JP2001106108A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which can enhance steering comfortability without deteriorating running stability of a vehicle and convergence of a steering wheel to a neutral position. SOLUTION: A current instruction value for controlling motor current running through a motor 4 is set to a value which is obtained by subtracting a brake current value ΔIbc produced from a brake current control part 34 from the sum of a desired current value I created from a torque motor current characteristic table 31 and a current correction value ΔI created from a derivative control table 32. Further, the brake current value ΔIbc produced by the brake current control part 34 is set by multiplying a basic brake current value Ibc corresponding to a motor speed N, with a vehicle speed correction coefficient corresponding to a vehicle speed V, and a torque coefficient value corresponding to a relationship between a direction of a torque applied to the steering wheel and a direction of rotation of the motor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for assisting steering by giving a torque generated by an electric motor to a steering mechanism.

[0002]

2. Description of the Related Art Conventionally, there has been used an electric power steering device which transmits torque generated by an electric motor to a steering mechanism of a vehicle and thereby assists steering. In this type of electric power steering device, a brake current value determined based on a rotation speed of an electric motor and a vehicle speed is subtracted from a target current value determined based on a steering torque or the like input by operating a steering wheel. The motor current supplied to the electric motor is controlled by using the obtained value as a motor current command value. The brake current value is set to a relatively small value when the vehicle speed is low, and is set to a large value when the vehicle speed is high. As a result, the stability of the vehicle during high-speed driving can be improved, and
The steering wheel can be quickly converged to the neutral position (the steering wheel position during straight running).

[0003]

However, in the above-mentioned prior art, since the brake current value is determined independently of the operation of the steering wheel, for example, when the steering wheel is cut in one direction from the neutral position, the electric motor is turned off. There was a possibility that sufficient torque was not generated, giving the driver a feeling of friction. Accordingly, an object of the present invention is to solve the above-mentioned technical problems and to provide an electric power steering device capable of improving the steering feeling without deteriorating the running stability of a vehicle and the convergence of a steering wheel to a neutral position. That is.

[0004]

According to the first aspect of the present invention, there is provided an electric power steering apparatus for assisting a steering by applying a torque generated by a motor to a steering mechanism. A motor rotation detecting means for detecting the rotation direction and the number of rotations of the motor; a steering torque detecting means for detecting a direction and a magnitude of the steering torque inputted to the steering mechanism; Current target value setting means for setting a motor current target value based on the magnitude of the steering torque detected by the means; and a rotation direction and a rotation speed detected by the motor rotation detection means and detected by the steering torque detection means. The mode set by the current target value setting means based on the direction and magnitude of the steering torque An electric power steering apparatus which comprises a brake current setting means for determining the brake current value to be subtracted from the current target value.

According to a second aspect of the present invention, the value obtained by subtracting the brake current value set by the brake current setting means from the motor current target value set by the current target value setting means, 2. The motor control device according to claim 1, further comprising a motor control unit that controls the motor as a current command value that is a current value to be supplied to the motor.
It is an electric power steering device as described in the above. According to the above invention, the brake current value to be subtracted from the motor current target value is determined in consideration of not only the rotation direction and the number of rotations of the motor, but also the direction and magnitude of the steering torque. Thus, as described in claim 2, by controlling the motor using a value obtained by subtracting the brake current value from the motor current target value as a current command value, the steering wheel is cut from the neutral position to the neutral position. When the steering wheel is returned to the normal position, the steering wheel is quickly converged to the neutral position, and when the steering wheel is turned rightward or leftward, it is possible to generate a torque capable of sufficiently performing steering assist from the motor. Therefore, when the steering wheel is turned rightward or leftward, it is possible to eliminate the possibility of giving the driver a feeling of friction, thereby improving the steering feeling.

According to a third aspect of the present invention, the brake current setting means includes a basic value setting means for setting a basic value of the brake current based on a rotation direction and a rotation speed detected by the motor rotation detection means. A direction difference determining means for determining whether the direction of the generated torque of the motor according to the rotation direction detected by the motor rotation detecting means is different from the direction of the steering torque detected by the steering torque detecting means; Torque correction coefficient setting means for determining a torque correction coefficient based on the determination result of the direction difference determination means and the magnitude of the steering torque detected by the steering torque detection means; and a brake current basic value set by the basic value setting means And first multiplication means for multiplying the torque correction coefficient set by the torque correction coefficient setting means. It is preferable.

For example, when returning the steering wheel from the incised state to the neutral position, the driver releases his / her hand or applies a slight force to the steering wheel to prevent the steering wheel from returning suddenly. Is opposite to the direction of the generated torque. On the other hand, when the steering wheel is turned rightward or leftward, the direction of the steering torque matches the direction of the torque generated by the motor. Therefore, if the direction of the steering torque and the rotation direction of the motor are opposite, the torque correction coefficient is set so that the brake current value increases,
If the direction of the steering torque and the rotation direction of the motor match, the torque correction coefficient is set so that the brake current value decreases, thereby deteriorating the running stability of the vehicle and the convergence of the steering wheel to the neutral position. Without this, the steering feeling can be improved.

According to a fourth aspect of the present invention, the electric power steering apparatus further includes a vehicle speed detecting means for detecting a running speed of the vehicle, and the brake current setting means detects the vehicle speed by the vehicle speed detecting means. Vehicle speed correction coefficient setting means for determining a vehicle speed correction coefficient based on the traveling speed of the vehicle, and a vehicle speed correction coefficient set by the vehicle speed correction coefficient setting means multiplied by a brake current basic value set by the basic value setting means. 4. The electric power steering apparatus according to claim 3, further comprising squaring means.

According to the present invention, for example, the vehicle speed correction coefficient is set so that the brake current value takes a large value during high-speed running, and the vehicle speed correction coefficient is set so that the brake current value takes a small value during low-speed running. This can prevent the running stability of the vehicle during high-speed running from being impaired.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electric configuration of an electric power steering apparatus according to one embodiment of the present invention. The steering mechanism is provided with a torque sensor 1 for detecting a steering torque. The control unit 2 controls a motor based on an output signal of the torque sensor 1 and an output signal of a vehicle speed sensor 3 for detecting a vehicle speed. 4 is controlled. The driving force generated by the motor 4 is transmitted to the steering mechanism as a steering assist force via an appropriate drive force transmitting mechanism including a speed reducer or the like, so that steering assist is performed.

The motor 4 is supplied with a current from a motor drive circuit 5. The motor current flowing through the motor 4 is detected by a motor current detection circuit 6, and the voltage between the terminals of the motor 4 is detected. Are detected by the motor terminal voltage detection circuit 7 and are input to the control unit 2 for feedback control. The control unit 2 is constituted by a microcomputer or the like, and realizes functions necessary for controlling the motor 4 by operating the microcomputer according to a predetermined operation program. Thus, the control unit 2 substantially has a plurality of functional blocks described below.

That is, the control unit 2 advances the phase of the output signal of the torque sensor 1 and sets an appropriate current command value based on the output of the phase compensation unit 21 for stabilizing the system. A generated current command value calculating unit 22, a subtraction unit 23 for calculating a deviation between the current command value and the motor current value detected by the motor current detection circuit 6, and a PWM drive pulse based on an output of the subtraction unit 23. Generated PW
M generation unit 24.

The current command value calculator 22 includes a phase compensator 21
Output a target current value I corresponding to the torque value T output by the motor, and a differential output a current correction value ΔI corresponding to a time differential value ΔT of the output torque value T of the phase compensator 21. A control table 32, a motor rotation detector 33 for detecting the rotation speed N of the motor 4 based on the outputs of the motor current detection circuit 6 and the motor terminal voltage detection circuit 7, and a rotation speed output by the motor rotation detection unit 33 N, a brake current control unit 34 that generates a brake current value ΔIbc based on the vehicle speed V detected by the vehicle speed sensor 3 and the torque value T output by the phase compensation unit 21. The torque-motor current characteristic table 31 has a plurality of tables in which different torque-motor current characteristics are set for each vehicle speed range, and one of the tables is selected based on the output signal of the vehicle speed sensor 3. It has become.

The torque-motor current characteristic table 31 is
A case where a target current I having a positive value is output when the motor 4 generates a torque in the direction of generating the assisting force for the rightward steering, and the motor 4 generates a torque in a direction of generating the assisting force for the leftward steering. Negative target current I
Is output. Further, the torque value T input from the phase compensator 21 takes a positive value when the right steering torque is acting on the steering wheel, and takes a negative value when the left steering torque is acting on the steering wheel. Take. Then, the target current value I
Is set such that the target current value I monotonically increases with respect to the torque value T within a certain range.

The differential control table 32 is for improving a response delay caused by inertia of the motor 4 and mechanical components related thereto. That is, when the absolute value of the time differential value ΔT of the torque value T takes a large value due to sudden steering, a current correction value ΔI having a large absolute value is generated accordingly. The current correction value ΔI is added to the torque-motor current characteristic table 31 in the adder 35.
Is added to the output target current value I, thereby obtaining a target current value I + ΔI corrected for improving the responsiveness.

The motor rotation detector 33 first calculates the average number Ia of the motor current detected by the motor current detection circuit 6 and the motor terminal voltage detection circuit 7 to calculate the rotation speed N of the motor 4. An average value Va of the inter-terminal voltage is obtained. Then, an instantaneous value R of the internal resistance of the motor 4 is calculated from the obtained motor current average value Ia and terminal voltage average value Va according to the following equation (1). R = Va / Ia (1) Next, the motor internal resistance instantaneous value R is integrated over time to obtain the motor 4
From the internal resistance value Ri, the motor current average value Ia and the terminal voltage average value Va.
The back electromotive voltage Vc of the motor 4 is obtained according to the equation (2).

Vc = Va−Ia · Ri (2) Then, according to the following equation (3), the back electromotive voltage Vc of the motor 4 obtained as described above is The number of rotations N of the motor 4 is calculated by multiplying the number of rotations by the motor power generation constant K. The rotation speed N has a sign corresponding to the sign of the back electromotive voltage Vc of the motor 4, and takes a positive value for, for example, rightward rotation of the motor 4, and has a positive value for leftward rotation of the motor 4. Takes a negative value. That is,
It can be said that the rotation speed N is a rotation speed including a rotation direction component of the motor 4.

N = K · Vc (3) The brake current control unit 34 outputs a basic brake current value Ibc corresponding to the rotation speed N output by the motor rotation detection unit 33. A setting table 41, a vehicle speed correction coefficient table 42 for multiplying a basic brake current value Ibc by a vehicle speed correction coefficient corresponding to the vehicle speed V and outputting the same, and an output torque value of the phase compensation unit 21 And a torque correction coefficient table 43 that generates a brake current value ΔIbc by multiplying the torque correction coefficient according to T and the rotation speed N of the motor 4.

The brake current value ΔIbc generated by the torque correction coefficient table 43 (brake current control unit 34) is subtracted from the target current value I + ΔI in the subtraction unit 36, and the value I + ΔI−ΔIbc obtained as a current command value is used. You. FIG. 2 is a diagram for explaining in detail the generation of the brake current value ΔIbc by the brake current control unit 34, and shows an example of the brake current basic value setting table 41, the vehicle speed correction coefficient table 42, and the torque correction coefficient table 43. ing.

The brake current basic value setting table 41 includes:
The absolute value of the rotation speed N of the motor 4 (see FIG. 1) is a fixed value + N
1, less than or equal to the absolute value of -N1, and the inequality -N1≤N≤ + N1
Is satisfied, the basic value of the brake current I
Set bc to zero. When the absolute value of the rotation speed N of the motor 4 is equal to or greater than the absolute values of the fixed values + N2 and -N2, the brake current basic value Ibc is set to a predetermined value.
Then, the rotational speed N of the motor 4 is equal to -N2 <N <-N1.
Alternatively, when + N1 <N <+ N2 is satisfied, the absolute value of the brake current basic value Ibc is set to increase as the absolute value of the rotation speed N of the motor 4 increases. The characteristics of the brake current basic value setting table 41 may be a straight line passing through the origin. However, the brake current basic value Ibc set in this way is set to a positive value when the motor 4 is rotating rightward, and is a negative value when the motor 4 is rotating leftward. Is set to

The vehicle speed correction coefficient table 42 is for achieving a good steering feeling according to the vehicle speed V. That is, when the vehicle is running at a low speed, it is preferable to supply a large current to the motor 4 to generate a large steering assist force. Therefore, the brake current value ΔIbc having a relatively small absolute value is appropriate. On the other hand, when the vehicle is running at a high speed, a brake current value ΔIbc having a relatively large absolute value is appropriate in order to suppress the fluctuation of the vehicle and increase the running stability.

Therefore, the vehicle speed correction coefficient table 42 sets the vehicle speed correction coefficient to 0 if the vehicle speed V is equal to or lower than the predetermined low speed V1, and sets the vehicle speed V to the predetermined high speed V
If it is 2 or more, the vehicle speed correction coefficient is set to 1, and if the vehicle speed V is within a range larger than the low speed V1 and smaller than the high speed V2, the vehicle speed correction coefficient is set to a value proportional to the vehicle speed V. Then, the vehicle speed correction coefficient set according to the vehicle speed V is multiplied by the basic brake current value Ibc given from the basic brake current value setting table 41 and output.

The torque correction coefficient table 43 stores the torque value T output from the phase compensating section 21 and the motor rotation detecting section 3.
The relationship between the direction of the steering torque acting on the steering wheel and the rotation direction of the motor 4 is determined from the rotation speed N output by the motor 3 and a torque correction coefficient is set based on this relationship and the absolute value of the torque value T. For example, when returning the steering wheel from the cut state to the neutral position, the brake current value ΔIbc having a relatively large absolute value is set to eliminate the influence of the inertia of the motor 4 and quickly converge the steering wheel to the neutral position. Preferably. On the other hand, when the steering wheel is turned rightward or leftward, it is preferable to supply a large current to the motor 4 to generate a large steering assist force. Therefore, it is preferable to set the brake current value ΔIbc to a relatively small absolute value. Is appropriate.

When returning the steering wheel from the cut-in state to the neutral position, the driver releases his / her hand or applies a light force to the steering wheel in order to prevent the steering wheel from returning suddenly. Torque value T
Is zero or a value having a sign opposite to the rotation speed N of the motor 4. On the other hand, when the steering wheel is turned rightward or leftward, the sign of the torque value T output by the phase compensation unit 21 matches the sign of the rotation speed N of the motor 4.

Therefore, the torque correction coefficient table 43
When the torque value T output by the phase compensating unit 21 is zero or a value having a sign opposite to the rotation speed N of the motor 4, the torque correction coefficient is set to 1, for example. Then, the set torque correction coefficient is multiplied by a value given from the vehicle speed correction coefficient table 42, and the obtained value is output as a brake current value ΔIbc. As a result, when returning the steering wheel from the cut state to the neutral position, the brake current value ΔIbc is set to a relatively large value of the absolute value, so that the steering wheel can be quickly converged to the neutral position.

When the sign of the torque value T output from the phase compensator 21 matches the sign of the rotation speed N of the motor 4, the torque correction coefficient table 43 stores the torque correction value based on the absolute value of the torque value T. Set the coefficient. For example, if the absolute value of the torque value T is equal to or less than a predetermined value T1, the torque correction coefficient is set to 1, and if the absolute value of the torque value T is equal to or more than the predetermined value T2, the torque correction coefficient is set to a constant value α. If the absolute value of the torque value T is larger than the value T1 and smaller than the value T2, the larger the absolute value of the torque value T, the smaller the torque correction coefficient is set. Then, the set torque correction coefficient is multiplied by a value given from the vehicle speed correction coefficient table 42, and the obtained value is output as a brake current value ΔIbc. This allows
When the steering wheel is turned rightward or leftward, the absolute value of the brake current value ΔIbc is set to a relatively small value in accordance with the absolute value of the torque value T, and a sufficient steering assist force (torque) is supplied from the motor 4. Can be generated.

As described above, according to this embodiment, the current command value for controlling the motor current flowing through the motor 4 is determined by the target current value I generated by the torque-motor current characteristic table 31 and the differential control table 32. The value is set to a value obtained by subtracting the brake current value ΔIbc generated by the brake current control unit 34 from the sum with the generated current correction value ΔI. The brake current value ΔIbc generated by the brake current control unit 34 is calculated by adding the vehicle speed correction coefficient corresponding to the vehicle speed V and the direction of the steering torque acting on the steering wheel to the basic value of the brake current Ibc corresponding to the motor speed N. Is set by multiplying by a torque correction coefficient according to the relationship with the rotational direction of the motor.

Thus, when returning the steering wheel from the cut state to the neutral position, the steering wheel is quickly converged to the neutral position, and when the steering wheel is turned rightward or leftward, the motor 4 generates a sufficient steering assist force. It becomes possible. Therefore, when the steering wheel is turned rightward or leftward, it is possible to eliminate the possibility of giving the driver a feeling of friction, thereby improving the steering feeling. Moreover, since the vehicle speed correction coefficient is set so that the absolute value of the brake current value ΔIbc takes a large value during high-speed running, the running stability of the vehicle during high-speed running is not impaired.

Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms. For example, in the above-described embodiment, the brake current basic value Ibc is multiplied by the vehicle speed correction coefficient and then multiplied by the torque correction coefficient. However, the brake current basic value Ibc is multiplied by the torque correction coefficient and then multiplied by the vehicle speed correction coefficient. Good. Further, in order to set the brake current value ΔIbc in consideration of the vehicle speed V, a plurality of brake current basic value setting tables different for each vehicle speed range are used instead of multiplying the vehicle speed correction coefficient according to the vehicle speed V by the brake current basic value Ibc. 41, one of the tables may be selected according to the vehicle speed V, and the basic brake current value Ibc may be determined based on the selected table.

In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electric configuration of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining in detail generation of a brake current value by a brake current control unit, and shows an example of a brake current basic value setting table, a vehicle speed correction coefficient table, and a torque correction coefficient table.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Torque sensor (steering torque detection means) 2 Control part 3 Vehicle speed sensor (vehicle speed detection means) 4 Motor 5 Motor drive circuit 6 Motor current detection circuit (motor rotation detection means) 7 Motor terminal voltage detection circuit (motor rotation detection means) 23 Subtraction unit 24 PWM generation unit (motor control unit) 31 Torque-motor current characteristic table (current target value setting unit) 32 Differential control table (current target value setting unit) 33 Motor rotation detection unit (motor rotation detection unit) 34 Brake current Control unit (brake current setting unit) 35 Addition unit (current target value setting unit) 36 Subtraction unit 41 Brake current basic value setting table (basic value setting unit) 42 Vehicle speed correction coefficient table (vehicle speed correction coefficient setting unit, second multiplication unit) 43) Torque correction coefficient table (direction difference determination means,
Torque correction coefficient setting means, first multiplication means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI theme coat ゛ (Reference) B62D 119: 00 B62D 119: 00 (72) Inventor Kiyoshi Sakamoto 3-1, Fuchu-cho, Shinchu, Aki-gun, Hiroshima Mazda F term in reference (reference) 3D032 CC08 DA15 DA23 DA63 DA64 DA65 DC17 DD10 DD17 EB08 3D033 CA13 CA16 CA20 CA28 5H550 AA16 DD01 EE03 GG03 GG05 GG06 JJ03 JJ23 JJ25 LL01 LL14 LL15 LL16 LL22 LL23 LL32

Claims (4)

[Claims] 1. An electric power steering apparatus for assisting steering by giving a torque generated by a motor to a steering mechanism, comprising: a motor rotation detecting means for detecting a rotation direction and a number of rotations of the motor; Steering torque detecting means for detecting the direction and magnitude of the steering torque input to the motor, and a current target value setting for setting a motor current target value based on the magnitude of the steering torque detected by the steering torque detecting means A motor current set by the current target value setting means based on a rotation direction and a rotation speed detected by the motor rotation detection means, and a direction and magnitude of a steering torque detected by the steering torque detection means. Brake current setting means for determining a brake current value to be subtracted from the target value. And an electric power steering device. 2. A value obtained by subtracting a brake current value set by said brake current setting means from a motor current target value set by said current target value setting means is a current value to be supplied to said motor. 2. The electric power steering apparatus according to claim 1, further comprising motor control means for controlling the motor as a certain current command value. 3. A brake current setting means comprising: a basic value setting means for setting a brake current basic value based on a rotation direction and a rotation speed detected by the motor rotation detection means; Direction difference judging means for judging the difference between the rotation direction of the steering wheel and the direction of the steering torque detected by the steering torque detecting means; the judgment result of the direction difference judging means; and the steering torque detected by the steering torque detecting means. A torque correction coefficient setting means for determining a torque correction coefficient based on the magnitude of: a brake current basic value set by the basic value setting means multiplied by a torque correction coefficient set by the torque correction coefficient setting means. 3. The electric power steering apparatus according to claim 1, further comprising a multiplication unit. . 4. The electric power steering apparatus according to claim 1, further comprising a vehicle speed detecting means for detecting a running speed of the vehicle, wherein the brake current setting means is based on the running speed of the vehicle detected by the vehicle speed detecting means. Vehicle speed correction coefficient setting means for determining a vehicle speed correction coefficient; and second multiplying means for multiplying the vehicle speed correction coefficient set by the vehicle speed correction coefficient setting means with a brake current basic value set by the basic value setting means. The electric power steering apparatus according to claim 3, wherein the electric power steering apparatus includes: