A three-phase permanent magnet-type synchronous motor configured to significantly reduce cogging torque. The motor includes a rotator and stator each having either permanents magnets or teeth. The number of magnetic poles of the rotator or stator is P and a number of slots of the stator or rotator is N, and a fraction of 2N/3P has a value greater than zero and less than one. The tooth width of the teeth of the stator or rotator in a circumferential direction is ½ of the slot pitch of the stator or rotator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a § 371 National Stage Application of International Application No. PCT/JP2012/069325 filed on Jul. 30, 2012, claiming the priority of Japanese Patent Application No. 2012-038656 filed on Feb. 24, 2012.

TECHNICAL FIELD

The present invention relates to a preferred three-phase permanent magnet-type synchronous motor that can obtain smooth rotation in a driving motor or similar portion in an electric car.

BACKGROUND ART

A three-phase permanent magnet-type synchronous motor typically employs a motor where 2N/3P is an integer assuming that the number of magnetic poles in a rotator is P and the number of slots in a stator is N. However, this type of motor has a problem with a large cogging torque. Therefore, to reduce this cogging torque, a technique is proposed. This technique employs a fractional-slot motor where 2N/3P is not an integer and specifies the combination of the number of magnetic poles P and the number of slots N so as to reduce the cogging torque.

For example, Patent Literature 1 discloses that N/P is set to satisfy 1<N/P≤1.2 assuming that the number of magnetic poles is P and the number of slots is N so as to reduce the cogging torque.

Patent Literature 2 discloses that the number of slots N is set to satisfy N=3×[P/2−INT (P/10)] assuming that the number of magnetic poles is P and the number of slots is N so as to reduce the cogging torque. However, INT (P/10) denotes a value of the quotient of P divided by 10.

CITATION LIST

Patent Literature

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2003-032983

SUMMARY OF INVENTION

Technical Problem

Patent Literatures 1 and 2 described above disclose that the fractional slot motor is employed and a predetermined relationship is provided between the number of magnetic poles and the number of slots so as to reduce the cogging torque of the motor. However, it is not possible to sufficiently decrease the cogging torque only by providing the predetermined relationship between the number of magnetic poles and the number of slots.

Therefore, in order to improve these conventional techniques, the present invention has been made to provide a three-phase permanent magnet-type synchronous motor that significantly reduces a cogging torque by employing a fractional slot motor and providing a specific relationship between a slot pitch and a slot width (tooth width) of a stator or a rotator in a permanent magnet-type synchronous motor.

Solution to Problem

The invention of claim1is a three-phase permanent magnet-type synchronous motor. In the three-phase permanent magnet-type synchronous motor, assuming that a number of magnetic poles of a rotator or a stator is P and a number of slots of the stator or the rotator is N, a fraction of 2N/3P is not an integer. The stator or the rotator includes a tooth facing a surface of a magnetic pole of the rotator or the stator via a void, and a tooth width of the tooth in a circumferential direction is approximately ½ of a slot pitch of the stator or the rotator.

The invention of claim2is the three-phase permanent magnet-type synchronous motor according to the invention of claim1in which the stator or the rotator has a tooth tip where corner portions on both sides have curved surfaces.

The invention of claim3is the three-phase permanent magnet-type synchronous motor according to the invention of claim1or2in which the number of magnetic poles of the rotator or the stator is 20 and the number of slots of the stator or the rotator is 24.

The invention of claim4is the three-phase permanent magnet-type synchronous motor according to any one of the inventions of claims1to3. In the three-phase permanent magnet-type synchronous motor, the three-phase permanent magnet-type synchronous motor employs an outer rotor type. The tooth of the stator has a radial cross section with an approximately uniform shape from a tooth tip portion to a tooth root portion or a radial cross section with a larger tooth root portion than a tooth tip portion so as to allow mounting a winding unit from the tooth tip portion. The winding unit is preliminarily wound by a coil.

The invention of claim5is any of the inventions of claims1to4in which the three-phase permanent magnet-type synchronous motor is an in-wheel motor for an electric car.

Advantageous Effects of Invention

According to the inventions of claims1to5, the motor is the fractional slot type. The tooth tip width in the circumferential direction of the stator or the rotator is designed to be ½ of the slot pitch. Thus, the cogging torque can become approximately zero. In particular, according to claim4, furthermore, the tooth of the stator has the cross section with an approximately uniform shape from the tooth tip portion to the tooth root portion or the cross section with the larger tooth root portion than the tooth tip portion. Thus, the winding unit that is preliminarily assembled by the coil can be mounted from the tooth tip. This can facilitate the winding work and ensures a high occupancy rate of the winding inside of the slot.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention is a three-phase permanent magnet-type synchronous motor. In the three-phase permanent magnet-type synchronous motor, assuming that a number of magnetic poles of a rotator or a stator is P and a number of slots of the stator or the rotator is N, a fraction of 2N/3P is not an integer. The stator or the rotator includes a tooth facing a surface of a magnetic pole of the rotator or the stator via a void, and a tooth width of the tooth in a circumferential direction is approximately ½ of a slot pitch of the stator or the rotator.

This allows significantly reducing the cogging torque.

The following describes an embodiment 1 of the present invention based on the drawings. This outer-rotor motor1is constituted of a stator2and a rotator3. The stator2has an approximately circular shape. The rotator3has a cylindrical shape, and rotates on the outer side of the stator2in the circumferential direction. The rotator3has an inner surface with multiple permanent magnets4. Facing the permanent magnets4, a plurality of teeth5is arranged. The plurality of teeth5is radially disposed at a predetermined interval on the outer periphery of the stator2. A slot6is formed between the teeth5adjacent to each other.

The number of magnetic poles in the rotator3is 20. The number of the slots6in the stator2is 24. Accordingly, assuming that the number of magnetic poles in the rotator3is P and the number of slots in the stator2is N, 2N/3P becomes 0.8, thus achieving a fractional slot. The tooth5of the stator2in the radial direction has a square cross section that has the same size and the same shape from the tooth tip portion to the tooth root portion. While the illustration is omitted, a coil is wound around the outer periphery of each tooth5in the stator2.

FIG. 2illustrates a relationship between a width L1and a pole pitch L2of the permanent magnet4in the rotator3and a tooth width L3of the tooth5and a slot pitch L4of the slot6in the stator2. The ratio of the magnet width L1to the pole pitch L2is generally set to about 0.6 to 0.8. However, during the analysis described later, ⅔ the magnet width L1is set to the pole pitch L2. The ratio of the slot pitch L4to the tooth width L3in the tooth5is approximately twice.

Both of a magnet magnetomotive force (A) on the rotator3side and a magnetic susceptance (X) of the stator2are multiplied together as a magnetic flux density (B). This magnetic flux density (B) is squared as a magnetic energy distribution (D=B2). Then, D is integrated over the whole circumference as the total amount of magnetic energy (Qm). When a displacement (x) in the rotation direction of the rotator3and an electromagnetic force (F) are defined, the algorithm for calculating the electromagnetic force (F) is as follows.

FIG. 3illustrates a result of analysis using mathematical analysis software (whose product name is “Mathematica”).FIG. 3is a graph illustrating a change in maximum value of a cogging torque by changing the tooth width L3with respect to the slot pitch L4.

In a simulation result where that the number of magnetic poles is set to 20 and the number of slots (the number of teeth) is set to 24, the cogging torque becomes substantiality zero when the tooth width L3/the slot pitch L4=½. Here, also in the case where the number of magnetic poles, the number of slots, and the relationship between the number of magnetic poles and the number of slots are changed, a similar trend is seen.

In the present invention, as illustrated inFIG. 1, wings projecting from a tooth tip portion5ain each tooth5to both sides are removed. In the case where the cross-sectional shape is the same from the tooth tip portion5ato a tooth root portion5blike this or the cross-sectional shape becomes gradually larger from the tooth tip portion5atoward the tooth root portion5b, as illustrated inFIG. 4, a large number of winding units25that are each formed by preliminarily wounding a coil24on a bobbin23are manufactured. This winding unit25is inserted into each tooth5of the stator2from the distal end so as to simply wind the coil.

A known method is used, for example, the outer side of the coil24in this winding unit25is fixed with a wrapping paper or the coil24is fixed with an adhesive such that the coil24wound on the bobbin23is not collapsed. After the winding units25are mounted on the respective teeth5, the winding units25are fixed to the teeth5as necessary and then the coils24are coupled to one another.

With the above-described configuration, the coil24is wound using a flyer or similar tool outside of the stator2. This allows sufficient winding without taking into consideration a conventional nozzle space and allows utilizing a conductor with a rectangular cross section or similar material for the coil. In a trial calculation, in the case where the number of magnetic poles is 20 and the number of slots is 24, a 1.5 times larger amount of coil can be housed compared with coil winding with a nozzle method.

After the winding units25are mount on the teeth5, as illustrated inFIG. 5, slot portions26disposed in distal end portions of the teeth5receive protruding portions27located at the distal ends23aof the bobbins of the winding units25. The protruding portions27are fitted into the slot portions26. This allows retaining and locking of the winding units25with respect to the teeth5such that the winding units are not displaced or thrown out from the slots6. It is preferred to round the distal end portions of the teeth (i.e. teeth tip portions5a) in the circumferential direction to prevent torque noise at high frequency and facilitate insertion of the winding units25. The rotator3has a base3cdefining an inner surface with a first set of transverse retaining slots3bfor multiple permanent magnets4and a set of transverse recesses3awhich are respective indentations between adjacent transverse retaining slots3b. A said transverse recess3ais between adjacent transverse retaining slots3b.FIG. 5shows one transverse recess between each pair of adjacent transverse retaining slots for the multiple permanent magnets. Each transverse recess3ais indented relative to a phantom circle3dconnecting the end points of the transverse recesses3a3a.FIG. 5shows a portion of the phantom circle3d. The permanent magnets4are provided with tapering side edges cooperating with inner tapering edges of transverse retaining slots3bprovided in a retaining surface of the rotator3together configured to retain and lock each permanent magnet4within each respective slot during operation of the motor. The retaining surface being the inner tapering edges of the transverse retaining slot3bas well as the back surface of the retaining slot in contact with the permanent magnet4. The permanent magnets4and slots are configured to retain only a base portion of each permanent magnet in each respective slot of the retaining surface while an exposed portion of each permanent magnet4protrudes outwardly from the retaining surface of the rotator3in a direction towards teeth tip portions5aof the teeth5of the stator2.FIG. 5also shows the rotator3is provided with a recess3afacing the stator2at a portion between the permanent magnets4which are adjacent.

FIG. 6illustrates an embodiment 2 for the shape of tooth of the present invention. As illustrated in the drawing, a tooth tip portion5a′ of a tooth5′ facing the permanent magnet4of the outer rotor has a width that is ½ of a slot pitch while the portion other than the tooth tip portion5a′ of the tooth5′ has a larger tooth width. The embodiment 2 is otherwise similar to the embodiment 1.

This embodiment 2 also employs a fractional slot and uses an outer rotor to allow inserting the winding unit25into each tooth5. With the fractional slot, a magnetic-flux utilization rate can be maintained even without tooth heads (wings). The tooth width can be actively adjusted so as to reduce the pulsation torque.

Next,FIG. 7illustrates a schematic configuration diagram when the three-phase permanent magnet-type synchronous motor of the present invention is applied to an in-wheel motor for an electric car.

As illustrated in the drawing, the outer-rotor motor1that includes the stator2and the rotator3outside of the stator2is housed in a wheel10. The wheel10includes a rim8in an approximately cylindrical shape and a disk9. The disk9of the wheel10is secured to a flange12with a bolt13. The flange12is disposed at the end portion of a shaft11. The flange12is secured to a motor cover15with a bolt14. The motor cover15covers the outer side of the motor1.

Accordingly, by rotation of the rotator3, this rotation is transmitted to the motor cover15, the flange12, and the wheel10in this order. Thus, a tire16mounted on the rim8is rotated. The stator2is secured to an inner frame17on the inner side of the stator2. Between the inner frame17and the shaft11, a bearing18intervenes. The inner frame17is secured to a knuckle20with a bolt19. Additionally, a disk caliper21is secured to the knuckle20with the bolt19so as to freely grip a brake disc22that is secured to the outer periphery of the shaft11.

While in the above-described embodiments the examples of the outer-rotor motor has been described, the present invention is applicable to an inner-rotor motor.

REFERENCE SIGNS LIST