Adjustment ring assembly for variable turbine geometry turbochargers

An adjustment ring (50) is configured to facilitate vane (30) position adjustment in a variable turbine geometry turbocharger (1), and is formed of an assembly of one or more first ring portions (60) that are formed of a first material, and one or more second ring portions (61) that are formed of a second material. The first material has different material properties than the second material. In some embodiments, high-wear portions of the adjustment ring (50) can selectively and cost-effectively be formed of wear-resistant material while remaining portions are formed of a conventional material. A cost-effective method of manufacturing multi-piece adjustment rings (50) is described.

FIELD OF THE INVENTION

Embodiments are generally related to turbochargers and, more particularly, to an improved adjustment ring for variable turbine geometry turbochargers.

BACKGROUND

Exhaust gas turbochargers are provided on an engine to deliver air to the engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.

Generally, an exhaust gas turbocharger includes a turbine section and a compressor section, and uses the exhaust flow from the engine exhaust manifold to drive a turbine wheel located in the turbine section. The turbine wheel drives a compressor wheel located in the compressor section via a shaft that extends between the sections. Air compressed by the compressor section is then provided to the engine intake as described above.

In some turbochargers, the turbine section may have variable turbine geometry (VTG) that permits adjustment of the amount of exhaust gas directed to the turbine wheel. In some examples, the VTG is implemented using a ring of aerodynamically shaped vanes that are disposed in the turbine housing at the inlet to the turbine wheel. The vanes rotate in unison to vary the inlet area and angle of approach of the exhaust gas directed to the turbine wheel. By altering the turbine housing geometry in this way, the turbocharger has reduced lag and increased efficiency at higher speeds. Moreover, the exhaust gas backpressure and the turbocharger speed can be controlled by modulating the exhaust gas flow to the turbine wheel via the VTG.

SUMMARY

In some aspects, an adjustment ring is configured to facilitate vane position adjustment in a variable turbine geometry turbocharger. The adjustment ring includes a first ring portion that is formed of a first material; and a second ring portion that is formed of a second material. The first ring portion and the second ring portion are configured to be assembled together into a single annular element, and the first material has different material properties than the second material.

The adjustment ring may include one or more of the following additional features: The first material is a different material than the second material. The first material has been subjected to a different heat treatment than the second material. The first material has a higher wear resistance than the second material. The first ring portion corresponds to a portion of the single annular element that, when in use, is subjected to the highest wear. The first ring portion is fixed to the second ring portion. The first ring portion includes a first ring mating edge having an irregular profile, the second ring portion includes a second ring mating edge having an irregular profile, and the irregular profile of the first ring mating edge is configured to matingly engage the irregular profile of the second ring mating edge.

In some aspects, a method of manufacturing an annular adjustment ring is provided. The annular adjustment ring is configured to facilitate vane position adjustment in a variable turbine geometry turbocharger. The method includes providing a cutting pattern for the adjustment ring, the cutting pattern incorporating sector patterns, and each sector pattern corresponds to a ring portion of the adjustment ring. The sector patterns are arranged within the cutting pattern such that the sector patterns are nested. The method further includes cutting a first sheet of source material in accordance with the cutting pattern to provide ring portions; and assembling the ring portions together to form at least one annular adjustment ring.

The method may include one or more of the following steps and/or features: The step of cutting comprises fine blanking. The step of cutting includes cutting at least one individual ring portion from a second sheet of source material, where the second sheet of source material has different material properties than the first sheet of source material. The first sheet of source material has different wear resistance than the second sheet of source material. The step of assembling the ring portions comprises assembling at least one ring portion formed from the first sheet of source material with at least one ring portion formed from a second sheet of source material to form the annular adjustment ring, the second sheet of source material having different material properties than the first sheet of source material. The second sheet of source material is less wear resistant than the first sheet of source material, and when the ring portions are assembled together to form the adjustment ring, the first ring portion is arranged within the adjustment ring at a location that corresponds to a portion of the adjustment ring that, when in use, is subjected to the highest wear.

The adjustment ring assembly of the variable turbine geometry (VTG) turbocharger is an important part of the overall VTG since it is the link between the vane ring assembly, which supports the vanes, and the adjustment shaft, which connects the VTG to an actuator. In particular, the adjustment ring assembly is used to control the position of the vanes relative to the turbine housing. As such, it plays a critical role in the structure and function of the VTG assembly, and can affect turbocharger efficiency. Several components, such as the adjustment ring, pivoted sliding blocks and large adjustment block, form the adjustment ring assembly.

In some aspects, the adjustment ring assembly includes a multi-piece adjustment ring that provides increased wear resistance, and reduced weight and manufacturing costs relative to some conventional single-piece adjustment rings. In particular, by manufacturing the adjustment ring in two, three, four or more individual pieces, and then assembling the individual pieces into the single adjustment ring, one or more of the pieces can be formed of a material different than that of the remaining pieces. For example, one piece can be made of a highly-wear resistant, and thus relatively expensive, material and incorporated into the assembly at a location requiring high wear resistance, whereas the remaining piece(s) can be made of a conventional, and thus relatively inexpensive, material. This approach reduces costs of manufacturing a wear resistant adjustment ring, and can be compared to some conventional adjustment rings which are stamped as a single piece from a sheet of material.

In this example, the individual pieces used to form the adjustment ring are generated by splitting a template adjustment ring into two or more pieces at strategic locations. This provides the benefit of permitting the designer to hand pick and combine relatively expensive materials with less expensive materials. By this technique, a relatively expensive wear resistant piece can be provided for use in the higher wear region of the adjustment ring, where the location of such a high wear region is determined based on historical experience and wear calculation estimations. In this technique, less wear resistant, and thus less expensive, materials and pieces can be used in non-critical locations. This can be compared to a conventional adjustment ring that, when entirely formed of the highly wear resistant material, is much more expensive than the multi-piece adjustment ring in which highly wear resistant material is only used at locations of high wear.

Moreover, by manufacturing the adjustment ring in multiple pieces, more pieces can be cut from single source sheet of material due to use of strategic cutting patterns, further reducing manufacturing costs. In some embodiments, the strategic cutting patterns employ a nested arrangement of the pieces to be cut. This can be compared to some conventional adjustment rings which are cut as a single piece from a sheet of material. Due to their annular shape, manufacture of such a conventional adjustment rings results in large amounts of wasted material relative to the manufacture of the multi-piece adjustment ring, due to wasted material corresponding to the center region and to poor packing density associated with its circular outer shape.

Advantageously, multiple adjustment rings can be stamped from the same sheet of source material, significantly reducing material wastage and scrap during manufacturing, and particularly with respect to fine blanking. In some embodiments, three or four adjustment rings having similar diameters and can be fine blanked in multiple pieces out of the same area of sheet metal required for fine blanking a single, unitary adjustment ring of the same diameter.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, an exhaust gas turbocharger1includes a turbine section2, the compressor section18, and a center bearing housing16disposed between and connecting the compressor section18to the turbine section2. The turbine section2includes a turbine housing4that defines an exhaust gas inlet (not shown), an exhaust gas outlet8, and a turbine volute10disposed in the fluid path between the exhaust gas inlet and the exhaust gas outlet8. A turbine wheel12is disposed in the turbine housing4between the turbine volute10and the exhaust gas outlet8. A shaft14is connected to the turbine wheel12, is supported for rotation about a rotational axis R within in the bearing housing16, and extends into the compressor section18. The compressor section18includes a compressor housing20that defines an axially-extending air inlet22, an air outlet (not shown), and a compressor volute26. A compressor wheel28is disposed in the compressor housing20between the air inlet22and the compressor volute26, and is connected to the shaft14.

In use, the turbine wheel12in the turbine housing4is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold of an engine (not shown). Since the shaft14connects the turbine wheel12to the compressor wheel28in the compressor housing20, the rotation of the turbine wheel12causes rotation of the compressor wheel28. As the compressor wheel28rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine's cylinders via an outflow from the compressor air outlet, which is connected to the engine's air intake manifold.

The turbocharger1is a variable turbine geometry turbocharger (VTG). In particular, the turbine section2includes a plurality of pivotable vanes30to control the flow of exhaust gas that impinges on the turbine wheel12and control the power of the turbine section2. The vanes30also therefore control the pressure ratio generated by the compressor section18. In engines that control the production of NOx by the use of High Pressure Exhaust Gas Recirculation (HP EGR) techniques, the vanes30also provide a means for controlling and generating exhaust back pressure.

Referring also toFIGS. 2-3, the vanes30are arranged in a circular array around the turbine wheel12, and are located between the turbine volute10and the turbine wheel12. The vanes30are pivotably supported in this configuration between a generally annular upper vane ring40and a generally annular lower vane ring42, where “upper” refers to being closer to the center bearing housing16, and “lower” refers to being closer to the turbine housing4. Each vane30rotates on a post32that protrudes from the opposed side faces of the vane30, with the post32defining a pivot axis35. The free ends of the post32are received in respective apertures in the upper vane ring40and the lower vane ring42. The angular orientation of the upper vane ring40relative to the lower vane ring42is set such that the corresponding apertures in the vane rings40,42are concentric with the axis35of the posts32, and the vane30is free to rotate about the axis35. On the upper vane ring-side of the vane30, the post32protrudes through corresponding aperture of the upper vane ring40and is affixed to a vane arm36, which controls the rotational position of the vane30with respect to the vane rings40,42. An adjustment ring assembly45is arranged adjacent to, and in parallel with, the upper vane ring40, and controls the position of all of the vane arms36in unison.

The adjustment ring assembly45includes the adjustment ring50, small slide blocks47rotatably disposed on the turbine-facing side of the adjustment ring50, and a large block46that is rotatably disposed on the compressor-facing side the adjustment ring50and is used to connect the adjustment ring50to an actuator. In use, the adjustment ring assembly45rotatably drives the vanes30via the vane arms36, which link the adjustment ring assembly45to the individual vanes30. In many configurations, forks37formed on the ends of the vane arms36drive the independently rotatable slide blocks47to minimize friction in the system and to accommodate distortion and corrosion in the turbine housing, and thus the linkages. The adjusting ring50is allowed to rotate circumferentially with minimal friction, and is aligned radially so that it remains concentric with the upper and lower vane rings40,42, and axially so that the slide blocks47remain in contact with the vane arms36.

In some embodiments the adjustment ring50is supported by ramparts38on the vane arms36. The large block46is connected by a shaft to the adjusting ring50. Circumferential motion of the large block46about the turbocharger rotational axis R causes the adjusting ring50to rotate about the turbocharger rotational axis R. Rotation of the adjusting ring50about the turbocharger rotational axis R causes the multiple small slide blocks47to rotate about the turbocharger rotational axis R while each of the slide blocks47also rotate about the rotational axis35of the vane posts32. This motion of the slide blocks47causes the vane arms36to rotate about the rotational axis35of the vane posts32and change the angle of attack of the vanes30relative to the exhaust flow. The slide blocks47are designed so that the interface between each slide block47and the corresponding fork37is predominantly sliding friction over the entire area of one cheek of the rotating block. This design provides uniform load distribution, which reduces wear and provides greater life than in line contact, but conversely raises friction over that of a line contact design.

The adjustment ring50is controlled by an actuator (not shown) which is operatively connected to the large block46via a linkage48(FIG. 1), whereby the adjustment ring50can rotated about the rotational axis R. The actuator receives commands from the engine electronic control unit (ECU).

Referring toFIG. 4, the adjustment ring50is annular in shape, and includes an outer edge51, an inner edge52, and opposed side faces53,54(opposite side face53, but not shown) that extend between the outer and inner edges51,52. The adjustment ring50is formed having three sets of through-openings55,56,57that extend between the opposed side faces53,54(opposite side face53, but not shown). The first set of through-openings consists of circular arm openings55, each of which is configured to receive one of the vane arms36. In the illustrated embodiment, there are thirteen arm openings55that are generally equidistantly spaced about the circumference of the adjustment ring50, and are radially located closer to the inner edge52than the outer edge51. The second set of through-openings consist of circular bolt openings56, each of which is configured to receive a bolt59that supports a spacer (not shown) used to control axial spacing between the adjustment ring50and the upper vane ring40. Three bolt openings56are equidistantly spaced about the circumference of the adjustment ring50, and are radially located closer to the inner edge52than the outer edge51. The third set of through-openings consists of weight reduction openings57that are disposed between pairs of adjacent arm openings55. The weight reduction openings57are elongated along the circumferential direction, and are radially located midway between the inner edge52and the outer edge51. In addition to the three sets of through-openings55,56,57, the adjustment ring50includes a circular securement opening58that extends between the opposed side faces53,54, and is configured to receive the shaft that secures the large block46to the adjustment ring50, whereby the adjustment ring50is connected to the actuator.

The adjustment ring50is an assembly of two pieces, including a first ring portion60and second ring portion61. The first ring portion60and the second ring portion61each have a peripheral shape which is an annular sector. In addition, the first ring portion60and the second ring portion61each have the same radius of curvature R1, and an arc length generally corresponding to an angle measure of the sector that is about 180 degrees, so that when assembled together, the first ring portion60and the second ring portion61form a single, complete annular element. Respective mating edges66of first ring portion60are secured to the corresponding mating edges68of the second ring portion61by conventional techniques such as welding, riveting (i.e., orbital riveting), etc.

Referring toFIGS. 5 and 6, in some embodiments, in order to provide a precise and reliable connection between respective ring portions60′,61′,60″,61″, the mating edges66′,68′,66″,68″ have an irregular, interlocking profile. For example, the first ring portion60′,60″ may include a first ring mating edge66′,66″ having an irregular profile including a slot, notch, groove or hole. In addition, the second ring portion61′,61″ may include a second ring mating edge68′,68″ having an irregular profile including a protrusion that is shaped and dimensioned to matingly engage with the profile of the first ring mating edge66′,66″. A press-fit dovetail joint or other mortise-and-tenon connection is an example of such an irregular, interlocking profile that can be used to form a secure assembly of the ring portions60′,61′,60″,61″.

Referring toFIGS. 7 and 8, by forming the adjustment ring50in multiple pieces, in this case two ring portions60,61, and then assembling the ring portions60,61together to form the single, annular element, material costs are reduced. This is because the ring portions60,61are cut, for example by fine stamping, from a single sheet S of source material. The source material may be, for example, a sheet metal suitable for use in high temperature applications, such as 321 stainless steel. Due to their curved shape and hemispherical arc length, the cutting patterns corresponding to the annular-sector shaped first and second ring portions60,61can be nested (FIG. 7). That is, the convex outer edge51aof one ring portion60can be arranged within the concave inner edge52bof another ring portion61during the cutting process. In one example, for a sheet S of source material having a length of x mm and a height of y mm, by using a nested arrangement during stamped cutting of multiple first and second ring portions60,61from the sheet S of source material, four adjustment rings50of radius R1(as shown inFIG. 4) can be obtained, with minimal waste material W1. This can be compared to stamping single-piece annular adjustment rings500from the same sheet S of source material, in which only two adjustment rings500can be obtained, and in which the amount of resulting waste material W2of the sheet S (FIG. 8) is much greater than the waste material W1.

Referring toFIG. 9further reductions in waste material can be gained by stamping adjustment rings50,150of dissimilar diameter from the same sheet S of source material. For example, the stamps corresponding to the annular-sector shaped first and second ring portions60,61corresponding to a first adjustment ring50having a radius R1can be nested. In addition, other stamps corresponding annular-sector shaped third and fourth ring portions160,161corresponding to a second adjustment ring150having a radius R2can be further nested within the stamps for the first and second ring portions60,61. In this example, by using a nested arrangement during stamped cutting of the first through fourth ring portions60,61,160,161from the sheet S of source material, two adjustment rings50of radius R1and two adjustment rings150of radius R2can be obtained, with minimal waste material W3.

Referring toFIG. 10, an alternative embodiment adjustment ring250is similar to the adjustment ring50illustrated above with respect toFIG. 3in that it is annular in shape, and includes an outer edge251, an inner edge252, and opposed side faces253,254(opposite side face253, side face254not shown) that extend between the outer and inner edges251,252, and is formed having three sets of through-openings55,56,57that extend between the opposed side faces253,254. In this embodiment, however, the adjustment ring250is an assembly of three pieces, including a first ring portion260, a second ring portion261, and a third ring portion262. The first ring portion260, the second ring portion261, and the third ring portion262each have a peripheral shape which is an annular sector. In addition, first ring portion260, the second ring portion261, and the third ring portion262each have the same radius of curvature R1, and an arc length generally corresponding to an angle measure of the sector that is about 120 degrees, so that when assembled together, first ring portion260, the second ring portion261, and the third ring portion262form a single, complete annular element.

Respective mating edges266,268,270of first ring portion260, the second ring portion261, and the third ring portion262are secured together by conventional techniques such as welding, riveting (i.e., orbital riveting), etc., and may also include an irregular, interlocking profile.

Referring toFIG. 11, by forming the adjustment ring250in multiple pieces, in this case three ring portions260,261,262, and then assembling the three ring portions260,261,262together to form the single, annular element, material costs are reduced. Like the previous embodiment, due to their curved shape and less than-hemispherical arc length, the stamps corresponding to the annular-sector shaped first, second, and third ring portions260,261,262can be nested. In one example, by using a nested arrangement during stamped cutting of multiple first, second, and third ring portions260,261,262from the sheet S of source material, four adjustment rings250of radius R1can be obtained, with minimal waste material W4. This can be compared to stamping single-piece annular adjustment rings500from the same sheet S of source material, in which only two adjustment rings500can be obtained, and in which the amount of resulting waste material W2of the sheet S (FIG. 8) is much greater than W4.

The adjustment rings50,150,250illustrated herein have been described as having multiple ring portions60,61,160,161,260,261,262formed from a single sheet S of source material, whereby each of the resulting ring portions are formed of the same material, and thus have the same material properties. However, the adjustment rings50,150,250and the corresponding ring portions ring portions60,61,160,161,260,261,262are not limited to this configuration. For example, the ring portions260,261,262of the adjustment ring250may be formed so that at least one ring portion (i.e., the third ring portion262) has material properties that are different that the material properties of the other ring portions (i.e., the first and second ring portions260,261). In some embodiments, the third ring portion262is formed of the same material as the material used to form the first and second ring portions260,261, but the third ring portion262is heat treated, for example to improve wear resistance or other desired material property, whereas the first and second ring portions260,261remain un-heat treated or are subjected to a different heat treatment. In other embodiments, the third ring portion262may be formed of a relatively expensive material, such as, for example, a highly wear resistant material such as GMR 235, a high alloy, Nickel-based alloy steel, whereas the first and second ring portions260,261are formed of another material, for example, a conventional material that is less expensive than the material used to form the third ring portion262, such as 321 stainless steel. In these embodiments, the third ring portion262having different material properties, such as for example improved wear resistance, can be assembled into the adjustment ring250, which in turn is arranged in the turbocharger1so that the third ring portion262is positioned at a location known to have relatively higher wear. This arrangement allows the use of one ring portion having higher wear properties, while the remaining ring portions are formed of the more cost-effective material and used in non-critical locations. Thus, this arrangement allows the designer to hand pick from materials of varying costs and material properties, and combine them in a single element as required by the specific application. By doing so, material costs can be reduced relative to the configuration in which the adjustment ring is entirely formed of a highly wear resistant material.

Referring toFIG. 12, another alternative embodiment adjustment ring350is annular in shape, and includes an outer edge351, an inner edge352, and opposed side faces353,354(opposite side face353, side face354not shown) that extend between the outer and inner edges351,352, and is formed having two sets of through-openings55,56that extend between the opposed side faces353,354. The adjustment ring350also includes a circular securement opening58, and in some instances, may further include weight reduction openings57(not shown). In addition, the adjustment ring350is an assembly of four pieces. In particular, the adjustment ring350includes a first ring portion360, a second ring portion361, and a third ring portion362, all formed of the same material, for example 321 stainless steel. When assembled together, first ring portion360, the second ring portion361, and the third ring portion362form a single, annular element. The adjustment ring350further includes a fourth piece, e.g., an insert363, formed of a different material having material properties that address the requirements of a specific application. For example, the insert363may be formed of GMR 235 high alloy steel, and may be attached to a side face353of the adjustment ring350so as to overlie one or more of the first, second and third ring portions360,361,362. The insert363may be strategically placed at a location requiring specific material properties, for example, improved wear resistance.

In the illustrated exemplary embodiment, the insert363has a peripheral shape which is an annular sector. In addition, the insert363has an arc length generally corresponding to the circumferential length of a region of high wear of the adjustment ring350. For example, the insert363may have an arc length that is less than the arc length of the ring portion362that it overlies (as shown), or that is the same as or greater than the arc length of the ring portion362that it overlies. In addition, the insert363has a radial dimension that is less than the radial dimension of the ring portion362that it overlies. The insert363is secured in the desired position relative to the ring portion362via welding, fasteners, adhesives, or a combination thereof. By providing the adjustment ring350as an assembly of three stamped ring portions360,361,362, manufacturing costs can be reduced as discussed above. Moreover, by addressing wear resistance requirements by including the insert363in the adjustment ring350, manufacturing costs can be further reduced by minimizing the amount of relatively expensive, high wear material included in the adjustment ring350, specifically, limiting it to those regions that require this feature.

A method of manufacturing an annular adjustment ring50,150,250,350that is configured to facilitate vane position adjustment in a variable turbine geometry turbocharger1includes providing an appropriate cutting pattern. The cutting pattern incorporates one or more annular patterns, or portions of annular patterns, where each annular pattern corresponds to a single adjustment ring. In the cutting pattern, each annular pattern is separated into at least two individual sectors corresponding to the ring portions60,61. The sectors may include features to provide any required features of the resulting device, for example the through-openings55,56,57,58, mating edges with an irregular, mating profile, etc.

The cutting pattern is configured in a way such that the sectors are provided in a nested arrangement. For example, the convex outer edge of a sector corresponding to one ring portion can be arranged within the concave inner edge of a sector corresponding of another ring portion. The nested sectors may correspond to the same ring portion (60,60or61,61) or may correspond to different ring portions60,61.

Multiple adjustment rings50are cut from a sheet of source material. Effectively, for each sector, the sheet of source material is cut along the periphery of the each sector used to form a ring portion60,61. Once the ring portions60,61are cut from the sheet of source material, one or more adjustment rings50are formed by assembling the ring portions60,61together by joining the respective mating edges66,68.

In some embodiments, the step of cutting the ring portion60,61from a sheet of source material comprises fine blanking (e.g., fine stamping). Alternatively, other cutting techniques can be used to form the ring portions60,61. Multiple ring portions may be cut simultaneously from a single sheet of source material, individual ring portions may be cut sequentially, or cutting may be a combination of both.

In some embodiments, all the ring portions60,61used to form the adjustment ring50are formed from the same material. In this case, the step of assembling the ring portions includes assembling connecting the ring portions60,61along their corresponding mating edges66,68to form a homogeneous, annular adjustment ring50.

In other embodiments, at least one individual ring portion60is cut from a first sheet of source material, and at least one other individual ring portion61is cut from a second sheet of source material, where the second sheet of source material has different material properties than the first sheet of source material. The different material properties may be inherent to the material used to form the second sheet, or may be provided to the material by heat-treatment, coating, or other process. In some embodiments, the first sheet of source material is formed of the same material as the second sheet of source material, but is heat treated differently than the second sheet of source material.

Where ring portions60,61of differing materials are used, the step of assembling the ring portions60,61includes assembling at least one ring portion (e.g., the first ring portion60) formed of the first sheet of source material with at least one ring portion (e.g., the second ring portion61) formed of the second sheet of source material to form a single, annular adjustment ring50. In some embodiments, the second sheet of source material may be formed of less wear resistant material that that of the first sheet. In this case, the annular adjustment ring50is then assembled within the turbocharger1such that the first ring portion60is arranged within the turbocharger at a location that corresponds to a portion of the adjustment ring50that, when in use, is subjected to the highest wear.

Although the adjustment ring50,150,250,350are described herein as having two or three ring portions, the adjustment ring is not limited to having two or three ring portions. For example, in some embodiments the adjustment ring50,150,250,350may have four or more ring portions.

Although the adjustment ring50,150,250,350are described herein as having multiple ring portions60,61,62, each ring portion60,61,62having an approximately equal circumferential dimension, the adjustment ring50,150,250,350is not limited to this configuration. For example, in some embodiments, one of the ring portions (e.g., the first ring portion60) may be larger or smaller than the other ring portions used to form the adjustment ring50,150,250,350. In some embodiments, each ring portion60,61,62may have a unique circumferential dimension.

Although the adjustment ring50,150,250,350is described herein as being formed of 321 stainless steel, GMR 235 alloy steel, or a combination thereof, these materials are exemplary and the adjustment ring50,150,250,350are not limited to these materials or a combination thereof. Materials selected to form the adjustment ring50,150,250,350will be determined by the requirements of the specific application.

Although the adjusting ring50is described herein as being constrained and supported by the axial and radial shapes fabricated on the ramparts38of the vane arms36, it is not limited to this configuration. For example, in some embodiments, the adjusting ring50may be radially supported and constrained by a set of rollers (not shown) which are themselves either constrained by the turbine housing or upper vane ring40. In this configuration, the vane arms36are flat and do not contain the ramparts of the illustrated embodiment.

Aspects described herein can be embodied in other forms and combinations without departing from the spirit or essential attributes thereof. Thus, it will of course be understood that embodiments are not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the following claims.