U.S. patent application number 11/803206 was filed with the patent office on 2008-01-10 for compressor wheel.
Invention is credited to David McKenzie.
Application Number | 20080008595 11/803206 |
Document ID | / |
Family ID | 33523680 |
Filed Date | 2008-01-10 |
United States Patent
Application |
20080008595 |
Kind Code |
A1 |
McKenzie; David |
January 10, 2008 |
Compressor wheel
Abstract
Compressor wheel (16) and techniques for manufacturing such a
wheel are provided. The wheel may include a hub (21) with a
counterbore (36) internally treated to impart residual compressive
stresses, for enhanced endurance to stress-induced fatigue. The
surface treatment allows extending the counterbore relatively
closer to a plane (30) of typical maximum stress of the wheel. This
design flexibility advantageously allows avoiding or reducing
overhang of the compressor wheel, thereby improving rotor dynamics
and reducing the axial length of the hub, and the overall foot
print of the compressor wheel.
Inventors: |
McKenzie; David;
(Huddersfield, GB) |
Correspondence
Address: |
John H. Allie;Krieg DeVault, LLP
Suite 2800
One Indiana Square
Indianapolis
IN
46204
US
|
Family ID: |
33523680 |
Appl. No.: |
11/803206 |
Filed: |
May 14, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/GB2005/004316 |
Nov 9, 2005 |
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11803206 |
May 14, 2007 |
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Current U.S.
Class: |
416/223B |
Current CPC
Class: |
C21D 7/04 20130101; C21D
2221/00 20130101; F04D 29/284 20130101; Y10T 29/49321 20150115;
C21D 7/08 20130101; F04D 29/266 20130101 |
Class at
Publication: |
416/223.00B |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 2004 |
GB |
GB0425088.2 |
Claims
1. A compressor wheel, the compressor wheel having an axis of
rotation and comprising a plurality of blades extending generally
radially away from said axis and generally axially from one face of
a disc-like support, the opposite face of the support defining a
wheel backface, wherein at least a portion of the backface is
provided with a layer of residual compressive stress extending to a
depth below the surface of the backface.
2. A compressor wheel according to claim 1, wherein said backface
portion is annular.
3. A compressor wheel according to claim 2, wherein said backface
portion extends radially from the axis of the compressor wheel.
4. A compressor wheel according to claim 1, wherein said portion of
the surface of the backface is a substantial portion of the surface
of the backface.
5. A compressor wheel according to claim 4, wherein the entire
surface of the backface is provided with said layer of residual
compressive stress.
6. A compressor wheel according to claim 1, wherein the layer of
residual compressive stress has a maximum depth of at least 300
.mu.m.
7. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a minimum depth of 300 .mu.m.
8. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a maximum depth of at least 500
.mu.m.
9. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a minimum depth of at least 500
.mu.m.
10. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a maximum depth of at least 800
.mu.m.
11. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a minimum depth of at least 800
.mu.m.
12. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a maximum depth of at least 1
mm.
13. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress has a minimum depth of at least 1
mm.
14. A compressor wheel according to claim 1, wherein the depth of
the layer of residual compressive stress varies across said portion
of the surface of the backface.
15. A compressor wheel according to claim 14, wherein said depth is
minimised in regions of said portion of the backface susceptible to
deformation under compressive forces required to produce said layer
of compressive stress.
16. A compressor wheel according to claim 1, wherein said layer of
residual compressive stress is induced by applying a cold working
technique to said portion of the backface.
17. A compressor wheel according to claim 16, wherein said cold
working technique comprises roller burnishing.
18. A compressor wheel assembly comprising: a compressor wheel
having an axis of rotation and comprising a plurality of blades
extending generally radially away from said axis and generally
axially from one face of a disc-like support, the opposite face of
the support defining a wheel backface, wherein at least a portion
of the backface is provided with a layer of residual compressive
stress extending to a depth below the surface of the backface.
19. A compressor wheel assembly according to claim 18, wherein a
second member is mounted to the shaft for rotation therewith in
abutment with a region of the wheel backface, and wherein said
portion of the wheel comprising said layer of residual compressive
stress includes at least said region.
20. A compressor wheel assembly according to claim 19, wherein said
second member comprises an oil control device such as an oil
slinger.
21. A compressor wheel assembly according to claim 19, wherein said
second member comprises a component of a thrust bearing assembly
mounted on said shaft.
22. A compressor wheel assembly according to claim 18, wherein the
compressor wheel is welded to said shaft, a transition region being
formed between the backface and shaft in the region of said weld,
said transition region being provided with said layer of
compressive residual stress.
23. A compressor wheel assembly according to claim 22, wherein said
transition region comprises a fillet radii.
24. A compressor wheel assembly, comprising a compressor wheel
welded to a shaft for rotation about an axis, the compressor wheel
comprising a plurality of blades extending generally radially away
from said axis and generally axially from one face of a disc-like
support, the opposite face of the support defining a wheel
backface, wherein a transition region is defined between the
backface and shaft in the region of said weld, said transition
region being provided with a layer of residual compressive stress
extending the depth below the surface of the backface.
25. A turbocharger comprising a compressor wheel having an axis of
rotation and comprising a plurality of blades extending generally
radially away from said axis and generally axially from one face of
a disc-like support, the opposite face of the support defining a
wheel backface, wherein at least a portion of the backface is
provided with a layer of residual compressive stress extending to a
depth below the surface of the backface.
26. A method of manufacturing a compressor wheel to provide
increased resistance to critical failure, the compressor wheel
having an axis of rotation and comprising a plurality of blades
extending generally radially away from said axis and generally
axially from one face of a disc-like support, the opposite face of
the support defining a wheel backface, wherein at least a portion
of the backface is treated to form a layer of residual compressive
stress extending to a depth below the surface of the backface.
27. A method according to claim 26, wherein said treatment
comprises applying a cold working technique to said portion of the
backface.
28. A method according to claim 27, wherein said cold working
technique comprises roller burnishing.
29. (canceled)
30. A turbocharger comprising a compressor wheel welded to a shaft
for rotation about an axis, the compressor wheel comprising a
plurality of blades extending generally radially away from said
axis and generally axially from one face of a disc-like support,
the opposite face of the support defining a wheel backface, wherein
a transition region is defined between the backface and shaft in
the region of said weld, said transition region being provided with
a layer of residual compressive stress extending the depth below
the surface of the backface.
31. A method of manufacturing a compressor wheel assembly
comprising: welding a compressor wheel to a shaft for rotation
about an axis, the compressor wheel comprising a plurality of
blades extending generally radially away from said axis and
generally axially from one face of a disc-like support, the
opposite face of the support defining a wheel backface, wherein a
transition region is defined between the backface and shaft in the
region of said weld; and treating said transition region to form a
layer of residual compressive stress extending the depth below the
surface of the backface.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to compressor wheels or
impellers as may be used in a turbocharger, supercharger, and the
like.
[0002] Locomotives equipped with internal combustion engines, e.g.,
diesel engines, designed to meet stringent emissions regulations
may require relatively high air flow rates and high manifold
pressures, as may be provided by a turbocharger, to meet air
quality targets while maximizing fuel economy and reliability. The
high boost ratios, typically 3.8 or higher, may require high tip
speeds on a turbocharger compressor wheel, which may lead to high
levels of tensile stress in a bore area and shortened wheel life
due to low cycle fatigue. It is known that compressor wheels have
used a through bore that extends through the center of the wheel
along a rotation axis, and where the wheel may be securely mounted
onto a shaft with a locking nut.
[0003] It is further known that so called boreless compressor
wheels are able to rotate at higher speeds than compressor wheels
having a through bore since a through bore removes load carrying
material and thereby increases the stress level in the remaining
material. That is, more wheel material exists at a point of maximum
centrifugal load that results in higher load carrying
capability.
[0004] In one known compressor wheel, a hub section of the
compressor wheel that axially corresponds with the radially
outermost portion of the wheel experiences the maximum centrifugal
load. That is, a plane indicative of typical maximum stress exists
in substantial axial alignment with the maximum radial extent of
the hub. In this known compressor wheel, a threaded counterbore is
provided in a hub extension for receiving the shaft. However, the
counterbore must terminate well short of the plane indicative of
typical maximum stress to avoid the high level of stress at that
location. Since the length of the shaft/threaded interface is
generally constant for any given application, the foregoing
arrangement (that causes the designer to position such an interface
away from the high stress plane) may result in excessive overhang
of the compressor wheel. This detrimentally affects rotor dynamics
and increases the axial length of the hub extension, thus
increasing the overall footprint of the compressor wheel and
turbocharger.
BRIEF DESCRIPTION OF THE INVENTION
[0005] Aspects of the present invention propose to improve
compressor life by using a hub with a counterbore including a base
surface treated to impart residual compressive stresses for
enhanced endurance to stress-induced fatigue. The surface treatment
allows extending the counterbore relatively closer to a plane
indicative of typical maximum stress. This design flexibility
advantageously allows avoiding or reducing overhang of the
compressor wheel, thereby improving rotor dynamics and reducing the
axial length of the hub, and the overall foot print of the
compressor wheel and turbocharger.
[0006] Generally, the present invention fulfills the foregoing
needs by providing in one aspect thereof, a method of manufacturing
a compressor wheel. The method allows providing a hub extension of
the compressor wheel that defines a counterbore. The method further
allows imparting residual compressive stresses to a base surface of
the counterbore.
[0007] In another aspect thereof, the present invention further
fulfills the foregoing needs by providing a compressor wheel
comprising a hub including a hub extension that defines a
counterbore. The counterbore includes a base surface and the base
surface of the counterbore is treated to impart residual
compressive stresses thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The features and advantages of the present invention will
become apparent from the following detailed description of the
invention when read with the accompanying drawings in which:
[0009] FIG. 1 illustrates a cutaway view of an exemplary
turbocharger that may benefit from the teachings of the present
invention.
[0010] FIG. 2 shows a cross-sectional view of an exemplary
compressor wheel embodying aspects of the present invention.
[0011] FIG. 3 shows configurational details regarding the
compressor wheel of FIG. 2 that allow positioning a mounting
counterbore relatively closer to a plane indicative of typical
maximum stress of the wheel.
[0012] FIG. 4 shows a rotatable shaft assembled into a counterbore
embodying aspects of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] FIG. 1 shows a cutaway view of an exemplary turbocharger
(10) that may benefit from the teachings of the present invention.
Turbocharger (10) generally comprises respective compressor and
turbine stages (12) and (14) including a compressor wheel (16) and
a turbine wheel (18) coupled through a rotatable shaft (20). The
turbine wheel (18) is disposed within a turbine housing, which
includes an inlet for receiving exhaust gases from an internal
combustion engine (not shown). The turbine housing guides the
engine exhaust gases for communication with and expansion through
the turbine wheel (18) for rotatably driving the turbine wheel.
Simultaneously, the turbine wheel rotatably drives the shaft (20)
and compressor wheel (16), as may be disposed within a compressor
housing. The compressor wheel (16) and housing allow drawing in and
compressing ambient air for supply to the intake of the engine.
[0014] Referring to FIG. 2, a cross-sectional view of an exemplary
embodiment of the compressor wheel (16) is shown. Compressor wheel
(16) includes a hub portion (21). The hub portion (21) defines a
front face surface (22) for the compressor wheel (16), and supports
a plurality of circumferentially spaced apart compressor blades
(23) (only two of which are visible in FIG. 2) extending both
radially outwardly and axially thereon. The hub portion (21) also
includes a radially enlarged disc-like portion (24) which serves to
support the compressor blades (23) as well as to define a floor
surface (25) for the air flow channels defined between blades (23).
The disc-like portion (24) also defines a radially outer
circumferential surface (26) for hub (21), as well as an axially
disposed back side or back face surface (27).
[0015] As will be recognized by those skilled in the pertinent art,
in operation of compressor wheel (16), a plane indicative of
typical maximum stress (30) typically exists substantially in axial
alignment with the maximum radial extent of the hub (21). That is,
the plane of maximum stress (30) is typically coincident with
surface 26 and reaches a maximum at the point where the rotation
axis (34) transects plane (30), approximately at point (31).
[0016] To avoid the undesirable stress concentration of a
conventional through bore and preserve the strength of solid metal
adjacent to point (31), compressor wheel (16) includes a hub
extension (38) integrally defined by hub (21) and extending axially
away from plane (30). Hub extension (38) defines an axially
extending counterbore (36).
[0017] The inventors of the present invention have innovatively
recognized that one may advantageously improve rotor dynamics as
well as reduce the axial length of the compressor wheel when a base
surface (40) of counterbore (36) is treated to impart residual
compressive stresses to such a base surface. Examples of
techniques, such as cold working techniques, that may be used to
treat the counterbore base surface may comprise shot peening, laser
peening, glass beading, roll burnishing, etc. Cold working provides
plastic deformation of a metal (e.g., aluminum) below its annealing
temperature to cause permanent strain hardening.
[0018] Peening, as understood in the art and as used herein, means
to compress a portion of a surface by forming a depression or
indentation on the surface. Peening equipment generally is utilized
to create a compressively stressed protection layer at the outer
surface of a workpiece. The protection layer considerably increases
the resistance of the workpiece to fatigue failure. A shot used in
shot peening may comprise spherical particles constructed from a
hard metal or any other suitable material. With shot peening
systems, a stream of shot particles traveling at a high velocity is
directed at an outer surface of a workpiece, e.g., the base of the
counterbore. Each shot particle that impacts with sufficient force
upon the outer surface of the workpiece causes plastic deformation
of the surface and a dimple is formed therein. In this manner, a
compressively stressed layer is formed at the outer surface of the
workpiece to increase fatigue strength of the workpiece.
[0019] In laser peening, a laser beam from a laser beam source is
used to produce a strong localized compressive force on a surface.
Laser peening may be utilized in lieu of shot peening to create a
compressively stressed protection layer at the outer surface of a
workpiece. This type of treatment also considerably increases the
resistance of the workpiece to fatigue failure. Thus, peening is
typically a very effective means for producing surface compression
residual stress, and therefore, prolonging the useful life of the
workpiece.
[0020] As shown in FIG. 3, the surface treatment of the base of the
counterbore allows extending the base surface (40) of counterbore
(36) relatively closer to the plane (30) indicative of typical
maximum stress. This is exemplarily illustrated in FIG. 3 by the
representation of the counterbore base (40') relative to the
representation of the counterbore base (40). This design
flexibility advantageously allows avoiding or reducing overhang of
the compressor wheel, thereby improving rotor dynamics and reducing
the axial length of the hub extension, and the overall foot print
of the compressor wheel and turbocharger. For example, assuming the
base (40) of counterbore (36) is configured to extend a distance L
towards plane (30), this would allow reducing the axial length of
the hub extension (38) by distance L.
[0021] In yet another aspect of the invention, as may be
appreciated in FIG. 4, the extended base (40) of the counterbore
allows deeper penetration of shaft (20) relative to the plane (30)
of typical maximum tensile stress, thereby reducing axial overhang
of the compressor wheel. In one exemplary embodiment, counterbore
(36) includes alignment pilots (42) disposed to facilitate the
centering of the shaft (20) received in counterbore (36). That is,
alignment pilots (42) are configured to minimize eccentricity of
shaft (20) relative to the walls of the counterbore. As will be
appreciated by those skilled in the art, the compressor wheel,
shaft, and thrust collar (44) may rotate relative to a bearing
configured to provide radial support to the rotating
structures.
[0022] While the preferred embodiments of the present invention
have been shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions will occur to those of skill
in the art without departing from the invention herein.
Accordingly, it is intended that the invention be limited only by
the spirit and scope of the appended claims.
* * * * *