| 摘要 |
<p>PROBLEM TO BE SOLVED: To suppress degradation of accuracy in air-fuel ratio feedback control caused by inconsistency of air-fuel ratios between an upstream side and a downstream side of a catalyst.SOLUTION: In executing diagnosis to estimate an oxygen storage capacity of a catalyst through measuring a lapse time from the change of an air-fuel ratio at an upstream side to the change of an air-fuel ratio at a downstream side, of the exhaust gas purification catalyst disposed in an exhaust passage of the internal combustion engine, an execution starting condition of the diagnosis is that an amount of fresh air charged into at least a cylinder is an upper limit value or less. When the diagnosis is executed in EGR for recirculating an exhaust gas from the exhaust passage to an intake passage, the EGR is stopped, and an amount of fresh air increased by stopping the EGR is estimated from an amount of EGR gas just before the stop, and availability of the start of execution of the diagnosis is determined while raising the upper limit value by the increased amount.</p> |
