JPH0460869B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a four-wheel steering system for a vehicle that steers the front and rear wheels of the vehicle.

Conventionally, in this type of steering system, which steers the rear wheels according to the turning state of the front wheels in order to improve the driving performance of the vehicle, a link type steering system that connects the front wheels and the rear wheels with a link mechanism is used. There are also hydraulically driven types in which the rear wheel steering device is independent of the steering device and the rear wheels are controlled by hydraulic pressure or the like. However, while the hydraulic drive type has the advantage of being able to control the rear wheels with a large degree of freedom, it does not have elements such as link mechanisms that restrict the rear wheel steering device.
When a servo valve in the hydraulic system or the control circuit that controls it malfunctions while driving and the servo valve is fixed at a position other than the neutral position, or when the steering position corresponds to the desired rear wheel steering. If the rear wheels are steered more than the above, there is a risk that the alignment between the front and rear wheels will be disrupted, causing a movement contrary to the outside of the vehicle while the vehicle is running, which poses problems in terms of stability and safety.

In view of the above, the present invention is designed to make the rear wheels independent of the front wheels and steer them using an actuator. It is an object of the present invention to provide a four-wheel steering device for a vehicle that is provided with a restriction device that limits the operation of a rear wheel steering device so that the rear wheels are not steered.

In order to achieve the above object, the present invention provides steering devices 10-16, 3 for steering the front wheels 18.
4, a rear wheel steering device 22-26, 32, 40-44 that is independent of the steering device and steers the rear wheels 28 by an actuator 52, and a sensor 50 that detects at least the steering angle of the front wheels. A four-wheel steering device for a vehicle, comprising: a control means 48 that receives a signal and controls the operation of the actuator so that the rear wheels are steered in a predetermined relationship with respect to the front wheels. Limiting device 6 that limits the operation of the rudder device
0-64, 34, 90, 94, the restriction device restricts the rear wheels from being steered beyond a certain tolerance range A, B, C, D with respect to the front wheels; The allowable range is configured to change depending on the steering angle of the front wheels.

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

In FIG. 1, which shows the entire system of a four-wheel steering device, a steering wheel 10 is connected to a piston rod 14 in a power cylinder 12 on the front wheel side by a rack and pinion mechanism, and both ends of the piston rod 14 are connected to a pair of knuckle arms 16.
It is connected to the front wheel 18 via. Also on the rear wheel side, a piston rod 24 is slidably fitted within the power cylinder 22, and both ends thereof are connected to the rear wheel 28 via a pair of knuckle arms 26. The rotating shaft 30 is adapted to control the operation of the piston rod 24 through the control of the control valve section 32.

Pressure oil in a hydraulic tank 40 is sucked up by a hydraulic pump 42 into the power cylinders 12 and 22 on the front wheel 18 side and the rear wheel 28 side, respectively, and is divided into two directions by a flow divider 44 to flow into the control valve section. 34 and 32, and after moving the piston rods 14 and 24 to the left or right, the oil is collected in a hydraulic tank 40.

The amount of steering of the steering wheel 10 is detected by a sensor 46 placed near the steering wheel 10, and the result is input to a controller 48. The controller 48 also receives the vehicle speed detected by another sensor 50, and the controller 48 controls the operation of the stepping motor 52 based on both inputs (steering amount and vehicle speed). is now under control. The rotation status of the motor 52 is detected by a meter 53 and fed back to the controller 48.
A bevel gear 54 is fixed to the output shaft of the motor 52.
This meshes with a bevel gear 56 fixed to the rotating shaft 30.

Hereinafter, the restriction device will be explained based on FIGS. 1 and 2.

Between the front wheel 18 and the rear wheel 28, a square frame-shaped cam member 60 is supported by four sets of rollers 62 and is disposed so as to be movable in the front-rear direction (vertical direction in FIG. 1). The front frame portion of the cam member 60 is connected to the cable 64
It is connected to a rod 66 fixed to the piston rod 14 on the front wheel 18 side by a cable 6.
4 are arranged along a predetermined path by a guide tube 68. Therefore, when the piston rod 14 moves to the left or right, the cam member 60 moves forward or backward via the cable 64.

On the inner surface of the cam member 60, as shown enlarged in FIG. 2, two congruent trapezoidal protrusions 70 and 80 protrude in the left-right direction and are formed point-symmetrically. One protrusion 70 has a short first flat surface 72 extending in the front-rear direction, a relatively steep and short first inclined surface 74 continuing from the front of the flat surface 72, and a first flat surface continuing from the inclined surface 74. It has a long second flat surface 76 parallel to the first flat surface 72 and a relatively gentle and long second inclined surface 78 continuing from the rear of the first flat surface 72. On the other hand, the other protrusion 80 is parallel to the first flat surface 72, but has a third flat surface 82 that is slightly shifted forward, and a third flat surface 82 that continues behind the third flat surface 82 and is relatively parallel to the first flat surface 72. Steep and short third slope 84
Continuing from this inclined surface 84, there is a long fourth flat surface 86 parallel to the third flat surface 82, and a third flat surface 86.
It has a relatively gentle and long fourth inclined surface 88 that continues in front of the second inclined surface.

A rack 90 is disposed below the cam member 60 so as to be movable in the left-right direction, and a rack portion 92 is formed at one end, and a pin 9 is formed at the other end.
4 is erected, and the pin 94 is located within a space surrounded by the first to fourth flat surfaces or the first to fourth inclined surfaces of the cam member 60. Further, a pinion 96 fixed to the rotating shaft 30 is meshed with the rack portion 92 .

The cam member 60, roller 62, cable 6
4, the pinion 34, the rack 90, the pin 94, etc. constitute a limiting device.

Next, the operation of this embodiment will be explained in Figs. 1 and 2.
The description will be made based on FIG. 3, which shows the relationship between the steering angle and the phase between the front wheels 18 and the rear wheels 28.

Assuming that the steering wheel 10 is now turned to the right, the piston rod 14 is moved to the left via the rack and pinion mechanism in accordance with the amount of steering, and the control valve section 34 is actuated to cause the hydraulic pump 42 to move the piston rod 14 to the left. The piston rod 14 is also powered by the supplied pressure oil.
moves to the left and steers the front wheels 18 to the right.
At this time, the controller 48 receives as input the steering amount, that is, the turning angle information of the front wheels 18 from the sensor 46 and the vehicle speed information from the sensor 50, and based on this, the rear wheels 28 are set in a predetermined relationship with respect to the front wheels 18. The stepping motor 52 is operated so that the vehicle is steered by the vehicle. The rotation of the motor 52 is caused by bevel gears 54 and 56.
The signal is transmitted to the rotating shaft 30 via the rotary shaft 30, thereby controlling the control valve section 32, which in turn controls the power cylinder 22 and steers the rear wheels 28.
The manner in which the rear wheels 28 are steered, that is, the predetermined relationship described above, may vary. For example, when the steering angle of the front wheels 18 is relatively small at a relatively high speed,
The rear wheels 28 are also steered in the same direction as the front wheels 18, and when the speed is relatively low and the steering angle of the front wheels 18 is relatively large, the rear wheels 28 are steered in the opposite direction to the front wheels 18.

However, the above predetermined relationship does not fall into the shaded area of the graph in FIG. 3 (θ _H is the front wheel steering angle, θ _R is the rear wheel steering angle) regardless of the vehicle speed, and furthermore, Even if a failure occurs in the hydraulic system of the wheel steering device or the like and the predetermined relationship is broken, it is mechanically ensured that the relationship will not fall into the shaded area.

That is, when the piston rod 14 is moved to the left as described above, the rod 66 is also moved to the left, pulling the cable 64 and moving the cam member 60 upward in FIG. At the same time, as described above, the rotating shaft 30 is also rotated by the stepping motor 52, and the rack 90 is moved leftward or rightward via the pinion 96 and the rack portion 92. This movement normally corresponds to the above-mentioned predetermined relationship, and the pin 94 of the rack 90 is in the first position.
The space is defined by the flat surface 72 , the second slope 78 , the third slope 84 , and the fourth flat surface 86 . This corresponds to the fact that the predetermined relationship is within the white area in the graph of FIG. In addition, the third inclined surface 84 corresponds to the boundary line C, and the fourth flat surface 86 corresponds to the boundary line D.

Therefore, as the cam member 60 is moved upward, the pin 94 of the rack 90 is moved either left or right, but the range of movement of the pin 94 to the left or right depends on the position of the cam member 60 at that time. is defined by a pair of points on planes 72 and 84, or 78 and 84, or 78 and 84, which are at the same left and right level. In this way, the movement of the pin 94 is restricted in the left-right direction by the cam member 60 which is immovable with respect to the vehicle body, which in turn restricts the movement of the rack 90, the movement of the rotating shaft 30, and the movement of the control valve section 32. Movement of the rear wheel 28 is limited within the blank area shown in FIG.

In the illustrated example, the first flat surface 72, that is, the boundary line A, prevents the rear wheel turning angle θ _R from being in the opposite phase with respect to the front wheel turning angle θ _H when the front wheel turning angle θ H is relatively small. , the third inclined surface 84, that is, the boundary line C, prevents the rear wheel turning angle θ _R from becoming excessive although it is in the same phase as the front wheel turning angle θ _R when the front wheel turning angle θ H is relatively small. Also, the second inclined surface 7
8, that is, the boundary line B, and the fourth plan view 86, that is, the boundary line D, prevent θ _R from being in an opposite phase to θ H or being excessively in phase with θ _H , respectively.

When the steering wheel 10 is turned to the left, the operation is substantially the same except that the operation is reversed.

As described above, according to the present invention, the operable range of the rear wheel steering device is limited by the limiting device whose allowable range changes in accordance with the front wheel steering angle. Therefore, even if there is some kind of failure in the rear wheel steering device or the control means, the rear wheels will not be steered beyond the allowable range relative to the front wheel steering angle. Furthermore, the size and direction of the allowable range are set in consideration of the steering angle of the front wheels.
Therefore, the correlation between the front and rear wheels can be maintained in a suitable state, and a high level of stability and safety can be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view showing one embodiment of the present invention, and FIG.
The figure is an enlarged view of the main part, and FIG. 3 is a graph showing the relationship between the steering angles of the front wheels and the rear wheels. Explanation of symbols of main parts, steering device...
10-16, 34, rear wheel steering device...22-2
6, 32, 40-44, restriction device...60-9
5.

Claims (1)

[Claims] 1. A steering device that steers the front wheels, a rear wheel steering device that is independent of the steering device and uses an actuator to steer the rear wheels, and a sensor that detects at least the steering angle of the front wheels. signal is input,
A four-wheel steering device for a vehicle, comprising: a control means for controlling operation of the actuator so that the rear wheels are steered in a predetermined relationship with respect to the front wheels, the operation of the rear wheel steering device being restricted. A restriction device is provided, the restriction device restricts the rear wheels from being steered beyond a certain tolerance range with respect to the rear wheels, and the tolerance range is dependent on the steering angle of the front wheels. A four-wheel steering device for a vehicle, characterized in that the four-wheel steering device is configured to change according to the direction of the vehicle.