Abstract:
An oil filter unit for arrangement in the oil sump of an oil circuit, particularly in an automatic transmission. The oil filter unit has a multi-part filter housing with a filter chamber disposed therein such that an oil inlet and an oil outlet communicate with the filter chamber. A filter element is sealingly mounted in the housing between the oil inlet and the oil outlet. The filter element has a pleated filter medium, which is sealingly enclosed by a frame, and the frame has seal contours designed to cooperate with the contours of the filter housing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an oil filter unit, which is disposed in an oil collection chamber, such as an oil pan or a housing. Oil filter units of this type are used, for example, to filter the lubricating oil of gears, e.g., automatic transmissions. To adapt the filter unit to the space available for installation, it is designed in the shape of a pan and can be positioned directly within the oil sump. The purpose is to separate impurities from the lubricating oil and thereby to increase the life of the lubricating oil and minimize the wear of the unit to be lubricated. The oil filter unit should have the greatest possible filter fineness and minimum flow resistance and at the same time adequate dirt holding capacity and, in motor vehicles with automatic transmissions, should be designed to last for the life of the vehicle. 
     Published US patent application no. US 2002/0121473 A1 (=EP 1,238,693) discloses an oil filter assembly having a filter chamber in a pan-shaped housing, which communicates with an oil inlet and an oil outlet. A replaceable filter element supported by ribs is disposed inside the filter chamber. The hollow filter element is spatially substantially parallel to the filter chamber, such that the fluid flows from the outside toward the inside. 
     A disadvantage of this design is that because of its replaceability, the replaceable filter element must have a complex seal relative to the housing at its opposite end faces. This seal requires corresponding contours on the filter element and the housing, which enable a releasable yet fluid-tight connection. Producing these contours places high demands on the manufacturing process. Furthermore, the size of the filter surface depends directly on the circumference of the filter chamber, which implies a substantial restriction with regard to the adjustment between dirt holding capacity and filter fineness. Because of this restriction, the described oil filter assembly cannot be used with a filter medium that ensures the filter fineness required for the operation of automatic transmissions. Use of such a filter medium would exceed the pressure differential required in suction operation. To meet this requirement in practice, a coarse particle filter is used on the inlet side and an additional fine particle filter downstream of the coarse filter is used on the pressure side. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an improved oil filter unit suitable for filtering the fluid of a motor vehicle transmission. 
     A further object of the invention is to provide an oil filter unit which has a both a high filter fineness and a high dirt holding capacity. 
     Another object of the invention is to provide an oil filter unit which has a long service life and can be designed for the life of a motor vehicle transmission. 
     Yet another object of the invention is to provide an oil filter unit which has a low pressure loss and is simple and economical to manufacture. 
     It is also an object of the invention to provide an oil filter unit which assures a reliable seal between the filter element and its housing. 
     These and other objects have been achieved in accordance with the present invention by providing an oil filter unit for arrangement in an oil sump of an oil circuit, the filter unit comprising an at least two-part filter housing having a filter chamber therein; an oil inlet and an oil outlet in communication with the filter chamber, and a filter element sealingly arranged in the housing between the oil inlet and the oil outlet; the filter element comprising a pleated filter medium sealingly enclosed by a frame, and the frame having seal contours configured to sealingly engage with contours of the filter housing. 
     The oil filter unit according to the invention aims to use a filter medium that makes maximum use of the space available within a filter chamber and forms the largest possible filter surface. This is achieved by using a zigzag-type pleated filter medium. Because of the flat, pan-shaped installation space, a flat pleated filter medium is preferred. To seal the filter medium relative to a housing, the filter medium is enclosed by a frame having seal contours that correspond to the housing or the seal contours of the housing. The frame is made of plastic, for example, such as polyamide or polypropylene, and is injection-molded directly around the filter medium. The injection molded seal contour may, for example, comprise a rib for engagement with a groove formed in the housing. The connection between the filter medium and the frame may, for example, be produced by adhesive bonding, joining or welding, particularly vibration welding. The frame or the seal contour may also be made of polyurethane foam or some other elastomer known in the art. A flat filter element of this type is inserted into the housing in longitudinal direction and divides the housing into a lower unfiltered liquid side and an upper filtered liquid side. On the unfiltered side of the housing, at least one oil inlet is disposed through which the oil from the oil sump flows into the housing. On the filtered side of the housing, an oil outlet is disposed through which the filtered oil is discharged, preferably through an outlet fitting which is fabricated as an integral part of the housing. 
     The filter element can be inserted into the housing through an installation opening formed in one end face. In this case, a cover may be disposed on the frame to seal the installation opening. The mounting may be releasable, e.g., by snap-in connections, or permanent, by welding or adhesive bonding. To support the seal function, additional seal elements, such as elastomers, may be disposed on the cooperating seal contours between the cover and the housing and/or also between the frame and the housing. 
     An advantage of the invention is that it substantially enlarges the dirt holding capacity while reducing the differential pressure of the filter medium and keeping the installation space identical. This ensures adequate dirt holding capacity for the coarse and fine particles that occur, so that no additional oil filter is necessary. The use of a frame that is firmly connected with the filter medium ensures a seal between the filter element and the housing which is simple and economical to produce. Because of the large filter surface, the pressure loss is low, such that the filter can be disposed on the inlet side and it is unnecessary to have a fine filter on the pressure side. 
     In accordance with one advantageous embodiment of the invention, the filter medium is made of a fully synthetic nonwoven material or of glass fibers. Fully synthetic nonwoven materials are well suited for a comparatively coarse filtration fineness. If finer particles need to be filtered, glass fiber media may be used. High demands with regard to filter fineness can be met by using either glass fiber or nonwoven media. Because of the high melting point of the media, the filter frame can be injection molded around them without problems. As a result, an oil filter with a high degree of filter fineness can be simply and economically manufactured, and a highly effective filtration capacity is assured. 
     In a further advantageous embodiment, the use of glass fiber media enables a filter fineness with a pore size of less than 25 μm. The resulting filter fineness makes it possible to further increase the filtration capacity without an additional filter unit. 
     In yet another advantageous embodiment, the filter medium is stabilized against the flow pressure by adding a support grid on the inflow and/or the outflow side. This support grid directly contacts the inflow and/or outflow side of the filter medium and extends parallel to the zigzag pleats. The purpose of the support grid is to mechanically stabilize the filter medium against the inflow pressure of the oil and to prevent any fiber particles from being flushed out of the medium. The support grid can furthermore stabilize the fold geometry of the filter medium or can itself form the fold geometry. The material used for the support grid is preferably metal, but a thermostable synthetic resin or a stable spunbound material may also be used. On the lateral faces of the medium, the grid mesh may be injection molded into the frame to ensure reliable mounting. 
     The support grid is a simple and reliable way to impart mechanical stability to the filter medium, such that the medium itself requires little stability, can be suitably designed and economically manufactured. 
     In accordance with yet another advantageous embodiment, the housing is made of two shells, such that a parting plane extends in a longitudinal direction of the filter housing between an upper shell and a lower shell. The parting plane preferably separates the housing along a horizontal plane and surrounds the filter medium completely. Thus, laterally reversed parting surfaces exist on the upper and lower shell. In the assembled state, the seal contours of the frame cooperate with the parting surfaces and are sealingly connected by the parting surfaces. The seal contours of the frame can thus be disposed in the parting plane. To stabilize this connection, the housing walls may be reinforced or expanded in width by forming a bead along the parting surfaces. The parting surfaces may be clamped together, for example by screws or clip connections, to create a compression force with the seal contours of the element. The seal contour may extend sandwich-style across the entire area of the separation face or may be integrated in a stepped seal profile formed by the parting surfaces. 
     The parting plane is situated in the largest circumferential area of the housing, such that the two housing shells may be advantageously fabricated without undercuts. As a result, all components can be manufactured simply and economically and assembly is reliable and controlled. 
     In one embodiment, the joint of the seal contour of the frame is non-releasable. The seal contours of the frame may for example be bonded or welded together with the parting surfaces of the shells. These joining methods eliminate the need for additional fasteners and the space required for such fasteners. Taking into account vibration and temperature loads, this embodiment represents a very cost-effective and reliable joint. 
     In one specific embodiment of the invention, a bypass valve is provided between the unfiltered liquid side and the filtered liquid side of the filter. Valves of this type typically comprise a valve body, a valve seat, a spring and a cage. The preferably spring-loaded valve opens a flow cross section between the unfiltered side and the filtered side, for example, at a defined pressure differential of 0.4 bar. This situation may occur if the oil to be filtered is still highly viscous because of low temperatures or if the flow resistance of the filter medium is increased because of inflowing particulate matter. The space required to install the bypass valve is preferably accommodated in the parting plane. To this end, the parting plane is extended beyond a filter medium region to form a valve space. In the valve space, the unfiltered side is separated from the filtered side by the frame, ensuring a communicating connection of the bypass valve in the direction of flow. The bypass valve can be inserted into the frame as a separate unit. On the other hand, a valve seat may be integrated into the frame and the additional valve components added prior to assembly. 
     The bypass valve has the advantage that the oil supply is ensured even if the flow resistance of the filter element is elevated. By disposing the bypass valve in the parting plane, it can be simply and economically integrated into the oil filter unit and requires a minimum of space. 
     A further advantageous embodiment is equipped with an anti-drain element. This element prevents the oil filter unit from emptying upon shutdown and ensures an immediate oil supply when the transmission is restarted. Anti-drain elements of this type are preferably constructed of a thin-walled metal, plastic or elastomer plate, which seals a valve seat radially or axially in a flow direction. To retain the entire amount of oil within the oil filter unit as far as possible, the anti-drain element may be disposed directly on the oil inlet. 
     The anti-drain element also advantageously ensures rapid oil supply of the oil filter unit after shutdown and may be integrated into the lower shell, the upper shell or the frame, so that it requires little space. 
     It is further advantageous to arrange a prefilter directly on the oil inlet, which keeps coarse particulate matter out of the oil filter unit. This prefilter is preferably constructed of a single-layer screen mesh with a mesh size of approximately 0.4 mm to 0.8 mm. To protect both the oil inlet and a bypass valve as described above from coarse particulate matter by using a single prefilter, the oil inlet may be positioned directly adjacent the valve space for the bypass valve. The prefilter may also be disposed on the bypass valve, so that it protects only the bypass valve and thereby prevents a completely unfiltered inflow of particulate matter into the oil circuit when the bypass valve is open. To secure the prefilter, it may, for example, be adhesively bonded, clipped, screwed or welded or injection molded onto or into the unit in the form of an insert. 
     In accordance with yet another advantageous embodiment of the invention, the frame extends across a given distance between the upper and lower shell of the oil filter unit and thereby forms a part of the housing wall of the filter housing. The frame may also protrude above the height of the filter medium. This creates a flexible clearance on the frame sides facing the shells, which may be used for fastening contours. These contours may be used to fasten the oil filter unit in an installation structure or to fasten the upper and/or lower shell to the frame. For example, contours for vibration welding or butt-welding with heat reflectors may be disposed on the frame. The clearance required for vibration welding may also be taken into account. 
     Because of the height of the frame, other functional components, such as the bypass valve, an anti-drain element or a prefilter may be integrated into the frame or manufactured integrally with the frame. Depending on the requirements, the frame may also be constructed as a two-part component which is made from different materials. This frame advantageously makes it possible to integrate essential functional elements and to produce the joint between the shells in a reliable and economically efficient manner. 
     In accordance with yet another advantageous embodiment, contours are provided for mounting the oil filter unit in an installation space of the transmission. These contours may comprise flat webs, eyelet-shaped protuberances, pins, clip-type hooks or other forms of fasteners known in the art. The fastening contours may be disposed on the lower shell, the upper shell or in the parting plane. Since the wall thickness in the region of the parting plane is preferably reinforced and may be further reinforced by the seal contour of the filter element, this region is particularly suitable for disposing fastening contours. These contours preferably cooperate with fastening elements of the transmission housing and secure the position of the oil filter unit. 
     It is particularly advantageous that the mounting of the oil filter unit can be optimally adjusted to the installation space and the installation process, so that assembly and affixation are made particularly convenient and economical. 
     In a further refinement of the invention, contours for connecting an intake flange of an oil pump are disposed on the oil outlet. The filtered oil preferably flows to an oil pump through an oil outlet fitting disposed on the upper shell. The oil outlet fitting is provided with contours for connection to a flange of the oil pump. These contours may for example comprise an annular collar, an annular groove, a latching contour or any other fastening contour for pipe fitting known in the art. This has the advantage that the entire oil filter unit may be adjusted to the installation situation to minimize the complexity of the connection to the oil pump. 
     These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either individually or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures, in which: 
         FIGS. 1   a  to  1   c  are an exploded view of an oil filter unit according to the invention; 
         FIG. 2  is a sectional view of an assembled oil filter unit; 
         FIGS. 2   a  and  2   b  are enlarged detail views of regions X and Y of  FIG. 2 ; 
         FIGS. 3   a  to  3   c  are an exploded view of another variant of the oil filter unit of the invention, and 
         FIGS. 4   a  and  4   b  are perspective views of an alternative embodiment of the oil filter unit of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1   a  to  1   c  show an exploded view of an oil filter unit  10  with the individual components disposed in assembly direction. Between an upper shell  11  shown in  FIG. 1   a  and a lower shell  12  shown in  FIG. 1   c  is disposed a filter element  13  depicted in  FIG. 1   b . A bypass valve  30  and a prefilter  31  are connected to the lower shell  12  when the unit is assembled ( FIG. 2 ). 
     The upper shell  11  forms one housing section of the two-part housing. On the upper side, it has a tubular oil outlet fitting  14 , on the discharge end of which there is a radial groove  15  to receive an O-ring  16 . In longitudinal direction of the upper shell  11 , on the lower side facing the filter element  13 , fins  17  are formed which stiffen the upper shell  11  and form a support for the filter element  13  as illustrated in the assembled state shown in  FIG. 2 . The lower pan-shaped opening of the upper shell  11  is enclosed by the flat parting surface  18  along its entire periphery. Within the upper shell  11 , a support wall  19  is disposed, which separates a first, unfiltered liquid side  20  from a second, filtered liquid side  21 . 
     The filter element  13  comprises a flat filter medium  23  enclosed along its lateral faces by a frame  24 . The filter medium  23  is pleated in zigzag fashion, such that the end face edges of the pleats are completely covered by the frame  24 . The longitudinal sides of the pleats are also sealingly fastened to the frame  24 , so that the entire periphery of the filter medium  23  is sealingly mounted inside the frame  24 . The frame  24  also has a stepped seal contour  25  around its entire periphery. 
     The lower shell  12  has a parting surface  18   b  mirroring the parting surface  18  of the upper shell. The lower shell  12  forms an unfiltered liquid chamber  28  which is separated from a valve space  27  by a transverse partition  26 . A cylindrical valve flange  33  communicating with the valve space  27  is provided to receive the bypass valve  30 . The oil inlet  29  molded onto the underside forms an oval contour disposed in the region of the partition  26  and thus communicates with the unfiltered space  28  and the valve space  27 . The prefilter  31  shown below the oil inlet  29  communicates with the oil inlet  29  through its circumferential contour and retains coarse particulate matter when installed. Mounting contours  22  disposed laterally on the upper shell  11  are used to secure the oil filter element  10  in an installation space. 
       FIGS. 2 ,  2   a  and  2   b  show the assembled oil filter unit  10  with the filter element  13  sealingly enclosed between the upper shell  11  and the lower shell  12 .  FIG. 2   a  shows a detail X of  FIG. 2 , and  FIG. 2   b  shows a detail Y of  FIG. 2 . The seal contours  25  of the frame  24  are inserted between the parting surfaces  18  and  18   b , which have seal shoulders  32  engaging the seal contours  25 . 
     Between the unfiltered liquid  28  and the second, filtered liquid side  21  there is a partition  26  which separates the unfiltered liquid space  28  from the second, filtered liquid side  21  via the seal contour  25  of the filter element  13 . The end face of the partition  26  is in the same plane as the parting surfaces  18  and  18   b . The joint between the parting surfaces  18  and  18   b  and between the shoulders  32  and the seal contour  25  may be adhesively bonded or welded, for example. As an alternative, the seal contour  25  may also be formed over the entire area of the parting surfaces  18  and  18   b , so that the shoulders  32  can be eliminated and the seal contour  25  lies sandwich-style between flat parting surfaces  18  and  18   b.    
     A valve space  27  which is separate from the filter element  13  and in which the bypass valve  30  is disposed, is formed in longitudinal direction of the oil filter unit  10 . The bypass valve  30  is sealingly enclosed within the valve space  27  and communicates on the bottom side with the oil inlet  29  and on the topside with the second, filtered liquid side  21 . Between a first filtered side  20  and the second filtered side  21 , a flow-permeable support wall  19  is disposed which only supports the seal contour  25  and allows cross-flow (see  FIG. 1 ). 
     To tightly seal the oil outlet fitting  14  relative to a connecting contour (not shown), an O-ring  16  is inserted into the radial groove  15 . 
     Oil which enters through the oil inlet  29  is cleaned from coarse particulate matter by the prefilter  31  disposed in the lower shell  12 . The oil flows through the filter medium  23 , which causes the filter medium to curve in the direction of flow while being supported by the ribs  17 . The oil then flows through the oil outlet fitting  14  to an oil pump (not shown). If the filter medium  23  is very dirty or if the oil is too viscous because of low temperatures, the bypass valve  30  opens as a result of the increased pressure differential, so that a supply of oil is assured. 
       FIGS. 3   a  to  3   c  are an exploded view of an oil filter unit  10  with a substantially higher frame  124 , which protrudes above the filter medium  123 . The figures show the upper shell  111  of  FIG. 1   a , the lower shell of  FIG. 1   c , and the filter element  113  of  FIG. 1   b  disposed therebetween. A valve flange  133  is formed on the frame  124  to receive the bypass valve  130 . The upper shell  111  and the lower shell  112  are substantially flat and have parting surfaces  118  which cooperate with the seal faces  125  of the frame. The fastening contours  122  are fabricated integrally with the frame  124  and enable central fastening inside an installation structure (not shown). 
       FIGS. 4   a  and  4   b  show an embodiment of the lower shell  212  in which a return flow of the oil is prevented.  FIG. 4   b  shows a detail of the region of the oil inlet  29  in a full section of the lower shell  212 . In this embodiment, the anti-drain valve  234  is an umbrella valve integrated into the lower shell  212 . A suitable material for this purpose is a thermostable and chemical-resistant elastomer, such as silicone. 
     The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.