CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 60/166,404, filed Nov. 19, 1999, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a fuel system having an integrated pressure management system that manages pressure and detects leaks in a fuel system. The present invention also relates to fuel system having an integrated pressure management system that performs a leak diagnostic for the headspace in a fuel tank, a canister that collects volatile fuel vapors from the headspace, a purge valve, and all associated hoses. 
     BACKGROUND OF INVENTION 
     In a conventional pressure management system for a vehicle, fuel vapor that escapes from a fuel tank is stored in a canister. If there is a leak in the fuel tank, canister or any other component of the vapor handling system, some fuel vapor could exit through the leak to escape into the atmosphere instead of being stored in the canister. Thus, it is desirable to detect leaks. 
     In such conventional pressure management systems, excess fuel vapor accumulates immediately after engine shutdown, thereby creating a positive pressure in the fuel vapor management system. Thus, it is desirable to vent, or “blow-off,” through the canister, this excess fuel vapor and to facilitate vacuum generation in the fuel vapor management system. Similarly, it is desirable to relieve positive pressure during tank refueling by allowing air to exit the tank at high flow rates. This is commonly referred to as onboard refueling vapor recovery (ORVR). 
     SUMMARY OF THE INVENTION 
     According to the present invention, a sensor or switch signals that a predetermined pressure exists. In particular, the sensor/switch signals that a predetermined vacuum exists. As it is used herein, “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. 
     The present invention is achieved by providing a fuel system for supplying fuel to an internal combustion engine of a vehicle. The fuel system comprises a fuel tank having a headspace; an intake manifold in fluid communication with the headspace; a charcoal canister in fluid communication with the headspace; a purge valve having a first side in fluid communication with the intake manifold and having a second side in fluid communication with charcoal canister and with the headspace; and an integrated pressure management system. The integrated pressure management system includes a housing connected to the charcoal canister and defining an interior chamber; a pressure operable device separating the chamber into a first portion and a second portion, the first portion communicating with the charcoal canister, the second portion communicating with a vent port, the pressure operable device permitting fluid communication between the charcoal canister and the vent port in a first configuration and preventing fluid communication between the charcoal canister and the vent port in a second configuration; and a switch signaling displacement of the pressure operable device in response to negative pressure at a first pressure level in the charcoal canister. 
     The present invention is also achieved by a fuel system that comprises a leak detector sensing negative pressure at a first pressure level in a headspace of a fuel tank, a charcoal canister, and fluid conduits interconnecting the fuel tank and charcoal canister; and a pressure operable device operatively connected to the leak detector, the pressure operable device relieving negative pressure below the first pressure level and relieving positive pressure above a second pressure level. 
     The present invention is further achieved by a method of managing pressure in a fuel system. The fuel system includes a fuel tank, a charcoal canister, and fluid conduits interconnecting the fuel tank and charcoal canister. The method comprises providing an integrated assembly including a switch actuated in response to the pressure and a valve actuated to relieve the pressure; and signaling with the switch a negative pressure at a first pressure level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the present invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention. Like reference numerals are used to identify similar features. 
     FIG. 1 is a schematic illustration showing the operation of an apparatus according to the present invention. 
     FIG. 2 is a cross-sectional view of a first embodiment of the apparatus according to the present invention 
     FIG. 3 is a cross-sectional view of a second embodiment of the apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 an integrated pressure management system (IPMA)  20 . 
     The IPMA  20  performs a plurality of functions including signaling  22  that a first predetermined pressure (vacuum) level exists, relieving pressure  24  at a value below the first predetermined pressure level, relieving pressure  26  above a second pressure level, and controllably connecting  28  the charcoal canister  18  to the ambient atmospheric pressure A. 
     In the course of cooling that is experienced by the fuel system  10 , e.g., after the engine is turned off, a vacuum is created in the tank  12  and charcoal canister  18 . 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 for indicating the integrity of the fuel system  10 , i.e., that there are no leaks. Subsequently relieving pressure  24  at a pressure level below the first predetermined pressure level protects the integrity of the fuel tank  12 , i.e., prevents it from collapsing due to vacuum in the fuel system  10 . Relieving pressure  24  also prevents “dirty” air from being drawn into the tank  12 . 
     Immediately after the engine is turned off, relieving pressure  26  allows excess pressure due to fuel vaporization to blow off, thereby facilitating the desired vacuum generation that occurs during cooling. During blow off, air within the fuel system  10  is released while fuel molecules are retained. Similarly, in the course of refueling the fuel tank  12 , relieving pressure  26  allows air to exit the fuel tank  12  at high flow. 
     While the engine is turned on, controllably connecting  28  the canister  18  to the ambient air A allows confirmation of the purge flow and allows confirmation of the signaling  22  performance. While the engine is turned off, controllably connecting  28  allows a computer for the engine to monitor the vacuum generated during cooling. 
     FIG. 2, shows a first embodiment of the IPMA  20  mounted on the charcoal canister  18 . The IPMA  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  34  is interposed between the charcoal canister  18  and the IPMA  20 . This attachment  32 , in combination with a snap finger  33 , allows the IPMA  20  to be readily serviced in the field. Of course, different styles of attachments between the IPMA  20  and the body  18  can be substituted for the illustrated bayonet attachment  32 , e.g., a threaded attachment, an interlocking telescopic attachment, etc. Alternatively, the body  18  and the housing  30  can be integrally formed from a common homogenous material, can be permanently bonded together (e.g., using an adhesive), or the body  18  and the housing  30  can be interconnected via an intermediate member such as a pipe or a flexible hose. 
     The housing  30  can be an assembly of a main housing piece  30   a  and housing piece covers  30   b  and  30   c . Although two housing piece covers  30   b , 30   c  have been illustrated, it is desirable to minimize the number of housing pieces to reduce the number of potential leak points, i.e., between housing pieces, which must be sealed. Minimizing the number of housing piece covers depends largely on the fluid flow path configuration through the main housing piece  30   a  and the manufacturing efficiency of incorporating the necessary components of the IPMA  20  via the ports of the flow path. Additional features of the housing  30  and the incorporation of components therein will be further described below. 
     Signaling  22  occurs when vacuum at the first predetermined pressure level is present in the charcoal canister  18 . A pressure operable device  36  separates an interior chamber in the housing  30 . The pressure operable device  36 , which includes a diaphragm  38  that is operatively interconnected to a valve  40 , separates the interior chamber of the housing  30  into an upper portion  42  and a lower portion  44 . The upper portion  42  is in fluid communication with the ambient atmospheric pressure through a first port  46 . The lower portion  44  is in fluid communication with a second port  48  between housing  30  the charcoal canister  18 . The lower portion  44  is also in fluid communicating with a separate portion  44   a  via first and second signal passageways  50 , 52 . Orienting the opening of the first signal passageway toward the charcoal canister  18  yields unexpected advantages in providing fluid communication between the portions  44 , 44   a . Sealing between the housing pieces  30   a , 30   b  for the second signal passageway  52  can be provided by a protrusion  38   a  of the diaphragm  38  that is penetrated by the second signal passageway  52 . A branch  52   a  provides fluid communication, over the seal bead of the diaphragm  38 , with the separate portion  44   a . A rubber plug  50   a  is installed after the housing portion  30   a  is molded. The force created as a result of vacuum in the separate portion  44   a  causes the diaphragm  38  to be displaced toward the housing part  30   b . This displacement is opposed by a resilient element  54 , e.g., a leaf spring. The bias of the resilient element  54  can be adjusted by a calibrating screw  56  such that a desired level of vacuum, e.g., one inch of water, will depress a switch  58  that can be mounted on a printed circuit board  60 . In turn, the printed circuit board is electrically connected via an intermediate lead frame  62  to an outlet terminal  64  supported by the housing part  30   c . An O-ring  66  seals the housing part  30   c  with respect to the housing part  30   a . As vacuum is released, i.e., the pressure in the portions  44 , 44   a  rises, the resilient element  54  pushes the diaphragm  38  away from the switch  58 , whereby the switch  58  resets. 
     Pressure relieving  24  occurs as vacuum in the portions  44 , 44   a  increases, i.e., the pressure decreases below the calibration level for actuating the switch  58 . Vacuum in the charcoal canister  18  and the lower portion  44  will continually act on the valve  40  inasmuch as the upper portion  42  is always at or near the ambient atmospheric pressure A. At some value of vacuum below the first predetermined level, e.g., six inches of water, this vacuum will overcome the opposing force of a second resilient element  68  and displace the valve  40  away from a lip seal  70 . This displacement will open the valve  40  from its closed configuration, thus allowing ambient air to be drawn through the upper portion  42  into the lower the portion  44 . That is to say, in an open configuration of the valve  40 , the first and second ports  46 , 48  are in fluid communication. In this way, vacuum in the fuel system  10  can be regulated. 
     Controllably connecting  28  to similarly displace the valve  40  from its closed configuration to its open configuration can be provided by a solenoid  72 . At rest, the second resilient element  68  displaces the valve  40  to its closed configuration. A ferrous armature  74 , which can be fixed to the valve  40 , can have a tapered tip that creates higher flux densities and therefore higher pull-in forces. A coil  76  surrounds a solid ferrous core  78  that is isolated from the charcoal canister  18  by an O-ring  80 . The flux path is completed by a ferrous strap  82  that serves to focus the flux back towards the armature  74 . When the coil  76  is energized, the resultant flux pulls the valve  40  toward the core  78 . The armature  74  can be prevented from touching the core  78  by a tube  84  that sits inside the second resilient element  68 , thereby preventing magnetic lock-up. Since very little electrical power is required for the solenoid  72  to maintain the valve  40  in its open configuration, the power can be reduced to as little as 10% of the original power by pulse-width modulation. When electrical power is removed from the coil  76 , the second resilient element  68  pushes the armature  74  and the valve  40  to the normally closed configuration of the valve  40 . 
     Relieving pressure  26  is provided when there is a positive pressure in the lower portion  44 , e.g., when the tank  12  is being refueled. Specifically, the valve  40  is displaced to its open configuration to provide a very low restriction path for escaping air from the tank  12 . When the charcoal canister  18 , and hence the lower portions  44 , experience positive pressure above ambient atmospheric pressure, the first and second signal passageways  50 , 52  communicate this positive pressure to the separate portion  44   a . In turn, this positive pressure displaces the diaphragm  38  downward toward the valve  40 . A diaphragm pin  39  transfers the displacement of the diaphragm  38  to the valve  40 , thereby displacing the valve  40  to its open configuration with respect to the lip seal  70 . Thus, pressure in the charcoal canister  18  due to refueling is allowed to escape through the lower portion  44 , past the lip seal  70 , through the upper portion  42 , and through the second port  46 . 
     Relieving pressure  26  is also useful for regulating the pressure in fuel tank  12  during any situation in which the engine is turned off. By limiting the amount of positive pressure in the fuel tank  12 , the cool-down vacuum effect will take place sooner. 
     FIG. 3 shows a second embodiment of the present invention that is substantially similar to the first embodiment shown in FIG. 2, except that the first and second signal passageways  50 , 52  have been eliminated, and the intermediate lead frame  62  penetrates a protrusion  38   b  of the diaphragm  38 , similar to the penetration of protrusion  38   a  by the second signal passageway  52 , as shown in FIG.  2 . The signal from the lower portion  44  is communicated to the separate portion  44   a  via a path that extends through spaces between the solenoid  72  and the housing  30 , through spaces between the intermediate lead frame  62  and the housing  30 , and through the penetration in the protrusion  38   b.    
     The present invention has many advantages, including: 
     providing relief for positive pressure above a first predetermined pressure value, and providing relief for vacuum below a second predetermined pressure value. 
     vacuum monitoring with the present invention in its open configuration during natural cooling, e.g., after the engine is turned off, provides a leak detection diagnostic. 
     driving the present invention into its open configuration while the engine is on confirms purge flow and switch/sensor function. 
     vacuum relief provides fail-safe operation of the purge flow system in the event that the solenoid fails with the valve in a closed configuration. 
     integrally packaging the sensor/switch, the valve, and the solenoid in a single unit reduces the number of electrical connectors and improves system integrity since there are fewer leak points, i.e., possible openings in the system. 
     While the 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 invention, as defined in the appended claims and their equivalents thereof. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.
A fuel system supplying fuel to an internal combustion engine of a vehicle. The fuel system includes an integrated pressure management system managing pressure and detecting leaks in the fuel system. The integrated pressure management system also performs a leak diagnostic for the headspace in a fuel tank, a canister that collects volatile fuel vapors from the headspace, a purge valve, and all associated hoses and connections.