Combustion – Process of combustion or burner operation – Starting or shutdown procedure
Utility Patent
1999-04-29
2001-01-02
Lazarus, Ira S. (Department: 3743)
Combustion
Process of combustion or burner operation
Starting or shutdown procedure
C431S067000, C431S073000, C431S256000, C137S514000, C200S034000, C251S048000
Utility Patent
active
06168418
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to gas ignition systems. In particular, the present invention is related to gas ignition systems for gas appliances and heating equipment, including gas ranges.
BACKGROUND
Conventional gas appliances and heating equipment, such as gas ranges, often use silicon carbide (SiC) hot surface ignitors. The SiC ignitor is normally placed in series with the gas valve. The gas valve is designed to open when the current supplied to it exceeds a certain value. The SiC ignitor has a carefully controlled resistance versus temperature characteristic such that: (1) when current is initially supplied to the ignitor and the ignitor is cold, it has a relatively high resistance that keeps the current low enough so the gas valve stays closed; and (2) when the ignitor heats up, the resistance drops so the current becomes sufficiently large to open the gas valve. When the current reaches this threshold point, the ignitor is hot enough to ignite the gas. This resistance versus temperature relationship serves as a “fail-safe” in that the ignitor must reach a certain temperature before the gas valve opens, thus avoiding the situation of gas flowing to an ignitor which is not hot enough to ignite the gas.
Conventional SiC gas range ignitors are produced by several commercial vendors, including Surface Igniter Co. of Chagrin Falls, Ohio and Saint-Gobain/Norton Co. of Milford, N.H. Some of the problems with these conventional ignitors are that they are porous, fragile, and expensive. In addition, the resistance versus temperature characteristics of these conventional SiC ignitors may alter or drift over time, thereby adversely affecting their reliability.
Ignitor materials which are more mechanically robust than SiC have also been developed. One such ignitor, the Mini-ignitor®, available from the Saint-Gobain/Norton Company of Milford, N.H., comprises a pressure sintered composite of aluminum nitride (“AIN”), molybdenum disilicide (“MoSi
2
”), and silicon carbide (“SiC”), and is designed for 8 volt through 48 volt applications. However, the resistance versus temperature characteristics of the pressure sintered composite material is different from the resistance characteristics of conventional ignitor materials such as SiC. Generally, the pressure sintered composite material has a resistance which increases with temperature (e.g., a metallic resistance characteristic). Accordingly, pressure sintered composite ignitors are not compatible with existing conventional ignition systems, which rely on a resistance fail safe region.
Thus, there is a need for an ignition system which is robust, which does not rely on a resistance fail safe region, and which is not susceptible to performance degradation due to temperature drifts.
SUMMARY
A delay switch for a gas appliance, according to an exemplary embodiment of the invention, comprises a first member, a second member which moves relative to the first member, an activator which moves the second member relative to the first member from a first relative position to a second relative position in a first time period, and a deactivator which moves the second member relative to the first member from the second relative position to the first position in a second time period less than the first time period, wherein the second member is coupled to the gas valve such that when the first and second members are in the second relative position, the gas valve is open, and when the first and second members are in the first relative position, the gas valve is closed.
Another embodiment of the invention relates to a method of controlling the opening of a gas valve comprising the steps of: (a) electrically coupling an ignitor to a delay switch, such that the delay switch is activated in response to the ignitor receiving a predetermined current level, wherein activation of the delay switch includes: driving a first member of the delay switch from a first position to a second position relative to a second member of the delay switch, and providing a resistive force which resists movement of the first member from the first position to the second position; and (b) coupling the first member of the delay switch to the gas valve such that when the first member reaches the second position, the gas valve is opened.
The delay switch is typically used in conjunction with an ignitor, a power source, a gas burner, and a gas valve. The first and second members of the delay switch may take the form of a cylinder and a piston which reciprocates within the cylinder. The chamber defined by the piston and cylinder includes a large aperture and a small aperture which influence the rate at which the piston moves.
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Cocks Josiah C.
General Electric Company
Johnson Noreen C.
Lazarus Ira S.
Stoner Douglas E.
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