Patent ID: 8904756

Claim:
An exhaust emission control system of an internal combustion engine, comprising: a bypass passage provided in an exhaust passage of the internal combustion engine and arranged to bypass a main passage that is a part of the exhaust passage; a NOx adsorbent provided in the bypass passage and adapted to adsorb at least NOx from among components contained in exhaust gas; a channel switching device that switches a channel of the exhaust gas between the main passage and the bypass passage; a first temperature sensor that detects a temperature of a portion of the NOx absorbent which is located on an upstream side as viewed in a direction in which the exhaust gas flows, as an upstream-side temperature; a second temperature sensor that detects a temperature of a portion of the NOx adsorbent which is located on a downstream side as viewed in the direction in which the exhaust gas flows, as a downstream-side temperature; and an electronic control unit programmed to; control the channel switching device, based on operating conditions of the internal combustion engine, so as to cause the exhaust gas to flow through the bypass passage, determine, when the adsorbing capability of the NOx adsorbent degrades, whether the degradation in the adsorbing capability is a surmountable degradation from which the NOx adsorbent can recover, or an insurmountable degradation from which the NOx adsorbent cannot recover, determine whether the degradation in the adsorbing capability is caused by oxidation of the NOx adsorbent, determine, when the degradation in the adsorbing capability is not caused by oxidation, whether the degradation in the adsorbing capability is caused by irreversible structural changes in the NOx adsorbent, compare changes in the upstream-side temperature with changes in the downstream-side temperature when the exhaust gas flows into the NOx adsorbent to cause the changes in the upstream-side temperature and the downstream-side temperature, and determine whether the degradation in the adsorbing capability is in insurmountable degradation from which the NOx adsorbent cannot recover, based on a result of the comparison.