Filler cap structure for a fuel tank

Abstract

A filler cap structure for a vehicular fuel tank particularly designed to prevent the discharge of fuel vapor to the ambient atmosphere and hence possible air pollution resulting therefrom upon filling of the fuel tank. The fuel tank has a filler tube closed by a filler cap. The filler tube is provided on its inner peripheral surface at a location inward of the bottom end of the filler cap with an annular seal seat. Defined by the annular seal seat, the inner peripheral surface of the fillter tube, and the bottom portion of the filler cap is an annular space which is connected through a communication tube with a canister. The annular space is sealed from the atmosphere by a first seal member disposed between the inner peripheral surface of the filler tube and the filler cap at a location outward of the annular space. The filler cap is provided on its bottom end with a second seal member which is adapted to be placed, upon complete closure of the filler cap against the filler tube, in sealing engagement with the annular seal seat on the inner peripheral surface of the filler tube for sealing of the fuel vapor in the fuel tank, the second seal member being moved away from the annular seal seat so as to place the fuel tank in communication with the canister when the filler cap is partially loosened.