JPH01266075A - Device for steering rear wheel of vehicle - Google Patents

Abstract

PURPOSE:To prevent the occurreoce of shifting in control in the captigned device in which a rear wheel steering lneans is held in a defined displaced position by means of a steering electric motir or a steering holding means by carrying out the steering holding action by meaos of both at the time of avitchover to the steering hoiding by means of the electric motor or to the steering flolding by means of the stiering holding means. CONSTITUTION:In a rear wheel steering device, a rear wheel steering means A is alwiys being eoergized toward a defined neutral position by a neutral position riturlliog means B. Oue to tbe action of au electric ]notor C linked to the rear wlleel steering means A, the rear wl)eel steering !neans A is displaced from the neutral position against the energizir!g force of the neutral position returning [neaDs B while holding the rear wheel sheering meaans A in a defined displaced condition. Also, by the action of a stiering bolding means D, the rear wheel steering means A is locked and held in the defirnd displaced condition. In this case, the holding of the defihed displaced condition is switched over between the electric motor C ani the steering hilding means D by a switchover means E and, at the time of carrying out the switchover by this lneans E, the holding is carried out for a certain time by both electric motor C and steering holding means D.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle that uses an electric motor as a drive source to steer rear wheels.

(Prior Art) A vehicle equipped with a four-wheel steering device or the like that steers the rear wheels in response to front wheel steering requires a rear wheel steering device for steering the rear wheels. Conventionally, this rear wheel steering device has been known to use hydraulic pressure or an electric motor as the driving source for steering the rear wheels, and the latter is disclosed in, for example, Japanese Utility Model Application Publication No. 62-25277. ing.

As described in the above-mentioned publication, the electric motor type rear wheel steering device generally moves the rear wheels by driving an electric motor to displace a rear wheel steering means such as a rear wheel steering rod connected to the electric motor. It is configured to steer, and it is possible to control rear wheel steering more precisely than a hydraulic type.

On the other hand, since the rear wheel steering is controlled exclusively electrically, sufficient consideration must be given to fail-safe against abnormalities such as failures in this control system. For this reason, conventionally,
As disclosed in Publication No. 1-202977, a neutral position return means such as a centering spring that always urges the rear wheel steering means toward a predetermined neutral position is provided, and when an abnormality occurs, this neutral position return means is attached. Efforts have been made to return the rear wheel steering means to the neutral position after being displaced from the neutral position due to the force.

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 return means. Furthermore, under certain driving conditions, it is also necessary to maintain the rear wheel steering means in a state displaced from the neutral position by a specified amount (that is, to hold the steering), but in order to do this with an electric motor, It is necessary to supply the electric motor with enough current to counter the biasing force of the position return means, and if the steering is held for a long time, the current consumption is large, which may cause problems such as a dead battery. In response to this, a steering means is provided which locks the rear wheel steering means and maintains the rear wheel steering means in a predetermined displacement state, so that it is possible to switch from steering by the electric motor to steering by the steering means as appropriate. By doing so, it is possible to reduce the amount of current consumption and eliminate the above-mentioned inconvenience.

(Problem to be Solved by the Invention) However, since the rear wheel steering means that has been displaced by a predetermined amount from the neutral position is always urged toward the neutral position by the neutral position return means, the steering control means is changed from the steering by the electric motor to the steering holding means. When switching to rudder holding or vice versa,
While there is some delay in the operational response, the rear wheel steering means may be displaced toward the neutral position due to the biasing force, which may cause a deviation in the rear wheel steering control.

The present invention has been made in view of the above circumstances, and is intended to prevent deviations in rear wheel steering control from occurring even if the steering of the rear wheel steering means is switched between the electric motor and the steering means. It is an object of the present invention to provide a rear wheel steering device for a vehicle that can prevent this.

(Means for Solving the Problems) The vehicle rear wheel steering device according to the present invention has the following features:
The above object is achieved by causing both the electric motor and the steering means to maintain the steering of the rear wheel steering means for a predetermined period of time.

That is, as shown in FIG. 1, a rear wheel steering means is connected to the rear wheels and steers the rear wheels by displacement, and the rear wheel steering means is always biased toward a predetermined neutral position. connected to a neutral position return means and the rear wheel steering means,
an electric motor capable of displacing the rear wheel steering means from the neutral position against the biasing force of the neutral position return means and maintaining the rear wheel steering means in a predetermined displacement state; a steering means for locking and holding the rear wheel steering means in the predetermined displacement state; and a switching means for switching maintenance of the predetermined displacement state between the electric motor and the steering means; The switching means is characterized in that the switching means is configured to cause both the electric motor and the steering holding means to perform the holding for a predetermined period of time during the switching.

The above-mentioned "steering means" is not particularly limited in its locking position with respect to the rear wheel steering means as long as it is capable of locking the rear wheel steering means. For example, it may be configured to lock the rear wheel steering means itself. Alternatively, the rear wheel steering means may be locked by locking the output shaft of the electric motor or the coupling mechanism between the electric motor and the rear wheel steering means.

The above-mentioned "predetermined time" is the time required for the steering holding operation of the rear wheel steering means by the steering holding means (or electric motor) to be completed when switching from the electric motor (or steering holding means) to the steering holding means (or electric motor). The length of time is not particularly limited as long as it is sufficient time.

(Function) As shown in the above configuration, an electric motor and a steering holding means are provided as means for maintaining (steering holding) the rear wheel steering means in a predetermined displacement state, and a switching means switches the steering holding between the two. Therefore, by switching the steering control as appropriate, it is possible to stop the power supply to the electric motor that consumes a large current and save power. Since the switching is performed in a lap manner, even if there is a slight delay in the operational response during the switching, it is possible to eliminate the possibility that the rear wheel steering means will be displaced by the biasing force of the neutral position return means.

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

(Examples) Examples of the present invention will be described in detail below with reference to the accompanying drawings.

2 and 3 are an overall configuration diagram and a detailed diagram of essential parts of an embodiment of a rear wheel steering device for a vehicle according to the present invention.

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

The rear wheel steering rod 4 extends in the vehicle width direction, and has both ends connected to a pair of left and right rear wheels 18L via a pair of left and right tie rods 14L, 14R and knuckle arms 16L, 16R.
18R, and when the rear wheel steering rod 4 is displaced in the vehicle width direction, the rear wheel 18L is connected to the rear wheel 18R.

It is designed to steer 18R.

The neutral position return means 6 is attached to the rear wheel steering rod 4,
As its cross section is shown in detail in FIG. 4, it has a casing 22 fixed to the vehicle body 20, and a pair of spring receivers 24a, 24b are loosely fitted into the casing 22. A compression spring 26 is arranged between 24b and 24b. The rear wheel steering rod 4 is connected to the casing 2
A pair of flanges 4a, 4b are formed at intervals on this rear wheel steering rod 4, and extend through the rear wheel steering rod 4.
b is configured to receive the spring receivers 24a and 24b, and the rear wheel steering rod 4 is always kept at a predetermined neutral position (i.e., the rear wheels 18L, 24B) by the compression spring 26.
18R is biased toward the position where the steering angle is zero and the steering wheel is in a straight-ahead state. The compression spring 26 has a spring force sufficient to overcome side forces during cornering.

The servo motor 8 is a step motor, and as shown in FIG. 3, its output shaft 8a is connected to the rear wheel steering rod 4 via a speed reduction mechanism 28 consisting of a gear train 28a and a ball screw 28b. As shown in FIG. 2, the rear wheel steering rod 4 is operated by a control signal from the control unit 12 to displace it from the neutral position against the biasing force of the neutral position return means 6, and the rear wheel steering rod 4 It is now possible to maintain the steering wheel at a predetermined displacement state (that is, to hold the steering wheel).

The brake 10 is an electromagnetic brake and is attached to the output 1d+8a of the servo motor 8 so as to be able to brake the rotation of the output shaft 8a. 8a (and by extension, the rear wheel steering rod 4) can be locked to maintain the rear wheel steering rod 4 in a predetermined displacement state (that is, to maintain the steering). The operation of this brake IO is
It is controlled by a 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, by activating the brake 10 and locking the output shaft 8a, the steering can be maintained even if the power supply to the servo motor 8 is stopped. This makes it possible to save power. In this way, the control unit 12 performs steering control switching between the servo motor 8 and the brake IO, which will be described in detail later. Note that the brake 10 is also utilized when a predetermined abnormality occurs.

A clutch 30 for disconnecting the rear wheel steering rod 4 and the servo motor 8 is provided between the output shaft 8a of the servo motor 8 and the gear train 28a.
Rear wheel steering rod 4 displaced from the neutral position due to the operation of
can be returned to the neutral position by the biasing force of the neutral position return means 6 when a predetermined abnormality occurs. The operation of this clutch 30 is controlled by the control unit 12.

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

The brake IO includes a ring plate 34 that is fixed to the output shaft 8a of the servo motor 8 and has an uneven groove that engages with an uneven groove on the servo motor 8 side of a disk 32, which has a plurality of uneven grooves extending radially on both sides. , and a solenoid 38 that attracts this ring plate 34 to a suction plate 3B fixedly installed on a casing 35. When the solenoid 38 is in the OFF state, in which electricity is not energized, the ring plate 34 rotates freely together with the disk 32, while the solenoid In the ON state where 38 is energized, the ring plate 3
The rotation of the disk 32, that is, the rotation of the output shaft 8a of the servo motor 8, is braked by attracting the disk 4 to the suction plate 3B while maintaining the meshing state with the disk 32.

The clutch 30 is a twin clutch in which two clutches are provided in series, and the clutch 30A is on the upstream side (brake 10 side).
The clutch 30B on the downstream side (gear train 28a side) is a normally closed type. That is, the clutch 30A includes a ring plate 40 having an uneven groove that engages with an uneven groove on the downstream side of the disk 32, and a rotating shaft 4 that is coaxial with the output shaft 8a.
2, and a solenoid 4B that is attracted to a disk 44 fixedly attached to the solenoid 4B.
In the FF state, the ring plate 40 and the disc 44 are disconnected, while in the ON state, where the solenoid 46 is energized, the ring plate 40 and the disc 44 are connected by surface contact. Note that the ring plate 40 always maintains a state of engagement with the disk 32. The clutch 30B also includes a ring plate 50 that is spline-coupled to a hub 48 that is fixed to the rotating shaft 42, and a ring plate 50 that comes into contact with the downstream surface of the ring plate 50 and is activated by the spring force of the spring 52.
0 upstream, and a rotating shaft that contacts the upstream surface of the ring plate 50 so as to prevent the ring plate 50 pressed by the pad 54 from moving more than a predetermined amount upstream. 42, and a solenoid 60 that sucks the ring plate 50 from the downstream side and separates the ring plate 50 and the drum 58. In this state, the ring plate 50 and the drum 58 are connected by surface contact, and in the ON state where the solenoid BO is energized, the connection between the ring plate 50 and the drum 58 is released.

However, 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 during normal times is performed in this state.

In addition, as the clutch 30, clutches 30A and 30
The twin clutch with two Bs installed in series is
Even if either one becomes inoperable due to seizure or the like, the connection between the servo motor 8 and the gear train 28a (and by extension the rear wheel steering rod 4) can be released by turning the other ON or OFF. In addition, one of the clutches is a normal oven type and the other is a normally closed type in order to release the connection when the power supply to both clutches 30A and 80B is stopped due to disengagement of the coverlet, etc. requires a normal oven type clutch, but using a normal oven type for both requires both clutches to be in the ON state for power transmission during normal times, which requires additional power consumption. It is.

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

In addition to the rear wheel steering device 2, the four-wheel steering device includes 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 driving conditions. Be prepared.

The front wheel steering mechanism 70 extends in the vehicle width direction, and has both ends connected to a pair of left and right front wheels 76L, 7 via a pair of left and right tie rods 72L, 72R and knuckle arms 74L, 74R.
8H, and a steering shaft 84, which is provided with a pinion 80 that engages with the rack 78 at one end and a steering wheel 82 at the other end. 78 in the vehicle width direction to steer the front wheels 76L and 78R.

Rear wheel steering control by the control unit 12 is performed in response to vehicle speed, and an example of changing the steering ratio (rear wheel steering angle/front wheel steering angle) according to vehicle speed is as shown in FIG. There are cases where When the control characteristics shown in FIG. 7 are applied, the rear wheel steering angle relative to the front wheel steering angle changes in the same phase direction as the vehicle speed increases, and this situation is shown in FIG.

In order to perform such rear wheel steering control, the control unit 12 includes a steering wheel angle sensor 86 and a vehicle speed sensor 8.
8 and a rotary encoder 62 that detects the rotational position of the servo motor 8, and the control unit 12 determines the target rear wheel based on the steering angle (theoretically equal to the front wheel steering angle) and the vehicle speed. The steering angle is calculated, and a control signal corresponding to the required amount of rear wheel turning is output to the servo motor 8. The rotary encoder 62 constantly monitors whether or not the servo motor 8 is operating properly, that is, the rear wheels 18L and 18R are steered under feedback control.

In the rear wheel steering control described above, the control system has a dual configuration for fail-safe purposes.

That is, a front wheel steering angle sensor 90 is added to the steering wheel steering angle sensor 86, and a second front wheel steering angle sensor 90 is added to the vehicle speed sensor 88.
A vehicle speed sensor 92 is added, and a rotary encoder 82
, a rear wheel steering angle sensor 84 is added that detects the mechanical displacement of a member closer to the rear wheel steering rod 4 than the clutch 30, and in these three sets of sensors, both corresponding sensors are the same. The rear wheels are steered only when the value is detected. Therefore, in the three sets of sensors, if 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, this means that an abnormality (failure) has occurred, and the predetermined By controlling the rear wheels 18L, 18
R is held in a neutral position.

In addition, to detect various abnormalities, ON/OFF signals from switches 94.9B and 98.100 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. be done. Here, the switch 94 is a neutral clutch switch, the switch 96 is an inhibitor switch, and the switch 98 is a neutral clutch switch.
is a brake switch, and switch 100 is an engine switch. Here, in a vehicle equipped with a manual transmission, the neutral switch 94 outputs an OFF signal when the shift position of the manual transmission is neutral or when the clutch pedal is depressed, and outputs an ON signal otherwise. It 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 ON signal when the range is in the driving range.
An FF signal is output. 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 in operation.

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

The microprocessor 104 has a double structure of I and ■, and this microprocessor 104 includes a vehicle speed sensor 8g.
, 92 and switches 94.96.98.100 and alternator terminals 102 are input via buffer 106 and also to sensor 86.9Q.

The signal from rotary encoder 64 is input via A/D converter 108, and the signal from rotary encoder 62 is input via interface 110. On the other hand, microprocessor 1
The signal generated in 04 is transmitted to the motor drive circuit 112.
The signal is sent to the servo motor 8 via the brake drive circuit 114, and the brake 10 via the brake drive circuit 114, or the clutch 30 via the clutch drive circuit 116. This rear wheel steering control is performed using the alternator terminal 10.
It is started on condition that the signal from 2 becomes high (Hl). In addition, in the figure, reference numeral 118 is a battery, 120 is an ignition key switch, and 12
Reference numeral 2 denotes a relay, and when a predetermined abnormality occurs, the relay drive circuit 124 is operated to stop supplying electricity to the coil 126, and as a result, the contacts of the relay 122 are switched, and the power supply to the motor drive circuit 112 is stopped. At the same time, the warning lamp 128 lights up. Furthermore, when an abnormality other than the above occurs, the microprocessor 104 causes a base current to flow through the transistor 130 and the warning lamp 128 lights up.

Next, the servo motor 8 is controlled by the control unit 12.
The steering control switching between the brakes 10 and the brakes 10 will be explained.

As shown in the timing chart in FIG. 9, a control signal corresponding to the target rear wheel steering angle θTR (calculated based on the steering wheel steering angle and vehicle speed) is output to the servo motor 8 to drive the servo motor. ), the rear wheel steering rod 4 is displaced from the neutral position, thereby controlling the actual rear wheel steering angle θR (detected by the rear wheel steering angle sensor 64) to match the target rear wheel steering angle. Then, when the target rear wheel steering angle θ R becomes a constant value and the actual rear wheel steering angle θ3 reaches a value that matches this value, the current value supplied to the servo motor 8 is held constant (servo lock), which causes the rear wheel steering angle θ to reach a constant value. The wheel steering rod 4 is maintained at a predetermined displacement state, that is, the steering is maintained. When this steering state is continued for a predetermined period of time under predetermined conditions to be described later, the brake lO is turned on and the brake 10 is used to maintain the steering. When a predetermined period of time T has elapsed since the start of steering operation using the brake 10, power supply to the servo motor 8 is stopped, and only steering operation using the brake IO continues.

Since the servo motor 8 is in an OFF state while the steering is maintained using only the brake 10, the rear wheels cannot be steered in immediate response to changes in driving conditions. For this reason,
When a change in running conditions is expected, power is supplied to the servo motor 8 again, and both the servo motor 8 and the brake 10 maintain the steering until a predetermined time T has elapsed, and then the brake 10 is turned off. Then, the servo motor 8 only maintains the steering, and the rear wheels are quickly steered by the drive of the servo motor 8.

In this way, by using only the brake 10 to maintain steering in a situation where the rear wheel steering angle is constant and the rear wheels are not likely to be steered for the time being, compared to the brake 10, Power can be saved as there is no need to feed power to the servo motor 8, which consumes a large amount of current. Furthermore, when changing the steering between the servo motor 8 and the brake 10, by providing a lap time T during which both maintain the steering, at least one of them can maintain the steering even if there is a certain delay in the operation response during the switching. Therefore, the spring force of the neutral position return means 6 causes the rear wheel steering rod 4 to
It is possible to prevent the inconvenience of displacement from occurring. Note that the lap time T may be set to about 0.1 degree, for example, if the operational response delay is about 0.02 seconds.

FIG. 10 is a flowchart showing an example of control for switching between the servo motor 8 and the steering means 10.

Steering holding using the brake lO (hereinafter referred to as brake holding) is performed only when predetermined conditions are met based on the determination from Sl to SIO.

At Sl, it is determined whether the actual rear wheel steering angle θR matches the target rear wheel steering angle θa8. That is, if the two do not match, it is necessary to continue the servo drive, so brake holding is prohibited.

In S2, it is determined whether the target rear wheel steering angle displacement amount δTR is zero. In other words, when the target rear wheel steering angle θ〒R changes, the servo drive is performed accordingly.
Brake-holding is prohibited.

In S3, it is determined whether the brake (for vehicle braking) drive circuit 114 is normal or not, and if it is abnormal, brake holding is prohibited. Note that the judgment as to whether or not it is normal is based on the ON (12
v), OFF (OV) monitor signal.

In S4, it is determined whether the wheels are locked. In other words, the wheel lock phenomenon occurs due to sudden braking action (the braking action here is a braking action caused by depressing the brake pedal, not the brake 10), but in such a case, the rear wheel rotation due to the driver's steering wheel operation, etc. Since it is expected that a rudder action will be made,
Brake-holding is prohibited. In addition, to determine that the wheels are locked, three conditions are met: the brake (vehicle) switch is ON, the vehicle speed signal (detected from the drive system) is zero, and the vehicle speed signal 30 is +m or more before one count (sampling time 13111s). This will be done when all are fulfilled.

In S5, it is determined whether or not the vehicle speed is rapidly increasing.

In other words, if the value of the vehicle speed signal increases rapidly due to noise, chattering of the vehicle speed sensor 88, etc., the vehicle speed signal may become temporarily constant after that, but if such an abnormal signal is input, the brake hold steering start condition is determined. In order to avoid an erroneous determination that there is a match, brake holding is prohibited when it is determined that the vehicle speed is rapidly increasing. In addition,
The reason why brake holding and steering is prohibited during a rapid increase in vehicle speed is because there is a high possibility that wheelspin will cause the vehicle to sway, and corrective steering will be performed in response to this phenomenon. The criteria for determining whether the vehicle speed is rapidly increasing is determined by considering whether the increase in vehicle speed is abnormally large in terms of the vehicle's ability to follow normal accelerator operation.

In S6, it is determined whether the vehicle speed signal is 40k11 or more. That is, in high-speed ranges, detailed steering operations are repeatedly performed and responsiveness is required for rear wheel steering, so brake-holding is prohibited. On the other hand, in the low speed range, even if the response is somewhat poor, it does not pose a particular problem in practice.

In S7, it is determined whether the brake (vehicle) switch is ON or not. In other words, the fact that the brake pedal is depressed or that the foot is lightly placed on it indicates that the driver has foreseen some kind of danger, and the next moment the brake pedal is pressed strongly. Being stepped into,
Alternatively, since a steering wheel operation is performed and a change in the rear wheel target steering angle θTR is expected due to a decrease in vehicle speed or a change in the front wheel steering angle, brake holding is prohibited. Note that in S4 as well, a determination is made as to whether the brake (vehicle) switch is ON or OFF to determine whether the wheels are locked, but in S4,
In order to continue the lock determination for a predetermined period of time even after the brake switch is determined to be ON or OFF, taking into account the control response delay, S7
In this embodiment, only ON/OFF determination of the brake switch is performed independently.

In S8, it is determined whether the throttle opening change amount 1ΔTVOl is less than a predetermined value α.

In other words, when the accelerator pedal depression amount changes, the throttle opening changes, which changes the vehicle speed and changes the target rear wheel steering angle θ7R. By prohibiting brake hold and steering when the vehicle speed is reached, changes in driving conditions can be predicted and appropriate countermeasures can be taken before an actual change in vehicle speed occurs.

In S9, it is determined whether the L terminal is Hi. In other words, if the engine stalls while the vehicle is running (the L terminal becomes Lo), it is expected that the target rear wheel steering angle θ□8 will change due to a decrease in vehicle speed, and it is also necessary to perform initial processing for rear wheel steering control. Since it becomes necessary to return the rear wheel steering rod 4 to the neutral position, brake holding is prohibited.

In S10, it is determined whether a predetermined time has elapsed in a state in which the actual rear wheel steering angle θ8 is held at the target rear wheel steering angle θ,R by the servo motor 8 (servo lock state). That is, when a predetermined period of time has elapsed in the locked state, it is assumed that one condition for transitioning to brake-holding mode has been met, and the transition to brake-steering mode is controlled. Note that the predetermined time is set to, for example, about 0.5 seconds by a timer.

The transition control to brake hold steering is performed as follows.

That is, the brake 10 is turned on with Sll, and S12
Set the brake ON flag B. And 51
3, it is determined whether the lap time T (see FIG. 9) has elapsed. In other words, both the servo motor 8 and the brake 10 are turned off until the lap time T elapses.
N, the steering is held by both of these, and when the lap time T has elapsed, the servo motor 8 is turned off (servo current 0 FF) in S14, and the steering is held by only the brake 10.

In this way, even after shifting to brake hold steering, the actual rear wheel steering angle θ
R is monitored, and it is determined in S15 whether or not the rear wheel actual steering angle θ has changed. In other words, the change in the rear wheel actual steering angle θR during brake holding is caused by abnormal external force acting on the rear wheel steering rod 4 or by brake 1 due to wear.
This can happen when the holding force of 0 is decreased, but even if the actual rear wheel steering angle θ8 changes like this, the steering is only held by the brake lO, not by the servo lock. Therefore, the actual rear wheel steering angle θ3 is the target rear wheel steering angle θT.
The state remains deviated from R. In order to avoid such a situation, if a change occurs in the rear wheel actual steering angle θR, a brake circuit abnormality is determined at 816, and control is performed to shift to steering holding by servo lock. On the other hand, if there is no change in the rear wheel actual steering angle θR, brake holding is continued as long as the conditions S1 to A9 described above are satisfied.

If even one of the conditions S1 to S9 is no longer satisfied, or if there is a change in the rear wheel actual steering angle θ7 while the brakes are being held, the following control is performed.

In S17, it is determined whether the B flag is set. When the determination is No, that is, when the steering is not maintained by the brake 10, 818
Normal feedback control (referring to servo control that follows the target rear wheel steering angle θTH, including not only servo drive but also servo lock) is performed at If so, control is performed to shift to rudder holding using servo lock.

Control of transition to rudder holding by servo lock is performed as follows.

That is, the servo motor 8 is turned on in S19, and the servo motor 8 is turned on in S19.
4, the same current value as the current value immediately before being turned off is supplied, and thereby, in addition to brake steering holding, steering holding is performed by servo lock. In S20, it is determined whether or not this double steering has been maintained continuously for a predetermined lap time T. When this lap time T has elapsed, the brake lO is turned off in S21, and only the steering is held by the servo lock. It is said that

Then, after the B flag is reset in S22, 818
Normal feedback control is performed.

[Brief explanation of the drawing]

FIG. 1 is a conceptual block diagram showing the configuration of the present invention, FIG. 2 is an overall configuration diagram showing an embodiment of a vehicle rear wheel steering device according to the present invention, FIG. 3 is a detailed view of the main parts of the device, Figure 4 is a detailed sectional view of the neutral position return means of the device, Figure 5 is a detailed sectional view of the brake and clutch of the device, and Figures 6 and 7 are a four-wheel steering system in which the device is a part of its components. Figure 8 is a block diagram of the control system of the device, Figures 9 and 10 are characteristic diagrams showing the action of the device.
The figure is 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 return means 8... Servo motor (electric motor) 8a... Output shaft lO... Brake (Steering means) 12... Control unit (switching means) 18L,
18R...Rear wheel 28...Reduction mechanism 28
a...Gear train 2111b...Ball screw 30...Clutch 30A...Normal oven type clutch 30B...
Normally closed type clutch 62...Low reencoder 64...Rear wheel steering angle sensor Fig. 2 76L
76F? Figure 6 Figure 7

Claims (1)

[Scope of Claims] Rear wheel steering means that is connected to a rear wheel and steers the rear wheel by displacement, and neutral position return means that always urges the rear wheel steering means toward a predetermined neutral position. and connected to the rear wheel steering means, for displacing the rear wheel steering means from the neutral position against the biasing force of the neutral position return means, and for maintaining the rear wheel steering means in a predetermined displacement state. a steering means for locking the rear wheel steering means to maintain the rear wheel steering means in the predetermined displacement state; and switching means for switching the vehicle, wherein the switching means is configured to cause both the electric motor and the steering holding means to perform the holding for a predetermined period of time during the switching. Rear wheel steering device.