Catalytic converter efficiency monitoring

Abstract

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/fuel ratio at which fuel is supplied to the engine in response to a fuel flow control signal. During normal operation mode, control signal means generate 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. During a test operation mode, preferably initiated and carried out during substantially steady state or normal operation of the engine, the output signal from the upstream EGO sensor is replaced by a zero mean value periodic function test signal. The output signal of the second (i.e., downstream) EGO sensor is compared to a stored value corresponding to minimum acceptable efficacy of the catalytic converter. For example, a value may be pre-stored and compared to the integral over the test interval of the absolute value of signal deviation from stoichiometry, preferably weighted or normalized, e.g., by dividing it by the integral over the test interval of the absolute value of fuel pulse width deviation from steady state. A failure signal is generated when the comparison indicates efficacy below the minimum acceptable level.