GB568054A - Improvements in or relating to speed governors - Google Patents

Abstract

568,054. Fluid-pressure servomotorcontrol systems. HOBSON (AIRCRAFT & MOTOR) COMPONENTS, Ltd., H. M., and RAMSAY, D. July 28, 1943, No. 12275. [Class 135] In a hydraulic governor of the type comprising an engine-driven pump supplying its whole output to an orifice of variable area, a control for varying the speed at which the governor is to control by varying the area of the orifice and a servomotor controlled by a device responsive to the pressure difference across the orifice arranged to actuate speed-changing mechanism, the pump delivers fuel to the engine and also operates the servomotor. Fig. 1 shows the invention applied to an installation in which fuel is fed to carburetters at low pressures of the order of 2 lbs./per sq. in. An enginedriven' fuel pump 10 delivers fuel through a variable orifice 11 controlled by a needle valve 12, a restricted orifice 32 byepassed by a non- return valve 33 and servomotor control valve 25, 26 to a pipe 27 leading to a carburetter or other fuel metering unit. The valve 25, 26 is actuated by a diaphragm 13 loaded by a tension spring 14 and subject to the pressures on the two sides of the variable orifice and controls the operation of a spring-loaded power piston 19 coupled by a bell-crank lever 28 and link 30 to the engine throttle. The bell-crank lever is mounted on an eccentric 29 actuated by a lever 31 linked to the needle valve so that when the servomotor is inoperative the throttle may be slightly opened by manipulating the lever 31. In a modification shown in Fig. 2, the fuel pump delivers fuel to the carburetter at 'a higher pressure and in greater quantity than that demanded by the engine. In this form, the non-return valve 33 is dispensed with and the piston valve 25, 26 is replaced by separate spring-loaded inlet and exhaust valves having lost-motion connections with a bellcrank lever coupled to the diaphragm 13. The piston 19 has a small leak orifice 43 to permit slow descent of the piston when both valves 35, 36 are closed. In both forms, a relief valve 34 is arranged in parallel with the variable orifice to prevent an excessive build-up of pressure in the event of the area of the orifice being rapidly reduced while the engine is running at high speed. The pressure of the fuel delivery is governed by a relief valve 16 which allows excess fuel to return to the suction side of the pump. The Provisional Specification describes several alternative arrangements. In one form, Fig. 2 (not shown), the bell-crank lever 28 is actuated by a spring-loaded bellows housed in a chamber connected through a conduit provided with a restriction with a conduit connecting the variable orifice with the carburetter and through a lift valve actuated by the diaphragm 13 with the outlet side of the pump 10. In another form, Fig. 3 (not shown), a spring-loaded non-return valve is arranged in the conduit connecting the variable orifice to the carburetter, the inlet side of which is connected to the bellows chamber through the control valve and the outlet connected to the same chamber through a restricted orifice. In a further form, a spring-loaded diaphragm actuated pressure regulator is inserted in the carburetter conduit, the inlet side being connected through a restriction with the inlet of the control valve and through a further restriction with the bellows chamber, while the outlet side is connected through a restriction with the back of the diaphragm, and through a further restriction with the outlet side of the control valve. In a modification of the form shown in Fig. 2, a diaphragm-actuated pressure regulator is inserted in the carburetter conduit, the pressure on the back of the diaphragm being controlled by a pair of valves similar to the valves 35, 36. Fluid from the variable orifice passes through a restriction byepassed by a non-return valve to the chamber below the diaphragm 13 and thence to the bellows chamber, which is also connected through a restriction with the carburetter conduit.