Patent ID: 9677490
Date: 2017-06-13
CPC Classifications: F01N,F02D,Y02T

Claim:
1. An abnormality diagnosis system of an internal combustion engine wherein the internal combustion engine includes an exhaust purification catalyst which is arranged in an exhaust passage of the internal combustion engine and which can store oxygen, the abnormality diagnosis system comprising: an electronic control unit configured to control the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst to become a target air-fuel ratio, and a downstream side air-fuel ratio sensor which is arranged at a downstream side of said exhaust purification catalyst in an exhaust flow direction and which can detect an air-fuel ratio of exhaust gas discharged from said exhaust purification catalyst, wherein the electronic control unit is configured to perform an active air-fuel ratio control which alternately controls said target air-fuel ratio to a rich air-fuel ratio which is richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio which is leaner than the stoichiometric air-fuel ratio at a given interval, and to diagnose abnormality of said exhaust purification catalyst based on an output air-fuel ratio of the downstream side air-fuel ratio sensor during execution of said active air-fuel ratio control, wherein the electronic control unit is configured to judge that said exhaust purification catalyst is abnormal when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes as rich as or richer than a rich judgment air-fuel ratio which is richer than the stoichiometric air-fuel ratio and becomes as lean as or leaner than a lean judgment air-fuel ratio which is leaner than the stoichiometric air-fuel ratio in a period where said target air-fuel ratio is successively made the rich air-fuel ratio and the lean air-fuel ratio due to said active air-fuel ratio control, and wherein the electronic control unit is configured to judge that the control of the air-fuel ratio is abnormal when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes only one of: (i) as rich as or richer than said rich judgment air-fuel ratio; and (ii) as lean as or leaner than said lean judgment air-fuel ratio, in the period where said target air-fuel ratio is successively made the rich air-fuel ratio and the lean air-fuel ratio due to said active air-fuel ratio control.