Patent Application
20120211687
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.
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.
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.
There is a desire for a system that ensures consistent seal operation while keeping the overall isolation valve structure simple.
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.
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.
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
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.
The operation of the isolation valve 10 will now be described with respect to
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).
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.
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.
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 14c since the small gap between the stopper 14c and the walls forming the vent path 12 chokes vapor flow.
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.
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.
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.
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.
