Patent GB-1229203-A (GB)
IPC: F02C7/277
Filed: 1967-05-18
Abstract: 1,229,203. Gas turbine plant; engine turning gear; turbines. ROLLS ROYCE Ltd. May 16, 1968 [May 18, 1967], No.23005/67. Headings F1G, F1K and F1T. A starting system for a main gas turbine engine comprises a starter engine consisting of a gas turbine type gas generator and a separate turbine having an output shaft which can be coupled to the main engine, there being a connection to supply compressed air to rotate the output shaft should the starter engine fail to operate normally. The main gas turbine engines to be started include the port outer and inner engines 1, 2, Fig. 1, of a four engined aircraft. The engines are normally started by using a gas turbine type starter 10 for engine 1 and by connecting a ground air supply to air starter 11 via pipes 25, 27 and valve 26 for engine 2. Alternatively, starter 11 can take its air supply from the compressor of engine 1 via pipes 27, 28 and valve 29. Gas turbine starter 10 is itself normally started by an electric motor but should it fail to start it can be rotated by standby air supplied via pipe 12 and valve 13. The starter 10 comprises a centrifugal compressor (31), Fig. 2, (not shown), a combustion chamber 32, a turbine 34 driving the compressor, and a separate turbine 37 connected to engine 1 through clutches 14, 16 and gearbox 15. The standby air may be led by pipe 12 to a scroll 42, Fig. 3, which directs the air past guide blades 43 to drive an additional set of blades 44 radially outwards of the normal blades of turbine 37. In a modification, Fig. 5, the standby air is supplied to a connection 46 on the combustion chamber 32 and is by-passed around the turbine 34 through an aperture 47 which is normally closed by an annular slide valve 48, a valve at the intake of the starter being closed to prevent the flow of air upstream. In this arrangement only turbine 37 is driven by the air, but in a further modification, Fig. 4 (not shown) aperture 47 and valve 48 are omitted so that the air passing from connection 46 through the combustion chamber 32 drives both turbines 34, 37, the former driving the compressor (31) through the shaft 35 to prevent the flow of air upstream. In a further embodiment Fig. 6 (not shown), the standby air is led into a scroll (50) and is directed past the guide vanes 36 to drive turbine 37, air-flow upstream being prevented by a flap valve (51) which closes off the scroll during normal starter operation. In a further modification, Figs. 7, 8 (not shown), a scroll (53) supplies the standby air to the hollow interiors of the guide vanes (55) of turbine 37, the air being directed through the trailing edges of the vanes to drive the turbine 37. At starting, the starter 10 also drives an alternator 17 and a hydraulic pump 18 through one-way clutch 14 and gear-box is. The clutch 16 comprises a oneway clutch in parallel with a two-way clutch such that when the engine 1 fires and runs up to speed the two-way clutch can be disengaged and the engine will drive the auxiliaries 17, 18 through the oneway clutch. The starter 10 can drive the auxiliaries in the event of failure of engine 1. The two-way portion of clutch 16 is hydraulically operated by pressure produced by an oil pump driven by starter 10. In the embodiments where the turbine 34 remains stationary and only turbine 37 is driven when standby air is supplied to starter 10, the oil pump (57) Fig. 9 (not shown), is driven by turbine 37 and delivers oil through a line (59) to a hydraulic accumulator (58). When the accumulator is fully charged a valve (60) is opened and the oil pressure causes the two-way portion of clutch 16 to engage, thus transmitting power from turbine 37 to engine 1. The pump (57) also provides lubricating pressure. The standby air may be supplied from a ground truck (61), and booster unit (63), Fig.10 (not shown), the latter comprising a turbine (65) driven by air from the truck and itself driving a centrifugal compressor (67) which boosts the pressure of some of the air from the truck before supplying it to the starter.