Abstract:
A vent fan for use with the dishwasher and providing a vent door covering the opening associated with a motorized fan employs a mechanical coupling between the fan motor and vent door to eliminate the need for a separate vent door actuator by using energy of the fan motor to accomplish the actuation.

Description:
CROSS REFERENCE TO RELATED CASE 
     This application is a National Phase of International Application Number PCT/US2012/050683 filed Aug. 14, 2012 and claims the benefit of U.S. provisional application 61/523,599 filed Aug. 15, 2011 hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to dishwashers and other appliances and in one embodiment to dishwashers providing forced airflow during the drying cycle. 
     BACKGROUND OF THE INVENTION 
     Dishwashers, such as those used in a home, may provide for a washing cycle followed by a drying cycle, the latter intended to dry the washed dishes sufficiently so that they may be immediately removed from the dishwasher and stored without additional manual drying. In many cases, the drying cycle includes activation of a heating element exposed at the bottom of the washing volume to heat the dishes and create an upward convective flow of hot air. 
     One drawback to vents is that they can increase the noise emitted from the dishwasher during the washing cycle and, accordingly, it is known to provide for vents having an electrically actuable door that may block the vents during the washing cycle thereby cutting emitted noise. One vent of this type is described in U.S. Pat. No. 6,293,289 entitled: “Surge Pressure Vent for Low Noise Dishwasher”. Venting can also be obtained by partially opening the door at the conclusion of the washing cycle as disclosed in U.S. Patent Application US 2004/0163684 entitled: “Automatic Door for Dishwasher”. Both of these patents are assigned to the assignee of the present invention and hereby incorporated by reference. 
     Venting systems can be improved by the addition of a blower to increase the passage of air through the washing volume. Generally, such blowers are arranged to reinforce the natural convective flow of air thereby obtaining the benefit from the blower and the convection action of the heated air during the drying cycle. 
     US patent application 2006/0231122, also assigned to the assignee of the present invention, describes a blower that obtains improved drying efficiency by operating at very low flow volumes in a direction counter to the natural convective flow of the air. This application also describes a vent door actuated by a solenoid or the like. 
     SUMMARY OF THE INVENTION 
     The present invention provides a vent door for a dishwasher blower that makes use of the energy of the blower fan to mechanically open or close a vent depending on the direction of that rotary action. In this way, a single electrical actuator (the fan motor) may provide mechanical energy both to turn the fan and to open and close the door eliminating the need for separate wiring for the fan and the door actuator. A direct mechanical coupling between the fan motor and the vent door permits a greater degree of opening and less back pressure than would be obtained, for example, in a design using air pressure to open the door. In addition, the greater strength of the motor permits a more positive sealing of the door for water tightness as well as acoustic damping. 
     Specifically, the invention provides a dishwasher vent having a housing with an inlet adapted to communicate with a washing volume for receiving dishes, and an outlet communicating with air outside of the dishwasher. The housing includes a channel for permitting airflow therethrough between the inlet and outlet. An electrical motor provides a rotating shaft extending along an axis attached to a fan positioned within the channel and rotatable in a first direction to move air through the channel from the inlet to the outlet. A vent door is provided that is movable between a closed position blocking the channel to prevent airflow therethrough and a open position opening the channel to permit airflow therethrough and a mechanical coupling is positioned between the motor and the vent door to cause rotation of the electrical motor driving the fan in the first direction to open the vent door. 
     It is thus a feature of at least one embodiment of the invention to eliminate the need for a separate vent door actuator while providing positive actuation displacement without the backpressure, and hence reduction in airflow, produced by a system where air pressure must be used to open the vent door. 
     The mechanical coupling may further cause rotation of the electrical motor to drive the fan in a second direction opposite the first direction to close the door. 
     It is thus a feature of at least one embodiment of the invention to use the same motor for a positive sealing of the vent door to provide improved resistance to sound and/or water leakage. 
     The dishwasher vent may further include a vent control providing a first polarity of electrical power to the electrical motor to cause the fan to move in the first direction when venting of the dishwasher is to occur and providing a second opposite polarity of electrical power to the electrical motor to cause the fan to move in the second direction when washing of dishes within the dishwasher is to occur. 
     It is thus a feature of at least one embodiment of the invention to permit motorized opening and closing of the vent door without the need for multiple wire pairs. 
     The mechanical coupling may be a collar fitting about a threaded shaft attached to the motor. 
     It is thus a feature of at least one embodiment of the invention to provide a simple coupling mechanism that may be tailored to produce the desired mechanical advantage and speed reduction necessary for using one motor for both a fan and a door actuator. 
     The collar may attach to a center of the vent door to move the vent door to engage or disengage from a vent door seat concentric about the fan with rotation of the motor. 
     It is thus a feature of at least one embodiment of the invention to permit mechanical coupling to provide both the motivation to and support for the vent door. 
     The threaded shaft may provide a non-threaded portion allowing rotation of the threaded shaft without movement of the collar in at least one extreme position of the collar with respect to the threaded shaft. 
     It is thus a feature of at least one embodiment of the invention to provide a vent cover that may be controlled in an “open loop” fashion in which the motors run for a predetermined period of time to ensure its opening or closing without the need for limit switches or the like. 
     Alternatively, the vent may include a spring element urging the vent door to the closed position when no power is applied to the electrical motor. 
     It is thus a feature of at least one embodiment of the invention to provide a vent door that may be operated with a unipolar control voltage whose absence serves to close the door. It is a further feature of at least one embodiment of the invention to provide a default door closure position desirable for shipping and the like when no power is applied to the dishwasher. 
     The vent door may be a plate slidable along the axis to cover or uncover an orifice in the housing. 
     It is thus a feature of at least one embodiment of the invention to provide a low-profile vent door and fan combination for use where space is at a premium, for example, at the top of the dishwasher for updraft venting. 
     The plate may include multiple openings spaced along the axis and the orifice includes multiple apertures spaced along the axis so that movement of the plate with respect to the orifice by a distance equal to the spacing between openings and apertures may move the vent door from a full open to a full close position. 
     It is thus a feature of at least one embodiment of the invention to permit a large open area of the event with relatively small amounts of plate movement. 
     The mechanical coupling may be a collar fitting about the threaded shaft attached to the motor and the vent cover and fan may be joined to a collar to rotate together. Rotation of the vent cover and fan in an open position then move air through the channel from the inlet to the outlet. 
     It is thus a feature of at least one embodiment of the invention to provide apparatus of limiting the need for separate vent cover and fan structure. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a standard residential dishwasher as positioned beneath a counter, the latter shown in cutaway and with the door opened; 
         FIG. 2  is a cross-sectional view through the dishwasher of  FIG. 1  along lines  2 - 2  of  FIG. 1  showing the door closed and a first embodiment of the invention providing counter-convection airflow using a top mounted intake fan; 
         FIG. 3  is an exploded perspective view of a dishwasher vent according to the present invention showing a helix drive, an elastomeric valve disk, a fan, and a valve seat/shroud arranged along an axis of a motor shaft; 
         FIG. 4  is a side elevational view in partial cross-section of the vent as assembled showing operation of the motor in a counterclockwise direction to close a vent door; 
         FIG. 5  is a figure similar to that of  FIG. 2  showing the motor operated in a clockwise direction to open the vent door and provide for airflow into the dishwasher cavity; 
         FIG. 6  is a figure similar to that of  FIG. 4  showing a more detailed embodiment; 
         FIG. 7  is a figure similar to that of  FIG. 5  showing a more detailed embodiment; 
         FIG. 8  is a figure similar to that of  FIG. 5  showing an alternative embodiment using a spring element for returning the vent door to the closed position; 
         FIG. 9  is an exploded perspective view in partial phantom of an alternative embodiment of the invention employing a horizontal motor and fan axis and a sliding vent plate; 
         FIG. 10  is a cross-sectional view through the housing and unexploded assembly of  FIG. 9  showing airflow therethrough; 
         FIG. 11  is a fragmentary detail of a screw thread for moving a sliding plate of  FIGS. 9 and 10 ; 
         FIGS. 12 and 13  are figures similar to those of  FIGS. 4 and 5  showing an embodiment in which the helix drive has a stop to prevent disengagement of the valve disk from the drive at the end of travel and in which air paddles presenting drag forces in the air are used to ensure relative movement between the components of the helix drive without a mechanical keying; 
         FIGS. 14 and 15  are figures similar to  FIGS. 12 and 13  wherein blades of the fan provide the function of the air paddles of  FIGS. 12 and 13 ; 
         FIGS. 16 and 17  are figures similar to  FIGS. 4 and 5  showing an embodiment in which a magnetic centering of the motor rotor within the stator that occurs with energization of the stator motor provides for opening of the valve disk; 
         FIG. 18  is an upper perspective view of an embodiment similar to that of  FIGS. 12 and 13 ; 
         FIG. 19  is a cross-section perspective view of the alternative embodiment of  FIG. 18 ; 
         FIGS. 20 and 21  are elevational cross-section views of the embodiments of  FIGS. 18 and 19  in an open and closed position, respectively; 
         FIGS. 22 and 23  are figures similar to  FIGS. 18 and 19  of an embodiment combining the fan and the vent plate on a single structure; and 
         FIGS. 24 and 25  are elevational cross-section views of the embodiments of  FIGS. 22 and 23  in the open and close position respectively. 
     
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a dishwasher  10  for fitting beneath a countertop  12  may include a cabinet  14  enclosing a washing volume  16 . The washing volume  16  may hold one or more racks  18  into which dishes may be loaded for cleaning as accessed through a front opening closeable by a door  20 . 
     Referring also to  FIG. 2 , the door  20  may be closed against door seals to contain water within the washing volume  16  during a wash cycle. During a wash cycle, heated water is sprayed on the dishes within the washing volume  16  by stationary or movable nozzles (not shown). At the conclusion of the wash and rinse cycles as determined by a cycle timer (not shown), water is drained from the lower portion of the washing volume  16  in preparation for drying of the dishes and, in a first embodiment of the invention, a heater element  43  is activated heating the air within the washing volume  16 . 
     At this time the cycle timer activates a vent fan assembly  29  positioned at a vent opening in a roof  19  of the cabinet  14  drawing intake air  21  from outside the washing volume  16  beneath a countertop  12  to produce a counter-convection or downward airflow  23  within the washing volume  16  with the air ultimately exhausting through the lower vent at the lower edge of the door  20  to flow along the floor as exhaust airflow  25 . Notably, no moist air is injected in between the dishwasher  10  and the countertop  12  or under other cabinet areas. The downward airflow  23  serves to preferentially exhaust the air at the bottom of the washing volume  16 . 
     Filtration of the intake air  21  may be provided by sound insulating batting  27 , for example, also serving to reduce the sound emitted by the dishwasher  10  and being, for example, a fiberglass mat or the like wrapped around the cabinet  14  and beneath the countertop  12 . Alternatively, a dedicated filter to be described can be used. 
     Referring now to  FIG. 3 , a vent fan assembly  29  of the present invention may provide a housing  31 , for example, having a lower wall being flush with an upper inner wall of the roof  19  of the dishwasher  10 . The housing  31  may have a passageway  33  through the housing  31 , the opening surrounded by a circular shroud/valve seat  35 , for example, in the form of a cylindrical tube. The shroud/valve seat  35  may surround a fan  38  having a hub  39  concentric within the shroud/valve seat  35  to rotate therein to move air through the passageway  33  when rotated. 
     The hub  39  of the fan  38  may be received on a downwardly extending post  22  of a helical drive  24 , the main body of the helical drive  24  being a cylinder having an outer helical thread  26  spiraling counterclockwise downward. 
     A socket  28  in the upper end of the helical drive  24 , in turn, may be received by a motor shaft  17  oriented generally along the vertical axis  32  and rotatable by a DC electric motor  34 . It will be understood that the DC electric motor  34  may be rotated in either of two directions simply by reversal of the polarity of the driving voltage provided on a single pair of wires  36  attached to the DC electric motor  34 . The wires  36  may attach to a cycle timer  37  of a type known in the art that may provide either a timed unipolar voltage pulse or timed bidirectional voltage pulses as will be described. 
     A threaded collar  40  may fit about the helical drive  24  between the DC electric motor  34  and the fan  38  and may include inner threads  42  engaging the threads  26  of the helical drive  24  when the collar  40  is at middle positions along the helical drive  24  but disengaging from the threads  26  at the top and bottom extent of its travel along the helical drive  24 . 
     The collar  40  may have radially outwardly extending arms  44  received by vertically extending grooves  46  attached to the housing  31  and generally parallel to the axis  32 . An interfitting between the arms  44  and grooves  46  prevents rotation of the collar  40  with rotation of the helical drive  24  from frictional engagement between the helical drive  24  and the collar  40  while allowing movement of the collar  40  along the axis  32 . Rotation of the helical drive  24  moves the collar  40  up or down to limits of this travel defined by this engagement between the inner threads  42  and the threads  26 . 
     A bottom surface of the collar  40  may be attached to an elastomeric valve disk  48  sized to have a diameter slightly larger than the shroud/valve seat  35  so that when the collar  40  is in its lowermost extreme position it fits against an upper lip  50  of the shroud/valve seat sealing the same and preventing sound and moisture from passing from inside the dishwasher through the passageway  33 . 
     Referring now to  FIGS. 4 and 6 , when the motor  34  is operated in a counterclockwise direction  52 , the threads  26  of the helical drive  24  push the collar  40  downward pressing the elastomeric valve disk  48  against the upper lip  50  sealing the housing  31  against moisture passing through the shroud/valve seat  35  and passageway  33 . In this position, the fan  38  is isolated from the motor  34  and effectively inside of the dishwasher  10 ; however, the materials of the fan  38  and the post  22  may be water resistant thermoplastic. In contrast, the electrical components of the motor  34  are protected from water spray in the volume of the dishwasher  10 . 
     When the motor  34  is operated in this counterclockwise direction  52 , the pitch of the fan  80  is such as to generally blow upward as indicated by arrows  56 . Thus, operation of the motor  34  in a counterclockwise direction may serve to close the vent door. The motor  34  may be stalled at this point of closure (through the use of current limiting resistance) or the threads may disengage as described above allowing free rotation of the helical drive  24 . Power may then be removed from the motor  34  with the elastomeric valve disk  48  staying in closed position through the agency of friction and the inertia of the motor or, for tighter seal, a continuous bias voltage may be provided to the motor  34  to press the elastomeric valve disk  48  downward. 
     Referring now to  FIGS. 5 and 7 , a reversal of the motor  34  to a clockwise direction  60  causes the helical drive  24  to pull the collar  40  upward. Initial engagement between the threads of the collar  40  and the helical drive  24  is provided by slight upward biasing of the collar  40  by flexure of the elastomeric valve disk  48  shown in  FIG. 4 . It will be understood that the elastomeric valve disk  48  may be moved an arbitrarily large distance by proper sizing of the helical drive  24  to provide minimum amounts of air resistance to downward airflow  23  caused by the reversal of the fan  38  to the clockwise direction  60 . At this point, air is free to move in through the passageway  33  in the shroud/valve seat  35  out of the dishwasher volume to be exhausted out of the dishwasher through an upper vent in the housing (not shown). It will be understood that the airflow direction may be easily reversed by changing the pitch of the fan  38  and/or that of the threads  26 . 
     Referring now to  FIG. 8 , in an alternative embodiment, springs  70 , for example helical compression springs, may be positioned to press downward on the collar  40 , for example, by agency of the arms  44  so that when no power is applied to the motor  34  the elastomeric valve disk  48  closes. In this case, the springs  70  cause a torsion on the helical drive  24  through the collar inner threads  42  which provide the necessary rotation  52  to close the elastomeric valve disk  48 . An advantage to this design is the ability to operate the motor  34  with only a single polarity of voltage and to firmly retain the elastomeric valve disk  48  in a closed position without electrical power and to be used with an AC or DC motor. This design also permits the use of a brushless DC motor. 
     Referring now to  FIG. 9 , in an alternative embodiment, the axis  32 ′ of the motor  34  may be oriented horizontally or perpendicular with respect to the downward airflow  23 . The motor  34  may be joined with the opposed fan  38  (now rotating in a vertical plane) by means of a horizontal driveshaft  82  having threaded portions  84  on opposite ends close to the motor  34  and close to the fan  38 . Vertically oriented follower pins  86  may extend downward from opposite ends of a comb-formed vent plate  90  to engage each of the threaded portions  84  respectively. 
     The comb-formed vent plate  90  may be a generally planar plate aligned with a generally horizontal plane, and extending substantially the length of the driveshaft  82 . The comb-formed vent plate  90  may provide for a series of regularly spaced apertures  92  between comb teeth. When the vent plate  90  is in an open position, as moved by the threaded portions  84  acting on the follower pins  86 , and when the driveshaft  82  turns so that the fan  38  blows downward airflow  23 , each aperture  92  aligns with a corresponding aperture  94  in the housing  31  providing a passageway for air  21 . 
     In contrast, when the driveshaft  82  is turned so that the fan  38  rotates in the opposite direction to pull air from the washing volume  16  of the dishwasher  10 , the vent plate  90  is moved to a closed position by the threaded portions  84  acting on the follower pins  86  so that the comb teeth between each aperture  92  each block a corresponding aperture  94  in the housing  31  preventing the flow of air  21  and sealing the washing volume  16  of the dishwasher  10  against the escape of moisture and sound. 
     Referring now to  FIGS. 8 and 10 , the threaded portions  84  may provide for a generally helical thread  98  separated by a helical groove  100  receiving a follower pin  86 . When the plate  90  is in the open position allowing free flow of air through the apertures  94  and  92 , the follower pin  86  arrives at a circumferential groove  102  communicating with the helical groove  100 . The circumferential groove  102  allows continuous rotation of the driveshaft  82  without further movement of the follower pin  86  in a leftward direction (as depicted). The circumferential groove  102  thus permits continuous rotation of the fan  38  in this direction without interference. 
     When the follower pin  86  is in the circumferential groove  102 , and the motor  34  changes direction to move the plate  90  toward the closed position closing the vent, engagement of the follower pin  86  and the helical groove  100  may be promoted through the use of a slight biasing spring  106 . 
     When the plate  90  is in the closed position blocking the free flow of air through apertures  92  and  94 , the follower pin  86  arrives at a dead-end  104  of the helical groove  100  and the motor  34  may stall ceasing motion of the fan  38 . The resistance of the motor  34  may be adjusted to permit a brief period of stalling without damage, the brief period as controlled by the cycle timer  37  (shown in  FIG. 1 ). 
     This embodiment may provide for a lower profile of the vent fan assembly  29  helpful when the thickness of the roof  19  of the dishwasher is limited and/or clearance between the dishwasher  10  and the countertop  12  is small (for example, shown in  FIG. 1 ). 
     While the present invention has been described in the context of a dishwasher, it will be understood that this design can also be used in other appliances where venting is required, including but not limited to, for example, clothes washing machines where the vent fan is used to dry residual water that may otherwise produce unpleasant odors. 
     Referring now to  FIGS. 12 and 13 , in an alternative embodiment, the thread  26  of the helical drive  24  may have a stop  108  preventing the collar  40  from disengaging from the thread  26  at its upper limit of travel when the motor  34  is turning in a clockwise direction. In this embodiment, the collar  40  is not stabilized against rotation by interengaging arms  44  and grooves  46  as shown in  FIG. 3  but is free to turn with the motor  34 . This permits the collar  40  to rotate with the helical drive  24  when it reaches the upper limit of travel as shown in  FIG. 13  and prevents a clicking sound that might otherwise occur were the collar  40  to remain stationary and pressing downward on the truncated end of the thread  26  rotating therebeneath. 
     Elimination of the inter-engaging arms  44  and grooves  46 , requires some means to prevent the collar  40  from rotating with the motor  34  when the motor  34  is operated in a clockwise direction  60  and has not yet reached the upper limits of its travel (for example as shown in  FIG. 12 ) such as would defeat operation of the helical drive  24 . Inhibition of rotation of the collar  40  is provided by air paddles  110  extending radially from the collar  40  about axis  32  above the valve disk  48 . The air paddles  110  which provide air resistance producing a net rotational speed difference between a collar  40  and threads  26  allowing the collar  40  climb the threads  26  to the point of the stop  108 . The air paddles  110  are sized to provide sufficient air resistance for this purpose of allowing the collar  40  to climb the threads  26  but small enough to provide low energy loss in the operation of the motor  34  when the collar  40  is rotating with the motor shaft  17  at the top of its travel. 
     When the motor  34  is reversed with the shaft  17  traveling in a counterclockwise direction  52 , the collar  40  is pressed downward by the threads  26  until the motor stalls as has been described above closing the valve disk  48  against the upper lip  50 . 
     Referring now to  FIGS. 14 and 15 , this same concept may be implemented by using the blades of the fan  38  as the air paddles  110  and locking the hub  39  and the blades of the fan  38  to the collar  40  to rotate therewith. When the valve disk  48  is in the closed position, as shown in  FIG. 14 , the fan  38  will be somewhat below the shroud/valve seat  35  but will climb into position as shown in  FIG. 15  within the shroud/valve seat  35  as the collar  40  rises on the threads  26  of the helical drive  24 . When the internal threads  42  of the collar  40  abut the stop  108 , the collar  40  begins to rotate with the motor shaft also causing rotation of the fan  38 . In this case there is no unnecessary dissipation of energy into the air as the natural resistance to rotation provided by the fan  38  is an inherent side effect of the useful function of causing airflow  23 . 
     Referring now to  FIGS. 16 and 17 , in an alternative embodiment the collar  40  may be locked to the shaft  17  of the motor  34  dispensing with the helical drive  24 . In this embodiment, the shaft  17  may move axially along axis  32  by an amount necessary to open the valve disk  48 . The motor rotor  112  attached to the shaft  17  may be offset along axis  32  downward from the center of the motor  34  with the effect of gravity as shown in  FIG. 16  or an auxilary spring (not shown). This downward offset displaces the rotor  112  from a magnetically stable position centered within the motor housing and aligned with the motor stator when the motor is being run, and serves to close the valve disk  48  against the upper lip  50  under the force of gravity. When the motor  34  is energized, the rotor  112  seeks its stable position upward in the motor  34  aligned with the stator causing the shaft  17  to rise pulling up on the collar  40 . Per the embodiment of  FIGS. 14 and 15 , the collar  40  may be fixed rotatably to the hub  39  and the fan  38  so that raising of the shaft  17  pulls the fan  38  into position within the shroud  58  and simultaneously rotates the fan  38 . Generally, the motor  34  may be operated in either direction to open the valve disk  48 . This optionally allows this design to be used either to draw air out of or blow air into the wash cavity as desired. The motor  34  may be, for example, an AC shaded pole motor or the like. 
     Referring now to  FIGS. 18-21 , in an alternative embodiment, the vent fan assembly  29  may be covered by a dome shaped shell  122  having an arcuate interior wall enclosing a volume containing the fan  38  and the valve disk  48 . The shell  122  connects to the housing  31  outside of the shroud/valve seat  35  so as not to interfere with airflow through passageway  33 . The shell  122  further provides an opening  124  at an upper end near the motor  34 , for example in the form of a circle, for allowing air passage there through when the vent fan assembly  29  is in a opened position. The motor  34  may be suspended in the opening  124  by a mounting bracket  126 , which is affixed to the housing  31  at a first and second attachment pylon  128 . 
     As described generally above with respect to  FIGS. 12-15 , the valve disk  48  may be supported on a collar  40  that threadably engages a helical drive  24  driven by the motor  34 . The valve disk  48  may have upwardly extending air paddles  110  attached thereto to engage in air held within the volume of the shell  122 . This air will tend to restrain rotation of the valve disk  48  with respect to the helical drive  24  causing the valve disk  48  to rise away from the shroud/valve seat  35  with a first direction of motor operation and causing the valve disk  48  to fall toward the shroud/valve seat  35  with a second direction of motion. 
     A resilient seal  130 , such as an O-ring, may be supported near the upper lip  50  of the shroud/valve seat  35  so that when the valve disk  48  moves downward it compresses the resilient seal  130  to improve the sealing between the valve disk  48  and the shroud/valve seat  35 . 
     A collar  40  providing internal threads engaging the external threads of the helical drive  24  may provide for the connection between the helical drive  24  and the valve disk  48  through a bellows  134  formed concentrically about the axis of the helical drive  24  on the valve disk  48 . The bellows  134  provides for a spring biased translation of the valve disk  48  along the axis of rotation with respect to the collar  40  so as to equalize pressure between the valve disk  48  and the resilient seal  130  and to reduce jamming forces between the collar  40  and the helical drive  24  when the valve disk  48  abuts the seal  130 . 
     Referring now to  FIGS. 22-25 , in a further embodiment, the resilient seal  130  described above may be eliminated while providing resistance to the passage of water and air through the vent fan assembly  29  when it is in the closed state by providing an overlapping engagement between the valve disk  48  and the shroud/valve seat  35  that provides a serpentine pathway between the two that resists water flow when the valve disk  48  is in the closed or nearly closed position. Specifically, the housing  31  provides a circular channel  140  outside and surrounding the shroud/valve seat  35  and concave upward toward the motor  34 . Conversely, the valve disk  48  provides a circular channel  142  at its outer periphery concave downward away from the motor  34  and staggered with respect to the circular channel  140  so that the two engage each other with a lowermost edge of the valve disk  48  contacting a center of the channel  140  and upper edge  55  of the channel  140  contacting a center of the channel  142 . 
     In this embodiment, the motor  34  may be supported directly on the shell  122  by means of radially inwardly extending support struts  144  passing through the opening  124 . The air paddles  110  extending from the upper surface of the valve disk  48  also provide the fan  38  so that both are joined on the same structure attached to collar  40 . When the helical drive  24  rotates in a first direction, the drag of the air paddles  110  against the air causes the collar  40  to rise upward on the helical drive  24  toward the motor  34  opening the passageway  33  for airflow downward through the passageway  33 . This air is impelled centrifugally by the rotation of the air paddles  110  when upward motion of the collar  40  is stopped by the threads causing the air paddles  110  to rotate. The radially expelled air is guided by the shell  122  through the open and overlapping channels  140  and  142 . When the helical drive  24  rotates in a second opposite direction, the drag of the air paddles  110  against the air causes the collar  40  to descend downward on the helical drive  24  away from the motor  34  closing the passageway  30  also for airflow downward through the passage. Downward motion of the fan  38  and valve disk  48  is prevented by an end cap  150  positioned at the end of the helical drive  24  furthest from the motor  34 . 
     Significantly, either direction of rotation of the motor  34  will generate the same centrifugal action and downward airflow thus preventing any draw of moisture upward into the motor area regardless of the rotation direction of the motor  34 . The elimination of the elastomeric seal and the use of the restricted serpentine channel formed between channels  140  and  142  prevents stalling of the motor in this closed position allowing simple open loop control of the opening and closing of the vent fan assembly  29  by timing of a control circuit. 
     Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
     The recitation of a fan in the present invention should be understood to broadly include rotating elements for air movement including propeller type fans and squirrel cage type of blowers. 
     When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.