JPH01285459A - Electric power steering control method - Google Patents

Abstract

PURPOSE:To make motor braking effort at the time of vehicle high speed controllable by making an armature circuit of an electric motor so as to be short- circuited on the basis of sensor signals including a car speed signal or the like. CONSTITUTION:An H bridge circuit, driving an electric motor of an electric power steering system has transistors 1-4, a motor 5, a relay RL or the like. At the time of high speed driving, this relay RL comes to be opened, and supply voltage is made so as not to be fed to the H bridge circuit. In this state, a duty ratio of a transistor driving PMW signal is calculated on the basis of car speed and steering force, and this calculated PMW signal is outputted to the electric motor. With this constitution, the motor 5 is given its braking effort by this signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control method for electric power steering in which steering force is assisted using an electric motor, and in particular, the present invention relates to a control method for electric power steering that uses an electric motor to assist the steering force. The present invention relates to an electric power steering control method that improves straight-line stability.

[Conventional technology]

Conventionally, an electromagnetic clutch has been used to cut off the mechanical connection between the output shaft of the electric motor and the reduction gear, and to cut off the electric power supplied to the electric motor, thereby stopping steering force assist when the vehicle is running at high speed, and improving safety. I was planning.

[Problem to be solved by the invention]

However, in such a method, due to the influence of the mechanical inertial system, convergence performance is poor when the vehicle is running at high speed, and there is a problem particularly in straight-line stability after sudden steering.

In contrast, no control method has been proposed that actively increases straight-line stability, and there has been a demand for this type of control method.

[Means to solve the problem]

In order to meet such demands, the electric power steering control method according to the present invention cuts off the power supply to the electric motor and drives a predetermined transistor with a PWM signal for driving a transistor with a duty ratio determined by a sensor signal such as a vehicle speed signal. This short-circuits the armature circuit of the motor to control the braking force of the motor when the vehicle is running at high speed.

[Effect]

In the electric power steering control method according to the present invention, the fluctuation of the vehicle after sudden steering during high-speed running is significantly reduced compared to the conventional method, and the straight-line stability is significantly improved.

〔Example〕

Figure 2 shows the H bridge circuit that drives the motor. In the figure, 1 to 4 are transistors, 5 is the motor, T is the power supply terminal to which the power supply voltage from the battery is supplied, RL is the relay, and E is the ground. be.

First, operations other than when traveling at high speed will be explained.

When the vehicle is not running at high speed, relay RL is "closed" and power supply voltage is supplied from terminal T to the H bridge circuit. In order to rotate the motor 5 in the forward direction, as shown in FIG. 3, the transistor 1 is turned on and off at a duty ratio, the transistor 4 is turned on, and the transistors 2 and 3 are turned off. As a result, current flows through the motor 5 as shown by the solid arrow API in FIG. 2, and the motor 5 rotates in one direction. To rotate the motor 5 in the opposite direction, as shown in FIG. 4, the transistor 2 is turned on and off at a given duty ratio, the transistor 3 is turned on, and the transistors 1.4 are turned off.

As a result, current flows through the motor 5 as shown by the broken arrow AR2 in FIG. 2, and the motor 5 rotates in the opposite direction.

Next, the operation during high-speed running will be explained. During high-speed driving, relay RL is "open" and no power supply voltage is supplied to the H-bridge circuit.
As shown in the figure, when transistors 1 and 2 are turned on and off with a duty ratio of
4 is in the OFF state), when the motor 5 is rotating by an external force, a current, that is, an armature circuit current flows as shown by the dashed-dotted arrow AR3 in FIG. occurs. This braking force is shown in Figure 5(a).
P that turns on and off the transistor 1.2 shown in (b)
It is determined by the duty ratio of the WM signal.

Therefore, the braking force can be controlled by controlling the duty ratio. This duty ratio control includes, for example, control using a vehicle speed signal and steering force. In addition, the second
In the figure and FIG. 5, transistor 1.2 is turned on.
Although the case where the braking force of the electric motor 5 is controlled by turning it off is shown,
A similar effect can be obtained by turning on and off the transistor 3.4.

FIG. 1 is a flowchart for explaining an embodiment of the electric power steering control method according to the present invention. First, C
Initialize the PU (step 11) and perform a self-check (step 12). Next, a fail check is performed (step 13), and it is determined whether the mode is electric motor assist mode or electric motor braking mode (step 14).

Since the mode is electric motor assist except when driving at high speed, the process moves from step 14 to step 15 to calculate the PWM value from the vehicle speed and steering force, determine the direction, and output this PWM value and direction to the H-bridge circuit.Step 16 ), the electric motor 5 is driven in a predetermined direction and with a predetermined torque.

When driving at high speeds, it is in electric braking mode, so
Shifting from step 14 to step 17, first relay R
It is determined whether L is off (open) or not, and if it is off, the duty ratio of the PWM signal for driving the transistor is calculated from the vehicle speed and steering force (step 18), and this calculated PWM signal is output (step 19). Gives braking force to the electric motor 5.

Figure 6 shows an example of the duty ratio of the PWM signal in the case of electric motor braking. In the figure, the horizontal axis is the steering force, and the vertical axis is the PWM signal.
This is the duty ratio of the WM signal, and uses vehicle speed as a parameter. Sl is the characteristic curve when the vehicle speed is 80 km/h, S
2 is a characteristic curve when the vehicle speed is 50 km/h.

FIG. 7 is a graph comparing a vehicle to which the present invention is applied and a conventional vehicle in terms of straight-line stability.

The characteristic curve S3 shows the characteristics of a conventional vehicle, and the characteristic curve S4
0 shows the characteristics of a vehicle to which the present invention is applied. It can be seen that the straight-line stability of the vehicle to which the present invention is applied is far superior to that of the conventional vehicle.

〔Effect of the invention〕

As explained above, the electric power steering control method according to the present invention cuts off power supply to the electric motor, and drives a predetermined transistor with a PWM signal for driving a transistor with a duty ratio determined by a sensor signal such as a vehicle speed signal. By short-circuiting the armature circuit to control the electric motor braking force when the vehicle is running at high speeds, vehicle fluctuations caused by sudden steering at high speeds are significantly reduced compared to before, and straight-line stability is greatly improved. It has the effect of

[Brief explanation of the drawing]

FIG. 1 is a flowchart for explaining an embodiment of the electric power steering control method according to the present invention, FIG. 2 is a circuit diagram showing a general H bridge circuit, and FIGS. FIG. 6 is a graph showing an example of the duty ratio of the PWM signal with respect to vehicle speed and steering force. FIG. 7 shows the characteristics of a vehicle to which the present invention is applied and a conventional vehicle. This is a comparison graph. 1 to 4...transistor, 5...motor, T...
Power terminal, RL...relay, E...earth.

Claims (1)

[Claims] The rotational direction of the steering force assist electric motor is controlled by on/off control of a transistor constituting an H-bridge circuit, and the torque of the electric motor is controlled by a transistor drive PW.
In an electric power steering control device that performs duty ratio control of the M signal, power supply to the electric motor is cut off, and a predetermined transistor is driven with the transistor driving PWM signal with a duty ratio determined by a sensor signal such as a vehicle speed signal. An electric power steering control method that short-circuits an armature circuit of the electric motor to control the braking force of the electric motor when the vehicle is running at high speed.