JPS62160961A - Control method of rear wheel steering angle - Google Patents

Abstract

PURPOSE:To achieve a smooth steering characteristic when advancing or backing by setting the steering angle ratio between the front and rear wheels to be determined in accordance with the vehicle speed such that it will have a symmetrical value for the front and rear wheel speeds lower than a predetermined value. CONSTITUTION:When a vehicle is advancing with a speed higher than a predetermined value, the front and rear wheels are steered in phase in accordance with a front wheel steering angle fed from a front wheel steering angle detector 16 and the vehicle speed, and when it is advancing with a speed lowr than the predetermined value, the front and rear wheels are steered in reverse phase in accordance with the vehicle speed and the front wheel steering angle. When the vehicle is backing, an absolute value of the backing vehicle speed is detected and the front/rear wheel steering angle ratio control completely symmetrical with that under advancing is performed with reference to the time point when the vehicle speed is 0. Consequently, the rotary radius of the vehicle can be reduced similarly even when the vehicle is backing, thereby the maneuverability of vehicle can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling a rear wheel steering angle of a vehicle, which steers the rear wheels in relation to vehicle speed in accordance with the steering of the front wheels.

(Prior art) As a conventional rear wheel steering angle control method, for example, Japanese Patent Application Laid-Open No. 1987-
There is one disclosed in Publication No. 11173. In other words, this control method is used to reduce the sideslip angle of the vehicle.
This system improves maneuverability by controlling the steering angle of the rear wheels, and as shown in Figure 5, the vehicle speed is approximately 30 km/h.
) In the above, the rear wheels are steered in the same phase as the front wheels, but at low speeds below a predetermined vehicle speed, the rear wheels are steered out of phase with the front wheels. Since the ratio of the steering angle of the rear wheels to the steering angle of the front wheels at low speeds is greatest near zero vehicle speed, so-called small turning performance is improved at low speeds.

(Problems to be Solved by the Invention) However, the conventional rear wheel steering control method described above uses signals obtained from the front wheel steering angle sensor and the vehicle speed sensor to improve the steering performance when the vehicle moves forward. Since the rear wheel control steering angle is calculated by the control circuit and the rear wheels are steered based on this, the rear wheel steering angle cannot be controlled when the vehicle is moving backward. Therefore, since the turning radius of the vehicle does not become smaller when reversing, for example, when entering a garage, if you steer the front and rear wheels in opposite phases to drive forward into a narrow garage and then try to pull the vehicle out of the garage by reversing, When reversing, the rear wheels were not steered in the opposite direction, making it impossible to make small turns and causing problems such as the inability to get the car out of the garage.

(Means for Solving the Problems) In order to solve the above-mentioned problems, in the present invention, when controlling the steering angle of the rear wheels according to the vehicle speed and the front wheel steering angle, when the vehicle speed is lower than a predetermined vehicle speed when moving forward, The rear wheels are steered in the opposite phase to the front wheels at a corresponding steering angle ratio, and the rear wheels are steered in the opposite phase to the front wheels at least at a predetermined vehicle speed or lower when reversing with the same control ratio as when moving forward.

(Function) As described above, in the present invention, even when the vehicle is reversing, the rear wheels are steered in the opposite phase to the front wheels with the same control ratio as when moving forward when the vehicle speed is below a predetermined speed. The turning radius of the vehicle can also be reduced in the same way as when moving forward.

Therefore, according to the present invention, the maneuverability of the vehicle can be improved when moving backward as well as when moving forward.

(Example) The present invention will be described in detail below with reference to FIGS. 1 to 4.

FIG. 1 is a route map showing an example of a device implementing the rear wheel steering angle control method of the present invention. In the figure, reference numeral 1 denotes an engine, and an oil pump 3 driven by the engine 1 via a Hertboog transmission 2 sends oil in a reservoir tank 4 to a servo valve 6 via an unloading valve 5. It is configured to send oil to the left or right oil chamber of the rear wheel steering hydraulic actuator tough.

8 is an accumulator, 9 is a hydraulic oil supply line, and 10 is a return line to the reservoir tank 4. 11 is an electronic control circuit, and this control circuit 11 includes a vehicle speed sensor 13 attached to a transmission 12 and a steering wheel 14.
A signal is input from a front wheel steering angle detector 16 attached to the steering column 15 of the servo valve 6, and the output of the control circuit 11 is electrically connected to the servo amplifier 17 to electrically drive the servo valve 6. ing. A displacement detection mechanism 18 detects the steering angle of the rear wheels, and is electrically connected to feed-hack a rear wheel steering angle signal to the servo amplifier 17.

19 and 20 are front tires, 21 and 22 are rear tires, and 23 and 24 are steering linkages for the front and rear wheels.

That is, in the device of this embodiment, the vehicle speed is detected by the vehicle speed sensor 13, the steering angle of the front wheels 19, 20 is detected by the front wheel steering angle detector 16, and the detected electric signal is sent to the electronic control circuit 1.
1, the output from the electronic control circuit 11 is input to the servo amplifier 17, and the output of the servo amplifier 17 controls the servo valve 6, thereby controlling the rear wheels 21 and 22 via the hydraulic actuator 7. In addition to controlling the angle, the displacement detection mechanism 18 detects the steering angle of the rear wheels 21 and 22, and the detected value is fed to the servo amplifier 17 as an electric signal to ensure control.

2 to 4 show examples of the method of the present invention, and are characteristic diagrams in which the abscissa represents the vehicle speed V (km/h) and the ordinate represents the steering angle ratio k of the front and rear wheels.

FIG. 2 shows a first embodiment of the method of the present invention, and this embodiment is based on a predetermined vehicle speed ν when the vehicle is moving forward. In the above, the rear wheels are steered in the same phase as the front wheels according to the vehicle speed and the front wheel steering angle, and the predetermined vehicle speed V is maintained. In the following, the rear wheels are steered in the opposite phase to the front wheels according to the vehicle speed and front wheel steering angle, and when the vehicle is reversing, the absolute value of the reversing vehicle speed is detected. It performs symmetrical front and rear wheel steering angle ratio control.

That is, even when reversing, the rear wheels are steered in the opposite phase to the front wheels when the vehicle speed V is in the range of O to L.

In this case, as a method for detecting the vehicle speed using the vehicle speed sensor 13, if the number of pulses of the pulse signal generated from the drive system of the vehicle is counted per a certain period of time corresponding to a certain traveling distance, the absolute value of the vehicle speed can be calculated. Convenient for measuring values.

Further, FIG. 3 shows a second embodiment of the method of the present invention, and the difference from the first embodiment is that the absolute value of the vehicle speed is a predetermined vehicle speed V +
This is the point where the steering angle ratio k of the front and rear wheels is kept constant below (V+ < Vo).

In other words, when vehicle speed is detected by counting pulse signals corresponding to a fixed traveling distance as described above, it is difficult to accurately detect extremely low vehicle speeds in a short period of time. Therefore, in this second embodiment, the predetermined vehicle speed range is v1 to -v.
1, the difficult detection of extremely low vehicle speeds was avoided by keeping the steering angle ratio k of the front and rear wheels constant.

FIG. 4 shows a third embodiment of the method of the present invention, and the differences from the first embodiment are as follows.

That is, in this embodiment, the first reverse vehicle speed is -Vl, the second reverse vehicle speed is -v2, and Q≦i−V+l≦1−
If V21< 1-VOI, then V≦l -Vl 1
In d, the steering angle ratio k is the same when reversing and when moving forward, and V≧
In l-V21, the steering angle ratio k is set to zero, and l-v+
l≦V≦l −V2 In l, k is gradually decreased as the backward vehicle speed increases.

The reason for doing this is that the driving posture is poor when the vehicle is reversing, so when the reversing vehicle speed becomes high, if the steering angle ratio is the same as when forwarding as in the first embodiment, the vehicle's co-rate gain becomes too large and This is because driving becomes difficult to control due to inexperience with driving, and the vehicle becomes unstable and dangerous.

Therefore, in this third embodiment, the steering angle ratio k of the front and rear wheels is set to zero at a predetermined reverse vehicle speed or higher.

(Effects of the Invention) As described above, according to the present invention, the steering angle ratio of the front and rear wheels, which is determined according to the vehicle speed, is made symmetrical at least below a predetermined vehicle speed in the forward and backward directions of the vehicle. It is possible to give continuity to the steering angle ratio of the front and rear wheels when the vehicle is moving forward and backward, and in practical terms smooth steering characteristics can be obtained when moving forward and backward.

In particular, the ability to make small turns when reversing is improved and maneuverability is improved. Furthermore, there is no need to detect vehicle speeds with different signs for forward and backward directions. Furthermore, since the steering angle ratio of the front and rear wheels can be used in common regardless of whether the vehicle speed is positive or negative, it is possible to reduce the burden on the memory capacity of the arithmetic unit.

In addition to the above-mentioned common effects, each embodiment has the following effects.

That is, in the second embodiment, since it is not necessary to detect the vehicle speed at extremely low speeds, the number of generated pulses can be reduced and the structure of the vehicle speed sensor can be simplified.

Furthermore, if the third embodiment is adopted, the effect of facilitating driving control when the vehicle is reversing can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a route diagram showing an example of a device implementing the rear wheel steering angle control method of the present invention; Figs. 2 to 4 are characteristic diagrams showing each embodiment of the present invention; FIG. 5 is a characteristic diagram of a conventional device. 1...Engine 3...Oil pump 6.
... Servo valve 7 ... Hydraulic actuator 1
1... 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 2
L 22...Rear wheel

Claims (1)

[Claims] 1. In controlling the steering angle of the rear wheels according to the vehicle speed and front wheel steering angle, when the vehicle speed is lower than a predetermined one when moving forward, the rear wheels are steered in the opposite phase to the front wheels at a steering angle ratio that corresponds to the vehicle speed, and when reversing, the rear wheels are steered in the opposite phase to the front wheels. A rear wheel steering angle control method characterized in that the rear wheels are steered in the opposite phase to the front wheels at a control ratio similar to that when moving forward when the vehicle speed is below a predetermined vehicle speed.