GB2525240A

GB2525240A - Variable geometry turbine

Info

Publication number: GB2525240A
Application number: GB1406957.9A
Authority: GB
Inventors: John F Parker
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2014-04-17
Filing date: 2014-04-17
Publication date: 2015-10-21
Anticipated expiration: 2034-04-17
Also published as: GB2525240B; GB201406957D0

Abstract

A variable geometry turbine having an annular inlet passageway defined by a radial surface of a first wall member mounted within a cavity. The first wall member is axially movable to vary the size of the inlet passageway. There is also a second wall member, which covers the opening of a cavity defined by the housing. The second wall member comprises an outer flange 127 defining a circumferential flange groove for receiving a retaining ring for securing the second wall member in the cavity. An array of inlet guide vanes 114 extend across the annular inlet passageway to define a radial vane passage, the radial wall 124 of the second wall member defining a radial second surface that opposes the first surface, wherein the second wall member further comprises an annular flange 162 that extends axially into the cavity and which supports a radially extending flange 163 that defines a radial third surface that is opposed to the radial second surface. This pressure balancing flange 163 allows the pressure in the cavity to produce an axial force on the second wall member and reduces the vibration on the second wall member, thus reducing the wear and fatigue.

Description

Variable Geometry Turbine The present invention relates to a varable geometry turbine. Particuarly, but not exclusively, the present invention relates to a variable geometry turbine for a turbocharger or other turbomachine.

A turbomachine comprises a turbine. A conventional turbine comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel drives either a compressor wheel mounted on the other end of the shaft within a compressor housing to deliver compressed air to an engine intake manifold, or a gear which transmits mechanical power to an engine flywheel or crankshaft. The turbine shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a bearing housing.

Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures).

Turbochargers comprise a turbine having a turbine housing which defines a turbine chamber within which the turbine wheel is mounted; an annular inlet passageway defined between opposed radial walls arranged around the turbine chamber; an inlet chamber arranged around the inlet passageway; and an outlet passageway extending from the turbine chamber. The passageways and chambers communicate such that pressurised exhaust gas admitted to the inlet chamber flows through the inlet passageway to the outlet passageway via the turbine and rotates the turbine wheel.

Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that the size of the annular inlet passageway can be varied to optimise gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suite varying engine demands. In this case, the annular inlet passageway is defined between opposed radial surfaces of respective radial walls of a movable annular nozzle ring and a fixed annular "shroud'.

For instance, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the annular inlet passageway. Turbochargers provided with a variable geometry turbine are referred to as variable geometry turbochargers.

It is known to improve turbine performance by providing vanes, referred to as inlet guide vanes, in the annular inlet passageway. The inlet guide vanes define a plurality of radial vane passages which deflect gas flowing through the inlet passageway towards the direction of rotation of the turbine wheel.

Inlet guide vane arrangements in variable geometry turbochargers can take different forms. In one type, the inlet guide vanes are fixed to the radial wall of the movable annular nozzle ring and extend into the annular inlet passageway and through vane slots provided in the fixed shroud to accommodate movement of the nozze ring. In an alternative arrangement, the inlet guide vanes are provided on the fixed shroud and the vane slots are provided in the nozzle ring to accommodate movement of the nozzle ring.

The radial wall of the nozzle ring is typically provided, at opposed radial ends, with radially inner and outer axially extending walls or flanges which extend into an annular cavity behind the radial wall of the nozzle ring. The cavity is formed in a part of the turbocharger housing (usually either the turbine housing or the turbocharger bearing housing) and accommodates axial movement of the nozzle ring. The flanges may be sealed with respect to the cavity walls to reduce or prevent leakage flow around the back of the nozzle ring.

In one arrangement of a variable geometry turbine the nozzle ring is supported on rods extending parallel to the axis of rotation of the turbine wheel and is moved by an actuator which axially displaces the rods. Nozzle ring actuators can take a variety of forms, including pneumatic, hydraulic and electric and can be linked to the nozzle ring in a variety of ways. The actuator will generally adjust the position of the nozzle ring under the control of an engine control unit (ECU) in order to modify the airflow through the turbine to meet performance requirements.

The shroud comprises an annular plate which seats in the mouth of an annular shroud cavity. The shroud plate is held in position by a retaining ring located in a circumferential groove provided in the outer periphery of the shroud plate and extending into a circumferential groove provided in the turbine housing around the mouth of the shroud cavity. The retaining ring is a split ring of a form commonly referred to as a "bevelled retaining ring.

At certain times during operation of the engine it is desirable to move the nozzle ring closer to the shroud so as to reduce the axial width of the inlet passageway and increase the speed of the gas flow. During a thermal management cycle (also referred to as thermal regeneration) the engine is usually at idle and the nozzle ring is positioned so as to be very close to the facing radial surface of the shroud, thereby defining an annular inlet passageway which is typically much narrower than during normal engine operation. Due to this constriction, as well as the constriction produced by the vanes, the speed of gas passing through the inlet passageway increases significantly and consequently has a very low pressure.

As a result, there is a large difference in pressure between the pre-turbine pressure of gas upstream of the inlet guide vanes extending across the inlet passageway and the pressure of gas downstream of the inlet guide vanes before it impinges upon the turbine wheel.

During use, as the gas flows through the annular inlet passageway it exerts a pressure on the opposed inboard (inboard relative to the annular inlet passageway) radial surfaces of the nozzle ring and shroud that produces opposed outboard forces (i.e. away from the annular inlet passageway) on the nozzle ring and shroud. Gas flowing through the annular inlet passageway also passes behind the shroud, into the shroud cavity (for example past the retaining ring and/or through any vane slot in the shroud plate). This gas exerts a pressure on a back wall of the shroud in the inboard direction, i.e. towards the annular inlet passageway.

During use, the pressure of the gas behind the shroud, within the shroud cavity, is at the pre-turbine pressure upstream of the vane passage and is therefore higher than the pressure within the inlet passageway due to the reduction in the pressure of gas flowing through the vane passages. This results in a pressure differential across the radial wall of the shroud that produces a net force on the shroud, in the inboard direction, i.e. towards the annular inlet passageway. The gas arrives at the annular inlet passageway, and in the shroud cavity, in pulsations that are out of phase with each other. This causes a pulsation, and variation, of the above pressure differential across the radial wall of the shroud which produces a net force on the shroud that changes direction between the axially inboard and outboard directions. This acts to vibrate the shroud in the axial direction, which results in wear and fatigue of the shroud retaining ring and/or the shroud itself.

It is one object of the present invention to obviate or mitigate the aforesaid disadvantages. It is also an object of the present invention to provide for an improved or alternative shroud.

According to a first aspect of the present invention there is provided a variable geometry turbine comprising: a housing comprising a turbine housing in which a turbine wheel is mounted for rotation about a turbine axis; an annular inlet passageway upstream of the turbine wheel; the annular inlet passageway being defined by a radial surface of a radially extending wall of an annular first wall member mounted within a cavity provided within the housing and a facing radial first surface of a radial wall of an annular second wall member; the first wall member being axially movable to vary the size of the inlet passageway; the second wall member being substantially fixed in the axial direction relative to the housing; the second wall member covering the opening of a cavity defined by the housing; the second wall member comprising an outer flange around its radially outer periphery, the outer flange defining a circumferential flange groove for receiving a retaining ring for securing the second wall member in the cavity; an array of inlet guide vanes extending across said annular inlet passageway to define a radial vane passage; the radial wall of the second wall member defining a radial second surface that opposes the first surface; wherein the second wall member further comprises an annular flange that extends axially into the cavity and which supports a radially extending flange that defines a radial third surface that is opposed to the radial second surface.

This is advantageous in that the pressure of the gas within the cavity, which is at a higher pressure than the gas within the inlet passageway downstream of the vane passage, acts on the third surface defined by the radially extending flange (pressure balance flange"). This acts in the opposite direction to the pressure of the gas on the radial second surface (i.e. the back face) of the second wall member, which acts to produce a net axial force on the second wall member in the outboard direction (i.e. away from the annular inlet passageway). This reduces the vibration of the second wall member caused by the pulsating gas, since the net axial forces produced by the pulsations are now substantially always in the outboard axial direction. This reduces the wear/fatigue on the retaining ring.

The above arrangement is also advantageous in that the radially extending flange acts as a heat sink. Accordingly, when the second wall member is provided with vane slots for receiving vanes provided on the first wall member, thermal stresses in the region of the inner diameter of the vane slots are reduced. This prevents cracking of the vane slots.

The outer flange may be located within the cavity.

The circumferential flange groove may be located within the cavity.

The outer flange may comprise first and second radially extending flange members connected by an axially extending flange member to form said circumferential flange groove. The circumferential flange groove may have a substantially square or rectangular cross-sectional shape. Alternatively, the circumferential flange groove may have any other suitable cross-sectional shape, including a curved or partly curved cross-sectional shape. The circumferential flange groove may extend substantially around or partly around the circumference of the outer flange.

A retaining ring may be received within the circumferential flange groove in the outer flange, the retaining ring being arranged to secure the second wall member in the cavity. The retaining ring may be partially received in the circumferential flange groove and partially received in a circumferential groove in the housing.

The use of the radially extending flange removes the need for the retaining ring to be pre-loaded to bias the second wall member in the outboard direction. This allows the retaining ring, the circumferential flange groove, and the circumferential groove in the housing to have a simpler cross-sectional shape than that required for a pre-loaded retaining ring. This therefore allows for simpler machining and assembly.

The retaining ring may not be pre-loaded within the circumferential flange groove. In this respect, the retaining ring may be arranged such that, when it is received within the circumferential flange groove, it does not act to bias the second wall member in an axial direction.

For example the retaining ring may have a cross-sectional shape that is substantially uniform in the radial direction of the retaining ring. The retaining ring may have a width that is substantially constant across the radius of the retaining ring.

Alternatively, the retaining ring may be pre-loaded in the circumferential flange groove so as to bias the second wall member in an axial direction, preferably in the axially outboard direction.

The retaining ring may have a radially outer periphery that tapers to define a conical surface which engages with a complimentary conical surface defined by a side wall of a groove defined by the housing such that the retaining ring biases the second wall member in an axial direction, preferably in the axially outboard direction.

The retaining ring may be mounted within the circumferential flange groove such that the second wall member is rotatable relative to the housing. In this regard the retaining ring may be rotatable relative to the second wall member and/or the housing. Where the retaining ring is rotatable relative to the housing, the second wall member may be rotationally fixed relative to the retaining ring. Where the retaining ring is fixed relative to the housing, the second wall member may be rotatable relative to the retaining ring.

Because the radially extending flange removes the need for the retaining rng to be pre-loaded, this allows the retaining ring to be mounted within the circumferential flange groove such that the second wall member is rotatable relative to the housing. This facilitates ease of assembly since the second wall member may be rotated relative to the first wall member, as it is secured in the cavity. Accordingly, vanes on the first or second wall members may be aligned with slots on the other of the first and second wall members by rotation of the second wall member relative to the first wall member, when the second wall member is secured within the cavity. This therefore provides for an easer and faster assembly process as it removes the need for the second wall member and first wall member to be accurately positioned relative to each other by a setting operation as the second wall member is secured within the cavity.

The radially extending flange may be located towards an outboard end of the cavity.

The radially extending flange may be located proximal to the outboard end of the cavity. The outboard end of the cavity may be substantially closed.

The radially extending flange may define a fourth surface that is opposed to the third surface. The fourth surface may be adjacently opposed to a surface that defines an outboard end of the cavity. Said surface may be a surface of the housing, or a surface of an intermediary member between the radially extending flange and the housing. The intermediary member may be an axial sleeve.

The second wall member may be sealed against a surface so as to define a first area within the cavity which includes the radial second and third surfaces and a second area within the cavity which includes the radial fourth surface. Said surface may be a surface of the housing, or a surface of an intermediary member between the radially extending flange and the housing. The intermediary member may be an axial sleeve.

Such a sealing arrangement restricts the transmission of the relatively high pre-turbine pressure to the fourth surface defined by the radially extending flange, which would otherwise negate the advantages provided by the radially extending flange. This also provides an additional efficiency gain as the gas is prevented from leaking past the radially extending flange.

The radially extending flange and/or the outer flange may be sealed against said surface such that the first area is substantially sealed from the second area.

The second area may be in fluid communication with a region of the annular inlet passageway downstream of the radial vane passage.

The intermediary member may be formed integrally with the turbne housing.

Alternatively, the intermediary member may be formed separately to the turbine housing and fixed to the turbine housing by any suitable means, e.g. brazing or welding. This is advantageous in that it allows the second wall member to be retro-fitted to existing turbines.

The radially extending flange may be formed integrally with the axially extending annular flange. The axially extending annular flange may be formed integrally with the radial wall of the second wall member.

The radially extending flange may be formed separately from the radial wall of the second wall member and fixed thereto attached by any suitable means, e.g. by brazing, welding, etc. In this respect, the radially extending flange may be formed separately from the axially extending annular flange and attached by any suitable means, e.g. by brazing, welding, etc. Alternatively, or additionally, the axally extending annular flange may be formed separately to the radially extending wall of the second wall member and attached by any suitable means, e.g. by brazing, welding, etc. This is advantageous in that it allows the pressure balancing flange" to be retro-fitted to existng turbines.

The outer flange may be located in the opening of the cavity. The axially extending flange member may extend from the second wall member. The axially extending flange member may extend axially outboard from the radial second surface defined by the radial wall of the second wall member. The axially extending flange member may extend axially outboard from a radially outer end of the radial second surface defined by the radial wall of the second wall member.

The circumferential flange groove defined by the outer flange may be located in the opening of the cavity.

The radially extending flange may define a circumferential seal groove for receiving a seal to seal the radially extending flange against said surface so as to define said first and second areas. The radially extending flange may comprise first and second radially extending flange members connected by an axially extending flange member to form said circumferential seal groove. The circumferential seal groove may have a substantially square or rectangular cross-sectional shape. Alternatively, the circumferential seal groove may have any other suitable cross-sectional shape, including a curved or partly curved cross-sectional shape. The circumferential seal groove may extend substantially or partly around the circumference of the radially extending flange.

A seal may be provided in said circumferential seal groove to as to seal the radially extending flange may against said surface. The seal may be an annular sealing ring, or by any other sealing member.

The outer flange may be located axially outboard of the opening of the cavity. The outer flange may be located towards an outboard end of the cavity. The outer flange may be located proximal to the outboard end of the cavity.

The outer flange may extend from the radially extending flange. The axially extending flange member may extend axially inboard from the radial third surface defined by the radially extending flange. The axially extending flange member may extend axially inboard from a radially outer end of the radial third surface defined by the radially extending flange.

The circumferential flange groove defined by the outer flange may be located axially outboard of the opening of the cavity. In this case, where a retaining ring is received within the circumferential flange groove, the retaining ring may be located axially outboard of the opening of the cavity such that a radial clearance is provided between the outer periphery of the radial wall of the second wall member and the housing that allows for gas to flow from the annular inlet passageway into the cavity. The radial clearance may be located axially inboard of the retaining ring. The radial clearance may extend substantially across the distance between the outer periphery of the radial wall of the second wall member and an opposed surface of the housing. Preferably the radial clearance extends substantially around the circumference of the second wall member to form a substantially annular shape. Preferably no intermediary member, such as a retaining ring, is provided within the annular clearance.

This is advantageous in that, due to the annular clearance, the gas arrives at the annular inlet passageway, and in the shroud cavity, in pulsations that are generally in phase with each other, or at least more in phase with each other than where the retaining ring is located in the cavity opening. This reduces the vibration on the second wall member, which reduces wear on the retaining ring and on the second wall member.

The circumferential flange groove defined by the outer flange may be located towards an outboard end of the cavity. The circumferential flange groove defined by the outer flange may be located proximal to the outboard end of the cavity.

The circumferential groove in the housing may be substantially axially aligned with the circumferential flange groove in the outer flange. In this respect, where the outer flange is located in the opening in the cavity, the circumferential groove in the housing may be located in the opening in the cavity. Where the outer flange is located towards an outboard end of the cavity, the circumferential groove in the housing may be located towards the outboard end of the cavity accordingly.

The outer flange may define a circumferential seal groove for receiving a seal to seal the outer flange against said surface so as to define said first and second areas. The outer flange may comprise first and second radially extending flange members connected by an axially extending flange member to form said circumferential seal groove. The circumferential seal groove may have a substantially square or rectangular cross-sectional shape. Alternatively, the circumferential seal groove may have any other suitable cross-sectional shape, including a curved or partly curved cross-sectional shape. The circumferential seal groove may extend substantially or partly around the circumference of the outer flange.

A seal may be provided in said circumferential seal groove so as to seal the radially extending flange against said surface. The seal may be an annular sealing ring, or any other sealing member.

The circumferential seal groove may be axially adjacent to the circumferential flange groove for receiving the retaining ring. The circumferential seal groove may be axially inboard of the circumferential flange groove for receiving the retaining ring.

Alternatively, the circumferential seal groove may be axially outboard of the circumferential flange groove for receiving the retaining ring.

Where the outer flange is located axially outboard of the opening of the cavity, the outer flange may define a radial fifth surface that is opposed to the radial second surface. The radial fifth surface may be substantially annular. The radial fifth surface may be substantially parallel to the radial third surface. The radial fifth surface may extend from a radially inner surface, located at a radial position that is substantially aligned with, or radially overlaps, a radially outer end of the radial third surface, to a radially outer surface. The radially outer surface of the radial fifth surface may be adjacent to a radially inner surface of the housing that defines the cavity The second wall member and/or housing may be arranged to define a path for gas to flow from the annular inlet passageway into the cavity, outboard of the radial wall of the second wall member. The retaining ring may be arranged to permit the flow of gas past the retaining ring into the cavity. In this way, such gas can flow around the radially outer edge of the second wall member to transmit the relatively high pre-turbine pressure to the radial second surface defined by the radial wall of the second wall member.

Additionally, or alternatively, one or more apertures may be defined by the second wall member, fluidly connecting the first radial surface to the second radial surface, to facilitate gas flow from the annular inlet passageway into the cavity. The one or more apertures may be defined in the second wall member upstream of the vane passage.

Alternatively, or additionally, the one or more apertures may be defined in a portion of the second wall member within the vane passage.

The one or more apertures may be a plurality of apertures distributed circumferentially around the second wall member.

The first wall member may be a nozzle ring and the second wall member a shroud.

Alternatively, the first wall member may be a shroud and the second wall member a nozzle ring.

The inlet guide vanes may be fixed to the first wall member, with the second wall member defining apertures for receipt of the vanes. Alternatively, the inlet guide vanes may be fixed to the second wall member, with the first wall member deIinng apertures for receipt of the vanes. The apertures may be slots.

The one or more apertures defined by the second wall member to facilitate gas flow into the cavity may be disposed between adjacent said inlet guide vanes or apertures for receipt of the vanes.

The radially extending flange may be disposed axially outboard of the outer flange. In this respect, the third radial surface may be disposed axially outboard of an axially outboard surface of the outer flange.

Preferably the second wall member is substantially fixed relative to the housing.

Preferably the radially extending flange is substantially fixed relative to the housing.

Preferably the third radial surface is substantially fixed relative to the housing.

Preferably the second wall member is not axially movable relative to the housing.

Preferably the second wall member is not connected to an actuator arranged to move the second wall member in the axial direction.

The second wall member may be received in the turbine housing. In this case, the second wall member may be substantially fixed in the axial direction relative to the turbine housing, with the second wall member covering the opening of a cavity defined by the turbine housing.

The variable geometry turbine may comprise a bearing housing which houses a bearing element that supports a shaft of the turbine for rotation about its axis. In this case, the second wall member may be received in the bearing housing. The second wall member may be substantially fixed in the axial direction relative to the bearing housing, with the second wall member covering the opening of a cavity defined by the bearing housing.

The radially outer periphery of the radially extending flange may be located radially inwardly of the radial vane passage. This is advantageous in that, where the guide vanes are provided on the first wall member, with the second wall member provided with apertures for receipt of the guide vanes, the radially extending flange does not obstruct the passage of the guide vanes into the cavity.

Alternatively, the radially outer periphery of the radially extending flange may be located radially outwardly of the radial vane passage. This is advantageous in that it provides said third radial surface with a relatively large cross-sectional area, thereby increasing the above-mentioned advantages provided by said radial third surface.

The second and/or third surfaces may be substantially parallel to each other.

According to a second aspect of the present invention, there is provided a turbomachine comprising a variable geometry turbine according to the frst aspect of the invention.

The second wall member may be received in the turbine housing.

The turbomachine may comprise a bearing housing which houses a bearing element that supports a shaft of the turbine for rotation about its axis. In this case, the second wall member may be received in the bearing housing. The second wall member may be substantially fixed in the axial direction relative to the bearing housing, with the second wall member covering the opening of a cavity defined by the bearing housing.

Preferably the turbomachine is a variable geometry turbocharger.

Specific embodiments of the present nvention 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 2A is a front view of a prior art shroud for use in a variable geometry turbine; Figure 2B is a cross-sectional view taken along line 0-0 of the shroud of Figure 2A; Fig. 3 is a schematic illustration of the prior art shroud of Figs. 2a and 2b installed in a turbine housing; Fig. 4 is a sectional view of a nozzle ring and of a shroud installed in a turbine housing of a variable geometry turbine according to a first embodiment of the present invention; Fig. 5 is a sectional view corresponding to that of Figure 4, but where the retaining ring is of a different arrangement; Fig. 6 is a sectional view of a shroud installed in a turbine housing of a variable geometry turbine according to a second embodiment of the present invention, and Fig. 7 is an enlarged view of the region crcled A' in Figure 6.

Referring to figure 1, there is shown a known variable geometry turbocharger comprising a variable geometry turbine housing 1 and a compressor housing 2 interconnected by a central bearing housing 3. A turbocharger shaft 4 extends from the turbine housing 1 to the compressor housing 2 through the bearing housing 3. A turbine wheel 5 is mounted on one end of the shaft 4 for rotation within the turbine housing 1, and a compressor wheel 6 is mounted on the other end of the shaft 4 for rotation within the compressor housing 2. The shaft 4 rotates about turbocharger axis 4a on bearing assemblies located in the bearing housing 3.

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 passageway 8 via an annular inlet passageway 9 and the turbine wheel 5. The inlet passageway 9 is defined on one side by an inboard surface of a radial wall of a movable annular first wall member 11, referred to as a nozzle ring" (inboard relative to the inlet passageway 9) and on the opposite side by an opposing inboard surface 50 (inboard relative to the inlet passageway 9) of a radial wall 24 of a second wall member comprising an annular shroud 12 which forms the wall of the inlet passageway 9 facing the nozzle ring 11. The shroud 12 is fixed to the turbine housing 1 (as discussed in more detail below) and covers the opening of an annular recess, or shroud cavity, 13 in the turbine housing 1.

The nozzle ring 11 supports an array of circumferentially and equally spaced inlet guide vanes 14 each of which extends across the inlet passageway 9. The vanes 14 are orientated to deflect gas flowing through the inlet passageway 9 towards the direction of rotation of the turbine wheel 5. The vanes 14 project through suitably configured slots 25 in the shroud 12, and into the shroud cavity 13, to accommodate movement of thenozzleringll.

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 passageway 9. For a fixed rate of mass of gas flowing into the inlet passageway 9, the gas velocity is a function of the width of the inlet passageway 9, the width being adjustable by controlling the axial position of the nozzle ring 11. Figure 1 shows the annular inlet passageway 9 fully open. The inlet passageway 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 turbine housing 1. Inner and outer sealing rings 20 and 21 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.

Gas flowing from the inlet volute 7 to the outlet passageway 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 in an air inlet 22 and delivers the pressurised air to an air outlet volute 23 from which it is ted to an internal combustion engine (not shown).

The shroud 12 of the turbocharger of Fig. 1 is shown in greater detail in Figs. 2A and 2B. The shroud 12 is an annular plate comprising a radially extending shroud wall 24.

The axially inboard surface 50 of the radial wall 24 opposes the axially inboard surface of the radial wall of the nozzle ring 11, with said opposing surfaces 50, 10 defining the inlet passageway 9.

The radially extending shroud wall 24 is provided with vane slots 25 for the receipt of the vanes 14 of the nozzle ring 11. The vane slots 25 are best seen in Fig. 2A, each slot having a leading end 25a and a trailing end 25b. The trailing end 25b of two of the slots 25 is visible in the cross-section of Fig. 2b. The radially inner periphery of the radial wall 24 is formed with an axially extending flange 26, which extends in an outboard direction away from the turbine inlet passageway 9 when the shroud 12 is in position in the turbine housing 1, and provides means for seating the inner periphery of the shroud 12 in the mouth of the shroud cavity 13.

The radially outer periphery of the radial wall 24 is formed with a grooved outer flange 27. The outer flange 27 extends axially inboard from the radial wall 24 to a greater extent than the radially inner axially extending flange 26, and defines an annular circumferential flange groove 28 around the radially outer periphery of the shroud 12.

In more detail, the outer flange 27 comprises an axially extending flange wall 27a and a radially extending flange wall 27b, the groove 28 being defined between the outer periphery of the radial wall 24 and the radially extending flange wall 27b, the base of the groove 28 being defined by the axially extending flange wall 27a. The overall configuration is generally h" shaped.

Figure 3 schematically illustrates mounting of the known shroud plate 12 of Figs. 2a and 2b to a turbine housing 1. Specifically, Fig. 3 schematically illustrates the manner in which the outer periphery of the shroud 12 is secured in the opening, or mouth, of the shroud cavity 13. A retaining ring 29 (which may have the form of a conventional piston ring") is located within the circumferential flange groove 28 of the shroud 12.

The retaining ring 29 is a split ring which can be radially compressed to allow the shroud 12 to be slid into the mouth of the shroud cavity 13. As the shroud 12 is fitted in position, the circumferential flange groove 28 aligns with an annular groove 30 in the turbine housing 1, defined around the mouth of the shroud cavity 13. The turbine housing 1 is also formed with a radial extending annular shoulder la. With the grooves 28 and 30 aligned, the retaining ring 29 springs radially outwards to engage the groove and secure the shroud 12 in position. The radially outer periphery of the retaining ring 29 tapers defining a conical inboard surface 32 which engages with a complimentary conical surface defined by an inboard side wall 33 of the groove 30.

Interaction of the surfaces 32 and 33 as the retaining ring 29 radially expands into the groove 30 biases the shroud 12 axially into the mouth of the shroud cavity 13 (in the outboard direction relative to the inlet passageway 9) to ensure the shroud 12 is firmly located in position. Accordingly, the shroud 12 is fixed to the housing 1.

Figure 4 is a sectional view of a nozzle ring 111 and of a shroud 112 installed in a turbine housing 101 of a variable geometry turbine according to a first embodiment of the present invention. The variable geometry turbine of figure 4 is the same as that shown n figures 1 to 3 except for the differences described below. Components of the variable geometry turbine shown in Figure 4 which correspond to those shown in Figures 1 to 3 will take the same reference numbers used in Figures to 1 to 3 but increased by 100.

It can be seen that the shroud 112 has many features in common with the shroud 12.

That is, the shroud 112 is an annular plate that is mounted within the turbine housing 1 and covers the annular opening 300 of an annular shroud cavity 113 in the turbine housing 101. The shroud 112 is substantially fixed in the axial direction relative to the turbine housing 101.

The shroud 112 comprises a radially extending wall 124. The inlet passageway 109 is defined on one side by the inboard surface 110 of the nozzle ring 11 (also referred to herein as the ront face" 110 of the nozzle ring 11) and on the opposite side by the opposing inboard radial surface 150 of the radial wall 124 of the shroud 112 (also referred to herein as the "first radial surface" 150 of the shroud 112).

A second radial surface 167 of the radial wall 124 of the shroud 112 is opposed to the first radial surface 150 of the radial wall 124 and faces into the shroud cavity 113.

The radial wall 124 is provided with a grooved outer flange 127 at its outer periphery.

The outer flange 127 is substantially annular and extends in a circumferential direction about the turbocharger axis 4a, as well as in the axial direction.

The outer flange 127 comprises an axially extending annular flange wall 127a that extends axially outboard from a radially outer portion of the second radial surface 167 and a radially extending annular flange wall 127b that extends radially outwardly from an outboard end of the axially extending flange wall 127a.

A circumferential flange groove 128 is defined between the radial wall 124 and the radially extending flange wall 127b, the base of the groove 128 being defined by the axially extending flange wall 127a.. The circumferential flange groove 128 extends substantially around the circumference of the outer flange 127.

The radial wall 124 is provided, at its radially inner periphery, with an axially extending flange 162. The axially extending flange 162 is substantially annular and extends in a circumferential direction about the turbocharger axis 4a, as well as in the axial direction. The axially extending flange 162 has a substantially constant radius to form a substantially cylindrical flange.

The axially extending flange 162 is longer, in the axial direction, than the outer flange 127. In this respect, the axially extending flange 162 extends axially outboard of the outer flange 127.

The axially extending flange 162 supports a radially extending flange 163 (a "pressure balancing flange"), provided at the outboard end of the axially extending flange 162.

The radially extending flange 163 extends radially outwardly from an outboard end of the axially extending flange 162. The radially extending flange 163 is substantially annular and extends in a circumferential direction about the turbocharger axis 4a.

The axially extending flange 162 is formed by first and second axial sections 162a, 162b. The first section 162a extends axially outboard from a radially inner end of the radial wall 124. The second axial section 162b extends axially outboard from the first axial section 1 62a. The pressure balancing flange 163 is provided at the outboard end of the second section 1 62b.

The second section 162b is formed separately to the first section 162a and is attached to the first section by any suitable means, for example brazing, welding, by one or more suitable fasteners such as screws, nuts and bolts, etc. Forming the second section 162b separately to the first section 162a is advantageous in that it allows the radially extending flange 163 to be retrofitted to existing shrouds 12 (such as those shown in Figures ito 3) by attaching the second axial section 162b to the radially inner flange 26 of the shroud 12 (which then forms the first section 162a of the radially inner flange 162). However, it will be appreciated that the second section 1 62b may alternatively be formed integrally with the first section 1 62a.

The radially extending flange 163 defines an annular seal groove 164 for receipt of an annular split seal ring 165. In more detail, the radially extending flange 163 comprises an axially extending flange wall 163a and front (inboard) and rear (outboard) radially extending flange walls 163c, 163b, the groove 164 being defined between the front and rear radially extending flange walls 1 63c, 1 63b, with the base of the groove 164 being defined by the axially extending flange wall 163a. The overall configuration is generally "h"shaped.

The radially extending flange 163 defines two opposing radially extending surfaces, a front (inboard) surface 171 of the front radially extending flange wall 163c (referred to herein as a Third radial surface') and a rear (outboard) surface 172 of the rear radially extending flange wall 1 63b (referred to herein as a fourth radial surface') A housing insert 200 is fixedly attached to the turbine housing 1 and forms a cylindrical sleeve 166 that extends axially inboard from the turbine housing 101 into the shroud cavity 113. A seal ring 165 is received within the seal groove 164 and seals the radially extending flange 163 against a radially inner surface of the sleeve 166 so as to prevent the gas from flowing from the cavity 113 in between the radially extending flange 163 and the cylindrical sleeve 166 to behind (outboard of) the radially extending flange 163.

The radially inner surface of the sleeve that the seal ring 165 seas against is substantially annular and has a substantially constant radius relative to the turbocharger axis 4a. In this regard, said surface is not indented radially inwardly. This provides for ease of assembly of the seal ring 165 since it allows the seal ring 165 to be installed in position by a push fit operation. The housing insert 200 is made from iron. However, it will be appreciated that any suitable material may be used. The housing insert 200 is fixedly attached to the turbine housing 1 by brazing. However it will be appreciated that any suitable means of attachment may be used, including by fasteners such as screws, by welding, etc. It will be appreciated that if a surface is exposed to gas at a certain pressure then the pressure causes a force to be exerted on that surface perpendicular to the surface. The force exerted on a surface is equal to the product of the pressure of the gas contacting that surface and the area of the surface contacted by the gas. Some of the surfaces of the shroud 112 are generally radial whereas other surfaces are generally axial. The shroud 112 is fixed to the turbine housing 1. Any force which is exerted on one of the radial surfaces of the shroud will act on the shroud 112 either in the axially inboard direction, towards the inlet passageway 9, or in the axially outboard direction away form the inlet passageway 9. A force which is exerted on an axial surface of the shroud 112 will not urge the shroud 112 to move axially in either direction so can be ignored for the purposes of the following description of a preferred embodiment of the present invention.

In order to determine the net axial force which is exerted on the shroud 112 the individual forces acting on each of the radial surfaces must be summed. A surface which experiences a force which urges the shroud 112 in the outboard direction, away from the inlet passageway 9 (i.e. away from the nozzle ring 111) is described herein as "opposing" a surface which experiences a force which urges the shroud 112 in the inboard direction, towards the inlet passageway 9 (i.e. towards from the nozzle ring 111) and vice versa. In order to determine the net axial force on the shroud 112 due to forces exerted on two opposing radial surfaces, the force exerted on one of the opposing radial surfaces is subtracted from the force exerted on the other opposing radial surface.

Relatively high pressure exhaust gas flows from the engine exhaust manifold to the turbine in the direction of arrow X via the inlet passageway 109. Gas within the inlet passageway 109 initially flows through area Al before impinging upon the vanes 114, which together define a vane passage in area A2. As the gas flows through area A2 its speed increases causing a reduction in its pressure such that the accelerated gas at area AS has a lower pressure than the gas in areas A2 or Al.

The retaining ring 129 and the groove 130 in the turbine housing 101 are arranged so that gas can flow past the retaining ring into the shroud cavity 113 behind the shroud 112.

In addition, the shroud 112 defines a plurality of pressure balancing apertures 104.

The pressure balancing apertures 104 extend from the first radial surface 150 of the radial wall 124 to the second radial surface 167 of the radial wall 124 of the shroud 112 (see below). Accordingly, the pressure balancing apertures fluidly connected said first and second radial surfaces 150, 167. The pressure balancing apertures 104 are located upstream of the vane passage between adjacent vanes 114. The pressure balancing apertures 104 are distributed circumferentially about the turbocharger axis 4a.

The pressure balancing apertures 104 facilitate the passage of gas from the inlet passageway 109, through the radial wall 124 of the shroud 112 into the shroud cavity 113.

The above arrangement of the retaining ring 129 and pressure balancing apertures 104 enables a quantity of the highest pressure gas entering the turbine from the engine to pass behind the shroud 112 into area A4 within the shroud cavity 113. Downstream of the seal ring 165 between the housing irsert 200 and the radially extending flange 163 and between the turbine housing 101 and the axially extending flange 162 defines a further area A5, which is in fluid communication with area A3.

The third radial surface 171, defined by the pressure balance flange 163, resides in area A4 which contains the relatively high pressure gas during use, and the fourth radial surface 172, defined by the pressure balance flange 163 resides in area AS which, by virtue of being in fluid communication with area A3, contans gas at a relatively low pressure during use. The seal ring 165 is arranged to seal the area A4 from the area AS.

As mentioned above, provision of the vanes 114 extending axially across the inlet passageway 109 establishes three different areas of differing pressure within the inlet passageway log: Al; A2; and A3. Consequently, the opposing front face 110 and first radial surface 150 of the nozzle ring 111 and shroud 112 respectively, are subjected to differing pressures within the three areas, Al, A2 and A3. The regions of these surfaces 110, 150 in area Al experience the highest pressure, which act on first radial surface 150 of the shroud 112 in the axial outboard direction, i.e. in the axial direction towards the shroud cavity 113. The regions of the these surfaces 110, 150 in area A2 experience a lower pressure, and the regions of these surfaces 110, 150 in area A3 experience the lowest pressure.

The second radial surface 167 of the radial wall 124 of the shroud 112 faces into the shroud cavity 113 and lies in area A4. Since the highest pressure gas upstream of the inlet passageway 109 can flow into area A4, the whole radial extent of the second radial surface 167 of the shroud 112 experiences the same gas pressure as the first radial surface 150 of the shroud 112 upstream of the vane passage, i.e. the region of the first radial surface 150 of the shroud 112 in area Al. Since the pressure of gas flowing through areas A2 and A3 of the inlet passageway 109 is lower than that within areas Al and A4, the regions of the second radial surface 167 of the shroud 112 in the vane passage and downstream of the vane passageway experience a higher gas pressure than the corresponding regions of the first radial surface 150 of the shroud 112.

As a result, in the absence of the pressure balancing arrangement of the present invention, which will now be explained, the net axial force acting on the radial wall 124 of the shroud 112 is in the inboard direction, i.e. towards the annular inlet passageway 109. The gas arrives at the inlet passageway 109, and in the shroud cavity 113, in pulsations that are out of phase with each other. This causes a pulsation, and variation, of the above pressure differential across the radial wall 124 of the shroud 112 which produces a net force on the shroud 112 that changes direction between the axially inboard and outboard directions. This acts to vibrate the shroud 112 in the axial direction, which results in wear and fatigue of the shroud retaining ring 129 and of the shroud 112 itself.

The above described radially extending flange 163 is provided so as to substantially remove, or at least reduce this problem, particularly when the spacing between the opposing surfaces 110, 150 of the nozzle ring 111 and shroud 112 is smalL In the embodiment shown in Figure 4, the radially extending flange 163 extends to a radially outer diameter that is located radially inwardly of the radial vane passage. This is advantageous in that the radially extending flange 163 does not obstruct the passage of the guide vanes 114 into the cavity 113.

The pressure balance flange 163 is advantageous in that the pressure of the gas within area A4 in the shroud cavity 113, which is at a higher pressure than the gas within areas A2 and A3 (within the inlet passageway within and downstream of the vane passage) acts on the third radial surface 171, defined by the radially extending flange 163. This acts in the opposite direction to the pressure of the gas on the second radial surface, defined by the radial wall 124 of the shroud 112, which acts to reduce the net axial force on the shroud 112 in the inboard axial direction. In fact, the net axial force on the shroud 112 is now in the outboard direction (i.e. away from the annular inlet passageway 109). This reduces the vibration of the shroud 112 caused by the pulsating gas, since the net axial forces produced by the pulsations are now substantially always in the outboard axial direction. This reduces the wear/fatigue on the retaining ring 129.

Arranging the seal ring 165 to seal the radially extending flange 163 against the sleeve 166, so as to prevent the gas from flowing from the cavity 113 in between the radially extending flange 163 and the cylindrical sleeve 166, to behind the radially extending flange 163, restricts the transmission of the relatively high pre-turbine pressure to the radial fourth surface defined 172 defined on the rear face of the flange 163, which would otherwise negate the advantages provided by the pressure balance flange 163.

This also provides an additional efficiency gain as the gas is prevented from leaking past the pressure balance flange 163.

An addtional advantage provided by the shroud 112, is that it can be quickly and easily retro-fitted to existing turbines, by fixing the second axial section 162b (with its attached radial flange 163) to the radially inner flange 26 of the shroud 12 of an existing turbine, and by attaching the housing insert 200 to the turbine housing 1, inside the shroud cavity 13.

A further advantage is that the pressure balancing flange 163 acts as a heat sink.

Accordingly, thermal stresses in the region of the inner diameter of the vane slots 125 are reduced. This prevents cracking of the vane slots 125.

Referring to Figure 5, there is shown a sectional view of a shroud 112 that is the same as that of Figure 4, but using a retaining ring 400 that is not pre-loaded. In more detail, the retaining ring 400 is not pre-loaded within the circumferential flange groove 128 and the groove 130 in the housing 101. The retaining ring 400 is arranged such that, when it is received within said grooves 128, 130, it does not act to bias the shroud plate 112 in the axially outboard (or inboard) direction.

In this regard, the retaining ring 400 has a cross-sectional shape that is substantially uniform in the radial direction of the retaining ring 400, i.e. it does not have the tapered arrangement of the retaining ring 129. The retaining ring 400 has a width that is substantially constant across the radius of the retaining ring 400. The radially outer surface of the retaining ring 400 engages with a surface 401 of the housing 101 that defines the groove 130. The groove 130 also has a width that is substantially constant across the radius of the groove 130.

The use of the radially extending flange 163 removes the need for the retaining ring 400 to be pro-loaded to bias the shroud 112 in the outboard direction. This allows the retaining ring 400 and the circumferential groove 401 in the housing to have a simpler cross-sectional shape than that required for a pre-loaded retaining ring (as described above). This therefore allows for simpler machining and assembly.

The retaining ring 400 is mounted within said grooves 128, 130 such that the shroud 112 is rotatable relative to the housing 101. In this regard the retaining ring 400 is rotatable relative to the shroud 112 and the housing 101.

Because the radially extending flange 163 removes the need for the retaining ring 400 to be pre-loaded, this allows the retaining ring 400 to be mounted within the said grooves 128, 130 such that the shroud 112 is rotatable relative to the housing 101.

This facilitates ease of assembly as the shroud 112 may be rotated relative to the nozzle 111 when the shroud is secured in the cavity 113. Accordingly, the vanes 114 on the nozzle ring 111 may be aligned with slots 125 in the shroud 112 by rotation of the shroud 112 relative to the housing 101 (and therefore relative to the nozzle ring 111) when the shroud 112 is secured within the cavity 113. This therefore provides for an easier and faster assembly process as it removes the need for the shroud 112 and the nozzle ring 111 to be accurately positioned relative to each other by a setting operation as the shroud 112 is secured within the cavity 113.

Referring now to figures 6 and 7, there is shown a sectional view of a shroud 212 installed in a turbine housing 201 of a variable geometry turbine according to a second embodiment of the present invention. The variable geometry turbine of figures 6 and 7 is the same as that shown in figures 3 and 4 except for the differences described below. Components of the variable geometry turbine shown in figures 6 and 7 which correspond to those shown in Figures 3 and 4 will take the same reference numbers used in Figures 3 and 4 but increased by 100.

In the embodiment shown in figures 5 and 6, the shroud 212 differs from the first embodiment in that the radially extending flange 263 extends further radially outwardly than the radially extending flange 163 of the first embodiment. In this respect, the radially extending flange 263 extends substantially across the radial extent of the cavity 213.

Furthermore, the outer flange 227 is supported by the radially extending flange 263. In this respect, the outer flange 227 comprises a first axially extending annular flange wall 227a that extends axially inboard from a radially outer end of the radial third surface 271 defined by the radially extending flange 263. The outer flange 227 further comprises first and second radially extending flange walls 227c, 227b connected by the axially extending annular flange wall 227a to form said circumferential flange groove 228. The second radially extending wall 227b is a radial extension of the radially extending flange 263. The first radially extending wall 227c is provided axially inboard of the second radially extending wall 227b.

The circumferential flange groove 228 is defined between the first and second radially extending flange walls 227c, 227b, with the base of the groove 228 defined by the first axially extending flange wall 227a. The overall configuration is generally "h" shaped.

Accordingly, in this embodiment, the outer flange 227, and the circumferential flange groove 228, is located axially inboard of the cavity opening 300 and is located proximal to the outboard end of the cavity 213.

A circumferential groove 230 in the housing is substantially axially aligned with the groove 228 in the outer flange 227. In this regard, the circumferential groove 230 in the housing is located towards the outboard end of the cavity 213. The circumferential groove 230 is substantially the same shape as the circumferential groove 130 of the first embodiment. In addition, in the same way as in the first embodiment, a retaining ring 229, identical to the retaining ring 129 of the first embodiment, is received within the groove 228 in the outer flange 227 and the groove 230 in the housing 201, to axially fix the shroud 212 relative to the housing 201.

The outer flange 227 is also provided with a corresponding sealing arrangement to the sealing arrangement of the radially extending flange 163 of the first embodiment. In this respect, the outer flange 227 further comprises a third radially extending wall 227d spaced axially inboard of the first radially extending wall 227c and connected by a second axially extending flange wall 227e.

A circumferential seal groove 264 is defined between the second and third radially extending flange walls 227c, 227d, with the base of the seal groove 264 defined by the second axially extending flange wall 227e. The overall configuration is generally h' shaped. The seal in groove 264 has substantially the same shape as the seal groove 164 of the first embodiment.

A seal ring 265, of substantially the same type and shape as the seal 165 of the first embodiment, is received within the circumferential seal groove 264. The seal ring 265 prevents gas from flowing from the cavity 213 in between the outer flange 227 and the housing 201 to behind (outboard of) the radially extending flange 163, in between the radially extending flange 263 and the housing 201.

As with the first embodiment, this restricts the transmission of the relatively high pre-turbine pressure to the radial fourth surface defined 272 defined on the rear face of the flange 263, which would otherwise negate the advantages provided by the pressure balance flange 263. This also provides an additional efficiency gain as the gas is prevented from leaking past the pressure balance flange 263.

Accordingly, in this embodiment, the outer flange 227 is provided both with the retaining ring 229 arrangement and the seal arrangement 265 of the first embodiment.

The radially outer periphery of the radially extending flange 263 is located radially outwardly of the radial vane passage. This is advantageous in that it provides the third radial surface 271 with a relatively large cross-sectional area, thereby increasing the above-mentioned advantages provided by said radial third surface 271.

The outer flange 227 defines a radial ffth surface 501 that is opposed to the radial second surface 267. The radial fifth surface 501 is defined by an inboard surface of the third radial flange wall 227d of the outer flange 227 and is substantially annular. The radial fifth surface 501 is substantially parallel to the radial third surface 271. The radial fifth surface 501 extends from a radially inner surface, located at a radial position that is substantially aligned with a radially outer end of the radial third surface 271, to a radially outer surface. The radially outer surface of the radial fifth surface is adjacent to the inner surface 500 of the housing 201 that defines the cavity 213.

As with the first embodiment, the pressure balance flange 263 is advantageous in that the pressure of the gas within area A4 n the shroud cavity 213, which is at a higher pressure than the gas within areas A2 and A3 (within the inlet passageway within and downstream of the vane passage) acts on the third radial surface 271, defined by the radially extending flange 263 and on the fifth radial surface 501 is defined by the outer flange 227. This acts in the opposite direction to the pressure of the gas on the second radial surface, defined by the radial wall 224 of the shroud 212, which acts to reduce the net axial force on the shroud 212 in the inboard axial direction. In fact, the net axial force on the shroud 212 is now in the outboard direction (i.e. away from the annular inlet passageway). This reduces the vibration of the shroud 212 caused by the pulsating gas, since the net axial forces produced by the pulsations are now substantially always in the outboard axial direction. This reduces the wear/fatigue on the retaining ring 229.

In this embodiment, the retaining ring is not located in the cavity opening 300 (as in the first embodiment) but is located axially outboard of the cavity opening 300, as described above. In this regard, a radial clearance 505 is provided between the outer periphery of the radial wall 224 of the shroud 212 and an inner surface 506 of the housing that defines the cavity opening 300. The radial clearance is located axially inboard of the retaining ring 229 and extends substantially across the radial distance between the outer periphery of the radial wall 224 of the shroud 212 and said inner surface 506 of the housing that defines the cavity opening 300. The radial clearance 505 extends substantially around the circumference of the shroud 212 to form a substantially annular shape.

The radial clearance 505 allows for gas to flow from the annular inlet passageway into the cavity 212. This is advantageous in that, due to the radial clearance 505, the gas arrives at the annular inlet passageway, and in the shroud cavity 212, in pulsations that are generally in phase with each other, or at least more in phase with each other than where the retaining ring is located in the cavity opening 300. This further reduces the vibration on the second wall member, which reduces wear on the retaining ring and on the second wall member.

Accordingly, it will be appreciated that the shroud 112, 212 of the first and second embodiments provides an arrangement that reduces the vibration of the shroud 112, 212 during use, thereby reducing wear/fatigue on the retaining ring 129,229 and the shroud 112, 212.

Furthermore, since the radially extending flange 163, 263 acts as a heat sink, thermal stresses in the region of the inner diameter of the vane slots 125, 225 are reduced.

This prevents cracking of the vane slots 125, 225.

In addition, the radially extending flange 163, 263 can be conveniently and cheaply retro-fitted to existing turbines, to provide the above-mentioned advantages.

Numerous modifications and variations may be made to the exemplary design described above without departing from the scope of the invention as defined in the claims.

For example, in the described embodiment, the inlet guide vanes 114 are attached to the nozzle ring 111, with the shroud 112 provided with apertures 125 for receiving the vanes 114 as the nozzle ring 111 moves towards the shroud 112. Alternatively, the inlet guide vanes 114 may be attached to the shroud 112, with the nozzle ring 111 provided with said apertures 125 for receiving the vanes 114 as the nozzle ring 111 moves towards the shroud 112.

Furthermore, in the described embodiment, the shroud 112 is mounted within a cavity 113 within the turbine housing 1, with the nozzle ring 111 mounted within a cavity in the bearing housing 3. Alternatively, the nozzle ring may be mounted within a cavity 113 within the turbine housing 1, with the shroud 112 mounted within a cavity in the bearing housing 3.

Claims

CLAIMS1. A variable geometry turbine comprising: a housing comprising a turbine housing in which a turbine wheel is mounted for rotation about a turbine axis; an annular inlet passageway upstream of the turbine wheel; the annular inlet passageway being defined by a radial surface of a radially extending wall of an annular first wall member mounted within a cavity provided within the housing and a facing radial first surface of a radial wall of an annular second wall member; the first wall member being axially movable to vary the size of the inlet passageway; the second wall member being substantially fixed in the axial direction relative to the housing; the second wall member covering the opening of a cavity defined by the housing; the second wall member comprising an outer flange around its radially outer periphery, the outer flange defining a circumferential flange groove for receiving a retaining ring for securing the second wall member in the cavity; an array of inlet guide vanes extending across said annular inlet passageway to define a radial vane passage; the radial wall of the second wall member defining a radial second surface that opposes the first surface; wherein the second wall member further comprises an annular flange that extends axially into the cavity and which supports a radially extending flange that defines a radial third surface that is opposed to the radial second surface.
2. A variable geometry turbine according to claim 1 wherein a retaining ring is received within the circumferential flange groove in the outer flange, the retaining ring being arranged to secure the second wall member in the cavity.
3. A variable geometry turbine according to claim 2 wherein the retaining ring is not pro-loaded within the circumferential flange groove.
4. A variable geometry turbine according to claim 2 wherein the retaining ring is pre-loaded in the circumferential flange groove so as to bias the second wall member in an axial direction.
5. A variable geometry turbine according to claim 4 wherein the retaining ring has a radially outer periphery that tapers to define a conical surface which engages with a complimentary conical surface defined by a side wall of a groove defined by the housing such that the retaining ring biases the second wall member in an axial direction.
6. A variable geometry turbine according to any of claims 2 to 5 wherein the retaining ring is mounted within the circumferential flange groove such that the second wall member is rotatable relative to the housing.
7. A variable geometry turbine according to any preceding claim wheren the radially extending flange is located towards an outboard end of the cavity.
8. A variable geometry turbine according to any preceding claim wheren the radially extending flange defines a radial fourth surface that is opposed to the radial third surface.
9. A variable geometry turbine according to claim 8 wherein the second wall member is sealed against a surface so as to define a first area within the cavity which includes the radial second and third surfaces and a second area within the cavity which includes the radial fourth surface.
10. A variable geometry turbine according to claim 9 wherein said surface is a surface of an intermediary member between the radially extending flange and the housing.
11. A variable geometry turbine according to claim 10 wherein the intermediary member is formed separately to the turbine housing and is fixed to the turbine housing.
12. A variable geometry turbine according to any of claims 9 to 11 wherein the second area is in fluid communication with a region of the annular inlet passageway downstream of the radial vane passage.
13. A variable geometry turbine according to any preceding claim wherein radially extending flange is formed separately from the radial wall of the second wall member and is fixed thereto.
14. A variable geometry turbine according to any preceding claim wherein the outer flange is located in the opening of the cavity.
15. A variable geometry turbine according to claim 14 wherein the outer flange comprises first and second radially extending flange members connected by an axially extending flange member to form said circumferential flange groove and the axially extending flange member extends axially outboard from the radial second surface defined by the radial wall of the second wall member.
16. A variable geometry turbine according to either of claims 14 or 15 wherein the circumferential flange groove defined by the outer flange is located in the opening of the cavity.
17. A variable geometry turbine according to any of claims 14 to 16 when dependent on claim 9, or any of claims 10 to 16 when dependent on claim 9, wherein the radially extending flange defines a circumferential seal groove for receiving a seal to seal the radially extending flange against said surface so as to define said first and second areas.
18. A variable geometry turbine according to claim 17 wherein a seal is provided in said circumferential seal groove to as to seal the radially extending flange against said surface.
19. A variable geometry turbine according to any of claims 1 to 13 wherein the outer flange is located axially outboard of the opening of the cavity.
20. A variable geometry turbine according to claim 19 wherein the outer flange is located towards an outboard end of the cavity.
21. A variable geometry turbine according to either of claims 19 or 20 wherein the outer flange extends axially inboard from the radial third surface defined by the radially extending flange.
22. A variable geometry turbine according to any of claims 19 to 21 wherein the circumferential flange groove defined by the outer flange is located axially outboard of the opening of the cavity.
23. A variable geometry turbine according to any of claims 19 to 22 wherein a retaining ring is received within the circumferential flange groove, the retaining ring is located axially outboard of the opening of the cavity such that a radial clearance is provided between the outer periphery of the radial wall of the second wall member and the housing that allows for gas to flow from the annular inlet passageway into the cavity.
24. A variable geometry turbine according to any of claims 19 to 23 when dependent on claim 9, or any of claims 10 to 23 when dependent on claim 9, wherein the outer flange defines a circumferential seal groove for receiving a seal to seal the outer flange against said surface so as to define said first and second areas.
25. A variable geometry turbine according to claim 24 wherein a seal is provided in said circumferential seal groove so as to seal the radially extending flange against said surface.
26. A variable geometry turbine according to claim 25 wherein the circumferential seal groove is axially adjacent to the circumferential flange groove for receiving the retaining ring.
27. A variable geometry turbine according to any of claims 19 to 26 wherein the outer flange defines a radial fifth surface that is opposed to the radial second surface.
28. A variable geometry turbine according to any preceding claim wherein the second wall member and/or housing are arranged to define a path for gas to flow from the annular inlet passageway into the cavity, outboard of the radial wall of the second wall member.
29. A variable geometry turbine according to claim 28 wherein the retaining ring is arranged to permit the flow of gas past the retaining ring into the cavty.
30. A variable geometry turbine according to either of claims 28 or 29 wherein one or more apertures are defined by the second wall member, fluidly connecting the first radial surface to the second radial surface, to facilitate gas flow from the annular inlet passageway into the cavity.
31. A variable geometry turbine according to any preceding claim wherein the first wall member is a nozzle ring and the second wall member is a shroud.
32. A variable geometry turbine according to any of claims 1 to 30 wherein the first wall member is a shroud and the second wall member is a nozzle ring.
33. A variable geometry turbine according to any preceding claim wherein the inlet guide vanes are fixed to the first wall member, with the second wall member defining apertures for receipt of the vanes.
34. A variable geometry turbine according to any preceding claim wherein the inlet guide vanes are fixed to the second wall member, with the first wall member defining apertures for receipt of the vanes.
35. A variable geometry turbine according to any preceding claim wherein the second wall member covers the opening of a cavity defined by the turbine housing.
36. A variable geometry turbine according to any preceding claim wherein the second wall member covers the opening of a cavity defined by the bearing housing.
37. A variable geometry turbine according to any preceding claim wheren the radially outer periphery of the radially extending flange is located radially inwardly of the radial vane passage.
38. A variable geometry turbine according to any of claims 1 to 36 wherein the radially outer periphery of the radially extending flange is located radially outwardly of the radial vane passage.
39. A turbomachine comprising a variable geometry turbine according to any preceding claim.
40. A turbomachine according to claim 39 wherein the turbomachine is a variable geometry turbocharger.
41. A variable geometry turbine substantially as described herein with reference to the accompanying drawings.
42. A turbomachine substantially as described herein with reference to the accompanying drawings.