Abstract:
A fan and shroud assembly has a rotatable hub and plural blades extending outward from the hub. A shroud surrounding the fan controls air blast resulting from rotation of the fan. The shroud includes a guide ring spaced a predetermined distance from the periphery of the fan. The ends of the blades are connected together. The guide ring includes continuous circular undulations having alternate differing radii of curvature to reduce air swirl along the periphery of the fan. The undulations surround the fan periphery.

Description:
RELATED APPLICATION 
   The present application is based on, and claims priority from, Korean Application Number 10-2005-0025221, filed Mar. 26, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fan and shroud assembly used for an air blast in an air conditioner of a car, and more particularly, to a fan and shroud assembly which can effectively reduce noise by controlling generation of swirling airflow and backflow during the air blast by rotation of a fan. 
   2. Background Art 
   In general, an air conditioner for a car comprises a radiator, and an axial fan for cooling heat exchange medium flowing through a heat exchanger such as a condenser. As shown in  FIG. 1 , the axial fan  200  generally comprises a hub  230  connected with a shaft of a driving source such as a motor, and a plurality of blades  210  radially arranged on the outer periphery of the hub  230 . The axial fan  200  may further include a fan band  220  connecting ends of the blades  210  to prevent transformation of the blades  210 . Therefore, air can be axially blown by the blades  210  while the axial fan  200  is rotated by rotational force transmitted from the driving source to the hub  230 . A shroud is fixed to the heat exchanger in order to effectively guide the blown air toward the heat exchanger. The shroud has a blast inlet as large as the axial fan can be rotatably inserted thereinto to guide the air blast in such a way as to support the motor. 
   As shown in  FIGS. 2 ,  3  and  4 , the shroud  100  of a puller type fan shroud assembly mounted on the rear of the heat exchanger to inhale air from the front of the heat exchanger and send air to the rear of the heat exchanger comprises: a housing  110  having a blast inlet  120  in which an axial fan  200  is rotatably inserted; a motor supporting ring  130  for supporting a motor (not shown) rotating the axial fan  200  at the center of the blast inlet  120  of the housing  110 ; and a plurality of guide vanes  140  for radially connecting the motor supporting ring  130  and the housing  110  with each other to support the motor supporting ring  130  and guide air discharged when the axial fan  200  is rotated. 
   The housing  110  is depressed to the rear to effectively guide sucked air toward the air blowing hole  120 , and comprises connection ribs formed on the edges for coupling between the housing  110  and the heat exchanger. 
   The blast inlet  120  is formed by a guide ring  150  protruding backwardly from the housing  110  and curved from the rear end of the guide ring  150  toward the inside of the guide ring  150 , and further comprises a bell mouth  180  for smoothly guiding a discharge of air. 
   Here, a plurality of swirl preventing saw teeth  160  are formed along the inner periphery of the blast inlet  120 , that is, inner periphery of the guide ring  150 . In the case where the bell mouth  180  is provided, the swirl preventing saw teeth  160  are formed integrally on the inner periphery of the guide ring  150  which is connected with the bell mouth  180 . 
   The swirl preventing saw teeth  160  are spaced apart at a predetermined interval from the ends of the blades  210  of the axial fan  200 . The swirl preventing saw teeth  160  comprise a first side  162  toward the rotational direction of the axial fan and a second side  164  toward the counter-rotational direction of the axial fan. 
   Such shroud having the swirl preventing saw teeth can reduce noise, but noise generated from the fan and shroud assembly is more increased when noise generated from the car is added. To solve the above problem, a configuration to which a bended bell mouth is provided to smoothly discharge air into the guide ring has been proposed. However, such configuration has a problem in that it is insufficient in reducing noise since it needs additional structure. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention has been made to solve the above problems occurring in the prior art, and it is an object of the present invention to provide a fan and shroud assembly, which can increase a noise reduction effect by installing swirl preventing means on a guide ring part of a shroud keeping a predetermined interval from the periphery of a fan connecting ends of blades. 
   To accomplish the above objects, according to the present invention, there is provided a fan and shroud assembly comprising: a fan having a hub rotatable on a shaft and a plurality of blades extending outward from the hub; and a shroud surrounding the fan for controlling air blast resulting from rotation of the fan, wherein the shroud comprises: (a) a guide ring part spaced apart at a predetermined interval from the periphery of the fan, wherein the ends of the blades are connected together at the periphery of the fan; and (b) a swirl preventer including round-corrugation structure formed on the guide ring part for preventing swirling airflow along the periphery of the fan where the ends of the blades are connected. 
   Furthermore, the swirl preventer comprises round furrows having a predetermined radius of curvature at a portion which is depressed in a radial direction and round projections having a predetermined radius of curvature at a portion extending toward the center of the shroud, the round furrows and the round projections being repeatedly arranged and having differing radii of curvature. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a front view of the prior art axial fan, as previously discussed; 
       FIG. 2  is a perspective view of the rear of the prior art shroud of the fan of  FIG. 1 ; 
       FIG. 3  is a front view and a partially enlarged view of the prior art shroud of  FIG. 2 ; 
       FIG. 4  is a partially side sectional view of the prior art fan and shroud assembly of  FIG. 1 ; 
       FIG. 5  is a front view of a fan and shroud assembly according to a preferred embodiment of the present invention; 
       FIG. 6  is an exploded perspective view of a fan and a shroud according to the preferred embodiment of the present invention; 
       FIG. 7  is a detailed view of part “A” of  FIG. 6 ; 
       FIG. 8  is a perspective view of the shroud according to the preferred embodiment of the present invention; 
       FIG. 9  is a view indicating the dimensions and arrangement of round corrugation formed on the shroud, as seen from part “B” of  FIG. 8 ; 
       FIG. 10  is a graph comparing noise spectra of the prior art fan and shroud assembly and the fan and shroud assembly of  FIGS. 5-8  in the same blast capacity; and 
       FIG. 11  is a P-Q graph comparing the shroud between the prior art fan and shroud assembly and the fan and shroud assembly of  FIGS. 5-9  with changes of pressure. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will be now made in detail to the preferred embodiment of the present invention with reference to the attached drawings. Terms and words used in this specification and claims are to be interpreted with a meaning and in accordance with the concepts corresponding to the technical idea of the present invention, based on the principle that the inventor can properly define the concept of words to explain the inventor&#39;s invention in the best way. 
     FIG. 5  is a front view of a fan and shroud assembly according to the preferred embodiment of the present invention,  FIG. 6  is an exploded perspective view of a fan and a shroud according to the preferred embodiment of present invention,  FIG. 7  is a detailed view of part “A” of  FIG. 6 ,  FIG. 8  is a perspective view of the shroud according to the preferred embodiment of the present invention, and  FIG. 9  is a view indicating dimensions and arrangement of a round corrugation formed on the shroud, as seen from part “B” of  FIG. 8 . 
   The fan and shroud assembly according to the preferred embodiment of the present invention comprises a fan  20  having a hub  21  rotatable on a shaft and a plurality of blades  22  extending outward from the hub  21 , and a shroud  10  surrounding the fan  20  for controlling the air blast resulting from rotation of the fan  20 . The shroud  10  comprises a guide ring part  11  spaced apart at a predetermined interval from the periphery of the fan. The periphery of the fan, defined by band  23 , connects the ends of the blades  22  together. Shroud  10  also includes swirl preventing means formed on the guide ring part  11 ; the swirl preventing means prevents swirling air from flowing along the peripheral band connecting the ends of the blades  22 . 
   The shroud  10  comprises a housing  12  having a blast inlet  13  in which the fan  20  is inserted, a motor supporting part  14  located at the center of the blast inlet  13  for supporting a motor (not shown) for driving the fan  20 , and ribs  15  for connecting the motor supporting part  14  and the housing  12  with each other. The swirl preventing means is round corrugations  16  formed on the guide ring part  11 . 
   Because the fan  20  comprises a band  23  for connecting the ends of the blades  22 , the round corrugations  16  are spaced a predetermined distance from the band  23 . 
   The round corrugations  16  have round furrows  16   a  having a predetermined radius of curvature (D/2) at portions which extend outwardly from the center of the shroud and round projections  16   b  having a predetermined radius of curvature (d/2) at the portions which extend toward the center of the shroud, where D&gt;d and the round furrows  16   a  and the round projections  16   b  are repeatedly arranged. 
   The fan and shroud assembly having the above configuration somewhat increases power consumption but can reduce noise since it minimizes generation of air swirl. 
   When the fan  20  is rotated, swirling air flows in the rotational direction of the fan  20  in a space between band  23  and the inner periphery of guide ring part  11 . Such swirling air has a circular flow with a small diameter as shown in  FIG. 9  due to a pressure difference between the round furrows  16   a  and the round projections  16   b . The circular flow serves as a shielding membrane in the space between the band  23  and the inner periphery of the guide ring part  11 , so as to prevent swirling airflow and backflow. Therefore, the present invention can reduce noise. 
   Moreover, the circular flow can progress smoothly progressed with little resistance since the furrows  16   a  are round. 
   The main factors for determining performance in relation with the noise reduction effect are a diameter D of the round furrow  16   a  and the number N of the round furrows  16   a  of the corrugation  16 . At this time, it is preferable that the diameter of the round furrow  16   a  is 5.0 mm˜30.0, and more preferably, within a range of 5.0˜15.0 mm. It is preferable that the number of the round furrows  16   a  formed along the peripheral direction of the guide ring part  11  is 20˜60. 
   Hereinafter, test results of the prior art fan and shroud assembly having the swirl preventing saw teeth and the fan and shroud assembly of the present invention will be described. 
   The test was carried out by the steps of mounting the fan and shroud assembly on a heat exchanger, applying a voltage of 12V, preheating the heat exchanger for 15 minutes, and measuring rotational frequency, blast capacity and noise at 12V, 13.5V and the same blast capacity. The test results are shown in the Table 1 and  FIG. 10 . 
   Furthermore, blast capacity was measured while pressure is lowered by 2 mmAq (where 1 atmosphere=10.332 mmAq=760 mmHg) within a range of constant pressure of 0.0˜12.0 mmAq in a single product state. The measured results are shown in  FIG. 11 . 
   
     
       
             
             
             
             
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
                 
                 
                 
                 
               Consumption 
                 
                 
               Blast 
                 
                 
                 
                 
                 
             
             
                 
                 
               Voltage 
               Current 
               power 
               Difference 
                 
               Capacity 
               Difference 
               Noise 
               Difference 
               1 st  peak 
               Difference 
             
             
               Terms 
               Sample 
               (volt) 
               (A) 
               (Watt) 
               (%) 
               Rpm 
               (CMH) 
               (%) 
               dB(A) 
               dB(A) 
               dB(A) 
               dB(A) 
             
             
                 
             
           
           
             
               12 V 
               Prior art 
               12.0 
               11.0 
               132.1 
               — 
               1732 
               1446 
               — 
               63.2 
               — 
               53.8 
               — 
             
             
                 
               Fan of 
               12.0 
               11.0 
               132.1 
               0 
               1732 
               1446 
               −1.4 
               61.9 
               −1.3 
               50.0 
               −3.8 
             
             
                 
               FIGS. 5-9 
             
             
               13.5 V 
               Prior art 
               13.5 
               12.8 
               172.7 
               — 
               1876 
               1592 
               — 
               64.9 
               — 
               55.1 
               — 
             
             
                 
               Present 
               13.5 
               12.8 
               172.7 
               0 
               1874 
               1570 
               −1.4 
               63.7 
               −1.2 
               52.5 
               −2.6 
             
             
                 
               invention 
             
             
               Same 
               Prior art 
               12.0 
               11.0 
               132.1 
               — 
               1732 
               1446 
               — 
               63.2 
               — 
               53.8 
               — 
             
             
               blast 
               Fan of 
               11.2 
               12.2 
               136.6 
                 3.4 
               1740 
               1446 
               — 
               62.1 
               −1.1 
               50.1 
               −3.7 
             
             
               capacity 
               FIGS. 5-9 
             
             
                 
             
           
        
       
     
   
   In the test results shown in the Table 1 and  FIG. 10 , at the same voltage (12V, and 13.5V), compared with the prior art, the fan and shroud assembly according to  FIGS. 5-9  had an overall noise reduction, and reduced first peak value of the noise spectrum. However, the blast capacity was reduced a little and the power consumption was equal to that of the prior art fan and shroud assembly. 
   Meanwhile, at the same blast capacity, compared with the prior art, the fan and shroud assembly according to  FIGS. 5-9  was greater in power consumption than the prior art, but the overall noise was reduced about 1.1 dB, and peak noise was reduced about 3.7 dB. 
   Moreover, referring to  FIG. 11  showing P-Q line graph, the shroud of  FIGS. 5-9  was equal in the entire constant pressure area (P) and the blast capacity (Q) with the saw teeth type shroud of the prior art. 
   As described above, the fan and shroud assembly according to the present invention can minimize generation of swirling airflow and backflow and provide improved noise-reduction effect by the round corrugation formed along the inner periphery of the blast inlet of the shroud. 
   While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.