Patent ID: 6470674
Filing Date: 2002-10-29
Classification: F01N,Y02T

Abstract:
A deterioration detecting apparatus for an engine having an exhaust purifying catalyst and oxygen responsive upstream and downstream sensors disposed upstream and downstream the catalyst, respectively, the apparatus comprising:air/fuel ratio feedback control means for effecting an air/fuel ratio feedback control based on an output of the upstream sensor; sub-feedback control means for effecting a sub-feedback control based on an output of the downstream sensor thereby to reflect the output of the downstream sensor in the air/fuel ratio feedback control; and catalyst deterioration detecting means for detecting deterioration of the catalyst based on the outputs of the downstream sensor and the upstream sensor; wherein the catalyst deterioration detecting means includes gain changing means for changing a feedback gain of the sub-feedback control during a catalyst deterioration detecting operation of the catalyst deterioration detecting means; the sub-feedback control means calculates a correction value of the sub-feedback control by using a proportional term and an integral term based on the downstream sensor; and the gain changing means changes gains of the proportional term and the integral term differently from each other.