Abstract:
A filter apparatus deposits impurities from a fluid stream by use of a filter element ( 10 ) accommodated in a filter casing ( 12 ). The filter casing ( 12 ) has a swirl space ( 14 ) such that the fluid stream to be filtered is conducted at least partly in a swirling flow around the filter element ( 10 ). The properties of a cyclone are utilized for the actual filtration operation to the extent that the swirl space of the filter casing brings about multiple deflection of the direction of motion of the fluid to be filtered.

Description:
FIELD OF THE INVENTION 
     The invention relates to a filter apparatus for separating impurities from a fluid stream by using a filter element accommodated in a filter housing. 
     BACKGROUND OF THE INVENTION 
     Similar hydraulic filters and filter apparatus are readily available on the market in a plurality of embodiments (e.g., DE 197 11 589 A1). In addition to suction filter apparatus, filter apparatus as return line filters, in-line filters, or ventilation filters are known. In generic terms they are often referred to as hydraulic filters. Generally, these hydraulic filters are devices for separation of solids, with fibrous, grainy, or lattice-shaped filter media being used to separate solids from liquids or for separating dusts from gases. 
     Furthermore, other separation devices in the prior art (e.g., DE 42 14 324 A1) are cyclones which are devices with which the action of a centrifugal force separates particles of solids from gases or liquids which are subsumed in the jargon under the generic term fluid. In the aforementioned solution, the cyclone is located in a ventilation path leading from a driving mechanism space (crank space) to the intake line of an internal combustion engine so that aerosols entrained by the air are separated in the cyclone and can be delivered by an outlet to an oil sump of the internal combustion engine. To be able to prevent unwanted feed of oil from the oil sump into the cyclone even under extreme operating conditions, a stop safeguard in the form of a float valve is on the outlet side. 
     This cyclone separation technology has also already been used in combination with filter devices. Thus, DE-OS 37 35 106 discloses a process for separating liquid particles from gases, in particular in the form of aerosols from exhaust gases, in which the gases are centrifuged first and then filtered. Some of the filtrate gases are then relayed to a cyclone. The liquid particles entrained in the gas flow are combined into droplets by frequent deflection of the direction of their motion (swirling flow). The droplets emerge by their own weight from of the separation device. 
     Furthermore, U.S. Pat. No. 6,129,775 A discloses a cyclone separator with a predominantly conically running separation housing in which, following the wall of the separation housing and with the formation of a swirl space spaced analogously, a usually self-contained guide body enables improved swirl guidance for separating the particles in the swirl space for a tangentially supplied fluid flow with particle fouling. Filtration by a filter element is not possible with the known solution. 
     The prior art (e.g., EP 06 59 462 A1) also discloses solutions in which, for further particle separation, in the bypass flow of a cyclone separator a filter element is held in a separate filter housing following in the direction of the fluid stream. The filtration line of these known solutions still leaves much to be desired. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a filter apparatus with improved filtration properties. 
     This object is basically achieved by a filter apparatus where the filter housing has a swirl space such that the fluid stream to be filtered is routed at least partially around the filter element in a swirling flow. For actual filtration operation, the properties of the cyclone are used in so far as the swirl space of the filter housing causes repeated deflection of the direction of motion of the fluid to be filtered. The associated swirling flow is able to be established along the entire filter surface of the filter element, with the result that the fluid stream to be filtered passes through the filter element to an increased degree and with high energy input, with simultaneous retention or separation of impurities. The swirling flow achieved in the filter housing caused by the action of the swirl space yields a laminar, helix-like fluid flow. In contrast to the otherwise conventional radial throughflow of a filter element transversely to its longitudinal axis, the filter apparatus of the invention leads to improved filtration performance and results. In this way, an increased throughput rate of the fluid to be filtered through the filter element can be achieved. 
     In one preferred embodiment of the filter apparatus according to the invention, the swirl space is formed by a conical widening of the filter housing in the direction of its one housing end. The feed inlet for the unfiltered medium extends through the filter housing off-center to the longitudinal axis of the filter element. This off-center feed causes improved generation of a cyclone-like flow under the action of the swirl space in the filter housing. 
     The conical widening of the filter housing in the region of the swirl space preferably undergoes transition into a cylindrical housing part or into one with a small conical tilt, with the result that partial damping of the swirl-like fluid flow occurs with reduced wall distances between the outside of the filter element and the inside of the filter housing. A kind of forced guidance for the purpose of a compressed fluid flow then results to increase the feed amount of fouled fluid for the filter element in this way. 
     In another preferred embodiment of the filter apparatus according to the invention, with a definable axial distance above on the free end of the filter element, a collecting space adjoins likewise contributing to making the fluid flow uniform in the upper region, and helping prevent supercritical turbulences within the fluid flow. This supercritical turbulence otherwise could adversely affect the filtration performance of the filter apparatus. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
     It has proven especially advantageous with respect to the described structure of the filter housing to use as filter elements those whose filter element extends conically. It has also proven especially advantageous to use slit screen tube filter elements as filter elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure and which are schematic and not to scale: 
         FIG. 1  is a perspective view in section of a filter apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  is a perspective view of the filter apparatus of in  FIG. 1  in the state closed on the housing side and in another viewing direction. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The filter apparatus according to the invention is used to separate impurities from a fluid stream, for example formed by a hydraulic medium. Fundamentally, the filter apparatus can also be used for gaseous media, aerosols, etc., which likewise form fluids.  FIGS. 1 and 2  correspond to the conventional installation direction. To the extent the terms “top” and “bottom” are used below in this respect, they relate to the representations of the operating situation of the filter apparatus as shown in  FIGS. 1 and 2 . 
     The filter element  10  shown in  FIG. 1  is accommodated by a filter housing  12  of the filter apparatus. The filter housing  12  on its top end has a swirl space  14  used to route the fluid to be filtered at least partially in a swirling flow or cyclone flow around the filter element  10 . In the illustrated solution, the swirl space  14  is formed by a conical widening of the filter housing  12  in the direction of its top end  16 . Instead of this conical widening produced by the housing wall, in addition or as an alternative, on the inside of the filter housing  12  flow baffles—also in the manner of turbulators—(not shown) could be used. To produce the swirling flow, the feed inlet  18  for the unfiltered media is located off-center to the longitudinal axis  20  of the filter element  10  and in this respect extends through the housing wall on the top end of the swirl space  14 . To the outside the feed inlet  18  is provided with a flange-like widening  22  for connecting other fluid-carrying pipe elements or other line elements (not shown). 
     After the fluid to be filtered flows from the outside to the inside through the filter element  10 , the filtrate stream, that is, the filtered fluid, is withdrawn from the filter housing  12  via the drain  24  in the housing top. The free end of the drain  24  is in turn provided with a flange  26  used like the flange  22  to connect fluid-carrying lines to the filter apparatus. The drain  24  is placed on the top end of the filter housing  12  and, viewed in cross section, has a slightly larger cross section at the top fluid exit site  28  out of the filter housing  12 . The feed inlet  18  and drain  24  can optionally be produced in one piece together with the filter housing  12 . The corresponding connection to the remaining filter housing  12  is possible by weld connections. 
     As furthermore follows especially from  FIG. 1 , the conical widening forming the swirl space  14  undergoes transition in the direction of the bottom of the filter apparatus into a cylindrical housing part  30  also having a smaller conical tilt (not shown) opposite the swirl space  14 . The swirling flow produced in the swirl space  14  is made uniform over the further housing part  30  in terms of the progression of the cyclone. This uniformly promotes fluid passage through the filter element  10 . The cross sectional reduction from the swirl space  14  to the housing part  30  also contributes to this fluid passage. The free end  32  of the filter element  10  is oriented in the direction of the closed end  34  of the filter housing  12 . At a definable axial distance to the filter element  10  the closed end forms a collecting space  36  which, in spite of the partially turbulent flow dictated by the swirl space  14 , leads to more uniformity of the fluid stream penetrating the filter element  10  and otherwise produces good filling in the interior  38  of the filter housing  12 . This arrangement promotes energy-efficient operation of the filter apparatus. 
     In particular, in this way fluid-free cavities do not form within the filter apparatus. This forming otherwise could lead to damaging cavities for the hydraulic circuit connected to the filter apparatus in operation. The closed end  34  can also be produced by a switch fitting  40  (cf.  FIG. 2 ) which, for example, made as a ball valve enables opening of the bottom end of the filter housing  12 . In this way, for example, it would be possible, with the switch fitting  40  closed, to carry out the already described filtration operation, and when the bottom end of the filter housing  12  is opened, for example, the impurities arising in a backflushing process to be carried out and discharged from the filter apparatus. In the pertinent backflushing operation, cleaned fluid is routed from the inside to the outside through the filter element, preferably from the clean side of the filter apparatus, that is, coming from the drain  24 . This operation leads to cleaning of the passages in the filter element  10 . The dirt backflushed in this way could then be discharged from the filter apparatus by way of the interior  38  of the filter housing  12  and by way of the lower bottom opening of the filter housing  12 . 
     Fundamentally, for backflushing a housing situation as shown in  FIG. 1 , the cleaned fluid is backflushed from the clean side (drain  24 ) in the direction of the unfiltered material side (feed inlet  18 ). The delivery of unfiltered material would have to be stopped. With a somewhat smaller tilt than applies to the housing wall of the swirl space  14 , the collecting space  36  tapers likewise conically in the direction of the free or closed end  34  of the filter housing  12 . This conical tapering allows a partial pressure rise in the collecting space  36  for operation of the apparatus, promoting complete filling for the filter apparatus. 
     The filter element  10 , as already addressed, is made as a slit screen tube filter element. DE 197 11 589 shows the more detailed structure of such a slit screen tube filter element. This element  10  includes individual supports bars around which a wire profile is wound in individual turns, leaving exposed gaps through which fluid can pass. A weld is in the region of each contact site of the wire profile with the assignable support bar. For improved filtration operation, the filter element  10  is made conical. The turns of the wire profile decrease in diameter in the direction of the tilted ends of the support bars. The length of the slit screen tube filter element measured in the direction of the longitudinal axis  20  is roughly 11 times greater than the largest exit cross section in the region of the outlet or drain  24 . Since slit screen tube filter elements are fundamentally prior art, the pertinent element  10  in  FIG. 1  is shown only in terms of its conical structure. 
     The conical structure of the slit screen tube filter element  10  results in less resistance being offered to the fluid stream entering the housing  30  from the swirl space  14 , relative to a solution with an exclusively cylindrically made element, with the result that the pressure difference for the entire filter apparatus is reduced in an energy-efficient manner. A constant liquid stream is also achieved by the conical structure when the element  10  is backflushed. Conversely for a cylindrical element (not shown) which could likewise be used in this embodiment, the speed in its longitudinal direction continuously increases. This increasing speed opposes uniform entry into the interior of the filter element. 
     The installation conditions are implemented such that viewed in the longitudinal direction (longitudinal axis  20 ) of the filter element  10 , the overall length of the swirl space  14  with its conical housing wall  16  and of the collecting space  36  corresponds to a least one third, but less than half, of the installation length of the filter element  10 . The overall length of the swirl space  14  corresponds essentially to the overall length of the collecting space  36  extending from the end  32  of the filter element  10  to the end  34  of the filter housing  12 . 
     The filter apparatus according to the invention, in particular when it is built essentially in one piece except for the filter element  10 , can be extremely economically produced and therefore operated as a disposable article. Depending on the pressures which arise, the filter apparatus can also be made as a plastic injection molding or can be made of metallic materials including sheet metal and casting materials. The housing wall  16  of the swirl space  14  can be made as a dished bottom. 
     In a further configuration of the filter apparatus according to the invention which is not shown, it can be additionally provided that potential light floating materials may be removed from the filter housing via another outlet site in the region of the top housing end  16  of the filter housing  12  with formation of a kind of overflow line. Preferably the respective sealing opening relative to the longitudinal axis  20  is diametrically opposite the feed inlet  18 . The overflow line, comparably to the other connection sites, can have a corresponding flange body, as shown. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.