GB2536399A

GB2536399A - Actuator rod for a variable geometry turbine

Info

Publication number: GB2536399A
Application number: GB1414043.8A
Authority: GB
Inventors: Stelfox Alexander; M Wood David; L Holroyd Robert
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2014-08-07
Filing date: 2014-08-07
Publication date: 2016-09-21
Anticipated expiration: 2034-08-07
Also published as: GB2536399B; GB201414043D0

Abstract

A variable geometry turbine actuator rod 116 comprising a head 127 for attachment to a moving wall, and a stem, or shaft 134, extending from the head and which is connected to an actuator. One of the head and stem defines a projection extending parallel to the longitudinal axis of the stem and the other defines a complementary recess for receipt of the projection so as to resist relative rotation between the head and the stem. The invention improves the alignment of the stem and head during the assembly process and allows the components to be assembled without a bespoke assembly fixture, providing flexibility in the production chain as to when to perform the assembly operation. Also disclosed is an actuator rod comprising a head and a stem, wherein the stem comprises a hollow bushing defining a bore; and a shaft defining a region, for receipt by the bore of the hollow bushing.

Description

ACTUATOR ROD FOR A VARIABLE GEOMETRY TURBINE

The present invention relates to an actuator rod for a variable geometry turbine.

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

In one known type of turbine, referred to as a variable geometry turbine, an axially moveable wall member, generally referred to as a "nozzle ring", defines one wall of the turbine 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 flows through the turbine decreases, the inlet passageway width may be decreased to maintain gas velocity and optimise turbine output.

In one common arrangement of a variable geometry turbine the nozzle ring is supported on rods extending parallel to the axis of rotation of the turbine wheel. The rods are moved by an actuator assembly, typically a pivoting yoke mechanism, which axially displaces the rods via a block attached to the end of each yoke arm received in a flat defined by one end of each rod. The opposite end of each rod has an enlarged head which defines one or more apertures for receipt of pins to secure the head of each rod to the back face of the nozzle ring, the front face being the face that faces into the turbine inlet passageway. During movement of the nozzle ring across the turbine inlet passageway the nozzle ring is exposed to very high temperature exhaust gases which can cause the nozzle ring to expand relative to components of the actuator assembly, including the rods, which are located further from the exhaust gases and are often located in the bearing housing, which is typically provided with cooling. In certain arrangements and operating conditions a portion of the exhaust gases are allowed to pass behind the nozzle ring such that the end of each rod connected to the nozzle ring is directly exposed to the very high temperature exhaust gases. Thus, not only must the actuator assembly accurately position and maintain the precise axial location of the nozzle ring to maximise turbine efficiency, but it must do so under varying and, often extreme, operating conditions, which place severe requirements on the various components of the actuator assembly, in particular the actuator rods, which extend between the very hot turbine housing into the much cooler bearing housing in a typical bearing side-mounted actuator assembly.

In order to address the above-mentioned issues, actuator rods in current variable geometry turbines which employ a sliding nozzle ring are currently manufactured from one of the small number of high performance alloys, e.g. TribaloyTM, which are capable of exhibiting the required high level of wear and corrosion resistance at the typical operating temperatures of a turbine. While such alloys are available, they are expensive and can be difficult to form, machine and, particularly, cast; an undesirably high occurrence of casting defects is not uncommon and rods formed from such materials can exhibit undesirably high residual stresses which can lead to cracks forming post-machining.

It is an object of the present invention to obviate or mitigate one or more of the problems with existing actuator rods and/or their method of manufacture.

According to a first aspect of the present invention there is provided a variable geometry turbine actuator rod. The rod comprises a head for attachment to a moving wall of a variable geometry turbine and a stem extending from the head and which is configured for connection to an actuator. One of the head and stem defines a projection extending parallel to the longitudinal axis of the stem.

The other of the head and stem defines a complementary recess for receipt of the projection so as to resist relative rotation between the head and the stem about the longitudinal axis of the stem.

In this way, the actuator rod can be accurately assembled with the head and stem correctly aligned without the need to hold the relative orientation of the components during subsequent assembly steps, e.g. a heat treatment process required if the components are brazed together. Another benefit is that the components can be assembled without a bespoke assembly fixture, which allows flexibility in the production chain as to when to perform the assembly operation.

The stem may comprise a hollow bushing defining a bore and a shaft having a proximal end nearest the head of the actuator rod and a distal end furthest from the head of the actuator rod. The shaft defines a first region in between the proximal and distal ends of the shaft. Said first region is configured for receipt by the bore of the hollow bushing.

The projection may be defined by an arcuate lip extending axially from the head of the actuator rod. The recess may be defined by a pair of axially extending flats, one flat on each side of an intermediate convex portion of the bushing.

The arcuate lip may have axially extending flat surfaces at each end which are complementary to a section of the pair of flats defined by the bushing. In this way, relative rotation between the head and the stem about the longitudinal axis of the stem can be resisted by the flat surfaces of the arcuate lip bearing against the pair of flats defined by the bushing.

The curvature of the arcuate lip orthogonal to the longitudinal axis of the stem may be complementary to the curvature of said convex portion of the bushing orthogonal to the longitudinal axis of the stem. In this way, said arcuate lip can receive a section of the convex portion.

A second aspect of the present invention provides a variable geometry turbine actuator rod. The actuator rod comprises a head for attachment to a moving wall of a variable geometry turbine and a stem extending from the head and which is configured for connection to an actuator. The stem comprises a hollow bushing defining a bore and a shaft having a proximal end nearest the head of the actuator rod and a distal end furthest from the head of the actuator rod. The shaft defines a first region in between the proximal and distal ends of the shaft. Said first region is configured for receipt by the bore of the hollow bushing.

In this way, it is possible to use a different material for the bushing and to position the bushing at any desirable location along the length of the shaft. For example, it is possible to employ a bushing that has a surface made from a wear resistant material, or to form the bushing from a wear resistant material, and to then design the shaft so as to locate the bushing in a potential wear region of the actuator rod. Since such wear resistant materials are typically expensive, this can eliminate the need to form any of the other components of the actuator rod from the expensive material and thereby reduce costs by reducing the amount of the expensive material that is required.

Typical actuator rods are currently formed as a single casting from a high performance low carbon cobalt-chromium-molybdenum alloy, such as a TribaloyTM. There may be additional benefits to changing the material for the head and/or shaft from such expensive, high performance materials. It is therefore now possible to select materials for the head and/or shaft that are less prone to casting defects, which is a recognised feature of alloys, such as TribaloyTM, and/or materials that exhibit a greater tensile strength.

Assembling the actuator rod from a head, bushing and shaft also allows modularity for future changes to the actuator rod, since any of these components can be substituted by a modified component as required in the future without having to modify the remaining component(s). For example, the material from which each component is manufacture could be changed to suit a particular application or to enable a particular braze alloy to be used in applications where components are brazed together. Moreover, the shape of any of the components can be varied without having to lay down new tooling for the remaining component(s) as long as the interface between the components remains essentially the same. This has the potential to reduce the costs associated with adapting the actuator rod to a particular application and also to improve supply chain efficiency.

The head may define an aperture for receipt of a second region of the shaft; said second region being closer to the proximal end of the shaft than the first region of the shaft. The aperture may be defined by an internal wall of the head. The internal wall of the aperture and the second region of the shaft may define complementary screw threads to facilitate connection of the shaft to the head. In this way, as the shaft is inserted through the bore of the bushing, the second region of the shaft nearer to its proximal end can be screwed into the aperture in the head of the actuator.

The first region of the shaft may have a reduced diameter as compared to a third region of the shaft; said third region being in between the first region and the distal end of the shaft. Providing the first region of the shaft, which is the region upon which the bushing is mounted, with a reduced diameter as compared to the third region of the shaft enables the outer diameter of the actuator rod in the region of the bushing to be smaller than if the first region of the shaft had the same or a larger diameter than the third region of the shaft. This is beneficial in terms of packaging since it allows the actuator rod to be received in a narrower cavity in a housing containing the actuator than would otherwise be the case.

A section of the stem adjacent the head may have a surface comprised of a material that has particular properties that are desirable for that section of the stem. An example of a material that is suitable in certain applications, e.g. where the section of interest is a potential wear surface, is a high performance low carbon cobalt-chromium-molybdenum alloy, such as a TribaloyTm. Reference to low carbon' is intended to refer to alloys which incorporate essentially no carbon or as close as practically possible, save for unavoidable impurities. In the present context of variable geometry turbines, 'high performance' is intended to refer to one or more properties or characteristics of a material which enable a component comprising that material to perform to a higher level as compared to the same component made from a material that is not a 'high performance' material and/or which enable the component comprising the material to perform to an acceptable standard in relatively extreme operating conditions, such as those experienced by components exposed to exhaust gases during operation of a variable geometry turbine, such as very high temperatures (e.g. approx. 700 °C or above) and/or highly corrosive species.

Another section of the stem may be formed from any other desirable material, which may be more suitable for use in other regions of the stem due to the operating requirements imposed on those regions of the stem and/or which may be cheaper, easier to manipulate (e.g. cast or machine), etc. A suitable material from which another section of the stem may be formed is a stainless steel, such as a high carbon stainless steel, for example, 440C stainless steel. A 'high carbon' stainless steel is considered to be one containing at least about 0.2 to 0.3 wt% carbon.

The bushing, shaft and/or stem may be formed from any suitable material. An example of a suitable material for the bushing is a high performance, low carbon cobalt-chromium-molybdenum alloy, such as a TribaloyTm. An example of a suitable material for the shaft and/or head is a stainless steel, such as a high carbon stainless steel, for example, 440C stainless steel. 440C stainless steel may be particularly preferred since it has a similar, though nominally lower, co-efficient of thermal expansion than a more costly, high performance material from which actuator rods are often manufactured, TribaloyTM 440. This ensures that the current clearances around the component made from TribaloyTM 440 remain suitable to prevent sticking when the component has been modified in accordance with the second aspect of present invention and a preferred embodiment of the first aspect of the present invention incorporating a stem comprising a bushing and a shaft. A further advantage of 440C stainless steel is that it improves casting efficiency where the actuator rod is to be produced by casting.

A third aspect of the present invention provides a variable geometry turbine actuator assembly comprising an actuator and an actuator rod according to the first or second aspect of the present invention. Any one or more of the optional features recited above in respect of the first and second aspects of the present invention may be incorporated into the actuator assembly of the third aspect of the present invention.

A fourth aspect of the present invention provides a variable geometry turbine comprising a turbine wheel rotationally mounted on a shaft and an actuator assembly according to the third aspect of the present invention. Any one or more of the optional features recited above in respect of the first and second aspects of the present invention may be incorporated into the actuator assembly forming part of the variable geometry turbine according to the fourth aspect of the present invention.

A fifth aspect of the present invention provides a variable geometry turbocharger comprising a variable geometry turbine according to the fourth aspect of the present invention, wherein there is further provided a compressor wheel rotationally mounted on the shaft upon which the turbine is also mounted. Any one or more of the optional features recited above in respect of the first and second aspects of the present invention may be incorporated into the variable geometry turbine forming part of the turbocharger according to the fifth aspect of the present invention.

It is preferred that the turbine or turbocharger of the above defined aspects of the present invention incorporates a housing within which the turbine wheel is received. It is preferred that said housing defines an annular radial gas flow inlet which is directed upstream of the turbine and that the actuator rod of the present invention is operatively connected to a slidable annular wall member which defines one wall of said inlet. In preferred embodiments in which a compressor wheel is mounted on the shaft which also supports the turbine wheel, the compressor wheel is driven by rotation of the shaft as a result of rotation of the turbine. As a result. the compressor wheel can be used to compress atmospheric air and deliver said air at above atmospheric pressure via a radial gas flow outlet defined by a compressor housing assembly to an engine intake manifold. Alternatively, the shaft which supports the turbine wheel may be connected to a gear, in place of the compressor wheel, to transmit mechanical power to an engine-flywheel or crankshaft. Moreover, it is preferred that an annular wall member operatively connected to an actuator rod according to the present invention supports a plurality of axially extending stators or vanes arranged to deflect gas flowing through the inlet passage so that the gas is flowing in the correct direction to drive the turbine wheel most efficiently. The turbine preferably further comprises an annular shroud plate located within the turbine housing and which defines a plurality of slots that are suitably arranged to receive the stators defined by the annular wall member. The shroud plate may be fixed such that axial displacement of the annular wall member relative to the shroud plate is achieved solely by axial displacement of the annular wall member by the actuator rods according to the present invention. Alternatively, the wall member carrying the stators or vanes may be fixed relative to the housing and the actuator rods may be operatively connected to the shroud plate so that the shroud plate can be slid axially to vary the effective width of the turbine inlet passageway and to receive the stators or vanes when the shroud plate is moved so as to radially overlie the stators or vanes.

Other advantageous and preferred features of the invention will be apparent from the following description.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an axial cross-section through a known variable geometry turbocharger; Figure 2 is a perspective schematic view of a variable geometry turbine actuator rod according to preferred embodiments of the first and second aspects of the present invention; Figure 3 is an alternative perspective schematic view of the actuator rod shown in Figure 2; Figure 4 is a side-on schematic view of the actuator rod shown in Figure 2; Figure 5 is a side-on schematic view of the actuator rod shown in Figure 2 where the head and bushing are shown in transparent outline to expose the configuration of the shaft; and Figure 6 is a side-on schematic part-sectioned view of the actuator rod shown in Figure 2.

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

The turbine housing 1 defines an inlet volute 7 to which gas from an internal combustion engine (not shown) is delivered. The exhaust gas flows from the inlet volute 7 to an axial outlet passageway 8 via an annular inlet passageway 9 and the turbine wheel 5. The inlet passageway 9 is defined on one side by a face 10 of a radial wall of a movable annular wall member 11, commonly referred to as a "nozzle ring", and on the opposite side by an annular shroud 12 which forms the wall of the inlet passageway 9 facing the nozzle ring 11. The shroud 12 covers the opening of an annular recess 13 in the turbine housing 1.

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

The position of the nozzle ring 11 is controlled by an actuator assembly of the type disclosed in US 5,868,552. An actuator (not shown) is operable to adjust the position of the nozzle ring 11 via an actuator output shaft (not shown), which is linked to a yoke 15. The yoke 15 in turn engages axially extending actuating rods 16 that support the nozzle ring 11. Accordingly, by appropriate control of the actuator (which may for instance be pneumatic or electric), the axial position of the rods 16 and thus of the nozzle ring 11 can be controlled.

The speed of the turbine wheel 5 is dependent upon the velocity of the gas passing through the annular inlet passageway 9. For a fixed rate of mass of gas flowing into the inlet passageway 9, the gas velocity is a function of the width of the inlet passageway 9, the width being adjustable by controlling the axial position of the nozzle ring 11. Figure 1 shows the annular inlet passageway 9 fully open. The inlet passageway 9 may be closed to a minimum by moving the face 10 of the nozzle ring 11 towards the shroud 12.

The nozzle ring 11 has axially extending radially inner and outer annular flanges 17 and 18 that extend into an annular cavity 19 provided in the turbine housing 1. Inner and outer sealing rings 20 and 21 are provided to seal the nozzle ring 11 with respect to inner and outer annular surfaces of the annular cavity 19 respectively, whilst allowing the nozzle ring 11 to slide within the annular cavity 19. The inner sealing ring 20 is supported within an annular groove formed in the radially inner annular surface of the cavity 19 and bears against the inner annular flange 17 of the nozzle ring 11. The outer sealing ring 20 is supported within an annular groove formed in the radially outer annular surface of the cavity 19 and bears against the outer annular flange 18 of the nozzle ring 11.

Gas flowing from the inlet volute 7 to the outlet passageway 8 passes over the turbine wheel 5 and as a result torque is applied to the shaft 4 to drive the compressor wheel 6. Rotation of the compressor wheel 6 within the compressor housing 2 pressurises ambient air present in an air inlet 22 and delivers the pressurised air to an air outlet volute 23 from which it is fed to an internal combustion engine (not shown).

Referring to Figures 2 and 3, this illustrates an embodiment of an actuator rod 116 according to the present invention which can be employed to interconnect the nozzle ring 11 and yoke 15 of Figure 1. The actuator rod 116 defines a notch 124 at its distal end 125, opposite to its proximal end 126 nearest the nozzle ring 11. The notch 124 is dimensioned to receive one of the ends of the yoke 15 of Figure 1 so that pivoting of the yoke 15 axially displaces the actuator rod 116 and thereby the nozzle ring 11 when mounted on a pair of actuator rods 116.

The actuating rod 116 incorporates an enlarged head 127 with a back face 128 and an opposite front face 129 which is arranged to contact a back face of the nozzle ring 11 between the axially extending radially inner and outer annular flanges 17, 18 of the ring 11. The enlarged head 127 has a curvature matching that of the nozzle ring 11 and defines a pair of bores 130a, 130b at its ends to receive rivets (not shown) to fixedly connect the actuator 116 to the back face of the nozzle ring 11 in between the radially inner and outer annular flanges 17, 18 of the ring 11.

The actuator rod 116 further defines a recess 131 which extends axially along one side of a section of the actuator rod 116 from just behind its enlarged head 127 towards its distal end 125. The prior art actuator rod 16 shown in Figure 1 also defines a broadly similar recess (not shown) but in that arrangement the recess is defined simply by a flat extending along a side of the actuator rod 16. The purpose of the recess in the prior art actuator rod 16 and the actuator rod 116 according to the present invention is to scrape any soot accumulated from components adjacent to the recess as the actuator rod 16, 116 moves axially across the turbine inlet passageway 9. The recess 131 in the actuator rod 116 according to the present invention differs from the flat employed in the prior art actuator rod 16 by virtue of the fact that the recess 131 is defined by a pair of radially narrow flats 132a, 132b which extend axially to each side of an intermediate axially extending convex portion 133. This arrangement is beneficial because it still provides the desired soot scraping function but also increases the diameter of that section of the actuator rod 116 as compared to the prior art actuator rod 16 which just incorporates a flat, thereby increases the strength of the soot scraper section 131 of the actuator rod 116.

As shown in Figures 2 and 3, the actuator rod 116 according to the present invention is assembled from three components: the enlarged head 127; a shaft 134; and a hollow bushing 135 mounted on the shaft 134 just behind the enlarged head 127. The bushing 135 is manufactured from TribaloyTM 440 and is provided at a location at which wear may occur during use of the actuator rod 116 in a variable geometry turbine. While any suitable wear-resistant material may be used in this region of the actuator rod 116, TribaloyTM 440 is particularly suitable since it exhibits excellent wear resistance, as well as corrosion resistance, which is important given the fact that the actuator rod 116 may be exposed to potentially corrosive exhaust gases during use. The enlarged head 127 is cast from 440C stainless steel and the shaft 134 is manufactured from wrought 4400 stainless steel. While any suitable material(s) may be used for the enlarged head 127 and/or shaft 134, 440C stainless steel is preferred because it possesses the desired balance of weight, strength and hardness, while also exhibiting excellent resistance to wear and corrosion. Assembling the actuator rod 116 from multiple components, rather than forming it as a single component, such as the cast TribaloyTM 440 actuator rod 16 shown in Figure 1, has a number of benefits. It allows modularity for future changes to the actuator rod 116, since any constituent component can be replaced with a modified component without having to modify the remaining component(s). The shape of any one or more of the constituent components can be varied without having to build new tooling as long as the interface between the components remains essentially the same. This can reduce costs associated with adapting the actuator rod 116 to a particular application and can also improve supply chain efficiency.

Referring now to Figures 4, 5 and 6, the enlarged head 127 defines a central aperture 136 for receipt of a proximal end 137 of the shaft 134. A first region 138 of the shaft 134 adjacent its proximal end 137 defines a screw thread 139 of complementary form to a screw thread 140 defined by an internal wall of the aperture 136. A second region 141 of the shaft 134 extending axially away from the enlarged head 127 is of reduced diameter compared to a third region 142 of the shaft 134 which extends from the narrower second region 141 towards the distal end 125 of the actuator rod 116. The bushing 135 defines an open internal bore 143 extending through the bushing 135 and which is dimensioned to form a close fit with the narrower second region 141 of the shaft 134 when the bushing 135 is mounted on to the shaft 134. Once the bushing 135 is mounted on to the shaft 134, the threaded first region 138 of the shaft 134 is then screwed into the threaded aperture 136 in the enlarged head 127 before components are brazed together. In this specific embodiment, the internal bore 143 of the bushing 135 is left as-cast, rather than having its surface honed, prior to insertion of the shaft 134. This removes a process from the overall manufacturing method, which saves on time and cost, and also improves adhesion of the bushing to the shaft, since an as-cast surface exhibits better braze adhesion than a honed surface.

A further feature of the actuator rod 116 is the provision of an arcuate lip 144 extending circumferentially around a segment of the aperture 136 so as to radially overlie a section of the bushing 135 when the shaft 134, bushing 135 and enlarged head 127 are assembled together. As described above in relation to Figures 2 and 3, the bushing 135 defines a pair of flats 132a, 132b extending axially across the length of the bushing 135 to each side of an intermediate convex portion 133 of reduced outer diameter as compared to the third region 142 of the shaft 134. The flats 132a, 132b are circumferentially spaced apart by just under half the total circumference of the bushing, as can best be seen in Figure 4 and 5. The arcuate lip 144 extends around a similar proportion of the total circumference of the aperture 136 such that when the enlarged head 127 is mounted on the shaft 134 carrying the bushing 135, the flats 132a, 132b on the bushing 135 engage ends 145a, 145b of the arcuate lip 144 to resist rotation of the enlarged head 127 relative to the shaft 134 and bushing 135. In this way, it is possible to conduct the necessary post-assembly heat treatment processes to fix the components of the actuator rod 116 together without concern that the components will move relative to one another. As a result, the relative location of the various features of the components can be accurately controlled so that the actuator rod 116 can be installed and operated correctly without having to re-align or re-configure any of the actuator rod 116 components prior to use.

The described and illustrated embodiments are 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.

In the embodiment of the actuator rod 116 of the present invention described above with reference to Figures 2 to 6 the entire bushing 135 is manufactured from TribaloyTm 440. In an alternative embodiment, just the external surface of the bushing 135 may be provided with a surface coating of a wear and/or corrosion resistant material, such as TribaloyTm 440, and the remainder of the bushing made from any other suitable material that exhibits the desired physical and chemical properties, and is amenable to the application of the required surface coating. Such a coating may be provided by any suitable method, for example plasma vapour deposition (PVD). Moreover, the coating may be applied to the entire external surface of the bushing 135 or may be applied to only the portion or portions of the external surface of the bushing at which wear and/or corrosion has been identified as likely to be a problem.

In the illustrated embodiment, the bushing 135 and the shaft 134 are manufactured as separate components that are then brazed together prior to use. In an alternative embodiment, the separate bushing may be omitted and instead the shaft produced as a one-piece component that defines the various necessary features (notch 124, soot scraper recess 131, flats 132a, 132b etc). If a wear and/or corrosion resistant region is required on the one-piece shaft, this may then be provided by way of an insert of a suitable material provided in a complementary recess defined by the one-piece shaft, or by way of a surface coating of the appropriate material provided on the exterior surface of the one-piece shaft at the correct location or locations using a suitable surface deposition technique, such as PVD.

Moreover, while the actuator rod 116 described above incorporated a projection/recess arrangement in the form of an arcuate lip 144 on the enlarged head 127 and a recess 131 defined by the bushing 135 when mounted on the shaft 134, it will be appreciated that relative rotation between the enlarged head 127 and the shaft (and bushing, if present as a separate component) can be achieved using any desirable male/female pair of formations that co-operate to provide the desired anti-rotation functionality. For example, the shaft or bushing may define a projection for receipt in a recess defined by the head. The shape of that projection/recess pair may be generally similar to the arcuate lip 144 and recess 131 described above with reference to Figures 2 to 6, or the projection/recess may take a different form provided the form chosen is capable of limiting rotation of the head relative to the shaft and/or bushing.

It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature 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

CLAIMS1. A variable geometry turbine actuator rod comprising: a head for attachment to a moving wall of a variable geometry turbine; and a stem extending from the head and which is configured for connection to an actuator; one of the head and stem defining a projection extending parallel to the longitudinal axis of the stem; and the other of the head and stem defining a complementary recess for receipt of the projection so as to resist relative rotation between the head and the stem about the longitudinal axis of the stem.
2. An actuator rod according to claim 1, wherein the stem comprises: a hollow bushing defining a bore; and a shaft having a proximal end nearest the head of the actuator rod and a distal end furthest from the head of the actuator rod; the shaft defining a first region in between the proximal and distal ends of the shaft, said first region being configured for receipt by the bore of the hollow bushing.
3. An actuator rod according to claim 2, wherein the projection is defined by an arcuate lip extending axially from the head of the actuator rod and the recess is defined by a pair of axially extending flats, one flat on each side of an intermediate convex portion of the bushing.
4. An actuator rod according to claim 3, wherein the arcuate lip has axially extending flat surfaces at each end which are complementary to a section of the pair of flats defined by the bushing; relative rotation between the head and the stem about the longitudinal axis of the stem being resisted by the flat surfaces of the arcuate lip bearing against the pair of flats defined by the bushing.
5. An actuator rod according to claim 3 or 4, wherein the curvature of the arcuate lip orthogonal to the longitudinal axis of the stem is complementary to the curvature of said convex portion of the bushing orthogonal to the longitudinal axis of the stem such that said arcuate lip can receive a section of the convex portion.
6. A variable geometry turbine actuator rod comprising: a head for attachment to a moving wall of a variable geometry turbine; and a stem extending from the head and which is configured for connection to an actuator; wherein the stem comprises: a hollow bushing defining a bore; and a shaft having a proximal end nearest the head of the actuator rod and a distal end furthest from the head of the actuator rod; the shaft defining a first region in between the proximal and distal ends of the shaft, said first region being configured for receipt by the bore of the hollow bushing.
7. An actuator rod according to any one of claims 2 to 6, wherein the head defines an aperture for receipt of a second region of the shaft; said second region being closer to the proximal end of the shaft than the first region of the shaft.
8. An actuator rod according to claim 7, wherein the aperture is defined by an internal wall of the head; said internal wall and the second region of the shaft defining complementary screw threads to facilitate connection of the shaft to the head.
9. An actuator rod according to any one of claims 2 to 8, wherein the first region of the shaft has a reduced diameter as compared to a third region of the shaft; said third region being in between the first region and the distal end of the shaft.
10. An actuator rod according to any preceding claim, wherein a section of the stem adjacent the head has a surface comprised of a high performance low carbon cobalt-chromium-molybdenum alloy, such as a TribaloyTm.
11. An actuator rod according to claim 10, wherein another section of the stem is formed from a stainless steel, such as a high carbon stainless steel, for example, 440C stainless steel.
12. An actuator rod according to any one of claims 2 to 9, wherein the bushing is formed from a high performance, low carbon cobalt-chromiummolybdenum alloy, such as a TribaloyTm.
13. An actuator rod according to any one of claims 2 to 9 or 12, wherein the shaft is formed from a stainless steel, such as a high carbon stainless steel, for example, 440C stainless steel.
14. An actuator rod according to any preceding claim, wherein the head is formed from a stainless steel, such as a high carbon stainless steel, for example, 440C stainless steel.
15. A variable geometry turbine actuator assembly comprising: an actuator and an actuator rod according to any preceding claim.
16. A variable geometry turbine comprising a turbine wheel rotationally mounted on a shaft and an actuator assembly according to claim 15.
17. A variable geometry turbocharger comprising a variable geometry turbine according to claim 16, wherein there is further provided a compressor wheel rotationally mounted on the shaft.