Patent ID: 7661264
Filing Date: 2010-02-16
Classification: F01N,F02D,Y02T

Abstract:
1. An air-fuel ratio control apparatus for an internal combustion engine, having a catalyst which is disposed in an exhaust system of the internal combustion engine and which purifies exhaust gas from the internal combustion engine, a first air-fuel ratio sensor which is disposed on an upstream side of the catalyst and which detects an air-fuel ratio in upstream-side exhaust gas, a second air-fuel ratio sensor which is disposed on a downstream side of the catalyst and which detects an air-fuel ratio in downstream-side exhaust gas, first air-fuel ratio feedback control means for adjusting an air-fuel ratio to be fed into the internal combustion engine, in accordance with the output value of the first air-fuel ratio sensor and a predetermined control constant, and for oscillating the air-fuel ratio in the exhaust gas on the upstream side of the catalyst cyclically in a rich direction and in a lean direction, and second air-fuel ratio feedback control means for changing the control constant so that the output value of the second air-fuel ratio sensor and a target value may agree, and for manipulating an average air-fuel ratio obtained by averaging the air-fuel ratio in the upstream-side exhaust gas as is cyclically oscillated, comprising fuel cut state detection means for detecting a state of fuel cut in which feed of a fuel into the internal combustion engine is stopped; and catalyst deterioration decision means for deciding deterioration of the catalyst on the basis of a period which is expended since said fuel cut state detection means has detected release of the state of the fuel cut, until the output value of the second air-fuel ratio sensor agrees with a predetermined resetting decision value near the target value, and a manipulation quantity of the average air-fuel ratio of the upstream side as is based on the second air-fuel ratio feedback control means.