Abstract:
An apparatus, system and method of establishing a threshold for a leak detection test that is performed on a headspace of a fuel system. A fuel vapor pressure management apparatus includes a housing, a pressure operable device, and a sensor. The housing defines an interior chamber. The pressure operable device separates the interior chamber into first and second portions, and includes a poppet that moves along an axis and a seal that is adapted to cooperatively engage the poppet. A first arrangement of the pressure operable device occurs during the leak detection test when the seal is in a first deformed configuration. A sensor detects the first arrangement of the pressure operable device during the leak detection test. And a processor is coupled to the sensor and reduces sensitivity of the fuel vapor pressure management apparatus during the leak detection test.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 60/452,651, filed 7 Mar. 2003, which is incorporated by reference herein in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    A fuel vapor pressure management apparatus that manages pressure and detects leaks in a fuel system. In particular, a fuel vapor pressure management apparatus that vents positive pressure, vents excess negative pressure, and uses evaporative natural vacuum to perform a leak diagnostic.  
         BACKGROUND OF THE INVENTION  
         [0003]    A known fuel system for vehicles with internal combustion engines includes 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.  
           [0004]    It is believed that excess fuel vapor can accumulate immediately after engine shutdown, thereby creating a positive pressure in the fuel 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  
         [0005]    The present invention provides a fuel vapor pressure management apparatus including a housing, a pressure operable device, a switch, an outlet terminal fixed to the housing, and an intermediate lead member. The housing defines an interior chamber and includes first and second ports that communicate with the interior chamber. The pressure operable device separates the chamber into a first portion and a second portion. The first portion communicates with the first port, and the second portion communicates with the second port. The pressure operable device permits fluid communication between the first and second ports in a first configuration, and prevents fluid communication between the first and second ports in a second configuration. The switch signals displacement of the pressure operable device in response to negative pressure at a first pressure level in the first portion of the interior chamber. And the intermediate lead member, which includes a resilient element, electrically couples the switch and the outlet terminal.  
           [0006]    The present invention also provides a fuel system for supplying fuel to an internal combustion engine. The fuel system includes a fuel tank having a headspace, a fuel vapor collection canister, an intake manifold of the internal combustion engine, a purge valve, and a fuel vapor pressure management apparatus. The fuel vapor collection canister has a first side being in fluid communication with the headspace, and has a second side. The purge valve includes an inlet and an outlet. The inlet is in fluid communication with the first side of the fuel vapor collection canister, and the outlet is in fluid communication with the intake manifold. The fuel vapor pressure management apparatus includes a first port that is in fluid communication with the second side of the fuel vapor collection canister, and a second port that is in fluid communication with atmosphere. A first arrangement of the fuel vapor pressure management apparatus occurs when there is a first negative pressure level in the fuel vapor collection canister relative to atmosphere, a second arrangement of the fuel vapor pressure management apparatus permits a first fluid flow from atmosphere to the fuel vapor collection canister when there is a second negative pressure level less than the first negative pressure level, and a third arrangement of the fuel vapor pressure management apparatus permits a second fluid flow from the fuel vapor collection canister to atmosphere when there is a positive pressure in the fuel vapor collection canister relative to atmosphere. The fuel vapor pressure management apparatus includes a housing, a pressure operable device, a switch, an outlet terminal fixed to the housing, and an intermediate lead member. The housing defines an interior chamber that is in fluid communication with the first and second ports. The pressure operable device separates the chamber into a first portion that communicates with the first port, and a second portion that communicates with the second port. The pressure operable device prevents fluid communication between the first and second ports in the first arrangement, and the pressure operable device permits fluid communication between the first and second ports in the second and third arrangements. The switch signals displacement of the pressure operable device in response to the first negative pressure level, and the intermediate lead member, which includes a resilient element, electrically couples the switch and the outlet terminal.  
           [0007]    The present invention further provides a method of assembling a fuel vapor pressure management apparatus. The fuel vapor pressure management apparatus includes a housing that has a main body piece and first and second cover pieces, an outlet terminal that is fixed to the first cover piece, and a cover terminal that is fixed to the second cover piece and electrically coupled to a switch. The method includes attaching the first cover piece to the main body piece such that the outlet terminal projects into the main body piece, positioning in the main body an intermediate lead member, and attaching the second cover piece to the main body piece. The intermediate lead member includes a first end that is contiguously engaged with and is electrically coupled with the outlet terminal, and a second end portion. The attaching the second cover piece to the main body piece causes the cover terminal to project into the main body piece, and the cover terminal engages the second end of the intermediate lead member and resiliently deforms the intermediate lead member.  
       
    
    
     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 showing a fuel system including an integrated pressure management apparatus according to the present invention.  
         [0010]    [0010]FIG. 2 is a cross-sectional view of a preferred embodiment of an integrated pressure management apparatus according to the present invention.  
         [0011]    [0011]FIG. 3 is a perspective view showing components of the integrated pressure management apparatus. Portions of the integrated pressure management apparatus have been omitted to facilitate understanding of the present invention.  
         [0012]    [0012]FIG. 4 is an alternate perspective view of the components shown in FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    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.  
         [0014]    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.  
         [0015]    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.  
         [0016]    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 fuel vapor collection canister  18  (also referred to as a “charcoal canister”), and an integrated pressure management apparatus (IPMA)  20 .  
         [0017]    The IPMA  20  performs a plurality of functions including signaling  22  that a first predetermined pressure (vacuum) level exists in the headspace of the fuel system  10 , relieving pressure  24  (also referred to as relieving excess vacuum) in the headspace of the fuel system  10  at a value below the first predetermined pressure level, and relieving pressure  26  (also referred to as pressure blow-off) in the headspace of the fuel system  10  above a second pressure level. Relieving pressure  24 , 26  refers to the relieving pressure in the fuel vapor collection canister  18  and throughout the headspace of the fuel system  10  relative to the ambient atmospheric pressure A.  
         [0018]    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 fuel vapor collection 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 appreciable 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 .  
         [0019]    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 pressure blow-off, air within the fuel system  10  is released while fuel molecules are retained in the fuel vapor collection canister  18 . Similarly, in the course of refueling the fuel tank  12 , relieving pressure  26  allows air to exit the fuel tank  12  at high flow.  
         [0020]    While the engine is turned on, controllably connecting  28  the fuel vapor collection canister  18  to the ambient air A allows confirmation of the purge flow and allows confirmation of the signaling  22  performance.  
         [0021]    [0021]FIG. 2 shows a preferred embodiment of the IPMA  20  mounted on the fuel vapor collection canister  18 . The IPMA  20  includes a housing  30  that can be mounted to the body of the fuel vapor collection canister  18  by a “bayonet” style attachment  32 . A seal  34  is interposed between the fuel vapor collection canister  18  and the IPMA  20 . This attachment  32 , in combination with a snap finger  36 , 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 fuel vapor collection canister  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 fuel vapor collection canister  18  and the housing  30  can be interconnected via an intermediate member such as a pipe or a flexible hose.  
         [0022]    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.  
         [0023]    Signaling  22  occurs when vacuum at the first predetermined pressure level is present in the fuel vapor collection 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 fuel vapor collection canister  18 .  
         [0024]    The lower portion  44  is also in fluid communicating with a separate portion  44   a  via a signal passageway that extends through spaces in the housing  30 , and through spaces between the intermediate lead frame  62  and the housing  30 . Sealing between the housing pieces  30   a , 30   b  for the signal passageway can be provided by a protrusion  38   a  of the diaphragm  38  that is penetrated by the signal passageway.  
         [0025]    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. A calibrating screw  56  can adjust the bias of the resilient element  54  such that a desired level of vacuum, e.g., a fraction of an inch of water, will depress a switch  58  that can be mounted on a printed circuit board  60 . 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.  
         [0026]    The printed circuit board  60  is electrically interconnected to an outlet terminal  64  that is supported by the housing piece cover  30   c . The electrical interconnect for each conductor can include a cover terminal  60   a  projecting from the printed circuit board  60 , and an intermediate lead member  62  electrically coupling the cover terminal  60   a  with a corresponding outlet terminal  64 . The cover terminal  60   a  can also, similar to the signal passageway, penetrate the protrusion  38   a  of the diaphragm  38 . The intermediate lead member  62  includes a resilient piece that ensures electrical coupling between the cover terminal  60   a  and the outlet terminal  64 .  
         [0027]    Referring additionally to FIGS. 3 and 4, a preferred embodiment of the electrical interconnect allows connection of the outlet terminal  64  to the switch  58  via a set of electrically conductive and resilient intermediate lead members  62 , e.g., two coil springs. The intermediate lead members  62  are resilient in that elastic deformation, which results in reshaping, resizing, or repositioning of the intermediate lead members  62 , is relied upon to grip or forcibly press against the cover and outlet terminals  60   a , 64 .  
         [0028]    A manufacturing assembly sequence in accordance with the present invention will now be described. First, the housing piece cover  30   c  with insert molded outlet terminals  64  is sub-assembled with the main housing piece  30   a . An O-ring  66  can seal the housing piece cover  30   c  with respect to the main housing piece  30   a . The inner ends of the outlet terminals  64  are supported underneath by support walls (not shown) that project inward from the housing cover piece  30   c . Next, electrically conductive, resilient intermediate lead members  62 , e.g., coil springs, are inserted vertically through access holes in the main housing piece  30   a . Preferably, after the resilient intermediate lead members  62  are inserted, the diaphragm  38  can be positioned with respect to the main housing piece  30   a . Then the housing cover piece  30   b  is attached to the sub-assembled combination of the housing piece cover  30   c  and the main housing piece  30   a . In the process of attaching the housing cover piece  30   b , the cover terminal end  60   a  enters into an end, which may be flared, of the intermediate lead member springs  62 . The entry of the terminal end  60   a  acts to expand the intermediate lead member spring  62 . With the housing cover piece  30   b  in its final position, each of the intermediate lead member springs  62  springs may also be compressed to approximately 50% of its free length. Compressing the intermediate lead member springs  62  acts to make a secure electrical connection at the lower end of the spring  62  to the outlet terminals  64 . This electrical connection is believed to be vibration and shock tolerant, when used in a fuel vapor pressure management apparatus that is mounted on a vehicle, since the elastic force supplied by the intermediate lead member springs  62  is continually acting to create the connection.  
         [0029]    According to a preferred embodiment, the intermediate lead member springs  62  may have a generally symmetrical hourglass shape, e.g., flared end portions and a relatively constricted central portion. Such a shape provides at least two advantages. First, the flared end portions help to guide the cover terminals  60   a  into the center of the intermediate lead member springs  62 . Second, the taper of the intermediate lead member springs  62  and the taper of the cover terminals  60   a  interact to effectively wedge the two components securely together. It should also be noted that the intermediate lead member springs  62  may be restrained on all four sides by walls (not shown) that protrude from the main housing piece  30   a.    
         [0030]    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 fuel vapor collection 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., one inch 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.  
         [0031]    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 fuel vapor collection canister  18 , and hence the lower portions  44 , experience positive pressure above ambient atmospheric pressure, the signal passageway communicates 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 fuel vapor collection canister  18 , e.g., 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  58 .  
         [0032]    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.  
         [0033]    The present invention has many advantages, including:  
         [0034]    providing relief for positive pressure above a first predetermined pressure value, and providing relief for vacuum below a second predetermined pressure value.  
         [0035]    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.  
         [0036]    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.  
         [0037]    excluding from the fuel vapor management apparatus an electromechanical actuator that would consume electrical power.  
         [0038]    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.