Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
1998-06-11
2001-05-29
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
C060S734000
Reexamination Certificate
active
06237324
ABSTRACT:
This invention relates to a fuel control system for a gas turbine engine, such as a jet engine, primarily for use in aircraft.
Fuel control systems have been proposed incorporating main and emergency fuel metering valves connected in series and arranged so that failure of one of the valves in a manner giving rise to potential upward runaway of fuel flow results in control being maintained or assumed by the other valve.
It can be desirable to provide a fuel control system with protection against a condition leading to downward failure of either valve and an object of the invention is to provide a fuel control system in which this is accomplished in a simple and efficient manner. In this specification, “downward failure” of a valve means failure in such a manner as to cause a potential reduction in fuel flow.
According to the present invention, a fuel control system comprises series-connected first and second metering valves for providing a metered fuel flow, means operable to detect a downward failure condition in the control or operation of either metering valve and to produce a signal representative of such failure, and means operable in response to said signal to place the system in a condition in which a sufficient metered fuel flow is maintained via the non-failed valve.
The first and second metering valves conveniently have respectively main and emergency functions with the metered flow normally provided by the main valve, said signal-responsive means being operable to transfer fuel supply control to the non-failed emergency valve upon downward failure of the main valve.
Preferably, the system is placed in said condition either by by-passing the failed valve or by placing the failed valve in an open condition such that a sufficient amount of fuel is supplied therethrough.
Preferably, the means operable in response to said signal is a changeover valve.
Typically, the system includes means serving to monitor position error signals from the valves and to cause operation of the signal-responsive means, upon the occurrence of an error signal in excess of a predetermined value, to place the system in said condition.
An arrangement can thus be envisaged in which downward failure of one of the valves will not lead to an undemanded reduction in fuel flow since the failed valve is rapidly placed in a condition in which supply control can be taken over or retained by the non-failed valve.
In one typical arrangement, one of the metering valves disposed downstream of the other is controlled to provide a fuel supply rate higher than the other valve, as described in our published application EP 0761948, enabling either valve to retain or assume control upon upward failure of the other. The system may thus be protected additionally against upward valve failure.
REFERENCES:
patent: 4969444 (1990-11-01), Zagranski et al.
patent: 0 436 513 A1 (1991-01-01), None
patent: 0 761 948 A2 (1996-07-01), None
patent: 2 300 451 (1996-11-01), None
Andrus Sceales Starke & Sawall LLP
Casaregola Louis J.
Lucas Industries Public Limited Company
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