Air-fuel ratio control system for changing the limit value of the target air-fuel ratio in the reduction treatment of the catalyst

摘要

PROBLEM TO BE SOLVED: To reduce the exhaust of an injurious ingredient in exhaust gas after a catalyst reducing treatment.;SOLUTION: An air-fuel ratio controller for controlling an air-fuel ratio of an internal combustion engine is provided with a reducing means for reducing a catalyst in a catalyst reducing mode conducted after finishing an operation with a lean air-fuel ratio, and an air-fuel control means for controlling the air-fuel ratio to converge the output of an exhaust gas sensor arranged in an exhaust pipe at a predetermined target value in an air-fuel ratio control mode executed after finishing the catalyst reducing mode. The air-fuel ratio means calculates an control input for controlling the air-fuel ratio. The control input is processed for a limit with a limiter using an upper limit and a lower limit. The air-fuel ratio is controlled using the control input processed for the limit. When the internal combustion engine is in the catalyst reducing mode, the limiter shifts the upper limit to a rich direction to prevent the air-fuel ratio from changing to the lean direction over the predetermined amount when the internal combustion engine shifts from the catalyst reducing mode into the air-fuel ratio control mode.;COPYRIGHT: (C)2004,JPO