US20120006839A1

US20120006839A1 - Fuel tank vent system

Info

Publication number: US20120006839A1
Application number: US12/830,539
Authority: US
Inventors: Peter D. Shears
Original assignee: Briggs and Stratton Corp
Current assignee: Briggs and Stratton Corp
Priority date: 2010-07-06
Filing date: 2010-07-06
Publication date: 2012-01-12

Abstract

An apparatus and method vent a fuel tank through an oleophobic membrane. In one embodiment, a pressure relief valve accommodates pressure buildups that may result from use of the oleophobic membrane. In one embodiment, a vacuum relief valve accommodates pressure drops within the fuel tank. that may result from use of the oleophobic membrane.

Description

BACKGROUND

Fuel tanks are often vented. However, liquid fuel sometimes undesirably enters the vent system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fuel tank vent system according to an example embodiment.

FIG. 2 is a schematic illustration of another embodiment of the fuel tank vent system of FIG. 1.

FIG. 3 is a schematic illustration of another embodiment of the fuel tank vent system of FIG. 1 according to an example embodiment.

FIG. 4 is a schematic illustration of another embodiment of the fuel tank vent system of FIG. 1 according to an example embodiment.

FIG. 5 is a draft illustrating operational characteristics of the fuel tank vent system of FIG. 4 according to an example embodiment.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

FIG. 1 schematically illustrates a fuel tank vent system 10 according to an example embodiment. As will be described hereafter, fuel tank vent system 10 vents a fuel tank through an oleophobic membrane which inhibits liquid fuel from entering the vent system. Fuel tank vent system can further includes one or both of a carburetor and a pressure release valve that accommodate pressure buildups while a vacuum relief valve accommodates pressure drops within the fuel tank that may result from use of the oleophobic membrane.
Fuel tank vent system 10 includes fuel tank 12, vent conduits 14A, 14B (collectively referred to as vent conduits 14), membranes 16A, 16B (collectively referred to as membrane 16), vapor system 18, fuel pump 20, carburetor 22 of fuel intake system 24, pressure relief valve 28 and vacuum relief valve 30. Fuel tank 12 comprises a tank configured to contain and supply fuel for use by an internal combustion engine having intake system 24. In one embodiment, fuel tank 12 comprises a plastic fuel tank. In other embodiments, fuel tank 12 may be formed from other materials.
Vent conduits 14 comprise openings within or passages extending from fuel tank 12 through which an interior of the fuel tank 12 is vented. Vent conduits 14 communicate with an interior of fuel tank 12 proximate to a top side of fuel tank 12, allowing fuel vapors to rise and pass through vent conduits 14. Vent conduits 14 direct vapors from fuel tank 12 to membranes 16.
Although system 10 is illustrated as including two vent conduits 14, in other embodiments, system 10 may include a single vent conduit 14 or more than two vent conduits 14. In one embodiment, vent conduits 14 comprise tubes extending from fuel tank 12 to membranes 16. In another embodiment, vent conduits 14 merely comprise openings within fuel tank 12, wherein membranes 16 are located within the openings and within the walls around the openings in fuel tank 12.
Membranes 16 comprise oleophobic membranes configured to allow the flow of vapors or gases therethrough while preventing or inhibiting the flow or movement of fuel and other liquids across such membranes. Membranes 16 have high gas permeabilities while repelling liquids. Membranes 16 extend between fuel tank 12 and vapor system 18 to inhibit fuel from entering vapor system 18 while permitting gases or vapors to pass to vapor system 18. Although system 10 is illustrated as including two membranes 16, in other embodiments, system 10 may include a single membrane 16 or more than two membranes 16.
In one embodiment, membranes 16 each comprise a filter medium substrate treated with a coating material including a cross-linked fluorosulfone-containing oligomer, which coats the surface of the substrate. This coating provides permanent oleophobicity and hydrophobicity to the filter. Examples of the material from which membrane 16 may be provided are found in U.S. Pat. No. 6,579,342 issued on Jun. 17, 2003 to Wang et al., the full disclosure of which is hereby incorporated by reference. In other embodiments, membranes 16 may be provided by other hydrophobic or oleophobic filters or materials.
Vapor system 18 comprises one or more mechanisms configured to inhibit or reduce the extent to which vapors are released to atmosphere. In one embodiment, vapor system 18 comprises one or more carbon canisters configured to collect and store hydrocarbons for later use or disposal. In another embodiment, vapor system 18 comprises one or more conduits which direct vapors back to fuel intake system 24 where the hydrocarbons are consumed. For example, in one embodiment, such conduits direct hydrocarbons back to an upstream side of carburetor 22. In some embodiments, vapor system 18 may additionally include one or more filters for filtering predetermined vapor components, wherein some predetermined vapor components, such as hydrocarbons, are redirected for storage or consumption and wherein other predetermined vapor components are permitted to be released to atmosphere. In some embodiments, vapor system 18 may have other configurations for filtering, consuming and/or storing vapors from fuel tank 12.
Fuel pump 20 comprises a fuel pump operatively coupled between fuel tank 12 and fuel intake system 24 so as to pump or pressurize the flow of fuel from tank 12 to intake system 24. Fuel pump 20 increases the flow of fuel from fuel tank 12 to overcome the otherwise restriction of fuel flow that may occur when membranes 16 become fuel wetted. In some embodiments, fuel pump 20 may be omitted.
Carburetor 22 is part of fuel intake system 24 and is configured to blend air and fuel from fuel tank 12 for use by an internal combustion engine including fuel intake system 24. As compared to internal combustion engines without membranes 16, carburetor 22 is configured to restrict intake of fuel to fuel intake system 24. In particular, carburetor 22 may have a smaller bowl inlet needle valve seat diameter to counteract high fuel supply pressures that may occur when membranes 16 become fuel wetted. In yet other embodiments, where fuel intake system 24 is part of a fuel injection system, carburetor 22 may be omitted.
Pressure relief valve 28 comprises a valve mechanism in pneumatic communication with an interior of fuel tank 12 which is configured to relieve or lessen pressure within an interior of tank 12 when pressures within tank 12 exceed a predetermined threshold. Pressure relief valve 28 inhibit excess pressure build up within fuel tank 12 which might occur during fuel heating on warm-up, during wetting of membrane 16 and during diurnal heating. Pressure relief valve 28 inhibit pressure buildups within fuel tank 12 that might otherwise damage, deform or expand tank 12 to an undesirable extent, such as when fuel tank 12 comprises a plastic fuel tank. For example, pressure relief valve 28 may prevent undesirable expansion of fuel tank 12 into contact with a hot part of an engine which might melt or damage fuel tank 12. Pressure relief valve 28 may additionally inhibit excessive pressurization of fuel being delivered to fuel intake system 24 such that a proper flow rate of fuel to fuel intake system 24 is achieved. Nominally the pressure relief valve 28 is closed forcing fuel tank vapors through vapor system 18.
Vacuum relief valve 30 comprises a valve mechanism in pneumatic communication with an interior of fuel tank 12 which is configured to relieve or lessen vacuum within an interior of tank 12 when the vacuum within tank 12 exceeds a predetermined threshold. Vacuum relief valve 30 inhibits excess vacuum within fuel tank 12 which might otherwise damage, deform or contract tank 12 to an undesirable extent, such as when fuel tank 12 comprises a plastic fuel tank. Vacuum relief valve 30 counteracts any vacuum that may occur during fuel use or diurnal tank cooling. In one embodiment, vacuum relief valve 30 is configured to limit vacuum within fuel tank 12 to less than three inches of water vacuum relative to atmosphere. In some embodiments, vacuum relief valve 30 may be omitted.
As schematically shown in FIG. 1, in the example illustrated, pressure relief valve 28 and vacuum relief valve 30 are both incorporated into and as part of a fuel tank cap 34. For example, 34, which includes valve 28 and 30, may screw or otherwise fit into a fill opening 36 through exterior walls of fuel tank 12 so as to close off the fill opening 36 of fuel tank 12. Cap 30 is configured to be removed or separated from fuel tank 12, allowing fuel to be filled into fuel tank 12, and then later reattached to fuel tank 12 covering the fill opening 36. As a result, the construction of fuel tank 12 is simplified and repair, replacement by subsequent addition of cap 34 including valve 28 and 30 is facilitated.
In other embodiments, pressure relief valve 28 may alternatively be incorporated into a wall of fuel tank 12. In other embodiments, the vacuum relief valve 30 may be incorporated as part of a wall of fuel tank 12. In yet other embodiments, both pressure relief valve 28 and vacuum relief valve 30 may be provided in a wall of fuel tank 12 rather than being incorporated into cap 34. In yet other embodiments, pressure relief valve 28 and vacuum relief valve 30 may be provided as part of a single valve mechanism which relieves pressure within fuel tank 12 at a predetermined pressure threshold within tank 12 and which also relieves vacuum within fuel tank 12 at a predetermined vacuum threshold within tank 12. For example, in one body, pressure relief valve 28 and vacuum relief valve 30 may be provided as part of a single duck bill umbrella valve mechanism.
Overall, fuel tank vent system 10 collects or consumes fuel vapors. One or both of a carburetor and a pressure release valve accommodate pressure buildups while a vacuum relief valve accommodates pressure drops within the fuel tank that may result from use of the oleophobic membrane. As a result, fuel tank vent system 10 counteracts negative side effects of such membranes 16 to prevent damage to fuel tank 12 and ensure proper fuel flow to the fuel intake system 24.
FIG. 2 schematically illustrates fuel tank vent system 110, another embodiment of fuel tank vent system 10. Fuel tank vent system 110 is similar to fuel tank vent system 10 except that fuel tank vent system 110 includes carbon canister 118, vacuum relief valve 130 and cap 134 in place of vapor system 18, vacuum relief valve 30 and cap 34, respectively. Those remaining components of fuel tank vent system 110 which correspond to components of fuel tank vent system 10 are numbered similarly.
Carbon canister 118 comprises a particular embodiment of vapor system 18. Carbon canister 118 comprises one or more carbon collection canisters or containers configured to collect and store hydrocarbons for later use or disposal. Carbon canister 118 receives hydrocarbon vapors that have passed through membranes 16. In other embodiments, carbon canister 118 may comprise other vapor collection and/or consumption mechanisms.
Vacuum relief valve 130 and cap 134 are similar to vacuum relief valve 30 and cap 34 except that vacuum relief valve 130 is not incorporated as part of cap 134, but is instead incorporated as part of wall 138 of fuel tank 12. Cap 134 merely includes pressure relief valve 28. Vacuum relief valve 130 and pressure relief valve 28 perform similar functions as those performed by pressure relief valve 28 and vacuum relief valve 30 described above.
FIG. 3 schematically illustrates fuel tank vent system 210, another embodiment of fuel tank vent system 10. Fuel tank vent system 110 is similar to fuel tank vent system 10 except that fuel tank vent system 110 includes vapor return conduit 218, pressure relief valve 228, vacuum relief valve 230 and cap 234 in place of vapor system 18, pressure relief valve 28, vacuum relief valve 30 and cap 34, respectively. Those remaining components of fuel tank vent system 110 which correspond to components of fuel tank vent system 10 are numbered similarly.
Vapor return conduit 218 comprises a particular embodiment of vapor system 18. Vapor return conduit 218 comprises one or more conduits configured to direct vapors back to fuel intake system 24 where the hydrocarbons are consumed. For example, in one embodiment, such conduits direct hydrocarbons back to an upstream side of carburetor 22. In some embodiments, vapor system 18 may additionally include one or more filters for filtering predetermined vapor components, wherein some predetermined vapor components, such as hydrocarbons, are redirected for consumption and wherein other predetermined vapor components are permitted to be released to atmosphere or are directed to collection canisters. In some embodiments, vapor system 218 may have other configurations for filtering, consuming and/or storing vapors from fuel tank 12.
Pressure relief valve 228, vacuum relief valve 230 and cap 134 are similar to pressure relief valve 28, vacuum relief valve 30 and cap 34 except that pressure relief valve 228 and vacuum relief valve 230 are not incorporated as part of cap 234, but are instead incorporated as part of wall 138 of fuel tank 12. Pressure relief valve 228 and vacuum relief valve 130 perform similar functions as those performed by pressure relief valve 28 and vacuum relief valve 30 described above.
FIG. 4 schematically illustrates fuel tank vent system 310, another embodiment of fuel tank vent system 210. Fuel tank vent system 310 is identical to fuel tank vent system 210 except that fuel tank vent system 310 is specifically illustrated as having a fuel tank 312 including a fill tube or fill neck 313. Fill neck 313 comprises a tube extending to a predetermined location or depth into an interior of fuel tank 212. Fill neck 313 assists in regulating the filling of tank 312 to inhibit over-filling of tank 312.
FIG. 5 is a graph or chart illustrating venting characteristics of pressure relief valve 228 and vacuum relief valve 230 when incorporated into fuel tank vent system 310. As shown by area 400, vacuum relief valve 230 is configured to vent air or gas into tank 312 at a flow rate greater than or equal to a maximum anticipated fuel consumption rate for the engine being supplied with fuel (F_fcmax). In the example illustrated, vacuum relief valve 230 vents air into tank 312 at a flow rate of at least 25 cubic centimeters per minute (ccm or sccm). As a result, vacuum relief valve 230 accommodates any vacuum that may result from an airflow restriction resulting from use of the oleophobic during start up of the engine so as to maintain a desired air to fuel ratio in the fuel being supplied to the engine.
As shown by area 402, pressure relief valve 228 is configured to vent out gas from the interior of fuel tank 312 during filling of tank 312 with fuel. Pressure relief valve 228 is configured to send out gas at a flow rate of no greater than V/T, wherein V is a volume of the fill neck 313 and wherein T is the desired recession time for a given capacity of tank 312 (the desired amount of time for fuel within fuel neck 3132 to recede when a desired percentage of the interior of the fuel tank 312 has been filled with fuel). Pressure relief valve 230 releases or vents gas from tank 312 at a maximum rate of V/T until the pressure within tank 312 attains a pressure of P_n. Pressure P_nis the neck head pressure or the distance between a rim of filler neck 313 and a desired fill capacity (nominally in a range from 2-6 inches). In the example illustrated, pressure relief valve 228 is configured to vent out gas from the interior of the fuel tank at a flow rate of between about 30 ccm and 170 ccm up to a pressure within the interior of the tank of 1.2 KPa. As a result, pressure relief valve 228 cooperates with fill neck 313 to provide a user with a positive indication of when fuel tank 312 is filled to its desired fill capacity, accommodating pressure changes resulting from membranes 16.
As shown by area 404, pressure relief valve 228 is further configured to vent vapors or gas from the interior of tank 312 at pressures exceeding P_n. As shown by area 406, when the pressure within tank 312 reaches a pressure which the air to fuel ratio being supplied to the engine is detrimentally impacted, pressure relief valve 228 vents gas at a flow rate of at least F_TMmaxstarting at a maximum pressure within the interior of the tank (P_AFI) that causes the air to fuel ratio to lie outside the air to fuel ratio operating range of the engine being supplied with fuel. In the example illustrated, the flow rate F_TMmaxis greater than or equal to a rate at which pressure increases within the interior from thermal expansion and motion generated vapors. As a result, pressure relief valve 228 accommodates pressure increases that may result from membranes 16 (shown in FIG. 3) to maintain an appropriate air to fuel ratio of the fuel being supplied to the engine from fuel tank 12.
Although the present disclosure has been described with example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.

Claims

1. An apparatus comprising:

a fuel tank;

a vent conduit extending from an interior of the fuel tank;

an oleophobic membrane across the vent conduit; and

a vacuum relief valve between the interior of the fuel tank and atmosphere.

2. The apparatus of claim 1 further comprising a pressure relief valve between the interior of the tank and atmosphere.

3. The apparatus of claim 2, wherein the pressure relief valve is configured to vent out gas from the interior of the fuel tank at a flow rate of between about 30 ccm and 170 ccm up to a pressure within the interior of the tank of 1.2 KPa.

4. The apparatus of claim 3, wherein the fuel tank is configured to supply fuel to an engine configured to operate using an air to fuel ratio within an intended range and wherein the pressure relief valve is configured to vent gas out of the interior of the tank at a flow rate of at least F_TMmaxstarting at a maximum pressure within the interior of the tank that causes the air to fuel ratio to lie outside the intended range and wherein the flow rate F_TMmaxis greater than or equal to the rate of thermal and vapor expansion within the fuel tank due to increasing thermal transients and motion generated vapors.

5. The apparatus of claim 2 further comprising a cap incorporating the pressure relief valve.

6. The apparatus of claim 5, wherein the cap incorporates the vacuum relief valve.

7. The apparatus of claim 1 further comprising a fuel tank incorporating the pressure relief valve.

8. The apparatus of claim 7, wherein the cap incorporates the vacuum relief valve.

9. The apparatus of claim 1, wherein the cap incorporates the vacuum relief valve.

10. The apparatus of claim 1, wherein the fuel tank has an outer wall incorporating the vacuum relief valve.

11. The apparatus of claim 1, wherein the vacuum relief valve is configured to vent gas into the interior of the fuel tank at a flow rate of at least 25 ccm.

12. The apparatus of claim 1 further comprising:

a second that conduit influence communication with the interior of the fuel tank; and

a second oleophobic membrane across the second vent conduit.

13. The apparatus of claim 1 further comprising a carbon canister connected to the vent conduit on an opposite side of the oleophobic membrane as the fuel tank.

14. The apparatus of claim 1, wherein the vent conduit is connected to an intake system of an engine including the carburetor.

15. An apparatus comprising:

a fuel tank;

a vent conduit extending from an interior of the fuel tank;

an oleophobic membrane across the vent conduit;

a pressure relief valve in fluid communication with the interior of the tank; and

a vacuum relief valve between the interior of the fuel tank and atmosphere.

16. The apparatus of claim 15, wherein the pressure relief valve is configured to vent out gas from the interior of the fuel tank at a flow rate of between about 30 ccm and 170 ccm up to a pressure within the interior of the tank of 1.2 KPa.

17. The apparatus of claim 15, wherein the fuel tank is configured to supply fuel to an engine configured to operate using an air to fuel ratio within a range and wherein the pressure relief valve is configured to vent gas out of the interior of the tank at a flow rate of at least F_TMmaxstarting at a maximum pressure within the interior of the tank that causes the air to fuel ratio to lie outside the range and wherein the flow rate F_TMmaxis greater than or equal to the rate of thermal and vapor expansion within the fuel tank due to increasing thermal transients and motion generated vapors.

18. The apparatus of claim 15 further comprising a carburetor operatively coupled to the fuel tank and a fuel pump operatively coupled between the fuel tank and the carburetor.

19. The apparatus of claim 15 further comprising a cap incorporating at least one of the pressure relief valve and the vacuum relief valve.

20. A method comprising:

venting an interior of a fuel tank across an oleophobic membrane to a vapor handling system; and

relieving a vacuum in the fuel tank through a vacuum relief valve.