Auxiliary oil system for geared gas turbine engine

A gas turbine engine comprises a fan drive turbine, a fan rotor, and a gear reduction driven by the fan drive turbine to, in turn, drive the gear architecture. A main oil supply system supplies oil to components within the gear reduction, and an auxiliary oil supply system. The auxiliary oil system operates to ensure that the gear reduction will be adequately supplied with lubricant for at least 30 seconds at power should the main oil supply system fail.

BACKGROUND OF THE INVENTION

This application relates to an auxiliary oil system to supplement a main oil supply system on a gas turbine engine with a gear drive for a fan.

Gas turbine engines are known and, typically, include a fan delivering air into a bypass duct as propulsion air and also delivering air into a core engine. The core engine flow passes into a compressor where it is compressed and then delivered into a combustion section. The compressed air is mixed with fuel and ignited in the combustion section and products of this combustion pass downstream over turbine rotors driving them to rotate.

Historically, a turbine rotor drove the fan rotor at a single speed. This led to compromise in the desired speed for both the fan rotor and the turbine rotor. The fan rotor could not rotate unduly fast and, thus, the turbine rotor typically rotated slower than would be desired.

More recently, it has been proposed to include a gear reduction between a fan drive turbine and the fan rotor. This has allowed the fan to rotate at slower speeds and results in many efficiencies.

However, the gear reduction requires adequate lubrication and must be lubricated even under extreme flight conditions.

SUMMARY OF THE INVENTION

In a featured embodiment, a gas turbine engine comprises a fan drive turbine, a fan rotor, and a gear reduction driven by the fan drive turbine to, in turn, drive the gear architecture. A main oil supply system supplies oil to components within the gear reduction, and an auxiliary oil supply system. The auxiliary oil system operates to ensure that the gear reduction will be adequately supplied with lubricant for at least 30 seconds at power should the main oil supply system fail.

In another embodiment according to the previous embodiment, the gear reduction includes a sun gear driven by the fan drive turbine to drive intermediate gears that engage a ring gear.

In another embodiment according to any of the previous embodiments, the sun gear, the intermediate gears and the ring gear are enclosed in a bearing compartment, which captures oil removed via a scavenge line connected to a main oil pump.

In another embodiment according to any of the previous embodiments, the main oil pump has a gutter that directs scavenged oil to a main oil tank.

In another embodiment according to any of the previous embodiments, oil in the main oil tank feeds a main pump pressure stage which then delivers oil to the gear reduction.

In another embodiment according to any of the previous embodiments, oil from the main pump pressure stage passes through a lubrication system that includes at least one filter and at least one heat exchanger to cool the oil.

In another embodiment according to any of the previous embodiments, the gear reduction is surrounded by an oil gutter that scavenges oil and directs it to an auxiliary oil tank.

In another embodiment according to any of the previous embodiments, the auxiliary oil tank has an overflow conduit that allows excess oil to fall to the bottom of the bearing compartment.

In another embodiment according to any of the previous embodiments, the auxiliary oil tank has a tube with holes at a vertically higher location thereon, such that oil is drawn from the auxiliary oil tank when it is full or under negative gravity conditions.

In another embodiment according to any of the previous embodiments, the gutter is at least 70% efficient, defined as the volume of oil captured in the gutter directed to the auxiliary oil tank compared to a volume of oil that falls out of the gutter and is scavenged by the main scavenge pump.

In another embodiment according to any of the previous embodiments, the auxiliary oil supply system includes an auxiliary pump.

In another embodiment according to any of the previous embodiments, the gear reduction drives auxiliary gears which, in turn, drive the auxiliary pump, such that whenever the gear reduction is turning, it drives the auxiliary pump.

In another embodiment according to any of the previous embodiments, the auxiliary pump draws oil from the bottom of an oil sump and the bottom of the oil sump is at lower elevation than a line leading from the oil sump to the main pump scavenge stage.

In another embodiment according to any of the previous embodiments, the auxiliary pump also draws oil from the auxiliary oil tank.

In another embodiment according to any of the previous embodiments, the oil sump traps residual oil in the bearing compartment, such that oil is supplied to the auxiliary pump under negative gravity conditions as well as positive gravity conditions.

DETAILED DESCRIPTION

FIG. 2shows an oil supply system99for the gear reduction such as gear reduction48in the gas turbine engine20ofFIG. 1. The gear reduction48includes a sun gear100which is driven by a fan drive turbine (such as turbine46ofFIG. 1) and engages a plurality of intermediate gears102. In some embodiments, the intermediate gears102may be planet gears of a planetary epicyclic gear system. In other embodiments, the intermediate gears102may be star gears of a star epicyclic gear system. In some embodiments, the intermediate gears102, in turn, drive a ring gear103which drives a fan drive shaft to, in turn, rotate a fan (such as fan rotor42). Other planetary gear arrangements would come within the scope of this application and the above is merely one example for a gear reduction which may be utilized to drive a fan rotor. For example, in other embodiments, a planetary gear carrier (not shown) driven by planetary gears may drive the fan shaft.

Oil supply104is shown schematically delivering oil to the planet gears102. It should be understood the oil is supplied to other components such as journal pins, bearings, etc. associated with the gear architecture illustrated inFIG. 2.

Oil is supplied from a line106delivered from a main oil supply pump108. A pressure stage of the main oil supply pump108receives oil from an oil tank142. The oil in the oil tank142feeds the main pump108and is then conditioned in a lubrication system110that may contain filters to clean the oil and heat exchangers to cool the oil, as known. The oil then passes back to the gear architecture48through the line106.

A bearing compartment112surrounds the gear reduction48. The bearing compartment112has oil removed via a scavenge line180, which returns the oil to a scavenge side109of the main pump108, which, in turn, delivers the oil back to the oil tank142.

The gear architecture is surrounded by an oil gutter114, shown schematically, that scavenges oil from the gear architecture and directs it to an auxiliary tank116. When tank116is full, an overflow conduit117allows excess oil to fall to the bottom of the bearing compartment112. The gutter114is at least 70% efficient. This means that up to 30% of the oil falls out of the gutter and is scavenged by the main scavenge pump109through line180. The 70% that is captured in the gutter is directed into the tank116.

The detail of the oil supply104, the gutter114and the gears generally may be as shown in U.S. Patent Application 2008/0116010, now U.S. Pat. No. 8,215,454, issued Jul. 10, 2012. The details of those features are incorporated herein by reference. The gear system and, in particular, the intermediate gears102drive auxiliary gears190and191which are shown schematically driving an auxiliary pump124. Thus, as long as the gears102or103are being rotated, the gears190and191will drive the auxiliary pump124.

The pump124draws oil from a sump126at a bottom of the compartment112through a line128. The sump126is at a lower elevation than the main scavenge line180and also draws oil from the tank116through the line122. Sump126will trap any residual oil in the bearing compartment112.

There are challenges with the auxiliary pump with regard to negative gravity conditions. Further, if there is a break in the main oil supply system or windmilling of the engine when the engine is otherwise shut down, it is desirable for the engine to be able to maintain operation for at least 30 seconds at power without damage if the main oil line (108/106, etc.) ruptures. This will provide a pilot time to shut the engine down.

It is also desirable to allow the engine to windmill in the air for up to 90 minutes without damage if it is shut down for other reasons than oil system failure. It is also desirable to allow the engine to windmill indefinitely on the ground with wind speeds below 85 mph or less. As known, windmilling refers to a condition where the engine is shut down, however, air being forced into the fan rotates the fan, in turn, causing components to rotate.

Finally, it is desirable to allow an aircraft to fly under negative gravity conditions for at least 20 seconds.

All of these raise challenges with regard to operating the engine and supplying oil to the gear components.

The arrangement of the components, as described above, allow these conditions to be met.

The auxiliary pump124draws oil from the sump126. Pump124also draws oil from a line122. The tank116has a tube118with holes120at a vertically higher location, such that oil is only drawn from the tank116to the line122when it is full or under negative gravity conditions. Otherwise, oil is drained from the tank116by overflow through the conduit117.

The auxiliary pump124supplies oil to the conduit130and then to a valve132. Valve132senses a pressure (through line140) in the main line144. If the pressure is acceptable, oil from the line130is sent by the valve132back to the tank142through a line199. Thus, if the pressure is acceptable, the oil is recycled for reuse during normal operation. On the other hand, if the pressure on the main line144is low, oil is sent into a conduit200and then passes into the conduit106to bypass the main lubrication system and feed the gear reduction48to ensure that the conditions as described above are met.

The conditions as described above are met in large part, since the auxiliary oil tank116, and the tube118, has the holes120only at the top, such that oil is only drawn from the tank116, through the line122when it is full, or under negative G conditions. Further, since the sump126is at a lower elevation than a main scavenge line180, the auxiliary pump124will always be supplied with oil, in both positive and negative G conditions. Further, the auxiliary pump124, in combination with the valve132, ensure that oil will be supplied in adequate amounts during the conditions set forth above.