JP2009044913A - Motor device and electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor capable of reducing cogging torque, while suppressing complication of the structure and enlargement of the outer shape. <P>SOLUTION: In a motor control circuit 40, a correction map is stored which stores a rotation angle of the motor 5 and the amplitude of the cogging torque generated in the motor 5, and a correction value, corresponding to an amplitude value read out from the correction map is calculated. Then, the cogging torque of a predetermined order is reduced, by adding the correction value to a current command value Iq*. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a motor device and an electric power steering device.

In recent years, electric power steering devices (EPS) using a motor as a drive source have been widely adopted as vehicle power steering devices. By the way, the output torque of the motor varies due to cogging torque or torque ripple caused by distortion of the induced voltage waveform generated in the winding coil. Moreover, in EPS, such fluctuations in output torque are directly reflected in the steering feeling. For this reason, many countermeasures for reducing the cogging torque have been proposed for motors used in EPS in order to improve the steering feeling. For example, Patent Document 1 discloses a rotating electrical machine including a plurality of cogging correctors. The cogging corrector is moved in the axial direction by adjustment after assembling the rotating electric machine, thereby removing the cogging with variations.
JP 2006-060879 A (paragraph [0017], FIG. 2)

  However, the rotating electric machine has a problem that the structure is complicated and the cost is increased. In addition, the rotating electrical machine has to be firmly fixed to prevent the adjusted cogging corrector from being displaced, and there is a problem in that the outer shape of the blanket or frame is increased. When the cogging corrector is displaced, there is a problem that the steering feeling at the time of low-speed steering of the EPS is deteriorated due to the fluctuation of the output torque of the motor due to the cogging torque and torque ripple generated thereby.

  An object of the present invention is to provide a motor capable of reducing the cogging torque while suppressing the complexity of the structure and the enlargement of the outer shape, and an electric power steering device using the motor.

  In order to solve the above-mentioned problems, the invention of claim 1 is a motor device comprising a brushless motor configured to have 10 poles and 12 slots or 14 poles and 12 slots, and a motor control circuit for controlling the brushless motor. The motor control circuit includes a storage unit that stores the rotation characteristics of the brushless motor, a current command value calculation unit that calculates a current command value for controlling the brushless motor, and a value stored in the storage unit. In response, a correction value calculation unit that calculates a correction value for correcting the rotation characteristic with an opposite phase, an addition unit that calculates the correction command value by adding the correction value to the current command value, and the correction command And a voltage supply unit that supplies a drive voltage to the motor device based on the value.

  According to this configuration, it is not necessary to provide a member for mechanically correcting the cogging torque in the motor device, and the cogging torque can be reduced without changing the mechanical structure of the motor device.

  According to a second aspect of the present invention, in the motor device according to the first aspect, the stator of the motor has a plurality of teeth protruding inward in the radial direction, and a distal end portion of each tooth along the circumferential direction. The protruding portion is formed, and the value of the ratio of the spacing between the teeth tips adjacent in the circumferential direction to the circumferential length per tooth is within a predetermined range determined by the characteristics of the cogging torque and the torque ripple. It is formed as follows.

  According to this configuration, when the ratio of the length between the tips of the protrusions (slot open) to the circumferential length per tooth (slot open ratio) is changed, the characteristic values of the cogging torque and the torque ripple are accordingly changed. Change. Therefore, by setting the slot open ratio within a predetermined range according to the required characteristics, it is possible to reduce the torque ripple and suppress the increase of the cogging torque of the predetermined order component, and to realize a motor device with a small torque ripple and cogging torque. .

  According to a third aspect of the present invention, in the motor device according to the second aspect, the cogging torque is a cogging torque of an order that is greatly affected by the change of the ratio, and the cogging torque of the order is a value of the ratio. The torque ripple decreases in inverse proportion to the value of the ratio, and the predetermined range is such that the order cogging torque is smaller than a first predetermined value, In addition, the torque ripple is a range set to be smaller than the second predetermined value.

  Increasing the ratio of the length between the tips of the protrusions (slot open) to the circumferential length per tooth (slot open ratio) increases the torque ripple and cogging of the order component that is greatly affected by changes in the slot open ratio When the torque is increased and the slot open ratio is reduced, the torque ripple is increased and the cogging torque of the order component is decreased. Therefore, by setting the slot open ratio to be a predetermined range set to be smaller than the first predetermined value set for the cogging torque and smaller than the second predetermined value set for the torque ripple. Thus, the torque ripple is reduced to suppress an increase in cogging torque of a predetermined order component, and a motor device with a small torque ripple and cogging torque can be realized.

According to a fourth aspect of the present invention, there is provided an electric power steering apparatus including the motor device according to any one of the first to third aspects.
According to this configuration, the cogging torque in the motor device is reduced, and vibration due to the cogging torque is not transmitted to the steering, so that the steering feeling can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the motor which can aim at reduction of a cogging torque, suppressing the complication of a structure and the enlargement of an external shape, and the electric power steering apparatus using the motor can be provided.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
Hereinafter, an embodiment in which the present invention is embodied in a coaxial rack assist type electric power steering apparatus (EPS) will be described with reference to the drawings.

  As shown in FIG. 1, the housing 2 of the EPS 1 is formed in a substantially cylindrical shape. The tip of a pinion shaft 3 that is rotated by a steering operation is inserted into the housing 2. In addition, a rack shaft 4 meshed with the pinion shaft 3 is supported by the housing 2 so as to be capable of reciprocating along the axial direction. The rack shaft 4 is penetrated along the axial direction of the housing 2. One end of the pinion shaft 3 is connected to a steering wheel (not shown) via a steering shaft (not shown) or the like. Then, the pinion shaft 3 rotates in accordance with the steering operation, and the rotational motion is converted into the reciprocating motion of the rack shaft 4, whereby the steering angle of the steered wheels (not shown) is changed.

  Further, a motor (motor device) 5 is arranged in the housing 2 coaxially with the rack shaft 4. In the present embodiment, the motor 5 is a rotating field motor (brushless motor) in which a field permanent magnet is provided on the rotor side. The EPS 1 applies an assist force to the reciprocating motion of the rack shaft 4 by driving and controlling the motor 5 in accordance with the steering operation.

  As shown in FIG. 2, the stator 11 of the motor 5 is formed in an annular shape and is fixed to the inner peripheral surface 2 a of the housing 2. The stator core 12 of the stator 11 has a cylindrical portion 13 formed in an annular shape, and a plurality of teeth 14 projecting from the cylindrical portion 13 inward in the radial direction. The teeth 14 are formed at equiangular intervals in the circumferential direction. A winding coil 17 is wound around each tooth 14 via an insulator 15. The stator core 12 includes a plurality of (in this embodiment, 12) divided cores 30 in which the cylindrical portion 13 is divided in the circumferential direction for each tooth 14. The stator core 12 is fixed to the housing 2 by so-called shrink fitting, in which the split cores 30 arranged in an annular shape are inserted into the heated housing 2.

  A rotor 21 is disposed inside the stator 11. The motor shaft 22 of the rotor 21 is formed in a hollow cylindrical shape, and the outer peripheral surface thereof is a field magnet having a plurality of magnetic poles (10 poles in the present embodiment) in the circumferential direction so as to face the tip of the tooth 14. A ring magnet 23 is externally fitted. As shown in FIG. 1, the rotor 21 is rotatably supported by the housing 2 by supporting the vicinity of both ends of the motor shaft 22 by bearings 6 a and 6 b. A rotating magnetic field is formed around the motor shaft 22 (ring magnet 23) by the three-phase alternating current supplied to the winding coil 17. The motor shaft 22 rotates due to the relationship between the field magnetic flux formed by the ring magnet 23 and the rotating magnetic field of the stator 11.

  As shown in FIG. 1, the rack shaft 4 is inserted into the motor shaft 22. A screw portion 4 a is formed on the outer periphery of the rack shaft 4, and a nut portion 22 a corresponding to the screw portion 4 a is formed on the inner periphery of the motor shaft 22. A plurality of steel balls 7 are inserted between the screw portion 4a and the nut portion 22a, and the ball screw mechanism 8 is configured by the screw portion 4a, the nut portion 22a, and the steel ball 7. The ball screw mechanism 8 converts the rotational motion of the motor shaft 22 into the reciprocating motion of the rack shaft 4 and applies assist force to the steering system.

  As shown in FIG. 3, each tooth 14 is formed so as to extend along the axial direction, and projecting portions 31a and 31b extending along the circumferential direction are formed on both sides in the circumferential direction of the radially inner end thereof. Furthermore, the inner peripheral side end of each tooth 14 is curved and formed in an arc shape along a circle centered on the central axis of the stator 11. A circle formed by connecting the inner circumferential side ends of the teeth 14 is referred to as an inner circumferential circle. Between the adjacent divided cores 30, a slot 32 extending in the axial direction is formed by two teeth 14 adjacent to each other in the circumferential direction and the cylindrical portion 13. That is, the motor 5 is a so-called 10-pole 12-slot motor having 12 slots 32.

  The length (arc length) along the circumferential direction from the tip of the protruding portion 31a to the tip of the protruding portion 31b is the length of the inner circle per slot 32 (between the circumferential centers of adjacent teeth 14). It is set shorter than (arc length). Accordingly, a gap 33 is formed between the protruding portions 31a and 31b formed in the adjacent teeth 14. The gap along the circumferential direction is called a slot open, and the ratio of the slot open length to the length of the inner circumferential circle per slot 32 is called the slot open ratio. This slot open ratio α is defined as D1 as the length of the inner circumference per slot 32 and D2 as the slot open length.

により求められる。

It is calculated by.

  In the present embodiment, the shape of the stator 11, particularly the slot open length, is determined by the cogging torque and torque ripple of the motor 5. When the physique of the motor 5, that is, the inner circumference of the stator 11 is made constant and the slot open length is changed, it has been experimentally obtained that the cogging torque and the torque ripple change according to the length. Furthermore, it was found that the predetermined order component of the cogging torque exhibited characteristics opposite to the torque ripple.

  FIG. 5 shows the relationship between the cogging torque and the torque ripple with respect to the slot open ratio. In FIG. 5, the slot open ratio α shown on the horizontal axis increases toward the right side, that is, the slot open length is large. The main components of the cogging torque that affect the operation of the motor 5 are a 10th-order component, a 12th-order component, and a 60th-order component, and the torque ripple is a 30th-order component. The 10th-order component and the 60th-order component of the cogging torque do not change much as the slot open ratio α changes. As the slot open ratio α is increased, the 12th order component of the cogging torque is increased, and the 30th order component of the torque ripple is decreased. That is, the 12th order component of the cogging torque and the 30th order component of the torque ripple are characteristics that are greatly affected by the change in the slot open ratio α. In other words, the value of the 12th order component of the cogging torque and the value of the 30th order component of the torque ripple can be controlled by the slot open ratio α.

  When the EPS 1 using the motor 5 is used, the first set value for the cogging torque and the second set value for the torque ripple are set. A range in which the 12th-order cogging torque is smaller than the first predetermined value and the 30th-order torque ripple is smaller than the second predetermined value, that is, the slot open ratio α is in the range from the value α1 to the value α2 (for example, The motor 5 is formed so as to be 9-11 [percent]). As a result, it is possible to obtain an electric power steering apparatus in which the cogging torque is reduced and the increase in torque ripple is suppressed and the operational feeling is improved.

The relationship between slot opening and torque ripple will be described.
When the slot opening is reduced, that is, when the tips of the protruding portions 31a and 31b of the teeth 14 are brought closer, the magnetic flux leaking from the protruding portions 31a and 31b to the adjacent teeth 14 increases, and the inductance increases. Conversely, if the slot open is widened, that is, the tips of the projecting portions 31a and 31b are separated, the leakage magnetic flux decreases and the inductance decreases. The inductance changes as shown in FIG. 7 according to the rotational position of the rotor 21, that is, the rotational position of the magnetic pole. FIG. 7 shows inductance waveforms B1 to B5 when the slot opening is changed. In FIG. 7, inductance waveforms B1 to B5 indicate waveforms when the slot open ratio α is increased in this order. FIG. 6 shows torque ripple (30th-order component) and inductance change rate with respect to the slot open ratio α.

  The inductance and torque relationship of the motor 5 is obtained by the following equation with the magnetic field energy formed by the ring magnet 23 being constant.

上記式において、Ｖ：相電圧、Ｒ：相抵抗、Ｌ：インダクタンス、Ｉ：相電流、ωe：モータ角速度（電気角）、ωm：モータ角速度（機械角）、Ｋe：逆起電圧定数、Ｐ：時間微分演算子、Ｔ：トルク、である。

In the above formula, V: phase voltage, R: phase resistance, L: inductance, I: phase current, ωe: motor angular velocity (electrical angle), ωm: motor angular velocity (mechanical angle), Ke: counter electromotive voltage constant, P: Time differentiation operator, T: torque.

  In this embodiment, the d and q axis current command values in the dq coordinate system, which are target values, are calculated based on the steering wheel operation, vehicle speed, and the like, and the command values are used as U, V, and W system phase voltage command values. (2 phase / 3 phase conversion) and a control method for generating a motor control signal based on the phase voltage command value is employed.

  Here, the dq coordinate system is an orthogonal coordinate system in which the same direction as the magnetic flux of the rotor of the motor is the d-axis, and the direction orthogonal to the d-axis is the q-axis. This is a technique that makes it possible to calculate alternating current as direct current by mapping the vector of each phase current supplied to the brushless motor to the dq coordinate system.

  The circuit equation on the dq axis is given by

トルクに寄与するのはｑ軸電流Ｉｑであるため、ｄ軸電流Ｉｄ＝０とすると、式１におけるｑ軸のインダクタンスＬｑは、

Since the q-axis current Iq contributes to the torque, when the d-axis current Id = 0, the q-axis inductance Lq in Equation 1 is

により求められる。このインダクタンスＬｑの変化によりトルクが変動する。従って、スロットオープン比を大きくすることにより、トルクリプルの３０次成分を減少させ得る。

It is calculated by. The torque varies due to the change of the inductance Lq. Therefore, the 30th-order component of torque ripple can be reduced by increasing the slot open ratio.

Next, control on the motor 5 will be described.
The motor 5 is controlled by a motor control circuit 40 shown in FIG. The motor control circuit 40 reduces the cogging torque of a predetermined order component of the motor 5 by energizing in a phase opposite to the cogging torque of the motor 5. In the present embodiment, among the cogging torque components, the controllable and dominant 10th order component is reduced.

  FIG. 4 is a block circuit diagram showing an example of a motor control circuit 40 that controls the motor 5. The motor control circuit 40 includes a current command value calculation unit 41, an addition unit 42, a two-phase / three-phase conversion unit 43, a PWM drive unit 44 as a voltage supply unit, a rotation angle calculation unit 45, and a correction value calculation unit 46. Yes.

  Signals input from various sensors are input to the current command value calculation unit 41. As the sensor, for example, a torque sensor capable of detecting an absolute angle (absolute steering angle) from the neutral position of the steering wheel, a vehicle speed sensor, and a rotation angle sensor 47 provided in the motor 5 are used. The current command value calculation unit 41 detects steering torque, vehicle speed, motor rotation angle (electrical angle) and the like based on signals output from the sensors, and calculates and outputs a current command value Iq * according to the detection result. To do. The current command value calculation unit 41 may be configured only to calculate the current command value according to the detection result.

  The adding unit 42 adds a correction value to the current command value Iq * (if the current command value is a positive value, the phase is controlled in the opposite phase, so the sign is opposite to that of the current command value and is subtracted). Command value Iq ** is output.

  The two-phase / three-phase converter 43 converts the corrected command value Iq ** and the d-axis current command value (= 0) into three-phase voltage command values Vu *, Vv *, Vw *, and the voltage Command values Vu *, Vv *, Vw * are output to a PWM (pulse width modulation) drive unit 44. The PWM drive unit 44 generates a drive voltage for each phase of u, v, and w by a drive circuit having an inverter configuration from a pulse signal having a pulse width corresponding to each of the input voltage command values Vu *, Vv *, and Vw *. The drive voltage is applied to the motor 5.

  A signal corresponding to the rotation position of the rotation angle sensor 47 provided in the motor 5 is output. The rotation angle calculation unit 45 calculates the rotation angle (electrical angle) of the motor 5 of the motor 5 based on the signal from the rotation angle sensor 47 and outputs the calculation result. This calculation result (motor electrical angle θ (θm)) is used for conversion in the two-phase / three-phase converter 43. The calculation result is used in the correction value calculation unit 46.

  The correction value calculation unit 46 stores a correction map. This correction map is provided by a rewritable (or detachable) storage unit such as an EEPROM. In the correction map, the amplitude of the cogging torque with respect to the electrical angle of the motor 5 is stored in association with each other. The value of this correction map is obtained by connecting the motor shaft 22 of the motor 5 assembled in advance to the rotation shaft of the servo motor via a torque sensor, giving a rotation command to the servo motor to rotate the motor shaft 22, and It is obtained by the electrical angle obtained by the provided rotation angle sensor 47 and the torque obtained by the torque sensor.

  The correction value calculation unit 46 reads the amplitude of the cogging torque corresponding to the calculation result (electrical angle) of the rotation angle calculation unit 45 from the correction map, and converts the amplitude value into a correction value. Then, the correction value is output to the adding unit 42. In the adder 42, a correction command value Iq ** corrected so as to reduce the cogging torque is calculated by adding a correction value to the current command value Iq *, and the drive supplied by the correction command value Iq **. The motor 5 is rotated by the voltage.

As described above, the present embodiment has the following effects.
(1) The motor control circuit 40 stores a correction map that stores the rotation angle of the motor 5 and the amplitude of the cogging torque generated in the motor 5, and calculates a correction value corresponding to the amplitude value read from the correction map. To do. Then, by adding the correction value to the current command value Iq *, the cogging torque of a predetermined order can be reduced. Therefore, it is not necessary to provide a member for mechanically correcting the cogging torque in the motor 5, and the cogging torque can be reduced without changing the mechanical structure of the motor 5. Further, since vibration due to cogging torque is not transmitted to the steering, the steering feeling can be improved.

  (2) Protrusions 31a and 31b are formed in the circumferential direction from the tip of the teeth 14 constituting the stator 11 of the motor 5. The slot open ratio α, which is the ratio of the slot open length to the length of the inner circumferential circle per slot 32, with respect to the slot open between the protruding portions 31a and 31b of the adjacent teeth 14 is set to a predetermined order. The stator 11 was formed to have a value within a predetermined range defined by the component cogging torque and torque ripple. Increasing the slot open ratio α decreases the torque ripple and increases the cogging torque of the order component (30th order component) that can be controlled by the slot. Decreasing the slot open ratio α increases the torque ripple and increases the cogging torque of the 30th order component. Decrease. Therefore, by setting the slot open ratio α within a predetermined range, it is possible to reduce the torque ripple and suppress the increase of the 30th-order component cogging torque, and to realize the motor 5 having a small torque ripple and cogging torque.

In addition, you may change embodiment of this invention as follows.
In the above embodiment, the invention is embodied in EPS 1 using a brushless motor having 10 poles and 12 slots, but may be embodied in a motor having another configuration, for example, a brushless motor having 14 poles and 12 slots, and EPS using the same.

  In the above embodiment, the correction value to be added to the current command value Iq * is calculated based on the value stored in the correction map, but the correction value for this command value is calculated using the torque command value or the like. Also good.

  In the above embodiment, the configuration of the motor control circuit 40 may be changed as appropriate. For example, the current value supplied to the motor 5 may be detected and feedback correction for correcting the command current value may be performed.

  In the above embodiment, the motor 5 (motor shaft 12) itself is embodied in the coaxial rack assist type EPS 1 arranged coaxially with the rack shaft 4. However, a so-called rack cross type or the like is provided by a motor provided outside the housing. Further, the present invention may be embodied in an EPS that drives a hollow shaft through which a rack shaft is inserted. Further, the present invention may be embodied as a column type EPS that applies assist force to a column shaft and a pinion type EPS that applies assist force to a pinion shaft as a steering force assisting device that applies assist force to a steering shaft.

Sectional drawing of an electric power steering device. AA sectional view taken on the line AA of FIG. The top view which shows the shape of teeth. The block diagram which shows the electric constitution of an electric power steering device. The characteristic view which shows the cogging torque and torque ripple with respect to slot open ratio. The characteristic view which shows the torque ripple and inductance with respect to a slot open ratio. The wave form diagram which shows the relationship between an electrical angle and an inductance.

Explanation of symbols

  Iq * ... current command value, Iq ** ... correction command value, 5 ... motor, 11 ... stator, 14 ... teeth, 31a, 31b ... projection, 40 ... motor control circuit, 41 ... current command value calculation unit, 42 ... Adder, 46... Correction value calculator.

Claims (4)

A motor device composed of a brushless motor configured in 10 poles and 12 slots or 14 poles and 12 slots, and a motor control circuit for controlling the brushless motor,
The motor control circuit is
A storage unit for storing rotational characteristics of the brushless motor;
A current command value calculation unit for calculating a current command value for controlling the brushless motor;
A correction value calculation unit that calculates a correction value for correcting the rotation characteristic in an opposite phase according to the value stored in the storage unit;
An adder for adding the correction value to the current command value to calculate a correction command value;
A voltage supply unit that supplies a drive voltage to the motor device based on the correction command value;
A motor device comprising: The motor device according to claim 1,
The stator of the motor has a plurality of teeth protruding inward in the radial direction, and a protruding portion is formed along the circumferential direction at the tip of each tooth. The value of the ratio of the distance between the teeth tips adjacent in the circumferential direction with respect to is formed to be within a predetermined range determined by the characteristics of the cogging torque and the torque ripple,
The motor apparatus characterized by the above-mentioned. The motor device according to claim 2,
The cogging torque is a cogging torque of an order greatly affected by the change of the ratio, and the cogging torque of the order increases in proportion to the value of the ratio, and the torque ripple is set to the value of the ratio. In contrast, it decreases in inverse proportion,
The predetermined range is a range set so that the cogging torque of the order is smaller than a first predetermined value and the torque ripple is smaller than a second predetermined value.
The motor apparatus characterized by the above-mentioned.   An electric power steering device comprising the motor device according to claim 1.

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