Patent Description:
Gas turbine engines are known, and typically include a fan delivering air into a bypass duct, as propulsion air, and into a core housing where it is delivered to a compressor. The air is compressed in the compressor, and delivered into a combustor where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, driving them to rotate. Turbine rotors in turn drive the fan and compressor rotors.

In one known engine type, a low pressure turbine drives a low pressure compressor and a high pressure turbine drives a high pressure compressor. The low pressure turbine also drives the fan. Historically the fan and low pressure turbine rotated at a common speed.

More recently a gear reduction gearbox has been placed between the fan and low pressure turbine such that fan can rotate at a slower speed. There are a number of efficiency advantages that flow from this arrangement. However, the gear reduction gearbox requires a complex lubrication system. A relatively high volume of lubricant is delivered to the gears within the gear reduction gearbox.

After the oil has lubricated gear interfaces it is scavenged and returned to an oil sump. In known geared gas turbine engines, the scavenge line is connected to a scavenge pump which returns the oil to the sump.

The gear reduction gearbox is mounted in a gear reduction bearing compartment. The bearing compartment has a bearing at each end of the gear reduction gearbox, and a seal outward of the bearing.

<CIT> discloses a lubricant system for a gas turbine engine having an ejector device, where part of a lubricant flow stream removed from a lubricant tank is supplied to the ejector device such that a negative pressure arises in the ejector device for returning the lubricant from a lubricant consumer to the lubricant tank.

<CIT> discloses a twin shaft geared turbofan engine.

According to an aspect of the present invention, a gas turbine engine includes a fan to deliver air into a bypass duct defined between an outer housing and a core housing as propulsion air. The fan further delivers air into the core housing where it communicates with a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The high pressure turbine drives the high pressure compressor and the low pressure turbine driving the low pressure compressor, and also drives the fan rotor through a gear reduction gearbox. The low pressure turbine has an input shaft driving a sun gear in the gear reduction gearbox. The sun gear drives intermediate gears. There is an output shaft driven by one of a carrier and a ring gear in the gear reduction to in turn drive a fan drive shaft to drive the fan. A bearing compartment housing encloses the gear reduction gearbox and has an inlet bearing supporting the inlet shaft from the low pressure turbine. A fan shaft bearing supports the fan drive shaft. An oil supply system communicates with a main oil pump. The oil supply system delivers oil to at least one of the sun gear, the intermediate gears and the ring gear. A scavenge system returns oil from the bearing compartment housing to a sump which communicates with the main oil pump. The scavenge system includes a scavenge tube. An ejector pump communicates with a source of pressurized fluid to assist in driving oil from within the bearing compartment housing into the scavenge tube.

Optionally, and in accordance with the above, a scavenge pump is positioned downstream of the scavenge tube, and downstream of the ejector pump.

Optionally, and in accordance with any of the above, a fan shaft seal is positioned outwardly of the fan shaft bearing and an input shaft seal is positioned outwardly of the input shaft bearing.

Optionally, and in accordance with any of the above, no vent hole is provided through the gear reduction bearing compartment housing.

Optionally, and in accordance with any of the above, the scavenge tube has an inlet communicating with an inner wall of the bearing compartment housing, and the ejector pump has an outlet downstream of the inlet to the scavenger tube.

Optionally, and in accordance with any of the above, the pressurized fluid is oil.

Optionally, and in accordance with any of the above, the pressurized fluid is tapped downstream of the main oil pump.

Optionally, and in accordance with any of the above, the scavenge tube has an inlet to communicate an inner wall of the bearing compartment housing, and the ejector pump has an outlet positioned upstream of the inlet to the scavenge tube.

Optionally, and in accordance with any of the above, the pressurized fluid is air.

Optionally, and in accordance with any of the above, the pressurized air is tapped from one of the low pressure compressor and the high pressure compressor.

The engine parameters described above and those in this paragraph are measured at this condition unless otherwise specified. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about <NUM>, or more narrowly greater than or equal to <NUM>. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]<NUM> , wherein °R = °K*<NUM>/<NUM>. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second (<NUM> meters/second), and can be greater than or equal to <NUM> ft / second (<NUM> meters/second).

<FIG> shows a first embodiment <NUM> having an outer housing <NUM> enclosing a gear reduction gearbox <NUM>.

An input shaft <NUM> is driven by a low pressure turbine (such as turbine <NUM> from <FIG>), to in turn drive a sun gear <NUM>. Sun gear <NUM> drives intermediate gears <NUM>. Gears <NUM> drive a ring gear <NUM>. The intermediate gears <NUM> are mounted in a carrier <NUM> which is schematically shown fixed at <NUM> to the housing <NUM>. The ring gear <NUM> in turn drives a fan drive shaft <NUM> that goes to drive a fan (such as fan <NUM> from <FIG>).

The arrangement as shown is a so called "star" epicyclic gear reduction. However, this disclosure would apply equally to a so called planetary epicyclic gear reduction. In a planetary system the ring gear <NUM> is fixed and the carrier <NUM> rotates to drive the shaft <NUM>.

Bearings <NUM>, <NUM> and <NUM> support the shafts <NUM> and <NUM> within the outer housing <NUM> and together serve to define the bearing compartment <NUM>. Seals <NUM> and <NUM> are positioned outwardly of the bearings <NUM> and <NUM>. Again, this is a schematic view. In practice bearings <NUM> and <NUM> may be inside the housing <NUM>.

It should be understood that the bearing compartment, the gear reduction, the housing, the bearings and all of what is depicted in <FIG> is shown highly schematically.

Oil is supplied through an oil supply <NUM> from a main oil pump <NUM>. In practice, the supply of oil to the gear reduction gearbox <NUM> is complex, and involves a number of components to accurately and efficiently deliver oil to gear interfaces which need lubrication. These features of this disclosure may be as known in the art. The main oil pump <NUM> communicates with an oil sump <NUM>. An oil scavenge tube <NUM> scavenges oil delivered from supply <NUM> across the gear reduction gearbox <NUM> and bearing compartment <NUM>.

In the past, the bearing compartment <NUM> has been maintained at a relatively high pressure. This pressure was deemed necessary to assist in driving the oil into the scavenge tube, and toward a scavenge pump. A vent to an outer chamber <NUM>, which is at a relatively high pressure, was formed through the prior art housing to assist in driving the scavenge oil flow.

Applicant has recognized that this is somewhat undesirable. The higher pressure encourages leakage of lubricant across the seals <NUM> and <NUM>. This has resulted in some concerns such as oil loss, with aircraft cabin odor issues.

In addition, there is significant windage or air drag due the prior art higher pressure in the bearing compartment <NUM> caused by the rotating components within the gear reduction <NUM>. Thus, Applicant has recognized that lowering the pressure in the compartment <NUM> may be desirable.

To this end, an ejector pump <NUM> is positioned within the scavenge tube <NUM>. The scavenge tube <NUM> communicates with a scavenge pump <NUM> which returns the oil to the sump <NUM>. The ejector pump <NUM> is shown communicating downstream of the main oil pump <NUM> through a connection <NUM>. Also, the prior art vent mentioned above may be eliminated.

The oil moved into connection <NUM> downstream of main oil pump <NUM> will be at a higher pressure than that found within the bearing compartment <NUM>.

Now, when oil is delivered outwardly of the ejector pump <NUM> it draws oil from the interior of the bearing compartment <NUM> through the scavenge tube <NUM>. This reduces the concerns mentioned above.

The position of the ejector pump <NUM> in <FIG> is shown schematically relative to a rotation axis of the gear reduction <NUM>. In fact, <FIG> better show the location.

As shown in <FIG>, in the first embodiment <NUM>, the ring gear <NUM> rotates in a direction R which is clockwise in this view. An opening <NUM> to scavenge tube <NUM> is shown to communicate oil outwardly of the housing <NUM> of the bearing compartment <NUM>. A direction of oil flow S into the tube <NUM> has a circumferential component in the direction of rotation R. With a planetary gear system the direction S will have a component in a circumferential direction of the carrier. This direction gains assistance from the rotation to aid in guiding oil into the tube <NUM>.

The ejector pump <NUM> communicates and delivers oil outwardly of an ejector outlet <NUM> which is downstream of the entrance <NUM>, and within the scavenge tube <NUM>.

<FIG> shows an alternative not claimed embodiment <NUM> where the ejector pump <NUM> has its outlet <NUM> spaced outward of the ejector tube <NUM> and spaced closely from its entrance <NUM>. In this embodiment, the ejector pump <NUM> communicates through a line <NUM> to a main compressor section <NUM> such that compressed air will drive the oil flow. Section <NUM> may be in the low or high pressure compressor such as shown in <FIG>.

While air is shown as the driving fluid in <FIG>, and oil is shown as the driving fluid in <FIG>, either fluid, or some other fluid can be used with either arrangement.

Under this disclosure a gas turbine engine could be said to include a fan delivering air into a bypass duct defined between an outer housing and a core housing as propulsion air. The fan further delivers air into the core housing where it communicates with a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine.

The high pressure turbine drives the high pressure compressor. The low pressure turbine drives the low pressure compressor, and also the fan rotor through a gear reduction gearbox. The low pressure turbine has an input shaft driving a sun gear in the gear reduction gearbox. The sun gear drives intermediate gears, and there is an output shaft driven by one of a carrier and a ring gear in the gear reduction gearbox to in turn drive a fan drive shaft to drive the fan rotor.

A bearing compartment housing encloses the gear reduction gearbox and has an inlet bearing supporting the inlet shaft from the low pressure turbine. A fan shaft bearing supports the fan drive shaft. An oil supply system communicates with a main oil pump. The oil supply system delivers oil to at least one of the sun gear, the intermediate gears and the ring gear.

A scavenge system returns oil from the bearing compartment housing to a sump which communicates with the main oil pump. The scavenge system includes a scavenge tube. An ejector pump communicates with a source of pressurized fluid to assist in driving oil from within the bearing compartment housing into the scavenge tube.

Claim 1:
A gas turbine engine (<NUM>) comprising:
a fan (<NUM>) to deliver air into a bypass duct defined between an outer housing (<NUM>) and a core housing as propulsion air, and further to deliver air into said core housing where it communicates with a low pressure compressor (<NUM>), a high pressure compressor (<NUM>), a combustor, a high pressure turbine (<NUM>), and a low pressure turbine (<NUM>), said high pressure turbine (<NUM>) driving said high pressure compressor (<NUM>) and said low pressure turbine (<NUM>) driving said low pressure compressor (<NUM>) and also driving said fan (<NUM>) through a gear reduction gearbox (<NUM>);
said low pressure turbine (<NUM>) having an input shaft (<NUM>) driving a sun gear (<NUM>) in said gear reduction gearbox (<NUM>), said sun gear (<NUM>) driving intermediate gears (<NUM>), and there being an output shaft being driven by one of a carrier (<NUM>) and a ring gear (<NUM>) in said gear reduction gearbox (<NUM>) to in turn drive a fan drive shaft (<NUM>) to drive said fan (<NUM>);
a bearing compartment housing (<NUM>) enclosing said gear reduction gearbox (<NUM>) and having an inlet bearing (<NUM>) supporting said inlet shaft (<NUM>) and a fan shaft bearing (<NUM>; <NUM>) supporting said fan drive shaft (<NUM>);
an oil supply system (<NUM>) communicating with a main oil pump (<NUM>), said oil supply system (<NUM>) delivering oil to at least one of said sun gear (<NUM>), said intermediate gears (<NUM>) and said ring gear (<NUM>); and
a scavenge system returning oil from said bearing compartment housing (<NUM>) to a sump (<NUM>) which communicates with said main oil pump (<NUM>), said scavenge system including a scavenge tube (<NUM>; <NUM>), and an ejector pump (<NUM>; <NUM>) communicating with a source of pressurized fluid to assist in driving oil from within said bearing compartment housing (<NUM>) into said scavenge tube (<NUM>; <NUM>).