The present invention relates to a motor provided with a twin rotor.
Stator 60 includes: annular yoke 61; a plurality of outer teeth 62 and outer slots 63 provided on an outer circumference of yoke 61; and a plurality of inner teeth 65 and inner slots 66 provided on an inner circumference of yoke 61. Yoke 61 is provided with a plurality of coils 64 wound in toroidal shape across outer slots 63 and inner slots 66.
Meanwhile, two rotors 70 and 75 are provided outside and inside of stator 60. Outer rotor 70 includes outer permanent magnet 72 facing outer teeth 62 and outer yoke 71, and is held outside of stator 60 rotatably. Inner rotor 75 includes inner permanent magnet 77 facing inner teeth 65 and inner yoke 76, and is held inside of stator 60 rotatably.
Coils 64 are formed in three-phase star or delta connection. When coils 64 are energized, outer rotor 70 and inner rotor 75 start rotating all together to a predetermined direction by a torque generated by magnetic field by current-flow through coils 64.
Stator 60 is provided with a plurality of mounting-holes 80 at intersections of outer teeth 62 and inner teeth 65 on annular yoke 61. Mounting-holes 80 run through yoke 61.
Since a twin rotor motor has outer rotor 70 and inner rotor 75 on outside and inside of stator 60 respectively, stator 60 cannot be fixed by usual fitting methods such as shrink-fitting or press-fitting. Therefore, mounting-holes 80 are provided so as to enable stator 60 to be fixed on a machine by inserting bolts or the like (not shown) through mounting-holes 80 as shown in
The conventional fitting method is disclosed in a technical document: IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 40, NO 3, MAY/JUNE 2004. In “Section A. Flux Distribution” of the paper: “Design and Parameter Effect Analysis of Dual-Rotor, Radial-Flux, Toroidally-Wound, Permanent-Magnet Machines” on page 774 in the document, it is described that the bolt-holes will increase leakage flux, causing stator core to decrease in flux density by 15%.
The conventional twin rotor motor can be provided with mounting-holes 80 to fix stator 60 on the machine, which however requires areas for forming mounting-holes somewhere in yoke 61.
To minimize influences on the motor performance, mounting-holes 80 should preferably be formed at intersections of outer teeth 62 and inner teeth 65 on annular yoke 61 as shown in
In cases like this, it sometimes occurs that the width required to keep mechanical strength for fixing is larger than widths of yoke 61, outer teeth 62 or inner teeth 65 that are required for magnetic circuit designing. Therefore, because for instance the larger the width of outer teeth 62 or inner teeth 65 the smaller the area of slots become, the current density will increase to cause reliability problems, and then, enlarging the slot area to restrict the increase in current density will shorten the outer diameter of inner rotor 75, causing the motor to decrease in torque force. Enlarged yoke width will also shorten the outer diameter of inner rotor 75, causing the motor to decrease in torque force. As a result, forming mounting-holes 80 will cause difficulty in obtaining full performance of the motor.
A twin rotor motor of the present invention has the following configuration.
A stator comprising: an annular yoke; a plurality of outer teeth and outer slots provided on an outer circumference of the yoke; a plurality of inner teeth and inner slots provided on an inner circumference of the yoke; and a plurality of toroidally-wound coils on the yoke.
A rotor comprising: an outer rotor provided with an outer permanent magnet facing the outer teeth; and an inner rotor provided with an inner permanent magnet facing the inner teeth.
Moreover, the stator is provided with a resin mold that seals the coils and has a mounting-tab. The configuration can provide the twin rotor motor with high performance without causing poor properties such as decrease in motor efficiency or torque force.
A preferred embodiments of the present invention are described below with reference to the drawings.
Stator 10 includes: annular yoke 11; a plurality of outer teeth 12 and outer slots 13 provided on an outer circumference of yoke 11; and a plurality of inner teeth 15 and inner slots 16 provided on an inner circumference of yoke 11. Yoke 11 is provided with a plurality of coils 14 wound toroidally across outer slots 13 and inner slots 16. Resin mold 30 is provided to seal coils 14 as indicated by hatching in
Meanwhile, two rotors 20 and 25 are provided outside and inside of stator 10. Outer rotor 20 includes outer permanent magnet 22 facing outer teeth 12 and outer yoke 21. Inner rotor 25 includes inner permanent magnet 27 facing inner teeth 15 and inner yoke 26. Both outer permanent magnet 22 and inner permanent magnet 27 are magnetized to form four poles (pole-pair number=2).
Stator 10 is provided with resin mold 30 so as to seal coils 14. Resin mold 30 improves the heat dissipation property of coils 14 effectively.
Furthermore, resin mold 30 has mounting-tab 31. Mounting-tab 31 should preferably be molded integrally with resin mold 30. Mounting-tab 31 can be fixed on a machine for instance by using bolts or the like into through-holes drilled axially. The fixing method on the machine is not limited to bolting only but crimping or welding are available. Though pedestal-shaped mounting-tab 31 is shown in
As described above, mounting-tab 31 molded integrally with resin mold 30 can eliminate through-holes provided on yoke 11 of the stator core and the shape of stator 10 can be determined by the design factors of the magnetic circuit only that have decisive influences on the motor properties. The configuration, therefore, can realize the twin rotor motor with a high performance without causing any decrease in motor properties due to taking the fixing method on the machine into account.
In
In this way, being the rotor output shafts united into a single output shaft, the motor output shaft will have the sum of output torques of outer rotor 20A and inner rotor 25A consequently. The motor, therefore, will have a higher output torques.
As described above, inner/outer rotor yoke 40, which is necessary for attaching outer rotor 20A with inner rotor 25A, is formed so as to cover one side in axial direction of stator 10. Therefore, it is very difficult to form through-holes on yoke 11 of stator core for fixing rotors on the machine. As described in this embodiment, however, the motor can be fixed on the machine very easily by using mounting-tab 31 molded on resin mold 30 integrally.
In this embodiment, the shape of resin mold 30A differs from embodiment 1 and 2. Namely, the structure is such that resin mold 30A is shortened radially so as to expose the respective tops of outer teeth 12 and inner teeth 15. The exposing structure can be applied to either or both of outer teeth 12 and inner teeth 15.
The resin mold 30A sealing coil 14 improves heat dissipation and acts to restrict temperature increase in coil 14. In this embodiment, however, the effect can be obtained sufficiently by resin mold 30A only that has the minimum necessary amount of resin, thus reducing material usages.
Moreover, the tops of outer teeth 12 and inner teeth 15 in the exposed structure can be used for positioning in motor assembling. Especially, the twin rotor motor such as described in the present invention needs a high accuracy in coaxiality or the like between stator and outer and inner rotors compared with normal motors. At this time, both radial surfaces of outer teeth 12 and inner teeth 15 and an axial end surface can be used for positioning in assembling, causing a great effect on assembling the motor highly accurately.
The embodiment shows a 20-pole/12-slot twin rotor motor with the combination ratio of pole-pair number P to slot number Ns of P:Ns=5:6.
Two rotors 20B and 25B are provided outside and inside of stator 10B respectively. Outer rotor 20B includes outer permanent magnets 22B facing outer teeth 12 and outer yoke 21. Inner rotor 25B includes inner permanent magnets 27B facing inner teeth 15 and inner yoke 26. Outer permanent magnets 22B and inner permanent magnets 27B are both magnetized to have 20 poles (pole-pair number P=10).
In case of the combination ratio of pole-pair number P to slot number Ns of P:Ns=5:6 as described in this embodiment, the torque constant of the motor is the same as that of P:Ns=1:6 in embodiment 1. Meanwhile, increase in pole-pair number causes stator core 12 to decrease in flux density. This means that iron loss generated in the stator core decreases, thus improving the motor efficiency consequently.
Meanwhile, coil 14B provided on yoke 11 can be formed by changing the coil arrangement only with the toroidal shape kept unchanged as shown in
Furthermore, the fact that the flux density decreases in the stator core means that teeth 12 and 15 or yoke 11 can be designed narrower in width without any decrease in torque force. When for instance teeth 12, 15 and yoke 11 are designed narrower in width while keeping the same slot area, the outer diameter of inner rotor can be enlarged to improve torque property or motor efficiency. Narrowing the width of yoke 11 is able to have an effect of a shorter perimeter length of coil 14B and accordingly a decrease in copper loss due to reduced coil resistance.
As described above, the configuration of this embodiment can realize the twin rotor motor with a high efficiency.
The twin rotor motor is provided with a resin mold to seal coils on a stator, and a mounting-tab formed integrally on the resin mold can eliminate through-holes in a yoke of stator core to fix the stator on a machine. The configuration can provide the twin rotor motor generating a high torque force efficiently without causing poor motor properties due to taking the fixing way on the machine into account.
Number | Date | Country | Kind |
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2005-209735 | Jul 2005 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2006/302464 | 2/13/2006 | WO | 00 | 12/6/2007 |