WO2011042695A2

WO2011042695A2 - Turbomachine

Info

Publication number: WO2011042695A2
Application number: PCT/GB2010/001869
Authority: WO
Inventors: Tom J. Roberts; John F. Parker; Simon Moore
Original assignee: Cummins Ltd
Priority date: 2009-10-06
Filing date: 2010-10-06
Publication date: 2011-04-14
Also published as: EP2486245A2; IN2012DN02723A; BR112012007831A2; CN102667071A; WO2011042695A3

Abstract

According to a first aspect of the present invention there is provided a variable geometry turbine comprising: a turbine wheel mounted for rotation about a turbine axis within a housing, the housing defining an annular inlet surrounding the turbine wheel and defined between first and second inlet sidewalls, the annular inlet being divided into at least two axially offset inlet portions; a cylindrical sleeve axially movable across the annular inlet to vary the size of a gas flow path through the inlet; wherein an axial extent of a leading end of the sleeve varies in magnitude around a circumference of the sleeve. The variation in the axial extent defines a plurality of recesses and/or protrusions located around the circumference of the leading end of the sleeve. The sleeve, or the axial extent thereof, is free of vanes.

Description

TURBOMACHINE

The present invention relates to a turbine suitable for, but not limited to, use in turbochargers and variable geometry turbochargers.

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 a housing in which is provided an exhaust gas driven turbine wheel mounted on a rotatable shaft connected downstream of an engine outlet manifold. A compressor impeller wheel is mounted on the opposite end of the shaft such that rotation of the turbine wheel drives rotation of the impeller wheel. In this application of a compressor, the impeller wheel delivers compressed air to the engine intake manifold. A power turbine also comprises an exhaust gas driven turbine wheel mounted on a shaft, but in this case the other end of the shaft is not connected to a compressor. For instance, in a turbocompound engine, two turbines are provided in series, both driven by the exhaust gases of the engine. One turbine drives a compressor to deliver pressurised air to the engine and the other, the "power turbine", generates additional power which is then transmitted to other components via a mechanical connection, such as a gear wheel to transmit power to the engine crankshaft, or via other types of connection, for instance a hydraulic or electrical connection.

It is an object of the present invention to obviate or mitigate one or more of the problems associated with existing turbines.

According to a first aspect of the present invention there is provided a variable geometry turbine comprising: a turbine wheel mounted for rotation about a turbine axis within a housing, the housing defining an annular inlet surrounding the turbine wheel and defined between first and second inlet sidewalls, the annular inlet being divided into at least two axially offset inlet portions; a cylindrical sleeve axially movable across the annular inlet to vary the size of a gas flow path through the inlet; wherein an axial extent of a leading end of the sleeve varies in magnitude around a circumference of the sleeve. The variation in the axial extent defines a plurality of recesses and/or protrusions located around the circumference of the leading end of the sleeve. The sleeve, or the axial extent thereof, is free of vanes. A maximum in the variation in magnitude of the axial extent may be substantially equal to: an axial width of an inlet portion; or an axial width of an inlet portion plus an axial width of a baffle that divides the inlet; or an axial width of an inlet passage through an inlet portion.

The variation in the axial extent is such that an area defined by recesses in, or between protrusions of, the leading end of the sleeve is substantially equal to an area of an opening of an inlet portion, or of openings through inlet passages formed in those inlet portions.

An inlet portion may comprise one or more vanes or other structures dividing the inlet portion into one or more inlet passages, and wherein the variation in magnitude of the axial extent in the circumferential direction is synchronised with a location of the one or more vanes or other structures, or a spacing between the one or more vanes or other structures.

A thickness of the sleeve, in the radial direction, may be less than an axial width of the annular inlet, or less than an axial width of an inlet portion or inlet passages formed in that inlet portion.

An inner diameter of the sleeve may be greater than an outer diameter, or outer radial extent, of the inlet portions.

The axial extent of the leading end of the sleeve may vary in: a castellated manner; and/or a wave-like manner. The variation may be periodic.

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 conventional turbocharger;

Figure 2 is an axial cross-section through a turbine volute and annular inlet of a turbine according to an embodiment of the present invention; Figures 3a to 3c each schematically depict a side-on view of different embodiments of a leading end of an axially moveable sleeve;

Figure 4 is a schematic side-on view of the leading end of an axially moveable sleeve according to another embodiment of the present invention; and

Figure 5 is a schematic side-on view of the leading end of an axially moveable sleeve according to a still further embodiment of the present invention.

Referring to Figure 1 , the turbocharger comprises a turbine 1 joined to a compressor 2 via a central bearing housing 3. The turbine 1 comprises a turbine wheel 4 for rotation within a turbine housing 5. Similarly, the compressor 2 comprises a compressor wheel 6 which can rotate within a compressor housing 7. The turbine wheel 4 and compressor wheel 6 are mounted on opposite ends of a common turbocharger shaft 8 which extends through the central bearing housing 3.

The turbine housing 5 has an exhaust gas inlet volute 9 located annularly around the turbine wheel 4 and an axial exhaust gas outlet 10. The compressor housing 7 has an axial air intake passage 1 1 and a compressed air outlet volute 12 arranged annularly around the compressor wheel 6. The turbocharger shaft 8 rotates on journal bearings 13 and 14 housed towards the turbine end and compressor end respectively of the bearing housing 3. The compressor end bearing 14 further includes a thrust bearing 15 which interacts with an oil seal assembly including an oil slinger 16. Oil is supplied to the bearing housing from the oil system of the internal combustion engine via oil inlet 17 and is fed to the bearing assemblies by oil passageways 18.

In use, the turbine wheel 4 is rotated by the passage of exhaust gas from the annular exhaust gas inlet 9 to the exhaust gas outlet 10, which in turn rotates the compressor wheel 6 which thereby draws intake air through the compressor inlet 1 1 and delivers boost air to the intake of an internal combustion engine (not shown) via the compressor outlet volute 12.

In Figure 2 there is shown a turbine volute 20 and an annular inlet 21 of a turbine 22 according to an embodiment of the present invention. Equiaxially spaced across the inlet 21 are two annular baffles 23a, 23b which, together with inner and outer sidewalls 24, 25 of the inlet, define three axially offset annular inlet portions 26a, 26b, 26c of equal axial width. Extending axially across each of the three inlet portions 26a, 26b, 26c are respective annular arrays of vanes 27a, 27b, 27c. The vanes 27a, 27b, 27c are optional, and in other embodiments may not be present in all inlet portions 26a, 26b, 26c. The vanes 27a, 27b, 27c divide each respective inlet portion 26a, 26b, 26c to form inlet passages in each inlet portion 26a, 26b, 26c. A cylindrical sleeve 28 is provided that is axially movable across the annular inlet 21 to vary the size of a gas flow path through the inlet 21 (i.e. to vary the geometry of the turbine). Movement of the cylindrical sleeve 28 may be undertaken, for example, to close or at least partially close, or open, or at least partially open, one or more of the inlet portions 26a, 26b, 26c.

The turbine 22 is also shown as comprising a turbine wheel 29 mounted on a turbine shaft 30 for rotation about a turbine axis.

Although not visible in Figure 2, an axial extent of a leading end (which includes a leading edge or face) of the sleeve 28 varies in magnitude around a circumference of the sleeve 28. Figures 3a to 3c depict different examples of such variation.

Figure 3a shows an embodiment of a sleeve 40. The axial extent of a leading end 42 of the sleeve 40 varies in magnitude around a circumference of the sleeve 40. The variation has a castellated configuration. The castellation might alternatively or additionally be described as axial variation in a square-wave like manner.

Figure 3b shows another embodiment of a sleeve 50. The axial extent of a leading end 52 of the sleeve 50 varies in magnitude around a circumference of the sleeve 50. The variation has a castellated-like configuration. In this embodiment, the castellation is not strictly angular, but involves a degree of curvature of side and base edges of the castellation. The castellation might alternatively or additionally be described as axial variation in a wave like manner.

Figure 3c shows another embodiment of a sleeve 60. The axial extent of a leading end 62 of the sleeve 60 varies in magnitude around a circumference of the sleeve 60. The variation has a wave-like property, for example varying in a sinusoidal manner. Because the axial extent of a leading end of the sleeve varies in magnitude around a circumference of the sleeve, the opening or closing of the inlet portions is not undertaken in a harsh step-wise manner, as might be the case if the axial extent exhibited no variation. This might result in associated or related step-wise characteristic in the performance of the turbine as a whole. Instead, the axial variation ensures that the opening or closing of the inlet portions is undertaken more gradually, which obviates or mitigates such a step-wise characteristic.

Referring to Figures 3a to 3c, a maximum 70 in the variation in magnitude of the axial extent may be substantially equal to: an axial width of an inlet portion; or an axial width of an inlet portion plus an axial width of a baffle that divides the inlet; or an axial width of an inlet passage through an inlet portion. This may facilitate a smooth change or transition in gas flow through the inlet portion as the sleeve is axially moved.

An inlet portion may comprise one or more vanes or other structures dividing the inlet portion into one or more inlet passages. The variation in magnitude of the axial extent in the circumferential direction (e.g. a pitch or wavelength 72) may be synchronised in some way with a location of the one or more vanes or other structures, or a spacing between the one or more vanes or other structures. The synchronisation may extend or continue around the circumference of the sleeve. For example, the synchronisation may be such that the variation in magnitude is in phase with the location of the vanes or other structures. Alternatively or additionally, an area defined between a maximum and minimum axial extent may be equal to an area defined between vanes or other structures in the vicinity of the variation. In other words, an area defined by recesses (or in other words between protrusions) of the leading end of the sleeve may be equal to an area of the opening or opening of inlet portions or inlet passages through those inlet portions. This may ensure that when a leading edge of the leading end of the sleeve is aligned with a baffle that divides the inlet, gas flow through an inlet portion which the sleeve has partially closed is optimised. The synchronisation may be used in combination with the concept described above relating to the maximum in the variation in magnitude of the axial extent.

Referring to figure 4, there is shown another embodiment of a sleeve 80 incorporating cut out areas A and B, only two of which are visible in figure 4. The total area of the cut out sections A and B has been designed to be substantially equal to the area of the throat defined by the vanes located radially inboard of the sleeve (not shown in figure 4). In this way, the axial location of the sleeve primarily controls the flow of gas through the turbine inlet rather than the vane throat. The axial depth of each area A is substantially equal to the distance between adjacent baffles within the turbine inlet. The purpose of each area B is to filter out or reduce the undesirable effect the baffle as far as possible by allowing more circumferential area to be exposed to the gas flow at the point at which area A starts to be concealed by a baffle, for this reason the axial depth of area B is equal to the axial thickness of each baffle.

Alignment of a single vane throat area with a radially overlying cut-away section of the sleeve may only be important if the number of cutaways is effectively equal to the number of vanes. It will be appreciated that this does not necessarily need to be the case in all embodiments. In alternative embodiments, more cutaways may be desired for example. In this case, the same basic theory can be applied, i.e. the total flow area defined by the sleeve cut-aways should be substantially similar or equal to the total flow area defined by the combination of all of the vane throats. The shape of the profile of the end of the sleeve defined by one or more cut-away sections can be tailored to meet a specific requirement. For example, a sleeve may be provided with a saw tooth, sinusoidal or semicircular prolife.

Referring to figure 5, a sleeve 90 with semicircular cut-aways 92 may be particularly desirable because semicircular cut-aways offer a good compromise between flow characteristic and design for manufacture. A semicircle profile can be machined relatively easily in comparison to some more complex profiles, but still offers a circumferential increase in flow area with respect to axial position, to filter out the baffle.

It is advantageous in certain embodiments for the axial depth of the cut-away sections of the sleeve to be substantially equal to the spacing between adjacent baffles within teh turbine inlet (including the width of one baffle). In such embodiments, it may also be advantageous that at least one or more, more preferably most, or all, of the baffles should have substantially equal axial spacing.

In some embodiments the cut-away sections at the end of the sleeve need not all be the same shape, size or have equal spacing, however it is generally preferred that their combined cross-sectional area relative to gas flow through the turbine inlet should be substantially equal to the cross-sectional area of the throat area of at least one annular array of inlet gas passages defined by the vanes.

The invention may be alternatively or additionally described or defined in many as will now be discussed. An axial extent of a leading end of the sleeve varies in magnitude around a circumference of the sleeve. This results in a plurality of recesses and/or protrusions being defined around the circumference of the leading end of the sleeve. The recesses (which may be defined as spaces between protrusions) extend through the entire thickness or the sleeve. The recesses and/or protrusions are present to, upon movement of the sleeve, selectively block or expose (e.g. close or open) inlet portions, or inlet passages provided in those portions by other structures.

It will be apparent that the sleeve is free of vanes. It is known in the prior art to provide a sleeve with vanes, for example to affect the angle of attack of gas flowing past the vanes. However, it is important to note that such a prior art sleeve is cylindrical, and this cylinder is then provided with vanes. In other words, an axial extent of a leading end of the prior art sleeve does not vary in magnitude around a circumference of the sleeve. In this prior art sleeve, a plurality of recesses and/or protrusions are not defined around the circumference of the leading end of the sleeve. Instead, vanes protrude from a circular face of that sleeve.

In another prior art sleeve, a leading portion (i.e. not end) of the sleeve extends further in an axial direction that another, adjacent portion (e.g. an outer diameter portion) to accommodate a vane structure upon appropriate movement of the sleeve. However, and again, an axial extent of a leading end of the prior art sleeve does not vary in magnitude around a circumference of the sleeve. Instead, the axial extent defines a circular structure. In this prior art sleeve, a plurality of recesses and/or protrusions are not defined around the circumference of the leading end of the sleeve.

Preferentially, the sleeve surrounds the inlet portions, which has been found to give an improved aerodynamic performance. In other words, the inner diameter of the sleeve is greater than an outer diameter (or outer radial extent) of the inlet portion or portions. In another embodiment, the sleeve may be surrounded by the inlet portions. In other words, the outer diameter of the sleeve may be less than inner diameter of the inlet portion or portions. In another embodiment, the sleeve may be moveable through the inlet portion or portions. In other words, the diameter (e.g. inner or outer, or average diameter) of the sleeve may be less than an outer diameter of the inlet portion or portions, and greater than an inner diameter of the inlet portion or portions. The extent of the sleeve in the radial direction (which may be described as a thickness of the sleeve) may be small, to reduce aerodynamic load on the sleeve, or actuators thereof. 'Small', may be defined as being less than an axial width of the annular inlet, or less than an axial width of an inlet portion or passage way. The sleeve may be less than 5mm thick, less than 4mm thick, less than 3mm thick, less than 2mm thick, or less than 1 mm thick, for example approximately 0.5mm thick.

Typically, exhaust gas flows to the annular inlet from a surrounding volute or chamber. The annular inlet is therefore defined downstream of the volute, with the downstream end of the volute terminating at the upstream end of the annular inlet. As such, the volute transmits the gas to the annular inlet, while the gas inlet passages or portions of the present invention receive gas from the volute. In some embodiments, the first and second inlet sidewalls which define the annular inlet are continuations of walls which define the volute. The annular inlet may be divided into at least two axially offset inlet passages or portions by one or more baffles located in the annular inlet, and which are therefore positioned downstream of the volute.

The turbine of the present invention has been illustrated in the Figures using a single flow volute, however it is applicable to housings that are split axially, whereby gas from one or more of the cylinders of an engine is directed to one of the divided volutes, and gas from one or more of the other cylinders is directed to a different volute. It is also possible to split a turbine housing circumferentially to provide multiple circumferentially divided volutes, or even to split the turbine housing both circumferentially and axially. It should be appreciated, however, that an axially or circumferentially divided volute is distinguished from the multiple gas inlet passages or portions present in the turbine of the present invention. For example, the gas inlet passages or portions relate to a nozzle structure arranged to accelerate exhaust gas received from the volute towards the turbine, and optionally to adjust or control the swirl angle of the gas as it accelerates. The multiple gas inlet passages or portions forming part of the present invention may be further distinguished from a divided volute arrangement in that, while the gas inlet passages or portions receive gas from the volute (or divided volute), and split the gas into an array of paths directed on to the turbine, a divided volute receives gas from the exhaust manifold so as to retain the gas velocity in gas pulses resulting from individual engine cylinder opening events. It will be appreciated that axially offset inlet passages or portions include inlet passages or portions with different axial positions and/or inlet passages with different axial extents. Axially offset inlet passages or portions may be spaced apart, adjacent or axially overlapping.

Claims

1. A variable geometry turbine comprising:

a turbine wheel mounted for rotation about a turbine axis within a housing, the housing defining an annular inlet surrounding the turbine wheel and defined between first and second inlet sidewalls, the annular inlet being divided into at least two axially offset inlet portions;

a cylindrical sleeve axially movable across the annular inlet to vary the size of a gas flow path through the inlet;

wherein an axial extent of a leading end of the sleeve varies in magnitude around a circumference of the sleeve.

2. The variable geometry turbine of claim 1 , wherein the variation in the axial extent defines a plurality of recesses and/or protrusions located around the circumference of the leading end of the sleeve.

3. The variable geometry turbine of claim 1 or claim 2, wherein the sleeve, or the axial extent thereof, is free of vanes.

4. The variable geometry turbine of any preceding claim, wherein a maximum in the variation in magnitude of the axial extent is substantially equal to:

an axial width of an inlet portion; or

an axial width of an inlet portion plus an axial width of a baffle that divides the inlet; or

an axial width of an inlet passage through an inlet portion.

5. The variable geometry turbine of any preceding claim, wherein the variation in the axial extent is such that an area defined by recesses in, or between protrusions of, the leading end of the sleeve is equal to an area of an opening of an inlet portion, or of openings through inlet passages formed in those inlet portions.

6. The variable geometry turbine of any preceding claim, wherein an inlet portion comprises one or more vanes or other structures dividing the inlet portion into one or more inlet passages, and wherein the variation in magnitude of the axial extent in the circumferential direction is synchronised with a location of the one or more vanes or other structures, or a spacing between the one or more vanes or other structures.

7. The variable geometry turbine of any preceding claim, wherein a thickness of the sleeve, in the radial direction, is less than an axial width of the annular inlet, or less than an axial width of an inlet portion or inlet passage formed in that inlet portion.

8. The variable geometry turbine of any preceding claim, wherein an inner diameter of the sleeve is greater than an outer diameter, or outer radial extent, of the inlet portions.

9. The variable geometry turbine of any preceding claim, wherein the axial extent of the leading end of the sleeve varies in:

a castellated manner; and/or

a wave-like manner.