Patent ID: 8079212

Claim:
An exhaust purifying method for an internal combustion engine on a vehicle, the method comprising: supplying fuel to an exhaust purification catalyst to increase a bed temperature of the catalyst, thereby regenerating the exhaust purification catalyst, wherein the fuel is supplied to exhaust gas via a fuel adding valve; determining whether the vehicle is driving downhill; and suspending the supply of fuel to the exhaust purification catalyst when the vehicle is determined to be driving downhill, wherein the supply of fuel to the exhaust purification catalyst is suspended only when the vehicle is continuously determined for a predetermined period to be driving downhill, wherein the determining includes determines that the vehicle is driving downhill when the amount of fuel injected by a fuel injection valve of the engine is equal to or less than a predetermined amount and a vehicle driving speed is equal to or greater than a predetermined driving speed, wherein the supplying fuel includes first heating control, in which the amount of fuel supplied to the exhaust purification catalyst is relatively small, and second heating control, in which the amount of fuel supplied to the exhaust purification catalyst is relatively large, and wherein the suspending the supply of fuel includes suspending at least the second heating control when it is determined that the vehicle is driving downhill.