JP2515966B2 - Rear wheel steering angle control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a rear wheel steering angle of a vehicle which steers rear wheels in relation to vehicle speed in accordance with steering of front wheels.

[0002]

2. Description of the Related Art A conventional rear wheel steering angle control method is disclosed, for example, in Japanese Patent Laid-Open No. 57-11173. In other words, this control method improves the steering performance by controlling the steering angle of the rear wheels in order to reduce the side slip angle of the vehicle. As shown in FIG. 3, a predetermined vehicle speed (about 30 km /
h) In the above, the rear wheels are steered in phase with the front wheels, but at low speeds below a predetermined vehicle speed, the rear wheels are steered in reverse phase with the front wheels. Since the ratio of the steered angle of the rear wheels to the steered angle of the front wheels at the low speed becomes maximum near the vehicle speed of zero, so-called small turning performance is improved at the low speed.

[0003]

However, in the above-mentioned conventional rear wheel steering control method, in order to improve the steering performance when the vehicle is moving forward, based on the signals obtained by the front wheel steering angle sensor and the vehicle speed sensor. Since the control circuit calculates the rear wheel control steering angle and steers the rear wheel by this, the steering angle control of the rear wheel cannot be performed when the vehicle moves backward. Therefore, since the turning radius of the vehicle does not become small when reversing, for example, when entering the garage, even if the front and rear wheels are steered in reverse phase to put the car forward in a narrow garage, and then try to move the car out of the garage, When the vehicle retreats, the rear wheels are not steered in the opposite phase, which makes it impossible to turn around a small amount and prevent the driver from leaving the garage.

Further, when the rear wheels are steered at the same steering angle control ratio as when the vehicle is moving backward when moving backward, the yaw rate gain of the vehicle when moving backward becomes too large and the running of the vehicle becomes unstable. There was a point.

[0005]

In order to solve the above-mentioned problems, in the present invention, in controlling the steering angle of the rear wheels in accordance with the vehicle speed and the steering angle of the front wheels, the rear wheels are kept below a predetermined vehicle speed during forward movement. While steering in reverse phase with the front wheels, the rear wheels are steered in reverse phase with the front wheels at a vehicle speed whose absolute value is lower than the predetermined vehicle speed when the vehicle is moving backward.

[0006]

As described above, in the present invention, even when the vehicle is moving backward, the rear wheels are steered in reverse phase to the front wheels at a vehicle speed whose absolute value is lower than the predetermined vehicle speed when moving forward. Also in, the turning radius of the vehicle can be reduced. Particularly, in the present invention, since the rear wheels are steered in the reverse phase of the front wheels only when the vehicle speed is lower than the predetermined vehicle speed when moving backward when the vehicle is moving backward, the yaw rate gain of the vehicle when moving backward increases. It is possible to prevent the vehicle from traveling instable by suppressing the passing.
Therefore, according to the present invention, it is possible to improve the steering performance of the vehicle when moving backward.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing an example of an apparatus for implementing the rear wheel steering angle control method of the present invention. In the figure, reference numeral 1 denotes an engine. An oil pump 3 driven by the engine 1 via a belt pulley transmission 2 sends oil in a reservoir tank 4 to a servo valve 6 via an unloading valve 5 and the servo valve 6 It is configured to feed oil into the left or right oil chamber of the rear wheel steering hydraulic actuator 7. Reference numeral 8 is an accumulator, 9 is a hydraulic oil supply line, and 10 is a return line to the reservoir tank 4. Reference numeral 11 denotes an electronic control circuit. The control circuit 11 inputs signals from a vehicle speed sensor 13 mounted on the transmission 12 and a front wheel steering angle detector 16 mounted on a steering column 15 of the steering wheel 14, and its control circuit 11
The output of is electrically connected to the servo amplifier 17 and the servo valve 6
Are connected so as to be electrically driven. Reference numeral 18 denotes a displacement detection mechanism that detects the steering angle of the rear wheel, and is electrically connected so that a rear wheel steering angle signal is fed back to the servo amplifier 17. Reference numerals 19 and 20 are front wheel tires, 21 and 22 are rear wheel tires, and 23 and 24 are front and rear wheel steering linkages.

That is, in the apparatus of this embodiment, the vehicle speed is detected by the vehicle speed sensor 13, the steering angles of the front wheels 19, 20 are detected by the front wheel steering angle detector 16, and the detected electric signals are input to the electronic control circuit 11, respectively. The output from the electronic control circuit 11 is input to the servo amplifier 17, and the servo valve 6 is controlled by the output of the servo amplifier 17, thereby controlling the steering angles of the rear wheels 21 and 22 via the hydraulic actuator 7. Together with this, the steering angle of the rear wheels 21, 22 is detected by the displacement detection mechanism 18,
The detected value is fed back to the servo amplifier 17 as an electric signal to ensure control.

FIG. 2 shows an embodiment of the method of the present invention.
FIG. 7 is a characteristic diagram in which a vehicle speed V (km / h) is taken on an abscissa and a steering angle ratio k of front and rear wheels is taken on an ordinate. In this embodiment, at a predetermined vehicle speed V ₀ or higher when the vehicle is moving forward, the rear wheels are steered in phase with the front wheels in accordance with the vehicle speed and the front wheel steering angle, and at a predetermined vehicle speed V ₀ or lower,
According to the vehicle speed and the steering angle of the front wheels, the rear wheels are steered in the opposite phase to the front wheels, and when the vehicle retreats, the absolute value of the reverse vehicle speed is detected so that the vehicle speed whose absolute value is lower than the predetermined vehicle speed V _0. It is to steer the rear wheels out of phase with the front wheels at -V ₂ or less.

That is, in this embodiment, the first reverse vehicle speed is −V ₁ , the second reverse vehicle speed is −V _2, and 0 ≦ | −V ₁ |
If ≦ | −V ₂ | <| −V ₀ |, then in V ≦ | −V ₁ |, the steering angle ratio k during reverse and forward is the same, and V ≧ | −V ₂ |
The steering ratio k is zero _{in, | -V 1 | ≦ V ≦} | -V 2
At │, k is gradually reduced as the reverse vehicle speed increases.

The reason for doing this is that since the driving posture is bad when the vehicle is moving backward, when the reverse vehicle speed becomes high, the yaw rate gain of the vehicle becomes too large at the same steering angle ratio as when moving forward, and the driver becomes unfamiliar with driving. This is because the driving control becomes difficult and the running of the vehicle becomes unstable, which is dangerous. Therefore, in this embodiment, the vehicle speed range in which the rear wheels are steered in the opposite phase with respect to the front wheels is set to a lower vehicle speed side when moving backward than when moving forward.

[0012]

As described above, according to the present invention, even when the vehicle is moving backward, the rear wheels are steered in reverse phase to the front wheels at a vehicle speed whose absolute value is lower than the predetermined vehicle speed when moving forward. The turning radius of the vehicle can be reduced even when the vehicle moves backward. Particularly, in the present invention, since the rear wheels are steered in the reverse phase of the front wheels only when the vehicle speed is lower than the predetermined vehicle speed when moving backward when the vehicle is moving backward, the yaw rate gain of the vehicle when moving backward increases. It is possible to prevent the vehicle from traveling instable by suppressing the passing. Therefore, according to the present invention, there is an effect that the steering performance of the vehicle at the time of backward movement can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of an apparatus for implementing a rear wheel steering angle control method according to the present invention.

FIG. 2 is a characteristic diagram showing an example of the present invention.

FIG. 3 is a characteristic diagram of a conventional device. DESCRIPTION OF SYMBOLS 1 Engine 3 Oil pump 6 Servo valve 7 Hydraulic actuator 11 Electronic control circuit 13 Vehicle speed sensor 14 Steering wheel 16 Front wheel steering angle detector 17 Servo amplifier 18 Displacement detection mechanism 19, 20 Front wheel 21, 22 Rear wheel

Claims (1)

(57) [Claims] 1. When controlling the steering angle of the rear wheels according to the vehicle speed and the front wheel steering angle, the rear wheels are steered in a reverse phase to the front wheels at a speed equal to or lower than a predetermined vehicle speed during forward movement, and when the vehicle moves backward, the absolute speed is more than the predetermined vehicle speed. A rear wheel steering angle control method comprising steering a rear wheel in a phase opposite to that of a front wheel at a vehicle speed having a low value or less.