CN120693473A

CN120693473A - Method for controlling a hydrostatic drive

Info

Publication number: CN120693473A
Application number: CN202480012725.4A
Authority: CN
Inventors: M·穆勒; A·巴雷拉维拉尔潘多; F·维尔纳; N·布里克斯; R·赫尔曼; E·伊尔克; P·蒙库; A·阿尔科利亚
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2023-02-16
Filing date: 2024-02-12
Publication date: 2025-09-23
Also published as: DE102023201325A1; DE102023201325B4; WO2024170487A1

Abstract

The invention relates to a method for actuating a hydrostatic travel drive (1), wherein the hydrostatic travel drive is provided with a first hydraulic machine (4) having an adjustable displacement volume and with a second hydraulic machine (6) and a third hydraulic machine (8) each having an adjustable displacement volume, wherein the first hydraulic machine is coupled or coupleable to a drive machine, wherein a pressure medium from the first hydraulic machine can be fed to the second and third hydraulic machines (6, 8) arranged in parallel to each other, wherein the second and third hydraulic machines (6, 8) are connected or connectable to at least one wheel (12) to be driven or a chain or shaft (14) to be driven, characterized in that the method comprises the steps of a. Determining a total target volume flow of the second and third hydraulic machines on the basis of the speed and/or the pressure prevailing in the hydrostatic drive, b. Determining the target volume flows of the second and third hydraulic machines on the basis of the total target volume flow determined in step a.

Description

Method for actuating a hydrostatic drive

Technical Field

The invention relates to a method for actuating a hydrostatic drive, preferably a working machine. Furthermore, the invention relates to a control unit, a work machine comprising the control unit and a computer program.

Background

Hydrostatic travel drives for mobile working machines are known, in which a hydraulic pump and one or more hydraulic motors are connected to one another in a closed hydraulic circuit. The hydraulic pump is driven by an internal combustion engine, for example a diesel engine, and the hydraulic motor finally drives the mobile working machine, for example via corresponding wheels.

The hydraulic pump and the hydraulic motor of such a travel drive are generally adjustable in terms of their delivery rate. In this way, for example, the volume flow rate delivered by the hydraulic pump in the closed circuit can be changed with a constant rotational speed of the internal combustion engine, and the output rotational speed of the hydraulic motor or of the wheels, i.e. the travel speed of the mobile working machine, can be set accordingly.

Hydrostatic travel drives have many applications, for example, in agriculture, in which work machines should perform work functions in addition to travel functions. A field cutter is one example. A field cutter is an agricultural device for receiving, crushing and loading harvests such as grass, alfalfa or corn, particularly when preparing silage or whole-plant silage.

In order to expand the transmission ratio range of a drive, hydrostatic transmissions are known, for example, which have at least two hydraulic motors that are operated in parallel in terms of flow. Their drive shaft power can be added by the additive drive of the hydrostatic drive and can be transmitted, for example, to the axle. Thus, for example, at low driving speeds, the two hydraulic motors are in parallel operation and thus allow high traction forces. In the case of a predetermined delivery rate of the hydraulic pump and in the background of a reduced efficiency caused by a reduced feed rate of the hydraulic motor, the travel speeds achievable with both motors are limited.

In order to achieve a higher driving range of the driving speed, one of the hydraulic motors can therefore be set to zero displacement volume and disconnected from the output by means of a clutch. The entire volume flow of the hydraulic pump is thereby conducted via the remaining, mostly smaller hydraulic motor, which enables higher rotational speeds and thus higher driving speeds.

The control of the previously known solutions allows for individual actuation logic of the hydraulic motor and accordingly for extensive adjustment of the core software for controlling the hydraulic motor of the hydraulic transmission with the hydraulic pump and the single hydraulic motor, which is very time-consuming. The previously known solutions require in particular a change in the manipulation of the core software, thereby increasing the effort in terms of integration and application of other functions (speed limitation, pressure regulator and overspeed protection, etc.).

Disclosure of Invention

In contrast, the object of the present invention is to provide a simpler solution in order to be able to control at least two hydraulic motors, in particular to adjust existing known methods to the minimum, in order to be able to achieve such a control, so that an already existing infrastructure can be used without adjustment thereof.

According to one embodiment of the invention, a method for actuating a hydrostatic travel drive (1) is provided, wherein the hydrostatic travel drive is provided with a first hydraulic machine (4) having an adjustable displacement volume and with a second hydraulic machine (6) and a third hydraulic machine (8) each having an adjustable displacement volume, wherein the first hydraulic machine is coupled or coupleable to a drive machine, wherein pressure medium from the first hydraulic machine can be fed to the second and third hydraulic machines (6, 8) arranged in parallel to each other, wherein the second and third hydraulic machines (6, 8) are connected or connectable to at least one wheel (12) to be driven or a chain or shaft (14) to be driven,

Characterized in that the method comprises the steps of:

a. determining a total target volume flow of the second hydraulic machine and the third hydraulic machine based on the speed and/or the pressure prevailing in the hydrostatic drive;

b. the target volume flows of the second hydraulic machine and of the third hydraulic machine are determined on the basis of the total target volume flow determined in step a.

Since the first, second and third hydraulic machines can theoretically be used not only as hydraulic motors but also as hydraulic pumps, they are collectively referred to as hydraulic machines in the claims. For the reasons mentioned, moreover, the volume flow is always mentioned in the claims (and not exclusively referred to as the feed-in volume of a hydraulic motor, for example). The invention is particularly advantageous in that with this solution the total target volume flow can be determined using existing methods. The existing method is a highly sophisticated and widely marketed control solution for hydraulic motors in hydraulic transmission mechanisms with a hydraulic pump and a single hydraulic motor in a closed circuit together with the hydraulic pump. This means that the invention enables the use of existing methods, in which an assembly has been added in addition, for determining the target volume flows of the second and third hydraulic machines.

Drawings

The present invention is described with reference to the accompanying drawings, wherein like reference numerals refer to like and/or similar components of the system and/or corresponding components. Regarding the drawings:

figure 1 shows a hydraulic circuit diagram of a hydrostatic travel drive according to the prior art,

Fig. 2 shows a scaling function f in a first driving mode, which is a power mode, according to an embodiment of the invention;

Fig. 3 shows the scaling function f in a second driving mode, which is a power saving mode, according to an embodiment of the invention.

Detailed Description

The invention will now be described with reference to specific embodiments as shown in the drawings. However, the invention is not limited to the specific embodiments described in the following detailed description and shown in the drawings, but the described embodiments merely illustrate some aspects of the invention, the scope of which is defined by the claims.

Other modifications and variations of the present invention will be apparent to those of skill in the art. Accordingly, this specification includes all modifications and/or variations of the present invention, the scope of which is defined by the claims.

According to fig. 1, the travel drive 1 has a hydrostatic transmission 2 with a hydraulic machine 4 which operates as a hydraulic pump in the traction operation of the travel drive 1 and two hydraulic machines 6 and 8 which operate as hydraulic motors in the traction operation mentioned. The two hydraulic motors 6, 8 are connected in fluid parallel with the hydraulic pump 4 in a closed hydraulic circuit via working lines 10 and 12 on the one hand and working lines 14 and 16 on the other hand. The hydraulic machines 4, 6, 8 are adjustable in terms of their displacement volume, wherein they are each configured as axial piston machines of swash plate construction or of inclined shaft construction. In general, the maximum volume flow (intake) of the first hydraulic motor 6 is significantly greater than the maximum volume flow of the second hydraulic motor 6. The ratio between the maximum volumetric flows of the two hydraulic motors is between 1.5 and 2.5.

The hydraulic pump 4 is connected by its drive shaft 18 to a drive machine 20 which is configured as a diesel engine. A first hydraulic motor 6 of the two hydraulic motors 6, 8 has a first drive shaft 22 and a second hydraulic motor 8 has a second drive shaft 24. Downstream of hydrostatic transmission 2, as a mechanical transmission, a summation transmission 26 having two input shafts 28 and 30 is connected. In this case, the first input shaft 28 is connected to the first drive shaft 22 in a rotationally fixed manner and the second input shaft 30 is connected to the second drive shaft 24 in a rotationally fixed manner. The output shaft 32 of the summation gear 26 is connected in a torque-proof manner to the differential 34 of the drive shaft 36.

The summation gear 26 includes a clutch 38 configured as a plate clutch. This clutch has a first clutch section 40 which is connected to the first input shaft 28 in a rotationally fixed manner. The clutch further has a second clutch section 42, which is connected in a rotationally fixed manner to the second input shaft 30 of the summation gear 26 via a gear assembly 44, which is shown purely schematically. The two input shafts 28 and 30 and thus the two drive shafts 22 and 24 can be connected to one another in a rotationally fixed manner by actuating the clutch 38, which is accompanied by engagement of the second clutch section 42.

For actuating the clutch 38, an actuating element 46 in the form of a hydraulic cylinder is provided. The piston 48 of the actuating element is coupled with the second clutch section 42 in a tensile and shearing-resistant manner by a piston rod. The hydraulic cylinder 46 has a piston chamber in which a pressure spring 50 is arranged. The piston chamber is permanently connected to the tank T by a tank line. On the piston rod side, the hydraulic cylinder 46 has an annular chamber 52 which is connected via a control pressure line 54 to a connection S of a regulating device 56 which is embodied as a pressure regulating valve. The last-mentioned regulating device has a pressure connection P, which is connected via a pressure line 58 to a feed pump 61, which is driven by the drive shaft 18 together with the hydraulic pump 4. The feed pump 61 here sucks pressure medium from the tank T. The pressure regulating valve 56 has a tank port T connected to the tank T.

The pressure regulating valve 56 can be continuously regulated and has two end positions a, b. In the first end position a, in which the valve body is preloaded by the spring 60, the pressure connection P is connected to the control pressure connection S and the connection T is blocked relative to the connection S. In the second end position b, the pressure regulating valve 56, more precisely the valve body of the pressure regulating valve, can be actuated by means of an electromagnet 62. When the electromagnet is energized and as long as the second end position b is fully occupied, the control pressure connection S is connected to the tank connection T and the pressure connection P is blocked. In this way, in the first end position a, only the annular space 52 is supplied or filled with pressure medium, while in the second end position b only the annular space 52 is emptied or drained of pressure medium. Between the two end positions a and b, there can be an adjustment position of the valve body in which the ports P, S and T are in a corresponding pressure medium connection with respect to one another. In order to return the control pressure present at the control pressure connection S and to be regulated in the annular chamber 52, the annular chamber 52 is fluidically connected via a control line or a control channel to a control surface of the valve body of the pressure regulating valve 56, which control surface acts identically to the spring 60.

Furthermore, the mechanical transmission 26 has a first rotational speed detection unit 64, by means of which the rotational speed of the first input shaft 28 and thus the rotational speed of the first clutch section 40 and thus the rotational speed of the first drive shaft 22 can be detected. The second rotational speed detection unit 66 of the mechanical transmission 26 can detect the rotational speed of the second clutch section 42 and thus indirectly the rotational speed of the second input shaft 30 and the rotational speed of the second drive shaft 24, with knowledge of the gear ratio of the gear assembly 44.

An adjusting device 70 is associated with the hydraulic pump 4, which cooperates with an adjusting mechanism 72 for adjusting the displacement volume of the hydraulic pump 4. The first hydraulic motor 6 and the second hydraulic motor 8 have an adjusting device 74 or 78 and an adjusting mechanism 76 or 80.

The drive machine 20, the regulating devices 70, 74 and 78, the electromagnet 62 and the rotational speed detection units 64, 66 are each connected to the control mechanism 68 via signal lines.

In the following paragraphs, a method for controlling two hydraulic motors according to an embodiment of the invention is described.

In a first step, the total target volume flow (Vg _{eff_t}) of the first hydraulic motor 6 (second hydraulic machine) and of the second hydraulic motor 8 (third hydraulic machine) is determined on the basis of the speed and/or the pressure prevailing in the hydrostatic drive. This means that the two hydraulic motors 6, 8 are regarded as the only hydraulic motor for determining the target volume flow (or target intake volume). In order to determine the total target volume flow, the actual pressure at the hydraulic pump 4 is taken into account, for example. Alternatively or additionally, speeds, for example, driving speeds or rotational speeds, are considered.

By means of this solution it is possible to determine the target volume flow (Vg _{eff_t}) using existing methods. The existing method is a highly sophisticated and widely marketed control solution for hydraulic motors in hydraulic transmission mechanisms with a hydraulic pump and a single hydraulic motor in a closed circuit together with the hydraulic pump. Since this method is well known, a detailed description of this method is not provided in this specification.

The target volume flows of the two hydraulic motors must then be determined from the total target volume flow determined. For this reason, a volume flow balance equation (see equation 90 below) is written that combines the total target volume flow with the volume flow of the first hydraulic motor and the volume flow of the second hydraulic motor.

Vg_{eff_t}＝Vg_{pem_t}+i_tp＊Vg_{temp_t} (90)

Where, correspondingly, vg _{eff_t} denotes the total target volume flow, vg _{perm_t} denotes the target volume flow of the second hydraulic motor 8, vg _{temp_t} denotes the target volume flow of the first hydraulic motor 6 and i _tp denotes the mechanical transmission ratio between the second hydraulic motor and the first hydraulic motor. As can be seen from equation 90, there are two parameters that must be determined. For this reason, the inventors have found a solution to determine one of the two unknown parameters and then in another step determine the other parameter by means of equation 90.

First, a maximum available volume flow (Vg _{eff_max}) is determined, which can be provided by means of the first and second hydraulic motors 6, 8.

Vg_{eff_max}＝Vg_{pem_max}+i_tp＊Vg_{temp_max} (91)

Where accordingly Vg _{perm_max} represents the maximum volume flow of the second hydraulic motor 8, vg _{temp_max} represents the maximum volume flow of the second hydraulic motor 8 and i _tp represents the mechanical transmission ratio between the second hydraulic motor and the first hydraulic motor. As can be seen from the equation, the maximum available volume flow (Vg _{eff_max}) can be calculated relatively easily from known variables and can be stored and does not have to be recalculated each time.

In a further step, the maximum available volume flow Vg _{eff_max} mentioned is combined with the total target volume flow Vg _{eff_t} calculated in order to calculate a normalized target volume flow α, which is used to calculate the scaling factor f as described in the description.

a=Vg_{eff_t}/Vg_{eff_max} (92)

The normalized volume flow α essentially describes how much volume flow is required compared to the maximum available volume flow. The mentioned scaling factor f is then found on the basis of this normalized volume flow.

The scaling factor f is determined by means of a scaling function, wherein the scaling function determines the value of the scaling factor on the basis of the combination of the maximum available volume flow Vg _{eff_max} mentioned and the total target volume flow Vg _{eff_t} determined.

In order to determine a scaling function that should be used for determining the scaling factor f, a driving pattern is preferably also detected in the method, wherein a scaling function is selected from a plurality of scaling functions in accordance with the detected driving pattern in order to determine the scaling factor f.

After the scaling factor f has been determined, it is combined with the maximum available volume flow of the second hydraulic machine or of the third hydraulic machine in order to determine the target volume flow of the second hydraulic machine or of the third hydraulic machine, respectively. In such an embodiment, the scaling factor f is combined with the maximum volumetric flow of the second hydraulic motor 8 in the following way:

Vg_{perm_t}＝Vg_{perm_max}*f(a) (93)

By means of this solution, the target volume flow of the second hydraulic motor 8 can be determined. However, it is clear to a person skilled in the art that the scaling factor can alternatively be applied to the maximum volume flow of the first hydraulic motor.

Since the target volume flow of the second hydraulic motor is now known, this information can be used to determine the target volume flow of the first hydraulic motor. To this end, equation 90 is rewritten as follows:

Vg_{temp_t}＝(Vg_{eff_t}-Vg_{perm_t})/i_tp (94)

The target volumetric flow rate of the first hydraulic motor can then also be determined by equation 94. The current signals, the signals IHM1 and IHM2 are then sent to the two hydraulic motors via the control means 68 on the basis of the determined target volume flow in order to control the respective pivot angles of the hydraulic motors.

In fig. 2 and 3 two different scaling functions are shown, which can be used to determine the scaling value.

Fig. 2 shows the scaling function f in a first driving mode, wherein the first driving mode is a Power mode (Power-Modus). In the power mode, the target volumetric flow of the second hydraulic machine or of the third hydraulic machine is kept substantially constant and the volumetric flow regulation is performed with the further hydraulic machine. In the example shown, the second hydraulic motor is kept substantially constant and the volume flow is regulated by the first hydraulic motor 6. To achieve this, a substantially constant function is selected, as shown in fig. 2. This driver mode is called "sequential adjustment" in that the second motor (permanent motor) is turned to the maximum volume flow and remains constant in this position. To perform an active adjustment, the first hydraulic motor 6 is then turned.

Fig. 3 shows the scaling function f in a second driving mode, wherein the second driving mode is an energy saving mode (Eco-Modus). In the energy saving mode, not only the target volume flow of the second hydraulic machine but also the target volume flow of the third hydraulic machine is changed in order to perform the volume flow adjustment. This driver mode is called "parallel regulation" in that the second motor (permanent motor) and the first motor (temporary motor) are gradually changed (more or less volume flow of the first hydraulic motor and the second hydraulic motor is required according to the standardized volume flow α).

Furthermore, the work machine can comprise an operating element (not shown in fig. 1), wherein the operating element is in signal connection with the control unit 40, wherein commands can be output to the control unit 40 via the operating element, wherein the commands include whether the driver wishes the power mode or the energy saving mode.

When the clutch 38 is closed and at the same time the hydrostatic travel drive 1 is decelerated by the second hydraulic motor 8, a sudden increase in the braking torque can occur, since the first hydraulic motor 6 suddenly also contributes to the deceleration of the hydrostatic travel drive 1. In particular when the driving speed falls below a limit value (for example 5 km/h), the control means 68 normally automatically send a signal I _V to the electromagnet 62 to enable the clutch 38 to be closed. However, this causes a significant increase in braking torque. For this reason, it is advantageous to apply a reduction factor R to the target volume flow of the first hydraulic motor 6 under such operating conditions, which is configured to reduce the target volume flow of the first hydraulic motor 6 when the clutch 38 is closed and at the same time when the hydrostatic travel drive is decelerated.

The reduction factor R is calculated from a function that is related to the time that begins with the closing of the clutch 38. The effect of the reduction factor on the target volumetric flow of the first hydraulic motor 6 decreases over time. This is a "ramp" that is utilized in order to reduce the abrupt change in retarding torque as the clutch 38 is closed, which reduces this effect. It is particularly preferred to correct the target volume flow of the second hydraulic motor using the following formula:

Vg_{temp_tc}＝(Vg_{temp_t}*R(t)) (95)

Where accordingly Vg _{temp_tc} represents the corrected target volume flow of the second hydraulic motor 8, vg _{temp_t} represents the already calculated target volume flow of the second hydraulic motor 8 and R (t) represents the time-dependent reduction factor.

The described method is stored in a memory unit and is executed by the control mechanism 68.

The described method can be used in different types of work machines. The method can be used in essentially all working machines with hydrostatic drives and controllable drives (e.g. diesel engines). Examples of applications can be, for example, field cutters, combine harvesters, snowploughs or road milling machines.

The invention has been described with reference to the embodiments described hereinbefore, it will be apparent to those skilled in the art that various modifications, variations and improvements of the invention can be effected on the basis of the teachings described hereinbefore and within the scope of the claims which follow.

Although the invention has been described with respect to two hydraulic motors at all times, it is clear to a person skilled in the art that the invention can also be applied to three or more hydraulic motors with some small adjustment, for example using two different scaling functions in two different hydraulic motors.

Furthermore, those skilled in the art will be familiar with the art and will not be described herein in order to avoid unnecessarily obscuring the invention.

Accordingly, the invention should not be limited by the specific illustrative embodiments, but rather by the scope of protection of the appended claims.

Claims

1. A method for controlling a hydrostatic travel drive (1), wherein the hydrostatic travel drive comprises: a first hydraulic machine (4) with an adjustable displacement volume and a second hydraulic machine (6) and a third hydraulic machine (8) each with an adjustable displacement volume, wherein the first hydraulic machine is coupled or can be coupled to a drive machine, wherein pressure medium from the first hydraulic machine can be supplied to the second and third hydraulic machines (6, 8) arranged in parallel with one another, wherein the second and third hydraulic machines (6, 8) are connected or can be connected to at least one wheel (12) to be driven or a chain or axle (14) to be driven,

Characterized in that the method comprises the following steps:

a. determining the total target volume flow of the second hydraulic machine and the third hydraulic machine based on the speed and/or pressure present in the hydrostatic drive;

b. Based on the total target volume flow ascertained in step a., the target volume flow of the second hydraulic machine and the third hydraulic machine is ascertained.

2 . The method according to claim 1 , wherein the target volume flows of the second and third hydraulic machines determined in step b. are also determined taking into account a maximum available volume flow of the second and/or third hydraulic machines.

3 . The method according to claim 2 , wherein, to determine the target volume flow of the second hydraulic machine and/or the third hydraulic machine, the maximum available volume flow is combined with the total target volume flow determined in step a. in order to determine a scaling factor.

4. The method according to claim 3, wherein the scaling factor is determined by means of a scaling function, wherein the scaling function determines a value for the scaling factor based on a combination of the maximum available volume flow and the total target volume flow determined in step a.

5 . The method according to claim 4 , wherein the method further comprises detecting a driving mode, wherein a scaling function is selected from a plurality of scaling functions in order to determine the scaling factor as a function of the detected driving mode.

6 . The method according to claim 5 , wherein the first driving mode is a power mode, wherein in the power mode a target volume flow of the second or third hydraulic machine is kept substantially constant and a volume flow control is performed using a further hydraulic machine.

7 . The method according to claim 5 , wherein the second driving mode is an energy-saving mode, wherein in the energy-saving mode not only the target volume flow of the second hydraulic machine but also the target volume flow of the third hydraulic machine is changed in order to perform a volume flow control.

8. The method according to claim 3, wherein the scaling factor is combined with the maximum available volume flow of the second hydraulic machine or the third hydraulic machine in order to determine a target volume flow of the second hydraulic machine or the third hydraulic machine, respectively.

9 . The method according to claim 8 , wherein, after determining a volume flow of the second or third hydraulic machine based on the scaling factor, a further volume flow is determined based on the volume flow and the total target volume flow determined in step a.

10. A method according to any one of claims 1 to 9, wherein the second hydraulic machine (6) is capable of being rotationally connected to the at least one wheel to be driven (12) or the chain or shaft to be driven (14) by means of a clutch (38), and wherein the third hydraulic machine (8) is rotationally connected to the at least one wheel to be driven (12) or the chain or shaft to be driven (14).

11. A method according to claim 10, wherein a reduction factor is applied to the target volume flow of the second hydraulic machine, the reduction factor being configured to reduce the target volume flow of the second hydraulic machine (6) when the clutch (38) is closed and simultaneously when the hydrostatic drive (1) is decelerated by the third hydraulic machine (8).

12. The method according to claim 11, wherein the reduction factor is calculated from a time-dependent function, wherein the time begins with the closing of the clutch (38), and wherein the influence of the reduction factor on the target volume flow of the second hydraulic machine (6) decreases over time.

13. A control unit (68) configured to carry out the method according to any one of claims 1 to 12.

14. A working machine, comprising a hydrostatic travel drive (1), wherein the hydrostatic travel drive is provided with: a first hydraulic machine (4) having an adjustable displacement volume and a second hydraulic machine (6) and a third hydraulic machine (8) each having an adjustable displacement volume, wherein the first hydraulic machine is coupled or can be coupled to a drive machine, wherein the pressure medium from the first hydraulic machine can be delivered to the second hydraulic machine and the third hydraulic machine (6, 8) arranged in parallel with each other, wherein the second hydraulic machine and the third hydraulic machine (6, 8) are connected or can be connected to at least one wheel (12) to be driven or a chain or shaft (14) to be driven, wherein the working machine comprises a control unit according to claim 13.

15 . A computer program designed to execute and/or control the method according to claim 1 .

16. A machine-readable storage medium having stored thereon the computer program according to claim 15.