The EGR system recirculates a part of the exhaust gas back into the inlet manifold, which results in reducing NOx emissions. Higher operability and emission reduction are both realized by controlling the EGR system. For the microprocessor in the EGR valve, a control current from the ECM operates a motor to control the lift amount of the EGR valve. In addition, the EGR position sensor is used for detection of the actual valve lift amount and for precision control of the EGR amount. The EGR is activated when the specified conditions of engine speed, engine coolant temperature, intake air temperature, and barometric pressure are met. Then, the valve opening position is calculated based on engine speed and the desired fuel injection quantity. The motor drive duty is determined from this valve opening position, and the valve is driven according to the motor drive duty. The intake throttle valve appropriately adjusts the inlet manifold vacuum and closes when the EGR is activated.
EGR control operating conditions