U.S. patent application number 12/618938 was filed with the patent office on 2010-05-20 for turbomachine.
Invention is credited to Pierre Bernard French, Jonathan David Wood.
Application Number | 20100124496 12/618938 |
Document ID | / |
Family ID | 41509313 |
Filed Date | 2010-05-20 |
United States Patent
Application |
20100124496 |
Kind Code |
A1 |
French; Pierre Bernard ; et
al. |
May 20, 2010 |
TURBOMACHINE
Abstract
A turbomachine such as a turbocharger comprises a housing 3
defining a bearing cavity and a turbine wheel 4 mounted to a shaft
8 for rotation about an axis. A housing wall 3a is disposed between
the bearing cavity and the turbine wheel 4, the shaft 8 extending
into the bearing cavity through a shaft passage 20 provided in the
housing wall 3a. The housing wall 3a comprises a first portion
defining an air gap with the turbine wheel 4 and a second annular
portion 3b defining the opening to the shaft passage 20 and which
is axially spaced from said turbine wheel 4 by a minimum distance
D. The housing wall 3a further comprises at least one third portion
32, such as an annular rib, radially spaced from the first portion
3a. The third portion is configured to bear load from a turbine
wheel rotating off axis in a failure condition.
Inventors: |
French; Pierre Bernard;
(Holmfirth, GB) ; Wood; Jonathan David; (West
Yorkshire, GB) |
Correspondence
Address: |
KRIEG DEVAULT LLP
ONE INDIANA SQUARE, SUITE 2800
INDIANAPOLIS
IN
46204-2079
US
|
Family ID: |
41509313 |
Appl. No.: |
12/618938 |
Filed: |
November 16, 2009 |
Current U.S.
Class: |
415/229 |
Current CPC
Class: |
F05D 2240/55 20130101;
F05D 2260/96 20130101; F05D 2270/09 20130101; F05D 2220/40
20130101; F02C 6/12 20130101; F05D 2260/84 20130101; F01D 25/162
20130101 |
Class at
Publication: |
415/229 |
International
Class: |
F04D 29/04 20060101
F04D029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2008 |
GB |
0820952.0 |
Dec 13, 2008 |
GB |
0822771.2 |
Claims
1. A turbomachine comprising: a housing defining a bearing cavity;
a turbine wheel mounted to a shaft for rotation about an axis; a
housing wall disposed between the bearing cavity and the turbine
wheel; the shaft extending into the bearing cavity through a shaft
passage provided in said housing wall; the housing wall including:
a first portion defining an air gap between the housing wall and
the turbine wheel; a second portion which is annular and protrudes
from the first portion into said air gap to define the opening to
said passage; and at least one third portion which is radially
distanced from second portion and which protrudes from said first
portion into said air gap; wherein the third portion is configured
to support the turbine wheel in a failure condition in which the
wheel rotates off-axis to thereby at least reduce the radial load
which would otherwise be applied to the annular second portion by
the shaft.
2. A turbomachine according to claim 1, wherein the second portion
is defined by a generally domed portion of the housing wall.
3. A turbomachine according to claim 2, wherein the or each third
portion is defined by a feature of the housing wall which extends
to the domed portion to directly reinforce the domed portion
against any radial load applied thereto by the shaft.
4. A turbomachine according to claim 1, wherein the or each third
portion is positioned at a radius less than or equal to the radius
of the turbine wheel.
5. A turbomachine according to claim 1, wherein the second portion
is spaced from the turbine wheel by a minimum distance D and the or
each third portion is spaced from the turbine wheel by minimum
distance d, wherein d is less than or equal to D.
6. A turbomachine according to claim 1, wherein the or each third
portion is at least substantially annular and at least
substantially surrounds the second portion.
7. A turbomachine according to claim 1, wherein the or each third
portion of the housing wall comprises a rib or other protrusion
which has a height extending from the housing wall towards the
turbine wheel.
8. A turbomachine according to claim 1, wherein the or each third
portion of the housing wall comprises a rib or other protrusion
which has a height extending from the housing wall towards the
turbine wheel, and the or each third portion has a length extending
in a linear or curved direction away from the second portion.
9. A turbomachine according to claim 8, wherein at least one third
portion extends in a generally radial or tangential direction away
from said second portion.
10. A turbomachine according to claim 1, comprising a plurality of
said third portions.
11. A turbomachine according to claim 1, wherein the turbine wheel
comprises a central body which supports turbine blades, and wherein
said central body defines a back face, the minimum distance d being
defined between the or each third portion of the bearing housing
and the turbine wheel back face.
12. A turbomachine according to claim 1, wherein the or each third
portion of the housing wall defines a turbine wheel contact surface
which lies in a plane substantially normal to the axis or which
lies on a conical surface defined about the axis.
13. A turbomachine according to claim 1, wherein said housing wall
defines a portion of the bearing cavity and wherein said shaft is
sealed with respect to said passage to prevent or obstruct leakage
of oil through said passage to said turbine wheel.
14. A turbomachine according to claim 1, wherein said housing wall
is defined by, or connected to, a housing comprising a further wall
portion which extends in a direction having a significant component
parallel to said axis.
15. A turbomachine according to claim 14, wherein said further wall
portion meets said housing wall at a radial location corresponding
to the radial location of the or each third portion of the housing
wall such that an axial force applied to the or each third portion
of the housing wall is reacted by said further housing wall
portion.
16. A turbomachine according to claim 1, wherein the turbomachine
is a turbocharger or a power turbine.
17. A turbomachine according to claim 2, wherein the or each third
portion is positioned at a radius less than or equal to the radius
of the turbine wheel.
18. A turbomachine according to claim 3, wherein the or each third
portion is positioned at a radius less than or equal to the radius
of the turbine wheel.
19. A turbomachine according to claim 2, wherein the second portion
is spaced from the turbine wheel by a minimum distance D and the or
each third portion is spaced from the turbine wheel by minimum
distance d, wherein d is less than or equal to D.
20. A turbomachine according to claim 1, wherein the second portion
is spaced from the turbine wheel by a minimum distance D and the or
each third portion is spaced from the turbine wheel by minimum
distance d, wherein d is less than or equal to D.
Description
[0001] The present invention relates to turbomachinery, such as for
instance a power turbine or turbocharger for an internal combustion
engine. In particular, the present invention relates to the
limitation of damage which may occur to the turbocharger as a
result of low cycle fatigue failure of the turbine wheel.
[0002] Turbochargers are well known devices for supplying air to
the intake of an internal combustion engine at pressures above
atmospheric (boost pressures). A conventional turbocharger
essentially comprises an exhaust gas driven turbine wheel mounted
on a rotatable shaft within a turbine chamber defined by a turbine
housing. Rotation of the turbine wheel rotates a compressor wheel
mounted on the other end of the shaft within a compressor housing.
The compressor wheel delivers compressed air to the intake manifold
of the engine, thereby increasing engine power.
[0003] The turbocharger shaft is conventionally supported by
journal and thrust bearings, including appropriate lubricating
systems, located within a central bearing housing connected between
the turbine and compressor housing. It is well known that providing
an effective sealing system to prevent oil leakage from the central
bearing housing into the turbine housing is problematic. It is
however important to prevent oil leaking into the turbine housing
where it will mix with the exhaust gas and increase exhaust
emissions and may cause damage to downstream components such as a
catalytic converter.
[0004] The turbine wheel comprises a central body or hub, having a
back face which faces towards the bearing housing. Turbine blades
extend generally radially from the hub and generally axially
relative to the back face. The turbine wheel may be friction welded
to a seal boss at the end of the turbocharger shaft, the seal boss
having a larger diameter than the shaft for rotation within an
passage through a housing wall separating the bearing housing from
the turbine housing. Known oil seal arrangements comprise a seal
ring located around the seal boss within the passage providing a
seal in the manner of a piston ring.
[0005] It is also common that a heat shield, frequently made of
sheet metal, is provided intermediate the turbine wheel and the
housing wall so as to reduce the amount of heat transfer (due to
hot exhaust gases) to the bearing housing
[0006] It is known that thermal and/or mechanical loading
conditions on parts of the turbocharger, particularly the turbine,
may cause premature failure of materials concerned. This is known
as fatigue. One type of fatigue is low cycle fatigue, which is
generally caused by repeated loading cycles as the turbocharger
changes between low and high operating speeds. In some cases low
cycle fatigue may cause the turbine wheel to fail and fracture,
which may result in catastrophic damage to the turbocharger. In
particular, damage to the bearing housing may result in oil leakage
from the bearing cavity into the turbine presenting a fire
risk.
[0007] It is an object of the present invention to obviate or
mitigate the problems of oil leakage from the turbocharger bearing
housing into the turbocharger turbine housing due to a turbine
wheel failure.
[0008] According to the present invention there is provided a
turbomachine comprising: [0009] a housing defining a bearing
cavity; [0010] a turbine wheel mounted to a shaft for rotation
about an axis; [0011] a housing wall disposed between the bearing
cavity and the turbine wheel; the shaft extending into the bearing
cavity through a shaft passage provided in said housing wall; the
housing wall including: [0012] a first portion defining an air gap
between the housing wall and the turbine wheel; [0013] a second
portion which is annular and protrudes from the first portion into
said air gap to define the opening to said passage; and [0014] at
least one third portion which is radially distanced from second
portion and which protrudes from said first portion into said air
gap;
[0015] wherein the third portion is configured to support the
turbine wheel in a failure condition in which the wheel rotates
off-axis to thereby at least reduce the radial load which would
otherwise be applied to the annular second portion by the
shaft.
[0016] Accordingly, the third portion of the housing wall is
configured, e.g. sized and located, to bear load (directly or
indirectly) from the turbine wheel in a failure condition which in
turn reduces off-axis load on the second annular portion of the
housing wall via the shaft. In some embodiments the turbine wheel
may directly contact the third portion of the housing wall. In
other embodiments a heat shield may be located between the third
portion and the turbine wheel which is sandwiched between the third
portion and the wheel when the wheel fails.
[0017] Turbine wheels may suffer low cycle fatigue in an asymmetric
manner. This is particularly the case when the failure originates
from the back face of the wheel (usually that which is adjacent the
bearing housing) or when a large portion of the wheel, for example
a blade, becomes detached. It is believed that when such a failure
occurs, the remainder of the turbine wheel (which is still attached
to the shaft) reacts by moving radially with respect to the axis of
rotation of the turbine wheel, and thereafter will become highly
unbalanced. The high torque on the shaft may even cause it to snap.
The turbine wheel and attached shaft may act as a lever,
particularly if the shaft has snapped, which applies a force to the
housing wall and/or any oil seal arrangement within the shaft
passage through the housing wall, causing possible fracture of the
housing wall around the passage and/or failure of the seal
arrangement. Either fracture of the bearing housing or failure of
the seal arrangement would result in high-pressure oil within the
bearing cavity leaking into the turbine and mixing with the exhaust
gas flow. As previously mentioned, this may severely contaminate
downstream emissions equipment, and may cause a fire.
[0018] The present invention reduces the likelihood of such
catastrophic failure of the turbine by provision of the third
portion (or portions) of the housing to provide some support to a
failed turbine wheel that may be rotating in an asymmetric manner.
Such support will reduce any off-axis, or lever, forces exerted on
the second portion of the housing wall around the shaft passage
(and on any seal arrangement present in the passage) thereby
reducing the risk of fracture to the housing wall (or damage of the
seal arrangement), thus reducing the likelihood of oil leakage into
the turbine.
[0019] In some embodiments the present invention further reduces
the likelihood of catastrophic failure of the turbine by
configuration of the third portion of the housing such that it
reinforces the second portion of the housing defining the aperture
shaft. That is, any axially forces exerted by the shaft as a result
of off-axis rotation of the turbine wheel will be transmitted to
the or each reinforcing portion. The or each third portion may for
instance be positioned to transmit any such force to a more robust
portion of the housing, such as a housing wall having at least a
substantial component extending in the axially direction.
[0020] In some embodiments, the or each third portion may be
configured to reinforce the second portion without necessarily
being configured to directly support the turbine wheel in a failure
condition. One aspect of the present invention provides a turbo
machine comprising: [0021] a housing defining a bearing cavity;
[0022] a turbine wheel mounted to a shaft for rotation about an
axis; [0023] a housing wall disposed between the bearing cavity and
the turbine wheel; the shaft extending into the bearing cavity
through a shaft passage provided in said housing wall; the housing
wall including: [0024] a first portion defining an air gap between
the housing wall and the turbine wheel; [0025] a second portion
which is annular and protrudes from the first portion into said air
gap to define the opening to said passage; and [0026] at least one
third portion which protrudes from said first portion into said air
gap;
[0027] wherein the third portion is configured (e.g. sized and
located) to reinforce the second portion of the housing defining
the aperture shaft.
[0028] For instance, the or each third portion of the housing may
comprise a rib or web portion connecting the second portion of the
housing to the first portion of the housing or to another portion
of the housing.
[0029] The second portion may be defined by a generally domed
portion of the housing wall.
[0030] The or each third portion may be positioned at a radius less
than or equal to the radius of the turbine wheel.
[0031] The second portion may be spaced from the turbine wheel by a
minimum distance D and the or each third portion is spaced from the
turbine wheel by minimum distance d, wherein d is less than or
equal to D.
[0032] In some embodiments the turbomachine may comprise a bearing
housing which defines at least a part of the bearing cavity and a
turbine which defines a turbine chamber within which the turbine
wheel rotates. The housing wall may be a wall of the bearing
housing which separates the bearing cavity from the turbine chamber
in which the turbine wheel rotates, the air gap between the two
reducing heat transfer to the bearing housing. In such embodiments
a heat shield may be located in the air gap between the housing
wall and the turbine wheel. Any such heat shield is preferably
spaced from the second portion of the housing wall to limit heat
transfer to the housing. In other embodiments the housing wall may
itself comprise a heat shield, for instance integrally cast with
the bearing housing.
[0033] The or each third portion of the housing wall may be
annular.
[0034] The or each third portion of the housing wall may be defined
by a rib or other protrusion which has a height extending from the
housing wall towards the turbine wheel. For instance, the or each
third portion may be a rib with a length extending in a linear or
curved direction away from the first portion of the housing wall.
Such a rib may extend to the second portion of the housing or may
terminate at a location spaced from the second portion of the
housing.
[0035] The height of height of the or each third portion may be
non-uniform to define a region or regions of the respective third
portion that will deform preferentially under impact.
[0036] The or each third portion may extend in a generally radial
direction away from the second portion of the housing wall. In some
embodiments at least one third portion may extend in a generally
tangential direction to the first portion.
[0037] The housing wall may comprise a plurality of said third
portions which may, for instance, be arranged circumferentially
around said second portion.
[0038] Whereas in some embodiments the or each third portion may be
defined by a discreet protrusion, such as for example a rib or the
like, provided on the surface of the housing wall, in other
embodiments the or each third portion may be defined by a contour
of the housing wall.
[0039] A typical turbine wheel may comprise a central body or hub
supporting turbine wheel blades, the hub having a back face which
faces towards the housing wall. Other forms of turbine wheel may
comprise a back plate supporting the wheel blades and which defines
the wheel back face. The minimum distance d may be defined between
the or each third portion of the housing wall and the turbine wheel
back face.
[0040] The or each third portion of the housing wall may define a
contact surface (which is contacted in the event of turbine wheel
failure) which lies in a plane substantially normal to the axis or
which lies on a conical surface defined about the axis--for
instance corresponding to the likely orientation of an
asymmetrically rotating turbine wheel following wheel failure as
described above.
[0041] In some embodiments the housing wall defines a portion of
the bearing cavity and the shaft may be sealed with respect to said
passage to prevent or obstruct leakage of oil through said passage
to the turbine wheel.
[0042] In other embodiments the housing wall comprises a heat
shield with a second housing wall which defines a portion of the
bearing cavity being disposed between the bearing cavity and the
heat shield. The shaft may be sealed with respect to a second
passage through said second housing wall to prevent or obstruct
leakage of oil to the turbine wheel.
[0043] The third portion of the housing wall may be radially spaced
from the dome or other feature defining the second portion, albeit
that the second portion may be defined by a feature of the housing
wall which contacts the dome.
[0044] The housing wall may be defined by, or connected to, a
housing comprising a further wall portion which extends in a
direction having a significant component parallel to said axis. The
further wall portion may meet said housing wall at a radial
location corresponding to the radial location of the third portion
of the housing wall such that any substantially axial force applied
to the second portion of the housing wall is transmitted to the
further housing wall portion. The further housing wall portion will
thus support the or each third portion of the housing wall in the
event of impact by the turbine wheel.
[0045] The or each third portion of the housing wall may be an
integral feature of the housing wall (eg integrally cast with the
housing wall or machined into the housing wall) or may be
fabricated as a separate component which is subsequently attached
to the housing wall.
[0046] The turbomachine may be a turbocharger or may for instance
be a power turbine.
[0047] Other preferred and particularly advantageous features of
the invention will be apparent from the following description.
[0048] Specific embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0049] FIG. 1 is a cross-section through a known turbocharger;
[0050] FIG. 2 is an expanded view of the turbine end bearing and
oil seal assemblies of the turbocharger of FIG. 1;
[0051] FIG. 3 shows details of part of another known turbocharger
bearing housing structure;
[0052] FIG. 4 shows a fractured dome portion of a known
turbocharger;
[0053] FIGS. 5a and 5b show details of a first embodiment of
present invention;
[0054] FIG. 6 is a cross-section through a turbocharger in
accordance with an embodiment of the present invention;
[0055] FIG. 7 is a simplified enlarged cross-sectional view of a
turbine wheel and bearing housing in accordance with the present
invention;
[0056] FIG. 8 is an end on view of a bearing housing in accordance
with a second embodiment of the invention; and
[0057] FIG. 9 is a cross-section through a turbine wheel and
bearing housing in accordance with the same embodiment of the
invention as shown in FIG. 6.
[0058] Referring to FIGS. 1 and 2, the illustrated turbocharger
comprises a turbine 1 joined to a compressor 2 via a central
bearing housing 3. The turbine 1 comprises a turbine wheel 4
rotating within a turbine housing 5. Similarly, the compressor 2
comprises a compressor wheel 6 which rotates within a compressor
housing 7. The turbine wheel 4 and compressor wheel 6 are mounted
on opposite ends of a common turbocharger shaft 8 which extends
through the central bearing housing 3.
[0059] The turbine housing 5 has an exhaust gas inlet volute 9
located annually around the turbine wheel 4 and an axial exhaust
gas outlet 10. The compressor housing 7 has an axial air intake
passage 11 and a compressed air outlet volute 12 arranged annually
around the compressor wheel 6.
[0060] Intermediate the turbine wheel 4 and the bearing housing 3
there is a heat shield 13a, made of sheet metal, which is installed
in the turbine housing 5 behind the turbine wheel 4. The purpose of
the heat shield 13a is to prevent overheating of the bearing
housing 3, due to the hot exhaust gases in the turbine housing 5,
which can for instance result in oil coking in the bearing housing
3. The heat shield 13a is spaced from the turbine wheel 4, not only
such that the heat shield 13a does not impede the movement of the
wheel 4, but also so that no heat can be conducted directly from
the wheel 4 to the heat shield 13a. A portion of the heat shield
13a is also spaced from the bearing housing 3 to minimise heat
conduction to the bearing housing.
[0061] The turbine wheel 4 typically comprises a generally
cylindrical main body or hub 4a, having a back face 4c which faces
towards the bearing housing/heat shield. A plurality of turbine
blades extend generally radially from the hub and generally axially
relative to the back face.
[0062] In use, the turbine wheel 4 is rotated by the passage of
exhaust gas from the annular exhaust gas inlet 9 to the exhaust gas
outlet 10, which in turn rotates the compressor wheel 6, which
thereby draws intake air through the compressor inlet 11 and
delivers boost air to the intake of an internal combustion engine
via the compressor outlet volute 12.
[0063] The turbocharger shaft 8 rotates on fully floating journal
bearings 13 and 14 housed towards the turbine end and compressor
end respectively of the bearing housing 3. The compressor end
bearing assembly 14 further includes a thrust bearing 15 which
interacts with an oil seal assembly including an oil slinger 16.
Details of the compressor end bearing and oil seal are not
important to an understanding of the present invention and will not
be described further. Oil is supplied to the bearing housing from
the oil system of the internal combustion engine via oil inlet 17
and is fed to the bearing assemblies by oil passageways 18.
[0064] The turbine wheel 4 is joined to the end of the turbocharger
shaft 8 at a seal boss 19. Generally, the seal boss 19 is formed
integrally with the shaft 8 and is joined (for instance by friction
welding) to a boss portion on the turbine wheel 4. The seal boss 19
extends through a passage 20 in a bearing housing wall 3a and into
the turbine housing. The bearing housing wall 3a is such that it is
generally convex in nature, the radially innermost portion (with
respect to the axis of shaft 8), which defines the opening of the
aperture 20, being closer to the back face than any other portion
of the bearing housing wall. The radially innermost portion is
sometimes referred to as the "dome" 3b. The seal boss 19 is sealed
with respect to the passage 20 by a seal ring 21 (piston ring),
which sits in an annular groove defined by the seal boss.
[0065] In more detail (referring in particular to FIG. 2) the
passage 20 through the bearing housing wall 3a is radially stepped
having a relatively narrow diameter inboard portion 20a and a
relatively large diameter outboard portion 20b. This provides an
annular abutment shoulder 22 for the ring seal 21 which sits within
an annular groove 23 provided in the outer surface of the seal boss
19. The seal ring 21 is stationary with respect to the bearing
housing 3 and is provided to prevent the leakage of air/oil through
the passage 20. The abutment shoulder 22 prevents the seal ring 21
creeping inboard towards the bearing housing 3. In order to provide
an abrupt, non-radiused change of diameter of the passage 20, a
slight annular recess 24 is cut back in to the surface of the
passage 20 to define the shoulder 22.
[0066] The turbine end journal bearing 13 is located between
circlips 25 and 26. Oil is fed to the bearing 13 via oil passageway
18 and the bearing 13 is provided with circumferentially spaced
radial holes 27 for oil to pass to the turbocharger shaft 8. An
annular oil return groove 28 is radially recessed into the bearing
housing wall adjacent the passage 20 through the housing wall 3a.
The oil return groove 28 surrounds the shaft 8 and has an entrance
29.
[0067] The seal boss 19 extends slightly into the bearing housing
18 beyond the inner surface of the bearing housing wall 3a and
axially overlaps the entrance 29 to the oil groove 28. The inboard
end of the seal boss 19 forms a radial shoulder around the shaft 8
having an annular face 30. As the turbocharger shaft 8 rotates, oil
reaching the annular face 30 is radially dispelled and propelled
from the face 30 of the boss 19 is into the oil groove 28 from
which it drains back to the engine crank case via an oil drain hole
31 (shown in FIG. 1). The provision of the oil groove 28 thus
prevents oil from accumulating in the region of the passage 20, and
similarly ensuring that the boss 19 protrudes into the bearing
housing 3 ensures that oil is projected into the oil groove 28 and
not towards the annular gap defined where the boss 19 passes
through the passage 20.
[0068] FIG. 3 shows part of another known turbocharger. The same
reference numerals are used to correspond to those provided above.
With the turbocharger of FIG. 3 it can be seen that the bearing
housing dome 3b is very much more pronounced that with the housing
design of FIGS. 1 and 2.
[0069] It has been found that under certain fatigue conditions,
such as low-cycle fatigue, the turbine wheel 4 may fail whilst it
is in use. Such a failure may involve the turbine wheel 4 cracking,
or in extreme cases, separating into a plurality of pieces. This
type of failure tends to be asymmetric in nature and is
particularly the case when the failure occurs from the back face of
the turbine wheel 4 or when a large portion of the wheel, for
example a blade 4b, becomes detached.
[0070] Either fracture of the bearing housing or failure of the
seal arrangement would result in high-pressure oil within the
bearing housing passing into the turbine housing, and hence the
engine exhaust system. As previously mentioned, this may severely
contaminate downstream emissions equipment, or may cause a
fire.
[0071] The result of such failure is to cause the rotating turbine
4 and shaft 8 to become unstable. The turbine 4 and shaft 8
experience a force which causes them to become highly unbalanced
and move radially outwards relative to their normal axis of
rotation. The torque produced by this movement, in combination with
any forces which may result from the turbine wheel 4 and shaft 8
abutting the turbine housing 5 and/or bearing housing 3, may cause
the shaft 8 to break or deform and thereafter will become highly
unbalanced. Deformation or breaking of the shaft usually occurs in
the region of the journal bearings 13, 14 (particularly the turbine
end bearing 13) or within the dome 3b. Once the shaft 8 has
deformed or broken, the wheel 4 and any portion of the shaft 8
attached thereto, continues to move radially outward. This exerts
radial force on the bearing housing and or seal 21 in the region of
the passage 20. The shaft 8 may effectively form a lever, which as
the turbine 4 moves radially outwards, causes a large force to be
applied to the dome 3b, which can break it open and/or cause
failure of the seal arrangement 21.
[0072] A dome 3b which has been broken in the above manner is shown
in FIG. 4. If the dome 3b or seal 21 are damaged, pressurised oil,
which is fed to the bearing 13 via inlet 17 and passageway 18, will
flow into the turbine and mix with the hot exhaust gas flow.
Exposure of the engine exhaust system, which is typically at a high
temperature, to oil is potentially hazardous as the oil may ignite.
In addition, the ingress of oil into the engine exhaust system may
lead to external oil leaks and/or contamination of downstream
emissions equipment, for instance a catalytic converter.
[0073] FIGS. 5a and 5b illustrate part of a turbocharger bearing
housing in accordance with a first embodiment of the present
invention. The illustrated housing structure in accordance with the
present invention is a modification of that shown in FIG. 3 and
like reference numerals are used where appropriate. In accordance
with the present invention the bearing housing is modified by the
provision of radially extending ribs or buttresses 3c which are
raised above the housing wall. In the illustrated example the
height of the ribs 3c above the housing wall is less than that of
the dome 3b but in other embodiments the height of the ribs 3c may
be equal to or greater than the height of dome 3b. Should a turbine
failure of the type discussed above occur, any radial and/or
levering movement of the turbine 4 and attached portion of shaft 8
will be limited by the abutment of the turbine 4 with the ribs 3c.
The ribs 3c protrude a sufficient distance towards the turbine 4
such that any nutating motion of a failed turbine 4 results in the
turbine 4 abutting the ribs 3c, inhibiting significant contact
between the dome 3b and the back face of the turbine 4. Limiting
the radial movement of the turbine wheel 4 reduces, and may even
prevent, off axis forces on the dome 35 and/or seal 21. This may
prevent the dome 3b from breaking and/or the seal from being
destroyed and may, for instance, prevent the shaft 8 from breaking.
This will thereby prevent or minimise the leakage of oil into the
exhaust system in the event of turbine wheel failure
[0074] Furthermore, in this embodiment the ribs 3c in the
illustrated embodiment are arranged to reinforce the dome 3b and to
transmit the force towards a radially outer portion of the housing
to be borne by a housing wall which extends generally axially and
is thereby better orientated to bear the load. Tests have shown
that this embodiment of the invention greatly reduces any tendancy
of the dome to fracture under turbine wheel failure conditions.
[0075] FIG. 6 shows a turbocharger in accordance with a second
embodiment of the present invention, wherein the bearing housing 3
has a raised annular portion 32 provided radially outward of the
dome 3b. Again, where appropriate, the same reference numbers are
used to identify corresponding features to those in previous
figures. Due to the convex dome shape of the bearing housing 3 the
spacing between the back face of the turbine wheel 4 and the
bearing housing 3 increases as radial distance from the axis of the
shaft 8 increases. The annular portion 32 protrudes from the
bearing housing 3 towards, depending on the radial location of the
annular portion, either the back face of the turbine wheel 4 or the
blades 4b of the turbine wheel 4. In the embodiment shown, the
portion 32 is annular and is concentric with the turbine wheel 4.
The heat shield 13a is intermediate the containment portion 32 and
the turbine wheel 4. It is desirable that, as shown, the
containment portion 32 is such that it does not contact the heat
shield 13a, so that there is no direct conduction of heat
therebetween.
[0076] Should a turbine failure of the type discussed above occur,
any radial and/or levering movement of the turbine 4 and attached
portion of shaft 8 will be limited by the abutment of the turbine 4
with the annular portion 32 (albeit via the heat shield 13a). As
with ribs 3c of the earlier embodiment, the annular portion 32
protrudes a sufficient distance towards the turbine 4 such that any
nutating motion of a failed turbine 4 results in the turbine 4
abutting the annular portion 32, inhibiting significant contact
between the dome 3b and the back face of the turbine 4. As
described above, limiting the radial movement of the turbine wheel
4 in this way reduces, and may even prevent, off axis forces on the
dome 35 and/or seal 21 and thereby prevent the dome 3b from
breaking and/or the seal from being destroyed (and may, also
prevent the shaft 8 from breaking)
[0077] As previously discussed, the turbine 4 comprises a main body
4a with a back face 4c and blades 4b. As seen best in FIG. 6, the
annular portion 32 is sized and positioned such that should the
turbine wheel 4 abut the annular portion 32 if the turbine 4 fails,
then it is the back face of the hub 4a of the turbine wheel 4 which
abuts the containment portion 32. This is advantageous in that the
main body 4a is capable of withstanding a greater force than the
blades 4b. As such, a greater reaction force can be imparted to the
turbine wheel 4 via the annular portion 32, so as to oppose the
force which urges the failed turbine 4 radially outwards. The
annular portion 32 may for instance lie at the same radius as the
outer periphery of the turbine wheel back face 4c. Alternatively,
in other embodiments the annular portion 32 may be radially inward
or outward of the periphery of the turbine wheel back face.
[0078] In some embodiments, such as those illustrated in FIGS. 6
and 7, the annular portion 32 is also sized and shaped such that
should the turbine 4 fail and impart a force to the portion 32, the
transmission of such a force will be through a side wall portion 3c
of the bearing housing 3 which extends generally axially away from
the turbine. Any transmitted force will thus have a significant
component parallel to the direction of the extension of the side
wall 3c away from the turbine, as shown by arrow A. The
transmission of any reaction force in this manner is advantageous
as it minimises the risk of fracturing the housing 3 whist it is
under the load of a failed turbine 4.
[0079] In a further embodiment of the invention shown in FIGS. 8
and 9 the raised portion comprises a plurality of parallel ribs 33
rather than the annular rib 32. The ribs 33 are adjacent the dome
3b and are connected thereto with ribs 33a extending radially from
the dome and ribs 33b extending tangentially to the dome 3b. The
dome 3b comprises a central nose portion 34, the surface of which
is substantially parallel to the back face of the turbine wheel 4.
The axial height of the ribs 33 is the same as that of the nose
portion 34. The individual ribs 33 are sized and positioned (in
relation to the turbine 4 and each other) such that a nutation of a
failed turbine 4 in any direction will result in the turbine 4
abutting the containment portion 32. As with the previous
embodiment of the invention, the abutment of the turbine 4 with the
ribs 33 inhibits significant off-axis forces on the dome 3b and
seal 21 in the event of turbine wheel failure. This structure
allows the bearing housing to be cast economically using a
conventional two-part cast process
[0080] In the above-described embodiments, the housing wall 3a,
which separates the turbine wheel 4 chamber from the bearing
cavity, is provided by the bearing housing 3. In other embodiments
the housing wall may be provided by the turbine housing 5. In yet
further embodiments the heat shield 13a, may be sufficiently robust
as to bear the load of a failed turbine wheel. For example in some
embodiments the heat shield may be an integrally cast wall of the
bearing housing, and as such may be the housing wall which is
provided with the portion 32 or ribs 33 etc.
[0081] Although embodiments of the invention described above have a
support portion provided as a protrusion from the housing wall, is
also envisaged that in other embodiments of the invention such a
support portion could be provided by a less prominent feature of
the shape or configuration of the bearing housing wall 3a. For
instance, the wall 3a may have a generally concave curving towards
the turbine wheel at a radius beyond the passage 20 or dome 3b if
present. Discreet protrusions are however preferred as they
typically involve only a small increase in weight of the
turbocharger housing
[0082] As mentioned above, the configuration and location of the
reinforcing or support portion of the housing wall may vary from
those shown in the illustrated embodiments of the invention. For
instance the annular protrusion 32 may be replaced by an annular
array of circumferentially spaced discreet protrusions. For
instance such discreet protrusions may be arced ribs lying on a
circle circumscribing the axis, or may be ribs curving generally
towards or away from the axis in the direction of rotation of the
turbine wheel. The radial width of the annular protrusion, or any
such ribs, may vary as may the orientation of the face of any such
protrusion. For instance an annular protrusion may define a surface
facing towards the turbine wheel which lies substantially
perpendicular to the axis or which lies on the surface of a cone
corresponding to the orientation the turbine wheel might assume if
it fails and contacts the protrusion.
[0083] An annular protrusion/rib or annular array of
protrusions/ribs may lie at a radius substantially corresponding to
the circumference of the turbine wheel back face, or may lie
between the circumference of the back face and the axis or between
the circumference of the back face and the outer extremity of the
turbine wheel blades. In some embodiments a protrusion or
protrusions positioned at a radius corresponding to that of the
main body 4a of the turbine wheel 4 my be most effective in
enabling the maximum reaction force to be exerted on a failed
turbine wheel 4, without significantly increasing the risk of
further blade fracture or deformation. In some embodiments the
possible location of the protrusion or other reinforcing or support
portion, might be to limited by other features of the configuration
of the bearing housing, turbine housing and/or heat shield.
[0084] In embodiments in which the support portion comprises ribs,
such ribs may extend radially away from the axis (similar to ribs
33a a shown in FIG. 6) or tangentially to a circle centred on the
axis (similar to ribs 33b shown in FIG. 6), or may extend in a
direction between these two directions. Such ribs may define a
surface facing the turbine wheel which lies in plane normal to the
axis or lies on the surface of a cone corresponding to the possible
orientation assumed by a failed turbine wheel contacting the
protrusions. In some embodiments such ribs may be combined with an
annular or similar protrusion or protrusions as described above.
Where the bearing housing wall has a dome, as illustrated, ribs may
contact the dome or be radially spaced therefrom.
[0085] Where the support portion comprises a protrusion or
plurality of protrusions, such protrusions may be integrally formed
(e.g. cast or machined) with the housing wall. Alternatively the
protrusions may comprise separately fabricated structures which are
subsequently attached to the housing wall (e.g. by welding or
securing with bolts, rivets or other fasteners). This would for
instance enable the protrusions to be formed of a different
material to that of the housing wall and may allow more flexibility
in the configuration of the protrusions.
[0086] It is also envisaged that the cross-sectional profile
(perpendicular to its longitudinal axis) of any protrusion which
forms part of the reinforcing or support portion may take different
forms. The protrusions of the above described embodiments have
substantially parallel side walls extending axially (and which are
radiused where they meet the bearing housing wall) and an end
surface facing towards the turbine wheel which is arcuate. The end
surface could alternatively be flat to increase the surface area
which will contact and support a failed turbine wheel. This not
only spreads any reaction force exerted by the reinforcing or
support portion on the turbine 4 over a greater area, but also
further limits the radial movement of a failed turbine 4. In
addition, if it is desired that the abutment of the reinforcing or
support portion with a failed turbine wheel 4 should cause the
rotation of the turbine 4 to stop, the stopping distance of the
failed turbine 4 will be reduced. The flat profile of the tip
portion of the protrusion may, for instance, be perpendicular to
the axis of rotation of the shaft 8, or may be at a fixed angle
relative to the axis of rotation of the shaft 8 which corresponds
to that of the back face of a notional failed turbine 4 as
mentioned above
[0087] It is additionally envisaged that any protrusion which forms
part of the support portion may be such that its radial distance
from the shaft 8 axis may decrease as it extends towards the
turbine 4. This may lead to improved transfer of impact (or
reaction) force to a load-bearing portion of the housing 3, for
example the housing sidewall 3c.
[0088] In some of the above-described embodiments, the minimum
axial separation between the support portion and the turbine wheel
4 is less than that the minimum axial separation between the nose
of the dome 3b (i.e. the portion of the dome defining the opening
of the passage 20) and the turbine wheel 4. The difference in
separation may vary between different embodiments of the invention.
In some embodiments the difference may be relatively small, and in
others it may be larger. The appropriate difference may to some
extent be dictated by the configuration of the bearing housing
and/or heat shield and/or distance between the turbine wheel and
housing wall and/or diameter of the turbine wheel relative to the
radial position of the protrusion or other housing feature defining
the reinforcing portion.
[0089] In some embodiments the protrusion or other housing feature
which forms the support portion may include a `crumple zone`, i.e.
a portion which will deform preferentially when a failed turbine 4
impacts on the support portion. Such a crumple zone may, for
instance, take the form of a portion of the protrusion or other
feature which has a fractionally greater axial height (i.e. extends
closer to the turbine wheel) than adjacent portions of the
protrusion or other support feature. Such a crumple zone may for
instance flatten on impact to absorb some of the force of the
impact
[0090] Whereas the present invention has been described in relation
to a turbocharger turbine it will be appreciated that it may be
applied to turbines of other turbomachinery such as for instance
power turbines. As will be known to the skilled person, a power
turbine is a turbine which drives a gear or other coupling for
deriving work from the turbine rather than a compressor wheel.
[0091] Other possible modifications and applications of the
invention will be readily apparent to the appropriately skilled
person.
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