Fuel vapor control apparatus

A fuel vapor control apparatus on a motor vehicle fuel tank including a vapor storage canister, a plurality of vent valves on the fuel tank, a plurality of vapor ducts between the vent valves and the vapor storage canister, a plurality of primary liquid traps, and a secondary liquid trap which cooperates with the primary liquid traps in preventing liquid fuel leaking through the vent valves from reaching and contaminating the vapor storage canister. The primary liquid traps are segments of respective ones of the vapor ducts defining standpipes above corresponding ones of the vent valves when the fuel tank is inclined. The primary liquid traps retain liquid fuel leaking through the vent valves and drain by gravity to the fuel tank when the incline of the fuel tank is reduced to zero. The secondary liquid trap is a secondary tank on the top of the fuel tank interposed between the vapor storage canister and the segments of the vapor ducts defining the standpipes. The secondary tank retains liquid fuel which overflows any one of the standpipes and also drains by gravity to the fuel tank when the incline of the fuel tank is reduced to zero.

TECHNICAL FIELD
 This invention relates to a fuel vapor control apparatus on a motor
 vehicle.
 BACKGROUND OF THE INVENTION
 A motor vehicle typically includes a fuel vapor control apparatus which
 exposes a vapor dome in a fuel tank of the vehicle to the atmosphere
 without releasing fuel vapor. The fuel vapor control apparatus commonly
 includes a vapor storage canister, a vent valve exposed to a vapor dome
 above a pool of liquid fuel in the fuel tank, and a vapor duct between the
 vent valve and the storage canister. A mixture of air and fuel vapor
 migrates from the vapor dome to the storage canister where an adsorbent,
 e.g. carbon granules, strips the fuel vapor from the mixture so that only
 uncontaminated air exhausts from the canister to the atmosphere. The fuel
 vapor is retained on the adsorbent until the canister is later purged by
 combustion air. In order to maintain exposure of the vapor dome to the
 atmosphere when the motor vehicle is parked on an incline, e.g. on a
 parking deck ramp or on a hill, it is known to mount a plurality of vent
 valves on the top of the fuel tank at locations which assure that at least
 one of the vent valves always communicates with the vapor dome even though
 others may be submerged in liquid fuel. Because the performance of
 adsorbents degrades when contaminated by liquid fuel, vent valves in fuel
 vapor control apparatuses are typically constructed to automatically close
 when submerged in liquid fuel Even when a vent valve is closed, however,
 there is a risk of leakage of liquid fuel through the vent valve if the
 motor vehicle remains parked on the incline for an extended period.
 Accordingly, the industry continues to seek improved fuel vapor control
 apparatuses which minimize the likelihood of adsorbent contamination by
 liquid fuel leaking through vent valves submerged in liquid fuel.
 SUMMARY OF THE INVENTION
 This invention is a new and improved fuel vapor control apparatus for
 suppressing release to the atmosphere of fuel vapor from a vapor dome in a
 fuel tank of a motor vehicle including a vapor storage canister, a
 plurality of vent valves on the fuel tank, a plurality of vapor ducts
 between the vent valves and the vapor storage canister, a plurality of
 primary liquid traps, and a secondary liquid trap which cooperates with
 the primary liquid traps in preventing liquid fuel leaking through the
 vent valves from reaching and contaminating the vapor storage canister.
 The primary liquid traps are segments of respective ones of the vapor
 ducts defining standpipes above corresponding ones of the vent valves when
 the fuel tank is inclined. The primary liquid traps retain liquid fuel
 leaking through the vent valves and drain by gravity to the fuel tank when
 the incline of the fuel tank is reduced to zero. The secondary liquid trap
 is a secondary tank on the top of the fuel tank interposed between the
 vapor storage canister and the segments of the vapor ducts defining the
 standpipes. The secondary tank retains liquid fuel which overflows any one
 of the standpipes and drains by gravity to the fuel tank through at least
 one of the vapor ducts when the incline of the fuel tank is reduced to
 zero.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to FIGS. 1-2, a motor vehicle fuel tank 10 includes a horizontal
 top 12, a horizontal bottom 14, a pair of vertical end walls 16A, 16B
 perpendicular to a longitudinal centerline of the motor vehicle, and a
 pair of vertical side walls 18A, 18B perpendicular to the end walls. A
 fill pipe 20 is supported on the fuel tank and includes an outboard end 22
 through which liquid fuel is introduced into the fuel tank to form a pool
 24 of liquid fuel having a horizontal surface 26. A vapor dome 28 filled
 with a mixture of air and fuel vapor is defined in the fuel tank above the
 surface 26 of the pool of liquid fuel The fuel tank is supported on a
 motor vehicle body, not shown, such that the vertical end walls 16A, 16B
 tip oppositely up and down when the motor vehicle is inclined in the fore
 and aft direction and the vertical side walls 18A,18B tip oppositely up
 and down when the motor vehicle is inclined laterally.
 A fuel vapor control apparatus 30 according to this invention includes a
 pair of schematically represented vent valves 32A, 32B on the top 12 of
 the fuel tank at diagonally opposite corners thereof Each vent valve 32A,
 32B includes an orifice 34 through which the mixture of air and fuel vapor
 in the vapor dome 28 is conducted out of the fuel tank. The vent valves
 32A, 32B are further constructed to close automatically, e.g. as by a
 schematically represented float 36 below the orifice 34 in each vent
 valve, when the vent valves are submerged in liquid fuel to prevent the
 escape of liquid fuel through the vent valves.
 A flat plastic secondary tank 38 of the fuel vapor control apparatus 30 is
 supported on the top 12 of the fuel tank 10 parallel to the plane of the
 top and at an elevation above the vent valves 32A, 32B. A first primary
 vapor duct 40 includes a longitudinal segment 42 parallel to the vertical
 sides 18A, 18B of the fuel tank and a lateral segment 44 is series with
 the longitudinal segment and parallel to the vertical ends 16A, 16B of the
 fuel tank. A first end 46 of the vapor duct 40 is connected to the vent
 valve 32A. A second end 48 of the vapor duct 40 is connected to the
 secondary tank 38 through an end 50 thereof facing away from the vent
 valve 32A. A second primary vapor duct 52 includes a longitudinal segment
 54 parallel to the vertical sides 18A, 18B of the fuel tank and a lateral
 segment 56 is series with the longitudinal segment and parallel to the
 vertical ends 16A, 16B of the fuel tank. A first end 58 of the vapor duct
 52 is connected to the vent valve 32B. A second end 60 of the vapor duct
 52 is connected to the secondary tank 38 through an end 62 thereof facing
 away from the vent valve 32B.
 A vapor storage canister 64 of the fuel vapor control apparatus 30 is
 supported on the motor vehicle body outside the fuel tank 10 and contains
 an adsorbent such as charcoal granules. The vapor storage canister 64
 communicates with the secondary tank 38 through a secondary vapor duct 66
 which opens into the secondary tank through a top side 68 thereof When the
 motor vehicle is parked with substantially zero fore and aft and lateral
 incline, FIG. 2, each of the vent valves 32A, 32B is open and exposed to
 the vapor dome 28 in the fuel tank. A mixture of air and fuel vapor
 migrates from the vapor dome to the vapor storage canister through the
 primary vapor ducts 40, 52, the secondary tank 38, and the secondary vapor
 duct 66. Fuel vapor is stripped from the mixture by the adsorbent in the
 vapor storage canister so that only uncontaminated air is vented or
 exhausted to the atmosphere. The adsorbent is later purged of retained
 fuel vapor by combustion air.
 When the fuel tank is full and the motor vehicle is parked on an incline,
 one of the vent valves 32A, 32B can be submerged below the surface 26 of
 the pool 24 of liquid fuel in the fuel tank while the other remains
 exposed to the vapor dome. For example, when the motor vehicle and the
 fuel tank thereon are inclined such that the vertical side wall 18A is
 tipped down and the vertical side wall 18B is tipped up, FIG. 3, the vent
 valve 32A constitutes a submerged or "tipped-down" valve and the vent
 valve 32B constitutes an exposed or "tipped-up" valve. In the tipped-down
 vent valve 32A, the float 36 seals closed the orifice 34 to prevent
 leakage of liquid fuel through the tipped down valve into the vapor duct
 40. At the same time, the tipped-up vent valve 32B remains open to expose
 the vapor dome to the atmosphere and to conduct the air and fuel vapor
 mixture from the vapor dome to the storage canister 64 through the vapor
 duct 52.
 With the fuel tank 10 inclined as illustrated in FIG. 3, the lateral
 segment 44 of the primary vapor duct 40 tips upward from the vent valve
 32A through a height dimension "H" and functions as a standpipe into which
 flows any liquid fuel leaking through the tipped down vent valve 32A. The
 lateral segment 44 of the primary vapor duct 40 extends substantially the
 full width of the fuel tank to maximize the height dimension H. The
 standpipe defined by the lateral segment 44 constitutes a primary liquid
 trap between the tipped-down vent valve 32A and the canister 64 when the
 fuel tank is inclined laterally which prevents any liquid fuel leaking
 through the tipped-down valve from migrating to the canister as long as
 the top of the standpipe is higher than the surface 26 of the pool 24 of
 liquid fuel in the fuel tank. The lateral segment 56 of the primary vapor
 duct 52 likewise defines a standpipe constituting a primary liquid trap
 above the other vent valve 32B when the fuel tank is inclined laterally in
 the opposite direction. Similarly, the longitudinal segments 42, 54 of the
 primary vapor ducts 40, 52 define standpipes constituting primary liquid
 traps when respective ones of the vent valves 32A, 32B are tipped down due
 to fore and aft incline of the fuel tank.
 The secondary tank 38 constitutes a secondary liquid trap between the
 canister 64 and each of the aforesaid primary liquid traps. That is, when
 the surface 26 of the pool 24 of liquid fuel in the fuel tank is higher
 than the height dimension H of the standpipe, any liquid fuel overflowing
 the standpipe flows into and is collected or aggregated m the secondary
 tank and thus prevented from flowing into the canister 64 and
 contaminating the adsorbent therein. Because leakage of liquid fuel
 through the tipped-down one of the vent valves 32A, 32B is relatively
 slow, the corresponding primary liquid trap will not overflow into the
 secondary liquid trap until after the motor vehicle has been parked for a
 reasonably extended period. The volume of the secondary tank 38 is
 calculated to aggregate liquid fuel for an additional period which,
 together with the initial period attributable to the primary liquid traps,
 exceeds the total period during which a motor vehicle may reasonably be
 expected to remain parked on an incline and still be in active service.
 As seen best in FIG. 2, the vent valves 32A, 32B are vertically below the
 vapor ducts 40, 52 and the secondary tank 38 when the incline of the fuel
 tank is zero so that liquid fuel aggregated in the standpipes and in the
 secondary tank drains by gravity back into the fuel tank when the motor
 vehicle returns to zero incline. Further, the location of the secondary
 vapor duct 66 above the secondary tank affords protection against a wave
 of liquid fuel being swept into the canister when the motor vehicle
 returns to zero incline.
 A modified fuel vapor storage apparatus 70 on a fuel tank 72 is
 schematically illustrated in FIG. 4 and includes a plurality of four vent
 valves 74A, 74B, 74C, 74D mounted on a top 76 of the fuel tank at the four
 corners thereof A flat plastic secondary tank 78 is supported on the top
 of the fuel tank at an elevation above the vent valves 74A, 74B, 74C, 74D.
 A vapor storage canister 80 is connected to the secondary tank 78 by a
 secondary vapor duct 82 above the secondary tank. A plurality of four
 primary vapor ducts 84A, 84B, 84C, 84D extend between respective ones of
 the vent valves 74A, 74B, 74C, 74D and the secondary tank 78.
 The four primary vapor ducts 84A, 84B, 84C, 84D include respective ones of
 a plurality of four longitudinal segments 86A, 86B, 86C, 86D parallel to
 the longitudinal centerline of the motor vehicle and the vertical sides of
 the fuel tank and a plurality of four lateral segments 88A, 88B, 88C, 88D
 perpendicular to the longitudinal segments. The longitudinal and lateral
 segments of the primary vapor ducts 84A, 84B, 84C, 84D define standpipes
 above respective ones of the vent valves when one or more of the vent
 valves are tipped down and submerged in liquid fuel. When the fuel tank 72
 is inclined, each standpipe constitutes a privy liquid trap between the
 tipped-down ones of the vent valves 74A, 74B, 74C, 74D and the canister 80
 which collects any liquid fuel leaking through the tipped down valves
 except when the top of the standpipe is below the surface of the pool of
 liquid fuel in the fuel tank. In that circumstance, the secondary tank 78
 constitutes a secondary liquid trap between the canister 80 and each of
 the aforesaid standpipes in the primary vapor ducts 84A, 84B, 84C, 84D
 which collects or aggregates liquid fuel overflowing the standpipes. The
 volume of the secondary tank 78 is calculated to aggregate liquid fuel for
 a period which, together with the initial period of liquid aggregation
 attributable to the primary liquid traps, exceeds the total period during
 which a motor vehicle may reasonably be expected to remain parked on an
 incline and still be in active service.