Abstract:
An isolation valve has a housing having a vent path and a sealing member that opens and closes the vent path. The sealing member is driven by a motor via a gear arrangement that links the sealing member with the motor. The motor drives the gear arrangement in a first direction to open the vent path and a second direction to close the vent path. During operation, a motor current rises when the sealing member reaches the first position and/or the second position. The controller detects the motor current rise and changes operation of the motor (e.g., stops the motor) in response.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a valve assembly for controlling fluid flow to and from a high-pressure fuel tank, and more particularly to such a valve assembly having a motor-driven seal. 
       BACKGROUND OF THE INVENTION 
       [0002]    High-pressure fluid reservoirs, such as high-pressure fuel tanks, may use an isolation valve to open and close a vapor path between the fuel tank and a purge canister. In a typical evaporative emissions system, vented vapors from the fuel system are sent to a purge canister containing activated charcoal, which adsorbs fuel vapors. During certain engine operational modes, with the help of specifically designed control valves, the fuel vapors are adsorbed within the canister. Subsequently, during other engine operational modes, and with the help of additional control valves, fresh air is drawn through the canister, pulling the fuel vapor into the engine where it is burned. 
         [0003]    For high-pressure fuel tank systems, an isolation valve may be used to isolate fuel tank emissions and prevent them from overloading the canister and vapor lines. In some systems, it may be desirable to isolate the fuel tank except during refueling or during extreme pressure conditions to avoid the potential risk of damage to the system. Due to the high-pressure environments in which isolation valves often operate, the sealing mechanisms in the isolation valve should operate consistently. 
         [0004]    There is a desire for a system that ensures consistent seal operation while keeping the overall isolation valve structure simple. 
       SUMMARY OF THE INVENTION 
       [0005]    An isolation valve according to one embodiment of the invention comprises a housing having a vent path and a sealing member aligned with the vent path and movable between a first position to open the vent path and a second position to close the vent path. The sealing member is driven by a motor that is controllable by a controller, and a gear arrangement couples the motor with the sealing member. The motor drives the gear arrangement in a first direction to open the vent path and a second direction to close the vent path. During operation, a motor current rises when the sealing member reaches one of the first position and the second position, and the controller detects the motor current rise and changes operation of the motor in response. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic diagram of an isolation valve according to one embodiment of the invention where a seal is in an open position; 
           [0007]      FIG. 2  is a schematic diagram of the isolation valve in  FIG. 1  where the seal is in a closed position; and 
           [0008]      FIG. 3  is a schematic diagram of an isolation valve according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]      FIG. 1  is a representative diagram of an isolation valve  10  according to one embodiment of the invention. In this example, the isolation valve  10  has a housing  11  and is arranged as an inline valve disposed in a vent path  12  formed in the housing  11  and opening into a fuel tank  13 . However, the isolation valve  10  can be disposed in a high-pressure fluid system in any way without departing from the scope of the invention. For example, the housing  11  can be configured to be mounted on or in the fuel tank  13 . 
         [0010]    In one embodiment, the isolation valve  10  may have a sealing member  14  disposed in the vent path  12  and aligned with a seat  15 . The sealing member  14  itself may have any appropriate structure that provides secure sealing in the isolation valve  10 .  FIGS. 1 and 3  show a sealing member  14  having a seal plate  14   a  and a gasket  14   b  to prevent leakage, while  FIG. 2  shows a sealing member  14  having a tapered stopper  14   c  with the gasket  14   b  to ensure good alignment between the sealing member  14  and the seat  15 . Those of ordinary skill in the art will recognize other possible sealing member  14  structures that may be used without departing from the scope of the invention. 
         [0011]    The sealing member  14  may be driven by an electric motor  16  that actuates a gear arrangement  18 . The gear arrangement  18  may be any appropriate gear system, such as planetary gears, worm drives, or other systems. The example shown in  FIG. 1  uses a worm drive, but those of ordinary skill in the art will understand that the gear arrangement  18  can have any configuration without departing from the scope of the invention. The sealing member  14 , seat  15 , motor  16 , and gear arrangement  18  are operatively coupled to open and close the vent path  12 . 
         [0012]    Operation of the isolation valve  10 , and more particularly operation of the motor  16 , may be controlled by a vehicle controller  24 . The controller  24  sends signals to the motor  16  to start and stop of the motor  16  as well as control its direction of operation based on various inputs such as, for example, a sensed tank pressure. Possible motor  16  operation modes will be described in more detail below. 
         [0013]    The operation of the isolation valve  10  will now be described with respect to  FIGS. 1 and 2 . To close the valve  10 , the controller  24  sends a signal to the valve  10  to start operation of the motor  16 . The motor  16  in turn operates the gear arrangement  18 , in turn lowers the sealing member  14  until the sealing member  14  contacts the seat  15 . In one embodiment, there is a hard stop  25  that limits the downward travel of the sealing member  14 . When the hard stop  25  is reached, the motor  16  stalls and the current through the motor  16  will spike, and this spike is detected by the controller  24 . The controller  24  then stops supplying current to the motor  16 , stopping the downward movement of the sealing member  14 . At this point, the sealing member  14  closes the vent path  12 . The location of the hard stop  25  dictates the location at which the sealing member  14  stop, which in turn affects the load applied by the sealing member  14  onto the seat  15 . If a lost motion member  26  is used as described in more detail below, the location of the hard stop  25  also controls the amount of spring force applied by the lost motion member  26  onto the sealing member  14  when it closes the vent path  12 . 
         [0014]    To open the vent path, the isolation valve  10  works the same way as described above but in reverse. More particularly, the controller  24  sends a signal to the motor  16  to open the valve  10 , causing the motor  16  to turn the gear arrangement  18  in the opposite direction and lift the sealing member  14  off the seat  15 . Note that a hard stop may be included to stop the motor  16  in this direction as well, but since the sealing member  14  operation does not necessarily need to be as precise in this direction, the motor  16  may be stopped in this direction simply when the moving parts in the motor  16  bottom out (e.g., when they are completely threaded together). 
         [0015]    Although the sealing member  14  provides a secure seal, it may be desirable to provide additional structures in the isolation valve  10  to ensure consistent sealing despite variations and changes in the motor  16  and/or the gear arrangement  18  due to, for example, wear, design, assembly, or manufacturing. Thus, the isolation valve  10  may also include the lost motion member  26 , such as a spring, that applies a downward biasing force to the sealing member  14  to bias the sealing member  14  toward the seat  15 . This biasing force helps the isolation valve  10  become less sensitive to positional and force variations in the motor  16  and gear arrangement  18 , ensuring consistent sealing action despite these variations. 
         [0016]    In one embodiment, the biasing force in the lost motion member  26  allows the isolation valve  10  to be used as an overpressure relief device. More particularly, the lost motion member  26  applies a spring force when the motor  16  bottoms out due to the hard stop  25  and stops operation. As noted above, this spring force, combined with the location of the sealing member  14  when in the closed position, controls the amount of load on the seat  15  when the isolation valve  10  is closed. 
         [0017]    The lost motion member  26  also allows the isolation valve  10  to act as a bleed valve by gradually allowing pressure to escape before opening completely. For example, to bleed pressure through the isolation valve  10 , the motor  16  and gear arrangement  18  may turn only slightly to lift the sealing member  14  slightly of the seat  15 . However, the biasing force from the lost motion member  26  tends to bias the sealing member  14  downward toward the seat  15 . As a result, the high vapor pressure in the vent path  12  may counteract the biasing force of the lost motion member  26  and allow vapor to escape, but the small space between the sealing member  14  and the seat  15  prevents vapors from rushing through the vent path  12  at full force. Thus, vapor can bleed in a controlled manner through the vent path  12 , gradually reducing the vapor pressure until, for example, the pressure level drops to a level where the valve  10  can be opened completely in a controlled manner without adverse effects elsewhere in the emissions system. This gradual bleeding can be controlled even further by incorporating the stopper  14   c  since the small gap between the stopper  14   c  and the walls forming the vent path  12  chokes vapor flow. 
         [0018]    In other words, the combination of the motor  16  and the biasing force of the lost motion member  26  allows close control over the amount of pressure relief provided by the isolation valve  10 . The specific degree of pressure relief may be fine-tuned by selecting the biasing force of the lost motion member  26  so that it has a predetermined degree of compression at a given motor  16  position. For example, the biasing force may be selected to provide a desired amount of pressure relief during an overpressure condition. 
         [0019]      FIG. 3  illustrates the isolation valve  10  according to another embodiment of the invention. In this embodiment, the isolation valve  10  may be disposed outside the fuel tank  13 , and the motor  16  itself is disposed outside the housing  11  of the isolation valve  10 . In this embodiment, a shaft  32  extends through the housing  11  to couple the motor  16  with the sealing member  14 . A shaft seal  34  may be used to prevent leakage through the housing  11 . The other components of the isolation valve  10  operate in the same manner as the embodiments described above. 
         [0020]    If the isolation valve  10  is used in an environment where vacuum pressures are a potential issue, a vacuum relief valve  36  may be incorporated into the emissions system or even within the isolation valve  10  itself. 
         [0021]    Because the operation of the isolation valve  10  is controlled by the controller  24 , its operation does not depend on responding to changes in tank pressure. Thus, the isolation valve  10  may also be used as a fuel limit valve. For example, a fuel level sensor (not shown) may be used to monitor a fuel level in a tank and send a signal to the controller  24  when the tank is full. The controller  24  then sends a signal to the isolation valve  10  to close, thereby allowing pressure to build up in the tank and induce shutoff in a refilling nozzle. 
         [0022]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.