Abstract:
A diesel exhaust fluid (DEF) delivery system includes a tank for DEF, usually a urea aqueous solution, and a pump receiving the DEF from the tank for pressurization and delivery through a nozzle to the exhaust system of a work machine. A breather assembly is provided for the DEF tank and includes a housing having an inlet for ambient air and a particle filter adjacent the inlet for filtering particles. A hydrophobic membrane is interposed between the particle filter and an outlet leading to the tank for preventing outflow of DEF vapor and condensate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to diesel exhaust fluid (DEF) delivery systems, and, more particularly, to breather assemblies for such systems. 
         [0003]    2. Description of the Related Art 
         [0004]    As the Environmental Protection Agency (EPA) regulations covering combustion engine emissions are applied to ever more applications, the agricultural art and more broadly work machines are being required to comply with the EPA emissions limits already applied to on-highway vehicle applications. Many approaches have been proposed, but a cost-effective one is utilizing diesel exhaust fluid (DEF) injected into the exhaust stream of a diesel engine and providing a chemical reaction with the exhaust stream to enable a downstream SCR to produce appropriate reductions in nitrous oxide emissions. 
         [0005]    One of the keys to this approach is the DEF delivery system. Current systems include a tank for the DEF, a pressure pump and a nozzle for injecting the DEF into the diesel exhaust system. Typical systems incorporate a control system for coordinating the injection of DEF with appropriate engine duty cycles so that the proper chemical reactions may take place. The DEF is typically a urea-aqueous solution that, while nonflammable, poses several application challenges. 
         [0006]    The tanks for the DEF are rigid and as a result must include a breather assembly to permit ingress of air as the DEF is depleted from the tank. While this approach has been relatively straightforward for on-highway applications, the use in a work machine such as an agricultural combine presents unique problems. These problems are associated with the ambient air which has significant particulate contaminants of both a microscopic and macroscopic size. Existing systems may utilize hydrophobic membranes on the breather assembly to prevent outflow of the DEF vapors and condensate. However, such a system does not take into account the particulates that may be drawn into the breather assembly and clog the hydrophobic membrane. Such a restriction can cause the interior pressure of the DEF tank to be lowered to a point where proper delivery of the DEF to the exhaust flow is inhibited. 
         [0007]    Likewise, breather assemblies that use a particulate filter permit DEF vapors and condensate to permeate the filter, thus causing crystal buildup and eventual clogging. 
         [0008]    What is needed in the art, therefore, is a system for breather assemblies that operates efficiently and effectively in the work machine environment. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a simplified and reliable DEF breather assembly for the work machine environment and more particularly for agricultural combines. 
         [0010]    The invention, in one form, is directed to a breather assembly for a diesel exhaust fluid (DEF) tank, including a housing having an inlet for ambient air, and interior chamber and an outlet fluidly connectable to the DEF tank. A particle filter is positioned adjacent the ambient air inlet for filtering particles from the air entering the interior chamber and an hydrophobic membrane in the chamber is interposed between the particle filter and the outlet for preventing the DEF vapors and condensate from passing to the ambient. 
         [0011]    The invention, in another form, is directed to a diesel exhaust fluid (DEF) delivery system including a tank for DEF, a pump receiving DEF from the tank and a nozzle for delivering the DEF to the exhaust system of a engine for a work machine. The DEF system includes a breather assembly fluidly connected to the DEF tank and having a housing with an inlet for ambient air, an interior chamber and an outlet connected fluidly connected to the DEF tank. A particle filter is positioned adjacent the ambient air inlet for filtering particles from the air entering the interior chamber. A hydrophobic membrane is positioned in the chamber and interposed between the particle filter and the outlet for preventing DEF vapors and condensate from reaching the particle filter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of several embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a perspective view of a DEF delivery system embodying the present invention. 
           [0014]      FIG. 2  is a cross-section view of one embodiment of a breather assembly used in the DEF delivery system of  FIG. 1   
           [0015]      FIG. 3  is a perspective view of the breather assembly of  FIG. 2 . 
           [0016]      FIG. 4  is a cross-sectional view of an alternate embodiment of the breather assembly utilized in the DEF delivery system of  FIG. 1 . 
           [0017]      FIG. 5  is a plan view, in an upward direction, of the breather assembly of  FIG. 4 . 
       
    
    
       [0018]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate several embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a DEF delivery system  10  including a storage tank  12  for DEF fluid for delivery to a nozzle  14  located in the exhaust stream  16  of a work machine which is not shown to enable a better understanding of the present invention. Typically, engines for work machines are compression ignition, or diesels because of their torque capacity, durability and fuel economy. 
         [0020]    Preferably the work machine is an agricultural combine which traverses a field containing crops and harvests them for collection and delivery to market. As stated above, EPA emission regulations applied to on-highway vehicles are being phased in to the off-highway field. 
         [0021]    The DEF delivered to nozzle  14  in the exhaust system  16  causes a chemical reaction with selective catalytic reduction (SCR) to achieve reductions in nitrous oxides and meet the EPA limitation. A discussion of the details of this process is not included to simplify the understanding of the present invention. 
         [0022]    The DEF delivery system  10  has a filler tube  18  extending from tank  12  to terminate in end fitting  20  having a removable cap  22  to permit filling of the tank  12  in a manner similar to other replenishable fluids in a work machine environment. In order to provide proper venting of tank  12  during the filling process, a vent conduit  24  extends from a vent passage (not shown) in end fitting  20  to a fitting  28  on the top surface  26  of tank  12 . Thus, when the tank  12  is being filled, the air above the liquid in tank  12  is expelled through conduit  24  to prevent an airlock. 
         [0023]    The upper surface  26  of tank  12  has a removeable access plate  30  providing interconnections with a bundle of conduits  32  leading to a pump  34 , usually electrically driven, that pressurizes DEF for injection and provides return flow. And outlet bundle of conduits  36  extends from the pump  34  to the nozzle assembly  14  in the exhaust  16 . Of special interest in the bundle  32  is the suction line  38  for DEF leading to pump  34 . In addition, there is a pressure line  40  in bundle  36  leading to nozzle assembly  14 . 
         [0024]    When tank  12  is full of DEF, cap  22  is secured on end fitting  20 , thus sealing that part of the system. Pump  34  is actuated in accordance with control inputs from a controller (not shown) to deliver pressurized DEF to nozzle  14  for minimizing emissions. As the tank  12  is depleted of DEF, the space in the tank above the DEF needs to be connected to ambient and this is done by a breather tube  42  fluidly connected to access plate  30  and leading to breather assembly  44  and secured thereto by a fitting  45 . Thus, when DEF is being delivered from tank  12 , air is passing into tank  12  via breather assembly  44  and tube  42  to prevent inappropriate suction on pump  34 . 
         [0025]    In accordance with the present invention, the breather assembly  44  shown in  FIGS. 2 and 3  is provided at the end of breather tube  42 . Breather assembly  44  includes an upper housing  46  and a lower housing  48  having an end nipple  50  that is received in the end of breather tube  42 . Upper housing  46  has an annular outer facing recess  52  that receives a foam ring  54  to prevent the ingress of particles to an interior chamber  58  of upper housing  46 . As shown particularly in  FIG. 3 , upper housing  46  has flats  56  to enable and facilitate removal and replacement of the annular foam filter  54 . A plurality of radially directed passages  60  extend from annular recess  52  to interior chamber  58  for the entry of ambient air. 
         [0026]    An annular disk  62  of hydrophobic material is sandwiched and held between a shoulder  66  on lower housing  48  and lower annular faces  64  of upper housing  46  to be interposed between chamber  58  and a chamber  68  fluidly connected to breather tube  42  Hydrophobic disk  62  is formed from appropriate hydrophobic material that has the property of permitting the passage of air but preventing passage of the vapors and condensates from chamber  68 . 
         [0027]    An example of suitable hydrophobic material is Polytetrafluoroethylene (PTFE). It is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co. PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE. 
         [0028]    The hydrophobic membrane  62  prevents outflow of DEF vapors and condensates to chamber  58  and the foam ring  54  prevents ingress of particles to chamber  58  and thus chamber  68  and the interior of tank  12 . This arrangement is particularly suited for a work machine environment, especially for a combine in which straw, chaff and other debris from the field is ever present. 
         [0029]      FIGS. 4 and 5  illustrate an alternative embodiment of the present invention. In these figures, a breather assembly  70  has a lower housing  72  and interior chamber  74  for connection with the breather tube  42 . An upper housing  76  extends from lower housing  72  and forms an interior chamber  78  in which an annular filter  80 , schematically illustrated, is positioned. Filter  80  may be formed from paper material of appropriate porosity and particle filtration for the breather application. The filter  80  surrounds a central passage  82  providing fluid flow to chamber  74 . Housings  86  and  72  are removeably connected at flanges  86 ,  90 , respectively by appropriate means (not shown) to enable replacement of paper filter  80 . 
         [0030]    A hydrophobic membrane  84  is received in an inwardly facing groove  85  in chamber  74  of housing  72 . Thus, the hydrophobic membrane  84  prevents flow of aerosols and condensate from chamber  74  to the interior of filter  80 . A series of openings  88 , shown in  FIG. 5 , provide entry of air from the ambient to the interior chamber  78  of upper housing  76 . The breather assembly  70  functions in a manner similar to that for breather assembly  44  in that it prevents the ingress of particulate matter ultimately into the interior of the tank and prevents outflow of DEF vapors or condensate which can cause crystallization and present flow restrictions in the system. 
         [0031]    Both embodiments provide an effective reliable and economic way of providing a breather assembly for a DEF tank while at the same time minimizing, if not eliminating, the problems incurred with current systems providing the tank breathing function. 
         [0032]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.