US Patent 7963105 Exhaust purification system for internal combustion engine

An exhaust purification system includes a catalyst disposed in an exhaust path of an internal combustion engine; a fuel pump that supplies fuel to a common rail; an exhaust-side fuel injection valve that is interposed in the exhaust path so as to be located upstream of the catalyst and injects into the exhaust path the fuel supplied from the fuel pump; and estimation section that estimates a clogging degree of an injection port of the exhaust-side fuel injection valve on the basis of fluctuations in pressure of the common rail and those in revolution speed of the internal combustion engine at the time of fuel injection by the exhaust-side fuel injection valve.