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An evaporative emissions control fuel cap system comprises a closure adapted to mate with a fuel tank. The closure includes a passageway formed therein to conduct vapors from the fuel tank to the atmosphere. The closure includes a filter configured to capture hydrocarbons positioned in the passagewa

An evaporative emissions control fuel cap system comprises a closure adapted to mate with a fuel tank. The closure includes a passageway formed therein to conduct vapors from the fuel tank to the atmosphere. The closure includes a filter configured to capture hydrocarbons positioned in the passageway so that fuel vapor flowing from the fuel tank is scrubbed of hydrocarbons before being discharged to the atmosphere.

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The invention claimed is: 1. An evaporative emissions control system comprising a closure structured to mate with and close a fuel tank filler neck, the closure being formed to include a fuel vapor entry port, an atmospheric air entry port, and a fuel vapor-conducting passageway interconnecting the

The invention claimed is: 1. An evaporative emissions control system comprising a closure structured to mate with and close a fuel tank filler neck, the closure being formed to include a fuel vapor entry port, an atmospheric air entry port, and a fuel vapor-conducting passageway interconnecting the fuel vapor entry port and the atmospheric air entry port, a hydrocarbon adsorbing filter unit positioned to lie in the fuel vapor-conducting passageway to adsorb hydrocarbon material entrained in fuel vapor passing from the fuel tank filler neck into the fuel vapor-conducting passageway through the fuel vapor entry port to produce a stream of filtered vapor exiting the fuel vapor-conducting passageway through the atmospheric air entry port, and wherein the fuel vapor-conducting passageway from the fuel vapor entry port extends along a first direction, a second direction generally perpendicular to the first direction and through a passageway portion substantially filled with adsorbent material and extending along a third direction different from the first and second directions wherein fuel vapor passes from the fuel tank into the fuel vapor-conducting passageway through the fuel vapor entry port and produces a stream of filtered vapor exiting the fuel vapor-conducting passageway through the atmospheric air port. 2. The system of claim 1, further comprising an engine intake manifold and wherein a tether is coupled at one end to the closure and at another end to the engine intake manifold to limit movement of the closure relative to the engine intake manifold upon separation of the closure from a fuel tank filler neck adapted to mate with the closure and the tether is a purge hose formed to include a fluid-conducting passageway interconnecting the vapor-discharge channel and the engine intake manifold in fluid communication to conduct the stream of fuel vapor to the engine intake manifold. 3. The system of claim 2, further comprising a cover arranged to overlie the closure and adapted to be gripped and moved by a user to remove the closure from a fuel tank filler neck, the vapor-discharge channel being arranged to extend through an aperture formed in the cover to mate with the tether. 4. The system of claim 3, further comprising a fresh-air filter interposed in a vapor-discharge passageway provided between the closure and the cover and opened to the atmosphere and configured to intercept and filter atmospheric air drawn into the hydrocarbon filter unit through the atmospheric air entry port during operation of the purge means. 5. The system of claim 1, wherein the hydrocarbon adsorbing filter unit includes a group of activated charcoal pellets, an upper sponge filter located above the group of activated charcoal pellets, and a lower sponge filter interposed between the group of activated charcoal pellets and the bottom wall of the lower housing, and the upper and lower sponge filters cooperate to provide means for retaining the activated charcoal pellets in a confined region in the fuel vapor-conducting passageway so that the activated charcoal pellets are unable to escape from the closure through the fuel vapor entry port and the atmospheric entry port during flow of fuel vapor through the fuel vapor-conducting passageway. 6. The system of claim 1, wherein the closure further includes rollover means for closing the fuel vapor entry port formed in the closure to prevent liquid fuel from passing into the fuel vapor-conducting passageway to reach the hydrocarbon adsorbing filter unit during rollover of the closure. 7. The system of claim 1, wherein the closure includes a lower housing configured to mate with the fuel tank filter neck and an upper housing arranged to extend into a container included in the lower housing, the container includes a side wall and a bottom wall coupled to a lower end of the side wall to form an interior region containing the hydrocarbon adsorbing filter unit, the lower housing is formed to include the fuel vapor entry port, the upper housing is formed to include the atmospheric air entry port, and the lower and upper housings cooperate to form the fuel vapor-conducting passageway therebetween. 8. The system of claim 7, wherein the upper housing includes an inner sleeve formed to define the vapor-discharge channel and an outer sleeve arranged to surround the inner sleeve to define a space therebetween containing the hydrocarbon filter unit and to cooperate with the side wall of the container to define a portion of the fuel vapor-conducting passageway therebetween. 9. The system of claim 8, wherein the hydrocarbon adsorbing filter unit includes a group of activated charcoal pellets trapped between an upper sponge filter and a lower sponge filter. 10. The system of claim 8, wherein the lower housing further includes at least one standoff coupled to the bottom wall and arranged to extend upwardly to engage an underside of the hydrocarbon adsorbing filter unit to define a portion of the fuel vapor-conducting passageway between the bottom wall and the hydrocarbon adsorbing filter unit so that fuel vapor admitted into the container can flow around the at least one standoff and then upwardly and through the hydrocarbon adsorbing filter unit to reach the atmospheric air entry port. 11. The system of claim 7, wherein the upper housing includes a top plate formed to include the atmospheric air entry port and arranged to lie in spaced-apart relation to the bottom wall of the container to locate the hydrocarbon adsorbing filter therebetween. 12. The system of claim 11, wherein the hydrocarbon adsorbing filter unit includes a group of activated charcoal pellets trapped between an upper sponge filter and a lower sponge filter. 13. An evaporative emissions control system comprising a closure adapted to mate with and close a fuel tank filler neck, the closure being formed to include a fuel vapor entry port, an atmospheric air entry port, and a fuel vapor-conducting passageway interconnecting the fuel vapor entry port and the atmospheric air entry port, a hydrocarbon adsorbing filter unit positioned to lie in the fuel vapor-conducting passageway to adsorb hydrocarbon material entrained in fuel vapor passing from the fuel tank filler neck into the fuel vapor-conducting passageway through the fuel vapor entry port to produce a stream of filtered vapor exiting the fuel vapor-conducting passageway through the atmospheric air entry port, purge means for applying a purge vacuum to a region in the fuel vapor-conducting passageway interposed between the fuel vapor entry port and the filter unit to draw atmospheric air through the atmospheric air entry port into and through the hydrocarbon adsorbing filter unit to entrain hydrocarbon material adsorbed in the filter unit to produce a stream of fuel vapor containing such hydrocarbon material and moving through a vapor-discharge channel formed in the closure toward an engine intake manifold associated with the closure, an engine intake manifold and wherein the purge means includes a tether coupled at one end to the closure and at another end to the engine intake manifold to limit movement of the closure relative to the engine intake manifold upon separation of the closure from a fuel tank filler neck adapted to mate with the closure and the tether is a purge hose formed to include a fluid-conducting passageway interconnecting the vapor-discharge channel and the engine intake manifold in fluid communication to conduct the stream of fuel vapor to the engine intake manifold, a cover arranged to overlie the closure and adapted to be gripped and moved by a user to remove the closure from a fuel tank filler neck, the vapor-discharge channel being arranged to extend through an aperture formed in the cover to mate with the tether, and wherein the cover is mounted for movement relative to the closure and the tether and further comprising a torque-override system interposed between and coupled to each of the cover and the closure and configured to establish a torque-limited connection between the cover and the closure during installation of the closure on the fuel tank filler neck and a direct-drive connection between the cover and the closure during removal of the closure from the fuel tank filler neck and a fresh-air filter interposed in a space provided between the closure and the cover to cause atmospheric air drawn into the hydrocarbon adsorbing filter unit through the atmospheric air entry port during operation of the purge means to have passed first from the atmosphere into a vapor-discharge passageway formed between the closure and the cover to contain the torque-override system and through the torque-override system and the fresh-air filter. 14. An evaporative emissions control system comprising a closure adapted to mate with and close a fuel tank filler neck, the closure being formed to include a fuel vapor entry port, an atmospheric air entry port, and a fuel vapor-conducting passageway interconnecting the fuel vapor entry port and the atmospheric air entry port, a hydrocarbon adsorbing filter unit positioned to lie in the fuel vapor-conducting passageway to adsorb hydrocarbon material entrained in fuel vapor passing from the fuel tank filler neck into the fuel vapor-conducting passageway through the fuel vapor entry port to produce a stream of filtered vapor exiting the fuel vapor-conducting passageway through the atmospheric air entry port, purge means for applying a purge vacuum to a region in the fuel vapor-conducting passageway interposed between the fuel vapor entry port and the filter unit to draw atmospheric air through the atmospheric air entry port into and through the hydrocarbon adsorbing filter unit to entrain hydrocarbon material adsorbed in the hydrocarbon adsorbing filter unit to produce a stream of fuel vapor containing such hydrocarbon material and moving through a vapor-discharge channel formed in the closure toward an engine intake manifold associated with the closure, and further comprising a cover arranged to overlie the closure and adapted to be gripped and moved by a user to remove the closure from a fuel tank filler neck and a fresh-air filter interposed in a vapor-discharge passageway provided between the closure and the cover and opened to the atmosphere and configured to intercept and filter atmospheric air drawn into the hydrocarbon adsorbing filter unit through the atmospheric air entry port during operation of the purge means. 15. The system of claim 14, wherein the fresh-air filter is formed to include a hole and the vapor-discharge channel is arranged to extend upwardly through the hole. 16. The system of claim 14, wherein the closure includes a top wall formed to include the atmospheric air entry port and the fresh-air filter is arranged to lie on the top wall to cover the atmospheric air entry port to cause fluid exiting and entering the atmospheric air entry port to pass through the fresh-air filter. 17. The system of claim 14, wherein the closure includes an upper housing formed to include the atmospheric air entry port and a downstream portion of the fuel vapor-conducting passageway containing the hydrocarbon adsorbing filter unit and communicating with the atmospheric air entry port, and the closure further includes a lower housing including a side wall formed to include the fuel vapor entry port and arranged to cooperate with the upper housing to form an upstream portion of the fuel vapor-conducting passageway surrounding the hydrocarbon adsorbing filter unit and a bottom wall lying in spaced-apart relation to the hydrocarbon adsorbing filter unit to define a midstream portion of the fuel vapor-conducting passageway underlying the hydrocarbon adsorbing filter unit and interconnecting the upstream and downstream portions of the fuel vapor-conducting passageway to provide fluid communication therebetween. 18. The system of claim 17, wherein the hydrocarbon adsorbing filter unit includes a group of activated charcoal pellets, an upper sponge filter interposed between the group of activated charcoal pellets and the fresh-air filter, and a lower sponge filter interposed between the group of activated charcoal pellets and the bottom wall of the lower housing. 19. The system of claim 17, wherein the upper housing includes a top wall formed to include the atmospheric air entry port and arranged to support the fresh-air filter, the top wall is also formed to include a central aperture, and the upper housing further includes an inner sleeve extending through the central aperture and including a lower portion passing through a central aperture formed in the hydrocarbon adsorbing filter unit to lie in fluid communication with the midstream portion of the fuel vapor-conducting passageway and an upper portion extending through a hole formed in the fresh-air filter and defining the vapor-discharge channel. 20. An evaporative emissions control system comprising a closure adapted to mate with and close a fuel tank filler neck, the closure being formed to include a fuel vapor entry port, an atmospheric air entry port, and a fuel vapor-conducting passageway interconnecting the fuel vapor entry port and the atmospheric air entry port, a hydrocarbon adsorbing filter unit positioned to lie in the fuel vapor-conducting passageway to adsorb hydrocarbon material entrained in fuel vapor passing from the fuel tank filler neck into the fuel vapor-conducting passageway through the fuel vapor entry port to produce a stream of filtered vapor exiting the fuel vapor-conducting passageway through the atmospheric air entry port, purge means for applying a purge vacuum to a region in the fuel vapor-conducting passageway interposed between the fuel vapor entry port and the filter unit to draw atmospheric air through the atmospheric air entry port into and through the filter unit to entrain hydrocarbon material adsorbed in the hydrocarbon adsorbing filter unit to produce a stream of fuel vapor containing such hydrocarbon material and moving through a vapor-discharge channel formed in the closure toward an engine intake manifold associated with the closure, and wherein the purge means further includes a valve seat associated with the vapor-discharge channel, a purge hose coupled to the vapor-discharge channel at one end and adapted to be coupled to an engine intake manifold at another end, and a vacuum-actuated regulator mounted for movement from a normally closed position engaging the valve seat to block flow of fuel vapor from the hydrocarbon adsorbing filter unit through the purge hose toward the engine intake manifold and to an opened position disengaging the valve seat to allow flow of fuel vapor laden with hydrocarbon material separated from the hydrocarbon adsorbing filter unit through the purge hose upon exposure of the vapor-discharge channel to a purge vacuum communicated by the purge hose. 21. The system of claim 20, wherein the hydrocarbon adsorbing filter unit is formed to include a central aperture and the vapor-discharge channel is arranged to extend downwardly through the central aperture to cause the hydrocarbon adsorbing filter unit to surround a portion of the vacuum-actuated regulator. 22. An evaporative emissions control system comprising a closure structured to mate with and close an open mouth of a filler neck for a fuel tank, the closure including a fuel vapor entry port adapted for communication with fuel vapor within the fuel tank when the closure is mated with the filler neck and a vapor discharge channel in communication with the fuel vapor entry port and adapted to vent vapor through the closure, the fuel vapor entry port and the discharge channel together defining a vapor passageway through the closure, the fuel vapor-conducting passageway extending along a first direction, a second direction generally perpendicular to the first direction and through a passageway portion substantially filled with adsorbent material and extending along a third direction generally parallel to the first direction, and a hydrocarbon adsorbing filter in the vapor passageway so that fuel vapor passing along the third direction is filtered before exiting the vapor passageway. 23. The system of claim 22, wherein the closure comprises a lower housing and an upper housing, the lower housing comprising a container having a side wall, the upper housing comprising an outer sleeve arranged to extend into the container and formed to define a vapor chamber between the outer sleeve and the side wall. 24. The system of claim 23, wherein the upper housing further comprises an inner sleeve surrounded by the outer sleeve and formed to define the vapor discharge channel, the inner sleeve and the outer sleeve are formed to define a hydrocarbon adsorbing filter bed storage area therebetween, and the filter is located in the hydrocarbon adsorbing filter bed storage area. 25. The system of claim 24, wherein the upper housing includes a top plate coupled to an upper end of the outer sleeve and an upper end of the inner sleeve and the top plate is formed to include an atmospheric air entry port adapted to conduct air from the atmosphere into the hydrocarbon adsorbing filter bed storage area to reach the filter. 26. The system of claim 24, wherein the filter comprises an upper sponge filter arranged to surround the inner sleeve and lie at an upper end of the hydrocarbon adsorbing filter bed storage area, a lower sponge filter arranged to lie at a lower end of the hydrocarbon adsorbing filter bed storage area, and a group of activated charcoal pellets located in a space between the upper and lower sponge filters. 27. The system of claim 24, wherein the lower housing includes a bottom wall coupled to a lower end of the side wall to form an interior region and a plurality of upwardly projecting standoffs coupled to the bottom wall and configured to support a lower filter arranged to lie at a lower end of the hydrocarbon adsorbing filter bed storage area, and the plurality of standoffs and the lower filter are spaced to form a chamber therebetween. 28. The system of claim 24, further comprising a purge hose coupled to the vapor discharge channel and adapted to channel vapor from the closure to an intake manifold of an engine. 29. The system of claim 22, further comprising means for tethering the closure to an associated engine coupled to the vapor discharge channel, the means for tethering being formed to provide a vapor path from the filter means to an intake manifold of the engine. 30. The system of claim 22, further comprising a purge hose coupled to the vapor discharge channel and adapted to channel vapor from the closure to an intake manifold of an engine. 31. An evaporative emissions control system comprising a closure adapted to mate with and close an open mouth of a filler neck for a fuel tank, the closure including a fuel vapor entry port adapted for communication with fuel vapor within the fuel tank when the closure is mated with the filler neck, the closure comprises a lower housing and an upper housing, the lower housing comprising a container having a side wall, the upper housing comprising an outer sleeve arranged to extend into the container and formed to define a vapor chamber between the outer sleeve and the side wall, the upper housing further comprises an inner sleeve surrounded by the outer sleeve and formed to define the vapor discharge channel, the inner sleeve and the outer sleeve are formed to define a hydrocarbon filter bed storage area therebetween, and the filter means is located in the hydrocarbon filter bed storage area, a vapor discharge channel in communication with the fuel vapor entry port and adapted to vent vapor through the closure, the fuel vapor entry port and the discharge channel together defining a vapor passageway through the closure, filter means in the vapor passageway for capturing hydrocarbons admitted into the vapor passageway through the fuel vapor entry port, a purge hose coupled to the vapor discharge channel and adapted to channel vapor from the closure to an intake manifold of an engine, and wherein the closure includes a check valve mounted in the vapor passageway, the check valve is movable between an opened position and a closed position, and the check valve is movable in response to a purge vacuum extant in the intake manifold to allow vapor to flow through the filter means and the purge hose for combustion in the engine. 32. The system of claim 31, wherein the check valve is biased to a closed position to prevent vapor flow through the purge hose when the engine is not in operation. 33. A fuel cap system for use with a fuel tank, the system comprising a closure structured to mate with and close an open mouth of the fuel tank, the closure including a passageway adapted for passage of vapors from the fuel tank to the atmosphere, a hydrocarbon adsorbing filter housed in the closure and configured to filter substantially all of the vapors passing from the fuel tank to the atmosphere via the passageway and to capture hydrocarbons passing through the passageway, and wherein the passageway is shaped to cause the vapors to flow along a first direction into the closure, along a second direction different from the first direction to advance toward the hydrocarbon adsorbing filter and then along a third direction different from the first direction and second direction to advance the fuel vapor flow through the hydrocarbon fuel filter. 34. The system of claim 33, wherein the closure comprises an upper housing and a lower housing, the upper housing comprises a top plate, an inner sleeve, and an outer sleeve, the top plate is coupled to the outer sleeve and the inner sleeve at upper ends thereof, the lower housing comprises a cylindrical side wall and a bottom wall coupled to a lower end of the cylindrical side wall, the bottom wall and the cylindrical side wall cooperate to define a container, the upper housing is arranged to extend into the container, the outer sleeve is arranged to surround the inner sleeve to define a chamber therebetween, and the chamber receives and stores hydrocarbon adsorbing filter material. 35. The system of claim 34, wherein the closure further comprises an upper sponge filter arranged to surround the inner sleeve and to lie under the top plate in the chamber and a lower sponge filter arranged to lie above the bottom wall in the chamber, the upper sponge filter and the lower sponge filter are spaced apart from one another, and the hydrocarbon adsorbing filter comprises a group of activated charcoal pellets located in a space between the upper and lower sponge filters. 36. The system of claim 33, further comprising a purge hose coupled to the vapor discharge channel and adapted to channel vapor from the closure to an intake manifold of an engine. 37. A fuel cap system for use with a fuel tank, the system comprising a closure adapted to mate with and close an open mouth of the fuel tank, the closure including a passageway adapted for passage of vapors from the fuel tank to the atmosphere, a hydrocarbon adsorbing filter housed in the closure and configured to capture hydrocarbons passing through the passageway, and a purge hose coupled to the closure and adapted to conduct hydrocarbons captured in the filter to an intake manifold coupled to an engine associated with the fuel tank, and further comprising a check valve positioned in the passageway and mounted for movement between an opened position and a closed position blocking discharge of vapor until a purge vacuum generated in the intake manifold is applied by the purge hose to the hydrocarbon adsorbing filter. 38. An evaporative emissions control fuel cap system comprising a closure structured to mate with a fuel tank filler neck of a fuel tank, the closure comprising an upper housing and a lower housing, the upper housing comprising a top plate, an inner sleeve, and an outer sleeve, the top plate being coupled to the outer sleeve and the inner sleeve at upper ends thereof, the outer sleeve being arranged to surround the inner sleeve to define a chamber therebetween, the lower housing comprising a side wall and a bottom wall coupled to a lower end of the side wall, the bottom wall and the side wall defining a container, the upper housing arranged to extend into the container, a passageway formed in the closure, the passageway being defined between a fuel vapor entry port adapted for communication with fuel vapor in the fuel tank when the closure is in a closed position and a vapor discharge port in communication with the fuel vapor entry port and adapted to conduct vapor from the closure to the atmosphere, and filter means for capturing hydrocarbons passing through the chamber wherein the passageway is shaped to cause the vapors to flow along a first direction into the closure, along a second direction different from the first direction to advance toward the hydrocarbon adsorbing filter and then along a third direction different from the first direction and second direction to advance the fuel vapor flow through the hydrocarbon fuel filter. 39. The system of claim 38, wherein the filter means comprises a hydrocarbon filtering material, the system further comprising a purge hose coupled to the vapor-discharge port and is adapted to conduct vapor from the closure to an intake manifold of an engine. 40. The system of claim 39, wherein hydrocarbons captured in the hydrocarbon adsorbing filtering material are drawn therefrom into the intake manifold under a purge vacuum extant in the intake manifold during engine operation. 41. The system of claim 39, wherein the closure further comprises an upper sponge filter arranged surround the inner sleeve and to lie under the top plate in the chamber and a lower sponge filter arranged to lie above the bottom wall in the chamber, the upper sponge filter and the lower sponge filter are spaced apart to contain the hydrocarbon filtering material therebetween, and the upper and lower sponge filters are adapted to minimize discharge of filtering material from the chamber through the fuel vapor entry port and the vapor discharge port. 42. The system of claim 39, wherein the purge hose acts as a tether to retain the closure in tethered relation to an apparatus containing the fuel tank. 43. An evaporative emissions control fuel cap system comprising a closure adapted to mate with a fuel tank filler neck of a fuel tank, the closure comprising an upper housing and a lower housing, the upper housing comprising a top plate, an inner sleeve, and an outer sleeve, the top plate being coupled to the outer sleeve and the inner sleeve at upper ends thereof, the outer sleeve being arranged to surround the inner sleeve to define a chamber therebetween, the lower housing comprising a side wall and a bottom wall coupled to a lower end of the side wall, the bottom wall and the side wall defining a container, the upper housing arranged to extend into the container, a passageway formed in the closure, the passageway being defined between a fuel vapor entry port adapted for communication with fuel vapor in the fuel tank when the closure is in a closed position and a vapor discharge port in communication with the fuel vapor entry port and adapted to conduct vapor from the closure to the atmosphere, hydrocarbon adsorbing filter means comprising a filtering material for capturing hydrocarbons passing through the chamber, a purge hose coupled to the vapor-discharge port and adapted to conduct vapor from the closure to an intake manifold of an engine, wherein hydrocarbons captured in the filtering material are drawn therefrom into the intake manifold under a purge vacuum extant in the intake manifold during engine operation, and further comprising a check valve mounted in the passageway, the check valve being movable between an opened position and a closed position, the check valve operable to the opened position by means of a purge vacuum applied by the intake manifold, and the check valve providing for discharge of vapor from the hydrocarbon filtering material to the intake manifold. 44. The system of claim 43, wherein the check valve is mounted for movement inside the inner sleeve and the check valve comprises a biasing spring to bias the check valve against a valve seat during periods of nonuse of the engine to block flow of fuel vapor through the purge hose.