Patent GB-762203-A (GB)
Title: Improvements in or relating to control systems for power plants driving variable pitch propellers
Inventor: WALL WILLIAM ALBERT JOHN
IPC: F02D29/00
Filed: 1954-02-04
Abstract: 762,203. Variable pitch propellers. ROTOL, Ltd. Jan. 31, 1955 [Feb. 4, 1954], No. 3391/54. Class 114. [Also in Groups XXVI and XXIX] In a control system for a power plant comprising an internal combustion engine driving a variable pitch propeller and including a variable datum speed governor to control the speed of rotation of the propeller by varying the pitch thereof and a fuel control to control the rate of flow of fuel to the engine, the fuel control and a control for adjusting the datum of the governor being inter-connected by a linkage so as to be normally operable together by a single master control which correlates fuel flow and propeller speed, and hence the power output of the engine, an auxiliary fuel governor is inter-connected with said control system in a manner such that so long as the engine speed is different from that selected by the master control, the auxiliary fuel governor adjusts the rate of flow of fuel to the engine relatively to that selected by the master control in a sense to reduce the said speed difference. In Fig, 1 a gas turbine engine comprising a compressor 1, a combustion chamber 2 and a turbine 4 drives a propeller 7 through a gearing 8, the pitch of the propeller being controlled according to the speed or datum setting of the centrifugal governor of a constant speed unit 9 driven by the engine through a drive 10. The fuel control 11 controls the amount of fuel delivered to the chamber 2. The auxiliary fuel governor 25 incorporates a centrifugal governor geared to a drive shaft 89 from the engine, and has levers 23 and 31. As shown in Fig. 2 the latter governor comprises flyweights 78, 79 mounted on a cup 82 connected by gear wheels 87, 88 to the drive 89, and lifts a hollow valve member 48 against the action of a spring 72 loaded by a sleeve 69 having a gear rack 70 in mesh with a pinion 71 mounted on a shaft which carries the lever 31. A ported piston 40 sliding over the valve member 48 has a hollow stem 39 with a rack 41 for actuating the lever 23. A hollow liner 62 is secured in the member 48 by a pin 68. Hydraulic fluid is supplied through apertures 33 and 34. When the pilot moves the control lever 12 rapidly to increase engine speed, the master control unit 14 resets shafts 15 and 16. Links 28, 30 move levers 29 and 31 to set the governors of the units 9 and 25. The shaft 15 displaces a lever 17, and since pivot 22a is held fixed by a link 22 connected to unit 25, link 20 moves lever 21 to increase fuel flow to the engine. Since pitch coarsening of the propeller by unit 9 is slower than acceleration of the engine under increased fuel supply, the engine accelerates to its new speed by the time movement of lever 12 ceases and before the pitch of the propeller has changed to that at which the full power of the engine is absorbed. The engine speed will therefore exceed that called for by the new datum setting of the governor in unit 25 and the flyweights 78, 79 will move outwardly to lift the valve member 48 against its spring, the resultant change in relative position of the various ports allowing hydraulic fluid to flow to the underside of piston 40, the fluid above same being connected to an annular passage externally of member 48 and thence via ports 84 to drain. Upward movement of the piston shuts off the ports, and the rack 41 moves lever 23 which in turn moves the link 22, and since the lever 17 is now fixed this movement is transmitted through link 20 to the lever 21 to adjust the setting of the fuel control 11 to reduce the fuel flow to the engine. Consequent reduction of engine speed causes flyweights 78, 79 to move back to their equilibrium setting, and piston 40 will follow up valve member 48 and move lever 23 back. This sequence of movements is repeated until the engine and propeller settle down to the new speed and pitch with the governors stabilised in their equilibrium settings. Specification 748,076 is referred to.