Fuel tank cap with charcoal canister

The fuel tank cap with charcoal canister includes a fuel tank inner cap and a fuel tank outer cap. A filling chamber is disposed in the fuel tank inner cap. The fuel tank outer cap wraps up the upper port of the filling chamber. The fuel tank inner cap has a volume chamber having an upper vent cap. Between the side wall of the upper vent cap and the inner wall of the volume chamber, there is an air gap. The filling chamber has a lower breathing panel. Between the lower breathing panel and the bottom of the filling chamber, there is a welding ring. The upper port is on the inner side of the welding ring. The lower surface of the lower breathing panel is fixed and connected with the filling chamber via the welding ring. The bottom surface of the volume chamber has an air inlet/outlet.