JPH06247331A - Motor-driven power steering device - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the instability when returning to the vehicle at high vehicle speed, while improving the steering speed and improving the steering feeling. [Structure] By utilizing the non-linearity of fuzzy calculation, the phase of a detected steering angular acceleration signal in a desired frequency range (a frequency range of 1 Hz to several tens Hz, which is a problem in an electric power steering device) is advanced and a noise removing function is provided. The detected steering angular acceleration signal is supplied to the fuzzy operation filter 52 having the following, and the inertial control signal is obtained based on the steering angular acceleration signal extracted thereby. Then, this inertial control signal is positively fed back to the assist command value for controlling the steering assist motor. On the other hand, the lowering of the gain in the frequency range below the frequency range (1 Hz or less) is compensated by the variable means 100.

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 an electric 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 apparatus, the tokle sensor detects the steering torque of the steering system, the vehicle speed sensor detects the vehicle speed, and the driving force of the motor connected to the steering system is controlled based on these detection results. , Power assist is done. In general, it is a vehicle speed sensitive type, and the assist force is controlled according to the torque sensor input so that it is light at low vehicle speed and heavy at high vehicle speed. Generally, it is a speed-sensitive type, and the assist force is controlled according to the torque sensor input so that it is light at low vehicle speeds and heavy at high vehicle speeds.

FIG. 11 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 wheel 1 is transmitted to a steering gear 2 including a pinion gear via a steering 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 shaft of the handle 1 and the motor 6 is a gear 2,
7 and the rack shaft 3 are mechanically connected. The steering torque (return torque) by the steering torque sensor 11.
Is detected, and the vehicle speed sensor 12 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.

As shown in FIG. 12, the control device 5 includes a motor current detection circuit 21, a motor drive circuit 22 for driving the motor 6, and a CPU for controlling the overall control of the motor 6.
23 (for example, a microprocessor), a memory 24, an interface circuit (not shown) between the computer and the input / output device, and the like.

In FIG. 12, the steering torque detected by the steering torque sensor 11 is converted into a digital signal by the A / D conversion circuit 25 and then taken into the CPU 23. The vehicle speed detected by the vehicle speed sensor 12 is counted by the counter 26, and the count value indicating the vehicle speed is fetched by the CPU 23. The CPU 23 creates an assist command based on the input steering torque and vehicle speed, outputs a control signal based on the assist command to the motor drive circuit 22, and the motor drive circuit 22 drives the motor 6. As a result, the assist torque value (or motor current command value) output from the motor drive circuit 22 becomes a value determined by the detected torque V _T and the detected vehicle speed V _S , as shown in FIG.

FIG. 13 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) depending on the steering torque V _T , and when the above range is exceeded. 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.

Returning to FIG. 12, the motor current is detected by the motor current detection circuit 21, converted into a digital signal by the A / D conversion circuit 27, and then taken into the CPU 23. The memory 24 stores programs and data necessary for the processing of the CPU 23.

As described above, the steering assist motor 6 is controlled based on the steering torque detection value and the vehicle speed detection value to generate the steering assist torque. in this case,
Since the inertial force of the motor 6 causes insufficient stability when the vehicle is released at high vehicle speeds, a braking device for braking the motor 6 near the neutral position of the steering wheel 1 is provided. This braking device is disclosed, for example, in Japanese Utility Model Publication No. 61-169675.

By the way, in this braking device, since the instability at the time of releasing the vehicle at high vehicle speed is stabilized by viscous braking, the stability can be improved.
There is a problem in that the return speed of the steering wheel 1 is insufficient and the driver feels uncomfortable. Therefore,
In order to solve this problem, it has been proposed to provide an inertial control unit that positively feeds back the steering angular acceleration to the assist command value.

[0012]

However, in the method of positively feeding back the steering angular acceleration to the assist command value, a low-pass filter for removing noise is detected when the steering angular acceleration is fed back positively. Since it is necessary to use it and it is necessary to sample at a predetermined time interval, there is a phase delay with respect to the assist command value.

Further, when the band is narrow, such as when the current controller is performing digital control, the assist torque output by the motor is output with a delay, so that the acceleration positive feedback gain is increased as shown in FIG. Can not do it. For this reason, since the influence of inertia cannot be sufficiently removed, the stability when the steering wheel 1 is released cannot be sufficiently obtained, the convergence speed to the steering wheel neutral position is slow, and the steering feeling is also increased due to the inertia feeling during steering. However, there is a problem that is worse.

Therefore, an object of the present invention is to provide an electric power steering apparatus which improves the steering speed and enhances the steering feeling while improving the instability when the vehicle is released at high vehicle speed. .

[0015]

To achieve the above object, an electric power steering apparatus according to the present invention is based on an assist motor connected to a steering system for generating a steering assist torque, a detected steering torque, and a detected vehicle speed. Assist command value creating means for creating an assist command value for assisting the assist motor, control means for controlling the assist motor based on the assist command value, and steering angle acceleration detection for detecting the steering angular acceleration of the steering system. Means and an inertial control means for generating an inertial control signal for compensating the inertia of the assist motor in accordance with the steering angular acceleration signal output from the steering angular acceleration detecting means, and for positively feeding back the assist command value to the inertial control signal. In an electric power steering device, the inertial control means is provided, and the steering angular acceleration signal is input to a desired frequency range. A fuzzy operation filter that advances the phase and has a noise removal function, a steering angular velocity detection unit that detects the steering angular velocity of the steering system, and a level of the inertial control signal based on the steering angular velocity output from the steering angular velocity detection unit. It is characterized in that variable means for varying is provided.

[0016]

In the present invention, the phase in the desired frequency range of the detected steering angular acceleration signal (the frequency range of 1 Hz to several tens Hz which is a problem in the electric power steering device) is advanced by utilizing the non-linearity of the fuzzy calculation. At the same time, the detected steering angular acceleration signal is supplied to the fuzzy arithmetic filter having a noise removing function. Then, an inertial control signal is obtained based on the steering angular acceleration signal extracted by the fuzzy operation filter, and this inertial control signal is positively fed back to the assist command value for controlling the steering assist motor.

In addition, a frequency range (1H
(z or less), the gain is reduced due to the characteristic of the fuzzy operation filter, so that the level of the inertial control signal is controlled to increase based on the steering angular velocity signal.

Therefore, a steering angle acceleration signal whose phase is advanced in a desired frequency range can be obtained, and the inertia control signal obtained based on this steering angle acceleration signal can be positively fed back to the assist command value. Assist torque without phase delay can be obtained even through the loop, and the acceleration gain can be sufficiently increased. As a result, the stability when the steering wheel is released is improved, the convergence speed when returning is increased, and a good steering feeling without inertia feeling is obtained.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing various functions of a computer incorporated in a control device 5A of an embodiment of an electric power steering device according to the present invention, along with blocks showing other input / output devices and various circuits. is there.

In the figure, the assist command section 30 includes a detection torque VT of the steering torque sensor 11 and a vehicle speed sensor 1.
The detected vehicle speed Vs of 2 is given. Assist command unit 30
The assist torque value instruction function unit 31 in the
A command value representing the assist torque to be generated by the motor 6 is output in accordance with the above.

Further, the multiplication constant function unit 32 detects the detected vehicle speed Vs.
A constant is generated in accordance with the above, and the constant is multiplied by the assist torque command value in the multiplication calculation unit 33. As a result, the assist torque value (or motor current command value) output from the multiplication calculator 33 becomes a value determined by the detected torque VT and the detected vehicle speed Vs, as shown in FIG.

The detected torque VT is also given to the phase compensator 34, and the differential value of the detected torque VT is added to the output of the multiplication calculator 33 by the phase compensator 34.
The output (assist command value) of the assist command unit 30 is supplied to the current control unit 35.

On the other hand, in addition to the output of the assist command section 30, the output of the inertia control section 50 is further added to the current control section 35. The inertia control unit 50 controls the rotor inertia of the motor 6 as if the rotor inertia has decreased. The inertia control unit 50 eliminates the weight generated when the motor 6 does not follow the rotation of the steering wheel when the steering wheel is abrupt, and the return speed when the steering wheel is released. Acts to speed up.

In the inertia control unit 50, the steering angular acceleration sensor 51 obtains the steering angular acceleration, and the steering angular acceleration is given to the fuzzy calculation filter 52. A predetermined frequency range (approximately 0 Hz to several tens of H
After the steering angular acceleration signal of z) is extracted, it is given to the inertia compensation unit indicator function unit 53. On the other hand, the steering angular velocity sensor 5
4, the steering angular velocity is obtained, and this steering angular velocity is given to the multiplication constant function unit 55. The multiplication constant function unit 55 generates a constant according to the detected steering angular velocity and gives it to the multiplication calculation unit 56. Then, this constant is the inertia compensation part indicator function part 53.
The inertial control signal obtained by multiplying the command value output from is added to the assist command value of the assist command unit 30 and supplied to the current control unit 35.

In the following description, the steering angular velocity and the steering angular acceleration are represented by dots using θ as usual in the drawings.
Double dots are added on top of the characters, but it is difficult to display the dots in the text of the specification.
It will be appropriately expressed as θ _m (k) ≡η.

FIG. 2 is a functional block diagram showing the fuzzy operation filter 52. In this figure, 60 is a first antecedent part membership function, and 61 is a second antecedent part membership function. First antecedent part membership function 6
The steering angular acceleration η is given to 0 by the steering angular acceleration sensor 51. Further, the second antecedent part membership function 61 includes the variation Δη (steering angular acceleration Aθ _m (k) and the steering angular acceleration Aθ _m (k) delayed by the delay unit 62. The difference from Aθ _m (k-1) is given. 63 is MIN_
It is a MAX calculation unit and performs an operation based on the membership function of the antecedent part. 64 is a consequent part, which performs a calculation for obtaining the position of the center of gravity.

The fuzzy rules of the fuzzy operation filter 52 will be described. 3 (a) and 3 (b) are membership functions of the antecedent part, of which FIG. 3 (a) is a membership function regarding the steering angular acceleration η, and FIG. 3 (b) is a membership function regarding the variation Δη. . In this case, the membership function has a triangular shape, but needless to say, not only this but any shape can be adopted. On the other hand, 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. NB: Negative Big NM: Negtive a medium NS: Negative Small ZO: zero PS: Positive Small PM: Positive medium PB: Positive Big

The fuzzy rule is shown in FIG. 4, and when expressed using an equation, it becomes as follows. The rule is so-called I
It is expressed in the form F, THEN (if any). R1. IF Steering angular acceleration η = PB AND Change Δη
= PB THEN fuzzy output = PB R2. IF Steering angular acceleration η = PB AND Change Δη
= PS THEN fuzzy output = PB

R3. IF steering angle acceleration η = PB AND
Change Δη = ZO THEN Fuzzy output = PM R4. IF Steering angular acceleration η = PB AND Change Δη
= NS THEN fuzzy output = PS R5. IF Steering angular acceleration η = PB AND Change Δη
= NB THEN fuzzy output = ZO

The fuzzy rule R1 means "if the steering angular acceleration η is positively large and the variation Δη is positively large, the fuzzy output is positively increased."

Further, the fuzzy rule R2 means "if the steering angular acceleration η is positively large and the variation Δη is small positively, the fuzzy output is positively increased."

Further, the fuzzy rule R3 means "if the steering angular acceleration η is positively large and the variation Δη is zero, the fuzzy output is positively slightly increased."

Further, the fuzzy rule R4 means "if the steering angular acceleration η is positively large and the variation Δη is small negatively, the fuzzy output is positively increased."

The fuzzy rule R5 means "if the steering angular acceleration η is positively large and the variation Δη is negatively large, the fuzzy output is set to zero". Hereinafter, other rules are determined by the same method.

This fuzzy rule is configured to advance the phase in the frequency range of 1 to 10 and several Hz which is a problem in the electric power steering system. By doing so, the phase delay in the current control unit 35 can be prevented. Here, FIG. 5 is a characteristic diagram of the fuzzy operational filter 52, of which FIG. 5A is a gain frequency characteristic and FIG. 5B is a phase frequency characteristic. As can be seen from FIG. 5 (b), the fuzzy arithmetic filter 52 has about 0.1 Hz.
The phase is advanced in the frequency range of ˜50 Hz.

By the way, when the phase is advanced in the frequency range of 1 to 10 Hz, the fuzzy operational filter 52 as a result, the gain decreases in the low frequency range of 1 Hz or less as shown in FIG. 5 (a). Resulting in. Therefore, when the detected angular velocity is less than or equal to a predetermined value to compensate for this decrease in gain, or when the rate of change in the sign of the detected angular velocity is less than or equal to a predetermined value (when the number of code changes in a certain fixed period is less than or equal to a predetermined number) In addition, the multiplication coefficient of the multiplication calculation unit 56 is increased to increase the output of the fuzzy calculation filter 52.

For reference, FIG. 6 is a characteristic diagram of a digital low-pass filter which has been conventionally used, in which FIG. 6 (a) is a gain frequency characteristic and FIG. 6 (b) is a phase frequency characteristic. In this conventional digital low-pass filter, the phase is delayed in the frequency range of 1 to 10 Hz. In this digital low pass filter, the current controller 35
If there is a phase delay at, this cannot be prevented.

Returning to FIG. 1, the current control unit 35 controls the drive of the motor 6 by a chopper operation using a PWM (Pulse Width Modulation) pulse according to the H-bridge drive method including, for example, four switching elements. ,
Performs current feedback control. That is, the armature current detector 36 detects the armature current of the motor 6,
The deviation between the assist command value given and the detected current is calculated in the current deviation calculator 37. The absolute value of this deviation is obtained by the absolute value converter 38, and the duty ratio of the PWM pulse is determined by the duty generator 39 based on this absolute value.

On the other hand, the polarity (positive or negative) of the deviation is discriminated by the positive / negative discriminating section 40, and the generated duty ratio and the discriminated polarity are given to the motor driving section 41, and the motor driving section 41 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.

The assist command section 30 corresponds to an assist command value creating means. The current control unit 35 corresponds to a control means. The inertia control unit 50 corresponds to the inertia control means. The steering angular acceleration sensor 51 corresponds to steering angular acceleration detecting means. The steering angular velocity sensor 54 corresponds to the steering angular velocity detecting means. Further, the multiplication constant function unit 55 and the multiplication operation unit 56 are arranged in the variable means 100.
Make up.

Next, the operation of the fuzzy operation filter 53 will be described. FIG. 7 is a main program showing the processing of the fuzzy operation filter 53. First, step S1
And read the steering angular acceleration η from the steering angular acceleration sensor 51,
In step S2, the steering angular acceleration η is fuzzy input. Then, based on the steering angular acceleration η and the variation Δη, fuzzy inference is performed according to a predetermined fuzzy rule,
Estimate the steering angle acceleration. Then, in step S3, the estimated value of the steering angular acceleration is output to the inertia compensation value instruction function unit 53 as a fuzzy output.

The fuzzy inference in step S2 is shown in FIG.
It is executed by the subroutine shown in. In FIG. 8, first, after the steering angular acceleration η and its variation Δη are set as fuzzy inputs, the processing of the antecedent part is performed in step S11. That is, the input value (steering angular acceleration η and its change Δη)
And from the first and second membership functions of the conditional part,
Find the fitness of the input. Next, in step S12, the processing of the conclusion section is performed.

That is, the fuzzy output for each conclusion part label 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.

FIG. 9 is a diagram showing a response of the steering system when the fuzzy operation filter 52 is used, and FIG. 10 shows a response of the steering system when a filter having a linear characteristic such as a conventional digital low-pass filter is used. It is a figure. From these figures, it is understood that the fuzzy operation filter 52 has better convergence.

In the above embodiment, the steering angular acceleration is obtained by the steering angular acceleration sensor 51, and the steering angular velocity is obtained by the steering angular velocity sensor 54. The motor rotation speed is calculated from the voltage / current of 6, and the steering angular speed is estimated from this calculation result.
Further, the steering angular acceleration may be estimated from the result of differentiating the calculated value and these estimated values may be used. This way,
The rudder angular acceleration sensor 51 and the rudder angular velocity sensor 54 are unnecessary, and the cost can be reduced.

[0048]

According to the present invention, the phase of the detected steering angular acceleration signal in the desired frequency range (the frequency range of 1 Hz to several tens Hz which is a problem in the electric power steering device) is advanced and the noise removing function is provided. While the fuzzy operation filter provided is provided, the variable means for compensating for the signal level in the frequency range which is lowered by providing the fuzzy operation filter is provided, so that the assist without phase delay even through the current loop having a low frequency band. Since the torque can be obtained and the acceleration gain can be sufficiently increased, the stability when the steering handle is released, the convergence speed at the time of returning is increased, and a good steering feeling without inertia feeling can be obtained.

[Brief description of drawings]

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

FIG. 2 is a functional block diagram of a fuzzy operation filter of the same embodiment.

FIG. 3 is a diagram showing a membership function of an antecedent part and a membership function of a consequent part of the fuzzy operation filter of the embodiment.

FIG. 4 is a diagram showing a fuzzy rule of the fuzzy operation filter of the embodiment.

FIG. 5 is a characteristic diagram of the fuzzy operational filter of the embodiment.

FIG. 6 is a characteristic diagram of a conventional digital low-pass filter.

FIG. 7 is a flowchart of a main program of the fuzzy operational filter according to the embodiment of the present invention.

FIG. 8 is a flowchart showing a fuzzy reasoning subroutine of the embodiment.

FIG. 9 is a diagram showing response characteristics of a steering system when the fuzzy arithmetic filter according to the embodiment of the present invention is used.

FIG. 10 is a diagram showing a response characteristic of a steering system when a conventional linear filter is used.

FIG. 11 is a configuration diagram showing an example of a mechanical system of a conventional power steering device.

FIG. 12 is a detailed block diagram of a control device of a conventional power steering device.

FIG. 13 is a diagram showing characteristics of assist torque of a conventional power steering device.

FIG. 14 is a diagram for explaining a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering handle 6 Assist motor 11 Steering torque sensor 12 Vehicle speed sensor 30 Assist command section (assist command value creating means) 35 Current control section (control means) 50 Inertial control section (inertial control means) 51 Steering angular acceleration sensor (steering angular acceleration) Detection unit) 52 Fuzzy calculation filter 53 Inertia compensation value instruction function unit 54 Steering angular velocity sensor (Steering angular velocity detection unit) 55 Multiplication constant functional unit 56 Multiplication arithmetic unit 100 Variable unit

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 137: 00

Claims (1)

[Claims] 1. An assist motor connected to a steering system for generating a steering assist torque, and an assist command value creating means for creating an assist command value for assisting the assist motor based on a detected steering torque and a detected vehicle speed, Control means for controlling the assist motor based on the assist command value, steering angle acceleration detection means for detecting the steering angular acceleration of the steering system, and the steering angle acceleration signal output from the steering angular acceleration detection means An electric power steering apparatus comprising: an inertial control means for generating an inertial control signal for compensating the inertia of an assist motor and positively feeding back to the assist command value; and the steering angle acceleration signal provided in the inertial control means. Is input, the phase is advanced in the desired frequency range, and a fuzzy operation filter that has a noise removal function and a steering system steering Rudder angular velocity detecting means for detecting an angular velocity, variable means for varying the level of the inertial control signal based on the steering angular velocity output from the rudder angular velocity detecting means,
An electric power steering device comprising: