GB2516688A - Turbine - Google Patents

Abstract

A turbine 1b for a turbocharger or power turbine comprises a turbine housing 5b, having an inlet for receiving exhaust gas from an engine, an outlet, a turbine chamber, and a turbine wheel 4b within the turbine chamber 20a for rotation about an axis. The inlet comprises first and second separate flow passages 22a, 24a which meet to define a substantially annular inlet passageway. The double flow turbine is configured to define first and second separate flow passages which meet to define a substantially annular inlet passageway, the passages forming unequal angles about the turbine wheel axis; or may be configured such that the mass flow of exhaust gases from each portion 28a, 30a of the inlet passageway towards the turbine wheel is unequal to each other. An additional aspect is also disclosed where each separate flow passage directs gas flow onto a separate portion of an array of adjustable vanes, where the first portion of the vanes has a different configuration to the second portion. The apparatus is beneficial where an EGR system is fitted so as to control the pressure differential across the EGR system.

Description

Turbine The present invention relates to a turbine. The turbine may form part of a turbocharger or power turbine. A turbocharger including a turbine according to the present invention may form part of an internal combustion engine.

Turbomachines are machines that transfer energy between a rotor and a fluid. For example, a turbomachine may transfer energy from a fluid to a rotor or may transfer energy from a rotor to a fluid. Two examples of turbomachines are a power turbine, which uses the rotational energy of the rotor to do useful work, for example, generating electrical power; and a turbocharger, which uses the rotational energy of the rotor to compress a fluid.

Turbochargers are well known devices for supplying air to an inlet 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 an engine inlet 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 of a conventional turbocharger comprises: a turbine chamber within which the turbine wheel is mounted; an inlet including an annular inlet passageway defined between facing radial walls arranged around the turbine chamber, and an inlet volute arranged around the annular 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 volute flows through the inlet to the outlet passageway via the turbine and rotates the turbine wheel. It is also known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet so as to deflect gas flowing through the inlet. That is, gas flowing through the annular inlet flows through inlet passages (defined between adjacent vanes) which induce swirl in the gas flow, turning the flow direction towards the direction of rotation of the turbine wheel.

Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that characteristics of the inlet (such as the inlet's size) 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 suit varying engine demands. For instance, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the inlet using a variable geometry mechanism. Turbochargers provided with a variable geometry turbine are referred to as variable geometry turbochargers.

Nozzle vane arrangements in variable geometry turbochargers can take different forms. Two known types of variable geometry turbine are swing vane turbochargers and sliding nozzle turbochargers.

Generally, in swing vane turbochargers the inlet size (or flow size) of a turbocharger turbine is controlled by an array of movable vanes in the turbine inlet. Each vane can pivot about an axis extending across the inlet parallel to the turbocharger shaft and aligned with a point approximately half way along the vane length. A vane actuating mechanism is provided which is linked to each of the vanes and is displaceable in a manner which causes each of the vanes to move in unison, such a movement enabling the cross sectional area available for the incoming gas and the angle of approach of the gas to the turbine wheel to be controlled.

Generally, in sliding nozzle turbochargers the vanes are fixed to an axially movable wall that slides across the inlet. The axially movable wall moves towards a facing shroud plate in order to close down the inlet and in so doing the vanes pass through apertures in the shroud plate. Alternatively, the nozzle ring is fixed to a wall of the turbine and a shroud plate is moved over the vanes to vary the size of the inlet.

The compressor of a conventional turbocharger comprises a compressor housing defining compressor chamber within which the compressor wheel is mounted such that it may rotate about an axis. The compressor also has a substantially axial inlet passageway defined by the compressor housing and a substantially annular outlet passageway defined by the compressor housing between facing radially extending walls arranged around the compressor chamber. A volute is arranged around the outlet passageway and an outlet is in flow communication with the volute. The passageways and compressor chamber communicate such that gas (for example, air) at a relatively low pressure is admitted to the inlet and is pumped, via the compressor chamber, outlet passageway and volute, to the outlet by rotation of the compressor wheel. The gas at the outlet is generally at a greater pressure (also referred to as boost pressure) than the relatively low pressure of the gas which is admitted to the inlet. The gas at the outlet may then be pumped downstream of the compressor outlet by the action of the compressor wheel.

Known types of turbine include double flow turbine and twin flow turbine. Double flow turbines and twin flow turbines have an inlet which includes two separate flow passages separated by a dividing wall. The two separate flow passages which define at least part of the volute meet at the generally annular inlet passageway. In the case of a twin flow turbine, the two separate flow passages meet at the generally annular inlet passageway such that each flow passage supplies a respective portion of the inlet passageway, the two respective portions being axially spaced from one another. In the case of a double flow turbine, the two separate flow passages meet at the generally annular inlet passageway such that each flow passage supplies a respective portion of the inlet passageway, the two respective portions being substantially in the same plane perpendicular to the axis, but being circumferentially separate (which may also be referred to as circumferentially segmented).

It is known to provide a turbocharger turbine with a valve controlled bypass port referred to as a wastegate, to enable control of the turbocharger boost pressure and/or shaft speed. A wastegate valve (typically a poppet type valve) is controlled to open the wastegate port (bypass port) when the boost pressure of the fluid in the compressor outlet increases towards a pre-determined level, thus allowing at least some of the exhaust gas to bypass the turbine wheel. Typically the wastegate port opens into a wastegate passage which diverts the bypass gas flow to the turbine outlet or vents it to atmosphere. The wastegate valve may be actuated by a variety of means, including electric actuators, but is more typically actuated by a pneumatic actuator operated by boost pressure delivered by the compressor wheel.

Some known internal combustion engines include Exhaust Gas Recirculation (EaR).

EGR is used to reduce nitrogen oxide (NOx) emissions of an internal combustion engine. EGR works by recirculating a portion of an exhaust gas produced by the internal combustion engine back to the engine cylinders, usually via the engine intake manifold. Recirculating a portion of the exhaust gas results in a reduction in temperature of the combustion which occurs in the engine cylinders. Because NOx production requires a mixture of nitrogen and oxygen (as found in the air) exposed to high temperatures, the lower combustion temperatures resulting from EGE reduces the amount of NOx generated by the combustion of the internal combustion engine. In some known internal combustion engines a variable geometry turbine (which forms part of a turbocharger) is used to increase the pressure (also known as back pressure) of the exhaust gas. This creates a pressure differential between the exhaust gas and the engine intake such that the exhaust gas will flow via an exhaust gas recirculation channel to the engine intake. However, the creation of back pressure by the variable geometry turbine can impair the operating performance of the internal combustion engine.

It is an object of the present invention to provide an alternative turbine. It is another object of the present invention to provide an alternative turbocharger or power turbine.

It is a further object of the present invention to provide an alternative internal combustion engine. A turbine, turbocharger, power turbine, or internal combustion engine according to the present invention may obviate or mitigate at least one disadvantage of prior art turbines, turbochargers, power turbines, or internal combustion engines respectively.

According to a first aspect of the present invention there is provided a turbine comprising a housing, the housing defining a turbine inlet for receiving exhaust gas from an engine, a turbine outlet and a turbine chamber between the turbine inlet and the turbine outlet; and a turbine wheel located within the turbine chamber and arranged for rotation about an axis; wherein the inlet comprises first and second separate flow passages which meet to define a substantially annular inlet passageway, the first flow passage forming a first portion of the substantially annular inlet passageway, and the second flow passage forming a second portion of the substantially annular inlet passageway; wherein the turbine is configured such that the mass flow of exhaust gas from the first portion of the inlet passageway towards the turbine wheel is substantially unequal to the mass flow of exhaust gas from the second portion of the inlet passageway towards the turbine wheel.

According to a second aspect of the invention there is provided a turbine comprising a housing, the housing defining a turbine inlet for receiving exhaust gas from an engine, a turbine outlet and a turbine chamber between the turbine inlet and the turbine outlet; and a turbine wheel located within the turbine chamber and arranged for rotation about an axis; wherein the inlet comprises first and second separate flow passages which meet to define a substantially annular inlet passageway, the first flow passage forming a first portion of the substantially annular inlet passageway which subtends a first angle about the axis, and the second flow passage forming a second portion of the substantially annular inlet passageway which subtends a second angle about the axis; and wherein the first angle and second angle are substantially unequal.

According to a third aspect of the invention there is provided a turbine comprising a housing, the housing defining a turbine inlet for receiving exhaust gas from an engine, a turbine outlet and a turbine chamber between the turbine inlet and the turbine outlet; and a turbine wheel located within the turbine chamber and arranged for rotation about an axis; wherein the inlet comprises first and second separate flow passages which meet to define a substantially annular inlet passageway; and the turbine further comprising a substantially annular array of vanes extending across the inlet passageway for directing gas flow towards the turbine wheel; wherein the first flow passage forms a first portion of the substantially annular inlet passageway which is configured to direct gas flow onto a first portion of the array of vanes, and the second flow passage forms a second portion of the substantially annular inlet passageway which is configured to direct gas flow onto a second portion of the array of vanes; and wherein the configuration of the vanes of the first portion of the array of vanes is substantially different to the configuration of the vanes of the second portion of the array of vanes.

The first portion of the substantially annular inlet passageway may be circumferentially offset about the axis from the second portion of the substantially annular inlet passageway.

The first portion of the substantially annular inlet passageway may be axially offset from the second portion of the substantially annular inlet passageway.

The configuration of the vanes of the first portion of the array of vanes may differ from the configuration of the vanes of the second portion of the array of vanes in that the circumferential spacing between the vanes of the first portion of the array is different to the circumferential spacing between the vanes of the second portion of the array.

The configuration of the vanes of the first portion of the array of vanes may differ from the configuration of the vanes of the second portion of the array of vanes such that the total throat area defined by the vanes of the first portion of the array of vanes differs from the total throat area defined by the vanes of the second portion of the array of vanes.

The configuration of the vanes of the first portion of the array of vanes may differ from the configuration of the vanes of the second portion of the array of vanes in that the throat area and/or throat width between adjacent vanes of the first portion of the array of vanes differs from the throat area and/or throat width between adjacent vanes of the second portion of the array of vanes.

The configuration of the vanes of the first portion of the array of vanes may differ from the configuration of the vanes of the second portion of the array of vanes in that the swirl angle of the vanes of the first portion of the array is different to the swirl angle of the vanes of the second portion of the array.

Each vane of the array of vanes may have a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the radial distance between the axis and the trailing edge of each of the vanes of the first portion of the array is less than the radial distance between the axis and the trailing edge of each of the vanes of the second portion of the array.

Each vane of the array of vanes may have a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the circumferential distance between the trailing edges of adjacent vanes of the first portion of the array is less than the circumferential distance between the trailing edges of adjacent vanes of the second portion of the array.

Each vane of the array of vanes may have a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the radial distance between the axis and the leading edge of each of the vanes of the first portion of the array is less than the radial distance between the axis and the leading edge of each of the vanes of the second portion of the array.

Each vane of the array of vanes may have a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the circumferential distance between the leading edges of adjacent vanes of the first portion of the array is less than the circumferential distance between the leading edges of adjacent vanes of the second portion of the array.

Each vane of the array of vanes may have a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the chord length between the leading and trailing edges of each of the vanes of the first portion of the array is less than the chord length between the leading and trailing edges of each of the vanes of the second portion of the array.

Each vane of the array of vanes may have a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that at least one of the following thicknesses: thickness of the leading edge, thickness of the trailing edge, and/or maximum circumferential thickness and thickness at a location half way along the chord between the leading edge and trailing edge, of each of the vanes of the first portion of the array is less than the equivalent thickness of each of the vanes of the second portion of the array.

The turbine may further comprise a variable geometry arrangement configured to selectively change at least one characteristic of the turbine inlet.

The inlet passageway may be defined between a first wall and a facing second wall, and wherein the variable geometry arrangement is configured to move the first wall relative to the second wall in a direction substantially parallel to the axis in order to vary the size of the inlet passageway.

According to a fourth aspect of the invention there is provided a turbocharger or power turbine comprising a turbine according to any of the preceding aspects.

According to a fifth aspect of the invention there is provided an internal combustion engine comprising a turbocharger having a turbine according to any of preceding aspects and a compressor configured to supply gas to an inlet manifold.

The internal combustion engine may further comprise an exhaust gas recirculation channel, the exhaust gas recirculation channel providing a flow conduit between one of the first and second flow passageways of the inlet and the inlet manifold.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross-section through a portion of a known turbocharger; Figure 2 shows a schematic cross-section through a portion of a known turbine; Figure 3 shows a schematic cross-section through a portion of a turbine according to an embodiment of the present invention; Figure 4 shows a schematic cross-section through a portion of another known turbine; Figure 5 shows a schematic cross-section through a portion of a turbine according to another embodiment of the present invention: Figure 6 shows a schematic cross-section through a portion of a turbine according to a further embodiment of the present invention; Figure 7 shows a schematic cross-section through a vane which forms part of a vane array in a turbine according to an embodiment of the present invention; and Figure 8 shows a schematic cross-section through a portion of a turbine according to a further embodiment of the present invention.

Figure 1 shows a schematic cross-section through a known turbocharger. 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 compressor housing 7 defines a compressor chamber within which the compressor wheel 6 can rotate. 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 11 and a volute 12 arranged annularly around the compressor chamber. The volute 12 is in gas flow communication with a compressor outlet 25. The turbocharger shaft 8 rotates about an axis A 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. The oil fed to the bearing assemblies may be used to both lubricate the bearing assemblies and to remove heat from the bearing assemblies.

In use, the turbine wheel 4 is rotated by the passage of exhaust gas from the exhaust gas inlet 9 to the exhaust gas outlet 10. Exhaust gas is provided to exhaust gas inlet 9 from an exhaust manifold (also referred to as an outlet manifold) of the engine (not shown) to which the turbocharger is attached. The turbine wheel 4 in turn rotates the compressor wheel 6 which thereby draws intake air through the compressor inlet 11 and delivers boost air to an inlet manifold of the engine via the volute 12 and then the outlet 25.

The exhaust gas inlet 9 is defined by a portion of the turbine housing 5 which includes a turbocharger mounting flange 27 at the end of the exhaust gas inlet 9 remote from the turbine wheel 4.

Figure 2 shows a cross-section through the turbine housing of a known turbocharger which is different to that shown in Figure 1. The turbine 1 a includes a housing 5a. The cross-section shown in Figure 2 is in a plane which is perpendicular to the turbocharger axis (not shown, also referred to as the turbine axis). That is to say, in the turbine according to an embodiment of the present invention shown in Figure 2, the turbocharger axis will be perpendicular to the plane of the Figure such that is passes directly into the plane of the Figure. The turbine housing 5a defines a turbine chamber within which the turbine wheel 4a is located. Within the Figure, detail of the turbine wheel is omitted but the outer circumference of the turbine wheel 4a is indicated by dashed lines 4b.

The turbine housing 5a of the turbine defines a volute having two separate flow passages 22 and 24 which are separated by a dividing wall 26. The two separate flow passages 22, 24 meet at a generally annular inlet passageway which is located radially outboard of the turbine wheel 4a. The turbine 1 a shown in Figure 2 is a double flow turbine because the two separate flow passages 22, 24 meet at the generally annular inlet passageway such that each flow passage supplies a respective portion of the inlet passageway, the two respective portions being substantially in the same plane perpendicular to the turbocharger axis, but being circumferentially separate. Within Figure 2, the first portion of the inlet passageway which is supplied by the first flow passage 22 is indicated by dotted line 28. The second portion of the inlet passageway, which is supplied by the second flow passage 24 is indicated generally by dashed line 30. The first portion 28 of the substantially annular inlet passageway is circumferentially offset about the axis from the second portion 30 of the substantially annular inlet passageway.

As previously discussed, it can be seen that the first portion of the annular inlet passageway (indicated generally by dotted line 28) is circumferentially separate from the second portion (indicated generally by dashed line 30) of the generally annular inlet passageway. It may also be said that the first portion and second portion of the inlet passageway are circumferentially unique. That is to say, at any point on the circumference around the turbocharger axis, there is located either the first portion of the inlet passageway or the second portion of the inlet passageway -i.e. there is no circumferential position at which both the first portion and second portion coexist.

Another way of referring to the first and second portions of the generally annular inlet passageway is that they are circumferentially segmented.

In the turbine shown in Figure 2, the first flow passage 22 is located generally radially outboard of the second flow passage 24. In other embodiments, this may be reversed.

The angular extent of the first and second portions 28, 30 of the inlet passageway are defined by the position of first and second tongues (32 and 34 respectively). The first tongue 32 is defined by the end of the dividing wall 26. The second tongue 34 is a portion of the turbine housing which divides the first flow passage 22 from the second flow passage 24 and is located at a position which is substantially circumferentially opposite the first tongue 32.

The turbine shown in Figure 2 is such that the first tongue 32 is substantially exactly circumferentially opposite to the second tongue 34. That is to say, there is a substantially straight line (dashed line 36) which passes through the first tongue 32, the second tongue 34 and the turbocharger axis. Another way of defining this is to say that the angle subtended between the first tongue 32 and the second tongue 34 about the turbocharger axis is substantially 180g. For this reason, the first portion 28 of the substantially annular inlet passageway subtends an angle about the turbocharger axis of about 180 and the second portion 30 of the generally annular inlet passageway subtends substantially the same angle (i.e. substantially 180°) as that of the first portion of inlet passageway. A further way of defining the nature of the double flow turbine shown in Figure 2, is that the circumference of the turbine wheel 4a which, in use, is exposed to exhaust gas which passes through the first flow passage 22 to the first portion of the generally annular inlet passageway is the same as the circumference of the turbine wheel which, in use, is exposed to exhaust gas which passes through the second flow passage 24 to the second portion 30 of the generally annular inlet passageway. This is a factor which results in the turbine shown in Figure 2 being referred to as a generally symmetric double flow turbine.

Figure 3 shows a schematic cross-section through a turbine lb according to an embodiment of the present invention. The turbine shown within Figure 3 is a double flow turbine which is similar to the double flow turbine shown in Figure 2. Again, the turbine lb comprises a housing Sb, the housing Sb defining a turbine inlet for receiving exhaust gas from an engine. The turbine includes a turbine outlet (not shown in Figure 3, but similar to that of the turbine of the known turbocharger shown in Figure 1) and a turbine chamber 20a between the turbine inlet and turbine outlet. A turbine wheel 4b (omitted within the Figure for clarity, but having an outer circumference indicated by dashed line 30a) which is located within the turbine chamber 20a and arranged for rotation about an axis which extends perpendicular to the plane of the Figure through point B. The turbine inlet comprises first and second separate flow passages 22a, 24a which meet to define a substantially annular inlet passageway. The first and second flow passages 22a, 24a are separated by a dividing wall 26a.

The first flow passage 22a forms a first portion (indicated generally by dotted line 28a) of the substantially annular inlet passageway and the second flow passage 24a forms a second portion (indicated generally by dashed line 30a) of the substantially annular inlet passageway. The first portion of the inlet passageway subtends a first angle C about the axis and the second portion of the inlet passageway subtends a second angle D about the axis.

Unlike the symmetric turbine shown in Figure 2, the first angle C and second angle D of the turbine shown in Figure 3 are substantially unequal. Consequently, the turbine lb shown in Figure 3 may be referred to an asymmetric double flow turbine. Because the turbine is asymmetric (i.e. because the angle subtended by the first portion of the inlet passageway and the angle subtended by the second portion of the inlet passageway are substantially unequal), the first tongue 32a and second tongue 34a are not substantially circumferentially opposite to one another. In addition, because the first angle C and second angle D are substantially unequal, the circumference of the turbine wheel 4b which, in use, is exposed to exhaust gas from the first inlet flow passage 22a is different (in this case less) than the circumference of the turbine wheel 4b which, in use, is exposed to exhaust gas from the second inlet flow passage 24a.

Figure 4 shows a schematic cross-section through a symmetric double flow turbine ic which is identical to the turbine la shown in Figure 2 except that the turbine ic includes a substantially annular array of vanes 40. The substantially annular array of vanes 40 includes a plurality of vanes (a number of which are indicated by 42a, 42b and 42c) which extend across the substantially annular inlet passageway. That is to say, the vanes extend generally in a direction which is generally parallel to the turbocharger axis such that the vanes (e.g. 42a, 42b and 42c) within the Figure extend in a direction perpendicular to the plane of the Figure. The vanes are configured to direct gas which flows through the first and second flow passages 22, 24 towards the turbine wheel 4a (which is omitted for clarity, but the outer circumference of which is indicated by dashed line 4b).

The array of vanes 40 is substantially uniform. That is to say, each of the vanes (e.g. 42a, 42b, 42c) which form part of the array of vanes 40 are substantially the same and the vanes are substantially uniformly spaced (e.g. circumferentially). The first flow passage 22 forms a first portion of the substantially annular inlet passageway which is configured to direct gas flow onto a first portion of the array of vanes 40. The first portion of the array of vanes is indicated generally by dotted line 44. The second flow passage 24 forms a second portion of the substantially annular inlet passageway which is configured to direct gas flow onto a second portion of the array of vanes 40. The second portion of the array of vanes 40 is indicated generally by dashed line 46. It can be seen that the configuration of the vanes of the first portion 44 of the array of vanes is the same as the configuration of the vanes of the second portion 46 of the array of vanes 40. The array of vanes 40 is rotationally symmetric about the turbocharger axis. The turbine shown in Figure 4 may be referred to symmetric double flow turbine.

Figure 5 shows a schematic cross-section through a turbine according to another embodiment of the present invention. The turbine ld shown in Figure 5 is substantially the same as the turbine shown in Figure 4 except that the substantially annular array of vanes 40a of the turbine shown in Figure 5 differs from the substantially annular array of vanes 40 shown in the turbine lc of Figure 4. In particular, the configuration of the vanes of the first portion 44a of the array of vanes 40a is substantially different to the configuration of the vanes of the second portion 46a of the array of vanes 40a. It will be appreciated that the dotted line 44a indicating the first portion of the array of vanes and the dashed line 46a indicated the second portion of the array of vanes are included to aid interpretation of the Figure and do not physically exist within the turbine itself.

In this embodiment the first portion of the substantially annular inlet passageway which is configured to direct gas flow onto the first portion of the array of vanes is circumferentially offset about the axis from the second portion of the substantially annular inlet passageway which is configured to direct gas flow onto the second portion of the array of vanes.

Because the configuration of the vanes of the first portion 44a of the array of vanes 40a differs from the configuration of the vanes of the second portion 46a of the array of vanes 40a, the total throat area defined by the vanes of the first portion 44a is different to the total throat area defined by the vanes of the second portion 46a. The total throat area is the minimum area, in a plane perpendicular to the direction of air flow, which air flows through as it passes through a portion the inlet passageway.

In the case of an inlet including vanes, the throat area between two adjacent vanes is usually the area between the vanes in a plane perpendicular to the flow direction of the air between the two vanes, the plane including the trailing edge of one of the vanes and a portion of the other of the vanes.

The throat area between two adjacent vanes may also be defined as the product of the axial height of the vanes within the inlet passageway and the throat width between the vanes. The throat width is the distance between the surface of one vane and the trailing edge of the other of the vanes in a direction perpendicular to the flow direction of the air between the two vanes.

For a number of vanes of the same configuration spaced from their adjacent vane(s) by the same throat width, the total throat area between the vanes will be given by the product of the throat area of a flow passage between two adjacent vanes and the number of flow passages between adjacent pairs of vanes. Normally the number of flow passages between adjacent pairs of vanes is one less than the number of vanes.

In the example shown in Figure 5, the configuration of the vanes of the first portion 44a of the array of vanes 40a differs from the configuration of the vanes of the second portion 46a of the array of vanes 40a in that the circumferential spacing between the vanes of the first portion 44a of the array is different to the circumferential spacing between the vanes of the second portion 46a of the array. In particular, the circumferential spacing between vanes in the first portion 44a of the array is greater than the circumferential spacing between the vanes of the second portion 46a of the array.

The different configuration of the vanes of the first portion of the array compared to the configuration of the vanes of the second portion of the array will give rise to the exhaust gas which, in use, passes through the first portion of the array having at least one different flow property to that of the gas which, in use, passes through the second portion of the array. For example, the speed of the gas which has passed through the first portion 44a of the array may have a slower speed than that of the gas which has passed through the second portion 46a of the array. Because at least one flow property of the gas which, in use, has passed through the first portion of the array is different to that of the gas which, in use, has passed through the second portion of the array, the turbine shown in Figure 5 may be said to be an asymmetric double flow turbine. That is to say, at least one flow property of the gas which, in use, is incident on the turbine wheel of the turbine is not uniform around the circumference of the turbine wheel. In other words, the exhaust gas which is incident on the turbine wheel in use has at least one flow property which is not rotationally symmetric about the turbocharger axis.

Figure 6 shows an alternative embodiment of turbine according to the present invention. In the turbine le shown in Figure 6, like the turbine id shown in Figure 5, the configuration of the vanes of the first portion 44b of the array 40b of vanes is substantially different to the configuration of the vanes of the second portion 46b of the array 40b of vanes. In the case shown in Figure 6, the vanes of the first portion 44b of the array and the vanes of the second portion 46b of the array are circumferentially spaced by the same amount. However, in this embodiment, the configuration of the vanes of the first portion of the array 44b differs from the configuration of the vanes of the second portion of the array 44b in that the swirl angle of the vanes of the first portion 44b of the array is different to the swirl angle of the vanes of the second portion 46b of the array. In particular, the swirl angle of the vanes of the first portion 40b of the array is greater than the swirl angle of the vanes of the second portion 46b of the array.

The swirl angle of gas which has passed the vanes at a particular point is generally defined as the angle subtended between the direction of gas flow at the particular point and a straight radial line (relative to the turbine axis) which passes through the particular point.

As previously discussed, because of the different configuration of the vanes of the first portion of the array compared to that of the vanes of the second portion of the array in the turbine shown in Figure 6, at least on flow property, in use, of the gas which has passed through the first portion of the array of vanes will be different to that of the gas which has passed through the second portion of the array of vanes. Consequently, the turbine shown in Figure 6 may also be said to be an asymmetric double flow turbine.

In Figure 5 and Figure 6 respectively, two different ways of producing an asymmetric turbine by having a first portion of the array of vanes which has a different configuration to that of a second portion of the array of vanes are shown. As previously discussed, it is the difference in configuration between the vanes of the first and second portions of the array which gives rise to the gas passing through these respective portions having at least one different flow property. It will be appreciated that, in order to produce this asymmetry, any appropriate difference in the configuration of the vanes of the first and second portions of the array of vanes may be used.

Figure 7 shows a schematic view of a single vane 50 which may form part of a turbine according to the present invention. The vane 50 is located in the annular inlet passageway and, in use, is supplied with exhaust gas travelling substantially in the direction indication by arrow E. The exhaust gas passes the vane 40 and is guided by the vane towards the turbine wheel, a portion of the outer circumference of which is indicated generally by the dashed line 52. The vane 50 has a leading edge 54 and a trailing edge 56. The leading edge 54 is the first edge of the vane 50 which, in use, comes into contact with the incoming exhaust gas F. The trailing edge 56 is the edge of the vane 50 which is last in contact with the exhaust gas as it passes the vane 50.

Consequently, in general, the trailing edge 56 is closer to the turbine wheel than the leading edge 54.

If the leading edge 54 and trailing edge 56 of the vane 50 are joined by a straight line, then this straight line is referred to as the chord of the vane. Within Figure 7, the chord is indicated as 58.

Further examples of ways in which the configuration of the vanes of the first portion of the array may differ from the configuration of the vanes of the second portion of the array so as to give rise to an asymmetric turbine are given below.

One example is that the radial distance (measured from the turbine axis) between the trailing edge of at least one of the vanes (or of each of the vanes) of the first portion of the array may differ from (e.g. be greater or less than) the radial distance between the trailing edge of one of the vanes (or each of the vanes) of the second portion of the array.

Another way in which the configuration of the vanes of the first portion of the array may differ from the configuration of the vanes of the second portion of the array is that the radial distance (measured from the turbine axis) between the leading edge of at least one of the vanes (or each of the vanes) of the first portion of the array may differ from (for example be greater or less than) the radial distance between the leading edge of at least one of the vanes (or each of the vanes) of the second portion of the array.

A further way in which the configuration of the vanes of the first portion of the array may differ from the configuration of the vanes of the second portion of the array is that the chord length of at least one (or each of) the vanes of the first portion of the array may differ from (for example be greater or less than) the chord length of at least one of (or each of) the vanes of the second portion of the array.

Another way in which the configuration of the vanes of the first portion of the array may differ from the configuration of the vanes of the second portion of the array is that the thickness of at least one of (or each of) the vanes of the first portion of the array may differ from (for example be greater or less than) the thickness of at least one of (or each of) the vanes of the second portion of the array. Examples of thicknesses which may differ include the thickness of the leading edge, the thickness of the trailing edge, the maximum circumferential (about the turbine axis) thickness, and the thickness at a location halfway along the chord between the leading edge and trailing edge. The thickness of the vane 50 within Figure 7 at a location halfway along the chord 58 between the leading edge 54 and trailing edge 56 is indicated by 60.

The thickness of the leading edge, thickness of the trailing edge and thickness of the location halfway along the chord may be measured in any appropriate way. For example, the thickness may be measured in a direction which is circumferential (relative to the turbine axis) or may be in a direction which is perpendicular to the chord.

It has already been discussed above that Figures 5 and 6 show two examples of producing an asymmetric turbine by having a first portion of the array of vanes which has a different configuration to that of a second portion of the array of vanes. Another way in which each of the embodiments shown in Figures 5 and B can be described as having a first portion of the array of vanes which has a different configuration to that of a second portion of the array of vanes is that the total throat area defined by the first portion of the array of vanes is different to the total throat area defined by the second portion of the array of vanes.

In the embodiments shown in Figures 5 and 6 the total throat area defined by the first portion of the array of vanes is different to the total throat area defined by the second portion of the array of vanes because the throat width between adjacent vanes in the first portion of the array of vanes differs to the throat width between adjacent vanes in the second portion of the array of vanes. In particular, in each of the embodiments shown in figures 5 and 6, the throat width between adjacent vanes in the first portion 44a, 44b of the array of vanes is greater than the throat width between adjacent vanes in the second portion 46a, 46b of the array of vanes.

In the embodiments shown in Figures 5 and 6, the axial height of each of the vanes within the inlet passageway is the same. Furthermore, the throat width and hence throat area between each pair of adjacent vanes in first portion of the array of vanes is substantially the same. Likewise, the throat width and hence throat area between each pair of adjacent vanes in second portion of the array of vanes is substantially the same.

In other embodiments, this may not be the case. For example, the throat area between adjacent vanes in first portion of the array of vanes may be different, for example, due to different vanes having different axial heights and/or their being different throat widths between different adjacent vanes. Likewise, the throat area between adjacent vanes in first portion of the array of vanes may be different. In these cases however, the total throat area defined by the first portion of the array of vanes is different to the total throat area defined by the second portion of the array of vanes.

Although none of the turbines according to the present invention previously described incorporate a variable geometry arrangement, it will be appreciated that other embodiments of the present invention may include a variable geometry arrangement.

For example, any of the embodiments described above may be modified so as to include a variable geometry arrangement.

The variable geometry arrangement may be configured to selectively change at least one characteristic of the turbine inlet. For example, the turbine may include a swing-vane-type arrangement, as is well-known in the art, which is capable of changing the swirl angle of the substantially annular array of vanes.

In another variable geometry arrangement the general annular inlet passageway may be defined between a first wall and a facing second wall. The variable geometry arrangement is configured to move the first wall relative to the second wall in a direction substantially parallel to the turbine axis in order to vary the size of the inlet passageway. Changing the size of the inlet passageway will change the speed, in use, of the gas which passes through the inlet passageway. For example, for a given mass flow rate of gas provided to the first and second flow passages, the larger the axial size of the inlet passageway, the slower gas will pass through the inlet passageway.

The way in which various variable geometry arrangements operate is well-known in the art. Consequently, further explanation of the operation of variable geometry arrangements is omitted. It will be appreciated that although only two types of variable geometry arrangement have been discussed, any appropriate variable geometry arrangement may be used provided it is capable of selectively changing at least one characteristic of the turbine inlet.

As previously discussed, a turbine according to the present invention may form part of a turbocharger which, in turn, may form part of an internal combustion engine. In this case, the turbine is supplied with exhaust gas from at least one of the cylinders of the internal combustion engine via an exhaust manifold, and the compressor is configured to supply gas to at least one of the cylinders of the internal combustion engine via an inlet manifold.

An internal combustion engine may include an exhaust gas recirculation channel in which the exhaust gas recirculation channel provides a flow conduit between at least one of the first and second flow passageways of the inlet of the turbine and an inlet manifold which is connected to at least one of the cylinders of the internal combustion engine.

The applicant has found that there is a synergistic benefit between a turbine according to the present invention and an internal combustion engine which includes an exhaust gas recirculation channel. In some internal combustion engines which include an exhaust gas recirculation channel, it may be beneficial to be able to control the pressure of the gas within the exhaust manifold to which one end of the exhaust gas recirculation channel is connected, such that this pressure is greater than the pressure of the inlet manifold to which the other end of the exhaust gas recirculation channel is connected. In this way, the pressure differential between the exhaust manifold at one end of the exhaust gas recirculation channel and the inlet manifold at the second end of the exhaust gas recirculation channel drives exhaust gas from the exhaust manifold to the inlet manifold via the exhaust gas recirculation channel as desired.

One problem which exists with increasing the pressure of the exhaust gas at the exhaust manifold (also sometimes referred to as the back pressure) is that high pressure in the exhaust manifold can oppose the forces produced by combustion within the cylinders of the internal combustion engine, thereby reducing the efficiency (or operating performance) of the internal combustion engine.

The use of an asymmetric turbine according to the present invention as part of an internal combustion engine including an exhaust gas recirculation channel can minimise the problem described above. The reason for this is discussed below.

An asymmetric turbine according to the present invention has first and second inlet flow passages. Of these flow passages, due to the asymmetry of the turbine, one of the flow passages will provide less resistance to the passage of exhaust gas through it than the other. For example, referring to the turbine shown in Figure 3, the second flow passage 24a will offer less resistance to exhaust gas passing through it than the first flow passage 22a. This is because the size of the inlet passageway portion 30a into which the second flow passage 24a feeds is greater than the size of the inlet passageway portion 28a into which the first flow passage 22a feeds.

Similarly, referring to Figure 5, the inlet flow passage which feeds the first portion 44a of the inlet passageway will offer less resistance to the passage of gas therethrough compared to the inlet flow passage which supplies the second portion 46a of the inlet passageway. This is because the greater number (i.e. circumferential density) of vanes in the second portion of the inlet passageway will provide more of an obstruction to gas passing through the inlet passageway when compared to the resistance offered by the relatively few vanes provided in the first portion 44a of the inlet passageway.

The inlet flow passage which offers the least resistance to gas flow therethrough, for a given mass flow of gas, will contain gas which is at a lower pressure than that within the inlet flow passage which provides the greater resistance to the flow of gas therethrough.

If the turbine according to the present invention forms part of an internal combustion engine which has a plurality of cylinders it would be possible to connect one of the inlet flow passages to at least one of the cylinders of the internal combustion engine and to connect the other inlet flow passage of the turbine to any (if not all) of the remaining cylinders.

In some applications it may be advantageous to connect one end of the exhaust gas recirculation channel to the inlet flow passage which has the most resistance to gas passing through it (and therefore a relatively high gas pressure). This inlet flow passage may be connected to only one or a few of the cylinders of the internal combustion engine. The remaining cylinders of the internal combustion engine are connected to the other inlet flow passage which has a relatively low resistance to the passage of gas therethrough (and therefore a relatively low gas pressure). In this way, the increased back pressure created in the inlet flow passage which is connected to one end of the exhaust gas recirculation channel only affects the efficiency (or operating performance) of the cylinder(s) of the internal combustion engine to which the inlet flow passage with relatively high resistance to the passage of gas therethrough is connected. The efficiency of the remaining cylinders of the internal combustion engine, which are connected to the other inlet flow passage having a relatively low gas pressure), are not adversely affected.

Consequently, the turbine according to the present invention can be utilised within an internal combustion engine which includes an exhaust gas recirculation channel so as to provide the pressure differential required for driving the exhaust gas recirculation system, whilst minimising the adverse effect the back pressure required for driving the exhaust gas recirculation system has on efficiency (or operating performance) of the internal combustion engine.

It can be seen that, in its broadest terms, all of the embodiments of the present invention described include a turbine comprising a housing, the housing defining a turbine inlet for receiving exhaust gas from an engine, a turbine outlet, and a turbine chamber between the turbine inlet and the turbine outlet. The turbine further comprises a turbine wheel located within the turbine chamber and arranged for rotation about an axis. The inlet comprises first and second separate flow passages which meet to define a substantially annular inlet passageway. The first flow passage forms a first portion of the substantially annular inlet passageway, and the second flow passage forms a second portion of the substantially annular inlet passageway. The turbine is configured such that the mass flow of exhaust gas from the first portion of the inlet passageway towards the turbine wheel is substantially unequal to the mass flow of exhaust gas from the second portion of the inlet passageway towards the turbine wheel.

In some embodiments, the mass flow of exhaust gas from the first portion of the inlet passageway towards the turbine wheel is different to the mass flow of exhaust gas from the second portion of the inlet passageway towards the turbine wheel because the first and second portions of the inlet passageway are of different sizes (i.e. subtend a different angle about the turbine axis). In some embodiments of the present invention, the mass flow of exhaust gas from the first portion of the inlet passageway towards the turbine wheel is different to the mass flow of exhaust gas from the second portion of the inlet passageway towards the turbine wheel because the configuration of vanes of a first portion of an array of vanes (which corresponds to the first portion of the inlet passageway) is different to the configuration of vanes of a second portion of the array of vanes (which corresponds to the second portion of the inlet passageway).

It is to be appreciated that numerous modifications to the above-described embodiments may be made without departing from the scope of the invention as defined in the appended claims.

It will be appreciated that a turbine according to an embodiment of the present invention, for example any of the turbines described above, may additionally include a valve controlled bypass port referred to as a wastegate The wastegate may be configured to enable control of the rotation speed of the turbine. Additionally, if the turbine forms part of a turbocharger, the wastegate may be used to control the boost pressure of the gas output by the compressor of the turbocharger. The bypass port provides a conduit between the inlet of a turbine and either the outlet of the turbine or atmosphere. Consequently, when the wastegate valve is opened, to thereby open the bypass port, in use, it allows at least some of the exhaust gas to bypass the turbine wheel. Within turbines according to the present invention, the bypass port may adjoin the first inlet flow passage and/or the second inlet flow passage. That is to say, the bypass port may adjoin the inlet flow passage which offers relatively greater resistance to the passage of gas therethrough and/or to the inlet flow passage which offers relatively less resistance to the passage of gas therethrough.

It will also be appreciated that although the turbines according to the present invention described above each utilise only one way of creating asymmetry (i.e. by the first and second portions of the inlet passageway supplied by the respective flow passages being of different sizes or by the configuration of the vanes in the first and second portions of the inlet passageway supplied by the respective flow passages having different configurations), in other embodiments of the present invention the turbine may utilise a combination of the two different methods in order to create asymmetry.

Some of the turbines according to the present invention described above utilise substantially different vane configurations in the first and second portions of the inlet passageway in order to create an asymmetric turbine. It will be appreciated that in some embodiments of the invention the configuration of the vanes of the first portion of the array of vanes may differ from the configuration of the vanes of the second portion of the array of vanes in that the first portion of the array of vanes does not include any vanes, whereas the second portion of the array of vanes does. That is to say, in such an embodiment, the first portion of the inlet passageway will not include any vanes, whereas the second portion of the inlet passageway will.

The embodiments of turbine according to the invention described above are referred to as double flow turbines. Such double flow turbines have a turbine housing which defines a volute having two separate flow passages which are separated by a dividing wall. The two separate flow passages meet at a generally annular inlet passageway such that each flow passage supplies a respective portion of the inlet passageway, the two respective portions being substantially in the same plane perpendicular to the turbocharger axis, but being circumferentially separate.

The configuration of double flow turbine described in the embodiments of the invention above is such that each of the flow passages which are configured to supply the inlet passageway are generally scroll (or volute) shaped and have a generally linearly reducing area schedule as you move towards the inlet passageway. The two flow passages are generally side-by-side and co-planar. The flow passages are configured such that gas flowing through each of the flow passages flows in the same rotational direction about the turbine axis (anti-clockwise in Figures 3, 5 and 6 -however, in other embodiments it may be clock-wise). In this configuration, the exhaust gas inlet of the turbine (at the opposite end of the flow passages to the inlet passageway) will be a coplanar inlet. That is to say the exhaust gas inlet will include two inlet openings, one for each flow passage, the inlet openings being generally adjacent one another, and generally co-planar with one another and both of the flow passages.

However, any appropriate configuration of turbine which comprises first and second separate flow passages which meet to define a substantially annular inlet passageway may be used in a turbine according to the present invention. Other examples of turbine configuration which may form part of an embodiment of the present invention are described below.

In some embodiments, the flow passages may be co-planar, but configured such that that gas flowing through each of the flow passages flows in the opposite rotational direction about the turbine axis (i.e. the flow in one of the flow passages is clockwise about the turbine axis, whereas the flow in the other one of the passages is anti-clockwise about the turbine axis). This type of configuration is shown in Figure 8, in which the turbine 801 is configured such that flow 802 in a first flow passage 803 is clockwise about the turbine axis 804, whereas the flow 805 in a second flow passage 806 is anti-clockwise about the turbine axis 804. The turbine wheel and nozzle ring within Figure 8 are indicated as 807 and 808 respectively. Again, in this arrangement, the exhaust gas inlet of the turbine (at the opposite end of the flow passages to the inlet passageway) will be a coplanar inlet. That is to say the exhaust gas inlet will include two inlet openings, one for each flow passage, the inlet openings being generally adjacent one another, and generally co-planar with one another and both of the flow passages.

The flow passages of turbines with this type of configuration may have a linearly reducing area schedule. Although the embodiment shown in Figure 8 has first and second flow passages which form first and second portions of the inlet passageway which subtends the same angle about the turbine axis, it will be appreciated that in other embodiments the turbine may be configured such that the first and second portions of the inlet passageway subtend different angles about the turbine axis.

Other arrangements are also possible. For example, in some embodiments portions of each of the flow passages may be generally scroll (or volute) shaped, generally side-by-side and co-planar. The flow passages may be configured such that gas flowing through the portions of the flow passages flow in the same rotational direction about the turbine axis. However, in this embodiment, the exhaust gas inlet of the turbine may be a non-coplanar inlet. For example, the inlet openings for each of the flow passages may be generally separated from one another -for example such that the inlet for one flow passage is generally perpendicular to the inlet for the other flow passage.

In other embodiments the inlet openings for both flow passages may be generally co-planar, and the inlet opening for one flow passage may be angularly spaced (about the axis) by about 1800 from the inlet opening for the other flow passage. Such an arrangement may be suitable for the turbine being mounted to an engine with cylinders in a V arrangement.

In the embodiments described above the first portion of the substantially annular inlet passageway is circumferentially offset about the axis from the second portion of the substantially annular inlet passageway. Consequently, in the embodiments described above which have first and second portions of an array of vanes which have substantially different configurations, the first portion of the substantially annular inlet passageway which is configured to direct gas flow onto the first portion of the array of vanes is circumferentially offset about the axis from the second portion of the substantially annular inlet passageway which is configured to direct gas flow onto the second portion of the array of vanes. Furthermore, the first portion of the array of vanes will also be circumferentially offset about the axis from the second portion of the array of vanes.

In the embodiments described above, the vanes are substantially uniform in the axial direction (i.e. across the inlet passageway). However, in other embodiments, this need notbethecase.

In some embodiments of turbine according to the present invention the first portion of the substantially annular inlet passageway may be axially offset from the second portion of the substantially annular inlet passageway. Consequently, in embodiments described which have first and second portions of an array of vanes which have substantially different configurations, the first portion of the substantially annular inlet passageway which is configured to direct gas flow onto the first portion of the array of vanes is axially offset from the second portion of the substantially annular inlet passageway which is configured to direct gas flow onto the second portion of the array of vanes. Furthermore, the first portion of the array of vanes will also be axially offset from the second portion of the array of vanes. In such embodiments, the vanes will be non-uniform in the axial direction (i.e. across the inlet passageway). That is to say the configuration of the vanes at a first axial position (i.e. at the first portion of the array of vanes) will differ from the configuration of the vanes at a second axial position (i.e. at the second portion of the array of vanes).

In embodiments in which the first portion of the substantially annular inlet passageway is axially offset from the second portion of the substantially annular inlet passageway, the separate flow passages configured to supply gas to the first and second portions of the inlet passageway respectively may or may not be coplanar. Likewise, the inlets of the flow massages may or may not be co-planar. That is to say the exhaust gas inlet, which includes two inlet openings, one for each flow passage, may include inlet openings being generally adjacent one another, and generally co-planar with one another and both of the flow passages, or may include inlet openings and/or flow passages which are axially offset from one another.

Although the previous description is related to an embodiment of a turbine according to the present invention which forms part of a turbocharger, it will be appreciated that a turbine according to the present invention may form part of any appropriate turbomachine. For example, a turbine according to the present invention may form part of a turbomachine which does not include a compressor. In particular, a turbine according to the present invention may form part of a power turbine, for example a power turbine which converts the rotation of a turbine wheel into electrical power.

Although the above described embodiment relates to a turbine which operates in conjunction with gas, it will be appreciated that turbines according to the present invention may operate in conjunction with any appropriate fluid, for example a liquid.

Claims (19)

1. CLAIMS: 1. A turbine comprising: a housing, the housing defining a turbine inlet for receiving exhaust gas from an engine, a turbine outlet and a turbine chamber between the turbine inlet and the turbine outlet; and a turbine wheel located within the turbine chamber and arranged for rotation about an axis; wherein the inlet comprises first and second separate flow passages which meet to define a substantially annular inlet passageway, the first flow passage forming a first portion of the substantially annular inlet passageway which subtends a first angle about the axis, and the second flow passage forming a second portion of the substantially annular inlet passageway which subtends a second angle about the axis; and wherein the first angle and second angle are substantially unequal.
2. 2. A turbine comprising: a housing, the housing defining a turbine inlet for receiving exhaust gas from an engine, a turbine outlet and a turbine chamber between the turbine inlet and the turbine outlet; and a turbine wheel located within the turbine chamber and arranged for rotation about an axis; wherein the inlet comprises first and second separate flow passages which meet to define a substantially annular inlet passageway; and the turbine further comprising a substantially annular array of vanes extending across the inlet passageway for directing gas flow towards the turbine wheel; wherein the first flow passage forms a first portion of the substantially annular inlet passageway which is configured to direct gas flow onto a first portion of the array of vanes, and the second flow passage forms a second portion of the substantially annular inlet passageway which is configured to direct gas flow onto a second portion of the array of vanes; and wherein the configuration of the vanes of the first portion of the array of vanes is substantially different to the configuration of the vanes of the second portion of the array of vanes.
3. 3. A turbine according to claim 2, wherein the first portion of the substantially annular inlet passageway is circumferentially offset about the axis from the second portion of the substantially annular inlet passageway.
4. 4. A turbine according to claim 2 or claim 3, wherein the first portion of the substantially annular inlet passageway is axially offset from the second portion of the substantially annular inlet passageway.
5. 5. A turbine according to any of claims 2 to 4, wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the circumferential spacing between the vanes of the first portion of the array is different to the circumferential spacing between the vanes of the second portion of the array.
6. 6. A turbine according to any of claims 2 to 5, wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes such that the total throat area defined by the vanes of the first portion of the array of vanes differs from the total throat area defined by the vanes of the second portion of the array of vanes.
7. 7. A turbine according to any of claims 2 to 6, wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the throat area and/or throat width between adjacent vanes of the first portion of the array of vanes differs from the throat area and/or throat width between adjacent vanes of the second portion of the array of vanes.
8. 8. A turbine according to any of claims 2 to 7, wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the swirl angle of the vanes of the first portion of the array is different to the swirl angle of the vanes of the second portion of the array.
9. 9. A turbine according to any of claims 2 to 8, wherein each vane of the array of vanes has a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the radial distance between the axis and trailing edge of each of the vanes of the first portion of the array is less than the radial distance between the axis and trailing edge of each of the vanes of the second portion of the array.
10. 1O.A turbine according to any of claims 2 to 9, wherein each vane of the array of vanes has a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the circumferential distance between the trailing edges of adjacent vanes of the first portion of the array is less than the circumferential distance between the trailing edges of adjacent vanes of the second portion of the array.
11. 11. A turbine according to any of claims 2 to 10, wherein each vane of the array of vanes has a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the radial distance between the axis and leading edge of each of the vanes of the first portion of the array is less than the radial distance between the axis and leading edge of each of the vanes of the second portion of the array.
12. 12. A turbine according to any of claims 2 to 11, wherein each vane of the array of vanes has a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the circumferential distance between the leading edges of adjacent vanes of the first portion of the array is less than the circumferential distance between the leading edges of adjacent vanes of the second portion of the array.
13. 13. A turbine according to any of claims 2 to 12, wherein each vane of the array of vanes has a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that the chord length between the leading and trailing edges of each of the vanes of the first portion of the array is less than the chord length between the leading and trailing edges of each of the vanes of the second portion of the array.
14. 14. A turbine according to any of claims 2 to 13, wherein each vane of the array of vanes has a leading edge and a trailing edge, the trailing edge being closer to the turbine wheel than leading edge, and wherein the configuration of the vanes of the first portion of the array of vanes differs from the configuration of the vanes of the second portion of the array of vanes in that at least one of the following thicknesses: thickness of the leading edge, thickness of the trailing edge, and/or maximum circumferential thickness and thickness at a location half way along the chord between the leading edge and trailing edge of each of the vanes of the first portion of the array is less than the equivalent thickness of each of the vanes of the second portion of the array.
15. 15. A turbine according to any preceding claim, further comprising a variable geometry arrangement configured to selectively change at least one characteristic of the turbine inlet.
16. 16.A turbine according to claim 15, wherein the inlet passageway is defined between a first wall and a facing second wall, and wherein the variable geometry arrangement is configured to move the first wall relative to the second wall in a direction substantially parallel to the axis in order to vary the size of the inlet passageway.
17. 17. A turbocharger or power turbine comprising a turbine according to any preceding claim.
18. 18. An internal combustion engine comprising a turbocharger having a turbine according to any of claims 1 to 16 and a compressor configured to supply gas to an inlet manifold.
19. 19. An internal combustion engine according to claim 18 further comprising an exhaust gas recirculation channel, the exhaust gas recirculation channel providing a flow conduit between one of the first and second flow passageways of the inlet and the inlet manifold.