Abstract:
A soil sensing system is provided for a dishwasher having an interior wash chamber receiving soiled dishes wherein during a wash cycle wash liquid is sprayed throughout the wash chamber through an upper wash arm and a lower wash arm and soils are collected in a soil collector. The soil collector includes a filter screen which is backwashed by the wash arm. A pressure sensor measures the pressure within the soil collector to provide an input which corresponds to the presence of soils. In order to improve the sensitivity of the pressure based soil sensing, the lower wash arm is deactivated. Deactivating the lower wash arm ceases the backflushing of the collection chamber&#39;s filter screen and allows pressure to build within the soil collector in the presence of only light or oily soils. A response is activated if the actual pressure within the collection chamber is greater than a predetermined limit pressure. The response may consist of the addition of heat to the water, the addition of time to the cycle, the draining of soiled wash liquid, the addition of detergent or possibly the addition of a wetting agent.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dishwasher and more particularly, to a system for sensing light soil loads to allow an accurate cycle response thus improving washability and energy efficiency. 
     2. Description of Related Art 
     Domestic dishwashers in use today draw wash liquid from a sump at the bottom of a wash tub and spray the wash liquid within the wash tub to remove soils from dishes located on racks in the tub. It is well known that the removal of soils from the recirculating wash liquid positively impacts the wash performance of the dishwasher. Accordingly, to improve performance and efficiency, some dishwashers employ a system for separating soils out of the recirculating wash liquid wherein the soils are retained in a soil collector. Frequently, a filter screen is used to retain soil in the soil collector. For example, in U.S. Pat. No. 5,165,433, a dishwasher system is disclosed that includes a centrifugal soil separator which sends soil laden wash liquid into a soil container then wash liquid passes through a fine filter disposed in the wall of the soil container while soils are retained by the screen. Typically, backwash jets are directed against the filter by the lower wash arm in an attempt to clear the filter and prevent clogging. 
     U.S. Pat. No. 4,559,959 discloses a dishwasher wherein soil load is measured by monitoring pressure in a soil collector in which soils are retained after the wash liquid passes through a filter mesh. If the pressure exceeds a predetermined limit, indicating that the filter mesh is clogged, the wash liquid is completely purged by draining all of the wash liquid out of the tub and refilling the tub with fresh water. However, this dishwasher uses excess water and concerns over energy consumption have led to dishwashers utilizing purge systems that only partially drain the dishwasher tub. For example, U.S. Pat. No. 4,346,723 discloses a dishwashing system wherein soils are collected in a bypass soil collector and the soil collector may be purged by draining small amounts of wash liquid in spurts during an early wash period by selectively opening and closing a drain valve. 
     Since wash performance is effected by the soiled condition of the wash liquid recirculated through the system, all or a portion of the wash liquid may be drained from the dishwasher chamber if it is sensed that the soil collector has reached a predetermined pressure as disclosed in U.S. Pat. No. 5,900,070 and clean water can be introduced into the chamber. However, since the soil collector is usually provided with a screen that is backwashed, pressure only builds when there is a heavy soil load in the collector. 
     Wash performance in a dishwasher is also related to the temperature of the wash liquid. It is known that hot water is more effective for washing than cold water, particularly for oily soils, which melt at higher wash liquid temperatures. Accordingly, dishwashers are commonly connected to a hot water supply such that the fill water supplied into the dishwasher has a relatively high temperature. Thermal inputs during the dishwasher cycle typically occur during a thermal hold wherein the cycle of operation is interrupted while a heater is energized until a thermostat is satisfied or a maximum default time limit elapses. A dishwasher may have a pressure sensor for sensing fluid pressure within the soil collector such as is shown in U.S. Pat. No. 5,900,070. A control means energizes a heater disposed in a sump region of the wash chamber when the pressure within the soil collector exceeds a predetermined limit pressure. Heat energy is then supplied to the wash liquid in response to the soil load. 
     Detergents and wetting agents can affect the wash performance in a dishwasher. Chemical energy can affect the breakdown of soils and thus the ability of the wash liquid to remove soils from dishes. It is well known that the use of detergents and wetting agents positively impacts wash performance, so varying amounts of detergents and wetting agents would be useful for varying soil loads. It would be beneficial if the amount of detergent and/or wetting agent added to the wash liquid was responsive to the soiled condition of the wash liquid. 
     Unfortunately, there is currently no means of measuring light soil loads. Pressure in the soil collector usually indicates the presence of heavy soil loads because the backwash provided by the lower wash arm keeps light soil loads from clogging the filter and thus, from increasing pressure in the collection chamber. 
     Accordingly, it would be an improvement in the art if a dishwasher wash system was provided which could sense light soil loads in the dishwasher so a response could be initiated, for example, the addition of heat to the water, the addition of time to the cycle, the draining of soiled wash liquid or the addition of detergent. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an automatic dishwasher wash system that is responsive to the presence of light or oily soil loads. It is an object of the invention to provide a dishwasher having an interior wash chamber for receiving wash liquid and a sump region disposed at the bottom of the wash chamber. A wash pump is disposed in the sump region and has an intake through which wash liquid is drawn from the sump. The wash pump has a main outlet and a secondary outlet. The dishwasher draws wash liquid through the sump region into the wash pump intake and selectively directs wash liquid from the wash pump main outlet to the wash arm. Wash liquid is directed from the wash pump secondary outlet to a soil collector having a filter screen along the top portion. Wash liquid is sprayed from the wash arm through at least one jet toward the filter when the wash liquid is directed to the wash arm. A valve is provided for selectively deactivating wash liquid to the lower wash arm such that when the valve is open in a first position wash liquid flows to the wash arm and when the valve is closed in a second position wash liquid is prevented from flowing to the wash arm. The wash liquid can be diverted to an upper wash arm when the valve is in the second position. A pressure sensor senses soils in the soil collector. The pressure within the soil collector is monitored when the wash liquid is not directed through the wash arm to backwash the filter screen. If the pressure measurement exceeds a predetermined limit, a response is activated 
     For example, it is an object of the invention to provide a response of energizing a heater disposed in the sump region for increasing wash liquid temperature if the pressure sensor exceeds a predetermined limit. 
     It is a further object of the invention to provide a response of adding a wetting agent into the wash chamber. 
     It is an object of the invention to provide a response of adding detergent into the wash chamber. 
     Further, it is an object of the invention to provide a response of adding wash liquid to the wash chamber to help rinse soils away. 
     It is an object of the invention to provide a response of partial or complete draining of wash liquid from the wash chamber and the addition of fresh wash liquid if the pressure sensor exceeds a predetermined limit. 
     It is a further object of the invention to provide a dishwasher that operates with a cleaning cycle having a fill period and a wash period. The length of the wash period time can be increased if the pressure sensor exceeds a predetermined limit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a dishwasher including a soil sensing system in accordance with the present invention. 
     FIG. 2 is a schematic illustration of the dishwasher pump and soil collector used in the dishwashing system illustrated in FIG.  1 . 
     FIG. 3 is a block diagram of the control elements for an electrical system used in the dishwashing system illustrated in FIG.  1 . 
     FIG. 4 is a flow chart showing the operation of a dishwasher according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The basic constructional features of the drain pump system of the present invention are disclosed in U.S. patent application Ser. No. 09/326,280 to Jozwiak et al., entitled “Automatic Purge Filtration System for a Dishwasher”, herein incorporated by reference. In this patent application, the operation of a drain pump system for purging wash liquid is fully explained. 
     FIG. 1 illustrates an automatic dishwasher  10  providing the environment of the invention. The dishwasher  10  includes an interior tub  12  forming an interior wash chamber or dishwashing space  14 . The tub  12  includes a sloped bottom wall  16  that defines a lower tub region or sump  18  of the tub. A soil collector and wash pump assembly  20  are centrally located in the bottom wall  16  and a lower wash arm assembly  22  extends upwardly from a portion thereof and an upper wash arm assembly  23  is positioned above the lower wash arm assembly. A heating element  24  may be disposed within the lower portion of the dishwashing space  14  and may be operated to heat wash liquid within the dishwasher  10 . The tub includes a door  36  that defines one of the walls of the tub. One or more dispensers  42  and  44  may be disposed along the door  36  for dispensing detergent and/or wetting agent within the wash chamber. 
     As illustrated in FIG. 2, the soil collector and wash pump assembly  20  include a motor  25  suspended below the tub  12 . A pump chamber  40  is supported within the sump region and houses a wash pump  31  having a wash impeller  38 . The motor has an output shaft  26  that extends up through the base to drivingly connect the wash impeller  38 . An annular soil collector, or soil separator,  46  is disposed about the pump chamber  40 . 
     During the wash mode, the wash impeller  38 , driven by motor  25 , draws wash liquid from the sump  18  through a pump inlet  63 , into the pump chamber and pressurizes the wash liquid within the pump chamber  40 . The majority of the pressurized wash liquid is directed by diffuser vanes (not shown) through the pump outlet  34 . The pump outlet  34  guides wash liquid to the lower wash arm assembly  22  and to an upper wash arm supply tube  52 . A valve  108  may be provided at the pump outlet to selectively direct wash liquid to the lower and upper wash arms. Wash liquid is repeatedly recirculated over the dishes for removing soils. 
     A portion of wash liquid within the pump chamber  40  is directed to a secondary outlet  54  and from there into the soil collector  46 . Wash liquid flows from the pump chamber  40  into the soil collector  46 . Fine mesh filter segments  56  are positioned along the top of the soil collector and permit flow of cleansed wash liquid to exit from the soil collector  46  and return to the dishwasher sump region  18 . In this manner, soils are captured within the soil collector  46 . 
     During the wash mode, the filter segments  56  are repeatedly backflushed. The lower wash arm assembly  22  has a lower wash arm  48  extending outwardly above the soil collector. The wash arm  48  rotates as pressurized wash liquid is emitted from downwardly directed jets  66 . Means may be provided for forming a fan-shaped spray from the flow of wash liquid through the jets  66 . As the lower wash arm  48  rotates, this fan shaped spray sweeps across the filter segments  56  providing a backwashing action to keep the filter screen segments  56  clear of soil particles which may impede the flow of cleansed wash liquid into the sump  18 . 
     In spite of backflushing, in conditions of a heavy soil load, the filter screen segments  56  may become clogged with food soils. When this occurs, pressure within the soil collector  46  increases. This pressure increase is sensed by a pressure sensor  60  which may be connected to a pressure dome or chamber via a pressure tap tube. The pressure sensor  60  can be either an analog device or a digital device. As the pressure within the soil collector  46  rises, the air within the pressure dome  62  is compressed and this increase in air pressure is sensed by the pressure sensor  60 . The pressure sensor  60  may be a single-pole, single throw pressure switch which is designed to trip or actuate at a predetermined limit pressure P L  or possibly it could be an analog pressure sensor. The pressure sensor  60  may be mounted to any suitable structure beneath the bottom wall  16  of the dishwasher. 
     When the actual pressure P A  in the soil collector exceeds the predetermined limit pressure P L , indicative of a clogged screen mesh  56 , a response R can be activated. The response may include a partial or complete drain of the wash liquid, or possibly an increase in the thermal input. As described in U.S. Pat. Nos. 5,900,070 and 5,909,743, these responses facilitate the wash process when there is a heavily soiled load. 
     Detecting the presence of light or oily soils is difficult to accomplish with the above-described system due to the effectiveness of the filter backflushing. When just a light soil load is present, the backflushing of the filter screens  56  keeps the lighter soils from clogging the filter and thus from increasing the pressure within the soil collector  46 . A pressure reading within the soil collector may not exceed the pressure limit P L  because pressure does not have an opportunity to build when the light and oily soils arc being backflushed. 
     In the present dishwasher system, through operation of the valve  108 , the lower wash arm  48  may be periodically deactivated; thus the backflushing action of the filter screens  56  will be discontinued. This allows pressure to build within the soil collector  46  when there is only a light or oily soil presence. The pressure can be measured during this lower wash arm  48  “off period” and a response R activated if the actual pressure P A  is greater than the light pressure limit P L . This dishwasher system allows the pressure limit P L  to be set relatively low so a response R can be initiated accordingly. The system also contemplates deactivating the lower wash arm  48  at defined times during the wash cycle to measure soils that are prevalent at different times. For example, the lower wash arm  48  may be deactivated when the wash liquid is at a lower temperature, perhaps less than 130 degrees F, to determine if soils exist that are difficult to remove at lower temperatures. It will be appreciated that the timing of the “off period” can be set to learn about the characteristics of the soils present. Thus, the washability of the dishwasher  10  is improved. 
     The lower wash arm  48  may be deactivated by the valve  108  that may be configured such that when the valve  108  is open in a first position wash liquid flows to the lower wash arm  48  and when the valve  108  is closed in a second position wash liquid is diverted to the upper wash arm assembly  23 . The upper wash arm assembly  23  has an upper wash arm  27  for spraying wash liquid on dishes within the wash chamber  14 . The valve  108  may be constructed such that wash liquid flows through the pump outlet  34  to both the upper and lower wash arms when the lower wash arm is activated or wash liquid may selectively flow between the upper  27  and lower  48  wash arms in an alternating fashion. If an alternating wash arm operation is implemented, the pressure within the soil collector  46  is measured when the lower wash arm  48  is deactivated. The measurement can be timed to occur when the wash liquid is being supplied to the upper wash arm  27 . 
     There are many configurations allowing wash liquid to alternate between the lower and upper spray arms or wherein the lower wash arm  48  may be deactivated by selectively diverting the flow of wash liquid to the upper wash arm. For example, U.S. Pat. No. 5,924,432, incorporated by reference herein, discloses a dishwasher utilizing a valve that selectively directs the flow of wash liquid between the upper and lower spray arms. Additionally, U.S. Pat. Nos. 5,752,533; 5,486,089; 5,924,432; 4,741,353 and 5,264,043 disclose configurations allowing wash liquid to alternate between multiple spray arms. The present invention may be found in a dishwasher in which the flow of wash liquid alternates between the upper and lower spray arms. This allows the actual pressure measurement to be taken during the period when the upper wash arm is activated and the lower wash arm is deactivated. 
     Besides the many configurations for allowing wash liquid to alternate between spray arms, there are other means of selectively stopping the backwash of the filter screen so light soils can be sensed. For example, the dishwasher  10  may have two lower spray arms, a rotating flush arm above the screen for flushing soils from an underside of the screen and a wash water arm above the flush arm for spraying dishes in the chamber  14 . Thus, the wash water arm can be flow separated from the flush water arm for selective operation. This configuration is detailed in U.S. Pat. No. 5,730,805, incorporated by reference herein. 
     Another means of selectively controlling the backwash action is achieved in wash arms having individual controls for the backwash jets, or nozzles. The lower wash arm is constructed with two separate inlets to two chambers within the wash arm. The upper chamber is used for spraying dishes and the lower chamber is used to backwash the filter screen. This configuration allows selective fluid control to the lower chamber and thus intermittent operation of the backwash jets. 
     Additionally, the dishwasher system might be constructed with individually controlled backwash jets. In this manner, the flow of liquid can be selectively controlled. Not only can each jet be selectively turned off and on, but also the force of the spray emitting from the jet can be used to control the effect of the jet. 
     The dishwasher system can either provide for a pressure measurement to be taken within the soil collector  46  during the lower wash arm “off period”, or both at a time when the screen filters  56  are being backflushed and during the “off period”. Providing different circumstances under which pressure measurements are taken allows for different responses R to be initiated in response to different pressure limits P L . 
     Once the lower wash arm has been deactivated, the actual pressure P A  within the soil collector  46  can be measured immediately or after a defined period of time T. A time period T can be set to allow pressure to build within the soil collector during the “off period”. If the actual pressure P A  exceeds the predetermined pressure limit P L , a first response R 1  is activated. The response may consist of a partial drain of wash liquid with the addition of some clean liquid R a ; the complete drain of wash liquid with a fresh fill of liquid R b ; the addition of heat to the wash liquid R c ; the addition of detergent to the wash liquid R d ; the addition of a wetting agent to the wash liquid R e ; or possibly the addition of time to the wash cycle R f . 
     Turning now to FIGS. 3 and 4, the operation of the dishwasher can be explained. Step  84  represents a conventional fill period wherein a fill valve  80  is energized for supplying water into the dishwasher. After water is added to the dishwasher, the motor  25  is energized for recirculating wash liquid throughout the dishwasher in a wash or recirculation mode as shown in step  86 . After fill liquid is initially supplied into the tub  12 , the wash pump  31  is energized. During the wash mode, there may be instances of monitoring pressure within the soil collector, as represented by step  88 . There, may be a first sensing period, as shown in step  90 , as the lower wash arm  48  operates to clean dishes on the lower rack and the jets  66  backwash the filter  56 . If the pressure sensor  60  provides a signal to the controller  70  indicating that the pressure within the soil collector exceeds a predetermined limit P L , then a response is activated, as shown in step  92 . Typically, that response will be a purging of the soil collector as described above. 
     Either at a fixed time, represented by step  94 , or at a time when the pressure sensor  60  no longer senses any heavy soil loads, most of the wash liquid is diverted to the upper wash arm  27  thus ceasing the backwash of the filter screens  56  as the lower wash arm  48  is deactivated in step  96 . There is then a second sensing period  98  wherein the controller  70  monitors the pressure sensor  60  to determine whether the actual pressure P A  exceeds the predetermined limit pressure P L  within the soil collector  46 . If the actual pressure exceeds the limit pressure, then a response R is activated, as represented in step  100 . The response may be any of the responses R a -R f  discussed below and the dishwasher system may be configured to respond with one or more of the responses R a -R f . Either before or after the response R has been completed, the lower wash arm  48  is reactivated in step  102  and it is determined whether the second sense period is complete, shown in step  104 . If the second sense period is complete, the wash cycle continues as represented in step  106 . 
     As will be appreciated, the complete dishwasher cycle may include additional steps such as rinsing and drying. During any of the sensing periods, an indicator light  94  (FIG.  3 ), such as an LED, can be energized to provide feedback to the consumer that a soil sensing operation is being executed. 
     It should be understood that the present invention may contemplate initiating a plurality of responses. For example, after a first response R is initiated, if during subsequent sensing, the actual pressure P A  in the soil collector  46  exceeds the predetermnined limit pressure P L , then a second response R 2  is initiated. This response R 2  may either be the same response as the first response R 1  or a different response. This dishwasher system of measuring the pressure in the soil collector  46  when the lower wash arm  48  is deactivated may occur a defined number of times during the wash process or may continue until the pressure measurement indicates the actual pressure P A  is less than the predetermined pressure limit P L . 
     If the response R is either a partial drain of wash liquid with the addition of some clean liquid R a  or the complete drain of wash liquid with a fresh fill of liquid R b , a drain pump  64  is energized to clear the filter screen segments  56 , as represented in FIG.  2 . The drain pump draws wash liquid, concentrated with soils, from the soil collector  46  through a drain conduit  58  and pumps it past a check valve  68  through a drain hose  32  to drain. If only partially drained, the amount of wash liquid drained may be controlled by time or by other means such as draining until the pressure within the soil collector  46  drops below the predetermined pressure limit P L . 
     In this manner, the soil collector  46  of the present invention is purged of soils and fresh wash liquid can be introduced through the water valve  80  (FIG.  3 ). It can be understood, moreover, that since the drain pump  64  is separate from the wash pump  31 , the purging of soils from the soil collector  46  can be accomplished while the wash pump impeller  38  continues to recirculate wash liquid through the dishwashing chamber  14 . 
     If the response is the addition of heat to the wash liquid R c  to increase the thermal input into the dishwasher, a control system can be provided for implementing a thermal hold in response to the soil level. For example, as shown in FIG. 3, a controller  70  may be provided comprising a comparator  72  and memory means  74 . The controller  70  may be an electromechanical sensor or a microprocessor connected to operation switches  76  such that the dishwasher operator can input cycle selections. The controller  70  also receives input from the pressure sensor  60  and from a temperature sensor  78  which may be mounted adjacent the dishwasher bottom wall  16  for sensing the temperature of wash liquid within the dishwasher. Alternatively, the temperature sensor  78  may be attached to a base plate which forms part of the tub or may be attached to the tub and have a sensing portion protruding through a hole in the base plate for directly sensing the temperature of the wash water in the dishwasher sump  18 . The temperature sensor may be a thermistor or a thermostat. A water valve  80  for supplying water into the dishwasher, the pump motor  25  and the heater  24  are connected to the controller  70  through a driver  82  such that these components can be selectively energized by the controller  70 . A system for increasing the thermal input in the dishwasher is explained in detail in U.S. Pat. No. 5,900,070, incorporated by reference herein. 
     If the response is the addition of detergent R d  or a wetting agent R e  to the wash liquid to increase the chemical input into the dishwasher, a control system can be provided for releasing detergent and/or wetting agent in incremental amounts. As illustrated in FIG. 3, a detergent dispenser  42  and a wetting agent dispenser  44  are connected to the controller  70  through a driver  82  such that these dispensers can be selectively energized by the controller. For example, the dispensers may be of the type disclosed in U.S. Pat. Nos. 4,820, 934; 5,205,304; or 5,839,454. 
     While the above description includes two sensing periods, it can be readily understood that the present invention is not limited to two sensing periods. The dishwasher cycle could be configured having one or more sensing periods. If the sensing period occurs more than once, there may be more than one response activated. The responses may be either the same response or different responses. For example, the first response R 1  may be a partial drain of wash liquid R a  and the second response R 2  may be the addition of heat to the wash liquid R c . 
     It will be understood that the system contemplates any response that increases wash performance of the dishwasher. For example, the responses R a -R f  are meant to be illustrative and not limiting. Additionally, it will be understood that there are different ways of draining wash liquid, adding detergents and/or wetting agents and heating wash liquid. For example, the process of completely draining the tub can be effected similarly to the method disclosed in U.S. Pat. No. 4,559,959, incorporated by reference herein. The process of partially draining the tub can be effected similarly to the method disclosed in U.S. Pat. No. 5,223,042, incorporated by reference herein. The addition of detergents and/or wetting agents can be effected by providing a dispenser  42  or  44  within the tub or perhaps on the inside wall of the door and signaling the dispenser to release a portion of the detergent and/or wetting agent in response to the sensor measurement. The process of heating the wash liquid can be effected similarly to the method disclosed in U.S. Pat. No. 5,900,070, incorporated by reference herein. 
     It can be seen, therefore, that the present invention provides a system for improving the washability of a dishwasher while minimizing energy consumption. It is possible to respond to light soils loads with an appropriate response to ensure a clean load of dishes. While the present invention has been described with reference to the above described embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the scope of the invention as set forth in the appended claims.