JPH04283167A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To not only perform feedforward control of a rear wheel steering angle but also feedback control thereof and to improve disturbance resistance. CONSTITUTION:When a vehicle is provide with a front wheel steering angle deltaf=theta/N corresponding to a steering wheel steering angle theta and a steering gear ratio N, it is also provided with a rear wheel steering angle deltar. The angle deltar is obtained by a total sum of a multiplying value between the angle deltaf and a feedforward control gain k1 (S), a multiplying value between a yaw angular velocity (d/dt)<2>phi and a feedback control gain k2 (S), and a multiplying value between a yaw angular velocity (d/dt)<2>phi and a feedback control gain k3 (S). The efficiency steering angle deltar is fixed by not only feedforward control but also feedback control which takes (d/dt)phi and (d/dt)<2>phi, to be changed by disturbance, into consideration. The change of (d/dt)phi and (d/dt)<2>phi owing to disturbance can be corrected through steering of rear wheels and disturbance resistance is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a vehicle.

0002

2. Description of the Related Art A rear wheel steering system improves the driving performance including the responsiveness of a vehicle by steering the rear wheels when the steering wheel is used to steer the front wheels. As such a rear wheel steering device, the applicant of the present application has previously proposed devices such as those shown in Japanese Patent Application Laid-Open Nos. 1-175575 and 1-145273. The former rear wheel steering device has a sideslip angle of 0 at any point.
The latter rear wheel steering device determines the rear wheel steering angle so that the point at which the sideslip angle is 0 can change depending on the vehicle speed.

0003

[Problems to be Solved by the Invention] However, such conventional rear wheel steering devices determine the rear wheel steering angle only by feedforward control according to the amount of front wheel steering by the steering wheel, without feedback of vehicle behavior. Therefore, there was a problem in that it lacked resistance to external disturbances. In other words, even if the vehicle experiences changes in behavior or disturbances due to crosswinds, rough roads, etc., these are not reflected in the determination of the rear wheel steering angle, resulting in poor autonomous stability.

The present invention aims to solve the above problem by adding feedback control to feedforward control.

[0005]

[Means for Solving the Problems] For this purpose, the rear wheel steering device of the present invention is provided in a vehicle in which the rear wheels are also steered when the front wheels are steered by the steering wheel. The system is configured to perform feedforward control based on the vehicle's yaw angular velocity and yaw angular acceleration.

[0006]

[Operation] When the front wheels are steered by the steering wheel, the rear wheel steering device also steers the rear wheels. At this time, the rear wheel steering angle is feedforward controlled based on the front wheel steering amount by the steering wheel, and the yaw angular velocity and yaw of the vehicle are controlled. Feedback control is performed based on angular acceleration.

Feedforward control of the rear wheel steering angle compensates for the dynamic performance including vehicle responsiveness as before, and feedback control of the rear wheel steering angle compensates for the yaw angular velocity and yaw angle that change in response to external disturbances such as crosswinds. Because the control is based on acceleration, even if the front wheel steering amount remains unchanged, disturbance compensation is performed by changing the rear wheel steering angle in a direction that corrects changes in vehicle behavior due to disturbances. Therefore, disturbance resistance (autonomous stability) can be improved while maintaining the dynamic performance of the vehicle.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram showing an embodiment of the rear wheel steering device of the present invention, and FIG. 2 is a system block diagram thereof.
L and 1R represent the left and right front wheels, 2L and 2R represent the left and right rear wheels, and 3 represents the steering wheel. The front wheels 1L, 1R can be steered by a steering wheel 3 via a steering gear 4, and the rear wheels 2L, 2R can be steered by a rear wheel steering actuator 5.

The rear wheel steering actuator 5 includes a rack-and-pinion type rear wheel steering mechanism 6 that is linked to the left and right rear wheels so as to steer these wheels, a reduction gear 7b that rotationally drives the pinion, and a motor 7b (see FIG. 2). ) consists of a geared motor 7. This motor 7 is driven by a controller 8 via a drive circuit 9.
Sensor 1 detects the steering wheel steering angle θ.
0, a signal from the sensor 11 that detects the vehicle's yaw rate (d/dt)φ, and a sensor 1 that detects the vehicle speed V.
2 and the output rotation of the motor 7 (rear wheel steering angle δR
) are respectively input from the sensors 13 that detect them.

As shown in FIG. 2, when the ignition switch 14 is turned on, the controller 8 is activated together with the drive circuit 9 by power from a power supply circuit 16 connected to a battery 15. And the controller 8 is the sensor 10
The steering angle θ, vehicle speed V, and yaw rate (d/
dt) A target rear wheel steering angle δr is calculated from φ based on the rear wheel steering angle control law described later, and the rear wheel steering angle δR detected by the sensor 13 is calculated via the circuit 9 so that the rear wheel steering angle δR detected by the sensor 13 becomes the target value δr. Drive the motor 7. The controller 8 also controls the steering angle regulating stopper 17 in the rear wheel steering mechanism 6, as shown in FIG.

Next, an example of the rear wheel steering angle control law used by the controller 8 will be explained. As shown in Figure 3, the front wheel is 1, the rear wheel is 2, and the linear 2-free in an x-y coordinate system (the x-axis is in the longitudinal direction of the vehicle and the y-axis is in the left-right direction) with the origin at the center of gravity of the vehicle. It is known that the equation of motion of the two-wheel model is expressed by the following equation. M{d/dt)2y+V(d/dt)φ}=
Ff + Fr... (1)
I(d/dt)2 φ= aFf − 6F r
・・・・・・ (2) Here, number 1

[Equation 1] By the way, the lateral velocity v at the yaw center P is v=(d/d
Since v=0, (d/dt)y = e(d/dt)φ
・・・・・・
The relationship (5) holds true. Here, rear wheel steering angle δr
If we perform feedforward control according to the front wheel steering angle δf and at the same time perform feedback control according to the yaw angular velocity (d/dt)φ, the respective control gains become k1,
k2, the rear wheel steering angle δr is δr = k1 ・δf +k2 ′・(d/d
t)φ... (6) It is shown as (
By substituting the relationships in equations 3) to (6) into equation (1) and summarizing them by Laplace transformation (S is Laplace operator), the following equation is obtained. MV{S(e/v)(d/dt)φ+ (d/dt
)φ}= Cf {δf −[e(d/dt) φ+a
(d/dt) φ〕/v}+ Cr { k1 δf
+k2'(d/dt)φ-[e(d/dt)φ-b(d
/dt) φ]/v} MV {(e/v)S+1}(
d/dt)φ=(Cf +k1C r ) δf +{
C r [k2'-(e-b)/v]-Cf (e
+a)/v }{ M(eS+V)+C f (a+e
)/v − Cr [k2′+(be-e)/v]}(
d/dt)φ − (C f + k1C r )
δf = 0...
(7) If (d/dt)φ and δf are arbitrary,
(7) For the formula to hold, M(es+V)+C f (a+e)/V − Cr
{k2′+ (be-e)/V }=0Cf +k1C
Since r = 0, the control gains k1 and k2' must each be expressed by the following equations. Number 2

[Equation 2] On the other hand, by also adding feedback control according to the yaw angular acceleration (d/dt)2φ, the rear wheel steering angle δr is calculated by the following equation.
When determining δr = k1δf +k2(d/dt)φ+k3
(d/dt)2 φ... (9)
The feedforward control gain k1 is as follows:
are the same as above, (d/dt)φ, (d/dt)
2 Feedback control gain k2, k according to φ
3 are as follows: Number 3

##EQU00003## Here, the control gains k1, k2, k3 are determined in consideration of balance, and by appropriately selecting them, it is possible to improve the maneuverability. and k2,
As k3 becomes larger, the yaw center can be moved backward, which improves the turning stability of the vehicle, and as k2 and k3 become smaller, the yaw center can be moved forward, thereby The turning response of the vehicle is improved, and it is also possible to increase the steady yaw rate gain and reduce the phase delay.

Regarding the yaw center position, as shown in FIG. 4, in the case of a two-wheel steering vehicle in which the rear wheels are not steered, the yaw center position changes as shown by the dotted line h1 depending on the vehicle speed, whereas it changes as shown by the dotted line h2. Control gains k2 and k3 are used to keep the yaw center position the same despite changes in vehicle speed, or to change the yaw center position as shown by h3 according to the vehicle speed.
can be given. In addition, it is better to move the yaw center position depending on the driving conditions and vehicle condition; the stronger the crosswind, the rainier the weather than sunny or cloudy days, and the more uneven the road, the further the yaw center position will be moved to the rear. It is good to have some, and for this purpose, the feedback control gains k2 and k3 are increased. Also, when accelerating, the power slide becomes larger,
Since tuck-in increases when decelerating, in order to reduce this, the yaw center position is shifted rearward as the acceleration/deceleration increases, and as the vehicle mass becomes heavier, the lateral grip of the tires becomes relatively insufficient. Since steering stability is relatively reduced, it is necessary to compensate for the decrease in lateral grip force, so it is better to shift the yaw center position backward as the vehicle mass increases. In addition, as the front and rear axle load distribution moves closer to the rear axle, the rear of the vehicle becomes more likely to slide outwards due to turning centrifugal force.
To compensate for this, it is better to move the yaw center further back as the weight of the rear axle increases.

Of course, it is preferable that the yaw center position be changed by the driver according to his/her preference, and for this purpose, the feedback control gains k2 and k3 can be changed manually by the driver. Furthermore, in order to improve both the stability against lateral force disturbances when traveling straight and the maneuvering response when turning, the steering wheel steering condition is detected and the yaw center position is moved backward when traveling straight and the yaw is adjusted when turning. It is also possible to change the feedback control gains k2 and k3 so as to move the center position further forward than when the vehicle is traveling straight.

Of course, it is possible to select the one with the highest priority among vehicle speed, crosswind, weather, road surface irregularities, acceleration/deceleration, vehicle mass, front/rear axle weight distribution, driver's preference, etc., or to weight them in descending order of priority. It is also possible to determine the values k2 and k3 so as to obtain a predetermined yaw center position.

As explained above, based on equation (9), the rear wheel steering angle δr is not only feedforward controlled according to the front wheel steering angle δf, but also the yaw angular velocity (d/dt)φ
and yaw angular acceleration (d/dt) 2 φ can be expressed as shown in FIG. 5, where the controller 8 in FIGS. (9) Target value δ obtained by formula
When controlling to match r, as is clear from Fig. 6, which shows the simulation results when a vehicle running at a vehicle speed of 120 km/h with a constant steering wheel angle is subjected to a crosswind disturbance, the crosswind disturbance caused by the crosswind disturbance The amount of displacement is i1
(For feedforward control only) from i2
It is possible to improve the resistance to external disturbances. The reason for this is that, as is clear from equation (9), the rear wheel steering angle is changed in accordance with the change in yaw angular velocity and the change in yaw angular acceleration caused by the crosswind disturbance so as to correct the change.

[0016]

As described above, the rear wheel steering system of the present invention not only performs feedforward control of the rear wheel steering angle according to the amount of front wheel steering, but also performs feedback control according to the yaw angular velocity and yaw angular acceleration. Therefore, changes in the yaw angular velocity and yaw angular acceleration due to disturbances are reflected in the determination of the rear wheel steering angle, and this change can be corrected by rear wheel steering, thereby improving resistance to disturbances.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of a rear wheel steering device of the present invention.

FIG. 2 is the same system block diagram.

[Figure 3] Linear 2 used to explain the rear wheel steering angle control law of the present invention
It is a two-wheel model diagram with degrees of freedom.

FIG. 4 is a characteristic diagram showing an example of yaw center position control by the rear wheel steering device of the present invention in comparison with changes in the yaw center position of a two-wheel steered vehicle.

FIG. 5 is a schematic diagram of a rear wheel steering angle control law by the device of the present invention.

FIG. 6 is a drawing showing a comparison of simulation results of the amount of lateral displacement when subjected to an external force of a cross wind between a case using the device of the present invention and a case using a conventional device.

[Explanation of symbols]

1L front left wheel 1R Right front wheel 2L left rear wheel 2R Right rear wheel 3 Steering wheel 4 Steering gear 5 Rear wheel steering actuator 6 Rear wheel steering mechanism 7 Geared motor 8 Controller 9 Drive circuit 10 Steering angle sensor 11 Yaw rate sensor 12 Vehicle speed sensor 13 Rear wheel steering angle sensor 14 Ignition switch 16 Power supply circuit

Claims (1)

[Claims] Claim 1: In a vehicle in which the rear wheels are also steered when the front wheels are steered by the steering wheel, the rear wheel steering angle is feedforward controlled based on the amount of front wheel steering by the steering wheel, and the yaw angular velocity and yaw angular acceleration of the vehicle are controlled. A rear wheel steering device for a vehicle, characterized in that it is configured to perform feedback control based on.