Abstract:
A permanent magnet rotor comprising a shaft, a rotor core fixed to the shaft, a magnet disposed around the core, and a linker fixed relative to the shaft and located at one end of the core; wherein an elastic clamping structure is arranged between the linker and the magnet such that rotational torque of the magnet can be transferred to the shaft via the linker.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 200910107313.6 filed in The People&#39;s Republic of China on May 12, 2009. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to the electric motors, and in particular, to a permanent magnet rotor of a brushless DC motor. 
       BACKGROUND OF THE INVENTION 
       [0003]    A permanent magnet brushless DC motor usually comprises a shaft, a rotor core fixed to the shaft and one or more magnets disposed around the core. In the prior art, the magnet and the rotor core are usually attached by a binder such as an epoxy resin. The binder is used as a torque transfer structure between the magnet and the rotor core for transferring the rotational torque of the magnet to the shaft, thereby driving the shaft. 
         [0004]    However, adhesion by means of a binder has following disadvantages: 
         [0005]    1) With changes in temperature and prolongation of the duration of usage, the binder is easily aged and may lose its adhesive strength, thereby resulting in failure of the rotor. 
         [0006]    2) The manufacturability is poor. A paste binder is difficult to apply evenly, in production which easily results in the magnet being eccentrically mounted to the rotor core, thereby generating one extra factor affecting the imbalance of the rotor. 
         [0007]    Hence, it is desirable to develop a new torque transfer structure between the magnet and the core. 
       SUMMARY OF THE INVENTION 
       [0008]    To solve the above problem, the present invention provides a permanent magnet rotor comprising: a shaft, a rotor core fixed to the shaft, a magnet disposed around the core, and a linker fixed relative to the shaft and located at one end of the core; wherein an elastic clamping structure is arranged between the linker and the magnet such that rotational torque of the magnet can be transferred to the shaft via the linker. 
         [0009]    Preferably, the elastic clamping structure comprises recesses formed in one end of the magnet proximate the linker and elastic pins arranged on one side of the linker facing the magnet, said elastic pins being resiliently pressed against side walls of the recesses by means of elastic deformation of the pins caused by pressing the pins into the recesses. 
         [0010]    Preferably, the recesses have side walls which are divergent with the axially inner side being narrower than the axially outer open side, and an axial slot is formed through the distal end of each of the elastic pins. 
         [0011]    Preferably, the linker is made of plastic or a combination of plastic and fiber. 
         [0012]    Preferably, the magnet is a unitary hollow cylinder and the recesses are arranged uniformly in the circumferential direction of the magnet and through the wall of the magnet in the radial direction of the magnet. 
         [0013]    Preferably, a plurality of grooves are formed on the outer surface of the rotor core, a plurality of positioning pins are arranged on the side of the linker facing the magnet, and the positioning pins are located in the grooves and have axially extending surfaces on which a plurality of teeth are formed, the teeth resiliently press against the inner surface of the magnet. 
         [0014]    Preferably, a plurality of ridges are formed on the surface of the positioning pins in contact with the grooves so that the positioning pins resiliently grip the grooves. 
         [0015]    Preferably, a mounting hole is formed in the center of the linker and the shaft passes through the mounting hole. 
         [0016]    Preferably, a plurality of balance pins are arranged on the side of the linker remote from the magnet. 
         [0017]    Preferably, the rotor further comprises a second linker fixed to the other end of the core and said second linker and the magnet are connected by means of elastic fixation. 
         [0018]    Advantages of embodiments of the present invention include that the linker and the magnet is fixed together by means of an elastic clamping structure while the traditional way of fixation by means of binder is avoided. The way of connection is simple, convenient, reliable and has good manufacturability and repeatability; the inner diameter of the magnet can have a relatively large tolerance because teeth formed on the surface of the positioning pins arranged on the linker press against the inner surface of magnet; and balance pins arranged on the linker can be used for dynamic balancing of the rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labelled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0020]      FIG. 1  is an exploded view of the motor rotor in accordance with an embodiment of the present invention; 
           [0021]      FIG. 2  is an enlarged perspective view of the linker of the motor rotor in accordance with an embodiment of the present invention; 
           [0022]      FIG. 3  is a partial enlarged view of the assembling drawing of the motor rotor in accordance with an embodiment of the present invention; 
           [0023]      FIG. 4  is a cross sectional view of the motor rotor in accordance with an embodiment of the present invention; and 
           [0024]      FIG. 5  is another cross sectional view of the motor rotor in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The technical problem to be solved, the technical solution and the beneficial effects of the present invention are best understood from the following detailed description with reference to the accompanying figures and embodiments. It is to be understood that the specific embodiments described here are merely examples to explain the invention and are not intended to limit the scope of the present invention. 
         [0026]    Referring to  FIG. 1 , a motor rotor according to the preferred embodiment of the present invention comprises a shaft  10 , a rotor core  20  fixed to the shaft  10 , a magnet  30  disposed around the core  20 , and a linker  40  fixed to one end of the core  20 . An elastic clamping structure is arranged between the linker  40  and the magnet  30  such that rotational torque of the magnet  30  is transferred to the shaft  10  via the linker  40  and the core  20 . 
         [0027]    Referring to  FIG. 2  and  FIG. 3 , optionally, recesses  32  are formed on one end of the magnet  30  proximate the linker  40 . Elastic pins  42  are arranged on the side of the linker  40  facing the magnet  30  and extend into the recesses  32 . The pins press against the side walls of the recesses due to elastic deformation force of the pins as they are pressed into the recesses. Preferably, side walls of the recesses are divergent such that the axially inner end of the recess is narrower that the open axially outer end. Thus the recesses  32  are preferably trapezoidal in shape so that the pins  42  can be guided into the recesses  32  easily. An axial slot  422  is formed through the distal end of elastic pin  42  so that the elastic pin  42  can generate an elastic deformation force after being inserted into the recess  32  and press against the side walls of the recess  32  reliably. The recesses  32  and elastic pins  42  form the elastic clamping structure for fixing the magnet  30  with the linker  40 . Preferably, the magnet  30  is a unitary hollow cylinder and the recesses  32  are arranged uniformly in the circumferential direction of the magnet. In this embodiment, the number of the recesses  32  is four and uniformly spaced apart by 90 degrees. Each recess  32  extends through the wall of the magnet  30  in the radial direction of the magnet. 
         [0028]    Referring to  FIG. 4  and  FIG. 5 , the linker  40  is made of plastic or a combination of plastic and other material such as fiber. A plurality of positioning pins  44 , four in this embodiment, are arranged on the side of the linker  40  facing the magnet  30 . The positioning pins  44  are cylindrical with axially extending surfaces on which several teeth  442  are formed for pressing against the inner surface of magnet  30  to position the magnet  30  in the radial direction. Because of the arrangement of the teeth  442 , the magnet  30  can have a relatively large tolerance on the dimension of the inner diameter. A plurality of axial extending grooves  22 , four in this embodiment, are formed on the outer surface of the core  20 . The four positioning pins  44  of the linker  40  clamp into the four grooves  22  respectively. Several ridges  444  may also be formed on the surface of positioning pins  44  in contact with the grooves  22  so that the positioning pins  44  can clamp into the grooves  22  elastically. A couple of cylindrical projections  45  are arranged on the side of the linker  40  facing the magnet  30 . The rotor core  20  has a couple of acceptance holes  24  for receiving the projections  45  therein such that the linker  40  is fixed to the rotor core  20 . A mounting hole  48  is formed in the center of the linker  40 . The shaft  10  passes through the mounting hole  48 . The projections  45  may have ridges as well to form a tight interference fit within the acceptance holes to securely fix the linker to the core. 
         [0029]    Optionally, the rotor further comprises a second linker  40  fixed to the other end of the core. The second linker  40  has the same structure and mates with the core and the magnet in the same way as the above first mentioned linker  40 . 
         [0030]    A plurality of balance pins  46  are arranged on the side of the linker  40  remote from the magnet  30 . Dynamic balance of the rotor can be achieved by cutting some of the balance pins  46 . 
         [0031]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
         [0032]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.