Patent Publication Number: US-6340292-B1

Title: Anti-fracture fan structure

Description:
FIELD OF THE INVENTION 
     The invention relates to an anti-fracture fan structure, particularly to an anti-fracture fan structure that has a plurality of ribs in predetermined shapes to prevent the fan from fracturing due to heat expansion. 
     BACKGROUND OF THE INVENTION 
     A fan is widely used to dissipate heat generated by electrical devices such as desktop computers or notebook computers. FIG. 1 is a schematic illustration that shows a conventional fan structure. Referring to FIG. 1, the fan includes a hub  11  and a shielding-can  12 . The hub  11  has an inner surface  111 . A plurality of blades  112  are arranged around the hub  11 . A plurality of ribs  113  are provided around the inner surface  111 . 
     The hub  11  is usually made of a material such as plastic or resin. The shielding-can  12  is usually made of a metallic material that has a high strength property, and is mounted inside the hub  11  by press fitting in order to prevent a ring-shaped magnet (not shown), that is situated around the inner surface of the hub  11 , from being deformed. Thus, the magnetic leakage phenomenon can be avoided. 
     The ribs  113  are useful for mounting the shielding-can  12  into the hub  11  and preventing the hub  11  from being fractured. 
     In general, the fan starts operating at a lower temperature. The temperature of the fan gradually rises owing to the heat energy generated from the fan or the heat energy transferred from a heat sink (not shown). For example, it is possible that the temperature of the fan rises from −10° C. to 50° C. 
     However, the hub  11  and the shielding-can  12  have different heat expansion coefficients because the hub  11  and the shielding-can  12  are made of different materials. For example, the heat expansion coefficient of a PC (poly carbonate) material constituting the hub  11  is about 2.5×10 −7  in/in °F., while the heat expansion coefficient of a metal material constituting the shielding-can  12  is about 6.5×10 −6  in/in °F., which is 26 times as large as that of the PC material. As a result, if the fan is subjected to heat energy, the shielding-can  12  expands faster than the hub  11 , causing the hub  11  to fracture from the pressure of the expanding shielding-can  12 . 
     SUMMARY OF THE INVENTION 
     To overcome the above drawback, it is therefore an object of the invention to provide an anti-fracture fan structure in which the hub is not easily fractured by the pressing force of the shielding-can when the fan expands. 
     To achieve the above objective, there is provided an anti-fracture fan structure including a hub, a plurality of blades, and a plurality of ribs. The hub has an inner surface formed inside and encircling it. The plurality of blades are arranged outside and around the hub. The plurality of ribs projects from the inner surface of the hub into the inside of the hub. Each of the plurality of ribs is not perpendicular to the inner surface of the hub. 
     Furthermore, the anti-fracture fan further includes a shielding-can situated inside the hub and in contact with the plurality of ribs. 
     Moreover, the hub can be formed of a plastic material and the shielding-can can be formed of a metal material. 
     The ribs can be easily warped when the shielding-can expands. Therefore, the hub is not easily fractured by the expansion of the shielding-can when the fan expands with heat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration showing a conventional fan. 
     FIG. 2 is a schematic illustration showing the structure of an anti-fracture fan of an embodiment in accordance with the invention. 
     FIG. 3 is a partially enlarged schematic illustration showing the deformation of the anti-fracture fan in FIG. 2, wherein the deformation is caused by heat expansion. 
     FIG. 4 is a schematic illustration showing a modification of the embodiment as shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An anti-fracture fan of a preferred embodiment in accordance with the invention is now described in detail with reference to the accompanying drawings. 
     FIG. 2 is a schematic illustration showing the structure of an anti-fracture fan. Referring to FIG. 2, the fan includes a hub  11  and a shielding-can  12 . The hub  11  has an inner surface  111 . A plurality of blades  112  are arranged around the hub  11 . A plurality of ribs  114  are provided on the inner surface  111 . 
     It should be noted that a line A indicates the direction of extension of one of the ribs  114  while a line B indicates the radial direction of the rib  114  and also indicates the direction of extension of one of the ribs  113  if the ribs  113  are arranged as in FIG.  2 . 
     The difference is that an angle θ between the line A and the line B is not zero degrees. In other words, each of the ribs is not perpendicular to the inner surface  111 . 
     Referring to FIG. 3 that is a partially enlarged schematic illustration showing the deformation of the anti-fracture fan caused by heat expansion. When the anti-fracture fan expands, the shielding-can  12  expands, becoming the shielding-can  12 ′ and exerting force on the rib  114 . The force that shielding-can  12  exerts on the rib  114  is indicated by an arrow F which is substantially parallel to the radial direction as indicated by the line B. 
     When the rib  114  is compressed, it is elastically deformed, becoming the rib  114 ′ because the rib  114  is not perpendicular to the inner surface  111 . In other words, the rib  114  will slightly warp when absorbing the force created by the expanded shielding-can  12 . 
     In the fan of the prior-art, as shown in FIG. 1, because the rib  113  is perpendicular to the inner surface  111  of the hub  11 , the expanded shielding-can  12  exerts a compression force on the rib  113 . In this situation, the compression force mainly acts on the hub  11 , causing the hub  11  to be fractured. 
     However, in the anti-fracture fan as shown in FIG. 3, the ribs  114  can absorb most compression force by warping. Therefore, the expanded shielding-can  12  does not easily fracture the hub  11 . 
     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it 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. For instance, the shapes of the ribs  114  can be modified to the shapes as shown in FIG.  4 . In this case, each of the ribs  114  in FIG. 4 extends in two directions but still retains the same function as that of the above embodiment as shown in FIG.  3 .