Patent ID: 7685871

Claim:
An apparatus for determining a residual burned gas fraction in a multi-cylinder internal combustion engine, comprising: a single-cylinder simulator configured to simulate a thermodynamic cycle for at least one of the cylinders and output said residual burned gas fraction, said simulator being responsive to a plurality of simulator input parameters to develop values for engine operating variables in accordance with a simulation model, said engine operating variables including a simulated mass air flow rate, a simulated cylinder pressure, a polytropic exponent and a simulated exhaust temperature; and an optimizer responsive to measured parameters associated with the operation of said one cylinder and being configured to produce values for said simulator input parameters including an intake pressure, one or more burned-gas parameters used to modulate simulated burned gas mass and a heat transfer multiplier, said measured parameters including a measured mass air flow rate, a measured intake air temperature, a measured exhaust temperature and a measured crankshaft-angular-position-resolved cylinder pressure, said optimizer being further configured (1) to estimate said intake pressure such that said simulated mass air flow rate corresponds to said measured mass air flow rate; (2) to estimate said burned gas mass trapped in said cylinder at an intake valve closing time such that said simulated cylinder pressure corresponds to said measured cylinder pressure; and (3) to estimate said heat transfer multiplier such said simulated exhaust temperature corresponds to said measured exhaust temperature; wherein said simulator is further configured to determine said residual burned gas fraction based on said estimated trapped burned gas mass.