Patent GB-595152-A (GB)
Title: Improvements in fuel supply systems
Filed: 1945-02-24
Abstract: 595,152. Fluid-pressure servomotor systems. DOWTY EQUIPMENT, Ltd., and GARY, F. H. Feb. 24, 1945, Noa. 4666 and 4667. f Class 135] [Also in Groups XXVI and XXVII] The fuel supply to a gas turbine is regulated by means comprising a follower member responsive to engine speed and a control member responsive to controllable variable-speed motor means which are related with means by which the fuel supply is regulated so that when said members are moved relatively to one another, the fuel supply is correspondingly varied. In the arrangement shown in Fig. 1, the fuel regulating valve 12 is operated by a control arm 24 on which is freely mounted a pinion 25 mating with two crown wheels 30 and 31. The crown wheel 30 is mounted on a shaft 27 driven by the engine and the wheel 31 on a shaft 28 driven by the motor 29, the speed of which is controlled by the unit 33 operated by the throttle lever 34. When the shafts 27 and 28 are driven in opposite directions at equal speeds, the pinion 25 and control arm 24 will remain stationary, but if either of the shafts 27 or 28 increase speed relative to the other, the control arm 24 will move to regulate the fuel supply to the turbine so as to bring them back to synchronism. The spring 23 operates to load the control plunger 13 into the minimum restriction setting so that fuel is available for starting. In a modified arrangement, Fig. 2, the quantity of fuel delivered to the burner ring 47 is regulated by varying the output of the variable delivery pump 35 by adjusting the eccentricity of the track ring 42 by means of a fluid-actuated piston 50 operating in a cylinder 53. The fluid supply to and from the cylinder 53 is controlled by a rotary control valve 60 which comprises an outer sleeve 69 driven by the engine and an inner sleeve 68 driven by an electric motor. Fluid pumped by a gear pump 57 is fed into the centre ports 59 of the valve 60, and the annulus 75 between the sleeves 68, 69 together with the spaces 77 in the fixed centre piece 78 are connected to the drain tank through the ports 82, 83. When the sleeves 68 and 69 are rotating at the same speed, the supply ports 71, 73 and 70, 72 are in the relative position shown in Figs. 4 and 6. With an increase of the motor speed relative to the engine speed the sleeve 68 rotates clockwise relative to the sleeve 69 and pressure fluid is supplied through the ports 71, 73, Fig. 4, to the annulus 79 through the conduit 55 to the cylinder 53 to move the piston 50 and increase the eccentricity of the track ring 42 and thereby increase the output of the pump. At the same time the conduit 54 is connected to the drain spaces 81 through the ports 70, 72a, Fig. 6. This will continue until the engine speed equals the motor speed when the sleeves will return to the position shown. With a decrease in motor speed relative to the engine speed, the sleeve 68 will rotate anti-clockwise relative to the sleeve 69 and the conduit 55 will be connected to the drain spaces 81 through the ports 71, 73, Fig. 4, and the conduit 54 to the pressure spaces 77 through the ports 70, 72, Fig. 6. This will reduce the eccentricity of the track ring 42 and so reduce the output of the pump and the speed of the turbine until it equals the motor speed. To start the engine, the lever 66 is set to the idling speed and the valve 45 is opened and the engine run up on the starter. The track ring 42 is urged by the spring 52 to the maximum eccentricity position to ensure an adequate supply of fuel. The burners have relief valves which open when a predetermined pressure is reached and until the pressure reaches this value, the pump 35 charges the accumulator 49 in which pressure is built up against a resilient device. On reaching this pressure, the fuel from the accumulator and the pump passes to the burners. The engine then starts and accelerates until the pre-set idling speed is reached when the control valve 60 comes into operation and operates as described above. The movement of the sleeves 68 and 69, relative to one another is limited by co-operating dog and slot connection between the two drives. The governor controlled valve 48 prevents the engine speed exceeding a predetermined maximum speed and when this speed is reached, the fuel is byepassed to the suction of the pump. The valve 45 may be used to control the speed of the engine if the control system fails. A relief valve 92 limits the pressure in the auxiliary hydraulic circuit. Although the invention has been described using an electric motor which is preferred, since the system may then be easily modified to take into account burner failures, e.g. by means of thermo-couples, hydraulic or airdriven motors may also be used. According to the first Provisional Specification, the control valve 60 can be used to control an auxiliary circuit which operates plunger or valve means varying the spring loading of a governor controlling the speed of the fuel pump or which operates some form of variable speed gear in the pump drive.