The present invention relates to tank pressure control apparatus, and particularly to venting apparatus which operates to seal the vapor space in the interior of a fuel tank during refueling and reopens at some point after refueling has been completed to vent the vapor space. More particularly, the present invention relates to a fill limit system for preventing overfilling of a fuel tank.
Fuel pump nozzles are known to include a fill-limiting sensor for shutting off the flow of fuel from the nozzle when the fuel tank is nearly filled. Typically, this fill-limiting sensor is triggered whenever the fuel tank is full and fuel "backs up" the filler neck to splash onto or reach the fill-limiting sensor located on the nozzle. Sometimes fuel pump operators overfill a fuel tank inadvertently in a good-faith effort to fill the tank "completely" or to purchase a quantity of fuel that can be paid for in cash without causing the operator to receive unwanted coinage in change.
It has been observed that fuel pump operators are able to manually override or bypass some fill-limiting sensors on nozzles by continuing to pump fuel after the pump nozzle has automatically shut off several times. This practice has come to be called the "trickle fill" method of introducing liquid fuel into a fuel tank. Using this well-known trickle fill method, the fuel pump operator "clicks" or squeezes the lever handle on the pump nozzle slowly two or three times in succession after automatic nozzle shutoff has occurred in order to introduce more fuel into the fuel tank without actuating the fill-limiting sensor right away. It will be appreciated that such trickle fill practices can result in overfilling the fuel tank which can effectively reduce the fuel vapor expansion capacity in the vapor space available within the filled fuel tank.
Vehicle fuel systems are known to include valves for venting the vapor space in a fuel tank. See, for example, U.S. Pat. Nos. 4,760,858; 4,991,615; and 5,028,255.
What is needed is a fill limit control system that is able to vent fuel vapor from the vapor space in a fuel tank during early stages of refueling but block introduction of any and all liquid fuel in excess of a maximum volume so as to preserve a minimum volume of the vapor space in the fuel tank once the fuel tank is filled to its maximum capacity with fuel. Ideally, this fill limit control system could be included as one component in a comprehensive Onboard Refueling Vapor Recovery (ORVR) vehicle fuel system. An ORVR system is used to manage fuel vapor recovery during all phases of vehicle use. In addition, a fill limit control system that is adaptable to permit customers some latitude to trickle-fill their fuel tanks without overfilling the fuel tanks would be welcomed by fuel customers and vehicle makers.
According to the present invention, an apparatus is provided for controlling discharge of fuel vapor from a vehicle fuel tank. The apparatus includes a valve housing mounted in a wall of the fuel tank. The valve housing is formed to include a vapor inlet opening communicating with an interior region of the fuel tank, a vapor outlet opening, and a passageway interconnecting the vapor inlet opening and the vapor outlet opening.
The apparatus also includes a float valve and a skirt. The float valve is disposed in the valve housing and movable between an open position allowing flow of tank fuel vapor through the vapor outlet opening and a closed position preventing flow of tank fuel vapor through the vapor outlet opening. The skirt is positioned to lie inside the fuel tank and extend around the valve housing and the vapor inlet opening in the valve housing to define an annular channel lying around the valve housing and conducting fuel vapor from the interior region of the fuel tank to the vapor inlet opening.
The skirt has a bottom edge lying in spaced-apart relation to the top wall of the fuel tank to locate the vapor inlet opening in the valve housing in a position between the top wall of the fuel tank and the bottom edge. The bottom edge of the skirt is positioned to lie in coextensive relation with a top surface of liquid fuel in the interior region of the fuel tank once the volume of liquid fuel in the fuel tank is equal to a predetermined maximum fuel capacity of the fuel tank.
In preferred embodiments, the skirt includes a top wall coupled to the valve housing and an annular side wall appended to the top wall. The annular side wall is positioned to surround the valve housing and define the annular channel therebetween. During refueling, fuel vapor in the fuel tank vapor space will be vented from the fuel tank along a path through the annular channel, vapor inlet opening, passageway, and the vapor outlet opening. Such venting will stop automatically once liquid fuel in the fuel tank rises to a level that is high enough to occlude or close the opening into the annular channel.
In effect, the skirt causes the pump nozzle to shut off at the proper time during refueling due to sudden restriction of the exit vapor flow as the rising level of liquid fuel in the fuel tank covers the annular opening into the annular channel at the bottom of the skirt. This allows the fuel pump operator a small amount of trickle fill without materially raising the liquid fuel level in the fuel tank.
The annular side wall of the skirt extends downwardly to position the bottom edge in spaced-apart relation to the top wall of the fuel tank. During refueling, the rising liquid fuel will reach the bottom edge of the skirt and close the annular opening into the annular channel before it ever reaches the top wall of the fuel tank. Once the opening into the annular channel is closed, no more fuel vapor can be vented from the vapor space in the fuel tank through the annular channel, vapor inlet opening, passageway, and vapor outlet opening. If a pump operator continues to pump fuel into the fuel tank through the filler neck, the pressure in the vapor space will rise and force some liquid fuel in the fuel tank up through the filler neck to reach and trigger the fill-limiting sensor on the pump nozzle.
Advantageously, it is possible to set the maximum fuel capacity of any fuel tank easily by simply mounting a fill-limiting valve assembly in accordance with the present invention so that the bottom edge of the skirt is fixed to lie in coextensive relation with a top surface of liquid fuel in the fuel tank once the volume of liquid fuel in the fuel tank is equal to a predetermined maximum fuel capacity of the fuel tank. It will be understood that use of a bottom edge of the skirt to prevent overfilling of the fuel tank also functions to preserve a minimum volume for the vapor space between the top wall of the fuel tank and the top surface of liquid fuel in the fuel tank.
In use, the float valve is expected to rise in the valve housing and close the vapor outlet opening only if a pump operator uses the trickle fill method to try and introduce more liquid fuel into the tank once the automatic shutoff sensor on the pump nozzle has operated to shut off the pump. In such a case, any extra fuel added into the fuel tank will cause the fuel level inside the annular channel to rise, thereby causing the float valve to rise to its closed position. Illustratively, a spring underneath the float valve provides a float-lifting force in addition to buoyancy forces generated by the rising liquid fuel to move the float valve in the annular channel to its closed position.
Avantageously, a limited amount of trickle fill is permitted by a fill limit valve in accordance with the present invention. In use, after the first automatic pump nozzle shutoff, a pump operator can click the pump nozzle a couple of times to introduce a bit more fuel into the tank. As noted above, this extra fuel displaces fuel already in the tank causing the level of fuel in the annular channel to rise without raising the level of the fuel in the fuel tank outside of the annular channel. In another embodiment, a vertical slot or a small aperture can be formed at the bottom edge of the skirt to allow additional limited trickle fill capability for pump operators without overfilling the tank.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.