JPS63184575A - Control method for rear wheel steering device for automobile - Google Patents

Abstract

PURPOSE:To suppress change of behavior of a body due to variation of frictional resistance of pavement, by detecting slip condition of rear right and left wheels upon rotary operation of a steering wheel, and controlling the steering angle of rear right and left wheels individually corresponding to said slip condition. CONSTITUTION:Upon rotary operation of a steering wheel 1, a control circuit 4 determines steering direction and angle of rear wheel based on a steering angle of front wheel detected through a steering angle sensor 2 and a vehicle speed detected through a vehicle speed sensor 3, so as to control a rear wheel steering mechanism. In such device, the rear wheel steering mechanism is constructed with independent steering mechanisms L, R for steering right and left rear wheels 14R, 14L individually. Respective steering mechanisms L, R are constructed such that a tie rod 12 is displaced axially through gear rows 6-9 by means of motors. Steering angle of rear wheel is corrected according to slip condition of right and left rear wheels 14R, 14L which is judged based on outputs from respective rear wheel rotation sensors 15, and respective motors 5 are controlled according to corrected steering angle of rear wheel.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of controlling a rear wheel steering system for an automobile.

Conventional Technology Various automobiles have been developed in which the rear wheels are simultaneously steered when the front wheels are steered by turning the steering wheel. For example, Japanese Patent Laid-Open No. 55-91457 It has already been published in etc.

Problems to be Solved by the Invention In the conventional rear wheel steering device as described above, the left and right rear wheels are connected, and the left and right rear wheels are steered together based on the steering angle of the front wheels and the vehicle speed at that time. It is common to take .

However, the driving performance of a vehicle is greatly affected by the road surface conditions, and especially when the end of the road surface (friction coefficient) differs between the left and right wheels or only one wheel, the driver may exhibit unexpected behavior. In contrast, the conventional type in which the left and right rear wheels are connected and the left and right rear wheels are steered together has the problem that it cannot accurately respond to the difference in road surface use between the left and right wheels. ing.

The main object of the present invention is to provide a control method for a rear wheel steering system that can overcome the conventional problems as described above.

Means for Solving the Problems The present invention provides a rear wheel steering mechanism in which a control circuit determines the direction and steering angle in which the rear wheels should be steered based on the steering angle of the front wheels and the vehicle speed at that time, and issues an output signal. In the rear wheel steering system of an automobile, which operates the rear wheels to steer the rear wheels, the left rear wheel steering mechanism and the right rear wheel steering mechanism, which respectively steer the left and right rear wheels separately, are made independent of each other. The control circuit determines the slip state of each of the left and right rear wheels from the rotation speed information of the left and right rear wheels, and adjusts the rear wheel steering angle determined from the front wheel steering angle and the vehicle speed according to the slip state. This is characterized by correction control.

Effect In the above, when the rear wheels are steered in the same direction as the front wheel steering direction based on the front wheel steering angle and vehicle speed during steering operation, for example, when the road resistance on either the left or right side is low, the road resistance Since the slip of the lower rear wheel is greater than the slip of the opposite rear wheel, the control circuit controls the rear wheel with lower road resistance to give a larger steering angle than the opposite rear wheel. The left and right rear wheels are always controlled to maintain optimal conditions against changes in road resistance, such as by increasing the resistance against uphill climbs. This makes it possible to improve stability.

Example An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a steering handle, and by rotating the steering handle 1 to the right or left, a known front wheel steering device (not shown) such as a rack and pinion type steering device is actuated to turn the front wheels to the right or left. It is now possible to operate the steering.

2 is a front wheel steering angle sensor that detects the front wheel steering angle from the steering angle of the steering handle 1 and generates a front wheel steering angle signal δf; and 3 is a vehicle speed sensor that detects the running speed from, for example, a speedometer cable and generates a vehicle speed signal V. The front wheel steering angle signal δf from the front wheel steering angle sensor 2 and the vehicle speed signal V from the vehicle speed sensor 3 are input to the control circuit 4.

The left and right rear wheels 14L and 14R are configured to be steered separately by independent steering mechanisms and R, respectively.

The steering mechanisms R and R each include an actuator such as an electric motor 5 controlled by an output signal from a control circuit 4, a cylindrical worm 6 fixed to the output shaft of the electric motor 5, and a worm wheel meshing with the cylindrical worm 6. 7, and a pinion gear 8 that rotates integrally with the worm wheel 7.
, a rack shaft 9 that meshes with the pinion gear 8, and a gear box 11 that houses these, and each rack shaft 9 is connected to left and right rear wheels 14L and 14R via tie rods 12 and knuckle arms 13, respectively. As the electric motor 5 rotates, the rack shaft 9 is actuated in the axial direction, so that the rear wheels 14L and 14R can be steered separately.

The steering mechanisms R and R are provided with a rear wheel steering angle sensor 10 that detects the actual steering angle of each rear wheel and outputs left rear wheel steering angle signals δrLT and δrRT to the control circuit 4.

15 detects the respective rotation speeds of the left and right rear wheels 14L and 14H, and outputs a left rear wheel rotation speed signal WL and a right rear wheel rotation speed signal WR.
The rear wheel rotation speed sensor 15 is a rear wheel rotation speed sensor that sends a signal to the control circuit 4, and the rear wheel rotation speed sensor 15 uses a rear wheel rotation speed detection device for the ABS, for example, in a car equipped with an anti-skid brake system, that is, ABS. can do.

As shown in FIG. 2, the control circuit 4 has a function f (V
) are set, as well as data on coefficients αL and α that gradually increase from 1 as the left and right rear wheels 14L, 14Rcr+, ;l-/proportions ΔvL and ΔvR increase, as shown in FIG. 3, for example. are set, and the control circuit 4 uses the information from the sensors 2, 3, 10.
The steering angle control for 4L and 14R is performed separately.

That is, the control circuit 4 first calculates f (V) based on FIG. 2 based on the input of the vehicle speed signal V from the vehicle speed sensor 3, and then calculates f (
V) is positive or negative, and then it is determined whether the front wheel steering direction is right or left from the front wheel steering angle signal δf input from the front wheel steering angle sensor 2, and if f(V)>0 The rear wheels are steered in the same direction as the front wheels, and if f(V)<0, the rear wheels are steered in the opposite direction to the front wheels.

Next, the left rear wheel rotation speed signal W and the right rear wheel rotation speed signal WR from the rear wheel rotation speed sensor 15 are used to calculate the slip ratios Δ■ and ΔVR of the left rear wheel and the right rear wheel.

Calculation of slip rate is l rWL-Vl l rWR-V
This can be easily done using the following equations: lΔVL=−■−−, ΔvR=−7−−. In the above formula, r is the tire radius.

The coefficients αL and αR are calculated from the above slip rates ΔvL and ΔVR based on the data shown in Figure 3, and the next iteration δfXf
(V) Xat = δr1.

Calculate the left rear wheel steering angle δrL + right rear wheel steering angle δrH to be steered using the formula δfXf(V)Xαa=δrR,
The left and right rear wheel actual steering angle signals δrLT and δrRT inputted from the left and right rear wheel steering angle sensors 10 and 10, respectively, are compared with the left and right rear wheel steering angles δrL+δ, R to be steered, respectively, and the left and right rear wheel steering angles are determined. Wheel steering machine Mejogo 7. It outputs an output signal to rotationally drive each electric motor 5.
The wheels are steered so that they almost match R.

In the above, the slip ratio increases as the front wheel steering angle and vehicle speed increase, and as the road surface becomes smaller, so even if you turn the steering in the same way at the same vehicle speed, the slip ratio will be different when the road surface p is large and small. different. Therefore, by setting the coefficients αL and αR to be calculated using increasing functions that gradually increase as the slip ratio increases as shown in Figure 3, if the left and right rear wheels are designed for different road surfaces, the The slip rate of the rear wheels on the lower side of the river is greater than the slip rate of the rear wheels on the higher side of the river, and the coefficient of the rear wheels on the lower side of the river becomes larger, causing the steering angle of the rear wheels on that side to be smaller than that of the rear wheels on the opposite side. This increases the resistance to build-up of the lower rear wheel (i.e. cornering force) and prevents unexpected changes in vehicle behavior such as vehicle spin.

That is, the left and right rear wheels are controlled to steering angles that match their respective slip rates, minimizing changes in vehicle behavior due to variations in road surface angle, and improving steering stability.

The embodiment shown in FIG. 4 above shows an example in which the slip ratio ΔVL+ΔVR of each rear wheel is calculated from the left and right rear wheel rotational speed and the vehicle speed, and each coefficient αL, αR is calculated from the slip ratio. In addition to the above method, the turning radius is estimated from the vehicle speed signal V and the front wheel steering angle signal δf, and the standard rotation speed of the left and right rear wheels is estimated from the difference in rotation speed of the inner and outer wheels that occurs at the turning radius. Compare the actual rotation speeds Wt and WR of the left and right rear wheels obtained from the wheel rotation speed sensors 15, 15, respectively, and if the actual rotation speed is lower than the rotation speed estimated above, it is determined that the road surface level is low and the A control method that provides a larger steering angle than in the case of a road surface may be adopted.

In the illustrated embodiment, an electric motor is used as the actuator for steering the rear wheels, and the rotation of the electric motor drives the reduction gear mechanism and the pinion gear.

Although a structure in which the rear wheels are steered through a rack shaft or the like is shown, the rear wheel steering actuator and the mechanism for transmitting the steering force from the actuator to the rear wheels are other than those in the above-illustrated embodiment. For example, any configuration may be adopted, such as a mechanism that steers the rear wheels using the hydraulic pressure of a hydraulic actuator.

Effects of the Invention As described above, according to the present invention, when steering by rotating the steering wheel, the slip state of each of the left and right rear wheels is detected, and the steering angle of the left and right rear wheels is adjusted according to the slip state. By adopting separate control methods, for example, even if the left and right road surfaces have different friction coefficients, the left and right rear wheels are always controlled to the optimal steering angle for the road surface conditions, and changes in vehicle behavior due to changes in road surface friction resistance are avoided. can be kept extremely small,
It can significantly improve steering stability,
This can bring about great practical effects.

[Brief explanation of the drawing]

Fig. 1 is an explanatory plan view showing an embodiment of the present invention, Fig. 2 is a diagram showing an example of a vehicle speed function for calculating the rear wheel steering angle, and Fig. 3 is a diagram showing the rear wheels when calculating the rear wheel steering angle. FIG. 4 is a flowchart showing an example of the rear wheel steering angle control '4JIJ mode according to the present invention. ■...Steering handle, 2...Front wheel steering angle sensor, 3...Vehicle speed sensor, 4...Control circuit, L. R... Rear wheel steering mechanism, 10... Rear wheel steering angle sensor, 1
4L, 14R...Rear wheel, 15...Rear wheel rotation speed sensor. that's all

Claims (3)

[Claims] (1) The control circuit determines the direction and steering angle in which the rear wheels should be steered based on the steering angle of the front wheels accompanying rotation of the steering wheel and the vehicle speed at that time, and issues an output signal to create a rear wheel steering mechanism. In the rear wheel steering system of an automobile, which operates the rear wheels to steer the rear wheels, the left rear wheel steering mechanism and the right rear wheel steering mechanism, which respectively steer the left and right rear wheels separately, are made independent of each other. The control circuit determines the slip status of the left and right rear wheels from the respective rotation speed information of the left and right rear wheels.
A method for controlling a rear wheel steering device for an automobile, characterized in that a rear wheel steering angle determined from the front wheel steering angle and the vehicle speed is corrected and controlled in accordance with the slip state. (2) The control circuit calculates each slip rate of the left and right rear wheels from the respective rotation speed information of the left and right rear wheels, and increases the rear wheel steering angle determined from the front wheel steering angle and the vehicle speed as the slip rate increases. 2. A method of controlling a rear wheel steering device for an automobile according to claim 1, wherein said correction control is performed as follows. (3) The control circuit uses standard rotational speed information for the left and right rear wheels, estimated from the turning radius estimated from the front wheel steering angle and vehicle speed, and taking into account the difference in rotational speed between the inner and outer rear wheels. The system compares the rotation speed and determines whether the frictional resistance of the road surface is high or low based on the slip state of the left and right rear wheels, and gives a large steering angle to the rear wheel on the side where the frictional resistance of the road surface is determined to be low. A method of controlling a rear wheel steering device for an automobile according to claim 1, characterized in that correction control is performed.