US Patent 7665297 Exhaust purifying apparatus for internal combustion engine

An internal combustion engine has a separate exhaust passage for each one of banks. An exhaust purifying catalyst is provided in each exhaust passage. The mass flow rates G1, G2 of exhaust gas that flow through the exhaust passages are individually estimated. The flow rate of exhaust gas is individually adjusted per each bank by controlling the operation of each one of exhaust gas recirculation valves such that the difference between the estimated mass flow rates G1, G2 is decreased.