Patent ID: 7021046

Claim:
A method for controlling an engine having at least a first and second group of cylinders, comprising: operating the engine in a first mode wherein the first cylinder group operates with air and substantially no injected fuel and the second cylinder group operates to combust air and injected fuel, where said first mode is selected at least based on a driver request; transitioning the engine to operating in a second mode wherein both the first cylinder group and the second cylinder group operate to combust air and injected fuel, combustion in one of said first and second cylinder groups including combustion of an air fuel ratio that oscillates about stoichiometry and combustion in the other of said first and second cylinder groups including combustion of an air fuel ratio that is rich of stoichiometry, wherein exhaust gasses from said second group pass to a first upstream emission control device and then mix with exhaust gasses from said first group, before passing to a second downstream emission control device; and adjusting valve operation on one of said first group and said second group to provide different valve operation in said first mode from said second mode.