JPH061251A - Rear wheel steering gear for vehicle - Google Patents

Abstract

PURPOSE:To provide a vehicle rear wheel steering gear capable of steering rear wheels by a large steering angle onto the same phase side and the opposite phase side and moreover reduced in the production cost. CONSTITUTION:A rear wheel steering gear 1 is provided with a hydraulic cylinder 4 capable of steering rear wheels 25 only by an angle corresponding to operating oil pressure, a hydraulic pump 3 for supplying the hydraulic cylinder 4 with operating oil pressure, a steering angle control valve 5 interposed between the hydraulic cylinder 4 and the hydraulic pump 3 so as to control operating oil pressure to operate the hydraulic cylinder 4, and a relief valve 6 for determining the maximum value of the operating oil pressure of the hydaulic cylinder 4. The relief valve 6 is provided with a pressure regulating means for changing the elastic deformation quantity of a pressure regulating spring for determining relief pressure, a closing means for closing a by-pass passage, and the like, and circulates operating oil pressure to a reservoir tank 16 through the by-pass passage to suppress the rise of operating oil pressure at the non-steering time of front wheels 73 while increasing the maximum value of operating oil pressure according to the increase of a front wheel steering angle at the steering time of the front wheels 73.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle rear wheel steering system, and more particularly to a rear wheel steering system mounted on a four-wheel steering vehicle.

[0002]

2. Description of the Related Art Conventionally, as a rear wheel steering system for a four-wheel steering vehicle, a hydraulic cylinder for steering the rear wheels, a steering angle control valve for controlling the hydraulic pressure of the hydraulic cylinder, and a steering angle control valve for operating 2 Some were equipped with operating means of the system. The first operation means includes an electric motor controlled by the controller, and can steer the rear wheels to the in-phase side and the anti-phase side at most once. Further, the second operating means is provided with a control cable connected to the front wheel steering device, and can steer the rear wheels to the opposite phase side up to 5 degrees. When the first and second operating means steer the rear wheels at the same time, the steering angle is limited to a maximum of 5 degrees.

FIG. 8 is a steering characteristic diagram of a four-wheel steering vehicle equipped with this rear wheel steering system. When the front wheels are steered small, only the first operating means steers the rear wheels, and therefore steers the rear wheels to the in-phase side and the anti-phase side by a slight angle. When the steering angle of the front wheels becomes large, the second operating means in addition to the first operating means steers the rear wheels, and therefore the rear wheels can be steered largely to the opposite phase side.

[0004]

By the way, when a vehicle parked in parallel on the side of a wall is started, the rear wheel is steered largely to the same phase side to facilitate the operation of the vehicle, while the rear wheel is operated. If the steering wheel is steered to the opposite phase side, it may be difficult to operate the vehicle. However, in the above-mentioned conventional rear wheel steering system, the rear wheel cannot be steered largely by the first operating means, and the rear wheel is steered to the same phase side by the second operating means for steering a large steering angle. Can not do it. Therefore, there is a problem that the rear wheels cannot be steered to the same phase side.

Further, in the above-mentioned rear wheel steering system, since the control cable is connected to the front wheel steering system, a large number of pulleys and the like for arranging this cable are required, and the number of constituent parts is increased and the assembly is increased. There is also a problem that the workability of attachment deteriorates and the production cost increases. The present invention has been made to solve the above-mentioned problems, and a vehicle capable of steering the rear wheels to a large steering angle to the in-phase side and the anti-phase side, and further capable of reducing the production cost. An object is to provide a rear wheel steering device.

[0006]

In order to achieve the above object, according to the present invention, a hydraulic actuator capable of steering a rear wheel by an angle corresponding to the hydraulic pressure, and a hydraulic fluid supplied to the hydraulic actuator. And a control valve interposed between the liquid pressure actuator and the liquid pressure source for controlling the operating liquid pressure to operate the liquid pressure actuator,
A relief valve mechanism for determining the maximum value of the operating liquid pressure of the liquid pressure actuator is provided, and the relief valve mechanism determines a relief pressure by pressing a fluid passage, a valve body capable of closing the fluid passage, and the valve body. Pressure adjusting spring, a pressure adjusting means that changes the elastic deformation amount of the pressure adjusting spring according to the front wheel steering angle, a bypass passage that connects the upstream side and the downstream side of the valve body of the fluid path, and the front wheel is steered. In the case where the front wheel is not steered, the closing means is provided to prevent the increase of the working fluid pressure supplied to the fluid pressure actuator when the front wheel is not steered, and the working fluid pressure is increased according to the increase of the front wheel steering angle. The rear wheel steering system of the vehicle is configured so as to increase the maximum value of.

[0007]

The control valve adjusts the magnitude of the working liquid pressure from the liquid pressure source, switches the flow direction thereof, and supplies it to the liquid pressure actuator. Therefore, the hydraulic actuator steers the rear wheel in a direction corresponding to the flow direction by an angle corresponding to the magnitude of the hydraulic pressure actuated by the control valve.

On the other hand, the bypass passage of the relief valve releases the working fluid pressure generated by the fluid pressure source when the front wheels are not steered. Therefore, the control valve cannot supply sufficient working fluid pressure to the hydraulic actuator, and the rear wheels are not steered. Also, the bypass passage of the relief valve is
When the front wheels are steered, they are closed by the closing means. In this state, the pressure adjusting means changes the elastic deformation amount of the pressure adjusting spring according to the front wheel steering angle, so that the relief pressure increases as the front wheel steering angle increases. Therefore, the working fluid pressure supplied from the liquid pressure source increases as the front wheel steering angle increases. Therefore, the maximum working hydraulic pressure that the control valve can supply to the hydraulic actuator increases as the front wheel steering angle increases, and when the front wheels are steered by a large steering angle, the rear wheels can be steered by a large steering angle. If the front wheel steering angle is small, the maximum steering angle of the rear wheels can be set small.

[0009]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a rear wheel steering system to which the present invention is applied. The rear wheel steering system 1 is composed of a hydraulic circuit, a controller 2 and the like. This hydraulic circuit includes a hydraulic pump 3, a hydraulic cylinder 4, a steering angle control valve 5, a relief valve 6 and the like, which are connected by an oil passage.

In other words, from the hydraulic pump 3 to the oil passages 11, 1
2 extends, and these oil passages 11 and 12 are connected to the steering angle control valve 5 and the relief valve 6, respectively. Further, oil passages 13 and 1 extending from the steering angle control valve 5 and the relief valve 6 respectively.
Both 4 are connected to the reserve tank 16. Further, a pair of oil passages 18 and 19 extend from the steering angle control valve 5, and these oil passages 4 a and 4 b of the hydraulic cylinder 4 are provided.
Respectively connected to. The oil passages 11 and 13 are connected by an oil passage 21, and in the middle of the oil passage 21,
An unload valve 22 is provided.

The hydraulic cylinder 4 has an operating rod 4c extending in the vehicle width direction. The operating rod 4c is attached to each rear wheel 25 via left and right tie rods 24 and knuckle arms (not shown). It is connected. This working rod 4
c reciprocates by a distance according to the magnitude of the operating hydraulic pressure adjusted by the steering angle control valve 5 described later. Therefore, the steering angle of the rear wheel 25 increases in proportion to the increase in the operating hydraulic pressure supplied from the steering angle control valve 5 to the hydraulic cylinder 4. For example, 35.
When the working hydraulic pressure of 0 kg / cm ² is supplied, the hydraulic cylinder 4 steers the rear wheels by 0.8 degrees, and the hydraulic pressure is 90.0 kg / c.
When the hydraulic pressure of m ² is supplied, the hydraulic cylinder 4 steers the rear wheels by 5.0 degrees.

The steering angle control valve 5 has, for example, a pair of solenoids, and is operated by a controller 2 which will be described later to switch the connection between the oil passages 11, 13, 18 and 19 and to connect the oil passages 18 to each other. , 19 can be reduced. For example, at the neutral position of the steering angle control valve 5, the oil passage 11 and the oil passage 13 and the oil passage 18 and the oil passage 19 are in communication with each other. Therefore, when the steering angle control valve 5 is switched to the neutral position, the pressures in the hydraulic chambers 4a and 4b of the hydraulic cylinder 4 become equal, and the operating rod 4c is moved to the neutral position by the spring force of the return spring (not shown). Will be restored.

Further, when the position of the steering angle control valve 5 is switched and the oil passage 11 and the oil passage 18 and the oil passage 13 and the oil passage 19 respectively communicate with each other, the operating hydraulic pressure supplied from the hydraulic pump 3 is supplied. Can be guided to the first hydraulic chamber 4a of the hydraulic cylinder 4, and the hydraulic oil in the second hydraulic chamber 4b can be guided to the reserve tank 16. Therefore, in this case, the operating rod 4c of the hydraulic cylinder 4 moves forward and steers each rear wheel 25 to the right. At this time, the steering angle control valve 5 can reduce the amount of oil flowing into the oil passage 18, adjust the magnitude of the operating hydraulic pressure introduced into the first hydraulic chamber 4a, and control the steering angle of the rear wheel 25. be able to.

Further, when the position of the steering angle control valve 5 is switched and the oil passage 11 and the oil passage 19 and the oil passage 13 and the oil passage 18 respectively communicate with each other, the operating hydraulic pressure supplied from the hydraulic pump 3 is supplied. Is guided to the second hydraulic chamber 4b of the hydraulic cylinder 4, and the hydraulic oil in the first hydraulic chamber 4a is stored in the reserve tank 16
Can lead to. Therefore, in this case, the operating rod 4c of the hydraulic cylinder 4 is returned to steer each rear wheel 25 to the left. At this time, the steering angle control valve 5 can throttle the amount of oil flowing into the oil passage 19, adjust the magnitude of the operating hydraulic pressure introduced into the second hydraulic chamber 4b, and control the steering angle of the rear wheel 25. be able to.

The unload valve 22 is, for example, a normally-open type electromagnetic opening / closing valve, which is opened / closed by the controller 2. That is,
When an engine (not shown) is started, the controller 2
The solenoid is energized to close the unload valve 22.
When the controller 2 detects any abnormality in the rear wheel steering system 1, the controller 2 deactivates the solenoid and opens the unload valve 22.

The controller 2 has a microcomputer, and the steering wheel angle sensor 2 is provided on the input side thereof.
7, the vehicle speed sensor 28, the front power steering pressure sensor 29, etc., and the solenoids of the steering angle control valve 5 and the unload valve 22 are electrically connected to the output side.
The controller 2 operates the steering angle control valve 5 based on the detection signals of the sensors 27 to 29, etc., according to a control program stored in advance in the storage device, and adjusts the steering angle suitable for the traveling state of the vehicle to the rear wheels. Give to 25.

The hydraulic pump 3 is driven by the engine. The relief valve 6 is attached to the steering gear box 64 of the front wheel steering device 31, and is composed of a valve body 36, a pressure adjusting mechanism 40, a bypass mechanism 80, etc., as shown in FIG. It is housed in each of the first to third spaces 35, 38, 39 therein.

An inflow port 33a and an outflow port 33b are provided at predetermined positions of the valve body 33. The inflow port 33a is opened to face an oil passage 47, which will be described later, and the oil passage 12 is connected thereto. Further, the outflow port 33b is opened to face the first space 35, and the oil passage 14 is connected thereto. The valve body 36 is provided with a valve seat 42 that is screwed and fixed to the valve body 33, a spring seat 43 that is axially movable with respect to the valve body 33, and is disposed between the spring seat 43 and the valve seat 42. A spool 44 movable in the axial direction with respect to the body 33,
The pressure adjusting spring 45 and the like are provided between the spring seat 43 and the spool 44.

The valve seat 42 is provided with a screw portion 42a. The screw portion 42a is provided on the outer peripheral surface of the base end side half portion and meshes with the screw portion 33d of the valve body 33. Therefore, when the valve seat 42 is rotated,
The amount of insertion into the valve body 33 changes, and the preload of the pressure adjusting spring 45 described later can be adjusted. Also,
The valve seat 42 is fixed with a nut 49. In addition, between the valve seat 42 and the valve body 33,
It is sealed with an O-ring 51.

The valve seat 42 has an inflow port 3
An oil passage 47 is formed which connects 3a and the first space 35. The oil passage 47 includes an annular groove 47a provided on the outer peripheral surface of the valve seat 42 so as to face the inflow port 33a.
A hole 47 extending in the axial direction from the front end surface of the valve seat 42.
b, and a plurality of holes 47c that penetrate the valve seat 42 in the radial direction and open the holes 47b facing the annular groove 47a. Width dimension of the annular groove 47a (valve seat 42
Is set to be larger than the diameter of the opening of the inflow port 33a. Therefore, the valve seat 4
Even when the insertion amount of 2 is changed, the annular groove 47a always faces the inflow port 33a.

A shaft 44a extending toward the spring seat 43 is integrally formed with the spool 44 that abuts the valve seat 42 and closes the oil passage 47. This axis 4
The tip of 4a is slidably inserted into a shaft hole 43a formed in the spring seat 43. Therefore, the spool 44 is relatively displaceable with respect to the spring seat 43 and is not detachable. Also, the spool 44
The notch 44b is provided in the outer peripheral part at a plurality of positions at predetermined intervals in the circumferential direction, and serves as a passage through which hydraulic oil flows.

A connecting portion 43b projecting into the second space 38 is integrally formed at the tip of the spring seat 43. A hole 43c extending in the axial direction from the tip end surface is formed in the connecting portion 43b, and the connecting portion 43b is radially penetrated, and
An elongated hole 43d communicating with the hole 43c is formed. The long hole 43d has a shape elongated in the axial direction (FIG. 3).

The pressure adjusting spring 45 is a coil spring, for example, and presses the spool 44 toward the valve seat 42 side. The pressure adjusting spring 45 is contracted between the spring seat 43 and the spool 44 and has a predetermined preload. When the pressure on the oil passage 12 side becomes larger than the preload of the pressure regulating spring 45, the oil passage 47
The hydraulic oil therein moves the spool 44 and flows into the first space, thus reducing the pressure on the oil passage 12 side. That is, the maximum value of the operating hydraulic pressure on the oil passages 12 and 11 side is determined by the pressure adjusting spring 45.

The pressure adjusting mechanism 40 comprises a shaft 53, an eccentric shaft 54, a connecting rod (hereinafter referred to as a connecting rod) 55 and the like. A gear 57 having a relatively small diameter is attached to the shaft 53 such that the gear 57 cannot rotate relatively. Also, this shaft 53 is used for the valve body 3
3 is rotatably supported at predetermined positions via bearings 58 and 59. A convex portion 53a extending in the radial direction is integrally formed at the base end of the shaft 53.
By inserting a into the groove 61a of the rotary shaft 61, these rotate integrally. The rotary shaft 61 extends from the front wheel steering device 31 and rotates integrally with a pinion gear (not shown) in the steering gear box 64 when the steering wheel 63 (FIG. 1) is rotationally operated. Therefore, the shaft 53 rotates in conjunction with the steering wheel 63.

The rotation angle of the steering wheel 63 is limited to 400 degrees in both left and right directions.
The eccentric shaft 54 includes a large diameter portion 54b, an eccentric portion 54a extending from the tip surface of the large diameter portion 54b, a small diameter portion 54c further extending from the tip surface of the eccentric portion 54a, and the like. There is. Large diameter part 54b and small diameter part 5
4c have the same axis, and these are the valve body 3
3 is rotatably supported at predetermined positions via bearings 66 and 67.

A gear 69 having a relatively large diameter is provided near the tip of the large diameter portion 54b. The gear 69 meshes with the gear 57 of the shaft 53. Therefore, when the shaft 53 rotates, the eccentric shaft 54 also rotates. In addition, when the steering wheel 63 is not operated, the eccentric portion 54a is not attached to the shaft 53.
When the steering wheel 63 is operated to the maximum angle (that is, 400 degrees), the eccentric portion 54a is eccentric to the valve body 36 side (FIG. 6). State).

A recess 90 of a bypass mechanism 80, which will be described later, is formed on the outer circumference of the large diameter portion 54b. Recess 9
0 is formed at a position facing the third space 39 when the steering wheel 63 is not operated. The base end of the connecting rod 55 is connected to the eccentric portion 54 a of the eccentric shaft 54 via a bearing 71 so as to be relatively rotatable. Further, a cylindrical connecting piece 55a extending horizontally in a substantially T shape is integrally formed at the tip of the connecting rod 55. The tip portion of the connecting rod 55 is inserted into the hole 43c of the connecting portion 43b of the spring seat 43, and the connecting piece 55a is arranged in the long hole 43d.

Therefore, the connecting rod 55 converts the rotational movement of the eccentric shaft 54 into the linear movement of the spring seat 43 in the axial direction. At this time, since the connecting piece 55a of the connecting rod 55 is arranged in the long hole 43d of the spring seat 43, when the eccentric shaft 54 rotates, the connecting piece 55a moves in the long hole 43d. At times, the connecting piece 55a may be attached to the spring seat 43.
Can not be moved. And the eccentric shaft 5
After 4 further rotates and the connecting piece 55a comes into contact with the side wall defining the long hole 43d, the connecting piece 55a can move the spring seat 43. In this case, the elasticity of the pressure adjusting spring 45 is increased. The amount of deformation, that is, the relief pressure of the relief valve 6 changes.

The bypass mechanism 80 is composed of a bypass passage 82 extending from the third space 39, steel balls 84 and 85, a push rod 87 and a coil spring 88 housed in the third space 39, and the recess 90 described above. ing. The bypass passage 82 connects the third space 39 to the oil passage 47.
The upstream passage 82a communicating with the third space 39
It is composed of a downstream passage 82b communicating with the space 35,
Specifically, the upstream passage 82a is opened to face the annular groove 47a, and the downstream passage 82b is opened to face the outflow port 33b. Therefore, the bypass passage 82 bypasses the oil passage 47 closed by the spool 44 and connects the inflow port 33a side and the outflow port 33b side.

The push rod 87 has an eccentric shaft 54.
And extends slidably with respect to the valve body 33. A steel ball 84 is provided at one end of the push rod 87, and a coil spring 8 is provided at the other end.
8 and a steel ball 85 are arranged respectively. When the steering wheel 63 is not operated, the steel ball 84 on one end side of the push rod 87 faces the recess 90 of the large diameter portion 54b. Therefore, in this state, as shown by the solid line in FIG. 4, the hydraulic oil in the upstream passage 82a moves the steel ball 85, the push rod 87, etc. to the large diameter portion 54b side, and enters the third space 39. Inflow. In addition, the steering wheel 63
Is rotated, the recess 90 is removed from the steel ball 84. Therefore, the outer peripheral surface of the large diameter portion 54b pushes the steel ball 84 toward the upstream passage 82a,
The steel ball 85 closes the upstream passage 82 a via the push rod 87 and the coil spring 88. The coil spring 88 has a predetermined elastic force and presses the steel ball 85 with a strong force.

The operation of the rear wheel steering system 1 will be described below. When the engine is started and the hydraulic pump 3 is driven, the operating hydraulic pressure of the hydraulic cylinder 4 is generated. The relief valve 6 sets the maximum value of this operating oil pressure to a value according to the steering angle of the front wheels 73. That is, when the steering wheel 63 is not operated, the upstream passage 82a and the downstream passage 82b of the bypass passage 82 of the relief valve 6 are in communication with each other, and the operating oil pressure generated in the hydraulic pump 3 is the oil passage 12. Flows into the inflow port 33a. The operating hydraulic pressure is applied to the annular groove 47a, the upstream passage 82a, the third space 39, the downstream passage 82b, the first space 35, and the outflow port 3.
It flows in the order of 3b, flows into the oil passage 14, and circulates to the reserve tank 16. Therefore, even if the spool 44 of the valve body 36 closes the oil passage 47, the relief valve 6 relieves the operating oil pressure on the oil passage 12 side to the oil passage 14 side, and controls the steering angle via the oil passage 11. The rise of the operating oil pressure supplied to the valve 5 is suppressed.

On the other hand, in this state, the pressure regulating mechanism 40 of the relief valve 6 has its eccentric shaft 54 as shown in FIG.
The eccentric part 54a is located on the shaft 53 side. Therefore, the spring seat 43 is not moved by the connecting rod 55, and the elastic deformation amount of the pressure adjusting spring 45 is minimum. When the amount of elastic deformation is the minimum, the relief pressure is set to the value P1 (for example, 35.0 kg / cm ² ).
In this case, as described above, the bypass passage 8
2 circulates the operating oil pressure on the oil passage 12 side to the reserve tank 16 side, the operating oil pressure on the oil passage 12 side does not rise to the value P1, and the pressure adjusting spring 45 causes the spool 44 to move the valve seat 42. Are pressed against.

When the steering wheel 63 is operated, the pinion gear in the steering gear box 64 rotates, so that the shaft 53 of the pressure adjusting mechanism 40 rotates. Therefore, the eccentric shaft 54 rotates and the recess 9
0 disengaged from steel ball 84, steel ball 8
5 closes the bypass passage 82. Therefore, the oil passage 12
The operating hydraulic pressure on the side is the valve main body 36 and the pressure adjusting mechanism 40, that is,
It is determined by the relief pressure of the relief valve 6.

On the other hand, when the eccentric shaft 54 rotates, the connecting piece 55a at the tip of the connecting rod 55 moves to the right side in the figure. Since the connecting piece 55a is arranged in the long hole 43d, the connecting piece 55a first moves in the long hole 43d. Therefore, the movement of the connecting piece 55a does not affect the position of the spring seat 43, and the spring seat 43 is pressed by the pressure adjusting spring 45 and is positioned at the left end of the first space 35 in the figure. Therefore, the elastic deformation amount of the pressure adjusting spring 45 does not change. Therefore, the relief pressure is maintained at the value P1 and the working hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 (that is, the maximum working hydraulic pressure of the hydraulic cylinder 4).
Becomes the value P1. This state is continued until the connecting piece 55a of the connecting rod 55 comes into contact with the wall on one side defining the elongated hole 43d and the spring seat 43 is moved.

Further, when the steering wheel 63 is operated and the angle thereof reaches, for example, 230 degrees, the eccentric shaft 54 of the pressure adjusting mechanism 40 is rotated to the position shown in FIG. 5, and the connecting piece 55a is elongated hole 43d. Abut one wall defining When the steering wheel 63 is further operated from this state, the connecting piece 55 of the connecting rod 55 is
a moves the spring seat 43 and pushes the pressure adjusting spring 45. Therefore, the elastic deformation amount of the pressure adjusting spring 45 increases, and the relief pressure increases. This allows
The hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 starts to increase from the value P1.

Then, when the rotation angle of the steering wheel 63 reaches its maximum value of 400 degrees, FIG.
As shown in, the eccentric portion 54a of the eccentric shaft 54 is located on the valve body 36 side, and the moving distance of the spring seat 43 is maximized. Therefore, the elastic deformation amount of the pressure adjusting spring 45 becomes the maximum, and the relief pressure has a value P2 (for example, 90.0).
reach kg / cm ² ). As a result, the hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 is set to the maximum value P2.

From this state, the steering wheel 63
When the return operation is performed, the eccentric shaft 54 starts to rotate in the direction opposite to the above case. Therefore, the connecting piece 55a of the connecting rod 55 moves to the left side in the figure, and accordingly, the spring seat 43 is pressed by the pressure adjusting spring 45 and moves toward the left end. As a result, the elastic deformation amount of the pressure adjusting spring 45 is reduced, and the relief pressure is also reduced. That is, the hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 decreases.

Then, when the rotation angle of the steering wheel 63 is returned to the aforementioned 230 degrees and the eccentric shaft 54 of the pressure adjusting mechanism 40 is returned to the position shown in FIG. 5, the spring seat 43 is moved to the left end of the first space 35. To reach. Therefore, the elastic deformation amount of the pressure adjusting spring 45 is minimized,
The relief pressure is reduced to the minimum value P1, and the hydraulic pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 is set to the minimum value P1.

When the steering wheel 63 is further returned from this state, the eccentric shaft 54 rotates and the connecting piece 55a of the connecting rod 55 moves further to the left. Since the spring seat 43 has already reached the left end, the connecting piece 55a moves within the elongated hole 43d. In this case, the movement of the connecting piece 55a does not affect the elastic deformation amount of the pressure adjusting spring 45, that is, the relief pressure. Therefore, the relief pressure is held at the value P1.

By the way, when the steering wheel 63 is operated and the spring seat 43 is moving to the right in the figure, the spring seat 43, the pressure adjusting spring 45, etc. are caught by the valve body 33, and a so-called stick phenomenon occurs. Sometimes. In the pressure adjusting mechanism 40 of the present embodiment, since the connecting piece 55a of the connecting rod 55 is arranged in the long hole 43d of the spring seat 43, when the spring seat 43 is returned to the left end of the first space 35, the connecting piece 55a is used. The spring seat 43 can be pulled, and the spring seat 43 can be reliably returned to the left end of the first space 35.

FIG. 7 shows the steering characteristics of the rear wheel steering system 1. When the steering wheel 63 is not operated, the bypass passage 82 of the relief valve 6 stores the working hydraulic pressure generated by the hydraulic pump 3 in the reserve tank. It is circulated to 16 to suppress an increase in the hydraulic pressure supplied to the steering angle control valve 5. Therefore, the hydraulic cylinder 4 cannot obtain sufficient working hydraulic pressure to steer the rear wheels 25, and the steering angle of the rear wheels 25 becomes zero.

From this state, the steering wheel 63
Is operated and the rotation angle (steering angle) is within 230 degrees in both left and right directions, the operating oil pressure supplied from the hydraulic pump 3 to the steering angle control valve 5 is the value P, as described above.
It is set to 1. The rudder angle control valve 5 supplies the operating oil pressure (that is, the value P1) to the first hydraulic chamber 4a or the second hydraulic chamber 4b of the hydraulic cylinder 4 while maintaining or reducing the pressure. Therefore, within the range of the steering angle, the rear wheels 25 are steered up to 0.8 degrees in the in-phase side and the anti-phase side depending on the running state of the vehicle.

From this state, the steering wheel 63 is further operated so that the steering angle is 23 in both left and right directions.
When the temperature exceeds 0 degrees, as described above, the spring seat 43 of the relief valve 6 starts to move and the pressure adjusting spring 45.
The amount of elastic deformation of is increased, and the operating oil pressure becomes larger than the value P1. Therefore, the distance that the operating rod 4c of the hydraulic cylinder 4 can reciprocate increases, and the maximum steering angle of the rear wheel 25 also increases to the in-phase side and the anti-phase side.

When the operating angle of the steering wheel 63 reaches a maximum of 400 degrees to the left and right, the relief pressure of the relief valve 6 becomes maximum and the operating oil pressure is set to the value P2. Therefore, the hydraulic cylinder 4 can steer the rear wheel 25 to the in-phase side and the anti-phase side up to 5.0 degrees.
In this way, the maximum steering angle of the rear wheels 25 is determined by the relief valve 6 that increases or decreases the relief pressure according to the steering angle. Therefore, when the steering operation is not performed, the rear wheels 25 are not steered, and the steering angle of the rear wheels 25 is maintained at 0 even if the controller 2 operates the steering angle steering valve 5 by mistake.

Further, when the vehicle having a relatively small steering angle travels at high speed, the maximum steering angle of the rear wheels 25 is set to a small value, and even if the controller 2 operates the steering angle control valve 5 by mistake, the vehicle travels at high speed. The rear wheel 25 is not steered at a large steering angle. Further, when the steering is largely operated, the rear wheels 25 can be steered to the in-phase side and the anti-phase side by a large steering angle, so that the driving operation of the vehicle becomes easy.

[0046]

As described above, according to the present invention, a rear wheel steering system of a vehicle is provided with a liquid pressure actuator capable of steering the rear wheels by an angle corresponding to the working liquid pressure, and the working liquid pressure is applied to the liquid pressure actuator. Is provided between the hydraulic pressure source and the liquid pressure actuator, and the control valve for controlling the hydraulic fluid pressure to operate the hydraulic pressure actuator is provided between the hydraulic pressure actuator and the hydraulic pressure source. A relief valve mechanism for determining the fluid path, the relief valve mechanism, a valve element capable of closing the fluid path, a pressure adjusting spring for pressing the valve element to determine the relief pressure, and a front wheel steering angle. Adjusting means for changing the elastic deformation amount of the pressure adjusting spring, a bypass passage for connecting the upstream side and the downstream side of the valve body of the fluid passage, and a closing means for closing the bypass passage when the front wheels are steered. It is configured such that an increase in the working fluid pressure supplied to the fluid pressure actuator is suppressed when the front wheels are not steered, and the maximum value of the working fluid pressure is increased in accordance with an increase in the front wheel steering angle. Therefore, the rear wheels can be steered to the in-phase side and the anti-phase side by a large steering angle, and the operability of the vehicle is improved. Further, since the maximum steering angle of the rear wheels is determined according to the steering angle of the front wheels, it is possible to improve safety. Further, there is an excellent effect that the assembling work of the rear wheel steering device becomes easy and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a vehicle rear wheel steering system to which the present invention is applied.

2 is a cross-sectional view of the relief valve of FIG.

3 is a cross-sectional view of the pressure adjusting mechanism as viewed in the direction of arrow III in FIG.

4 is a cross-sectional view showing the bypass mechanism of FIG. 2 and taken along the line IV-IV.

FIG. 5 shows the pressure regulating mechanism of FIG. 3 with a steering angle of 23.
It is sectional drawing in the state which reached 0 degree.

FIG. 6 shows the pressure adjusting mechanism of FIG. 3 with a steering angle of 40.
It is sectional drawing in the state which reached 0 degree.

FIG. 7 is a steering characteristic diagram of the rear wheel steering system of FIG.

FIG. 8 is a steering characteristic diagram of a four-wheel steering vehicle equipped with a conventional rear wheel steering system.

[Explanation of symbols]

 1 Rear Wheel Steering Device 2 Controller 3 Hydraulic Pump 4 Hydraulic Cylinder 5 Steering Angle Control Valve 6 Relief Valve 16 Reserve Tank 25 Rear Wheel 40 Pressure Regulator 43 Spring Seat 44 Spool 45 Pressure Adjusting Spring 54 Eccentric Shaft 55 Connecting Rod 80 Bypass Mechanism 82 Bypass passage

Claims (1)

[Claims] 1. A liquid pressure actuator capable of steering a rear wheel by an angle corresponding to an operating liquid pressure, a liquid pressure source for supplying an operating liquid pressure to the liquid pressure actuator, and a liquid pressure actuator and the liquid pressure source. An intervening control valve for controlling the working liquid pressure to operate the liquid pressure actuator, and a relief valve mechanism for determining the maximum value of the working liquid pressure of the liquid pressure actuator, wherein the relief valve mechanism is a fluid passage and a fluid A valve body capable of closing the passage, a pressure adjusting spring for pressing the valve body to determine a relief pressure, a pressure adjusting means for changing an elastic deformation amount of the pressure adjusting spring according to a front wheel steering angle, and a fluid passage The fluid pressure actuator is provided with a bypass passage that connects the upstream side and the downstream side of the valve body, and a closing means that closes the bypass passage when the front wheels are steered. It suppresses an increase in supply is the hydraulic fluid pressure, rear wheel steering apparatus for a vehicle, characterized in that to increase the maximum value of the working fluid pressure in accordance with an increase in the front-wheel steering angle.