GB2620975A

GB2620975A - Variable geometry turbine

Info

Publication number: GB2620975A
Application number: GB2211048.0A
Authority: GB
Inventors: Pridham Ian
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2022-07-28
Filing date: 2022-07-28
Publication date: 2024-01-31
Also published as: GB202311683D0; GB2622482A; GB202211048D0

Abstract

A nozzle ring 110 for a variable geometry turbine, e.g. of a turbocharger, comprises an array of circumferentially spaced inlet vanes 114 supported by a generally annular wall 112. At least a portion of each inlet vane has a cross section, in a plane perpendicular to an axis of the annular wall, of generally uniform shape. An orientation of the uniform shape is dependent on its axial position on the inlet vane, i.e. each inlet vane is twisted. The vanes may be twisted linearly or non-linearly and may be integrally formed with the annular wall. A shroud 111 for the variable geometry turbine comprises an array of rotatable members 124 provided on and rotatable relative to a generally annular wall 122. Each rotatable member has a slot for receipt of at least a portion of an inlet vane of the nozzle ring. Each rotatable member may be provided in a respective aperture of the annular wall of the shroud.

Description

Variable Geometry Turbine The present invention relates to a variable geometry turbine and component parts thereof. In particular, the present invention relates to a new nozzle ring and a new shroud that together form part of a new nozzle assembly for a variable geometry turbine. The variable geometry turbine may, for example, be for use in a turbocharger for an internal combustion engine.

Turbochargers are 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 that is mounted on the other end of the shaft and within a compressor housing. The compressor wheel delivers compressed air to the engine intake manifold. 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 housings.

In known turbochargers, the turbine comprises a turbine chamber within which the turbine wheel is mounted, an inlet passageway defined between facing radial walls arranged around the turbine chamber, an inlet volute arranged around the inlet passageway, and an outlet passageway extending from the turbine chamber. The passageways and chambers communicate in such a way that pressurised exhaust gas admitted to the inlet volute flows through the inlet passageway to the outlet passageway via the turbine and rotates the turbine wheel. It is also known to trim turbine performance by providing vanes, referred to as nozzle vanes or inlet vanes, in the inlet passageway so as to deflect gas flowing through the inlet passageway towards the direction of rotation of 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 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 suit varying engine demands. 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 that ensures efficient turbine operation by reducing the size of the inlet passageway.

In one known type of variable geometry turbine, an axially moveable wall member, generally referred to as a "nozzle ring", defines one wall of the inlet passageway. The position of the nozzle ring relative to a facing wall of the inlet passageway is adjustable to control the axial width of the inlet passageway. Thus, for example, as gas flowing through the turbine decreases, the inlet passageway width may also be decreased to maintain gas velocity and to optimise turbine output. Such nozzle rings comprise a generally annular wall and inner and outer axially extending flanges. The flanges extend into a cavity defined in the turbine housing, which is a part of the housing that in practice is provided by the bearing housing, which accommodates axial movement of the nozzle ring.

The nozzle ring may be provided with vanes that extend into the inlet passageway and through slots provided on the facing wall of the inlet passageway to accommodate movement of the nozzle ring. Alternatively, vanes may extend from the fixed wall through slots provided in the nozzle ring. Generally the nozzle ring is supported on rods extending parallel to the axis of rotation of the turbine wheel and is moved by an actuator that axially displaces the rods. Various forms of actuators are known for use in variable geometry turbines, including pneumatic, hydraulic and electric actuators that are mounted externally of the turbocharger and connected to the variable geometry system via appropriate linkages.

In one known type of variable geometry turbine, the vanes of the nozzle ring can be pivoted by an actuator and suitable mechanical linkages such that the angle at which the exhaust gas being delivered to the turbine can be varied. Said pivotable vanes require a large number of components to put into effect and are complicated to manufacture and assemble into the turbocharger.

It may be desirable to provide a variable geometry turbine at least partially addresses one or more problems associated with known variable geometry turbines, whether identified herein or otherwise.

According to a first aspect of the present disclosure there is provided a nozzle ring for a variable geometry turbine, the nozzle ring comprising: a generally annular wall; and an array of circumferentially spaced inlet vanes supported by the generally annular wall, each of which extends axially from a first surface of the generally annular wall, wherein each of the inlet vanes is shaped such that, for at least a portion of the inlet vane, in cross section in a plane perpendicular to an axis of the generally annular wall the inlet vane has a generally uniform shape that is independent of an axial position on the inlet vane and wherein an orientation of the generally uniform shape is dependent on the axial position on the inlet vane.

In use, the nozzle ring is disposed within a variable geometry turbine such that the generally annular wall faces another generally annular wall (which may be referred to as a shroud) so as to define an inlet passageway therebetween. Exhaust gas is directed via said inlet passageway to a turbine wheel. The speed of the turbine wheel is dependent upon the velocity of the gas passing through the inlet passageway. For a fixed mass flow rate of exhaust gas passing through the inlet passageway, the velocity of the exhaust gas is a function of the width of the inlet passageway, the width being controllable by moving the position of the nozzle ring and/or the shroud. If it is desired to increase the speed of the turbine wheel, the width of the inlet passage may be decreased.

The speed of the turbine wheel is also dependent on an inlet angle of the exhaust gas. The inlet angle of the exhaust gas is determined by an orientation of the inlet vanes with respect to the turbine wheel (in particular, an orientation of a trailing edge of the inlet vanes). For a fixed mass flow rate of exhaust gas passing through the inlet passageway, the speed of the turbine wheel is a function of the effective inlet angle. This is because torque applied by the exhaust gas flow on the turbine wheel is a function of the effective inlet angle. Introducing the exhaust gas flow to the turbine wheel tangentially will result in the exhaust gas flow exerting a larger torque on the turbine wheel compared to if the exhaust gas is introduced radially. Therefore, a more tangential inlet angle will increase the speed of the turbine wheel more than a more radial inlet angle.

The orientation of the generally uniform cross-sectional shape of each of the inlet vanes of the nozzle ring according to the first aspect is dependent upon the axial position on the inlet vane. Therefore, in general, the inlet angle of gas leaving the trailing edge of the inlet vanes is dependent on axial position on the inlet vane. An effective inlet angle of gas may be an average inlet angle, averaged over a portion of the trailing edge of the inlet vane that the exhaust gas flows over in use. Said portion of the trailing edge of the inlet vane that the exhaust gas flows over may, for example be a portion of the inlet vane from the generally annular wall it extends from to an opposing generally annular wall of a shroud. Therefore, in use, as a distance between the generally annular walls of the nozzle ring and the shroud are varied, the effective inlet angle of gas leaving the nozzle ring will vary.

Therefore, advantageously, the nozzle ring according to the first aspect allows for an arrangement wherein both the effective inlet angle of the inlet vanes and the size and position of the inlet passageway can be changed by virtue of relative movement of the nozzle ring and an opposed shroud. For example, when the inlet passageway is fully open, the effective inlet angle provided may be less tangential than when the inlet passageway is only partially open.

It will be appreciated that a plane perpendicular to an axis of the generally annular wall may be any plane that is generally parallel to the first surface of the generally annular wall.

In general, the shape of a vane is defined by two opposed surfaces (which may be referred to as the pressure and suction surfaces of the vane) extending between a leading edge and a trailing edge. The leading edge of a vane shall be understood to be a radially outer end of the vane and the trailing edge of a vane shall be understood to be a radially inner end of the vane. A straight line connecting the leading edge to the trailing edge may be referred to as a chord. Similarly, a line connecting the leading edge to the trailing edge which bisects the vane (i.e. is halfway between the two opposed surfaces of the vane) may be referred to as a camber or camber line. It will be appreciated that, in general, the camber of a vane is curved. The inlet angle of gas leaving the trailing edge of a vane is intended to mean an angle between a tangent to the camber line at the trailing edge and a radial direction (relative to the axis of the generally annular wall).

Each of the inlet vanes may be shaped such that it is more tangential towards an axial end that is proximal the generally annular wall and less tangential towards a distal end of the inlet vane. Advantageously, this can increase the speed of the turbine wheel as an axial extent of the inlet passageway defined between the nozzle ring and an opposing shroud is decreased (which is typically when mass flow rate through the turbine is reduced).

Each of the inlet vanes may be shaped such that an angle of the or each of the inlet vanes varies linearly between a proximal end and a distal end.

Alternatively, each of the inlet vanes may be shaped such that an angle of the or each of the inlet vanes varies non-linearly between a proximal end and a distal end.

For example, each of the inlet vanes may be shaped such that a rate of change of the angle of the or each of the inlet vanes with respect to axial position along that inlet vane is greater towards an axial end that is proximal the generally annular wall. That is, the twisted inlet vanes have more twist near their base at the generally annular wall of the nozzle ring.

From a proximal end of each of the array of circumferentially spaced inlet vanes to a distal end of each such inlet vane, the generally uniform shape of the inlet vanes may rotate through at least 5 degrees.

In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane rotates through at least 10 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane rotates through at least 20 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane rotates through at least 30 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane rotates through at least 40 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane rotates through at least 45 degrees.

The inlet vanes may be integrally formed with the generally annular wall. Since the inlet vanes are integrally formed with the generally annular wall, the strength of the inlet vanes is improved due to the absence of a joint between the generally annular wall and the inlet vane.

The nozzle ring may further comprise: an inner flange that is generally perpendicular to the generally annular wall, and which extends from a radially inner edge of the generally annular wall; and an outer flange that is generally perpendicular to the generally annular wall, and which extends from a radially outer edge of the generally annular wall.

The array of circumferentially spaced inlet vanes may be considered to be axially stacked. "Axially stacked" is used herein to refer to inlet vanes which comprise an axis which is parallel to an axis of the generally annular wall, each point of which resides within the cross-section of the inlet vane. Since the inlet vanes are axially stacked, this increases the rigidity of the inlet vanes compared to non-axially stacked vanes.

According to a second aspect of the present disclosure there is provided a shroud for a variable geometry turbine, the shroud comprising: a generally annular wall; and an array of rotatable members provided on the generally annular wall, the rotatable members being rotatable relative to the generally annular wall, and each rotatable member having a slot for receipt of at least a portion of an inlet vane.

In use, the slot of each rotatable member may receive at least a portion of an inlet vane of the nozzle ring according to the first aspect. A shape of the slot of each rotatable member may generally match the generally uniform shape of such an inlet vane of a nozzle ring in cross section in a plane perpendicular to an axis of the nozzle ring.

The generally annular wall may define a plurality of apertures, each of the plurality of apertures being for engagement with one of the rotatable members.

Each of the plurality of apertures may comprise a central portion that is generally circular but is provided with two flat portions on opposite sides of the circle. The flat portions provide engagement features for releasable engagement with the rotatable members.

Each of the plurality of apertures may further comprise: a first end portion radially outboard of the central portion; and a second end portion radially inboard of the central portion. In use, the first end portion and the second end portion (and a part of the central portion) accommodate the inlet vanes of the nozzle ring. In particular, the first end portion may accommodate the leading edge of an inlet vane and the second end portion may accommodate the trailing edge of the inlet vane.

The shroud may further comprise: an inner flange that is generally perpendicular to the generally annular wall, and which extends from a radially inner edge of the generally annular wall; and an outer flange that is generally perpendicular to the generally annular wall, and which extends from a radially outer edge of the generally annular wall. Together, the generally annular wall, the inner flange and the outer flange define a recess adjacent a surface of the generally annular wall that, in use, may be distal from the nozzle ring.

Each rotatable member may comprise: a main body portion which defines the slot; and a pair of engagement features for releasable engagement with the generally annular wall.

In some embodiments, when engaged with the generally annular wall the main body portion of each rotatable member may be adjacent to, and sit proud of, the generally annular wall. A first surface of the main body portion may, in use, face a nozzle ring and a second surface may be adjacent and in contact with the generally annular wall of the shroud. It will be appreciated that the main body portion of each rotatable member may therefore extend from the generally annular wall and may, in use, be disposed in the inlet passageway defined between the generally annular walls of the nozzle ring and the shroud.

The main body portion of each rotatable member may be provided with rounded edges.

The rounded edges may be arranged to reduce turbulent flow through an inlet passageway partially defined by the generally annular wall of the shroud. Advantageously, this can reduce turbulent flow through the inlet passageway defined between the generally annular walls of the nozzle ring and the shroud.

In some embodiments, the main body portion of each rotatable member may be recessed into, or countersunk into, the generally annular wall such that together the generally annular wall and the rotatable members form a generally flat annular surface. In use, said generally flat annular surface (formed by the generally annular wall and the rotatable members together) partially defines an inlet passageway of a turbine. For such embodiments, to allow relative rotation of the rotatable members and the generally annular wall while forming such a generally flat annular surface of the inlet passageway, the main body portions (and the counter bores that receive them) may be generally circular or disc-shaped.

The pair of engagement features may extend from the main body portion on either side of the slot.

A first portion of each engagement feature may extend generally perpendicularly to the main body portion adjacent the slot and a second portion of each engagement feature may extend generally parallel to the main body portion and away from the slot.

A shape of a footprint of the second portions of the pair of engagement features may generally match, but may have slightly smaller dimensions than, the shape of the central portion of the apertures in the generally annular wall.

Each of the array of rotatable members may be rotatable between at least: a first range of positions in which it is not engaged with the generally annular wall; and a second range of positions in which it is engaged with the generally annular wall.

That is, engagement between each of the rotatable members and the generally annular wall may be achieved by inserting the rotatable member into a recess in the rotatable member when disposed in a first orientation such that it is in the first range of positions in which it is not engaged with the generally annular wall. Once received in the recess, the rotatable member can then be rotated to a second orientation such that it is in the second range of positions in which it is engaged with the generally annular wall. That is, the engagement between each of the rotatable members and the generally annular wall may be achieved by a bayonet-type fitting arrangement.

According to a third aspect of the present disclosure there is provided a nozzle ring assembly for a variable geometry turbine, the nozzle ring assembly comprising: a first wall member and a second wall member; wherein the second wall member faces the first wall member so as to define an inlet passageway between a face of the first wall member and a face of the second wall member; wherein one of the first wall member and the second wall member is an axially moveable wall such that axial movement of the axially movable wall member varies an axial width of the inlet passageway; wherein one of the first wall member and the second wall member comprises the nozzle ring of the first aspect of the present disclosure and the other one comprises the shroud of the second aspect of the present disclosure; and wherein, in use, the slot of each rotatable member of the shroud receives at least a portion of one of the array of inlet vanes of the nozzle ring, a shape of the slot generally matching the generally uniform shape of said one or the array of inlet vanes in cross section in a plane perpendicular to the axis of the generally annular wall of the nozzle ring.

It will be appreciated that the one of the first wall member and the second wall member that is axially moveable may be referred to as a moveable wall. The width of the inlet passageway can be varied by axially moving the moveable wall member.

Axial movement of the moveable wall member either retracts or inserts the inlet vanes into the slots of the rotatable members. Therefore, changing the axial position of the moveable wall member will result in a change in the axial section of the inlet vanes which are located in the inlet passageway. As noted above, the orientation of the uniform shape of the inlet vanes is dependent upon the axial position on the inlet vane.

The inlet angle at a particular axial position is dependent upon the orientation of the generally uniform shape of the inlet vanes. Therefore, the inlet angle of each inlet vane can vary axially, and so axial movement of the moveable wall member results in a change in the effective vane angle. The effective vane angle of the inlet vanes in the inlet passageway determines how the flow of exhaust gas is influenced by the vanes.

Therefore, the moveable wall member can be moved axially in order to change the portions of the inlet vanes which are in the inlet passageway, and therefore change the angle that the exhaust gas is turned through by virtue of the inlet vanes.

In addition, axial movement of the moveable wall member changes the size and axial position of the inlet passageway. The inlet vanes of the nozzle ring can be configured, by virtue of the orientation of the uniform cross-sectional shape of the inlet vanes, such that when the moveable wall member is at a given axial position the desired effective vane angle provided by the inlet vanes is provided for the portion of the turbine wheel on which the exhaust gas flow is incident. It is desirable to configure the inlet vanes such that the effective blade angle of the inlet vane corresponds with the region of the turbine wheel on which exhaust gas is incident. For example, when the moveable wall member is in the fully open position, the effective blade angle provided can be less tangential than when the moveable wall member is closer to the opposing (or non-moveable) wall (i.e. the axial width of the inlet passage is reduced).

The inlet vanes each define a first axis, wherein the first axis is generally parallel to the axis of the generally annular wall of the nozzle ring. A centre of area of the generally uniform shape of the inlet vane resides on the first axis at all axial positions of the inlet vane.

The rotatable members each define a second axis about which the rotatable members rotate. The second axis is generally parallel to the axis of the generally annular wall of the shroud. The second axis extends through a centre of area of the slot of the rotatable member. When a slot of a rotatable member receives an inlet vanes the first axis of the inlet vane and the second axis of the rotatable member are coaxial.

Some conventional variable geometry turbines can change the effective inlet angle of the inlet vanes by using what are known as pivot vanes. Pivot vanes are vanes which can be pivoted about an axis. The orientation of each pivot vane may be controlled independent of one another or a common linkage may control the orientation of all of the pivot vanes of a variable geometry turbine. Variable geometry turbines which comprise pivot vanes require a large number of components as each vane must be assembled separately into the variable geometry turbine. In addition, variable geometry turbines which comprise pivot vanes require control via control system in order to control the orientation of the pivot vanes. The inlet vanes of the nozzle ring of the present disclosure provide a much simpler way in which to change the effective inlet angle of the inlet vanes. The inlet vanes of the present disclosure can either be formed as an integral part of a generally annular wall or can be attached to a generally annular wall as a separate component. In order to change the effective angle of the inlet vanes of the nozzle ring, the nozzle ring is moved axially such that the inlet vanes are either retracted from slots of the rotatable members or inserted into the slots.

According to a fourth aspect of the present disclosure there is provided a variable geometry turbine comprising: a housing; a turbine wheel supported in the housing for rotation about a turbine axis; and the nozzle ring assembly of the third aspect of the present disclosure, wherein the nozzle ring assembly is arranged around the turbine wheel such that the inlet passageway defined between the face of the first wall member and the face of the second wall member extends radially inwards towards the turbine wheel.

The axially moveable one of the first wall member and the second wall member may be moveable between a fully open position and a fully closed position.

According to a fifth aspect of the present disclosure there is provided a turbocharger comprising the variable geometry turbine of the fourth aspect of the present disclosure.

It will be appreciated that features described above with reference to one aspect of the disclosure may be combined with another aspect of the invention as appropriate.

Specific embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section view of a known type of turbocharger incorporating a variable geometry turbine having a nozzle assembly comprising a nozzle ring and a shroud; Figure 2 is an enlarged portion of the cross-section shown in Figure 1, showing details of the nozzle assembly; Figure 3 is a perspective view of the movable wall member shown in Figures 1 and 2; Figure 4 is a perspective view of a new nozzle assembly for a variable geometry turbine of the type included in the turbocharger shown in Figure 1; Figure 5A is a perspective view of a nozzle ring that forms part of the new nozzle assembly shown in Figure 4; Figure 5B is a plan view of the nozzle ring shown in Figure 5A; Figure 6A is a first perspective view of a shroud that forms part of the new nozzle assembly shown in Figure 4; Figure 6B is a second perspective view of the shroud shown in Figure 6A; Figure 60 is a plan view of the shroud shown in Figures 6A and 6B; Figure 7A is a plan view of a generally annular wall member that forms part of the new shroud shown in Figures 6A to 60; Figure 7B is a first perspective view of the generally annular wall member shown in Figure 7A; Figure 70 is a second perspective view of the generally annular wall member in Figures 7A and 7B; Figure 8A is a top view of a rotatable member that forms part of the new shroud shown in Figures 6A to 60; Figure 8B is a bottom view of the rotatable member shown in Figure 8A; Figure 80 is a first side view of the rotatable member shown in Figure 8A from the direction indicated on Figure 8A as 8C; Figure 80 is a second side view of the rotatable member shown in Figure 8A from the direction indicated on Figure 8A as 8D; Figure BE is a first perspective view of the rotatable member shown in Figure 8A; Figure 8F is a second perspective view of the rotatable member shown in Figure 8A; and Figure 9 is a partial cross section view of the shroud shown in Figures 6A to 60 through the line A-A (the line A-A is shown in Figures 60 and 7A).

An embodiment of a known type of turbocharger 1 incorporating a variable geometry turbine is now described with reference to Figures 1 to 3.

Figure 1 shows a known type of turbocharger 1 incorporating a variable geometry turbine. Figure 2 is an enlarged portion of the cross-section of the turbocharger 1 shown in Figure 1. The turbocharger 1 comprises a turbine housing 2 and a compressor housing 3 interconnected by a central bearing housing 4. A turbocharger shaft 5 extends from the turbine housing 2 to the compressor housing 3 through the bearing housing 4. A turbine wheel 6 is mounted on one end of the shaft 5 for rotation within the turbine housing 2, and a compressor wheel 7 is mounted on the other end of the shaft 5 for rotation within the compressor housing 3. The shaft 5 rotates about turbocharger axis 8 on bearing assemblies located in the bearing housing 4.

It will be appreciated that the turbine housing 2 and an axial end of the bearing housing 4 together form a housing of the variable geometry turbine, in which the turbine wheel 6 is supported for rotation about turbocharger axis 8.

The turbine housing 2 defines an inlet volute 9 to which exhaust gas from an internal combustion engine (not shown) is delivered. The exhaust gas flows from the inlet volute 9 to an axial outlet passage 10 via an inlet passageway 11 and the turbine wheel 6. The inlet passageway 11 is defined between two axially spaced walls. In particular, the inlet passageway 11 is defined on one side by a face of a movable wall member 12, commonly referred to as a "nozzle ring," and on the opposite side by a shroud 13. Together, the nozzle ring 12 and the shroud 13 may be considered to form a nozzle ring assembly. The shroud 13 covers the opening of a generally annular recess 14 in the turbine housing 2.

As will be appreciated by the skilled person, the inlet volute 9 may comprise a generally toroidal volume (defined by the turbine housing 2) and an inlet arranged to direct exhaust gas from an internal combustion engine tangentially into the generally toroidal volume. As exhaust gas enters the inlet volute 9 it flows circumferentially around the generally toroidal volume and radially inwards towards the inlet passageway 11. In the vicinity of the inlet, there is provided a wall or "tongue" 18 which serves to separate the generally toroidal volume in the vicinity of the inlet of the volute 9 from the inlet passageway 11 of the turbine. The tongue 18 may help to guide the exhaust gas circumferentially around the generally toroidal volume and may also aid the mixing of the generally linear gas flowing into the volute 9 with the circumferential gas flow around the generally toroidal volume. In the cross section shown in Figure 1, the tongue 18 is visible on one side of the axis 8 only.

Figure 3 shows a perspective views of the movable wall member 12.

The movable wall member 12 supports an array of circumferentially and equally spaced inlet vanes 15 each of which extends across the inlet passageway 11. The vanes 15 are orientated to deflect gas flowing through the inlet passageway 11 towards the direction of rotation of the turbine wheel 6. The shroud 13 is provided with suitably configured slots for receipt of the vanes 15 such that as the movable wall member 12 moves axially towards the shroud 13, a distal end of each of the vanes 15 moves through one of said slots and protrudes into the recess 14. In alternative embodiments, the shroud 13 may be provided with circumferentially and equally spaced inlet vanes 14 and the movable wall member 12 may be provided with suitably configured slots for receipt of the vanes.

Accordingly, by appropriate control of an actuator (which may for instance be pneumatic or electric), the axial position of the movable wall member 12 can be controlled. The speed of the turbine wheel 6 is dependent upon the velocity of the gas passing through the inlet passageway 11. For a fixed rate of mass of gas flowing into the inlet passageway 11, the gas velocity is a function of the width of the inlet passageway 11, the width being adjustable by controlling the axial position of the movable wall member 12. As the width of the inlet passageway 11 is reduced, the velocity of the gas passing through it increases. Figure 1 shows the nozzle ring 12 disposed between a fully open position and a fully closed position such that the width of inlet passageway 11 is greater that a minimum width and smaller than a maximum width.

Gas flowing from the inlet volute 9 to the outlet passage 10 passes over the turbine wheel 6 and as a result torque is applied to the shaft 5 to drive the compressor wheel 7. Rotation of the compressor wheel 7 within the compressor housing 2 pressurises ambient air present in an air inlet 16 and delivers the pressurised air to an air outlet volute 17 from which it is fed to an internal combustion engine (not shown).

The movable wall member (or nozzle ring) 12 comprises a generally annular wall 20 and radially inner and outer flanges 21, 22 extending axially from the generally annular wall 20.

A cavity 25 is provided in the housing of the variable geometry turbine for receipt of the radially inner and outer flanges 21, 22 of the moveable member 12. It will be appreciated that in this embodiment the cavity 25 is formed on an axial end of the bearing housing 4, which cooperates with the turbine housing 2 to form the housing of the variable geometry turbine.

As the movable wall member 12 moves axially, the extent to which the radially inner and outer flanges 21, 22 of the moveable member 12 are received in the cavity 25 varies. The moveable wall member 12 is moveable between a fully opened position and a fully closed position. When disposed in the fully opened position, the radially inner and outer flanges 21, 22 of the moveable member 12 may contact a portion of a base surface 28 of the cavity 25. That is, a portion of the base surface 28 of the cavity 25 may serve as a physical stop to limit the range of axial movement of the moveable member 12.

Inner and outer sealing rings 30 and 31 are provided to seal the movable wall member 12 with respect to inner and outer curved surfaces of the cavity 25 respectively, whilst allowing the movable wall member 12 to slide within the cavity 25. The inner sealing ring 30 is supported within an annular groove formed in the radially inner curved surface of the cavity 25 and bears against the inner flange 21 of the movable wall member 12. The outer sealing ring 31 is supported within an annular groove formed in the radially outer curved surface of the cavity 25 and bears against the outer flange 22 of the movable wall member 12.

As can be seen in Figure 3, in some embodiments, a plurality of axially extending apertures 32, 33 are provided through the generally annular wall 20 of the moveable wall member 12. The apertures 32, 33 may be referred to as balancing apertures 32, 33. The apertures 32, 33 connect the inlet passageway 11 to the cavity 25, such that the inlet passageway 11 and the cavity 25 are in fluid communication via the apertures 32, 33. In use, the apertures 32, 33 serve to reduce pressure differences across the generally annular wall 20 of the movable wall member 12 and thereby reduce loads applied to the face of the generally annular wall 20 of the movable wall member 12.

It will be appreciated that as gas flows through the inlet passageway 11 the pressure of the gas flow drops as it moves across the face of the movable wall member 12 towards the turbine wheel 6. Therefore, by selecting a particular radial position for the balance apertures 32, 33, an average pressure within the cavity 25 (which will be substantially equal to the local average pressure in the inlet passageway 11 proximate to the balance apertures 32, 33) can be maintained.

In use, as air flows radially inwards through the inlet passageway 11, it flows between adjacent vanes 15, which can be regarded as defining a vane passage. The inlet passageway 11 has a reduced radial flow area in the region of the vane passage with the effect that the inlet gas speed increases through the vane passage with a corresponding drop in pressure in this region of the movable wall member 12.

Accordingly, a first set of balancing aperture 32 may be located between pairs of adjacent vanes 15 in the sense that the inner and outer radial extremity of these balancing apertures 12 lie within the inner or outer radial extent of the vane passage. In this embodiment, a balancing aperture 32 is located between each pair of adjacent vanes 15.

In addition, in this embodiment, a smaller number of balancing apertures 33 are provided upstream of (i.e. at a larger radius than) the balance apertures 32 located between pairs of adjacent vanes 15. These balance apertures 33 can result in a reduction in the force amplitude at an actuator interface caused by an exhaust pulse passing through the inlet passageway 11 when compared with the provision of the balance apertures 32 located between pairs of adjacent vanes 15 alone. It will be understood that although the described embodiment comprises balance apertures 32, 33 these balance apertures 32, 33 are optional. In other, alternative embodiments, these apertures 32, 33 may be absent.

The movable wall member 12 further comprises two supports 34, each of the supports being generally of the form of a shaft or rod. The two supports 34 may be referred to as push rods. Each of the two supports 34 is attached to the inner surface of the generally annular wall 20 (i.e. the surface that is distal from the inlet passageway 11).

The connection between each of the two supports 34 and the inner surface of the generally annular wall 20 may, for example, be generally of the form described in EP0917618.

The supports 34 extend through apertures in the base surface 28 of the cavity 25 for connection to an actuation mechanism. The position of the movable wall member 12 is controlled by an actuator assembly, which may be generally of the type disclosed in US 5,868,552. An actuator (not shown) is operable to adjust the position of the movable wall member 12 via a mechanical linkage. For example, an actuator may be connected by a lever system to a bar upon which a generally C-shaped yoke is mounted. The ends of the generally C-shaped yoke may engage with the two supports 34 via notches 37.

Embodiments of the present invention relate to a new nozzle ring and a new shroud that together form part of a new nozzle assembly for a variable geometry turbine of the type included in the turbocharger 1 shown in Figure 1 and described above with reference to Figures 1 to 3. An embodiment of such a new nozzle assembly 100 is shown in Figure 4; a new nozzle ring 110 that forms part of the new nozzle assembly 100 shown in Figure 4 is shown in Figures 5A and 5B; and a new shroud 120 that forms part of the new nozzle assembly 100 shown in Figure 4 is shown in Figures 6A to 6C.

The nozzle ring 110 comprises a generally annular wall 112 an array of circumferentially spaced inlet vanes 114. The generally annular wall 112 defines an axis 116, which passes through a centre of the generally annular wall 112 and which is generally perpendicular to the generally annular wall 112.

The new shroud 120 comprises: a generally annular wall 122; and an array of rotatable members 124 provided on the generally annular wall 122. The rotatable members 124 are rotatable relative to the generally annular wall 122. Each rotatable member 124 has a slot 126 for receipt of at least a portion of an inlet vane 114.

The nozzle ring 110 shown in Figures 4 to 5B is generally equivalent to the movable wall member 12, or nozzle ring, shown in Figures 1 to 3 and described above. In particular, the nozzle ring 110 shown in Figures 4 to 5B is generally equivalent to the generally annular wall 20 of the movable wall member 12, or nozzle ring, shown in Figures 1 to 3 and described above. It will be appreciated that the nozzle ring 110 shown in Figures 4 to 5B may additionally have any of the features of the movable wall member 12, or nozzle ring, shown in Figures 1 to 3 and described above although such optional features are omitted from Figures 4 to 5B merely for ease of understanding.

For example, the nozzle ring 110 shown in Figures 4 to 5B may further comprise radially inner and outer flanges 21, 22 extending axially from the generally annular wall 112 (on an opposite side of the generally annular wall 112 to the inlet vanes 114). Similarly, the nozzle ring 110 shown in Figures 4 to 5B may further comprise any of: apertures in the generally annular wall 112 (for example of the form of balancing apertures 32, 33) and/or supports (for example of the form of push rods 34).

The inlet vanes 114 are supported by the generally annular wall 112. Each inlet vane 114 extends axially from a first surface of the generally annular wall 112. It will be appreciated that as used here axial is intended to mean a direction generally parallel to the axis 116 of the generally annular wall 112.

The inlet vanes 114 shown in Figures 4 to 5B are generally equivalent to the inlet vanes 15 shown in Figures 1 to 3 and described above. However, each of the inlet vanes 114 of the new nozzle ring 110 is twisted, as can be best seen in Figure 5B and as now described.

Each of the inlet vanes 114 is shaped such that, for at least a portion of the inlet vane 114, in cross section in a plane perpendicular to the axis 116 of the generally annular wall 112 the inlet vane 114 has a generally uniform shape that is independent of an axial position on the inlet vane 114. However, an orientation of the generally uniform shape is dependent on the axial position on the inlet vane 114. This generally uniform shape can be seen in Figure 5B (which is a plan view in a plane perpendicular to the axis 116 of the generally annular wall 112) as the shape of a distal end of the inlet vanes 114.

It will be appreciated that a plane perpendicular to the axis 116 of the generally annular wall 112 may be any plane that is generally parallel to the first surface of the generally annular wall 112.

That the inlet vanes 114 of the new nozzle ring 110 are twisted, can also be best seen in Figure 5B.

In general, the shape of a vane 114 is defined by two opposed surfaces (which may be referred to as the pressure and suction surfaces of the vane) extending between a leading edge 114a and a trailing edge 114b. The leading edge 114a of a vane 114 shall be understood to be a radially outer end of the vane 114 and the trailing edge 114b of a vane shall be understood to be a radially inner end of the vane 114. A straight line connecting the leading edge 114a to the trailing edge 114b may be referred to as a chord. Similarly, a line connecting the leading edge 114a to the trailing edge 114b which bisects the vane 114 (i.e. is halfway between the two opposed surfaces of the vane) may be referred to as a camber or camber line. It will be appreciated that, in general, the camber of a vane is curved. The inlet angle of gas leaving the trailing edge 114b of a vane 114 is intended to mean an angle between a tangent to the camber line at the trailing edge and a radial direction (relative to the axis of the generally annular wall 112).

To more clearly indicate the twist of the vanes, in Figure 5B, on one of the inlet vanes is also shown: a first line 117 connecting the leading edge 114a to the trailing edge 114b at an end of the inlet vane 114 proximal to the generally annular wall 112; and a second line 118 connecting the leading edge 114a to the trailing edge 114b at an end of the inlet vane 114 distal from the generally annular wall 112. It can be seen that direction of the vane 114 rotates between these proximal and distal ends of the vane 114.

In this embodiment, the inlet vanes 114 are shaped such that, in cross section in a plane perpendicular to the axis 116 of the generally annular wall 112 the inlet vane 114 has a generally uniform shape along the entire axial extent of the inlet vane 114.

However, in alternative embodiments the inlet vanes 114 may be shaped such that, in cross section in a plane perpendicular to the axis 116 of the generally annular wall 112 the inlet vane 114 has a generally uniform shape along the a portion of the axial extent of the inlet vane 114. For example, a distal portion of the inlet vane 114 may have a different cross sectional shape (for example a smaller footprint) to a portion of the inlet vane 114 adjacent the generally annular wall 112, for example as is the case for the inlet vanes 15 shown in Figure 3. In general, the inlet vanes 114 are shaped such that, in cross section in a plane perpendicular to the axis 116 of the generally annular wall 112, a portion of the inlet vane 114 adjacent the generally annular wall 112 has a generally uniform shape that is independent of an axial position on the inlet vane 114.

In use, the nozzle ring 110 is disposed within a variable geometry turbine (of the type shown in Figure 1) such that the generally annular wall 112 faces a generally annular wall 122 of the new shroud 120 so as to define an inlet passageway therebetween. Exhaust gas is directed via said inlet passageway to a turbine wheel. The speed of the turbine wheel is dependent upon the velocity of the gas passing through the inlet passageway. For a fixed mass flow rate of exhaust gas passing through the inlet passageway, the velocity of the exhaust gas is a function of the width of the inlet passageway, the width being controllable by moving the position of the nozzle ring and/or the shroud. If it is desired to increase the speed of the turbine wheel, the width of the inlet passage may be decreased.

The speed of the turbine wheel is also dependent on an inlet angle of the exhaust gas. The inlet angle of the exhaust gas is determined by an orientation of the inlet vanes 114 with respect to the turbine wheel On particular, an orientation of a trailing edge 114b of the inlet vanes 114). For a fixed mass flow rate of exhaust gas passing through the inlet passageway, the speed of the turbine wheel is a function of the effective inlet angle. This is because torque applied by the exhaust gas flow on the turbine wheel is a function of the effective inlet angle. Introducing the exhaust gas flow to the turbine wheel tangentially will result in the exhaust gas flow exerting a larger torque on the turbine wheel compared to if the exhaust gas is introduced radially.

Therefore, a more tangential inlet angle will increase the speed of the turbine wheel more than a more radial inlet angle.

The orientation of the generally uniform cross-sectional shape of each of the inlet vanes 114 of the new nozzle ring 110 is dependent upon the axial position on the inlet vane 114. Therefore, in general, the inlet angle of gas leaving the trailing edge 114b of the inlet vanes 114 is dependent on axial position on the inlet vane 114. An effective inlet angle of gas may be an average inlet angle, averaged over a portion of the trailing edge 114b of the inlet vane 114 that the exhaust gas flows over in use. Said portion of the trailing edge 114b of the inlet vane 114 that the exhaust gas flows over may, for example, be a portion of the inlet vane 114 from the generally annular wall 114 it extends from to an opposing generally annular wall of the shroud 120. Therefore, in use, as a distance between the generally annular walls of the nozzle ring 110 and the shroud 120 are varied, the effective inlet angle of gas leaving the nozzle ring will vary.

Therefore, advantageously, the new nozzle ring 110 allows for an arrangement wherein both the effective inlet angle of the inlet vanes 114 and the size and position of the inlet passageway can be changed by virtue of relative movement of the nozzle ring 110 and an opposed shroud 120. For example, when the inlet passageway is fully open, the effective inlet angle provided may be less tangential than when the inlet passageway is only partially open.

In some embodiments, each of the inlet vanes 114 may be shaped such that it is more tangential towards an axial end that is proximal the generally annular wall 112 and less tangential towards a distal end of the inlet vane 114. It can be seen from Figure 5B that embodiment shown in the Figures is such an embodiment, as the first line 117 is more tangential (less radial) than the second line 118 relative to the axis 116 of the generally annular body 112 (a radial line is shown as a dotted line in Figure 5B). Advantageously, such an arrangement can increase the speed of the turbine wheel as an axial extent of the inlet passageway defined between the nozzle ring 110 and an opposing shroud 120 is decreased (which is typically when mass flow rate through the turbine is reduced).

In some embodiments, each of the inlet vanes 114 may be shaped such that an angle of the inlet vane 114 varies linearly between a proximal end (adjacent the generally annular wall 112) and a distal end.

Alternatively, in some embodiments, each of the inlet vanes 114 may be shaped such that an angle the inlet vane 114 varies non-linearly between a proximal end (adjacent the generally annular wall 112) and a distal end. For example, in some embodiments, each of the inlet vanes 114 may be shaped such that a rate of change of the angle of the inlet vane 114 with respect to axial position along that inlet vane 114 is greater towards an axial end that is proximal the generally annular wall 112. That is, the twisted inlet vanes 114 have more twist near their base at the generally annular wall 112 of the nozzle ring 110.

In the embodiment shown in the Figures, from a proximal end of each of the array of circumferentially spaced inlet vanes 114 to a distal end of each such inlet vane 114, the generally uniform shape of the inlet vanes 114 rotates through a twist angle of 25 degrees.

In some embodiments, from a proximal end of each of the array of circumferentially spaced inlet vanes 114 to a distal end of each such inlet vane 114, the generally uniform shape of the inlet vanes 114 may rotate through a twist angle of at least 5 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane 114 may rotates through a twist angle of at least 10 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane 114 may rotate through a twist angle of at least 20 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane 114 may rotate through a twist angle of at least 30 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane 114 may rotate through a twist angle of at least 40 degrees. In some embodiments, between the proximal and distal ends, the generally uniform shape of each inlet vane 114 may rotate through a twist angle of at least 45 degrees.

The inlet vanes 114 may be integrally formed with the generally annular wall 112. With such an arrangement, since the inlet vanes 114 are integrally formed with the generally annular wall 112, the strength of the inlet vanes 114 is improved due to the absence of a joint between the generally annular wall 112 and the inlet vane 114.

As discussed above, although not shown in Figures 4 to 5B (for ease of understanding) the nozzle ring 110 may further comprise: an inner flange that is generally perpendicular to the generally annular wall 112, and which extends from a radially inner edge of the generally annular wall 112; and an outer flange that is generally perpendicular to the generally annular wall 112, and which extends from a radially outer edge of the generally annular wall 112.

The array of circumferentially spaced inlet vanes 114 may be considered to be axially stacked. "Axially stacked" is used herein to refer to inlet vanes 114 which comprise an axis which is parallel to the axis 116 of the generally annular wall 112, each point of which resides within the cross-section of the inlet vane 114. Since the inlet vanes are axially stacked, this increases the rigidity of the inlet vanes 114 compared to non-axially stacked vanes.

As shown in Figure 4, in use, the slot 126 of each rotatable member 124 receives at least a portion of an inlet vane 114 of the new nozzle ring 110. A shape of the slot 126 of each rotatable member 124 generally matches the generally uniform shape of the inlet vanes 114 of a nozzle ring 110 in cross section in a plane perpendicular to an axis 116 of the nozzle ring 110.

The new shroud 120 shown in Figures 4 and 6A to 6C is generally equivalent to the shroud 13 shown in Figures 1 to 3 and described above. In use, the new shroud 120 may also cover the opening of a generally annular recess 14 in the turbine housing 2 (see Figure 1).

The generally annular wall 122 of the new shroud 120 is now described with reference to Figures 7A to 7C. The generally annular wall 122 defines a plurality of apertures 128. Each of the plurality of apertures 128 is for engagement with one of the rotatable members 124.

Each of the plurality of apertures comprises a central portion 130, a first end portion 132 and a second end portion 134. The central portion is generally circular but is provided with two flat portions 136, 138 on opposite sides of the circle (the full circle is shown as a dotted line 140 overlaid on one of the apertures). The first end portion 132 is generally radially outboard of the central portion 130 and is continuous with the central portion 130. The second end portion 134 is generally radially inboard of the central portion 130 and is continuous with the central portion 130. The first end portion 132 and the second end portion 134 are on opposite sides of the circle 140 and are not aligned with the two flat portions 136, 138 (i.e. the first end portion 132 and the second end portion 134 are adjacent to and continuous with portions of the circle 140 other than the locations of the flat portions 136, 138).

In use, as explained further below, the flat portions 136, 138 provide engagement features for releasable engagement with the rotatable members 124. The first end portion 132 and the second end portion 134 (and a part of the central portion 130) accommodate the inlet vanes 114 of the nozzle ring 110. In particular, the first end portion 132 accommodates the leading edge 114a of an inlet vane 114 and the second end portion 134 accommodates the trailing edge 114b of the inlet vane 114.

In this embodiment, the shroud 120 further comprises: an inner flange 142 that is generally perpendicular to the generally annular wall 122, and which extends from a radially inner edge of the generally annular wall 122; and an outer flange 144 that is generally perpendicular to the generally annular wall 122, and which extends from a radially outer edge of the generally annular wall 122. Together, the generally annular wall 122, the inner flange 142 and the outer flange 144 define a recess 146 adjacent a surface of the generally annular wall that, in use, is distal from the nozzle ring 110.

The rotatable members 124 of the new shroud 120 are now described with reference to Figures 8A to 8F.

Each rotatable member 124 comprises a main body portion 148 which defines the slot 126. The main body portion 148 is generally of the form of a rectangular plate having two opposed surfaces 148a, 148b (the slot 126 extending between the two opposed surfaces 148a, 148b). In use, a first surface 148a faces the nozzle ring 110 and a second surface is adjacent and in contact with the generally annular wall 122 of the shroud 120 (see Figure 4). It will be appreciated that the main body portion 148 of each rotatable member 148 therefore extends from the generally annular wall 122 and is, in use, disposed in the inlet passageway defined between the generally annular walls 112, 122 of the nozzle ring 110 and the shroud 120. The first surface 148a of the main body portion 148 is provided with rounded edges. Advantageously, this can reduce turbulent flow through the inlet passageway defined between the generally annular walls 112, 122 of the nozzle ring 110 and the shroud 120. The second surface 148b of the main body portion 148 is flat.

Each rotatable member further comprises a pair of engagement features 150, 152. The pair of engagement features 150, 152 extend from the second surface 148b of the main body portion 148 on either side of the slot 126. A first portion 150a, 152a of each engagement feature 150, 152 extends generally perpendicularly to the main body portion 148 adjacent the slot 126. A second portion 150b, 152b of each engagement feature 150, 152 extends generally parallel to the main body portion 148 and away from the slot 126. Together with the main body portion 148 and each engagement feature 150, 152 defines a recess 154, 156 for receipt of a portion of the generally annular wall 122 of the nozzle 122.

As can be seen from Figure 8B, in a plane parallel to that of the second surface 148b of the main body portion 148, a footprint of the second portions 150b, 152b of the pair of engagement features 150, 152 generally falls within a shape that is a circle with two flat portions on opposite sides of the circle (except there is no material in the region corresponding to the slot 126). This shape is indicated in Figure 83 only by a semitransparent cross-hatched region 158.

The releasable engagement between the rotatable members 124 and the generally annular wall 122 of the shroud 120 is now discussed with reference to Figure 9, which shows a partial cross section view of the shroud 120 shown in Figure 6C through the line A-A The shape 158 of the footprint of the second portions 150b, 152b of the pair of engagement features 150, 152 generally matches, but has slightly smaller dimensions than, the shape of the central portion 130 of the apertures 128 in the generally annular wall 122.

Engagement between each of the rotatable members 124 and the generally annular wall 122 may be achieved by inserting part of the rotatable member 124 through an aperture 128 in the generally annular wall 122 and into a recess 146 defined by the shroud 120 when disposed in a first orientation such that it is in a first range of positions in which it is not engaged with the generally annular wall 122. Once part of the rotatable member 124 is so received in the recess 146, the rotatable member 124 can then be rotated to a second orientation such that it is in a second range of positions in which it is engaged with the generally annular wall 122. That is, the engagement between each of the rotatable members 124 and the generally annular wall 122 may be achieved by a bayonet-type fitting arrangement.

In order to engage a rotatable member 124 with the generally annular wall 122, the rotatable member 124 is orientated such that the shape 158 of the footprint of the second portions 150b, 152b of the pair of engagement features 150, 152 is aligned with that of the central portion 130 of an aperture 128 in the generally annular wall 122. In this position, the second portions 150b, 152b of the pair of engagement features 150 are not aligned with the flat portions 136, 138 of the central portion 130 of the aperture.

The engagement features 150, 152 are then inserted into the aperture 128 in the generally annular wall 122 such that the second surface 148b of the main body portion 148 is adjacent to, and contacts, a surface of the generally annular wall 122 that, in use, faces the nozzle ring 110. Once in this position, the second portions 150b, 152b of the pair of engagement features 150, 152 are received in the recess 146 adjacent a surface of the generally annular wall that, in use, is distal from the nozzle ring 110. While in this position, the rotatable member 124 is rotated relative to the generally annular wall 122 so that the second portions 150b, 152b of the pair of engagement features 150 are aligned with the flat portions 136, 138 of the central portion 130 of the aperture. In this position, the parts of the generally annular wall 122 that define the flat portions 136, 138 of the central portion 130 of the aperture 128 are received in the recesses 154, 156 defined by the with the main body portion 148 and the engagement features 150, 152. In this way, the rotatable member 124 is retained engaged with the generally annular wall 122 and will remain so unless the rotatable member 124 is rotated relative to the generally annular wall 122 so that the second portions 150b, 152b of the pair of engagement features 150 no longer are aligned with the flat portions 136, 138 of the central portion 130 of the aperture 128.

At least when no inlet vanes 114 are received in the slots 126, each of the array of rotatable members 124 may be rotatable between at least a first range of positions in which it is not engaged with the generally annular wall 122 and at least a second range of positions in which it is engaged with the generally annular wall 122.

Note that, in use, once one of the inlet vanes 114 of the nozzle ring 110 is disposed in the slot 126 of a rotatable member 124, the rotatable member 124 is prevented from disengaging from the generally annular wall 122.

In the embodiment shown in Figures 4 to 9, the main body portion 148 of each rotatable member 124 sits proud of the surface of the generally annular member 122 of the shroud 120 that faces the nozzle ring 110. As mentioned above, the main body portion 148 of each rotatable member 124 is provided with rounded edges so as to reduce turbulence in the inlet passageway. However, in an alternative embodiment, the main body of the rotatable members may be recessed into, or countersunk into, the generally annular wall 122 such that together the generally annular wall and the rotatable members form a generally flat annular surface of the inlet passageway. For such embodiments, to allow relative rotation of the rotatable members and the generally annular wall while forming such a generally flat annular surface of the inlet passageway, the main body portions (and the counter bores that receive them) may be generally circular or disc-shaped. An example shape is indicated on Figure 7A by circles 160. However, with such an arrangement, as can be seen from the circles 160 in Figure 7A, it may be desirable or necessary to increase a spacing between the vanes so that two adjacent circles 160 do not interfere with each other, which may be undesirable. Therefore, it is an advantage of the embodiment shown in Figures 4 to 9 that a smaller spacing between adjacent vanes can be achieved than with an arrangement with full circular or disc-shaped rotatable members.

In the nozzle ring assembly 100 shown in Figure 4, the generally annular wall 112 of the nozzle ring 110 faces the generally annular wall 122 of the shroud 120 so as to define an inlet passageway 111 between a face of the generally annular wall 112 of the nozzle ring 110 and a face of the generally annular wall 122 of the shroud 120. At least one of the nozzle ring 110 and the shroud 120 is axially moveable wall so as to vary an axial width of the inlet passageway 111. In use, the slot 126 of each rotatable member 124 of the shroud 120 receives at least a portion of one of the array of inlet vanes 114 of the nozzle ring 110. A shape of the slot 126 generally matches the generally uniform shape of the inlet vanes 114 in cross section in a plane perpendicular to the axis 116 of the generally annular wall 112 of the nozzle ring 110.

It will be appreciated that the one of the generally annular wall 112 of the nozzle ring 110 and the generally annular wall 122 of the shroud 120 that is axially moveable may be referred to as a moveable wall. The width of the inlet passageway 111 can be varied by axially moving the moveable wall member.

Axial movement of the moveable wall member either retracts or inserts the inlet vanes 114 into the slots 126 of the rotatable members 124. Therefore, changing the axial position of the moveable wall member will result in a change in the axial section of the inlet vanes 114 which are located in the inlet passageway 111. As noted above, the orientation of the uniform shape of the inlet vanes 114 is dependent upon the axial position on the inlet vane 114. The inlet angle (of exhaust gas onto a turbine wheel) at a particular axial position is dependent upon the orientation of the generally uniform shape of the inlet vanes 114. Therefore, the inlet angle of each inlet vane 114 can vary axially, and so axial movement of the moveable wall member results in a change in the effective vane angle. The effective vane angle of the inlet vanes 114 in the inlet passageway determines how the flow of exhaust gas is influenced by the vanes 114. Therefore, the moveable wall member can be moved axially in order to change the portions of the inlet vanes 114 which are in the inlet passageway, and therefore change the angle that the exhaust gas is turned through by virtue of the inlet vanes 114.

In addition, axial movement of the moveable wall member changes the size and axial position of the inlet passageway 111. The inlet vanes 114 of the nozzle ring 110 can be configured, by virtue of the orientation of the uniform cross-sectional shape of the inlet vanes 114, such that when the moveable wall member is at a given axial position the desired effective vane angle provided by the inlet vanes 114 is provided for the portion of the turbine wheel on which the exhaust gas flow is incident. It is desirable to configure the inlet vanes 114 such that the effective blade angle of the inlet vane 114 corresponds with the region of the turbine wheel on which exhaust gas is incident. For example, when the moveable wall member is in the fully open position, the effective blade angle provided can be less tangential than when the moveable wall member is closer to the opposing (or non-moveable) wall (i.e. the axial width of the inlet passage 111 is reduced).

The inlet vanes 114 each define a first axis, wherein the first axis is generally parallel to the axis 116 of the generally annular wall 112 of the nozzle ring 110. A centre of area of the generally uniform shape of the inlet vane 114 resides on the first axis at all axial positions of the inlet vane 114.

The rotatable members 124 each define a second axis about which the rotatable members 124 rotate. The second axis is generally parallel to an axis 125 of the generally annular wall 122 of the shroud 120. The second axis extends through a centre of area of the slot 126 of the rotatable member 124. When a slot 126 of a rotatable member 124 receives an inlet vane 114 the first axis of the inlet vane 114 and the second axis of the rotatable member 124 are coaxial.

Some conventional variable geometry turbines can change the effective inlet angle of the inlet vanes by using what are known as pivot vanes. Pivot vanes are vanes which can be pivoted about an axis. The orientation of each pivot vane may be controlled independent of one another or a common linkage may control the orientation of all of the pivot vanes of a variable geometry turbine. Variable geometry turbines which comprise pivot vanes require a large number of components as each vane must be assembled separately into the variable geometry turbine. In addition, variable geometry turbines which comprise pivot vanes require control via a control system in order to control the orientation of the pivot vanes. The inlet vanes 114 of the nozzle ring 110 of the present disclosure provide a much simpler way in which to change the effective inlet angle of the inlet vanes 114. The inlet vanes 114 of the present disclosure can either be formed as an integral part of a generally annular wall 112 or can be attached to a generally annular wall 112 as a separate component. In order to change the effective angle of the inlet vanes 114 of the nozzle ring 110, the nozzle ring 110 is moved axially such that the inlet vanes 114 are either retracted from slots 126 of the rotatable members 124 or inserted into the slots 126.

In use, the nozzle ring assembly 100 shown in Figure 4 is arranged around a turbine wheel such that the inlet passageway 111 defined between the face of the generally annular wall 112 of the nozzle ring 110 and the face of the generally annular wall 122 of the shroud 120 extends radially inwards towards the turbine wheel. Such an arrangement may form part of a turbocharger.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS: 1. A nozzle ring for a variable geometry turbine, the nozzle ring comprising: a generally annular wall; and an array of circumferentially spaced inlet vanes supported by the generally annular wall, each of which extends axially from a first surface of the generally annular wall, wherein each of the inlet vanes is shaped such that, for at least a portion of the inlet vane, in cross section in a plane perpendicular to an axis of the generally annular wall the inlet vane has a generally uniform shape that is independent of an axial position on the inlet vane and wherein an orientation of the generally uniform shape is dependent on the axial position on the inlet vane.
2. The nozzle ring of claim 1 wherein each of the inlet vanes is shaped such that it is more tangential towards an axial end that is proximal the generally annular wall and less tangential towards a distal end of the inlet vane.
3. The nozzle ring of claim 1 or claim 2 wherein each of the inlet vanes is shaped such that an angle of the or each of the inlet vanes varies linearly between a proximal end and a distal end.
4. The nozzle ring of claim 1 or claim 2 wherein each of the inlet vanes is shaped such that an angle of the or each of the inlet vanes varies non-linearly between a proximal end and a distal end.
5. The nozzle ring of claim 4 wherein each of the inlet vanes is shaped such that a rate of change of the angle of the or each of the inlet vanes with respect to axial position along that inlet vane is greater towards an axial end that is proximal the generally annular wall.
6. The nozzle ring of any preceding claim wherein from a proximal end of each of the array of circumferentially spaced inlet vanes to a distal end of each such inlet vane, the generally uniform shape of the inlet vanes rotates through at least 5 degrees.
7. The nozzle ring of any preceding claim, wherein the inlet vanes are integrally formed with the generally annular wall.
8. The nozzle ring of any preceding claim further comprising: an inner flange that is generally perpendicular to the generally annular wall, and which extends from a radially inner edge of the generally annular wall; and an outer flange that is generally perpendicular to the generally annular wall, and which extends from a radially outer edge of the generally annular wall.
9. A shroud for a variable geometry turbine, the shroud comprising: a generally annular wall; and an array of rotatable members provided on the generally annular wall, the rotatable members being rotatable relative to the generally annular wall, and each rotatable member having a slot for receipt of at least a portion of an inlet vane.
10. The shroud of claim 9 wherein the generally annular wall defines a plurality of apertures, each of the plurality of apertures being for engagement with one of therotatable members.
11. The shroud of claim 10 wherein each of the plurality of apertures comprises a central portion is generally circular but is provided with two flat portions on opposite sides of the circle.
12. The shroud of claim 11 wherein each of the plurality of apertures further comprises: a first end portion radially outboard of the central portion; and a second end portion radially inboard of the central portion.
13. The shroud of any one of claims 9 to 12 further comprising: an inner flange that is generally perpendicular to the generally annular wall, and which extends from a radially inner edge of the generally annular wall; and an outer flange that is generally perpendicular to the generally annular wall, and which extends from a radially outer edge of the generally annular wall
14. The shroud of any one of claims 9 to 13 wherein each rotatable member comprises: a main body portion which defines the slot; and a pair of engagement features for releasable engagement with the generally annular wall.
15. The shroud of claim 14 wherein when engaged with the generally annular wall the main body portion of each rotatable member is adjacent to, and sits proud of, the generally annular wall.
16. The shroud of claim 15 wherein the main body portion of each rotatable member is provided with rounded edges.
17. The shroud of claim 14 wherein the main body portion of each rotatable member is recessed into, or countersunk into, the generally annular wall such that together the generally annular wall and the rotatable members form a generally flat annular surface.
18. The shroud of any one of claims 14 to 17 wherein the pair of engagement features extend from the main body portion on either side of the slot.
19. The shroud of any one of claims 14 to 18 wherein a first portion of each engagement feature extends generally perpendicularly to the main body portion adjacent the slot and a second portion of each engagement feature extends generally parallel to the main body portion and away from the slot.
20. The shroud of any one of claims 14 to 19 when dependent either directly or indirectly on claim 11 wherein a shape of a footprint of the second portions of the pair of engagement features generally matches, but has slightly smaller dimensions than, the shape of the central portion of the apertures in the generally annular wall.
21. The shroud of any one of claims 9 to 20 wherein each of the array of rotatable members is rotatable between at least: a first range of positions in which it is not engaged with the generally annular wall; and a second range of positions in which it is engaged with the generally annular wall.
22. A nozzle ring assembly for a variable geometry turbine, the nozzle ring assembly comprising: a first wall member and a second wall member; 20 25 30 wherein the second wall member faces the first wall member so as to define an inlet passageway between a face of the first wall member and a face of the second wall member; wherein one of the first wall member and the second wall member is an axially moveable wall such that axial movement of the axially movable wall member varies an axial width of the inlet passageway; wherein one of the first wall member and the second wall member comprises the nozzle ring of any one of claims 1 to 8 and the other one comprises the shroud of any one of claims 9 to 21; and wherein, in use, the slot of each rotatable member of the shroud receives at least a portion of one of the array of inlet vanes of the nozzle ring, a shape of the slot generally matching the generally uniform shape of said one or the array of inlet vanes in cross section in a plane perpendicular to the axis of the generally annular wall of the nozzle ring.
23. A variable geometry turbine comprising: a housing; a turbine wheel supported in the housing for rotation about a turbine axis; and the nozzle ring assembly of claim 22, wherein the nozzle ring assembly is arranged around the turbine wheel such that the inlet passageway defined between the face of the first wall member and the face of the second wall member extends radially inwards towards the turbine wheel.
24. The variable geometry turbine of claim 23 wherein the axially moveable one of the first wall member and the second wall member is moveable between a fully open position and a fully closed position.
25. A turbocharger comprising the variable geometry turbine of claim 23 or claim 24.