Abstract:
A seal actuated by generally atmospheric pressure helps protect the motor bearing of a vacuum appliances, such as a dry air vacuum cleaner, a wet/dry vacuum cleaner, a water extractor (e.g., carpet cleaner), etc. The generally atmospheric air pressure on a motor side of the seal and a vacuum on an opposite turbine side of the seal urges the seal in an axial direction toward an impeller of the vacuum appliance and presses the seal firmly against an axially abutting sealing surface. Sliding sealing contact between a broad axial surface of the seal and the abutting sealing surface helps prolong the life of the seal and the bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application Ser. No. 61/207,774, filed Feb. 17, 2009 by the present inventors. 
    
    
     FIELD OF THE INVENTION 
     The subject disclosure generally pertains to wet vacuum motors and more specifically to means for protecting a bearing of such a motor. 
     BACKGROUND 
     Vacuum appliances, such as a dry air vacuum cleaner, a wet/dry vacuum cleaner, a water extractor (e.g., carpet cleaner), etc., often include an electric motor that drives an impeller to draw in dirty or moist air. Air contaminated with dirt or moisture, unfortunately, can damage a motor bearing that is near the impeller, particularly if the bearing is of a high speed universal motor, such as those typically found in lightweight portable appliances. Various means for protecting a motor bearing are disclosed in U.S. Pat. Nos. 4,226,575; 4,527,960; 5,482,378; 3,733,150; 3,932,070; 4,088,424; Re. 32,027; and 6,472,786. In spite of the current bearing protection schemes, there is an ongoing need to further prolong the life of motor bearings in a vacuum appliance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an example motor for a vacuum appliance, wherein the motor includes a seal according to some examples of the invention. 
         FIG. 2  is a top view of  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional view of the seal in  FIG. 1 , wherein the motor is de-energized. 
         FIG. 4  is a cross-sectional view similar to  FIG. 2  but with the motor energized. 
         FIG. 5  is a cross-sectional view similar to  FIG. 2  but showing another seal example. 
         FIG. 6  is a cross-sectional view similar to  FIG. 3  but showing the seal example of  FIG. 4 . 
         FIG. 7  is a cross-sectional view similar to  FIGS. 2 and 4  but showing another example seal design. 
         FIG. 8  is a cross-sectional view similar to  FIGS. 2 ,  4  and  6  but showing yet another example seal design. 
         FIG. 9  is a cross-section view similar to  FIG. 1  but showing another example of a motor. 
         FIG. 10  is a top view of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     An example wet vacuum motor  10 , shown in  FIGS. 1-4 , comprises a stator  12 , a rotor  14  in proximity with stator  12  to be driven by the stator&#39;s electromagnetic field, a housing assembly  16  that supports stator  12 , a shaft  18  extending from rotor  14 , at least one impeller  20  and  22  mounted to shaft  18  (the vacuum motor can have any number of impellers), at least one bearing  26  attached to housing assembly  16  and supporting shaft  18 , and a pressure-reactive external seal  24  proximate to bearing  26  and encircling shaft  18 . 
     Seal  24  is referred to herein as an “external” seal because seal  24  is outside of bearing  26  (i.e., seal  24  is beyond the axial outer face of bearing  26 ). In comparison, some examples of bearing  26  include an internal seal/shield  66  captured radially between an inner race  92  and an outer race  72  of bearing  26 . The term “seal/shield” is used herein to encompass both a polymeric bearing insert known as a seal and a metallic bearing insert known as a shield. 
     In the example of  FIGS. 1-4 , housing assembly  16  includes a motor bracket  28 , a discharge housing  30 , and a two-stage impeller housing  32 . In the example of  FIGS. 1 and 2 , discharge housing  30  includes a tangential discharge horn  31  for discharging air  42  from a discharge area  56  out through a discharge opening  48 . In the example of  FIGS. 9 and 10 , however, a discharge housing  30 ′ includes an impeller housing  32 ′, which provides a series of peripheral discharge openings  48 ′ for releasing discharge air  42 . In some examples, impeller housing  32  comprises a plurality of nested impeller sections to facilitate assembly. In some multi-stage examples, conventional air guides and/or stationary guide vanes are axially interposed between impellers to help guide the air discharged from one impeller to the suction inlet of the next stage impeller. Since the actual design of impeller housing  32  can vary greatly while still remain within the scope of the invention,  FIG. 1  shows impeller housing  32  illustrated somewhat schematically. Examples of other design features of multi-stage impeller housings and/or other conventional components related thereto are disclosed in U.S. Pat. Nos. 4,226,575; 4,527,960; 5,482,378; 3,733,150; 3,932,070; 4,088,424; Re. 32,027; and 6,472,786; all of which are specifically incorporated by reference herein. 
     Shaft  18  can be a unitary piece or an assembly. In the illustrated example, shaft  18  comprises a main shaft  34 , a sleeve  36  (sleeve  36 ′ in  FIGS. 5-8 ) slid over main shaft  34  and axially clamped between bearing  26  and impeller  20 , and a second sleeve  38  slipped over main shaft  34  and axially clamped between impellers  20  and  22 . Sleeves  36 ,  36 ′ and  38  serve as spacers that establish the axial positions of impellers  20  and  22  within housing  32 . In this example, a nut  40  holds impellers  20  and  22  to shaft  18  (shaft  18  comprises main shaft  34 , sleeve  36 , and sleeve  38 ). 
     Rotation of rotor  14  and shaft  18  rotates impellers  20  and  22  to centrifugally force air  42  sequentially through a vacuum appliance  44 , a suction port  46  of impeller housing  32 , first stage impeller  22 , second stage impeller  20 , area  56  of discharge housing  30 , and out through discharge opening  48 . Vacuum appliance  44  (which happens to be shown being adjacent a floor surface  50 ) is schematically illustrated to represent any device for sucking air  42 . Examples of appliance  44  include, but are not limited to, a dry air vacuum cleaner, a wet/dry vacuum cleaner, a water extractor (e.g., carpet cleaner), etc. 
     The rotation of impellers  20  and  22  creates subatmospheric pressure at suction port  46 , while air just beyond appliance  44  (at an area  52 ) is at generally atmospheric pressure, thus air flows from area  52 , through an inlet gap  54  between appliance  44  and surface  50 , to suction port  46 . In various examples of the invention, one or more appliance components exist between inlet gap  54  and suction port  46 . Examples of such appliance components include, but are not limited to, a filter, screen, guarding, shield, baffle, hose, tube, conduit, stationary brush, rotating brush, vortex tube, etc. Impellers  20  and  22  centrifugally increase the air&#39;s pressure from subatmospheric pressure at suction port  46  to something above atmospheric pressure at discharge area  56  within discharge housing  30 . With the air at discharge area  56  being greater than atmospheric pressure, the air readily flows out through discharge opening  48  ( FIG. 2 ) to exhaust to an area  58  at generally atmospheric pressure just beyond discharge opening  48 . In various examples of the invention, one or more appliance components exist between discharge opening  48  and area  58 . Examples of such appliance components include, but are not limited to, a filter, vortex tube, screen, guarding, shield, baffle, hose, tube, conduit, muffler, etc. 
     To cool motor  10 , housing assembly  16  includes vents  60  or other openings that allow ambient air to circulate among rotor  14 , stator  12 , and an open space  62  between bearing  26  and rotor  14 . In some embodiments, a fan  64  attached to shaft  18  helps promote the circulation of air for cooling motor  10 . 
     To help prevent dirty and/or moisture laden air in discharge area  56  from entering bearing  26 , motor  10  includes a flexible annular external seal  24  encircling shaft  18  near bearing  26 . Although bearing  26  might include its own internal seal/shields  66 , external seal  24  provides bearing  26  with remarkably better protection, partially due to external seal  24  having a greater axial sealing contact area than internal seal/shield  66 . In some examples, external seal  24  has an outer radial periphery  70  (outermost radial periphery) that is greater than an outer diameter  71  of internal seal/shield  66 , and/or in some examples, external seal  24  has an inner radial periphery  76  (innermost radial periphery) that is smaller than an inner diameter  73  of internal seal/shield  66 . Radial air clearance at a radial periphery of seal  24  minimizes the seal&#39;s drag on the motor&#39;s rotation and allows an axial face of seal  24  to deflect and seal against an axial abutment surface on bearing  26 , shaft  18  or housing assembly  16 . 
     In the example shown in  FIGS. 1-4 , external seal  24  is axially interposed between bearing  26  and impeller  20 . Bearing  26  can be held in place by any suitable means including, but not limited to, a press fit, adhesive, mechanical clamping, etc. In some examples, for instance, a bearing retainer  68  axially clamps the seal&#39;s outer radial periphery  70  (e.g., seal&#39;s outside diameter) between housing assembly  16  and outer race  72  of bearing  26 . 
     Radial air clearance  74  between the seal&#39;s inner radial periphery  76  (e.g., the inside diameter of seal  24 ) and an outer diameter of shaft  18  (e.g., sleeve  36  of shaft  18 ) allows a turbine side  78  of seal  24  the freedom to deflect (in some examples of the invention) and seal against an axial abutment surface  80  on shaft  18  (e.g., sleeve  36  of shaft  18 ). Such deflection is driven by a pressure differential across  24 , wherein the pressure differential is due to a motor side  86  of seal  24  being exposed to generally atmospheric pressure at open space  62  and turbine side  78  of seal  24  being exposed to a vacuum in a dead-space area  82 . The term, “vacuum” means subatmospheric pressure, i.e., pressure less than atmospheric pressure. The expression, “generally atmospheric pressure” in open space  62  includes pressure slightly above atmospheric pressure due to inconsequential pressure effects caused by fan  64 . In other words, “generally atmospheric pressure” means that even if the pressure in open space  62  were exactly equal to atmospheric pressure, such zero pressure would still be sufficient to urge seal  4  against abutment surface  80 . 
     Since discharge area  56  is at a discharge air pressure that is greater than atmospheric pressure, one might expect that dead-space area  82 , between bearing  26  and impeller  20 , would also be greater than atmospheric pressure, as areas  82  and  56  are in open fluid communication with each other (turbine side  78  of seal  24  is in open fluid communication with discharge opening  48 ). And if the pressure at dead-space  82  were greater than atmospheric pressure while area  62  above bearing  26  is at generally atmospheric pressure, one might expect an air pressure differential across seal  24  to urge seal  24  toward rotor  14 , but actually just the opposite is true. 
     An axial clearance  84  between impeller  20  and housing assembly  16  is sufficiently small (e.g., about 0.5 inches or less) that the rotation of impeller  20  (e.g., about 4.5 inches in diameter more or less and rotating at about 20,000 rpm more or less) induces a centrifugal airflow pattern within clearance  84  to create a vacuum in dead-space  82 . thus the absolute air pressure or subatmospheric pressure in dead-space  82  is less than the positive pressure in discharge area  56  at discharge opening  48  and is also less than the generally atmospheric pressure in open space  62  (which is on the motor side of bearing  26 ). 
     When appreciable axial clearance exists at the seal&#39;s inner radial periphery  76  (e.g., seal&#39;s inside diameter), then the seal&#39;s inner periphery  76  will have the freedom to deflect, as shown in  FIGS. 3 and 4 .  FIG. 3  shows motor  10  de-energized with seal  24  at its relaxed, undeflected state.  FIG. 4  shows motor  10  energized with the upstream air pressure (generally atmospheric pressure) pushing down against the seal&#39;s motor side  86  to deflect seal  24  such that turbine side  78  of seal  24  engages axial abutment surface  80  of shaft  18 . Deflecting seal  24  by way of generally atmospheric pressure is possible due to the vacuum on the opposite side of seal  23  at dead space area  82 . In the example shown in  FIGS. 1-4 , axial abutment surface  80  on shaft  18  is a shoulder on sleeve  36  (shaft  18  comprises main shaft  34  and sleeve  36 ). 
     In other examples where no appreciable axial clearance exists at the seal&#39;s inner periphery  76  (e.g., abutment surface  80  engages the seal&#39;s turbine side  78  even when motor  10  is de-energized), the axial pressure differential across seal  24  will still urge seal  24  away from rotor  14  and toward impeller  20 ; however, there might not be any appreciable seal deflection. 
     In the example shown in  FIGS. 5 and 6 , a housing assembly  16 ′ includes a step  88  that serves as an axial abutment surface against which an outer periphery  90  of a seal  24 ′ can deflect in response to a pressure differential across seal  24 ′.  FIG. 5  shows a motor  10 ′ de-energized with seal  24 ′ at its relaxed, undeflected state.  FIG. 6  shows motor  10 ′ energized with the upstream air pressure (generally atmospheric pressure) pushing down against the seal&#39;s motor side  86 ′ to deflect seal  24 ′ such that a turbine side  78 ′ of seal  24 ′ engages step  88 . 
     In the example shown in  FIG. 7 , seal  24  is axially interposed between bearing  26  and rotor  14  with motor side  86  facing rotor  14  and turbine side  78  facing toward impeller  20 . In this example, outer radial periphery  70  is axially clamped between a bearing retainer  68 ′ and the bearing&#39;s outer race  72 . At the seal&#39;s inner radial periphery  76 , the seal&#39;s turbine side  78  rests upon the bearing&#39;s inner race  92 , thus the bearing&#39;s inner race  92  provides as an axial abutment surface against which turbine side  78  seals, particularly in response to a pressure differential across seal  24 . In this example, upstream air pressure (generally atmospheric pressure) in open space  62  urges seal  24  down away from rotor  14  toward impeller  20 . 
     In the example shown in  FIG. 8 , seal  24 ′ is axially interposed between bearing  26  and rotor  14  with motor side  86 ′ facing rotor  14  and turbine side  78 ′ facing toward impeller  20 . In this example, inner radial periphery  76   a  is axially clamped between a shaft shoulder  94  and the bearing&#39;s inner race  92 . At the seal&#39;s outer radial periphery  90 , the seal&#39;s turbine side  78 ′ rests upon the bearing&#39;s outer race  72 , thus the bearing&#39;s outer race  72  provides an axial abutment surface against which turbine side  78 ′ seals, particularly in response to a pressure differential across seal  24 ′. In this example, upstream air pressure (generally atmospheric pressure) in area  62  urges seal  24 ′ down away from rotor  14  toward impeller  20 . 
     In some examples, seal  24  has an outer diameter of about 1.0 inches, an inner diameter of about 0.5 inches, a thickness of about 0.032 inches, and seal  24  is comprised mostly or entirely of polytetrafluoroethylene. To achieve desired wear resistance or lubricity, some examples of seal  24  are comprised of polytetrafluoroethylene impregnated with an additive such as molybdenum disulfide, graphite, brass powder, or combinations thereof. Other examples of seal  24  are made of other materials and/or different dimensions. 
       FIGS. 9 and 10  shows another example of the invention, wherein external seal  24  is installed in a motor  10 ″ having a housing assembly  16 ″ that includes a peripheral discharge.  FIGS. 9 and 10  correspond to  FIGS. 1 and 2 , respectively. In the example of  FIGS. 9 and 10 , however, discharge housing  30 ′ includes impeller housing  32 ′, which provides the series of peripheral discharge openings  48 ′ for releasing discharge air  42 . The structure and function of seal  24  is otherwise basically the same for motors  10  and  10 ′. 
     In at least some of the aforementioned examples include one or more features and/or benefits including, but not limited to, the following: 
     In some examples, a motor for a vacuum appliance includes a bearing seal that is urged axially toward an impeller under the pressure of air at generally atmospheric pressure. 
     In some examples, a motor for a vacuum appliance includes a bearing seal that is urged axially toward an impeller under the pressure of air at generally atmospheric pressure, wherein radial clearance at the inner or outer periphery of the seal provides the seal with greater axial flexibility. 
     In some examples, seal wear is minimized by virtue of the seal relying on sliding sealing contact of a broad axial surface external to a bearing. 
     Although certain example methods, apparatus, and articles of manufacture have been described herein, the scope of the coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.