Patent ID: 7783408

Claim:
A controller for an internal combustion engine having a plurality of cylinders, wherein said internal combustion engine including: a plurality of intake manifolds connected to said plurality of cylinders respectively, introducing external air to a combustion chamber of a corresponding cylinder of said plurality of cylinders, a fuel injection mechanism provided corresponding to each of said plurality of cylinders, injecting fuel to said combustion chamber, a plurality of exhaust manifolds connected to said plurality of cylinders respectively, discharging exhaust gas emitted from said combustion chamber of the corresponding cylinder to the outside, and an exhaust gas recirculating device recirculating part of said exhaust gas to each of said plurality of intake manifolds through a recirculation valve; said controller comprising: an air-fuel ratio detecting unit detecting cylinder-by-cylinder air-fuel ratio of each of said plurality of cylinders, and an imbalance determining unit determining whether or not there is any imbalance among air-fuel ratios of said plurality of cylinders, based on the detected cylinder-by-cylinder air-fuel ratios; wherein said imbalance determining unit stops recirculating operation of said exhaust gas if there is an imbalance among air-fuel ratios of said plurality of cylinders, and again determines, while said recirculating operation is stopped, whether there is any imbalance among air-fuel ratios of said plurality of cylinders.