The exhaust gas control apparatus and method of an internal combustion engine

Exhaust gas control apparatus of an internal combustion engine comprising: a NOx catalyst (50b) which is on an exhaust passage (18, 19) is provided; a NOx catalyst temperature detecting means (48a, 48b) for detecting a temperature of the NOx catalyst (50b); an exhaust air-fuel ratio detecting means (47) for detecting an air-fuel ratio of the exhaust gas in the exhaust passage (18, 19); and an exhaust air-fuel control means (30) for controlling the air-fuel ratio of the exhaust gas in the exhaust passage (18, 19) on the basis of the temperature of the NOx catalyst (50b) by the NOx catalyst temperature detecting means (48a, 48b) is detected, and the air-fuel ratio of the which is detected by the exhaust air-fuel ratio detecting means (47) exhaust gas, wherein when the air-fuel ratio of the exhaust gas detected by the exhaust air-fuel ratio detecting means (47) from a first predetermined air-fuel ratio, wherein an upper limit of an allowable amount of smoke produced is achieved and that is greater than a stoichiometric air-fuel ratio, is starting lean, the exhaust air-fuel ratio control means (30) controls the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio and it intermittently the air-fuel ratio of the exhaust ...