JPH10203389A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power steering device by which durability of a pump part and a pressure oil supply hose or the like can be improved by reducing relief pressure of a pump to supply pressure oil to a steering assisting force generating hydraulic cylinder without enlarging the whole device. SOLUTION: Oil pressure of pressure oil supplied from a pump to a steering assisting force generating hydraulic cylinder 18, is controlled by a control valve according to steering resistance. Rightward steering assisting force is imparted by a unidirectional movement of a piston 20 by oil pressure of pressure oil supplied to one oil chamber 21 partitioned by the piston 20 in a cylinder tube 19 of its hydraulic cylinder 18, and leftward steering assisting force is imparted by the other directional movement of the piston 20 by oil pressure of pressure oil supplied to the other oil chamber 22. The pressure receiving area of its piston 20 changes so that the pressure receiving area of the piston 20 in a condition where a steering angle is not less than a preset value becomes larger than the pressure receiving area of the piston 20 in a condition where it is less than its preset value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for generating a steering assist force by a hydraulic cylinder.

[0002]

2. Description of the Related Art The force required for steering a vehicle is maximized when the steering is performed up to just before the left and right steering limit, because the greater the steering angle, the greater the reaction force acting on the tire from the road surface.

[0003] Therefore, in a power steering apparatus including a hydraulic cylinder that generates a steering assist force by pressure oil from a pump, in order to generate a steering assist force commensurate with the force required for the steering, the hydraulic cylinder is supplied from the pump to the hydraulic cylinder. A control valve is provided for controlling the hydraulic pressure of the pressurized oil according to the steering resistance. Thus, as shown in FIG. 8, the hydraulic pressure acting on the hydraulic cylinder is maximized immediately before the steering limit. When the steering is performed to the steering limit angle θ, the hydraulic pressure acting on the hydraulic cylinder is released to prevent an impact.

[0004]

The relief pressure of the pump in the power steering apparatus needs to be larger than the maximum value of the hydraulic pressure acting on the hydraulic cylinder. However, if the relief pressure of the pump is increased, the durability of the pump parts, the pressure oil supply hose, and the like decreases.

In addition, a pump for supplying pressure oil to the hydraulic cylinder is driven by an electric motor, and to save energy, the rotation speed of the motor is set to a steering assist speed when assisting steering and to a standby speed when canceling steering assist. In the power steering apparatus, in order to increase the hydraulic pressure acting on the hydraulic cylinder, it is necessary to increase the output torque of the motor, so that the drive current value increases, and energy saving cannot be sufficiently achieved.

An object of the present invention is to provide a power steering device that can solve the above-mentioned problems.

[0007]

According to the present invention, there is provided a hydraulic cylinder for generating a steering assist force by pressure oil from a pump;
A control valve that controls the hydraulic pressure of the hydraulic oil supplied to the hydraulic cylinder in accordance with the steering resistance.
It has a cylinder tube and a piston that forms a pair of oil chambers by partitioning the inside of the cylinder tube, and a right steering assist force is applied by one-way movement of the piston by hydraulic pressure of pressure oil supplied to one oil chamber. The present invention is applied to a power steering device in which a left steering assist force is applied by the piston moving in the other direction by the hydraulic pressure of the pressure oil supplied to the other oil chamber.

[0008] The power steering apparatus of the present invention is arranged such that the pressure receiving area of the piston when the left and right steering angles are equal to or greater than the set value is larger than the pressure receiving area of the piston when the left and right steering angles are less than the set value. It is characterized in that the pressure receiving area changes.

According to the present invention, the pressure receiving area of the piston is
When the left and right steering angles are larger than the set value, the steering resistance is reduced by increasing the steering assist force without increasing the hydraulic pressure of the hydraulic oil supplied to the hydraulic cylinder by making it larger than the state below the set value. it can. Therefore, the maximum value of the hydraulic pressure applied to the hydraulic cylinder can be reduced, and the relief pressure of the pump can be reduced.

[0010] The cylinder tube has a portion in one of the oil chambers whose inner diameter gradually increases toward one end;
The other oil chamber has a portion whose inner diameter gradually increases as it goes to the other end, and the piston has a piston body and a piston ring fitted on the outer periphery of the piston body, and the piston moves. The piston ring is elastically deformable in the radial direction so that the outer diameter of the piston ring changes according to the change in the inner diameter of the cylinder tube, and the pressure receiving area of the piston changes due to the change in the outer diameter of the piston ring. Is preferred. Thus, the pressure receiving area of the piston can be changed with a simple configuration. In this case, a plurality of piston rings parallel to the movement direction of the piston are fitted around the outer periphery of the piston body, and each piston ring is elastically deformable so as to change its outer diameter by being divided at one place. It is preferable that the divided end positions in the circumferential direction of the piston ring are different from each other. As a result, leakage of pressure oil between the two oil chambers can be reliably prevented.

The hydraulic cylinder generates a steering assisting force by pressure oil from a pump driven by an electric motor, and sets the rotation speed of the motor to the steering assisting speed at the time of steering assist, and the standby speed at the time of canceling the steering assisting. It is preferable to provide a means for performing the following. In this case, the maximum value of the hydraulic pressure applied to the hydraulic cylinder can be reduced, so that the output torque of the drive motor of the pump can be reduced.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

A rack and pinion type power steering apparatus 1 shown in FIG. 1 includes an input shaft 2 connected to a steering wheel H, and an output shaft 4 connected to the input shaft 2 via a torsion bar 3. The torsion bar 3 is connected to the input shaft 2 via a pin 5 and to the output shaft 4 via a serration 6. Its output shaft 4
A rack 8 meshing with the pinion 7 is connected to steering wheels (not shown). The input shaft 2 is connected to a valve housing 10 via a bearing 9.
a and is supported by the output shaft 4 via a bush 11. The output shaft 4 is supported by the rack housing 10b via bearings 12 and 13. As a result, the rotation of the input shaft 2 due to the steering is transmitted to the pinion 7 via the torsion bar 3, and the rack 8 moves in the vehicle width direction, and the wheels are steered by the movement of the rack 8. Note that oil seals 14, 15 are provided between the input / output shafts 2, 4 and the valve housing 10a. Also,
A support yoke 16 for supporting the rack 8 is provided. The support yoke 16 is pressed against the rack 8 by the elastic force of a spring 17.

A hydraulic cylinder 18 is provided for generating a steering assist force by pressure oil from a pump 37. The hydraulic cylinder 18 has a cylinder tube 19 formed by a part of the rack housing 10b, and an annular piston 20 formed integrally with the rack 8. The piston 20 partitions the inside of the cylinder tube 19 to form a pair of oil chambers 21 and 22. Each oil chamber 21, 2
2, a rotary hydraulic control valve 23 that controls the hydraulic pressure of the hydraulic oil supplied to the hydraulic cylinder 18 according to the steering resistance is connected. The control valve 23 includes a cylindrical first valve member 24 and a second valve member 25 inserted into the first valve member 24 so as to be relatively rotatable. The first
The valve member 24 is rotatably attached to the output shaft 4 via a pin 26. The second valve member 25 is formed integrally with the outer periphery of the input shaft 2.

As shown in FIG. 2, a plurality of recesses along the axial direction are formed on the inner periphery of the first valve member 24 and the outer periphery of the second valve member 25 at equal intervals in the circumferential direction. The first valve member-side recess is composed of four right steering recesses 27 located at equal intervals in the circumferential direction and four left steering recesses 28 located at equal intervals in the circumferential direction. The second valve member-side recess is composed of four pressure oil supply recesses 29 located at equal intervals in the circumferential direction and four pressure oil discharge recesses 30 located at equal intervals in the circumferential direction. Each right steering recess 27 and each left steering recess 28 are alternately arranged in the circumferential direction, and each pressure oil supply recess 29 and each pressure oil discharge recess 30 are alternately arranged in the circumferential direction. Each right steering recess 27 is
As shown in FIG. 1, one of the oil chambers 2 of the hydraulic cylinder 18 passes through a first flow path 31 formed in the first valve member 24 and a first port 32 formed in the valve housing 10a.
Lead to 1. Each left steering recess 28 is provided with the first valve member 2.
2 and the second flow path 33 formed in the valve housing 1
Through the second port 34 formed at 0a, the oil port 22 communicates with the other oil chamber 22 of the hydraulic cylinder 18. Each pressure oil supply recess 29
Is a third flow path 35 formed in the first valve member 24 and an inlet port 36 formed in the valve housing 10a.
Through the pump 37 as shown in FIG. The pump 37 is driven by an electric motor 50, and can be configured by, for example, a vane pump or a gear pump that discharges hydraulic oil at a flow rate corresponding to the rotation speed of the motor 50. A relief valve 8 is provided between the pump 37 and the inlet port 36.
0 is provided. Each pressure oil discharge recess 30 is formed in the first discharge passage 38 formed in the second valve member 25, the passage 47 between the input shaft 2 and the inner and outer circumferences of the torsion bar 3, and the input shaft 2 shown in FIG. 1. It communicates with the tank 41 via a second discharge path 39 and a discharge port 40 formed in the valve housing 10a. Thus, the pump 37, the tank 41, and the oil chambers 21 and 22 of the hydraulic cylinder 18 communicate with each other through the inter-valve flow path 42 between the inner and outer circumferences of the first valve member 24 and the second valve member 25. Between the first valve member side concave portion and the second valve member side concave portion in the inter-valve flow path 42,
The throttle portions A, B, C, and D whose opening degree changes by the relative rotation of the two valve members 24 and 25 are defined as the throttle portions A, B,
The hydraulic pressure acting on the hydraulic cylinder 18 is controlled by the change in the opening degree of C and D.

FIG. 2 shows the relative positions of the two valve members 24 and 25 in a straight steering state where steering is not performed. In this state, since each pressure oil supply recess 29 and each pressure oil discharge recess 30 communicate with each other through the throttle portions A, B, C, and D, the pressure oil supplied from the pump 37 is directly sent to the tank 41. The motor does not return and no steering assist force is generated.
It is not necessary to drive 0 at the steering assist speed required for steering assist.

When the vehicle is steered rightward from the straight steering state, the torsion bar 3 is twisted in accordance with the steering resistance, and the two valve members 24 and 25 rotate relatively elastically. As a result, the throttle portion A between each right steering recess 27 and each pressure oil supply recess 29 is formed.
Of opening and each left steering recess 28 and each pressure oil discharge recess 3
The opening of the throttle portion B between 0 and 0 increases, the opening of the throttle portion C between each left steering recess 28 and each pressure oil supply recess 29, and each right steering recess 27 and each pressure oil. The degree of opening of the throttle portion D between the discharge recess 30 and the discharge recess 30 is reduced. As a result, pressure oil is supplied from the pump 37 to one oil chamber 21 of the hydraulic cylinder 18, the piston 20 moves in one direction due to the oil pressure of the hydraulic oil, and the piston 20 moves from the other oil chamber 22 of the hydraulic cylinder 18 to the tank 41. The pressure oil is recirculated, and a steering assist force to the right of the vehicle is applied to the rack 8.

When the vehicle is steered to the left from the straight steering state, the opening of each of the throttles A, B, C, and D changes in the opposite direction to the case of steering to the right. The pressure oil is supplied to the chamber 22, and the hydraulic pressure of the pressure oil causes the piston 20 to move in the other direction, whereby the pressure oil is returned from one oil chamber 21 of the hydraulic cylinder 18 to the tank 41, and the vehicle is steered to the left. An auxiliary force is applied to the rack 8.

As shown in FIG. 1, the motor 50 is connected to a controller 60. The controller 60 has a control circuit 61 and a drive circuit 62. The control circuit 6
Reference numeral 1 is mainly composed of a computer, and is connected to a steering angle sensor 51 for detecting a steering angle of the steering wheel H from a straight steering state and a vehicle speed sensor 53. In accordance with the stored control program, the control circuit 61 outputs to the drive circuit 62 an instruction signal for setting the rotation speed of the motor 50 to the steering assist speed at the time of steering assist, and instructing to set the rotation speed of the motor 50 to the standby speed at the time of canceling the steering assist. The signal is output to the drive circuit 62. That is, the control circuit 61 stores a preset reference steering angle. The reference steering angle is, for example, a play angle from the steering wheel midpoint of the steering wheel H. When the steering angle of the steering wheel H detected by the steering angle sensor 51 is equal to or larger than the reference steering angle, it is determined that the steering is being performed. If there is no change in the steering angle or if a predetermined time has elapsed after the steering angle has returned to the play range, it is determined that the steering assist has been released. The drive circuit 62 includes the motor 50
A known device including a transistor such as an FET can be used as a power control switching element connected to the battery power source 63 and the battery power source 63. The drive circuit 62 supplies a drive current to the motor 50 in response to an instruction signal from the control circuit 61 that sets the rotation speed of the motor 50 to the steering assist speed. The steering assist speed is a speed preset so that the flow rate of the pressure oil sent from the pump 37 becomes a flow rate necessary for steering assist. The steering assist speed of the motor 50 is
Until the set vehicle speed is reached, it decreases in proportion to the vehicle speed. Thus, at low vehicle speeds, the steering assist force is increased to improve the turning performance of the vehicle, and at high vehicle speeds, the steering assist force is reduced to improve the running stability of the vehicle. The vehicle speed is detected by the vehicle speed sensor 53. The control circuit 6
When an instruction signal for setting the rotation speed of the motor 50 to the standby speed from 1 is output to the drive circuit 62, the drive circuit 62 cuts off the current to the motor 50, whereby the steering assist is released. The standby speed is a preset speed lower than the steering assist speed, and is zero in the present embodiment.

As shown in FIG. 3, the hydraulic cylinder 18
The space between the inner periphery of both ends of the cylinder tube 19 and the outer periphery of the rack 8 is closed by seal members 82 and 83.
The inner diameter of the cylinder tube 19 is a portion 19a between both ends.
In the portion 19b near one end, it is gradually increased toward one end, and in the portion 19c near the other end, it is gradually increased toward the other end.

The piston 20 of the hydraulic cylinder 18 is
The rack 8 is fitted to the outer periphery of the rack 8
Has a retaining portion 20 'which is in contact with the inner surface of a peripheral groove 8' on the outer periphery of the outer periphery of the rack 8 and is integrated with the rack 8 by fitting a retaining ring 81 between the rack 8 and the rack. This piston 20 has an annular piston main body 20a and, as shown in FIG.
a 'having a single annular piston ring 20b fitted with a gap therebetween. (1), (2),
As shown in (3), the piston ring 20b is divided at one location and is elastically deformable in the radial direction. Due to the elastic deformation, the piston ring 20b
From the natural state having a large diameter shown in (2) of FIG. 5, (3) of FIG.
Can be reduced to the state shown in FIG. The outer diameter of the piston ring 20b is larger than the maximum value of the inner diameter of the portions 19b and 19c near both ends of the cylinder tube 19 in a natural state. In the present embodiment, in the vicinity of each divided end of the piston ring 20b, the wall thickness is reduced toward the divided end, and the divided ends are surface-joined to each other via a surface 20b 'inclined with respect to the radial direction. It is supposed to.

When the left-right steering angle exceeds a set value, the piston ring 20b reaches the portions 19b and 19c near both ends where the inner diameter of the cylinder tube 19 changes. As a result, the outer diameter of the piston ring 20b is reduced by the movement of the piston 20 from the straight-ahead steering state shown by the solid line in FIG. 3 to the vicinity of the steering limit shown by the two-dot chain line.
The outer diameter changes according to the change in the inner diameter at. Due to the change in the outer diameter of the piston ring 20b, the piston 2
The pressure receiving area of 0 changes so as to be larger when the steering angle is equal to or larger than the set value than when the steering angle is smaller than the set value.
In the present embodiment, when the piston 20 is steered to the steering limit, the piston ring 20b passes through the pipe connection port 19 ″ with the control valve 23 in the cylinder tube 19, and thereby the two oil chambers 21 and 22 Are communicated with each other, and the hydraulic pressure acting on the hydraulic cylinder 18 can be released.

According to the above configuration, the pressure receiving area of the piston 20 is made larger when the left and right steering angles are larger than the set value than when the left and right steering angles are smaller than the set value. Without increasing the steering assist force, the steering resistance can be reduced by increasing the steering assist force. Therefore, the maximum value of the hydraulic pressure applied to the hydraulic cylinder 18 can be reduced, and the relief pressure of the pump 37 can be reduced. Thereby, the relief pressure of the pump 37 can be reduced, and the durability of the pump parts, the pressure oil supply hose, and the like can be improved. Further, since the output torque of the drive motor 50 of the pump 37 can be reduced, the motor drive current value can be reduced to improve energy saving.

The present invention is not limited to the above embodiment. For example, the set value of the steering angle at which the pressure receiving area of the piston changes is not particularly limited as long as the above-mentioned effect can be obtained. For example, by setting the set angle to zero, as shown by a two-dot chain line in FIG. And cylinder tube 1
The inner diameter of the piston 9 may gradually change from the straight steering position of the piston 20. As shown in FIG. 6A, a pair of circumferential grooves 20a 'are formed on the outer periphery of the piston main body 20a in parallel with the moving direction of the piston 20, and each circumferential groove 20a' is formed.
a ′, a single circumferential groove 20a ″ wider than the above embodiment is formed on the outer periphery of the piston body 20a, as shown in FIG. A pair of piston rings 20b arranged in parallel in the movement direction of the piston 20 may be fitted into the circumferential groove 20a ″ via a backup washer 20d.
In each of the modified examples (1) and (2) of FIG. 6, one divided end position of the pair of piston rings 20b and the other divided end position are different from each other in the circumferential direction. The leakage of pressure oil between the chambers 21 and 22 is reliably prevented. Also, (1), (2), and (3) in FIG.
As shown in FIG. 7, the step 20b 'is formed near each divided end of the piston ring 20b to reduce the wall thickness, and the portions near both divided ends are in contact with each other via a radially parallel surface 20b ". Further, the pump of the power steering apparatus to which the present invention is applied may be driven by an engine of a vehicle, and the present invention may be applied to a power steering apparatus other than a rack and pinion type power steering apparatus. The present invention may be applied to, for example, a ball screw type power steering device.

[0025]

According to the present invention, the relief pressure of a pump for supplying pressure oil to a hydraulic cylinder for generating a steering assist force can be reduced with a simple configuration without increasing the size of the entire device, and the pump parts and the pressure oil can be reduced. The durability of the supply hose and the like can be improved, and when the pump is driven by an electric motor, the motor drive current value can be reduced to improve energy saving, and the current load on the motor and its drive circuit can be reduced. A power steering device capable of improving durability can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a power steering device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a sectional view of a hydraulic cylinder in the power steering device according to the embodiment of the present invention.

FIG. 4 is a sectional view of a main part of a hydraulic cylinder in the power steering device according to the embodiment of the present invention.

FIG. 5 is a front view of a piston ring of a hydraulic cylinder in a power steering apparatus according to an embodiment of the present invention, (1) is a front view, (2) is a cross-sectional view in a natural state, and (3) is a cross-sectional view in a contracted state.

FIG. 6 is a sectional view of a main part of a hydraulic cylinder in a power steering device according to an embodiment of the present invention;
(2) is a cross-sectional view of a different modification.

FIG. 7 shows a modification of the piston ring of the hydraulic cylinder in the power steering device according to the embodiment of the present invention (1).
Is a front view, (2) is a sectional view in a natural state, and (3) is a sectional view in a reduced state.

FIG. 8 is a diagram showing a relationship between a steering angle of a conventional power steering device and a hydraulic pressure acting on a hydraulic cylinder for generating a steering assist force.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power steering device 18 Hydraulic cylinder 19 Cylinder tube 20 Piston 20b Piston ring 21, 22 Oil chamber 23 Control valve 37 Pump 50 Motor 60 Controller

Claims (4)

[Claims] A hydraulic cylinder for generating a steering assist force by hydraulic oil from a pump; and a control valve for controlling a hydraulic pressure of hydraulic oil supplied to the hydraulic cylinder in accordance with a steering resistance. A cylinder tube and a piston that forms a pair of oil chambers by partitioning the inside of the cylinder tube. One-way movement of the piston by the hydraulic pressure of the pressure oil supplied to one of the oil chambers increases the right steering assist force. In a power steering device in which the left steering assist force is given by the piston moving in the other direction by the hydraulic pressure of the pressure oil supplied to the other oil chamber, the pressure receiving area of the piston when the left and right steering angles are equal to or greater than a set value But the pressure receiving area of the piston changes so as to be larger than the pressure receiving area of the piston in a state of being less than the set value. Apparatus. The cylinder tube has a portion in one of the oil chambers whose inner diameter gradually increases toward one end, and a portion in the other oil chamber whose inner diameter gradually increases toward the other end. Has a piston main body and a piston ring fitted on the outer periphery of the piston main body. The movement of the piston causes the outer diameter of the piston ring to change according to the change in the inner diameter of the cylinder tube. The power steering apparatus according to claim 1, wherein the piston ring is elastically deformable in a radial direction, and a pressure receiving area of the piston changes according to a change in an outer diameter of the piston ring. 3. A plurality of piston rings arranged in parallel in the movement direction of the piston are fitted around the outer periphery of the piston body, and each piston ring is elastically deformable so as to change its outer diameter by being divided at one location. The power steering apparatus according to claim 2, wherein the divided ends of the piston rings in the circumferential direction are different from each other. 4. The hydraulic cylinder generates a steering assist force by pressure oil from a pump driven by an electric motor, and sets the rotation speed of the motor to the steering assist speed at the time of steering assist and to the steering assist speed at the time of canceling the steering assist. The power steering device according to any one of claims 1 to 3, further comprising a unit for setting a standby speed.