Air/fuel ratio control system having an evaporated fuel purging control arrangement

In an air/fuel ratio control system for performing feedback control of the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion engine having an intake pipe, said system including means for detecting the concentration of an exhaust gas ingredient emitted from said engine, fuel quantity adjusting means for producing said mixture being supplied to said engine, and an electrical circuit operatively connecting said concentration detecting means with said fuel quantity adjusting means in a manner effecting feedback control operation to control the air/fuel ratio of said mixture to a predetermined value in response to an output signal produced by said concentration detecting means, the combination comprising:

• a canister having evaporated fuel absorbed therein;
• a purge conduit connecting said canister to said intake pipe of said engine for allowing said fuel absorbed in said canister to be purged into said intake pipe;
• a purge control valve having means actuatable by negative pressure and arranged across said purge conduit;
• a control circuit connecting said negative pressure-actuatable means of said purge control valve to said intake pipe;
• a solenoid valve arranged to selectively close and open said control conduit;
• means for driving said solenoid valve;
• a temperature sensor responsive to a change in the temperature of engine coolant to produce an output continuously variable with said change;
• and circuit means provided within said electrical circuit and operable to detect an operating condition of said engine;
• said circuit means being connected to said temperature sensor to be supplied with said output of said temperature sensor;
• said electrical circuit being operable to carry out control of the air/fuel ratio of said mixture in response to said output of said temperature sensor supplied to said circuit means;
• said circuit means being connected to said solenoid valve driving means and adapted to supply a control signal thereto when said output of said temperature sensor exceeds a predetermined value;
• said solenoid valve driving means being operable upon said control signal to actuate said solenoid valve to cause said negative pressure-actuatable means of said purge control valve to communicate with atmospheric air.