Patent ID: 6463735
Filing Date: 2002-10-15
Classification: F01N,F02D,Y02T

Abstract:
A deterioration detection apparatus for detecting deterioration of a catalyst of an engine having an upstream-side catalyst and a downstream-side catalyst provided for purifying exhaust gas, the deterioration detection apparatus comprising:a first sensor, provided on an upstream side of the upstream-side catalyst, for detecting an air-fuel ratio of exhaust gas flowing in the upstream side of the upstream-side catalyst; a second sensor, provided on a downstream side of the upstream-side catalyst, for detecting an air-fuel ratio of exhaust gas flowing in the downstream side of the upstream-side catalyst; a third sensor, provided on a downstream side of the downstream-side catalyst, for detecting an air-fuel ratio of exhaust gas flowing in the downstream-side of the downstream-side catalyst; and a catalyst deterioration diagnosing unit for determining existence and non-existence of a deteriorating state of the upstream-side catalyst based on at least a signal output of the second sensor, wherein the catalyst deterioration diagnosing unit controls the air-fuel ratio of the exhaust gas flowing in the downstream side of the downstream-side catalyst in a predetermined range during a period of time to diagnose the deteriorating state of the upstream-side catalyst, and wherein the catalyst deterioration diagnosing unit starts the diagnosis of the deteriorating state of the upstream-side catalyst after a signal output of the third sensor has been sustained in the predetermined range for a predetermined period of time continuously.