Patent GB-1095109-A (GB)
Title: Improvements in or relating to gas turbine engines
Inventor: ALLEN ROY
IPC: F01D3/00
Filed: 1966-10-03
Abstract: 1,095,109. Fluid-pressure servomotor systems. ROLLS-ROYCE Ltd. Oct.3, 1966 No. 44120/66. Heading G3P. [Also in Division F1] A gas turbine engine comprises a rotor mounted on a shaft thereof, there being means for subjecting a substantially radially-extending part of the rotor to a pressure differential in a sense to oppose the axial load in operation of the engine on a bearing or bearings supporting the shaft, there being also servocontrol means for controlling the said pressure differential so as to maintain the axial load between predetermined limits. In the embodiment shown the turbine and compressor rotor assembly is supported in bearings 15 and a thrust bearing 16. An annular housing 18 is supported by fixed structure adjacent the downstream side of the turbine rotor disc 17 so as to define an annular chamber 19 therewith, air under pressure tapped from the engine compressor being passed through duct 20 to the chamber, the air pressure being controlled by a servocontrol device 21 in response to engine speed. The control device comprises an obturating member 25 having a profiled portion 26 which is disposed in the line 20 so as to control the pressure of the air supplied to chamber 19. The member 25 is integral with a piston 28 which is disposed within a cylinder 30, the space 31 at the right hand side of piston 28 being supplied with fuel at high-pressure and the space at the left hand side of the piston being supplied with fuel at high-pressure through a restriction 33. The space at the left of the piston 28 is connected through duct 47 and valve-controlled orifice 46 to a low-pressure point in the fuel system through return line 54. The valve 41 controlling the orifice 46 is carried by a rod 37 on which is mounted a plate 38, a spring 39 being disposed between the plate 38 and the piston 28. The rod 27 also carries a flexible diaphragm 43 which is disposed in a chamber formed between walls 36 and 40. The right hand side of the diaphragm 43 is subject to a reference pressure derived from highpressure fuel supplied through restriction 34 and regulated by an altitude responsive device 48, while the left hand side of the diaphragm is subject to pressure which is proportional to engine speed and which is derived from a device 45. The device 45 comprises a casing 55 within which is mounted a rotor 57 which is driven by shaft 58 at a speed proportional to turbine rotor speed, the rotor comprising an internal partition 59, a diaphragm 60 and a valve member 62 pivotally mounted at 63 and having a centrifugal weight 64, the valve controlling fuel flow through an opening 61 in the partition 59. High-pressure fuel is supplied to the housing 55 through restriction 56 and leak off from the housing to a lowpressure line 54 through the orifice 61 is controlled by the pivoted valve 62 in response to engine speed, the resulting pressure being communicated through line 44 to the left hand side of the diaphragm 43, the pressure in the line 44 being a measure of the rotational speed of the shaft 14. The altitude responsive control 48 comprises an evacuated capsule 50 disposed in a chamber which is connected to compressor inlet pressure P 1 , the capsule controlling the opening of valve 53 and so the value of the reference pressure in the line 35. An increase in the shaft rotational speed or an increase in altitude will cause the diaphragm 43 to move to the right, so that the valve 41 moves away from the seat 42. The servopressure within the cylinder 30 will therefore fall and the piston 28 will move to the left thus varying the restriction to flow presented by the restriction 26. As the piston 28 moves to the left so also will the rod 37 thus moving the valve member 41 back on its seat.