JP2008062816A - 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 improved in functions thereof by processing signals of a low pass filter to improve responsiveness and to reduce the noise. <P>SOLUTION: The control device of an electric power steering device controls a motor giving the steering assist force to a steering mechanism based on a current control value computed by using a steering assist command value computed based on the steering torque generated in a steering shaft and a current value of the motor. The control device comprises the structure for passing a signal for controlling the steering assist force to the low pass filter 332, and a switching means for switching output by inputting an input signal and an output signal of the low pass filter. The switching means is switched based on a difference between the input signal and the output signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering apparatus in which a steering assist force (assist force) by a motor is applied to a steering system of a vehicle, and more particularly, a signal that achieves both noise reduction and ensuring responsiveness of signals used for control. The present invention relates to a control device for an electric power steering device that is improved in function by performing processing.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor energizes an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally performed by a PWM (pulse width modulation) control duty. This is done by adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. It is connected to the tie rod 6. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque T of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is connected to the column shaft 2 via the reduction gear 3. Has been. The control unit 30 that controls the power steering apparatus is supplied with electric power from the battery 14 and also receives an ignition key signal from the ignition key 11. The control unit 30 calculates an assist command steering assist command value I 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 calculated steering assist command value I is calculated. Is used to control the current supplied to the motor 20.

  The control unit 30 is mainly composed of a CPU (including MPU and MCU), and FIG. 9 shows general functions executed by programs in the CPU. For example, the phase compensation unit 32 does not represent a phase compensation unit as independent hardware, but represents a phase compensation function executed by the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 9. The steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12 are input to the steering assist command value calculation unit 31, and the steering assist is performed. The steering assist command value Iref1 calculated by the command value calculation unit 31 is input to the phase compensation unit 32 for enhancing the stability of the steering system and phase compensated, and the phase-compensated steering assist command value Iref2 is input to the addition unit 39A. Entered. Further, the steering torque T is input to the center response improvement unit 33 for improving the control response in the vicinity of the neutral position of the steering to realize smooth and smooth steering, and the steering torque Ta with improved response is added. It is input to 39A. A compensation signal CM3, which will be described later, is input to the adding unit 39A, and the steering assist command value Iref3 added by the adding unit 39A is added to the subtracting unit 39B, and the deviation (Iref3-Im) from the motor current Im is the current. Input to the control unit 34, the current control unit 34 supplies the motor current Im through the motor winding 35.

  An angle sensor 36A for measuring the motor rotation angle θ is attached to the motor, and the angle θ is input to the angular velocity calculation unit 36B to calculate the angular velocity ω. The angular velocity ω is input to the yaw rate estimation unit 37A and the inertia compensation unit 38, and the yaw rate Yr estimated by the yaw rate estimation unit 37A is input to the convergence control unit 37B. In order to improve the yaw convergence of the vehicle, the convergence control unit 37B brakes the motion of the steering wheel, and the inertia compensation unit 38 assists the force equivalent generated by the inertia of the motor. Or deterioration of control responsiveness is prevented. The inertia compensation signal CM1 from the inertia compensation unit 38 and the convergence control signal CM2 from the convergence control unit 37B are input to the addition unit 39C and added, and the compensation signal CM3 as a result of the addition is input to the addition unit 39A. Yes.

  Here, the configurations of the center response improvement unit 33 and the inertia compensation unit 38 are as shown in FIG. FIG. 10 shows the center response improvement unit 33, but the same applies to the inertia compensation unit 38. In the center responsiveness, a steering assist force based on a signal obtained by differentiating the steering torque T is applied to prevent fluctuations in the steering torque T, so that the steering torque T does not increase rapidly even when sudden steering is performed. The inertia compensator 38 acts to accelerate and decelerate the motor inertia by applying a steering assist force based on a signal obtained by differentiating the angular velocity ω, that is, the angular acceleration, so that the driver does not feel the inertia.

  The center responsiveness improvement unit 33 includes a difference calculation unit 33A, a low-pass filter 33B, and a compensation gain unit 33C. The difference calculation unit 33A differentiates the steering torque T and passes the low-pass filter 33B to reduce noise by differentiation. The V-sensitive compensation gain unit 33C multiplies the compensation gain to obtain the steering torque Ta.

In the electric power steering apparatus described in Japanese Patent Laid-Open No. 2002-234454 (Patent Document 1), a low-pass filter is inserted in the current command value in order to achieve both noise and vibration reduction and a steering feeling, thereby cutting off the low-pass filter. The frequency is changed by the steering speed and the vehicle speed.
JP 2002-234454 A

  In the center response improvement unit and the inertia compensation unit having the low-pass filter as shown in FIG. 10, it is necessary to achieve both the response improvement by differentiation and the noise reduction. However, both characteristics are in a trade-off relationship, and there is a compromise. The point must be adjusted. Moreover, even if the cut-off frequency of the low-pass filter is changed by some information as described in Patent Document 1, it is not sufficient to eliminate the trade-off relationship.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide an electric power steering apparatus that achieves high functionality by performing signal processing of a low-pass filter that can achieve both responsiveness and noise reduction. It is to provide a control device.

  The present invention controls the motor that applies a steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated based on a steering torque generated in a steering shaft and a current value of the motor. The above-described object of the present invention relates to a control device for an electric power steering device configured as described above, and has a structure in which a signal for controlling the steering assist force is passed through a low-pass filter, and inputs an input signal and an output signal of the low-pass filter. This is achieved by providing a judgment switching means for judging the difference and switching the output based on the judgment result.

  In addition, the object of the present invention is that the low-pass filter includes the center and the determination switching unit in the response improvement unit, or the low-pass filter and the determination switching unit are included in the inertia compensation unit. Alternatively, when the low-pass filter and the determination switching unit are included in the back electromotive force compensation unit, or when the absolute value of the difference is larger than a first predetermined value, the determination switching unit is input to the low-pass filter. When the absolute value of the difference is smaller than a second predetermined value (<first predetermined value), the determination switching means outputs the output signal of the low-pass filter more effectively. Is done.

  According to the control device for the electric power steering apparatus according to the present invention, the input signal and the output signal to the low-pass filter are supplied to the center response improvement unit and the inertia compensation unit provided with the low-pass filter, or the counter electromotive voltage compensation unit. By performing the process of switching according to the determination result based on the difference between the two, it is possible to achieve both improvement in response by differentiation and reduction in noise, and increase the functionality of the electric power steering apparatus.

  Although the overall configuration of the present invention is the same as that of FIG. 9, the configuration of the center response improvement unit 33 of the present invention is as shown in FIG. 1, and the configuration of the inertia compensation unit 38 is as shown in FIG. It has become.

  As shown in FIG. 1, the center response improvement unit 33 includes a difference calculation unit 331, a low-pass filter 332, a determination unit 333, a signal switching unit 334, and a compensation gain unit 335. The difference calculation unit 331 differentiates the steering torque T. Then, the differential torque Fi1 is input to the low-pass filter 332 for noise reduction, the signal switching unit 334, and the determination unit 333 that compares and determines the magnitude of the signal. The determination unit 333 and the signal switching unit 334 constitute a determination switching unit. The output value Fo1 of the low-pass filter 332 is input to the signal switching unit 334 and the determination unit 333. The signal switching unit 334 switches the output S1 to Fi1 or Fo1 by the switching signal SW1 from the determination unit 333, and the output S1 is the vehicle speed V. The sensitive compensation gain unit 335 multiplies the compensation gain and outputs it as a steering torque Ta.

Here, the determination unit 333 determines the magnitude and elapsed time between the input value Fi1 of the low-pass filter 332, that is, the output value Fi1 of the difference calculation unit 331, and the output value Fo1 of the low-pass filter 332, and switches based on the determination result. The signal SW1 is output, and the signal switching unit 334 performs switching as in the following (a1) to (d1) and outputs the output S1. The predetermined value A1> the predetermined value B1.

(A1) When (Fi1-Fo1)> A1 is continued for a predetermined time,
The output S1 is set as the input value Fi1.

(B1) When (Fi1-Fo1) <-A1 is continued for a predetermined time,
The output S1 is set as the input value Fi1.

(C1) When | Fi1-Fo1 | <B1 is continued for a predetermined time,
The output S1 is set as an output value Fo1.

(D1) In cases other than the above, the output S1 is set as the previous output value.

When the difference between the input value Fi1 and the output value Fo1 of the low-pass filter 332 is large, it can be considered that the change of the input value Fi1 is large. Therefore, when (Fi1-Fo1) is larger than the predetermined value A1 for a predetermined time, or when (Fi1-Fo1) is smaller than the predetermined value -A1 for a predetermined time, the input value Fi1 is larger. And the input value Fi1 is set as the output S1. When the difference between the input value Fi1 and the output value Fo1 is small, it can be considered that the change in the input value Fi1 is small. Therefore, when | Fi1-Fo1 | is smaller than the predetermined value B1, the output value Fo1 is set. The output is S1. A1> B1 so that chattering does not occur in signal switching.

  As shown in FIG. 2, the inertia compensation unit 38 includes a difference calculation unit 381, a low-pass filter 382, a determination unit 383, a signal switching unit 384, and a compensation gain unit 385, and the difference calculation unit 381 differentiates the angular velocity ω. The differentiated angular acceleration Fi2 is input to the low-pass filter 382 for noise reduction, the signal switching unit 384, and the determination unit 383 that compares and determines the magnitude of the signal. The determination unit 383 and the signal switching unit 384 constitute a determination switching unit. The output value Fo2 of the low-pass filter 382 is input to the signal switching unit 384 and the determination unit 383. The signal switching unit 384 switches the output S2 to Fi2 or Fo2 by the switching signal SW2 from the determination unit 383, and the output S2 is the vehicle speed V. The sensitive compensation gain unit 385 multiplies the compensation gain and outputs it as an inertia compensation signal CM1.

Here, the determination unit 383 determines the magnitude and elapsed time of the input value Fi2 of the low-pass filter 382, that is, the output value Fi2 of the difference calculation unit 381, and the output value Fo2 of the low-pass filter 382, and switches based on the determination result. The signal SW2 is output, and the signal switching unit 384 switches as follows (a2) to (d2) and outputs the output S2. The predetermined value A2> the predetermined value B2.

(A2) When (Fi2-Fo2)> A2 is continued for a predetermined time,
The output S2 is set as the input value Fi2.

(B2) When (Fi2-Fo2) <-A2 is continued for a predetermined time,
The output S2 is set as the input value Fi2.

(C2) When | Fi2-Fo2 | <B2 is continued for a predetermined time,
The output S2 is set as an output value Fo2.

(D2) In cases other than the above, the output S2 is set as the previous output value.

When the difference between the input value Fi2 and the output value Fo2 of the low-pass filter 382 is large, it can be considered that the change of the input value Fi2 is large. Therefore, when (Fi2-Fo2) is larger than the predetermined value A2 for a predetermined time, or when (Fi2-Fo2) is smaller than the predetermined value -A2 for a predetermined time, the input value Fi2 is larger. And the input value Fi2 is set as the output S2. When the difference between the input value Fi2 and the output value Fo2 is small, it can be considered that the change in the input value Fi2 is small. Therefore, when the state where | Fi2-Fo2 | is smaller than the predetermined value B2 continues for a predetermined time, the output value Fo2 is set. The output is S2. In order to prevent chattering in signal switching, A2> B2.

  As described above, according to the present invention, the center responsiveness improvement unit 33 can improve the responsiveness of compensation by using the signal before the low-pass filter when the steering torque T is large, that is, when the steering response is sudden. Thus, the sudden increase in the steering torque T at the time of sudden steering can be suppressed. Further, in the inertia compensator 38, when the change of the motor angular velocity ω is large, for example, when the motor angular velocity ω suddenly decelerates at the rack end, the response of the inertia compensation is improved by using the signal before the low-pass filter. The ability to decelerate inertia can be increased, and the impact force can be reduced.

  As described above, according to the present invention, when the change in the low-pass filter input signal is not large, the noise reduction performance is prioritized, so the trade-off relationship between noise reduction and responsiveness can be relaxed.

  Since the present invention can also be applied to an electric power steering apparatus having a back electromotive force compensation function using a low-pass filter, an example of performing back electromotive force compensation will be described below.

First, back electromotive force compensation will be described with reference to FIG. FIG. 3A shows an actual motor. Since the back electromotive voltage EMF = Ke · ω is a non-linear element, the motor model is a non-linear element. Linearizing this motor model means that if an EMF estimated value (calculated value) is estimated and added to the voltage command value Vref as shown in FIG. And the motor model can be linearized to 1 / (R + s · L). The back electromotive force EMF is expressed as in the following formula 1.
(Equation 1)
EMF = V- (R + s · L) · I

Here, if the back electromotive force EMF is completely compensated, EMF = 0 and the above formula 1 is expressed as the following formula 2.
(Equation 2)
I / V = 1 / (Rn + s · Ln) = Pn
Here, Rn is a constant motor resistance value, Ln is a constant motor inductance value, and Pn is a rated motor model.

The feature of the above formula 2 is that it is a linear form. When the formula 2 is transformed, the following formula 3 is obtained.
(Equation 3)
V = I · (Rn + s · Ln) = I · Pn ⁻¹

When Expression 3 is expressed as a control target, the following Expression 4 is obtained.
(Equation 4)
Vref = Iref · (Rn + s · Ln) = Iref · Pn ⁻¹

Therefore, the voltage command value Vref can be calculated by inputting the steering assist command value Iref, and a first-order lag low-pass filter is inserted in order to remove noise from the input signal. That is, the following formula 5 is established.
(Equation 5)
Vref = Iref · (Rn + s · Ln) / (1 + s · T)
= Iref · Pn ^-1 / (1 + s · T)
Here, T = 1 / 2πfc, T is a time constant of the low-pass filter, and fc is a cutoff frequency.

Based on the above assumptions, a configuration example of feedforward control that compensates for the back electromotive force will be described. The back electromotive force EMF of the brushless motor has a waveform that is a function of an electrical angle (angle) θ and an amplitude that is a function of an angular velocity ω. Become. From this, for example, if the back electromotive voltage waveform having an electrical angle corresponding to 1 [rad / s] is “E1”, the back electromotive voltage EMF is expressed by the following equation (6).
(Equation 6)
EMF = E1 (electrical angle [rad / s]) × electrical angular velocity [rad / s]

If the counter electromotive voltage waveform E1 is prepared in accordance with the unit of the angular velocity ω that is actually used, it can be handled regardless of the unit of the angular velocity ω.

  The control device of the electric power steering apparatus having such a back electromotive force compensation function is as shown in FIG. 4 corresponding to FIG. 9, and the back electromotive force compensation value EMF is inputted by inputting the rotation angle θ and the angular velocity ω. Is provided. The back electromotive force compensation value EMF is added to the voltage command value Ic1 in an adding unit 39D provided at the subsequent stage of the current control unit 34, and the added voltage command value Ic2 is input to the motor winding 35.

  The details of the back electromotive force compensation unit 50 are as shown in FIG. 5. The rotation angle θ is input to the waveform generation unit 51, and the angular velocity ω is input to the contact point b of the low pass filter 52, the subtraction unit 53, and the switching unit 54. Is done. The waveform generation unit 51 generates a waveform W as shown in FIG. 6 according to the rotation angle θ, and the waveform W is input to the multiplication unit 57 to determine the amplitude and sign of the back electromotive voltage EMF.

  Further, the angular velocity ωf filtered for noise removal by the low-pass filter 52 is subtracted and input to the subtractor 53 and also input to the contact a of the switching unit 54. The subtractor 53 obtains a difference ωd (= ω−ωf) between the angular velocity ω before the low-pass filter 52 and the angular velocity ωf after the low-pass filter 52, and obtains an absolute value | ωd | The value | ωd | is input to the acceleration / deceleration state detection unit 56. As shown in FIG. 7, the acceleration / deceleration state detection unit 56 detects the acceleration / deceleration state based on the predetermined angular speeds ω1 and ω2, and switches the contacts a and b of the switching unit 54 by the acceleration / deceleration state signal CS. That is, in the non-acceleration / deceleration state that is not the acceleration / deceleration state, the acceleration / deceleration state signal CS is not output, the switching unit 54 is in the contact point a, the angular velocity ωf is output from the switching unit 54, and the acceleration / deceleration state is detected. Then, the acceleration / deceleration state signal CS is output, the switching unit 54 is switched from the contact point a to b by the acceleration / deceleration state signal CS, and the angular velocity ω that does not pass through the low-pass filter 52 is output from the switching unit 54. The subtraction unit 53, the absolute value conversion unit 55, the acceleration / deceleration state detection unit 56, and the switching unit 54 constitute a determination switching unit.

  The waveform generation unit 51 generates the waveform W with the characteristics of FIG. 6 according to the rotation angle θ, and the multiplication unit 57 outputs the waveform W and the output of the switching unit 54, that is, the angular velocity ω in the acceleration / deceleration state and the angular velocity ωf in the non-acceleration / deceleration state. Multiplication is performed to calculate the back electromotive force EMF whose amplitude and sign are determined. The back electromotive voltage EMF is input to the adder 39D.

  As a result, the motor is controlled in a state in which the back electromotive force EMF, which is a non-linear element, is compensated in advance, so that an electric power steering apparatus with less control error and less torque ripple can be obtained, and acceleration / deceleration that requires responsiveness is required. At the time of steering, the back electromotive force is compensated by the angular velocity ω before the low-pass filter 52, and when the change in steering speed that requires noise removal is small, the back electromotive force is compensated by the angular velocity ωf after the low-pass filter 52. It is possible to increase the reliability by reducing the overcurrent when applied to.

It is a block diagram which shows the structural example of the center response improvement part which concerns on this invention. It is a block diagram which shows the structural example of the inertia compensation part which concerns on this invention. It is a figure for demonstrating back electromotive force compensation. It is a block block diagram which shows an example of the apparatus which has a back electromotive force compensation function which can apply this invention. It is a block diagram which shows the structural example of a back electromotive force compensation part. It is a figure for demonstrating operation | movement of a back electromotive force compensation part. It is a figure for demonstrating operation | movement of a back electromotive force compensation part. It is a figure showing an example of composition of a general electric power steering device. It is a block diagram which shows the structural example of a general control apparatus. It is a block which shows the structural example of a center response improvement part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 2 Column axis | shaft 3 Reduction gear 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 14 Battery 20 Motor 30 Control unit 31 Steering assistance command value calculating part 32 Phase compensation part 33 Center response improvement part 34 Current control part 36A Angle sensor 36B Angular velocity calculation unit 38 Inertia compensation unit 50 Back electromotive force compensation unit 51 Waveform generation unit 52, 332, 382 Low pass filter 54 Switching unit 55 Absolute value conversion unit 56 Acceleration / deceleration state detection unit 331, 381 Difference calculation unit 333, 383 Determination unit 334, 384 Signal switching unit 335, 385 Compensation gain unit

Claims (4)

An electric motor comprising a current command value calculation unit that calculates a current command value based on the steering torque value and the vehicle speed, and a motor drive control unit that controls a motor that applies a steering assist force to the steering mechanism based on the current command value. The control device for the power steering device includes a rack end determination unit that determines whether the rack end is approached in consideration of the rack movement amount and the rack movement speed, and limits the current command value when approaching the rack end. And a controller for an electric power steering device, wherein the motor is electromagnetically braked at a timing when the limited current command value becomes zero. The control device for the electric power steering apparatus according to claim 1, wherein the current command value is gradually limited. The control device for an electric power steering apparatus according to claim 1 or 2, wherein when the electromagnetic brake is applied, the terminals of the motor are short-circuited. 4. The control device for an electric power steering apparatus according to claim 2, wherein the rack end determination unit inputs a steering angle and an angular velocity to determine that the rack end is approaching.

Images