Abstract:
The present invention relates to an exhaust end cone assembly including an outer end cone which is formed from a cast iron alloy and an inner end cone disposed within the outer end cone which is formed from a heat resistant material. The inner end cone is shaped such that an air gap occurs along a significant portion of the area between the inner and outer end cones to provide thermal advantages to the assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/527,314, filed on Dec. 5, 2003. The disclosure(s) of the above application(s) is (are) incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     End cones for exhaust conversion assemblies, otherwise referred to herein as hot end systems, employing catalytic converters increasingly require accommodations for thermal heat management. One of the chief functions of the end cones is to transition the diameter from the inlet/outlet pipes to the diameter of the substrate and to evenly distribute the exhaust gas over the face of a catalytic converter substrate. In so doing, the end cones are invariably subjected to extreme exhaust gas impingement, high exhaust gas flow velocities and temperatures.  
         [0003]     If the design geometry is not optimized, turbulence invariably occurs which accelerates the heat transfer from the exhaust stream into the end cones. These facts have several detrimental effects to the durability of the converter. Most significant is the exhaust heat has a direct path from the end cone into the main body (container) of the converter, thus raising the exterior temperature of the container and mounting mat. The mounting mat is designed to hold the substrate by “taking up” and limiting the thermal growth differential between the converter housing and the substrate. One way it accomplishes this is by insulating the converter housing, otherwise known in the art as the converter can, from the hot substrate thus lowering the temperature of the can and limiting its thermal growth. The mat is under compression, which with its friction provides the holding force for the substrate and expands to fill the gap differential between the substrate and can caused by their differing thermal growths. Therefore, any mechanism that increases the can temperature is detrimental to the converter durability as it will increase the gap between the can and substrate, which decreases the holding force, imparted by the mat and raises the overall mat temperature reducing its life. Other detrimental effects in more extreme cases are from erosion of the end cones due to exhaust gas impingement and thermal heat loss of the exhaust gas before it reaches the substrate causing increased lit off times and reduced conversion efficiency.  
       DISCUSSION OF PRIOR ART  
       [0004]     Currently known end cones use rolled and formed stainless steel for both inner and outer cones. Further, such end cones do not employ air gaps and/or insulation in the manner described in the present invention.  
         [0005]     Still other prior art employs cast-in heat shields that require special casting processes that may be prohibitively expensive. The construction of various known end cone assemblies are unduly complicated and often require welding with expensive alloys to accomplish a robust weld.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention relates to exhaust system end cone assemblies comprising an outer end cone and an insertable inner end cone which is disposed within the outer end cone in at least partially spaced relationship to provide a gap between the inner and outer end cones. The air gap, which serves as a thermal barrier, optionally including thermal insulation, protects the cast iron end cone and converter housing from extreme temperatures and may eliminate the need for external heat shields to protect other under hood components. More particularly, the present invention describes a way of capturing an inner cone, made of heat resistant material, in a way that requires no welding, crimping or fastening in a conventional way.  
         [0007]     The inner cone is not called upon to have great strength, it only needs to have enough strength to support itself and some light insulation. Therefore a fairly light section is usually all that&#39;s required, which helps improve thermal inertia. Its main function is to protect the outer cone from direct exhaust gas impingement lowering its temperature and therefore reducing the heat transfer into the main body of the converter. 
     
    
     DESCRIPTION OF THE FIGURES  
       [0008]      FIG. 1  is a sectional view of an exhaust system end cone assembly embodiment including an insertable inner cone according to the teachings of the present invention;  
         [0009]      FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 ;  
         [0010]      FIG. 3  is a cross-sectional view demonstrating an alternative outer end cone flange design taken along the same cross-section as line  2 - 2 ;  
         [0011]      FIG. 4  is a partial cross-sectional view of the outer end cone flange design of  FIG. 3  including an inner end cone having outwardly projecting beads;  
         [0012]      FIG. 5  is a sectional view of an alternative exhaust system end cone assembly according to the teachings of the present invention; and  
         [0013]      FIG. 6  is a cross-sectional view taken along line  6 — 6  of  FIG. 5  absent the inner end cone. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     A catalytic converter end cone assembly  10  having a dual wall air gap for improved thermal heat management is illustrated in  FIG. 1 . While the end cone assembly described herein is considered to be applicable to either the inlet side or outlet side of a catalytic converter assembly, as should be appreciated by those of ordinary skill in the art reference will now be made to an inlet end application for purposes of describing the invention.  
         [0015]     The end cone assembly  10  includes an outer end cone  12  which transitions the inner diameter between the catalytic converter housing  16  and an exhaust gas inlet portion  14 . The end cone of the inlet side is intended to assist in evenly distributing the exhaust gas over the face of the catalytic substrate  18  contained within the converter housing that filters the exhaust gases. The inlet portion  14 , shown in the form of a transition pipe may include a flange  24  provided along one end  22  for mounting the catalytic converter end cone assembly to other components such as an exhaust manifold (not shown) by way of non-limiting example. The pipe  14  may also include one or more apertures  26  for hosting exhaust gas monitoring sensors (not shown).  
         [0016]     At an opposite end  28 , the pipe  14  transitions to the outer end cone  12  wherein the internal diameter of the end cone expands to the transition point  30  of the converter housing  16 . As shown, the internal diameter of the outer end cone has a substantially fluted shape. The pipe  14 , outer end cone  12  and converter housing  16  can be a multiple piece cast assembly or as shown in the form of a one piece casting such as those described in co-pending U.S. patent application Ser. No. 10/812,009 entitled “One Piece Catalytic Converter Housing With Integral End Cone”, which is hereby incorporated by reference. Among the preferred alloys for casting are those known in the art as SiMo cast iron alloys.  
         [0017]     The end cone assembly  10  includes means for cooperatively securing the insertable inner cone  44  within the outer end cone  12 . As depicted in  FIG. 1 , such means include an inwardly extending flange  36  disposed in proximity to the transition point  30  between the outer end cone  12  and converter housing  16 . The flange  36  which is typically a cast in feature generally includes a shelf  38  and an inner wall  40 . The flange  36  may be continuous as depicted in  FIG. 2  or intermittent including various flange sections  36   a  as depicted in  FIG. 3 . The inner end cone  44  may optimally include outwardly projecting leads  62  which engage the corners  66  of the intermittent flange sections  36   a  which prevent the inner core from rotating within the outer end cone  12 .  
         [0018]     The inner cone  44 , which is formed from a heat resistant material such as 439 or 409 stainless steel or ceramics by way of non-limiting example, is sized and shaped to fit within the outer cone  12 . More particularly, the second end  48  of the inner cone  44  as shown in  FIG. 1 , is sized to fit securely against the inner wall  40  of the inwardly projecting flange  36  provided along the inner wall of the outer cone or is sized to fit securely against the inner wall sections  40   a  of the flange sections  36   a  of the embodiment of  FIG. 3 . The second end  48  also includes an outwardly extending lip  56  which rests upon the shelf  38  and is captured, i.e., entrapped along an end  60  of the mounting mat  58  upon full insertion into the converter housing  16 .  
         [0019]     At the opposite end  46  the inner cone  44  is sized to seat against the inner wall  34  of the outer end cone  12 . The body  50  of the inner cone diverges from the second end  48  toward the first end  46  such that an air gap  52  is provided between the inner wall  34  of the outer end cone and the outer wall  54  of the inner end cone  44 . Except for connection points along the ends  46 ,  48  and the inner cone the air gap is preferably continuous to minimize heat transfer to the outer end cone. The spacing between the inner wall of the outer end cone and the outer wall of the inner end cone may vary between the first and second ends  46 ,  48  but on average should be a distance of at least about 2 mm over the length of the assembly. Depending upon the thermal requirements of the end cone assembly  10 , insulation  66  may be provided within the air gap for enhanced thermal dispersion. The insulation can be selected from various known insulation materials but a preferred type of insulation includes ceramic fibers. In addition to effective thermal properties, ceramic fiber insulation tends to dampen vibration.  
         [0020]     Referring to  FIG. 5 , an alternative exhaust system end cone assembly employing a snap fit inner end cone  144  is presented. Under this embodiment, the inner end cone  144  includes a circumferential recess  162  which is engaged by the intermittent inwardly projecting flange sections  136   a  shown most clearly in  FIG. 6 . The flange sections  136   a  are substantially rounded to mimic the contour of the recess  162 . Essentially all other elements of the assembly remain the same as described above with reference to  FIGS. 1-4 .  
         [0021]     Since the inner cone does not need to function as a structural member of the end cone assembly per se, the inner cone  44  generally only needs enough strength to support itself and some light insulation. Thus, the average thickness of the inner cone  44 , when formed from a lightweight stainless steel is typically less than about 1.4 mm, and preferably is between about and 0.8 mm and 1.25 mm. As should now be appreciated, the primary functions of the inner cone are to protect the outer cone from direct exhaust gas impingement thereby lowering its temperature, reducing the heat transfer into the main body of the converter, reducing overall temperature of the main body and mat, and enhancing durability.  
         [0022]     The inner cone allows for the outer cone (the main structural piece) to be cast and provide for a gap between the inner and outer cones. The gap can host thermal insulation, which may further protect the cast iron from extreme temperatures. This also protects the exterior of the converter from radiating extreme temperatures and may eliminate the need for external heat shields to protect other under hood components.  
         [0023]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.