JP2605977B2 - 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 is to improve 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 the same phase as the front wheels, but at low speeds equal to or lower than a predetermined vehicle speed, the rear wheels are steered in the opposite phase to the front wheels. Then, the ratio of the steering angle of the rear wheels to the steering angle of the front wheels at the low speed becomes the largest near zero vehicle speed, so that the so-called small turning performance is improved at the low speed.

[0003]

However, the above-described conventional rear wheel steering control method is intended to improve the steering performance when the vehicle is moving forward based on signals obtained by a front wheel steering angle sensor and a vehicle speed sensor. The control circuit calculates a rear wheel control steering angle and thereby steers the rear wheels. In this case, as a method of detecting the vehicle speed by a vehicle speed sensor, the vehicle speed is generated from a drive system of the vehicle corresponding to a certain traveling distance. It is convenient to measure the absolute value of the vehicle speed if the number of pulses per fixed time of the pulse signal is counted, but in this way, the detection of the vehicle speed is performed by counting the pulse signal corresponding to the constant traveling distance. In such a case, it is difficult to accurately detect an extremely low vehicle speed in a short time, and if a vehicle speed detection error occurs, the rear wheel control steering ratio becomes inappropriate. .

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a rear wheel steering angle such that a steering angle ratio of a rear wheel to a front wheel has a predetermined characteristic according to an absolute value of a vehicle speed. In the control, the rear wheels are steered in the same phase as the front wheels in the high vehicle speed region where the absolute value of the vehicle speed is equal to or greater than the first predetermined value, and the rear wheels are steered in the low vehicle speed region where the absolute value of the vehicle speed is equal to or less than the first predetermined value. Steering is performed in a phase opposite to that of the front wheels, and in a vehicle speed region in which the absolute value of the vehicle speed is equal to or less than a second predetermined value that is lower than the first predetermined value, the value of the steering angle ratio is kept constant, and In the vehicle speed region, the steering angle ratio is set so as to continuously change in accordance with the vehicle speed, and the rate of change of the steering angle ratio at a first predetermined value or more is set at a value equal to or less than the first predetermined value. Make it smaller than the change rate.

[0005]

As described above, in the present invention, in the low vehicle speed region where the absolute value of the vehicle speed is equal to or less than the first predetermined value, the rear wheels are in the opposite phase to the front wheels, and the steering angle ratio is continuously changed according to the vehicle speed. The steering is performed so as to change, and when the absolute value of the vehicle speed is equal to or less than a second predetermined value lower than the first predetermined value, the steering angle ratio of the rear wheels to the front wheels is kept constant. Since it is possible to avoid difficult detection of an extremely low vehicle speed when moving forward and backward, the structure of the vehicle speed sensor can be simplified.
Further, it is possible to prevent inappropriate steering control of the rear wheels due to an excessive steering angle ratio caused by a vehicle speed detection error. Further, as shown in FIG. 3, if the steering angle ratio is made to be constant when the absolute value of the vehicle speed is equal to or less than the second predetermined value and the steering angle ratio is continuously changed in the other portions, as shown in FIG. The device of the present invention can be easily achieved by only partially changing the conventional device.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 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, and an oil pump 3 driven by the engine 1 through a belt pulley transmission 2 serves as a reservoir tank 4.
The internal oil is sent to a servo valve 6 via an unloading valve 5, and the servo valve 6 is used to feed oil into a left or right oil chamber of a rear wheel steering hydraulic actuator 7. 8 denotes an accumulator, 9 denotes a hydraulic oil supply line, and 10 denotes a return line to the reservoir tank 4. 11 is an electronic control circuit, and this control circuit 11 is a transmission
Vehicle speed sensor 13 and steering wheel 14 mounted on 12
A signal is input from a front wheel steering angle detector 16 mounted on a steering column 15 of the vehicle, and an output of the control circuit 11 is electrically connected to a servo amplifier 17 to electrically drive the servo valve 6. ing. Reference numeral 18 denotes a displacement detection mechanism that detects a steering angle of a rear wheel, and then outputs a wheel steering angle signal to a servo amplifier 17.
Is electrically connected to provide feedback. 19
Reference numerals 20 and 20 denote front wheel tires, 21 and 22 denote rear wheel tires, and 23 and 24 denote steering linkages of front and rear wheels.

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 to control the steering angles of the rear wheels 21 and 22 via the hydraulic actuator 7. At the same time, the steering angle of the rear wheels 21 and 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, when the vehicle speed at the time of forward movement of the vehicle is equal to or greater than a first predetermined value V ₀ , the rear wheels are steered in phase with the front wheels according to the vehicle speed and the front wheel steering angle, and the first predetermined value
V ₀ In the following, the vehicle speed and the rear wheel to the front and reverse phase in response to front wheel steering angle, and steered to continuously change in accordance with the steering angle ratio is the vehicle speed of the front and rear wheels, in particular the vehicle speed is first of lower than a predetermined value V ₀ second predetermined value V ₁ below to constant steering ratio k of the front and rear wheels.

In this embodiment, when the vehicle is moving backward, the absolute value of the reversing vehicle speed is detected so that the front and rear wheel steering angle ratio control, which is completely symmetric with the case of moving forward with V = 0 as the center, is performed. I have. That is, in this embodiment, the steering angle ratio k of the front and rear wheels is kept constant when the absolute value of the vehicle speed is equal to or less than V ₁ (V ₁ <V ₀ ).

As described above, when the vehicle speed is detected by counting pulse signals corresponding to a certain traveling distance, it is difficult to accurately detect an extremely low vehicle speed in a short time. Therefore, in the present invention, it is possible to avoid difficult detection of an extremely low vehicle speed and maintain the steering angle ratio k between the front and rear wheels in a predetermined vehicle speed range of V ₁ to −V _1. An inappropriate steering control of the rear wheels due to an excessive steering angle ratio is prevented.

[0011]

[Effect of the Invention] In the present invention, as described above, the absolute value of the rear wheel is at a first predetermined value V ₀ or lower vehicle speed range of the vehicle speed and the front and reverse-phase, and the vehicle speed is steering angle ratio of the front and rear wheels in conjunction with continuous steering to such changes in accordance, a constant steering ratio k of the rear wheel with respect to the absolute value of the first front wheel at a lower than the predetermined value V ₀ second predetermined value V ₁ the following vehicle speed Therefore, according to the present invention, it is possible to avoid difficult detection of an extremely low vehicle speed when the vehicle moves forward and backward, so that the structure of the vehicle speed sensor can be simplified. In addition, an effect is obtained that inappropriate steering control of the rear wheels due to an excessive steering angle ratio caused by a vehicle speed detection error can be prevented. Furthermore as in the present invention, the absolute value of the vehicle speed is the second predetermined value V ₁ or less is a constant steering ratio k, if such is the steering angle ratio k varies continuously with the other portions, FIG. The effect that the device of the present invention can be easily obtained by only partially changing the conventional device shown in FIG.

[Brief description of the 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] When controlling a rear wheel steering angle so that a steering angle ratio k of a rear wheel to a front wheel has a characteristic set in advance according to an absolute value of a vehicle speed, the absolute value of the vehicle speed is set to a first predetermined value V ₀ or more in the high vehicle speed region to steer the rear wheels to the front wheels and in phase, the absolute value of the first predetermined value V ₀ or lower vehicle speed range of the vehicle speed steering the rear wheels to the front wheels in the opposite phase, the absolute value of the vehicle speed together but in the first lower than the predetermined value V ₀ second predetermined value V ₁ the following vehicle speed region is a constant value of該舵angle ratio k, the rudder is at a second predetermined value V ₁ higher vehicle speed range angle ratio k is set to continuously change according to the vehicle speed, and steering angle ratio of the steering angle ratio rate of change k of the first predetermined value greater than or equal _to V ₀ at a first predetermined value V ₀ below A rear wheel steering angle control method characterized in that the rate of change is smaller than a change rate of k.