JPH05201343A - Steering control method for rear wheel for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To perform transition to 2WS as while holding running stability even when abnormality occurs to a rear wheel steering mechanism by stopping control of rear wheel steering after rear wheels are automatically returned to neutral by a control means when an overcurrent flows in an electric motor for steering rear wheels. CONSTITUTION:A rear wheel steering mechanism 10 is driven with the aid of an electric motor 28, and the electric motor 28 is controlled by a control means 29. When an overcurrent flows in the electric motor 28, a control means 29 first effects control so that the electric motor 28 is reversed. When the overcurrent is still generated, an off-relay 44 and an electromagnetic brake 31 is operated and the electric motor 28 is stopped. Meanwhile, when the overcurrent is still generated, an alarm is sounded after rear wheels are automatically returned to neutral, and the electric motor 28 is stopped and brought into an 2WS state. Thus, in addition to prevention of the occurrence of seizure owing to the overcurrent, running is effected in a 2WS state even when abnormality occurs to the rear wheel steering mechanism 10 and running stability can be held even in case of emergency arising.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering control method for a four-wheel steering vehicle.

[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 Japanese Patent Publication No. 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, the rear wheel steering mechanism is mechanically completely separated from the front wheel steering mechanism and is independent, and the steering Based on information detected by a steering angle sensor that detects a steering angle, a vehicle speed sensor, and the like, the electric motor must be driven to steer the rear wheels. Usually, a control unit for driving the electric motor is provided, and a microcomputer is often adopted as the control unit.

[0006]

By the way, in a four-wheel steering system of the type in which the rear wheel steering mechanism is driven by the electric motor, a motor drive current is supplied from the motor driver controlled by the control means to the electric motor. At the same time, the steered angle of the rear wheels is fed back to the control means by the rear wheel steered angle sensor, and highly precise steered control of the rear wheels is performed.

However, when foreign matter is caught in the rear wheel steering mechanism and the rear wheels are not steered to a predetermined steering angle, the motor drive current supplied from the motor driver to the electric motor is increased to drive the electric motor. Often controlled to increase output. However, there is no problem when the rear wheel steering mechanism operates normally due to the increase in the output, but when the rear wheel steering mechanism does not operate even if the output of the electric motor is increased, the motor of the electric motor The drive current becomes too large, and the electric motor may be burnt in.
The rear wheel steering mechanism may be damaged. Further, even when a failure occurs in the motor driver itself, a large motor drive current may flow in the electric motor, and the same problem as described above occurs.

In order to solve the above problems, for example, as disclosed in Japanese Patent Publication No. 1-297373, when a large motor drive current flows in the drive circuit of the electric motor, the motor drive current flowing in the electric motor. There has been proposed a control method for limiting the electric shock and preventing the seizure of the electric motor. However, the above control method is configured so that the rear wheel steering mechanism is kept operating as long as possible so that the running stability is not adversely affected.

Therefore, before the electric motor burns and is damaged, the drive current supplied to the electric motor can be limited to protect the rear wheel steering mechanism. However, an abnormal motor drive current flows to the electric motor. There is a risk that the steering angle of the rear wheels may be further increased by operating the steering wheel. That is, since the operation of the rear wheel steering mechanism is continued, there is a risk that the traveling stability will be reduced. Moreover, in the conventional rear wheel steering control method, even if an abnormal motor drive current once flows, the rear wheel steering control is terminated unless the rear wheel steering mechanism stops operating completely. Configured to not. For this reason, even if the motor driver itself fails, the rear wheel steering mechanism continues to be driven, and the rear wheel steering mechanism may be seriously damaged.

The present invention has been devised under the circumstances described above, solves the above-mentioned conventional problems, and should a large motor drive current flow through the electric motor for driving the rear wheel steering mechanism. It is an object of the present invention to provide a rear wheel steering control method capable of shifting to the 2WS state while preventing the driving stability from decreasing as much as possible even in the case of the above.

[0011]

In order to solve the above problems, the present invention takes the following technical means. That is, the present invention includes a front wheel steering mechanism that steers the front wheels according to a steering operation, and a rear wheel steering mechanism that is driven by an electric motor, and the electric motor is controlled by a motor driver controlled by a control unit. In a four-wheel steering vehicle driven by a supplied motor drive current, when a motor drive current of a predetermined value or more flows in the electric motor, the control means sets the electric motor in a direction in which the motor drive current flows. The motor is controlled to rotate in the reverse direction, and when the motor drive current in the control of rotating the electric motor in the reverse direction is equal to or more than a predetermined value, the drive of the electric motor is controlled to be stopped immediately. ,
When the motor drive current in the rotation control of the electric motor in the reverse direction is equal to or less than a predetermined value, after controlling the rear wheels to be in the neutral position, control is performed to stop the drive of the electric motor. It has a feature.

[0012]

In the steering control method for rear wheels according to the present invention, first, the current flowing through the electric motor is detected, and when the motor driving current of a predetermined value or more flows through the electric motor, the control means , The electric motor is controlled to rotate in a direction opposite to the direction in which the motor drive current flows. An abnormal motor drive current of a specified value or more flows in the electric motor when a failure occurs in the motor driver itself.
Alternatively, it is conceivable that foreign matter may be caught in the rear wheel steering mechanism and the rear wheel steering may be hindered.

In the latter case, when the electric motor is reversed,
It can be expected that the foreign matter caught in the rear wheel steering mechanism will come off.

Next, even when the electric motor is controlled to rotate in the reverse direction, if a large motor drive current flows through the electric motor, the driving of the electric motor is immediately stopped. In this case, the electric motor cannot rotate in either direction, that is, the rear wheels cannot steer in either the left or right direction, and the electric motor is immediately stopped by supplying the motor drive current. It is possible to prevent image sticking. In addition, even when the motor driver itself has a failure, a large motor drive current may flow regardless of the rotation direction of the electric motor. The supply of drive current is stopped.

Further, in the present invention, when the abnormality of the motor drive current is resolved by the reverse rotation of the electric motor, the control of the electric motor is stopped after returning the rear wheels to the neutral position. That is, in the control method according to the present invention, when the electric motor can rotate in the opposite direction, the control for automatically returning the rear wheels to the neutral position is performed. Then, after the rear wheels have returned to the neutral position, the supply of the motor drive current is forcibly cut off and the control of the rear wheel steering mechanism is stopped.

Therefore, unlike the conventional case, the control of the rear wheels is terminated in the state where the rear wheels are largely steered, and the state is not shifted to the 2WS state while adversely affecting the running stability. In particular, foreign matter is caught in the rear wheel steering mechanism and a large current is supplied to the electric motor because the rear wheels are often steered in the opposite phase to the front wheels.In this state, the rear wheel steering control is performed immediately. If you control it to stop,
Although it is necessary to continue traveling while the traveling stability is reduced, in the control method according to the present invention, the rear wheels are controlled so as to be returned to the neutral position as much as possible, so that the above-mentioned inconvenience occurs. It can be avoided.

As described above, in the present invention, even when a large motor drive current flows through the electric motor, the control means automatically makes an effort to return the rear wheels to the neutral position, and thereafter the rear wheels are steered. Control is terminated. As a result, even if an abnormality occurs in the rear wheel steering mechanism, the steering control of the rear wheels can be terminated and the state can be shifted to the 2WS state without reducing the traveling stability as much as possible. It will be possible.

[0018]

Description of Embodiments An embodiment of a four-wheel steering system to which a rear wheel steering control method according to the present invention is applied 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 by the gear box 4 into the movement of the rack rod 5 in the vehicle width direction, and the movement of the rack rod 5 in the vehicle width direction is changed at both ends. The knuckle arms 7, 7 are converted into rotations about the axes 8, 8 via the tie rods 6, 6. 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 9 in a range where the steering angle of the steering wheel 3 is small and to steer the steering wheels 3 in the opposite phase when the steering angle of the steering wheel 3 becomes a predetermined value or more, for example, as shown in FIG. As shown in FIG. 5, the cam surface 13 that pushes one of the cam followers 14 when the cam body 13 rotates from the neutral rotation position, and the other cam follower 14 when the rotation angle further increases. It can be easily constructed by providing the cam surface 25 for pushing. Also,
The turning amount of the rear wheel 21 can also be increased / decreased according to the steering angle of the steering wheel 3 by forming the cam surfaces 25 and 26 so that the distance from the rotational axis O thereof changes depending on the rotational angle position. ..

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.
0 is driven by an electric motor 28 whose rotation is controlled by a control unit 29 including a microcomputer. 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. In the present embodiment, the electric motor 28 is driven by the motor drive current supplied from the motor driver 28b controlled by the control means 29.

The control means 29 determines the steered angle and steered direction of the rear wheels 21 according to, for example, the vehicle speed and the steered angle of the steering wheel 3. In the range where the steered angle of the steering wheel 3 is small, the rear wheel 21 is determined. Is turned in the same phase as the front wheels 9, and the steering angle of the steering wheel 3 is a predetermined value (for example, about 240 °).
When it becomes larger, the drive of the electric motor 28 is controlled so as to steer the rear wheels 21 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 suppress the skid and enable a quick direction change, and at the same time, it is possible to enhance the running stability during turning. 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, 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. The direction in which the cam body 13 should be rotated and its rotation amount are determined based on the rear wheel steering angle sensor 3
5 receives the feedback signal from the motor driver 28b, the rear wheel steering angle information (rotation angle information of the cam body) from the rear wheel steering angle sensor 35, and the rear wheel 21 has a predetermined shape. Brake control means for activating the electromagnetic brake 31 when the steering angle is reached is provided.

Further, in this embodiment, as shown in FIG. 5, the rear wheel steering control 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 the abnormality is provided. The fail-safe circuit 36 detects an abnormality in the control means 29 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 equal to or higher than a certain value, the rear wheels 21
Must be steered in the same phase, and the steered angle of the rear wheels 21 in the same phase does not exceed a preset constant value. Moreover, the maximum turning angle of the rear wheels 21 allowed in the in-phase turning region is much smaller than the maximum turning angle allowed in the anti-phase turning region, and therefore, before the traveling stability is impaired. The fail-safe function can be demonstrated.

Moreover, the fail-safe circuit 36 according to this embodiment is provided independently of the control means 29 so that the outputs from the vehicle speed sensor 32 and the rear wheel steering angle sensor 35 are directly input. Is configured. Then, when the rear wheel turning angle and the vehicle speed exceed preset threshold values, a control output is output from the fail-safe circuit 36, and the OFF relay 44 and the electromagnetic brake 31 that stop the operation of the electric motor 28 are stopped. O to drive
The N relays are activated at the same time. In the present embodiment, the OFF relay 44 is provided between the motor driver 28b that drives the electric motor 28 and the electric motor 28, and is electrically connected to the motor driver 28b by the control output from the fail-safe circuit 36. The circuit with the motor 28 is opened to stop the driving of the electric motor 28. That is, the OFF relay 4
4, the drive of the electric motor 28 is forcibly stopped 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 may be adopted as the ON relay 45, and the electromagnetic brake 31 may be operated for a predetermined time (for example, 1 second). In the present embodiment, each of the relays 44 and 45 outputs the control output from the fail-safe circuit 36 or the control output from the control means 29 when a large motor drive current flows through the electric motor 28. O to be activated when at least one of the outputs is output
It is connected using an R circuit. In addition, each of the above relays 4
An alarm output means 50 is provided to inform the driver of an abnormality when the valves 4, 45 are activated.

Next, the steering control method for the rear wheels of the present invention, which is realized by the four-wheel steering system having the above-mentioned configuration, will be specifically described with reference to FIGS. Note that these drawings are obtained by dividing one flowchart.

First, the control when the rear wheel steering mechanism 10 is operating normally will be described. When the ignition switch key is turned on to start the engine, the control means 29 is initialized (s101). Then,
During traveling, vehicle speed information from the vehicle speed sensor 32 and steering steering angle information from the steering angle sensor 33 are read (s104, s109), and the lateral acceleration G (hereinafter referred to as lateral G) is calculated from these ( 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 if the steering angle of the steering wheel is equal to or greater than the predetermined angle (for example, 240 °) (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 in accordance with the steering angle of the steering wheel, the driving feeling of the driver and the behavior of the vehicle can be matched, and the steering feeling of the steering wheel can be improved.

On the other hand, when the magnitude of the lateral G is within a certain range (YES in s112, NO in s113), the magnitude of 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 s114), 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. Will be returned. 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 magnitude of 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, as shown in FIG. 3, the steering amount of the rear wheels 21 in the same phase direction is also controlled according to the size of the lateral G (s203, s204, s205) (s206,
s207, s208, 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 the present 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.

Next, the control when an abnormality occurs in the rear wheel steering mechanism will be described. In the rear wheel steering mechanism according to the present embodiment, as shown in FIGS. 1 and 4, the current flowing through the motor driver 28b that supplies the motor drive current to the electric motor 28 is detected and fed back to the control means 29. It is configured to do. Then, in the control means 29, a current monitoring means 29a for monitoring the magnitude of the motor drive current is provided in the control means 29, and the motor drive current is detected (s102).
When a current of a certain value or more (a current of 30 amperes or more in the embodiment) flows in 8 (YES in s103), the steering control of the rear wheels 21 described below is performed.

That is, as shown in FIG. 2 and FIG.
When a large current (hereinafter referred to as an overcurrent) of a certain level or more flows through the electric motor 28, first, the control unit 29 controls the electric motor 28 to rotate in the reverse direction (s3).
01). When an overcurrent flows through the electric motor 28 due to foreign matter being caught in the rear wheel steering mechanism 10 by the above control, the electric motor 28 is rotated in the reverse direction, that is, the rear wheel 21 is steered in the opposite direction. By doing so, it can be expected that the foreign matter will come off.

Further, the motor drive current supplied to the electric motor 28 is detected even when the reverse rotation control is performed (s302). Even if the electric motor 28 is rotated in the reverse direction, if the overcurrent flows in the electric motor 28 (YES in S303), the rear wheel steering mechanism 10
Is considered not to operate at all, or the motor driver 28b itself is out of order. Therefore, in such a case, as in the case of the fail-safe circuit 36, an alarm output is issued to inform the driver of the abnormality (s304), and the current supply to the electric motor 28 is stopped OFF. The ON relay 45 that operates the relay 44 and the electromagnetic brake 31 is driven to stop the electric motor 28 and operate the electromagnetic brake 31 (s305).
As a result, the steering control of the rear wheels 21 is immediately stopped (s306).

On the other hand, if the overcurrent disappears when the electric motor 28 is rotated in the reverse direction (NO in s303), it means that the rear wheel steering control in the reverse direction of the electric motor 28 is permitted. .. In this case, the rotation direction of the electric motor 28, that is, the steering direction of the rear wheels 21 is detected (s30
7). When the steered direction of the rear wheels 21 is toward the neutral direction due to the reverse rotation of the electric motor 28 (YES in s308), the rear wheels 21 are returned to the neutral state (s31).
2) An abnormal alarm output is output (s304), the OFF relay 44 and the ON relay 45 are operated to stop the driving of the electric motor 28, and the electromagnetic brake 31 is operated (s305). Then, the control of the rear wheels is stopped (s306).

On the other hand, when the rear wheels 21 are steered in the direction away from the neutral position by the reverse rotation of the electric motor 28 (NO in s308), the electric motor 28 is rotated.
Is reversed again (s309), and the rear wheel 21 is controlled to return to the neutral position. Then, the motor drive current is detected during the returning operation of the rear wheel 21 to the neutral position (s310),
Also in this case, if the overcurrent occurs again (s3
(YES in 11), an abnormal alarm output is issued at that stage to notify the driver (s304), the driving of the electric motor 28 is stopped, and the electromagnetic brake 31 is operated (S3).
04), the control of the rear wheels is stopped (s306).

If the re-reverse rotation is performed, the electric motor 2
If no overcurrent occurs in 8 (N in s311)
O), after returning the rear wheel 21 to the neutral position (s311),
An abnormality warning output is issued to inform the driver of the abnormality (s30
4). Then, similarly to the above, the drive of the electric motor 28 is stopped and the electromagnetic brake 31 is controlled to be activated (s304), and the control of the rear wheels is stopped.

In this embodiment, as shown in FIGS. 4 and 5, the OR circuit 42 outputs the output of the fail-safe circuit 36 and the output of the control means 29 when an overcurrent flows through the electric motor 28. Connected to each of the relays 44, 4 when at least one of these outputs is output.
5 is configured to operate.

In the control method according to this embodiment,
When foreign matter is caught in the rear wheel steering mechanism 10 and the steering of the rear wheels 21 is hindered, or an abnormally large current flows through the electric motor 28 due to a failure of the motor driver 28b itself,
The rear wheel 21 is returned to the neutral position as much as possible, and then the drive of the electric motor 28 is stopped and the electromagnetic brake 31 is operated. That is, the rear wheel steering mechanism 10
If some abnormality occurs in the electric motor 28 and a large current flows through the electric motor 28, the control means 29 automatically operates the rear wheel 21.
After making an effort to return the vehicle to the neutral position, it switches to the 2WS state.

Therefore, due to the overcurrent, the electric motor 2
Not only can the burn-in of the rear wheel 8 be prevented, but also the rear wheel 21 can be effectively prevented from being switched to the 2WS state when the rear wheel 21 is largely steered. If something goes wrong,
It becomes possible to automatically return the rear wheels 21 to the neutral position and run in the 2WS state, and in the event of an emergency, running stability is maintained.

The scope of the present invention is not limited to the above embodiments. In the embodiment, the current monitor 29a means for monitoring the motor drive current is provided inside the control means 29, but a current monitor means may be provided separately from the control means 29. Further, a current monitoring means may be provided inside the fail-safe circuit 36. Further, in the embodiment, the relays 44 and 45 are operated when an overcurrent of 30 amperes or more flows, but it can be changed according to the output of the electric motor 28 or the like.
In addition, the criteria of lateral G shown in the flowchart are
It is a rough one, and the rear wheel steering conditions can be determined by further subdividing it.

Further, in the embodiment, a fail-safe circuit 36 is provided, and the output signal of the fail-safe circuit 36 and the output signal output from the control means 29 when an overcurrent flows through the electric motor 28 are selected. The electric motor 28 is stopped and the electromagnetic brake 31 is operated when at least one output signal is received.
The fail-safe circuit 36 may be omitted. Further, in the embodiment, the electromagnetic brake 31 is activated at the same time that the motor drive current of the electric motor 28 is shut off, but the electromagnetic brake 31 may be deactivated.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic diagram of the 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 flowchart showing an example of rear wheel steering control according to the present invention.

FIG. 5 is a system block diagram of a control method 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.

[Explanation of symbols]

 1 Front Wheel Steering Mechanism 2 Steering Wheel 9 Front Wheel 10 Rear Wheel Steering Mechanism 28 Electric Motor 29 Control Means

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B62D 113: 00 117: 00 125: 00

Claims (1)

[Claims] 1. A front wheel steering mechanism for steering front wheels according to a steering operation, and a rear wheel steering mechanism driven by an electric motor, wherein the electric motor is supplied from a motor driver controlled by a control means. In a four-wheel steering vehicle driven by the motor drive current, when the motor drive current of a predetermined value or more flows in the electric motor, the control means reverses the direction in which the motor drive current flows in the electric motor. While controlling to rotate in the direction, when the motor drive current in the rotation control of the electric motor in the reverse direction is a predetermined value or more, while controlling to stop the drive of the electric motor immediately, When the motor drive current in the reverse rotation control of the electric motor is equal to or less than a predetermined value, after the rear wheels are steered to the neutral position, A method for controlling steering of rear wheels in a four-wheel steering vehicle, comprising: controlling to stop driving of the electric motor.