Fuel-vapor emission-control system for controlling the pressure in a system

A fuel-vapor emission-control system for an internal combustion engine wherein fuel vapor generated in a fuel tank is adsorbed and, while the engine is running, is subsequently returned to the intake manifold of an engine, said fuel-vapor emission-control system comprising:

• refueling detection means for detecting refueling of the fuel tank;
• a canister having a housing enclosing adsorbing material for adsorbing vaporized fuel, wherein a tank port, into which fuel vapor flows from the fuel tank, is located at one end of said housing, and wherein the canister includes a purge port from which fuel vapor is exhausted to said intake manifold, and wherein an atmospheric port is located on another end of said housing and is connected to the atmosphere;
• an atmospheric release surface area changing mechanism including an electromagnetic valve provided at a prescribed position on said atmospheric port side of said canister for varying the atmospheric release surface area of said canister by varying an opening of the valve so that, when the internal pressure inside said fuel tank is large, the atmospheric release surface area is greater than when the internal pressure inside said tank is small;
• and
• control means coupled to the refueling detection means and to the atmospheric release surface area changing mechanism for controlling the degree of opening of the valve so that the degree of opening of the valve is increased when the refueling condition is detected.