Abstract:
An oil seal for an end bearing of an electric motor with one or more internal cooling fans. The oil seal includes: (a) a non-contact floating ring seal, forming a first stage integrated into the bearing housing; (b) an adjacent labyrinth seal with three lands and two grooves, forming a second and third stage; and (c) air conduits that pressurize the groove of the third stage with air discharged from the stator during operation of the motor, forming an air seal room that inhibits the effect of fan suction that could otherwise draw oil from the bearing housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to an internal seal for electric motors that provides a static seal between a rotatable shaft and a housing. In particular, the present invention relates to an axially-split labyrinth seal for an electric motor having an internal cooling fan. 
         [0003]    2. Description of the Related Art 
         [0004]    End bearings that support a motor&#39;s rotating shaft are typically provided with a seal that prevents oil from escaping from the bearing housing. A secondary, but important consideration is that the seal should inhibit contaminants from working their way into the housing. 
         [0005]    The prior art includes metal sealing rings which are fixed to the bearing housing, the rings incorporating internal labyrinth-type grooves which tend to scrape oil moving axially along the shaft and thereby prevent the oil from escaping the housing. The prior art also includes floating seals that rotate with the shaft to retain the lubricant and exclude foreign matter, and floating shafts that do not rotate with the shaft. 
         [0006]    If properly lubricated and foreign matter is prevented from contacting bearing surface(s), the life of the bearings can be prolonged. However, if the internal seal is ineffective and allows oil to escape from the housing, the life of the bearings may be greatly reduced. Similarly, if the internal seal allows contaminants to work their way into the housing, the contaminants can mix with the oil and cause premature wear of the bearings. 
         [0007]    Oil can escape bearing housings through the outside of the motor or into contact with the motor&#39;s stator and/or rotor. In electric motors that incorporate internal cooling fans, oil leaks into the motor are a particular concern. 
         [0008]    It is therefore an object of the present invention to provide an improved internal seal for an electric motor with an internal cooling fan that will inhibit oil from escaping the bearing housing. 
       SUMMARY OF THE INVENTION 
       [0009]    The above objects and other advantages are achieved by the present invention which comprehends an improved oil seal for an end bearing of an electric motor with one or more cooling fans that provides for greater retention of oil in the bearing housing, and which includes (a) a non-contact floating ring seal, forming a first stage; (b) a labyrinth seal with three lands and two grooves, forming a second stage (adjacent to the first stage) and a third stage (closest to the motor windings); and (c) conduits that pressurize the groove of the third stage closest to the internal fan with air removed from the stator housing during operation of the motor, via bore holes that communicate to the third stage, thus creating a seal air room. 
         [0010]    The first, second and third stages, are axially split into upper and lower semi-circular sections for ease of assembly and mounted around the motor shaft and bolted together to form a unitary structure. 
         [0011]    In a preferred embodiment, the lower semi-circular section of the labyrinth seal of the second and third stages is provided with a radial bore hole arranged for receiving an oil drain tube. 
         [0012]    Any of various types of metals can be used in the present invention, including, for example, iron, steel, stainless steel, and aluminum. In a preferred embodiment, the oil seal is machined from aluminum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will be further described in detail below and with reference to the attached drawings which are provided by way of illustration and example only, where the same or similar elements are referred to by the same number, and in which: 
           [0014]      FIG. 1  is side view of an electric motor incorporating one embodiment of the invention; 
           [0015]      FIG. 2A  is a cross-sectional side view of the upper semi-circular sections of the three stages of the internal seal; 
           [0016]      FIG. 2B  is a cross-sectional side view of the lower semi-circular sections of the three stages of the internal seal; 
           [0017]      FIG. 3  is a perspective view of the internal configuration of the second and third stages of the internal seal; and 
           [0018]      FIG. 4  is a perspective view of the external configuration of the assembled internal seal. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  illustrates one embodiment of the invention, in which a very large motor  100 , for example 6500 HP, has its frame  160  mounted on skid  105 . Shaft  130  is supported by two end bearings  110  that are situated outside motor frame  160 . Terminal box  120  provides terminal blocks for electrical feeder cables. Internal fans  140  are mounted on shaft  130  and pull in outside air through intake vents in motor frame  160 , which is directed to cool windings  170 . The discharge air then exits through exhaust vents in motor frame  160 .  FIGS. 2 through 4  and the accompanying detailed description describe the oil seal provided for each end bearing  110 . As may be seen in  FIG. 1 , the oil seal for end bearing  110  is provided with oil drain  440  and upper and lower air conduits  420  and  430 , which are shown in greater detail in  FIG. 4 . 
         [0020]      FIGS. 2A and 2B  show the upper and lower semi-circular sections of the three stages of the oil seal. The upper semi-circular section  240  of the first stage can be seen in  FIG. 2A , while the lower semi-circular section  230  of the first stage can be seen in  FIG. 2B . Both  FIGS. 2A and 2B  show a preferred embodiment in which the first stage is incorporated into the bearing housing. The first stage includes a floating oil seal insert  250 , such as a model commercially available from RENK AG, in which the seal is a two-piece design of rubber, polymer, etc., held together by a circumferential spring. An anti-rotation key molded into the housing of floating oil seal insert  250  is held in place in a keyway machined into the housing of the first stage, preventing the floating oil seal insert  250  from rotating. Therefore, the shaft (not shown) rotates through the seal i.e., the seal floats on the shaft, preferably picking up any oil which flows axially and draining it back into the bearing housing. 
         [0021]    The internal seal  200  also includes a combined second and third stage, with the upper semi-circular section  220  of the combined second and third stages shown in  FIG. 2A  and the lower semi-circular section  210  of the combined second and third stages shown in  FIG. 2B . The combined second and third stages are located adjacent (and bolted to) the side of the bearing housing closest the cooling fan and motor windings. The combined second and third stages comprise a labyrinth seal that provides a tortuous path that prevents leakage. Included are lands  260 ,  270 , and  280 , and grooves  265  and  275 . Groove  265  forms the second stage, which is adjacent to the first stage semi-circular sections  230 ,  240 . Groove  275  forms the third stage, which is closest to the motor windings. Lands  260 ,  270  and  280  press tightly against the rotating shaft, with a very small clearance between the shaft and the tip of each land. Any oil that escapes the first stage and passes land  260  will be drawn by centrifugal motion and the formation of controlled fluid vortices into groove  265 . This acts to prevent its escape past land  270 . 
         [0022]    The lower semi-circular section  210  ( FIG. 2B ) and upper semi-circular section  220  ( FIG. 2A ) include two or more holes  215  for bolting the semi-circular sections together. Lower semi-circular section  210  includes bore hole  290  ( FIG. 2B ) in groove  275  of the third stage, and upper semi-circular section  220  (FIG,  2 A) includes bore hole  292  in groove  275  of the third stage. Bore holes  290  and  292  are arranged for accepting air conduits to pressurize the third stage as an air seal room. In addition to the previously mentioned tight clearance between land  270  and the shaft, and the action of centrifugal force and the formation of controlled fluid vortices into groove  265 , the pressurized air seal room of the third stage further prevents oil from being drawn out of the second stage via land  270 . 
         [0023]      FIG. 2B  also shows that lower semi-circular section  210  includes a bore hole  296  in groove  265  of the second stage for receiving an oil drain tube. Thus, upper semi-circular section  220 , as shown in  FIG. 2A , is identical to lower semi-circular section  210 , as shown in  FIG. 2B , except that upper semi-circular section  220  does not require an oil drain tube bore hole comparable to  296 . 
         [0024]      FIG. 3  shows a perspective view of lower and upper semi-circular sections  210  and  220 , joined together as they would be when mounted around the motor shaft  245 . As noted above, lower semi-circular section  210  and upper semi-circular section  220  include two or more holes  215  (shown in  FIGS. 2A and 2B ) for bolting the semi-circular sections together.  FIG. 3  also shows that lower and upper semi-circular sections  210  and  220  are provided with holes  310  for bolting the sections  210  and  220  to the bearing housing. 
         [0025]      FIG. 4  shows the assembled internal seal  200 , with upper semi-circular section  240  of the first stage (incorporated into the bearing housing). In this figure, lower semi-circular section  230  of the first stage is not visible, being placed behind and bolted to upper semi-circular section  240  of the first stage. Similarly, upper semi-circular section  220  of the combined second and third stages is shown. Lower semi-circular section  210  of the combined second and third stages is not shown in this figure, since it is positioned behind and bolted to upper semi-circular section  220  of the combined second and third stages. Bolt holes  310  may be seen, by which the semi-circular sections  210  and  220  of the combined second and third stages are bolted to the bearing housing. 
         [0026]    Oil drain line  440  extends from bore hole  296  of the lower semi-circular section  210  (not shown). Any oil that escapes past the first stage to the second stage will drain through bore hole  296  and oil drain line  440  due to gravity. Oil drain line  440  extends to outside the motor, to a convenient place where maintenance staff can observe if a leak is present. 
         [0027]    One end of air conduits  420  and  430  terminate penetrations of wall  410  of the motor frame, where they draw pressure produced by the internal fans. The other ends of air conduits  420  and  430  terminate, respectively, at bores hole  292  and  290  (not shown) of the upper and lower semi-circular sections of the second and third stages, where they pressurize the air seal room. 
         [0028]    As noted previously, the first stage and also the labyrinth seal of the second and third stages are each split into upper and lower semi-circular sections for ease of assembly around the motor shaft. For the labyrinth seal of the second and third stages, the orientation of the upper and lower semi-circular sections  210 ,  220  is important, as bore hole  296  should be positioned closest to the ground, allowing any oil leak to escape through the action of gravity. Bore holes  290  and  292  are arranged for accepting air conduits to pressurize the third stage as an air seal room. 
         [0029]    The orientation of the upper and lower semi-circular sections  230 ,  240  for the first stage does not matter, except as noted upper and lower semi-circular sections  210 ,  220  are supplied with holes  310  for bolting the sections  210  and  220  to the bearing housing. 
         [0030]    The present invention has been described in the foregoing specification with reference to specific embodiments. It will, however, be evident to one of ordinary skill in the art that various modifications and additions can be made without departing from the broader scope of the invention, which is to be determined by reference to the claims that follow. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.