EXHAUST EMISSION CONTROL FOR ENGINE

摘要

An engine exhaust emission control arrangement has a catalytic converter including a three-way catalyst. Two oxygen sensors detect the oxygen concentration of exhaust gas upstream and downstream of the catalyst. A microprocessor calculates a maximum oxygen storage amount of a catalyst while the upstream oxygen concentration is higher than the stoichiometric concentration and the downstream oxygen concentration is in a predetermined concentration range which has a value approximately equal to the stoichiometric oxygen concentration. The microprocessor also calculates a maximum oxygen release amount of a catalyst while the upstream oxygen concentration is lower than the stoichiometric concentration and the downstream oxygen concentration produces an indication of a predetermined concentration range. The engine air-fuel ratio is controlled to cause the oxygen storage amount of the catalyst to coincide with a target value which is set at approximately half of an average value of the maximum oxygen storage amount and the maximum oxygen release amount.