Patent ID: 8769931

Claim:
A low pressure exhaust gas recirculation (EGR) cooler efficiency diagnosis method for an EGR system, the method comprising: measuring a speed and a load of an engine; using an ECU to perform the following steps; setting a threshold of a difference between a model temperature and a detected temperature downstream of a low pressure EGR cooler according to the speed and the load of the engine; measuring a pressure difference between an upstream side and a downstream side of a low pressure EGR valve; calculating a mass flow rate of an exhaust gas passing through the low pressure EGR cooler based on the measured pressure difference; calculating an efficiency of the low pressure EGR cooler based on the calculated mass flow rate; calculating the model temperature downstream of the low pressure EGR cooler based on the calculated efficiency; and comparing the model temperature downstream of the low pressure EGR cooler with the detected temperature downstream of the low pressure EGR cooler, wherein the mass flow rate of the exhaust gas is calculated according to a first equation of =ρ exh Q exh =C·A Flap √{square root over (2ρ exh ΔP )}= f (Δ P ,valve position)√{square root over (2ρ exh ΔP )} Eq. (1) wherein, the is a mass flow rate of the exhaust gas flowing in a low pressure EGR line, wherein the ρ exh is a density of the exhaust gas, wherein the Q exh is a volume flow rate of the exhaust gas, wherein the C is a coefficient, wherein the A Flap is a cross-section of the low pressure EGR valve, wherein the ΔP is the pressure difference between the upstream and the downstream of the low pressure EGR valve, wherein the efficiency of the low pressure EGR cooler is calculated according to a second equation of η= f ( , T coolant −T in ), Eq. (2) wherein the T coolant is a coolant temperature flowing in or flowing out of the low pressure EGR cooler, and wherein the T in is an exhaust gas temperature of an upstream side of the low pressure EGR cooler, and wherein the calculating of the model temperature downstream of the low pressure EGR cooler is performed by substituting the second equation into a third equation of T out =T in −η( T in −T coolant ), Eq. (3) wherein the T out is the model temperature of a downstream side of the low pressure EGR cooler, and wherein the η is the efficiency of the low pressure EGR cooler.