Patent GB-1136584-A (GB)
Title: Gas turbine engine accessory drive systems
Inventor: SNELL LEONARD STANLEY
IPC: F02C7/27
Filed: 1966-01-19
Abstract: 1,136,584. Gas turbine engines. ROLLSROYCE Ltd. Jan 19, 1967 [Jan. 19, 1966], No.2525/66. Heading F1G. The invention relates to the combination of a main gas turbine engine which is adapted to be started by impingement of a gas against a rotor assembly of the engine with a system which comprises an auxiliary turbine arranged to be driven by gas tapped from the main engine and connected to drive engine accessories. A gas generator is provided and is arranged to drive the accessories either through the auxiliary turbine or through a separate power turbine, there being means for conveying gas from the gas generator or from an auxiliary air compressor driven by the gas generator, to the main engine for starting it, and for conveying gas bled from the main engine to the auxiliary turbine to drive it. In a first embodiment the main gas turbine engine is indicated at 10, the auxiliary turbine at 27 and the gas generator (which may be a gas turbine type gas generator) at 25. The gas generator 25 is started and gases pass through valve 35 to the duct 26 thence through the valve 37 to the auxiliary turbine 27 which drives through shaft 29 and gear-box 28 accessories such as hydraulic pump 30, fuel pump 31 and electric generator 32. When the main engine is to be started the valve 40 is opened so that gases from the gas generator 25 pass through duct 21 and nozzle 19, Fig. 2 by which they are directed on to the blades of the high-pressure turbine 15. When the engine has started, the valve 41 is opened whereby exhaust gases from the main engine downstream of the low-pressure turbine pass to the duct 24 and so to the auxiliary turbine 27 which is driven thereby, the gas generator 25 then being shut-down. Air for aircraft cabin air conditioning may be provided by the gas generator 25 when the aircraft is on the ground either by tapping air from the compressor unit of the gas generator or by air supplied from an auxiliary air compressor driven by the turbine 27. Alternatively, the gas generator 25 may be continued in operation so that the turbine 27 is driven by gases therefrom instead of by gases tapped from the main engine. In Fig. 3 a gas generator 25 is again provided but a free power turbine 25A is incorporated being connected to the gear-box 28 through a freewheel coupling 56. The auxiliary turbine 27 is connected to the gearbox by a shaft 29 as in Fig. 1 In this embodiment air is tapped from the gas generator 25 through a duct 52 and may pass through duct 55 for cabin air supply when the aircraft is on the ground. When the engine 10 is to be started, the valve 53 is actuated so that air under pressure passes through the duct 54 to the impingement starter. When the engine is running air under pressure is tapped from the compressor thereof and passed through duct 51 to drive the auxiliary turbine 27, the gas generator 25 then being shut-down. Alternatively, the gas generator 25 may be continued in operation and no air tapped from the engine compressor; air could be tapped from the engine compressor in the event of failure of the gas generator. In Fig.4 (not shown) a separate air compressor 60 driven from the gear-box 28 through a clutch 61 is provided to supply cabin air and air for impingement starting. The power turbine 25A of the gas generator 25 is connected to the gear-box 28 through a freewheel device 56 as in Fig. 3, and the auxiliary turbine 27 is also connected to the gear-box through a freewheel device 62. In Fig. 5 (not shown) a device 70 is connected to the gear-box 28 by a clutch and reverse gear 71, the device 70 operating either as in air compressor or an air turbine. When the gas generator 25 is started, the power turbine 25A thereof drives the accessories also the device 70 which now operates as a centrifugal compressor the air from which is first used for cabin supply them for impingement starting of the main engine. When the main engine starts high-pressure air is tapped from the compressor and passes to the device 70 which now operates as an air turbine and drives the accessories. A valve device 75 is provided to control air-flow to and from the device 70. In Fig. 6 an aircraft has two main engines 100, 101, a gas turbine type gas generator 25 and two auxiliary turbines 27 connected to a common gear-box 28 to which aircraft and engine accessories are connected. The gas generator 25 is first started and air tapped through the manifold 82 passes to the aircraft cabin; the valve 83 is then actuated whereby air under pressure passes through the lines 84 and valves 84a to the impingement starters of the main engines which start up. At the same time combustion gases from the gas generator 25 pass through ducts 81, 87 to the auxiliary turbines 27 which thereby drive the accessories 31, 50 &c., the exhaust gases finally discharging through ducts 88 into the jet pipes of the main engines. When the main engines start gas under pressure tapped therefrom passes through ducts 91, 87 to the auxiliary turbines 27 which are thereby driven and the gas generator 25 is shut-down.