JPS62187657A - Front and rear wheels steering device for vehicle - Google Patents

Abstract

PURPOSE:To make it possible to control the steering of the rear wheels rapidly without producing a hunting, by making the ratio of the steering control of the rear wheels larger when the steering angle control amount of the rear wheels is larger than when it is smaller. CONSTITUTION:While the front wheels 1 are steered by a handle 2 through a front side power steering unit 3, the rear wheels 4 are steered by a servomotor 5 through a rear side power steering unit 6, and the servomotor 5 is controlled by a motor driving device 7. And a control unit 11 computes the rear wheel steering angle ratio to the front wheel steering angle responding to the car speed, depending on the signals from various sensors 12 and 13, and inputs the resultant signal to the motor driving device 7. In this case, when the control error of the rear wheel steering angle is smaller, the ratio of the control voltage of the servomotor 5 to the control error is made smaller. On the other hand, when the control error is larger, the ratio of the control voltage is made larger.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a front and rear wheel steering device for a vehicle.

(Prior art) A front and rear wheel steering system for a vehicle that variably controls the ratio of the rear wheel steering angle to the front wheel steering angle in accordance with the vehicle speed is disclosed in Tokuko Sho Go-4.
No. 4185, which states that at low speeds, the rear wheels are steered in the opposite phase to the front wheels to improve the vehicle's turning performance, and at high speeds, the rear wheels are steered in the same phase as the front wheels. The steering response performance of the vehicle can be improved.

Specifically, the optimal value for the rear wheel steering angle is determined based on the vehicle speed and front wheel steering angle data, and the rear wheel steering angle is adjusted so that the rear wheel steering angle reaches that value (hereinafter referred to as the target value). Control the motor.

Conventionally, as a control method for this purpose, a control voltage proportional to the difference (hereinafter referred to as control error) between the target value and the current rear wheel steering angle (hereinafter referred to as current value) is applied to the motor, and the control error is eliminated. As the value becomes smaller, the motor control voltage is lowered, and even when the error is 0, the motor control voltage is set to 0 to achieve control to the target value. In this control method, the ratio of the motor control voltage to the control error is constant as shown in FIG.

This is called a proportional control method.

(Problems to be Solved by the Invention) However, such a proportional control method has the following problems.

1) When increasing the coefficient of proportional rAa (increasing the ratio of motor control voltage to control error) in order to increase control speed (shorten control delay time), hunting occurs in a region where control error is small.

11) Conversely, if the coefficient is made sufficiently small to prevent hunting, the motor control voltage will not rise sufficiently in a region where the control error is large, resulting in a slow control speed.

That is, in driving conditions, the steering delay of the rear wheels does not pose much of a problem at low speeds, but at high speeds, the steering delay of the rear wheels affects the steering response. Therefore, the rear wheels are steered to eliminate the steering delay. If the 11JJ control output is increased, hunting will occur if the steering angle control amount is small.

(Means for solving the problem) In order to solve the problem, the present invention provides a front and rear wheel steering system for a vehicle that variably controls a rear wheel steering angle ratio to a front wheel steering angle in accordance with vehicle speed. The rear wheel steering control device controls the steering angle of the rear wheels by increasing the ratio of the control output for steering the rear wheels when the steering angle side 4.1 is large than when the steering angle side 4.1 is small.

(Function) In the region where the rear wheel steering angle I control is small, the ratio of the fl control output is small, so hunting can be prevented.
On the other hand, in a region where the steering angle control amount is large, the control output ratio is large, so the control speed can be increased.

Therefore, the steering control of the rear wheels can be quickly performed without causing hunting.

(Example) Examples will be described below based on the accompanying drawings.

Figure 1 is a schematic perspective view of the front and rear wheel steering system, showing the front wheels (1),
(1) is steered via the front power steering device (3) in response to the operation of the steering wheel (2), and the rear wheels (4)
, (4) are steered via a power steering device (8) corresponding to the drive of a servo motor (5), the operation of the servo motor (5) is controlled by a motor drive device (7), and (8) ) is a tacho generator. Detection signals from the vehicle speed sensor (12) and front wheel steering angle sensor (13) are input to the control unit (11), and the control unit (11) calculates the ratio of the rear wheel steering angle to the front wheel steering angle corresponding to the vehicle speed. The output signal is the motor drive device (
7). Also control tips) (11
) is switched between normal front wheel steering (2WS) and front and rear wheel steering (4WS) by selecting the operation switch (14).

Here, in the example, the control unit is used.) In (11), if the front wheel steering angle is (δsw) and the vehicle speed is (V), the optimal steering angle of the rear wheels (δr) is 1+CV2 However, (A), (B ) and (C) are determined by constant arithmetic processing.

In the above control unit (11), the ratio of the control voltage of the motor (5) to the control error of the rear wheel steering angle is determined as shown in FIG. That is, in the region (S) where the control error is small, the control voltage ratio, that is, the slope in the figure, is reduced to prevent hunting, and in the region (M+) and (M2) where the control error is large, the slope is increased. The control speed is improved and the rear wheel steering is controlled according to this map.

FIG. 3 shows a curve in which the sudden change in slope at the boundary between regions (S) and (M) in FIG. 2 is eliminated, and a gentle curve is created, and control may be performed in this manner.

(Effects of the Invention) As described above, according to the present invention, the rear wheels can be quickly steered without causing hunting.

[Brief explanation of drawings]

Figure 1 is a schematic perspective view of the front and rear wheel steering system, Figures 2 and 3
The figure is a characteristic diagram of the control voltage according to the present invention, and FIG. 4 is a conventional characteristic diagram. In the drawings, (5) is a servo motor, (7) is a motor drive device, (11) is a control unit, (I2) is a vehicle speed sensor, and (13) is a front wheel steering angle sensor.

Claims (1)

[Claims] In a vehicle front and rear wheel steering system that variably controls the rear wheel steering angle ratio to the front wheel steering angle in response to vehicle speed, the control output for steering the rear wheels is greater when the rear wheel steering angle control amount is large than when the rear wheel steering angle control amount is small. 1. A front and rear wheel steering device for a vehicle, comprising: a rear wheel steering control device that controls the steering angle of the rear wheels by increasing the ratio of the front and rear wheels.