Abstract:
An improved electric motor cooling construction where the motor stator is contained within the motor housing. The motor covers and motor housing are designed to provide direct increased airflow to the motor stator, and coil windings to provide better airflow through the motor resulting in improved cooling.

Description:
This application is a Continuation of U.S. application Ser. No. 10/234,530 filed on Sep. 3, 2002. 

   FIELD OF THE INVENTION 
   This invention relates to cooling of electric motors. More specifically, the present invention relates to an apparatus and method to improve the cooling of electric motors by creating a more even airflow over the motor coil windings and stator laminations. 
   BACKGROUND OF THE INVENTION 
   The majority of all commercial and industrial electric fans have an electric motor. These motors generate heat from the motor windings. This heat, when excessive, can degrade overall performance and longevity of the motor. Typically fan designers try to use the “suction” on the rear of the blade and blade hub to help pull the air through the rear of the motor towards the front. This airflow is important in providing cooling for the motor windings, however, there are many structurally necessary elements that are part of the motors which limit the amount of airflow that can help cool the motor. 
   One of these structurally necessary elements is the motor housing. The motor housing is used to mount the bearings, which support the shaft for rotation. The housing also protects the windings from damage after the motor is assembled, and also acts as an enclosure. The housing has openings, the size of which is mandated by standards organizations such as Underwriters Laboratories. If the openings in the housings exceed a certain mandated size, special cover materials or additional enclosures are required. Motors housings can be cast aluminum, zinc or stamped metal. Motor housings are in contact with the stator, and, in the prior art, closely surround the windings/coils, which leaves little to no area for “air flow” through the motor. 
   A second structural element, which limits airflow through the motor, consists of the stator and rotor. The stator consists of a stack of steel laminations which have copper magnet wire wound on them. Conventionally, the steel is normally sandwiched between the front and the rear housings. 
   Looking through the rear housing, the wire and stator laminations block the airflow through the motor. The area of opening for air movement through the stator is generally quite small even in relationship to the mandated holes in the motor housings and the motor covers. The prior art housings are so tight against the outside of the laminations that they generally do not allow adequate airflow through the housings and by the coils. The two motor housings typically have a gap where the stator sits, which also allows some of the air entering the rear motor housing to escape, thereby completely bypassing the front coil. 
   A third structural element, which effects airflow through the motor, is the outside motor cover. For safety purposes most electric motors are surrounded by “motor covers.” Common materials for motor covers are metal and plastic. These covers are usually aesthetic and cover any electrical materials and/or hot motor surfaces. These, motor covers may additionally impede airflow through the motor. Motor covers have vent structures which are usually located at the rear and the front of the motor. Venting provides an airflow path that will enter the “rear motor cover” and flow mostly around the outside of the motor housing drawing heat from the housings, which in turn draws heat from the stator/windings. This prior art airflow path  30 , as illustrated in  FIG. 2 , has little to no effect on the front coil area of the motor, resulting in uneven heat dissipation throughout the windings. Accordingly, the prior art airflow pattern enters the rear motor cover  11  and travels mainly between the inside of the motor cover walls and the outside of the motor housings  14  and  15 . This prior art construction and its resultant airflow does not provide adequate and even cooling of the motor. 
   The inventive design, set forth in detail below, forces a greater amount of air to be drawn into the motor housing and flow in a path that contacts both the front and rear windings and provides more even cooling of both the front and rear windings and the stator. 
   SUMMARY OF THE INVENTION 
   In view of the shortcomings of the prior art, the present invention provides a method and apparatus for improved electric motor cooling. 
   It has now been found that an improved electric motor cooling construction is available wherein the motor housing and covers draw in more air and channel it into an air path that directly contacts the motor stator and coil windings to remove the heat and to more evenly cool the motor. 
   The improved electric motor comprises a first housing having a first wall defining a first interior space, and at least one opening disposed on a surface of the first housing; a second housing having a second wall defining a second interior space, and at least one opening disposed on a surface of the second housing; and a stator having a plurality of laminations a first portion of windings and a second portion of windings, the plurality of laminations disposed substantially within the first interior space and the second interior space, such that air flows i) into the at least one opening in the first housing, ii) over the first portion of windings, substantially all an exterior portion of the stator laminations, and the second portion of windings, and iii) out the at least one opening in the second housing. 
   According to another aspect of the invention, a front cover having openings is coupled to the surface of the second housing, and a rear cover having openings is coupled to the front cover and substantially surrounds the first and second housings. The openings in the rear cover are in fluid communication with the openings in first housing, and the openings in the front cover are adjacent and in fluid communication with the openings in the second housing. 
   According to a further aspect of the invention, the stator is substantially square. 
   According to yet a further aspect of the invention, the at least one opening in the first housing is a first plurality of openings and the at least one opening in the second housing is a second plurality of openings, at least a portion of the first plurality of openings and at least a portion of the second plurality of openings in respective planes substantially parallel to one another. 
   According to another aspect of the invention, the motor housings are in contact with the stator and have airflow channels therebetween. 
   According to yet another aspect of the invention, the stator is substantially round. 
   According to still another aspect of the invention, the front motor cover contacts the front motor housing to seal off airflow, forcing air through the motor. 
   According to yet a further aspect of the invention, the front and rear motor housings have a reduced gap therebetween so that airflow is inhibited from escaping from between the motor housings. 
   According to another aspect of the invention, the electric motor has a reduced operating temperature and a more even cooling of the stator windings and laminations. 
   These and other aspects of the invention are set forth below with reference to the drawings and the description of exemplary embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following Figures: 
       FIG. 1  is an exploded perspective view of a prior art electric motor assembly; 
       FIG. 2  is a sectional view of the prior art motor assembly of  FIG. 1 ; 
       FIG. 3A  is a perspective view of an electric motor incorporating a first exemplary embodiment of the present invention; 
       FIG. 3B  is a perspective view of an electric motor incorporating a second exemplary embodiment of the present invention; 
       FIGS. 3C and 3D  are sectional views illustrating details of the exemplary embodiment of  FIG. 3B ; 
       FIG. 4  is a sectional view of the motor of  FIGS. 3A and 3B ; 
       FIG. 5  is a chart showing the performance characteristics of a prior art electric motor; 
       FIG. 6  is a chart showing the performance characteristics of an electric motor which incorporates an exemplary embodiment of the present invention, and; 
       FIG. 7  is an illustration of an oscillating fan incorporating an exemplary embodiment of the present invention. 
   

   It should, of course, be understood that the description and drawings herein are merely illustrative and that various modifications and changes can be made in the structures disclosed without departing from the spirit of the invention. Like numerals refer to like parts throughout the several views. 
   DETAILED DESCRIPTION 
   The entire disclosure of U.S. patent application No. 10/234,530 filed on Sep. 3, 2002 is expressly incorporated by reference herein. 
   When referring to the preferred embodiment, certain terminology will be utilized for the sake of clarity. Use of such terminology is intended to encompass not only the described embodiment, but also technical equivalents which operate and function in substantially the same way to bring about the same result. 
   Referring now more particularly to the drawings and  FIGS. 1 and 2  thereof, a prior art electric motor assembly  10  is therein illustrated. 
   As shown in  FIG. 1 , motor assembly  10  includes rear cover  11 , front cover  12  of a generally circular configuration, with motor  50  contained therein. 
   Motor  50  includes front and rear motor housings  15  and  14 , respectively, which are in contact with and are secured to the outside surfaces of motor stator  17 , in a conventional manner, retaining it therebetween, such as by screws  18  extending into spaced bosses  20 , on motor housings  14  and  15 . 
   Motor stator  17  is of square configuration and extends outside motor housings  14  and  15 . 
   Referring now to  FIG. 2 , motor assembly  10  is also provided with rotor (not shown) and output shaft  22 , which has a hub  23  of fan blade assembly  24  secured thereto in a conventional well known manner. Motor stator  17  includes a plurality of laminated sheets of steel  25 , with rear coil windings  26 , and front coil windings  27 , secured thereto in a well known manner. 
   Referring again to  FIG. 2 , the airflow pattern for cooling motor  50  is illustrated by curved lines  30 , which show air entering through openings  31  in rear cover  11 , over a motor capacitor  32 , over the exterior of rear motor housing  14 , over the exterior of front motor housing  15  and exiting through openings  35  in front cover  12  (best shown in FIG.  1 ). 
   As is clearly shown in  FIG. 2 , airflow  30  does not directly contact the laminated sheets  25 , and the rear coil windings  26  and the front coil windings  27  to provide cooling. Rather, airflow  30  ineffectively attempts to draw heat away by contacting front motor housing  15  and rear motor housing  14 . 
   Referring now more particularly to  FIGS. 3A and 4 , a fan motor assembly  300  incorporating a first exemplary embodiment of the present invention is shown. As shown in  FIG. 3A , fan motor assembly  300  includes rear cover  101 , rear motor housing  102 , front cover  104 , and motor  100 . Each of front and rear motor housing  103 ,  102  have at least one respective opening ( 122  as shown in  FIG. 3   a  for rear motor housing  102 ) therein to allow for the passage of air therein (explained in detail below with respect to FIG.  4 ). Opening  122  may be formed in a variety of shapes and orientations, such as slots formed circumferencially and/or radially, or circular openings, for example. 
   Motor  100  includes rear motor housing  102  and front motor housing  103  defining interior spaces  132  and  133 , respectively. The front and rear motor housings  103  and  102  are fastened together by fasteners  105 , such as screws, which may extend through bosses  106  in rear motor housing  102  into bosses  107  in front motor housing  103 , securing the motor housings in fluid tight relation with one another. Motor housings  102  and  103  are preferably of cast or stamped metal such as aluminum, zinc or steel. Alternatively, either or both motor housings  102 ,  103  may be formed from a polymer, if desired. 
   Rear cover  101  is secured to the rear motor housing  102  by a fastener  108  (best shown in FIG.  4 ), such as a screw, engaged in boss  109  which is in turn coupled to housing  102 . Front and rear motor covers  104  and  101  are preferably of metal or plastic. 
   Referring now to  FIG. 4 , motor stator  110  is provided, of a generally square configuration, with a plurality of laminated sheets of steel  111 , with rear coil windings  112 , and front coil windings  114  secured thereto in a well known manner. In this exemplary embodiment, motor stator  110  is contained substantially within interior spaces  132 ,  133  of motor housing  102  and  103 , with only corners  127  of stator  110  extending beyond the confines of motor housing  102  and  103  (best shown in FIG.  3 A). Motor  100  has a rotor  113 , output shaft  134 , and hub  115  of fan blade assembly  116  secured thereto. 
   Front cover  104  has inside and outside rims  117  and  118 , which receive rear cover  101  therebetween, to couple front cover  104  to rear cover  101  and form a seal between front cover  104  and rear cover  101 . As shown in  FIG. 4 , front cover  104  is in close contact with the front motor housing  103  and is attached thereto in a conventional manner, using screws, for example (not shown). 
   Referring now to  FIG. 3B , fan motor  200  incorporating a second exemplary embodiment of the present invention is shown. As shown in  FIG. 3B , the significant differences between the first and second exemplary embodiments is the containment of the entirety of stator  210  within interior  232 ,  233  of motor housings  202 ,  203 , respectively, forming airflow cavity  234  between the inner walls of motor housings  202 ,  203  and stator  210 . This is best illustrated in FIG.  3 C. Similar to the first exemplary embodiment, the front and rear motor housings  203  and  202  are fastened together by fasteners  105 , such as screws, which may extend through bosses  206  in rear motor housing  202  into bosses  207  in front motor housing  203 , securing the motor housings in fluid tight relation with one another. 
   In one version of this exemplary embodiment, stator  210  is substantially round and attached to at least one of housings  202 ,  203  using conventional means, such as staking through the walls of either or both housings  202 ,  202 , press fit within either or both housings  202 ,  202 , or stops incorporated within interior spaces  132  and  133  of the motor housings, for example. Alternately, and as shown in  FIG. 3D , stator  310  may be substantially square. 
   In an exemplary embodiment of the present invention, motor  100  may be a permanent split capacitor (PSC) motor having any of a variety of pole configurations, such as 4 poles and 6 poles. The invention is not so limited, however, and it is contemplated that motor  100  may be of other types, such as a shaded pole motor, for example. 
   As shown in  FIG. 4 , air, depicted by air flow lines  128 , is drawn toward and enters motor  100  by action of fan blade  116 , through openings  120  in rear cover  101 , and through openings  122  in rear motor housing  102 , over and in contact with rear coil windings  112 , the exterior portions of laminated sheets  111 , front coil windings  114 , exiting through openings  125  in front housing  103 , and finally out the front cover  104  through openings  126 , thereby drawing heat out of fan motor  100 . This improved airflow is substantially identical in each of the two exemplary embodiment described above. 
   Referring now to  FIG. 5 , a fan motor, such as motor  50  was tested for efficiency and measured temperature. As shown in  FIG. 5 , at column  502 , the heat distribution with a conventional cooling construction was very uneven, with an 11.3° C. differential between front coils  27  and rear coils  26 . 
   In  FIG. 6 , motor  100  was tested where the only difference between motor  100  and motor  10  was the improved cooling provided by motor housings  102 ,  103 , front cover  104  and rear cover  101 . As shown in  FIG. 6 , at column  602 , the temperatures of the front and rear coil windings  114  and  112  were the same and were significantly lower than the temperatures recorded for motor  10  by greater than 19° C. for the rear coils and by greater than 30° C. for the front coils. As shown in  FIG. 7 , it is contemplated that this improved motor assembly  300  may be used in an oscillating fan  700 , for example. 
   Although the invention has been described with reference to exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the true spirit and scope of the present invention.