Dual-sensor type air-fuel ratio control system for internal combustion engine and catalytic converter diagnosis apparatus for the same

Claim 1

A dual-sensor type air-fuel ratio control system for an internal combustion engine, comprising: a catalytic converter disposed within an exhaust pipe of said engine for purifying an exhaust gas; a first air-fuel ratio disposed upstream of said catalytic converter for detecting the upstream concentration of a particular component of said exhaust gas to output a first air-fuel ratio signal indicating said upstream concentration; a second air-fuel ratio sensor disposed downstream of said catalytic converter for detecting the downstream concentration of said particular component of said exhaust gas to thereby output a second air-fuel ratio signal indicating said downstream concentration; and an electronic control unit for controlling a target air-fuel ratio of a mixture supplied to said engine by arithmetically determining a target air-fuel ratio control quantity on the basis of said first and second air-fuel ratio signals; wherein said electronic control unit includes: first arithmetic means for determining a first air-fuel ratio control quantity on the basis of said first air-fuel ratio signal; second arithmetic means for determining a second air-fuel ratio control quantity on the basis of said second air-fuel ratio signal; correcting means for correcting said first air-fuel ratio control quantity with said second air-fuel ratio control quantity to thereby determine said target air-fuel ratio control quantity on the basis of said correction of said first air-fuel ratio control quantity; and filtering means for filtering said first air-fuel ratio signal.