Regenerable Diesel Exhaust Filter and Heater

The present invention relates to a filter system for purifying the exhaust gases of an internal combustion engine. In particular, it relates to a regenerating filter for removing particulates from the exhaust gases of a diesel engine.

There is an increasing awareness of the health hazards presented by many common air pollutants. Perhaps in response to these concerns, governments are increasingly regulating the exhaust emissions of vehicles. In the United States, Environmental Protection Agency requirements relate to the exhaust of vehicles, rather than the device or method used to control the exhaust. Two predominant methods are currently used to control emissions; they are the utilization of alternative fuels, and solid particulate removal, as with a filter.

In particular, diesel engines, such as those utilized in trucks, buses, and passenger cars, produce a tremendous amount of soot. As there are in excess of 1.2 million diesel-powered vehicles in the United States alone, diesel engines pose significant health and air pollution problems. Over the next several years, vehicles powered by such diesel engines must meet more and more stringent regulations. As a result, there is increasing interest in the efficient and effective limitation of emission of particulate material, generally carbon and hydrocarbon particles, from the exhaust gases of diesel engines.

Various types of filtering devices have been proposed to filter diesel engine exhaust. Usually, such devices comprise filter systems which retain and collect the particulates in the exhaust gas. As soot particles are reported to range in size upward from 2500 .ANG. (0.25 micron), a high efficiency filter is required to effectively filter out such contaminants. A number of filters are known. For example, cellular ceramic filters and honeycomb filters of porous ceramic material, such as those disclosed in U.S. Pat. Nos. 4,872,889 and 4,948,403 to Lepperhoff et al., have been recognized as being useful in trapping particulates from exhaust emissions.

However, particulates retained in the filter generally lead to an increase in the flow resistance in the exhaust and a resultant increase in the back pressure of the exhaust. Excessive back pressure can develop quickly, particularly when high efficiency filters are utilized. This unacceptable increase in exhaust back pressure can lead to an increase in fuel consumption, and, in extreme cases, to engine shut-off or failure. This result is particularly troublesome with truck and bus diesel engines inasmuch as any filter of a practical size would quickly become loaded and develop high back pressure which would result in engine shut-off.

As a result, it necessary to intermittently regenerate the filter to remove the carbon particles from the filter during operation of the diesel engine. This is generally accomplished by providing sufficient heat to combust the particulates. Consequently, filter materials must withstand temperatures of over 600.degree. C. (1112.degree. F.) repeatedly. A number of methods of regeneration are known, such as the utilization of electric heating elements, as disclosed in, for example, U.S. Pat. No. 5,053,062 to Barris et al., U.S. Pat. No. 4,791,785 to Hudson et al., and U.S. Pat. Nos. 4,872,889 and 4,948,403 to Lepperhoff et al. Another means of regenerating the filter includes turbo enriched fuel injection to raise the temperature in the filter to initiate auto-combustion of trapped soot particles. These methods may suffer, however, from difficulties in the ignition of deeply trapped soot particles during regeneration or require an excessive energy input to regenerate the filter material.

Ceramic honeycomb filter designs are particularly susceptible to rapid development of excessive back pressure. There are a number of additional disadvantages, however, associated with the use of ceramic materials. Ceramic materials, particularly filters, are inherently brittle, and, consequently, subject to fracture from shock and mechanical stresses. Therefore, when ceramic materials are used in filters, it is necessary to design the filters with greater depth thickness than ordinarily desirable. Further, because ceramic materials are fragile and not deformable, it is not feasible to utilize standard engineering edge-sealing, gasketing methods due to the heating that is required. Ceramics are also costly to manufacture as they are difficult to shape. Additionally, inasmuch as the uniformity of ceramic particles is difficult to control, particularly for sintering and pre-forming, manufacturing quality is difficult to control.

The general object of the invention is to provide an improved exhaust filter for diesel engines. A more particular object of the invention is to provide a reliable, high efficiency filter which provides a low change in pressure across the filter.

An additional object is to provide an exhaust filter that does not significantly impair engine performance. A related object is to provide an exhaust filter with reduced susceptibility to development of back pressure.

Another object is to provide an exhaust filter that is highly resistant to heat, and is regenerable.

A further object is to provide an exhaust filter of an uncomplicated design that may be easily serviced. A more specific object is to provide an exhaust filter that may be easily assembled and disassembled to facilitate maintenance or replacement of filter elements in the field.

Yet another object is to provide a diesel exhaust purification system which accommodates a large flow of gas but features a small, compact design.

Another object of the invention is to provide an exhaust filter assembly which facilitates the ignition of trapped soot particles during regeneration of the filter.

An additional object is to provide a modular diesel exhaust filter arrangement which may be sized to fit a variety of different engines.

In accomplishing these objects, there is provided an improved diesel exhaust filter having a high efficiency, self-contained filter arrangement disposed within a housing that may be connected in-line with the exhaust system of the vehicle to provide a flow of exhaust gases therethrough. The housing, which may be of any appropriate shape, includes an inlet pipe, which may be connected to an exhaust pipe from the engine, and an outlet pipe, which may be open to the atmosphere. Disposed within the housing is a self-contained filtering means.

In one embodiment of the invention, the filtering means is a flat filter arrangement having inlet and outlet cells and filter elements compressed between opposite impervious endplates. Exhaust gas enters the inlet cells along the inlet end of the housing, flows through the filter elements, and out of the filter arrangement through the outlet cells to be exhausted to the atmosphere through the outlet pipe. In another embodiment of the invention, a pleated cylindrical filter is utilized, the exhaust gas flowing from the inlet pipe outward through the cylindrical filter from the interior, or, alternately, inward from the perimeter of the cylindrical filter to its interior, and out of the housing through the outlet pipe. Another embodiment combines the flat and cylindrical filters of the first and second embodiments, respectively, to provide an arrangement where the exhaust gas flows through the flat filters and outward from the interior of the cylindrical filter to its perimeter to be passed to the atmosphere through the outlet pipe. Another embodiment of the invention comprises a housing having a rectangular plenum having an open top portion into which seats a topplate having substantially flat and upwardly and outwardly extending sides. This embodiment utilizes a flat filter arrangement, the components of which are compressed between the lower, inner surface of the plenum and the flat surface of the topplate by nuts and carriage bolts that extend through openings in the flat surface of the topplate, the lower surface of the plenum, and the components of the filter arrangement. Another embodiment of the invention comprises a similar flat filter arrangement, and housing comprising a plenum having dual components that are secured together along outwardly extending flanges by bolts. Flat plates, each having an outwardly extending pipe are secured to the ends of the plenum to seal the housing.

Another embodiment of the invention includes a housing having an inlet pipe and an outlet pipe, which defining an exhaust gas flow path through the housing, and a filter arrangement is disposed within the gas flow. The filtering arrangement includes a plurality of inlet cells, microporous filter elements and outlet cells, which are alternately arranged with at least one microporous filter element disposed between each inlet cell and adjacent outlet cell. A portion of the filter elements extend past the inlet and outlet cells. The inlet and outlet cells, and the microporous filter elements comprise materials that are resistant to high temperatures such that the filtering arrangement may be regenerated by heat.

In any of the embodiments of the present invention, the filter assembly may further include an insulating material coupled to the housing. The insulating material is resistant to the high temperatures to which it may be exposed during regeneration of the filtering means. The insulation of the housing, in addition to lessening heat dissipation within the plenum, serves to enhance the safety of the filter assembly by reducing the surface temperature of the housing.

Each of the filter arrangements utilizes materials that are highly resistant to excess temperature so that the exhaust filter may be regenerated by heat provided by any appropriate method. Further, the filters, while having a much higher efficiency than present ceramic and metal trap filter designs, provide effective filtration of soot expelled from the diesel engine with a minimal pressure drop across the filter. The filter arrangements preferably comprise a fiber filter sandwiched between woven wire mesh. The fiber filter preferably comprises quartz, borosilicate-E or aluminosilicate.

Further, the structure of the exhaust filter is such that it may be easily disassembled to facilitate service, even after the device has been installed on a vehicle. The housing includes a plenum and at least one removable endplate. Once the endplate has been disassembled from the plenum, the self-contained filter arrangement may be removed to permit replacement or further cleaning. The filter arrangement may then be reinserted and the housing easily reassembled.

The exhaust filter may also incorporate an electric heater in the plenum, which may be operated from an electric source in the vehicle. The electric heater may serve to heat the plenum in order to initiate the regeneration of the filter assembly.

An exhaust gas filter assembly for removing particulates from the exhaust gas of an engine in accordance with the present invention includes a housing having an inlet pipe configured to receive the exhaust gas from the engine and an outlet pipe configured to vent exhaust gas to the atmosphere and defining an exhaust gas flow path through the housing. A filter arrangement is disposed within the housing in the gas flow path. The filter arrangement includes a plurality of inlet cells, microporous filter elements, and a plurality of outlet cells which are alternately arranged. At least one microporous filter element is disposed between each inlet cell and adjacent outlet cell. The inlet and outlet cells, and the microporous filter elements include materials that are resistant to high temperatures for allowing the filter arrangement to be regenerated by heat. At least one of the inlet cells or outlet cells is electrically conductive. The exhaust gas filter includes a heater associated with the filter arrangement to regenerate the filter arrangement by heating the filter arrangement or gas in the housing to combust the particulates removed from the exhaust gas of the engine. The heater includes an electrical connection means for electrically connecting the electrically conductive inlet cell or outlet cell to an electrical power source.

An exhaust gas filter assembly in accordance with the invention may also include a housing having an inlet pipe for receiving exhaust gas and an outlet pipe for venting exhaust gas to the atmosphere. A filter arrangement is disposed within the housing and includes a plurality of inlet cells, microporous planar filter elements and outlet cells which are alternately arranged with at least one microporous planar filter element disposed between each inlet cell and adjacent outlet cell. The inlet and outlet cells, and the microporous planar filter elements comprise materials that are resistant to high temperatures so that the filter arrangement may be regenerated by heat. At least one of the filter elements includes a filter support and a filter medium. An electrically resistive heating wire is mounted to the filter support to regenerate the filter arrangement by heating the filter arrangement or gas in the housing to combust the particulates removed from the exhaust gas.

An exhaust gas filter assembly in accordance with the invention may also include a housing having an inlet pipe for receiving exhaust gas and an outlet pipe for venting exhaust gas to the atmosphere. A filter arrangement is disposed within the housing and includes a plurality of inlet cells, microporous planar filter elements and outlet cells which are alternately arranged with at least one microporous planar filter element disposed between each inlet cell and adjacent outlet cell. The inlet and outlet cells, and the microporous planar filter elements comprise materials that are resistant to high temperatures so that the filter arrangement may be regenerated by heat. At least one of the filter elements includes a filter support and a filter medium. An electrically resistive heating wire is mounted to the filter medium to regenerate the filter arrangement by heating the filter arrangement or gas in the housing to combust the particulates removed from the exhaust gas.

An exhaust gas filter assembly according to the invention also includes a housing having an inlet and outlet pipe. A filter arrangement is disposed within the housing and includes a plurality of inlet cells, microporous filter elements and outlet cells which are alternately arranged with at least one microporous filter element disposed between each inlet cell and adjacent outlet cell. The inlet and outlet cells, and the microporous filter elements comprise materials that are resistant to high temperatures such that the filter arrangement may be regenerated by heat. At least one of the filter elements includes a filter support and a filter medium. An electrically resistive heating wire is disposed within at least one of the microporous filter elements and mounted to the filter medium to regenerate the filter arrangement by heating the filter arrangement or gas in the housing to combust the particulates removed from the exhaust gas.

The foregoing and other features of the present invention will become apparent to one of ordinary skill in the art to which the invention pertains from the following detailed description when read in conjunction with the drawings, in which:

FIG. 1 is a perspective view of an exemplary filter system embodying the invention;

FIG. 2 is an exploded view of the filter system of FIG. 1;

FIG. 3 is an exploded view of a portion of the filter arrangement of FIG. 2;

FIG. 4 is a cross-sectional view of the filter system taken along line 4--4 in FIG. 1;

FIG. 5 is a cross-sectional view of an alternate embodiment of the filter system shown in FIG. 1;

FIG. 6 is a cross-sectional view of an alternate embodiment of the filter system shown in FIG. 1;

FIG. 7 is a cross-sectional view of the filter system taken along line 7--7 in FIG. 6;

FIG. 8 is a view of an alternate embodiment of the embodiment of the filter system shown in FIG. 1;

FIG. 9 is a cross-sectional view of the filter system taken along line 9--9 in FIG. 8;

FIG. 10 is a perspective view of the filter arrangement of FIG. 9;

FIG. 11 is a top view of an inlet cell of FIG. 10;

FIG. 12 is a top view of an alternate embodiment of inlet cell;

FIG. 13 is a side view of the inlet cell taken along line 13--13 of FIG. 12;

FIG. 14 is a side view of the inlet cell taken along line 14--14 of FIG. 12;

FIG. 15 is a perspective view of an alternate embodiment of the invention of FIG. 1;

FIG. 16 is a partially cutaway top view of the inlet end of an alternate embodiment of the filter system of the present invention;

FIG. 17 is a cross-sectional view of the filter system of FIG. 16;

FIG. 18 is a cross-sectional view of a modification of a portion of the housing of the filter system of FIG. 16;

FIG. 19 is a cross-sectional view of an alternate embodiment of the filter system of the present invention;

FIG. 20 is a cross-sectional view of a filter system;

FIG. 21 is a top view of an inlet cell;

FIG. 22 is an exploded view of a portion of a filter arrangement; and

FIG. 23 is a cross-sectional view of an alternate filter system.

While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, there is shown in FIG. 1 an exhaust filter system 20 for use in the exhaust system of a diesel powered vehicle. The filter system 20 includes a housing 22 having an inlet pipe 24 and an outlet pipe 26. The housing 22 may be connected in-line with the exhaust system of a diesel powered vehicle to provide a flow of exhaust gases from the engine into the inlet pipe 24, through the housing 22, and out of the outlet pipe 26 to the atmosphere. In a currently preferred embodiment, the inlet and outlet pipes 24, 26 are on the order of two inches, or fifty millimeters in diameter.

In accordance with one aspect of the invention, there is provided a self-contained filter arrangement 28 in line with the gas flow through the housing 22, as shown in the exploded view in FIG. 2. The filter arrangement 28 provides high efficiency filtration of the gases passing therethrough, while providing a relatively low pressure drop across the filter system 20. Further, the filter arrangement 28, and, indeed, the filter system 20 is comprised of materials that are highly resistant to heat required for the regeneration process.

In the embodiment shown in FIGS. 1-4, the housing 22 comprises a plenum 30, which is generally configured as a rectangular parallelepiped. It will be appreciated, however, that the housing 22 as well as the self-contained filter arrangement 28, may be of a suitable alternate geometric design. In the preferred embodiment, the inlet pipe 24 and the outlet pipe 26 are formed integrally with the endplates 32, 34, respectively. The endplates 32, 34 are provided with flanges 33 for coupling the endplates 32, 34 to the plenum 30 by way of bolts 36 or other suitable fastening devices, which extend through the flanges 33 and the plenum 30. Accordingly, those skilled in the art will appreciate that the housing 22 may be easily disassembled for maintenance or replacement of the filter arrangement 28, even after installation. Although the housing 22 may be of any appropriate dimensions, a currently preferred design is on the order of eight inches (20.32 cm) by fifteen inches (38.1 cm) by six inches (15.24 cm). However, for larger engines, or different vehicles, these dimensions may be effectively altered to different proportions to fit the space provided.

The housing 22 may be coupled to an insulating material, which is resistant to the high temperatures to which such material may be exposed during regeneration of the filtering arrangement 28. Typically, the plenum is wrapped with the insulating material and preferably all of the outer side of the housing is wrapped with the insulating material. In a preferred embodiment, the insulation may be sandwiched between inner and outer walls of the housing 22. FIG. 18 shows a cross-sectional view of a portion of the plenum 30 of this embodiment. The insulating material 210 is sandwiched between inner and outer walls 30A, 30B of the plenum 30. In an alternate embodiment, the insulating material may be a blanket wrapped around the interior or exterior of the housing 22. Suitable insulation material may comprise inorganic fibers capable of withstanding the temperatures produced during regeneration of the filtering means, e.g., calcium silicate fibers.

The presence of the layer of insulating material minimizes heat loss from the housing. This allows the high temperatures required to burn off soot collected in the filtering means to be achieved with a lower energy input. By preventing the dissipation of heat from the filter assembly, the insulation also increases the efficiency of the soot burn off once combustion of the soot has been initiated and enhances the safety of the filter assembly by reducing the surface temperature of the housing.

Further, in order to facilitate installation of the filtering system 20 on the vehicle, the housing 22 may be provided with mounting brackets (not shown). The mounting brackets may be formed integrally with one of the components of the housing 22, or may be formed as separate components, which may be then be coupled to the housing 22.

The self-contained filter arrangement 28 is shown in greater detail in FIG. 3. The filter arrangement 28 is configured as a rectangular parallelpiped and generally comprises an assembly of inlet cells 40, outlet cells 42, and filter elements 44 compressed between opposite impervious endplates 46, 48, which may be integrally formed with the inlet and outlet cells 40, 42, as shown in FIG. 3. The inlet and outlet cells 40, 42, which may be identical to each other, are relatively thin structures. The configuration of the self-contained filtering means provides access to both sides of the microporous filter elements, thereby increasing the soot load capacity and life of the filter assembly.

Each cell 40, 42 includes four frame members 40a-40d, 42a-42d joined in a rectangular frame and a number of support members. In the embodiment illustrated in FIG. 3, each cell 40, 42 includes two support members 40e-40f, 42e-42f connected between opposite frame members 40b, 40d, 42b, 42d. However, any number of support members arranged in any appropriate configuration or geometry may be utilized. Small cells may not require support members.

For both the inlet and outlet cells 40, 42, one of the opposite frame members 40b, 42d contains several apertures 50, 52, which interconnect the exterior of the cells 40, 42 and the interior or internal spaces 54, 56 between the frame and support members 40a-40f, 42a-42f, respectively. In the embodiment shown in FIGS. 2-4, the apertures 50, 52 are of a rectangular shape. The rectangular shape provides highly efficient air flow through the cells 40, 42. It will be appreciated, however, that the apertures 50, 52 may be of any appropriate shape.

Likewise, the cells 40, 42 may be fabricated by any appropriate method; for example, the cells 40, 42 may be milled, machined, or cast. According to one low cost method, the cells 40, 42 may be flame cut or machined from flat sheet metal. The apertures may then be drilled in one of the frame members. Another low cost method is to cast the cells in steel or iron.

The inlet and outlet cells 40, 42 are distributed alternately within the filter arrangement 28 with the frame and support members 40a-f of the inlet cells 40 lying similarly to the frame and support members 42a-42f of the outlet cells 42, respectively. The inlet and outlet cells 40, 42 are further arranged so all of the inlet apertures 50 and none of the outlet apertures 52 open onto one surface of the filter arrangement 28, defining an inlet surface 58 facing the endplate 32, as shown in FIG. 2. In the exemplary filter system 20, all of the outlet apertures 52 open onto the opposite surface of the filter arrangement 28, defining an outlet surface 60 facing 180 degrees from the inlet surface 58. Alternately, the outlet apertures 52 may open onto a side surface or surfaces of the filter arrangement 28, or any appropriate combination thereof, so long as the inlet apertures 50 are sealed from the outlet apertures 52.

Returning now to FIG. 3, disposed between the inlet and outlet cells 40, 42, the filter elements 44 each comprise one or more layers of a microporous filter 57 for removing particulate contaminants, e.g., carbon and hydrocarbon particles. The filters 57 are exposed to excessive temperatures, as well as hydrocarbons, chlorides, and acid forming exhaust. Consequently, the filter material must be highly resistant to high temperatures and chemical deterioration. A variety of microporous filter materials or combinations thereof are suitable for use in the filter element 44, including ceramic fibers, porous metal fiber, or porous metal powder. Such materials as high purity silica, aluminosilicate or borosilicate-E glass, powdered metal alloys, boron, and carbon fibers, as well as other synthetic fibrous or matrix-forming materials may likewise be used. In general, any inorganic fibrous material that has a service temperature of at least 1200.degree. F. may be used if the material is capable of forming a filter media that will permit the efficient removal of solid contaminants, such as soot particles, at a low pressure drop. It will be appreciated, however, that the filter medium utilized preferably provides a high efficiency filter and is able to withstand repeated heating to high temperatures. Typically, the filter elements of the present invention comprise fibers having an average fiber diameter of from about 0.25 micron to about 15 microns and preferably of from about 0.5 micron to about 2.0 microns. Additionally, the filter element is preferably fashioned as a compressible material to allow the filter elements to be sealingly compressed when pressure is applied to the inlet and outlet cells.

A preferred filter 57 comprises quartz fiber, which is able to withstand extremely high temperatures, and has a high efficiency. Quartz fibers, such as Manville Corning type 104, 106, 108, 110 grades, or blends thereof, may be used. This filter is advantageous in that it blends fibers from under one-half micron in diameter to four microns into a highly porous sheet with low air resistance, while retaining integrity without the addition of binders. Further, these quartz fibers have melting points over 2500.degree. F., and a wide range of chemical resistance.

Borosilicate-E glass fibers, aluminosilicate fibers or chromium-containing aluminosilicate fibers are also preferred as materials which may be used in the filter elements of the present invention. These materials are commercially available in blends of very fine fibers. For instance, borosilicate-E glass fibers are commercially available in a variety of average fiber diameters, such as 104, 106 and 108B grade fibers, available from Johns-Manville Corporation. The filter elements 57 may preferably include a blend of borosilicate-E glass fibers having an average fiber diameter of 0.65 microns and a surface area of 2.3 m.sup.2 /g. Borosilicate-E glass fibers have a service temperature of 1200.degree. F., a softening point of over 1500.degree. F., and excellent chemical resistance. Aluminosilicate fibers and chromium-containing aluminosilicate fibers, such as are available from Johns-Manville Corporation with an average fiber diameter of 3-4 microns, may also be used in the filter elements of the present invention. Aluminosilicate fibers and chromium-containing aluminosilicate fibers have melting points above 3200.degree. F., and a wide range of chemical resistance.

It will likewise be appreciated that alternate filter arrangements may be utilized. One or more grades of filters may be utilized to act as a prefilter. For example, the filter arrangement may include a multi-layered structure, where the first layer to be contacted by the exhaust gas flow has a larger pore size than the adjacent downstream layer. This arrangement provides efficient removal of soot particles at a low pressure drop while making the filter element less susceptible to clogging. Such arrangements may serve to extend the life of the filters.

Further, filter element 44 may further comprise support elements 59 which may be provided adjacent the microporous filters 57 in order to provide additional support thereto, as shown in FIG. 3. In general, any metal mesh, which is capable of providing support to the areas of the filter elements unsupported by the frame members of the inlet and outlet cells, may be used. Preferably, the support elements are able to withstand the temperatures produced during the regeneration of the filter elements and typically have a service temperature of at least 1200.degree. F. In some applications, where the filter assembly is subjected to higher temperatures during use, a service temperature of at least 1500.degree. F. is preferred. Currently, preferred embodiments of the invention utilize a woven metal wire mesh, sintered metal fibers, or a sintered, woven metal mesh, such as RIGIMESH, a product available from Pall Corporation. Other support materials may also be suitable as support elements 59, so long as such materials are able to withstand extremely high temperatures and do not result in rapid development of excessive back pressure. The woven wire mesh is typically formed of a metal such as a carbon steel or low-alloy steel. Woven wire mesh formed from stainless steel (e.g., 304, 316 or 347 stainless steel) or higher alloys may also be used, particularly where enhanced corrosion resistance is desired. Mesh sizes such as 100 mesh, 90.times.100 mesh or 70 mesh are typically used. These mesh sizes have a very fine wire size and a pore size that is small enough to retain the fibers of the filter element but large enough to avoid creating a large pressure drop across the filter element. A porous metal media, such as PMM media, available from Pall Corporation, may likewise be suitable.

The impervious endplates 46, 48 are preferably fashioned from sheet metal to provide additional structural integrity. Each endplate 46, 48 is located adjacent an inlet or outlet cell, 40, 42, preferably with a gasket or other supplemental sealant disposed between them.

To compress the filter elements 44 between the inlet and outlet cells 40, 42 and to provide structural integrity to the self-contained filter arrangement 28, the endplates 46, 48 are disposed on opposite ends of an interconnecting frame assembly 64. While a variety of interconnecting frame assemblies 64 may be suitable, including a spring biased clamping assembly, in the exemplary exhaust filter system 20, the interconnecting frame assembly 64 comprises tie rods or carriage bolts 66 running through holes 68 in the corners of the cells 40, 42 and endplates 46, 48 and through cut-outs or holes 70 in the corners of the filter elements 44. Wing nuts 72 are threaded onto the threaded ends of the carriage bolts 66 and may be tightened to provide the desired compression.

Gaskets may be provided between the filter elements 44, the support screens 59, and the inlet and outlet cells 40, 42 to eliminate or minimize leakage. However, the fine fiber materials of the filter elements 44 and openings in the mesh support screen 59 may seal together in a manner that prevents leakage, thus eliminating the need for gasket materials in these locations.

A gasket 74, as shown in FIG. 2, is disposed between the plenum 30 and the filter arrangement 28 to prevent leakage of the air from between them. The gasket 74 may also dampen vibrations and noise. The gasket 74 may be formed of any suitable high temperature material, including quartz sheets, magnesium fiber, or other mineral compositions. Alternately, the gasket 74 may be a commercial high temperature metallic-type gasket, such as, for example, the type available from Flexetallic Company. Likewise, the gasket 74 may be constructed of any appropriate cross-section. For example, metal gaskets may be constructed of a ">" cross-section, wherein the deflection of the open end will create a self-adjusting seal between the two surfaces. Such an "elastic" metal seal would also accommodate variations of manufacturing tolerances of the components.

As shown in FIG. 4, from the inlet apertures 50, the exhaust flows generally parallel to the adjacent filter elements 44 into the interior or internal spaces 54 of the inlet cells 40. It then changes direction and passes through either of the adjacent filter elements 44 where particulate contaminants are removed. After passing through the filter elements 44, the purified air flows into the interior or internal spaces 56 of the outlet cells 42 and again changes direction, flowing generally parallel to the adjacent filter elements 44 through the outlet apertures 52.

The air is evenly distributed along the filter elements 44 as it flows generally parallel to the filter elements 44. The air then flows substantially perpendicularly through the filter elements 44. In this way, particulates are substantially evenly distributed along the filter elements 44.

The filter arrangement 28 may include a large number of filter elements 44, and, therefore, present a large filtering area, in a relatively small space. Further, as the adjacent frame members and filters elements 44 provide sufficiently large contact area, leakage of air between the frame members and the filter elements 44 is prevented when the assembly of cells 40, 42 and filter elements 44 is compressed by tightening the wing nuts 72 onto the carriage bolts 66. Thus no gaskets or supplemental sealants are required between the filter elements 44 and the inlet or outlet cells 40, 42.

It will be appreciated by those in the art that the self-contained filter arrangement 28 is easy to service. With either of the endplates 32 or 34 removed, as explained above, the self-contained filter arrangement 28 may be easily removed from the plenum 30. One or more of the filter elements 44 may be removed and cleaned or replaced simply by loosening the wing nuts 72 on the carriage bolts 66. The flexible filter elements 44 may be removed from the filter arrangement 28 by simply loosening the wing nuts 72, rather than completely removing them, inasmuch as the corners of the filter elements 44 have cutouts 70, rather than holes. Once the filter elements 44 have been reinserted in the filter arrangement 28, the wing nuts 72 are than tightened onto the carriage bolts 66 until the filter elements 44 are again adequately compressed against the inlet and outlet cells 40, 42.

FIG. 19 shows an alternative embodiment of the present invention which is configured substantially as in the first embodiment of the present invention and those elements corresponding to elements in the first embodiment of the present invention retain the reference numerals. In contrast to the first embodiment, in which the configuration of the filter elements is substantially parallel (see e.g., FIG. 4), the embodiment shown in FIG. 19 includes "wedge-shaped" inlet and outlet cells 40x, 42x. The inlet cells 40x have inlet end frame members 220 that are thicker than the blind outlet end frame members 221. Similarly, the outlet cells 42x have outlet end frame members 222 that are thicker than the blind inlet end frame members 223. The side frame members (not shown) of the inlet and outlet cells are tapered accordingly. For a given number of filter elements, this configuration permits the construction of a filter assembly having smaller external dimensions than would be possible with an assembly having the parallel filter element configuration.

Another embodiment of the invention is shown in FIGS. 16 and 17. The filter assembly of this embodiment is configured substantially as in the first embodiment of the present invention and those elements corresponding to elements in the first embodiment of the present invention retain the reference numerals. As shown in FIGS. 16 and 17, the housing 22 includes a diffuser baffle 200. The inlet chamber 204 may be partitioned by a diffuser baffle 200 into an outer inlet chamber 202 communicating with the inlet pipe, and an inner inlet chamber 203 communicating with the inlet cells. The baffle 200 has perforations 206 therethrough and comprises materials that are resistant to the high temperatures that may be produced during regeneration of the filtering arrangement. Preferably, the total area of the perforations 206 is no less than about 25% and preferably about one-half the total surface area of the baffle 200. In a typical embodiment of the invention, the baffle 200 has 1/4 inch (0.635 cm) diameter perforations 206, the total area of which is about 50% of the total surface area of the baffle 200. The baffle 200 serves to better distribute incoming gases in the inlet chamber 204 without significantly increasing back pressure in the exhaust system. This allows higher incoming exhaust gas velocities to be accommodated and enhances the efficiency of the filter system.

The filter arrangement 28, a portion of the filter element 57 extends past the inlet and outlet cells 40, 42. In one embodiment, the filter arrangement includes a filter support element 59 disposed along each side of each filter element 57. In a preferred embodiment, the filter element 57 is disposed between two adjacent support elements 59, which may be fastened together, e.g., with staples, along the inlet edge 207 to prevent damage to the filter element 57. Preferably, portions of the filter element 57 and the filter support element 59 disposed adjacent the microporous filter element 57, extend past the inlet and outlet cells 40, 42 into the inlet chamber 204 to form an initiator section 201. The initiator section 201 extends a sufficient distance beyond the inlet and outlet cells 40, 42, typically, about 1/2 inch (1.27 cm) to 1 inch (2.54 cm), to permit the initiator section 201 to be heated by entering exhaust gas without a substantial dissipation of heat, thereby, to facilitate combustion of the solid contaminants. The inlet cells 40, the outlet cells 42, the microporous filter elements 57, and the filter support elements 59 comprise materials that are resistant to high temperatures such that the filtering arrangement may be regenerated by heat.

During operation, exhaust gas flows from the inlet port into inlet chamber 204, past initiator sections 201, into the inlet cells 40, through the filter elements 57 and filter support elements 59 and out through the outlet cells 42. Solid contaminants, such as soot particles, are collected on the initiator sections 201 as well as on the portions of the filter elements 57 between the inlet and outlet cells 40, 42. The initiator sections 201, which extend into the inlet chamber 204 contact hot incoming gases before heat can be dissipated through the inlet and outlet cells 40, 42. This allows the initiator sections 201 to be heated more rapidly and to a higher temperature than the remaining portions of the filter elements and support elements during the regeneration phase of a filter cycle. The initiator sections facilitate the ignition of soot particles during the initial stage of the regeneration phase and as a result, the efficiency of combustion of trapped soot particles is enhanced.

An alternate embodiment of the invention is shown in FIG. 5. In this embodiment, the housing 22A comprises a generally cylindrical shaped plenum 30A to which the inlet endplate 32A is secured by nuts and bolts 36A along an outwardly extending flange 80. The self-contained filter arrangement 28A is likewise of a generally cylindrical shape. In order to retain the filter arrangement 28A in an appropriate position within the housing 22A, post spacers 84 are provided along the inlet side of the housing 22A. It will be appreciated that the incoming exhaust flows into the housing 22A through the inlet pipe 24A, past the post spacers 84, and through the filter arrangement 28A, and out of the outlet pipe 26A.

The cylindrical filter arrangement 28A is preferably of pleated design, sandwiching a filter medium 57A between alloy mesh supports 59A. Preferably, filter medium 57A may include Tissuquartz.TM., sandwiched between stainless steel 40-60 mesh 59A, of the types available from Pall Corporation. Other preferred filter media comprise quartz fibers, borosilicate-E fibers, aluminosilicate fibers or chromium-containing aluminosilicate fibers.

Another embodiment of the invention, which is shown in FIGS. 6 and 7, provides a combination of a flat filter 90, as in the first embodiment, and a cylindrical filter 92, as with the second embodiment in a single exhaust filter system. The flat filter 90 may be supported on a flat frame 94 within the housing, while the cylindrical filter 90 may be held in position by the post spacers 84B. It will thus be appreciated, that air enters the housing 22B through the inlet pipe 24B, passes through the flat filter 90 and the cylindrical filter 92, and passes out of the housing 22B through the outlet pipe 26B to the atmosphere. As with the embodiments above, the housing 22B may include endplates that may be secured to the plenum by any appropriate method.

Another embodiment of the invention is shown in FIGS. 8-11. As shown in FIG. 8, the filter system 20C includes a housing 22C having an inlet pipe 24C and an outlet pipe (not shown). As shown more clearly in FIG. 9, the housing 22C comprises a plenum 100 having a rectangular box shape with an open top. The housing 22C further comprises a topplate 102 having a flat surface 104 and upwardly and outwardly extending sides 106. The lower surface 108 of the plenum 100 and the topplate 102 are provided with corresponding holes 110, 112 through which tie rods or carriage bolts 114 may be inserted. Nuts 116 may then be tightened onto the bolts 114 to tighten the topplate 102 onto the plenum 100 and secure the components together. Those skilled in the art will appreciate that as the topplate 102 is pressed downward within the open top of the plenum 100, the upwardly and outwardly extending sides 106 of the topplate 102 will form a seal between the plenum 100 and the topplate 102.

Disposed within the plenum 100 is a self-contained filter arrangement 28C, which is shown in more detail in FIG. 10. The filter arrangement 28C comprises an arrangement of inlet and outlet cells 40C, 42C, filter elements 44C, and support screens 59C, similar to those shown in FIGS. 2-4. To compress the components of the filter arrangement, the components are provided with a plurality of openings 118, similar to the holes 68 and holes 70 in the embodiment shown in FIGS. 2-4.

As shown in FIG. 9, the assembly bolts 114 may be inserted through the openings 110 in the lower surface 108 of the plenum 100, the openings 118 of the filter arrangement 28C, and the openings 112 in the topplate 102 and the nuts 116 tightened down to assemble the filter system 20C. In this embodiment, the system 20C may be assembled without the use of gaskets, as the filter arrangement 28C seats directly against the lower surface of the plenum 100 and the topplate 102, and tightening the assembly bolts 114 and nuts 116 compress the assembly, including the filter elements 44C, cells 40C, 42C, and support screens 59C. This type of arrangement provides easier maintenance and extends the life of the system 20C.

Alternate methods of sealing the arrangement may be utilized that do not necessarily provide for easy field maintenance. For example, a method of sealing porous metal support screens and sintered filters is by swaging the edges with a forming press and dies. Alternately, metal edges may be sealed by welding.

Returning now to the filter arrangement 28C shown in FIGS. 9-10, it may be seen that the inlet apertures 50C and outlet apertures (not shown) are round. The inlet and outlet cells 40C, 42C may be more easily understood with reference to FIG. 11, which shows an inlet cell 40C. It will be appreciated, however, that the outlet cell 42C may be of a similar construction. During operation, gas enters the cell 40C through the apertures 50C and flows parallel to the support members 40eC-40fC, passes through the support screens 59C and the filter element 44C, and enters the outlet cell 42C to be passed out of the filter arrangement 28C.

An alternate inlet/outlet cell 40D arrangement is shown in FIGS. 12-14. In this arrangement, gas enters the cell 40D through apertures 50D. As illustrated in FIG. 13, the apertures are round; the apertures, however, may be of an alternate configuration. It will be appreciated that in this configuration, rather than flowing parallel, the gas flows through the cell 40D substantially perpendicularly to the support members 40eD-40fD.

Therefore, in order to provide a smooth flow of gas through the cell 40D, the support members 40eD-40fD are of a configuration that permits the gas to flow perpendicularly past the support member. Although alternate designs may be appropriate, the "alternating step" design shown in FIG. 14 is particularly suitable for permitting gas flow past the support member 40eD-40fD by way of openings 120.

Thus, during operation, gas flows into the cell 40D through the apertures 50D. The gas may then flow directly through the adjacent support screens and filter element (not shown), or, may pass one or more support members 40eD-40fD by way of openings 120 and then flow through the adjacent support screens and filter element. It will be appreciated that if the gas flows past only one support member 40eD of the inlet cell 40D or flows directly through the adjacent support screens and filter element, the gas must pass similarly one or more similar support members of the outlet cell before flowing out of the apertures of the outlet cell (not shown).

Another embodiment of the invention is shown in FIG. 15. In this embodiment, the housing 22E comprises a substantially rectangularly shaped plenum 30E that is formed in two mating sections 124, 126 with outwardly extending flanges 128, 130. In order to secure the sections 124, 126 together, nuts 134 and bolts 132 are tightened together through openings in the flanges 128, 130. The housing 22E further comprises endplates 32E (the outlet endplate is substantially identical to the inlet endplate), which include a flat plate 136 from which extends an inlet pipe 24E or outlet pipe (not shown) for coupling to the exhaust system. The flat plate 136 is coupled to the plenum 30E by any appropriate method to provide a seal of the mating surfaces of the sections 124, 126. In the embodiment shown, the flat plate 136 is bolted to the plenum 30E. The filter arrangement 28E may be of any of the designs discussed above.

A test, which was conducted to determine the ability of a specific embodiment of the present invention to efficiently remove solid contaminants from diesel exhaust, is described in the example set forth below. This example is offered by way of illustration and not by way of limitation.

A test was carried out to determine the ability of a filter assembly of the present invention to remove solid contaminants from the exhaust gases of a diesel engine. The filter assembly was fitted on the exhaust discharge of a Lombardini 6LD 435/B1 monocylindrical, direct injection, 4 phase, air cooled type diesel engine. The engine, which is representative of the "Light Duty" class of diesel engines, was run at two air/fuel ranges on a stationary bench. The filter assembly was configured substantially as shown in FIG. 1-4 and included microfibrous filter elements disposed between two woven wire mesh support elements. The filter elements were formed from borosilicate-E glass fibers having an mean fiber diameter of 0.65 micron and a surface area of 2.3 m.sup.2 /g. The support elements were made of a 90.times.100 woven wire mesh of 304 stainless steel. The filter arrangement contains 35 filter elements, each of which have an exposed area of about 1.4 square feet (1300 square cm), since both sides of each filter element are exposed.

During the test, engine discharge temperatures, hydrocarbon and NO.sub.x gas emissions, solid contaminant output and the pressure difference between the inlet and outlet of the filter assembly were measured. The engine was run for a period of about 150 minutes, during which the filter assembly demonstrated close to 100% solid contaminant removal. This highly efficient removal of solid contaminants was achieved while maintaining a pressure drop of less than 150 mm (H.sub.2 O) across the filter assembly. During the test, the filter had no influence on hydrocarbon or NO.sub.x emissions and did not affect the performance of the engine, both in terms of specific consumption and torque.

In accordance with another aspect of the invention, a heater may be incorporated in an exhaust gas filter system to facilitate regeneration of the filter assembly. The heater preferably heats to a sufficient temperature to facilitate combustion of the particulates in the filter system, for example, a temperature which ignites particulates in the filter elements, typically a temperature of up to about 600.degree. C. or more. The heater may heat the particulates via any suitable mechanism. The heater may radiantly heat the particulates directly; the heater may heat the filter arrangement which in turn conductively heats the particulates; and/or the heater may heat the gas in the housing or filter arrangement which in turn convectively heats the particulates.

The heater may be variously configured. For example, the heater may comprise a burner mounted to the housing or the filter arrangement, a fuel line extending between a fuel source and the burner, and a control arrangement including various valves and pilots for delivering a combustible fuel to the burner and igniting it. Fuel may be delivered to the burner recurrently or continuously. The burner may include a plurality of fuel outlets, disposed, for example, on a manifold or in different portions of the housing or the filter arrangements. Fuel may be delivered to the fuel outlets and ignited substantially simultaneously or sequentially under the control of the control arrangement.

In preferred embodiments, the heater comprises an electrical resistance element and an electrical connection arrangement extending between the electrical resistance element and a source of electrical energy. The electrical resistance element may be any element which, upon being supplied with electrical energy, heats to a sufficient temperature to facilitate combustion of the particulates. The electrical resistance element may be an electrically conductive component of the filter system itself, such as the baffle or the filter support. However, high temperature electrical resistance wiring is preferred. The electrically resistive heating wires may be alloys selected for corrosion resistance and power dissipation characteristics that allow the wires quickly to heat up and cool down. Suitable exemplary materials for the electrically resistive heating wires include nichrome and/or calorite. One electrically resistive heating wire suitably disposed within the filter system may suffice for effective regeneration. Alternatively, the electrically resistive heating wire may be a plurality of resistive wire segments connected in series or in parallel and disposed in different portions the filter system.

The electrical energy source may be an electrical outlet, a battery, or a generator or alternator or any other device which provides, stores, and/or generates electrical energy.

The electrical connection arrangement includes any wires, bushings, insulators, connectors, switches, or other structures used to transfer electrical energy continuously or recurrently from the electrical energy source to the electrical resistance element. For example, a supply wire may pass through insulated bushings disposed in the filter housing, the bushing providing electrical and/or thermal insulation.

The heater may also include a control arrangement which controls the supply of energy to the electrical resistance element, for example, by means of timers on a fixed time basis or by means of sensors, such as differential pressure sensors or temperature sensors, such as thermocouples, on a variable time basis. For example, a controller, such as a microprocessor programmed appropriately, may receive temperature information input from a temperature sensor, and/or pressure information input from a pressure sensor, and controls the energizing of the electrical resistance heating elements, based on the microprocessor programming and/or sensor information inputs. For example, the electrically resistive heating wires may all be electrically connected to the same electrical power source or they may each be electrically connected to separate electrical power sources, and may be energized substantially simultaneously or sequentially by means of the control arrangement. The electrically resistive heating wires may be energized sequentially via a switching arrangement under control of the control arrangement. If the energy of the power source is limited, for example, is available only from a vehicular battery, sequential energizing may be desirable to heat the filter arrangement or the gas in the housing to a temperature high enough to regenerate the filter.

The heater may be operatively associated with the exhaust gas filter system in a variety of ways. For example, the heater may be coupled to any of the previously described embodiments of the exhaust gas filter system. In the embodiment illustrated in FIG. 20, which is similar to many of the previous embodiments, the heater preferably comprises an electrical resistance heating wire 250 electrically coupled to an electrical energy source 251 via an electrical connection arrangement 252. The heater is mounted to the housing 20 and/or the filter arrangement 28 in any suitable manner. For example, the electrical resistance heating wire 250 may be mounted within the inlet pipe 24 and/or outlet pipe 26 and/or within the housing 20 in the inlet chamber 204, to the baffle 200, between the baffle 200 and the filter arrangement 28, and/or in the outlet chamber 205.

Alternatively or in addition the electrical resistance heating wire 250 may be mounted to the filter arrangement 28 at the initiator section 201 of the filter elements, to the inlet cells 40, to the filter supports 59, to the filter media 57, and/or to the outlet cells 42. Where the electrical resistance heating wire is mounted to the filter medium, it may be attached to the upstream face and/or the downstream face of the filter medium or it may be within the filter medium. Where the electrical resistance heating wire is mounted to the inlet or outlet cells, it may extend between frame members 40a-40d and support members 40e, 40f through the interior space or spaces 54 defined by the cell, as shown, for example, in FIG. 21. In addition, the electrical resistance heating wires 250 may be connected to the electrical energy source 251 in series, in parallel or through a switching arrangement S which may, for example, connect each heating wire sequentially, as shown in FIG. 20.

As shown in FIG. 22, one or more of the components of the filter system may serve as the electrical resistance element, if they are formed from a suitably electrically conductive material. For example, the electrical connection arrangement 252 may be connected to an inlet cell 40, a filter support 59, the filter medium 57, or an outlet cell 42 which is preferably electrically insulated from the remainder of the filter assembly. Electrical energy supplied from the source 251 then directly heats the component to a temperature sufficient to facilitate regeneration of the filter medium.

The heater may similarly be operatively associated with cylindrical embodiments of the filter arrangement. For example, as shown in FIG. 23, electrical resistance heating wires 250 may be mounted to the housing 22A and/or the filter arrangement 28A, e.g., in the inlet chamber 204A, to the spacer 84, between the spacer 84 and the filter arrangement 28A, to a filter support 59A, to the filter medium 57A, and/or to the outlet chamber 205A. Alternatively, or in addition, suitably conductive components of the filter system may themselves serve as the electrical resistance elements. For example, the electrical connection arrangement 252 may be connected directly to the spacer 84, a filter support 59A, and/or the filter medium 57A.

In a preferred mode of operation, exhaust gas is directed through the inlet pipe and the filter arrangement to the outlet pipe, while particulates are trapped in the filter medium. Recurrently, the heater is activated to burn particulates off the filter medium and thereby regenerate the filter medium. The heater may be activated, e.g., by the control arrangement, according to any suitable parameter. For example, the heater may be activated on a fixed time basis or a fixed fuel consumption basis. Alternatively, the differential pressure across the filter arrangement may be sensed and the heater may be activated once the differential pressure exceeds a predetermined value.

Upon activation of the heater, the flow of exhaust gas through the filter arrangement may be continued or terminated, for example, by diverting the exhaust gas to a second filter arrangement (not shown). The heater then heats the gas in the housing and/or the components of the filter system to a temperature sufficient to facilitate combustion of the particulates in the filter medium. For example, the heater may increase the temperature of the particulates sufficient to initiate combustion of the particulates. Once a combustion is initiated, the heater may be deactivated to conserve energy or it may remain activated to supplement the heat generated by the combustion of the particulates. In addition, atmospheric air may be introduced into the filter arrangement to enhance combustion of the particulates. For example, atmospheric air may be fed into the filter arrangement via the outlet pipe or a separate vent (not shown) by means of a blower (not shown). Alternatively, atmospheric air may be enticed to enter the filter arrangement via the outlet pipe by diverting exhaust gas past the inlet pipe through a Venturi tube (not shown), thereby creating a low pressure zone at the inlet pipe.

One the particulates have been burned off the filter media, the heater, if it remained activated, may be deactivated and the flow of exhaust gas, if it was terminated, may be redirected through the regenerated filter arrangement.

The present invention has been described above in terms of specific embodiments. It will be readily appreciated by one of ordinary skill in the art, however, that the invention is not limited to these embodiments, and that, in fact, the principles of the invention may be embodied and practiced in devices and methods other than those specifically described above. Therefore, the invention should not be regarded as being limited to these specific embodiments, but instead should be regarded as being fully commensurate in scope with the following claims.