JPH05213223A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To prevent deterioration of running safety of a vehicle by returning a four-wheel steering state to a 2WS state by immediately stopping control of the rear wheel steering mechanism as well as detecting the occurrence of abnormality in a control means for controlling an electric motor, when such abnormality occurs. CONSTITUTION:A fail safe circuit 36 which detects abnormality of control of rear wheel steering based on car speed information outputted from a car speed sensor 32 and rear wheel steering angle information outputted from a rear wheel steering angle 35 and stops running of an electric motor 28 is provided independently from a control means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system, and more specifically, to a fail that detects an abnormality in a control means for controlling the steering of rear wheels and stops an electric motor that drives a rear wheel steering mechanism. The present invention relates to a four-wheel steering device provided with a safety circuit.

[0002]

2. Description of the Related Art A four-wheel steering system configured to steer not only front wheels but also rear wheels in order to obtain optimum traveling performance according to various traveling situations is widely used. In general, a four-wheel steering system is used when the steering angle is small.
The rear wheels are steered in the same direction as the front wheels, that is, in the same phase, but when the steering angle of the steering is larger than a predetermined value, the rear wheels are steered in the opposite direction to the front wheels, that is, in the opposite phase. Is configured.

When turning or changing lanes at medium and high speeds, the steering angle of the steering wheel is generally small. At this time, the rear wheels are steered in the same phase as the front wheels, so that the vehicle is caused by centrifugal force. It is possible to suppress skidding and improve running stability. On the other hand, when making a relatively steep turn such as a U-turn at a low speed, the steering angle of the steering becomes large, and at this time, the rear wheels are steered in the opposite phase to reduce the turning radius of the vehicle. It is possible to improve the small turning ability.

In such a four-wheel steering system, for example,
A device configured to mechanically transmit the rotation of a steering wheel to a rear wheel steering mechanism to steer the rear wheels, as described in JP-B-60-44186, and JP-A-1-204867. There are various types such as the one disclosed in Japanese Patent Publication No. JP-A-2003-138, which is configured to drive the rear wheel steering mechanism by an electric motor or a hydraulic actuator.

In a four-wheel steering system of the type in which the rear wheel steering mechanism is driven by an electric motor or the like, the rear wheel steering mechanism is
It is mechanically completely separated from the front wheel steering mechanism and independent, and it drives the electric motor based on information detected by a steering angle sensor for detecting the steering angle of the steering wheel, a vehicle speed sensor, etc. You have to steer the wheels. Usually, a control unit for driving the electric motor is provided, and a microcomputer is often adopted as the control unit.

[0006]

However, when an abnormality occurs in the microcomputer constituting the above control means, even if a sensor such as a steering angle sensor is operating normally,
The rear wheels cannot be properly steered. That is, there is a possibility that the rear wheels should be steered in the opposite phase to the front wheels but steered in the same phase, or control such that the steered angle of the rear wheels does not reach a predetermined value. In particular, in the in-phase region where the rear wheels are steered in the same phase as the front wheels, if the steered angle of the rear wheels becomes too large, running stability may be impaired.

[0007] Conventionally, for example, Japanese Patent Application Laid-Open No. 1-20486 discloses a device for detecting the above-mentioned abnormality of a four-wheel steering system.
When an abnormality such as a short circuit or a disconnection occurs in the steering angle sensor or various circuits connected to the control means as described in Japanese Patent No. 7, the abnormality is detected and the control is determined. A fail-safe device is provided.

However, the above-mentioned conventional fail-safe device does not judge the abnormality of the control means itself, but the failure for judging the abnormality of the detection output output from the sensor or the control output for driving the electric motor. Since it is a safety device, it was not possible to judge the abnormality of the control means itself such as a microcomputer. Therefore, even if an abnormality occurs in the control means itself, the control of the rear wheels cannot be immediately stopped, and it cannot be said that the fail-safe function is sufficiently exerted.

The present invention has been devised under the circumstances described above, solves the above-mentioned conventional problems, and detects when an abnormality occurs in the control means itself for controlling the electric motor. At the same time, it is an object of the present invention to provide a four-wheel steering device in which the control of the rear wheel steering mechanism is immediately stopped and returned to the 2WS state, and the running stability of the vehicle is not impaired.

[0010]

In order to solve the above problems, the present invention takes the following technical means. That is, the invention described in claim 1 of the present application includes a front wheel steering mechanism that steers the front wheels in response to a steering operation, and a rear wheel steering mechanism that is driven by an electric motor controlled by the control means. The control means is a four-wheel steering device configured to control the electric motor based on at least vehicle speed information output from the vehicle speed sensor and rear wheel steering angle information output from the rear wheel steering angle sensor, A fail-safe that detects an abnormality in the rear-wheel steering control based on the vehicle speed information output from the vehicle speed sensor and the rear-wheel steering angle information output from the rear-wheel steering angle sensor and stops the driving of the electric motor. A circuit is provided separately from the control means.

The invention described in claim 2 of the present application is
A front wheel steering mechanism that steers the front wheels in response to a steering operation, and a rear wheel steering mechanism that is driven by an electric motor controlled by a control means, and the control means is at least a lateral G sensor that outputs a lateral G sensor. In a four-wheel steering system configured to control the electric motor based on the acceleration information and the rear wheel turning angle information output from the rear wheel steering angle sensor, the lateral acceleration information output from the lateral G sensor. And a fail-safe circuit that detects the abnormality of the rear-wheel steering control based on the rear-wheel steering angle information output from the rear-wheel steering angle sensor and stops the driving of the electric motor.
It is characterized in that it is provided separately from the control means.

[0012]

In the four-wheel steering system according to the present invention, the rear wheel steering control abnormality is based on the vehicle speed information output from the vehicle speed sensor and the rear wheel steering angle information output from the rear wheel steering angle sensor. Is provided and a fail-safe circuit for stopping the drive of the electric motor for steering the rear wheels is provided.

The fail-safe circuit detects an abnormality in the control means by utilizing the relationship that should be established between the vehicle speed and the rear wheel turning angle. That is, when the vehicle speed is a certain value or more, the rear wheels should be steered in the same phase, and the steered angle of the rear wheels in this case is
The relationship is that a certain value set in advance is not exceeded. Moreover, the maximum steering angle of the rear wheels allowed in the in-phase steering area is much smaller than the maximum steering angle allowed in the anti-phase steering area, and therefore, the running stability is impaired. The fail-safe function can be demonstrated.

The vehicle speed information is the most basic input information input to the control means, and the rear wheel turning angle information is the most basic output information achieved by the control means. Moreover, the vehicle speed sensor for detecting the vehicle speed and the steering angle sensor for detecting the rear wheel turning angle are highly reliable and are unlikely to fail. For this reason, it becomes possible to judge highly reliably whether or not the control circuit is abnormal.

The fail-safe circuit determines that an abnormality has occurred in the control means when the rear wheels are steered beyond a predetermined threshold steering angle within the in-phase steering region. The threshold steering angle is set to be slightly larger than the maximum steering angle in the in-phase steering area, and the fail-safe circuit detects an abnormality of the control means and at the same time, the electric motor for driving the rear wheel steering mechanism is detected. Stop driving. The above-mentioned control achieved by the fail-safe circuit according to the present invention is a very simple operation of stopping the drive of the electric motor, and therefore a highly reliable fail-safe function can be exhibited.

Moreover, the fail-safe circuit is provided separately from the control means. That is, the determination is made by directly using the outputs of the vehicle speed sensor and the rear wheel steering angle sensor without using the data calculated by the control means. Therefore, even if an abnormality occurs in the control means, the function of the fail-safe circuit is not affected at all, and a highly reliable fail-safe function can be obtained.

In addition, the fail-safe circuit according to the present invention is configured to detect an abnormality in the steering angle within the in-phase steering region of the rear wheels, so that the threshold steering angle can be set small. Therefore, the fail-safe function can be exerted before the rear wheels are largely steered. Therefore, it is possible to prevent the traveling performance from significantly deteriorating.

[0018]

Description of Embodiments An embodiment of a four-wheel steering system according to the present invention will be specifically described below with reference to the drawings. FIG. 1 schematically shows the overall configuration of a four-wheel steering vehicle equipped with a four-wheel steering system according to the present invention.

As the front wheel steering mechanism, a general one can be used. In this embodiment, the rack and pinion type front wheel steering mechanism 1 is adopted. This is because the rotation of the steering wheel 3 transmitted through the steering shaft 2 is converted into the movement of the rack rod 5 in the vehicle width direction within the gear box 4, and the movement of the rack rod 5 in the vehicle width direction is
Knuckle arms 7, 7 via tie rods 6, 6 at both ends
Is converted into rotation about the axes 8 and 8. The front wheels 9, 9 are steered by the rotation of the knuckle arms 7, 7.

On the other hand, in the case of the present embodiment, the rear wheel steering mechanism 10 is
A cam body 13 is used which employs a cam mechanism, and is connected and fixed to a rear end portion of a transmission shaft 12 that extends in the vehicle front-rear direction inside a housing 11 that is fixed to a lower surface of a body floor and the like. A pair of left and right rotating roller-like cam followers 14, 14 arranged on both sides of 13, and supporting these cam followers 14, 14 in an intermediate portion, and
The housing 11 is provided with a frame-shaped moving rod 15 which is slidably supported in the vehicle width direction.

As shown in FIG. 6, the cam body 13 according to the present embodiment is formed in a profile having a substantially diaper shape, and the cam followers 14, 14 are formed on the outer peripheral surface thereof at a predetermined rotational direction position. There are provided cam surfaces 25 and 26 for pushing in the vehicle width direction. In order to steer the rear wheels 21 in the same phase as the front wheels in the range where the steering angle of the steering wheel 3 is small and to steer the wheels in the opposite phase when the steering angle of the steering wheel 3 becomes a predetermined value or more, for example, the above cam body is used. 13, a cam surface 26 that pushes one of the cam followers 14 when it rotates from the neutral rotation position.
Can be easily configured by providing the cam surface 25 that pushes the other cam follower 14 when the rotation angle further increases. Further, the turning amount of the rear wheel 21 is also formed by forming the cam surfaces 25 and 26 so that the distance from the rotation axis O thereof changes depending on the rotation angle position.
It can be increased or decreased according to the steering angle of the steering wheel 3.

A housing 11 is provided at both ends of the moving rod 15.
The slide shafts 17, 17 slidably supported by the shaft support parts 11a, 11a are integrally projectingly provided, and the tie rod 23 and the knuckle arm 22 are provided at the tip of the slide shafts 17, 17 via The rear wheels 21 are connected to each other. Therefore, the cam body 13 is rotated by a predetermined amount so that the cam surfaces 25, 26 of the cam body 13 are rotated.
When 4 is pushed, the moving rod 15 is thereby moved in a predetermined direction in the vehicle width direction, and accordingly, the rear wheels 21, 21 are steered in a predetermined direction by a predetermined amount.

In this embodiment, the rear wheel steering mechanism 1 is used.
As shown in FIG. 4, 0 is driven by an electric motor 28 controlled by control means 29 including a microcomputer or the like. Further, an electromagnetic brake 31 is connected to the electric motor 28 so that the rotation of the electric motor 28 can be appropriately braked. Further, a deceleration mechanism 30 is provided between the electric motor 28 and the transmission shaft 12 so that a sufficient rotation torque can be obtained for the cam body 13. Note that reference numeral 2
A motor driver 8b supplies a drive current to the electric motor 28.

The control means 29 determines the turning angle and the turning direction of the rear wheels 21 in accordance with the vehicle speed, the steering angle of the steering wheel 3, and the like. In the range where the vehicle speed is above a certain level and the steering angle of the steering wheel 3 is small, the rear wheels 21 are steered in the same phase, and when the vehicle speed is below a certain level, the steering angle of the steering wheel 3 becomes larger than a predetermined value (for example, about 240 °). First, the drive of the electric motor 28 is controlled so that the rear wheels 21 are steered in the opposite phase.

The steering angle of the steering wheel is small at the time of turning traveling at medium and high speeds and at the time of lane change. At this time, by steering the rear wheels 21 in the same phase, the vehicle is caused by centrifugal force. It is possible to improve the running safety during turning while suppressing the skidding and enabling a quick direction change. Further, in such in-phase steering, the steering amount of the rear wheels 21 is increased or decreased according to the vehicle speed, and the steering amount of the rear wheels 21 is increased as the vehicle speed becomes higher. This is because the effect of centrifugal force increases as the speed increases, and the tendency of the vehicle to skid becomes stronger.

On the other hand, when making a turn such as a U-turn at a low speed, the steering angle of the steering wheel is relatively large,
At this time, by turning the rear wheels 21 in the opposite phase, it is possible to reduce the turning radius of the vehicle and improve the small turning ability. The control means 29 detects the steering angle of the rear wheel 21 by detecting the vehicle speed sensor 32, the steering angle sensor 33 that detects the steering angle of the steering wheel 3, the shift position sensor 34, and the rotation angle of the electric motor 28. A signal from the rear wheel steering angle sensor 35 or the like is input as control information.

The control means 29 is not shown in the drawing,
Based on the information from the vehicle speed sensor 32 and the steering angle sensor 33, a lateral G calculating means for calculating a lateral G (lateral acceleration acting on the center point of the vehicle) theoretically generated at the time of turning, and the lateral G calculating means. Based on the lateral G calculated by the above, etc., the rear wheel turning angle determining means for determining the direction in which the rear wheel 21 should be turned and the amount of turning thereof, and the rear wheel turning angle information received from the rear wheel turning angle determining means. Motor control means for determining the direction in which the cam body 13 should be rotated and the amount of rotation thereof, and for controlling the motor driver 28b by receiving a feedback signal from the rear wheel steering angle sensor 35 for the rear wheel. Brake control means or the like for actuating the electromagnetic brake 31 when the rear wheel 21 reaches a predetermined steering angle by receiving rear wheel steering angle information (rotation angle information of the cam body) from the wheel steering angle sensor 35. Is provided There.

Next, a rear wheel steering control method of the present invention, which is realized by the four-wheel steering system having the above structure, will be described with reference to the flowcharts shown in FIGS. 2 and 3 are obtained by dividing one flow chart.

When the ignition switch key is turned on to start the engine, the control means 29 is initialized (s101). Next, when traveling, vehicle speed sensor 3
The vehicle speed information from 2 and the steering operation steering angle information from the steering angle sensor 33 are read (s102, s10
9) From these, lateral acceleration G (hereinafter, referred to as lateral G).
Is calculated (s110). Then, the rear wheels 21 are steered in a predetermined direction by a predetermined angle according to the size of the lateral G and the like.

The lateral G is 0.1 G or less (YES in s112, YES in s113), and the shift position is first or reverse (YE in s114).
S) and the steering angle of the steering wheel is at a predetermined position (for example, 240 °) or more (YES in s115), the rear wheels 21 are steered in the opposite phase with respect to the front wheels 9 (s11).
6). As described above, when the lateral G is small, the shift position of the transmission is in the first or reverse, and the steering is relatively large, it is generally the case that a turn such as a U-turn is made at low speed. By steering the rear wheels 21 in the opposite phase, the radius of gyration of the vehicle can be reduced and the maneuverability can be improved. Further, in this case, by increasing or decreasing the turning angle of the rear wheels 21 according to the steering angle of the steering wheel 3, it is possible to match the driving feeling of the driver with the behavior of the vehicle and improve the steering feeling of the steering wheel. ..

On the other hand, when the lateral G is in a certain range (YES in s112, NO in s113), the lateral G is equal to or less than the predetermined value, but the shift position is other than the first or reverse ( NO in s113), and
The magnitude of the lateral G is equal to or smaller than a predetermined value, and the shift position is first or reverse, but when the steering angle is smaller than the predetermined value (NO in s115), the rear wheel 21 is in the neutral position. It is returned (s104). This is because the vehicle travels in a straight line and the like, and the traveling stability is better when the vehicle is traveling in the 2WS state with the rear wheels 21 returned to the neutral position.

When the lateral G is larger than the predetermined value (NO in s112), the rear wheels 21 are steered in the same phase as the front wheels. When the size of the lateral G is relatively large, the lane change or turning is generally performed in the middle / high speed range. At this time, the rear wheels 21 are steered in the same phase to prevent the vehicle from slipping sideways. It is possible to suppress the speed change and to promptly change the direction to improve the traveling safety. In this case, (s
203, s204, s205) and the steering amount of the rear wheels 21 in the same phase direction is also controlled (s206, s207, s20).
8, s209). This is because the tendency of the vehicle to skid becomes stronger as the lateral G becomes larger, so that it is necessary to increase or decrease the steering amount of the rear wheels 21 according to the lateral G.

Further, in the present embodiment, when the rear wheels 21 are steered in the same phase, the steering start timing is delayed by a predetermined time with respect to the start of steering (front wheel steering) (s201). The delay time is set to be longer as the steering angular velocity of the steering wheel is higher. As a result, an appropriate amount of yawing can be promoted at the initial stage of turning, and sufficient yaw angular acceleration can be obtained during the turning transition period. As a result, the turning ability is enhanced, and the direction can be changed quickly. Further, the higher the speed, the smaller the delay time is set. This is because the steerer the steering becomes slower as the speed increases, in other words, the yawing rises faster, so if the delay time at high speed is set to the same as at medium speed, the steering of the rear wheels will be too late. This is because a situation occurs and the running stability becomes worse.

Further, in this embodiment, when the rear wheels 21 are steered in the same phase, the steered speed of the rear wheels 21 is controlled according to the magnitude of the steering steering angular velocity. (S
202). That is, the steering feeling of the driver is improved by matching the driving feeling of the driver with the behavior of the vehicle by controlling the steering speed of the rear wheels to increase as the steering angular velocity of the steering increases.

In the present embodiment, as shown in FIG. 4, the rear wheel rolling is performed based on the vehicle speed information output from the vehicle speed sensor 32 and the rear wheel steering angle information output from the rear wheel steering angle sensor 35. A fail-safe circuit 36 for detecting an abnormality in the rudder control is provided. Fail-safe circuit 3 above
As shown in FIG. 1 and FIG.
The vehicle speed sensor 32 is provided separately from the vehicle speed sensor 32.
The output from the rear wheel steering angle sensor 35 is directly input. In the present embodiment, the rear wheel steering angle is indirectly detected by detecting the rotation angle or the rotation position of the electric motor 28.

That is, as shown in FIG. 5, the fail-safe circuit 36 according to the present embodiment counts the pulse signals from the rear-wheel steering angle sensor 35 to calculate the rear-wheel steering angle signal UP-DOWN. Counter 37 and vehicle speed sensor 3
And a vehicle speed signal calculating means 38 for calculating a vehicle speed signal from the average pulse width of the pulse signal from No. 2. Further, the fail-safe circuit 36 uses the threshold angle signal preset by the threshold angle setting switch 39 and the UP-D.
A comparison means 40 that digitally compares the rear wheel steering angle signal detected by the OWN counter 37 and generates an output signal when the rear wheel steering angle is larger than a predetermined threshold angle (for example, 1.25 °). And a vehicle speed signal calculated by the vehicle speed signal calculating means 38 and a threshold vehicle speed signal corresponding to a preset vehicle speed (for example, 20 km / h), and an output signal when the vehicle speed is higher than the threshold vehicle speed. And a comparison means 41 for generating

In the embodiment, in order to improve reliability, two vehicle speed sensors 32 are provided and the vehicle speed signal calculating means 3 corresponding to these vehicle speed sensors 32, 32.
8 and two comparison means 41 are provided.
Further, an OR circuit 42 for generating an output signal when a signal is generated from one of the two comparing means 41, 41 is provided, and even if one vehicle speed sensor should fail, the fail-safe circuit 36 will be It is configured to work.
Further, the output signal from the comparison means 40 and the OR
An AND circuit 43 is provided which generates a signal when both output signals from the circuit 42 are present.

That is, the signal from the fail-safe circuit 36 is output only when the rear wheel turning angle and the vehicle speed exceed predetermined threshold values. The signal output from the AND circuit 43 is input to the control output unit 46, and the OFF relay 44 that stops the operation of the electric motor 28 and the ON relay 45 that operates the electromagnetic brake 31 are controlled by the control output output from the control output unit 46. Operated at the same time.

In this embodiment, the OFF relay 4 is used.
As shown in FIG. 4, 4 is provided between the motor driver 28b for driving the electric motor 28 and the electric motor 28, and the motor driver 28b and the electric motor 28 are controlled by the control output from the fail-safe circuit 36. It is configured to open the circuit between and to stop the driving of the electric motor 28. That is, the OFF relay 44 forcibly stops the drive of the electric motor 28 regardless of the drive output of the motor driver 28b.

On the other hand, the ON relay 45 is provided between the electromagnetic brake 31 and the battery 48, and the circuit between the electromagnetic brake 31 and the battery 48 is closed by the control output from the fail-safe circuit 36. Then, the electromagnetic brake 31 is driven. That is, the above O
The N relay 45 forces the electromagnetic brake 31 to operate regardless of the output of the control means 29. A timer relay is used as the relay 45, and the electromagnetic brake 31 is operated for a predetermined time (for example,
It may be configured to operate only for 1 second). Also,
In the embodiment, when the fail-safe circuit 36 operates, abnormality warning means 50 is provided to inform the driver of abnormality.

In the control means 29, although the vehicle speed is within the rear wheel in-phase steering region (20 km / h or more), the rear wheel 21 has a predetermined steering angle or more (1.25 ° or more).
When the steering is turned to, it means that there is an abnormality in the control performed by the control means 29. In this case, the control of the rear wheel steering mechanism 10 is stopped and the state of 2WS is immediately held. With the above control, when abnormal control is being performed, the steering angle of the rear wheels is maintained in that state, and further rear wheel steering is not performed. The steering control of the rear wheels 21 is not performed until the engine is restarted while the rear wheels 21 are returned to the neutral position.

With the above configuration, the abnormality of the control means 29 can be detected promptly and the control of the rear wheels 21 can be immediately stopped, so that the running stability is not seriously impaired. Moreover, the maximum steering angle (1.2 °) of the rear wheels allowed in the in-phase steering region is much smaller than the maximum steering angle allowed in the anti-phase steering control region. Since the threshold steering angle (1.25 °) can be set on the basis of the wheel turning angle, the fail-safe function can be exerted before the traveling stability is significantly reduced.

The vehicle speed information is the most basic input information input to the control means 29, and the rear wheel turning angle information is the most basic output information achieved by the control means 29. is there. Moreover, the vehicle speed sensor 32 for detecting the vehicle speed and the rear wheel steering angle sensor 3 for detecting the rear wheel steering angle
No. 5 is very reliable and is less prone to failure. For this reason, it becomes possible to judge highly reliably whether or not the control circuit is abnormal. Furthermore, the comparison means 40, 4
Since the fail-safe circuit 36 can be configured with an extremely simple circuit configuration such as 1 and the AND circuit 43,
There are very few failures of the fail-safe circuit 36 itself.

Furthermore, the fail-safe circuit 36 is also provided.
Is provided separately from the control circuit 29, and the outputs of the vehicle speed sensor 32 and the rear wheel steering angle sensor 35 are directly input to the fail-safe circuit 36. Therefore, even if an abnormality occurs in the control means 29, it is not affected at all. Therefore, the abnormality of the control means 29 can be determined reliably and quickly, and the reliability is extremely high.

In addition, when an abnormality is found in the control means 29, the electric motor 28 can be immediately stopped and switched to 2WS. For this reason, it is possible to prevent the deterioration of the running stability and to exert the fail-safe function by extremely simple control.

FIG. 7 shows a system block diagram according to the second embodiment of the present invention. In the first embodiment, the abnormality of the rear wheel steering control is detected based on the vehicle speed information detected by the vehicle speed sensor 35 and the rear wheel steering angle information output by the rear wheel steering angle sensor 35. As shown, a lateral G sensor 47 is provided instead of the vehicle speed sensor 32 and the steering angle sensor 33, and steering control of the rear wheels is performed based on the lateral G information directly output from the lateral G sensor 47.
It is also possible to detect an abnormality in the rear wheel steering control. That is, as shown in FIG. 2, when the lateral G is a predetermined value or more (0.2 G or more in the embodiment), the relationship that the rear wheels 21 are steered in the same phase is used. Yes,
Based on the lateral acceleration information and the rear-wheel steering angle information detected by the rear-wheel steering angle sensor 35, the fail-safe circuit 36a having the same fail-safe function as that of the first embodiment can be configured.

The scope of the present invention is not limited to the above embodiments. In the embodiment, the maximum value of the rear wheel turning angle in the same phase region is set to 1.2 °, and
The threshold rudder angle at which the fail-safe circuit operates is 1.25 °
However, these values can also be changed according to the characteristics of the vehicle. In addition, the reference of the lateral G and the like shown in the flowchart is a rough one, and the rear wheel steering condition can be determined by further subdividing. Further, the structure of the four-wheel steering device is not particularly limited, and the present invention can be applied to, for example, a four-wheel steering device in which the rear wheels are driven by a hydraulic actuator or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an overall configuration of a four-wheel steering vehicle according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of rear wheel steering control according to the present invention.

FIG. 3 is a flowchart showing an example of rear wheel steering control according to the present invention.

FIG. 4 is a system block diagram showing an example of a control method according to the present invention.

FIG. 5 is a system block diagram showing an example of a fail-safe circuit according to the present invention.

FIG. 6 shows a cam body and a cam follower according to the embodiment.
FIG. 6 is a view as seen from the direction of arrow A in FIG.

FIG. 7 is a system block diagram showing a second embodiment of the present invention.

[Explanation of symbols]

 1 Front Wheel Steering Mechanism 3 Steering Wheel 9 Front Wheel 10 Rear Wheel Steering Mechanism 28 Electric Motor 29 Control Means 32 Vehicle Speed Sensor 35 Rear Wheel Steering Angle Sensor 36, 36a Fail Safe Circuit 47 Lateral G Sensor

Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location B62D 117: 00 125: 00 (72) Inventor Takashi Inaba 1-1, Showa-cho, Kariya city, Aichi Nidec stock In the company

Claims (2)

[Claims] 1. A front wheel steering mechanism that steers front wheels according to a steering operation, and a rear wheel steering mechanism driven by an electric motor controlled by a control means, wherein the control means includes at least a vehicle speed sensor. In a four-wheel steering system configured to control the electric motor based on the vehicle speed information output and the rear wheel steering angle information output from the rear wheel steering angle sensor, a vehicle speed output from the vehicle speed sensor is provided. A fail-safe circuit that detects an abnormality in the rear-wheel steering control based on the information and the rear-wheel steering angle information output from the rear-wheel steering angle sensor and that stops the drive of the electric motor is provided separately from the control means. A four-wheel steering device, characterized in that 2. A front wheel steering mechanism for steering front wheels in response to a steering operation, and a rear wheel steering mechanism driven by an electric motor controlled by a control means, wherein the control means includes at least a lateral G sensor. In the four-wheel steering apparatus configured to control the electric motor based on the lateral acceleration information output from the rear wheel steering angle sensor and the rear wheel steering angle information output from the rear wheel steering angle sensor, the four-wheel steering device outputs the lateral G sensor. The fail-safe circuit that detects an abnormality in the rear-wheel steering control based on the lateral acceleration information and the rear-wheel steering angle information output from the rear-wheel steering angle sensor and that stops the drive of the electric motor. A four-wheel steering device, which is separately provided.