Patent Publication Number: US-7909936-B2

Title: Dishwasher final steam rinse method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of dishwashing, and more particularly, to a steam sanitation method for a dishwasher. 
     2. Description of the Related Art 
     Maintaining a high sanitation level in connection with the washing of dishes has been a long standing priority in commercial settings. However, the public has also become particularly concerned with minimizing the presence of germs in the home such that it is increasingly desirable to include sanitation options in domestic dishwashers. Typically, performing a sanitation operation in connection with a domestic dishwasher constitutes controlling a heating element during an overall washing cycle such that the washed dishware will be subject to high temperature washing, drying and sanitizing operations. To further address enhance the degree to which dishware is cleaned, it has also been proposed to introduce steam into a dishwashing tub. Basically, steam has been utilized in dishwashers in order to aid in the removal of food debris from dishware. One such known dishwasher arrangement, as set forth in International Patent Application No. WO 2006/129963, incorporates a dedicated steam generator into the dishwasher, with the steam generator directing steam through pipes into a wash chamber containing the dishware. 
     Although the addition of steam can be advantageous, the requirement for additional components in a domestic dishwasher can add significantly to the manufacturing cost. In addition to the added component costs, the effectiveness of the added use of steam can greatly vary depending on both the manner in which the steam is provided and the time at which the steam is introduced in the overall washing cycle. Based on at least these reasons, it is considered desirable to effectively incorporate steam as part of an overall dishware cleaning strategy in a dishwasher, particularly in connection with a sanitation operation in a dishwasher, while avoiding the costs associated with the need for dedicated steam generating components. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a steam purge and sanitation method for a dishwasher. In general, the dishwasher includes a tub defining a wash chamber, a door movably mounted relative to the tub for selectively sealing the wash chamber, a heating element supported by the tub and exposed to the wash chamber, and a washing assembly for supplying fluid to dishware within the wash chamber. The dishwasher also includes a control panel that allows a consumer to choose between numerous washing cycles and options, including a sanitizing option. 
     In accordance with the invention, it is desired to provide a steam cleaning operation as part of an overall dishwasher cycle, particularly when the sanitize option is selected. When the sanitize option is initiated, a main washing cycle is performed wherein washing fluid is introduced into the tub to a level substantially at or preferably above the heating element, the washing fluid is heated by activation of the heating element, and the heated washing fluid is distributed throughout the wash chamber via the washing assembly. Thereafter, the tub is drained. Preferably, the washing fluid has a minimum temperature of approximately 145° F. This washing cycle may be repeated multiple times, depending on the type of washing cycle selected by the consumer. Next, a purge cycle is actuated, wherein the tub is filled with water, and the water used to flush or purge the washing assembly before the tub is drained. After purging, one or more rinse cycles are actuated, wherein the tub is filled with water, heated by the heating element and utilized to rinse dishware within the wash chamber. Preferably, the rinse water has a minimum temperature of approximately 156° F. In accordance with the invention, during a final rinse cycle, fluid within the tub is partially drained to below the level of the heating element and the heating element is actuated to transform some of the fluid into steam which is dispersed within the wash chamber. After a predetermined period of time, a final drain of the tub occurs. When the heated dry option is selected, the heating element continues to operate for a period of time after the final drain has occurred in order to provide a drying heat to dishware within the dishwasher. If the heated dry option is not selected, the heating element will be deactivated after the steam generation step. 
     With this arrangement, the same heating element effectively utilized for heating the washing fluid, heating rinse water, and drying the dishware is employed to generate the desired steam such that a very cost effective arrangement is established. In addition, by linking the steam generation with the final rinse and possibly the heated dry option, the overall cycle time is not substantially increased and the steam is provided at an effective time in the overall dishwashing cycle. Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an upper right perspective view of a dishwasher utilized in conjunction with the present invention, with a door of the dishwasher being open; 
         FIG. 2  is a front view of a control panel of the dishwasher of  FIG. 1 ; and 
         FIG. 3  is a flowchart illustrating the steam sanitation method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to  FIG. 1 , a dishwasher for use with the present invention is indicated at  10 . As shown, dishwasher  10  includes a tub  12  which is preferably injection molded of plastic or formed of stainless steel so as to include integral bottom, side, rear and top walls  14 - 18  respectively. Within the confines of walls  14 - 18 , tub  12  defines an interior  20  within which soiled kitchenware or dishware is adapted to be placed, such as upon shiftable upper and lower racks (not shown), with the kitchenware being cleaned during a washing operation in a manner widely known in the art. Tub  12  has attached thereto a frontal frame  22  which pivotally supports a door  24  used to create a seal during a washing operation. As shown, door  24  is pivotally supported to frame  22  at a bottom portion  26 . In connection with the washing operation, door  24  is preferably provided with a detergent tray assembly  28  within which a consumer can place liquid or particulate washing detergent for dispensing at predetermined portions of the washing operation. Bottom, side and rear walls  14 - 17  of tub  12 , as well as door  24  define a wash chamber indicated at  30  which is adapted to be filled with fluid for washing dishware. 
     Disposed within wash chamber  30  is a washing assembly generally indicated at  32 . In the preferred embodiment and as illustrated in these figures, washing assembly  32  includes a main housing  34 , and an annular, radial outermost strainer  36 . Extending about a substantial portion of washing assembly  32 , at a position raised above bottom wall  14 , is a heating element  44 . Heating element  44  preferably takes the form of a sheathed, electric resistance-type heating element. In a manner known in the art, washing assembly  32  is adapted to direct washing fluid to at least a lower wash arm  48  and a conduit  52 , which leads to an upper spray arm (not shown). See, for example, U.S. Pat. No. 6,997,193, which is hereby incorporated by reference. 
     As depicted in  FIG. 2 , a control panel  56  for dishwasher  10  is linked to a controller  58  and provides a user with a variety of washing options. More specifically, control panel  56  preferably includes a start/cancel button  60 , a delay programming button  62  and an auto clean button  64 . Additionally, control panel  56  preferably includes a plurality of cycle options, such as heavy wash  66 , normal wash  68 , light wash  70  and rinse only  72 , as well as washing options including high temperature wash  74 , tough scrub  76  and heated dry  78 . In accordance with the present invention, control panel  56  also includes a sanitize option  80  into which the final rinse cycle with steam of the invention is incorporated as will now be described in detail. 
     With reference to  FIG. 3 , upon a user selecting a sanitize cycle through button  80  and pushing start/stop button  60  as indicated at  101 , a washing cycle is performed wherein wash chamber  30  is initially filled with a washing fluid as indicated at step  102  to a level preferably above heating element  44 . The fluid is heated by turning on the wash system and activating heating element  44  at step  103  to circulate the washing fluid over and about heating element  44 . When sanitize option  80  is selected, the fluid in wash chamber  30  is preferably heated to a disinfecting temperature of approximately 145° Fahrenheit (° F.), although lower temperatures could be employed as long as the final rinse target temperatures, as discussed below, are met. Washing assembly  32  is then activated and fluid from tub  12  is distributed throughout wash chamber  30  by wash arm(s)  48  and conduit  52  in a manner known in the art to wash dishware within interior  20  as indicated at step  104 . The washing fluid is then drained from wash chamber  30  at step  105 . As indicated at step  106 , steps  102 - 105  of washing cycle  100  can be repeated if desired, based on the cycle options chosen by the consumer. For example, if heavy wash  66  is selected, steps  102 - 105  may be repeated two or three times. Next, a purge cycle  107  is initiated, wherein wash chamber  30  is filled with water at step  108 , and the water is pumped through wash arm(s)  48  and conduit  52  to flush or purge dishwashing fluid from washing assembly  32  as indicated at step  109 . Once this flushing or purging operation is complete, the pump associated with washing assembly  32  is deactivated and the flushed fluid is drained at  110 . If desired, multiple, short purge cycles can be performed as indicated at  111 . One or more rinse cycles may then be initiated, wherein tub  12  is filled with water to a level substantially at or preferably above heating element  44  at step  112 , heating element  44  is activated to heat the rinse water at step  113 , then the rinse water is pumped through washing assembly  32  to rinse out wash chamber  30  at step  114 . When sanitize option  80  is selected, it is preferred to heat the rinse water to a disinfecting temperature of approximately 156° F. during step  113  for use in rinse step  114 . 
     In accordance with the present invention, it is desired to incorporate a steam generation operation or cycle within a final rinse cycle. Therefore, after rinse step  114 , it is determined whether a final rinse cycle has been entered at  115 . If the overall dishwashing operation calls for multiple rinse cycles, a drain step  116  follows rinse step  114  and the rinse cycle in steps  112 - 116  may be repeated. However, during a final rinse cycle, drain step  116  is performed such that tub  12  is only partially drained in order to lower the rinse water level within tub  12  below a level of heating element  44 . Thereafter, heating element  44  is activated at step  117  for a predetermined period of time and the rinse water remaining in tub  12  is transformed into high-temperature steam at step  118 . During steam generating step  118 , steam interacts with dishware within wash chamber  30 , effectively loosening any hardened soils and disinfecting the dishware. After a predetermined time period, a final drain of tub  12  is initiated to drain tub  12  of remaining liquid as indicated at  119 . At this point, if heated dry option  78  or sanitizing option  80  has been selected, heating element  44  is activated at step  120  after a predetermined drainage period of time. Therefore, heating element  44  continues to be actuated after steam generating step  118  to heat air within wash chamber  30  and expedite drying of dishware therein at step  120  before the overall cycle ends at step  121 . Again, the final rinse with steam generation cycle is preferably, automatically performed when a user selects sanitize option  80 , and steam generated at step  117  has a temperature effective to disinfect dishware within wash chamber  30 . 
     Based on the above, it should be readily apparent that heating element  44  is advantageously utilized in accordance with the invention for each of the washing, rinsing, steam generating and heat drying operations. Therefore, additional, dedicated steam generating components are not required. For this reason, dishwashers already on the market or in production may be readily programmed in accordance with the method described above and the invention can be implemented in an extremely cost effective manner. In addition, given that the steam generation utilizes fluid already heated during the final rinse step, less energy is need to transform fluids within tub  12  into steam, and energy is conserved. Furthermore, with the steam generation being performed at the end of the final rinse cycle, there will be no more, relatively cool water introduced into tub  12  and circulated over heating element  44  such that there is no risk of thermally shocking heating element  44  and heating element  44  does not have to be allowed to cool before further operations are performed. Thus, the steam generation step can be added without any major modifications or substantial increase in overall cycle time. 
     Although described with reference to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, although not discussed, the number of purge and rinse cycles prior to the steam cycle may be varied without departing from the invention. Additionally, various pre-wash and pre-rinse cycles may be implemented prior to the washing cycle without departing from the invention. Furthermore, it should be recognized that a user option for steam generation could be directly added on control panel  56  such that the steam generation can be used in connection with other, non-sanitize cycles. Finally, although the invention has been described for use in a more conventional dishwasher arrangement including a pivoting front door, the invention can be employed in a wide range of dishwashers, including drawer dishwashers. In general, the invention is only intended to be limited by the scope of the following claims.