ACTUATING MECHANISM FOR A SLIDABLE NOZZLE RING

Abstract: An actuating mechanism for a slidable nozzle ring (8) of a variable geometry turbine contains linking elements which allow radial dilatation of the nozzle ring (8). The nozzle ring (8) is connected via pivotable bridge members (15) to axial actuator rods (14) thus allowing free radial dilatation of the nozzle ring (8) while maintaining axial alignment with the actuator rods (14).

Description: ACTUATING MECHANISM FOR A SLIDABLE NOZZLE RING This invention relates to a linkage mechanism, and in particular to a linkage mechanism suitable for connecting components in a manner which can accommodate differential expansion between interconnected components. Mechanisms which operate over a wide temperature range must be designed to take account of thermally induced expansion and contraction of their components. Different components can experience different rates of expansion or contraction, which may be caused either by differences between the coefficients of thermal expansion of the components, or by variations in any temperature differential between different parts of the mechanism. For example, in a known variable geometry turbocharger a displaceable nozzle ring is held within a housing through which hot gases flow. The nozzle ring will generally reach a higher temperature than the housing and its temperature will also vary much more rapidly than that of the housing. As a result, the ring will expand and contract radially relative to the housing. An example of a variable geometry turbocharger of the above type is described in European Patent No. EP0095853. The described structure comprises an annular nozzle ring supported on a pair of rods that are displaceable relative to a housing in a direction parallel to the lengths of the rods. The housing is water-cooled, and therefore the spacing between the rods varies as a result of temperature changes much less than the diameter of the ring to which the rods are connected. If the rods were securely fixed to the ring, this differential expansion could only be accommodated by mechanical distortion of the interconnected components and this is not acceptable. To overcome this problem, in turbochargers of the above type the rods have been connected to the ring in a way which allows for limited relative movement in the radial direction. The allowed movement must be sufficient to accommodate the maximum expected differential expansion, but limited so that the mechanism is still able to position the ring accurately in the housing. In some known arrangements, one rod is connected to the ring so as to permit relatively limited pivotal movement between the rod and the ring, whereas the other rod is loosely connected to the ring so as to allow for substantially all of the expected differential expansion. The interconnections between the ring and rods which allow for the expected differential expansion have to prevent excessive tilt of the nozzle ring relative to a plane perpendicular to the rods as such tilting would affect the operating clearances of the mechanism and thereby reduced performance. In addition, the ring must be accurately positioned in the axial direction to ensure that the mechanism responds in a predictable manner to a control input. This means that the mechanism must have limited backlash to ensure proper operation and control. All this has to be achieved in a linkage mechanism that is robust enough to last for several thousands of hours running in the corrosive exhaust gas of an engine, at high temperatures, with no lubrication and in conditions in which mechanical vibration of the interconnected components in inevitable. Such performance has proved difficult to achieve. It is an object of the present invention to provide an improved linkage mechanism which at least partially fulfils the above requirements. According to the present invention, there is provided a linkage mechanism comprising at least two links displaceable in a predetermined direction relative to a first component and connected at spaced apart locations to a second component, wherein at least one of the links incorporates an element which is pivotal relative to the first component about a first axis and pivotal relative to the second component about a second axis, the two axes being parallel to each other and to the predetermined direction and being offset relative to each other. Each link may incorporate a pivotal element, means being provided to limit the positions between which the pivotal element may move relative to one of the components. Alternatively, two links may be provided, one permitting pivotal movement between the link and one of the components about a single axis and the other link incorporating the said pivotal element. Preferably the pivotal element comprises a transverse member mounted on one end of an axially displaceable rod, the elongate member being linked to one component by a pivot at one of its ends and defining at its other end a slot which receives a pin mounted on that one component. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which; Figure 1 is a cut-away perspective view of a variable geometry turbocharger incorporating a linkage in accordance with the invention; and Figure 2 is an exploded perspective view of component parts of the linkage incorporated in the structure illustrated in Figure 1. Referring to Figure 1, the turbocharger comprises an air inlet 1 and an air outlet 2 connected to a chamber in which a compressor wheel 3 is mounted to rotate about an axis 4. The wheel 3 is mounted on a shaft which extends into a turbine housing and supports a turbine wheel 5 such that the wheels 3 and 5 rotate about the common axis 4. The wheel 5 is located in a chamber interconnecting an exhaust inlet 6 and an exhaust outlet 7. Exhaust gases flowing into the inlet 6 and out of the outlet 7 drive the turbine wheel 5 which in turn drives the compressor wheel 3. Such an arrangement is conventional. Exhaust gas flows radially inwards to the turbine wheel 5 between a nozzle ring 8 and a facing radial surface defined by the turbine housing. Vanes 9 mounted on the nozzle ring extend into a recess 10 defined in the turbine housing and facing the nozzle ring. In Figure 1, the nozzle ring 8 is shown as defining a minimum gap between itself and the facing surface of the turbine housing. The axial position of the nozzle ring is controlled by an actuator 11 connected by a lever system to a bar 12 upon which a C-shaped yoke 1 is mounted. The ends of the C-shaped yoke engage in respective rods 14 only one of which is visible in Figure 1. Each of the rods 14 is connected to a transverse arcuate component 15 (hereinafter referred to as a foot) which in turn is connected to the nozzle ring 8. Each rod 14 is slidably received within a suitable bush mounted in the housing. Thus it will be appreciated that each rod 14 is axially displaceable and can rotate about its axis relative to the housing. Referring to Figure 2, this illustrates the linkage interconnecting the nozzle ring 8 and the rods 14. Each of the rods 14 defines a notch 16 in which a respective one of the ends of the yoke 13 of Figure 1 engages. Figure 2 shows only part of the nozzle ring 8 and one of the actuator rods 14 the axial position of which controls the position of the ring. The opposite section of the ring 8 to that shown in Figure 2 is connected to an identical actuator rod linkage. The nozzle ring 8 supports a limiting stop 17 and a cylindrical pivot 18 extending from an inwardly extending radial flange 19 of the ring 8. The foot 15 has a curvature matching that of the nozzle ring 8 and is provided with bores 20 and 21 at its ends. The bores 20 and 21 are positioned on the foot 15 such that they can be aligned with the stop 17 and pivot 18. The rod 14 is secured to a central portion of the foot 15. The stop 17 and pivot 18 are secured to the nozzle ring 8 by washers 22 and rivets 23. The foot 15 is retained between the flange 19 of the ring and the washers 22. The pivot 18 is a close fit in the bore 21. In contrast, the stop 17 is a loose fit in the bore 20. Accordingly the foot 15 can rotate on the pivot 18 to an extent determined by the clearance between the stop 17 and the wall of the bore 20. One face of the foot 15 bears against the flange 19 of the nozzle ring. Given the relatively large surface area of the foot in contact with the nozzle ring a significant bearing area is defined between the components and as a result wear between the contacting surfaces will not rapidly result in the nozzle ring being free to move axially relative to the rod 14. Similarly, the side of the foot 15 remote from the nozzle ring flange 19 runs against the washers 22 which are held against the ends of the stop 17 and pivot 18 by the rivets 23. Again the contact areas are relatively large so that wear rates are reduced to acceptable levels. A further benefit of the illustrated design is that a bearing of increased dimensions further benefit of the illustrated design is that a bearing of increased dimensions can be provided to carry the torsional loads on the nozzle ring that result from acceleration of the exhaust gas flowing across the face of the nozzle ring. It will be appreciated that, assuming two substantially identical rod assemblies are provided which are located symmetrically about the centre of the nozzle ring, if the ring expands more than the housing the differential expansion will be accommodate by the feet 15 pivoting in the radially inwards direction and vice versa. It will also be appreciated that a single linkage as illustrated in Figure 2 could be used with a second linkage which provides only for pivotal movement of the ring about a single bearing defined by the other rod. Alternatively, three or more linkages of the type illustrated could be used. If three of more such linkages were used, the linkages would prevent any displacement of the axis of the nozzle ring in a transverse direction. Although the illustrated embodiment of the invention interconnects a ring and axially displaceable rods, it will be appreciated that the linkage of the invention could be used in circumstances where for example a ring was to be connected to fixed rods or the like.

Claims: CLAIMS 1. A linkage mechanism comprising at least two links extending in a predetermined direction relative to a first component and connected at spaced apart locations to a second component, wherein at least one of the links incorporates a member which is pivotal relative to the first component about a first axis and pivotal relative to the second component about a second axis, the two axes being parallel to each other and to the predetermined direction and being offset relative to each other. 2. A linkage mechanism according to claim 1 , wherein each link incorporates a said pivotal element, means being provided to limit the positions between which the pivotal element may move relative to one of the components. 3. A linkage mechanism according to claim 1 , wherein two linkages are provided, one linkage incorporating said pivotal element and the other linkage permitting relative pivotal movement between the components about a single axis. 4. A linkage mechanism according to any preceding claim, wherein the pivotal element is an elongate transverse member mounted on an axially displaceable rod, the pivotal element being pivotably mounted on one component at one of its ends and defining a slot at its other end which receives a pin mounted on the said one component. 5. A linkage mechanism according to claim 4, wherein the elongate transverse member is retained on the pivot and on the pin by washers secured against the ends of the pivot and pin. 6. A linkage mechanism substantially as hereinbefore described with reference to the accompanying drawing.

Inventors: FRANKLIN PHILIP C, FRANKLIN, PHILIP, C.
Applicants: FRANKLIN PHILIP C, HOLSET ENGINEERING CO, FRANKLIN, PHILIP, C., HOLSET ENGINEERING CO. LTD.
Application year: 1998
Main classification: F01D17
IPC codes: F01D17