JPH01301465A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve disconnecting reliability of a driving force transmission system using a clutch and to improve safety when abnormality occurs by interposing two clutches in a series in the driving force transmission system between an electric motor and a rear wheel steering member. CONSTITUTION:A clutch 48 is controlled by a control unit, so that when a designated abnormality occurs, a driving force transmission system between a servo motor 32 and a rear wheel steering shaft 30 is disconnected to let the rear wheel steering shaft 30 be free, whereby the steering shaft 30 is returned to the neutral position by centering spring means 36 to be put in the two-wheel state, thereby accomplishing fail-safe. The clutch 48 is a twin-electromagnetic clutch where two clutches are disposed in a series. An upper clutch 48A is of a normal-open type and a low clutch 48B is of a normal-close type.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle that steers the rear wheels by driving a rear wheel steering member connected to the rear wheels using an electric motor.

(Prior art) Vehicles include two-wheel steering (2ws) vehicles that steer the front wheels, and four-wheel steering (4ws) vehicles that steer the rear wheels along with the front wheels.
There is a vehicle.

As a rear wheel steering device in the above-mentioned four-wheel steering, for example, as described in Japanese Utility Model Application Publication No. 82-25277, a rear wheel steering member connected to the rear wheels is driven by an electric motor to steer the rear wheels. There are known electric motor-type devices that can be used in a similar manner.

In addition, in such an electric motor-type rear wheel steering device, the rear wheel steering is controlled exclusively electrically, so sufficient consideration must be given to fail-safe against abnormalities such as failure of this control system. JP-A-61-202
As described in Publication No. 977, a neutral position return means such as a centering spring is provided that always biases the rear wheel steering member toward a predetermined neutral position, and when an abnormality occurs, the biasing force of this neutral position return means is used. A device has been devised to return the rear wheel steering member to the neutral position, that is, to return the rear wheels to the neutral position (straight ahead position) to perform two-wheel steering.

(Problem to be Solved by the Invention) Various methods can be employed to return the rear wheel steering member to the neutral position when an abnormality occurs using the biasing force of the neutral position return means, one of which is as follows. As such, a clutch is installed in the drive power transmission system between the electric motor and the rear wheel steering member to connect and disconnect the transmission system, and when an abnormality occurs, the clutch disconnects the drive power transmission system to free the rear wheel steering member. A method can be considered in which the rear wheel steering member is returned to the neutral position by the urging force of the neutral position return means.

However, in this method of returning the rear wheel steering member to the neutral position using a clutch, there is a possibility that the on/off control, especially the disengagement control, may become impossible due to failure, seizure, disconnection, etc. of the clutch. If such a situation occurs, a problem arises in that the rear wheel steering member cannot be returned to the neutral position by the neutral position return means even when an abnormality occurs.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a rear wheel steering device for a vehicle that can return a rear wheel steering member to a neutral position using a clutch when an abnormality occurs, and that can sufficiently improve the reliability of returning to the neutral position. There is a particular thing.

(Means for Solving the Problems) In order to achieve the above object, a rear wheel steering device for a vehicle according to the present invention includes: a rear wheel steering member connected to a rear wheel; and a rear wheel steering member that is placed in a neutral position. a neutral position return means for biasing toward the neutral position; an electric motor for driving the rear wheel steering member against the biasing force of the neutral position return means to steer the rear wheels; and a space between the electric motor and the rear wheel steering member. The driving force transmission system is characterized by comprising two clutches arranged in series to connect and disconnect the driving force transmission system.

For example, if the two clutches are electromagnetic clutches, one is a normally closed clutch that connects the driving force transmission system when no power is applied, and the other is a normally open clutch that disconnects the driving force transmission system when no current is applied. It is better to configure it as a type clutch.

(Function) By arranging two clutches in series in the drive power transmission system between the electric motor and the rear wheel steering member as described above, even if one clutch becomes uncontrollable, for example due to sticking due to seizure, etc. Even if it becomes impossible to disconnect due to the above reasons, it becomes possible to disconnect the driving force transmission system using the other clutch. In other words, by using a double cutting system, cutting reliability can be greatly improved.

In addition, by arranging the two clutches, one of which is the normally open type electromagnetic clutch and the other is the normally closed type electromagnetic clutch, the disconnect reliability of the drive power transmission system is improved and power consumption is saved. be able to. In other words, the normally open type must be energized to connect, so if both clutches are normally open, it will be necessary to continue energizing both clutches under normal conditions (when no abnormality occurs), resulting in increased power consumption. .

On the other hand, if both clutches are of the normally closed type, there is no need to energize both clutches during normal times, making it possible to significantly save power consumption. However, if both are normally closed types, it becomes impossible to disconnect the driving force transmission system in both cases, for example, when the clutch power supply fails. Therefore, as mentioned above, by making one of them a normally closed type, it is possible to save power consumption, and by making the other one a normally open type, it can be disconnected even when the clutch power supply fails, improving disconnection reliability. can be done.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an overall outline of a four-wheel steering system according to an embodiment of the present invention, and FIG. 2 is a detailed cross-sectional view of a portion of the rear-wheel steering system shown in FIG.

The illustrated four-wheel steering device includes a front wheel steering device 4 that steers left and right front wheels 2L, 2R, and a rear wheel steering device 8 that steers left and right rear wheels 6L, 6R.

The front wheel steering device 4 includes a front wheel steering shaft 14 that extends in the vehicle width direction and has both ends connected to a pair of left and right front wheels 2L and 2H via a pair of left and right tie rods IOL and IOR and knuckle arms 12L and 12R. and a steering shaft 20 having a pinion 16 at one end that meshes with rack teeth (not shown) formed on the steering shaft 14 and a steering wheel 18 at the other end. By operating the steering wheel 18, the front wheel steering shaft 14 is displaced in the vehicle width direction to steer the front wheels 2L and 2R.

The rear wheel steering device 8 is rotated by a rear wheel steering shaft 30 that is a rear wheel steering member that connects the left and right rear wheels 6L and 6R, an electric servo motor 32 that is an electric motor, and the servo motor 32. Drive control of the pole screw means 34 for displacing the rear wheel steering shaft 30, the centering spring means 36 which is a neutral position return means for urging the rear wheel steering shaft 30 to return to the neutral position, and the servo motor 32. The rear wheel steering shaft 30, the pole screw means 34, the centering spring means 36, etc. are housed in a housing 40 fixed to the vehicle body (not shown) as shown in FIG. ing.

The rear wheel steering shaft 30 extends in the vehicle width direction, and has both ends connected to a pair of left and right rear wheels 6L via a pair of left and right tie rods 42L, 42R and knuckle arms 44L, 44R.
6R, and the stroke displacement of the rear wheel steering shaft 30 in the vehicle width direction (axial direction) causes the rear wheel 6L.

6R is steered.

Stroke displacement of the rear wheel steering shaft 30 in the axial direction is performed by the servo motor 32. That is, the servo motor 32 is composed of a step motor, and is driven and controlled by the control unit 38, and the brake 4 is controlled by the control unit 38.
6. Rotation is transmitted to the pawl screw means 34 through a driving force transmission system consisting of a clutch 48 and a reduction gear 50, and the rotation is transmitted to the rear wheel through the pawl screw means 34 against the biasing force of the centering spring means 42. The steering shaft 30 is configured to be driven from a neutral position, that is, to be subjected to stroke displacement.

The brake 46 is controlled by the control unit 38 and is connected to the servo motor 32 and the rear wheel steering shaft 30.
The rear wheel steering shaft 30 is held in a predetermined displacement state by locking the driving force transmission system between the rear wheel steering shaft 30 and the rear wheel steering shaft 30.

That is, during steady steering (when the target steering angle does not change), it is necessary to maintain the rear wheel steering shaft 30 in a predetermined displacement state, but this is done by the brake 46 instead of the servo lock by the servo motor 32. This is an attempt to save power consumption.

The clutch 48 is controlled by the control unit 38, and when a predetermined abnormality occurs, disconnects the driving force transmission system between the servo motor 3z and the rear wheel steering shaft 30, freeing the rear wheel steering shaft 30, and thereby frees the rear wheel steering shaft 30. The steering shaft 30 is returned to the neutral position by the centering spring means 3B, and the 2WS
This is intended to provide a so-called fail-safe system.

The brake 46 and clutch latch 48 will be described in detail below with reference to FIG.

The brake 46 includes a disc 52 that is fixed to the output shaft 32a of the servo motor 32, and has a plurality of grooves extending radially on both sides of the disc 52, and the servo motor 32 of the disc 52.
Ring plate 5 having an uneven groove that engages with an uneven groove on the side
4, and a solenoid 58 that causes the ring plate 54 to be attracted to a suction plate 56 fixed to the housing 40. When the solenoid 58 is in the OFF state in which electricity is not energized, the ring plate 54 is allowed to freely rotate together with the disk 52. In the ON state where the solenoid 58 is energized, the ring plate 54 is attracted to the suction plate 5B while maintaining the meshing state with the disc 52, and the rotation of the disc 52, that is, the rotation of the output shaft 32a of the servo motor is Braking is applied to lock the output shaft 32a.

The clutches 48 are two twin electromagnetic clutches provided in series, with the upstream clutch 48A being a normally open type (disconnected when no current is applied), and the downstream clutch 48B being a normally closed type (connected when no current is applied). has been done. That is, the clutch 48A includes a ring plate 60 having an uneven groove that engages with an uneven groove on the downstream side of the disk 52, and a ring plate 60 that is attached to a disk 64 fixed to a rotating shaft 62 coaxial with the output shaft 32a. When the solenoid 66 is not energized, the connection between the ring plate 60 and the disk 64 is released, while when the solenoid 66 is energized, the ring plate 60 is disconnected from the disk 64. solenoid 6
6, and the ring plate 60 and the disk 64 are connected by surface contact. Note that the ring plate 60 is in a state of meshing with the disc 52.
, is maintained. Further, the clutch 48B is connected to the rotating shaft 6
a ring plate 70 spline-coupled to a hub 68 fixed to the ring plate 2; a pad 74 that contacts the downstream surface of the ring plate 7o and presses the ring plate 70 upstream by the spring force of the spring 72; This pad 7
A rotating shaft 76 coaxial with the rotating shaft 62 contacts the upstream surface of the ring plate 70 so as to restrict movement of the ring plate 70 pressed by the ring plate 4 to the upstream side by more than a predetermined amount.
It consists of a drum 78 fixed to the drum 78 and a solenoid 80 that sucks the pad 74 from the downstream side to release the ring plate 70 from pressing the drum 78. In the OFF state where the solenoid 80 is not energized, the ring plate 70 The ring plate 70 and the drum 78 are connected by surface contact, and in the ON state where the solenoid 80 is energized, the ring plate 70 and the drum 78 are disconnected from each other.

The rotation of the output shaft 32a caused by the operation of the servo motor 32 is transmitted to the pole screw means 34 only when the brake 46 and clutch 48B are OFF and the clutch 48A is ON, but under normal conditions Rear wheel steering is performed in this state.

The pole screw means 34, as shown in FIG. 82 is fixed to a gear 88 that meshes with the reduction gear 50 and rotates integrally with the gear 88, and cannot be displaced in the axial direction of the steering shaft 30, so that the servo motor 32 rotates the pole nut 82. and the steering shaft 30 accordingly.
is subjected to a stroke displacement in the axial direction.

The centering spring means 36, as shown in FIG.
A pair of stoppers 90 and 92 are provided on the steering shaft 30 at a predetermined interval, and both stoppers 9 are loosely fitted on the steering shaft 30.
a pair of spring receivers 94.9 disposed within 0.92 mm and whose movement in the expansion direction is regulated by both stoppers 90.92;
8, a centering spring 98 disposed in a compressed state between both spring receivers 94.98, and the stopper 90.92 in a state where both the spring receivers 94.96 are in contact with the stoppers 90.92. Similarly, housing-side stopper portions 100 and 102 are provided which abut against both spring receivers 94 and 96 in order to restrict the movement of both spring receivers 94 and 96 in the expansion direction. Further, one of the stoppers 92 is connected to the steering shaft 30.
The one housing-side stopper part 102 is formed on a screw cap member 104 screwed to the housing 40, so that by adjusting the screwing amount of the stopper 92 and the screw cap member 104, The compressive load (preset load) of the centering spring 98 can be set appropriately, and the set preset load always biases the steering shaft 30 toward the neutral position. Note that this preset load needs to be large enough to at least overcome the side force during cornering.

The rear wheel steering by the servo motor 32 is controlled by the control unit 38 as described above.

The rear wheel steering control by the control unit 38 is performed in response to the vehicle speed, and an example of changing the steering ratio (rear wheel steering angle/front wheel steering angle) according to the vehicle speed is as shown in FIG. There are cases. When the control characteristics shown in the figure are applied, the rear wheel steering angle relative to the front wheel steering angle will be larger than the vehicle speed (
As the phase increases, the phase changes toward the same phase direction, and this situation is shown in FIG.

In order to perform such rear wheel steering control, signals from the steering wheel angle sensor 1101, vehicle speed sensor 112, and rotary encoder 114 that detects the rotational position of the servo motor 32 are input to the control unit 38. Then, a target rear wheel steering angle is calculated based on the steering wheel steering angle (theoretically equal to the front wheel steering angle) and the vehicle speed, and a control signal corresponding to the required rear wheel steering angle is output to the servo motor 32. . The rotary encoder 114 constantly monitors whether or not the servo motor 32 is operating properly, that is, the rear wheels 6L and 6R are steered under feedback control.

The control unit 38 controls the servo motor 3.
2, a brake 46 and a clutch 48 as described above.
It also controls the operation of the

As described above, the brake 46 is controlled to lock the output shaft 32a of the servo motor during steady steering to maintain the rear wheel steering shaft 30 in a predetermined displacement state, and the clutch 48 is controlled as described above when a predetermined abnormality occurs. This is done so that the rear wheel steering shaft 30 is returned to the neutral position by the centering spring means 36 as a disconnection state at the time of occurrence.

Note that in controlling the clutch 48, both clutches 48A and 48B may be in a connected state during normal times, and both clutches 48A and 48B may be in a disengaged state when a predetermined abnormality occurs, or either one may be in a disengaged state. You may also do this.

In addition, in the rear wheel steering device in this embodiment, when an abnormality occurs in the rear wheel steering device, the rear wheels are placed in the neutral position (straight-ahead position).
The control unit 88 performs fail-safe control to return the vehicle to a two-wheel steering state, and two modes are set for the fail-safe control.

In the first fail-safe control mode, as described above, the clutch 48 is disengaged and the centering spring means 36
This control is performed by the servo motor 32 and the control unit 38.
This is performed when rear wheel control by the servo motor 32 is impossible, such as in the case of a failure of the encoder 114 or the like.

In the second fail-safe control mode, the servo motor 32
This control returns the rear wheels to the neutral position by using the servo motor 32 and the control, although it is difficult to perform appropriate four-wheel steering control as in the case of a failure of the vehicle speed sensor system or steering angle sensor system. This is performed when the unit 38, encoder 114, etc. are normal, and therefore the servo motor 32 can return the rear wheels to the neutral position.

The control unit 38 includes a front wheel steering angle sensor 118 relative to the steering wheel steering angle sensor 110 in order to improve reliability of rear wheel steering control and to reliably detect various abnormalities (failures) in the rear wheel steering device. A second vehicle speed sensor 118 is added to the vehicle speed sensor 112, and a rear wheel steering angle sensor 120 is added to the encoder 114 to detect the rear wheel steering angle based on the displacement of the rear wheel steering shaft 30. Therefore, the vehicle speed signal, front wheel steering angle signal, and rear wheel steering angle signal are configured to be inputted twice, and various other signals, ie, the neutral clutch switch 12
2, inhibitor switch 124, brake switch 1
ON/OFF from 26 and engine switch 128
It is configured so that a signal indicating the presence or absence of power generation from the L terminal 130 of the alternator is input.

The rear wheel steering angle sensor 120 is constituted by a potentiometer, and as shown in FIG.
It is installed to detect the amount of rotation of the Furthermore, failure detection based on input signals from the various sensors and switches mentioned above can be carried out as appropriate, and the detection method itself is not directly related to the present invention, so a detailed explanation thereof will be omitted. .

FIG. 5 is a block diagram showing the above control system. The microprocessor 150 has a dual structure of I and
18 and switches 122, 124, 126.12
8 and the alternator terminal 130 are inputted via the buffer 152, and the sensors 110,
11[1, 120 is input via the A/D converter 154, and the signal from the low-resolution encoder 114 is input via the interface 156. On the other hand, the signals generated in microprocessor 150 are sent to servo motor 32 via motor drive circuit 158,
It is also sent to the brake 46 via the brake drive circuit 160 or to the clutch 48 via the clutch drive circuit 162. This rear wheel steering control is started on the condition that the signal from the alternator terminal 130 becomes high (Hl). In addition, the reference numeral 132 in the figure indicates the microprocessor 150 when an abnormality occurs.
This is a warning lamp that is turned on when a base current is caused to flow through the transistor 166.

Further, reference numeral 168 is a battery, 170 is an ignition key switch, and 172 is a relay. When an abnormality occurs in the first fail-safe mode described above, the relay drive circuit 174 is activated to stop supplying electricity to the coil 176, and as a result, When the contacts of the relay 172 are switched, the power supply to the motor drive circuit 158 is stopped and the warning lamp 132 is turned on without going through the transistor 166.

FIG. 6 is a diagram showing a drive circuit portion of the normally open type clutch 48A in the clutch drive circuit 162.

In the drive circuit portion, a microprocessor 150
A control signal for the clutch 48A is output from the output section of the clutch 48A.

This control signal is a clutch connection signal (Hi level signal)
and the clutch disconnection signal (Lo level signal), and when the clutch connection signal is output, each transistor 200,
202 and 204 are turned on, and as the transistor 204 is turned on, current flows from the power supply 206 to the solenoid 66 of the clutch 48A, and the ring plate 60 is attracted by the excitation of the solenoid 66, so that the clutch 48A is connected. Furthermore, when the clutch disengagement signal is output, each transistor 200, 202, 204 is off, so no current flows through the solenoid 66, the ring plate 60 is not attracted, and the clutch 48A is disengaged.

Further, a monitor circuit 208 is provided in this drive circuit portion. This monitor circuit 208 is a transistor 204
A predetermined point 210 on the energized line between and the solenoid 66
and the input section of the microprocessor 150, and when the clutch connection signal is output from the output section and the solenoid 6B is energized, the predetermined point 210 is set to Lo.
Therefore, the transistor 212 is off, and therefore a <Hi level signal is input to the input section of the microprocessor 150 based on the power supply 214, and
When the clutch disengagement signal is output and the solenoid 66 is not energized, the predetermined point 210 is at Hi level, so the transistor 212 is turned on, and current flows from the power supply 214 through the transistor 212, so that no current is applied to the input section. is configured so that a Lo rerel signal is input.

The monitor circuit 208 as described above is attached, and when the output section of the microprocessor 150 outputs a clutch connection signal (Hi level signal), for example, once every 10 seconds, as shown in FIG. 7A. The signal is inverted for 0.1 seconds to output a clutch disengagement signal (L level signal). By doing so, in the event that the power supply 206 fails for some reason, the solenoid 66 is disconnected, or the energizing line to the solenoid 66 is disconnected and the solenoid 66 is not energized, this will be prevented. can be detected. That is, in the monitor circuit 208, when the clutch is connected, a clutch connection signal is output from the output section of the microprocessor 150, and in this case, the potential at the predetermined point 210 is Lo rerel, and the failure of the power supply 208 as described above is detected. Even if this occurs, the potential at the predetermined point 210 is at the L0 level. Therefore, simply continuing to output the clutch connection signal will cause the monitor input to the input unit to fail even if the power supply 206 fails when the clutch is connected. The signal is still a Hi-level signal, so such a power failure cannot be detected. However, if the clutch disconnection signal is output for 0.1 seconds once every 10 seconds as described above, the monitor signal will be . level, and if a power supply failure occurs during the process, the monitor signal level is used when the clutch disconnection signal is output. level. Therefore, by providing the monitor circuit 208 as described above and inverting the control signal for a short time every predetermined time interval, it is possible to detect a failure of the power supply. Note that even if the control signal is reversed as described above, the clutch disconnection signal output time is extremely short, so the clutch 48A will not be disconnected due to mechanical response delay.

Although the drive circuit portion of the normally open type clutch 48A has been described above, the drive circuit portion of the normally closed type clutch 48B is also configured in exactly the same manner. However, in the case of the normally closed clutch 48B, a L0 level signal is output as a clutch connection signal, and a Hi level signal is output as a clutch disconnection signal. Furthermore, it serves as a clutch connection signal. When outputting a level signal, as shown in Figure 7B, the signal is inverted for 0.1 seconds once every 10 seconds and a clutch disengagement signal (Hi level signal) is output, as in the case above. has been completed. By doing so, it is possible to detect a failure of the transistors 200, 202, 204 when the clutch is connected. In other words, in the case of a normally closed type clutch, the connection signal is used when the clutch is connected. A level signal is output, and the potential at the predetermined point 210 is Hi level,
Monitor signal beam. It becomes a level signal. In that case, even if the transistors 200, 202, and 204 fail, the potential at the predetermined point 210 remains at Hi level,
Therefore, the monitor signal remains the same. It remains a level signal.

Therefore, when the clutch is connected, the above transistor 200°2
Even if 02, 204 fails, the failure cannot be detected if it simply continues to output the clutch connection signal, but if the control signal is reversed at predetermined time intervals as described above, the above Transistors 200, 202,
When 204 is normal, the monitor signal becomes a Hi level signal when the inverted signal is output, but if a failure occurs, the monitor signal becomes a Lo rerel signal even when the inverted signal is output, and it is therefore difficult to detect the failure. can.

Note that the above-mentioned outskirts monitor circuit is the motor drive circuit 158.
and the brake drive circuit 180 as well.

In the above embodiment, as described above, the centering spring means 3B is provided on the rear wheel steering shaft 30, and the clutch 48 is provided in the driving force transmission system between the servo motor 32 and the rear wheel steering shaft 30, and the centering spring means 3B is provided on the rear wheel steering shaft 30. When an abnormality occurs, the clutch 48 disconnects the driving force transmission system, and the centering spring means 36 returns the rear wheel steering shaft 30 to the neutral position, resulting in a two-wheel steering condition.

The two clutches 48 are arranged in series and are composed of a normally open type clutch 48A and a normally closed type clutch 48B, thereby improving the disconnection reliability of the driving force transmission system and reducing power consumption. This makes it possible to achieve both savings.

That is, by providing two clutches in series, cutting reliability can be greatly improved. In other words, by providing two clutches in series, even if one of the clutches becomes unable to disconnect due to various reasons such as sticking due to seizure, the other clutch can disconnect the driving force transmission system. , cutting reliability can be significantly improved.

Furthermore, by configuring the two clutches as a normally open type and a normally closed type, it is possible to improve disconnection reliability and save power consumption.

In other words, both clutches must be in a connected state under normal conditions, and in a normally open type clutches, electricity must be applied in order to connect them, so if both clutches are normally open types, it is necessary to continue energizing both clutches during normal times. This results in high power consumption.

In devices such as this rear wheel steering device that use an electric motor to steer the rear wheels, since the electric motor consumes a large amount of power, there is a need to save as much power as possible in other devices. It is not appropriate to make both of them normally open type from the viewpoint of saving power consumption. On the other hand, if both of the above-mentioned clutches are of the normally closed type, there is no need to energize them in order to bring them into the normally connected state, which is extremely advantageous in terms of saving power consumption.

However, if both clutches are normally closed, if the clutch power supply fails, the energizing line to both clutches is disconnected, the coverlet comes off, etc., and it becomes impossible to energize both clutches, both clutches will be disconnected. cutting reliability decreases. Therefore, by making one of them a normally open type and the other a normally closed type as described above, it is possible to both improve cutting reliability and save power consumption.

(Effects of the Invention) In the vehicle rear wheel steering system according to the present invention, two clutches are interposed in series in the driving force transmission system between the electric motor and the rear wheel steering member as described above. This greatly improves the cutting reliability of the drive force transmission system, thereby improving safety in the event of an abnormality.

Furthermore, by using the two clutches as a normally open type and a normally closed type, it is possible to improve the disconnection reliability of the driving force transmission system and to save power consumption.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a schematic diagram showing an example of a four-wheel steering device equipped with an embodiment of the present invention, and Fig. 2 is a sectional view showing details of the rear wheel steering device portion in Fig. 1. , Fig. 3 and Fig. 4 are diagrams showing an example of rear wheel steering control, Fig. 5 is a block diagram of a control unit portion for rear wheel steering control, Fig. 6 is a diagram showing a clutch drive circuit, Fig. 7A and FIG. 7B is a diagram showing an example of a clutch control signal. 6L, 6R...Rear wheel 8...Rear wheel steering device 30
...Rear wheel steering member 32...Electric motor 48.
...Latch 48A...Normally open type clutch 48B...
Normally closed type clutch Fig. 1 +20 Fig. 3 Fig. 5 Fig. 6 Fig. 78

Claims (2)

[Claims] (1) a rear wheel steering member connected to a rear wheel; a neutral position return means for biasing the rear wheel steering member toward a neutral position; and a biasing force of the neutral position return means to apply the rear wheel steering member to the neutral position return means. an electric motor that is driven in opposition to steer the rear wheels; and two clutches that connect and connect the driving force transmission system, which are arranged in series in the driving force transmission system between the electric motor and the rear wheel steering member. A rear wheel steering device for a vehicle, comprising: (2) One of the two clutches mentioned above is a normally closed type clutch that connects the driving force transmission system when no power is applied, and the other is a normally open type clutch that disconnects the above driving force transmission system when no current is applied. Claim 1 characterized by
Rear wheel steering device for the vehicle described.