JPH0445389B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a device for steering both the front wheels and the rear wheels in a four-wheeled vehicle such as an automobile, that is, by steering the front wheels, which are steering wheels, the rear wheels as well as the front wheels are steered. The present invention relates to a wheel steering device, and particularly relates to a four-wheel steering device equipped with a device for returning rear wheels to a neutral position.

Conventionally, steering devices in four-wheeled vehicles steer only the front wheels, and the rear wheels tend to steer actively, although they do some toe-in or toe-out depending on the driving situation, regardless of the steering of the front wheels. I haven't gotten used to it. However, recently, a four-wheel steering device has been proposed in which both the front wheels and the rear wheels are steered (for example, Japanese Patent Laid-Open No. 55-91458), and research on this type of device is being carried out.

According to the four-wheel steering system, convenient maneuvering that was previously impossible and driving with improved steering performance are possible depending on various driving conditions of the vehicle. for example,
When maneuvering a vehicle at extremely low speeds, such as parallel parking or parking in a garage, by steering the rear wheels in the opposite direction to the front wheels (this is called anti-phase), it is possible to significantly change the direction of the vehicle. This makes it possible or easy to park in narrow spaces, which was previously impossible or extremely difficult. Also,
This is advantageous in U-turns as well, since the minimum turning radius can be made small. Furthermore, by steering the rear wheels in a phase opposite to that of the front wheels, the difference between the inner wheels can be minimized or eliminated, which is advantageous when turning a narrow corner. Also,
When steering a vehicle at such extremely low speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase), it is possible to move the entire vehicle in parallel, making it easier to park or park the vehicle. It is often useful when

On the other hand, when changing lanes while driving at medium to high speeds, if four-wheel steering is performed in the same phase, lateral force is applied to the front and rear wheels at the same time, making it possible to change lanes smoothly without phase lag, thereby suppressing yawing. This allows you to change lanes at high speed without fear. Furthermore, when cornering, the direction of the vehicle can be effectively changed by steering the rear wheels in opposite phases.

Furthermore, when driving straight ahead, if the rear wheels are steered in a direction that counteracts the effect of external disturbances such as crosswinds, stable driving can be maintained against external disturbances, and stable high speeds can be maintained. It is also possible to obtain straightness.

In addition, even if you accelerate or decelerate while keeping the steering angle of the front wheels constant during a turn, the steering angle of the rear wheels will change according to the acceleration or deceleration, so that you will not deviate from the course and make a stable turn. It can also be done.
In other words, in conventional vehicles, the steering characteristics are adjusted to slightly understeer in order to maintain straight-line stability, and when accelerating during a turn, there is a tendency for the vehicle to deviate outward from the course. By doing so, the deviation can be corrected and stable turning can be achieved.

In terms of comfort, it is possible to obtain a smaller minimum turning radius with the same wheelbase, so the wheelbase can be increased, and in addition to this, the actual steering angle of the front wheels can be reduced. It has many advantages, including the ability to experiment with new designs.

As described above, four-wheel steering has many practical advantages and is extremely useful.

When performing four-wheel steering as described above, a rear wheel steering device for steering the rear wheels is provided in addition to the conventional steering device for front wheels. This rear wheel steering device is configured to steer the rear wheels in a desired direction (i.e., in the same phase or in opposite phase) with respect to the front wheels using a hydraulic device or a mechanism that works with the front wheel steering device. However, since steering may become impossible due to failure of the rear wheel steering device or hydraulic system, it is desirable to combine a rear wheel restoring device that always restores the rear wheels to a safe neutral position.

The above-mentioned rear wheel restoring device is, for example,
This has been known for a long time as shown in Japanese Patent No. 147968. However, this conventional rear wheel restoring device presses the other ends of two springs, one end of which is supported on the vehicle body side, onto an actuating rod connected to the rear wheel, and utilizes the balance of the forces of these springs to restore the rear wheel. Since the wheels are configured to be set in a neutral position, even if a slight disturbance (lateral force caused by a crosswind, uneven road surface, etc.) acts on the rear wheels, the rear wheels are allowed to steer. . Therefore, this conventional rear wheel restoring device does not actually set the rear wheels firmly in the neutral position to enable the vehicle to run when the rear wheel steering device fails, and it also does not allow the vehicle to maintain straight-line stability. It was something that would damage the.

The present invention has been made in view of the above circumstances, and provides a safe four-wheel steering system for a vehicle that prevents the rear wheels from being easily steered by external force when the rear wheel steering system malfunctions. The purpose is to

The four-wheel steering device of the present invention includes a steering device that steers the front wheels, a hydraulic cylinder that receives hydraulic pressure to steer the rear wheels, and a preset load that biases and holds the rear wheels in a neutral position. a rear wheel steering device having a set neutral position biasing device; a control device for controlling hydraulic pressure supplied to a hydraulic cylinder of the rear wheel steering device according to predetermined conditions; The neutral position biasing means includes a spring loosely fitted to an actuating rod connected to the rear wheel, and a valve that acts to eliminate the pressure difference between the left and right cylinder chambers of the hydraulic cylinder. is,
a first regulating member that comes into contact with both ends of the spring and receives a spring reaction force; a spring seat that is slidably and loosely fitted on the actuating rod and whose sliding is regulated by the first regulating member; and a second regulating member for regulating the sliding of the spring seat, and the spring seat compresses and deforms the spring under the action of the second regulating member as the actuating rod is displaced when the rear wheels are steered. The invention is characterized in that it is configured to

With the above configuration, since the rear wheels are steered by hydraulic pressure, it is possible to reliably steer the rear wheels with a large force, and when securing the neutral position of the rear wheels, the control means uses a signal By controlling the valve to release hydraulic pressure to the reservoir and eliminate the differential pressure between the left and right cylinder chambers, the rear wheels will maintain the neutral position using the neutral position biasing means to which the preset load is set. , the rear wheels will not be steered by the disturbance unless an extremely large disturbance that exceeds this preset load acts on the rear wheels.

The mechanism by which the above preset load is applied will be explained below. In the above configuration, the first regulating member fixed to the vehicle body of the neutral position biasing means is
Hold both ends of the spring while receiving the spring reaction force.
The second regulating member provided on the actuating rod regulates the position of the spring seat, which is regulated in position by the first regulating member.
The position of the actuating rod is regulated by the end of the spring compressed and held by the regulating member and held at the neutral position. When the actuating rod whose position has been regulated in this manner attempts to move, the reaction force of the compressed and held spring is applied to the actuating rod, and the force exerted by this spring becomes a preset load.

FIG. 4 shows the relationship between the spring force acting on the actuating rod and the actuating rod stroke when such a preset load is applied. As shown in the figure, in this device, as long as the applied external force a is smaller than the preset load Fp, the actuating rod does not move at all, and therefore the neutral position of the rear wheel can be reliably maintained.

In the conventional rear wheel restoring device that utilizes the balance of spring forces, the relationship between the spring force acting on the actuating rod and the actuating rod stroke is shown in FIG. 3. In other words, in this case, the preset load described above cannot be applied, and if an external force of magnitude a is applied to the actuating rod, the rear wheels will easily turn by the amount that causes stroke b to move. Become.

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

FIG. 1 shows a four-wheel steering system for a vehicle according to one embodiment of the present invention. Front wheels 1, 1 and rear wheels 2,
The output 4a of the front wheel steering angle sensor 4, which is mechanically separated from the steering wheel 2 and detects the steering angle θ _H of the steering wheel 3, is inputted to the controller 10 of the rear wheel steering device. I am trying to steer 2,2. As is well known, the front wheel steering device moves a rack 6 in the width direction of the vehicle (indicated by arrow A) by means of a pinion 5 fixed to a steering shaft 3A to which a steering wheel 3 is fixed. The knuckle arms 8, 8 of the left and right front wheels 1, 1 are rotated around their shafts 8a, 8a via tie rods 7, 7 connected to the wheels, thereby steering the front wheels 1, 1 left and right. . That is, when the steering wheel 3 in the figure is rotated in the direction of arrow L, the steering shaft 3
A rotates in the direction of the arrow L, rotates the pinion 5 in the L direction, and moves the rack 6 in the L direction. As a result, the left and right front wheels 1, 1's knuckle arms 8, 8 rotate in the L direction via the tie rods 7, 7, and the front wheels 1, 1
Rotate in the L direction around a and 8a and steer to the left. At this time, the steering angle sensor 4
The output signal 4 indicates that the has rotated by an angle θ _H in the L direction.
a, and input this to the front wheel steering angle input 10A of the controller 10 of the rear wheel steering device.

The controller 10 is supplied with power by a power source 11, and in addition to the front wheel steering angle input 10A, the controller 10 has a vehicle speed input 10B connected to a vehicle speed sensor 12, and a feedback input 10C connected to a rear wheel steering angle sensor 13. and a steering direction output 1 connected to a solenoid 20 that controls the steering direction of the rear wheels.
0D and a hydraulic pump motor output 10E connected to the motor 21A of the hydraulic main pump 21 that controls the steering angle θ _R of the rear wheels.

The hydraulic main pump 21 includes a pump 21B that discharges oil (hydraulic oil), and this pump 21B is connected to a hydraulic actuator 23 via a steering direction switching valve 22, and between this valve 22 and the pump 21B. In the oil column 24A
and oil return path 24C and orifice 2 on the way.
4b is provided, and an oil reservoir 25 is provided in the middle of the oil return path 24C.
are arranged.

The steering direction switching valve 22 is connected to the oil outgoing path 24A.
and a valve part consisting of two inlets connected to the oil return path 24C and two outlets communicating with the inlets,
It has three valve parts 22A, reverse 22B, and stop 22C that can be switched in parallel, and by operating the solenoid 20, these three valve parts 22A, 22
Either one of B and 22C is the oil outgoing path 24.
A, it is designed to be connected to the return route 24C.
The two outlets of this valve 22 are connected to a right oil passage 23R and a left oil passage 23L of a hydraulic actuator 23, respectively, and these right oil passage 23R and left oil passage 23L are connected to the outgoing path 24A through this valve 22. It is connected to the return route 24C.

The hydraulic actuator 23 moves the rod 26, which is its output shaft, in the width direction of the vehicle (indicated by arrow B) due to the pressure difference between the right and left oil passages 23R, 23L, and moves the rod 26, which is the output shaft, in the width direction of the vehicle (indicated by arrow B). The knuckle arms 28, 28 of the wheels 2, 2 are rotated around their shafts 28a, 28a, thereby steering the rear wheels 2, 2 left and right.

In the illustrated example, when the front wheels 1, 1 are steered in the left direction L and the rear wheels 2, 2 are steered in the same phase as the front wheels 1, 1, the steering direction switching valve 22 is set to the positive 22A position. The oil flows from the home passage 24A to the return passage 24C via the orifice passage 24B, and returns to the pump 21B via the reservoir 25. This results in
The pressure in front of the orifice 24b, that is, on the outward path 24A side, becomes high, and the pressure behind the orifice 24b, that is, on the return path 24C side, becomes low, and the valve 22
The pressure in the right oil passage 23R becomes higher than the pressure in the left oil passage 23L through the positive 22A portion of the hydraulic actuator 23.
is driven in the L direction. The amount of drive at this time is determined by the amount of current input to the main pump motor 21A. As a result, the rear wheels 2, 2 are steered in the left direction L via the tie rods 27, 27, and the rear wheels 2, 2 are steered in the same phase as the front wheels 1, 1.

When the front wheels 1, 1 are steered to the right and the rear wheels 2, 2 are steered in the same phase as the front wheels 1, 1, the steering direction switching valve 22 is set to the reverse 22B position, and the right oil The pressure relationship between the passage 23R and the left oil passage 23L is reversed to that described above, and the actuating rod 26 is driven rightward. As a result, the rear wheels 2, 2 are the front wheels 1,
Turn to the right in the same phase as 1.

In addition, when steering the rear wheels 2, 2 in the opposite phase to the front wheels 1, 1, the correspondence between the steering direction and the forward direction 22A and reverse direction 22B of the steering direction switching valve 22 is reversed from the case of the same phase. That is, when steering the front wheels 1, 1 to the left, it is set to reverse 22B, and when steering the front wheels 1, 1 to the right, it is set to forward 22A.

The steering direction of the front wheels 1, 1 is determined by the front wheel steering angle sensor 4.
It is input to the controller 10 by the output 4a of The controller 10 makes the determination according to the set vehicle speed corresponding pattern.

To make the steering angle θ _R of the rear wheels 2, 2 zero, connect the stop 22C of the valve 22 to the oil passage, cut off the communication between the pump 21B and the hydraulic actuator 23, and turn the left and right of the hydraulic actuator 23. The pressure difference between the oil passages 23L and 23R is eliminated, and the actuating rod 26 is set in a neutral position. At this time, in order to ensure that the actuating rod 26 is set at the neutral position, and furthermore, to enable the vehicle to travel by steering only the front wheels 1, 1 in the event of oil pressure failure, the hydraulic actuator 23 is installed at the rear. A neutral position biasing means is provided for biasing and holding the wheels 2, 2 in a neutral position. The neutral position biasing means will be explained in detail below with reference to FIG. 2.

The hydraulic actuator 23 described above includes a cylindrical case 23a and a hydraulic chamber 23 inside this case 23a.
The piston 23c is slidably housed in the actuating rod 26, and the piston 23c is fixed to the large diameter portion 26a at the center of the actuating rod 26. A spring seat 70 is fitted into a small diameter portion 26b continuous to both left and right ends of the large diameter portion 26a of the actuating rod 26 so as to be slidable relative to the small diameter portion 26b. The small diameter portion 26b of the actuating rod 26 is inserted into a nut 71 screwed onto both ends of the case 23a. The small diameter portion 26b is slidable on the nut 71, and a seal member 72 is provided on the inner peripheral surface of the nut 71 to maintain airtightness between the inside and outside of the case 23a. As will be described later, the nut 71 is provided on the vehicle body side and supports a coil spring 73.
It also acts as a stopper that supports each outer end of L and 73R.

Between the spring seat 70 and the nut 71 are coil springs 73 as first and second biasing members, respectively.
L, 73R are compressed, and these coil springs 73L, 73R are connected through spring seats 70, respectively.
The actuating rod 26 is elastically pressed against the left and right ends of the large diameter portion 26a serving as the first regulating member, respectively.
It is biased to the left. However, there are stoppers 74 at both left and right ends of the hydraulic chamber 23b of the case 23.
L and 74R are fixed, and the spring seat 70 comes into contact with these stoppers 74L and 74R. The stoppers 74L, 74R are each provided at a position that sets the piston 23c to the center position of the case 23c (at this time, the rear wheels 2, 2 are set to a neutral position where the steering angle is zero). In other words, the actuating rod 26 sets the rear wheels 2, 2 to the neutral position while receiving preset loads from the coil springs 73L, 73R from both left and right directions. In this way, the stopper 74L, 7
4R, each coil spring 73L, 73
Since the biasing force of R is prevented from acting on the other coil springs 73R and 73L, the actuating rod 26
is always set to the neutral position. Stopper 74L,
Without 74R, the biasing force of each of the above coil springs would be acting on the other coil spring, so
If there is a difference in the biasing forces of these coil springs, the differential rod 26 will not be set at the neutral position, and the actuating rod 26 will move due to a small external force.

As is clear from the above description, in this embodiment, the nut 71 and the stopper 74L constitute a first regulating member located at both ends of the coil spring 73L, and similarly, the nut 71 and the stopper 74R constitute a first regulating member that controls the coil spring 73R. A first regulating member is configured to regulate the position of both ends. Further, the large diameter portion 26a of the actuating rod 26 constitutes a second regulating member that regulates the sliding movement of the spring seats 70, 70.

As mentioned above, the actuating rod 26 is set in the neutral position by the rear wheel restoring device consisting of the coil springs 73L, 73R and the stoppers 74L, 74R.
As mentioned above, when hydraulic oil is supplied from the oil passages 33L and 23R and hydraulic pressure exceeding the preset load acts on the piston 23c, it moves to the left or right and steers the rear wheels 2, 2 (the spring seat 70 includes the spring chamber 23d of the case 23 and the hydraulic chamber 2.
A small hole 70a communicating with the spring chamber 23b is provided to prevent the hydraulic fluid in the spring chamber 23d from being excessively compressed during hydraulic operation).

However, even if a lateral force due to a crosswind or uneven road surface is applied to the rear wheels 2, 2 when the vehicle is traveling straight, as long as this lateral force does not exceed the preset load, the rear wheels 2, 2,
2 is not steered. The larger the preset load is set, the more the straight-line stability of the vehicle is improved, but on the other hand, a stronger hydraulic actuator 23 is required. Therefore, the preset load may be appropriately set in consideration of both.

As explained in detail above, the four-wheel steering system for a vehicle according to the present invention opens the hydraulic reservoir for steering the rear wheels, and controls the valve to eliminate the differential pressure between the left and right cylinder chambers. Since the rear wheels are reliably brought to the neutral position by the neutral position biasing means to which a preset load is established, the rear wheels will not be steered even if some disturbance acts. Therefore, according to the device of the present invention, the straight-line stability of the vehicle in the event of a failure can be significantly improved, and the vehicle can be safely driven by steering only the front wheels.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of the four-wheel steering device of the present invention using hydraulic pressure, Fig. 2 is a cross-sectional view showing an enlarged part of the device in Fig. 1, and Fig. 3 is the operation of the conventional device. FIG. 4 is a graph showing the relationship between the spring force applied to the rod and the actuating rod stroke. FIG. 4 is a graph showing the relationship between the spring force applied to the actuating rod and the actuating rod stroke in the device of the present invention. 1...Front wheel, 2...Rear wheel, 3...Steering wheel, 5...Pinion, 6...Rack, 7,
27... Tie rod, 8, 28... Knuckle arm, 10, 50... Controller, 20... Solenoid, 21... Main pump, 22... Rear wheel steering direction switching valve, 23... Hydraulic actuator, 25... Reservoir , 26... Actuation rod, 2
6a...Large diameter part of actuation rod (second regulating member),
70... Spring seat, 71... Nut, 73... Coil spring, 74... Stopper.

Claims (1)

[Scope of Claims] 1. A steering device that steers the front wheels, a hydraulic cylinder that receives hydraulic pressure to steer the rear wheels, and a preset load set to bias and hold the rear wheels in a neutral position. a rear wheel steering device having a neutral position biasing means; a control device for controlling hydraulic pressure supplied to the hydraulic cylinder of the rear wheel steering device according to predetermined conditions; The neutral position biasing means includes a spring loosely fitted to an actuating rod connected to the rear wheel, and a valve fixed to the vehicle body,
a first regulating member that comes into contact with both ends of the spring and receives a spring reaction force; a spring seat that is slidably and loosely fitted on the actuating rod and whose sliding is regulated by the first regulating member; and a second regulating member for regulating the sliding of the spring seat, and the spring seat adjusts to the second regulating member as the actuating rod is displaced when the rear wheels are steered.
A four-wheel steering device for a vehicle, characterized in that it is configured to compress and deform a spring under the action of a regulating member.