JP2014093914A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce torque ripples while improving output, in a magnet auxiliary type reluctance motor.SOLUTION: A motor 1 is a magnet auxiliary type reluctance motor that makes a rotor rotate with reluctance torque and magnet torque, and comprises a stator 2 having tooth parts 9, and a rotor 3 in which magnets 16 are buried. The stator 2 has bridge parts 32 connecting between front end parts 9a of the tooth parts. The rotor 3 has arcuate slits 34 for housing the magnets 16, and a 4-pole magnetic pole part 35 formed of the magnets 16. When a length in a circumferential direction of the bridge parts 32 is defined as W1, and an interval between the slits 34 of the magnetic pole part 35 is defined as W2, W1 and W2 are set to have a relation of W1≤W2, and thereby, a change in reluctance torque accompanied by the rotation of the rotor 3 is made moderate, and torque ripples are reduced.

Description

  The present invention relates to a brushless motor that rotates a rotor using reluctance torque, and more particularly, to a magnet-assisted reluctance motor that embeds a magnet in the rotor and rotates the rotor by using the magnetic force of the magnet in an auxiliary manner.

  2. Description of the Related Art Conventionally, a reluctance motor is known as a type of electric motor that generates a rotational force by utilizing a magnetic resistance difference between a stator and a rotor. In such a reluctance motor, the rotor is rotated by a reluctance torque generated by a magnetic resistance difference. However, since the reluctance torque is smaller than the torque obtained by the magnet, the output torque of the reluctance motor tends to be smaller than that of the same-sized motor using the magnet. Therefore, in recent years, a magnet-assisted reluctance motor has been proposed in which a basic configuration is a reluctance motor and a magnet is arranged on a rotor. For example, Patent Document 1 describes such a magnet-assisted reluctance motor, and shows a configuration in which a magnet is embedded in the rotor of the reluctance motor.

JP 2011-83066 JP

  On the other hand, in the magnet-assisted reluctance motor, the reluctance torque changes with the rotation of the rotor, so that a torque ripple is generated with the rotation of the rotor. For this reason, for example, in Patent Document 1, the change of the reluctance torque is reduced by adopting a closed stator structure in which the front end portions of the stator are connected to reduce torque ripple. However, even when such a closed stator structure is adopted, in the motor in which the rotor core outside the magnet becomes a magnetic path when current is applied, it is unavoidable that the magnetic flux from the stator is biased and torque ripple remains. In particular, the magnet-assisted reluctance motor has a problem in that the effect of torque ripple is increased because the ratio of reluctance torque is large.

  In addition, when a magnet-assisted reluctance motor is used as a motor for an electric power steering apparatus, torque ripple causes a deterioration of steering feeling and causes a driver to feel uncomfortable. For this reason, from the viewpoint of comfortable driving, reduction of torque ripple in the motor has been demanded.

  An object of the present invention is to reduce torque ripple while improving output in a brushless motor, in particular, a magnet-assisted reluctance motor.

  The brushless motor of the present invention, a stator comprising a plurality of teeth portions projecting radially inward, and a coil wound around the teeth portions through slots formed between the teeth portions, A brushless motor having a rotor rotatably disposed inside the stator, wherein the stator includes a bridge portion that is provided at a distal end portion on the radially inner side of the tooth portion and connects adjacent tip portions. And the rotor is provided along a circular arc having a center point on the outer side of the rotor, and a plurality of arc-shaped slits formed in the rotor in a shape in which a convex side portion is directed toward the central side of the rotor. A plurality of magnets housed in each of the slits, and a plurality of magnetic pole portions formed by the magnets and disposed along a circumferential direction of the rotor. When the circumferential length of the wedge portion is W1, and the interval between the slits in the magnetic pole portion of the same polarity is W2, the W2 is set not to be smaller than the W1 (W1 ≦ W2). Features.

  In the present invention, since the relationship between W1 and W2 is set so as to satisfy W1 ≦ W2, the direction and magnitude of the reluctance torque gradually change as the rotor rotates. Therefore, a sudden change in the reluctance torque can be suppressed, and torque ripple can be reduced.

  In the brushless motor, the interval W2 between the slits may be set to the same dimension between the slits belonging to the magnetic pole portion having the same polarity, thereby suppressing torque ripple and improving the workability of the slit. improves. In consideration of the workability of the slit, the circumferential length W1 of the bridge portion may be set to 0 or more and not more than the interval between the tip portions of the adjacent tooth portions.

  The stator may be configured by laminating a plurality of steel plate materials, and the radial width t1 of the bridge portion may be set to substantially the same value as the plate thickness of the plate material, and the slit in the rotor The width t2 between the outer diameter side end of the rotor and the outer peripheral edge of the rotor may be set to a value substantially the same as the plate thickness of the plate member, thereby improving the torque.

  Both ends of the bridge portion in the circumferential direction on the slot side may be connected to the teeth portion and the chamfered portion, thereby improving the workability of the slit.

  On the other hand, opposing inner surfaces in the circumferential direction of the slots may be provided parallel to each other along the radial direction, and the distance between the inner surfaces may be set to be substantially the same as the thickness of the wire constituting the coil. As a result, the coil wire can be arranged well within the slot, and the coating of the wire is hard to be damaged at the time of forming the coil, and the insulation is improved.

  According to the brushless motor of the present invention, in the magnet-assisted reluctance motor, the teeth of the stator are connected to each other at the bridge portion, and a slit for accommodating the magnet is provided in the rotor. By forming the magnetic pole portion along the circumferential direction, W1 as the circumferential length of the bridge portion, and W2 as the interval between the slits in the magnetic pole portion of the same polarity, by setting W1 and W2 as W1 ≦ W2, The change in reluctance torque accompanying the rotation of the rotor becomes gradual, and torque ripple can be reduced. Thereby, for example, it becomes possible to provide a motor for electric power steering with reduced torque ripple, and the steering feeling in electric power steering can be improved.

It is sectional drawing of the brushless motor which is one Example of this invention. It is sectional drawing along the AA line of FIG. It is explanatory drawing which shows the structure of the X section of FIG. It is explanatory drawing which shows the mode of the coil | winding accommodated in the slot, (a) is the structure in the motor by this invention using a parallel slot structure in the case of the conventional structure where the slot became a fan shape. Each case is shown. It is a graph which shows the experimental result of the present inventors, and has shown the relationship between a rotor rotation angle and a torque. It is explanatory drawing which compared and showed the average torque of the conventional motor and the motor of this invention based on the experimental result of FIG. It is explanatory drawing explaining the torque ripple reduction effect | action by this invention. It is explanatory drawing which compared and showed the torque ripple of the conventional motor and the motor of this invention based on the experimental result of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a brushless motor 1 (hereinafter abbreviated as “motor 1”) according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA of FIG. The motor 1 is based on a reluctance motor, and is a magnet-assisted reluctance motor that uses the magnet's magnetic force by arranging magnets on the rotor, and is used as a drive source for an electric power steering device. The As shown in FIG. 1, the motor 1 is an inner rotor type brushless motor in which a stator (stator) 2 is disposed on the outside and a rotor (rotor) 3 is disposed on the inside, similarly to a normal reluctance motor.

  The stator 2 is fixed inside a bottomed cylindrical motor case 4 (hereinafter abbreviated as case 4). The stator 2 includes a stator core 5, a stator coil 6 (hereinafter abbreviated as a coil 6) wound around a tooth portion 9 of the stator core 5, and a bus bar unit (terminal) attached to the stator core 5 and electrically connected to the coil 6. Unit) 7. The case 4 is formed in a bottomed cylindrical shape with iron or the like, and an aluminum die cast bracket 8 is attached to an opening of the case 4 with a fixing screw (not shown).

  The stator core 5 is formed by laminating steel plate materials (for example, electromagnetic steel plates), and a plurality of teeth portions 9 are provided projecting radially inward. Slots 31 are formed between adjacent tooth portions 9, in which the coils 6 are accommodated in distributed winding. An insulator 11 made of synthetic resin is attached to the stator core 5, and a coil 6 is wound around the outside of the insulator 11.

  FIG. 3 is an enlarged view of the tooth portion 9 portion, that is, the X portion of FIG. As shown in FIG. 3, on the inner peripheral side of the teeth portion 9, a bridge portion 32 that connects adjacent tooth tip portions 9 a is provided. The bridge portion 32 is provided with a chamfered portion 33 (R or C chamfer) between the teeth tip portion 9a so that the magnetic flux on the stator side can easily flow and press working is facilitated. The bridge portion 32 has a radial width t <b> 1 set to a value substantially the same as the thickness of the electromagnetic steel plate constituting the stator core 5. The reason why the coil 6 is distributed winding as described above is that there is less leakage of magnetic flux at the bridge portion 32 compared to concentrated winding, and the maximum torque can be increased compared to concentrated winding.

  Further, the tooth portion 9 has a width B in the circumferential direction that is narrower toward the distal end portion, and the tooth portion 9 is generally fan-shaped with a central angle θ. Thereby, the slot 31 will be in the state where the inner surface 31a of the opposing circumferential direction is mutually parallel along radial direction. Conventionally, in a magnet-assisted reluctance motor, teeth have a straight shape with an equal width, and slots have a fan shape. For this reason, when the winding is accommodated in the slot, as shown in FIG. 4A, the coil does not fit, and when the coils are welded, the coils may slip and cause insulation failure. In particular, in the case of the configuration in which the teeth inner peripheral side is connected like the motor 1, since coiling by the winding machine is difficult, a method of inserting a thick coil into the slot and then welding between the coils is adopted. In such a motor, it is necessary to twist the coil during welding, and if there is play in the coil in the slot, the coil may slide and damage the coil coating.

  On the other hand, in the motor 1, since the inner surface 31 a of the slot 31 is in a parallel state, as shown in FIG. In this case, the width SW of the slot 31 is set to be approximately the same (or slightly larger) than the thickness of the wire constituting the coil 6, and the coil 6 is accommodated in the slot 31 with little play. For this reason, even if it twists a coil in the case of welding, a coil does not move easily and it also becomes difficult for a coil to slide. Therefore, it is possible to prevent damage to the coil film and improve the insulation of the coil.

  On the other hand, in the motor 1, as described above, the width on the root side of the tooth portion 9 is wide. For this reason, the flow of magnetic flux in the teeth becomes smooth, and magnetic flux saturation in the tooth portion is less likely to occur. Further, since the space of the back core portion in the stator core 5 is widened and the magnetic resistance is reduced as compared with the case where the teeth are straight, it is possible to increase the torque as compared with the motor of the same size. . FIG. 5 is a graph showing experimental results by the inventors, and FIG. 6 is an explanatory diagram showing comparison of average torques of the conventional motor and the motor of the present invention based on the experimental results. As can be seen from FIGS. 5 and 6, the motor according to the present invention has an improved torque compared to the conventional motor, and the average torque can be increased by about 5%.

  A bus bar unit 7 is attached to one end side of the stator core 5. The bus bar unit 7 has a structure in which a copper bus bar is insert-molded in a synthetic resin main body. Around the bus bar unit 7, a plurality of power supply terminals 12 project in the radial direction. When the bus bar unit 7 is attached, the end 6 a of the coil 6 drawn out from the stator core 5 is welded to the power feeding terminal 12. In the bus bar unit 7, the number of bus bars corresponding to the number of phases of the motor 1 (here, three for the U phase, V phase, W phase and one for connecting each phase) is provided. Yes. Each coil 6 is electrically connected to a power supply terminal 12 corresponding to the phase. The stator core 5 is press-fitted and fixed in the case 4 after the bus bar unit 7 is attached.

  A rotor 3 is inserted inside the stator 2. The rotor 3 has a rotor shaft 13, and the rotor shaft 13 is rotatably supported by bearings 14a and 14b. The bearing 14 a is fixed to the center of the bottom of the case 4, and the bearing 14 b is fixed to the center of the bracket 8. A cylindrical rotor core 15 and a rotor (resolver rotor) 22 of a resolver 21 serving as a rotation angle detection unit are attached to the rotor shaft 13. A stator (resolver stator) 23 of the resolver 21 is accommodated in a resolver bracket 24 made of synthetic resin, and is fixed to the inside of the bracket 8 by an attachment screw 25.

  The rotor core 15 is also formed by laminating a large number of disk-shaped electromagnetic steel plates. The steel plate constituting the rotor core 15 is provided with a plurality of slits 34 as flux barriers for varying the magnetic resistance of the rotor 3 along the rotation direction. The slit 34 is bent in an arc shape, and the inside of the slit 34 is a space. The slit 34 is provided along an arc centered on a virtual point (not shown) set outside the outer periphery of the rotor 3, and the slit 34 is formed in the rotor so that the convex side portion faces the center side of the rotor 3. Yes. A width t2 between the outer diameter side end portion 34a of the slit 34 and the outer peripheral edge 15a of the rotor core 15 is set to a value substantially the same as the plate thickness of the electromagnetic steel sheet.

  When the direction of the magnetic flux generated by the magnetic pole (center axis of the permanent magnet) is d-axis and the axis magnetically orthogonal to it (axis between the permanent magnets) is q-axis, the slit 34 is orthogonal to the rotor shaft 13. A plurality of sets are provided with the q axis as the boundary. In the motor 1, four sets of a plurality of slits 34 are provided in an arc shape, and a plurality of layers of magnetic paths are formed in each set.

  In the motor 1, in order to improve the output, a plurality of magnets (permanent magnets) 16 are embedded in the slits 34, and magnetic pole portions 35 are formed along the circumferential direction at the portions of the respective magnets 16. . In the motor 1, the reluctance torque is main and the magnet torque is auxiliary, and an inexpensive ferrite magnet is used as the magnet 16. However, a rare earth magnet such as a neodymium bond magnet may be used for the magnet 16 in order to further increase the output.

  In the rotor 3, as a plurality of magnets 16 forming the magnetic pole portion 35, a magnet 16s having an S pole on the outer peripheral side and a magnet 16n having an N pole on the outer peripheral side are provided. The rotor 3 has a 4-pole configuration including four magnetic pole portions 35, and the motor 1 is formed in a 4-pole 24-slot configuration. The magnets 16 of each pole are formed in an arc shape, and three are provided along the radial direction, and a plurality of d-axis and q-axis are alternately provided in the circumferential direction on the rotor 3. Thereby, torque reinforcement by magnet torque is achieved while using reluctance torque effectively.

  In the rotor 3, as described above, the direction of the magnetic flux generated by the magnetic pole is set as the d axis, the axis magnetically orthogonal thereto is set as the q axis, and a plurality of d axes and q axes are set in the rotor 3. At that time, the d-axis and the q-axis are alternately provided along the circumferential direction. The rotor 3 is provided with an arc-shaped slit 34 to facilitate passage of the q-axis magnetic flux, and an arc-shaped magnet 16 is embedded therein. That is, the rotor 3 has a structure in which the q-axis magnetic flux easily passes and the inductance Lq can be increased. Therefore, the magnet torque by the magnet 16 can be increased, and a sufficient torque can be obtained even with the ferrite magnet.

  On the other hand, in the motor 1, a relationship of W 1 ≦ W 2 is set between the circumferential width dimension W 1 of the stator side bridge portion 32 and the dimension W 2 between the slits 34 of the rotor core 15. In this case, W <b> 1 is the distance between the tips of the double-sided chamfered portion 33 in the bridge portion 32. W2 is the distance between adjacent slits 34 in the same pole, and is the circumferential length of the magnetic path portion 36 formed between the slits 34. The motor 1 has a closed stator structure that cancels out the change in reluctance torque, and the torque ripple is kept relatively small. However, the dimension setting W1 ≦ W2, that is, the stator-side bridge portion 32 is replaced with the rotor-side magnetic path portion. By setting it not to be wider than 36, the fluctuation of the reluctance torque is moderated, and further the torque ripple is reduced.

  FIGS. 7A and 7B are explanatory diagrams for explaining the torque ripple reduction effect by the above setting according to the present invention. FIG. 7A shows a case where W1> W2, and FIG. 7B shows a case where W1 ≦ W2 as in the present invention. Yes. As shown in FIG. 7A, when W1 and W2 are set to W1> W2, when the rotor 3 rotates and enters the state as shown in (a), the magnetic path portion 36p of the rotor 3 Since it is close to the tooth portion 9p, reluctance torque in the direction opposite to the rotation direction is generated by the magnetic flux φ1 flowing from the tooth portion 9p to the magnetic path portion 36p. Next, when the rotor 3 rotates (b) (when the centers of the rotor-side magnetic path portion 36 and the stator-side bridge portion 32 are coincident with each other), the magnetic resistance increases. Therefore, the magnetic flux φ2 rapidly decreases, and the right magnetic flux φ3 that cancels the magnetic flux φ2 also decreases. Although the change in the amount of magnetic flux is improved by the closed stator structure, the reluctance torque suddenly decreases between (a) and (b).

  Further, when the rotor 3 further rotates (C), the magnetic path portion 36p is now closer to the right tooth portion 9q side, so that the magnetic flux φ4 flowing from the tooth portion 9q to the magnetic path portion 36p suddenly increases. Reluctance torque is generated in the same direction (forward direction) as the rotational direction. In other words, when W1> W2, the direction and magnitude of the reluctance torque changes abruptly, such as (a) reluctance torque generation in the reverse direction → (b) sudden decrease in reluctance torque → (c) reluctance torque generation in the forward direction. To do. For this reason, although it is suppressed by the closed stator structure, it is difficult to avoid the occurrence of torque ripple due to a sudden change in the reluctance torque.

  On the other hand, as shown in FIG. 7 (b), when W1 and W2 are set to W1 ≦ W2, in the state of (A), as in (a), the direction opposite to the rotation direction is caused by the magnetic flux φ1. Reluctance torque is generated. On the other hand, when the rotor 3 is rotated (B), W2 is larger than W1 here, so that the facing portion R exists between the tip portion of the tooth portion 9 and the magnetic path portion 36p of the rotor 3. For this reason, the magnetic resistance does not decrease rapidly, and the magnetic fluxes φ2 and φ3 increase compared to the case (a). That is, the left and right magnetic fluxes φ2 and φ3 are gently canceled while effectively utilizing the magnetic flux entering by the closed stator structure and suppressing the change of the magnetic flux amount.

  Further, when the rotor 3 further rotates (c), a magnetic flux φ4 is generated as in (a), and at the same time, a magnetic flux φ5 flowing from the tooth portion 9p to the magnetic path portion 36p also remains. Therefore, the magnetic flux φ4 increases while canceling out by φ5, and the reluctance torque in the forward direction is gradually generated. That is, even in the case of W1 ≦ W2, the process follows (i) reverse reluctance torque generation → (b) reluctance torque decrease → (c) forward reluctance torque generation, but the right and left magnetic fluxes cancel each other as appropriate. The direction and magnitude of the reluctance torque changes slowly. Therefore, the sudden change of the reluctance torque as shown in (a) is suppressed, and the torque ripple is reduced. FIG. 8 is an explanatory diagram showing experimental results by the inventors (comparing the ripples in FIG. 5). As can be seen from FIG. 8, the motor according to the present invention reduces torque ripple as compared with the conventional motor. It is possible.

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, the circumferential width dimension W1 of the bridge portion 32 is 0, that is, when the facing chamfered portions 33 are continuously in contact with each other, the distance between adjacent tooth tip portions 9a (the chamfered portion 33 is not provided). If you can take up). Further, the brushless motor according to the present invention can be applied to other electric machines and devices such as a hybrid vehicle and an electric vehicle in addition to the electric power steering device.

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Stator 3 Rotor 4 Motor case 5 Stator core 6 Stator coil 6a Coil end part 7 Bus bar unit 8 Bracket 9 Teeth part 9a Teeth tip part 9p, 9q Teeth part 11 Insulator 12 Power supply terminal 13 Rotor shaft 14a, 14b Bearing 15 Rotor core 15a Outer peripheral edge 16 Magnet 16n N pole magnet 16s S pole magnet 21 Resolver 22 Resolver rotor 23 Resolver stator 24 Resolver bracket 25 Mounting screw 31 Slot 31a Inner surface 32 Bridge portion 33 Chamfered portion 34 Slit 34a Outer diameter side end portion 35 Magnetic pole portion 36 Magnetic path portion 36p Magnetic path portion R Opposing portion W1 Bridge portion circumferential length W2 Spacing t1 between magnetic pole portions of the same polarity t1 Bridge portion radial width t2 Slit Width θ teeth central angle between the outer diameter side end portion and the rotor core outer periphery 15a

Claims (7)

A stator comprising a plurality of teeth portions projecting radially inward, and a coil wound around the teeth portions via slots formed between the teeth portions;
A brushless motor having a rotor rotatably disposed inside the stator,
The stator has a bridge portion that is provided at a radially inner tip portion of the teeth portion and connects adjacent tip portions.
The rotor is provided along a circular arc having a center point on the outside of the rotor, and a plurality of arc-shaped slits formed in the rotor in a shape in which a convex side portion faces the central side of the rotor, A plurality of magnets housed in the slit, and a plurality of magnetic pole portions formed by the magnets and disposed along the circumferential direction of the rotor,
When the circumferential length of the bridge portion is W1 and the interval between the slits in the magnetic pole portion having the same polarity is W2, W2 is set not to be smaller than W1 (W1 ≦ W2). Features a brushless motor. The brushless motor according to claim 1,
The brushless motor is characterized in that the interval W2 between the slits is set to the same dimension between the slits belonging to the magnetic pole part having the same polarity. The brushless motor according to claim 1 or 2,
A circumferential length W1 of the bridge portion is set to be not less than 0 and not more than an interval between the tip portions of the adjacent teeth portions. The brushless motor according to any one of claims 1 to 3,
The stator is configured by laminating a plurality of steel plate materials,
A brushless motor, wherein when the width of the bridge portion in the radial direction is t1, the t1 is set to a value substantially equal to the plate thickness of the plate member. In the brushless motor according to any one of claims 1 to 4,
The stator is configured by laminating a plurality of steel plate materials,
Brushless, wherein t2 is set to be substantially the same as the plate thickness of the plate material, where t2 is the width between the outer diameter side end of the slit and the outer peripheral edge of the rotor in the rotor. motor. The brushless motor according to any one of claims 1 to 5,
Both ends of the bridge portion in the circumferential direction on the slot side are connected to the teeth portion and chamfered portions at a brushless motor. In the brushless motor according to any one of claims 1 to 6,
The slots have inner surfaces facing each other in parallel to each other along a radial direction, and the distance between the inner surfaces is set to be substantially the same as the thickness of the wire constituting the coil. Brushless motor.

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