Filter and forming system

A filter includes first and second sheets of filter media, the second sheet being pleated and forming with the first sheet a plurality of axially extending flow channels having lateral cross-sectional shapes with two adjacent included angles each greater than 45° and less than 75°. Forming apparatus and methods are provided.

BACKGROUND AND SUMMARY

The invention relates to filters for filtering fluid, including air, exhaust, liquid, and other fluids, and to forming apparatus and methods for such filters.

The filter is formed by alternating layers of flat and pleated filter media. In one embodiment, the layers are rolled into a cylindrical or other closed loop shape, such as oval, racetrack shaped, etc. The channels formed by the intersection of the rolled pleated and flat layers run in an axial direction to the cylindrical structure along its length. Lower restriction and greater structural strength is provided, including crush strength, which is desirable for packaging and sleeving where appropriate. Particular geometries have been found to improve performance.

The invention further provides forming apparatus for the filter and methods of configuring and shaping same. In various applications, it may be desirable that the filter use pleated media with either triangular or trapezoidal cross-sections, rather than corrugated media with a sinusoidal shaped cross-section. The difference is significant for greater strength, stability, and structural integrity. This is particularly desirable in applications where force is applied in a radial direction to seal and hold the filter element in place, including in applications where the pleat height is less than 10 mm, and preferably less than 6 mm.

Conventional methods, including score-roll pleating and corrugation, cannot produce media with the noted desired geometry and structure. Pleating is commonly done by score-rolling, wherein the media passes between two rollers with male and female spikes and slots that score the media. The media then passes through downstream gathering wheels that feed the media against an opposing force. The inherent stiffness of the media causes the media to fold or crease into pleats along the score lines. For this reason, score-roll pleating is unsuitable for pliable media with insufficient stiffness. Another limitation is that desired small pleat heights in certain applications, e.g. less than 10 mm, cannot be obtained by the score-roll pleating method. Furthermore, creasing along the noted score lines can damage the media pleat tips for some types of filter media.

Another possibility is to use corrugation for producing a filter. In this method, corrugated rollers are used to imprint a shape onto the media, instead of creasing and folding the media as is done with other pleating methods. The limitation of the noted corrugation method is that the pleats have a sinusoidal cross-section, rather than triangular or trapezoidal. As above noted, triangular or trapezoidal flutes or channels are desired, with cross-sectional geometries which are more structurally stable and provide for more laminar flow.

In one aspect of the invention, a star gear pleating method is used to produce the pleated media filter. Particularly designed interlocking gears pass the media between one or more sharp tips of a gear tooth on one gear and a particularly formed root of the opposing gear. The teeth can be modified to provide triangular or trapezoidal pleats. The gears fold and gather the media without crushing it and without adversely affecting the performance of the filter. As the media is released from the interlocking gears, it is directed forward and out of the gears by guide bars which prevent the media from tending to follow the gears and become damaged. The present method does not rely on media stiffness to fold and crease the media, and hence it can be used on more pliable media without damage to the pleat tips. The media is partially gathered and folded between the interlocking teeth of the gears, which partial gathering helps prevent unwanted jams or reverse pleating otherwise common with score-roll pleating. The present method and forming apparatus allows much shorter pleat heights and faster pleating without damaging the media or breaking media fibers. In contrast to corrugation, the present technique provides straight sided triangular or trapezoidal pleats.

DETAILED DESCRIPTION

FIG. 1shows a filter10for filtering fluid flowing axially thereinto as shown at arrow11. The filter includes first and second filter media sheets12and14. Sheet14has a plurality of pleats such as16defined by wall segments18,20, etc. extending in zig-zag manner between pleat tips22,24,26, etc.,FIGS. 1,2, at axially extending bend lines. The pleat tips such as22and26on one side of sheet14are in contiguous relation with sheet12and preferably bonded thereto with an adhesive or other binder, and define axial flow channels such as28. Sheets12and14are preferably, though not necessarily, wound or rolled into a spiral,FIG. 1. In a spiral-wound or other multilayer stack, the pleat tips such as24on the other side of sheet14engage sheet12of the next layer, for example as shown at12a,FIG. 2.

The noted flow channels such as28have a lateral cross-sectional shape having two adjacent included angles each greater than 45° and less than 75°. In one embodiment, sheets12and14, including wall segments18and20, have a thickness less than 0.8 mm, a porosity greater than 80%, and an extension b between pleat tips less than 10 mm. In the preferred form of such embodiment, the noted thickness is less than 0.5 mm, the noted porosity is greater than 85%, and the noted extension or length b is less than 6 mm.

The noted two adjacent included angles are provided by a first angle34,FIG. 2, between first sheet12and wall segment18of second sheet14, and a second angle36between first sheet12and second wall segment20of second sheet14. As noted above, each of angles34and36is greater than 45° and less than 75°. In the embodiment ofFIG. 2, the noted lateral cross-sectional shape of flow channel28consists of three pleat tips22,24,26and three included angles34,36,38. Third angle38is between first and second wall segments18and20. In preferred form, the lateral cross-sectional shape of flow channel28is an isosceles triangle wherein45⁢°<θ<75⁢°0.5⁢⁢mm<2⁢b·sin⁢⁢12⁢θ·cos⁢⁢12⁢θ1+sin⁢⁢12⁢θ<2.9⁢⁢mm
where θ is angle38between wall segments18and20, and b is the noted extension or length of each of wall segment20between pleat tips26and24and wall segment18between pleat tips22and24, as measured along the inside dimension of the wall,FIGS. 2,3.

FIG. 4shows an alternate embodiment and uses like reference numerals from above where appropriate to facilitate understanding. InFIG. 4, the lateral cross-sectional shape of flow channels such as46consists of four pleat tips48,50,52,54and four included angles56,58,60,62. Each of first and second angles56and58is greater than 45° and less than 75°. Each of third and fourth angles60and62is greater than 90°. The lateral cross-sectional shape is a trapezoid having first and second distally opposite sides64and66provided by wall segments68and70of pleats20and slanted towards each other. The trapezoid has distally opposite substantially parallel major and minor bases72and74extending laterally between sides64and66. Major base72is longer than minor base74. Wall segment68of second sheet42provides side64of the trapezoid. Wall segment70of second sheet42provides side66of the trapezoid. First sheet40provides major base72of the trapezoid. Second sheet42has a truncated wall segment76spanning first and second wall segments68and70and providing minor base74of the trapezoid. The ratio of the length of minor base74to the length of major base72is less than 0.27.

The flow channel lateral cross-sectional trapezoid shape ofFIG. 4consists of four walls, namely a first wall provided by first sheet40along major base72, a second wall provided by first wall segment68of second sheet42along first side64, a third wall provided by truncated wall segment76of second sheet42along minor base74and by a section of the next layer18of the first sheet at40ain the spiral pattern along minor base74, and a fourth wall provided by the second wall segment70of second sheet42along the noted second side66. The noted first, second and fourth walls72,64,66have a single sheet thickness. The noted third wall at74has a double sheet thickness. The single sheet thickness of the first wall at72provided by first sheet40is less than 0.8 mm. The single sheet thickness of the second wall64provided by second sheet42at wall segment68is less than 0.8 mm. The double sheet thickness of the third wall74provided by first and second sheets40and42at40aand76is less than 1.6 mm. The single sheet thickness of the fourth wall66provided by second sheet42at wall segment70is less than 0.8 mm. Walls72and64meet at pleat tip48and define angle56. Walls64and74meet at pleat tip52and define angle60. Walls74and66meet at pleat tip54and define angle62. Walls66and72meet at pleat tip50and define angle58. The length or height of wall64along wall segment68between pleat tips48and52is less than 10 mm, and preferably less than 6 mm. The length of wall66along wall segment70between pleat tips50and54is less than 10 mm, and preferably less than 6 mm.

In the preferred form of the embodiment ofFIG. 3,45⁢°<θ<75⁢°,⁢0.5⁢⁢mm<2⁢b·(w-b·sin⁢⁢12⁢θ)·cos⁢⁢12⁢θb+w-b·sin⁢⁢12⁢θ<2.9⁢⁢mm
where θ is the included angle at the intersection of projections of wall segments68and70, b is the length of each of trapezoid sides64and66as measured along the inside dimension,FIGS. 4,5, and w is the length of major base72as measured along the inside dimension,FIGS. 4,5.

In one embodiment the noted wall segments are alternately sealed to each other by a first upstream set of plugs such as78,FIG. 1, to define a first set of flow channels80closed by plugs78, and a second set of flow channels81interdigitated with first set of flow channels80and having open upstream ends. The wall segments are alternately sealed to each other by a second downstream set of plugs such as shown in dashed line at82, and as is known, closing the second set of flow channels81. The first set of flow channels80have open downstream ends. This forces the flow from intake11to flow through the wall segments of the media, i.e. to flow into the open upstream ends of flow channels81, and then cross through the filter media wall segments, and then flow through the open downstream ends of flow channels80.

FIG. 6illustrates forming apparatus for the above noted filter. First and second star gears83and84each have a plurality of teeth85and86interdigitated with a plurality of roots88and90therebetween. The gears rotate in intermeshed relation with the tooth of one gear in the root of the other. Gear83rotates clockwise as shown at arrow92about rotation axis94. Gear84rotates counterclockwise as shown at arrow96about rotation axis98. Gears83and84pass second sheet42therebetween, and gather and fold second sheet42along crease lines at pleat tips26,28,30, etc., which crease lines provide the noted axially extending bend lines. Each root such as90has a given arcuate length along an inner hub surface100spanning between and separating a respective pair of teeth such as86and102having sides104and106extending generally radially outwardly from opposite arcuate ends of spanning root hub surface100. Side104meets spanning root hub surface100at a first angle108at a first junction point110. Side106meets spanning root hub surface100at the second arcuate end thereof at a second angle112at a second junction point114. First and second junction points110and114are spaced from each other by the noted given arcuate length of spanning root hub surface100. Each of angles108and112is greater than 90°.

Each tooth of at least one of the gears has an outer end with a pointed tip116extending into a respective root and spaced from first junction point110by a first triangular shaped gap, and spaced from second junction point114by a second triangular shaped gap. In one preferred embodiment, the teeth of each of the gears have pointed tips116and118at the outer ends of the teeth. In another embodiment, each tooth of at least one of the gears has an outer end which is truncated as shown in dashed line at120, to have first and second pointed tips122and124extending into a respective root. In a further embodiment, the teeth of the other gear may also be truncated as shown at dashed line126, with first and second pointed tips128and130extending into a respective root.

The noted given arcuate length of spanning root hub surface100defines minor base74. Sides104and106of the teeth diverge from each other as they extend radially outwardly from spanning root hub surface100and are spaced from each other at their outer ends along a second given arcuate length defining major base72. In preferred form, the sides of the teeth, for example sides132and134of tooth85, bow convexly as they extend from the outer end of the tooth generally radially inwardly to respective roots spaced on opposite sides of the tooth.

A pair of parallel guide bars140and142are spaced on opposite sides of the intermeshing of gears83and84. Bars140and142extend parallel to the direction of travel144of second sheet42through the gears. The bars are spaced from each other by a gap146less than 10 mm along a direction perpendicular to travel direction144and perpendicular to the gear rotation axes94,98. The bars receive pleats20and engage pleat tips26,28,30, etc. Sheet42is fed forwardly, leftwardly inFIG. 6, through the gears from an inlet region148to an outlet region150. The guide bars have respective upstream ends152,154at the gears, and downstream ends156and158at outlet region150and spaced leftwardly from the gears. It is preferred that upstream ends152and154of the guide bars be upstream of rotation axes94and98, i.e. rightwardly of the rotation axes inFIG. 6. In the orientation ofFIG. 6, the guide bars are spaced behind the gears, as illustrated in dashed line. The forming apparatus provides the preferred method of configuring and shaping the noted filter. In spiral wound configurations, the noted cross-sectional specifications of the channels are not met in the first several layers of pleats starting at the center.

In one embodiment in accordance with the noted parent application, the filter is initially a pre-form which is cured and rigidized, as in the noted parent patent, to an exhaust aftertreatment filter for filtering engine exhaust from an engine such as shown in U.S. Pat. No. 6,444,006 in FIG. 1 at diesel engine 30 receiving engine exhaust flowing axially therethrough at 32. The cured and rigidized filter is regenerable by heat to burn-off contaminant particulate collected from the engine exhaust. The pre-form may be rigidized with sol-gel, chemical vapor infiltration, ceramic bond phase, silicon carbide, or in other suitable manner.

It is recognized that various equivalents, alternatives and modifications are possible within the scope of the appended claims. For example, spiral wound, annular, concentric, and so on, include shapes such as cylindrical, oval, racetrack shaped, and the like. The filter and forming system hereof may be used for various filters for filtering fluid, including air, exhaust, liquid, and other fluids.