Evaporative fuel recovery systems are used to recover volatile fuel vapors from the airspace in automotive vehicle fuel tanks. Some evaporative fuel recovery systems use vapor collection canisters filled with an activated carbon mixture. These canisters are in gaseous communication with the vehicle fuel tanks to allow the activated carbon mixture to adsorb fuel vapor from the airspace above the fuel disposed in the tanks. The adsorbed fuel vapor must be purged periodically from the vapor collection canisters to preclude over-saturation of the carbon mixture and to allow additional vapor adsorption to take place. In a number of such systems a purge line connects the canister to the engine intake manifold to allow the intake manifold vacuum to purge the canister by drawing adsorbed fuel from the canister into the engine combustion chambers. A purge valve is disposed between the engine intake manifold and the canister to control and regulate fuel vapor flow from the canister to the intake manifold. Canister purging is therefore accomplished by opening the purge valve to allow the engine intake manifold vacuum to draw air and fuel vapor into the intake manifold from the canister. From the intake manifold the air and fuel vapor are drawn into an engine combustion chamber to be burned. During normal purge operations, an atmosphere vent admits atmospheric air into the canister to replace the air and fuel vapor that the intake manifold has drawn out of the canister.
In some systems, to permit diagnostic leak detection, a vent valve is disposed inline with the atmosphere vent to control the flow of gasses between the canister and the atmosphere. Where a negative pressurization leak detect system is used, the vent valve is closed and the canister evacuated. A vacuum sensor then measures either the rate of vacuum loss, or how much energy is required to maintain the vacuum. Where a positive pressurization leak detect system is used, the vent valve is closed and a sensor measures either the rate of pressure dissipation or the amount of energy required to maintain a given pressure differential.
In systems that include both purge valves and vent valves, the two valves are physically separated. In addition, these systems include separate actuators to operate the respective valves. Therefore, the valves are actuated independently. Each of the following patents includes a system of this type having separate valves and a separate actuator for each valve:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 5,411,004 Busato, et al. 5,437,257 Giacomazzi, et al. 5,450,833 Denz, et al. 5,460,141 Denz, et al. 5,499,614 Busato, et al. 5,542,397 Takahata, et al. 5,560,347 Reddy, et al. 5,562,084 Shimamura 5,562,757 Brun, et al. 5,613,477 Maeda 5,614,665 Curran, et al. 5,623,911 Kiyomiya, et al. 5,629,477 Ito 5,635,630 Dawson et al. ______________________________________
What is needed is an evaporative fuel recovery system that includes both a purge valve and a vent valve, is easier to assemble and operate and requires fewer parts.