JPH05131941A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To generate a proper assist force according to a running mode, achieve a stable steering feeling, improve the operatiliby, reduce fatigue of a driver, and achieve a safe and comfortable drive. CONSTITUTION:A motor 6 connected to a steering system for generating a steering auxiliary torque, a torque sensor 11 to detect a steering torque of the steering system, a velocity sensor 12 to detect a velocity, and a control means 70 to control drive of the motor 6 based on outputs of the torque sensor 11 and the velocity sensor 12 are provided for an electric power steering device. A steering angle sensor 41 for detecting a steering angle of the steering system, and a running mode estimating means 60 for performing fuzzy inference corresponding to predetermined fuzzy rules based on the detected velocity and the steering angle and estimating a running mode are provided, where the control means 70 corrects a control value to control drive of the motor 6 based on the estimated running mode by the running mode estimating 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 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, the above-mentioned conventional electric power steering device is of the vehicle speed sensitive type, and controls the assist force according to the torque sensor input so that it is light in the low speed range and heavy in the high speed range. However, there is a problem in that an appropriate assisting force according to the driving mode cannot be obtained and the steering feeling is unstable.

That is, in order to control the steering force suitable for the traveling mode, the vehicle speed sensitive control alone is not sufficient.
The operability was reduced and the driver's fatigue was increased, which was not enough to drive safely and comfortably.

Therefore, according to the present invention, an appropriate assisting force according to the driving mode is generated to stabilize the steering feeling, improve operability, reduce driver's fatigue, and perform safe and comfortable driving. It is an object of the present invention to provide an electric power steering device that can be used.

[0016]

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. An electric power steering system including: steering torque detecting means for detecting the vehicle speed; vehicle speed detecting means for detecting the vehicle speed; and control means for controlling the drive of the motor based on the outputs of the steering torque detecting means and the vehicle speed detecting means. In the device, there are provided steering angle detecting means for detecting a steering angle of a steering system, and traveling mode estimating means for estimating a traveling mode by performing fuzzy inference according to a predetermined fuzzy rule based on the vehicle speed and the steering angle. The means corrects the control value for controlling the drive of the motor based on the traveling mode estimated by the traveling mode estimating means. To.

Further, as a preferred mode, the traveling mode estimating means performs fuzzy inference using the average vehicle speed obtained from the output of the vehicle speed detecting means and the average steering amount obtained from the output of the steering angle detecting means as a fuzzy input. It is characterized in that the driving mode is estimated. Further, the driving mode estimating means performs the fuzzy inference, and estimates a driving mode such as an urban area, a suburb, a curved road, or a high speed mode.

[0018]

In the present invention, fuzzy inference is performed according to a predetermined fuzzy rule based on the vehicle speed and the steering angle to estimate the traveling mode, and the drive of the motor is controlled according to the estimated traveling mode. Therefore, an appropriate assist force is generated according to the traveling mode, and the steering feeling becomes stable.

[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 is 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 a steering angle for detecting a steering angle of the steering wheel 1. An output signal from a sensor (steering angle detection means) 41 and a temperature sensor 42 that detects the temperature of the motor 6 is input, and the control device 40 includes an ignition switch 43.
And connected to 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 required for drive control of the motor 6 based on signals from the steering torque sensor 11, the vehicle speed sensor 12, the steering angle 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. CPU51
Calculates the rotation speed and the rotation acceleration of the motor 6 based on the detected motor current value and the motor voltage value, and uses the vehicle speed, the steering torque, the rotation speed and the rotation acceleration of the motor as input parameters according to a predetermined fuzzy rule. Perform fuzzy inference, estimate the driving mode, and adjust the assist force according to the estimated driving mode.
Control the M drive pulse.

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 traveling mode estimating unit.

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 drawing and the conventional example is that the output of the fuzzy inference unit (corresponding to the running mode estimating means) 60 is added to the output of the multiplication operation unit 15 in the assist command unit 10. The fuzzy inference unit 60 receives the output signal of the vehicle speed sensor 12 to calculate the average vehicle speed (ie, the average vehicle speed) and the output signal of the steering angle sensor 41 to input the average steering. The output of the average steering amount calculation unit 62 for calculating the amount (that is, the average steering amount) is input. The output signal of the steering angle sensor 41 is the angle at which the steering wheel 1 is steered, and this corresponds to the steered amount, that is, the steering amount.

The fuzzy inference unit 60 uses the average vehicle speed and the average steering amount as fuzzy inputs to perform fuzzy inference according to a predetermined fuzzy rule to estimate the running mode of the vehicle and add the estimated value to the output of the multiplication calculation unit 15. Output to the current control unit 20. The assist command unit 10
The current control unit 20 constitutes the control means 70.

Here, a fuzzy rule for estimating the driving mode will be described. 3A and 3B are membership functions of the antecedent part, of which FIG. 3A is a membership function relating to the average vehicle speed, and FIG. 3B is a membership function relating to the average steering amount. Further, FIG. 3C is a fuzzy output in the consequent part, which is a membership function represented by a single tone position. The meaning of the label in each membership function is as follows. PS: Positive Small (small) PM: Positive Medium (somewhat small) PML: Positive Medium Large (somewhat large) PL: Positive Large (some)

The fuzzy rule is shown in FIG. 4, 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 average vehicle speed = PS AND average steering amount = PS THEN fuzzy output = PL (city area) R2. IF Average vehicle speed = PM AND Average steering amount = PS THEN Fuzzy output = PM (Suburbs)

The fuzzy rule R1 means "if the average vehicle speed is small and the average steering amount is small, the fuzzy output is large and the driving mode is the city area."

Further, the fuzzy rule R2 means "if the average vehicle speed is a little low and the average steering amount is a little, the fuzzy output is a little small and the driving mode is the suburb". Hereinafter, other rules are determined by the same method.

Next, the operation of the power steering control will be described. FIG. 5 is a main program showing the processing of the power steering control. Ignition switch 4
When 3 is turned on, first, in step S1, the vehicle speed and the steering angle are read from the sensors 12 and 41, respectively, and then in step S2.
Calculate the average vehicle speed and average steering angle. Then, in step S3, the average vehicle speed and the average steering angle are used as fuzzy inputs to perform fuzzy inference according to a predetermined fuzzy rule to estimate the traveling mode of the vehicle.

After that, in step S4, the estimated value of the running mode is added to the output of the multiplication calculation section 15 as a fuzzy output and output to the current control section 20. Thereby, the PWM drive pulse is controlled so as to correct the assist force by the motor 6 according to the estimated traveling mode, and an appropriate assist force corresponding to the traveling mode is generated.

The fuzzy inference in step S3 is shown in FIG.
It is executed by the subroutine shown in. In FIG. 3, first, the average vehicle speed and the average steering angle are set as fuzzy inputs, and then the processing of the condition section is performed in step S11. That is, the fitness of the input is obtained from the input values (average vehicle speed and average steering angle) and the condition part membership function. Next, in step S12, the processing of the conclusion section is performed. That is, the fuzzy output for each label of the conclusion part is found by comparing the rule suitability found by the condition part processing with other suitability. Next, in step S13, weighting processing is performed to adjust the degree of influence of each rule on the conclusion part. For example, the one having the smaller matching degree is selected and given to the consequent part. Then, in step S14, one definite value representing the fuzzy output is calculated.

That is, in the consequent part, the membership functions are superposed by the MAX synthesizing process to generate a synthetic output, and then the defuzzifier obtains one definite value from the center of gravity of the synthetic output. In this way, the running mode is estimated, and as shown in FIG. 4, the modes of urban area, suburb, curved road, and high speed are obtained.

As described above, in this embodiment, the driving mode is estimated by performing the fuzzy inference based on the vehicle speed and the steering angle according to the predetermined fuzzy rule, and the drive of the motor is controlled according to the estimated driving mode. Therefore, it is possible to generate an appropriate assisting force in accordance with the driving mode rather than a mere vehicle speed-sensitive type, and to make the steering feeling stable. As a result, the operability is improved, the driver's fatigue is reduced, and safe and comfortable driving can be performed.

Although the average steering angle is calculated from the output of the steering angle sensor in the above embodiment, the invention is not limited to this. For example, the motor rotation speed is calculated from the voltage / current of the motor 6,
Further, the average steering angle may be obtained from the integrated value. With this configuration, the steering angle sensor is not needed, and the cost can be reduced.

That is, first, when the rotation speed dθ / dt of the motor 6 is obtained from the values of the motor voltage V _M and the motor current I _M , the rotation speed dθ / dt of the motor 6 represents the steering angular velocity, which is the steering amount. Will correspond to. afterwards,
The average steering amount is obtained by integrating the calculated value of the rotation speed dθ / dt of the motor 6. The rotation speed of the motor 6 dθ / dt
Is an observer output calculated from the motor voltage V _M and the value of the motor current I _M according to the following equation, which eliminates the need for a steering angle sensor. V _M = R _a I _M + K _e dθ / dt where R _{a is the} armature current, K _{e is the} induced voltage constant.

In this embodiment, the running mode estimating means for performing fuzzy inference is realized by software, but it may be realized by hardware using a fuzzy chip, for example.

[0039]

According to the present invention, since the driving mode is estimated by fuzzy inference, an appropriate assisting force can be generated according to the driving mode, and the steering feeling can be made stable. .. As a result, operability is improved,
The driver's fatigue can be reduced and safe and comfortable driving can be performed.

[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 diagram showing a fuzzy rule of the embodiment.

FIG. 5 is a flowchart of a main program for power steering control according to the same embodiment.

FIG. 6 is a flowchart showing a fuzzy reasoning subroutine 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]

6 Motor 10 Assist Command Unit 11 Steering Torque Sensor (Steering Torque Detecting Means) 12 Vehicle Speed Sensor (Vehicle Speed Detecting Means) 20 Current Control Unit 40 Control Device 43 Ignition Switch 51 CPU (Run Mode Estimating 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 reasoning section 70 control means

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Claims (3)

[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 angle detection unit that detects a steering angle of a steering system; and a steering angle detection unit that detects the steering angle based on the vehicle speed and the steering angle. A fuzzy inference is performed according to a predetermined fuzzy rule, and a driving mode estimating means for estimating a driving mode is provided, and the control means controls the drive of the motor based on the driving mode estimated by the driving mode estimating means. The electric power steering device is characterized in that 2. The traveling mode estimating means performs fuzzy inference with the average vehicle speed obtained from the output of the vehicle speed detecting means and the average steering amount obtained from the output of the steering angle detecting means as fuzzy input to determine the traveling mode. The electric power steering apparatus according to claim 1, which is estimated. 3. The driving mode estimating means performs the fuzzy inference to estimate a driving mode such as city, suburb, bend road, or high speed mode.
The electric power steering device described.