Abstract:
An engine assembly includes an intake assembly, an internal combustion engine defining a plurality of cylinders and configured to combust a fuel and produce exhaust gas, and an exhaust assembly in fluid communication with a first subset of the plurality of cylinders. Each of the plurality of cylinders are provided in fluid communication with the intake assembly. The exhaust assembly is provided in fluid communication with a first subset of the plurality of cylinders, and a dedicated exhaust gas recirculation system in fluid communication with both a second subset of the plurality of cylinders and with the intake assembly. The dedicated exhaust gas recirculation system is configured to route all of the exhaust gas from the second subset of the plurality of cylinders to the intake assembly. Finally, the engine assembly includes a turbocharger having a variable geometry turbine in fluid communication with the exhaust assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/762,581, filed Feb. 8, 2013, which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under DOE/NETL grant number DE-EE0005654. The invention described herein may be manufactured and used by or for the U.S. Government for U.S. Government (i.e., non-commercial) purposes without the payment of royalties thereon or therefore. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to turbocharged internal combustion engines with dedicated exhaust gas recirculation. 
     BACKGROUND 
     Internal combustion engines may combust a mixture of air and fuel within one or more combustion chambers to produce a mechanical output. During the combustion, various exhaust gases are produced and expelled to the atmosphere. In some instances, a portion of the exhaust gas may be recirculated back into the engine cylinders (via an exhaust gas recirculation system). In a gasoline engine, this inert exhaust may displace an amount of combustible mixture in the cylinder resulting in increased engine efficiency. In a diesel engine, the exhaust gas may replace some of the excess oxygen in the pre-combustion mixture. In either instance, the recirculated exhaust may reduce the combustion temperature in the cylinder and/or reduce the creation of certain gaseous byproducts. 
     SUMMARY 
     An engine assembly includes an intake assembly, an internal combustion engine defining a plurality of cylinders and configured to combust a fuel and produce exhaust gas, and an exhaust assembly in fluid communication with a first subset of the plurality of cylinders. Each of the plurality of cylinders is provided in fluid communication with the intake assembly. 
     The exhaust assembly is provided in fluid communication with a first subset of the plurality of cylinders, and a dedicated exhaust gas recirculation system in fluid communication with both a second subset of the plurality of cylinders and with the intake assembly. The dedicated exhaust gas recirculation system is configured to route all of the exhaust gas from the second subset of the plurality of cylinders to the intake assembly. 
     Finally, the engine assembly includes a turbocharger that includes a compressor in fluid communication with the intake assembly, and a variable geometry turbine in fluid communication with the exhaust assembly. The compressor and variable geometry turbine are operatively connected through a shaft. 
     The variable geometry turbine includes a rotatable turbine wheel disposed within a housing, and a plurality of articulating veins circumferentially disposed about the rotatable turbine wheel. The articulating veins are configured to articulate between a substantially open and a substantially closed position to controllably nozzle the exhaust gas to the turbine wheel. 
     The exhaust assembly may further include a first exhaust manifold and a second exhaust manifold, and the first subset of the plurality of cylinders includes a first cylinder and a second cylinder. The first exhaust manifold may receive the produced exhaust gas from the first cylinder, and the second exhaust manifold may receive the produced exhaust gas from the second cylinder. In this manner the design may separate the exhaust pulses generated between the respective first and second cylinders. 
     In one configuration, the first exhaust manifold and the second exhaust manifold may converge at a manifold interface, wherein the manifold interface defines a first manifold flow path in fluid communication with the first exhaust manifold and defines a second manifold flow path in fluid communication with the second exhaust manifold. In this configuration, the first manifold flow path may be internally separated from the second manifold flow path by a manifold flow divider. 
     The variable geometry turbine may include a turbine housing defining a turbine inlet. The turbine inlet may be coupled with the manifold interface and may be in fluid communication with the manifold interface. A turbine flow divider may be disposed within the turbine inlet, and may partially define a first turbine channel and a second turbine channel. The first turbine channel may be in fluid communication with the first manifold flow path, and the second turbine channel may be in fluid communication with the second manifold flow path. In this configuration, the turbine flow divider may then abut the manifold flow divider. 
     In another embodiment, the plurality of cylinders may more specifically include a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder. The exhaust assembly may then includes a first exhaust manifold, a second exhaust manifold, and an EGR manifold. The first exhaust manifold may receive the produced exhaust gas from the first cylinder. The second exhaust manifold may receive the produced exhaust gas from both the second cylinder and the third cylinder, and the EGR manifold may receive all of the produced exhaust gas from the fourth cylinder. Additionally, the plurality of cylinders may combust fuel sequentially in the order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder. 
     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 
         FIG. 1  is a schematic diagram of an internal combustion engine assembly with a variable geometry turbocharger and dedicated exhaust gas recirculation. 
         FIG. 2A  is a schematic cross-sectional view of a variable geometry turbocharger turbine during a period of high exhaust flow. 
         FIG. 2B  is a schematic cross-sectional view of a variable geometry turbocharger turbine during a period of low exhaust flow. 
         FIG. 3  is a schematic cross-sectional view, taken along line  3 - 3  of  FIG. 2A , showing a manifold interface for coupling a first and second exhaust manifold to a turbocharger turbine housing. 
         FIG. 4  is a schematic cross-sectional view, taken along line  4 - 4  of  FIG. 2A , illustrating a first embodiment of a variable geometry turbocharger turbine. 
         FIG. 5  is a schematic cross-sectional view, such as taken along line  5 - 5  of  FIG. 2A , illustrating a second embodiment of a variable geometry turbocharger turbine. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numerals are used to identify like or identical components in the various views,  FIG. 1  schematically illustrates an engine assembly  10  including an internal combustion engine  12 , an air intake system  14 , and an exhaust system  16 . The air intake system  14  and the exhaust system  16  may each respectively be in fluid communication with the engine  12 , and may be in mechanical communication with each other through a turbocharger  18 . 
     The internal combustion engine  12  (i.e., engine  12 ) may be a spark-ignited internal combustion engine, and may define a plurality of cylinders  20  (referenced as cylinders 1-4). Each of the respective cylinders  20  may include one or more fuel injectors  22  that may selectively introduce liquid fuel (as an aerosol) into each cylinder for combustion. Each of the cylinders  20  may be in selective fluid communication with the air intake system  14  to receive fresh/oxygenated air, and several of the cylinders  20  may be in selective fluid communication with the exhaust system  16  to expel the byproducts of combustion. While the illustrated engine  12  depicts a 4-cylinder engine, the present technology is equally applicable to inline three and six cylinder engines, V-8, V-10, and V-12 configuration engines, among others. 
     The air intake system  14  may generally include a fresh-air inlet  24 , an exhaust gas recirculation (EGR) mixer  26 , a charge air cooler  28 , a throttle  30 , and an intake manifold  32 . As may be appreciated during operation of the engine  12  fresh air  34  may be ingested by the air intake system  14  from the atmosphere (or from an associated air-cleaner assembly) via the fresh-air inlet  24 . The throttle  30  may include a controllable baffle configured to selectively regulate the total flow of air through the intake system  14 , and ultimately into the cylinders  20  (via the intake manifold  32 ). 
     The exhaust system  16  may include at least a first exhaust manifold  36  and a second exhaust manifold  38  that may channel flowing exhaust gasses  40  away from the engine  12 . The exhaust gasses  40  may pass through an aftertreatment device  42  to catalyze and/or remove certain byproducts prior to exiting the exhaust system  16  via a tailpipe  44 . 
     As mentioned above, the air intake system  14  and the exhaust system  16  may be in mechanical communication through a turbocharger  18 . The turbocharger  18  may include a variable geometry turbine  60  (“VGT  60 ” or “turbine  60 ”) in fluid communication with the exhaust system  16  and a compressor  62  in fluid communication with the intake system  14 . The turbine  60  and the compressor  62  may be mechanically coupled via a rotatable shaft  64 . The turbocharger  18  may utilize the energy of exhaust gasses  40  flowing from the engine  12  to spin the turbine  60  and compressor  62 . The rotation of the compressor  62  may then draw fresh air  34  in from the inlet  24  and compress it into the remainder of the intake system  14 . 
     The engine assembly  10  may further include a dedicated EGR system  50  that may directly route (e.g., via an EGR manifold  52 ) the exhaust gas  54  from one or more cylinders of the engine  12  back into the intake system  14 . This recirculated exhaust gas  54  may mix with the fresh air  34  at the EGR mixer  26 , and may correspondingly dilute the oxygen content of the mixture. The use of EGR is known to increase efficiency in spark ignition engines. EGR is also known to reduce the combustion temperature and NOx production from the engine  12 . Using a separate EGR manifold  52  to route the entire exhaust of one or more cylinders back to the intake assembly  14  is referred to herein as “dedicated EGR.” 
     As illustrated in  FIG. 1 , one of the cylinders  20  (i.e., cylinder 4) is a dedicated EGR cylinder that may supply 100% of its exhaust gas  54  back to the intake assembly  14 . The exhaust gas  40  of the remaining three cylinders  20  (i.e., cylinders 1-3) is expelled from the engine  12  via the exhaust assembly  16 . 
       FIGS. 2A and 2B  illustrate two states of the variable geometry turbine  60 . In each case, the turbine  60  includes a housing  70  that defines a turbine inlet  72 . The turbine inlet  72  is configured to couple the turbine housing  70  with the first and second exhaust manifolds  36 ,  38  via a common manifold interface  74 . In one configuration, the common manifold interface  74  may be a single tube that may be in fluid communication with each of the first exhaust manifold  36  and the second exhaust manifold  38 . A rotatable turbine wheel  78  is disposed within the housing  70 , and is mechanically coupled with the compressor  62 . A plurality of individually articulating veins  80  are disposed about the rotatable turbine wheel  78 , and are configured to controllably nozzle the flow of exhaust gas  40  to the turbine wheel  78 , where the exhaust gas  40  may then exit the housing in a direction generally aligned with the axis of rotation of the wheel  78 . 
       FIG. 2A  illustrates the variable geometry turbine  60  in a high-flow exhaust state  82 , and  FIG. 2B  illustrates the variable geometry turbine  60  in a low-flow exhaust state  84 . In the high-flow state  82 , each of the plurality of veins  80  are articulated to an “open” position, whereby the exhaust gas  40  may be more freely allowed to contact the turbine wheel  78 . In the low-flow state  84 , each of the plurality of veins  80  are articulated to a “substantially closed” position, whereby the exhaust gas  40  is nozzled toward the turbine wheel  78 . By nozzling the exhaust gas  40  toward the turbine wheel  78 , the variable geometry turbine  60  may attempt to maintain a minimum turbine wheel speed, even despite the low flow rate. Referring to  FIG. 1 , a controller  86  may be in electronic communication with the throttle  30 , fuel injectors  22 , and/or various mass/flow sensors within the intake assembly  14  or exhaust assembly  16  to determine the most efficient angular state of the various veins  80 . Once this is determined, the controller  86  may continuously command the veins  80  to rotate to the proper angle. In this manner, the variable geometry turbine  60  may provide an improved transient response at substantially lower flow rates (when compared with a standard turbocharger). 
     Referring again to  FIG. 1 , in a typical 4-cylinder engine, the firing order may sequentially be: cylinder 1; cylinder 3; cylinder 4; cylinder 2. As may be appreciated, the engine  12  may then expel gas from the cylinders in the same sequential order. Therefore, the exhaust flow more closely resembles a series of pulses than a continuous flow. 
     It has been found that engine efficiency is maximized when exhaust pulses are separated from each other. In addition to reducing interference between the pulses, the separation may reduce the occurrence of knocking and/or abnormal combustion. In an effort to achieve sufficient pulse separation, the exhaust flow may be divided into different flows, which may be separately introduced to the turbocharger  18 . In an ideal 4-cylinder engine with the firing order previously noted, this separation would pair cylinder 1 with cylinder 4, and cylinder 3 with cylinder 2. In the present configuration, however, cylinder 4 is a dedicated EGR cylinder, with 100% of its exhaust returning to the intake assembly  14 . Therefore, cylinders 2 &amp; 3 may remain paired (via the second exhaust manifold  38 ), while cylinder 1 may be isolated (via the first exhaust manifold  36 ), and cylinder 4 may be independently recirculated. 
       FIG. 3  illustrates a cross-sectional view  90  of an embodiment of the manifold interface  74  shown in  FIG. 2A , and taken along line  3 - 3 . As shown, the first exhaust manifold  36  and the second exhaust manifold  38  may converge to a single physical tube  76 , yet may still remain independent. Said another way, the manifold interface  74  may define a first manifold flow path  92  in fluid communication with only the first exhaust manifold  36 , and may define a second manifold flow path  94  in fluid communication with only the second exhaust manifold  38 . A manifold flow divider  96  may separate the first manifold flow path  92  from the second manifold flow path  94 . In this manner, assembly may only require the attachment of one part to the housing  70  of the turbine  60 , yet the exhaust pulses may be separated to a greater degree than with one single flow-path. In an alternative embodiment, the manifold interface  74  may be integrally formed with the housing  70 . 
     To maximize efficiency, it may be desirable to maintain the exhaust flow separation up to the introduction of the exhaust flow to the turbine wheel  78  (ideally where each flow would act on a physically different portion of the wheel  78 . Unfortunately, however, the plurality of articulating veins  80  in the variable geometry turbocharger may prevent the flows from being isolated to that extent. 
       FIG. 4  schematically illustrates a cross-sectional view  100  of an embodiment of the variable geometry turbine  60  shown in  FIG. 2A , and taken along line  4 - 4 . As shown, the turbine housing  70  may include a housing flow divider  102  that may partially separate a first turbine channel  104  from a second turbine channel  106 . The turbine flow divider  102  may surround, or substantially surround the turbine wheel  78  and plurality of articulating veins  80 , and may further extend through the turbine inlet  72  and mate with/abut the manifold flow divider  96 . In this manner, the first turbine channel  104  may be in fluid communication with the first manifold flow path  92 , and the second turbine channel  106  may be in fluid communication with the second manifold flow path  94 . 
     Each of the first and second turbine channels  104 ,  106  may be open to the articulating veins  80  such that exhaust gas may pass from the respective turbine channels  104 ,  106  across the respective veins  80  and to the turbine wheel  78 . The turbine flow divider  102  may extend from the turbine housing  70  to a point that is at or immediately proximate to the furthest outward radial distance  108  the articulating veins  80  can extend (also accounting for thermal expansion). In this manner, when the veins  80  are rotated to their fully opened state, they closely approach the divider  102 , though do not make contact. 
       FIG. 5  schematically illustrates a cross-sectional view  110  of another embodiment of a variable geometry turbine  60 . This cross-sectional view  110  may be taken from a turbine  60  similar to that shown in  FIG. 2A , and taken along line  5 - 5 . As shown, the turbine housing  70  may include a turbine flow divider  102  that may partially separate a first turbine channel  104  from a second turbine channel  106  only within the turbine inlet  72 . Said another way, the flow divider  102  may terminate prior to entering the volute portion of the turbine housing  70 , wherein the two exhaust flows may join to present a uniform flow to the turbine wheel. In one configuration, the flow divider  102  may twist (e.g., in a screw or helicoid shape) or include any other such geometry that may aid in promoting a uniform distribution of exhaust flow to the turbine wheel. 
     The presently described engine assembly  10  employs the dedicated EGR system  50 , which has been shown to reduce the average exhaust gas temperature by promoting more efficient combustion. In doing so, the dedicated EGR system  50  may enable the use of a variable geometry turbine  60  on a spark-ignited combustion engine without the need to over-design the articulating veins  80  to withstand typical elevated spark-ignited engine combustion temperatures (which are generally hotter than any current uses of a VGT). Additionally, employing the present pulse separation techniques within the VGT housing may provide an additional efficiency increase beyond mere application of the VGT. The combination of these techniques may be used to increase the efficiency of the spark-ignited gasoline engine assembly  10  without adding a substantial amount of weight or cost to the vehicle. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. Any directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, above, below, vertical, and horizontal) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.