US3871814A

US3871814A - Electric ignition system

Info

Publication number: US3871814A
Application number: US394204A
Authority: US
Inventors: Nalini R Das; Edwin H Strain
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1973-09-04
Filing date: 1973-09-04
Publication date: 1975-03-18
Anticipated expiration: 1992-03-18

Abstract

An electric ignition system which employs as a key element a thermal relay which is responsive to electric current from an ignition coil only when the current equals or exceeds an established minimum whereby resultant opening of a valve will occur to supply fuel to a burner only when the supply voltage is sufficient to provide the minimum current through the coil.

Description

United States Patent 1191 Das et al.

1451 Mar. 18, 1975 1 ELECTRIC IGNITION SYSTEM [75] Inventors: Nalini R. Das, Bethlehem; Edwin Strain, Allentown; both of Pa.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: Sept. 4, 1973 [21] Appl. No.: 394,204

[52] U.S. Cl. 431/66 [51] Int. Cl. F23n 5/14 [58] Field of Search 431/66, 67; 317/98 [56] References Cited I UNITED STATES PATENTS 3,551,083 12/1970 Michaels 431/66 3,584,987 6/1971 Michaels 431/66 3,594,107 7/1971 Willson et a1 431/66 3,609,072 9/1971 1 Willson. 431/66 3,776,684 12/1973 Wright 431/66 FOREIGN PATENTS OR APPLICATIONS France 431/66 Primary Examiner-Edward G. Favors Attorney, Agent, or Firm-Harold A. Murphy; Joseph D. Pannone; John T. Meaney [57] ABSTRACT I An electric ignition system which employs as a key element a thermal relay which is responsive to electric current from an ignition coil only when the current equals or exceeds an established minimum whereby resultant opening of a valve will occur to supply fuel to a burner only when the supply voltage is sufficient to provide the minimum current through the coil.

6 Claims, 2 Drawing Figures PATENTEU MR1 1 5 ELECTRIC IGNITION SYSTEM BACKGROUND OF THE INVENTION Burners utilizing fiuid fuel have conventionally employed ignitors in the form of fluid-fueled pilots which are undesirable for many reasons. For example, pilot outage can occur by drafts, lack of air, and the like. Pilot ignitors also have the disadvantage of fuel wastage because of the necessity that conventional pilots must be constantly burning, consequently also creating unnecessary heat.

Various kinds of ignition systems have been tested and used by different appliance industries but many of them have proved to be unreliable, and others are too expensive for incorporation in most household gas ranges, for example.

SUMMARY OF THE INVENTION In accordance with the present invention there is provided a novel electric ignition system which is completely reliable, which is completely fail-safe, and which can be made and installed at a cost comparable to a standard pilot ignition system.

The inventive system employs an ignition coil in the form of a high resistance wire which glows when electric current is applied to it. The coil is connected to the low voltage secondary of a transformer in series with the heater element of a normally open thermal relay.

The contacts of the relay are series-connected between a thermostat and gas valve to the power supply.

The thermal relay is a current activated relay designed specially to work with the ignition coil whereby the contacts will close if the current through the ignition coil is approximately equal to or greater than a required minimum such as about 3.5 amperes, for example.

Closing of the thermostat in a conventional manner causes current to flow through the ignitor coil and the relay heater coil. After a predetermined time interval the relay contacts will close, supplying power to the gas valve, which will open to allow gas to flow to the burner, whereupon the burner gas will be ignited by the ignitor coil. After the thermostat is satisfied, it will open, terminating the flow of power to the ignitor-coil, relay heater coil, and gas valve, whereupon the gas valve will close and the burner will be extinguished.

Such an ignition system is safe, reliable, and economical in both manufacture and use.

BRIEF DESCRIPTION OF THE DRAWINGS Referring more particularly to the drawings,

FIG. 1 is a schematic diagram of an ignition system embodying the invention; and

FIG. 2 is a diagram similar to FIG. 1 showing a modi fication of the ignition system of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, the ignition system of FIG. 1 may be used with a burner of any type suitable for use in a fluid-fueled appliance such as a cooking range, furnace or the like. Flow of fuel, such as gas, from a supply indicated diagrammatically at 12 is controlled by a conventional electric valve 14 which is inserted in a line 16 leading from the supply 12 to the burner 10. The valve 14 has a coil 15 which is connected into an electric circuit, as will be described, so as to automatically open when electric power is supplied to it and to automatically close when the power is disrupted. In this manner gas or other fuel may be supplied to the burner on demand.

A thermostat 18 is connected to one side of .a source of AC power via line 20 which also contains a fuse 22. Line 20 is connected to a low voltage stepdown transformer 24, as is a line 26 which constitutes the second side of the power source. Line 26 is also connected to the transformer 24 as shown.

Power is supplied to the coil 15 of valve 14 by a lead 28, which is connected to line 26, and by a second lead 30 which is connected to line 20 at one end and to one contact 34 of a thermal relay 32 at its other end, the other contact 36 of the relay being connected via lead 38 to the valve 14.

It will be obvious that since the relay contacts 34-36 are normally open, no power at this time is being supplied to the valve coil 15. Therefore, valve 14 is closed. In order to ignite burner 10 it is first necessary to supply it with fuel from supply 12. This requires that the contacts of relay 32 be closed to supply power to the valve coil. It also requires that an ignition coil 40 be heated to incandescence or radiation in the vicinity of the burner 10.

In order to achieve these functions in a fail-safe manner, the ignitor coil 40, which may be an electrically conductive high-resistance wire, is connected at one side to'one side of the low voltage secondary winding of the transformer 24 by a lead 42, and is connected at its other side to the transformer secondary through the heater coil 44 of the relay 32 via leads or

conductors

46 and 48.

The heating coil 44 and the contacts 34-36 of the relay are designed to cooperatively function to close the contacts only if an amount of current flows to the heater coil 44 which is equal to or greater than a predetermined valve such as 3.5 amperes, for example. Thus, if the supply voltage is too low to maintain the required minimum current through the ignitor coil 40, the contacts 3436 of the thermal relay 32 will not be closed and the gas valve 14 will not be energized. The required minimum current through the ignitor coil 40 to successfully ignite the gas in the burner 10 thus has to be the required minimum current through the heater coil 44 of the thermal relay which will effect closing of contacts 34-36.

It will be apparent that an open circuit caused by any defect in the ignitor coil 40 or in the heating element 44 of the thermal relay 32 will keep the contacts 34-36 open, preventing the valve 14 from being energized.

It will also be apparent that once sufficient heat has been supplied to satisfy the thermostat 18, the thermostat will disrupt the supply of power to the system.

, Upon resultant deenergization of the valve 14, the

source. This permits the transformer to be eliminated.

From the foregoing it will be apparent that a novel, efficient, safe and economical electric ignition system has been produced in accordance with the objectives of this invention. It is to be understood, however, that various changes may be made in the system shown and described and in its manner of operation without departing from the spirit of the invention as expressed in the accompanying claims. Therefore, all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

'We claim:

1. An electric ignition system for a fluid-fueled burner comprising an electrically operable valve for controlling flow of fuel to the burner, an electrical resistance type ignition wire for igniting fuel at the burner when at least a predetermined minimum amount of electric current is passing through it, and a currentactivated relay connected directly to said wire and said valve, said relay being sensitive to current passing to it from said ignition wire and being operable to energize said valve only when at least said predetermined minimum amount of current is passing through said ignition wire.

2. An electric ignition system as set forth in claim 1 wherein said relay includes a pair of normally open contacts electrically connected respectively to said valve and a source of electrical power, and a heating element electrically connected at one end directly to said ignition wire and at its other end connected to a source of power and operable to close said contacts only when at least said predetermined minimum amount of current is passing through the wire.

3. An electric ignition system as set forth in claim 2 wherein a thermostat is located in the system for controlling flow of current to the wire and relay.

4. An electric ignition system for a fluid-fueled burner comprising an electrically operable normally closed fuel supply valve for controlling flow of fuel to the burner, an electrical resistance wire which assumes ignition temperature when a predetermined minimum current passes through it connected at a first side to a source of electrical power, and a current-activated thermal relay having a heater element and first and second normally open contacts, said heater element having one side connected directly to a second side of the wire and its other side connected to the power source,

said first contact being connected to the power source,

the fuel supply valve being connected to said second contact and to said power source, said relay heater element being operable only when the current passing through the wire is of an amount at least equal to said predetermined minimum.

5. An electric ignition system as set forth in claim 4 wherein a thermostat is located between the source of power and the wire and relay.

6. An electric ignition system as set forth in claim 5 wherein a low voltage step-down transformer is provided with a primary winding connected to said power source and with a secondary winding connected at opposite ends respectively to the ignition coil and the heater element of the relay.

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Claims

1. An electric ignition system for a fluid-fueled burner comprising an electrically operable valve for controlling flow of fuel to the burner, an electrical resistance type ignition wire for igniting fuel at the burner when at least a predetermined minimum amount of electric current is passing through it, and a current-activated relay connected directly to said wire and said valve, said relay being sensitive to current passing to it from said ignition wire and being operable to energize said valve only when at least said predetermined minimum amount of current is passing through said ignition wire.

4. An electric ignition system for a fluid-fueled burner comprising an electrically operable normally closed fuel supply valve for controlling flow of fuel to the burner, an electrical resistance wire which assumes ignition temperature when a predetermined minimum current passes through it connected at a first side to a source of electrical power, and a current-activated thermal relay having a heater element and first and second normally open contacts, said heater element having one side connected directly to a second side of the wire and its other side connected to the power source, said first contact being connected to the power source, the fuel supply valve being connected to said second contact and to said power source, said relay heater element being operable only when the current passing through the wire is of an amount at least equal to said predetermined minimum.