Abstract:
A fan system includes a motor; a driven fan, driven by the motor; and a dummy fan, freely rotatable around a bearing support shaft. The fans have blade rings at their external surfaces. The blade rings include gears, engaged with each other such that rotation of the driven fan rotates the dummy fan.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is based on, and claims priority from, Korean Application Serial Number 10-2007-0067895, filed on Jul. 6, 2007, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a cooling fan system, and more particularly, to a dual cooling fan system driven by single motor. 
       BACKGROUND OF THE INVENTION 
       [0003]    In general, a vehicle is cooled with coolant or cooling water. The cooling water circulates such that after it is heated in the engine, it is cooled using both a fan and a radiator, and is then supplied back to the engine. The radiator uses a separate fan to more quickly and efficiently cool the heated cooling water. 
         [0004]    If the capacity of the motor of the fan is increased, or more than one fan is used, cooling efficiency increases, but noise, manufacturing cost, and weight also increase. If the capacity of the motor of the fan is reduced, less noise is generated, but the cooling efficiency of the radiator suffers. 
       SUMMARY OF THE INVENTION 
       [0005]    A fan system includes a motor; a driven fan, driven by the motor; and a dummy fan, freely rotatable around a bearing support shaft. The fans have blade rings at their external surfaces. The blade rings include gears, engaged with each other such that rotation of the driven fan rotates the dummy fan. 
         [0006]    The fans may blow air toward a vehicle radiator, and may be attached to a fan cover provided at the front side of the radiator. The driven fan may be near the transmission, and the dummy fan may be near the engine. 
         [0007]    The dummy fan may be larger than the driven fan, and more particularly, the ratio of the diameter of the driven fan to the diameter of the dummy fan may be 7:10. 
         [0008]    The driven fan may include fewer fan blades than the dummy fan. More particularly, the driven fan may have five fan blades and the dummy fan may have six. 
         [0009]    The gear ratio of the gears of the driven fan to the gears of the dummy fan may be approximately 10:7. 
         [0010]    The fan blades may be made of polyacetylene 66 or polypropylene. The blade rings and/or the gears may be made of aluminum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0011]    For a better understanding of the nature and objects of the present invention, reference should be made to the following detailed description with the accompanying drawing, in which: 
           [0012]      FIG. 1  is a view showing the structure of a dual cooling fan system driven by a single motor according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    A dual cooling fan system driven by single motor according to an embodiment of the present invention includes a Down Flow type radiator  1  and a fan assembly  5 . Down Flow type radiator  1  is provided at the front side of an engine. Fan assembly  5  cools radiator  1  with air from dual fans  6 ,  13  that are rotated using one motor controlled by an ECU. 
         [0014]    Fan assembly  5  includes a driven fan  6  and a dummy fan  13 . The driven fan is provided in a first fan receiving hole  3  in a fan cover  2  provided at the front side of radiator  1 . The dummy fan  13  is provided in a second fan receiving hole  4  adjacent first fan receiving hole  3 . The dummy fan  13  rotates together with the driven fan  6 . 
         [0015]    Diameter d of first fan receiving hole  3  is smaller than diameter D of second fan receiving hole  4 . More air thus flows into the second hole  4 . For this reason, even though the fans are not rotated while a vehicle runs, ambient air flows to the engine. 
         [0016]    For example, the ratio of diameter d of first fan receiving hole  3  to diameter D of second fan receiving hole  4  is 7:10. 
         [0017]    The diameter of second fan receiving hole  4  should be selected so as to be projected onto the area of the core of the radiator  1  to the maximum extent. 
         [0018]    Further, first fan receiving hole  3  is positioned close to a transmission, and second fan receiving hole  4  is positioned close to the engine. The motor is positioned close to first fan receiving hole  3 ; the motor is thus less affected by heat radiated from the engine. 
         [0019]    Driven fan  6  includes a driving motor  7 , a blade ring  10 , and an external gear  11 . The driving motor is received in a housing that is supported by stays  8  fixed to fan cover  2 . The driving motor is connected to a power supply connector  12 , and is controlled by the ECU. Blade ring  10  is attached to ends of blades  9  that are rotated by driving motor  7  so as to allow air to flow to radiator  1 . External gear  11  is formed on the outer surface of blade ring  10 . 
         [0020]    Stays  8  are fixed to fan cover  2  in order to support the housing in which motor  7  is received. Accordingly, each of the stays has a small diameter so that a sufficient space is ensured and airflow is not prevented when motor  7  is driven. For example, stays  8  are fixed to the fan cover at 90° intervals. 
         [0021]    Driving motor  7  may have a capacity to rotate the fan  6  at 1000 rpm or less in consideration of fan noise. 
         [0022]    Blades  9  may be made of polyacetylene 66 or polypropylene, and the number of the blades is selected in consideration of the entire performance of the motor. 
         [0023]    Blade ring  10  and external gear  11  may be made of aluminum, or any light material. 
         [0024]    Dummy fan  13  includes a bearing support shaft  14 , blades  16 , a blade ring  17 , and an external gear  18 . The bearing support shaft freely rotates using a bearing received in a housing that is supported by stays  15  fixed to fan cover  2 . Blades  16  rotate together with bearing support shaft  14  and blow air to radiator  1 . Blade ring  17  is attached to ends of blades  16 . External gear  18  is formed on the outer surface of blade ring  17 , and meshes with external gear  11  on blade ring  10  to rotate dummy fan  13 . 
         [0025]    Stays  15  may have a structure similar to that of stays  8  of driven fan  6 . 
         [0026]    The bearing provided on bearing support shaft  14  allows dummy fan  13  to rotate with a small force of driving motor  7  at low rpm. 
         [0027]    Blades  16  may be made of polyacetylene 66 or polypropylene. Blade ring  17  and external gear  18  may be made of aluminum or any light material. 
         [0028]    External gears  11  and  18  may be applied with grease or another material that can improve durability and prevent noise. 
         [0029]    The number of blades  9  and  16  of driven fan  6  and dummy fan  13  is determined depending on the gear ratio, to avoid resonance of blades  9  and  16 , and to prevent bit sound from being generated during the rotation of the fans. The number of the blades of the driven fan and the dummy fan is selected so that the difference between main components of frequency is in the range of about 30 to 40 Hz. 
         [0030]    In one example, the gear ratio of d:D is 7:10, the number of blades  9  of driven fan  6  is 5, and the number of blades  16  of dummy fan  13  is 6. A driving motor  7  having capacity of 100 W is used, and the motor speed is 1200 rpm at 12V. Main components of peak values of driven fan  6  are experimentally 100 Hz and 200 Hz. Dummy fan  13  is rotated at 840 rpm, and main components of peak values are 84 Hz and 168 Hz. 
         [0031]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.