Patent Application
20050089809
This invention relates to control of gas appliances in general and more specifically to an electronically actuated gas cooktop flame proportioning control with flame sequencing simmer system.
While easily achieved in electric cooktops, simmer temperatures have until now been complicated issues for gas cooking apparatus. Conventional gas cooktops are generally operated by using manually activated mechanical actuator knobs, with infinitely varying settings of the flow of gas by rotating associated gas proportional valves. Most often, adjustment of cooking level is achieved by comparing level indicators printed on the knob, to a fixed pointer printed on the cooktop surface, immediately surrounding the knob. With such knobs and associated infinite valves, it often becomes difficult for the user to precisely re-adjust the valve to a predetermined preferred level of BTU output and thus repeatability is rarely achieved. This effect is of an even greater concern in simmer mode of cooking where delicate food such as chocolate or sauces can be spoiled, if cooked at slightly higher temperatures than those recommended. Additionally, mechanical knobs are also usually susceptible to wear and tear and are often vulnerable to contaminants normally present in cooking areas, such as greases and moisture infiltration that generally find their way through open areas, necessary for the mechanical valve installation in the cooking surface. Spark igniters are typically used to ensure ignition of the gas and are generally activated upon rotation of the above-mentioned mechanical knobs. Most often, integrated sensors, such as flame detectors, are used to continuously monitor proper combustion of the gas. Such sensors typically provide feedback to the spark ignition module, to ensure re-ignition of the gas, should it fail to combust. However, very low flames have been proven hard to detect by such sensor types and are often a cause for spark igniters to unnecessarily generate discharges in response to false detection incidents. Spark igniters are also known, by those in the industry, to emit powerful electromagnetic interference (EMI) that often disturbs electronic equipment working in their vicinity. Microcontrollers used in electronic controls are also known to be highly susceptible to EMI emission, and hence generally need additional protection when used in conjunction with spark igniter modules in gas cooking apparatuses. Due to their large orifice size, burners that are capable of high BTU output are usually not suitable for simmer, one of the reasons being that smaller flames have the tendency to self-extinguish in such conditions. Therefore, some cooktops have been equipped with simmer burners, featuring smaller orifice diameters and capable of delivering stable low-to-medium BTU output. This has often had the effect of reducing the number of available burners capable of high BTU output on a given cooking surface. Various methods involving flame sequencing have been used to provide gas-cooking appliances with low temperature output to provide a simmer. Sequencing the flame on and off in a timely fashion provides for an elegant solution to achieve very low is BTU output from a burner also capable of high BTU output, but simmer systems of the prior art generally involve synchronized re-ignition of the gas following each flame on/off cycle, complicating even further the design of simmer controls in gas cooktops. Moreover, repeated re-ignitions of the gas during simmer mode often have the undesirable effect of continuously generating harmful electromagnetic interference. As mechanical valves are traditionally used to adjust the gas flow, additional electrically controlled “on/off” cycling solenoid valves are generally added to provide the “on/off” sequencing of the flame in simmer mode, contributing to higher system cost and reliability issues.
U.S. Pat. No. 4,376,626 to Rossi et al. (Device for the control of a sequential burner of a cooking apparatus) discloses a control device for at least one sequential burner of a cooking apparatus, comprising in combination: a geared-down synchronous motor and a drum which can be driven in rotation by this motor, an electric circuit associated with this drum, comprising at least one electric contact pressing upon the surface of the drum and at least one electrically conductive track arranged on the drum in such manner as to permit operation of the burner according to heating sequences which are variable as a function of the position of the electric contact on the drum, and means for adjusting the position of the contact in relation to the conductive track in order that the duration of the heating sequences of the burner may be varied progressively and continuously.
U.S. Pat. No. 5,575,638 to Witham et al. (Stove burner simmer control) discloses a burner control which provides a pulsed flame sequence in response to a user's selective manipulation of an actuator through a range of response. A microcontroller-based control module switches both a burner igniter control and an electric valve for gas supply to the burner in a predetermined time sequence depending upon the actuator position within the predetermined range. Preferably, one or more of a plurality of burners on a single cooking top are controlled for pulsed sequence operation, and a single actuator for each channel, preferably in a form of a rotary knob, provides a simple user interface for utilizing the pulsed flame sequence, preferably in a low gas flow or simmer cooking range.
U.S. Pat. No. 6,116,230 to Clifford et al. discloses a gas appliance comprising a burner, a conduit, a control circuit, and a valve. The control circuit is adapted to provide a pulse-width-modulated signal to the valve, whereby the valve provides a substantially linear flow rate of fuel from a fuel source to the burner. The gas appliance of Clifford et al. employs a spark igniter.
Thus, there is a need for an electronically controlled gas cooktop appliance capable of delivering true simmer temperatures from gas burners that are also capable of high BTU output. There is also a need for an electronic gas cooktop appliance that is capable of fine, precise, and repeatable control of heating levels, provided by a direct level-dialing control, thus providing the user with a more precise selection of available and controllable temperatures. There is also a need for a gas cooktop appliance capable of assuring flame re-ignition without generating harnful electromagnetic interference. There is equally a need for a gas cooktop flame-sequencing simmer system integrating gas-flow modulation and “on/off” sequencing ability into a single gas valve. Finally, there is a need for a gas cooktop appliance integrating an electronic user touch interface for burner activation and selection of temperature settings.
The present invention is intended to provide practical solutions to problems in the existing art, thus globally fulfilling the above-mentioned needs.
A major object of the invention is a gas cooktop appliance capable of delivering very low heat power while maintaining capability of delivering very high BTU output, in each available burner, and also capable of fine, precise and repeatable control over the entire span of cooking levels. Another object of the present invention is to provide a gas cooktop appliance with an innovative electronic control featuring a capacitive touch user interface, thus featuring a flat, smooth and sealed cooking surface. Such a capacitive touch interface facilitates the maintenance of surfaces that are generally prone to become dirty and that are also difficult to reach. A capacitive touch interface offers the additional benefit of eliminating the wear and tear associated with mechanical devices and also of preventing contaminants such as greases and moisture from reaching sensitive components internal to the cooktop apparatus.
Another object is an electronic control capable of handling simultaneously both modulation of the valve(s) for metering the gas flow delivered to the burners from medium to high BTU output, and sequencing of the flame “on” and “off” at a predetermined medium level of flame, to provide efficient simmer temperatures. An additional object is to provide electronic control of a gas cooktop featuring a direct-dial keyboard-entry system and a digital visual user interface such that repeatability and precise re-selection of predetermined cooking levels is achieved. Yet another object is to provide an initial gas ignition and a flame sequencing re-ignition system that does not need to be synchronized with the flame on/off cycling during simmer cook mode and that does not generate harmful electromagnetic interference.
The present invention relates to the field of gas cooking appliances in general and more specifically to a micro-controller-based electronic controller and simmer system for a gas cooktop appliance. In a preferred embodiment, the present invention is presented as a gas residential cooktop with controls, but it will be understood that the teachings of the present invention are also applicable to industrial and commercial gas cooktop appliances.
Among features provided by this invention are: a capacitive touch keyboard interface, an entirely electronic control system controlling the gas flow through modulating valves; an innovative modulating valve activated through a pulse-width-modulation (PWM) port, capable of infinitely controlling the flow of gas while also providing for an “off” position, the electrical modulating valve therefore eliminating the need for an additional in-line solenoid valve to sequence the flame “on” and “off” during simmer operation; and ceramic hot-surface igniter(s) controlled and monitored by the electronic control system, capable of constant gas re-ignition without generation of electromagnetic interference.
Natural or propane gas is selectively provided to each individual burner, through the use of electrically actuated modulating valves, thus eliminating the need for mechanical valves and actuator knobs protruding through the user console and facilitating the maintenance of such surfaces. Ignition of the gas is monitored through temperature sensing, and ceramic hot-surface igniters are also monitored through current sensing. Safety features such as main in-line valve closure and de-energizing of the igniters are supported in the event that a fault condition occurs. Features such as visual and audible alarms are also generated, providing the user with positive indications of serious error conditions.
The user interface panel 110, placed in registry with a silk-screened portion of a ceramic glass panel 109, preferably firther includes one or more visual indicator(s) 116, such as seven-segment LED displays, discrete LED displays, bar-graph LED displays, LCD displays, and vacuum fluorescent displays, for displaying information 120 concerning the status of the cooktop to the user; an audible annunciator 125 such as an external drive or built-in drive piezo-acoustic element, magnetic transducer or Mylar speaker, used to provide audible indication 124 that a touch key is selected and also to provide for an audible alarm whenever a system error is detected; and an array of capacitance sensitive keypads 115, each one having a capacitive field 119, produced, detected and analyzed by a capacitive-keyboard decoding interface module 102, and capable of electrically reacting to a human hand or finger 121, placed in proximity with any one capacitive field 119 associated with one of the capacitance sensitive keypads 115.
The microcontroller-based control 111 comprises an array of modules, dedicated to the driving and monitoring of the various elements of the system, controlled by the microcontroller 101.
The display elements of the visual indicators 116 are driven by a display-power-driver module 103 preferably comprising serial output shift registers (integrated circuits), multiple channels of source-driver integrated circuits, multiple channels of sink-driver integrated circuits, and may also include driver circuits using discrete transistors.
A power module 126 consisting of discrete transistor circuitry drives the audible interface 125. Power module may be unnecessary if the audible interface is made with one or more built-in drive acoustic annunciators.
A valve-power driving module includes a power relay or a triac module 107 for driving main safety valve 112 and a Darlington array integrated circuit or an array of discrete transistors 108 for driving the modulating valve(s) 113.
An igniter-power driving module 105 is also provided and includes a power relay or a triac module for driving one or more ceramic hot-surface igniter(s) 117. A current sensor module 104 is also provided for monitoring the current flowing through the hot-surface igniter(s) 117.
Appropriate amplification module 106 is provided to deliver reliable temperature sensor data, at the proper voltage span, to an analog-to-digital input port of microcontroller 101. Amplification may not be needed for some sensors, and thus module 106 may also be a simple voltage divider circuitry, e.g., if the temperature sensor used is a thermistor.
A sine-to-square-wave converter input module 127 is preferably included in the microcontroller-based control 111 to provide the microcontroller 101 with a reliable time base for proper timing of “on/off” flame sequencing periods, during simmer mode. The sine-to-square wave converter input module 127 may consist of a diode rectifying input circuitry, tapping a portion of the conventional AC supply voltage and feeding a transistor based circuit. That circuit, connected to a pull-up resistor, provides as an output a square wave representative of the 50 Hz or 60 Hz signal carried by the AC voltage supply line.
Additionally, the microcontroller-based control 111 preferably includes a capacitive-keyboard decoding interface module 102 with a serial or parallel communication interface, capable of detecting and analyzing a user touch condition. The capacitive-keyboard decoding module preferably includes: a capacitive matrix decoder integrated circuit with a serial or parallel communication interface, a portion of the ceramic glass panel 109 (preferably silk-screened) used to provide for a user touch interface, and an array of capacitive sensing keypads 115 placed in registry with the user touch interface portion of the ceramic glass panel 109. Key sensitivity may be made individually trinrnable for adaptation to key size, key shape, and key location on the user interface keyboard. Capacitive sensing for the keyboard interface may be done as described in U.S. Pat. No. 5,730,165 to Philipp, the entire disclosure of which is hereby incorporated by reference. In U.S. Pat. No. 5,730,165, a capacitive field sensor employs a single coupling plate to detect a change in capacitance to ground. The apparatus comprises a circuit for charging a sensing electrode and a switching element acting to remove charge from the sensing electrode and to transfer it to a charge detection circuit.
A suitable capacitive-keyboard decoding interface 102 is the model QM1, available from Quantum Research Group Ltd. of Southampton, England and Pittsburgh, Pa, or preferably the models QT60320 and QT 60321 Matrix Scan IC's available from that company. The QT60320 family of Matrix Scan IC's is a family of capacitive-keyboard decoding interfaces, based on the Philipp invention mentioned above, utilizing dual coupling capacitive plate sensors, disposed in a key matrix configuration.
The microcontroller-based control 11 also preferably includes a microcontroller integrated circuit 101 having integrated features, as per the following list:
Those skilled in the art will recognize that multiple ports of any of the types listed may be provided.
The valve portion of the system preferably includes an in-line gas valve assembly having a single main in-line solenoid safety valve 112, commonly found in the industry and an in-line modulating valve 113 for each burner. One suitable modulating valve is disclosed in U.S. Pat. No. 5,458,294 to Zachary et al., in which a variable orifice solenoid has a plurality of positions, and the positions are controlled by the application of a voltage signal to the modulating valve. The entire disclosure of U.S. Pat. No. 5,458,294 to Zachary et al. is incorporated herein by reference, as is the entire disclosure of U.S. Pat. No. 6,116,230 to Clifford et al., mentioned above.
U.S. Pat. No. 5,458,294 discloses an apparatus for accurately controlling gas fuel flow to a combustion device to control gas flow to a burner of the combustion device. A variable orifice solenoid-operated valve serves as a control element. The valve includes a poppet having a fixed control surface at an end received in an insert element having a variable control surface. The poppet has a plurality of positions within the insert element, including a full open position and a full closed position. Maximum fuel flow is measured in the full open position and minimum fuel flow is measured in the full closed position. Intermediate partially open positions are adjustable by a signal of an electronic controller connected to the solenoid valve operating as a function of actual and desired temperature of the combustion device. If desired, the fixed control surface can contact the variable control surface at some point as the fixed control surface moves into the insert, to completely seal the valve and shut off the flow of gas to the burner means.
The flame ignition portion of the system preferably includes a resistive hot-surface igniter 117, preferably fixed to the burner base 128, capable of producing a temperature of 1350° C. in a time-to-design-temperature equal to or less than 3 seconds. U.S. Pat. No. 5,892,201 to Croucher et al., discloses a ceramic igniter, comprising: (a) a pair of electrically conductive portions, each portion having a first end, (b) a hot zone disposed between and in electrical connection with each of the first ends of the electrically conductive portions, the hot zone having an electrical path length of less than 0.5 cm, and (c) an electrically non-conductive heat sink material contacting the hot zone. The entire disclosure of U.S. Pat. No. 5,892,201 to Croucher et al. is incorporated herein by reference. One suitable resistive ceramic hot-surface igniter is the Norton Igniter model No. M-401 manufactured by Saint-Gobain Industrial Ceramics Inc. of Milford, N.H.
Additionally, the invention provides for one or more temperature sensor(s) 118, each one fixed to the burner base 128 and directed at the flame area of the burner to detect a flame, thus monitoring proper ignition of the gas delivered to the burner 114 by the modulating valve(s) 113. The temperature sensor may be of any suitable type, such as: thermistors, thermocouples, or infrared temperature sensors.
Operation
A continuous flame modulation mode of operation, described below, is used for the portion of the total span of gas output levels that can be safely modulated by the modulating valve, where the flame is continuously present and not sequenced “on” and “off” by the controller. This continuous flame modulation mode is associated with cooking levels ranging from medium-low to high BTU output. Furthermore, medium-low level of flame is defined here as being the lowest level of flame that can be safely maintained without self-extinguishing, can be safely ignited by a ceramic hot-surface igniter, and can be easily sensed by the flame detector, for any particular burner orifice size.
In continuous-flame-modulation mode of operation the microcontroller 101 first sends a signal to the power-driving portion 107 of the controller, driving the safety valve 112 “on” to permit the gas entering the system 122 to reach the in-line modulating valve(s) 113, then the microcontroller 101 sends a pulse-width-modulation signal to the power-driving portion 108 of the controller 111 driving the modulating valve 113, to proportionally modulate the valve opening size to the desired gas flow level, as selected by the user and, thus, to permit the gas to reach the burner. Hence, this mode of operation adjusts the flame height to any desired level of BTU output ranging from medium-low to high BTU output. Furthermore, in this particular mode of operation, the hot-surface igniter 117 is powered only during the first phase of the continuous-flame modulation mode of operation. Ignition is provided and maintained from the time that the gas is permitted to reach the burner, until a flame is detected by the appropriate temperature sensor 118 associated with the controlled burner. Ignition process can also be aborted if one of the following error conditions occurs: no hot-surface igniter current is sensed, and/or flame is not detected for a predetermined period of time. In any of these error condition cases, the controller 111 automatically turns off the safety valve 112, the hot-surface igniter 117, and the modulating valve 113 corresponding to the faulty burner. Then, visual and audible signals are generated to alert the user of the faulty condition.
Simmer mode of operation is defined here as being the mode of operation used for the lowest portion of the total span of BTU output levels. In simmer mode of operation, the microcontroller 101 first sends a signal to the power-driving portion 107 of the controller, driving the safety valve 112 “on”, to permit the gas entering the system 122 to reach the in-line modulating valve(s) 113. Then, the microcontroller 101 sends a predetermined pulse-width-modulation signal to the power-driving portion 108 of the controller 111 driving the modulating valve 113, to proportionally modulate the valve opening size to a predetermined level of gas flow, and, thus, to permit the gas to reach the burner. In simmer mode of operation, the pulse-width-modulation (PWM) output level is set to provide a predetermined medium-low height level of flame that can safely be maintained without self-extinguishing, can safely be ignited by the ceramic hot-surface igniter, and can easily be sensed by the flame detector, for any particular burner orifice size. In that particular mode of operation the pulse-width-modulation output, which drives the modulating valve associated with the burner working in simmer mode, is continuously being sequenced “on” and “off” by the microcontroller 101 A time-based sequencer, ruled by appropriate software program and 60 Hz detection module 127, is activated, toggling the PWM output driving the modulating valve, and thus turning the flame “on” and “off” in a timely fashion. During the “off” portion of the sequencing, while no PWM signal is provided to the modulating valve, the valve reverts to its “off” position, sealing the opening and thus preventing the gas from reaching the gas burner under simmer mode of operation. During the “on” time portion of the sequencing, the PWM output is set to the medium-low level of BTU output, providing the safest low level of flame that can be ignited, maintained, and sensed by the temperature sensor. The “on” and “off” periods are produced to correspond to a desired simmer level as selected by the user. As an example of this, for a particular output level, as selected by the user; “on” time, when the flame is present, can be equal to 1 second, and “off” time, when the flame is not present, can be equal to 7 seconds, to produce a 1 over 8 or 1:8 ratio of BTU output in relation to an hypothetical constant flame produced at the same predetermined flame height level. Additionally, during that particular mode of operation, the hot-surface igniter 117 is continuously powered by the igniter power module 105, and constantly monitored by the igniter-current sensor module 104 to provide for an instantaneous ignition process, bypassing the time-to-design-temperature period. Furthermore, the temperature sensor output is read during each “on” portion of the flame sequencing activities. Ignition is thus provided and maintained until the user selects a burner powering level other than those provided within the span of simmer mode of operation, and can also be aborted if one of the following error condition occurs: no hot-surface igniter current is sensed and/or flame is not detected during the “on” periods of the sequencing cycles. In any of these error condition cases, the controller 111 automatically turns off the safety valve 112, the hot-surface igniter 117, and the modulation valve 113. Then, visual and audible signals are generated to alert the user of the faulty condition.
Total span of BTU output can range from very low to very high and have an infinite number of steps from which many can operate in simmer mode of operation and many others in the continuous flame modulation mode of operation. For example, a particular control could arbitrarily offer 44 levels of BTU output, from which the lowest fourteen levels could be operating in a simmer mode of operation and the remaining 30 levels could be modulated in a continuous flame modulation mode of operation. The above-mentioned example is given here only as one possible embodiment of the present invention and does not intend to constitute a limitation to the present invention. One of ordinary skill in the art would readily perceive that the total number of possible cooking-level steps, as well as the portion of these steps predetermined to work either in the simmer mode or in the continuous flame modulation mode of operation, are readily defined by appropriate software programming alone. Control software programming is described next.
Control Software
a and 3b together show a flowchart of control software for a preferred embodiment of the invention, using conventional flowchart symbols. Table I below shows the steps used in the control software illustrated in
It can be seen in
If no current flows through the igniters while activated and/or no flame is sensed while gas is conducted to the burner under control, then visual and audible alarms are generated 317, and the faulty burner is deactivated by stopping appropriate PWM output, shutting off the appropriate igniter and clearing the appropriate burner display 305.
In simmer mode of operation shown by the series of actions identified by reference numeral 311, i.e., when a simmer level of BTU output is selected by the user, the microcontroller energizes the hot surface igniter, energizes the main solenoid valve, outputs a predetermined PWM level to the appropriate modulating valve, sets the PWM output sequencer to selected BTU output level, shows the selected burner level in the burner display and leaves the igniter continuously “on” during the entire simmer operation.
In continuous-flame-modulation mode of operation, shown by the series of actions identified by reference numeral 312, i.e., when a level of BTU output other than simmer level is selected by the user, the microcontroller then energizes the hot surface igniter, energizes the main solenoid valve, outputs the selected PWM level to the appropriate modulating valve, shows the selected burner level in the burner display and further de-energizes the hot surface igniter once the ignition of the flame is achieved 318.
Use of the Invention
To use the invention, a user touches desired control keys on the cooktop keyboard similar to the one illustrated in
Industrial Applicability
The invention is useful in domestic and commercial cooking, providing an electronically controlled gas cooktop with multiple heating modes, including precisely controlled simmering and safety features.
Although specific embodiments of the present invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the particular embodiments described herein, but is capable of numerous rearrangements, modifications, and substitutions without departing from the scope of the invention. One skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
| Number | Date | Country | |
|---|---|---|---|
| 0045142 A1 | Apr 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60159885 | Oct 1999 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US00/28624 | Oct 2000 | US |
| Child | 09884828 | Jun 2001 | US |
