1 Title: Labyrinth screw sealing for aero engine application
2 Field of the Invention
The invention relates to a bearing sealing arrangement for an aero engine
and more particularly to an Auxiliary Power Unit (APU) sealing using a
labyrinth screw.
3 Background of the Invention
Aero engine rotor system is supported through bearings which reduces the
friction between the components in contact‘ Further reduction in friction is
achieved by using lubricants. These lubricants gets retained within the
bearings. Lubricant leakage results in increased friction, bearing failures
and contamination of nearby components. This necessitates the usage of
a seal to keep the lubricants within the bearings.
Different sealing arrangements are available. Contact type seals such as
lip seals are one of the examples of the seals used. The wear experienced
by these type of seals make them not desirable for cases where the
diameter is large. The replacement of worn out seals is difficult and costly.
Sub dividing or segment the seal helps to ease the difficulties associated
with the replacement, but this aggravated the leakage issues by
introducing a weak zone for leakage in the segment joints.
Labyrinth seals are the alternate to the contact type seals discussed
earlier. They are used to reduce / eliminate the undesired oil leakage
between cavities of an aero engine. The precise manufacturing tolerances
makes it not economically practical to employ the labyrinth seals for large
diameter applications. The working of labyrinth seal is by forming vortices
against the fluid flow to greatly reduce fluid leakage. This is achieved by
maintaining pressure difference between the two cavities separating the pressure developed‘across the labyrinth seal reduces, for example idle
condition of engine operation, oil leakage increase.
These problems are addressed by introducing a labyrinth screw to seal the
oil leakage in an aero engine by pumping the oil back to the bearing.
3.1 Prior Art
Patent no. 3347554 disclosed a lip sealing with a pair of frustoconical
surfaces. Helical pumping ribs are provided to seal the fluid. The problem
associated with the design is that the pumping capacity is reduced with
increased wear.
Patent no. 4094519 disclosed an oil seal and the ribs used for pumping
are bilge- shaped, Each of the pumping ribs is defined by a pair of curved
side faces meeting with each other to define a curved working edge. The
reduction in pumping capacity with wear is addressed through this design‘
However manufacturing of these ribs are extremely difficult.
4 Brief Summary of the Invention
It is therefore an object of the present invention is to provide an improved
dynamic sealing arrangement for aero engine application. Another object
of the invention is to provide a sealing arrangement with improved
dynamic sealing performance. Another object of the invention is to provide
an oil seal with manufacturing easiness.
These objects are achieved according to the current invention wherein the.
labyrinth screw seal is introduced. A labyrinth screw seal (11) returns the
fluid that escapes from the bearings (9) back to the bearings (9). The
arrangement is particularly useful in aero engine application.
Present design addressed the problems associated with prior arts. The wear and manufacturing difficulties are addressed through the labyrinth
screw sealing design. The introduction of an abradable coating made of NiCrAIY undercoat of thickness 0.2 mm and a carbide projection of 0.6mm thickness reduced the wear‘ The difficulty in manufacturing of bilge
shaped ribs is that the accuracy of positioning trimming knife for trimming
the sealing lips is having a tolerance of 0.2-0.3 mm. This requirement is
eliminated in the present invention through the design of saw teeth of
helical construction which doesn’t require the trimming knife.
These features and advantages of the invention, as well as other features
and advantages thereof, will become apparent from the following
description.
5 Detail Description of the Drawings
The invention with its advantages is illustrated with reference to Figures 1.
2 and 3.
Figure 1 represents the APU.
Figure 2 shows the incorporated new bearing sealing arrangement by
introducing labyrinth screw.
Figure 3 shows the labyrinth screw arrangement.
6 Detail Description of the Invention
The preferred embodiments of the present invention will be hereafter
described in detail with reference to the accompanying drawings.
Figure 1 is an illustration of a gas turbine engine with a seal assembly of
the current invention. The view in Figure 1 is a longitudinal sectional view
along an engine center line. Figure 1 shows gas turbine engine including a
gear box (1), an air intake (2), a compressor (3), a combustor (4), turbines
(5), and exhaust (6).
A shaft (10) supported by the bearing (9) for rotation is shown in Figure 2. Gas turbine engine rotor and stator components interface on bearings (9). The arrangement for oil supply to the bearing is through a pipe line (7) and
pipe line (8) is the oil outlet. A group. of seals (11) on either side of the bearing (9) prevents the escape of lubricant from the bearing. Each group
of seals uses a labyrinth screw sealing (11) as shown in Figure 2 which
represents the present invention. It consists of a labyrinth screw (15) on
the rotor (13) and an abradable coating (14) on stator (12) as seen in
Figure 3.
Labyrinth screw (15) is having a plurality of saw teeth (16) to ensure that it
captures the advantages of labyrinth as well as screw‘ The saw teeth is of
helical construction with saw shaped cross section. Abradable coating (14)
is made of NiCrAIY undercoat of thickness 0.2 mm and a carbide
projection of 06 mm thickness.
The advantages of using a labyrinth screw sealing for aero-engine are
listed below:
0 Labyrinth screw seal pumps the fluid back to the bearings due to
the pumping action of screw.
- Labyrinth screw seal produces region of higher pressure within the
seal arrangement itself and reduces the passage of oil across the
seal.
The labyrinth seal requires the arrangement of two cavities with differential pressure between them -for effective sealing. This is achieved by air venting from higher pressure zone to one of the cavities. Labyrinth screw seal reduces this requirement of higher pressure air, thus making this air available for higher engine thrust
and efficiency.
- Viscous fluids produce foam due to turbulence of flow in various seals and measures are to be taken to address this issue. However in labyrinth screw seals, the fluid flow is in axial direction without turbulence and hence no foaming.
. The fluid is pumped without any decrease in flow rate independent
of viscosity.
. The flow doesn't pulsate much and is typically very even‘ This
reduces losses in the flow.
- Operates better in sub-idle condition compared to labyrinth seals
which experience problems at ground idle conditions where the
delta pressure developed across the labyrinth seal becomes too
low.
While the present invention has been described herein with reference to the specific embodiment thereof, it is considered that the present invention is not limited thereby and numerous changes and alterations may be made therein for those skilled in the art without departing from the scope of the invention.
We Claim,
1. A labyrinth screw sealing (11) for aero engine application comprising a labyrinth screw (15) on the rotor (13) and an abradable coating (14) on
5 stator (12).
2. The labyrinth screw sealing as claimed in claim 1, characterized in that, the labyrinth screw (15) is having a plurality of saw teeth (16). 3. The labyrinth screw sealing as claimed in claim 1, characterized in that, the saw teeth (16) is of helical construction with saw shaped
10 cross section.
4. The labyrinth screw sealing as claimed in claim 1, characterized in that, abradable coating (14) is made of NiCrAlY undercoat of thickness 0.2 mm and a carbide projection of 0.6 mm thickness.