JPH10338152A - Control device for electric power steering device - Google Patents

Abstract

(57) [Summary] In a control device for an electric power steering device, compensation of motor inertia, control of vehicle convergence, etc. are fully performed by estimating a motor angular velocity with high accuracy to improve steering performance. improves. SOLUTION: The motor which applies a steering assist force to a steering mechanism based on a current command value calculated from a steering assist command value calculated based on a steering torque generated in a steering shaft and a current value of the motor is controlled. The control device for an electric power steering device is configured to define an impedance model of each motor drive system in an intermittent mode and a continuous mode and estimate a motor angular velocity.

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, and more particularly to a control device for controlling a motor angular velocity without being affected by temperature. The present invention relates to a control device for an electric power steering device, which is capable of improving steering characteristics such as overall control accuracy and followability by estimating the accuracy.

[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 uses a transmission mechanism such as a gear or a belt through a speed reducer to transmit the driving force of the motor to a steering shaft or the like. 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 device 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. 9 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 the current supplied to the motor 20 based on the input steering torque TA and the vehicle speed V. Is provided with a memory 33. The memory 33 stores a steering assist command value I corresponding to the steering torque using the vehicle speed V as a parameter, and is used for calculating the steering assist command value I by the steering assist command value calculator 32. The steering assist command value I is input to a subtractor 30A, and also to a feedforward differential compensator 34 for increasing the response speed.
The deviation (I-i) of the subtractor 30A is input to a proportional calculator 35, and the proportional output is input to an adder 30B and an integral calculator 3 for improving the characteristics of the feedback system.
6 is input. The outputs of the differential compensator 34 and the integration compensator 36 are also added to the adder 30B, and the current control value E, which is the result of the addition in the adder 30B, 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 the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A and fed back.

A configuration example of the motor drive circuit 37 will be described with reference to FIG. 10. The motor drive circuit 37 is based on a current control value E from an adder 30B and is a field effect transistor (FE).
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 boost 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.

FIG. 3 shows ON / OFF of the FETs 1 to 4 of the H-bridge circuit as shown in FIG.
Shows, for example, when the FET 3 is in a conductive state, the current is the FET 1, the motor 20,
Flow through FET3, resistor R1 (mode A), motor 2
A current in the positive direction flows through 0. When the FET 4 is in the conductive state, the current flows through the FET 2, the motor 20, the FET 4,
The current flows through the resistor R2 (mode A), and a negative current flows through the motor 20. Therefore, the current control value E from the adder 30B is also a PWM output. FET1 is OFF
When FET3 is ON, current flows through the regenerative diode of FET4 (mode B), and FET1 and FE
When both T3 are OFF, the magnetic energy stored in the motor 20 is converted into electric energy, and FE
A current flows through the regenerative diodes of T2 and FET4 (mode C). Then, the motor current detection circuit 38 detects the magnitude of the forward current based on the voltage drop across the resistor R1, and detects the magnitude of the negative current based on the voltage drop across the resistor R2. The motor current value i detected by the motor current detection circuit 38 is input to the subtractor 30A and fed back.

The effective current Ie and effective voltage Ve in modes A to C are as shown in FIGS. 4A and 4B. That is, the mode B is a regenerative mode in the H-bridge circuit.
There is a loss due to the N voltage, which causes a difference in the occurrence times of modes A and C. As a result, an effective voltage Ve is generated and the impedance has R = Ve / Ie.

[0008] In such a control device for an electric power steering device, in order to compensate for the influence of the inertia of the motor or to control the yaw rate of the vehicle, the estimated value or detected value of the motor angular velocity or the motor angular acceleration is used. Control. As disclosed in JP-A-3-74262, there is generally known a method of estimating an angular velocity from a back electromotive force generated in a motor for the purpose of cost reduction. That is, the estimation of the conventional motor angular velocity is performed by detecting the voltage between the terminals of the motor and the motor current, calculating the motor back electromotive force based on the impedance model of the motor,
This is because the motor back electromotive force is generated in proportion to the motor angular velocity.

[0009]

Generally, when the frequency of the PWM drive is sufficiently high with respect to the electric time constant of the motor, the characteristics of the drive system can be ignored. However, when a method of driving the motor by PWM driving the upper and lower FETs located diagonally by an H-bridge circuit as shown in FIG. 10 is employed, as shown in FIG. A dead zone DB is generated. A curve B1 in FIG. 11 indicates normal steering (angular velocity ω = 0), and a curve A1 indicates steering in which the steering wheel returns. In this dead zone DB, the current intermittently flows in a PWM cycle. Mode. In the intermittent mode, the current I = 0 within one PWM cycle as shown in FIG.
When I = 0 does not occur within one cycle as shown by the broken line in the figure, the current is superimposed sequentially by the current, and the "continuous mode" in which the current I increases as shown in FIG. . In this continuous mode, when the PWM cycle is sufficiently shorter than the electric time constant of the motor, a transient response according to the electric characteristics of the motor is exhibited. Further, in the intermittent mode, since the driving method affects the current and the effective applied voltage to the motor, as a result, the effect of the driving method on the impedance of the driving system cannot be ignored.

Therefore, in the conventional estimation method in which the influence of the drive system is not taken into consideration, a motor angular velocity estimation error occurs due to the fact that the impedance model is different from the actual one. That is, in the conventional estimation method, since the motor applied voltage is estimated from the duty ratio and the battery voltage, an error occurs in the estimated value of the motor applied voltage. As a result, FIG.
As shown in the characteristic V1, there is a problem that the motor is estimated to be running even though the motor is not running, or the angular velocity is estimated to be small in a region where the current is small. In other words, back EMF in the graph of the current I versus motor terminal voltage V _M as shown in FIG. 2, it is determined as the difference between the actual characteristic V1 and characteristics V2 when the omega = 0. Therefore, the difference e between the model V2 and the actual characteristic V1 when ω = 0 is an offset error, and it is estimated that the motor is rotating regardless of ω = 0. Conventional estimation model V
In No. 2, an offset error occurs because the impedance in the intermittent mode is not considered. FIG.
, R1 is Ve / Ie, and r2 is an impedance substantially equal to the internal resistance of the motor. In the above control system, compensation of motor inertia, control of vehicle yaw rate convergence, and compensation of friction of electric power steering are performed based on the estimated angular velocity of the motor. The steering performance was poor.

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances described above, and an object of the present invention is to estimate motor angular velocity of an electric power steering device with high accuracy, thereby compensating for motor inertia and vehicle convergence. An object of the present invention is to provide a control device for an electric power steering device in which control and the like are fully performed and steering characteristics of a steering wheel are improved.

[0012]

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 applying an assisting force. The object of the present invention is to compensate for the inertia of the motor by estimating the motor angular velocity with high accuracy, This is achieved by improving the steering performance by sufficiently exerting the convergence control and the like.
Further, a dead zone proportional to the motor current value may be set, and the gain of the dead zone may be switched between the intermittent mode and the continuous mode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, by defining different motor drive system impedance models for the intermittent mode and the continuous mode, the influence of the drive system on the drive system impedance is considered, and the motor angular velocity estimation is performed. By doing so, highly accurate motor angular velocity estimation is enabled. Further, a dead zone proportional to the current value is set to compensate for an estimation error caused by a change in the impedance characteristic of the motor drive system due to a temperature change, and the gain of the dead zone is switched between the intermittent mode and the continuous mode. or,
The motor temperature may be measured or estimated to compensate for the estimation error due to the temperature fluctuation.

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

First, FIG. 1 shows the estimation of the motor angular velocity ω and its compensation mode according to the present invention, corresponding to FIG. Motor angular velocity estimator 301 in control unit 30A
Estimates the motor angular velocity ω from the current control value E (corresponding to the motor terminal voltage) and the motor current value i, and inputs the estimated motor angular velocity ω 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 30A, respectively. The convergence controller 304 applies a brake to the steering operation of the steering wheel in order to improve the convergence of the yaw of the vehicle. 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 30A. I have.
The inertia compensator 305 assists the force corresponding to the force generated by the inertia of the motor 20, and prevents the feeling of inertia or the control response from deteriorating.

In the present invention, the reason why the impedance is generated in the intermittent mode is that the time constant in the regenerative mode (mode B) is smaller than the time constant at the time of rising and falling as shown in FIG. Increase due to the influence of the ON voltage of the diode and the ON resistance of the FET, and as a result, the effective voltage Ve is generated. Incidentally, (C) of FIG. 5 shows a voltage V _M between the motor terminals, FIG. (D) shows the motor current value (effective current) Ie, FIG. (E) shows a current detection value Id. In the control unit,
The intermittent effective current value Ie and the current detection value Id are shown in FIG.
(D) and (E) are monitored, and it is recognized that the motor drive system has the impedance determined by these effective current values Ie. As a result, the impedance is recognized as an impedance represented by a current-voltage characteristic as shown in FIG. In FIG. 2, V1 is the actual characteristic,
Reference numeral 2 denotes a conventional model, and an estimation error e occurs.

Here, in the intermittent mode, when the impedance Rd is obtained based on FIG. 5, it is expressed as a function of the duty ratio D1 as shown in the following Expression 1. In FIG. 2, the current I
_The area smaller than _O indicates the impedance in the intermittent mode, and the area equal to or higher than the current I _O indicates the impedance in the continuous mode.

[0018]

Rd = (m1 · D1 ² + m2 · D1) / (m3
D1 ² + m4D1 + m5 where m1, m2, m3, m4, and m5 are constants determined by the battery voltage (Vb), the PWM cycle, and the time constant of the motor.

However, in practice, the impedance can be approximated to a constant value of impedance R1. The inflection point from the intermittent mode to the continuous mode actually changes according to the motor angular velocity.
However, since the impedance in the intermittent mode is sufficiently large, it can be considered that an inflection occurs when a constant current value is reached. Therefore, in order to detect the current _IO and switch the impedance model for estimation, the following impedance model can be defined.

[0020]

[Number 2] I <For _{I O} For _{K T · ω = V M -R1} · i I ≧ I O K T · ω = V M - (R2 · i + b) However, _{K T} · ω counter electromotive force , _IO is the current value for switching from the intermittent mode to the continuous mode, R1 is the impedance of the intermittent mode at the reference temperature, and R2 is the impedance of the continuous mode at the reference temperature.

On the other hand, the characteristics of the actual motor drive system are affected by temperature fluctuations. Conventionally, measures have been taken by setting a dead zone in proportion to the current value in order to eliminate the influence of temperature fluctuation. Also in the present invention, by setting the dead zone in proportion to the current value, it is possible to eliminate the modeling error of the motor internal resistance and the influence of the temperature fluctuation. Here, it is qualitatively known that the impedance straight line in the discontinuous mode always passes through the origin regardless of the temperature fluctuation as shown in FIG. 6 and always passes through the intercept b in the continuous mode, and the dead zone is set under the following conditions. You know what to do. Note that in FIG. 6, W denotes a width that there is impedance characteristic undergoing temperature variations, V _O is the voltage value across the motor terminals impedance characteristics inflection.

[0022]

## EQU3 ## When I <I _O / K * K _T · ω = K _T · ω−K1 · i When I ≧ I _O / K * K _T · ω = K _T · ω−K2 · i where, K1 is a dead zone proportional constant in the intermittent mode, K
2 is a dead zone proportional constant in the continuous mode, and K is a ratio between the intermittent mode impedance at the reference temperature and the impedance after receiving the temperature fluctuation.

In the above example, the influence of the temperature fluctuation is compensated by setting the dead zone. However, when the temperature fluctuation is large, it is preferable to compensate by estimating or measuring the motor temperature.
By the way, as shown in FIG. 6, the inflection position is substantially constant irrespective of the temperature ( _VO ) as viewed from the voltage applied to the motor. This is because the inflection point is dominated by the duty ratio of the upper and lower FETs, and the motor applied voltage is determined by a function of only the duty ratio and the battery voltage. On the other hand, the current in the intermittent mode decreases as the internal resistance of the motor increases. Therefore, the temperature fluctuation of the motor drive system changes as shown by the broken line in FIG. Therefore, temperature compensation can be performed under the following condition (4).

[0024]

Equation 4] _{I <I} O / _{K Y} when _{K T · ω = V M -R} 1T · i I ≧ I O / K Y when _{K T · ω = V M -} (R 2T · i + b) However, R _1T is the impedance of the intermittent mode at the temperature T, R _2T is the impedance of the continuous mode at the temperature T, and K _Y = R _1T / R _2T .

The change in the impedance model of the motor is
In addition to temperature fluctuations, there are also manufacturing errors. Therefore, by performing the correction together with the correction method based on the dead zone,
More accurate estimation can be performed. Conventionally, a method of estimating the applied voltage of the motor from the duty ratio has been adopted. However, the relationship between the motor applied voltage and the duty ratio using the motor angular velocity as a parameter is different from the nonlinear characteristic shown in FIG. Therefore, it is preferable to directly use the motor applied voltage for monitoring. The solid line in FIG. 7 indicates normal steering, and the chain line indicates steering with the steering wheel returned.

[0026]

According to the present invention, the influence of the drive system on the drive system impedance is considered by defining different motor drive system impedance models for the intermittent mode and the continuous mode. Thus, the motor angular velocity can be estimated with high accuracy. This makes it possible to compensate for the influence of the inertia of the motor and the friction with high accuracy. In addition, a dead band proportional to the current value is set to compensate for an estimation error caused by a change in impedance characteristics of the motor drive system due to temperature fluctuation, and the gain of the dead band is switched between the intermittent mode and the continuous mode.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a relationship between a motor current and a voltage between motor terminals according to the present invention in comparison with a conventional example.

FIG. 3 is a diagram illustrating an example of a current path in an H-bridge circuit.

FIG. 4 is a diagram showing an example of an effective voltage and an effective current in modes A to C.

FIG. 5 is a diagram for explaining the operation of the present invention.

FIG. 6 is a diagram for explaining a change in impedance with temperature.

FIG. 7 is a diagram showing a relationship between a duty ratio and a motor terminal voltage with the motor angular velocity as a parameter.

FIG. 8 is a block diagram showing an example of an electric power steering device.

FIG. 9 is a block diagram showing a general internal configuration of a control unit.

FIG. 10 is a connection diagram illustrating an example of a motor drive circuit.

FIG. 11 is a diagram illustrating an example of a duty ratio versus motor current (terminal voltage) characteristic;

FIG. 12 is a diagram for explaining an intermittent mode and a continuous mode.

[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

Continued on the front page (72) Inventor Hideaki Kawada 78 Tobacho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd. (72) Inventor Yusuke 78 Tobacho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd.

Claims (3)

[Claims] 1. A motor for applying a steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated based on a steering torque generated on a steering shaft and a current value of the motor. A control apparatus for an electric power steering apparatus, comprising: defining an impedance model of each motor drive system in an intermittent mode and a continuous mode to estimate a motor angular velocity; . 2. The control device for an electric power steering device according to claim 1, wherein a dead zone proportional to the motor current value is set, and a gain of the dead zone is switched between the intermittent mode and the continuous mode. 3. The control device for an electric power steering apparatus according to claim 2, wherein the motor temperature is measured to compensate for an estimation error due to temperature fluctuation.