JP2003175837A - Control device for electric power steering device - Google Patents

Abstract

(57) [Problem] To provide a control device for an electric power steering device in which a setting of a dead zone width is varied according to a steering torque, thereby avoiding an influence due to a measurement error of a back electromotive force and improving a steering feeling. provide. SOLUTION: A steering assist command value calculated by a calculation means based on a steering torque generated in a steering shaft;
A control device for an electric power steering device adapted to control the motor for applying a steering assisting force to a steering mechanism based on a current control value calculated from the current value of the motor and a motor angle based on a voltage and a current of the motor. A function of estimating acceleration and providing a dead band width that assumes angular acceleration to be zero when the motor angular acceleration estimated value is within a predetermined minute range is provided, and the dead band width of the motor angular acceleration estimated value is set as a function of steering torque. .

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 assisting force by a motor to a steering system of an automobile or a vehicle, and more particularly to setting a dead band width for an angular acceleration by a steering torque ( The present invention relates to a control device for an electric power steering device that is made variable by a function of input torque) or a function of a yaw rate and lateral acceleration of a vehicle to improve driving cleanliness and stability.

[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 apparatus performs feedback control of the motor current in order to accurately generate the assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally PWM (pulse width modulation).
This is done by adjusting the duty ratio of control.

Here, a general structure of the electric power steering apparatus will be described with reference to FIG. 9, in which the shaft 2 of the steering wheel 1 passes through a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5 to form a traveling wheel. It is connected to the tie rod 6. The shaft 2 has a torque sensor 10 for detecting the steering torque of the steering wheel 1.
Is provided and a motor 20 for assisting the steering force of the steering wheel 1 is coupled to the shaft 2 via a reduction gear 3. Electric power is supplied to the control unit (ECU) 30 that controls the power steering device from the battery 14 via the ignition key 11, and the control unit 30 detects the steering torque T detected by the torque sensor 10 and the vehicle speed sensor 12. The steering assist command value I of the assist command is calculated based on the vehicle speed V, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.

The control unit 30 is mainly a CP
Although it is composed of U, the general function executed by the program inside the CPU is shown in FIG.

To explain the function and operation of the control unit 30, the steering torque T detected and input by the torque sensor 10 is phase-compensated and phase-compensated by the phase compensator 31 in order to enhance the stability of the steering system. The steering torque TA is input to the steering assist command value calculator 32. Also,
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 is
The motor 2 based on the input steering torque TA and vehicle speed V
Steering assist command value I which is the control target value of the current supplied to 0
To decide. 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, and the deviation (I-i) of the subtractor 30A is input to the proportional calculator 35. At the same time, it is input to the 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, 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 detected motor current value i is input to the subtractor 30A and fed back.

Here, in the electric power steering device, in order to improve the steering feeling, the motor angular acceleration is estimated from the current and voltage of the motor, or a separate sensor is provided to detect the motor angular acceleration. The value of the motor angular acceleration detected or estimated in this way may be used for motor control calculation.However, when the angular acceleration is obtained by estimation, in order to avoid the influence of the measurement error of the back electromotive force, A dead zone is provided in a region where the acceleration is small (for example, Japanese Patent Laid-Open No. 10-338152 and Japanese Patent No. 28249).
26, JP-A-8-175404). Even if the steering angle sensor is used, some dead zone is necessary due to the influence of noise due to differentiation and LSB. When this estimated angular acceleration value is used for control for improving the steering feeling, this control is also affected by the dead zone.

[0007]

When the dead zone is provided in the area where the angular acceleration is small as described above, if the dead zone width is narrowed, even if the angular acceleration is small such as when steering with a light force, the angular acceleration is small. It is possible to make effective the control utilizing, and to enhance the steering feeling. However, when the dead zone width is narrowed, an error in the estimated value of angular acceleration when the angular acceleration is small is conspicuous, which causes minute vibration of the steering wheel and deterioration of feeling. In other words, if the dead band width is narrowed,
Although it is possible to control the steering feeling improvement in the vicinity of the neutral point with high accuracy, unevenness or vibration is caused due to the problem of the accuracy. If the dead zone width is set wide, the opposite problem will occur. Since the estimated value of angular acceleration is obtained from (differential of) the estimated value of angular velocity, this error becomes larger due to the influence of the error of the resistance value model as the motor current increases.

The present invention has been made under the circumstances as described above, and an object of the present invention is to change the setting of the dead band width for the estimated value of the angular acceleration in accordance with the steering torque, the yaw rate of the vehicle, and the lateral acceleration. An object of the present invention is to provide a control device for an electric power steering device that can improve the cleanliness and stability of constant driving.

[0009]

The present invention is directed to steering based on a current control value calculated from a steering assist command value calculated by a calculation means based on a steering torque generated on a steering shaft and a motor current value. The present invention relates to a control device for an electric power steering device configured to control the motor that applies a steering assist force to a mechanism. The object of the present invention is to estimate a motor angular acceleration from a voltage and a current of the motor, This is achieved by providing a function of giving a dead band width in which the angular acceleration is regarded as zero when the motor angular acceleration estimated value is within a predetermined minute range, and using the dead band width as a function (for example, a linear function) of the steering torque.

Further, by making the dead zone a function of the yaw rate and lateral acceleration of the vehicle, it is possible to reduce the influence of the vehicle alignment and the friction coefficient of the road surface.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In an electric power steering apparatus, a motor angular acceleration detected by a sensor or a motor angular acceleration value estimated by calculation may be used for motor control calculation in order to improve steering feeling. . In this case, when the estimated value of angular acceleration is within a predetermined minute range, it is common to have a dead zone width in which the angular acceleration is treated as zero.

In the present invention, the setting of the dead band width of the motor angular acceleration estimated value is made a function of the steering torque, the vehicle yaw rate, and the lateral acceleration, and the dead band width is reduced when the steering torque, the vehicle yaw rate, and the lateral acceleration are small, By increasing the dead band width when the steering torque is large, the control for enhancing the steering feeling is enabled even when the driver is steering near the neutral point with a light force such as when going straight, and the high torque The unevenness and vibration when steering is also suppressed.

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

FIG. 1 is a control function block diagram of the present invention. The steering torque T from a torque sensor is input to a steering assist command value calculation unit 100 and a center responsiveness improvement unit 101, and each output is input to an adder 102. The addition result is input to the torque control calculation unit 103. The center responsiveness improving unit 101 secures stability in the assist characteristic dead zone and compensates for static friction. The output signal of the torque control calculation unit 103 is input to the motor loss current compensation unit 104, the output thereof is input to the maximum current limiting unit 106 via the adder 105, and the maximum current limiting unit 106 limits the maximum current value to control the current. It is input to the section 110. The motor loss current compensating unit 104 improves the rise from the motor output torque 0 by adding a current that does not appear in the motor output even if the motor current flows, and the maximum current limiting unit 106 sets the maximum value of the current command value to the rated value. It is limited to the current. Current control unit 1
The output of 10 is input to the current drive circuit 112 via the H-bridge characteristic compensating section 111, whereby the motor 11
Drive 3

The motor current i of the motor 113 passes through the motor current offset correction unit 120 and the motor angular velocity estimation unit 1
21, current drive switching unit 122 and current control unit 110
The motor terminal voltage Vm is input to the motor angular velocity estimation unit 121. The angular velocity ω estimated by the motor angular velocity estimation unit 121 is the motor angular acceleration estimation unit / inertia compensation unit 1
23, the motor loss torque compensating unit 124, and the yaw rate estimating unit 125, and the output of the yaw rate estimating unit 125 is input to the convergence control unit 126, and the convergence control unit 126.
And each output of the motor loss torque compensation unit 124 is an adder 1
The addition is performed at 27, and the addition result is input to the adder 102. The motor angular acceleration estimator / inertia compensator 123 removes the torque that accelerates / decelerates the motor inertia from the steering torque,
In order to make the steering feeling without inertia, and to improve the convergence of the yaw of the vehicle, the convergence control unit 126 applies a brake to the swinging motion of the steering wheel. Motor 113
In the direction in which the loss torque is generated, that is, in the rotation direction of the motor 113, assistance corresponding to the loss torque is performed. The loss torque is a friction loss based on the structure of the motor and a loss due to a magnetic factor in the output torque of the motor, and such a loss torque is a steering direction when a slight steering is performed during straight running. An unintended force is applied to the steering wheel or a force in the opposite direction is applied to the steering wheel to deteriorate the steering feeling. Further, a current dither signal generation unit 130 is provided, and the outputs of the current dither signal generation unit 130 and the motor angular acceleration estimation unit / inertia compensation unit 123 are added by an adder 131.
Is added and the addition result is input to the adder 105. The current dither signal generator 130 prevents the motor from sticking due to static friction.

According to the present invention, in the estimation of the motor angular acceleration of the motor angular acceleration estimator / inertia compensator 123, a dead zone is provided in which the angular acceleration is regarded as zero when the estimated value of the motor angular acceleration is within a predetermined minute range. There is. That is, the motor angular acceleration estimation unit / inertia compensation unit 123 obtains the angular acceleration estimated value * ω by differentiating the angular velocity estimated value ω from the motor angular velocity estimation unit 121, but as shown in FIG.
The estimated value of angular acceleration * ω (estimated value of angular acceleration 1) further provided with a dead zone width a (estimated value of angular acceleration 2) is the adder 1
It is output to 31 and used for control calculation. Even when the rudder angle sensor is used, a similar dead zone is provided and the adder 131
Output to. The setting of the dead zone width a shown in FIG. 2 is changed based on the linear function of the following equation (1) using the steering torque T and the constant b.

A = b × T (1) Therefore, the dead zone a increases as the steering torque T increases, and the dead zone a decreases as the steering torque T decreases.

Alternatively, similarly, the dead zone width a is set by using the yaw rate γ and the constant b of the vehicle or the lateral acceleration G and the constant b of the vehicle based on the linear functions of the following equations (2) and (3). Change.

A = b × γ (2) a = b × G (3) Alternatively, the dead zone width a is combined with two or more of the steering torque T, the yaw rate γ, and the lateral acceleration G as follows. It can also be a function.

A = f (T, γ, G) (4) The motor angular velocity ω [rad / sec] is estimated as follows. The motor terminal voltage Vm [V] is expressed by the following formula (5), where the motor back electromotive force constant is Ke [Vs / rad], the motor current is i [A], and the motor winding resistance is Rm [Ω]. expressed.

Vm = Keω + iRm (5) Therefore, the motor angular velocity ω [rad / sec] is expressed by the following equation (6).

Ω = (Vm−i · Rm) / Ke (6) As described above, in the present invention, the dead zone width a for the estimated angular acceleration value * ω is narrow when the steering torque T is small and the steering torque T is small. When the driver is steering near the neutral point with a light force, the control for enhancing the steering feeling works effectively. In addition, dead zone width a in steering with high torque such as stationary steering and high G turning.
Since it becomes wider, unevenness and vibration can be suppressed. Further, when the dead zone width a is set by a function of the yaw rate or lateral acceleration of the vehicle, the above effect can be obtained without being affected by the alignment of the vehicle and the change of the friction coefficient of the road surface.

Next, the structure of the other parts of FIG. 1 will be briefly described. In this example, first, the center responsiveness improving unit 101 is provided with a phase compensating unit 101A and an approximate differentiating unit 101B as shown in FIG.
And the gain setting unit 101C, and the phase compensation unit 10
1A is the frequency characteristic shown in FIG.
Are frequency characteristics shown in FIG. As a result, the combined characteristic of the phase compensation and the approximate differentiation is as shown in FIG. The gain setting unit 101C switches and sets the gain according to the vehicle speed V and the steering torque T. Further, in order to reduce the uncomfortable steering feeling such that the steering wheel is suddenly returned and stabilize the steering, the gain is reduced when the steering torque is large, the steering torque change rate is large, and the steering torque is decreasing.

Further, in the present invention, the steering assist command value calculation unit 1
In the calculation of the assist amount at 00, the assist characteristics at three representative vehicle speeds (0, V1, V2Km / h) are set as the basic characteristics, and at other vehicle speeds, the vehicle speeds of 2 km / h are set between the basic characteristics according to the vehicle speed interpolation gain. Interpolate for each. Then, the vehicle speed setting range of the assist characteristic is 0 to V2Km.
/ H, and the resolution is 2 km / h. The basic assist characteristic (torque vs. current) is shown in FIG. 7, and 0 km / h = I
o characteristics, V1 = Ia characteristics, and V2 = Ib characteristics. Then, the vehicle speed interpolation calculation for other vehicle speeds is performed by the vehicle speed (Km / h) vs. vehicle speed interpolation coefficient γ shown in FIG.
Perform every Km / h. When the vehicle speed is 0 to V1, the assist current I is I = Ia (T) + γ (V) (Io (T) −Ia
(T)), and when the vehicle speed is (V1 + 2) to V2Km / h, the assist current I is I = Ib (T) + γ (V) (Ia
(T) -Ib (T)).

Although the dead zone width a is changed by the linear function of the steering torque T, the yaw rate γ and the lateral acceleration G in the above description, it may be changed by a non-linear function.

[0026]

According to the present invention, the dead band width of the estimated motor angular acceleration is set as a function of the steering torque, and the dead band width is reduced when the steering torque is small and the dead band width is increased when the steering torque is large. There is. Therefore, even when the driver is steering near the neutral point with a light force such as when going straight, the control for enhancing the steering feeling effectively works, and in steering with high torque such as stationary steering and high G turning. Also, unevenness and vibration can be suppressed, and a comfortable steering feeling can always be obtained.

By using the functions of the yaw rate and the lateral acceleration of the vehicle, it is possible to reduce the influence of the vehicle alignment and the friction coefficient of the road surface.

[Brief description of drawings]

FIG. 1 is a control function block diagram of the present invention.

FIG. 2 is a diagram for explaining a dead zone of the present invention.

FIG. 3 is a block configuration diagram of a center response improving unit.

FIG. 4 is a diagram showing a characteristic example of a phase compensation unit.

FIG. 5 is a diagram showing a characteristic example of an approximate differentiating unit.

FIG. 6 is a diagram showing a combined characteristic of a phase compensation unit and an approximate differentiation unit.

FIG. 7 is a diagram showing basic assist characteristics.

FIG. 8 is a diagram showing an example of a vehicle speed interpolation calculation.

FIG. 9 is a mechanism diagram showing a general example of electric power steering.

FIG. 10 is a block diagram showing a general internal configuration of a control unit.

[Explanation of symbols] 10 Torque sensor 12 vehicle speed sensor 20 motor 30 control unit 100 Steering assistance command value calculator 101 Center Response Improvement Section 103 Torque control calculation unit 110 Current controller 112 Current drive circuit 113 motor 121 Motor angular velocity estimation unit 124 Motor loss torque compensation unit 125 Yaw rate estimation unit 126 Convergence controller

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) B62D 137: 00 B62D 137: 00 (72) Inventor Shuji Endo 78 Toba-cho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd. (72) Inventor Masahiro Murata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor, Victory Sakata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Naoki Kobayashi 1200, Onjuku, Susono-shi, Shizuoka Toyota Motor Corporation F-term (reference) 3D032 CC08 DA15 DA23 DA29 DA33 DA64 DA65 EB06 3D033 CA13 CA16 CA20

Claims (3)

[Claims] 1. A steering assist force is applied to a steering mechanism on the basis of a current control value calculated from a steering assist command value calculated by a calculating means 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 adapted to control a motor, the motor angular acceleration is estimated from the voltage and current of the motor, and the angular acceleration is estimated when the estimated motor angular acceleration value is within a predetermined minute range. A control device for an electric power steering system, which has a function of giving a dead band width that is regarded as zero, wherein the dead band width is a function of the steering torque. 2. A steering assist force is applied to a steering mechanism based on a current control value calculated from a steering assist command value calculated by a calculation means 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 adapted to control a motor, the motor angular acceleration is estimated from the voltage and current of the motor, and the angular acceleration is estimated when the estimated motor angular acceleration value is within a predetermined minute range. A control device for an electric power steering device, having a function of giving a dead band width regarded as zero, wherein the dead band width is a function of a yaw rate and a lateral acceleration of a vehicle. 3. The control device for an electric power steering system according to claim 1, wherein the function is a linear or non-linear function.