LOW PRESSURE EGR SYSTEM AND EXAMINING METHOD FOR EFFICEINCY OF LOW EGR COOLER

摘要

PURPOSE: A method for diagnosing the efficiency of an LP(Low Pressure) EGR(Exhaust Gas Recirculation) cooler is provided to predict the temperature of the rear end of the LP EGR cooler using the temperature of exhaust gas flowing into an inlet of the LP EGR cooler and the gas flow passing through the LP EGR cooler. CONSTITUTION: A method for diagnosing the efficiency of an LP EGR cooler comprises following steps. An engine speed and load are measured(S10). A limit value of the difference between measured temperature and the model temperature of the rear end of the LP EGR cooler is set(S20). The differential pressure between the front and rear ends of an LP EGR valve is measured. A mass flow passing through the LP EGR cooler is calculated using the measured differential pressure. The efficiency of the LP EGR cooler is calculated using the measured mass flow. The temperature of the rear end of the LP EGR cooler is calculated using the measured efficiency. The temperature of the rear end of the LP EGR cooler is compared with the real measured temperature of the rear end of the LP EGR cooler(S40). [Reference numerals] (AA) START; (S10) Measuring the Engine Speed/Load(Fuel); (S20) Setting the Limit about the difference between measured temperature and the model temperature of the rear end of the LP EGR cooler on the basis of an engine state; (S30) Predicting the temperature of the rear end of the LP-EGR cooler by the LP-EGR system model; (S40) Measured temperature - model temperature > Limit; (S50) Maintaining predetermined time (Debounce Time); (S60) LP-EGR system shut-off (alarm if necessary); (S70) Operating the LP-EGR system normally