Patent GB-846358-A (GB)
Title: Combination engine starter and accessory drive apparatus
IPC: F02C7/277
Filed: 1958-06-11
Abstract: 846,358. Engine turning-gear. GARRETT CORPORATION. June 11, 1958 [June 12, 1957], No. 18701/58. Class 7(5). [Also in Group XXVI] A combination engine starter and accessory drive apparatus for installation in an aircraft and which can alternatively deliver power to a main shaft 15, Figs. 1 and 6, for starting a jet engine connected thereto or receive power from the main shaft to drive a generator 12, comprises a gear train 14 connected to the shaft 15, an air turbine 13 directly connected to the gear train to provide continuous driving power thereto when the shaft 15 is both receiving and delivering power, an accessory shaft 42 to which the generator 12 is connected, the shaft 42 being directly connected with the gear train and driven both when the shaft 15 is delivering and receiving power, and speed sensitive means controlling means for modifying the operation of the gear train so that the shaft 15 receives a substantial share of the power output of the turbine 13 when the speed of the shaft is below a predetermined speed and the load on the shaft 42 is shared between the turbine 13 and the shaft 15 after the shaft 15 attains a predetermined speed. As shown, the gear train 14 comprises an epicyclic differential gear including a ring gear assembly 22 and two sets of planet gears 28, 27 and 26, 38 mounted on stub shafts 30 extending from a rotatable spider 21 mounted on bearings 43 and to which is splined the shaft 15. Air is supplied to the turbine wheel 36 through a conduit 49 via an annular inlet passage 50 and a nozzle 54, the speed of the turbine being varied by regulating the flow of air through the turbine by adjustable vanes 57 pivotably mounted in the nozzle and connected to a lever 61 operated by a control system 63 including a combination servo and hydraulic actuator 70 which is supplied by fluid under pressure from a gear pump 64 driven from the generator shaft 42 and which is pneumatically controlled by a speed sensing governor 71 also driven from the shaft 42. In operation, the governor 71 is arranged to produce a predetermined constant speed of the generator and any change thereof is compensated by the governor transmitting a signal to the actuator 70 causing the latter to adjust the vanes 57 to increase or decrease the speed of the turbine 13. For starting the engine, the ring gear assembly 22 is held stationary by a brake device 73 actuated by an annular piston 80 provided in an annular chamber 79 to which fluid under pressure is supplied, so that rotary motion transmitted by the turbine 13 to the planets 28, 27 is imparted to the shaft 15 through the spider 21, the generator shaft 42 being simultaneously driven by the planets 38. An air regulator and shut-off valve 82 are connected to the conduit 49 and a conduit 84 connected to the conduit 49 and comprising a pressure regulator 83 is connected to a starting selector valve 85, which includes a spool 86 connected with a wall 87 spring loaded on one side and having a chamber 94 on the other side to which air is supplied from the conduit 84 through a branch pipe 90, the air supply being controlled by a speed sensor 91 driven from the shaft 42 which permits air to bleed from the passage 90 to atmosphere until the shaft 42 attains a predetermined speed. The conduit 84 leads from the valve 85 to the piston chamber 79 of the brake 73. When the chamber 94 is not pressurized the spool 86 is urged by the spring 88 to the position shown in Fig. 6 and fluid pressure is supplied to operate the brake 73 when the engine is started as described above. When the shaft 15 is rotated at a speed sufficient to start the engine the speed sensor 91 prevents air being bled from the passage 90 whereupon the chamber 94 is pressurized and the spool 86 is moved to a second position in which a conduit 95 branching from the conduit 84 communicates with the speed governor 71, the chamber 79 being simultaneously vented and the brake 73 released. The switch for loading the generator is then actuated and the constant speed drive mechanism operates normally. In a modification of the control system, Fig. 7, the speed of the turbine 102 is controlled by a variable exit nozzle 104 in which a movable element 105 moves in response to fluid pressure in a chamber 106 to vary the flow of exhaust fluid through the passage 101. Variable pressure is supplied to the chamber 106 through a passage 107 connected to the exhaust passage 101, a bleed outlet 108 to atmosphere from the passage 107 being controlled by a valve 110 controlled by the governor 71 through the conduit 95 which extends to an actuator 109. To prevent the generator or the turbine from overspeeding both control systems are provided with a speed sensor 111 driven by the shaft 42 and with an overspeed sensing device 114 in the turbine shaft which are both connected through a conduit 112 to the valve 82. If either the generator or the turbine overspeeds the respective speed sensor 111 or 114 operates to vent the conduit 112 to atmosphere and the valve 82 interrupts fluid flow to the turbine. In a modified form of the invention, Fig. 4, the differential gearing 115 consists of two sets of planets 116, 117 rotatably,mounted on a spider 118 secured to the shaft 15, the set 116 being driven from a torsion shaft 121 connected to the turbine wheel 36 and the set 117 being driven from the shaft 42 and both sets meshing with the ring gear assembly 22. A brake mechanism 125 is axially offset from the ring gear assembly 22 and is splined to a conically shaped ring plate 127 which is in turn splined to the assembly 22, the brake being actuated by an annular piston 134 in a chamber 135 to which fluid under pressure is supplied. Means for utilising the residual energy in the turbine exhaust include (a) conducting the exhaust to the tail pipe of the aircraft main engine; (b) conducting the exhaust to the intermediate stage of the compressor of the main engine; (c) discharging the exhaust to atmosphere through a jet nozzle. Specifications 710,095, 760,656 and 837,833 are referred to.