JPH0339860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control device for an electric power steering device for an automobile.

Prior Art In automobiles, in order to reduce the need for steering wheel operations when turning the steering wheel, a torque sensor is provided to detect the steering torque during the steering operation, and this converts the steering torque into an electrical quantity. An electric power steering device has already been developed that variably controls the output of the electric device in response to changes in the steering torque and performs power assist in accordance with the steering torque (see, for example, Japanese Patent Publication No. 41246/1983).

Problems to be solved by the invention: In an electric power steering system that uses the output of an electric motor to assist the steering force of the vehicle's steering wheel to reduce the steering force, it is difficult to return the steering wheel after turning the steering wheel. However, there is a problem in that the inertia force of the electric motor is significantly deteriorated by friction of the motor speed reducer.

The present invention improves the return characteristic of the steering wheel to the straight-ahead position, that is, the neutral position, by extremely simple means, and also enables the driver to select the return characteristic according to his/her preference.

Means for Solving the Problems The present invention provides an electric power steering device that performs power assist for steering using the output of an electric motor, in which an assist direction motor current command value is issued based on a torsional torque signal of a steering shaft. a motor current instruction section; a return direction motor current instruction section that issues a return direction motor current command value of a predetermined value in the direction of returning to the straight running direction according to the steering angle; and a return direction motor current command of the return direction motor current instruction section. a multiplication coefficient setting section that issues a multiplication coefficient signal that is multiplied by the value and changes its magnitude; A control circuit is provided which adds a value obtained by multiplying a current command value by a multiplication coefficient signal from a multiplication coefficient setting section and controls a current value supplied to the electric motor based on the added value. be.

Function The present invention operates as follows by employing the above configuration.

The control circuit is driven by an addition signal of a return direction motor current command value having a predetermined magnitude in the direction of returning to the straight direction according to the steering angle and an assist direction motor current command value based on the torsional torque signal of the steering shaft. Therefore, when the assist direction motor current command value of the steering shaft is zero or close to zero, the above return direction motor current command value causes the electric motor to output in the direction of returning to the straight forward direction, thereby overcoming the resistance to the movement of the steering wheel in the return direction. In addition, by setting the multiplication coefficient signal according to the driver's preference, it is possible to provide the steering system with a steering wheel return torque that matches each person's driving sense.

Embodiments The present invention will be described in detail with reference to embodiments shown in the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, in which reference numeral 1 denotes a steering angle sensor 11 that detects the steering wheel angle, and a return torque value instruction function unit that issues a return direction motor current command value based on the signal. In the return direction motor current instruction section 12, the return torque value instruction function section 12 continuously changes the turning angle within a certain angle |θ°|, and returns to the straight direction when it exceeds |θ°| It is configured to generate a return direction motor current command value iθ having a constant value in the direction.

Reference numeral 2 denotes an assist direction motor current instruction section which includes a torsional torque sensor 21 that detects the torsional torque of the steering shaft, and an output torque value instruction function section 22 that issues an assist direction motor current command value based on the torsional torque sensor 21.

Reference numeral 3 denotes a multiplication coefficient setting section which generates a multiplication coefficient signal which is multiplied by the return direction motor current command value of the return torque value instruction function section 12 and changes its magnitude. It is configured to be multiplied by the directional motor current command value.

4 is a positive/negative discrimination section 41, an electric motor drive section 42,
A control circuit for a conventional electric power steering device consisting of an absolute value conversion section 43, a duty control section 44, and an armature current detection section 45. The output of the control circuit 4 drives the electric motor 5 and provides power assist to the steering mechanism 6. give.

That is, an addition signal is obtained by adding the multiplication signal obtained by multiplying the return direction motor current command value of the return direction motor current instruction section 1 by the multiplication coefficient signal of the multiplication coefficient setting section 3 and the signal from the assist direction motor current instruction section 2. When input to the control circuit 4, the positive/negative discriminator 41
The polarity of the signal is determined, and the electric motor drive section 42 determines the output direction of the electric motor.The absolute value conversion section 43 takes the absolute value of the signal, and the duty control section 44 converts it into the absolute value of the signal. The electric motor drive section 42 is controlled by comparing the output of the armature current detection section 45 to determine the duty ratio so that the motor current matches the indicated value (absolute value of the signal).

Before explaining the operating conditions of the device of the present invention, a general control mode of the electric power steering device will be explained.

In principle, conventional electric power steering devices use a torsional torque sensor 21 that detects the torsional torque of the steering shaft and generates _{a torsional torque signal V T as} shown in FIG. Power assist control during driving is performed by inputting the command value i of the output torque value instruction function unit 22 which issues the assist direction motor current command value i to the electric motor as shown in FIG. 3 into the control circuit 4. It's on.

In other words, when turning the steering wheel slightly during steering, the torsional torque signal V _T changes as shown in Figure 2.
When V _R1 or V _L1 is reached, the signal V _R1 or V _L1 determines whether the steering wheel is operated to the right or to the left, and determines the direction of the current to be applied to the electric motor. Further, when the handle is rotated and the torsional torque signal V _T reaches the level of V _R2 or V _L2 , the control circuit starts operating according to that signal, and from then on, the control circuit operates as shown in Fig. 3 according to the torsional torque signal. The electric motor is designed to provide power assist to the electric motor according to the torsional torque of the steering shaft.

In the present invention, as shown in FIG. 1, a torsional torque sensor 21 detects the torsional torque of a conventional steering shaft, and an output torque value instruction function section 22 which issues an assist direction motor current command value i based on the torsional torque signal V _T thereof. In addition to the assist direction motor current instruction section 2 consisting of the assist direction motor current instruction section 2, a steering angle sensor 11 that detects the steering wheel angle, and the return torque value instruction function section 12 that issues the return direction motor current command value iθ based on the signal. A motor current instruction section 1, and a multiplication coefficient setting section 3 for emitting a multiplication coefficient signal K that is multiplied by the return direction motor current command value and changes its magnitude,
The sum of the assist direction motor current command value i of the assist direction motor current instruction section 2 and the value K·iθ obtained by multiplying the return direction motor current command value iθ of the return direction motor current instruction section 1 by the multiplication coefficient signal K. The present invention is characterized in that a control circuit 4 is provided to control the current value supplied to the electric motor at the value i+K·iθ.

The multiplication coefficient setting section 3 can freely select and set the multiplication coefficient signal K within a setting range.

That is, as shown in FIG. 4, the return direction motor current indicator 1 changes continuously in the range below a certain angle |θ°|, and returns to a constant value in the straight direction when it exceeds |θ°|. It is configured to generate a directional motor current command value iθ.

For example, when the steering wheel is turned to the right, a multiplication value -K·iθ obtained by multiplying the return direction motor current command value −iθ by this steering angle by the multiplication coefficient signal K is added to the assist direction motor current command value i in FIG. As a result of this addition, the assist direction motor current command value i gradually moves downward in parallel, and when the steering angle exceeds θ°, the assist direction motor current command value i moves downward by K·iθ as shown in FIG. You will get a parallel shifted signal.

Based on this output signal, the control circuit 4 controls the electric motor 5 by changing the conventional current control characteristic shown by the solid line in FIG. The steering mechanism 6 performs rotation control and provides power assist to the steering mechanism 6.

As described above, when the steering with power assist by the electric motor 5 is completed and the vehicle returns to straight-ahead running, the assist direction motor current command value i becomes zero for the operation force of the steering wheel. At that time, the steering angle is naturally greater than θ°, so the control characteristic of the control circuit 4 is in a state in which the steering angle is shifted downward in parallel by an amount corresponding to K·iθ, as shown by the dotted line in FIG. When the torsional torque is less than a predetermined value, the electric motor 5 generates an output in the left-turning direction represented by -K·iθ, and the electric motor 5 generates an output in the steering wheel return direction. The rotational torque of the electric motor 5 cancels the resistance to the movement of the steering wheel in the return direction due to the inertia of the electric motor, the friction of the reducer, etc., so the steering mechanism 6 can accurately move straight due to the caster effect on the wheel side. Return to direction.

When the steering mechanism approaches the straight-ahead position and the steering angle enters the range within θ°, the return direction motor current command value gradually approaches zero as shown in Figure 4, so the control characteristics of the control circuit 4 are as shown in Figure 5. The control characteristic of the control circuit 4 becomes as shown by the solid line in FIG. It returns to the same state as before.

In the above, the return direction motor current command value iθ that should generate the return direction torque when the assist direction motor current command value i is zero is determined by the return torque value instruction function section 12, so the return torque value instruction By appropriately setting the function of the function section 12, it is possible to generate a motor torque that exactly cancels the element that resists the steering wheel return force from the wheel side due to the caster effect or the like.

In the above embodiment, a steering angle sensor that detects the steering angle of the steering wheel was used, but in the case of a rack and pinion gearbox, the stroke amount of the rack shaft or the rotation angle of the king pin can be used. Of course.

Also, the return direction motor current indicator 12 is at a certain angle |
θ゜｜In the above, we have mentioned the one that issues a constant return direction motor current command value in the direction of returning to the straight traveling direction.
It is also possible to use one that issues a return direction motor current command value that increases or decreases as the steering angle increases.

Note that the present invention can be applied to a vehicle in which the assist direction motor current command value or the return direction motor current command value is variably controlled in accordance with the vehicle speed, and the power assist amount is gradually decreased as the vehicle speed increases. Of course.

Effects of the Invention The present invention provides a return direction motor current instruction unit that issues an assist direction motor current command value based on a torsional torque signal of the steering shaft and a return direction motor current command value of a predetermined value in the direction of returning to the straight traveling direction according to the steering angle. The value obtained by multiplying the return direction motor current command value by the multiplication coefficient signal of the multiplication coefficient setting section is added, and the added value of both signals changes the current control characteristics to the electric motor so that the steering direction is turned to the right. In the case of , the motor is moved downward in parallel, and in the case of a left-hand turn, it is moved upward in parallel, thereby generating an electric motor output in the steering wheel return direction when the assist direction motor current command value is zero or close to zero. , the resistance to the return direction of the steering wheel caused by the inertia of the electric motor, the friction of the speed reducer, etc. can be canceled, and the return characteristics of the steering wheel of the electric power steering device can be significantly improved.

Further, by selecting and setting the multiplication coefficient signal within a set range by the driver, the steering wheel return force can be adjusted according to the driver's preference, so that the desired steering feel can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Figs. 2 and 3 show control modes of a conventional electric power steering device, and Fig. 2 is a torsional torque signal characteristic diagram of a steering shaft. FIG. 3 is a characteristic diagram of current control to the electric motor based on the torsional torque signal. 4 and 5 are diagrams showing an example of the control mode of the electric power steering device according to the present invention, in which FIG. 4 is a steering angle signal characteristic diagram, and FIG. 5 is a diagram showing assist direction motor current command value and return direction. FIG. 4 is a characteristic diagram of current control to the electric motor based on a signal added to a motor current command value. DESCRIPTION OF SYMBOLS 1... Return direction motor current instruction section, 11... Rudder angle sensor, 12... Return torque value instruction function section, 2
... Assist direction motor current instruction section, 21 ... Torsional torque sensor, 22 ... Output torque value instruction function section, 3 ... Multiplication coefficient setting section, 31 ... Multiplication calculation section, 4 ... Control circuit, 5 ... Electric motor, 6...
Steering mechanism.

Claims (1)

[Claims] 1. In an electric power steering device that performs power assist for steering using the output of an electric motor, there is provided an assist direction motor current instruction section that issues an assist direction motor current command value based on a torsional torque signal of the steering shaft; a return direction motor current instruction section that issues a return direction motor current command value of a predetermined value in the direction of returning to the straight traveling direction in accordance with the return direction motor current instruction section; a multiplication coefficient setting unit that issues a multiplication coefficient signal to cause Add the values obtained by multiplying the coefficient signals,
A control device for an electric power steering device, comprising a control circuit that controls a current value supplied to an electric motor based on the added value.