Diesel exhaust fluid tank venting system

1. A diesel exhaust fluid storage unit adapted to supply a metered amount of diesel exhaust fluid provided in a diesel exhaust fluid tank to a mixing zone in an exhaust pipe coupled to a diesel engine, the diesel exhaust fluid storage unit comprising

a diesel exhaust fluid tank venting control unit formed to include a fill-limit valve module adapted to receive diesel exhaust fluid from a diesel exhaust fluid tank, a breather-valve module exposed to the atmosphere, and a vapor-transfer module interposed between and coupled in fluid communication to each of the fill-limit valve module and the breather-valve module, wherein the breather-valve module includes an interior chamber and a semi-permeable membrane having a topside exposed to atmospheric air admitted into the interior chamber and an underside exposed to fluid vapor associated with diesel exhaust fluid in the diesel exhaust fluid tank and fluid vapor conducted through vapor transfer module.

2. The diesel exhaust fluid storage unit of claim 1 , wherein the vapor-transfer module is formed to include

a first fluid-conducting passageway configured to provide means for carrying fluid vapor associated with diesel exhaust fluid extant in the diesel exhaust fluid tank and discharged from the fill-limit valve module and an interior region of the diesel exhaust fluid tank to a recirculation line coupled to a tank filler neck associated with the diesel exhaust fluid tank during normal use and refilling of the diesel exhaust fluid tank until the level of diesel exhaust fluid in an interior region of the tank has risen to a fill-limit closure level causing a fill-limit valve included in the fill-limit valve module to move to close an inlet opening into the first fluid-conducting passageway so that tank pressure in the diesel exhaust fluid tank rises and forces diesel exhaust fluid up the tank filler neck to trigger a shut-off mechanism included in a fluid-dispensing pump nozzle used to discharge fluid from a diesel exhaust fluid supply into the tank filler neck and

a second fluid-conducting passageway configured to provide means separate from the first fluid-conducting passageway for conducting fluid vapor extant in the interior region of the diesel exhaust fluid tank and extant in the fill-limit valve module to the underside of the semi-permeable membrane included in the breather-valve module.

3. The diesel exhaust fluid storage unit of claim 2 , wherein the semi-permeable membrane is configured to provide breathing means for regulating discharge of fluid vapor through the semi-permeable membrane to the atmosphere and also for regulating admission of atmospheric air through the semi-permeable membrane into the interior region of the diesel exhaust fluid tank to dissipate any unwanted negative pressure developed in the interior region of the diesel exhaust fluid tank without exposing diesel exhaust fluid in the diesel exhaust fluid tank to enough air to cause that diesel exhaust fluid to change from a liquid state to an unwanted crystalline state.

4. The diesel exhaust fluid storage unit of claim 1 , wherein the vapor-transfer module is formed to include a first fluid-conducting passageway arranged to communicate fluid vapor from the fill-limit valve module to an external recirculation line and a separate second fluid-conducting passageway arranged to communicate fluid vapor and atmospheric air between the fill-limit valve module and the breather-valve module and the semi-permeable membrane is arranged to communicate fluidly with each of the second fluid-conducting passageway formed in the vapor-transfer module and the interior chamber formed in the breather-valve module.

5. The diesel exhaust fluid storage unit of claim 4 , wherein the semi-permeable membrane is configured to provide means for blocking flow of liquid fluid from the second fluid-conducting passageway into the interior chamber and for allowing some fluid vapor to pass from the second fluid-conducting passageway formed in the vapor-transfer module to the atmosphere through the interior chamber formed in the breather-valve module as long as a positive pressure is maintained in the interior region of the diesel exhaust fluid tank and for allowing some atmospheric air to pass from the atmosphere into the interior region of the diesel exhaust fluid tank in sequence through the interior chamber formed in the breather-valve module, the second fluid-conducting passageway formed in the vapor-transfer module, and the fill-limit valve module to dissipate an unwanted negative pressure that might develop in the interior region of the diesel exhaust fluid tank without causing crystallization of liquid diesel exhaust fluid stored in the interior region.

6. The diesel exhaust fluid storage unit of claim 4 , wherein the vapor-transfer module includes an endless outer wall arranged to extend between the fill-limit valve module and the breather-valve module, an interior tube arranged to extend through a space bounded by the endless outer wall and formed to define a portion of the first fluid-conducting passageway, and first and second fins coupled to the interior tube and to the endless outer wall and arranged to lie in spaced-apart relation to one another to define the second fluid-conducting passageway therebetween.

7. The diesel exhaust fluid storage unit of claim 1 , wherein the semi-permeable membrane in the breather-valve module is configured to provide breathing means for regulating flow of atmospheric air into the interior region of the diesel exhaust fluid tank through the vapor-transfer and fill-limit valve modules to maintain a selected positive vapor pressure in the interior region of the diesel exhaust fluid tank without exposing diesel exhaust fluid in the interior region to enough air to change from a normal liquid state to an unwanted crystalline state and also for regulating discharge of fluid vapor from the interior region of the diesel exhaust fluid tank to the atmosphere through the fill-limit valve and vapor-transfer modules to block development of a vapor pressure in the interior region in excess of a selected maximum pressure.

8. The diesel exhaust fluid storage unit of claim 7 , wherein the breather-valve module includes a membrane housing formed to include an interior chamber and a tank breather unit comprising the semi-permeable membrane and a membrane-support frame coupled to the membrane housing and to the semi-permeable membrane to cause the topside of the semi-permeable membrane to be exposed to atmospheric air admitted into the interior chamber and the underside of the semi-permeable membrane to be exposed to the fluid vapor extant in the fuel vapor-module.

9. The diesel exhaust fluid storage unit of claim 8 , wherein the diesel exhaust fluid tank venting control unit further includes a sleeve including, in series, upper, middle, and lower portions, the membrane housing defines the upper portion of the sleeve, the fill-limit valve module includes a fill-limit valve mounted for movement in the lower portion of the sleeve to regulate flow of fuel vapor from the fill-limit valve module into the vapor-transfer module, and the vapor-transfer module is located in the middle portion of the sleeve.

10. The diesel exhaust fluid storage unit of claim 9 , further comprising a diesel exhaust fluid tank formed to include an interior region and a sleeve-receiving aperture opening into the interior region and wherein the sleeve is arranged to extend into the interior region through the sleeve-receiving aperture to locate the fill-limit valve module in the interior region and the breather-valve module outside of the interior region.

11. The diesel exhaust fluid storage unit of claim 10 , wherein the fuel-vapor transfer module is located outside of the interior region and above the fill-limit valve module and below the breather-valve module.

12. The diesel exhaust fluid storage unit of claim 10 , wherein the diesel exhaust fluid tank includes a top wall formed to include the sleeve-receiving aperture and the breather-valve module is located above and in spaced-apart relation to the top wall of the diesel exhaust fluid tank.

13. A diesel exhaust fluid storage unit adapted to supply a metered amount of diesel exhaust fluid provided in a diesel exhaust fluid tank to a mixing zone in an exhaust pipe coupled to a diesel engine, the diesel exhaust fluid storage unit comprising

an elongated sleeve including, in series, a lower portion, a middle portion, and an upper portion,

wherein the lower portion of the elongated sleeve is formed to include a float chamber and a fill-limit valve mounted for up-and-down movement in the float chamber to open and close an inlet into a first fluid-conducting passageway formed in the middle portion of the elongated sleeve,

wherein the middle portion of the elongated sleeve is also formed to include a second fluid-conducting passageway separate from the first fluid-conducting passageway and arranged to communicate fluid vapor and atmospheric air between the fill-limit valve module and the upper portion of the sleeve, and

wherein the upper portion of the elongated sleeve is formed to include an interior chamber open to atmospheric air and a semi-permeable membrane having a topside exposed to atmospheric air admitted into the interior chamber and an underside exposed to fluid vapor conducted through the second fluid-conducting passageway.

14. The diesel fuel exhaust fluid storage unit of claim 13 , further comprising a diesel exhaust fluid tank formed to include an interior region and a sleeve-receiving aperture opening into the interior region and wherein the sleeve is arranged to extend into the interior region through the sleeve-receiving aperture to locate the fill-limit valve in the interior region and the semi-permeable membrane outside of the interior region.

15. The diesel fuel exhaust fluid storage unit of claim 14 , wherein the diesel exhaust fluid tank includes a top wall formed to include the sleeve-receiving aperture and the semi-permeable membrane is located above and in spaced-apart relation to the top wall of the diesel exhaust fluid tank.

16. A diesel exhaust fluid storage unit adapted to supply a metered amount of diesel exhaust fluid provided in a diesel exhaust fluid tank to a mixing zone in an exhaust pipe coupled to a diesel engine, the diesel exhaust fluid storage unit comprising

a diesel exhaust fluid tank formed to include an interior region and a unit-mount aperture formed in a top wall of the diesel exhaust fluid tank to open into the interior region and

a tank venting control unit arranged to extend into the interior region of the diesel exhaust fluid tank through the unit-mount aperture, wherein the tank venting control unit includes a fill-limit valve module located in the interior region of the diesel exhaust fluid tank, a breather-valve module located outside of the interior region of the diesel exhaust fluid tank in spaced-apart relation to the top wall of the diesel exhaust fluid tank, and a vapor-transfer module located outside of the interior region of the diesel exhaust fluid tank and interposed between and in fluid communication with each of the fill-limit valve and breather-valve modules.