This disclosure relates to a lubrication system, and more particularly, to a lubrication system for a fan drive gear system in gas turbine engines.
In many gas turbine engines, a low pressure spool includes a low pressure turbine connected to and driving a low pressure compressor, and a high pressure spool includes a high pressure turbine connected to and driving a high pressure compressor. A main pump is typically driven by the high pressure spool, connected through gearing, and is used to pump lubricating and cooling fluid to all engine components that require lubrication and cooling.
The main pump typically pumps fluid from a passage connected to a main reservoir that holds both liquid and air. During normal operating conditions, the fluid settles at the bottom of the main reservoir and displaces air to the top. However, in a gas turbine engine mounted on an aircraft, the main reservoir may experience “negative gravity” conditions such as the aircraft turning upside down, the aircraft accelerating toward the Earth at a rate equal to or greater than the rate of gravity, or the aircraft decelerating at the end of a vertical ascent. Under negative gravity conditions, the fluid in the main reservoir can rise to the top, which can expose an opening of the passage to air and interrupt the supply of fluid to the main pump and, consequently, interrupt supply to the engine components. Certain engine components, such as gears and bearings, can be damaged by a relatively short period of non-lubricated operation during negative gravity conditions.
In some gas turbine engines, a fan at the front of the engine is connected to the low pressure spool through a fan drive gear system. When the high pressure spool stops rotating or rotates at a reduced rpm (revolutions per minute), the fan drive gear system can continue rotating even though the main pump will ordinarily provide little or no fluid during this time. For example, wind may rotate the fan and corresponding gears and bearings while the aircraft is parked on the ground or during an in-flight engine shutdown. Certain gears and bearings can also be damaged by a relatively short period of non-lubricated operation during windmilling as well.