There are several advantages as follows that the permanent magnet motor possesses such as: the simplified structure, the reliable motion, the small volume, the light weight, the lower losses and the highly efficiency etc. Furthermore, the shape and the size of the motor are easily variable such that it is wildly applicable to the field of the aviation industry, the national defense, the industry, the agriculture and the respective field in the daily life.
Please referring to FIG. 1, which is a cross-sectional view illustrating the rotary structure of a conventional outer rotor permanent magnet motor, in which a permanent magnet motor with eight poles and six slots is presented as an example for addressing the rotary structure 801 of a permanent magnet motor. The rotary structure 801 of a permanent magnet motor includes a stator 30 and a rotor 40, in which the cylindrical stator 30 is fixed inside the inner space of permanent magnet motor in order to produce a rotating magnetic field, the stator 30 with the rotating magnetic field is encircled by the rotor 40 that is in circular shape and is coaxial with the stator 30. The magnetic field of the rotor 40 interacts with the rotating magnetic field provided by the stator 30 to cause the rotor 40 rotating.
The stator 30 of the rotary structure 801 includes a stator core 1, a stator shaft 2 and six windings 3, in which the stator core 1 is fixed to the stator shaft 2 and includes the magnetic materials, six windings 3 are winded on the six salient teeth 5, and the driving current flows through the six windings 3 in order to produce the rotating magnetic field of the stator 30.
The rotor 40 of the rotary structure 801 includes a rotor yoke 7 and eight permanent magnets 8, in which the rotor yoke 7 is in circular shape and the eight permanent magnets 8 are uniformly distributed in a round shape along the inner surface of the rotor yoke 7. The N pole and the S pole of the eight permanent magnets 8 are alternatively exchanged and each of the eight permanent magnets 8 is a magnetic pole including the magnetic material. The rotor 40 rotates around the stator shaft 2 of the stator 30 and an air gap is formed among the outer surface of the salient teeth 5 of the stator 30, the winding slot openings 6 and the permanent magnets 8 of the rotor 40.
In FIG. 1, sufficient electric current is injected into the windings 3 for driving the rotor 40 rotating in accordance with the demands. A cogging torque is produced since the winding slots 4 formed by the permanent magnets 8 and the stator 30 interacts with the winding slot openings 6. The cogging torque refers to the torque variations induced by the interaction between the distribution of the magnetomotive force and the distribution of the air gap permeance for the existence of the slots of the stator. Therefore, in accordance with the preceding definition, the corresponding torque produced by the rotation of the rotor while no driving current exists in the windings is the cogging torque.
The issues raised by the cogging torque are the variation of the output torque of the electric machine such that the smooth operation of the electric machine is influenced, and the speed of the motor becomes unstable and the noise and vibration are thus generated.
Please refer to FIG. 2, which is a cross-sectional view illustrating the rotary structure of a second kind of a conventional outer rotor permanent magnet motor. In FIG. 2, a permanent magnet motor with ten poles and twelve slots is presented as an example for addressing the rotary structure 802. As compared with FIG. 1, both figures share the same reference numerals for addressing the identical element. The only difference between these two figures is the total number of poles and slots.
Please refer to FIG. 3, which is a cross-sectional view illustrating the rotary structure of a third kind of a conventional outer rotor permanent magnet motor. In FIG. 3, an arc-cut permanent magnet motor with eight poles and six slots is presented as an example for addressing the rotary structure 803. As compared with FIG. 1, the present preferred embodiment is based on the embodiment disclosed in FIG. 1 and further includes a pair of arc-cut surfaces formed at two sides of each permanent magnet 8 so as to reduce the cogging torque. The present preferred embodiment shares the same reference numerals with those of FIG. 1 for addressing the identical element and what is different is that a pair of arc-cut surfaces 11 is formed at two sides of each permanent magnet 8. The pair of arc-cut surfaces 11 are symmetrically distributed to each other along the radial direction of each permanent magnet 8 and the thickness at the terminal side of each permanent magnet 8 gradually becomes thinner along the circumference direction.
Please refer to FIG. 4, which is a cross-sectional view illustrating the rotary structure of a fourth kind of a conventional outer rotor permanent magnet motor. In FIG. 4, an arc-cut permanent magnet motor with ten poles and twelve slots is presented as an example for addressing the rotary structure 804. As compared with FIG. 3, both figures share the same reference numerals for addressing the identical element and the only difference between these two figures is the total number of poles and slots.
Please refer to FIG. 5, which is a cross-sectional view illustrating the rotary structure of a fifth kind of a conventional outer rotor permanent magnet motor. In FIG. 5, an arc-cut permanent magnet motor with ten poles and twelve slots is presented as an example for addressing the rotary structure 805. As compared with FIG. 4, the difference between these two figures is that the corresponding angular range of the arc-cut surface 11 in the present preferred embodiment is smaller than that illustrating in FIG. 4. The present preferred embodiment shares the same reference numerals with those of FIG. 4 for addressing the identical element.
Subsequently, a permanent magnet motor with eight pole and six slots is presented as an example for addressing the rotary structure of a conventional permanent magnet motor. The rotary structure of the inner rotor permanent magnet motor includes a stator and a rotor, in which the circular stator is fixed so as to form an external structure of the permanent magnet motor and to produce a rotating magnetic field. The cylindrical rotor having a rotor magnetic field is encircled by the stator and is coaxial with the stator. The magnetic field of the rotor interacts with the rotating magnetic field provided by the stator 30 whereby the rotor 40 is thus driven to rotate.
The stator of the inner rotor permanent magnet motor includes a stator ring and six windings, in which the stator ring is in circular shape, symmetric to a central axis and includes the magnetic material. The stator ring includes an outer stator yoke and six salient teeth. The six salient teeth are extended from the stator yoke to the rotor shaft and are uniformly distributed corresponding to the rotor shaft. Six winding slots and six winding slot openings are formed by the six salient teeth, and six windings 3 are winded on the six salient teeth 5. The driving current flows through the six windings 3 such that the rotating magnetic field of the stator is produced accordingly.
The rotor of the inner rotor permanent magnet motor includes a stator core and eight permanent magnets, in which the stator core is in circular shape and the eight permanent magnets 8 are uniformly distributed at the surface of the rotor core corresponding to the rotor shaft. The N pole and the S pole of the eight permanent magnets 8 are alternatively exchanged. Each of the eight permanent magnets 8 is a magnetic pole including the magnetic material. The rotor rotates with the rotor shaft and an air gap is formed among the inner surface of the salient teeth of the stator, the winding slot openings and the permanent magnets of the rotor.
Although the rotary structure of a conventional outer rotor permanent magnet motor introduced in the preceding FIG. 3, FIG. 4 and FIG. 5 and the rotary structure of a conventional inner rotor permanent magnet motor corresponding to what is introduced in the preceding FIG. 3, FIG. 4 and FIG. 5 possess the efficiency of reducing the cogging torque, however, the efficiency thereof is still unable to meet the requirements. Hence, improving the preceding drawbacks existing in the conventional technique is one of the critical motivations to inspire this invention.
To overcome the mentioned drawbacks of the prior art, a novel permanent magnet rotary structure of electric machine is provided.