Strategy For Control Of Recirculated Exhaust Gas To Null Turbocharger Boost Error

A method for coordinating control of exhaust gas recirculation from a exhaust system of a turbocharged internal combustion engine to an intake system of the engine with control of engine boost, the method comprising:

• developing data representing the mass flow rate of fresh air that is entering the intake system;
• calculating data representing the mass flow rate of recirculated exhaust gas that is entraining with the fresh air entering the intake system by calculating data representing mass flow rate through the engine cylinders and calculating the difference between the data representing the calculated mass flow rate through the engine cylinders and the data representing the mass flow rate of fresh air entering the intake system;
• calculating data representing expected mass flow rate through the engine cylinders that would occur if boost were equal to a desired set-point;
• calculating data representing actual mass flow rate through the engine cylinders using actual boost;
• calculating data representing the difference between the data representing actual mass flow rate through the engine cylinders and the data representing the expected mass flow rate through the engine cylinders;
• using an initial set of data comprising at least the data representing the difference between the data representing actual mass flow rate through the engine cylinders and the data representing the expected mass flow rate through the engine cylinders as a feed-forward adjustment of the mass flow rate of recirculated exhaust gas in a direction;
• and
• using a second set of data, at least a portion of which differs from the initial set of data, to further adjust the mass flow rate of recirculated exhaust gas in a direction of adjustment that seeks to further null out the difference between desired boost set point and actual boost.

An engine system comprising:

• an engine having cylinders;
• a turbocharger;
• an intake system, including a compressor of the turbocharger, for delivering charge air to the engine cylinders;
• an exhaust system, including a turbine of the turbocharger, for conveying exhaust gas from the engine cylinders;
• an exhaust gas recirculation system, including an EGR valve, for recirculating exhaust gas from the exhaust system to the intake system;
• and a control system for coordinating control of exhaust gas recirculation comprising a processor for:
• a) developing data representing the mass flow rate of fresh air that is entering the intake system, b) calculating data representing the mass flow rate of recirculated exhaust gas that is entraining with the fresh air entering the intake system by calculating data representing mass flow rate through the engine cylinders and calculating the difference between the data representing the calculated mass flow rate through the engine cylinders and the data representing the mass flow rate of fresh air entering the intake system, c) calculating data representing expected mass flow rate through the engine cylinders that would occur if boost were equal to a desired set-point, d) calculating data representing actual mass flow rate through the engine cylinders using actual boost, e) calculating data representing the difference between the data representing actual mass flow rate through the engine cylinders and the data representing the expected mass flow rate through the engine cylinders, and
• performing feed-forward adjustment of the mass flow rate of the EGR valve by processing the data representing the difference between the data representing actual mass flow through the engine cylinders and the data representing the expected mass flow rate through the engine cylinders and the data representing the expected mass flow rate through the engine cylinders to develop a feed-forward adjustment signal that is applied to the EGR valve to adjust the mass flow rate of recirculated exhaust gas in a direction of adjustment that seeks to null out the difference between desired boost set point and actual boost;
• and
• a PID controller which develops an error signal by subtracting the calculated data representing the mass flow rate of recirculated exhaust gas that is entrained with the fresh air entering the intake system from a desired set-point for mass flow rate of recirculated exhaust gas in a direction of adjustment that seeks to null out the difference between desired boost set point and actual boost.