JPH06127416A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To reopen rear wheel steering control directly after reset of a CPU due to noise or the like, and prevent sudden steering at the time so as to enable smooth rear wheel steering without giving a sense of incongruity to a driver, in the rear wheel steering device of a vehicle. CONSTITUTION:This rear wheel steering device of a vehicle is provided with a main motor 9 and additionally a sub-motor 13 as the mechanism, a memory 41 to store generation of reset in the CPU in the past, and a memory 43 to store generation of abnormality in the CPU in the past. The motors 9, 13 are constituted so as not to be operated without allowance signals ADMM, ADSM from a changeover control circuit 35. The changeover control circuit 35 monitors a reset signal RST and a rising signal STcpu and writes generation of reset and abnormality in the CPU in the past in the memory 41, 43. The CPU sets the main motor driving speed directly after resetting to be low speed based on the content of the memory 41. Further, returning to the neutral of rear wheels is performed with the sub-motor 13 at anormality of the CPU or the main motor.

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 system for a vehicle which steers the front wheels and steers the rear wheels in response to the vehicle speed.

[0002]

2. Description of the Related Art Conventionally, as a rear wheel steering system for a vehicle, a system is known in which an electronic control unit is mounted and a rear wheel is steered by driving and controlling an electric motor according to a front wheel steering angle and a vehicle speed. . By the way, a central processing unit (hereinafter referred to as CPU) of the electronic control device may run away due to noise or the like.

Therefore, for example, Japanese Patent Laid-Open No. 61-108066.
When the CPU runs out of control like the device described in the publication, the rear wheel steering is stopped and the rear wheels are returned to the neutral position.
A technique for switching to S control is known. According to this technique, unstable rear wheel steering control due to CPU runaway can be avoided.

[0004]

However, in the device described in this publication, once it is determined that the CPU is abnormal and switched to the 2WS control, the vehicle speed becomes zero even if the CPU is reset and returns to normal. Until then, it was not possible to return to 4WS control. Therefore, there is a problem that the original operation and effect of the 4WS control cannot be obtained for a long period of time. This problem is particularly noticeable on highways where vehicles are not stopped for a long time.

Therefore, it is desired that the 4WS control by the electric motor is restarted when the CPU is reset and returns to the normal state. However, suddenly 4W
Returning to S control has the following problems. That is, when the 4WS control is suddenly restarted, the rear wheels are steered in some cases, which gives the driver a feeling of strangeness. In particular, if such a state occurs during high-speed traveling, a very strong sense of discomfort will be given.

Therefore, the vehicle rear wheel steering system of the present invention enables smooth rear wheel steering without causing the driver a sense of discomfort when the rear wheel steering control is restarted after such a CPU reset reset. The purpose is to

[0007]

As shown in FIG. 1, a vehicle rear wheel steering system according to the present invention includes an actuator for driving a rear wheel steering mechanism, a front wheel steering operation for the actuator, and a vehicle speed. A rear wheel steering control means for steering the rear wheels by controlling the drive in accordance with the above, an abnormality determination means for determining an abnormality of the rear wheel steering control means, and when an abnormality is determined by the abnormality determination means, Disconnection means for disconnecting the actuator from the drive control by the rear wheel steering control means, abnormality elimination determination means for determining whether or not the abnormality of the rear wheel steering control means is eliminated, and the abnormality elimination by the abnormality elimination determination means And a return control means for restarting the drive control of the actuator by the rear wheel steering control means at a low speed.

According to this vehicle rear wheel steering system, when the rear wheel steering control means is abnormal, the actuator is disconnected from the drive control by the rear wheel steering control means to prevent abnormal control. Then, when the abnormality of the rear wheel steering control means is resolved, the drive control of the actuator by the rear wheel steering control means is restarted at a low speed. Therefore, when recovering from the abnormality, the actuator can operate only at a low speed, and the original rear wheel steering state is smoothly changed. As a result, there is no sudden turning when returning from an abnormality, and the driver does not feel uncomfortable. Then, after shifting to the original rear wheel steering state, the actuator will resume operation at a normal speed.

By the way, if the rear wheels are left as they are during the occurrence of an abnormality, the rear wheels may be largely steered, impairing the straight running performance or impairing the steering stability. Therefore, in the present invention described above, it is desired that the actuator is also provided with a configuration for preventing such a problem after the actuator is separated from the rear wheel steering control means.

The vehicle rear wheel steering system according to claim 2 is completed there. That is, in the vehicle rear wheel steering system according to claim 1, further, a sub-actuator for driving a rear wheel steering mechanism independently of the actuator and the rear wheel steering control means are provided separately, A sub-steering control means for driving and controlling an actuator, and a sub-steering permission means for enabling a drive control of the sub-actuator by the sub-steering control means when the disconnecting means operates are provided. That is the rear wheel steering system.

According to the vehicle rear wheel steering system of the present invention, the drive control of the sub-actuator is permitted when the actuator is separated from the rear wheel steering control means by the disconnecting means. Therefore, despite adopting the configuration described in claim 1, it is possible to accurately switch to 2WS when an abnormality occurs. Of course, instead of switching to 2WS, 4WS control by the sub-actuator may be performed.

Here, as in claim 3, in the vehicle rear wheel steering system according to claim 2, it is further determined whether or not the actuator itself driven and controlled by the rear wheel drive control means is abnormal. Actuator abnormality determination means,
If an abnormality is determined by the actuator abnormality determining means, the drive control of the auxiliary actuator is stopped and the switching means for permitting the drive control of the sub-actuator is provided. Even if the actuator fails, the abnormal control can be prevented and the sub-actuator can be driven to switch to the 2WS control or the 4WS control can be continued.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a rear wheel steering system of a vehicle will be described below with reference to the drawings. As shown in FIG. 2, the rear wheel steering apparatus according to the embodiment includes a rack 3 provided on a shaft 1 of a rear wheel of a vehicle and a pinion gear 5 that meshes with the rack 3.
A main motor 9 for rotationally driving the pinion gear 5 via a worm gear type speed reducer 7; a sub motor 13 engaged / disengaged with the worm gear type speed reducer 7 via an electromagnetic clutch 11; Steering sensor 17 for detecting the front wheel steering angle θF
And a potentiometer type rear wheel steering angle sensor 19 provided on the worm gear type speed reducer 7 for detecting the steering angle θR of the rear wheels.
A motor angle sensor 21 for detecting a rotation angle θMM of the main motor 9, a vehicle speed sensor 23 for detecting a vehicle speed V, and an engine speed sensor 25 for detecting an engine speed NE.
And the detection signals .theta.F, .theta.R, .theta.MM, V, NE from these sensors 17, 19, 21, 23, 25 are input to execute predetermined arithmetic processing, and the main motor 9, electromagnetic clutch 1
1 and an electronic control device for controlling the sub motor 13 (hereinafter,
(Referred to as ECU) 30. The motors 9 and 13 used here may be DC motors or brushless motors.

The worm gear type speed reducer 7 is shown in FIG.
As shown in, the worm gear 7a is directly connected to the rotor shaft 9a of the main motor 9, and the worm wheel 7b meshes with the worm gear 7a. The pinion gear 5 is directly connected to the rotary shaft of the worm wheel 7b. The submotor 13 has a reduction gear 13
a is attached. The electromagnetic clutch 11 engages / disengages the shaft of the reduction gear 13a and the worm gear 7a. In addition, the sub motor 13 is the worm gear 7
The speed of rotating a is lower than that of the main motor 9.

The ECU 30, as shown in FIG.
1 and a drive circuit 33 that receives a main motor drive command QMM output from the CPU 31 and outputs a control signal DMM to the main motor 9, and a control signal may be output to the drive circuit 33. A switching control circuit 35 that outputs a prohibition signal NDMM when a control signal should not be output as the permission signal ADMM, and a reset generation circuit that monitors whether the CPU 31 is out of control and resets the CPU 31 when the control signal is out of control. And 37.

The CPU 31 has two dedicated memories 4
1, 43 are connected. The first memory (hereinafter, referred to as past reset generation memory) 41 is writable by both the CPU 31 and the switching control circuit 35, and the CP
The contents can be read from the U31 side. The past reset generation memory 41 has a parameter indicating whether or not a reset of the CPU 31 has occurred in the past (hereinafter, referred to as past reset determination parameter).
MRST is stored. The second memory (hereinafter referred to as backup CPU abnormal memory) 43 has a switching control circuit 35.
Is writable from the CPU 31 side and read from the switching control circuit 35 side. The backup CPU abnormality memory 43 has a parameter M (hereinafter, referred to as an abnormality determination parameter) M indicating whether the CPU 31 is in an abnormal state and should not be used.
The CPU is stored.

The switching control circuit 35 thus executes the process of writing predetermined information in the memories 41 and 43. Then, the switching control circuit 35 includes the drive circuit 3 for the main motor.
3, an electromagnetic clutch drive circuit 45 that outputs a control signal DCL to the electromagnetic clutch 11, a submotor drive circuit 47 that outputs a control signal DSM to the submotor 13, and a submotor command that outputs a drive command signal QSM to this submotor drive circuit 47. The circuit 49 also outputs the permission signal ADSM or the inhibition signal NDSM for permitting / inhibiting the operation.

Next, main motor drive control processing executed by the CPU 31 will be described with reference to the flow charts of FIGS. After starting up, the CPU 31 first reads the abnormality determination parameter MCPU of the backup CPU abnormality memory 43, and if "MCPU = 1", stops the main motor drive command QMM (S501 → S).
515). “MCPU = 1” means that there is a high possibility that the CPU 31 is abnormal and the rear wheel drive control cannot be normally performed.

On the other hand, if "MCPU = 1" is not satisfied, initial processing (for example, register initialization) is performed (S5
02), the switching control circuit 35 to the CPU rising signal STCPU
Is output (S503). Then, the detection signals θF and V are input from the steering sensor 17 and the vehicle speed sensor 23, and the rear wheel steering angle target θRM is set from these signals (S50).
4).

Thereafter, the past reset determination parameter MRST of the past reset generation memory 41 is read (S50
5) If "MRST = 1", the control speed of the main motor 9 is set to a low speed (S506). "MRST = 1" means
It means that the CPU 31 has been reset due to a runaway or the like caused by noise in the past.

On the other hand, if "MRST = 0", the control speed is set to the normal speed (S507). Then, the detection signal θMM of the motor angle sensor 21 is read (S508), and the positioning control of the main motor 9 is performed toward the rear wheel steering angle target θRM (S509). And if the goal is reached (S
510: YES), past reset determination parameter MRST
Is cleared to "0" (S511). This step S5
By performing the processing of 11, in the next positioning control, “step S505 → step S507” is passed,
Control by the normal speed will be restarted. Further, since the past reset determination parameter MRST is not reset unless the target is reached (S510: NO), even if the front wheels are steered or the vehicle speed changes and the rear wheel steering angle target θRM changes in step S504, The control to approach the new rear wheel steering angle target θRM at low speed is repeated.

Thus, in step S511, "MRST =
After clearing to "0", the operation is checked by the motor rotation speed and the motor current value of the main motor 9 (S512),
If normal, “step S513 → step S504”
And the positioning control of the main motor 9 is repeated. If it is determined to be abnormal, the main motor abnormality signal ERRMM is output to the switching control circuit 35 (S514), and the main motor drive command QMM is stopped (S515).

The CPU 31 also sends to the reset generation circuit 37 a watchdog signal WD for turning the pulse on and off within a fixed time. When the CPU 31 runs out of control, this watchdog signal WD is not output, so the reset signal RST is generated from the reset generation circuit 37, and the CP
U31 is reset. This reset signal RST is
As shown in FIG. 4, it is also input to the switching control circuit 35. The switching control circuit 35 switches the drive of the main motor 9 and the sub motor 13 based on the reset signal RST or the like. This switching is performed by the permission signal A as shown in FIG.
This is executed in the form of outputting DMM, ADSM or outputting inhibit signals NDMM, NDSM.

The switching control circuit 35 operates according to the flow of FIG. First, at the time of rising after the ignition is turned on for the first time, drive prohibition signals NDMM and NDSM for both the main motor 9 and the sub motor 13 are output (S701).
At this time, as shown in FIG. 3, since the rear wheel steering angle mechanism is configured using the worm gear 7a and the worm wheel 7b, the main motor 9 is stopped due to the non-reciprocal characteristic of the worm gear 7a and the worm wheel 7b. Sometimes the rear wheels cannot be moved (ie the rear wheels cannot be moved to turn the main motor 9). Therefore, this step S
The rear wheel is fixed by the processing of 701.

Thereafter, the switching control circuit 35 causes the past reset determination parameter MRST of the past reset generation memory 41 to be set.
"0" is written in (S702). The past reset determination parameter MRST is a parameter for notifying that a reset has occurred after the ignition is turned on. The past reset generation memory 41 can also be accessed from the CPU 31, as described above. Further, the memory 41 is configured so that the stored contents are lost when the ignition is turned off.

Next, the switching control circuit 35 causes the backup C
The abnormality determination parameter MCPU of the PU abnormality memory 43 is read, and it is determined whether or not "MCPU = 1" (S
703). This backup CPU abnormality memory 43 is
Even if the ignition is turned off, the stored contents are held by the battery voltage. At this point, "MCPU
In the case of “= 1”, it means that an abnormality was detected during the previous travel before the ignition was turned on this time.
In this case, the process jumps to step S720, "MCPU = 1" is written again in the backup CPU abnormality memory 43, the detection signal θR of the rear wheel steering angle sensor 19 is read, and it is determined whether or not it is neutral (S721).

If it is determined to be "NO", the sub motor drive permission signal ADSM is output and step S72 is performed.
It returns to 1 (S723). At this time, as shown in FIG. 4, the electromagnetic clutch drive circuit 45, the sub motor drive circuit 47, and the sub motor command circuit 49 are turned on by the permission signal ADSM, and the sub motor command circuit 49 is activated based on the detection value of the rear wheel steering angle sensor 19. The control signal QSM is output to return to the neutral position (S721 → S723 → S721 → ...). At this time, the neutral return speed is set to a low speed so that the driver does not feel uncomfortable with the reduction gear 13a, as shown in FIG. If it returns to neutral, the sub motor is stopped (S72
2), the operation ends.

On the other hand, if it is determined that the abnormality determination parameter MCPU is not "1" at the time of turning on the ignition (S703: NO), the switching control circuit 35 clears the built-in watchdog counter WDC (S70).
4). Then, it is determined whether or not the CPU rising signal STCPU has come (S705). As shown in FIG. 4, CP
U31 is a rising signal STCPU when it rises normally.
Is sent to the switching control circuit 35, but this signal is not sent unless the CPU 31 has normally started up.

When it is determined in step S705 that the CPU rising signal STCPU has not come, it is determined whether the predetermined time T1 has elapsed (S706). Then, within the predetermined time T1, the determination of whether or not the rising signal STCPU has arrived (S705) is repeated. Predetermined time T1
Repeatedly determine whether or not to stand up
This is to accurately determine whether the PU 31 is delayed in rising by nature or does not start in nature.

If the CPU rising signal STCPU does not come even after the elapse of the predetermined time T1, it is determined that the CPU is abnormal, the process jumps to step S720, and the abnormality determination parameter MCPU
Write "1" to. If the CPU rising signal STCPU comes within the predetermined time T1, the CPU 31 determines that it has started normally, and outputs the main motor drive permission signal ADMM (S707).

The drive of the main motor 9 is executed by outputting a drive command QMM from the CPU 31, as shown in FIG. 4, but the main motor drive circuit 33 does not output the drive signal DMM by itself. The main motor 9 can be driven only when the permission signal ADMM from the switching control circuit 35 is input to the main motor drive circuit 33.

As described above, the CPU 31 constantly checks the main motor 9 in the control flow (S5).
12) If it is determined to be abnormal, the main motor abnormality signal ERRMM is output to the switching control circuit 35 (S514).
When the switching control circuit 35 detects the abnormal signal ERRMM in step S708, the switching control circuit 35 outputs the main motor drive prohibition signal ND.
After outputting MM (S709), the process jumps to step S720.

Main motor abnormality signal ER from CPU 31
If the RMM does not come, it is determined whether or not the reset RST is generated by checking the watchdog signal in the reset generation circuit 37 (S710). When the rear wheel steering is normally performed, the switching control circuit 35 performs the "step S7".
"07 → S708 → S710 → S707 → ..." is repeated. On the other hand, when a reset occurs due to CPU runaway, the main motor drive prohibition signal NDMM is output (S711) and the watchdog counter WDC is incremented (S712). In the present embodiment, the reset occurrence from the ignition on to the threshold value N times is regarded as an accidental runaway due to a disturbance due to power source noise or the like.

This watchdog counter WDC shows ">
In the case of “N”, it is determined that an abnormality has occurred in the CPU 31,
Write "1" to the abnormality determination parameter MCPU (S71
3 → S720), neutral return is performed by the sub motor (S72)
1 to S723). That is, the 4WS control by the CPU 31 is stopped. When the abnormality determination parameter MCPU becomes "1", this value is backed up even after the ignition is turned off. Therefore, even if the CPU 31 is able to start up thereafter, the control processing by the CPU 31 is performed in step S5.
The process proceeds from 01 to S515 and the 4WS control is not executed.

On the other hand, when "WDC≤N", the CPU
After returning to normal, the abnormality determination parameter MCPU remains "0" in order to return to normal control. However, "1" is written in the past reset determination parameter MRST (S71).
3 → S714). If the vehicle is not stopped (S
715: NO), jump to step S705 and wait for the rising of the CPU 31. When it is determined that the vehicle is stopped, that is, the pulse of the vehicle speed sensor 23 is not output,
If the engine speed NE is below the threshold value (S
715: YES), and after confirming that the rear wheels are not in the large steering angle in the reverse phase of the front wheels, the neutral return is performed by the sub motor 13 (S716 → S717). This neutral return does not make the driver feel uncomfortable because the vehicle is stopped.

Further, even if the vehicle is stopped, if the rear wheels are in the large steering angle in the reverse phase, it is determined that the reset has occurred during the stationary steering such as putting in the garage. , Turning the rear wheel to neutral changes the turning radius and gives the driver a feeling of strangeness.
Wait for the return of (S716 → S705). Switching control circuit 3
5 performs the above operation independently of the CPU 31.

As described above, according to this embodiment, C
Even if the PU31 has been reset in the past,
The rear wheel steering control is immediately restarted when the vehicle normally starts up again. Therefore, unlike the device disclosed in Japanese Patent Laid-Open No. 61-108066, the 4WS control cannot be restarted until the vehicle is once stopped, and the original function of the 4WS control is
It is possible to solve the problem that the effect cannot be obtained for a long time.

Further, in addition to the action and effect, according to the present embodiment, the rear wheel steering control is restarted at a low speed when the CPU 31 is reset in the past (S506). Therefore, when the CPU 31 stands up, the rear wheels are not steered suddenly, and the rear wheels can smoothly approach the target, so that the driver does not feel uncomfortable. That is, according to the present embodiment, the original operation and effect of the 4WS control can be exerted to the maximum and without any trouble.

If it is determined that the CPU 31 is abnormal rather than due to mere noise, the rear wheel steering by the main motor 9 is stopped (S501 → S).
515). Therefore, it is possible to prevent the abnormal CPU 31 from performing the control, and the unintended sudden turning due to the CPU runaway does not occur.

Then, when such a CPU abnormality occurs, the fact is stored in the backup CPU abnormality memory 43, and the sub motor 13 is switched to perform neutral return (S720 to S723). Therefore, when it is determined that an abnormality has occurred, even if the rear wheels have been steered by a relatively large amount, they can be returned to neutral, and the operation can be continued with the rear wheels cut off. Absent. Further, since the sub-motor 13 originally uses a rear wheel that can be steered only at a low speed, this neutral return does not result in sudden turning. In addition, since the sub motor 13 is provided, the neutral return can be performed even if the main motor 9 fails (S708 → S709 → S720).

Further, the neutral return by the sub motor 13 is not performed during high speed running (S715 → S).
705), even if the vehicle is traveling at a low speed, it is not performed if it is in a reverse phase (S716 → S705).
As a result, even if a CPU abnormality or a main motor abnormality occurs during high-speed traveling, the steering state of the rear wheels is fixed and the rear wheels are not steered. Further, since the rear wheel steering angle during high-speed traveling is small, the driver does not feel uncomfortable even if fixed. Therefore, when an abnormality of the CPU or the like occurs during high-speed traveling, an unstable traveling state that causes a strong discomfort to the driving vehicle does not occur.

Further, since the neutral return is prohibited when the vehicle is being steered in the reverse phase at a low speed, the rear wheels are not suddenly returned while the vehicle is being put in the garage, and the driver's intention is avoided. It is possible to continue garage entry in this turning state and to drive without feeling discomfort.

Although the vehicle rear wheel steering system according to the embodiment has been described above, the rear wheel steering system according to the present invention is not limited to the above embodiment, and is not a DC motor or a brushless motor, but a hydraulic cylinder. If the main motor 9 is abnormal and the CPU 31 is normal, the 4WS control is continued by the drive control from the CPU 31. The present invention can be modified into various forms without departing from the gist of the present invention.

[0044]

As described in detail above, according to the vehicle rear wheel steering system of the present invention, the temporary CPU due to noise or the like is used.
The rear-wheel steering control can be immediately executed when the vehicle is reset and recovered from the abnormality, and the rear-wheel steering control is restarted at low speed. Can be controlled to.

Further, according to the apparatus of claim 2, if the rear wheel steering state before the occurrence of the abnormality continues as it is, there is a possibility that the straight running performance may be impaired or the steering stability may be impaired. It can be dealt with accurately. Further, according to the vehicle rear wheel steering system of claim 3, abnormal control is prevented even when the actuator itself is out of order, and the auxiliary actuator is driven to switch to the 2WS control. Or 4WS
Control can be continued.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram illustrating the configuration of a vehicle rear wheel steering system according to the present invention.

FIG. 2 is an overall configuration diagram showing an overall configuration of a rear wheel steering system according to an embodiment.

FIG. 3 is an overall configuration diagram showing an overall configuration of a rear wheel steering system according to an embodiment.

FIG. 4 is a block diagram of a control system in the rear wheel steering system according to the embodiment.

FIG. 5 is a flowchart showing a main processing routine of rear wheel steering control in the embodiment.

FIG. 6 is a flowchart showing a main processing routine of rear wheel steering control executed by a CPU in the embodiment.

FIG. 7 is a flow chart showing a processing routine for abnormality determination / neutral return performed by the switching circuit in the embodiment.

FIG. 8 is a flowchart showing a processing routine for abnormality determination / neutral return performed by the switching circuit in the embodiment.

FIG. 9 is a flowchart showing a processing routine executed by the switching circuit for abnormality determination / neutral return in the embodiment.

[Explanation of symbols]

3 ... Rack, 5 ... Pinion gear, 7 ... Worm gear type speed reducer, 79 ... Main motor, 11 ...
・ Electromagnetic clutch, 13 ... Sub motor, 17 ... Steering sensor, 19 ... Rear wheel steering angle sensor, 21 ...
..Motor angle sensor, 23 ... Vehicle speed sensor, 25 ...
・ Engine speed sensor, 31 ・ ・ ・ CPU, 33 ・ ・
・ Main motor drive circuit, 35 ... Switching control circuit, 3
7 ... Reset generation circuit, 41 ... Past reset generation memory, 43 ... Backup CPU abnormal memory,
45 ... Electromagnetic clutch drive circuit, 47 ... Sub motor drive circuit, 49 ... Sub motor command circuit.

Claims (3)

[Claims] 1. An actuator for driving a steering mechanism for a rear wheel, a rear wheel steering control means for steering a rear wheel by driving and controlling the actuator according to a steering operation of a front wheel and a vehicle speed, and the rear wheel steering control. Abnormality determining means for determining abnormality of the means, disconnection means for disconnecting the actuator from drive control by the rear wheel steering control means when the abnormality is determined by the abnormality determining means, and abnormality of the rear wheel steering control means And a recovery control for restarting the actuator drive control by the rear wheel steering control means at a low speed when it is determined that the abnormality is resolved by the abnormality resolution determination means. And a rear wheel steering device for a vehicle. 2. The vehicle rear wheel steering system according to claim 1, further comprising a sub-actuator for driving a rear wheel steering mechanism independently of the actuator and the rear wheel steering control means. A sub-steering control unit that drives and controls the sub-actuator; and a sub-steering permission unit that enables drive control of the sub-actuator by the sub-steering control unit when the disconnecting unit operates. Rear wheel steering system for vehicles. 3. The vehicle rear wheel steering system according to claim 2, further comprising actuator abnormality determining means for determining whether or not the actuator itself driven and controlled by the rear wheel drive control means is abnormal, and the actuator abnormality. A rear wheel steering device for a vehicle, comprising: a switching unit that stops drive control of the actuator and permits drive control of the sub-actuator when an abnormality is determined by the determination unit.