Patent ID: 7693645

Claim:
A method for controlling a low pressure EGR valve that mixes an EGR gas into an intake air, the method comprising: detecting temperature of an intake air passing through an air cleaner; detecting a mass flow rate of the intake air passing through the air cleaner; detecting temperature and pressure of the intake air at a downstream side of an intercooler; detecting temperature and pressure of an EGR gas at an upstream side of an EGR cooler; determining a control duty of the low pressure EGR valve on the basis of the detected temperature and mass flow rate of the air passing through the air cleaner, the detected temperature and pressure at the downstream side of the intercooler, and the detected temperature and pressure at the upstream side of the EGR cooler; and controlling the low pressure EGR valve based on the determined control duty; wherein the determining control duty of the low pressure EGR valve comprises: estimating temperature, pressure, and mass flow rate at the upstream side of the intercooler on the basis of the temperature and mass flow rate at the downstream side of the intercooler; estimating temperature, pressure, and mass flow rate at the upstream side of the turbocharger on the basis of the estimated temperature, pressure, and mass flow rate at the upstream side of the intercooler; estimating temperature, pressure, and mass flow rate of the EGR gas at the downstream side of the EGR cooler on the basis of the EGR gas temperature and pressure at the upstream side of the EGR cooler; and calculating the control duty of the low pressure EGR valve on the basis of the estimated mass flow rate at the upstream side of the turbocharger, the estimated temperature and mass flow rate of the EGR gas at the downstream side of the EGR cooler, and the detected temperature and mass flow rate of the air passing through the air cleaner.