JP3770297B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus for applying a steering assist force to a steering mechanism of a vehicle using a rotational force of a motor.
[0002]
[Prior art]
Conventionally, an electric power steering apparatus that assists the operation of a steering wheel by using the rotational force of a motor has been used. In such an electric power steering apparatus, a steering assist force according to the steering torque when the driver performs steering by rotating the steering wheel is applied from the motor to the steering mechanism.
[0003]
Specifically, the motor is composed of, for example, a three-phase AC motor, and the magnitude of the steering assist force generated from this motor is controlled by the controller controlling the sine wave current flowing in each phase of the motor. It has come to be adjusted. The controller receives an output signal from a torque sensor for detecting steering torque and an output signal from a motor rotation angle sensor for detecting the rotation angle of the motor. 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, the controller receives an output signal from a motor current detection circuit for detecting a current value flowing in each phase of the motor. The controller controls the motor drive circuit so that the peak value of the sine wave current flowing in each phase of the motor matches each target current value. As a result, a steering assist force corresponding to the steering torque is generated from the motor.
[0004]
[Problems to be solved by the invention]
However, in the conventional electric power steering apparatus, there is a possibility that torque ripple of the motor is generated and unpleasant vibration is generated in the steering mechanism.
That is, when the motor is used continuously for a long time, the winding temperature of the motor rises and the winding resistance increases with the temperature rise. 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, the peak portion of the sine wave current waveform flowing through the phase is distorted as shown by the solid line in FIG. Torque ripple will occur.
[0005]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electric power steering device that solves the above technical problem and can suppress the occurrence of unpleasant vibration of the steering mechanism due to torque ripple of the motor.
[0006]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, the present invention drives an electric motor (M) based on a target current and transmits the driving force of the motor to a steering mechanism (1) to assist steering (2 ), A target current setting means (41, S3) for setting a target current to be supplied to the motor, a motor current detection means (70, S5) for detecting an actual current flowing through the motor, and the target current setting means. Calculating means (43U, 43V, 43W) for calculating the deviation between the target current set by the motor current detecting means and the actual current detected by the motor current detecting means, and when the deviation calculated by the calculating means is a predetermined value or more The electric power steering apparatus includes means (41, 46, S6, S7) for reducing and correcting the target current according to the deviation.
[0007]
In the parentheses, symbols such as corresponding components in the embodiments described later are represented. Hereinafter, this is the same in this section.
The winding current value flowing through the motor winding satisfies the relationship of winding resistance value × winding current value + motor induced voltage × motor rotation speed ≦ battery voltage. Therefore, for example, when the winding temperature of the motor rises, the winding resistance increases with this temperature rise, and the allowable current value of the winding becomes smaller. 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 is distorted. This distortion of the current waveform causes a torque ripple of the motor and causes an unpleasant vibration of the steering mechanism.
[0008]
According to this 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 greater than or equal to a predetermined value, the deviation should be supplied to the motor according to the deviation. The target current is corrected for reduction. As a result, even if the winding resistance of the motor is increased, the target current value can be kept smaller than the allowable winding current value, and distortion of the current waveform flowing through the motor winding can be prevented. be able to. Therefore, it is possible to prevent the occurrence of torque ripple due to the distortion of the current waveform flowing in the motor winding, thereby eliminating the possibility of causing unpleasant vibration in the steering mechanism.
[0009]
The motor is preferably an AC motor, and more preferably a three-phase AC motor.
When a three-phase AC motor is applied as the motor, the means for reducing and correcting the target current is at least one of the U phase, V phase, and W phase of the motor, and each phase target current. When the deviation between the value and each phase actual current value is equal to or larger than a predetermined value, it is preferable to reduce and correct the target current to be given to the motor in accordance with the deviation.
[0010]
Furthermore, it is preferable that the means for reducing and correcting the target current is for correcting and reducing the target current so that the current waveform supplied to the motor becomes a sine wave waveform. By doing this, even if the winding resistance is increased and the allowable current value of the winding is reduced, the peak portion of the sine wave current waveform flowing through the motor is not distorted.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electrical 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 is coupled to a rack 11 disposed along the vehicle width direction, a pinion shaft 12 having a pinion portion meshing with the rack 11 in a gear box 17 at a tip, and both ends of the rack 11 to be rotatable. The tie rod 13 is provided, and a knuckle arm 14 is rotatably coupled to the tip of the tie rod 13.
[0012]
The knuckle arm 14 is rotatably provided around the kingpin 15, and a steering wheel 16 is attached to the knuckle arm 14. A base end portion of the pinion shaft 12 is coupled 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, when the steering wheel is rotated, the rack 11 is displaced in the longitudinal direction thereof, the knuckle arm 14 is rotated around the kingpin 15, and the direction of the steering wheel 16 is changed.
[0013]
The electric power steering apparatus 2 has a three-phase brushless motor M provided in association with the middle part of the rack 11. The motor M includes a case 21 fixed to the vehicle. In the case 21, a rotor 22 is disposed so as to surround the rack 11, and a stator 23 is disposed so as to surround the rotor 22. .
[0014]
A ball nut 31 is connected to one end of the rotor 22. The ball nut 31 is screwed into a screw shaft portion 32 formed in the middle of the rack 11 via a plurality of balls, whereby a ball screw mechanism 30 is formed. Further, 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.
[0015]
With this configuration, when the motor M is energized and torque is applied to the rotor 22, the applied torque is transmitted to the ball nut 31 connected to the rotor 22. The torque transmitted to the ball nut 31 is converted into a driving force in the vehicle width direction of the rack 11 by the ball screw mechanism 30. Thus, the force generated from the motor M is applied to the steering mechanism 1.
[0016]
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. The controller 40 includes a vehicle speed sensor 61 for detecting the vehicle speed, a torque sensor 62 for detecting the steering torque, a motor rotation angle sensor 63 for detecting the rotation angle of the motor M, and the magnitude of the current flowing through the motor M. An output signal of the motor current detection circuit 70 for detecting the length is inputted. The controller 40 obtains a current value to be supplied to the motor M based on each output signal, and controls the motor driver 50 based on the current value, thereby controlling the current flowing in each phase of the motor M.
[0017]
The vehicle speed sensor 61 is realized, for example, by a wheel speed sensor that is provided in association with a wheel and outputs a pulse signal at a cycle corresponding to the rotation speed of the wheel. In this case, the vehicle speed that 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 quantity. That is, since the torque applied to the steering wheel and the torsion amount of the torsion bar correspond one-to-one, the steering torque can be detected by detecting the torsion amount with an appropriate detection mechanism such as a potentiometer.
[0018]
The motor rotation angle sensor 63 is composed of a rotary encoder or the like, and is provided in association with the rotor 22. Based on the pulse signal output from the rotary encoder, the rotational position of the rotor 22, that is, the rotational angle of the motor M can be detected.
FIG. 2 is a block diagram showing the configuration of the controller 40, the motor driver 50, and the motor current detection circuit 70. The controller 40 is composed of, for example, a microcomputer including a CPU, a RAM, and a ROM. In FIG. 2, the function is shown in blocks.
[0019]
The controller 40 calculates the target current value to be applied to the motor M based on the outputs of the vehicle speed sensor 61 and the torque sensor 62, and outputs the target current calculation unit 41 and the motor rotation angle sensor 63 as output signals. And a three-phase phase separation processing unit 42 for performing the three-phase phase separation processing based on the above. In the three-phase phase separation process, the target current value of each motor phase (U phase, V phase, W phase) corresponding 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.
[0020]
The U-phase target current value, the V-phase target current value, and the W-phase target current value output from the three-phase phase separation processing unit 42 are given to the subtraction units 43U, 43V, and 43W, respectively. The subtractors 43U, 43V, and 43W are also provided with actual current values of the U phase, V phase, and W phase of the motor M detected by the motor current detection circuit 70. Subtraction units 43U, 43V, and 43W calculate the difference between each phase target current value and the actual current value for each phase of the motor, and calculate the calculation results as U-phase PI (Proportional-Integral) control unit 44U and V-phase PI, respectively. Provided to control unit 44V and W-phase PI control unit 44W.
[0021]
The PI control units 44U, 44V, 44W perform PI calculation based on the outputs from the subtraction units 43U, 43V, 43W, respectively. The result of this PI calculation is given to a U-phase PWM (Pulse Width Modulation) control unit 45U, a V-phase PWM control unit 45V, and a W-phase PWM control unit 45W. The PWM control units 45U, 45V, 45W each create a PWM control signal corresponding to the PI calculation result, and output the created PWM control signal to the motor driver 50.
[0022]
The outputs of the subtracting units 43U, 43V, and 43W are given to the deviation determining unit 46. The deviation determination unit 46 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 subtraction units 43U, 43V, and 43W is greater than or equal to a predetermined value, and the determination result is a target. This is given to the current calculation unit 41. The target current calculation unit 41 gives 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 according to the output from the deviation determination unit 46, or The value is corrected for reduction and given to the three-phase phase separation processing unit 42.
[0023]
The motor driver 50 is configured by connecting a series circuit of FETs (Field-Effect Transistor) 51U and 52U, a series circuit of FETs 51V and 52V, and a series circuit of FETs 51W and 52W in parallel. The voltage (for example, 12V) from the battery mounted in the vehicle is applied. The connection point 53U between the FETs 51U and 52U is connected to the U-phase winding of the motor M, the connection point 53V between the FETs 51V and 52V is connected to the V-phase winding of the motor M, and the connection point 53W between the FETs 51W and 52W. Is connected to the W-phase winding of the motor M.
[0024]
The PWM control signals from the PWM control units 45U, 45V, and 45W are input to the FETs 51U and 52U, the FETs 51V and 52V, and the FETs 51W and 52W, respectively.
The motor current detection circuit 70 includes current transformers 71U, 71V, 71W using Hall elements, for example. The current transformers 71U, 71V, 71W are arranged so as to detect currents flowing from the connection points 53U, 53V, 53W toward the phase windings of the motor M, respectively. The outputs of the current transformers 71U, 71V, 71W are respectively amplified by amplifiers (Amp) 72U, 72V, 72W, and then supplied to the subtracting units 43U, 43V, 43W.
[0025]
FIG. 3 is a flowchart for explaining a 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 and acquires 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 according to the rotation angle of the motor M with respect to the target current value (step S4).
[0026]
Next, the controller 40 takes in the output from the motor current detection circuit 70 and checks the actual current values flowing in the U phase, V phase, and W phase of the motor M (step S5). Then, a deviation between each phase target current value and each phase actual current value is calculated for each motor phase, and it is determined whether or not the deviation is equal to or greater than a predetermined value (step S6).
The winding current value that flows through each phase winding of the motor M satisfies the relationship of the following formula, assuming that the maximum voltage of the battery mounted on the vehicle is 12V.
[0027]
Winding resistance value × winding current value + motor induced voltage × motor rotation speed ≦ 12V (formula)
Therefore, for example, when the temperature of each phase winding of the motor M rises, each phase winding resistance increases with this temperature rise, and the allowable current value of the winding becomes smaller. If this winding allowable current value becomes smaller than the target current value of each phase of the motor obtained in step S4, distortion is generated at the peak portion of the waveform of the sine wave current flowing through that phase as shown by the solid line in FIG. It will occur. This distortion of the current waveform causes a torque ripple of the motor M.
[0028]
Therefore, in this embodiment, when the deviation between each phase target current value and each phase actual current value is a predetermined value or more in any of the U phase, V phase, and W phase of the motor M, The target current value to be given to the motor M at a ratio according to the deviation is suppressed (step S7). Thereby, even if each phase winding resistance of the motor M increases, the target current value for each phase of the motor can be suppressed to be smaller than the allowable winding current value, and there is no distortion in each phase of the motor. A sinusoidal current (indicated by a two-dot chain line in FIG. 4) can be input.
[0029]
The controller 40 again calculates 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 S8). Then, the controller 40 performs PI calculation based on the deviation between each phase target current value and each phase actual current value detected by the motor current detection circuit 70 (step S9), and PWM corresponding to the result of the PI calculation. A control signal is created, and the created PWM control signal is output to the motor driver 50 (step S10).
[0030]
On the other hand, if the deviation between the target current value and the actual current value is less than the predetermined value in any of the U phase, V phase, and W phase of the motor M (NO in step S6), the controller 40 Steps S7 and S8 are skipped, and PI calculation is performed based on the deviation between each phase target current value set in step S4 and each phase actual current value detected by the motor current detection circuit 70 (step S9). . Then, a PWM control signal corresponding to the PI calculation result is created, and the created PWM control signal is output to the motor driver 50 (step S10).
[0031]
After the process of 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 controller 40 returns to step S1, and performs the processes after step S1 described above. When the ignition switch is turned off, the process is terminated.
As described above, according to this embodiment, even if the winding resistance increases with an increase in the winding temperature of each phase of the motor M, the target current value for each phase of the motor is set as the winding allowable current. The sine wave current without distortion can be inputted to each phase of the motor. As a result, it is possible to prevent the occurrence of torque ripple due to distortion of the current waveform flowing in each phase of the motor, and to eliminate the possibility of causing unpleasant vibration in the steering mechanism 1.
[0032]
In the above description, the target current value for each phase of the motor can be kept smaller than the allowable winding current value. However, the target current value for each phase of the motor becomes equal to the allowable winding current value. It may be reduced and corrected. Even in this case, a sine wave current without distortion can be input to each phase of the motor, and the occurrence of torque ripple due to distortion of the current waveform flowing through each phase of the motor can be prevented.
[0033]
The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described 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 electrical 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.
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 for explaining a motor control operation by a controller.
FIG. 4 is a diagram showing a waveform of an input current 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]
DESCRIPTION OF SYMBOLS 1 Steering mechanism 2 Electric power steering apparatus 40 Controller 41 Target current calculation part 43U, 43V, 43W Subtraction part 46 Deviation judgment part 50 Motor driver 70 Motor current detection circuit M Motor

Claims (1)

In the electric power steering device that drives the motor based on the target current and transmits the driving force of the motor to the steering mechanism to assist the steering,
Target current setting means for setting a target current to be supplied to the motor;
Motor current detecting means for detecting an actual current flowing through the motor;
Arithmetic means for calculating a deviation between the target current set by the target current setting means and the actual current detected by the motor current detection means;
And a means for reducing and correcting the target current in accordance with the deviation when the deviation calculated by the calculating means is equal to or greater than a predetermined value.

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