JPH05131942A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To perform fuzzy inference correctly, control a motor to generate assist force properly, and generate the optimum assist force by performing the fruzzy inference based on a velocity, a steering torque and a steering quantity of a steering system for estimating a condition of a road surface. CONSTITUTION:A motor-driven power steering device controls a motor, unillustrated, which generates a steering auxiliary torque, based on detection signals from a torque sensor 11 for detecting a steering torque of a steering system, and a car speed sensor 12 for detecting car speed. In this case, a motor current and voltage are detected by detection means 53, 54 respectively. An average steering quantity of the steering system is computed by a computation means 55 based on the detected current value and voltage value. An average estimatioan torque is computed by a computation means 52 based on the average steering quantity and an average speed computed by a computation means 51. A condition of a road surface is determined by fuzzy inference by a fuzzy computation part 33 based on the car speed, steering torque, and average estimation torque.

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. 9 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.
0), the steering torque (return torque) is detected, and the vehicle speed sensor 12 (see FIG. 10) 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 are supplied with operating power from a battery 8 mounted on the vehicle.

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. 10 is a block diagram showing various functions of a computer incorporated in the control device 5, together with blocks showing other input / 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. 11.

[0008] Figure 11 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.

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.

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 deviation is discriminated by the positive / negative discriminating section 22, and the generated duty ratio and the discriminated polarity are 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.

[0012]

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. Therefore, there is a problem in that the assisting force becomes excessive and the steering feeling becomes unstable on a road surface having a low friction coefficient μ such as a frozen road or a wet asphalt road. On the other hand, on dry asphalt roads and bad roads, the assisting power was weak and a light steering feeling could not be obtained.

That is, in order to control the steering force to match the actual running road surface condition of the vehicle, the vehicle speed sensitive type alone is insufficient. Therefore, it is desirable to be able to estimate the road surface condition.

Therefore, an object of the present invention is to provide an electric power steering apparatus capable of appropriately estimating a traveling road surface state and generating an assisting force corresponding to the road surface state.

[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. 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, a current detection unit that detects a motor current of the motor, a voltage detection unit that detects a motor voltage of the motor, and a motor current value and a motor voltage value detected by the current detection unit and the voltage detection unit. Steering amount calculation means for calculating the steering amount of the steering system based on the above, and based on the vehicle speed, the steering torque and the steering amount of the steering system A fuzzy inference is performed according to a fixed fuzzy rule, and a road surface state estimating means for estimating the state of the traveling road surface is provided, and the control means sets a control value for controlling the drive of the motor based on the estimated value of the road surface state estimating means. It is characterized by correction.

According to another aspect of the present invention, there is provided an electric power steering apparatus, which is connected to a steering system to generate a steering assist torque, a steering torque detecting means for detecting a steering torque of the steering system, and a vehicle speed. Vehicle speed detecting means for detecting, and control means for controlling driving of the motor based on outputs of the steering torque detecting means and the vehicle speed detecting means,
In an electric power steering apparatus including: a steering amount detecting means for detecting a steering amount of the steering system; a vehicle body yaw rate detecting means for detecting a yaw rate of a vehicle body; and a predetermined amount based on the vehicle speed, the steering amount and the vehicle body yaw rate. A fuzzy inference according to the fuzzy rule of (1) to provide a road surface condition estimating means for estimating the condition of the traveling road surface, and the control means corrects the control value for controlling the drive of the motor based on the estimated value of the road surface condition estimating means. It is characterized by doing.

[0017]

According to the first aspect of the invention, fuzzy inference is performed based on the vehicle speed, the steering torque, and the steering amount of the steering system.
The condition of the road surface is estimated. Then, the drive current of the motor is corrected based on the estimated value of the road surface condition. That is, the steering force is controlled to be suitable for the actual traveling road surface condition of the vehicle. Therefore, the assisting force is weakened on a road surface having a low friction coefficient μ, such as a frozen road or a wet asphalt road, so that an unstable steering feeling disappears. On the other hand, on dry asphalt roads and rough roads, the assisting power is slightly stronger and a lighter steering feel is obtained. That is, the steering force is controlled to be suitable for the actual traveling road surface condition of the vehicle.

According to the third aspect of the invention, fuzzy inference is performed based on the vehicle speed, the steering amount, and the yaw rate of the vehicle body, the state of the traveling road surface is similarly estimated, and the motor state is estimated based on the estimated value of the road surface state. The drive current is corrected. Therefore, the assist force is weakened on a road surface having a low friction coefficient μ, and the unstable steering feeling is lost, and the assist force is slightly strengthened on a dry asphalt road or a bad road, and a light steering feeling is obtained.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 5 are views showing an embodiment of an electric power steering apparatus according to the invention described in claim 1. In the description of the present embodiment, the same components as those of the conventional example will be denoted by the same reference numerals and redundant description will be omitted. FIG. 1 is a block diagram showing the hardware configuration of this apparatus. In this figure, reference numeral 40 denotes an assist command section, and a fuzzy inference section (road surface state estimating means) 30 and a multiplication calculation section 31 are added to the assist command section 40, and a multiplication calculation section 32 is provided. The contents are different.

Average vehicle speed, average steering amount, average steering torque, and other data are input to the fuzzy inference unit 30, and the fuzzy inference unit 30 performs fuzzy inference according to a predetermined fuzzy rule based on these input data. ,
The state of the traveling road surface is estimated, and the estimated value is multiplied by the multiplication calculation unit 31.
Output to. The multiplication calculation unit 31 multiplies the output of the multiplication constant function unit 14 by the estimated value of the fuzzy inference unit 30 and outputs the result to the multiplication calculation unit 32 in the subsequent stage. The multiplication calculation unit 32 multiplies the output of the assist torque value instruction function unit 13 by the output of the multiplication calculation unit 31 and outputs the result to the current control unit 20. The current control unit 20
Also, the assist command section 40 constitutes the control means 50.

FIG. 2 is a diagram showing a system of input data for performing fuzzy inference. The output of the vehicle speed sensor (vehicle speed detecting means) 12 is input as it is to the fuzzy operation section 33 as the vehicle speed SP and also to the average vehicle speed operation means 51. The average vehicle speed calculation means 51 calculates the average vehicle speed from the output of the vehicle speed sensor 12 and outputs it to the average estimated torque calculation means 52. On the other hand, the current and voltage of the motor 6 are detected by the motor current detection means 53 and the motor voltage detection means 54, and the detected values are input to the average steering amount calculation means 55.

Average steering amount calculation means (steering amount calculation means) 5
5 is a motor 6 based on the values of the motor voltage V _M and the motor current I _M.
The rotational speed dθ / dt of the motor 6 is obtained, and the rotational speed dθ / dt of the motor 6 represents the steering angular velocity, which corresponds to the steering amount. After that, the rotation speed dθ / dt of the motor 6
The calculated value of is integrated to obtain the average steering amount. The rotation speed dθ / dt of the motor 6 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 makes the steering angle sensor unnecessary. V _M = R _a I _M + K _e dθ / dt where R _{a is the} armature current, K _{e is the} induced voltage constant.

The average steering amount calculated by the average steering amount calculation unit 55 is input to the average estimated torque calculation unit 52, and the average estimated torque calculation unit 52 calculates the average estimated torque value Te from the average steering amount and the above-mentioned average vehicle speed. To do.
Thereafter, the steering torque T detected by the torque sensor (steering torque detecting means) 11 from the average estimated torque value Te
r is subtracted, and the value of Te−Tr is input to the fuzzy calculation unit 33. The fuzzy calculation unit 33 performs fuzzy inference using the vehicle speed SP and the torque deviation (Te-Tr) as fuzzy inputs to estimate the state of the traveling road surface, and outputs a multiplication calculation unit gain according to the estimated value to the multiplication calculation unit 31. ..

Here, a fuzzy rule for estimating the road surface condition will be described. Using the above-mentioned data as input parameters, fuzzy inference is performed according to the following rules to estimate the state of the road surface. 3A and 3B are membership functions of the antecedent part, of which FIG. 3A is a membership function of torque deviation (Te-Tr), and FIG. 3B is a membership of detected vehicle speed SP. Is a function. Also, FIG.
(C) is a membership function of the multiplication operation part gain in the consequent part.

The fuzzy rules are shown in FIG. 4 and expressed by the following equation. The rule is so-called I
It is expressed in the form F, THEN (if any). R1. IF Te−Tr = NL AND SP = ZR THEN Gain = PL The fuzzy rule R1 is “if the torque deviation (Te
When −Tr) is relatively large in the reverse direction and the vehicle speed SP is very small, the multiplication calculation unit gain is increased in the forward direction (that is, the assist force in the forward direction is increased). It means "." Hereinafter, similarly, the state of the traveling road surface is estimated according to the fuzzy rule of FIG.

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 state of the traveling road changes, the road surface state is estimated by fuzzy reasoning and the assist force is controlled. Figure 5 shows the program for fuzzy inference
As shown.

In FIG. 5, first, in step S1, evaluation by the membership function shown in FIG. 3, that is, how much the torque deviation (Te-Tr) and the detected vehicle speed SP are used as input parameters to evaluate the membership function. I do. Then, in step S2, a fuzzy logic operation is performed according to the fuzzy rules shown in FIG.

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 the smaller conformity is selected and the consequent is selected. 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. Next, in step S3, the membership functions are superposed by a MAX combining process to generate a combined output, and thereafter, a center of gravity of the combined output is determined as a final output by a defuzzifier, and a multiplication operation unit according to the estimated value of the road surface condition is obtained. The gain is calculated and output to the multiplication calculator 31 as a variable to be controlled.

In the multiplication calculation unit 31, the output of the multiplication constant function unit 14 is multiplied by the estimated value (multiplication calculation unit gain) of the fuzzy inference unit 30 and output to the multiplication calculation unit 32 in the subsequent stage. The output of the value instruction function unit 13 is multiplied by the output of the multiplication calculation unit 31 to obtain the current control unit 20.
Is output to. 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.

Therefore, the assisting force is weakened on a road surface having a low friction coefficient μ such as a frozen road or a wet asphalt road, so that an unstable steering feeling can be eliminated.
On the contrary, on dry asphalt roads and bad roads, the assisting power is slightly strengthened and a light steering feeling can be obtained.
That is, it is possible to control the steering force to match the actual traveling road surface condition of the vehicle. Further, in this embodiment, the rotation speed d of the motor 6 is calculated from the values of the motor voltage V _M and the motor current I _M.
Since θ / dt is obtained and the rotation speed dθ / dt of the motor 6 is used as data representing the steering angular velocity, there is an advantage that the steering angular velocity can be detected without installing a special sensor.

Next, FIGS. 6 to 8 are views showing an embodiment of the electric power steering apparatus according to the invention of claim 3. In the description of the present embodiment, the same components as those of the conventional example will be denoted by the same reference numerals and redundant description will be omitted. FIG. 6 is a diagram showing a system of input data to the fuzzy calculation unit 60. In this figure, the output of the vehicle speed sensor 12 is directly input to the fuzzy calculation unit 60 as the vehicle speed SP. On the other hand, the steering angle (corresponding to the steering amount) of the steering wheel 1 is detected by the steering angle detecting means 61, and the steering angle change dθ /
While being input to the fuzzy calculation unit 60 as dt,
It is input to the frequency characteristic calculation means 62.

In the following description, a change in the steering angle is represented by adding a dot on the character by using θ as usual in the drawings. However, since it is difficult to display the dot in the text of the specification, the steering angle is changed. The change dθ / dt will be appropriately represented as Sθ.

Further, the yaw rate (for example, rolling) of the vehicle body is detected by the yaw rate detecting means 63 and is also input to the frequency characteristic calculating means 62. The yaw rate detecting means 63 calculates the frequency characteristic of the vehicle body yaw rate with respect to the steering angle change Sθ, and outputs the calculation result to the fuzzy calculation section 69 using the gain and the phase delay as parameters. The fuzzy operation unit 60 uses the above-mentioned data as fuzzy inputs and performs fuzzy inference according to the following rules to estimate the state of the traveling road surface.

7A to 7D are membership functions of the antecedent part, of which FIG. 7A is a membership function of the detected vehicle speed SP, and FIG. 7B is a membership of the steering angle change Sθ. 7C is a membership function of the gain G, and FIG. 7D is a membership function of the phase φ. Further, FIG. 7E is a membership function of the multiplication operation unit gain in the consequent part.

The fuzzy rules are shown in FIG. 8 and expressed by the following equation. The rule is so-called I
It is expressed in the form F, THEN (if any).

This fuzzy rule R1 is "if the vehicle speed SP is very small, the steering angle change Sθ is very small, the gain G is large, and the phase φ delay is large, the multiplication operation unit gain is large. In the opposite direction so that the friction coefficient μ of the road surface is small to correspond to the state (that is, the assist force is weakened). " Hereinafter, similarly, the state of the traveling road surface is estimated according to the fuzzy rule of FIG.

Therefore, although the fuzzy input parameters are different in this embodiment as well, similar to the previous embodiment,
The assist force is weakened on a road surface with a low friction coefficient μ such as an icy road or a wet asphalt road, and the unstable steering feeling can be eliminated, and the assist power becomes slightly stronger on a dry asphalt road or a bad road. It is possible to obtain a light steering feeling. In particular, since the yaw rate of the vehicle body is detected in addition to the steering angle change Sθ, the steering force can be controlled more finely than that in the above-described embodiment so as to match the actual running road surface condition of the vehicle.

Although the fuzzy inference unit for performing the fuzzy inference is realized by software in the above embodiments, it may be realized by hardware using a fuzzy chip, for example.

[0039]

According to the first aspect of the present invention, the assist force is weakened on a road surface having a low friction coefficient μ such as a frozen road or a wet asphalt road, so that an unstable steering feeling can be eliminated and a dry feeling can be obtained. On asphalt roads and rough roads, the assist force can be slightly increased to provide a light steering feel. That is, it is possible to control the steering force to match the actual traveling road surface condition of the vehicle. In addition, when detecting the steering angular velocity, there is an advantage that the steering angular velocity can be detected without installing a special sensor, and the cost can be reduced. According to the invention of claim 3, in addition to the above effect, the steering angle change and the yaw rate of the vehicle body are detected.
The steering force can be controlled more finely so as to match the actual running road surface condition of the vehicle.

[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 invention of claim 1.

FIG. 2 is a functional block diagram of a portion for performing fuzzy inference according to the embodiment.

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 used in fuzzy inference according to the embodiment.

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

FIG. 6 is a block diagram showing a hardware configuration of an embodiment of an electric power steering apparatus according to the invention of claim 3;

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

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

FIG. 9 is a configuration diagram showing an example of a mechanical system of a conventional power steering device.

FIG. 10 is a block diagram showing various functions of a computer incorporated in a control device of a conventional power steering device.

FIG. 11 is a diagram showing characteristics of assist torque of a conventional power steering device.

[Explanation of symbols]

 1 Steering Handle 6 Motor 11 Steering Torque Sensor (Steering Torque Detecting Means) 12 Vehicle Speed Sensor (Vehicle Speed Detecting Means) 20 Current Control Unit 30 Fuzzy Calculating Unit (Road Surface Condition Estimating Means) 33, 60 Fuzzy Calculating Unit 40 Assist Command Unit 50 Controlling Means 51 average vehicle speed calculation means 52 average estimated torque calculation means 53 motor current detection means 54 motor voltage detection means 55 average steering amount calculation means 61 steering angle detection means (steering amount detection means) 62 frequency characteristic calculation means 63 yaw rate detection means

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Claims (4)

[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 current detection unit that detects a motor current of the motor; and a voltage that detects a motor voltage of the motor. Detection means, steering amount calculation means for calculating a steering amount of the steering system based on the motor current value and the motor voltage value detected by the current detection means and the voltage detection means, the vehicle speed, the steering torque, and the steering A road surface condition estimating means for estimating the condition of the traveling road surface by performing fuzzy inference according to a predetermined fuzzy rule based on the steering amount of the system; Provided, the control means, electric power steering apparatus characterized by correcting the control value for controlling driving of the motor based on the estimated value of the road surface state estimating means. 2. The road surface state estimating means obtains an average vehicle speed from the output of the vehicle speed detecting means, and calculates a motor rotation speed based on the motor current value and the motor voltage value detected by the current detecting means and the voltage detecting means, respectively. At the same time, the calculated value is integrated to obtain the average steering amount, the average estimated torque is calculated from the average vehicle speed and the average steering amount, and the calculated average estimated torque and the torque detected by the steering torque detecting means are calculated. 2. The electric power steering apparatus according to claim 1, wherein the difference and the vehicle speed detected by the vehicle speed detecting means are used as fuzzy inputs to perform fuzzy inference to estimate the state of the road surface on which the vehicle is running. 3. A motor connected to a steering system for generating steering assist torque, a steering torque detecting means for detecting 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 the drive of the motor based on the output of the detection unit; a steering amount detection unit that detects the steering amount of the steering system; and a vehicle body that detects the yaw rate of the vehicle body. The yaw rate detection means and the road surface state estimation means for estimating the state of the traveling road surface by performing fuzzy inference according to a predetermined fuzzy rule based on the vehicle speed, the steering amount, and the yaw rate of the vehicle body are provided, and the control means estimates the road surface state. An electric power steering system characterized in that a control value for controlling the drive of the motor is corrected based on the estimated value of the means. Location. 4. The road surface condition estimating means calculates the gain and phase delay of the frequency characteristic of the vehicle body yaw rate with respect to the change in the steering amount from the outputs of the steering amount detecting means and the vehicle body yaw rate detecting means, and changes in the vehicle speed and the steering amount. 4. The electric power steering apparatus according to claim 3, wherein fuzzy inference is performed by using the gain of the frequency characteristic of the vehicle body yaw rate and the phase delay of the frequency characteristic of the vehicle body yaw rate as fuzzy inputs to estimate the state of the traveling road surface.