Evaporative fuel-purging control system for internal combustion engines

Claim 1

In an evaporative fuel-purging control system for an internal combustion engine having an intake system, an exhaust system, a fuel tank, a canister in which evaporative fuel from said fuel tank is adsorbed, purge control valve means arranged between said canister and said intake system for controlling a flow rate of said evaporative fuel supplied from said canister to said intake system, an exhaust gas ingredient concentration sensor arranged in said exhaust system, and air-fuel ratio control means responsive to an output from said exhaust gas ingredient concentration sensor for calculating an air-fuel ratio correction coefficient based upon said output from said exhaust gas ingredient concentration sensor and controlling the air-fuel ratio of a mixture supplied to said engine by the use of said air-fuel ratio correction coefficient, the improvement comprising: calculating means for calculating an average value of said air-fuel ratio correction coefficient; and purge control means responsive to said average value calculated by said calculating means for controlling said purge control valve means in a manner such that when said average value of said air-fuel ratio correction coefficient is below a predetermined value, the flow rate of said evaporative fuel supplied by said purge control valve means is decreased, said purge control means including means for correcting said predetermined value by a second average value of said air-fuel ratio correction coefficient calculated when the supply of said evaporative fuel to said intake system is stopped.