Control method for a variable geometry turbocharger in a diesel engine having exhaust gas recirculation

A method of controlling the airflow into a compression ignition engine having an exhaust gas recirculation (EGR) system including a valve connecting an intake manifold and exhaust manifold of the engine, and a variable geometry turbocharger (VGT) including a compressor connected to a turbine having an adjustable inlet guide vane responsive to a VGT actuator signal, the compressor in communication with the intake manifold and the turbine guide vane in communication with the exhaust manifold, the method comprising the steps of:

• determining a temperature value (T.sub.2) indicative of the exhaust manifold temperature;
• determining a turbine flow value (W.sub.2t) indicative of the mass flow rate through the turbocharger turbine;
• determining a pressure value (p.sub.2) indicative of the exhaust manifold pressure;
• determining a back-pressure value (p.sub.exs) indicative of the turbine back-pressure;
• generating an VGT actuator position estimate (.alpha..sub.vgt) as a function of W.sub.2t, T.sub.2, p.sub.2, and p.sub.exs ;
• retrieving a desired VGT inlet guide vane position value (.alpha..sub.vgt *) from a table of values indexed by engine speed and fueling rate;
• generating a VGT actuator position command (U.sub.vgt) as a function of the difference between the desired and estimated VGT actuator position values;
• and
• applying U.sub.vgt to the turbine guide vane to drive the inlet guide vane to the respective desired values.

In a compression ignition engine system having an exhaust gas recirculation (EGR) passage including an EGR valve connecting an intake manifold and exhaust manifold of the engine, and a variable geometry turbocharger (VGT) including a compressor connected to a turbine, said turbine including an adjustable inlet guide vane, the compressor in communication with the intake manifold and the guide vane in communication with the exhaust manifold, said guide vane responsive to a VGT actuator signal for regulating the intake manifold pressure, an engine control unit for regulating the airflow into said engine, said engine control unit comprising:

• memory for storing a map of engine volumetric efficiency as a function of engine operating parameters, a map of the EGR valve effective flow area as a function of said EGR valve position, and a map of the VGT effective flow area as a function of the VGT guide vane position;
• and
• a feedback controller for generating said said VGT actuator signal, said feedback controller programmed to:
• determine a temperature value (T.sub.2) indicative of the exhaust manifold temperature;
• determine a turbine flow value (W.sub.2t) indicative of the mass flow rate through the turbocharger turbine;
• determine a pressure value (p.sub.2) indicative of the exhaust manifold pressure;
• determine a back-pressure value (p.sub.exs) indicative of the turbine back-pressure;
• generate an VGT actuator position estimate (.alpha..sub.vgt) as a function of W.sub.2t, T.sub.2, p.sub.2, and p.sub.exs ;
• retrieve a desired VGT inlet guide vane position value (.alpha..sub.vgt *) from a table of values indexed by engine speed and fueling rate;
• generate a VGT actuator position command (U.sub.vgt) as a function of the difference between the desired and estimated VGT actuator position values;
• and
• transmit U.sub.vgt to the turbine guide vane to drive the inlet guide vane to the respective desired value.