Patent ID: 6076353
Filing Date: 2000-06-20
Classification: F02B,F02D,F02M,Y02T

Abstract:
A method of controlling the air-fuel ratio and burnt gas fraction in a compression ignition engine having an EGR system including a valve connecting an intake manifold and exhaust manifold of the engine, and a variable geometry turbocharger including a compressor connected to a turbine having guide vanes, the compressor in communication with the intake manifold and the turbine guide vanes in communication with the exhaust manifold, the method comprising the steps of:determining an engine speed value (N(t)) indicative of the current engine speed;determining a fueling rate value (W.sub.F (t)) to be injected as a function of N(t) and the operator-requested fueling rate;retrieving desired values for the intake manifold pressure (P.sub.1 *) and compressor mass flow rate (W.sub.a *) from a table of values indexed by W.sub.F (t) and N(t) said table of values corresponding to desired values for the air-fuel ratio and burnt gas fraction at each value of W.sub.F (t) and N(t);determining an intake pressure value (P.sub.1) indicative of the intake manifold pressure;determining a mass airflow value (W.sub.a) indicative of the compressor mass flow rate;generating an EGR valve position command (X.sub.egr (t)) and VGT guide vane position command (X.sub.vgt (t)) as a function of the weighted sum of the difference between P.sub.1 and P.sub.1 *, and the difference between W.sub.a and W.sub.a *; andapplying X.sub.egr (t) and X.sub.vgt (t) to the EGR valve and turbine guide vanes, respectively, to drive the EGR valve and turbine guide vanes to the respective desired values.