Abstract:
A sensor arrangement and a method of verificating leaks in a fuel system including an integrated pressure management apparatus. The sensor arrangement comprises a chamber having an interior volume varying in response to fluid pressure in the chamber, a first switch, and a second switch. The chamber includes a diaphragm that is displaceable between a first configuration in response to fluid pressure above a first pressure level, a second configuration in response to fluid pressure below the first pressure level but above a second pressure level, and a third configuration in response to fluid pressure below the second pressure level. The third pressure level being lower than the second pressure level, and the second pressure level being lower than the first pressure level. The first switch is actuated by the diaphragm in the second configuration. And the second switch is actuated by the diaphragm in the third configuration.

Description:
FIELD OF THE INVENTION  
         [0001]    This disclosure relates to a sensor arrangement for an Integrated Pressure Management Apparatus (IPMA) that manages pressure and detects leaks in a fuel system. This disclosure also relates to a sensor arrangement for 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. And this disclosure also relates to controlled duty cycle purging that provides active leak detection recognition by the IPMA while the engine is operating and able to accept evaporative purging.  
         BACKGROUND OF THE INVENTION  
         [0002]    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 as a result of a 0.5 millimeter or greater break in the vapor handling system.  
           [0003]    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  
         [0004]    The present invention provides a sensor arrangement for an integrated pressure management apparatus. The sensor arrangement comprises a chamber having an interior volume varying in response to fluid pressure in the chamber, a first switch, and a second switch. The chamber includes a diaphragm that is displaceable between a first configuration in response to fluid pressure above a first pressure level, a second configuration in response to fluid pressure below the first pressure level, and a third configuration in response to fluid pressure below a second pressure level. The third pressure level being lower than the second pressure level, and the second pressure level being lower than the first pressure level. The first switch is actuated by the diaphragm in the second configuration. And the second switch is actuated by the diaphragm in the third configuration.  
           [0005]    The present invention also provides an integrated pressure management apparatus. The integrated pressure management apparatus comprises a housing defining an interior chamber, a pressure operable device, a first switch, and a second switch. The housing includes the first and second ports that communicate with the interior chamber. The pressure operable device separates the chamber into a first portion that communicates with the first port, a second portion that communicates with the second port, and a third portion that has an interior volume that varies in response to fluid pressure in the first portion. The pressure operable device is displaceable between a first configuration in response to fluid pressure in the third portion above a first pressure level, a second configuration in response to fluid pressure in the third portion below the first pressure level, and a third configuration in response to fluid pressure in the third portion below a second pressure level. The third pressure level is lower than the second pressure level, and the second pressure level is lower than the first pressure level. The first switch is actuated by the pressure operable device in the second configuration. And the second switch is actuated by the pressure operable device in the third configuration  
           [0006]    The present invention further provides a method of detecting detecting leaks in a fuel system for an internal combustion engine that has an engine control unit. The fuel system includes a purge valve and an integrated pressure management apparatus. The integrated pressure appratus has a first switch that is activated at a first pressure level below ambient pressure, a second switch that is activated at a second pressure level below ambient, and a pressure operable device relieving excess vacuum at a third pressure level below ambient. The third pressure level is lower than the second pressure level, and the second pressure level is lower than the first pressure level. The method comprises operating the purge valve according to a first controlled duty cycle purge during operation of the internal combustion engine, indicating a gross leak, operating the purge valve according to a second controlled duty cycle purge during operation of the internal combustion engine, indicating a sealed fuel system, indicating a small leak, and indicating a large leak. The operating the purge valve according to the first controlled duty cycle purge draws a first vacuum between the first and second pressure levels. The operating the purge valve according to the second controlled duty cycle purge draws a second vacuum between the first and second pressure levels. The second vacuum is greater than the first vacuum. A gross leak is indicated if the first switch is not activated. A sealed fuel system is indicated if the first and second switches are activated. A small leak is indicated if the second switch is not activated and the first switch remains activated. And a large leak is indicated if the second switch is not activated and the first switch is intially activated and is subsequently deactivated. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    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.  
         [0008]    [0008]FIG. 1 is a schematic illustration showing the operation of an integrated pressure management system.  
         [0009]    [0009]FIG. 2 is a cross-sectional view of an embodiment of an integrated pressure management system.  
         [0010]    [0010]FIG. 3 is a graph illustrating the operation principles of the integrated pressure management system shown in FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    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 .  
         [0012]    The IPMA  20  performs a plurality of functions including signaling  22  that a first predetermined pressure (vacuum) level exists, relieving negative pressure  24  at a value below a third predetermined pressure level, relieving positive pressure  26  above a second pressure level, and controllably connecting  28  the charcoal canister  18  to the ambient atmospheric pressure A.  
         [0013]    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  by virtue of the IPMA  20  isolating the fuel system  10 . 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 second 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 through a fuel cap (not shown) into the tank  12 .  
         [0014]    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.  
         [0015]    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.  
         [0016]    [0016]FIG. 2, shows a first embodiment of the IPMA  20  that can be directly 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 . 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.  
         [0017]    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.  
         [0018]    Signaling  22  occurs when vacuum at the first and second predetermined pressure levels 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 diaphragm  38  includes a bead  38   a  that provides a seal between the housing pieces  30   a , 30   b . 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 a signal passageway that extends through spaces between a solenoid  72  (as will be further described hereinafter) and the housing  30 , through spaces between an intermediate lead frame  62  (as will be further described hereinafter) and the housing  30 , and through a penetration in a protrusion  38   b  of the diaphragm  38 . Orienting the opening of the signal passageway toward the charcoal canister  18  yields unexpected advantages in providing fluid communication between the portions  44 , 44   a.    
         [0019]    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., one inch of water, will depress a first 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 . The intermediate lead frame  62  penetrates the protrusion  38   b  of the diaphragm  38 . 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 first switch  58 , whereby the first switch  58  resets.  
         [0020]    If, rather than releasing the vacuum, a further vacuum is drawn, as will be further described hereinafter, a second switch  59  is activated, e.g., by contact with either the diaphragm  38  or the resilient element  54 . Thus, activation of the second switch is indicative that the fuel system  10  has achieved an increased vacuum level, i.e., exceeding the calibration level for activating the first switch  58 . The second switch  59  facilitates active on-board leak detection during engine operation, as will be described hereinafter.  
         [0021]    Negative 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  59 . 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, e.g., six inches of water, in excess of the levels for activating the switches  58 , 59 , 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 so as to prevent a collapse in the fuel system  10 .  
         [0022]    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 . A ferrous strap  82  that serves to focus the flux back towards the armature  74  completes the flux path. 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 .  
         [0023]    Relieving positive 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 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 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 .  
         [0024]    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 and fuel tank explosion can be avoided.  
         [0025]    By virtue of the second switch  59  and the controlled duty cycle purging, the IPMA  20  is also able to perform additional functions including leak detection recognition while the engine is operating and able to accept evaporative purging.  
         [0026]    Referring additionally to FIG. 3, the evaporative space in the fuel system  10  is initially charged, i.e., a vacuum is drawn according to a first controlled duty cycle purge by the purge valve  16 , until the first switch  58  is activated, and then the fuel system  10  is allowed to stabilize. Upon successful stabilization, a second controlled duty cycle purge by the purge valve  16  is initiated to draw a further vacuum in the evaporative space. As discussed above, the IPMA  20  provides excess vacuum relief that prevents a implosion of the evaporative space.  
         [0027]    The second switch  59  being activated indicates a sealed system. A “small” threshold leak is indicated if, after a set time period of the controlled duty cycle purge by the purge valve  16 , the first switch  58  remains activated but the second switch  59  is not activated. A “large” leak is indicated if activation of the first switch  58  cannot be maintained.  
         [0028]    However, certain operating conditions could cause false indications. For example, operating conditions of an IPMA equipped vehicle that result in decreasing engine load and increasing engine speed, e.g., when the vehicle is being driven down an incline, can cause a false indication that the fuel system  10  is sealed. Conversly, operating conditions that result in increasing engine load and decreasing engine speed, e.g., when the vehicle is being driven up an incline, can cause a false indication that there is a leak in the fuel system  10 . These types of false indications can be identified by an Engine Control Unit (ECU) based on the engine load/speed maps that are stored in the ECU. A false indication that there is a leak can also result from excessive fuel vapors that are generated by a hot fuel cell. This type of false indication can be identified by the ECU based on a “lambda” sensor detecting an O 2  shift as a result of controlled duy cycle purging.  
         [0029]    Thus, active leak detection can be performed while the engine is operating using an IPMA  20  comprising a second pressure switch  58  and using duty cycle controlled purging by the purge valve  16 .  
         [0030]    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.