Control method for turbocharged diesel engines having exhaust gas recirculation

A method of controlling the air-fuel ratio and exhaust gas recirculation (EGR) 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(k)) indicative of the current engine speed;
• determining a fueling rate value (F(k)) to be injected as a function of N(k) and the operator-requested fueling rate;
• generating a desired compressor airflow value (m.sub.comp,d (k) ) as a function of F(k) and N(k);
• generating a desired exhaust manifold pressure value (P.sub.exh,d (k)) as a function of F(k) and N(k);
• determining an exhaust pressure value (P.sub.exh (k)) indicative of the exhaust manifold pressure;
• determining an mass airflow value (m.sub.comp (k)) indicative of the compressor mass airflow;
• generating a commanded EGR mass flow value (m.sub.egr,c (k)) and a commanded turbine mass flow value (m.sub.turb,c (k)) as a function of m.sub.comp,d (k), P.sub.exh,d (k), m.sub.comp (k) , and P.sub.exh (k);
• determining an intake pressure value (P.sub.m (k)) indicative of the intake manifold pressure;
• generating an EGR valve percent opening command (EGR.sub.p,c (k)) and a variable geometry turbocharger percent open command (VGT.sub.p,c (k)) as a function of m.sub.egr,c (k) and m.sub.turb,c (k), respectively;
• and
• applying EGR.sub.p,c (k) and VGT.sub.p,c (k) to the EGR valve and turbine guide vanes, respectively, to drive the EGR valve and turbine guide vanes to the respective desired percent open values.