Patent GB-904938-A (GB)
Title: Improvements relating to gas turbine engines
Inventor: JOHNSTON CHRISTOPHER LINLEY
IPC: F02K1/15
Filed: 1960-07-01
Abstract: 904,938. Fluid-pressure servomotor-control systems. ROLLS-ROYCE Ltd. June 26, 1961 [July 1, 1960], No. 23184/60. Class 135. [Also in Group XXVI] A gas-turbine engine comprises a plurality of adjustable engine components which require to be adjusted in accordance with engine-operating conditions, pressure-responsive means being provided, the opposite faces of which are open to two different pressures prevailing either in or at the ends of the engine compressor. Adjustment means, controlled by the pressureresponsive means, are provided for successively adjusting the various engine components as the ratio between the two different pressures increases or decreases. The engine shown is a gas-turbine jet-propulsion engine and comprises an air compressor 11, combustion equipment 12, a turbine 13, a jet pipe 14 in which is disposed reheat equipment (not shown), and a variable area propulsion nozzle 19. The pressure-responsive means is indicated at 61 in Fig. 1, and is connected to the compressor outlet pressure P 2  and an intermediate compressor pressure PINT by lines 76 and 67 respectively. The operating rod 60 of the pressureresponsive means acts through links 58, 57 to impart angular movement to a shaft 46 on which are mounted cam-plates having cam grooves 40, 41, 42, 48 and 48<SP>1</SP>, the cam groove 40 serving to control a link 15 which adjusts the angular positions of the compressor intake guide vanes 17, the cam groove 41 serving to control a link 16 which adjusts the angular positions of the outlet guide vanes 18, the cam groove 42 serving to control the lever 20 which controls the opening of a bleed valve through which air may be bled from an intermediate stage of the compressor during starting of the engine, the cam groove 48 controlling a lever 55 which controls supply of reheat fuel to the jet pipe 14 by means of fuel control unit 56, and the cam groove 48<SP>1</SP> controlling a lever 55<SP>1</SP> which controls an air motor 39<SP>1</SP> which is supplied with air from the compressor 11 through line 39 and which actuates the variable area propulsion nozzle 19. The unit 61 is shown in detail in Fig. 2 and comprises a piston 63 mounted within a cylinder 62, the space 65 at the left-hand side of the piston being connected to the pressure PINT at an intermediate point of the compressor, and the space 70 at the righthand side of the piston being connected to pressure P 2  at the outlet of the compressor. The piston-rod 77 is secured to a gear 82 which is driven by means of the shaft 81 through worm gearing, the piston being rotated so as to prevent sticking. A tubular member 84 is disposed within the hollow piston-rod 77 and is connected thereto by splines, the opposite end of the tubular member being drivingly connected to a sleeve 86 which is disposed therearound, the sleeve 86 being spaced from the piston-rod 77 by a gap 88. The sleeve 86 is slidably mounted within a central cavity 87 within the piston-rod 60, the sleeve being formed with radial holes 90, 91 which co-operate with annular grooves 92, 93 within the piston-rod 60. The piston 94 is formed integrally with the piston-rod 60 and is disposed within a cylinder 95 and defines a chamber 97 at its left-hand face and a chamber 100 at its righthand face. High pressure fuel is supplied to the chambers 97 and 100 through bores 101, 102, the chamber 97 communicating with the annular groove 93 by means of the bore 103, and the chamber 100 communicating with the annular groove 92 by means of the bore 104. Lowpressure fuel is communicated to the chamber 80 in which the gear 82, also the annular gap 88, are disposed, through the hollow shaft 81. The piston 63 carries at its right-hand face a needle valve 105 which controls an outlet 107 to atmosphere pressure P 0 , the needle valve having a bore 106 by which the space 108 within the piston-rod 60 is vented to atmosphere for pressure balancing purposes. In operation, as the engine is speeded up, the pressure ratio P 2 /P INT  will gradually rise and the piston 63 will therefore move towards the left so moving the sleeve 86 to the left until the holes 91 are brought into alignment with the annular groove 93. When this occurs, high pressure fuel in the chamber 97 at the left side of the piston 94 is communicated with low-pressure fuel in the space 80 by way of the bore 103, groove 93, holes 91, the annular space 89 between the sleeve 86 and the tubular member 84 and the gap 88. The piston 94 will therefore move towards the left, whereby the annular groove 93 will move out of alignment with the holes 91, and the needle valve 105 will open outlet 107 so that the pressure in the chamber 70 will fall. If the pressure ratio P 2 /P INT  rises to and remains at an increased value, therefore, the parts of the servo mechanism 61 will swiftly become pressure balanced in their new positions. If the ratio P 2 / INT  decreases, however, the pressure difference produced across the piston 94 will cause the piston to move towards the right.