Patent ID: 7089730

Claim:
An internal combustion engine exhaust gas purification method for changing an oxygen concentration in exhaust gas flowing into an NOx absorption catalyst provided inside an exhaust passage of an internal combustion engine, making the NOx absorption catalyst absorb the NOx under a first oxygen concentration condition in which the oxygen concentration in the exhaust gas becomes excessive, and releasing and simultaneously reducing the NOx from the NOx absorption catalyst under a second oxygen concentration condition in which the oxygen concentration in the exhaust gas declines, the exhaust gas purification method comprising: a first step for, under the first oxygen concentration condition, calculating an inflow NOx amount flowing into the NOx absorption catalyst per unit time, and a processable NOx amount that can be processed by the NOx absorption catalyst per unit time; a second step for comparing the inflow NOx amount and the processable NOx amount calculated in the first step; and a third step for reducing the oxygen concentration in the exhaust gas flowing into the NOx absorption catalyst in a case where it was determined in the second step that the inflow NOx amount is greater than the processable NOx amount.