Abstract:
A flow control valve including a passage, and first and second valve devices disposed in the passage and comprising first and second valve members, valve seats, and seal members, respectively. Each valve member is movable for opening and closing the passage. Each seal member may seal between the corresponding valve member and seat. The first valve member moves in a first direction toward a closing position of the first valve device. The second valve member moves in a second direction, opposite the first closing direction, toward a closing position of the second valve device. The first or the second seal member may include a base portion attached to one of the corresponding valve member and the corresponding valve seat, a lip extending from the base portion, and a turning-up inhibiting device configured to inhibit the lip from turning up when the corresponding valve member is in the closing position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims priority to Japanese Patent Application Serial No. 2014-263146 filed on Dec. 25, 2014, the contents of which are incorporated herein by reference in their entirety for all purposes. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    This disclosure generally relates to a flow control valve and also relates to a fuel processing apparatus incorporating the flow control valve. 
         [0004]    U.S. Patent Application Publication No. 2014/0216574A1 (also published as Japanese Laid-Open Patent Publication No. 2014-149035) discloses a flow control valve that may be used for a fuel vapor processing apparatus. The flow control valve is a relief valve including a positive pressure relieve valve and a negative pressure relief valve for maintaining a pressure within a fuel tank at an appropriate level when the fuel tank is closed. In each of the positive and negative pressure relief valves, an annular seal member is disposed between a valve member and a valve seat. The valve member can move to be seated on the valve seat and can move away from the valve seat. The annular seal member may elastically seal between the valve member and the valve seat when the valve member is seated on the valve seat for closing the valve. The seal member includes an annular base portion attached to the valve member. A seal lip protrudes obliquely inwards in the axial direction from the base portion for elastically contacting the valve seat. 
         [0005]    To ensure the sealing property of the seal lip of the seal member, it may be necessary for the seal lip to be formed so as to allow easy elastic deformation to some extent. If, however, the seal lip can easily deform, the seal lip may be turned up when the valve member is in a closing position. The seal lip may be turned up due to the fluid pressure acting on the seal lip in the opposite direction, i.e., a direction radially from the outer side to the inner side. If this occurs, the sealing properties or performance of the seal lip may be deteriorated. 
         [0006]    In view of the challenges discussed above, there is a need in the art for a technique of inhibiting turning-up of a seal lip of a seal member to make it possible to achieve an improvement in terms of sealing performance. 
       SUMMARY 
       [0007]    In one aspect according to the present disclosure, a flow control valve may include a valve housing defining a flow passage. The flow control valve may further include a first valve device and a second valve device disposed in the flow passage and each comprising a valve member, a valve seat and a seal member. The valve member may be movable relative to the corresponding valve seat for opening and closing the flow passage. The seal member may be disposed between the corresponding valve member and the corresponding valve seat and may be configured to elastically seal therebetween when the corresponding valve member is in a closing position. The valve member of the first valve device may move in a first closing direction toward the closing position. The valve member of the second valve device may move in a second closing direction toward the closing position. The second closing direction may be opposite to the first closing direction. The seal member of at least one of the first valve device and the second valve device may include a base portion configured to be attached to one of the corresponding valve member and the corresponding valve seat, a seal lip extending from the base portion and configured to elastically contact the other of the corresponding valve member and the corresponding valve seat, and a turning-up inhibiting device configured to inhibit the seal lip from turning up due to a difference in pressure between an upstream side and a downstream side of the flow passage with respect to the seal member of the at least one of the first valve device and the second valve device when the corresponding valve member is in the closing position. 
         [0008]    In one embodiment, a flow control valve may include a valve housing defining a flow passage including a first passage portion and a second passage portion communicating with each other, and a first valve device and a second valve device each comprising a valve member, a valve seat, an urging device and an annular seal member. The valve member may be movable relative to the corresponding valve seat for opening and closing the flow passage. The seal member may be disposed between the corresponding valve member and the corresponding valve seat and may elastically seal therebetween when the corresponding valve member is in a closing position. The urging device of the first valve device may urge the corresponding valve member in a first closing direction that is opposite to a direction of flow of fluid from the first passage portion to the second passage portion. The urging device of the second valve device may urge the corresponding valve member in a second closing direction that is opposite to the first closing direction. The seal member of at least one of the first valve device and the second valve device may include an annular base portion configured to be attached to one of the corresponding valve member and the corresponding valve seat, a conical tubular seal lip protruding obliquely inwards in an axial direction from the base portion and configured to elastically contact the other of the corresponding valve member and the corresponding valve seat, and an annular rib-shaped protrusion arranged to surround an outer periphery of the seal lip and configured to elastically contact the other of the corresponding valve member and the corresponding valve seat. In this way, the seal member of the first valve device may include the seal member including the base portion, the conical tubular seal lip and the annular rib-shaped protrusion; and/or the seal member of the second valve device may include the seal member including the base portion, the conical tubular seal lip and the annular rib-shaped protrusion. 
         [0009]    With this arrangement, when the valve member of the at least one of the first valve device and the second valve device is in the closed position, the seal lip may elastically contact the other of the corresponding valve member and the corresponding valve seat, and the rib-shaped protrusion may elastically contact the other of the corresponding valve member and the corresponding valve seat at a position on the outer peripheral side of the seal lip. Therefore, a seal may be formed between the corresponding valve member and the corresponding valve seat. In addition, the rib-shaped protrusion may shut off the fluid pressure acting radially from the outer side to the inner side. As a result, potential turning-up of the seal lip of the seal member may be suppressed, making it possible to achieve an improvement in terms of sealing property or performance. 
         [0010]    When no load is applied to the seal member of the at least one of the first valve device and the second valve device, a leading end in the axial direction of the rib-shaped protrusion may be positioned on a side of the base portion with respect to a leading end in the axial direction of the seal lip. 
         [0011]    With this arrangement, as the valve member of the at least one of the first valve device and the second valve device moves toward the open position, the rib-shaped protrusion may be separated or move away from the other of the corresponding valve member and the corresponding valve seat before the seal lip is separated or moves away from the other of the corresponding valve member and the corresponding valve seat. On the other hand, as the valve member of the at least one of the first valve device and the second valve device moves toward the closing position, the seal lip may contact the other of the corresponding valve member and the corresponding valve seat before the rib-shaped protrusion contacts the other of the corresponding valve member and the corresponding valve seat. 
         [0012]    The valve member of the first valve device and the valve member of the second valve device may be coaxially fitted with each other. The valve seat of the first valve device may be disposed at the valve housing, while the valve seat of the second valve device may be disposed at the valve member of the first valve device. 
         [0013]    With this arrangement, it may be possible to achieve a reduction in the size of the flow control valve. 
         [0014]    The first valve device may be a positive pressure release valve configured to be opened when a pressure within the first passage portion is not less than (i.e., greater than or equal to) a predetermined positive pressure value, while the second valve device may be a negative pressure release valve configured to be opened when the pressure within the first passage portion is less than a predetermined negative pressure value. 
         [0015]    With this arrangement, it may be possible to achieve an improvement in terms of the valve-opening accuracy of the negative pressure relief valve. That is, in many cases, the predetermined positive pressure value of the positive pressure relief valve and the predetermined negative pressure value of the negative pressure relief valve may be set such that the “predetermined positive pressure value”&gt;the “predetermined negative pressure value”. In this case, the urging force of the urging device of the second valve device may be smaller than the urging force of the urging device of the first valve device, so that it is possible to achieve an improvement in the accuracy in the valve-opening operation of the negative pressure relief valve. 
         [0016]    The seal member of the first valve device and the seal member of the second valve device may be integrated to form a single seal member, and the single seal member may be disposed at the valve member of the first valve device. 
         [0017]    With this arrangement, it may be possible to achieve a reduction in the number of components of the seal member, and to achieve an improvement in terms of the ease of mounting to the valve member of the first valve device. 
         [0018]    The urging device of the at least one of the first valve device and the second valve device may be a coil spring arranged coaxially with the rib-shaped protrusion and having a coil diameter that is the same or substantially the same as a diameter of the rib-shaped protrusion. 
         [0019]    With this arrangement, the urging force of the coil spring may be efficiently act on the rib-shaped protrusion, making it possible to improve the sealing property of the rib-shaped protrusion. 
         [0020]    In another aspect according to the present disclosure, the flow control device may be one component of a fuel vapor processing apparatus. The fuel vapor processing apparatus may include a vapor passage configured to allow communication of a fluid between a fuel tank and a canister, and a closing valve disposed in the vapor passage and configured to open and close the vapor passage. The closing valve may include the flow control valve and may further include an electric valve electrically controlled for adjusting a flow rate of the fluid, and a bypass passage connected to the vapor passage to bypass the electric valve. The flow control device may be disposed in the bypass passage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic view illustrating the construction of a fuel vapor processing apparatus according to a first embodiment; 
           [0022]      FIG. 2  is a cross sectional view of a flow control valve of the fuel vapor processing apparatus; 
           [0023]      FIG. 3  is an enlarged view of a portion III in  FIG. 2 ; 
           [0024]      FIG. 4  is a bottom view of valve members of the flow control valve; 
           [0025]      FIG. 5  is a bottom view of a seal member of the flow control valve; 
           [0026]      FIG. 6  is a cross sectional view taken along line VI-VI in  FIG. 5 ; 
           [0027]      FIG. 7  is an enlarged view of a portion VII in  FIG. 6 ; 
           [0028]      FIG. 8  is a cross sectional view as viewed from a front side of a positive pressure relief valve of the flow control valve in an open state; 
           [0029]      FIG. 9  is a cross sectional view as viewed from a front side of a negative pressure relief valve of the flow control valve in an open state; 
           [0030]      FIG. 10  is a cross sectional view of a flow control valve according to a second embodiment; 
           [0031]      FIG. 11  is a cross sectional view of a flow control valve according to a third embodiment; 
           [0032]      FIG. 12  is a cross sectional view of a flow control valve according to a fourth embodiment; and 
           [0033]      FIG. 13  is a cross sectional view of a flow control valve according to a fifth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0034]    A first embodiment will now be described with reference to  FIGS. 1 to 9 . A flow control valve  56  according to a first embodiment may be used for a fuel vapor processing apparatus  12  that may be mounted to a vehicle, such as an automobile. For the sake of convenience, the flow control valve  56  will be described after the description of the fuel vapor processing apparatus  12 . 
         [0035]    As shown in  FIG. 1 , the fuel vapor processing apparatus  12  may be used for an engine system  10  of a vehicle. The engine system  10  may include an engine  14 , such as an internal combustion engine, and a fuel tank  15  for storing fuel to be supplied to the engine  14 . The fuel tank  15  may include an inlet pipe  16 . The inlet pipe  16  may have a refueling port at its upper end, so that fuel may be filled into the fuel tank  15  via the refueling port. A tank cap  17  may be detachably attached to the refueling port for opening and closing the same. A breather pipe  18  may provide communication between the interior of the upper end portion of the inlet pipe  16  and a gaseous space portion in the fuel tank  15 . 
         [0036]    A fuel supply device  19  may be dispose inside the fuel tank  15 . The fuel supply device  19  may include a fuel pump  20  that may pump and pressurize the fuel in the fuel tank  15  before discharging the fuel from the fuel pump  20 . The fuel supply device  19  may further includes a sender gauge  21  for detecting the surface level of the fuel stored in the fuel tank  15 , and a tank inner pressure sensor  22  that can detect a pressure of fuel stored in the fuel tank  15  (hereinafter called a “tank internal pressure”). For example, the tank internal pressure sensor  22  may detect the tank inner pressure as a relative pressure value to the atmospheric pressure. The fuel pumped from within the fuel tank  15  by the fuel pump  20  may be supplied to the engine  14  via a fuel supply passage  24  and a delivery pipe  26 . The delivery pipe  26  may include injectors (fuel injection valves)  25 , so that fuel may be injected into an intake passage  27  from each injector  25 . The number of the injectors  25  may correspond to the number of combustion chambers of the engine  14 . An air cleaner  28 , an airflow meter  29 , a throttle valve  30 , etc. may be disposed in the intake passage  27 . 
         [0037]    The fuel vapor processing apparatus  12  may include a vapor passage  31 , a purge passage  32 , and a canister  34 . One end (upstream end) of the vapor passage  31  may be in fluid communication with the gaseous space in the fuel tank  15 . The other end (downstream end) of the vapor passage  31  may be in fluid communication with the interior of the canister  34 . One end (upstream end) of the purge passage  32  may be in fluid communication with the interior of the canister  34 . The other end (downstream end) of the purge passage  32  may be in fluid communication with a part of the intake passage  27  on the downstream side of the throttle valve  30 . The canister  34  may contain activated carbon (not shown) as an adsorbent material. The fuel vapor produced in the fuel tank  15  may flow into the canister  34  via the vapor passage  31  and may be adsorbed by the adsorbent material (activated carbon) contained in the canister  34 . 
         [0038]    At the upstream end portion of the vapor passage  31 , there may be provided an on-board refueling vapor recovery valve (ORVR valve)  35  and a fuel cut-off valve  36 . The ORVR valve  35  and the fuel cut-off valve  36  may be disposed in the gaseous space of the fuel tank  15 . The ORVR valve  35  may be a filling-up preventing valve. The filling-up preventing valve  35  may include a float valve (not shown) that may be opened and closed according to the movement of a float (not shown) floating on the fuel surface due to its buoyancy. When the fuel level of the fuel tank  15  is less than a full level, the float valve may be opened. If the fuel is refueled into the fuel tank  15  until the fuel surface level is raised to the full level, the float valve may be closed, so that the vapor passage  31  may be shut off. When the vapor passage  31  is shut off by the ORVR valve  35 , the inlet pipe  16  may be partially filled with the fuel to activate an auto stop mechanism of a fuel supply gun (not shown) for stopping the supply of fuel. The fuel cut-off valve  36  may also include a float valve (not shown) that may be opened and closed according to the movement of a float (not shown) floating on the fuel surface due to its buoyancy. The float valve may be normally maintained in the open position and may be closed, for example, when the vehicle has accidentally overturned, whereby the fuel in the fuel tank  15  can be prevented from flowing into the vapor passage  31 . 
         [0039]    A closing valve  38  may be disposed in the vapor passage  31  at a position along the vapor passage  31 . The closing valve  38  may include an electric valve  52 , a bypass passage  54 , and a flow control valve  56 . The electric valve  52  may be a motor-driven valve that includes, for example, a stepping motor and a controller that can adjust a valve-opening amount of a valve member (not shown) by controlling a stroke movement of the valve member. That is, the electric valve  52  can adjust the flow rate of a mixture of air and fuel vapor (hereinafter called a “fuel vapor containing gas”) flowing through the vapor passage  31  under the electrical control of the stepping motor. The electric valve  52  may be opened and closed based on a drive signal that may be output from an engine control unit (hereinafter referred to as an “ECU”)  45 . The bypass passage  54  may be connected to the vapor passage  31  so as to bypass the electric valve  52 . The flow control valve  56  may be disposed in the bypass passage  54  at a position along the bypass passage  54 . The flow control valve  56  may serve to maintain the pressure in the fuel tank  15  at an appropriate level when the electric valve  52  is closed. The flow control valve  56  will be described later in detail. 
         [0040]    A purge valve  40  may be disposed in the purge passage  32  at a position along the purge passage  32 . The purge valve  40  may be opened and closed under the control of the ECU  45  such that the valve-opening amount of the purge valve  40  corresponds to the flow rate of a purge gas (i.e., the fuel vapor containing gas to be purged to the engine  14 ) calculated by the ECU  45 , whereby a so-called purge control may be performed. The purge valve  40  may include a stepping motor (not shown) and a controller (not shown) that can adjust a valve-opening amount of a valve member (not shown) by controlling a stroke movement of the valve member. Alternatively, the purge valve  40  may include an electromagnetic valve or a solenoid valve that may be closed in the non-exited state and may be opened when exited. 
         [0041]    An atmospheric passage  42  may have one end in fluid communication with the canister  34 . The other end of the atmospheric passage  42  may be opened to the atmosphere. An air filter  43  may be disposed in the atmospheric passage  42  at a position along the atmospheric passage  42 . 
         [0042]    In addition to the tank inner-pressure sensor  22 , the electric valve  52  of the closing valve  38  and the purge valve  40 , a lid switch  46 , a lid opener  47 , a display device  49 , etc. may be connected to the ECU  45 . A lid manual opening/closing device (not shown) may be coupled to the lid opener  47  and may allow manual opening and closing of a lid  48  that may be attached to the refueling port. The lid  48  may include a lock mechanism (not shown) that can releasably lock the lid  48  at a close position for closing the refueling port. The lid opener  47  may be operable to release the lock of the lock mechanism of the lid  48 . The lid switch  46  may output a signal for releasing the lock of the lid  48  to the ECU  45 . When a signal for releasing the lock is supplied from the ECU  45  to the lid opener  47 , and/or when the lid manual opening/closing device is operated for manually opening the lid  48 , the lid opener  47  may release the lock of the lid  48 . 
         [0043]    Next, the basic operations of the fuel vapor processing apparatus  12  will be described. In the following explanation, it is assumed that, in the normal state, the flow control valve  56  of the closing valve  38  is in the closed state. 
         [0044]    (1) Operation when the vehicle is not traveling (i.e., during parking or when the vehicle is at rest). 
         [0045]    When the vehicle is not traveling, the electric valve  52  of the closing valve  38  may be maintained in the closed state. Therefore, no fuel vapor in the fuel tank  15  may flow into the canister  34 . In addition, no air may flow from the canister  34  into the fuel tank  15 . The purge valve  40  may be also maintained in the closed state. When the electric valve  52  is closed, for example, due to non-traveling of the vehicle, the pressure in the fuel tank  15  may be maintained at an appropriate value by the flow control valve  56  as will be described later. 
         [0046]    (2) Operation when the vehicle is traveling. 
         [0047]    If a predetermined purge condition is established when the vehicle is traveling, the ECU  45  may execute a purge control for desorbing the fuel vapor from the canister  34  and purging the purge gas (i.e., the mixture of air and fuel vapor) to the engine  14 . In the purge control, the purge valve  40  may be opened and closed. When the purge valve  40  is opened, a negative pressure of intake air produced in the intake passage  27  of the engine  14  may act to the interior of the canister  34  via the purge passage  32 . As a result, the fuel vapor adsorbed by the canister  34  may be desorbed and purged to the intake passage  27  together with the atmospheric air supplied via the atmospheric passage  32 . The purge gas purged to the intake passage  27  may flow into the engine  14 , so that fuel contained in the purge gas may be burned in the engine  14 . The ECU  45  may control the electric valve  52  of the closing valve  38  to be opened as long as the purge operation of the fuel vapor is being performed. Therefore, the tank inner pressure of the fuel tank  15  may be maintained at a value that is close to the atmospheric pressure. 
         [0048]    (3) Operation during refueling of the vehicle. 
         [0049]    If the lid switch  46  is operated when the vehicle is not traveling, the ECU  45  may control the electric valve  52  of the closing valve  38  to be opened. In this case, if the tank inner pressure of the fuel tank  15  is higher than the atmospheric pressure, the fuel vapor in the fuel tank  15  may flow into the canister  34  via the vapor passage  31  and may be adsorbed by the adsorption material in the canister  34 , simultaneously with the opening of the electric valve  52  of the closing valve  38 . This may prevent the fuel vapor from dissipation into the atmosphere. At the same time, the tank inner pressure of the fuel tank  15  may be reduced to a value that may be close to the atmospheric pressure. When the tank inner pressure of the fuel tank  15  is reduced to the value close to the atmospheric pressure, the ECU  45  may output a signal to the lid opener  47  for releasing the lock of the lid  48 . The lid opener  47  having received the signal for releasing the lock of the lid  48  may unlock the lid  48  to allow opening of the lid  48 . Refueling to the fuel tank  15  may be started when the tank cap  17  is opened after the lid  48  is opened. The ECU  45  may control the electric valve  52  of the closing valve  38  such that the electric valve  52  is maintained in the open position until the refueling operation is completed (more specifically, until the lid  48  is again closed). In this way, during the refueling operation, the fuel vapor produced in the fuel tank  15  may flow through the vapor passage  31  to be adsorbed by the adsorbent material in the canister  34 . 
         [0050]    Next, the flow control valve  56  will be described with reference to  FIGS. 2 to 4 . For the purpose of explanation, the up-down direction (i.e., the vertical direction) of the flow control valve  56  will be determined based on the cross sectional view of  FIG. 2 . Preferably, the flow control valve  56  may be arranged such that its axial direction is oriented in the up-down direction (i.e., the vertical direction) of the vehicle. 
         [0051]    As shown in  FIG. 2 , the flow control valve  56  may include a valve housing  58 , a positive pressure relief valve  60 , and a negative pressure relief valve  62 . In the state of  FIG. 2 , both relief valves  60  and  62  are closed. The valve housing  58  may include a cylindrical tubular side wall portion  64 , a top wall portion  65  closing the upper end of the tubular side wall portion  64 , and a bottom wall portion  66  closing the lower end of the tube side wall portion  64 . At the center of the bottom wall portion  66 , a first port  68  may be formed. At the center of the top wall portion  65 , a second port  69  may be formed. Inside the valve housing  58 , there may be formed a fluid communication space  70  for fluid communication between the first port  68  and the second port  69 . A tank-side passage portion on the side of the fuel tank  15  of the bypass passage  54  may be connected to the first port  68 . A canister-side passage portion on the side of the canister  34  of the bypass passage  54  may be connected to the second port  69 . 
         [0052]    At the inner circumference of the lower end portion of the valve housing  58 , there may be formed a first valve seat  72  by decreasing the inner diameter of the fluid communication space  70 . A first valve hole  74  may be defined inside of the first valve seat  72 . The first port  68  and the first valve hole  74  may jointly define a first passage portion  76 . The remaining space defined in the valve housing  57  and the second port  69  may jointly define a second passage portion  78 . That is, the fluid communication space  70  defined inside of the valve housing  58  may include the first passage portion  76  and the second passage portion  78  communicating with each other. 
         [0053]    Inside the fluid communication space  70 , there may be disposed a first valve member  80  and a second valve member  82  that are arranged coaxially with each other. Each of the first valve member  80  and the second valve member  82  may be movable in the up-down direction (i.e., the vertical direction) along an up-down axis (i.e., a vertical axis). The positive pressure relief valve  60  may include the first valve member  80 . The negative pressure relief valve  62  may include the second valve member  82 . The first valve member  80  may include an annular valve plate  84 , an inner tubular portion  85  and an outer tubular portion  86 . The inner tubular portion  85  and the outer tubular portion  86  may form an inner and outer double tubular structure. An outer peripheral portion of the valve plate  84  extending radially inward by a given distance from the outer peripheral edge of the valve plate  84  may be defined as a first valve portion  87  for seating on the first valve seat  72  of the valve housing  58 . The first valve portion  87  may open the first valve hole  74  when the first valve portion  87  moves upward away from the first valve seat  72 . The first valve portion  87  may close the first valve hole  74  when the first valve portion  87  moves downward to be seated on the valve seat  72 . 
         [0054]    The inner tubular portion  85  may extend vertically upward from the inner peripheral portion of the valve plate  84 . At the connection portion between the valve plate  84  and the inner tubular portion  85 , there may be formed a plurality of communication holes  89  arranged in the circumferential direction and spaced from each other at equal intervals for communication between the first passage portion  76  and the second passage portion  78 . In this embodiment, two communication holes  89  may be formed (see  FIG. 2 ). The outer tubular portion  86  may extend vertically upward from the outer peripheral portion of the valve plate  84  at a position spaced radially inward from the outer peripheral edge by a given distance. A plurality of stopper members  90  may be formed on the lower surface of the outer peripheral edge portion of the first valve portion  87  and may be arranged at equal intervals in the circumferential direction. In this embodiment, eight stopper members  90  may be formed as shown in  FIG. 4 . The stopper members  90  may contact the first valve seat  72  when the first valve member  80  is in a closed position. The inner peripheral portion of the valve plate  84  may form a second valve seat  92 . The space within the inner tubular portion  85  and the communication holes  89  may jointly define a second valve hole  93 . A seal member  95  may be attached to the lower surface of the valve plate  84 . The seal member  95  will be described later. 
         [0055]    A first coil spring  97  may be interposed between the upper surface of the valve plate  84  of the first valve member  80  and the lower surface of the top wall portion  65  of the valve housing  58 . The first coil spring  97  may be arranged so as to be coaxial with the valve plate  84 . The first coil spring  97  may urge the first valve member  80  downwards, i.e., in the closing direction. The first coil spring  97  may be fitted within the outer tubular portion  86  of the first valve member  80 . 
         [0056]    The second valve member  82  may include a disc-shaped valve plate  99 , and a shaft portion  100  having a shape of a round rod (i.e., a cylindrical rod). The shaft portion  100  may be fitted into the inner tubular portion  85  of the first valve member  80  from below. The outer peripheral portion of the valve plate  99  may form a second valve portion  102  for seating on the second valve seat  92  of the first valve member  80 . The valve plate  99  may open the second valve hole  93  when the valve plate  99  moves downward away from the second valve seat  92 . The valve plate  99  may close the second valve hole  93  when the valve plate  99  moves upward to be seated on the second valve seat  92 . A spring receiving member  104  may be attached to the leading end portion (upper end portion) of the shaft portion  100 . As the second valve member  82  moves downward in a valve opening direction, the spring receiving member  104  may contact the inner tubular portion  85  of the first valve member  80 , so that a maximum valve-opening amount of the second valve member  82  may be defined. 
         [0057]    A second coil spring  106  may be interposed between the upper surface of the valve plate  84  of the first valve member  80  and the lower surface of the spring receiving member  104  so as to be coaxial with these members  80  and  104 . The inner tubular portion  85  of the first valve member  80  may be arranged inside the second coil spring  106 . The second coil spring  106  may urge the second valve member  82  upwards, i.e., in the closing direction. The second coil spring  106  and the first coil spring  97  may be arranged so as to form an inner-outer double spring structure. The coil diameter, the coil length, and the coil wire diameter of the second coil spring  106  may be set to be smaller than those of the first coil spring  97 . Thus, the urging force of the second coil spring  106  may be smaller than the urging force of the first coil spring  97 . 
         [0058]    Next, the seal member  95  will be described. As shown in  FIGS. 5 and 6 , the seal member  95  may include a first seal member  108  and a second seal member  110  arranged on the inner peripheral side of the first seal member  108 . The first seal member  108  and the second seal member  110  may be integrated together. The seal member  95  may be formed of rubber or a like elastic material. The first seal member  108  may include a first base portion  112  having an annular plate shape, and a first seal lip  113  formed on the outer peripheral portion of the lower surface of the first base portion  112 . The first seal lip  113  may have a shape of a conical tube protruding obliquely inwards in the axial direction from the lower surface of the first base portion  112 . The second seal member  110  may have a second base portion  115  having a shape of an annular plate, and a second seal lip  116  formed on the outer peripheral portion of the lower surface of the second base portion  115 . The second seal lip  116  may have a shape of a conical tube protruding obliquely inwards in the axial direction from the lower surface of the second base portion  115 . 
         [0059]    As shown in  FIG. 7 , the second base portion  115  of the second seal member  110  may be formed in series with the inner peripheral side part of the first base portion  112  of the first seal member  108 . In this embodiment, the upper surfaces of the two base portions  112  and  115  may be flush with each other and extend within a same plane. Similarly, the lower surfaces of the two base portions  112  and  115  may be flush with each other and extend within a same plane. Therefore, the two base portions  112  and  115  may have a same thickness in the vertical direction. The second seal member  110  may further include a rib-shaped protrusion  118 . The rib-shaped protrusion  118  may have an annular shape surrounding the outer periphery of the second seal lip  116 . The rib-shaped protrusion  118  may be formed in series with the outer peripheral side part of the base portion of the second seal lip  116 . In this embodiment, the rib-shaped protrusion  118  may have an inverted-triangular sectional shape. 
         [0060]    In the free state (no-load state) of the seal member  95 , assuming that the protruding height of the second seal lip  116  from the lower surface of the second base portion  115  is “A”, and that the protruding height of the rib-shaped protrusion  118  is “B” as shown in  FIG. 7 , there may be a relationship of “A&gt;B”. That is, the leading end (lower end) of the second seal lip  116  may be positioned below the leading end (lower end) of the rib-shaped protrusion  118 . Further, assuming that the protruding height of the first seal lip  113  from the lower surface of the first base portion  112  is “C”, there may be a relationship of “A&gt;C&gt;B”. That is, the leading end (lower end) of the first seal lip  113  may be positioned between the leading end (lower end) of the second seal lip  116  and the leading end (lower end) of the rib-shaped protrusion  118 . 
         [0061]    As shown in  FIG. 2 , both base portions  112  and  115  of the seal member  95  may be attached to the lower surface of the first valve member  80  by an appropriate attaching device such as an adhesive. The first seal lip  113  of the first seal member  108  may be opposed to the first valve seat  72  of the valve housing  58  in the vertical direction. When the first valve member  80  is in the closing position, the first valve member  80  may be downwardly urged by the urging force of the first coil spring  97 , whereby the leading end (lower end) of the first seal lip  113  of the first seal member  108  may elastically contact (i.e. closely contact) the first valve seat  72  (See  FIG. 3 ). 
         [0062]    The second seal lip  116  and the rib-shaped protrusion  118  of the second seal member  110  may be opposed to the second valve portion  102  of the second valve member  82  in the vertical direction. When the second valve member  82  is in the closing position, the second valve member  82  may be upwardly urged by the urging force of the second coil spring  106 , whereby the second valve portion  102  of the second valve member  82  may elastically contact (i.e., closely contact) the leading end (lower end) of the second seal lip  116  of the second seal member  110  and may also elastically contact (i.e., closely contact) the leading end (lower end) of the rib-shaped protrusion  118  (See  FIG. 3 ). 
         [0063]    A predetermined positive side pressure value that is a valve-opening pressure value on the positive pressure side necessary for opening the positive pressure relief valve  60  (See  FIG. 2 ) may be set by the first coil spring  97 . If the pressure in the first passage portion  76  of the fluid communication space  70  (i.e., the pressure on the side of the fuel tank  15 ) is not less than (i.e., greater than or equal to) the predetermined positive side pressure value (i.e., the valve-opening pressure value on the positive pressure side), the first valve member  80  may move upward against the urging force of the first coil spring  97 , whereby the positive pressure relief valve  60  may be opened (See  FIG. 8 ). Then, the first seal lip  113  may be separated (move away) from the valve seat  72  so as to be brought into a free state or a no load state. 
         [0064]    A predetermined negative side pressure value that is a valve-opening pressure value on the negative pressure side necessary for opening the negative pressure relief valve  62  may be set by the second coil spring  106 . If the pressure within the first passage portion  76  of the fluid communication space  70  (i.e., the pressure on the side of the fuel tank  15 ) is less than the predetermined negative side pressure value (i.e., the valve-opening pressure value on the negative pressure side), the second valve member  82  may move downward against the urging of the second coil spring  106 , whereby the negative pressure relief valve  62  may be opened (See  FIG. 9 ). Then, the second seal lip  116  and the rib-shaped protrusion  118  may be separated (move away) from the second valve portion  102  of the second valve member  82  so as to be brought into a free state or a no load state. 
         [0065]    Next, the operation of the flow control valve  56  of the closing valve  38  of the fuel vapor processing apparatus  12  (See  FIG. 1 ) will be described. For the purpose of explanation, the state where the electric valve  52  of the closing valve  38  is in the closed state, and where both relief valves  60  and  62  of the flow control valve  56  are in the closed state (See  FIG. 2 ) will be assumed to be an initial state. In this initial state, if a positive pressure not less than (i.e., greater than or equal to) the predetermined positive side pressure value (i.e., the valve-opening pressure value on the positive pressure side) is generated on the side of the fuel tank  15 , the positive pressure relief valve  60  may be opened (See  FIG. 8 ). Therefore, fluid may flow from the side of the fuel tank  15  to the side of the canister  34  via the first passage portion  76  and the second passage portion  78  (See arrows in  FIG. 8 ). As a result, the pressure in the fuel tank  15  may be lowered. 
         [0066]    If a negative pressure less than the predetermined negative pressure value (i.e., the valve-opening pressure value on the negative pressure side) for the negative pressure relief valve  62  is generated on side of the fuel tank  15 , the second valve member  82  may be opened (See  FIG. 9 ). Therefore, fluid may flow from the canister  34  to the side of the fuel tank  15  via the second passage portion  78  and the first passage portion  76  (See arrows in  FIG. 9 ). As a result, the pressure in the fuel tank  15  may be raised. 
         [0067]    With the flow control valve  56  of this embodiment (See  FIG. 2 ) described above, when the second valve member  82  of the negative pressure relief valve  62  is in the closing position, the second seal lip  116  of the second seal member  110  of the seal member  95  may elastically contact the second valve portion  102  of the second valve member  82 . In addition, the rib-shaped protrusion  118  may elastically contact the second valve portion  102  of the second valve member  82  on the outer peripheral side of the second seal lip  116  (See  FIG. 3 ). As a result, a seal may be formed between the second valve member  82  and the second valve seat  92  of the first valve member  80 . Further, the rib-shaped protrusion  118  may shut off the fluid pressure acting radially from the outer side to the inner side, i.e., the pressure on the positive pressure side in the first passage portion  76 . As a result, potential turning-up of the second seal lip  116  of the second seal member  110  may be suppressed, making it possible to achieve an improvement in terms of sealing property or performance of seal lip  116 . 
         [0068]    Furthermore, the leading end (lower end) of the rib-shaped protrusion  118  in the free state of the second seal member  110  may be positioned on the side of the second base portion  115  with respect to the leading end (lower end) of the second seal member  110  of the second seal member  110  in the free state (See  FIG. 7 ). Therefore, as the second valve member  82  moves to be opened from the closing position, the rib-shaped protrusion  118  may be separated from the second valve portion  102  of the second valve member  82  before the second seal lip  116  is separated from the second valve portion  102 . Further, as the second valve member  82  moves to be closed from the open position, the second seal lip  116  may contact the second valve portion  102  of the second valve member  82  before the rib-shaped protrusion  118  contacts the second valve portion  102 . 
         [0069]    Furthermore, the first valve member  80  and the second valve member  82  may be coaxially fitted with each other such that the first valve seat  72  is arranged in the valve housing  58  and that the second valve seat  92  is arranged at the first valve member  80  (See  FIG. 2 ). Therefore, it is possible to achieve a reduction in the size of the flow control valve  56 . 
         [0070]    Furthermore, the first valve member  80  may serve as a valve member of the positive pressure relief valve  60  and may be opened when the pressure in the first passage portion  76  is not less than (i.e., greater than or equal to) the predetermined positive pressure value, while the second valve member  82  may serve as a valve member of the negative pressure relief valve  62  and may be opened when the pressure in the first passage portion  76  is less than the predetermined negative pressure value (See  FIG. 2 ). Therefore, it is possible to achieve an improvement in terms of the valve-opening accuracy of the negative pressure relief valve  62 . That is, in many cases, the predetermined positive pressure value of the positive pressure relief valve  60  and the predetermined negative pressure value of the negative pressure relief valve  62  may be set such that the “predetermined positive pressure value” &gt;the “predetermined negative pressure value”. In this case, the urging force of the second coil spring  106  may be smaller than the urging force of the first coil spring  97 , so that it is possible to achieve an improvement in the accuracy in the valve-opening operation of the negative pressure relief valve  62 . 
         [0071]    Furthermore, in the above embodiment, the first seal member  108  and the second seal member  110  may be integrated into the seal member  95  as a single seal member, and the seal member  95  may be arranged at the first valve member  80  (See  FIGS. 2 and 3 ). Therefore, it is possible to achieve a reduction in the number of components of the seal member, and to achieve an improvement in terms of ease of mounting to the first valve member  80 . 
         [0072]    Furthermore, the fuel vapor processing apparatus  12  may include the vapor passage  31  for communication between the fuel tank  15  and the canister  34 , and the closing valve  38  operable for opening and closing the vapor passage  31 . In addition, the closing valve  38  may include the electric valve  52  electrically controlled for adjusting the flow rate, the bypass passage  54  for bypassing the electric valve  52 , and the flow control valve  56  disposed in the bypass passage  54  (See  FIG. 1 ). Therefore, the fuel vapor processing apparatus  12  may have the flow control valve  56  in which potential turning-up of the second seal lip  116  of the second seal member  110  is inhibited to achieve an improvement in terms of sealing property. 
         [0073]    A second embodiment will now be described with reference to  FIG. 10 . This embodiment is a modification of the first embodiment and may be different from the first embodiment only in the construction of the flow control valve  56 , in particular the seal member  95  and the first coil spring  97 . In  FIG. 10 , members that are different from corresponding members of the first embodiment are labeled with the same reference numerals but with the additional letter “A” being affixed at the end thereof. The other components that are the same or similar to those of the first embodiment are labeled with the same reference numerals as the first embodiment and a redundant description will be omitted. As shown in  FIG. 10 , in the present embodiment, a diameter of a second seal lip  116 A of a second seal member  110 A may be smaller than the diameter of the second seal lip  116  of the second seal member  110  of the first embodiment (See  FIG. 2 ). Further, a diameter of a rib-shaped protrusion  118 A of a seal member  95 A may be smaller than the diameter of the rib-shaped protrusion  118  of the seal member  95  of the first embodiment (See  FIG. 2 ). More specifically, the diameter of the rib-shaped protrusion  118 A may be set to be the same or substantially the same as the coil diameter of the second coil spring  106 . As a result, the urging force of the second coil spring  106  may efficiently act on the rib-shaped protrusion  118 A of the second seal member  110 A, making it possible to improve the sealing property of the rib-shaped protrusion  118 A. 
         [0074]    Further, the first seal member  108 A may include a rib-shaped protrusion  120  that may be similar in shape to the rib-shaped protrusion  118 A. Further, the coil diameter of the first coil spring  97 A may be larger than that of the first coil spring  97  of the first embodiment. More specifically, the coil diameter of the first coil spring  97 A may be set to be the same or substantially the same as the diameter of the rib-shaped protrusion  120  of the first seal member  108 A. As a result, the urging force of the first coil spring  97 A may efficiently act on the rib-shaped protrusion  120  of the first seal member  108 A, making it possible to improve the sealing property of the rib-shaped protrusion  120 . With the increase in the coil diameter of the first coil spring  97 A, the diameter of the outer tubular portion  86  of the first valve member  80  may be increased. 
         [0075]    A third embodiment will now be described with reference to  FIG. 11 . Also, this embodiment is a modification of the first embodiment and may be different from the first embodiment only in the construction of the flow control valve  56 , in particular the seal member  95 . Therefore, in  FIG. 11 , members that are different from corresponding members of the first embodiment are labeled with the same reference numerals but with the additional letter “B” being affixed at the end thereof. The other members that are the same or similar to those of the first embodiment are labeled with the same reference numerals as the first embodiment and a redundant description will be omitted. As shown in  FIG. 11 , in this embodiment, a seal member  95 B of a flow control valve  56 B may include a first seal member  108 A and a second seal member  110 B that are separated from each other in the radial direction. That is, each of the two seal members  108 B and  110 B is formed as an independent seal member. 
         [0076]    A fourth embodiment will now be described with reference to  FIG. 12 . This embodiment is a modification of the third embodiment. Therefore, in  FIG. 12 , like members components that are the same or similar to those of the third embodiment are labeled with the same reference numerals as the third embodiment and a redundant description will be omitted. As shown in  FIG. 12 , in a flow control valve  56 C of this embodiment, a first seal member  108 C of a seal member  95 C may be different from the first seal member  108 B in that the orientation of the first seal member  108 C is reversed upside down such that the base portion  112  is positioned on the lower side of the first lip  113 . In this connection, the base portion  112  may be attached to the first valve seat  72  of the valve housing  58 . Therefore, the first seal lip  113  may elastically contact the first valve portion  87  of the first valve member  80 . 
         [0077]    A fifth embodiment will now be described with reference to  FIG. 13 . This embodiment is a modification of the fourth embodiment. Therefore, in  FIG. 13 , like members components that are the same or similar to those of the fourth embodiment are labeled with the same reference numerals as the third embodiment and a redundant description will be omitted. As shown in  FIG. 13 , in a flow control valve  56 D of this embodiment, a second seal member  110 D of a seal member  95 D may be different from the second seal member  110 B in that the second seal member  110 D is reversed upside down such that the base portion  115  is positioned on the lower side of the second seal lip  116  and the rib-shaped protrusion  118 . In this connection, the base portion  115  may be attached to the second valve portion  102  of the second valve member  82 . Therefore, the second seal lip  116  and the rib-shaped protrusion  118  may elastically contact the second valve seat  92  of the first valve member  80 . 
         [0078]    The above embodiments may be modified in various ways. For example, the flow control valve  56  ( 56 A,  56 B,  56 C,  56 D) may be used not only for the fuel vapor processing apparatus  12  but also for the other machines and apparatuses that require a control of flow of fluid. Further, as the electric valve  52 , it may be possible to use an electromagnetic valve. For example, the electromagnetic valve may include an electromagnetic solenoid and may be configured to be closed in the non-exited state and to be opened when exited. Further, the seal lip and the rib-shaped protrusion of the seal member may be arranged so as to be spaced away from each other in the radial direction. 
         [0079]    The various examples described above in detail with reference to the attached drawings are intended to be merely representative and thus not limiting. The detailed description is intended to teach a person of skill in the art to make, use and/or practice various aspects of the present teachings and thus is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above may be applied and/or used separately or with other features and teachings to provide improved flow control valves, and/or methods of making and using the same. 
         [0080]    Moreover, the various combinations of features and steps disclosed in the above detailed description may not be necessary to practice the present teachings in the broadest sense, and are instead taught to describe representative examples. Further, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. 
         [0081]    All features disclosed in the description and/or the claims are intended to be disclosed as informational, instructive and/or representative and may thus be construed separately and independently from each other. In addition, all value ranges and/or indications of groups of entities are also intended to include possible intermediate values and/or intermediate entities for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.