Patent GB-949031-A (GB)
Title: Improvements in the pitch control of variable pitch vanes in axial flow compressors
Inventor: TYLER STANLEY RALPH
IPC: F04D27/00
Filed: 1959-02-17
Abstract: 949,031. Fluid-pressure servomotor systems. DOWTY FUEL SYSTEMS Ltd. May 17,1960 [Feb.17, 1959], No. 5497/59. Heading G3P. [Also in Division F1] A control system for variable pitch vanes 66 of the compressor of a gas turbine includes means responsive both to compressor speed N and compressor inlet temperature T 1  to control the vanes in accordance with either of the expressions N<SP>1</SP>/T 1  or N<SP>2</SP> - f(T 1 ), a stop 80 being provided to prevent the means responding to increase in T 1  above a predetermined value but to permit response to variations in the compressor speed N. A radial cylinder fuel pump 1 has its displacement adjusted by a track ring 2 of variable eccentricity connected to a servo piston 3 controlled by a restrictor 27 and a half ball valve 24 on a lever 21 pivoted at 22. The position of the lever and hence of the vlave 24 is controlled by the pressure drops in a valve-controlled part 8 in the fuel supply line 6, 12 to the engine and by a cam 49 whose angular position corresponds to engine speed, the cam acting on the lever through an adjustable spring 31 co-operating with a pre-set spring 29. A second servo piston 32 controlled by a restrictor 35 and a half ball valve 37 on a lever 39 actuated by compressor output pressure operates a valve 11 in the bore 8, the valve being connected to the lever by a feed back spring 44 cooperating with a pre-set spring 45. To position the vanes 66 in response to engine speed a cam 48 mounted together with the cam 49 on a shaft 47 controls a pilot valve 61 for a jack 65, the pilot valve being connected to the fuel supply line 6 through a pressure-regulating valve 84. The cam controls the valve through a lever 56 having its fulcrum 78 connected to the jack 65 by a feedback linkage including a cam 73 rotated by a plunger 79 and a bellows 87 in response to compressor inlet temperature, the movement of the cam being limited by the stop 80 while continued expansion of the bellows is accommodated by a spring-loaded stop 83. A roller 72 actuated by the jack 65 through a linkage 67... 69 is interposed between the cam 73 and a plunger 74 connected by cranks 75, 77 and a shaft 76 to the fulcrum 78. The shaft 47 carrying the cams 48, 49 is rotated through a rack and pinion 96, 97 by a servo piston 94 controlled in the same way as the other servo pistons, the half ball valve 92 being adjusted by centrifugal flyweights 88 through a plunger 89 and a lever 91. The pinion 97 also meshes with rack teeth on a plunger 98 carrying a spring 99 to form a feedback connection while the flyweights include auxiliary weights so that the centrifugal force produced is independent of fuel density. A by-pass valve 101 connected to a servo piston 105 controlled by an all-speed governor on a minimum flow control regulates the fuel flow during deceleration on constant-speed operation. In Fig. 2, a speed sensing device 121 adjusts a valve 124 governing the flow through a restrictor 127 and hence the position of a piston 125 which operates a cam 131 and compresses a spring 132 opposing the movement of the valve 124. The cam 131 controls the guide vane jack 139 through a valve 137 and a floating lever 134 whose fulcrum is controlled both by a feedback movement through a cable 143 connected with the vanes 141 and by a bellows 149 responding to compressor inlet temperature. A second bellows 152 prevents fulcrum adjustment due to ambient temperature changes while a stop 154 limits the inlet temperature response, a spring 155 absorbing further movement of the bellows. According to the Provisional Specification, the cable 143 may be connected to a roller unit interposed between a link 146 and a member adjusted angularly by the bellows 149.