Abstract:
A vent system for a dishwasher provides a mixing chamber receiving high humidity air from a downdraft dishwasher vent system or the like and mixes this air with dry air before discharging it from the dishwasher to reduce the humidity of the discharged air moderating condensation problems

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     CROSS REFERENCE TO RELATED APPLICATION 
     BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to automatic dishwashing machines (dishwashers) and in particular to a dishwasher providing improved dish drying. 
         [0002]    Dishwashers, such as those found in many homes, provide a wash cavity holding one or more racks into which eating utensils and cookware may be placed for cleaning. The wash cavity may be sealed by a door opening at the front of the wash cavity 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 wash cavity and used to wash items placed in the racks. Upon completion of the washing cycle, a drying cycle is initiated during which water is drained from the wash cavity and moist air is discharged through a vent. Cool air, pulled by convection or a fan into the chamber through a lower vent, dries the heated dishes. 
         [0003]    Recent dishwasher designs may employ a one-piece tub, for example of stainless steel, that defines the wash cavity and, when closed by the door, is sealed from communication with the outside air. The sealed nature of this chamber makes the promotion of air circulation for proper venting particularly difficult. 
         [0004]    Co-pending U.S. application Ser. No. 11/108,525, entitled: “Dishwasher With Counter-Convection Air Flow”, assigned to the same assignee as the present invention, and hereby incorporated by reference, describes a downdraft venting system in which low-turbulence down-flow is created within the wash cavity to more efficiently remove moisture laden air from the wash cavity and dishes. In one embodiment, a relatively small fan placed at the top of the wash cavity pushes air out of existing vents near the bottom of the washing machine door. 
         [0005]    The greater efficiency of this design in removing moisture from the wash cavity and contained dishes can create condensation problems when high humidity air is exhausted from the dishwasher and contacts cool surfaces, such as a metal-faced dishwasher door. This condensation may cause the undesirable collection of water on surfaces near the vent outlet. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides an improved vent system for a dishwasher that may accommodate high humidity air such as produced by downdraft venting systems. The vent provides a mixing chamber that mixes the humid air from the washing chamber with drier outside air before discharging it from the dishwasher. This cooling, and reduction of humidity by this cooling and dilution, greatly minimizes condensation problems. A dual fan embodiment also may be used for low drying efficiency systems where it is desired to reduce external condensation. 
         [0007]    Specifically, the present invention provides a dishwasher with a venting system having a first opening leading into an upper area of a wash cavity and a second opening leading from a lower area of the wash cavity. A mixing chamber has a first inlet for receiving moist air from the second opening, a second inlet for receiving drier air from outside of the wash cavity, and an outlet displaced from the second inlet for venting the moist air to outside of the wash cavity. A fan communicates with one of the mixing chamber and the wash cavity to move air through the first and second inlets to be mixed within the mixing chamber and exhausted through the outlet. Air drawn through the first inlet, in turn, pulls air through the first opening leading into the wash cavity to flush moist air out of the wash cavity in a downward direction. 
         [0008]    Thus it is one feature of at least one embodiment of the invention to provide a vent system that better accommodates high humidity air exhausted from high-efficiency downdraft venting systems. 
         [0009]    In one embodiment of the invention, a first fan communicates with one of the mixing chamber and the wash cavity to move the moist air from the wash cavity into the first inlet of the mixing chamber, and a second fan communicates with the mixing chamber and operates independently of the first fan to move drier air into the mixing chamber via the second inlet to mix with the moist air prior to exit of the moist air from the outlet. 
         [0010]    It is thus one feature of at least one embodiment of the invention to blow dry air directly into the mixing chamber with a second fan that is independent of a first fan venting the wash cavity to provide improved air mixing. 
         [0011]    The mixing chamber may include a reservoir for capturing water condensing from the moist air and a control communicating with the first and second fan to operate the second fan when the first fan is not operating to dry the water collected in the reservoir. 
         [0012]    It is thus one feature of at least one embodiment of the invention to condense water within the mixing chamber and then to operate the second fan to disperse this condensed moisture over a period extending beyond the time of the drying cycle. 
         [0013]    The first fan may communicate with the wash cavity to receive dry air from outside the wash cavity and to blow the dry air into the wash cavity. Likewise, the second fan may communicate with the mixing chamber to receive dry air from outside the wash cavity and to blow drier air into the mixing chamber. 
         [0014]    It is thus a feature of at least one embodiment of the invention to position the fans removed from the path of humid air flow, preventing corrosion or damage to the fans or the need for moisture resistant fans and fan components. 
         [0015]    The second fan may be a brushless DC motor muffin fan. 
         [0016]    It is thus another feature of at least one embodiment of the invention to make use of low-voltage, low power, quiet fans, of a type used for cooling in the computer industry, to reduce noise, power consumption, and risk of electrical shock in the dishwasher environment. 
         [0017]    The second fan is displaced upward on the mixing chamber to be removed from a path of condensation draining down walls of the mixing chamber. 
         [0018]    It is thus one feature of at least one embodiment of the invention to permit the use of water intolerant fans in a condensing system. 
         [0019]    The first inlet in the mixing chamber may connect with a flow separator communicating through a wall of the wash chamber and also accepting a water line, wherein water from the water line also communicates through the flow separator into the wash chamber. The flow separator operates to prevent water from passing into the mixing chamber from the water line. 
         [0020]    It is thus a feature of at least one embodiment of the invention to avoid the need to cut additional apertures in the walls of the wash cavity near the bottom of the tub, and thus the need for additional components and seals in a downdraft type system. 
         [0021]    The mixing chamber may provide for a substantially horizontal airflow. 
         [0022]    It is thus a feature of at least one embodiment of the invention to provide a simple method for producing a high surface area reservoir that may promote the evaporation of water contained in the reservoir. 
         [0023]    The mixing chamber may be positioned in a wall of the dishwasher or in a door of the dishwasher. 
         [0024]    It is thus a feature of at least one embodiment of the invention to provide a vent system that may be easily incorporated into a variety of dishwasher designs. 
         [0025]    The invention may include a watertight tub defining the wash cavity for receiving dishes to be sprayed with water for washing, and the tub may be a single piece stainless steel tub. 
         [0026]    It is thus a feature of at least one embodiment of the invention to provide a venting system particularly suited to sealed stainless steel tubs which present a venting problem and a condensation problem if aggressively vented. 
         [0027]    These particular features 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 
         [0028]      FIG. 1  is a perspective view of a wash cavity of a dishwasher showing the dishwasher housing and door in phantom and further showing the position of a first and second vent of the present invention; 
           [0029]      FIG. 2  is a perspective view in partial phantom of the lower vent of  FIG. 1  showing a flow separator receiving air from the wash cavity and a mixing chamber mixing fresh air with the moist air from the wash cavity; 
           [0030]      FIG. 3  is an elevational cross-section of the flow separator of  FIG. 2  showing a U-shaped channel providing for separation of water and airflow through a single aperture leading to the wash cavity; 
           [0031]      FIG. 4  is an elevational schematic representation of the dishwasher of  FIG. 1  showing humidity concentrations inside and outside the wash cavity as managed by the present invention under the control of a controller executing a timing cycle; 
           [0032]      FIG. 5  is a perspective view of a dishwasher, with the door in partial phantom, showing an alternative placement of the invention within the door; 
           [0033]      FIG. 6  is a schematic representation of an alternative embodiment of the invention using a single fan to draw air through the mixing chamber and/or the wash cavity; and 
           [0034]      FIG. 7  is a figure similar to that of  FIG. 6  of an alternative embodiment of the invention using a single fan to push air through the mixing chamber and/or the wash cavity. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]    Referring now to  FIG. 1 , a dishwasher  10  may include a wash cavity  12  into which dishes and cutlery may be placed for washing on racks (not shown). The wash cavity  12  may be defined by a generally rectangular tub  14 , for example, of drawn stainless steel, providing a single piece sealable volume open at the front to be covered by a door  16  that seals against a front lip of the tub  14 . 
         [0036]    An opening  19  may be cut in the tub  14 , for example, at a right rear edge of the top of the tub  14 , for the attachment of a vent unit  18 . The vent unit  18  includes a fan and an electrically actuable door (not shown) operating together to allow dry air  20  from outside of the wash cavity  12  to be blown into the tub  14  to cause a downward evacuation of the humid air within the tub  14  at the conclusion of the washing cycle when drying of the dishes is desired. The fan in the vent unit  18  may be so-called “muffin fan” using a low voltage brushless DC motor with the door protecting the brushless DC motor from exposure to water from inside the tub  14 . A vent unit  18  suitable for this purpose is described in detail in the above cited co-pending application Ser. No. 11/108,525 incorporated by reference. 
         [0037]    A second tub opening  22  may be cut in the lower left wall of the tub  14  allowing the connection of a second vent unit  24 . The second vent unit  24  receives moist air  26  from inside the tub  14  and conducts it via a conduit  28  down a side of the tub  14  to a mixing chamber  30  positioned below the tub  14 . The mixing chamber  30  provides a generally horizontal tube of rectangular cross section extending from the front to the back of the tub  14 . At the front of the tub  14 , the mixing chamber provides an exhaust port  32  underneath the door  16  for exhausting reduced humidity air  36 . 
         [0038]    The tub opening  22  connects to the conduit  28  by means of a flow separator  34  which also receives a source of water controlled by a solenoid valve (not shown) through hose  37 . The water from the hose  37  is introduced into the tub  14  during a wash cycle for washing of the dishes and is controlled and dispersed within the wash cavity  12  according to methods well known in the art. 
         [0039]    Referring now to  FIG. 2 , the moist air  26  from inside the tub  14  received from the tub opening  22  enters the flow separator  34  and is conducted downward through the conduit  28  which extends into the mixing chamber  30  passing through an upper wall of the mixing chamber  30 . The end of the conduit  28  within the mixing chamber  30  has an opening  40  centered within the cross-section of the mixing chamber  30  and directed toward the exhaust port  32  to direct the moist air  26  exiting the conduit  28  toward the exhaust port  32 . The conduit  28  is sealed at its point of entry into the mixing chamber  30  to prevent the escape of moist air  26  at the connection between the conduit  28  and the mixing chamber  30 . 
         [0040]    A second fan  44  of similar construction to the fan of vent unit  18 , and being in the preferred embodiment a second brushless DC motor fan, is attached at an intake port  76  at an end of the mixing chamber opposite the exhaust port  32 . The use of a brushless DC motor allows the fan  44  to operate on a low-voltage that may be readily routed in the environment of the dishwasher with considerable safety and allows positioning of the fan motor within the hub of the fan to provide an extremely compact package. 
         [0041]    The fan  44  is positioned to draw dry air  20  from beneath the tub  14  into the mixing chamber  30  through the intake port  76  and to direct that dry air along the axis of the mixing chamber toward the exhaust port  32 . Downstream from the opening  40  of the conduit  28  is a mixing region at which the moist air  26  and dry air  20  mix. Airflow from the fan  44  serves to draw the moist air  26  out of the conduit  28  into turbulent mixing with the dry air  20 . This mixing cools the moist air  26  causing some condensation within the mixing chamber  30  and diluting the moist air  26  to lower its average humidity and thus its dew point, a measure of its propensity to cause condensation outside of the dishwasher  10  on the metallic surfaces of the door  16  or elsewhere in the kitchen environment. The reduced humidity air  36  exits the exhaust port  32 . 
         [0042]    A lower wall of the mixing chamber  30  beneath the conduit  28  provides a shallow reservoir  42  in the form of a depression that may collect water condensing out of the moist air  26  while the moist air  26  is within the conduit  28  and the mixing chamber  30 . The fan  44  may be positioned on a top surface of the mixing chamber  30  to be removed from the water in the reservoir  42  and from any drip path of condensation on the inner walls of the mixing chamber  30 . 
         [0043]    Referring also now to  FIG. 3 , the flow separator  34  may receive a water hose  37  at a hose fitting  46  leading to a downwardly curved diverter section  48  directing water  50  received horizontally from the hose  37  downward through a chimney  52 . The chimney  52  connects at its lower end to a base  51  of the flow separator  34 , the base covering and communicating with the tub opening  22  so that the water  50  within the base may pass into the tub  14 . A bifurcation in the upper end of the chimney  52  provides a second anti-siphon chimney  54  having a small vent  55  admitting dry air  20  when water  50  is flowing downward in the chimney  52  so as to form a siphon break preventing the siphoning of water out of the flow separator  34  into the hose  37  (and then into the water supply) in the event of a possible decrease in water pressure on the hose  37 . 
         [0044]    The base  51  also communicates with a third chimney  56  leading upward to join with conduit  28 . The third chimney provides an upward path from the tub opening  22  that may conduct moist air  26  through the tub opening  22  (when water is not flowing through the tub opening  22 ) and out of the tub  14 . The small vent  55  in the second anti-siphon chimney  54  is small enough that no significant amounts of moist air  26  will flow out of the small vent  55 . 
         [0045]    Water flowing into the hose fitting  46  is sufficiently restricted in comparison to the size of the aperture  33  so that that water  50  will never rise sufficiently within the base to enter the chimney  56  and thus flow through the conduit  28 . In this way, the flow separator  34  allows a dual use of tub opening  22  at different times: first, for admission of water  50  during washing cycle and, second, for the extraction of moist air  26  during a drying cycle. 
         [0046]    Referring now to  FIG. 4 , the dishwasher may include a cycle timer  60  of a type known in the art communicating with a fan  62  of the vent unit  18  and the fan  44  on the mixing chamber  30  to provide electrical signals switching these fans on and off at different times. During a first wash stage  64 , the cycle timer  60  may provide a signal to a flapper valve (not shown) within the vent unit  18  closing that flapper valve to protect the fan  62  from moisture. At this time, fans  62  and  44  are turned off and a solenoid valve communicating with the hose  37  of  FIG. 2  is opened to allow water to flow into the tub  14 . 
         [0047]    At the conclusion of the wash stage  64 , a dish dry stage  66  is begun and the cycle timer stops water flow through the hose  37 , opens the flapper valve and turns fans  62  and  44  on to flush the wash cavity  12  with dry air  20  and to mix dry air  20  with the exhausting moist air  26  in the mixing chamber  30 . During the dish dry stage  66 , fan  62  introduces dry air  20  into the wash cavity  12  at a low velocity that preferentially exhausts the high humidity air from the bottom of the wash cavity  12  downward through the conduit  28  into the mixing chamber  30  without disruption of the stratification of moisture within the wash cavity  12 . 
         [0048]    The mixing chamber  30  accommodates the high moisture content of the air exhausted from the wash cavity  12  by dilution and condensation as described above. 
         [0049]    An evaporator dry stage  70  occurs after the dishes are dry and fan  62  is turned off. During the evaporator dry stage  70 , the fan  44  may optionally remain on. No significant amount of moist air  26  enters the mixing chamber  30 , but the dry air  20  is used to provide for evaporation of moisture collected in the reservoir  42 , drying the reservoir  42  for future use. 
         [0050]    Referring now to  FIG. 5 , the present invention provides a vent system that may be flexibly located within the door  16  of the dishwasher  10 . In this case, the vent unit  18  is positioned high within the door  16  to communicate through an opening in the inner surface of the door  16  with an upper portion of the wash cavity  12 . Similarly, the conduit  28  is positioned low in the door  16  to communicate through an opening in the inner surface of the door  16  with a lower portion of the wash cavity  12 . The horizontal mixing chamber  30  is placed along the bottom of the door  15  extending from right to left. This positioning reduces wiring harness lengths. 
         [0051]    Referring now to  FIG. 6 , in an alternative embodiment, fan  44  may be removed leaving intake port  76  open to admit dry air  20  into the mixing chamber  30 . A moisture tolerant fan  78  may then be placed at the exhaust port  32  to draw the mixed moist air  26  and dry air  20  together out of the exhaust port  32 . A similar mixing and condensing process may occur however with less baffling of the noise of the fan  78 . With such an approach and the proper sizing of the tub opening  22 , conduit  28 , opening  40  and intake port  76 , it may be possible to remove the fan  62  to provide a single fan system achieving the benefits of downdraft venting. 
         [0052]    Referring now to  FIG. 7 , in yet an alternative embodiment, a fan  80  may be placed to both introduce dry air  20  into the mixing chamber  30  at intake port  76 , and by means of a duct  82 , to also conduct dry air  20  through an upper opening  84  in the wash cavity  12 . Like the embodiment of  FIG. 6 , a single fan may thus provide the benefits of downdraft venting together with the humidity reducing effect of the mixing chamber  30 . Unlike the embodiment of  FIG. 6 , the fan  80  need not be moisture tolerant and is removed from exhaust port  32  reducing fan noise. 
         [0053]    In each of the embodiments of  FIGS. 6 and 7 , the fans  78  and  80  may be conventional blowers employing either DC or AC motors. 
         [0054]    The terms moist air and dry air as used herein are not intended to convey any absolute level of humidity but to broadly characterize the air within a dishwasher after washing dishes and the normal level of humidity of air outside of the dishwasher. 
         [0055]    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.