Abstract:
The disclosure is directed to a flow distributor for use to maximize the efficiency and working life of a catalytic converter. The flow distributor is configured such that it directs the gas flow in the center of the exhaust gas stream to the periphery of the gas stream thereby resulting in a more uniform velocity flow pattern.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/615,180, filed Oct. 1, 2004, which application is hereby incorporated by reference in its entirety. 

   TECHNICAL FIELD 
   The present disclosure relates generally to an exhaust flow distribution device. More particularly, the disclosure relates to a device capable of altering the exhaust gas velocity profile upstream of an exhaust aftertreatment device. 
   BACKGROUND 
   The natural velocity profile of exhaust gas in a muffler flowing towards the inlet of an exhaust aftertreatment device (e.g., a catalytic converter or diesel particulate filter) resembles a parabolic curve with the velocity maximum at the center of the flow distribution and decreasing significantly outwardly towards the periphery of the flow distribution. This non-uniform velocity flow distribution shortens the useful lives of the aftertreatment devices, and reduces their operational efficiency. 
   Various flow distribution devices have been used to create a more uniform velocity flow profile. U.S. Pat. Nos. 5,355,973; 5,732,555; 5,185,998; and 4,797,263 disclose exemplary flow distribution devices that can be used to prolong the useful life and efficiency of exhaust aftertreatment devices. However, these flow distribution devices typically either impede fluid flow causing an undesirable increase in backpressure or do not adequately distribute flow across the face of their corresponding exhaust aftertreatment device. Consequently, there is a need for improved flow distribution devices that provide an effective flow distribution while at the same time generating reduced backpressure. 
   SUMMARY 
   One aspect of the present disclosure is to provide a flow distribution device that is constructed such that it effectively distributes flow without generating unacceptable levels of backpressure. In particular, the flow distribution device includes a plate adapted to be disposed across the flow path of exhaust gas in an exhaust system. The flow distribution device includes a plurality of apertures that define open spaces in the plate. The open spaces are largest adjacent the periphery region of the flow path where the natural flow velocity is slowest and are smallest adjacent the center region of the flow path where the natural flow velocity is fastest. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a portion of a vehicle exhaust assembly having a flow distributor that includes features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
       FIG. 2  is a plan view of the flow distributor of  FIG. 1 ; 
       FIG. 3  is a flow model showing an example flow pattern generated by a flow distributor of the type shown in  FIGS. 1 and 2 ; 
       FIG. 4  shows an example catalytic converter muffler having a flow distribution device that includes features that are examples of inventive aspects in accordance with the principles of the present disclosure; and 
       FIG. 5  shows an example exhaust aftertreatment component having a flow distribution device that includes features that are examples of inventive aspects in accordance with the principles of the present disclosure. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic illustration of a portion of a vehicle exhaust system  10  that includes, among other elements, an exhaust conduit  11 , an aftertreatment device  30  and a flow distributor element  40 . Flow arrows  13 ,  15 , and  19  illustrate that the direction of exhaust gas flow is from an upstream end  1  of the aftertreatment device  30  to a downstream end  2  of the aftertreatment device  30 . 
   The flow distribution element  40  is preferably configured to improve exhaust flow uniformity across the upstream end  1  of the aftertreatment device  30  without generating significant back pressure in the exhaust system  10 . The aftertreatment device  30  can include a structure such as a catalytic converter, diesel particulate filter, a lean NOx catalyst device, a selective catalytic reduction (SCR) catalyst device, a lean NOx trap, or other device for removing for removing pollutants from the exhaust stream. 
   Catalytic converters are commonly used to convert carbon monoxides and hydrocarbons in the exhaust stream into carbon dioxide and water. Diesel particulate filters are used to remove particulate matter (e.g., carbon based particulate matter such as soot) from an exhaust stream. Lean NOx catalysts are catalysts capable of converting NOx to nitrogen and oxygen in an oxygen rich environment with the assistance of low levels of hydrocarbons. For diesel engines, hydrocarbon emissions are too low to provide adequate NOx conversion, thus hydrocarbons are required to be injected into the exhaust stream upstream of the lean NOx catalysts. SCR&#39;s are also capable of converting NOx to nitrogen and oxygen. However, in contrast to using HC&#39;s for conversion, SCR&#39;s use reductants such as urea or ammonia that are injected into the exhaust stream upstream of the SCR&#39;s. NOx traps use a material such as barium oxide to absorb NOx during lean burn operating conditions. During fuel rich operations, the NOx is desorbed and converted to nitrogen and oxygen by catalysts (e.g., precious metals) within the traps. 
   Diesel particulate filters can have a variety of known configurations. An exemplary configuration includes a monolith ceramic substrate having a “honey-comb” configuration of plugged passages as described in U.S. Pat. No. 4,851,015 that is hereby incorporated by reference in its entirety. Wire mesh configurations can also be used. In certain embodiments, the substrate can include a catalyst. Exemplary catalysts include precious metals such as platinum, palladium and rhodium, and other types of components such as base metals or zeolites. 
   For certain embodiments, diesel particulate filters can have a particulate mass reduction efficiency greater than 75%. In other embodiments, diesel particulate filters can have a particulate mass reduction efficiency greater than 85%. In still other embodiments, diesel particulate filters can have a particulate mass reduction efficiency equal to or greater than 90%. For purposes of this specification, the particulate mass reduction efficiency is determined by subtracting the particulate mass that enters the filter from the particulate mass that exits the filter, and by dividing the difference by the particulate mass that enters the filter. 
   Catalytic converters can also have a variety of known configurations. Exemplary configurations include substrates defining channels that extend completely therethrough. Exemplary catalytic converter configurations having both corrugated metal and porous ceramic substrates/cores are described in U.S. Pat. No. 5,355,973, that is hereby incorporated by reference in its entirety. The substrates preferably include a catalyst. For example, the substrate can be made of a catalyst, impregnated with a catalyst or coated with a catalyst. Exemplary catalysts include precious metals such as platinum, palladium and rhodium, and other types of components such as base metals or zeolites. 
   In one non-limiting embodiment, a catalytic converter can have a cell density of at least 200 cells per square inch, or in the range of 200-400 cells per square inch. A preferred catalyst for a catalytic converter is platinum with a loading level greater than 30 grams/cubic foot of substrate. In other embodiments the precious metal loading level is in the range of 30-100 grams/cubic foot of substrate. In certain embodiments, the catalytic converter can be sized such that in use, the catalytic converter has a space velocity (volumetric flow rate through the DOC/volume of DOC) less than 150,000/hour or in the range of 50,000-150,000/hour. 
   Still referring to  FIG. 1 , the depicted exhaust system  10  includes an inlet tube  14  positioned at an upstream end  13  of the conduit  11 . The inlet tube  14  is aligned with a central longitudinal axis  3  of the conduit  11  and supported relative to the conduit  11  by an annular end cap  18 . The inlet tube  14  includes a generally cylindrical construction having an upstream end  17  that is coincident with an inlet aperture  16  and a downstream end  19  that is connected to a tapered inlet conduit  20  (e.g., a truncated cone having a major diameter end  22  and a minor diameter end  21 ). The flow distributor element  40 , which will be discussed in greater detail below, is positioned adjacent the major diameter end  22  of the tapered inlet conduit  20 . The aftertreatment device  30  is located between the flow distributor element  40  and the downstream end  22  of the conduit  11 . In one example embodiment, the upstream face of the aftertreatment device  30  is spaced a distance d from the flow distributor element  40 , the distance d being in the range of 1-6 inches. 
   In use, the exhaust gases are directed into the exhaust conduit  11  through the inlet aperture  16  as indicated by arrows  13 . The exhaust gases are then directed though the tapered inlet conduit  20  which allows for expansion of the gases as they flow toward the major diameter end  22  of the tapered conduit  20  and the approach the flow distributor element  40 . The diffused exhaust gas interacts with and flows through the distributor element  40  and enters into an internal region or volume  24  of the exhaust system  10  defined by the conduit  11 . Finally, the exhaust gas flows through the aftertreatment device  30  and out the downstream end of the conduit  11 . 
   Now referring to both  FIGS. 1 and 2 , the flow distribution element  40  will be discussed in greater detail. The flow distribution element  40  is sized and configured such that it effectively distributes exhaust gas flow across the entire front or upstream end  1  (i.e., the upstream face or side) of the aftertreatment device  30  without generating an excessive amount of backpressure (i.e., without excessively impeding the forward flow of the exhaust gas) and without occupying a large amount of space. The distribution of exhaust flow on the upstream end  1  decreases the likelihood of exhaust gas overload to any given portion of the aftertreatment device  30  which also increases the effective lifetime of the aftertreatment device  30 . 
   Still referring to both  FIGS. 1 and 2 , the flow distribution element  40  includes a plate  54  having a first major surface  42  facing in a downstream direction, and a second major surface  44  facing in an upstream direction. As shown, the plate  54  has a peripheral edge  46  that is sized and shaped to engage the inner surface of the exhaust conduit  11 . The peripheral edge  46  can include a flange  48  that is arranged coaxially and adjacent the inner surface of the conduit  11  to aid in positioning and supporting the plate  54  within the conduit  11 . The plate  54  is positioned adjacent the major diameter end  22  of the diffuser  20 . The major diameter end  22  of the diffuser  20  contacts the flow distribution element  40  at an intermediate peripheral boundary  58 . The area of the plate  54  surrounded by the intermediate periphery boundary  58  is directly in the path of the gas flow stream passing through the tapered inlet conduit  20 . 
   Referring specifically to  FIG. 2 , the plate  54  includes a plurality of flow-distribution holes  50 . The holes  50  are elongated along lengths L that extend radially outwardly from a central region  51  of the plate  54 . The central region  51  is preferably aligned generally with the central longitudinal axis  3  of the conduit  11 . The holes  50  have widths W 1  that continuously increase as the lengths L extend radially away from central region  51 . Thus, the sizes of the holes  50  increase as the holes extend away from the central region  51 . Also, the percentage of open area of the plate  54  increases as the openings extend away from the central region  51 . This hole configuration assists in distributing exhaust gas flow radially outwardly to provide improved flow distribution at the aftertreatment device  30 . The region of the plate  54  between the boundary  58  and the outermost peripheral edge  46  preferably does not include holes. 
   In the embodiment shown, the plate  54  includes a generally circular aperture  52  disposed at the center of the plate  54  and twelve pie or wedge shaped flow-distribution holes  50  disposed evenly around the circular aperture  52 . The wedge shaped apertures are separated by radially extending strips of plate referred to herein as deflectors  64 . In the embodiment shown, the deflectors  64  are uniform in shape with a width W 2  that remains relatively constant from a first end  60  near the center of the plate  54  to a second end  62  near the periphery of the plate  54 . However, it will be appreciated that the shapes of the deflectors can be varied without departing from the principles of the present invention. 
   It is also noted that a majority of the region of the plate  54  defined within the intermediate peripheral boundary  58  is open to allow exhaust flow to pass therethrough. In certain embodiments, the sum of the open spaces within the boundary  58  divided by the overall area defined inside the boundary  58  is greater than or equal to 75 percent. In other words, the plate  54  is at least seventy-five percent open and less than twenty-five percent closed within the boundary  58 . It should be appreciated that a number of different arrangements and shapes of apertures are possible. The open configuration of the plate assists in minimizing the backpressure generated by the plate  54 . The tapered transition provided by the tapered inlet conduit  20  also assists in minimizing backpressure. 
   Referring to  FIG. 1 , to further enhance flow distribution, the upstream side  44  of the plate  54  is convex and the downstream side  42  of the plate is concave. However, in other embodiments the plate could be flat, conical or any number of different shapes. 
   The above-described convex configuration is advantageous since it inhibits “oil canning” or fluctuation under heavy flow and vibration conditions. In addition, the convex configuration allows the plate  54  to direct the flow to the periphery of the flow path without impeding the flow by abruptly changing its direction. In the embodiment shown, no major surface of the plate  54  within the intermediate periphery edge  58  is disposed perpendicular to the longitudinal axis  3  of the muffler assembly  10 . Such a construction enables the plate  54  to modify the natural non-uniform flow profile to a more uniform flow profile without significantly decreasing the overall flow rate. 
     FIG. 3  shows flow modeling for a flow distribution device having features in accordance with the principles of the present disclosure. The depicted embodiment includes an exhaust conduit having a diameter in the range of 10-14 inches, and a flow distribution device having flow distribution openings that have radial lengths of about 9 inches. The modeling shows that such a configuration provides substantially uniformly distributed flow across the upstream face of the aftertreatment device. The flow distribution device provides effective flow distribution while causing reduced back pressure as compared to conventional flow distribution techniques. 
     FIG. 4  shows a vertical catalytic converter muffler  200  incorporating the flow distribution element  40  and tapered inlet conduit  20 . The muffler  200  includes a muffler body  211  having an inlet end  201  and an outlet end  203 . The tapered inlet conduit  20  and flow distribution element  40  are mounted at an inlet pipe  207  of the muffler  200 . The element  40  distributes exhaust flow across a diesel oxidation catalyst  210  (i.e., a catalytic converter) mounted within the muffler body  211 . The muffler  200  also includes an outlet pipe  220  mounted at the outlet end  203  of the muffler body  211 . The outlet pipe  220  has a capped lower end that prevents water from wetting the diesel oxidation catalyst  210 . The outlet pipe  220  also includes a first perforated region  221  for allowing exhaust gas from within the body  211  to enter the outlet pipe  220 , and a second perforated region  223  in fluid communication with an expansion chamber  225  for muffling exhaust noise. 
     FIG. 5  shows a double-walled exhaust aftertreatment component  300  having an inlet piece  302 , an intermediate piece  304 , and an outlet piece  306 . The pieces  302 ,  304  and  306  are secured together by clamps (e.g., v-band clamps). A catalytic converter  310  is mounted in the inlet piece  302  and a diesel particulate filter  312  is mounted in the intermediate piece. The flow distributor  40  is mounted within the inlet piece  302  at a location upstream from the catalytic converter  310 . Further details regarding the aftertreatment component  300  can be found at U.S. patent application Ser. No. 11/223,460, entitled “Construction for an Engine Exhaust System Component”, filed on Sep. 8, 2005, which application is hereby incorporated by reference in its entirety. 
   It will be appreciated that flow distribution element  40  can also be used with other muffler configurations such as horizontal mufflers. Also, in other embodiments, multiple aftertreatment devices (e.g., multiple catalytic converters, multiple diesel particulate filters, or combinations of catalytic converters and diesel particulate filters) can be mounted in the muffler downstream from the flow distributor. Moreover, flow distribution elements in accordance with the present disclosure can be used in other types of exhaust conduits in addition to muffler bodies. 
   The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.