JPH05131947A - Motor-operated power steering device - Google Patents

Abstract

PURPOSE:To perform simple detection of a neutral position at a low cost without using any expensive steering angle sensor by performing fuzzy inference based on a car speed, steering torque, and the rotation speed and rotation acceleration of a motor and estimating the neutral position of a steering handle. CONSTITUTION:A motor 6 which generates steering auxiliary torque is driven and controlled, by a control device 40 through a motor drive circuit 53 with the aid of a CPU 51 based on detected signals respectively from a steering torque sensor 11 and a car speed sensor 12. In this case, the current and the voltage of the motor are detected by a motor current/voltage detecting circuit 54 based on a drive pulse from the motor drive circuit 53 and inputted to the CPU 51. The rotation speed and rotation acceleration of the motor 6 are computed by the CPU 51 based on an input signal. Fuzzy inference is performed based on the car speed, the steering torque, and the rotation speed and rotation acceleration of the motor to estimate the neutral position of a steering handle. Further, the control value of the motor 6 is corrected according to an estimated value.

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.

FIG. 7 is a block diagram showing an example of a mechanical system of a conventional electric power steering apparatus. In this figure, the rotational force of a steering handle 1 is transmitted to a steering gear 2 including a pinion gear via a handle shaft. At the same time, it is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned through the knuckle arms and the like. Further, 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 shaft 7 including the pinion gear and the rack shaft 3, and the steering wheel 1 is used. 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 11 (see FIG.
Steering torque (return torque) is detected by
The vehicle speed is detected by the vehicle speed sensor 12 (see FIG. 8). 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. 8 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 10 is supplied with the detected torque V _T of the torque sensor 11 and the detected vehicle speed V _{S of the} vehicle speed sensor 12. 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. As a result, the assist torque value (or motor current command value) output from the multiplication calculator 15 becomes a value determined by the detected torque V _T and the detected vehicle speed V _S , as shown in FIG. 9.

FIG. 9 shows that when the steering torque V _T is in a certain range, a motor current almost proportional to the steering torque V _T flows (assist torque is generated) and 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.

The detected torque V _T is also given to the phase compensator 16, and the phase compensator 16 adds the differential value of the detected torque V _T to the output of the multiplication calculator 15,
The output (reference current command value) of the assist command unit 10 is supplied to the current control unit 20.

On the other hand, in addition to the assist command unit 10, the output of the regenerative brake command output unit 30 is added to the current control unit 20. The regenerative braking instruction output unit 30 includes a steering angle sensor 31 that detects the steering angle of the steering wheel 1.
The command value for detecting the neutral position of the steering wheel 1 based on the output of the steering wheel 1 and for instructing the motor 6 to apply the regenerative brake near the neutral position of the steering wheel 1 based on the above-described detected torque V _T and the detected vehicle speed V _S. Is added to the output of the assist command unit 10 and is supplied to the current control unit 20 as a final current command value.

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 generated duty ratio and the discriminated polarity are given to the motor drive section 23, and the motor drive section 23 determines these values. Based on the above, the four switching elements wired in the H-bridge type are turned on / off to drive the motor 6.

[0013]

However, in the above-mentioned conventional electric power steering apparatus, the regenerative braking of the motor is applied near the neutral position of the steering wheel and the viscous viscosity is improved in order to improve the steering performance, particularly the convergence. Since the structure is controlled, in this case, a detector such as an expensive steering angle sensor is required to detect the neutral position of the steering wheel, which causes a problem of increasing the cost of the device.

Therefore, an object of the present invention is to provide an electric power steering apparatus which can detect the neutral position of the steering wheel by utilizing an existing sensor without using an expensive steering angle sensor.

[0015]

In order to achieve the above object, an electric power steering apparatus according to a first aspect of the present invention is provided with an electric power steering apparatus, which is connected to a steering system and generates a steering assist torque, and a steering torque of the steering system. And a steering torque detecting means for detecting the vehicle speed, a vehicle speed detecting means for detecting the vehicle speed, and a control means for calculating a control value for controlling the motor based on the outputs of the steering torque detecting means and the vehicle speed detecting means. Type power steering apparatus, current detection means for detecting a motor current of the motor, voltage detection means for detecting a motor voltage of the motor, motor current value detected by the current detection means and voltage detection means, and motor The rotation speed of the motor based on the voltage value,
Rotation data calculation means for calculating rotation acceleration, and neutral position estimation means for determining the neutral position of the steering wheel by performing fuzzy inference according to a predetermined fuzzy rule with the vehicle speed, steering torque, motor rotation speed and rotation acceleration as input parameters. And the control means corrects the control value for controlling the motor based on the estimated value of the neutral position estimating means.

In a preferred embodiment, the control means is characterized in that when the neutral position estimating means estimates that the steering wheel is in the neutral position, the motor is regeneratively braked or the viscosity is controlled.

[0017]

In the present invention, the motor current value and the motor voltage value are detected, and the rotational speed and rotational acceleration of the motor are calculated based on these detected values. Then, using the vehicle speed, steering torque, rotation speed and rotation acceleration of the motor as input parameters, fuzzy inference is performed according to a predetermined fuzzy rule, the neutral position of the steering wheel is estimated and calculated, and if the steering wheel is near the neutral position. When it is estimated, regenerative braking is applied to the motor or viscosity control is performed to improve the steering performance, especially the convergence.

Therefore, an expensive detector such as a steering angle sensor is unnecessary for detecting the neutral position of the steering wheel, and the cost of the apparatus is reduced.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 6 are views showing an embodiment of an electric power steering apparatus according to the present invention. In explaining the present embodiment,
The same components as those of the conventional example are designated by the same reference numerals, and duplicate description will be omitted. FIG. 1 is a block diagram showing the hardware configuration of this apparatus.

In the figure, reference numeral 40 denotes a control device, and the control device 40 includes a steering torque sensor (steering torque detecting means) 11, a vehicle speed sensor (vehicle speed detecting means) 12, and an engine rotation sensor 41 for detecting an engine speed. An output signal from the temperature sensor 42 that detects the temperature of the motor 6 is input, and the control device 40 is connected to the ignition switch 43 and the battery 8.

The control device 40 is composed of a CPU 51 which controls the overall control of the motor 6, a relay drive circuit 52, a motor drive circuit 53, a motor current / voltage detection circuit 54 and a fail safe circuit 55. CPU
Reference numeral 51 calculates a processing value necessary for drive control of the motor 6 based on signals from the steering torque sensor 11, the vehicle speed sensor 12, the engine rotation sensor 41, the motor temperature sensor 42, and the ignition switch 43, and outputs a PWM pulse to the motor drive circuit. Then, the motor drive circuit 53 drives the motor 6 in accordance with the PWM pulse.

The motor current / voltage detection circuit 54 detects the motor voltage and the motor current from the PWM drive pulse of the motor drive circuit 53 and outputs them to the CPU 51. In response to this, the CPU 51 calculates the rotation speed and rotation acceleration of the motor 6 based on the detected motor current value and motor voltage value, and uses the vehicle speed, steering torque, rotation speed and rotation acceleration of the motor as input parameters. Fuzzy inference is performed according to a predetermined fuzzy rule to estimate the neutral position of the steering wheel 1, and when it is estimated that the steering wheel 1 is near the neutral position, the motor 6 is regeneratively braked or the viscosity is controlled. ..

The fail-safe circuit 55 performs control such as stopping the operation of the motor drive circuit 53 based on the output of the motor current / voltage detection circuit 54 when the motor current or the like is abnormal. The relay drive circuit 52 operates the power relay 56 based on a command from the CPU 51 when the ignition switch 43 is in the ON state, and the motor drive circuit 5
The power of the battery 8 is supplied to 3.

The motor current / voltage detection circuit 54 has a function as a current detection means for detecting a motor current and a voltage detection means for detecting a motor voltage. The CPU 51 has a function as a rotation data calculation means, a neutral position estimation means, and a control means.

FIG. 2 is a block diagram showing various functions of the computer incorporated in the control device 40, together with blocks showing other input / output devices and various circuits. The difference between this figure and the conventional example is that the output of the fuzzy inference unit 60 is added to the output of the assist command unit 10. The fuzzy inference unit 60 is supplied with the rotation speed dθ / dt and the rotation acceleration d ² θ / dt ² of the motor 6, and the detection torque V _T of the torque sensor 11 and the detection vehicle speed V _{S of the} vehicle speed sensor 12.

In the following description, the rotational speed and rotational acceleration are represented by dots using θ as usual in the drawings,
Double dots are added above the characters to represent them, but since it is difficult to display the dots in the text of the specification, the rotation speed d
θ / dt will be appropriately represented as Sθ, and rotational acceleration d ² θ / dt ² will be represented as Aθ.

The fuzzy inference unit 60 performs fuzzy inference according to a predetermined fuzzy rule using the detected torque V _T , the detected vehicle speed V _S , the rotation speed Sθ of the motor 6 and the rotation acceleration Aθ as input parameters, and determines the neutral position of the steering wheel 1. In addition to the estimation, when it is estimated that the steering wheel 1 is near the neutral position, a compensation value Ka for applying regenerative braking to the motor 6 or performing viscosity control.
current control unit 2 by adding v to the output of the assist command unit 10.
Output to 0.

The fuzzy rule for neutral position estimation will be described below. First, the rotation speed Sθ and the rotation acceleration Aθ of the motor 6 become an observer output calculated from the motor voltage V _M and the value of the motor current I _M according to the following equation,
As a result, the steering angle sensor is unnecessary. V _M = R _a I _M + K _e Sθ where R _{a is the} armature current and K _{e is the} induced voltage constant.

Then, using the above-mentioned data as input parameters, fuzzy inference is carried out according to the following rules to estimate the neutral position of the steering wheel 1. FIG. 3 (A),
(B) is the membership function of the antecedent part, of which Figure 3
(A) is the membership function of the steering wheel neutral position with the detected torque V _T , the rotational speed Sθ of the motor 6, and the rotational acceleration Aθ as input parameters, and FIG. 3B shows the detected vehicle speed V _S.
It is a membership function of the steering wheel neutral position that takes as an input parameter. Further, FIG. 3C is a membership function of the compensation value Kav in the consequent part.

The fuzzy rules can be expressed as follows. The rule is so-called IF, THEN (if
If) is expressed in the form of.

The fuzzy rule R1 is "if the vehicle speed V _S
Is large to some extent, the steering torque V _T is very small (for example, zero), the rotation speed Sθ of the motor 6 is large, and the rotation acceleration Aθ is very small, the compensation value Kav is increased in the opposite direction ( That is, apply regenerative braking or perform viscosity control by negative velocity feedback). It means "."

Further, the fuzzy rule R2 states that "if the vehicle speed V _S is high to some extent, the steering torque V _T is very low, and the rotation speed Sθ of the motor 6 is high in the opposite direction,
And when the rotational acceleration Aθ is very small, the compensation value Ka
Increase v in the opposite direction. It means "."

Next, the operation of the power steering control will be described. FIG. 4 is a main program showing processing of power steering control. Ignition switch 4
When 3 is turned on, a normal power assist process is first executed in step S1. As a result, normal steering of the steering wheel 1 by the motor 6 is performed. Next, in step S2, fuzzy estimation is performed on the neutral position of the steering wheel 1.

This estimation processing is performed according to the subroutine shown in FIG. Moving to FIG. 5, first, in step S11, evaluation by the membership function shown in FIG.
Detected torque V _T , detected vehicle speed V _S , and rotation speed S of the motor 6
The degree with respect to the membership function is obtained using θ and the rotational acceleration Aθ as input parameters. Then, in step S12, a fuzzy logic operation is performed according to the fuzzy rules described above. In the fuzzy logic operation process, the input parameters are given in the antecedent part of the fuzzy logic operation, and the degree of conformity to the corresponding membership function of the fuzzy rule is obtained.

Then, the one having a smaller fitness is selected and given to the consequent part. In the consequent part, the membership function of the output is restricted from the selected conformance, and for example, a trapezoidal membership function is selected. obtain. Then, step S13
Then, the membership functions are superposed by the MAX synthesizing process to generate a synthetic output, and then the defuzzifier calculates the compensation value Kav with the center of gravity of the synthetic output as a definite output and outputs it as a variable to be controlled. In this way, while the neutral position of the steering wheel 1 is being estimated, the compensation value Kav is obtained and a control command is issued to improve the steering performance, particularly the convergence.

Returning to the main program again, after step S2, it is determined in step S3 whether or not the steering wheel 1 is in the converged state and the steering wheel 1 is in the neutral position during traveling. The process returns to S1 and repeats the same process. If YES, the process proceeds to step S4 to execute at least one process of control for improving the convergence, for example, regenerative braking control of the motor 6 or viscosity control, and thereafter. It returns to step S2.

FIG. 6 shows the convergence state of the steering wheel 1 at a high vehicle speed.
Waveform in steering mode (steering torque V T, rotation of motor 6
Speed Sθ, rotational acceleration Aθ, steering angle θ)
In the figure, Td represents a damping vibration period. Thus, for example, a car
Speed V_SIs large (high vehicle speed) and steering torque V_TIs small
The rotation speed Sθ of the motor 6 is high,
When the speed Aθ is small, the steering wheel 1 is attached to the neutral position.
It is estimated that they are close to each other, and the compensation value Kav is largely compensated in the opposite direction.
To be corrected. This allows regenerative braking to be applied or
Or one of the viscosity control by velocity negative feedback is executed.
Characteristics when the steering wheel 1 is released while driving
Is improved.

Although the neutral position estimating means for performing fuzzy inference is realized by software in this embodiment, it may be realized by hardware using a fuzzy chip, for example.

[0039]

According to the present invention, since the neutral position of the steering wheel is estimated by fuzzy reasoning, it is possible to easily obtain the steering wheel neutral position information necessary for the control for improving the convergence of the steering wheel, for example. As a result, an expensive detector such as a steering angle sensor for detecting the neutral position of the steering wheel can be eliminated, and the cost of the device can be reduced.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing various functions of a computer incorporated in the control device shown in FIG.

FIG. 3 is a diagram showing a membership function used in fuzzy inference according to the embodiment.

FIG. 4 is a flowchart of a main program for power steering control according to the same embodiment.

FIG. 5 is a flowchart showing a fuzzy reasoning subroutine of the embodiment.

FIG. 6 is a waveform chart explaining the operation of the embodiment.

FIG. 7 is a configuration diagram showing an example of a mechanical system of a conventional power steering device.

FIG. 8 is a block diagram showing various functions of a computer incorporated in a control device of a conventional power steering device.

FIG. 9 is a diagram showing characteristics of assist torque of a conventional power steering device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steering handle 6 Motor 10 Assist command part 11 Steering torque sensor (steering torque detection means) 12 Vehicle speed sensor (vehicle speed detection means) 20 Current control part 40 Control device 43 Ignition switch 51 CPU (rotation data calculation means, neutral position estimation means, Control means) 52 Relay drive circuit 53 Motor drive circuit 54 Motor current / voltage detection circuit (current detection means, voltage detection means) 55 Fail-safe circuit 60 Fuzzy inference section

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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 comprising: a control unit that calculates a control value for controlling the motor based on the output of the detection unit, a current detection unit that detects a motor current of the motor, and a motor voltage of the motor. Voltage detection means for detecting, rotation data calculation means for calculating the rotation speed and rotation acceleration of the motor based on the motor current value and the motor voltage value detected by these current detection means and voltage detection means, and the vehicle speed, Fuzzy inference according to predetermined fuzzy rules with steering torque, motor rotation speed and rotation acceleration as input parameters And a neutral position estimating means for determining the neutral position of the steering wheel, wherein the control means corrects the control value for controlling the motor based on the estimated value of the neutral position estimating means. Steering device. 2. The control means, when the steering wheel is estimated to be in the neutral position by the neutral position estimating means,
The electric power steering apparatus according to claim 1, wherein a regenerative brake is applied to the motor or viscosity control is performed.