Abstract:
In one approach, a method for measuring exhaust gas recirculation flow in an engine is provided. The method comprises separating EGR flow into at least a first flow and a second flow, passing the separated first flow through a restriction region, where the first flow passes through the restriction region separately from the separated second flow, combining the separated second flow and inducting the combined flows into a cylinder of the engine, where the EGR flow is separated and then combined within a common EGR passage.

Description:
BACKGROUND/SUMMARY 
     Exhaust gas recirculation (EGR) is a technique that may reduce NO x  (e.g., nitrogen oxide and nitrogen dioxide) gases in an exhaust stream produced by diesel turbocharged engines. EGR works by recirculating a portion of the exhaust gas flow discharged by an engine back to the cylinders of the engine. The overall combustion process is thereby slowed and cooled. As NO x  gases are more readily formed at higher temperatures, the formation of NO x  gases may thus be reduced. Errors in the flow of recirculated gas, however, may cause various issues. For example, the introduction of higher amounts of recirculated exhaust gas may result in retarded engine performance while lower amounts may increase NOx gas formation and the creation of engine ping. 
     Metering of the amount of recirculated gas processed by an EGR system may be achieved in part by measuring the overall volumetric flow rate of recirculated gas through the system. Typically, this measurement may be made by passing the entire recirculated gas flow stream through an orifice that is formed by an orifice plate and measuring the resulting pressure drop across the plate. An overall EGR volumetric flow rate may then be calculated via application of Bernoulli&#39;s equation, for example. 
     Such orifice plate flow measurement configurations may introduce excessive flow restriction to an EGR system and may therefore require that a larger orifice be utilized to ameliorate flow restriction effects. With larger orifice diameters, however, the capability of such a configuration to accurately measure a pressure drop across the orifice at lower volumetric flow rates is reduced, and overall packaging issues may arise in the engine compartment. 
     The inventors herein have realized that a flow measurement configuration that decreases restriction to flow and allows for a larger dynamic flow measurement range may be advantageous. In one approach, a method for measuring exhaust gas recirculation flow in an engine is provided. The method comprises separating EGR flow into at least a first flow and a second flow, passing the separated first flow through a restriction region, where the first flow passes through the restriction region separately from the separated second flow, combining the separated second flow and inducting the combined flows into a cylinder of the engine, where the EGR flow is separated and then combined within a common EGR passage. 
     In this way, it may be possible to maintain sufficient dynamic measurement range (for higher and lower EGR flows), while reducing overall EGR restriction. Thus, desired overall EGR system packaging may be achieved. 
     Note that various approaches may be used for separating the EGR flow, such as dividing a tubular passage of the EGR system, providing a plurality of EGR passages, etc. Further, note that various restrictions may form the restriction region, such as via an integrated or separately formed orifice. Finally, note that the common EGR passage may be a common tubular assembly, separate tubes coupled together via various valves, etc. 
     In another approach, another method for measuring exhaust gas recirculation (EGR) flow in an engine may be used. The method may comprise: separating EGR flow into two separated flows including a first separated flow and a second separated flow; passing the separated first flow through a flow restriction region, where the first flow passes through the flow restriction region separately from the second flow; combining the first and second separated flows and inducting the combined flows into a cylinder of the engine, where the EGR flow is controlled by a common EGR valve, and where the second separated flow includes a greater mass flow than the first separated flow; and correlating the first separated flow to the combined flow and adjusting the EGR valve in response thereto. 
     In this way, accurate control of both higher and lower EGR flows through the EGR valve can be achieved, while reducing impacts on engine packaging in the engine compartment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exhaust system for processing exhaust gases of an internal combustion engine. 
         FIG. 2  illustrates a side view of an exhaust gas recirculation system of the exhaust system of  FIG. 1  in greater detail as a longitudinal cross-section. 
         FIG. 3A  illustrates a perspective view of the flow measurement area of  FIG. 2  in greater detail as a longitudinal cross-section. 
         FIG. 3B  illustrates a cross-sectional view of the flow measurement area of  FIG. 2  that is configured with a flow restriction region that has a cross-section that is substantially round in shape. 
         FIG. 3C  illustrates a cross-sectional view of the flow measurement area of  FIG. 2  that is configured with a flow restriction region that has a cross-section that is substantially rectangular in shape. 
         FIG. 4  shows a flow chart depicting an example routine  400  for processing the flow of an engine exhaust gas stream through a flow measurement region of an EGR system. 
         FIG. 5  shows a flow chart depicting an example routine for adjusting an amount of exhaust gas recirculation based on vehicle operating parameters and a differential pressure measured within a flow restriction region. 
         FIG. 6  depicts a graphical representation of a theoretical flow curve through an EGR system flow measurement area. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exhaust system  100  for processing exhaust gases of an internal combustion engine  102 . As one non-limiting example, engine  102  includes a diesel engine that produces a mechanical output by combusting a mixture of air from the intake system  140  and diesel fuel that it receives from fuel system  128  via fuel passage  134 . Alternatively, engine  102  may include other types of engines such as gasoline-burning engines, alcohol-burning engines and combinations thereof, among others. Further, engine  102  may be configured in a propulsion system for a vehicle. Alternatively, engine  102  may be operated in a stationary application, for example, as an electric generator. While exhaust system  100  may be applicable to stationary applications, it should be appreciated that exhaust system  100  as described herein, is particularly adapted for vehicle applications. 
     Exhaust system  100  may also include one or more of the following: an exhaust gas recirculation (EGR) system  104  that receives a portion of an exhaust gas stream exiting engine  102  and an air intake manifold  112  that supplies fresh air and recirculated exhaust gas to engine  102 . Under some conditions, EGR system  104  may be used to regulate the temperature and or dilution of the air and fuel mixture within the combustion chamber, thus providing a method of controlling the timing of ignition during some combustion modes. Further, during some conditions, a portion of combustion gases may be retained or trapped in the combustion chamber by controlling exhaust valve timing. Also, EGR system  104  is shown forming a common EGR passage from the exhaust system to the intake system. 
     Exhaust system  100  may also include a turbocharger  106 . Turbocharger  106  may be include a turbine  108  and a compressor  110  coupled on a common shaft. The blades of turbine  108  may be caused to rotate about the common shaft as a portion of the exhaust gas stream discharged from engine  102  impinges upon the blades of the turbine. Compressor  110  may be coupled to turbine  108  such that compressor  110  may be actuated when the blades of turbine  108  are caused to rotate. When actuated, compressor  110  may then direct pressurized fresh air to air intake manifold  112  where it may then be directed to engine  102 . While  FIG. 1  shows a high pressure EGR system, the EGR system may also be coupled between downstream of the turbine and upstream of the compressor. 
     Engine  102  may be controlled at least partially by a control system including controller  116  and by input from a vehicle operator via an input device  130 . In this example, input device  130  includes an accelerator pedal and a pedal position sensor  132  for generating a proportional pedal position signal PP. As non-limiting examples, controller  116  may also at least partially control EGR system  104  via inputs from engine  102 , input device  130 , and EGR system  104 . 
     Additionally, exhaust system  100  may include a plurality of passages for fluidically coupling the various exhaust system components. For example, as illustrated by  FIG. 1 , turbocharger  106  may be fluidically coupled to engine  102  by exhaust passage  118  and EGR system  104  may be fluidically coupled to engine  102  via exhaust passages  118  and  122 . Additionally, EGR system  104 , turbocharger  106 , and engine  102  may be fluidically coupled to air intake manifold  112  via exhaust passages  122 ,  124 , and  114 , respectively. Exhaust gases may be permitted to flow from turbocharger  106  via exhaust passage  126  to a selective catalytic reduction (SCR) catalyst and/or to a noise suppression device, neither of which are illustrated by  FIG. 1 . Subsequently, exhaust gases may then be released to the ambient environment via an exhaust passage that is also not illustrated by  FIG. 1 . 
     Furthermore, it should be appreciated that the various portions of the exhaust system coupling the various exhaust system components may include one or more bends or curves to accommodate a particular vehicle arrangement. Further still, it should be appreciated that in some embodiments, exhaust system  100  may include additional components not illustrated in  FIG. 1 , such as various valves, pumps, restrictions, etc., or may omit components described herein, or combinations thereof. 
       FIG. 2  illustrates a side view of exhaust gas recirculation system  104  in greater detail as a longitudinal cross-section. A portion of the exhaust gas flow stream discharged by engine  102  may be diverted to EGR system  104  via exhaust passage  122 . As exhaust gas enters EGR system  104 , it may first be directed through flow measurement area, or region,  212  having a diameter  226 . The recirculated exhaust gas stream flowing through flow measurement area  212  may then be separated into a first separated flow along a first parallel flow path and a separated second flow along a second parallel flow path as a portion of the exhaust flow stream entering the flow measurement area may be diverted through a flow restriction region  208 . The first flow, diverted through flow restriction region  208 , may then flow through an orifice  230  formed by orifice plate  210  within flow restriction region  208 . The second separated flow may then be allowed to flow adjacent to and/or around flow restriction region  208  depending upon the location of the flow restriction region. 
     Although shown arranged at a location not coincident with the center region of flow measurement area  212 , other embodiments may arrange for the center longitudinal axis  316  of flow restriction region  208  (see  FIG. 3A ) to be arranged at various other locations within flow measurement area  212  such as a location where the separated first flow would be at least partially and/or fully surrounded by the separated second flow. Also, the separated flows may occur within a common exterior tubular region, or occur in separate tubes. Further, the separated flows may have an equal or unequal flow length, and may have a similarly or differently shaped flow region, length, and/or cross section. 
     Additionally, in some embodiments the separated second flow may be substantially larger than the separated first flow. For instance, the volumetric flow rate of the separated second flow may be ten times (or more) larger than the volumetric flow rate of the separated first flow (e.g., due to differently sized flow areas, flow resistances, etc.). Correspondingly, in some embodiments the separated second flow may include a greater mass flow than the first separated flow. In other embodiments, the ratio defined by the volumetric flow rates of the second and first separated flows may be smaller or larger. For example ratios such as 12:1, 8:1, 7.5:1, 5:1, or other suitable ratios may be used. Likewise, the volumetric flow rate ratio may be proportional to a separated flow area ratio which may be defined as the ratio of the cross-sectional flow area of flow measurement area  212  less the cross-sectional flow area of flow restriction region  208  to the cross-sectional area of flow restriction region  208 . 
     As illustrated by  FIG. 2 , pressure taps  204  and  206  may be arranged upstream and downstream of orifice plate  210 , respectively. Pressure taps  204  and  206  may also be linked to pressure sensor  202  which may be configured to sense a pressure differential, P a , across orifice  230 . Flow restriction region diameter  228 , the diameter of orifice  230 , and P a  may be utilized by controller  116  to calculate the volumetric flow rate of the first separated flow (the flow through flow restriction region  208 ) via application of Bernoulli&#39;s equation, for example. The volumetric flow rate of the second separated flow may then be calculated by multiplying the calculated volumetric flow rate through flow restriction region  208  by the separated flow area ratio. An overall volumetric flow rate through flow measurement area  212  may then be arrived at by summing the volumetric flow rates of the first and second separated flows. 
     By utilizing a flow restriction region that is proportionally smaller than the overall flow measurement area, a more consistent, less variable overall volumetric flow rate calculation may be realized. Additionally, the dynamic range of accurate orifice pressure differential measurement in such configurations may be greater than that of larger, center-of-flow stream orifice flow measurement configurations that directly measure the overall volumetric flow rate through a flow measurement area. Typically, larger, substantially center-of-flow stream orifice flow measurement configurations require greater flow through an orifice to accurately measure the pressure drop across the orifice and hence calculate the overall volumetric flow rate through the flow measurement area. Therefore, at lower overall flow rates, volumetric flow rate calculations with such a configuration may be rife with inaccuracies. Furthermore, the restriction to EGR flow produced by larger in-stream orifice flow measurement configurations may not be accurately predicted or accounted for in EGR system calibration and may lead to additional overall EGR flow rate calculation error. 
     The packaging of an EGR system that utilizes a flow restriction region that is proportionally smaller than the overall flow measurement area may also be smaller than that of a larger in-stream orifice flow measurement configuration. Thus, restriction to flow may be decreased and desired packaging characteristics may be realized. 
     After exiting flow restriction region  208 , the separated first flow may be combined with the separated second flow to form a single EGR flow stream within flow measurement area  212 . The combined exhaust flow may then be directed (via EGR valve  214  and exhaust passage  220 ) to an exhaust oxidation catalyst (EOC)  216  that may reduce unburned hydrocarbons and carbon monoxide in the recirculated exhaust gas flow stream. The portion of the exhaust gas flow discharged by engine  102  that is allowed to pass through EGR system  104  and returned to engine  102  may be metered by the measured actuation of EGR valve  214  which may be controlled by controller  116 . The actuation of EGR valve  214  may be based on various vehicle operating parameters and the calculated overall EGR flow rate through flow measurement area  212  (as described in greater detail in regards to  FIG. 5 ). 
     Once processed by EOC  216 , the EGR flow stream may then be directed to EGR cooler  218  via exhaust passage  222 . EGR cooler  218  may act to lower the overall temperature of the EGR flow stream before passing the stream on to air intake manifold  112  via exhaust passage  122  where it may be combined with fresh air and directed to engine  102  via exhaust passage  114 . 
     In an alternate approach, one or more of the separated flows may pass through an oxidation catalyst, EGR cooler, additional valve, or other device before being combined in the EGR passage and entering the intake manifold. Also, the EGR valve may be located upstream of the flow measurement area. 
       FIG. 3A  illustrates one particular embodiment via a perspective view as a longitudinal cross-section of an example flow measuring area that may be used as flow measuring area  212  of  FIG. 2 . As illustrated, longitudinal axis  316  of restricted flow region  208  is parallel to longitudinal axis  314  of flow measurement area  212 . In some embodiments, restricted flow region  208  may be arranged within flow measurement area  212  such that the smallest distance between longitudinal axis  316  and the outer wall of flow measurement area  212  is less than the distance between longitudinal axis  316  and longitudinal axis  314 . 
     In other embodiments, restricted flow region  208  may be arranged within flow measurement area  212  such that the smallest distance between longitudinal axis  316  and the outer wall of flow measurement area  212  is greater than or equal to the distance between longitudinal axis  316  and longitudinal axis  314 . By configuring flow restriction region  208  within flow measurement area  212  (and not separate from flow measurement area  212 ) in this example, overall packaging dimensions may be decreased and additional componentry costs may be reduced. 
     Additionally, alternative embodiments may utilize flow restriction regions with different geometries. For example, in some embodiments, the overall length of flow restriction area  208  may be three inches. In other embodiments, the overall length of flow restriction area  208  may be two inches, four inches or other suitable length. Also, alternative embodiments may differ as to the location of flow restriction area  208  relative to longitudinal axis  314  of flow measurement area  212 . For example, the point at which exhaust gases enter flow restriction area  208  may be arranged at a location coincident with a line bisecting longitudinal axis  314 . In other embodiments, the point at which exhaust gases enter flow restriction area  208  may be arranged at a location on either side of the line bisecting longitudinal axis  314 . 
     As shown, pressure taps  204  and  206  may be arranged upstream and downstream of orifice plate  210 , respectively. In various embodiments, the distance between the pressure taps and orifice plate may vary. For example, in one embodiment, pressure tap  204  may be arranged one inch upstream of orifice plate  210  and pressure tap  206  may be arranged one inch downstream of orifice plate  210 . In another embodiment, pressure tap  204  may be arranged 0.5 inch, 2 inches, or another suitable distance upstream of orifice plate  210  and pressure tap  206  may be arranged one-half inch, two inches, or another suitable distance downstream of orifice plate  210 . 
       FIGS. 3B and 3C  illustrate alternative embodiments of the cross-sectional shape of flow restriction region  208  and orifice plate  210 .  FIG. 3B  illustrates the cross-sectional shape of flow restriction region  208  and orifice plate  210  as being substantially circular. Orifice  230 , as formed by orifice plate  210  may be configured with a diameter of one inch, for example. Other embodiments may configure orifice  230  with a 0.5 inch diameter, a 2 inch diameter, or other suitable diameter. 
       FIG. 3C  illustrates the cross-sectional shape of flow restriction region  208  and orifice plate  210  as being substantially rectangular. Other embodiments may configure the cross-sectional shape of flow restriction region  208  and orifice plate  210  as being substantially elliptical, octagonal, hexagonal, triangular, or other suitable shape. Additionally, some embodiments may disclose orifice plate  210  as having a nominal thickness of 0.25 inches. Other embodiments may disclose orifice plate  210  as having a nominal thickness of 0.10 inches, 0.5 inches, 1.5 inches, 2 inches, or other suitable thickness. 
       FIG. 4  shows a flow chart depicting an example routine  400  for processing the flow of an exhaust gas stream through flow measurement area  212  of EGR system  104 . At  402 , a portion of the exhaust gas flow stream exited by engine  102  may be diverted from exhaust passage  118  to EGR system  104  via exhaust passage  122 . At  404 , the exhaust gas flow stream diverted to EGR system  104  may enter flow measurement area  212  and may then be separated into a first separated flow and a second separated flow via flow restriction area  208 . At  406 , the first separated flow may be directed through flow restriction region  208  where it may be directed through an orifice formed by orifice plate  210 . At  408 , a pressure drop across orifice plate  210  may be sensed by pressure sensor  202  via pressure taps  204  and  206  which may be located upstream and downstream of orifice plate  210 , respectively. An overall volumetric flow rate through flow measurement area  212  may then be ascertained (as described in greater detail herein). 
     At  410 , the first separated flow, after traversing flow restriction region  208 , may be combined with the second separated flow that has bypassed flow restriction region  208 . Finally, at  412 , the combined flow may be directed through recirculation valve  214 , EOC  216 , cooler  218 , and air intake manifold  112  where it may be combined with fresh air and directed to engine  102  via exhaust passage  114  (as described in greater detail herein). 
       FIG. 5  shows a flow chart depicting an example routine for adjusting an amount of exhaust gas recirculation based on vehicle operating parameters and a differential pressure measured within flow restriction region  208 . At  502 , a vehicle PCM may read various operating parameters such as vehicle speed, engine load, air/fuel ratio, and exhaust temperature, for example. Based on the operating parameters read at  502 , a desired amount of exhaust gas recirculation may be determined at  504 . At  506 , the vehicle PCM may read a differential pressure across orifice plate  210  that may then be used to calculate an overall volumetric flow rate through flow measurement area  212 . 
     At  508 , EGR valve  214  may be adjusted based on the EGR volumetric flow rate calculated at  506  to produce the desired amount of exhaust gas recirculation determined at  504 . An engine load/speed look-up table may be utilized to determine a desired percentage of the overall gas stream directed to engine  102  that is comprised of recirculated exhaust gases. The following equation may then be utilized to calculate a desired EGR mass flow rate, DES EM:
 
 DES EM= Am*% EGR /(1−% EGR )
 
where Am represents an air mass flow rate entering air intake manifold  112  and % EGR represents the desired percentage of the overall gas stream directed to engine  102  that is comprised of recirculated exhaust gases. A look-up table that relates DES EM to a desired pressure differential across orifice plate  210 , P d , may then be utilized to determine a desired differential pressure across orifice plate  210 . Controller  116  may then utilize the actual pressure differential sensed across orifice plate  210  by pressure sensor  202  via pressure taps  204  and  206 , P a , to control EGR valve  214  to actuate so as to produce a pressure differential across orifice plate  210  that is closer to the desired pressure differential, P d . In this way, the EGR valve may be adjusted to accurately control the total EGR flow, even though only a portion of the EGR flow is measured.
 
       FIG. 6  depicts a graphical representation of a theoretical flow curve  602  through flow measurement area  212  of exhaust gas recirculation system  104 . In this graphical representation, horizontal axis  604  represents the pressure differential across orifice plate  210  as measured by pressure sensor  202  via pressure taps  204  and  206 . Additionally, vertical axis  606  represents the mass flow rate of the separated first flow through flow restriction region  208  and vertical axis  608  represents the mass flow rate of the separated second flow next to and/or around flow restriction region  208  (through flow measurement area  212 ). 
     In this representation, the mass flow rate of the separated second flow is shown to be approximately ten times larger than the mass flow rate of the separated first flow. In other embodiments, the ratio defined by the mass flow rates of the second and first separated flows may be smaller or larger, such as 12:1, 8:1, 7.5:1, 5:1, or other suitable ratio. At lower overall EGR mass flow rates, a configuration that utilizes a smaller orifice plate that receives a separated first flow that is proportionally smaller than a separated second flow may produce a more pronounced, measurable pressure drop across an orifice plate than may be exhibited by a larger, substantially center-of-flow stream orifice flow measurement configuration at the same lower overall EGR mass flow rate. A more reliable, robust configuration for measuring EGR mass flow at both higher and lower EGR mass flow rates may thus be realized. Correspondingly, the actuation of EGR valve  214  may be based on more accurate real-time EGR flow calculations which may result in finer, more precise control of overall EGR flow. 
     Note that the example routines included herein can be used with various engine and/or vehicle system configurations. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various acts, operations, or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts may graphically represent code to be programmed into the computer readable storage medium in the engine control system, where the code is executable by the computer. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.