JP3032849B2 - Power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering apparatus using an electric hydraulic pump as a source of steering assist force.
More specifically, the present invention relates to a power steering apparatus that enables a driver to obtain an appropriate steering feeling according to a slow vehicle speed.

[0002]

2. Description of the Related Art In recent years, a power steering device that assists a steering operation by a hydraulic actuator such as a hydraulic cylinder disposed in a steering mechanism is not limited to large vehicles such as trucks and buses.
It is also widely used in small vehicles such as ordinary passenger cars.

[0003] By the way, the steering of an automobile is performed against a road surface reaction force acting on a steered wheel, and it is known that the magnitude of the road surface reaction force corresponds to a slower vehicle speed.
When the road surface reaction force is large and the vehicle is stopped or running at low speed, a large force is required for steering operation for steering. On the other hand, when the road surface reaction force is small in the middle speed region or at high speed, the steering operation is relatively small. obtain. Therefore, in the power steering device, it is required to generate a steering assist force that is large when the vehicle is stopped and running at a low speed, and is small when the vehicle is running at a high speed, that is, a steering assist force that becomes large or small according to the slowdown of the vehicle speed.

On the other hand, there is a problem of responsiveness of a steering assist force as a steering sensation experienced by a driver. The response of the steering assist force is closely related to the pressure oil flow rate, and the conventional relationship between the vehicle speed and the pressure oil flow rate is set as shown in FIG. FIG.
Is a graph showing the relationship between the vehicle speed and the pressure oil flow rate, with the horizontal axis representing the vehicle speed and the vertical axis representing the pressure oil flow rate. As is clear from the graph, the pressure oil flow rate gradually increases in a range from the state where the vehicle speed is zero to the medium speed area, the pressure oil flow rate becomes highest in the medium speed area, and the pressure oil flow rate increases further from here to the high speed area. It is decreasing rapidly.

[0005] The reason why the pressure oil flow rate is rapidly decreased from the middle speed range to the high speed range is to prevent the risk that a slight rotation of the steering wheel due to a camera shake or the like causes a meandering when the response is increased. Reduce the flow rate to increase the rigidity of the steering wheel,
In addition, reducing the hydraulic oil flow rate in the stop / low speed range does not require high responsiveness at the time of so-called stationary operation under such a condition, but rather reduces waste and reduces the load on the motor, thereby reducing power consumption. To save money.

[0006]

The pressure oil flow rate changes as shown in FIG. 5 in the stop / low speed range, for example, in relation to the discharge pressure of the hydraulic pump. FIG. 5 is a graph showing the relationship between the discharge side pressure and the pressure oil flow rate. The horizontal axis indicates the discharge side pressure of the hydraulic pump, and the vertical axis indicates the pressure oil flow rate. As apparent from this graph, when no special control is performed on the hydraulic pump, the discharge side pressure,
In other words, when the load on the hydraulic pump increases, the rotation speed of the motor that is the driving source of the hydraulic pump decreases, and the flow rate of the hydraulic oil also decreases.

As a result, FIG. 6 shows the relationship between the force applied to the steering wheel by the driver, that is, the steering torque and the hydraulic pressure (steering assist force).
It becomes as shown in. FIG. 6 shows the steering torque on the horizontal axis and the hydraulic pressure on the vertical axis. The solid line in the graph stops
The relationship in the low speed range, the broken line in the middle speed range, and the two-dot chain line in the high speed range. As is clear from this graph, the rigidity of the steering wheel should be increased as the vehicle speed increases, but in actuality, the operating torque in the medium speed range, in other words, the rigidity becomes lower than the rigidity in the stop / low speed range, and the driver There has been a problem that a deviation occurs in the sense of steering experienced. As a countermeasure against this, conventionally, as shown by a dashed line in FIG. 5, means has been proposed for keeping the flow rate of the feed pressure oil constant irrespective of the fluctuation of the discharge side pressure (Japanese Patent Laid-Open No. 59-112968) Gazette). However, with such means, although a slight improvement in the hydraulic pressure in the stop / low speed range can be expected, the hydraulic pressure in the medium speed range is always lower than the hydraulic pressure in the stop / low speed range for the same steering torque. It is not possible to eliminate the unnatural feeling of steering.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and enables an appropriate relationship between a steering torque and a steering assist force to be obtained in accordance with a slow vehicle speed, thereby eliminating unnatural steering feeling. It is an object of the present invention to provide a power steering device that can be obtained.

[0009]

According to the power steering apparatus of the present invention, the opening degree of the throttle portion interposed between the valve body and the casing is changed by the relative displacement generated between the valve body and the casing in response to the steering operation. In a power steering apparatus that controls an electric motor of a hydraulic pump so as to change a hydraulic pressure supplied to a hydraulic actuator for steering assistance according to a vehicle speed, a discharge pressure of the hydraulic pump is detected. a pressure sensor that, with an increase of the discharge pressure of the hydraulic pump in the middle speed range, the discharge pressure oil beyond the reduction ratio of the discharge pressure oil flow rate based on the reduction of the electric motor speed with an increase in the discharge pressure of the hydraulic pump A control unit that controls the electric motor to reduce the flow rate.

[0010]

According to the present invention, the flow rate of the hydraulic oil in the medium speed range is reduced at a rate exceeding the reduction rate of the flow rate of the hydraulic oil caused by the decrease in the number of revolutions of the electric motor caused by the increase in the pressure on the discharge side of the hydraulic pump. Thus, the steering torque in the middle speed range becomes relatively higher than the steering torque in the stop / low speed range, and a steering sensation corresponding to the slowdown of the vehicle speed can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic diagram showing the overall configuration of a power steering device according to the present invention (hereinafter referred to as the present device).

This figure shows a steering wheel (steering wheel) 1
The rotation of the pinion 3 interlocking with the rack shaft 6 is converted into sliding in the axial direction of a rack shaft 6 extending left and right at the lower part of the vehicle body via the rack 4, and wheels (not shown) connected to both ends of the rack shaft 6. Is a configuration example in a vehicle provided with a rack and pinion type steering mechanism that steers the oil, and discharges oil from a hydraulic pump P driven by a motor M from a steering wheel 1 to a pinion 3. Is sent to the hydraulic cylinder S formed in the middle of the rack shaft 6 through the hydraulic control valve 2 formed in the middle of
The hydraulic pressure (steering assist force) generated by the hydraulic cylinder S assists the sliding of the rack shaft 6.

The hydraulic control valve 2 coaxially connects an input shaft connected to the steering wheel 1 and an output shaft connected to the steering mechanism via a torsion bar, and a casing which rotates in conjunction with one of the connecting portions, And a valve body that rotates in conjunction with the other inside the cylinder, and is disposed between a hydraulic cylinder S disposed in the steering mechanism and a hydraulic pump P serving as a hydraulic pressure generation source. Between the casing and the valve element of the hydraulic control valve 2, there is formed a throttle portion whose opening degree changes according to the relative angular displacement of both, although not specifically shown in the figure. Of the hydraulic pump P from the port 2a of the hydraulic control valve 2 into the internal control groove due to the change in the opening degree of the
Is returned to the oil tank T, and is selectively supplied to the oil chamber of the hydraulic cylinder S from the port 2c or 2d in accordance with the operation of the steering wheel 1. The pressure oil in the oil chamber on the opposite side of the hydraulic cylinder S is supplied to the port 2c or 2d. The oil is selectively returned to the oil tank T via the port 2b from 2d or 2c.

The relative angular displacement is caused by the torsion of the torsion bar according to the steering torque applied to the steering wheel 1. As a result, the hydraulic cylinder S generates hydraulic pressure according to the steering torque applied to the steering wheel 1. The hydraulic pressure assists the force required for steering operation for steering. Reference numeral 5 denotes a control unit for the motor M of the hydraulic pump P. The control unit 5 controls the vehicle speed detected by the vehicle speed sensor 5a and the hydraulic pressure detected by the pressure sensor 5b provided on the discharge side oil passage from the hydraulic pump P to the hydraulic control valve 2 and the motor M. The driving current of the motor M is controlled based on the motor rotation speed by the rotation speed detector 5c.

The control by the control unit 2 is the same as the conventional case shown in FIG. 4 in terms of the relationship between the vehicle speed and the supply pressure oil flow rate.・ The pressure oil flow rate in the low speed range is slightly lower than that in the medium speed range, and the supply pressure oil flow rate in the high speed range is controlled by the control unit 5 so as to be lower than that in the medium speed range and stop / low speed range. The drive current of the motor M is controlled. FIG. 2 shows the relationship between the discharge pressure of the hydraulic pump and the flow rate of the supply pressure oil. FIG. 2 is a graph showing the control contents of the control unit 5, in which the horizontal axis indicates the discharge side pressure (pump load) of the pump P, and the vertical axis indicates the supply pressure oil flow rate. A broken line a in the graph indicates a control mode in the medium speed range by the device of the present invention. The solid line b shows the conventional relationship in the uncontrolled state in the stop / low speed range.
(The same as in FIG. 5), and the dashed line c shows the relationship when the pressure oil flow rate constant control is performed in the stop / low speed range, respectively.

As is apparent from this graph, control is performed in the middle speed range so that the flow rate of the hydraulic oil is reduced at a rate exceeding the reduction rate of the flow rate caused by the decrease in the number of revolutions of the motor M due to the increase of the normal discharge side pressure. . Specifically, in the range where the discharge side pressure in the medium speed range is small, the pressure oil flow rate in the medium speed range is higher than the pressure oil flow rate in the stop / low speed range, but with the increase in the discharge side pressure thereafter, The pressure oil flow rate in the medium speed range is made lower than the pressure oil flow rate in the stop / low speed range.

FIG. 3 is a graph showing the relationship between the steering torque and the hydraulic pressure (steering assist force) under the control as shown in FIG. 2 by the control unit 5, wherein the horizontal axis represents the steering torque, and the vertical axis represents the steering torque. The hydraulic pressure is shown in FIG. As is clear from this graph, in the region where the steering torque is small, there is a reverse rotation state in which the oil pressure in the middle speed region is still larger than the oil pressure in the stop / low speed region. It can be seen that the hydraulic pressure decreases in the order of the range, the middle speed range, and the high speed range, in other words, the rigidity of the steering wheel increases in this order, and a steering feeling according to the vehicle speed can be obtained.

[0018]

As described above, in the device of the present invention, in the medium speed range, the pressure oil is reduced at a reduction rate larger than the reduction rate of the pressure oil flow rate caused by the decrease in the rotation speed of the electric motor with the increase of the discharge side pressure. Since the flow rate is reduced, the stiffness of the steering wheel in the medium speed range is relatively increased compared to the stiffness in the low speed range, and an excellent effect of obtaining a steering sensation corresponding to the vehicle speed is achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a steering mechanism and a control system thereof in the device of the present invention.

FIG. 2 is a graph showing a relationship between a discharge side pressure of a hydraulic pump and a supply pressure oil flow rate in the device of the present invention.

FIG. 3 is a graph showing a relationship between a steering torque and a hydraulic pressure (steering assist force) as a control result of a control unit in the device of the present invention.

FIG. 4 is a graph showing a relationship between a vehicle speed and a supply pressure oil flow rate of a conventional device.

FIG. 5 is a graph showing a relationship between a discharge side pressure of a hydraulic pump of a conventional device and a supply pressure oil flow rate.

FIG. 6 is a graph showing a relationship between a steering torque and a hydraulic pressure (a steering assist force) in a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Hydraulic control valve 3 Pinion 4 Rack 5 Control part 5a Vehicle speed sensor 5b Pressure sensor 5c Speed detector P Hydraulic pump M Motor

Claims (1)

(57) [Claims] A hydraulic actuator for assisting steering by changing the opening degree of a throttle portion interposed between an electric hydraulic pump and a valve body and a casing in response to steering operation by a relative displacement generated between the valve body and the casing. A hydraulic control valve that changes the supply hydraulic pressure to the hydraulic control valve, and a supply pressure oil flow rate to the hydraulic actuator is higher in the middle speed range than in the stop / low speed range according to the vehicle speed. A power steering device having a control unit that controls an electric motor of the electric hydraulic pump so as to be lower than in a middle speed range, wherein the control unit includes a vehicle speed sensor and a pressure sensor that detects a discharge side pressure of the hydraulic pump. with the increase in discharge pressure of the hydraulic pump in the mid-speed range based on the detected value, decrease the feed pressure oil flow beyond the reduction ratio of the feed pressure oil flow electric motor rotation speed reduction in the results due to Before A power steering device for controlling the electric motor.