GB783880A - Control apparatus for internal combustion power units - Google Patents

Abstract

783,880. Gas turbine plant. NAPIER & SON, Ltd., D. Jan. 31, 1955 [Feb. 16, 1954], No. 4571/54. Class 110 (3). [Also in Groups XXVII and XXIX] A power unit of the internal combustion type, more especially a gas turbine engine for aircraft propulsion, in which a substantial part at least of the power developed by the unit is transmitted through transmission mechanism has means responsive to a substantial reduction or a reversal of the torque for reducing or cutting off the supply of fuel to the unit. In an embodiment an axial flow compressor 1 is driven by a two-stage turbine 5 whilst a third-stage turbine 6 drives a variable-pitch propeller 9 through epicyclic reduction gearing 8. The internally toothed annulus 15 of the latter is, as shown at the top of the Figure, connected by a torque arm 20 with a piston 22, chambers A, B on either side of which are connected by conduits to ports 34, 35 which are controlled by lands 31, 32 on a piston valve which is attached to the piston 22. The arrangement is such that the resultant of the pressures in the chambers A, B balances the torque transmitted through the gearing 8, and the pressure in A is led through a conduit 40 to a cylinder 41 where the pressure acts on a spring-loaded piston 42 which is connected through linkage 48 &c. to a fuel control valve 50, and also to an electric switch 45 which controls feathering of the propeller. An override valve 52 is connected to the pilot's main control lever 53 which also governs the main fuel controller 54 so that the conduit 40 is closed to render the torque responsive mechanism inoperative when the control 53 is set for low power output. Under normal running conditions, however, the valve 52 is opened and the arrangement is such that a reduction of torque will result in an increase of pressure in the chamber A causing the piston 42 to be moved to the right to cut off or substantially reduce the fuel supply to the engine by means of the valve 50 and also to feather the propeller. A manual control 51 is associated with the valve 50 and the latter may also act as a dump valve. The valve 50 and switch. 47 are also operable by an overspeed governor 55 driven by the turbine 5. In a modification, the invention is applied to a power unit of a kind suitable for use in a helicopter and comprising first and second stage turbines driving a second stage axial flow compressor whilst a free, third stage turbine drives the first stage axial flow compressor and, through the epicyclic reduction gearing, the propeller and in addition drives through an hydraulic coupling another axial flow compressor which supplies air to burners in reaction jets arranged at the tips of the rotor blades. In this embodiment the fuel is not cut off completely in the event of a substantial reduction of torque since a supply of compressed air to the rotor is necessary to obtain lift. The rotor that is not directly connected to the reduction gearing is provided with an overspeed governor which may act on the fuel control valve and/or the propeller pitch control mechanism. In a further embodiment, also suitable for a helicopter, the power unit consists of a single spool which drives the additional compressor for the rotor jets through an hydraulic coupling. In this case the supply of compressed air from the additional compressor is augmented by the exhaust from the turbine. Specification 743,418, [Group XIX], is referred to.