Abstract:
A water separating screen for a filter element in a liquid filter, the water separating screen including: a screen fabric having end faces; and a fabric carrier; a screen fabric arranged on the fabric carrier and encircling a longitudinal axis, the screen fabric having axial end faces, the longitudinal axis defining an axial direction; wherein the fabric carrier in an area between the end faces exclusively has longitudinal struts, which at least substantially extend in the direction of the longitudinal axis and which are elastic in a radial direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a water separating screen for a filter element in a liquid filter. 
       BACKGROUND OF THE INVENTION 
       [0002]    A filter system for diesel fuel including an annular particle filter in a filter housing, which has an also annular coalescing element connected upstream, is known from the publication WO 2004/082804 A1. In order to facilitate the water separation, dispersively present droplets of water in the fuel are accumulated to larger droplets via the coalescing element. The coalescing element and the filter element are mounted about a center pipe centrally situated in the receiving space of the filter housing, which serves to discharge the cleaned fuel. 
         [0003]    The publication DE 20 2011 002 684 U1 describes a filter for insertion into a fuel tank, which has a filter sock made out of a fabric braced by web-like stiffening elements, which are flexibly deformable. In this way, it is to be achieved that, when inserting the filter into a curvedly formed filler neck, the filter may follow the run without damage. The sock-like filter, however, only serves for filtering particles; a water separation can not be achieved in this manner. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention is, when filtering liquids over a long period of operation, to effectively separate dispersively contained droplets of water with simple, constructive measures. 
         [0005]    The water separating screen according to the present invention can be used in filter elements in liquid filters, preferably in fuel filters, for example, in diesel fuel filters. An application for, for example, filtering hydraulic oil is, however, also possible. 
         [0006]    In a filter housing, the liquid filter has an annular filter element, which particularly serves as a particle filter and which is radially through-flown from the outside to the inside by the fluid to be cleaned. The interior of the hollow cylindrical filter element forms the clean space via which the cleaned fluid is axially discharged. A center pipe may be inserted into the clean space, adding stability to the filter medium of the filter element which, for example, is embodied in a pleated manner. 
         [0007]    A water separating screen according to the present invention, which is formed separately from the filter element and is connected to the filter element or a component situated at the filter element, may be inserted into the filter element of the liquid filter. The droplets of water, which are included in the liquid to be cleaned, thus, for example, in the fuel or the hydraulic oil, are separated at the water separating screen. The clean space in the filter element may be axially flow-connected at one end to a water collecting space which is situated in the filter housing and into which the separated water from the water separating screen is discharged. In contrast, the cleaned fluid is advantageously discharged from the clean space of the filter element via a liquid outflow line axially situated at the other end. This, for example, enables to situate the liquid filter having the water collecting space in the bottom area of the filter housing, whereas the cleaned fluid is discharged axially upwards from the clean space. The water received into the water collecting space may, for example, be discharged from the filter housing via a valve. Thus, the outflow of separated droplets of water from the water separating screen into the water collecting space is carried out in the direction of the weight force of the droplets of water. 
         [0008]    The water separating screen includes a screen fabric and a fabric carrier at which the screen fabric is held and which lends the screen fabric a defined form, for example, a cylindrical form or a conical form. The water separating screen is located at the clean side of the filter element; it is inserted into the cylindrical clean space of the filter element. If a center pipe is situated at the interior wall of the clean space at the filter medium of the filter element, the center pipe engages around the water separating screen. In particular, a gap, for example, of at least  5  mm, is provided between the water separating screen and the center pipe. 
         [0009]    The fabric carrier extends between the end faces of the screen fabric and, in this area, has exclusively longitudinal struts which at least substantially extend in the direction of the longitudinal axis of the filter element or of the water separating screen situated coaxially to the filter element. Owing to the at least substantially axial alignment of the longitudinal struts in the direction of the longitudinal axis, the angle of the longitudinal struts to the longitudinal axis is smaller than 45°. It may be expedient to align the longitudinal struts exactly in the direction of the longitudinal axis or at an only small angle of, for example, a maximum of 10° or 20°. 
         [0010]    Only the longitudinal struts, but no cross struts, run in the area between the end faces of the screen fabric. Owing to the abstaining from cross struts, the structure of the fabric carrier has a high radial elasticity and may, in particular, be compressed radially inward. This enables the screen fabric, which is carried by the fabric carrier and located in particular at the outside of the longitudinal struts of the water separating screen, to give way also in the radially inward direction when the pressure radially abutting at the outside of the water separating screen is correspondingly high. Such an elevated pressure is, for example, present when using the liquid filter for filtering diesel at low temperatures and for separating out paraffins from the diesel fuel, as a result of which the screen fabric has a force radially applied from the outside to the inside. The radially elastic yielding of the longitudinal struts and of the screen fabric may prevent a tearing of the screen fabric. 
         [0011]    Once the outer pressure diminishes, the water separating screen resumes its original position in that its radially elastic longitudinal struts return into their original position. The screen fabric, which preferably is situated on the outside of the longitudinal struts, also returns into its original position. 
         [0012]    In principle, it is also possible that the screen fabric is situated on the inside of the longitudinal struts. In this case, it may be expedient to at least spot-connect the screen fabric with the longitudinal struts. In contrast, when the screen fabric is situated on the outside of the longitudinal struts, it is not mandatory to connect the screen fabric with the longitudinal struts, even though this is categorically possible. 
         [0013]    Advantageously, the fabric carrier is made out of plastic. Furthermore, it is expedient that the fabric carrier has a carrier ring or collar at each end face of the water separating screen and that the longitudinal struts run between the carrier rings and are connected with said carrier rings. It is particularly possible to integrally form the end face carrier rings and the in-between lying longitudinal struts. The end face carrier rings are each connected to the screen fabric. The water separating screen is, for example, to be connected via one of the carrier rings with one of the end plates situated at an end face of the filter element. 
         [0014]    It may be expedient to keep the number of longitudinal struts relatively small to ensure a sufficient radial elasticity of the fabric carrier and, moreover, to keep the area, which is covered by the longitudinal struts and, thus, is not available for the liquid to be cleaned to pass through, as small as possible. For example, it suffices to provide four longitudinal struts uniformly distributed over the circumference in the fabric carrier. 
         [0015]    According to a further expedient embodiment, a coalescing element expediently integrated in the filter element is, in addition to the filter element, situated in the liquid filter. The fluid to be cleaned is a dispersive mixture of two liquids, for example, fuel having dispersively embedded water, which are to be separated from each other. With the aid of the coalescing element, fine droplets of water may be joined to larger droplets, however, without causing a separation. Thus, only larger droplets of water are generated in the coalescing element, which, after through-flowing the coalescing element, are separated at the water separating screen located in the clean space. Preferably, the coalescing element is situated on the clean side of the filter element, particularly between the radial interior side of the filter medium of the filter element and the center pipe. 
         [0016]    It may be expedient to provide a sealing element between the water separating screen and the component at the filter element, at which the water separating screen is held. Insofar as the water separating screen is connected to the end plate, the sealing element may be situated between a collar or carrier ring and the end plate. The collar or carrier ring is preferably located at the end face of the water separating screen. The sealing element between the water separating screen and the component of the filter element is either integrally formed with the collar or the carrier ring, for example, as a sealing lip molded onto the collar or the carrier ring, or separately formed as a sealing element in the form of a sealing ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Further advantages and expedient embodiments may be concluded from the further claims, the description of the figures and the drawings. 
           [0018]      FIG. 1  shows a perspective view of a liquid filter for filtering fuel; 
           [0019]      FIG. 2  shows a longitudinal section through the liquid filter having marked flow arrows to indicate the flow path; 
           [0020]      FIG. 3  shows a perspective, partially sectional view of a filter element, which is part of the liquid filter, having a water separating screen situated in the inside lying clean space; 
           [0021]      FIG. 4  shows a further, partially sectional illustration of the filter element; 
           [0022]      FIG. 5  shows an enlarged view of Part V from  FIG. 4 ; 
           [0023]      FIG. 6  shows a water separating screen in a side view; 
           [0024]      FIG. 7  shows a water separating screen in a longitudinal section; 
           [0025]      FIG. 8  shows a water separating screen in a perspective view. 
       
    
    
       [0026]    In the figures, same components are provided with the same reference characters. 
       DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 1  perspectively shows a fluid filter  1  for filtering fuel, preferably diesel fuel. In a filter housing  2 , liquid filter  1  has a filter element for filtering the fuel. In the upper end face region of filter housing  2 , a heating device  3  is located, in which the supplied fuel is preheated before it is fed into the filter element in filter housing  2 . A radial inflow line  4  for supplying the unfiltered fuel and a radial outflow line  5  for discharging the filtered fuel is also located in the upper region of filter housing  2 . 
         [0028]      FIG. 2  shows liquid filter  1  in a longitudinal section. Filter housing  2  accommodates annular filter element  6 , which is through-flown radially from the outside to the inside by the fluid to be filtered. Accordingly, the cylindrical interior in filter element  6  forms clean space  7  from which the cleaned fluid is axially discharged. 
         [0029]    A center or support pipe  8 , which preferably is made out of plastic and braces the filter medium of filter element  6  and which provides stability to said filter medium, is inserted into clean space  7  of filter element  6 . Central pipe  8  lines clean space  7 . 
         [0030]    A coalescing element  9  delimited radially inwards by center pipe  8  is located on the radially interior side of the filter medium of filter element  6 . A coalescence or agglomeration of finely distributed droplets of water in the fuel occurs in coalescing element  9  so that said droplets accumulate into larger droplets. 
         [0031]    A water collecting space  10 , in which water separated when filtering the fluid is collected, is located in the bottom region near the ground in filter housing  2 . The collected water can be discharged from water collecting space  10  in the filter housing via a bottom sided opening and a valve. 
         [0032]    A water separating screen  11 , embodied as a hollow cylinder and having an outer diameter which is smaller than the interior diameter of center pipe  8 , is inserted into clean space  7  so that an intermediate annular space is formed. Water separating screen  11  extends axially like center pipe  8  over the complete length of clean space  7  or of filter element  6 . It is, however, also possible that water separating screen  11  only extends over a part of the length of clean space  7  or filter element  6 . The droplets of carried along in the fuel are separated at the outer surface shell of water separating screen  11 . As indicated by the vertical downward pointing arrow, the separated droplets of water are discharged via the bottom axial end face of clean space  7  into water collecting space  10 . 
         [0033]    The wall of water separating screen  11  has a plurality of passage openings, via which the cleaned fuel may through-flow radially inwards from the annular space between center pipe  8  and water separating screen  11  into the interior of water separating screen  11 . In particular, a screen fabric  23  ( FIGS. 6 through 8 ) of water separating screen  11  has a mesh having a defined mesh width of, for example, 10 to 30 μm. Subsequently, the cleaned fuel liberated from the water droplets is axially discharged via the end face of clean space  7  lying axially on the top, which is flow-connected to outflow line  5 . 
         [0034]      FIG. 3  shows filter element  6  in a perspective and partially sectional view. Filter medium  12  of filter element  6  is embodied as a pleated filter and is enclosed on both end faces by respectively one end plate  13 ,  14 . In the area of upper end plate  6 , via the central opening of which the cleaned fluid is discharged from clean space  7 , water separating screen  11  has a radially widened collar or carrier ring  15 , which is connected in a latch-closing manner via snap or latch hooks  16  to end plate  13 . Latch hooks  16  are molded at the inward facing side at end plate  13  or integrally formed with end plate  13  (see also  FIGS. 4, 5 ). In the connected state, latch hooks  16  engage behind a circumferential, radially outer ring shoulder at collar or carrier ring  15 . 
         [0035]    As may particularly be concluded from  FIG. 5 , a sealing lip  17 , which abuts at the radially interior side of latch hooks  16 , is molded adjacent to the free end face and, in the radially outside area, to collar or carrier ring  15 . Latch hooks  16  may optionally also be configured as a continuous circumferential latch ring at the bottom side of end plate  13 . A flow-proof seal between the radially outer clean side having water containing fuel and the radially interior clean side having fuel not containing water is provided via sealing lip  17 . 
         [0036]    End plate  13  has on its axially outward facing end face an axially protruding support collar  20 , onto which a cover  18  is fitted. On the radially inner side of support collar  20 , a sealing ring  19  is located, which, as may be concluded from  FIG. 3 , is braced radially inwards at a section of end plate  13 . 
         [0037]    As may further be concluded from  FIG. 5 , the free end face of collar  15  is located in the assembled state directly below end plate  13 . During assembly, water separating screen  11  has to be inserted axially from the opposite side into clean space  7  or center pipe  8 . 
         [0038]      FIGS. 6 through 8  show water separating screen  11  in isolation. Water separating screen  11  includes a fabric carrier  22  made out of plastic and a screen fabric  23  which is held and carried by fabric carrier  22 . Fabric carrier  22  has two end face collars or carrier rings  15 ,  25  and longitudinal struts  24 , which run between carrier rings  15 ,  25  and which extend in the direction of longitudinal axis  26 . Longitudinal struts  24  are integrally formed with end face carrier rings  15 ,  25 . Longitudinal axis  26  of cylindrically embodied water separating screen  11  coincides in the assembled state with the longitudinal axis of the liquid filter. 
         [0039]    Fabric screen  23  abuts on the radially outer outside at longitudinal struts  24  and is connected at the end faces to each carrier ring  15 ,  25 . In the area between carrier rings  15 ,  25 , fabric carrier  22  exclusively has longitudinal struts  24 , but no connecting cross struts, so that a radial elasticity is provided and longitudinal struts  24 , which preferably are made out of plastic, may give way inwards from radially outside if the pressure applied at the outside is correspondingly high. This also makes it possible that screen fabric  23  deforms radially inward when pressure is applied. In this way, the risk of the screen fabric tearing is significantly reduced. 
         [0040]    Distributed over the circumference, four longitudinal struts  24  in total, which respectively run exactly in the direction of longitudinal axis  26  and which are situated in a uniformly distributed manner over the circumference, are provided in fabric carrier  23 . Longitudinal struts  24  only have a relatively small thickness to ensure, on the one hand, the desired radial elasticity and, on the other hand, to restrict the through-flow area at the screen fabric available for through-flowing the fluid to be cleaned as little as possible. 
         [0041]    After the radially outside pressure has lapsed, longitudinal struts  24  may, owing to their own elasticity, return into the original position, in which longitudinal struts  24  run in a straight line. Along with the return to the original position, the screen fabric  23  also is returned into its original position.