US3030575A - Thermocouple circuit - Google Patents

Description

April 1962 R. R. BOCKEMUEHL ET AL 3,030,575

THERMOCOUPLE CIRCUIT Original Filed Jan. 11, 1954 f a z??? z/ we WK BY 25;? 12522212 ATTORNEY United States Patent 3,030,575 THERMOCOUPLE CIRCUIT Robert R. Bockemuehl, Birmingham, and Robert J. Moiiat, Oak Park, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application Jan. 11, 1954, Ser. No. 403,398. Divided and this application Sept. 29, 1958, Ser. No. 764,034

3 Claims. (Cl. 324-51) This application is a division of application S.N. 403,398 filed January 11, 1954 (now abandoned).

Our invention relates to controls for gas turbine engines and other combustion devices or thermal plants. The preferred embodiment of the invention in a safety control for a gas turbine engine with two combustion chambers is described herein.

In brief, the control described herein employs two temperature responsive devices such as thermocouples, one in each combustion chamber, the responsive devices being connected in opposition and operative through suitable relay mechanism to shut off fuel to the engine when significant temperature unbalance occurs.

The invention which is the subject of this application lies particularly in a thermocouple circuit including means for checking the continuity of the circuit to assure that it is in condition to perform its function.

The principles and advantages of the invention will be apparent to those skilled in the art from the succeeding detailed description and the accompanying drawing which is a schematic diagram of a gas turbine fuel system embodying the invention.

The fuel system is illustrated in combination with a gas turbine engine which comprises a compressor supplying combustion chambers 11 and 12, and a turbine wheel 13 driven by combustion products from the chambers and driving the compressor through a shaft 14. This part of the engine serves as a gas generator for a power turbine wheel 16 driving a shaft 17. Fuel nozzles 18 in the combustion chambers are supplied from a fuel tank 19 through pump 21, fuel control 22, a normally closed solenoid-opened valve 23, and line 24.

Thermocouples 31 and 32, which may be of a known quick-response high-temperature type, are mounted adjacent the discharge ends of combustion chambers 11 and 12. These couples are in reverse series connection so that the thermoelectric E.M.F.s of the two are opposed, and the resultant is substantially zero when the two are at the same temperature. The series circuit may be traced through thermocouple 31, lead 33, switch 36, coil 37 of a sensitive relay 35, resistor 38, lead 39, thermocouple 32, and lead 41. Relay 35 is of a known galvanometric type. Coil 37 operates an armature 44 in either direction in response to direction of current in the coil. A contact arm 46 actuated by the armature will engage either of two fixed contacts 47 in response to excitation of coil 37 above a predetermined value. The contact arm is magnetically urged into, and held in, engagement with the contacts until released by energization of a reset coil 48.

Closure of contacts 46, 47 energizes solenoid valve 23 to close the fuel line by means of the following circuit: A battery 51 is connected to ground, and through switch 52, line 53, relay coil 54, switch 56, and contacts 47 (when closed) to ground. The battery also is connected through line 53, switch 58, back contacts 59 which may be opened by coil 54, and solenoid 61 of valve 23 to ground. Relay coil 54 is shunted by a resistor 63 and a signal light Patented Apr. 17, 1962 64 which is energized when contacts 47 close. The reset coil 48 is energized from the battery through line 53, resistor 66, and normally open push button switch 67.

In normal operation of the electrical system, switches 52, 36, and 56 are closed. Switch 58 is closed to energize valve solenoid 61 to admit fuel to the engine upon starting. Contacts 47 are normally open and contacts 59 normally closed. If, however, the differential of the thermocouples 31 and 32 exceeds the threshold of relay 35, contacts 47 close, energizing warning light 64 and relay coil 54, opening contacts 59 and cutting off the fuel at valve 23. Because of the inherent thermal lag of thermocouples, the response of the relay is a function of both the magnitude and duration of the temperature dif ference between the combustion chambers. J

Light 64 is energized to indicate that the dilferential temperature safety circuit has cut out the engine. It re mains cut out until switch 67 is closed to reset relay 35. Switch 56 may be opened to disable the energizing circuit of relay 54, if desired. Thus, switch 56 may he closed only when starting the engine if the system is desired to be operative only then. Switch 52 is an overall energizing switch for the system. v

A test circuit for the thermocouple circuit is provided, Energized line 53 is connected through high resistance 71 to the circuit on one side of switch 36 while the circuit is grounded through high resistance 72 on the other side of switch 36. With switch 36 closed, the small current bled through resistors 71 and 72 in series passes through this switch and does not aiiect the relay 35. To test eon tinuity of the thermocouple circuit, switch 36 i opened, whereupon the battery 51 is connected through resistor 71, relay coil 37, the thermocouples, and resistor 72 to ground. If the circuit is complete, relay 35 operates, en ergizing lamp 64.

It will be apparent that the invention may be employed in other environments than that described and may be embodied in diverse combinations of apparatus within the Y scope of the invention.

We claim:

1. In combination, a control circuit comprising at least one thermocouple, a galvanometer, and a normally closed switch in series, and means for testing continuity of the circuit comprising a low-current supply means connected to opposite ends of the switch so that the galvanometer is energized by the said source through the thermocouple when the switch is opened.

2. A control circuit comprising, in combination, thermocouple means, current-responsive means, and a normally closed switch connected in series, and means for testing the continuity of the series circuit comprising a limited current supply means connected to the series circuit at 0pposite sides of the switch so that the current-responsive means is energized by the source through the thermocouple means when the switch is opened and the series circuit is continuous.

3. A circuit as recited in claim 2 in which the thermocouple means comprises two thermocouples in series opposition.

Podell Dec. 18, 1956

Images