Patent ID: 7239954

Claim:
A method for controlling an engine to maintain stable torque during rapid air/fuel (A/F) ratio transitions between a normal lean combustion mode and a temporary rich combustion mode, said engine having a means for determining intake air mass flow, at least one combustion chamber, and a fuel injector in fluid communication with the combustion chamber, said method comprising: operating said engine in a normal lean combustion mode wherein the intake air and the quantity of injected fuel, and the timing of injected fuel have selected values; determining rich combustion initial values for intake air, fuel quantity and injection timing, said rich combustion initial fuel quantity and injection timing being sufficient to maintain engine torque stability for said rich combustion initial value of intake air; determining a target air/fuel ratio and injection timing for operation in a defined temporary rich combustion mode; abruptly reducing intake air mass flow to the determined rich combustion initial value; determining the concentration of oxygen in a selected cylinder; simultaneously abruptly increasing the quantity of fuel injected into said selected cylinder and abruptly retarding the timing of fuel injection into the cylinder, said quantity of fuel and said timing of fuel injection being their respective determined rich combustion initial values, and subsequently proportionally decreasing the quantity of fuel injected into said cylinder to maintain the target air/fuel ratio for a coexisting oxygen concentration in said cylinder during said transition from said lean combustion mode to said rich combustion mode while simultaneously proportionally advancing the timing of fuel injected into said cylinder to said determined target injection timing value.