US Patent 7174706 Exhaust emission control system for internal combustion engine

An exhaust emission control system for an internal combustion engine is located on a vehicle and provided with a particulate filter to accumulate particulate matters in an exhaust gas of the engine. The system has a pressure difference detector, an exhaust flow rate detector, a regeneration controller and a detection accuracy increaser. The pressure difference detector detects a differential pressure in the particulate filter. The exhaust flow rate detector detects an exhaust flow rate of the engine. The regeneration controller determines to regenerate the particulate filter based on the differential pressure and the exhaust flow rate. The detection accuracy increaser increases a detection accuracy of the differential pressure.