Patent ID: 6732503
Filing Date: 2004-05-11
Classification: F01N,F02D

Abstract:
An air/fuel ratio controller for an internal combustion engine, comprising:a upstream catalyst disposed upstream along an exhaust passage; a hydrocarbon-adsorbent exhaust purification catalyst that is disposed downstream from said upstream catalyst and has the function of adsorbing hydrocarbons at low temperatures and releasing the adsorbed hydrocarbons as the temperature rises; upstream air/fuel ratio detection means disposed upstream from said upstream catalyst, for detecting the exhaust air/fuel ratio of exhaust gas flowing into the upstream catalyst; downstream air/fuel ratio detection means disposed downstream from the hydrocarbon-adsorbent exhaust purification catalyst, for detecting the exhaust air/fuel ratio of exhaust gas flowing out of the hydrocarbon-adsorbent exhaust purification catalyst; middle air/fuel ratio detection means disposed downstream from said upstream catalyst and upstream from the hydrocarbon-adsorbent exhaust purification catalyst, for detecting the exhaust air/fuel ratio of exhaust gas flowing into the hydrocarbon-adsorbent exhaust purification catalyst; air/fuel ratio main feedback control means for performing main feedback control such that the exhaust air/fuel ratio detected by the upstream air/fuel ratio detection means is kept at a specific main feedback target air/fuel ratio; and air/fuel ratio sub-feedback control means for performing sub-feedback control such that the exhaust air/fuel ratio detected by the downstream air/fuel ratio detection means is kept at a specific sub-feedback target air/fuel ratio while the adsorbed hydrocarbons are being desorbed from the hydrocarbon-adsorbent exhaust purification catalyst, and for performing sub-feedback control such that the exhaust air/fuel ratio detected by the middle air/fuel ratio detection means is kept at a specific sub-feedback target air/fuel ratio after the adsorbed hydrocarbons have been desorbed from the hydrocarbon-adsorbent exhaust purification catalyst.