Patent Publication Number: US-2011067680-A1

Title: Turbocharger and Air Induction System Incorporating the Same and Method of Making and Using the Same

Description:
FIELD OF THE INVENTION 
     Exemplary embodiments of the present invention are related to a turbine housing and turbocharger incorporating the same, as well as a method of using the same, and, more specifically, to a turbine housing having an integral wastegate/exhaust gas recirculation (EGR) outlet, and turbocharger incorporating the same, as well as a method of using the same. 
     BACKGROUND 
     The efficient use of exhaust gas recirculation (EGR) is very important to all modern internal combustion engines, including both gasoline and diesel engines. Efficient use of EGR generally supports the objectives of realizing high power output from these engines while also achieving high fuel efficiency and economy, and achieving increasingly stringent engine emission requirements. The use of forced-induction, particularly including turbochargers, in these engines is also frequently employed to increase the engine intake mass airflow and the power output of the engine. However, turbochargers are also powered by exhaust gas, so the efficient use of EGR and turbocharged forced-induction necessitates synergistic design of these systems. 
     Turbocharged diesel engines must be particularly efficient in the use of the energy available in EGR and exhaust gas flows in order to improve overall engine efficiency and fuel economy. Diesel EGR systems are required to deliver high volumes of EGR to the intake air system of the engine. In order to do so, the EGR system must provide enough pressure change through the system, including the flow control valve, bypass valve and cooler to drive the desired EGR flow into the boosted intake system. The exhaust system must also provide adequate exhaust gas energy so that the turbine has sufficient power to provide the desired boost. Typical diesel engine EGR systems feed EGR passages off various exhaust system components. EGR feed passages off the turbine housing have been proposed; however, such EGR feed passages have generally been at less than optimal angles to the desired gas flow direction within the turbine volute, through the use of elbows and the like, thereby creating high flow losses and low efficiency, thereby reducing the amount of EGR flow available for use in the air intake system. Such arrangements do not provide a sufficient volume of intake EGR. 
     In U.S. Pat. No. 6,430,929, a design has been proposed to associate an EGR outlet with a turbine volute and EGR valve. This design locates the EGR outlet tangentially to the volute and substantially linearly along the flowstream entering the turbine housing inlet. Thus, the EGR outlet is located at the volute inlet and the EGR outlet appears to define the volute inlet. The turbocharger described in this patent incorporates an EGR valve having a flanged elbow, where the hole pattern on the flange can be adjusted to orient the elbow to accommodate varying engine arrangements. The use of the elbow may also be necessitated by the in-line or linear arrangement of the EGR outlet and turbine inlet. However, use of the elbow configuration has an efficiency loss associated therewith. The turbocharger of the &#39;929 patent also incorporates a variable geometry nozzle that is used to increase back pressure in the EGR system. While potentially useful, the costs of variable nozzle turbochargers are significantly higher than those having fixed nozzles. Further, increases in back pressure observed by closing the turbine vanes of a variable nozzle are nearly outweighed by the resultant increase in boost pressure of the intake air, such that the desired increases in EGR flow in the induction system are not achievable. 
     Accordingly, it is desirable to provide turbine housings, turbochargers and intake air systems that use them and associated methods of use that enhance EGR available for use in the induction system while at the same time providing sufficient exhaust gas flow to drive the turbine and generate the desired pressure boost and air induction into the air intake system, regardless of whether the turbochargers use either fixed or variable nozzle turbines. 
     SUMMARY OF THE INVENTION 
     In accordance with an exemplary embodiment of the present invention, a turbocharger for an internal combustion engine is provided, including a turbine comprising a turbine wheel attached to a turbine shaft, the turbine wheel and shaft rotatably disposed in a turbine housing, the turbine housing comprising a turbine volute conduit, the turbine volute conduit having a turbine volute inlet and a wastegate/EGR conduit inlet, the wastegate/EGR conduit inlet radially spaced from the turbine volute inlet along the turbine volute conduit and opening into an EGR conduit that is joined to the turbine volute conduit. The turbine volute inlet is configured for fluid communication of an exhaust gas received from an engine to the turbine wheel, the EGR conduit configured for fluid communication of the exhaust gas to an engine intake conduit. 
     In accordance with another exemplary embodiment of the present invention, an intake air system for an internal combustion engine is provided. The intake air system includes a turbocharger comprising a turbine and a compressor, the turbine comprising a turbine wheel attached to a turbine shaft, the turbine wheel and shaft rotatably disposed in a turbine housing, the turbine housing comprising a turbine volute conduit, the turbine volute conduit, having a turbine volute inlet and a wastegate/EGR conduit inlet, the wastegate/EGR conduit inlet radially spaced from the turbine volute inlet along the turbine volute conduit and opening into an EGR conduit that is joined to the turbine volute conduit. The turbine volute inlet is configured for fluid communication of an exhaust gas received from an engine to the turbine wheel, the wastegate/EGR conduit is configured for fluid communication of the exhaust gas to an engine intake conduit. The compressor comprising a compressor wheel attached to the turbine shaft, the compressor wheel and turbine shaft rotatably disposed in compressor housing, the compressor comprising a compressor volute conduit, the compressor volute conduit having a compressor volute inlet, a compressor volute outlet, the compressor volute outlet in fluid communication with the engine intake conduit. The intake air system also includes an EGR valve switchable between at least an open and a closed position and having an EGR valve inlet and an EGR valve outlet, the EGR valve inlet in fluid communication with the EGR conduit, the EGR valve outlet also in fluid communication with the engine intake conduit, the open position in a blank fluid communication from the EGR conduit to the engine intake conduit and defining a first operating mode, in the closed position disabling fluid communication from the EGR conduit to the engine intake conduit and defining a second operating mode, wherein the in the first mode an EGR gas flow from the EGR conduit is promoted within the engine intake conduit and in the second mode of pressurized airflow is promoted within the engine intake conduit. 
     In accordance with yet another exemplary embodiment of the present invention, a method of using an intake air system for an internal combustion engine is provided. The method includes providing an internal combustion engine having a turbocharger in fluid communication with an intake manifold of the engine and configured to provide a forced-induction airflow thereto having a first pressure, the turbocharger comprising a turbine housing, the turbine housing comprising a turbine volute conduit, the turbine volute conduit having a turbine volute inlet and a wastegate/EGR conduit inlet, the wastegate/EGR conduit inlet radially spaced from the volute inlet along the turbine volute conduit and opening into an EGR conduit that is disposed on the turbine housing, the EGR conduit configured for fluid communication of an EGR flow to an EGR valve switchable between an open and a closed position, the open position enabling fluid communication of the EGR flow having a second pressure to the intake manifold and defining a first operating mode, and the closed position disabling fluid communication from the EGR conduit to the intake manifold and defining a second operating mode, wherein in the first mode the second pressure is greater than the first pressure and an EGR flow to the engine is promoted within the intake manifold. The method also includes operating the engine to produce an exhaust gas flow into the turbine volute inlet. The method also includes selecting the first mode or the second mode while operating the engine. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which: 
         FIG. 1  is a schematic view of an exemplary embodiment of a forced-induction intake air system as disclosed herein; 
         FIG. 2  is a front view of an exemplary embodiment of a turbine housing for a turbocharger, as disclosed herein; 
         FIG. 3  is a perspective view of the turbine housing of  FIG. 2 , 
         FIG. 4  is a top view of the turbine housing of  FIG. 2  and an exemplary embodiment of a turbocharger incorporating the same as disclosed herein; 
         FIG. 5  is a side view of the turbine housing and turbocharger of  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of the turbine housing of  FIG. 5  taken along section  6 - 6 ; and 
         FIG. 7  is a cross-sectional view of the turbine housing of  FIG. 2  taken along section  7 - 7 ; 
         FIG. 8  is a cross-sectional view of the turbine housing of  FIG. 2  taken along section  8 - 8 ; 
         FIG. 9  is a cross-sectional view of the turbine housing of  FIG. 2  taken along section  9 - 9 ; and 
         FIG. 10  is a flowchart of an exemplary method of using an intake air system as described herein. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention discloses an exemplary embodiment of a turbine housing, and exemplary embodiments of a turbocharger and air induction system for an internal combustion engine that incorporate the turbine housing, as well as associated methods of their use, that enhance EGR available for use in the air induction system while at the same time providing sufficient exhaust gas flow to drive the turbine and generate the desired pressure boost and induction airflow into the air intake system, regardless of whether the turbocharger uses a fixed or variable nozzle turbine. 
     The present invention includes a turbine housing having a wastegate-like conduit or passage which directly bypasses or shunts a portion of the exhaust gas energy from the turbine wheel and reduces the effective efficiency of the turbine stage, which consequently reduces the boost pressure of the intake airflow available from the compressor and allows for EGR flow pressures which are higher than the intake airflow pressures, thus promoting the EGR flow to enter and be intermixed with the intake airflow to produce a combustion airflow that includes EGR, including a predetermined amount or flow of EGR. 
     A wastegate or EGR conduit inlet is located in the turbine volute and an associated EGR conduit is integrally formed in the turbine housing with a connection to the EGR system such that the EGR valve also effectively serves as a wastegate valve. In this instance; however, the term wastegate is somewhat of a misnomer, since the exhaust shunted through the “wastegate” is in fact available for use as EGR flow. What would otherwise normally be wastegate flow and would bypass the turbine volute and turbine wheel altogether to be exhausted from the vehicle through its exhaust system is instead passed into the turbine volute conduit, where a portion is available for use as desirable EGR flow while the remaining portion may be used to drive the turbine wheel, albeit at a reduced efficiency relative to that which would be available from the entire exhaust flow. The wastegate may be associated with the EGR conduit or flow passage in the form of an EGR valve attached to the EGR conduit, including both two-position (fully open and closed) and variable position EGR valves, such that the EGR valve serves as a wastegate valve and the action of opening the EGR valve also opens the wastegate. When EGR flow is desired to support the combustion process, the engine control system opens the EGR valve. Opening the EGR valve simultaneously reduces turbine efficiency and promotes EGR flow. This synergistic interaction to promote EGR flow is an advantageous aspect of the turbine housing disclosed herein, as well as turbochargers and intake air systems that incorporate them. This synergistic arrangement enables incorporation of a wastegate function while also enabling integrated balancing of the EGR flow and forced-induction intake airflow requirements. 
     The present invention enhances EGR available for use in the induction system, while at the same time providing sufficient exhaust flow to drive the turbine and generate the desired pressure boost and air induction into the air intake system, and effectively resolves the issue of inhibited EGR flow due to excessive turbine boost by directly reducing the turbine efficiency by “wastegating” exhaust flow directly from within the turbine volute when necessary as EGR flow. This reduces the total energy available in the exhaust stream to drive the turbine wheel and compressor wheel, thereby reducing the turbine efficiency and boost pressure. This may be used, for example, to prevent the development of undesirable intake air boost pressures, particularly those that result from the use of variable nozzle turbines to increase backpressures, which are intended to promote EGR flow, but which actually generate increases in the boost pressures that offset gains in the EGR flow, thereby preventing EGR flow into the forced-induction intake airflow. While the invention is particularly useful in conjunction with variable nozzle turbines (VNT&#39;s), the devices and methods disclosed can be used with both (VNT) and fixed nozzle turbines. The present invention enables the controlled, repeatable, and temporary reduction of the turbocharger efficiency while at the same time promoting EGR flow in the combustion air mixture. 
     As illustrated in  FIG. 1 , in accordance with an exemplary embodiment of the present invention an internal combustion engine  10  includes a forced-induction system  12 , including turbocharger  14 , and an EGR system  16  that respectively supply intake air or EGR, or a combination or mixture thereof, to air intake system  18 . Air intake system  18  includes EGR intake conduit  20  configured for fluid communication of a pressurized or forced-induction EGR flow represented by arrow  22  and engine intake conduit  24  configured for fluid communication of a pressurized, forced-induction airflow represented by arrow  26 . EGR flow  22  and airflow  26  are used to make up the pressurized or forced-induction combustion flow  28  that provides pressurized, forced-induction air or EGR, or a combination or mixture thereof, to engine  10  for combustion. Air intake system  18  also includes an intake manifold  30 , or plurality of manifolds, that receives combustion flow  28  and distributes the combustion flow  28  to the engine cylinders (not shown). Air intake system  18  may also, optionally, include other intake system devices downstream of EGR intake conduit  20  and engine intake conduit  24  and upstream of intake manifold  30 , including EGR flow  22  and forced-induction airflow  26  coolers, as well as mixers for combining these airflows, as described herein. 
     Referring to  FIG. 1 , engine  10  includes intake manifold  30 , or a plurality of manifolds, and an exhaust manifold  32 , or a plurality of manifolds  32 . Engine  10  also includes a turbocharger  14  that includes a turbine  34  contained in a turbine housing  36  and a compressor  38  contained in a compressor housing  40 , for compressing ambient intake air illustrated by arrow  41  and producing the pressurized, forced-induction airflow  26  for combustion in engine  10 . Intake airflow  41  is heated during the turbocharger compression process and may be cooled to improve their volumetric efficiency by increasing intake air charge density through isochoric cooling. That cooling may be accomplished by routing the forced-induction airflow  26  discharged from the turbocharger  14  to a turbocharger air cooler  42 , which may also be referred to as an inter cooler or after cooler, via engine intake conduits  24 . Turbocharger air cooler  42  may be engine mounted. The forced-induction air flow  26  is then routed from the turbocharger air cooler  42  through engine intake conduit  24  and intake manifold  30  for distribution to the cylinders of engine  10 . 
     Engine  10  and forced-induction system  12  also includes an EGR system  16 . EGR system  16  includes an EGR control valve  46 . EGR control valve  46  is in fluid communication with and regulates the release of exhaust gas as EGR from the turbine housing  36  through EGR conduit  48 , as further explained herein. EGR control valve  46  acts as a wastegate and is configured to divert a portion of the exhaust gas flow  52  from the exhaust manifold  32  and associated conduits  33 , that would otherwise pass through turbine housing  36  via turbine volute conduit  50  (See  FIG. 6 ), for use as EGR flow  22  through EGR conduit  48 . EGR flow  22  exits EGR conduit  48  through EGR conduit outlet  90  ( FIG. 6 ) where it is routed to EGR control valve  46  as part of EGR system  16 . By controlled opening and closing of the valve, EGR flow  22  is mixed with the forced-induction airflow  26  in intake charge mixer  56 . EGR system  16  may also include an EGR cooler  54 , or heat exchanger, that may also be engine-mounted for cooling the EGR flow  22  passing through the system. By providing a heat exchanger in the EGR system  16 , EGR cooler  54  may also provide for increased efficiency of engine  10 . EGR cooler  54  may also include a bypass valve  55  that permits the EGR flow  22  to bypass the cooler during periods when cooling is not needed or desirable, such as at cold engine startup. The EGR flow  22  passing through or bypassing EGR cooler  54  is combined with the forced-induction airflow  26  that has in turn passed through the turbocharger air cooler  42  to provide force-induction combustion (air or air+EGR) flow  28 . The gas flows  22  and  26  may be combined using intake charge mixer  56  to improve the homogeneity of the combustion flow  28  before the flow enters the intake manifold  30  of the engine  10 . Forced induction system  12  may be operated without affecting the efficiency of turbocharger  14  when EGR control valve  46  is closed, and forced induction combustion flow  28  includes just forced-induction airflow  26 . When EGR control valve  46  is opened, the efficiency of turbine  34  and turbocharger  14  is reduced, thereby promoting introduction of EGR flow  22  into forced-induction combustion flow  28  so that flow  28  includes a mixture of forced-induction airflow  26  and EGR flow  28 , as described herein. By using a variable EGR control valve  46 , the reduction of efficiency of turbocharger  14  and the mixture of forced-induction airflow  26  and EGR flow  28  can be controlled. 
       FIGS. 1-9  show an exemplary embodiment of a turbine housing  36 , and turbocharger  14  that uses the housing, in greater detail. Turbine housing  36  may include one or more mounting flanges  37  for mounting the housing to the engine  10 . Turbine housing  36  includes one or more turbine inlets  76 , a housing body  78  that includes a turbine volute  75  that defines the turbine volute conduit  50  and associated turbine volute passage  58  and the turbine outlet  80 . Housing  36  also includes an EGR conduit inlet  74  that is radially spaced away from the turbine volute inlet  82  along the turbine volute conduit  50 . 
     Referring to  FIGS. 1-6 , turbine housing inlets  76  may be attached directly to the exhaust manifold  32 , or a plurality of manifolds, of the engine  10 , or maybe attached indirectly through additional exhaust conduits (not shown). The one or more turbine inlets  76  may be associated with one or more branches  92 ,  94  of inlet conduit  77 . For example, in the embodiment of  FIGS. 1-6 , there are two turbine inlets  76  and two respective branches  92 ,  94  that merge into a single inlet conduit  77 . Turbine housing inlets  76  may be incorporated into one or more mounting flanges  84  for detachable attachment, as described, using a plurality of threaded bolts, clamps or the like (not shown). Exhaust gas flows  52  ( FIG. 6 ) entering the turbine housing inlet  76  are combined into a single exhaust gas flow  52  that flows into turbine volute conduit  50  at turbine volute inlet  82 . Referring to  FIG. 6 , turbine volute conduit  50  has an inwardly curving and converging turbine volute passage  58 , such as a spiroidal-shaped curving passage. As turbine volute passage  58  converges away from turbine volute inlet  82 , as shown in  FIGS. 7-9 , the cross-sectional area of the passage is progressively reduced. The progressive reduction of turbine volute passage  58  progressively increases the speed of exhaust gas flow  52  within the passage. The turbine volute conduit  50  spirals inwardly about turbine wheel  60 , which is in fluid communication with conduit  50  and turbine volute passage  58  through circumferentially extending turbine nozzle  25 . Nozzle  25  directs exhaust gas flow  52  across turbine blades (not shown) on turbine wheel  60  where it is exhausted through turbine conduit outlet  80 , thereby causing rotation of turbine wheel  60  and turbine shaft  64  to which it is attached, which in turn rotates the compressor wheel  66  that is attached to the opposite end of shaft  64 . Rotation of the compressor wheel  66  draws air into the compressor intake  68  which is then compressed as it passes through the compressor nozzle (not shown) and expelled through compressor volute conduit  70  and compressor volute conduit outlet  72  as forced-induction airflow  26 . 
     Referring to FIGS.  1  and  6 - 9 , EGR conduit inlet  74  opens into EGR conduit  48  that is disposed on turbine housing  36  over the EGR conduit inlet  74 . In the exemplary embodiment of  FIG. 6 , EGR conduit  48  is disposed over EGR conduit inlet and extends tangentially outwardly from turbine volute  75  as an integral portion of turbine housing  36 . EGR conduit  48  has an EGR conduit passage  86 . EGR conduit  48  may have a substantially similar size and shape, or cross-sectional area, as EGR conduit inlet  74  so that a smooth transition occurs between turbine conduit  50  and EGR conduit  48 . Alternately, EGR conduit  48  may have a cross-sectional area that is less than the cross-sectional area of EGR conduit inlet  74 . EGR conduit passage  86  and EGR conduit inlet  74  may have any suitable cross-sectional area and orientation with respect to the turbine volute conduit  50  and turbine volute passage  58  sufficient to provide a predetermined EGR flow  22 , as well as a predetermined exhaust gas flow through nozzle  25 , including a cross-sectional area of the EGR conduit passage  86  that is less than or equal to the cross-sectional area of the turbine volute passage  58  proximate the EGR conduit inlet  74 . Further, the cross-sectional area of EGR conduit passage  86  may be the same along its length away from the EGR conduit inlet  74 , or alternately, may progressively converge or diverge away from the EGR conduit inlet. In the exemplary embodiment of  FIG. 6 , a central axis  49  of EGR conduit  48  and EGR conduit passage  86  may be substantially tangential to and co-planar with a central axis  51  of turbine volute conduit  50  and turbine volute passage  58  in order to minimize losses in EGR flow  22 . Further, in this embodiment, the cross-sectional area of EGR conduit passage  86  may be less than the cross-sectional area of the turbine volute passage  58  proximate the EGR conduit inlet to provide the predetermined EGR flow  22  and predetermined exhaust gas flow  52  through turbine nozzle  25 . The EGR conduit passage  86  and turbine volute passage  58  should be sized to obtain a predetermine EGR flow  22  and a reduction in the forced-induction airflow  26 , wherein the pressure of EGR flow  22  is greater than the pressure of forced-induction airflow  26 , thereby promoting a predetermined EGR flow  22  portion of forced-induction flow  28 . EGR conduit  48  may also include a mounting flange  88  proximate EGR conduit outlet  90  for detachable attachment to EGR intake conduit  20 , as described herein, using a plurality of threaded bolts, clamps or the like (not shown). 
     EGR conduit inlet  74  is radially spaced away from the turbine volute inlet  82  along turbine volute conduit  50 . The radial spacing may be characterized as an angle (α) between the centers of EGR conduit inlet  74  and turbine volute inlet  82  ( FIG. 6 ). In an exemplary embodiment, the spacing may be between about 80° to about 270°. As the radial spacing (a) increases, the speed of exhaust gas flow  52  within turbine volute passage  58  increases, hence the speed of EGR flow  22  also increases, when EGR control valve  46  is opened. As described herein, the opening of EGR control valve  46  also reduces exhaust gas flow  52  within turbine volute conduit  50 , thereby reducing the amount of work done by exhaust gas flow  52  on turbine wheel  60  and a concomitant reduction of the work that may be performed by compressor wheel  66 , thereby lowering the pressure or boost available from the turbocharger. As described, the balance of increasing the EGR flow  22  pressure and reducing the forced-induction airflow  26  may be used to increase the amount of EGR available in forced-induction combustion flow  28  and provide a predetermined amount of EGR in forced-induction combustion flow  28 . The radial spacing, orientation, size and other aspects of EGR conduit  48  and EGR conduit inlet  74  may be used to control the predetermined amount of EGR in forced-induction combustion flow  28 . 
     In the exemplary embodiment of  FIGS. 1-9 , the turbine nozzle  25  is a fixed geometry nozzle. In another exemplary embodiment, turbine nozzle  25  may be a variable geometry nozzle. The nozzle geometry may be varied to control back pressure in the turbine volute passage and associated upstream conduits, including the exhaust manifold, wherein reducing the nozzle opening increases backpressure and increasing the nozzle opening reduces backpressure. The nozzle geometry and backpressure may be controlled by various actuator mechanisms. 
     Turbine housing  36  and the portions thereof described above may be made individually, in any combination, and assembled together to make turbine housing. Alternately, turbine housing  36 , as described herein, may be formed as an integral whole, such as by casting the housing. Suitable materials for use as turbine housing  36  include various grades and alloys of cast iron and steel. Further, housing may receive any suitable secondary finishing operation, including cleaning, machining and the like. 
     Referring to  FIGS. 1-10 , in accordance with yet another exemplary embodiment of the present invention, a method  100  of using an intake air system  18  for an internal combustion engine  10  is provided. Method  100  includes providing  110  an internal combustion engine  10  having a turbocharger  14  in fluid communication with an intake manifold  30  of the engine and configured to provide a forced-induction airflow  26  thereto having a first pressure. The turbocharger  14  includes a turbine housing  36  that includes turbine volute conduit  50 . Turbine volute conduit  50  has a turbine volute inlet  82  and an EGR conduit inlet  74  that is radially spaced from the volute inlet along the turbine volute conduit and opens into an EGR conduit  48  that is disposed on the turbine housing  36 . The EGR conduit  48  is configured for fluid communication of EGR flow  22  to an EGR control valve  46  that is switchable between an open and a closed position. EGR flow  22  is received at EGR control valve  46  through EGR valve inlet  45 . The open position of EGR control valve  46  enables fluid communication of EGR flow  22 , having a second pressure, through EGR valve outlet  47  to the intake manifold  30  and defines a first operating mode. The closed position disables fluid communication from the EGR conduit  48  to the intake manifold  30  and defines a second operating mode. In the first mode, the second pressure is greater than the first pressure and EGR flow  22  to the engine is promoted within the intake manifold  30 . Method  100  also includes operating  120  the engine  10  to produce exhaust gas flow  52  in the turbine volute conduit  50  at turbine volute inlet  82 . Method  100  also includes selecting  130  the first mode or the second mode while operating the engine. Selecting  130  may be performed using a suitable controller (not shown), such as an engine control unit (ECU). In the first mode, the efficiency of the turbocharger and the first pressure are reduced in conjunction with providing the EGR flow  22  to the intake manifold  30 . Optionally, method  100  also includes selecting  140  the radial spacing of the turbine volute inlet  82  and EGR conduit inlet  74  to obtain a predetermined EGR flow  22 , as described herein. Optionally, the EGR control valve  46  is a variable EGR control valve  46  switchable between the open position, the closed position and a plurality of partially open positions therebetween that define a corresponding plurality of operating modes, wherein the method further comprises selecting  150  one of the plurality of operating modes, and wherein in the first operating mode and the plurality of operating modes, the second pressure is greater than the first pressure, thereby promoting a corresponding plurality of EGR flows into the intake manifold  30 . 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the present application.