WO2008139130A1

WO2008139130A1 - Variable geometry turbine

Info

Publication number: WO2008139130A1
Application number: PCT/GB2008/000996
Authority: WO
Inventors: Stephen Garrett
Original assignee: Cummins Turbo Technologies Limited
Priority date: 2007-05-10
Filing date: 2008-03-20
Publication date: 2008-11-20
Also published as: GB2461216A; GB0919127D0; GB2461216B; GB0708975D0

Abstract

A turbocharger has a variable geometry turbine (1) of the swing vane kind. The vanes (24) are pivotally mounted on a vane carrier (23) and extend into an annular passageway (13) defined between a first surface (21) of the vane carrier and the turbine housing or the bearing housing. The carrier has a second surface (28) that is connected to a supporting wall (30) of the bearing housing (3) or the turbine housing (4) by means of a plurality of substantially radially extending key connections (41,43). These resist the rotational force applied to the carrier by the passage of the exhaust gas over the vanes and also permit thermal expansion of the vane carrier (23) relative to the supporting wall.

Description

VARIABLE GEOMETRY TURBINE

The present invention relates to a variable geometry turbine and a turbocharger incorporating the same for use with an internal combustion engine.

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 to in line with varying engine demands.

One common form of variable geometry turbine is the "swing vane" type. This comprises an array of moveable vanes concentrically disposed around the turbine wheel and pivotally supported on an annular vane carrier in the turbine inlet passageway. Each vane is 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. The redirection of the gas by the vanes means that an aerodynamic load is applied to each vane and the cumulative effect is to impart a rotational force on the vane carrier. In view of this the carrier is generally fixed relative to the turbine or bearing housings by means of pins or bolts interspersed with the vanes. One of the problems with such an arrangement is differential thermal expansion of the various components that leads to thermal stresses and distortions and ultimately cracking of the components and, on occasions, jamming or binding of the swing vane mechanism. In particular, the vanes and one side of the carrier are disposed directly in the hot exhaust gas flow of a turbocharger whilst the supporting structure is shielded from it. Moreover, the bearing housing is generally cooled by oil (and, in some applications, by water). These factors and differences in thermal inertia of the components (primarily owing to the different masses of the components) lead to different thermal responses.

The use of variable geometry turbines in turbochargers became particularly important when the general thrust of turbine development was to maximise turbine efficiency; either to extract the maximum boost pressure from the exhaust gas pressure available, or to achieve a required boost pressure for a minimum exhaust manifold back pressure. In more recent times, such turbines have been modified to reduce their efficiency in certain circumstances so as to render them suitable for use in turbochargers intended for internal combustion engines having exhaust gas recirculation systems. The variable geometry turbine efficiency reduction is used to increase the back pressure to drive a recirculation of exhaust gas to the engine intake thereby reducing emissions.

It is one object of the present invention to obviate or mitigate the aforementioned disadvantages. It is another object to provide for an improved variable geometry turbine in general.

According to a first aspect of the present invention there is provided a variable geometry turbine comprising: a turbine housing defining a turbine chamber within which a turbine wheel is mounted for rotation about a turbine axis; the turbine chamber having a substantially radially extending annular inlet disposed radially outboard of said turbine wheel; an annular swing vane carrier disposed adjacent to the annular inlet and having a wall with first and second surfaces, one side of the annular inlet being defined by a first surface of said carrier wall, an array of swing vanes mounted on the carrier such that they are pivotable within the inlet; each vane being arranged to pivot about a respective pivot axis extending across the inlet to adjust the effective cross-section area of the annular inlet; wherein the second surface of said carrier has a plurality of substantially radially extending keys or keyways.

According to a second aspect of the present invention there is provided a turbocharger comprising a variable geometry turbine as defined above and a bearing housing, the swing vane carrier being connected to a wall of either the bearing housing or the turbine housing by means of a plurality of substantially radially extending key connections.

The keys may be integrally formed in the bearing or turbine housing for engagement with keyways in the carrier or, alternatively, they may be integrally formed in the carrier for engagement with keyways in the bearing or turbine housing.

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 turbocharger with a swing vane variable geometry turbine in accordance with one embodiment of the present invention;

Figure 2 is a schematic exploded perspective of the swing vane mechanism of the variable geometry turbine of figure 1;

Figure 3 is a schematic rear view of a nozzle carrier of the mechanism of figure 2;

Figure 4 is a partial front view of the nozzle carrier with vanes fitted;

Figure 5 is a partial rear view of a nozzle carrier of the mechanism illustrating a modification to the version shown in figure 3; and Figures 6a-6b are schematic representations illustrating different keyway designs for connecting the nozzle carrier.

The exemplary turbocharger of figure 1 comprises a turbine 1 joined to a compressor 2 via a central bearing housing 3. The turbine 1 comprises a turbine housing 4 that houses a turbine wheel 5 rotatable about an axis. Similarly, the compressor 2 comprises a compressor housing 6 that houses a compressor wheel 7. The turbine wheel 5 and compressor wheel 7 are mounted on opposite ends of a common turbocharger shaft 8 which is supported on bearing assemblies 9 within the bearing housing 3.

The turbine housing 4 is provided with an exhaust gas inlet (hidden in figure 1) and an exhaust gas outlet 11. The inlet directs incoming exhaust gas to an annular inlet chamber, i.e. volute 12, surrounding the turbine wheel 5 and communicating therewith via a radially extending annular inlet passageway 13. Rotation of the turbine wheel 5 rotates the compressor wheel 7 which draws in air through an axial inlet 14 and delivers compressed air to the engine intake (not shown) via an annular outlet volute 15. Exhaust gases flow to the turbine wheel 5 from the inlet volute 12 via the inlet passageway 13

The inlet passageway 13 is defined between facing annular walls 20, 21, one of which is provided by the turbine housing 4 and the other 21 by part of a nozzle ring assembly 22 disposed partly in the turbine housing 4 around the turbine wheel 5 and partly in the bearing housing 3, the walls 20, 21 extending in a plane normal to the turbine axis. The nozzle ring assembly 22 is used to redirect gas flow towards the turbine wheel 5 and to vary the size of the inlet passageway 13 by changing the cross- sectional area available for the incoming gas. As illustrated in figures 1 to 4, the assembly comprises an annular nozzle vane carrier 23 that supports an annular array of pivotal nozzle vanes 24. Each of the vanes 24 is formed with a respective integral vane axle 25 that projects through a corresponding bore 26 in the wall of the carrier 23 and is pivotal therein. An actuator mechanism 26a is coupled to the vane 24 so as to control its rotation on the axle 25. The mechanism will typically comprise a ring, referred to as a unison ring, rotation of which, via a crank arm A, controls pivoting of all vanes simultaneously. Movement of the unison ring may be controlled by various forms of actuator, including pneumatic and electric actuators. Such details, which are not relevant to an understanding of the present invention, will be well known to the skilled person and will not be described. The vanes 24 are pivotal between a substantially closed position (represented in dotted line in figure 4) in which the cross sectional area of the annular passage is significantly reduced so as to restrict the flow of exhaust gas, and a fully open position (shown in solid line in figure 4) in which the cross sectional area is a maximum.

The nozzle vane carrier 23 is fixed to a wall 27 of the bearing housing 3 by a key arrangement shown in figures 2 and 3. The carrier 23 is in the form of an annular wall having a front surface that defines the wall 21 from which the vanes extend into the passageway 13, a rear surface 28 that faces the bearing housing 3 and a central circular opening 29 that is designed to locate over a projecting boss 30 on the bearing housing wall 26, the boss being configured to support the turbine wheel 5 in rotation. The front surface 27 of the carrier effectively forms one of the walls of the annular passageway 13 with the other being provided, in this instance, by a wall 31 of the turbine housing. The turbocharger shaft 8 passes through a central aperture 32 in the boss and into the bearing housing 3. Immediately surrounding the boss 30 there is a shallow annular projection 40 with three equi-angularly spaced, radially extending keyway slots 41. Three keys 42 of complementary cross section are designed to be received in these slots 41 and corresponding recessed keyway slots 43 provided in an annular projection 44 on the rear surface 28 of the carrier as shown in figure 3, thus fixing the nozzle carrier 23 to the bearing housing 3. It is to be appreciated that any other suitable number of keys and keyways may be used. Only two keys (and two sets of keyways) are theoretically required to ensure that the carrier is centrally disposed but it is envisaged that three or four key connections would be most practical and cost efficient. The keys 42 are shorts lengths of hard material typically of square or rectangular cross section. They fit precisely in the complementary keyway slots 41, 43 in both the bearing housing 3 and the nozzle carrier 23. In one embodiment the keyway slots 41 may be provided on a separate component that is fixed to the bearing housing 3. It is to be understood that the carrier 22 may be fixed to the turbine housing 4 instead of the bearing housing 3 in which case the keyway slots 41 are provided on the turbine housing 4 or a component fixed thereto. The radial direction of the key connections renders them able to resist the rotational forces applied to the carrier 22 without resisting its thermal expansion in a radial direction.

The nozzle vane arrangement is assembled by mounting the vanes 24 on to the carrier 23 and inserting the keys 42 into slots 41. The keyway slots 43 in the nozzle carrier 22 are then aligned with those in the bearing housing 3 so that the keys 41 can be forced into the slots in an axial direction.

The key connection arrangement provides an unrestrained fixing that rigidly attaches the carrier to the supporting structure so as to position the vanes concentrically around the turbine wheel axis as is conventional, but allows the carrier and vanes to expand and contract freely relative to the support.

An alternative keyway slot configuration for the bearing housing is illustrated in figure 4. In this modification the radially outer end of the slots 143 on the carrier 122 are closed so as to prevent the keys from falling out of the slots in a radial direction.

It is to be understood that an inner end of the slots in the bearing housing may also be closed. In practice any arrangement can be adopted that ensures the keys are prevented from escaping radially in either direction can be used.

In use, the gas flow to the turbine can be optimised for instantaneous operating conditions via appropriate adjustment of the positioning of the vanes 24 as is well known.

It will be appreciated the numerous modifications or variations to the particular embodiments of the invention described may be made without departing from the scope of the present invention as defined in the appended claims. For example, the shallow annular projection 40 on the bearing housing could be replaced by a planar annular surface. The keyways 41 could be defined by any appropriate formation such as, for example, those depicted in figures 6a to 6c. In figure 6a the keyway is a radial slot 41a milled into the bearing housing wall. In the embodiment of figure 6b the radial slot 41b is formed in a raised boss 60 and in figure 6c the radial slot 41c is formed between a pair of parallel ribs 61. Of course, it will be understood that such keyway designs could also be adopted on the nozzle carrier 22.

Claims

1. A variable geometry turbine comprising: a turbine housing defining a turbine chamber within which a turbine wheel is mounted for rotation about a turbine axis; the turbine chamber having a substantially radially extending annular inlet disposed radially outboard of said turbine wheel; an annular swing vane carrier disposed adjacent to the annular inlet and having a wall with first and second surfaces, one side of the annular inlet being defined by a first surface of said carrier wall, an array of swing vanes mounted on the carrier such that they are pivotable within the inlet; each vane being arranged to pivot about a respective pivot axis extending across the inlet to adjust the effective cross-section area of the annular inlet, wherein the second surface of said carrier has a plurality of substantially radially extending keys or keyways.

2. A variable geometry turbine according to claim 1, wherein the second surface of the vane carrier has a plurality of radially extending keyways.

3. A variable geometry turbine according to claim 2, wherein the keyways are defined in an annular projection on the second surface of the carrier.

4. A variable geometry turbine according to claim 3, wherein at least one of the keyways is closed at its radially outermost end.

5. A variable geometry turbine according to any one of claims 1 to 4, wherein the keys or keyways are provided at a position radially inboard of the swing vanes.

6. A variable geometry turbine according to claim 1, wherein the second surface defines a plurality of integrally formed keys.

. A variable geometry turbine according to any preceding claim, wherein the first and second surfaces are opposed.

8. A turbocharger comprising a variable geometry turbine according to any preceding claim and a bearing housing, the swing vane carrier being connected to a supporting wall of either the bearing housing or the turbine housing by means of a plurality of substantially radially extending key connections.

9. A turbocharger according to claim 8, wherein the supporting wall is defined on the bearing housing

10. A turbocharger according to claim 8, wherein the supporting wall is defined on the turbine housing.

11. A turbocharger according to any one of claims 8 to 10, wherein the key connections comprise a plurality of keyways defined in the supporting wall and/or the second surface of the vane carrier.

12. A turbocharger according to claim 11, wherein the keyways are defined in an annular projection.

13. A turbocharger according to any one of claims 8 to 12, wherein there is provided means for pivoting each vane about a respective pivot axis extending across the inlet to adjust the effective cross-section area of the annular inlet, each vane being pivotable 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.