Muffler with catalytic converter arrangement; and method

An apparatus for modifying an exhaust stream of a diesel engine is provided. The apparatus includes a muffler arrangement having an exhaust inlet and an exhaust outlet in construct and arrange for sound attenuation therein. The apparatus also includes a catalytic converter arrangement positioned within the muffler arrangement between the exhaust inlet and exhaust outlet. During operation, the exhaust flow is directed both through the muffler arrangement and the catalytic converter arrangement, to advantage.

FIELD OF THE INVENTION

The present invention relates to muffler assemblies and in particular to muffler assemblies of a type used to dampen exhaust noise produced by internal combustion engines. The invention specifically concerns such an arrangement having a catalytic converter therein.

BACKGROUND OF THE INVENTION

Catalytic converters have been widely utilized with internal combustion engines, typically gasoline powered engines. In operation an oxidizing catalytic converter comprises a post combuster through which emissions from the internal combustion process are directed. The catalyst promotes the conversion of carbon monoxides and hydrocarbons in the emissions to carbon dioxide and water vapor.

In a typical application, the catalytic converter is located in the exhaust system as close to the exhaust engine manifold as practical. In this manner, advantage is taken of available heat in the exhaust gases to minimize the time lag in reaching the desired operating (reaction) temperature. The typical catalyst is a noble metal such as platinum or palladium.

As indicated above, typically catalytic converters have been utilized with gasoline powered internal combustion engines, rather than diesel engines such as truck engines. There are numerous reasons for this. For example, trucks typically have very limited space for the placement of catalytic equipment in the exhaust system. The largest space available is occupied by the muffler, leaving little if any room for effective placement of a catalytic converter. It is not generally reasonable to reduce the size of the muffler to allow for placement of a converter assembly. This is because reduction in the size of the muffler will generally lead to less sound attenuation and higher backpressure.

In addition, in a diesel powered truck system the acceptable amount of resistance to flow in the exhaust stream is strictly limited. More specifically, an effective muffler system for a diesel engine truck typically provides a backpressure close to the maximum backpressure allowable for efficient engine use. The added backpressure which would be introduced by placement of a conventional catalytic converter arrangement in the exhaust stream (in addition to the conventional muffler) would typically be unacceptably close to (if not over) the maximum backpressure allowable and would reduce fuel efficiency.

Nevertheless, there are reasons why it may be desirable to introduce a catalytic converter into a diesel exhaust flow stream. In particular, the catalyst allows for the oxidation of hydrocarbons in the gaseous phase, thereby reducing the concentration of hydrocarbons in the exhaust stream. Due to the concentration reduction, a lower amount of hydrocarbons would be adsorbed onto the surface of carbonaceous particles or soot in the stream. Thus there will be a mass reduction in the tailpipe emissions, if a catalytic converter can be efficiently utilized.

SUMMARY OF THE INVENTION

According to the present invention an apparatus is provided for modifying an exhaust stream of an engine. Herein the term “modifying” in this context is meant to refer to the conduct of at least two basic operations with respect to the exhaust stream: sound attenuation (muffling); and, catalytic conversion (catalyzed combustion of hydrocarbons in the exhaust gas stream). In typical preferred applications the apparatus is utilized for the modification of an exhaust stream of a diesel engine. In most typical applications, the apparatus is utilized as a muffler arrangement for the diesel engine of a vehicle, such as an over-the-highway truck.

The preferred apparatus according to the present invention comprises a muffler arrangement, a catalytic converter arrangement and flow direction means. The muffler arrangement generally has an exhaust inlet, exhaust outlet and means for sound attenuation. That is, exhaust gas is passed through the muffler arrangement from the inlet end through to the outlet end, with sound attenuation occurring within the muffler.

The catalytic converter arrangement is preferably positioned within the muffler arrangement between the exhaust inlet and the exhaust outlet. In general it is operatively positioned such that as exhaust gas is passed through the muffler arrangement, then passed through the catalytic converter. The catalytic converter is constructed and arranged such that in use it will effect a catalyzed conversion in the exhaust gas flow stream, i.e., oxidation of hydrocarbon components in the exhaust gas flow.

The means for flow direction generally comprises means directing the exhaust gases through the catalytic converter arrangement whenever the gases operably flow through the muffler arrangement from the exhaust inlet to the exhaust outlet. In a typical system this means comprises appropriate construction and configuration for the apparatus so that gas flow cannot bypass the catalytic converter arrangement while passing through the muffler.

A variety of arrangements may be utilized as the means for sound attenuation. Among them are included arrangements utilizing one or more resonating chambers for sound attenuation, within the muffler. Resonating chambers may be positioned both upstream and downstream of the catalytic converter arrangement. In typical constructions, substantial use would be made of downstream resonating chambers (or other downstream acoustic elements) to achieve substantial sound attenuation.

In one preferred apparatus, the means for sound attenuation includes a “sonic choke” arrangement operably positioned within the muffler arrangement, as part of the downstream acoustics. A detailed description of a sonic choke arrangement is provided hereinbelow. In general, a sonic choke arrangement comprises a tube having a converging portion to a neck, with an expanded flange on an end thereof. The expanded flange is positioned on the most upstream end of the sonic choke, with the shape of the choke or tube converging rapidly from the flange to a narrowest portion in the neck, and then with a relatively slow divergence in progression from the neck toward the exhaust outlet.

In selected arrangements according to the present invention the catalytic converter arrangement is operatively positioned between an exhaust inlet and the downstream acoustics. The catalytic converter may comprise a metal foil core having an effective amount of catalyst dispersed thereon. In this context the term “effective amount” is meant to refer to sufficient catalyst to conduct whatever amount of conversion is intended under the operation of the assembly. The term “dispersed thereon” is meant to refer to the catalyst operably positioned on the catalytic converter core, regardless of the manner held in place.

When the catalytic converter arrangement comprises a metal foil core, generally the core comprises corrugated foil coiled in arrangement to form a porous tube having an outer surface. In preferred arrangements, the outer surface is generally cylindrical and an outer protective sheet such as a metal sheet may be positioned around the core outer cylindrical surface. Preferred metal foil cores have a cell density, i.e., population density of passageways therethrough, of at least about 200 cells/in2and more preferably about 400 cells/in2. Such an arrangement can be formed from corrugated stainless sheeting of about 0.0015 inches (0.001-0.003 inch) thick.

A variety of catalysts may be utilized in assemblies according to the present invention including platinum, palladium, rhodium and vanadium.

In certain alternate embodiments the catalytic converter core may comprise a porous ceramic core. A typical such core will be formed from extruded cordierite (a magnesia alumina silicate) and have an effective amount of catalyst dispersed thereon. Preferably the cell density of passageways through such a ceramic core is at least about 200 cells/in2and preferably at least about 400 cells/in2.

In preferred arrangements wherein the catalytic converter core comprises ceramic, the ceramic core is provided in a generally cylindrical configuration, with an outer cylindrical surface. The ceramic core is preferably protected by the catalytic converter arrangement being provided with a flexible, insulating mantle wrapped around the core outer surface. The insulating mantle will preferably be secured in place by the positioning of an outer metal wrap therearound. In preferred arrangements the outer metal wrap is provided with side flanges, operably folded over upstream and downstream faces of the catalytic converter core. Preferably a soft, flexible insulating rope gasket is positioned adjacent any such folds or flanges, to inhibit crumbling of the ceramic core during the manufacture and installation process and to provide a seal for the less durable insulating mantle materials.

Preferred arrangements according to the present invention include a flow distribution arrangement constructed and arranged to direct the exhaust flow substantially evenly against the catalytic converter. In particular, the catalytic converter core member may be described as having a most upstream face. Preferably the flow distribution element is constructed and arranged to direct flow relatively evenly across the upstream face of the catalytic converter core member. In one preferred embodiment, which is described and shown the flow distribution element comprises a porous tube having an end with a “star crimp”, i.e. a type of folded end closure, therein. In another, a domed, perforated baffle member positioned between the exhaust inlet and the porous core member upstream face serves as a flow distribution element. In still another, curved surfaces are used to generate a radial diffuser inlet.

It has been determined that there is a preferred positioning of the porous core member between the flow distribution element and the downstream acoustics. More specifically, preferably the porous core member is positioned within about 1 inch to 6 inches from the flow distribution element; and, preferably the core member is also positioned within about 1 inch to 6 inches from the re-entrant tube inlet for the downstream acoustics. Also, a preferred open area fraction for the flow distribution element can be defined. Detailed descriptions with respect to this is provided herein below.

In addition, according to the present invention an apparatus for providing a relatively even fluid (typically gas) flow velocity across a conduit (typically having a substantially circular cross section) is provided. In general the apparatus is adapted for generating even flow in a situation in which gases pass into an arrangement through an inlet tube having a first diameter (cross-sectional size) to a chamber having a second diameter (cross-sectional size) greater than the first diameter. Typically, a domed perforated diffusion baffle having a second diameter greater than the first (inlet) diameter, is located downstream from the inlet tube. What is needed, is an arrangement to provide for direction of gases against the domed perforated diffusion baffle in such a manner that as the fluid or gases pass therethrough, an even flow distribution (i.e. velocity of gases or volume of gases directed against any point in cross section) is provided. This is accomplished by positioning a bell shaped radial diffuser element upstream from the domed perforated diffusion baffle and downstream from the inlet tube. The bell shaped radial diffuser element generally comprises an expanding bell having a shape similar to the bell of a musical instrument. Preferred sizes and curvatures are described herein. In general the bell allows for expansion of the gases as they approach the dome perforated diffusion baffle for even flow distribution. Such arrangements may be utilized in a variety of muffler constructions including ones having catalytic converters therein.

The invention also includes within its scope a method of modifying the exhaust stream of a diesel engine for both sound attenuation and catalytic conversion. The method includes a step of conducting catalytic conversion within a muffler assembly. Preferred manners of conducting these steps are provided herein below.

DETAILED DESCRIPTION OF THE INVENTION

As required, a detailed description of preferred and alternate embodiments is presented herein. The description provided is not intended to be limiting, but rather to serve as a presentation by example of embodiments in which the subject matter claimed may be applied.

The General Configuration of the Overall Assembly

The reference numeral1,FIG. 1, generally designates a muffler assembly according to the present invention. The muffler assembly1has defined therein three general regions: an exhaust introduction, distribution and upstream acoustics region5; a catalytic converter region6; and a downstream acoustical or attenuation region7. Each of regions5,6and7may be constructed separately, with the overall assembly prepared through utilization of appropriate clamps, segments, etc. However, in preferred applications as shown inFIG. 1, it is foreseen that the segments5,6and7will be constructed in an overall unit10having an outer shell11with no segment seams or cross seams therein. By “cross seam” in this context it is meant that the shell11is not segmented into longitudinally aligned segments, rather it comprises one longitudinal unit, typically (but not necessarily) having at least one and possibly more than one longitudinal seam.

Herein a unit10which is constructed with no cross seams, i.e., as a single longitudinal unit, will be referred to as an “integrated” unit. To a certain extent, it may be viewed as a muffler assembly having a catalytic converter positioned operably therein. A unit constructed in segments aligned coaxially and joined to one another along cross seams will be referred to as a “segmented” arrangement. It will be understood that to a great extent the principles of the present invention may be applied in either “integrated” or “segmented” units or arrangements. It is an advantage of the preferred embodiment of the present invention, however, that it is well adapted for arrangement as an “integrated” unit.

As will be understood from the following descriptions, the muffler assembly1according to the present invention is constructed to operate effectively and efficiently both as an exhaust noise muffler and as a catalytic converter. With respect to operation as an exhaust noise muffler, many of the principles of operation are found in, and can be derived from, certain known muffler constructions. With respect to these principles, attention is directed to U.S. Pat. Nos. 3,672,464; 4,368,799; 4,580,657; 4,632,216; and 4,969,537, the disclosure of each being incorporated herein by reference.

Still referring toFIG. 1, muffler assembly1comprises a cylindrical casing or shell11of a selected predetermined length. Annular end caps13and14respectively define an inlet aperture17and an outlet aperture18. The shell11is generally cylindrical and defines a central longitudinal axis20. An inlet tube22is positioned within inlet aperture17. The inlet tube22has a generally cylindrical configuration and is aligned with its central longitudinal axis generally coextensive or coaxial with axis20. It is noted that end portion24of inlet tube22is configured in a manner non-cylindrical and described in detail hereinbelow, for advantage.

Outlet tube26is positioned within outlet aperture18. Outlet tube26includes a generally cylindrical portion27aligned with a central longitudinal axis thereof extending generally coextensive with or coaxially with longitudinal axis20.

In use, the exhaust gases are directed: (1) into assembly1by passage through inlet tube22as indicated by arrows30; (2) into the internal region or volume31defined by casing or shell11; and, (3) outwardly from assembly1by passage outwardly through outlet tube26as indicated by arrows33. Within assembly1both sound attenuation (muffling) and emission improvement (catalytic conversion) occurs.

Referring to region5, and in particular inlet tube22positioned therein, the inlet tube22is positioned and secured in place by end cap13and internal baffle35. Preferably baffle35is constructed so as not to be permeable to the passage of the exhaust gases therethrough or thereacross. Thus, baffle35in cooperation with end cap13and shell11define a closed volume37.

For the embodiment shown inFIG. 1, inlet tube22is perforated along its length of extension within assembly1, i.e., that portion of the tube22positioned internally of end cap13(that is positioned between end cap13and end cap14) is perforated, as indicated by perforations38. Certain of the perforations allow gas expansion (and sound travel) into volume37, which assists in attenuation of sound to some degree. Regions such as volume37may be generally referred to as “resonating chambers” or “acoustics”, and similar structure positioned upstream of region6and also constructed and arranged for sound attenuation, will be referred to herein as “upstream acoustics.”

The portion42of inlet tube22which projects inwardly of baffle35; i.e., which extends over a portion of the volume between baffle35and outlet end cap18operates as a flow distribution construction or element44. The flow distribution element44generates distribution of exhaust gas flow within volume45, i.e., the enclosed volume of shell11positioned immediately inwardly of baffle35, for advantage. Portion42of inlet tube22includes previously defined end portion24.

Positioned immediately downstream of inlet tube22is catalytic converter50. Catalytic converter50includes a substrate51having catalyst appropriately positioned thereon. The substrate51is gas permeable, i.e., the exhaust gases pass therethrough along the direction of arrow53. The catalytic converter50includes sufficient catalyst therein to effect the desired conversion in the exhaust gases as they pass therethrough. Herein this will be referred to as “an effective amount” of catalyst. The substrate51is sized appropriately for this. Greater detail concerning the preferred catalytic converter50is provided hereinbelow.

Preferably the flow distribution element44is sized and configured appropriately to substantially evenly distribute exhaust flow against the entire front or upstream surface55of the catalytic converter50. In this manner, lifetime of use in the catalytic converter50is enhanced. Also, the more effective and even the distribution, the less likelihood of overload in any given portion of the catalytic converter50. This will facilitate utilization of a catalytic converter minimal or relatively minimal thickness, which is advantageous. By the term “substantially evenly” in this context it is meant that flow is distributed sufficiently to avoid substantial “dead” or “unused” volume in converter50. Generally, as even a distribution as can be readily obtained, within acceptable backpressure limits is preferred.

In general, the catalytic converter50provides for little or no sound attenuation within the muffler. Thus, the space utilized by the catalytic converter is space or volume of little or no beneficial effect with respect to muffler operation. Under such conditions, minimal thickness or flow path catalytic converter will be preferred, so as not to substantially inhibit muffler (attenuation) operation.

It has been determined that there is a preferred positioning of the catalytic converter50relative to the flow distribution element44, for advantageous operation. In particular, most preferred operation occurs when the catalytic converter50is not positioned too close to the flow distribution element44, but is also not positioned too far therefrom. Discussion of studies with respect to optimizing the position of the catalytic converter50relative to the flow distribution element44are provided hereinbelow, in detail.

For the arrangement shown inFIG. 1, flow distribution element44comprises end24of tube22crimped or folded into a “star” or “four finned” configuration. Such an arrangement has been used in certain types of muffler assemblies before, see for example Wagner et al. '537 referred to above and incorporated herein by reference. In general, the crimping creates closed edges56and facilitates flow distribution. Unlike for conventional muffler arrangements, for the embodiment ofFIG. 1this advantageous distribution is applied in order to achieve relatively even cross-sectional distribution of airflow into and through a catalytic converter50, to advantage. As will be understood from alternate embodiments described hereinbelow, alternative flow distribution arrangements may be utilized in some applications.

The portion60of the muffler assembly1in extension between the downstream surface61of the catalytic converter50and the outlet end cap14is referred to herein as the downstream acoustical or attenuation segment or end7of the assembly1. It is not the case that all sound attenuation which occurs within the assembly1occurs within this region. However, the majority of the sound attenuation will occur in this portion of the assembly1.

In general, the downstream acoustical segment7comprises structure placed to facilitate sound attenuation or sound control. In typical constructions, resonating chambers or the like will be included therein. One such construction is illustrated in FIG.1. The particular version illustrated inFIG. 1utilizes a sonic choke arrangement65therein in association with resonating chambers, to achieve sound attenuation. It will be understood that a variety of alternate arrangements may be utilized.

Referring more specifically toFIG. 1, acoustical or attenuation segment7includes therein a converging or sonic choke arrangement65supported by sealed baffle66. In general, the volume68upstream from sealed baffle66will be constructed or tuned for advantageous low frequency sound attenuation. Such tuning will in general concern the precise location of the sealed baffle66, i.e., adjustment in the size of volume68. Constructions in which a sonic choke assembly similar to that illustrated as65are positioned within a muffler assembly1by a sealed baffle66advantageously, are described in U.S. Pat. Nos. 3,672,464 and 4,969,537 incorporated herein by reference.

In general, sonic choke assembly65comprises a tube member75mounted coaxially with outlet tube26and, together with outlet tube26, supported by baffles66and77, and outlet end cap18. In certain constructions such as that shown inFIG. 1, tube member75may comprise an extension of an overall tube having no cross seam which includes both the tube member75and the outlet tube26as portions thereof. Alternately stated, for the embodiment shown inFIG. 1, the outlet tube26comprises an end portion of tube member75. In the alternative, the outlet tube26may comprise a separate extension of material from tube member75; the outlet tube and tube member being joined along a cross seam such that they are oriented substantially coaxial with one another.

For the embodiment shown, the tube member75defines a central longitudinal axis positioned generally coextensive and coaxial with axis20. In some constructions, a tube member75with a longitudinal axis off-set from alignment with the inlet axis may be used.

Still referring toFIG. 1, tube member75in combination with outlet tube26defines exit flow for exhaust gases passing along the direction of arrow53through catalytic converter50. More specifically, such gases pass through an interior80of the tube member75and outwardly through outlet tube26, as indicated at arrows33.

Between baffles66and77, and externally of tube member75, a volume85is defined within shell11. An extension88of the combination of tube member75and outlet tube26extending through volume85is perforated as shown by perforations84, to allow for expansion of gases into volume85. Volume85will operate as a resonator or resonating chamber for attenuation of sound, in particular continued attenuation of low frequency and much of the medium frequency attenuation. The size of the volume85may be selected so that it is tuned for preferred sound attenuation including some high frequency attenuation as well.

Similarly, between baffle77and end cap14chamber90is defined, externally of tube member75and outlet tube26, and internally of shell11. The portion91of outlet tube26extending between baffle77and end cap14is perforated, to allow expansion of gases (and leakage of soundwaves) into volume90. The size and configuration of volume90may be tuned for selected medium and high frequency sound attenuation.

Still referring toFIG. 1, tube member75includes a conical end92which converges from point93to neck94, i.e., it converges in extension toward the catalytic converter. On the opposite side of neck94from point91, the tube member75diverges at flange95to lip96; lip96defining a re-entry port for gasses passing through assembly1. Such a construction is advantageous for preferred muffler operation and sound attenuation. As indicated above, such a construction is referred to herein as a sonic choke. Sonic chokes are described generally in Rowley et al. U.S. Pat. No. 3,672,494, incorporated herein by reference.

In general, a portion of the soundwaves existing in the gaseous medium of volume31are inhibited from passing through the tube member75by increased acoustical impedance encountered at the narrow neck94. Such waves are reflected back, which serves to attenuate the sound level.

The Construction of the Catalytic Converter

As indicated generally above, a variety of constructions may be utilized for the catalytic converter50. One such construction is illustrated inFIGS. 1 and 3. An alternate construction is presented byFIGS. 6 and 7.

For the embodiment ofFIGS. 1 and 3, the catalytic converter50comprises a ceramic structure having a honeycomb-like configuration defining a plurality of longitudinal flow channels extending therethrough. Referring toFIG. 3, the ceramic construction is indicated generally at100. For mounting within the assembly1, the ceramic core100is provided in a circular configuration, i.e., core100defines a cylindrically shaped item. Although alternate configurations are possible, the cylindrical one described and shown is advantageous for positioning within a cylindrical shell11.

A ceramic cylinder having a large plurality of longitudinal channels extending therethrough is a somewhat brittle configuration. It is therefore preferably mounted such that it will be dampened from the shocks and vibrations generally associated with a muffler assembly in a diesel powered vehicle. For the arrangement ofFIGS. 1 and 3, the ceramic core100is provided with a dampening mantle or wrap101in extension around an outer periphery102thereof. The mantle101should be provided from a flexible, heat resistant material, such as a vermiculite pad. The material Interam® Mat III available from 3M, St. Paul, Minn. 55144 is usable. In general, for the arrangement shown the mantle101would be about 0.12 in. (0.3 cm) to 0.25 in. (0.64 cm) thick.

For the preferred embodiment the mantle101is retained against the core100by retaining means such as a cylindrical casing105of sheet metal. Preferably the casing105is provided not only in extension around the outside of the mantle101, but also with a pair of side flanges bent toward the front face55and rear face61, respectively, of the core100to contain the mantle101. That is, casing105has first and second side lips or rims106and107folded toward opposite sides of the core100. Preferably a circular loop of rope or O-shaped gasket109is provided underneath each of the rims106and107, to facilitate secure containment of the core100and mantle101within the casing105, without damage.

Referring toFIGS. 1 and 3, it will be understood that the preferred catalytic converter50illustrated is a self-contained or “canned” unit, positioned within shell11. The converter comprises a ceramic core100positioned within a casing105, and protected therein by the mantle101and rope rings109. The converter50can thus be readily welded or otherwise secured and placed within shell11, with good protection of the core100from extreme vibrations within the assembly1. In addition, the mantle101and rings109will help protect the converter50from premature deterioration due to flow erosion.

In a typical system, it is foreseen that the ceramic core100will comprise an alumina magnesia silica (crystalline) ceramic, such as cordierite, extruded from a clay, dried and fired to a crystalline construction. Techniques for accomplishing this are known in the ceramic arts. In many, crystalline ceramics are prepared as catalytic converter cores by application of a wash coat thereto and then by dipping the core into a solution of catalyst. In some, the wash coat and catalyst are applied simultaneously. Typical catalysts utilized would be noble or precious metal catalysts, including for example platinum, palladium and rhodium. Other materials such as vanadium have also been used in catalytic converters.

In general, for use within a diesel engine muffler assembly, it is foreseen that the core100should be extruded with a cell density of longitudinal passageways of 200 cells/in2to 600 cells/in2and preferably at least about 400 per square inch of front surface area.

As indicated above, alternate constructions for the catalytic converter may be utilized. One such alternate construction would be to construct the core from a metallic foil substrate, rather than a ceramic. This will be understood by reference toFIGS. 6 and 7.

InFIG. 6, a side or edge view of a corrugated metal substrate120usable to provide a catalytic converter is shown. In general the substrate120should comprise a relatively thin metal such as a 0.001-0.003 inch (0.003-0.005 cm) thick sheet of stainless steel that has been corrugated to make wells of a size such that when coiled around itself, as indicated inFIG. 7, about 200 cells/in2to 600 cells/in2and preferably at least about 400 cells per square inch will result. Thus, referring toFIG. 7, the catalytic converter125depicted comprises a sheet of material, such as that illustrated inFIG. 6, which has been coiled upon itself and braised to retain the cylindrical configuration. Since the construction is not brittle, but rather is formed from sheet metal, a mounting mantle is not needed around the outside of the construction, for protection from vibration. The coil or construction may be surrounded with an outer casing126if desired, and then mounted within a muffler assembly such as that shown inFIG. 1, similarly to catalytic converter50. It is foreseen that in general the catalyst can be applied to the metal substrate120in a manner similar to that for the substrate, i.e., by use of a wash coat followed by dipping in a catalyst.

Alternate Constructions for the Flow Distribution Element

As indicated generally above, it is foreseen that alternate constructions and configurations for the flow distribution element may be utilized in assemblies according to the present invention. First, second and third such alternate configurations are illustrated inFIGS. 4,5and8.

Referring toFIG. 4, a muffler assembly150according to the present invention is depicted. The assembly150is in many ways analogous to that illustrated at reference numeral1, in FIG.1. InFIG. 4the assembly150is depicted fragmentary; the portion of the assembly not concerning the flow distribution element and catalytic converter, but rather concerning the downstream acoustics being fragmented (not shown). It will be understood that the portion of the assembly150not depicted inFIG. 4may be substantially the same as that illustrated for assembly1inFIG. 1or it may be according to variations such as those mentioned above.

Referring toFIG. 4, the assembly150comprises an outer shell155which contains therein a catalytic converter156positioned between a flow distribution element160and a downstream acoustics161. The flow distribution arrangement160is mounted within shell155by end cap163and comprises in part inlet tube164.

In the arrangement shown inFIG. 1, flow distribution arrangement160comprises cylindrical tube170perforated in a portion thereof positioned within shell155. Flow distribution element160is not crimped as is the arrangement of FIG.1. Rather, the cylindrical end171is closed by perforated cover173. Cover173is of a bowed, domed or radiused configuration, with a convex side thereof projected toward end cap163and a concave side thereof projected toward catalytic converter156. This configuration is advantageous, since it inhibits “oil canning” or fluctuation under heavy flow and vibration conditions.

It will be understood that flow distribution arrangement160operates by allowing gas expansion through apertures174into volume175. The distribution of apertures174(and the distribution of apertures in domed cover173) may be used to define a preferred, even distribution of gas flow in region175and thus toward surface176of catalytic converter156.

As indicated above, still another alternate construction is illustrated in FIG.5. Similar toFIG. 4, the depiction ofFIG. 5is of that portion of the assembly concerning the flow distribution arrangement and catalytic converter.

For the construction ofFIG. 5, inlet tube193comprises a cylindrical tube extending through end cap190to interior volume195. Flow distribution arrangement186comprises a domed baffle197extending completely across shell181and oriented with a convex side thereof projected toward tube193. The baffle197is perforated and acts to distribute flow evenly, in direction toward surface198of catalytic converter185. The population density and arrangement of perforations in the domed baffle197can be selected to ensure even flow distribution.

Radial Diffuser Inlets

InFIGS. 8,9and10unique radial diffuser inlets or constructions are illustrated. A radial diffuser allow for controlled expansion of gases passing from an inlet of a first diameter to a volume of a second, larger, diameter. In general, radial diffuser inlets are presented herein as new designs for the inlet section of a muffler, whether the muffler is an acoustic exhaust muffler or catalytic converter muffler. That is, while they may be utilized mufflers containing catalytic converters therein, they may also be utilized in other types of mufflers. When used as part of an arrangement having catalytic converter therein, generally the radial diffuser inlet would be located immediately upstream of the catalyst substrate.

In general a radial diffuser inlet directs and guides the inlet fluid (typically exhaust gas) into the muffler. The result of this is a relatively uniform fluid (gas) velocity distribution across the diameter of the muffler shell (i.e. the face of the converter for an arrangement having catalytic converter therein) in the region downstream of the inlet baffle. A uniform velocity distribution is highly desirable at the inlet, especially of a catalytic substrate or core. In general, it is foreseen that a catalyst core would preferably be located within about 2 to 4, most preferably about 2 to 3, inches of the inlet baffle.

The radial diffuser construction may be utilized at the inlet end of an arrangement similar to that previously described with respect toFIG. 1, or variations mentioned herein. The radial diffuser inlet200ofFIG. 8comprises inlet member201, flow distribution element202, and end cap203. Assembly200is shown mounted within shell205.

End cap203defines an aperture210through which air inlet member201projects. Air inlet member201includes an inlet portion211and a flow distribution portion212.

Flow distribution element202is generally curved in cross-section (preferably radial) with a concave side thereof directed toward downstream acoustics. The member is sufficiently perforated (preferably evenly) to allow desired gas flow therethrough. The extent of curvature should generally be sufficient to avoid “oil canning” and achieve desired distribution of flow.

The unique construction of radial diffuser inlet200is greatly attributable to diffusion flange212(or bell-shaped flange) which extends outwardly from inlet tube211, as a bell, around curve225to obtain a bell portion spaced from and generally juxtaposed with the concave side of member202. The bell portion of member212is generally indicated at230.

Radial diffuser inlet construction200generally allows for a good even flow of air against porous distribution element202, with effective flow distribution over the cross-section of shell205, for efficiency. It will be understood that highest efficiency can be obtained from modification of various dimensions and parameters. From the following recited example, general principles of construction will be understood.

Assuming a shell having an inside diameter of 11 inches (27.4 cm) and a radial diffuser intended to operate across the full diameter of the shell, the inside diameter of the inlet portion211would be about 4 inches (11 cm). Curve225to form bell230would be constructed on a radius of 1.5 inches (3.81 cm). The overall length of the straight portion of inlet tube211would be about 3.75 inches (9.4 cm). The distance between bell230and diffusion element202, if measured as illustrated at “A” would be about 0.38 inches (0.96 cm).

InFIG. 9an alternate design of a radial diffuser inlet is indicated. In general, the inlet is indicated at reference numeral302. It is foreseen that the design indicated inFIG. 9would be somewhat less expensive to manufacture than the design atFIG. 8due to simplified integration of its perforated baffle303with the sidewalls305. Otherwise, it is foreseen that the dimensions the dimensions may be generally as indicated above. More specifically, it is foreseen that the radius of curvature for curve306would be about 1.5 inches (3.8 cm); and, the diameter of inlet end307would be about 4 inches (11 cm), for an arrangement wherein the diameter of the shell is about 11 inches (27.4 cm).

If the catalyst substrate downstream from the radial diffuser inlet is substantially smaller than the muffler body, a design similar to that indicated inFIG. 10could be utilized for the radial diffuser. In particular, inFIG. 10the muffler is indicated generally400; and, the radial diffuser inlet is indicated generally at401. The curved perforated baffle402in combination with bell403provides the diffusion of gases across region405. A converter core having a smaller diameter than the shell400is indicated generally at406.

The arrangement shown inFIG. 10is also a resonator. In particular, some sound attenuation is provided by holes407which allow expansion into volume408. Through various methods, the construction can be tuned to muffle desired frequencies, especially those likely to be presented by an engine with which arrangement400would be associated.

Operation of the radial diffusers was tested. In particular, flow through an 11 inch diameter shell fitted with a resonator generally corresponding to the design illustrated inFIG. 9, with a perforated bell having a diameter of 9.5 inches (24 cm) was conducted. InFIG. 11a velocity of flow measured across the core width is indicated. It is apparent that except for at the edges, there was substantially uniform velocity of flow across the width of the core.

From these examples of dimensions, one of skill can create a variety of sizes of radial diffuser inlets for utilization in a variety of muffler constructions.

Size of the Catalytic Converter and Its Positioning Relative to the Downstream Acoustics and Flow Distribution Element

In general, catalyst activity is a function of temperature. That is, a catalytic converter generally operates best when it is hottest (within design limits). Thus, since the inlet end of a muffler assembly is hotter than the outlet end, it is generally preferable to position the catalytic converter toward the inlet end of the arrangement to the extent possible. Thus, for the arrangements shown inFIGS. 1,4,5and8the catalytic converter is generally positioned adjacent the flow distribution element.

However, if the catalytic converter is positioned too close to the flow distribution element, inefficient use will result, due to inefficient spread of flow across the front surface of the catalytic converter. In general it is foreseen that for diesel engine truck muffler assemblies according to the present invention, the catalytic converter will be generally preferably positioned within a distance of about 2-4 inches (5-10 cm), preferably about 2.0-3.0 inches and most preferably around 2.0 inches (5.0 cm) from the flow distribution element. The results of some simulated modeling and calculations with respect to this are presented hereinbelow.

Also, in general the catalytic converter takes up space in the muffler assembly otherwise utilizable for low-frequency sound attenuation. Since the catalytic converter does not facilitate sound attenuation and since sound attenuation will not generally take place in the space occupied by the catalytic converter, a problem with the catalytic converter positioning is that it interferes with sound attenuation. It is desirable, therefore, to render the catalytic converter as short as reasonably possible. This is facilitated by assuring good flow distribution across the front surface of the catalytic converter, as indicated above, and also by positioning the catalytic converter where it will operate at the hottest and thus most efficient. In general it is foreseen that a catalytic converter utilizable in assemblies according to the present invention (as converters in muffler assemblies for diesel trucks) will need to be about 3.0-8.0 inches (7.6-20.3 cm) long and generally preferably about 5.0-6.0 inches (12.7-15.2 cm) long. It is foreseen that, therefore, in preferred constructions according to the present invention (for diesel engine mufflers) the muffler assembly will be about 5.0-6.0 inches (12.7-15.2 cm) longer than would a muffler assembly not having a catalytic converter positioned therein but utilized to achieve the same level of sound attenuation in a diesel engine exhaust stream.

To improve efficiency, and thus shorten the length of core needed, it is also preferred that the population density of pores through the core be as high as reasonably obtainable. Thus, high porosity (with a large population of very small pores) is generally preferred.

As indicated generally above, it is preferred that the catalytic converter be integrated with the muffler assembly, i.e., positioned therein, rather than positioned simply in a flow stream in series with a muffler assembly. The reasons for this include that it is foreseen that less overall backpressure will be generated by such a system.

Experiments

To examine the importance of the distance between the converter element (core member) and the flow distribution element, computer models were developed. The models were based upon an arrangement corresponding generally to that shown in FIG.5.

In the following table the value of X is the distance (in inches) between the end of inlet element193and domed distribution element197. Y is the distance (inches) between the center of dome distribution element197and the upstream face198of core member185. Z is the distance (inches) between the core member185and the re-entry port of the downstream acoustics190. A is the open area fraction (in %) of the flow distribution element.

The substrate for the purposes of the experiment was a 10.5 in. by 6 in. substrate comprising a ceramic with a platinum catalyst. It was 400 cells/in2with a wall thickness of 0.0065 inches. The conditions assumed for the computer modeling were 938° F., 637 standard cubit feet per min (SCFM).

The flow distribution analysis indicated that the distance X and the open area A have a strong influence on flow distribution and the distances Y and Z have weaker but correlated affects on flow distribution. Thus optimization is feasible.