JPS6325180A - power steering device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power steering device, and more particularly, to a power steering device that provides power assist to a vehicle such as an automobile.

(Conventional technology) As automobiles become more popular, especially in urban areas, it has become inevitable to use them in poor parking and garage environments. is also increasing. Reducing the driver's burden leads to less fatigue, which means more margin for safe driving.

As the width of tires increases, the steering force itself tends to increase. Against this background, so-called power steering devices have recently been installed in vehicles from the viewpoint of maneuverability and stability, and their use has become remarkable.

The purpose of power steering is to reduce the burden on the driver regarding steering, and the various functions required include reduction of steering force, feedback of appropriate reaction force in response to steering, and smooth steering. Furthermore, it is also required that the power required for devices that implement these various functions be small.

There are, for example, the following three types of power steering devices applied to this type of conventional power steering device, and these will be explained below with reference to FIGS. 11 to 13.

(1) Hydraulic type (see Figure 11) In Figure 11, 1 is a handle, and the steering force of the handle 1 is transmitted to a hydraulic servo valve 3 via a steering shaft 2, and also to a steering gear mechanism 4. be done. In the steering gear mechanism 4, the rotational displacement of the handle 1 is converted into a linear displacement of the rod 5, and this linear displacement is transferred via a hydraulic cylinder 6 to a predetermined linkage mechanism 7 (
(not shown) to the steering wheel 8 (not shown), and the steering wheel 8 is steered in accordance with the rotational displacement of the handle 1.

On the other hand, discharge oil from a hydraulic pump 11 that is constantly driven by an engine 10 is guided to the hydraulic servo valve 3, and the hydraulic servo valve 3 controls switching of the discharge oil pressure supplied to the hydraulic cylinder 6 according to the steering direction of the handle 1. The piston of the hydraulic cylinder 6 is moved by applying so-called hydraulic pressure to the operation to increase the steering force. Note that 12 is a return tank.

(Problem to be Solved by the Invention) However, in such hydraulic type devices, the hydraulic pump is driven by the power of the engine, and the direction and pressure of the discharge amount of the pump are controlled by a hydraulic servo valve to perform steering. Since the structure is such that the power to be fed to the hydraulic cylinder of the device is assisted, there are the following problems.

b) Since the hydraulic pump is constantly driven by the engine, it is necessary to provide a flow control valve to control the flow rate.

Since the pump is driven to discharge a large flow rate even at high speeds where power assistance is not required, engine power loss is large.

c) High-precision machining is required for the servo valve that performs hydraulic control, resulting in high costs.

2) In order to set the hydraulic characteristics, special edge machining is required for the spool valve in the hydraulic servo valve. in this case,
There are limits to processing, and there are also limits to the degree of freedom in properties.

e) Since it is a mechanical hydraulic control, there is a limit to implementing control suitable for vehicle driving conditions.

f) Since the hydraulic pressure is determined by the pump discharge flow rate, throttle, piping, etc., the hydraulic pressure decreases during sudden steering, and the auxiliary force decreases.

On the other hand, in order to overcome some of the drawbacks of the hydraulic type as mentioned in (I) above, the following electric type has been proposed.

(n) Electric type (see FIG. 12) In FIG. 12, the displacement of the steering shaft 2 is detected by a steering force detector 21 and input to a control circuit 22. The control circuit 22 receives information from this steering force detector 21,
That is, the output of the electric motor 23 is controlled according to the rotational direction of the handle 1 and the magnitude of the steering force, and the power of the electric motor 23 is transmitted to the steering gear mechanism 25 via the speed reduction mechanism 24. In this way, the mechanical power of the electric motor 23 increases the steering force.

However, although such an electric type solves the drawbacks of the hydraulic type described above, the following new problems arise, which hinders its practical use.

f) Since a coupling device such as an electric motor and a reduction gear that couples the rotation of the electric motor to the steering gear mechanism is attached to the steering device, the device becomes large.

g) The installation space for the steering device is generally installed in a very narrow area, and it is difficult to place an electric type in this space because it will interfere with the vehicle body. Additionally, installation requires significant changes to the vehicle body.

Furthermore, in order to improve the drawbacks of N) and (II) above, the following motor-driven pump type has been proposed. II) The aim is to improve the ease of installation, which is a drawback of the electric type.

(III) Motor-driven pump type (see Figure 13) No. 13
In the figure, the displacement of the steering shaft 2 is detected by a steering switch 31 and input to a control circuit 32.

The control circuit 32 controls the output of the electric motor 33 based on this detection information, that is, the information that the steering wheel 1 has been steered, and the driving of the electric motor 33 drives the hydraulic pump 11 similar to the above-mentioned (1) hydraulic pump method. be done.

However, in such a system, the pump drive is only ON-OFF controlled by an electric motor, and the conventional hydraulic servo valve is used for pressure control, and the above-mentioned drawbacks in this respect cannot be solved.

Further, in the above methods (1), (II), and (I[I), since the road reaction force caused by steering is not applied to the control, sudden steering becomes unstable, especially when driving at high speed.

(Objective of the Invention) Therefore, the present invention drives the hydraulic pump with an electric motor only when necessary according to the steering condition, detects the rotational speed of the steering wheel, and corrects the output of the electric motor, thereby adjusting the rotational speed of the steering wheel. The purpose of this system is to generate hydraulic pressure according to the steering force regardless of the steering force, to provide appropriate power assistance, as well as to improve steering stability, improve device installation, and reduce the power required for power assist.

(Means for Solving the Problems) In order to achieve the above object, the power steering system according to the present invention, as shown in FIG. A steering speed detection means for detecting the rotational speed of the steering wheel, a discrimination means C for determining the steering direction and steering force of the steering wheel based on the output of the operation state detection means, and a hydraulic pump according to the steering direction and steering force of the steering wheel. a control means d that calculates an output control value to an electric motor that drives the motor and corrects the output control value according to the steering speed; an electric motor e that outputs a driving force according to the output control value from the control means; Driven by an electric motor,
It includes a hydraulic pump f that generates hydraulic pressure corresponding to the output of the electric motor, and a hydraulic actuator g that generates auxiliary power that assists the steering force of the steering wheel based on the discharge pressure from the hydraulic pump.

(Function) In the present invention, the steering direction, steering force, and rotational speed of the steering wheel are detected, and the hydraulic pump is driven by the electric motor only when necessary according to the detection results, and the electric motor output is adjusted according to the rotational speed of the steering wheel. will be corrected. therefore,
Regardless of the rotational speed of the steering wheel, an appropriate hydraulic pressure is generated according to the steering force, providing appropriate power assistance, improving steering stability, improving the ease of installing the device, and reducing the required power.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 10 are diagrams showing one embodiment of the present invention, and are examples in which the present invention is applied to a power steering device for a vehicle such as an automobile.

First, the configuration will be explained. In FIG. 2, 41 is a handle, and the steering force TM of the handle 41 is transmitted via a steering shaft 42 to a pinion 44 that constitutes a part of a steering device 43. The pinion 44 is rotatably supported by bearings 46 and 47 fixed to the housing 45, and its center meshes with a rack 48. Therefore, when the handle 41 is steered, the pinion 44 rotates, and the rack 48 is engaged with the rack 48.
8 moves left and right in the figure. That is, the rotational displacement of the handle 41 is converted into a linear displacement of the rack 48. The pinion 44, housing 45, bearings 46, 47, and rack 48 constitute a steering device 43. In addition, 4
9 is a dust seal.

A hydraulic cylinder 51 is integrally disposed on the right side of the steering device 43 in the figure, and the hydraulic cylinder 51 has a loft 52 formed integrally with the rack 48 . A piston 53 is fixed to the rod 52.
is slidably movable within the outer cylinder 54 of the hydraulic cylinder 51. Further, the inside of the outer cylinder 54 is divided into an A chamber 55 and a B chamber 56 by a piston 53, and each chamber 55, 56
A seal 57, 58 is provided on each side. Each chamber 55, 56 is connected to a main oil passage 61, 62 through a port 59, 60, and the main oil passage 61, 62 is connected to a hydraulic pump 63 that can rotate in forward and reverse directions. Branch oil passages 64.65 are connected to each middle of the main oil passages 61.62, and the branch oil passages 64.65
is connected to the oil tank 66. Check valves 67, 68 and fixed throttles 69, 70 are disposed in the middle of each of these branch oil passages, and the fixed throttles 69, 70 create a pressure difference before and after the hydraulic oil passes through them.

The hydraulic pump 63 is driven by an electric motor 71, and the electric motor 71 is rotated by a drive signal V from a control circuit 72. The control circuit 72 receives a signal vI from the steering force sensor 73, signals S9 and St from the steering speed sensor 74, a signal (2) from the vehicle speed sensor 75, and a signal T0 from the oil temperature sensor.

The steering force sensor 73 is attached to the steering shaft 42 and detects the direction and magnitude of the steering force of the handle 41. Devices that detect such steering force include, for example, a strain gauge type that detects the amount of distortion caused by torque as an electrical quantity, a potentiometer type that electrically detects the amount of torsion caused by torque as a displacement amount, or a type that detects torsional displacement. A device using a Hall element that detects the amount of change in the magnetic field is used. Further, as a device for detecting the steering angle, for example, a method of detecting light passing through a slit in a rotary plate as a pulse signal is used.

The steering speed sensor 74 is attached to the steering shaft 42 together with the steering force sensor 73, and detects the rotational speed and rotational acceleration of the steering wheel 41. On the other hand, the vehicle speed sensor 74 detects the speed (vehicle speed) of the vehicle, and uses, for example, a signal from a speedometer.

Further, the oil temperature sensor 76 is provided in the middle of the passage connected to the oil tank 66, and detects the temperature T0 of the hydraulic oil.

The control circuit 72 has functions as a determination means and a control means, and is constituted by a microcomputer. Then, the control circuit 72 calculates a processing value necessary for assisting the steering force of the vehicle according to a program stored therein, and outputs a drive signal V to the electric motor 71 as necessary. Electric motor 7
1 generates a rotational force according to the drive signal (2) to rotate the hydraulic pump 63 forward or reverse. A type of hydraulic pump 63 that can be rotated in forward and reverse directions is used, and generates hydraulic pressure corresponding to the rotational driving force of the electric motor 71, and pumps the main oil passage 61.
．． 62 to the hydraulic cylinder 51. The hydraulic cylinder 51 moves the piston 53 linearly from side to side in the figure in response to the oil pressure supplied to each chamber 55, 56, and steers the steering wheel 76 via a linkage mechanism 75 connected to the rod 52.

The hydraulic cylinder (including the piston and outer cylinder) 51, the rod 52, the main oil passage 61.62, the branch oil passage 64.65,
Oil tank 66, check valve 67, 68 and fixed throttle 6
9.70 constitutes a hydraulic actuator 79 as a whole, and the hydraulic actuator 79 generates auxiliary power for assisting the steering force T□ of the handle 41 based on the discharge pressure from the hydraulic pump 63.

FIG. 3 is a block diagram showing the overall configuration described above.

In this figure, the application of steering force T by the driver via the steering wheel 41 is detected by the steering force sensor 73,
The steering force sensor 73 uses this as a signal (■) and sends it to the control circuit 72.
Output to. The control circuit 72 is composed of a signal amplification processing circuit 81, an arithmetic circuit (such as a CPU) 82, and a motor drive circuit 83. The signal amplification processing circuit 81 amplifies the signal (1) by the necessary amount and outputs it as a signal (2) to the arithmetic circuit 82.The arithmetic circuit 82 also receives the rotational speed signal Sl and rotational acceleration signal from the steering speed sensor 74 as other inputs. S2,
Vehicle speed signal V from vehicle speed sensor 75 and oil temperature sensor 7
The oil temperature signals T0 from 6 are respectively input. Based on these signals Vz, S+, St, Vz, and To, the arithmetic circuit 82 outputs a signal (4) necessary for controlling the steering force assistance of the vehicle to the motor drive circuit 83 in accordance with the aforementioned program.

The motor drive circuit 83 converts the signal V to the level necessary to drive the motor 71 based on the signal 4 to the motor 7.
Output to 1. The electric motor 71 rotates forward or reverse depending on the signal V, and the hydraulic pump 63 generates a hydraulic pressure P according to the driving force of the electric motor 71 to drive the steering device 43 including the hydraulic cylinder 51 (indicated by a hydraulic actuator 79 in this figure). ) to generate auxiliary steering force F. and,
This auxiliary steering force F is detected again by the steering force sensor 73 as a rotational displacement of the steering shaft 42, and is feedback-controlled so that the steering wheel is steered to a desired position.

Next, the effect will be explained.

FIG. 4 is a flowchart showing a steering force assistance program executed by the control circuit 72. This program is executed once every predetermined time.

First, the steering force TH% of the handle 41 at P
The rotational speed SI of the handlebar 41, the rotational acceleration S2 of the steering wheel 41, the vehicle speed 3, and the oil temperature T0 are read. Next, the output (2) of the steering force sensor 73 representing the steering force T is converted and amplified to obtain a signal (2). In P3, the current steering force conversion value ■2 is set to a predetermined value ■. Compare with. Here, the predetermined value ■. is set to a value corresponding to the case where the steering force T of the steering wheel 41 is extremely small and so-called power assist is not required, and takes into consideration, for example, vibrations of the vehicle etc. and rattles due to wear of various members constituting the steering device. It has become.

V, <V. In this case, it is determined that there is no need to assist the steering force T of the steering wheel 41, and the current routine is ended. Therefore, in this case, the drive signal (2), which will be described later, is not output, and no power is supplied to the motor 71. This is the case when the hydraulic actuator 77 does not need to perform power assist.
This means that there is no need to constantly generate hydraulic pressure to drive the engine.

Incidentally, in conventional hydraulic types, the hydraulic pump rotates even when power assist is not applied.

Therefore, this leads to a reduction in driving power.

On the other hand, in step P above, v2≧■. In this case, it is determined that power assist is necessary, and the steering direction (steered direction) is determined in P4. Signal ■2 represents the steering direction and the magnitude of the steering force; when V2>o, it indicates that the vehicle is being steered to the right, and when v2〉o, it indicates that the vehicle is being steered to the left.

■When the value is 0, the control signal is P, and the control signal is V when steering to the right.
4 is calculated, and when Vz<O, the control signal -■ at the time of left steering toward P is calculated.

As shown in FIG. 5, the control signals V4 and -V are set so as not to assist the steering within a certain range from the start of steering, taking into account the amount of play in the steering wheel. When the fixed range is exceeded, the value (also an absolute value) increases as the steering force conversion value v2 increases (increases in absolute value).

When ps or P is obtained, the drive signal ① is outputted to the electric motor 71 in response to the control signal V4, -V4 corresponding to the above-mentioned calculation result at P. Control signal V4, V
The relationship between a and the drive signal V has linearity as shown in FIG. 6, but this characteristic may be set arbitrarily depending on the control mode.

Also, in this step P, the rotational speed S3 mentioned above is
, rotational acceleration S2, vehicle speed (2), and oil temperature T0. Each correction value will be explained later.

In this way, the control signal signal v4, −
A drive signal V is output to the electric motor 71 based on
3 in forward or reverse rotation. As a result, the hydraulic pump 63 is driven in accordance with the rotation speed N of the electric motor 71,
A pump discharge amount Q as shown in FIG. 8 is generated and supplied to the hydraulic actuator 77.

The hydraulic oil discharged from the hydraulic pump 63 causes the hydraulic cylinder 51 to slide left and right in FIG.

When the main oil passage 61 is set as the discharge side in the hydraulic pump 63, the hydraulic oil flows into the A chamber 55 and returns to the oil tank 66 through the branch oil passage 64 and the fixed throttle 69.

On the other hand, the main oil passage 62 is on the suction side, and the hydraulic oil passes through the check valve 68, the fixed throttle 70, and the branch oil passage 65, and is sucked into the hydraulic pump 63 again by the main oil passage 62.

At this time, the rod 52 moves to the right in the figure as the piston 53 receives hydraulic pressure, and the steering force is assisted. On the other hand, if the discharge side and suction side are reversed,
The passage route of hydraulic oil is reversed.

In the above case, when the hydraulic oil discharged by the hydraulic pump 63 passes through the fixed throttles 69, (70), a pressure difference occurs before and after the throttles. For example, if the downstream side of the throttle is set to approximately atmospheric pressure (because it is open to the oil tank 66), the pressure PD will be generated on the upstream side.

This pressure PD is determined by the flow rate Q passing through the fixed throttles 69, (70), and its characteristics tend to increase rapidly as the pump discharge rate increases, as shown in FIG. Note that since the flow rate Q passing through the fixed throttles 69 and (70) is approximately the discharge flow rate of the hydraulic pump 63, this flow rate Q is proportional to the pump rotation speed N (=motor rotation speed), and this characteristic is the same as the eighth It will look like the figure.

On the other hand, during sudden steering, the pressure PD is
The rotation speed S is corrected based on the rotation speed S outputted from the rotation speed S. For example, the pressure PD decreases as the rotation speed of the handle increases under a constant pump discharge flow rate because the flow rate passing through the fixed throttles 69, (70) decreases. In this state, the control circuit 72 increases the rotation speed of the electric motor 71 according to the rotation speed signal S1 of the steering speed sensor, and
, (70) can be kept constant to obtain the desired pressure PD.

Furthermore, as the hydraulic fluid passes through each member constituting the hydraulic actuator 79, its viscosity changes under the influence of frictional heat, outside temperature, and the like. At this time, if the fixed throttle 69, (70) that generates the hydraulic pressure PD is an orifice, it is less susceptible to changes in viscosity, but the fixed throttle 69, (70)
The oil passages before and after are affected by viscosity. Therefore, even if the discharge flow rate of the hydraulic pump 63 is constant, the hydraulic pressure PD
changes. Generally, when the temperature of the hydraulic oil increases, the oil pressure P
D decreases, and conversely, when the temperature of the hydraulic oil decreases, the oil pressure PD increases.

As a result, the hydraulic actuator 77 cannot provide power assistance corresponding to the rotational speed N of the electric motor 71. Therefore, by giving the output of the oil temperature sensor 75 as data to the control circuit 71 and using this data information for feedback control of the discharge pressure, the oil pressure PD corresponding to the steering force T is output.

Furthermore, the oil pressure PD is corrected by the vehicle speed signal V.

The characteristics are shown in FIG. 10, and as the vehicle speed increases, the oil pressure PD decreases. Therefore, the auxiliary force is controlled to be large when the vehicle is running at low speeds and when the vehicle is stationary, and to be small when the vehicle is running at high speeds. Moreover, large lateral acceleration is applied to the vehicle due to sudden steering during high-speed driving, and a road reaction force is generated in accordance with the acceleration. In this case, the control circuit 72 calculates the lateral acceleration based on the vehicle speed signal V described above and information on the rotational acceleration S2 detected by the steering speed sensor 74. The control circuit 72 controls the electric motor 63 based on the calculated value so that a steering feeling corresponding to the road reaction force is obtained. At this time, the rotational speed of the electric motor 71 becomes smaller as the rotational acceleration St increases under a constant vehicle speed. Therefore, the auxiliary power becomes smaller and the steering force becomes heavier, allowing stable steering.

From the above, the hydraulic pressure PD corresponding to the steering force T is appropriately corrected by the rotational speed SI, the rotational acceleration S2, the vehicle speed V, and the oil temperature T0, and the power assist according to the steering condition is applied to the hydraulic actuator during steering. Granted by 79.

Based on the above effects, the effects of this embodiment will be compared with the conventional example from the viewpoints of problems (a) to (h).

(A) Since the hydraulic pump 63 is driven by the electric motor 71 only when power assistance is required depending on the steering wheel 41, the hydraulic pump 63 is stopped when the vehicle is not being steered. In addition to this, the pump can also be stopped regardless of the steering force, for example in high speed ranges where power assist is not required, resulting in no loss of engine power and a significant energy saving effect.

This means that the problem (b) above is solved.

(B) Hydraulic servo valves and flow control valves that require precision machining as in the past are no longer necessary, and all control can be performed electrically. Therefore, the above problems (a), (c), (
D) and (TI[) can be resolved.

(C) Electrical control makes it possible to easily create steering characteristics that are optimal for various vehicle running conditions.

Therefore, the above problem (e) can be solved.

(D) By controlling the rotational speed of the steering wheel, the desired oil pressure can be obtained regardless of the steering speed. Therefore, the above-mentioned problem can be solved.

(E) Since the hydraulic pressure generation source composed of the electric motor 71 and the hydraulic pump 63 is connected to the hydraulic cylinder of the steering device through hydraulic piping, it can be installed anywhere in a vacant space of the vehicle.

In other words, the wearability is extremely good. Therefore, since a coupling device such as a speed reducer is not required, the above-mentioned problem (g) can be solved, and problem (h) can be solved as well.

In addition, by providing power assistance in accordance with the road reaction force based on the vehicle speed and the rotational acceleration of the steering wheel, the sense of instability caused by sudden steering during high-speed driving is eliminated.

In this embodiment, a hydraulic pump capable of forward and reverse rotation is used, but the present invention is not limited to this. In short, any device that generates a constant operating pressure depending on the steering condition of the steering wheel may be used. Therefore, a hydraulic pump that rotates only in a fixed direction may be used, and the discharge operating pressure thereof may be switched by a predetermined hydraulic mechanism to operate the hydraulic cylinder.

(Effects) According to the present invention, since the hydraulic pump is driven by the electric motor only when necessary according to the steering condition, it is possible to generate the desired hydraulic pressure according to the steering force and provide appropriate power assistance. . As a result, it is possible to improve steering stability, improve device attachment, and reduce the power required for power assist.

[Brief explanation of drawings]

Fig. 1 is a basic conceptual diagram of the present invention, Figs. 2 to 10 are diagrams showing an embodiment of the present invention, Fig. 2 is an overall configuration diagram thereof, Fig. 3 is a block diagram thereof, and Fig. 4 is a diagram showing an embodiment of the present invention. A flowchart showing the steering force assistance program; FIG. 5 is a diagram showing the characteristics of the control signal; FIG. 6 is a diagram showing the characteristics of the drive signal;
Figure 7 is a diagram showing the characteristics of the motor rotation speed, Figure 8 is a diagram showing the characteristics of the pump discharge amount, Figure 9 is a diagram showing the oil pressure in relation to the pump discharge rate, and Figure 10 is a diagram showing the relationship between the pump discharge amount and the oil pressure. Figures 11 to 13 are diagrams showing the relationship between hydraulic pressure and steering force; Figures 11 to 13 are diagrams for explaining a conventional power steering system; Figure 11 is a schematic configuration diagram showing the hydraulic power steering system; Figure 12 is a schematic diagram showing the hydraulic power steering system; 13 is a schematic configuration diagram showing the electric power steering device, and FIG. 13 is a schematic configuration diagram showing the motor-driven pump drive type power steering device. 63... Hydraulic pump, 71... Electric motor, 72... Control circuit (discrimination means, control means), 7
3...Steering force sensor (steering state detection means), 7
4...Steering speed sensor (steering speed detection means),
77...Hydraulic actuator.

Claims (1)

[Scope of Claims] a) Steering state detection means for detecting the steering state of the steering wheel; b) Steering speed detection means for detecting the rotational speed of the steering wheel; c) Steering of the steering wheel based on the output of the operation state detection means. a determining means for determining the direction and steering force; and d) calculating an output control value to an electric motor that drives the hydraulic pump according to the steering direction and steering force of the steering wheel, and correcting the output control value according to the steering speed. e) an electric motor that outputs a driving force according to the output control value from the control means; f) a hydraulic pump driven by the electric motor and generating hydraulic pressure corresponding to the output of the electric motor; and g) hydraulic pressure. A power steering device comprising: a hydraulic actuator that generates auxiliary power to assist steering force of a steering wheel based on discharge pressure from a pump;