Patent Publication Number: US-2012025655-A1

Title: Motor rotor and motor having the motor rotor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to motor rotors, and particularly, to a motor rotor that an air gap between the motor rotor and a stator is uneven, and a motor having the motor rotor. 
     2. Description of Related Art 
     In modern society, motors have been applied to a variety of products. In general, a motor forms an inductive magnetic field by using currents. The inductive magnetic field interacts with an inner permanent magnet to generate a rotational movement. In addition to providing the rotational movement, the motor may also output rotational mechanical energy that may be converted into a linear movement or vibrating movement by certain mechanisms. 
       FIG. 1A  (PRIOR ART) is an oblique view of an outer rotor motor of the prior art. The outer rotor motor comprises a stator  11  installed in a central region and a rotor  12  surrounding an outer periphery of the stator  11 . The stator  11  is a stationary part. The stator  11  comprises a field coil  111 , and generates a magnetic field by inputting currents into the field coil  111 . The rotor  12  includes an annular body  121  and a plurality of permanent magnets  122  installed on an inner lateral surface of the annular body  121 . The permanent magnets  122  provides another magnetic field. The rotor  12  generates a rotational movement according to an interaction of the two magnetic fields. 
       FIG. 1B  (PRIOR ART) is a top view of the outer rotor motor shown in  FIG. 1A  (PRIOR ART). As shown in the figure, each of the permanent magnets  122  has a first curved surface  122   a  fastened to the inner lateral surface of the annular body  121  and a second curved surface  122   b  opposing the first curved surface  122   a . The second curved surface  122   b  faces the stator  11 , and the first curved surface  122   a  is parallel to the second curved surface  122   b.    
     However, the permanent magnets of the motor rotor of the prior art have the same thickness, and the magnetic fields generated by the permanent magnets for the stator are average. Accordingly, the action forces (cogging torques) applied to a region where the magnetic forces change direction when the rotor is rotating cause the motor to vibrate and make noises, and affect the operation quality of the motor. 
     Therefore, how to solve the drawbacks of the prior art to reduce the noises generated by an operating motor is becoming one of the most urgent issues in the art. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned drawbacks of the prior art, the present invention provides a motor rotor including an annular body having an inner lateral surface and a magnetic body installed on the inner lateral surface of the annular body, the magnetic body having a first curved surface with a first curvature fastened to the inner lateral surface of the annular body and a second curved surface with a second curvature opposing the first curved surface, wherein the second curvature greater than the first curvature. 
     The magnetic body of the motor rotor of an embodiment according to the present invention is fastened to the inner lateral surface of the annular body by a locking, a riveting or an adhering technique. 
     In the motor rotor of an embodiment of according to the present invention, the annular body is a sheet metal part. 
     According to the motor rotor of an embodiment, the annular body comprises non-magnetoconductive metal or plastic, and the non-magnetoconductive metal is one selected from the group consisting of aluminum, copper, zinc, tantalum and stainless steel. 
     In the motor rotor of the embodiment according to the present invention, the magnetic body is a permanent magnet. 
     The present invention further provides a motor, comprising a stator and a motor rotor surrounding an outer periphery of the stator, the motor rotor comprising an annular body having an inner lateral surface, and a magnetic body installed on the inner lateral surface of the annular body, the magnetic body having a first curved surface with a first curvature fastened to the inner lateral surface of the annular body and a second curved surface with a second curvature opposing the first curved surface, wherein the second curvature is different to the first curvature. 
     Compared with the prior art, the magnetic body of the motor rotor of the present invention has an uneven thickness, and an air gap between the motor rotor and a stator thus has an uneven width, resulting in the decrease of cogging torques and the decrease of the vibration generated by the motor when the magnetic forces change direction. Therefore, the noises generated by an operating motor is reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein: 
         FIG. 1A  (PRIOR ART) is an oblique view of an outer rotor motor of the prior art; 
         FIG. 1B  (PRIOR ART) is a top view of the outer rotor motor shown in  FIG. 1A  (PRIOR ART); and 
         FIG. 2  is a planar view of a motor rotor and its corresponding stator of an embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparently understood by those in the art after reading the disclosure of this specification. The present invention can also be performed or applied by other different embodiments. The details of the specification may be on the basis of different points and applications, and numerous modifications and variations can be devised without departing from the spirit of the present invention. 
     Please refer to  FIG. 2 , which is a planar view of a motor rotor and its corresponding stator of an embodiment according to the present invention. 
     As shown in the figure, the motor rotor of the embodiment according to the present invention comprises an annular body  21  having an inner lateral surface  210 , and a plurality of magnetic bodies  22  installed on the inner lateral surface  210  of the annular body  21 . Each of the magnetic bodies  22  has a first curved surface  22   a  and a second curved surface  22   b  opposing the first curved surface  22   a . Each of the magnetic bodies  22  is fastened to the inner lateral surface  210  of the annular body  21  via the first curved surface  22   a . The second curved surface  22   b  faces the stator  23 , and the first curved surface  22   a  has a first curvature not equal to a second curvature of the second curved surface  22   b . In the embodiment, the first curvature is preferably less than the second curvature. Note that the embodiment is exemplified with 12 magnetic bodies, while other embodiments may contain any number of magnetic bodies. 
     In the embodiment, the magnetic bodies  22  are selectively fastened, riveted or adhered to the inner lateral surface  210  of the annular body  21 . 
     In the embodiment, the annular body  21  may be preferably a sheet metal part, non-magnetoconductive metal or plastic, and the non-magnetoconductive metal is one selected from the group consisting of aluminum, copper, zinc, tantalum and stainless steel, but is not limited thereto. 
     In the embodiment, the magnetic bodies  22  are permanent magnets. 
     In conclusion, since the first curvature of the first curved surface  22   a  is different from the second curvature of the second curved surface  22   b;  that is, each of the magnetic bodies  22  has an uneven thickness, an air gap between the motor rotor and a stator also has an uneven width, resulting in the decrease of cogging torques and the generation of a counter electromotive force that is close to a sine or cosine wave. Under a condition that the energy density of the magnetic bodies  22  is not reduced, the influence of the tolerance of the magnetic bodies  22  on the magnetic path may still be reduced. In addition, the motor rotor may reduce the noises generated by an operating motor effectively. 
     Note that the motor rotor of embodiments according to present invention may be applied to a variety of motors, such as, but not limited to, a brushless DC motor (BLDC motor), a permanent magnet synchronous motor (PMSM) or a ceiling fan motor. For example, the motor rotor of the present invention may be applied to the motor shown in  FIGS. 1A and 1B . Accordingly, the motor of the present invention comprises the stator  11  and the motor rotor surrounding an outer periphery of the stator  11 , wherein the motor rotor comprises the annular body  21  having an inner lateral surface  210 , and the magnetic bodies  22  installed on the inner lateral surface  210  of the annular body  21 . 
     The foregoing descriptions of the detailed embodiments are only illustrated to disclose the features and functions of the present invention and not restrictive of the scope of the present invention. It should be understood to those in the art that all modifications and variations according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims.