Turbomachine

Abstract

A turbine 10 comprising a wastegate chamber 28 and a turbine housing 12 that defines a turbine inlet 14 and comprises a wastegate assembly 26 having an inlet passageway 30 that defines a flow path B b

Description

TECHNICAL FIELD The present invention relates to a turbine, and to a turbomachine comprising the turbine. BACKGROUND Turbines convert the potential energy of a fluid into mechanical work. Conventional turbines comprise a turbine housing defining a turbine inlet, a turbine chamber and a turbine outlet. A turbine wheel is mounted within the turbine chamber. The turbine inlet commonly comprises an annular inlet defined between facing radial walls arranged around the turbine chamber and an inlet volute arranged around the annular inlet. In use, fluid enters the turbine through the turbine inlet, where it is passed to the turbine wheel in the turbine chamber. The fluid impinges upon one or more blades defined by the turbine wheel, which exerts a force upon the turbine wheel causing the turbine wheel to rotate about a turbine axis. Once the fluid has passed the turbine wheel, it exits the turbine via the turbine outlet. Turbochargers are well known turbomachines for supplying air to an inlet of an internal combustion engine at pressures above atmospheric pressure (boost pressures). Turbochargers increase the pressure of atmospheric air entering into an internal combustion engine using a turbine and a compressor mounted to a common shaft. Exhaust gasses from an outlet manifold of the internal combustion engine are passed through the turbine. Rotation of the turbine wheel causes rotation of the shaft and thus the compressor wheel. Air is drawn through the compressor and compressed by the compressor wheel to a boost 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. It is known to provide a turbine with a bypass, typically referred to as a wastegate assembly, which permits fluid to flow from the turbine inlet to the turbine outlet without passing through the turbine wheel. Wastegate assemblies typically include a wastegate valve (e.g. a poppet type valve or a swing type valve) configured to permit or prevent flow from bypassing the turbine wheel. When used in a turbocharger, the wastegate is opened to permit fluid to bypass the turbine wheel. The wastegate may be opened when the boost pressure of the fluid in the compressor outlet increases above a pre-determined level, or to support the thermal requirements of an emission aftertreatment system of the vehicle to which the turbocharger is provided. A bypass ratio of the turbine is controlled by varying the position of the wastegate valve (i.e., by controlling the degree to which the wastegate valve is open). It is an object of the present invention to address one or more problems associated with known wastegate assemblies SUMMARY According to a first aspect of the invention there is provided a turbine. The turbine comprises a wastegate chamber. The turbine further comprises a turbine housing that defines a turbine inlet. The turbine housing comprising a wastegate assembly. The wastegate assembly comprises a wastegate inlet passageway that defines a flow path between the turbine inlet and the wastegate chamber, wherein the wastegate inlet passageway comprises a turbine port adjacent the turbine inlet and a valve port adjacent the wastegate chamber. A first sealing surface surrounds the valve port. The wastegate assembly further comprises a valve member. The valve member comprises a valve plate that defines a second sealing surface, and a protrusion that extends from the valve plate to define a protrusion height and a protrusion width. The protrusion height is less than half of the protrusion width. The valve member is pivotable between a closed position in which the second sealing surface engages the first sealing surface and the protrusion is disposed in the wastegate inlet passageway, and an open position in which the second sealing surface is spaced apart from the first sealing surface. The central axis of the wastegate inlet passageway may extend through a centre of area at each position along the length of the wastegate inlet passageway. A maximum protrusion height may be less than half of half of a maximum protrusion width. With the valve in the open position, fluid is able to flow along the flow path in use. The wastegate assembly may comprise an actuator. The valve member may be operatively coupled to the actuator. The actuator may be operable to pivot the valve member. The actuator may be remote from the turbine housing. The actuator may be directly coupled to the valve member. The actuator may be indirectly coupled to the actuator, such as via a shaft. A bypass ratio of the turbine may be described as the ratio of mass flow rate of fluid through the wastegate inlet passageway to the mass flow rate of fluid through the turbine (i.e., the sum of the mass flow rate of fluid through the wastegate inlet passageway and the mass flow rate of fluid that is incident upon a wheel of the turbine). Increasing an opening angle of the valve member typically increases the bypass ratio. Decreasing the opening angle of the valve member typically decreases the bypass ratio. Since the valve member comprises a protrusion, the wastegate assembly can be seen to operate (or open) in two phases: a first phase in which the protrusion is disposed in the wastegate inlet passageway; and a second phase in which the protrusion is not disposed in the wastegate inlet passageway. The rate of change of the mass rate of fluid flow through the wastegate inlet passageway with respect to the opening angle of the valve member (i.e., the degree to which the valve member is spaced apart from the closed position) in the first phase of operation is less than in the second phase of operation. This is because the protrusion restricts the flow of fluid through the wastegate passageway during the first phase of operation. Since the protrusion height is less than half of the protrusion width, the opening angle of the valve member at which operation transitions from the first phase to the second phase is at a low opening angle of the valve member (as compared to if the height of the protrusion were greater than half of the width). This advantageously provides improved control of the mass flow rate of fluid through the wastegate inlet passageway. In conventional wastegate assemblies, the rate of change of the mass flow rate of fluid through the wastegate inlet passageway with respect to the opening angle of the valve member is greatest at low opening angles. This can make the mass flow rate of fluid through the wastegate inlet passageway difficult to control. By providing the protrusion, which restricts the flow of fluid at low opening angles of the valve member, the rate of change of the mass flow rate of fluid through the wastegate inlet passageway with respect to the opening angle of the valve member is reduced during the first phase of operation. The second phase of operation provides an increased (relative to the first phase of operation) rate of change of the mass flow rate of fluid through the wastegate inlet passageway with respect to the opening angle of the valve member. The valve port may define a valve port central axis. The valve port central axis may extend through a centre of area of the valve port. The valve port central axis may extend parallel to the flow path at least in the region of the flow path that adjoins the valve port. A wastegate inlet passageway central axis may be coincident with the valve port central axis. The wastegate inlet passageway central axis may extend through a centre of area of the wastegate inlet passageway. It will be appreciated that turbulence may occur in the region of the valve port. However, the direction of the flow path may be understood to refer to a direction of the bulk of the fluid flow through the valve port. The valve port central axis may be at an oblique angle to the first sealing surface. Where the valve port central axis is at an oblique angle to the first sealing surface, control of fluid flow through the valve port, in particular during the first phase of operation, is further improved. This is because the flow of fluid through the valve port is impeded as a result, which reduces the rate of change of mass flow rate of fluid through the valve port with respect to the opening angle of the valve member. Because of this, the mass flow rate of fluid through the valve port can be controlled with greater accuracy. The valve port central axis may be perpendicular to the first sealing surface. The protrusion may comprise a first protrusion end. The first protrusion end may be disposed proximal the valve plate. The protrusion may comprise a second protrusion end. The second protrusion end may be disposed distal the valve plate. The protrusion may define a protrusion central axis. The protrusion central axis may extend perpendicular to the valve plate. The protrusion central axis may extend through a centre of area of the first protrusion end. The protrusion central axis may extend parallel to a valve stem central axis of a valve stem of the valve member. The protrusion may be non-axisymmetric about the protrusion central axis. Where the protrusion is non-axisymmetric about the protrusion central axis, the protrusion can be shaped such that the extent to which the protrusion impedes, or otherwise influences, the flow of fluid through the valve port is non-uniform. This advantageously allows the flow of fluid through the valve port to be more uniform. This is because other factors, such as the position of a pivot axis of the valve member, can result in the flow of fluid through the valve port being non-uniform. Where the protrusion is non-axisymmetric about the protrusion central axis, the protrusion can be shaped to account for the other factors that influence the uniformity of flow through the valve port. The protrusion may define a first protrusion portion and a second protrusion portion. The height of the first protrusion portion may be greater than a height of the second protrusion portion. The first protrusion portion and the second protrusion portion may each comprise half of the circumferential length of the protrusion. The height of each protrusion portion may be measured in a direction that is parallel to the protrusion central axis. The height of the first protrusion portion may be at least 20% greater than the height of the second protrusion portion. The height of the first protrusion portion may be at least 25% greater than the height of the second protrusion portion. The height of the first protrusion portion may be up to two times greater than the height of the second protrusion portion. The height of the first protrusion portion may be up to three times greater than the height of the second protrusion portion. The first protrusion portion may be disposed distal a pivot axis of the valve member. The second protrusion portion may be disposed proximate to the pivot axis of the valve member. Where the first protrusion portion is disposed distal the pivot axis of the valve member and the second protrusion portion is disposed proximate the pivot axis of the valve member, control of fluid flow through valve port is further improved. This is because the rate of change of displacement of the distal portion of the valve member, with respect to the opening angle of the valve member, is greater than that of the proximal portion of the valve member. Because of this, each protrusion portion may vacate the wastegate inlet passageway at the same or similar opening angle of the valve member. Therefore, this arrangement allows more uniform change of fluid flow through the valve port while the valve member is pivoted. With the valve member in the closed position, the protrusion central axis may be at an oblique angle to the valve port central axis. Where the protrusion central axis is at an oblique angle to the valve port central axis, this help further reduce rate at which the clearance between the protrusion and the wastegate inlet passageway changes when the valve member is pivoted in use. This reduces the rate at which the clearance between the protrusion and the wastegate inlet passageway, as compared to if the protrusion central axis were not at an oblique angle to the valve port central axis. This allows for more accurate control of the bypass ratio. The valve member may comprise a valve stem that defines a valve stem central axis. The protrusion central axis and the valve stem central axis may be non-coaxial. Where the protrusion central axis and the valve stem central axis are non-coaxial, the rate at which the clearance between the protrusion and a wall of the wastegate inlet passageway changes as the valve member is pivoted is more uniform about a periphery of the protrusion. This allows for more accurate control of the bypass ratio of the turbine. The protrusion central axis may extend beyond the protrusion. The valve stem central axis may extend beyond the valve stem. The protrusion central axis may be parallel to the valve stem central axis. A distance from the protrusion central axis to a pivot axis of the valve member may be greater than a distance from the valve stem central axis to the pivot axis. The above distances may be understood to refer to a minimum distance. Where a distance from the protrusion central axis to the pivot axis is greater than a distance from the valve stem central axis to the pivot axis, the rate at which the clearance between the protrusion and a wall of the wastegate inlet passageway changes as the valve member is pivoted is more uniform about a periphery of the protrusion. This is because the rate at which the separation between the protrusion and the wall of the wastegate inlet passageway changes as the valve member is pivoted is greater at positions that are further away from the pivot axis, as compared to positions that are closer to the pivot axis. This allows for more accurate control of the bypass ratio of the turbine. The valve member may defines a set angle. The set angle may extend between the second sealing surface and a plane on which the second protrusion end is disposed. A first flow area may be defined between a wall of the wastegate inlet passageway and the first portion of the protrusion. A second flow area may be defined between the first sealing surface and the second sealing surface in the region of the first portion of the protrusion. When the valve member is angularly spaced apart from the closed position by a magnitude that is less than the set angle, the first flow area may be smaller than the second flow area. When the valve member is angularly spaced apart from the closed position by a magnitude that is greater than the set angle, the protrusion may not be located in the wastegate inlet passageway. The first flow area may be a minimum flow area defined between the protrusion and the valve port. The second flow area may be a minimum flow area between the first sealing surface and the second sealing surface. The protrusion being removed from the wastegate inlet passageway may be understood to mean that the protrusion is no longer disposed in the wastegate inlet passageway. Where used, this arrangement allows for improved control of the flow of fluid from the turbine inlet to the wastegate chamber. This is because, with the valve member angularly spaced apart from the closed position by less than the set angle, the flow of fluid through the valve port is impeded by the protrusion. As a result, the rate of change of the mass flow rate of fluid through the valve port with respect to the opening angle is reduced. This makes the mass flow rate of fluid through the valve port easier to control. Furthermore, once the valve member is angularly spaced apart from the closed position by more than the set angle, the rate of change of the mass flow rate of fluid through the valve port with respect to the opening angle is increased, as compared to where the valve member is angularly spaced apart from the closed position by less than the set angle. This allows for more coarse adjustments to the mass flow rate of fluid through the valve port to be made. A third flow area may be defined between the wall of the wastegate inlet passageway and the second portion of the protrusion. A fourth flow area may be defined between the first sealing surface and the second sealing surface in the region of the second portion of the protrusion. When the valve member is angularly spaced apart from the closed position by a magnitude that is less than the set angle, the fourth flow area may be smaller than the third flow area. The wastegate inlet passageway may define a wastegate inlet passageway plane. The wastegate inlet passageway plane may be is perpendicular to the flow path in the region of the flow path that adjoins the valve port. With the valve member in the closed position, an angle from the wastegate inlet passageway plane to the second sealing surface, measured in a direction of pivot of the valve member, may be at least 5 degrees and / or up to 70 degrees. Where the above arrangement is used, the flow of fluid is impeded as a result of the orientation of the flow path with respect to the second sealing surface. This allows for the flow of fluid through the valve port to be better controlled. The angle from the wastegate inlet passageway plane to the second sealing surface may be an included angle. The angle from the wastegate inlet passageway plane to the second sealing surface may be at least 5 and / or up to 45 degrees. An angle between a sidewall of the protrusion and the second sealing surface may be within 10% of the angle between the wastegate inlet passageway plane and the second sealing surface. The angle between a sidewall of the protrusion and the second sealing surface may be equal to the angle between the wastegate inlet passageway plane and the second sealing surface The protrusion may define a recess. The recess may extend into the second protrusion end. The recess may extend to the valve plate. The recess may extend to a plane on which the second sealing surface is disposed. The recess may extend only part way to the valve plate. According to a second aspect of the invention there is provided a turbomachine comprising a turbine according to the first aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of a turbine including a wastegate assembly in accordance with an embodiment of the present invention; Figure 2 shows a perspective view of a valve member of the wastegate assembly of Figure 1; Figure 3 shows a side view of the valve member of Figure 2; Figure 4 shows a close-up view of the wastegate assembly of Figure 1 with the valve member in a closed position; Figure 5 shows a close-up view of the wastegate assembly of Figure 1 with the valve member in an open position; Figure 6 shows a close-up view of the wastegate assembly of Figure 1 with the valve member in an open position; and Figure 7 shows a close-up view of a wastegate assembly according to a second embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS Referring to Figure 1, a turbine 10 comprises a turbine housing 12 defining a turbine inlet 14, a turbine chamber 16, and a turbine outlet 18. The turbine 10 further comprises a turbine wheel 20 that is disposed within the turbine chamber 16 and is rotatable about a turbine axis 17 on a shaft 24. In use, there is provided a conventional flow path A through the turbine. Fluid flows into the turbine 10 via the turbine inlet 14 and impinges on the turbine wheel 20 thereby causing rotation of the turbine wheel 20 around the turbine axis 17. The fluid is redirected by the turbine wheel 20 to flow out of the turbine 10 via the turbine outlet 18. In order to regulate the volume of fluid impinging on the turbine wheel 20, and therefore control the speed of rotation of the turbine wheel 20, the turbine is provided with a wastegate assembly 26 that defines a bypass flow path B. The wastegate assembly 26 provides a way of controlling the speed of the turbine wheel 20 by selectively diverting an amount of fluid away from the turbine wheel 20. The wastegate assembly 26 comprises a wastegate chamber 28 having a wastegate inlet passageway 30 and a chamber outlet 32. The wastegate inlet passageway 30 provides a flow path between the turbine inlet 14 and the wastegate chamber 28. The wastegate inlet passageway 30 comprises a turbine port 31 (or wastegate port) adjacent the turbine inlet 14. The wastegate inlet passageway 30 comprises a valve port 33 adjacent the wastegate chamber 28. A first sealing surface 36 surrounds the valve port 33. The chamber outlet 32 provides a flow path between the wastegate chamber 28 and the turbine outlet 18. Fluid flowing along the bypass flow path B flows from the turbine inlet 14, through the wastegate inlet passageway 30 to the wastegate chamber 28, and through the chamber outlet 32 to the turbine outlet 18. In other embodiments, the chamber outlet may provide a flow path between the wastegate chamber and the atmosphere, and the bypass flow path may end in the atmosphere rather than the turbine outlet. The wastegate assembly 26 further comprises a valve member 34 and an actuator 35. The valve member 34 is operatively coupled to the actuator 35. In the depicted embodiment, the valve member 34 is coupled to the actuator 35 via a shaft 41. However, in other, non-depicted, embodiments, the valve member 34 may be coupled to the actuator via any other suitable support member. The valve member 34 has an open position and a closed position to control fluid flow along the bypass flow path B. The valve member 34 is pivotable between the open and closed positions. The valve member 34 may be understood to be pivotable between a closed position and a fully open position. The valve member 34 can be positioned at any position between the closed position and the fully open position. Each position between the closed position and the fully open position may be understood to be an open position. The valve member 34 may be pivoted from the closed position when a boost pressure of the turbine exceeds a predetermined value. Alternatively or additionally, the valve member 34 may be pivoted from the closed position based on a command from an engine management system of a vehicle that the turbine 10 forms a part of. The actuator 35 is operable to pivot the valve member 34. In the closed position, the valve member 34 blocks the wastegate inlet passageway 30 to prevent fluid flow along the bypass flow path B. In the open position, the valve member 34 is spaced from the wastegate inlet passageway 30 to permit fluid flow along the bypass flow path B. The degree to which the valve member 34 is spaced apart from the closed position determines a bypass ratio of the turbine 10. The bypass ratio of the turbine 10 may be described as the ratio of mass flow rate of fluid through the wastegate inlet passageway 30 to the mass flow rate of fluid that is incident upon a turbine wheel 20 of the turbine 10 when the valve member 34 is in the closed condition The valve member 34 has a valve stem 39. The valve stem 39 defines a valve stem central axis 37. The valve member 34 is free to rotate around the valve stem central axis 37. This may reduce the valve stem 39 wear and wear of the sealing surfaces. In some embodiments, the degree to which the valve member 34 is able to rotate may be limited. Figure 2 shows a perspective view of the valve member 34. The valve member 34 comprises a valve plate 38. The valve plate 38 is generally disc shaped. However, in other, non-depicted, embodiments, the valve plate 38 may take any other suitable shape. The valve plate 38 defines a second sealing surface 40. The second sealing surface 40 engages the first sealing surface (not shown in Figure 2) with the valve member in a closed position. The valve stem 39 extends from the valve plate 38. The valve stem 39 extends from a side of the valve plate 38 that is opposed to the second sealing surface 40. The valve member 34 further comprises a protrusion 42. The protrusion 42 extends from the valve plate 38. The protrusion 42 extends from a side of the valve plate 38 that is opposed to the side form which the valve stem 39 extends. The protrusion 42 defines a first protrusion end 44. The first protrusion end 44 is disposed proximal the valve plate 38. The first protrusion end 44 is sized to be received by the valve port (not shown in Figure 2). The protrusion 42 defines a second protrusion end 46. The second protrusion end 46 is disposed distal the valve plate 38. The protrusion 42 defines a protrusion central axis 48. The protrusion central axis 48 extends perpendicular to the valve plate 38. The protrusion central axis 48 may extend perpendicular to the second sealing surface 40. The protrusion central axis 48 may also be considered to extend parallel to the valve stem central axis 37. The protrusion central axis 48 extends through a centre of area of the first protrusion end 44. The protrusion 42 encircles the protrusion central axis 48. The protrusion 42 is non-axisymmetric about the protrusion central axis 48. This advantageously allows the protrusion 42 to influence the flow of fluid through the valve port 3 in a non-uniform manner. This is desirable because the flow of fluid through the valve port in conventional assemblies is typically non-uniform. By influencing the flow of fluid in a non-uniform manner, the flow can be more uniform as a result. In some, non-depicted, embodiments, the protrusion 42 may be axisymmetric about the protrusion central axis 48. The protrusion 42 of the valve member 34 defines a recess 70. The recess 70 extends in a direction that is parallel to the protrusion central axis 48. However, this need not be the case. The recess 70 is generally cylindrical. However, the recess 70 may take any suitable shape. The recess 70 extends to the valve plate 38. The recess 70 extends to a plane upon which the second sealing surface 40 is disposed. In some embodiments, the recess 170 need not be provided, and the protrusion 42 may be formed as a solid piece of material. That is to say, the second protrusion end 46 may define a planar surface. The protrusion defines a first protrusion portion 50 and a second protrusion portion 52. Each of the first protrusion portion 50 and the second protrusion portion 52 may be considered to comprise half of the circumferential length of the protrusion 42. Referring to Figure 3, the protrusion 42 defines a protrusion height 54 and a protrusion width 56. The height of the protrusion 42 may be measured from the valve plate 38, in particular from the second sealing surface 40, in a direction that is parallel to the protrusion central axis 48. The protrusion width 56 may be measured in a direction that is parallel to the second sealing surface 40. The protrusion height 54 is less than half of the protrusion width 56. The protrusion 42 allows operation, or opening, of the wastegate assembly 26 to be seen to operate in two phases: a first phase in which the protrusion 42 is disposed in the wastegate inlet passageway 30; and a second phase in which the protrusion 42 is not disposed in the wastegate inlet passageway 30. The rate of change of the mass rate of fluid flow through the wastegate inlet passageway 30 with respect to the opening angle of the valve member in the first phase of operation is less than in the second phase of operation. This is because the protrusion 42 impedes the flow of fluid through the wastegate inlet passageway 30 during the first phase of operation. Since the protrusion height 54 is less than half of the protrusion width 56, the transition from the first phase of operation to the second phase of operation occurs at a low opening angle of the valve member 34 (as compared to is the protrusion height 54 were greater than half of the protrusion width 56). This provides improved control of the flow of fluid through the wastegate inlet passageway 30 because fine adjustments to the mass flow rate of flow through the wastegate inlet passageway 30 can be made in the first phase of operation, and coarse adjustments can be made in the second phase of operation. The protrusion height 54 may refer to a maximum protrusion height. The protrusion width 56 may refer to a maximum protrusion width. In the depicted embodiment, a height of the first protrusion portion 50 is greater than a height of the second protrusion portion 52. Generally, the height of the first protrusion portion 50 may be at least 20% greater than the height of the second protrusion portion 52. In some embodiments, the height of the first protrusion portion 50 may be at least 25% greater than the height of the second protrusion portion 52. In some embodiment, the height of the first protrusion portion 50 may be up to two or three times greater than the height of the second protrusion portion 52. The height of the first protrusion portion 50 relative to the second protrusion portion 52, and vice versa, may be chosen based on the desired relationship between the bypass ratio of the turbine and the opening angle of the valve member 34. In some embodiments, the minimum height of the second protrusion portion 52 may be zero. Where the minimum height of the second protrusion portion 52 is zero at least part of the second protrusion 52 may define a height that is non-zero. The height of the first protrusion portion 50 being greater than the height of the second protrusion portion 52 advantageously improves the control of the passage of fluid through the valve port 33. This is because the rate of change of displacement of the valve member 34 in the region of the first protrusion portion 50 with respect to the degree to which the valve member 34 is open is greater than that of the second protrusion portion. The protrusion 42 comprises a sidewall 59. The sidewall 59 is tapered such that the width of the first protrusion end 44 is greater than the width of the second protrusion end 46. However, in some, non-depicted, embodiments, the sidewall 59 of the protrusion 42 may extend perpendicular to the second sealing surface 40 of the valve plates 38. The angle of the sidewall 59 with respect to the second sealing surface 40 may be at least 30 degrees and / or up to 90 degrees. The angle of the sidewall 59 with respect to the second sealing surface 40 may be chosen based on the geometry of the chamber inlet (not shown in Figure 2). In some, non-depicted, embodiments, opposed portions of the sidewall may extend parallel to one another. In such embodiments, the protrusion central axis may be considered to extend parallel to the sidewall, and through a centre of area of the second protrusion end. In such embodiments, the protrusion central axis may or may not extend perpendicular to the valve plate. Alternatively, in such embodiments, the protrusion central axis may be considered to extend perpendicular to the second sealing surface and through a centre of area of the first protrusion end, as above. The valve member 34 defines a set angle S. The set angle S extends between the second sealing surface 40 and a plane on which the second protrusion end 46 is disposed. Referring now to Figure 4, which shows a close up view of the wastegate assembly 26 with the valve member 34 in the closed position. The valve port 33 defines a valve port central axis 58. The valve port central axis 58 extends through a centre of area of the valve port 33. The valve port central axis 58 extends parallel to the bypass flow path B at least in the region of the bypass flow path that adjoins the valve port 33. In some embodiments, the valve port central axis 58 may be parallel to an entirety of the bypass flow path B. The valve port central axis 58 is perpendicular to the first sealing surface 36. However, in other embodiments, this need not be the case, as will be discussed in more detail below. The wastegate inlet passageway 30 defines a wastegate inlet passageway plane 72. The wastegate inlet passageway plane 72 is perpendicular to the flow path B at least in the region of the flow path B that adjoins the valve port 33. With the valve member 34 in the closed position, as shown in Figure 4, the wastegate inlet passageway plane 72 is parallel to the second sealing surface 40. However, in other embodiments, discussed below, the wastegate inlet passageway plane 72 may be at an oblique angle (measured in a direction of pivot of the valve member 34) with respect to the second sealing surface 34. The protrusion central axis 48 and the valve stem central axis 37 are non-coaxial. This allows for more accurate control of the bypass ratio. In other, non-depicted, embodiments, this may not be the case, and the protrusion central axis 48 may be coaxial with, or extend from, the valve stem central axis 37. The protrusion 42 may be described as being eccentric with respect to the valve stem ventral axis 37. The protrusion central axis 48 extends parallel to the valve stem central axis 37. However, in some embodiments the protrusion central axis 48 may be at an oblique angle with respect to the valve stem central axis 37. The protrusion central axis 48 is disposed outboard (i.e., radially outwards of) of the valve stem central axis 37 with respect to a pivot axis 60 of the valve member 34. Put another way, the protrusion central axis 48 is further away from the pivot axis 60 of the valve member 34 than the valve stem central axis 37. This allows for more accurate control of the bypass ratio because, during pivoting of the valve member 42, the rate at which the clearance between a periphery of the protrusion 42 and the sidewall 59 of the wastegate inlet passageway 30 is more uniform about the periphery of the protrusion 42. The first protrusion portion 50 is disposed distal the pivot axis 60. The second protrusion portion 52 is disposed proximate the pivot axis 60 of the valve member 34. In this embodiment, the protrusion central axis 48 is disposed outboard of (i.e., radially outwards of) the valve port central axis 58 with respect to the pivot axis 60 when the valve member 34 is in the closed configuration. Figure 4 shows the valve member 34 in a closed position. In the closed position, the second sealing surface 40 and the first sealing surface 36 are in contact with one another. Figure 5 shows the valve member 34 in an open position. In Figure 5, the valve member 34 is angularly spaced apart from the closed position by a magnitude that is less than the set angle. A first flow area 62 is defined between a wall 64 of the wastegate inlet passageway 30 and the first protrusion portion 50. A second flow area 66 is defined between the first sealing surface 36 and the second sealing surface 40 in the region of the first protrusion portion. With the valve member 34 spaced apart from the closed position by a magnitude that is less than the set angle, the first flow area 62 may be less than the second flow area 66 (i.e., the magnitude of the first flow area 62 may be less than the second flow area 66). Therefore, with the valve member 34 spaced apart from the closed position by a magnitude that is less than the set angle, the first flow area 62 dictates the rate at which fluid can flow through the wastegate inlet passageway 30. In some embodiments, when the valve member 34 is angularly spaced apart from the closed position by a magnitude that is less than the set angle, the second flow area 66 may be less than the first flow area 62. A third flow area 68 is defined between the wall 64 of the wastegate inlet passageway 30 and the second protrusion portion 52. A fourth flow area 70 is defined between the first sealing surface 36 and the second sealing surface 40 in the region of the second protrusion portion 52. When the valve member 34 is angularly spaced apart from the closed position by a magnitude that is less than the set angle, as shown in Figure 5, the fourth flow area 70 is less than the third flow area 68. In some embodiments, when the valve member 34 is angularly spaced apart from the closed position by a magnitude that is less than the set angle, the third flow area 68 may be less than the fourth flow area 70. In Figure 6, the valve member 34 is angularly spaced apart from the closed position by a magnitude that is greater than the set angle. As can be seen from Figure 6, with the valve member 34 angularly spaced apart from the closed position by a magnitude that is greater than the set angle, the protrusion 42 is not disposed in the wastegate inlet passageway 30. With the valve member 34 angularly spaced apart from the closed position by a magnitude that is greater than the set angle, the entirety of the protrusion 42 is disposed in the wastegate chamber 28. Figure 7 shows a cross-sectional view of a wastegate assembly 126 according to a second embodiment of the invention. Unless noted otherwise, the above discussion in relation to the first embodiment of the invention applies to the second embodiment of the invention. Like numerals will be used for the features of the second embodiment as were used in relation to the first embodiment. The valve port central axis 158 is at an oblique angle with respect to the first sealing surface 136. In addition, with the valve member 134 in the closed position, the protrusion central axis 148 is at an oblique angle to the valve port central axis 158. However, in some, non-depicted embodiments, the protrusion central axis 148 may be parallel to the valve port central axis 158. In this embodiment, with the valve member 134 in the closed position, the sidewall 159 of the protrusion 142 in the region of the first protrusion portion 150 extends parallel to the wall 164 of the wastegate inlet passageway 130, at least in the region of the wastegate inlet passageway 130 that adjoins the valve port 133. Where the valve port central axis 158 is at an oblique angle with respect to the first sealing surface, the flow of fluid through the wastegate inlet passageway 130 is impeded. This reduces the rate of change of the mass flow rate of fluid through the wastegate inlet passageway 130 with respect to the degree to which the valve member 134 is open. This allows for improved control of the mass flow rate of fluid through the wastegate inlet passageway 130. The wastegate inlet passageway 130 defines a wastegate inlet passageway plane 172. The wastegate inlet passageway plane 172 is perpendicular to the flow path B at least in the region of the flow path B that adjoins the valve port 133. With the valve member 134 in the closed position, as shown in Figure 7, an angle from the wastegate inlet passageway plane 172 to the second sealing surface 140, measured in a direction of pivot of the valve member 134 is at least 5° and / or up to 70°. With the valve member 134 in the closed position, an angle from the wastegate inlet passageway plane 172 to the second sealing surface 140, measured in a direction of pivot of the valve member 134 may be at least 5 degrees and / or up to 40 degrees. An angle between the sidewall 159 of the protrusion 142 and the second sealing surface 140 may be within 10% of, or equal to, the angle between the wastegate inlet passageway plane 172 and the second sealing surface 140. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. A turbine comprising:a wastegate chamber;a turbine housing that defines a turbine inlet, the turbine housing comprising a wastegate assembly that comprises:a wastegate inlet passageway that defines a flow path between the turbine inlet and the wastegate chamber, wherein the wastegate inlet passageway comprises a turbine port adjacent the turbine inlet and a valve port adjacent the wastegate chamber, wherein a first sealing surface surrounds the valve port;a valve member, the valve member comprising a valve plate that defines a second sealing surface, and a protrusion that extends from the valve plate to define a protrusion height and a protrusion width, wherein the protrusion height is less than half of the protrusion width;wherein the valve member is pivotable between a closed position in which the second sealing surface engages the first sealing surface and the protrusion is disposed in the wastegate inlet passageway, and an open position in which the second sealing surface is spaced apart from the first sealing surface.

2. The turbine of claim 1, wherein the valve port defines a valve port central axis that extends through a centre of area of the valve port and parallel to the flow path at least in the region of the flow path that adjoins the valve port.

3. The turbine of claim 2, wherein the valve port central axis is at an oblique angle to the first sealing surface.

4. The turbine of claim 2, wherein the valve port central axis is perpendicular to the first sealing surface.

5. The turbine of any preceding claim, wherein the protrusion comprises a first protrusion end that is disposed proximal the valve plate, and a second protrusion end that is disposed distal the valve plate, and wherein the protrusion defines a protrusion central axis that extends perpendicular to the valve plate and through a centre of area of the first protrusion end.

6. The turbine of claim 5, wherein the protrusion is non-axisymmetric about the protrusion central axis.

7. The turbine of any preceding claim, wherein the protrusion defines a first protrusion portion and a second protrusion portion, and wherein the height of the first protrusion portion is greater than a height of the second protrusion portion.

8. The turbine of claim 7, wherein the first protrusion portion is disposed distal a pivot axis of the valve member and the second protrusion portion is disposed proximate to the pivot axis of the valve member.

9. The turbine of any of claims 2 to 4 and any of claims 5 to 8, wherein, with the valve member in the closed position, the protrusion central axis is at an oblique angle to the valve port central axis.

10. The turbine of any of claims 5 to 9, wherein the valve member comprises a valve stem that defines a valve stem central axis, and wherein the protrusion central axis and the valve stem central axis are non-coaxial.

11. The turbine of claim 10, wherein a distance from the protrusion central axis to a pivot axis of the valve member is greater than a distance from the valve stem central axis to the pivot axis.

12. The turbine of any of claims 5 to 11, wherein:the valve member defines a set angle that extends between the second sealing surface and a plane on which the second protrusion end is disposed,a first flow area is defined between a wall of the wastegate inlet passageway and the first portion of the protrusion, and a second flow area is defined between the first sealing surface and the second sealing surface in the region of the first portion of the protrusion;when the valve member is angularly spaced apart from the closed position by a magnitude that is less than the set angle, the first flow area is smaller than the second flow area; andwhen the valve member is angularly spaced apart from the closed position by a magnitude that is greater than the set angle, the protrusion not located in the wastegate inlet passageway.

13. The turbine of claim 12, wherein a third flow area is defined between the wall of the wastegate inlet passageway and the second portion of the protrusion, and a fourthflow area is defined between the first sealing surface and the second sealing surface in the region of the second portion of the protrusion; andwherein, when the valve member is angularly spaced apart from the closed position by a magnitude that is less than the set angle, the fourth flow area is smaller than the third flow area.

14. The turbine of any preceding claim, wherein the wastegate inlet passageway defines a wastegate inlet passageway plane that is perpendicular to the flow path in the region of the flow path that adjoins the valve port, and wherein, with the valve member in the closed position, an angle from the wastegate inlet passageway plane to the second sealing surface, measured in a direction of pivot of the valve member, is at least 5 degrees and / or up to 70 degrees.

15. The turbine of claim 3 and claim 12, wherein an angle between a sidewall of the protrusion and the second sealing surface is within 10% of the angle between the wastegate inlet passageway plane and the second sealing surface.

16. The turbine of any of claims 6 to 15 when dependent upon claim 5, wherein the protrusion defines a recess that extends into the second protrusion end.

17. The turbine of claim 16, wherein the recess extends to the valve plate.

18. A turbomachine comprising the turbine of any preceding claim.

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