Abstract:
An electrically powered axial-flow fan has a hub to house the motor and support the fan blades. Small blades or vanes on the inside of the hub function as a radial-flow blower to draw cooling air through cooling ports on the electric motor housing. The vanes inside the hub cooperate with a flange surrounding the motor to form a low pressure chamber under the hub to improve cooling flow through the motor. This motor cooling air flow is then ejected into the exhaust stream of the axial-flow fan.

Description:
[0001]     The invention concerns a specially designed fan hub and a flange around the motor which combine to provide cooling air flow for an electric motor which drives the fan.  
       BACKGROUND OF THE INVENTION  
       [0002]     An engine cooling fan and electric motor assembly is used to provide radiator and A/C condenser cooling airflow in engine compartments of many vehicles. The engine compartment itself is a high-temperature environment. To complicate matters, the motor generates its own internal heat during the normal course of operation. The internally generated heat is primarily due to Joule heating caused by electric current passing through its rotor and stator coils, and brush losses. High temperatures can greatly increase the wear of motor brushes and bearings, and significantly reduce motor life.  
         [0003]     One solution to these problems is to provide cooling holes  44   a,    44   b  in Figure to admit cooling air through the motor  22 . The invention provides additional strategies to cool motor  22 .  
       SUMMARY OF THE INVENTION  
       [0004]     The object of the invention is to provide an improved cooling system for electric motors which drive a fan.  
         [0005]     In one aspect of the invention, a fan with a specially designed hub is provided, which is powered by an electric motor. By this design, the inside of the hub becomes a radial-flow blower. The radial-flow blower draws cooling air through the electric motor, and exhausts the spent cooling air into the exhaust stream of the engine cooling fan.  
         [0006]     In one aspect, this invention comprises a cooling system for use in a vehicle, comprising an electric motor comprising a housing and an airflow path through the motor for cooling the motor, a fan comprising a hub having a connector for mounting to a shaft of the electric motor, a plurality of fan blades extending radially from the hub, a plurality of ribs situated between the connector and the hub; and the plurality of ribs cooperating with the housing to define a pathway for channeling air from the motor cooling airflow path into the exit stream of the main flow stream created by the plurality of fan blades.  
         [0007]     In yet another aspect this invention comprises a method for cooling an electric motor, the method comprising the steps of providing an electric motor having an airflow passageway, and situating a fan comprising a hub for mounting on a shaft of the electric motor, the hub cooperating with a cover on the electric motor to form a low pressure area that draws cooling airflow through the airflow passageway inside the motor.  
         [0008]     In yet another aspect this invention comprises An electric fan for use on a vehicle comprising: an electric motor having an airflow passageway, and a fan assembly mounted on a shaft of the electric motor, the fan assembly comprising: a hub on which a plurality of fan blades are situated for creating an axial air flow, and the hub further comprising a plurality of vanes at least partially surrounding a cover of the electric motor for creating a radial air flow used for cooling the motor and then directed toward the axial air flow.  
         [0009]     These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is view of a hub in accordance with one embodiment of the invention;  
         [0011]      FIG. 2  is an exploded view showing the hub and motor;  
         [0012]      FIG. 3  is a fragmentary view of the hub and motor assembly; and  
         [0013]      FIG. 4  is a perspective fragmentary view of the hub and motor assembly with several blades removed for ease of illustration. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIG. 1  illustrates a fan assembly or fan  10  in accordance with one embodiment of the invention. The fan  10  comprises a plurality of fan blades  12  that extend radially between a hub  14  and a ring shroud  15 . The hub  14  comprises a circumferential ring  18  to which the fan blades  12  are integrally formed and a front wall  17  ( FIG. 2 ). A plurality of radial vanes or ribs  20  rise from the front wall  17  and extend between the connector  16  and circumferential ring  18 , as illustrated in  FIG. 2 . It should be understood that the fan  10  may be a one-piece construction molded from plastic or other suitable material.  
         [0015]      FIG. 3  illustrates an exploded fragmentary view illustrating an electric motor  22  for rotatably driving fan  10 . The electric motor  22  comprises a shaft  24  which is received in the aperture  26  defined by connector  16  and secured thereto by conventional means, such as a nut or spring clip attachment design. Air holes  44   a  and  44   d  ( FIG. 4 ) permit air to flow through the motor  22  as is conventionally known.  
         [0016]     For ease of description, one of the ribs  20  will be described, but it should be understood that each of the ribs  20  are similarly constructed. Note that each rib  20  is generally L-shaped, as shown in  FIG. 3 , and comprises a portion  21  having a first surface or edge  27  and second portion  23  having surface or edges  23   a  and  23   b.  The edge or surface  27  and the inner surface of the hub wall  17   a  ( FIGS. 2 and 3 ) cooperates with a front face  22   a  of motor  22  to define a low-pressure area or chamber  27   a  ( FIG. 3 ). The axial gap between surfaces  17   a  and  22   a  and between adjacent ribs  20  is the low pressure chamber and the motor cooling airflow pathway.  
         [0017]     Note that the motor  22  comprises a housing or casing  25  having a circumferential flange or bulkhead  30  ( FIGS. 2 and 3 ) that extends radially outward from the casing  25  of motor  22 . Note that the flange  30  comprises a surface  30   a  that is situated in proximate relation to edge  27  of vane  20 , as illustrated in  FIG. 3 . Thus, as best illustrated in  FIG. 3 , notice that the edges  27 ,  23   a  and  23   b  of each rib or vane  20  and the surface  17   a  cooperate with the surfaces  22   a,    25  and  30   a,  respectively, to define a low pressure channel or area  27   a  through which air may flow. Ideally, it is desired to have a distance or gap  28   a  be small or minimized to facilitate creating a low-pressure chamber between the hub  14  and the motor  22  and flange  30 . It is desirable to have the axial gap  28   a  between surface  23   b  and  30   a  to be optimized and dimensioned along with the respective diameter of the inside of the hub wall  18  and outside diameter of the flange. There is also an optimum relationship between the constraints defining the region  28   a  as shown in  FIG. 3  that maximizes the low pressure level of the said low pressure channel or area. The defining constraints of the region  28   a  are the rear edge of the rib  20  defined as  23   b,  the forward surface of the flange  30 , indicated by  30   a,  the inner diameter of the hub wall  18 , defined by  18   a  and expressed as double arrow E, and the outer edge of the flange  30 , defined by  30   b  and also expressed as the double arrow F. The relationship between the axial gap and the respective diameters of the inner hub wall and the outer diameter of the flange must be jointly optimized to maximize the cooling flow drawn through the motor.  
         [0018]     As best illustrated in  FIGS. 1 and 2 , the generally L-shaped vanes  20  and wall  18  make up or define an area  36  for receiving the electric motor  22  such that the vanes, or at least portions  23  ( FIG. 3 ) of vanes  20  surround the housing  25 . In the embodiment being described, the clearance between the surfaces  22 ,  23   a  and  23   b  and the surface  22   a,    25  and  30   a  should be minimized as much as possible. It has been found that a channel  27   a  having a relatively small clearance  28  will increase a rotational speed (i.e., in the direction of arrow B in  FIG. 3 ) of air confined within the area or chamber  36 , which further reduces the pressure in area  27   a  relative to the area outside of area  36 .  
         [0019]     Thus, it should be appreciated that the invention provides a cooling system for use in a vehicle. Note that the plurality of fan blades  12  direct air flow in the direction of arrow A in  FIG. 3  which indicates a mixed axial and radial exit airflow character. The plurality of ribs  20  direct air flow in a radial direction indicated in arrow B in  FIG. 3 . Note that the channel  27   a  directs the air flow generally radially across the face  22   a  of motor  22 , then axially along the housing  25  of motor  22  and then again radially along surface  30   a  toward the air flow A. Thus, one feature of the invention is that that the ribs or vanes  22  ultimately direct air flow toward the plurality of blades  12  which direct air flow in a mixed axial and radial character per direction arrow A. The motor cooling exit flow is assisted or entrained by the presence of the higher velocity airflow generated by the plurality of blades  12 . This entrainment by the higher velocity main cooling fan airflow that occurs in the general area  40  that increases cooling airflow through the motor, which further improves cooling of the electric motor  22 .  
         [0020]     Advantageously, this invention provides an electric motor having an air flow passageway and further comprising a fan assembly having a hub that cooperates with the cover of the motor to form a low pressure area referred to above and that communicates with the air flow passageway to facilitate improving air flow through the electric motor.  
         [0021]     Another advantage of the invention is that it provides an electric fan for use on a vehicle which is designed to generate cooling airflow through the motor  22  that moves radially across the front face  22   a  of motor  22  and toward the area  40  ( FIG. 3 ) where the air flowing through channel  27   a  which is directed toward area  40  where it meets and is entrained by the air flow generated by fan blades  12  and indicated by arrow A in  FIG. 3 .  
         [0022]     Notice also that the invention provides an electric fan having a hub  14  that extends or partially surrounds the housing  25 , as illustrated in  FIG. 3 . Notice also that the fan blades or a portion of the fan blades  12  may also extend over the motor  22  as shown. Thus, the ribs  20  are formed to surround at least a portion of the surface  25  to further facilitate creating the low pressure area and the channel  27   a  for providing a controlled air flow across surfaces  22   a,    25  and  30   a.    
         [0023]     The motor  22  comprises the holes or openings  44   a  and  44   b  that permit air to flow through motor  22 . Notice that the invention facilitates causing air to flow in the direction of dashed arrow D in  FIGS. 3 and 4 . In operation, the hub  14  rotates as indicated by arrow C in  FIG. 4 . Each portion  21  and portion  23  sweeps air across the surfaces  22   a  and  33   a  ( FIG. 3 ). Centrifugal force pushes the swept air radially through channel  27   a  and generally radially outward in the direction of dashed arrow D in  FIG. 3 . As the air exits channel  27   a,  it is further urged toward the fan blades  12  which forces the air in the direction of arrow A. Further, the pressure at area  40  ( FIG. 4 ) is greater than the pressure in channel  27   a.  The flange  30  helps reduce flow recirculation across area  44  and maintains the low pressure in the channel  27   a  between the hub  14  and motor  22 .  
         [0024]     The low pressure in area or channel  27   a  air to pass through holes  44   a,    44   b  ( FIG. 4 ) in the motor casing  25 . While within the motor  22 , the air passes along the rotor (not shown), cooling the rotor, the associated stator (not shown) and other internal components of the motor  22 . This air is then expelled from the displacement and injected toward the area  40  in the direction of dashed arrow D ( FIG. 3 ).  
         [0025]     The shape and number of ribs  20  within the hub  14  and the clearance between the ribs  28  and casing  23  and flange  30  must be selected to ensure air in the area  28   b  closely follows the rotation of the hub  14 . The number of vanes  20  must also not be so high as to severely block motor cooling air flow passage. Increased rotational speed of the fan  10  will increase the air flow in the direction of arrow D ( FIG. 4 ) and should resultingly increase cooling flow through motor  22 . An increase in an overall diameter of the hub  14  will also work to lower the pressure in the area  36  and therefore, increase motor cooling flow.  
         [0026]     Advantageously, this system and method provides a hub having a plurality of vanes or ribs  20  that cooperate with a motor casing  23  to define the coupling channel  36 . The channel  36  defines a low-pressure area around the motor casing  23  which facilitates urging air through the motor casing  23  which, in turn, facilitates cooling of the motor  22 .  
         [0027]     While the system and method described, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise system and method, and that changes may be made in either without departing from the scope of the inventions, which is defined in the appended claims.