JPH02117466A - Method for preventing steering wheel from moving - Google Patents

Abstract

PURPOSE:To make it possible to effectively prevent a steering wheel from moving by making an electric motor for steering dynamic braking at the time of sudden starting or sudden acceleration in an electric power steering device of a FF vehicle. CONSTITUTION:In a system in which an electric motor 5 for steering is driven and controlled by a H bridge circuit consisting of transistors 1-4, at the time of sudden starting an sudden acceleration of a vehicle, the motor 5 is dynamically braked by turning on and off the transistors 1, 1 at PWM value. Namely, in case that the transistor 1 is turned on, a short-circuit current flows like the arrow AR3 of a solid line, and in case that the transistor 2 is turned on, a short-circuit current flows like the arrow AR4 of a solid line. Hereupon, both of the transistors 1, 2 are turned on to make the short-circuit currents freely flow in any direction, brake fore is thereby applied to a steering wheel to prevent the steering wheel from moving.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for preventing steering wheel shake during sudden start or sudden acceleration of an FF (front engine front drive) vehicle, and in particular to a method for preventing steering wheel shake in an electric power steering device. It is about the method.

[Conventional technology]

Generally, in front-wheel drive cars, the engine is often placed horizontally, and due to constraints in its placement, the drive shafts that transmit rotational driving force to the front wheels may have unequal lengths on the left and right.
This causes a moment difference between the left and right sides around the king pin due to the rotational driving force, which causes a phenomenon called torque steer where the steering wheel is held in a fixed direction, especially during sudden starts and accelerations, resulting in a worsening of the steering feeling. was there.

A steering device that solved the above problem was developed in 1986.
It is described in Publication No. 82873. This device prevents steering wheel shake when the vehicle suddenly starts or accelerates by using a steering torque correction value, that is, reverse assist.

[Problem to be solved by the invention]

However, since conventional steering wheel shake prevention is based on reverse assist, there is a problem in that steering wheel shake is not sufficiently prevented when the amount of reverse assist changes depending on the characteristics of the vehicle or the like.

The present invention has been made in view of these points, and an object of the present invention is to provide a method for preventing steering wheel shake that is not affected by the characteristics of a vehicle or the like.

[Means to solve the problem]

In order to solve these problems, the present invention provides an electric power steering system for a front-wheel drive vehicle, in which a steering electric motor is dynamically braked during a sudden start or sudden acceleration.

[Effect]

In the method for preventing steering wheel shake according to the present invention, the steering electric motor is dynamically braked during a sudden start or sudden acceleration, and steering wheel shake is effectively prevented without being affected by the characteristics of the vehicle or the like.

〔Example〕

In an electric power steering device, a steering electric motor is normally driven by an H-bridge circuit.

The operation of the H bridge circuit will be explained using FIGS. 4 to 9.

FIG. 4 shows an H bridge circuit for explaining the assist operation. In the figure, 1 to 4 are transistors, 5 is a steering electric motor, T is a power supply terminal, RL is a relay, and E is a ground. FIG. 5 is a time chart showing the operation of each transistor for rotating the motor 5, for example, in the forward direction.

In FIG. 5, the transistor 1 is in an on-off operation, and the transistor 4 is in an on-operation, and a current flows through the motor 5 as indicated by the solid arrow API in FIG. FIG. 6 is a time chart showing the operation of each transistor for rotating the motor 5, for example, in the reverse direction. In FIG. 6, the transistor 2 is in an on-off operation, and the transistor 3 is in an on-operation, and a current flows through the motor 5 as indicated by a dotted arrow AR2 in FIG.

FIG. 7 shows an H-bluff circuit for explaining the operation when preventing steering wheel shake, and in this figure, the same or equivalent parts as in FIG. 4 are given the same reference numerals. FIG. 8 is a time chart showing one method of dynamically braking the electric motor 5, in which the electric motor 5 is dynamically braked by turning on and off transistors 1 and 2 according to a PWM value. When transistor 1 is turned on, a short circuit current flows as shown by the solid arrow AR3, and when transistor 2 is turned on, the short circuit current flows as shown by the solid arrow AR4.
Short-circuit current flows as follows. Therefore, transistor 1.
2 are both on, the short circuit current is free to flow in either direction. This short-circuit current generates a braking force on the steering wheel, preventing the steering wheel from shaking.

FIG. 9 is a time chart showing another method of dynamically braking the electric motor 5, in which the electric motor 5 is dynamically braked by turning on and off the transistor 3.4 at a PWM value. transistor 3
When transistor 4 is turned on, a short circuit current flows as shown by the dotted arrow AR5, and when transistor 4 is turned on, the short circuit current flows as shown by the dotted arrow AR5.
A short circuit current flows as shown in 6. Therefore, transistor 3
．． 4 are both on, the short circuit current is free to flow in either direction.

FIG. 1 is a flowchart for explaining an embodiment of a method for preventing steering wheel shake according to the present invention. First, C.P.
Initialize U (step 11) and perform self-check and fail check (step 12.13). Next, it is determined whether or not there is a sudden start (step 14). A sudden start is determined based on the amount of change in vehicle speed per unit time, that is, the magnitude of acceleration. When the acceleration exceeds a predetermined value, it is determined that the vehicle has started suddenly, and the process proceeds to step 15. Therefore,
Even if the vehicle suddenly accelerates while driving, the process may proceed to step 15.

In step 15, relay RL (see FIG. 7) is turned off. Next, the PWM vs. vehicle vs. train bull (hereinafter referred to as "table A") shown in FIG. 2 or the PWM vs. time table (hereinafter referred to as "table B") shown in FIG.
The WM value is calculated (step 16), and the PWM value is output (step 17). Table A is PWM depending on vehicle speed.
Table B controls the PWM value based on the elapsed time since the sudden start. Although it was assumed that relay RL was turned off in step 15, when the short-circuit current indicated by the dotted arrows AR5 and AR6 in FIG. do not have to. Further, control for preventing blurring can be performed when the steering wheel angle immediately before sudden start is within a predetermined value. That is, when the steering wheel angle is large enough to make the steering wheel angle (for example, 30 degrees or more left and right), the steering wheel operation can be regarded as the driver's intention, and control for preventing camera shake can be stopped.

If it is determined that there is no sudden start, the process moves to step 18,
A PWM value is calculated from the vehicle speed and steering force, and the PWM value is output together with a rotation direction command for the electric motor 5 (step 19).
.

〔Effect of the invention〕

As explained above, the present invention applies dynamic braking to the steering electric motor at the time of a sudden start or sudden acceleration, so that the magnitude of the braking force that prevents steering wheel shake is not affected by changes in the characteristics of the vehicle, etc. This has the effect of preventing insufficient blur prevention.

[Brief explanation of the drawing]

FIG. 1 is a flowchart for explaining the method for preventing steering wheel shake according to the present invention, FIGS. 2 and 3 are graphs showing examples of the relationship between PWM value versus vehicle speed and PWM value versus time, and FIG. 4 is a flowchart for explaining the steering wheel shake prevention method according to the present invention. 5 and 6 are circuit diagrams showing the H-bridge circuit for explaining the control of the steering electric motor.
The figures are a time chart for explaining the operation of the circuit in Fig. 4, Fig. 7 is a circuit diagram showing the H-bridge circuit for explaining the control of the steering electric motor when preventing steering wheel shake, and Figs. 8 and 9. The figure is a time chart for explaining the operation of the circuit of FIG. 7. 1 to 4...Transistor, 5...Steering electric motor, T
...Power terminal, RL...Relay, E...Earth.

Claims (1)

[Claims] A method for preventing steering wheel shake in an electric power steering device for a front-wheel drive vehicle, characterized by dynamically braking a steering electric motor during a sudden start or sudden acceleration.