JPH05208683A - Electrically-driven power steering device - Google Patents

Abstract

PURPOSE:To improve a return characteristic of a handle and a driving feeling at the time of low car speed by performing fuzzy inference based on two parameters of a steering condition of steering system, calculating a correction value in accordance with a return condition of steering, and previously correcting a drive control value of a motor when steering is returned. CONSTITUTION:In addition to giving outputs of a car speed sensor 12 and a torque sensor 11 to a fuzzy inference part 30, it is given an output from a steering angular speed sensor 31 and a differentiation value of detected torque VT from a phase compensation part 17. The fuzzy inference part 30 performs fuzzy inference with a car speed, steering torque, differentiation value of the torque VT and a steering angular speed serving as input parameters, to estimate a return condition of steering and to calculate a return time assist gain output to a multiplication arithmetic part 16. In the multiplication arithmetic part 16, an output of a multiplication arithmetic part 15 is multiplied by the return time assist gain from the fuzzy inference part 30 and output to a current control part 20 in the late stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus suitable for use in a vehicle, and more particularly to a power steering apparatus which assists a steering force with a rotational output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering systems using a motor instead of a hydraulic type have been used as a vehicle power steering device, and the motor has an increasing tendency in the future due to advantages such as small size and light weight as an actuator.

In the conventional power steering system, the torque sensor detects the steering torque of the steering system, the vehicle speed sensor detects the vehicle speed, and the drive of the motor connected to the steering system is controlled based on the detection results. , Power assist is done. Generally, it is a vehicle speed sensitive type, and the assist force is controlled according to the torque sensor input so that it is light in the low speed range and heavy in the high speed range.

By the way, in the above-mentioned conventional apparatus, since the torque of the assisting motor is reduced by the gears and transmitted to the rack shaft or the like, the moment of inertia of the assisting motors acts as if they were large, and the gears act as if they were geared. There is a problem that the astringency at high vehicle speed is deteriorated due to the friction of the vehicle and the steering wheel return at low vehicle speed is deteriorated.

Therefore, in order to solve such a problem, for example, a device for braking a assist motor in the vicinity of the neutral position of the steering wheel has been considered, for example, by providing a circuit for braking when the vehicle speed is high (for example, actual opening 61). -169
675).

[0006]

However, in the conventional device of such an improvement, since the instability at high vehicle speed is stabilized by viscous braking, the stability cannot be improved. However, there is a problem that the driver feels tired and anxious because the returning speed of the steering wheel is insufficient especially at low vehicle speed.

Therefore, an object of the present invention is to provide an electric power steering apparatus which can improve the steering wheel return characteristic at a low vehicle speed to improve the driving feeling.

[0008]

To achieve the above object, an electric power steering apparatus according to the present invention comprises a motor connected to a steering system for generating a steering assist torque,
Steering torque detecting means for detecting the steering torque of the steering system,
A steering state of the steering system in an electric power steering apparatus comprising: vehicle speed detecting means for detecting a vehicle speed; and control means for controlling driving of the motor based on outputs of the steering torque detecting means and the vehicle speed detecting means. Based on at least two parameters of the steering state detection means for detecting the steering torque, the vehicle speed, and the steering state of the steering system detected by the steering state detection means, and fuzzy inference is performed according to a predetermined fuzzy rule. Return correction calculation means for calculating a correction value according to the return state of the motor, and the control means corrects the drive control value of the motor when the steering wheel returns based on the calculated value of the return correction calculation means. And

[0009]

According to the present invention, at least two parameters (for example, vehicle speed, steering torque, differential value of steering torque, steering angle, steering angular velocity) of the steering torque, the vehicle speed, and the steering state of the steering system detected by the steering state detection means are used. , At least two or more parameters of the steering angular acceleration) are fuzzy inputs, fuzzy inference is performed, a correction value is calculated according to the return state of the steering wheel, and the assist at the time of returning the steering wheel is calculated based on the calculated value. The motor control value is corrected.

Therefore, fine control can be performed in a non-linear manner, and the assist torque is reduced when the steering wheel returns at a low vehicle speed, so that the steering wheel return speed is improved and the residual steering wheel angle is reduced, resulting in good return characteristics. Become.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 8 are views showing an embodiment of an electric power steering apparatus according to the present invention. FIG. 1 is a block diagram functionally showing the entire apparatus. FIG. 2 is a configuration diagram showing an example of a steering mechanical system to which the power steering device is applied.

First, the power steering mechanical system shown in FIG. 2 will be described. In FIG. 2, the rotational force of the steering wheel 1 is transmitted to the steering gear 2 including the pinion gear via the handle shaft, is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned through the knuckle arm and the like. To be done.

The rotational force of the steering assist (auxiliary) motor (DC motor) 6 controlled and controlled by the control device 5 is transmitted to the rack shaft 3 by the meshing of the steering gear 7 including a pinion gear and the rack shaft 3. The steering by the steering wheel 1 is assisted. The rotating shafts of the handle 1 and the motor 6 are mechanically connected by gears 2 and 7 and a rack shaft 3.

On the other hand, a steering torque sensor 11 (see FIG.
Steering torque (return torque) is detected by
The vehicle speed is detected by the vehicle speed sensor 12 (see FIG. 1). Then, the motor 6 is controlled by the control device 5 based on the detected torque, the vehicle speed, and the like. The control device 5 and the motor 6 have a battery 8 mounted on the vehicle.
Is supplied with its operating power.

The control device 5 includes detectors such as a current detector and a voltage detector, a drive circuit for driving the motor 6, a computer (CPU, for example, microprocessor) that controls the motor 6 as a whole, a memory, and a computer. It is composed of an interface circuit with the input / output device.

Next, FIG. 1 is a block diagram showing various functions of a computer incorporated in the control device 5 in a different manner.
It is drawn together with blocks showing output devices and various circuits. In this figure, the assist command section 10 includes a torque V detected by a torque sensor (steering torque detecting means) 11.
_T and the vehicle speed V _S detected by the vehicle speed sensor (vehicle speed detecting means) 12 are given. The assist torque value instruction function unit 13 in the assist command unit 10 outputs a command value representing the assist torque to be generated by the motor 6 according to the detected torque V _T.

Further, the multiplication constant function unit 14 detects the detected vehicle speed V _S
A constant is generated according to the above, and this constant is multiplied by the above-mentioned assist torque command value in the multiplication calculator 15. further,
The output of the multiplication calculation unit 15 is multiplied by the return assist gain from the fuzzy inference unit 30 described later in the multiplication calculation unit 16, and the output of the multiplication calculation unit 16 is supplied to the current control unit 20 as a reference current command value.

Here, the assist torque value (or motor current command value) output from the multiplication calculator 15 is a value determined by the detected torque V _T and the detected vehicle speed V _S , as shown in FIG.

[0019] Figure 3, according to the steering torque V _T, which substantially proportional to the motor current (assist torque is generated) flows against the steering torque V _T of a range, when it exceeds the above range, as constant motor current flows (the assist torque is generated), also according to the vehicle speed V _S, the motor current (assist when when the vehicle speed V _S is high to reduce the motor current (assist torque), the vehicle speed V _S is low It indicates that an assist command for controlling the motor 6 is generated so that the torque is increased.

On the other hand, the detected torque V _T is also given to the phase compensator 17, which detects the detected torque V _T.
The differential value of _T is added to the output of the multiplication calculation unit 16 to become the output of the assist command unit 10 (reference current command value), which is supplied to the current control unit 20. The current control unit 20 may be entirely configured by a hardware circuit, or a part of the current control unit 20 may be implemented by computer software.

The current control unit 20 includes a PWM (Pulse) that follows the H-bridge drive method including, for example, four switching elements.
The motor 6 is driven and controlled by a chopper operation using a (Width Modulation) pulse, and current feedback control is performed. That is, the armature current detector 26 detects the armature current ia of the motor 6, and the target current command value and the detected current ia given by the current deviation calculator 21.
The deviation from and is calculated. The absolute value of the deviation is obtained by the absolute value converter 24, and the duty generator 25 determines the duty ratio of the PWM pulse based on the absolute value.

On the other hand, the polarity (positive or negative) of the above-mentioned deviation is discriminated by the positive / negative discriminating section 22, and the polarity determined as the generated duty ratio is given to the motor driving section 23, and the motor driving section 23 determines these values. Based on the above, the four switching elements wired in the H bridge type are controlled to be turned on / off to drive the motor 6.

Reference numeral 30 denotes a fuzzy inference unit. The fuzzy inference unit 30 is supplied with the output of the vehicle speed sensor 12 and the output of the torque sensor 11, and also with the output from the steering angular velocity sensor 31 for detecting the steering angular velocity. With
The differential value of the detected torque V _T is given by the phase compensator 17. The steering angular velocity sensor 31 constitutes steering state detecting means.

A fuzzy inference section (corresponding to return correction calculation means) 30 performs fuzzy inference according to a predetermined fuzzy rule using vehicle speed, steering torque, a differential value of torque V _T and steering angular velocity as input parameters, and estimates a steering return state. Then, the return assist gain is calculated and output to the multiplication calculator 16. The multiplication calculation unit 16 multiplies the output of the multiplication calculation unit 15 by the return assist gain from the fuzzy inference unit 30 and outputs the result to the current control unit 20 in the subsequent stage. The rudder angular velocity detecting means may be, for example, a tacho generator or an encoder, or an observer for estimating the rudder angular velocity may be provided instead of the sensor. This observer estimates the steering angular velocity based on the terminal voltage of the motor 6 and the armature current, or based on the current command value to the motor 6 and the measured armature current.

Then, the differential value of the detected torque V _T detected by the phase compensator 17 is added to the output of the multiplication calculator 16 and the result is supplied to the current controller 20 as the output of the assist commander 10. The current control unit 20 and the assist command unit 10 constitute a control means 40.

Here, the fuzzy rule of the return assist gain calculation will be described. FIG. 4A is a membership function of the antecedent part in the return assist gain calculation, which uses the steering torque and the torque differential value as input parameters. Further, FIG. 4B is a fuzzy output in the consequent part, which is a membership function represented by a single tone position and has an assist decrease constant as an output value.

The assist gain at the time of return has a relationship represented by the following equation with respect to the assist decrease constant. [Return assist gain] = 1- [Assist decrease constant] The membership function is such that the assist decrease constant is set large when the handle 1 returns, so the return assist gain becomes small when the handle 1 returns. .. The meaning of the label in each membership function is as follows.

PL: Positive Large PS: Positive Small ZR: Zero (neutral) NS: Negative Small NL: Negative Large

The fuzzy rule is shown in FIG. 5, and is expressed by the following equation. The rule is so-called I
It is expressed in the form F, THEN (if any). R1. IF torque = PL AND torque derivative value =
NS THEN Fuzzy output = PL (larger in the positive direction) R2. IF torque = PS AND torque differential value =
NS THEN Fuzzy output = PS (smaller in the positive direction)

The fuzzy rule R1 is "if the steering torque is large in the positive direction and the torque differential value is small in the negative direction, the fuzzy output is large in the positive direction (ie,
Assist decrease constant is large in the positive direction). It means "."

Further, the fuzzy rule R2 is "if the steering torque is small in the positive direction and the torque differential value is small in the negative direction, the fuzzy output is small in the positive direction (that is, the assist decrease constant is in the positive direction). Small). " Hereinafter, other rules are determined by the same method. In each of the fuzzy rules shown in FIG. 5, the power assist is reduced when the steering wheel 1 returns to improve the return.

Next, the operation of the power steering control will be described. When the ignition switch is turned on, the normal power assist process is executed first,
The assist force is controlled according to the torque sensor input so that the vehicle speed sensitive control is performed, that is, it is light in the low speed range and heavy in the high speed range.

On the other hand, when the handle 1 returns, the return state is estimated by fuzzy inference, the return assist gain is calculated, and the result is output to the multiplication calculator 16. And
In the multiplication calculation unit 16, the output of the multiplication calculation unit 15 is multiplied by the return assist gain from the fuzzy inference unit 30 and output to the current control unit 20 in the subsequent stage, and finally the assist force is corrected and controlled.

Specifically, the membership function shown in FIG. 4 is evaluated, that is, the steering torque and the torque differential value are used as input parameters to evaluate how well the membership function is satisfied. Fuzzy logic operations are performed according to the fuzzy rules.

In the fuzzy logic operation process, the above-mentioned input parameters are given in the antecedent part of the fuzzy logic, the degree of conformity to the corresponding membership function of the fuzzy rule is determined, and the one with a small degree of conformity is selected and the consequent In the consequent part, the membership function of the output is restricted by the selected fitness in the consequent part to obtain, for example, a trapezoidal membership function. Then, the membership function is MA
The composite output is generated by superimposing the composite output by the X composite processing, and then the return assist gain according to the estimated value of the return state of the handle 1 is calculated by the defuzzifier using the center of gravity of the composite output as the definite output, and the multiplication calculator 16 is output.

In the multiplication calculation unit 16, the multiplication calculation unit 15 of the preceding stage is used.
Is multiplied by the calculated value from the fuzzy inference unit 30 (assist gain at return: assist decrease constant in FIG. 4B) and output to the current control unit 20 in the subsequent stage. After that, the current controller 20 controls the drive of the motor 6 by the chopper operation using the PWM pulse to assist the steering system.

Here, when the steering wheel 1 returns, the assist output works in a direction to stop the rotation of the steering wheel 1. In this embodiment, when the return of the steering wheel 1 is detected, the assist output is reduced by the calculation correction by the fuzzy inference.

FIG. 6A shows a control waveform when the control of this embodiment is not performed, and the return speed when the handle 1 is released is not sufficient. On the other hand, FIG. 6B shows a control waveform when the control of the present embodiment is performed, and the assist output is reduced, so that the return speed when the handle 1 is released is improved.

As described above, in this embodiment, since the return assist gain when the steering wheel 1 is released is determined by fuzzy inference, fine control can be performed in a non-linear manner. In particular, the assist torque is returned when the steering wheel is returned at a low vehicle speed. By decreasing, the steering return speed is improved, and the residual steering wheel angle is reduced, resulting in good return characteristics.

In this case, by using fuzzy inference,
It is possible to accurately determine at the time of returning, and the interpolation function, which is a feature of fuzzy reasoning, can obtain sufficient assisting force at the time of steering, while providing good returning characteristics at the time of returning.

Further, the interpolation function makes it possible to smoothly connect the steering torque at the time of shifting to so-called steering wheel turning, turning back and returning, and it is possible to obtain a good feeling and a good steering feeling.

Next, FIG. 7 is a diagram showing a first modification of the fuzzy rule in the fuzzy inference unit 30. In this first modified example, the steering torque and the steering angular velocity are used as input parameters, and are expressed as follows using an equation. Rules are expressed in the form of so-called IF, THEN (if, if). R1. IF torque = PL AND Steering angular velocity = NS THEN Fuzzy output = PL (large in positive direction) R2. IF torque = PS AND Steering angular velocity = NS THEN Fuzzy output = PS (small in the forward direction)

The fuzzy rule R1 is "if the steering torque is large in the positive direction and the steering angular velocity is small in the negative direction, the fuzzy output is large in the positive direction (that is, the assist reduction constant is large in the positive direction). It means "."

The fuzzy rule R2 states that "if the steering torque is small in the positive direction and the steering angular velocity is small in the negative direction, the fuzzy output is small in the positive direction (that is, the assist decrease constant is small in the positive direction). ). " Hereinafter, other rules are determined by the same method. In each of the fuzzy rules shown in FIG. 7, when the steering wheel 1 returns, the power assist is reduced to improve the return.

Also in this first modified example, since the steering torque and the steering angular velocity are used as the input parameters for detecting the steering state, it is possible to perform fine control in a non-linear manner as in the case of the above-described embodiment, and particularly at a low vehicle speed. By decreasing the assist torque when returning the steering wheel at this time, the returning speed of the steering wheel is improved, and the residual steering wheel angle is reduced, so that good returning characteristics can be obtained.

Next, FIG. 8 is a diagram showing a second modification of the fuzzy rule in the fuzzy inference unit 30. In the second modified example, the steering angle and the steering angular velocity are used as input parameters, and are expressed as follows using an equation. Rules are expressed in the form of so-called IF, THEN (if, if). R1. IF rudder angle = PL AND rudder angular velocity = NS THEN fuzzy output = PL (large in positive direction) R2. IF rudder angle = PS AND rudder angular velocity = NS THEN fuzzy output = PS (small in positive direction)

The fuzzy rule R1 is "if the steering angle is large in the positive direction and the steering angular velocity is small in the negative direction, the fuzzy output is large in the positive direction (that is, the assist reduction constant is large in the positive direction). It means "."

Further, the fuzzy rule R2 is "if the steering angle is small in the positive direction and the steering angular velocity is small in the negative direction, the fuzzy output is small in the positive direction (that is, the assist decrease constant is small in the positive direction). ). " Hereinafter, other rules are determined by the same method. Figure 8
In each of the fuzzy rules shown in (1), the power assist is reduced when the steering wheel 1 returns to improve the return.

Also in this second modified example, since the steering angle and the steering angular velocity are used as the input parameters for the steering state detection,
As in the case of the above embodiment, it is possible to perform fine control in a non-linear manner. By reducing the assist torque when returning the steering wheel at a low vehicle speed, the steering return speed is improved and the residual steering wheel angle is reduced. Therefore, the effect of good return characteristics can be obtained.

In the above embodiment, the fuzzy inference unit 30 which performs fuzzy inference is actually realized by software using a microcomputer, but it may be realized by hardware using a fuzzy chip, for example.

[0051]

According to the present invention, since the return assist gain when the steering wheel is released is determined by fuzzy inference, it is possible to perform fine control in a non-linear manner, and particularly to assist torque when returning the steering wheel at low vehicle speed. By making it smaller, the returning speed of the steering wheel can be improved, and the residual steering wheel angle can be made smaller to obtain good returning characteristics.

Further, since the fuzzy reasoning is used for the assist control, the determination at the time of returning can be accurately performed,
Furthermore, the interpolation function, which is also a feature of fuzzy inference, makes it possible to obtain a sufficient return force when returning while obtaining a sufficient assist force during steering. In addition, the interpolating function smoothly connects the steering torque at the time of shifting to so-called steering wheel turning, turning back and returning, and it is possible to obtain a good feeling and a good steering feeling.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an embodiment of an electric power steering apparatus according to the present invention.

FIG. 2 is a diagram showing an example of a power steering mechanical system of the same embodiment.

FIG. 3 is a diagram showing characteristics of assist torque in the same example.

FIG. 4 is a diagram showing a fuzzy rule used in fuzzy inference according to the embodiment.

FIG. 5 is a diagram showing a membership function used in fuzzy inference according to the embodiment.

FIG. 6 is a diagram showing a control waveform according to the embodiment.

FIG. 7 is a diagram showing a first modification of the fuzzy rule used in the fuzzy inference according to the embodiment.

FIG. 8 is a diagram showing a second modification of the fuzzy rule used in the fuzzy inference according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering wheel 6 Motor 11 Steering torque sensor (steering torque detection means) 12 Vehicle speed sensor (vehicle speed detection means) 20 Current control section 30 Fuzzy calculation section (return correction calculation means) 31 Steering angular velocity sensor (steering state detection means) 40 Control means

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Claims (2)

[Claims] 1. A motor connected to a steering system for generating a steering assist torque, a steering torque detecting means for detecting a steering torque of the steering system, a vehicle speed detecting means for detecting a vehicle speed, the steering torque detecting means and the vehicle speed. In an electric power steering apparatus including: a control unit that controls driving of the motor based on an output of a detection unit, a steering state detection unit that detects a steering state of the steering system, the steering torque, the vehicle speed, and Among the steering states of the steering system detected by the steering state detecting means, fuzzy inference is performed according to a predetermined fuzzy rule based on at least two parameters including the steering state, and a correction value according to the steering return state is calculated. A return correction calculation means, and the control means controls the steering wheel return time based on the calculated value of the return correction calculation means. 2. An electric power steering device according to claim 1, wherein the drive control value of the motor is corrected. 2. The steering state detecting means includes at least one of a steering angle detecting means for detecting a steering angle of a steering system and a steering angular velocity detecting means for detecting a steering angular velocity of the steering system, and the return correction calculating means. Fuzzy inference using at least two or more parameters of the vehicle speed, steering torque, differential value of steering torque, steering angle, and steering angular velocity as fuzzy inputs, and calculating a correction value according to the return state of steering. The electric power steering apparatus according to claim 1, wherein