Patent ID: 8336294

Claim:
A fuel addition control method for an exhaust emission purifier of an internal combustion engine, the exhaust emission purifier including an exhaust emission purifying device that includes a catalyst and purifies exhaust emission of an internal combustion engine and a fuel addition device that adds fuel upstream of the exhaust emission purifying device, cycles being repeated in the fuel addition control method in order that the exhaust emission purifying device is to be regulated at a target temperature, the cycle starting when a temperature control of the exhaust emission purifying device is requested, and ending when the requested fuel addition amount coincides with the really added fuel addition amount, the cycle being a combination of an addition period during which fuel is added from the fuel addition device and a halt period during which fuel addition from the fuel addition device is halted, and the fuel addition device being operated such that the halt period is split to sandwich the addition period in each of the cycles, wherein the fuel addition device is manipulated such that the length of a pre-addition halt period, which is a halt period disposed before the addition period, is varied in accordance with the temperature of the exhaust emission purifying device at the start point of the cycle and degradation of the catalyst, so that the pre-addition halt period can be different to a post-addition halt period.