GB860848A - Improvements in or relating to control mechanisms and to uses thereof - Google Patents

Abstract

860,848. Fluid-pressure servomotor-control systems. ROLLS-ROYCE Ltd. July 11, 1958 [July 25, 1957], No. 23666/57. Class 135. [Also in Group XXVI] A gas turbine engine having both a variablearea nozzle at the outlet of its jet pipe and a reheat system in the latter is provided with a control mechanism which, when the reheat system is inoperative, enables the nozzle to be set to a minimum area A, Fig. 1, maximum area C or an intermediate area B. When the reheat system is operative the nozzle area is in a range E, D, Fig. 2, which lies between positions B, C, Fig. 1, and is dependent upon the rate of delivery of reheat fuel. The control mechanism comprises a number of pistons, as shown, two differential pistons 11, 12, which divide a cylinder 10 into spaces 13-16, spaces 13, 14 being supplied with air from the engine compressor 24 via, solenoid valves 22, 23, space 15 being supplied directly from the compressor 24 whilst space 16 is open to atmosphere; valves 22 and 23 are spring opened and closed, respectively, when the solenoids are de-energized. The compressor 24 supplies air through a pipe 30 and a turbine 32 that drives the reheat fuel pump, the pipe 30 including a cock 31 and being connected to the valve 23 by a pipe 27 in which is a spring-loaded valve 28 embodying a bleed orifice 29. The piston 12, which has a rod 37 that extends through the piston 11 and is attached to the nozzle, is also provided with a tubular extension 38 that controls a port 39. The nozzle assumes position A when both valves 22, 23 are closed ; position B is attained when the valves are in the position shown and position C is reached when both valves are open. During reheat operation the position of piston 12 and hence rod 37 in the range E, D, Fig. 2, is determined by an abutment 40 movable by a piston 42, the supply and exhaust of reheat fuel to either side of which is controlled by a piston valve 54 ; the fuel enters a chamber 47 from whence the bulk flows to a chamber 71 past a non-return valve whilst the remainder flows into a duct 51 which has two outlets 52, 55, the former leading to the valve 54 and the latter being under the control of another piston valve 57. When outlet 55 is uncovered all the fuel in duct 51 flows to drain 61 so that no fuel is available to operate the piston 42; upon closing the outlet 55 all the fuel in duct 51 is supplied to valve 54 and is available for moving the piston 42. The piston 42 and valves 54, 57 are interconnected by a floating lever 62 in turn joined to a pilot's selector-lever 63. In the range 64a, Fig. 1, the outlet 55 is open and the engine operates without reheat. With the cock 31 and both valves 22, 23 open, reheat operation is obtained by turning the lever 63 into the range 64b, Fig. 2, any position in this range resulting in the rod 37 assuming a given position in the nozzle area range E, D. Should the solenoid of valve 23 fail, air is conveyed to space 14 via pipe 27 and orifice 29. Chamber 71 contains a shuttle valve 74 that controls the distribution of fuel to pipes 48, 49, 50 leading to the pilot, inner and outer ring injector means in the jet pipe. With the piston 12 in the nozzle-area position D the port 39 is covered and flexible bellows 88 maintain a half-ball valve 82 on the outlet from a duct 79 supplied with fuel from the chamber 47 through a restriction 80, which duct is also open to the right-hand end of the valve 74 so that the valve is maintained in the position shown and only pipes 48, 49 are supplied with fuel. When the piston 12 assumes a position whereby port 39 is open to space 15, a diaphragm unseats the valve 82 and connects the duct 79 to drain, the shuttle valve 74 moves to the right and all the pipes 48, 49, 50 are supplied with fuel although the supply flowing to the pipe 49 is reduced since it passes through a restricted bore 77.