Patent GB-1251955-A (GB)
IPC: F01D7/00
Filed: 1967-12-29
Abstract: 1,251,955. Gas turbine ducted fan engines; axial-flow fans. ROLLS-ROYCE Ltd. Jan.10, 1969 [Dec. 29, 1967 (4)], Nos.59024/67, 59025/67, 59026/67 and 59027/67. Headings F1C and F1J. A rotor for a fluid-flow machine comprises a hub at least two fluid-flow blades and for each blade a self-aligning bearing connecting the blade to the hub, there being means for varying the pitch of the blades during rotation of the rotor. The invention is described with reference to the fan assembly of a gas turbine ducted fan engine, the assembly comprising a turbine 14 which receives turbine exhaust gases and by-pass air flowing through ducts 11, 12 from an engine, (not shown). The assembly comprises fan blades 15 each of which comprises a spoke portion 16 which extends through an aerofoil rotational guide vane 17, the spoke being supported at its inner end in a bearing 18 which allows angular movement of the blade about its axis also pivotal movement centred on the bearing. The fan assembly comprises also fan inlet guide vanes 15a and outlet guide vanes 15b all disposed within duct 15c. The turbine 14 comprises four stages. Each fan blade is angularly rotatable by means of an annular member 26 which is mounted for rotation on bearings 64, 65, the member 26 being connected to each blade spoke 16 by means of linkage 27, 28. An actuator 21 is provided for changing the pitch of the fan blades 15, the actuator driving through gearing 22 to cause relative rotation between the shafts 23, 24 which relative rotation acts through gearing 60 to cause angular movement of the annnular member 26 and thus angular movement of the fan blades about their longitudinal axes. The gearing 22 comprises attached gears 40, 41 and attached gears 45, 46, the gears 40, 41 being rotatably mounted on a fixed stub shaft 44 by bearings 42, 43 and the gears 45, 46 being rotatably mounted by bearings 47, 48 on a stub shaft 49 which is mounted in a carrier 55 which is mounted for rotation in bearings 56, 57 and which is splined to shaft 58. The gear 40 engages ring gear 50 on outer shaft 23 and gears 41, 45 engage ring gear 51 which is mounted for rotation on shaft 23. The gear 46 engages ring gear 52 on annular member 53 which is in splined engagement with inner shaft 24. Normally the shafts 23, 24 rotate at the same speed but when fan blade pitch variation is required the actuator 21 causes relative rotation between the two shafts. Assuming the shafts 23, 24 are not rotating and shaft 23 is held stationary so that gears 40, 41 and annular member 51 are thus held stationary so that when carrier 55 is rotated by the actuator 21 gear 45 rolls on the stationary ring 51 and the member 53 and so inner shaft 24 are rotated relative to the shaft 23 by means of the gear 46 engaging ring gear 52. In operation this angular movement is superimposed on the otherwise equal rotation of the two shafts. Means are provided to offset axial thrust on the bearings 83 when the fan blades are moved to reverse pitch position for reverse thrust. The shaft 58 is in splined engagement with a member 77 which is in screwed engagement 80, 81 with stator structure so that when the shaft 58 is rotated by the actuator 21 as the fan blades move to reverse pitch the member 77 opens the port 79 whereby air under pressure passes from chamber 84 through ports 85, 86, 87 to chambers such as 96 formed between members 90, 91, 92 and members 93, 94, 95. The members 90, 91, 92 engage structure in which the bearing inner members are mounted, while the members 93, 94, 95 are carried by structure 82 in which the bearing outer members are mounted so that supply of pressure air to chambers 96 acts to offset axial thrust on the bearings 83. The chambers 97 are open to atmosphere through ports 88.