JPS632772A - Power-steering device - Google Patents

Abstract

PURPOSE:To improve the fittability of an adequate power-subsidiary-device and lessen the power required by providing a control means operating an output control value to an electric motor which drives a hydraulic pump according to the steering direction and steering force of a 'handle'. CONSTITUTION:A hydraulic pump 63 is driven by an electric motor 71, which rotates according to a drive signal from a control circuit 72. Signals from a steering force sensor 73 and a vehicle speed sensor 74 are inputted at the control circuit 72. And the control circuit 72 operates a processing value necessary for supporting the steering force of a vehicle in conformity to a program housed therein, and outputs the drive signal to the electric motor 71 as occasion calls. The electric motor 71 generates rotational force according to this drive signal and reciprocates the hydraulic pump 63 and generates hydraulic pressure, which is supplied to a hydraulic cylinder 51 through main hydraulic passages 61, 62. The cylinder 51 steers a steering control wheel 76 through a linkage mechanism 75.

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 suitable for use in power steering of vehicles such as automobiles.

(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, from the viewpoint of maneuverability and stability, so-called power steering devices have recently been installed in vehicles, and their popularity 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, appropriate reaction force feed pack 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.

([) Hydraulic type (see Fig. 11) In Fig. 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 according to the rotational displacement of the handle 1.

On the other hand, the hydraulic servo valve 3 is filled with discharge oil from a hydraulic pump 11 that is constantly driven by the engine 10, and the hydraulic servo valve 3 switches the discharge oil pressure supplied to the hydraulic cylinder 6 according to the steering direction of the handle 1. Control is performed to move the piston of the hydraulic cylinder 6 and apply 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.

- 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.

(II) 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 a23 is controlled according to the rotation 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 disadvantages of the hydraulic type, 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 (T) and (II) above,
The following motor-driven pump type has been proposed, which has the following advantages: (1) improvement of power loss, which is a drawback of hydraulic type;
) The aim is to improve the ease of installation, which is a drawback of electric types.

(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 turned. : [II, by driving the electric motor 33, the above (
1) A hydraulic pump 11 similar to the hydraulic pump system is driven.

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

(Purpose of the Invention) Therefore, the present invention generates hydraulic pressure according to the steering force by driving the hydraulic pump with an electric motor only when necessary according to the steering state, and at the same time, it is possible to provide appropriate power assistance to the device. The aim is to improve installation ease 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 has a steering state B detection means for detecting the steering state of the /% steering wheel, as shown in FIG. a, and a determining means for determining the steering direction and steering force of the steering wheel based on the output of the steering state detecting means a, which determines an output control value to the electric motor that drives the hydraulic pump in accordance with the steering direction and steering force of the steering wheel. A control means C that performs calculations, an electric motor d that outputs a driving force according to an output control value from the control means C, and a hydraulic pump e that is driven by the electric motor d and generates hydraulic pressure corresponding to the output of the electric motor d. The hydraulic actuator f generates auxiliary power to assist the steering force of the steering wheel based on the discharge pressure from the hydraulic pump e.

(Function) In the present invention, the steering direction and steering force of the steering wheel are detected, and the hydraulic pump is driven by the electric motor only when necessary according to the detection results.

Therefore, an appropriate hydraulic pressure is generated according to the steering force, providing appropriate power assistance, improving the ease of mounting 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 TH 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 47 and 48 fixed to the housing 45, and its central portion meshes with a rack 49. Therefore, when the knob 41 is steered, the pinion 44 rotates, and the rack 49 is engaged with it, causing the rack 49 to move left and right in the figure. That is, the rotational displacement of the handle 41 is converted into a linear displacement of the handle 49. The above pinion 44, No. 1 housing 45, bearing 46.47.
48 and rack 49 constitute the steering device 43 (note that 46 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 rond 52 that is integrally formed with the rack 49. 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 via a boat 59.60, respectively.
62 is connected to a hydraulic pump 63 capable of forward and reverse rotation. Branch oil passages 64 are provided in the middle of each of the main oil passages 61 and 62.
．． 65 are connected, and branch oil passages 64 and 65 are connected to an oil tank 66. Check valves 67, 68 and fixed throttles 69, 7 are located in the middle of each of these branch oil passages.
0 is provided, and the fixed throttle 69.70 creates a pressure difference before and after the fixed throttle when the hydraulic oil passes through it.

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. Signals V, , V, from a steering force sensor 73 and a vehicle speed sensor 74 are input to the control circuit 72 . The steering force sensor 73 is attached to the steering shaft 42,
The direction and magnitude of the steering force of the handle 41 are detected. Devices for detecting 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 twist caused by torque as an amount of displacement, or a mirror displacement type. 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.

-4. The vehicle speed sensor 74 detects the speed (vehicle speed) (3) of the vehicle, and uses, for example, a signal from a speedometer. 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.

The electric motor 71 generates a rotational force according to the drive signal (2) to rotate the hydraulic pump 63 forward or reverse. hydraulic pump 6
3 is a type that can rotate in forward and reverse directions, and the electric motor 7
Hydraulic pressure corresponding to the rotational driving force of No. 1 is generated and supplied to the hydraulic cylinder 51 through main oil passages 61 and 62.

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 moves the steering wheel 7 via a linkage mechanism 75 connected to the rod 52.
Steer 6.

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 as a whole constitutes a hydraulic actuator 77, and the hydraulic actuator 77 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 1 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 (2) by the necessary amount and outputs it as the signal (2) to the arithmetic circuit 82.The arithmetic circuit 82 also receives the vehicle speed sensor 7 as another input.
A vehicle speed signal V from 4 is input. Based on these signals (2) and (V3), 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 is a signal ■
4, the signal V is converted to a level necessary to drive the motor 71 and is output to the motor 71. The electric motor 71 rotates forward or reverse depending on the signal V, and the hydraulic pump 63
generates a hydraulic pressure P corresponding to the driving force of the electric motor 7I, operates the steering device 43 (indicated by a hydraulic actuator 77 in this figure) including the hydraulic cylinder 51, and generates an auxiliary steering force F. Then, this auxiliary steering force F is returned to the steering force sensor 7 as a rotational displacement of the steering shaft 42.
3, and feedback control is performed 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 T of the steering wheel 41 and the vehicle speed ■3 are determined by Pl.
Load. Next, a steering force sensor 7 representing the steering force T
3's output ■1 is converted and amplified to obtain signal ■2. At P, the current steering force conversion value ■2 is set to a predetermined value ■. Compare with. Here, the predetermined value V. 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.

V2<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, a drive signal v5, which will be described later, is not output, and no power is supplied to the electric 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, if V>V in step P, it is determined that power assist is necessary, and the forward direction (steering direction) is determined in P4. The signal vt represents the steering direction and the magnitude of the steering force, and when 2>0 indicates that the vehicle is being steered to the right, and when V2<0, it indicates that the vehicle is being steered to the left.

■, When >0, use P, the control signal when steering to the right■
4, and when vz<0, P is used to calculate the control signal -v4 during left steering.

As shown in FIG. 5, the control signals V, -V4 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 specified range is exceeded, the steering force conversion value v2
As the value increases (the absolute value increases), the value (also the absolute value) becomes thicker (becomes thicker).

If we get P5 or P6, then P? Then, a control signal V4 corresponding to the above calculation result and a drive signal V according to V4 are output to the electric motor 71. Control signal V, , -
The relationship between V and the drive signal V is as shown in FIG.
Although it has linearity, this characteristic may be arbitrarily set depending on the control mode.

Further, in this step P1, a correction is made based on the information of the vehicle speed V mentioned above. This correction value is specifically shown in FIG. 10, which will be described later.

In this way, the control signal V, which is differentiated into positive and negative values,
-V4, the drive signal V is output to the electric motor 71, so the electric motor 71 rotates at a rotation speed N corresponding to the steering direction and the magnitude of the steering force as shown in FIG. Drives forward or reverse. As a result, the hydraulic pump 63 is driven in accordance with the rotational speed N of the electric motor 71 to generate a pump discharge amount Q as shown in FIG. 8 and supply it 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 equal to the flow I passing through the fixed throttle 69, (70).
It is determined by Q, and its characteristics tend to increase rapidly as the steering force increases, as shown in FIG. Note that the flow rate Q passing through the fixed throttle 69, (70)
is approximately the discharge flow rate of the hydraulic pump 63, so this flow i
1Q is proportional to the pump rotation speed N (=motor rotation speed), and this characteristic is as shown in FIG. 8 above.

From the above, the operating pressure PD is determined according to the steering force T, and the characteristics are appropriately corrected based on the vehicle speed (2), as shown in FIG. Therefore, power assist according to the steering force T and vehicle speed V is applied by the hydraulic actuator 77 during steering.

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

(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 valves and flow control valves that require precision machining as in the past are no longer required, and all control can be performed electrically. Therefore, the above problems (a), (c), (
D) and (Ill) 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) 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 an empty space of the vehicle.

In other words, the wearability is extremely good. Therefore, since a coupling device such as a speed reducer is unnecessary, the above-mentioned problem (f) can be solved, and problem (g) can be solved as well.

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 the - fixed direction may be used, and the discharge operating pressure 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 state, it is possible to generate hydraulic pressure according to the steering force and provide appropriate power assistance. As a result, it is possible to improve the ease of mounting the device and reduce the power required for power assist.

[Brief explanation of the drawing]

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
7...Hydraulic actuator.

Claims (1)

[Scope of Claims] a) Steering state detection means for detecting the steering state of the steering wheel; b) Discrimination means for determining the steering direction and steering force of the steering wheel based on the output of the steering state detection means; c) Discrimination means for determining the steering direction and steering force of the steering wheel. a control means that calculates an output control value to an electric motor that drives a hydraulic pump according to a steering direction and a steering force; d) an electric motor that outputs a driving force according to an output control value from the control means; and e) an electric motor. (f) a hydraulic pump that is driven to generate hydraulic pressure corresponding to the output of the electric motor; and (f) a hydraulic actuator that generates auxiliary power that assists the steering force of the steering wheel based on the discharge pressure from the hydraulic pump. Characteristic power steering device.