Abstract:
A motor having a magnetic bearing. The motor includes a base provided with a bearing seats, a stator fixed to the base, a rotor equipped with a rotation shaft and able to rotate relative to the stator by magnetic forces generated from excitation, a bearing fastened to the bearing seat of the base for accommodating the rotation shaft of the rotor, and a magnetic unit composed of a first, a second and a third magnetic elements. The second magnetic element is located below the first magnetic element. The third magnetic element is located below the second magnetic element. By employing the magnetic force, the second magnetic element is restrained between the first and third magnetic elements, thereby limiting a shift range of the rotation shaft.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a motor structure and, more particularly, to a motor having a magnetic bearing using magnetic forces to avoid rotation friction. 
   2. Description of the Related Art 
   Referring to the prior fan motor structure shown in  FIGS. 1 and 2 , the structure includes a base  12 , a stator  13 , a rotor  14  and a bearing  15 . 
   Referring to  FIG. 1 , the base  12  is located in the center of a fan frame  201  and the base  12  and the fan frame  201  are integrally formed together. A bearing seat  21  is located in the center of the base  12 . An accommodation portion  31  is provided in the center of the stator  13 . Outside the accommodation portion  31  are a coil  32  and a piece of silicon steel  33 , with a circuit board  34  underneath. The coil  32 , the silicon steel  33  and the circuit board  34  are electrically connected. The accommodation portion  31  is telescoped to the outer surface of the bearing seat  21  of the base  12 . 
   Referring to  FIG. 2 , the rotor  14  includes a hollow cylinder  44  that has an open end. A set of fan blades  43  are attached to the outer wall of the hollow cylinder  44  while a ring-shaped magnet  41  is allocated at its inner wall. A rotation shaft  42  is provided at the center of the ring-shaped magnet  41  and is accommodated in the bearing  15 . When the coil  32  of the stator  13  is electrically excited, the rotor  14  is able to rotate relatively to the stator  13  due to the magnetic forces. 
   The bearing  15  is a self-lubricating bearing fixed onto the bearing seat  21  of the base  12 . It accommodates the rotation shaft  42  of the rotor  14 . 
   The elastic washer  7  is telescoped on the upper part of the rotation shaft  42  to act as an elastic buffer between the rotor  14  and the bearing  15 . 
   The C-ring  16  is jointed with a groove  133  situated near the lower end of the rotation shaft  42  to prevent the rotor  14  from disengaging from the base  12 . 
   It is observed from the above structure that, in prior structures, the C-ring  16  is employed to axially position the rotation shaft  42  of the rotor  14 . To describe at length, when the rotor  14  rotates due to the electric excitation of the coil  32 , the wind force F 1  acts downwards towards the bottom of the base  12 , and as a result of the counterforce F 2 , the rotor  14  disengages from the base  12 . Therefore, the presence of the C-ring  16  prohibits the rotor  14  from disengaging from the base  12 . 
   However, in the first prior technique, when the fan rotates, wear and heat due to friction occur between the C-ring  16  and the rotation shaft  42 , thereby shortening the operational life span. Also, the friction between the C-ring  16  and the rotation shaft  42  generates noise, or unsteady rotation speed may occur depending on the degree of friction. Over the above description, the rotor  14  and the stator  30  are designed with magnetic bias therebetween. Therefore, when the rotor  14  rotates, magnetic levitation is created, resulting in magnetic equilibrium between the rotor  14  and the stator  30  at a stable position. However, during the rotation, the rotor  14  deviates the rotation shaft  42  consequent on the external forces, such as wind forces, it receives, in such a manner that the rotor  14  and the stator  30  are no longer in previous equilibrium positions, but are in new equilibrium positions depending on the degree of the received external forces. This gives rise to a comparatively great difficulty in the design. 
   SUMMARY OF THE INVENTION 
   One object of the invention is to provide a motor having a magnetic bearing that employs magnetic forces to adjust the position of rotation shaft and then form a non-contact axial positioning, hence avoiding contact wear during operation. 
   Another object of the invention is to provide a motor having a magnetic bearing that utilizes magnetic forces to compensate the original magnetic bias insufficiency, and hence the rotor is able to stay in a stationary equilibrium position during operation. 
   Another object of the invention is to provide a motor having a magnetic bearing, in which the rotor is designed to rotate in reverse without deviating the original magnetic equilibrium. 
   The other object of the invention is to provide a motor having a magnetic bearing, which uses the repulsion principle between the magnetic elements so as to allow the rotor to axially shift within the allowable range formed between the rotor and the magnetic elements, so that when the motor incurs vibration or collision, the magnetic elements do not shatter. 
   To accomplish the above objects, the motor having a magnetic bearing of the invention includes: a base provided with a bearing seat; a stator fixed onto the base; a rotor equipped with a rotation shaft and able to rotate relative to the stator by magnetic forces generated from excitation; a bearing fastened onto the bearing seat of the base for accommodating the rotation shaft of the rotor; and a magnetic unit composed of a first, a second and a third magnetic elements, wherein the first magnetic element is anchored to the bearing seat, the second magnetic element is fastened onto the outside of the bearing seat and is located below the first magnetic element, and the third magnetic element is fixed onto the base and is located below the second magnetic element. In addition, the first and second magnetic elements are of the same pole and repulsive to each other; likewise, the second and the third magnetic elements are of the same pole and repulsive to each other. With the aid of the magnetic unit, the second magnetic element is refrained between the first and third magnetic elements, and therefore the axial shift range of the rotation shaft is limited. 
   By the above structure, the movement force towards one direction produced by the rotation of the rotor, is counterbalanced by the magnetic forces in the opposite direction brought out by the magnetic unit, thus avoiding contact wear of rotation and at the same time recovering the magnetic bias insufficiency, so that the rotor is able to stay at a stationary equilibrium position during rotation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, advantages and features of the invention will become apparent from the following description with reference to the accompanying drawings that illustrate examples of the invention, in which: 
       FIG. 1  is a three-dimensional exploded view of a conventional fan motor; 
       FIG. 2  is a sectional view of a fan motor structure in accordance with the prior art; 
       FIG. 3  is a sectional view of the motor having a magnetic bearing in accordance with a first embodiment of the invention; 
       FIG. 4  is a sectional view of the motor having a magnetic bearing in accordance with a second embodiment of the invention; 
       FIG. 5  is a sectional view of the motor having a magnetic bearing in accordance with a third embodiment of the invention; 
       FIG. 6  is a sectional view of the motor having a magnetic bearing in accordance with a fourth embodiment of the invention; 
       FIG. 7  is a sectional view of the motor having a magnetic bearing in accordance with a fifth embodiment of the invention; and 
       FIG. 8  is a sectional view of the motor having a magnetic bearing in accordance with a sixth embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring the first embodiment of the invention shown in  FIG. 3 , the embodiment is a fan motor structure including a base  12 , a stator  30 , a rotor  14 , a bearing  50  and a magnetic unit. The bearing  50  is fastened to the bearing seat of the base for accommodating and supporting the rotation shaft of the rotor. 
   The magnetic unit is composed of a first magnetic element  1 , a second magnetic element  2  and a third magnetic element  3 . The first and second magnetic elements  1  and  2  are of the same pole and repulsive to each other. The second magnetic element  2  is ring-shaped with its center hole telescoped near the lower end of the rotation shaft  42 . The first magnetic element  1  is secured to the bottom part of the bearing  50  and is located above the second magnetic element  2 , and it has a hole with a diameter comparatively larger than that of the rotation shaft  42  such that when the rotation shaft  42  passes through the center hole of the first magnetic element  1 , both of them do not come into contact with each other. The third magnetic element  3  is fixed onto the base  12  and is located below the second magnetic element  2 . The second and third magnetic elements  2  and  3  are of the same pole and repulsive to each other. 
   By the structure described above, during the rotation of the rotor  14 , a wind force F 1 , which is produced by the fan blades  43  shown in  FIG. 3 , acts downwards towards the bottom of the base  12 , and a counterforce F 2  disengages the rotation shaft  42  from the base  12 . However, as a lower surface  510  of the first magnetic element  1  and a upper surface  521  of the second magnetic element  2  are magnetically repulsive to each other, the first magnetic element  1  is anchored onto the bearing seat  21  and is situated above the second magnetic element  2 , and therefore a force shifting the rotation shaft downwards (that is, towards the base  12 ) is generated, thereby counterbalancing the counterforce F 2 . Consequently, the rotor  14  does not disengage from the base  12  in the presence of the counterforce F 2 . 
   When the rotor  14  is designed to rotate in reverse, a wind force F 6  is produced acting upwards towards the top of the base  12 , and a counterforce F 5  acting towards the base is also created at the same time. To avoid friction between the rotor  14  and the bearing  50 , the lower surface  520  of the second magnetic element  2  and the upper surface  530  of the third magnetic element  3  of the magnetic unit in the embodiment are magnetically repulsive. The second magnetic element  2  is telescoped near the lower end of the rotation shaft  42 , and the third magnetic element  3  is fixed onto the base  12 . In such a manner, the repulsion of the second and third elements  2  and  3  respectively, is employed to counterbalance the counterforce P 5 , and the friction between the rotor  14  and the bearing  50  is thus avoided. In addition, according to the structure described above, the bearing  50  also has the function of supporting the rotation shaft  42  to assist in maintaining the rotor  14  and the stator  30  at their equilibrium positions. Thus, the motion of the rotor  14  can be limited along the axial direction and stabilized. According to  FIG. 3 , the self-lubricating bearing  16  is fastened to the bearing seat of the base for accommodating and supporting the rotation shaft of the rotor to limit the rotation shaft along the axial direction. Furthermore, the rotor  14  will be balanced in accordance with the wind force and the magnetically repulsive force, which is provided by the magnetic elements, along the axial direction. 
   For the reason that the closer the first and second magnetic elements  1  and  2  approach each other, the greater the repulsive force gets (the repulsive force is directly proportional to 1/(distance 2 )), the contact and friction do not occur between the first and second magnetic elements  1  and  2 , thus achieving a non-contact positioning effect during rotation. In the meanwhile, the repulsive force resisting the external force (counterforce F 2 ) compensates the magnetic bias insufficiency between the rotor  14  and the stator  30  so that the original magnetic equilibrium during rotation is not deviated because of external forces. Similarly, the closer the second and third magnetic elements  2  and  3  approach each other, the greater the repulsive force gets (the repulsive force is directly proportional to 1/(distance 2 )), so that contact and friction do not occur between the second and third magnetic elements  2  and  3 , thus achieving a non-contact positioning effect during rotation. In the meanwhile, the repulsive force resists the external force (counterforce F 5 ), so the second magnetic element  2  is able to locate itself in the center of the first and third magnetic elements  1  and  3  to obtain equilibrium and is not deviated towards either of them, hence attaining the axial positioning of the rotation shaft  42 . 
   Referring now to the second preferred embodiment of the invention shown in  FIG. 4 , the fan motor structure in the embodiment includes a base  12 , a stator  30 , a rotor  14 , a bearing  50  and a magnetic unit. 
   The magnetic unit is composed of a first magnetic element  1 , a second magnetic element  2  and a third magnetic element  3 . The first and second magnetic elements  1  and  2  are of the same pole and repulsive to each other. The first magnetic element  1  is ring-shaped with its center hole telescopically fitted to the rotation shaft  42 . The second magnetic element  2  is secured to the bearing seat  21  and is located below the first magnetic element  1 . The second magnetic element  2  has a hole with a diameter larger than that of the rotation shaft  42  such that when the rotation shaft  42  passes through the center hole of the second magnetic element  2 , both of them do not come into contact with each other. The third magnetic element  3  is ring-shaped with its center hole telescopically fitted to the lower end of the rotation shaft  42  and is located below the second magnetic element  2 . The second and third magnetic elements  2  and  3  are of the same pole and repulsive to each other. 
   Because the magnetic unit of the second preferred embodiment operates in the same fashion as that of the first preferred embodiment, the detailed description is omitted. 
   Alternatively, the first and third magnetic elements  1  and  3  can be of same pole different from that of the second magnetic element  2 . The attractive magnetic forces between the first and second magnetic elements  1  and  2  and the second and third magnetic elements  2  and  3  can also achieve magnetic equilibrium so as to obtain the axial positioning. 
   Referring to the third preferred embodiment of the invention shown in  FIG. 5 , the fan motor structure in the embodiment includes a base  12 , a stator  30 , a rotor  14 , a bearing  50  and upper and lower magnetic units. 
   The upper magnetic unit is composed of a first magnetic element  61  and a second magnetic element  62 . The first and second magnetic elements  61  and  62  are of the same pole and repulsive to each other. The second magnetic element  62  is secured to the upper end of the bearing  50  and has a center hole with a diameter larger than that of the rotation shaft  42 , to such an extent that when the rotation shaft  42  passes through the center hole of the second magnetic element  62 , both of them do not come into contact with each other. The first magnetic element  61  is ring-shaped with its center hole telescopically fitted to the rotor  14  and is located above the second magnetic element  62 . 
   The lower magnetic unit is composed of a third magnetic element  63  and a fourth magnetic element  64 . The third and fourth magnetic elements  63  and  64  are of the same pole and repulsive to each other. The third magnetic element  63  is ring-shaped with its center hole telescopically fitted to the lower end of the rotation shaft  42 . The third magnetic element  63  is secured to the lower end of the bearing  50  and is located above the fourth magnetic element  64 , and it has a center hole with a diameter larger than that of the rotation shaft  42 , to such an extent that when the rotation shaft passes through the third element  63 , both of them do not come into contact with each other. 
   By the above-mentioned structure of the third preferred embodiment of the invention, a magnetically repulsive force F 2  (F 6 ) is produced between the first and the second magnetic elements  61  and  62 ; and a magnetically repulsive force F 1  (F 5 ) is produced between the third and fourth magnetic elements  63  and  64  at the same time. Therefore, the magnetically repulsive force F 2  (F 6 ) that pushes the rotation shaft  42  towards the base  2  and the force F 1  (F 5 ) that pushes the rotation shaft  42  out of the base  2  cooperatively provide an axial positioning effect to the rotation shaft  42 . 
   Referring now to the fourth preferred embodiment of the invention shown in  FIG. 6 , the motor fan structure includes a base  12 , a stator  30 , a rotor  14 , a bearing  50  and upper and lower magnetic units. 
   The upper magnetic unit is composed of a first magnetic element  61  and a second magnetic element  62 . The first and second magnetic elements  61  and  62  are of the same pole and repulsive to each other. The second magnetic element  62  is fastened to the upper end of the bearing  50  and has a center hole with a diameter larger than that of the rotation shaft  42 , to such an extent that when the rotation shaft  42  passes through the center hole of the second magnetic element  62 , the two do not come into contact with one another. The first magnetic element  61  is ring-shaped with its center hole telescopically fitted to the rotor  14  and above the second magnetic element  62 . 
   The lower magnetic unit is composed of a third magnetic element  63  and a fourth magnetic element  64 . The third and fourth magnetic elements  63  and  64  are of the same pole and repulsive to each other. The third magnetic element  63  is ring-shaped with its center hole telescopically fitted to the rotation shaft  42 . The fourth magnetic element  64  is secured to the bearing seat  21  and is located below the third magnetic element  63 , and it has a center hole with a diameter larger than that of the rotation shaft  42 , to such an extent that when the rotation shaft passes through the third element  63 , the two do no come into contact with one another. 
   By the above-mentioned structure of the fourth preferred embodiment of the invention, a magnetically repulsive force F 2  (F 6 ) is produced between the first the second magnetic elements  61  and  62 ; and a magnetically repulsive force F 1  (F 5 ) is produced between the third and fourth magnetic elements  63  and  64  at the same time. Therefore, the magnetically repulsive force F 2  (F 6 ) that pushes the rotation shaft  42  towards the base  2  and the force F 1  (F 5 ) that pushes the rotation shaft  42  out of the base  2  cooperatively provide an axial positioning effect to the rotation shaft  42 . 
   Referring to the fifth preferred embodiment of the invention shown in  FIG. 7 , the fan motor in the embodiment includes a base  12 , a stator  30 , a rotor  14 , a bearing  50  and a magnetic unit. 
   The magnetic unit is composed of a first magnetic element  1  and a second magnetic element  2 . The first and second magnetic elements  1  and  2  are of the same pole and repulsive to each other. The second magnetic element  2  is ring-shaped with its center hole telescopically fitted near the lower end of the rotation shaft  42 . The first magnetic element  1  is secured to the lower end of the rotation shaft  42  and is located above the second magnetic element  2 , and it has a center hole with a diameter larger than that of the rotation shaft  42 , to an extent that when the rotation shaft  42  passes through the first magnetic element  1 , both of them do not come into contact with each other. 
   A magnetic centerline C 1  of a magnetic body  300  of the stator  30  and a magnetic centerline C 2  of a magnetic body  400  of the rotor  14  are not on the same level surface. Mutual deviation magnetism is utilized to provide axial magnetism, coupled with the magnetic unit, to achieve magnetic equilibrium. 
   Referring to  FIG. 8  in accordance with the sixth preferred embodiment of the invention, the fan motor structure of the embodiment includes a base  12 , a stator  30 , a rotor  14 , a bearing  50  and a magnetic unit. 
   The magnetic unit is composed of a first magnetic element  1  and a second magnetic element  2 . The first and second magnetic elements  1  and  2  are of the same pole and repulsive to each other. The first magnetic element  1  is ring-shaped with its center hole telescopically fitted to the rotation shaft  42 . The second magnetic element  2  is secured to the bearing seat  21  and is located below the first magnetic element  51  and it has a center hole with a diameter larger than that of the rotation shaft  42 , to an extent that when the rotation shaft  42  passes through the second magnetic element  52 , both of them do not come into contact with each other. As shown in  FIGS. 3-8 , the bearing  50  is a self-lubricating bearing. 
   The magnetic centerlines C 1  and C 2  of the magnetic body  300  of the stator  30  and the magnetic body  400  of the rotor  14 , respectively, are not on the same level surface. The mutual deviation magnetism is utilized to provide axial magnetism, coupled with the magnetic unit, to achieve magnetic equilibrium. 
   The repulsive magnetic forces of the magnetic units in the first to sixth preferred embodiments may also be replaced by attractive magnetic forces of opposite poles for magnetism so as to obtain the axial positioning. 
   Conclusive from the above structures, the advantages of the invention are summarized as the following: 
   1. Magnetism is utilized to achieve axial positioning, and therefore there are no contact and friction during rotation. 
   2. External magnetic forces may be applied to compensate the insufficiency of magnetic bias between the rotor  14  and the stator  30 , in a way that the rotor  14  and the stator  30  are unaffected by external forces and able to maintain a stationary equilibrium so as to achieve the purpose of gaining an excellent stability during rotation. 
   While the present invention has been particularly described, in conjunction with specific preferred embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.