Method And Associated Device For Sensing The Air/fuel Ratio Of An Internal Combustion Engine - PDF

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Method And Associated Device For Sensing The Air/fuel Ratio Of An Internal Combustion Engine - PDF Powered By Docstoc
Description: FIELD OF THEINVENTION This invention relates to control systems for the operating parameters of internal combustion engines, and, more particularly, to a method and associated device for sensing the air/fuel ratio (briefly AFR) of an internal combustion engine, andan associated control system that uses this sensing device.BACKGROUND OF THE INVENTION In the last twenty years, fundamental goals of engine manufacturers are to achieve significant reductions of the amounts of pollutants emitted at the engine exhaust, and lower fuel consumption without compromising speed and torque performances. For these reasons, an efficient engine control based on a comprehensive monitoring of the many engine working parameters is desired. To maintain a strict control of the engine working parameters, Engine Management Systems (EMS) or Engine Control Units (ECU) are used. The EMS implements control strategies which achieve the optimum trade-off between several contradictoryobjectives: high output power when required by the driver, low emission levels and low fuel consumption. At the same time, in a spark-ignition engine, the EMS brings and maintains the engine in a specified operating range such that the three-waycatalytic converter can further reduce the undesired content of the exhaust gases. The EMS controls the amount of fuel injected in the engine combustion chamber (fuel pulse width), the point in the engine cycle at which the mixture air fuel is ignited(ignition timing) and in advanced engine designs, other parameters, such as the valve timing. The EMS determines values for these parameters from measured quantities such as speed, torque, air mass flow rate, inlet-manifold pressure, temperatures atseveral critical points and throttle angle. FIG. 1 illustrates the EMS function. The EMS determines values for Controlled Variables from knowledge of the Measured Variables to achieve the System Aims. EMS essentially includes three components: engine maps (look-up tables stored in