Abstract:
An internal combustion engine includes a block defining at least one combustion cylinder. An intake manifold is fluidly coupled with at least one combustion cylinder, and an exhaust manifold is also fluidly coupled with at least one combustion cylinder. An exhaust gas recirculation system is fluidly coupled between the exhaust manifold and the intake manifold. A turbocharger includes a variable geometry turbine fluidly coupled with the exhaust manifold. The variable geometry turbine is movable to a first position effecting fluid flow of exhaust gas from the exhaust manifold to the intake manifold, and movable to a second position effecting fluid flow of charge air to the variable geometry turbine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 11/242,100 entitled “TURBOCHARGED INTERNAL COMBUSTION ENGINE WITH EGR SYSTEM HAVING REVERSE FLOW”, filed Oct. 3, 2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to internal combustion engines, and, more particularly, to exhaust gas recirculation systems in such engines. 
       BACKGROUND OF THE INVENTION 
       [0003]    An internal combustion (IC) engine may include an exhaust gas recirculation (EGR) system for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the IC engine. 
         [0004]    An IC engine may also include one or more turbochargers for compressing a fluid which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the fluid to be compressed and supplies the fluid to the combustion chambers. The fluid which is compressed by the compressor may be in the form of combustion air or a fuel and air mixture. 
         [0005]    The operating behavior of a compressor within a turbocharger may be graphically illustrated by a “compressor map” associated with the turbocharger in which the pressure ratio (compression outlet pressure divided by the inlet pressure) is plotted on the vertical axes and the flow rate is plotted on the horizontal axes. In general, the operating behavior of a compressor is limited on the left side of the compressor map by a “surge line” and on the right side of the compressor map by a “choke line”. The surge line basically represents “stalling” of the air flow at the compressor inlet. With too small a volume flow and too high a pressure ratio, the flow will separate from the suction side of the blades on the compressor wheel, with the result that the discharge process is interrupted. The air flow through the compressor is reversed until a stable pressure ratio by positive volumetric flow rate is established, the pressure builds up again and the cycle repeats. This flow instability continues at a substantially fixed frequency and the resulting behavior is known as “surging”. The choke line represents the maximum centrifugal compressor volumetric flow rate, which is limited for instance by the cross-section at the compressor inlet. When the flow rate at the compressor inlet or other location reaches sonic velocity, no further flow rate increase is possible and choking results. Both surge and choking of a turbocharger compressor should be avoided. 
         [0006]    When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted by a poppet-type EGR valve directly from the exhaust manifold. The percentage of the total exhaust flow which is diverted for introduction into the intake manifold of an internal combustion engine is known as the EGR rate of the engine. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides an EGR system which is configured such that exhaust gas is circulated to the intake manifold, or, alternatively, charge air is bypassed in a reverse direction through the EGR system to the turbocharger. 
         [0008]    The invention comprises, in one form thereof, an internal combustion engine including a block defining at least one combustion cylinder. An intake manifold is fluidly coupled with at least one combustion cylinder, and an exhaust manifold is also fluidly coupled with at least one combustion cylinder. An exhaust gas recirculation system is fluidly coupled between the exhaust manifold and the intake manifold. A turbocharger includes a variable geometry turbine fluidly coupled with the exhaust manifold. The variable geometry turbine is movable to a first position effecting fluid flow of exhaust gas from the exhaust manifold to the intake manifold, and movable to a second position effecting fluid flow of charge air to the variable geometry turbine. 
         [0009]    The invention comprises, in another form thereof, an exhaust gas recirculation system for an internal combustion engine including an intake manifold having an inlet, an exhaust manifold having an outlet, and a turbocharger coupled with the exhaust manifold outlet. The exhaust gas recirculation system includes at least one fluid line for interconnecting the exhaust manifold outlet and the intake manifold inlet; and a pressure differential generator for selectively generating an EGR flow of exhaust gas through the at least one fluid line from the exhaust manifold outlet to the intake manifold inlet, and a reverse EGR flow of charge air through the at least one fluid line to the turbocharger. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of an embodiment of an internal combustion engine of the present invention; and 
           [0011]      FIG. 2  is a graphical illustration of a compressor map for the turbocharger shown in  FIG. 1 , illustrating the effect of the present invention on the compressor map. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown an embodiment of an IC engine  10  of the present invention, which generally includes a block  12  having a plurality of combustion cylinders  14 , intake manifold  16 , exhaust manifold  18 , charge air cooler  20 , turbocharger  22 , EGR valve  24  and EGR cooler  26 . In the embodiment shown, IC engine  10  is a diesel engine which is incorporated into a work machine, such as an agricultural tractor or combine, but may be differently configured, depending upon the application. 
         [0013]    Block  12  is typically a cast metal block which is formed to define combustion cylinders  14 . In the embodiment shown, block  12  includes six combustion cylinders  14 , but may include a different number depending upon the application. Intake manifold  16  and exhaust manifold  18  are also typically formed from cast metal, and are coupled with block  12  in conventional manner, such as by using bolts and gaskets. Intake manifold  16  and exhaust manifold  18  are each in fluid communication with combustion cylinders  14 . Intake manifold  16  receives charge air from charge air cooler  20  at intake manifold inlet  28 , and supplies charge air (which may be air or a fuel/air mixture) to combustion cylinders  14 , such as by using fuel injectors (not shown). 
         [0014]    Similarly, exhaust manifold  18  is in fluid communication with combustion cylinders  14 , and includes an outlet  30  from which exhaust gas from combustion cylinders  14  is discharged to turbocharger  22 . 
         [0015]    Turbocharger  22  includes a variable geometry turbine (VGT)  32  and a compressor  34 . VGT  32  is adjustably controllable as indicated by line  36 , and includes an actuatable element which is controlled electronically using a controller (not shown). For example, VGT  32  may be actuated by changing the position of turbine blades, a variable size orifice, or other actuatable elements. The turbine within VGT  32  is driven by exhaust gas from exhaust manifold  18 , and is exhausted to the environment, as indicated by arrow  38 . 
         [0016]    VGT  32  mechanically drives compressor  34  through a rotatable shaft  40 . Compressor  34  is a fixed geometry compressor in the embodiment shown. Compressor  34  receives combustion air from the ambient environment as indicated by line  42 , and discharges the compressed combustion air via line  44  to charge air cooler  20 . As a result of the mechanical work through the compression of the combustion air, the heated charge air is cooled in charge air cooler  20  prior to being introduced at inlet  28  of intake manifold  16 . 
         [0017]    EGR valve  24  and EGR cooler  26  are part of an EGR system which also includes a first fluid line  46 , second fluid line  48  and third fluid line  50 . The term fluid line, as used herein, is intended broadly to cover a conduit for transporting a gas such as exhaust gas and/or combustion air, as will be understood hereinafter. 
         [0018]    First fluid line  46  is coupled at one end thereof with a fluid line  52  interconnecting exhaust manifold outlet  30  with VGT  32 . First fluid line  46  is coupled at an opposite end thereof with EGR cooler  26 . Second fluid line  48  fluidly interconnects EGR cooler  26  with EGR valve  24 . Third fluid line  50  fluidly interconnects EGR valve  24  with fluid line  54  extending between charge air cooler  20  and inlet  28  of intake manifold  16 . 
         [0019]    In the embodiment shown in  FIG. 1 , first fluid line  46  is fluidly coupled with fluid line  52  extending between exhaust manifold  18  and VGT  32 . However, it will also be understood that first fluid line  46  may be fluidly coupled directly with exhaust manifold  18  for certain applications. Similarly, third fluid line  50  is fluidly coupled with fluid line  54  interconnecting charge air cooler  20  and inlet  28  of intake air manifold  16 . However, it will also be understood that third fluid line  50  may be coupled directly with intake air manifold  16  in certain applications. 
         [0020]    During operation, IC engine  10  is operated to recirculate a selective amount of exhaust gas from exhaust manifold  18  to intake manifold  16  using an EGR system defined by first fluid line  46 , EGR cooler  26 , second fluid line  48 , EGR valve  24  and third fluid line  50 . The EGR system could also be defined by first fluid line  46 , EGR valve  24 , second fluid line  48 , EGR cooler  26 , and third fluid line  50 , in that order connecting fluid line  52  to fluid line  54 . A controller selectively actuates EGR valve  24  to provide EGR flow of the exhaust gas in the EGR flow direction indicated by the large directional arrows on first fluid line  46  and third fluid line  50 . 
         [0021]    Conversely, the EGR system is also configured to provide a reverse flow of fluid in the form of charge air from fluid line  54  to fluid line  52  leading to VGT  32 . More particularly, VGT  32  may be controllably actuated to provide a pressure within fluid line  52  which is less than the pressure within fluid line  54 . When EGR valve  24  is opened, charge air thus flows from fluid line  54  through EGR valve  24  and EGR cooler  26  to fluid line  52 , and ultimately to VGT  32 . Under certain operating conditions, it is desirable to mix cooled charge air with the exhaust which is discharged from outlet  30  of exhaust manifold  18 . The reverse flow direction of charge air through the EGR system is indicated by the smaller directional arrows on second fluid line  48  and first fluid line  46 . 
         [0022]    Conventional operation of an EGR system deactivates the EGR system, or prevents any through flow, during engine operating conditions when no EGR flow is desired. On the other hand, the present invention utilizes an EGR system in a reverse flow mode to bypass fresh air around combustion cylinders  14  to VGT  32  during appropriate engine operating conditions when no EGR flow is desired. For this reverse flow to occur, it is apparent that VGT  32  is configured in a way to obtain a positive engine delta pressure (higher intake manifold pressure than exhaust manifold pressure). The process of configuring the turbocharger to obtain a positive engine delta pressure also allows a more efficient operation of turbocharger  22 . 
         [0023]    The present invention has been shown to provide improved fuel efficiency, air to fuel ratio, smoke emissions, and compressor surge margin, as well as reduce exhaust temperatures, at low to intermediate engine speeds when IC engine  10  is delivering moderate to high torque output. Due to these engine performance improvements, maximum engine output torque at certain engine speeds can also be increased, if desired. 
         [0024]      FIG. 2  is a graphical illustration of a compressor map for compressor  34  of turbocharger  22  when using EGR reverse flow of the present invention as described above. The left most line on the curve represents the surge line of the compressor. Using EGR reverse flow with the present invention, the operating point is shifted upward and to the right away from the surge line, as indicated by any particular one of the three arrows. This effectively reduces the possibility of surge of compressor  34  of turbocharger  22 . 
         [0025]    In the embodiment of the present invention described above, IC engine  10  includes a VGT  32  which is controlled to provide a delta engine pressure between intake manifold  16  and exhaust manifold  18  allowing reverse flow through the EGR system. However, it is also possible to use a pressure differential generator in the form of a differently configured turbocharger, such as a turbocharger with a wastegate, a multiple turbocharger system, a multi-stage turbocharger system, or even a fixed geometry turbocharger at low engine speeds. 
         [0026]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.