Exhaust gas condensate control method and exhaust gas recirculation system thereof

An exhaust gas recirculation system where an exhaust gas condensate control method is applied, the system comprising:

• an LP-EGR line that is connected with a turbine of a turbo charger, diverges from an exhaust line connected to an exhaust manifold of an engine, and allows an exhaust gas to flow;
• a mixing pipe line that is connected with the LP-EGR line at an front end of the turbo charger, mixes an intake air drawn inside from outside with the exhaust gas flowing out of the LP-EGR line to form a gas mixture, and sends the gas mixture to the turbo charger;
• an intake pipe line connected the mixing pipe line to an intake manifold of the engine;
• and
• an electronic control unit (ECU) including an EGR base control logic that controls an LP-EGR valve and an LP-EGR cooler in the LP-EGR line and an intercooler in the intake pipe line using an intake air flow rate control by matching a base map, and an EGR advanced control logic that controls the LP-EGR valve and the LP-EGR cooler in the LP-EGR line and the intercooler in the intake pipe line to remove condensate in the EGR system;
• wherein an allowable relative humidity limit K1 required for the EGR advanced control logic is calculated from the gas mixture composed of the exhaust gas flowing in the EGR system and the intake air sucked from outside;
• an estimated relative humidity value K2 is calculated from calculated or measured factors, including exhaust gas passing mass Na of the LP-EGR valve, temperature Tout, pressure Pout, absolute humidity Ha1, relative humidity Hr1, and partial water vapor pressure Sp1 of the LP-EGR cooler, temperature Mt and mass Mm of the gas mixture in the mixing pipe line, and absolute humidity Ha2, relative humidity Hr2, partial water vapor pressure Sp2, and saturated water vapor pressure Hp2 of the intercooler;
• a current relative humidity value K3 is calculated from the exhaust gas flowing into the EGR line from the LP-EGR valve and passing through the LP-EGR cooler;
• and
• the control objects of the EGR advanced control logic are the mixing pipe line in which an amount of the intake air to be drawn is controlled, the LP-EGR valve in which an flow rate of the exhaust gas distributed to the LP-EGR line is controlled by controlling an opening amount of the valve, and a boost pressure that is changed by operations of the engine and the EGR system.