JP2012227989A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a consequent type brushless motor useful as the drive source of an electric power steering device, by reducing the cogging torque or torque ripple of the consequent type brushless motor.SOLUTION: The consequent type brushless motor 1 is used as the drive source of an electric power steering device, and has a stator 2 and a rotor 3. The stator 2 has a stator core 5 in which teeth 43 are formed, and a field coil 6 wound around the teeth 43 and housed in a slot 44. The rotor 3 has a shaft 13, and a rotor core 15 with a core 15a and iron poles 15b, and a magnet 16 placed between the iron poles 15b. The stator core 5 has a skew structure, and the slot 44 is provided while inclining in the extension direction of the shaft 13 at a skew angle θ=17°-22°, preferably 24°.

Description

  The present invention relates to a continuous brushless motor, and more particularly, to a technique for reducing cogging and torque ripple of a continuous brushless motor.

  In recent years, in an electric power steering apparatus (hereinafter abbreviated as EPS) mounted on a vehicle such as an automobile, a magnet using a rare metal such as neodymium as a driving source motor in response to a demand for miniaturization and high output. Is used. However, rare metals are highly dependent on imports, making it difficult to obtain materials, and the price is very high. For this reason, in recent years, in order to reduce the amount of rare metal used, a so-called continuous-type permanent magnet motor that uses an iron core as a magnetic pole in a pseudo manner is being sought as an EPS motor.

  In general, in such a continuous motor, magnets and iron poles are alternately arranged on the outer periphery of the rotor. The magnet has an N pole on the outside, and the magnetic flux emitted from the magnet enters an adjacent iron pole to form a magnetic circuit. At this time, the iron pole becomes an S pole, and as a result (consequent), the iron pole between the magnets becomes a magnetic pole to form a pole pair. Thereby, the N pole and the S pole are alternately arranged on the outer periphery of the rotor, and the rotor functions as a rotor of the permanent magnet motor.

JP 9-327139 A

  Here, in a normal permanent magnet motor that uses magnets for both the N and S poles, the magnetic pole itself generates magnetic flux. Therefore, if the magnets have the same shape, it is relatively easy to reduce cogging and torque ripple. That is, by adjusting the magnet shape, the line-induced voltage waveforms of the respective phases can be made similar to each other, and cogging and the like can be reduced relatively easily. However, in the continuous permanent magnet motor, the iron pole is converted into a magnetic pole through the magnetic flux of the magnet, and it is difficult to set the shape of the iron pole so that the induced voltage waveforms are uniform. Further, since the rotor is composed of a magnet and iron, unnecessary harmonic components are easily included in the induced voltage between lines, and the cogging / torque ripple tends to increase.

  In this way, the continuous motor can reduce the amount of magnets to about half that of a normal motor and can reduce the amount of expensive rare metal magnets used, but it has large cogging and torque ripple. There is a problem of becoming. For this reason, the current situation is that the continuous motor is difficult to be used for the EPS motor, which has strict requirements for cogging and torque ripple, and a countermeasure to reduce them has been demanded.

  An object of the present invention is to provide a continuous brushless motor useful as a drive source for an electric power steering apparatus for a vehicle by reducing cogging and torque ripple of the continuous motor.

  A brushless motor of the present invention is a brushless motor having a cylindrically formed stator and a rotor rotatably disposed inside the stator, wherein the stator extends radially inward. A plurality of stator cores formed along the circumferential direction; and a field coil wound around the teeth and accommodated in a slot formed between the adjacent teeth. A rotor core comprising a shaft rotatably supported, a core portion attached to the shaft and having a circular cross section, and a plurality of iron electrode portions projecting radially from the outer periphery of the core portion; A magnet disposed between the iron poles on the outer periphery of the rotor core, the stator core having a skew structure, and the slot being the shuffling Characterized in that it is provided obliquely at a predetermined skew angle with respect to the stretching direction.

  In the present invention, a so-called continuous brushless motor in which iron poles and magnets are alternately arranged on the outer periphery of the rotor core, a skew structure is adopted on the stator core side, which is compared with a step skew structure on the rotor side. Thus, cogging and torque ripple can be reduced.

  In the brushless motor, the brushless motor has a 6-pole 9-slot structure, and the skew angle in the skew structure may be set to 17 ° to 22 °, preferably 24 °.

  Further, a segment magnet may be used as the magnet, and it may be attached to the outer periphery of the rotor core. Since the shape of the segment magnet can be changed as appropriate, the magnetic flux can be easily adjusted. For this reason, even in a continuous motor in which the balance between the magnet and the iron electrode is difficult, the shapes of both the magnet and the iron electrode can be adjusted, the induced voltage waveform can be easily adjusted, and the degree of design freedom is improved. In this respect, since the embedded magnet has a fixed shape, it can only be changed on the iron pole side, the adjustment of the induced voltage waveform is very difficult, and the reduction of torque ripple is also difficult.

  Further, the brushless motor may be used as a drive source for the electric power steering apparatus. The brushless motor according to the present invention is excellent in low cogging and low torque ripple, and can be used in EPS motors that require strict specifications.

  According to the brushless motor of the present invention, since a skew structure is employed on the stator core side of a so-called continuous brushless motor, it is possible to provide a brushless motor with low cogging and low torque ripple that could not be achieved with the rotor step skew structure. It becomes. As a result, the number of magnets can be reduced by about half compared to a conventional permanent magnet motor, the amount of expensive rare metal magnets used can be reduced, and the product cost of the motor can be reduced. Further, by using the continuous motor according to the present invention as an EPS motor, it is possible to provide an EPS system that is inexpensive and has low cogging and torque ripple.

It is sectional drawing of the motor for EPS which is one Example of this invention. It is explanatory drawing which shows the outline | summary of the cross section along the AA of FIG. It is a perspective view which shows the structure of a rotor. It is explanatory drawing which shows the structure of a stator core. It is explanatory drawing which shows the overlapping relationship of the magnet and rotor core in a step skew. It is a graph which shows the relationship between skew angle (theta) and the cogging torque in the motor of a status cue and rotor step skew. It is a graph which shows the relationship between skew angle (theta) and total harmonic distortion (THD) in the motor of a status cue and rotor step skew. It is explanatory drawing which compared and showed the case of no skew, and the torque ripple of a rotor step skew and a status cue.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an EPS motor according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing an outline of a cross section taken along line AA of FIG. The EPS motor 1 (hereinafter abbreviated as “motor 1”) is used, for example, as a power source of a column assist type EPS, and applies an operation assisting force to a steering shaft of an automobile. The motor 1 is a continuous brushless motor, and has an inner rotor type configuration in which a stator (stator) 2 is disposed on the outside and a rotor (rotor) 3 is disposed on the inside, as shown in FIGS. . The motor 1 is attached to a reduction mechanism (not shown) provided on the steering shaft, and the rotation of the motor 1 is reduced and transmitted to the steering shaft by the reduction mechanism.

  The stator 2 includes a bottomed cylindrical housing 4, a stator core 5, a field coil 6 (hereinafter abbreviated as a coil 6) wound around the stator core 5, and a bus bar unit 7 attached to the stator core 5. Yes. The housing 4 is formed in a bottomed cylindrical shape with iron or the like, and also serves as a motor yoke. A bracket 8 made of synthetic resin is attached to the opening of the housing 4 with a fixing screw 10. A synthetic resin insulator 11 is attached to the stator core 5, and a coil 6 is wound around the insulator 11. An end portion 6 a of the coil 6 is drawn out at one end side of the stator core 5.

  A bus bar unit 7 in which a copper bus bar 9 is insert-molded in a synthetic resin main body is attached to one end side of the stator core 5. A plurality of power feeding terminals 12 project from the bus bar 9 in the radial direction, and the power feeding terminals 12 project radially around the bus bar unit 7. On the other hand, the end of the bus bar 9 extends in the axial direction from the end face of the bus bar unit 7 to form a bus bar terminal 33. When the bus bar unit 7 is attached, the coil end 6 a is welded to the power feeding terminal 12. In the bus bar unit 7, the number of bus bars 9 corresponding to the number of phases of the motor 1 (here, three for the U phase, V phase, and W phase) is provided, and each coil 6 corresponds to that phase. It is electrically connected to the power supply terminal 12. The stator core 5 is press-fitted and fixed in the housing 4 after the bus bar unit 7 is attached.

  A rotor 3 is inserted inside the stator 2. FIG. 3 is a perspective view showing the configuration of the rotor 3. The rotor 3 has a shaft 13 that serves as a motor rotation shaft. The shaft 13 is rotatably supported by ball bearings (hereinafter abbreviated as bearings) 14a and 14b. The rear-side bearing 14 a is press-fitted and fixed in a bearing housing portion 40 formed at the center of the bottom of the housing 4. The front-side bearing 14 b is fixed to the central portion of the bracket 8 by a metal bearing holder 19.

  A rotor core 15 formed by laminating electromagnetic steel plates is fixed to the shaft 13. As shown in FIGS. 2 and 3, the rotor core 15 includes a core portion 15 a having a circular cross section and an iron electrode portion 15 b protruding from the outer periphery of the core portion 15 a. The iron electrode part 15b is equally divided into three places along the circumferential direction. A segment type magnet (permanent magnet) 16 is attached between the adjacent iron electrode portions 15b. The magnet 16 is held on the outer periphery of the core portion 15a by a synthetic resin magnet holder 17. A bottomed cylindrical magnet cover 18 is attached to the outside of the magnet 16 and the iron pole portion 15b.

  A rotor (resolver rotor) 22 of a resolver 21 serving as a rotation angle detection unit is attached to the end of the magnet holder 17. On the other hand, a stator (resolver stator) 23 of the resolver 21 is press-fitted into a metal resolver holder 24 and accommodated in a bracket holder 25 made of synthetic resin. The resolver holder 24 is formed in a bottomed cylindrical shape, and is lightly press-fitted into the outer periphery of the end portion of the rib 26 provided in the center portion of the bracket 8. The bracket holder 25 is fixed to the inside of the bracket 8 by a tapping screw (not shown).

  The bracket holder 25 and the bracket 8 are fixed by the aforementioned tapping screw in a form in which the flange portion 24a of the resolver holder 24 is interposed therebetween. The flange portion 24a is attached between the bracket holder 25 and the bracket 8 so as to be slightly movable in the circumferential direction. After the position of the stator 23 is adjusted, the resolver holder 24 is attached to the bracket holder 25 by a resolver fixing screw 28. Fixed. As shown in FIG. 1, a metal resolver fixing nut 27 is attached to the bracket holder 25. A resolver fixing screw 28 is screwed into the resolver fixing nut 27 from the outside of the bracket 8, and the bearing holder 19 and the resolver holder 24 are fastened together with the bracket 8. Thereby, the resolver holder 24 is fixed to the inside of the bracket 8 in a state where the position in the circumferential direction is adjusted.

  A power terminal 31 is also insert-molded in the bracket 8. The power terminal 31 is provided for each of the U, V, and W phases, and one end side 31 a thereof is disposed in the opening 32. The other end 31 b of the power terminal 31 is disposed in the power connector 34. When the bracket 8 is assembled to the housing 4, the bus bar terminal 33 extending in the axial direction from the bus bar unit 7 faces the power terminal 31 in parallel. In the motor 1, after the bracket 8 is attached to the housing 4, the bus bar terminal 33 and the power terminal 31 are fixed by welding in the opening 32.

  Here, in the motor 1 of the present invention, the stator core 5 of the stator 2 has a skew structure. FIG. 4 is an explanatory view showing the structure of the stator core 5. As shown in FIGS. 1, 2, and 4, the stator core 5 has a configuration in which a plurality of stator pieces 41 made of electromagnetic steel plates are arranged in a ring shape along the circumferential direction, and the stator pieces 41 are stacked along the axial direction. ing. The motor 1 further realizes a status cue structure by laminating the stator pieces 41 with a predetermined angle shifted in the circumferential direction.

  The stator piece 41 includes an arcuate yoke portion 41a and a teeth portion 41b projecting from the yoke portion 41a toward the center of the arc. A plurality of grooves 42 forming a pseudo slot are formed at the tip of the tooth portion 41b to reduce cogging torque. In the stator core 5, a plurality of teeth 43 extending in the central direction along the radial direction are formed along the circumferential direction by the teeth portions 41b. A slot 44 is formed between the teeth 43, and the coil 6 wound around the teeth 43 is accommodated in the slot 44. The stator core 5 has a skew structure as described above, and the axial center line M of the slot 44 is inclined by an angle θ (skew angle) with respect to the extending direction (axial direction) O of the shaft 13. .

  As described above, the continuous type motor has a problem that cogging and torque ripple are increased although the amount of magnet used can be reduced. On the other hand, the use of a skew structure is effective for canceling out harmonic components of the induced voltage that adversely affects cogging. In addition, it is generally known that driving a motor with a sine wave is effective for reducing torque ripple, but in order to obtain a significant effect of reducing torque ripple, harmonic components of the induced voltage waveform are reduced. It is necessary to reduce as much as possible. In a continuous motor using a segment magnet, the magnetic flux shape can be adjusted by the magnet shape, and the iron pole portion 15b can also adjust the magnetic flux by adjusting the curvature of the outer diameter, but there is always a harmonic component. In order to reduce this, a skew structure is still necessary.

  That is, even in the continuous motor, it is effective to employ a skew structure in order to reduce cogging and torque ripple. However, in the case of a motor using a segment magnet, there is a merit that the magnetic flux can be adjusted in a magnet shape, but in order to configure a rotor skew, a stacked structure (step skew) is used. In such a step skew structure, as shown in FIG. 5, since the magnet 51 and the iron pole portion 52 of the rotor core overlap (arrow P) between adjacent stages, the magnetic flux from the magnet is distorted. In addition to being difficult to obtain the skew effect, cogging may be worsened.

  Accordingly, in the motor 1 according to the present invention, the rotor 3 side has a linear magnetic pole configuration without skew and prevents distortion of magnetic flux, while the stator 2 side has a skew structure to reduce cogging and torque ripple. FIG. 6 is a graph showing the relationship between the skew angle θ and the cogging torque in the motor of the status queue (motor 1) and the rotor skew (step skew). Note that the skew angle θ referred to here is the inclination angle of the center line (axial direction) of the slot 44 with respect to the extending direction (axial direction) of the shaft 13 in the case of a status cue, and each adjacent step in the case of a rotor step skew. This means the sum of the shift angles of the magnets in the circumferential direction. FIG. 7 is a graph showing the relationship between the status queue, the skew angle θ and the total harmonic distortion (THD) in the motor of the rotor step skew, and FIG. 8 is the case of no skew, the rotor step skew, and the status. It is explanatory drawing which compared and showed the torque ripple of the cue | queue.

  As can be seen from FIG. 6, the cogging torque of the motor 1 is suppressed to be lower than that of the rotor step skew motor. In a 6-pole 9-slot motor such as the motor 1, the minimum is theoretically around a mechanical angle of 20 ° obtained by dividing the mechanical angle of 360 ° by the least common multiple of 6P9S. However, in the case of the rotor step skew, the cogging torque does not become so small even in the vicinity of 20 ° due to the overlap problem between the magnet 51 and the iron pole portion 52 as described above. Further, when the skew angle is increased, the amount of overlap between the magnet 51 and the iron pole portion 52 is increased, and the cogging is deteriorated. In the case of an EPS motor, the cogging torque is generally preferably 10 mNm or less, but as is apparent from FIG. 6, it is difficult to achieve the specifications of a rotor step skew motor. On the other hand, in the motor 1 having the status queue structure, the above-described condition can be cleared by setting the skew angle to about 15 ° to 27 °.

  Next, with respect to the harmonic component, in the 6P9S motor, the minimum is around 24 degrees where the fifth-order component is minimized. However, in the case of the rotor step skew, as in the case of cogging, the harmonic component does not become so small due to the distortion of the magnetic flux, so that the induced voltage waveform does not become a sine wave and the torque ripple becomes large. In EPS motors, it is generally considered that THD is preferably less than 1%, but as is clear from FIG. 7, it is difficult to achieve the specifications with a rotor step skew motor. On the other hand, in the motor 1 having the status queue structure, if the skew angle is set to about 17 ° to 27 °, the above-described conditions can be cleared. In particular, if the skew angle is set to 24 °, the torque ripple can be suppressed to a minimum value. it can.

  Further, in the EPS motor, it is desired to suppress the torque ripple rate to 5% or less. However, as can be seen from FIG. 8, in the case of no skew or the rotor step skew, it cannot be suppressed to 5% or less. In that respect, if the status queue is employed and the skew angle is set to 24 °, the torque ripple rate can be suppressed to about 3%, and the specifications required for the EPS motor can be satisfied.

  As described above, the motor 1 of the present invention can provide a brushless motor with low cogging and low torque ripple that cannot be achieved with the rotor step skew structure by adopting the status cue structure for the continuous permanent magnet motor. It becomes possible. As described above, the continuous motor can reduce the number of magnets to about half that of a conventional permanent magnet motor, thus reducing the amount of expensive neodymium magnets used and reducing the product cost of the motor. Is possible. Therefore, by adopting the continuous motor as the EPS motor, it is possible to provide an EPS system that is inexpensive and has low cogging and torque ripple.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.
For example, in the above-described embodiment, an example in which the rotor side has a step skew structure has been shown, but by using a segment magnet magnetized by a parallel magnetic field, a smooth skew structure that is not a step structure is formed on the rotor side. You may do it. However, magnetizing with a parallel magnetic field makes it difficult to increase the magnetic flux density of the magnet, so the magnet may become large in order to obtain the required magnetic flux. In EPS, where a small and high-performance motor is required, status A queue structure is preferred.

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Stator 3 Rotor 4 Housing 5 Stator core 6 Field coil 6a Coil end 7 Bus bar unit 8 Bracket 9 Bus bar 10 Fixing screw 11 Insulator 12 Feeding terminal 13 Shaft 14a, 14b Bearing 15 Rotor core 15a Core part 15b Iron pole part 16 Magnet 17 Magnet holder 18 Magnet cover 19 Bearing holder 21 Resolver 22 Rotor 23 Stator 24 Resolver holder 24a Flange 25 Bracket holder 26 Rib 27 Resolver fixing nut 28 Resolver fixing screw 31 Power terminal 31a One end side 31b The other end 32 Opening 33 Bus bar terminal 34 Power connector 40 Bearing housing part 41 Stator piece 41a Yoke part 41b Teeth part 42 Groove 43 Teeth 4 slot 51 magnet 52 iron poles unit θ skew angle

Claims (4)

A brushless motor having a cylindrically formed stator, and a rotor rotatably disposed inside the stator,
The stator includes a stator core in which a plurality of teeth extending radially inward are formed along a circumferential direction, and a field coil that is wound around the teeth and accommodated in a slot formed between the adjacent teeth. With
The rotor includes a shaft that is rotatably supported by the stator, a core portion that is attached to the shaft and has a circular cross section, and a plurality of irons that project radially from the outer periphery of the core portion. A rotor core having a pole portion, and a magnet disposed between the iron pole portions on the outer periphery of the rotor core,
The brushless motor according to claim 1, wherein the stator core has a skew structure, and the slot is inclined at a predetermined skew angle with respect to the extending direction of the shaft.   2. The brushless motor according to claim 1, wherein the brushless motor has a 6-pole 9-slot structure, and the skew angle in the skew structure is 17 [deg.] To 22 [deg.].   3. The brushless motor according to claim 1, wherein a segment magnet attached to an outer periphery of the rotor core is used as the magnet.   The brushless motor according to any one of claims 1 to 3, wherein the brushless motor is used as a drive source of an electric power steering device.

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