JP2686956B2 - Vehicle rear wheel steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering device for turning a rear wheel using an electric motor as a drive source.

(Prior Art) In a vehicle including a four-wheel steering device that also steers the rear wheels in response to front-wheel steering, a rear-wheel steering device for steering the rear wheels is required. As the rear wheel steering device, a device using hydraulic pressure or a motor as a drive source for rear wheel steering is conventionally known, and the latter is disclosed in, for example, Japanese Utility Model Laid-Open No. 62-25277. ing.

The electric motor type rear wheel steering device generally displaces rear wheel steering means such as a rear wheel steering rod connected thereto by driving an electric motor to drive the rear wheels as described in the above publication. Since it is configured to steer, it is possible to perform finer control of the rear wheel steering compared to the hydraulic type. On the other hand, since the control of the rear wheel steering is performed exclusively electrically, it is necessary to give sufficient consideration to the fail-safe against the abnormality such as the failure of the control system. Therefore, conventionally, as disclosed in JP-A-61-202977, a neutral position returning means such as a centering spring for always biasing the rear wheel steering means toward a predetermined neutral position is provided. The urging force of the neutral position returning means has been devised so that the rear wheel steering means displaced from the neutral position can be returned to the neutral position.

Therefore, in the electric motor type rear wheel steering device, the displacement of the rear wheel steering means from the neutral position by the electric motor must be performed against the biasing force of the neutral position returning means. Further, under a predetermined traveling condition, it is necessary to hold the rear wheel steering means in a state of being displaced from the neutral position by a predetermined amount (that is, to hold the steering wheel). It is necessary to supply a sufficient current to the electric motor to withstand the urging force of the position returning means, and if the steering is held for a long time, the current consumption is large, which may cause problems such as battery exhaustion. On the other hand, the rear wheel steering means is locked so that the rear wheel steering means is held in a predetermined displacement state, so that it is possible to appropriately switch from the steering by the electric motor to the steering by the steering means. If so, it is possible to reduce the current consumption amount and solve the above inconvenience.

(Problems to be Solved by the Invention) However, since the rear wheel steering means displaced by a predetermined amount from the neutral position is always urged toward the neutral position by the neutral position returning means, the steering from the steering by the electric motor to the steering holding means. It is possible that the biasing force may cause the rear wheel steering means to be displaced toward the neutral position during a slight delay in the operation response when switching to steering holding by the steering wheel and vice versa. There is a risk that a deviation will occur in the wheel steering control.

The present invention has been made in view of such circumstances, and even if the steering of the rear wheel steering means is switched between the electric motor and the steering means, the switching causes a shift in the rear wheel steering control. It is an object of the present invention to provide a rear wheel steering system for a vehicle capable of preventing the above.

(Means for Solving the Problem) In the vehicle rear wheel steering system according to the present invention, the rear wheel steering means is held by both the electric motor and the steering holding means for a predetermined time during the switching. The above-mentioned purpose is achieved. That is, as shown in FIG. 1, a rear wheel steering means that is connected to the rear wheel and steers the rear wheel by displacing the rear wheel, and always urges the rear wheel steering means toward a predetermined neutral position. Neutral position returning means,
The rear wheel steering means is connected to the rear wheel steering means, and the rear wheel steering means can be displaced from the neutral position against the biasing force of the neutral position returning means, and the rear wheel steering means can be held in a predetermined displacement state. An electric motor, and a steering holding means that locks the rear wheel steering means and holds the rear wheel steering means in the predetermined displacement state,
Switching means for switching holding of the predetermined displacement state between the electric motor and the steering holding means, the switching means holding the predetermined displacement state from one of the electric motor and the steering holding means to the other. When switching to, the holding of one of the two is released after a predetermined lap time set in advance after the start of the holding by the other.

As long as the above-mentioned "holding means" can lock the rear wheel steering means, the lock position or the like with respect to the rear wheel steering means is not limited at times, and for example, as a configuration for locking the rear wheel steering means itself. Or the output shaft of the electric motor,
Alternatively, the rear wheel steering means may be locked by locking the connecting mechanism between the electric motor and the rear wheel steering means.

The above "predetermined lap time" means that the steering operation of the rear wheel steering means by the steering holding means (or the electric motor) is completed when the steering holding is switched from the electric motor (or the steering holding means) to the steering holding means (or the electric motor). The length is not particularly limited as long as it is a sufficient time.

(Operation) As shown in the above configuration, the electric motor and the steering holding means are provided as means for holding (holding) the rear wheel steering means in a predetermined displacement state, and the steering holding can be switched between the two by the switching means. Therefore, it is possible to stop the power supply to the electric motor that consumes a large current to save power by appropriately changing the steering holding, and to keep the predetermined displacement state of the electric motor and the steering holding means. When switching from one to the other, the holding of the one is canceled after a predetermined lap time set in advance after the start of the holding by the other, and as a rule, a predetermined time (the predetermined lap time) Since the steering is lapped, the rear wheel steering means is displaced by the urging force of the neutral position returning means even if there is some operational response delay during the switching. You can eliminate the fear.

(Effects of the Invention) Therefore, according to the present invention, it is possible to prevent the rear wheel steering control from deviating due to the steering control switching, thereby obtaining the power saving effect by utilizing the steering control means and then the rear wheel control. The rudder control can be smoothly performed.

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

2 and 3 are an overall configuration diagram showing an embodiment of a rear wheel steering device of a vehicle according to the present invention, and a detailed view of main parts thereof.

As shown in FIG. 2, the rear wheel steering device 2 constitutes a part of a four-wheel steering device that also turns the rear wheels in accordance with the front wheel turning, and includes a rear wheel turning device as a rear wheel turning means. Rudder rod 4,
A neutral position return means 6, a servomotor 8 as an electric motor,
A brake 10 as a steering holding means and a control unit 12 as a switching means are provided.

The rear wheel steering rod 4 extends in the vehicle width direction, and both ends thereof are connected to a pair of left and right rear wheels 18L, 18R via a pair of left and right tie rods 14L, 14R and knuckle arms 16L, 16R. The rear wheels 18L and 18R are steered by displacing the rear wheel steering rod 4 in the vehicle width direction.

The neutral position returning means 6 has a casing 22 attached to the rear wheel steering rod 4 and fixed to the vehicle body 20, as shown in detail in FIG. The spring supports 24a and 24b are loosely fitted, and these spring supports 2
A compression spring 26 is provided between 4a and 24b. The rear wheel steering rod 4 extends through the casing 22. The rear wheel steering rod 4 is formed with a pair of flanges 4a and 4b at intervals, and the spring supports 24a are formed by the flanges 4a and 4b. , 24b, and the rear wheel steering rod 4 is always attached by the compression spring 26 toward a predetermined neutral position (ie, a position where the rear wheels 18L, 18R are in a straight traveling state with a steering angle of zero). It is being rushed. The compression spring 26 has a spring force enough to overcome the side force during cornering.

The servo motor 8 is a stepping motor, and as shown in FIG. 3, its output shaft 8a is connected to a rear wheel steering rod 4 via a speed reduction mechanism 28 comprising a gear train 28a and a ball screw 28b.
As shown in FIG. 2, it is operated by a control signal from the control unit 12 to displace the rear wheel steering rod combination from the neutral position against the biasing force of the neutral position returning means 6, and The wheel-turning rod 4 can be held in a predetermined displacement state (that is, can be held).

The brake 10 is an electromagnetic brake, which is attached to the output shaft 8a of the servo motor 8 so that braking can be applied to the rotation of the output shaft 8a. (Consequently, the rear wheel steering rod 4) can be locked to hold the rear wheel steering rod 4 in a predetermined displacement state (that is, to maintain the steering). The operation of the brake 10 is controlled by the control unit 12. That is, when the rear wheel steering rod 4 is displaced by a predetermined amount from the neutral position by the servo motor 8, the brake 10 is operated to lock the output shaft 8a, so that the steering can be maintained even when the power supply to the servo motor 8 is stopped. This makes it possible to save power. In this way, the control unit 12 switches the steering holding between the servo motor 8 and the brake 10, which will be described in detail later. The brake 10 is also used when a predetermined abnormality occurs.

Between the output shaft 8a of the servo motor 8 and the gear train 28a, a clutch 30 for releasing the connection between the rear wheel steering rod 4 and the servo motor 8 is provided. The displaced rear wheel steering rod 4 can be returned to the neutral position by the urging force of the neutral position return means 6 when a predetermined abnormality occurs. The operation of the clutch 30 is controlled by the control unit 12.

FIG. 5 is a sectional view showing the brake 10 and the clutch 30 in detail.

The brake 10 is fixed to the output shaft 8a of the servomotor 8, and has a ring rate 34 having a concave-convex groove that meshes with the concave-convex groove on the servomotor 8 side of the disk 32 in which a plurality of concave-convex grooves extending radially are formed. , A solenoid 38 for attracting the ring plate 34 to a suction plate 36 fixed to the casing 35, and the solenoid 38 is not energized.
In the F state, the ring plate 34 is freely rotated together with the disc 32, while in the ON state where the solenoid 38 is energized, the ring plate 34 is attracted to the attraction plate 36 while maintaining the meshed state with the disc 32. The rotation of the disk 32, that is, the rotation of the output shaft 8a of the servomotor 8 is braked.

The clutch 30 is a twin clutch provided in series. The clutch 30A on the upstream side (the brake 10 side) is a normally open type, and the clutch 3A on the downstream side (the gear train 28a side)
0B is a normally closed type. That is, the clutch 30A includes a ring plate 40 having an uneven groove that meshes with the uneven groove on the downstream side of the disk 32,
40, a disk fixed to a rotating shaft 42 coaxial with the output shaft 8a
It consists of a solenoid 46 that is adsorbed on 44
In the OFF state where power is not supplied to 46, the ring plate 40
Is disconnected from the disk 44 and the solenoid 46
In the ON state where power is supplied to the ring plate 40, the ring plate 40 and the disk 44 are connected by surface contact.
Note that the ring plate 40 always maintains the meshing state with the disk 32. Further, the clutch 30B contacts the hub 48 fixed to the rotary shaft 42 and the ring plate 50 spline-coupled, and contacts the downstream surface of the ring plate 50 to move the ring plate 50 upstream by the spring force of the spring 52. A pad 54 that is pressed to the side, and contacts the upstream surface of the ring plate 50 so as to restrict the movement of the ring plate 50 pressed by the pad 54 to the upstream side by a predetermined amount or more,
The drum 58 fixed to the rotary shaft 56 coaxial with the rotary shaft 42 and the ring plate 50 are sucked from the downstream side, and the ring rate 50
In the OFF state where the solenoid 60 is not energized, the ring plate 50 and the drum 58 are connected by surface contact, and in the ON state where the solenoid 60 is energized, the ring plate The connection between the drum 50 and the drum 58 is released.

Therefore, the rotation of the output shaft 8a due to the operation of the servo motor 8 is transmitted to the gear train 28a only when the brake 10 and the clutch 30B are in the OFF state and the clutch 30A is in the ON state. Rear wheel steering is performed in this state. This, clutch 30
As a twin clutch in which two clutches 30A and 30B are provided in series, even if one of them becomes inoperable due to seizure, etc.
Servo motor 8 and gear train 28A by setting to F state
(Hence, the rear wheel steering rod 4) can be released from the coupling. One of the normally open type and the other is normally closed type is because the clutch 30A Normally open type clutches are required to release the above connection when power supply to the 30B and 30B is stopped, but both normally open type clutches are required to be in the ON state for power transmission in normal times. This is because power consumption is required extra.

As described above, as shown in FIG. 2, the control unit 12 controls the operation of the servo motor 8, the brake 10 and the clutch 30, but the control by the control unit 12 is the same. As shown in the figure, since the rear wheel steering system 2 constitutes a part of the four-wheel steering system, the rear-wheel steering system 2 is designed to perform a required four-wheel steering function.

The four-wheel steering system includes, in addition to the rear-wheel steering system 2, a front-wheel steering mechanism 70 and various sensors that send various information to the control unit 12 for appropriate rear-wheel steering control according to the traveling conditions. Be prepared.

The front wheel steering mechanism 70 extends in the vehicle width direction, and has a pair of left and right tie rods 72L, 72R and knuckle arms 74L, 74R at both ends.
Rack 7 connected to a pair of left and right front wheels 76L, 76R via 4R
8 and a steering shaft 84 provided with a pinion 80 meshing with a rack 78 at one end and a steering wheel 82 at the other end, and the steering wheel 82 is operated to move the rack 78 in the vehicle width direction. The front wheels 76L and 76R are steered by being displaced.

The rear wheel steering control by the control unit 12 is performed in response to the vehicle speed. 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. It may be. When the control characteristics shown in the figure are added, the rear wheel steering angle with respect to the front wheel steering angle changes in the same direction as the vehicle speed increases, and this is shown in FIG.

In order to perform such rear wheel turning control, the control unit 12 includes a steering wheel angle sensor 86, a vehicle speed sensor 88,
Also, a signal from the rotary encoder 62 that detects the rotational position of the servo motor 8 is input, and in the control unit 12, the 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. Is calculated, and a control signal corresponding to the required rear wheel turning amount is output to the servo motor 8. Then, while constantly monitoring whether or not the operation of the servo motor 8 is proper by the rotary echoda 62, that is, under the feedback control, the rear wheels 18L, 18L
The R is turned.

In the rear wheel turning control, the control system has a double configuration for fail-safe. That is, the steering angle sensor 90 is added to the steering wheel steering angle sensor 86, the second vehicle speed sensor 92 is added to the vehicle speed sensor 88, and the rear wheel steering is performed with respect to the rotary encoder 62 rather than the clutch 30. A rear wheel steering angle sensor 64 for detecting the mechanical displacement of the member on the rod 4 side is added, and the rear wheel steering angle is detected only when both of the three corresponding sensors detect the same value. I am supposed to do it. Therefore, when the vehicle speed detected by the first vehicle speed sensor 88 and the vehicle speed detected by the second vehicle speed sensor 92 are different from each other, for example, an abnormality (failure) occurs, , The rear wheels 18L and 18R are held at the neutral position.

Further, for detection of various abnormalities, ON / OFF signals from the switches 94, 96, 98, and 100 are input to the control unit 12, and a signal indicating the presence or absence of power generation is input from the L terminal 102 of the alternator. . Here, the switch 94 is a neutral clutch switch, the switch 96 is an inhibitor switch, the switch 98 is a brake switch, and the switch 100 is an engine switch. Here, in the vehicle equipped with a manual transmission, the neutral switch 94 outputs an OFF signal when the shift position of the manual transmission is in neutral or when the clutch pedal is depressed, and otherwise outputs an ON signal. Has become. In a vehicle equipped with an automatic transmission, the inhibitor switch 96 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 98 outputs an ON signal when the brake pedal is depressed, and the engine switch 100 outputs an ON signal when the engine is operating.

FIG. 8 is a block diagram showing the control system.

The microprocessor 104 has a dual structure of I and II, and the microprocessor 104 includes vehicle speed sensors 88 and 92.
And switches 94, 96, 98, 100 and alternator L
A signal from the terminal 102 is input via the buffer 106, a signal from the sensor 86, 90, 64 is input via the A / D converter 108, and a signal from the rotary encoder 62 is input via the interface 110. Is done. Microprocessor 1
The signal generated at 04 is sent to the servomotor 8 via the motor drive circuit 112, and the brake drive circuit 11
It is delivered to the brake 10 via 4 or to the clutch 30 via the clutch drive circuit 116. The rear wheel turning control is started on condition that the signal from the L terminal 102 of the alternator becomes high (Hi). In the figure, reference numeral 118 denotes a battery, 120 denotes an ignition key switch, and 122 denotes a relay.When a predetermined abnormality occurs, the energization of the coil 126 is stopped by the operation of the relay drive circuit 124. The contact is switched, the power supply to the motor drive circuit 112 is stopped, and the warning lamp 128 is turned on. Also,
When an abnormality other than the above occurs, the microprocessor 104 supplies a base current to the transistor 130 to turn on the warning lamp 128.

Next, the servo motor 8 by the control unit 12 is used.
A description will now be given of steering switching control between the brakes 10 and the brakes 10.

As shown in the timing chart of FIG. 9, a control signal corresponding to the target rear wheel steering angle θ _TR (calculated based on the steering wheel steering angle and the vehicle speed) is output to the servo motor 8 to drive it ( (Servo drive), the rear wheel steering rod 4 is displaced from the neutral position, and thereby the control is performed so that the actual rear wheel steering angle θ _R (detected by the rear wheel steering angle sensor 64) matches the target rear wheel steering angle. . Then, the target rear wheel steering angle θ _TR
Becomes a constant value, and when the rear wheel actual steering angle θ _R becomes a value that matches this, the current value supplied to the servo motor 8 is kept constant (servo lock), whereby the rear wheel steering rod 4 is displaced by a predetermined value. The state is maintained, that is, the steering is held. When this steering holding state is continuously performed for a predetermined time under a predetermined condition described later, the brake 10 is turned on to perform the steering holding by the brake 10. When a predetermined lap time T that has been set in advance has elapsed from the start of the steering operation by the brake 10, the power supply to the servo motor 8 is stopped and only the steering operation by the brake 10 is continuously performed.

Since the servomotor 8 is in the OFF state while the steering is being performed by the brake 10 alone, the rear wheels cannot be steered immediately in response to a change in running conditions. Therefore, when a change in traveling conditions is expected, power is supplied to the servo motor 8 again, and both the servo motor 8 and the brake 10 are held until the lap time T elapses, and then the brake 10 is released. Is turned off and only the steering holding by the servo motor 8 is performed, so that the rear wheels can be quickly steered by driving the servo motor 8.

In this way, by maintaining the rear wheel steering angle at a constant and for the time being, it is considered that the rear wheel is not to be steered by the brake 10, only the brake 10 is used. It is not necessary to supply power to the servo motor 8 that consumes a large current, thereby saving power. Further, when the steering holding is switched between the servo motor 8 and the brake 10, by providing the lap time T in which the steering holding is performed by both of them, the steering can be held by at least one of them even if some operation response delay occurs at the time of switching. Because it will be
It is possible to prevent the disadvantage that the rear wheel steering rod 4 is displaced by the spring force of the neutral position return means 6. The lap time T may be set to about 0.1 seconds if the operation response delay is about 0.02, for example.

FIG. 10 is a flow chart showing a control example of the steering holding switching between the servo motor 8 and the steering holding means 10.

Steering by brake 10 (hereinafter referred to as brake steering)
Is performed only when the predetermined conditions are satisfied by the determinations from S1 to S10.

At S1, it is determined whether the actual rear wheel steering angle θ _R matches the target rear wheel steering angle θ _TR . In other words, if they do not match, it is necessary to continue the servo drive, so that brake steering is prohibited.

In S2, it is determined whether or not the target rear wheel steering angle displacement amount _TR is zero. That is, when the target rear wheel steering angle θ _TR changes, the servo drive is performed accordingly, and thus the brake holding is prohibited.

In S3, it is determined whether the brake (for vehicle braking) drive circuit 114 is normal, and if abnormal, the brake steering is prohibited. In addition, the determination of whether it is normal,
This is performed by an ON (12v) and OFF (0V) monitor signal input to the microprocessor 104 from a monitor circuit provided in the brake circuit 114.

At S4, it is determined whether the wheels are locked. That is, the wheel locking phenomenon occurs due to a sudden braking operation (the braking operation here is a braking operation by depressing the brake pedal, not the brake 10). In such a case, the rear wheel rolling caused by the steering wheel operation by the driver is performed. Since it is expected that rudder movement will be made,
Brake hold is prohibited. In addition, the determination that the wheels are locked satisfies all three conditions: the brake (vehicle) switch is ON, the vehicle speed signal (detected from the drive system) is zero, and the vehicle speed signal is 30 km or more before one count (sampling time 131 ms). Done when

At S5, it is determined whether or not the rapid increase is in progress.
That is, when the value of the vehicle speed signal increases sharply due to noise or chattering of the vehicle speed sensor 88, the vehicle speed signal may temporarily become constant thereafter. In order to avoid erroneous determination that they match, brake holding is prohibited when it is determined that the vehicle speed is rapidly increasing. It should be noted that the reason why the brake holding is prohibited during the rapid increase of the vehicle speed is that there is a high possibility that the tail swing phenomenon of the vehicle will occur due to the wheel spin and the correction steering for the phenomenon will be performed. The criterion for determining whether or not the vehicle speed is rapidly increasing is determined in consideration of whether or not the increase in vehicle speed is abnormally large in view of the followability of the vehicle to a normal accelerator operation.

In S6, it is determined whether the vehicle speed signal is 40 km or more. In other words, in the high speed region, fine steering operation is repeatedly performed and the responsiveness is also required for the rear wheel steering, so that the brake steering is prohibited. On the other hand, in the low speed region, even if the response is somewhat poor, there is no practical problem.

In S7, it is determined whether the brake (vehicle) switch is ON. In other words, the fact that the brake pedal is stepped on, or that the foot is lightly placed on it, suggests that the driver or the user has predicted some danger, and the next moment the brake pedal is pressed hard. ,
Since the rear wheel target rudder angle θ _TR is expected to change due to a decrease in vehicle speed or a change in the front wheel rudder angle when the steering wheel is operated, the brake steering is prohibited. Even in S4, the brake (vehicle) switch is turned on to determine the wheel lock.
Although it is judged to be OFF, in S4, since the lock judgment is continued for a predetermined time in consideration of the control response delay even after the ON / OFF judgment of the brake switch, only the ON / OFF judgment of the brake switch is independent in S7. It was done by doing.

In S8, it is determined whether or not the throttle opening change amount | ΔTVO | is less than a predetermined value α. That is, when the accelerator pedal depression amount changes, the throttle opening changes, which changes the vehicle speed and the target rear wheel steering angle θ _TR, but the throttle opening change amount | ΔTVO | α
When it becomes above, by prohibiting the brake steering,
Before the actual vehicle speed change occurs, it is possible to anticipate the change in the driving condition and take appropriate countermeasures.

At S9, it is determined whether the L terminal is Hi. That is, when the engine stalls while the vehicle is running (L terminal becomes L ₀ )
Since it is expected that the target rear-wheel steering angle θ _TR will change due to the decrease in vehicle speed, and that the rear-wheel steering rod 4 needs to be returned to the neutral position because the initial processing of the rear-wheel steering control needs to be performed. Brake hold is prohibited.

In S10, the state where the actual rear wheel steering angle θ _R is maintained at the target rear wheel steering angle θ _TR by the servo motor 8 (servo lock state)
Then, it is determined whether or not a predetermined time has elapsed. That is, when the predetermined time has passed in the servo lock state, it is assumed that the conditions for shifting to the brake holding state are complete,
Transition control to brake holding is performed. The predetermined time is set to about 0.5 seconds by the timer.

The shift control to brake holding is performed as follows.

That is, the brake 10 is turned on in S11, and the brake ON B flag is set in S12. Then, in S13, it is determined whether or not the lap time T (see FIG. 9) has elapsed. That is, until the lap time T elapses, both the servo motor 8 and the brake 10 are turned on to hold the steering, and after the lap time T elapses, the servo motor 8 is turned off (servo current OFF) and brake
Only 10 will be held.

In this way, the rear wheel actual steering angle θ _R is monitored even after shifting to the brake steering, and it is determined in S15 whether the rear wheel actual steering angle θ _R has changed. That is, the change of the rear wheel actual steering angle θ _R during the brake holding may occur when an abnormal external force acts on the rear wheel steering rod 4 or when the holding force of the brake 10 is reduced due to wear. , even in this way changes the rear wheel steer angle theta _R occurs, because only the holding steering is being performed by the brake 10 instead of the steering-held by the servo lock, the rear wheel steer angle theta _R after goal The wheel steering angle θ _{TR is} still off. In order to avoid such a situation, if the rear wheel actual steering angle θ _R changes, S1
In 6 it is judged that the brake circuit is abnormal and shift control to the steering holding by servo lock is performed. On the other hand, if there is no change in the rear wheel actual steering angle θ _R , the brake steering is continuously maintained as long as the above conditions S1 to A9 are satisfied.

When any one of the conditions S1 to S9 is no longer satisfied, or when the rear wheel actual steering angle θ _R changes during brake holding, the following control is performed.

In S17, it is determined whether or not the B flag is set. Then, when the determination is NO, that is, when the steering by the brake 10 is not performed, the normal feedback control (servo control that follows the target rear wheel steering angle θ _TR is performed in S18, not only the servo drive but also the servo control. (Including locking), on the other hand, when the determination is YES, that is, when the steering by the brake 10 is being performed, the shift control to the steering by the servo lock is performed.

The shift control to the steering hold by the servo lock is performed as follows.

That is, the servo motor 8 is turned on in S19, and OF in S14.
The same current value as that immediately before being set to F is supplied, so that the steering is held by the servo lock in addition to the brake holding. In S20, this double rudder holds for a predetermined lap time T
It is determined whether or not the operation is continued, and when this lap time T has elapsed, the brake 10 is turned off in S21 and only the steering holding by the servo lock is performed. Then, after the B flag is reset in S22, normal feedback control is performed in S18.

[Brief description of the drawings]

FIG. 1 is a conceptual block diagram showing a configuration of the present invention, FIG. 2 is an overall configuration diagram showing an embodiment of a rear wheel steering system for a vehicle according to the present invention, and FIG. 3 is a detailed view of a main part of the system, FIG. 4 is a detailed sectional view of a neutral position returning means of the device, FIG. 5 is a detailed sectional view of a brake and a clutch of the device, and FIGS. 6 and 7 are four-wheel steering devices including the device as a part of constituent elements. FIG. 8 is a block diagram of a control system of the device, and FIGS. 9 and 10 are a characteristic diagram and a flowchart showing an example of control by the control unit of the device. 2 ... Rear wheel steering device 4 ... Rear wheel steering rod (rear wheel steering means) 6 ... Neutral position returning means 8 ... Servomotor (electric motor), 8a ... Output shaft 10 ... Brake (steering means) 12 …… Control unit (switching means) 18L, 18R …… Rear wheel, 28 …… Reduction mechanism 28a …… Gear train, 28b …… Ball screw 30 …… Clutch 30A …… Normal open type clutch 30B …… Normal close type Clutch 62 …… Rotary encoder 64 …… Rear wheel steering angle sensor

Claims (1)

(57) [Claims] 1. A rear wheel steering means connected to the rear wheel for steering the rear wheel by displacing the rear wheel, and a neutral position returning means for constantly urging the rear wheel steering means toward a predetermined neutral position. , Coupled to the rear wheel steering means, capable of displacing the rear wheel steering means from the neutral position against the biasing force of the neutral position returning means, and maintaining the rear wheel steering means in a predetermined displacement state An electric motor, a steering holding means for locking the rear wheel steering means, and holding the rear wheel steering means in the predetermined displacement state, and holding the predetermined displacement state between the electric motor and the steering holding means. And a switching means for switching, wherein the switching means, when switching the holding of the predetermined displacement state from one of the electric motor and the steering holding means to the other,
A rear wheel steering system for a vehicle, characterized in that the one holding is released after a predetermined lap time set in advance has elapsed after the other holding is started.