Patent ID: 7536852

Claim:
A combustion air-fuel ratio control system for an internal combustion engine comprising: exhaust guiding means for guiding exhaust from the internal combustion engine; exhaust purification means, arranged downstream of the exhaust guiding means, for purifying the exhaust; fresh air supplying means for supplying fresh air to the exhaust guiding means at a fresh air supplying position upstream of the exhaust purification means; exhaust air-fuel ratio sensing means for detecting an exhaust air-fuel ratio of the exhaust at a location between the exhaust purification means and the fresh air supplying position; exhaust air-fuel ratio sensor activation determining means for determining whether or not the exhaust air-fuel ratio sensing means is active; and combustion air-fuel ratio control means for controlling a combustion air-fuel ratio of the internal combustion engine based on the exhaust air-fuel ratio that is detected by the exhaust air-fuel ratio sensing means by controlling the fresh air from the fresh air supplying means to the exhaust guiding means when warming up of the exhaust purification means is requested, the combustion air-fuel ratio control means further performing a function of open controlling the combustion air-fuel ratio in a combustion chamber to be a primary combustion air-fuel ratio which is between a theoretical air-fuel ratio and a combustion limit air-fuel ratio that is richer than the theoretical air-fuel ratio upon the exhaust air-fuel ratio sensor activation determining means determining the exhaust air-fuel ratio sensing means to be inactive, and the combustion air-fuel ratio control means further performing a function of feedback controlling the combustion air-fuel ratio to be a secondary combustion air-fuel ratio that is richer than the primary combustion air-fuel ratio and upon the exhaust air-fuel ratio sensor activation determining means determining the exhaust air-fuel ratio sensing means to be active.