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Nox control for an internal combustion engineRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust GasNox control for an internal combustion engine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070012027, Nox control for an internal combustion engine. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF INVENTION [0001] This invention relates to internal combustion engines and emissions standards for internal combustion engines and more particularly to calibration, control and operation of direct injection engines and lean burn stratified charge engines so as to comply with certain emissions standards. BACKGROUND [0002] A majority of fuel injected engines/vehicles currently produced by the major engine and vehicle manufacturers of the world are of the conventional manifold multipoint or port fuel injection (MPI/PFI) type. However, with the ongoing efforts to extract better performance from internal combustion engines and the emerging requirements to meet stringent emission laws, more and more engine manufacturers are investigating and developing direct fuel injection engine technologies. Such direct injection (DI) engine technologies are considered by some to be the next evolutionary step for internal combustion engines and examples of automotive vehicles incorporating DI engines are in fact already available to the consumer in certain automotive markets. [0003] Almost all current design MPI and DI engines include a catalytic converter or exhaust gas after treatment system of some nature located in the exhaust system of the vehicle. The catalytic converter typically acts to convert undesirable exhaust emissions such as hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) into non-harmful substances such as carbon dioxide, nitrogen, oxygen and water. Increasingly stringent internal combustion engine emissions legislation around the world, such as the proposed US ULEV II & SULEV emissions regulations and European Euro IV regulations, is placing increasing pressure on engine and vehicle manufacturers to reduce engine emissions. [0004] In meeting these stringent emissions standards most MPI and PFI vehicles suffer a fuel consumption penalty even though overall tail pipe emission levels decrease. This increase in fuel consumption arises for various reasons including increased engine hardware requirements that serve to increase the level of parasitic loading on the engine, increased fuel consumption due to the catalyst light-off strategies used and an increase in fuel consumption that arises when the engine is calibrated to produce reduced levels of hydrocarbon emissions and NOx emissions. DI engines promise fuel economy savings and are being looked to as a potential technology to offset increases in fuel consumption that are likely to result from the introduction of low emissions vehicles. [0005] A significant portion of the current activity taking place in respect of DI engine technology development is in relation to lean burn engines. A lean burn engine is able to operate with a lean air fuel ratio. Typically this occurs at lower load operating points. Lean operation allows significant fuel consumption reductions to be realised. Typically, lean burn engines also operate with a stoichiometric air/fuel ratio at higher operating load points. [0006] Lean operation is typically associated with the provision of a stratified fuel-air charge in the combustion chamber whilst stoichiometric operation is typically associated with a homogenous fuel-air charge. [0007] There are however certain challenges to be faced when effecting lean burn engines. In particular, lean operation often results in the formation of NOx emissions. Reduction of NOx emissions by after treatment systems can be difficult to effect. In this regard, conventional three-way catalytic converters (TWC's) have been found to be unsatisfactory for efficiently treating NOx emissions. One present way of addressing this is by incorporating a further Lean NOx catalyst (LNC) catalyst which acts to adsorb NOx gases emitted from the engine until its operating conditions are more favourable for reduction of the trapped NOx gases by the exhaust gas treatment system. The favourable engine condition is typically when the engine is operating with a rich or stoichiometric air/fuel ratio. Accordingly, in current systems incorporating an LNC, it has been found necessary for the engine to temporarily run with a rich air/fuel ratio to promote reduction of NOx stored/trapped on the LNC. However, these rich excursions impose a fuel consumption penalty that detracts from the fuel consumption benefits available from DI engines. Accordingly, it is desirable to reduce the extent of any rich excursion used in regenerating an LNC. [0008] It is therefore an object of the present invention to provide improved NOx control for an internal combustion engine. SUMMARY OF INVENTION [0009] With this in mind, there is provided in accordance with a first aspect of the present invention a method of operating an internal combustion engine having a first catalyst with NOx storage capability; said method comprising the steps of determining the composition of gasses input to said catalyst to thereby determine an aggregate quantity of nitrogen oxide compounds (NOx) stored on said catalyst. [0010] Preferably said estimate of said aggregate quantity of NOx stored on said catalyst is performed at intermittent time intervals. [0011] Preferably said intermittent time intervals further comprise a background loop of an electronic control unit of said engine. [0012] Preferably said method further comprises the step of estimating a quantity of NOx that has either been stored onto said catalyst or reduced from said catalyst over a recent one of said intermittent time intervals, and summing said quantity of NOx estimated to have been stored or reduced over said recent one of said intermittent time intervals with an aggregate quantity of NOx estimated to have been stored on said catalyst over a previous one of said intermittent time intervals. Preferably said step of estimating the quantity of NOx stored on said catalyst further comprises the step of estimating NOx flow to said catalyst. [0013] Preferably said NOx flow is derived from at least engine speed and engine load [0014] Preferably said step of estimating the quantity of NOx stored on said catalyst further comprises the step of estimating engine temperature. [0015] Preferably said NOx flow and said intermittent time interval is used to determine a total quantity of NOx input to said catalyst during a recent one of said intermittent time intervals. [0016] Preferably said step of estimating the quantity of NOx stored on said catalyst further comprises the step of estimating the space velocity of said gasses input to said catalyst. [0017] Preferably said space velocity and said total quantity of NOx input to said catalyst are used to determine said quantity of NOx stored on said catalyst. [0018] Preferably said step of estimating NOx reduced from said catalyst further comprises the step of estimating a NOx purge time period based on said aggregate quantity of NOx stored on said catalyst. [0019] Preferably said NOx purge time comprises the time required to purge a pre-determined quantity of NOx from said catalyst under predetermined engine operating conditions. [0020] Preferably said step of estimating NOx reduced from said catalyst comprises the further step of estimating a NOx reduction flow to said catalyst. Continue reading about Nox control for an internal combustion engine... Full patent description for Nox control for an internal combustion engine Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Nox control for an internal combustion engine patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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