JP2011063114A - Rear wheel steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress encouragement of an advancing direction of a vehicle body in an uncontrollable steering wheel direction, even when uncontrollable steering wheel is generated during low speed traveling by a four-wheel steering automobile. <P>SOLUTION: This rear wheel steering device includes a steering angular velocity calculating part 22a, a steering state deciding part 22b for deciding a steering state from a steering angle and steering angular velocity, a rear wheel turning control part 22c for determining controls of rear wheel turning from the steering angle and vehicle speed, and a reverse phase gain adjusting part 22d for adjusting gain of reverse phase controls of the rear wheels by a steering state decision signal and a rear wheel turning signal. When the steering state becomes an uncontrollable steering wheel state, reverse phase gain is reduced. The increase of behaviors of the vehicle by the uncontrollable steering wheel due to steering increases of the rear wheels can be suppressed, and thereby driving can be continued without generating unnatural feeling, even if the uncontrollable steering wheel is generated in a front wheel steering traveling state during the low speed traveling. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rear wheel steering device that enables steering of rear wheels in accordance with front wheel steering.

  Some four-wheeled vehicles include a rear-wheel steering control device that changes the steering angle of the left and right rear wheels for the purpose of improving the turning performance and running stability of the vehicle. This type of rear-wheel steering control device steers the rear wheels in the opposite direction to the front-wheel steering direction at low speeds, and steers the rear wheels in the same direction as the front-wheel steering direction at high vehicle speeds. There is one that improves running stability at high vehicle speeds (for example, Patent Document 1).

JP-A-62-113649

  On the other hand, in the driving state of an automobile, for example, when driving on a road with a step in the width direction or a road with a fence, an external force that steers the front wheel acts when the front wheel crosses the step diagonally or enters a fence. The handle may be removed. In a four-wheel steering vehicle such as that described above, the front wheel steering direction and the rear wheel steering direction are opposite when traveling at low speeds. Therefore, when the steering wheel is removed as described above, the steering wheel (steering wheel) is removed. There was a problem that the car body would turn further in the specified direction.

  In order to solve such a problem and suppress the driving direction of the vehicle body from being promoted in the direction in which the steering wheel is taken even when the steering wheel is taken at low speed in a four-wheel steering vehicle, the present invention In this case, the front wheel steering angle detecting means (26) for detecting the steering angle of the front wheels (4L, 4R), the vehicle speed detecting means (24) for detecting the vehicle speed, and the rear wheels (6L, 6R) are steered. Rear wheel steering control for controlling the actuator (21L, 21R) and at least the rear wheel (6L, 6R) to be steered in the direction opposite to the steering direction of the front wheel (4L, 4R) by the actuator (21L, 21R). A rear wheel steering device having a means (22), wherein an external force detection means (27) for detecting an external force input from the front wheels (4L, 4R) to the steering shaft (12) is provided, and the external force detection means ( Change of the external force is detected and the steering angle by 7) if it becomes more than a predetermined threshold value, it was assumed to inhibit the steering to the opposite direction of the rear wheel (6L, 6R).

  According to this, when the vehicle is traveling with the rear wheel steered in the reverse direction with respect to the front wheel steering direction during low-speed traveling, the steering wheel is removed due to the front wheel passing through a step or a saddle, causing the front wheel to rotate. Even if the rudder angle increases in the steering direction, the steering of the rear wheels in the reverse direction is suppressed, so that the behavior of the vehicle due to the steering wheel being taken can be suppressed from increasing due to the increase in steering of the rear wheels.

  In particular, the suppression of the steering of the rear wheels (6L, 6R) in the reverse direction may be to switch the gain in the reverse steering control of the rear wheels (6L, 6R) to a low gain.

  As described above, according to the present invention, it is possible to suppress an increase in the behavior of the vehicle due to the steering wheel being increased due to an increase in steering of the rear wheel. You can continue driving without any discomfort.

It is a schematic block diagram of the motor vehicle which applied the rear-wheel steering apparatus with which this invention was applied. It is a principal part control block diagram based on this invention. It is a flowchart which shows the control point. It is a typical wave form diagram explaining rear-wheel steering control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an automobile 1 to which a rear wheel steering device 20 to which the present invention is applied is applied. In the description, for the wheels and members arranged for them, that is, tires, electric actuators, etc., subscripts L or R indicating left and right are attached to the numerals, respectively, for example, rear wheel 6L (left), For example, the rear wheel 6R (right) is referred to as the rear wheel 6 when collectively referred to. The vehicle body 1 is used as a reference for front and rear, left and right, and top and bottom.

  The vehicle 1 is equipped with tires 3L and 3R, front wheels 4L and 4R suspended from the vehicle body 2 by left and right front suspensions 7L and 7R, and tires 5L and 5R. 2 and rear wheels 6L and 6R suspended from the vehicle. While the front wheels 4L and 4R are rotatably supported by the knuckles 7aL and 7aR, respectively, the rear wheels 6L and 6R are also rotatably supported by the knuckles 8aL and 8aR, respectively.

  The automobile 1 includes a front wheel steering device 10 that directly steers the left and right front wheels 4 </ b> L and 4 </ b> R by steering the steering wheel 11. The front wheel steering device 10 includes a pinion 13 that is integrally connected to a steering wheel 11 via a steering shaft 12 and a rack shaft 14 that is meshed with the pinion 13 and can reciprocate in the vehicle width direction. A rack and pinion mechanism having both ends of the rack shaft 14 is connected to the knuckles 7a via the left and right tie rods 15, and the left and right front wheels 4 are rotated to the left and right by rotating the steering wheel 11. It is to be steered.

  The front wheel steering device 10 is equipped with an electric power steering (EPS) device 16 that provides an assist force for reducing the manual steering force. The electric power steering device 16 includes an electric motor 17 that generates an assist force for steering operation, a power transmission mechanism 18 that transmits the assist force generated by the electric motor 17 to the steering shaft 12, and an EPS control unit 19 that controls the drive of the electric motor 17. And as a main component.

  The steering shaft 12 is provided with a steering angle sensor 26 as front wheel steering angle detection means for detecting the steering angle of the steering wheel 11 in order to calculate the steering angle (including the steering direction) of the front wheel 5, and in the vicinity of the pinion 13. Is provided with a steering torque sensor 27 as an external force detecting means for detecting a steering torque acting on the pinion 13 (steering shaft 12). Further, a vehicle speed sensor 24 as a vehicle speed detecting means for detecting the vehicle speed is provided at an appropriate place.

  The detection signals from these are input to the EPS control unit 19 and used for steering assist control. Specifically, the base current of the electric motor 17 is calculated based on the steering torque by the steering torque sensor 27 and the vehicle speed by the vehicle speed sensor 24. The EPS control unit 19 includes a microcomputer, ROM, RAM, peripheral circuit, input / output interface, various drivers, and the like, and drives and controls the electric motor 17 based on the calculated current value.

  In addition, the automobile 1 includes a rear wheel steering device 20. The rear wheel steering device 20 drives and controls the left and right rear wheel steering actuators 21L and 21R whose base end is connected to the vehicle body 2 and whose front end is connected to the rear part of the knuckle 8a, and left and right rear wheel steering actuators 21L and 21R. A rear wheel steering control unit 22 as a rear wheel steering control means, and left and right stroke sensors 23L, 23R installed in the rear wheel steering actuators 21L, 21R, respectively, for detecting the stroke amounts of the rear wheel steering actuators 21L, 21R; It has. Based on the detection signals of the stroke sensors 23L and 23R, the turning angles of the left and right rear wheels 5L and 5R can be obtained.

  In the rear wheel steering device 20 configured as described above, the steering angles of the left and right rear wheels 6L and 6R can be individually changed by driving the left and right rear wheel steering actuators 21L and 21R to extend and contract. In the rear wheel steering control, the detection signals of the stroke sensors 23L and 23R are input to the rear wheel steering control unit 22, so that the rear wheel steering control unit 22 performs feedback control of the rear wheel steering actuators 21L and 21R.

  The automobile 1 is further provided with an ECU (Electronic Control Unit) 28 for overall control of various systems, a yaw rate sensor 25 for detecting the yaw rate (vehicle behavior) of the vehicle, and other various sensors (not shown). The ECU 28 is connected to the sensors 23 to 27, the EPS control unit 19, the rear wheel steering control unit 22 and the like via a communication line (CAN), and detection signals of the sensors 23 to 27 are input to the ECU 28. It is used for various control of vehicles.

  The ECU 28 calculates the rear wheel steering angle based on these various signals input, determines the stroke amount of each of the rear wheel steering actuators 21L and 21R, and then outputs a drive control signal to the rear wheel steering control unit 22. Then, the steering control of the rear wheel 6 is performed.

  The rear wheel steering control unit 22 includes a microcomputer, peripheral circuits, various drivers, and the like, and drives and controls the rear wheel steering actuator 21 based on a drive control signal output from the ECU 28. As a result, the rear wheel turning actuators 21L and 21R expand and contract to the stroke amount determined by the ECU 28, and change the left and right rear wheels 6L and 6R to a desired turning angle.

  According to the vehicle 1 configured as described above, if one of the left and right rear wheel steering actuators 21L and 21R is extended and the other is contracted, both the rear wheels 6L and 6R can be steered left and right. By simultaneously and symmetrically displacing the rear wheel steering actuators 21L and 21R, the toe-in / to-out of the rear wheels 6L and 6R can be freely controlled under appropriate conditions. For example, the automobile 1 has the rear wheel 6 in the same direction (in-phase) as the front wheel turning direction during high-speed turning traveling and the rear wheel 6 in the front-wheel steering direction during low-speed turning traveling based on the vehicle motion state grasped by various sensors. It is possible to improve maneuverability by steering in the opposite direction (reverse phase). Further, stability during acceleration / deceleration can be improved by controlling the toe angle so that the rear wheel 6 is changed to toe-out during acceleration and the rear wheel 6 is changed to toe-in during braking.

  Next, a control procedure based on the present invention will be described below with reference to FIG. 2 showing a principal circuit block of the rear wheel steering control unit 22 and FIG. 3 showing a control flow.

  As shown in FIG. 2, the steering angle detection signal from the steering torque sensor 27 and the steering angular velocity calculation unit 22 a to which the steering angle detection signal from the steering angle sensor 26 is input are input to the rear wheel steering control unit 22. A steering state determination unit 22b that receives a steering angular velocity signal from the steering angular velocity calculation unit 22a, a rear wheel steering control unit 22c that receives the steering angle detection signal and a vehicle speed signal from the vehicle speed sensor 24, and a steering state determination unit. There is provided a reverse phase gain adjusting unit 22d to which a determination signal from 22b is inputted and a rear wheel turning signal from the rear wheel turning control unit 22c is inputted.

  The steering angular velocity calculation unit 22a calculates the front wheel steering angular velocity from the time change of the steering angle detection signal. For example, when the right steering direction is set to + and the left steering direction is set to-, the left and right directions of the front wheel steering angle can be processed as signals.

  The steering state determination unit 22b determines the steering state from the steering torque and the front wheel steering angular velocity. In the case of normal steering, the steering direction and the direction in which the steering torque (assist torque) is applied are the same. On the other hand, when the steering wheel is removed, the damping amount is increased in the direction opposite to the steering direction by the damping control in the normal electric steering apparatus. In this case, the steering torque is applied in the opposite direction. Therefore, when the result of integration of the sign (+ −), which is the direction in which the steering direction and the steering torque are generated, becomes −, it can be determined that the external force is input to the steering shaft 12 (the handle is removed). .

  In the rear wheel steering control unit 22c, the steering direction and the rear wheel steering angle of the rear wheel 5 with respect to the front wheel steering angle are obtained according to the front wheel steering angle and the vehicle speed. Also in this case, for example, when the right steering direction is set to + and the left steering direction is set to −, the signals can be processed as signals that distinguish the left and right directions of the rear wheel steering angle.

  In the reverse phase gain adjustment unit 22d, as a gain in the control of steering the rear wheel 6 in the reverse direction with respect to the steering direction of the front wheel 4 according to the steering state determination signal from the steering state determination unit 22b and the rear wheel turning angle. Adjust the negative phase gain to be used. The reverse phase gain is a gain that is used when the rear wheel steering direction is reversely controlled (reverse phase) with respect to the front wheel steering direction in the normal traveling state. Then, when a steering wheel determination by an external input and a determination signal is input by the determination of the steering state, the negative phase gain adjustment unit 22d makes the negative phase gain smaller than 1 (for example, 0.5). In addition, the magnitude of the steering angular velocity is included in the steering wheel take determination signal, and it can be variably set so that the reverse phase gain decreases as the steering angular velocity increases.

  The rear wheel steering angle signal determined by the rear wheel steering control unit 22c is set to a gain by the reverse phase gain adjusting unit 22d and output to the rear wheel steering actuator 21, and the rear wheel steering actuator 21 responds to the rear wheel steering angle signal. The rear wheels 5L and 5R are steered to a steering angle corresponding to the control. In addition, control by well-known feedback control is performed using each turning angle detection value by the stroke sensor 23. FIG.

  The control point based on this invention in the rear-wheel steering apparatus comprised in this way is demonstrated with reference to the flowchart of FIG. The program may be executed in the rear wheel steering control unit 22.

  In step ST1 of FIG. 3, the front wheel steering angle is detected, and in the next step ST2, the steering torque is obtained. The steering torque may be a value detected by the steering torque sensor 27. When the steering torque sensor 27 is not used, for example, the current of the electric motor 17 may be detected, and the steering torque may be estimated from the current value. In this case, as the steering control of the electric power steering device 16, when the steering assist force is mainly determined and the damping effect is added, the current when the steering torque is generated when the external force is input by the damping control is used. it can.

  In the next step ST3, the relationship between the steering direction of the front wheel steering angle θf and the generation direction of the front wheel steering torque Tf is determined. As described above, when the right steering direction is set to + and the left steering direction is set to-, the determination can be made based on the result of integration of positive and negative signs. That is, when the same sign (accumulation result is +), the steering torque (assist torque) is generated in the steering direction, which is the normal steering state. On the other hand, when the sign is different (accumulation result is-), the steering torque opposite to the steering direction is generated, and the steering torque in the reverse direction is generated by the input of the external force. This is because, as described above, by the damping control, a damping effect opposite to the steering direction of the steering wheel 11 (steering shaft 12) is generated. Therefore, such a state can be discriminated by the code integration result as described above.

  If it is determined in step ST3 that the integration result has the same sign, the gain is reset (for example, returned to 1 if it is 1) in step ST7, and this control is terminated (normal steering control is performed). ), If it is determined that the sign is different, the process proceeds to step ST4.

  In step ST4, it is determined whether or not the rear wheel steering control is in reverse phase control. The reverse phase control means that the rear wheel 5 is steered with the rear wheel steering direction opposite to the front wheel steering direction in order to improve the turning ability at the time of low speed traveling, which is the object of control of the present invention. It is that you are. When it is determined that the reverse phase control is not being performed (in-phase control is being performed), the control is outside the target of the main control, so the gain is reset in step ST7 and the main control is terminated. If it is determined in step ST4 that the reverse phase control is being performed, the process proceeds to step ST5.

  In step ST5, the gain correction amount in the negative phase gain adjustment unit 22d is determined. As described above, when the correction amount is uniformly set to 0.5, 0.5 is substituted for the gain coefficient, and when the correction amount is set to a value inversely proportional to the magnitude of the front wheel steering speed, the coefficient is set to, for example, the front wheel. The coefficient is obtained from a map in which the relationship between the steering speed and the coefficient is set. In the determination of the gain correction amount in step ST5, the correction amount is determined when the steering angle θf detected in step ST1 is greater than or equal to a predetermined threshold θd (θf ≧ θd). The threshold value θd may be a value that prevents the main control from being performed, for example, when the degree of play of the handle is changed.

  In step ST6, adjustment is performed to set a gain using the coefficient determined in step ST5, and this routine is terminated. In another routine, damping control is performed using the changed anti-phase control gain.

  As a result, when the steering wheel is removed while the rear wheel is steered in the opposite direction to the front wheel steering direction during low-speed traveling, the normal rear according to the change in the front wheel steering angle due to the steering wheel is taken. If the wheel steering control is to be performed, the steering angle of the rear wheel 5 is greatly changed to the opposite phase side as indicated by a two-dot chain line in FIG. On the other hand, according to the control of the present invention described above, since the rear wheel reverse phase gain is adjusted to be small, the amount of change to the reverse phase side is suppressed as shown by the solid line in FIG. As a result, the steering wheel is not increased, so that it is possible to continue the steering operation without a sense of incongruity.

  In the above-described rear wheel steering suppression control, the reverse phase gain is reduced. However, for example, the rear wheel turning angle may be maintained.

4L, 4R Front wheel 6L, 6R Rear wheel 12 Steering shaft 21L, 21R Rear wheel steering actuator (actuator)
24 Vehicle speed sensor (vehicle speed detection means)
22 Rear wheel steering control unit (rear wheel steering control means)
26 Steering angle sensor (front wheel steering angle detecting means)
27 Steering torque sensor (external force detection means)

Claims (2)

Front wheel steering angle detection means for detecting the steering angle of the front wheel, vehicle speed detection means for detecting the vehicle speed, an actuator for turning the rear wheel, and at least the rear wheel in a direction opposite to the steering direction of the front wheel by the actuator A rear wheel steering device having a rear wheel steering control means for performing steering control,
An external force detection means for detecting an external force input from the front wheel to the steering shaft is provided;
The rear wheel steering control means suppresses the steering of the rear wheel in the reverse direction when the external force is detected by the external force detection means and the change in the steering angle exceeds a predetermined threshold value. A rear wheel steering device characterized by the above.   2. The rear wheel steering device according to claim 1, wherein the suppression of the steering of the rear wheel in the reverse direction is to switch the gain in the reverse steering control of the rear wheel to a low gain.

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