GB654263A - Speed governor mechanisms for aircraft internal combustion turbine engines - Google Patents

Abstract

654,263. Gas turbine plant. DOWTY EQUIPMENT, Ltd. Dec. 3, 1947, No. 31950. [Class 110(iii)] [Also in Group XXIX] A fuel system for an aircraft gas turbine having between the throttle or metering valve and the pilot's control member a governing mechanism whereby the setting of the control member corresponds with a definite engine speed under all operating conditions, has variable speed limiting means comprising a preselecting member operated by the control member and a follow-up member responsive to engine speed which co-operate to limit the quantity of fuel reaching the engine irrespective of an overshot position of the throttle or metering valve. The fuel system shown comprises an engine driven fuel pump 13 which delivers fuel from a tank 11 to the burners 12 through a pressure balanced fuel byepass valve 31 and a metering valve 14. The metering valve 14 is controlled by the pilot's control lever 18 through a governing mechanism 15, such as that described in Specification 595,152 so that each position of the control lever corresponds to a definite engine speed. The operation of the pressure balanced fuel valve 31 and the associated altitude control is described in Specification 654,256. The valve maintains the pressure in the fuel supply line 32 to the metering valve 14 constant a,t a value which varies with altitude. A speed limiting device comprising a preselecting member 23 and a follow-up member 24 is embodied in the system. The preselecting member is connected to the control lever 18 and the follow-up member 24 to a spring loaded piston 26 which moves in response to changes in pressure in the casing of. the engine driven fuel pump 13 and/ therefore indirectly to changes in engine speed. When the control lever 18 is moved to give a large increase in speed, the governing mechanism 15 causes opening movement of the metering valve 14. At the same time, the setting of the preselecting member 23 is altered. The engine then accelerates and if its speed exceeds that set by the preselecting member.23, the pressure acting on the piston 26 causes the follow-up member 24 to move into the cylinder formed in the preselecting member and open the port 25. The fluid pressure above the piston of the valve 31 will then be relieved and fuel will be byepassed back to the fuel tank 11 through the conduits 36, 37 and 38. The engine will then slow down and the piston 26 move back under the action of the spring 28 to close the port 25. An overspeed control valve 42, which also operates by relieving the fluid pressure above the piston of the valve 31, may also be employed. The end of the conduit 45 is opened and closed by a spring loaded lever 43 controlled by a diaphragm 44 responsive to the pressure in the conduit 29. In a modification, the preselecting member comprises an abutment which varies the spring loading on a diaphragm which includes the follow-up member. The diaphragm carries a closure disc which controls a vent of the fuel byepass valve. The Provisional Specification describes arrangements in which the speed limiting device is used to control the eccentricity of a track ring of a variable displacement type of fuel pump and in which the speed limiting device is used to control the speed at which the overspeed control valve 42 operates by means of a wedge or cam member connected to the control lever which varies the spring loading on the lever 43.