Patent Application
20050161063
The present invention relates to a method for measuring the water level in a residential dishwasher.
Providing and maintaining a precise water level in a dishwasher is important for many reasons, including for example, assuring that the dishwasher does not experience either an underfill or an overfill condition. The underfill condition can result in a poor wash performance. The overfill condition can cause damage to the dishwasher.
Typically, most dishwashers employ two methods for filling the dishwasher. One method is by using a timer in connection with a microprocessor that controls the operation of a water-inlet valve connected to a water supply. The timer generally opens and closes the water valve at a predetermined length of time to fill the dishwasher to a desired water level. Another method is by using a float switch device. The float switch is generally cylindrical in shape and is located inside the dishwasher at the bottom of the dishwashing tank. In operation, as the water level in the dishwasher rises, the float rises accordingly. When the float reaches a predetermined level, the float activates its switch, cutting the electricity to the water-inlet valve, thereby terminating the fill cycle. However, these two methods do not provide for the most accurate water level measurement. The timer and the float switch have a wide tolerance range due to the different water pressures experienced in every household. As a result, an accurate water level is often not obtained, thereby enabling an overfill or underfill condition to occur in the dishwasher.
Therefore, there is a need for a method for more accurately measuring the water level in a residential dishwasher independent of influences such as water pressure. In addition, there is also a need for a method for more accurately filling the dishwasher to a desired water level.
The invention provides an apparatus for controlling the water level in a dishwasher comprising a heating element having a resistance adapted to change in response to a change in the water level of the dishwasher. A data processing unit is coupled to the heating element and measures the resistance of the heating element, determines the water level based on the resistance measurement, and fills the dishwasher to a desired water level, accordingly.
In another aspect of the invention, a method for controlling the water level in a dishwasher comprising the steps of determining a desired water level, measuring a resistance of a heating element, and filling the dishwasher to the desired water level using the resistance measurements. The water level of the dishwasher thereby corresponds to the resistance of the heating element.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.
The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The present invention provides a dishwashing system that employs an apparatus and method for measuring the water level in a residential dishwasher and accurately filling the dishwasher to a desired water level. The apparatus employs a main control panel for selecting a wash cycle, a water valve for filling the dishwasher based on the selected wash cycle, a heating element adapted to change in resistance in response to the water level in the dishwasher, and a data processing unit for determining a fill rate and measuring a precise water level. The method includes using the heating element of the dishwasher and directly measuring the resistance of the heating element to determine the fill rate for filling the dishwasher to a desired water level and to measure the precise water level.
It should be readily understood that the dishwasher 10 according to the present invention does not include a float switch that is typically employed in a current dishwasher to fill the dishwasher to the desired water level. Rather, a fill rate is calculated by measuring the resistance of the heating element itself, and the calculated fill rate is used to fill the dishwasher to the desired water level.
The dishwasher 10 generally comprises a data processing unit 12 with a timer 14, a main control panel 16, a water-inlet valve 18, a conduit 20, a dishwashing chamber 22, and a heating element 24. The data processing unit 12 is in communication with the main control panel 16, the water-inlet valve 18, and the heating element 24. Specifically, the data processing unit 12 performs the functions of receiving an input and sending an output to either one of the components. It should be understood that the data processing unit 12 can be any type of commercially available processor for executing instructions and processing data.
The timer 14 is generally located behind the main control panel 16 and is connected with the data processing unit 12. The timer 14 can be an electronic device capable of providing a digital signal to the data processing unit 12. The timer 14 is used as a standard counting device. The timer 14 helps provide power to all of the dishwasher components at a pre-set time and for a pre-set period of time as computed by the data processing unit 12.
The user operated main control panel 16 is generally located at the front top of the dishwasher. The main control panel 16 includes one or more selector switches. The switches provide options among wash cycles, drying cycles (heat or no heat), temperatures for the wash or rinse, and so on. The wash cycle selected from the switches of the panel 16 is used to calculate the pre-set time for the timer 14. These switches may include, for example, an option for a heavy, medium, and a light cycle. For instance, when the user selects the heavy cycle, the data processing unit 12 automatically determines the desired water level. The desired water level varies according to the selected wash cycle. Each wash cycle can have a different water level. It should be understood that the main control panel 16 may include a number of options that can be considered as a factor in determining the desired water level.
The water-inlet valve 18 is generally located at the bottom left or right of the dishwasher and is in communication with the data processing unit 12. The water-inlet valve 18 is connected to a water supply 26 by conduit 20 to allow water to flow into the dishwashing chamber 22 for the selected wash cycle. The water-inlet valve 18 is typically attached to a hot-water supply line of the water supply 26. The timer 14 and the data processing unit 12 control the water-inlet valve 18. The timer 14 turns the water-inlet valve 18 on and off for a length of time calculated by the data processing unit 12. Specifically, the timer 14 opens and closes the water-inlet valve 18 for the calculated length of time to allow water into the dishwashing chamber 22. The water-inlet valve 18 closes when the timer 14 cuts off the flow of power to the water-inlet valve 18. The timer 14 keeps the water-inlet valve 18 open for the length of time to fill the dishwashing chamber 22 to the desired water level.
The dishwashing chamber 22 is located within the body of the dishwasher 10. The dishwashing chamber 22 is the region where the washing and rinsing takes place. The dishwashing chamber 22 includes a number of components that are not shown, such as supporting racks for loading dishes, a pump assembly and spray arms for spraying water onto the dishes, a soap dispenser for providing soap, a drain and a solenoid drain valve for draining the wash water through a hose and out to a plumbing waste system. The volume of water the dishwashing chamber 22 can hold is pre-stored in the data processing unit 12 and is used to calculate a fill rate. It should be understood that the dishwashing chamber 22 can be any size and shape suitable for the different washing cycles.
The heating element 24 is located within the body of the dishwashing chamber 22 and is adapted to be submerged in water. The heating element 24 is generally located in a sump area of the dishwashing chamber 22. The heating element 24 is made of wire wrapped around a core and is nearly entirely resistive. As such, the resistance of the heating element 24 changes in response to the water level. The heating element 24 essentially acts as a resistor with positive temperature coefficient (PTC) characteristics and a sensor. The data processing unit 12 enables the heating element 24 to turn on and off for a calculated length of time.
The data processing unit 12 determines the fill rate for the dishwasher 10 by measuring the length of time elapsed from the time the end positions 30a, 30b are exposed to water till the time the main body 32 is submerged with water. This is accomplished with the use of the timer 14. Specifically, the timer 14 begins counting as soon as water is introduced to the dishwashing chamber 22 and contacts end positions 30a, 30b. The data processing unit 12 measures the resistance of the heating element 24 when the timer 14 is actuated to begin counting. The data processing unit 12 continually measures the resistance of the heating element 24 until the water level reaches the main body 32 of the heating element 24. At this point, a dramatic change of resistance is measured. Once the water reaches the main body 32 of the heating element 24, the data processing unit 12 computes the fill rate. The fill rate is the volume of water over time. The volume of water up to the main body 32 of the heating element 24 is pre-stored in the data processing unit 12. The known volume can vary depending where the main body 32 is positioned relative to the bottom surface of the chamber 22. The main body 32 can be positioned at any convenient level of the dishwashing chamber 22.
The data processing unit 12 also computes a water-valve turn-off time. The valve turn-off time is used by the timer to keep the water-inlet valve 18 open for the remaining time in which to fill the dishwasher to the desired water level. The known water level is referred to as level A, where the main body 32 of the heating element 24 is positioned. The desired water level is shown as level B. The desired water level B is reached by using the fill rate to compute the water-valve turn off time. Specifically, the data processing unit determines the remaining volume of water needed to fill the dishwashing chamber 22 from level A to level B. The data processing system uses the water-inlet valve turn off time to fill the chamber 22 to the desired water level. This results in a controlled amount of water in the dishwasher 10.
With this configuration, the water level can be controlled anywhere between the minimum fill level to the maximum fill level because the water level can be measured anywhere between the minimum and maximum fill levels. The minimum and maximum levels are pre-selected according to the wash cycles of the dishwasher 10. The data processing unit 12 is operative to interpret the resistance of the heating element 24 as a specific water level and terminate the operation of the water-inlet valve 18 at the desired level.
It should be understood that the method for measuring the resistance of a heating element to determine the water level can be employed to other systems, such as, for example, a washing machine. The present invention provides a method for accurately filling a dishwasher and measuring the water level of the dishwasher.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.
