Ford Motor Company Limited

Gerald G Stock

Peter John Grutter

Alexander Y Gopp

John A Cushing

Apparatus and method are disclosed for monitoring catalytic converter efficiency in treating exhaust gas from an internal combustion engine having fuel control means for controlling the air to fuel ratio at which fuel is supplied to the engine in response to a fuel flow control signal. During a normal operation mode, the control signal means generates the fuel flow control signal based at least in part on output signals from first and second EGO sensors exposed to the exhaust gas upstream and downstream, respectively, of the catalytic converter. The normal operation mode is periodically interrupted by a test operation mode, preferably initiated during substantially steady state operation of the engine, during which the engine is controlled in response to the output signal from the first EGO sensor without the signal from the second EGO sensor. Air to fuel ratio perturbations about a mean value corresponding to stoichiometry are introduced, comprising an initial lean interval of air to fuel ratio higher than stoichiometry, typically for about 5 seconds, followed by a series of rich intervals alternating with lean intervals. An efficiency value for the catalytic converter corresponding to its emissions treatment efficiency is determined based on the number of perturbations detected by the upstream EGO sensor versus the number detected by the downstream EGO sensor.

Method and apparatus of on-board catalytic converter efficiency

An exhaust gas oxygen sensor downstream of a catalytic converter is used to control a closed loop air/fuel ratio control system. A measured limit cycle frequency at various engine speed/load conditions is compared to stored benchmark limit cycle frequencies as functions of engine speed/load conditions. If the measured frequency is higher, the catalytic converter is considered to be degraded.

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Whitmore Lake, MI, United States of America

Gerald G Stock