Patent GB-968795-A (GB)
Title: Gas turbine power plant
IPC: F02C7/36
Filed: 1963-02-21
Abstract: 968,795. Measuring torque. GENERAL MOTORS CORPORATION. Feb. 21, 1963 [March 7, 1962], No. 7038/63. Heading G1W. [Also in Divisions F1, F2 and G3] In a gas turbine engine of the type comprising a compressor driving turbine and a separate power turbine, the power turbine may be connected to the compressor driving turbine by a torque responsive device which is responsive to a condition indicative of turbine temperature so as to load the compressor driving turbine variably with decrease in engine power level thereby maintaining a high compressor driving turbine temperature at light loads. The plant is shown in Fig. 1 and comprises a centrifugal air compressor 11 which is driven by means of the turbine 13 through shaft 14. The gases discharging from the turbine 13 action the separate power turbine 17 which drives the output shaft 18. The engine comprises a fuel pump 24 and fuel control circuit 23, a gas generator speed responsive device 39, also a power transfer and accessory drive shaft 37, the compressor-turbine shaft 14 being connected to the shaft 37 by means of gearing 32, 33, 34, 35, 36 the gearing incorporating a torque-sensing device 111. The shaft 37 is connected to a further shaft 45 in alignment therewith by means of a power transfer clutch 44 the shaft 45 being connected to the turbine output shaft 18 by gearing 46, the clutch being automatically engaged when excess power is available from the compressor driving turbine whereby this turbine is connected to the output shaft 18, also when the load turbine tends to overrun the compressordriving turbine whereby the load turbine tends to assist in driving the compressor thus producing a braking effect on a vehicle in which the engine is mounted. An oil pump 42 is also driven from the shaft 37, the pump supplying cooling oil through line 108 to the torque sensor 111 and to other components. The torque sensor 111 indicated in Fig. 1 is shown in Fig. 3 and comprises a pair of helical gears 34, 35 formed integrally on a common shaft 112 which is mounted in bearings 113, 114, there being provision for some axial movement of the shaft as indicated by the clearances 118, 119. The inclinations of the gear teeth of the two gears 34, 35 are of opposite hand so that the shaft 112 takes up an axial position which is a measure of the torque being transferred. The shaft 112 is connected by means of a ball thrust bearing 121 to an open-ended cylinder 122 which moves axially with the shaft 112, the cylinder being formed with stepped bores 127, 128 in which is disposed a fixed stepped piston 129. Servo-oil is supplied through line 108 to a central bore 136 in the fixed piston 129 and thence through bore 137 and the groove 138 into the pressure chamber 133. Under normal torque, the shaft 112 and cylinder 122 are biased to the right so the fluid in the chamber 133 is pressurised to a pressure which is a measure'of the torque. This pressure signal indicative of torque is communicated through bore 141 and line 142 to the torque programmer shown in Fig. 4. When the shaft 112 and cylinder 122 are urged to the left as occurs when the power turbine tends to overrun the gas generator turbine, the servo-fluid entering the bore 136 is caused to flow through duct 152 and line 153 and enters the braking cylinder 74 of the clutch 44 (Fig. 2 not shown) whereby the clutch is engaged sufficiently to brake the power turbine. The torque programmer 161 is shown in Fig. 4 and comprises a cylinder bore 166 in which is disposed a servo-oil control valve 167 which is loaded to the right by an adjustable spring 169 and to the left by fluid pressure in the chamber 173A the chamber being connected to the line 142, the pressure in the line 142 being a measure of engine torque. Servo fluid supplied through line 108 is controlled by the axial position of the spool valve 167 and the fluid may pass through the outlet to line 173 which is the power transfer clutch control line. When the servo fluid inlet port 171 is closed off by the spool valve 167, the clutch cylinder is connected to drain by way of line 173, duct 191 and outlet 188. The loading of the spring 169 is controlled by a cam 177 acting on the follower 168, the axial position of the cam being controlled by a fluid pressure which is applied to the piston 178 which is loaded in the opposite direction by a spring 183, the pressure of the fluid being a measure of the speed of the gas generator turbine and which is conveyed through line 162 from the speed responsive device 39.