JP2000118424A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of uncomfortable vibration of a steering mechanism due to the torque ripple of a motor. SOLUTION: Subtraction parts 43U, 43V, and 43W compute a deviation between each phase target current value computed by a three-phase processing part 42 and each phase actual current value detected by a motor current detecting circuit 70, and the computing result is provided to PI control parts 44U, 44V, and 44W and a deviation deciding part 46. The deviation deciding device 46 decides it relating to each motor phase whether a deviation between each of phase target current values determined by the subtraction parts 43U, 43V, and 43W and each phase actual current value exceeds a given value, and respective deciding results are provided to a target current computing part 41. The target current computing part 41 provides a target current value as it is computed based on outputs from a car speed sensor 61 and a torque sensor 62 with the three-phase split-phase processing part 42 on the basis of an output from the deviation deciding part 46 and a target current value is reduced for correction and the result is provided for the three-phase split-phase processing part 42.

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 applying a steering assisting force to a steering mechanism of a vehicle by using a rotational force of a motor.

[0002]

2. Description of the Related Art Conventionally, using the rotational force of a motor,
2. Description of the Related Art An electric power steering device that assists operation of a steering wheel is used. In such an electric power steering device, a steering assist force corresponding to a steering torque when a driver turns a steering wheel to perform steering is provided from a motor to a steering mechanism.

More specifically, the motor is, for example, a three-phase AC motor. The magnitude of the steering assist force generated by the motor is controlled by a controller which controls a sine wave current flowing through each phase of the motor. It is adjusted by doing. An output signal of a torque sensor for detecting a steering torque and an output signal of a motor rotation angle sensor for detecting a rotation angle of a motor are input to the controller. Based on the output signals of the torque sensor and the motor rotation angle sensor, the controller calculates a target current value to be given to each phase of the motor. Further, an output signal from a motor current detection circuit for detecting a current value flowing through each phase of the motor is input to the controller. The controller controls the motor drive circuit so that the peak value of the sinusoidal current flowing through each phase of the motor matches the respective target current values. As a result, a steering assist force corresponding to the steering torque is generated from the motor.

[0004]

However, in the conventional electric power steering apparatus, there is a possibility that torque ripple of the motor occurs and unpleasant vibration occurs in the steering mechanism. That is, when the motor is used continuously for a long time, the winding temperature of the motor increases, and the winding resistance increases with the temperature increase. Since the maximum applied voltage to the motor is limited by the voltage generated by the battery mounted on the vehicle, when the winding resistance of the motor increases, the allowable current value that can flow through the winding decreases. If the allowable current value is smaller than the target current value in any one phase of the motor, as shown by a solid line in FIG. Torque ripple will occur.

An object of the present invention is to solve the above-mentioned technical problems and to provide an electric power steering apparatus capable of suppressing generation of unpleasant vibration of a steering mechanism due to torque ripple of a motor.

[0006]

In order to achieve the above object, the present invention drives a motor (M) based on a target current, and applies a driving force of the motor to a steering mechanism (1). A target current setting means (41, S3) for setting a target current to be supplied to the motor in an electric power steering device (2) for transmitting and assisting steering.
A motor current detecting means (70, S5) for detecting an actual current flowing through the motor; and calculating a deviation between a target current set by the target current setting means and an actual current detected by the motor current detecting means. Calculation means (43
U, 43V, 43W) and means (41, 46, S6, S6, S6, S6, S6) for reducing and correcting the target current according to the deviation when the deviation calculated by the calculating means is equal to or larger than a predetermined value.
7) An electric power steering apparatus comprising:

[0007] In the parentheses, reference numerals such as corresponding components in the embodiments described later are shown. Hereinafter, the same applies in this section. The winding current value flowing through the motor winding is: winding resistance value × winding current value + motor induced voltage × motor rotation speed ≦
The battery voltage relationship is satisfied. Therefore, for example, when the winding temperature of the motor rises, the winding resistance increases with the rise in temperature, and the allowable current value of the winding decreases. If the winding allowable current value is smaller than the target current value to be supplied to the winding, the current waveform flowing through the winding will be distorted. The distortion of the current waveform causes torque ripple of the motor, and causes unpleasant vibration of the steering mechanism.

According to the present invention, when the deviation between the target current set by the target current setting means and the actual current detected by the motor current detection means is equal to or larger than a predetermined value, the motor is controlled according to the deviation. The target current to be supplied is reduced and corrected. Thereby, even if the winding resistance of the motor increases, the target current value can be suppressed to be smaller than the winding allowable current value, and the current waveform flowing through the motor winding is prevented from being distorted. be able to. Therefore, it is possible to prevent the occurrence of torque ripple due to the distortion of the current waveform flowing through the motor winding, and it is possible to eliminate the possibility of causing unpleasant vibration in the steering mechanism.

The motor is preferably an AC motor, and more preferably a three-phase AC motor. In the case where a three-phase AC motor is applied as the motor, the means for reducing and correcting the target current includes at least one of the U, V, and W phases of the motor.
When the deviation between the target current value of each phase and the actual current value of each phase is equal to or more than a predetermined value, it is preferable that the target current to be supplied to the motor is reduced and corrected in accordance with the deviation.

Further, it is preferable that the means for reducing and correcting the target current reduce and correct the target current so that the current waveform supplied to the motor has a sine wave waveform. By doing so, even if the winding resistance increases,
Even if the allowable current value of the winding becomes small, no distortion occurs in the peak portion of the sinusoidal current waveform flowing through the motor.

[0011]

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 an embodiment of the present invention, together with a cross-sectional structure of a steering mechanism. The steering mechanism 1 includes a rack 11 arranged along the width direction of the vehicle, a pinion shaft 12 having a pinion at its tip for meshing with the rack 11 in a gear box 17, and rotatably coupled to both ends of the rack 11. And a knuckle arm 14 rotatably connected to the tip of the tie rod 13.

The knuckle arm 14 is rotatably provided around a king pin 15, and a steering wheel 16 is mounted on the knuckle arm 14. Pinion shaft 1
The base end of the steering wheel 2 is connected to a steering shaft via a universal joint, and a steering wheel (not shown) is fixed to one end of the steering shaft. With this configuration, by rotating the steering wheel, the rack 11 is displaced in its longitudinal direction,
The knuckle arm 14 rotates around the king pin 15 and the direction of the steered wheels 16 changes.

The electric power steering device 2 has a three-phase brushless motor M provided in connection with an intermediate portion of the rack 11. The motor M includes a case 21 fixed to the vehicle.
1, a rotor 22 is arranged, and a stator 23 is arranged so as to surround the rotor 22.

A ball nut 3 is provided at one end of the rotor 22.
1 are connected. The ball nut 31 is screwed through a plurality of balls to a screw shaft portion 32 formed at an intermediate portion of the rack 11, whereby the ball screw mechanism 3
0 is formed. Bearings 33 and 34 are interposed between the ball nut 31 and the case 21 of the motor M, and a bearing 35 is interposed between the case 21 and the vicinity of the other end of the rotor 22. ing.

With this configuration, when the motor M is energized and a torque is applied to the rotor 22, the applied torque is applied to the ball nut 3 connected to the rotor 22.
1 is transmitted. The torque transmitted to the ball nut 31 is converted by the ball screw mechanism 30 into a driving force in the vehicle width direction of the rack 11. Thus, the force generated by the motor M is given to the steering mechanism 1.

The magnitude of the steering assist force is adjusted by controlling the drive current of the motor M. The drive current of the motor M is controlled by the controller 40 via the motor driver 50. Controller 40
Include a vehicle speed sensor 61 for detecting a vehicle speed, a torque sensor 62 for detecting a steering torque, a motor rotation angle sensor 63 for detecting a rotation angle of the motor M, and a magnitude of a current flowing through the motor M. An output signal of the motor current detection circuit 70 for detection is input. The controller 40 obtains a current value to be supplied to the motor M based on the output signals described above, and controls the motor driver 50 based on the current value, thereby controlling the current flowing through each phase of the motor M.

The vehicle speed sensor 61 is realized, for example, by a wheel speed sensor provided in connection with a wheel and outputting a pulse signal at a cycle corresponding to the rotation speed of the wheel. In this case, the vehicle speed, which is the speed of the vehicle, can be obtained by measuring the period or frequency of the pulse signal.
The torque sensor 62 divides the pinion shaft 12 into an input shaft on the steering wheel side and an output shaft on the rack 11 side, connects the input shaft and the output shaft with a torsion bar, and twists the torsion bar. This is realized by a configuration for detecting the amount. That is, since the torque applied to the steering wheel and the amount of twist of the torsion bar correspond one-to-one, the steering torque can be detected by detecting the amount of twist with an appropriate detection mechanism such as a potentiometer.

The motor rotation angle sensor 63 is constituted by a rotary encoder or the like, and is provided in association with the rotor 22. The rotation position of the rotor 22, that is, the rotation angle of the motor M can be detected based on the pulse signal output from the rotary encoder. FIG. 2 shows a controller 40, a motor driver 50, and a motor current detection circuit 7.
FIG. 3 is a block diagram showing a configuration of a 0. Controller 40
Is constituted by a microcomputer including, for example, a CPU, a RAM and a ROM, and its functions are shown by blocks in FIG.

A controller 40 calculates a target current value to be supplied to the motor M based on the outputs of the vehicle speed sensor 61 and the torque sensor 62. The target current calculation unit 41 and the motor rotation angle sensor 63 Three-phase splitter 4 that performs three-phase splitter processing based on the output signal
2 is provided. In the three-phase phase separation process, the target current value of each motor phase (U phase, V phase, W phase) according to the rotation angle of the motor M is calculated with respect to the target current value obtained by the target current calculation unit 41. Is done.

The U-phase target current value, V-phase target current value, and W-phase target current value output from the three-phase splitting processing unit 42 are given to subtraction units 43U, 43V, 43W, respectively. The subtraction units 43U, 43V, and 43W are also provided with the actual U-phase, V-phase, and W-phase current values of the motor M detected by the motor current detection circuit 70. Subtraction units 43U, 43V,
43W calculates the difference between the target current value of each phase and the actual current value for each phase of the motor, and outputs the calculation result to the U-phase PI
(Proportional-Integral) control unit 44U, V-phase PI control unit 44V, and W-phase PI control unit 44W.

The PI control units 44U, 44V and 44W perform PI calculations based on the outputs from the subtraction units 43U, 43V and 43W, respectively. The result of this PI operation is the U-phase PW
M (Pulse Width Modulation) control unit 45U, V-phase PWM
Control unit 45V and W-phase PWM control unit 45W. Each of the PWM control units 45U, 45V, and 45W creates a PWM control signal corresponding to the PI calculation result, and outputs the created PWM control signal to the motor driver 50.

The outputs of the subtractors 43U, 43V, 43W are provided to a deviation determiner 46. Deviation judgment unit 4
6 determines whether or not the deviation between the target current value and the actual current value for each phase of the motor obtained by the subtractors 43U, 43V, 43W is equal to or greater than a predetermined value, and determines the result of the determination as a target current calculator. Give to 41. The target current calculation unit 41 supplies the target current value calculated based on the outputs of the vehicle speed sensor 61 and the torque sensor 62 to the three-phase phase separation processing unit 42 as it is, in accordance with the output from the deviation determination unit 46, The value may be reduced and corrected and applied to the three-phase phase separation processing unit 42.

The motor driver 50 has an FET (Field-Eff)
ect Transistor) 51U, 52U series circuit and FET
A series circuit of 51 V and 52 V and a series circuit of FETs 51 W and 52 W are connected in parallel, and a voltage (for example, 12 V) from a battery mounted on a vehicle is applied to each series circuit. . And FET51U,
A connection point 53U between the 52Us is connected to the U-phase winding of the motor M, and a connection point 53V between the FETs 51V and 52V is connected to the motor M
, And a connection point 53W between the FETs 51W and 52W is connected to the W-phase winding of the motor M.

FETs 51U and 52U, FETs 51V and 5
2V and the FETs 51W and 52W have PWM respectively.
PWM control signals from the control units 45U, 45V, 45W are input. The motor current detection circuit 70 includes current transformers 71U, 71V, 71W using, for example, Hall elements. The current transformers 71U, 71V, and 71W are arranged so that currents flowing from the connection points 53U, 53V, and 53W toward the respective phase windings of the motor M can be detected. Outputs of the current transformers 71U, 71V, and 71W are supplied to subtraction units 43U, 43V, and 43W after being amplified by amplifiers (Amp) 72U, 72V, and 72W, respectively.

FIG. 3 is a flowchart for explaining the motor control operation by the controller 40. First, the controller 40 refers to the output signals of the vehicle speed sensor 61 and the torque sensor 62 to obtain data on the vehicle speed and the steering torque (Steps S1 and S2). Next, the controller 40 calculates a target current value to be given to the motor M based on the vehicle speed and the steering torque (Step S3). When the target current value is determined, the controller 40 calculates the target current value of each phase of the motor corresponding to the rotation angle of the motor M with respect to the target current value (Step S4).

Next, the controller 40 fetches the output from the motor current detection circuit 70 and outputs the U phase of the motor M,
Check the actual current values flowing in the V and W phases (step S
5). Then, a deviation between each phase target current value and each phase actual current value is calculated for each phase of the motor, and it is determined whether the deviation is equal to or more than a predetermined value (step S6). The value of the winding current flowing through each phase winding of the motor M satisfies the following equation, assuming that the maximum voltage of the battery mounted on the vehicle is 12V.

Winding resistance value × winding current value + motor induced voltage × motor rotation speed ≦ 12V (Equation) Therefore, for example, when the temperature of each phase winding of the motor M rises, each phase winding rises with this temperature rise. Wire resistance increases,
The allowable current value of the winding becomes smaller. If the winding allowable current value becomes smaller than the target current value of each phase of the motor obtained in step S4, as shown by a solid line in FIG. 4, distortion occurs at the peak portion of the waveform of the sine wave current flowing through that phase. Will happen. This current waveform distortion causes torque ripple of the motor M.

Therefore, in this embodiment, in any one of the U-phase, V-phase and W-phase of the motor M, the deviation between each phase target current value and each phase actual current value is not less than a predetermined value. In step S7, the target current value to be supplied to the motor M at a ratio corresponding to the deviation is suppressed. Thereby, even if the winding resistance of each phase of the motor M is increased, the target current value for each phase of the motor can be suppressed to be smaller than the allowable current value of the winding, and there is no distortion in each motor phase. A sine wave current (indicated by a two-dot chain line in FIG. 4) can be input.

The controller 40 calculates again the target current value of each phase of the motor corresponding to the rotation angle of the motor M with respect to the newly set target current value (step S).
8). Then, the controller 40 performs a PI calculation based on the deviation between the target current value of each phase and the actual current value of each phase detected by the motor current detection circuit 70 (step S9), and further performs PWM corresponding to the result of the PI calculation. Create a control signal,
The generated PWM control signal is output to the motor driver 50 (step S10).

On the other hand, if the deviation between the target current value and the actual current value is less than a predetermined value in any of the U, V, and W phases of the motor M (NO in step S6), the controller 40 skips the processing of steps S7 and S8 and performs PI calculation based on the deviation between the target current value of each phase set in step S4 and the actual current value of each phase detected by the motor current detection circuit 70 ( Step S9). And P
A PWM control signal corresponding to the result of the I operation is created, and the created PWM control signal is output to the motor driver 50 (step S10).

After the process in step S10, the controller 40 determines whether or not the ignition switch of the vehicle has been turned off. If the ignition switch remains on, the process returns to step S1, and the above-described processes after step S1 are performed. Is performed, and the process ends when the ignition switch is turned off. As described above, according to this embodiment, the target current value for each phase of the motor M is set to the allowable winding current even if the winding resistance increases in accordance with the increase in the temperature of each phase winding of the motor M. Value can be kept below
A sine wave current without distortion can be input to each motor phase. As a result, it is possible to prevent the occurrence of torque ripple due to the distortion of the current waveform flowing through each phase of the motor, and it is possible to eliminate the possibility that unpleasant vibration is generated in the steering mechanism 1.

In the above description, the target current value for each motor phase can be suppressed to be smaller than the winding allowable current value. However, the target current value for each motor phase becomes the winding allowable current value. The reduction correction may be made to be equal. Even in this case, it is possible to input a sine wave current without distortion to each phase of the motor, and it is possible to prevent the occurrence of torque ripple due to the distortion of the current waveform flowing through each phase of the motor.

As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above embodiment, and 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, together with a cross-sectional structure of a steering mechanism.

FIG. 2 is a block diagram illustrating a configuration of a controller, a motor driver, and a motor current detection circuit.

FIG. 3 is a flowchart illustrating a motor control operation performed by a controller.

FIG. 4 is a diagram showing input current waveforms to each phase of a motor.

FIG. 5 is a diagram for explaining distortion of an input current waveform to a motor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering mechanism 2 electric power steering device 40 controller 41 target current calculation unit 43U, 43V, 43W subtraction unit 46 deviation determination unit 50 motor driver 70 motor current detection circuit M motor

Claims (1)

[Claims] 1. An electric power steering apparatus for driving a motor based on a target current and transmitting a driving force of the motor to a steering mechanism to assist in steering, wherein a target current for setting a target current to be supplied to the motor. Setting means; motor current detecting means for detecting an actual current flowing in the motor; and calculating means for calculating a deviation between a target current set by the target current setting means and an actual current detected by the motor current detecting means. An electric power steering apparatus comprising: a means for reducing and correcting the target current according to the deviation when the deviation calculated by the calculation means is equal to or greater than a predetermined value.