Patent GB-566285-A (GB)
Title: Improvements in exhaust-driven superchargers for internal combustion engines
IPC: F02B37/18
Filed: 1942-09-14
Abstract: 566,285. Fluid-pressure servomotor-control systems. HOBSON (AIRCRAFT & MOTOR) COMPONENTS, Ltd., H. M., STOKES, P. H., GREENLAND, L. S., PLESSEY CO., Ltd., and PUGH, C. A. Sept. 14, 1942, Nos. 12938/42 and 744/43. [Class 135] A fluid pressure servomotorcontrol system for aircraft engine superchargers driven by an exhaust gas turbine includes a control device for increasing the flow of exhaust gas to the turbine with increased altitude and a speed governor which, when the speed of the turbine reaches a given upper limit, comes into action and operates to over-ride the altitude control and thereby prevent the turbine from exceeding the critical speed. Fig. 2 shows the invention applied to the control of a supercharger system including an engine-driven supercharger controlled by a throttle valve 14 and an exhaust-driven supercharger controlled by a waste gate 18. The pilot's lever 19 is coupled by a divided link 25 to the throttle 14 and' carries a cam 20 adapted to vary the central point of a boostcontrol capsule stack 21. The junction of the split link 25 is coupled by a link 24 to the rod 23 of a spring-loaded power piston 22 controlled by a piston valve actuated by the capsule stack. The two ends of the cylinder 29 are connected by pipes 34, 35 with a second power cylinder 36 housing a piston 37 adapted to actuate the waste gate 18. A speed governor 54 driven through gearing by the exhaust-gas turbine actuates a piston valve having lands 48, 49 slidable against the action of an adjustable spring 44 in a casing connected to the pipe 34 and the ends of the cylinder 36. As the aircraft climbs the piston 22 is moved downwards against the action of the spring 32 to open the throttle. When the piston 22 has reached the end of its stroke pressure builds up to overcome the stronger spring 40 and move the piston 37 to gradually close the waste gate. Should the turbine exceed the critical speed, the governor moves the valve 45 away from the stop 58 causing the land 48 to throttle the pipe 34 and permit the spring 40 to move the gate towards its open position. A rapid overspeeding closes the pipe 34 and connects the two ends of the cylinder to permit rapid opening of the gate. To prevent hunting the pipe 35 is provided with a restriction and a non-return valve opening away from the cylinder 36, the restriction and valve being byepassed by a pipe with a second restriction. This device may be placed in the pipe 34 in which case the non-return valve is reversed. The pistons 22, 37 and land 49 have bleed ports to permit a small continuous flow of warm engine oil. In a modification, the governor actuates a lift valve in the pipe 35 or in the pipe 34. The control device may be used in association with a carburetter or fuel injection system and in one arrangement a third power piston loaded by a spring stronger than the spring 40 is coupled to one end of a floating lever having a tappet at the other end engaging the cam 20 and an intermediate point connected to a fuel-metering valve and the anchorage of the capsule stack. In the arrangement shown in Fig. 7, the valve 95 for overriding the altitude control is actuated by fluidpressure under the control of a valve 45 actuated by the speed governor, In the position of the valve 95 shown in full lines high pressure oil passes through the valve 45 to hold the valve 95 depressed against the action of a spring 94 to allow high pressure oil to act beneath the piston 37 and lift it against the action of a spring to close the waste gate. Above the critical speed, the governor moves the valve towards its closed position reducing the pressure above the valve 95 which is then moved by the spring into the position shown in broken lines more or less completely blocking the conduits 134, 135 so permitting the spring to return the waste gate to the open position. In another form the valve 95 is replaced by a piston-actuated lift valve adapted to open a byepass connecting the conduits 134, 135 when the critical speed is exceeded. Specifications 419,113, [Group XXVII], and 553,117 are referred to.