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  Intake oxygen estimator for internal combustion engineUSPTO Application #: 20060241849Title: Intake oxygen estimator for internal combustion engine Abstract: An internal combustion engine system includes an intake manifold, a combustion chamber, an exhaust manifold and exhaust gas recirculation apparatus for recirculating a portion of the exhausted gases from the exhaust manifold to the intake manifold. An estimate intake manifold oxygen concentration is determined from the air fraction within the intake manifold which is determined from an engine system model that provides interdependent air mass fractions at various locations within the engine system. (end of abstract) Agent: General Motors Corporation Legal Staff - Detroit, MI, US Inventor: Anupam Gangopadhyay USPTO Applicaton #: 20060241849 - Class: 701108000 (USPTO) Related Patent Categories: Data Processing: Vehicles, Navigation, And Relative Location, Vehicle Control, Guidance, Operation, Or Indication, With Indicator Or Control Of Power Plant (e.g., Performance), Internal-combustion Engine, Digital Or Programmed Data Processor, Control Of Air/fuel Ratio Or Fuel Injection, Exhaust Gas Circulation (egc) The Patent Description & Claims data below is from USPTO Patent Application 20060241849. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention is related to lean burn internal combustion engines. More particularly, the invention is concerned with estimations of intake manifold gas composition. BACKGROUND OF THE INVENTION [0002] Most of the time a diesel engine operates significantly lean of stoichiometry wherein gases expelled from the combustion chambers are characterized by excess oxygen. Richer air/fuel ratios may be controlled during brief periods for the purposes of particulate or oxides of nitrogen (NOx) trap regenerations where such apparatus are utilized as part of the engine emission control system. Diesel engines may also use exhaust gas recirculation (EGR) in the emission controls to reduce the NOx produced in the diesel engine's combustion process by lowering the effective combustion temperature and reducing the oxygen component of the cylinder charge. [0003] Oxygen concentration in the intake manifold is a key parameter in controlling the make up of the exhaust gases expelled from a combustion chamber. Exhaust gases recirculated back into the intake manifold will vary the oxygen concentration in the intake manifold and, in turn, the oxygen concentration in the intake manifold will affect the oxygen concentration in the combustion chambers established during cylinder filling periods. Therefore, the total pre-combustion trapped charge within the combustion chamber may contain different amounts of oxygen depending on the prevailing intake concentration of oxygen during the cylinder filling period. The amount of oxygen affects both the amount of fuel that can be injected before unacceptable levels of particulate emissions (i.e. smoke) are produced and the level of NOx production. [0004] Combustion controls which rely upon post-combustion oxygen sensing are generally satisfactory for managing steady state or slowly varying oxygen levels. EGR dynamics are therefore limited by the effectiveness of such controls in accounting for rapid changes in EGR levels. Additional factors including intake temperature and pressure also affect the oxygen levels. Intake boosting, such as by turbocharging or supercharging, also have limited dynamics in accordance with the effectiveness of such controls in accounting for rapid changes in boost levels. [0005] Ideally, pre-combustion oxygen sensing in the intake manifold would alleviate much of the dynamic limitations mentioned by providing substantially instantaneous intake oxygen concentration measurements thus accounting for rapid changes in EGR concentrations and intake boost pressures. However, known wide range oxygen sensing technologies are effective at substantially elevated temperatures. Whereas they work well in a high temperature exhaust environment, substantial heat would need to be added thereto to achieve light-off in the much cooler intake environment. A supplemental electrical heater would likely result in an unacceptably high power consumption penalty. Also, known wide range oxygen sensing technologies are effective at substantially ambient pressure levels and require proper pressure compensation to produce accurate oxygen concentration information. SUMMARY OF THE INVENTION [0006] This invention enables the estimation of instantaneous levels of oxygen at various locations within an internal combustion engine system that uses exhaust gas recirculation, including within the intake manifold. A real-time, transient-responsive model of the internal combustion engine includes interdependent sub-system models effective to estimate air or oxygen fractions at various locations within the system including at combustion chamber exhaust ports and intake and exhaust manifolds. [0007] An internal combustion engine system includes a combustion chamber, an exhaust manifold, an intake manifold and exhaust gas recirculation apparatus for variable recirculation of exhaust gases from the exhaust manifold to the intake manifold. A method for estimating oxygen concentration at points within the internal combustion engine system includes reticulating the engine system into a plurality of interconnected engine sub-systems. The interconnected engine sub-systems are modeled to provide interdependent air mass fractions at predetermined points within the internal combustion engine. Oxygen concentration at the predetermined points within the internal combustion engine are then estimated as a function of the respective modeled air mass fractions at said predetermined points. Preferably, an empirically determined data set correlating combustion chamber air mass fraction to a plurality of engine operating parameters is used to model the air mass fraction at the combustion chamber exhaust port. Engine speed, fuel mass flow, combustion timing, intake manifold pressure, exhaust manifold pressure, intake manifold temperature and intake manifold air fraction are among the engine operating parameters used in the empirical determination of the data set. [0008] A method for estimating oxygen concentration in the intake manifold of an internal combustion engine includes reticulating the engine system into a plurality of interconnected engine sub-systems including an intake manifold, an exhaust manifold, an exhaust gas recirculation apparatus and combustion chambers. All significant mass flows corresponding to the engine sub-systems are identified, including combustion chamber exhaust mass flows. Similarly, all significant pressure nodes corresponding to the engine sub-systems are identified, including the intake manifold and the exhaust manifold. Interdependent air mass fractions at the identified pressure nodes, including at the intake manifold, and at the combustion chamber exhaust mass flow are modeled. Oxygen concentration in the intake manifold is then estimated as a function of the modeled air mass fraction at the intake manifold. The engine sub-systems may further include intake pressure boost apparatus such as turbochargers and superchargers. The modeling of the interdependent air mass fractions at the identified pressure nodes may further include modeling of the air mass fraction at the exhaust manifold and the modeling of the air mass fraction at the intake manifold may include determining recirculated exhaust gas mass flow and determining recirculated exhaust gas air mass flow based on the recirculated exhaust gas mass flow and the air mass fraction at the exhaust manifold. Combustion transport delay is preferably accounted for in the modeling of the air mass fraction at the combustion chamber exhaust mass flow, and exhaust gas recirculation transport delay is preferably accounted for in the determination of recirculated exhaust gas mass flow. [0009] A control system for an internal combustion engine includes means for providing respective measures of a plurality of engine operating parameters and a microprocessor based controller includes computer code stored in a storage medium for applying the engine operating parameter measures to a model to estimate interdependent air mass fractions at locations within the internal combustion engine. The control system further includes at least one actuator controlled in response to at least one of the interdependent air mass fractions. One of the interdependent air mass fractions is estimated at the intake manifold and an actuator may comprise an intake boost control actuator (e.g. variable geometry turbocharger, variable nozzle turbocharger) or an exhaust gas recirculation actuator. BRIEF DESCRIPTION OF THE DRAWINGS [0010] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [0011] FIG. 1 is a schematic illustration of an internal combustion engine system and engine controller in accordance with one embodiment of the present invention; [0012] FIG. 2 is a schematic illustration of a model the engine system shown in FIG. 1 reticulated into engine sub-systems; [0013] FIG. 3A is a schematic illustration of an exhaust manifold sub-system model including inputs and outputs in accordance with the present invention; [0014] FIG. 3B is a schematic illustration of a combustion chamber sub-system model including inputs and outputs in accordance with the present invention; [0015] FIG. 3C is a schematic illustration of an intake manifold sub-system model including inputs and outputs in accordance with the present invention; [0016] FIG. 3D is a schematic illustration of an EGR and cooler sub-system model including inputs and outputs in accordance with the present invention; [0017] FIG. 3E is a schematic illustration of a turbocharger and intercooler sub-system model including inputs and outputs in accordance with the present invention; [0018] FIG. 4 is a proportional-integral control for providing a closed loop correction term to the EGR and cooler model in accordance with the present invention; and [0019] FIG. 5 is a proportional-integral control for providing a closed loop correction term to the combustion chamber model in accordance with the present invention. 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