Abstract:
A dishwasher having a washing chamber includes at least one prewash cycle for removing loose soil from associated kitchenware, a steam cycle instituted after the at least one prewash cycle for softening soil not removed in the at least one prewash cycle, a main wash cycle commenced after the steam cycle cleaning the associated kitchenware, and at least one rinse cycle commenced subsequent to the main wash cycle for rinsing detergent and remaining soil off of the associated kitchenware. The dishwasher includes a housing having a wash chamber that receives associated kitchenware therein and a controller for selectively controlling water supply from an associated source, water removal to an associated drain, and energization of a heating element contained in the wash chamber. A wash routine having a pulse routine periodically introduces wash fluid into the wash chamber to wet an inner surface of the chamber and the associated kitchenware received therein and a steam routine in which the wash fluid is retained in the wash chamber and the heating element remains energized to generate steam in the wash chamber environment by droplets of the wash fluid contacting exposed surface portions of the heating element.

Description:
BACKGROUND OF THE DISCLOSURE 
       [0001]    The present disclosure is generally directed toward a dishwasher and more particularly a dishwasher that runs a steam algorithm, preferably as a prewash, and a method of removing adhered food soils on kitchenware. 
         [0002]    Conventional dishwasher routines include various wash cycles, each of which achieves a specific function. A wash routine typically initiates with at least one pre-wash cycle. The pre-wash cycle performs several functions: (1) flushing water from the fluid delivery lines; (2) circulating wash fluid at a pressure which removes loose soil from kitchenware; and, (3) raising a temperature of the wash chamber by heating the wash fluid delivered thereto. The pre-wash cycle is followed by a main wash cycle, which is dedicated toward mixing detergent with wash fluid for cleaning the kitchenware. At least one rinse cycle rinses detergent residue from the kitchenware while also sanitizing the kitchenware with wash fluid delivered at a high temperature. 
         [0003]    A problem associated with conventional systems is that there is no method to soften hardened or carbonized food soils that are ineffectively removed from kitchenware in the pre-wash cycles. Known embodiments rely on a spray injected into a dishwasher chamber immediately after the pre-wash cycle to release these adhered or stuck-on food soils. The spray provides humidity for softening these soils and in combination with enzymatic activity of the spray, aids in removing the soils. 
         [0004]    A need exists for creating and maintaining a chamber environment in which steam can be effectively generated without any hardware changes or additions to presently manufactured dishwashers. 
       SUMMARY OF THE DISCLOSURE 
       [0005]    A first exemplary method of the present disclosure for a dishwasher having a washing chamber includes at least one prewash cycle for removing loose soil from associated kitchenware. A steam cycle is instituted after the at least one prewash cycle for softening soil not removed in the at least one prewash cycle. Subsequently, a main wash cycle is commenced after the steam cycle for cleaning the associated kitchenware. At least one rinse cycle then rinses detergent and remaining soil off of the associated kitchenware. 
         [0006]    An exemplary embodiment of the present disclosure includes a dishwasher having a housing with a wash chamber that receives associated kitchenware therein and a controller for selectively controlling water supply from an associated source, water removal to an associated drain, and energization of a heating element. The controller is configured to implement (i) a wash routine introducing wash fluid into the wash chamber to wet an inner surface of the chamber and the associated kitchenware received therein and (ii) a steam routine in which the wash fluid is retained in the wash chamber and the heating element is energized to generate steam in the wash chamber environment by droplets of the wash fluid contacting exposed hot surface portions of the heating element. 
         [0007]    Another exemplary method of the present disclosure includes cycles for removing food or soil from kitchenware supported on at least one rack in a dishwasher chamber. The method includes removing loose soil from the kitchenware in at least one prewash cycle, which includes the stages of pumping heated wash fluid in the wash chamber, and draining the wash fluid from the wash chamber until at least a portion of a heating element is exposed, and softening soil not removed from the kitchenware in a steam cycle. The steam cycle includes the stages of spraying wash fluid on inner surfaces of the wash chamber and on the associated kitchenware while energizing the heating element to a temperature of at least 100° C. (212° F.), and, keeping the heating element energized for at least a remainder of the steam cycle. A remainder of a main wash cycle includes washing the kitchenware with detergent and rinsing the detergent and remaining soil from the kitchenware. 
         [0008]    A primary benefit of the disclosure relates to providing a steam cycle option to a dishwasher. 
         [0009]    Another advantage is that the steam cycle can be incorporated into a dishwasher without adding or changing hardware or components. 
         [0010]    Still another benefit is the ability to heat certain types of soils on kitchenware including, for example, improving lipstick removal and/or softening difficult-to-remove soils. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a partial elevational view of a dishwasher according to an exemplary embodiment of the present disclosure. 
           [0012]      FIG. 2  is a flow-chart illustrating a wash routine provided by a dishwasher of the present disclosure. 
           [0013]      FIG. 3  is a chart illustrating comparative plots of temperature of the heating element and wattage of the heating element as it is energized over time during the pre-wash and steam cycles. 
           [0014]      FIG. 4  is a plot showing temperature of the heating element during a steam cycle of approximately five minute duration. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    For purposes of the present disclosure, the term “vaporization” is the phase transition (of a wash fluid) from a liquid phase to a gas phase. The “vaporization” described herein can be of the boiling type for its rapid occurrence. Vaporization can also be of the evaporation type, where the wash fluid repeatedly evaporates and condenses to visible droplets over a slower period. The vaporization occurs in a closed dishwasher chamber, and as the temperature of a heating element and the environment rises, the pressure similarly rises until the temperature and the pressure reestablish equilibrium. Likewise, for purposes of the present disclosure, the term “condensation” is the phase change (of the wash fluid) from the gaseous to the condensate (i.e., liquid) form. 
         [0016]    The present disclosure is directed toward a method and a dishwasher implementing such method for softening certain soils not quite loose enough for easy removal in pre-wash or main wash cycles. An exemplary embodiment of a dishwasher  100  according to the present disclosure is provided in  FIG. 1 . The dishwasher  100  includes a housing  102  that surrounds a chamber  104  containing racks  106  for supporting kitchenware (not shown) deposited for washing therein. A door  108  or a drawer provides access to the chamber  104 . A sump system (not shown) communicates with floor of the chamber. This sump system filters and/or disposes of the wash fluid and soil from the dishwasher into a drainage system. A fluid circulation system (not shown) includes delivery conduits (fixed and/or rotating arms) that deliver pressurized wash fluid, which distributes and sprays the wash fluid into the chamber. The dishwasher also includes a heater or heating element  110 , which in the embodiments herein described is a conventional commercially available sheathed or tubular resistive electric heating element used in household automatic dishwashers for heating the interior of the dishwasher chamber and the wash fluid that is sprayed throughout the chamber. 
         [0017]    The heating element  110  is situated within the chamber  104  at a position that optimizes the amount of liquid droplets that can fall onto an exposed surface of the heating element for reasons which will become more apparent below. In the preferred embodiment, the heating element  110  is generally centrally situated in the chamber adjacent a bottom (i.e., floor) surface. Preferably, the heating element  110  is situated above the sump system and other components so that droplets falling from the racks and kitchenware supported above the heating element land directly on the exposed top and side surfaces of the heating element. 
         [0018]    A thermistor  112  and other dishwasher components, such as, for example, a turbidity sensor and/other sensors, can also be included in the wash chamber, and preferably in a sump area of the wash chamber. The thermistor monitors a temperature of wash fluid circulating in the wash chamber for purposes of energizing and deenergizing the heating element, actuating a release of a detergent from a dispenser, or initiating and/or terminating a cycle. For purposes of the present disclosure, temperatures of the heating element  110  are not monitored and maintained for energization and de-energization of the heating element  110  in the steam cycle disclosed herein; rather, wattage and voltage of the heating element and sheath is known to establish a temperature of up to about 600° F. (315° C.). No feedback system is required for achieving the steam cycle herein because the heating element  110  utilized with the present dishwasher preferably reaches a temperature of at least 100° C. (212° F.) under one minute duration after energization of the heating element  110 . 
         [0019]    The controller  114  (e.g., a microprocessor or microcomputer) effectively operates various components of the dishwasher. The controller works in conjunction with a memory (not shown), a display (not shown), thermistor  112  and a user interface (not shown) all coupled thereto. The memory stores instructions, calibrations and constants, etc., and other information necessary to complete a wash routine. The user interface provides a means for an operator to enter instructions, variables, and selections for activation of a wash routine. The controller operates components of the fluid circulation assembly and controls energization of the heating element  110 . The controller also controls activation of caps to dispenser cups (singular and multiple-cup dispensers) and valves to a bulk dispenser  116  for release of detergent into the chamber during different stages of the wash routine. 
         [0020]    The present disclosure provides a means to soften adhered food soils or other difficult-to-remove soils from kitchenware without subjecting the kitchenware to unnecessary scouring, greater wash fluid pressures, or wash fluid at higher temperatures. In the present manner, the kitchenware is exposed to wash fluid droplets and vaporized wash fluid for a duration of time. The heating element  110  is energized to reach high temperatures to assist in a steam cycle that is achieved in the dishwasher without adding further components. 
         [0021]      FIG. 2  shows a method of the disclosure, which is representative of a wash routine incorporated in a program of the dishwasher. The wash routine starts at step S 200 . An operator initiates actuation of the present routine, for example, upon a user-input into an interface of the dishwasher. At least one pre-wash cycle (step S 202 ) introduces wash fluid into the dishwasher chamber. This wash fluid is delivered to and sprayed about the chamber by means of a fluid circulation system (e.g., a spray arm(s) that may or may not rotate or move in the chamber). The wash fluid first introduced to the dishwasher chamber may be cool in temperature because of the standing water in the fluid delivery conduits. However, a heater (“heating element”) is energized preceding commencement of or during the at least one pre-wash cycle to raise the wash fluid temperature 
         [0022]      FIG. 3  is a chart illustrating comparative plots of (i) temperature of the heating element and (ii) wattage of the heating element as it is energized (i.e., powered) over time during the pre-wash S 202  and later discussed cycles. As illustrated, the a steady plot shows the heating element energized to about 800 Watts. The energized heating element causes the temperature of the heating element to climb over the same period, as is shown with the steady increase in the temperature plot to about 125° F. (52° C.). The rise in temperature occurs during the pre-wash cycle S 202 . 
         [0023]    During the at least one pre-wash cycle S 202 , a detergent is released or dosed at least once into the dishwasher chamber (step S 204 ). The fluid circulation system provides for the wash fluid to come into contact with the detergent and distribute the detergent on the kitchenware. The detergent can be contained and released from a detergent cup or container in the dishwasher, or alternatively from a bulk dispenser which stores larger quantities of liquid or gel detergent for multiple wash cycles. The bulk dispenser provides for multiple releases of detergent during different stages of a wash routine if desired. Each release of detergent may be in a variable amount based on the stage, an algorithm, and/or optional sensor readings. Each amount dispensed need not be identical to other release amounts of detergent at different stages of the wash cycle. The detergent released in the pre-wash cycle S 202 , for example, is the first of at least two detergent releases during the wash routine. Detergent will be released again during the main wash cycle for proper cleansing of the kitchenware. 
         [0024]    The pre-wash cycle(s) S 202  removes loose food soils from the kitchenware by spraying the wash fluid toward the kitchenware at a pulsed, varied, or a constant pressure sufficient to force the loose food soils to detach from the kitchenware surfaces. In the present routine, the at least one pre-wash or combination of pre-wash cycles S 202  run for a preselected duration, for example, of up to approximately 15 minutes. The loose food soil falls to the dishwasher chamber floor, where the wash fluid carries it toward a drain/sump and drainage system. The pre-wash S 202  effectively removes substantially all loose soils so that there is a minimized probability that the loose food soils will remain on the kitchenware until the next cycle in sequence in the wash routine. 
         [0025]    In the present exemplary method, the wash fluid is then at least partially drained (step S 206 ) from the dishwasher chamber to dispose of the soil and other matter removed from the kitchenware in the pre-wash cycle(s) S 202 . At least a portion of the heating element surfaces are exposed. Alternatively, the wash fluid from the pre-wash cycle may be totally removed and a supply of fresh wash fluid may be introduced into the wash chamber sufficient for the ensuing cycle.  FIG. 3  shows rather coincident dips in both plots illustrated for the period in which the wash fluid drains from the chamber at conclusion of the pre-wash cycle S 202 . The heating element de-energizes during the draining period, as is shown by a drop in the wattage to 0 Watts and a simultaneous dip in the temperature. The heating element, however, energizes again as wash fluid is reintroduced into the wash chamber, as is representative in the temperature plot with the steady increase in temperature to between about 120° F. (48° F.) and 130° F. (54° C.) simultaneous to the steady power plot of wattage above 800 W. At approximately the five minute mark, the pump system that circulates the wash fluid deactivates, but the heating element remains energized. The arc in the power plot is representative of the steam cycle which is preferably a part of the prewash option, wherein the wash fluid droplets fall onto the hot, exposed surface of the energized heating element and thus generate steam. 
         [0026]    The steam cycle S 208  is directed toward softening the harder food soils not removed in the foregoing pre-wash cycle(s)  202 . The steam cycle provides a chamber environment in which vaporized water molecules interact with the more-difficult-to-remove soils over a duration to essentially loosen the soils. For example, food soils such as baked-on or burned-on food, or lip-stick on glassware, are soils of the type that are more effectively treated by the steam cycle. 
         [0027]      FIG. 3  shows that at a power of approximately 800 Watts, the temperature of the sheath of the heating element will climb to above 100° C. within a short period of energization of the heating element.  FIG. 4  is a graph that plots sheath temperature relative to time and illustrates a rise in temperature (degree-Fahrenheit) over a steam cycle of approximately five minute duration. The plot illustrates that the sheath reaches a boiling temperature of 212° F. (100° C.) within a first minute of the steam cycle S 208 . Steam is first observed when the sheath reaches boiling temperatures. Therefore, steam will be observed throughout the remainder of the steam cycle S 208  because the heating element remains energized. The plot illustrates that the sheath temperature of the heating element continues to climb in temperature for the duration of the cycle as the heating element remains energized. A power of 800 Watts is known to raise a temperature of a heating element to approximately 600° F. (315° C.). There is no proactive monitoring and controlling of the temperatures of the heating element for the steam cycle; rather, the energization periods of the heating element are controlled at predetermined times based on the power characteristics of the heating element utilized in the dishwasher in the preferred arrangement of the present disclosure. 
         [0028]    The first preselected period S 210  of the steam cycle S 208  effectively wets the surfaces of the kitchenware, racks, etc., so that they are covered with droplets of water. The pump system that circulates wash fluid to wet the foregoing surfaces is deactivated (i.e., shut off (step S 212 ) while the heating element remains energized. Deactivation of the pump system causes a sufficient area of the heating element to become exposed. In one embodiment, a sufficient portion of the wash fluid retained in the sump area of the chamber floor is simultaneously drained (step S 212 ) and a sufficient area of the heating element is exposed. This step S 212  ensures that at least a portion of the heating element surface is exposed for the second, steam period (step S 214 ) and that there is sufficient wash fluid in the chamber to be vaporized. 
         [0029]    In the second period S 214  of the steam cycle S 208 , circulation of the wash fluid is preferably terminated. The second period S 214  furthermore includes energizing and raising a temperature of the sheath of the heating element to at least 100° C. (212° F.) for a predetermined duration after the fluid circulation system ceases to circulate wash fluid, for example, on the order of approximately five minutes. To maintain the temperature, the heating element preferably heats the wash chamber during the entirety, or substantially the entirety, of the second period S 214 . The heating element preferably remains energized such that the temperature of the sheath continues to rise above at least 100° C. (212° F.) for about four minutes to about five minutes in one exemplary implementation of the steam cycle. 
         [0030]    The temperature of the heating element continues to remain at a temperature that vaporizes water and/or wash fluid as the heating element remains energized. The vaporized wash fluid (steam) forms a fog of liquid particles formed by (finely divided) condensation or a blanket of steam. Droplets of the wash fluid dispersed on the kitchenware and throughout the chamber collect, coalesce, or fall when the droplet becomes too large. At least some of the water droplets drop onto the exposed heating element surface. In the present steam cycle S 208 , however, the heating element is energized during the second period S 214 , so the droplets of wash fluid that fall onto the heated, exposed heating element surfaces “boil”. The boiling has an effect of causing the droplets of wash fluid to rapidly vaporize. The vaporized wash fluid becomes wet steam, i.e., steam containing intermingled moisture. The fine liquid particles of the steam interact with the hardened soils to loosen the matter from the kitchenware. 
         [0031]    It is envisioned and desired that the wash fluid circulated for the present disclosure is water; hence, the wash fluid boils at about 100° C. (212° F.) in normal atmospheric conditions. However, the heating element can be utilized including different power characteristics that raise temperatures according to different atmospheric pressures and for dishwashers that utilize wash fluids other than water, s.a., e.g., wash fluids containing a combination of water and an active agent. 
         [0032]    In one embodiment, the second period S 214  of the steam cycle S 208  can further include periodic pulsing (step S 216 ) of wash fluid to ensure that there are sufficient droplets of wash fluid available for vaporization by the heating element. The fluid circulation system can intermittently or periodically reactivate for limited durations of a few seconds to distribute more droplets of wash fluid on to the surfaces of the kitchenware and the dishwasher racks above a top exposed surface of the heating element. Pulsing S 216  is beneficial because some of the original droplets that fall from the kitchenware and rack surfaces reach the chamber floor and not the exposed heating element. The droplets that fall onto the heating element boil quickly (i.e., through rapid vaporization), while droplets that instead fall onto the chamber floor take more time to vaporize. These droplets may eventually evaporate from the chamber floor. Because the steam cycle is of a limited duration, the evaporation may not occur within the steam cycle time frame. Thus, pulsing S 216  can disperse additional droplets for falling onto the heating element. 
         [0033]    The steam cycle S 208  can further include a pre-heat period (step S 218 ) of predetermined duration for raising the temperature in the dishwasher chamber environment before commencement of the first circulation period S 210 . Alternatively, the controller may be operative to monitor the ambient temperature in the chamber and terminate the pre-heat period upon sensing a temperature which at least equals a pre-determined reference temperature. In this manner, the chamber temperature is raised to a desired level that aids in evaporation (in the second period S 214 ) of the wash fluid that is subsequently circulated (in the first period S 202 ). Evaporation is more likely to occur on surfaces of the chamber floor because of the large surface area as compared to boiling of fallen droplets that fall on surfaces of the heating element. Therefore, exposing the chamber to the predetermined duration at an elevated temperature by simply energizing the heating element without operation of the fluid circulation system may be desirable. 
         [0034]    After the steam cycle S 208  concludes, at least one main wash cycle (step S 220 ) initiates. The main wash cycle S 220  is not limited to any particular embodiment; rather, the wash cycle includes release of a detergent that mixes with circulating wash fluid to clean the kitchenware contained in the dishwasher chamber. The main wash cycle S 220  can include one or multiple detergent releases, various stages at different temperature ranges, fluid circulation at varied pressures and pulsing speeds, etc. Varying the pressure and circulation of the wash fluid directed toward the kitchenware will facilitate removal of soils that have been softened in the preceding steam cycle S 208 . 
         [0035]    At least one rinse cycle (step S 222 ) follows the main wash cycle S 220 . The at least one rinse cycle S 222  aids in rinsing detergent and remaining soil from the kitchenware, sanitizing the kitchenware, and raising a temperature of the chamber environment. The wash routine concludes with a dry cycle (step S 224 ). This dry cycle S 224  can take the form of a dry session, wherein an elevated temperature of the chamber environment expedites drying of the kitchenware by a fan mixing dry air pulled into the chamber with the moist air contained in the chamber. More specifically, the wash fluid sprayed on the kitchenware in the rinse cycle S 222  is at a high temperature to sanitize the kitchenware. The higher temperature wash fluid causes the interior chamber environment to warm up as it is sprayed thereabout. The chamber environment is thus heated when the spraying ceases. Dry air is pulled into the chamber and mixes with the warmer air. The mixed air is vented from the chamber while condensation is collected and returned to a sump. Hence, the heating element does not remain energized after the spraying of the wash fluid ceases. The dry cycle can alternatively include a predetermined period wherein the kitchenware in the chamber is allowed to cool. 
         [0036]    Although the wash routine is illustrated and described above in the form of a series of stages or cycles, it will be appreciated that the various methods or periods of the present disclosure are not limited by the illustrated ordering of such cycles. In this regard, except as specifically provided hereinafter, some periods and/or cycles may occur in different order and/or concurrently with other acts or events apart from those illustrated and described herein in accordance with the disclosure. It is further noted that not all illustrated periods and/or cycles may be required to implement a wash routine or a method in accordance with the present disclosure, and one or more such acts may be combined. The illustrated methods and other methods of the disclosure may also be implemented in any system including but not limited to the illustrated dishwasher  100 . 
         [0037]    Advantageously, the present method does not require engineering, redesigning, or incorporation of additional components into a dishwasher for manufacturing such a dishwasher capable of achieving the present wash routine. The present method is commanded by a controller, wherein a program for the routine can be incorporated therein that utilizes components already used and add the novel steam cycles described herein to the pre-wash, wash, rinse, and dry cycles already used in most commercially available dishwashers. 
         [0038]    The disclosure has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the disclosure be construed as including all such modifications and alterations.