JPH06239256A - Front and rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To perform an initial stage self-diagnosis for the front and rear wheel control of a vehicle, a check for control results, and another check at the time of control change-over, respectively only with a sensor in a system. CONSTITUTION:This mechanism performs a power steering function for front wheels at the time of a slow speed travel, and steers rear wheels at the time of medium and high speed travel. Also, the mechanism is caused to perform a control function related to self-diagnosis function for failure mode assumed with an ECU 15 on the basis of each sensor output. First, the mechanism performs an initial check and, when a condition is found normal, enters power steering control mode. When a travel speed is equal to or less than the preset value, the power steering control mode continues and the result of the control is checked, every time the control is effectuated. When the travel speed exceeds the preset value, the mechanism undertakes the confirmation of the disengagement of a front wheel electromagnetic clutch 8, and enters rear wheel steering control mode. While the travel speed continues to be larger than the preset value, the rear wheel steering control mode continues, and the result of the control is checked, every time the control is effectuated. When the travel speed drops to below the preset value, the mechanism confirms the disengagement of a rear wheel electromagnetic clutch 10 and again continues the power steering control mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle wheel steering system, and in a vehicle equipped with a so-called 4WS (four-wheel steering) mechanism, one motor power is used for front wheel steering (front wheel power steering) and rear wheel steering. The present invention relates to a steering device that is used by switching to and.

[0002]

2. Description of the Related Art As a conventional technique, there is a four-wheel steering system disclosed in Japanese Patent Publication No. 4-63771. This is an invention of the basic structure of the above-mentioned device, and when the vehicle is traveling at low speed, the power is connected to the front wheel steering mechanism with a clutch in accordance with the front wheel steering and used as a steering assistance device (front wheel power steering). By connecting power to the rear wheel steering mechanism with another clutch, the rear wheel steering is performed corresponding to the front wheel steering to improve the running performance of the vehicle. In order to control this device, a vehicle speed sensor, steering angle sensor,
The structure is equipped with a torque sensor, a rear wheel steering angle sensor, and a motor rotation angle sensor.

[0003]

However, the above-mentioned device has no countermeasure against the abnormality of the clutch which is the power transmission mechanism, and for example, the detection when the clutch is seized and stuck is not performed.

Therefore, an object of the present invention is to provide an apparatus having highly safe system operation in consideration of fail-safe in this system.

[0005]

In order to solve the above-mentioned problems, the structure according to claim 1 has a front wheel steering mechanism and a rear wheel steering having one motor, a front wheel electromagnetic clutch and a rear wheel electromagnetic clutch. A structure for transmitting the output of the motor to a mechanism, and has a vehicle speed sensor, a rotation angle sensor of the motor, a steering angle sensor provided in the front wheel steering mechanism, and a rear wheel steering angle sensor provided in the rear wheel steering mechanism. In a front / rear wheel steering system of a vehicle, the front / rear wheel steering system is controlled by switching between a front wheel steering mode and a rear wheel steering mode according to a predetermined speed value of a vehicle speed sensor after the engine of the vehicle is started and while the vehicle is running. The steering speed and the motor speed are calculated from the output of the steering angle sensor and the value of the rotation angle sensor every time the control means and the control of the front wheel steering that is repeated in the front wheel steering mode are performed. The first diagnostic means for diagnosing whether or not the front wheel electromagnetic clutch is securely connected, and the output of the rear wheel steering angle sensor and the rotation angle sensor for each control of the rear wheel steering repeated in the rear wheel steering mode. It is characterized by further comprising a second diagnosis means for obtaining the position of the motor and the rear wheel steering angle position from the value and comparing both the positions to diagnose whether or not the connection of the rear wheel electromagnetic clutch is reliable.

According to a second aspect of the present invention, there is provided one motor, a front-wheel electromagnetic clutch, and a rear-wheel electromagnetic clutch for transmitting the output of the motor to the front-wheel steering mechanism and the rear-wheel steering mechanism. The vehicle speed sensor, the motor rotation angle sensor and the motor drive current detection means, the steering angle sensor and torque sensor provided in the front wheel steering mechanism, the front wheel electromagnetic clutch drive current detection means, and the rear wheel steering mechanism In a front and rear wheel steering system for a vehicle having a wheel steering angle sensor and a rear wheel electromagnetic clutch drive current detection means, the output of each sensor is within a normal range at the start of use of the vehicle and when the controller is powered on. The sensor diagnostic means for determining whether or not the value of, and the front and rear electromagnetic clutches drive the motor in a control state in which the rotation is not transmitted,
The output of the rotation angle sensor and the motor drive current value are used to determine if there is no load.If it is determined that there is a load, the outputs of the rear wheel steering angle sensor, steering angle sensor and torque sensor are detected. Then, only the clutch-off diagnosis means for determining which electromagnetic clutch is abnormal and the electromagnetic clutch for the rear wheel are connected, and the values of the rear wheel steering angle sensor and the rotation angle sensor and the driving of the rear wheel electromagnetic clutch are driven. Based on the magnitude of the current value, the rear-wheel clutch connection diagnosis means for determining whether or not the rear-wheel clutch connection is reliable, and the magnitude of the drive current value of the front-wheel electromagnetic clutch with only the front-wheel electromagnetic clutch in the connected state. It is characterized by having an initial self-diagnosis means constituted by a front-wheel clutch connection diagnosis means for judging whether or not the front-wheel electromagnetic clutch is operating normally.

According to a third aspect of the present invention, there is provided one motor, a front wheel electromagnetic clutch and a rear wheel electromagnetic clutch, and the motor output is transmitted to the front wheel steering mechanism and the rear wheel steering mechanism. A front and rear wheel steering system for a vehicle having a vehicle speed sensor, a motor rotation angle sensor, and a motor drive current detecting means, wherein a front wheel steering mode and a rear wheel steering mode are set according to a predetermined speed value of the vehicle speed sensor after the engine is started and while the vehicle is running. Control means for controlling the front and rear wheel steering device by switching between the wheel steering modes and the motor drive current detection in the control state in which the rotation of both electromagnetic clutches is not transmitted while the control shifts from the front wheel steering mode to the rear wheel steering mode. Means for determining whether or not the front-wheel electromagnetic clutch is reliably disengaged based on the output of the means and the rotation angle sensor, and the rear-wheel steering mode to the front-wheel steering mode. While the two electromagnetic clutches are in a control state where the rotation is not transmitted, the second judging means for judging whether or not the disengagement of the rear wheel electromagnetic clutch is reliable by the output of the motor drive current detecting means and the output of the rotation angle sensor. And having.

[0008]

According to the first aspect of the invention, the assist torque is output from the motor to the front wheel steering mechanism as steering control in the front wheel steering mode. After that step is executed, the speeds calculated by the output result of the motor rotation angle sensor and the output result of the steering angle sensor are calculated and compared.If they match within an appropriate range, it is determined that the control was performed without abnormality. , Continue control. As the steering control in the rear wheel steering mode, the rotational force of the motor serves as a drive source of the rear wheel steering mechanism, and the motor is rotated by an angle corresponding to the front wheel steering. After that step is executed, the angle calculated by the output result of the rotation angle sensor of the motor and the output result of the rear wheel steering angle sensor is calculated and compared,
If the two match within an appropriate range, it is determined that the control is performed without abnormality, and control is continued. If any of them is determined to be abnormal, the clutch transmission is abnormal, so the warning lamp is turned on and the control is stopped.

According to the second aspect of the invention, when the front and rear wheel steering device is used for the first time, an initial check is performed immediately after the system is energized in order to check the condition of the entire device. First, it is detected whether the output value of each sensor is appropriate. Next, it is determined whether the motor is normal or not, and the motor is idled to determine whether the current value is within the no-load value range. Then each clutch is operated independently and the signal from each sensor is checked to see if the engagement is secure. If there is any abnormality, the warning lamp is turned on and the control is stopped.

According to the third aspect of the present invention, when the control switching between the front wheel steering mode and the rear wheel steering mode is performed, both clutches are disengaged. Therefore, the disengaged state of each clutch is confirmed by the output of the rotation angle sensor. Since the motor is in an unloaded state, rotate it to determine if the current value is within the unloaded state. If it is abnormal, the warning lamp will light up and control will be interrupted.

[0011]

As a result of the above operation, in the invention according to claim 1, since the system is constantly checked during the control, even if the system becomes abnormal, it can be detected immediately and may fall into a dangerous state. Absent. According to the second aspect of the invention, since the check is performed when the system is started, it is possible to avoid a dangerous state. According to the third aspect of the invention, the system is checked even when the control is switched, so that the control is switched. As described above, since the failure monitoring of the device works from the start of the control, it is possible to provide the front and rear wheel steering device having the control in which the safety is considered in consideration of the fail safe.

[0012]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a configuration diagram of a front and rear wheel steering device for a four-wheel vehicle showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram schematically showing a power switching mechanism thereof. In FIG. 1, a steering wheel 1 is connected to a steering column (steering column) 3, and a steering wheel operation of a driver is transmitted to a front wheel steering mechanism 4 through a steering column 3 via a pinion in a pinion gear housing 5 and a rack gear mechanism. It has a structure to move wheels not shown. A steering angle sensor (steering sensor) 2 that detects the rotation of the steering wheel 1 is attached to the steering culvert 3. Further, here, the torque sensor 6 is mounted in the pinion gear housing 5, and two systems of main and sub are installed for safety. On the other hand, as shown in FIG. 2, the motor 7 is connected to the front wheel steering mechanism 4 via the front wheel clutch 8, the front wheel reduction gear 9, and the pinion rack gear mechanism 19, and the rear wheel clutch 10 and the rear wheel reduction gear 1 are connected.
1. The structure is such that it can be connected to the rear wheel steering mechanism 13 via the pinion / rack gear mechanism 20. A rear wheel steering angle sensor 12 is attached to the rear wheel steering mechanism 13 (FIG. 1). These mechanisms are controlled by an ECU (Electronic Control Unit) motor driver (hereinafter referred to as ECU) 15.
Therefore, wiring for energizing the electromagnetic clutches 8 and 10 and the motor 7 from the ECU 15 is formed, and the signals of the above-mentioned sensors are connected thereto. The signal from the vehicle speed sensor 14 mounted on the engine of the vehicle is also connected to the ECU 15.

With this steering mechanism, the motor 7 is connected to the front wheel steering mechanism 4 by the front wheel electromagnetic clutch 8 when the vehicle is stopped or running at a low speed, and when the driver operates the steering wheel 1, the front wheel steering mechanism 4 is operated. Based on signals from the torque sensor 6 attached to the included pinion gear housing 5 and the steering angle sensor (steering sensor) 2 attached to the steering column (steering column) 3, the motor 7 is operated so that the steering wheel 1 can be operated easily. Rotational force is used (front wheel power steering). Further, when the vehicle is traveling at medium and high speeds, the motor 7 is disconnected from the front wheel steering mechanism 4 and the rear wheel electromagnetic mechanism 1 is operated by the rear wheel electromagnetic clutch 10.
3 and the rear wheel steering is performed in accordance with the front wheel steering based on the output of the rear wheel steering angle sensor 12 (so-called 4WS,
Four-wheel steering). The output of the motor 7 is transmitted by the clutches 8 and 10, but is too high speed as it is, and thus is transmitted using the speed reducers 9 and 11. As can be seen from FIG. 2, since the steering angle is swung left and right, the motor 7 is of a type that reverses rotation.

Each sensor as shown in FIG. 3 is connected to the ECU 15, and the electric power of the motor 7, the front wheel electromagnetic clutch 8 and the rear wheel electromagnetic clutch 10 is controlled by the ECU 15. Therefore, these drive currents are also detected by the ECU 15. Among the sensors connected to the ECU 15, the non-contact photointerrupter type sensor is used because the steering angle sensor 2 and the rotation angle sensor 16 mounted in the motor have a structure that makes one rotation or more. . These sensors output the two-phase rectangular signals A and B shown in FIG. 4, and detect the amount of rotation and the direction of rotation by detecting the phase and counting the number of pulses. The rear wheel steering angle sensor 12 uses a potentiometer-type sensor here, and its output is regulated as shown in FIG. 5 (a). The output of the torque sensor 6 is also shown in FIG.
As shown in (b), the output range is also specified, and if there is a difference between the main and sub signals, it is not shown in the flowchart below, but it is detected and warned during control. Has become. As the vehicle speed sensor 14, a sensor that outputs a pulse signal for turning on / off the contact of the switch according to the vehicle speed is used.

Although the present apparatus functions as configured and operated as described above, a failure mode that is assumed to occur during the operation of the system at that time is conceivable. Therefore, control based on the self-diagnosis function that characterizes the present invention is performed. To execute. FIG. 6 shows it in a flowchart. First, when the driver turns on the ignition, the ECU 15 is started, an initial check described later is performed in step 6-1, and if normal, the power steering control mode in step 6-2 is entered. If the vehicle speed is equal to or lower than the predetermined value, the power steering control 6-22 is continued. Each time step 6-22 is completed, the control result is checked in step 6-24. When the predetermined vehicle speed is exceeded, in step 6-3 it is confirmed that the front wheel electromagnetic clutch 8 is disengaged, and then in step 6-4 the rear wheel steering control mode is entered. Again, the rear wheel steering control 6-42 is continued while the vehicle speed is higher than the predetermined value. Each time the control is completed once, the control result is checked in step 6-44. When the vehicle speed decreases and becomes equal to or lower than the predetermined value, after confirming the disengagement of the rear wheel electromagnetic clutch 10 in step 6-5, the power steering control 6-2 is continued again. This flow indicates that the vehicle power is O
Continue until FF.

In the initial check step, it is inspected whether the system is normal. The steps are shown in order in the flowcharts shown in FIGS. 7 to 11. First, the sensor itself is checked, and then the actuators are checked. When the initial check starts, first clear the internal check flag (7-1). In order to confirm the operation of the motor 7, the inspection is performed at a vehicle speed of 0 in order to ensure safety, so after checking whether the vehicle speed is 0 (7-2), first the rear wheel steering angle sensor 12 is normal. It is checked whether it is within the output range (7-3), then whether the torque sensor 6 is within the normal output range (7-4).
Go to step and set the corresponding check flag
(11-1) The warning lamp 17 is turned on and (11-4) the control ends. If it is normal, the motor 7 inspection mode shown in FIG. 8 is entered, and the motor 7 is driven with both clutches off (8-1) (8-2) Waiting for the start of rotation (8-3) Check the current value to see if the current is 0 (8-4)
, Check the abnormal condition of lock value or more (8-5), and
Check if it is in the no-load range that should be normal (8-6). If both are abnormal, the process moves to the step of FIG. 11 and a corresponding check flag is set and the warning ends. If it is not in the no-load range, it is assumed that both clutches 8 and 10 are engaged even though they are in the OFF state. Therefore, the rear wheel steering angle sensor 12 (8-7), the steering angle sensor 2, the torque sensor 6
(8-8) It is determined which clutch is abnormal, and the process proceeds to the step in FIG. If the motor 7 is normal, also check the output of the rotation angle sensor 16 attached to the motor 7 (8-9). If it is normal, the step of FIG. 9 is entered to check the rear wheel steering related. If the outputs of the steering angle sensor 2 and the torque sensor 6 do not match in step 8-8, it is determined that the steering angle sensor is abnormal, although not shown.

In FIG. 9, after stopping the motor 7 (9-1),
The rear wheel electromagnetic clutch 10 is turned on (9-2), first the driving current value of the clutch is checked (9-3), and if it is abnormal, it is checked whether the current is 0 (9-4) Go to step. If the current is normal, the output of the rear wheel steering angle sensor 12 is checked to determine whether it is in the neutral position (9-5). If it is not neutral, the motor is driven to the neutral position (9-6), and the This also determines whether drive control is normal (9-7). If it is in the neutral position from the beginning, slightly drive the motor (9-8) and check the movement and sensor output to determine whether it is functioning normally.
(9-9). If normal, return the rear wheels to the neutral position (9-10) and
Check the power steering side of 0. If abnormal, check the motor current (9-11). Even if it is determined in step 9-7 that the motor drive current is not in the neutral position, it is checked in step 9-11 whether the motor drive current is the lock value, and if abnormal, the process proceeds to the abnormality processing step in FIG. If it is the lock value, it is considered to be normal with the rear wheels fixed, and the process proceeds to FIG. After stopping the motor (10-1) in FIG. 10, the rear wheel electromagnetic clutch 10 is turned on.
FF (10-2), then turn on the front wheel electromagnetic clutch 8 (1
0-3), check the drive current value (10-4,5). At this time, confirming the connection state of the front wheel clutch can be understood by driving the motor, but at this point the vehicle is stopped and the power steering device will drive the front wheel steering mechanism. From the perspective of the driver, the steering wheel will move without permission, which may give the driver anxiety. Therefore, the connection status is not checked here only during traveling. If the clutch current is normal, the initial check ends. Then, the process proceeds to the steering control step at low speed.

The front wheel steering control step at low speed is shown in FIG.
It is shown in the flowchart of FIG. First check the vehicle speed (1
2-1) If the speed is equal to or higher than the predetermined speed, the front wheel steering control step is ended (12-7, 8). If the speed is less than the specified speed, turn on the front wheel electromagnetic clutch (12-2) and check the torque sensor value (1
2-3), the motor is driven according to the force applied to the steering wheel 1 by the driver's operation (12-4). Then, the speeds of the steering angle sensor 2 of the steering wheel 1 and the rotation angle sensor 16 of the motor shown in FIG. ), It is determined whether the value obtained by dividing the motor speed by the gear ratio, which is the deceleration relation of the front wheel steering mechanism 4, is equal to the steering speed value (12-
6). If they match, it means that the control was performed correctly, and the process returns to step 12-1 for checking the vehicle speed again. If the control is abnormal, the process proceeds to the step of FIG. 13, checks which part is abnormal (13-1, 2) and issues a warning (13-3 to 8), and terminates the control.

When the speed of the vehicle is increased and the vehicle is in a high speed state, the control is switched to the rear wheel steering mode by the signal from the vehicle speed sensor. Then, the disengagement check of the front wheel electromagnetic clutch is performed in the same manner as the initial check (see FIG. 8).
If there is no problem, the rear wheel steering control step is entered. 14 and 15 are flowcharts of the rear wheel steering control. First, it is confirmed whether the vehicle speed is equal to or higher than a predetermined threshold value (14-1), and if it is equal to or lower than the threshold value, the rear wheels are returned to the neutral position, which is not shown in the flowchart, and the rear wheel steering control step is ended (14- 10, 11). If the threshold is exceeded, turn on the electromagnetic clutch for the rear wheels (14-2) and check the value of the rear wheel steering angle sensor to see if it is normal (14-
3). When executing this step for the first time, it is necessary to know the absolute position of the motor, so the value obtained by multiplying the gear ratio from the value of the rear wheel steering angle sensor is stored (14-4,5).
This is because the motor rotation angle sensor outputs only relative values. As a result, it is used for control in correspondence with the rear wheel steering angle sensor. Then, the rear wheel steering amount corresponding to the front wheel steering amount is calculated from the signals of the steering angle sensor, the rotation angle sensor, and the vehicle speed sensor (14-6) and output to the motor (14-7).
If the motor position matches the value of the rear wheel steering angle sensor value × gear ratio, it is determined that the control was successful (14-8), the vehicle speed check is returned again, and the rear wheel steering control is continued. If there is an abnormality, check the rear wheel steering angle sensor (14-9), move to the warning step in Fig. 15 and set a check flag (15-1), disconnect the power (15-2, 3) and turn on the warning lamp. Then (15-4) the control is stopped and terminated.

As described above, in controlling this system,
According to the present invention, the initial self-diagnosis is performed because only the sensor included in the system includes the step of constantly monitoring the system at the beginning of use of the vehicle and during the running of the vehicle, and two clutches and sensors having particularly important functions. It was shown that the front and rear wheel steering control with high safety is performed by checking the control result and checking when the control is switched.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a motor drive switching mechanism.

FIG. 3 is a connection diagram of an ECU (electronic control unit).

FIG. 4 is an explanatory diagram showing output values of a steering angle sensor and a rotation angle sensor.

FIG. 5 is an explanatory diagram showing output values of a rear wheel steering angle sensor and a torque sensor.

FIG. 6 is a flowchart of the overall control of the present invention.

FIG. 7 is a flowchart of the initial check of the present invention. (Sensor diagnostic means)

FIG. 8 is a flowchart of the initial check of the present invention. (Clutch-off diagnosis means)

FIG. 9 is a flowchart of the initial check of the present invention. (Clutch connection diagnosis means for rear wheels)

FIG. 10 is a flowchart of the initial check of the present invention. (Clutch connection diagnosis means for front wheels)

FIG. 11 is a flowchart of the initial check of the present invention.

FIG. 12 is a flowchart of power steering control according to the present invention.

FIG. 13 is a flowchart of power steering control according to the present invention.

FIG. 14 is a flowchart of rear wheel steering control according to the present invention.

FIG. 15 is a flowchart of rear wheel steering control according to the present invention.

[Explanation of symbols]

1 steering wheel 2 steering angle sensor (steering sensor) 3 steering stalk (steering column) 4 front wheel steering mechanism 5 pinion gear housing 6 torque sensor 7 motor 8 electromagnetic clutch for front wheels 9 front speed reducer 10 rear wheel electromagnetic clutch 11 rear wheel speed reducer Machine 12 Rear wheel steering angle sensor 13 Rear wheel steering mechanism 14 Vehicle speed sensor 15 ECU (electronic control unit) motor drive 16 Rotation angle sensor 17 Warning lamp 19, 20 Pinion rack mechanism Step 6-2 (front wheel steering mode) Step 6- 4 (rear wheel steering mode) Step 6-1 and FIGS. 7 to 11 (initial self-diagnosis means) Step 6-24, and FIGS. 12 to 13 (first diagnosis means) Step 6-44, and 14 to 15 (second diagnosis means) Step 6-3 (first determination means) Flop 6-5 (second determination means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 117: 00 119: 00

Claims (3)

[Claims] 1. A structure having one motor, an electromagnetic clutch for front wheels and an electromagnetic clutch for rear wheels to transmit the output of the motor to a front wheel steering mechanism and a rear wheel steering mechanism, a vehicle speed sensor and the motor. In the front and rear wheel steering system of a vehicle having a rotation angle sensor, a steering angle sensor provided in the front wheel steering mechanism, and a rear wheel steering angle sensor provided in the rear wheel steering mechanism. And a control means for controlling the front and rear wheel steering device by switching between a front wheel steering mode and a rear wheel steering mode according to a predetermined speed value of the vehicle speed sensor, and a control of front wheel steering repeated during the front wheel steering mode. Each time, the steering speed and the motor speed are calculated from the output of the steering angle sensor and the value of the rotation angle sensor, and the contact of the front wheel electromagnetic clutch is determined by comparing the two speeds. A first diagnosis means for diagnosing whether or not is reliable, and the motor from the output of the rear wheel steering angle sensor and the value of the rotation angle sensor for each control of the rear wheel steering repeated in the rear wheel steering mode. And a rear wheel steering angle position, and a second diagnostic means for diagnosing whether or not the connection of the rear wheel electromagnetic clutch is reliable by comparing the both positions, and the front and rear of the vehicle. Wheel steering device. 2. A structure having one motor, an electromagnetic clutch for front wheels and an electromagnetic clutch for rear wheels to transmit the output of the motor to a front wheel steering mechanism and a rear wheel steering mechanism, a vehicle speed sensor and the motor. Rotation angle sensor and motor drive current detection means, steering angle sensor and torque sensor provided in the front wheel steering mechanism, front wheel electromagnetic clutch drive current detection means, rear wheel steering angle sensor provided in the rear wheel steering mechanism, In a front and rear wheel steering system for a vehicle having an electromagnetic clutch drive current detection means for the rear wheels, whether the output of each sensor is within a normal range when the control unit is powered on at the start of use of the vehicle. The sensor diagnosis means for determining whether or not the front and rear wheels, both of the electromagnetic clutches drive the motor in a control state in which the rotation is not transmitted, and the output of the rotation angle sensor is output. The motor drive current value is used to determine whether there is no load, and when it is determined that a load is applied, the output of the rear wheel steering angle sensor and the steering angle sensor and the torque sensor is detected to determine which electromagnetic Clutch-off diagnosis means for determining whether the clutch is abnormal, only the rear wheel electromagnetic clutch is in a connected state, the value of the rear wheel steering angle sensor and the value of the rotation angle sensor, and the drive current of the rear wheel electromagnetic clutch. The rear wheel clutch connection diagnosis means for determining whether or not the clutch connection is reliable based on the magnitude of the value, and only the front wheel electromagnetic clutch is in a connected state, and the driving current value of the front wheel electromagnetic clutch is determined according to the magnitude. Front and rear wheels of a vehicle having initial self-diagnosis means configured by front-wheel clutch connection diagnosis means for determining whether or not the front-wheel electromagnetic clutch is operating normally Rudder system. 3. A structure having one motor, an electromagnetic clutch for front wheels and an electromagnetic clutch for rear wheels to transmit the output of the motor to a front wheel steering mechanism and a rear wheel steering mechanism, a vehicle speed sensor and the motor. In a front-rear wheel steering system for a vehicle having a rotation angle sensor and a motor drive current detection means, a front-wheel steering mode and a rear-wheel steering mode according to a predetermined speed value of the vehicle speed sensor after the engine of the vehicle is started and while the vehicle is running. And a control means for controlling the front and rear wheel steering device by switching between the front and rear wheels, and the motor drive in a control state in which rotation of both the electromagnetic clutches is not transmitted while the control shifts from the front wheel steering mode to the rear wheel steering mode. First determination means for determining whether or not the front wheel electromagnetic clutch is reliably disengaged from the output of the current detection means and the output of the rotation angle sensor; and the rear wheel steering mode. While the control shifts from the front wheel steering mode to the front wheel steering mode, the electromagnetic clutches for the rear wheels are disengaged by the output of the motor drive current detection means and the output of the rotation angle sensor in a control state where both the electromagnetic clutches have not transmitted rotation. A front / rear wheel steering device for a vehicle, comprising: a second determination means for determining whether or not the vehicle is reliable.