CN115667802A

CN115667802A - Gas safety valve opening keeping circuit of cooking range surface with ceramic heater

Info

Publication number: CN115667802A
Application number: CN202180039417.7A
Authority: CN
Inventors: 布莱恩·C·多尔蒂; 埃里克·博特; 杰克·A·欣德勒; 刘殷
Original assignee: Scp Research And Development Co ltd
Current assignee: Scp Research And Development Co ltd
Priority date: 2020-07-01
Filing date: 2021-06-30
Publication date: 2023-01-31
Also published as: EP4176206A1; JP2023531886A; US20220003419A1; CA3177140A1; WO2022006213A1

Abstract

A cooking gas safety device is shown and described. The apparatus includes a cooking gas safety valve assembly that supplies cooking gas to one or more burners. The cooking gas safety assembly includes at least one coil that is energizable to maintain the valve assembly in an open position when subjected to a current exceeding a threshold, and a hold-open circuit. The hold-open circuit includes a coil and a hot surface igniter in electrical communication with the coil.

Description

Gas safety valve opening keeping circuit of cooking range surface with ceramic heater

Cross Reference to Related Applications

This application claims benefit of U.S. provisional application No. 63/047,088, filed on 1/7/2020, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to a gas safety valve having a hold open circuit (hold open circuit) that holds the valve open when a threshold current sufficient to heat a hot surface igniter to the auto-ignition temperature of the gas is reached.

Background

Some cooktops include safety features to ensure that cooking gas is supplied to the burner only after ignition is complete. This ensures that unburned cooking gas is not supplied to the surroundings, which could otherwise cause a fire or explosion.

In one known system, a user operates a gas control knob to manually actuate a gas valve and supply current to a spark igniter adjacent a burner. The thermocouple acts as a flame detector, which produces a direct current upon ignition success. At a certain threshold current, the current generates a magnetic field that holds the gas valve in the open position so that the user can release the knob. The gas valve is configured to close upon failure such that when no flame is present, the magnetic force drops below the characteristic force required to keep the gas valve open, causing it to close. The threshold current is sufficient to hold the valve in the open position, but insufficient to open it. Requiring user intervention to open the valve by manually actuating it. The integrated gas valve and electromagnet is known in europe as a "gas tap".

A spark igniter is a user-actuated igniter that produces a brief discharge and a spark that ignites the gas. Therefore, they cannot be kept 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 unburned gas to the burner. However, because the thermocouple must heat long enough to reach the temperature at which the threshold current is generated, there is a significant amount of lag time and/or dead time in generating the threshold current after ignition that is required to keep the gas valve open. Typically, due to the thermal response of the thermocouple, the user needs to continue manually holding the gas valve open for five to ten seconds after ignition occurs.

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 clothes dryers. Some hot surface igniters, such as silicon carbide igniters, include a semi-conductive ceramic body having terminals across which a potential difference is applied. The current flowing through the ceramic body causes the ceramic body to heat and increase in temperature, thereby providing an ignition source for the combustion gases. Other types of hot surface igniters, such as silicon nitride igniters, include a ceramic body with an embedded circuit that applies a potential difference across it. The current flowing within the embedded circuit causes the ceramic body to heat and increase in temperature, thereby providing an ignition source for the combustion gases.

Unlike spark igniters, hot surface igniters can be continuously energized to ignite the cooking gas because it is the igniter surface temperature that causes ignition rather than discrete electrical potential bursts. When used in conjunction with the gas safety valve assembly described above, the energized state of the hot surface igniter provides an indication that ignition has occurred (or will occur), which allows for elimination of the thermocouple. However, some means is required to link the current used to energize the igniter to the current required to keep the gas burner valve open. Therefore, there is a need for a cooking gas safety device that solves the aforementioned problems.

Disclosure of Invention

According to a first aspect of the present disclosure, there is provided a cooking gas safety device comprising: a valve assembly that can be manually actuated to an open position to allow gas to be allowed to cook. The valve assembly includes at least one coil that is energizable to maintain the valve in an open position only when subjected to a current exceeding a threshold current value. The device also includes: a hold-open circuit comprising a hot surface igniter and a coil, wherein the hot surface igniter is in electrical communication with the coil, and wherein a surface of the hot surface igniter reaches at least an auto-ignition temperature of the cooking gas no later than about eight seconds after at least one coil is subjected to a current having a threshold current value. According to some examples, the coil is a direct current coil. According to other examples, the coil is an alternating current coil. According to an additional example, the keep-alive circuit may operate in a full power mode and a reduced power mode. In a preferred example, the surface of the hot surface igniter reaches at least the auto-ignition temperature of the cooking gas no later than about six seconds, and more preferably no later than four seconds, after the at least one coil is subjected to the current having the threshold current value.

According to a second aspect of the present disclosure, a method of supplying cooking gas to a cooktop burner is provided. The method comprises the following steps: a valve assembly is provided that includes a valve having an open position and a closed position, wherein cooking gas passes through the valve when the valve is in the open position. The valve assembly also includes at least one coil that can be energized to maintain the valve in an open position. The method further comprises the following steps: the valve is manually actuated to an open position and an alternating current is supplied to a hold open circuit comprising a hot surface igniter and at least one coil, thereby holding the valve in the open position. In some examples, the at least one coil comprises a direct current coil, and the method comprises: the alternating current is converted to a time-varying direct current that is supplied to a 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 an auto-ignition temperature of the cooking gas.

According to a third aspect of the present disclosure, there is provided a cooking gas safety device comprising a valve assembly comprising a valve and at least one coil. The valve comprising a fluid inlet and a fluid outlet and being manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to maintain the valve in an open position only when subjected to an electrical current exceeding a threshold current value; and the apparatus further comprises: a hot surface igniter electrically connectable to the at least one coil to define a keep-open circuit, and wherein the hot surface igniter reaches a surface temperature of at least 1400 ° F no more than eight seconds after the at least one coil is subjected to the threshold current when subjected to an alternating current of 120VAC rms.

According to a fourth aspect of the present disclosure, there is provided a cooking gas safety device comprising a valve assembly comprising a valve and at least one coil. The valve comprising a fluid inlet and a fluid outlet and being manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to maintain the valve in an open position only when subjected to an electrical current exceeding 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 the hot surface igniter reaches an auto-ignition 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 a threshold current when subjected to an alternating current of 120VAC rms.

Drawings

FIG. 1 is a cross-sectional view of a gas valve assembly in a closed position, wherein the gas safety valve assembly includes a valve that is manually actuatable to an open position, and the valve further includes a hold open coil that holds the valve assembly open when a threshold current through the coil is reached;

fig. 2 is a cross-sectional view of the gas safety valve assembly of fig. 1 in an open position.

FIG. 3 is a cross-sectional view of the gas safety valve assembly of FIG. 1 in the open position of FIG. 2, with the tapered sleeve having the metering hole removed;

FIG. 4 is a first example of a hold-open circuit including a hot surface igniter and a DC coil of a gas safety valve assembly;

FIG. 5 is a second example of a hold-open circuit including a hot surface igniter and a DC coil of a gas safety valve assembly;

FIG. 6 is a template circuit configured to energize a hot surface igniter to two different energization states and equipped with a plurality of different circuit components operable to provide various indications of burner status and control operation thereof;

FIG. 7 is the template circuit of FIG. 6 modified to hold open a gas safety valve assembly including a DC coil for holding the valve assembly open;

FIG. 8 is an example of a hold open circuit including a hot surface igniter and an AC coil for holding open a gas safety valve assembly;

FIG. 9 is an illustrative depiction of the voltage versus time of the capacitor input voltage in the hold-on circuit of FIG. 4 superimposed on the diode output voltage of the hold-on circuit;

FIG. 10A is a graph depicting analog voltage versus time data for the input voltage of the hot surface igniter in the hold-open circuit of FIG. 4 when operating at full power;

FIG. 10B is a graph depicting simulated current versus time data for the hot surface igniter in the hold-on circuit of FIG. 4 when operating at full power;

FIG. 10C is a graph depicting analog voltage versus time data for the input voltage of the resistor in the hold-open circuit of FIG. 4 when operating at full power;

FIG. 10D is a graph depicting simulated current versus time data for the DC coil in the hold-open circuit of FIG. 4 when operating at full power;

FIG. 11A is a graph depicting analog voltage versus time data for the input voltage of the hot surface igniter in the hold-on circuit of FIG. 4 when operating at reduced power;

FIG. 11B is a graph depicting simulated current versus time data for the hot surface igniter in the hold-on circuit of FIG. 4 when operating at reduced power;

FIG. 11C is a graph depicting analog voltage versus time data for the input voltage of the resistor in the hold-open circuit of FIG. 4 when operating at reduced power;

FIG. 11D is a graph depicting simulated current versus time data for the DC coil in the hold-on circuit of FIG. 4 when operating at reduced power;

FIG. 12A is a graph depicting simulated voltage versus time data for the input voltage of the hot surface igniter of FIG. 5 when operating at full power;

FIG. 12B is a graph depicting simulated current versus time data for the hot surface igniter in the hold-on circuit of FIG. 5 when operating at full power;

FIG. 12C is a graph depicting analog voltage versus time data for the input voltage of resistor 80 in the hold-open circuit of FIG. 5 when operating at full power;

FIG. 12D is a graph depicting simulated current versus time data for the DC coil in the hold-open circuit of FIG. 5 when operating at full power;

FIG. 13A is a graph depicting analog voltage versus time data for the input voltage of the hot surface igniter in the hold-on circuit of FIG. 5 when operating at reduced power;

FIG. 13B is a graph depicting simulated current versus time data for the hot surface igniter in the hold-on circuit of FIG. 5 when operating at reduced power;

FIG. 13C is a graph depicting analog voltage versus time data for the input voltage of resistor 80 in the hold-open circuit of FIG. 5 when operating at reduced power;

FIG. 13D is a graph depicting simulated current versus time data for the DC coil in the hold-open circuit of FIG. 5 when operating at reduced power;

FIG. 14 is a third example of a hold-open circuit including a hot surface igniter and a DC coil of a gas safety valve assembly;

FIG. 15 is a fourth example of a hold-open circuit including a hot surface igniter and a DC coil of a gas safety valve assembly;

FIG. 16A is a graph depicting simulated voltage versus time data for the input voltage of the hot surface igniter in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when operating at full power;

FIG. 16B is a graph depicting simulated current versus time data for the input current of the hot surface igniter in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when operating at full power;

FIG. 16C is a graph depicting analog voltage versus time data for the input voltage of the resistors in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when operating at full power;

FIG. 16D is a graph depicting simulated current versus time data for the DC coil in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when operating at full power;

FIG. 17A is a graph depicting analog voltage versus time data for the input voltage of the hot surface igniter in the hold-on circuit of FIG. 15 when operating at reduced power;

FIG. 17B is a graph depicting simulated current versus time data for the hot surface igniter in the hold-on circuit of FIG. 15 when operating at reduced power;

FIG. 17C is a graph depicting analog voltage versus time data for the input voltage of the resistor in the hold-open circuit of FIG. 15 when operating at reduced power; and

fig. 17D is a graph depicting simulated current versus time data for the dc coil in the hold-open circuit of fig. 15 when operating at reduced power.

In the drawings, like reference numerals refer to like parts.

Detailed Description

Examples of gas safety valve devices are described below, including a valve assembly and a "hold open" circuit. The valve assembly includes a valve and at least one coil that is energizable to maintain the valve in an open position only when subjected to a current exceeding a threshold current value. The hold open circuit ensures that the valve only allows gas to enter the burner when the user actuates the gas control knob or when the burner is lit. More specifically, if the hot surface igniter used to ignite the burner is not energized sufficiently to reach (or maintain) a surface temperature at or above the auto-ignition temperature of the cooking gas, holding the circuit open causes the valve to close, thereby reducing the likelihood of gas inadvertently flowing to the un-ignited burner. In some examples, the igniter is energized by an ac power source and at least one of the coils is a dc coil that keeps the valve open only when subjected to a threshold dc current. According to such an example, the hold-open circuit is configured to: the threshold direct current is supplied to the at least one coil only when the igniter is supplied with current sufficient to cause the igniter surface to reach a cooking gas auto-ignition temperature.

Referring to fig. 1-3, a cooking gas safety valve assembly 20 is provided. The cooking gas safety valve assembly 20 includes a valve 21, a dc coil 40 and a magnetic core 42. The valve assembly 20 has a proximal end P and a distal end D spaced apart along the length axis l. The valve 21 comprises a rigid metal housing 23 in which an air inlet 22 and an air outlet 24 are defined and spaced apart along a radial axis r. The valve 21 has an open position (fig. 2) in which the inlet port 22 is in fluid communication with the outlet port 24, and a closed position (fig. 1) in which the inlet port 22 is not in fluid communication with the outlet port 24. A tapered sleeve 28 having an inlet metering orifice 29 is provided and includes an outlet 31 through which combustion gases may pass 31 when the valve disc 36 is unseated from the shoulder 45 of the axial fluid passage 43 (fig. 2). In fig. 1 and 2, not all of the apertures 29 are visible, but the air inlet 22 is in fluid communication with the apertures 29.

The shaft engaging surface 38 is disposed on the valve disc 36 and is engaged by a shaft 44 (fig. 2) that passes through the tapered sleeve 28 along the longitudinal (l) axis of the gas safety valve assembly 20. The shaft 44 is operatively connected to a gas knob stem 26 (the knob is removed in the figures) which knob stem 26 is axially depressible in a distal direction along the longitudinal (l) axis of the cooking gas safety valve assembly 20. Axially pressing the gas knob stem 26 in a distal direction causes the shaft 44 to axially move the valve disc 36 distally in the longitudinal direction (l) and out of engagement with the shoulder 45 of the axial fluid passage 43. The diameter of the shaft 44 along the radial axis r is narrower than the diameter of the axial fluid passage 43 at the shoulder 45 and distal to the shoulder 45. The fluid passage 43 has a diameter along the radial axis r that is greater than the diameter of the open area defined radially within the shoulder 45. As a result, when the valve disc 36 is moved out of engagement with the shoulder 45, combustion gases exiting the outlet 31 of the conical sleeve 28 may exit the valve assembly outlet 24. The shaft 44 is biased in a proximal direction along the longitudinal axis l by a spring 46 (fig. 3). Since the gas knob stem 26 is operatively connected to the shaft 44, the gas knob stem 26 is also biased in a proximal direction along the longitudinal axis l.

The valve disc 36 is connected to a distal valve shaft 32, which distal valve shaft 32 is in turn connected to a magnetic disc 30 housed in an electromagnet housing 41. The electromagnet housing 41 houses a direct current coil 40 wound around a corresponding magnetic core 42. It is also possible to provide a plurality of coils, each coil being wound around their respective core. The valve disc 36 is biased in a proximal direction along the length/axis by a spring 34, which spring 34 is attached to the proximal end of the solenoid housing 41. The distal valve shaft 32 passes through the spring 34 and a hole (not shown) in the proximal end of the electromagnet housing 41. When the gas relief valve 21 is in the closed position (fig. 1), the valve disc 36 is biased by the biasing spring 34 away from the solenoid housing 41 and into engagement with the shoulder 45 of the axial fluid passage 43. When the user depresses the gas knob stem 26 in a distal direction along the length/axis, the distal end 47 (FIG. 3) of the shaft 44 engages the shaft engaging surface 38 of the valve disc 36 and displaces the valve disc 36 in the distal direction along the length/axis to the open position of FIG. 2. Displacement of the valve disc 36 along the length/axis also displaces the distal valve shaft 32 in a distal direction along the length/axis, thereby displacing the magnetic disc 30 distally into engagement with the magnetic core 42. When a threshold current is supplied to the dc coil 40, the magnetic force generated will hold the magnetic disk 30 of the valve 21 in engagement with the magnetic core 42 even if the user releases the gas knob stem 26. In the absence of magnetic force, releasing the gas knob stem 26 will cause the biasing force of the spring 34 to push the valve disc 36 in a proximal direction along the length/'axis and into engagement with the axial fluid passage shoulder 45, which in turn will cause the shaft engaging surface 38 to push the shaft 44 in a proximal direction along the length/' axis. As long as the dc current through the coil 40 remains above the threshold current characteristic of the gas safety valve assembly 20, the magnetic force engages the valve-retaining magnetic disc 30 with the magnetic core 42, thereby retaining the valve 21 in the open position of fig. 2. The magnetic field generated by the dc coil 40 is strong enough to hold the magnetic disk 30 in engagement with the magnetic core 42, but not strong enough to pull the magnetic disk 30 into engagement with the magnetic core 42.

As previously mentioned, it is desirable to modify the flame detection scheme typically used with cooking gas safety valve assemblies 20 to shorten the duration of manual actuation of the gas knob stem 26 by the user before the valve disc 36 remains in the open position of fig. 2, while still ensuring that gas is supplied to the cooktop burner only when the ignition source is energized. As previously mentioned, flame detection schemes typically use thermocouples to generate direct current for the coil 40 when a flame is present.

In the following example, instead of a spark igniter, one or more burners used with the cooking gas safety valve assembly 20 are ignited by a ceramic hot surface igniter 52. Ceramic hot surface igniters for use in conjunction with the gas valve assemblies described herein include those described in U.S. patent application No. 16/366,479, the entire contents of which are incorporated herein by reference.

Although shown as a resistor in fig. 4-8, a preferred ceramic hot surface igniter 52 useful in the gas heating systems described herein includes a hot surface igniter having a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis. The ignitor 52 includes first and second ceramic tiles having respective outer surfaces. A conductive ink pattern is disposed between the first and second tiles. In certain examples, the igniter 52 has a thickness along the thickness axis of about 0.047 inches to about 0.060 inches, preferably about 0.050 inches to about 0.058 inches, and more preferably about 0.052 inches to about 0.054 inches. See FIGS. 3A-3H and corresponding text of U.S. patent application Ser. No. 16/366,479.

The preferred ceramic hot surface igniter 52 described herein is generally in the shape of a cuboid and includes two major facets, two minor facets, a top portion and a bottom portion. The main facet is defined by first (length) and second (width) longest dimensions of the ceramic hot surface igniter body. The secondary facet is defined by the first (length) and third (thickness) longest dimensions of the igniter body. The igniter body also includes a top surface and a bottom surface defined by a second (width) and a third (thickness) longest dimension of the igniter body. The ceramic hot surface igniter 52 may have a resistance with a positive or negative temperature coefficient. However, a positive temperature coefficient of resistance is preferred.

According to an example where the ceramic hot surface igniter 52 has a positive temperature coefficient of resistance, the igniter brick is ceramic and preferably comprises silicon nitride. Conductive ink circuits are disposed between the tiles and generate heat when energized. The ceramic tiles are electrically insulating, but sufficiently thermally conductive to achieve, within a desired period of time, the external surface temperature necessary to ignite a combustible mixture of air and fuel gas selected from the group consisting of natural gas, propane, butane 1400 (heating value 1400 Btu/ft) ³ Butane and air mixtures of (a) and mixtures thereof.

As described in more detail below, in certain examples, the ceramic tiles include silicon nitride, ytterbium oxide, and molybdenum disilicide. In the same or other examples, the conductive ink circuit includes tungsten carbide, and in certain embodiments, the conductive ink additionally includes ytterbium oxide, silicon nitride, and silicon carbide.

In certain examples, the ceramic hot surface igniter 52 described herein achieves a surface temperature of at least 1400 ° F, preferably not less than 1800 ° F, more preferably not less than 2100 ° F, even more preferably not less than 2130 ° F, when subjected to a potential difference of 120VAC (rms). These temperatures are preferably reached in no more than eight seconds, more preferably in no more than six seconds, and still more preferably in no more than four seconds after application of the 120VAC (rms) potential difference.

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, still more preferably does not exceed 2450 ° F, at any time after a potential difference of full wave 132VAC (rms) is applied to the igniter, including after the steady state temperature is reached.

In the same or other examples of ceramic hot surface igniters according to the disclosure, the ceramic hot surface igniters described herein, when subjected to a potential difference of 102VAC (rms), reach a surface temperature of at least 1400 ° F, preferably at least 1800 ° F, and more preferably at least 2100 ° F within no more than seventeen seconds, preferably no more than ten seconds, more preferably no more than about seven seconds, after the first application of the potential difference of 102VAC (rms). These temperatures are preferably reached in no more than 4 seconds, more preferably in no more than 3 seconds.

In the same or additional examples, the thickness (along the thickness axis) of the conductive ink circuit of the hot surface igniter is no more than about 0.002 inches, preferably no more than about 0.0015 inches, and more preferably no more than about 0.0009 inches. In the same or additional examples, the thickness (along the thickness axis) of the conductive ink circuit is not less than about 0.00035 inches, preferably not less than about 0.0003 inches, and more preferably not less than about 0.0004 inches.

The green body density of the hot surface igniter 52 of the present disclosure is preferably at least 50% of theoretical density, more preferably at least 55%, and still more preferably at least 60% of theoretical density.

As discussed in U.S. patent application Ser. No. 16/366,479, the ceramic hot surface igniter 52 used in the gas fired heating system described herein is prepared by sintering ceramic components. In certain examples, after sintering, the tile used to form the igniter 52 (excluding the conductive ink circuit) has a room temperature resistivity of no less than 10 ¹² Omega-cm, preferably not less than 10 ¹³ Omega-cm, more preferably not less than 10 ¹⁴ Omega-cm. In the same or other examples, the tile has a thermal shock value according to ASTM C-1525 of not less than 900 ° F, preferably not less than 950 ° F, more preferably not less than 1000 ° F.

In other examples, the conductive ink comprising the conductive ink circuit has a (post-firing) room temperature resistivity of about 1.4 x 10 ^-4 Omega cm to about 4.5X 10 ^-4 Ω · cm, preferably about 1.8 × 10 ^-4 Omega cm to about 4.1X 10 ^-4 Ω · cm, more preferably about 2.2 × 10 ^-4 Omega cm to about 3.7X 10 ^-4 Omega cm. In the case of a material having a constant cross-sectional area along its length, the resistivity ρ at a given temperature T is related to the resistance R at the same temperature T according to the well-known formula:

(1) R (T) = ρ (l/A), wherein

ρ = resistivity of the conductive circuit material at temperature T (Ω -cm);

r = resistance at temperature T in ohms (Ω);

t = temperature (° F or ℃);

a = cross-sectional area (cm) of conductive ink circuit perpendicular to current direction ² ) (ii) a And

l = total length of conductive ink circuit in current direction (cm).

In the case where the cross-sectional area varies along the length of the conductive circuit, the resistance can be expressed as:

(2)

where L = the total length of the circuit in the current direction (cm), and the remaining variables are as defined in equation (1).

In certain examples, the ceramic body comprised of the ceramic hot surface igniter 52 herein preferably includes 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 aid may be provided as a co-dopant selected from the aforementioned rare earth oxides and one or more of silica, alumina and magnesia. It is also preferred to include a sintering aid protectant, which also enhances densification. The preferred sintering aid protectant is molybdenum disilicide. The rare earth oxide sintering aid (with or without the co-dopant) is preferably present at a level (by weight of the ceramic body) in a range of about 2% to about 15%, more preferably about 8% to about 14%, and still more preferably about 12% to about 14%. The molybdenum disilicide is preferably present in an amount ranging from about 3% to about 7%, more preferably from about 4% to about 7%, still more preferably from about 5.5% to about 6.5% (by weight of the ceramic body). The balance being silicon nitride.

The conductive ink circuit is preferably printed on the face of one of the tiles to produce a ceramic hot surface igniter (after sintering) Room Temperature Resistance (RTR) of about 60 Ω to about 120 Ω, preferably about 70 Ω to about 110 Ω, more preferably about 80 Ω to about 100 Ω. Meanwhile, the ceramic hot surface igniter High Temperature Resistance (HTR) is typically about 300 Ω to about 500 Ω, preferably about 400 Ω to about 480 Ω, and more preferably about 430 Ω to about 450 Ω over a temperature range of 2138 ° F to 2700 ° F.

The conductive ink in the igniter 52 should include tungsten carbide in an amount ranging from about 20% to about 80%, preferably from about 30% to about 80%, and more preferably from about 70% to about 75%, by weight of the ink. The silicon nitride is preferably provided at a content ranging from about 15% to about 40%, preferably from about 15% to about 30%, more preferably from about 18% to about 25% by weight of the ink. It is also preferred to include the same sintering aid or co-dopant as described for the ceramic body in a content ranging from about 0.02% to 6%, preferably from about 1% to about 5%, more preferably from about 2% to about 4% by weight of the ink.

In the example of the cooking gas safety device described herein, the hot surface igniter 52 is used to ignite the cooking gas supplied to the burner, and the gas flow to the burner is regulated by the cooking gas safety valve assembly 20, which safety valve assembly 20 remains open only when the current supplied to the hot surface igniter is sufficient to cause the igniter to reach the auto-ignition temperature of the cooking gas. The "auto ignition temperature" is the lowest temperature at which the gas-air mixture will ignite and continue to combust. In a preferred example, the igniter 52 may also operate in full power and reduced power modes. During ignition, the igniter 52 will be operating at full power. After ignition, the igniter will operate at reduced power, even if the power is sufficient to heat the igniter at least to the auto-ignition temperature of the cooking gas.

Referring to fig. 4, a portion of a cooking gas safety device is depicted. The cooking gas safety device includes a hold-open circuit 50 and a cooking gas safety valve assembly 20 that includes a dc coil 40 (as shown). The valve assembly 20 is manually actuatable to an open position (fig. 2) using a gas knob stem 26 as previously described. While the valve disc 36 is in the open position of FIG. 2 and when the DC coil 40 is energized to a current exceeding the threshold DC current, the magnetic force of the DC coil 40 maintains the valve disc 36 open by maintaining the disk 30 in engagement with the magnetic core 42 without requiring the user to continue to depress the gas knob stem 26. In the case of a time-varying current, the threshold direct current is the RMS value of the time-varying current.

The keep-alive circuit 50 includes a hot surface igniter 52 and a dc coil 40. As shown, the hot surface igniter 52 is in electrical communication with the dc coil 40 such that when the dc coil 40 is subjected to a current having a threshold current value, the surface of the igniter 52 at least reaches the auto-ignition temperature of the cooking gas. Providing the igniter 52 that reaches the auto-ignition temperature of the gas only when the dc coil 40 is at or below the threshold current better ensures that the gas to the burner is cut off when the igniter is not hot enough to ignite the cooking gas. As a result, flame detection devices with significant dead time or lag time, such as thermocouples, can be eliminated, which significantly reduces the amount of time during which a user must press the gas knob stem 26 in a distal direction along the length/axis to hold the gas valve assembly in an open state (fig. 2).

The hot surface igniter 52 is powered by an ac power source 51. According to the example of fig. 4, the alternating current supplied to the direct current coil 40 by the alternating current power supply 51 is converted into a time-varying direct current. As used herein, "direct current" refers to a current having one polarity. The "direct current" may have a constant value or a time-varying value as long as it has one polarity. Because the ac power source 51 has two polarities, the hold-on circuit 50 is configured to: the potential is stored when the ac power cycle is of one polarity and made available to the dc coil 40 when the ac power cycle is of the opposite polarity. Although not shown in fig. 4, another switch would be provided to selectively energize the hold open circuit 50 in response to depression of the gas knob stem 26 in a distal direction along the length/axis (fig. 2). Thus, although not specifically depicted, it should be understood that the AC power source 51 is in selective electrical communication with the hot surface igniter 52 and the DC coil 40.

As shown in fig. 4, the hot surface igniter 52 is combined in series and parallel with the dc coil 40. The terms "series-parallel" and "parallel-series" refer to components that do not have a strict series or parallel relationship with each other. The term "in series" as used to describe the relationship between two components in a circuit means that current flows through each component in turn. The term "parallel" as used to describe the relationship between two components of a circuit means that current is split between the components and then recombined. Referring to fig. 4, a portion of the current flowing through the igniter 52 will flow through the dc coil 40, another portion of the current flowing through the igniter 52 will flow through the resistor 56, and the two currents will recombine.

In fig. 4, the alternating current supplied to the hot surface igniter 52 is rectified and preferably half-wave rectified. As is known in the art, a diode allows current flow with only one polarity. The diode 64 is combined in series and parallel with the hot surface igniter 52 because the portion of the current flowing through the diode 64 during the portion of the AC cycle in which the diode is forward biased will also flow through the hot surface igniter 52. The diode 64 is not directly in series with the hot surface igniter 52 because the current flowing from the diode 64 to the igniter 52 during each half of the AC cycle will drop to zero, causing the dc coil 40 to release the valve disc 36 to the closed position of fig. 1 when the current passes through the pole-zero. As a result, one or more capacitors are provided that charge when diode 64 is forward biased and discharge when diode 64 is reverse biased. The voltage and current rating of diode 64 are preferably selected to balance cost and life of circuit 50, as lower voltage or current ratings will tend to reduce the life of circuit 50.

The half-wave rectified voltage, such as the voltage 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 referred to as a "ripple". The ripple has a characteristic factor called the "ripple coefficient", which is the ratio of the Root-Mean-Square (RMS) value of the AC component to the overall average value. The 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, the RMS value of a time-varying signal is the square root of the mean of the square function. In the context of time-varying current or voltage, the corresponding RMS current or voltage value is a DC value that has an effect equivalent to a time-varying value. The RMS voltage and current may be calculated from equations (2 a) and (b), respectively:

(2a)

where v (T) is a periodic time varying voltage (volts) having a period T ₂ -T ₁ (seconds);

t1= time value at the beginning of the cycle (seconds);

t2= time value (seconds) at the end of the period starting at T1; and

v _rms is the root mean square voltage (volt) of the function v (t)

(2b)

Where i (T) is a periodic time varying current (amperes) having a period T ₂ -T ₁ (seconds);

t1= time value at the beginning of the cycle (seconds);

t2= time value (seconds) at the end of the period starting at T1; and

i _rms is the root mean square voltage (volt) of the function i (t)

In the example of fig. 4, two

capacitors

58 and 60 are provided.

Capacitors

58 and 60 help smooth the dc ripple voltage and increase the Root Mean Square (RMS) voltage seen by igniter 52 and dc coil 40 after rectification. The capacitor 60 is in selective electrical communication with the hot surface igniter 52 and the dc coil 40. Switch 62 is in series with capacitor 60. When the switch 62 is open, the capacitor 60 is disconnected from the hold open circuit 50 and is in electrical communication with neither the hot surface igniter 52 nor the dc coil 40, i.e., only the capacitor 58 reduces the ripple factor. When the switch 62 is closed and in contact with the electrode 63, the capacitor 60 is in electrical communication with both the hot surface igniter 52 and the dc coil 40.

Referring first to the situation when switch 62 is open, when diode 64 is forward biased, capacitor 58 will charge and will draw current until it reaches its saturation voltage. When the AC source voltage begins to drop from its maximum value, the capacitor 58 will begin to discharge when the AC source voltage drops below the saturation voltage of the capacitor 58. Thus, when AC source 51 switches polarity and diode 64 is reverse biased, capacitor 58 will continue to discharge and ignite towards the hot surfaceThe current is supplied by the transformer 52 and the dc coil 40. The result is that the hot surface igniter 52 and the DC coil 40 effectively see a smoothed ripple, i.e., their voltage is equivalent to an AC voltage sine wave superimposed on a DC voltage signal. Fig. 9 depicts how capacitor 58 alone or in parallel with capacitor 60 (when switch 62 is closed) smoothes the ripple voltage produced by diode 64. The rectified waveform in FIG. 9 is the output voltage signal from the diode 64, which is also the hot surface igniter 52 and node N ₅₂ The input voltage at (c). During the time that the waveform portion of the output voltage of diode 64 is increasing, capacitor 58 is charging (and capacitor 60 will also charge if switch 62 is closed) until the saturation voltage is reached or until the AC source reaches its peak voltage. Thus, when the capacitor 58 is charging, the input voltage to the hot surface igniter 52 tracks the AC waveform from the AC source 51. As the AC source reaches its peak voltage and begins to drop below the saturation voltage of capacitor 58, capacitor 58 begins to discharge and supply current to hot surface igniter 52, as shown in the upper line segment of FIG. 9. Once the capacitor 58 voltage drops below the AC source voltage, the capacitor 58 begins to charge again. As a result, the hot surface igniter 52 experiences a voltage represented by the upper curve in fig. 9, rather than the rectified voltage output from the diode 64, thereby smoothing the ripple of the rectified waveform. The resulting voltage and current seen by the hot surface igniter 52 and the dc coil 40 is a time varying dc voltage and current that enables the dc coil 40 to keep the valve disc 36 (fig. 2) open despite the AC source reversing polarity every half cycle. As the total capacitance of the circuit 50 increases, it "smoothes" or suppresses the ripple. When switch 62 is closed, the total capacitance is the sum of the capacitances of capacitor 58 and capacitor 60. When switch 62 is open, the total capacitance is that of capacitor 58. The smoothing effect of the capacitance is indicated by equation (2C), which shows the dependence on the total capacitance C _total Increasing, the difference (Δ V) between the maximum and minimum voltages experienced by the hot surface igniter 52 decreases:

(2c) ΔV＝0.7i/((f)C _total )

where Δ V = the voltage difference (volts) between the voltage and the adjacent peak in the time signal;

i = DC load current (amps) seen by the hot surface igniter 52; and

f = ripple frequency (Hz (full wave typically 120Hz or half wave typically 60 Hz)).

In equation (2 c), 0.7 is the complement of the rectifier current duty cycle, which is assumed to be 0.3. Node N increases as the capacitance of capacitor 58 increases ₅₂ The igniter 52 input voltage at (a) shows less ripple (becomes flatter) in both the full power mode and the reduced power mode (as described below). Node N increases as the capacitance of capacitor 60 increases ₅₂ The igniter 52 input voltage at (a) will only show a small ripple during full power and the igniter 52 will heat up to a higher temperature. In addition, as the capacitance of the capacitor 60 increases, the likelihood of subjecting the components of the circuit 50 to exceeding their rating increases. Conversely, when circuit 50 is in the reduced power mode, node N decreases as the capacitance of capacitor 60 decreases ₅₂ The igniter 52 input voltage at (a) will show a larger ripple (become "less flat") and the RMS current through the igniter 52 will decrease, resulting in the igniter 52 reaching a lower steady state temperature. The dc coil 40 tends to have a much lower resistance and inductance than the other circuit components. Therefore, the selection of those properties for the coil 40 is often of less importance to the overall performance of the circuit 50.

The hot surface igniter 52 is in full power mode when the switch 62 is closed. The hot surface igniter 52 is in the reduced power mode when the switch 62 is open. The full power mode is preferably used during ignition operation. The reduced power mode is preferably used during cooking operations and provides a means to re-ignite the cooking gas in the event that the flame is extinguished. When switch 62 is closed,

capacitors

58 and 60 act as a single capacitor having a total capacitance equal to the sum 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 achieved during reduced power operation. In some examples, releasing the gas valve stem 26 after the dc coil 40 has been latched in the open position of fig. 2 will cause the switch 62 to open and place the circuit 50 in the reduced power mode. In certain examples, the power provided to the igniter 52 in the reduced power mode is from about 70% to about 90%, preferably from about 75% to about 85%, and more preferably from about 78% to about 82% of the power provided to the igniter 52 in the full power mode.

The power dissipated in the surface igniter 52 is proportional to the total capacitance of the

capacitors

58 and 60 in the full power mode and the capacitor 58 in the reduced power mode. Thus, as the capacitance of capacitor 60 increases relative to the capacitance of capacitor 58, the ratio of igniter power dissipation in the reduced power mode to igniter power dissipation in the full power mode decreases. As with the reduced power mode, when diode 64 is forward biased,

capacitors

58 and 60 will charge until a saturation voltage is reached. Once the capacitors are saturated, no current will flow to them until the voltage of AC source 51 drops below its saturation voltage (which may differ between capacitors 58 and 60). As the output voltage from the diode 64 drops below the saturation voltage of either capacitor (or below the peak source voltage if less than the saturation voltage), the capacitor will begin to discharge, causing current to flow from the capacitor 58 and/or the capacitor 60 through the igniter 52 and to the dc coil 40. When diode 64 is reverse biased, no current from AC source 51 will flow through it. However, the

capacitors

58, 60 will continue to provide current to the igniter 52 and the dc coil 40.

In the hold-open circuit 50 of fig. 4, the hot surface igniter 52 is not directly connected in series with the dc coil 40 because the threshold current required to hold the valve assembly 20 open is less than the hot surface igniter 52 current required for the igniter surface to reach the auto-ignition temperature of the cooking gas. Resistor 56 is a shunt resistor that makes circuit 50 more sensitive and responsive by shunting current away from dc coil 40, which results in dc coil 40 being switched off and valve 21 being closed at a higher current than would be required without resistor 56. Particularly in full power mode, the igniter 52 may receive a current that is much greater than the threshold current of the dc coil 40 to magnetically hold open the valve assembly 20 (fig. 1-3). Thus, shunt resistor 56 shunts some of this current around dc coil 40. As the resistance of the resistor 56 increases, the dc coil 40 will receive most of the current received by the igniter 52, in which case a lower igniter 52 current will be required to reach the trigger current of the dc coil 40. Conversely, as the resistance of the resistor 56 decreases, the dc coil 40 will receive a smaller portion of the current received by the igniter 52, in which case a higher igniter 52 current will be required to reach the trigger current of the dc coil 40. Accordingly, the resistance of the shunt resistor 56 may be selected to provide a safety margin between the igniter 52 current when the igniter 52 reaches the auto-ignition temperature of the cooking gas and the trigger current when the dc coil 40 remains open to the valve 21. The resistor 54 is arranged to provide an additional voltage drop between the igniter 52 and the coil 40. At a given resistance value of the resistor 56, increasing the resistance of the resistor 54 will result in a lower portion of the current received by the igniter 52 being received by the dc coil 40, while decreasing the resistance of the resistor 54 will have the opposite effect. The fuse 66 provides an additional layer of protection in the event of a failure of the shunt resistor 56. The higher the current rating of the fuse 66, the longer it takes for the circuit 50 to open in the event of a catastrophic failure. However, an excessively low rating may cause the fuse to undesirably blow during normal circuit 50 operation.

The hold-open circuit of fig. 4 may be described as several equivalent circuits comprising various series and parallel combinations of components. The fuse 66, the resistor 54 and the dc coil 40 form a first series combination that forms a first parallel combination with the shunt resistor 56. The first parallel combination forms a second series combination with the hot surface igniter 52.

Capacitors

58 and 60 form a second parallel combination with each other 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 an AC source 51 voltage ranging from 90VAC (rms) to about 135VAC (rms), preferably from about 110VAC (rms) to about 130VAC (rms), more preferably from about 115VAC (rms) to about 125VAC (rms), and to provide sufficient current to the igniter 52 to reach the cooking gas auto-ignition temperature. In certain examples, the hot surface igniter 52 is designed to have a high temperature resistance (i.e., resistance at the ignition temperature of the cooking gas) ranging from about 330 Ω to about 500 Ω, preferably from about 400 Ω to about 480 Ω, and more preferably from about 430 Ω to about 450 Ω. The dc coil 40 has a threshold (rms) current ranging from about 30mA to about 90mA, preferably from about 40mA to about 80mA, and more preferably from about 50mA to about 70 mA. The dc coil 40 also has an inductance ranging from about 0.005mH to about 0.010mH, preferably from about 0.006mH to about 0.009mH, more preferably from about 0.007mH to about 0.008 mH.

Capacitors

58 and 60 may have exemplary values ranging from about 15 μ F to about 30 μ F, preferably from about 18 μ F to about 25 μ F, more preferably from about 20 μ F to about 24 μ F. The dc coil 40 has a threshold (rms) current ranging from about 30mA to about 90mA, preferably from about 40mA to about 80mA, and more preferably from about 50mA to about 70 mA.

Resistors

54 and 56 may have exemplary resistance values ranging from about 20 Ω to about 40 Ω, preferably from about 25 Ω to about 35 Ω, and more preferably from about 28 Ω to about 32 Ω. The fuse 66 may be rated, for example, from about 0.5A to about 1.5A, preferably from about 0.6A to about 1.3A, and more preferably from about 0.8A to about 1.2A.

Example 1

A hold open circuit 50 is provided as shown in fig. 4. The hot surface igniter 52 includes a silicon ceramic body having a rare earth sintering aid and a molybdenum disilicide sintering aid protectant. The rare earth oxide sintering aid is present in an amount ranging from about 12% to about 14% by weight of the ceramic body. The molybdenum disilicide sintering aid protective agent is present in an amount ranging from about 5.5% to about 6.5% by weight of the ceramic body. The balance (79.5% to about 82.5% by weight of the ceramic body) is silicon nitride. The conductive ink in the igniter 52 includes tungsten carbide in an amount ranging from about 70% to about 75% by weight of the ink. Silicon nitride is provided in an amount ranging from about 18% to about 25% by weight of the ink. The same sintering aids or co-dopants described for the ceramic body are also included at levels ranging from about 2% to about 4% by weight of the ink. The thickness (taken along the thickness axis) of the conductive ink circuit of the hot surface igniter is no greater than about 0.002 inches, preferably no greater than about 0.0015 inches, and more preferably no less than about 0.0004 inches and no greater than about 0.0009 inches.

The capacitance values of the

capacitors

58 and 60 are 22 μ F, respectively. The

resistors

54 and 56 have a resistance value of 30 Ω. The inductance value of the dc coil 40 is 0.0074mH. The circuit was simulated using a 120VAC (rms) 60Hz voltage source signal. Fig. 10A depicts the input voltage (in volts) at the igniter 52 versus time. The circuit 50 operates in a full power mode (where the switch 62 is closed).

Capacitors

58 and 60 each have 22 muf and collectively behave like a single capacitor with a capacitance of 44 muf. The rms value of the voltage signal seen by the igniter is 130V, which is higher than the rms value of the AC source signal due to the smoothing effect of the capacitor on the ripple produced by the diode 64. Fig. 10B shows the current through the igniter 52 and has a similar pattern with an rms value of about 267 mA. At these voltage and current values, the high temperature resistance of the igniter was about 471 Ω, and the estimated surface temperature of the igniter reached about 2430 ° F at steady state.

Fig. 10C and 10D show the output voltage from the igniter 52 and the current received by the dc coil 40, respectively. As expected, the waveform has a shape similar to that in fig. 10A and 10B. However, the rms output voltage from the igniter 52 is 4.4V. The rms current to the dc coil 40 is 201mA, which is sufficient to lock the dc coil 40 and the cooking gas safety valve assembly 20 in the open position of fig. 2.

Fig. 11A-11D are simulation results in reduced power mode (where switch 62 is open). As previously mentioned, the reduced power mode is preferably used after ignition and during cooking operations as a way to prevent flame extinction while reducing energy costs and extending the life of the igniter 52 relative to a full power mode in which the igniter 52 is operated constant. Fig. 11A shows the input voltage of the igniter 52. The waveform is similar to that in fig. 10A. However, the input rms voltage of the igniter 52 is 109V. Referring to FIG. 11B, the rms current of the average igniter 52 is 245mA. The high temperature resistance of the igniter 52 is about 429 Ω.

Fig. 11C-11D show reduced power mode conditions for the igniter 52 output voltage and dc coil 40 current. The average output rms voltage of the igniter 52 was 4.1V. The average dc coil 40rms current was 185mA. At these estimated current and voltage values, the igniter 52 will reach a surface temperature of about 2150 ° F at steady state. Referring to fig. 5, a portion of another exemplary cooking gas safety device is depicted. The cooking gas safety device includes a hold open circuit 70 and a cooking gas safety valve assembly 20 that includes a dc coil 40 (as shown). Just as the hold-open circuit 50, the hold-open circuit 70 is powered by an ac power source 71 and converts it to a time-varying dc power so that known gas taps having dc coils like coil 40 can be used. Although not shown, an additional switch may be provided to selectively connect the ac power source 71 to the remainder of the hold open circuit 70 when the user actuates the valve assembly 20 by depressing and rotating the gas knob stem 26. The hot surface igniter 52 is in selective electrical communication with the dc coil 40 (as described below) depending on the state of the zener diode 72.

The hold-open circuit 50 of fig. 4 uses two parallel capacitors, one of which may be selectively connected to the circuit 50 to provide full power and reduced power modes for the igniter 52. In contrast, the hold-open circuit 70 of fig. 5 uses two

parallel resistors

82 and 84, one of which (84) may be selectively connected to the hold-open circuit (via switch 86) to provide full power and low power modes. When switch 86 is closed,

resistors

82 and 84 are connected in parallel with each other. When the switch 86 is open, the resistor 84 is not in electrical communication with the ac power source 71 and is effectively outside of the hold open circuit 70. The parallel combination of

resistors

82 and 84 corresponds to a single resistor having a resistance equal to the product of their resistances divided by the sum of their resistances. The combined resistance will always be lower than each individual resistance. Thus, closing switch 86 places circuit 70 in a full power mode, while opening switch 86 places circuit 70 in a reduced power mode. The full power mode is preferably used during ignition operation. The reduced power mode is preferably used during cooking operations and provides a means to re-ignite the cooking gas in the event that the flame is extinguished. In certain examples, the power provided to the igniter 52 in the reduced power mode is from about 70% to about 90%, preferably from about 75% to about 85%, and more preferably from about 78% to about 82% of the power provided to the igniter 52 in the full power mode.

In some examples, releasing the gas valve stem 26 after the dc coil 40 has been locked in the open position of fig. 2 will cause the switch 86 to open (to place the circuit 70 in the reduced power cooking mode). Otherwise, switch 86 will remain closed.

The dc coil 40 is connected in series with the zener diode 72 and the 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 connected in series with the first parallel combination to form a second series combination. The second series combination forms a third series combination with the hot surface igniter 52. The third series combination and capacitor 74 form a third parallel combination in series with diode 76 and fuse 88.

When the switch 86 is open, the second series combination consists of the first parallel combination and the resistor 82 alone (i.e., without the resistor 84). Thus, when the switch 86 is closed, the hot surface igniter 52 is in series with its equivalent circuit component having a lower total resistance than when the switch 86 is open. This means that more voltage is available to the igniter 52 and, therefore, it consumes more power. The resistor 82 determines how hot the igniter 52 will become in the reduced power mode and affects the temperature of the igniter 52 in the full power mode.

When the switch 86 is closed, the resistor 84 allows more current to flow through the circuit 70, causing the igniter 52 to become hotter in the full power mode. An increase in the resistance of the resistor 84 will tend to decrease the power dissipated by the igniter 52 in the full power mode, while a decrease in the resistance of the resistor 84 will tend to increase the power dissipated by the igniter 52 in the full power mode.

As with the hold-open circuit 50, the 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 the cost and expected life of circuit 70. Diodes having higher voltage ratings tend to be more expensive, but as the voltage rating of the diode 76 decreases, the life of the circuit 70 also decreases. Because of diode 76, as with circuit 50Ripple is also present in the circuit 70. Here, a capacitor 74 is placed in series-parallel relationship with the diode 76 and the hot surface igniter 52 to smooth the ripple voltage and reduce the ripple factor. The capacitor 74 is not selectively connected to the hold-open circuit 70, but rather is maintained in electrical communication with the hot surface igniter 52 and the dc coil 40 at all times. When the diode 76 is forward biased, the capacitor 74 will charge until the saturation voltage is reached. Once the capacitor is at its saturation voltage, if the voltage of the ac power source 71 drops below the saturation voltage, the capacitor 74 will begin to discharge until the ac voltage exceeds the voltage of the capacitor 74, at which point the capacitor 74 will begin to charge again. Generally, increasing the capacitance of capacitor 74 will cause node N to operate in both full power and reduced power modes ₅₂ The ripple of the input voltage to the igniter 52 at (a) flattens out and will also reduce the AC supply voltage at which the valve assembly 20 releases to the closed position of fig. 1, i.e., at lower supply voltages, the dc coil 40 will still experience the threshold current required to hold the valve disc 36 in the open position of fig. 2. At higher capacitance values, the power dissipated by the igniter 52 will increase in both full power and reduced power modes relative to lower capacitance values.

The resistor 80 acts as a current setting resistor. As the current through the igniter 52 increases, the voltage at the resistor 80 increases. When the voltage at resistor 80 reaches the breakdown voltage of zener diode 72, dc coil 40 will receive current. The fuse 78 provides an additional layer of protection for the dc coil 40 in the event of a failure of the resistor 80. At too high a current rating, the dc coil 40 may not be able to shut down when the circuit 70 fails. If the fuse 78 current rating is too low, the dc coil 40 may close the valve 21 during normal operation. The fuse 88 provides overall circuit protection.

The hold-open circuit 70 includes a zener diode 72 in series with the dc coil 40 rather than using a current limiting resistor in series with the dc coil 40 as is the case with the hold-open circuit 50. The zener diode 72 operates in a reverse bias mode. When the voltage input to the zener diode drops below the zener breakdown voltage, it stops allowing current to flow to the dc coil 40, causing it to release the valve disk 30 so that it is biased to the closed position of fig. 1. Thus, the zener diode 72 acts as a low voltage switch that ensures that the dc coil 40 does not keep the valve disc 36 open when the ignitor 52 is not hot enough to ignite the cooking gas.

The hold-open circuit 70 advantageously includes several features that prevent the valve assembly 20 from remaining open in the event of a circuit component failure. For example, if the diode 76 fails due to a short circuit, alternating current will flow through the dc coil 40 causing it to discharge. Because the valve assembly 20 is a valve assembly that remains open, gas will stop flowing to the burner unless and until manual actuation of the gas knob stem 26 is performed. If the diode 76 fails to open, the dc coil 40 will cease generating the magnetic field and the valve assembly 20 will fail to reach the closed position of fig. 1, thereby shutting off gas flow to the burner.

If the capacitor 74 fails due to a short circuit, all of the current will flow through the capacitor 74 causing the fuse 88 to blow and the valve assembly 20 will not reach the closed position of FIG. 1. If the capacitor 74 fails to open when the AC signal is 60Hz, the current to the DC coil will drop to zero, causing the valve assembly 20 to fail to reach the closed position of FIG. 1.

If the igniter 52 fails due to a short circuit, excessive current will flow through the circuit 70 and the fuse 78 will blow, causing the valve assembly 20 to fail to the closed position of FIG. 1. If the igniter 52 fails to open, no current will reach the dc coil 40, again causing the valve assembly 20 to shut off gas flow to the burner by failing to reach the closed position of fig. 1.

If the zener diode 72 fails due to a short circuit, the current through the dc coil 40 will rapidly increase significantly, causing the fuse 78 to blow and the valve assembly 20 to fail to reach the closed position of fig. 1. If the zener diode 72 fails to open, no current can reach the dc coil 40, resulting in the failure of the valve assembly 20 to reach the closed position.

If the shunt resistor 80 fails due to a short circuit, no current will reach the dc coil 40 causing it to release the valve disc 36 and shut off gas flow to the burner. If the shunt resistor 80 fails to open, the current to the dc coil 40 will increase dramatically, causing the fuse 78 to blow and the valve assembly 20 to fail to close.

If the resistor 82 fails to open with the switch 86 open, nothing will happen because there will be no closed path for current to flow through the dc coil 40. If the resistor 82 fails due to a short circuit with the switch 86 open or closed, the igniter 52 will experience a large current spike causing it to heat up significantly, which may cause the igniter 52 to malfunction. If the resistor 82 fails to open with the switch 86 closed, the igniter 52 will only operate in the reduced power mode. If the resistor 84 fails to open with the switch 86 open or closed, the igniter 52 will only operate in the reduced power mode. If the resistor 84 fails to close with the switch 86 closed, the igniter 52 will experience a large current spike causing it to heat up significantly, which may cause the igniter 52 to malfunction.

The capacitance and resistance values of the various components of the keep-open circuit 70 may be selected to achieve the desired operation of the circuit 70. In general, if it is desired to have the DC coil 40 remain open more quickly upon actuation of the gas knob stem 26, the resistance of the resistor 80 may be increased. Increasing the resistance of the resistor 80 will increase the input voltage to the zener diode 72 and the resistor 80 and will cause relatively more of the total current through the igniter 52 to pass through the dc coil.

If it is desired to operate 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. Simultaneously or alternatively, the capacitance value of the capacitor 74 may be increased. Increasing the capacitance of the capacitor 74 provides more stored electrical energy when the capacitor 74 discharges (i.e., when the output voltage from the diode 76 drops below the saturation voltage of the capacitor 74). As a result, the rms voltage experienced by the igniter 52 increases, thereby increasing its surface temperature.

The hold-open circuit 70 is preferably designed to operate at an AC voltage ranging from 90VAC (rms) to about 135VAC (rms), preferably from about 110VAC (rms) to about 130VAC (rms), and more preferably from about 115VAC (rms) to about 125VAC (rms). In certain examples, the hot surface igniter 52 is designed to have a high temperature resistance (i.e., resistance at the ignition temperature of the cooking gas) ranging from about 330 Ω to about 500 Ω, preferably from about 400 Ω to about 480 Ω, and more preferably from about 430 Ω to about 450 Ω.

Meanwhile, the capacitor 74 may have an exemplary capacitance value ranging from about 60 μ F to about 80 μ F, preferably from about 65 μ F to about 75 μ F, and more preferably from about 66 μ F to about 70 μ F. The dc coil 40 has a threshold (rms) current ranging from about 30mA to about 90mA, preferably from about 40mA to about 80mA, and more preferably from about 50mA to about 70 mA. The dc coil 40 also has an inductance ranging from about 0.005mH to about 0.010mH, preferably from about 0.006mH to about 0.009mH, more preferably from about 0.007mH to about 0.008 mH. In addition, at the higher capacitance value of capacitor 74, node N ₅₂ The igniter 52 voltage at (a) will show less ripple (become "flatter") in both power modes. This in turn will reduce the current in the circuit 70 and the steady state temperature of the igniter 52, and the valve 21 may not remain open during lower power mode operation. The resistance and impedance of the dc coil 40 is typically much lower than the resistance and impedance of the other circuit components and is negligible in practice.

Meanwhile, the resistor 82 may have an exemplary resistance value ranging from about 80 Ω to about 120 Ω, preferably from about 90 Ω to about 110 Ω, and more preferably from about 95 Ω to about 105 Ω. Resistor 84 preferably has an exemplary resistance value ranging from about 30 Ω to about 70 Ω, preferably from about 40 Ω to about 60 Ω, and more preferably from about 45 Ω to about 55 Ω. An increase in the resistance value of the resistor 82 will primarily affect the current flowing through the circuit 70 in the reduced power mode and will generally reduce the power dissipated by the igniter 52 (and reduce the temperature of the igniter 52). An increase in the resistance value of resistor 84 will generally decrease the temperature of igniter 52 in full power mode, while a decrease in the resistance value will increase the temperature.

Meanwhile, the resistor 80 may have an exemplary resistance value ranging from about 65 Ω to about 95 Ω, preferably from about 70 Ω to about 90 Ω, and more preferably from about 75 Ω to about 85 Ω. Increasing the resistance value of resistor 80 will tend to decrease the discharge voltage of dc coil 40 (i.e., the input voltage of resistor 80 required by dc coil 40 to generate a magnetic field sufficient to maintain valve assembly 20 in the open position of fig. 2) by allowing more current to flow through coil 40 for a given input voltage of resistor 80. By way of example, the fuse 88 may be rated from about 0.5A to about 1.5A, preferably from about 0.6A to about 1.3A, and more preferably from about 0.8A to about 1.2A. By way of example, the fuse 78 may be rated from about 100mA to about 300mA, preferably from about 150mA to about 250mA, and more preferably from about 180mA to about 220mA.

Example 2

A hold open circuit 70 is provided as shown in fig. 5. The hot surface igniter 52 is described in example 1. The breakdown voltage of the zener diode 72 is 5.1V. The capacitance value of the capacitor 74 is 68 μ F. The resistance value of the resistor 80 is 80 Ω. The resistance value of the resistor 82 is 100 Ω, and the resistance value of the resistor 84 is 50 Ω. The inductance of the dc coil 40 is 7.4 muh. The circuit was simulated using a 120VAC (rms) 60Hz voltage source signal. Fig. 12A depicts input voltage (in volts) at the igniter 52 versus time. Circuit 70 operates in a full power mode (where switch 86 is closed). The rms value of the input voltage signal seen by the igniter 52 is 141.8V, which is higher than the rms value of the AC source signal due to the smoothing effect of the capacitor on the ripple produced by the diode 64. Fig. 12B shows the current through igniter 52 and has a similar pattern with an rms value of 269 mA. At these voltage and current values, the igniter 52 high temperature resistance is about 476 Ω and the estimated igniter 52 surface temperature will reach about 2460 ° F at steady state.

Fig. 12C and 12D show the voltage output from igniter 52 (i.e., the input voltage to resistor 80) and the current received by dc coil 40, respectively. As expected, the waveform has a shape similar to that in fig. 12A and 12B. However, the output rms voltage of the igniter 52 is 14.1V and the rms current to the DC coil is 100mA, which is sufficient to lock the DC coil 40 and the cooking gas safety valve assembly 20 in the open position of FIG. 2.

Fig. 13A-13D are simulation results in reduced power mode (i.e., when switch 86 is open). As previously mentioned, the reduced power mode is preferably used after ignition and during cooking operations as a way to prevent flame extinction while reducing energy costs and extending the life of the igniter 52 relative to operating the igniter 52 in a constant full power mode. Fig. 13A shows the input voltage of the igniter 52. The waveform is similar to that in fig. 12A. However, the input rms voltage of the igniter 52 is 143.2V. Referring to FIG. 13B, the rms current of the igniter 52 is 253mA. At these estimated current and voltage values, the igniter 52 will have a high temperature resistance of about 446 Ω and will reach a surface temperature of about 2260 ° F at steady state.

Fig. 13C-13D show reduced power mode conditions for the igniter 52 output voltage and dc coil 40 current. The average rms current of the dc coil 40 is about 85mA and the output rms voltage of the igniter 52 is 30.5V.

The hold-

open circuits

50 and 70 are particularly well suited for situations where the igniter 52 can be energized and remain part of the hold-open circuit, but receives insufficient current to reach the auto-ignition temperature of the cooking gases. However, it has been determined that this is unlikely to occur for some igniters 52. In this case, if the igniter 52 fails to reach the auto-ignition temperature, the

circuit

50 or 70 will not act as an open circuit. The hold-open circuits of fig. 14 and 15 below are particularly suitable for situations where the igniter 52 is unlikely to reach auto-ignition temperature unless it fails to act as an open circuit. Referring to fig. 14, a portion of another exemplary cooking gas safety device is depicted that includes a single mode valve driver hold open circuit 130. The circuit 130 is powered by an ac power source 131. The hold-open circuit 130 converts the alternating current to a time-varying direct current so that known gas taps having a dc coil like coil 40 can be used. Although not shown, an additional switch may be provided to selectively connect the ac power source 131 to the remainder of the hold open circuit 130 when the user actuates the valve assembly 20 by depressing and rotating the gas knob stem 26. The hot surface igniter 52 is in electrical communication with the dc coil 40. The term "single mode" refers to the fact that keep-open circuit 130 has a full power mode but no reduced power mode. Accordingly, the igniter 52 may reignite the cooking gas after the flame is extinguished by remaining at full power.

The igniter 52 is connected in series with the dc coil 40. The series combination of the igniter 52 and the dc coil 40 is connected in parallel with the capacitor 136. The parallel combination of the capacitor 136 and the series combination of the igniter 52 and the dc coil 40 are in series with the diode 132. The diode 132 provides half-wave rectification to the AC signal of the AC source 131 so that the igniter 52 is at node N ₅₂ Where the voltage experienced has only a dc component. The diode 132 is preferably selected to balance cost and life of the circuit 130, as diodes with higher current ratings tend to be more expensive, while diodes with lower current ratings tend to shorten the life of the circuit 130.

The capacitor 136 smoothes out ripples in the DC signal provided by the diode 132. When diode 132 is forward biased, capacitor 136 will charge until a saturation voltage is reached, at which point charging stops. When the voltage of the diode 132 drops below the saturation voltage of the capacitor 136, the capacitor 136 will begin to discharge until the AC voltage exceeds the voltage of the capacitor 136, at which point it will begin to charge again. The capacitance value of the capacitor 136 is from about 20 μ F to about 40 μ F, preferably from about 25 μ F to about 35 μ F, and more preferably from about 28 μ F to about 32 μ F. Node N increases as the capacitance of capacitor 136 increases ₅₂ The input voltage to the igniter 52 will tend to be flat (showing "less ripple"). Conversely, as the capacitance of capacitor 136 decreases, node N ₅₂ The igniter 52 input voltage at will tend to be uneven ("more ripple"); the inductance of the dc coil 40 ranges from about 6 μ H to about 9 μ H, preferably from about 6.5 μ H to about 8.5 μ H, and more preferably from about 7.0 μ H to about 8.0 μ H.

Example 3

A hold open circuit 130 is provided as shown in fig. 15. The hot surface igniter 52 is described in example 1. The capacitance of the capacitor 136 is 30 μ F. The inductance of the dc coil 40 is 7.5 muh. The circuit was simulated using a 120VAC (rms) 60Hz voltage source signal. FIG. 16A depicts node N ₅₂ Input voltage (in volts) at the igniter 52 and timeThe relationship (2) of (c). The rms value of the input voltage signal seen by the igniter 52 is 118V. Fig. 16B shows the current through the igniter 52 with an rms value of 259mA. At these voltage and current values, the high temperature resistance of the igniter 52 is approximately 457 Ω, and the surface temperature of the igniter 52 reaches approximately 2340 ° F at steady state.

Fig. 16C and 16D show the voltage output from the igniter 52 and the current received by the dc coil 40, respectively. As expected, the waveform has a shape similar to that in fig. 16C and 16D. The rms current to the dc coil 40 is 259mA, which is sufficient to lock the dc coil 40 and the cooking gas safety valve assembly 20 in the open position of fig. 2.

Referring to fig. 15, an exemplary portion of a cooking gas safety device is depicted that includes a dual mode valve driver hold open circuit 140. Unlike the hold-on circuit 130 of fig. 14, the hold-on circuit 140 can operate in both full power and reduced power modes. In certain examples, the power provided to the igniter 52 in the reduced power mode is from about 70% to about 90%, preferably from about 75% to about 85%, and more preferably from about 78% to about 82% of the power provided to the igniter 52 in the full power mode.

The ac power supply 141 supplies ac power to the diode 140, and the diode 140 converts the ac power into time-varying dc power.

Capacitors

146 and 148 are provided and are connected in parallel with each other when switch 150 is closed to electrically connect capacitor 148 to the remainder of hold open circuit 140. When the hold-on circuit 140 is in the full or low power mode, the capacitor 146 leads to the igniter 52 (i.e., node N) ₅₂ Where) the ripple in the input voltage and current becomes smooth or flat. Capacitor 148 passes to igniter 52 (i.e., node N) when hold-on circuit 140 is in full power mode ₅₂ Where) the ripple in the input voltage and current becomes smooth or flat. When the 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 the switch 150 is open, the capacitor 148 is not in circuit and the total capacitance of the parallel combination of the

capacitors

146 and 148 is equal to the capacitance of the capacitor 146. In certain

exemplary embodimentsCapacitors

146 and 148 have capacitance values ranging from about 10 μ F to about 20 μ F, preferably from about 12 μ F to about 18 μ F, and more preferably from about 14 μ F to about 16 μ F. The dc coil 40 has the inductance value described above. When in full power mode, the igniter 52 input voltage and current tend to have less ripple (become flatter) as the capacitance of one or both of the

capacitors

146 and 148 increases, however at smaller values the situation is reversed.

The hot surface igniter 52 is in series with the dc coil 40. When the switch 150 is open, the capacitor 146 forms a parallel combination with the series combination of the igniter 52 and the dc coil 40. When the switch 150 is closed, the parallel combination of the

capacitors

146 and 148 forms a parallel combination with the series combination of the igniter 52 and the dc 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 the switch is open. When AC source 141 is electrically connected to circuit 140,

capacitors

146 and 148 will charge until a saturation voltage is reached. When the AC source signal drops below the saturation voltage, the

capacitors

146 and 148 will begin to discharge and supply current to the igniter 52, thereby ensuring that the igniter input voltage at node 52 does not drop below the highest saturation voltage of the

capacitors

146 and 148.

Example 4

A hold open circuit 140 is provided as shown in fig. 15. The hot surface igniter 52 is described in example 1. The

capacitors

146 and 148 each have a capacitance of 15 μ F. The inductance of the dc coil 40 is 7.5 muh. The circuit was simulated using a 120VAC (rms) 60Hz voltage source signal. At full power, the hold-open circuit 140 is equivalent to the hold-open circuit 130 of example 3. Thus, fig. 16A depicts the input voltage (in volts) of the igniter 52 versus time at full power. Igniter 52 at node N ₅₂ Where the rms value of the input voltage signal experienced is 118V. Fig. 16B shows the current through igniter 52 with a similar pattern of rms values of 259mA. At these voltage and current values, the high temperature resistance of igniter 52 is about 457 Ω and the estimated igniter surface temperature reaches about 2330 ° F at steady state.

As with example 3, fig. 16C and 16D show the voltage output from the igniter 52 and the current received by the dc coil 40, respectively, when the hold-open circuit 140 is operating in the full power mode. As expected, the waveform has a shape similar to fig. 16C and 16D. The rms current to the dc coil 40 is 259mA, which is sufficient to lock the dc coil 40 and the cooking gas safety valve assembly 20 in the open position of fig. 2.

The simulation at 120VAC source power is performed with the hold-on circuit 140 in the reduced power mode, i.e., with the switch 150 turned off using the same igniter 52 and component values as in the full power mode. Fig. 17A depicts the input voltage (in volts) at the igniter 52 versus time at reduced power. The rms value of the voltage seen by the igniter 52 is 98V. Fig. 17B shows the current through igniter 52 in the reduced power mode, which has a similar mode with an rms value of 238mA. At these voltages and currents, the estimated high temperature resistance of the igniter 52 is about 414 Ω, and the igniter 52 will reach an estimated surface temperature of about 2050 ° F. Fig. 17C shows the output voltage of the igniter 52. Fig. 17D shows the current of the dc coil 40, the rms value of which is 238mA.

Example 5

Three igniters 52, each of the same composition and size, were used, these igniters falling within the range described in example 1, but with conductive ink thickness variations on the order of 0.0004 to 0.002 inches, keeping the open circuit 140 subjected to different AC source voltage signals ranging from 90VAC rms to 135VAC rms. The AC power supply rms voltage value, igniter input rms voltage value, igniter rms current value, igniter power consumption, and measured igniter temperature are set forth in tables I-III below:

TABLE I

Igniter 1

TABLE II

Igniter 2

TABLE III

Igniter 3

Example 6

A hot surface igniter as described in example 1 was provided having a room temperature resistance of 87 omega. The igniter is placed in the hold-open circuit 140 with the previously described component values and subjected to a source voltage of 120VAC rms. In table 4, the time (in seconds) required to reach 1800 ° F and 2138 ° F is provided:

TABLE 4

The keep-

open circuits

50, 70, 130, and 140 are designed to: allowing the hot surface igniter 52 to be powered by an ac power source while still being compatible with the dc coil 40. Because of the relationship between the igniter 52 and the dc coil 40 in the

circuits

50, 70, 130 and 140, the dc coil 40 only receives sufficient current to maintain the cooking gas safety valve assembly 20 in the open position of fig. 2 when the igniter 52 receives sufficient current to ignite the combustible mixture of air and cooking gas supplied by the valve assembly 20 to the associated burner. However, unlike known hold-open circuits, the

circuits

50, 70, 130, and 140 do not use a thermocouple to determine when the igniter is hot enough to warrant holding the gas valve 21 open. In this known system, the thermocouple introduces a significant amount of lag time due to the dynamic response of the thermocouple to the ignited flame. Instead, the

circuits

50, 70, 130 and 140 rely on the electrical condition of the igniter 52 to indicate that ignition has occurred or will occur quickly enough to allow the gas valve 21 to remain open after the user releases the gas knob. This is possible, at least in part, because the hot surface igniters disclosed herein have superior ignition temperature time characteristics relative to known hot surface igniters, suitable for use as the igniter 52. Thus, in a preferred example, the hot surface igniter 52 is not operatively connected to the thermocouple of the flame sensor.

Referring to fig. 8, an alternative example of a hold-open circuit 120 is provided in which the hold-open coil 132 operates on alternating current, i.e., it can generate a consistent magnetic field to maintain the cooking gas safety valve assembly 20 in the open position of fig. 2 even when the source voltage crosses zero during a polarity change. As known to those skilled in the art, the shield ring is equipped with a standard dc coil 40 to produce a magnetic field that is inferior and out of phase with the magnetic field produced by the dc coil 40. As a result, the secondary magnetic field created by the shield ring holds the valve assembly 20 in the open position of fig. 2 as the primary magnetic field begins to weaken due to the voltage at the hold open coil 132 approaching zero. Referring to FIG. 8, an alternating current holds the open coil 132 in series with the hot surface igniter 52. The diode 124 may be selectively connected to the igniter 52 and the ac coil 132 to allow the hold-on circuit 120 to operate in a low power mode, such as during a cooking operation after ignition. Just as

circuits

50 and 70 remain open, the ability to operate in a low power mode reduces the likelihood of extinguishment by providing an ignition source (igniter 52) that is constantly energized, while reducing power consumption and increasing igniter life relative to operating igniter 52 constantly at full power. A switch 130 may be selectively connected to the electrode 128 to place the hold-open circuit in a full power mode and to the electrode 126 to place the igniter 52 in a reduced power mode. In certain examples, the switch 130 is operatively connected to the gas knob stem 26 such that when the gas knob stem 26 is released with the valve assembly 20 in the open position of fig. 2, the switch 130 is connected to the electrode 126 to operate in the reduced power mode.

As previously described, one benefit of using the hot surface igniter 52 to ignite the cooktop burner gases, as opposed to a spark igniter, is that the igniter can remain continuously energized (at full or reduced power) to provide ignition in the event the flame is extinguished. This property of hot surface igniters also enables many other features.

Referring to fig. 6, a template circuit 90 including a hot surface igniter 52 is depicted, and fig. 6 does not show a hold-open circuit or a gas valve with a hold-open coil. However, a gas valve would be provided and the circuit 90 would be configured such that when the gas valve is actuated the hot surface igniter 52 would be energized via the switch 94 to coordinate the flow of gas to the burner with the supply of electrical power to the igniter 52. The diode 92 may be selectively connected to the circuit 90 via a switch 94. When the switch 94 is in contact with the switch pole 96, the diode 92 is connected to the circuit 90 and half-wave rectifies the current supplied to the igniter 52. The elimination of the reverse polarity current reduces the power supplied to the igniter 52, thereby providing a reduced power mode of operation. When the switch 94 is in contact with the switch pole 98, the circuit 90 is in full power mode. In a preferred example, the full power mode is used during ignition operation, while the reduced power mode is used after ignition and during cooking operation. The template circuit 90 is referred to as such because it includes locations 102 and 104 where a number of different circuit components may optionally be provided.

Referring to FIG. 6, one component that may be used in locations 102 or 104 is a flame sensor. As is known in the art, a flame sensor determines whether the burner is lit. Many different flame sensor technologies exist and can be used, including optical flame detectors and thermocouples. The optical flame sensor may include a UV detector, a near IR array detector, and an IR detector. If a flame sensor is provided, it may be operatively connected to a gas valve assembly for supplying gas to the burner, so that the gas flow is disconnected when no flame is present. The flame sensor may also be used with a temperature control relay, an open coil, and a bimetallic gas safety valve ("safety cans") to prevent the flow of burner gas in the absence of a flame.

A number of sensors or indicators may also be used at locations 102 and 104 to record information about the electrical status of the igniter 52. The sensors or indicators may be used alone or in combination with one another. In one example, a timer may be provided that accumulates the total time that the igniter 52 is energized. The energization time data can then be used to determine how much life expectancy of the igniter 52 remains so that the igniter 52 can be replaced before failure. This collected information may also be wirelessly transmitted to the user's smart phone, personal computer, laptop or server via wi-fi, bluetooth and other known wireless communication techniques to remotely provide information about the status of the igniter 52.

Audible indicators may also be used at locations 102 and 104. Current spark igniters produce an audible and noticeable sound during ignition, and many consumers have become accustomed and willing to hear this sound as an indication of ignition. The hot surface igniter 52 does not emit an audible sound during ignition. However, a sound generator may be provided at location 104 that is energized only when the ignitor 52 is initially energized and emits a click or other type of sound to indicate that the ignitor 52 is receiving ignition current.

A number of additional sensors and indicators may be used at locations 102 or 104. For example, a fire sensor may be provided. Fire sensors differ from flame sensors in that they are intended to determine whether a flame other than the desired cooking is present. The flame sensor is typically an optical sensor with a field of view above the burner. In some examples, it may be integrated into a control scheme that shuts off gas to the burner when a fire is detected.

A pan sensor can also be provided. The pan sensor determines when a pan is present on the burner (e.g., by sensing weight changes). The pot sensor may include or be operatively connected to a pressure switch or piston that completes the circuit 90 only when a pot is present on the burner, which may help prevent a fire.

Further, because the ignitor 52 can be continuously energized (to full power or reduced power) and re-ignited at any airflow, a variety of different cooking functions can be provided by turning the burner on and off for a particular period of time (i.e., by turning on and off a gas valve to the burner). In some examples, a timer is provided that accumulates the amount of time the burner is turned on or off. A flame sensor of the type described previously may be used to switch the timer state between on and off. Alternatively, the timer may simply be configured to: the igniter 52 is energized only when energized, and the on and off times are accumulated when the user sets the gas valve to a position indicating a desired cooking mode (e.g., "simmer"). A preprogrammed algorithm residing in the associated controller may open and close the burner gas valve based on the selected cooking mode.

The circuit component options described with respect to fig. 6 may also be used with the dc hold-on coil circuit previously described. Referring to fig. 7, the hold-open circuit 110 is similar to the circuit of fig. 4. The dc coil 40 is part of the gas safety valve assembly 20 of fig. 1 and 2. Various sensors and indicators may be used at

locations

114 and 116. The hold-on circuit 110 includes a diode 130 that functions similar to the diode 64 of fig. 4. When switch 126 contacts electrode 128 (full power mode),

parallel capacitors

120 and 124 smooth the ripple voltage of diode 130. The capacitor 120 smoothes the ripple voltage in the reduced power mode (with the switch 126 open). Resistor 122 is in series with dc coil 40 and limits the current received by dc coil 40. The shunt resistor 118 shunts excess current required to operate the igniter 52 relative to the current required to keep the cooking gas safety valve assembly 20 (fig. 2) open.

Claims

1. A cooking gas safety device comprising:

a valve assembly that can be manually actuated to an open position to allow gas to be allowed to be cooked, and that includes at least one coil that is energizable to maintain the valve in the open position only when subjected to a current that exceeds a threshold current value; and

a hold-open circuit comprising a hot surface igniter and the at least one coil, wherein the hot surface igniter is in electrical communication with the at least one coil, and wherein a surface of the hot surface igniter reaches at least an auto-ignition temperature of the cooking gas no later than eight (8) seconds after the at least one coil is subjected to the current having the threshold current value.

2. The cooking gas safety device of claim 1, wherein the at least one coil is at least one alternating current coil.

3. The cooking gas safety device of claim 1, wherein the at least one coil is at least one direct current coil.

4. The cooking gas safety device of claim 3, wherein the hot surface igniter is in a first series combination with the at least one DC coil.

5. The cooking gas safety device of claim 4, further comprising: a first capacitor, wherein the first capacitor is in a first parallel combination with the first series combination.

6. The cooking gas safety device of claim 5, further comprising: a second capacitor in selective electrical communication with a hold open circuit such that the first capacitor and the second capacitor are in a second parallel combination with the first series combination when the second capacitor is in electrical communication with the hold open circuit.

7. The cooking gas safety device of claim 6, further comprising: a diode in a second series combination with the second parallel combination.

8. The cooking gas safety device of claim 5, further comprising: a diode in a second series combination with the first parallel combination.

9. The cooking gas safety device of claim 3, wherein the hot surface igniter is in selective electrical communication with the at least one DC coil.

10. The cooking gas safety device of claim 3, wherein the hot surface igniter and the at least one DC coil are in a first series-parallel combination.

11. The cooking gas safety device of claim 3, wherein the hold-open circuit further comprises a Zener diode in a first series combination with the at least one DC coil.

12. The cooking gas safety device of claim 11, wherein the hold open circuit further comprises a diode in a second series-parallel combination with the hot surface igniter.

13. The cooking gas safety device of claim 3, wherein the hold open circuit further comprises a first capacitor in parallel with the hot surface igniter to form a first parallel combination.

14. The cooking gas safety device of claim 13, wherein the hold open circuit further comprises a second capacitor and a switch, the second capacitor selectively connected in series with the switch to form a first series combination, and the first series combination connected in parallel with the first parallel combination.

15. The cooking gas safety device of claim 3, wherein the hold-open circuit further comprises a first resistor, the at least one DC coil is in series with the first resistor to form a first series combination, and the hot surface igniter is in a first series-parallel combination with the first series combination.

16. The cooking gas safety device of claim 15, wherein the hold open circuit further comprises a second resistor connected in parallel with the first series combination to form a first parallel combination, and connected in series with the hot surface igniter to form a second series combination.

17. The cooking gas safety device of claim 1, wherein the hold-open circuit further comprises a first resistor, and the dc coil is connected in series with the first resistor to form a first series combination.

18. The cooking gas safety device of claim 17, wherein the hold-open circuit further comprises a second resistor, and the first series combination is in parallel with the second resistor to form a first parallel combination.

19. The cooking gas safety device of claim 18, wherein the first parallel combination is in series with the hot surface igniter to form a second series combination.

20. The cooking gas safety device of claim 19, wherein the hold open circuit further comprises a first capacitor, and the second series combination is in parallel with the first capacitor to form a second parallel combination.

21. The cooking gas safety device of claim 20, wherein the hold open circuit further comprises a second capacitor and a switch, the second capacitor selectively connected in series with the switch to form a third series combination, and the third series combination connected in parallel with the second parallel combination to form a third parallel combination.

22. The cooking gas safety device of claim 10, wherein the hold-open circuit further comprises a diode in a second series-parallel combination with the hot surface igniter.

23. Cooking gas safety device according to any one of the preceding claims, wherein the at least one coil is not electrically connected to a thermocouple.

24. Cooking gas safety device according to any one of the preceding claims, wherein the at least one direct current coil is not electrically connected to a flame sensor.

25. Cooking gas safety device according to any one of the preceding claims, wherein the hot surface igniter has a positive temperature coefficient of resistance.

26. The cooking gas safety device according to any preceding claim, wherein the hot surface igniter is a ceramic igniter.

27. The cooking gas safety device according to any preceding claim, wherein the hot surface igniter is a silicon nitride igniter.

28. The cooking gas safety device of claim 26, wherein the ceramic igniter has a room temperature resistance of from about 20 ohms to about 60 ohms.

29. The cooking gas safety device of claim 26, wherein the ceramic igniter has a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis, the ceramic igniter comprising:

first and second tiles having respective outer surfaces;

a conductive ink pattern disposed between the first and second tiles, wherein the igniter has a thickness along a thickness axis of from about 0.047 inches to about 0.060 inches and at least one of the respective igniter outer surfaces reaches a temperature of at least 1400 ° F in no more than 8 seconds when subjected to a potential difference of 120V AC rms.

30. The cooking gas safety device of claim 29, wherein the ceramic igniter conductive ink has a thickness along a thickness axis of from about 0.0004 inches to about 0.002 inches.

31. The cooking gas safety device of claim 29 or 30, wherein the conductive ink comprising the conductive ink pattern of the ceramic igniter comprises silicon nitride and tungsten carbide.

32. The cooking gas safety device according to any one of claims 29 to 31, wherein the conductive ink pattern has a positive temperature coefficient of resistivity.

33. The cooking gas safety device of claim 3, wherein the hold-open circuit further comprises a Zener diode in series with the DC coil to form a first series combination.

34. The cooking gas safety device of claim 33, wherein the hold open circuit further comprises a first resistor in parallel with a second resistor to be selectively connectable to the hold open circuit to form a first parallel combination.

35. The cooking gas safety device of claim 34, wherein the hold open circuit further comprises a third resistor in parallel with the first series combination to form a second parallel combination.

36. The cooking gas safety device of claim 35, wherein the first parallel combination is in series with the second parallel combination to form a second series combination.

37. The cooking gas safety device of claim 36, wherein the hot surface igniter is in series with the second parallel combination to form a third series combination.

38. The cooking gas safety device of claim 37, wherein the hold open circuit further comprises a capacitor in parallel with the third series combination to form a third parallel combination.

39. The cooking gas safety device of claim 38, further comprising: a diode in series with the third parallel combination to form a fourth series combination.

40. A method of supplying cooking gas to a cooktop burner, comprising:

providing a valve assembly comprising a valve having an open position and a closed position, wherein cooking gas passes through the valve when the valve is in the open position, and further comprising at least one coil energizable to maintain the valve in the open position;

manually actuating the valve to an open position;

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 an open position.

41. The method of claim 40, wherein the at least one coil is an alternating current coil.

42. The method of claim 40, wherein the at least one coil is at least one direct current coil, and further comprising: converting the alternating current to a time-varying direct current and supplying the time-varying direct current to the at least one direct current coil to thereby maintain the valve in an open position.

43. The method of claim 42, wherein the step of converting the alternating current to a time-varying direct current comprises: the alternating current is rectified.

44. The method of claim 42, wherein the step of converting the alternating current to a time-varying direct current further comprises: charging and discharging a first capacitor in electrical communication with the hot surface igniter and the DC coil.

45. The method of claim 44, further comprising: selectively placing a second capacitor in electrical communication with the hot surface igniter and the at least one dc coil, and charging and discharging the second capacitor when it is in electrical communication with the hot surface igniter and the at least one dc coil.

46. The method of claim 45, wherein the first capacitor is connected in parallel with the second capacitor to form a first parallel combination.

47. The method of claim 46, wherein the second capacitor is in selective electrical communication with the hold open circuit.

48. The method of any one of claims 42 to 47, wherein the hot surface igniter and the at least one DC coil are connected in series to form a first series combination.

49. The method of claim 42, wherein the time-varying direct current is a first time-varying direct current, and further comprising: supplying a second time-varying direct current to the hot surface igniter.

50. The method of claim 40, wherein the valve remains in the open position no earlier than eight (8) seconds before the hot surface igniter reaches the auto-ignition temperature of the cooking gas.

51. The method of claim 40, further comprising: switching the hold-on circuit from an igniter full power mode during ignition operation to an igniter reduced power mode during cooking operation.

52. The method of claim 51, wherein the hold-open circuit comprises a first resistor in series with a switch to form a first series combination and a second resistor in series with the first series combination to form a first parallel combination, and the step of switching the hold-open circuit from the igniter full power mode to the igniter reduced power mode comprises: the switch is opened.

53. The method of claim 51 wherein the hold-open circuit further comprises a first capacitor in series with a switch to form a first series combination and a second capacitor in series with the first series combination and in combination to form a first parallel combination, and the step of switching the hold-open circuit from the igniter full power mode to the igniter reduced power mode comprises: the switch is opened.

54. A cooking gas safety device comprising:

a valve assembly comprising a valve and at least one coil, the valve comprising a fluid inlet and a fluid outlet and being manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to maintain the valve in an open position only when subjected to an electrical current exceeding a threshold current value; and

a hot surface igniter electrically connectable to the at least one coil to define a hold open circuit such that when subjected to a potential difference of 120V AC rms, the hot surface igniter reaches a surface temperature of at least 1400 ° F no more than eight seconds after the at least one coil is subjected to a threshold current.

55. The cooking gas safety device of claim 54, wherein the hot surface igniter reaches a surface temperature of at least 1800 ° F no more than four seconds after the at least one coil is subjected to the threshold current when subjected to a potential difference of 120V AC rms.

56. The cooking gas safety device of claim 54 or 55, wherein the at least one coil is at least one alternating current coil.

57. The cooking gas safety device of claim 54 or 55, wherein the at least one coil is at least one direct current coil.

58. The cooking gas safety device of claim 57, further comprising: a diode electrically connectable to the at least one coil, and an alternating current power source supplying a time-varying direct current to the at least one direct current coil.

59. The cooking gas safety device of any one of claims 57 or 58, further comprising: at least one capacitor, wherein the at least one capacitor is connectable in parallel with the hot surface igniter and the at least one DC coil.

60. The cooking gas safety device of any one of claims 54 to 59, wherein the at least one coil is not electrically connected to a thermocouple.

61. The cooking gas safety device of any one of claims 54 to 60, wherein the hot surface igniter is a silicon nitride igniter having a room temperature resistance of from about 20 ohms to about 60 ohms.

62. The cooking gas safety device of any one of claims 54 to 61, wherein the ceramic igniter has a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis, the ceramic igniter comprising:

first and second tiles having respective outer surfaces; and

a conductive ink pattern disposed between the first and second tiles, wherein the igniter has a thickness along a thickness axis of from about 0.047 inches to about 0.060 inches and at least one of the respective igniter exterior surfaces reaches a temperature of at least 1400 ° F in no more than 8 seconds when subjected to a potential difference of 120V AC rms.

63. The cooking gas safety device of claim 62, wherein the conductive ink pattern has a positive temperature coefficient of resistivity.

64. A cooking gas safety device comprising:

a hot surface igniter electrically connectable to the at least one coil to define a hold open circuit such that when subjected to a potential difference of 120V AC rms, a surface of the hot surface igniter reaches an auto-ignition temperature of at least one of butane, butane 1400, propane, natural gas, and mixtures thereof no more than eight (8) seconds after the at least one coil is subjected to a threshold current.

65. The cooking gas safety device of claim 64, wherein the surface of the hot surface igniter reaches an auto-ignition temperature of at least one of butane, butane 1400, propane, natural gas, and mixtures thereof no more than four seconds after the at least one coil is subjected to the threshold current.

66. The cooking gas safety device of claim 64 or 65, wherein the at least one coil is at least one alternating current coil.

67. The cooking gas safety device of claim 64 or 65, wherein the at least one coil is at least one direct current coil.

68. The cooking gas safety device of claim 67, further comprising: a diode electrically connectable to the at least one coil, and an alternating current power supply supplying a time-varying direct current to the at least one direct current coil.

69. The cooking gas safety device of claim 67 or 68, further comprising: at least one capacitor, wherein the at least one capacitor is connectable in parallel with the hot surface igniter and the at least one DC coil.

70. The cooking gas safety device of any one of claims 64 to 69, wherein the at least one coil is not electrically connected to a thermocouple.

71. The cooking gas safety device of any one of claims 64 to 70, wherein the hot surface igniter is a silicon nitride igniter having a room temperature resistance of from about 20 ohms to about 60 ohms.

72. The cooking gas safety device of any one of claims 64 to 71, wherein the ceramic igniter has a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis, the ceramic igniter comprising:

first and second tiles having respective outer surfaces;

73. The cooking gas safety device of claim 72, wherein the conductive ink pattern has a positive temperature coefficient of resistivity.