Patent Application
20070278319
1. Field of the Invention
This invention relates generally to a gas valve for a consumer appliance, and more specifically to a proportional gas valve allowing the gas flow rate to be proportionally adjusted by a control system.
2. Description of the Related Art
Gas-supplied household appliances, such as gas ranges or ovens, typically employ one or more valves to regulate the flow of gas to the appliance. The gas is specifically delivered to a heating element, such as a gas burner. In the case of a gas oven, the appliance also has a control system that regulates the temperature of the oven cavity in accordance with a temperature set point programmed by a user. The control system acts to maintain the oven cavity at the temperature set point by opening and closing the valve to raise and lower, respectively, the oven cavity temperature. Traditionally, only ON/OFF valves are used in ovens. ON/OFF valves function just as their name implies. When the valve is open, it is completely open and gas flows through at a maximum rate. When the valve is closed, no gas flows through. These valves are normally solenoid valves that have only the two ON and OFF positions.
Controllers for the ON/OFF valves open and close the valve to maintain the oven temperature at a user-selected set point. Most controllers are programmed to avoid rapid cycling of the burner because each cycle requires ignition and the ignitions are typically audible, which can be an annoyance for some users. Also, the repeated cycling of the valve reduces the life of the valve and ignition components.
The desire to reduce the number of ignitions is made more difficult in that the heat output of the gas burner is normally selected such that it can quickly reach and easily maintain the highest anticipated cooking temperature, which is usually around 350° F. For self-cleaning ovens, the heat output is selected to reach the very high temperatures, around 830° F., necessary for pyrolytic cleaning.
As the burner output is selected to meet the highest anticipated temperature and the burner can only be ON or OFF, the oven temperature often quickly rises above the user-selected set point for the traditional cooking temperatures of around 350° F. To avoid rapid ON/OFF cycling of the burner, the controller normally cycles the valve between upper and lower trip points relative to the user-selected set point. The upper trip point is greater than the set point and the lower trip point is less than the set point. This cycling of valve between the trip points results in the oven temperature that is rarely at the temperature set point, and instead oscillates above and below the temperature set point. This is illustrated in
The trip points are selected as a compromise between minimizing the cycling of the burner and maintaining an average temperature close to the set point. The trip points must also take into account that the response of gas burner is not instantaneous for a variety of reasons. Thus, the burner will introduce some heat after the upper trip point is reaches and the burner will not immediately begin heating when the lower trip point is reached. The result is that the oven cavity will often cycle between a temperature slightly above the upper trip point and slightly be the lower trip point.
Therefore, current oven and their temperature control systems are a compromise between temperature accuracy and life cycle of the temperature control system.
The invention addresses the compromise of current temperature control systems by providing a gas oven comprising a housing defining a cooking chamber, a temperature sensor outputting a temperature signal indicative of the air temperature of the cooking chamber, a gas heating element heating the air in the cooking chamber, a proportional valve regulating the supply of gas to the heating element in response to a control signal, and a controller operably coupled to the temperature sensor to receive the temperature signal and operably coupled to the proportional valve, where the controller generates the control signal in response to the temperature signal to maintain the air temperature of the cooking chamber at a temperature set point.
The gas oven can further comprise a user interface operably connected to the controller that is configured to permit a user to input a user-selected set temperature as the set point. The controller can repeatedly receive the temperature signal and generate the corresponding control signal. The proportional valve can comprise a motor to selectively open the valve in response to the control signal. The motor can be infinitely adjustable to move the proportional valve to one of an infinite number of positions between closed and completely open. The motor can be discretely adjustable to move the proportional valve to one of a discrete number of positions between closed and completely open. The motor can be a stepper motor.
According to another aspect of the invention, a method is provided for maintaining the cooking temperature of a gas oven having a cooking chamber heated by a gas heating element at a user-selected set temperature. The method comprises sensing the air temperature of the cooking chamber, and proportionally controlling the supply of gas to the gas heating element in response to the sensed air temperature to maintain the air temperature of the cooking chamber at the set temperature.
The method can further comprise repeatedly sensing the air temperature of the cooking chamber and proportionally controlling the supply of gas in response to the repeatedly sensed air temperatures. The repeated sensing of the air temperature and corresponding proportional controlling can be conducted throughout an operational cycle. The supply of gas can be proportionally controlled by moving a proportional valve. The proportional control of the supply of gas can be infinitely adjustable. The proportional control of the supply of gas can be discretely adjustable. The discretely adjustable supply of gas can be discretely adjustable in predetermined increments. The predetermined increments can be equal or non-equal.
A gas-supplied household appliance, such as a gas oven, according to the invention is provided with a proportional valve for regulating the supply of gas to the oven and a control system for controlling the proportional valve to regulate the temperature of a cooking chamber to alleviate problems caused by the use of ON/OFF valves. Because the use of a proportional valve allows the gas flow rate to be adjusted from 0-100% of the maximum flow rate, the temperature of the cooking chamber can be maintained closer to a set temperature for improved cooking performance.
Referring now to the drawings, and in particular to
A user interface 22 is provided on the exterior of the housing 12 in a location that is convenient for a user to access. The user interface 22 is configured to allow the user to input a temperature set point, where the temperature set point is the temperature that the user desires the cooking chamber 14 to reach for a cooking operation. A suitable user interface is disclosed in U.S. Pat. No. 6,786,058 to Sanna, whose disclosure is incorporated by reference. However, any of the well known user interfaces can be used, including: mechanical knobs and dials, and electronic user interfaces, such as touch buttons or capacitance touch panels.
A controller 24 is operably coupled to the proportional valve 20 for controlling to opening and closing of the valve, thus controlling the gas flow rate through the valve. The controller 24 employs a control system algorithm to provide proper valve positioning. Any of the currently used controllers may be used, which include, but are not limited to, proportional, PI, PID, and fuzzy logic controllers. A suitable controller is disclosed in U.S. Pat. No. 6,163,017 to Corda et al., whose disclosure is incorporated by reference.
The controller 24 receives information from one or more temperature sensor(s) 26 positioned within the oven 10 to detect the air temperature in the cooking chamber 14. The temperature sensor 26 provides an indication of the cooking chamber temperature to the controller 24 in the form of a temperature signal that can be received by the controller 24. The controller 24 uses the temperature signal to determine the appropriate valve position and generates a control signal corresponding to the determined appropriate valve position. The control signal prompts the proportional valve 20 to move to the position defined by the control signal. The controller 24 repeatedly received information from the temperature sensor 26 and adjusts the position of the proportional valve 20 as needed through an operational cycle of the gas oven. The operational cycle can be any predetermined or user-inputted heating program that the oven performs, such as, but not limited to cooking cycles, self-cleaning cycles, warming cycles, and bread-proofing cycles.
The proportional valve 20 may be an infinitely adjustable proportional valve that can be set at any desired flow rate between 0% and 100%. The proportional valve 20 may also be discretely adjustable in sufficiently small amounts. For example, the proportional valve 20 may be adjustable in 1% increments. The degree of adjustability of the proportional valve 20 need only be fine enough to maintain the oven temperature at the desired set point within the desired range of accuracy, which can be limited by the controller 24 and the user interface 22. For example, the user interface 22 may only permit temperature adjustments in steps of 5° F. Under such circumstances, the resolution of the adjustability of the proportional valve 20 need only be fine enough to resolve the 5° F. temperature adjustments.
The proportional valve 20 may also be discretely adjustable in non-equal increments. For example, cooking cycles may be commonly preformed within a known range of cooking temperatures, such as between 170 and 550° F., while self-cleaning cycles may be commonly preformed within a higher known range of self-cleaning temperatures, such as between 800 and 850° F. As such, there is no need to regulate the temperature of the cooking chamber 14 between the range of cooking temperatures and the range of self-cleaning temperatures, in this example, between 550 and 800° F. Within the 550 to 800° F. temperature range, the proportional valve 20 may, for example, be adjustable in relatively large increments as compared to the incremental adjustments made in the cooking and self-cleaning temperature ranges. Additionally, the relationship between energy input to the oven 10 and resulting air temperature in the cooking chamber 14 is a non-linear function due to factors such as burner efficiencies (at different flow rates), the temperature gradient between air in the oven 10 and ambient air exterior of the oven 10, the design of the oven air intake system and design of oven venting system. Thus, it may be desirable for the proportional valve 20 to also provide a non-linear position vs. flow rate response curve to provide better performance.
The valve 20 is illustrated in a closed position, where no gas flows through the valve. In an open position, the valve element 30 is raised, thus permitting gas to flow from inlet 34, which is fluidly connected to the gas source 18, and through outlet 36, which is fluidly connected to the heating element 16. The extent to which the valve element 30 is raised corresponds to the rate of gas flow through the proportional valve 20.
It will be understood that the particular proportional valve is not germane to the invention. Furthermore, the valve position may be controlled by a variety of devices other than a motor 28, including, but not limited to, a solenoid actuator, an analog control that provides an analog voltage output to a motor winding, which acts to the change the valve position in an manner directly or inversely proportional to the voltage, and a binary linear coil actuator.
Referring to
It should be noted that the controller 24 can be programmed to take account of circumstances in the operational cycle. For example, at start-up, the controller 24 may maintain the proportional valve 20 100% open until the set point is reached as this will provide the fastest warm up of the oven. Once the set point is reached, the controller 24 will control the proportional valve 20 to maintain the temperature at the set point.
Referring to
While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.
