EXHAUST GAS PURIFICATION APPARATUS FOR INTERNAL COMBUSTION ENGINE

摘要

In an internal combustion engine, an NO x selective reduction catalyst (14) is arranged in an engine exhaust passage, and an NO x storage catalyst (12) is arranged in the engine exhaust passage upstream of the NO x selective reduction catalyst (14). When the amount of NO x stored in the NO x storage catalyst (12) exceeds a predetermined allowable value, the NO x storage catalyst (12) is raised in temperature to make the NO x storage catalyst (12) release the NO x . The amount of urea feed is decreased by exactly the amount of reduction of the calculated stored NO x amount with respect to the amount of urea feed determined from the engine operating state, and the amount of urea feed is increased by exactly the amount of reduction of the calculated released NO x amount with respect to the amount of urea feed determined from the engine operating state.