JP2003312509A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an electric power steering device capable of preventing a sudden decrease in assist force by gradually reducing an assist before and after the control device and a motor reach temperature limits (regardless of high temperature or low temperature) on the electric power steering device. <P>SOLUTION: This electric power steering device is provided with a torque sensor to detect steering torque generated at least at a steering shaft and a motor to give steering an auxiliary force corresponding to the steering torque to a steering mechanism and recognizes from a temperature sensor or a temperature estimated value that the control device and the motor approach their temperature limit and multiplies an assist command value with a specified value to gradually become smaller than 1 as they approach the temperature limits when it is determined that the control device and the motor approach the temperature limits. <P>COPYRIGHT: (C)2004,JPO

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 assist force by a motor to a steering system of an automobile or a vehicle, and the temperature of the control device or the motor reaches a temperature limit. The present invention relates to a control device for an electric power steering device that avoids a sudden change in steering force.

[0002]

2. Description of the Related Art An electric power steering system for urging an auxiliary load on a steering system of an automobile or a vehicle by a rotational force of a motor uses a transmission mechanism such as a gear or a belt for transmitting a driving force of the motor through a reduction gear. Alternatively, 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 an 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, and the motor applied voltage is generally adjusted by PW.
It is performed by adjusting the duty ratio of M (pulse width modulation) control.

Here, the general structure of the electric power steering apparatus will be described with reference to FIG. 11, in which the shaft 2 of the handle 1 has a reduction gear 3 and universal joints 4a and 4a.
b, it is connected to the tie rods 6 of the traveling wheels via the pinion rack mechanism 5. A torque sensor 10 that detects the steering torque of the steering wheel 1 is provided on the shaft 2, and a motor 20 that assists 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 controls the torque sensor 1
The steering assist command value I of the assist command is calculated based on the steering torque T detected at 0 and the vehicle speed V detected at the vehicle speed sensor 12, and is supplied to the motor 20 based on the calculated steering assist command value I. Control the current.

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.

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 determines 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
Is determined using a preset data table or functional expression. 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. Integral calculator 36 for improving the characteristics of the feedback system
Entered in. 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.

[0007]

By the way, the control device and the motor of the electric power steering device are limited in the operable temperature. For example, in the case of a motor, the temperature is
If the temperature rises above the high temperature limit, an accident may occur due to burning or the like, whereas if the temperature falls below the low temperature limit, a problem of low temperature demagnetization due to a rack end or a large back electromotive force occurs. Therefore, when the controller or motor reaches the temperature limit, the output to the motor is limited,
It is common to protect control devices and motors. However, if this protection suddenly operates, the assisting force sharply decreases, which causes a driver to feel uncomfortable.

Therefore, in order to smooth the decrease in the assist force when the control device or the motor exceeds the temperature limit, the temperature sensor attached to the control device, the temperature sensor attached to the motor or the motor temperature estimated value is JP-A-10-100913, JP-A-12-34411
8), it is judged whether the control device and the motor are close to the temperature limit, and if they are close to the temperature limit,
A predetermined value that gradually becomes smaller than 1 is multiplied by a steering assist command value obtained by using preset table data or a functional formula based on the steering torque to prevent a sudden decrease in the assist force. .

That is, an object of the present invention is to gradually reduce the assist before and after the control device and the motor reach the temperature limit (whether high temperature or low temperature) in the electric power steering device, and prevent a sudden decrease in the assist force. An object of the present invention is to provide a control device for such an electric power steering device.

[0010]

The above object of the present invention is to provide an electric power provided with a torque sensor for detecting at least a steering torque generated in a steering shaft, and a motor for applying a steering assist force corresponding to the steering torque to a steering mechanism. When the steering device recognizes from the temperature sensor or the estimated temperature value that the temperature limits of the control device and the motor are approaching, and when it is determined that the control device and the motor are approaching the temperature limit, the value gradually increases as the temperature limit is approached.
This is effectively achieved by multiplying the assist command value by a smaller predetermined value.

Further, the above-mentioned object of the present invention is such that when the control device is judged to be approaching the high temperature limit, or when the motor is judged to be approaching the high temperature limit or the low temperature limit, the value gradually increases as the temperature limit is approached. This is achieved more effectively by multiplying the assist command value by a smaller predetermined value.

That is, when it is determined that the control device is close to the high temperature limit, or when it is determined that the motor is close to the high temperature limit or the low temperature limit, as the temperature limit is approached, a predetermined value gradually smaller than 1 is assisted. Multiply the characteristics. As a result, the assist amount is gradually reduced to protect the system without making the driver feel uncomfortable. The determination that the temperature is close to the temperature limit is made based on the temperature sensor attached to the control device and the motor, or in the case of the motor, based on the estimated temperature value calculated by the control device.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In an electric power steering system, a motor current according to a steering torque is calculated and an appropriate current is given to a motor. This current value is a preset data based on the steering torque. It is determined using a table or a function formula. In this case, the operating temperature of the control device and the motor is limited, and when the temperature approaches the temperature limit, the output of the control device or the motor is limited. It makes the steering feel worse. However, in the present invention, when the control device and the motor reach the temperature limit, in order to smooth the decrease of the assist gain, the control device and the motor temperature estimated value are attached to the control device and the motor temperature estimated value attached to the control device and the motor. Is approaching the temperature limit, and when approaching the temperature limit, a coefficient that gradually becomes smaller than 1 is multiplied to prevent a rapid decrease in the assist gain. This makes it possible to maintain a good steering feel even when the control device or the motor approaches the temperature limit.

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. Steering torque TA 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. In addition, the vehicle speed V and the temperature T of the control device or the motor are input to the steering assist command value calculation unit 100. 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
Is also input to the motor output limit detection unit 200. The motor terminal voltage Vm is the motor angular velocity estimation unit 1
21 and the motor output limit detection unit 200.
Entered in. Further, the angular velocity ω estimated by the motor angular velocity estimation unit 121 is input to the motor angular acceleration estimation unit / inertia compensation unit 123, the motor loss torque compensation unit 124, and the yaw rate estimation unit 125, and the output of the yaw rate estimation unit 125 is convergent control. Is input to the unit 126, and the convergence control unit 12
6 and each output of the motor loss torque compensator 124 are added by the adder 127, and the addition result is input to the adder 102.

Motor angular acceleration estimation unit / inertia compensation unit 123
Eliminates torque for accelerating and decelerating the motor inertia from the steering torque to provide a steering feeling without inertia, and the convergence control unit 126 applies a brake to the steering wheel swinging motion to improve the yaw convergence of the vehicle. The motor loss torque compensating section 124 provides a loss torque assist in the direction in which the loss torque of the motor 113 is generated, that is, in the rotation direction of the motor 113. 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 the adder 131, and the addition result is added to the adder 105. It has been entered. The current dither signal generator 130 prevents the motor from sticking due to static friction.

The motor output detection unit 200 performs the following calculation.

The output P of the motor is such that the output torque of the motor is T _m [N · m] and the angular velocity of the motor is ω [rad /
s], it is calculated by the following equation (1).

P = T _m × ω (1) When the motor torque constant is K _T [N · m / A] and the motor current is i [A], the output torque T _m of the motor is as follows. It is expressed by equation (2).

T _m = K _T × i (2) When the above equation (2) is substituted into the equation (1), the motor output P becomes the following equation (3).

P = K _T × i × ω (3) Since the torque constant K _T is known, the motor output P can be estimated from the motor current i and the angular velocity ω. The estimation of the angular velocity ω is performed, for example, in Japanese Patent Laid-Open No. 10-10965
No. 5 publication.

For example, if the motor terminal voltage is Vm [V], the motor winding resistance is Rm [Ω], and the motor electromotive force constant is Ke [V · s / rad], the motor angular velocity ω is given by the following (4). It is calculated by the formula.

Ω = (Vm−i · Rm) / Ke (4) Here, since the torque constant K _T and the electromotive force constant Ke have the same value in the same motor, the formula (4) is changed to the formula (3). Substituting into the equation, the motor output P is expressed by the following equation (5).

P = i · (Vm−i · Rm) (5) Since the winding resistance Rm is known, the motor output P can also be estimated by the motor current i and the motor terminal voltage Vm. Further, if there is a motor angular velocity sensor or a steering angle sensor, the angular velocity may be obtained from this.

As a feature of the present invention, the steering assist command value calculation unit 100 receives the temperature T from the temperature sensor that constantly detects the temperature of the control device and the motor during the operation of the electric power steering device. As shown in FIG. 2, a steering assist command value calculation unit 100A that calculates a steering assist command value SS1 based on the steering torque TA, and a steering assist command value SS.
1 is multiplied by the gain based on the vehicle speed V to obtain the steering assist command value S
A vehicle speed gain multiplication unit 100B that outputs S2 and a temperature limit range gain multiplication unit 100C that multiplies the steering assist command value SS2 by a gain based on the temperatures of the control device and the motor. The multiplication of the vehicle speed gain is disclosed in, for example, Japanese Patent Laid-Open No. 8-150954.

During operation of the electric power steering,
The temperature of the control device and the motor are always detected. Wherein the temperature control device, the temperature sensor in the control device, the motor temperature (hot or _{cold) T LIM,} the temperature sensor or the above-mentioned publication in the motor (JP-A 10-100913,
It is obtained from the motor temperature estimated value estimated in JP-A-12-344118). Then, the difference between the temperature T of this control device or the motor and the temperature limit T _LIM (T _LIM −T)
Is calculated, and the gain characteristic as shown in FIG. 3 is set in advance so that it becomes smaller as the difference becomes smaller.
That is, the temperature T of the controller or the motor and the temperature limit T
_The gain Gain is "1" or a value close to "1" in the region where the difference with the _LIM is large, and the gain Gain is "1" in the region where the difference between the temperature T of the control device or the motor and the temperature limit T _LIM is small. It is a non-linear function that changes to become smaller. Then, by multiplying the steering assist command value SS2 after the vehicle speed gain multiplication by the gain characteristic as shown in FIG. 3, in the region where the temperature T of the control device or the motor is away from the temperature limit T _LIM , the steering assist command is obtained. Value SS3
Is larger, the temperature T of the controller or motor is the temperature limit T
_In a region close to _LIM , the steering assist command value SS3 is output small.

The characteristic of FIG. 3 is an example, and the gain Gain is large (maximum value "1") in the region where the temperature T of the control device or the motor is far from the temperature limit, and the temperature T of the control device or the motor is Gain near the temperature limit T _LIM
The function expression may be non-linear or linear as long as it is a functional expression in which the gain changes small (greater than “0”).

Further, in the case of a motor, in order to eliminate the adverse effects of low temperature demagnetization due to the rack end at a low temperature and a large back electromotive force, the motor approaches the low temperature limit not only at the high temperature limit but also at the low temperature limit. When it is determined, the assist command value is multiplied by a predetermined value that gradually becomes smaller than 1 as the low temperature limit is approached. That is, by multiplying the assist command value by the gain characteristic shown in FIG. 4, the assist force is gradually reduced when the motor approaches the low temperature limit.

Next, the structure of the other parts of FIG. 1 will be briefly described. In the present example, first, as shown in FIG. 5, the center response improving unit 101 includes a phase compensating unit 101A and an approximate differentiating unit 101B.
And a gain setting unit 101C, and a phase compensation unit 101
Let A be the frequency characteristic shown in FIG. 6, and let the approximate differentiator 101B have the frequency characteristic shown in FIG. As a result, the combined characteristic of the phase compensation and the approximate differentiation is as shown in FIG. Also,
In the gain setting unit 101C, the vehicle speed V and the steering torque TA
Use to switch and set the gain. Further, in order to reduce an uncomfortable steering feeling such that the steering wheel is suddenly returned and stabilize the steering, a large steering torque and a large steering torque change rate are set, and the gain is reduced when the steering torque is decreasing.

In the present invention, the steering assist command value calculation unit 1
In the calculation of the assist amount at 00, the assist characteristic based on the representative vehicle speed (0, V1, V2Km / h) is set as the basic characteristic, and at other vehicle speeds, the interpolation between the basic characteristics is performed according to the vehicle speed interpolation gain. The basic assist characteristic (torque vs. current) is shown in FIG. 9, and is 0 km / h.
= Io characteristic, V1 = Ia characteristic, V2 = Ib characteristic. 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.
Done in. When the vehicle speed is 0 to V1, the assist current I is I = I
a (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)).

Therefore, in the above embodiment, the temperature limit T _LIM of the control device or the motor is measured in advance, and the difference between the temperature T of the control device or the motor and the temperature limit value T _LIM is known. Even if the control device or the motor approaches the temperature limit at which it can operate by presetting such a gain (for example, gain setting as shown in FIG. 1) and multiplying it by the current command value after the vehicle speed interpolation gain multiplication, By gradually reducing the assist, it is possible to prevent a sudden decrease in the assist force.

[0033]

As described above, according to the control device for the electric power steering apparatus of the present invention, the temperature of the control device and the motor is constantly detected, and the temperature of the control device or the motor is gradually increased as the temperature approaches the temperature limit. By multiplying the assist command value by a predetermined smaller value, the assist amount is gradually reduced, and the sudden decrease in assist force due to the temperature of the control device and motor is prevented, giving the driver a feeling of strangeness. You can avoid it.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration example of a steering assist command value calculation unit of the present invention.

FIG. 3 is a diagram showing an example of gain multiplication characteristics in a high temperature limit region according to the present invention.

FIG. 4 is a diagram showing an example of gain multiplication characteristics in a low temperature limit region according to the present invention.

FIG. 5 is a block configuration diagram of a center response improving unit.

FIG. 6 is a diagram showing a characteristic example of a phase compensation unit.

FIG. 7 is a diagram showing a characteristic example of an approximate differentiating unit.

FIG. 8 is a diagram showing a combined characteristic of a phase compensation unit and an approximate differentiation unit.

FIG. 9 is a diagram showing basic assist characteristics.

FIG. 10 is a diagram showing an example of vehicle speed interpolation calculation.

FIG. 11 is a mechanism diagram showing a general example of electric power steering.

FIG. 12 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 100A steering assist command value calculation unit 100B vehicle speed gain multiplication section 100C High temperature limit gain multiplication section 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

[Procedure amendment]

[Submission date] May 28, 2002 (2002.5.2)
8)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

Here, the general structure of the electric power steering apparatus will be described with reference to FIG. 11, in which the shaft 2 of the handle 1 has a reduction gear 3 and universal joints 4a and 4a.
b, it is connected to the tie rods 6 of the traveling wheels via the pinion rack mechanism 5. A torque sensor 10 that detects the steering torque of the steering wheel 1 is provided on the shaft 2, and a motor 20 that assists the steering force of the steering wheel 1 is coupled to the shaft 2 via a reduction gear 3. A control unit (ECU) 30 for controlling the power steering device includes a battery 14, an ignition key 11 and a relay 13.
The electric power is supplied through the control unit 30,
The steering assist command value I of the assist command is calculated 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 the motor 20 is controlled based on the calculated steering assist command value I. Controls the current supplied.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

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 determines 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
Is determined using a preset data table or functional expression. 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. Integral calculator 36 for improving the characteristics of the feedback system
Entered in. The outputs of the differential compensator 34 and the integration calculator 36 are also input to the adder 30B, and the current control value E, which 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.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

By the way, the control device and the motor of the electric power steering device are limited in the operable temperature. For example, in the case of a motor, the temperature is
If the temperature rises above the high temperature limit, burnout will occur, while
If the temperature drops below the low temperature limit, problems of low temperature demagnetization due to rack ends and large back electromotive force will occur. Therefore, when the controller or motor reaches the temperature limit,
It is common to limit the output to the motor to protect the controller and the motor. However, if this protection suddenly operates, the assisting force sharply decreases, which causes a driver to feel uncomfortable.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

During operation of the electric power steering,
The temperature of the controller and the motor are always detected. Temperature where the controller from the temperature sensor in the control device, the motor temperature (hot or _{cold) T LIM} is a temperature sensor or the above-mentioned publication in the motor (JP-A 10-100913, JP-A-12-344118) Obtained from the estimated motor temperature estimate. As calculates the difference between the temperature T and the temperature limit T _{L IM} of the control unit or the motor (T _{LIM -T),} decreases as the difference becomes smaller,
The gain characteristic as shown in FIG. 3 is set in advance. That is, the temperature T of the controller or the motor and the temperature limit T
_The gain Gain is "1" or a value close to "1" in the region where the difference with the _LIM is large, and the gain Gain is "1" in the region where the difference between the temperature T of the control device or the motor and the temperature limit T _LIM is small. It is a non-linear function that changes to become smaller. Then, by multiplying the steering assist command value SS2 after the vehicle speed gain multiplication by the gain characteristic as shown in FIG. 3, in the region where the temperature T of the control device or the motor is away from the temperature limit T _LIM , the steering assist command is obtained. Value SS3
Is larger, the temperature T of the controller or motor is the temperature limit T
_In a region close to _LIM , the steering assist command value SS3 is output small.

Continued front page    (72) Inventor Shuji Endo             78 Toba-cho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd.             In the company (72) Inventor Masahiro Murata             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Victory Sakata             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Naoki Kobayashi             1200 Onjuku, Susono City, Shizuoka Prefecture Toyota Motor Corporation             Within the corporation F term (reference) 3D032 CC34 CC38 CC40 DA15 DA23                       DA64 DA67 DC01 DC02 DC03                       DC17 DD17 DE02 DE09 EC23                       GG01                 3D033 CA03 CA13 CA16 CA20 CA21                       CA31

Claims (3)

[Claims] 1. An electric power steering apparatus comprising at least a torque sensor for detecting a steering torque generated on a steering shaft and a motor for applying a steering assist force according to the steering torque to a steering mechanism. When recognizing that the temperature limits of the control device and motor are approaching, and if it is determined that the control device and motor are approaching the temperature limit, the assist command value is multiplied by a predetermined value that gradually becomes less than 1 as the temperature limit is approached. A control device for an electric power steering device characterized by the above. 2. The electric power steering device according to claim 1, wherein the control device multiplies the assist command value by a predetermined value that gradually becomes smaller than 1 as the temperature limit is approached, when it is determined that the temperature limit is approached. Control device. 3. The electric power steering system according to claim 1, wherein, when it is determined that the motor is approaching a high temperature limit or a low temperature limit, the assist command value is multiplied by a predetermined value that gradually becomes smaller than 1 as the temperature limit is approached. The control device of the device.