| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To accurately execute an abnormality diagnosis of an exhaust gas sensor at a downstream side of a catalyst (hereinafter referred to as 'downstream side exhaust gas sensor') without receiving an influence of the catalyst. <P>SOLUTION: A gas introduction device 21 for diagnosing an abnormality is constituted by connecting a gas introduction pipe 25 for diagnosing an abnormality and an atmosphere release pipe 26 onto the midway of a secondary air introduction pipe 21 of a secondary air introduction device 23 through a secondary air directional control valve 24. At the time of realization of the abnormality diagnosis execution condition of the downstream side exhaust gas sensor 20, the secondary air directional control valve 24 is switched between a gas introduction position for diagnosing the abnormality and an atmosphere release position to switch the state that the secondary air (abnormality diagnosis gas) is introduced to an upstream side of the downstream side exhaust gas sensor 20 of an exhaust pipe 17b at a downstream side of the catalyst and the state that the introduction of the secondary air is stopped. Thereby, an air/fuel ratio of the exhaust gas flowing around the downstream side exhaust gas sensor 20 is varied without receiving the influence of the catalyst 18 and the abnormality diagnosis of the downstream side exhaust gas sensor 20 is carried out by measuring a response time of the downstream side exhaust gas sensor 20 at this time. <P>COPYRIGHT: (C)2003,JPO</p> |
