JP2019213417A - Brushless motor - Google Patents

Abstract

To reduce thrust electromagnetic force and fluctuation of a motor having such a specification that the lowest common multiple of the number of poles including skew structure and the number of slots is small.SOLUTION: A brushless motor 2 has a quadrupole 6 slot configuration, and has a stator 11, and a rotor 12 including skew structure. At both ends of a magnet 19 in the axial direction, first and second overhang parts 31, 32 are provided. The overhang parts 31, 32 have different overhang amounts OH1, OH2 from the axial end of a stator core 14. A rare-earth magnet is used in the magnet 19, and magnetic orientation thereof is pole orientation. A skew angle θ is set to 30° to 50° (electrical angle), and the ratio OH2/OH1 of overhang amounts is set to 1.5 to 2.5.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a reduction in thrust electromagnetic force generated in a brushless motor, and more particularly, to a thrust electromagnetic force reduction technique in a brushless motor having a skew structure.

  Conventionally, as a means to reduce torque ripple and cogging of a brushless motor (hereinafter abbreviated as “motor”), the so-called skew structure in which the magnetic pole polarity switching position (magnetic pole boundary position) is shifted in the rotational direction along the axial direction. It has been known. However, in the skew structure motor, torque ripple and the like can be reduced. On the other hand, along with the inclination of the magnetic pole boundary position, along with the rotational force due to magnetic attraction and repulsion, the axial component causes the force in the thrust direction (rotating axis extending direction). Force (thrust electromagnetic force) is generated.

JP 2009-213282 A

  When such thrust electromagnetic force is generated in the motor, vibrations are generated in the thrust direction due to increase / decrease (ripple). As a result, for example, in a motor equipped with a gear transmission mechanism, there has been a problem that the meshing state of the gear becomes discontinuous due to thrust vibration, which causes generation of sound and vibration. In particular, such thrust electromagnetic force and the ripple thereof become prominent in a motor having a small number of magnetic poles, and further increases when a magnet using a rare earth element having a large magnetic force (hereinafter referred to as a rare earth magnet) is used. There was a problem.

FIG. 10A is an explanatory diagram showing the relationship between the inclination angle of the magnetic poles and the number of magnetic poles, and FIG. 10B shows the relationship between the number of magnetic poles and the PP (peak-to-peak) value of the thrust electromagnetic force. It is explanatory drawing shown. As can be seen from FIG. 10 (a), the magnetic pole inclination angle θm is Dm as the magnet outer diameter, θs (mechanical angle) as the skew angle, and Lm as the magnet axial length.
θm = tan ⁻¹ [{Dm × π × (θs / 360)} / Lm]
Can be expressed as In this case, when the electrical angle skew angle is constant, the mechanical angle skew angle θs decreases as the number of magnetic poles increases.

  Accordingly, when the skew angle (electrical angle) is made constant in a motor of 2 poles 3 slots (2P3S) × n (integer) specification, (a) 4 poles (6 slots: 4P6S), (A) 6 poles (9 In a motor with each specification of slot: 6P9S) and (c) 8 poles (12 slots: 8P12S), the skew angle θs (mechanical angle) is the least common multiple of the number of poles and the number of slots (A: 12, A: 18, C). : 24) increases as it decreases, and θm also increases. Since the thrust electromagnetic force is an axial component of the rotational force generated by the skew, it increases as the magnetic pole inclination angle θm increases. For this reason, as shown in FIG. 10B, the 4-pole specification and 8-pole specification motors have a difference of about 5 times in the PP value of the thrust electromagnetic force, and the least common multiple of the number of poles and the number of slots is The smaller the specification, the larger the ripple of thrust electromagnetic force.

  In addition, when a rare earth magnet having a high magnetic flux density is used as the magnet for the magnetic pole, magnetic attraction is reduced compared to a case where a magnet using a non-rare earth element such as a ferrite magnet (hereinafter referred to as a non-rare earth magnet) is used. The rebound is strengthened. For this reason, although the use of the rare earth magnet can reduce the size and output of the motor, there is a problem that the thrust electromagnetic force is further increased and the ripple is also increased. FIG. 11A is an explanatory diagram showing the magnitude of the thrust electromagnetic force when a rare earth magnet is used and when a non-rare earth magnet is used, and FIG. 11B is a diagram illustrating the rotation angle (mechanical angle) and the thrust electromagnetic force. It is explanatory drawing which shows the relationship of force. As can be seen from FIG. 11, the rare earth magnet has a thrust electromagnetic force about 3.5 times larger than that of the non-rare earth magnet, and its fluctuation is also large. For this reason, a motor using a rare earth magnet also increases thrust vibration, and is likely to generate sound and vibration.

  An object of the present invention is to reduce the thrust electromagnetic force of a brushless motor having a skew structure, in particular, the thrust electromagnetic force of a motor having a specification with a small least common multiple of the number of poles and the number of slots and its ripple.

  The brushless motor of the present invention includes a stator core in which six teeth extending radially inward are formed along the circumferential direction, and a winding housed in a slot formed between the adjacent teeth wound around the teeth. A brush provided with a stator, and a rotor provided with a magnet that is rotatably arranged radially inward of the stator and has four magnetic poles formed along the circumferential direction. Is formed of a ring magnet using a rare earth magnet, and the ring magnet has a skew structure in which the switching position of the magnetic pole is shifted in the rotational direction along the axial direction, and the shaft of the stator core is provided at both axial end portions thereof. A first overhang portion and a second overhang portion extending in the axial direction from each of the end portions in the direction, The structure is characterized in that a skew angle is set to an electrical angle of 30 ° to 50 °, and the first and second overhang portions have different extension amounts with respect to the axial end portion of the stator core. To do.

  In the present invention, in a motor having a 4-pole 6-slot configuration, the skew angle is set to an electrical angle of 30 ° to 50 °, and the axial direction from the axial end of the stator core to each of both axial end portions of the magnet. By providing an overhang portion that extends to the surface, the thrust electromagnetic force generated by the skew structure can be reduced, and the thrust electromagnetic force can be suppressed even when a rare earth magnet is used. As a result, it is possible to reduce the thrust electromagnetic force and the ripple while suppressing the occurrence of torque ripple and cogging by the skew structure.

  In the brushless motor, as the ring magnet, a magnet having a magnetic orientation of polar orientation magnetized so that a magnetic pole is formed only on the outer peripheral surface may be used. Thereby, it becomes possible to further suppress the ripple of the thrust electromagnetic force.

  Further, the ratio OH 2 / the ratio of the extension amount OH 1 of the first overhang portion formed on one end side of the ring magnet to the extension amount OH 2 of the second overhang portion formed on the other end side of the ring magnet. OH1 may be set to 1.5 to 2.5. Thereby, it is possible to effectively suppress the ripple of the thrust electromagnetic force.

  According to the brushless motor of the present invention, in the brushless motor having a 4-pole 6-slot configuration, the skew angle is set to an electrical angle of 30 ° to 50 °, and the axial end portions of the stator core are respectively disposed at both axial end portions of the magnet. Since the overhang portion extending in the axial direction is provided, the thrust electromagnetic force generated by the skew structure and its PP value can be reduced. For this reason, even in a brushless motor using a rare earth magnet, it is possible to suppress the thrust electromagnetic force and its ripple.

It is sectional drawing which shows the structure of the motor unit which is one embodiment of this invention. It is sectional drawing which shows the structure of the brushless motor currently used for the motor unit of FIG. It is explanatory drawing which shows the magnetization form of a magnet. It is explanatory drawing which shows the skew structure of a magnet. It is explanatory drawing which shows the relationship between a rotor and a stator. It is explanatory drawing which shows the relationship between skew angle (theta) (electrical angle) and PP value of thrust electromagnetic force in the motor of 4 pole 6 slot structure. It is explanatory drawing which shows the relationship between ratio of the overhang amount in the motor of 4 pole 6 slot structure, and PP value of thrust electromagnetic force. It is explanatory drawing which shows the relationship between the magnetic orientation of a magnet, and PP value of thrust electromagnetic force. It is explanatory drawing which shows the relationship between a rotor rotational angle and a thrust electromagnetic force in the case of setting it as polar orientation, skew angle 40 degrees, and overhang amount ratio = 2. (A) is explanatory drawing which shows the relationship between the inclination angle of a magnetic pole, and the number of magnetic poles, (b) is explanatory drawing which shows the relationship between the number of magnetic poles and PP value of thrust electromagnetic force. (A) is explanatory drawing which showed the magnitude | size of the thrust electromagnetic force at the time of using a rare earth magnet and a non-rare earth magnet, (b) is the relationship between a rotation angle (mechanical angle) and thrust electromagnetic force. It is explanatory drawing shown.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a configuration of a motor unit 1 using a brushless motor according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a configuration of a brushless motor used in the motor unit of FIG. It is. A motor unit 1 in FIG. 1 includes a brushless motor 2 (hereinafter abbreviated as a motor 2) and a speed reduction mechanism (transmission mechanism) 3. For example, a sunroof, a wiper device, a power window, a power Used as a driving source for sheets and the like. In the motor unit 1, the rotation of the rotating shaft 4 of the motor 2 is shifted within the speed reduction mechanism unit 3 and is output from the output shaft 5 to the outside of the unit.

  As shown in FIGS. 1 and 2, the motor 2 is a brushless motor, and includes a stator 11 and a rotor 12 that is rotatably disposed in the stator 11. The stator 11 includes a bottomed cylindrical motor housing 13 and a stator core 14 fixed to the inner surface of the motor housing 13. The stator core 14 is formed by laminating a plurality of plates made of a magnetic material, and has a hexagonal yoke portion 15 and a radial projection from the yoke portion 15 toward the radially inner side (center direction). The teeth 16 are configured. In the motor 2, six teeth 16 are provided along the circumferential direction. A slot 17 is formed between adjacent teeth 16. A winding 18 is wound around the outer periphery of the tooth 16, and the winding 18 is accommodated in the slot 17. The winding 18 is wound by concentrated winding, and three-phase windings are connected by Δ connection.

  A rotor 12 is inserted inside the stator 11. The rotor 12 includes a rotating shaft 4 and a magnet 19 fixed to the rotating shaft 4, and one end side (one end on the motor side) of the rotating shaft 4 is a bearing 21 disposed at an end portion of the motor housing 13. Is rotatably supported by. The magnet 19 is magnetized to 4 poles, and the motor 2 is a brushless motor having a 4 pole 6 slot (4P6S) configuration. Here, as the magnet 19, a permanent magnet (rare earth magnet) using rare earth elements such as neodymium, dysprosium, and samarium is used. The magnet outer peripheral surface 19a is disposed so as to oppose the tip end surface 16a of the tooth 16, and the motor 2 has an SPM (Surface Permanent Magnet) type configuration.

  The magnet 19 is a polar anisotropic ring magnet that is magnetized so as to have different polarities along the circumferential direction. FIG. 3 is an explanatory view showing a magnetized form of the magnet. As shown in FIG. 3A, the magnet 19 is a pole-oriented magnet in which the magnetic poles N and S are formed only on the magnet outer peripheral surface 19a. That is, unlike the radially oriented magnet 41 in which the magnetic field direction is radial as shown in FIG. 3B, the magnet 19 has magnetic poles formed only on the magnet outer peripheral surface 19 a facing the stator 11.

  Further, in the motor 2, skew magnetization is performed in which the magnetic pole boundary line P of the magnet 19 is shifted in the radial direction along the axial direction. FIG. 4 is an explanatory diagram showing a skew structure in the magnet 19. As shown in FIG. 4, in the magnet 19, the magnetic pole boundary line P is inclined along the axial direction, and the angle θ between the start point Q1 and the end point Q2 of the magnetic pole boundary line P is a skew angle. In the motor 2, the skew angle θ is set in a range of 30 ° to 50 ° (electrical angle). Note that either point Q1 or point Q2 may be the start point or the end point.

  The speed reduction mechanism unit 3 includes a worm 6 formed on the rotary shaft 4 and a worm wheel (driven gear) 6 that meshes with the worm (drive gear) 5, and is formed of synthetic resin or aluminum die casting. Arranged in the gear case 22. As shown in FIG. 1, one end opening side of the motor housing 13 is fixed to the gear case 22. The rotating shaft 4 of the motor 2 extends into the gear case 22, and the rotating shaft 4 is rotatably supported by a bearing 23 and a bearing 24 provided in the gear case 22. The worm wheel 7 is fixed to the output shaft 5, and the output shaft 5 rotates together with the worm wheel 7.

  Here, in the motor 2 according to the present invention, the axial length Lm of the magnet 19 on the rotor 12 side is longer than the axial length Lc of the stator core 14 on the stator 11 side. FIG. 5 is an explanatory diagram showing the relationship between the rotor 12 and the stator 11. As shown in FIG. 5, overhang portions (a first overhang portion 31 and a second overhang portion 32) that extend in the axial direction without facing the stator core 14 are provided at both axial end portions of the magnet 19. Each is provided.

  In the motor 2, the overhang amounts (extension amounts) OH1 and OH2 of the first overhang portion 31 on one end side and the second overhang portion 32 on the other end side are different. That is, the first and second overhang portions 31 and 32 are provided asymmetrically in the axial direction. Further, the overhang amount OH2 of the second overhang portion 32 is larger than the overhang amount OH1 of the first overhang portion 31 (OH1 <OH2), and OH2 is 1.5 to 2.5 times that of OH1. (OH2 / OH1 = 1.5 to 2.5).

  In the motor 2 having such a configuration, the thrust electromagnetic force and its PP value can be reduced by setting the asymmetric first and second overhang portions 31 and 32 while adopting the skew structure. it can. Therefore, the ripple of the thrust electromagnetic force due to the PP value is also reduced. In the case of no overhang portion (and no skew), the thrust electromagnetic force is almost 0. On the other hand, if an asymmetric overhang portion is provided, a constant thrust electromagnetic force is always generated in a certain direction. Thereby, it is considered that the thrust electromagnetic force generated by the skew is canceled out.

  FIG. 6 is an explanatory view showing the relationship between the skew angle θ (electrical angle) and the PP value of the thrust electromagnetic force in the motor 2 having a 4-pole 6-slot configuration, and FIG. It is explanatory drawing which shows the relationship between OH2 / OH1) and PP value of thrust electromagnetic force. As shown in FIG. 6, according to the analysis by the inventors, it was found that the PP value of the thrust electromagnetic force in the motor of 4P6S configuration takes a minimum value when the skew angle θ is 40 °. As shown in FIG. 7, the P-P value of the thrust electromagnetic force takes a minimum value when the overhang ratio is 2 (OH2 / OH1 = 2). I understand.

  On the other hand, when investigating the relationship between the P-P value of the thrust electromagnetic force when the first and second overhang portions 31 and 32 are set and the magnetic orientation of the magnet 19, the magnet 19 is more or less polar. It was found that the thrust electromagnetic force was lower than in the case of radial orientation. FIG. 8 is an explanatory diagram showing the relationship between the magnetic orientation of the magnet and the PP value of the thrust electromagnetic force. According to the analysis by the inventors, it has been found that by making the magnet 19 polar, the PP value of the thrust electromagnetic force can be suppressed to almost half as compared with the radial orientation.

  Here, as described above, the thrust electromagnetic force generated by the skew is generated by converting the electromagnetic force (torque) in the rotation direction into the thrust force by the skew. Therefore, if the torque ripple is small, the thrust electromagnetic force ripple is also small. Therefore, considering the torque ripple of the motor, the magnitude of the torque ripple is “radial orientation magnet> polar orientation magnet”. For this reason, it is presumed that the ripple magnitude (PP value) of the thrust electromagnetic force also becomes “radial orientation> polar orientation” as shown in FIG.

  FIG. 9 is an explanatory diagram showing the relationship between the rotor rotation angle and the thrust electromagnetic force when the polar orientation, the skew angle is 40 °, and the overhang amount ratio OH2 / OH1 = 2. In FIG. 9, the broken line indicates only the thrust electromagnetic force generated only by the overhang portion, and the alternate long and short dash line indicates only the thrust electromagnetic force generated only by the portion where the magnet 19 and the stator 11 face each other (non-overhang portion). (The vertical axis is the right scale). The solid line is a combination of the two, and indicates the thrust electromagnetic force of the motor according to the present invention (the vertical axis is the left scale).

  As shown in FIG. 9, the thrust electromagnetic force indicated by the broken line and the alternate long and short dash line is substantially in antiphase, and the combined solid electromagnetic force is small because both cancel each other and rotational fluctuation is also small. It is running low. As shown in FIG. 9, in order to reduce the synthetic thrust electromagnetic force and suppress fluctuations, it is necessary to finely adjust the cancellation balance between the broken line and the alternate long and short dash line. Based on the analysis results of each element as described above, A well-balanced result such as 9 was obtained.

Therefore, from these results, in a 4-pole 6-slot motor using rare earth magnets,
(1) The magnet is polar oriented,
(2) The skew angle θ is set to 30 ° to 50 ° (electrical angle), preferably 40 °,
(3) While providing an asymmetric overhang portion, the ratio of each overhang amount is set to 1.5 to 2.5, preferably 2.
Thus, it was found that the thrust electromagnetic force and its PP value can be reduced.

  Therefore, by adopting the above-described configurations (1) to (3), the thrust electromagnetic force generated by the skew structure and its PP value can be reduced in the motor having the 4-pole 6-slot configuration, and the rare earth magnet Even when is used, the thrust electromagnetic force and its PP value can be suppressed. As a result, it is possible to reduce the thrust electromagnetic force while suppressing the occurrence of torque ripple and cogging by the skew structure. Further, since the PP value of the thrust electromagnetic force is also reduced, the fluctuation (ripple) of the thrust electromagnetic force can be suppressed and the thrust position of the rotor can be stabilized. As a result, for example, it is possible to suppress noise and vibration caused by discontinuity of meshing teeth in a speed reduction mechanism such as a worm, and it is possible to suppress motor noise and vibration.

It goes without saying that the present invention is not limited to the above-described embodiment, 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 a polar anisotropic magnet is used as the magnet 19 has been shown. However, a polar isotropic magnet is used as the magnet 19, and a magnetic pole is formed only on the outer peripheral surface of the magnet. It is also possible to use a pole-oriented magnet magnetized as described above. In the above-described embodiment, the brushless motor in which the magnet 19 is fixed to the rotating shaft 4 is shown. However, the present invention is not limited to the form in which the magnet is directly fixed to the rotating shaft, but also the rotor core or the like. It is applicable also to the brushless motor of the form which attaches a magnet to a rotating shaft via. Furthermore, although the motor 2 has an SPM configuration in which the magnet 19 is directly opposed to the stator core 14, the present invention is also applied to a motor having an IPM (Interior Permanent Magnet) configuration in which a steel rotor core is provided on the rotor side and a magnet is embedded on the inner side. The invention is applicable.

  In the present invention, the magnet is “fixed to the rotating shaft” means not only the form in which the magnet is directly fixed to the rotating shaft, but also the inner or outer periphery of the rotor core attached to the rotating shaft, etc. The meaning includes a form in which a magnet is fixed to a rotating shaft via a rotor core or the like.

  The brushless motor according to the present invention can be widely applied not only to an in-vehicle motor of an automobile but also to an electric motor used for home appliances, industrial machines and the like.

DESCRIPTION OF SYMBOLS 1 Motor unit 2 Brushless motor 3 Deceleration mechanism part 4 Rotating shaft 5 Output shaft 6 Worm 7 Worm wheel 11 Stator 12 Rotor 13 Motor housing 14 Stator core 15 Yoke part 16 Teeth 16a Tip surface 17 Slot 18 Winding 19 Magnet 19a Magnet outer peripheral surface 21 Bearing 22 Gear case 23 Bearing 24 Bearing 31 First overhang portion 32 Second overhang portion 41 Magnet Lc Stator core axial length Lm Magnet axial length θm Magnetic pole boundary inclination angle θs Skew angle OH1 First overhang portion overhang amount OH2 Second overhang portion overhang amount P Magnetic pole boundary line Q1 Magnetic pole boundary start point Q2 Magnetic pole boundary end point X Thrust direction

Claims (3)

A stator comprising six stator cores extending radially inward along the circumferential direction, and a winding wound around the teeth and housed in a slot formed between the adjacent teeth; ,
A brushless motor having a rotor that is rotatably arranged radially inward of the stator and includes a magnet in which four magnetic poles are formed along the circumferential direction,
The magnet is formed of a ring magnet using a rare earth magnet,
The ring magnet has a skew structure in which the switching position of the magnetic pole is shifted in the rotational direction along the axial direction, and extends axially from both axial end portions of the stator core at both axial end portions. Having one overhang part and a second overhang part,
In the skew structure, the skew angle is set to an electrical angle of 30 ° to 50 °,
The brushless motor according to claim 1, wherein the first and second overhang portions have different extension amounts with respect to the axial end portion of the stator core. The brushless motor according to claim 1,
The brush magnet according to claim 1, wherein the ring magnet has a magnetic orientation of polar orientation magnetized so that a magnetic pole is formed only on an outer peripheral surface. The brushless motor according to claim 1 or 2,
The ratio OH2 / OH1 between the extension amount OH1 of the first overhang portion formed on one end side of the ring magnet and the extension amount OH2 of the second overhang portion formed on the other end side of the ring magnet is A brushless motor set to 1.5 to 2.5.

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