EGR CONTROL: STEPPER MOTOR EGR VALVE

摘要

Exhaust gas recirculation (EGR) is used to control NO_x formation and, on some cars, to improve highway gas mileage. A vacuum-powered EGR valve is usually operated by the PCM using a pulse width modulated solenoid valve to control the vacuum. These work well enough, but with increased demand for tighter EGR control over a broad range of throttle openings, the time has come for an electric EGR valve. Digital electric EGR valves were first used on General Motors (GM) engines in the 1980s. They were actually just solenoid valves that were opened or closed by the electronic control module (ECM) to provide different set levels of EGR flow. They were effective, but not without problems, nor flexible enough for today's demands.