Abstract:
A device for a fuel vapor pressure management apparatus of a fuel system supplying fuel to an internal combustion engine. The fuel vapor pressure management apparatus performs leak detection on a headspace of the fuel system, performs excess negative pressure relief of the headspace, and performs excess positive pressure relief of the headspace. The device includes a housing defining an interior chamber, and a poppet movable along an axis. The poppet includes a perimeter that has a plurality of notches. Interposed between each adjacent pair of the notches is a corresponding tab, and each tab includes a radially outer edge that is adapted to cooperate with the housing so as to guide movement of the poppet that is associated with the performing excess positive pressure relief.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 60/298,255, filed Jun. 14, 2001, U.S. Provisional Application No. 60/310,750, filed Aug. 8, 2001, and the U.S. Provisional Application identified as “System For Fuel Vapor Pressure Handling,” Attorney Docket No. 051481-5093-PR, filed May 30, 2002, all of which are incorporated by reference herein in their entirety.  
           [0002]    Related co-pending applications filed concurrently herewith are identified as “ Fuel System Including an Apparatus for Fuel Vapor Pressure Management ,” Attorney Docket No. 051481-5093, filed on Jun. 14, 2002 ; “Apparatus for Fuel Vapor Management ,” Attorney Docket No. 051481-5094, filed on Jun. 14, 2002 ; “Method for Fuel Vapor Management ,” Attorney Docket No. 051481-5095, filed on Jun. 14, 2002 ; “Apparatus and Method for Calibrating a Fuel Vapor Pressure Management Apparatus ,” Attorney Docket No. 051481-5097, filed on Jun. 14, 2002 ; “Bi-directional Flow Seal for a Fuel Vapor Pressure Management Apparatus ,” Attorney Docket No. 051481-5100, filed on Jun. 14, 2002 ; “A Method of Managing Fuel Vapor Pressure in a Fuel System ,” Attorney Docket No. 051481-5104, filed on Jun. 14, 2002 ; “Apparatus and Method for Preventing Resonance in a Fuel Vapor Pressure Management Apparatus ,” Attorney Docket No. 051481-5107, filed on Jun. 14, 2002; all of which are incorporated by reference herein in their entirety.  
         FIELD OF THE INVENTION  
         [0003]    A fuel vapor pressure management apparatus and method that manages pressure and detects leaks in a fuel system. In particular, a fuel vapor pressure management apparatus and method that vents positive pressure, vents excess negative pressure, and uses evaporative natural vacuum to perform a leak diagnostic.  
         BACKGROUND OF THE INVENTION  
         [0004]    Conventional fuel systems for vehicles with internal combustion engines can include a canister that accumulates fuel vapor from a headspace of a fuel tank. If there is a leak in the fuel tank, the canister, or any other component of the fuel system, fuel vapor could escape through the leak and be released into the atmosphere instead of being accumulated in the canister. Various government regulatory agencies, e.g., the U.S. Environmental Protection Agency and the Air Resources Board of the California Environmental Protection Agency, have promulgated standards related to limiting fuel vapor releases into the atmosphere. Thus, it is believed that there is a need to avoid releasing fuel vapors into the atmosphere, and to provide an apparatus and a method for performing a leak diagnostic, so as to comply with these standards.  
           [0005]    In such conventional fuel systems, excess fuel vapor can accumulate immediately after engine shutdown, thereby creating a positive pressure in the fuel vapor pressure management system. Excess negative pressure in closed fuel systems can occur under some operating and atmospheric conditions, thereby causing stress on components of these fuel systems. Thus, it is believed that there is a need to vent, or “blow-off,” the positive pressure, and to vent, or “relieve,” the excess negative pressure. Similarly, it is also believed to be desirable to relieve excess positive pressure that can occur during tank refueling. Thus, it is believed that there is a need to allow air, but not fuel vapor, to exit the tank at high flow rates during tank refueling. This is commonly referred to as onboard refueling vapor recovery (ORVR).  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a device for a fuel vapor pressure management apparatus of a fuel system supplying fuel to an internal combustion engine. The fuel vapor pressure management apparatus performs leak detection on a headspace of the fuel system, performs excess negative pressure relief of the headspace, and performs excess positive pressure relief of the headspace. The device includes a housing defining an interior chamber, and a poppet movable along an axis. The poppet includes a perimeter that has a plurality of notches. Interposed between each adjacent pair of the notches is a corresponding tab, and each tab includes a radially outer edge that is adapted to cooperate with the housing so as to guide movement of the poppet that is associated with the performing excess positive pressure relief.  
           [0007]    The present invention also provides a device for a fuel vapor pressure management apparatus of a fuel system supplying fuel to an internal combustion engine. The fuel vapor pressure management apparatus performs leak detection on a headspace of the fuel system, performs excess negative pressure relief of the headspace, and performs excess positive pressure relief of the headspace. The device includes a poppet movable along an axis between a first position, a second position, and an intermediate position between the first and second positions. The poppet is adapted to cooperatively engage a seal such that a first arrangement includes the poppet in the second position and the seal in a substantially symmetrically deformed configuration, a second arrangement includes the poppet in the second position and the seal in a generally asymmetrically deformed configuration, a third arrangement includes the poppet in the first position and the seal in an undeformed configuration, and a fourth arrangement includes the poppet in the intermediate position and the seal in the substantially symmetrically deformed configuration. The first arrangement performs the leak detection, the second arrangement performs the excess negative pressure relief, the third arrangement performs the excess positive pressure relief; and the fourth arrangement substantially prevents fluid flow through the seal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention.  
         [0009]    [0009]FIG. 1 is a schematic illustration of a fuel system, in accordance with the detailed description of the preferred embodiment, which includes a fuel vapor pressure management apparatus.  
         [0010]    [0010]FIG. 2A is a first cross sectional view of the fuel vapor pressure management apparatus illustrated in FIG. 1.  
         [0011]    [0011]FIG. 2B are detail views of a seal for the fuel vapor pressure management apparatus shown in FIG. 2A.  
         [0012]    [0012]FIG. 2C is a second cross sectional view of the fuel vapor pressure management apparatus illustrated in FIG. 1.  
         [0013]    [0013]FIG. 3A is a schematic illustration of a leak detection arrangement of the fuel vapor pressure management apparatus illustrated in FIG. 1.  
         [0014]    [0014]FIG. 3B is a schematic illustration of a vacuum relief arrangement of the fuel vapor pressure management apparatus illustrated in FIG. 1.  
         [0015]    [0015]FIG. 3C is a schematic illustration of a pressure blow-off arrangement of the fuel vapor pressure management apparatus illustrated in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    As it is used in this description, “atmosphere” generally refers to the gaseous envelope surrounding the Earth, and “atmospheric” generally refers to a characteristic of this envelope.  
         [0017]    As it is used in this description, “pressure” is measured relative to the ambient atmospheric pressure. Thus, positive pressure refers to pressure greater than the ambient atmospheric pressure and negative pressure, or “vacuum,” refers to pressure less than the ambient atmospheric pressure.  
         [0018]    Also, as it is used in this description, “headspace” refers to the variable volume within an enclosure, e.g. a fuel tank, that is above the surface of the liquid, e.g., fuel, in the enclosure. In the case of a fuel tank for volatile fuels, e.g., gasoline, vapors from the volatile fuel may be present in the headspace of the fuel tank.  
         [0019]    Referring to FIG. 1, a fuel system  10 , e.g., for an engine (not shown), includes a fuel tank  12 , a vacuum source  14  such as an intake manifold of the engine, a purge valve  16 , a charcoal canister  18 , and a fuel vapor pressure management apparatus  20 .  
         [0020]    The fuel vapor pressure management apparatus  20  performs a plurality of functions including signaling  22  that a first predetermined pressure (vacuum) level exists, “vacuum relief” or relieving negative pressure  24  at a value below the first predetermined pressure level, and “pressure blow-off” or relieving positive pressure  26  above a second pressure level.  
         [0021]    Other functions are also possible. For example, the fuel vapor pressure management apparatus  20  can be used as a vacuum regulator, and in connection with the operation of the purge valve  16  and an algorithm, can perform large leak detection on the fuel system  10 . Such large leak detection could be used to evaluate situations such as when a refueling cap  12   a  is not replaced on the fuel tank  12 .  
         [0022]    It is understood that volatile liquid fuels, e.g., gasoline, can evaporate under certain conditions, e.g., rising ambient temperature, thereby generating fuel vapor. In the course of cooling that is experienced by the fuel system  10 , e.g., after the engine is turned off, a vacuum is naturally created by cooling the fuel vapor and air, such as in the headspace of the fuel tank  12  and in the charcoal canister  18 . According to the present description, the existence of a vacuum at the first predetermined pressure level indicates that the integrity of the fuel system  10  is satisfactory. Thus, signaling  22  is used to indicate the integrity of the fuel system  10 , i.e., that there are no appreciable leaks. Subsequently, the vacuum relief  24  at a pressure level below the first predetermined pressure level can protect the fuel tank  12 , e.g., can prevent structural distortion as a result of stress caused by vacuum in the fuel system  10 .  
         [0023]    After the engine is turned off, the pressure blow-off  26  allows excess pressure due to fuel evaporation to be vented, and thereby expedite the occurrence of vacuum generation that subsequently occurs during cooling. The pressure blow-off  26  allows air within the fuel system  10  to be released while fuel vapor is retained. Similarly, in the course of refueling the fuel tank  12 , the pressure blow-off  26  allows air to exit the fuel tank  12  at a high rate of flow.  
         [0024]    At least two advantages are achieved in accordance with a system including the fuel vapor pressure management apparatus  20 . First, a leak detection diagnostic can be performed on fuel tanks of all sizes. This advantage is significant in that previous systems for detecting leaks were not effective with known large volume fuel tanks, e.g., 100 gallons or more. Second, the fuel vapor pressure management apparatus  20  is compatible with a number of different types of the purge valve, including digital and proportional purge valves.  
         [0025]    [0025]FIG. 2A shows an embodiment of the fuel vapor pressure management apparatus  20  that is particularly suited to being mounted on the charcoal canister  18 . The fuel vapor pressure management apparatus  20  includes a housing  30  that can be mounted to the body of the charcoal canister  18  by a “bayonet” style attachment  32 . A seal (not shown) can be interposed between the charcoal canister  18  and the fuel vapor pressure management apparatus  20  so as to provide a fluid tight connection. The attachment  32 , in combination with a snap finger  33 , allows the fuel vapor pressure management apparatus  20  to be readily serviced in the field. Of course, different styles of attachments between the fuel vapor pressure management apparatus  20  and the body of the charcoal canister  18  can be substituted for the illustrated bayonet attachment  32 . Examples of different attachments include a threaded attachment, and an interlocking telescopic attachment. Alternatively, the charcoal canister  18  and the housing  30  can be bonded together (e.g., using an adhesive), or the body of the charcoal canister  18  and the housing  30  can be interconnected via an intermediate member such as a rigid pipe or a flexible hose.  
         [0026]    The housing  30  defines an interior chamber  31  and can be an assembly of a first housing part  30   a  and a second housing part  30   b . The first housing part  30   a  includes a first port  36  that provides fluid communication between the charcoal canister  18  and the interior chamber  31 . The second housing part  30   b  includes a second port  38  that provides fluid communication, e.g., venting, between the interior chamber  31  and the ambient atmosphere. A filter (not shown) can be interposed between the second port  38  and the ambient atmosphere for reducing contaminants that could be drawn into the fuel vapor pressure management apparatus  20  during the vacuum relief  24  or during operation of the purge valve  16 .  
         [0027]    In general, it is desirable to minimize the number of housing parts to reduce the number of potential leak points, i.e., between housing pieces, which must be sealed.  
         [0028]    An advantage of the fuel vapor pressure management apparatus  20  is its compact size. The volume occupied by the fuel vapor pressure management apparatus  20 , including the interior chamber  31 , is less than all other known leak detection devices, the smallest of which occupies more than 240 cubic centimeters. That is to say, the fuel vapor pressure management apparatus  20 , from the first port  36  to the second port  38  and including the interior chamber  31 , occupies less than 240 cubic centimeters. In particular, the fuel vapor pressure management apparatus  20  occupies a volume of less than 100 cubic centimeters. This size reduction over known leak detection devices is significant given the limited availability of space in contemporary automobiles.  
         [0029]    A pressure operable device  40  can separate the interior chamber  31  into a first portion  31   a  and a second portion  31   b . The first portion  31   a  is in fluid communication with the charcoal canister  18  through the first port  36 , and the second portion  31   b  is in fluid communication with the ambient atmosphere through the second port  38 .  
         [0030]    The pressure operable device  40  includes a poppet  42 , a seal  50 , and a resilient element  60 . During the signaling  22 , the poppet  42  and the seal  50  cooperatively engage one another to prevent fluid communication between the first and second ports  36 , 38 . During the vacuum relief  24 , the poppet  42  and the seal  50  cooperatively engage one another to permit restricted fluid flow from the second port  38  to the first port  36 . During the pressure blow-off  26 , the poppet  42  and the seal  50  disengage one another to permit substantially unrestricted fluid flow from the first port  36  to the second port  38 .  
         [0031]    The pressure operable device  40 , with its different arrangements of the poppet  42  and the seal  50 , may be considered to constitute a bi-directional check valve. That is to say, under a first set of conditions, the pressure operable device  40  permits fluid flow along a path in one direction, and under a second set of conditions, the same pressure operable device  40  permits fluid flow along the same path in the opposite direction. The volume of fluid flow during the pressure blow-off  26  may be three to ten times as great as the volume of fluid flow during the vacuum relief  24 .  
         [0032]    The pressure operable device  40  operates without an electromechanical actuator, such as a solenoid that is used in a known leak detection device to controllably displace a fluid flow control valve. Thus, the operation of the pressure operable device  40  can be controlled exclusively by the pressure differential between the first and second ports  36 , 38 . Preferably, all operations of the pressure operable device  40  are controlled by fluid pressure signals that act on one side, i.e., the first port  36  side, of the pressure operable device  40 .  
         [0033]    The pressure operable device  40  also operates without a diaphragm. Such a diaphragm is used in the known leak detection device to sub-partition an interior chamber and to actuate the flow control valve. Thus, the pressure operable device  40  exclusively separates, and then only intermittently, the interior chamber  31 . That is to say, there are at most two portions of the interior chamber  31  that are defined by the housing  30 .  
         [0034]    The poppet  42  is preferably a low density, substantially rigid disk through which fluid flow is prevented. The poppet  42  can be flat or formed with contours, e.g., to enhance rigidity or to facilitate interaction with other components of the pressure operable device  40 .  
         [0035]    The poppet  42  can have a generally circular form that includes alternating tabs  44  and recesses  46  around the perimeter of the poppet  42 . The tabs  44  can center the poppet  42  within the second housing part  30   b , and guide movement of the poppet  42  along an axis A. The recesses  46  can provide a fluid flow path around the poppet  42 , e.g., during the vacuum relief  24  or during the pressure blow-off  26 . A plurality of alternating tabs  44  and recesses  46  are illustrated, however, there could be any number of tabs  44  or recesses  46 , including none, e.g., a disk having a circular perimeter. Of course, other forms and shapes may be used for the poppet  42 .  
         [0036]    The poppet  42  can be made of any metal (e.g., aluminum), polymer (e.g., nylon), or another material that is impervious to fuel vapor, is low density, is substantially rigid, and has a smooth surface finish. The poppet  42  can be manufactured by stamping, casting, or molding. Of course, other materials and manufacturing techniques may be used for the poppet  42 .  
         [0037]    The seal  50  can have an annular form including a bead  52  and a lip  54 . The bead  52  can be secured between and seal the first housing part  30   a  with respect to the second housing part  30   b . The lip  54  can project radially inward from the bead  52  and, in its undeformed configuration, i.e., as-molded or otherwise produced, project obliquely with respect to the axis A. Thus, preferably, the lip  54  has the form of a hollow frustum. The seal  50  can be made of any material that is sufficiently elastic to permit many cycles of flexing the seal  50  between undeformed and deformed configurations.  
         [0038]    Preferably, the seal  50  is molded from rubber or a polymer, e.g., nitrites or fluorosilicones. More preferably, the seal has a stiffness of approximately 50 durometer (Shore A), and is self-lubricating or has an anti-friction coating, e.g., polytetrafluoroethylene.  
         [0039]    [0039]FIG. 2B shows an exemplary embodiment of the seal  50 , including the relative proportions of the different features. Preferably, this exemplary embodiment of the seal  50  is made of Santoprene 123-40.  
         [0040]    The resilient element  60  biases the poppet  42  toward the seal  50 . The resilient element  60  can be a coil spring that is positioned between the poppet  42  and the second housing part  30   b . Preferably, such a coil spring is centered about the axis A.  
         [0041]    Different embodiments of the resilient element  60  can include more than one coil spring, a leaf spring, or an elastic block. The different embodiments can also include various materials, e.g., metals or polymers. And the resilient element  60  can be located differently, e.g., positioned between the first housing part  30   a  and the poppet  42 .  
         [0042]    It is also possible to use the weight of the poppet  42 , in combination with the force of gravity, to urge the poppet  42  toward the seal  50 . As such, the biasing force supplied by the resilient element  60  could be reduced or eliminated.  
         [0043]    The resilient element  60  provides a biasing force that can be calibrated to set the value of the first predetermined pressure level. The construction of the resilient element  60 , in particular the spring rate and length of the resilient member, can be provided so as to set the value of the second predetermined pressure level.  
         [0044]    A switch  70  can perform the signaling  22 . Preferably, movement of the poppet  42  along the axis A actuates the switch  70 . The switch  70  can include a first contact fixed with respect to a body  72  and a movable contact  74 . The body  72  can be fixed with respect to the housing  30 , e.g., the first housing part  30   a , and movement of the poppet  42  displaces movable contact  74  relative to the body  72 , thereby closing or opening an electrical circuit in which the switch  70  is connected. In general, the switch  70  is selected so as to require a minimal actuation force, e.g., 50 grams or less, to displace the movable contact  74  relative to the body  72 .  
         [0045]    Different embodiments of the switch  70  can include magnetic proximity switches, piezoelectric contact sensors, or any other type of device capable of signaling that the poppet  42  has moved to a prescribed position or that the poppet  42  is exerting a prescribed force on the movable contact  74 .  
         [0046]    Referring now to FIG. 2C, there is shown an alternate embodiment of the fuel vapor pressure management apparatus  20 ′. As compared to FIG. 2A, the fuel vapor pressure management apparatus  20 ′ provides an alternative second housing part  30   b ′ and an alternate poppet  42 ′. Otherwise, the same reference numbers are used to identify similar parts in the two embodiments of the fuel vapor pressure management apparatus  20  and  20 ′.  
         [0047]    The second housing part  30   b ′ includes a wall  300  projecting into the chamber  31  and surrounding the axis A. The poppet  42 ′ includes at least one corrugation  420  that also surrounds the axis A. The wall  300  and the at least one corrugation  420  are sized and arranged with respect to one another such that the corrugation  420  telescopically receives the wall  300  as the poppet  42 ′ moves along the axis A, i.e., to provide a dashpot type structure. Preferably, the wall  300  and the at least one corrugation  420  are right-circle cylinders.  
         [0048]    The wall  300  and the at least one corrugation  420  cooperatively define a sub-chamber  310  within the chamber  31 ′. Movement of the poppet  42 ′ along the axis A causes fluid displacement between the chamber  31 ′ and the sub-chamber  310 . This fluid displacement has the effect of damping resonance of the poppet  42 ′. A metering aperture (not show) could be provided to define a dedicated flow channel for the displacement of fluid between the chamber  31 ′ and the sub-chamber  310 ′.  
         [0049]    As it is shown in FIG. 2C, the poppet  42 ′ can include additional corrugations that can enhance the rigidity of the poppet  42 ′, particularly in the areas at the interfaces with the seal  50  and the resilient element  60 .  
         [0050]    The signaling  22  occurs when vacuum at the first predetermined pressure level is present at the first port  36 . During the signaling  22 , the poppet  42  and the seal  50  cooperatively engage one another to prevent fluid communication between the first and second ports  36 , 38 .  
         [0051]    The force created as a result of vacuum at the first port  36  causes the poppet  42  to be displaced toward the first housing part  30   a . This displacement is opposed by elastic deformation of the seal  50 . At the first predetermined pressure level, e.g., one inch of water vacuum relative to the atmospheric pressure, displacement of the poppet  42  will actuate the switch  70 , thereby opening or closing an electrical circuit that can be monitored by an electronic control unit  74 . As vacuum is released, i.e., the pressure at the first port  36  rises above the first predetermined pressure level, the elasticity of the seal  50  pushes the poppet  42  away from the switch  70 , thereby resetting the switch  70 .  
         [0052]    During the signaling  22 , there is a combination of forces that act on the poppet  42 , i.e., the vacuum force at the first port  36  and the biasing force of the resilient element  60 . This combination of forces moves the poppet  42  along the axis A to a position that deforms the seal  50  in a substantially symmetrical manner. This arrangement of the poppet  42  and seal  50  are schematically indicated in FIG. 3A. In particular, the poppet  42  has been moved to its extreme position against the switch  70 , and the lip  54  has been substantially uniformly pressed against the poppet  42  such that there is, preferably, annular contact between the lip  54  and the poppet  42 .  
         [0053]    In the course of the seal  50  being deformed during the signaling  22 , the lip  54  slides along the poppet  42  and performs a cleaning function by scraping-off any debris that may be on the poppet  42 .  
         [0054]    The vacuum relief  24  occurs as the pressure at the first port  36  further decreases, i.e., the pressure decreases below the first predetermined pressure level that actuates the switch  70 . At some level of vacuum that is below the first predetermined level, e.g., six inches of water vacuum relative to atmosphere, the vacuum acting on the seal  50  will deform the lip  54  so as to at least partially disengage from the poppet  42 .  
         [0055]    During the vacuum relief  24 , it is believed that, at least initially, the vacuum relief  24  causes the seal  50  to deform in an asymmetrical manner. This arrangement of the poppet  42  and seal  50  are schematically indicated in FIG. 3B. A weakened section of the seal  50  could facilitate propagation of the deformation. In particular, as the pressure decreases below the first predetermined pressure level, the vacuum force acting on the seal  50  will, at least initially, cause a gap between the lip  54  and the poppet  42 . That is to say, a portion of the lip  54  will disengage from the poppet  42  such that there will be a break in the annular contact between the lip  54  and the poppet  42 , which was established during the signaling  22 . The vacuum force acting on the seal  50  will be relieved as fluid, e.g., ambient air, flows from the atmosphere, through the second port  38 , through the gap between the lip  54  and the poppet  42 , through the first port  36 , and into the canister  18 .  
         [0056]    The fluid flow that occurs during the vacuum relief  24  is restricted by the size of the gap between the lip  54  and the poppet  42 . It is believed that the size of the gap between the lip  54  and the poppet  42  is related to the level of the pressure below the first predetermined pressure level. Thus, a small gap is all that is formed to relieve pressure slightly below the first predetermined pressure level, and a larger gap is formed to relieve pressure that is significantly below the first predetermined pressure level. This resizing of the gap is performed automatically by the seal  50  in accordance with the construction of the lip  54 , and is believed to eliminate pulsations due to repeatedly disengaging and reengaging the seal  50  with respect to the poppet  42 . Such pulsations could arise due to the vacuum force being relieved momentarily during disengagement, but then building back up as soon as the seal  50  is reengaged with the poppet  42 .  
         [0057]    Referring now to FIG. 3C, the pressure blow-off  26  occurs when there is a positive pressure above a second predetermined pressure level at the first port  36 . For example, the pressure blow-off  26  can occur when the tank  12  is being refueled. During the pressure blow-off  26 , the poppet  42  is displaced against the biasing force of the resilient element  60  so as to space the poppet  42  from the lip  54 . That is to say, the poppet  42  will completely separate from the lip  54  so as to eliminate the annular contact between the lip  54  and the poppet  42 , which was established during the signaling  22 . This separation of the poppet  42  from the seal  50  enables the lip  54  to assume an undeformed configuration, i.e., it returns to its “as-originally-manufactured” configuration. The pressure at the second predetermined pressure level will be relieved as fluid flows from the canister  18 , through the first port  36 , through the space between the lip  54  and the poppet  42 , through the second port  38 , and into the atmosphere.  
         [0058]    The fluid flow that occurs during the pressure blow-off  26  is substantially unrestricted by the space between the poppet  42  and the lip  54 . That is to say, the space between the poppet  42  and the lip  54  presents very little restriction to the fluid flow between the first and second ports  36 , 38 .  
         [0059]    At least four advantages are achieved in accordance with the operations performed by the fuel vapor pressure management apparatus  20 . First, providing a leak detection diagnostic using vacuum monitoring during natural cooling, e.g., after the engine is turned off. Second, providing relief for vacuum below the first predetermined pressure level, and providing relief for positive pressure above the second predetermined pressure level. Third, vacuum relief provides fail-safe purging of the canister  18 . And fourth, the relieving pressure  26  regulates the pressure in the fuel tank  12  during any situation in which the engine is turned off, thereby limiting the amount of positive pressure in the fuel tank  12  and allowing the cool-down vacuum effect to occur sooner.  
         [0060]    While the present invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.