Abstract:
A filter composed of a filter medium ( 10 ) formed from a corrugated filter layer ( 11 ) and a flat filter sheet ( 12 ) which are interconnected by embossing points ( 15 ). This eliminates the need for an additional joining agent. Production of the filter is simplified because no additional materials are required to be supplied or cured.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a filter comprising a spirally wound filter medium formed from a corrugated filter layer and a flat filter sheet for separating particles from a fluid stream. In a preferred aspect the invention relates to a diesel particle filter for separating particles from the exhaust stream of an internal combustion engine. 
     Filters having a spirally wound filter medium are known in the art. The filter medium is formed from a corrugated filter layer and a flat filter sheet. The corrugated filter layer has corrugation valleys and peaks. To connect the filter layer to the filter sheet, the corrugation valleys are glued to the filter sheet. Thus, channels are formed between the corrugation peaks and the filter sheet. As the filter medium is wound, channels are also formed between the corrugation valleys and the filter sheet wound on top of them. The end faces of the channels are alternately closed, so that the fluid to be cleaned can flow into a channel, flow through the filter sheet or the filter layer and flow out of the filter through the adjacent channel. Adhesive is used to connect the corrugated filter layer to the filter sheet and close the end faces of the channels. When the corrugation valleys are connected to the filter sheet, the filtering surface is blocked by the adhesive applied. To alternately close the channels, adhesive is applied between the filter sheet and the filter layer. This adhesive fills the volume formed between the corrugation peaks and the filter sheet, which requires a large amount of adhesive. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an improved spirally wound filter. 
     Another object of the invention is to provide a spirally wound filter which can be produced cost-effectively. 
     A further object of the invention is to provide a spirally wound filter in which the filtering surface is not reduced by adhesive used for assembly. 
     These and other objects are achieved in accordance with the present invention by providing a filter comprising a spirally wound filter medium formed of a corrugated filter layer having valleys and peaks and a flat filter sheet, wherein the valleys of the corrugated filter layer are connected to the flat filter sheet by a form-fit connection, and alternately closed channels are formed between the peaks and the filter sheet. 
     In accordance with a further aspect of the invention, the objects are achieved by providing a filter comprising a spirally wound filter medium formed of a corrugated filter layer having valleys and peaks and a flat filter sheet, wherein the valleys of the corrugated filter layer are connected to the flat filter sheet, and alternately closed channels are formed between the peaks and the filter sheet, and wherein the filter sheet and the filter layer are each formed of a weldable material and the connection between the valleys of the corrugated layer and the flat filter sheet is a welded connection. 
     In accordance with a still further aspect of the invention the objects are achieved by providing a diesel particle filter for an internal combustion engine, which filter comprises a sintered ceramic body with channel structures, the sintered ceramic body having a porosity suitable for removing solid combustion residues from an engine exhaust gas stream, and the ceramic body being formed by impregnating a filter structure as described above with a fluid ceramic precursor and subsequently drying or sintering the ceramic precursor to produce the ceramic body with channel structures. 
     The filter according to the invention can be used to separate particles from a fluid stream, particularly from gases, such as air. To this end, the filter comprises a spirally wound filter medium which is formed from a corrugated filter layer and a flat filter sheet, both of which are made of a filter material permeable to the fluid to be cleaned. Filter materials of this type include, for example, nonwovens, cellulose papers or mixtures thereof. These filter materials have sufficient dimensional stability that any corrugation impressed on them will persist even after removal of a forming die. This dimensional stability can also be achieved by a subsequent process step, such as curing or coating, for example. The corrugated filter layer has valleys and peaks, and the valleys of the corrugated filter layer are connected to the flat filter sheet. Channels are formed between the peaks and the filter sheet, and the channels are closed at their end faces. As the filter medium is wound, the peaks of the corrugated filter layer contact the underside of the filter sheet of the subsequent layer. This causes further channels to form between the valley and the subsequent layer. 
     To connect the filter sheet to the filter layer, a form-fit connection is provided between the valleys and the flat filter sheet. This is achieved by a partial overlap of the filter sheet and the filter layer. This overlap can be obtained, for example, by a fold or crease, such that the two parts, because of their dimensional stability, are fixed relative to each other. This form of connection eliminates the need for an additional joining agent, so that the entire filtering surface is available for cleaning the fluid stream. It also saves the cost of adhesives. In addition, disposability is improved because the filter is a single-material component. As a result, the filter can be simply incinerated without creating residues of other substances. 
     In one advantageous embodiment of the invention, the closure of the channels at the end face area is produced by a form-fit connection, such that the peaks are pressed onto the filter sheet. Pressing the peaks onto the filter sheet substantially reduces the volume to be closed. Furthermore, the peaks are connected to themselves and to the filter sheet by turned-over folds or creases. As a result, no additional material is required to close the channels, which saves cost of material. In addition, the production cycle is shortened because no curing times for adhesives or other components are required. By pressing the peaks onto the filter sheet, the flow into the channels is improved because the flow resistance of the closed channels is reduced. 
     It is advantageous to produce the form-fit connection by embossing the filter sheet or filter layer such that indentations in the sheet or layer engage indentations in the other member, i.e., the layer or sheet. These indentations may be formed as round, oval or angular embossing points, such that both filter strata (filter sheet and filter layer) are simultaneously in contact with the embossing die. The upper filter strata, which contacts one die, is pressed into the lower filter strata, which is supported on a bottom die. The two filter strata are thus embossed together in a precise fit. Embossing indentations into the filter layer and the filter sheet eliminates the need for additional folds, so that the entire installation space and the entire filter medium can be used for filtration. 
     To produce the form-fit connection it is advantageous to use an embossing roll. An embossing roll makes it possible to produce uniform embossing points quickly and easily. The spacing between the individual points and the configuration of the embossing points are regular. This creates a uniform connection across the entire filter medium. 
     In an alternative embodiment of the filter according to the invention, a filter medium is wound in spiral form, as already described above. The filter medium comprises a corrugated filter layer and a flat filter sheet, and the filter medium is weldable. Both a polyester nonwoven and cellulose paper with synthetic fibers are suitable for this purpose. The proportion of synthetic fibers must be selected in such a way that the cellulose paper can be thermally bonded. Preferably, both filter strata are formed of the same material. It is also possible, however, to weld different materials together. 
     In yet another embodiment of the filter according to the invention, the one filter stratum is formed of a weldable medium and the other filter stratum of a non-weldable medium. To connect the two strata, the weldable medium is melted and penetrates the non-weldable medium to produce the bond. With regard to the dimensional stability of the filter medium, the filter strata formed by the filter sheet and the filter layer are stable enough so that the applied corrugation is permanent. The corrugated filter layer has valleys and peaks, such that the valleys of the corrugated filter layer are connected to the flat filter sheet by a weld. The channels formed between the peaks and the filter sheet are closed at one of the end faces. The other end face remains open. The channels formed between the valleys and the underside of the adjacent filter sheet by winding the filter medium are closed on the opposite side, so that alternately closed channels are formed. No additional materials are introduced into the filter medium by the welded connection, so that the filter medium in the filter is a single-component material. This facilities disposal of the used filter after filter replacement. 
     In accordance with another embodiment of the invention, the closure of the channels in the end face area is produced by a weld, such that the peaks are pressed onto the filter sheet. Pressing the peaks onto the filter sheet substantially reduces the volume to be closed off. Furthermore, the peaks are welded to themselves and to the filter sheet. As a result, no additional material is required to close the channels, which saves cost of materials. In addition, the production cycle is shortened because no curing times for adhesives or other components are required. By pressing the peaks onto the filter sheet, the flow into the channels is improved because the flow resistance of the closed channels is reduced. 
     In one advantageous embodiment of the invention, the welded joint is produced by ultrasound. A sonotrode is used for this purpose, and the filter sheet and the filter layer are jointly guided past the sonotrode. After welding, the filter medium can be wound and subsequently cut to length as required. An ultrasonically welded joint is easy to produce and can be produced even in small components. 
     The diesel particle filter according to the invention is intended particularly for motor vehicles and comprises a sintered ceramic body with channel structures. A filter such as the one described above is used to produce the sintered ceramic body. The filter has alternately closed channels. This closure and the connection of the filter layer to the filter sheet are produced without adding any additional components. 
     In another embodiment of the filter, the channels are not alternately closed. Thus the filter medium has identical particle collection properties in all the areas. This means that the filter can be impregnated with a ceramic mass and the ceramic mass settles uniformly within the entire filter. The filter merely forms the support structure for the ceramic mass. In a subsequent drying or sintering process, the filter medium is combusted and removed from the ceramic mass. The porosity of the sintered ceramic body can be influenced by the porosity and structure of the filter medium, particularly paper. The sintered ceramic body furthermore has the same geometry as the filter. Thus, the channels of the channel structure are also alternately closed or open. In a filter with open channels, the alternate channel closure is produced by the ceramic mass. The exhaust gas streaming in at one end face flows into the channels that are open on this side. Since the channels on the opposite side are closed, the exhaust gas must pass through the porous wall of the channels. The diesel particles are thereby retained and the cleaned exhaust gas can exit the sintered ceramic body through the adjacent channels. Since the filter is produced without using additional joining agent, the ceramic mass homogenously penetrates the filter, so that all the adjacent filter strata have good contact with each other. The formation of defects is prevented, so that the sintered ceramic body has good shatter resistance and can withstand shocks, such as may occur in motor vehicles, without being destroyed. 
    
    
     
       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: 
         FIG. 1  is a detail view of a filter medium according to the invention; 
         FIG. 2  is a cross-sectional view of an embossing point; 
         FIG. 3  illustrates a filter medium during winding; 
         FIG. 4  is a detail view of a filter medium of the invention with closed end faces; 
         FIG. 5  illustrates the process of welding the filter medium; 
         FIG. 6  is a top view of a diesel particle filter, and 
         FIG. 7  is a longitudinal section of a diesel particle filter. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a detail perspective view of a filter medium  10 , which depicts a partial manufacturing step. The filter medium  10  shown in this view will be further processed in a subsequent step. The filter medium  10  comprises a corrugated filter layer  11  and a flat filter sheet  12 . Both filter strata  11 ,  12  are formed of the same dimensionally stable cellulose paper. The corrugated filter layer  11  has valleys  13  and peaks  14 . The valleys  13  are connected to the flat filter sheet  12  by embossing points  15 , so that the filter layer  11  is fixed to the filter sheet  12 . The embossing points  15  are disposed in a line only in partial areas along the valley floor, which is the lowest point of the valley  13 . Between the peaks  14  and the filter sheet  12 , parallel-extending channels  16  are formed. Since the embossing points  15  do not form a sealing connection between the filter strata  11 ,  12 , volume flows are able to pass from one channel  16  to the next channel  16  extending parallel thereto. A leakage flow from one channel  16  to another channel  16  is unimportant because the parallel channels  16  carry the same unfiltered or filtered fluid. 
       FIG. 2  shows the embossing point  15  in cross-section. The embossing point  15  forms a positive-locking connection between the corrugated filter layer  11  and the filter sheet  12 . Both filter strata  11 ,  12  are deformed in such a way that the indentations are permanent and remain even after removal of the strata from the embossing dies. The indentation in the flat filter sheet  12  forms the seat for the indentation of the filter layer  11 . Since the two filter strata  11 ,  12  interengage, the holding forces are sufficient to prevent accidental detachment of the filter strata  11 ,  12  from each other. 
       FIG. 3  shows the filter medium  10  depicted in  FIG. 1  during winding. Components corresponding to those of  FIGS. 1 and 2  are identified by the same reference numerals. The filter strata  11 ,  12 , which are joined as illustrated in  FIG. 1 , are rolled up to form a winding  17 . In this process, the channels  16  are closed along their end faces. To this end, the peaks  14  are pressed onto the filter sheet  12  and fixed with embossing points  15 . Outside the pressed areas at the end faces the channels  16  remain. On the opposite end face, the channels  16  have their corrugated shape. The process of closing the channels  16  will be described below with reference to  FIG. 4 . 
       FIG. 4  shows a detail view of the filter medium  10  with closed channels  16 . Again, components corresponding to those depicted in  FIGS. 1 and 3  are identified by the same reference numerals. The end faces of the channels  16  are closed by pressing or crimping the peaks  14 . Pressing causes the peaks  14  to form folds, such that the accumulation of material is fixed by the embossing points  15 . This creates a connection to the filter layer  11  itself as well as to the filter sheet  12 . To secure the connection, a plurality of embossing rows  18  is provided, which extend parallel to each other. 
       FIG. 5  illustrates a process sequence for welding the filter medium  10 . The filter strata  11 ,  12  to be connected are each unwound from an endless roll  19 . Both filter strata  11  and  12  are formed of the same weldable material. The material for the corrugated filter layer  11  is guided over profiled rolls  20 , which produce the required corrugation. After the filter layer  11  has been corrugated, the filter sheet  12  is fed over a guide pulley  21  and is pressed onto the corrugated filter layer  11 . The corrugated filter layer  11  continues to be guided in the profiled roll  20  to prevent damage to the corrugated shape. The strata  11 ,  12  thus brought together are welded to the filter sheet  12  in the contact zones of the valleys  13  using a sonotrode  22 . The closing of the end faces of the channels  16  can be effected by expanding the production plant or by using another machine in a subsequent process. To close the channels  16 , they are pressed by an anvil  23  at their end face and are welded by an additional sonotrode  24 . Outside the pressed-down end faces the channels  16  remain. 
       FIG. 6  shows a top view of a diesel particle filter according to the invention. The diesel particle filter comprises a sintered ceramic body  25 , which has porous walls  26  that are permeable to the internal combustion engine exhaust gas which is to be cleaned by the filter. The walls  26 , as shown in  FIG. 7 , form alternately closed channels  16  that extend parallel to each other. The channels  16  that are open in the left half of the figure are closed at the opposite end face (right half of the figure). The closure  27  of the, channels  16  is indicated schematically. The channels  16  that are closed on the left end face are open on the opposite end face (right end face), so that the gas to be cleaned flows through the sintered ceramic body  25  in the direction of the arrows, as shown. 
     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.