Patent ID: 7467511

Claim:
An engine control system that regulates fuel to an engine after lean idle operation, comprising: a first module that determines a rich mass fuel rate based on a lean operation mass air flow and a stoichiometric air to fuel ratio (AFR) and that calculates a time rich based on said rich mass fuel rate, a mass of oxygen stored in a catalytic converter stored during said lean idle operation, and an oxygen to fuel ratio (OFR); and a second module that regulates fuel to said engine during a rich operation period after said lean idle operation to provide said rich mass fuel rate for said time rich, wherein said first module determines said OFR based on said stoichiometric AFR, calculates a product of a % oxygen content of air by mass, said lean operation mass air flow and a lean time, and determines said mass of oxygen stored as a minimum of said product and a target mass of oxygen stored.