Turbine

There is provided a turbine comprising: a turbine housing; a turbine wheel; an inlet upstream of the turbine wheel, the inlet defining a first inlet portion and a second inlet portion; an outlet downstream of the turbine wheel, the outlet defining a first outlet portion and a second outlet portion; and a wastegate arrangement configured to selectively vent exhaust gas from the first inlet portion to the first outlet portion via a first bypass passage, and further configured to selectively vent exhaust gas from the second inlet portion to the second outlet portion via a second bypass passage; wherein the first outlet portion and the second outlet portion are separated by a baffle of the turbine housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase filing under 35 U.S.C. § 371 of International Application No. PCT/GB2018/052995, titled “TURBINE,” filed on Oct. 17, 2018, which claims priority to British Patent Application No. 1717127.3, filed on Oct. 18, 2017, the entire disclosures of which being expressly incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a turbine, and in particular to a turbine having a baffle separating a first outlet portion and a second outlet portion of the turbine.

BACKGROUND

Turbines are used to harness power from a working fluid by converting fluid pressure into rotational motion using a turbine wheel. This rotary motion can be used to do useful work, such as for example by generating electrical power or by powering a compressor within a turbocharger of which the turbine forms part.

Turbochargers are used to increase the pressure of air entering into an internal combustion engine using a turbine wheel and a compressor wheel mounted to a common shaft. Exhaust gasses from the internal combustion engine are passed through the turbine wheel, which causes rotation of the turbine wheel, shaft and compressor wheel. Air is drawn through the compressor wheel and compressed to a boost pressure which is above atmospheric pressure. By providing higher pressure air to the internal combustion engine, more oxygen is available within the internal combustion engine for the combustion of fuel. As such, the turbocharger permits more fuel to be combusted, and hence the internal combustion engine may produce more power.

Turbines, as part of a turbocharger or otherwise, are typically provided with either an axial or radial turbine arrangement. In axial turbine arrangements, a working fluid (such as exhaust gas) passes through the turbine wheel in a direction parallel to the axis of rotation of the turbine wheel. In radial turbine arrangements, the working fluid circulates around the turbine wheel in an inwardly directed spiral, before being deflected by the turbine wheel along a path parallel to the axis of rotation of the turbine wheel.

Radially arranged turbines typically comprise an inlet in the shape of a hollow spiral, referred to as a volute, which is shaped to encourage circulation of the working fluid around the turbine wheel. Some radial turbines are provided with a twin entry arrangement comprising two such volutes arranged to be either side-by-side or radially overlapping. Where such a twin volute turbine is used within a turbocharger, each volute is typically connected to a separate bank of cylinders of an internal combustion engine. Exhaust gasses from each bank of cylinders are fed to one of the inlet volutes by separate exhaust manifolds. The exhaust manifolds may be tuned using pressure wave superposition to provide more efficient flow of exhaust gasses through the exhaust manifolds and inlet volutes. In order to prevent interference between the tuned exhaust gasses in each manifold, the two streams of exhaust gasses are kept separate until they reach the turbine wheel, at which point both streams of exhaust gasses are directed through the turbine wheel.

Some turbines, particularly those used in turbochargers, comprise wastegates which are used to bypass exhaust gasses to a position downstream of the turbine wheel such that the exhaust gasses do not pass through the turbine wheel. Such wastegates are used to reduce the amount of exhaust gas impinging on the turbine wheel so as to regulate the power produced by the turbine wheel. In this manner, detrimental flow conditions in the turbocharger compressor, such as compressor surge, can be avoided.

It is known to provide a twin volute radial turbine with a wastegate, such as of the type disclosed in U.S. Pat. No. 5,046,317. In the case of U.S. Pat. No. 5,046,317, the wastegate is positioned in the outlet of the turbine and comprises a pair of valve members which are configured to selectively cover and uncover a pair of wastegate passages connected to either inlet volute. Depending upon the configuration of the internal combustion engine and the exhaust manifolds, it is common that only one of the exhaust manifolds is pressurised at any one time (i.e. because a cylinder which feeds that manifold has just fired). As such, when the wastegate is opened, pressure pulses from each wastegate passage are able to interfere with the pressure pulses from the other wastegate passage. Any pressure difference between the two passages can result in an impedance to gas flow through the less pressurised passage as the pressure of the pressurised passage is transmitted into region downstream the unpressurised passage. The increased local pressure downstream of the unpressurised passage reduces the velocity of the exhaust gasses travelling through the unpressurised passage, and thus the amount of exhaust gas which can be transmitted through the wastegate overall (i.e. the wastegate efficiency). It is therefore desirable to reduce such interference between the wastegate passages.

SUMMARY

It is an object of the present disclosure to obviate or mitigate at the problems prevalent in the prior art, whether identified herein or elsewhere.

According to a first aspect of the disclosure there is provided a turbine comprising: a turbine housing; a turbine wheel; an inlet upstream of the turbine wheel, the inlet defining a first inlet portion and a second inlet portion; an outlet downstream of the turbine wheel, the outlet defining a first outlet portion and a second outlet portion; and a wastegate arrangement configured to selectively vent exhaust gas from the first inlet portion to the first outlet portion via a first bypass passage, and further configured to selectively vent exhaust gas from the second inlet portion to the second outlet portion via a second bypass passage; wherein the first outlet portion and the second outlet portion are separated by a baffle of the turbine housing.

Because the baffle separates the first outlet portion and the second outlet portion, when the wastegate arrangement is opened, pressure pulses from the first outlet portion must travel around the baffle in order to interfere with the pressure pulses from the second outlet portion. Interference between the pressure pulses in either outlet portion therefore occurs at a distal end of the baffle and not at the points where the first and second bypass passages connect to the first and second outlet portions. It will be appreciated that the distal end of the baffle is defined as the most downstream point of the baffle relative to the flow of fluid through the outlet. As such, this structure prevents pulse wave interference occurring within (or immediately downstream of) the first and second bypass passages themselves, and therefore the corresponding impedance to flow through the first and second bypass passages is reduced. That is to say, by creating a more tortuous path for exhaust gas flow between the first and second bypass passages, the location of any interference between the pressures of the exhaust gasses in the first and second bypass passages is displaced away from the first and second bypass passages themselves. As such, the efficiency of the flow through the first and second bypass passages is increased.

It will be appreciated that the first and second inlet portions are separate portions of the turbine which are positioned upstream of the turbine wheel. The first and second inlet portions may be fully or partially defined by the turbine housing and may include some or all of an exhaust manifold connected to an internal combustion engine.

It will be appreciated that the first and second outlet portions are separate portions of the turbine which are positioned downstream of the turbine wheel. The first and second outlet portions are regions of the turbine outlet which are separated from one another by the baffle. The turbine outlet may comprise additional regions which do not form part of the either the first or second outlet portions. For example, the first and second outlet portions may feed into a common region of the turbine outlet downstream of the first and second outlet portions.

By the term “configured to selectively vent” it will be understood that the wastegate arrangement is configurable between a first state in which gas flow communication between the first and second inlet portions and the first and second outlet portions via the first and second bypass passages is substantially prevented, and a second state in which such gas flow communication is permitted. As such, the wastegate arrangement may comprise one or more valve members configured to selectively block the path of exhaust gasses through the first and second bypass passages.

The baffle may extend in a generally axial direction with respect to a rotational axis of the turbine wheel.

The baffle may be an annular baffle. Where the baffle is annular, the baffle acts to encourage circulation of the exhaust gasses in the first and second outlet portions around the axis of the turbine wheel. As such, at the point immediately downstream of the baffle where the exhaust gasses in the first and second outlet portions are no longer separated by baffle, the exhaust gasses will be circulating around the axis of the turbine wheel in the same direction and at approximately the same speed. As such, detrimental flow effects such as turbulence at a distal end of the baffle are avoided, and the two streams of fluid are smoothly mixed.

The baffle may be arranged concentrically in relation to the turbine wheel and turbine housing. Where the baffle is concentric to the turbine wheel, the circulation of exhaust gasses around the axis of the turbine wheel may be symmetric.

The first bypass passage may be vented to a central region of the baffle, such that the central region of the baffle defines the first outlet portion. It will be appreciated that the term “vented” is intended to mean that the first bypass passage directs exhaust gasses from the first inlet portion and into the central region of the annular baffle.

The central region of the baffle may define a proximal end adjacent to the turbine wheel and a distal end opposite the proximal end and positioned further away from the turbine wheel, and wherein the central region of the baffle is open at both said distal end and said proximal end. As such, the central region may receive exhaust gasses from the turbine wheel and/or first bypass passage and transmit these exhaust gasses to the turbine outlet.

The first bypass passage may be vented to a position at or near the proximal end of the turbine wheel. That is to say, an exit of the first bypass passage may be positioned adjacent to an outlet of the turbine wheel. As such, exhaust gasses from the first bypass passage may enter the first outlet portion at an upstream part of the first outlet portion which is spaced apart from the distal end of the baffle.

The first bypass passage may be configured to direct exhaust gasses into the first outlet portion in a non-radial direction relative to an axis of rotation of the turbine wheel. That is to say, the exhaust gasses may enter the first outlet portion from the first bypass passage in a direction which is inclined relative to the radial direction of the axis of the turbine wheel in a plane which is normal to the axis of the turbine wheel. As such, circulation of the exhaust gasses around the axis of the turbine wheel is induced by the first bypass passage.

The second outlet portion comprises an annular region defined between the baffle and the turbine housing, and wherein the second bypass passage is vented to the annular region. It will be appreciated that the term “vented” is intended to mean that the second bypass passage directs exhaust gasses from the second inlet portion and into the annular region between the exterior of the baffle and the interior of the turbine housing. Furthermore, it will be appreciated the exterior of the baffle is defined by a radially outer surface of the baffle and the interior of the baffle is defined by a radially inner surface of the baffle.

Said annular region may have an upstream end and a downstream end spaced apart from the upstream end, and wherein the annular region is closed at the upstream end and open at the downstream end. That is to say, the annular region may define two ends, once of which is closed and the other of which is open. As such, exhaust gasses may be transmitted through the annular region to the turbine outlet.

The second bypass passage may be vented to the upstream end of the annular region. That is to say, an exit of the second bypass passage may be positioned such that it is spaced apart from the distal end of the baffle and towards the closed end of the annular region.

The second bypass passage may be vented to a position which is spaced apart from the upstream end of the annular region. It will be appreciated that by being spaced apart from the upstream (i.e. closed) end of the second outlet portion, the spacing may be tuned so as to reduce resonance of any pressure pulses present in the second outlet portion. As such, the exit of the second bypass passage is spaced apart from both the closed end of the second outlet portion and the distal end of the baffle. The second bypass passage may be vented to a position equidistant between the ends of the annular region, or may be vented to a position which is further towards one of the upstream or downstream ends of the annular region.

The second bypass passage may be configured to direct exhaust gasses into the second outlet portion in a non-radial direction relative to an axis of rotation of the turbine wheel. That is to say, the exhaust gasses may enter the second outlet portion (e.g. the annular region) from the second bypass passage in a direction which is inclined relative to the radial direction of the axis of the turbine wheel in a plane which is normal to the axis of the turbine wheel. As such, circulation of the exhaust gasses around the axis of the turbine wheel may be induced by the first bypass passage.

The baffle may be formed as an insert separable from the turbine housing. Alternatively, the baffle may be integrally formed with the turbine housing, such as for example by casting or welding. The first inlet portion may comprise a first volute and the second inlet portion may comprise a second volute separate to the first volute. The wastegate arrangement may comprise a first wastegate valve configured to open and close the first bypass passage and a second wastegate valve configured to open and close the second bypass passage. The first and second wastegate valves may be integrally formed with the turbine housing. The first and second wastegate valves may be external to the turbine housing. The turbine may form part of a turbocharger.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

Referring toFIG. 1, this illustrates a turbocharger provided with a divided turbine inlet and twin wastegate valve assembly as disclosed in U.S. Pat. No. 5,046,317 referred to above. The illustrated turbocharger comprises a turbine1and a compressor2interconnected by a central bearing housing3. The turbine1comprises a turbine wheel4mounted on one end of a shaft5within a turbine housing6. The compressor2comprises a compressor wheel7mounted on the other end of the turbo shaft5within a compressor housing8. The shaft5rotates about the turbocharger axis on bearing assemblies (not shown) located within the bearing housing3.

The turbine housing comprises a divided inlet volute having parallel exhaust gas inlet paths9and10which deliver exhaust gas to the turbine wheel4via an annular inlet passage11and exits the turbine housing via an axial outlet passage12.

The compressor housing2defines an axial inlet13and an outlet volute14.

Exhaust gas flow through the turbine1causes rotation of the turbine wheel4which in turn rotates the compressor wheel7mounted to the opposite end of the shaft5. As the compressor wheel7rotates, air is drawn in through the axial inlet13, and delivered to the cylinders of an internal combustion engine (not shown) via outlet volute14at a boosted pressure above atmospheric pressure.

The turbine1is a wastegated turbine and as such each exhaust gas inlet path9and10is provided with a respective bypass passage15and16which communicate with a common outlet passage17via a dual wastegate valve assembly. The dual wastegate valve assembly comprises a pair of wastegate valve members, i.e. poppets18and19loosely mounted to opposite ends of a linking support member20. Each poppet has a limited freedom of movement allowing the precise position of each poppet to shift slightly to accommodate small variations in the height of the respective valve seats defined around the opening of each bypass passage15,16.

The support member20is mounted to one end of the support arm21which extends through a wall22of the turbine housing and is connected at its opposite end to an actuator arm23. A bushing24is provided in the turbine housing wall22to accommodate rotation of the support arm21.

The end of the support arm21which is fixed to the support member20is bent at right angles to the axis of rotation of the support arm21. The opposite end of the support arm21is linked to the actuator arm23so that reciprocal movement of the actuator arm (as indicated by arrow25) causes rotation of the support arm21which in turn moves the linking support member20and the poppets18,19to simultaneously open or close the bypass passages15,16. The tip of the support arm21is secured to the support member20so as to allow limited angular movement between the two. In particular, the pivotal connection between the tip of the support arm21and the support member20is intended to provide a centering action to improve accurate seating of the poppets.

The wastegate valve assembly is controlled to open as boost pressure produced by the compressor2reaches a predetermined level to permit a portion of exhaust gas flowing through the turbine inlet paths9and10to bypass the turbine wheel4and thus limit any further increase in boost pressure produced by the compressor. The outlet passage17may communicate to atmosphere (as suggested in U.S. Pat. No. 5,046,317) or may for instance communicate with the turbine outlet passage12so that the bypass gas flow merges with the main exhaust gas flow downstream of the turbine wheel4.

Each of the exhaust gas inlet paths9,10is fluidly connected to a separate bank of cylinders of the internal combustion engine via conduits or piping (not shown). As such, under normal operating conditions it is usual for a pressure pulse to be present in one of the inlet paths9,10and not the other such that one inlet path is pressurised and the other is unpressurised. That is to say, the pressure in one of the inlet paths9,10may be substantially greater than the pressure in the other inlet path for a short period of time, for example approximately 20 milliseconds.

It will be appreciated that when the bypass passages15,16are opened (i.e. by actuation of the poppets18,19) the pressure pulses from the inlet paths9,10are transmitted through the bypass passages15,16to the outlet passage17. This causes the pressure of the exhaust gas in the region of the outlet passage17immediately downstream of the unpressurised one of the bypass passages15,16to be higher than the pressure of the exhaust gas within the unpressurised one of the bypass passages15,16. This localised pressure increase results in a corresponding drop in velocity of the exhaust gasses and therefore acts to choke the flow out of the unpressurised one of the bypass passages15,16. The ability of the wastegate to discharge exhaust gasses from the turbine1is therefore impeded by slowing of the exhaust gasses in the outlet passage17as a result of interference between the two streams of exhaust gasses. That is to say, cross-communication between the exhaust gasses leaving the bypass passages15,16within the outlet passage17reduces the rate at which exhaust gasses can be transmitted through the wastegate.

FIG. 2shows a schematic cross sectional view of a turbine30according to the present disclosure. The turbine30may be used within a turbocharger such as that exemplified inFIG. 1above with reference to U.S. Pat. No. 5,046,317, or may be used in any suitable application as would be apparent to the skilled person (e.g. within a power turbine or otherwise). The turbine30comprises a turbine wheel32contained within a turbine housing34. The turbine wheel32is fixedly connected to a turbine shaft36which is supported for rotation by a bearing housing (not shown). The turbine housing34defines an inlet volute38divided into a first inlet path40and a second inlet path42. The first and second inlet paths are fluidly connected to two separate banks of cylinders of an internal combustion engine (not shown) by piping. The first and second inlet paths40,42deliver exhaust gasses from an internal combustion engine to the turbine wheel32via an annular inlet passage44. Mixing between the first and second inlet paths40,42is substantially prevented by the presence of a divider wall43within the inlet volute38.

The turbine30comprises a turbine outlet46defined by a tubular portion35of the turbine housing34and having a baffle50positioned therein. The baffle50is generally tubular in shape and comprises a generally annular cross section. The baffle50comprises a distal end51which is defined as the most downstream point of the baffle50relative to the flow of fluid through the turbine outlet46. The baffle50divides the turbine outlet46into an inner outlet portion52and an outer outlet portion54. The inner outlet portion52is defined as the cylindrical region bounded by the baffle50, whilst the outer outlet portion54is defined as the annular region bounded between the tubular portion35of the turbine housing34and the baffle50. The inner outlet portion52is open at an upstream end to receive exhaust gasses from the turbine wheel32and is open at a downstream end to transmit fluid to the turbine outlet46. The outer outlet portion54is closed at an upstream end by the turbine housing34and is open at a downstream end to transmit fluid to the turbine outlet46.

The turbine30comprises a wastegate arrangement48which connects the first and second inlet paths40,42to the turbine outlet46by bypassing the turbine wheel32. The wastegate arrangement48comprises a first bypass passage56which connects the first inlet path40to the inner outlet portion52. The first bypass passage56comprises an exit57which is defined by the baffle50as an aperture of the baffle50. The first bypass passage56comprises a conduit which extends through part of the outer outlet portion54to the exit57. The wastegate arrangement48further comprises a second bypass passage58which connects the second inlet path42to the outer outlet portion54. The second bypass passage58comprises an exit59which is defined by the turbine housing34as an aperture of the tubular portion35.

The exit57of the first bypass passage56is positioned at an upstream end of the baffle50such that it is slightly downstream from the turbine wheel32. That is to say, the exit57of the first bypass passage56is immediately adjacent to an outlet of the turbine wheel32, such that it is spaced away from the distal end51of the baffle50in an axial direction relative to an axis of rotation64of the turbine wheel32. The exit59of the second bypass passage58is positioned at an upstream end of the outer outlet portion54. That is to say, the exit59of the second bypass passage56is also spaced away from the distal end51of the baffle50in the axial direction and towards the turbine wheel32.

The first bypass passage56comprises a first wastegate valve60disposed between the first inlet path40and the exit57of the first bypass passage56. Likewise, the second bypass passage58comprises a second wastegate valve62disposed between the second inlet path42and the exit59of the second bypass passage58.

The first and second wastegate valves60,62are each configurable between an open state in which exhaust gasses are permitted to vent through the respective one of the first and second bypass passages56,58to the turbine outlet46whilst bypassing the turbine wheel32and a closed state in which such venting is substantially prevented. It will be appreciated that the first and second wastegate valves60,62may be any suitable wastegate valve, for example a poppet valve. Furthermore, the first and second wastegate valves60,62may be either integral with or external to the turbine housing34. That is to say, the first and second wastegate valves62,60may be at least partially defined by the turbine housing34(such as that shown with respect to the prior art inFIG. 1) or may be entirely separate to the turbine housing34. Where the first and second wastegate valves60,62are external to the turbine housing34, the first and second wastegate valves60,62may be connected between the inlet volute38and the turbine outlet46by conduits or piping which at least partially define the first and second bypass passages56,58.

During use, exhaust gasses from the internal combustion engine are passed from the first and second inlet paths40,42through the annular inlet44and are directed onto turbine wheel32. The kinetic energy of the exhaust gasses causes the turbine wheel32to rotate and thereby extract useful work from the exhaust gasses. As explained above with reference to the prior art, where the turbine30is part of a turbocharger this rotation is used to drive a compressor wheel which acts to compress intake air to a boost pressure substantially above atmospheric pressure.

Where rotation of the turbine wheel is required to be slowed, such as for example to avoid detrimental operating conditions such as compressor surge, the first and second wastegate valves60,62are opened. Opening of the first and second wastegate valves60,62permits some or all of the exhaust gasses in the first and second inlet passages40,42to bypass the turbine wheel32and vent directly to the turbine outlet46. As such, the kinetic energy imparted on the turbine wheel32by the exhaust gasses is reduced and the rotational velocity of the turbine wheel slowed accordingly.

It will be appreciated that because the first and second inlet paths40,42are connected to separate banks of cylinders of the internal combustion engine, under normal operating conditions it is usual for a pressure pulse to be present within the one of the inlet paths40,42and not the other. For example, if a cylinder which is fluidly connected to the first inlet path40has just fired and the cylinders which are fluidly connected to the second inlet path42are between firing intervals, a relatively high pressure will be present within the first inlet path40whilst a relatively low pressure will be present in the second inlet path42(i.e. lower than the pressure in the first inlet path40). When the first wastegate valve60is opened, the pressure within the first inlet path40is transferred to the inner outlet portion52via the first bypass passage56. Likewise, when the second wastegate valve62is opened, the pressure within the second inlet path42is transferred to the outer outlet portion54via the second bypass passage58.

Pressure pulses from the first inlet path40and second inlet path42are introduced into the turbine outlet46at the exits57,59of the first bypass passage56and the second bypass passage58respectively. It will be appreciated that because the baffle50separates the inner outlet portion52and the outer outlet portion54, interference between any pressure pulses emanating from the exits57,59of the bypass passages may only occur downstream of the baffle50. That is to say, the pressure pulses from either the first or second bypass passages56,58must travel around the distal end51of the baffle50relative to the turbine wheel32before encountering a corresponding pressure pulse from the other of the first or second bypass passages56,58. Any resulting pressure increases will therefore be local to the distal end51of the baffle50. It follows that flow through the region surrounding the distal end51of the baffle50will be slowed due to the increased pressure of the exhaust gasses in this region. However, because the restriction to flow occurs at a location of the turbine outlet46which is spaced apart (i.e. away) from the exits57,59of the first and second bypass passages56,58the impact of this restriction to flow is substantially reduced. In other words, the baffle50moves the restriction to flow away from the exits57,59of the first and second bypass passages60,62and therefore flow out of the exits57,59is less restricted than the situation where the exits57,59are not separated by a baffle.

The exit59of the second bypass passage58is spaced from the closed end of the outer outlet portion54. As such, a pressure pulse transmitted out of the exit59of the second bypass passage58may be reflected from the closed end of the outer outlet portion54. It will be appreciated that the spacing between the exit59of the second bypass passage58may be selected such that the reflected pressure pulse is tuned to the typical operating frequencies of the internal combustion engine. The spacing may therefore act to prevent resonance of the pressure pulses of the exhaust gasses in the outer outlet portion54, and hence further reduce any impedance to flow through the wastegate arrangement48.

FIG. 3shows a cross sectional end view of the turbine30ofFIG. 2. The first bypass passage56is angled relative to the baffle50such that it is non-normal to an inner surface of the baffle50. Likewise the second bypass passage58is angled relative to the tubular portion35of the turbine housing34such that it is non-normal to an inner surface of the tubular portion35. Because the first and second bypass passages are angled relative to the baffle50and the tubular portion35of the turbine housing34swirling of the exhaust gasses about the axis of rotation64(seeFIG. 2) of the turbine wheel32is induced as the exhaust gasses enter the inner and outer outlet portions52,54. That is to say, because the exhaust gasses from the first and second bypass passages56,58are directed into the inner outlet portion52and outer outlet portion54in a non-radial direction with respect to the axis64of the turbine wheel this encourages the exhaust gasses to circulate around the axis64of the turbine wheel32, as shown by the arrows A and B.

During normal use when the wastegate valves60,62are closed, the exhaust gasses present in the inner outlet portion52circulate around the axis64of the turbine wheel32due to the rotation of the turbine wheel32. As such, by inducing swirling of the exhaust gasses entering the inner outlet portion52the exhaust gasses transmitted via the wastegate arrangement48are able to smoothly join the flow of any exhaust gasses leaving the outlet of the turbine wheel32. Furthermore, turbulence at the distal end51of the baffle50is also avoided because both streams of fluid are circulating in the same direction and at similar speeds. That is to say, by inducing swirling in both the inner and outer outlet portions52,54, when the two circulating streams of exhaust gasses join one another they move in unison and therefore disturbances to the flow in the turbine outlet46are avoided. In this manner, a smooth mixing of exhaust gasses from the inner and outer outlet portions52,54downstream of the baffle50is achieved.

In order to induce swirl within the inner outlet portion52, the first bypass passage56is inclined at an angle relative to the circumference of the baffle50at the point where the bypass passage56intersects the baffle50. The angle of the first bypass passage56relative to the circumference of the baffle50may vary substantially anywhere in the range of 0° (such that is tangential to the circumference of the baffle50) to 45°. Likewise, in order to induce swirl within the outer outlet portion54, the second bypass passage58is inclined at an angle relative to the circumference of the tubular portion35of the turbine housing34. The angle of the second bypass passage58relative to the circumference of the tubular portion35may also vary substantially anywhere in the range of 0° to 45°. It will be understood that the precise angles of the first and/or second bypass passages56,58are not critical, provided that the angles are sufficient to induce swirling of the exhaust gasses within the inner and outer outlet portions52,54. It will be appreciated that the first and second bypass passages56,58may be inclined at the same or different angles.

Furthermore, in order to induce flow of the exhaust gasses in an axial direction relative to the axis64of the turbine wheel32, in alternative embodiments of the disclosure the first and/or second bypass passages56,58may also be inclined at a non-normal angle relative to the axis64of the turbine wheel32. That is to say, the first and/or second bypass passages may be arranged such that they point towards the turbine outlet46. In an example embodiment, the angle of the first and/or second bypass passage relative to the axis64may be varied substantially anywhere within the range of 45° to 90°. It will be appreciated that by being inclined at a non-normal angle relative to the axis64of the turbine wheel32, exhaust gasses in the inner and outer outlet portions52,54are encouraged to travel away from the turbine wheel32, so as to result in a helical or spiral-like flow path. As such, the exhaust gasses transmitted through the wastegate38are carried with the flow of the exhaust gasses which have passed through the turbine wheel32and hence turbulence in the regions where the bypass passages56,58connect to the inner and outer outlet portion52,54is avoided.

It will be appreciated that in alternative embodiments of the disclosure the baffle50could be substantially any cross sectional shape. For example, the baffle may be rectangular in cross section. Additionally or alternatively, the baffle50may be tapered along its length. For example, the baffle50may be configured to define a wider cross section at the distal end51of the baffle50relative to the turbine wheel32such that the baffle50acts to diffuse exhaust gasses in the inner outlet portion52. In such embodiments, the outer outlet portion54may be correspondingly tapered.

Furthermore, in alternative embodiments of the disclosure the outer outlet portion54may not surround the inner outlet portion52in an annular manner. For example, the baffle50may define a conduit of the turbine outlet46which runs parallel to the axis64of the turbine wheel32. In particular, the baffle50may define a chord dividing the tubular portion35of the turbine housing34into two separate outlet portions. Alternatively, the baffle50may extend into the tubular portion35of the turbine housing34in the manner of a pitot tube (although oriented away from the direction flow out of the turbine wheel32). It will be appreciated that exhaust gasses in either of the outlet portions are prohibited from mixing until they are downstream of the distal end51of the baffle50.

It will be appreciated that the length of the baffle50comprises a length parallel to the axis64of the turbine wheel32which may be substantially any suitable length, provided that the baffle50acts to divide the turbine outlet46to prevent mixing between the inner and outer outlet portions52,54. That is to say, the baffle50may be any length as would be apparent to the skilled person, and may, in particular, be dependent upon one or more of: a diameter of the tubular portion35of the turbine housing34, a diameter of the turbine wheel32, a length of the tubular portion35of the turbine housing34in a direction parallel to the axis64of the turbine wheel32, an axial length of the turbine wheel32parallel to the axis64of the turbine wheel32, the velocity, pressure, temperature or density of the exhaust gasses through the turbine outlet46, or any other characteristic of the construction of the turbine30or its operating conditions. Likewise, the baffle50defines a thickness in a radial direction relative to the axis64of the turbine wheel32which may be substantially any suitable thickness as would be apparent to the skilled person and/or based upon any one or more of the parameters listed above. For example, the thickness of the baffle50in the radial direction may be approximately 2 to 5 mm.

In the embodiment shown, the first bypass passage56comprises a conduit which extends through part of the outer outlet portion54. However, it will be appreciated that in alternative embodiments of the disclosure the base of the outer outlet portion54and the first bypass passage56may be arranged such that the first bypass passage56is wholly or partially upstream of the base of the outer outlet portion54.

It will be appreciated that in alternative embodiments of the disclosure, the exits57,59of the first and second bypass passages40,42may be located at any suitable position within the inner outlet portion52and outer outlet portion54respectively. For example, the exit59of the second bypass passage58may be positioned at the same point along the axis64as the exit57of the first bypass passage56, or may even be positioned upstream of the exit57of the first bypass passage56. That is to say, the precise position of the exits57,59is may be varied provided that the baffle50acts to provide a tortuous path for any gas flow communication between the exits57,59. Furthermore, any axial spacing between the exits57,59such as that shown inFIG. 2may be selected so as to promote improved joining of flow at the distal end51of the baffle50. In particular, such axial spacing between the exits may be selected in dependence upon the operating parameters of the engine, such as the incoming magnitude and/or frequency of the incoming pressure pulses.

It will further be appreciated that the exits57,59of the first and second bypass passages56,58may intersect the baffle50and tubular portion35respectively at substantially any angular position with respect to the axis64. That is to say, the exits57,59may be positioned on the same side as one another relative to the axis64(such as that shown inFIG. 3), on opposite sides of the axis64or at any arbitrary position around the axis64.

It will be appreciated that the first and second wastegate valves may be operated independently from one another, or may be configured to actuate simultaneously.