JP2008006919A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good responsiveness even to a sudden steering operation in an electric power steering apparatus that feedback-controls energization of an electric motor based on a deviation between a target current value and an actual current value.
A proportional-integral control unit 41 calculates a q-axis command voltage Vq * based on a q-axis command current ΔIq obtained by subtracting a q-axis actual current value Iq from a corrected q-axis target current value Iq * ′. The proportional integration control unit 42 calculates the d-axis command voltage Vd * based on the d-axis command current ΔId obtained by subtracting the d-axis actual current Id from the corrected d-axis target current Id *. The PI gain calculation unit 50 decreases the control gain (proportional term gain, integral term gain) in the proportional integral control units 41 and 42 as the q axis actual current Iq and d axis actual current Id increase. Set to.
[Selection] Figure 2

Description

  The present invention relates to an electric power steering apparatus including an electric motor for assisting a steering operation of a steering wheel by a driver.

2. Description of the Related Art Conventionally, an electric power steering device for a vehicle in which a steering torque applied to a steering wheel is detected and an assist torque corresponding to the detected steering torque is generated in an electric motor is well known.
For example, in the electric power steering device disclosed in Patent Document 1, a target current value of an electric motor is set based on a steering torque applied to a steering wheel and a vehicle speed, and the motor is detected by the target current value and a current detector. Based on the deviation from the current value (actual current value), the electric motor is feedback controlled so that the deviation becomes zero. The control gain (proportional gain and integral gain) in feedback control is changed based on the target current value. That is, the smaller the target current value, the larger the proportional gain and the integral gain, and the smaller the target current value, the smaller the proportional gain and the integral gain. This attempts to compensate for a response delay when a small current is to flow through the electric motor.
JP2001-1917

  However, in the thing of patent document 1, the responsiveness at the time of steering operation of a steering handle rapidly is bad. In other words, when the steering wheel is steered rapidly, the target current value increases as the steering torque suddenly increases, and the control gain is set to be small accordingly. For this reason, although the deviation between the target current value and the actual current value becomes large, the electric motor current is feedback-controlled based on the control gain set to be small, and the current value can be increased quickly. As a result, the responsiveness deteriorates. Therefore, a good steering feeling cannot be obtained.

  An object of the present invention is to provide an electric power steering device that is responsive to a sudden steering operation.

  In order to achieve the above object, the present invention is characterized by a steering mechanism that steers a steered wheel by steering a steering handle, and a steering assist force that is provided in the steering mechanism and that is provided for steering operation of the steering handle. A target current value calculating means for calculating a target current value for controlling the operation of the electric motor according to a steering operation of the steering handle, and a current value flowing through the electric motor is detected. With respect to the target current value calculated by the actual current value detection means and the target current value calculation means, the current value flowing through the electric motor detected by the actual current value detection means is fed back to energize the electric motor. An electric power steering apparatus including feedback control means for controlling, based on a value of a current flowing through the electric motor detected by the actual current detecting means; In further comprising a control gain changing means for changing the control gain of the feedback control by the feedback control means.

  In this case, the control gain changing means sets the control gain to be smaller as the current value flowing through the electric motor detected by the actual current detecting means is larger, or is applied to the electric motor detected by the actual current detecting means. When the flowing current value is larger than the predetermined current value, the control gain may be set smaller than when the flowing current value is less than the predetermined current value.

  According to the present invention configured as described above, the feedback control means feeds back the actual current value flowing through the electric motor to the target current value, that is, the deviation between the target current value and the actual current value becomes zero. Thus, the energization of the electric motor is controlled. At this time, the control gain changing means changes the control gain of the feedback control based on the value of the current flowing through the electric motor. For example, the control gain is decreased as the value of the current flowing through the electric motor detected by the actual current detecting means increases.

Thereby, at the time of an abrupt steering operation, the control gain is not rapidly reduced, and the responsiveness can be improved. That is, during a sudden steering operation, the target current value increases instantaneously, but the actual current value increases as a control result. Therefore, the control gain set based on this actual current value is It does not decrease as rapidly as the current value changes.
Accordingly, during a sudden steering operation, feedback control can be performed using a large deviation between the target current value and the actual current value and a large control gain, so that the responsiveness is good. Since the control gain is reduced when the actual current value is increased by this feedback control, this time, it is suppressed that the actual current value hunts the target current value.
Further, since the control gain is set to be large under the condition where the actual current value flowing through the electric motor is small, good response can be obtained even in this case.
As a result, the steering feeling is improved.

In changing the control gain, for example, when the current value flowing through the electric motor detected by the actual current detecting means is larger than a predetermined current value, the control gain is set smaller than when the current value is smaller than the predetermined current value. You may do it. In this case, a plurality of predetermined current values for switching the control gain may be set, and the control gain may be switched to a plurality of stages. Note that the target current value calculated by the target current value calculating means is, for example, a steering that works on the steering wheel. It may be calculated based on at least two detection values of a torque detection means for detecting torque and a vehicle speed detection means for detecting vehicle speed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an electric power steering apparatus according to the present invention.

  This electric power steering apparatus for a vehicle includes a steering shaft 12 connected to a steering handle 11 so as to rotate integrally with an upper end thereof, and a pinion gear 13 is connected to a lower end of the shaft 12 so as to rotate integrally. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1, FW2 are steerably connected to both ends of the rack bar 14 via tie rods and knuckle arms (not shown). The left and right front wheels FW1 and FW2 are steered left and right in accordance with the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis.

An electric motor 15 for steering assist is assembled to the rack bar 14. The electric motor 15 is configured by an AC motor that is a three-phase synchronous permanent magnet motor (brushless motor). The rotating shaft of the electric motor 15 is connected to the rack bar 14 via the ball screw mechanism 16 so that power can be transmitted, and assists the steering of the left and right front wheels FW1, FW2 by the rotation.
The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter. The ball screw mechanism 16 reduces the rotation of the electric motor 15 and converts it into a linear motion and transmits it to the rack bar 14. Further, instead of assembling the electric motor 15 to the rack bar 14, the electric motor 15 is assembled to the steering shaft 12, and the rotation of the electric motor 15 is transmitted to the steering shaft 12 via the speed reducer so that the shaft 12 is axially connected. You may comprise so that it may drive around.

Next, an electric control device that controls the operation of the electric motor 15 will be described. The electric control device includes a steering torque sensor 21, a vehicle speed sensor 22, and a rotation angle sensor 23. The steering torque sensor 21 is assembled to the steering shaft 12 and detects the steering torque T acting on the steering shaft 12 by the turning operation of the steering handle 11. The steering torque T represents the magnitude of the steering torque when the steering handle 11 is steered in the right direction and the left direction by positive and negative values, respectively.
Further, instead of assembling the steering torque sensor 21 to the steering shaft 12, the steering torque T may be detected from the amount of distortion in the axial direction of the rack bar 14 by being assembled to the rack bar 14. The vehicle speed sensor 22 detects the vehicle speed V and outputs a detection signal representing the vehicle speed V.

  The rotation angle sensor 23 is composed of an encoder incorporated in the electric motor 15, and is a two-phase pulse train signal having a phase different by π / 2 according to the rotation of the rotor of the electric motor 15 and a zero representing the reference rotation position. Outputs a phase pulse train signal. The detection signal from the rotation angle sensor 23 is used to calculate the rotation angle θ and the angular velocity ω of the electric motor 15. On the other hand, since the rotation angle θ of the electric motor 15 is proportional to the steering angle of the steering handle 11, the rotation angle θ is commonly used as the steering angle of the steering handle 11 in this specification.

  In addition, since the angular velocity ω of the electric motor 15 is proportional to the steering angular velocity of the steering handle 11, the angular velocity ω is also commonly used as the steering angular velocity of the steering handle 11 in this specification. Instead of using the detection output of the rotation angle sensor 23, a sensor for detecting the rotation angle of the steering shaft 12 or the axial position of the rack bar 14 is prepared, and the rotation angle and displacement detected by the sensor are prepared. The amount may be used as the steering angle of the steering handle 11 and the differential value thereof may be used as the steering angular velocity of the steering handle 11. The steering angle θ and the steering angular velocity ω thus detected also represent the right and left steering angles and steering angular velocities of the steering handle 11 based on positive and negative values.

These steering torque sensor 21, vehicle speed sensor 22 and rotation angle sensor 23 are connected to the electronic control unit 30. The electronic control unit 30 includes a microcomputer including a CPU, ROM, RAM, and the like as main components, and also includes a drive control circuit for the electric motor 15.
Next, the electronic control unit 30 will be described in detail. FIG. 2 is an overall block diagram of the electronic control unit 30 including functional blocks representing the functions of the microcomputer realized by executing the program.
The electronic control unit 30 controls the rotation of the electric motor 15 by vector control described in a two-phase rotating magnetic flux coordinate system in which the rotation direction of the electric motor 15 is the q axis and the direction orthogonal to the rotation direction is the d axis. . In addition, regarding the q-axis and the d-axis, when the expression method is changed, the d-axis is a field direction by the permanent magnet of the electric motor 15 and the q-axis is a direction orthogonal thereto.

  The electronic control unit 30 includes a basic assist force calculation unit 31 and a compensation value calculation unit 32. The basic assist force calculation unit 31 has a basic assist force table that stores a basic assist force Tas that changes as shown in the characteristic graph of FIG. 3 according to the steering torque T and the vehicle speed V. The basic assist force calculation unit 31 inputs the steering torque T from the steering torque sensor 21 and the vehicle speed V from the vehicle speed sensor 22, and calculates the basic assist force Tas by referring to the basic assist force table. In this case, the basic assist force Tas increases as the steering torque T increases and decreases as the vehicle speed V increases.

  The characteristic graph of FIG. 3 shows only the relationship between the positive region, that is, the steering torque T in the right direction and the basic assist force Tas, but the negative region, that is, the left direction steering torque T and the basic assist force Tas, The characteristic graph of FIG. 3 is moved to a point-symmetrical position around the origin. In this embodiment, the basic assist force Tas is calculated using the basic assist force table. However, instead of the basic assist force table, a basic assist force Tas that changes according to the steering torque T and the vehicle speed V is defined. Alternatively, the basic assist force Tas may be calculated using the same function.

  The compensation value calculation unit 32, together with the vehicle speed V, a rotation angle θ of an electric motor 15 described later (corresponding to a steering angle θ of the steering handle 11) and an angular velocity ω of the electric motor 15 (corresponding to a steering angular velocity ω of the steering handle 11). To calculate a compensation value Trt for the basic assist force Tas. That is, the compensation value calculation unit 32 basically responds to the return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θ and the rotation of the steering shaft 12 that increases in proportion to the steering angular velocity ω. The sum of the return torque corresponding to the resistance force is calculated as the compensation value Trt. The compensation value Trt increases as the vehicle speed V increases. The compensation value Trt may be calculated by adding signals from other various sensors.

  The calculated basic assist force Tas and compensation value Trt are input to the calculation unit 33. The calculation unit 33 adds the basic assist force Tas and the compensation value Trt, and supplies the addition result to the q-axis target current calculation unit 34 as the target command torque T *. The q-axis target current calculation unit 34 calculates a q-axis target current Iq * that is proportional to the target command torque T *. The q-axis target current Iq * is a q-axis component current in vector control described in the two-phase rotating magnetic flux coordinate system, and controls the magnitude of the rotational torque generated by the electric motor 15.

  The electronic control unit 30 includes a field-weakening control parameter calculation unit 35 related to field-weakening control for increasing the efficiency and reducing the size and output of the electric motor 15. The field weakening control parameter calculation unit 35 inputs, in detail, an angular velocity ω of the electric motor 15, which will be described later, a q-axis command voltage Vq * ′ for the electric motor 15, and a q-axis actual current Iq of the electric motor 15, and first to third parameters. Referring to the table, first to third parameters Cw, Cq, Ci corresponding to the angular velocity ω, q-axis command voltage Vq * ′, and q-axis actual current Iq are calculated. These first to third parameters Cw, Cq, and Ci are supplied to the d-axis target current calculation unit 36. The d-axis target current calculator 36 multiplies the first to third parameters Cw, Cq, and Ci by a positive coefficient k to calculate a d-axis target current Id * (= k · Cw · Cq · Ci). This d-axis target current Id * is a d-axis component current in vector control described in the two-phase rotating magnetic flux coordinate system, and is used to weaken the field of the electric motor 15.

  Next, the first to third parameters Cw, Cq, and Ci will be described. As shown in the characteristic graph of FIG. 4, the first parameter table shows “0” when the angular velocity ω of the electric motor 15 is small, and shows a substantially constant positive value when the angular velocity ω is large. Is remembered. In other words, the first parameter Cw indicating a value that increases as the angular velocity ω increases is stored. Therefore, the first parameter Cw determined according to this characteristic means that the field-weakening current is increased in a region where the rotational speed of the electric motor 15 is large. Change to characteristics. Further, the first parameter Cw prevents useless field weakening current from flowing when the rotation speed of the electric motor 15 is low, that is, when the rotation speed of the steering handle 11 is low.

  As shown in the characteristic graph of FIG. 5, the second parameter table indicates “0” when the q-axis command voltage Vq * ′ of the electric motor 15 is small, and is substantially constant when the q-axis command voltage Vq * ′ is large. The second parameter Cq indicating the positive value of is stored. In other words, the second parameter Cq indicating a value that increases as the q-axis command voltage Vq * ′ increases is stored. The large q-axis command voltage Vq means that the q-axis command current ΔIq, which will be described in detail later, is large. This means that the deviation from Iq is large, and the field weakening current of the electric motor 15 increases as the deviation increases. As a result, the second parameter Cq increases the rotational speed of the electric motor 15 by performing field-weakening control when the steering handle 11 is slowly and smallly rotated while the vehicle is running, and the deviation is large. Prevents the field-weakening current from flowing when it is small.

  As shown in the characteristic graph of FIG. 6, the third parameter table shows a substantially constant positive value in a portion where the q-axis actual current Iq is small, and “0” in a portion where the q-axis actual current Iq is large. The parameter Ci is stored. In other words, the first parameter Ci indicating a value that decreases as the q-axis actual current Iq increases is stored. The third parameter Ci is the steering torque of the steering handle 11 when the steering assist force by the electric motor 15 is controlled to decrease when the steering handle 11 is rotated faster while the angular velocity ω of the electric motor 15 is large. To avoid increasing. In the present embodiment, the first to third parameters Cw, Cq, and Ci are calculated using the first to third parameter tables. However, instead of these tables, the angular velocity ω, q-axis command is calculated. Functions that respectively define first to third parameters Cw, Cq, and Ci that change according to the voltage Vq * ′ and the q-axis actual current Iq are prepared, and the first to third parameters Cw, Cq and Ci may be calculated.

The calculated q-axis target current Iq * and d-axis target current Id * are supplied to the q-axis target current correction calculation unit 37.
The q-axis target current correction calculation unit 37 receives the q-axis target current Iq * from the q-axis target current calculation unit 34 and the d-axis target current Id * from the d-axis target current calculation unit 36. Then, the q-axis target current correction calculation unit 37 calculates the correction coefficient α corresponding to the d-axis target current Id * with reference to the correction coefficient table shown in FIG. 7, and corrects the q-axis target current Iq *. By dividing by the coefficient α, the corrected q-axis target current Iq * ′ obtained by correcting the q-axis target current Iq * is calculated (Iq * ′ = Iq * / α), and the corrected q-axis target current which is the calculation result is calculated. Iq * ′ is output to the calculation unit 38.
This correction coefficient table is provided in the q-axis target current correction calculation unit 37, and stores a positive correction coefficient α that decreases as the d-axis target current Id * increases.
As a result, the corrected q-axis target current Iq * ′ indicates a value obtained by correcting the q-axis target current Iq * so as to increase as the d-axis target current Id * increases.
In this embodiment, the correction coefficient α is calculated using the correction coefficient table. However, a function that defines a correction coefficient α that changes according to the d-axis target current Id * is prepared instead of the correction coefficient table. In addition, the correction coefficient α may be calculated using the same function.

  The calculation unit 38 subtracts the q-axis actual current Iq from the corrected q-axis target current Iq * ′, and supplies the subtraction result to the proportional-integral control unit (PI control unit) 41 as the q-axis command current ΔIq. The calculation unit 39 subtracts the d-axis actual current Id from the d-axis target current Id * and supplies the subtraction result to the proportional-integral control unit (PI control unit) 42 as the d-axis command current ΔId. The proportional-integral control unit 41 and the proportional-integral control unit 42 correct the q-axis actual current Iq and the d-axis actual current Id based on the q-axis command current ΔIq and the d-axis command current ΔId, and correct the q-axis target current Iq * ′ and d. The q-axis command voltage Vq * and the d-axis command voltage Vd * are calculated so as to follow the target shaft current Id *. For example, the proportional-integral control units 41 and 42 calculate the q-axis command voltage Vq * and the d-axis command voltage Vd * according to the following proportional-integral arithmetic expressions (1) and (2).

The control gains Kpq, Kiq, Kpd, and Kid in the arithmetic expressions (1) and (2) calculated by the proportional integration control units 41 and 42 are set by the PI gain calculation unit 50. The PI gain calculation unit 50 inputs a q-axis actual current Iq and a d-axis actual current Id representing an actual current value flowing through the electric motor 15 from a three-phase / two-phase coordinate conversion unit 53 described later, and this q-axis actual current Control gains Kpq, Kiq, Kpd, and Kid are calculated by referring to the control gain table based on the current Iq and the d-axis actual current Id.
8 to 11 show control gain tables stored in the PI gain calculation unit 50. FIG.

The control gain Kpq represents the control gain of the proportional term of the calculation formula (1) for calculating the q-axis command voltage Vq *, and is set to a value corresponding to the q-axis actual current Iq by the control gain table shown in FIG. The In the present embodiment, the control gain Kpq is set to a smaller value as the q-axis actual current Iq increases.
The control gain Kiq represents the control gain of the integral term of the calculation formula (1) for calculating the q-axis command voltage Vq *, and is set to a value corresponding to the q-axis actual current Iq by the control gain table shown in FIG. The Similar to the control gain Kpq, the control gain Kiq is set to a smaller value as the q-axis actual current Iq increases.

Further, the control gain Kpd represents the control gain of the proportional term of the calculation formula (2) for calculating the d-axis command voltage Vd *, and is set to a value corresponding to the d-axis actual current Id by the control gain table shown in FIG. Is set. In the present embodiment, the control gain Kpd is set to a smaller value as the d-axis actual current Id increases.
The control gain Kid represents the control gain of the integral term of the calculation formula (2) for calculating the d-axis command voltage Vd *, and is set to a value corresponding to the d-axis actual current Id by the control gain table shown in FIG. The Similar to the control gain Kpd, the control gain Kid is set to a smaller value as the d-axis actual current Id increases.

  The actual currents Id, Iq and the target currents Iq * ′, Iq *, Id * on the q-axis and the d-axis represent current values that specify the rotation direction of the motor 15 with a positive / negative sign, but this control gain Kpq , Kiq, Kpd, and Kid are calculated based on their magnitudes (absolute values).

  In this embodiment, the control gains Kpq, Kiq, Kpd, and Kid are calculated using the control gain table. Instead of the control gain table, the q-axis actual current Iq and the d-axis actual current Id are calculated. A function defining the values of the control gains Kpq, Kiq, Kpd, and Kid that change in response may be prepared, and the control gains Kpq, Kiq, Kpd, and Kid may be calculated using this function.

The q-axis command voltage Vq * and the d-axis command voltage Vd * calculated by the proportional integration control unit 41 and the proportional integration control unit 42 are corrected by the non-interference correction value calculation unit 43 and the calculation units 44 and 45 to be q-axis corrected. The command voltage Vq * and the d-axis correction command voltage Vd * ′ are supplied to the two-phase / three-phase coordinate conversion unit 46. The non-interference correction value calculation unit 43 performs non-interference correction for the q-axis command voltage Vq * and the d-axis command voltage Vd * based on the q-axis actual current Iq, the d-axis actual current Id, and the angular velocity ω of the rotor. The values -ω · (φa + La · Id) and ω · La · Iq are calculated. The inductance La and the magnetic flux φa are predetermined constants.
The calculation units 44 and 45 subtract the non-interference correction values −ω · (φa + La · Id) and ω · La · Iq from the q-axis command voltage Vq * and the d-axis command voltage Vd *, respectively, to obtain the q-axis correction command voltage. Vq * ′ (= Vq * + ω · (φa + La · Id)) and d-axis correction command voltage Vd * ′ (= Vd * −ω · La · Iq) are calculated.

  The two-phase / three-phase coordinate conversion unit 46 converts the q-axis correction command voltage Vq * ′ and the d-axis correction command voltage Vd * ′ into the three-phase command voltages Vu *, Vv *, Vw * and performs the conversion 3 The phase command voltages Vu *, Vv *, Vw * are supplied to the PWM voltage generator 47. The PWM voltage generator 47 outputs PWM control voltage signals UU, VU, WU corresponding to the three-phase command voltages Vu *, Vv *, Vw * to the inverter circuit 48. The inverter circuit 48 generates three-phase excitation voltage signals Vu, Vv, Vw corresponding to the PWM control voltage signals UU, VU, WU, and generates the three-phase excitation voltage signals Vu, Vv, Vw. Are supplied to the electric motors 15 respectively.

  Current sensors 51 and 52 are provided in two of the three-phase excitation current paths, and each of the current sensors 51 and 52 is an excitation of two of the three-phase excitation currents Iu, Iv, and Iw for the electric motor 15. The currents Iu and Iw are detected and output to the three-phase / two-phase coordinate conversion unit 53. The three-phase / two-phase coordinate conversion unit 53 is also supplied with the excitation current Iv calculated by the calculation unit 54 based on the actual currents Iu and Iw. The three-phase / two-phase coordinate conversion unit 53 converts these three-phase actual currents Iu, Iv, Iw into two-phase actual currents Id, Iq. The two-phase actual current values Id and Iq are supplied to the calculation units 38 and 39, the PI gain calculation unit 50, and the non-interference correction value calculation unit 43. The two-phase actual current value Iq is also supplied to the field weakening control parameter calculation unit 35.

  Further, the two-phase pulse train signal and the zero-phase pulse train signal from the rotation angle sensor 23 are continuously supplied to the electrical angle converter 55 at a predetermined sampling period. The electrical angle conversion unit 55 calculates an electrical angle of the rotor of the electric motor 15 with respect to the stator based on each pulse train signal and supplies the calculated electrical angle to the angular velocity conversion unit 56. The angular velocity conversion unit 56 calculates the angular velocity of the rotor relative to the stator by differentiating the electrical angle. These electric angles and angular velocities correspond to the rotation angle (steering angle of the steering handle 11) θ and the angular velocity (steering angular velocity of the steering handle 11) ω of the electric motor 15, and these rotation angles θ and angular velocity ω are described above. The compensation value calculation unit 32, the field weakening control parameter calculation unit 35, the 2-phase / 3-phase coordinate conversion unit 46, the 3-phase / 2-phase coordinate conversion unit 53, and the like are also used.

  Next, the operation of the embodiment configured as described above will be described. When the driver turns the steering handle 11, the turning operation is transmitted to the rack bar 14 via the steering shaft 12 and the pinion gear 13, and the left and right front wheels FW1 and FW2 are moved by the axial displacement of the rack bar 14. Steered. At the same time, the steering torque sensor 21 detects the steering torque T applied to the steering shaft 12, and the electric motor 15 is servo-controlled by the electronic control unit 30 so that the rack bar 14 is driven with the assist torque corresponding to the steering torque T. Since it is driven, the left and right front wheels FW1, FW2 are steered while being assisted by the driving force of the electric motor 15.

  In the servo control by the electronic control unit 30, the basic assist force calculation unit 31, the compensation value calculation unit 32, and the calculation unit 33 perform the detected steering torque T, the vehicle speed V, the rotation angle of the electric motor 15 (the steering of the steering handle 11). Angle) θ and the angular velocity of the electric motor 15 (steering angular velocity of the steering wheel 11) ω, the target command torque T * is calculated, and the q-axis target current calculation unit 34 calculates the q-axis based on the target command torque T *. A target current Iq * is calculated. Further, the d-axis target current calculation unit 36 calculates the first to third parameters Cw calculated by the field weakening control parameter calculation unit 35 based on the angular velocity ω of the electric motor 15, the q-axis command voltage Vq, and the q-axis actual current Iq. , Cq, and Ci, the d-axis target current Iq * is calculated.

  The calculation units 38 and 39, the proportional integration control units 41 and 42, the two-phase / three-phase coordinate conversion unit 46, the PWM voltage generation unit 47, and the inverter circuit 48 are converted into the current sensors 51 and 52, the three-phase / two-phase coordinate conversion. The electric motor 15 is controlled using the d-axis actual current Id and the q-axis actual current Iq fed back by the unit 53 and the calculation unit 54. In this case, the PI gain calculation unit 50 sets the control gains Kpq, Kiq, Kpd, and Kid of the proportional-plus-integral control units 41 and 42 based on the d-axis actual current Id and the q-axis actual current Iq. Further, the non-interference correction value calculation unit 43 and the calculation units 44 and 45 are used to cancel the velocity electromotive force that interferes between the d and q axes, and the q axis command voltages Vq * and d from the proportional integration control units 41 and 42, respectively. The axis command voltage Vd * is corrected.

  According to the electric power steering apparatus of the present embodiment described above, the proportional integral control units 41 and 42 are electrically driven based on the deviations ΔIq and ΔId between the final target currents Iq * ′ and Id * and the actual currents Id and Iq. The command voltages Vq * and Vd * of the motor 15 are calculated, and the control gains Kpq, Kiq, Kpd, and Kid used for this proportional integration calculation become smaller as the actual currents Id and Iq increase by the PI gain calculation unit 50. Set as follows. Accordingly, the responsiveness when the steering handle 11 is suddenly turned is improved.

  That is, during a sudden steering operation, the target currents Iq * ′ and Id * increase suddenly due to a sudden increase in the steering torque T, but the actual currents Id and Iq increase as a control result. , Iq, the control gains Kpq, Kiq, Kpd, Kid set based on the magnitude of Iq do not decrease rapidly. Therefore, the electric motor 15 is feedback-controlled using the large deviations ΔIq and ΔId between the target currents Iq * ′ and Id * and the actual currents Id and Iq and the large control gains Kpq, Kiq, Kpd, and Kid. High nature.

When the actual currents Id and Iq are increased by this feedback control, the control gains Kpq, Kiq, Kpd, and Kid are reduced by the PI gain calculation unit 50 accordingly. Overshoots with respect to Iq * ′ and Id * and downshoots associated therewith are suppressed, and hunting can be prevented. Further, by preventing hunting, it is possible to prevent the generation of abnormal noise and vibration.
Furthermore, in a situation where the actual currents Id and Iq flowing through the electric motor 15 are small, the control gains Kpq, Kiq, Kpd, and Kid are set large, so that responsiveness can be improved.
As a result, a good steering feeling can be obtained for the driver.

  In the present embodiment, the rotation of the electric motor 15 is controlled by vector control described in a two-phase rotating magnetic flux coordinate system in which the rotation direction of the electric motor 15 is the q axis and the direction orthogonal to the rotation direction is the d axis. Be controlled. In this vector control, the d-axis target current calculation unit 36 calculates the d-axis target current Id * based on the first to third parameters Cw, Cq, and Ci calculated by the field weakening field control parameter calculation unit 35. Thus, field weakening control of the d-axis current of the electric motor 15 is performed according to the angular velocity ω, the q-axis command voltage Vq, and the q-axis actual current Iq. Therefore, efficiency and electric power of the electric motor 15 are expected to be increased by the field weakening control, and a useless field weakening current is prevented from flowing.

  The q-axis target current Iq * calculated by the q-axis target current calculation unit 34 is corrected by the q-axis target current correction calculation unit 37 according to the d-axis target current Id *. In the correction of the q-axis target current Iq *, the d-axis target current Id * or the d-axis actual current Id is increased, so that the q-axis target current Iq * is corrected. Therefore, according to the above-described embodiment, the output assist torque of the electric motor 15 is ensured even if the field weakening control of the electric motor is performed to increase the efficiency of the electric motor 15 and to increase the size and output, so that the steering assist force is insufficient. It is possible to avoid such a situation, and the deterioration of the steering feeling of the driver can be avoided.

  Furthermore, the present invention is not limited to the above-described embodiment and its modifications, and various modifications can be employed within the scope of the present invention.

For example, in the above embodiment, the current feedback control of the electric motor 15 is performed by the PI control, but the P control using only the proportional term by omitting the integral term and the PID control including the differential term are adopted. May be. Further, the adjustment of the control gain in the PI control may be only the control gain of the proportional term or only the control gain of the integral term, as long as it adjusts at least one control gain.
In this embodiment, the control gain is changed according to the actual current for the d-axis current as well as the q-axis current that generates torque. However, the control gain is not changed for the d-axis current. May be.

  Furthermore, in this embodiment, the control gains Kpq, Kiq, Kpd, and Kid are set to smaller values as the current values Iq and Id flowing through the electric motor 15 are larger. For example, as shown in FIG. 12 or FIG. In addition, when the actual current values Iq and Id are larger than the predetermined current value, the control gains Kpq, Kiq, Kpd, and Kid may be set smaller than when the actual current values Iq and Id are smaller than the predetermined current value. Further, as shown in FIG. 14 or FIG. 15, even if a plurality of predetermined current values for switching the control gains Kpq, Kiq, Kpd, and Kid are set and the control gains Kpq, Kiq, Kpd, and Kid are switched and set in a plurality of stages, Good.

  The q-axis target current calculation unit 34, the q-axis target current correction calculation unit 37, and the d-axis target current calculation unit 36 in the present embodiment correspond to the target current value calculation unit of the present invention, and the current sensor 51 in the present embodiment. 52, the arithmetic unit 54, and the three-phase / two-phase coordinate conversion unit 53 correspond to the actual current value detecting means of the present invention, and the arithmetic units 38 and 39 and the proportional-plus-integral control units 41 and 42 in the present embodiment are the present invention. It corresponds to feedback control means, and the PI gain calculation unit 50 in this embodiment corresponds to control gain changing means of the present invention.

1 is a schematic view of an electric power steering apparatus according to an embodiment of the present invention. It is a block diagram which shows the detail of the electronic control unit of FIG. It is a characteristic graph which shows the relationship between steering torque and basic assist force. It is a characteristic graph which shows the relationship between the angular velocity of an electric motor, and the 1st parameter Cw in the field-weakening control parameter. It is a characteristic graph which shows the relationship between the q-axis command voltage of an electric motor, and the 2nd parameter Cq in a field-weakening control parameter. It is a characteristic graph which shows the relationship between the q-axis real current of an electric motor, and the 3rd parameter Ci in the field-weakening control parameter. It is a characteristic graph which shows the relationship between d-axis target electric current Id * and a correction coefficient. It is a characteristic graph which shows the relationship between the q-axis actual electric current Iq of an electric motor, and control gain Kpq. It is a characteristic graph which shows the relationship between the q-axis actual electric current Iq of an electric motor, and the control gain Kiq. It is a characteristic graph which shows the relationship between the d-axis actual electric current Id of an electric motor, and control gain Kpd. It is a characteristic graph which shows the relationship between the d-axis actual electric current Id of an electric motor, and control gain Kid. It is a characteristic graph which shows the relationship between the q-axis actual electric current Iq of the electric motor as a modification, and control gain Kpq, Kiq. It is a characteristic graph which shows the relationship between the d-axis actual electric current Id of the electric motor as a modification, and control gain Kpd, Kid. It is a characteristic graph which shows the relationship between the q-axis actual electric current Iq of the electric motor as another modification, and the control gains Kpq and Kiq. It is a characteristic graph which shows the relationship between the d-axis actual current Id of the electric motor as another modification, and control gain Kpd, Kid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Steering handle, 15 ... Electric motor, 21 ... Steering torque sensor, 22 ... Vehicle speed sensor, 23 ... Rotation angle sensor, 30 ... Electronic control unit, 31 ... Basic assist force calculating part, 34 ... q-axis target current calculating part, 36 ... d-axis target current calculation unit, 37 ... q-axis target current correction calculation unit, 38, 39 ... calculation unit, 41, 42 ... proportional-integral control unit, inverter 48, 50 ... PI gain calculation unit, 51, 52 ... current Sensor, Kpq, Kiq, Kpd, Kid ... control gain, FW1, FW2 ... left and right front wheels (steered wheels).

Claims (2)

A steering mechanism that steers the steered wheels by steering the steering wheel;
An electric motor that is provided in the steering mechanism and generates a steering assist force with respect to a steering operation of the steering handle;
Target current value calculating means for calculating a target current value for controlling the operation of the electric motor in accordance with a steering operation of the steering wheel;
An actual current value detecting means for detecting a current value flowing through the electric motor;
Feedback control means for feeding back the current value flowing through the electric motor detected by the actual current value detecting means to control the energization of the electric motor with respect to the target current value calculated by the target current value calculating means; In the electric power steering apparatus provided,
An electric power steering apparatus comprising control gain changing means for changing a control gain of feedback control by the feedback control means based on a value of a current flowing through the electric motor detected by the actual current detecting means. The control gain changing means sets the control gain to be smaller as the current value flowing through the electric motor detected by the actual current detecting means is larger, or the current value flowing through the electric motor detected by the actual current detecting means. 2. The electric power steering according to claim 1, wherein when the value is larger than a predetermined current value, the control gain is set smaller than when the current is less than the predetermined current value.

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