JPH0725345A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To reduce manufacturing cost and enable minute rear wheel steering by constituting front and rear wheel steering mechanisms of equal units, and controlling rear wheel steering through a motor driven according to front wheel steering. CONSTITUTION:Front wheel steering mechanism 100 has a first pinion shaft 109, a first control valve 110 disposed around the first pinion shaft 109, a first rack shaft 102 engaged with the first pinion shaft 109, and a first power cylinder 105 formed around the first rack shaft 102. Rear wheel steering mechanism 200 is formed of a unit equal to the front wheel steering mechanism and has a second pinion shaft 209, a second control valve 210, a second rack shaft 202 and a second power cylinder 205. An electric motor 430 for adjusting the opening of the second control valve 210 is provided and driven by a control means 400 according to a front wheel steering angle. With this constitution, minute rear wheel steering can be performed, and the whole system can be made compact and lightweight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system for a vehicle, and more particularly to a steering system capable of steering rear wheels in response to front wheel steering.

[0002]

2. Description of the Related Art In recent years, a four-wheel steering system, a so-called 4WS, has also been installed in passenger vehicles. Particularly in recent years, this 4WS has been designed to steer the front wheels and steer the rear wheels according to the traveling condition by electronic control, which can improve the handling of the vehicle and the safety during traveling. Generally, the 4WS is a hydraulic power steering, and the steering mechanisms for the front wheels and the rear wheels are incorporated in the vehicle as dedicated units. The reason for using the rear wheel steering mechanism as a dedicated unit is that the steering angle range of the rear wheels is very narrow compared to the steering angle range of the front wheels. In addition, the steering angle control of the rear wheels needs to be performed more finely than that of the front wheels, and moreover, the influence of the hydraulic pressure on the rear wheels on the front wheels must be suppressed, so it is not necessary for the rear wheel steering unit to be special. This is because a hydraulic control device is required.

[0003]

Therefore, it is necessary to specially design the steering mechanism for the rear wheels, so that the steering mechanism for the rear wheels costs four to five times as much as the steering mechanism for the front wheels. I will end up. As a result, the cost of 4WS is significantly increased, and there has been a problem that the spread of the 4WS is delayed although it is an excellent device that improves the handling performance and running stability of the vehicle. Further, conventionally, since the hydraulic pressure on the front wheel side is guided to the rear wheel side and the rear wheel steering is controlled by the hydraulic pressure, the front wheel side may be affected by the hydraulic pressure generated on the rear wheel side. In some cases, it was difficult to carry out four-wheel steering.

SUMMARY OF THE INVENTION An object of the present invention is to provide a practical four-wheel steering system which has a sufficient rigidity and is capable of performing fine four-wheel steering, and which is substantially cost-effective.

[0005]

A four-wheel steering system according to the present invention is a four-wheel steering system for steering a rear wheel in response to steering of a front wheel, and a first pinion shaft connected to a steering wheel and the first pinion shaft. 1st arranged around the 1-pinion shaft
A front wheel steering mechanism having a control valve, a first rack shaft that meshes with the first pinion shaft, and a first power cylinder formed around the first rack shaft, and a second pinion shaft connected to a motor. A second control valve disposed around the second pinion shaft,
A rear wheel steering mechanism having a second rack shaft that meshes with the pinion shaft and a second power cylinder formed around the second rack shaft, and a control unit that drives the motor in response to steering of the front wheels. The front-wheel steering mechanism and the rear-wheel steering mechanism are composed of the same unit.

[0006]

According to the four-wheel steering system of the present invention, since the front wheel steering mechanism and the rear wheel steering mechanism are composed of the same unit, there is no need to design the rear wheel steering mechanism as a special unit. Further, since the control means controls the steering of the rear wheels via the motor driven in response to the steering of the front wheels, the hydraulic pressure generated on the rear wheels does not affect the front wheels and the rear wheels are finely tuned. Can be controlled.

[0007]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a diagram schematically showing a drive system of a four-wheel steering system according to an embodiment of the present invention. Referring to FIG. 1, the four-wheel steering system includes a hydraulic front wheel steering mechanism 100, a hydraulic rear wheel steering mechanism 200, and these steering mechanisms 100, 20.
Hydraulic circuit 30 that supplies hydraulic pressure to 0 to assist steering force
0, and a control means 400 for controlling the hydraulic pressure. Note that the up, down, left, and right described below indicate the up, down, left, and right in the drawings.

The hydraulic front wheel steering mechanism 100 steers the front wheels while assisting the steering force of the front wheels by hydraulic pressure, and is a known one configured as follows. First
The first rack shaft 102 is passed through the rack housing 101 so as to be movable in the left-right direction. First rack shaft 1
Tie rods 104 are connected to the left and right ends of 02 via ball joints 103. This tie rod 104
Are connected to the front wheels, and the front wheels are steered by moving the tie rods 104 to the left and right.

A first power cylinder 105 is formed in a part of the first rack housing 101. The first rack shaft 10 of the first power cylinder 105 portion
2 is provided with a piston (not shown), and the inside of the first power cylinder 105 is divided into left and right oil chambers with the piston separated. Further, 111 and 112 are ports for allowing oil to flow in and out of each oil chamber of the first power cylinder 105.

In a part of the first rack housing 101,
A gear box 106 is formed that extends obliquely up and down so as to intersect with the rack housing 101. A first pinion shaft 109 that meshes with the rack of the first rack shaft 102 is rotatably supported on the gear box 106. The first pinion shaft 109 has an input shaft portion 107 at one end and a pinion portion 119 at the other end.
These are connected by a torsion bar (not shown). The input shaft portion 107 projects upward from the gear box 106, and this projecting portion is connected to a steering wheel (steering wheel) not shown. Further, 110 is a first control valve, which operates by the torsion of the torsion bar and adjusts the amount of pressure oil supplied to the first power cylinder 105 to assist the steering force. The first control valve 110 has a pump port PP to which pressure oil is sent,
Return port DP for returning oil and the first power cylinder 105
A port AP1 and B port BP1 connected to the ports 111 and 112, respectively. further,
The lower part of the gearbox 106 has a control means 400 described later.
The steering angle detection device 410 is attached.

The hydraulic rear wheel steering mechanism 200 steers the rear wheels while assisting the steering force of the rear wheels by hydraulic pressure, and has exactly the same construction as the hydraulic front wheel steering mechanism 100. That is, the hydraulic rear wheel steering mechanism 200 is passed through the second rack housing 201 so that the second rack shaft 202 can move in the left-right direction, and a part of the second rack housing 201 is provided with the second rack housing 201. A power cylinder 205 is formed. Note that 211 and 212 are ports for supplying pressure oil to the second power cylinder 205. A gear box 206 is formed in a part of the second rack housing 201, and a second pinion shaft 209 meshing with the rack of the second rack shaft 202 is rotatably supported by the gear box 206. ing. The second pinion shaft 209 has an input shaft portion 207 on one end side and a pinion portion 219 on the other end side,
These are connected by a torsion bar (not shown). Then, the gearbox 2 of the input shaft portion 207.
The control means 40, which will be described later, is provided at a portion projecting upward from 06.
Zero gear 440 is attached. The lower part of the gear box 206 is plugged with a plug screw PB. Reference numeral 210 denotes a second control valve, which is the same as the above-described first control valve 110, and the amount of pressure oil supplied to the second power cylinder 205 to assist the steering force of the rear wheels. Adjust.

Next, the hydraulic circuit 300 will be described.
The hydraulic circuit 300 includes a hydraulic pump 118, a flow divider FD, and the first control valve 1
The hydraulic pressure is supplied to the control valve 10 and the second control valve 210, and the pressure oil is supplied to the first power cylinder 105 and the second power cylinder 205 when required.

The hydraulic piping on the front wheel side will be described below.
Reference numeral 16 denotes a pump line in which hydraulic pressure is supplied from the hydraulic pump 118 to the first control valve 110, and 115
From the first control valve 110 to the oil tank 1
It is a return line where oil is returned to 17. Also, 113
Is the A port AP1 of the first control valve 110.
And one port 11 of the first power cylinder 105
1 is a conduit for connecting the B port BP1 of the first control valve 110 and the other port 112 of the first power cylinder 105.

The hydraulic piping on the rear wheel side is the same as that on the front wheel side. 216 is a pump line, 215 is a return line, and 21 is a return line.
3 is the A port AP2 of the second control valve 210
And one port 211 of the second power cylinder 205
The conduit 214 for connecting to the second control valve 2
10 B port BP2 and the second power cylinder 205
Is a conduit connecting to the other port 212 of the.

The first control valve 110 determines the opening degree of the valve 110 according to the direction and size of the torsion of the torsion bar, and sends the pressure oil supplied from the oil pump 118 to the first power cylinder 105. is there. Therefore, when the torsion bar is not twisted, all the pressure oil supplied from the oil pump 118 is relieved to the return line 115. The same applies to the second control valve 210.
The valve 210 is opened by the torsion of the torsion bar of the control valve 210, and the pressure oil supplied from the oil pump 118 is sent to the second power cylinder 205.

The control means 400 includes a rudder angle detecting device 410.
And a control device 420 including a microcomputer,
It includes an electric motor 430 and a gear 440. Figure 2
FIG. 6 is a diagram showing a cross section of a steering angle detection device 410. Figure 1
2, the steering angle detection device 410 is a device for detecting the rotation angle of the steering wheel connected to the input shaft portion 107 of the first pinion shaft 109, and includes a casing 411 and a pulley. The shaft 417, the first pulley 413, the second pulley 414, the belt 415, and the potentiometer 416 are provided. The casing 411 is fixed to the lower portion of the gear box 106, and the first pulley 413, the second pulley 414, and the belt 415 are housed in the casing 411. One end of the pulley shaft 417 is connected to the lower portion 109a of the first pinion shaft 109. And the pulley shaft 417
Is inserted in the casing 411, and both ends are rotatably supported by the casing 411 via bearing members 418a and 418b. The first pulley 413 is integrally attached to the pulley shaft 417. The potentiometer 416 is fixed to the outer wall surface of the casing 411, and the rotary shaft 416a of the potentiometer 416 is inserted into the casing 411. This rotating shaft 416a
A second pulley 414 is integrally attached to the tip of the. Then, the first pulley 413 and the second pulley 41
4 and 4 are connected by a belt 415.

FIG. 3 is a partially enlarged sectional view showing the vicinity of the gear box 206 on the hydraulic rear wheel steering mechanism 200 side.
With reference to FIGS. 1 and 3, the gear 440 is integrally attached to the input shaft portion 207. A worm gear 431 is integrally attached to the rotating shaft of the electric motor 430, and the worm gear 431 is the worm gear 431.
It meshes with 40. The electric motor 430 is fixed at a predetermined position on the vehicle body (not shown).

Referring to FIG. 1, the control device 420 controls the steering of the rear wheels in accordance with the steering of the front wheels.
Although not specifically shown, the steering angle detection device 4
10 based on the steering angle information of the front wheels sent from the potentiometer 416 and the speed information of the vehicle body sent from the vehicle speed sensor 421; And a command unit for issuing a command to the electric motor 430.

Next, the operation of this four-wheel steering system will be described. When the engine is started, the hydraulic pump 118 is activated to supply hydraulic pressure to the control valves 110 and 210 of the front and rear wheel steering mechanisms 100 and 200, and to supply power to the control means 400 to control wheel steering. Is possible. In this state, all the pressure oil supplied to the control valves 110 and 210 is relieved and returned to the oil tank 117.

When the steering wheel is cut, the first rack shaft 102 meshing with the first pinion shaft 109 on the front wheel side is slid to steer the front wheels. At this time,
A twist occurs in the first pinion shaft 109, and the direction and magnitude of this twist are detected by a torsion bar. And
For example, if the handle is turned to the right, the pump port PP and the A port A of the first control valve 110
P1 is communicated with and pressure oil is transferred to the first power cylinder 105.
It is supplied from the port 111 of the above and assists the steering force.
At this time, the other port 112 of the first power cylinder 105 serves as a return port, and the oil on the low pressure side of the first power cylinder 105 is the first control valve 1
The oil is returned to the oil tank 117 via the B port BP1 and the return port DP of 10. Further, when the steering wheel is turned to the left, the pressure oil is supplied from the B port BP1 of the first control valve 110 from the port 112 of the first power cylinder 105 to assist the steering force.

The rotation angle of the first pinion shaft 109 is detected by the steering angle detection device 410. That is, the first
The rotation angle of the pinion shaft 109 is transmitted to the potentiometer 416 by the first pulley 413 and the second pulley 414 connected by the belt 415, and the potentiometer 4
It is detected by the rotation angle of the 16 rotation shafts 416a. The detected rotation angle of the first pinion shaft 109 is sent to the control device 420 as steering angle information of the front wheels. Further, speed information of the vehicle is sent from the speed sensor 421 to the control device 420.

The calculation unit of the control device 420 determines the steering angle direction, the steering angular velocity and the size of the steering angle of the rear wheels based on the steering angle information and the speed information. Then, the command unit issues a command to the electric motor 430 to steer the rear wheels based on the determination of the calculation unit. The electric motor 430 operates according to the command, and rotates the gear 440 meshing with the electric motor 430. When the gear 440 rotates, the second pinion shaft 209 on the rear wheel side rotates, the second rack shaft 202 slides, and the rear wheel is steered. At this time, similarly to the steering of the front wheels described above, the second pinion shaft 20
Twist occurs in 9 and the direction and magnitude of this twist are detected by a torsion bar. Then, for example, if the front wheels are steered to the right and the rear wheels are steered in the same phase as the front wheels, the pump port P of the second control valve 210 is
The P and A ports AP2 are communicated with each other, and pressure oil is supplied from the port 211 of the second power cylinder 205 to assist the steering force. Further, if the steering is performed in the opposite phase to the front wheels, the pressure oil is supplied from the B port BP2 of the second control valve 210 from the port 212 of the second power cylinder 205 to assist the steering force.

According to this embodiment, the front wheel steering mechanism 100, which is already mass-produced and has a low cost, is replaced with the rear wheel steering mechanism 200.
By using the same unit as the front and rear steering mechanisms, the cost of the four-wheel steering device can be significantly reduced. As a result, although the handling performance and running stability of the vehicle can be improved, it is possible to promote the spread of 4WS, which has been delayed in spread due to its high price. As a result, it is possible to provide a wide range of vehicles with excellent running performance.

Further, the control means 400 can control the steering of the rear wheels via the electric motor 430 in response to the steering of the front wheels. Therefore, the rear wheel can be finely steered, and the second power cylinder 2 of the rear wheel steering mechanism 200 can be used.
The front wheels are not affected by the hydraulic pressure generated in 05, and four-wheel steering with sufficient rigidity can be performed. Moreover, when steering the rear wheels by the electric motor 430, the steering force is assisted by the hydraulic pressure, so that the electric motor 430 substantially only adjusts the opening degree of the second control valve 210 of the rear wheel steering mechanism 200.
Therefore, as the electric motor 430, a small, lightweight, and inexpensive one can be used, which can contribute to weight reduction of the entire apparatus and further cost reduction.

The present invention is not limited to the above embodiment, and various design changes can be made without changing the gist of the present invention.

[0026]

According to the present invention, since the front wheel steering mechanism and the rear wheel steering mechanism are composed of the same unit, the manufacturing cost of the four-wheel steering device can be greatly reduced. Further, since the control means controls the steering of the rear wheels via the motor in response to the steering of the front wheels, the rear wheels can be finely steered, and the hydraulic pressure generated on the rear wheel steering mechanism side affects the front wheel steering mechanism side. It is possible to carry out four-wheel steering with sufficient rigidity without receiving the steering force. Moreover, since the motor only adjusts the opening degree of the second control valve that substantially controls the hydraulic pressure supplied to the second power cylinder of the rear wheel steering mechanism when steering the rear wheels, a small and lightweight motor is used. As a result of being able to be used, the entire device can be made compact and lightweight.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a drive system of a four-wheel steering system according to an embodiment of the present invention.

FIG. 2 is an enlarged side view of a partial cross section of a hydraulic front wheel steering mechanism.

FIG. 3 is a partially sectional enlarged side view of a hydraulic rear wheel steering mechanism.

[Explanation of symbols]

 100 hydraulic front wheel steering mechanism 102 first rack shaft 105 first power cylinder 109 first pinion shaft 110 first control valve 200 hydraulic rear wheel steering mechanism 202 second rack shaft 205 second power cylinder 209 second pinion shaft 210 second 2 control valve 400 control means 410 rudder angle detection device 420 control device 430 electric motor 440 gear

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B62D 113: 00 117: 00

Claims (1)

[Claims] 1. A four-wheel steering system for steering rear wheels according to front wheel steering, comprising: a first pinion shaft connected to a steering wheel;
It has a first control valve arranged around the first pinion shaft, a first rack shaft that meshes with the first pinion shaft, and a first power cylinder formed around the first rack shaft. A front wheel steering mechanism; a second pinion shaft connected to the motor; a second control valve arranged around the second pinion shaft; a second rack shaft that meshes with the second pinion shaft;
A rear wheel steering mechanism having a second power cylinder formed around the rack shaft, and a control means for driving the motor in response to steering of the front wheels are provided, and the front wheel steering mechanism and the rear wheel steering mechanism are provided. A four-wheel steering system characterized by being composed of equal units.