GB1228297A - - Google Patents

Abstract

1,228,297. Engine turning gear. GARRETT CORP. Sept.16, 1969, No.45683/69. Heading F1K. [Also in Division F2] Transmission gearing between a starter and a gas turbine engine includes a planetary train having a ring gear 23 Fig. 1 or 60 Fig. 2 associated with a one-way detent which holds the ring gear during starting but becomes inoperative when the ring gear rotates in its permitted direction above a predetermined speed, i.e. when the engine is self-sustaining, to prevent wear and drag in the detent during normal engine running. The detent comprises ratchet pawls 35 Fig. 1A pivoted to the ring gear 23, each with a nose 36 urged by a spring 38 into engagement with fixed ratchet teeth 37. When the ring gear rotates anti-clockwise above the predetermined speed, centrifugal action on the tail 40 of the pawl overcome the spring 38 to move the nose 36 clear of the ratchet teeth 37. In Fig. 1, a constant speed drive to an alternator (not shown) is provided by combining inputs from a gas turbine engine (not shown) and an air turbine starter motor 10 the inlet guide vanes 13 of which are controlled in accordance with alternator and engine speeds. A planet carrier 21 splined to the engine shaft 28 carries a first set of stepped planets 20 having teeth 19 meshing a sun gear 18 on the air turbine shaft 17 and teeth 22 meshing internal teeth of a ring 23d splined to an annulus 23a, and a second set of stepped planets 26 having teeth 32 meshing teeth 23c of the annulus 23a and teeth 33 meshing a sun gear 34 on an alternator drive-shaft. For engine starting, the air turbine motor 10 drives the engine shaft, the annulus 23 being held stationary by the one-way detent 35, 37. When the engine is self-sustaining, the air supply to the motor 10 is reduced, the two power sources then driving the alternator conjointly, with the ring gear 23 rotating freely anti-clockwise Fig. 1A. In Fig. 2, an air turbine starter motor 47 is connected to an engine drive shaft 58 by gearing comprising a pinion 48 on the air turbine shaft, idlers 50 mounted in the casing 42, a ring gear 52 coupled to a sum pinion 53, and planets 56 in a carrier 57 rigid with the shaft 58. The planets mesh a ring gear 60 held by a one-way detent during starting. (For Figures see next page)