Abstract:
A vapor purge system having a tank isolation valve and a canister vent valve, where each valve includes a latching mechanism for maintaining the valves in an open position. A diagnostic test is performed on the purge system to prove that each of the valves are functioning correctly. Using latching valves in these applications reduces electricity draw from the battery and reduces electrical interference with integrated pressure sensors. The fuel tank is sealed by the tank isolation valve between the fuel tank and a vapor storage canister, and the canister vent valve provides sealing between the canister and the atmosphere, and controls venting of the canister. The tank isolation valve reduces power consumption from the battery, while the valve is being held in either an open position or a closed position by the latching mechanism, and uses only a single pulse of voltage to change the state of the valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/891,018 filed Oct. 15, 2013. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to a vapor purge system having a fuel tank isolation valve assembly integrated with a pressure sensor, as well as a canister vent valve, where the fuel tank isolation valve assembly includes a latching mechanism which maintains the fuel tank isolation valve assembly in an open position or closed position when no current is used. 
       BACKGROUND OF THE INVENTION 
       [0003]    Current fuel systems for vehicles include a valve which opens and closes to allow vapor from the fuel tank to escape when the tank is being re-fueled. The vapor flows from the fuel tank, through the valve, and into a canister, where the vapor is stored until it is dispensed back into the intake of the engine. The valve is also able to provide relief of vacuum pressure that builds up in the fuel tank as the fuel levels decrease during operation of the vehicle, and also functions to seal the fuel tank between the fuel tank and the vapor storage canister. 
         [0004]    The valve is typically operated using an actuation device, such as a solenoid, which is energized to open the valve, and hold the valve in an open position while the vehicle is being refueled. Current designs for solenoids used in these applications remain energized while the valve is opened during the time the vehicle is being re-fueled. This drains power from the battery, and reduces the overall efficiency of the vehicle. Additionally, the fuel tank, and the portion of the airflow system outside the fuel tank must be tested for leaks, so the airflow system must also be sealed with a valve on the fresh air side of the canister, such as a vent valve. These valves must also be tested to make sure they are functioning properly and that their positions (e.g. open or closed) may be verified, with minimal costs. This type of diagnostic testing may be required when the valves are first installed on a vehicle (during the manufacturing process or after repair), or after the battery has been disconnected. 
         [0005]    Accordingly, there exists a need for a valve assembly which is able to remain in an open position while the vehicle is being re-fueled to allow vapors to flow out of the fuel tank, while at the same time minimizing the amount of energy used to maintain the valve in an open position. There is also a need for a valve assembly which meets current packaging requirements, and is capable of performing diagnostic tests to ensure that the valves are working correctly after installation, or after the battery has been disconnected. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is a type of airflow system, or more specifically, a vapor purge system, having a tank isolation valve and a canister vent valve, where each valve includes a latching mechanism for maintaining the valves in an open position. A diagnostic test is performed on the vapor purge system to prove that each of the valves are functioning correctly. Using latching valves in these applications reduces the electricity draw from the battery and reduces electrical interference with integrated pressure sensors. The fuel tank is sealed by the tank isolation valve between the fuel tank and a vapor storage canister, and the canister vent valve provides sealing between the canister and the atmosphere, and controls venting of the canister. The diagnostic test is performed using the tank isolation valve and the canister vent valve under different operating conditions. 
         [0007]    The tank isolation valve reduces power consumption from the battery, while the valve is being held in either an open position, or a closed position, and uses only a short, single pulse of voltage, to change the state of the valve. The most common time that the valve is held open is during refueling. During refueling, the engine is typically shut off. The valve is held open without battery power because of the latching mechanism. A solenoid used with the latching mechanism avoids having to use continuous battery power. 
         [0008]    This invention describes the on-board diagnostic check used to ensure that the valves are functioning correctly. The invention also provides a method for proving both functionality and the current state of the valves (e.g., open or closed) using only the pressure sensors that are part of the vapor purge system. 
         [0009]    In one embodiment, the present invention is a latching mechanism for a fuel tank isolation valve. The latching mechanism includes a bobbin, a coil substantially surrounding the bobbin, and an inner stator insert partially surrounded by the bobbin. An armature is at least partially surrounded by the inner stator insert, and has a large diameter portion and a small diameter portion. An indexing latch is connected to a portion of the small diameter portion of the armature, such that the indexing latch moves with the armature. An index mechanism substantially surrounds a portion of the small diameter portion of the armature, and is selectively engaged with the indexing latch. 
         [0010]    A spring cup also substantially surrounds part of the small diameter portion of the armature, and the spring cup is adjacent the index mechanism. A load spring is disposed between the inner stator insert and the spring cup, such that the load spring is in contact with the spring cup and biases the spring cup away from the inner stator insert. A return spring also substantially surrounds part of the small diameter portion of the armature, such that the return spring is disposed between the large diameter portion of the armature and the spring cup. The return spring biases the spring cup away from the large diameter portion of the armature. 
         [0011]    There is also a reservoir cavity, and the valve, the valve seat, the indexing latch, the index mechanism, and the spring cup are all disposed in the reservoir cavity. An overmold assembly cavity is in fluid communication with the reservoir cavity, and the coil and the bobbin are adjacent the overmold assembly cavity. A guide is also located in the reservoir cavity. The guide is in contact with and adjacent the bobbin, and the index mechanism is selectively engaged with the guide. 
         [0012]    The small diameter portion of the armature is connected to a valve. The valve is in contact with a valve seat when the valve is in a closed position, and the valve is moved away from the valve seat then the valve is in an open position. The coil is energized to move the armature and the valve away from the valve seat against the force of the load spring and the return spring when the indexing latch is engaged with the index mechanism, and the valve is in contact with the valve seat and in the closed position. When the armature, the valve, and the indexing latch are moved far enough away from the valve seat, the index mechanism rotates about the armature and becomes engaged with the guide, maintaining the valve in the open position when the coil is then de-energized. 
         [0013]    When the valve is in the open position, the coil is again energized to move the armature, the valve, and index mechanism away from the guide, such that the index mechanism disengages from the guide, rotates about the armature, and reengages with the indexing latch. When the coil is then again de-energized, the valve moves to the closed position. 
         [0014]    In one embodiment, the fuel tank isolation valve is in fluid communication with a fuel tank and a canister, and the valve is changed between the open position and the closed position to control vacuum pressure in the fuel tank, and the flow of purge vapor from the fuel tank to the canister. 
         [0015]    In one embodiment, the spring cup includes an inner cylindrical portion located next to the index mechanism, a central flange integrally formed with the inner cylindrical portion, and an outer cylindrical portion integrally formed with the central flange such that the outer cylindrical portion is circumscribed by part of the load spring. An outer flange is integrally formed with the outer cylindrical portion, and the load spring is in contact with the outer flange. The load spring is disposed between the outer flange and the inner stator insert, and biases the spring cup and the index mechanism away from the inner stator insert, such that the valve is biased towards a closed position when the index mechanism is engaged with the indexing latch. 
         [0016]    A first plurality of teeth is formed as part of the indexing latch, a second plurality of teeth and a plurality of slots are formed as part of the guide, and a plurality of indexing teeth is formed as part of the index mechanism. Each of the plurality of indexing teeth are disposed in a corresponding one of the plurality of slots and engaged with the first plurality of teeth when the valve is in the closed position. The plurality of indexing teeth are removed from the plurality of slots and engaged with the second plurality of teeth when the valve is in the open position. 
         [0017]    Additionally, the first plurality of teeth are positioned relative to the second plurality of teeth such that when the valve is in the closed position and the coil is energized, the indexing latch and the index mechanism are moved away from the valve seat such that the first plurality of teeth move the plurality of indexing teeth out of the plurality of slots, causing the index mechanism to rotate relative to the armature, and engage the second plurality of teeth when the coil is de-energized, allowing the first plurality of teeth to disengage from the plurality of indexing teeth. 
         [0018]    When the plurality of indexing teeth are engaged with the second plurality of teeth and the valve is in the open position, the coil is again energized to reengage the first plurality of teeth with the indexing teeth such that the plurality of indexing teeth are disengaged from the second plurality of teeth, causing the index mechanism to rotate relative to the armature, allowing each of the plurality of indexing teeth to move back into a corresponding one of the plurality of slots, which then allows the armature and the valve to move toward and contact the valve seat when the coil is again de-energized, placing the valve back in the closed position. 
         [0019]    There is also a plurality of indexing splines formed as part of the indexing latch, and each one of the plurality of indexing splines slides is located in one of the plurality of slots as the indexing latch moves relative to the guide. 
         [0020]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0022]      FIG. 1  is a diagram of a vapor purge system for a vehicle having at least one valve incorporating a latching mechanism, according to embodiments of the present invention; 
           [0023]      FIG. 2  is a perspective view of an isolation valve assembly, according to embodiments of the present invention; 
           [0024]      FIG. 3  is a graph depicting the voltage versus valve position of an isolation valve assembly, according to embodiments of the present invention; 
           [0025]      FIG. 4  is a sectional side view of an isolation valve assembly, according to embodiments of the present invention; 
           [0026]      FIG. 5A  is a perspective view of a latching mechanism, used as part of a tank isolation valve assembly, according to embodiments of the present invention; 
           [0027]      FIG. 5B  is a sectional side view of a latching mechanism, used as part of a tank isolation valve assembly, according to embodiments of the present invention; 
           [0028]      FIG. 6A  is a first diagram of a latching mechanism used as part of an isolation valve assembly, where the tank isolation valve is in a closed position, according to embodiments of the present invention; 
           [0029]      FIG. 6B  is a diagram of a latching mechanism used as part of a tank isolation valve, where the latch mechanism is configured such that the tank isolation valve is moved to an open position, according to embodiments of the present invention; 
           [0030]      FIG. 6C  is a diagram of a latching mechanism used as part of a tank isolation valve, where the latch mechanism is configured such that the tank isolation valve is held in an open position, according to embodiments of the present invention; 
           [0031]      FIG. 6D  is a first diagram of a latching mechanism used as part of a tank isolation valve, where the latch mechanism is configured such that the tank isolation valve is being released from an open position, according to embodiments of the present invention; 
           [0032]      FIG. 6E  is a second diagram of a latching mechanism used as part of a tank isolation valve, where the latch mechanism is configured such that the tank isolation valve is being released from an open position, according to embodiments of the present invention; 
           [0033]      FIG. 6F  is a second diagram of a latching mechanism used as part of a tank isolation valve, where the tank isolation valve is in a closed position, according to embodiments of the present invention; 
           [0034]      FIG. 7  is a flowchart having the steps used to perform a diagnostic test on a vapor purge system under a first set of operating conditions, according to embodiments of the present invention; 
           [0035]      FIG. 8  is a flowchart having the steps used to perform a diagnostic test on a vapor purge system under a second set of operating conditions, according to embodiments of the present invention; 
           [0036]      FIG. 9  is a flowchart having the steps used to perform a diagnostic test on a vapor purge system under a third set of operating conditions, according to embodiments of the present invention; and 
           [0037]      FIG. 10  is a flowchart having the steps used to perform a diagnostic test on a vapor purge system under a fourth set of operating conditions, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0039]    A diagram of a vapor purge system according to the present invention is shown in  FIG. 1  generally at  10 . The system  10  includes a fuel tank  18 , where fuel  20  is stored. The fuel tank  18  is in fluid communication with an isolation valve assembly, shown generally at  22  in  FIGS. 1-2 . The isolation valve assembly  22  includes a tank isolation valve  24 , a pressure sensor  26 , and a temperature sensor  28 . The valve  24  is in fluid communication with the fuel tank  18  through the use of a first conduit  30 . Both the pressure sensor  26  and temperature sensor  28  are integrated with the isolation valve assembly  22 , and are in fluid communication with the first conduit  30  in between the valve  24  and the fuel tank  18 . 
         [0040]    The tank isolation valve  24  is in fluid communication with a vapor canister  32  through the use of a second conduit  34 . The vapor canister  32  is also in fluid communication with a purge valve  36  because of a third conduit  38 . The purge valve  36  is also connected to and in fluid communication with a fourth conduit  40 , where the fourth conduit  40  is connected to another component of the system, such as a turbocharger unit (not shown). 
         [0041]    The canister  32  is also in fluid communication with a canister vent valve  42  through the use of a fifth conduit  44 . Also connected to and in fluid communication with the fifth conduit  44  is a pressure sensor  46  and a temperature sensor  46 A. A sixth conduit  48  is also connected to, and in fluid communication with, the canister vent valve  42  and an air filter  50 . 
         [0042]    During operation, the tank isolation valve  24  is in a closed position such that the vapors in the fuel tank  18  cannot escape. When the tank  18  is being re-fueled, the tank isolation valve  24  is opened to allow vapors in the tank  18  to flow into the canister  32 . The canister vent valve  42  is typically in an open position during normal operation, and closed during different steps of an on-board diagnostic test, the function of which will be described later. The purge vapor is typically stripped of hydrocarbons in the canister  32 , and the air that flows out of the canister  32  passes through the canister vent valve  42 . 
         [0043]    The canister vent valve  42  and the isolation valve  24  are of substantially similar construction and have substantially the same components as shown in  FIGS. 2 ,  4 ,  5 A- 5 B, and  6 A- 6 F, and therefore only the construction of the isolation valve  24  is described. The isolation valve  24  includes a first port, which in this embodiment is an inlet port  74  connected to the first conduit  30 , and the inlet port  74  is formed as part of a reservoir  76 , and also formed as part of the reservoir  76  is a cap  78 , and the cap  78  is connected to an overmold assembly  80 . The overmold assembly  80  includes an overmold assembly cavity, shown generally at  82 , and a second port, or outlet port  84 , in fluid communication with the overmold assembly cavity  82 . The outlet port  84  is connected to and in fluid communication with the second conduit  34 . 
         [0044]    Disposed within the overmold assembly  80  is a solenoid assembly, shown generally at  86 , which is part of the isolation valve assembly  22 . The solenoid assembly  86  is disposed within a cavity, shown generally at  88 , formed as part of the overmold assembly  80 , and the cavity  88  includes an inner wall portion  90 . Also forming part of the cavity  88  is an outer wall portion  92  of the overmold assembly  80 . A retention feature  90 A is formed as part of both the inner wall portion  90  and outer wall portion  92 , and circumscribes the solenoid assembly  86 , for securing the solenoid assembly  86  in the cavity  88 . 
         [0045]    The solenoid assembly  86  includes an outer stator insert  94  which is in contact with an upper wall  98  formed as part of the overmold assembly  80 . The outer stator insert  94  is partially disposed in an aperture  96  formed as part of a housing  104 , and the outer stator insert  94  is disposed between the upper wall  98  and a bobbin  100 . The housing  104  is part of the solenoid assembly  86 , and the inner wall portion  90  and outer wall portion  92  also form part of the housing  104 . The bobbin  100  is surrounded by a coil  102 , and there is a first bushing  164  which is surrounded by the bobbin  100 , where the first bushing  164  has a shorter overall length than the bobbin  100 , as shown in  FIG. 4 . The bushing  164  partially surrounds a moveable armature  54 , and is adjacent an inner stator insert  166 . 
         [0046]    The armature  54  includes a large diameter portion  106  which extends into the solenoid assembly  86 , and is partially surrounded by the inner stator insert  166 , the first bushing  164 , and the bobbin  100 . The large diameter portion  106  also includes a tapered section  108  which selectively moves towards and away from a corresponding tapered section  110  formed as part of the outer stator insert  94 . Disposed between a lower washer  170  and a load spring  64  is an outer flange portion  166 A formed as part of the stator insert  166 . The outer flange portion  166 A is formed as part of the stator insert  166  between a small diameter portion  166 B and a large diameter portion  166 C of the stator insert  166 . The small diameter portion  166 B of the stator insert  166  is surrounded by the bobbin  100 , and is adjacent the first bushing  164 . The large diameter portion  166 C is surrounded by part of the load spring  64 , and the large diameter portion  166 C surrounds a second bushing  168 . Furthermore, mounted on the small diameter portion  166 B is the lower washer  170 , and the lower washer  170  is located between the outer flange portion  166 A and the bobbin  100 . 
         [0047]    The second bushing  168 , the small diameter portion  166 B, and the first bushing  164  surround the large diameter portion  106  of the armature  54 , where the large diameter portion  106  of the armature  54  is in sliding contact with and is supported by the bushings  164 , 168 , and the armature  54  is able to move relative to the second bushing  168 , the small diameter portion  166 B, and the first bushing  164 . 
         [0048]    The armature  54  also includes a small diameter portion  116  which is integrally formed with the large diameter portion  106 . The small diameter portion  116  extends into a reservoir cavity, shown generally at  124 , formed as part of the reservoir  76 , and is connected to a core portion  118  of a valve member, shown generally at  120 . The valve member  120  also includes a stopper portion  122  connected to the core portion  118 . The stopper portion  122  is made of rubber, or another type of flexible material, and includes a flange portion  126  which selectively contacts a contact surface  128  formed as part of the reservoir  76 , where the contact surface  128  functions as a valve seat. The valve member  120  is moved by the armature  54  such that the flange portion  126  selectively contacts the contact surface  128 , selectively placing the inlet port  74  in fluid communication with the reservoir cavity  124 . 
         [0049]    Disposed within the reservoir cavity  124  is a latching mechanism, shown generally in  FIGS. 4 ,  5 A- 5 B, and  6 A- 6 F at  52 . The latching mechanism  52  is connected to the valve member  120  of the isolation valve  24 , which is moveable between an open position and a closed position. The latching mechanism  52  is used with the armature  54  to hold the valve member  120  in an open position even if the coil  102  is not energized. The armature  54  is part of the solenoid assembly  86 , and a current is applied to the coil  102  to energize coil  102 , and move the armature  54  and the valve member  120  away from the contact surface  128 . 
         [0050]    In  FIGS. 4 and 6A , the valve member  120  is in a closed position. The mechanism  52  also includes an indexing latch  56  connected to the armature  54  such that the latch  56  moves with the armature  54 , as shown in  FIG. 4 , and the latch  56  includes a first plurality of teeth  58  and several indexing splines  68 . The mechanism  52  also includes several slots  60  formed as part of a guide  142 , where the guide  142  also includes a second plurality of teeth  66 . The mechanism  52  also includes an index mechanism  62  having at least one indexing tooth  62   a  (in this embodiment, the mechanism  62  has multiple teeth  62   a , but only one is shown in  FIGS. 6A-6F  for demonstrative purposes), where the index mechanism  62  also surrounds the small diameter portion  116  of the armature  54 , but is able to slide and move relative to the small diameter portion  116  of the armature  54 . Force is applied to the index mechanism  62  by the load spring  64 . The index mechanism  62  is also adjacent a spring cup, shown generally at  132 . More specifically, the spring cup  132  includes an inner cylindrical portion  134  located next to the index mechanism  62 . The inner cylindrical portion  134  also surrounds the small diameter portion  116 , but is not connected to the small diameter portion  116  such that the spring cup  132  is also able to slide and move relative to the small diameter portion  116 . The inner cylindrical portion  134  is connected to an outer cylindrical portion  136  with a central flange  138 . Part of the load spring  64  surrounds the outer cylindrical portion  136  and is in contact with an outer flange  140  integrally formed with the outer cylindrical portion  136 . 
         [0051]    In addition to the load spring  64 , there is also a return spring  144  which surrounds the small diameter portion  116 , and is located between the spring cup  132  and the large diameter portion  106  of the armature  54 . More specifically, the return spring  144  is between the inner cylindrical portion  134  of the spring cup  132  and the large diameter portion  106  of the armature  54 , and the return spring  144  biases the spring cup  132  away from the large diameter portion  106  of the armature  54 . The load spring  64  is between the outer flange  140  and the outer flange portion  166 A of the inner stator insert  166 , and biases the spring cup  132  and the index mechanism  62  away from the outer flange portion  166 A of the inner stator insert  166 . Depending on the configuration of the latching mechanism  52 , the load spring  64  causes the spring cup  132  and index mechanism  62  to apply force to the latch  56  or the guide  142 . Therefore, the latching mechanism  52  is biased in two different ways, one way is the return spring  144  biasing the spring cup  132  and the index mechanism  62  away from the large diameter portion  106  of the armature  54  (which is movable), and the other is the load spring  64  biasing the spring cup  132  and the index mechanism  62  away from the outer flange portion  166 A of the inner stator insert  166  (which is stationary). 
         [0052]    In addition to the slots  60  and the teeth  66 , the guide  142  also includes an inner housing  146  which partially surrounds the indexing latch  56  and the index mechanism  62 . Part of the inner housing  146  is surrounded by the spring cup  132 . Integrally formed with the inner housing  146  is an outer shield  148 , where the outer shield  148  partially surrounds the load spring  64 . The outer shield  148  is integrally formed with several support members  150 , and the support members  150  are integrally formed with an upper bracket member  152 . There are apertures, shown generally at  154 , between each of the support members  150  which allow for the passage of air and purge vapor between the reservoir cavity  124  and the overmold assembly cavity  82 . The upper bracket member  152  is in contact with the lower washer  170 . There are also several outer bracket members  172  integrally formed with the upper bracket member  152 . 
         [0053]    More specifically, the diameter of the lower washer  170  is larger than the diameter of the outer flange portion  166 A, such that the upper bracket member  152  is in contact with the lower washer  170 , and the retention feature  90 A is in contact with the lower washer  170 . The cap  78  has an outer surface  160  in contact with a lower surface  162  of each outer bracket member  172 . The outer bracket members  172  are therefore between the lower washer  170  and the outer surface  160  of the cap  78 , and this location of the bracket members  152 , 172  relative to the overmold assembly  80  and the cap  78  properly positions the guide  142 . 
         [0054]    The latching mechanism  52  functions to hold the valve member  120  in an open position, even when the coil  102  is not energized. Referring to  FIGS. 4 and 6A , the latching mechanism  52  is shown in a position which corresponds to the valve member  120  being in a closed position. When the coil  102  is energized enough to generate a magnetic force to overcome the force from the springs  64 , 144 , the armature  54  and the indexing latch  56  move toward the stator insert  94 , moving the valve member  120  away from the contact surface  128 , placing the valve member  120  in an open position. The movement of the armature  54  towards the stator insert  94  causes force to be applied to the teeth  62   a  of the index mechanism  62  from at least one of the first plurality of teeth  58  formed as part of the indexing latch  56 . The movement of the indexing latch  56  is guided by the movement of the indexing splines  68  moving in the slots  60 . The force applied to the index mechanism  62  from the indexing latch  56  overcomes the force applied to the index mechanism  62  from the spring  64  by way of the spring cup  132  and moves the teeth  62   a  of the index mechanism  62  out of the slot  60 , as shown in  FIG. 6B . 
         [0055]    It is shown in  FIGS. 6A-6F  that the vertexes  58 A of the first plurality of teeth  58   a  are not in alignment with the vertexes  66   a  of the second plurality of teeth  66 , which facilitates the rotation of the index mechanism  62 . Each of the teeth  62   a  has an angled portion which also facilitates the rotation of the index mechanism  62 . The coil  102  is energized to move the armature  54  and the indexing latch  56  toward the stator insert  94  enough to move the teeth  62   a  of index mechanism  62  out of the slot  60 . Once the indexing latch  56  has moved the teeth  62   a  of the index mechanism  62  out of the slot  60 , the pressure applied to the index mechanism  62  from the spring cup  132  and the load spring  64  and the return spring  144  pushes each tooth  62   a  towards a corresponding vertex  58   a . This causes the index mechanism  62  to move (i.e., rotate about the small diameter portion  116  of the armature  54 ) as each tooth  62   a  slides towards one of the vertexes  58   a  in between two of the first plurality of teeth  58 , as shown in  FIG. 6B . 
         [0056]    Once each tooth  62   a  is in contact with one of the vertexes  58   a  of the first plurality of teeth  58 , each tooth  62   a  of the index mechanism  62  is also positioned such that each tooth  62   a  is between two of the second plurality of teeth  66  formed as part of the guide  142 , also shown in  FIG. 6B . The coil  102  is then de-energized, but the valve member  120  remains in the open position because the index mechanism  62  (and therefore the spring cup  132  and armature  54 ) is held in place by the guide  142 . More specifically, after the coil  102  is de-energized, the indexing latch  56 , and therefore the armature  54 , move away from the index mechanism  62  enough to allow the teeth  58  of the indexing latch  56  to disengage from the teeth  62   a  of the index mechanism  62 , while at the same time, the force of the springs  64 , 144  forces the teeth  62   a  to move toward the vertexes  66   a  of the second plurality of teeth  66  formed as part of the guide  142 , as shown in  FIG. 6C , rotating the index mechanism  62 . Since the guide  142  is stationary, and the teeth  62   a  of the index mechanism  62  are interlocked with the teeth  66  of the guide  142 , the index mechanism  62 , spring cup  132 , and armature  54  are not allowed to move to place the valve member  120  back in the closed position, but rather are held in place by the guide  142  (and the teeth  58  of the indexing latch  56  are disengaged from the teeth  62   a  of the index mechanism  62 ), to maintain the valve member  120  in the open position. This allows the purge vapor to escape from the tank  18  to the canister  32  as the valve member  120  is held in the open position, but does not draw any power from the vehicle battery to maintain the position of the valve  24  in the open position since the coil  102  is not energized. 
         [0057]    Once it is desired to change the valve member  120  from the open position back to the closed position, the coil  102  is again energized, moving the armature  54  and the indexing latch  56  toward the stator insert  94  such that the first plurality of teeth  58  again engage and apply force to the teeth  62   a  of the index mechanism  62  to overcome the force applied to the index mechanism  62  from the springs  64 , 144  and lift the index mechanism  62  away from the second plurality of teeth  66 . As mentioned above, the vertexes  58 A of the first plurality of teeth  58   a  are not in alignment with the vertexes  66   a  of the second plurality of teeth  66 . When the valve member  120  is in the open position, and the teeth  62   a  of the index mechanism  62  are held in place by the teeth  66  of the guide  142 , the teeth  62   a  of the index mechanism  62  are not in alignment with the vertexes  58   a  of the first plurality of teeth  58 , shown in  FIG. 6C . Once the teeth  62   a  of the index mechanism  62  have disengaged from the second plurality of teeth  66 , and are only engaged with the first plurality of teeth  58 , the teeth  62   a  move toward the corresponding vertexes  58   a  (because of the force from the springs  64 , 144 ), rotating the index mechanism  62 , such that the teeth  62   a  are no longer in alignment with the vertexes  66   a  of the second plurality of teeth  66 . The coil  102  is then again de-energized, and the armature  54  and indexing latch  56  move away from the stator insert  94 , and the teeth  62   a  reengage with the second plurality of teeth  66  of the guide  142 . However, instead of moving towards the vertexes  66   a  due to the force of the springs  64 , 144 , the each tooth  62   a  moves towards a corresponding slot  60 , allowing the index mechanism  62  to move further away from the stator insert  94 , and each tooth  62   a  to move into a corresponding slot  60 , as shown in  FIG. 6F , which also results in the force from the springs  64 , 144  moving the armature  54 , indexing latch  56 , index mechanism  62 , and spring cup  132  further away from the stator insert  94 , and the valve member  120  to move back to the closed position, as shown in  FIGS. 4 ,  6 A, and  6 F. 
         [0058]    The solenoid assembly  86  and therefore the coil  102  is only energized when the valve member  120  is being changed between the open position and the closed position. Once the valve member  120  is in the open position, the coil  102  is de-energized. Furthermore, once the valve member  120  is in the closed position, the coil  102  is de-energized. An example of this is shown in  FIG. 3 , where voltage  70  of the solenoid assembly  86  and the position  72  of the valve member  120  are shown. The voltage  70  is applied to the coil  102 , and therefore the armature  54 , for about 30 milliseconds, the armature  54  moves the indexing latch  56  and the index mechanism  62 , allowing the valve member  120  to change to the open position, as described above. Once the valve member  120  is in the open position, the coil  102  is then de-energized, the voltage  70  then drops to zero, and the valve member  120  is held in the open position by the latching mechanism  52 . The voltage  70  is then re-applied to the coil  102 , which then re-energizes the coil  102 , and the latching mechanism  52  is actuated to change the valve member  120  from the open position to the closed position. The function of the latching mechanism  52  allows to the coil  102  of the solenoid assembly  86  to be de-energized, and therefore no power is drained from the battery of the vehicle, while still providing for the valve member  120  to be held in the open position or closed position. Energy is only used in intervals of about 30 milliseconds when changing the valve member  120  between the open and closed positions, as shown in  FIG. 3 , and energy is not used when the valve member  120  is held in the open position or the closed position. 
         [0059]    Another feature of the system  10  is that the pressure sensor  26  and temperature sensor  28  may be integrated with the tank isolation valve  24 , as shown in  FIGS. 1 ,  2 , and  4 . This eliminates at least one hose, and two hose connections, improving the overall design of the isolation valve assembly  22 , allowing the isolation valve assembly  22  to meet more stringent packaging requirements. Referring again to  FIGS. 2 and 4 , the pressure sensor  28  and temperature sensor  28  are formed as a single sensing unit, shown generally at  174 . Integrally formed as part of the inlet port  74  is a side port  176 , which is perpendicular to the inlet port  74 . The sensing unit  174  includes a port  174 A, which includes a groove  174 B having an O-ring  174 C disposed in the groove  174 B. The port  174 A is disposed in the side port  176 , and the O-ring  174 C provides a sealing function between the ports  174 A, 176 . The port  174 A is integrally formed with a housing  174 D, and also integrally formed with the housing  174 D is a connector  174 E, which is connectable with a corresponding connector to place the sensing unit  174  in electrical communication with another device, such as the ECU of the vehicle, or the like. 
         [0060]    Disposed in the port  174 A is a sensing element  174 F, and the sensing element  174 F in this embodiment may include a pressure sensing element and a temperature sensing element, which may be used for detecting both pressure and temperature in the port  174 A. The sensing element  174 F is in electrical communication with a circuit board, shown generally at  174 G, and the circuit board  174 G is also in electrical communication with the connector  174 E. The location and integration of the sensing unit  174  with the tank isolation valve  24  (more specifically, the connection of the sensing unit  174  with the inlet port  74 ), not only provides the advantages mentioned above, the sensing unit  174  is able to detect the pressure and temperature in the inlet port  74 , first conduit  30 , and fuel tank  18 . Because the voltage  70  is only applied to the coil  102  in intervals of about 30 milliseconds, as mentioned above, interference with the operation of the pressure sensor  26  when the coil  102  is energized is minimized or eliminated. 
         [0061]    In other embodiments, another latching mechanism  52  is also incorporated for use with the canister vent valve  42  also having a valve member  120 . The pressure sensor  46  and temperature sensor  46 A may also be integrated with the canister vent valve  42  in the same way as the pressure sensor  28  and temperature sensor  28  are integrated with the tank isolation valve  24 , as previously described. The latching mechanism  52  also allows for the valve member  120  of the canister vent valve  42  to change between the open position and closed positions, and remain in the open or closed positions, without drawing power from the vehicle battery. This operation also minimizes the interference with the operation of the pressure sensor  46 . 
         [0062]    The latching mechanism  52  is not limited to having the components described above. In still other embodiments, the latching mechanism  52  may be a permanent magnet with a double coil. In yet another embodiment, the latching mechanism  52  may include a permanent magnet, where the polarity is reversed at the terminals to open and close the valve member  120 . 
         [0063]    The system  10  also includes on-board diagnostic (OBD) check functions as well. Referring to FIGS.  1  and  7 - 10 , the isolation valve assembly  22  is located between the fuel tank  18  and the vapor canister  32 , and the canister vent valve  42  is located between the vapor canister  32  and the filter  50 . During the operation of the system  10 , the pressure sensor  26  provides a reading of the pressure in the first conduit  30  and the fuel tank  18  (hereafter referred to as “P1”), and the other pressure sensor  46  provides a reading of the pressure in the fifth conduit  44 , the canister  32 , the second conduit  34 , and the third conduit  38  (hereafter referred to as “P2”). The two valves  24 , 42  are opened and closed in different configurations and under different conditions to perform the various OBD check functions. There are four different sets of conditions, and therefore four possible configurations of the two valves  24 , 42 , which are used to perform the different OBD check functions. In order to determine if the system  10  is functioning correctly, and for the diagnostic test to be complete, the system  10  must pass the test under each of the four conditions described below, and shown in  FIGS. 7-10 . 
         [0064]    Referring to  FIGS. 1 and 7 , the first set of conditions that are used to perform the diagnostic test as shown at step  200 A occur when P1 is not equal to P2, and that P2 is substantially equal to atmospheric pressure. At step  202 A, it is presumed that the isolation valve  24  and the purge valve  36  are closed, and that the vent valve  42  is open. At step  202 A, the vent valve  42  is commanded to close, and the purge valve  36  is commanded to open. At step  204 A, a reading is taken by the second pressure sensor  46  to determine if P2 is substantially equal to atmospheric pressure. If P2 is still substantially equal to atmospheric pressure, then at step  206 A an indication is provided that either the vent valve  42  or the purge valve  36  are malfunctioning, or the third conduit  38  is plugged. If P2 is no longer equal to atmospheric pressure, then the vent valve  42  is functioning correctly, and at step  208 A, the vent valve  42  is closed, and the isolation valve  24  is opened. 
         [0065]    Once the vent valve  42  is closed, the isolation valve  24  is commanded to open, another measurement is taken by the sensors  26 , 46  at step  210 A to determine if P1 is substantially equal to P2. If P1 is not equal to P2, this is an indication that the isolation valve  24  is malfunctioning, and an indication is provided that the isolation valve  24  is malfunctioning at step  212 A. If, at step  210 A, P1 is substantially equal to P2, then at step  214 A, the isolation valve  24  is functioning correctly, and the system  10  passes this part of the diagnostic test. Also at step  214 A, the isolation valve  24  is closed, and the vent valve  42  is opened. 
         [0066]    Referring to  FIGS. 1 and 8 , the second set of conditions that are used to perform the diagnostic test as shown at step  200 B occur when P1 is not equal to P2, and P2 is not equal to atmospheric pressure. It is presumed, at step  202 B, that the isolation valve  24  and the vent valve  42  are both closed, and the isolation valve  24  is then commanded to open. A pressure reading is taken at step  204 B to determine if P1 is substantially equal to P2 after the isolation valve  24  is commanded to open. If P1 is not equal to P2, then an indication is provided at step  206 B that the isolation valve  24  is malfunctioning. If P1 is substantially equal to P2, then the isolation valve  24  is functioning correctly, and at step  208 B the vent valve  42  is then commanded to open. 
         [0067]    Once it is known that the isolation valve  24  is functioning correctly, and the vent valve  42  is commanded to open at step  208 B, another pressure reading is taken at step  210 B by the sensors  26 , 46  to determine if P2 is substantially equal to atmospheric pressure. If P2 is not equal to atmospheric pressure, then at step  212 B an indication is provided that either the vent valve  42  is malfunctioning, the purge valve  36  leaks, or the filter  50  is plugged. If, at step  210 B, P2 is substantially equal to atmospheric pressure, then the vent valve  42  is functioning correctly and in the open position, the conduits are clear, and the isolation valve  24  is placed in the closed position. 
         [0068]    Referring to  FIGS. 1 and 9 , the third set of conditions that are used to performed the diagnostic test at shown at step  200 C occur when P1 is substantially equal to P2, and P2 is not equal to atmospheric pressure. Under these conditions, at step  202 C it is presumed that both valves  24 , 42  are in closed positions, the isolation valve  24  is energized to change to the open position, and the purge valve  36  is then energized to change to the open position. Then, at step  204 C, a pressure reading is taken by the sensors  26 , 46  to determine if P1 is still substantially equal to P2. If P1 is still substantially equal to P2 at step  204 C, then at step  206 C an indication is provided that either the isolation valve  24  or the purge valve  36  is malfunctioning, or that the third conduit  38  is plugged. If P1 is not equal to P2 at step  204 C, then the isolation valve  24  is functioning correctly, and at step  208 C, the vent valve  42  is energized to open the vent valve  42 , and the purge valve  36  is closed. 
         [0069]    Once the purge valve  36  is closed and the vent valve  42  is opened at step  208 C, another pressure measurement is taken by the sensors  26 , 46  at step  210 C to determine if P2 is substantially equal to atmospheric pressure. If, at step  210 C, P2 is not equal to atmospheric pressure, then at step  212 C an indication is provided that either the vent valve  42  is malfunctioning properly, there is a leak in the purge valve  36 , or the filter  50  is plugged. If, at step  210 C, P2 is substantially equal to atmospheric pressure, then the vent valve  42  is functioning correctly and in an open position, the sixth conduit  48  is clear, and the system  10  passes this part of the diagnostic test. 
         [0070]    Referring to  FIGS. 1 and 10 , the fourth set of conditions that are used to perform the diagnostic test at step  200 D occur when P1 is substantially equal to P2, and P2 is substantially equal to atmospheric pressure. Under these conditions, at step  202 D it is presumed that the isolation valve  24  is open, the vent valve  42  is also open, and the vent valve  42  is commanded to change to a closed position, and additionally, the purge valve  36  is commanded to change to an open position. A pressure measurement is taken by the sensors  26 , 46  at step  204 D, and if P2 is still substantially equal to atmospheric pressure, then an indication is provided that either the vent valve  42  or the purge valve  36  is malfunctioning, the cap for the fuel tank  18  has been removed, or the third conduit  38  is plugged. If, at step  204 D, P2 is no longer equal to atmospheric pressure, then the vent valve  42  is functioning correctly and in a closed position, the third conduit  38  is clear, and at step  208 D, the isolation valve  24  and purge valve  36  are changed to a closed position, and the vent valve  42  is changed to an open position. 
         [0071]    Once the isolation valve  24  and the purge valve  36  are closed, and the vent valve  42  is opened, another pressure reading is taken, at step  210 D, to determine if P1 is substantially equal to P2. If, at step  210 D, P1 is substantially equal to P2, then an indication is provided that the isolation valve  24  is malfunctioning at step  212 D. If P1 is not equal to P2, then, at step  210 D, the isolation valve  24  is functioning correctly and in the open position, and the system  10  passes the diagnostic test. 
         [0072]    In addition to being able to perform the diagnostic test, the vapor purge system  10  also functions to configure the tank isolation valve  24  and canister vent valve  42  to allow for the removal of purge vapor during refueling, and for relief of vacuum pressure as the fuel levels in the fuel tank  18  decrease as fuel is consumed during vehicle travel. The tank isolation valve  24  and the canister vent valve  42  may also be configured to relieve positive pressure build up in the fuel tank  18  due increases in temperature, or relief of vacuum pressure build up in the fuel tank  18  due to decreases in temperature. 
         [0073]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.