JP2000095131A - Control device for electrically driven power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve steering performance of a steering wheel by differentiating a steering wheel torque signal to add it to a steering assist command value, thereby providing a continuous, stable steering feel. SOLUTION: A steering wheel torque TA from a position compensator 31 is input to an arithmetic and logical unit 310 that performs arithmetic operations of a steering assist command value I. The arithmetic and logical unit 310 performs arithmetic operations of steering assist command value I with a vehicle speed V used as a parameter. The steering assist command value I output from the arithmetic and logical unit 310 is input to an adder 313. The steering wheel torque TA is differentiated by an approximation differentiator 312 and the resulting differentiated torque STA is input to the adder 313. A current command value Iref added by the adder 313 is input to an adder-subtracter 314. Since the signal STA, which is a torque value differentiated by the differentiator, is added to the steering assist command value I, a negative gain is applied when a steering wheel is returned, i.e., a steering angle is reduced. This effectively prevents the steering assist command value I from decreasing sharply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device which applies a steering assisting force by a motor to a steering system of an automobile or a vehicle. The present invention relates to a control device for an electric power steering device which provides a safe steering ability.

[0002]

2. Description of the Related Art An electric power steering apparatus for energizing a steering apparatus of an automobile or a vehicle with an auxiliary load by the rotational force of a motor is provided with a steering shaft or a transmission mechanism such as a gear or a belt through a speed reducer. An auxiliary load is applied to the rack shaft. Such a conventional electric power steering apparatus performs feedback control of a motor current in order to accurately generate an assist torque (a steering assist torque). The feedback control adjusts the motor applied voltage so as to reduce the difference between the current control value and the motor current detection value. Generally, the adjustment of the motor applied voltage is performed by a PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

Here, a general configuration of an electric power steering apparatus will be described with reference to FIG.
Is connected to a tie rod 6 of a steered wheel via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5. The shaft 2 is provided with a torque sensor 10 for detecting a steering torque of the steering wheel 1. A motor 20 for assisting the steering force of the steering wheel 1 is coupled to the shaft 2 via a clutch 21 and a reduction gear 3. Have been. The control unit 30 for controlling the power steering device includes an ignition key 1 from the battery 14.
1 is supplied with power through the control unit 30
Calculates the steering assist command value I of the assist command based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and calculates the steering assist command value I based on the calculated steering assist command value I. The current supplied to the motor 20 is controlled. The clutch 21 is turned on / off by the control unit 30.
It is OFF controlled and is ON (coupled) in a normal operation state. Then, when the control unit 30 determines that the power steering device has failed, and when the ignition key 11 is used to supply power (voltage Vb) to the battery 14
Is off, the clutch 21 is turned off (disengaged).

The control unit 30 is mainly composed of a CP
FIG. 8 shows a general function executed by a program inside the CPU.
For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU. The function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by a phase compensator 31 in order to enhance the stability of the steering system. TA is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I which is a control target value of a current supplied to the motor 20 based on the input steering torque TA and vehicle speed V. The steering assist command value I is subtracted by a subtractor 30.
A, and also to a feed-forward type differential compensator 34 for increasing the response speed,
The deviation (I-i) of 0A is input to a proportional calculator 35 and also to an integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integral compensator 36 are also added and input to the adder 30B.
The current control value E, which is the result of the addition at B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by a motor current detection circuit 38,
The motor current value i is input to the subtractor 30A and fed back.

An example of the configuration of the motor drive circuit 37 will be described with reference to FIG. 9. The motor drive circuit 37 uses a field effect transistor (FE) based on a current control value E from an adder 30B.
T) An FET gate drive circuit 371 for driving the gates of FET1 to FET4, an H bridge circuit composed of FET1 to FET4, a step-up power supply 372 for driving the high side of FET1 and FET2, and the like. FET1 and FET2 are turned ON / OFF by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E.
It is turned off, and the magnitude of the current Ir actually flowing to the motor 20 is controlled. FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function expression (D2 = a · D1 + b where a and b are constants) in a region where the duty ratio D1 is small, and the duty ratio D2 is also 10%.
After reaching 0%, it is turned ON / OFF according to the rotation direction of the motor 20 determined by the sign of the PWM signal.

On the other hand, a widely used hydraulic power steering apparatus has a characteristic that the friction of the cylinder portion increases in proportion to the cylinder pressure P (the horizontal axis T is the steering torque) as shown in FIG. Due to this frictional characteristic, the steering wheel has a hysteresis. For example, the steering wheel is prevented from being returned suddenly by a self-aligning torque at the time of cornering, which contributes to improving the steering feeling of the driver. FIG.
1 shows the situation, in which the steering torque T suddenly increases by ΔT
If there is only a change, the cylinder pressure P1 will change if there is no hysteresis, but if there is hysteresis, the change will be P2 (<P1). Therefore, if there is a hysteresis, the change in the cylinder pressure P can be made gradual with respect to the change in the steering torque T. here,
It is known that the hysteresis width changes according to the magnitude of the friction. In rubber packing of a hydraulic cylinder, the rubber is pressed with the rise of the cylinder pressure, so that Coulomb friction increases and the hysteresis width increases. . And
It is important for the driver to feel a strong self-aligning torque near the neutral point and not to feel much self-aligning when cornering.
In this sense, it is ideally desirable that the friction (hysteresis) is small in a region where the steering angle θ is small and that the friction (hysteresis) is large in a region where the steering angle θ is large, as in a hydraulic power steering device.

On the other hand, the electric power steering apparatus has a constant friction regardless of the assist torque AT as shown in FIG. In the case of the electric power stearing device, the Coulomb friction of the motor is mainly dominant, so that it has a characteristic that it has a constant friction characteristic regardless of the steering force. Therefore, as shown in FIG. Characteristics. However, the hysteresis width is smaller than the hysteresis width of the hydraulic power stearing device at high torque. Therefore, in the electric power steering apparatus, the friction is compensated by giving importance to the friction characteristics in a region where the steering torque T is small. However, in the case of such a compensation, as shown in FIG. 13, in a region where the steering torque T is large, the friction becomes too small. As a result, when the steering torque T is large at the time of cornering or the like, a stable steering feeling is lost. Was supposed to.

[0008]

As a control device which has solved the above-mentioned problems, for example, Japanese Patent Application Laid-Open No. 9-156526
There is one shown in Japanese Patent Publication No. In the vehicle steering control device, a steering torque detection unit that detects a steering torque is provided, and an assist amount of an electric power assist unit is controlled based on a detection signal output from the steering torque detection unit. An adjusting means for providing a hysteresis to a detection signal of the torque detecting means is provided. By providing the adjusting means, the detection signal of the steering torque detecting means can be given a hysteresis. Therefore, the hysteresis characteristic of the power assist means that operates can be changed according to the steering state based on the steering torque detection signal, and the torque assist amount can be optimized.

[0009] However, the above-mentioned conventional apparatus has a drawback that the steering operation has a feeling of intermittent operation, the torque control system is unstable, and the cost is increased due to the provision of a new hardware configuration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electric power steering apparatus with an inexpensive software configuration and a continuous hysteresis characteristic with an adjustable width. Accordingly, it is an object of the present invention to provide a control device for an electric power steering device in which a continuous and stable steering feeling is obtained and steering characteristics of a steering wheel are improved.

[0011]

SUMMARY OF THE INVENTION The present invention provides a steering mechanism for steering a steering mechanism based on a steering assist command value calculated based on a steering torque generated in a steering shaft and a current control value calculated from a current value of a motor. The present invention relates to a control device for an electric power steering device adapted to control the motor for providing an assisting force, and an object of the present invention is to provide an assisting device for differentiating the steering torque signal and adding the signal to the steering assist command value. This is achieved by providing arithmetic means. The auxiliary calculation means is connected in parallel with the calculation means and comprises an approximate differentiator and an adder.
Further, the gain of the approximate differentiator is changed according to the magnitude of the steering torque.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a value proportional to the derivative of a steering torque signal with respect to an assist amount (a steering assist command value) is intended to improve the response of an assist torque and the stability of a torque control system. , To increase the response of the control system. Since the signal obtained by differentiating the torque amount is added to the assist amount, a negative gain is applied when the steering wheel returns, that is, when the steering angle θ decreases, and the assist amount (steering assist command value) Is prevented, and as a result, a large hysteresis characteristic is provided in a high torque region, and a small hysteresis characteristic is provided in a low torque region near a neutral point.

An embodiment of the present invention will be described below with reference to the drawings.

First, the control unit 3 according to the present invention
The configuration of 0A is shown in FIG. 1 corresponding to FIG. In the present invention, the steering torque TA from the phase compensator 31 is input to a calculator 310 for calculating a steering assist command value I, and the calculator 310 uses the vehicle speed V as a parameter to set the steering assist command value I
Is calculated. The steering assist command value I output from the calculator 310 is input to the adder 313, and the steering torque TA
Is differentiated by the approximate differentiator 312 and its differential torque STA
Is input to the adder 313, and the current command value Iref added by the adder 313 is input to the adder / subtractor 314. The vehicle speed V is also input to the approximate differentiator 312.

Further, the motor angular velocity estimator 301 in the control unit 30A calculates the motor angular velocity ω from the current control value E (corresponding to the voltage between the motor terminals) and the motor current value i.
Is input to the loss torque compensator 303 and the convergence controller 304. The outputs of the loss torque compensator 303 and the convergence controller 304 are input to the adder / subtractor 314, respectively.
Reference numeral 03 denotes an assist corresponding to the loss torque in the direction in which the loss torque of the motor 20 is generated, that is, the rotation direction of the motor 20. The convergence controller 304 operates the steering wheel in order to improve the convergence of the yaw of the vehicle. The brakes are applied to The motor angular velocity ω is input to a motor angular acceleration estimator (differentiator) 302 to estimate the motor angular acceleration. The motor angular acceleration is input to an inertia compensator 305, and the compensation signal is input to an adder / subtractor 3
14 has been entered. The inertia compensator 305 is a motor 20
This assists the force equivalent to the force generated by the inertia of the motor, and prevents deterioration of the feeling of inertia or control responsiveness.

Here, the operation of the steering assist command value I by the calculator 310 is calculated and output with a function characteristic as shown in a block 310A of FIG. 2, and △ I / △ TA = K.
For the sake of simplicity, assume that K∝TA. Approximate differentiator 3
A transfer function 12 is represented by a block 312 in FIG. 2 where the gain is Kdd. Note that T1 is an integration time constant, and s is a Laplace variable. From the block diagram of FIG.
The following equation 1 holds for the current command value Iref.

[0017]

Iref = K + Kdd · s / (T1 · s + 1)
= (K · T1 · s + K + Kdd · s) / (T1 · s +
1) = {(K · T1 + Kdd) s + K} / (T1 · s +
1) = {K / (T1 · s + 1)｝ ｛K · T1 + Kdd)
s / K + 1｝ Here, the following Expression 2 is established.

[0018]

## EQU2 ## (K.T1 + Kdd) / K> T1 Therefore, the frequency characteristic of the above equation 1 is as shown in FIG. As shown in FIG. 3, comparing the case where the assist characteristic gain K is small and the case where the assist characteristic gain K is large, when the assist characteristic gain K is large, the assist characteristic gain K Is small regardless of the magnitude of the gain G. That is, in the band equal to or higher than the frequency a, almost constant responsiveness is obtained regardless of the magnitude of the assist characteristic gain K. As shown in FIG. 4, the steering assist command value I, which is the output of the arithmetic unit 310, has a small assist characteristic gain K when the steering torque TA is small, and a large assist characteristic gain K when the steering torque TA is large. It has become. As a result, when the steering torque TA is small, the responsiveness is lower than when the steering torque TA is large. Accordingly, by providing the characteristics as shown in FIG. 3, the response in the high frequency band can be maintained, and the influence of the friction and the inertia of the motor can be compensated.

FIG. 5 is a flowchart showing an operation example of the present invention. When the steering torque TA decreases, K2 (> K
1) or a gain Kdd of K1 (≦ 0) is applied to define a current command value Iref in a direction that prevents a decrease in the steering torque TA (a direction in which hysteresis occurs). First, it is determined whether or not the absolute value of the steering torque TA is larger than a predetermined value α (step S1). If the torque value is smaller than the small predetermined value α, the gain Kdd is increased to obtain a stable steering in the center. K2 is set (step S4). If the torque value is larger than the predetermined value α, a magnitude relationship with a past value is determined (step S2). That is, the past absolute value | TA (k-1) | one sample before is subtracted from the absolute value | TA (k) | of the current value of the steering torque TA to determine whether it is smaller than "0". judge. If the subtracted value is smaller than “0”, that is, if the past torque value is larger, a large gain K2 is set. In step S2, when the difference between the current value and the past value is “0” or more, that is, when the current torque value is larger, the gain Kdd is set to a small negative gain K1 (≦ 0). (Step S3). The gain K2 is a function of the vehicle speed V.

As described above, according to the present invention, when the steering angle θ decreases, a negative gain Kdd is applied to prevent a sharp decrease in the current command value Iref. Hysteresis characteristics equivalent to the hydraulic power stearin device as shown can be obtained.

Here, the reason why the electric power steering apparatus has a hysteresis characteristic in the steering torque TA-current (steering assist command value I) characteristic when the electric power steering device has the Coulomb friction will be described below.

Assuming that the angular velocity of the steering shaft is ω, the friction Fc has a Coulomb friction f as shown in FIG. 14, and the reaction force from the road surface is a simple spring (spring constant: α) proportional to the steering angle θ. Then, the following equation 3
Is obtained.

[0023]

Equation 3] _{K T · I + TA-f} · sign (ω) = α · θ In this case, the steering is when gently smooth performed, characteristics of the steering torque TA versus steering angle theta is as shown in Figure 15. That is,
In order to steer and move the steering wheel, a force exceeding the frictional force f is always required. Where K _T · I≫TA, K _T · I
Since ≫f, it can be approximately regarded as K _T · I∝α · θ, and FIG. 15 has a hysteresis characteristic as shown in FIG.

Next, hysteresis in the case where the derivative of the steering torque TA is subtracted from the assist current will be described in a simplified manner except for the term f · sign (ω) from the above model. Ignoring all input friction,

[Number 4 is a _{K T · I + TA = α} · θ, and referred to the differential in *

K _T · (−Kd · * TA + K · TA) + TA = α · θ,

[6] _{-K T · Kd · * TA +} K T · K · TA = α · θ is true. Here, a Iαθ than K _T · IαK · θ, since it is TAαθ than _{K T · I = K · TA} , the following Expression 7 is satisfied.

[0025]

-Β1 ** θ + β2 • θ + TA = α · θ Therefore, the following Expression 8 is obtained.

[0026]

(Α−β2) · θ + β1 * θ = TA Based on Equation 8, the characteristic of the steering torque versus the steering angle in the steering pattern is shown in FIG. In FIG. 17, part A shows the case where (α−β2) · θ is added,
Part shows a case where (α−β2) · θ is not added,
By adding −Kd · TA to the output of the arithmetic unit 310, an effect equivalent to providing viscous friction can be obtained. K _T
From I∝α · θ, a similar hysteresis characteristic can be provided in the steering torque TA versus current I characteristic.
Although the case where Kd * TA has been subtracted has been described above,
Under normal conditions, K2 (V) * TA is added,
By adding the gain K1 that satisfies K2 (V)> K1, an effect of increasing the hysteresis with respect to a similar normal state can be obtained.

[0027]

According to the present invention, for the purpose of improving the responsiveness of the assist torque and the stability of the torque control system, a value proportional to the derivative of the steering torque with respect to the assist amount (steering assist command value) is determined. Are added to increase Since the differentiated value is added to the assist amount, a negative gain is applied when the steering angle θ decreases, thereby preventing a rapid decrease in the assist amount (steering assist command value), and as a result, Hysteresis characteristics similar to those of the hydraulic electric power steering device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of the present invention.

FIG. 2 is a transfer function block diagram showing a main part of the present invention.

FIG. 3 is a diagram for explaining the operation of the present invention.

FIG. 4 is a diagram illustrating a characteristic example of a computing unit.

FIG. 5 is a flowchart showing an operation example of the present invention.

FIG. 6 is a diagram showing the effect of the present invention.

FIG. 7 is a block diagram showing an example of an electric power steering device.

FIG. 8 is a block diagram showing a general internal configuration of a control unit.

FIG. 9 is a connection diagram illustrating an example of a motor drive circuit.

FIG. 10 is a diagram showing an operation example of the hydraulic power steering device.

FIG. 11 is a diagram for explaining the effect of the hysteresis characteristic.

FIG. 12 is a diagram showing an operation example of the electric power steering device.

FIG. 13 is a characteristic diagram illustrating an operation example of the electric power steering device.

FIG. 14 is a diagram showing Coulomb friction characteristics.

FIG. 15 is a diagram illustrating an example of a steering torque versus steering angle characteristic.

FIG. 16 is a characteristic diagram showing a hysteresis characteristic of a steering torque versus a steering angle.

FIG. 17 is a diagram illustrating an example of a steering torque versus steering angle characteristic.

[Explanation of symbols]

 Reference Signs List 1 steering handle 5 pinion rack mechanism 10 torque sensor 12 vehicle speed sensor 20 motor 30, 30A control unit 310 arithmetic unit 311 memory

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D032 CC08 DA15 DA23 DA64 DC01 DC02 DC03 DC17 DC22 DD02 DD17 DE10 EA01 EB11 EC23 3D033 CA03 CA13 CA16 CA20 CA21 CA23 CA28

Claims (3)

[Claims] A steering assist command value calculated by a calculating means based on a steering torque generated on a steering shaft;
In a control device of an electric power steering device adapted to control the motor for applying a steering assist force to a steering mechanism based on a current control value calculated from a current value of the motor, a signal of the steering torque is differentiated. A control device for an electric power steering device, further comprising auxiliary calculation means for adding the steering assist command value. 2. The control device for an electric power steering device according to claim 1, wherein said auxiliary operation means is connected in parallel with said operation means, and comprises an approximate differentiator and an adder. 3. The control device for an electric power steering device according to claim 2, wherein a gain of said approximate differentiator is changed according to a magnitude of said steering torque.