JPH01240377A - Apparatus for steering rear wheel of vehicle - Google Patents

Abstract

PURPOSE:To enable abnormal steering of rear wheels to be detected in an early stage, improving safety by a method wherein difference between a target rotation angle of an electric motor of a rear wheel steering mechanism corresponding to a target steering angle of a rear wheel and an actual rotation angle is compared with a reference value so that malfunction of the electric motor can be identified. CONSTITUTION:Output signals of steering angle sensors 21, 22 which detect steering angles of front wheels respectively according to the amount of steering of a steering wheel 6 and a rack and pinion mechanism 8 and speed sensors 23, 24 which detect vehicle speed respectively according to rotation speed of rear wheels and rotation speed of a thrust shaft are input to a control unit 5. In this control unit 5, a target steering angle of a rear wheel is calculated on the basis of a specific steering angle rate characteristic so as to control an electric motor 14 and steer the rear wheel. The control unit is provided with an identifying device in this case, and when the steering wheel 6 is maintained at a constant steering angle, difference between a target rotation angle of the electric motor 14 which corresponds to the target steering angle and an actual rotation angle detected by a rotation angle detecting device 28 is compared with a reference value so that malfunction of the electric motor is identified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rear wheel steering device for a vehicle that steers the rear wheels according to the driving condition of the vehicle.

[Prior Art] Conventionally, as shown in, for example, Japanese Utility Model Application Publication No. 62-25277, a rear wheel steering mechanism including an electric motor and a deceleration mechanism is used to steer the rear wheels according to the driving condition of the vehicle. Wheel steering devices are known. In the electrically driven rear wheel steering system mentioned above, in order to prevent malfunction of the electric motor due to a failure in the control system, etc., the steering status of the rear wheels is constantly detected, and it is confirmed that the rear wheels are being steered abnormally. When this occurs, the operation of the electric motor is stopped, and the rear wheels are maintained at zero steering angle using a neutral position biasing means or the like, resulting in a two-wheel steering state.

[Problems to be Solved by the Invention] In the conventional device described above, countermeasures are taken after detecting that the rear wheels have been abnormally steered, so the effects of the abnormal steering on the vehicle body can be prevented in advance. The problem is that it cannot be prevented.

The present invention has been made in view of the above points, and detects a failure in the control system of the electric motor before the rear wheels are steered abnormally, and eliminates the failure before it affects the vehicle body. It is an object of the present invention to provide a rear wheel steering device for a vehicle that can perform safe control and the like.

[Means for Solving the Problems 1] The present invention provides a rear wheel steering device for a vehicle that steers the rear wheels by a rear wheel steering mechanism including an electric motor and a speed reduction mechanism. A rear wheel steering angle setting means for setting a target steering angle and a rotation angle detecting means for detecting a rotation angle of the electric motor are provided, and when the steering wheel is held at a constant steering angle, the rear wheel steering angle is set. By comparing the difference between the target rotation angle of the electric motor corresponding to the target turning angle set by the angle setting means and the rotation angle of the electric motor detected by the rotation angle detection means with a preset reference value, This system is equipped with a discriminating means for discriminating whether a malfunction has occurred.

[Function] According to the above configuration, the difference between the rotation angle of the electric motor directly detected by the rotation angle detection means and the target rotation angle of the electric motor corresponding to the target turning angle set by the rear wheel steering angle setting means. By comparing this with a preset reference value, it is possible to determine that a failure has occurred in the electric motor's control system, causing the electric motor to malfunction, before the rear wheels are abnormally steered via the deceleration mechanism. Fail-safe control and the like can be performed so that the vehicle body is not affected.

[Embodiment] FIG. 1 shows an embodiment of a rear wheel steering device for a vehicle according to the present invention. This rear wheel steering position is the left and right front wheels IL, 1
A steering mechanism 2 that steers R, left and right rear wheels 3L,
A rear wheel steering mechanism 4 that steers 3R, and this rear wheel steering mechanism 4
and control means 5 for controlling.

The steering mechanism 2 includes a steering shaft 7 that is rotatably driven by a steering handle 6, a rack and pinion mechanism 8 that converts the rotational motion of the steering shaft 7 into linear motion, and a front wheel that is driven by the rack and pinion mechanism 8. Left and right tie rods 9.9 and knuckle arms 10.1 for steering IL and IR left and right
0.

The rear wheel steering mechanism 4 includes a rear wheel operating rod 13 whose both ends are connected to the rear wheels 3L and 3R via tie rods 11.11 and knuckle arms 12.12, and a rear wheel operating rod 13 that is connected to the rear wheels 3L and 3R in the vehicle width direction. It is equipped with an electric motor 14 consisting of a stepping motor or the like that causes sliding displacement, and a speed reduction mechanism 15 that transmits the driving force of the electric motor 14 to the rear wheel operating rod 13.

The rear wheel operating rod 13 is provided with a neutral position biasing means 16 that biases the rear wheels 3L, 3R in a direction to return to a neutral position, that is, a zero steering angle state when a failure occurs in the rear wheel steering mechanism 4. There is. As shown in FIGS. 2 and 3, the neutral position biasing means 16 includes holders 1 fixed to the rear wheel operating rod 13 at predetermined intervals with set bolts or the like.
7, 17, a centering spring 18 installed between this holder 17, 17, and a retainer 19a, 19 installed at both ends of this centering spring 18.
b, and a stopper 20.20 fixed to the vehicle body, etc., and when the front wheels IL, IR are in the neutral position, the left and right retainers 19a, 19b are held in a state in contact with the stopper 20.20, respectively. It is configured to For example, as shown in FIG. 3, the rear wheel operating rod 13
When the rear wheels 3L and 3R are steered by sliding in the right direction, the left retainer 19a is separated from the stopper 20, the centering spring 18 is compressed, and the right retainer 19b is pressed against the stopper 20. As a result, the rear wheel operating rod 13 is urged to the neutral position by the reaction.

The control means 5 that outputs a control signal to the electric motor 14 includes:
A steering angle signal from the first steering angle sensor 21 detects the front wheel turning angle according to the amount of steering of the steering wheel 6, and a first steering angle sensor 21 detects the front wheel turning angle according to the operating amount of the front wheel rack and pinion mechanism 8. 2 The steering angle signal from the steering angle sensor 22 and the front wheel I
A vehicle speed signal from a first vehicle speed sensor 23 that detects the vehicle speed according to the rotational speed of the L and IR, and a vehicle speed signal from the second vehicle speed sensor 24 that detects the vehicle speed according to the rotational speed of the thrust shaft are input. . Then, the control means 5 reads target steering angles of the rear wheels 3m and 3R according to the steering angle signal and the vehicle speed signal in a rear wheel steering angle setting means described below, based on the steering ratio characteristic set in advance, By outputting a control signal corresponding to this target steering angle to a drive means to be described later to drive the electric motor 14, the rear wheel operating rod 13 is slidably displaced against the urging force of the neutral position urging means 16. The vehicle is configured to steer the rear wheels 3L and 3R.

That is, the pole nut gear 15a of the reduction mechanism 15 converts the rotational force of the electric motor 14 into a sliding driving force and transmits it to the rear wheel operating rod 13, and the rear wheel operating rod 13 is slid left and right to control the rear wheels 3L, It is designed to perform 3R steering.

The amount of steering of the rear wheels 3L and 3R is determined by the stroke sensor 27 that detects the amount of operation of the reduction mechanism 15 and the electric motor 14.
The operation state of the rear wheel steering mechanism 4 is controlled based on the detection signal output from the rotation angle detection means 28, which is a rotary encoder or the like that detects the rotation angle of the rear wheel steering mechanism 4. Further, a brake 29 and a clutch 3 are provided between the electric motor 1114 and the deceleration mechanism 15.
0 is set.

As shown in FIG. 4, the control means 5 includes a rear wheel that reads out a target turning angle of the rear wheels 31.3R corresponding to the driving state of the vehicle based on the output signals of the steering angle sensors 21, 22, etc. a steering angle setting means 31; and a driving means 3 for driving the electric motor 1114 in response to a control signal output from the rear wheel steering angle setting means 31.
In addition to 2, a determination means 3 for detecting malfunction of the electric motor 14
3 is provided. The determining means 33 receives the steering angle signals from the first steering angle sensor 21 and the second steering angle sensor 22 and determines whether the steering wheel 6 is held at a constant steering angle, and also determines whether the steering wheel 6 is held at a constant steering angle. Electric motor 1 corresponding to the target steering angle set by angle setting means 31
By comparing the difference between the target rotation angle of No. 4 and the actual rotation angle of the electric motor 14 detected by the rotation angle detection means 28 consisting of the rotary encoder or the like with a predetermined constant reference value, This is to determine whether or not there has been a malfunction.

In other words, the steering wheel 6 is held at a constant steering angle, and the rear wheels 3 m are kept at a correspondingly set target steering angle.
When the electric motor 1fi 14 is feedback-controlled so as to match the steering angles of the motors 14 and 3R, if there is a difference between the target rotation angle of the electric motor 14 and the actual rotation angle that exceeds the above reference value, the control system etc. It is determined that the electric motor 14 malfunctions due to a failure. The electric motor 14
The rotation angle detection means 28 for detecting the rotation angle of
It is configured to detect the rotation angle of the electric motor 14 every 36 rotations (100). Therefore, in theory, it is possible to set the above reference value to 1/36 rotation, but if this reference value is too small, even if the drive shaft of the electric 1a14 overruns due to inertia, it will cause a failure. There is a risk that it will be erroneously determined that the electric motor 14 has malfunctioned, so in consideration of this, the above reference value is set to 176, for example.
It is desirable to set the rotation (600) to a certain degree.

When the determination means 33 confirms that the electric motor 14 has malfunctioned, a control signal is output to a display section (not shown) to display a warning of the occurrence of a failure, and the electric motor 114
By engaging the brake 29 provided between the brake and the deceleration mechanism 15 and disengaging the clutch 30, a control signal for stopping the operation of the rear wheel steering mechanism 4 is transmitted from the determining means 33 to the brake. 29 and the clutch 30.

The control operation of the rear wheel steering system configured as described above is performed as follows.
This will be explained based on the flowchart shown in the figure. When the control operation starts, first in step S1, based on the detection signals output from the first steering angle sensor 21 and the second steering angle sensor 22, the rear wheels 3L, Electric motor 1 that steers 3R
It is determined whether or not the target rotation angle change amount ΔθTG of No. 4 is O, and it is confirmed whether or not the steering wheel 6 is maintained at a constant steering angle. As a result of this determination, if it is confirmed that the target rotation angle change amount ΔθTG is not O but that the steering wheel 6 is being steered, the rear wheel 3L is set to the target rotation angle according to the driving state of the vehicle in step S2. , 3R, the driving means 32 executes normal servo drive control to control the electric motor 14 so as to steer the motors 3R.

As a result of the determination in step S1, if it is confirmed that the target rotation angle change amount ΔθTG is O,
In step S3, the rear wheel 3L.

Target rotation angle θ of the electric motor 14 corresponding to the target steering angle of 3R
It is determined whether TG is equal to the actual rotation angle θR of the electric current 114 detected by the rotation angle detection means 28. As a result of this determination, the target rotation angle θTG and the actual rotation angle θ
If it is confirmed that R is equal, step S1
Return to and repeat the above flow. Further, as a result of the determination in step S3 above, if it is confirmed that the target rotation angle θTG and the actual rotation angle θR are different, step S4
, the difference D (lθTG - θR1) between the target rotation angle θTG and the actual rotation angle θR is a preset reference value 6.
It is determined whether the value is smaller than 00 or not.

As a result of this determination, if it is confirmed that the difference is smaller than the reference value 600, the electric motor 14 is servo driven in step S5 so that the rotation angle θR of the electric motor 14 matches the target rotation angle θTG. Execute position correction control. Furthermore, as a result of the determination in step S4 above,
If it is confirmed that the above-mentioned difference is larger than the reference 11i600, it is determined that the electric motor 14 has malfunctioned, and the process proceeds to step S6, where the fail-safe control shown in FIG. 6 is executed.

When the fail-safe control starts, first, in step $7, a control signal is output from the determining means 33 to the display section to display a warning of the occurrence of a failure. Next, step S
In step S9, the determining means 33 outputs a control signal to disengage the clutch 30 to release the connection between the electric motor 14 and the speed reduction mechanism 15, and in step S9, the determining means 33 outputs a control signal to engage the brake 29. The rotation of the drive shaft of the electric motor 14 is forcibly stopped.

Then, in step S10, a control signal for stopping the operation of the electric motor Vs14 is output from the determining means 33 to the driving means 32, and in step S11, it is determined whether a predetermined time set by a timer has elapsed.

As a result of the above determination, when it is confirmed that the timer has timed up and the time necessary for automatically returning the rear wheels 3L and 3R to the neutral position by the biasing force of the neutral position biasing means 16 has elapsed, step In S12, a control signal for connecting the clutch 30 is output from the determining means 33, and the control operation is ended.

In this manner, the determining means 33 compares the difference between the target rotation angle θTG and the actual rotation angle θR of the electric motor 14 with a preset reference value (for example, 600), thereby determining whether the electric motor 14 exceeds the reference value. Since the configuration is configured to determine that a malfunction has occurred and detect a failure in the lbl control system of the electric motor 14, the rear wheel steering mechanism 4
By stopping the operation of L and 3R before they are abnormally steered, it is possible to prevent the vehicle body from being affected in advance. That is, like the conventional device, the turning angle of the rear wheels 3m and 3R is detected according to the output signal of the stroke sensor 2f, etc., and malfunction of the electric motor 14 is determined according to the actual turning angle of the rear wheels. In this case, the rear wheels 3L and 3R are affected by external force, causing the actuating rod 13 etc. to deform and the rear wheels 3L and 3R to be steered by approximately 0.10. 0.3
It is necessary to configure the vehicle so that it is determined that the electric IJ 14 has malfunctioned when the vehicle is steered to 0, and it is impossible to avoid causing a negative impression on the vehicle body. On the other hand, when malfunction of the electric motor 14 is determined according to the rotation angle of the electric motor 14 as described above, the rotation speed trace of the electric EL 114 is usually decelerated to about 1/30 by the deceleration mechanism 15. Therefore, even if the drive shaft of the electric motor 14 rotates 600 times, the rear wheels 3L and 3R will only be steered by about 0.10 through the tie rods 11, etc., and there will be no major effect on the vehicle body. do not have.

Further, in the embodiment described above, when it is determined that the electric motor 14 has malfunctioned, the clutch 30 provided between the electric motor 14 and the speed reduction mechanism 15 is disengaged, and the neutral position biasing means provided with the centering spring 18 16, rear wheel 3
Since L and 3R are configured to automatically return to the neutral position, there is an advantage that the heavy vehicle can be easily and quickly shifted to the two-wheel steering state. Furthermore, in the above embodiment, since the clutch 30 is configured to shift to the engaged state again after the rear wheels 3L and 3R return to the neutral position, the holding torque of the electric motor 14 is This has the advantage that the rear wheels 3L and 3R are held in the neutral position by the force exerted by the rear wheels 3L and 3R, thereby making it possible to maintain the vehicle in a more stable two-wheel steering condition.

[Effects of the Invention] As explained above, the present invention provides a rear wheel steering mechanism that corresponds to the target steering angle set by the rear wheel steering angle setting means when the steering wheel is held at a constant steering angle. By comparing the difference between the target rotation angle of the electric motor and the rotation angle of the electric motor detected by the rotation angle detection means with a preset reference value, it is determined that the electric motor has malfunctioned. Before the rear wheels are steered abnormally by the mechanism and the vehicle body is affected, a 7-ail safety control is executed, such as displaying a warning that a failure has occurred, or returning the rear wheels to a neutral position to enter a two-wheel steering state. be able to.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the structure of the neutral position biasing means, FIG. 3 is a cross-sectional view showing the operating state of the neutral position biasing means, and FIG. FIG. 4 is a block diagram showing a main part of an embodiment of the present invention, FIG. 5 is a flowchart showing a malfunction determination operation, and FIG. 6 is a diagram showing a fail-safe control operation. 3L, 3R...Rear wheel, 4...Rear wheel steering mechanism, 5...
- Control means, 31... Rear wheel steering angle setting means, 33...
Discrimination means. Figure 5 Figure 6

Claims (1)

[Claims] 1. In a rear wheel steering device of a vehicle that steers the rear wheels by a rear wheel steering mechanism including an electric motor and a speed reduction mechanism, a rear wheel steering angle that sets a target steering angle of the rear wheels according to the driving state of the vehicle. A setting means and a rotation angle detection means for detecting the rotation angle of the electric motor are provided, and when the steering wheel is held at a constant steering angle, the target turning angle set by the rear wheel steering angle setting means is provided. By comparing the difference between the target rotation angle of the electric motor corresponding to the rotation angle and the rotation angle of the electric motor detected by the rotation angle detection means with a preset reference value,
A rear wheel steering device for a vehicle, characterized in that it is provided with a determining means for determining whether an electric motor has malfunctioned.