GB2540762B

GB2540762B - A variable exhaust gas recirculation diffuser

Info

Publication number: GB2540762B
Application number: GB1513093.3A
Authority: GB
Inventors: John Mallard Will
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-07-24
Filing date: 2015-07-24
Publication date: 2019-11-27
Anticipated expiration: 2035-07-24
Also published as: GB2540762A; GB201513093D0

Description

A variable exhaust gas recirculation diffuser

Technical Field

The present disclosure relates to an Exhaust Gas Recirculation (EGR) diffuser and is particularly, although not exclusively, concerned with an EGR diffuser comprising variable geometry.

Background A motor vehicle may be fitted with an Exhaust Gas Recirculation (EGR) system configured to recirculate a portion of the exhaust gases of an engine back to an inlet of the engine. Replacing a portion of the oxygen rich inlet air with burnt exhaust gases reduces the proportion of the contents of each cylinder of the engine which are available for combustion. This results in a lower heat release and lower peak cylinder temperature and thereby reduces the formation of NOX.

In order for the engine to continue operating efficiently, it is desirable for the reintroduced EGR gases to be mixed homogenously with the inlet air. An EGR diffuser may be provided within the inlet air duct to facilitate mixing of the EGR gases and inlet air. The geometry of the EGR diffuser may be defined to provide the best mixing of EGR gases and inlet air at a specific operating condition of the vehicle.

Statements of Invention

According to an aspect of the present disclosure, there is provided an Exhaust Gas Recirculation (EGR) system for an internal combustion engine, the EGR system comprising: an inlet air duct configured to provide the internal combustion engine with inlet air; an EGR diffuser configured to provide recirculated exhaust gases from the internal combustion engine to the inlet air duct through an outlet, the EGR diffuser comprising: a body portion; a movable element, movable relative to the body portion, the movable element configured to vary the size of the outlet, the movable element comprising a pressure surface, arranged such that at least one of inlet air and recirculated exhaust gases act on the pressure surface thereby causing the movable element to move in a first direction and vary the size of the outlet; and wherein the movable element is biased to move in a second direction.

The size of the outlet of the EGR diffuser may vary in response to changes in the flow of EGR gases and/or inlet air, e.g. in response to a change of pressure of the EGR gases and/or inlet air. Allowing the size of the outlet of the EGR diffuser to vary may allow the EGR diffuser to introduce a desirable quantity of EGR gases according to the current engine running condition. Additionally or alternatively, varying the geometry of the EGR diffuser in this way may allow the EGR gases to be mixed more homogenously across a broad range of engine running conditions.

The body portion of the EGR diffuser may comprise a portion of an EGR duct, configured to carry recirculated exhaust gases. The outlet may be between the body portion and the movable portion.

The EGR system may further comprise a resilient element configured to resist movement of the movable element. The resilient element may be provided between the movable element and the body portion of the EGR diffuser.

The movable element may be provided in the inlet air duct and may be configured to restrict the flow of air within the inlet air duct. For example, by inducing a pressure drop in the flow of inlet air. Movement of the pressure surface may vary the restriction of the flow of air within the inlet air duct.

The movable element is movable between a first position and a second position. The outlet flow area may be greater in the first position compared to the second position.

The movable element may be configured to restrict the flow of air within the inlet air duct least when the movable element is in the first position. For example, by presenting a reduced projected area in the direction of inlet air flow in the first position compared to the second position.

The outlet flow area may vary linearly with the movement of the movable element between the first and second positions. Alternatively, the outlet flow area may vary non-linearly with the movement of the movable element between the first and second positions. The rate of change of the outlet flow area with the movement of the movable element may increase as the movable element moves from the first position to the second position. Alternatively, the rate of change of the outlet flow area with the movement of the movable element may decrease as the movable element moves from the first position to the second position.

The movable element may comprise a sleeve. The sleeve may be arranged co-axially with the body portion of the EGR diffuser. The sleeve may be provided radially outside the body portion. Alternatively, the sleeve may be provided radially inside the body portion. The body portion and the sleeve may comprise respective openings and the outlet may be at least partially formed by an overlapping area of the respective openings.

The openings may each comprise two substantially straight edges. The straight edges may or may not be parallel to the coincident axes of the body portion and the sleeve. The openings may comprise semi-circular end profiles. Alternatively, the openings may be substantially triangular shaped. The openings provided on the body portion and sleeve may be oriented in opposite directions, e.g. the peaks of triangular openings on the body portion and sleeve may point in opposite directions.

The resilient element may comprise a coil spring provided between the body portion and the sleeve.

The pressure surface may be provided on an end cap of the sleeve.

The movable element may comprise a plate configured to cover an opening provided on the body portion. The outlet may be at least partially formed by a flow area between the plate and the body portion. The pressure surface may comprise a surface of the plate.

The resilient element may be provided between the plate and the body portion.

The plate may be provided within the inlet duct and may restrict the flow of inlet air.

The plate may comprise one or more fins, which may be acted upon by the flow of inlet air. The pressure surface may comprise a surface of the one or more fins.

According to another aspect of the present disclosure, there is provided a vehicle comprising the EGR system according to a previously mentioned aspect of the disclosure.

Brief Description of the Drawings

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which;

Figure 1 is a schematic view of the air and exhaust paths in an engine with an EGR system according to arrangements of the present disclosure;

Figures 2a and 2b are perspective views showing previously proposed EGR diffusers;

Figures 3a and 3b are perspective views of an EGR diffuser according to a first arrangement of the present disclosure, in open and closed configurations respectively;

Figures 4a and 4b are perspective views of an EGR diffuser according to a second arrangement of the present disclosure, in closed and open configurations respectively; and

Figures 5a and 5b are perspective views of an EGR diffuser according to a third arrangement of the present disclosure.

Detailed Description

With reference to Figure 1, a typical air path for an internal combustion engine 10 of a motor vehicle is described. Air may enter through an inlet 12 and then pass through an air filter 13 via an inlet duct 46. The air may be throttled by a valve 36 before being passed through a compressor 14a of a turbocharger 14. The turbocharger 14 may improve the engine power output and reduce emissions. Typically, the turbocharger 14 is arranged with an exhaust gas driven turbine 14b driving the compressor 14a mounted on the same shaft. A charge air cooler 16 may further increase the density of the air entering the internal combustion engine 10, thereby improving its performance.

The air may then enter the internal combustion engine 10 via a throttle 18 configured to vary the mass flow of air into the internal combustion engine.

In a particular arrangement of the present disclosure, the internal combustion engine 10 comprises a diesel engine, however it is equally envisaged that the engine 10 may be a spark ignition engine. As depicted in Figure 1, the internal combustion engine 10 may comprise a number of cylinders 10a-d and the air may flow into each of these cylinders at an appropriate time in the engine’s cycle as determined by one or more valves (not shown).

The exhaust gases leaving the internal combustion engine 10 may pass through the turbine 14b of the turbocharger. One or more exhaust treatment modules 20 may be provided downstream of the turbine 14b, e.g. to reduce emissions from the engine exhaust. The exhaust treatment modules 20 may comprise one or more of an oxidation catalyst, e.g. a diesel oxidation catalyst, and a particulate filter, e.g. a diesel particulate filter. A further exhaust treatment module 21 may be provided, e.g. downstream of the exhaust treatment module 20. A first EGR loop 22 configured to selectively recirculate exhaust gases from the internal combustion engine 10 back into the internal combustion engine via a first EGR duct 42 may also be provided. The first EGR loop 22 may be provided about the turbocharger 14 such that exhaust gases leaving the turbine 14b may be recirculated into the inlet of compressor 14a. An EGR diffuser 50 may be provided to improve mixing of the exhaust gases with the inlet air. The first EGR loop 22 may be diverted from the main exhaust flow path, e.g. upstream or downstream of the exhaust treatment module 20. The first EGR loop 22 may comprise a first recirculation valve 24, which may control the amount of recirculation through the first EGR loop 22.

A second EGR loop 32 configured to selectively recirculate exhaust gases from the internal combustion engine 10 back into the internal combustion engine via a second EGR duct 44 may also be provided. The second EGR loop 32 may be provided about the engine 10 with exhaust gases leaving the engine 10 being recirculated to the air inlet of the engine 10. An EGR diffuser 50, may be provided to improve mixing of the exhaust gases with the inlet air. The second exhaust gas recirculation loop 32 may be diverted from the main exhaust flow path, e.g. at a point between the engine 10 and the turbine 14b of the turbocharger. Accordingly, the exhaust gases in the second EGR loop 32 may be at a higher pressure than the exhaust gases in the first EGR loop 22. The second exhaust gas recirculation loop 32 may comprise a second recirculation valve 34 which may control the amount of recirculation in the second EGR loop 32.

With reference to Figure 2a, a previously-proposed EGR diffuser 50 may be provided within the inlet air duct 46 and receive EGR gases via the EGR duct 42, 44. The EGR diffuser 50 may comprise a diffuser body 52 provided within the inlet duct 46. As shown in Figure 2a, the diffuser body may be cylindrical. An end cap 56, may be provided on the diffuser body to prevent EGR gases leaving the diffuser body in an axial direction relative to the diffuser body 52. A plurality of radial openings 54 may be provided, e.g. circumferentially distributed, around the diffuser body to allow EGR gases to leave the diffuser body 52 radially relative to the diffuser body 52 (and thus axially relative to the inlet duct 46. The openings may be provided in one or more rows of openings, distributed axially along the length of the diffuser body 52. The size of the openings 54 may be selected to promote optimal injection quantities and mixing of EGR gases at a specific operating condition of the vehicle.

With reference to Figure 2b, rather than providing the radial openings 54, another previously-proposed EGR diffuser 50 may alternatively comprise one or more axial openings 58, provided in the end cap 56 of the diffuser body 52. As shown in Figure 2b, the diffuser may further comprise a diffuser plate 60 which is supported from the diffuser body 52 by one or more support legs 62. The support legs 62 may couple to the end cap 56 of the diffuser body 52 and may be arranged circumferential around the perimeter of the end cap 56. The lengths of the support legs may vary with respect to one another and may be configured to support the diffuser plate 60 at an angle relative to the flow of inlet air and/or EGR gases. Additionally or alternatively, the diffuser plate 60 may be coupled directly to the diffuser body at one or more locations. The diffuser plate 60 may be configured to improve the mixing of EGR gases with the inlet air. The size of the axial openings 58 and/or the position and angle of the diffuser plate 60 may be configured to promote optimal injection quantities and mixing of EGR gases at a specific operating condition of the vehicle.

With reference to Figures 3a and 3b, a variable EGR diffuser 100, according to a first arrangement of the present disclosure is described. The variable EGR diffuser 100 may be provided within the inlet duct 46 and may receive EGR gases from the EGR duct 42, 44.

The variable EGR diffuser 100 may comprise a diffuser body 102. The diffuser body may comprise a portion of the EGR duct 42, 44 which may extend into the inlet duct 46. Alternatively, as shown in Figures 3a and 3b, the diffuser body 102 may be a separate component, coupled to the EGR duct 42, 44. The diffuser body 102 may be coupled to a wall of the inlet duct 46. The diffuser body 102 may be substantially cylindrical, with a substantially constant circular cross-section along its length. The longitudinal axis of the cylinder may define an axis of the EGR diffuser 100. Additionally or alternatively, the diffuser body 102 may comprise one or more sections of any prism or cone formed on any regular or irregular polygonal base. The diffuser body 102 may be formed in an aerodynamic shape to minimise disturbance to the flow of inlet air in the inlet duct 46.

The variable EGR diffuser 100 may further comprise a sleeve 104. The sleeve 104 may be slidably coupled to the diffuser body 102. As depicted in Figure 3a and 3b, the sleeve 104 may be provided within the diffuser body 102, however it is equally envisaged that the sleeve 104 may be provided externally to the diffuser body 102. In either case, there may be a close fit between the sleeve 104 and the diffuser body 102, to limit the flow of exhaust gases between the components.

The diffuser body 102 may comprise one or more openings 102a. The openings may extend into the diffuser body 102 in a substantially radial direction, e.g. relative to the longitudinal axis of the EGR diffuser. The openings may be circumferentially distributed, e.g. partially or fully, around the diffuser body. The openings may be evenly or variably spaced around the circumference of the diffuser body. For example, the openings may be arranged such that there is a greater number on an upstream side of the variable EGR diffuser 100, with respect to the flow of inlet air within the inlet duct 46, compared to on a downstream side, or vice versa.

The sleeve 104 may be provided with corresponding openings 104a. The corresponding openings 104a may be configured to overlap with the openings 102a to define one or more outlets of the variable EGR diffuser 100. As shown in Figure 3a, when the sleeve 104 is located in a particular position relative to the diffuser body 102, each of the corresponding openings 104a, provided in the sleeve 104, may align with, e.g. substantially fully overlap, the openings 102a, provided in the diffuser body 102. In this position, the size of the outlets of the variable EGR diffuser 100 may be at a maximum, e.g. the outlets may be substantially fully open.

The sleeve 104 may comprise an end cap 104b, which closes a distal end of the sleeve 104. The end cap 104b may be arranged such that EGR gases exiting the EGR duct 42, 44 impinge upon a pressure face 104c provided on the inside of the end cap 104b.

As shown in Figures 3a, and 3b, the diffuser body 102 may comprise an end cap 102b to prevent EGR gases exiting the diffuser body in an axial direction. However, if the sleeve 104 is provided externally to the diffuser body 102, the diffuser body may not comprise an end cap in order to allow the EGR gases to exit the EGR diffuser body axially and impinge upon the pressure face 104c of the sleeve 104.

The pressure force resulting from the EGR gases impinging upon the pressure face 104c may affect the position of the sleeve relative to the diffuser body, e.g. the pressure force may cause the sleeve to be displaced axially relative to the diffuser body. As depicted in Figure 3b, displacing the sleeve 102 relative to the diffuser body 104 may cause the openings 102a and corresponding openings 104a to move relative to one another and hence the area of the outlet of the variable EGR diffuser 100 may change. In a particular arrangement, displacing the sleeve 102 relative to the diffuser body 104 may cause the openings 102a and corresponding openings 104a to move out of alignment and hence the area of the outlet of the variable EGR diffuser 100 may be reduced.

The variable EGR diffuser 100 may further comprise a resilient element, e.g. a coil spring 106, which may configured to resist movement of the sleeve 104 relative to the diffuser body 102. The resilient element may be configured to return the variable EGR diffuser 100 to a position in which the outlet size is greatest when the pressure force applied to the pressure surface 104c is lowest. The coil spring 106 may be provided between the end cap 102b of the diffuser body, and the end cap 104b of the sleeve.

The stiffness of the spring 106 may be selected in order to control the effect of a change in EGR flow pressure on the size of the outlets of the variable EGR diffuser 100. Additionally or alternatively, the stiffness of the spring 106 may be selected such that the maximum pressure experienced by the pressure face 104c causes the sleeve 104 to be displaced into a closed (fully or partially) position, in which the size of the outlets of the EGR diffuser is smallest, as shown in Figure 3b. Additionally or alternatively, the length of the spring may be selected such that, when the sleeve 104 is displaced into the closed (fully or partially) position, the spring is compressed to its shortest length. Again additionally or alternatively, the diffuser body 102 and the sleeve 104 may comprise a shoulder and a corresponding abutment face (not shown), which may prevent the sleeve 104 being displaced beyond the closed position, regardless of whether the pressure force increases and the spring 106 is able to be compressed further.

Additionally or alternatively to providing a resilient element, such as the coil spring 106, the sleeve 104 may be weighted. The sleeve 104 may thereby be biased to return to the position in which the outlet size is greatest, when the pressure force applied to the pressure surface 104c is reduced.

As the sleeve 104 moves relative to the diffuser housing 102, the area of the variable EGR diffuser outlets may vary linearly with the displacement of the sleeve at least for a portion of the sleeve’s travel. Such variation may be achieved by providing openings 102a, 104a that comprise straight, parallel sides aligned in the direction of movement of the sleeve 104. For example, as shown in Figures 3a and 3b, the openings 102a, 104a may be substantially rectangular and may comprise profiled ends, such as semicircular ends as depicted. The semi-circular ends of the openings may provide outlets that are substantially circular when the outlets are fully closed, as shown in Figure 3b. Alternatively, the openings may be any other shape, such as triangular. Each of the openings may be a different shape and/or orientation compared to the other openings.

In one alternative arrangement, not shown, the openings 102a, 104a are triangular and the openings 104a provided on the sleeve 104 are arranged at an angle of 180° relative to the openings 102a on the diffuser body 102. By providing openings of different shapes and/or orientations, the rate of change of the size of the outlets may vary as the sleeve 104 is displaced. For example the rate of change of the outlet size may increase or decrease linearly or quadratically with the displacement of the sleeve 104.

With reference to Figures 4a and 4b, a variable EGR diffuser 200, according to a second arrangement of the present disclosure is described. The variable EGR diffuser 200 may be coupled, at a first end 200a, to the wall of the inlet duct 46. The variable EGR diffuser 200 may extend into the inlet duct 46 to a second end 200b. The variable EGR diffuser 100 may receive EGR gases from the EGR duct 42, 44.

The EGR diffuser 200 may comprise a diffuser body 202, which may be similar to the EGR body 102 described above, however the diffuser body 202 may not comprise radial openings. The diffuser body 202 may comprise an end cap 202b, which may be provided with one or more openings 202a. The openings 202a may be provided in an axial direction of the diffuser body 202 to allow EGR gases to exit the diffuser body axially. Alternatively, the end cap 202b may be omitted and the opening 202a may correspond to an open second end of the diffuser body 202.

The EGR diffuser 200 may further comprise a diffuser plate 208. The diffuser plate may be provided at or near the second end 200b of the EGR diffuser. The diffuser plate 208 may be supported from the diffuser body 202 by one or more resilient support members 206. The resilient support members 206 may be elongate and may extend from the diffuser body 202 towards the diffuser plate 208. The diffuser plate 208 may be configured to rotate relative to the diffuser body 202. For example, the resilient support member 206 may be elastically deformable to allow the angle of the diffuser plate 208 to vary. The resilient support member 206 may comprise a leaf spring or another form of natural spring. In an alternative arrangement, the resilient support member may comprise a hinge, flexure bearing or other pivot, which allows the diffuser plate 208 to rotate relative to the diffuser body 202. The gap between the diffuser body 202 and the diffuser plate 208 may define an outlet 201 of the variable EGR diffuser 200.

The resilient support member 206 may be provided at or near an edge of the end cap 202b. In the arrangement shown in Figures 3a and 3b, the resilient support member 206 is provided at an upstream position relative to the flow of inlet air. However, it is equally envisaged that the support member could be provided at a downstream position, or any other position on the end cap 202b.

As shown in Figure 4a, the diffuser plate 208 may be angled with respect to the flow of EGR gases leaving the EGR diffuser via the openings 202a and the flow of inlet air within the inlet duct 46. In a neutral position of the diffuser plate 208, in which the resilient support member 206 is substantially undeformed, the plate may be angled such that an upstream end of the diffuser plate is arranged further from the end cap 202b than a downstream end of the diffuser plate, e.g. the diffuser plate may be angled downwards relative to the flow of inlet air.

The diffuser plate 208 may be biased into the neutral position due to the stiffness of the resilient support member. Additionally or alternatively, for example if the resilient support member 206 comprises a hinge, flexure bearing or pivot, a spring may be provided to bias the diffuser plate 208 into the neutral position. Again additionally or alternatively, the diffuser plate 208 may be weighted, which may bias the diffuser plate into the neutral position.

In the configuration shown in Figure 4a, the diffuser plate is provided within the flow of inlet air within the inlet duct 46, 48. The diffuser plate may restrict the flow of inlet air and may induce a pressure drop in the inlet air. The diffuser plate may be configured to provide optimised mixing of EGR gases with the inlet air in a particular vehicle operation condition.

The diffuser plate 208 may comprise an inferior face 208a, which is provided adjacent the diffuser body 202, and a superior face 208b on the opposite side of the plate. EGR gases exiting the diffuser body 202 may impinge upon the inferior face 208a of the diffuser plate 208. Inlet air within the inlet duct 46 may also impinge upon the inferior face 208a. The impinging gases may increase the pressure on the inferior face of the diffuser plate, which may create a net pressure difference between the inferior and superior face of the diffuser plate. Additionally, inlet air, which is deflected by the diffuser plate 208, may form a low pressure region adjacent to the superior face 208b of the diffuser plate, which may increase the net pressure difference. The net pressure difference may result in a pressure force which causes a deflection of the resilient support member 206, e.g. bending of the resilient support member. As shown in Figure 4b, deflection of the resilient support member 206 may alter the angle of the diffuser plate 208 relative to the flows of EGR gases and inlet air.

In the configuration shown in Figure 4b, the flow area of the outlet 201 of the variable EGR diffuser 200, between the diffuser body 202 and the diffuser plate 208, may be larger than in the configuration shown in Figure 4a. The configuration shown in Figure 4a may be considered a first configuration and the configuration shown in Figure 4b may be a second configuration in which the outlet 201 is more open than in the first configuration.

In the second configuration, the projected area of diffuser plate, in the direction of the flow of inlet air, may be reduced compared to the first configuration. The diffuser plate 208 may therefore restrict the flow of inlet air less and the pressure drop induced in the inlet air flow by the diffuser plate may also be reduced. Such a configuration may be desirable when high efficiency of the inlet air system is desired.

In another arrangement, not shown, the diffuser plate 208 and/or resilient support member 206 may be configured such the pressure forces caused by impinging EGR gases and inlet air, act to reduce the size of the outlet 201 between the diffuser body 202 and the diffuser plate 208. For example, the diffuser plate 208 and/or resilient support member 206 may be configured such the inlet air impinges upon the superior face 208b of the diffuser plate 208. This may be achieved by orienting the diffuser plate 208 the other way round to that shown in Figure 4a, e.g. such that the downstream end of the diffuser plate 206 is arranged further from the end cap 202b than the upstream end, when the diffuser plate 206 is in the neutral position. Additionally or alternatively, the diffuser plate 208 and/or the resilient support member 206 may be configured such that the projected area of the diffuser plate, in the direction of the flow of inlet air, is smallest when the diffuser plate is in the first configuration.

As described above, the flow area of the outlet 201 of the EGR diffuser 200, and the effect of the diffuser plate 208 on the pressure drop of the inlet flow may be affected by the angle of the diffuser plate. In some configurations of the inlet and/or EGR system, it may be desirable to increase the effect of the inlet air flow on the angle of the diffuser plate, without altering the effect of the EGR gas flow. In this case, one or more diffuser fins 210 may be provided on the diffuser plate 208. The fins 210 may be provided on an edge of the diffuser plate 208, and may extend radially outwards from the diffuser plate 208. The fins 210 may extend in a plane parallel with the diffuser plate 208. Alternatively, the fins 210 may be provided at an angle relative to the diffuser plate 208. The angle of the fins 210 relative to the diffuser plate 208 may vary with distance from the diffuser plate 208, e.g. the fins may curve and/or bend away from the plane of the diffuser plate 208. Inlet air within the inlet duct 46 may impinge upon an inferior and/or superior surface of the diffuser fins 210, which may affect the pressure force on the diffuser plate 208 acting to deflect the resilient support members 206. The angle of the diffuser fins 210 relative to the diffuser plate 208 may be adjusted to alter the effect of the fins 210 on the pressure force. The fins 210 may be arranged such that the flow of exhaust gases from the diffuser body 202 does not impinge upon the fins 210.

With reference to Figures 5a and 5b, a variable EGR diffuser 300, according to a third arrangement of the present disclosure is described. The variable EGR diffuser 300 may be coupled, at a first end 300a, to the wall of the inlet duct 46. The variable EGR diffuser 300 may extend into the inlet duct 46 to a second end 300b. The variable EGR diffuser 300 may receive EGR gases from the EGR duct 42, 44.

The variable EGR diffuser 300 may comprise a diffuser body 302 and a sleeve 304. The diffuser body 302 may be configured similarly to the diffuser body 102 and may comprise one or more radial openings 302a. The sleeve 304 may be configured similarly to the sleeve 104 and may comprise corresponding openings 304a, which align with the openings 302a when the sleeve is arranged in an open configuration, as shown in Figure 5a.

The sleeve 304 may further comprise an end cap 304b. An inner surface of the end cap 304b may be a pressure face 304c of the sleeve 304. EGR gasses may impinge upon the pressure face 304c, as described above with reference to the sleeve 104, which may cause a displacement of the sleeve 304 relative to the diffuser body 302.

As described above with reference to Figures 3a and 3b, one or more outlets of the variable EGR diffuser 300 may be defined by the overlap of the openings 302a and the corresponding openings 304a. The shape and/or orientation of the openings 302a and/or corresponding openings 304a may be configured, as described above, to determine the size and/or shape of the outlets of the variable EGR diffuser 300, as well as the rate of change of outlet size and/or shape as the sleeve 304 is displaced relative to the diffuser body 302.

The variable EGR diffuser 300 may further comprise a resilient element 306a configured to resist movement of the sleeve 304 relative to the diffuser body 302. The resilient element may comprise a coil spring and may be configured similarly to the resilient element 106 described above.

The diffuser body 302 may comprise an end cap 302b, at or near the second end 300a of the variable EGR diffuser. The end cap 302b may be configured similarly to the end cap 202b and may comprise one or more axial openings 302c. As described above with reference to Figures 4a and 4b, the diffuser body 302 may not comprise the end cap 302b, and the axial opening 302c may correspond to an open second end of the diffuser body 302.

The variable EGR diffuser 300 may further comprise a diffuser plate 308 and resilient support member 306b, which may be configured similarly to the diffuser plate 208 and resilient support member 206 described above. The variable EGR diffuser 300 may therefore also comprise an outlet 301 defined between the diffuser body 302 and the diffuser plate 308.

The diffuser plate 308 may comprise an inferior surface 308a adjacent to the diffuser body 302 and a superior surface 308b on the opposite side of the diffuser plate 308. As described above with reference to the diffuser plate 208, the EGR gases and the inlet air may impinge upon the inferior surface 308a and may cause a pressure difference between the inferior surface 308a and the superior surface 308b.

The pressure difference may produce a pressure force, which deforms the resilient support member 306b and affects the angle of the diffuser plate 308 relative to the flows of inlet air and EGR gases. The angle of the diffuser plate 308 may affect the size of the outlet 301 of the variable EGR diffuser 300 defined between the diffuser body 302 and the diffuser plate 308. The angle of the diffuser plate may also affect a restriction on the flow of inlet air within the inlet duct and/or a pressure drop of the inlet air caused by the diffuser plate 308. When the diffuser plate is in an open configuration, as shown in Figure 5b, the size of the outlet 301 may be greatest and the restriction on the inlet air and the induced pressure drop may be smallest.

In order to allow EGR gases to impinge upon the inferior surface 308a of the diffuser plate 308, the end cap 304b of the sleeve 304 may comprise one or more axial openings (not shown) to permit a flow of EGR gases axially though the variable EGR diffuser 300.

Providing the axial opening may reduce the effect of the EGR gases on the displacement of the sleeve 304 relative to the diffuser body 302. The stiffness of the resilient element 306a may therefore be reduced compared to the stiffness of the resilient element 106 described above.

The diffuser plate 308 may be provided with one or more optional diffuser fins 310, which may allow the effect of the inlet air on the angle of the diffuser plate 308 to be adjusted independently to the effect of EGR gases, as described above with reference to the diffuser fins 210.

As shown in Figure 5a, when the EGR gas pressure and inlet air flow rate are both low, the outlets defined by the overlapping of the openings 302a and corresponding openings 304a may be in a fully open configuration, whilst the outlet 301 defined between the diffuser body 302 and the diffuser plate 308 may be in a substantially fully or partially closed configuration.

As shown in Figure 5b, when the EGR gas pressure and inlet air flow rate are both high, the outlets defined by the overlapping of the openings 302a and corresponding openings 304a may be in a fully or partially closed configuration, whilst the outlet 301 defined between the axial opening diffuser body 302 and the diffuser plate 308 may be in a substantially fully open configuration.

When the variable EGR diffuser 300 is configured as shown in Figures 5a and 5b, if the EGR pressure is low and the inlet air flow rate is high, the outlets defined by the overlapping of the openings 302a and corresponding openings 304a, and the outlet 301 defined between the diffuser body 302 and the diffuser plate 308 may both be in a substantially fully open position at the same time. Similarly, the variable EGR diffuser 300 may be configured such that, under certain conditions, the outlets are both in substantially fully or partially closed configurations at the same time.

It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more examples, it is not limited the disclosed examples and that other examples may be constructed without departing form the scope of the invention, as defined by the appended claims.

Claims

1. An Exhaust Gas Recirculation (EGR) system for an internal combustion engine, the EGR system comprising: an inlet air duct configured to provide the internal combustion engine with inlet air; an EGR diffuser configured to provide recirculated exhaust gases from the internal combustion engine to the inlet air duct through an outlet, the EGR diffuser comprising: a body portion; and a movable element movable relative to the body portion, the movable element configured to vary the size of the outlet, the movable element comprising a pressure surface arranged such that at least one of inlet air and recirculated exhaust gases act on the pressure surface thereby causing the movable element to move in a first direction and vary the size of the outlet; wherein the movable element is biased to move in a second direction.

2. The EGR system of claim 1 further comprising a resilient element configured to resist movement of the movable element.

3. The EGR system of claim 2, wherein the resilient element is provided between the movable element and the body portion of the EGR diffuser.

4. The EGR system of any of the preceding claims, wherein the movable element is provided in the inlet air duct and is configured to restrict the flow of air within the inlet air duct; and wherein movement of the movable element varies the restriction of flow of air within the inlet air duct.

5. The EGR system of any of claims 1 to 4, wherein the movable element is movable between a first position and a second position, the flow area through the outlet being greater in the first position.

6. The EGR system of claims 4 and 5, wherein the movable element is configured to restrict the flow of air within the inlet air duct least when the movable element is in the first position.

7. The EGR system of claim 5 or 6, wherein the flow area through the outlet varies non-linearly with the movement of the movable element between the first and second positions.

8. The EGR system of any of claims 5 to 7, wherein the rate of change of the outlet flow area with the movement of the movable element increases as the movable element moves from the first position to the second position.

9. The EGR system of claim 5 or 6, wherein the flow area through the outlet varies linearly with the movement of the movable element between the first and second positions.

10. The EGR system of any of the preceding claims, wherein the movable element comprises a sleeve arranged co-axially with the body portion of the EGR diffuser, wherein the body portion and the sleeve comprise respective openings; and wherein the outlet is at least partially formed by an overlapping area of the respective openings.

11. The EGR system of claim 10, wherein the sleeve is provided radially outside the body portion.

12. The EGR system of claim 10, wherein the sleeve is provided radially inside the body portion.

13. The EGR system of any of claims 10 to 12, wherein the openings each comprise two substantially straight edges, which are parallel to the coincident axes of the body portion and the sleeve.

14. The EGR system of any of claims 10 to 13, wherein the openings comprise semicircular end profiles.

15. The EGR system of any of claims 10 to 12, wherein the openings are substantially triangular shaped.

16. The EGR system of any of claims 10 to 15, wherein the pressure surface is provided on an end cap of the sleeve.

17. The EGR system of any of claims 10 to 16 when depending on claim 2, wherein the resilient element comprises a coil spring provided between the body portion and the sleeve.

18. The EGR system of any claims 1 to 16, wherein the movable element comprises a plate configured to cover an opening provided on the body portion, wherein the outlet is at least partially formed by a flow area between the plate and the body portion.

19. The EGR system of claim 18, when dependent on claim 2, wherein the resilient element is provided between the plate and the body portion.

20. The EGR system of claim 17, wherein the EGR system comprises a further movable element comprising a plate configured to cover an opening provided on the body portion, wherein the outlet is at least partially formed by a flow area between the plate and the body portion, wherein the EGR system comprises a further resilient element provided between the plate and the body portion.

21. The EGR system of any of claims 18 to 20, wherein the plate is provided within the inlet duct and restricts the flow of inlet air.

22. The EGR system of any of claims 18 to 21, wherein the plate further comprises one or more fins, which are acted upon by the flow of inlet air, and wherein the pressure surface comprises a surface of the plate and a surface of the fin.

23. A vehicle comprising the EGR system according to any of the preceding claims.