Abstract:
A filter element, in particular for filtering exhaust gases of an internal combustion engine, includes mutually parallel flow channels, at least two filter segments being provided which each have a subset of flow channels, the filter segments having a spacing from one another and being interconnected via connecting device(s) arranged integrally with the filter segments.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a filter element, in particular for filtering exhaust gases of an internal combustion engine, and to a particle filter and to an exhaust emissions control system having a filter element. The present invention further relates to a method for manufacturing a filter element. 
     BACKGROUND INFORMATION 
     These filter elements can be manufactured by extrusion, in which context a ceramic material is pressed through an extrusion tool so that a prismatic body having a plurality of flow channels arranged in mutually parallel fashion is created. The extrusion operation is followed by a firing or sintering operation. 
     Both cordierite and silicon carbide can be used for the known filter elements. A difference between these two materials is that the thermal expansion of cordierite is substantially less than the thermal expansion of silicon carbide. For this reason, filter elements manufactured from silicon carbide are not produced “en bloc,” i.e. as a monolith, but instead are assembled from multiple filter segments. Each filter element encompasses a subset of mutually parallel flow channels. These filter segments form subunits (“bricks”) that are manufactured individually and then assembled into a filter element using a ceramic adhesive bonding agent. 
     SUMMARY 
     Example embodiments of the present invention provide a filter element that is as easy as possible to manufacture. 
     In the context of a filter element, the filter segments have a spacing from one another, and are interconnected via connecting device(s) arranged integrally with the filter segments. 
     The filter element can be manufactured in the context of only one extrusion operation, with no need for the individual filter segments subsequently to be interconnected via separate connecting devices, for example an adhesive. The fact that the filter segments are spaced apart from one another creates a space permitting a filter segment to expand during a firing or sintering operation, without thereby being itself exposed to large internal stresses or exposing an adjacent filter segment to a large compressive stress. 
     The fact that the filter element can be manufactured in only one extrusion operation also means that only one corresponding extrusion tool needs to be made available. With conventional filter elements, on the other hand, either specific tools must be made available for the respective filter segments, or filter segments initially identical in cross section must be adapted in terms of their contour by grinding, after they have been adhesively bonded to one another. This is associated with a large loss of material, which can be avoided with the filter element according to example embodiments of the present invention. 
     The geometry of the filter element is advantageous especially in the context of filter elements that are constituted at least in part from silicon carbide. The fact that the filter segments can also be made, at least in part, of cordierite or also of another material is nevertheless within the present context. 
     The filter segments can complement one another to yield a filter element that is cylindrical in its entirety. The diameter of this filter element can be, for example, between 10 and 18 cm, in particular 5.66 inches. The filter segments can be in cross section, for example, between 400 and 1600 square millimeters in size. 
     The filter element has at least two filter segments, but preferably at least four filter segments. Formed between the respectively mutually adjacent filter segments are interstices, into which filter segments that heat up during manufacture of the filter element or upon operation thereof can expand. 
     The filter segments have a cross section that is at least sufficiently large that a number of mutually parallel flow channels can be received. At least for a centrally disposed filter segment, however, square or circular cross sections can be advantageous in order to permit a globally uniform distribution of filter segments over the cross section of the filter element. 
     The spacing between the filter segments can be comparatively small as compared with the size of the cross section of one filter segment, for example between 0.5 and 10 mm, in particular between 1 and 5 mm. The spacing is intended to make available a sufficiently large expansion space for the filter segments, but on the other hand should not be unnecessarily large so as not to reduce too greatly the total available filter area. 
     Mutually adjacent filter segments can be interconnected in only one region or also via multiple connecting means. Advantageously, a connecting device is arranged as a strut that extends parallel to the flow channels. Such a strut has a width that corresponds to the spacing between mutually adjacent filter segments. The material thickness present perpendicular thereto can be between 0.5 and 10 mm. It is advantageous, however, if the material thickness of the strut is less than the wall thickness of a filter wall, adjoining a flow channel, of a filter segment. 
     In order further to reduce the stresses that occur during heating of the filter element, it is proposed that the strut have in a central region a material thickness that is less than in the outer regions directly adjacent to the filter segments. As a result, the strut can deform to a limited extent in its central region without thereby causing permissible limit stresses to be exceeded. In order to provide good protection for the filter segments from mechanical overloads, it is proposed that the flexural strength of the strut, in particular in its central region, be equal to at most 60% of the flexural strength of a filter segment. 
     An example embodiment provides that the interstice resulting from the spacing between two interconnected filter segments is filled up at least in sections with a filler material. With the filler material, the mechanical stability of the interconnected filter segments, and thus of the filter element, can be enhanced. The filler material used can be, for example, ceramic powder, inorganic binder, and/or ceramic fibers. The filler material need not completely fill up the interstice formed between the filter segments in the direction parallel to the flow channels. It is preferred, however, if at least 20% of the length of the flow channel is filled up. 
     Further features and aspects of example embodiments of the present invention are described in more detail below. All features described in the drawings and the description thereof may be provided both individually and in any combination with one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically depicts an internal combustion engine having an exhaust emissions control system and having a filter element; 
         FIG. 2  is a longitudinal section through a conventional filter element; 
         FIG. 3  is a cross section through a filter element according to an example embodiment of the present invention having filter segments connected via struts; 
         FIG. 4  is a cross section through a strut depicted in enlarged fashion; 
         FIG. 5  is a cross section through the filter element according to  FIG. 3  having filled-up interstices; 
         FIG. 6  is a longitudinal section through the filter element according to  FIG. 5 ; and 
         FIG. 7  is a cross section through a filter element according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , an internal combustion engine bears the reference character  10 . Exhaust gases are directed through an exhaust pipe  12  to an emissions control system  14 . The latter encompasses a particle filter  16  with which carbon particles are filtered out of the exhaust gas flowing in exhaust pipe  12 . This is necessary especially in diesel internal combustion engines in order to comply with regulatory stipulations. 
     Particle filter  16  encompasses a filter element  18  that is substantially cylindrical in its entirety. 
       FIG. 2  depicts, in a longitudinal section, a conventional filter element  18 . Through this, exhaust gas of internal combustion engine  10  flows in the direction of arrows  20 . In  FIG. 2 , an entrance surface for the exhaust gas to be filters bears the reference character  22 , and an exit surface for filtered exhaust gas bears the reference character  24 . 
     Multiple flow channels  28  and  30  proceed parallel to a longitudinal axis  26  of filter element  18 . Flow channels  28  are open at entrance surface  22  and closed at exit surface  24 . Conversely, flow channels  30  are open at exit surface  24  and closed in the region of entrance surface  22 . 
     The flow path of the unpurified exhaust gas is thus into one of flow channels  28  and from there through a filter wall  32  into one of flow channels  30 , This is depicted by way of example by arrows  34 . 
     In  FIG. 3 , a filter element according to an example embodiment of the present invention is labeled in its entirety with the reference character  18 . It has, in totality, filter segments, of which four filter segments are labeled in  FIG. 3  with the reference characters  36  to  42 . These filter segments are delimited by segment boundaries  44 . The segment boundaries of mutually adjacent filter segments, for example of filter segments  38  and  40 , are spaced apart from one another so that an interstice  46  is constituted in this region. This interstice  46  is spanned by strut-shaped connecting means  48  that interconnect the filter segments. 
     In the example embodiment depicted in  FIG. 3 , the centrally disposed filter segment  36  is square in cross section. This filter segment preferably has a cross section of from 400 to 1600 square millimeters. The individual filter segments have a spacing  52  from one another of, for example, 0.5 to 10 mm. 
       FIG. 4  depicts in further detail a strut-shaped connecting device  48  and its connection to the segment boundaries  44  of mutually adjacent filter segments  40  and  42 . Connecting device  48  has a central region  54  that has a material thickness which is less than that of the laterally contiguous outer regions  56  that are disposed directly adjacent to segment boundaries  44 . In the exemplifying embodiment depicted in  FIG. 4 , the lesser material thickness in central region  54  is produced by trough-shaped notches located opposite one another. 
     Filter element  18  is depicted in  FIG. 5  with interstices  46  that are filled with a filler material  58 . Referring to  FIG. 6 , filler material  58  does not extend along the entire length of a flow channel  28  or  30 , but instead only in a respective region adjacent to entrance surface  22  or exit surface  24 . 
       FIG. 7  shows a further example embodiment of a filter element  18  according to the present invention. Provided in this filter element is a centrally arranged filter segment  60  that is circular in cross section and is surrounded by multiple filter segments  62 . Filter segments  62  are assembled in the shape of circle segments and form a ring surrounding central filter segment  60 . Each two of the individual filter segments  60 ,  62  are in turn interconnected via connecting device  48  arranged integrally with the filter segments. 
     Diameter  64  of this filter element  18  can be, for example, 5.66 inches.