Patent ID: 7377273

Claim:
An air-fuel ratio control apparatus for an internal combustion engine that is capable of performing a rich burn process or a lean burn process for each cylinder group, the air-fuel ratio control apparatus comprising: a first exhaust path connected to a first cylinder group; a second exhaust path connected to a second cylinder group; a NOx catalyst positioned downstream of a confluence of the first exhaust path and the second exhaust path; a fuel injection valve for injecting fuel into each of cylinders of the first and second cylinder groups; an intake air amount adjustment mechanism for changing an intake air amount for each of the cylinders; poisoning recovery means for performing sulfur poisoning recovery of the NOx catalyst by causing the first cylinder group to perform a rich burn or lean burn process and causing the second cylinder group to perform a lean burn or rich burn process; and exhaust air-fuel ratio control means for changing the intake air amount for each cylinder by operating the intake air amount adjustment mechanism at the time of performing the sulfur poisoning recovery while providing substantially the same fuel injection amount for all cylinders of the first and second cylinder groups.