This disclosure relates to gas safety valves with a hold open circuit that holds the valve open when a threshold current sufficient to heat a hot surface igniter to an autoignition temperature of the gas is reached.
Certain cooktops include safety features to ensure that cooking gas is only supplied to the burner once ignition is achieved. This ensures that uncombusted cooking gas is not supplied to the surrounding environment, which could lead to a fire or explosion.
In one known system, the user operates a gas control knob to manually actuate a gas valve and supply current to a spark igniter adjacent the burner. A thermocouple acts as a flame detector that generates a direct current when ignition is successful. At a certain threshold current, the current generates a magnetic field that holds the gas valve in the open position so the user can release the knob. The gas valve is configured to fail closed such that when no flame is present, the magnetic force drops below a characteristic force required to hold the gas valve open, causing it to close. The threshold current is sufficient to hold the valve in the open position, but not sufficient to open it. User intervention is required to open the valve by manually actuating it. The integrated gas valve and electromagnet is referred to as a “gas tap” in Europe.
Spark igniters are user-actuated igniters that create a brief electric discharge and a spark that ignites the gas. Thus, they cannot remain on to ensure continuous ignition. As a result, it is important to detect the presence of a flame, such as by using a thermocouple, to avoid supplying burners with uncombusted gas. However, there is a significant amount of lag time and/or dead time in generating the threshold current needed to hold the gas valve open following ignition because the thermocouple must be heated long enough to reach a temperature at which threshold current is generated. Typically, the user is required to continue to manually hold the gas valve open for five to ten seconds after ignition occurs due to the thermal response of the thermocouple.
Hot surface igniters are a possible alternative to spark igniters. Hot surface igniters are used to ignite combustion gases in a variety of appliances, including furnaces and clothing dryers. Some hot surface igniters, such as silicon carbide igniters, include a semi-conductive ceramic body with terminal ends across which a potential difference is applied. Current flowing through the ceramic body causes the body to heat up and increase in temperature, providing a source of ignition for the combustion gases. Other types of hot surface igniters, such as silicon nitride igniters, include a ceramic body with an embedded circuit across which a potential difference is applied. Current flowing in the embedded circuit causes the ceramic body to heat up and increase in temperature, providing a source of ignition for combustion gases.
Unlike spark igniters, hot surface igniters can be continuously energized to ignite cooking gas because it is the igniter surface temperature, and not a discrete burst of electric potential, that causes ignition. When used in conjunction with the gas safety valve assembly described above, the energization state of the hot surface igniter provides an indication that ignition has occurred (or will occur) which allows for the elimination of the thermocouple. However, some means is required to link the current used to energize the igniter to the current required to hold the gas valve open. Thus, a need has arisen for a cooking gas safety apparatus that addresses the foregoing issues.
In accordance with a first aspect of the present disclosure, a cooking gas safety apparatus is provided which comprises a valve assembly that is manually actuatable to an open position to allow the passage of the cooking gas. The valve assembly includes at least one coil that is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value. The apparatus further comprises a hold open circuit comprising a hot surface igniter and the coil, wherein the hot surface igniter is in electrical communication with the coil, and wherein no later than about eight seconds after the at least one coil is subjected to a current having the threshold current value, a surface of the hot surface igniter reaches at least an autoignition temperature of the cooking gas. In accordance with certain examples, the coil is a direct current coil. In accordance with other examples, the coil is an alternating current coil. In accordance with additional examples, the hold open circuit is operable in a full power mode and a reduced power mode. In preferred examples, no later than about six seconds and more preferably no longer than four seconds after the at least one coil is subjected to a current having the threshold current value, a surface of the hot surface igniter reaches at least an autoignition temperature of the cooking gas.
In accordance with a second aspect of the present disclosure, a method of supplying cooking gas to a cooktop burner is provided. The method comprises providing a valve assembly comprising a valve having an open position and a closed position, wherein when the valve is in the open position, the cooking gas passes through the valve. The valve assembly further comprises at least one coil that is energizable to hold the valve in the open position. The method further comprises manually actuating the valve to the open position, and supplying an alternating current to a hold open circuit comprising a hot surface igniter and the at least one coil, thereby holding the valve in the open position. In certain examples, the at least one coil comprises a direct current coil, and the method comprises converting the alternating current to a time-varying direct current which is supplied to the direct current coil. In other examples, the at least one coil comprises an alternating current coil. In certain examples, the step of manually activating the valve is performed until the hot surface igniter reaches at least the autoignition temperature of the cooking gas.
In accordance with a third aspect of the present disclosure, a cooking gas safety apparatus is provided which comprises a valve assembly comprising a valve and at least one coil. The valve comprises a fluid inlet and a fluid outlet and is manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value; and the apparatus further comprises a hot surface igniter electrically connectable to the at least one coil to define a hold-open circuit, and wherein when subjected to an alternating current of 120 V AC rms, the hot surface igniter reaches a surface temperature of at least 1400° F. in no more than eight seconds after the at least one coil is subjected to the threshold current.
In accordance with a fourth aspect of the present disclosure, a cooking gas safety apparatus is provided which comprises a valve assembly comprising a valve and at least one coil. The valve comprises a fluid inlet and a fluid outlet and is manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value; and the apparatus further comprises a hot surface igniter electrically connectable to the at least one coil to define a hold-open circuit, and wherein when subjected to an alternating current of 120 V AC rms, the hot surface igniter reaches an autoignition temperature of at least one of butane, butane 1400, propane, and natural gas no more than eight seconds after the at least one coil is subjected to the threshold current.
Like reference numerals refer to like parts in the figures.
Described below are examples of gas safety valve apparatuses that comprise a valve assembly and a “hold open” circuit. The valve assembly comprises a valve and at least one coil that is energizable to hold the valve in the open position only when the at least one coil is subjected to a current that exceeds a threshold current value. The hold-open circuit ensures that the valve only admits gas to a burner when a user actuates a gas control knob or when the burner is lit. More specifically, the hold open circuit causes the valve to close if a hot surface igniter used to ignite the burner is not energized sufficiently to reach (or maintain) a surface temperature at or above the autoignition temperature of the cooking gas, thereby reducing the likelihood that gas will unintentionally flow to an unlit burner. In certain examples, the igniter is energized by a source of alternating current, and the at least one coil is a direct current coil that only holds the valve open when subjected to a threshold direct current. In accordance with such examples, the hold open circuit is configured to supply the threshold direct current to the at least one coil only when the igniter is supplied with a current sufficient to cause a surface of the igniter to reach an autoignition temperature of the cooking gas.
Referring to
A shaft engagement surface 38 is provided on the valve disk 36 and is engaged by a shaft 44 (
The valve disk 36 is connected to a distal valve shaft 32 which is in turn connected to a magnetic disk 30 that is housed in electromagnet housing 41. Electromagnet housing 41 houses a direct current coil 40 wrapped around a corresponding magnetic core 42. Multiple coils each wrapped around their own respective core may also be provided. The valve disk 36 is biased in the proximal direction along the length l axis by spring 34 which is attached to the proximal end of electromagnet housing 41. The distal valve shaft 32 runs through the spring 34 and through a hole (not shown) in the proximal end of the electromagnet housing 41. When the gas safety valve 21 is in the closed position (
As mentioned previously, it would be desirable to modify the flame detection scheme typically used with cooking gas safety valve assembly 20 to shorten the duration of the manual actuation of gas knob stem 26 by the user prior to the valve disk 36 being held in the open position of
In the examples that follow, instead of a spark igniter, the burner(s) with which cooking gas safety valve assembly 20 are used are ignited by a ceramic, hot surface igniter 52. Ceramic hot surface igniters useful in connection with the gas valve assemblies described herein include those described in U.S. patent application Ser. No. 16/366,479, the entirety of which is hereby incorporated by reference.
Although represented as a resistor in
The preferred ceramic hot surface igniters 52 described herein are generally in the shape of a rectangular cube and include two major facets, two minor facets, a top and a bottom. The major facets are defined by the first (length) and second (width) longest dimensions of the ceramic hot surface igniter body. The minor facets are defined by the first (length) and third (thickness) longest dimensions of the igniter body. The igniter bodies also include a top surface and a bottom surface which are defined by the second (width) and third (thickness) longest dimensions of the igniter body. The ceramic hot surface igniter 52 may have a positive or negative temperature coefficient of resistance. However, positive temperature coefficients of resistance are preferred.
In accordance with examples in which ceramic hot surface igniter 52 has a positive temperature coefficient of resistance, the igniter tiles are ceramic and preferably comprise silicon nitride. The conductive ink circuit is disposed between the tiles and generates heat when energized. The ceramic tiles are electrically insulating but sufficiently thermally conductive to reach the outer surface temperature necessary to ignite combustible mixtures of air and gases selected from natural gas, propane, butane, butane 1400 (a butane and air mixture with a heating value of 1400 Btu/ft3), and mixtures thereof, within the desired period of time.
As described in greater detail below, in certain examples, the ceramic tiles comprise silicon nitride, ytterbium oxide, and molybdenum disilicide. In the same or other examples, the conductive ink circuit comprises tungsten carbide, and in certain specific implementations, the conductive ink additionally comprises ytterbium oxide, silicon nitride, and silicon carbide.
In certain examples, when subjected to a potential difference of 120V AC (rms), the ceramic hot surface igniters 52 described herein reach a surface temperature of at least 1400° F., preferably no less than 1800° F., more preferably no less than 2100° F., and even more preferably no less than 2130° F. These temperatures are preferably reached in no more than eight seconds, more preferably reached in no more than six seconds, and still more preferably, reached in no more than four seconds after the 120V AC (rms) potential difference is applied.
In the same or additional examples, the surface temperature of the ceramic hot surface igniters herein does not exceed 2600° F., preferably does not exceed 2550° F., more preferably does not exceed 2500° F., and still more preferably 2450° F. at any time after a full wave 132V AC (rms) potential difference is applied to the igniter, including after a steady-state temperature is reached.
In the same or other examples of ceramic hot surface igniters in accordance with the present disclosure, when subjected to a potential difference of 102V AC (rms), the ceramic hot surface igniters described herein reach a surface temperature of at least 1400° F., preferably at least 1800° F., and still more preferably at least 2100° F. in no more than seventeen, preferably more than ten, and more preferably no more than about seven seconds after the 102V AC (rms) potential difference is first applied. These temperatures are preferably reached in no more than four seconds and are more preferably reached in no more than three seconds.
In the same or additional examples, the thickness of the conductive ink circuit of the hot surface igniter (taken along the thickness axis) is not more than about 0.002 inches, preferably not more than about 0.0015 inches, and more preferably, not more than about 0.0009 inches. In the same or additional examples, the thickness of the conductive ink circuit (taken along the thickness axis) is not less than about 0.00035 inches, preferably not less than about 0.0003 inches, and more preferably, no less than about 0.0004 inches.
The hot surface igniters 52 of the present disclosure also preferably have a green body density of at least 50 percent of theoretical density, more preferably, at least 55 percent, and still more preferably at least 60 percent of theoretical density.
As discussed in U.S. patent application Ser. No. 16/366,479, ceramic hot surface igniters 52 used in the gas heating systems described herein are prepared by sintering ceramic compositions. In certain examples, post-sintering, the tiles used to form the igniter 52 (not including conductive ink circuit) have a room temperature resistivity that is no less than 1012 Ω-cm, preferably no less than 1013 Ω-cm, and more preferably, no less than 1014 Ω-cm. In the same or other examples, the tiles have a thermal shock value in accordance with ASTM C-1525 of no less than 900° F., preferably no less than 950° F., and more preferably, no less than 1000° F.
In other examples, the conductive ink comprising the conductive ink circuit has a (post-sintering) room temperature resistivity of from about 1.4×10−4 Ω·cm to about 4.5×10−4 Ω·cm, preferably from about 1.8×10−4 Ω·cm to about 4.1×10−4 Ω·cm, and more preferably from about 2.2×10−4 Ω·cm to about 3.7×10−4 Ω·cm. In the case of a material with a constant cross-sectional area along its length, resistivity ρ at a given temperature T is related to resistance R at the same temperature Tin accordance with the well-known formula:
R(T)=ρ(T)(I/A), (1)
where
In the case of a cross-sectional area that varies along the length of the conductive circuit, the resistance may be represented as:
In certain examples, the ceramic bodies comprising the ceramic hot surface igniters 52 herein preferably comprise silicon nitride and a rare earth oxide sintering aid, wherein the rare earth element is one or more of ytterbium, yttrium, scandium, and lanthanum. The sintering aids may be provided as co-dopants selected from the foregoing rare earth oxides and one or more of silica, alumina, and magnesia. A sintering aid protective agent is also preferably included which also enhances densification. A preferred sintering aid protective agent is molybdenum disilicide. The rare earth oxide sintering aid (with or without the co-dopant) is preferably present in an amount ranging from about 2 to about 15 percent by weight, more preferably from about 8 to about 14 percent by weight, and still more preferably from about 12 to about 14 percent by weight of the ceramic body. Molybdenum disilicide is preferably present in an amount ranging from about 3 to about 7 percent, more preferably from about 4 to about 7 percent, and still more preferably from about 5.5 to about 6.5 percent by weight of the ceramic body. The balance is silicon nitride.
The conductive ink circuit is preferably printed onto the face of one of the ceramic tiles to yield a ceramic hot surface igniter(post-sintering) room temperature resistance (RTR) of from about 60Ω to about 120Ω, preferably from about 70Ω to about 110Ω, and more preferably from about 80Ω to about 100Ω. At the same time, the ceramic hot surface igniter high temperature resistance (HTR) over the temperature range 2138° F. to 2700° F. is generally from about 300Ω to about 500Ω, preferably from about 400Ω to about 480Ω, and more preferably from about 430Ω to about 450Ω.
The conductive ink in the igniter 52 should comprise tungsten carbide in an amount ranging from about 20 to about 80 percent, preferably from about 30 percent to about 80 percent, and more preferably from about 70 to about 75 percent by weight of the ink. Silicon nitride is preferably provided in an amount ranging from about 15 to about 40 percent, preferably from about 15 to about 30 percent, and more preferably from about 18 to about 25 percent by weight of the ink. The same sintering aids or co-dopants described for the ceramic body are also preferably included in an amount ranging from about 0.02 to about 6 percent, preferably from about 1 to about 5 percent, and more preferably from about 2 to about 4 percent by weight of the ink.
In the examples of cooking gas safety apparatuses described herein, a hot surface igniter 52 is used to ignite cooking gas supplied to a burner, and the flow of gas to the burner is regulated by a cooking gas safety valve assembly 20 that is held open only when the current supplied to the hot surface igniter is sufficient for the igniter to reach the autoignition temperature of the cooking gas. The “autoignition temperature” is the lowest temperature at which a gas-air mixture will ignite and continue to burn. In preferred examples, the igniter 52 is also operable in a full power and a reduced power mode. During ignition, the igniter 52 would operate at full power. Following ignition, the igniter would operate at reduced power, albeit a power sufficient to heat the igniter to at least the autoignition temperature of the cooking gas.
Referring to
The hold open circuit 50 includes hot surface igniter 52 and direct current coil 40. As shown in the figure, the hot surface igniter 52 is in electrical communication with the direct current coil 40 such that when the direct current coil 40 is subjected to a current having the threshold current value, a surface of the igniter 52 reaches at least an autoignition temperature of the cooking gas. Providing an igniter 52 that only reaches the gas autoignition temperature when the direct current coil 40 is at or below threshold current better ensures that gas is shut-off to the burner when the igniter is not hot enough to ignite the cooking gas. As a result, flame detection devices such as thermocouples which have significant dead time or lag time may be eliminated, which significantly reduces the amount of time during which the user must depress the gas knob stem 26 in the distal direction along the length l axis to keep the gas valve assembly in the open condition (of
The hot surface igniter 52 is powered by an alternating current source 51. In accordance with the example of
As shown in
In
A half-wave rectified voltage such as that provided by diode 64 is a time-varying, unidirectional voltage and has the appearance of an AC sine wave superimposed on a DC signal, which is known as a “ripple.” A ripple has a characteristic factor called the “ripple factor” which is the ratio of the root-mean-square (RMS) value of the AC component to the mean value of the total. A single phase, half-wave rectified signal such as the output of diode 64 has a ripple factor of 1.21. As known to those skilled in the art, an RMS value of a time-varying signal is the square root of the mean value of a squared function. In the context of a time-varying current or voltage, the respective RMS current or voltage value is the DC value that has an effect equivalent to the time-varying value. The RMS voltage and current can be calculated from equations (2a) and 2(b), respectively:
In the example of
Referring first to the case when switch 62 is open, when the diode 64 is forward biased, capacitor 58 will charge and will draw current until reaching its saturation voltage. When the AC source voltage begins to drop from its maximum, capacitor 58 will begin to discharge when the AC source voltage falls below the capacitor 58 saturation voltage. Thus, when the AC source 51 switches polarity and diode 64 is reverse biased, the capacitor 58 will continue to discharge and supply current to hot surface igniter 52 and direct current coil 40. The result is that the hot surface igniter 52 and the direct current coil 40 effectively see a smoothed ripple, i.e., their voltages are equivalent to an AC voltage sinewave superimposed on a DC voltage signal.
ΔV=0.7i/((f)Ctotal) (2c)
In equation (2c), 0.7 is the complement of the rectifier-current duty cycle, which is assumed to be 0.3. As the capacitance of capacitor 58 increases, the igniter 52 input voltage at node N52 shows less ripple (becomes flatter) in both the full and reduced power modes (described below). As the capacitance of capacitor 60 increases, the igniter 52 input voltage at node N52 shows less ripple during the full power only, and igniter 52 will heat to a higher temperature. Also, as the capacitance of capacitor 60 increases the likelihood of stressing the components of circuit 50 beyond their ratings increase. Conversely, when circuit 50 is in reduced power mode, as the capacitance of capacitor 60 decreases, the igniter 52 input voltage at node N52 will show more ripple (become “less flat”), and the RMS current through igniter 52 will decrease, causing igniter 52 to reach a lower steady-state temperature. The direct current coil 40 tends to have a much lower resistance and inductance than the other circuit components. Thus, the selection of those properties for the coil 40 tends to be less critical to the overall performance of circuit 50.
When switch 62 is closed, the hot surface igniter 52 is in full-power mode. When switch 62 is open, hot surface igniter 52 is in reduced power mode. Full power mode is preferably used during an ignition operation. Reduced power mode is preferably used during a cooking operation and provides a means of reigniting the cooking gas in the event of a flame out. When switch 62 is closed, capacitors 58 and 60 act as a single capacitor having a total capacitance that equals the sum of each of their respective capacitances, meaning that the parallel combination is equivalent to a single capacitor having a capacitance equal to the sum of both capacitances. The capacitance values of capacitors 58 and 60 will affect the percentage of full power that is achieved during reduced power operation. In certain examples, releasing the gas valve stem 26 after the direct current coil 40 has latched in the open position of
The power dissipated in surface igniter 52 is proportional to the total capacitance of capacitors 58 and 60 in full-power mode and capacitor 58 in reduced power mode. Thus, the ratio of igniter power dissipation in reduced-power mode to the igniter power dissipation in full-power mode decreases as the capacitance of capacitor 60 increases relative to the capacitance of capacitor 58. As is the case with reduced power mode, while the diode 64 is forward-biased, the capacitors 58 and 60 will charge until reaching their saturation voltages. Once the capacitors are saturated, no current will flow to them until the AC source 51 voltage drops below their saturation voltages (which may differ between capacitors 58 and 60). As the output voltage from diode 64 falls below either capacitor's saturation voltage (or falls below the peak source voltage if it is less than the saturation voltage), that capacitor will begin to discharge, causing current to flow from the capacitor 58 and/or 60 through the igniter 52 and to direct current coil 40. When the diode 64 is reverse-biased, no current from the AC source 51 will flow through it. However, capacitors 58, 60 will continue to provide current to the igniter 52 and the direct current coil 40.
In hold-open circuit 50 of
The hold open circuit of
Capacitors 58 and 60 form a second parallel combination with one another, and the second parallel combination forms a third parallel combination with the second series combination. The third parallel combination forms a third series combination with diode 64.
The hold open circuit 50 is preferably designed to operate at AC source 51 voltages ranging from 90 V AC (rms) to about 135V AC (rms), preferably from about 110V AC (rms) to about 130 V AC (rms), and more preferably from about 115V AC (rms) to about 125 V AC (rms) and supply sufficient current for igniter 52 to reach the autoignition temperature of the cooking gas. In certain examples, hot surface igniter 52 is designed to have a high temperature resistance (i.e., a resistance at the ignition temperature of the cooking gas) that ranges from about 330Ω to about 500Ω, preferably from about 400Ω to about 480Ω, and more preferably from about 430Ω to about 450 a Direct current coil 40 has a threshold (rms) current ranging from about 30 mA to about 90 mA, preferably from about 40 mA to about 80 mA, and more preferably from about 50 mA to about 70 mA. Direct current coil 40 also has an inductance ranging from about 0.005 mH to about 0.010 mH, preferably from about 0.006 mH to about 0.009 mH, and more preferably from about 0.007 mH to about 0.008 mH.
Capacitors 58 and 60 may have exemplary values ranging from about 15 μF to about 30 μF, preferably from about 18 μF to about 25 μF, and more preferably from about 20 μF to about 24 μF. Direct current coil 40 has a threshold (rms) current ranging from about 30 mA to about 90 mA, preferably from about 40 mA to about 80 mA, and more preferably from about 50 mA to about 70 mA. Resistors 54 and 56 may have exemplary resistance values ranging from about 20Ω to about 40Ω, preferably from about 25Ω to about 35Ω, and more preferably from about 28Ω to about 32Ω. Fuse 66 may be rated, for example, for about 0.5 A to about 1.5 A, preferably from about 0.6 A to about 1.3 A, and more preferably from about 0.8 A to about 1.2 A.
A hold-open circuit 50 as shown in
Capacitors 58 and 60 have respective capacitance values of 22 μF. Resistors 54 and 56 have resistance values of 3052. Direct current coil 40 has an inductance value of 0.0074 mH. The circuit is simulated with a 120 VAC (rms) 60 Hz voltage source signal.
Hold open circuit 50 of
In certain examples, releasing the gas valve stem 26 after the direct current coil 40 has latched in the open position of
Direct current coil 40 is in series with a Zener diode 72 and fuse 78 to form a first series combination. The first series combination forms a first parallel combination with resistor 80. When switch 86 is closed, the second parallel combination of resistors 82 and 84 is in series with the first parallel combination to form a second series combination. The second series combination forms a third series combination with hot surface igniter 52. The third series combination and capacitor 74 form a third parallel combination that is in series with diode 76 and fuse 88.
When switch 86 is open, the second series combination consists of the first parallel combination and resistor 82 alone (i.e., without resistor 84). Thus, when switch 86 is closed, hot surface igniter 52 is in series with an equivalent circuit component having an overall resistance lower than when switch 86 is open. This means that more voltage is available for the igniter 52, and hence, it draws more power. Resistor 82 determines how hot igniter 52 will get in reduced power mode and impacts the igniter 52 temperature in full power mode.
When switch 86 is closed, resistor 84 allows more current to flow through the circuit 70, causing the igniter 52 to get hotter in full power mode. Increased values of the resistance of resistor 84 will tend to decrease the power dissipated by igniter 52 in full power mode, whereas decreased resistance values of resistor 84 will tend to increase the power dissipated by igniter 52 in full power mode.
As with hold open circuit 50, hold open circuit 70 includes a diode 76 to half-wave rectify the AC power source 71. Diode 76 is preferably selected to have a voltage rating that balances cost and the desired lifetime of circuit 70. Higher voltage rating diodes tend to be more expensive, but as the voltage rating of diode 76 decreases, the lifetime of circuit 70 decreases. Because of diode 76 and as with circuit 50, a ripple is also present in circuit 70. Here, capacitor 74 is placed in a series-parallel relationship to the diode 76 and the hot surface igniter 52 to smooth the ripple voltage and reduce the ripple factor. Capacitor 74 is not selectively connected to the hold open circuit 70 but rather remains in electrical communication with the hot surface igniter 52 and direct current coil 40 at all times. When diode 76 is forward-biased, capacitor 74 will charge until it reaches its saturation voltage. Once the capacitor is at its saturation voltage, if the AC source 71 voltage drops below the saturation voltage, capacitor 74 will begin discharging until the AC voltage exceeds the capacitor 74 voltage, at which point capacitor 74 will begin charging again. In general, increasing values of the capacitance of capacitor 74 will flatten the ripple in the igniter 52 input voltage at node N52 in both the full and reduced power modes of operation and will also lower the AC supply voltage at which the valve assembly 20 releases to the closed position of
Resistor 80 acts as a current set resistor. As the current through igniter 52 increases, the voltage at resistor 80 increases. When the voltage at resistor 80 reaches the breakdown voltage of Zener diode 72, direct current coil 40 will receive current. Fuse 78 provides an extra layer of protection for direct current coil 40 in the event that resistor 80 fails. At excessively higher current ratings, direct current coil 40 may fail to close when circuit 70 fails. If the fuse 78 current rating is too low, the direct current coil 40 may shut valve 21 during normal operation. Fuse 88 provides overall circuit protection.
Instead of using a current limiting resistor in series with the direct current coil 40—as in the case of hold open circuit 50—hold open circuit 70 includes a Zener diode 72 in series with direct current coil 40. The Zener diode 72 is operated in reverse-biased mode. When the voltage input to the Zener diode drops below the Zener breakdown voltage, it stops allowing current to flow to the direct current coil 40, causing it to release valve magnetic disk 30 so that it is biased to the closed position of
Hold open circuit 70 beneficially includes several features that prevent valve assembly 20 from remaining open in the case of circuit component failures. For example, if diode 76 fails by shorting, alternating current will flow through the direct current coil 40, causing it to release. Because the valve assembly 20 is a hold open valve assembly, gas will cease to flow to the burner(s) unless and until manual actuation of the gas knob stem 26 is performed. If diode 76 fails open, the direct current coil 40 will cease to generate a magnetic field, and valve assembly 20 will fail to the closed position of
If capacitor 74 fails by shorting, all the current will flow through capacitor 74 causing fuse 88 to blow and the valve assembly 20 to fail to the closed position of
If igniter 52 fails by shorting, too much current will flow though the circuit 70 and fuse 78 will blow, causing the valve assembly 20 to fail to the closed position of
If Zener diode 72 fails by shorting, the current through the direct current coil 40 will increase quickly and significantly causing fuse 78 to blow and valve assembly 20 to fail to the closed position of
If the shunt resistor 80 fails by shorting, no current will reach the direct current coil 40 causing it to release the valve disk 36 and shut off gas flow to the burner(s). If the shunt resistor 80 fails open, the current to the direct current coil 40 will increase precipitously, causing fuse 78 to blow, and valve assembly 20 to fail closed.
If resistor 82 fails open with switch 86 open, nothing will happen because there will be no closed path for current flow through direct current coil 40. If resistor 82 fails by shorting with switch 86 open or closed, igniter 52 will see a large spike in current, causing it to heat up significantly, which could lead to an igniter 52 failure. If resistor 82 fails open with switch 86 closed, igniter 52 will be operable in reduced power mode only. If resistor 84 fails open with switch 86 open or closed, igniter 52 will operate in reduced power mode only. If resistor 84 fails closed with switch 86 closed, the igniter 52 will see a large spike in current, causing it to heat up significantly, which may lead to an igniter 52 failure.
The capacitance and resistance values of the various components of hold-open circuit 70 may be selected to achieve the desired circuit 70 operation. In general, if it is desired to make the direct current coil 40 hold open sooner upon actuating the gas knob stem 26, the resistance of resistor 80 may be increased. Increasing the resistance of resistor 80 will increase the input voltage to Zener diode 72 and resistor 80, plus it will cause relatively more of the total current going through igniter 52 to go through the direct current coil.
If it is desired to operate the igniter 52 at a higher temperature, the resistance values of resistors 82 and 84 may be decreased, which will increase the current flowing through igniter 52. At the same time, or alternatively, the capacitance value for capacitor 74 may be increased. Increasing the capacitance of capacitor 74 provides more stored electrical energy when capacitor 74 discharges (i.e., when the output voltage from diode 76 falls below the saturation voltage of capacitor 74). As a result, the rms voltage seen by the igniter 52 increases, thereby increasing its surface temperature.
The hold open circuit 70 is preferably designed to operate at AC voltages ranging from 90 V AC (rms) to about 135V AC (rms), preferably from about 110V AC (rms) to about 130 V AC (rms), and more preferably from about 115V AC (rms) to about 125 V AC (rms). In certain examples, hot surface igniter 52 is designed to have a high temperature resistance (i.e., a resistance at the ignition temperature of the cooking gas) that ranges from about 330Ω to about 500Ω, preferably from about 400Ω to about 480Ω, and more preferably from about 430Ω to about 450Ω.
At the same time, capacitor 74 may have exemplary capacitance values ranging from about 60 μF to about 80 μF, preferably from about 65 μF to about 75 μF, and more preferably from about 66 μF to about 70 μF. Direct current coil 40 has a threshold (rms) current ranging from about 30 mA to about 90 mA, preferably from about 40 mA to about 80 mA, and more preferably from about 50 mA to about 70 mA. Direct current coil 40 also has an inductance ranging from about 0.005 mH to about 0.010 mH, preferably from about 0.006 mH to about 0.009 mH, and more preferably from about 0.007 mH to about 0.008 mH. In addition, at higher capacitance values for capacitor 74 the igniter 52 voltage at node N52 will show a smaller ripple (become “flatter”) in both power modes. This in turn will decrease the currents in the circuit 70 along with the steady-state temperature of igniter 52, and valve 21 may not remain open during lower power mode operation. The resistance and impedance of direct current coil 40 will typically be much lower than that of the other circuit components, and will be effectively negligible.
At the same time resistor 82 may have exemplary resistance values ranging from about 80Ω to about 120Ω, preferably from about 90Ω to about 110Ω, and more preferably from about 95Ω to about 105Ω. Resistor 84 preferably has exemplary resistance values ranging from about 30Ω to about 70Ω, preferably from about 40Ω to about 60Ω, and more preferably from about 45Ω to about 55Ω. Increased values of the resistance of resistor 82 will primarily affect the current that flows through the circuit 70 in reduced power mode and generally decreases the power dissipated by the igniter 52 (and decreases the igniter 52 temperature). Increased resistance values of resistor 84 will generally decrease the igniter 52 temperature in full power mode, and decreased resistance values will increase it.
At the same time, resistor 80 may have exemplary resistance values ranging from about 65Ω to about 95Ω, preferably from about 70Ω to about 90Ω, and more preferably from about 75Ω to about 85Ω. Increased resistance values for resistor 80 will tend to decrease the release voltage (i.e., the resistor 80 input voltage required for the direct current coil 40 to generate a magnetic field sufficient to hold the valve assembly 20 in the open position of
A hold-open circuit 70 as shown in
Hold open circuits 50 and 70 are particularly suited for situations where the igniter 52 may be energized and remain part of the hold open circuit but receive insufficient current to reach the autoignition temperature of the cooking gas. However, it has been found that with certain igniters 52 that scenario is less likely. In such cases, if the igniter 52 fails to reach the autoignition temperature, the circuit 50 or 70 will have failed as an open circuit. The following hold-open circuits of
Igniter 52 is in series with direct current coil 40. The series combination of igniter 52 and direct current coil 40 is in parallel with capacitor 136. The parallel combination of capacitor 136 and series combination of igniter 52 and direct current coil 40 is in series with diode 132. Diode 132 provides half-wave rectification to the AC signal of AC source 131 so that the voltage seen by igniter 52 at node N52 only has a direct current component. The diode 132 is preferably selected to balance cost and circuit 130 lifetime as diodes with higher current ratings tend to be more expensive while diodes with lower current ratings tend to shorten the lifetime of circuit 130.
Capacitor 136 smooths the ripple in the DC signal provided by diode 132 When diode 132 is forward-biased, capacitor 136 will charge until it reaches is saturation voltage, at which point charging stops. When the diode 132 voltage drops below the saturation voltage of capacitor 136, capacitor 136 will begin to discharge until the AC voltage exceeds the capacitor 136 voltage, at which point it will start charging again. Capacitor 136 has a capacitance value of from about 20 μF to about 40 μF, preferably from about 25 μF to about 35 μF, and more preferably from about 28 μF to about 32 μF. As the capacitance of capacitor 136 increases, the igniter 52 input voltage at node N52 will tend to flatten (show “less ripple”). Conversely, as the capacitance of capacitor 136 decreases, the igniter 52 input voltage at node N52 will tend to be less flat (“more ripple”); The direct current coil 40 has an inductance ranging from about 6 μH to about 9 μH, preferably from about 6.5 μH to about 8.5 μH, and more preferably from about 7.0 μH to about 8.0 μH.
A hold-open circuit 130 as shown in
Referring to
Alternating current source 141 supplies alternating current to diode 140 which converts the alternating current to a time-varying direct current. Capacitors 146 and 148 are provided and are in parallel with one another when switch 150 is closed to electrically connect capacitor 148 to the remainder of hold-open circuit 140. Capacitor 146 smooths or flattens the ripple in the input voltage and current to igniter 52 (i.e., at node N52) when hold open circuit 140 is in either the full or reduced power modes. Capacitor 148 smooths or flattens the ripple in the input voltage and current to igniter 52 (i.e., at node N52) when hold open circuit 140 is in the full power mode. When switch 150 is closed, the two parallel capacitors 146 and 148 act as a single capacitor having a capacitance equal to the sum of their respective capacitance values. When switch 150 is open, capacitor 148 is not in the circuit and the total capacitance of the parallel combination of capacitors 146 and 148 equals the capacitance of capacitor 146. In certain exemplary implementations, capacitors 146 and 148 have capacitance values that range from about 10 μF to about 20 μF, preferably from about 12 μF to about 18 μF, and more preferably from about 14 μF to about 16 μF. Direct current coil 40 has the inductance values described previously. When in full power mode, as the capacitance of either or both capacitors 146 and 148 increases, the igniter 52 input voltage and current tend to have less ripple (become flatter), whereas at lower values the converse is true.
Hot surface igniter 52 is in series with direct current coil 40. When switch 150 is open, capacitor 146 forms a parallel combination with the series combination of igniter 52 and direct current coil 40. When switch 150 is closed, the parallel combination of capacitors 146 and 148 forms a parallel combination with the series combination of igniter 52 and direct current coil 40.
When switch 150 is closed, the total capacitance of the parallel combination of capacitors 146 and 148 is higher than the capacitance of capacitor 146 when switch is open. When AC Source 141 is electrically connected to circuit 140 capacitors 146 and 148 will charge until they reach their saturation voltages. When the AC Source signal drops below their saturation voltages, capacitors 146 and 148 will begin to discharge and supply current to igniter 52, thus ensuring that the igniter input voltage at node 52 does not drop below the highest saturation voltage of the capacitors 146 and 148.
A hold-open circuit 140 as shown in
As with Example 3,
A simulation at 120 VAC source power is carried out with hold-open circuit 140 in reduced power mode, i.e., with switch 150 open using the same igniter 52 and component values as in the full power mode.
Using three igniters 52 each having the same compositions and dimensions which fall within the ranges described in Example 1 but with conductive ink thickness variations on the order of 0.0004-0.002 inches, hold-open circuit 140 is subjected to different AC source voltage signals ranging from 90 VAC rms to 135 VAC rms. The AC power source rms voltage values, igniter input rms voltage values, igniter rms current values, igniter power consumption and measured igniter temperatures are set forth in Tables I-III below:
A hot surface igniter as described in Example 1 is provided and which has a room temperature resistance of 87Ω. The igniter is placed in hold-open circuit 140 having the component values previously described and subjected to a 120 VAC rms source voltage. The time in seconds required to reach 1800° F. and 2138° F. is provided in Table 4:
Hold-open circuits 50, 70, 130, and 140 are designed to allow the hot surface igniter 52 to be powered by an alternating current source while still being compatible with a direct current coil 40. Because of the relationship between the igniter 52 and the direct current coil 40 in the circuits 50, 70, 130, and 140 the direct current coil 40 only receives sufficient current to hold cooking gas safety valve assembly 20 in the open position of
Referring to
As indicated previously, one benefit of using a hot surface igniter 52, as opposed to a spark igniter, to ignite cooktop burner gas is that the igniter can stay continuously energized (at full or reduced power) to provide ignition in the event of a flame-out. This property of hot surface igniters also makes a number of other features possible.
Referring to
Referring to
A number of sensors or indicators may also be used in positions 102 and 104 to document information about the electrical status of igniter 52. The sensors or indicators may be used alone or in combination with one another. In one example, a timer may be provided which accumulates the total time the igniter 52 is energized. The energization time data may then be used to determine how much of the expected igniter 52 life remains so that the igniter 52 may be replaced before failing. Such collected information may also be transmitted wirelessly by wi-fi, Bluetooth, and other known wireless communication technologies to a user's smart phone, a personal computer, a laptop, or a server to provide information about the status of the igniter 52 remotely.
Audible indicators may also be used in positions 102 and 104. Current spark igniters make a distinct audible sound during ignition, and many consumers have become accustomed to and prefer hearing the sound as an indication of ignition. Hot surface igniter 52 does not make an audible sound during ignition. However, a sound generator may be provided at position 104 which is energized only when igniter 52 is initially energized and which makes a clicking sound or another type of sound to indicate that the igniter 52 is receiving ignition current.
A number of additional sensors and indicators may be used in either position 102 or 104. For example, a fire sensor may be provided. A fire sensor differs from a flame sensor in that it is intended to determine whether a flame other than that desired for cooking is present. The fire sensor is typically an optical sensor with a field of view above the burner. In certain examples, it may be incorporated into a control scheme that shuts of gas to the burner when a fire is detected.
A pot sensor may also be provided. A pot sensor determines when a pot is present on the burner (e.g., by sensing a weight change). The pot sensor may include or be operatively connected to a pressure switch or a plunger that completes circuit 90 only when a pot is present on the burner, which may help prevent fires.
In addition, because igniter 52 may be continuously energized (to full or reduced power) and relit at any gas flow, a number of different cooking functions may be provided by turning the burner on and off (i.e., by opening and closing the gas valve to the burner) for specified periods of time. In certain examples, a timer is provided which accumulates the amount of time the burner is on or off. A flame sensor of the type described previously may be used to toggle the timer state between on and off. Alternatively, the timer may simply be configured to be energized only when the igniter 52 is energized and to accumulate the on and off time when the user sets the gas valve to a certain position that is indicative of a desired cooking mode, e.g., “simmer”. Pre-programmed algorithms present in an associated controller may open and close the burner gas valve based on the selected cooking mode.
The circuit component options described with respect to
This application claims the benefit of U.S. Provisional Application No. 63/047,088, filed on Jul. 1, 2020, the entirety of which is hereby incorporated by reference.
Number | Date | Country | |
---|---|---|---|
63047088 | Jul 2020 | US |