GB817395A - Improvements in speed governors for use with gas turbines - Google Patents

Abstract

817,395. Gas-turbine plant. DOWTY FUEL SYSTEMS Ltd. Feb. 11, 1957 [Feb. 13, 1956], No. 4467/56. Class 110 (3). [Also in Group XXIX] A speed governor for a gas-turbine engine which acts to maintain a selected engine speed by controlling fuel flow to the engine has means for providing a stabilizing signal which varies with fuel flow and acts in conjunction with the speed governor on fuel flow to prevent unstable governing. As shown, an engine-driven centrifugal governor 7 is opposed by an adjustable spring 24 and acts on a lever 36 pivoted at 37 and carrying a half-ball valve 38 which coacts with an orifice 39 controlling the escape of fuel from a chamber above a piston 43 which operates a fuel by-pass valve 44, the chamber below the piston 43 being connected to the delivery side of a fuel pump 46 and the chambers on each side of the piston 43 being interconnected through a restriction 51. The arrangement is such that an increase of engine speed causes the orifice 39 to be opened to reduce the pressure above the piston 43 to cause the latter to increase the amount of fuel being by-passed. Fuel flowing from the pump 46 to the engine passes through chambers 57, 58 between which is an orifice 55 controlled by a valve member 54 connected to a servopiston 56. The pressures in the chambers 57, 58 are communicated through passages 57a and 58a to pressure pads 59, 61 which are interconnected by a member 62 bearing against an extension of the lever 36 above the pivot 37 whereby a change of fuel flow through the orifice 55 consequent upon an action of the governor gives rise to a stabilizing feed-back on to the lever 36. To maintain the speed setting of the governor substantially constant with variation in ambient pressure, or to provide a desired droop, the orifice 55 is adjusted in accordance with ambient pressure by the servo-piston 56 which is controlled by a halfball valve 71 carried by a lever 64 pivoted at 69 and acted upon by an evacuated bellows 75 and a bellows 74 subject internally to jet pipe pressure, this pressure varying with ambient pressure. Since the jet pipe pressure also varies with engine speed the arrangement provides for a progressive change in governor speed datum thereby bringing about an anticipation of the final speed selection. The lever 64 has an extension between which and the end of the valve member 54 extends a spring 66. Also acting on the end of the lever 64 is another spring 67 whilst a third spring 68 reacts between the end of the valve member 54 and the lever 36. The bellows assembly 74, 75 is adjustable towards or away from the pivot 69 by means of a screwed rod 79 having a squared end 81. In a modification increased speed of response without instability is obtained by interposing a servo relay between the governor 7 and the lever 36. It is stated that an hydraulic governor embodying a centrifuge may be employed instead of a mechanical governor.