A method and system for controlling an engine operating over a range of operating conditions.

摘要

A method and system for controlling an engine operating over a range of operating conditions, with air-fuel mixtures which are rich and lean of a stoichiometric ratio, wherein the engine produces exhaust gas which is directed through an upstream emission control device 34 and a downstream sensor 40 that generates an output signal indicative of the concentration of reductants in the exhaust gas exiting the emission control device, the method comprising; determining a first value during a lean operating condition which is representative of a cumulative amount of a selected exhaust gas component generated by the engine; comparing this first value to a stored second value, which is periodically updated as a function of the output of the downstream sensor and at least one predetermined reference value, representing the capacity of the emission control device to store said exhaust gas component and; selecting an engine operating condition as a function of the first and second values. The determination of the first value may include the step of estimating an instantaneous amount of the selected exhaust gas component generated by the engine as a function of at least one of its load, ignition timing or air-fuel ratio. The method may include indicating emission control degradation if a predetermined number of desulfating operations are conducted without a significant increase in the maximum for the first value.