METHOD OF MANUFACTURING A COMPRESSOR HOUSING
The present invention relates to a method of manufacturing a compressor housing for
receiving an impeller to provide a compressor and relates particularly, but not
exclusively, to a method of manufacturing a compressor housing for use in a
turbocharger, such as a variable geometry turbocharger. The present invention also
relates to a method of manufacturing a compressor and particularly, but not
exclusively, to a method of manufacturing a compressor for use in a turbocharger, such
as a variable geometry turbocharger.
A compressor comprises an impeller wheel, having a plurality of blades (or vanes)
mounted on a shaft for rotation within a compressor housing. In the case of a
centrifugal compressor, rotation of the impeller wheel causes gas (e.g. air) to be drawn
into the impeller wheel and delivered to an outlet volute defined, at least in part, by the
compressor housing around the impeller wheel.
One use of a compressor is in a turbocharger. Turbochargers are well known devices
for supplying air to the intake of an internal combustion engine at pressures above
atmospheric pressure (boost pressures). A conventional turbocharger essentially
comprises a housing in which is provided an exhaust gas driven turbine wheel mounted
on a rotatable shaft connected downstream of an engine outlet manifold. A compressor
impeller wheel is mounted on the opposite end of the shaft such that rotation of the
turbine wheel drives rotation of the impeller wheel. In this application of a compressor,
the impeller wheel delivers compressed air to the engine intake manifold. The
turbocharger shaft is conventionally supported by journal and thrust bearings, including
appropriate lubricating systems.
A known centrifugal compressor housing comprises an axial intake, an annular diffuser
and an annular outlet volute in the form of a scroll volute. An impeller, with a plurality of
blades, is mounted on a shaft, for rotation about a longitudinal axis of the compressor
housing, and is received between the axial intake and the outlet volute.
A radially inner surface of the axial intake forms an annular intake passage that
extends axially inboard from an intake port to the impeller wheel.
The diffuser comprises first and second wall members having respectively opposed
first and second surfaces that define an annular diffuser passage that surrounds the
impeller and extends in a radially outward direction from an annular diffuser inlet
downstream of said plurality of blades, the tips of the blades sweeping across said
diffuser inlet during use, to an annular diffuser outlet communicating with the annular
outlet volute. The diffuser outlet is formed by respective annular outlet ends of the first
and second surfaces.
An inner surface of the outlet volute defines an annular outlet volute passage that
extends, along a circumferentially extending volute passage axis, about the
compressor housing longitudinal axis.
In use, as the impeller rotates, air is drawn in from the intake port, through the axial
intake, to the impeller and passes from the impeller through the diffuser passage to the
annular outlet volute passage. The compressed air passes along the outlet volute
passage and out through a volute outlet to a desired location, e.g. to an engine intake
manifold.
The inner surface of the volute extends, in a circumferential direction about the volute
passage axis, from the annular outlet end of the first surface that defines the diffuser
passage to the annular outlet end of the second surface that defines the diffuser
passage. The inner surface has a generally constant radius, relative to the volute
passage axis, such that the inner surface of the volute has a generally circular crosssectional
shape about the volute passage axis.
The inner surface of the volute has an annular first section that extends axially
outboard (i.e. away from the diffuser passage) from the annular outlet end of the first
surface that defines the diffuser passage.
It is known to form the first section of the inner surface of the volute such that it extends
radially inwardly (relative to the compressor housing longitudinal axis) of the annular
outlet end of the first surface that defines the diffuser passage to form a radially
outwardly protruding annular lip, curved along its radial extent, that extends along the
annular inlet end of the first surface. Providing this curved lip is advantageous in that it
acts to better align the circulating flow in the outlet volute, as it passes from the first
section of the inner surface of the volute towards the diffuser outlet, with the flow
leaving the diffuser outlet, thereby reducing losses. The shape of the first section to
form the lip is produced by appropriate shaping of the outer surface of a core around
which the compressor housing is cast (for example a sand core or metal core, as
described below).
An outlet volute may be formed from a single piece or from multiple pieces that are
subsequently attached together.
It is known to use sand casting to produce a single piece closed volute with a cross
sectional shape having this lip. In sand casting, a die is located around a sand core. A
suitable bonding agent (usually clay) is typically mixed with the sand and the mixture is
moistened, typically with water, but sometimes with other substances, to provide the
strength and plasticity of the core suitable for moulding. The sand is compacted
around a mould to provide the required shape of the core.
The die is positioned to enclose the sand core to define a mould cavity between an
inner surface of the die and an outer surface of the sand core. Accordingly, an inner
surface of the die defines the shape of the outer surface of the outlet volute (as well as
of the diffuser and axial intake) and an outer surface of the sand core defines the
shape of the inner surface of the outlet volute (as well as of the diffuser and axial
intake).
Molten metal is injected into the mould cavity. Once the molten metal cools and
solidifies, the die is removed and the sand core is removed from the inside of the
compressor housing by tipping the sand particles out through the volute outlet.
Sand casting is disadvantageous in that, during the casting process, the shape of the
sand core can change, resulting in dimensional inconsistency. In addition, it produces a
relatively poor surface finish which, during use, results in losses in the flow.
It is also known to use pressure die casting to produce a multiple piece closed volute
with this cross sectional shape. In pressure die casting molten metal is forced under
pressure into a mould cavity. The mould cavity is defined between an inner surface of a
die and an outer surface of a metal core located within the die.
In this process, multiple sections of the compressor housing (axially opposed sections)
are formed separately, using pressure die casting, and are then assembled together to
form a volute inner surface with the above cross sectional shape (a circular crosssectional
shape provided with said lip). Pressure die casting is advantageous in that it
provides a better surface finish than sand casting, which gives better performance and
reduces losses in the flow. However, due to the interfaces between the multiple
sections, the volute has problems of leakage and containment issues, resulting in
losses and inefficiencies in the flow.
Furthermore, it is currently not possible to use pressure die casting to form a single
piece volute having a cross sectional shape provided with said lip, since the lip would
prevent the metal core from being removed out of the volute after the casting process
is complete.
In addition, due to the relatively high tooling costs with pressure die casting, it is
necessary for high volumes of the compressor housing to be manufactured in order for
the manufacturing process to be economically viable.
It is an object of the present invention to obviate or mitigate one or more of the
problems set out above. A further object of the present invention is to provide an
alternative method of manufacturing a compressor housing, compressor and
turbocharger. A yet further object of the present invention is to provide a compressor
housing, compressor and turbocharger manufactured according to the alternative
method.
According to a first aspect of the invention there is provided a method of manufacturing
a compressor housing comprising:
arranging a core with a die so as to define a mould cavity between a surface of
the core and a surface of the die, the mould cavity having the shape of a compressor
housing;
providing a molten metal within the mould cavity and solidifying the molten
metal to form a compressor housing;
the compressor housing having a longitudinal axis and being for receipt of an
impeller wheel, mounted for rotation about an axis;
the compressor housing comprising an annular diffuser first wall member
having a surface for defining, with an opposed surface of an annular diffuser second
wall member, an annular diffuser passage;
the surface of the first wall member of the diffuser extending radially outwardly
from an annular inlet end to an annular outlet end and having an annular outlet section
extending radially inwardly from the outlet end;
the compressor housing further comprising an annular outlet volute first wall
member having a surface for defining, with a surface of an annular outlet volute second
wall member, an annular outlet volute passage;
the surface of the annular outlet volute first wall member defining a volute
channel that extends, along a circumferentially extending volute channel axis, about
the compressor housing longitudinal axis;
the surface of the annular outlet volute first wall member having an annular inlet
end, provided at the outlet end of the surface of the first wall member of the diffuser,
the surface of the annular outlet volute first wall member having an annular first section
that extends axially outboard from the annular inlet end ;
the compressor housing being formed such that for at least one circumferential
position about the compressor housing longitudinal axis, a first angle is subtended
between the outlet section of the surface of the diffuser first wall member and the first
section of the surface of the outlet volute first wall member;
the outlet volute first wall member being formed with an opening ;
wherein after the compressor housing has been formed in the mould cavity, the
core is removed from the volute channel;
once the core has been removed from the volute channel, a cut is applied,
through the opening, to the first section of the surface of the outlet volute first wall
member, at the least one circumferential position, to produce a cut section such that a
second angle is subtended between the cut section and the outlet section of the
surface of the diffuser first wall member, at said at least one circumferential position,
that is greater than the first angle.
Applying a cut to the at least one circumferential position of the first section of the
surface of the outlet volute first wall member that increases the angle subtended
between this surface and the outlet section of the surface of the diffuser first wall
member, at said at least one circumferential position, acts to better align the circulating
flow in the outlet volute, as it passes from the first section of the inner surface of the
volute towards the diffuser outlet, with the flow leaving the diffuser outlet, thereby
reducing losses.
Accordingly, casting the compressor housing around a core within a die, removing the
core and applying the above described cut through the opening in the outlet volute first
wall member allows pressure die casting to be used to produce a single piece volute
with a cross sectional shape that better aligns the circulating flow in the outlet volute
with the flow leaving the diffuser, than was otherwise possible, since the core may be
removed through the opening in the outlet volute, before the cut is made.
The method may be used with pressure die casting, which is advantageous in that it
provides a good surface finish, which reduces losses in the flow.
The method is also advantageous when a core of a particulate material (such as sand)
is used since the core may be supported through the opening in the outlet volute first
wall member. This reduces any shifting of the particular core during the casting
processes, providing increased dimensional consistency.
It will be appreciated that references to the surface of the first wall member of the
diffuser extending radially outwardly from the inlet end to the outlet end, and to the
annular outlet section extending radially inwardly from the outlet end, refer to the
surface/section extending generally in the radial direction and do not necessarily
require that the surface/section is substantially parallel to the radial direction. The
surface of the first wall member of the diffuser may be curved.
In this regard, the surface of the first wall member of the diffuser may extend radially
outwardly from the inlet end to the outlet end in a direction which is substantially
parallel to the radial direction. Alternatively, the surface of the first wall member of the
diffuser may extend radially outwardly from the inlet end to the outlet end in a direction
which is inclined relative to the radial direction. The annular outlet section of the
surface of the first wall member of the diffuser may extend radially inwardly from the
outlet end in a direction which is substantially parallel to the radial direction.
Alternatively, the annular section may extend radially inwardly from the outlet end in a
direction which is inclined relative to the radial direction.
Similarly, it will be appreciated that references to something (e.g. a surface or wall
member) extending in the radial or axial direction do not necessarily require that the
surface is substantially parallel to the radial or axial direction respectively, but merely
require that they have at least a component in the radial or axial direction respectively.
Similarly, it will be appreciated that references to the surface of the first wall member of
the outlet volute having an annular first section that extends in the axially outboard
direction refer to the surface extending generally in the axially outboard direction and
do not necessarily require that the surface is substantially parallel to the axially
outboard direction. In this regard, it will be appreciated that the outboard direction
refers to the direction away from the diffuser passageway (the surface of the first wall
member of the diffuser), and the inboard direction refers to the direction towards the
diffuser passageway.
The cut may extend radially inwardly of the outlet end of the surface of the first wall
member of the diffuser, at the at least one circumferential position. In this regard, the
cut section may extend radially inwardly of the outlet end of the surface of the first wall
member of the diffuser, at the at least one circumferential position. The cut section
may form a lip that extends in the circumferential direction about the volute channel
axis.
The cut may be at an oblique angle to the outlet section of the surface of the diffuser
first wall member, at the at least one circumferential position. In this regard, the cut
section may be at an oblique angle to the outlet section of the surface of the diffuser
first wall member, at the at least one circumferential position. Preferably the cut section
extends in a direction which has a component in both the axial and radial directions
(relative to the longitudinal axis of the compressor housing) .
The cut section may be at an angle to the outlet section of the surface of the diffuser
first wall member, at the at least one circumferential position, that is greater than or
equal to 270°, preferably greater than 270°. The cut section may be at an angle to said
outlet section that is greater than 270° and less than or equal to 350°. Preferably the
cut section is at an angle to said outlet section that is greater than or equal to 280° and
less than or equal to 320° . Preferably the cut section is at an angle to said outlet
section of substantially 290°.
It will be appreciated that angle of the cut made will be the same as the angle of the cut
section.
Preferably the surface of the first wall member of the outlet volute extends in a
circumferential direction about the volute channel axis, from the inlet end of said
surface to a radially outer end of said surface (radially outer relative to the compressor
housing longitudinal axis) .
The surface of the first wall member of the outlet volute may have a radius, relative to
the volute channel axis, that varies with the circumferential position of said surface
about the volute channel axis.
Optionally, before the cut is applied, the first section of the surface of the first wall
member of the outlet volute has a substantially constant radius, relative to the
compressor housing longitudinal axis, substantially along its length in the direction of
the compressor housing longitudinal axis, the surface of the first wall member of the
volute outlet has a radially outer section that extends axially outboard of the radially
outer end of said surface and has a substantially constant radius across its length in
the direction of the compressor housing longitudinal axis, said surface also having a
base section extending between the first section and the radially outer section.
Preferably the base section is curved along its length in the circumferential direction
about the volute channel axis. Preferably, along its length in the circumferential
direction about the volute channel axis, the base section has a substantially constant
radius, relative to the volute channel axis.
In this regard, before the cut is made, the surface of the outlet volute first wall member
may form a substantially D-shaped cross-sectional shape, about the volute channel
axis.
Alternatively, before the cut is made, the surface of the first wall member of the outlet
volute may have a radius, relative to the volute channel axis, that is substantially
constant with the circumferential position of said surface (about the volute channel
axis) . In this regard, the surface of the outlet volute first wall member may form a
substantially circular cross-sectional shape, about the volute channel axis.
The cut section may extend from a first end, to a second end, in the circumferential
direction about the volute channel axis.
The first end of the cut section may be provided at the inlet end of the surface of the
first wall member of the outlet volute, at the at least one circumferential position.
Alternatively, the first end of the cut section may be disposed at a point between the
inlet end of the surface of the first wall member of the outlet volute and the radially
outer end of said surface.
It will be appreciated that the angles referred to above (and below) are the external
angles subtended by the outwardly facing respective surfaces (as opposed to the
internal angle subtended by these surfaces) .
The cut section may have a length in the circumferential direction, about the volute
channel axis, that is less than or equal to half the length of the surface of the first wall
member of the outlet volute in the circumferential direction, about the volute channel
axis. Said length of the cut section may be less than or equal to 50% of said length of
the surface of the first wall member of the outlet volute, preferably less than or equal to
50% and greater than or equal to 5%, more preferably less than or equal to 40% and
greater than or equal to 10% and even more preferably less than or equal to 30% and
greater than or equal to 20% of said length.
The angle of the cut section relative to the outlet section of the surface of the first wall
member of the diffuser, at the at least one circumferential position, may vary along its
length in the circumferential direction about the volute channel axis. In this case, the
cut section may comprise a plurality of portions extending in said circumferential
direction that are inclined at different angles relative to said outlet section.
The angle of the cut section relative to the outlet section of the surface of the first wall
member of the diffuser, at the at least one circumferential position, may be substantially
constant along its length in the circumferential direction about the volute channel axis.
The cut section may be substantially straight in the circumferential direction about the
volute channel axis. At least one, or each, portion may be substantially straight in the
circumferential direction about the volute channel axis.
The plurality of portions may be arranged in an end to end configuration, in the
circumferential direction about the volute channel axis. Where the cut section
comprises said plurality of portions, the second angle may be the angle subtended
between the portion that is nearest the inlet end of the surface of the first wall member
of the outlet volute, and the outlet section of the surface of the diffuser first wall
member, at said at least one circumferential position.
The plurality of portions may approximate a concave curve that faces into the volute
channel.
The surface of the outlet volute first wall member may be at least partially curved from
the inlet end of the surface of the first wall member of the outlet volute to the radially
outer end of said surface and the plurality of portions may approximate a curve of
substantially the same radius as the curvature of the surface of the outlet volute first
wall member.
The cut section may be curved, or at least partially curved, along its length in the
circumferential direction, about the volute channel axis.
Alternatively, the angle of the cut section relative to the outlet section of the surface of
the first wall member of the diffuser may be substantially constant along its length in
the circumferential direction, about the volute channel axis.
The cut may be made by a single cutting operation or by a plurality of cutting
operations.
The at least one circumferential position may be a plurality of circumferential positions
about the compressor housing longitudinal axis. The at least one circumferential
position is preferably substantially every circumferential position about the compressor
housing longitudinal axis. In this regard, the cut may be made at least partially around
the circumference of the first section of the surface of the outlet volute first wall
member, about the compressor housing longitudinal axis. Preferably the cut is made
substantially around the entire said circumference of the first section of the surface of
the outlet volute first wall member. Accordingly, the cut section may extend at least
partially around the said circumference of the first section of the surface of the outlet
volute first wall member. Preferably the cut section extends around substantially the
entire said circumference of the first section (the circumference about the compressor
housing longitudinal axis). The cut section may form a lip that extends in the
circumferential direction about the compressor housing longitudinal axis.
In this regard the, or each portion, may be an annular portion that extends about the
longitudinal axis of the compressor housing.
Preferably the cut section has a substantially constant shape with circumferential
position about the compressor housing longitudinal axis. The length of the cut section,
in the circumferential direction about the volute channel axis, is preferably substantially
constant with circumferential position about the compressor housing longitudinal axis.
The second angle is preferably substantially constant with circumferential position
about the compressor housing longitudinal axis. This is advantageous in that it allows
for a simpler machining operation to machine the cut. Specifically, it allows the cut to
be machined in a single operation. This allows the cuts to be made using a lathe.
Alternatively, the cut section may have a varying shape with circumferential position
about the compressor housing longitudinal axis, with said length of the cut section
and/or said second angle, varying with said circumferential position. In order to produce
such a circumferentially varying cut, a CNC lathe may be used.
Preferably the outlet end of the surface of the first wall member of the diffuser outlet
has a radius that is substantially constant with circumferential position about the
compressor housing longitudinal axis. This is advantageous in that it allows for a
simpler machining operation to machine the cut. Specifically, it allows the cut to be
machined in a single operation.
The cut may be made by applying a cutting surface of a cutting tool to the first section
of the surface of the outlet volute first wall member and rotating the cutting tool relative
to said surface. In this regard, the cutting surface may be stationary, with said surface
of the outlet volute rotated, or vice versa. Preferably the cutting surface and/or the
compressor housing is rotated about the longitudinal axis of the compressor housing.
The cut may be made by a single continuous rotation of said first section relative to the
cutting surface.
Alternatively, the cut may be made by a plurality of rotations of said first section relative
to the cutting surface.
Before the cut is made, the first section of the surface of the first wall member of the
outlet volute, at the at least one circumferential position, may be of a substantially
constant radius, relative to the compressor housing longitudinal axis, across the length
of the first section in the circumferential direction about the volute channel axis. In this
respect, before the cut is made, the first section may define a cylinder that extends in
the axial direction, along a longitudinal axis that is centred on and coincident with the
longitudinal axis of the compressor housing.
Before the cut is made, the first section may be substantially perpendicular to the outlet
section of the surface of the diffuser first wall member, at the at least one
circumferential position. In this regard, the first angle may be substantially 270 °.
The outlet section of the surface of the diffuser first wall member, at the least one
circumferential position, may be substantially planar. The outlet section, at the at least
one circumferential position, may extend in a radial plane that is substantially
perpendicular to the longitudinal axis of the compressor housing.
Preferably the compressor housing is formed as a single piece. The outlet volute is
preferably formed as a single piece.
The core may be a solid core, such as a core made of metal or a metal alloy. The core
may be made of any suitable material, including stainless steel or any suitable metal
alloy. The molten metal may be injected into the mould cavity under pressure. In this
respect, the compressor housing may be formed by a pressure die casting.
The core may be a core of a particulate material. In this respect, the core may be made
of sand, or of any other suitable material. The molten metal may be provided in the
mould cavity by being injected, or poured, into the mould cavity. The molten metal may
be gravity fed into the mould cavity.
Preferably where the core is a core of a particulate material, the core is supported
through the opening in the outlet volute first wall member. Preferably the core is
supported through the opening across substantially the entire circumferential length of
the core, about the compressor housing longitudinal axis. This is advantageous in that
it reduces any shifting of the particular core during the casting processes, providing
increased dimensional consistency.
Preferably the core is removed from the compressor housing through the opening in
the outlet volute first wall member. Preferably where the core is a solid core, the core
is removed from the compressor housing through the opening. This is advantageous
as it allows pressure die casting to be used to produce a single piece volute with a
cross sectional shape that better aligns the circulating flow in the outlet volute with the
flow leaving the diffuser, than was otherwise possible. Where the core is a particulate
core, such as sand, the core may be removed through the opening and/or through an
outlet of the volute.
Preferably the opening is an annular opening. Preferably the opening extends about
substantially the entire circumference of the longitudinal axis of the compressor
housing. Preferably the opening extends across substantially the entire radial extent of
the volute channel, relative to the longitudinal axis of the compressor housing.
The compressor housing preferably comprises an axial intake and an intermediary
section that extends between the axial intake and the annular diffuser first wall
member. The axial intake and/or the intermediary section may be integrally formed with
the remainder of the compressor housing (e.g. the annular diffuser first wall member)
or may be formed separately and subsequently attached thereto.
According to a second aspect of the invention there is provided a method of
manufacturing a compressor comprising:
manufacturing a compressor housing according to the first aspect of the
invention;
providing a body having an annular diffuser second wall member and an
annular outlet volute second wall member, assembling the body with the compressor
housing such that the surface of the annular diffuser first wall member and a surface of
the annular diffuser second wall member define an annular diffuser passage and the
surface of the annular outlet volute first wall member and a surface of the annular outlet
volute second wall member define an annular outlet volute that is downstream of and in
fluid communication with the diffuser passage;
mounting an impeller within the compressor housing, the impeller being
mounted on a shaft for rotation about said longitudinal axis, the impeller having a
plurality of blades, the diffuser passage surrounding the impeller, with the tips of the
blades sweeping across said diffuser inlet during use.
The body may be a component of a turbo-machine, including a bearing housing and/or
a diffuser plate.
The surface of the annular diffuser second wall member may be substantially parallel to
the radial direction (relative to the compressor housing longitudinal axis). Alternatively,
the surface of the annular diffuser second wall member may be inclined relative to the
radial direction. The surface of the annular diffuser second wall member may be
substantially parallel to the surface of the annular diffuser first wall member. The
surface of the annular diffuser second wall member may be curved.
According to a third aspect of the invention there is provided a method of
manufacturing a turbocharger comprising manufacturing a compressor according to the
second aspect of the invention and assembling the compressor with a turbine and
bearing assembly to form a turbocharger.
According to a fourth aspect of the invention there is provided a compressor housing
manufactured by the method of the first aspect.
According to a fifth aspect of the invention there is provided a compressor
manufactured by the method of the second aspect.
According to a sixth aspect of the invention there is provided a turbocharger
manufactured by the method of the third aspect.
Other advantageous and preferred features of the invention will be apparent from the
following description.
Specific embodiments of the present invention will now be described, by way of
example only, with reference to the accompanying drawings, in which:
Figure 1 is an axial cross-section through a known variable geometry turbocharger;
Figure 2 is a rear perspective view of a slightly different version of the compressor
housing shown in figure 1 (with the impeller wheel omitted for illustrative purposes);
Figure 3 is a cross-sectional view of an upper half of the compressor housing shown in
figure 2 , taken along an axial plane;
Figure 4 is an axial cross-sectional view of a die and core for use in a method of
manufacturing a compressor housing according to the method of the present invention
Figure 5 is an axial cross-sectional view of an upper half of a compressor housing
manufactured according to the method of the present invention but before a cut,
according to the method, is made to the compressor housing;
Figure 6 is an enlarged cross-sectional view of the diffuser and volute of the
compressor housing shown in Figure 5 , after the cut according to the method of the
present invention has been made to the compressor housing;
Figures 7a to 7d show views corresponding to that of figure 6 , but taken along axial
planes at 0° , 90° , 180 ° and 270° respectively, relative to the volute outlet.
Figure 8 is a view corresponding to the of Figure 6 , but where the compressor housing
is assembled with a wall member of a bearing housing to form a compressor;
Figure 9 is a schematic flow diagram showing the direction of flow in the compressor of
Figure 8 , during use;
Figure 10 is a graph showing the variation of total pressure ratio (t-t) across the
compressor (i.e. between the compressor inlet and volute outlet) with normalised mass
flow for a compressor with an open 'D-section' volute (such as the compressor housing
shown in Figure 5 (i.e. before the cut is made)) and for the compressor of Figure 8 (i.e.
after the cut has been made);
Figure 11 is a graph showing the variation of total efficiency (t-t) across the compressor
(i.e. between the compressor inlet and volute outlet) with normalised mass flow for a
compressor with an open 'D-section' volute (such as the compressor housing shown in
Figure 5 (i.e. before the cut is made)) and for the compressor of Figure 8 (i.e. after the
cut has been made), and
Figure 1 is a view corresponding to that of Figure 4 , but where the core is a sand core
301 ' .
Referring to Figures 1 to 3 , this illustrates a known variable geometry turbocharger
comprising a turbine 4 1 and a compressor 40 interconnected by a bearing assembly
60.
The turbine 4 1 comprises a turbine wheel 5 mounted on one end of a shaft 4 for
rotation within a turbine housing 1. The compressor 40 comprises an impeller wheel 6
mounted on the other end of the shaft 4 for rotation within a compressor housing 2 . The
compressor housing 2 has a central longitudinal axis 4a.
The turbine housing 1 and the compressor housing 2 are interconnected by a central
bearing housing 3 . The turbocharger shaft 4 extends from the turbine housing 1 to the
compressor housing 2 through the bearing housing 3 . The shaft 4 rotates about an
axis that is substantially parallel and co-incident with the longitudinal axis 4a of the
compressor housing 2 , on bearings located in the bearing housing 3 .
In between the compressor housing 2 and the bearing housing 3 is a diffuser plate 2a
which is recessed to accommodate an inboard portion of the compressor wheel 6 , i.e. a
portion nearest to the bearing housing 3 , to increase the efficiency of the compressor
40.
The turbine housing 1 defines an inlet volute 7 to which gas from an internal
combustion engine (not shown) is delivered. The exhaust gas flows from the inlet
volute 7 to an axial outlet passage 8 via an annular inlet passage 9 and the turbine
wheel 5 . The inlet passage 9 is defined on one side by a face 10 of a radial wall of a
movable annular wall member 11, commonly referred to as a "nozzle ring", and on the
opposite side by an annular shroud 1 which forms the wall of the inlet passage 9
facing the nozzle ring 11. The shroud 12 covers the opening of an annular recess 13 in
the turbine housing 1.
The nozzle ring 11 supports an array of circumferentially and equally spaced inlet
vanes 14 each of which extends across the inlet passage 9 . The vanes 14 are
orientated to deflect gas flowing through the inlet passage 9 towards the direction of
rotation of the turbine wheel 5 . When the nozzle ring 11 is proximate to the annular
shroud 12, the vanes 14 project through suitably configured slots in the shroud 12, into
the recess 13.
The position of the nozzle ring 11 is controlled by an actuator assembly of the type
disclosed in US 5,868,552. An actuator (not shown) is operable to adjust the position of
the nozzle ring 11 via an actuator output shaft (not shown), which is linked to a yoke
15. The yoke 15 in turn engages axially extending actuating rods 16 that support the
nozzle ring 11. Accordingly, by appropriate control of the actuator (which may for
instance be pneumatic or electric), the axial position of the rods 16 and thus of the
nozzle ring 11 can be controlled. The speed of the turbine wheel 5 is dependent upon
the velocity of the gas passing through the annular inlet passage 9 . For a fixed rate of
mass of gas flowing into the inlet passage 9 , the gas velocity is a function of the width
of the inlet passage 9 , the width being adjustable by controlling the axial position of the
nozzle ring 11. Figure 1 shows the annular inlet passage 9 fully open. The inlet
passage 9 may be closed to a minimum by moving the face 10 of the nozzle ring 11
towards the shroud 12.
The nozzle ring 11 has axially extending radially inner and outer annular flanges 17
and 18 that extend into an annular cavity 19 provided in the bearing housing 3 . Inner
and outer sealing rings 20 and 2 1 are provided to seal the nozzle ring 11 with respect
to inner and outer annular surfaces of the annular cavity 19 respectively, whilst allowing
the nozzle ring 11 to slide within the annular cavity 19. The inner sealing ring 20 is
supported within an annular groove formed in the radially inner annular surface of the
cavity 19 and bears against the inner annular flange 17 of the nozzle ring 11. The outer
sealing ring 20 is supported within an annular groove formed in the radially outer
annular surface of the cavity 19 and bears against the outer annular flange 18 of the
nozzle ring 11.
Referring to Figures 2 and 3 , the compressor housing 2 defines an axial intake 42 and
an annular diffuser passage 43. The compressor housing 2 also comprises an annular
outlet volute 44 defining an outlet volute passage 9 1 .
The axial intake 42 is defined by a substantially annular radially inner surface 67 of the
compressor housing 2 that is substantially centred on the compressor housing
longitudinal axis 4a. The radially inner surface 67 extends axially inboard (i.e. towards
the annular diffuser passage 43) from an intake port 66 to an annular intermediary
surface 50.
The intermediary surface 50 extends from the axially inboard end of the radially inner
surface 67 and is an extension of said inner surface 67. As the intermediary surface 50
extends from the axially inboard end of the inner surface 67, it curves from the axial
direction 4a to the radial direction (relative to the compressor housing longitudinal axis
4a).
The annular diffuser passage 43 extends in the radial direction from a diffuser inlet 48,
that is in fluid communication with the impeller wheel 6 , to a diffuser outlet 5 1 that is in
fluid communication with the annular outlet volute 44. The annular diffuser passage 43
is defined by a surface 8 1 of an annular diffuser first wall member 82 and an opposed
surface 83 of an annular diffuser second wall member 84. In the described
embodiment the annular diffuser second wall member 84 is formed by the diffuser plate
2a. The opposed surfaces 8 1 , 83 are substantially parallel to each other and are
substantially perpendicular to the longitudinal axis 4a of the compressor housing 2 .
The surface 8 1 of the annular diffuser first wall member 82 has the general shape of a
ring, substantially centred on the longitudinal axis 4a of the compressor housing 2 . The
surface 8 1 of the annular diffuser first wall member 82 extends radially outwardly from
an inlet end 81a to an outlet end 81b. The surface 8 1 of the annular diffuser first wall
member 82 has an outlet section 101 that extends radially inwardly from the outlet end
81b.
The surface 83 of the annular diffuser second wall member 84 is a substantially planar
disc that is substantially continuous along its radial extent. The surface 83 has a
radially outer end that forms an annular outlet end 83b.
The impeller wheel 6 is mounted on the shaft 4 between the axial intake 42 and the
annular outlet volute 44. The impeller wheel 6 has a plurality of blades 45, each having
a front radial edge 46 which in use rotates within the axial intake 42, a tip 47 which
sweeps across the annular inlet 48 of the annular diffuser passage 43 and a curved
edge 49 defined between the front radial edge 46 and the tip 47 which sweeps across
the intermediary surface 50 of the compressor housing 2 . In this regard, the
intermediary surface 50 has a curved profile that is substantially matches that of the
impeller wheel blades 45.
Gas flowing from the turbine inlet volute 7 to the outlet passage 8 passes over the
turbine wheel 5 and as a result torque is applied to the shaft 4 to drive the compressor
wheel 6 . Rotation of the compressor wheel 6 within the compressor housing 2
pressurises ambient air present draws air in through the intake port 66, through the
axial intake 42 to the impeller wheel 6 , which delivers the pressurised air through the
annular diffuser passage 43 to the outlet volute 44. The air then delivered from an
outlet 75 of the volute 44 from which it is fed to an internal combustion engine (not
shown).
An inner surface 90 of the outlet volute 44 defines an annular outlet volute passage 9 1
that extends, along a circumferentially extending volute passage axis 99, about the
compressor housing longitudinal axis 4a from a volute tail to the volute outlet 75. The
volute 44 has a general scroll shape.
The inner surface 90 of the volute 44 extends, in a circumferential direction about the
volute passage axis 99, from an inlet end 103, provided at the outlet end 81b of the
surface 8 1 of the first annular diffuser wall member 82 to an annular radially outer end
104, provided at the outlet end 83b of the surface 83 of the second annular diffuser
member 84. The inner surface 90 has a substantially constant radius, relative to the
volute passage axis 99, such that the inner surface 90 has a substantially circular
cross-sectional shape about the volute passage axis 99.
The inner surface 90 of the volute 44 has an annular first section 102 that extends
axially outboard (i.e. away from the diffuser passage 43) from the annular outlet end
8 1b of the surface 8 1 of the first annular diffuser wall member 82.
It is known to form the first section 102 such that it extends radially inwardly (relative to
the compressor housing longitudinal axis 4a) of the annular outlet end 81b of the
surface 8 1 of the first annular diffuser wall member 82 to form a radially outwardly
protruding annular lip 200 (see Figure 1), curved along its radial extent, that extends
along the annular outlet end 81b of the first surface 8 1 . Providing this curved lip 200 is
advantageous in that it acts to better align the circulating flow in the outlet volute 44, as
it passes from the first section 102 of the inner surface 90 of the volute 44 towards the
diffuser outlet 5 1 , with the flow leaving the diffuser outlet 5 1 , thereby reducing losses.
The shape of the first section 102 to form the lip 200 is produced by appropriate
shaping of the outer surface of a core around which the compressor housing is cast (for
example a sand core or metal core, as described below).
An outlet volute may be formed from a single piece or from multiple pieces that are
subsequently attached together.
It is known to use sand casting to produce a single piece closed volute with a cross
sectional shape having the lip 200 shown in Figures 1 to 3 . In sand casting, a die is
located around a sand core. A suitable bonding agent (usually clay) is typically mixed
with the sand and the mixture is moistened, typically with water, but sometimes with
other substances, to provide the strength and plasticity of the core suitable for
moulding. The sand is compacted around a mould to provide the required shape of the
core.
The die is positioned to enclose the sand core to define a mould cavity between an
inner surface of the die and an outer surface of the sand core. Accordingly, an inner
surface of the die defines the shape of the outer surface of the outlet volute (as well as
of the diffuser and axial intake) and an outer surface of the sand core defines the
shape of the inner surface of the outlet volute (as well as of the diffuser and axial
intake).
Molten metal is injected into the mould cavity. Once the molten metal cools and
solidifies, the die is removed and the sand core is removed from the inside of the
compressor housing by tipping the sand particles out through the volute outlet.
Sand casting is disadvantageous in that, during the casting process, the shape of the
sand core can change, resulting in dimensional inconsistency. In addition, it produces a
relatively poor surface finish which, during use, results in losses in the flow.
It is also known to use pressure die casting to produce a multiple piece closed volute
with this cross sectional shape. In pressure die casting molten metal is forced under
pressure into a mould cavity. The mould cavity is defined between an inner surface of a
die and an outer surface of a metal core located within the die.
In this process, multiple sections of the compressor housing (opposed axial sections)
are formed separately, using pressure die casting, and are then assembled together to
form a volute inner surface with the above cross sectional shape (a circular crosssectional
shape provided with said lip). Pressure die casting is advantageous in that it
provides a better surface finish than sand casting, which gives better performance and
reduces losses in the flow. However, due to the interfaces between the multiple
sections, the volute has problems of leakage and containment issues, resulting in
losses and inefficiencies in the flow.
Furthermore, it is currently not possible to use pressure die casting to form a single
piece volute having a cross sectional shape provided with said lip 200, since the lip 200
would prevent the metal core from being removed out of the volute after the casting
process is complete.
In addition, due to the relatively high tooling costs with pressure die casting, it is
necessary for high volumes of the compressor housing to be manufactured in order for
the manufacturing process to be economically viable.
Referring to Figure 4 there is shown a die 300 and a core 301 suitable for forming the
compressor housing shown in Figure 5 , using a method according to the first aspect of
the present invention. The core 301 has an outer surface 303 that is shaped to define
the inner surface of the compressor housing. The die 300 has an inner surface 304
shaped to define an outer surface of the compressor housing. In accordance with the
method of the present invention, the core 301 is arranged with the die 300 so as to
define a mould cavity 302 between said surfaces 303, 304 of the core 301 and die 300.
The mould cavity 302 has a shape corresponding to that of the compressor housing to
be formed.
In the described embodiment, the core is a solid core made of metal and the
compressor housing is formed using pressure die casting. In this respect, molten metal
is forced under pressure into the mould cavity 302. The molten metal is cooled and
solidified within the mould cavity 302 to form the compressor housing 500 shown in
Figure 5 .
Once the compressor housing 500 has been formed in the mould cavity 302, it is
removed from the mould cavity 302. In this respect, the mould 301 comprises a volute
forming portion 305 that has an outer surface which defines the inner surface 190a of
the volute 144 of the compressor housing 500 (see Figure 5). As the core 301 is
removed from the die 300 it is removed, in the direction of the longitudinal axis 4a of
the compressor housing 500 through a radially extending opening 306 defined by the
first wall member 185 (as described in more detail below).
Referring to Figure 5 there is shown a compressor housing 500 formed by the above
described pressure die casting method in relation to Figure 4 . The compressor
housing 500 is similar to that of the compressor housing 2 shown in Figures 1 to 3 and
corresponding features will be labelled with the same reference numerals incremented
by 100. The differences between the compressor housing 500 of Figure 5 and that
shown in Figures 1 to 3 will be described below.
The compressor housing 500 has a longitudinal axis 104a. As with the compressor
housing of Figures 1 to 3 , the compressor housing 500 defines an axial intake 142.
The axial intake 142 is defined by a substantially annular radially inner surface 167 of
the compressor housing 500 that is substantially centred on the compressor housing
longitudinal axis 4a. The radially inner surface 167 extends axially inboard (i.e.
towards the annular diffuser passage 143) from an intake port 166 to an annular
intermediary surface 150.
The intermediary surface 150 extends from the axially inboard end of the radially inner
surface 167 and is an extension of said inner surface 167. As the intermediary surface
150 extends from the axially inboard end of the inner surface 167, it curves from the
axial direction 4a to the radial direction (relative to the compressor housing longitudinal
axis 4a).
The compressor housing 500 comprises an annular diffuser first wall member 182
having a surface 181 for defining, with an opposed surface 183 of an annular diffuser
second wall member 184 (as described below in relation to Figure 8).
The surface 181 of the annular diffuser first wall member 182 extends radially
outwardly from an annular inlet end 181a, provided at a radially outer end of the
intermediary surface 150, to an annular outlet end 181b.
The surface 181 is substantially planar, extending in a radial plane relative to the
compressor housing longitudinal axis 104a. The surface 181a has the general shape
of a ring, substantially centred on the longitudinal axis 104a. The surface 181 extends
in a plane that is substantially perpendicular to the longitudinal axis 104a.
The surface 181 has an outlet section 201 that extends radially inwardly from the outlet
end 181b.
For the avoidance of doubt, the outlet section 201 extends in a radial plane that is
substantially perpendicular to the longitudinal axis 104a of the compressor housing
500.
The section of the compressor that defines axial intake 142 is formed integrally with the
annular diffuser first wall member 182. The compressor housing 500 is formed as a
single piece.
The compressor housing 500 also comprises an annular outlet volute first wall member
185. The annular outlet volute first wall member 185 has a surface 190a for defining,
with an opposed surface 190b of an annular outlet volute second wall member 187, an
annular outlet volute 144 (as described below in relation to Figure 8). The surface
190a of the first wall member 185 of the outlet volute defines a volute channel 350 that
extends along a volute channel axis 2 15 , in the circumferential direction about the
compressor housing longitudinal axis 104a, terminating at a volute outlet (not shown).
The inner surface 190a of the annular outlet first wall member 185 extends in a
circumferential direction about the volute channel axis 2 15 , from an inlet end 203,
provided at the outlet end 18 1b of the surface 18 1 of the annular diffuser first wall
member 182, to an annular radially outer end 204.
The surface 190a of the outlet volute first wall member 185 has an annular first section
202 that extends axially outboard (i.e. away from diffuser passage 143 formed when
the diffuser first wall member 182 is assembled with the diffuser second wall member
187, as described below) from the inlet end 203. Referring to Figure 5 , the first section
202 is a section of the surface 190a that is substantially parallel to the axial direction
104a.
The surface 190a also has a radially outer section 190c that extends axially inboard
from the radially outer end 204 of the surface 190a. The radially outer section 190c is
substantially parallel to the axial direction 104a.
The first section 202 and the radially outer section 190c are joined by an annular base
section 190d. The base section 190d is curved along its length in the circumferential
direction about the volute channel axis 2 15 and has a substantially constant radius of
curvature. In this regard, the surface 190a of the outlet volute first wall member 185
forms a substantially D-shaped cross-sectional shape about the volute channel axis
2 15 .
The first section 202 is substantially perpendicular to the outlet section 201 of the
surface 18 1 of the annular diffuser first wall member 182.
The first section 202 of the surface 190a of the first wall member 185 of the outlet
volute is of a substantially constant radius, relative to the compressor housing
longitudinal axis 104a, across the length of the first section 202 in the circumferential
direction about the volute channel axis 2 15 . In this respect, the first section 202
defines a cylinder that extends in the axial direction 104a, along a longitudinal axis that
is centred on and coincident with the longitudinal axis 104a of the compressor housing
500.
A first angle (A1 ) is subtended between the outlet section 201 of the surface 18 1 of the
annular diffuser first wall member 182 and the first section 202 of the surface 190a of
the annular outlet volute first wall member 185. The first angle is substantially 270 °.
A radial extending opening 306 is provided in the annular outlet volute first wall
member 185. In more detail, the surface 190a of the volute first wall member 185
defines an annular opening 306 that extends radially between the inlet end 203 and the
radially outer end 204 of the surface 190a.
After the compressor housing has been formed in the mould cavity 302, the volute
forming portion 305 of the core 301 is removed from the volute passage 350 out
through the opening 306. Because the first section 202 is substantially planar and
extends in the axial direction 104a, this allows the volute forming portion 305 of the
core 301 to be removed from within the volute passage 350.
The die 300 is also removed from the outer surface of the compressor housing 500.
As will now be described, a cut is then applied to a portion of the first section 202 of the
surface 190a of the annular outlet first wall member 185. The shape of the surface
190a after the cut has been made is shown in Figure 6 .
The cut is applied through the opening 306 in the annular outlet volute first wall
member 185 by the insertion of a cutting tool 700 (shown schematically in axial crosssection
in Figure 6) through the opening 306. A cutting surface 701 of the cutting tool
is brought into contact with a portion of the first section 202 of the surface 190a.
The applied cut produces a cut section 2 10 of the surface 190a. The cut section 2 10
comprises three portions 2 10a to 2 10c. The portions 2 10a - 2 10c are arranged in an
end to end configuration, in the circumferential direction about the volute channel axis
2 15 . In this regard, the first portion 2 10a extends from a first end provided at the inlet
end 203 of the surface 190a to a second end. The first portion 2 10a is inclined at a
second angle (A2), relative to the outlet section 201 of the surface 18 1 of the annular
diffuser first wall member 182. The second angle (A2) is substantially 290 °.
By reference to the axial plane shown in Figure 6 , it will be appreciated that the first
and second angles (A1 , A2) refer to the angles subtended at the same circumferential
position about the longitudinal axis 104a of the compressor housing 500. In this
regard, the first and second angles (A1 , A2) are the angles subtended by the
respective said surfaces in the same axial plane relative to the compressor housing
longitudinal axis 104a.
A first end of the second portion 2 10b extends from the second end of the first portion
2 10a to a second end. A first end of the third portion 2 10c extends from the second
end of the second portion 2 10b to a second end.
The cut section 2 10 has a length in the circumferential direction, about the volute
channel axis 2 15 , that is substantially 20% of the length of the surface 190a of the first
wall member 185 of the outlet volute in the circumferential direction, about the volute
channel axis 2 15 .
The cut section 2 10 extends radially inwardly (relative to the longitudinal axis 104a of
the compressor housing 500) of the outlet end 18 1b of the surface 18 1 of the annular
diffuser first wall member 182. In this regard, the cut section 2 10 extends radially
inwardly of the inlet end 203 of the surface 190a of the annular outlet first wall member
185.
In this respect, the first portion 2 10a of the cut section 2 10 extends radially inwardly of
the outlet end 18 1b of the surface 18 1 of the annular diffuser first wall member 182,
from said outlet end 18 1b.
Each of the portions 2 10a - 2 10c is at a different angle relative to the outlet section 201
of the surface 18 1 of the annular diffuser first wall member 182. As stated above, the
first portion 2 10a is inclined relative to the outlet section 201 of the surface 18 1 of the
annular diffuser first wall member 182 at an angle (A2) of substantially 290 °. The
second portion 2 10b is inclined relative to the outlet section 201 of the surface 18 1 of
the annular diffuser first wall member 182 at an angle of substantially 270 °. The third
portion 2 10c is inclined relative to the outlet section 201 of the surface 18 1 of the
annular diffuser first wall member 182 at an angle of substantially 250 °.
The portions 2 10a - 2 10c of the cut section 2 10 approximate a concave curve, relative
to the volute passage axis 2 15 , that faces into the volute channel 350 and has
substantially the same radius as the radius of the base section 190c, relative to the
volute passage axis 2 15 .
The cut is made using a single cutting operation. In this regard, the cutting tool 700 is
a lathe having an annular cutting surface that engages with the first section 202 of the
surface 190a to form the cut section 2 10 .
The cut is made by rotating the cutting surface 701 of the cutting tool 700 relative to the
annular outlet volute first wall member 185, about the compressor housing longitudinal
axis 104a. In this regard, the annular outlet first wall member 185 is held stationary
and the cutting tool is rotated about the longitudinal axis 104a of the compressor
housing 500. It will be appreciated that alternatively, or additionally, the compressor
housing 500 may be rotated.
The cut is made substantially around the entire circumference of the first section 202 of
the surface 190a of the outlet volute first wall member 185. Accordingly, the cut
section 210 extends around substantially the entire circumference of the first section
202 (the circumference about the compressor housing longitudinal axis 104a). The cut
section forms a lip 600 that extends in the circumferential direction about the
compressor housing longitudinal axis 104a. The lip 600 also extends in the
circumferential direction about the volute channel axis.
Figures 7A to 7D show the shape of the cut made at different circumferential positions
relative to the compressor housing longitudinal axis 104a, specifically, taken along axial
planes at 0° , 90° , 180 ° and 270° respectively, relative to the volute outlet.
The cut section 210 has a substantially constant shape with circumferential position
about the compressor housing longitudinal axis 104a. In this regard, the length of the
cut section 210, in the circumferential direction about the volute channel axis 215 is
substantially constant with circumferential position about the compressor housing
longitudinal axis 104a. Furthermore, the second angle (A2) is substantially constant
with circumferential position about the compressor housing longitudinal axis. This is
advantageous in that it allows for a simpler machining operation to machine the cut.
Specifically, it allows the cuts to be machined in a single operation using the lathe.
The second angle (A2) is greater than the first angle (A1) subtended between the outlet
section 201 of the surface 181 of the annular diffuser first wall member 82 and the
uncut first section 202 of the surface 190a of the annular outlet volute first wall member
185. This acts to better align the circulating flow in the outlet volute as it passes from
the first section 202 (i.e. the cut section 210) of the surface 190a towards the diffuser
outlet 151 , with the flow leaving the diffuser outlet 151 thereby reducing losses.
The cut is made using a single cutting operation using a single continuous rotation of
the cutting surface relative to the surface 190a.
It will be appreciated that the angles referred to in this description (and the claims) are
the external angles subtended by the outwardly facing respective surfaces (as opposed
to the internal angle subtended by the surfaces).
The outlet end 181b of the surface 181 of the annular diffuser first wall member 82 has
a radius, relative to the compressor housing longitudinal axis 104a, that is substantially
constant with its circumferential position about said longitudinal axis 104a. This is
advantageous in that it allows for a simpler machining operation to machine the cut.
Specifically, it allows the cut to be machined in a single turning operation. This allows
the cut to be made using a lathe.
Referring to Figures 7a to 7d, there is shown the position of the centroid (C) of the
cross-sectional area (A) (taken in an axial plane) of the volute at each circumferential
position shown. The centroid (C) has a centroid radius (R), which is the radius of the
centroid (C) relative to the longitudinal axis 104a. The volute is shaped such that the
ratio of the volute cross-sectional area (A) (taken in an axial plane) to the centroid
radius (R) decreases linearly with circumferential position from the volute outlet 175 to
the volute tail.
The above described method of casting the compressor housing 500 around a core
301 , removing the core through the opening 306 and applying the described cut
through the opening 306 in the outlet volute first wall member 185 allows pressure die
casting (or any suitable type of casting) to be used to produce a single piece volute
with a cross-sectional shape that better aligns the circulating flow in the outlet volute
with the flow leaving the diffuser than was otherwise possible. Pressure die casting is
advantageous in that it provides a good surface finish, which reduces losses in the
flow.
Referring to Figure 8 , the cut compressor housing 500 of Figure 6 is assembled with a
body 501 , and an impeller (not shown) is mounted within the compressor housing 500,
to form a compressor.
In more detail, the body 501 is a wall member of a bearing assembly of a turbocharger
(such as the bearing assembly 60 of the turbocharger of Figure 1). The body 501 is a
radially extending substantially planar body.
The body 501 has a radially inner section that forms an annular diffuser second wall
member 184. The annular diffuser second wall member 184 has a surface 183 that is
substantially parallel to the radial direction, relative to the compressor housing
longitudinal axis 104a, and the body 501 is mounted to the compressor housing 500
such that the surface 183 of the annular diffuser second wall member 184 is opposed
to the surface 181 of the annular diffuser first wall member 182 and defines an annular
diffuser passage 143 therewith.
The annular diffuser passage 143 extends from an inlet to an outlet 151 as with the
diffuser passageway of Figures 1 to 3 .
A radially outer section of the body 501 forms an annular volute second wall member
187. The body 501 is mounted to the annular outlet first wall member 185 such that
the radially outer section of the body forms an annular outlet volute second wall
member 187 with a surface 190b of the annular outlet volute second wall member 187
being opposed to the surface 190a of the annular outlet first wall member 185 and
defining a volute passage 191 therewith. In this regard, the surface 190b closes the
opening 306 in the annular outlet first wall member 185, with the volute channel 350
now forming the volute passage 19 1 .
In this regard, the surface 190b of the second annular outlet volute wall member 187
abuts the radially outer end 204 of the surface 190a of the annular outlet volute second
wall member 187 provides a closed radially outer end of the volute passage 19 1 .
The compressor may be assembled with a turbine to form a turbocharger (e.g. using
the arrangement of a compressor, bearing assembly and turbine as shown in Figure 1).
Figure 9 is a flow diagram showing the direction and magnitude of the flow being the
volute 144 of Figure 8 at the circumferential position of Figure 8 . It can be seen from
Figure 9 that, due to the cut, a flow passing along the cut section 210 towards the
diffuser outlet 151 is better aligned with the flow leaving the diffuser outlet (than if the
cut had not been made). This reduces losses in the flow, thereby improving the
performance of the compressor.
The improvement in performance obtained by making the cut is shown in Figures 10
and 11.
Figure 10 is a graph showing the variation of total pressure ratio (t-t) across the
compressor with normalised mass flow for a compressor with an open 'D-section'
volute (such as the compressor housing shown in Figure 5 (i.e. before the cut is
made)), shown by the line 'A' and for the compressor of Figure 8 (i.e. after the cut has
been made) , shown by the line 'B'.
From Figure 10 it can be seen that for the compressor of Figure 8 (i.e. where the cut
has been made), the total to total pressure ratio is higher across the entire range of
normalised mass flow through the compressor, than for the compressor housing shown
in Figure 5 (i.e. where the cut has not been made) .
Figure 11 is a graph showing the variation of total efficiency (t-t) across the compressor
with normalised mass flow for a compressor with an open 'D-section' volute (such as
the compressor housing shown in Figure 5 (i.e. before the cut is made)), shown by the
line 'A' and for the compressor of Figure 8 (i.e. after the cut has been made) , shown by
the line 'B'.
From Figure 11 it can be seen that for the compressor of Figure 8 (i.e. where the cut
has been made) , the total to total efficiency ratio is higher across the entire range of
normalised mass flow through the compressor, than for the compressor housing shown
in Figure 5 (i.e. where the cut has not been made) .
As can be seen from the above, the above method of manufacture is advantageous in
that casting the compressor housing around a core within a die, removing the core and
applying the above described cut through the opening in the outlet volute first wall
member allows pressure die casting to be used to produce a single piece volute with a
cross sectional shape that better aligns the circulating flow in the outlet volute with the
flow leaving the diffuser, than was otherwise possible, since the core may be removed
through the opening in the outlet volute, before the cut is made. Pressure die casting is
advantageous in that it provides a good surface finish, which reduces losses in the
flow.
It will be appreciated that numerous modifications to the above described method may
be made without departing from the scope of the invention as defined by the claims.
For example, in the described embodiment, the cut section 2 10 extends from the outlet
end 18 1b of the surface 18 1 of the annular diffuser first wall member 182.
Alternatively, the cut section may extend from a first end disposed at a point between
said outlet end 18 1b (i.e. the inlet end 203 of the surface 190a) and the radially outer
end 204 of the surface 190a.
In the described embodiments, the cut section comprises a plurality of said portions
2 10a - 2 10c. Alternatively, the cut section 2 10 may comprise more or fewer cut
portions. For example, the cut section may comprise only a single portion, for example
the portion 2 10a.
In the described embodiments, the angle of the cut portion 2 10a relative to the outlet
section 201 of the surface 18 1 is substantially 290 °. The second angle may be greater
than or equal to 270 °, preferably greater than 270 °. The cut section may be at an
angle to said outlet section that is greater than 270 ° and less than 350 °. Preferably the
cut section is at an angle to said outlet section that is greater than or equal to 280 ° and
less than or equal to 320 °. Preferably the cut section is at an oblique angle to the outlet
section of the surface of the diffuser first wall member, at the at least one
circumferential position.
In the described embodiments, each cut portion 2 10a - 2 10c is substantially planar.
However, it will be appreciated that one or more of said cut portions may be curved in
the circumferential direction relative to the volute passage axis 2 15 .
Before the cut is made, the surface 190a of the outlet volute first wall member 185 may
have a radius relative to the volute channel axis 2 15 that is substantially constant with
the circumferential position of said surface (about the volute channel axis). In this
regard, before the cut is made, the surface of the outlet volute first wall member 185
may form a substantially circular cross-sectional shape about the volute channel axis
2 15 . The surface 198 may have any suitable cross-sectional shape.
The cut section 2 10 may have a length in the circumferential direction, about the volute
channel axis 2 15 , that is less than or equal to half the length of the surface 190b of the
first wall member 185 of the outlet volute in the circumferential direction, about the
volute channel axis. Said length of the cut section may be less than or equal to 50% of
said length of the surface 190b, preferably less than or equal to 50% and greater than
or equal to 5%, more preferably less than or equal to 40% and greater than or equal to
10% and even more preferably less than or equal to 30% and greater than or equal to
20% of said length.
In the described embodiment the cut, and therefore the cut section, extends
substantially around the circumference of the first section 202 of the surface 190a in
the circumferential direction about the compressor housing longitudinal axis 104a.
Alternatively, the cut, and therefore the cut section 210, may extend only partly around
said longitudinal axis 104a in the circumferential direction.
In the above described embodiment, the cut section has a substantially constant crosssectional
shape in the circumferential direction about the compressor housing
longitudinal axis 104a. Alternatively, the cut section may have a varying crosssectional
in said circumferential direction.
Furthermore, the outlet end 181b of the surface 181 of the annular diffuser first wall
member 182 may have a varying radius with circumferential position about the
compressor housing longitudinal axis 104a.
In the above described embodiments, pressure die casting is used to form the
compressor housing 500.
Alternatively, the core may be a core of a particulate material. In this respect, the core
may be made of sand or of any other suitable particulate material. The molten metal
may be provided in the mould cavity by being injected, or poured into the mould cavity.
The molten metal may be gravity-fed into the mould cavity.
Referring to Figure 12, there is shown a view corresponding to that of Figure 4 , but
where the core is a sand core 301 ' . Where the core is a core of a particulate material,
such as a sand core 301 ' , the core is supported through the opening 306 in the outlet
volute first wall member 185 by an annular support member 800. In this respect, the
sand core 301 ' is supported through the opening 306 substantially across the entire
circumferential length of the core 301 ' , about the compressor housing longitudinal axis
104a. This is advantageous in that it reduces any shifting of the sand core 301 ' during
the casting process, providing increased dimensional consistency.
The sand core 301 ' can primarily be removed from the compressor housing 500
through the opening 306, but may alternatively, or additionally, be removed through an
outlet 175 of the volute.
In the described embodiments, the body 501 is formed by a bearing assembly.
Alternatively, the body may be formed by any suitable component of a turbocharger
including a diffuser plate.
In the described embodiments, the compressor housing 500 is cut using a single
continuous cutting operation. Alternatively, a plurality of different cutting operations
may be used.
In the described embodiments, the section of the compressor housing forming the axial
intake 142 is formed integrally with the annular diffuser first wall member 182.
Alternatively, the axial intake 142 may be formed separately with the annular diffuser
first wall member 182 and attached thereto by any suitable attachment means.
In the described embodiments, the surface 181 of the annular diffuser first wall member
is substantially perpendicular to the longitudinal axis 104a. Alternatively, the surface
181 may be inclined relative to the perpendicular to the longitudinal axis 104a, i.e.
relative to the radial direction.
Furthermore, the outlet section 201 may be inclined relative to the perpendicular to the
longitudinal axis 104a, i.e. relative to the radial direction.
In addition, the surface 181 of the annular diffuser first wall member, including the
outlet section 201 , may be curved.
CLAIMS
1. A method of manufacturing a compressor housing comprising :
arranging a core with a die so as to define a mould cavity between a surface of
the core and a surface of the die, the mould cavity having the shape of a compressor
housing ;
providing a molten metal within the mould cavity and solidifying the molten
metal to form a compressor housing ;
the compressor housing having a longitudinal axis and being for receipt of an
impeller wheel, mounted for rotation about an axis;
the compressor housing comprising an annular diffuser first wall member
having a surface for defining, with an opposed surface of an annular diffuser second
wall member, an annular diffuser passage;
the surface of the first wall member of the diffuser extending radially outwardly
from an annular inlet end to an annular outlet end and having an annular outlet section
extending radially inwardly from the outlet end;
the compressor housing further comprising an annular outlet volute first wall
member having a surface for defining, with a surface of an annular outlet volute second
wall member, an annular outlet volute passage;
the surface of the annular outlet volute first wall member defining a volute
channel that extends, along a circumferentially extending volute channel axis, about
the compressor housing longitudinal axis;
the surface of the annular outlet volute first wall member having an annular inlet
end, provided at the outlet end of the surface of the first wall member of the diffuser,
the surface of the annular outlet volute first wall member having an annular first section
that extends axially outboard from the annular inlet end ;
the compressor housing being formed such that for at least one circumferential
position about the compressor housing longitudinal axis, a first angle is subtended
between the outlet section of the surface of the diffuser first wall member and the first
section of the surface of the outlet volute first wall member;
the outlet volute first wall member being formed with an opening ;
wherein after the compressor housing has been formed in the mould cavity, the
core is removed from the volute channel;
once the core has been removed from the volute channel, a cut is applied,
through the opening, to the first section of the surface of the outlet volute first wall
member, at the least one circumferential position, to produce a cut section such that a
second angle is subtended between the cut section and the outlet section of the
surface of the diffuser first wall member, at said at least one circumferential position,
that is greater than the first angle.
2 . A method of manufacturing a compressor housing according to claim 1 wherein
the cut section extends radially inwardly of the outlet end of the surface of the first
wall member of the diffuser, at the at least one circumferential position.
A method of manufacturing a compressor housing according to either of claims 1
or 2 wherein the cut section forms a lip that extends in the circumferential direction
about the volute channel axis.
A method of manufacturing a compressor housing according to any preceding
claim wherein the cut section is at an oblique angle to the outlet section of the
surface of the diffuser first wall member, at the at least one circumferential
position.
A method of manufacturing a compressor housing according to any preceding
claim wherein the cut section is at an angle to the outlet section of the surface of
the diffuser first wall member, at the at least one circumferential position, that is
greater than or equal to 270° .
A method of manufacturing a compressor housing according to claim 5 wherein
the cut section is at an angle to said outlet section that is greater than 270° and
less than or equal to 350° .
A method of manufacturing a compressor housing according to claim 6 wherein
the cut section is at an angle to said outlet section that is greater than or equal to
280° and less than or equal to 320° .
8 . A method of manufacturing a compressor housing according to claim 7 wherein
the cut section is at an angle to said outlet section of substantially 290° .
A method of manufacturing a compressor housing according to any preceding
claim wherein the surface of the first wall member of the outlet volute extends in a
circumferential direction about the volute channel axis, from the inlet end of said
surface to a radially outer end of said surface and the surface of the first wall
member of the outlet has a radius, relative to the volute channel axis, that varies
with the circumferential position of said surface about the volute channel axis.
10 . A method of manufacturing a compressor housing according to claim 9 wherein,
before the cut is made, the first section of the surface of the first wall member of
the outlet volute has a substantially constant radius, relative to the compressor
housing longitudinal axis, substantially along its length in the direction of the
compressor housing longitudinal axis, the surface of the first wall member of the
volute outlet has a radially outer section that extends axially outboard of the
radially outer end of said surface and has a substantially constant radius across its
length in the direction of the compressor housing longitudinal axis, said surface
also having a base section extending between the first section and the radially
outer section.
A method of manufacturing a compressor housing according to claim 10 wherein
the base section is curved along its length in the circumferential direction about the
volute channel axis.
A method of manufacturing a compressor housing according to any preceding
claim wherein the cut section extends from a first end, to a second end, in the
circumferential direction about the volute channel axis wherein the first end of the
cut section is provided at the inlet end of the surface of the first wall member of the
outlet volute, at the at least one circumferential position.
A method of manufacturing a compressor housing according to any preceding
claim wherein the cut section has a length in the circumferential direction, about
the volute channel axis, that is less than or equal to half the length of the surface of
the first wall member of the outlet volute in the circumferential direction, about the
volute channel axis.
A method of manufacturing a compressor housing according to any preceding
claim wherein the angle of the cut section relative to the outlet section of the
surface of the first wall member of the diffuser, at the at least one circumferential
position, is substantially constant along its length in the circumferential direction
about the volute channel axis.
A method of manufacturing a compressor housing according to any of claims 1 to
13 wherein the angle of the cut section relative to the outlet section of the surface
of the first wall member of the diffuser, at the at least one circumferential position,
varies along its length in the circumferential direction about the volute channel
axis.
16 . A method of manufacturing a compressor housing according to claim 15 wherein
the cut section comprises a plurality of portions extending in said circumferential
direction that are inclined at different angles relative to said outlet section.
A method of manufacturing a compressor housing according to claim 16 wherein
the plurality of portions approximate a concave curve that faces into the volute
channel.
A method of manufacturing a compressor housing according to claim 17 wherein
the surface of the outlet volute first wall member is at least partially curved from the
inlet end of the surface of the first wall member of the outlet volute to the radially
outer end of said surface and the plurality of portions approximate a curve of
substantially the same radius as the curvature of the surface of the outlet volute
first wall member.
19 . A method of manufacturing a compressor housing according to any preceding
claim wherein the cut is made by a single cutting operation.
20. A method of manufacturing a compressor housing according to any preceding
claim wherein the at least one circumferential position is a plurality of
circumferential positions about the compressor housing longitudinal axis.
2 1 . A method of manufacturing a compressor housing according to claim 20 wherein
the cut section extends around substantially the entire said circumference of the
first section about the compressor housing longitudinal axis.
22. A method of manufacturing a compressor housing according to either of claims 20
or 2 1 wherein the cut section has a substantially constant shape with
circumferential position about the compressor housing longitudinal axis.
23. A method of manufacturing a compressor housing according to any of claims 20 to
22 wherein the second angle is substantially constant with circumferential position
about the compressor housing longitudinal axis.
24. A method of manufacturing a compressor housing according to any of claims 20 to
23 wherein the outlet end of the surface of the first wall member of the diffuser
outlet has a radius that is substantially constant with circumferential position about
the compressor housing longitudinal axis.
25. A method of manufacturing a compressor housing according to any preceding
claim wherein, before the cut is made, the first section of the surface of the first
wall member of the outlet volute, at the at least one circumferential position, is of a
substantially constant radius, relative to the compressor housing longitudinal axis,
across the length of the first section in the circumferential direction about the volute
channel axis.
26. A method of manufacturing a compressor housing according to any preceding
claim wherein, before the cut is made, the first section is substantially
perpendicular to the outlet section of the surface of the diffuser first wall member,
at the at least one circumferential position.
27. A method of manufacturing a compressor housing according to any preceding
claim wherein the outlet volute is formed as a single piece.
28. A method of manufacturing a compressor housing according to any preceding
claim wherein the core is a solid core.
29. A method of manufacturing a compressor housing according to claim 28 wherein
the molten metal is injected into the mould cavity under pressure.
30. A method of manufacturing a compressor housing according to any of claims 1 to
26 wherein the core is of a particulate material.
3 1. A method of manufacturing a compressor housing according to claim 30 wherein
the core is supported through the opening in the outlet volute first wall member.
32. A method of manufacturing a compressor housing according to any preceding
claim wherein the core is removed from the compressor housing through the
opening in the outlet volute first wall member.
33. A method of manufacturing a compressor comprising:
manufacturing a compressor housing according to the method of any preceding
claim;
providing a body having an annular diffuser second wall member and an
annular outlet volute second wall member, assembling the body with the compressor
housing such that the surface of the annular diffuser first wall member and a surface of
the annular diffuser second wall member define an annular diffuser passage and the
surface of the annular outlet volute first wall member and a surface of the annular outlet
volute second wall member define an annular outlet volute that is downstream of and in
fluid communication with the diffuser passage;
mounting an impeller within the compressor housing, the impeller being
mounted on a shaft for rotation about said longitudinal axis, the impeller having a
plurality of blades, the diffuser passage surrounding the impeller, with the tips of the
blades sweeping across said diffuser inlet during use.
A method of manufacturing a compressor according to claim 33 wherein the body
is a component of a turbo-machine.
35. A method of manufacturing a turbocharger comprising manufacturing a
compressor according to claim 34 and assembling the compressor with a turbine
and bearing assembly to form a turbocharger.
36. A compressor housing manufactured by the method of any of claims 1 to 32.
37. A compressor manufactured by the method of either of claims 33 or 34.
38. A turbocharger manufactured by the method of claim 35.
39. A method of manufacturing a compressor housing substantially as described
herein with reference to the accompanying drawings.
40. A method of manufacturing a compressor substantially as described herein with
reference to the accompanying drawings.
4 1 . A method of manufacturing a turbocharger substantially as described herein with
reference to the accompanying drawings.