JPH068834A - Motor-driven type power steering device - Google Patents

Abstract

PURPOSE:To improve the stability of automatic drive at a high vehicle speed without applying an instable feeling and fatigue feeling to a driver without adding the unnecessary viscosity in the return of steering. CONSTITUTION:A motor-driven type power steering device is equipped with an assisting motor 6, torque sensor 21, car speed sensor 22 and a control means 100 for controlling the drive of the motor 6 on the basis of the outputs of the sensors 21 and 22. A motor speed detecting means 30 for detecting the revolution speed of the motor 6, steering state detecting means 50 for detecting the cut-in time of a steering system on the basis of the outputs of the torque sensor 21 and the motor speed detecting means 30, and a viscosity compensation means 60 for calculating the viscosity compensation value for compensating the viscosity of the motor 6 so as to apply brake to the motor 6, when the steering state detecting means 50 detects the cut-in time of the steering system are provided. The control means 100 corrects the control value for controlling the drive of the motor 6 on the basis of the viscosity compensation value calculated by the viscosity compensation means 60.

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 device suitable for use in a vehicle, and more particularly to a power steering device for assisting steering force by the 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 gear and transmitted to the rack shaft or the like, the assisting motor acts as if the moment of inertia of the assisting motor were large, and the gears also acted as if they were geared. There is a problem that the astringency at high vehicle speed deteriorates due to the friction of the vehicle and the steering wheel return at low vehicle speed deteriorates.

Therefore, in order to solve such a problem, the present applicant adds a viscosity compensation value according to the steering angular velocity (for example, the viscosity is added at a high vehicle speed and the viscosity is canceled at a low vehicle speed) to assist the vehicle. A device that appropriately corrects the viscosity of the motor and reduces the aggregating property at high vehicle speed and the steering wheel returning characteristic at low vehicle speed has been previously proposed (for example, see Japanese Patent Laid-Open No. 3-178868). .

[0006]

However, in the improved conventional device, the viscosity compensation value of the motor is changed only in accordance with the vehicle speed. Also, the same viscosity was added, and unnecessary viscosity was added even when the steering wheel returned. As a result, there is a problem in that the returning speed at the time of returning without releasing is reduced, the steering is not immediately returned to neutral, and the driver feels anxious and tired. In this case, the hand-over stability (convergence) is deteriorated especially at high vehicle speeds.

Therefore, the present invention does not add unnecessary viscosity when returning the steering wheel, and can improve the hand-release stability at high vehicle speed without giving the driver a feeling of anxiety and fatigue. Is intended to provide.

[0008]

In order to achieve the above object, an electric power steering apparatus according to the present invention includes 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,
In an electric power steering apparatus including a vehicle speed detecting means for detecting a vehicle speed, and a control means for controlling driving of the motor based on outputs of the steering torque detecting means and the vehicle speed detecting means, a rotation speed of the motor is controlled. Motor speed detecting means for detecting, steering state detecting means for detecting when the steering system is turned based on the outputs of the steering torque detecting means and the motor speed detecting means, and the steering state detecting means for detecting the steering system being turned. And a viscosity compensating means for calculating a viscosity compensating value for compensating the viscosity of the motor so as to apply braking to the motor, and the control means is based on the viscosity compensating value calculated by the viscosity compensating means. The control value for controlling the driving of the motor is corrected.

[0009]

According to the present invention, when the steering system is turned on by using the steering torque and the motor speed as input data, the viscosity of the motor is corrected and the braking is applied.

Therefore, an appropriate viscosity is added only at the time of cutting, and on the contrary, unnecessary viscosity is not added at the time of returning the steering wheel, etc., and the returning speed at the time of releasing the hand is improved. Further, the steering immediately returns to neutral, and the driver does not feel anxious or tired. On the other hand, friction is added only when the steering system is turned, and an appropriate texture is obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 11 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 a pinion gear via the handle shaft, is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned via the knuckle arm and the like. To be done. Further, the rotational force of a steering assist (auxiliary) motor (DC motor) 6 controlled and driven by the control device 5 is transmitted to the rack shaft 3 by meshing between the steering shaft 7 including a pinion gear and the rack shaft 3, and the steering wheel 1 is operated. It will assist steering. 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 21 (see FIG.
Steering torque (return torque) is detected by
The vehicle speed sensor 22 (see FIG. 1) detects the vehicle speed. 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 unit 20 includes a detection torque V of a torque sensor (steering torque detection means) 21.
_T and the vehicle speed V _S detected by the vehicle speed sensor (vehicle speed detecting means) 22 are given. The assist torque value instruction function unit 23 in the assist command unit 20 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 24 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 25. As a result, the assist torque value (or motor current command value) output from the multiplication calculator 25 becomes a value determined by the detected torque V _T and the detected vehicle speed V _S , as shown in FIG.

[0017] 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 as to increase the torque.

The detected torque V _T is also given to the phase compensator 26. In the phase compensator 26, the detected torque V _T
Is calculated, and a signal obtained by multiplying the differential value by a constant corresponding to the vehicle speed V _S generated in the differential multiplication constant function unit 27 is output. Then, the output of the phase compensation unit 26 is added to the output of the multiplication calculation unit 25, whereby the assist command unit 2
The output of 0 (reference current command value) is supplied to the current controller 40.

A command value for viscosity compensation, which will be described later, is added to the reference current command value, and then added to the current control section 40 as a target current command value. The current control unit 40 may be entirely configured by a hardware circuit, or a part thereof may be realized by computer software.

The current control section 40 is a PWM (Pulse) that follows the H-bridge drive method including, for example, four switching elements.
The motor 6 is driven and controlled by the chopper operation using the (Width Modulation) pulse, and the PWM pulse is determined so that the current target value and the current detection value im match.

For example, in the case of current feedback P (proportional) control, the armature current detector 46 detects the armature current of the motor 6, and the current target value and the current given by the voltage manipulated variable calculator 41 are detected. The deviation from the detected value im is calculated. The absolute value of this deviation is obtained by the absolute value conversion unit 44, and P is generated by the duty generation unit 45 based on this absolute value.
The duty ratio of the WM pulse is determined.

The polarity (positive or negative) of the deviation is discriminated by the positive / negative discriminating unit 42, and the polarity discriminated as the generated duty ratio is given to the motor driving unit 43 and the motor driving unit 43.
Drives ON / OFF the four switching elements wired in the H-bridge type based on these values to drive the motor 6.

The above shows the case of the current feedback P (proportional) control, but there are other feedback control methods such as PI (proportional / integral) control and PID (proportional / integral / derivative) control. . In addition, the current control unit 4
A current control method in which a disturbance with respect to 0 is estimated and the disturbance is feedforward may be used.

On the other hand, the control value of the motor drive section 43 described above is inputted to the motor speed detection means 30 for detecting the rotation speed of the motor 6, and the motor speed detection means 30 calculates the motor voltage detection section 31 and the motor speed. It is configured by the unit 32.

Motor voltage detector 31 Based on the control value from the motor driver 43, the motor terminal voltage Vm is detected and output to the motor speed calculator 32. Motor speed calculator 32
In addition, from the armature current detection unit 46, the current detection value im
Has been entered. The motor speed calculator 32 calculates the motor speed ω based on the motor terminal voltage Vm and the detected current value im.
Is calculated according to the following formula. ω = Vm− (R × im) ………… where R is a constant

The detection of the motor speed ω is not limited to the method of calculating based on the motor terminal voltage Vm and the detected current value im, and it is needless to say that a sensor such as an encoder or a tachogenerator may be used. Not obvious.

The calculated motor speed ω is input to the steering state detecting means 50 and the viscosity command section 60. The steering state detecting means 50 detects a steering state of the steering system, for example, a cut, a return, a steering hold, and a hand-release neutrality.

Here, the notch of the steering system means
An operation in which a driver grips the steering wheel 1 and applies force to steer the steering wheel in an arbitrary direction (that is, turning the steering wheel).
The return of the steering system means that the steered steering wheel 1 that has been steered returns to the neutral direction. Steering of the steering system refers to an operating state in which the driver holds the steering wheel 1 and applies force to hold the steering wheel at a constant steering angle. The steering system released neutral is a state in which the steered steering wheel 1 that has been steered returns to the neutral position and the driver releases the steering wheel 1.

There are various methods for detecting the steering state, but in the present embodiment, they are detected by fuzzy inference.
That is, the detected torque V _T from the torque sensor 21 and the motor speed ω from the motor speed calculator 32 are input to the steering state detection means 50 that performs fuzzy inference.
The steering state detection means 50 performs fuzzy inference according to a predetermined fuzzy rule using the detected torque V _T and the motor speed ω (corresponding to the steering angular velocity) as input parameters, estimates the steering state of the steering wheel, and sets the steering state detection value S to the viscosity command It is output to the unit 60.

Next, a fuzzy rule for steering state estimation will be described. FIG. 4 is a membership function of the antecedent part in steering state estimation, which uses the detected torque V _T as an input parameter, and FIG. 5 uses the motor speed ω as an input parameter. Further, FIG. 6 is a fuzzy output in the consequent part, which is a membership function represented by a single tone position, and uses the steering state detection value S as an output value.

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. 7, and is expressed as follows using an equation. The rule is so-called I
It is expressed in the form F, THEN (if any). R1. IF torque = PL AND motor speed = N
S THEN Fuzzy output = RL (large in the positive direction: that is, a large steering cut) R2. IF torque = PS AND motor speed = N
S THEN Fuzzy output = RS (small in the positive direction: that is, the steering cut is small)

The fuzzy rule R1 shown in FIG. 7 states that "if the steering torque is large in the positive direction and the motor speed, that is, the steering angular speed is small in the negative direction, the fuzzy output is large in the positive direction (that is, steering The control is such that the notch is large and, as a result, the viscous braking is greatly increased. "

Further, if the steering torque is small in the positive direction and the motor speed, that is, the steering angular speed is small in the negative direction, the fuzzy output is small in the positive direction (that is, the steering cut is It is small, and as a result, control is performed so as to reduce viscous braking). " Hereinafter, other rules are determined by the same method.

In the fuzzy output (steering state detection value S) of the consequent portion in FIG. 6, ZR is a neutral position of the steering wheel, RL is a large steering return value, and RS is a small steering return value. Therefore, as a result, control is performed without applying braking to the motor 6.

The steering state detection value S, which is the output of the steering state detection means 50, is input to the viscosity command section 60, and the viscosity command section (corresponding to the viscosity compensation means) 60 is in the viscosity constant calculation section 6.
1, a vehicle speed multiplication constant function unit 62 and a multiplication calculation unit 63. The viscosity constant calculation unit 61 calculates the viscosity constant Kv according to the steering state detection value S from the steering state detection means 50, and multiplies this viscosity constant Kv by the vehicle speed multiplication constant Kf or Kr from the vehicle speed multiplication constant function unit 62. And outputs it to the multiplication calculator 63. The vehicle speed multiplication constant function unit 62 sets vehicle speed multiplication constants Kf and Kr as shown in FIG. 8 according to the vehicle speed.

The multiplication calculator 63 calculates the viscosity compensation value of the motor 6 according to the motor speed ω from the motor speed calculator 32, and multiplies this viscosity compensation value by the viscosity constant Kv from the viscosity constant calculator 61. Is set as the command value of the viscosity command unit 60, and this command value is added to the reference current command value of the assist command unit 20 and given to the current control unit 40 in the subsequent stage. The viscosity compensation value is, for example, such that the larger the motor speed ω, the larger the absolute value and the opposite torque is generated.

That is, the viscosity command unit 60 applies a viscous force to the movement of the steering angle, and basically generates a force for returning the steering angle to the neutral position, that is, a restoring force.
The assist command unit 20 and the current control unit 40 constitute the control means 100.

Next, the operation of this apparatus will be described. First, the torque sensor 21 detects the steering torque V _T of the steering system, the vehicle speed sensor 22 detects the vehicle speed V _S , and the drive of the motor 6 connected to the steering system is controlled based on these detection results. Power assist is performed. In this control, general vehicle speed-sensitive control, that is, the assist force is controlled according to the steering torque V _T so that it is light in the low speed range and heavy in the high speed range.

On the other hand, the steering state of the steering wheel 1 is detected by the steering state detection means 50 by fuzzy reasoning, and the viscosity command value is calculated by the viscosity command section 60 in accordance with the steering state, and the reference current of the assist command section 20 is calculated. It is added to the command value and given to the current control unit 40 in the subsequent stage, and finally the assist force is corrected and controlled.

FIG. 9 shows the viscosity constant K in the viscosity command section 60.
It is a flowchart which shows the process of v calculation. Explaining this flowchart, first, in step S1, a process of estimating a steering state and calculating a detection value S is performed. Specifically, the membership function shown in FIGS. 4 and 5 is evaluated, that is, the motor speed ω and the detected torque V _T are used as input parameters to evaluate how well the membership function is satisfied. Fuzzy logic operations are performed according to the fuzzy rules shown.

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 obtained, and the one having the smaller degree of conformity is selected and the consequent is selected. In the consequent part, the membership function of the output is limited by the selected fitness in the consequent part to obtain, for example, a trapezoidal membership function. Then, the membership function is
A composite output is generated by superimposing it by the X composition processing, and thereafter, the steering state detection value S of the steering wheel is obtained by the defuzzifier with the center of gravity of this composite output as the definite output, and is output to the viscosity constant calculation unit 61.

Next, in step S2, it is determined whether or not the steering is being turned. If the steering is being turned, the detected value S is S> 0. Therefore, in the subsequent step S3, the viscosity constant Kv is Kv = S ×. It is calculated according to the expression Kf. On the other hand, when the cutting is not performed, the detected value S is S
Since ≦ 0, in the subsequent step S4, the viscosity constant K
v is calculated according to the equation Kv = S × Kr.

In comparison with the prior art, conventionally, the viscosity was uniformly added only according to the vehicle speed. Therefore, if the viscosity is set to a large value, the addition of the large viscosity is originally necessary. Not even when the steering wheel returned, unnecessary viscosity was added, resulting in braking. As a result, the return speed at the time of releasing the handwheel is reduced, the steering is not immediately returned to the neutral state, and the driver feels anxious and tired.

On the other hand, the present embodiment is based on the idea that the viscosity is not added, or is set to a small value and the viscosity is increased only when necessary. That is, when the turning of the steering system is detected, the viscosity constant Kv is calculated according to the equation Kv = S × Kf, the viscosity of the motor 6 is corrected, and braking is added. The vehicle speed multiplication constant Kr becomes a large positive value as the vehicle speed increases. Therefore, a large friction is applied to the motor 6 according to the vehicle speed, and the rotation of the motor 6 is braked. Therefore, it is possible to obtain an appropriate texture when cutting.

On the other hand, when the steering system is not being turned, on the contrary, unnecessary viscosity is not added, and the returning speed at the time of releasing the hand is improved. As a result, the steering immediately returns to neutral, and the driver does not feel anxious or tired. In addition, it is possible to improve the hand-over stability (convergence) at a high vehicle speed.

Furthermore, since the amount of friction applied to the motor 6 is changed according to the vehicle speed, it is possible to obtain a convergence and a feeling of resilience according to the vehicle speed.

Explaining an actual driving example, FIG. 10 shows a control waveform when the steering wheel is released by pulse steering at a high vehicle speed (100 km / h). The figure shows a state in which the steering angle θ, the steering torque V _T , and the motor speed ω repeatedly oscillate after being released due to the influence of the inertia of the motor 6. Focusing on the steering state detection value S, after detecting a cut (S> 0) during pulse steering, it is also detected as a cut (S> 0) when the steering angle θ moves away from the midpoint.

FIG. 11 shows a control waveform when the vehicle is returned to the released state at a low vehicle speed (20 km / h). The return is detected (S <0) until the steering angle returns to the neutral position after the steering wheel is released (S = 0). Conventionally, as indicated by a broken line, the rudder angle θ has been gradually changed at the time of returning without releasing it, but in the present embodiment, unnecessary viscosity is not added, so that the returning speed is improved.

[0050]

According to the present invention, when the steering system is turned, the viscosity of the motor is corrected and the braking is applied. Therefore, an appropriate feeling of touch can be obtained when the steering is turned. On the contrary, when the steering system is not turned, unnecessary viscosity is not added, and the return speed at the time of releasing the hand is improved. As a result, the steering immediately returns to neutral, and the driver does not feel anxious or tired. Further, the hand-over stability (convergence) at high vehicle speed can be improved.

[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 membership function of an antecedent part of fuzzy inference using the detected torque of the embodiment as an input parameter.

FIG. 5 is a diagram showing a membership function of an antecedent part of fuzzy inference using a motor speed as an input parameter in the embodiment.

FIG. 6 is a diagram showing a membership function of a consequent part used in the fuzzy inference of the example.

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

FIG. 8 is a diagram showing a relationship between a vehicle speed and a vehicle speed multiplication constant in the embodiment.

FIG. 9 is a flowchart showing the processing of the viscosity constant calculation of the same embodiment.

FIG. 10 is a diagram showing a control waveform when pulse steering is performed and the wheel is released at a high vehicle speed in the embodiment.

FIG. 11 is a diagram showing a control waveform when the vehicle is released and returned at a low vehicle speed in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering wheel 6 Motor 20 Assist command part 21 Steering torque sensor (steering torque detection means) 22 Vehicle speed sensor (vehicle speed detection means) 30 Motor speed detection means 31 Motor voltage detection part 32 Motor speed calculation part 50 Steering state detection means 60 Viscosity command Part (viscosity compensation means) 61 viscosity constant calculation part 62 vehicle speed multiplication constant function part 63 multiplication calculation part 100 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. An electric power steering apparatus comprising: a control unit that controls driving of the motor based on an output of the detection unit; a motor speed detection unit that detects a rotation speed of the motor; a steering torque detection unit and a motor speed. Steering state detecting means for detecting the turning time of the steering system based on the output of the detecting means, and when the turning state of the steering system is detected by the steering state detecting means, braking of the motor is applied to the motor. A viscosity compensating means for calculating a viscosity compensating value for compensating viscosity is provided, and the control means uses the viscosity compensating means. Electric power steering apparatus characterized by correcting the control value for controlling the drive of the motor based on the issued viscosity compensation value. 2. The electric power steering apparatus according to claim 1, wherein the viscosity compensating means changes the braking amount according to the output of the vehicle speed detecting means.