VARIABLE GEOMETRY TURBINE
A variable geometry turbine for a turbocharger has a plurality of vanes disposed in an inlet passageway of a turbine housing outboard of the turbine wheel. The vanes are movable so as to adjust the effective cross-section area of the inlet between a first position in which the area of the inlet is a minimum and a second position in which the area of the inlet is a maximum. The movement of one end of the vanes is supported by a plurality of first guide tracks, such as slots, defined in a guide member. A vane actuator such as, for example a unison ring, effects movement of the vanes. The vane actuator has a plurality of actuation tracks (e.g. slots) for engagement with the vanes and is rotatably disposed in the housing. When it rotates the vane actuator induces sliding translation of the vanes relative to the first guide tracks in a first direction and sliding translation of the vanes relative to the actuation tracks in a second direction so as to adjust the cross-section area of the inlet. The swirl angle changes between the first and second positions.
The present invention relates to a variable geometry turbine, a turbocharger incorporating such a variable geometry turbine for use with an internal combustion engine, and a variable geometry mechanism for varying the gas flow through such a turbine.
Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft 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.
The turbine stage of a conventional turbocharger comprises: a turbine housing defining a turbine chamber within which the turbine wheel is mounted; an annular inlet passageway defined in the housing between facing radially extending walls arranged around the turbine chamber; an inlet arranged around the inlet passageway; and an outlet passageway extending from the turbine chamber. The passageways and chamber communicate such that pressurised exhaust gas admitted to the inlet flows through the inlet passageway to the outlet passageway via the turbine chamber and rotates the turbine wheel. It is known to improve turbine performance by providing vanes, referred to as nozzle 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 of this kind 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 in line with varying engine demands.
Nozzle vane arrangements in variable geometry turbochargers can take different forms. In one type, known as a sliding “nozzle ring”, the vanes are fixed to an axially movable wall that slides across the inlet passageway. The axially movable wall moves towards a facing shroud plate in order to close down the inlet passageway and in so doing the vanes pass through apertures in the shroud plate. In another type the nozzle vanes are of the “swing vane” type. This comprises an array of movable vanes that is concentrically disposed around the turbine wheel with each vane pivotally supported on an annular vane carrier in the turbine inlet passageway. The vanes are each pivotable about a respective axle extending across the inlet parallel to the turbine axis and projecting through a wall of the inlet. The axle supports a crank or lever outside the inlet and a vane actuating mechanism connected to each crank is displaceable in a manner that causes each of the vanes to move in unison, such a movement enabling the cross-sectional area available for the incoming gas, and also the angle of approach of the gas to the turbine wheel, to be controlled. For instance, orientating the vanes so that their chords are generally radial to the wheel increases the spacing between adjacent vanes, thus increasing the cross-sectional flow area of the passageway—referred to as the turbine “throat”. On the other hand, pivoting the vanes so that their chords extend generally circumferentially to the wheel reduces the space between adjacent vanes thus reducing the turbine throat. The product of the throat dimension and the fixed axial length of the vanes extending across the inlet passageway, determines the flow area for any given vane angle.
In conventional swing vane mechanisms of the kind described above the change in angle of the vanes affects blade vibration as the distance between the trailing edges of the vanes and the turbine wheel changes as the vanes pivot. As the inlet passageway of the turbine is opened by pivoting the vanes the trailing edges of the vanes move closer to the periphery of the turbine wheel with the result that vibration occurs in the vanes. This results in metal fatigue over prolonged periods of use.
It is one object of the present invention to provide for an improved variable geometry turbine.
According to a first aspect of the present invention there is provided a variable geometry turbine comprising: a housing defining a chamber within which a turbine wheel is mounted for rotation about a turbine axis such that its outer periphery substantially describes a swept circumference; the chamber having a gas inlet disposed radially outboard of an outer periphery of said turbine wheel; a plurality of vanes arranged around the turbine axis, each vane having a vane height extending between a first end and a second end in a direction across the inlet in a substantially axial direction and each vane being movable so as to adjust the effective cross-section area of the inlet between a first position in which the area of the inlet is a minimum and a second position in which the area of the inlet is a maximum; at least one guide member having a plurality of first guide tracks for engagement with the first ends of the vanes; a vane actuator for effecting translational movement of the plurality of vanes relative to the housing between the first and second positions, the vane actuator having a plurality of actuation tracks for engagement with the plurality of vanes, the vane actuator being rotatably disposed in the housing such that rotation of the vane actuator induces sliding translation of each of the plurality of vanes relative to a respective first guide track in a first direction and sliding translation of each of the plurality of vanes relative to the respective actuation track in a second direction, the second direction being different to the first direction; wherein in the first position the vanes are disposed such that at a given turbine pressure ratio they direct the gas to the turbine wheel such that it has a first swirl angle at the swept circumference of the turbine wheel and in the second position the vanes are disposed such that at the same turbine press ratio they direct the gas to the turbine wheel such that it has a second swirl angle at the swept circumference, the first swirl angle being greater than the second swirl angle.
The swirl angle is defined by the angle of the gas incident on a radial plane that intersects the axis of the turbine wheel, as will be understood by those skilled in the art. The first swirl angle being greater than the second angle means that it is closer to a tangent to the circumference swept by the turbine wheel as it rotates.
The change in swirl angle means that trailing edges of the vanes do not move significantly away from the turbine wheel in the radial direction as the vanes move from the second to the first position and may in some embodiments move closer.
The guide and/or actuation tracks may be in the form of slots that receive a projection on the vanes or alternatively may be in the form of projections that engage with corresponding slots in the vanes. The slots may be through slots that penetrate through the guide member or blind slots that do not penetrate through. The guide member may be a ring that is fixed (releasably or otherwise) to the housing or may be an integral part of the housing.
The plurality of vanes may all move together in the same angular direction relative to the radial direction. It is to be understood that in one embodiment there may be one or more other vanes besides the plurality of vanes that are fixed or which do not move in the same manner. However, in another embodiment all of the vanes move in unison.
The first aspect of the invention provides for a variable geometry turbine in which the vanes translate in a sliding movement at both ends upon movement by the actuator. This allows for accurate control of the trailing edge position of the vanes relative to the periphery of the turbine wheel and accurate control of the size of the exposed inlet area. The variation of the inlet area may be independent of the change in vane angle. The change in swirl angle may assist in reducing turbine wheel blade vibration and resulting blade fatigue.
The first ends of the plurality of vanes may have at least one projection and the plurality of first guide tracks may be in the form of first guide slots, the at least one projection of each vane may be received in a respective first guide slot. The at least one projection may be in the form of an elongate tab that extends in the direction between leading and trailing edges of each vane.
The plurality of first guide slots may extend substantially in a direction that is substantially tangential to an imaginary circle about the turbine axis. Alternatively they may be inclined to the tangential direction by up to 40 degrees. The direction may have both tangential and radial components and the relationship between the two components may be linear such that the slot extends in a linear fashion. The tangential component may be dominant. Alternatively the relationship may be non-linear such that the slot extends in a curve.
The plurality of actuation tracks in the vane actuator may be in the form of slots. The actuation tracks may extend in a substantially radial direction or otherwise.
The guide member and the vane actuator may be spaced apart in the axial direction, the plurality of vanes being disposed between them. Alternatively they may be disposed at one end of the vanes, such as, the first end of the vanes.
The second ends of the vanes may each have at least one projection and the actuation tracks may be in the form of slots, the at least one projection of the second ends being received in a respective slot in the vane actuator. The slots may be through slots in that they penetrate through the vane actuator. The at least one projection may comprise a pin that extends into the respective slot.
The guide member may be defined by a wall of the turbine housing that is adjacent to the inlet.
The first guide member may be substantially annular.
There may be provided a first guide member that may have the plurality of first guide tracks and a second guide member that may be spaced apart from the first guide member in an axial direction and may have a plurality of second guide tracks for engagement with the second end of the plurality of vanes. The second guide tracks may be slots which penetrate the second guide member. Each of the second ends of the vanes may have a projection for receipt in the guide tracks. The pins may extend from the projections and may be integrally formed therewith. The projection may be in the form of elongate tabs extending in a direction between leading and trailing edges of the vanes. The pins may translate in the respective actuation tracks during movement of the vanes.
The first and second guide tracks may be substantially identical.
The plurality of vanes may have a flange at one or both of the first and second ends. The vane projections may extend from the flanges at each end.
The plurality of vanes may be disposed in a generally circumferential array concentric with the turbine wheel.
The plurality of vanes may each have a pair of projections at a first end for receipt in the first guide tracks. There may be a pair of first guide tracks for each of the plurality of vanes and the pair of first guide tracks may have substantially identical profiles or they may have different profiles.
The vane actuator may be a unison ring that may be substantially annular. The unison ring may have a formation that is couplable to an actuator drive member. The actuator drive member may be coupled to the unison ring by means of a link that engages with a formation defined on the unison ring. The formation may be in the form of a pin. The drive member may be a reciprocal piston rod that is coupled to the formation. It may be coupled to the formation by means of a cranked arm. The piston rod may have a boss in which one end of the cranked arm is pivotally connected. The other end of the cranked arm may have a spindle that is coupled to the formation. The spindle may support a disc for coupling to the formation. The disc may have a slot for engagement with the pin such that the pin may slide relative to the slot during driving of the vane actuator.
The unison ring may be supported on a flange of the second guide member.
The vanes may define trailing edges proximate the turbine wheel. In the first position the trailing edges of the vanes may be at a first distance from the turbine wheel swept circumference, in the second position the trailing edges of the vanes may be at a second distance from the swept circumference, the first distance being shorter than the second distance. This helps to reduce turbine wheel blade vibration and resulting blade fatigue.
According to a second aspect of the present invention there is provided a turbocharger comprising a compressor driven by an exhaust gas variable geometry turbine as defined above.
According to a third aspect of the present invention there is provided a variable geometry mechanism for varying the gas flow through a turbine as defined above.
According to a fourth aspect of the present invention there is provided an internal combustion engine fitted with a turbocharger as defined above such that compressed air is deliverable from the compressor to an inlet manifold of the engine and exhaust gas from an exhaust manifold is delivered to the inlet of the variable geometry turbine of the turbocharger.
Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Referring now to
The turbine housing 4 is provided with an exhaust gas inlet 7 and an exhaust gas outlet 8. The inlet directs incoming exhaust gas to an annular inlet chamber, i.e. volute 9, surrounding the turbine wheel 5 and communicating therewith via a radially extending annular inlet passageway 10. Rotation of the turbine wheel 5 rotates the compressor wheel, which in turn draws in air through an axial inlet 11 and delivers compressed air to the engine intake (not shown) via an annular outlet volute 12.
The turbine 1 is a variable geometry turbine in which the exhaust gas flows from the inlet chamber 9 to the outlet 8 via a variable geometry mechanism 13 that is disposed radially outboard of the turbine wheel 5.
Referring now to
The first guide ring 15 is fixed to a wall 17 of the turbine housing 4 and has a first surface, facing the inlet passageway 13, with a plurality of elongate first guide slots 18 arranged in an annular array. Each of the first guide slots 18 is substantially linear and extends along an axis that is substantially tangential to an imaginary concentric circle on the first surface of the first guide ring 15. In an alternative embodiment the first guide slots may be inclined to the tangential direction. In the particular embodiment shown each of the first guide slots 18 is blind i.e. its depth is such that it does not penetrate through the guide ring 15. The second guide ring 16 is penetrated by a corresponding arrangement of elongate second guide slots 19. At its inner periphery the second guide ring 16 has a flange 20 that extends in an axial direction away from the first ring 15 and supports a unison ring 21, rotation of which by an actuator 22 effects movement of the vanes 14. The unison ring 21 is guided in rotation by the flange 20 and has a plurality of slots 23, each of which extends in a substantially radial direction and is open to the inner periphery of the ring 21.
The actuator 22 may take any suitable form but in the embodiment shown it comprises a pneumatic actuator with a reciprocating piston rod 25 terminating in a bush 26 that is connected to a first end of a pivotal cranked arm 27 in such a manner that it permits lost motion between the arm 27 and the rod 25. A second end of the cranked arm 27 comprises a spindle 28 that terminates in disc 29 having a surface traversed by a slot 30 for connected to the unison ring 21.
An annular retaining plate 31 serves to retain the variable geometry mechanism 13 in the turbine housing 4 and is fixed relative to the bearing and turbine housings 3, 4. It is penetrated by a small bore 32 in which the spindle 28 of the cranked arm 27 is received such that its second end (disc 29) is positioned between the retaining plate 31 and the unison ring 21. The slot 30 (
In operation, reciprocal translation of the piston rod 25 causes the cranked arm 27 to rotate about the spindle 28 and therefore the disc 29. The pin 33 is offset from the centre of rotation of the disc 29 (i.e. the axis through the spindle 28) such that rotation of the disc 29 causes the displacement of pin 33 around the spindle 28 and relative to the slot 30. This movement causes the unison ring 21 to rotate about its centre axis to effect movement of the vanes 14 relative to the guide rings 15, 16 so as to increase or decrease the cross sectional area of the inlet passageway 13
Each of the vanes 14 has an aerofoil profile with an upstream leading edge distal from the turbine wheel 5, a downstream trailing edge proximate the outer periphery of the turbine wheel 5, and a vane height that extends in the axial direction across the inlet passageway 10. A first end of each vane defines a first tab 35 for receipt in a corresponding one of the first guide slots 18 in the first guide ring 15 and a second end of each vane 14 defines a second tab 36 for receipt in one of the second guide slots 19 in the second guide ring 16. An integral pin 37 extends from each second tab 36, passes through the respective second guide slot 19 in the second guide ring 16 and into a radial slot 23 of the unison ring 21. Each of the first and second tabs 35, 36 is designed to translate relative to the respective first and second guide slots 18,19 in which it resides by a sliding movement and may therefore be made from, or coated with, a suitable wear-resistant bearing material.
Angular displacement of the unison ring 21 about its central axis of rotation by the actuator 22 causes a corresponding angular displacement of the radial slots 23 and therefore the pivot pins 37 of the vanes 14 that reside in the slots 23. This displacement of the pins 37 causes the vanes 14 to move relative to the guide rings 15, 16 by virtue of a translational movement of the first and second tabs 35, 36 in the first guide slots 18 of the first guide ring 15 and the second guide slots 19 of the second guide ring 16 respectively. At the same time, the pins 37 travel along the radial slots 23 of the unison ring 21. The movement of the vanes 14 is illustrated in
The arrangement allows for accurate control of the cross-sectional area of the passageway and the vane angle with respect to the exhaust gas thus improving flow conditions and turbine efficiency. It also allows for accurate control of the trailing edge of the vane with respect to the periphery of the turbine wheel. This can be important as if the gap between the two is too small the turbine wheel blades may be subject to vibration by passing through the wakes of the vanes. If such vibration occurs over repeatedly it can lead to high cycle fatigue of the blades. On the other hand a reduction of the gap may be desirable in some circumstances to improve turbine efficiency.
A schematic representation illustrating the movement of the unison ring 21 is shown in
The first guide slots 18 in the first guide ring 15 and the corresponding second guide slots 19 in the second guide ring 16 may be inclined to the tangential direction by an angle of up to 40 degrees. In such an instance the radial slots 23 in the unison ring 21 may be correspondingly inclined to the radial direction.
An alternative embodiment of the variable geometry mechanism is depicted in schematic form in
In a variation to the immediately preceding embodiment, flanges are provided at each end of the vanes 214 as depicted in the schematic representations of
In the embodiment of
The embodiment of
In
In a modification to the embodiment of
In the embodiment of
Any of the preceding embodiments may be provided with an array of fixed splitter vanes 655 upstream of the main vanes 614. An example is shown in
The movement of the vanes may be achieved by rotation of the guide ring as well as the unison ring, the two rings being rotated in opposite directions.
The variable geometry mechanism may be assembled as a cartridge as, for example, shown in the embodiment of
For aerodynamic efficiency in all embodiments the slots are preferably hidden from the gas flow path by the vanes at all times.
In the first position, trailing edges T of the vanes 714, 814, 914 are proximate the circumference C swept by the outer periphery of the turbine wheel 704, 804, 904 as it rotates. This distance is represented by arrow Y. In the second position the trailing edges T′ are relatively distal as represented by distance Y′. In the arrangement shown in
The arrangements shown in
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the scope being defined by the claims that follow. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.
Claims
1. A variable geometry turbine comprising:
- a housing defining a chamber within which a turbine wheel is mounted for rotation about a turbine axis such that its outer periphery substantially describes a swept circumference;
- the chamber having a gas inlet disposed radially outboard of an outer periphery of said turbine wheel;
- a plurality of vanes arranged around the turbine axis, each vane having a vane height extending between a first end and a second end in a direction across the inlet in a substantially axial direction and each vane being movable so as to adjust the effective cross-section area of the inlet between a first position in which the area of the inlet is a minimum and a second position in which the area of the inlet is a maximum;
- at least one guide member having a plurality of first guide tracks for engagement with the first ends of the vanes;
- a vane actuator for effecting translational movement of the plurality of vanes relative to the housing between the first and second positions, the vane actuator having a plurality of actuation tracks for engagement with the plurality of vanes, the vane actuator being rotatably disposed in the housing such that rotation of the vane actuator induces sliding translation of each of the plurality of vanes relative to a respective first guide track in a first direction and sliding translation of each of the plurality of vanes relative to the respective actuation track in a second direction, the second direction being different to the first direction;
- wherein in the first position the vanes are disposed such that at a given turbine pressure ratio they direct the gas to the turbine wheel such that it has a first swirl angle at the swept circumference of the turbine wheel and in the second position the vanes are disposed such that at the same turbine press ratio they direct the gas to the turbine wheel such that it has a second swirl angle at the swept circumference, the first swirl angle being greater than the second swirl angle.
2. A variable geometry turbine according to claim 1, wherein the first ends of the plurality of vanes have at least one projection and the plurality of first guide tracks are in the form of first guide slots, the at least one projection of each vane being received in a respective first guide slot.
3. A variable geometry turbine according to claim 1, wherein the plurality of first guide slots extend in a substantially tangential direction.
4. A variable geometry turbine according to claim 1, wherein the plurality of actuation tracks in the vane actuator are in the form of slots.
5. A variable geometry turbine according to claim 4, wherein the actuation tracks extend in a substantially radial direction.
6. A variable geometry turbine according to claim 1, wherein the guide member and the vane actuator are spaced apart in the axial direction, the plurality of vanes being disposed between them.
7. A variable geometry turbine according to claim 6, wherein the second ends of the vanes each have at least one projection and the actuation tracks are in the form of slots, the at least one projection of the second ends being received in a respective slot in the vane actuator.
8. A variable geometry turbine according to claim 1, wherein the guide member and the vane actuator are disposed at the first end of the vanes.
9. A variable geometry turbine according to claim 1, wherein the guide member is defined by a wall of the turbine housing.
10. A variable geometry turbine according to claim 1, wherein the guide member is annular.
11. A variable geometry turbine according to claim 1, wherein there is provided a first guide member having the plurality of first guide tracks and a second guide member spaced apart from the first guide member in an axial direction and having a plurality of second guide tracks for engagement with the second end of the plurality of vanes.
12. A variable geometry turbine according to claim 1, wherein the plurality of vanes have a flange at one or both of the first and second ends.
13. A variable geometry turbine according to claim 12, wherein the vane projections extend from the flanges at each end.
14. A variable geometry turbine according to claim 1, wherein the plurality of vanes each have a pair of projections at a first end for receipt in the first guide tracks.
15. A variable geometry turbine according to claim 14, wherein the pair of guide tracks are substantially identically shaped.
16. A variable geometry turbine according to claim 14, wherein the pair of guide tracks have different profiles.
17. A variable geometry turbine according to claim 1, wherein the vane actuator is a substantially annular unison ring.
18. A variable geometry turbine according to claim 1, wherein the first guide tracks are substantially linear.
19. A variable geometry turbine according to claim 11, wherein the second guide track are substantially linear.
20. A variable geometry turbine according to claim 1, wherein the vanes define trailing edges proximate the turbine wheel and in the first position the trailing edges of the vanes are at a first distance from the turbine wheel swept circumference, in the second position the trailing edges of the vanes are at a second distance from the swept circumference, the first distance being shorter than the second distance.
21. A variable geometry turbine according to claim 1, wherein the plurality of vanes are movable in unison.
22. A variable geometry turbine according to claim 1, wherein the vanes translate without pivoting about a fixed point.
23. A variable geometry turbine according to claim 1, wherein all of the vanes disposed around the turbine axis are movable between the first and second positions.
24. A turbocharger comprising a compressor driven by an exhaust gas variable geometry turbine according to claim 1.
Type: Application
Filed: Jun 18, 2011
Publication Date: Apr 5, 2012
Inventor: Khimani Mohiki (Huddersfield)
Application Number: 13/163,679
International Classification: F04D 29/46 (20060101);