JP3525681B2 - Control device for 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 a control device for an electric power steering system which applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and particularly to a motor angular velocity which is high without being influenced by temperature. The present invention relates to a control device for an electric power steering device, which can be estimated accurately to improve steering performance such as overall control accuracy and followability.

[0002]

2. Description of the Related Art An electric power steering system for energizing a steering system of an automobile or a vehicle with an auxiliary load by a rotational force of a motor uses a transmission mechanism such as a gear or a belt to transmit a driving force of the motor through a reduction gear to a steering shaft or An auxiliary load is applied to the rack shaft. Such a conventional electric power steering device performs feedback control of the motor current in order to accurately generate the assist torque (steering assist torque). The feedback control is for adjusting the motor applied voltage so that the difference between the current control value and the motor current detection value is small. The adjustment of the motor applied voltage is generally performed by PWM (pulse width modulation) control duty. It is done by adjusting the tee ratio.

Here, a general structure of the electric power steering apparatus will be described with reference to FIG.
The shaft 2 is connected to a tie rod 6 of a steering 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 the steering torque of the steering wheel 1, and 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. Has been done. The control unit 30 for controlling the power steering device includes a battery 14 and an ignition key 1
Power is supplied via 1 and 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 based on the calculated steering assist command value I. The current supplied to the motor 20 is controlled. The clutch 21 is turned on by the control unit 30 /
It is turned off, and is turned on (coupled) in a normal operating state. Then, when the control unit 30 determines that the power steering device has a failure, and when the ignition key 11 is used, the power source (voltage Vb) of the battery 14 is supplied.
When is off, the clutch 21 is turned off (disengaged).

The control unit 30 is mainly a CP
Although it is composed of U, a general function executed by a program inside the CPU is shown in FIG.
For example, the phase compensator 31 does not represent a phase compensator as an independent hardware but a phase compensating 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 the phase compensator 31 to enhance the stability of the steering system, and the steering torque is phase-compensated. 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 the steering assist command value I, which is the control target value of the current supplied to the motor 20, based on the input steering torque TA and vehicle speed V, and the steering assist command value calculator 32 stores it. Is provided with a memory 33. The memory 33 stores the steering assist command value I corresponding to the steering torque with the vehicle speed V as a parameter, and is used by the steering assist command value calculator 32 to calculate the steering assist command value I. The steering assist command value I is input to the subtractor 30A and also to the feed-forward differential compensator 34 for increasing the response speed,
The deviation (I-i) of the subtractor 30A is input to the proportional calculator 35, and its proportional output is input to the 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 integral compensator 36 are also added and input to the adder 30B, and the current control value E that is the addition result of 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.

An example of the configuration of the motor drive circuit 37 will be described with reference to FIG. 10. The motor drive circuit 37 is based on the current control value E from the adder 30B and is based on the field effect transistor (FE).
T) An FET gate drive circuit 371 that drives each gate of FET1 to FET4, an H bridge circuit that includes FET1 to FET4, and a boosting power supply 372 that drives the high side of FET1 and FET2. 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.
When turned off, the magnitude of the current Ir that actually flows through 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 equation (D2 = a · D1 + b with a and b as 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 an ON / OFF state of the FET1 to FET4 of the H bridge circuit as shown in FIG.
Shows the relationship with the current flowing through, for example, when the FET3 is in the conducting state, the current is the FET1, the motor 20,
Flows through FET3 and resistor R1 (mode A), motor 2
A positive current flows to 0. When the FET4 is in the conductive state, the current is FET2, the motor 20, the FET4,
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. Also, FET1 is OFF
When FET3 is ON, current flows through the regenerative diode of FET4 (mode B), 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 each regenerative diode of T2 and FET4 (mode C). Then, the motor current detection circuit 38 detects the magnitude of the positive current based on the voltage drop across the resistor R1 and 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 the effective voltage Ve in the modes A to C are as shown in FIGS. 4 (A) and 4 (B). That is, mode B is a regeneration mode in the H bridge circuit, and in this mode B, the substrate resistance and the diode O
There is a loss due to the N voltage, which causes a difference in the time of occurrence of modes A and C. As a result, the effective voltage Ve is generated and the impedance is R = Ve / Ie.

In such a control device for an electric power steering system, in order to compensate for the influence of the inertia of the motor and to control the convergence of the yaw rate of the vehicle, the controller is based on the estimated value or the detected value of the motor angular velocity or the motor angular acceleration. Control. As disclosed in Japanese Patent Laid-Open No. 3-74262, a method of estimating the angular velocity from the back electromotive force generated in the motor is generally known for the great purpose of cost reduction. That is, in the conventional estimation of the motor angular velocity, the voltage between the terminals of the motor and the motor current are detected, and the motor back electromotive force is calculated based on the impedance model of the motor.
The motor back electromotive force is generated in proportion to the motor angular velocity.

[0009]

Generally, when the frequency of 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 the method of PWM driving the upper and lower FETs diagonally located in the H bridge circuit as shown in FIG. 10 is adopted as the motor driving method, as shown in FIG. Produces a dead zone DB. A curve B1 in FIG. 11 indicates normal steering (angular velocity ω = 0), and a curve A1 indicates steering for steering wheel return . In the dead zone DB, the current flows intermittently in the PWM cycle, and is referred to herein as the "intermittent mode". The intermittent mode is shown in FIG.
As shown in, the current I becomes 0 within one PWM cycle.
This is a mode having sections . On the other hand, if I = 0 is not satisfied within one cycle as indicated by the broken line in the figure, the current is sequentially superimposed by that amount, and the current I rises as shown in FIG.
Therefore, it is called “continuous mode” here . In this continuous mode, when the PWM cycle is sufficiently shorter than the electric time constant of the motor, it exhibits a transient response according to the electric characteristics of the motor. Further, in the intermittent mode, the drive system affects the current and the effective applied voltage to the motor, and as a result, the effect of the drive system on the impedance of the drive 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 impedance model being 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,
As indicated by the characteristic V1 of 1., there is a problem that the motor is estimated to be rotating even though the motor is not rotating, or the angular velocity is estimated to be small in a region where the current is small. That is, the counter electromotive force is obtained as the difference between the characteristic V2 when ω = 0 and the actual characteristic V1 on the graph of the current I versus the voltage V _M between the motor terminals as shown in FIG. Therefore, the difference e between the model V2 and the actual characteristic V1 when ω = 0 becomes an offset error, and it is estimated that the motor is rotating regardless of ω = 0. Conventional estimation model V
In No. 2, since the impedance in the intermittent mode is not taken into consideration, an offset error occurs. Incidentally, FIG.
In, r1 is Ve / Ie and r2 is an impedance that is approximately equal to the internal resistance of the motor. The control system performs compensation of the inertia of the motor, control of the convergence of the yaw rate of the vehicle, and compensation of the friction of the electric power steering based on the estimated value of the angular velocity of the motor, but these controls do not function sufficiently. The steering performance was poor.

The present invention has been made under the circumstances as described above, and an object of the present invention is to accurately estimate the motor angular velocity of an electric power steering apparatus to compensate for the inertia of the motor and the convergence of the vehicle. It is an object of the present invention to provide a control device for an electric power steering device in which control and the like are sufficiently exerted to improve steering performance of a steering wheel.

[0012]

According to the present invention, a steering mechanism is steered 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 motor current value. said motor providing an auxiliary force, relates controller of an electric power steering device adapted to control the PWM period, the object of the present invention, current is zero at the PWM period
In the intermittent mode and the PWM cycle
There is achieved by current performing motor angle <br/> speed Do推 constant defines the impedance model of the motor drive system in continuous mode with no interval becomes zero. Also, the above
A dead band proportional to the motor current value may be set in the back electromotive force calculation unit in the motor angular velocity estimation, and the gain of the dead band may be switched between the intermittent mode and the continuous mode.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, by defining different impedance models of a motor drive system for the intermittent mode and the continuous mode, the influence of the drive system on the drive system impedance is taken into consideration to estimate the motor angular velocity. By doing so, it is possible to estimate the motor angular velocity with high accuracy. Further, a dead band proportional to the current value is set in order to compensate for an estimation error caused by a change in impedance characteristic of the motor drive system due to a temperature change, and the dead band gain is switched between the intermittent mode and the continuous mode. or,
The motor temperature may be measured or estimated to compensate the estimation error due to the temperature fluctuation.

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

First, the estimation of the motor angular velocity ω according to the present invention and its compensation form are shown in FIG. 1 in correspondence with 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 voltage between the motor terminals) 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 respectively input to the adder / subtractor 30A, and the loss torque compensator 303 assists the loss torque of the motor 20 in the direction in which the loss torque is generated, that is, the rotation direction of the motor 20. The agility controller 304 brakes the steering wheel swinging motion in order to improve the agility of the yaw of the vehicle. The motor angular velocity ω is input to the motor angular acceleration estimator (differentiator) 302 to estimate the motor angular acceleration, the motor angular acceleration is input to the inertia compensator 305, and the compensation signal is input to the adder / subtractor 30A. There is.
The inertia compensator 305 assists the force equivalent to the force generated by the inertia of the motor 20, and prevents deterioration of the sense of inertia or the responsiveness of control.

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 greater than the time constant in the rising and falling as shown in FIG. 5 corresponding to FIG. Is increased 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. 5C shows the voltage V _M between the motor terminals, FIG. 5D shows the motor current value (effective current) Ie, and FIG. 5E shows the current detection value Id. In the control unit,
The effective current value Ie flowing intermittently and the detected current value Id are shown in FIG.
(D) and (E) are monitored, and it is recognized that the motor drive system has the impedance obtained by these effective current values Ie. As a result, it is recognized as an impedance represented by a current-voltage characteristic as shown in FIG. In FIG. 2, V1 is the actual characteristic, and V1
2 shows the conventional model, and the estimation error e has occurred.

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
_A region smaller than _O indicates impedance in the intermittent mode, and a region equal to or higher than the current I _O indicates impedance in the continuous mode.

[0018]

[Formula 1] Rd = (m1 · D1 ² + m2 · D1) / (m3
* D1 ² + m4 * D1 + m5) However, 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, it can be approximated to a constant 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 the inflection occurs at a constant current value. Therefore, in order to detect the current I _O and switch the impedance model for estimation, an impedance model such as the following equation 2 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 estimate of, I _O is the current value switches from intermittent mode to continuous mode, R1 is the impedance of the intermittent mode at the reference temperature, R2 is the impedance of the continuous mode at the reference temperature.

On the other hand, the actual characteristics of the motor drive system are affected by temperature fluctuations. Conventionally, in order to eliminate the influence of temperature fluctuation, a dead zone proportional to the current value has been set. Also in the present invention, by setting the dead zone proportional to the current value, it is possible to eliminate the influence of the modeling error of the motor internal resistance and its 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 variation 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 you need to do. In FIG. 6, W indicates the width in which the impedance characteristic is present due to the temperature change, and V _O is the voltage value between the motor terminals where the impedance characteristic changes.

[0022]

[Expression 3] I <IO / K * KT · ω = KT · ω-K1 · i I ≧ IO / K * KT · ω = KT · ω-K2 · i where K1 is a dead zone in the intermittent mode Proportional constant, K
2 is a dead zone proportional constant in the continuous mode, K is a ratio between the impedance of the intermittent mode at the reference temperature and the impedance after the temperature variation, and K1 · i and K2 · i
But that shows the dead zone.

In the above example, the influence of the temperature variation is compensated by setting the dead zone, but when the temperature variation is large, it is better to estimate or measure the motor temperature to compensate.
By the way, as shown in FIG. 6, the position of inflection viewed from the voltage applied to the motor is almost constant regardless of the temperature (V _O ). This is because the inflection point is dominated by the duty ratios 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 condition of the following expression 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 manufacturing errors. Therefore, by performing the correction in combination with the dead zone correction method,
More accurate estimation can be performed. The applied voltage of the motor has conventionally been estimated from the duty ratio, but the relationship between the applied voltage and the duty ratio of the motor with the motor angular velocity as a parameter has a non-linear characteristic as shown in FIG. Therefore, it is preferable to directly use the motor applied voltage for monitoring. The solid line in FIG. 7 indicates the normal steering operation, and the alternate long and short dash line indicates the steering wheel return steering operation.

[0026]

According to the present invention, the influence of the drive system on the drive system impedance is taken into consideration by defining different impedance models of the motor drive system for the intermittent mode and the continuous mode. Since the motor angular velocity is estimated by using the above method, it is possible to estimate the motor angular velocity with high accuracy. Thereby, the influence of the inertia of the motor and the friction can be compensated with high accuracy. Further, a dead zone proportional to the current value is set in order 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 dead zone gain is switched between the intermittent mode and the continuous mode.

[Brief description of drawings]

FIG. 1 is a block diagram showing 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 showing an example of a current path in an H-bridge circuit.

FIG. 4 is a diagram showing an example of effective voltage and 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 impedance change due to temperature.

FIG. 7 is a diagram showing a relationship between a duty ratio and a voltage between motor terminals using a 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 showing an example of a motor drive circuit.

FIG. 11 is a diagram showing an example of a duty ratio vs. motor current (terminal voltage) characteristic.

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

[Explanation of symbols]

1 Steering handle 5 pinion rack mechanism 10 Torque sensor 12 vehicle speed sensor 20 motor 30,30A control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideaki Kawada, 78 Toba-cho, Maebashi, Gunma Prefecture, Nippon Seiko Co., Ltd. (72) Inventor, Yusuke Itakura 78, Toba-cho, Maebashi, Gunma, Japan 56) References JP-A 9-39808 (JP, A) JP-A 8-67261 (JP, A) JP-A 3-176272 (JP, A) JP-A 5-338544 (JP, A) Flat 3-74262 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B62D 5/04 B62D 6/00

Claims (3)

(57) [Claims] 1. A motor for applying a steering assist force to a steering mechanism on the basis of a current control value calculated from a steering assist command value calculated based on a steering torque generated on a steering shaft and a motor current value , In a control device for an electric power steering device that is controlled in a PWM cycle, the current is zero in the PWM cycle.
In the intermittent mode having the following section and the PWM cycle
The motor angular velocity is defined by defining an impedance model for each motor drive system in continuous mode that does not have a section where the current becomes zero.
Control device for an electric power steering apparatus characterized by performing Do推 constant. 2. A back electromotive force factor for estimating the motor angular velocity.
In the calculation unit, set a dead zone proportional to the motor current value,
The control device for the electric power steering device according to claim 1, wherein the gain of the dead zone is switched between the intermittent mode and the continuous mode. 3. The control device for an electric power steering system according to claim 2, wherein the motor temperature is measured and an estimation error due to temperature fluctuation is compensated.