GB864712A - Improved load-balancing servo device and gas turbine engine fuel system embodying the same - Google Patents

Abstract

864,712. Mechanical servomotors; reverse gear. ROLLS-ROYCE Ltd. Sept. 24, 1958 [Nov. 8, 1957], No. 34977/57. Class 80 (2). [Also in Group XXVI] A mechanical servomotor is operated by a fluid-pressure-sensitive element and comprises a spring between its input and output members. In one form, the inlet and outlet pressures of a gas turbine compressor are applied across restrictions 28, 29, Fig. 2, connected to a pressure-sensitive bellows 26 tending to turn an input lever 25, an evacuated bellows 27 being associated with the bellows 26. The lever 25 has a forked end connected to a lever 24 splined upon a hollow shaft carrying a frame 22 in which is journalled an axle 21 and a ball 21a. A constantly-rotating power input shaft 18 drives through gearing 19 to a contrate gear 20 meshing a gear fast with the axle 21 to rotate the ball 21a, which engages a friction disc 30 rotatable in the forked end of a cranked control-arm 31. A spring 32 connects the input lever 25 to the arm 31. A gear 33 on the end of the controlarm 31 meshes an output rack 34 connected by links &c. to a throttle valve 60 controlling the gas turbine engine, as described in Specification 850,477. The frame 22 and the arm 24 are rotatable about the axis of the contrate gear 20, and are relatively movable against the bias of the power shaft 18 applied through gearing 23 and the gearing 19. On a change in the pressure applied to the bellows 26, the input lever 25 moves, and turns the arm 24 which accordingly adjusts the axis of rotation of the ball 21a. The friction disc 30 is accordingly driven and tends to turn the cranked control-arm 31, thus stressing the spring 32 to restore the arm 25 to a position of equilibrium, and simultaneously driving through the rack 34 and the links 35 &c. to vary the setting of the gas turbine throttle 60. In a modification, a continuously-rotated power shaft 60a, Fig. 3, drives through reversing gearing 62, 63 to rotate pinions 37, 38 in opposite directions. A driven friction clutch disc 39a secured to an axially slidable input shaft 39 lies between the two pinions 37, 38 and can be engaged selectively therewith. A gear 41a at the end of the shaft 39 meshes at all times a planet pinion 44, meshing a ring of teeth in a surrounding casing and mounted upon a control carrier 45. An externally-threaded and axially slidable output sleeve 46 is screwed into the planet carrier 45, and is connected by a spring 49 to a bearing on the end of the shaft 39. Links 47, 48 connect the output. sleeve 46 to a throttle 60 through which fuel is supplied to the gas turbine. A bellows 42 sensitive to the pressure of oil or fuel in the space 43 surrounding the mechanism is connected by an input lever 41 to the shaft 39, and an impeller 40 rotates with this shaft. On a change of pressure in the space 43, the bellows 42 slides the shaft 39 to engage the clutch disc 39a with one or other of the oppositely rotating gears 37, 38. The shaft 39 then rotates the control carrier 45 and screws the output sleeve 46 one way or the other, to adjust the gas turbine throttle 60 and simultaneously bias the spring 49 to oppose the axial movement of the shaft 39. At the same time, the impeller 40 rotating in the liquid within the space 43 also tends to oppose the axial movement of the shaft 39. Ultimately, a position of equilibrium is achieved, and the clutch disc 39a disengages from the gears 37 or 38 with which it has been rotating. In a modification, two impellers 140a, 140b, Fig. 3a, are secured to a shaft 139 corresponding to the shaft 39, these impellers rotating within spaces in oppositelyrotating gears 137, 138.