Abstract:
A motor having a magnetic bearing comprises a base formed with a bearing seat; a stator fixed to the base; a rotor provided with a rotation shaft and rotatable with respect to the stator by magnetic forces generated from excitation; a bearing fixed to the bearing seat of the base for receiving the rotation shaft of the rotor; and a magnetic element pair including a first element and a second element. The first element is telescopically interference-fitted on the rotation shaft, the second element is fixed relative to the bearing seat and lets the rotation shaft insert therethrough, and a magnetic force is generated between the first element and the second element. When the rotor rotates and an external force acts on the rotor in a direction, a magnetic force between the magnetic element pair counteracts the external force to achieve an axial positioning effect and avoid the contact wear.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a motor, and especially a motor having a magnetic bearing that incurs no rotation wear. 
     BACKGROUND OF THE INVENTION 
     In most prior art motors, the positioning of the rotation shaft is achieved by a heatproof washer or a metallic C-ring. A conventional self-lube bearing fan motor, as shown in FIG. 1, comprises: a base  11 , a stator  12 , a rotor  13 , a bearing  14 , an elastic washer  15 , and a C-ring  16 . 
     The base  11  is located at the central location of a fan frame  10 . The base  11  and the fan frame  10  are integrally formed. In the central location of the base  11  is provided a bearing seat  111 . The stator  12  is telescopically fitted on the bearing seat  111  and is fixed relative to the base  11 . The stator  12  includes a plurality of coils  121  and a plurality of silicon steel sets  122 . The bearing  14  is a self-lube bearing fitted in the bearing seat  111  of the base  11 . The rotor  13  includes a hollow cylinder  130  having an open end. The outer wall of the cylinder  130  engages with a fan blade set  134  and on the inner wall of the cylinder  130  is provided a magnet  131 . At the central location of the cylinder  130  is provided a rotation shaft  132 . A groove  133  is formed near the lower end of the rotation shaft  132 . The rotation shaft  132  is received by the bearing  14 . The elastic washer  15  is telescopically fitted on the rotation shaft  132  at an upper location thereof to provide an elastic buffer. The C-ring  16  is engaged in the groove  133  near the lower end of the rotation shaft  132  so that rotation shaft  132  is prevented from being disengaged from the base  11 . 
     From the above description, it can be know that in the prior art motor, the C-ring  16  is used to axially position the rotation shaft  132  of the rotor  13  so that when the rotor  13  rotates after the excitation of the coil  121  and generates airflow F 1 , the C-ring  16  prevents the bearing  14  from disengaging from the base  111  due to the force F 2  exerted on the fan blade set  134 . 
     The positioning of the rotation shaft in the aforementioned prior art motor involves the following drawbacks: 
     1. When the motor operates, the contact wear and friction between the C-ring  16  and bearing  14  are incurred and the life of the motor will be reduced. 
     2. The friction between the C-ring  16  and the bearing  14  incurs noises or varied rotation speeds. 
     3. The rotor  13  and the stator  12  are designed with a magnetic bias. However, when the rotor  13  rotates, the rotation shaft  132  is moved by an external force and the equilibrium position of the rotor relative to the stator is determined by the external force. This results in a big problem in motor design. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a motor having a magnetic bearing that utilizes a magnetic force to adjust the position of the rotation shaft to achieve a non-contact axial positioning effect and to avoid contact wear when the motor operates. 
     Another object of the invention is to provide a motor having a magnetic bearing that utilizes a magnetic force to adjust the radial position of the rotation shaft to achieve a non-contact radial positioning effect and to avoid contact wear when the motor operates. 
     Yet another object of the invention is to provide a motor having a magnetic bearing that utilizes a magnetic force to avoid the insufficiency of the original magnetic bias so that a stationary equilibrium position of the rotor can be achieved when the motor operates. 
     To achieve the above-mentioned objects, a motor having a magnetic bearing in accordance with the invention comprises a base formed with a bearing seat; a stator fixed to the base; a rotor provided with a rotation shaft and rotatable with respect to the stator by magnetic forces generated from excitation; a bearing fixed to the bearing seat of the base for receiving the rotation shaft of the rotor; and a magnetic element pair including a first element and a second element. The first element is telescopically interference-fitted on the rotation shaft, the second element is fixed relative to the bearing seat and letting the rotation shaft insert therethrough, and a magnetic force is generated between the first element and the second element. The magnetic force pushes the rotation shaft toward or out of the base. 
     When the above-mentioned motor rotates, an external force acts on the rotor in a direction and a magnetic force between the magnetic element pair is utilized to counteract the external force so that the axial positioning of the rotation shaft can be achieved and the contact wear can be avoided. In addition, the insufficiency of the magnetic bias between the rotor and the stator can be avoided and the rotor can be kept in a stationary equilibrium position when the motor operates. 
     Furthermore, a magnetic bearing can be used to replace the bearing of the above-mentioned motor for radially positioning the rotation shaft. The magnetic bearing is provided in the bearing seat and comprises at least one magnetic element pair including a first element and a second element. The first element is telescopically interference-fitted on the rotation shaft and the second element is fixed relative to the bearing seat and lets the rotation shaft insert therethrough. Each of the first element and the second element is formed with a tapered contact surface, and a magnetic force is generated between the first element and the second element. The first element and the second element can achieve not only an axial positioning effect but also a radial positioning effect. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and the features and effects of the present invention can be best understood by referring to the following detailed description of the preferred embodiment and the accompanying drawings, wherein: 
     FIG. 1 shows a conventional fan motor. 
     FIG. 2 is an exploded view of a motor in accordance with the first preferred embodiment of the invention. 
     FIG. 3 is a sectional view of a motor in accordance with the first preferred embodiment of the invention. 
     FIG. 4 is a sectional view of a motor in accordance with the second preferred embodiment of the invention. 
     FIG. 5 is a sectional view of a motor in accordance with the third preferred embodiment of the invention. 
     FIG. 6 is a sectional view of a motor in accordance with the fourth preferred embodiment of the invention. 
     FIG. 7 is a sectional view of a motor in accordance with the fifth preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 2 and 3, a fan motor in accordance with the first preferred embodiment of the invention comprises a base  2 , a stator  3 , a rotor  4 , a bearing  5 , a magnetic element pair  6 , and an elastic washer  7 . 
     The base  2  is located at the central location of and is integrally formed with a fan frame  201 . At the central location of the base  2  is formed a bearing seat  21 . 
     At the central location of the stator  3  is provided an accommodation portion  31 , and at each of a plurality of peripheral locations around the accommodation portion  31  are provided a coil  32  and a silicon steel set  33 . At the bottom of the stator  3  is provided a circuit board  34 . The coils  32  are electrically connected with the circuit board  34 . The accommodation portion  31  is telescoped on the outer surface of the bearing seat  21  of the base  2 . 
     The rotor  4  is generally a hollow cylinder  44  having an open end. The outer wall of the rotor  4  is attached with a plurality of fan blades  43 . On the inner surface of the rotor  4  is provided a ring-typed magnet  41 . A rotation shaft  42  is provided at the central location of the rotor  4  and is accommodated in the bearing  5 . When the coils  32  of the stator  3  are supplied with electricity and cause excitation, magnetic forces are generated and cause the rotor  4  to rotate relative to the stator  3 . 
     The bearing  5  is self-lube and is secured within the bearing seat  21  of the base  2 . The bearing  5  accommodates the rotation shaft  42  of the rotor  4 . 
     The magnetic element pair  6  comprises a first element  61  and a second element  62 . Each of the facing poles between the first element  61  and the second element  62  is an S pole so that the two elements are repulsive to each other. The first element  61  is in the form of a circular ring formed with a central hole  611  within which the lower end of the rotation shaft  42  is interference-fitted. The second element  62  is secured to the bottom end of the bearing  5  and is located over the first element  61 . The second element  62  is formed with a central hole  621  that is bigger than the rotation shaft  42  in diameter so that the rotation shaft  42  is inserted through the central hole  621  of the second element  62  without contact therewith. 
     The elastic washer  7  is telescoped on the rotation shaft  42  at its upper section to provide an elastic buffer between the rotor  4  and the bearing  5 . 
     When the rotor  4  rotates, a downward force F 1  is caused by airflow and a force F 2  exerts on the rotation shaft  42  to push it outward from the base  2 . In addition, a magnetic force F 3  is exerted on the first element  61  that transmits the magnetic force F 3  onto the rotation shaft  42  to move it in a downward direction in FIG.  3 . The magnetic force F 3  reacts against the force F 2  and prevents the rotation shaft  42  from escaping from the bearing  5 . 
     Due to that the magnetic force F 3  increases when the first element  61  and the second element  62  move closer to each other, i.e. the magnetic force F 3  is inversely proportional to the square of the distance between the first element  61  and the second element  62 . Therefore, the first element  61  and the second element  62  do not contact, and no contact wear between the first element  61  and the second element  62  is incurred. Thereby, a positioning effect without incurring contact wear can be achieved. In addition, the magnetic force F 3  acts against the force F 2  so that the insufficiency of the magnetic bias between the rotor  4  and the stator  3  can be avoided. 
     Referring to FIG. 4 that shows the motor in accordance with the second embodiment of the invention, the first element  61  and the second element  62  of the magnetic element pair  6  generate an attractive magnetic force F 4  between them. The first element  61  is a circular magnet and is interference fitted on the rotation shaft  42  near the upper end thereof The second element  62  is a circular iron plate and is fixed on the upper end of the bearing  5  below the first element  61 . A C-ring  202  is provided near the lower end of the rotation shaft. 
     When the rotor  4  rotates, a downward force F 1  is caused by airflow and a force F 2  exerts on the rotation shaft  42  to push it outward from the base  2 . However, due to that there is an attractive force F 4  between the first element  61  and the second element  62 , and the second element  62  is fixed to the bearing  5  below the first element  61 , the rotation shaft  42  is moved downward into the base  2  so that the contact wear between the C-ring  202  and the bearing  5  can be prevented. In this preferred embodiment, a magnet is adopted as the first element  61  and an iron plate as the second element  62  in order to reduce the material cost. However, two magnets instead of one magnet can be adopted to obtain a greater attractive force. 
     Referring to FIG. 5 that shows the motor in accordance with the third embodiment of the invention, the rotor  4  rotates in such a direction that the airflow generated, as indicated by arrow F 6 , flows upward from the base  2 . In this case, a reaction force F 7  is exerted on the rotor  4  to push it toward the base  2 . To avoid the contact wear between the rotor  4  and the bearing  5 , a magnetic element pair  6  consisting of a first magnetic element  61  and a second magnetic element  62  is provided. The first magnetic element  61  and a second magnetic element  62  are two magnets in the same magnetic orientation. The first element  61  is telescopically interference-fitted on the rotation shaft  42  near the lower end thereof; the second element  62  is fixed to the lower end of the bearing  5  over the first element  61 . The diameter of the central hole  621  of the second element  62  is greater than that of the rotation shaft  42  so that the rotation shaft  42  is inserted through the central hole  621  of the second element  62  without coming into contact with it. Thereby, the attractive force F 8  between the first and second magnetic elements  61  and  62  counteracts the force F 7  to avoid the contact wear between the rotor  4  and the bearing  5 . 
     Referring to FIG. 6 that shows the motor in accordance with the fourth embodiment of the invention, the rotor  4  rotates in such a direction that the airflow generated, as indicated by arrow F 6 , flows upward from the base  2 . In this case, a reaction force F 7  is exerted on the rotor  4  to push it toward the base  2 . The first magnetic element  61  and the second magnetic element  62  are two magnets in opposite orientations respectively. The first element  61  is telescopically interference-fitted on the rotation shaft  42  near the upper end thereof; the second element  62  is fixed on the upper end of the bearing  5  below the first element  61 . The diameter of the central hole  621  of the second element  62  is greater than that of the rotation shaft  42  so that the rotation shaft  42  is inserted through the central hole  621  of the second element  62  without coming into contact with it. Thereby, the repulsive force F 9  between the first and second magnetic elements  61  and  62  counteracts the force F 7  to avoid the contact wear between the rotor  4  and the bearing  5 . 
     Referring to FIG. 7 that shows the motor in accordance with the fifth embodiment of the invention, a magnetic bearing  8 , instead of a conventional bearing such as a self-lube bearing, is adopted. The magnetic bearing  8  comprises two magnetic element pairs. The first magnetic element pair comprises a first element  81  and a second element  82  that are two magnets in opposite orientations respectively and generate a repulsive force F 10  between them. The first element  81  is telescopically interference-fitted on the lower portion of the rotation shaft  42 . The second element  82  is located over the first element  81  and is fixed to the bearing seat  21 . The diameter of the central hole of the second element  82  is greater than that of the rotation shaft  42  so that the rotation shaft  42  can be inserted through the second element  82  without contact therewith. The first and second elements  81  and  82  are formed with tapered contact surfaces  811  and  821  respectively. The second magnetic element pair comprises the first element  83  and the second element  84  that are also two magnets in opposite orientations respectively and generate a repulsive force F 11  between them. The first element  83  is telescopically interference-fitted on the upper portion of the rotation shaft  42 . The second element  84  is located below the first element  83  and is fixed to the bearing seat  21 . The central hole of the second element  84  is bigger than the rotation shaft  42  in diameter so that the rotation shaft  42  can be inserted through the second element  84  without contact therewith. The first and second elements  83  and  84  are formed with tapered contact surfaces  831  and  841 . 
     Due to the repulsive force F 10  (F 11 ) between the tapered contact surfaces  811  and  821  ( 831  and  841 ) of the first and second elements  81  and  82  ( 83  and  84 ), the rotation shaft  42  can be radially positioned at the central of the second element  82  ( 84 ). 
     Additionally, the repulsive magnetic force F 10  that pushes the rotation shaft  42  toward the base  2  and the force F 11  that pushes the rotation shaft  42  out of the base  2  cooperatively provide an axial positioning effect to the rotation shaft  42 . 
     In sum, the following advantages can be achieved by the invention: 
     An axial positioning effect can be achieved by a magnetic force so that contact wear can be avoided the motor in accordance with the invention operates. 
     The axial positioning effect of the rotation shaft  42  can be achieved by magnetic forces and the rotation shaft  42  has no need to be supported by a bearing. 
     A magnetic force is used to compensate the insufficiency of the magnetic bias between the rotor  4  and the stator  3  so that a good stability in rotation can be achieved. 
     Although the preferred embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the scope and spirit of the invention defined by the appended claims.