Dual-sensor type air-fuel ratio control system for internal combustion engine and catalytic 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 sensor disposed upstream of said catalytic converter for detecting concentration of a particular component of said exhaust gas to thereby generate a first air-fuel ratio signal indicating said concentration; a second air-fuel ratio sensor disposed downstream of said catalytic converter for detecting concentration of said particular component of said exhaust gas to thereby generate a second air-fuel ratio signal indicating said concentration; deviation calculating means for arithmetically determining a deviation of said second air-fuel ratio signal from a first comparison value; proportional value calculating means for arithmetically determining a proportional value which is proportional to said deviation determined by said deviation calculating means; integrating means for calculating an integration value corresponding to said deviation; comparison value calculating means for arithmetically determining a second comparison value on the basis of said integration value and said proportional value; comparison means for comparing said first air-fuel ratio with said second comparison value; and air-fuel ratio correcting means for regulating an air-fuel ratio correcting quantity on the basis of the result of the output of said comparison means.