JPS63176778A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To securely hold the lock of rear wheels by preventing a working fluid from an actuator cylinder from flowing backward even when a lateral force is applied to said rear wheels under a condition that a feed oil pressure for steering rear wheels is lowered due to an oil pressure failure. CONSTITUTION:A lock means 35 for holding rear wheels in a straight advance condition at the time of the failure of oil pressure, etc. consists of a fixedly held lock cylinder 39, a lock piston 36 which is slidably provided in the lock cylinder 39, and a spring 37 for energizing the lock piston 36 upward. Oil pressure passages 56, 57 are connected to upper and lower oil pressure chambers 38a, 38b of the lock cylinder 39 which is partitioned by the lock piston 36, respectively. A one-way valve 50 is provided in an oil pressure passage 53 from the connecting part 56a between the oil pressure passage 56 and the oil pressure passage 53 to a control valve 20. And, this valve 50 permits the feed of oil pressure from the connecting part 56a to the control valve 20, while preventing the back flow of a working fluid through this oil pressure passage.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a four-wheel steering device that can also steer the rear wheels in accordance with the steering of the front wheels. The present invention relates to a four-wheel steering device that allows the steering to be performed.

(Prior art) Conventionally, four-wheeled vehicles were typically steered by using a steering wheel to steer only the front wheels. However, steering only the front wheels may cause the rear wheels to skid depending on the driving conditions, or the turning radius may be affected. Problems have been pointed out in terms of maneuverability and steering, such as the limited ability to make small turns, and in light of this, a four-wheel steering system that steers the rear wheels as well as the front wheels has recently been proposed and researched. .

In other words, with a four-wheel steering system, when driving at relatively high speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase steering), the front and rear wheels are simultaneously steered in the lateral direction. Since the force is applied, there is no phase lag from the steering wheel steering, and the vehicle's attitude can be maintained almost on the tangent to the turning circle, making it possible to smoothly change lanes at high speeds, for example.

Also, if the rear wheels are steered in the opposite direction to the front wheels when driving at very low speeds (this is called reverse phase steering), the direction of the vehicle can be changed significantly, which is convenient for parallel parking or parking in a garage.

Furthermore, considering that the front wheels are not steered significantly at relatively high speeds, and the front wheels are steered significantly when driving at relatively low speeds, the rear wheels are also steered within the range where the front wheels are steered small. It can be seen that a four-wheel steering system is required that steers the rear wheels in the same direction and steers the rear wheels in the opposite direction when turning a large amount.

For this reason, we have provided a mechanism that can arbitrarily variably control the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, that is, the steering ratio, and adjust the steering ratio according to vehicle speed, front wheel steering angle, etc. It has been proposed to perform variable control to improve maneuverability, driving stability, etc. In such a four-wheel steering system, when the front wheels are steered by operating the steering wheel, the front wheel steering angle and vehicle speed are detected so that, for example, the rear wheel steering angle can be obtained in accordance with the vehicle speed at that time. Based on this detection signal, a hydraulic actuator for steering the rear wheels is often operated to steer the rear wheels.

In this case, in order to ensure driving safety when a hydraulic pressure failure occurs and the hydraulic pressure supplied to the rear wheel actuator decreases, a mechanism is installed to keep the rear wheels facing straight ahead in the event of a hydraulic failure. It becomes necessary. For this reason, for example, as disclosed in Japanese Unexamined Patent Publication No. 61-77570, a four-wheel steering device is provided with a centering spring that urges a rear wheel steering rod of a rear wheel steering means to a neutral position. Proposed.

Further, for the same purpose, the vehicle body may be provided with a locking means that can be engaged with the rear wheel steering wheel.

This locking means is designed to disengage from the rear wheel steering rod by hydraulic pressure supplied to the actuator for rear wheel steering, and as a result, oil pressure failure occurs and the supply to the rear wheel steering means is interrupted. When the oil pressure decreases, the locking means engages the vehicle, and locks the rear wheel steering rod to the vehicle body in a state in which it faces straight ahead.

(Problem to be Solved by the Invention) When such a locking means is used, the rear wheel steering rod is reliably locked and held in the straight-ahead direction by the locking means, so that in the event of oil pressure failure, the rear wheels will not move in the straight-ahead direction. This prevents the vehicle from running on two wheels using only the front wheels, which would impair driving safety. However, this locking means must be held while the rear wheel steering wheel is in the straight-ahead position; When a hydraulic failure occurs while the wheels are being steered, the lock is held by the locking means while waiting for the rear wheels to return to the straight-ahead state. However, in this case, the rear wheels may be forcibly steered by a lateral external force acting on the rear wheels, and in this case, the rear wheel steering rod is forcibly moved and the actuator Hydraulic oil in the cylinder may flow backwards. When this backflow of hydraulic fluid occurs, the hydraulic pressure in the hydraulic path from the hydraulic supply source to the actuator becomes temporarily high, and the lock by the locking means is operated in the unlocking direction, completely locking the rear wheel in the straight-ahead direction. The problem is that there is a risk that it will no longer be possible.

(Means for Solving the Problems) The present invention provides a four-wheel steering system using a locking means as described above, in which when a hydraulic pressure failure occurs and the hydraulic pressure supplied for rear wheel steering decreases, the rear In view of the problem that when a lateral external force is applied to the wheels, the backflow of hydraulic oil from the actuator cylinder may occur, and the locking of the rear wheel may not be completely maintained, we have developed a system in which the backflow of hydraulic oil from the actuator cylinder occurs. The purpose is to solve the above problem by preventing the oil pressure of the locking means from increasing even if the four-wheel steering device of the present invention is configured as follows.

That is, this device transmits the hydraulic pressure supplied to the actuator for rear wheel steering to the locking means via the first hydraulic path, and when the hydraulic pressure is equal to or higher than a predetermined value, the locking means receives this hydraulic pressure. When the engagement with the rear wheel steering rod is released and the hydraulic pressure decreases, the locking means locks and holds the rear wheel steering rod in the straight traveling direction. and,
from a connecting portion with a second hydraulic path that supplies the hydraulic pressure to a hydraulic control valve that is arranged upstream of the actuator and controls the hydraulic pressure supplied to the actuator;
A one-way valve is disposed in the second hydraulic path leading to the hydraulic control valve, and is configured to allow the hydraulic pressure to be supplied only from the connecting portion to the hydraulic control valve.

(Function) If the four-wheel steering device with the above configuration is used, if the hydraulic pressure is normally supplied from the hydraulic supply source to the hydraulic control valve of the rear wheel steering means and a predetermined hydraulic pressure is obtained, the first
This hydraulic pressure is transmitted to the locking means via the hydraulic path, and the rear wheel steering rod is not locked and held by the locking means, but a predetermined rear wheel steering is performed by the rear wheel steering actuator. On the other hand, when a hydraulic pressure failure occurs and the above-mentioned hydraulic pressure decreases, the hydraulic pressure supplied to the locking means via the first hydraulic path also decreases, so that the locking means causes the rear wheel steering wheel to face in the straight direction. Locked and held. In this case, oil pressure failure occurs while the rear wheels are steered,
In addition, when a lateral external force acts on the rear wheel and the hydraulic oil in the actuator cylinder flows backwards, the one-way valve disposed in the second hydraulic path prevents the backward flow of the hydraulic oil.
The hydraulic oil is prevented from flowing back into the hydraulic path, and the locking means reliably locks and holds the rear wheel steering rod.

(Embodiments) Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing one embodiment of a four-wheel steering system according to the present invention. The steering wheel 1 is connected to a first pinion 2 via a steering shaft 1a, and the first pinion 2 is connected to the first pinion 2 of a front wheel steering rod 3 that is slidable in the vehicle width direction.
It meshes with rack 3a.

Right and left circular tie rods 4 are installed at both ends of the front wheel steering rod 3.
Tie rods 4a, 4b are connected to arms of knuckles 5a, 5b which support right and left circular front wheels 6a, 6b with respect to the vehicle body so as to be steerable. Therefore, the front wheel steering rod 3 moves in the vehicle width direction in response to the operation of the steering wheel 1, and this movement causes the tie rod 4a,
4b to the knuckles 5a, 5b and the front wheel 6a.
, 6b is steered.

On the other hand, a second rack 3b is formed on the front wheel steering rod 3, and a second pinion 8 meshes with the second rack 3b for obtaining a steering force to be transmitted to the rear wheels.

Therefore, when the front wheel steering rod 3 is moved in the vehicle width direction in response to the operation of the steering wheel 1 and the front wheels 6a, 6b are steered as described above, the second and second wheels 8 are also rotated at the same time. The rotation of the second pinion 8 is transmitted to the variable steering ratio mechanism 10 via a rotation transmission shaft 9 connected to the second pinion 8, and the rotation is adjusted according to the steering phase and steering ratio adjusted here. The wheels are steered as described below. That is, in this way, the rear wheels can be steered in accordance with the front wheels steered.

Next, the rear wheel steering means steered by the variable steering ratio mechanism 10 will be explained. Left and right rear wheels 26a, 26b
are supported by knuckles 25a, 25b so as to be freely steerable, and one ends of the left and right tie rods 24a, 24b are connected to the arms of these knuckles 25a, 25b, and the narrow ends are connected to the left and right ends of the rear wheel steering rod 23. There is. This rear wheel steering rod 23 is connected to a variable steering ratio mechanism 10 via connecting arms 11 and 22, and this variable steering ratio mechanism 10 allows the rear wheel steering rod 23 to be connected to the vehicle via connecting arms 11 and 22. The left and right rear wheels 26a are moved in the width direction.
, 26b are steered. The variable steering ratio mechanism 10 detects the steering angle of the front wheels from the amount of rotation transmitted by the rotation transmission shaft 9, and connects the steering ratio so that the rear wheels are steered by a predetermined amount in accordance with the front wheel steering angle. The rear wheel steering rod 23 is moved in the vehicle width direction via the arms 11.22. The specific operation of this mechanism includes, for example, variable control of the steering phase and steering ratio depending on the vehicle speed, increasing the steering ratio with opposite phases at low vehicle speeds, and increasing the steering ratio with the same phase and steering ratio at high vehicle speeds. Or, the steering ratio can be variably controlled according to the front wheel turning angle, so that when the front wheel turning angle is large, anti-phase steering is performed, and when the front wheel turning angle is small, the steering ratio is performed in the same phase. It is often done. There are various possible structures for this purpose, such as a mechanical type that mechanically changes the rotation of the rotation transmission rod 9, and a type that uses an electric motor or a hydraulic motor, but a detailed explanation of the structure will be omitted here. .

In this variable steering ratio mechanism 10, rotation of the rotation transmission rod 9 is detected and sent to the controller 60 via the line 60C. This controller 60 has a battery 6
1 through a key switch 62, and receives a signal from a vehicle speed sensor 63 that detects vehicle speed. Therefore, the controller calculates the steering phase and steering ratio of the rear wheels based on the vehicle speed signal and the signal corresponding to the front wheel steering angle sent from the line 60c, and sends this signal to the step motor 12. , the step motor 12 is driven so that the variable steering ratio mechanism 10 sets the rear wheels to the calculated steering phase and steering ratio.

As described above, the steering ratio and steering phase of the rear wheels are set with respect to the steering of the front wheels, and the rear wheels are steered to perform four-wheel steering. A hydraulic actuator 30 and a control valve 20 are provided to smoothly move the rear wheel steering rod 23 via the connecting arm 11.22. The hydraulic actuator 30 is
A cylinder 31 that is fixed to the vehicle body and slidably inserts and holds the rear wheel steering rod 23, a piston plate 32 that is fixed to the rear wheel steering rod 23 and is slidably fitted into the cylinder 31, and a piston plate 32. The springs 34a and 34b are arranged in the left and right hydraulic chambers 33a and 33b, which are partitioned by the hydraulic pressure chambers 33a and 33b. The piston plate 32 is moved in the vehicle width direction by the applied hydraulic pressure, and the rear wheel steering rod 23 is smoothly moved in the vehicle width direction.

The control valve 20 controls the supply of hydraulic pressure to each hydraulic chamber 33a, 33b of the hydraulic actuator 30 so as to assist the movement of the connecting arm 11, 22. Since it is the same as the valve of the device, the explanation of its structure will be omitted. A pump 52 is connected to this control valve 20.
A second hydraulic path 53 to which the hydraulic oil in the reservoir tank 51 is pressurized and supplied is connected thereto, and a fourth hydraulic path 54 for returning return oil to the reservoir tank 51 is also connected. And these second and fourth hydraulic passages 53,54
A safety valve 55 is disposed therein. Normally, this safety valve 55 is biased to the right by a solenoid 55b to keep both side pressure passages 53 and 54 in communication with each other, but when an electrical abnormality is detected by the controller 60, the safety valve 55 is actuated by the controller 60. Upon receiving the signal, the solenoid 55b is deactivated, the valve 55 is moved to the left by the urging force of the spring 55a, and the oil supplied from the pump 52 is returned to the tank 51 as it is, and the hydraulic actuator 30 due to an abnormality in the electrical system is moved.
It is designed to prevent abnormal operation.

This four-wheel steering system has locking means 35 for holding the rear wheels in a straight-line state in the event of oil pressure failure or the like. This locking means 35 consists of a lock cylinder 39 that is held fixed, a lock piston 36 that is slidably disposed within the lock cylinder 39, and a spring 37 that biases the lock piston 36 upward in the figure. lock piston 36
The upper and lower hydraulic chambers 38 of the lock cylinder 39 are partitioned by
First and third hydraulic passages 56 and 57 in a and 38b, respectively.
is connected. The first hydraulic path 56 connected to the upper reservoir pressure chamber 38a is connected to the second hydraulic path 53, and this first hydraulic path 5
A one-way valve 50 is disposed in the second hydraulic path 53 from a connecting portion 56a between the connecting portion 56a and the second hydraulic path 53 to the control valve 20, and hydraulic pressure supply from the connecting portion 56a to the control valve 20 is permitted. However, the reverse flow of hydraulic fluid in this hydraulic path is prevented.

Further, the third hydraulic path 57 connected to the lower hydraulic path 38b is connected to the fourth hydraulic path 54 described above. Furthermore, the lock piston 3
A protrusion that can engage with a lock groove 23a formed in the rear wheel steering rod 23 is formed at the upper end of the rear wheel steering rod 6, and the engagement and disengagement between this protrusion and the lock groove 23a is achieved by vertical movement of the lock piston 36. When this protrusion engages with the lock groove 238, the rear wheel steering rod 23 is held locked with the rear wheels 26a, 26b fixed in the straight traveling direction.

The operation of the locking means 35 in the four-wheel steering system having the above configuration will be explained.

This four-wheel steering system is operating normally, and the hydraulic pump 5
2 to the control valve 20 through the second hydraulic path 53, this hydraulic pressure is supplied to the upper reservoir pressure chamber 38a of the locking means 35 through the first hydraulic path 56. . Therefore, the lock piston 36 is moved downward against the biasing force of the spring 31 by this oil pressure, and the engagement between the protrusion at its tip and the lock groove 23a of the rear wheel steering rod 23 is released, and the rear wheel steering rod 23 is disengaged from the lock groove 23a of the rear wheel steering rod 23. is steered according to the steering of the front wheels at a predetermined steering phase and steering ratio. Here, when a hydraulic pressure failure occurs and the hydraulic pressure in the second hydraulic path 53 decreases, the hydraulic pressure in the first hydraulic path 56 also decreases, so that the lock piston 36 is moved upward by the biasing force of the spring 37. The protrusion at the tip is the lock groove 238
, and the rear wheel steering rod 23 is fixedly held in a straight-ahead state. Note that when the oil pressure failure occurs, the rear wheels 26a, 26
In the case where the vehicle b has been steered, the tip of the lock piston 36 engages with the lock groove 23a when the rear wheels return to the straight-ahead state. In this case, a lateral external force is applied to the rear wheels, and the rear wheel steering shaft is pushed sideways, causing the hydraulic actuator 3
If the hydraulic oil in the hydraulic chamber 0 flows backward, this backward flow is blocked by the one-way valve 50, so that the first hydraulic path 56
The oil pressure inside the lock piston 36 does not become high, and there is no fear that the engagement between the tip protrusion of the lock piston 36 and the lock groove 23a becomes incomplete, which has been a problem in the past.

(Effects of the Invention) As described above, according to the present invention, hydraulic pressure is supplied via the first hydraulic path to the hydraulic pressure control valve that controls the hydraulic pressure supplied to the actuator for steering the rear wheels, and Since the hydraulic pressure is transmitted to the locking means via the second hydraulic path, if the hydraulic pressure is normally supplied from the hydraulic supply source to the hydraulic control valve of the rear wheel steering means and a predetermined hydraulic pressure is obtained. In this case, this hydraulic pressure is transmitted to the locking means via the first hydraulic path, and the rear wheel steering rod is not locked and held by the locking means, but a predetermined wheel turning is performed by the rear wheel steering actuator. ,
When a hydraulic pressure failure occurs and the above-mentioned hydraulic pressure decreases, the hydraulic pressure supplied to the locking means via the first hydraulic path also decreases, so the locking means locks the rear wheel steering rod in the straight-ahead direction. However, in this case, if a hydraulic pressure failure occurs while the rear wheels are being steered and a lateral external force acts on the rear wheels, causing the hydraulic fluid in the actuator cylinder to flow backwards, the first Since a one-way valve is disposed in the second hydraulic path from the connecting part between the hydraulic path and the second hydraulic path to the hydraulic control valve, this one-way valve prevents the backflow of hydraulic fluid and operates the hydraulic fluid to the first hydraulic path. This prevents oil from flowing backwards, and the locking means reliably holds the rear wheel steering rod locked in the event of oil pressure failure.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a four-wheel steering system according to the present invention. 1... Steering wheel 3... Front wheel steering rod 6a, 6b... Front wheel 9.
...Rotation transmission shaft 10...Variable steering ratio flu2
0... Control valve 23... Rear wheel steering rod 30... Hydraulic actuator 35... Lock means 50... One-way valve 52... Hydraulic pump 53... Second hydraulic path 56... First hydraulic path 60... Controller 1st rXJ

Claims (1)

[Scope of Claims] 1) Front wheel steering means for steering the front wheels by steering operation of a steering wheel, and hydraulic pressure for controlling the supply of hydraulic pressure for steering the rear wheels using hydraulic pressure in response to the steering of the front wheels. 4 of a vehicle comprising a rear wheel steering means equipped with a control valve;
In the wheel steering device, the rear wheel steering means has a locking means that can be engaged with a rear wheel steering rod that is moved in the vehicle width direction in response to the hydraulic pressure and steers the rear wheels, The hydraulic control valve disengages from the rear wheel steering rod in response to hydraulic pressure, causing the hydraulic control valve to steer the rear wheels, and engages with the rear wheel steering rod when the hydraulic pressure decreases. The rear wheel is fixedly held in the straight-ahead direction, and the hydraulic pressure is supplied from a connecting portion between a first hydraulic path that transmits the hydraulic pressure to the locking means and a second hydraulic path that transmits the hydraulic pressure to the hydraulic control valve. A four-wheel steering system for a vehicle, characterized in that a one-way valve capable of supplying the hydraulic pressure from the connecting portion only to the hydraulic control valve side is disposed in the second hydraulic path leading to the control valve.