Patent GB-704849-A (GB)
Title: Improvements in or relating to multi-stage axial-flow compressors
Inventor: LOVESEY ALFRED CYRIL
IPC: F04D27/02
Filed: 1949-10-28
Abstract: 704,849. Axial-flow compressors; gas turbine plant. ROLLS-ROYCE, Ltd. Oct. 16, 1950 [Oct. 28, 1949], No. 27748/49. Classes 110 (1) and 110 (3). [Also in Groups XXVIII and XXIX] A multi-stage axial-flow compressor has at least one ring of adjustable-pitch stator blades controlled in such a manner that the blades have a pitch corresponding to each rotational speed of the compressor, and the pitch-controlling means comprise a pressure-sensitive element arranged to be loaded in one sense by a fluid pressure which is a function of the compressor rotational speed and in the opposite sense by a force which is a function of the pitch of the blades. The compressor supplies combustion air to a gas turbine, and the ring of interconnected adjustable-pitch blades is connected by a linkage to the stem 32a, Fig. 2, of the piston 32 of a hydraulic ram, progressive variation in the pitch being effected by movement of the piston in the ram cylinder 31 from one end to the other. The piston stem is hollow and houses a compression spring 50. When the piston moves from left to right the spring transmits an increasing force, which is a function of the blade pitch, to a flexible diaphragm 45 by means of a push rod 53 provided with fluid-sealing lands 53a. The diaphragm, which is also loaded by an auxiliary spring 55, divides a chamber into compartments 43, 44. Fluid under pressure from the delivery pipe 19 of the turbine fuel pump 14 is supplied to opposite ends of the ram cylinder by passages 40, 41 in the cylinder block. Passage 40 leading to the right hand side of the piston, which is of greater effective area than the left hand side, is provided with a constriction 42. The fuel pump, which is of the swash-plate variable delivery type and is gear driven from the turbine shaft, comprises a rotor 15 formed with radial drillings 22 communicating centrally with the pump suction pipe 18 and peripheral:y with a chamber 23. The rotor thereby acts as a centrifugal pump and the pressure in chamber 23 is a function of the rotational speed of the turbine and thus of the compressor. Chamber 23 is connected by a pipe 47 to compartment 44 and the diaphragm is thus loaded, in a direction opposite to the spring loading, with a force which is a function of. the compressor speed. Compartment. 43 is connected by a pipe 46 to the suction pipe 18. The right hand end of the ram cylinder is connected by a passage 60 and bleed port 63 to a chamber 61, and the latter is connected by a pipe 65 to the suction pipe 18. Chamber 61 houses a carrier 59 for a half-ball valve 62 which normally closes the bleed port, and also a spring 66 which tends to unseat the valve. The carrier extends as a push rod 57 which bears against the diaphragm and is provided with fluid sealing lands 57a. When the turbine is stationary the ram piston is at the left hand end of its cylinder and the bleed port is closed. With increasing turbine speed, pressure in compartment 44 rises until it overcomes the spring loading on the diaphragm, when spring 66 opens the bleed port to allow a flow of fluid from the right hand end of the ram cylinder to the suction pipe 18. Owing to constriction 42, pressure on the right hand side of the ram piston will then fall and the piston will thereby move to the right until it reaches a position of stability, when spring and fluid-pressure loadings on the diaphragm balance each other and the bleed port is closed. The arrangement is also modified in a manner designed to provide a corresponding blade pitch for each " corrected rotational speed " equal to the actual rotational speed divided by the square root of the absolute temperature at the turbine air inlet. In one modification the push rod 53 is provided, in compartment 43, with a radially extending disc. Between the disc and the left hand end of the compartment is arranged an expansible fluid-filled capsule communicating by a capillary with a temperaturesensitive bulb in the turbine air intake. Between the disc and an abutment extending peripherally into the compartment adjacent the diaphragm is arranged an evacuated capsule. Compartment 44 houses a compression spring tending to urge the diaphragm towards the left to counteract the resilient load exerted by the capsules. In a second modification fluid-pressure loading of the diaphragm is effected by an arrangement comprising a fixed-capacity positive-displacement pump driven at a speed proportional to the compressor speed, the inlet and outlet of the pump being connected to spaced-apart points on the suction pipe 18, and the outlet branch of the pump containing a restricting orifice the effective area of which is controlled by an expansible fluid-filled capsule connected by a capillary to a temperature-sensitive bulb in the air intake, compartment 44 being connected between the pump and restricting orifice, and compartment 43 being connected downstream of the orifice. In a further modification, Fig. 5, valve 62 is carried on one end of a lever 90, the fulcrum of which is formed by a flexible diaphragm 91 separating compartment 44 from chamber 61 which communicates with compartment 43 by a passage 165. The other end of the lever is connected in such a manner by a tappet member 93 to diaphragm 45 so that movement of the latter towards the right tends to allow the valve to close. A spring 94 housed in a chamber 95 tends to close the valve by means of a push rod 96. The end of the spring remote from the valve abuts a second push rod 97 loaded by means of an expansible fluid-filled capsule 173 connected by a capillary 75 to a temperature-sensitive bulb in the air intake. Specifications 652,095 and 704,936 are referred to.