Patent ID: 6840036

Claim:
A system for controlling an engine, comprising: a first oxygen sensor disposed in an exhaust gas stream of said engine upstream of a first emission control device, said first oxygen sensor generating a first feedgas air fuel signal; a second oxygen sensor disposed in said exhaust gas stream of said engine downstream of said first emission control device; said second oxygen sensor generating a first tailpipe air fuel signal; a third oxygen sensor disposed in said exhaust gas stream of said engine upstream of a second emission control device, said third oxygen sensor generating a second feedgas air fuel signal; a fourth oxygen sensor disposed in the exhaust gas stream of said engine downstream of said second emission control device, said fourth oxygen sensor generating a second tailpipe air fuel signal; and, an electronic control unit configured to obtain a first adjusted feedgas air fuel ratio responsive to said first feedgas air fuel signal and said first tailpipe air fuel signal, to obtain an estimate of an oxygen storage level in said first emission control device responsive to said first adjusted feedgas air fuel ratio and said first tailpipe air fuel signal, and to generate first control signal for said engine responsive to said first adjusted feedgas air fuel ratio and said oxygen storage level estimate for said first emission control device, to obtain a second adjusted feedgas air fuel ratio responsive to said second feedgas air fuel signal and said second tailpipe air fuel signal, to obtain an estimate of an oxygen storage level in said second emission control device responsive to said second adjusted feedgas air fuel ratio and said second tailpipe air fuel signal, and to generate a second control signal for said engine responsive to said second adjusted feedgas air fuel ratio and said oxygen storage level estimate for said second emission control device.