Abstract:
A mechanized vent for a dishwasher employs a vent plate moving about a hinge axis as driven by a cam mechanism at a surface of the vent plate removed from the hinge axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application 60/579,883 filed Jun. 15, 2004, and hereby incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to automatic dishwashing machines (dishwashers) and in particular to a dishwasher vent for use in a low noise dishwasher. 
     Dishwashers, such as those found in many homes, provide a chamber holding one or more racks into which eating utensils and cookware may be placed for cleaning. The chamber may be closed by a door opening at the front of the chamber to allow loading and unloading of the chamber. 
     The door is closed during a washing cycle to prevent the escape of water sprayed within the volume of the chamber to wash items placed in the rack. Upon completion of the washing cycle, a drying cycle is initiated during which water is drained from the chamber and moist air is discharged through a vent. Cool air pulled into the chamber through a lower vent rapidly dries the heated dishes. 
     Dishwashers can be loud, particularly during the washing cycle, with noise coming from the agitated water, movement of the dishes, and the dishwasher mechanism of pump and motor. Some of this noise can be reduced by properly shrouding the washing chamber with acoustically absorbent material, nevertheless, even with a properly shrouded chamber, a substantial amount of noise can escape through the vent by diffraction. 
     One method of reducing vent-transmitted noise is by offsetting the inlet and outlet of the vent to provide a baffling that prevents direct passage of sound through the vent opening. This approach can also prevent water from passing through the vent. 
     A second method of reducing vent-transmitted noise is to close the vent with a valve plate or similar mechanism during the washing cycle and open the vent only during the drying cycle. A vent suitable for this purpose is described in U.S. Pat. No. 6,293,289 filed Nov. 8, 1999, assigned to the assignee of the present invention, and hereby incorporated by reference. This patent describes, in one embodiment, a wax motor operating a hinged valve plate that opens and closes to control air and sound flow through the vent. The hinged plate may also be independently opened by excess pressure in the washing machine so as to accommodate “surge pressures” resulting, for example, from pressure build up caused by an opening and closing of the dishwasher in mid-cycle where introduced cold air is rapidly heated by dishes and hot water when the door is resealed. 
     Superior drying requires that the vent area be made as large as possible when the vent is open and that the valve plate provide minimal obstruction to the flowing air. This may be done by placing the hinge axis of the valve plate generally parallel to the front and rear surfaces so that the valve plate opens to align with the natural flow lines of air. 
     The actuator for a valve plate in a vent may be positioned outside of the vent housing (defining the vent passage) to improve airflow and to protect the actuator from water. This may be accomplished by extending the shaft about which the vent plate rotates out of the vent housing through a journal hole in one wall of the vent to be engaged by an actuator. The journal hole is kept small to prevent the escape of water from the vent and may include a seal. 
     Mechanically, passing the shaft through a wall of the vent housing requires either that the vent plate be detachable from the shaft, so that the shaft may be inserted through a journal hole into the housing without obstruction, or that the housing be separable into two halves to allow an integral vent plate/shaft assembly to be positioned in the vent body and the housing closed over that. Both of these approaches increase the complexity of manufacturing the vent: the former requiring assembly of the shaft and vent plate from inside of the vent, and the latter requiring assembly of the vent housing from several pieces. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention employs a cam drive mechanism moving a valve plate within a dishwasher vent without the need for a direct connection between an actuator and the shaft about which the valve plate rotates. This approach allows the valve plate shaft to be retained wholly within the vent housing eliminating leaks along a rotating shaft passing through the housing or excess shaft friction, and allowing the vent housing to be molded or preassembled as one piece with the valve plate is snapped into place subsequent to the molding. 
     The drive mechanism allows the axis of the valve plate and the drive actuator (preferably a wax motor) to be parallel and closely adjacent to the valve plate pivot axis, providing an extremely compact mechanism that may fit easily between the front and rear panel of a dishwasher door. This advantage also applies to an embodiment in which the valve plate is supported by externally inserted pins or the like. 
     In one embodiment, the cam mechanism may open and close the valve plate without the need for a biasing spring element or reliance on gravity, and may accommodate over travel common in wax motors while still providing a large amount of mechanical amplification to fully open and close the valve plate with small amounts of actuator travel. 
     In one embodiment, the operator may extend along an axis parallel to, but displaced from, a pivot axis of the valve plate to provide an extremely compact assembly. 
     In one embodiment, a spring biases the valve plate to allow the valve plate to open independently of the wax motor to relieve surge pressures. 
     In one embodiment, an elastomeric seal is held in cantilevered fashion at the valve seat to provide a compliant seal blocking sound transmission. 
     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified view of a dishwasher in perspective showing location of a door vent for venting moist air; 
         FIG. 2  is an exploded perspective view of the door vent of  FIG. 1  as viewed from the inside of the dishwasher and as may be positioned between the front and rear door surfaces; 
         FIG. 3  is a cross-sectional view of the inlet port of the vent of  FIG. 2  taken along lines  3 - 3  showing a snap-in engagement of an integrated vent plate and shaft at the inlet port; 
         FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 3  showing the vent plate in a closed configuration for blocking sound and the flow of air; 
         FIG. 5  is a perspective view of the engagement between a wax motor actuator and a cam surface on the vent plate of  FIG. 4  as viewed from inside the vent housing; 
         FIGS. 6   a  through  6   c  are rear elevational views of the cam surface with the vent plate in three states of closed, transition, and open; 
         FIG. 7  is a figure similar to that of  FIG. 4  showing an alternative embodiment of the door vent in which the valve plate may move independently in response to surge pressures; and 
         FIG. 8  is a figure similar to  FIG. 7  showing an alternative embodiment in which the valve plate has a default open position if the wax motor is removed. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a dishwasher  10  may include a housing  12  holding a washing chamber and a front door  14  that may be opened to obtain access to the washing chamber for loading and unloading of dishes. A door vent  16  provides an outlet port  18  in the front surface  20  of the door  14  to allow for the escape of moist air  22 . 
     Referring now to  FIG. 2 , a vent housing  24  provides an air passage between the outlet port  18  on the front surface  20  and an inlet port  26  opening at the rear surface  28  of the door  14  facing the washing chamber. The outlet port  18  is positioned higher on the door than the inlet port  26 , both to provide a serpentine path for muting sound passing through the vent housing  24  and to cause water splashed into and condensation forming within the vent housing to drain downward out of inlet port  26  back into the wash chamber. Preferably, the vent housing  24  is manufactured as a single injection molded part avoiding a need for subsequent assembly of multiple components using screws or welds and eliminating the need to test for leakage of the seams or to provide expensive gasketing at the seams. 
     The air passage of the vent housing  24  is substantially continuous to prevent leakage of water into the door  14 , with the exception of a bore  30  opening between inlet port  26  and outlet port  18 , generally perpendicular to the airflow. The bore  30  may be created during the molding of the vent housing  24  using an injection mold with a removable core pin as is understood in the art. 
     The bore  30  allows an operator  32  of a wax motor  34  (the wax motor  34  positioned outside the vent housing  24 ) to enter the air passage. The operator  32  of the wax motor  34  has an o-ring seal  36  allowing movement of the operator within the bore  30  without the leakage of liquid there through as will be described below. 
     Referring still to  FIG. 2 , the inlet port  26  is covered at the rear surface  28  of the door  14  by a removable vent cap  40  that attaches to the vent housing  24  by a twist lock formed from a set of interengaging tabs  41  molded into both the vent cap  40  and the inlet port  26 . The vent cap  40  provides an aperture  42  aligning with the opening of the inlet port  26  and the aperture  42  is covered by a grating  44  so as to deflect water and food particles away from the passageway of the vent housing  24 . 
     The vent cap  40  also provides a rear facing valve seat ring  46  extending into the inlet port  26 . This valve seat ring  46  cooperates with a valve plate  48  removably attached within the inlet port  26  to hinge about a hinge axis  51 . The hinge axis  51  is located beneath the valve plate  48  in a horizontal plane and is parallel to the front surface  20  and rear surface  28 . 
     When the valve plate  48  is in a closed position as shown in  FIG. 4 , a rubber disk  50  forming the inner surface of the valve plate  48  abuts the edge of the valve seat ring  46  blocking the flow of moist air  22  into the vent passageway and providing a barrier against sound  52 . The rubber disk  50  is supported from front and its side removed from the vent cap  40  by a support disk  54  of slightly smaller diameter than the rubber disk  50  so that the peripheral edge of the rubber disk  50  extends in cantilevered fashion from the peripheral edge of the support disk  54  so as to flex to accommodate slight irregularities in the valve seat ring  46  of the vent cap  40 . 
     Referring now to  FIG. 3 , the support disk  54  of the valve plate  48  includes four hooked tabs  56  extending through corresponding holes in the rubber disk  50 . The rubber disk  50  may be stretched to fit over the hooked tabs and thereby retained against the support disk  54  by the hooks on the hooked tabs  56 . Sizes of the openings  58  in the rubber disk  50  are relatively small being typically substantially less than 1/10th the total area of the rubber disk  50 . Accordingly, as shown in  FIG. 4 , the rubber disk  50  covers the majority and the center of the support disk  54  providing improved sound absorption when the valve plate  48  is closed in comparison to systems which use an annular rubber gasket. Using a substantially continuous rubber disk  50  also provides a cost savings by eliminating the need for a thicker support disk  54  for sound absorption and by making use of the center portions of the rubber disk  50  that might otherwise be removed and discarded in the fabrication of a washer shape. 
     Referring now to  FIGS. 2 and 3 , the support disk  54  has downwardly extending legs  60  supporting horizontal and opposed outwardly extending pivot pins  62  defining the hinge axis  51  described above. The support disk  54 , the leg  60 , and the pins  62  may be constructed of a material, such as injection moldable thermoplastic, providing sufficient flexibility so that the legs  60  may be compressed inward in order for the pins  62  to snap into corresponding pivot sockets  64  molded in the interior of the housing  24  adjacent to the inlet port  26 . The sockets  64  are blind, that is, they do not lead from the inside of the vent housing  24  to the outside of the vent housing  24 , and therefore the sockets  64  provide no passage for water or moisture splashing into the vent housing  24  to leak into the door  14 . Eliminating the need for the shaft supporting the valve plate  48  to pass wholly through the vent housing  24  simplifies single piece injection molding of the vent housing  24 , improves the integrity of the vent housing  24 , and reduces resistance of valve plate  48  to movement about the hinge axis  51  by allowing a small contact area between the pins  62  and sockets  64 . 
     The present invention also contemplates an alternate embodiment in which one or more metal pins (not shown) may be pressed into through holes aligned with but replacing the sockets  64  and serving as an axle for the valve plate  48 . As before, the advantages of being able to produce a single piece molding of the vent housing  24 , of limiting the path of water leakage, and of avoiding the excess resistance of a rotating drive shaft may be obtained. 
     Referring now to  FIGS. 4 and 5 , actuation of the valve plate  48  is accomplished without external access to a supporting shaft of the valve plate  48  by a cam drive mechanism. As mentioned above, the operator  32  of the wax motor  34  may extend into the vent housing  24  through bore  30 . The end of the operator  32  has a ball tip  70  that engages a cam  72  extending from the side of the support disk  54  removed from the vent cap  40 . The cam  72  provides actuation surfaces that form a Z-shaped channel capturing the ball tip  70  and thus allowing opening and closing of the valve plate  48  with extension and retraction of the operator  32  by the wax motor  34 . The ball tip  70  may include a hook (not shown) to provide improved engagement with the cam  72  as will be understood to those of ordinary skill in the art. 
     Generally, the extension axis  74  of the operator  32  is parallel to the hinge axis  51  with the ball tip  70  of the operator  32  positioned closely to the hinge axis  51 . This produces an extremely compact mechanism and one that is desirably sensitive to small motions of the operator  32 . Yet the range of travel of the operator  32  of a wax motor  34  can vary over time, so capture of the ball tip  70  by the cam  72  requires an accommodation of assembly tolerance and over travel of the operator  32 . 
     Referring now to  FIG. 6 , this accommodation is provided by creating over travel and under travel portions of the cam  72 . When the ball tip  70  is in its further extent from the wax motor (to the left in  FIG. 6   a ), it is in the over travel position  79  and contacts cam surface  76  which extend generally horizontally so that further travel of the ball tip  70  does not provide further torsion or twisting of the valve plate  48  about the hinge axis  51 . In this over travel position  79 , the valve plate  48  is closed against the valve seat ring  46  as shown in  FIG. 4 . Surface  77  may lie on a radius about axis  51  to allow free rotation of valve plate  48  in a closing direction without interference between the ball tip  70  and surface  77 , reflecting the constant radial distance between ball tip  70  and axis  51 . Ultimately, closing of the valve plate  48  is limited by the engagement of the valve plate  48  and the valve seat ring  46 . 
     When the ball tip  70  is retracted somewhat, it moves to an actuation position  82  as shown in  FIG. 6   b , the ball tip  70  now held captive between upper surface  84  and lower cam surface  78  diagonal to the hinge axis  51  and causing an opening or closing of the valve plate  48  with retraction or extension of the ball tip  70 . This actuation position  82  may be relatively short and may be fit easily within the assured operating range of the wax motor  34  during its lifetime or caused by unit-to-unit variation. 
     As shown in  FIG. 6   c , when the ball tip  70  is closest to the wax motor  34 , for example, prior to closure of the valve plate  48  or after opening of the valve plate  48 , it is held captive between surfaces  90  and  92  on its top and bottom sides in an under travel position  86 . The surfaces  90  and  92  are essentially horizontal so that the ball tip  70  may be threaded into engagement with the cam  72  when the wax motor  34  is installed on the housing  24 . Thus, over travel and under travel may be accommodated while maintaining a close coupling between the ball tip  70  and the cam  72 . 
     Referring now to  FIG. 7 , in a second embodiment, the cam  72  may be modified to remove the surfaces  76 ,  84 , and  90  shown in  FIGS. 6   a ,  6   b , and  6   c . As described above, these surfaces are used to allow extension of the ball tip  70  to close the valve plate  48 . Surfaces  78  and  92  which allow the ball tip  70  to open the valve plate  48 , remain in place. As a result, the entire surface of the cam  72  above surfaces  78  and  92  is lies on a constant radius about axis  51  to allow free rotation of valve plate  48  in a closing direction without interference between the ball tip  70  and surface  77   
     Closing of the valve plate  48  is performed in this embodiment by a helical compression spring  94  placed between the rear surface of the support disk  54  and a front surface of the rear wall of the housing  24 . Normally this spring  94  causes the valve plate  48  to close against the valve seat ring  46  absent contact between the ball tip  70  and the cam surfaces  78  or  92 . Moist air  22  of a predetermined pressure (for example, one half inch of water) as selected by varying the force of the spring  94  and the area of the valve plate  48 , will allow the valve plate  48  to swing open independent of the position of the ball tip  70  to relieve surge pressures as required. 
     In the absence of surge pressure, the valve plate  48  may be opened by the ball tip  70  interacting with cam surfaces  78  and  92  as described above. Other methods of biasing the valve plate  48  closed including gravity or other types of springs may also be employed as will be understood to those of ordinary skill in the art. 
     Referring now to  FIG. 8 , an alternative embodiment of the door vent  16  provides both the surge pressure release, described above, and a default open position for the valve plate  48 . This default to an open position allows air to pass through the door vent  16  should the wax motor  34  (described above) be removed or the ball tip  70  and/or its connecting shaft be broken or damaged in such a way as to disengage from the cam  72 . In this way, the risk of suffocation to a child entrapped in a dishwasher that has been abandoned or partially disassembled is reduced. 
     In contrast to the embodiment shown in  FIG. 7  in which compression spring  94  is used to close the valve plate  48 , in the embodiment of  FIG. 8 , a torsion spring  100  is placed about pivot axis  51  so as to provide a clockwise bias  109  to the cam  72  about the hinge axis  51 . The bias provided by torsion spring  100  opens the valve plate  48  absent countervailing force by the ball tip  70  on the cam surface  76  (also shown in  FIGS. 6   a - c ). 
     In this embodiment, the support disk  54  of the valve plate  48  is not rigidly attached to the cam  72 , but may pivot with respect to the cam  72  about a second hinge axis  102  on the cam  72 . A helical compression spring  104  fits between the rear surface of the support disk  54  and the front surface of an extension  106  to the cam  72 , so that the support disk  54  is biased forward toward the valve seat ring  46  in a counter-clockwise direction  108  about hinge axis  102 . 
     Movement of the support disk  54  in the counter-clockwise direction  108  is limited by a stop  110  extending rearward from the support disk  54  to oppose a rear surface of the upward extension  106 , allowing only limited relative travel between the support disk  54  and the cam  72  in a counter-clockwise direction  108 . 
     It will be understood from this description, that removal of the ball tip  70  will cause the cam  72  to move in a clockwise direction under the bias of the torsion spring  100 . This will cause valve plate  48  to open after its forward travel in a counter-clockwise direction  108  under the urging of spring  104  and is stopped by stop  110 . 
     Conversely in normal operation, when the ball tip  70  is fully extended from the wax motor  34 , the cam  72  is rotated in a counter-clockwise direction pressing the valve plate  48  and the rubber disk  50  against the valve seat ring  46  to close the vent. The helical compression spring  104  allows some over-travel of the cam  72  with no adverse effect. 
     In this position, a surge pressure of moist air  22  can nevertheless push against the valve plate  48  causing clockwise rotation against the spring  104  as described previously to open the valve plate  48  without movement of the cam  72 . 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.