Abstract:
In one aspect, a dishwasher comprising a control mechanism coupled to a sensor for generating an output representative of an amount of soil in the dishwasher water is described. The dishwasher comprises a tub, at least one filter for filtering water in the tub, and a fluid circulation assembly for circulating water in the tub. The control mechanism is configured to determine whether corrective action is needed to unclog the filter based on a signal output by the sensor.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to dishwashers, and, more particularly, to utilizing a turbidity sensor to facilitate ensuring consistent and thorough cleaning in a dishwasher. 
     Known dishwasher systems include a main pump assembly and a drain pump assembly for circulating and draining wash fluid within a wash chamber located in a cabinet housing. The main pump assembly feeds washing fluid to various spray arm assemblies for generating washing sprays or jets on dishwasher items loaded into one or more dishwasher racks disposed in the wash chamber. Fluid sprayed onto the dishwasher items is collected in a sump located in a lower portion of the wash chamber, and water entering the sump is filtered through one or more coarse filters to remove soil and sediment from the washing fluid. 
     If a filter is clogged, the cleaning performance of the dishwasher can decrease as compared to the cleaning performance of the dishwasher if the filter is not clogged. Specifically, food particles from the clogged filter as well as food particles that would otherwise be captured by the filter are recirculated and redeposited onto the dishes. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, a dishwasher comprising a control mechanism coupled to a sensor for generating an output representative of an amount of soil in the dishwasher water is provided. The dishwasher comprises a tub, at least one filter for filtering water in the tub, and a fluid circulation assembly for circulating water in the tub. The control mechanism is configured to determine whether corrective action is needed to unclog the filter based on a signal output by the sensor. 
     In another aspect, a method for controlling operation of a dishwasher is provided. The dishwasher comprises a tub, at least one filter for filtering water in the tub, a sensor in flow communication with the tub, and a fluid circulation assembly for circulating water in the tub. The method comprising the steps of determining whether the filter is clogged based on an output signal from the sensor, and if the filter is clogged, taking corrective action. 
     In yet another aspect, a kit comprising a turbidity sensor for coupling to a tub of a dishwasher is provided. The sensor is configured to couple to a control mechanism comprising a processor programmed to determine whether corrective action is needed to unclog a filter in the tub based on an output of said sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a side elevational view of an example dishwasher system partially broken away; 
     FIG. 2 is a top plan view of a portion of the dishwasher system shown in FIG. 1 along line  2 — 2 ; 
     FIG. 3 is a partial side elevational view of the portion of the dishwasher system shown in FIG. 2; 
     FIG. 4 is a cross sectional schematic view of the portion of the dishwasher system shown in FIG. 3 along line  4 — 4 ; 
     FIG. 5 is a schematic illustration of a sump and a turbidity sensor coupled thereto; and 
     FIG. 6 is a graphical representation of an example signal output by the turbidity sensor shown in FIG. 5 during a wash cycle. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side elevational view of an exemplary domestic dishwasher system  100  partially broken away, and in which the present invention may be practiced. It is contemplated, however, that the invention may be practiced in other types of dishwashers and dishwasher systems other than just dishwasher system  100  described and illustrated herein. Accordingly, the following description is for illustrative purposes only, and the invention is not limited to use in a particular type of dishwasher system, such as dishwasher system  100 . 
     Dishwasher  100  includes a cabinet  102  having a tub  104  therein and forming a wash chamber  106 . Tub  104  includes a front opening (not shown in FIG. 1) and a door  120  hinged at its bottom  122  for movement between a normally closed vertical position (shown in FIG. 1) wherein wash chamber is sealed shut for washing operation, and a horizontal open position (not shown) for loading and unloading of dishwasher contents. 
     Upper and lower guide rails  124 ,  126  are mounted on tub side walls  128  and accommodate upper and lower roller-equipped racks  130 ,  132 , respectively. Each of upper and lower racks  130 ,  132  is fabricated from/known materials into lattice structures including a plurality of elongate members  134 , and each rack  130 ,  132  is adapted for movement between an extended loading position (not shown) in which at least a portion of the rack is positioned outside wash chamber  106 , and a retracted position (shown in FIG. 1) in which the rack is located inside wash chamber  106 . Conventionally, a silverware basket (not shown) is removably attached to lower rack  132  for placement of silverware, utensils, and the like that are too small to be accommodated by upper and lower racks  130 ,  132 . 
     A control input selector  136  is mounted at a convenient location on an outer face  138  of door  120  and is coupled to known control circuitry (not shown) and control mechanisms (not shown) for operating a fluid circulation assembly (not shown in FIG. 1) for circulating water and dishwasher fluid in dishwasher tub  104 . The fluid circulation assembly is located in a machinery compartment  140  located below a bottom sump portion  142  of tub  104 , and its construction and operation is explained in detail below. 
     A lower spray-arm-assembly  144  is rotatably mounted within a lower region  146  of wash chamber  106  and above tub sump portion  142  so as to rotate in relatively close proximity to lower rack  132 . A mid-level spray-arm assembly  148  is located in an upper region of wash chamber  106  in close proximity to upper rack  130  and at a sufficient height above lower rack  132  to accommodate items such as a dish or platter (not shown) that is expected to be placed in lower rack  132 . In a further embodiment, an upper spray arm assembly (not shown) is located above upper rack  130  at a sufficient height to accommodate a tallest item expected to be placed in upper rack  130 , such as a glass (not shown) of a selected height. 
     Lower and mid-level spray-arm assemblies  144 ,  148  and the upper spray arm assembly are fed by the fluid circulation assembly, and each spray-arm assembly includes an arrangement of discharge ports or orifices for directing washing liquid onto dishes located in upper and lower racks  130 ,  132 , respectively. The arrangement of the discharge ports in at least lower spray-arm assembly  144  results in a rotational force as washing fluid flows through the discharge ports. The resultant rotation of lower spray-arm assembly  144  provides coverage of dishes and other dishwasher contents with a washing spray. In various alternative embodiments, mid-level spray arm  148  and/or the upper spray arm are also rotatably mounted and configured to generate a swirling spray pattern above and below upper rack  130  when the fluid circulation assembly is activated. 
     FIG. 2 is a top plan view of a dishwasher system  100  just above lower spray arm assembly  144 . Tub  104  is generally downwardly sloped beneath lower spray arm assembly  144  toward tub sump portion  142 , and tub sump portion is generally downwardly sloped toward a sump  150  in flow communication with the fluid circulation assembly (not shown in FIG.  2 ). Tub sump portion  142  includes a six-sided outer perimeter  152 . Lower spray arm assembly is substantially centered within tub  104  and wash chamber  106 , off-centered with respect to tub sump portion  142 , and positioned above tub  104  and tub sump portion  142  to facilitate free rotation of spray arm  144 . 
     Tub  104  and tub sump portion  142  are downwardly sloped toward sump  150  so that water sprayed from lower spray arm assembly  144 , mid-level spray arm assembly  148  (shown in FIG. 1) and the upper spray arm assembly (not shown) is collected in tub sump portion  142  and directed toward sump  150  for filtering and re-circulation, as explained below, during a dishwasher system wash cycle. In addition, a conduit  154  extends beneath lower spray arm assembly  144  and is in flow communication with the fluid circulation assembly. Conduit  154  extends to a back wall  156  of wash chamber  106 , and upward along back wall  156  for feeding wash fluid to mid-level spray arm assembly  148  and the upper spray arm assembly. 
     FIG. 3 illustrates fluid circulation assembly  170  located below wash chamber  106  (shown in FIGS. 1 and 2) in machinery compartment  140  (shown in phantom in FIG.  3 ). Fluid circulation assembly  170  includes a main pump assembly  172  established in flow communication a building plumbing system water supply pipe (not shown) and a drain pump assembly  174  in fluid communication with sump  150  (shown in FIG. 2) and a building plumbing system drain pipe (not shown). 
     FIG. 4 is a cross sectional schematic view of dishwasher system  100 , and more specifically of fluid circulating assembly  170  through drain pump assembly  174 . Tub  104  is downwardly sloped toward tub sump portion  142 , and tub sump portion is downwardly sloped toward sump  150 . As wash fluid is pumped through lower spray arm assembly  144 , and further delivered to mid-level spray arm assembly  148  (shown in FIG. 1) and the upper spray arm assembly (not shown), washing sprays are generated in wash chamber  106 , and wash fluid collects in sump  150 . 
     Sump  150  includes a cover  180  to prevent larger objects from entering sump  150 , such as a piece of silverware or another dishwasher item that is dropped beneath lower rack  132  (shown in FIG.  1 ). A course filter  182  is located to filter wash fluid for sediment and particles of a predetermined size before flowing into sump  150  over tub sump portion  142 . Wash fluid flowing through cover  180  flows through coarse inlet filter  183  into sump  150 . 
     A drain check valve  186  is established in flow communication with sump  150  and opens or closes flow communication between sump  150  and a drain pump inlet  188 . A drain pump  189  is in flow communication with drain pump inlet  188  and includes an electric motor for pumping fluid at inlet  188  to a pump discharge (not shown in FIG. 4) and ultimately to a building plumbing system drain (not shown). When drain pump is energized, a negative pressure is created in drain pump inlet  188  and drain check valve  186  is opened, allowing fluid in sump  150  to flow into fluid pump inlet  188  and be discharged from fluid circulation assembly  170 . 
     A fine filter assembly  190  is located below lower spray arm assembly and above tub sump portion  142 . As wash fluid is pumped into lower spray arm  144  to generate a washing spray in wash chamber  106 , wash fluid is also pumped into fine filter assembly  190  to filter wash fluid sediment and particles of a smaller size than coarse filters  182  and  183 . Sediment and particles incapable of passing through fine filter assembly  190  are collected in fine filter assembly  190  and placed in flow communication with a fine filter drain tube  192  received in a fine filter drain docking member  194 , which is, in turn, in flow communication with drain pump inlet  188 . Thus, when pressure in fine filter assembly  190  exceeds a predetermined threshold, thereby indicating that fine filter assembly is clogged with sediment, drain pump  189  can be activated to drain fine filter assembly. Down jets (not shown) of lower spray arm assembly  144  spray fluid onto fine filter assembly  190  to clean fine filter assembly during purging or draining of fine filter assembly  190 . 
     FIG. 5 is a schematic illustration of sump portion  150  of tub  104  and a turbidity sensor  200  coupled thereto. A first outlet  202  of sump portion  150  is in flow communication with drain pump inlet  188  (FIG. 4) and a second outlet  204  of sump portion  150  is in flow communication with an auxiliary pump (not shown). 
     Turbidity sensor  200  is coupled to the dishwasher control mechanism, and sensor  200  generates an output signal representative of a level of sediment in tub  104 . Turbidity sensors are commercially available. An example turbidity sensor is Model TS15, commercially available from Elektromanufaktur Zangenstein Hanauer GmbH &amp; Co., KgaA Siemensstrabe 1, Nabburg D-92507. 
     Generally, turbidity sensor  200  generates a signal representative of the soil level in water by sensing light transmittance from a light emitting diode (LED) at a known wavelength. Any particles in the water inhibit light transmittance. Therefore, as the soil level in the water rises, the voltage level of the signal output by sensor  200  decreases. Air bubbles also inhibit light transmittance. When sensor  200  is fully submerged in static or smooth dynamic (i.e., without bubbles) water, the output signal from sensor  200  is stable. 
     FIG. 6 is a graphical representation of an example signal output by sensor  200  during a wash cycle. The x-axis is time, and the y-axis is the magnitude of the voltage level of the signal output by sensor  200 . The example wash cycle includes four fill operations, four circulation operations, and four pump outs. 
     As shown in FIG. 6 in the example wash cycle, during a first fill (1 st  Fill) operation, the sensor output signal increases due to the sensor getting submerged by water. During circulation, however, the sensor output signal decreases due to the increase of particles that have been rinsed off the dishes into the water. The water is then pumped out of the dishwasher and a second fill (2 nd  Fill) operation is performed. The presence of air in the tub, and then clean water results in the sensor output signal increasing until the next circulation operation. As with the first circulation operation, the sensor output signal again decreases due to the increase of particles in the water. The water is then pumped out and a third fill (3 rd  Fill) operation is performed. Comparing the sensor output signal subsequent to the third fill operation to the sensor output signal subsequent to the first and second fill operations, less soil is present in the water subsequent to the third fill operation. 
     During circulation, if the output signal from sensor  200  decreases rapidly, heavy soil is present on the dishes and corrective measures are executed to prevent filter clogging. For example, in one embodiment, the control mechanism includes a microprocessor programmed to compare the magnitude of the voltage signal output from sensor  200  to a previously output voltage signal magnitude from sensor  200 . This comparison can be performed at a selectable rate, e.g., once every 1-60 seconds the immediately preceding voltage magnitude is compared to the current magnitude. If the voltage magnitude remains within a band for a selected number of comparisons, e.g., if the voltage signal magnitude is plus or minus 0.50 volts for 5 comparisons, then a decrease rate is determined for the sensor signal and corrective action is performed. 
     The corrective action can take many different forms. Generally, the objectives of the corrective action include unclogging the filter and/or washing off the sensor so that inaccurate readings are avoided. For example, upon identification of a low output signal as described above, a drain sequence can be initiated and water can be pumped onto the filter to wash off the filter. 
     The above described process facilitates enhancing the effectiveness of dishwasher filters since clogged filters are predicted and corrective action can be taken. Such sensing and corrective action facilitate consistent and thorough cleaning of dishes. As explained above, utilizing a turbidity sensor as described herein is not limited to practice with a specific dishwasher such as the three level dishwasher described above. A turbidity sensor as described above can be utilized in many different types and models of dishwashers. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.