Abstract:
The present invention provides a fan including a stator and a rotor coupled to the stator. The stator has a base and a bearing disposed inside the base. The rotor has a shaft supported by the bearing. Furthermore, the shaft has a concave structure formed on a surface thereof, or the bearing has a groove structure formed on a surface thereof.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 097101494, filed in Taiwan, Republic of China on Jan. 15, 2008, and Patent Application No(s). 097101495, filed in Taiwan, Republic of China on Jan. 15, 2008, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fan, and relates to a bearing structure of the fan. 
     2. Description of the Prior Art 
     Fans are usually used in dissipating heats generated by interior electric components during operation all the time. A conventional fan shown in  FIG. 1  includes a stator and a rotor. The stator includes a base  12  and a ball bearing  14  disposed inside the base  12 . The base  12  and the ball bearing  14  support the shaft  16  of the rotor together. The ball bearing  14  includes an inner ring and an outer ring rotating relative to each other. The outer ring urges against the base  12 , and the inner ring urges against the shaft  16 . Therefore, the cooperation elements must allow certain of deformation to achieve a tight press. However, the deformation causes the variation of the size of the element, and causes a non-uniform stress induced by the element. During the fan operation process, the inner ring of the ball bearing  14  rotates corresponding to the shaft  16  so as to generate heat because of the friction, and the heat will enlarge the variation. Additionally, when the shaft is in operation, the size of the shaft varies because of heats, and the abrasion becomes serious, such that the lifetime of the shaft and the ball bearing is lowered. Therefore, after the fan operates in a period of time, the stability of the fan will be lowered by the variation. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a fan and a bearing structure therein. 
     According to the design of the present invention, a fan includes a stator and a rotor. The stator includes a base and a bearing disposed inside the base. The rotor is coupled to the stator, and includes a shaft supported by the bearing. Therein, a concave structure is formed on a surface of the shaft. The concave structure includes a section plane, an annular concave, a spiral concave, a transversal concave, a longitudinal concave, an oblique concave, a polygonal concave, or a combination thereof. 
     Additionally, the fan further includes an impeller coupled to an end of the shaft. Therein, multiple airflow-guiding plates are formed on an inner surface of a hub of an impeller. When the impeller rotates, the airflow-guiding plates can guide airflows to pass through the concave structure. 
     Preferably, the bearing has a top end-surface, a bottom end-surface, and at least one groove structure. The groove structure extends out of the top end-surface or the bottom end-surface to allow airflows to pass through the groove structure. 
     According to another design of the present invention, the fan includes a stator and a rotor coupled to the stator. The stator includes a base and a bearing disposed inside the base, and a groove structure is formed on a surface of the bearing. The rotor includes a shaft supported by the bearing. 
     A groove structure is formed on a surface of the bearing. The groove structure can be a spiral groove, an annular groove, a transversal groove, a longitudinal groove, an oblique groove, a polygonal groove, or a combination thereof. The groove structure of the bearing is formed on a surface of an inner ring or a surface of an outer ring. Or, the groove structure is formed on both surfaces of an inner ring and an outer ring of the bearing. 
     Therefore, compared with the prior art under a condition of the same engagement, there is a smaller contacting area between the shaft and the bearing of the present invention and/or between the bearing and the base of the present invention. Such that, the size variation of the fan caused by the engagement is reduced, the whole structure becomes more stable, and the shaft can rotate smoothly. Further, airflows can be allowed to pass through the groove structure of the bearing to dissipate the heat generated by the fan during operation. According, the size variation of the fan is reduced, and the stability of rotation is kept. Additionally, the airflow-guiding plates disposed around the engagement between the shaft and the impeller can enhance the convection of airflows through the groove structure. Thus, the size variation caused by heat is highly reduced, and the stability of rotation is raised. 
     The advantage and spirit of the present invention can be understood by the following recitations together with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         FIG. 1  is a cross-sectional view of a conventional fan. 
         FIG. 2A  is a cross-sectional view of a fan according to a first embodiment of the present invention. 
         FIG. 2B  is a cross-sectional view of a fan according to a second embodiment of the present invention. 
         FIG. 2C  is a cross-sectional view of a fan according to a third embodiment of the present invention. 
         FIG. 2D  is a cross-sectional view of a fan according to a fourth embodiment of the present invention. 
         FIG. 3A  is a cross-sectional view of a fan according to a fifth embodiment of the present invention. 
         FIG. 3B  is a schematic illustration showing the shaft of the fan shown in  FIG. 3A . 
         FIG. 3C  is a schematic illustration showing the impeller of the fan shown in  FIG. 3A . 
         FIG. 4A  is a cross-sectional view of a fan according to a sixth embodiment of the present invention. 
         FIG. 4B˜4D  are schematic illustrations showing different kinds of bearing of the fan shown in  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 2A ,  FIG. 2A  is a cross-sectional view of the fan  1  according to the first embodiment of the present invention. The fan  1  includes a base  12 , a bearing  14 , a shaft  16 , an impeller  18 , and an electromagnetic element  19 . The fan  1  connects to a fixed part  2  (shown as dotted lines) of a system via the base  12 . 
     The base  12  is used for accommodating the bearing  14 . The bearing  14  is a ball bearing and includes an inner ring  142 , an outer ring  144 , and multiple balls  146  disposed between the inner ring  142  and the outer ring  144 . The outer ring  144  of the bearing  14  urges against the base  12 . A concave structure is formed on the shaft  16 , and the concave structure is an annular structure  164  in this embodiment. The shaft  16  passes through the inner ring  142  of the bearing  14  and urges against the inner ring  142 . The bearing  14  thereon defines two opposite surfaces  148   a  and  148   b , and the annular concave  164  includes two parts  164   a  and  164   b  respectively protruding out of the aforesaid surfaces  148   a  and  148   b . Accordingly, airflows can be allowed to pass through the annular concave  164 , such that the heat generated by the fan  1  during operation can be dissipated. It should be additionally remarked that the impeller  18  is coupled to an end of the shaft  16 , the fan  1  further includes a magnetic ring  182  cooperated with the electromagnetic element  19  to actuate the fan  1  to rotate. When the fan  1  rotates, the shaft  16  rotates with the inner ring  142  of the bearing  14  at the same time. 
     In the second embodiment of the present invention, the concave structure can be an oblique concave  164 ′ as shown in  FIG. 2B . In the third embodiment, the concave structure includes one or multiple spiral concave  164 ″ as shown in  FIG. 2C . 
     In the fourth embodiment, the concave structure includes multiple transversal concaves  164   a ′″ and multiple longitudinal concaves  164   b ′″ connected to the transversal concaves  164   a ′″, as shown in  FIG. 2D . The aforesaid transverse and longitude are relative to the central axis of the shaft (shown as the dotted line in  FIG. 2D ). Although the transversal concaves  164   a ′″ are not directly connected to exterior air, the whole concave structure via the engagements of the longitudinal concaves  164   b ′″ can allow airflows to pass through the transversal concaves  164   a ′″ and the longitudinal concaves  164   b ′″. Additionally, the aforesaid annular concave  164 , the oblique concave  164 ′, and the spiral concave  164 ″ can be combined alternatively and formed on the surface of the shaft  16 . 
     Please refer to  FIG. 3A ,  FIG. 3A  is a cross-sectional view of the fan  3  according to a fifth embodiment of the present invention. Compared with the aforesaid first embodiment, the concave structure includes multiple section-planes  364   a  and multiple concaves  364   b , and an enlarged schematic illustration of the shaft  36  of the fan  3  is shown in  FIG. 3B . When the impeller  38  rotates, the airflow-guiding plates  384  on the impeller  38  will guide airflows to pass between the section-plane  364   a  and the bearing  34 . The schematic path of airflow F is shown as a dotted line with an arrow in the  FIG. 3A . The design of the airflow-guiding plates  384  is shown in  FIG. 3C , the airflow-guiding plates  384  is formed on an inner surface of the cup-shaped hub  381  of the impeller  38 , and help guiding airflow F to pass through the concave structure. Therefore, the heat generated by the fan  3  during operation can be quickly dissipated by the airflow F. 
     According to the aforesaid embodiments, when the shaft has a concave structure, not only the contacting area between the shaft and the bearing can be reduced, but also the size variation can be reduced. Furthermore, the dissipation is enhanced by the concave structure with a penetration structure, the size variation caused by heat is reduced, and the durability and stability can be raised. 
     The concave structure of the fan of the present invention is formed on the shaft, and the groove structure can also be formed on the bearing to achieve a purpose of the reduction of the size variation. Further, the dissipation of heat can be enhanced as well.  FIG. 4A  is a fan according to the sixth embodiment of the present invention. The sixth embodiment is similar in structure to the first embodiment, and the difference is that the groove structure in the sixth embodiment is formed on the ball bearing  54 . As shown in  FIG. 4B , multiple longitudinal grooves  5422  (parallel to the extension direction of the shaft) are formed on the inner ring  542  of the ball bearing  54 , therefore the contacting area between the ball bearing  54  and the shaft is reduced. Additionally, the longitudinal grooves  5422  penetrate through two opposite surfaces  5424  (a top end-surface and a bottom end-surface) of the ball bearing  54 . Thereby, when the shaft is engaged to the ball bearing  54 , the longitudinal groove  5422  can be formed as a tunnel, and airflows can pass through the tunnel to dissipate the heat generated by the ball bearing  54  during operation. The path of airflows is shown as a dotted line with an arrow in  FIG. 4A . 
     Of course, the aforesaid longitudinal groove  5422  can be replaced with the spiral groove or the oblique groove  5422 ′ shown in  FIG. 4C . The groove structure can also be a combination of the aforesaid grooves  5422  and  5422 ′. 
     Additionally, as shown in  FIG. 4D , multiple grooves  5422 ′ and  5442  can also be formed on the inner ring  542  and the outer ring  544  of the ball bearing. Although the grooves  5422 ′ and  5442  are spiral grooves, the present invention is not limited to this. For example, the groove structure can have two oblique grooves and the two oblique grooves are disconnected and formed as V-shaped. In another example, the groove structure can have four oblique grooves are disconnected and formed as V-shaped, or the groove structure can have at least two spiral grooves. In another example, the groove structure can have a plurality of transversal grooves and longitudinal grooves connected to the transversal grooves. 
     Because the ball bearing urges against the base of the present invention, there is also a problem of a size variation in the cooperation between the ball bearing and the base. Therefore, the formation of the multiple grooves on the outer ring of the ball bearing of the present invention can reduce the contacting area between the ball bearing and the base, and further to reduce the size variation caused by engagement. Furthermore, the engagement between the ball bearing and the base has less effect on the ball bearing and on the engagement between the bearing and shaft. Similarly, when the grooves  5442  on the outer ring  544  penetrate through two opposite surfaces  5444  of the ball bearing  54 ′, the groove  5442  also has the same heat-dissipation effect as the groove  5422 ′ on the inner ring  542 , and it is not described here again. 
     Although the groove structures penetrating two opposite surfaces of the bearing are mostly described in the aforesaid embodiments, but the present invention is not limited to this. The groove structure of the fan of the present invention can also be a polygonal groove, and the structure can reduce the contacting area between the shaft and the bearing or between the bearing and the base as well. Further, the size variation caused by the engagement can be reduced as well. 
     As a whole, the shaft and the bearing of the present invention having concave structures and groove structures respectively, such that the contacting area between the shaft and the bearing or between the bearing and the base is reduced. Further, the size variation caused by the engagement is highly reduced, the whole structure is more stable, and the shaft can rotate smoothly. Additionally, airflows can be allowed to pass through the groove structure penetrating two opposite surfaces of the bearing to dissipate heat generated by the fan during operation, such that the size variation is reduced and the stability of the rotation is kept. Finally, the airflow-guiding plates disposed around the engagement between the impeller and the shaft can enhance the convection of airflows through the concave structure, and the size variation caused by heat can be highly reduced to raise the stability of the rotation. 
     With the example and explanations above, the features and spirits of the present invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the present invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.