GB2135740A

GB2135740A - Gas turbine engine lubrication systems

Info

Publication number: GB2135740A
Application number: GB08303903A
Authority: GB
Inventors: Stanley Smith
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1983-02-11
Filing date: 1983-02-11
Publication date: 1984-09-05
Also published as: GB8303903D0; JPS59153926A; FR2540936B1; DE3403401A1; JPH0423096B2; US4576001A; GB2135740B; FR2540936A1

Description

1

SPECIFICATION

Improvements in gas turbine engine oil systems 65 The present invention relates togas turbine engine oil systems.

In conventional oil systems the main oil pump picks up oil from the oil tankand directs itto the bearing chambers, scavenge pumps remove itfrom the bearing chambers and direct itto an airloil separator, also known as the breather, in a chamberwhich is at low pressure and from which the separated air is vented to atmosphere. From the breather chamberthe oil is pumped backto the tank usually via filters and coolers. Each pumping operation adds heatto the oil It has been proposed in our U.K. Patent Application No. 7,944,038thatthe centrifugal separatorcan also be used as an oil pump. From our U.K. Patent Application No. 7,907,710 it is known that by directing the pressurised airfrom the engine bearing chambers to the separator, the aircarriesthe oil with itto the separatorand the scavenge pumps can be eliminated, allowing the separatorto directthe oil backtothe oil tank.

Also in conventional oil systems, in which the main oil pump takes its supplyfrom thetank, special arrangements have to be madeto ensure thatthe bearings are supplied with oil when the aircraft makes aerobatic manoeuvres and, for example,the oil tank becomes inverted uncovering the pump inlet. These special arrangements have involved the use of auxiliary pumps, or modifications to the oil tank or other parts of the system, all of which add complications to the system.

One object of the present invention is to provide a fully aerobatic oil system with a minimum amount of complication.

Another object of the present invention is to provide an oil system for a gas turbine engine which reduces the number of gear pumps required, and which can operate using a single centrifugal pump in all aerobaticconditions.

Another object of the present invention isto provide an oil system for a gas turbine engine in which there are no valves.

According to the present invention a gas turbine engine oil system comprises a tank, a centrifugal separator, and scavenge means for removing oil from the bearing chambers and directing it to the centrif ug- al separator, characterised in that the tank is pressurised to a f irst pressu re by air f rom the engine, conduit means are provided for conveying oil from the interior of thetankto the interior of the centrifugal separator, oil circulating means are provided for directing at least a portion of the oil passing through the separatorto the engine bearing chambers under centrifugal action and at a pressure greaterthan said first pressure, and meansare provided for directing excess oil not used bythe oil circulating means, and at a pressure higher than the first pressure, backto the tank.

Bythis means itcan be seen thatas long as oil is returned to the centrifugal separator from the bearing GB 2 135 740 A 1 chambers, this oil will be continuously circulated, and shouldtheoil supply pressurefall belowthe pressure inthetank, indicating an interruption to the oil supply, thetankwill automatically supplyoiltothe separator duetothe pressure difference.

The oil circulating means preferably comprises a static scoop within a compartment& the rotating separatorwhich picks up spinning oilfrom thewall of the compartment and directs ittothe bearing chambers.

Also in a preferred embodimentof the invention each bearing chamberhasa plurality of scavenge openings atdifferent locationsto ensurethatoil is removedfromthe bearing chambers whatever attitude they adopt during aerobatic manoeuvres.

In a further preferred embodimentthe oil tank is provided with a vent at a location on the opposite side of the tank to the conduit means, and which is also arranged to communicate with the interior of the centrifugal separator, to provide an alternative oil supplyfor aerobatic manoeuvres.

The invention will now be more particularly de- scribed with referenceto the accompanying drawings in which:

Figure 1 is a diagrammatic layout of the essential elements of the oil system of the present invention, Figure 2 is an enlarged view of a part of the system go shown in Figure 1, and, Figure 3 shows detail of the arrangement of scoops shown in Figure 2.

Referring nowto the drawings a gas turbine engine 1 has an oil system which includes a tank 2, bearing chambers 3, only one of which is illustrated, a centrifugal separator4, which also acts as a pump, and an oil cooler 5. The bearing chamber 3 is scavenged by means which includes ducting 10 having a main inlet 12 and a plurality of auxiliary inlets 14which communicate with the interior of the chamber at a plurality of locations so that at least one will be supplied with oil whateverthe attitude of the engine in flight. Air under pressure is supplied to the bearing chamberfrom outside the chambervia non-contacting seals 16,the air serving not onlyto prevent leakage of oil from the chamberthrough the seals, but also to provide a pressurised flowto blow the oil from the chamber intothe scavenge ducting 10. The ducting communicating with the bearing cham- bervia inlets 14, includes a restriction 18to prevent excessive airflowsfrom the bearing chamber3when no oil is passing through the inlets.

The scavenge ducting conveysthe air-oil mixture fromthe bearing chamberstothe inlet of the centrifugal separatorwhere it is ejectedthrough nozzles 20 at high velocityto impinge on vanes 22, on the separator, in a direction such asto assistin driving the separator.

The separator itself consists of a main body 24 which is connected to a driving shaft 26for rotation, and includes within it one or more compartments 28 each containing a rigid porous material, for example, the material sold underthetrade name RETIMET (Regd. Trade Mark) by Dunlop Limited.

The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy.

2 GB 2 135 740 A 2 A suitable separator isdescribed in our U.K. Patent No. 1,508,212 so that it is notclescribed in detail. It sufficesto saythatthe air-oii mixtureafter impinging onthevanes22 enters the separatorth rough an inlet aperture30and passes intothe poresofthe porous material which causes itto be rotated so that the oil is urged radially outwardly. The air, being lessdense, passesthrough an airoutlet32 in a radiallyinner region, and escapes from the separator via one or more apertures 34 in the driving shaft. From therethe 75 air is vented from the engine.

The oil onthe otherhand, is now spinning with the radial ly outer wall, of the separator and the only way outisfrom a compartment 36 at the oppositeend of the separator in which is mounted a static scoop 38.

The scoop extends radially outwardlyto a radius at which the centrifugal pressure on the liquid together with its rotational velocity enables the required p;essure to be developed in the oil in the scoop, and 2G the inlet area of the scoop is sized to allow the scoop to 85 collect sufficientflowfor the bearings atthat pressure.

From the scoop 38 the oil passes via a diffuser 39 to the main oil supply ducting 40 leading to the bearing chambers. The diffuser 39 converts the velocity of the oil entering the scoop to pressure. Any oil in excess of 90 thattaken by the scoop wil 1 spill into a second outlet 41, which may be a simple pipe, or a second scoop, Figure 3, and is passed backto the oil tank. The height of the second outlet 41 is arranged such that the pressu re developed at this outlet is corn patible with the pressure in the oil tank as will be explained later.

Turning now to the oil tank 2, compressed air is fed to the tank via a pi pe 42 to ma intain the tan k at a pre-selected pressure, referred to as the first pressure, and a condu it 43 corn m u nicates between the floor of 100 the tank and the second outlet 40 in the separator. The purpose of this is to allow a two way flow of oil between the separator and the tank depending on the pressu res at the two ends of the condu it 43. The tank may need to be vented a rid a vent pipe 44 is provided 105 wh ich passes di rectly to the i nlet of the sepa ratorto vent the ai r overboa rd. The dia meter of the pi pe is kept as small as possible to avoid excessive loss of tank pressurisation air. The vent pipe 44 also provides an additional supply of oil to the separator during 110 invertedflight.

In operation the system acts as follows:

The velocity of the oil entering the scoop 38 in conjunction with the centrifugal pressure due to the depth of the separated oil on the radial ly outer wall of 115 theco partment, generates enough pressure to drive the oil along the supply ducting 40to the bearing chambers 3. The oil is arranged to pass th rough the cooler 5, in the supply ducting 40. After lubricating the bearings, the oil is blown back along the scavenge 120 ducting 10 as an air-oil mixture to the separator inlet, where, after doing work on the vanes 22, it gets caught up in the porous material of the separator in the compartment 28. By doing work on the separatorto assist in driving it the air loses energy and is cooled thus reducing the heat to oil as well as reducing the energy required to drive the separator. The separated oil is re-circulated to the bearings via the scoop 38 as described above. Any excess oil in the compartment will buildup on the outer wall increasing the 130 centrifugal head, and hencethe oil pressure, until it submergesthe second outlet41.The radius of this outlet is arrangedto be such thatwhen the oil reaches it,the centrifugally generated pressure on the outlet is equal tothefirst pressure inthe oil tank. Asthe oil depth continuesto increase on the outerwall of the compartment,the increasing oil pressure atthe second outlet drivesthe oil intothe oil tank.

Ifforany reason, e.g. aerobat[c manoeuvres, less oil returns to the separator, than passes outthroughthe scoop 38,the level of oil on the outerwall of compartment 36will drop and uncoverthe second outlet,thus allowingthe pressurisedcil in the oiltank toflow into, andtop up,the separatorwith oil.The system isthus completely self-regufating and fully aerobatic. Itwill continueto operate even when the tankis empty, provided thatthere is a scavengeflow fromthe bearing chambersto theseparator inlet.

Depending on the pressure in the oil tanka higher pressure may be required atthe second outletthan can be generated bythe centrifugal pressure head alone, so thatthe second outlet may be in theform of a second scoop to take advantage of some or all of the velocity head available in the rotating oil to increase the pressure.

Various additional refinements may be added to the above-described general system. For example, in the separator, another compartment 50 may be provided which has a radial depth greaterthan that of the other compartments 28 and 36, and an orifice 51 is provided to allow oil to enterthe chamber 50 where any foreign matter can collectfor subsequent inspection.

Claims

Also, in the bearing chambers, a radially inwardly facing channel 54 may be provided at a small distance from the radially outerwall thereof, and which is connected to rotating structure in the chamber. On start-up in cold conditions, when the air pressure in the bearing chamber may be insufficieritto blowthe cold viscous oil along the scavenge system,the oil level will build up in the chamber until the oil spills into the rotating channel which will energisethe oil by centrifugal action. Astatic scoop 56 extending into the channel and connected to direct oil straight into the scavenge ducting will thus drivethe oil backto the separator. Asthe oil warms upthe pressurisation air will increasingly take overthe scavenging function and the oil level will drop until no oil remains in the channel. As an alternative to the static scoop 56the oil from the channel can be passed through apertures in the base of the channel to a diffusing scroll leading to the scavenge ducting. CLAIMS

1. A gas turbine engine oil system comprising a tank, a centrifugal separator, and scavenge means for removing oil from the bearing chambers and directing itto the centrifugal separator, characterised in that the tank is pressurised to afirst pressure by airfrom the engine, conduit means are provided for conveying oil from the interior of the tankto the interior of the centrifugal separator, oil circulating means are provided for directing at least a portion of the oil passing through the separatorto the engine bearing chambers under centrifugal action and at a pressure greaterthan said first pressure, and means are provided for directing excess oil not used bythe oil circulating Al 4 iw - 3 GB 2 135 740 A 3 means, and ata pressure higher than the first pressure, backto the tank.

2. A gas turbine engine oil system as claimed in Claim 1 and in which the oil circulating means comprises a static scoop disposed within a compartment of the rotating separator and arranged to collect oil from adjacent the radial ly outer wall of the compartment.

3. A gas turbine engine oil system as claimed in Claim 2 and in which the scoop includes a diffuser.

4. A gas turbine engine oil system as claimed in Claim 2 and in which the means for directing excess oil back to the tank comprises a second outlet from the compartment containing the scoop, and which is arranged to collect oil from adjacentthe radially outer wall of the compartment but at a radius less than that of the scoop.

5. A gas turbine engine oil system as claimed in any preceding claim and in which each of the bearing chamber scavenge means comprises a plurality of scavenge openings atclifferent locations to ensure that oil is removed from the bearing chambers whatever attitude they adopt during operation.

6. A gas turbine engine oil system as claimed in any preceding claim and in which the oil tank is provided with a vent at a location on the opposite side of the tank to the conduit means, and which is also arranged to communicate with the interior of the centrifugal separator.

7. A gas turbine engine oil system as claimed in any preceding claim and in which the scavenge means comprises a radially inwardlyfacing annularchannel connected to rotating structure in the bearing chamber and positioned closeto the outerwall of the bearing chamber, and meansfor directing oil collecting in the annularchannel to an outletfirom the bearing chamberwhich communicates with the centrifugal separator.

8. A gas turbine engine oil system as claimed ill Claim 7 and in which a static scoop positioned close to the radial ly outer wall of the cha nnei constitutes the means for directing oil collecting in the channel to the outlet.

9. A gas turbine engine oil system substantially as hereinbefore more particularly described with referenceto the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office, 8818935, 8184, 18996. Published at the Patent Office, 25 Southampton Buildings, London WC2A lAY, from which copies may be obtained.