Patent GB-743324-A (GB)
Title: Improvements in or relating to gas-turbine engines
Inventor: FLETCHER ARTHUR HOLMES
IPC: F02C7/36
Filed: 1952-01-14
Abstract: 743,324. Gas turbine plant. ROLLS-ROYCE Ltd. Jan. 2, 1953 [Jan, 14, 1952], No. 1091/52. Class 110(3) A gas turbine plant comprising a compressor supplying air to combustion equipment feeding a turbine driving the compressor and a useful power turbine which turbines rotate independently of one another, has means arranged to couple the useful power turbine and compressor driving turbine together when the power absorbed from the output shaft falls below a selected value so as to allow the compressor driving turbine to deliver power to the output shaft. The invention is described with reference to a gas turbine plant comprising a high pressure compressor driven by a high pressure turbine, an intermediate presure supplying useful power and a low pressure compressor driving a low pressure turbine. The air from the low pressure compressor is cooled before entering the high pressure compressor and the air from the high pressure compressor is heated in a heat-exchanger by the exhaust gases of the low pressure turbine before entering the combustion chamber. The shaft 12, Fig. 2, connecting the high pressure compressor to the high pressure turbine is connected to the useful output shaft 18 through two sets of gear and clutch mechanism A and B. The shafts 12, 18 may run independently of one another or be coupled through the mechanism A in which case the shaft 12 runs at approximately twice the speed of shaft 18 or alternatively be coupled through the mechanism B in which case the speed ratio is approximately 3. The shaft 18 carries a pinion 24 and the shaft 12 a pinion 25 which mesh with pinions 26, 27 respectively. The pinion 26 rotates with a structure 28 which houses a friction clutch and its operating mechanism. Each friction clutch comprises friction elements 30 rotatable with the pinion 27 which co-operate with friction surfaces 31 in the structure 28. A pressure plate 32 splined to the structure 28 is operated by cam surfaces 33 on pivoted levers 34. The inner ends of the levers 34 engage a channelled piston 35 which is actuated by pressure fluid supplied through ducts 37, 38 in recesses 39. The supply of pressure fluid is controlled in accordance with the load and in the arrangement shown in Fig. 3 is controlled in accordance with the delivery pressure of the high pressure compressor 10. The pressure fluid is supplied at a constant pressure by a pump 40 to a pair of solenoid operated piston valves 44A, 44B associated with the mechanisms A and B respectively which control the supply to the ducts 37, 38. When the solenoid 46A or 46B is energized the corresponding clutch is engaged. The air from the discharge of the compressor 10 operates three pressure responsive devices 48, 49 and 50 each of which comprises a flexible diaphragm 51 loaded by a spring 56. When the air pressure falls below a first selected valve the pressure responsive device 48 closes the switch 58 and energizes the solenoid 46A which causes the clutch mechanism A to be engaged When'the air pressure falls below a second selected value which is lower than the first, the presure responsive device 49 operates 'hrough a toggle mechanism 60 a pair of switches 61, 62. The switch 61 opens and cuts off the supply to the solenoid 46A and the switch 62 closes and energizes the solenoid 46B which causes the clutch mechanism A to be disengaged and the clutch mechanism B to be engaged. On a further decrease of air pressure the pressure responsive device 51 operates a switch 65 through a toggle 66 to cut off the supply to the solenoid 46B so that both of the clutch mechanisms A and B disengage. The toggle mechanisms 60, 66 prevent hunting of the mechanism. A valve 67 enables the control mechanism to be cut out of operation. In a modification, a free wheel clutch is inserted in the mechanisms A and B so that power can be transmitted from the shaft 12 to the shaft 18 but not in the reverse direction. This arrangement allows the control mechanism shown in Fig. 3 to be modified in that only two pressure responsive devices are required. The first pressure responsive device referred to above is dispensed with and the drive taken up automatically by the free wheel of the mechanism A at the first selected value. The second and third pressure responsive devices 49, 50 are used to deenergize the solenoids 46A and 46B at the second and third selected values. It is stated that the devices 48, 49, 50 may be replaced by governors responsive to the speed of the power turbine or by devices responsive to the turbine inlet temperature or by the compressor compression ratio. Specification 641,377 is referred to.