Fuel fill vapor recovery system with differential pressure control valve

In a vehicle having a fuel tank that is filled through a fill pipe having a filler neck that is open to atmosphere when a gas cap is removed therefrom for refueling, a vapor recovery system for storing vapor displaced from the fuel tank by liquid fuel from a refueling nozzle inserted in the filler neck comprising, in combination:

• vapor storage canister means;
• a valve assembly having a housing defining first and second chambers separated by a diaphragm carrying a valve member, the housing further defining an internal conduit separate from the first and second chambers and having an end defining a valve seat adjacent the valve member, the valve member being movable with the diaphragm in response to varying differential pressure into and out of engagement with the valve seat to close and open the internal conduit to the first chamber, and spring means biasing the valve member toward engagement with the valve seat;
• a vapor vent conduit communicating a vapor collection region of the fuel tank with the first chamber of the valve assembly;
• a vapor recovery conduit communicating the internal conduit with the vapor storage canister means;
• a vapor recirculation conduit communicating the second chamber of the valve assembly with the filler neck;
• and
• means communicating the first and second chambers of the valve assembly through a restricted orifice to allow equalization of pressure across the diaphragm when the filler neck is closed from the atmosphere by the gas cap so as to allow the spring means to maintain the valve member in engagement with the valve seat to close the internal conduit from the first chamber, the vapor recirculation conduit providing communication of atmospheric pressure to the second chamber when the gas cap is removed from the filler neck with the restricted orifice in the means communicating the first and second chambers allowing the diaphragm to be activated by a differential pressure during refueling so as to move the valve member out of engagement with the valve seat and thus permit relatively unrestricted vapor flow from the fuel tank to the vapor storage canister means, with a portion of the vapor flow from the fuel tank flowing at a controlled rate through the restricted orifice and the recirculation conduit to the filler neck for recirculation by entrainment in incoming liquid fuel.