CLAIMS:

1. A turbine assembly for a turbocharger, the turbine assembly comprising:

a housing which defines a flow path between an inlet and an outlet, the housing extending around an axis, the housing comprising:

first and second volutes which define a respective first and second flow passage, a circumferential outlet portion of each of the first and second volutes being defined by first and second tongues; and

a first aperture in which a vane assembly is received;

the vane assembly comprising:

a plurality of vanes circumferentially distributed about a turbine wheel receiving bore, each of the plurality of vanes comprising a leading edge and a trailing edge, each of the plurality of vanes having a fixed orientation; and

wherein the plurality of vanes comprises a first vane and a second vane, the first vane being the vane having its leading edge disposed in closest proximity to a tip of the first tongue, the second vane being the vane having its leading edge disposed in closest proximity to a tip of the second tongue, and wherein, for each of the first vane and the second vane, the leading edge at least partly overlaps the tip of the proximate tongue circumferentially.

2. The turbine assembly according to claim 1 , wherein each of the first and second vanes comprises an at least partially convex surface, and an at least partially concave surface, each extending between the leading and trailing edge thereof.

3. The turbine assembly according to either of claims 1 or 2, wherein the plurality of vanes further comprises a first array of vanes, and a second array of vanes; and wherein the first array of vanes comprises the first vane, and the second array of vanes comprises the second vane, each of the first and second arrays of vanes further comprising a plurality of secondary vanes.

4. The turbine assembly according to claim 3, wherein the first and second vanes have leading edges which extend radially beyond the leading edges of the secondary vanes, the first and second vanes thereby having comparatively longer chord lengths than the secondary vanes.

5. The turbine assembly according to either of claims 3 or 4, wherein each of the two arrays of vanes comprises the same number of vanes.

6. The turbine assembly according to any preceding claim, wherein the first and second vanes are diametrically opposed relative to one another.

7. The turbine assembly according to any preceding claim, wherein each of the tongues comprises a body portion and a tapering portion, the tip being disposed at an outermost end of the tapering portion.

8. The turbine assembly according to any preceding claim, wherein, for each of the tongues, the tip extends to within about 0.5 mm to about 15 mm of the first aperture of the housing.

9. The turbine assembly according to any preceding claim, wherein the vane assembly is a fixed vane assembly comprising a mounting portion to which each of the vanes are mounted.

10. The turbine assembly according to any preceding claim, wherein the housing comprises:

a volute housing, the volute housing comprising the first and second volutes and the first aperture; and

a wall member engageable with the volute housing.

11. The turbine assembly according to claim 10, wherein the vane assembly is a nozzle ring and the wall member is a shroud.

12. The turbine assembly according to claim 11 , wherein the shroud comprises a plurality of vane apertures in which the vanes of the nozzle ring are receivable, the shroud being disposed in a recess within the volute housing, the shroud plate defining one side of an annular passage between the circumferential outlet portions of the volutes and the turbine wheel-receiving bore, a face of the nozzle ring defining the other side of the annular passage;

wherein the nozzle ring is axially displaceable, relative to the shroud, to adjust the extent to which the annular passage is open.

13. The turbine assembly according to claim 12, wherein the shroud is generally annular and incorporates a shroud wall which defines a periphery of the shroud, the shroud wall being outwardly offset in two positions.

14. The turbine assembly according to any of claims 10 to 13, wherein the first tongue is formed of a single body which forms part of the volute housing, and wherein the second tongue is also formed of a single body which forms part of the volute housing.

15. The turbine assembly according to any of claims 10 to 13, wherein the first tongue is formed of two portions, a first portion forming part of the volute housing and a second portion forming part of the wall member, the two portions being aligned with one another.

16. A turbine comprising the turbine assembly of any preceding claim, further comprising a turbine wheel received in the turbine wheel-receiving bore.

17. A turbocharger comprising:

a compressor comprising a compressor housing and a compressor wheel; the turbine according to claim 16;

a bearing housing interposing the compressor and the turbine; and

a shaft connected to both the compressor impeller and the turbine wheel, such that rotation of the turbine wheel is configured to drive rotation of the compressor wheel.

18. A nozzle ring for a turbocharger, the nozzle ring comprising a plurality of vanes, wherein the plurality of vanes comprises a first vane, a second vane and a plurality of secondary vanes, and wherein the first and second vanes have a longer chord length than the plurality of secondary vanes.

19. A shroud for a turbocharger, the shroud comprising:

a plate, the plate defining:

a first vane aperture in which a first vane of a nozzle ring is receivable; and

a second vane aperture in which a second vane of the nozzle ring is receivable;

the plate comprising first and second radially extending projections, the first projection being circumferentially aligned with at least a leading edge of the first vane aperture, the second projection being circumferentially aligned with at least a leading edge of the second vane aperture.

20. The shroud according to claim 19, wherein the shroud further comprises at least a tip of first and second tongues.

21. The shroud according to claim 20, wherein the at least a tip of first and second tongues extend from the first and second projections respectively.

22. The shroud according to either of claims 20 or 21 , wherein the tip of the at least a tip of the first and second tongues is misaligned relative to the leading edges of the first and second vane apertures respectively.

23. A shroud for a turbocharger, the shroud comprising:

a first vane aperture in which a first vane of a nozzle ring is receivable;

a second vane aperture in which a second vane of the nozzle ring is receivable; at least a tip of a first tongue associated with a leading edge of the first vane aperture; and

at least a tip of a second tongue associated with a leading edge of the second vane aperture.

24. A turbine assembly for a turbocharger, the turbine assembly comprising:

a housing which defines a flow path between an inlet and an outlet, the housing extending around an axis and defining a first aperture in which a vane assembly and turbine wheel are receivable, the housing further defining first and second tongues, the housing comprising a volute housing and a shroud according to claim 23;

the volute housing comprising first and second volutes which define a respective first and second flow passage, a circumferential outlet portion of each of the first and second volutes being defined by the first and second tongues;

the shroud engaging the volute housing; and

wherein the first tongue is formed of a first portion and a second portion, the first portion forming part of the volute housing and the second portion forming part of the shroud, wherein the first and second portions cooperate to define the first tongue; and

wherein the second tongue is formed of a first portion and a second portion, the first portion forming part of the volute housing and the second portion forming part of the shroud, wherein the first and second portions cooperate to define the first tongue.

25. A turbine assembly for a turbocharger, the turbine assembly comprising:

a housing which defines a flow path between an inlet and an outlet, the housing extending around an axis, the housing comprising:

first and second volutes which define a respective first and second flow passage, a circumferential outlet portion of each of the first and second volutes being defined by first and second tongues;

a wall member; and

a first aperture in which a vane assembly is received;

wherein the vane assembly defines a turbine wheel-receiving bore; and wherein the wall member and vane assembly define an annular passage between the circumferential outlet portions and the turbine wheel-receiving bore, at least one of the vane assembly and the wall member being axially displaceable relative to the other to adjust the extent to which the annular passage is open.

TURBINE ASSEMBLY FOR A TURBOCHARGER

The present invention relates to a turbine assembly and a shroud.

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 comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to the intake manifold of the engine, thereby increasing engine power.

The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housing.

It is known to provide double entry turbines in which two volutes each define two flow passages (i.e. each volute defines a flow passage). Exhaust gas enters the volutes at an inlet, and exits the volutes at an outlet. Exhaust gas flows, or pulses, through each volute in an alternating manner (i.e. a first volute pulses whilst a second does not, and then the second volute pulses whilst the first does not). Vanes may interpose the outlets and a turbine wheel, so as to direct exhaust gas flow onto the turbine wheel.

In known turbochargers, the leakage of exhaust gas flow from one volute into the other, as exhaust gas pulses through one volute but not the other, can decrease engine performance. This is due to an increased pumping work required from the engine in order to overcome the back pressure in the non-pulsing volute caused by the leaked flow. In some engines, the leakage of exhaust gas into the non-pulsing volute may also prevent the complete exhaustion of exhaust gas from a firing cylinder at the end of an ignition cycle. This is due to the exhaust gas having to be pumped against a back pressure gradient, due to exhaust gas having leaked into the non-pulsing volute. This can lead to an undesirable reduction in engine efficiency.

The extent to which the exhaust gas flows through a pulsing volute, and does not leak into a non-pulsing volute, may be referred to as scroll separation. That is to say, each volute may otherwise be referred to as a scroll, and it is desirable that scroll separation is increased i.e. that exhaust gas flowing through a pulsing volute does not leak into a non-pulsing volute. It is desirable to increase scroll separation for reasons of improved performance.

There exists a need to provide an alternative turbine assembly which overcomes one or more of the disadvantages of known turbine assemblies, whether set out above or not. Additionally, there is a need for an alternative turbine assembly.

According to a first aspect of the invention there is provided a turbine assembly for a turbocharger, the turbine assembly comprising:

a housing which defines a flow path between an inlet and an outlet, the housing extending around an axis, the housing comprising:

first and second volutes which define a respective first and second flow passage, a circumferential outlet portion of each of the first and second volutes being defined by first and second tongues; and

a first aperture in which a vane assembly is received;

the vane assembly comprising:

a plurality of vanes circumferentially distributed about a turbine wheel receiving bore, each of the plurality of vanes comprising a leading edge and a trailing edge, each of the plurality of vanes having a fixed orientation; and

wherein the plurality of vanes comprises a first vane and a second vane, the first vane being the vane having its leading edge disposed in closest proximity to a tip of the first tongue, the second vane being the vane having its leading edge disposed in closest proximity to a tip of the second tongue, and wherein, for each of the first vane and the second vane, the leading edge at least partly overlaps the tip of the proximate tongue circumferentially.

Advantageously, this arrangement reduces flow leakage into the other circumferential outlet portion. In order to leak into the other circumferential outlet portion, the flow must traverse a more tortuous path. That is to say, flow is more effectively directed towards the desired circumferential outlet portion which is associated with the volute through which the flow passes. The leading edge of the first and second vanes at least partly overlapping the tip of the proximate tongue is an example of as a positively

clocked arrangement. Put another way, the leading edges of the first and second vanes are positively clocked relative to the tips of the proximate tongues.

For each of the first and second vanes, the leading edge can be said to be disposed radially inwards of the tip of the tongue and to overlap with the tongue to at least some extent. For example, if a line extends from the axis radially outwards, the line would first pass through the leading edge of the vane and would then pass through the tongue (specifically through a portion of the tongue upstream of the tip). As flow passes along the tongue, past the tip thereof, the flow could be said to cascade onto, and along, the vane, owing to the overlap. The overlapping arrangement may therefore be referred to as a cascading arrangement, or alignment, of tongue and vane, specifically of the tip of the tongue and the leading edge of the vane. A positively clocked arrangement, with circumferential overlap, may be one in which, in use, the first tongue directs flow onto a generally convex side of the first vane. That is to say, if a high pressure side of the associated tongue was to be extended, it may impact, or pierce, the generally convex, or pressure, side of the first vane.

The presence of a circumferential overlap is indicative of a‘positively clocking’ of the vane assembly. In the field of turbines, clocking refers to a rotational displacement of a vane assembly due to the impingement of a flow thereon. In this instance, the clocking refers to the vane assembly being intentionally rotated relative to an otherwise aligned relationship with the tongues, specifically tips thereof. The positive of the positive clocking denotes the direction of rotation. When the turbine assembly forms part of a turbocharger, and the turbine assembly is viewed from the turbine-end, positive clocking may refer to a clockwise direction of rotation of the vane arrangement assembly relative to the housing (specifically the tongues thereof). Alternatively, positive clocking refers to a direction of rotation of a leading edge of a first vane relative to a tip of a first tongue which is the opposite direction to that which the turbine wheel rotates in use.

Proximate tongue is intended to refer to a tongue in closest proximity to the vane in question. For the first vane, the proximate tongue is the first tongue. Likewise, for the second vane, the proximate tongue is the second tongue. It is the proximate tongue which the vane may generally form an extension of, a gap being defined therebetween.

A preferred positive clocking rotational position may be a position in which a radial offset between a tip of the tongue and a leading edge of the vane is at its lowest. For example, the preferred positive clocking rotational position may be when the tip of the tongue and the leading edge of the vane are radially aligned with one another. The preferred arrangement may therefore be an arrangement in which the clearance between the leading edge and tip is minimised to as low a value as possible.

Misalignment refers to there being a relative circumferential offset between the tip of the tongue and the leading edge of the vane. In the case where the tip and leading edge are aligned, extending a high pressure side of the associated tongue would impact, or pierce, the leading edge of the vane. Misalignment refers to a relative orientation in which extending a high pressure side of the tongue does not impact, or pierce, the leading edge of the vane. Positive clocking is an example of misalignment as referred to in this document.

Advantageously, orienting the vane assembly such that the leading edge of the first vane at least partly circumferentially overlaps the tip of the first tongue increases scroll separation in use. Specifically, in use, an exhaust gas flow is pulsed, in an alternating manner, through each of the first and second volutes. This may be because, for example, an inlet associated with each volute is in fluid communication with a different bank of cylinders. It is desirable that all of the flow through a first volute inlet does not leak beyond the first circumferential outlet portion of that volute. It is therefore desirable that all of the flow through the first volute passes through the first circumferential outlet portion, and generally through an associated array of vanes. The overlap of the leading edge of the first vane relative to the tip of the first tongue reduces the risk that, in use, the exhaust gas flow through the first volute, and so along the first tongue, impinges upon a leading edge of the vane and leaks into the adjacent circumferential outlet portion. The overlap also reduces that risk of, as may be the case for a negatively clocked arrangement, flow passing between the leading edge of the first vane and the tip of the first tongue and impinging upon an adjacent vane disposed in the other circumferential outlet portion.

By reducing leakage into the adjacent circumferential outlet portion, i.e. increasing the scroll separation of the volutes, the pumping work required from the engine is reduced. This is due, at least in part, to a reduction in back pressure which the engine must

overcome when exhaust gas is exhausted from a cylinder at the end of a combustion cycle. Overall engine performance is therefore increased as a result.

The housing may be a double entry housing. The housing may be said to be circumferentially divided, or sector divided. The divisions may be equal e.g. in two halves, or may be unequal. Alternatively, the turbine assembly may be said to be a double entry turbine assembly. Similarly, when incorporated in a turbine, the turbine may be said to be a double entry turbine.

The first and second vanes may be referred to as long vanes. The first and second vanes may be referred to as tongue-associated vanes, owing to their proximity to the tongues.

The leading edge of the vane being in closest proximity to a tip of the tongue is intended to mean that the leading edge of that vane is closer to the tip of the tongue than the leading edges of all of the other vanes are to the tip of the tongue. A vane having its leading edge disposed in closest proximity to a tip of a tongue may be considered to generally extend in the same or a similar direction to the tongue. It will be appreciated that due to the misalignment between the vane and the tip of the tongue, the vane will not extend in exactly the same direction as the tongue. However, despite the misalignment between the vane and the tip of the tongue, the vane may still be considered to be an extension of the tongue. In use, the tongue directs flow towards the vane. The vane directs flow towards the turbine wheel-receiving bore, and so turbine wheel when assembled. The vane is therefore upstream of the turbine wheel-receiving bore. In turn, the tongue is upstream of the vane.

Each of the first and second volutes are defined, at least in part, by each of the first and second tongues. For the first volute, the first tongue is upstream of the second tongue. That is to say, for flow passing through the first volute, and so through the first flow passage, the flow first passes the first tongue before subsequently passing the second tongue. The second tongue is therefore downstream of the first tongue for the first volute. However, owing to the geometry of the housing, when considering the second volute, the second tongue is upstream of the first tongue. The first volute comprises a first circumferential outlet portion. The second volute comprises a second circumferential outlet portion.

The extent to which the leading edge of the first vane circumferentially overlaps the tip of the tongue may be of the order of up to 10%, 25% or 50% of the chord length of the vane. That is to say, the tip of the tongue may be disposed at a position which is radially outward of a position along a chord length of the vane up to 10%, 25% or 50% of the chord length of the vane in a direction moving from the leading edge to the trailing edge. That is to say, for an extent of overlap of 10%, the tip of the tongue radially aligns with a position along the chord length of the vane which is 10% of the distance along the chord from the leading edge.

The tip of the tongue may be an outer end of the tongue. The tip of the tongue may be the point at which a low pressure side of the tongue meets a high pressure side of the tongue. Where the tongue is rounded, the tip of the tongue may be substantially halfway along a circumference of an end of the tongue.

Each of the first and second vanes may comprise an at least partially convex surface, and an at least partially concave surface, each extending between the leading and trailing edge thereof.

The vanes may be entirely arcuate. Alternatively, the vanes may incorporate flat, or straight, geometries. The vanes may therefore be entirely arcuate, entirely flat, or anywhere in between. The vanes may be of a wing-like geometry e.g. with a pressure side and a suction side.

The vanes may be described as curved vanes, or arcuate vanes.

The at least partially convex and at least partially concave surfaces may be described as high and low pressure surfaces respectively. The high and low pressure surfaces may otherwise be referred to as high and low pressure sides respectively.

Where the first and second vanes comprise an at least partially convex surface, that surface may be a high pressure side of the vane. For the first vane, for example, the first tongue is preferably configured to direct flow onto the high pressure side of the vane in use. The first tongue, specifically a high pressure side thereof, may therefore be angled towards the at least partially convex surface, or high pressure side, of the first vane. The above is equally applicable to the second vane and tongue.

The plurality of vanes may further comprise a first array of vanes, and a second array of vanes; and

wherein the first array of vanes may comprise the first vane, and the second array of vanes may comprise the second vane, each of the first and second arrays of vanes may further comprise a plurality of secondary vanes.

The first array of vanes is therefore formed of the first vane and a plurality of secondary vanes. Similarly, the second array of vanes is formed of the second vane and a plurality of secondary vanes. Accordingly, there are two groups, or arrays, of secondary vanes. In alternative arrangements, there may be more than two groups, or arrays, of secondary vanes.

The presence of secondary vanes is advantageous in more evenly directing the flow towards the turbine wheel-receiving bore.

The first and second vanes may have leading edges which extend radially beyond the leading edges of the secondary vanes, the first and second vanes thereby having comparatively longer chord lengths than the secondary vanes.

The secondary vanes may all be of the same geometry. The secondary vanes may therefore have the same chord length i.e. a uniform chord length shared by all secondary vanes. Furthermore, the secondary vanes may all have the same angle of attack.

The first and second vanes having comparatively longer chord lengths is advantageous because there is less of a gap between the tip of the tongue and the leading edge of the proximate first or second vane. This means the exhaust gas flow is more accurately directed into the corresponding circumferential outlet portion. Undesirable leakage is therefore reduced as a result, and scroll separation is increased accordingly. Furthermore, surface friction, or skin friction, resulting from the flow passing over comparatively longer vanes is not unduly increased by the first and second vanes

having comparatively longer chord lengths, in comparison to all of the vanes having comparatively longer chord lengths.

Each of the two arrays of vanes may comprise the same number of vanes.

Each array preferably comprises one long vane, and six other vanes. That is to say, each array of vanes preferably comprises a first, or second, vane, and a plurality of secondary vanes. However, more, or fewer, vanes may otherwise be used.

The diametric position of a trailing edge of all of the vanes may be uniform. For example, the trailing edge of all of the plurality of vanes may be disposed at the same radius from the axis.

The first and second vanes may be diametrically opposed relative to one another.

The first and second vanes, or the long vanes, being diametrically opposed may be advantageous for reasons of a more even distribution of flow. When the turbine assembly is assembled in a turbine, incorporating a turbine wheel, the wheel may be easier to balance if the two vanes are diametrically opposed. This is typically preferred in arrangements where EGR is not utilised.

Alternatively, it may be desirable that the first and second vanes are not diametrically opposed, particularly in arrangements where EGR is utilised. Where EGR is used on only one bank of cylinders, i.e. flow is taken from only one of the first or second volutes, an uneven circumferential distribution of the first and second tongues may be used to counteract a flow imbalance otherwise caused by the EGR bleeding off a portion of the flow which otherwise pass through one of the first and second volutes.

Each of the tongues may comprise a body portion and a tapering portion, the tip being disposed at an outermost end of the tapering portion.

The tongues may otherwise be said to narrow to a tip. This may be advantageous because the flow is more accurately directed to the circumferential outlet portion of that volute. Leakage may therefore be reduced as a result, and scroll separation thereby increased.

The tongues may be formed of a single, monolithic body. Put another way, the tongues may be homogenous. Alternatively, the tongues may be formed of a plurality of constituent parts (e.g. be modular).

For each of the tongues, a high pressure side of the tapering portion may extend at an angle of between about 5° and about 70° relative to a tangent at that diameter.

The high pressure side of the tapering portion refers to a side of the tongue which is upstream of the circumferential outlet portion of the volute. Put another way, the high pressure side of the tapering portion of the tongue is the side of the tongue which exhaust gas flows along before reaching the circumferential outlet portion of the volute.

The tongue may otherwise be said to extend inwardly in at least the tapering portion. That is to say, the flow passing over the tongue has more of a radial component i.e. is directed towards the axis to a greater extent. This is advantageous in more effectively directing the flow over the plurality of vanes and towards the turbine wheel-receiving bore.

More preferably, the high pressure side of the tapering portion extends at an angle of between about 15° and about 50° relative to the tangent at that diameter.

For each of the tongues, the tip may extend to within about 0.5 mm to about 15 mm of the first aperture of the housing.

In other words, the tongues extend, to a greater extent, towards the first aperture. Given that the vane assembly is received in the first aperture, the tongues may be said to extend, to a greater extent, towards the vane assembly. The tongues may be said to extend to within about 0.5 mm to about 15 mm radially of the first aperture of the housing.

By having the tip extend to within 0.5 mm to 15 mm of the first aperture, the size of any leakage path around the first/second vanes is reduced. That is to say, flow is more accurately directed into/towards the correct circumferential outlet portion. Scroll separation is increased as a result.

In other arrangements, the tongue may extend beyond the first aperture. That is to say, the tongue, or a portion thereof, may extend into the first aperture. Alternatively, the tip may extend up to the first aperture. That is to say, the tip may terminate at the first aperture.

Preferably the tip extends to within about 1 mm to about 5 mm of the first aperture.

Defined another way, if a tip of the tongue(s) is disposed at a first radius relative to the axis, and the first aperture is at a second radius relative to the axis, the first radius may extend beyond the second radius by a distance of up to 5%, 10% or 20% of the second radius. This may result in, for example, a 3 mm offset between the tip and the first aperture. The above definition can also be applied where the leading edge of the first and second vanes is at a second radius relative to the axis.

The vane assembly may be a fixed vane assembly comprising a mounting portion to which each of the vanes are mounted.

Fixed is intended to mean that the vane assembly is not displaceable in any direction. For example, the vane assembly cannot be axially displaced to provide variable geometry functionality.

Advantageously the vanes may be fixed in position to reduce complexity and cost where not required. The vanes and mounting portion may be manufactured as a single, uniform body. Alternatively, the vanes may be manufactured separately from the mounting portion and then attached thereto. The mounting portion may be generally U-shaped in cross-section i.e. a channel may be defined by radially inner and outer flanges.

The housing may comprise:

a volute housing, the volute housing may comprise the first and second volutes and the first aperture; and

a wall member engageable with the volute housing.

For a fixed geometry turbocharger, the wall member may be an end portion of a bearing housing. That is to say, a generally annular face of the bearing housing may define the wall member. The combination of the bearing housing annular face and the volute housing therefore define the housing.

The engagement of the wall member and volute housing may be direct or indirect. Indirect may refer to another component interposing the wall member and volute housing.

The vane assembly may be a nozzle ring and the wall member may be a shroud.

The invention has been found to be particularly advantageous when the vane assembly is a nozzle ring because a clearance is desirable between the leading edge of the vanes and the tip of the tongues. This is to enable to nozzle ring to be displaced axially relative to the housing. Displacement of the nozzle ring relative to the housing allows the turbine wheel speed to be controlled by varying the throat of an annular passage disposed between the volutes and the turbine wheel.

By incorporating the misalignment as specified above, in combination with a variable geometry turbine, the turbine can be more readily controlled whilst scroll separation is still improved. In other words, the variable geometry nature of the turbine does not mean that scroll separation is decreased undesirably.

In other arrangements, the shroud may be displaceable relative to a fixed nozzle ring to provide variable geometry functionality.

The shroud may be a shroud plate. The shroud refers to a component which incorporates one or more vane apertures in which vanes are receivable.

The shroud may comprise a plurality of vane apertures in which the vanes of the nozzle ring are receivable, the shroud being disposed in a recess within the volute housing, the shroud plate defining one side of an annular passage between the circumferential outlet portions of the volutes and the turbine wheel-receiving bore, a face of the nozzle ring defining the other side of the annular passage;

wherein the nozzle ring is axially displaceable, relative to the shroud, to adjust the extent to which the annular passage is open.

Relative adjustment between a nozzle ring and a shroud is indicative of a variable geometry turbine. In other words, the turbine geometry can be varied to provide improved control of the speed (specifically the RPM) of the turbine wheel, and so compressor wheel.

The recess in the volute housing may be annular.

The shroud may be generally annular and incorporate a shroud wall which defines a periphery of the shroud, the shroud wall being outwardly offset in two positions.

The outward offset of the shroud plate in wall in two positions may otherwise be referred to as a radial offset. The two positions are preferably diametrically opposed form one another. By offsetting the shroud wall in two positions, which correspond with the circumferential positions of the first and second vanes, existing turbocharger assemblies can be used in combination with the first and second, or two long, vanes. This is desirable for reasons of reduced component proliferation.

Put another way, the outwardly offset shroud wall defines two recesses in which the first and second vanes, specifically leading edge regions thereof, are receivable. Due to the increased chord length of the first and second vanes, leading edge regions thereof may interfere with the shroud wall if the shroud wall was not offset. The recesses in the shroud wall, or shroud wall being outwardly offset in two positions, thereby reduces the risk of, or prevents, the first and second vanes clashing with the shroud wall.

Outwardly offset may mean radially offset.

The first tongue may be formed of a single body which forms part of the volute housing, and wherein the second tongue may also be formed of a single body which forms part of the volute housing.

Put another way, both tongues are disposed entirely on the volute housing. The volute housing therefore comprises first and second tongues. The first and second tongues may form a homogenous, or uniform, body with the volute housing. The first and second tongues may be said to be integrally formed with the volute housing.

The first tongue may be formed of two portions, a first portion forming part of the volute housing and a second portion forming part of the wall member, the two portions being aligned with one another.

The second tongue may also be formed of two portions, a first portion forming part of the volute housing and the second portion forming part of the wall member. The first and second portions of the second tongue may be aligned with one another. The tongue portion forming part of another component may otherwise be expressed as the tongue portion being a constituent feature of another component.

The portions being aligned with one another may be said to define a single geometry. That is to say, contours common to both portions define the overall tongue. The portions therefore fit together, or tessellate, to form a substantially continuous tongue. The two portions of the tongue may be said to engage one another, cooperate or mate.

The first portion may be referred to as a base portion. The second portion may be referred to as a tip portion because it incorporates a greater proportion of the tongue than just the tip. The first portion may be longer than the second portion.

The first and second tongues may therefore each be formed of two distinct portions. The portions of the tongues may align with one another to form a substantially continuous outer geometry.

Incorporating the second portion of the tongue on the wall member is advantageous because the tip of the tongue can then be positioned closer to the leading edge of the proximate vane aperture, and so vane. If the second portion of the tongue was not part of the wall member, the tip of the tongue would be distanced from the leading edge of the proximate vane aperture by at least the thickness of any perimeter wall of the wall member. Where the wall member is a shroud incorporating a shroud wall, the tip of the tongue would be distanced from the leading edge of the proximate vane aperture by at least the thickness of the shroud wall unless (at least) the tip of the tongue is incorporated as part of the shroud.

According to a second aspect of the invention there is provided a turbine comprising the turbine assembly according to the first aspect of the invention, further comprising a turbine wheel received in the turbine wheel-receiving bore.

According to a third aspect of the invention there is provided a turbocharger comprising:

a compressor comprising a compressor housing and a compressor wheel; the turbine according to the second aspect of the invention;

a bearing housing interposing the compressor and the turbine; and

a shaft connected to both the compressor impeller and the turbine wheel, such that rotation of the turbine wheel is configured to drive rotation of the compressor wheel.

The turbocharger may be a fixed geometry turbocharger. The turbocharger may be a variable geometry turbocharger.

The turbocharger may form part of an engine arrangement. The engine arrangement may be part of a vehicle, such as an automobile. The engine arrangement may have a static application, such as in a pump arrangement or in a generator.

According to a fourth aspect of the invention there is provided a nozzle ring for a turbocharger, the nozzle ring comprising a plurality of vanes, wherein the plurality of vanes comprises a first vane, a second vane and a plurality of secondary vanes, and wherein the first and second vanes have a longer chord length than the plurality of secondary vanes.

According to a fifth aspect of the invention there is provided a shroud for a turbocharger, the shroud comprising:

a plate, the plate defining:

a first vane aperture in which a first vane of a nozzle ring is receivable; and

a second vane aperture in which a second vane of the nozzle ring is receivable;

the plate comprising first and second radially extending projections, the first projection being circumferentially aligned with at least a leading edge of the first vane aperture, the second projection being circumferentially aligned with at least a leading edge of the second vane aperture.

The first and second projections may define first and second recesses. The first and second recesses may be circumferentially aligned with at least the leading edges of the first and second vane apertures respectively.

The shroud may further comprise a shroud wall. The shroud wall may define a periphery of the shroud. The shroud wall may project radially to form at least part of the first and second projections. The shroud wall may seat, or secure, the shroud in the volute housing.

The shroud may be generally annular. Specifically, the plate may be generally annular. The two recesses enable comparably longer vanes of a nozzle ring to be received by the shroud. The shroud may be a shroud plate.

The first and second recesses may be adjacent leading edges of the first and second vane apertures. The first and second recesses may receive leading edge regions of the first and second vanes. The first and second recesses may be said to receive the leading edges of the first and second vane apertures. The first and second recesses may be said to at least partially surround, or enclose, the leading edges of the first and second vane apertures respectively.

The leading edges of the vane apertures may be the radially outermost tips of the vane apertures. The leading edge of the vane apertures may be a radially outermost point of the vane apertures.

The locations may otherwise be referred to as positions.

Advantageously the first and second projections also serve as anti-rotation features to prevent undesirable rotation of the shroud about the volute housing in which it is

received. This is desirable because if the shroud was able to rotate, the vanes received therein may wear due to contact between the components. That is to say, a clearance around a vane aperture, to allow the vane to be received therein, may be reduced in certain positions, leading to wear of the vane. The projections also enable a modified vane assembly to be utilised with existing variable geometry components, reducing part proliferation.

The shroud may be manufactured by an additive manufacture method, such as 3D printing. This may be particularly advantageous for efficiently creating the first and second radially extending projections (which may otherwise require the removal of a significant amount of material if created using a machining process, for example).

The shroud may further comprise at least a tip of first and second tongues.

The tip of the first and second tongues may be said to be integrally formed with the shroud. In other words, the tip of the first and second tongues and the shroud are a homogenous body.

The shroud may comprise a portion of the tongue, or the second portion of the tongue. That is to say, the shroud may comprise more than just the tips of the first and second tongues.

Advantageously, incorporating at least the tip of the first and second tongues on the shroud allows the offset between a leading edge of the vane apertures and the tip of the tongues to be decreased. This can provide a more effective means of directing flow towards the turbine wheel-receiving bore, and so turbine wheel, which reduces flow leakage and increases scroll separation.

The at least a tip of first and second tongues may extend from the first and second projections respectively.

Preferably the at least a tip of the first tongue extends from the first projection. Preferably the at least a tip of the second tongue extends from the second projection. Each of the offset plate wall portions may be referred to as projections or tabs.

The at least a tip of the tongues may extend from a side of the projections which opposes the recesses. That is to say, the first and second recesses may be formed in a first side of the shroud and the at least a tip of the tongues may be formed in a second side of the shroud.

When assembled as part of a turbocharger, the first and second recesses may be disposed on an outwardly-facing side of the shroud. The at least a tip of the tongues may be disposed on a compressor-facing side of the shroud. The at least a tip of the tongues may therefore extend in a direction of the axis. The at least a tip of the tongues may extend towards a central region of the turbocharger, which may be a bearing housing.

The tip of the at least a tip of the first and second tongues may be misaligned relative to the leading edges of the first and second vane apertures respectively.

Preferably the leading edge of the first vane aperture at least partly circumferentially overlaps the at least a tip of the first tongue. Preferably the leading edge of the second vane aperture at least partly circumferentially overlaps the at least a tip of the second tongue.

According to a sixth aspect of the invention there is provided a shroud for a turbocharger, the shroud comprising:

a first vane aperture in which a first vane of a nozzle ring is receivable;

a second vane aperture in which a second vane of the nozzle ring is receivable; at least a tip of a first tongue associated with a leading edge of the first vane aperture; and

at least a tip of a second tongue associated with a leading edge of the second vane aperture.

The at least a tip of the tongues may be misaligned with the leading edge of the respective vane aperture. Preferably the leading edges of the respective vane apertures at least partly circumferentially the at least the tips of the tongues.

The at least a tip of the tongues may be a projection which extends axially away from the shroud. In use, the projection may form part of a tongue in a housing forming part of a turbine assembly.

Advantageously, incorporating at least the tip of the first and second tongues on the shroud allows the offset between a leading edge of the vane apertures and the tip of the tongues to be decreased. This can provide a more effective means of directing flow towards the turbine wheel-receiving bore, and so turbine wheel, which reduces flow leakage and increases scroll separation.

Associated in this context is intended to mean a leading edge of a vane aperture in closest proximity to the at least a tip of the tongue. Associated includes the at least a tip being aligned with the leading edge of the vane aperture, as well as the vane aperture being positively or negatively clocked relative to the at least a tip of the tongue. Associated also includes the leading edge of the vane aperture at least partly circumferentially overlapping the at least a tip of the tongue.

According to a seventh aspect of the invention there is provided a turbine assembly for a turbocharger, the turbine assembly comprising:

a housing which defines a flow path between an inlet and an outlet, the housing extending around an axis and defining a first aperture in which a vane assembly and turbine wheel are receivable, the housing further defining first and second tongues, the housing comprising a volute housing and a shroud according to the sixth aspect of the invention;

the volute housing comprising first and second volutes which define a respective first and second flow passage, a circumferential outlet portion of each of the first and second volutes being defined by the first and second tongues;

the shroud engaging the volute housing; and

wherein the first tongue is formed of a first portion and a second portion, the first portion forming part of the volute housing and the second portion forming part of the shroud, wherein the first and second portions cooperate to define the first tongue; and

wherein the second tongue is formed of a first portion and a second portion, the first portion forming part of the volute housing and the second portion forming part of the shroud, wherein the first and second portions cooperate to define the first tongue.

Advantageously by providing a two-part tongue, formed of first and second portions, a tip of the tongue can be disposed closer to a leading edge of a vane of the vane assembly. This can provide a more effective means of directing flow towards the turbine wheel, which reduces flow leakage and increases scroll separation.

The cooperation between first and second portions of the tongue may otherwise be described as engagement, or mating. In effect, the first and second portions define a single tongue geometry.

The shroud may be received in a recess in the volute housing. The recess may be annular.

According to an eighth aspect of the invention there is provided a turbine assembly for a turbocharger, the turbine assembly comprising:

a housing which defines a flow path between an inlet and an outlet, the housing extending around an axis, the housing comprising:

first and second volutes which define a respective first and second flow passage, a circumferential outlet portion of each of the first and second volutes being defined by first and second tongues;

a wall member; and

a first aperture in which a vane assembly is received;

wherein the vane assembly defines a turbine wheel-receiving bore; and wherein the wall member and vane assembly define an annular passage between the circumferential outlet portions and the turbine wheel-receiving bore, at least one of the vane assembly and the wall member being axially displaceable relative to the other to adjust the extent to which the annular passage is open.

Put another way, a double entry variable geometry turbine is provided in which a wall member, or vane assembly, is axially displaceable.

The wall member may be a shroud. The vane assembly may be a nozzle ring. The nozzle ring may be axially displaceable relative to the shroud. Alternatively, the shroud may be axially displaceable relative to the nozzle ring.

The annular passage may otherwise be referred to as a nozzle.

A double entry turbine assembly with an axially-displaceable variable geometry mechanism has been found to be particularly effective in comparison to twin-entry turbine assemblies. One advantage of the double entry turbine assembly is that scroll separation is increased in comparison to twin-entry examples. Engine efficiency is therefore improved.

The extent to which the annular passage is open may otherwise be described as an extent to which a flow passage is constricted. The annular passage defines a cross-sectional area through which exhaust gas can flow circumferentially towards the turbine wheel. The extent to which the annular passage is open may otherwise be described as changing, or varying, the size of the annular passage.

The optional and/or preferred features for each aspect of the invention set out herein are also applicable to any other aspects of the invention.

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 a cross sectional view of a prior art variable geometry turbocharger;

Figure 2a is a perspective cutaway view of a turbine assembly according to a first aspect of the invention;

Figure 2b is a magnified view of an area of interest of the turbine assembly of Figure 2a;

Figure 2c is an alternative cross section view of the turbine assembly of Figure 2a; Figure 2d is a magnified view of an area of interest of the turbine assembly of Figure 2c;

Figure 2e is a rotated perspective view of the area of interest shown in Figure 2d;

Figure 3a is an end view of a nozzle ring of the turbine assembly of Figure 2a;

Figure 3b is a rotated perspective view of the nozzle ring of Figure 3a;

Figure 4a is an end view of a portion of the turbine assembly of Figure 2a;

Figure 4b is a close up view of an area of interest of the portion of the turbine assembly of Figure 4a;

Figure 5 shows a volume which is occupied by flow within at least a portion of the turbine assembly of Figure 2a;

Figure 6 is a magnified view of a portion of a turbine assembly in accordance with the invention;

Figures 7a and 7b show areas of interest of a turbine assembly;

Figure 7c shows an area of interest of a turbine assembly in accordance with the invention;

Figures 8a to 8d are computer simulation results indicating an absolute pressure profile of flow in each of the arrangements depicted in Figures 6 and 7a to 7c;

Figures 9a and 9b are plots which correspond with the arrangements depicted in Figure 6 and 7a to 7c;

Figures 10a to 10c are computer simulation results indicating a velocity profile of flow through a turbine assembly in each of the arrangements depicted in Figures 7a to 7c respectively;

Figures 11a to 11c are computer simulation results indicating a velocity profile of flow through a turbine assembly in the arrangements depicted in Figures 7a to 7c respectively, magnified to show flow at a high pressure tongue;

Figures 12a to 12c are computer simulation results indicating a velocity profile of flow through a turbine assembly in the arrangements depicted in Figures 7a to 7c respectively, magnified to show flow at a low pressure tongue;

Figures 13a to 13c are computer simulation results indicating a total pressure profile of flow in each of the arrangements depicted in Figures 7a to 7c respectively;

Figure 14a is a magnified, perspective, cutaway view of an area of interest of a turbine assembly according to another embodiment of the invention;

Figure 14b is a side view of the turbine assembly of Figure 14a;

Figure 14c is an alternative cross section view of the turbine assembly of Figure 14a; Figure 14d is a magnified view of an area of interest of the turbine assembly of Figure 1 4c;

Figure 14e is a rotated perspective view of the area of interest shown in Figure 14d; and

Figure 15 is a plot indicating a pressure difference between manifold banks in a double entry turbine, in comparison to a single entry turbine, at various rotor speeds.

Figure 1 illustrates a known variable geometry turbocharger. The turbocharger comprises 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 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 12 which forms the wall of the inlet passageway 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 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. 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.