JP3293047B2 - Electric power steering device - Google Patents

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 an electric power steering apparatus for assisting a steering force by a rotation output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering devices using motors have been used in place of hydraulic power steering devices, and motors are increasing in the future because of their advantages such as small size and light weight as actuators.

In a conventional power steering apparatus, a steering torque of a steering system is detected by a torque sensor, a vehicle speed is detected by a vehicle speed sensor, and a driving force of a motor connected to the steering system is controlled based on the detection results. , Power assist. The vehicle is generally of a vehicle speed sensitive type, and the assist force is controlled in accordance with the input of the torque sensor so that the vehicle is light at a low vehicle speed and heavy at a high vehicle speed. In general, it is a speed-sensitive type, and the assist force is controlled in accordance with the input of the torque sensor so as to be light at a low vehicle speed and heavy at a high vehicle speed.

FIG. 11 is a block diagram showing an example of a mechanical system of a conventional electric power steering apparatus. In this figure, the turning force of a steering wheel 1 is transmitted to a steering gear 2 including a pinion gear via a handle shaft. At the same time, the power is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned through a knuckle arm or the like. The torque of a steering assist (auxiliary) motor (DC motor) 6 controlled and driven by the control device 5 is transmitted to the rack shaft 3 by meshing the steering gear 7 including a pinion gear with the rack shaft 3, and the steering wheel 1 This will assist steering.

[0005] The rotating shaft of the handle 1 and the motor 6 are gears 2,
7 and the rack shaft 3. Steering torque (return torque) by the steering torque sensor 11
Is detected, and the vehicle speed is detected by the vehicle speed sensor 12.
Then, the control device 5 controls the motor 6 based on the detected torque, vehicle speed, and the like. The operating power is supplied to the control device 5 and the motor 6 from a battery 8 mounted on the vehicle.

As shown in FIG. 12, a 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, and an interface circuit (not shown) between the computer and the input / output device.

In FIG. 12, a steering torque detected by a steering torque sensor 11 is converted into a digital signal by an A / D conversion circuit 25, and then is taken into a CPU 23. The vehicle speed detected by the vehicle speed sensor 12 is counted by the counter 26, and a count value representing the vehicle speed is taken into the CPU 23. The CPU 23 generates 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 6 is driven by the motor drive circuit 22. As a result, the assist torque value output from the motor driving circuit 22 (or the electric current value), as shown in FIG. 13, a value determined by the detected torque V _T and the detected vehicle speed V _S.

[0008] Figure 13 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 This 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 and is converted into a digital signal by the A / D conversion circuit 27 before being 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 detected steering torque and the detected vehicle speed to generate the steering assist torque. in this case,
Since the release stability at high vehicle speed is insufficient due to the inertial force of the motor 6, 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 Laid-Open No. 61-169675.

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

[0012]

However, in such a method of positively feeding back the steering angular acceleration to the assist command value, a low-pass filter for removing noise when detecting the steering angular acceleration to be fed back positively is used. Since it is necessary to use it and it is necessary to perform sampling at a predetermined time interval, the assist command value has a phase delay.

When the band is narrow, such as when the current control unit 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, the influence of inertia cannot be sufficiently removed, so that the stability when the steering wheel 1 is released cannot be sufficiently obtained, the speed of convergence to the neutral position of the steering wheel is slow, and the steering feeling due to the inertia during steering is reduced. Is worse.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric power steering device in which the steering wheel return speed is increased and the steering feeling is improved while improving the instability at the time of returning at a high vehicle speed. .

[0015]

In order to achieve the above object, an electric power steering apparatus according to the present invention is connected to a steering system and generates an assist motor for generating a steering assist torque, based on 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 angular acceleration detection for detecting a steering angular acceleration of a steering system. Means for generating an inertial control signal for compensating for the inertia of the assist motor in accordance with a steering angular acceleration signal output from the steering angular acceleration detecting means, and inertia control means for positively feeding back the assist command value. In the electric power steering apparatus, the steering angle acceleration signal is provided in the inertial control means, and the desired frequency range is provided. A fuzzy calculation filter having a noise removal function with advancing the phase, and the steering angular velocity detecting means for detecting a steering angular velocity of the steering system, the level of the inertia control signal based on the steering angular velocity output from the steering angular velocity detecting means And a variable means for correcting so as to increase .

[0016]

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

In addition, the frequency range (1H
At z or less), the gain is reduced due to the characteristics 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 having a phase advanced in a desired frequency range can be obtained, and the inertia control signal obtained based on the steering angle acceleration signal can be positively fed back to the assist command value. An assist torque with no 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 from the hand is improved, the convergence speed when returning is increased, and a good steering feeling without a feeling of inertia can be obtained.

[0019]

DETAILED 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 built in a control device 5A of an electric power steering apparatus according to an embodiment of the present invention, together with blocks showing other input / output devices and various circuits. is there.

In FIG. 1, an assist command unit 30 includes a detection torque VT of a steering torque sensor 11 and a vehicle speed sensor 1.
2 detected vehicle speed Vs. Assist command section 30
The assisting torque value indicating function section 31 in the figure indicates the detected torque VT
And outputs a command value indicating an assist torque to be generated by the motor 6 in response to the command.

The multiplication constant function unit 32 calculates the detected vehicle speed Vs
, And the constant is multiplied by the multiplying operation unit 33 with the assist torque command value. As a result, the assist torque value (or the motor current command value) output from the multiplication operation unit 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 applied to a phase compensator 34, and the differential value of the detected torque VT is added to the output of the multiplying operation unit 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, the output of the inertia control unit 50 is added to the current control unit 35 in addition to the output of the assist command unit 30. The inertia control unit 50 controls the motor 6 as if the rotor inertia became small. The inertia control unit 50 eliminates the weight caused by the motor 6 not following the rotation of the steering wheel at the time of sudden steering, and the return speed at the time of releasing. It acts as if it is faster.

In the inertial controller 50, a steering angle acceleration is obtained by a steering angle acceleration sensor 51, and this steering angle acceleration is given to a fuzzy operation filter 52. A predetermined frequency range (approximately 0 Hz to several tens H
After the extraction of the steering angle acceleration signal of z) is performed, the steering angle acceleration signal is supplied to the inertia compensating unit indicating function unit 53. On the other hand, the steering angular velocity sensor 5
The steering angular velocity is obtained by 4, 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 supplies the constant to the multiplication operation unit 56. Then, this constant is used as the inertial compensation unit indicating function unit 53.
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,
Although double dots are added above the characters, it is difficult to display dots in the text of the specification.
θ _m (k) ≡η as appropriate.

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

Here, 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 relating to the steering angular acceleration η, and FIG. 3 (b) is a membership function relating to the change Δη. . In this case, the membership function has a triangular shape, but it goes without saying that the membership function may have any shape. On the other hand, FIG. 3C shows 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 (negatively large) NM: Negtivea medium (negatively large) NS: Negative Small (negatively small) ZO: zero (zero) PS: Positive Small (positively small) PM: Positive medium (positively small) PB: Positive Big

The fuzzy rule is shown in FIG. 4 and is expressed as follows using an equation. The rule is the so-called I
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 angular 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 change Δη is positively large, the fuzzy output is positively increased".

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

The fuzzy rule R3 means "if the steering angular acceleration η is positively large and the change Δη is zero, the fuzzy output is made slightly large positively".

The fuzzy rule R4 means that if the steering angular acceleration η is large and the change Δη is small, the fuzzy output is made large.

The fuzzy rule R5 means "if the steering angle acceleration η is positively large and the change Δη is negatively large, the fuzzy output is set to zero". Hereinafter, other rules are determined in the same manner.

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

When the phase is advanced in a frequency range of 1 to several tens Hz, the fuzzy operation filter 52 results in a decrease in gain in a low frequency range of 1 Hz or less, as shown in FIG. Resulting in. Therefore, when the detected angular velocity is equal to or less than a predetermined value, or when the rate of change of the sign of the detected angular velocity is equal to or less than a predetermined value (when the number of sign changes during a certain period is equal to or less than a predetermined number), in order to compensate for this decrease in gain. The output of the fuzzy operation filter 52 is increased by increasing the multiplication coefficient of the multiplication operation unit 56 (the level is increased).
) .

For reference, FIG. 6 is a characteristic diagram of a conventionally used digital low-pass filter, of which FIG. 6A shows a gain frequency characteristic and FIG. 6B shows a phase frequency characteristic. In this conventional digital low-pass filter, the phase is delayed in a frequency range of 1 to several tens Hz. In this digital low-pass filter, the current control unit 35
However, this cannot be prevented when a phase delay occurs.

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 an H-bridge drive method including, for example, four switching elements. ,
Perform current feedback control. That is, the armature current of the motor 6 is detected by the armature current detection unit 36,
The current deviation calculator 37 calculates a deviation between the applied assist command value and the detected current. The absolute value of the 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 the absolute value.

On the other hand, the polarity (positive or negative) of the deviation is determined by the positive / negative determining unit 40, and the generated duty ratio and the determined polarity are given to the motor driving unit 41. , The four switching elements wired in an 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. Further, the current control unit 35 corresponds to a control unit. Further, the inertia control unit 50 corresponds to inertia control means. The steering angle acceleration sensor 51 corresponds to a steering angle acceleration detecting means. The steering angular velocity sensor 54 corresponds to a steering angular velocity detecting means. The multiplication constant function unit 55 and the multiplication operation unit 56 are
Is configured.

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
Reads the steering angle acceleration η from the steering angle acceleration sensor 51,
In step S2, this steering angular acceleration η is used as a fuzzy input. Then, fuzzy inference is performed according to a predetermined fuzzy rule based on the steering angular acceleration η and the change Δη,
Estimate the steering angular acceleration. Then, in step S3, the estimated value of the steering angular acceleration is output to the inertial compensation value indicating function unit 53 as a fuzzy output.

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

That is, the fuzzy output for each conclusion part label is obtained by comparing the rule suitability obtained by the condition part processing with other suitability. Next, a weighting process is performed in step S13 to adjust the degree of influence of each rule on the conclusion part. For example, an item having a low degree of matching is selected and given to the consequent part. Thereafter, in step S14, one definite value representing the fuzzy output is calculated.

That is, in the consequent part, the membership functions are superimposed by the MAX combining process to generate a combined output, and thereafter, one determinate value is obtained from the center of gravity of the combined output by the defuzzifier.

FIG. 9 is a diagram showing a response of the steering system when the fuzzy operation filter 52 is used, and FIG. 10 is a diagram showing a response of the steering system when a filter having a linear characteristic such as a conventional digital low-pass filter is used. FIG. These figures show 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 speed is obtained by the steering angular speed sensor 54. However, the present invention is not limited to these. 6, the motor rotational speed is calculated from the voltage / current, and the steering angular speed is estimated from the calculation result.
Further, the steering angle acceleration may be estimated from the result of differentiating the calculated value, and these estimated values may be used. This way,
The steering angle acceleration sensor 51 and the steering angular velocity sensor 54 become unnecessary, and the cost can be reduced.

[0048]

According to the present invention, the phase of the detected steering angular acceleration signal in a desired frequency range (frequency range of 1 Hz to several tens Hz which is a problem in the electric power steering apparatus) is advanced and a noise removing function is provided. While the fuzzy operation filter provided is provided, the variable means for compensating the signal level in the frequency range that is reduced by providing the fuzzy operation filter is provided, so that there is no phase delay even through a 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 wheel is released is improved, the convergence speed when returning is increased, and a good steering feeling without a feeling of inertia is obtained.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram illustrating a membership function of a consequent 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 operation 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 a fuzzy operation filter according to one embodiment of the present invention.

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

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

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

FIG. 11 is a configuration diagram illustrating 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 an assist torque of a conventional power steering device.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering handle 6 assist motor 11 steering torque sensor 12 vehicle speed sensor 30 assist command unit (assist command value creation unit) 35 current control unit (control unit) 50 inertia control unit (inertia control unit) 51 steering angle acceleration sensor (steering angular acceleration) Detection means) 52 fuzzy operation filter 53 inertia compensation value indicating function unit 54 steering angular velocity sensor (steering angular velocity detection means) 55 multiplication constant function unit 56 multiplication operation unit 100 variable means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 137: 00 B62D 137: 00 (56) References JP-A-63-291769 (JP, A) (58) Fields investigated (Int. .Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (1)

(57) [Claims] An assist motor connected to a steering system for generating a steering assist torque; assist command value generating means for generating 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 an assist command value; steering angle acceleration detecting means for detecting a steering angular acceleration of a steering system; and a steering angular acceleration signal output from the steering angular acceleration detecting means. An inertia control means for generating an inertia control signal for compensating for the inertia of the assist motor and positively feeding back to the assist command value, comprising: an electric power steering apparatus provided in the inertia control means, the steering angle acceleration signal And a fuzzy operation filter that advances the phase in a desired frequency range and has a noise removal function, and a steering system It is corrected so as to increase the steering angular velocity detecting means for detecting an angular velocity, a level of the inertia control signal based on the steering angular velocity output from the steering angular velocity detecting means
Electric power steering device comprising a variable means, that was provided that.