Patent ID: 12228221

Throughout the following description, like reference numerals have been used to refer to equivalent or corresponding features of the different embodiments of the disclosure. Where a reference numeral has a suffix, this indicates that the feature in question is one of a plurality of equivalent or corresponding features which are present in the same embodiment of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

FIG.1shows a cross-sectional schematic view of a seal assembly2which separates a first environment4from a second environment6. The first and second environments4,6both contain fluid, such as for example a liquid or a gas. The pressure of the fluid in the first environment4is greater than the pressure of the fluid in the second environment6. The first environment4may therefore be referred to as a high pressure environment and the second environment6may be referred to as a low pressure environment. The seal assembly2defines a lateral direction oriented horizontally in the plane ofFIG.1, a longitudinal direction normal to the plane ofFIG.1, and a vertical direction oriented vertically in the plane ofFIG.1.

The seal assembly2comprises a first component8and a second component10. The first and second components8,10are moveable relative to one another in the longitudinal and lateral direction. However, in other embodiments the first component8and the second component10may be fixed relative to one another. The first component8may be, for example, a fixed wall member, and the second component10may be, for example, a movable actuating member. For clarity, only part of the first component8and the second component10are shown in the Figures. The first and second components8,10may have substantially any shape suitable for their particular application. However for the sake of simplicity the first and second components8,10can be assumed to be generally prismatic along the longitudinal direction of the seal assembly2. However, in alternative embodiments the first and second components8,10may have generally revolved configurations. For example, the one of the first and second components8,10may be generally cylindrical and the other of the first and second components8,10may comprise a bore.

The first component8and the second component10are spaced apart from one another so as to define a passage12therebetween. The passage12defines an inlet14on the side of the high pressure environment4and an outlet16on the side of the low pressure environment6. The passage12fluidly connects the high pressure environment4to the low pressure environment8via the inlet14and the outlet16. The first component8comprises a recess18and the second component10comprises a recess19. The recess18is a concavity formed by the first component8, and the recess19is a concavity formed by the second component10. No part of the first component8(or any intermediate component positioned between the first and second components8,10) extends into region of space bounded by the recess19of the second component10, and no part of the second component10or any (or any intermediate component positioned between the first and second components8,10) extends into the region of space bounded by the recess18of the first component8. The recesses18,19of the first and second components8,10may be manufactured in any suitable way, such as for example by casting, machining, chemical etching, additive manufacturing or the like.

The recesses18,19of the first and second components8,10extend in the longitudinal direction of the first and second components8,10. The recesses18,19are in fluid flow communication with the passage12such that the recesses18define part of the boundary of the passage12. The recesses18,19are generally semi-circular in cross-section but may define any suitable cross-section, as discussed below. The first component8further comprises an upstream dwell portion20aand a downstream dwell portion20b. The dwell portions20a,20bare positioned either side of the recesses18of the first component8, such that the upstream dwell portion20ais on the side of the high pressure environment4and the downstream dwell portion20bis on the side of the low pressure environment6. The second component10also comprises an upstream dwell portion21aand a downstream dwell portion20bpositioned either side of the recess19of the second component10.

FIG.1shows an aligned configuration of the seal assembly2. In the aligned configuration, the first component8and the second component10are positioned such that the upstream dwell portions20a,21a, the recesses18,19and the downstream dwell portions20b,21bare aligned opposite one another. The recesses18,19of the first embodiment are generally semi-circular in cross-section. The upstream dwell portions20a,21adefine an upstream throat section22aof the passage12, and the downstream dwell portions20b,21bdefine a downstream throat section22b. The throat sections22a,22bdefine the portions of the passage12having the narrowest clearance between the first component8and the second component10. The recess18of the first component8and the recess19of the second component10define a chamber24which defines the widest part of the passage12. During use, high pressure fluid from the first environment4enters the passage12via the inlet14. The upstream throat section22aguides the fluid to the chamber24, whereupon the fluid expands to fill the chamber24. After passing through the chamber24, the fluid subsequently enters the downstream throat section22band exits the passage12via the outlet16.

As shown inFIG.1, the width of the passage12in the vertical direction at the cavity24is large in comparison to the width of the passage12in the vertical direction along the upstream and downstream throat sections22a,22b. From the perspective of the fluid, as the fluid enters the cavity24, the available flow area increases by a large amount over a relatively short distance. As such, the Reynolds number of the fluid in the cavity24will be higher than that of the fluid flowing through the throat sections22a,22b. Due to the increase in Reynolds number, the fluid within the cavity24will become turbulent, such that vortices will form in the chamber24. Furthermore, it can be seen fromFIG.1that at the point at which the upstream throat section22ajoins the chamber24, the walls of the recesses18,19extend away from the direction of flow of the incoming fluid by approximately 90°. The sharp edges of the recesses18,19relative to the upstream dwell portions20a,21aand downstream dwell portions20b,21bcause the flow to “trip” and begin to recirculate as it expands into the chamber24, thus aiding the formation of vortices. That is to say, due to the sharp edge of the recesses18,19the boundary layer of the fluid passing through the throat sections22a,22bdetaches as the fluid enters the recesses24a,24b, resulting in turbulence.

The vortices are localised areas of low pressure around which portions of the fluid circulate. The circulating portions of the fluid lose energy to frictional interaction with other portions of the fluid. Because the vortices are low pressure, the vortices also act to draw in fluid, causing the fluid to meander as it crosses the chamber24. Because the fluid meanders, the path taken by each portion of the fluid increases in length, and therefore increases the amount of energy that is lost to friction. Thus, the presence of the vortices in the chamber24impedes the flow of fluid through the seal assembly2, reducing the overall flow rate through the seal assembly2. Turbulence dissipates kinetic energy within the flow, the dissipated energy being lost as heat energy due to friction and resulting in a lower flow rate. The vortices in the chamber24are transient, such that the vortices generate and dissipate over time. The number, size and transience of the vortices generated will depend on a wide range of factors, including inter alia the type, pressure, density, compressibility, and temperature of the fluid flowing through the chamber24and the geometry of the chamber24itself.

In general, the more sharply the width of the passage12increases, the more effective the passage will be at generating vortices. As such, it is preferable for the recesses18,19to join the throat sections22a,22bat around 90°, however shallower angles may also be effective at generating vortices, as discussed below.

In order to create turbulence effectively, the recesses18must be sized so that they are large compared to the width of the upstream and downstream throat sections22a,22b. The spacing between the dwell portions20a,20bof the first component8and the dwell portions21a,21bof the second component in the vertical direction defines the minimum clearance between the first and second components8,10. The recesses18,19define a maximum depth, the maximum depth being the distance between the between the deepest point of the recesses18,19and the adjacent dwell portions20a-b,21a-b. In order to generate sufficient turbulence within the recesses18,19, the ratio of the maximum depth of the recesses18,19to the minimum clearance between the first and second components8,10is preferably in the range of around 2.5:1 to around 3.75:1, and is preferably at least around 3:1 (however turbulence may still occur outside of this range). In some embodiments, the ratio may be at least around 4:1. It will be appreciated that, in general, the larger the ratio of the maximum depth of the recesses18,19to the minimum clearance between the first and second components8,10the more effective the seal assembly2will be at generating turbulence. However, it has been found that in some circumstances it is practical if the ratio of the maximum depth of the recesses18,19to the minimum clearance between the first and second components8,10is no larger than around 15:1. In some embodiments, the ratio may be less than around 8:1 or 5:1. For example, the recesses18,19may define a diameter of around 0.5 mm, 1.0 mm, or 1.5 mm. It has been found that when the diameter of the recess is less than around 0.5 mm the seal is less effective. Generally speaking, sealing is more effective when the recesses18,19are larger, however the maximum size of the recesses18,19may be dictated by packaging constraints. The minimum clearance between the first and second components8,10may be around 0.1 mm, 0.2 mm, 0.3 mm or 0.4 mm.

Because the minimum clearance between the first and second components8,10is relatively small in relation to the maximum depth of the recesses18,19, the flow is accelerated as it passes through the throat sections22a,22b. The size of the minimum clearance can be chosen so as to ensure that the fluid passing through the first throat section22areaches a minimum velocity before entering the cavity24. Once the flow enters the cavity24it is decelerated, resulting in turbulence. Furthermore, because the minimum clearance between the first and second components8,10is generally small in relation to the size of the cavity24, the upstream throat section22aand the downstream throat section22balso provide resistance to flow due to friction. The narrower the distance between the first and second components8,10at the upstream and downstream throat sections22a,22b, the higher the frictional resistance imparted by the throat sections22a,22bon the flow. As such, it is beneficial to choose the minimum clearance distance between the first and second components8,10so that it is as small as possible. The frictional resistance provided by the throat sections22a,22bwill contribute to the overall resistance to flow provided by the seal assembly2.

The first component may define a seal length in the direction of fluid flow direction (i.e. from left to right inFIG.1). In particular, the seal length is the distance from the inlet14of the passage12to the outlet16of the passage12. Preferably the ratio of the seal length in the aligned configuration to the maximum depth of the recesses18,19is at least 20:1.

FIG.2shows the seal assembly2of the first embodiment of the disclosure in an unaligned configuration. In particular, first component8is positioned relative to the second component10such that the upstream dwell portion20aof the first component8is opposite the recess19of the second component10, and the recess18of the first component8is opposite the downstream dwell portion21bof the second component10. During use, fluid enters the inlet14and passes into a first throat section22aof the passage12defined between the upstream dwell portion20aof the first component8and the upstream dwell portion21aof the second component10. The fluid then passes into a first chamber24adefined between the upstream dwell portion20aof the first component8and the recess19of the second component10. When the fluid enters the first chamber24a, the cross-sectional area available for fluid flow increases sharply over a short distance, and thus the fluid in the first chamber24abecomes turbulent and results in the formation of vortices. As set out above in relation to the aligned configuration, the vortices in the first chamber24aform a barrier impeding the flow of fluid out of the first chamber24a.

The fluid in the first chamber24athen passes into a second throat section22bdefined between the upstream dwell portion20aof the first component8and the downstream dwell portion21bof the second component10. After the second throat section, the fluid passes to a second chamber24bdefined between the recess18of the first component8and the downstream dwell portion21bof the second component10. As with the first chamber24a, when the fluid enters the second chamber24bthe cross-sectional area available for fluid flow increases sharply over a short distance, and hence the fluid in the second chamber24bbecomes turbulent. As for the first chamber24a, the turbulent fluid in the second chamber24bwill also comprise vortices which impede the flow of fluid into and out of the second chamber24b. The fluid in the second chamber24bthen passes into a third throat section22cdefined between the downstream dwell portion20bof the first component8and the downstream dwell portion21bof the second component10. Once the fluid has passed through the third throat section22c, it leaves the seal assembly via the exit16.

As shown inFIG.2, the geometry of the recesses18,19at the point at which the fluid enters the first and second chambers24a,24bdiverges from the overall direction of fluid flow by approximately 90°. As such, from the perspective of the fluid, the available area for fluid flow increases sharply over a relatively short distance, even though one side of the first and second chambers24a,24bis defined by a dwell portion20a,21band therefore remains “flat”. Therefore, even though the recesses18,19of the first and second components8,10are not aligned, the expansion in flow area provided by the geometry of the recesses18,19still produces sufficient turbulence to impede the flow of fluid through the seal assembly2. Furthermore, the sharp edges of the recesses18,19as the flow enters the first and second chambers24a,24balso causes the flow to “trip” resulting in additional turbulence impeding flow through the seal assembly2. In order to provide sufficient sealing ability when the recesses18,19are unaligned, it is beneficial to choose the dimensions of the recesses18,19and the minimum clearance between the first and second components8,10based upon the desired sealing performance in the unaligned configuration.

FIG.3shows the seal assembly2of the first embodiment of the disclosure in an overlapped configuration. The overlapped configuration is any configuration of the first and second components8,10in which the recesses18,19are laterally overlapped but are not fully aligned. In the configuration ofFIG.3, the first component8is positioned relative to the second component10such that part of the recess18of the first component8is opposite part of the second dwell portion21bof the second component10and part of the recess19of the second component10. Likewise, part of the recess19of the second component10is opposite part of the first dwell portion20aof the first component8and part of the recess18of the first component8. The recesses18,19therefore define a generally S-shaped configuration.

During use, in the overlapped configuration fluid enters the seal assembly2via the inlet14and passes into a first throat section22adefined between the upstream dwell portions20a,21aof the first and second components8,10. The fluid then passes into a chamber24defined between the recesses18,19, the upstream dwell portion20aof the first component8and the downstream dwell portion21bof the second component. As the fluid enters the chamber24from the first throat section22a, the available flow area defined between the recess19of the second component10and the first dwell portion20aof the first component8increases sharply, causing vortex generation in the flow. In addition, the sharp edge between the first dwell portion21aand the recess19of the second component10also causes the flow to “trip”, resulting in further turbulence. Furthermore, the sharp edge between the first dwell portion20and the recess18of the first component8and the sharp edge between the second dwell portion21band the recess19of the second component10also act to “trip” the flow, causing further turbulence and vortex generation. The flow through the chamber24in the overlapped configuration is therefore sufficiently turbulent to impede flow through the seal assembly2.

It can be seen that in all of the aligned, unaligned and overlapped configurations, the seal assembly2is able to provide resistance to fluid flow. However, because the resistance to flow is caused by the vortices, and the vortices are formed by the fluid itself, no additional sealing members are required in order to impede flow through the seal assembly. Furthermore, as discussed above, the vortices are generated by sharp increases in the available flow area between the first and second components8,10. As such, the seal arrangement2does not need to define a tortuous path in order to impede the flow. Consequently, the first and second components8,10do not require features which overlap in the vertical direction ofFIGS.1to3in order to provide a seal. Put another way, no part of the first component8extends into the recess19of the second component10, and no part of the second component10extends into the recess18of the first component8. Furthermore, no intermediate components, such as for example a sealing element, extends into the recess18,19of the first or second components8,10. As such, the recesses18,19are substantially free of solid objects, and only fluid passes into and out of the recesses18,19.

Because the first and second components8,10are substantially free of solid objects, the first component8and the second component10are free to move relative to one another in both the lateral and longitudinal directions whilst the minimum clearance between the first component8and the second component10(i.e. the vertical distance between the dwell portions20a,20bof the first component and the dwell portions21a,21bof the second component10) remains the same. The seal arrangement2therefore provides increased freedom of movement between the first and second components8,10as compared, for example, to a labyrinth type seal.

The fluid passing through the seal assembly defines a direction of fluid flow from the inlet14to the outlet16. With reference toFIGS.1to3, the direction of fluid flow is generally parallel to the lateral direction. As described above, because no part of the first component8extends into the recess19of the second component10, and because no part of the second component10extends into the recess18of the first component10this means that the first and second components8,10are free to move relative to one another generally towards and against the direction of fluid flow. As such, the seal assembly2is particularly suited to applications in which movement of the first and second components in the direction of fluid flow is required.

The surfaces of the recesses18,19may be rough or smooth. It has been found that sealing performance is improved when the recesses18,19have a surface roughness (Ra) within the range of around 10 μm to around 50 μm, and preferably around 25 μm. where the roughness is lower than this range not enough turbulence is created to dissipate energy to create the seal. Where the roughness is higher than this range flow begins to stagnate and prevents the formation of vortexes. It has been found that surface roughness (Ra) of 25 μm provides the optimum sealing effect. Surface roughness for these purposes is measured in terms of the arithmetical mean deviation, Ra, however substantially any suitable measure of surface roughness may be used (e.g. root mean squared, Rq, or the like). The dwell portions20a,20b,21a,21bmay have any suitable surface roughness, however preferably the dwell portions20a,20b,21a,21bare smooth so as to avoid any possible grinding or wearing effects in the event that the first component8engages the second component10as the two are moved relative to one another.

In alternative embodiments, the first and second components8,10of the seal assembly2may comprise a plurality of recesses18,19. One such embodiment is shown inFIG.4, which depicts a schematic cross-section of a second embodiment of a seal assembly2according to the present disclosure. The second embodiment of the disclosure differs from the first embodiment in that the first component8comprises a plurality of recesses18a-c, and the second component10comprises a plurality of recesses19a-c. The seal assembly2of the second embodiment is shown in the aligned configuration, such that a first recess18aof the first component8is positioned opposite a first recess19aof the second component10, a second recess18bof the first component8is positioned opposite a second recess19bof the second component10, and a third recess18cof the first component8is positioned opposite a third recess19cof the second component10. The plurality of recesses18a-cof the first component8and the plurality of recesses19a-cof the second component10define a plurality of cavities24a-ctherebetween. The recesses18a-cof the first component8are separated by a plurality of dwell portions20a-d, and the recesses19a-cof the second component10are separated by a plurality of dwell portions21a-d. The dwell portions20a-dof the first component8and the dwell portions21a-dof the second components10define a plurality throat sections22a-dtherebetween, in a corresponding manner to that set out above in relation to the first embodiment.

During use, fluid enters the seal assembly2from the high pressure environment4via the inlet14and passes into a first throat section22a. The fluid then subsequently passes out of the first throat section22a, and through a first cavity24a, a second throat section22b, a second cavity24b, a third throat section24c, a third cavity24cand a fourth throat section24d. Finally, the fluid passes out of the seal assembly2via the outlet16and into the low pressure environment6. It will be appreciated that the first and second components8,10may be moved relative to one another so that they define unaligned and overlapped configurations in the same manner as for the first embodiment.

As discussed above in relation to the first embodiment, the throat sections22a-dwill provide resistance to fluid flow due to the narrow clearance between the first and second components8,10in combination with the frictional force exerted on the fluid by the dwell portions20a-d,21a-d. Furthermore, each cavity24a-cwill allow the fluid to expand, thus causing vortex formation in the same way as for the first embodiment. However, because the seal assembly of the second embodiment comprises a plurality of throat sections22a-dand cavities24a-carranged in series, the overall resistance to flow through the seal assembly2of the second embodiment is higher than that of the first embodiment. Put another way, each of the throat sections22a-dand cavities24a-dwill cause the fluid to lose an associated amount of energy. The total amount of energy lost by the fluid as is passes from the inlet14to the outlet16is the sum of the associated amounts of energy for each of the throat sections22a-dand cavities24a-d. Therefore, by increasing the number of throat sections22a-dand cavities24a-dthrough which the fluid must pass, the total amount of energy loss through the seal assembly2can be increased. Because more energy is lost by the fluid as it passes through the seal assembly2, the resistance to flow through the seal assembly2is increased and therefore the sealing effectiveness of the seal assembly2is improved. However, it will be appreciated that for most operating conditions the cavities24a-cwill cause the fluid to lose more energy than the throat sections22a-d, and therefore the total resistance can be increased by increasing the number of cavities24a-d.

The first and second components8,10may comprise substantially any number of recesses18,19. However, it has been found that sealing performance is improved where the first component8and/or the second component10comprises a minimum of four or five recesses18,19. Generally, sealing performance will be improved as the number of recesses18,19increases. However, a minimum number of four or five recesses18,19provides an effective seal whilst saving the cost of manufacturing further recesses18,19. For a given seal length, it is generally preferable to increase the number of recesses18,19than to increase the size (e.g. diameter) of the individual recesses18,19as this will produce a more effective seal. However, the total number of recesses18,19may be dependent upon packaging constraints.

The recesses18a-c,19a-cmay be spaced apart from one another in the lateral direction by any suitable distance. In particular, the recesses may be arranged so that the centre of each recess is spaced from the centre of the adjacent recess by a distance equal to the width of the recess, 1.5 times the width of the recess, twice the width of the recess, 2.5 times the width of the recess or more. However, it has been found that the optimum lateral spacing between the centres of each recess is approximately at least twice the width of the recess. In particular, in the embodiment ofFIG.4each of the recesses18a-cof the first component8the recesses19a-cof the second component10defines a width in the lateral direction, and the width of each recess18a-c,19a-cis approximately the same. Furthermore, the second and third dwell portions20b,20cof the first component8and the second and third dwell portions21b,21cof the second component10each define a width in the lateral direction that is approximately equal to the width of the recesses18a-c,19a-c. As such, the centre of the first recess18aof the first component8is spaced apart from the centre of the second recess18bof the first component8by approximately twice the width of the recesses18a-c. The same applies for the spacing between the second the third recesses18b,18cof the first component8and the spacing between the recesses19a-cof the second component10. When the lateral spacing between the recesses is at least twice the width of each recess, this ensures that in all positions of the first component8relative to the second component10a throat section will exist. The presence of the throat section acts as a restrictor causing greater resistance to flow. However, it will be appreciated that when the lateral spacing between the recesses is increased beyond twice the width of the recesses, fewer recesses can fit on the first and second components8,10. As such, it is desirable to maintain the lateral spacing of the recesses18a-c,19a-cto as close to twice their width as possible.

In some embodiments, the recesses18of the first component8maybe a different size and shape to the recesses19of the second component10.FIG.5shows a schematic cross-sectional view of a third embodiment of a seal assembly2according to the present disclosure. The third embodiment of the disclosure differs from the second embodiment of the disclosure in that the recesses18a-cof the first component8are larger than the recesses19a-cof the second component10. In the embodiment shown inFIG.5, when the first and second components8,10are in an aligned configuration, the recesses18a-cof the first component8and the recesses19a-cof the second component10together define generally circular cavities24a-c. However, the recesses18a-cof the first component8define major segments of the circular cavities24a-cand the recesses19a-cof the second component define minor segments of the circular cavities24a-c. As such, the throat sections22a-dare not aligned with the centres of the circular cavities24a-c. The throat sections22a-dmay be displaced away from the centres of the circular passages by any suitable distance, for example by a distance equal to around half of the radius of the circular cavities24a-c.

Because the recesses18a-cof the first component8are a different size and shape to the recesses19a-cof the second component, the throat sections22a-dare vertically offset from the centres of the cavities24a. This may be advantageous for example in situations where it is not possible to create large cavities on the surface of the second component10, for example where the thickness of the second component10in the vertical direction is relatively thin.

FIG.6shows a fourth embodiment of a seal assembly2according to the present disclosure. The fourth embodiment of the seal assembly2differs from the third embodiment in that the second recess18bof the first component8is smaller than the second recess19bof the second component10. As such, the relationship regarding which of the recesses of the first and second component8,10is larger than the other is reversed for the second recess18b,19b. In other embodiments, this relationship may be reversed for any of the plurality of recesses18,19.

FIG.7shows a fifth embodiment of a seal assembly2according to the present disclosure. The fifth embodiment of the seal assembly2differs from the first to fourth embodiments of the seal assembly2in that the recesses18,19of the first and second components8,10define a generally sawtooth-like profile. That is to say, the recesses18,19are asymmetric from upstream to downstream. With reference to the second recess18bof the first component8, the sawtooth-like profiles comprise a sloped portion26, a flat portion28, and a vertical portion30. The sloped portion26extends between an upstream dwell portion, such as the second dwell portion20bof the first component8, and the flat portion28. The sloped portion26is angled away from the lateral direction such that the width of the passage12increases in the direction from the upstream dwell portion20bto the flat portion28. The angle of the sloped portion26relative to the lateral direction is preferably within the range of around 20° to around 70°, and more preferably is in the range of around 30° to around 60°. The flat portion28extends between the sloped portion26and the vertical portion30. The flat portion28is generally parallel to the lateral direction, however in alternative embodiments the flat portion28may be sloped towards or away from the lateral direction by a small amount, for example plus or minus an angle in the range of around 0° to around 5°. The vertical portion30extends between the flat portion28and a downstream dwell portion, such as the third dwell portion20cof the first component8. The vertical portion30extends generally in the vertical direction. That is to say, the vertical portion30extends generally normal to the lateral direction within the plane ofFIG.7. However, in alternative embodiments the vertical portion30may be angled relative to the vertical direction by a small amount, for example plus or minus an angle in the range of around 0° to around 5°.

With reference to the second cavity24b, during use, the fluid enters the second cavity24bfrom the second throat section22b. The sloped portions26of the recesses18b,19bcause the passage12to widen, thus increasing the Reynolds number of the fluid in the second cavity24b, resulting in turbulent flow and the formation of vortices. Because the vertical portion30is inclined generally normal to the lateral direction, some of the fluid in the second cavity24bwill impinge upon the vertical portion30. The vertical portion30prevents further movement of the fluid in the lateral direction, and causes the impinged fluid to recirculate, thus creating further vortices and leading to additional frictional losses. It will be appreciated that in alternative embodiments, one or more (or all) of the sloped portions26and the vertical portions30may be swapped around so that the sawtooth profile is reversed. In such embodiments the fluid will enter the cavities24a-con the side of the vertical portions30, such that rapid expansion of the fluid will occur in the cavities24a-ccreating turbulence.

FIG.8shows a sixth embodiment of a seal assembly2according to the present disclosure. The sixth embodiment of the seal assembly2differs from the fifth embodiment of the seal assembly2in that the recesses18,19define generally scooped profiles. Such scooped profiles are another example of an asymmetric recess. With reference to the second recess18bof the first component8, the scooped profiles comprise a diverging portion32, an apex34, and a backflow portion36. The diverging portion32extends between an upstream dwell portion, such as the second dwell portion20bof the first component8, and the apex34. The diverging portion32is angled away from the lateral direction such that the width of the passage12increases in the direction from the upstream dwell portion20bto the apex34. The angle of the diverging portion32relative to the lateral direction at the join between the upstream dwell portion20band the diverging portion32is preferably within the range of around 20° to around 70°, and more preferably is in the range of around 30° to around 60°. The apex34extends between the diverging portion32and the backflow portion36. The backflow portion36extends between the apex34and a downstream dwell portion, such as the third dwell portion20cof the first component8. At the join between the backflow portion36and the downstream dwell portion20cof the first component8, the backflow portion36is preferably angled relative to the vertical direction by an angle in the range of around 0° to around 30°, around 5° to around 20°, or around 10° to around 15°.

With reference to the second cavity24b, during use, the fluid enters the second cavity24bfrom the second throat section22b. The diverging portion32of the recesses18b,19bcause the passage12to widen, thus increasing the Reynolds number of the fluid in the second cavity24b, resulting in turbulent flow and the formation of vortices. Furthermore the apex34and the backflow portion36act to scoop the fluid in the chamber around so that a portion of the fluid begins to flow back towards the second (i.e. upstream) throat section22b. The “scooped” fluid acts to form a barrier which impedes flow through the cavity24b. Furthermore, the “scooped” fluid will mix with the fluid entering the second cavity24bfrom the upstream throat portion22b, thus resulting in further turbulence and vortex formation. It will be appreciated that in alternative embodiments, one or more (or all) of the diverging portions32and the backflow portions36may be swapped around so that the scooped profile is reversed. In such embodiments the fluid will enter the cavities24a-con the side of the backflow portions36, such that rapid expansion of the fluid will occur in the cavities24a-ccreating turbulence.

FIG.9shows a seventh embodiment of a seal assembly2according to the present disclosure. The seventh embodiment of the seal assembly2differs from the second to sixth embodiments of the seal assembly2in that the recesses18a-c,19a-cof the first and second components8,10are varied in size. In particular, the first recesses18a,19aare larger than the second recesses18b,19b, which are in turn larger than the third recesses18c,19c. As such, the first cavity24ais larger than the second cavity24bwhich is larger than the third cavity24c. This is advantageous where the pressure differential between the high pressure environment4and the low pressure environment6driving the flow through the passage12is highly variable. In particular, when the pressure differential is large, the velocity of the fluid flowing through the passage12will be relatively high, and when the pressure differential is small the velocity of the fluid flowing through the passage12will be relatively low. The size of the first cavity24amay be chosen so that the Reynolds number of the fluid flowing through the first cavity24ais large enough to result in turbulent flow even when the velocity of the fluid is relatively high. Likewise, the size of the third cavity24cmay be chosen so that it is able to generate turbulence when the velocity of the fluid is relatively low. As such, the seal assembly2of the seventh embodiment is able to ensure that turbulence is generated across a range of different flow conditions. Furthermore, the difference in size between adjacent recesses18a-c,19a-ccan be chosen so that a constant pressure drop occurs over each recess18a-c,19a-c.

FIG.10shows an eighth embodiment of a seal assembly2according to the present disclosure. In eighth embodiment of the seal assembly2, the second component10comprises a plurality of dimples38. The dimples38differ from the recesses of the previous embodiments in that the dimples38are discrete concave indentations formed on the surface of the second component10, and as such the dimples38are examples of concavities. The dimples38are generally circular such that, for a given dimple38, the width of the dimple38in the lateral direction is approximately the same as the width of the dimple38in the longitudinal direction. Collectively, the dimples38have the effect that they create a roughened surface on the second component10. The roughened surface generates turbulence in the fluid flowing through the passage12. The turbulent flow generated by the dimples38contains vortices and therefore increases the resistance to fluid flow through the seal assembly2. The dimples38may be formed by machining or pressing the surface of the second component10.

FIG.11shows a ninth embodiment of a seal assembly2according to the present disclosure. In the seal assembly2of the ninth embodiment, the first component comprises three semi-circular recesses18a,18c,18dinterspaced with sawtooth-like recesses18b,18d. Likewise, the second component10comprises three semi-circular recesses19a,19c,19dinterspaced with sawtooth-like recesses19b,19d. As such, the recesses of the first and second components8,10form an alternating pattern of semi-circular and sawtooth-like profiles. Furthermore, the semi-circular recesses define a depth in the vertical direction which is greater than a corresponding depth defined by the sawtooth-like recesses. It will be appreciated that a given recess size and geometry will be suited to creating vortices for a particular range of flow conditions. Because the seal assembly2of the ninth embodiment comprises two different kinds of recess that are of different shapes and sizes to one another, the seal assembly2will cause vortex formation across a larger range of flow conditions.

FIG.12shows a tenth embodiment of a seal assembly2according to the present disclosure. In the seal assembly2of the tenth embodiment, the first component8comprises four recesses18a-dand the second component10comprises four recesses19a-d. The recesses18a-dof the first component8and the recesses19a-dof the second component smoothly transition between peak points (at which the distance between the first and second components8,10is minimal) and trough points (at which the distance between the first and second components8,10is largest). The recesses18a-d,19a-dact to diffuse and then constrict flow through the passage12. This causes turbulence which impedes flow through the seal assembly2.

Although a number of embodiments of a seal assembly2according to the present disclosure have been discussed above, it will be appreciated that further embodiments of the seal assembly2are contemplated as forming part of the disclosure. For example, in alternative embodiments the recesses18,19may comprise cross-sectional profiles aside from those illustrates above, including for example: triangular, square, rectangular or any other suitable cross-sectional profile. Such profiles may be symmetric, such as in the first to fourth embodiments, or may be asymmetric, such as in the fifth and sixth embodiments. The first and second components8,10may comprise substantially any suitable number of recesses18,19. Furthermore, it will be appreciated that the size and shape of the recesses18,19may be chosen to be most effective at creating turbulence over a range of flow conditions that correspond to the operating conditions of the seal assembly.

In some embodiments the number of recesses18of the first component8may be unequal to the number of recesses19of the second component10. In some embodiments one of the first or second components8,10may comprise no recesses, such that that side of the passage12defined by that component consists entirely of a single extended dwell portion. Furthermore, in alternative embodiments one or both of the first and second components8,10may comprise recesses which are not separated by dwell portions. In further embodiments the seal assembly2may comprise more than one type of recess size or geometry, for example three or more types. The different recess types may be arranged in substantially any suitable pattern. The recesses18,19may extend in the longitudinal direction of the first and/or second components8,10for only a portion of or for the entire longitudinal extend of the first and/or second component8,10. The seal assembly2may comprise a mixture of longitudinally extending recesses18,19and dimples32. The recesses18,19themselves may also comprise dimples32form on their surfaces. It will further be appreciated that in the recesses18,19need not define straight paths but could define curved, sinusoidal or zig-zagged paths or any other suitable path geometry.

In yet further embodiments, the recesses18or the first component8and/or the recesses19of the second component10may be generally hemispherical or domed. The recesses18,19may be substantially any spherical cap shape, and need not necessarily be a hemisphere. It has been found that where the recesses are shaped as spherical caps (including hemispheres), the sealing effectiveness is approximately the same as embodiments where the recesses18,19are elongate grooves. The spherical caps may be spaced apart by the same distances and proportions as described above in relation to the embodiments in which the recesses18,19are elongate grooves.

The seal assembly2of the embodiments described above may be implemented in a range of different applications. One such application is to improve sealing of a rotary bypass valve for a turbine, such as for example within a turbocharger system. However, it will be appreciated that the seal assembly2could be implemented in substantially any suitable valve.

FIGS.13to15depict a rotary valve100for use as a turbine control valve. The rotary valve100may be used, for example, within an engine system comprising a turbocharger. The rotary valve100comprises an outer housing102, an inner housing103, a sleeve105, and a valve member104. The outer housing102, inner housing103, and the sleeve105are generally tubular. The sleeve105is received within the inner housing103and the inner housing103is received within the outer housing102. The outer housing102, inner housing103and sleeve105are rotationally fixed in relation to one another. The sleeve105defines a valve chamber106within which the valve member104is positioned.

The outer housing102, inner housing103and sleeve105define an inlet108, a primary outlet110and a secondary outlet112. The inlet108, primary outlet110and secondary outlet112lie within a common plane and extend from an exterior of the rotary valve100to the valve chamber106via openings formed in the outer housing102, inner housing103and sleeve105. The valve chamber106is generally cylindrical and defines a longitudinal axis114of the rotary valve100that extends generally transverse to the common plane defined by the inlet108, primary outlet110and secondary outlet112(i.e. orthogonal to the perspective ofFIG.13). During use, the inlet108is connected to an exhaust of an internal combustion engine (not shown) so that it receives exhaust gas from the internal combustion engine. The primary outlet110is connected to an inlet of a turbine (not shown), for example forming part of a turbocharger. The secondary outlet112is connected to a bypass passage (not shown) for delivering exhaust gas to a position downstream of the turbine without passing through the turbine. The portions of the outer housing102defining the inlet108, primary outlet110and/or secondary outlet112may additionally comprise mounting flanges.

As shown most clearly inFIG.15, the valve member104is generally cylindrical and comprises end walls126positioned at longitudinally opposite ends of the body105which are connected by a longitudinally extending web130. The diameter of the valve member104may be any suitable size, however in the present embodiment the diameter of the valve member104is in the range of around 30 mm to around 100 mm. The end walls126and the web130define a channel124that penetrates the body105in a direction generally perpendicular to the longitudinal axis114. The end walls126are received within end caps116having longitudinally extending shafts118aligned with the longitudinal axis114. The end caps116are rotationally fixed with respect to the valve member104, for example by using an interference fit or an adhesive, such that the valve member104rotates with the end caps116.

As shown inFIGS.14and15, the inner housing103comprises a first housing portion119and a second housing portion120. The first housing portion119, second housing portion120and sleeve105are shown in cross-section inFIG.14for ease of reference. However the valve member104and end caps116are not shown in cross-section, such that their external surfaces are visible inFIG.14. The first and second housing portion119,120are generally cup-shaped such that the first and second housing portions119,120at least partially receive the valve member104. The first housing portion119comprises a stepped section122for receiving the sleeve105, and the second housing portion120abuts the sleeve105to axially retain the sleeve105between the first and second housing portions119,120. The shafts118of the end caps116extend through a bore142of the first housing portion119and a bore144of the second housing portion120. The shafts118support the valve member104for rotation within the valve chamber106about the longitudinal axis114. At least one of the shafts118of the end caps116extends out of the rotary valve100and is connected to an actuation mechanism (not shown) so as to control the rotational position of the valve member104within the valve chamber106. The bores142,144may further comprise bearings or bushings to support the valve member104for rotation. Although not shown inFIG.14or15, the outermost diameters of the end caps116may be sealed against the first and second housing portions119,120using a physical contact seal. The end caps116function to retain the valve member104within the rotary valve100and to support the valve member104for rotation.

The valve member104defines a closed-bypass configuration and an open-bypass configuration. The closed-bypass configuration is shown inFIG.13and corresponds to a position of the valve member104in which the web130blocks the entrance to the secondary outlet112(and hence to the bypass passage) whilst permitting fluid to flow from the inlet108to the primary outlet110(and hence to the turbine). The open-bypass configuration corresponds to a position of the valve member104in which the valve member104has been rotated so that the web130is no longer blocking the entrance to the secondary outlet112(so that fluid can flow to the bypass passage) whilst also permitting fluid flow to the primary outlet110. This corresponds to a position in which the valve member104shown inFIG.13has been rotated approximately 90° in an anti-clockwise direction.

With reference toFIG.13, the sleeve105comprises a plurality of inwardly-facing recesses138and the valve member104comprises a corresponding plurality of outwardly-facing recesses140. The recesses138,140have a diameter of approximately 1.5 mm. Both sets of recesses138,140extend generally parallel to the longitudinal axis114of the rotary valve100. The inwardly-facing recesses138of the sleeve105are formed on a generally cylindrical inner surface of the sleeve105, and the outwardly-facing recesses140of the valve member104are formed on a generally arcuate outer surface of the web130. The outer surface of the web130and the inner surface of the sleeve105are spaced apart from one another by a narrow clearance154. The clearance154is a relatively narrow gap which ensures that the valve member104is free to rotate within the valve chamber106relative to the sleeve105.

Due to the presence of the clearance154, during use, some exhaust gas is able to leak past the valve member104between the valve member104and the sleeve105. When the valve member104is in the closed position, a portion of the exhaust gas may leak from the inlet108to the secondary outlet112. The leaked exhaust gas does not pass through the turbine, and therefore the amount of energy absorbed by the turbine and the efficiency of the turbine is decreased. However, due to the presence of the outwardly-facing recesses138of the sleeve105and the corresponding inwardly-facing recesses140of the valve member104, the overall rate of leakage into the secondary outlet112via the clearance154is reduced. In particular, as described above in relation to the seal assembly2, the recesses138,140cause the formation of vortices which act to substantially impede the flow of exhaust gas through the space between the valve member104and the sleeve105. As such, the sleeve105and the valve member104may be considered to correspond to the first and second components8,10of the seal assembly2described above.

Because the recesses138,140generate vortices that impede leakage of exhaust gas into the secondary outlet112, the rotary valve100does not require a contact seal between the sleeve105and the valve member104. By contrast, if a contact seal were used between the sleeve105and the valve member106, this would exert a relatively large frictional force that would resist rotation of the valve member104. Furthermore, because the recesses138,140are concave features formed on opposing surfaces of the sleeve105and the valve member104, no part of the sleeve105extends into the recesses140of the valve member104and no part of the valve member104extends into the recesses138of the sleeve105. As such, the valve member104is free to rotate relative to the housing102about the longitudinal axis114. By contrast, a conventional labyrinth seal would not be appropriate for creating a seal between the valve member104and the sleeve105because in order to create the labyrinth seal a portion of the valve member104(or an intermediate component) would need to extend into a portion of the sleeve105(or vice versa), which would prevent rotation of the valve member104about the longitudinal axis114. The rotary valve100therefore provides improved sealing without constraining movement of the valve member104.

The use of a sleeve105to define the inwardly-facing recesses is beneficial because the sleeve can by manufactured more cheaply than the outer housing102or inner housing103. The sleeve105can be manufactured, for example, by casting, machining or chemical etching. In some embodiments, the sleeve105may be made from a corrugated sheet of material to define the inwardly-facing recesses138. It will be appreciated that because the sleeve105surrounds the valve member104, the sleeve105may be considered to form part of a housing of the rotary valve100. Furthermore, some embodiments may not comprise an inner housing103. However, the benefit of using an inner housing103is that the valve member104, end caps116, sleeve105, and inner housing103can be pre-assembled into a cartridge which is then simply inserted into the outer housing102thus improving the ease of assembly. Furthermore, because the components of the cartridge are generally smaller than the outer housing102it is easier to control the geometry (i.e. tolerances) of the components in the cartridge, and thereby avoid the need to tightly control the geometry of the relatively large outer housing.

However, in alternative embodiments, the outer housing102or the inner housing103may define the plurality of inwardly facing recesses138. Such embodiments may therefore not comprise a sleeve105. In yet further embodiments, the shafts118may be integrally formed with the valve member104such that the rotary valve100does not comprise end caps116(or, put another way, the end caps116may be integrally formed with the valve member104). By eliminating the end caps116and/or the sleeve105, fewer components are required to define the rotary valve100, and therefore the rotary valve100is simpler and cheaper to manufacture and assemble.

The housing102and/or the sleeve105may comprise a single concavity or a plurality of concavities for generating vortices. The concavity (or concavities) may have substantially any geometry for generating vortices, such as for example any of the geometries described above in relation to the seal assembly2.

In some embodiments, the rotary valve100may be for use with a twin-entry turbine. As such, the inlet108, the primary outlet110and secondary outlet112may be divided into two axially separated sections (for example, by the presence of a dividing wall in the plane normal to the longitudinal axis114of the valve chamber106). In such embodiments, the valve member104may comprise a dividing wall positioned between the end walls126so as to split the channel124into two axially separated sections. The dividing wall acts to prevent transient pressure fluctuations causing interference between the exhaust gasses passing through the two separated sections of the rotary valve100.

FIG.24shows rotary valve100′ which is an alternative embodiment of the rotary valve100described above. In rotary valve100′ the primary outlet110′ is positioned opposite the inlet108and the secondary outlet112′ is positioned at approximately 90° to the inlet108and the primary outlet110′.

It has been found that around five consecutively arranged recesses138,140provide the optimum sufficient sealing effect. As such, the recesses138,140may be positioned in groups of five at or near to a point of leakage, whilst saving the cost of machining further recesses into the valve member104or the sleeve105. Such an arrangement is shown inFIG.24. In particular, it can be seen fromFIG.24that the web130of the valve member104comprises five recesses140arranged in a first grouping141and five further recesses140arranged in a second grouping143. The first grouping141is positioned adjacent to a first edge of the web130and the second grouping143is positioned adjacent to a second edge of the web130. Furthermore, the sleeve105comprises five recesses138positioned in a third grouping145positioned in a first grouping145adjacent to the primary outlet110′ and five recesses138positioned in a fourth grouping147adjacent to the inlet108. The third and fourth groupings are positioned on the opposite side of the sleeve105to the secondary outlet112′. The sleeve105further comprises five recesses138positioned in a fifth grouping149between the inlet108and the secondary outlet112′, and five recesses138positioned in a sixth grouping151between the primary outlet110′ and the secondary outlet112′.

An important sealing position of the valve member104is when the valve member104is blocking the primary outlet110′. As such, it is preferable that the valve100′ comprises at least the first and second groupings141,143, the third grouping145and the sixth grouping151. That is to say, preferably a grouping of around five recesses is present on the sleeve105either side of the outlet connected to the bypass passage to improve the seal effect when the web130is blocking the bypass passage. However, it will be appreciated that in alternative embodiments the valve100′ may comprise substantially any suitable number of groupings. The groupings may be placed in any suitable position within the valve member104. Furthermore, the groupings may comprise any suitable number of recesses (e.g. three, four, six or more recesses). The groupings need not all comprise the same number of recesses, and the number of recesses in each grouping may be varied in dependence upon packaging constraints.

FIG.23shows a turbine146comprising a generally volute-shaped turbine housing150having an integrated rotary valve100. The turbine housing defines an inlet152and an outlet154. The valve member104is connected to an actuator156that is configured to control the angular position of the valve member104. The actuator156is supported by a bracket157mounted to the turbine housing150. The valve member104is visible through a cut-out portion of the turbine housing150. The valve member104of the turbine146does not comprise end caps116, and the shafts118are integrally formed with the valve member104. The turbine146is a twin volute (twin entry) turbine, and therefore the valve member104comprises a dividing wall148positioned approximately halfway between the end walls126.

The turbine housing150is equivalent to the first housing portion119of the previous embodiment of the rotary valve100described above (that is to say, the turbine housing150may define the first housing portion119). The turbine housing150may therefore define one of the first and second components8,10of the seal assembly2described above. The turbine146comprises a cover plate158which is equivalent to the second housing portion120of the previous embodiment of the rotary valve100described above (that is to say, the cover plate158may define the second housing portion120). The cover plate158may therefore define the other of the first and second components8,10of the seal assembly2. Alternatively, the valve member104may define one of the first and/or second components8,10of the seal assembly2.

Because the rotary valve100is integrated with the turbine housing150, the rotary valve100can be positioned closer to the turbine wheel (not shown) than in alternative arrangements where the entire rotary valve is positioned upstream of the turbine housing150. It will be appreciated that because the turbine housing is generally volute-shaped, the cross-sectional area available for fluid flow decreases around the turbine wheel. Due to the Bernoulli principle, the pressure of the fluid will be higher where the cross-sectional area available for flow is reduced. Because the rotary valve100is closer to the turbine wheel, the rotary valve100may be positioned at a point where the flow area is reduced, and hence the fluid pressure in the passage is lower. The lower fluid pressure in the passage creates a larger pressure differential across the seal assembly2(formed by the turbine housing150and the valve member104) which drives turbulence creation within the recesses138,140thus improving the effectiveness of the seal. Furthermore, integrating the rotary valve100with the turbine housing150reduces the complexity of the turbine148, saving costs during manufacture and assembly.

Another specific application of the seal assembly2is shown inFIG.16, which depicts a schematic cross-sectional view of a turbocharger200. The turbocharger200comprises a compressor202, a bearing housing204and a turbine206. The compressor202comprises a compressor wheel208, and a compressor housing210. The compressor housing210defines a compressor volute211. The compressor wheel208comprises a back face227positioned opposite a compressor end213of the bearing housing204so as to define a compressor leakage passage219therebetween. The turbine206comprises a turbine wheel212and a turbine housing214. The turbine housing214defines a turbine volute215. The turbine wheel221comprises a back face229positioned opposite a turbine end217of the bearing housing204so as to define a turbine leakage passage231therebetween. It will be appreciated that the compressor202and the turbine206are each an example of an impeller assembly. In particular, the compressor wheel208and the turbine wheel212are examples of impeller wheels.

The turbine wheel212is integrally formed with a turbocharger shaft216which extends through the bearing housing204to the compressor202. The compressor wheel208is mounted to an opposite end of the turbocharger shaft216to the turbine wheel212and is held in place by a compressor nut218. The turbocharger shaft216is supported for rotation about a turbocharger axis220by a pair of bearings222disposed in the bearing housing204. During use exhaust gas from an internal combustion engine (not shown) is fed to the turbine206which causes the turbine wheel212to spin, thus driving the compressor wheel218. The compressor wheel218compresses air so that it is at a pressure above atmospheric pressure, and the compressed air is fed to the intake of the internal combustion engine so as to increase the power output of the internal combustion engine, as would be known to a person skilled in the art.

The bearing housing comprises lubrication channels224which feed lubricant to the bearings222. This reduces the friction experienced by the turbocharger shaft216as it rotates, and improves power transmission from the turbine wheel212to the compressor wheel218(i.e. by reducing frictional losses). In general, the pressure of the intake air in the compressor volute211will be higher than the pressure within the bearing housing204. As such, fluid from the compressor volute211will leak into the bearing housing204via the compressor leakage passage219. Likewise, the pressure of the exhaust gas in the turbine volute215will be higher than the pressure within the bearing housing204and therefore fluid from the turbine volute215will leak into the bearing housing204via the turbine leakage passage231. However, under some operating conditions the pressure in the one of the compressor or turbine volutes211,215may be substantially higher than the other. In such circumstances, the fluid pressure from the higher pressure volute can be transferred through the beating housing204to the lower pressure volute. It is therefore possible for lubricating fluid to flow from the bearing housing204and into the compressor or turbine volutes211,215where it can be problematic for operation of the turbocharger200, the engine, or any aftertreatment systems.

In order to solve this problem, the compressor end213of the bearing housing204comprises a plurality of recesses226positioned behind the back face227of the compressor wheel208. The recesses226of the compressor end213of the bearing housing204extend circumferentially around the turbocharger axis220and are arranged concentrically to one another. Additionally, the back face227of the compressor wheel208comprises a corresponding series of recesses228. The recesses228of the back face227of the compressor wheel208extend circumferentially around the turbocharger axis220and are arranged concentrically to one another. During use, compressed air which leaks from the compressor volute211into compressor leakage passage219will be disrupted by the presence of the recesses226,228of the compressor wheel208and the compressor end213of the bearing housing204. The recesses226,228will cause the air within the compressor leakage passage219to become turbulent, leading to the formation of vortices and causing the air to lose energy (as explained above in relation to the seal assembly2). As such, the recesses226,228form act to impede fluid flow through the compressor leakage passage219. Because the compressor wheel208and the compressor end213of the bearing housing204comprise recesses226,228, it will be appreciated that the compressor wheel208and the compressor end213of the bearing housing204correspond to the first component8and/or second component10of the seal assembly2described above.

Likewise, the turbine end217of the bearing housing204comprises a plurality of recesses230positioned behind the back face229of the turbine wheel212, and the back face229of the turbine wheel212comprises a plurality of recesses232. The recesses230,232of the turbine end217of the bearing housing204and the turbine wheel212extend circumferentially around the turbocharger axis220and are arranged concentrically to one another. The recesses230,232of the turbine housing214and the turbine wheel212will cause vortex formation in any fluid that flows through the turbine leakage passage231, which will impede fluid leakage from through the turbine leakage passage231. Because the turbine wheel212and the turbine end217of the bearing housing204comprise recesses230,232, it will be appreciated that the turbine wheel212and the turbine end217of the bearing housing correspond to the first component8and/or second component10of the seal assembly2described above.

In alternative embodiments, the recesses226,228,230,232may be arranged so that they are directed radially outwards from the turbocharger axis220. Additionally or alternatively, the recesses226,228,230,232may be arranged so that they are spirals extending outwardly from the turbocharger axis220, or may be a plurality of dimples. It will be appreciated that any component of the compressor202which defines at least a portion of the compressor leakage passage219and any component of the turbine206which defines at least a portion of the turbine leakage passage231may comprise recesses configured to generate vortices. For example, the compressor housing210, turbine housing214, and/or bearing housing204may comprise recesses and may therefore correspond to the first component8and/or the second component10of the seal assembly2.

FIG.17discloses another embodiment of a turbocharger200. The compressor wheel208comprises a plurality of compressor blades240. The compressor blades define a generally curved axial cross-section such that incoming air enters the compressor202in an axial direction exits in a radially outward direction. That is to say, the curved cross-section is defined between an inducer portion and an exducer portion of the compressor wheel208. The compressor housing210comprises a curved profile242that closely conforms to the cross-axial cross-section of the compressor blades240. So that the compressor wheel208is rotatable relative to the compressor housing210, a clearance243is present between the compressor blades240and the curved profile242of the compressor housing210. Often, air passing through the compressor is able to pass through the clearance243. Air passing through the clearance243will not be compressed as much as the air passing through the compressor wheel208, and thus the efficiency of the compressor202will be reduced.

However, as shown inFIG.17the curved profile242of the compressor housing210comprises a plurality of recesses244. The recesses244extend circumferentially around the turbocharger axis220and are arranged concentrically to one another. However, in alternative embodiments the recesses244may extend parallel to the turbocharger axis220or may be spiral shaped or may be a plurality of dimples. The recesses generate turbulence in the clearance243which acts to impede air flow through the clearance243and thereby increase the efficiency of the compressor202.

Likewise, the turbine wheel212comprises a plurality of turbine blades246separated from a curved profile248of the turbine housing214by a clearance250. During use, a portion of the exhaust gas can pass through the clearance250, thus reducing the efficiency of the turbine206as this portion of the exhaust gas does not impart any energy on the turbine blades246. To solve this problem, the curved profile248of the turbine housing214comprises a plurality of recesses252, which may be the same as the recesses244of the compressor202. The recesses252of the turbine206cause turbulent flow in the clearance250of the turbine202thus reducing leakage through the clearance250and improving the efficiency of the turbine202in the same way as described above for the compressor202.

FIG.18shows a front view of a portion impeller wheel260for use as the compressor wheel208or the turbine wheel212of the turbocharger200. The impeller wheel260comprises a plurality of impeller blades262extending generally radially outwards from an impeller axis264to an impeller circumference266. For clarity, only one impeller blade262is shown inFIG.18. The impeller blades262comprise recesses268which extend along the tips of the impeller blades generally from the impeller axis264to the impeller circumference266. As such, it will be appreciated that the tips of the impeller blades262may comprise the first component8and/or the second component10of the seal assembly2.

As discussed above in relation toFIG.17, during use some fluid may leak through the region of space between the compressor blades240and the compressor housing210or between the turbine blades246and the turbine housing214. This leakage means that less energy is imparted on the fluid by the compressor wheel208and less energy is imparted on the turbine wheel212by the fluid passing through the turbine206. However, if the impeller wheel260ofFIG.18is used for the compressor wheel208and/or the turbine wheel212, the recesses268of the impeller wheel will cause turbulence in the regions of space through which fluid leaks, this impeding fluid leakage and improving the performance of the compressor202and/or the turbine206.

The radially outermost part of the impeller blades262further comprise a pair of winglets270extending away from the recesses268in a generally circumferential direction. The winglets270increase the surface area over which fluid must flow in order to leak out over the radially outer ends of the blades262. As such, the winglets270act to further impede leakage.

It will be appreciated that the above described embodiments of the turbocharger200may be combined to impede leakage from behind the compressor wheel208and/or turbine wheel212and to impede leakage over the tips of the compressor blades240and/or turbine blades246.

It will be appreciated that the seal assembly2may be applied in any application where there is a pressure differential across a gap defined between two relatively moving components. One such example is depicted inFIG.19, which shows a schematic cross-sectional view of a wastegate assembly300for a turbine. The wastegate assembly300comprises a wastegate valve member302, a wastegate shaft304, and an actuator linkage306. The wastegate shaft304passes through a bush308held securely within a bore310of a turbine housing312. The outer diameter of the wastegate shaft304fits tightly against but is slightly narrower than the inner diameter of the bush310so as to leave a clearance313therebetween. The clearance313allows the wastegate shaft304to rotate relative to the bush308. The turbine housing312defines an interior side314and an exterior side316. The interior side314contains high temperature and pressure exhaust gas, and the exterior side316is open to atmosphere.

During use, the actuator linkage exerts a torsional force upon the wastegate shaft304to cause the wastegate shaft304to rotate relative to the bush308and the turbine housing312. This causes the wastegate valve member302to cover or uncover a wastegate passage (not shown) which permits exhaust gas to vent from a position upstream of a turbine wheel to a position downstream of the turbine wheel without passing through the turbine wheel. In this way, the wastegate assembly300can be used to control the amount of rotational energy produced by the turbine wheel.

However, because the pressure of the exhaust gas on the interior side314of the turbine housing312is higher than the atmospheric pressure the air on the exterior side316of the turbine housing312, exhaust gas will leak through the clearance313between the wastegate shaft304and the bush308. The leaked exhaust gas will not pass through the exhaust gas aftertreatment system, and is therefore potentially harmful to the environment. In order to solve this problem, the wastegate shaft304comprises a plurality of circumferentially extending groves318axially spaced apart from one another along the shaft304, and the bush308comprises a corresponding plurality of circumferentially extending grooves320axially spaced apart from one another along the bush308. The corresponding sets of grooves318,320cause the formation of vortices within the exhaust gas flowing through the clearance313, which acts to impede the flow of exhaust gas from the interior side314to the exterior side316of the turbine housing312. It is advantageous for the grooves318,320to be arranged circumferentially so that the exhaust gas leaking through the clearance313will pass over each of the grooves318,320in series.

Because the wastegate shaft304comprises grooves318and the bush308comprises grooves320, the wastegate shaft304and the bush308may be considered to correspond to the first component8and/or the second component10of the seal assembly2. It will be appreciated that in alternative embodiments, the bush308may not be present, and therefore the turbine housing312may comprise a plurality of grooves configured to generate vortices. In such embodiments, the turbine housing312may be considered to correspond to the first component8and/or the second component10of the seal assembly2. It will be appreciated that the wastegate shaft304, the bush308, and/or the turbine housing312may comprise substantially any suitable geometry for the grooves318,320, such as those discussed above in relation to the seal assembly2. For example, the wastegate shaft304may comprise a plurality of dimples, and the bush308may comprise grooves320, or vice versa.

In some embodiments, the wastegate assembly300may additionally comprise one or more sealing elements (e.g. O-rings or piston rings) to create a contact seal between the wastegate shaft304and the turbine housing312and/or bush308. In such embodiments, the grooves318,320provide the advantage that the wastegate assembly is still able to impede leakage through the clearance313in the event that the sealing elements break. As such, the grooves318,320may be used as a back-up or auxiliary sealing means.

FIG.20shows a further application of the seal assembly2. In particular,FIG.20shows a turbocharger400comprising a turbine402and a bearing housing404. The turbine402comprises a turbine housing406defining an inlet volute408. The turbine402further comprises a turbine wheel410which is mounted to a turbocharger shaft412supported for rotation about a turbocharger axis413by bearings414. In order to permit the turbocharger shaft412to rotate relative to the bearing housing404, the shaft412and the bearing housing404define a clearance416therebetween.

As described above, during use the pressure of the air in the bearing housing404will be less than the pressure of the fluid in the inlet volute408, and therefore during use some exhaust gas will leak from the inlet volute408through the clearance416and into the bearing housing404, reducing the efficiency of the turbine402. In order to solve this problem, the bearing housing404comprises a plurality of circumferentially extending grooves418spaced axially along the turbocharger axis413, and the turbocharger shaft412comprises a plurality of circumferentially extending grooves420spaced axially along the turbocharger axis413. The presence of the grooves418,420will cause turbulence and vortex formation within the fluid passing through the clearance416, thus impeding leakage from the inlet volute408to the bearing housing404.

In addition, the turbocharger400comprises a pair of circumferential sealing elements422which are received within sealing element grooves424of the turbocharger shaft412. The grooves418of the bearing housing404and the grooves420of the turbocharger shaft412provide the advantage that they further impede any fluid leakage through the clearance413, and provide a back-up sealing means in the event of failure of the sealing elements422.

It will be appreciated that because the bearing housing404comprises the plurality of circumferentially extending grooves418and the turbocharger shaft412comprises the plurality of circumferentially extending grooves420, the bearing housing404and the turbocharger shaft412may be considered to correspond to the first component8and/or the second component10of the seal assembly2.

FIG.21shows a cross-sectional side view of a turbine500. The turbine500comprises a wastegate assembly502and a turbine housing504. The wastegate assembly502comprises wastegate valve member506and a wastegate actuator508. The turbine housing504defines a wastegate passage510and a valve seat511. During use, the wastegate valve member506contacts the valve seat511so that it covers the wastegate passage510to prevent fluid flowing through the wastegate passage. The wastegate valve member506can be lifted out of contact from the valve seat511by the wastegate actuator508to selectively permit exhaust gas to flow from an upstream side512of the wastegate passage510to a downstream side514of the wastegate passage so as to bypass a turbine wheel (not shown).

The pressure of the exhaust gas on the upstream side512of the wastegate passage510is generally higher than the pressure of the exhaust gas on the downstream side514of the wastegate passage. Although the wastegate valve member506contacts the valve seat511, some exhaust gas may leak between the wastegate valve member506and the valve seat511. The leaked exhaust gas will not pass through the turbine wheel, and therefore no energy is extracted from the leaked exhaust gas, decreasing the efficiency of the turbine500.

In order to solve this problem, the valve seal511comprises a plurality of circumferentially extending grooves520and the wastegate valve member506comprises a corresponding set of circumferentially extending grooves522. During use, the grooves520,522will cause turbulence in the fluid that leaks between the wastegate valve member506and the valve seat511and will impede the flow of leaked fluid, thus reducing the overall leakage. Furthermore, the grooves520,522also act to impede leakage where the wastegate valve member506is open by a relatively small amount, which is advantageous when opening and closing the wastegate assembly502.

Because the wastegate valve member506comprises grooves522and because the valve seat511of the turbine housing504comprises grooves520, the wastegate valve member506and the turbine housing504may be considered to correspond to the first component8and/or the second component10of the seal assembly2.

FIG.22shows a schematic cross-sectional side view of a portion of a variable geometry turbine600which may form part of a turbocharger. The variable geometry turbine comprises a turbine wheel602, a turbine shaft604, a turbine housing606and a bearing housing608. The turbine wheel602is supported for rotation within the turbine housing606about a turbine axis609by the turbine shaft604. The turbine shaft604extends through the bearing housing608and is supported for rotation by bearings610. The turbine housing606defines an inlet volute612which receives air, for example, from the outlet of an internal combustion engine (not shown).

The turbine600further comprises a variable geometry mechanism614having a nozzle ring616and a shroud618. The nozzle ring616defines a generally U-shaped cross-section having an inner wall617and an outer wall619. The nozzle ring616comprises a plurality of nozzle vanes620(of which only one is shown) circumferentially spaced about the turbine axis609. The nozzle ring616is disposed within an annular nozzle ring passage622formed between the turbine housing606and the bearing housing608. The nozzle ring616is movable along the turbine axis609by an actuation mechanism (not shown) which may be positioned within the bearing housing608. The nozzle vanes620extend along the turbine axis609and across an annular inlet passage624positioned upstream of the turbine wheel602and downstream of the inlet volute612.

The shroud618is fixedly positioned within a shroud cavity626defined by the turbine housing606such that the shroud618is positioned opposite the nozzle ring616along the turbine axis609. The shroud618is generally U-shaped and comprises an inner wall621and an outer wall623. The shroud618is prevented from moving axially by a circlip630received between a circumferential groove632of the turbine housing606and a corresponding groove634of the outer wall623. The shroud618comprises a plurality of apertures628which receive the nozzle vanes620of the nozzle ring616. During use, the nozzle ring616is moved along the turbine axis609to vary the width of the inlet passage624and thereby control the flow of fluid to the turbine wheel602.

It has been found that fluid from the inlet volute612is able to leak into the bearing housing608via the nozzle ring passage622, which is detrimental to the efficiency of the turbine600. The turbine housing606therefore comprises a plurality of circumferentially extending grooves636and the outer wall619of the nozzle ring616comprises a plurality of circumferentially extending grooves638. The grooves636,638lead to the formation of vortices which impedes fluid flow through the nozzle ring passage622. As such, the turbine housing606and the outer wall619of the nozzle ring616may be considered to define the first component8and/or second component10of the seal assembly2. Likewise, the inner wall617of the nozzle ring616also comprises a plurality of circumferentially extending grooves640and the bearing housing608comprises a corresponding plurality of circumferentially extending grooves642. The grooves640,642of the inner wall617and bearing housing608create vortices so as to impede flow through the nozzle ring passage622. As such, the inner wall617of the nozzle ring616and the bearing housing608may be considered to define the first component8and/or second component10of the seal assembly2.

Fluid may also leak between the shroud618and the turbine housing606into and/or out of the shroud cavity626. As such, the turbine housing606comprises a plurality of circumferentially extending grooves644and the outer wall623of the shroud618comprises a corresponding plurality of circumferentially extending grooves646which generate vortices to impede fluid flow therebetween. The turbine housing606and the outer wall623of the shroud618may be considered to define the first component8and/or second component10of the seal assembly2. Likewise, the inner wall621of the shroud618comprises a plurality of circumferentially extending grooves648and the turbine housing606comprises a corresponding plurality of circumferentially extending grooves650which generate vortices to impede fluid flow therebetween. The inner wall621of the shroud618and the turbine housing606may therefore be considered to define the first component8and/or the second component10of the seal assembly2.

Fluid may leak between the nozzle vanes620and the apertures628of the shroud618. As such, the nozzle vanes620may comprise one or more grooves652and the aperture628may comprise one or more corresponding grooves654configured to generate vortices so as to impeded fluid flow therebetween. The grooves652of the nozzle vanes620may extend around the entire perimeter of the nozzle vanes602, or may be positioned in localised groups, such as for example at the leading edge and/or the training edge of the nozzle vanes620. The nozzle vanes620and the apertures628of the shroud618may therefore be considered to define the first component8and/or the second component10of the seal assembly2.

It has been found that during use when the nozzle vanes620are received within the apertures628, some fluid may leak between the leading edge of the nozzle vanes620and the apertures628into the shroud cavity626, over the tips of the nozzle vanes620and then out of the shroud cavity626between the inner wall621of the shroud and the turbine housing606. This leakage detrimentally affects the performance of the turbine and the leaked fluid does not pass between the nozzle vanes620and therefore is not conditioned at the correct pressure, velocity and angle relative to the turbine wheel602. However, the variable geometry turbine600avoids this problem due to the presence of the grooves652of the nozzle vanes620and the grooves654of the apertures628of the shroud618, and the grooves648of the inner wall621of the shroud618and the grooves650of the turbine housing606act to impede fluid flow and thus reduce leakage along this leakage path.

It will be appreciated that the grooves discussed above in relation to the variable geometry turbine600may have substantially any suitable geometry as previously discussed in relation to the seal assembly2(including for example dimpled geometries). Although the variable geometry turbine600described above comprises nozzle ring616that is axially movable, it will be appreciated that the seal assembly2could be used to provide improved sealing in substantially any variable geometry turbine, such as for example a swing-vane variable geometry turbine. Alternatively, the shroud618may be movable along the turbine axis609and the nozzle ring616may be axially fixed. It will be appreciated that the variable geometry turbine600need not comprise all of the corresponding pluralities of grooves described above for reducing leakage. In particular, the turbine600may be configured so that leakage is only reduced between the nozzle ring616and the turbine housing606or the bearing housing608, between the shroud618and the turbine housing606, and/or between the nozzle vanes620and the apertures628.

In general, throughout this disclosure it will be appreciated that the features of any of the above described embodiments may be combined with any of the other described embodiments.