JP2522888Y2 - Four-wheel steering system - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The four-wheel steering device according to the invention is used as a vehicle steering device, and when changing the course of the vehicle, not only the front wheels but also the direction of the rear wheels are changed. By changing it, the turning radius can be reduced, or the stability of the vehicle can be maintained.

(Prior Art) To reduce the turning radius of a car so that the course can be easily changed on a narrow road, or to maintain the stability of the vehicle even when the course is changed during high-speed driving. Therefore, four-wheel steering devices that move not only the front wheels but also the rear wheels when operating the steering wheel have been used in recent years.

Further, the rear wheel steering shaft is located (offset) behind the rear wheel steering point (ground point) in the forward direction of the vehicle, and a steering angle is given to the rear wheel. Is elastically supported so that it can be displaced slightly in the axial direction, so that when the course changes during high-speed running, the steering angle is given to the rear wheels in the same phase as the front wheels based on the centrifugal force to stabilize the vehicle. For example, as described in Japanese Utility Model Publication No. 1-41656, it has been proposed to maintain the properties, and some of them have been used.

(Problems to be Solved by the Invention) However, in the case of the conventional structure described in the above-mentioned publication, the steering mechanism for the front wheels and the steering mechanism for the rear wheels are mechanically connected to each other so that the front wheels have a certain degree of steering. When the angle is given, the steering angle is given to the rear wheels in a fixed relationship regardless of the vehicle speed. Therefore, depending on the vehicle speed, an optimum steering angle may not always be given to the rear wheels.

If the steering mechanism for the front wheels and the steering mechanism for the rear wheels are electrically related, and the steering angle given to the rear wheels is changed not only according to the steering angle given to the front wheels but also according to the vehicle speed, the rear The steering angle can be always given to the wheels under optimal conditions. However, if the steering mechanism for the front wheels and the steering mechanism for the rear wheels are simply electrically connected, a so-called fail-safe mechanism is required to be enriched, which inevitably increases the cost.

In other words, when the steering mechanism for the front wheels and the steering mechanism for the rear wheels are electrically related to each other, and the steering angle application to the rear wheels during high-speed running is also electrically controlled, the controller breaks down during high-speed running. In this case, a double or triple fail-safe mechanism must be incorporated in order to prevent the vehicle from being in a dangerous state, which increases costs.

For this reason, the inventor first electrically controls the application of the steering angle to the rear wheels only when the traveling speed of the vehicle is relatively low, and when changing the course during high-speed traveling, the centrifugal force is applied. A four-wheel steering device that solves the above-mentioned inconvenience by devising a steering angle to the rear wheels by applying a steering angle to the rear wheels based on the so-called compliance steering mechanism based on the above-mentioned method has been devised (Japanese Patent Application No. Hei.
235553).

In the case of the four-wheel steering device according to the present invention, when the vehicle runs at high speed, only the mechanical control is performed, and the electrical control is not performed. Therefore, even if the controller breaks down at high speed, the vehicle does not become in a dangerous state. However, if a part of the controller breaks down during low-speed running, there may be a case where an extra steering angle that is not necessary for the rear wheels is applied.

When driving at low speeds, even if an extra steering angle is applied to the rear wheels, it does not immediately become a dangerous state, but the vehicle will draw a trajectory different from the driver's intended trajectory, and Driving at the time of changing course or entering a garage becomes difficult.

The four-wheel steering system according to the present invention returns the rear wheels to the neutral position when a rear wheel is given an unnecessary steering angle due to a failure of a controller or the like at a low speed. The configuration described above solves the above-mentioned inconvenience.

(Means for Solving the Problems) The four-wheel steering device of the present invention includes a steering angle sensor that detects a steering angle applied to a front wheel, and a rear wheel that applies a steering angle to a rear wheel by being displaced in an axial direction. Output shaft, an electric motor for displacing the rear wheel output shaft in the axial direction, a vehicle speed sensor for detecting a vehicle speed, and a rotary drive shaft of the electric motor and the rear wheel output shaft. A clutch for electrically connecting and disconnecting, a displacement sensor for detecting a steering angle given to a rear wheel based on a displacement of the rear wheel output shaft, and a signal from the steering angle sensor and a vehicle speed sensor. A controller for controlling energization of the electric motor and connection / disconnection of the clutch.

At the same time, the steering center of the rear wheel is positioned rearward in the forward direction of the vehicle from the point of application of the rear wheel, and the rear wheel output shaft is elastically displaceable with respect to the vehicle body so as to be slightly displaceable in the axial direction. I support it.

In addition, the controller connects the clutch so that the steering angle can be freely applied to the rear wheels based on the energization of the electric motor only when the vehicle speed detected by the vehicle speed sensor is equal to or lower than a predetermined value.

Furthermore, a damper mechanism is provided to provide resistance to the rear-wheel output shaft from being displaced in the axial direction. In this case, the connection of the clutch is immediately disconnected.

(Operation) In the four-wheel steering device of the present invention configured as described above, when the vehicle is running at a certain speed or less, the controller connects the clutch, and based on signals from the steering angle sensor and the vehicle speed sensor. To control the energization of the electric motor to give a desired steering angle to the rear wheels as necessary.

When the vehicle travels beyond a certain speed, the controller disconnects the clutch and applies the steering angle to the rear wheels by the electric motor regardless of the signals from the steering angle sensor and the vehicle speed sensor. Not in a state.

As described above, when the course is changed when the vehicle travels beyond a certain speed, the steering angle is given to the rear wheels in the same phase as the front wheels based on the centrifugal force, and the vehicle at the time of the course change is changed. Stability is ensured.

A simple mechanism for stopping the application of the steering angle by the electric motor when the running speed of the vehicle exceeds a certain value is sufficient. Therefore, the reliability of the mechanism can be sufficiently ensured, and the fail-safe mechanism added to this mechanism can be made simple and extremely reliable.

Further, if a part of the controller fails and the rear wheel is given an unnecessary steering angle while the traveling speed of the vehicle is equal to or less than the predetermined value, the controller may control the rear wheel. Is canceled, and the rear wheels are returned to the center position (a state in which steering angle is not applied in any direction).

That is, when an abnormality is detected, the controller disconnects the clutch. The output shaft for the rear wheel and the rear wheel mechanically coupled to the output shaft for the rear wheel are moved to the neutral position by the elasticity of an elastic member that elastically supports the output shaft for the rear wheel with respect to the vehicle body. Return to At this time, the output shaft for the rear wheel and the rear wheel slowly move toward the neutral position by the function of the damper mechanism.

(Embodiment) FIGS. 1 to 4 show a first embodiment of the four-wheel steering device of the present invention. The movement of the steering wheel 1 provided in the driver's seat is transmitted to the steering gear 3 by the steering shaft 2, and displaces the front wheel output shaft 4 in the axial direction (the left-right direction in FIG. 1). Then, a desired steering angle is given to the front wheels 6, 6 via a pair of left and right knuckle arms 5, 5, respectively connected to both ends of the front wheel output shaft 4.

Steering angle sensors 8, 8 are supported on a steering column 7 through which the steering shaft 2 is inserted. From the rotation angle of the steering shaft 2 detected by the steering angle sensors 8, 8, The angle can be detected easily. The two steering angle sensors 8 are provided for fail-safe operation so that desired control can be performed even when one of the steering angle sensors 8 fails.

On the rear floor of the vehicle, a housing 10 for accommodating a steering angle imparting mechanism for the rear wheels 9, 9 is provided in the width direction of the vehicle (first to first).
(Horizontal direction in FIG. 2). A rear wheel output shaft 11 is provided inside the housing 10.
Through the right and left direction (the width direction of the vehicle). The rear wheel output shaft 11 imparts a steering angle to the rear wheels 9 along with displacement in the axial direction (lateral direction). The rear wheels 9 are connected to each other by knuckle arms 13. As the rear wheel output shaft 11 is displaced in the axial direction, the rear wheels 9, 9 swing about the steering centers 14, 14, and the displacement of the rear wheel output shaft 11 is changed. The steering angle suitable for the rear wheels 9, 9
To be given to In addition, the steering center 14, 14 of each rear wheel 9, 9 is a distance 1 more than the applied point 12, 12 (the center of the contact surface between the tire lower surface and the ground) of each rear wheel 9, 9 in the forward direction of the vehicle. It is located rearward (upward in FIG. 1) (downward in FIG. 1).

On the other hand, rack teeth 15 are fixedly provided in a portion located inside the housing 10 at an intermediate portion of the rear wheel output shaft 11. A transmission shaft rotatably supported inside the intermediate portion of the housing 10 with the rear wheel output shaft 11 in a twisted positional relationship.
At one end (the upper end in FIGS. 1 and 2) of the pinion 16, pinion teeth 17 are provided.
Are fixed, and the pinion teeth 17 are meshed with the rack teeth 15. A worm wheel 18 is fixed to the other end of the transmission shaft 16 (the lower end in FIGS. 1 and 2).

Also, an electric motor 19 fixed to the outer surface of the housing 10
A worm 21 is fixed to the output shaft 20 which is rotationally driven via an electromagnetic clutch 31 by a rotary drive shaft (not shown). Then, use this worm 21 as the worm wheel
A speed reduction mechanism is configured so that the output shaft 20 is displaced in the axial direction by the rotation of the output shaft 20 by meshing with the output shaft 20. This speed reduction mechanism has reversibility in the power transmission direction. That is, in addition to displacing the rear wheel output shaft 11 in the axial direction with the rotation of the output shaft 20, the output shaft 20 is rotated in accordance with the axial displacement of the rear wheel output shaft 11. ing. However, by suppressing the reverse efficiency of the speed reduction mechanism to be low, a load due to compression of a centering spring 25 described later is not applied to the electric motor 19 as it is. A rotation angle sensor 32 is attached to the electric motor 19 so that the rotation amount of the electric motor 19 can be detected, and the detected value is input to a controller 24 described below.

Two displacement sensors 22, 22 are provided at one end of the transmission shaft 16 so that the displacement of the rear wheel output shaft 11 can be detected via the transmission shaft 16. These two displacement sensors 22, 22
The detection signal sent from the controller is input to a controller 24 for controlling the energization of the electric motor 19 together with the detection signals from the steering angle sensors 8 and 8 and the detection signal from a vehicle speed sensor 23 for detecting the vehicle speed. . The reason why two displacement sensors 22 and 22 are provided is also to achieve fail-safe.

The controller 24 connects the electromagnetic clutch 31 only when the traveling speed of the vehicle detected by the vehicle speed sensor 23 is equal to or lower than a predetermined value (for example, 40 km / h). Based on a signal from the vehicle speed sensor 23, the electric motor 19 applies a steering angle to the rear wheels 9, 9. At this time, energization of the electric motor 19 is controlled based on a signal from the rotation angle sensor 32. Also, the displacement sensors 22 provided at the end of the transmission shaft 16 actually
The controller detects the steering angle given to the
Enter 24.

In addition to the electromagnetic clutch 31, a viscous damper 33, which is a damper mechanism, is connected in series with the electromagnetic clutch 31 between the rotary drive shaft of the electric motor 19 and the output shaft 20 to which the worm 21 is fixed. And the viscous damper 33 with an electromagnetic clutch
It is provided so as to be located closer to the output shaft 20 than to 31. The viscous damper 33 provides resistance to the rotation of the output shaft 20.

The controller 24 has a function of immediately disconnecting the electromagnetic clutch 31 when an abnormality is detected by a signal from each of the sensors 8, 22, 23, and 32, and when the vehicle speed is equal to or lower than a predetermined value. Have.

Further, a housing 10 for fixing the rear wheel output shaft 11 to the vehicle body.
In contrast to this, it is slightly and freely displaceable and elastically supported in the axial direction (the horizontal direction in FIGS. 1 and 2).

That is, a pair of seat plates 26, 26 are externally fitted to the intermediate portion of the rear wheel output shaft 11 so as to be able to freely displace in the axial direction of the rear wheel output shaft 11 with an interval therebetween. . With this,
A centering spring 25 is provided between the inner side surfaces of the two seat plates 26, 26 for returning the rear wheel output shaft 11 to the neutral position even when the electric motor 19 fails. A pair of stepped portions are provided on the inner peripheral surface of the housing 10 at intervals.
27, 27 are formed, and portions of the pair of seat plates 26, 26 near the outer periphery of the outer surfaces are opposed to the step portions 27, 27, respectively. or,
The pair of seat plates 2 is provided on the outer peripheral surface of the intermediate portion of the rear wheel output shaft 11.
A pair of stop rings 28, 28 are fixed at positions sandwiching 6, 26 to limit the movement of each seat plate 26, 26 with respect to the rear wheel output shaft 11. Further, disc leaf springs 29, 29 are provided between the outer surfaces of the pair of seat plates 26, 26 and the step portions 27, 27 and the stop rings 28, 28.

The elasticity of each disc spring 29, 29 is smaller than the elasticity of the centering spring 25. When the rear wheel output shaft 11 is displaced with respect to the housing 10, the third
As shown by the straight line a in the figure, first, the plate springs 29, 29 are displaced,
After any one of the disc springs 29 (the tip side in the displacement direction) is completely crushed, the centering spring 25 is compressed between the pair of seat plates 26, 26 as shown by a straight line b in FIG. I'm trying to get started. However, the spring load when each disc spring 29, 29 is completely compressed is expected to be applied to the rear wheel output shaft 11 based on the centrifugal force generated in the expected operating state. It is slightly larger than the maximum lateral load F _MAX .

In the four-wheel steering system of the present invention configured as described above, when the vehicle runs at a constant speed (for example, 40 km / h) or less, the controller 24 detects the steering angle sensors 8 and 8 and the vehicle speed sensor 23. Is supplied to the electric motor 19, and a desired steering angle is applied to the rear wheels 9, 9 as required. At this time, power is supplied to the electromagnetic clutch 31 so that the electromagnetic clutch 31 remains connected.

That is, when the vehicle travels at low / medium speed, the rear wheels 9 are given steering angles opposite to those of the front wheels 6 in order to improve the turning performance of the vehicle. At this time, the steering angle given to the rear wheels 9, 9 decreases as the vehicle speed increases, as shown by the solid line c in FIG. In this case, the steering angle given to the rear wheels 9, 9 is determined by displacement sensors 22, 22 provided at one end of the transmission shaft 16.
And the detected value is input to the controller 24 to achieve fail-safe.

It should be noted that the steering angle ratio represented on the vertical axis in FIG. 4 is the ratio (θ) between the steering angle θ _{R applied} to the rear wheels and the steering angle θ _{F applied} to the front wheels.
_R / θ _F ) indicates that the larger the absolute value, the larger the steering angle given to the rear wheels. Further, in the region above the horizontal axis, the steering angles of the front and rear wheels are in phase, and in the region below, they are in opposite phase.

As described above, when the steering angle is applied to the rear wheels 9 and 9 by the electric motor 19 while the steering angle is applied to the rear wheels 9 and 9 due to some failure, ,
The controller 24 detects this abnormal state based on signals from the sensors 8, 22, 23, and 32, and disconnects the electromagnetic clutch 31. When the connection of the electromagnetic clutch 31 is disconnected in this manner, the centering spring 25 and the plate springs 29, 29 that elastically support the rear wheel output shaft 11 with respect to the housing 10 fixed to the vehicle body. Due to the elasticity, the rear wheel output shaft 11 is returned to the neutral position. As a result, the rear wheels 9, 9 mechanically connected to the rear wheel output shaft 11, return to the neutral position.

When the rear wheels 9, 9 return to the neutral position, the rack teeth 15
The transmission shaft 16 rotates based on the engagement between the pinion 17 and the
Further, the output shaft 20 rotates based on the engagement between the worm wheel 18 and the worm 21. The rotation of the output shaft 20 is performed slowly by the action of the viscous damper 33. As a result, the axial displacement of the rear wheel output shaft 11 is performed relatively slowly, and the rear wheels 9, 9 are rotated. It is possible to eliminate the unnatural feeling accompanying the sudden removal of the steering angle given to the vehicle. As a result of returning the rear wheels 9, 9 to the neutral position in this manner, the rear wheels 9, 9
No steering angle is applied to the vehicle, and the vehicle can be operated in the same state as a vehicle having a normal two-wheel steering device.

On the other hand, when the vehicle travels beyond a certain speed, the power supply to the electromagnetic clutch 31 is stopped, and the connection of the electromagnetic clutch 31 is disconnected. Accordingly, regardless of the signals from the steering angle sensors 8 and 8 and the vehicle speed sensor 23, the controller 24
Does not control the steering angle of the rear wheels 9, 9. Also, if necessary, the power supply to the electric motor 19 is stopped.

As described above, when the course is changed in a case where the vehicle travels beyond a certain speed, the steering angle is given to the rear wheels 9, 9 in the same phase as the front wheels 6, 6, based on the centrifugal force, The stability of the vehicle during the course change is maintained.

For example, when the front wheels 6, 6 are displaced in the direction of the arrow α in FIG. 1 based on the operation of the steering wheel 1, the rear wheels 9, 9 are moved rightward in FIG. 1 by the centrifugal force accompanying the change in the course of the vehicle. As shown by an arrow β in the figure, a lateral force F is applied to each of the rear wheels 9, 9 by friction between the rear wheels 9, 9 and the road surface.
Is added. This force F is applied to the contact surface between the rear wheels 9, 9 and the road surface,
That is, the rear wheels 9, 9 are applied on the vertical plane including the force application points 12, 12, respectively. On the other hand, since the steering centers 14 and 14 of the rear wheels 9 and 9 are located behind the landing points 12 and 12 by a distance l in the forward direction of the vehicle, the rear wheels 9 and 9 are F · l. The steering is performed in the direction of arrow γ in FIG.

As the rear wheels 9, 9 are steered in the direction of arrow γ in this manner, the rear wheel output shaft 11 is displaced in the axial direction, and the one (left side in FIGS. The leaf spring 29 is compressed. Accordingly, the steering angle applied to each rear wheel 9 is determined by the force applied in the axial direction of the rear wheel output shaft 11 based on the lateral force F and the compression of the disc spring 29 by the rear wheel. The force applied to the output shaft 11 is maintained in a balanced state.

Therefore, when the vehicle speed exceeds a certain value, the rear wheels 9, 9
Is always in the same phase as the front wheels, as shown by the broken line d in FIG. Also, in this case, the rear wheel 9,
9 is determined only by the magnitude of the lateral force F applied to the rear wheels 9 and 9 due to the centrifugal force accompanying the change of course of the vehicle, and is applied to the vehicle speed and the front wheels 6 and 6. The magnitude of the steering angle is not directly related (although largely related indirectly).

Also, since the compression allowance of the disc springs 29, 29 is limited, an excessive steering angle is not given to the rear wheels 9, 9.

As described above, the steering angle is not applied to the rear wheels 9, 9 by the electric motor 19 at the time of high-speed running, and the steering angle is applied to the rear wheels 9, 9 only by physical force. The mechanism for stopping the supply of power to the electromagnetic clutch 31 and the electric motor 19 when the running speed of the vehicle exceeds a certain value can be simple, and the reliability of the mechanism can be sufficiently secured. The fail-safe mechanism added to the mechanism can be simple and extremely reliable.

In the case of the illustrated embodiment, the reverse efficiency of the speed reduction mechanism is reduced by configuring the speed reduction mechanism provided between the electric motor 19 and the rear wheel output shaft 11 by the worm 21 and the worm wheel 18. I have. For this reason, the electric motor 19
When the steering angle is given to the rear wheels 9 and 9 and the state is maintained as it is, the large load is not applied to the electric motor 19 by the elasticity of the centering spring 25.

In the case of the illustrated embodiment, the housing 10 is supported on the vehicle body so as not to be displaceable in the width direction of the vehicle, and a plate plate made of an elastic material is provided between the housing 10 and the output shaft 11 for the rear wheel. Springs 29, 29 are provided. On the other hand, the plate springs 29, 29 between the housing 10 and the rear wheel output shaft 11 are omitted, and instead, the housing 10 is attached to the vehicle body, and the shaft of the rear wheel output shaft 11 is It can also be supported elastically displaceable in the direction (width direction of the vehicle).

Next, FIG. 5 shows a second embodiment of the four-wheel steering device of the present invention. In the case of this embodiment, a viscous damper as a damper mechanism is provided between a housing 10 fixed to the vehicle body and a rear-wheel output shaft 11 supported so as to be displaceable in the axial direction with respect to the housing 10. 34 are provided.

That is, one end of the housing 10 (the left end in FIG. 5)
A cylinder 35 with viscous oil sealed inside is provided,
A piston portion 36 provided at an intermediate portion of the rear wheel output shaft 11 is oil-tightly fitted inside the cylinder portion 35. The supply / drain ports 37 provided at both ends of the cylinder portion 35 are connected to each other by an oil feed pipe 38, and the oil feed pipe 38
A flow regulating valve 39 is provided at an intermediate portion of.

The flow rate adjusting valve 39 adjusts the amount of viscous oil flowing in the oil supply pipe 38 depending on whether or not the solenoid 40 is energized.For example, when the solenoid 40 is not energized, the flow of the viscous oil flows in the oil supply pipe 38. When the amount of the viscous oil is not reduced, and when the solenoid 40 is energized, the throttle nozzle 41 is
And functions to reduce the amount of viscous oil flowing in the oil feed pipe 38.

A controller 24 (see FIG. 1; omitted in FIG. 5) is provided with steering angle sensors 8 and 8 (see FIG. 1) for detecting a rotation angle of the steering shaft 2 and a rear wheel via a transmission shaft 16. Output shaft
Displacement sensors 22, 22, which detect the amount of displacement of 11, vehicle speed sensor 23
When an abnormal state of the four-wheel steering device is detected by a signal from a rotation angle sensor 32 for detecting the rotation angle of the electric motor 19, the connection of the electromagnetic clutch 31 is immediately disconnected (see FIG. 1). , The solenoid 40 that was in the non-energized state until then
The function is to start energization of the oil supply pipe and reduce the amount of viscous oil flowing in the oil supply pipe.

In the case of this embodiment, when an abnormality is detected during low-speed running of the vehicle and the connection of the electromagnetic clutch 31 is disconnected, the output shaft for the rear wheel is used.
A centering spring 25 and plate springs 29, 29 elastically supporting the housing 11 on the housing 10 fixed to the vehicle body;
, The rear wheel output shaft 11 is returned to the neutral position. As a result, the rear wheels 9, 9 mechanically connected to the rear wheel output shaft 11, return to the neutral position.

When the rear wheels 9, 9 return to the neutral position in this way, the piston portion 36 fixed to the rear wheel output shaft 11 is moved to the housing fixed to the vehicle body.
It is displaced inside the cylinder part 35 provided on the 10. Piston section
With the displacement of 36, the viscous oil sealed in the cylinder portion 35 flows through the oil feed pipe 38, and at this time, the flow rate passing through the flow control valve 39 with the energization of the solenoid 40 is reduced. Therefore, the displacement of the rear wheel output shaft 11 is performed slowly.
As a result, the steering angle given to the rear wheels 9, 9 is also gradually eliminated, and an unnatural feeling accompanying the sudden removal of the steering angle can be eliminated.

On the other hand, in a normal state where no failure has occurred,
Since the flow rate adjusting valve 39 is switched so that a sufficient amount of viscous oil can pass with no power supplied to the solenoid 40, the resistance to the displacement of the rear wheel output shaft 11 is unnecessarily large. It will not be. Accordingly, the rear wheel 9 and the electric motor 19 can be used without using a motor having a particularly large output.
9 can be quickly given a steering angle.

(Effects of the Invention) Since the four-wheel steering device of the present invention is configured and operates as described above, it is possible to give an optimum steering angle to the rear wheels according to the situation, and furthermore, a relatively simple failure Only by providing a safe mechanism, sufficient safety can be ensured.

Further, when a failure occurs during low-speed traveling, the steering angle given to the rear wheels is released, and stable operation can be performed.

In addition, since the steering angle applied to the rear wheels is slowly released, the sense of incongruity felt by the driver can be minimized.

[Brief description of the drawings]

1 to 4 show a first embodiment of the present invention. FIG. 1 is a partial cross-sectional plan view showing the entire structure, and FIG.
3 is a diagram showing the relationship between the axial displacement of the rear wheel output shaft and the spring load applied to the rear wheel output shaft in the axial direction, and FIG. 4 is a vehicle speed and steering angle ratio. FIG. 5 shows a second embodiment of the four-wheel steering system of the present invention.
FIG. 1: steering wheel, 2: steering shaft, 3:
Steering gear, 4: output shaft for front wheels, 5: knuckle arm, 6: front wheels, 7: steering column, 8: steering angle sensor, 9:
Rear wheel, 10: Housing, 11: Output shaft for rear wheel, 12: Force point, 1
3: Knuckle arm, 14: Steering center, 15: Rack teeth, 16: Transmission shaft, 17: Pinion teeth, 18: Worm wheel, 19: Electric motor, 20: Output shaft, 21: Worm, 22: Displacement sensor, 23 :
Vehicle speed sensor, 24: controller, 25: centering spring,
26: Seat, 27: Step, 28: Stop ring, 29: Disc spring,
31: electromagnetic clutch, 32: rotation angle sensor, 33, 34: viscous damper, 35: cylinder, 36: piston, 37: supply / discharge port, 38: oil supply pipe, 39: flow control valve, 40: solenoid, 41 : Aperture nozzle.

Claims (1)

(57) [Scope of request for utility model registration] 1. A steering angle sensor for detecting a steering angle applied to a front wheel, an output shaft for a rear wheel for applying a steering angle to a rear wheel by displacing in an axial direction, and an output shaft for the rear wheel. An electric motor for displacing in the direction, a vehicle speed sensor for detecting a vehicle speed, a clutch provided between the rotary drive shaft of the electric motor and the output shaft for the rear wheel, and electrically connected and disconnected; A displacement sensor that detects a steering angle given to a rear wheel based on a displacement of an output shaft, and based on signals from the steering angle sensor and a vehicle speed sensor, energizes the electric motor and disconnects / engages the clutch. And a damper mechanism that serves as a resistance to the rear-wheel output shaft being displaced in the axial direction.The steering center of the rear wheel is positioned rearward in the forward direction of the vehicle from the point of application of the rear wheel. Position the rear wheel output shaft with respect to the vehicle body. The controller engages the clutch only when the vehicle speed detected by the vehicle speed sensor is equal to or lower than a predetermined value, and controls the controller based on the energization of the electric motor. A four-wheel steering system in which the steering angle can be freely applied to the rear wheels, and when the abnormality is detected by a signal from each of the sensors and the vehicle speed is equal to or lower than a predetermined value, the connection of the clutch is immediately disconnected. apparatus.