Evaporative fuel-purging control system for internal combustion engines

In an evaporative fuel-purging control system for an internal combustion engine having a fuel tank and an intake passage, said evaporative fuel-purging control system including a canister for adsorbing evaporative fuel generated from said fuel tank, a purging passage connecting between said canister and said intake passage for purging a mixture of said evaporative fuel and air therethrough into said intake passage, and a purge control valve arranged across said purging passage for controlling a flow rate of said evaporative fuel supplied to said intake passage,

• the improvement comprising:
• evaporative fuel flow rate-detecting means for detecting a flow rate of said evaporative fuel contained in said mixture;
• desired evaporative fuel flow rate-setting means for setting a desired flow rate of said evaporative fuel commensurate with an operating condition in which said engine is operating;
• purge control means for comparing between the detected flow rate of said evaporative fuel and the set desired flow rate of said evaporative fuel and being responsive to results of said comparison for controlling valve opening of said purge control valve;
• evaporative fuel concentration-detecting means for detecting the concentration of said evaporative fuel in said mixture;
• and
• valve opening change rate-varying means responsive to the detected concentration of said evaporative fuel for varying a change rate of valve opening of said purge control valve.