ES2930125T3 - Apparatus comprising a hydraulic circuit - Google Patents

Abstract

An apparatus comprising a prime mover and a plurality of hydraulic actuators, a hydraulic machine having a rotary shaft in engagement driven by the prime mover and comprising a plurality of working chambers having a volume that varies cyclically with rotation of the shaft rotary, a hydraulic circuit that extends between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprising a low-pressure valve that regulates the flow of hydraulic fluid between the work chamber and a low pressure pressure manifold valve and a high pressure valve that regulates the flow of hydraulic fluid between the work chamber and a high pressure manifold, the hydraulic machine being configured to actively control the minus the low pressure valves of the group of one or more working chambers to select the net flow displacement hydraulic flow for each work chamber in each volume cycle of the work chamber and, therefore, the net displacement of hydraulic fluid through the group of one or more work chambers, in response to a demand signal, comprising the apparatus a controller configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators, where the demand signal is quantized, having one of a plurality of discrete values, and hence the net displacement of hydraulic fluid by the group of one or more working chambers, in response to a demand signal, the apparatus comprising a controller configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators, in in which the demand signal is quantized, having one of a plurality of discrete values, and therefore the net displacement of hydraulic fluid through the group of one or more chambers. as of work, in response to a demand signal, the apparatus comprising a controller configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators, in which the demand signal is quantized, having one of a plurality of discrete values. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Apparatus comprising a hydraulic circuit

field of invention

The invention relates to industrial machines and vehicles, such as excavators, with hydraulic actuators driven by an electronically switched hydraulic machine driven in turn by a main motor.

Background of the Invention

Industrial vehicles with multiple hydraulically powered actuators are in common use around the world. Industrial vehicles, such as excavators, usually have at least two tracks to move, a rotary actuator (for example, a motor) to rotate the cab of the vehicle with respect to the base comprising the tracks, rams to control the movement of an arm (for example, an excavator arm), including at least one ram for the boom, and at least one for the stick (arm), and at least two actuators to control the movement of a tool such as a bucket .

Each of these actuators represents some hydraulic load on a prime mover (for example, a motor such as an electric motor or, more typically, a diesel engine) of the vehicle and must be powered by one or more working chambers (for example, chambers defined by cylinders, within which the pistons rotate in use) of a hydraulic machine driven by the prime mover.

The invention is intended to provide improved hydraulic control systems for controlling multiple hydraulically powered actuators. Some aspects of the invention seek to provide hydraulic control systems that have energy efficiency advantages. Advantageously, the implementation of improved hydraulic control systems means that the power provided by a prime mover is used more efficiently to carry out work functions, thereby providing fuel savings.

Document WO2013/130768 refers to a digital hydraulic transformer and a method for recovering energy and leveling the hydraulic system. With special reference to Figure 13, a hydraulic transformer is shown comprising a radial piston pump with a number of cylinders constituting fluid chambers for supplying pressurized fluid to a hydraulic system of a construction machine that may be in the form of a a hydraulic excavator. The radial piston pump comprises a crankshaft with an eccentric mass. Document WO 2017/144875 refers to a hydraulic fluid power transmission.

Summary of the invention

According to a first aspect of the invention, there is provided an apparatus (for example, an excavator) comprising a main motor (for example, a motor) and a plurality of hydraulic actuators, a hydraulic machine having a rotary axis in which engagement driven with the main engine and comprising a plurality of working chambers having a volume that varies cyclically with the rotation of the rotating shaft (for example, each chamber is defined by a cylinder within which a piston moves in use),

a hydraulic circuit that runs between a group of one or more (optionally two or more) working chambers of the hydraulic machine and one or more (optionally two or more) of the hydraulic actuators,

each working chamber of the hydraulic machine comprises a low-pressure valve that regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve that regulates the flow of hydraulic fluid between the working chamber and a high pressure manifold,

the hydraulic machine is configured to actively control at least the group low-pressure valves of one or more working chambers to select the net displacement of hydraulic fluid per each working chamber in each working chamber volume cycle, and by Therefore, the net displacement of hydraulic fluid through the group of one or more working chambers, in response to a demand signal.

The hydraulic machine can be one or more electronic commutation machines (ECM). By ECM we mean a hydraulic fluid working machine comprising a rotating shaft and one or more working chambers (for example, chambers defined by cylinders, within which pistons move in use) having a volume that varies cyclically with the rotation of the rotating shaft, each work chamber has a low-pressure valve that regulates the flow of hydraulic fluid between the work chamber and a low-pressure manifold and a high-pressure valve that regulates the flow of hydraulic fluid between the working chamber and a high pressure manifold. The reciprocating movement of the pistons can be caused by direct interaction with an eccentric on the rotary axis, or with a second rotary axis, the second rotary axis being rotatively connected to the rotary axis. A plurality of ECMs with linked rotary axes (eg, common axes) driven by the main motor can work together as the hydraulic machine.

The apparatus may be a vehicle, typically an industrial vehicle. For example, the apparatus may be an excavator, telehandler, or backhoe loader.

It may be that the apparatus is configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators. Typically, the apparatus comprises a controller that is configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators.

The invention also extends to a method of operating said apparatus comprising calculating the demand signal in response to a measured property of the hydraulic circuit or of one or more actuators.

Typically, the method comprises sensing the flow and/or pressure demand of at least one of the groups of hydraulic actuators, or receiving a demand signal indicative of a demanded pressure or flow based on a pressure and/or demand. or flow of the group of one or more hydraulic actuators, and the control of the flow of hydraulic fluid from or to each of the groups of one or more working chambers that is fluidly connected to the group of one or more hydraulic actuators, responding thereto .

The apparatus (typically an excavator) may comprise a fluid manifold extending from said group of one or more working chambers to a group of one or more said hydraulic actuators and to a fluid container (for example, a tank or conduit). ) through a throttle, and a pressure monitor configured to measure the pressure of the hydraulic fluid in the manifold between the throttle and the group of one or more of said hydraulic actuators. The controller may be configured to regulate the displacement of the group of one or more of said working chambers that are in communication (for example, through a fluid manifold) with the group of one or more of said hydraulic actuators in response to the measured pressure to thereby regulate the pressure of the hydraulic fluid in the pressure monitor (for example, through feedback control). The method may comprise regulating the displacement of the group of one or more work chambers as a function of the measured pressure in order to thereby regulate the pressure of the hydraulic fluid in the pressure monitor. Thus, the apparatus often has a negative flow control loop. Optionally, the apparatus may comprise a feedback controller configured to calculate the demand signal in response to feedback of a measured property of the hydraulic circuit or one or more actuators (for example, in addition to or as an alternative to a feedback controller configured to calculate the demand signal in response to feedback from a measured property of the hydraulic circuit or one or more actuators).

The apparatus may comprise a (hydraulic) throttle connected in series with the open center of one or more open center control valves, said open center control valves located in the intermediate hydraulic circuit of the group of one or more working chambers and the actuator(s). Open center control valves typically divert fluid flow from the throttle to the actuator(s) when actuated. It may be that the demand signal is determined in response to a measurement of hydraulic fluid pressure at the throttle.

For example, the demand signal can be determined in response to a pressure measurement and/or a flow measurement. The demand signal may comprise a pressure measurement, the pressure measurement being measured at the throttle. The demand signal can be indicative of a fraction of the maximum displacement of hydraulic fluid by the group of one or more work chambers to be displaced per revolution of the rotary axis. It is referred to herein as Fd. (Fraction of maximum displacement per revolution).

Typically the controller (which may be a feedback controller) comprises a filter. The controller may calculate the demand signal in response to the measured property of the hydraulic circuit or one or more actuators by filtering a control signal based on the measured property of the hydraulic circuit or one or more actuators. The method may comprise calculating the demand signal in response to the measured property of the hydraulic circuit or one or more actuators, by filtering a control signal based on the measured property of the hydraulic circuit or one or more actuators. . For example, the control signal that is filtered can be a pressure signal, a flow signal, an actuator position signal, etc.

The filter can be selected to reject frequencies in the measured property and/or to attenuate noise (for example, beat noise) in the measured property, thereby generating a filtered input and subsequently determining the demand signal based on of said filtered input.

The method may comprise measuring and/or modulating the main engine operating parameters to thereby control the speed of the main engine. The prime mover (usually an engine) typically includes a prime mover control unit (PMCU), which typically includes a prime mover speed governor. The main engine speed controller may be operable to measure and/or modulate the operating parameters of the main engine to thereby control the speed of the main engine. The main engine speed controller may be operable to receive (and the method may comprise receiving) one or more inputs from a user (optionally via joystick) and/or a predefined set of instructions (for example, to prevent the main engine speed from increasing beyond a predetermined upper threshold, optionally to prevent the main engine speed from decreasing below a predetermined lower threshold).

The method may comprise varying one or more operating parameters of the apparatus (for example, one or more parameters of the prime mover or hydraulic machine) in response to an electrical signal received from one or more sensors. The PMCU may be configured to receive electrical signals from one or more sensors and optionally to further evaluate the signals and optionally vary one or more vehicle operating parameters (optionally one or more main engine parameters (eg, motor) and/or one or more parameters of the hydraulic machine). For example, the PMCU may be configured to receive (and the method may comprise receiving) electrical signals indicative of the position of the crankshaft and/or the speed of rotation of the rotating shaft (for example, measured by means of a speed sensor). axle), one or more temperatures (for example, a fuel temperature, an engine temperature, an exhaust air temperature, measured by means of one or more thermometers or other temperature sensors), an air mass flow, a charge air pressure, a fuel air pressure, an accelerator pedal position, etc.

The prime mover is typically in driving engagement with the hydraulic machine. The main motor has a rotating shaft which is usually coupled to the ECM rotating shaft (and to which the main motor can apply torque). The main motor (for example, the motor) and the hydraulic machine may have a common shaft.

When the apparatus is an excavator, the plurality of hydraulic actuators typically comprises (for example, at least) two actuators for moving the tracks (for example, for moving a vehicle, typically an excavator), a rotary actuator (for example, for a motor) (for example to rotate the excavator cab, relative to the excavator base, the base typically comprising the tracks), at least one ram actuator (for example to control an excavator arm , for example, for the pen and/or the stick), and at least two more actuators (for example, to control the movement of a tool such as a spoon).

One or more low pressure manifolds can be extended to the working chambers of the hydraulic machine. One or more high pressure manifolds can extend to the working chambers of the hydraulic machine. The hydraulic circuit typically comprises a high pressure manifold that extends between said group of one or more working chambers and said one or more actuators. The low pressure manifold can form part of one or more of said hydraulic circuits. By low-pressure manifold and high-pressure manifold we mean the relative pressures in the manifolds.

It may be that at least the low pressure valves (optionally the high pressure valves, optionally both the low pressure valves and the high pressure valves) are electronically controlled valves, and the apparatus comprises a controller that controls the valves (for example , electronically controlled) in step relation to the cycles of the work chamber volume to thereby determine the net displacement of hydraulic fluid by each work chamber in each cycle of the work chamber volume. The method may comprise controlling valves (eg, electronically controlled) in relation to cycles of the working chamber volume to thereby determine the net displacement of hydraulic fluid through each working chamber in each cycle of the working volume. the working chamber.

The flow rate and/or pressure requirement of a group of one or more hydraulic actuators can be determined by measuring the flow rate of hydraulic fluid to or from the group of one or more hydraulic actuators, or the pressure of hydraulic fluid at or at an output or input of the one or more hydraulic actuators, for example. The flow rate and/or pressure requirement can be determined from one or more measured flow rates and/or measured pressures that decrease or are below an expected value. A decrease in the flow and/or measured pressure with respect to an expected value indicates that the flow to or from the group of one or more hydraulic actuators is insufficient. For example, the flow rate of hydraulic fluid to an actuator may be determined to be below an expected (eg, target) value and a flow rate of hydraulic fluid to the actuator may be increased in response thereto. The hydraulic fluid flow rate of an actuator can be determined to be above an expected (for example, target) value (for example, when an arm or other weight is lowered) and an actuator flow rate can be reduce in response to it. It may be that an increase or decrease in pressure in one or more hydraulic actuators is detected and the group of one or more working chambers connected to the one or more hydraulic actuators is controlled to change (for example, increase or decrease) the pressure. flow rate of the hydraulic fluid from the group of one or more working chambers to the one or more hydraulic actuators, or vice versa.

Groups of one or more working chambers can be dynamically assigned to respective groups of one or more hydraulic actuators to thereby change which one or more working chambers are connected to (for example, a group of) hydraulic actuators, e.g. for example, by opening or closing electronically controlled valves (eg high pressure valves and low pressure valves, described below), eg under the control of a controller. Groups of (eg one or more) working chambers are often dynamically assigned to the (respective) groups of (eg one or more) actuators to thereby change which working chambers of the machine are coupled to which actuators hydraulic, eg by means of opening and/or closing valves (eg electronically controlled), eg under the control of a controller. The net displacement of the hydraulic fluid through each working chamber (and/or each hydraulic actuator) can be regulated by means of regulating the net displacement of the working chamber(s) which are connected to the hydraulic actuator(s). Groups of one or more working chambers are typically connected to a respective group of one or more of said hydraulic actuators through said manifold. Typically, the connection extends through one or more valves, such as normally open valves and/or spool valves (which may be open center spool valves or closed center spool valves in different embodiments).

The apparatus typically comprises a controller. The controller comprises one or more processors in electronic communication with the memory, and the program code stored in the memory. The controller may be distributed and comprise two or more controller modules (eg two or more processors), for example the controller may comprise a hydraulic machine controller (comprising one or more processors in electronic communication with memory, and program code stored in memory) that controls the hydraulic machine, and an apparatus controller (comprising one or more processors in electronic communication with memory, and program code stored in memory) that controls the other components of the apparatus (for example, valves for changing the flow path of hydraulic fluid).

Typically, the fluid manifold extends through a plurality of normally open valves. For example, the plurality of normally open valves may comprise one or more open-center control valves having at least one inlet and more than one outlet, in which fluid can flow (for example, directly) through the al least one inlet and at least one of more than one outlets, unless a force is applied to close the valve. Open center control valves may comprise (eg be) normally open valves, eg normally open spool valves, such as open center spool valves.

Open center spool valves comprise one or more openable ports (eg, a normally open port and one or more actuator ports). Typically, the fluid connection between the group of one or more working chambers and the group of one or more hydraulic actuators extends through another normally open valve, again typically a normally open spool valve, such as a spool valve. open center spool. A manually operable control (eg, joystick) is typically coupled to one or both of the normally open valves to regulate flow through them. Optionally, one or more hydraulic actuators may act in opposition, eg fluid may be directed to either end of a double acting piston or ram.

Typically, open center spool valves comprise one or more flow outlets through which the fluid in use is directed. Open center control valves typically comprise a predetermined valve position configured to cause fluid displaced by one or more cylinders to flow (eg, directly) through a central flow outlet to a tank. Open-center control valves typically comprise one or more fluid diversion positions, configured to cause fluid displaced by one or more cylinders to flow (for example, directly) through a flow outlet to one or more actuators. . In use, an input provided by a user (optionally by a controller) causes the position of the open center spool valve to be adjusted and thereby causes flow to be diverted to the tank and/or one or more actuators.

It may be that the pressure or flow rate of the hydraulic fluid accepted by, or produced by, each working chamber is independently controllable. It may be that the pressure of, or the flow rate of hydraulic fluid accepted by, or produced by each working chamber can be controlled independently by selecting the net displacement of hydraulic fluid per each working chamber in each volume cycle. of the working chamber. This selection is normally carried out by the controller.

The flow demand can, for example, be determined by means of detecting a drop in pressure (for example, through the use of pressure sensors) across a flow restriction (for example, an orifice) arranged in such a way by reducing the flow through the orifice when the total flow demand of all hydraulic actuators increases, or by direct measurement of the same flow through the use of a flow sensing means, such as a flowmeter.

Flow and/or pressure demand can be detected by measuring the pressure of the hydraulic fluid at the inlet of a hydraulic actuator. When a hydraulic actuator is a hydraulic machine, the flow demand can be detected by measuring the rotational speed of a rotating shaft or the translational speed of a ram or the angular velocity of a joint, for example. The sum of the measured pressures or flows can be added or find the maximum of the measured pressures or flows.

The demand signal indicative of a demanded pressure or flow based on a pressure and/or flow demand of the hydraulic actuator may be a signal representing a quantity of flow of hydraulic fluid, or pressure of hydraulic fluid, or torque. on the shaft of the machine or the shaft of a hydraulic actuator driven by the machine, or the power output of the machine or any other signal indicative of a demand related to the pressure or flow requirements of one or more hydraulic actuators.

Typically, the hydraulic machine is operable as a pump in a pump mode of operation or is operable as a motor in a motor mode of operation. It may be that some of the working chambers of the hydraulic machine can pump (and therefore some working chambers can release hydraulic fluid) while other working chambers of the hydraulic machine can motorize (and therefore some chambers work can enter hydraulic fluid).

The controller can control the hydraulic machine (for example, electronically commutated). The controller can be configured to calculate the power available from the prime mover and limit the net displacement of hydraulic fluid by the hydraulic machine driven by the prime mover so that the net power demand does not exceed that available from the prime mover.

The controller typically comprises one or more processors and memory that stores program code executed by the controller in operation. The controller can calculate a power limit value, or a value related to it (for example, a maximum pressure, a motor torque, a flow, etc.). The controller may be configured to implement a maximum rate of flow of hydraulic fluid through or pressure in a group of one or more hydraulic actuators.

An electronically commutated hydraulic machine is known to have a very short response time. Although short response times are useful in certain scenarios, they can also have drawbacks. For example, in some circumstances, when response times are too short, this can have a negative impact on controllability.

Accordingly, another aspect of the invention provides a method of operating an apparatus, comprising a hydraulic machine (for example, electronically commutated) with one or more working chambers, a prime mover (for example, a motor, optionally a motor diesel) coupled to the hydraulic machine, in which the method comprises selecting between two or more operating modes, at least a first mode having a first response time and/or comprising a first time constant and at least one second mode comprising a second response time and/or having a second time constant different from the first time constant. The second mode may further comprise a modified negative flow control system, the modified negative flow control system emulating an analog pump and/or the response time of the first mode. There may be other modes (eg, a third mode, a fourth mode, a fifth mode, etc.), each associated with a different stage response time and/or a different time constant.

Typically, the controller has at least two modes of operation, each mode of operation characterized by a filter (eg, low-pass) with a different stage response time and/or a different time constant.

Thus, there is at least one mode of operation in which the hydraulic machine responds more slowly to changes in the measured property. It may be that there are at least two modes with step change response times and/or time constants that differ by a factor of at least 2, or at least 4, or at least 10.

The at least two modes of operation may comprise at least one override mode characterized by a response time and/or a time constant that is shorter than the time constant of any other mode, in which the controller is operable to implementing the override mode in response to determining that a prime mover operating condition meets one or more override criteria. The operating condition may comprise (eg at least one of) a measured torque and/or a measured speed and/or a measured power. The operating condition may comprise a combination of a measured torque and/or a measured speed and/or a measured power. The override criterion could be, for example, that a measured torque and/or a measured speed and/or a measured power exceed a threshold or fall below a threshold.

The at least two modes of operation may comprise a second mode, wherein the second mode may comprise (for example, be) a "slow mode" with a reaction time of more than 200 ms, or preferably more than 250 ms, or preferably more than 300 ms. When the prime mover is a motor, the procedure may comprise activation of a "slow mode" when engine droop is detected and, optionally, subsequent activation of a "fast mode", for example, when engine speed recovers. engine. This has the advantage of preventing the engine from stalling.

By engine droop we mean a sustained decrease in engine speed from engine set point as engine load increases.

When the feedback loop has high gain and proportional control and the hydraulic circuit has low compliance it can be very prone to instability. Such a system can be very sensitive to delays, perhaps even 2 or 3 ms for example, either due to signal measurement and/or filtering of hardware responses. Accordingly, in some embodiments, the filter may be a low pass filter with a time constant of 100 to 300 ms or a filter with a step response of 100 to 300 ms.

Torque demand is known to be satisfied by sharing the output between multiple hydraulic machines (for example, electronically commutated). For example, an industrial machine that has two hydraulic machines (for example, electronically commutated) can be limited so that each hydraulic machine provides (at most) half of the required output (for example, torque) to satisfy the demand. In addition, to prevent stalling, a safety factor is often introduced to prevent the combined (eg added) torque of the two or more hydraulic machines from exceeding a maximum torque. When the prime mover is an engine, this safety factor also helps reduce engine droop and transient reductions in engine speed. This is inefficient because it is not possible to use the full power of the machine.

Typically, the procedure comprises selecting a main motor speed set point (for example, example, a motor speed setpoint), ^Ssetpoint . At any time, the main motor may be running at a speed that may be, but is not necessarily, the same as the main motor speed set point.

Consequently, the method comprises measuring or determining the current speed of the main engine, ^Sactuai. The controller may be configured to select a main motor setpoint (for example, a motor speed setpoint), ^Ssetpoint . The controller can be configured to receive a measurement or determine the current speed of the main motor, ^Sactual.

The motor can be made to operate at a main motor speed lower than the main motor speed set point (for example, at least 90% of the main motor speed set point, preferably at least 95% of the main motor speed set point).

Typically, the method comprises calculating a main motor speed error (eg motor speed error) (AS). The controller may be configured to calculate a main motor speed error (eg motor speed error) (AS). The main motor speed error can be calculated according to the following equation:

^Sset point - ^{Sactual =} AS (Equation 1)

Accordingly, in another aspect of the invention, the method may comprise selective regulation of the demand signal to implement a torque limit of the hydraulic machine. The controller may be configured to selectively regulate the demand signal to implement a hydraulic machine torque limit. The torque limit of the hydraulic machine can be variable. Normally, the torque limit of the hydraulic machine varies with the speed of the main motor, since the torque that the main motor can produce is also a function of the speed of the main motor.

The torque limit of the hydraulic machine can be calculated based on a speed error of the main motor (for example, a motor speed error), optionally, wherein the speed error of the main motor is determined by means of the comparison of a main motor speed measurement (eg, motor speed) and a main motor speed set point (eg, motor speed set point).

Typically, the prime mover comprises a prime mover governor (eg, an engine governor) that regulates the prime mover to a determined target speed in response to operator input. The target speed can be determined based on a torque limit defined in a database.

The method may comprise receiving a displacement signal from the input hydraulic machine and outputting a displacement signal from the output hydraulic machine that is selectively restrained to prevent a torque limit from being exceeded, which takes into account a torque limit function and a main motor speed error (for example, a motor speed error). The controller may be configured to process a hydraulic machine travel signal and compute (eg, output) a hydraulic machine travel signal that is selectively restrained to prevent a torque limit from being exceeded, which takes into account a torque limit function and a main motor speed error (for example, a motor speed error)

The displacement signal of the hydraulic machine may be representative (for example, it may comprise a numerical value proportional to) of a fraction of the maximum displacement per revolution of the rotary axis of the hydraulic machine (Fd).

It is known to supply industrial vehicles (eg excavators) comprising a plurality of pressure relief valves. Pressure relief valves prevent damage due to excess pressure during moving functions of industrial vehicles. It is also known that a plurality of pressure relief valves are provided in which different pressure relief valves have different functions. For example, the respective pressure relief valves could be associated with the movement of each of the arms, a caterpillar motor, a swing motor, etc.

When the pressure limit (“PRV pressure”, or pressure relief valve pressure) is reached, a PRV opens, allowing excess hydraulic fluid to escape, thereby preventing further pressure increases. Prevents pressures from reaching unsafe levels in the system. However, this results in inefficiencies in the system, as energy from the fluid is converted to heat over the valve and is subsequently lost.

Consequently, some embodiments of the invention seek to provide a method by which to avoid reaching the PRV pressure during the use of a machine, or in some embodiments even to bypass one or more (or all) of the PRVs. The controller can be configured to receive a measured pressure and compare the measured pressure to a pressure limit (default) and limit travel when the measured pressure is within a range (which may be, for example, in the 70% range). to 100%) of the pressure limit. The procedure may comprise receiving a measured pressure and comparing the measured pressure to a pressure limit. (default) and limitation of displacement when the measured pressure is within a range (which may be, for example, in the range of 70% to 100%) of the pressure limit. The pressure limit may be a pressure limit of a system pressure limiter, such as a pressure relief valve. The method may comprise sensing the current pressure, comparing the pressure with a PRV pressure, and limiting the displacement when the current pressure is within the range of the PRV pressure.

Optionally, the controller can be configured to receive a measured pressure and compare the measured pressure to a pressure limit. Optionally, the controller can be configured to receive a measured pressure and compare the measured pressure to the pressure limit and limit travel when the measured pressure approaches or is substantially equal to the pressure limit.

Optionally, the pressure limit (and/or pressure threshold) can be the pressure at which a pressure relief valve will actuate to release the pressurized fluid. The limited pressure (and/or threshold pressure) may be a predetermined acceptable pressure.

Optionally, pressure can be measured at a location in the hydraulic circuit that is not in fluid communication with a pressure relief valve.

In some embodiments, the vehicle (optionally an excavator) may not have any pressure relief valves, however typically the vehicle will comprise a plurality of pressure relief valves (eg where dictated by safety regulations).

Typically, different PRVs are associated with different functions and therefore will have different PRV opening pressures (for example, the PRV opening pressure to raise an excavator arm may be different (for example, higher or lower) than the PRV opening pressure to lower an excavator arm).

The controller may be configured to receive the user's demand and/or commands and to take the user's demand and/or commands into account when determining whether the measured pressure is within a range of the pressure limit. The method may comprise taking into account user demand and/or commands (for example, commands entered via one or more joysticks) in calculating where the measured pressure lies within a pressure limit range. (ie the opening pressure of the respective PRV). For example, the pressure limit and/or the margin can vary with the demand and/or the commands of the user or other parameters, for example, the position of the actuator or the speed of movement.

It is known that a vehicle (eg excavator) can be provided in which flux is supplied to allow performance of numerous functions (eg excavator functions) simultaneously. In some circumstances, excessive flow can be directed to one or more functions (for example, if a flow value stored in a lookup table associated with that function is inaccurate). This could result in the pressure reaching a PRV limit and excessive flow out through a PRV to prevent damage to hydraulic machine parts or other components in the hydraulic circuit. However, when the flow exits through a PRV, the energy associated with that flow is lost, leading to inefficiencies. Another adverse effect of excess flow to a function could be increased pressure drop over the spool (but not reaching PRV pressure). This causes a large loss of power on the reel.

The method may comprise measuring an input from a user (for example, an input supplied via a joystick) to generate a control signal that is used to determine a displacement of the hydraulic machine, or at least the group of a or more working chambers. The controller can receive input from the user and generate a control signal that is used to determine a displacement of the hydraulic machine, or at least the group of one or more working chambers. This works in open loop mode, so there is no feedback system with which to correct an error. These machines are usually very accurate.

The control signal can be a manifold control signal (for example, a pilot pressure or a proportional activation signal) that determines the opening degree of the manifolds. The control signal can be used to regulate a flow rate of hydraulic fluid from the group of one or more working chambers to the actuator(s).

It may be that the apparatus further comprises at least one distributor in the hydraulic circuit, through which the hydraulic fluid flows in use from the group of one or more working chambers to one or more of the hydraulic actuators, and pressure sensors configured to measure the pressure of the hydraulic fluid before and after the at least one distributor, for example at the outlet of the hydraulic machine and at the one or more actuators.

The controller is typically configured to determine a pressure drop across the at least one spool valve from pressure measurements from the pressure sensors, and to receive a position signal (measurement) from the spool valve, indicative of the position of the spool valve, or a spool valve control signal, and to limit the displacement of the one or more working chambers if the determined pressure drop exceeds a pressure drop threshold whose threshold of Pressure drop is determined as a function of the spool valve position signal or the spool valve control signal, respectively. The method typically comprises determining a pressure drop across the at least one spool valve from the pressure measurements from pressure sensors, and receiving a spool valve position signal (measurement), indicative of spool valve position, or a spool valve control signal, and limitation of the displacement of the one or more working chambers if the determined pressure drop exceeds a threshold pressure drop, the threshold pressure drop of which is determined as a function of the spool valve position signal or the control signal of the spool valve, respectively.

The threshold pressure drop is or is related to (eg, within a predetermined range of) an expected pressure drop. The expected pressure drop can be calculated based on the manifold position signal or the manifold control signal. The pressure drop threshold can be determined by looking up a lookup table. The pressure drop threshold can be an acceptable pressure drop. The pressure drop threshold may be an acceptable pressure drop given the flow indicated by the spool valve position signal or the spool valve control signal. Pressure drop is indicative of flow, and therefore excessive flow is indicative of higher than expected flow given the manifold valve position signal or manifold valve control signal, respectively. If an excess of flow is detected, the movement of the group of one or more working chambers is limited. The pressure drop threshold can be determined based on one or more additional factors, as well as the manifold position signal or manifold control signal.

The pressure sensors can comprise a pressure sensor at the outlet of the group of one or more working chambers of the hydraulic machine and a pressure sensor at the inlet of one or more of the hydraulic actuators.

Typically, valves (eg, spool) are normally closed and configured to open in response to a user command (eg, user command input via joystick) to thereby direct flow, optionally (for example), to one or more actuators. Spool valves typically have a primary port (eg, center) that can be default open (ie, normally open) to provide a default flow path (eg, conduit) through which fluid displaced by one or more working chambers may flow, optionally to a tank and one or more additional ports (for example, connected to one or more actuators) which may be closed by default and which may open in response to a user command or the controller. Spool valves typically include one or more additional ports that can be closed by default (ie, normally closed) and can be opened in response to a user command (optionally a controller command). Normally, when another port is opened, the main one is closed (for example, the central one). It is possible to determine the degree of opening of a manifold port by measuring a control signal associated with the manifold (for example, the control signal may be a pilot pressure). It is also possible to test a spool valve position sensor (which can, for example, determine the position of a spool valve member relative to a valve body).

The group of one or more working chambers may be connected to one or more actuators through a specific port of a spool valve having a plurality of ports. In that case, it is the opening of that specific port that will determine the flow rate leading to the head loss to be measured.

Distributors typically comprise a main port, which may be open by default, to thereby provide a default flow path through which fluid displaced by the group of one or more working chambers may flow, optionally towards a tank, and one or more additional ports that can be closed by default and that can be opened in response to a user or controller command. Said specific port can be a main port or an additional port.

The controller may be configured to receive a user input, a measurement of a control signal from the timing valve and a measurement of the rotational speed of the rotary shaft, to thereby determine (eg calculate), optionally with reference to a lookup table, an open-loop estimate of the required displacement, and typically also to determine (e.g. compute) an estimate of flow based on the rotational velocity measurement of the rotary shaft and the open-loop estimate of the required displacement. Accordingly, the method may comprise receiving and processing a spool valve control signal (for example, pilot pressure), in response to user input, and measuring the speed of rotation of the shaft. rotary to thereby compute (eg, with reference to a lookup table) an open-loop estimate of the required displacement and to compute an estimated flow based on the shaft velocity measurement and the open-loop estimate of the displacement required.

Instead of the control signal of the distributors, a feedback signal of the distributors, for example the position of the distributor, can be used.

The method may comprise determining a value representative of a pressure drop across the distributor on the basis of the control signal (and therefore on the basis of the distributor opening), and measuring the drop actual pressure drop (for example, by receiving pressure measurements from pressure sensors in the hydraulic machine and in the actuator) and comparing the actual pressure drop with a threshold pressure drop and the displacement reduction if the actual pressure drop exceeds the threshold pressure drop. The controller may be configured to determine a value representative of a pressure drop across the manifold based on the control signal (and therefore on the basis of manifold opening), and to measure the actual pressure drop (for example, by means of receiving pressure measurements from pressure sensors in the hydraulic machine and in the actuator) and to compare the actual pressure drop with a pressure drop threshold and to reduce the offset if the actual pressure drop exceeds the pressure drop threshold.

The power dissipated over the distributor is a function of the flow through the distributor and the pressure drop over the distributor. The pressure drop over the distributor is proportional to the square of the flow through the distributor. Therefore, if the pressure drop is high, it indicates that a lot of energy is being wasted through the spool. Accordingly, the pressure drop threshold for a given spool valve position or spool valve control signal is set based on what is considered an acceptable power loss at a given spool position. Thus, when the pressure drop exceeds the pressure drop threshold, the flow to one or more actuators can be reduced (eg, limited) to thereby limit power loss. This has the effect of improving efficiency. In use, an operator can adjust the spool valve control signal (for example, the pilot signal), typically via a joystick, to thereby increase the opening of the (for example, the spool valve). spool) and therefore to cause a speed increase in the one or more actuators. The pressure drop for a given flow rate through a larger valve opening (eg spool) is less.

Typically, the controller causes the flow to be reduced if the actual pressure drop exceeds the pressure drop threshold by using a proportional-integral control loop. The method may comprise causing the flow to be reduced if the actual pressure drop exceeds the pressure drop threshold by use of a proportional-integral control loop. This proportional-integral control loop is configured such that the integral part of the control loop can only integrate when the actual pressure drop exceeds the pressure drop threshold or return the integrated value to zero in the event that the actual pressure drop exceeds the pressure drop threshold. actual pressure drop is less than the acceptable pressure drop. The proportional part of the control loop is applied when the actual pressure drop does not exceed the acceptable pressure drop. Typically, the proportional part of the control loop is set to cause no change in flow if the actual pressure drop does not exceed the pressure drop threshold. Consequently, the controller (i.e. via the integral-proportional control loop) normally only acts to reduce the flow (eg displacement), i.e. the proportional-integral control loop does not act to increase the flow . The procedure usually includes flow reduction only.

It may be that, when the controller selectively restricts the displacement of the group of one or more working chambers to give less flow, the displacement is reduced below (for example, by a predetermined margin) the displacement indicated by the control signal of the spool valve (which in turn is typically determined by the position of a manually operable control) and/or below (for example, by a predetermined margin) the offset that the measured pressure drop would be expected to give during normal operation . In this way, the controller can overlimit the movement of the group of one or more working chambers. The method may comprise reducing the displacement below (for example, by a predetermined margin) the displacement indicated by the spool valve control signal (which in turn is typically determined by the position of a manually operable control) by below (eg, by a predetermined margin) the displacement that the measured pressure drop would be expected to give during normal operation. Thus, the method may comprise over-limiting the displacement of the group of one or more working chambers.

This has the effect of prompting the operator to move the manually operable control to a position that causes the spool valve to be more open and/or the one or more working chambers to displace more fluid. This has the advantage of allowing more efficient operation and avoiding the inefficiencies associated with proportional distributors.

When the displacement is regulated (eg increased, decreased or limited) this typically comprises (eg achieved by means of) regulating (eg increased, decreased or limiting) the demand signal.

Resonant oscillations in vehicles have a number of negative effects, for example component damage, unacceptable noise and vibrations experienced by the operator. Vehicles with hydraulic transmissions can be damaged by resonant oscillations from the operation of a hydraulic machine within or connected to the hydraulic transmission, including resonant oscillations from operation of the hydraulic transmission. However, it has been found that when hydraulic machines and motors of the type described above are used, vibrations may arise, resulting from the pulsatile nature of the flow through the hydraulic machine, which can give rise to oscillations if they coincide with a resonant frequency. of one or more components. Vibration of a component at its resonant frequency will only occur if there is a mechanical transmission path from the excitation source to the component. Vibrations may occur depending on the frequency with which active cycles are selected. For example, if ten active cycles per second, equally spaced in time, are selected, vibrations may arise at 10 Hz. Similarly, problems may also arise from vibrations associated with the frequency of chamber volume inactive cycles. of work. For example, if at each revolution of the shaft, all work chambers perform an active cycle but one work chamber every 0.1 seconds performs an idle cycle, where the idle cycles are spaced apart in time by the same, there may be a vibration of 10 Hz, as a result.

These vibrations can be more detrimental, simply because they become relevant when the machine is running at a high ratio of maximum displacement, and therefore in circumstances where there is high power output, and greater forces are at work.

Normally, the operation of a hydraulic machine inside a vehicle (for example, an excavator) will generate vibrations that can be classified into three groups: unacceptable, undesirable and acceptable vibrations. The controller may be configured to determine (and the method may comprise the determination) whether vibrations are classified as unacceptable vibrations, undesirable vibrations, or acceptable vibrations based on factors including the magnitude of these vibrations and/or the frequency of these vibrations and /o is the presence of a mechanical transmission path for these vibrations to allow the excitation of other components. When the demand is quantized, the output pulsations of the hydraulic machine may contain a certain frequency content comprising frequencies that are not considered unacceptable or undesirable, since they do not cause vibrations perceived by the driver, or do not give rise to audible noise, or give rise to vibrations that could cause damage to components. However, the frequency content can cause pulsations in pressure that we do not want to use when calculating the torque of the hydraulic machine. The frequency content of the pressure is known, which can be removed by means of a moving average filter. (In the event that the window size is dynamically adjusted so that the moving average filter removes this particular acceptable frequency, the filter will also remove harmonics at that frequency, and since the moving average filter is a type of low pass filter, it will also partially attenuate all frequencies above the acceptable frequency.

The demand signal is used by the hydraulic machine (for example, by a controller of the hydraulic machine) to make decisions about whether each work chamber in the group of one or more work chambers performs an active cycle or an inactive cycle. for each working chamber in each working chamber volume cycle. When the demand signal is calculated in response to a measured property of the hydraulic circuit or one or more actuators, we have found that there may be unwanted vibrations or oscillations due to the on/off frequencies of the cylinders resulting from the on-cycling pattern. and inactive implemented by the hydraulic machine in response to the demand signal. This can occur, for example, if the measured property is the pressure or flow at a location in the hydraulic circuit in fluid communication with the group of one or more working chambers, and/or a position or movement speed of one or more of the actuators in fluid communication with the group of one or more work chambers. It would be advantageous to remove these frequencies from the feedback loop.

It may be that the demand signal to which the hydraulic machine responds is quantized, having one of a plurality of discrete values. It may be that a demand signal (optionally continuous) is received and quantized, for example, by selecting the closest discrete value to the received demand, or the next discrete value above or below the received demand. Hysteresis can be applied in the quantization stage, to avoid flicker. The plurality of discrete values can be representative of the average fraction of the total fluid displacement through the group of one or more working chambers). There may be a step of determining the discrete values, for example by calculating or reading them from memory, and they may be variable, for example as a function of the speed of rotation of the rotary axis.

The controller may be configured to calculate, and the method may comprise calculating, the demand signal by filtering a control signal based on the measured property of the hydraulic circuit or one or more actuators by using a filter. , in which the filter attenuates one or more frequencies arising from a pattern of on-and-off cycling of the working chamber volume that results from the hydraulic machine selecting the net displacement of hydraulic fluid per each working chamber that responds to the demand signal. It may be that said one or more filters comprise at least one moving average filter. It may be that the measured property of the hydraulic circuit is a measured pressure (for example, at a hydraulic machine outlet, at one or more actuators, before or after one or more control valves, etc.)

The filter can be varied based on a current or previous value of the demand signal to thereby suppress frequencies derived from the pattern of working chambers cycling on or off derived from the (quantized) demand signal.

The plurality of discrete values of the demand signal may or may not be equally spaced. The discrete values may or may not vary with the speed of rotation of the rotating shaft. If they vary with the speed of rotation of the rotary axis, they can be selected to reduce the generation of low-frequency components. For example, there may be fewer than 1000 or fewer than 100 discrete values. When the demand signal is digital, we are not referring to the possible values imposed by binary logic, but to a subset of the values that could be represented digitally given the bit size of the demand signal. Thus, the discrete values typically represent less than 10%, less than 1%, or less than 0.1% of the digital values that the demand signal could have, given its bit length.

It may be that the values of the discrete values vary with the speed of rotation of the rotary axis and are selected to avoid the generation of undesirable and/or unacceptable frequencies when the hydraulic machine controls the net movement of the group of one or more working chambers to implement the quantified demand.

The moving average filter usually has a filter window. It may be that the filter window has a filter window length selected as a function of the discrete value of the demand signal and the speed of rotation of the rotary axis to attenuate a frequency arising from the group of one or more working chambers that they carry out active or inactive cycles of volume of the working chamber at that discrete value of the demand signal and at that speed of rotation of the rotary axis. It may be that the filter window has a filter window length corresponding to an inverse value of a predetermined minimum frequency. In this way, the filter will remove the components of the predetermined minimum frequency and, normally, it will also attenuate the lower frequency components. Typically, the predetermined minimum frequency is proportional to the rotational speed of the rotating shaft, for a given pattern of on/off cycles/given demand. The predetermined minimum frequency can be determined from a parameter stored in memory for a given discrete value of the demand signal and the speed of rotation of the rotary shaft.

Although the filter window length may be fixed, typically the hydraulic machine controller is configured to cause periodic adjustments of the filter window length based on the demand signal. The method may comprise making periodic adjustments to the length of the filter window based on the demand signal, for example once for each rotation of the rotary shaft.

Moving average filters are known that take the average of a specified function over a given number of previous data points (for example, data in a given data window). When calculating the average, a different weight can be assigned to different data points, or a substantially equal weight can be assigned to each data point (for example, when the moving average is effectively a moving average). The averages can be arithmetic, harmonic or geometric, the median, the mode, etc. When a moving average filter has a fixed filter period (for example, a data window of fixed size) it is unlikely that the moving average filter will effectively filter out all unwanted frequencies. However, when a function's waveform contains a signal with a given frequency that has the same period as the moving average window size, that frequency is completely attenuated (ie, filtered out) from the function. Therefore, it is possible to remove any frequency by selecting the window size of a moving average filter to match the period of that frequency. Since the moving average filter acts as a low pass filter, any frequency above that frequency will be at least partially attenuated. Another aspect of the invention provides a moving average filter with a dynamically changing window size.

The individual working chambers are selectable, for example, by a valve control module, at each working chamber volume cycle, to displace a predetermined fixed volume of hydraulic fluid (an active cycle), or to undergo a idle cycle (also called idle cycle) in which there is no net displacement of hydraulic fluid, thereby allowing the net fluid performance of the machine to dynamically adapt to the demand indicated by the demand signal. The controller and/or valve control module may be operable to cause individual work chambers to cycle on or cycle off by running an algorithm (eg, for each work chamber volume cycle ). The method may comprise running an algorithm to determine whether individual working chambers are cycled on or cycled off (eg, for each volume cycle of the working chamber). The algorithm usually processes the demand signal (eg quantized).

The pattern of on and off cycling of the working chamber volume carried out by the working chambers has a frequency spectrum with one or more intensity peaks. For example, if the working chambers were to alternately cycle on and off, an intensity peak would occur at a frequency equal to half the frequency of cycling the volume of the working chamber. More generally, the working chambers will undergo a more complex pattern of active and inactive cycles, which has a frequency spectrum with one or more intensity peaks.

The pattern of cycling the work chamber volume on and off performed by the work chambers typically has a finite period, wherein the finite period can vary within a range of acceptable values. For example, the pattern of on and off cycles may have a minimum period of at least 0.001 s, or at least 0.005 s, or at least 0.01 s and/or may have a maximum period of at least 0.1 s, or at least 0.5s.

On an example machine, the minimum period might be 2 ms (caused by the firing frequency of all 12 cylinders at a maximum speed of 2050 RPM). Those skilled in the art will appreciate that with higher main engine speeds, or with more cylinders, the minimum period could be 1ms (or less). In a first embodiment, it is preferred to remove all frequencies below 5 Hz, which corresponds to a period of 0.2 s.

Typically, the range of acceptable periods is selected based on the acceptable frequency content. From this maximum acceptable period, a finite acceptable range of displacement demands will be selected which will depend on the number of cylinders and the operating range of the main engine. For example, the range of acceptable Fd values may be selected to comprise a finite number of integer fractions of the displacement demand. The denominators of the finite number of integer fractions can be selected as a function of the rate of rotation of the axis of rotation, eg the denominators can be selected such that the period is less than a maximum period. Normally, the acceptable values of the denominators of the number finite to whole fractions vary as a function of the speed of rotation of the rotating shaft. It is beneficial to have a short period because this corresponds to more frequent cycling of the working chamber volume on or off and thus eliminates low frequency content from chamber activations.

Typically, the moving average filter window size is selected based on the frequency of the pattern of on-off cycles of the working chamber volume. For example, if the pattern of cycling the working chamber volume has a frequency of 10.5 Hz, the window size of the moving average filter can be selected to have a period of 0.095 s.

The frequency of the working chambers that carry out active or inactive cycles is proportional to the speed of rotation of the rotary axis (revolutions per second). This is because there will typically be a point during each work chamber volume cycle at which a given work chamber commits to either an active cycle or an inactive cycle. For example, it is often decided whether or not to close an electronically controlled valve that regulates the flow of hydraulic fluid between a working chamber and the low-pressure hydraulic fluid manifold. In this way, the (potentially undesirable) frequencies derived from a certain sequence of active and inactive cycles are proportional to the speed at which the cycles occur, that is, proportional to the speed of rotation of the rotating shaft. Thus, the window size of the moving average filter is typically selected as a function of the demand signal and the speed of rotation of the rotary shaft.

However, there may be unwanted frequencies (eg, a range of frequencies) comprising one or more resonant frequencies of a portion of a hydraulic machine and/or one or more resonant frequencies of a portion of the vehicle (eg, excavator ), which is part of or in mechanical communication with (for example, mechanically coupled to) the hydraulic machine, whose resonant frequencies do not vary proportionally to the speed of rotation of the rotating shaft.

What is important is the frequency with which the number of work chambers that carry out active (or inactive, depending on the case) cycles varies. If the number of working chambers that cycle on (or off, as the case may be) has been changed by a constant amount, this does not affect the fundamental frequency. For example, if at successive decision points (i.e., points in time at which it is decided whether one or more working chambers should be cycled on or off), it is determined that a sequence of working chambers may be represented by 1's and 0's, where 0 represents an inactive chamber cycle and 1 represents an active chamber cycle, for example: 0, 0, 0, 1, 0, 0, 0, 1 (this sequence has the same frequency fundamental than the sequence 1, 1, 1, 0, 1, 1, 0).

Consequently, the invention recognizes that the hydraulic machine will generate vibrations with intensity peaks at frequencies that depend on the pattern of active and inactive cycles carried out by the working chambers and that, for a given sequence of active and inactive cycles, it is proportional at the speed of rotation of the rotating shaft. In accordance with the invention, the pattern of the valve command signals is controlled to reduce unwanted vibrations by avoiding certain ranges of Fd, which means that the target net displacement is sometimes not met exactly. However, in closed-loop feedback systems, the errors derived from it can be corrected. The pattern of the valve command signals often affects the frequency with which the one or more intensity peaks in the frequency spectrum occur by determining whether each working chamber is cycled on or off. However, if the amount of hydraulic fluid displaced by the working chambers varies between cycles, then the net displacement determined by the pattern of valve control signals during each cycle of the working chamber volume also affects the frequency a which the one or more intensity peaks of the frequency spectrum occur.

When the demand signal is quantized, the patterns of on and off cycles at these discrete offsets ("quantized offsets") cause cylinder enable patterns with known frequency content, and as such, the lowest frequency pattern of the demand signal is known. the cylinder enable patterns present. Accordingly, the method may comprise dynamically adjusting (and the controller may be configured to adjust) the size of the moving average filter window such that the moving average filter fully attenuates the lowest known frequency. The method may comprise adjusting (and the controller may be configured to adjust) the moving average filter window size as a function of rotational speed of the rotary shaft and/or current hydraulic fluid displacement. For example, if the quantization results in a period of 10 ms, the window size of the moving average filter can be selected to also have a period of 10 ms, thus attenuating, for example, the filter) a 10 Hz cylinder enable pattern.

It may be that the controller receives a demand signal (typically a continuous demand signal) and determines a corresponding series of values, said series of values corresponds to a pattern of cycling on and/or off the volume of the working chamber to satisfy thereby the demand signal (ie, when the demand signal (Fd) resulting from the pattern of on/off cycling of the working chamber volume is averaged over a period of time). The procedure can comprise the reception of a demand signal (typically a continuous demand signal) and the determination of a series of corresponding values, said series of values corresponding to a pattern of active and/or inactive cycles of the volume of the storage chamber. work to thereby satisfy the demand signal (i.e., when the demand signal (Fd) resulting from the pattern of active cycles and/or idle chamber volume is averaged over a period of time).

For example, the controller may receive a continuous demand signal for 90% of maximum displacement and may determine a series of values comprising at least 100 values, or preferably at least 500 values, or more preferably at least 1000 values. The series of values may comprise a repetitive sequence and therefore the pattern of active and/or inactive cycles may comprise a period corresponding to the repetitive sequence.

The method may comprise selecting a minimum allowable frequency (eg 5 Hz, 10 Hz), and subsequently creating a quantized list of the plurality of discrete demand values (eg Fd), said values (eg example, of Fd) selected to cause one or more patterns of cylinder activation, wherein said patterns only have frequency content above the minimum allowable frequency. The controller may be configured to determine a minimum allowed frequency (eg, 5 Hz, 10 Hz), and subsequently create a quantized list of the plurality of discrete demand values (eg, Fd), those values (eg, of Fd) selected to cause one or more cylinder activation patterns, wherein said patterns only have frequency content above the minimum allowed frequency.

The quantified list of allowable demand values may depend on the number of cylinders in the machine and/or the operating speed of rotation of the rotating shafts of the machine (as the speed of rotation of the rotary shaft and the number of cylinders will affect the frequencies present for a given demand value) For each demand value in the list it is possible to calculate the minimum frequency present. While the machine is running, the (filtered) demand signal is transmitted to the hydraulic machine controller. The method may comprise receiving a value representative of a request (for example Fd) and a measured speed of rotation of the rotary axis and consulting a lookup table (in order to thereby determine the lowest frequency present as a result). of the patterns of active and inactive cycles of the volume of the working chamber for said demanded Fd), by means of the selection of a size of window corresponding to the lowest frequency present, the calculation of a moving average (for example, the mean) of a measured control signal (e.g. pressure) (i.e. from the measured pressures within the window) and thereby fully attenuate the lowest frequency present in the control signal (derived of the pattern of active or inactive cycles of the volume of the working chamber). Since the moving average filter is a type of low-pass filter, all other frequencies above the minimum frequency will also be partially attenuated.

Typically, the method comprises dynamically adjusting the size of the selected window. The controller may be configured to dynamically adjust the size of the selected window.

Normally, the size of the window depends on the lowest frequency present (which in turn depends on the speed of rotation of the rotary axis). The window size can be timed (ie adjusted) once per revolution signal.

By dynamically adjusting the window size (typically to match the inverse of the lowest known frequency), the moving average filter can fully attenuate this frequency from the received demand or control signal. This has the advantage of improving prime mover speed and allowing a hydraulic machine to run closer to the speed (or torque) limit of the prime mover for a greater percentage of the time it is in use.

It may be that one or more of the resonant frequencies (and/or ranges of undesirable frequencies) do not vary with the speed of rotation of the rotating shaft. However, it may be that one or more of the resonant frequencies (and/or ranges of undesirable frequencies) vary with the speed of rotation of the rotating shaft. One or more of the resonant frequencies (and/or ranges of undesirable frequencies) may vary as a function of a parameter, which may be independent of the speed of rotation of the rotating shaft. For example, one or more of said resonant (eg ram) frequencies may depend on the position of a ram or boom. The one or more parameters may be parameters measured by one or more sensors.

This procedure is useful for attenuating the known frequencies of a hydraulic machine that is controlled to produce a quantized displacement. The low-frequency pattern of continuous scrolling can, in some cases, cause large window sizes (for example, if the frequency is very low) and, as such, considerable delay in control. Furthermore, since the displacement is continuous (and not in fixed steps) the actuation patterns of the working chamber do not reach a state of repetitive pattern.

It may be that at least one of said filters receives a signal and outputs a signal, where the output signal does not change as a result of the input signal changing within a band. Typically, the input signal is the control signal (for example, measured pressure, flow, or actuator position or speed) or a signal derived from it. Normally the output is the demand signal or is further processed to give the demand signal.

Contributions from individual working chamber drives can cause a pulsatile pressure ripple. Since changes in pressure are used to enable decision making (for example, an Fd change decision, etc.), small changes in pressure caused by pulsatile pressure ripple they could be misinterpreted as real and deliberate pressure changes, which could lead to a wrong decision.

It may be that the output of the filter remains at a substantially constant value until the input value changes to be outside a predetermined rejection interval ("deadband") of the output. It may be that the output of the filter does a step change (for example, to the current value of the input) when the input values change to be outside the default rejection range of the output.

This has the advantage that pulsatile pressure ripple (or variations in other measured variables used for feedback) do not influence the torque control of the hydraulic machine, but large changes in pressure (not ripple), or other control signals, are taken into account.

The default rejection interval may be selected in response to an expected interval of pressure pulsing. The predetermined rejection range may comprise a pressure range of at least 10 bar, at least 20 bar or at least 30 bar (eg 20 bar). Those skilled in the art will appreciate that the predetermined reject range is typically selected based on the specific hydraulic system in which it is intended to be used. However, the predetermined rejection interval can be optionally adjustable, for example, if the compliance and/or rigidity of the hydraulic system changes (for example, when an accumulator is provided).

Motors and pumps take a finite amount of time to respond to a change in demand. Pumps (eg ECMs) tend to respond more quickly than motors.

Accordingly, another aspect of the invention provides an apparatus comprising a prime mover (eg an engine) and a plurality of hydraulic actuators, a hydraulic machine having a rotatable shaft driven by the prime mover and comprising a plurality of chambers working chambers that have a volume that varies cyclically with the rotation of the rotary axis, a hydraulic circuit that extends between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators,

each working chamber of the hydraulic machine comprises a low-pressure valve that regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve that regulates the flow of hydraulic fluid between the working chamber and a high pressure manifold,

the hydraulic machine is configured to actively control at least the group low-pressure valves of one or more working chambers to select the net displacement of hydraulic fluid per each working chamber in each working chamber volume cycle, and by Therefore, the net displacement of hydraulic fluid through the group of one or more working chambers, in response to a demand signal,

The apparatus comprises a main engine speed controller operable to regulate the main engine speed in response to a main engine control signal, wherein the apparatus is configured to regulate the main engine control signal by means of a signal. related to a demand for pair.

The invention extends to a method of operating the apparatus comprising regulating the speed of the prime mover in response to a prime mover control signal, wherein the prime mover control signal is regulated by means of power supply. a signal related to a demand for torque.

The torque demand is typically a torque demand from the hydraulic machine, although it may be a torque demand from another component, for example from a component that is driven by the hydraulic machine.

The method may comprise regulating the prime mover at a target speed responsive to input from the operator (usually setting the target speed). Typically, the prime mover's speed governor regulates the desired speed based on input from the operator (who usually sets the desired speed). The signal related to a torque demand may be the measured property of the hydraulic circuit or of one or more actuators, or an operating input. The signal related to the motor torque demand may be associated with a certain pressure or flow rate. The signal related to the torque demand may be a filtered signal. The prime mover speed governor may be a prime mover controller (eg, comprising one or more processors executing stored program code).

Typically, the prime mover control signal is regulated to cause the prime mover governor to increase the applied prime mover torque in response to an increase in torque demand.

Typically, the method comprises regulating, and the apparatus is configured to regulate, the prime mover control signal to cause the prime mover governor to increase the applied prime mover torque and then, after a delay period, (and optionally depending on speed and/or pressure and/or Fd, etc.), regulate the demand signal to increase the displacement of the working fluid and the torque exerted by the group of one or more working chambers. Typically this is such that the increase in torque exerted by the one or more work chambers is applied simultaneously with (eg at the same time as) the increase in torque from the main motor.

The procedure may comprise calculating a demand from the hydraulic machine, making the motor prime mover increases torque to meet the demand, delaying the torque demand of the hydraulic machine until the point where the prime mover can meet the demand, and thereafter both the pump load and the prime mover torque are applied to the prime mover. same time without causing any net torque on the y-shaft to thereby maintain prime mover speed. The apparatus may be configured to calculate a hydraulic machine demand and cause the prime mover to increase torque to meet the demand, while delaying the hydraulic machine torque demand until the point where the prime mover can meet the demand. demand, and subsequently both the pump load and the prime mover torque are applied at the same time without causing any net torque on the shaft and thereby maintain the prime mover speed.

When the prime mover is an engine, this has the advantage of improving the stability of the engine by preventing it from falling.

The invention extends to a method of operating the apparatus comprising applying a torque limit to the one or more hydraulic machines. The apparatus may comprise a controller that may be operable to apply a torque limit to the one or more hydraulic machines.

Typically, the torque limit of the hydraulic machine will be below a torque limit of the main motor in dependence on a current speed of the main motor (for example, the rotational speed of the rotary shaft). The controller (eg, a prime mover controller (eg, motor controller) or hydraulic machine controller) may be operable to receive a measurement of current prime mover speed and determine a torque limit. of the prime mover, typically with reference to a lookup table containing a torque speed curve. The method may comprise receiving a current speed measurement from the main motor and determining a corresponding torque limit from the main motor, typically with reference to a lookup table containing a torque speed curve.

Alternatively or additionally, the controller (of the prime mover or hydraulics) may be operable to receive a measurement of the current speed of the machine and determine a corresponding torque limit of the machine, typically with reference to a lookup table containing a torque speed curve. The method may comprise receiving a current speed measurement from the machine and determining a corresponding torque limit from the machine, typically with reference to a lookup table containing a torque speed curve.

When the prime mover is an engine having a turbocharger, the prime mover controller may further take into account, and the method may comprise taking into account, one or more parameters associated with the turbocharger. For example, where the turbocharger limits how quickly an engine changes its torque output (for example, due to turbocharger induction system time constant and/or turbocharger inertia), the main engine controller can applying, and the method may comprise applying, an additional temporary torque limit that is less than the torque limit of the main motor. The hydraulic machine controller may be operable to cause the hydraulic machine to implement, and the method may comprise implementing one or more (typically two or more) rates of change of torque, optionally RPM dependent, the current torque , the additional temporary torque limit, the maximum torque of the main motor and/or a safety factor. The one or more torque rates typically comprise (eg, at least) a first torque rate and a second torque rate. The hydraulic machine controller may be operable to implement, and the method may comprise implementing, a first rate of change of hydraulic machine torque when the prime mover is operating below an additional temporary torque limit and a second rate of change. torque change when the main motor is operating at or above the additional temporary torque limit, optionally (eg, typically) wherein the first rate of torque change is faster than the second rate of torque change.

When the prime mover is configured to provide displacement to two or more actuators, the controller (for example, the hydraulic machine controller) may be configured to apply, and the procedure may comprise, applying a different torque limit in the ECM in response to a demand associated with each actuator. Alternatively, the controller (eg, the hydraulic machine controller) may be configured to apply, and the method may comprise applying, substantially the same torque limit to the prime mover in response to a demand associated with each actuator.

The controller (for example, the hydraulic machine controller) may receive one or more signals (for example, signals associated with a measurement of speed error, available torque, motor load, one or more pressure measurements, etc.) in use and therefore determines the current torque applied to the ECM and can subsequently increase or decrease the torque limit in response to the one or more signals. The method may comprise receiving one or more signals (for example, signals associated with a measurement of speed error, available torque, motor load, one or more pressure measurements, etc.) and thereby determining mode the current torque applied to the ECM and may comprise the further increase or decrease of the torque limit in response to the one or more signals.

The controller (for example, the hydraulic machine controller) can be configured to receive a measurement of the outlet pressure and a value representative of the displacement demand, and can therefore calculate an estimate of the exerted torque (for example , by calculating a product of outlet pressure and displacement demand). The procedure may comprise receiving an outlet pressure measurement and a representative value of the displacement demand and the calculation of an estimate of the exerted torque (for example, by means of the calculation of a product of the outlet pressure and the displacement demand).

The controller (for example, the hydraulic machine controller) may be configured to receive a measurement of the rotational speed of the rotary shaft and a value representative of the displacement demand, and thereby calculate an estimate of the delivered flow (for example , by calculating a product of the displacement demand and the speed of rotation of the rotary shaft). The procedure may comprise the receipt of a measurement of the rotation speed of the rotary axis and of a representative value of the displacement demand and, therefore, the calculation of an estimate of the delivered flow (for example, by means of the calculation of a product of the displacement demand and the speed of rotation of the rotating shaft).

When the controller (for example, the controller of the hydraulic machine) is configured to receive a measurement of the speed of rotation of the rotating shaft and to calculate an estimate of the exerted torque, the controller can also calculate an estimate of the absorbed mechanical power. The method may comprise receiving a measurement of the speed of rotation of the rotating shaft and calculating an estimate of the exerted torque and, optionally, calculating an estimate of the absorbed mechanical power.

When the controller (eg, hydraulic machine controller) is configured to receive an outlet pressure measurement and calculate an estimate of delivered flow, the controller may further calculate an estimate of fluid power. The method may comprise receiving an outlet pressure measurement and calculating an estimate of the delivered flow rate and, optionally, calculating an estimate of fluid power.

Optionally, when the controller (for example, the hydraulic machine controller) is configured to calculate an estimate of the torque exerted and/or the flow delivered and/or the mechanical power absorbed and/or the power of the fluid, the controller may be configured to receive one or more additional parameters associated with the hydraulic machine (for example, volumetric displacement and mechanical efficiency, optionally as a function of pressure, speed, temperature, etc.) and may take into account one or more additional parameters to thereby improve the accuracy of the estimate. The procedure may comprise receiving one or more additional parameters associated with the hydraulic machine (for example, volumetric displacement and mechanical efficiency, optionally taking into account (for example, measurements of) pressure, speed, temperature , etc.) to thereby improve said estimation of the absorbed mechanical power or the power of the fluid.

The controller (for example, the hydraulic machine controller) may be configured to receive a measurement of the actual pressure, calculate a limit of displacement required to exert torque at that pressure, and limit the output displacement so that it does not exceed the travel limit to thereby limit the torque. The method may comprise receiving a measurement of the current pressure, calculating a displacement limit required to exert torque at that pressure, and limiting the output displacement so that it does not exceed the displacement limit to limit the current pressure. thus the torque.

The controller (for example, the hydraulic machine controller) may be configured to receive a measurement of the current rotational speed of the rotary shaft, calculate a travel limit required to deliver a flow at that rotational speed of the rotary shaft, and limit the output displacement so that it does not exceed the displacement limit to thereby limit the flow. The method may comprise receiving a measurement of the current rotational speed of the rotary shaft, calculating a displacement limit necessary to deliver a flow at that rotational speed of the rotary shaft, and limiting the output displacement so that it does not exceed the offset limit to thereby limit the flow.

The controller (for example, the hydraulic machine controller) may be configured to receive a measurement of the current pressure, and the current speed of rotation of the rotating shaft, and calculate a limit of displacement required to absorb a power at that pressure and rotation speed and limit the output displacement (so that it does not exceed the displacement limit to thereby limit the power). The method may comprise receiving a measurement of the current pressure, and current rotational speed of the rotating shaft, and calculating a displacement limit necessary to absorb a power at said pressure and rotational speed and limit the displacement of output (so that it does not exceed the offset limit to thereby limit the power).

The controller (eg, the hydraulic machine controller) may be configured to receive, and the method may comprise receiving, one or more signals indicative of a displacement, flow, pressure, power, and/or torque demand. The one or more signals may be limited by one or more limiting functions, the one or more limiting functions typically being dependent on one or more additional parameters (eg, temperature). For example, the controller may receive, and the method may comprise receiving, a signal indicative of a flow demand of 100 L/min, wherein the signal indicative of a flow demand is limited by a pressure limit of 200 bar and a power limit of 20 kW, and the machine can be configured to output flow in response to that flow demand, up to a limit of 100 L/min, only when a pressure measurement indicates that the pressure is at or below 200 bar and a power measurement indicates that the power output is at or below 20 kW. The one or more limiting functions may be non-limiting functions. linear.

The controller (eg, the hydraulic machine controller) may be configured to receive (and/or calculate) an estimate of the available torque from the main motor (eg, the motor) and set a hydraulic machine torque limit in in which the torque limit depends on the speed of the main motor. The method may comprise receiving and/or calculating an estimate of the available torque from the prime mover (eg motor) and setting a hydraulic machine torque limit where the torque limit is speed dependent. of the main engine. For example, at relatively low main motor speeds, the hydraulic machine torque limit can be selected to be zero to prevent stalling (eg, motor stalling); on the contrary, at relatively high speeds of the main motor, the torque limit of the hydraulic machine can be selected to prevent damage to the machine. Alternatively, at relatively high main engine speeds, the machine's hydraulic torque limit can be increased to thereby increase the machine load, causing the main engine speed to decrease until the machine load matches the main engine speed. torque available from the main motor. This has the advantage of providing a temporary increase in available power until the main engine speed is reduced. Those skilled in the art will appreciate that a relatively high or low main engine speed will depend on the individual main engine and/or vehicle.

Where a vehicle comprises a prime mover in the form of an engine, the engine has a controller comprising an engine governor, the engine governor may comprise a variable speed set point, and the controller may be configured to receive a droop measurement. of engine speed to thereby calculate an estimate of engine load. The method may comprise implementing a variable engine speed set point. The method may comprise receiving a measurement of engine speed droop and therefore calculating an estimate of engine load. Accordingly, the torque limit of the hydraulic machine may be limited by a limiting function in which the limiting function depends on the measurement of engine speed droop.

It may be that there are a plurality of said groups of working chambers having respective demand signals, and the controller implements the torque limit while independently varying the demand signals of two or more of said groups of working chambers. This allows the controller to prioritize, and the method may comprise prioritizing, the pairing of one or more of said working camera groups, or keeping the pairing of one or more of said working camera groups to a predetermined pair (for example, guaranteed, as long as sufficient motor torque is available).

It may be that there are a plurality of said groups of working chambers (typically connected to a plurality of respective groups of one or more actuators) having respective demand signals, and in which the controller implements the torque limit, and the procedure comprises implementing the torque limit, while prioritizing the pair of one or more of said groups of working chambers over the pair of one or more of said groups of working chambers by varying the respective demand signals of the respective groups of one or more chambers of work.

It may be that there are a plurality of said groups of working chambers having respective demand signals, and in which the controller implements the torque limit, and the method comprises implementing the torque limit, while prioritizing the torque of one or more than said groups of working chambers on the pair of one or more of said groups of working chambers.

It may be that there are a plurality of such groups of working chambers and where, at least in some circumstances, the controller causes, and the method comprises causing, one or more of said groups of working chambers to perform cycles. motorization while another or other of said groups of work chambers carry out pumping cycles, in order to thereby use the motor torque to complement the motor torque and thus help the torque generated by said pumping.

It may be that the controller limits the torque, and the method may comprise limiting the torque, to implement a maximum torque rate of rotation, either of the group of one or more working chambers or of the hydraulic machine as a whole.

Description of the drawings

An exemplary embodiment of the present invention will now be described with reference to the following Figures, in which:

Figure 1 is a hydraulic circuit diagram for an excavator with negative feedback control, which has an ECM;

Figure 2 is a schematic diagram of an ECM in accordance with the invention;

Figure 3A is a flowchart showing changing response time for an ECM;

Figure 3B is a flowchart showing changing response time for an ECM;

Figure 4 is a diagram of the hydraulic circuit of a forward control excavator, which has an ECM;

Figure 5 is a logic diagram of the inputs supplied to an excavator;

Figure 6 is a schematic diagram of the hydraulic motor valve control module;

Figure 7 is a schematic diagram of a hydraulic excavator.

Figure 8A is a plot of engine torque vs. RPM for a system that operates a factor of safety at an open loop torque limit set point to prevent engine droop or stall (as described). known in the art) and Figure 8B is a plot of engine torque vs. RPM for a system in accordance with the invention, the system operating an engine below its engine speed set point to avoid thereby engine stall or stall mode;

Figure 9 is a graph of input and output over time in response to step demand, indicating the time constant of the system;

Figure 10 is a graph of an example torque limit curve as a function of pressure;

Figure 11A is a graph of pressure vs. flow for a given flow demand and Figure 11B is a graph of pressure vs. flow for a given displacement demand;

Figure 12 is a graph of engine torque versus RPM indicating power demand and taking into account minimum and maximum engine speeds to prevent stalling and internal machine damage; Figure 13 is a graph of engine torque vs. RPM indicating engine torque vs. speed limit of a machine and engine torque vs. speed limit of an engine where the torque limit of a machine increases at high speed;

Figure 14 is a graph of engine torque vs. RPM, where an engine governor provides an engine speed set point so that total engine load can be estimated with reference to engine droop ;

Figure 15 is a graph of engine torque versus RPM for an engine with a limited rate of change of engine torque output;

Figure 16 is a graph of torque versus time with various imposed torque limits;

Figures 17A and 17B are graphs of torque as a function of time for varying demands of two hydraulic actuators in a system having a torque limit; Y

Figure 18 is a graph of the quantized output in response to a received demand signal as a function of time.

It must be recognized that hydraulic circuit schematics for practical designs of mobile and static hydraulic equipment, especially heavy construction equipment, are notoriously complex. For the sake of simplicity and clarity, the figures omit features that those skilled in the art will appreciate may be present, such as the usual pressure relief valves, drain lines, flow control, load hold hydraulics, the damping of the hydraulic load, the accumulators, the conforming fluid volumes, among other aspects.

Detailed description of an exemplary embodiment

A number of exemplary embodiments in which the prime mover is a motor will be described below. Those skilled in the art will appreciate that other prime movers may also be selected as appropriate.

Referring to Figure 1, a first exemplary embodiment of the invention is a vehicle in the form of an excavator. Known excavators usually have fluid manifolds which extend through a central passage in the valve 8 to a fluid container 2 (usually an atmospheric pressure tank) via a butterfly valve 5. Such excavators usually also have at minus a pressure monitor 4, an engine 22 (in this example, a diesel engine having an engine controller 26), which functions as the main engine, a controller 14, and a number of user input means (in this example , joysticks 10). The user input means is typically located in an operator's cab and coupled to the open center manifolds 8 through which the fluid manifold extends. The actuators 6 (for example, the actuators of a ram, a swing motor, caterpillar motors, etc.) can be hydraulically connected to the pump outlet when their respective valves 8 are activated by means of the joysticks 10.

In the first embodiment of the invention, the machine further has (for example, at least) two electronically commutated hydraulic machines 32 of the type generally shown in Figure 2, in rotational mechanical communication with the motor 22 to transfer torque. through one or more rotational axes.

Figure 2 is a schematic diagram of a hydraulic machine 32 in the form of an electronically commutated hydraulic machine (ECM) comprising a plurality of working chambers with cylinders 34 having working volumes 36 defined by the inner surfaces of the cylinders and pistons 40. which are driven from a rotary shaft 42 by an eccentric cam 44 and which move within the cylinders to cyclically vary the working volume of the cylinders. The rotating shaft is firmly connected to a drive shaft and rotates with it. A shaft position and velocity sensor 46 determines the instantaneous angular position and rotational speed of the shaft, and via a signal line 48 informs the machine controller 14, which enables the machine controller to determine the instantaneous phase of the cycles of each cylinder.

Each of the working chambers is associated with low pressure valves (LPVs) in the form of electronically actuated front sealing poppet valves 52, which have an associated working chamber and are operable to selectively seal a channel extending from the working chamber to a low pressure hydraulic fluid manifold 54, which may connect one or more, or even all of the working chambers as shown here, to the ECM low pressure hydraulic fluid manifold 54. LPVs are normally open solenoid-actuated valves that open passively when the pressure inside the working chamber is less than or equal to the pressure inside the low-pressure hydraulic fluid manifold, i.e., during an intake stroke, to put the working chamber in fluid communication with the low pressure hydraulic fluid manifold, but can be selectively shut off under active control of the controller through the lines Control areas 56 of the ^l P ^v to remove the work chamber from fluid communication with the low pressure hydraulic fluid manifold. The valves may alternatively be normally closed valves.

The working chambers are each associated with a respective high pressure valve (HPV) 64, each in the form of a pressure actuated delivery valve. The HPVs open outwardly from their respective working chambers and each is operable to seal a respective channel extending from the working chamber to a high pressure hydraulic fluid manifold 58, which may connect one or more working chambers, or even all of them as shown in Figure 2, to the high pressure hydraulic fluid manifold 60. HPVs function as normally closed pressure opening check valves that open passively when the pressure within the working chamber work exceeds the pressure inside the high pressure hydraulic fluid manifold. The HPVs also function as normally closed solenoid-actuated check valves which can be selectively held open by the controller via the HPV control lines 62 once the HPV is opened by pressure within the associated working chamber. Normally, the regulator cannot open the high pressure valve against the pressure in the high pressure hydraulic fluid manifold. In addition, the high-pressure valve can be opened under the control of the controller when there is pressure in the high-pressure hydraulic fluid manifold but not in the working chamber, or it can be partially opened.

In a pumping mode, the controller selects the net rate of displacement of hydraulic fluid from the working chamber to the high pressure hydraulic fluid manifold by the hydraulic motor actively closing one or more of the LPVs typically near the point of maximum volume. in cycling the associated working chamber, closing the path to the low pressure hydraulic fluid manifold and thereby directing hydraulic fluid out through the associated HPV on the subsequent contraction stroke (but not actively holding open HPV). The controller selects the number and sequence of LPV closings and HPV openings to produce flow or create shaft torque or power to satisfy a selected net rate of travel.

In a powered mode of operation, the hydraulic machine controller selects the net rate of displacement of hydraulic fluid, displaced by the hydraulic machine, through the high-pressure hydraulic fluid manifold to actively close one or more of the LPVs. shortly before the minimum volume point in the cycle of the associated working chamber, closing the path to the low pressure hydraulic fluid manifold which causes the hydraulic fluid in the working chamber to be compressed for the remainder of the contraction stroke . The associated HPV opens when the pressure across it equalizes and a small amount of hydraulic fluid is directed out through the associated HPV, which is held open by the hydraulic machine controller. The controller then actively holds the associated HPV open, typically to near the maximum cycle volume of the associated working chamber, to admit hydraulic fluid from the high-pressure hydraulic fluid manifold to the working chamber and apply torque. of torque to the rotating shaft.

In addition to determining whether to close or hold open the LPVs on a cycle-by-cycle basis, the controller is operable to vary the precise phase of HPV closure with respect to the variation in working chamber volume and thereby select the net rate displacement of the hydraulic fluid from the high pressure manifold to the low pressure manifold or vice versa.

Arrows on ports 54, 60 indicate hydraulic fluid flow in power mode; in pump mode the flow is reversed. A pressure relief valve 66 can protect the hydraulic machine from damage.

Returning to Figure 1, each joystick 10 is coupled to an open center spool valve 8 to regulate the flow through it. The pressure monitor 4 measures the pressure 24 of the hydraulic fluid in the line at a position upstream of the accelerator (ie, at a position downstream of the group of hydraulic actuators). The controller 14 regulates the displacement of the hydraulic fluid through a group of working chambers defined by cylinders in which the pistons move in use (the working chambers are in fluid communication with the group of hydraulic actuators 6) in response to pressure. measurement 24. This can be done in a feedback loop (for example, if the pressure monitor 4 registers a pressure that is below a desired level, the controller 14 can increase the displacement of the hydraulic fluid and thus the pressure 24 will increase). In some excavators, the controller 14 may also take into account a flow demand 16 and an output pressure from the hydraulic machine 18 and may include a torque control module 20 and a negative flow control module 12.

The two ECMs 32 are each controlled by an ECM controller 50 so that cycle-by-cycle decisions can be made as to whether or not an ECM will displace hydraulic fluid. Each ECM can transmit hydraulic fluid through a fluid manifold and through two open center manifolds 8 and to a reservoir 2 at atmospheric pressure. Each open center spool valve is in electronic communication with a joystick 10 through which the user can enter a command. The manifolds have normally open centers, operable to close when a command is entered via a joystick, in which case the hydraulic fluid is diverted to a hydraulic actuator 6 (in this case shown as a single hydraulic actuator although it will be appreciated that it would be possible to divert hydraulic fluid to multiple hydraulic actuators) to thereby meet a demand. Pressure sensors 4 detect the pressure of the hydraulic fluid between each ECM 32 and reservoir 2. Although two open center manifolds are shown connected to each of the two machines 32, it will be appreciated that this number can vary up or down. and may differ between the two electronic commutation machines.

The oil, which functions as hydraulic fluid, is supplied from a reservoir at the inlet side of the hydraulic machine through a low-pressure fluid working manifold. The pressure in the high pressure manifold is detected by means of a pressure sensor.

The excavator also has an engine controller 26 and a system controller 14. The system controller controls the ECM by sending control signals (for example, travel demand signals 16) to the machine controller to regulate the displacement. The control signals demand a displacement from the ECM, expressed as a fraction of the maximum displacement, Fd, (the displacement demand). The absolute volume of displacement (volume of hydraulic fluid displaced per second) is the product of the fraction of the maximum displacement, the maximum volume that can be displaced per cycle of one working chamber, the number of working chambers, and the rate of cycles. of the volume of the working chamber. Thus, the hydraulic machine controller can regulate the applied torque and the pressure in the high pressure hydraulic fluid manifold. The pressure in the high pressure hydraulic fluid manifold increases when the displacement rate of the hydraulic fluid increases faster than the hydraulic fluid is supplied to a hydraulic actuator and vice versa. Multiple hydraulic actuators may be in fluid communication with the high pressure fluid manifold. The hydraulic machine controller takes into account the displacement of each ECM to regulate the torque.

The controllers 50 of the ECMs 32 are operable to make cycle-by-cycle decisions as to whether each cylinder in the machine should complete an on or off cycle. These decisions are made based on a hydraulic fluid displacement demand associated with a given hydraulic actuator (or combination of hydraulic actuators). Consequently, there is a high frequency of decisions during the operation of such an ECM, and a correspondingly short response time of the machine when a hydraulic fluid displacement demand is applied or changed.

Referring to Figure 4, in an alternative example of an excavator, each joystick 10 is (in addition to being coupled to an open central distributor 8) in electronic communication with the system controller 14. This example of an excavator can therefore function without the feedback loop shown in Figure 1, in which case the system controller receives signals from the joysticks indicative of a demand and increases or decreases the displacement of the hydraulic fluid in response to that demand.

Referring to Figure 5, for an ECM such as that of Figure 2, decisions are made regarding the displacement of the pump 124A, 124B (for each electronically commutated hydraulic machine) based on various inputs including (although they are not necessarily limited to) an engine speed set point 126, an actual engine speed 128, an engine torque safety factor 130, an outlet pressure of each hydraulic machine 132A, 132B, and a system pressure negative flow control valve associated with each hydraulic machine 134A, 134B.

By subtracting an engine speed set point from an actual engine speed 136, an engine speed error 138 is calculated. The engine speed set point 126 is further supplied to a lookup table 140 for calculating from In this mode the maximum available engine torque 142 is compared 144 with a torque safety factor of 130 to calculate a maximum ECM torque 146 that can be applied to cause an acceptable level of engine droop.

The output pressure of each hydraulic machine is filtered 150A, 150B to remove the lowest frequencies that arise due to quantization and the flow control negative pressure is input to another lookup table 152A, 152B to thereby calculate a maximum flow offset 154A, 154B. One of the filtered outlet pressures is also limited to 158. The maximum flow displacement for each hydraulic machine is added to 156, and the corresponding torque is calculated. The difference between the actual engine speed and the speed setpoint is determined, a gain is applied, and a torque offset is applied to the maximum torque allowed by the ECM. This torque limit is compared to the engine's maximum torque output 148 and the ECM's torque demand is limited to this value (to ensure that excessive engine droop and stall can be avoided) before sending the start signal. torque demand to the hydraulic machine controller. In response to the torque demand signal, the hydraulic machine controller makes a 160 cycle-by-cycle decision as to whether each hydraulic machine should complete an active cycle or an inactive cycle. Depending on current conditions (including engine speed set point, actual engine speed, engine torque safety factor, outlet pressure and negative flow control pressure, and/or other factors) The hydraulic machine controller can cycle the first hydraulic machine on while the second hydraulic machine is cycled off, or it can cycle the first hydraulic machine on while the second hydraulic machine is cycled off. it is cycled on, or it can cause both the first hydraulic machine and the second hydraulic machine to be cycled off.

Figure 6 is a schematic diagram of the machine controller 50 of the motor 32. A processor 70, such as a microprocessor or microcontroller, is in electronic communication via a bus 72 with memory 74 and an input-output port 76. Memory 74 stores a program 78 that implements execution of a displacement determination algorithm to determine the net volume of hydraulic fluid to be displaced by each working chamber in each working chamber volume cycle, as well as one or more variables 80 that store an accumulated offset error value. The memory also stores a database 82 that saves data relating to each working chamber, such as the angular position of each working chamber 84 and whether or not it is deactivated 86 (for example, because it is broken). The database may store the number of times each working chamber has been subjected to an active cycle 88. The database may store one or more lookup tables. The program may comprise program code 90, which functions as the resonance determining module, which calculates one or more undesirable frequencies and/or intervals of undesirable frequencies.

The controller receives input signals that include a displacement demand signal 94, an axis position (ie, yaw) signal 90, and typically a pressure measurement 92 in the high pressure manifold. It can also receive a speed signal, as well as control signals (such as start or stop commands, or high pressure fluid manifold pressure increase or decrease before or during start or stop). , or other data as necessary.

Figure 7 is a schematic diagram of an example embodiment of a vehicle 170, in this case an excavator with a hydraulically powered arm. The hydraulic drive arm is formed by a first articulated portion 174A and a second articulated portion 174B. Each of the first and second hinged portions can be independently actuated. Other examples of suitable vehicles include telehandlers, backhoes, etc.

Figure 3A is a flow diagram of a system according to the invention, in which the system takes an initial pressure value 114 in the negative flow control system 100, the output of which is compared to a maximum pressure 116 giving a value of Fd 118 that is fed to a low pass filter 102 (in this case a low pass filter with a time constant of 300 ms). The output of this filter is passed to a speed limiter 106 which also takes a pressure measurement 104, an actual motor speed measurement 110, and a motor speed setpoint 112. This allows calculation of a torque limit by of a torque limiter 108 and therefore a final output demand is transmitted to the electronically switched machine(s) 118. Therefore, the present invention provides the function of emulating the behavior of an analog pump (for example, a conventional swash plate pump).

Electronic switching machines often have very short response times. This is because it can be decided whether a working chamber is to be cycled on or cycled off for each working chamber in each volume cycle of the working chamber. The working chambers are typically distributed around the rotary axis, so there are multiple decision points (eg, 8 or more or 12 or more) per rotation of the rotary axis. An electronic switching machine rotating at 1,500 rpm with working chambers spaced 24° apart around the rotary axis can react to a change in demand in 2.7 ms, for example. This very fast response time may be preferable in some cases, but can sometimes cause undesirable instabilities in the system that can have a negative impact on controllability.

For example, when a system is provided with high gain proportionally with low compliance, the system will be sensitive to delays (for example, delays caused by the time it takes to carry out a measurement of the signal (caused by filtering). or delays caused by hardware response times). When such a system is sensitive to delays of 2 to 3 ms, it may be impractical to reduce such delays to an acceptable level. Accordingly, the invention provides a method whereby the output response is delayed to allow time for the system to stabilize. A low-pass filter is used to filter the output demand (for example, with approximately 100 to 300 ms). As a result, the time it takes for the system to respond to a stage input it is longer, however in practice in many applications this is not noticeable to an operator (eg user of an excavator) in use.

Figure 3B is a flowchart of a system with the characteristics of 3A and additional inputs of currently measured motor speed 120 and a motor speed set point 122. These are compared to calculate a motor speed error. . In addition, a database 124 is provided, which contains a lookup table indicating an engine speed dependent torque limit.

Figure 9 is a graph indicating how a time constant is typically calculated (and defined) in the art. When a step demand is introduced into a system, it usually takes a finite amount of time for the system to respond to the demand. The time constant is defined as the time it takes for the output of the system to reach approximately 63% (ie 1-1/e) of the total change required by the input.

Because ECMs can react quickly (in the sense that decisions are made on a cycle-by-cycle basis for each cycle of each work chamber and, optionally, independently of each cycle of each other work chamber) flow control systems negative that operate with ECM can become unstable in response to rapidly changing demands. To avoid this, the invention applies a response damper (in this example, in the form of a filter). This response damper introduces a 300 ms delay in the response time of the ECM. Those skilled in the art will appreciate that any delay time may be selected to meet the requirements of particular machines.

In addition, the invention also provides an override mode that overrides the response damper to prevent engine stalling and to prevent engine droop.

The ECU controls the engine speed so that the engine speed is as close as possible to an engine speed set point, in order to respond to changes in torque demand. When an increase in demand is applied to the engine, a reduction in engine speed (i.e. engine droop) typically occurs and the ability to recover engine speed after such an increase in demand depends (at a minimum) on the engine speed. engine speed set point, ECU response time and fuel system.

During operation, the ECU receives a signal indicative of a desired value of torque or speed from an external sensor, for example an external sensor configured to measure the position of a pedal, or via a signal provided by a CANbus. The ECU receives signals from a rotational speed sensor and calculates a rotational speed of the rotating shaft. Therefore, the ECU is operable to maintain the rotational speed of the rotary shaft to meet a desired speed demand through closed-loop control.

The ECU is also configured to control the fuel injection components of the engine through control of one or more hydraulic machines, injectors, and/or nozzles in response to one or more received signals, including a signal indicative of crankshaft position. , a fuel temperature, a fuel pressure and/or a mass-air flow, to thereby satisfy a desired torque demand.

In embodiments where the engine has one or more turbochargers (or, for example, superchargers and/or exhaust gas recirculators), the ECU is configured to monitor one or more received signals indicative of mass-air flow and/or or from the air charge pressure and to regulate the flow of air supplied to the cylinders in response to thereby satisfy a desired torque demand.

In addition, the ECU is configured to receive signals from and supply signals to additional systems including a traction control system (in some embodiments a transmission shift control system). The ECU receives signals from additional systems and supplies them via a CANbus and can modify vehicle and/or engine behavior in response.

Referring to Figure 8A, in order to prevent engine stall, or stall, industrial vehicles (eg excavators) are known to operate with an open loop torque limit. This open loop torque limit is below the maximum torque of the motor 224 and represents the maximum summed torque that all hydraulic machines in combination can provide for a given engine speed (optionally for an engine speed set point). Consequently, there is a range 228 of acceptable engine speeds for a given engine torque. For example, if a vehicle had two hydraulic machines powered by the same motor, each hydraulic machine could be limited in such a way that it could provide at most 45% of the torque limit, thus the sum of the torque of both hydraulic machines would be 90% of the maximum torque (ie a safety margin of 226 is provided). This choice is made so that the absolute torque limit of the machine is never exceeded (for example, when excessive demands are introduced) to thereby prevent the vehicle from stalling.

However, by necessity this introduces inefficiencies (since the machine cannot operate at its maximum torque 224 for a given motor speed set point). Accordingly, referring to Figure 8B, the present invention provides a method of modulating torque limit as a function of motor speed error (where motor speed error is defined in equation 1, above). In this case, an increase in hydraulic machine torque above the available instantaneous torque 234 causes the engine speed to decrease, resulting in a proportional increase in engine speed error 240. The engine speed controller detects the error of engine speed and responds 236, providing more fuel to thereby maximize available torque. The result is that the engine speed approaches a stable value (below the engine speed set point 232) and the engine delivers its maximum torque.

During operation, the change in motor speed in response to an applied load is motor droop. Droop is usually expressed in percent and can be calculated from engine no-load speed ( ^Snoload ) and full-load speed (Sfullload) ^, according to the following equation:

% droop = ( S ^noload _ — S ^{full load} ) ^X 100 (2)

^{full charge}

In an example embodiment of the invention, a power torque demand is sent from the hydraulic machine controller to the ECU and the ECU calculates what engine load the engine demand will require before the hydraulic machine applies the load. This has the advantage of avoiding (or at least limiting) engine droop.

The maximum torque that a motor can supply does not have to be the same as the maximum torque of a hydraulic machine driven by the motor. In the event that a hydraulic machine has a shorter characteristic response time than a motor, it is advantageous to artificially delay the response time of the ECM. Thus, a demand is anticipated before load is applied to the engine, allowing time for engine speed to increase to the point where it can meet the demand, and load is applied to the engine only when engine speed has increased. up to that point.

Those skilled in the art will appreciate that the response time of the motor will depend on the current speed of the motor (ie, the response time is typically shorter when the motor is operating at a higher speed).

It is known in the art to provide engines with a turbocharger. These turbochargers have response times, that is, the period required for the turbocharger to respond to a demand from the engine. The response time of a turbocharger depends on a number of factors such as the inertia of the turbocharger rotor unit, intake pressure, airflow and energy transfer from the intercooler. This is significant because the response time of the turbocharger is a further limit to the speed with which the engine can apply high torque, since it takes some time to create a sufficient mass air flow to the cylinders. Turbochargers are known in the art for their slow response and the lag they cause is referred to as "turbo lag". It is important to take into account the effects of the turbocharger when considering the torque response of the engine as a whole. However, it is also possible that some motors have other characteristics that also slow down motor response and these characteristics must also be considered.

The use of pressure reducing means, such as pressure relief valves (PRVs) in hydraulic machines (eg excavators, etc.) is well known in the art. When the pressure in a fluid manifold reaches a PRV limit, the PRV opens to allow hydraulic fluid to exit the system (usually through an auxiliary passage to an atmospheric pressure tank) thereby reducing the pressure . It is a safety element that prevents the machine from being damaged.

However, the hydraulic fluid that exits through a PRV represents an inefficiency in the sense that that hydraulic fluid can no longer do work in the system and therefore energy is lost. Thus, in one embodiment of the invention, a system is provided to prevent reaching the limit of the check valve and therefore prevent the check valve from opening.

To achieve this, in an example embodiment of the invention, the control signal to the hydraulic machine is limited such that the pressure output by the hydraulic machine cannot exceed a predetermined maximum pressure (for example, 95% of the pressure of the PRV). The ECU receives a demand signal (for example, a signal input by a user via a joystick) and limits Fd so that the predetermined maximum is not reached.

Typically, at least one PRV will be associated with each actuator of a vehicle. For example, when the vehicle is an excavator, at least one PRV will be provided for each track actuator, swing actuator, arm actuator, boom actuator, etc. Since each actuator is associated with a different demand, each PRV associated with each actuator optionally has a different PRV limit. In addition, there may be different PRV limits associated with different movements (for example, a higher PRV limit may be associated with raising one arm and a lower PRV limit associated with lowering one arm). Accordingly, each vehicle actuator according to an exemplary embodiment of the invention is provided with a predetermined maximum pressure that corresponds to the safety valve limit of said actuator. Furthermore, an exemplary embodiment of the invention that limits pressure involves a PRV associated with a group or groups of actuators, where the limit is associated with one or more groups. The limit selected for the group may reflect the lower of the respective actuator pressure limits within the group. The group can encompass all actuators.

In an exemplary embodiment of the invention, this replaces traditional hardware PRVs. Consequently, some exemplary embodiments of the vehicle according to the invention may require fewer (or even no) PRV valves, however, in most exemplary embodiments, such valves will still be required, possibly to meet the requirements of safety. Furthermore, one can omit optionally from feedback control to the tank.

In another exemplary embodiment of the invention, open-center manifolds are replaced with closed-center manifolds. In use, a user inputs commands (eg, through the use of a joystick) and these inputs are used to determine displacement demand. This can be done by measuring or monitoring a control signal pressure, such as pilot pressure.

Since the input commands can correspond to multiple different shift demands simultaneously, for example to cause multiple different actuators to actuate simultaneously, the ECU calculates the expected sum of shift demands based on the user input commands. In an exemplary embodiment, the spool valves are controlled by hydraulic joysticks to open in proportion to the command to travel (this does not require electronic control). In an alternate example, the ECU uses proportional solenoids to cause the valves to open in proportion to displacement demand.

In one embodiment, the distributors do not have an open center; this represents an open loop feedback control procedure (i.e. there is no pressure measurement on either side of the open center port, as is the case when an open center manifold is provided, with which to provide feedback to correct for that way any error). Accordingly, a control signal is measured instead. This control signal can be in the form of a pilot pressure and is in the form of a measurement of the pressure in the open ports of the distributors and is used to determine the degree of opening of the same (the pressure is measured in each distributor side and a lookup table is referenced to determine the opening of the port). The pressure and gap provide information with which the ECU determines the flow and an expected pressure drop caused by the flow.

This avoids the inefficiencies associated with proportional distributors.

The controller is configured to receive a demand signal and determine a series of discrete values where the discrete values represent the displacement of fluid through one or more working chambers, that is, a pattern of on and off cycles of the volume of the working chamber. Figure 18 is a graph of the output as a result of a series of example discrete values (and thus an example pattern of working chamber volume on and off cycles). Over time, the total volume output of the work chamber is averaged such that the hydraulic machine (ie, Fd) meets the demand in response to the demand signal.

A user can enter a command (eg via a joystick) that causes some displacement demand that is less than 100% of the maximum possible displacement output of the motor. For example, the demand may be for a displacement of 88.9% of the maximum possible and the engine may have 12 cylinders with which to meet that demand. This demand is met through a pattern of activation of the work chambers that causes each individual work chamber to cycle on or off. In this example, the pattern would be 111 1 1 1 10 11 11 1 10 1 1 1 11 1 10, etc. (where a 1 represents an active cycle carried out by a working chamber and a 0 represents an inactive cycle carried out by a working chamber).

If this pattern of on and off cycles occurs when the rotational speed of the rotary shaft is 1200 rpm, this means that 240 decisions (i.e., choices between an on cycle and an inactive cycle for a single working chamber) and, in the above example, every 37.5 ms there is an idle cycle (a “0” in the pattern). This causes a vibration at 26.6 Hz.

As such, the series of discrete values (and/or the pattern of on/off cycling of the working chamber volume) can be represented as a non-linear function. Optionally, the set of discrete values may be determined with reference to a number of predetermined discrete values or from a database, or the controller may perform one or more calculations to thereby determine the set of discrete values. Those skilled in the art will appreciate that the non-linear function is not simply a transfer function and/or a low pass filter.

Low-frequency vibrations caused in this way can cause damage to machine (or vehicle) parts and inconvenience to the user. To avoid this, the present invention applies a moving average filter with a variable period to filter out low-frequency vibrations. By adjusting the period of the moving average filter to be equal to the period of the decision pattern causing the chatter (in the example above, the period would be 37.5 ms) the low frequency chatter is completely attenuated (as well as the harmonics of the vibration). If the period of the on/off cycle pattern is changed, or if the rotation speed of the rotary axis is changed, the period of the moving average filter is also changed depending on it.

The contributions of the individual drives of the working chamber cause a pulsatile pressure ripple. This causes vibrations in the vehicle, hydraulic machine, cab, etc. Although these vibrations usually start with a relatively low amplitude, the amplitude of the vibrations can increase over time, especially if the frequency of the vibrations is at (or close to) a resonant frequency of the vehicle (or a part of the vehicle). ). These vibrations can cause damage if the amplitude increases beyond a predetermined maximum amplitude.

Also, as changes in pressure are used to enable decisions to be made (eg a decision to change Fd, etc.) small changes in pressure caused by pulsatile pressure ripple could be misinterpreted as pressure changes. real and deliberate, which could lead to a decision being made in error. A low amplitude ripple rejection filter prevents this.

The low amplitude ripple rejection filter is a non-linear function (not a transfer function or low pass filter). These are two ways, ie a common goal, of suppressing ripple in a higher level system.

To control the torque of a hydraulic machine, it is necessary to know the pressure at the outlet of the hydraulic machine. The hydraulic machine torque arising from a variable displacement hydraulic machine is a function of the hydraulic machine displacement and the hydraulic machine outlet pressure. There is an inherent pulsatile pressure ripple in the output due to contributions from individual cylinder actuations. Using the unfiltered pressure could result in a rapid decrease or increase in hydraulic machine torque, which would be beneficial for motor stability and maximizing hydraulic machine productivity. However, due to pressure ripple, using the unfiltered pressure for torque control would result in unstable travel. To remove this pressure ripple from torque calculations, a heavily averaged or filtered pressure could be used, but this would result in a delayed torque response (undesirable lag).

An ideal pressure filter for torque control would therefore reject low amplitude pressure ripples, but accept high amplitude pressure changes. Consequently, the low amplitude ripple rejection filter retains the previous output value of the filter and compares the new inlet pressure with this retained value. If the difference between the new pressure and the held pressure value is within a rejection band (“dead band”), the outlet pressure is held constant and does not change. If the new pressure is outside the rejection band, the outlet pressure is changed to this new value. In this way, the pressure ripple does not influence the torque control of the hydraulic machine, but large pressure changes (not the ripple) are taken into account. The dead band range is established based on the expectation of a particular range of pressure pulsation - eg 20 bar pressure pulsation. The dead band is usually adjusted and configured for the specific hydraulic system in which it is installed. However, the band may change if the compliance / rigidity of the hydraulic system changes (for example, if an accumulator is provided).

The hydraulic machine controller applies a torque limit when the hydraulic machine torque limit is above a motor torque limit. The torque limit depends on the current engine speed. Therefore, the motor controller receives a measurement of the current speed of the motor and determines a corresponding motor torque limit, with reference to a lookup table (for example, a lookup table stored in a database) containing a torque-speed curve.

Furthermore, at all engine speeds, the maximum torque that can be applied by the engine will be less than the maximum torque that can be applied by the hydraulic machine. As a result, a torque limit is applied to the hydraulic machine.

For example, the demand signal may be a signal containing parameters associated with displacement, flow, pressure, power, or torque demand. These parameters are limited in their dependency on other parameters. Referring to Figure 11A, in one example, displacement can be reduced from maximum flow 310 to zero displacement through a range of pressures 308, resulting in a non-linear function representing a limit on demand for power 306 which is dependent on pressure demand 302 and flow demand 304. Referring to Figure 11B, in another example, torque demand 314 can be similarly limited so that maximum torque can be applied for certain values of pressure 308 and displacement 312, but can be reduced to zero torque over a pressure range based on displacement pressure demand 302 and displacement demand 316.

Figure 12 is a graph of an example power demand function 306 as a function of motor speed 326 and torque 324, with reference to a minimum speed demand 322 and a maximum speed demand 320. The drive controller hydraulic machine applies a torque limit depending on the engine speed. At low speed, the machine's hydraulic controller reduces torque limit to prevent engine stalling. On the contrary, at high speed, the hydraulic machine controller increases the torque limit to prevent damage to the hydraulic machine.

In one example, the torque limit can be set as a function of speed to match the available torque of the motor. Figure 13 is a graph of an example of torque functions; a torque function representing torque determined in accordance with available engine speed 330 and a torque function determined in accordance with available hydraulic machine speed 328, wherein torque 324 is plotted as a function of both engine speed of the motor 326 as with reference to a minimum speed request 322 and a maximum speed request 320. At low speed, the torque of the hydraulic machine is limited to prevent the motor from stalling. On the contrary, at high speed, the torque of the hydraulic machine is limited to prevent internal damage.

In an alternate example, at high speed the hydraulic machine torque can be increased (as shown at curve 328) to cause the engine speed to drop until the hydraulic machine load matches the available engine torque. This takes place for a short period of time until the engine speed is reduce.

Figure 14 is a graph of motor torque 342 versus motor 348 speed to indicate the change in torque with motor 350 droop, as is known. In an example of the invention where the engine governor applies an engine speed setpoint 346, the total engine load is determined by measuring engine droop. The hydraulic torque of the machine is limited in response to the measured droop, so that the engine torque limit is not exceeded. The constant torque vs. maximum speed of the motor 352 follows the torque vs. maximum speed of the hydraulic machine 344.

Figure 15 is a graph of motor torque 342 versus motor 348 speed to indicate the change in torque with motor 350 droop as a result of an example embodiment of the invention. The constant torque vs. maximum engine speed 352 can be compared to the instantaneous torque vs. engine speed 354. The hydraulic machine controller may apply an instantaneous torque limit less than the constant torque capability of the engine. This is advantageous when an engine has a turbocharger, since a turbocharger will have some inertia which, in turn, causes an increase in the time it takes for the engine to increase its output torque.

Figure 16 is a graph of torque 362 versus time 360 indicating an example of torque response to constant torque limit 364, instantaneous torque limit 366, and slew rate limit 368.

Figures 17A and 17B are graphs of torque 362 as a function of time 360 indicating the torque response associated with a first and second output of a hydraulic machine without exceeding a predetermined torque slewing limit 368. 370 is the actual torque associated with the first output of the hydraulic machine and 372 is the actual torque associated with the second output of the hydraulic machine. 374 is the torque demand associated with the first output of the hydraulic machine. 376 is the guaranteed amount of torque associated with the first output. As understood in the art, these outputs are simply fluid connections to (one or more working chambers of) the hydraulic machine that act as outputs when the machine is operating in a pumping mode and as inputs when the hydraulic machine is operated in pump mode. an engine mode. In one example, the torque demand of a second actuator may be restricted and de-prioritized because the first actuator is of greater importance and as such the total torque is split so that more torque is available to the first actuator than to the second. second.

Figure 18 is a graph indicating an example of how a continuous demand signal 380 can be quantized 382 in discrete steps. Although the quantized steps may be equally spaced in the amount of demand (eg, displacement) this is not necessary.

Claims (15)

An apparatus comprising a prime mover and a plurality of hydraulic actuators (6), a hydraulic machine (32) having a rotating shaft (42) driven by the prime mover and comprising a plurality of working chambers (84) with a volume (36) that varies cyclically with the rotation of the rotary axis, a hydraulic circuit that extends between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprises a low-pressure valve (52) that regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold (54) and a high-pressure valve (64) that regulates the hydraulic fluid flow between the working chamber and a high pressure manifold (58), the hydraulic machine is configured to actively control at least the low pressure valves of the group of one or more working chambers to select the net displacement of fluid hydraulic fluid for each working chamber in each working chamber volume cycle, and therefore the net displacement of hydraulic fluid through the group of one or more working chambers, in response to a demand signal (94, 380) , the apparatus comprises a controller (14) configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators, wherein the demand signal is quantized (382), which e has one of a plurality of discrete values. An apparatus according to claim 1, wherein the demand signal (94, 380) is received and quantized (382), optionally by selecting the discrete value, from the plurality of discrete values, plus close to the demand received. An apparatus according to claim 1, wherein the demand signal (94, 380) is received and quantized (382), said demand signal being indicative of a fraction of maximum displacement of hydraulic fluid by the group. of one or more working chambers to be displaced per revolution of the rotary axis, optionally wherein a range of acceptable values of the demand signal is selected to comprise a finite number of integer fractions of the maximum displacement of hydraulic fluid by the group of one or more working chambers to move per revolution of the rotary axis. An apparatus according to claim 1 or claim 2, wherein the plurality of discrete values varies with the speed of rotation of the rotary shaft (42). An apparatus according to one of the preceding claims, wherein there are fewer than 1,000 discrete values. An apparatus according to any preceding claim, wherein the discrete values represent less than 10% of the digital values the demand signal (94, 380) could have, given its bit length. An apparatus according to any of the preceding claims, wherein the controller is configured to determine a minimum allowable frequency and then to create a quantized list of the plurality of discrete demand values, said values selected for cause one or more cylinder firing patterns, wherein said patterns only have frequency content above the minimum allowable frequency. 8. A method of operating an apparatus, comprising a main motor and a plurality of hydraulic actuators (6), a hydraulic machine (32) having a rotating shaft (42) driven by the main motor and comprising a plurality of work chambers (84) with a volume (36) that varies cyclically with the rotation of the rotary axis, a hydraulic circuit that extends between a group of one or more work chambers of the hydraulic machine and one or more of the hydraulic actuators , each working chamber of the hydraulic machine comprises a low-pressure valve (52) that regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold (54) and a high-pressure valve (64) that regulates the hydraulic fluid flow between the working chamber and a high pressure manifold (58), the hydraulic machine is configured to actively control at least the low pressure valves of the group of one or more working chambers to select the net displacement of fluid hydraulic fluid for each working chamber in each working chamber volume cycle, and therefore the net displacement of hydraulic fluid through the group of one or more working chambers, in response to a demand signal (94, 380) , the method includes the step of calculating the demand signal in response to a measured property of the hydraulic circuit or one or more actuators, wherein the method comprises a quantization step, the quantization step comprises calculating a demand signal quantized that has one or a plurality of discrete values. A method according to claim 8, wherein the method comprises receiving the demand signal (94, 380) and quantizing the demand signal, optionally wherein quantizing the demand signal comprises selecting the discrete value , of the plurality of discrete values, closest to the demand received. A method according to claim 8 or 9, wherein the method comprises running an algorithm to determine whether individual work chambers (84) will cycle on (88) or off. A method according to any one of claims 8 to 10, wherein the method comprises receiving a demand signal (94, 380) and determining a corresponding set of values, said set of values corresponding to the pattern of active cycles (88) and/or idle the volume of the working chamber (36) to thereby satisfy the demand signal. A method according to claim 11, wherein the pattern of on (88) and/or off cycles of the working chamber (36) volume has a finite period, wherein the finite period can vary within from a range of acceptable values with a maximum period of at most 0.1 s, the range of acceptable values is selected based on the acceptable frequency content, and wherein, from the maximum period, an acceptable finite range of displacement demands (316) is selected depending on the number of cylinders (34) and the main engine operating range, the acceptable range of displacement demands that is selected to comprise a finite number of integer fractions of the displacement demand, wherein the denominators of the finite number of integer fractions of the displacement demand are selected as a function of the speed of rotation of the axis of rotation (42), optionally, where the denominators are selected such that the period is less than the maximum period. A method according to claim 11 or 12, wherein the series of values comprises a repeating sequence. A method according to any of claims 8 to 13, wherein the method comprises selecting a minimum allowable frequency and then creating a quantized list of the plurality of discrete demand values, said values selected to cause one or more cylinder activation patterns, wherein said patterns only have frequency content above the minimum allowable frequency. A method according to any one of claims 8 to 13, wherein the method comprises selecting a minimum allowable frequency and creating a quantized list of the plurality of discrete demand values, or a method of according to claim 14, wherein the quantified list of demand values depends on the number of cylinders (34) of the machine (32) and/or on the operating speed of rotation of the rotary axes (42) of the machine .