Abstract:
A motor rotor includes a magnetic yoke and a rubber magnet located within the magnetic yoke. At least one pattern is formed on a surface of the rubber magnet, which faces the magnetic yoke. The manufacturing method of the motor rotor is to provide a rubber magnet having flat surfaces, and at least one pattern is formed on a surface of the rubber magnet. The rubber magnet is curved to correspond with the inner surface of the magnetic yoke by the way that the patterned surface of the rubber magnet faces outside. The rubber magnet is put inside the magnetic yoke.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a motor rotor and its manufacturing method, and more particularly to a motor rotor having a rubber magnet with a pattern formed on the outer surface thereof for improving the flexibility of the rubber magnet of the motor rotor. 
   2. Description of the Related Art 
   A magnet is one of the essential components of a rotary machine, such as a motor. To reduce cost, cheap rubber magnets are used in conventional rotary machine structures. 
   The schematic structure of a conventional motor rotor adopting rubber magnets is illustrated in  FIG. 1 . As shown in  FIG. 1 , the band-shaped rubber magnet  100  with a predetermined dimension is bent into a ring in the manufacturing process of a motor adopting a rubber magnet  100 . Then, the ring-shaped rubber magnet  100  is pressed into a magnetic yoke  102  to complete the assembly of a motor rotor  104 . 
   However, in the process mentioned above, the rubber magnet  100  is not so flexible that the two end surfaces of the rubber magnet  100  cannot be jointed perfectly after the rubber magnet  100  is bent. This phenomenon becomes more significant as the thickness of the rubber magnet  100  increases. When the above phenomenon takes place, the motor suffers from the non-uniform distribution of the magnetic field or magnetic leakage, which results in the flutter of the motor. When this happens, not only the operation efficiency of the motor is reduced, but also high frequency noises are generated when the motor operates at high a speed. 
   SUMMARY OF THE INVENTION 
   In view of the above, an objective of the invention is to provide a motor rotor and the manufacturing method thereof for improving the flexibility of the rubber magnet to make the joint in the bent rubber magnet smoother and also improving the uniformity of the distribution of the magnet field to prevent fluttering and high frequency noises during motor operation and also to prevent low operation efficiency of the motor. 
   To achieve the above-mentioned objective, the invention provides a motor rotor including a magnetic yoke and a rubber magnet provided in the magnetic yoke in which a first surface of the rubber magnet facing the magnetic yoke has at least one first pattern. The first surface may be the outer surface of the rubber magnet. 
   Since patterns are formed on the outer surface of the rubber magnet, the flexibility of the rubber magnet is significantly improved and further the flatness of the joint in the rubber magnet is improved. Therefore, the mass distribution of the rubber magnet becomes more uniform and the rotational unbalance is reduced. Furthermore, due to better uniformity of the mass distribution, it is possible to improve the magnetic flux distribution of the rubber magnet after magnetizing. 
   Furthermore, an adhesive layer may be provided between the rubber magnet and the magnetic yoke. Since the outer surface of the rubber magnet is formed with patterns, the adhesive layer can increase the contact area to improve the adhesive strength between the rubber magnet and the magnetic yoke. 
   Moreover, in the motor rotor of the invention, besides formed on the first surface, patterns may be formed also on a second surface that is opposite to the first surface to further improve the flexibility of the rubber magnet. 
   The invention also provides a method of manufacturing a motor rotor in which a rubber magnet with a smooth surface is selected and at least one first pattern is formed on a first surface of the rubber magnet. Then, the rubber magnet is bent into a shape corresponding to an inner surface of a magnetic yoke by keeping the first surface facing outside, and is then put inside the magnetic yoke. The first surface is the outer surface of the rubber magnet. 
   In the method of manufacturing a motor rotor of the invention, since the outer surface of the rubber magnet is formed with patterns, the bending moment required can be reduced and the flexibility of the rubber magnet can be significantly improved. 
   Furthermore, an adhesive layer may be provided between the rubber magnet and the magnetic yoke. Since the outer surface of the rubber magnet is formed with patterns, the adhesive layer can increase the contact area so as to improve the adhesive strength between the rubber magnet and the magnetic yoke. 
   Moreover, in the method of manufacturing a motor rotor of the invention, patterns may be formed also on a second surface that is opposite to the first surface besides formed on the first surface to further improve the flexibility of the rubber magnet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram showing the structure of a motor rotor in the prior art. 
       FIG. 2A  is a schematic diagram showing the structure of a motor rotor according to an embodiment of the invention. 
       FIG. 2B  is a schematic diagram showing the patterns of the surfaces of the rubber magnet according to another embodiment of the invention. 
       FIG. 3A  is a schematic diagram showing a part of the pattern of the surface of the rubber magnet according to the embodiment of the invention. 
       FIG. 3B  is a schematic diagram showing a part of the pattern of the surface of the rubber magnet according to another embodiment of the invention. 
       FIG. 4A  is a schematic diagram showing a part of a rubber magnet in the prior art. 
       FIG. 4B  is a schematic diagram showing a part of a rubber magnet according to an embodiment of the invention. 
       FIG. 5  is a graph showing the relationships between the bending moment and the curvature radius of different rubber magnets. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2A  is a schematic diagram showing the structure of the motor rotor according to an embodiment of the invention. As shown in FIG  2 A, the motor rotor  204  includes a magnetic yoke  202  and a rubber magnet  200  provided inside the magnetic yoke  202 . The magnetic yoke  202  with a shape, for example a ring shape, is made of conductive material such as metal. In the fabrication of the motor rotor  204 , at first, a strip of the rubber magnet  200  made of magnetic rubber material with a smooth surface is selected. Then, one or more patterns  206  are formed on a first surface of the rubber magnet  200  that faces the magnetic yoke  202 . The first surface is the outer surface of the rubber magnet. The patterns  206  can be formed and distributed uniformly or fragmentarily on the whole surface or on portions of the surface. Moreover, the patterns  206  may be formed by various methods, such as press molding. 
   It should be noted that the patterns  206  may be embossing patterns  206   a  shown in  FIG. 3A , notch patterns  206   b  shown in  FIG. 3B , or any other patterns. The shape of the rubber magnet  200  is fit with the shape of the inner surface of the magnetic yoke  202 , such as a ring shape. Furthermore, the patterns  206  can be formed at the same time the rubber magnet  200  is made. This can reduce the number of steps for preparing the rubber magnet  200 . 
   The rubber magnet  200  is then bent into the shape corresponding to the inner surface of the magnetic yoke  202  by keeping its patterned surface facing outside. At this time, the joint  208  of the two ends of the rubber magnet  200  have improved flatness and fitness. Subsequently, the bent rubber magnet  200  is placed into the magnetic yoke  202 . Finally, the rubber magnet  200  is magnetized to complete the fabrication of the motor rotor  204 . 
   Since the outer surface of the rubber magnet  200  is formed with patterns  206 , the flexibility of the rubber magnet  200  is significantly improved that can be illustrated by  FIGS. 4A and 4B .  FIG. 4A  is a schematic diagram showing a part of a prior-art rubber magnet  100  and  FIG. 4B  is a schematic diagram showing a part of the rubber magnet according to the preferred embodiment of the invention. As shown in  FIGS. 4A and 4B , when the rubber magnets  100  and  200  are bent to have the same radius (that is, ρ R =ρ′ R ), the surface of the magnetic rubber  100  would be dented inwardly (that is, the curvature radius ρ T  is smaller). On the other hand, the surface of the magnet rubber  200  has no significant change (that is, the curvature radius ρ′ T  is smaller). It is shown that the magnet rubber  200  has a better flatness than the rubber magnet  100 . 
   Furthermore, in another embodiment, patterns can be formed also on the inner surface (opposite to the outer surface mentioned previously) of the rubber magnet  200 . The patterns formed on the inner surface of the rubber magnet can be embossing patterns, notch patterns or any other patterns. Thus, the flexibility of the rubber magnet  200  can be further improved. The patterns formed on the inner surface and the outer surface can be the same or different. 
   Using the conventional bending moment-bending angle measurement method, the results of the bending moment-bending angle tests of the prior-art rubber magnet, the rubber magnet of the first embodiment, and the rubber magnet of the second embodiment of the invention are shown in  FIG. 5 . In  FIG. 5 , the bending characteristics of the prior-art rubber magnet  100 , the rubber magnet  200  of the first embodiment, and the rubber magnet  200  of the second embodiment are represented by curve a, b, and c, respectively. When the bending moment is set to M 0 , the bending angles of the prior-art rubber magnet  100 , the rubber magnet  200  of the first embodiment and the rubber magnet  200  of the second embodiment are α 1 , α 2  and α 3 , respectively. As shown in  FIG. 5 , the relationships of the bending angles are α 1 &lt;α 2 &lt;α 3 , and the relationships of the curvature radiuses are ρ R1 &gt;ρ R2 &gt;ρ R3 . The result shows that the flexibility of the rubber magnet  200  of the second embodiment is better than that of the rubber magnet  200  of the first embodiment, and the flexibility of the rubber magnet  200  of the first embodiment is better than that of the prior-art rubber magnet  100 . 
   Furthermore, an adhesive layer (not shown in the figures) may be provided between the rubber magnet  200  and the magnetic yoke  202  to avoid the unfavorable conditions between the rubber magnet  200  and the magnetic yoke  202 , such as looseness and clearances, and to enhance their adhesive strength. The adhesive layer may be made of an adhesive or materials including adhesives. Since the outer surface of the rubber magnet  200  (that is, the surface contacts with the magnetic yoke  202 ) is formed with the patterns  206 , the adhesive layer can be provided at the dents or protrusions of the patterns  206  to increase the contact area of the adhesive layer and to improve the adhesive strength between the rubber magnet  200  and the magnetic yoke  202 . 
   Since the outer surface of the rubber magnet is formed with patterns, the flexibility of the rubber magnet can be significantly improved. Therefore, the mass distribution of the rubber magnet would be more uniform, and the rotational unbalance would be reduced. Furthermore, due to better uniformity of the mass distribution, it is possible to improve the magnetic flux distribution of the rubber magnet after magnetizing. 
   Moreover, patterns can be formed both on the first surface of the rubber magnet that contacts with the magnetic yoke and on a second surface opposite to the first surface to further improve the flexibility of the rubber magnet, as shown in  FIG. 2B . The patterns formed on the first or second surface of the rubber magnet can be a notch or embossing pattern. 
   While the invention has been described by way of examples and in terms of embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, and is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.