A fuel cap for a filler neck on a fuel tank includes a cap body having threads for engaging the filler neck when the fuel cap is installed on the filler neck and a cap handle rotatably mounted on the cap body. A clutch acts between the cap handle and the cap body to permit the cap handle to rotate freely on the cap body when the clutch is disengaged. When the clutch is engaged, rotation of the cap handle will rotate the cap body so that the user can remove the fuel cap from the filler neck to refuel the vehicle. A pressure-sensing diaphragm disengages the clutch when the pressure differential between the fuel vapor pressure and the atmospheric pressure exceeds a predetermined threshold and engages the clutch when the pressure differential between the fuel vapor pressure and the atmospheric pressure is less than the predetermined threshold.
1. A fuel cap for capping a filler neck on a fuel tank having fuel stored therein, said filler neck venting a volume of fuel vapor to the atmosphere when the cap is removed by a user, and the volume of fuel vapor escaping depending upon the difference between the fuel vapor pressure and the atmospheric pressure, comprising:
a cap body having threads for engaging and disengaging the filler neck when the cap body is rotated;
a cap handle rotatably mounted on the cap body; said cap handle having a window opening therein;
a first set of clutch teeth provided on the cap body;
a clutch plate mounted on the cap handle for up and down movement within the cap handle and rotation with the cap handle;
a pressure-sensing diaphragm of flexible material mounted within the cap body and having a first side of the diaphragm exposed to fuel vapor pressure and a second side of the diaphragm exposed to atmospheric pressure, said pressure-sensing diaphragm being operably coupled to the clutch plate for moving the clutch plate up and down within the cap handle;
a second set of clutch teeth provided on the clutch plate for engaging and disengaging with the first set of clutch teeth provided on the cap body so that rotation of the cap handle will be either effective or ineffective to rotate the cap body depending upon the pressure differential sensed by the pressure-sensing diaphragm;
said clutch plate having a post thereon that engages with the cap handle to limit the upward movement of the clutch plate when the second set of clutch teeth provided on the clutch plate are disengaged from the first set of clutch teeth provided on the cap body;
and said post that engages with the cap handle having an indicator surface thereon that is visible to the user through the window opening provided in the cap handle to indicate that the second set of clutch teeth is not engaged with the first set of clutch teeth so that the user is informed that turning the handle will not rotate the cap body unless an implement is inserted through the window opening to manually engage the second set of clutch teeth provided on the clutch plate with the first set of clutch teeth provided on the cap body irrespective of the pressure differential between the fuel vapor pressure and the atmospheric pressure.