Patent GB-677249-A (GB)
Title: Improvements in speed governors
IPC: F02D1/00
Filed: 1949-06-27
Abstract: 677,249. Speed-governors; gas-turbine plan t. HOBSON, Ltd.; H. M., McCOURTY, W. D. and TYLER; S. R. June 21, 1950 [June 27, 1949; Nov. 4, 1949], Nos. 16967/49 and 28278/49 Classes 57 and 110(iii) [Also in Group XXIX] A hydraulic speed governor comprises a shaft driven by the body being governed, a freely rotatable flywheel, a member fixed to the shaft and defining with the fiywheel an enclosure containing liquid and arranged to maintain the flywheel in rotation, a device responsive to the variations in pressure in said enclosure occasioned by relative movement of the flywheel and member due to acceleration of the shaft, the pressure responsive device being subject also to an hydraulic pressure varying in accordance with the rotati'onal speed of the shaft, an hydraulic servomotor to vary the speed of the governed body and having a control valve which is coupled to the pressure responsive device, and an adjustable speed-selecting spring acting on the latter in opposition to the hydraulic pressure acting thereon. A speed and acceleration-responsive device comprises a vane 23, Fig. 2, fast on an engine-driven shaft and a flywheel 25 loose on the shaft, the vane being accommodated ,in a cavity in the flywheel and being connected to the flywheel by springs 27. Liquid under pressure is led into the centre of the vane through a passage 31, and when the vane and flywheel are running at the same speed the outlet from passage 31 to the cavity housing the vane is closed. When the shaft accelerates, relative movement takes place between the vane and the flywheel and liquid flows from passage 31 to a pressure chamber 26 which is interconnected with a similar chamber on the diagonally opposite side of the vane by a passage 28. The exhaust or low pressure chambers 29 are similarly connected by a passage 30. The difference in the pressures in the high and low pressure chambers taken at the root of the vane will be indicative of the acceleration of the shaft, the difference in the pressures taken at the root and the tip of the vane in either the high or the low pressure chamber will be indicative of the speed of the shaft, and the difference between the pressures at the tip of the vane on the high pressure side and at the root on the exhaust side will give an indication of speed and acceleration together. A control effect is obtained by applying the last mentioned indication to a single diaphragm, or the two previous pressure differences are applied to two separate but interconnected diaphragms actuating ,a hinged control valve of a servomotor system, and in this lattercase the speed component could be detected by means of a separate centrifugal impeller an the same governor shaft. In a modified construction of acceleration and speed detector, a casing 140, Fig. 20, driven at engine speed contains a freely rotatable dumb-bell shaped flywheel 142, the latter being driven from the casing by springs 160 interposed between projections 144, 145 on the casing and the flywheel. Pressure liquid is supplied to the interiors of the projections 144, 145, and relative movement between the flywheel and casing due to acceleration will vary the amount of liquid escaping into the casing past a valve 152 carried by the flywheel. This venting of liquid will cause a corresponding varying pressure in the supply which can be detected by a pressure responsive device. The chamber formed in projection 145 is bounded by a diaphragm 149, and a rod 161 carried by the flywheel is maintained in contact with the diaphragm to establish a datum'pressure difference across the latter. The liquid in casing 140 escapes through apertures 156 into a fixed housing 157 where it is subjected to the pressure imposed by an impeller carried by casing 140. In applying the invention to the control of a constant speed unit of an airscrew, the liquid pressures produced by the engine-driven governor 25, Fig. 4, as indicative of the speed and acceleration of the engine are applied to opposite sides of a diaphragm 34, the latter being loaded by spring 49 which can be adjusted by a speed-selecting lever 65. The diaphragm 34 actuates a valve 63 controlling the venting of liquid from a circuit comprising a supply line 56, chamber 59 on one side of a diaphragm 58 carrying a relay valve 53, a restriction 60, chamber 61 on the opposite side of diaphragm 58, and the interior of valve 53. The variations of pressure in chamber 61 consequent on movements of valve 63, cause movement of valve 53 to control the operation of a servomotor piston 51 which, in its turn, controls the pitch of the airscrew blades In another application, the servomotor piston actuates a variable valve in a system for the supply of fuel to a gas turbine engine. The pressures derived from the speed and acceleration governor 25 are applied to two separate diaphragms which are, however, interconnected and actuate a hinged valve controlling the servomotor piston. The speed-responsive diaphragm works between stops restricting the acceleration or deceleration obtainable but the positions of the stops are automatically adjustable in accordance with the air intake pressure. An alternative acceleration limiting device comprises an apertured auxiliary piston contained in the servomotor cylinder and resiliently restrained in its movement in either direction. In a modified system for supplying fuel to a gas turbine engine, fuel from a tank 10, Fig. 12, passes a cut-off valve 11 and is fed from a pump 105, past a pressure boost valve 106, to a line 109, leading to the burners. For starting purposes, fuel from a boost pump is fed in from a line 110 past a non-return valve 111. When a linkage 112 is operated, an engine stop-valve 107 closes off line 109 and returns the output of pump 105 to the suction side, and a dump valve 108 is opened to allow fuel remaining in the burner ring to drain away through line 114. In an embodiment, valve 107 consists of a rotary cylindrical valve carrying an eccentric to actuate a poppet type valve 108. The fuel supplied to the burners is controlled by a needle valve 115 which byepasses a variable amount of fuel back to the pump inlet past a pressurizing valve 119. Some of the flow downstream of the needle valve passes through a restriction in a piston 116 carried by the needle valve to a control chamber 117, the pressure in which is controlled by a leak-off valve 123. This latter valve is carried on a beam 164 which is actuated by diaphragms 162, 163, controlled in accordance with the speed and acceleration, respectively, of the engine, diaphragm 162 being subject to the output pressure of an impeller 141 and diaphragm 163 to the control pressure produced by an acceleration detector 142, shown in Fig. 20. The spring loading of diaphragm 162 is adjusted by a speed selecting lever 172. The control pressure due to the acceleration is also applied to a diaphragm 217 which controls a leak-off valve 214 in parallel with the valve 123 whereby an over-ride to prevent over-fuelling during acceleration is provided, and the value at which the override operates is determined by the spring 220 loading valve 214. A further spring- loaded diaphragm 221 subject to impeller tip pressure carries an abutment 224, and at low speeds this abutment will be kept out of contact with valve 214 to allow full over-ride control by that valve. In order that the acceleration limit may be reduced as nacelle pressure decreases with altitude, the full speed responsive pressure developed by the impeller is reduced by a needle valve 226 under the control of an evacuated bellows 229 subject to static and ram pressures applied through a conduit 228. These pressures are also applied to balance diaphragms 232 which serve to seal off the needle actuating mechanism. This reduction in speed-responsive pressure will, of course, affect the operation of diaphragm 221. A modified form of acceleration-limiting device is described.