Abstract:
A fan guard has a function of supercharging a fan in addition to supporting a rotor device is disclosed. The fan guard is to be mounted beside the rotor device for supporting the rotor device, and additionally, the fan guard interacts with an airflow generated by the revolution of the rotor blades to supercharge the fan. The fan guard essentially includes a main frame, and a set of guard blades radially arranged inside the main frame and fixed onto an inner surface of the main frame by each one end thereof. Each of the guard blades is preferred to have a shape similar to the shape of the rotor blades, and the set of guard blades can be arranged either upstream or downstream of the rotor blades.

Description:
FIELD OF THE INVENTION 
     The present invention is related to a fan guard structure, and more particular to an improved fan guard structure which imparts a supercharging function to a fan for efficient heat dissipation. 
     BACKGROUND OF THE INVENTION 
     Currently, heat-dissipating fans commonly used in personal computers include an axial-flow fan, a centrifugal fan and a cross-flow fan. Of these, the most popular one is supposed to be an axial-flow fan. 
     A fan is primarily consisted of a rotor device and a fan guard arranged beside the rotor device for supporting the rotor device. Referring to  FIG. 1 , the fan guard  10  of a conventional axial-flow fan is constructed by a main frame  101 , a motor holder  102  and a plurality of ribs  103  arranged between the main frame  101  and the motor holder  102 . The rotor device  11  includes a motor (not shown) received in the motor holder  102 , a shaft ring  111  connected to and driven by the motor to revolve, and a plurality of rotor blades  112  fixed on the circumferential surface of the shaft ring  111  and revolving with the shaft ring  111  to work on the surrounding air to generate an airflow. Through the work of the rotor blades on the surrounding air, the blast pressure is changed from a relatively low value on the air inlet side into a relatively high value on the air outlet side. That is, there is a blast pressure enhancement on the air outlet side. 
     Unfortunately, when the airflow further flows through the fan guard having the structure as shown in FIG.  1  and as described above, turbulent flows will be generated after the airflow encounters the ribs so as to have an adverse effect on the blast pressure enhancement. Consequently, the efficiency of the fan is reduced. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide an improved fan guard structure which has a function of supercharging a fan in addition to supporting a rotor device. 
     The present invention is related to a fan guard to be mounted beside a rotor device of a fan for supporting the rotor device. Additionally, the fan guard according to the present invention interacts with an airflow generated by the revolution of the rotor blades to supercharge the fan. 
     The fan guard essentially includes a main frame, and a set of guard blades radially arranged inside the main frame and fixed onto an inner surface of the main frame by each one end thereof. Generally but not definitely, a count of the guard blades is about 1-2 times of that of the rotor blades. Preferably, the other ends of the guard blades are fixed onto a cylindrical motor holder which is located at the center of the main frame, and is hollow for receiving therein a motor used for driving the rotor blades to revolve. Especially preferred, at least one reinforcing ring connecting all of the guard blades is provided for strengthening the far guard. In general, the guard blades are made of plastic. Nevertheless, the guard blades can also be made of a material other than plastic for a desired purpose. For example, they can be made of a metal which is advantageous for heat dissipation. 
     To assemble the fan, the main frame of the fan guard is coupled to the frame of the rotor device. Alternatively, the main frame of the fan guard is integrally formed with the frame of the rotor device so that the fan can be assembled by installing the non-integrally formed parts into the common frame. The fan guard can be arranged either upstream or downstream of the rotor device. Preferably, the fan guard includes two sets of frame and guard blades respectively arranged by both sides of the rotor device. By properly designing the shapes and the position arrangement of the guard blades relative to the rotor blades, the upstream guard blades can guide air into the rotor device at an angle to make an air inflow to the rotor device have an additional tangential velocity which increases the work of the rotor blades on air, and on the other hand, the downstream guard blades can transform a tangential velocity of an air outflow from the rotor device into a static pressure, both advantageous for supercharging the fan. For example, all of the guard blades are made to have a shape identical to the shape of the rotor blades. As for the position arrangement of the downstream guard blades relative to the upstream rotor blades, one of the guard blades and one of the rotor blades constitute a near letter C configuration in a cross-sectional view instantaneously. Contrarily, the position arrangement of the upstream guard blades relative to the downstream rotor blades makes one of the guard blades and one of the rotor blades constitute a near letter S configuration in a cross-sectional view instantaneously. 
     Furthermore, by taking the combination of a fan guard according to the present invention and a rotor device as a fan unit, a fan can be designed to include a plurality of such fan units to enhance efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention may best be understood through the following description with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram showing a conventional axial flow fan; 
         FIG. 2A  is a resolving diagram of a first preferred embodiment of a fan according to the present invention; 
         FIG. 2B  is a perspective diagram of the assembled fan of  FIG. 2A  with the rotor device facing forwards; 
         FIG. 2C  is a bottom view of the fan shown in  FIG. 2B ; 
         FIG. 2D  is a bottom view of the fan guard shown in FIG.  2 A; 
         FIG. 3  is a cross-sectional view of a rotor blade and a guard blade of the fan of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of a rotor blade and a guard blade of a second preferred embodiment of a fan according to the present invention; 
         FIG. 5A  is a resolving diagram of a third preferred embodiment of a fan according to the present invention; 
         FIG. 5B  is a cross-sectional view of a rotor blade and a guard blade of the fan of  FIG. 5A ; 
         FIG. 6  is a cross-sectional view of a rotor blade and a guard blade of a fourth preferred embodiment of a fan according to the present invention; 
         FIG. 7  is a partially resolving diagram of a fifth preferred embodiment of a fan according to the present invention; and 
         FIG. 8  is a perspective diagram of a sixth preferred embodiment of a fan according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. On the other hand, all arrows shown in the drawings are used for schematically illustrating the directions of airflows and velocities, and the length of the arrows does not indicate the measure of the corresponding items. 
     Please refer to  FIG. 2A    FIGS. 2A and 2D  which schematically shows a rotor device and a preferred embodiment of a fan guard according to the present invention. The rotor device  21 , as conventionally used, includes a motor  211 , a shaft ring  212  connected to the motor  211 , and a plurality of rotor blades  213  fixed on the circumferential surface of the shaft ring  212 . The fan guard  20  includes a main frame  201 , a motor holder  202 , and a plurality of guard blades  203 . The motor holder  202  is a hollow cylinder located at the center inside the frame for receiving therein the motor  211 . The guard blades  203  are radially disposed within the main frame  201 . One end  2031  of each of the guard blades  203  is fixed onto the inner surface  2011  of the main frame  201  and the other end  2032  thereof is fixed onto the circumferential surface  2021  of the motor holder  202 . In this embodiment, the frames of the fan guard and the rotor device are integrally formed as the main frame  201 . In other words, the motor  211 , shaft ring  212 , rotor blades  213 , motor holder  202 , and guard blades  203  are all positioned inside the main frame  201 . 
     The assembled fan is shown on  FIG. 2B    FIGS. 2B and 2C . In this embodiment, the rotor blades are located upstream of the guard blades. When the fan operates, the motor  211  (see  FIG. 2A ) drives the shaft ring  212  with the rotor blades  213  to revolve. The revolution of the rotor blades  213  results in work on the surrounding air to generate an airflow. The arrows Fi and Fo in the figure indicates the air inflow and the air outflow, respectively. Through the work of the rotor blades on the surrounding air, the blast pressure is changed from a relatively low value on the air inlet (Fi) side into a relatively high value on the air outlet (Fm,  FIG. 3 ) side. That is, there is a blast pressure enhancement on the air outlet (Fm) side. According to the present invention, the blast pressure can be further increased on the air outflow (Fo) side through the guard blades of the fan guard for the reason described as follows. 
     Please refer to FIG.  3 . In order to concretely illustrate the arrangement of the guard blades, an upstream rotor blade  313  which can be any one of the rotor blades and a downstream guard blade  303  which can be any one of the guard blades, are shown in a cross-sectional view, and a specific moment that a leading point A of the guard blade  303  is moved to be axially aligned with the trailing point B of the rotor blade  313  is taken to facilitate to describe the position relationship between the selected rotor blade and guard blade. As shown, the rotor and the guard blades  313  and  303  constitute a near letter C configuration. 
     When the rotor device operates to have the rotor blade  313  revolve at a tangential velocity Vr, the airflow arriving at the guard blade  303  has an axial velocity and a tangential velocity. Due to conservation of mass, the axial velocity will not change through the entire guard blade  303 , and is represented by a reference symbol Va in FIG.  3 . The tangential velocity, however, varies from a relatively high value Vt approximating the velocity Vr of the rotor blade to a relatively low value Vt′ down to zero. According to the Bernoulli&#39;s Law, the pressure will increase with the decrease of velocity. The tangential velocity of the airflow Fm will be transformed into a static pressure. Accordingly, the blast pressure further rises through the fan guard, and the fan is thus supercharged. 
     Although such a near C configuration is exemplified as above to describe a preferred embodiment, other configurations are acceptable as long as the purpose of transforming a tangential velocity into a static pressure can be achieved. 
     In another embodiment according to the present invention, the guard blades are arranged upstream of the rotor blades. As shown in  FIG. 4 , the position relationship between an upstream guard blade  403  and a downstream rotor blade  413  is illustrated at a moment that a leading point C of the rotor blade  403  is moved to follow the camber line CL of the guard blade  403 . The guard and rotor blades  403  and  413  at such moment constitute a near letter S configuration. 
     When the rotor device operates to have the rotor blade  413  revolve at a tangential velocity Vr, the guard blade  403  guide air into the rotor blade  413  at an angle. Consequently, the air outflow from the guard blade  403  has an axial velocity Va and a tangential velocity Vt, and thus the airflow arriving at the rotor blade  413  has a tangential velocity of Vr+Vt. As known, the increase of the tangential velocity enhances the work of the rotor blades on air, so in this way, the fan is supercharged. 
     Although such a near S configuration is exemplified as above to describe a preferred embodiment, other configurations are acceptable as long as the purpose of providing an additional tangential velocity can be achieved. 
     Please now refer to  FIGS. 5-8  which schematically show several composite fans which include a plurality of fan guards according to the present invention and/or rotor devices to further enhance fan efficiency. 
     The composite fan shown in  FIGS. 5A and 5B  is assembled by screwing the frames  511 ,  521  of the rotor devices  51 ,  52  and the frame  501  of the fan guard  50  together ( FIG. 5A ) so that the guard blades  503  can be upstream of the rotor blades  523  and downstream of the rotor blades  513  ( FIG. 5B ) to simultaneously enhance the efficiencies of the upstream rotor device  51  and downstream rotor device  523  so as to supercharge the composite fan. 
       FIG. 6  schematically shows another embodiment of composite fan according to the present invention. In this embodiment, there are a set of guard blades  603  located upstream of rotor blades  613  and another set of guard blades  623  located downstream of the rotor blades  613  to both enhance the efficiency of the rotor device. By this way, the composite fan is supercharged. 
     A further embodiment of a composite fan is shown on  FIG. 7  wherein two fan units, each consisting of a fan guard  70  according to the present invention and a rotor device  71 , are directly coupled to form the composite fan. 
     On the basis of the above fan guard skeletons, at least one reinforcing ring connecting the guard blades are preferably arranged for strengthening the fan guard. Referring to  FIG. 8 , the fan guard  80  includes two reinforcing rings  814 . 
     Although the guard blades in the above embodiments are exemplified to have a shape identical to the shape of the rotor blades, they can be plane plates or any other suitable shapes as long as the efficiency of the fan can be enhanced thereby. 
     The number of the guard blades need not be particularly limited, but one to two times of the count of the rotor blades will result in satisfactory performance. 
     The guard blades can be made of plastic. Nevertheless, the guard blades can also be made of a material other than plastic for a desired purpose. For example, when they are made of metal, the guard blades can serve as efficient heat-dissipating plates to further enhance the heat-dissipating efficiency. 
     To sum up, according to the present invention, the performance of a fan can be easily improved by changing the structure of the fan guard conventionally only used for supporting the fan. On the other hand, it is even advantageous because for the application to compact products, the high performance of the fan according to the present invention allows the fan size to be reduced so as to be installed properly. 
     While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.