Patent ID: 7217309

Claim:
A paper filter for filtering particulates emitted together with the exhaust gases of internal combustion engines, which comprises a filtering element ( 11 ) made in the form of a folded up sheet to form a “Greek key”, having several filtering layers ( 13 ) placed substantially parallel, connected by means of folds ( 14 ), said filtering layers ( 13 ) being separated and maintained equidistant through the interposition of spacers ( 20 ) of such a rigidity as to prevent the collapse of the filtering layers ( 13 ) said spacers being arranged parallel to the direction of the inlet gas flow (F 1 ) in the filtering element ( 11 ) wherein said spacers ( 20 ) comprise two corrugated boards, each one consisting, in turn, of a sheet of corrugated paper ( 21 ) stuck along a generatrix to a corresponding cover ( 22 ), said spacer ( 20 ) formed by two covers ( 22 ) which are stuck to one another to form said spacer ( 20 ) which therefore presents corrugated surfaces both on its upper and lower side, wherein the disposition of filtering layers ( 13 ) and spacers ( 20 ) defines an alternated series of “dirty” cells ( 15 ) in which the gas to be filtered circulates and is sent to the filtering layers ( 13 ) through ducts ( 25 ) delimited by the waves of the corrugated paper ( 21 ) and by the filtering layers ( 13 ), alternated in the “Greek key” disposition of the filter, with “clean” cells ( 16 ), in which the filtered gas (F 2 ) circulates and is sent to the atmosphere through ducts ( 26 ), in turn delimited by the waves of the corrugated paper ( 21 ) and by adjacent filtering layers ( 13 ).