Degradation discrimination system of internal combustion engine exhaust gas purification system

Abstract

A system for discriminating degradation of an exhaust purification system of an internal combustion engine having an adsorbent installed at a bypass exhaust gas passage branched from an exhaust pipe of the engine, which is opened by a switch-over valve at starting of the engine to introduce the exhaust gas such that the adsorbent adsorbs unburned HC in exhaust gas generated by the engine and is closed such that the adsorbent desorbs the adsorbed HC and the desorbed HC is thereafter recirculated at a position upstream of a catalyst. In the system, an inflow amount and outflow amount of HC flowing in and out of the adsorbent are determined based at least on the engine operating conditions and the detected concentration of HC. Then, the ratio therebetween is calculated and compared with a threshold value and if the ratio is less than the threshold value, the adsorbent is discriminated to be degraded, thereby enabling to improve the discrimination accurately.