Power plants – Combustion products used as motive fluid – Multiple fluid-operated motors
Patent
1995-03-28
1997-12-09
Thorpe, Timothy
Power plants
Combustion products used as motive fluid
Multiple fluid-operated motors
60 39161, 60396, F02C 106
Patent
active
056947658
DESCRIPTION:
BRIEF SUMMARY
This invention relates to gas turbine engine transmission systems. In particular the invention concerns transmission systems suitable for effecting power transfer between independently rotatable engine shafts in multispool gas turbine engines.
A multispool gas turbine 10 having a conventional transmission system is shown schematically in FIG. 1. The gas turbine engine shown comprises, in flow series, a front fan assembly 12 and a core engine 14. The engine is of the ducted fan by-pass type and has three relatively rotatable spools including a low pressure spool 16, an intermediate pressure spool 18, and a high pressure spool 20. The low pressure spool includes a fan 12, a multistage turbine assembly 22 located at the downstream end of the core engine, and an interconnecting load transmitting shaft 24 rotatable about engine axis 26. The intermediate pressure spool 18 includes a multistage axial flow compressor 28, a turbine rotor assembly 30, and a hollow interconnecting shaft 32 concentrically disposed around engine shaft 24. The engine's high pressure spool 20 similarly includes a multistage axial flow compressor 34, a turbine rotor assembly 36, and an interconnecting shaft 38 concentric with engine shafts 32 and 24.
The transmission includes a radial power off-take shaft 40, a so called step-aside gearbox 42 drivingly connected to the engine's high pressure spool by the drive shaft 40, an externally mounted accessory gearbox 44, and a drive shaft 46 connecting the accessory gearbox to the step-aside gearbox 42. Various accessories (not shown), both engine and aircraft, are mounted on the accessory gearbox 44 so as to be driven by the transmission during engine operation.
This configuration is found in many ducted fan multispool gas turbine engines. It has the advantage over other configurations in that it allows the same transmission system to be utilised for transferring engine starter torque to the engine's high pressure spool during ground starting, as well as engine power to the accessories during self sustained operation. There is a drawback, however, with this type of arrangement.
Following an in-flight combustion flame out condition, aircraft mounted gas turbine engines typically rely upon the free rotation of the engine spools to generate sufficient core engine flow to support combustion and rapid engine acceleration at re-light. In arrangements where the accessories are driven by the engine's high pressure spool this capability can be significantly reduced. During periods of extinguished engine operation the additional load imposed by the accessories reduces the free rotational speed of the spool, and as a result the airflow through the core engine. One way of improving the re-light characteristics of ducted fan gas turbine engines is disclosed in our co-pending International Patent Application GB92/01179. This patent application discloses an aircraft mounted gas turbine engine having an accessory drive linked to the engine's low pressure spool. The arrangement ensures that in the event of a flame-out condition the engine's windmilling fan continues to drive the accessory gearbox. Under these conditions the power available from the windmilling is significantly greater than that required by the accessories and as such the accessory load impacts far less on the core engine flow.
Another method involves transferring power to the high pressure spool of an extinguished engine from a source external to the engine. Generally this is achieved using bleed air from a neighbouring engine to drive the starter of the extinguished engine. The power transferred augments that of the freely rotating high pressure spool and as such causes the spool to rotate faster, improving the chances of successful re-light. A major drawback with this is that it relies on the continued functioning of at least one other engine.
One way of overcoming this would be to utilise power from the windmilling fan of the extinguished engine, instead of bleed flow energy from the neighbouring engine, to accelerate the engine spool.
Accord
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Cundy John M.
Hield Paul M.
Midgley Ronald A.
Newton Arnold C.
Rowe Arthur L.
Kim Ted
Rolls-Royce plc
Thorpe Timothy
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