US20100028127A1

US20100028127A1 - Turbine engine lubrication method and system

Info

Publication number: US20100028127A1
Application number: US12/518,665
Authority: US
Inventors: Albert Cornet; Nicolas Raimarckers
Original assignee: Techspace Aero SA
Current assignee: Safran Aero Boosters SA
Priority date: 2006-12-12
Filing date: 2007-12-10
Publication date: 2010-02-04
Also published as: EP1933077B1; CA2671839A1; CA2671839C; WO2008071651A3; WO2008071651A2; EP1933077A1; ATE467080T1; DE602006014177D1

Abstract

A method and a system for lubricating a turbomachine including an oil tank, an oil feed pump, an oil/air separator, and at least two enclosures closed by air flow rate seals, each including a low outlet and housing shaft-supporting rolling bearings. The method injects oil from the tank into the enclosures by the pump to lubricate the bearings, introduces compressed air at a low flow rate into the enclosures via the seals to pressurize the enclosures, recuperates all of the air and the oil introduced into the enclosures via their low outlet, uses gravity and the pressurization of the enclosures to convey the oil/air mixture as recovered in this way to the oil/air separator, separates the oil and the air of the mixture by the oil/air separator, returns the oil to the tank, and exhausts the air to outside the turbomachine.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the general field of lubricating an aviation turbomachine.
An aviation turbomachine has numerous elements that need to be lubricated; these include in particular rolling bearings used for supporting the rotary shafts, and also the gearing, of the accessory drive gearbox.
In order to reduce friction, wear, and heating due to the high speed of rotation of the turbomachine shafts, the bearings that support them need to be lubricated. Since providing lubrication merely by injecting oil during maintenance of the turbomachine is not sufficient, use is generally made of so-called “dynamic” lubrication.
Dynamic lubrication consists in causing oil to circulate continuously in a lubrication circuit. A flow of lubricating oil from a tank is thus delivered to the bearings by a pump, which bearings are housed in enclosures that are closed by seals. In order to avoid lubricating oil leaking from the enclosures to the remainder of the turbomachine via the seals, a flow of air is taken from one of the compressors of the turbomachine and is injected through the seals. The enclosures are thus pressurized at a pressure higher than atmospheric pressure.
The major fraction of the air introduced into the enclosures is then exhausted to the outside of the turbomachine by following a special circuit designed to de-oil the air and to control the pressure inside the enclosures. The lubricating oil injected into the enclosures is recovered from the bottoms thereof by recovery pumps via another special circuit. In order to ensure that the enclosure is completely dry, a small fraction of the air is also sucked out by these pumps and the oil/air mixture as recovered in this way needs to be separated before the purified oil can be returned to the tank.
An example of such a lubrication system for a turbomachine is described in particular in document EP 0 513 957. That system presents numerous drawbacks. In particular, it requires a large number of recovery pumps to be used (one pump per enclosure), thereby increasing the weight of the turbomachine. It also requires a non-negligible quantity of air to be taken from one of the compressors of the turbomachine in order to pressurize the enclosures, and that is penalizing in terms of the specific fuel consumption of the turbomachine. Finally, it consumes a large amount of lubricating oil because the efficiency of de-oiling is a decreasing function of air flow rate.
U.S. Pat. No. 4,525,995 discloses a system for lubricating the front enclosure of a turbomachine in which the oil/air mixture injected into the enclosure flows into the accessory drive gearbox, which gearbox contains at its outlet a recovery pump and an oil/air separator. That system also presents numerous drawbacks. In particular it requires a pump to be present for recovering the oil/air mixture, thereby increasing the weight of the turbomachine. Furthermore, that system applies only to the front enclosure of the turbomachine, with nothing being provided for lubricating other enclosures of the engine.

OBJECT AND SUMMARY OF THE INVENTION

A main object of the present invention is thus to mitigate such drawbacks by proposing a lubrication method that is simplified, light in weight, and consumes little oil or compressed air.
This object is achieved by a method of lubricating a turbomachine comprising: at least two distinct enclosures closed at their ends by low air flow rate seals, having low outlets and containing rolling bearings for supporting shafts; an oil tank; an oil feed pump; and an oil/air separator, the method consisting, in accordance with the invention, in injecting the oil from the tank into the enclosures by means of the pump in order to lubricate the bearings; introducing compressed air at a low flow rate into the enclosures through the seals in order to pressurize said enclosures; recuperating all of the air and the oil introduced into the enclosures via their low outlet; using gravity and pressurization of the enclosures by the air introduced therein to convey the oil/air mixture as recovered in this way to the oil/air separator; separating the oil and the air of said mixture by means of the oil/air separator, the operation of the oil/air separator being controlled so as to be triggered only when oil is present at its inlet; returning the oil to the tank; and exhausting the air to outside the turbomachine.
The use of gravity and the pressurization of the enclosures for recovering all of the injected oil and oil makes it possible to avoid having recourse to recovery pumps such as those disclosed in the prior art. In addition, all of the oil and air injected into the enclosures is recovered via a single common air and oil circuit, thereby avoiding having recourse to a special circuit for removing and de-oiling the air introduced into the enclosures as described in the prior art. The method of lubrication is thus lighter and simpler.
According to the invention, the method consists in controlling the operation of the oil/air separator so as to operate it only when oil is present at its inlet. Controlling the oil/air separator thus makes it possible to save power.
In an advantageous disposition, the method also consists in controlling the operation of the oil feed pump to regulate the flow rate of oil conveyed to the enclosures as a function of the pressure and/or the temperature inside the enclosures. For this purpose, the oil feed pump may be started only when the temperature inside the enclosures rises above a given temperature. Controlling the pump makes it possible to avoid feeding the enclosures with oil when the oil/air mixture is no longer being recovered by gravity.
Preferably, the method further consists in cooling the oil prior to conveying it to the enclosures.
The present invention also provides a turbomachine lubrication system, characterized in that it comprises at least two distinct enclosures closed at their ends by low air flow rate seals and housing rolling bearings for supporting shafts; an oil tank; an oil feed pump for feeding the enclosures with lubricating oil from the tank; means for introducing compressed air at a low flow rate into the enclosures through the seals in order to pressurize them; means for recovering under gravity and under the effect of the enclosures being pressurized, all of the air and the lubricating oil introduced into the enclosures; an oil/air separator for separating the oil and the air of the mixture; means for controlling the operation of the oil/air separator; means for returning the oil to the tank; and means for exhausting the air to outside the turbomachine.
Preferably, the lubrication system further comprises means for controlling the operation of the oil feed pump.
According to another advantageous characteristic, the oil/air separator includes a pumping function to assist sucking the oil/air mixture recovered from the enclosures and returning the oil to the tank.
According to yet another advantageous characteristic, the oil feed pump and/or the oil/air separator are electrically driven.
The invention also provides a turbomachine including a lubrication system as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appear from the description below made with reference to the accompanying drawings that show an embodiment having no limiting character. In the figures:

FIG. 1 is a diagrammatic longitudinal section view of a turbomachine showing the environment of the invention; and

FIG. 2 is a diagram showing the flow of oil and air in an aviation bypass turbomachine in application of the method of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 is a diagram showing a portion of an aviation bypass turbomachine 2 in which the lubrication method and system of the invention can be implanted. Naturally, the present invention applies to any other type of turbomachine (single spool, triple spool, single-flow, industrial, etc.).
In well-known manner, the turbomachine 2 of longitudinal axis X-X comprises in particular a fan casing 4, a low-pressure spool 6, a high-pressure spool 8, a combustion chamber 10, and an accessory drive gearbox 12.
The low-pressure spool 6 comprises a low-pressure shaft 14 centered on the longitudinal axis X-X, a fan 16 mounted at the front end of the low-pressure shaft, a low-pressure compressor 18 fastened to the fan, downstream therefrom, and a low-pressure turbine 20 mounted on the rear end of the low-pressure shaft.
The high-pressure spool 8 comprises a high-pressure shaft 22 disposed concentrically around the low-pressure shaft 14, a bevel gear 24 mounted at the front end of the high-pressure shaft, the high-pressure compressor 26 mounted on the high-pressure shaft downstream from the gear 24, and a high-pressure turbine 28 mounted on the rear end of the high-pressure shaft.
For reasons of clarity, the various compressors and turbines of the high- and low-pressure spools of the turbomachine are represented in FIG. 1 as having blades in single stages. Naturally, and in well-known manner, these elements could have blades in several stages.
The accessory drive gearbox 12 comprises an angle transmission box 12 a and the accessory drive gearbox 12 b proper, these units being fastened under the fan casing 4, e.g. on a bottom face 4 a thereof. The accessory drive gearbox 12 b is generally driven by the high-pressure shaft 22 via an intermediate shaft 30 carrying a bevel gear 32 at its top end and a bevel gear 34 at its bottom end.
In order to withstand the radial and axial loads, the low- and high- pressure shafts 14 and 22 of the turbomachine are supported by rolling bearings (ball bearings or roller bearings). Thus, the low-pressure shaft 14 is supported at its front end by a front bearing 36 a and at its rear end by a rear bearing 36 b. Similarly, the high-pressure shaft 22 is supported at its front end by a front bearing 38 a and at its rear end by a rear bearing 38 b.
In order to reduce friction, wear, and heating, due in particular to the high speeds of rotation of the shafts of the turbomachine, the front and rear bearings 36 a & 38 a and 36 b & 38 b need to be lubricated by continuously injecting oil between the rings of these bearings via injection nozzles (not shown in the figures).
In order to prevent the lubricating oil that is injected in this way escaping from the turbomachine, the front bearings 36 a and 38 a and the rear bearings 36 b and 38 b are confined in respective front and rear enclosures 40 a and 40 b. These enclosures 40 a and 40 b are distinct from each other and they are hermetically closed at their upstream and downstream ends by annular seals 42 a, 42 b.
The seals 42 a, 42 b are leaktight with low air flow rates. For example they may be dynamic gaskets on cushions of air (also referred to as carbon gaskets with lift). By way of example, reference can be made to European patent application EP 1 055 848 which describes such gaskets. This type of gasket is particularly good at withstanding leaks, even when the enclosures are at slightly raised pressures and they essentially comprise labyrinth seals together with a static ring of carbon segments associated with a rotary surface having grooves for creating lift.
Each enclosure 40 a, 40 b includes in its bottom (or low) portion a specific outlet 44 a, 44 b enabling the oil/air mixture injected into the enclosure to be recovered in a manner that is described below.
The method of lubricating such a turbomachine in accordance with the invention is described below with reference in particular to FIG. 2, which is a highly diagrammatic representation of the oil and air flow in the turbomachine described with reference to FIG. 1.
In FIG. 2, lines referenced O represent a flow of lubricating oil, lines referenced A represent a flow of air, and lines referenced O/A represent a flow of an oil/air mixture.
Still in FIG. 2, there can be seen in addition to certain elements of FIG. 1, a lubricating oil tank 46, an oil feed pump 48 (e.g. of the electrically driven type), an oil/air separator 50 (e.g. of the electrically driven type), and an oil cooler device 52. In known manner, these elements are generally fastened under the turbojet, e.g. against the accessory drive gearbox 12. For reasons of clarity in FIG. 2, these elements 46 to 52, the accessory drive gearbox 12, and the turbomachine are nevertheless shown as being spaced apart from one another.
The method of the invention consists in particular in injecting oil of from the tank 46 into each of the enclosures 40 a and 40 b of the turbomachine by means of the feed pump 48, the oil being for lubricating the rolling bearings.
A flow of compressed air A is also introduced into the enclosures 40 a and 40 b via seals to pressurize these enclosures (this flow of air being taken for example from the high-pressure compressor of the turbomachine). Since the enclosures are closed by low air flow rate seals, it suffices to inject air at a low flow rate into the enclosures in order to pressurize them.
All of the air and the oil as introduced in this way into the enclosures 40 a and 40 b is then recovered via their low outlets 44 a and 44 b. The oil/air mixture O/A is conveyed merely under gravity and under the effect of the enclosures being under pressure to the oil/air separator 50 that is situated below the enclosures.
In practice, the oil/air mixture O/A recovered from the front enclosure 40 a can be taken to the oil/air separator by flowing along a removal pipe (not shown in the figures) that runs parallel to the intermediate shaft 30 for driving the accessory drive gearbox 12 and leading to the separator.
Likewise, the oil/air mixture O/A recovered from the rear enclosure 40 b can be conveyed to the oil/air separator by flowing along another removal pipe (not shown in the figures) that is incorporated in an arm of the turbomachine structure and that opens out into the separator.
Recovery of all of the oil/air mixture by gravity and under the effect of the enclosures being pressurized is made possible in particular by the fact that the pressure inside the enclosures is greater than the pressure in the separator and the separator is situated lower than the enclosures.
The oil/air mixture O/A is introduced into the separator 50 in order to separate the oil from the air, the purified oil then being returned to the tank 46. An oil cooler device 52 located downstream from the pump 48 serves to cool the purified oil (alternatively, the oil cooler device could be interposed between the separator 50 and the tank 46). The air that is recovered at the outlet from the separator is exhausted to outside the turbomachine.
The oil/air separator 50 may be of the dynamic type, i.e. operating on the principle of dynamically centrifuging the oil/air mixture in order to recover the oil and the air separately. Alternatively, the oil/air separator could be of the static type.
The oil/air separator 50 may incorporate a pumping function to assist in sucking in the oil/air mixture O/A recovered from the bottom portions of the enclosures and in order to deliver purified oil to the tank. Such a function may be made necessary if the pressure in the enclosures is too small or if the tank 46 is at an unsuitable height relative to the separator 50.
In an advantageous disposition of the invention, provision is made to control the operation of the oil/air separator 50 so as to trigger such operation only when oil is present at its inlet. For this purpose, an oil presence detector 50 a can be mounted at the inlet to the separator and coupled to its electrical power supply (when the separator is of the electrically driven type).
The oil/air separator can be controlled because it is electrically driven and thus powered independently of the speed of operation of the turbomachine. By means of such control, it is possible to guarantee that the oil/air mixture is removed from the enclosures and that purified oil is returned to the tank regardless of the operating speed of the turbomachine. Controlling the separator also makes it possible to save power when the separator is not powered continuously.
In another advantageous disposition of the invention, provision can also be made to control the operation of the oil feed pump 48 to regulate the flow rate of oil delivered to the enclosures as a function of the pressure and the temperature inside the enclosures. Controlling the pump makes it possible to avoid feeding oil to the enclosures when the oil/air mixture is no longer being recovered by gravity.
In practice, the operation of the oil feed pump can be controlled by starting the pump directly on the basis of the oil pressure measured inside the enclosures. Alternatively, the pump may be triggered solely above a given temperature inside the enclosures (sensed by appropriate measurement devices).
It should be observed that the oil feed pump may be controlled independently of or together with the above-described control of the oil/air separator.
It is also possible to observe that the lubrication method as described above can also be applied to lubricating the gearing of the accessory drive gearbox 12.
As shown in FIG. 2, the lubricating oil of from the tank 46 is injected via a feed pump 48 into the angle transmission box 12 a and the accessory drive gearbox 12 b proper. In addition, a flow of air A taken from the front enclosure 40 a is taken to these units 12 a and 12 b in order to pressurize them. After lubricating the gearing in the unit 12 a and 12 b, the oil flows to a low point thereof. Under the effect of these units being pressurized, the oil/air mixture that is formed is then discharged via a low outlet 54 to be conveyed to the inlet of the oil/air separator 50 and thus return to the lubrication circuit of the turbomachine.

Claims

1-9. (canceled)

10. A method of lubricating a turbomachine including at least two distinct enclosures closed at their ends by low air flow rate seals, low outlets and containing rolling bearings for supporting shafts, an oil tank, an oil feed pump, and an oil/air separator, the method comprising:

injecting oil from the tank into the enclosures by the oil feed pump to lubricate the bearings;

introducing compressed air at a low flow rate into the enclosures through the seals to pressurize the enclosures;

recuperating all of the air and the oil introduced into the enclosures via their low outlet;

using gravity and pressurization of the enclosures by the air introduced therein to convey the oil/air mixture as recovered in this way to the oil/air separator;

separating the oil and the air of the mixture by the oil/air separator, operation of the oil/air separator being controlled so as to be triggered only when oil is present at its inlet;

returning the oil to the tank; and

exhausting the air to outside the turbomachine.

11. A method according to claim 10, further comprising controlling operation of the oil feed pump to regulate the flow rate of oil conveyed to the enclosures as a function of pressure and/or temperature inside the enclosures.

12. A method according to claim 11, wherein the oil feed pump is started only when the temperature inside the enclosures rises above a given temperature.

13. A method according to claim 10, further comprising cooling the oil prior to conveying the oil to the enclosures.

14. A turbomachine lubrication system comprising:

at least two distinct enclosures closed at their ends by low air flow rate seals and housing rolling bearings for supporting shafts;

an oil tank;

an oil feed pump for feeding the enclosures with lubricating oil from the tank;

means for introducing compressed air at a low flow rate into the enclosures through the seals to pressurize the enclosures;

means for recovering, under gravity and under effect of the enclosures being pressurized, all of the air and the lubricating oil introduced into the enclosures;

an oil/air separator for separating the oil and the air of the mixture;

means for controlling the operation of the oil/air separator;

means for returning the oil to the tank; and

means for exhausting the air to outside the turbomachine.

15. A system according to claim 14, further comprising means for controlling operation of the oil feed pump.

16. A system according to claim 14, wherein the oil/air separator includes a pumping function to assist sucking the oil/air mixture recovered from the enclosures and returning the oil to the tank.

17. A system according to claim 14, wherein the oil feed pump and/or the oil/air separator are electrically driven.

18. A turbomachine, comprising a lubrication system according to claim 14.