GB2519977A

GB2519977A - Centrifugal oil and air separator for a gas turbine engine

Info

Publication number: GB2519977A
Application number: GB1319397.4A
Authority: GB
Inventors: Robert Thies
Original assignee: Rolls Royce Deutschland Ltd and Co KG
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 2013-11-04
Filing date: 2013-11-04
Publication date: 2015-05-13
Anticipated expiration: 2033-11-04
Also published as: GB2519977B; GB201319397D0

Abstract

An arrangement for separating oil particles from vent air in a gas turbine comprises a hollow shaft 2 defining a volume 22 having an inlet 20 through which air with entrained oil particles enters the volume 22 and an outlet through which, in use, air substantially free of entrained oil leaves the volume. The radially inner surface of the volume 22 may be provided by a hollow tube 12 which provides the outlet. The volume has an oil separator (breather) body 10, eg of wire mesh or metal foam, between the inlet and the outlet and through which the air passes, the separator body being attached to the hollow shaft 2 through a geared drive system, eg a planetary gear drive 100 so that the separator body 10 rotates faster than the shaft 2. The planetary gear drive 100 has a planetary outer ring (4, fig.2) driven by the shaft 2 and driving planet gears 6 which in turn drive a centre (sun) gear (9) which carries the breather drive arm 8.

Description

Centrifugal Oil and Air Separator for a Gas Turbine Engine The invention relates to a centrifugal oil separator arrangement for a gas turbine engine for separating the oil particles contained in vent air.

In order to avoid excess air pressure in the oil tank, the gearbox and the bearing chamber of a gas turbine have a venting arrangement integrated into the lubrication system. However, the air in the bearing chamber and gearbox contains entrained oil particles which must be removed as completely as possible from the air flow before the air is discharged to the atmosphere to both keep oil losses and the disadvantageous consequences of high oil consumption low and minimise the negative effects of air with high oil content entering the environment.

Centrifugal separators that are used to separate the oil from the air are known and use a porous metallic foam to arrest the oil and separate it from the airflow. These separators are known as breathers and are driven directly from the low pressure, or fan, shaft in an aero engine. The speed of rotation of the breathers and consequently its separation capacity is set by the rotational speed of the shaft.

Modern, and future engines, have larger fan diameters than those typically used in the past and concomitantly slower rotational speeds. Higher volumes of breather material may be used to improve the quality of separation but this adds to the weight of the engine and as there is finite space available within the complex engine there is a limit to the amount of material that can be used.

Bearing chamber seals could be improved to limit the volume of oil that needs to be separated from the air but more complex seals are likely to be heavier and more expensive to manufacture.

It is an object of the present invention to seek to provide an improved separator arrangement for separating oil from air in a gas turbine engine.

According to a first aspect of the invention there is provided an air and oil separator arrangement for a gas turbine for separating oil particles entrained in an air flow, the arrangement comprising: a hollow shaft defining a volume having an inlet through which, in use, air with entrained oil particles enters the volume and an outlet through which, in use, air substantially free of entrained oil leaves the volume, the volume having an oil separator body between the inlet and the outlet and through which the air passes, characterised in that the separator body is attached to the hollow shaft through a geared drive system.

The term "geared drive system" in this context means a drive system which offers a gearing ratio greater than 1:1. Advantageously, this allows the separator body to rotate at a faster speed than the hollow shaft and provide improved separation of the oil from the air flow.

Preferably the radially outer surface of the volume is provided by the hollow shaft.

The geared drive system and the separator body are advantageously located within the hollow shaft providing a good utilisation of space.

The radially inner surface of the volume is defined by a hollow tube with an orifice providing the outlet. The hollow tube may also provide support to the geared drive system. It is desirable that the tube does not rotate with the shaft or the drive system and is preferably isolated from both by respective bearing sets. The hollow tube may be attached to a static engine casing at the rear of the engine.

Preferably the geared drive system is a planetary gear drive. Advantageously, the radially inner surface of the hollow shaft has an outer ring gear attached to or otherwise integrated on its radially inner surface. One or more planet gears may be located between the outer ring and a centre gear supporting the separator body. The centre gear may be supported by the hollow tube through a bearing.

Preferably a support plate is mounted to the hollow tube to carry the planet gears.

Advantageously, the hollow tube may act to react torque and axial loads and can have one or more openings that permit air separated from the oil to enter the bore of the tube and be transferred along the tube to a vent at the rear ot the tube. The vent may open to the ambient air outside the engine or preferably to the engine thrust exhaust. Further forces and moments may be applied from the torque tube through the gearing into the shaft The separator body may have a carrier which connects to the centre gear through a conical drive arm having a smaller diameter at the gear and a larger diameter at the carrier. The drive arm may be closed i.e. a solid surfaced cone that prevents the passage of oil. Alternatively, the separator body may have a carrier which connects to the centre gear through a plurality of drive arms spaced around the periphery of the carrier and the periphery of the centre gear.

Preferably the shaft has a flow passage to supply oil separated in the separator body to the geared drive system.

The shaft may be a fan shaft. The separator body may comprise a porous metallic foam.

According to a second aspect of the invention there is provided a planetary drive system for a gas turbine engine air and oil separator for separating oil particles entrained in an air flow, the system comprising: a hollow fan shaft having an outer ring gear on its radially inner surface, a centre gear having a drive arm supporting a separator body, and one or more planetary gears between the outer ring gear and the centre gear.

The invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 depicts a geared breather within a hollow drive shaft; Fig. 2 depicts the geared drive system of Fig. 1 in greater detail Figure 1 depicts a geared breather within a gas turbine engine. The arrangement has a hollow drive shaft 2 and a tube 12, attached statically to an engine casing 25.

A planetary gear drive 100 attached to the static tube drives a rotary oil breather 10.

A vent 20 allows air, which can contain oil particles, from a gearbox or bearing chamber of the engine past the drive shaft 2 into the volume 22. The air passes through the oil breather 10 separation material where the oil particles are removed from the air and into the tube 12 which delivers the separated air to the rear of the engine where it is vented to ambient. Passages 34 are provided in the tube 12 for the transfer of separated air into the tube bore. Oil separated from the air is returned to the bearing chambers through a conduit 24 or used to lubricate the gear drive 100.

A seal 26, located behind volume 22, seals between shaft 2 and tube 12 preventing the escape of oil containing air from the separator volume 22. Further supports 30 between the shaft 2 and the tube 12 may be provided in addition or to replace the support 28, which may be provided with a seal element 27 between the support element and the hollow shaft. The front of the volume is closed by a cover 32 which is fixed to and rotates with the shaft 2.

The oil breather is mounted to an annular drive arm 8 located by a piston ring or locking plate 16, which is attached in a goove of the axial extension of the annular drive arm 8onto which the breather element 10 is mounted. The breather is cylindrical and the axially extension of the annular drive arm 8 has a number of apertures that direct captured oil from the breather element 10 onto the radially inner wall of the shaft 2 and subsequently through conduit 24 into the bearing chamber.

The breather element 10 is preferably a wire mesh or other porous material which can capture the oil elements and separate them from the air flow. A suitable material is a metal foam, sold under the trade name RETIMETTM, by DuPont and is sufficiently robust to withstand the rotational and temperature conditions required yet can be formed into an appropriate shape.

The radially outer surface of the drive arm 21 is provided with a seal 21 of an appropriate form which, in the embodiment shown in Fig. 2 is located at the fore end of the axial extension and is provided within an annular cavity in the radially inner surface of the drive shaft 2.

The breather element is preferably cylindrical and coaxially arranged to rotate about the centreline of the engine 1. As the vent air enters the chamber 22 and passes through the breather element 10 a rotation of the air is induced which advantageously moves the oil particles away from the central tube 12 by centrifugal force and improves the oil separation from the vent air. In conventional separators the speed of rotation of the breather element is limited requiring larger volumes of material to generate sufficient separation capability. It is to be appreciated that larger volumes of material add weight to the engine and can require undesired structural changes in order to provide a sufficiently large volume to contain the separation material.

The drive arm carrying the separation material is part of a planetary gear drive that is driven from the shaft 2. The gear drive is geared to allow the separator body lOto be driven significantly faster than if it was driven directly from the shaft 2.

Advantageously, the gear drive can be located in a currently under-utilised volume within the gas turbine making an efficient use of the space available. Where the shaft 2 is a fan shaft the planetary gear system allows the breather material to rotate at a sufficiently high velocity to separate the oil even if the speed of rotation of the fan shaft is reduced as may be required for large fan diameters used by current and future engines.

The gear system is shown in more detail in Figure 2. A planetary outer ring 4 is mounted to and driven by the shaft 2. The ring has a plurality of gear teeth on its radially inner surface which drive planet gears 6 that are held in position by a spindle 18 secured to a front plate 14. The front plate is carried by the tube 12 which is supported by bearing 28 to the shaft 2 and also to the rear casing of the engine (not shown). A centre gear 9 carries the breather drive arm 8 and is driven by the planet gears 6. A bearing 11 supports the radially inner surface of the centre gear 9 and prevents the rotational movement of the centre gear being transmitted to the tube 12.

Advantageously, the support fastener 13, washer 17 and anti-rotation pin 19 which mounts the front plate 14 to the tube 12 closes the front end of the tube to ensure that the air entering the tube does not escape forward into the volume 23 between the front plate and the front cover. It is desirable that the planetary gear drive permits a flow of air between volumes 22 and 23 to equalise their relative pressures. The anti rotation pin helps to restrict rotation of the front plate 14 that could result in the component releasing from the tube 12.

It will be appreciated that the arrangement offers a number of advantages. In particular the ability to drive the air and oil separation material at a higher velocity allows the amount of separator material used to be reduced whilst still maintaining an adequate separation. The reduction in material saves both weight and cost. The location of the drive system within a hollow shaft allows optimal utilisation of space.

The high efficiency of the separation means that essentially oil free air is discharged to the outside of the engine, neither constituting a danger to health by inhalation or skin contact nor producing visible, fog-like, oil mist contaminating the exterior of the engine nacelle or the aircraft.

Claims

CLAIMS1. An air and oil separator arrangement for a gas turbine for separating oil particles entrained in an airflow, the arrangement comprising: a hollow shaft defining a volume having an inlet through which, in use, air with entrained oil particles enters the volume and an outlet through which, in use, air substantially free of entrained oil leaves the volume, the volume having an oil separator body between the inlet and the outlet and through which the air passes, characterised in that the separator body is attached to the hollow shaft through a geared drive system.
2. An air and oil separator according to claim 1, wherein a radially outer surface of the volume is provided by the hollow shaft.
3. An air and oil separator according to claim 1 or claim 2, wherein a radially inner surface of the volume is defined by a hollow tube with an orifice in the hollow shaft providing the outlet.
4. An air and oil separator arrangement according to any preceding claim, wherein the geared drive system is a planetary gear drive.
5. An air and oil separator according to claim 4, wherein the planetary gear drive has an outer ring gear on a radially inner surface of the hollow shaft.
6. An air and oil separator according to claim 5, wherein the planetary gear drive has one or more planet gears between the outer ring and a centre gear supporting the separator body.
7. An air and oil separator according to claim 6, when dependent on claim 2, wherein the centre gear is supported by the hollow tube through a bearing.
8. An air and oil separator according to claim 7, wherein the hollow tube provides a load path that transmits torque and axial loads to the engine casings and further forces and moments are applied from the hollow tube through a support bearing into the hollow shaft.
9. An air and oil separator according to claim 7 or claim 8, wherein a support plate is mounted to the hollow tube to carry the planet gears.
10. An air and oil separator according to any of claims 6 to 9, wherein the separator body has a carrier which connects to the centre gear through a conical drive arm having a smaller diameter at the gear and a larger diameter at the carrier.
11. An air oil separator according to claim 10, wherein the tapering portion of the conical drive arm provides a non-porous shield.
12. An air and oil separator according to any of claims 6 to 9, wherein the separator body has a carrier which connects to the centre gear through a plurality of drive arms, spaced around the periphery of the carrier and the periphery of the centre gear.
13. An air and oil separator according to any preceding claim, wherein the shaft has a flow passage to supply oil separated in the separator body to the geared drive system.
14. An air and oil separator according to any preceding claim, wherein the shaft is a fan shaft.
15. An air and oil separator according to any preceding claim, wherein the separator body comprises a porous metallic foam.
16. A planetary drive system for a gas turbine engine air and oil separator for separating oil particles entrained in an airflow, the system comprising: a hollow fan shaft having an outer ring gear on its radially inner surface, a centre gear having a drive arm supporting a separator body, and one or more planetary gears between the outer ring gear and the centre gear.