Patent Publication Number: US-6712582-B1

Title: Centrifugal fan

Description:
FIELD OF THE INVENTION 
     The present invention is related to a centrifugal fan, and more particularly to a centrifugal fan mounted in a laptop computer. 
     BACKGROUND OF THE INVENTION 
     In the modern era, the computer has become an indispensable tool for the people in their daily lives. The market of the laptop computer has rapidly expanded, together with the rise of the living standard and with the rise in living standard and with the demands of business. In recent years, the major manufacturers of laptop computers have dedicated money and manpower to research and development the laptop computer to increase. One bottleneck imposed on the development of the laptop computer is the issue of the heat dissipation. The key feature of the laptop computer is that the user can carry it and use it at anytime, usually by placing it on the lap for operation. If the laptop computer becomes overheated in such situations, it will not be usable and it will also be inconvenient to transport. Thus, the key feature of the laptop computer will be degraded. 
     Most of the current laptop computers use a fan to dissipate the heat generated in the laptop computer. The heat generated in a laptop computer is expelled out of the laptop computer by way of air convection. The fan expels the hot air out of the laptop computer and draws the cooling air into the laptop computer for lowering the temperature of the a laptop computer. Because the laptop computer must be small and thin for portability, it is somewhat difficult to incorporate a fan inside the laptop computer. If a common axial flow fan is adopted for dissipating the heat generated in a laptop computer, the airflow will not be smooth and the heat-dissipation efficiency will be low owing to the forced air convection induced by the axial flow fan. If a centrifugal fan is adopted to dissipate the heat generated in a laptop computer, the centrifugal fan is able to match the natural fundamentals of airflow and thus is feasible for dissipating the heat generated in a laptop computer. 
     Please refer to FIG. 1 which is the top view of the conventional centrifugal fan. An outlet opening is located on the side of the casing  11 , which is not shown in the drawing. It can be seen from FIG. 1 that an impeller  13  facing the intake opening of the casing  11  (not shown) is rotatably mounted in the casing  11 , and the fan blades  12  are attached to the impeller  13 . The cooling air will flow into the intake opening by means of the rotation of the impeller  13  as well as the fan blades  12  and then blow off through the outlet opening on the side of the casing  11 . 
     While the centrifugal fan is operating, noise will be inevitably generated as long as the air is flowing inside the centrifugal fan. Moreover, the faster the fan rotates, the louder noise will be generated. Therefore, if one desires to increase the rotating speed of the centrifugal fan in order to improve the heat-dissipating efficiency, the noise will become louder as well. 
     Accordingly, it is desirable to modify the centrifugal fan to solve the dilemma of whether to improve the heat-dissipating efficiency or to lower the noise. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a centrifugal fan with an increased air capacity and a lower noise. 
     It is another object of the present invention to provide a centrifugal fan with an improved heat-dissipating efficiency. 
     The centrifugal fan of the present invention includes a casing having an intake opening and a horn-shaped outlet opening for increasing the air outflow, an impeller rotatably mounted in the casing with a reduced diameter and bared inner space for increasing the air capacity, and fan blades attached to the impeller, wherein each of the fan blades is chipped at the rim for lowering the noise. 
     In accordance with the present invention, the fan blades are protruded from the rim of the impeller. 
     In accordance with the present invention, the gap of the fan blade is near the intake opening of the casing. 
     In accordance with the present invention, the inner periphery of the horn-shaped outlet opening will be reduced toward the inner space of the casing. 
     Now the foregoing and other features of the present invention may best be understood through the following descriptions with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of the conventional centrifugal fan; 
     FIG. 2 is a top view of the centrifugal fan of the present invention; 
     FIG. 3 is a cross-sectional view of the outlet opening of the conventional centrifugal fan; 
     FIG. 4 is a cross-sectional view of the outlet opening of the centrifugal fan according to the present invention; 
     FIG. 5 is a cross-sectional view of the fan blades of the conventional centrifugal fan; 
     FIG. 6 is a cross-sectional view of the fan blades of the centrifugal fan according to present invention; and 
     FIG. 7 is a characteristic curve of an exemplary embodiment of the centrifugal fan of the present invention, in comparison with a conventional axial flow fan. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 shows the top view of the centrifugal fan of the present invention. In comparison with the conventional centrifugal fan of FIG. 1, the centrifugal fan shown in FIG. 2 has an impeller rotatably mounted in a casing  21 , the impeller including plural fan blades  22  arranged and disposed on a base  23 , the fan blades protrude from the base of the attached impeller, and wherein each of said plural fan blades  22  has a gap at its&#39; rim. 
     FIG. 3 is a cross-sectional view of the outlet opening of the conventional centrifugal fan, and FIG. 4 is a cross-sectional view of the outlet opening of the centrifugal fan according to the present invention. One characteristic of the centrifugal fan according to the present invention can be understood that the outlet opening  31  of the conventional centrifugal fan is a flat and rigid structure, but the outlet opening  41  of the centrifugal fan according to the present invention is a horn-shaped structure. Remarkably, the inner periphery of horn-shaped opening  41  will be reduced toward the inner space of the casing. Consequently, the airflow inside the centrifugal fan can be diffused rapidly and the air outflow is increased further. 
     FIG.  5  and FIG. 6 are cross-sectional views of the fan blades of the prior art and the present invention, respectively. It can be known that the fan blades  52  of the conventional centrifugal fan are extended to the extent of the impeller  53 . To contrast FIG. 5 with FIG. 6, it is obvious that the fan blades  62  of the centrifugal fan according to the present invention are protruded from the rim of the impeller  63 . Moreover, it is worthy to note that each of the fan blades  62  is chipped at the rim so as to have a gap  61  at the rim. While the fan blade  62  and the impeller  63  are mounted in the casing, the gap  61  of the chipped fan blade  62  is near the intake opening of the casing such that the noise will be lowered while the centrifugal fan is operating. 
     Please refer to FIG.  7 . As can be seen from FIG. 7, the axial flow fan curve  73  will have a relatively high air capacity  71  as the windage  72  is low. However, if the windage  72  is risen up to a certain degree, the axial flow fan will be much likely to be stalled, which will lead to a low heat-dissipating efficiency and a high noise. 
     On the contrary, it can be seen from the centrifugal fan curve  74  of the present invention that the centrifugal fan of the present invention will be more unlikely to be stalled as the windage  72  is raised. Thus, the working range of the centrifugal fan is enlarged and the heat-dissipating efficiency is much better than that of the axial flow fan. 
     In summary, the centrifugal fan of the present invention has the following three advantages: 
     (a) The outlet opening of the centrifugal fan is horn-shaped for increasing the air outflow. 
     (b) The impeller of the centrifugal fan has a reduced diameter and bared inner space such that the fan blades attached to the impeller are protruded from the rim of the impeller for increasing the air capacity. 
     (c) each of the fan blades is chipped at the rim, and the gap of the fan blade is near the intake opening of the casing for lowering noise. 
     Those of skill in the art will recognize that these and other modifications can be made within the spirit and scope of the invention as defined in the appended claims.