JPH01269674A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent the excessive consumption of electric power by controlling the operation of an electric motor for auxiliary steering so that the steering angle for rear wheels is held at the steering angle corresponding to a prescribed steering wheel steering angle, when the steering wheel steering angle becomes over a prescribed steering wheel steering angle. CONSTITUTION:A rear wheel steering device 2 which steers rear wheels according to the front wheel steering shifts a rear wheel steering rod 4 through a reduction gear mechanism 28 against the exciting power of a neutral position returning means 6 by the operation of a servomotor 8 controlled by a control unit 12, and steers rear wheels. The rear wheel steering rod 4 can be held at a prescribed shift state by the operation of a rudder holding means (brake) 10. In this case, the output signals of a steering wheel steering angle sensor 86, car speed sensor 88, etc., are inputted into the control unit 12, and when the steering wheel steering angle becomes over a prescribed steering angle set according to the car speed, the servomotor 8 is controlled so that the steering angle for rear wheels is held at the steering angle corresponding to a prescribed steering angle.

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 that steers the rear wheels in response to front wheel steering requires a rear wheel steering device for steering the rear wheels. As this rear wheel steering device, conventionally,
It is known to use hydraulic pressure or an electric motor as the drive source for steering the rear wheels, and the latter is disclosed in, for example, Japanese Utility Model Application Publication No. 82-25277.

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

(Problem to be Solved by the Invention) However, in the conventional electric motor type rear wheel steering device, control for steering the rear wheels according to the steering wheel angle is performed over the entire steering wheel angle range. Therefore, the electric motor always consumes current. In particular, from the viewpoint of ensuring safety, electric motor-type rear wheel steering systems generally adopt a fail-safe structure in which the rear wheels are always biased toward a predetermined neutral position using spring force or the like. The electric current consumed by the electric motor during rear wheel steering in a large steering angle region becomes extremely large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rear wheel steering device for a vehicle that can perform rear wheel steering control without requiring excessive current consumption. It is something to do.

(Means for Solving the Problems) The vehicle rear wheel steering device according to the present invention is capable of achieving a large steering wheel steering angle region exceeding a predetermined steering wheel steering angle even if rear wheel steering control is strictly performed in the entire steering wheel steering angle region. The rear wheel steering control performed in the Considering that there is little significance in performing this, the rear wheels are not steered in the above-mentioned large steering wheel steering angle range, and instead, the rear wheels are kept at a steering angle corresponding to the above-mentioned predetermined steering angle. It was designed to achieve the goal. That is, as shown in FIG. 1, it is equipped with an electric motor that steers the rear wheels from a predetermined neutral position, and a control means that operates this electric motor according to the steering angle of the steering wheel. The electric motor is configured to operate when the steering angle exceeds a predetermined steering angle, the steering angle of the rear wheels is maintained at a steering angle corresponding to the predetermined steering angle. It is something.

The above-mentioned "predetermined steering wheel angle" takes into consideration the influence of rear wheel steering control in a large steering angle region greater than or equal to the predetermined steering angle on the driver's sensibilities, or the amount of current consumed to drive the electric motor. However, it is possible to set the
It is effective to make this predetermined steering angle variable depending on the vehicle speed.

(Function) As shown in the above configuration, the control means operates the electric motor according to the steering wheel steering angle to perform control to steer the rear wheels from a predetermined neutral position, and when the steering wheel steering angle is set to a predetermined steering angle. When the steering angle exceeds the specified value, control is performed to maintain the rear wheels at a steering angle corresponding to the predetermined steering angle, so this has little effect on the driver's sensibilities, and the electric motor drive is significantly affected. Rear wheel steering is not performed in a large steering wheel angle region where a large amount of current is likely to be consumed.

(Effects of the Invention) Therefore, according to the present invention, by not performing rear wheel steering control in a large steering angle region where there is little practical necessity, control can be simplified and unnecessary current consumption can be prevented. can be achieved.

Further, according to the present invention, the rear wheels are held at a steering angle corresponding to a predetermined steering angle in place of rear wheel steering control in a large steering wheel steering angle region, so that the rear wheel steering device has the following functions: If a steering holding means is provided separately from the electric motor to lock the rear wheel steering means or the like and maintain the rear wheels at a predetermined steering angle,
It is also possible to switch from the electric motor to the steering means as appropriate to keep the steering at a specified steering angle, and when switching to the steering holding means, the steering angle is 1. It is possible to maintain the rudder with significantly less current consumption.

Note that the range of steering wheel angles that require rear wheel steering control in practical use depends on the magnitude of the vehicle speed (7 is also not constant, so if the above-mentioned predetermined steering angle is made variable according to the vehicle speed, Rear wheel steering control becomes possible within a necessary and sufficient steering angle range, and the above effects can be further enhanced.

(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 comprises a rudder rod 4, a neutral position return means 6, a servo motor 8 as an electric motor, a brake lO as a steering means, and a control unit 12 as a control means.

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

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 2B is arranged between 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 shaft 8a of the servo motor 8, and is capable of applying braking to the rotation of the output shaft 8a. (In turn, 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 ■0 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 IO is activated and the output shaft 8a is
lock. This makes it possible to maintain the steering even if the power supply to the servo motor 8 is stopped, thereby saving power. In this way, control unit 1
2, the steering is switched 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 is provided between the output shaft 8a of the servo motor 8 and the gear train 211a to release the connection between the rear wheel steering rod 4 and the servo motor 8. The displaced rear wheel steering rod 4 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 10 and clutch 30 in detail.

The brake lO is fixed to the output shaft 8a of the servo motor 8, and includes a ring plate 34 having 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
4 is attracted to a suction plate 36 while maintaining the meshing state with the disk 32, and the rotation of the disk 32, that is, the rotation of the output shaft 8a of the servo motor 8 is braked.

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 lO 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.
and a solenoid 46 that is attracted to a disk 44 fixedly attached to the solenoid 4B.
In the FF state, the connection between the ring plate 40 and the disc 44 is released, while in the ON state where the solenoid 46 is energized, the ring plate 40 and the disc 44 are disconnected.
and are connected by surface contact. In addition,
The ring plate 40 always maintains a state of engagement with the disk 32. Further, the clutch 30B is connected to the rotating shaft 42.
a ring plate 50 spline-coupled to a hub 48 fixed to the ring plate 50; a pad 54 that contacts the downstream surface of the ring plate 50 and presses the ring plate 50 upstream by the spring force of the spring 52; pad 54
Fl toward the upstream side of the ring plate 50 pressed by
The ring plate 50
A rotating shaft 5 coaxial with the rotating shaft 42 and in contact with the upstream surface of the
A drum 58 fixed to C and a ring plate 50 are suctioned from the downstream side] 7 and the ring plate 50 and drum 58
and a solenoid 60 that separates the
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 50 and the drum 58 are disconnected. It has become.

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. In addition, as the clutch 30, clutches 30A and 3
The reason for the twin clutch, which has two 0Bs installed in series, is that even if one of them becomes inoperable due to seizure, the other can be turned on or off to maintain the servo motor 8 and gear train 28a. (and thus the rear wheel steering rod 4). In addition, one of the clutches is a normal oven type and the other is a normally closed type, so that when the power supply to both clutches 30A and 30B is stopped due to disengagement of the coverlet, etc., the above connection is released. For this purpose, a normal oven type clutch is required, but if both clutches are normally open type, it means that both clutches are turned on for power transmission in normal conditions.
This is because it is necessary to set the state to the state, which requires additional power consumption.

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 j2 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, 72R via a pair of left and right tie rods 72L, 72R and knuckle arms 74L, 74R.
Rack 78 connected to 761J and rack 7 at one end.
A steering shaft 84 is provided with a pinion 80 that meshes with the steering wheel 82, and a steering wheel 82 is provided at the other end of the steering shaft 84.
By operating the steering wheel, the rack 78 is displaced in the vehicle width direction to steer the front wheels 76L and 7BR.

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 θR/front wheel steering angle θP) according to vehicle speed is shown in FIG. There are cases like this.

When the control characteristics shown in the figure are applied, the front wheel steering angle θF
The rear wheel steering angle θ□ relative to the vehicle speed changes in the same phase direction as the vehicle speed increases, and this situation is shown in FIG. 7a.

That is, FIG. 7a shows the steering wheel steering angle θH (front wheel steering angle θ
2 is a graph showing the relationship between the rear wheel steering angle θR and the rear wheel steering angle θR using the vehicle speed V as a parameter.

As shown by the straight lines with multiple slopes in the figure, when the steering wheel angle θH is within a predetermined range, the rear wheel steering control is performed so that the steering ratio at each vehicle speed is constant. There is. That is, in a low speed region where the vehicle speed is less than 40kffl/h, the steering wheel steering angle θH changes from 60'' to 360@
The steering ratio is constant (opposite phase) for each vehicle speed in the steering angle range up to, and in the high speed range of 40 km/h or more, the steering wheel steering angle θ□ is from 01' to the angle shown for each vehicle speed in the figure. The steering ratio is constant (same phase) for each vehicle speed in the steering angle range.

On the other hand, when the steering wheel steering angle θH exceeds the maximum value of the above steering angle region (hereinafter referred to as the predetermined steering wheel steering angle), the rear wheel steering angle corresponds to the above predetermined steering angle regardless of the steering wheel steering angle θH. The rudder angle is maintained (rudder held).

The reason why the control to keep the steering ratio constant is canceled and the steering is maintained in the large steering angle region is as follows. In other words, if the steering ratio -
Even if control is performed to maintain a constant steering angle, it has little effect on giving the driver the feeling that the rear wheels are being steered faithfully in accordance with the steering wheel angle θH, and is of little practical value. In order to keep the steering ratio constant in the large steering angle region, it is necessary to increase the rear wheel steering angle θ3 accordingly, but when the rear wheel steering angle θR becomes large, the rear wheel steering rod 4 is moved to the neutral position. This is because the current consumed by the servo motor 8 for further displacement against the spring force of the position return means 6 becomes extremely large.

Further, the reason why the predetermined steering wheel steering angle differs depending on the vehicle speed V is that the influence exerted on the driver's sensibilities differs depending on the magnitude of the vehicle speed V when the steering ratio is controlled to be constant. From this point of view, if a predetermined steering angle is set, (θH2θR) - (1
This is the steering wheel steering angle θ□ near the intersection of the circular arc centered on the coordinates of 40", Oo) (the curve shown by the two-dot chain line in the figure) and the straight line with a constant steering ratio at each vehicle speed. In this case, the circular arc The radius is set within a range in which the rear wheel steering angle θ3 does not exceed 5'' (a range in which the spring force of the neutral position return means 6 does not become excessive). On the other hand, in the low speed range, the predetermined steering angle is uniformly set to 360'. The reason why the predetermined steering angle was not set differently for each vehicle speed as in the high-speed range is that the steering wheel must be operated more than 380" from the neutral position when parking, making a U-turn, etc. This is because there is little need to finely differentiate the predetermined steering wheel steering angle for each vehicle speed. However, it goes without saying that this does not prohibit making it variable according to the vehicle speed. , rear wheel steering angle θ, is −
It is set within a range not exceeding 5°.

In addition, in the low speed region, the steering wheel steering angle θ□ is 00~
A dead zone of the rear wheel steering angle θ, l-0 is provided in the range of 60'', which means that a slight steering operation performed at low speed will cause the rear wheels 18L and 18R to be steered in opposite phases. This is in consideration of the fact that it is difficult to imagine steering wheel operation under conditions where driving is required, and that in such cases it is more important to improve driving stability.

In order to perform such rear wheel steering control, as shown in FIG. The control unit 12 calculates a target rear wheel steering angle based on the steering wheel steering angle and vehicle speed, and outputs a control signal corresponding to the required rear wheel steering amount to the servo motor 8.

The rotary encoder 62 constantly monitors whether or not the servo motor 8 is operating properly, that is, under feedback control, the rear wheel 18L, 1
8R steering is performed.

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

That is, the steering wheel angle sensor 86 has a value of 1. A front wheel steering angle sensor 90 is added to the vehicle speed sensor 88, a second vehicle speed sensor 92 is added to the vehicle speed sensor 88, and a rear wheel steering rod 4 is added to the rotary encoder 62 than the clutch 30.
A rear wheel steering angle sensor 64 is added to detect mechanical displacement of the side member, and rear wheel steering is performed only when both corresponding sensors detect the same value among these three sets of sensors. is being used. 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 control unit 12 Rear wheel 11 by predetermined control!
L and 18R are held in neutral positions.

In addition, to detect various abnormalities, 0N-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 94 is a neutral clutch switch.
8 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. inhibitor switch 96
In a vehicle equipped with an automatic transmission, an ON signal is output when the range is in neutral (N) or parking (P), and an OFF signal is output when the range is in the driving range. The brake switch 98 outputs an ON signal when the brake pedal is depressed, and the engine switch 10O outputs an ON signal when the engine is in an operating state.

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

The microprocessor 104 has a dual structure of I and ■, and this microprocessor 104 includes a vehicle speed sensor 88.
．． 92 and switches 94, 98, 98, 100 and the alternator terminal 102 are sent to buffer 1.
06 and also sensor 8B, 90°64
A signal from the rotary encoder 62 is input via the A/'D converter 108, and a signal from the rotary encoder 62 is input via the interface 110. On the other hand, the signal generated by the microprocessor 104 is transmitted to the motor drive circuit 11.
2 to the servo motor 8, the brake drive circuit 114 to the brake 1o, or the clutch drive circuit 11G to the clutch 30. This rear wheel steering control is performed by alternator terminal 1.
It is started on condition that the signal from 02 becomes high (Hl). In addition, in the figure, reference numeral 118 is a battery, 120 is an ignition key switch, and 1
22 is 1 NO, and when a predetermined abnormality occurs, the relay drive circuit 124 is activated to stop supplying electricity to the coil 12B, and as a result, the contacts of the relay 122 are switched, and power is supplied to the motor drive circuit 112. is stopped and the warning lamp 128 lights up. Additionally, when an abnormality other than the above occurs, the microprocessor 104
As a result, a base current flows 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. drive), rear wheel steering rod 4
17 from the neutral position, thereby changing the actual rear wheel steering angle θ.
Control is performed to make R (detected by the rear wheel steering angle sensor 64) coincide with the target rear wheel steering angle. Then, when the target rear wheel steering angle θ78 reaches a constant value and the actual rear wheel steering angle θ2 reaches a value that matches this value, the current value supplied to the servo motor 8 is held constant (servo lock), and the rear wheel is steered. The rod 4 is held in a predetermined displacement state, that is, the steering is held. When this steering holding state continues for a predetermined period of time under a predetermined condition, the brake lO is turned on and the steering is held using the brake 10. When a predetermined period of time T has elapsed since the start of the steering operation using the brake 10, power supply to the servo motor 8 is stopped, and only the steering operation using the brake 10 is continued.

Since the servo motor 8 is in an OFF state while the steering is maintained using only the brake lO, the rear wheels cannot be steered in immediate response to changes in driving conditions. For this reason,
When a change in driving conditions is expected, power is supplied to the servo motor 8 again, and both the servo motor 8 and the brake IO maintain the steering until the predetermined time T has elapsed, and then the brake IO 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 lO 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, the steering angle is significantly improved compared to the brake 10. Power can be saved by eliminating the need to feed power to the servo motor 8, which consumes a large amount of current. Furthermore, when switching between the servo motor 8 and the brake IO, by providing a lap time T during which both of them 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.

The steering control switching control by the control unit 12 is as follows:
In the rear wheel steering control to keep the steering ratio constant, this is not only carried out under a predetermined condition, but also when the steering wheel steering angle θ□ exceeds the predetermined steering angle, the rear wheel steering angle θ3 is held at a predetermined value by the servo motor 8. It is also done when the

That is, as shown in Fig. 7b, the brake IO is turned ON when the steering wheel angle θH becomes 390'' or more.
After that, the operation is controlled so that it turns off when it becomes 380' or less, and accordingly, the servo motor 8 turns on and off.
are also being controlled. In this case, the steering wheel angle θu when the brake is ON/OFF is
The reason for providing the 1:10'(390°-380'') wrap was to take play in the handle into account.

FIG. 1O is a flowchart illustrating an example of control of steering-holding switching performed in a large steering angle region.

Steering holding by the brake 10 (hereinafter referred to as brake holding) is performed only when predetermined conditions are met based on the determination of Sl and Sl.

At Sl, it is determined whether the actual rear wheel steering angle θ8 matches the target rear wheel steering angle θ7R. That is, if the two do not match, it is necessary to continue the servo drive, so brake holding is prohibited.

In Sl, it is determined whether the steering wheel steering angle θH is 390° or more, and if the determination is YES, in S3, the brake IO is turned on and steering is maintained using both the servo motor 8 and the brake lO. let

When the lap time T has elapsed in S4, the servo motor 8 is turned OFF (servo current 0 OFF) in S5 to hold the steering using only the brake ■0, and then the brake is turned ON in S6.
set the flag.

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 S7 whether or not the rear wheel actual steering angle θ7 has changed. That is, the change in the rear wheel actual steering angle θ2 during brake steering is caused by abnormal external force acting on the rear wheel steering rod 4 or by wear of the brake 10.
This can happen when the holding force decreases, but even if the actual rear wheel steering angle θR changes like this, the steering is only held by the brake 10, not by the servo lock. Therefore, the actual rear wheel steering angle θR is the target rear wheel steering angle θTR.
It may remain deviated from the current state. To avoid this situation, if there is a change in the rear wheel actual steering angle θR,
The transition control to steering holding is performed again by servo lock.

On the other hand, if there is no change in the rear wheel actual steering angle θ3, brake holding is continued as long as the above-mentioned condition S2 is satisfied.

If the condition in S2 is no longer met, it is determined in S8 whether the flag is set. and,
When the determination is No, that is, when the steering is not held by the brake 10, normal feedback control (
It refers to servo control that follows the target rear wheel steering angle θTR, and includes not only servo drive but also servo lock).
On the other hand, when the determination is YES, that is, when the steering is held by the brake IO, it is determined in S9 whether the steering angle of the steering wheel is 380° or less. and 8
If the determination in step 9 is No, the process returns to S2 again, while YE
In the case of S, the transition to steering holding is controlled by servo lock.

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

That is, the servo motor 8 is turned on with SlO, and S5
Supplies the same current value as the current value just before it was turned off,
As a result, in addition to braking and steering, steering is maintained by the servo lock. At S11, it is determined whether or not this double steering has been continued for a predetermined lap time T. When this lap time T has elapsed, the brake 10 is turned to O at SL2.
It is set to FF and the rudder is only maintained by servo lock. After the flag is reset in S13, normal feedback control is performed.

As described in detail above, according to this embodiment, in a large steering wheel steering angle region equal to or greater than a predetermined steering angle set according to the vehicle speed, rear wheel steering control is not performed according to the vehicle speed, but instead Since the servo motor 8 is operated and controlled so as to maintain the rear wheel steering angle at the steering angle corresponding to the predetermined steering wheel steering angle, the control can be simplified and unnecessary current consumption can be prevented. Moreover, when the steering angle reaches a predetermined steering angle larger than the above-mentioned predetermined steering angle, the steering is switched from holding the steering by the servo motor 8 to holding the steering by the brake lO, so that the servo motor 8, which consumes a large current, is This makes it possible to eliminate the need for current supply, resulting in further power savings.

In this embodiment, the steering wheel angle at which the steering control is switched between the servo motor 8 and the brake 10 is set to a constant value in the entire vehicle speed range, but the steering wheel angle may vary depending on the above-mentioned predetermined steering angle, etc. It may be made variable for each vehicle speed.

[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 cross-sectional view of the neutral position return means of the device, Figure 5 is a detailed cross-sectional view of the brake and clutch of the device, and Figures 6.7a and 7 show the device as part of its components. FIG. 8 is a block diagram of the control system of the wheel steering device, and FIGS. 9 and 10 are characteristic diagrams and flowcharts showing examples of control by the control unit of the device. 2... Rear wheel steering device 4... Rear wheel steering rod 6... Neutral position return means 8... Servo motor (electric motor) 8a... Output shaft 10... Brake 12... Control unit (control means) 18L,
18R...Rear wheel 28...Reduction mechanism 2
8a...Gear train 28b...Ball screw 30...Clutch 30A...Normal oven type clutch 30B...
Normally closed type clutch 62...Rotary encoder 64...Rear wheel steering angle sensor Fig. 1 Fig. 2 Fig. 6 Fig. 8 Fig. 10

Claims (1)

[Scope of Claims] 1) An electric motor that steers a rear wheel from a predetermined neutral position, and a control means that operates the electric motor according to a steering angle of the steering wheel, the control means controlling the steering angle of the steering wheel. The vehicle is characterized in that the motor is configured to operate so as to maintain the steering angle of the rear wheels at a steering angle corresponding to the predetermined steering angle when the steering angle becomes equal to or greater than a predetermined steering angle. Rear wheel steering device. 2) The rear wheel steering device for a vehicle according to claim 1, wherein the predetermined steering angle is variable depending on vehicle speed.