GB885542A - Improvements relating to engine starting systems - Google Patents

Abstract

885,542. Gas turbine plants. GARRETT CORPORATION. May 27, 1958 [May 29, 1957], No. 16922/58. Class 110 (3). [Also in Group XXVII] An engine starting system for starting a gas turbine power plant comprises two turbine rotor units mechanically interconnected and arranged to be driven from different sources of motive fluid, means being provided whereby the inlet and outlet of one of the turbine rotors are connected to spaces at substantially the same pressure so that this rotor will act as a compressor to provide a braking effect to prevent overspeeding when the second turbine rotor is being driven. The starter shown comprises a rotor 12 having centripetal-type turbine blades 13 on one face and impulse-type turbine blades 14 on its other face. The rotor comprises a stub shaft 30 mounted in bearings 32, 33 and formed with gear teeth 34 which mesh with gears 35 each mounted on a shaft 36 rotatably mounted in bearings 40, 41 in a fixed casing part. The shafts 36 also carry pinions 42 which engage with internal teeth on a ring gear 43, the ring gear being rotatably mounted on a bearing 44 and forming the inner member 45 of an overrunning clutch. The outer member 46 of the clutch is rotatably secured to the output shaft 11 by means of a spline connection 50. Air under pressure may be supplied through duct 23 controlled by valve 84 and passes through inlet nozzles 62 to act on the centripetal turbine blades 13, the air discharging through outlets 60 to atmosphere. Air may alternatively be supplied to the inlet nozzles 62 through duct 24 under the control of valve 81. When using air under pressure there is no risk of overspeeding when the starter turbine is disconnected upon the engine starting. Starting may alternatively be effected by the firing of a cartridge 27 in the breech chamber 20, the high-pressure combustion gases discharging through nozzles 16 to impinge on the turbine impulse blades 14, the gases discharging to atmosphere through outlet 23. To prevent overspeeding of the rotor when the starter becomes disconnected from the engine, the rotor blades 13, during this operation act as an inefficient centrifugal air compressor, air being drawn in through ducts 60 and being discharged together with the turbine exhaust gases through duct 23. Two gas turbine engines 71, 72 are shown mounted on the wing 70 of an aircraft, each engine having a starter 73, 74. At least one of the starters has a cartridge unit similar to that shown in Figs. 1 and 2 and once its associated engine has been started, air is tapped from its compressor through duct 76 to the common manifold 75, and the other engines may be started by means of this low-pressure air through duct 80. The engines may alternatively be started by means of air from an external supply through inlets 83.