JP2758166B2 - Vehicle rear wheel steering system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rear wheel steering device for a vehicle that steers rear wheels.

(Prior Art) Some vehicles, such as so-called four-wheel steering (4WS), steer not only front wheels but also rear wheels.

In this four-wheel steering, as a rear wheel steering mechanism, as shown in Japanese Utility Model Publication No. 62-25275, a mechanical system in which a front wheel steering mechanism and a rear wheel steering mechanism are mechanically connected,
Electromagnetic driving means such as an electric motor is linked to the rear wheel turning mechanism, and is roughly classified into an electric type in which the rear wheels are steered by the driving force of the driving means. In this electromagnetic type, it has also been proposed to interpose a speed reduction mechanism between the driving means and the rear wheel steering mechanism so that the capacity of the driving means can be reduced as much as possible. No. 25277).

In the electronic type, since the rear wheel steering is exclusively controlled electrically, it is necessary to sufficiently consider a fail safe such as a failure of the control system. From this point of view, as disclosed in Japanese Patent Application Laid-Open No. 61-202977, it has been proposed to provide the rear wheel steering mechanism with neutral holding means for constantly biasing the rear wheel steering mechanism in the neutral direction. This proposal is based on the idea that when any trouble occurs in the control system, the rear wheel steering control is stopped and the rear wheels are forcibly returned to the neutral position by the neutral holding means.

(Problems to be Solved by the Invention) When a rear wheel is steered by a motor, feedback control is generally performed so as to attain a target rear wheel steering angle. A sensor for detecting the steering angle is required.

In this case, if the sensor that detects the actual turning angle of the rear wheel breaks down, the steering control of the rear wheel cannot be performed accurately, and some measures are desired in this regard.

Therefore, an object of the present invention is to turn the rear wheels using a motor as a drive source, and to sufficiently secure safety when a failure occurs in rear wheel turning angle detection for detecting an actual turning angle of the rear wheels. It is an object of the present invention to provide a rear wheel steering device for a vehicle which can be secured.

(Means and Actions for Solving the Problems) In order to achieve the above object, the present invention has the following configuration. That is, a rear wheel steering mechanism for steering a rear wheel, a motor as a drive source that is linked to the rear wheel steering mechanism via a clutch, and displaces the rear wheel steering mechanism, First rear wheel turning angle detecting means for detecting the rotational position of the motor on the side, and second rear wheel turning angle detection for detecting a mechanical displacement of the rear wheel turning mechanism closer to the rear wheel turning mechanism than the clutch. Means for detecting an abnormality of the clutch by comparing the output of the first rear wheel turning angle detecting means with the output of the second rear wheel turning angle detecting means.

(Example) Hereinafter, an example of the present invention will be described with reference to the attached drawings.

In FIG. 1, 1R is a right front wheel, 1L is a left front wheel, 2R is a right rear wheel, 2L is a left rear wheel, left and right front wheels 1R and 1L are linked by a front wheel steering mechanism A, and left and right rear wheels. 2R and 2L are linked by a rear wheel steering mechanism B.

In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R and 3L and tie rods 4R and 4L, respectively, and a relay rod 5 connecting the pair of left and right tie rods 4R and 4L. The steering mechanism C is linked to the front wheel steering mechanism A, and the steering mechanism C
Is a rack-and-pinion type in the embodiment, and a component pinion 6 is connected to a handle 8 via a shaft 7. Thereby, when the steering wheel 8 is turned to the right, the relay rod 5 is moved to the first position.
The knuckle arms 3R and 3L are displaced to the left in the figure, and the knuckle arms 3R and 3L are steered clockwise about the rotation centers 3R 'and 3L' by an amount corresponding to the amount of operation displacement of the handle 8, that is, the steering angle. Is done. Similarly, when the operation of turning the steering wheel 8 to the left is performed, the left and right front wheels 1R and 1L are steered to the left according to the amount of operation displacement.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also has a pair of left and right knuckle arms 10R and 10L and a tie rod.
The tie rods 11R and 11L have a relay rod 12 for connecting the tie rods 11R and 11L, and the relay rod 12 is provided with a neutral holding means 13. The neutral holding means 13 has a casing 15 fixed to the vehicle body 14, as shown in FIG.
A pair of spring supports 16a and 16b are loosely fitted in the casing 15, and a compression spring 17 is disposed between the spring supports 16a and 16b. The relay rod 12 extends through the casing 15, and a pair of flanges 12a, 12b are formed on the relay rod 12 at intervals, and the flanges 12a, 12b receive the spring supports 16a, 16b. The relay rod 12
Is always biased in the neutral direction by the compression spring 17.
Needless to say, the compression spring 17 has a spring force enough to overcome the side force during cornering.

The rear wheel turning mechanism B is linked to a servomotor 20 as a drive source for turning the rear wheels 2R and 2L. More specifically, a speed reduction mechanism 21 including a gear train 21a and a ball screw 21b, a clutch 22, and a brake mechanism 23 are interposed in the linkage mechanism between the relay rod 12 and the servomotor 20 in order from the relay rod 12 side. Have been. Thus, the linkage between the servo motor 20 and the rear wheel steering mechanism B can be mechanically disconnected by the clutch 22 as appropriate.
23 allows the output shaft of the servo motor 20 to be gripped and the rotation of the output shaft to be locked.

With the above configuration, when the clutch 22 is in the connected state, the forward rotation or the reverse rotation of the servomotor 20 causes
The relay rod 12 is displaced leftward or rightward in FIG. 1 so that the knuckle arms 10R, 10L are pivoted about
The steering wheel is turned clockwise or counterclockwise in the figure by an amount corresponding to the rotation amount of the servo motor 20 around L '. On the other hand, when the clutch 22 is in the disengaged state, the rear wheels 2R and 2L are forcibly returned to the neutral position by the neutral holding means 13 and held at the neutral position. That is, when the clutch 22 is disconnected, only the front wheels 1R and 1L are steered, which is a so-called 2WS vehicle.

Here, the control of the rear wheel steering is made to be vehicle speed-sensitive, and there is a case as shown in FIG. 3 as an example of the change of the steering ratio according to the vehicle speed. When the control characteristics shown in FIG. 3 are provided, the rear wheel turning angle with respect to the steering wheel angle changes in the same phase direction as the vehicle speed increases. This is shown in FIG. In order to perform such control, basically, signals from a steering wheel angle sensor 30, a vehicle speed sensor 31, and an encoder 32 for detecting the rotational position of the servo motor 20 are input to the control unit U, and the control unit U performs control. The unit U calculates a target rear wheel steering angle based on the steering wheel steering angle and the vehicle speed, and outputs a control signal corresponding to a required rear wheel steering amount to the servo motor 20. Then, while the encoder 32 constantly monitors whether the servo motor 20 is properly operated, that is, the rear wheels 2R and 2L are steered under feedback control.

The basic control has a double control system for fail-safe. That is, a front wheel steering angle sensor 34 is added to the steering wheel steering angle sensor 30, a second vehicle speed sensor 35 is added to the vehicle speed sensor 31, and the encoder 32 is located closer to the relay rod 12 than the clutch 22. A rear wheel steering angle sensor 36 for detecting a mechanical displacement of a member is added, and in these sensors 30 to 36, rear wheel steering is performed only when both corresponding sensors detect the same value. I have. That is, when the vehicle speed detected by the first vehicle speed sensor 31 and the vehicle speed detected by the second vehicle speed sensor 35 are different from each other in the sensors 30 to 36, it means that a failure has occurred. The rear wheels 2R and 2L are held in a neutral state.

To detect various failures, on / off signals from the switches 37 to 40 are input to the control unit U, and a signal indicating the presence or absence of power generation is input from the L terminal 41 of the alternator. Here, the switch 37 is a neutral clutch switch, the switch 38 is an inhibitor switch, the switch 39 is a brake switch, and the switch 40 is an engine switch. Here, in a vehicle equipped with a manual transmission, the neutral switch 37 outputs an off signal when the shift position of the manual transmission is neutral or depresses a clutch pedal, and outputs an on signal otherwise. Has become. In a vehicle equipped with an automatic transmission, the inhibitor switch 38 outputs an ON signal when the range is in neutral (N) or parking (P), and outputs an OFF signal when the range is in the travel range. ing. The brake switch 39 outputs an ON signal when the brake pedal is depressed, and the engine switch 40 outputs an ON signal when the engine is operating.

FIG. 5 is a block diagram showing the control system. That is, the microprocessor 50 has a double structure of I and II, and the microprocessor 50 receives signals from the vehicle speed sensors 31, 35, the switches 37 to 40 and the L terminal 41 of the alternator via the buffer 51. The signals from the sensors 30, 34 and 36 are input via an A / D converter 52, and the signal from the encoder 32 is input via an interface 53. On the other hand, the signal generated by the microprocessor 50 is sent to the servomotor 29 via the drive circuit 54, sent to the motor brake 23 via the brake drive circuit 55, or sent to the clutch 22 via the clutch drive circuit 56. Sent out. This rear wheel steering control is started on condition that the signal from the L terminal 41 of the alternator becomes high (Hi). In the figure, reference numeral 57 denotes a battery, 58 denotes an ignition key switch, and 59 denotes a relay.When any failure occurs in the control system of the four-wheel steering, the energization of the coil 61 is stopped by the operation of the relay drive circuit 60. As a result, the B contact of the relay 59 is closed, and the warning lamp 62 is turned on.

Next, the failure and its countermeasures will be described.
It is assumed that a measure corresponding to the location of the failure is performed, and the form of the measure includes the following two forms.

Treatment mode A (control in first fail mode) This is a mode in a case where control of rear wheels 2R and 2L and position determination thereof are still possible. That is, when it is possible to return to neutral by the motor 20, the neutral return is performed by the motor 20. Specifically, the contents of this treatment are as follows. After the warning lamp 62 is turned on, the rear wheels 2R and 2L are returned to the neutral position by driving the servo motor 20, and then the motor brake 23 is engaged. Done.

Treatment Mode B (Control in Second Fail Mode) This is a mode in which the control of the rear wheels 2R and 2L and the position determination thereof are disabled. The contents of this treatment are as follows.

After the warning lamp 62 is turned on, the clutch 22 is turned off, the linkage between the servomotor 20 and the rear wheel steering mechanism B is disconnected, and the rear wheels 2R, 2L return to the neutral position by the spring force of the neutral holding means 13. After that, the connection of the clutch 22 is made.

Preferably, the motor brake 23 is engaged after the clutch 22 is disconnected. As a result, the turning of the rear wheels 2R, 2L accompanying the runaway of the motor 20 is physically prohibited. Then, the supply of power to the motor 20 is cut off thereafter.

Below, the failure modes and their setting conditions are classified into each system,
The corresponding treatment mode will be described.

Vehicle speed signal system When it is determined that a failure has occurred in the present system, the treatment of the above-described mode A is performed.

(1) A change amount error of the first vehicle speed sensor 31.

This determination is based on the condition that the brake switch 39 is off (OFF) and the first vehicle speed sensor 31 detects the deceleration of | dV ₁ / dt |> a (constant). Where V ₁ is the first
Represents the vehicle speed detected by the vehicle speed sensor 31. That is, when the vehicle decelerates by a predetermined amount or more even though the vehicle is not braked, it is determined that the first vehicle speed sensor 31 is out of order.

(2) A change amount error of the second vehicle speed sensor 35.

This determination is performed in the same manner as in the case of the first vehicle speed sensor 31 described above.
The condition is that the brake switch 39 is off (OFF) and the second vehicle speed sensor 35 detects the deceleration of | dV ₂ / dt |> a (constant). Here, V ₂ is the first vehicle speed sensor 31
Represents the detected vehicle speed.

(3) Vehicle speed mismatch error This determination is based on the condition that the detection values of the first and second vehicle speed sensors 31 and 35 do not match as represented by, for example, | V ₁ −V ₂ |> b (constant). Is done.

In this case, since it is considered that an abnormality of at least one of the vehicle speed sensors has occurred, regardless of whether the abnormality has occurred in any of the sensors 31 and 35, it is determined that a failure has occurred, and as described above, , The processing of the aspect A is performed.

(4) Simultaneous failure of both vehicle speed sensors 31, 35.

This determination is based on the fact that the signal from the L terminal 41 of the alternator is high (Hi) and that the outputs of the first and second vehicle speed sensors 31 and 35 are zero (V ₁ = V ₂ = 0). As a premise, in a vehicle with a manual transmission, on the condition that the ON state of the neutral switch 37 continues for a fixed time, on the other hand, in a vehicle with an automatic transmission, the inhibitor switch 38 is turned off,
Engine switch 40 is on and brake switch 39
Both sensors must be turned off for a certain period of time.
31 and 35 are judged as simultaneous failures.

In other words, the vehicle speed is zero, despite the fact that it is possible to run the vehicle from the shift position based on the engine speed at which the vehicle can run based on the amount of power generation, which means that some abnormality has occurred in the sensors 31 and 35. No.

Rear wheel steering mechanism system When it is determined that a failure has occurred in this system,
The treatment of Embodiment B is performed.

(1) Control Deviation (Part 1) This determination is based on a mismatch between the output (EN) of the encoder 32 and the output of the sensor 36, that is, the rear wheel steering angle (θR), for example, | f (E
N) −G (θR) |> c (constant).

(2) Control Deviation (No. 2) This determination is based on the discrepancy between the target rear wheel steering angle (θr) set by the control unit U and the actual rear wheel steering angle (θR), for example, | θr−θR |> c ( (Constant).

(3) Rear Wheel Reference Position Error This determination is based on the condition that a rear wheel sensor reference cannot be found at the start of control (at the time of initialization). Here, the initialization is performed on condition that the engine key is turned on.

DC servo motor system When it is determined that a failure has occurred in this system.
The treatment of Embodiment B is performed.

(1) Rotation amount error This determination is based on the control amount and the rotation amount of the motor 20 (encoder 32
Are not the same.

(2) Motor monitor error This determination is made in the following cases.

Disconnection or short circuit of motor coil.

Disconnection or short circuit of the harness.

Failure of motor drive circuit 52.

Rear wheel steering angle sensor system When it is determined that a failure has occurred in the present system, the treatment of mode B is performed.

(1) Rotary encoder monitor error This determination is made on the condition that an error is detected in the code output from the encoder 32.

(2) Rear wheel steering angle sensor monitor error This determination is made on condition that the output of the rear wheel steering angle sensor 36 exceeds a set range.

Front wheel steering angle sensor system When it is determined that a failure has occurred in this system,
The treatment of aspect A is performed.

(1) Steering angle sensor monitor error This determination is made on condition that the output of the steering angle sensor 30 exceeds a set range.

(2) Front wheel steering angle sensor monitor error This determination is made on condition that the output of the front wheel steering angle sensor 36 exceeds a set range.

(3) Front Wheel Steering Angle Mismatch Error This determination is based on the condition that the difference between the output of the steering wheel steering angle sensor 30 and the output of the front wheel steering angle sensor 34 has reached a certain value or more.

When it is determined that the disconnection operation of the electromagnetic clutch is defective, the treatment of the aspect A is performed.

This determination is performed when an off signal is output to the clutch 22 and the servo motor 20 is operated, and the rear wheel steering angle sensor
The condition is that the output of 36 fluctuates more than a certain value.

Control unit system When it is determined that a failure has occurred in this system,
The treatment of Embodiment B is performed.

(1) RAM error This determination is made on the condition that an abnormality is found in the RAM read / write check.

(2) ROM error This judgment is based on the condition that an abnormality is found in the dumb sum check of the ROM.

(3) FRC error This determination is made on the condition that an abnormality is found in the initial check of the self-propelled counter.

(4) A / D Error This determination is made on condition that an abnormality is recognized in the I / O check of the A / D converter 52.

Microprocessor System (1) Calculation Error This determination is made on condition that the calculation result of the microprocessor I and the calculation result of the microprocessor II do not match.

(2) Communication error This determination is made on condition that mutual communication between the microprocessors I and II is disabled.

Brake When the brake 23 breaks down, the treatment of the mode B is performed. The failure determination of the brake 23 may be performed, for example, as follows.

(1) When the motor 20 remains locked by the brake 23.

Control is performed to rotate the motor 20 while the brake 23 is not operated (unlocked).
32, when there is no output from the sensor 36 (the rear wheels 2R and 2L are not steered).

(2) When the motor 20 cannot be locked by the brake 23.

When the control for locking the brake 23 is performed and the braking for rotating the motor 20 is performed, the encoder 3
2. When there is an output from the sensor 36 (the rear wheels 2R and 2L are steered).

Next, the failure mode as described above and the control for fail-safe according to this will be described with reference to the flowcharts of FIGS. 7 to 10. In the following description, P, Q, R or S indicates a step.

Overall Control (FIG. 9) First, a system initialization is performed at PO in FIG. At this time, a failure that can be known at the time of the initialization is detected (for example, an error check of the rear wheel reference position, an error check of the ROM, RAM, and the like of the control unit).

In this P1, the reference position of the motor 70, the encoder 32, and the sensor 36 is adjusted as shown in FIG. 10, and particularly, the abnormality of the encoder 32 is detected. This point will be described sequentially. First, in Q1 of FIG. 10, the encoder output value EN and the sensor 36 output value θR
And the target rear wheel turning angle θ from the control unit U
In both cases, r is initialized to a value (zero) when the rear wheels 2R and 2L are at the neutral position. Then, by changing the target rear wheel steering angle θr to a predetermined value theta ₁ direction to the motor 20 180 ° forward example, in Q3 accordingly, the motor 20
Is driven by a value corresponding to θ ₁ .

After Q3, in Q4, the output EN of the encoder 32, whether or not a value corresponding to the theta ₁ (a value within the allowable error range) is determined. If the determination in Q5 is YES, it is determined in Q5 whether the output θR of the sensor 36 matches the output EN of the encoder 30. If the determination in Q5 is YES, EN and θR are normally changed according to the change in θr.
Processing after P1 is continued.

If the determination in Q4 is NO, in Q6, it is determined whether or not the rate of change of EN matches the rate of change of θR.
If YES in this Q6, the Q7, whether a predetermined time has elapsed from the start of driving the motor 20 to the theta ₁ direction is determined. Since when this Q7 is determined when the NO of the possibility of mismatch between accompanying EN and theta ₁ to the control delay, the control described above returns to Q4 is repeated. Conversely, if NO in the determination of Q7, when not a mismatch the accompanying EN and theta ₁ to the control delay, i.e., the encoder 32 or the sensor 36
In this case, control for fail-safe operation (corresponding to P12 in FIG. 9 and corresponding to FIG. 8) is performed in this case.

If the determination in Q5 is NO, there is a possibility that the clutch 20 has worn and slipped, so it is preferable to store information that the clutch 20 should be checked (RAM writing). .

After the failure detection at the time of initializing the encoder 32 and the sensor 36 as shown in FIG. 10 described above, the process proceeds to P1 in FIG. The signals from the P1 sensors or switches are input, and the above-described failure determination is sequentially performed.
That is, when there is an abnormality in the vehicle speed signal state (in the determination of P2,
(When YES), if there is an abnormality in the front wheel steering angle sensor system (P
If it is determined that the clutch 22 has an abnormality (YES in the determination of P4), the process proceeds to P5, and the process mode A (described below) is performed. Braking in one fail mode) is performed in principle.

If all of the determinations in P2 to P4 are NO, failure determinations in P6 to P11 are made. In the determination of P6 to P11, if the rear wheel steering mechanism system is abnormal (YES in the determination of P6), if the motor 20 is abnormal (YES in the determination of P7), the rear steering angle sensor When there is an abnormality in the system (when YES is determined in P8), when there is an abnormality in the control unit system (when YES is determined in P9), when there is an abnormality in the microprocessor system (when YES is determined in P10) ), Brake 23
If there is an abnormality (YES in the determination of P11), if any one of the above applies, the process proceeds to P12. In this case, a processing mode B described later (control of the second fail mode)
Is made.

When all of the above P2 to P4 and P6 to P11 are NO,
This is when there is no abnormality, and in this case, normal control is performed in P13. That is, control is performed to realize the steering ratio characteristics shown in FIG.

Processing Mode A (FIG. 7) Details of the control at P5 are shown in FIG.

First, in S1, the warning lamp 62 is turned on to notify the driver that an abnormality has occurred. Next, in order to check whether the rear wheel control and the position determination are performed normally, S2,
The determination at S3 is made. That is, the rearward turning sensor 36 is normal (when the determination of S2 is YES), and the encoder 32
Is normal (when the determination in S3 is YES), in S4, the motor 20 is controlled to gradually return the rear wheels 2R, 2L to the neutral position. Thereafter, it is confirmed in S5 that the motor 20 itself is normal (when the determination in S5 is YES),
After confirming that the rear wheels 2R and 2L have actually reached the neutral position (when the determination in S6 is YES), the brake is activated in S7, and the rear wheels 2R and 2L are in the neutral position. To lock the operation of the motor 20. Of course, at this time,
The clutch 22 remains connected, and
2R and 2L are the urging force of the neutral holding means 13 and the speed reduction mechanism 21.
, And the locking action of the brake 23 firmly maintains the neutral position.

On the other hand, if the determination in any of S2, S3 and S5 is NO, it means that the motor 20 cannot accurately return the rear wheels 2R and 2L to the neutral position. In this case, the processing shifts to S11 in the processing mode B in FIG. 8 described later.

Processing Mode B (FIG. 8) First, after turning on the warning lamp 62 in S10, the clutch 22 is disconnected in S11. Thereby, the neutral holding means 13
As a result, the rear rotations 2R and 2L are forcibly returned to the neutral position. Thereafter, in S12, the brake 23 is operated to lock the motor 20, and then, in S13, the power supply to the motor 20 is cut off (prevention of runaway of the motor 20). Wait for a predetermined time to elapse in S14, that is, wait for this time to elapse in consideration of the time required for the reverse rotation 2R, 2L to return to the neutral position, and then reconnect the clutch 20 in S15. (Neutral position is held firmly).

Here, when both the encoder 32 and the sensor 36 are normal, the feedback control at P13 is performed by the output E of the encoder 32.
N by giving priority to this encoder 32
When a failure occurs, feedback control may be performed using the output θR of the sensor 36. An example of such control is shown in the flowchart of FIG.
That is, when it is determined that the encoder 32 is normal in R1 of FIG. 11, the output of the encoder 32 is determined in R2.
The feedback control of the motor 20 is performed so that EN and the target rear wheel turning angle θr match. If the above R1 is NO,
Assuming that the sensor 36 is normal in the determination of R3, feedback control is performed so that the output θR of the sensor 36 matches the target rear wheel turning angle θr in R4. When the determination of R3 is NO, the position determination of the rear wheels 2R and 2L is impossible, so that the control for fail safe shown in FIG. 8 is performed.

Of course, when performing the control as shown in FIG. 11, P8 shown in FIG. 9 becomes unnecessary.

(Effects of the Invention) As is clear from the above description, according to the present invention, in the case where the steering of the rear wheels is performed by using the motor as the drive source, the actual detection of the rear wheel steering angle is performed by two systems. The reliability for the reverse rotation control is improved, and a failure can be detected using the outputs of the two systems, which is preferable in terms of safety measures.

Further, a clutch is interposed between the motor and the rear wheel steering mechanism to prevent undesired rear wheel steering from being performed by disconnecting the clutch when the motor is abnormal or the like. By comparing the outputs of the angle detecting means, the abnormality of the clutch can also be detected, which is extremely preferable in terms of fuel safety.

[Brief description of the drawings]

FIG. 1 is an overall system diagram showing one embodiment of the present invention. FIG. 2 is a configuration diagram of a rear wheel steering mechanism. FIG. 3 is an enlarged sectional view of the neutral holding means. FIG. 4 is a control characteristic diagram of a vehicle speed sensitive type which is an example of rear wheel steering. FIG. 5 is a characteristic diagram showing a change in the rear wheel steering angle according to the vehicle speed. FIG. 6 is a block diagram of a control system according to the embodiment. 7 to 11 are flowcharts showing control examples of the present invention. 1: front wheel 2: rear wheel 20: servo motor 32: encoder (first rear wheel turning angle detecting means) 36: sensor (second rear wheel turning angle detecting means) U: control unit B: rear wheel turning mechanism

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 7/14 B62D 5/04

Claims (1)

(57) [Claims] 1. A rear wheel turning mechanism for turning a rear wheel, a motor as a drive source that is linked to the rear wheel turning mechanism via a clutch, and displaces the rear wheel turning mechanism; First rear wheel turning angle detecting means for detecting the rotational position of the motor on the motor side; and second rear wheel turning detecting a mechanical displacement of the rear wheel turning mechanism on the rear wheel turning mechanism side of the clutch. A steering angle detecting means, and an abnormality detecting means for comparing an output of the first rear wheel turning angle detecting means with an output of the second rear wheel turning angle detecting means to detect an abnormality of the clutch. A rear wheel steering device for a vehicle, comprising: