Abstract:
A flexible bellows tube connecting pipes in a system such as a vehicle exhaust system. Various embodiments are disclosed, with each including two conduit sections having mating corrugations that overlap to provide a seal while allowing the two sections to rotate in response to torsion loading. Different configurations of the interfitting corrugations and related structure are disclosed in the different embodiments.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional patent application Ser. No. 60/318,516 filed Sep. 10, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to flexible hoses, and in particular to a flexible hose section which controls dynamic stresses in a system with components which are subjected to different dynamic forces. 
     2. Description of the Related Art 
     Conduit and piping systems for conveying fluids and bulk materials are used in a wide variety of applications. Various components for such systems have been devised to accommodate different fluids and materials and to operate in particular environments. For example, some of the components of such systems are fabricated from flexible metal hose, which offers the advantages of durability, flexibility, relatively low cost and adaptability to various sizes, configurations and materials. 
     Flexible metal hose has been used for many years to interconnect components which move relative to each other. Some of the common configurations of flexible mental hose include spiral-wound, edge-interlocked hose wherein the edges of a strip of sheet metal are interlocked on a hose winding machine to permit limited deflection of the resulting flexible metal hose. Corrugated flexible metal hose is another type of hose that can be used. The corrugations provide flexibility and permit a corrugated pipe or hose section to be bent and shaped more easily than a comparable hose section with smooth walls. Moreover, corrugations can dissipate dynamic stresses associated with the vibration of the components to which the flexible hose section is attached. 
     Corrugated flexible hose sections can have corrugations of different diameters, such as bellows-type arrangement with the largest-diameter corrugations in the center and corrugations of decreasing diameters towards the ends whereby maximum flexibility is achieved in the center with increasing stiffness toward the ends (see U.S. Pat. No. 5,769,463 to Thomas). Such bellows-type configurations tend to be relatively efficient at dissipating vibrational energy toward their centers for dissipation. 
     Hybrid flexible metal hose sections have also been fabricated from corrugated sheet metal bands which are spiral wound with their edges interlocked. The resulting hose sections can provide the advantages of both interlocked-edge and corrugated types of flexible metal hose. Such hybrid hose designs can combine the advantages of both of these flexible metal hose types. For example, see the Thomas U.S. Pat. No. 5,494,319. 
     The disclosure of this patent, and also of the Thomas U.S. Pat. No. 5,882,046, are incorporated herein by reference. 
     Exhaust systems for internal combustion engines are examples of relatively severe environments in which the operating characteristics of flexible metal hoses can be used to advantage. Flexible metal hose sections are often used for connecting exhaust pipes from vehicle internal combustion engines with manifold mufflers, tail pipes and other exhaust system components. Flexible metal hose sections are commonly used in exhaust systems of tractors of tractor-trailer truck rigs and off road and construction vehicles because of their flexibility, temperature resistance and corrosion resistance when fabricated from suitable materials, such as stainless steel, galvanized steel or other metals. 
     Exhaust systems in general and vehicle exhaust systems in particular must perform reliably under relatively severe operating conditions, which can include temperature extremes, corrosive environmental factors and dynamic stress loading. Dynamic stresses in an exhaust system can originate from vibrations associated with the engine and movement of the vehicle. Such dynamic stresses include axial, lateral and angular forces, all of which can normally be effectively attenuated and controlled by flexible metal hose with corrugations and/or edge interlocking. However, torsional forces caused by the differential rotation of the exhaust system components connected by a flexible metal hose section can inflict significant damage, particularly when the flexible hose section ends are fixedly secured and the flexible section design is rigid with respect to rotational forces. Such dynamic torsional forces can lead to premature metal fatigue, cracking and failure of exhaust system components, including previous designs of flexible metal hose. 
     The present invention addresses these considerations in connection with the application of the flexible metal hose to applications involving dynamic stresses. Heretofore there has not been available a dynamic stress controlling flexible metal hose section with the advantages and features of the present invention. 
     SUMMARY OF THE INVENTION 
     In the practice of the present invention, a flexible hose section is provided which includes a body with a corrugated medial portion and first and second ends with first and second mouths. The body mouths receive the ends of upstream and downstream exhaust system pipe sections and are secured therein by suitable connectors, such as weldments, clamps, gaskets and the like. The hose section, through the arrangements of its corrugations and/or its end connections, permits relative rotational displacement between the exhaust pipe sections whereby dynamic torsional stress is attenuated in and controlled by the hose section. Alternative embodiments of the present invention include various arrangements of corrugations, end connections and multiple hose section body layers, which can include intermediate insulation layers and outer sleeves for greater dynamic stress control and heat resistance. 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     The principal objects and advantages of the present invention include providing a flexible hose section adapted to control dynamic stresses; providing such a hose section which is adapted to control axial, lateral, angular and rotational stresses; providing such a hose section which attenuates and dissipates forces associated with differential rotational forces in a system; providing such a hose section which dissipates heat; providing such a hose section which can be either rigidly or flexibly connected to other components in a system; providing such a hose section which can be fabricated from a variety of different materials; providing such a hose section which can operate effectively in relatively severe operating conditions, such as those associated with vehicle exhaust systems; providing such a hose section which is economical to manufacture, efficient in operation, capable of a long operating life and particularly well adapted for the proposed usage thereof. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal, cross-sectional view of an exhaust bellows embodying the present invention. 
         FIG. 1   a  is an enlarged, cross-sectional view thereof taken generally within Circle A in FIG.  1 . 
         FIG. 2  is a longitudinal, cross-sectional view of an exhaust bellows comprising a first alternative embodiment of the present invention with a shortened inner section. 
         FIG. 2   a  is an enlarged, fragmentary view thereof taken generally within the Circle A in FIG.  2 . 
         FIG. 3  is a longitudinal, cross-sectional view of an exhaust bellows comprising a second alternative embodiment of the present invention, a tapered corrugation configuration at the bellows ends. 
         FIG. 3   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  3 . 
         FIG. 4  is a longitudinal, cross-sectional view of an exhaust bellows comprising a third alternative embodiment of the present invention with a tapered corrugation at one end of the bellows. 
         FIG. 4   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in  FIG. 4  (with an annular protrusion at one end of the bellows). 
         FIG. 5  is a longitudinal, cross-sectional view of an exhaust bellows comprising a fourth alternative embodiment of the present invention. 
         FIG. 5   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A of FIG.  5 . 
         FIG. 6  is a longitudinal, cross-sectional view of an exhaust bellows comprising a fifth alternative embodiment with tapered corrugations and double annular protrusions at one end of the bellows. 
         FIG. 6   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  6 . 
         FIG. 7  is a longitudinal, cross-sectional view of an exhaust bellows comprising a sixth alternative embodiment of the present invention, with tapered corrugations and a single annular protrusion at one end of the bellows. 
         FIG. 7   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  7 . 
         FIG. 8  is a longitudinal, cross-sectional view of an exhaust bellows comprising a seventh alternative embodiment of the present invention, with annular packing captured within an annular protrusion at one end of the bellows. 
         FIG. 8   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  8 . 
         FIG. 9  is a longitudinal, cross-sectional view of an exhaust bellows comprising an eighth alternative embodiment of the present invention, with an annular gasket captured within an annular protrusion and with tapered corrugations at one end of the bellows. 
         FIG. 9   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  9 . 
         FIG. 10  is a longitudinal, cross-sectional view of an exhaust bellows comprising a ninth alternative embodiment of the present invention, with tapered corrugations at both ends of the bellows and with the inner section extending for the entire length of the bellows. 
         FIG. 10   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  10 . 
         FIG. 11  is a longitudinal, cross-sectional view of an exhaust bellows comprising a tenth alternative embodiment of the present invention, with a tapered corrugation at one end of the bellows and with the inner section extending substantially the entire length of the bellows. 
         FIG. 11   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  11 . 
         FIG. 12  is a longitudinal, cross-sectional view of an exhaust bellows comprising an eleventh alternative embodiment of the present invention, with an annual protrusion located at one end of the bellows and with the inner section extending for substantially the entire length thereof. 
         FIG. 12   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  12 . 
         FIG. 13  is a longitudinal, cross-sectional view of an exhaust bellows comprising an twelfth alternative embodiment of the present invention, with tapered corrugations and two annular protrusions located at one end of the bellows and with the inner bellows section extending for substantially the entire length thereof. 
         FIG. 13   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  13 . 
         FIG. 14  is a longitudinal, cross-sectional view of an exhaust bellows comprising a thirteenth alternative embodiment of the present invention, with a tapered corrugation and an annular protrusion at one end of the bellows, and with the inner section extending for substantially the entire length thereof. 
         FIG. 14   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  14 . 
         FIG. 15  is a longitudinal, cross-sectional view of an exhaust bellows comprising a fourteenth alternative embodiment of the present invention, with an annular sealing gasket located in an annular protrusion at one end of the bellows and with the bellows inner section extending for substantially the entire length thereof. 
         FIG. 15   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  15 . 
         FIG. 16  is a longitudinal, cross-sectional view of an exhaust bellows comprising a fifteenth alternative embodiment of the present invention, with an annular gasket captured within an annular protrusion and with a tapered corrugation at one end of the bellows and with the bellows inner section extending for substantially the entire length thereof. 
         FIG. 16   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  16 . 
         FIG. 17  is a longitudinal, cross-sectional view of an exhaust bellows comprising a sixteenth alternative embodiment of the present invention, with an annular gasket captured within an annular protrusion at one end of the bellows and with the inner section extending for substantially the entire length thereof. 
         FIG. 17   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  17 . 
         FIG. 18  is a longitudinal, cross-sectional view of an exhaust bellows comprising a seventeenth alternative embodiment of the present invention, with a double-ply construction at a tapered bellows end and a stainless ring located at both ends thereof. 
         FIG. 18   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  18 . 
         FIG. 19  is a longitudinal, cross-sectional view of an exhaust bellows comprising an eighteenth alternative embodiment of the present invention, which is similar to the eighth alternative embodiment but comprised of a different material with different proportions. 
         FIG. 19   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally with Circle A in FIG.  19 . 
         FIG. 20  is a longitudinal, cross-sectional view of an exhaust bellows comprising a nineteenth alternative embodiment of the present invention, with tapered bellows and sealing rings located at both ends thereof. 
         FIG. 20   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  20 . 
         FIG. 21  is a longitudinal, cross-sectional view of an exhaust bellows comprising a twentieth alternative embodiment of the present invention, which is similar to the tenth alternative embodiment but with liners extending further into the bellows. 
         FIG. 21   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  21 . 
         FIG. 22  is a longitudinal, cross-sectional view of an exhaust bellows comprising a twenty-first alternative embodiment of the present invention with a liner located within the bellows and a single corrugation overlapping. 
         FIG. 22   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally with Circle A in FIG.  22 . 
         FIG. 23  is a longitudinal, cross-sectional view of an exhaust bellows comprising a twenty-second alternative embodiment of the present invention, which is similar to the twelfth alternative embodiment but with a shorter liner. 
         FIG. 23   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally. 
         FIG. 24  is a longitudinal, cross-sectional view of an exhaust bellows comprising a twenty-third alternative embodiment of the present invention, with an intermediate liner layer. 
         FIG. 24   a  is an enlarged, fragmentary, cross-sectional view thereof taken generally within Circle A in FIG.  24 . 
         FIG. 25  is an elevational view of an exhaust bellows comprising a twenty-fourth alternative embodiment of the present invention, with an interlock located between two bellows sections. 
         FIG. 26  is an elevational view of an exhaust bellows comprising a twenty-fifth alternative embodiment of the present invention having relatively lengthy bellows sections and an interlock on one end. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed Description of the Preferred Embodiments 
     I. Introduction and Environment 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     II. Primary Embodiment Bellows  2 . 
     Referring to the drawing in more detail, the reference numeral  2  generally designates an exhaust bellows for an exhaust system  4  embodying the present invention. The exhaust system  4  includes upstream and downstream exhaust pipe sections  4   a,b  with ends  4   c,d  whereat bores  4   e,f  are open. The bellows  2  includes an upstream, inner section  6  with corrugations  8  including alternating lands  8   a  and grooves  8   b . The inner section  6  has an upstream end  10   a  adapted to be received within the upstream exhaust pipe section  4   a  and a downstream end  10   b . A downstream, outer section  12  of the bellows  2  telescopically receives a downstream portion of the upstream, inner section  6  and includes a downstream end  14   b  with a bore  16  extending through the exhaust bellows. The downstream, outer section  12  includes corrugations  18  with alternating lands  18   a  and grooves  18   b . The corrugations  8 ,  18  of the inner and outer sections  6 ,  12  overlie at a two-ply section  20  which is located adjacent to the outer section upstream end  14   a  and extends through approximately two corrugation lands  8   a ,  18   a . However, the two-ply section  20  could extend for a greater or lesser distance and can assume various configurations, as will be described in more detail below. A coating of lubricant  22  can be provided between the inner and outer sections  6 ,  12  within the two-ply section  20  to facilitate relative movement (i.e., rotation) therebetween. The materials comprising the sections  6 ,  12  can be chosen from a wide range of suitable materials chosen for corrosion resistance, strength, flexibility and ability to accommodate temperature changes. Price is also a factor in selecting the appropriate material. Examples include stainless steel number 304, 316, 321, 316TI (Titanium), 316L (low carbon) and various alloys. 
     The bellows  2  can be hydro-formed or mechanically formed to produce the corrugations  8 ,  18 . The corrugated portions of the sections  6 ,  12  are preferably tightly fit to provide an effective seal therebetween but the annular corrugated configurations thereof facilitate relative rotation therebetween in response to torsional stress loads on the bellows  2 . Such relative rotation can be further facilitated by utilizing a lubricant coating  22  therebetween, as described above. Still further, various liners and coatings, including high temperature plastics, metals or other materials could be located between the corrugations  8 ,  18 . 
     III. First Alternative Embodiment Bellow  102 . 
       FIG. 2 and 2   a  show a bellows  102  comprising a first alternative embodiment of the present invention with a shortened inner section  106  terminating at a downstream end  110   b  located within the corrugated portion of the outer section  112 . 
     IV. Second Alternative Embodiment Bellows  202 . 
       FIGS. 3 and 3   a  show a bellows comprising a second alternative embodiment of the present invention. The bellows  202  includes a shortened inner section  204  terminating at a downstream end  210   b  and a corrugated section  208  located in proximity thereto. The corrugated section  208  includes an upstream, reduced-diameter corrugation  208   a  and a downstream increase-diameter corrugation  208   b.    
     A downstream outer section  212  also includes a corrugated section  218  with reduced-diameter corrugations  219  corresponding to the inner section reduced-diameter corrugations  209  and enlarged-diameter corrugations  221  corresponding to the inner section enlarged-diameter corrugations  211 . The smaller-diameter corrugations  209 ,  219  tend to be stiffer than the larger-diameter corrugations  211 ,  221  and thus tend to transmit the vibrational forces towards the middle portion of the bellows  212 . 
     V. Third Alternative Embodiment Bellows  302 . 
       FIGS. 4 and 4   a  show a bellows  302  comprising a third alternative embodiment of the present invention, with a construction similar to the bellows  202  described above except that an outer section  312  is provided with a corrugated section  318  with a single reduced-diameter corrugation  319  at an upstream end of the corrugated section  318  and enlarged-diameter corrugations  321  comprising the remainder of the corrugated section  318 . 
     VI. Fourth Alternative Embodiment Bellows  402 . 
       FIGS. 5 and 5   a  show a bellows  402  comprising a fourth alternative embodiment of the present invention. The bellows  402  includes inner and outer sections  406 ,  412  respectively. The sections  406 ,  412  include corresponding annular, outwardly-convex protrusions  407  and  413  respectively. The annular protrusions  407 ,  413  closely overlie each other and provide an additional area of sealing contact between the inner and outer sections  406 ,  412 . 
     VII. Fifth Alternative Embodiment Bellows  502 . 
     A bellows  502  comprising a fifth alternative embodiment of the present invention is shown in  FIGS. 6 and 6   a . The bellows  502  includes inner and outer sections  506 ,  512  respectively. The inner section  506  includes a pair of protrusions  507  similar to the protrusions described above. The outer section  512  also includes a pair of protrusions  513 , also similar to the protrusion  413  described above. The sections  506  and  512  also include reduced and enlarged-diameter corrugations  509 ,  511  and  519 ,  521  respectively, which are similar to those described above. 
     VIII. Sixth Alternative Embodiment Bellows  602 . 
       FIGS. 7 and 7   a  show a bellows  602  comprising a sixth alternative embodiment of the present invention. The bellows  602  is similar to the bellows  502  described above, except that only single protrusions  607 ,  613  are provided on an inner section  606  and an outer section  612  respectively. 
     IX. Seventh Alternative Embodiment Bellows  702 . 
       FIGS. 8 and 8   a  show a bellows  702  comprising a seventh alternative embodiment of the present invention. The bellows  702  includes an inner section  706  and an outer section  712 . The inner section  706  includes an annular projection  707  with an annular channel  709  formed therein. The outer section  712  includes an annular projection  713  which encloses the annular channel  709  to provide an internal raceway  711  which receives an annular packing ring  715 . The packing ring  715  can comprise a suitable material, such as fabric or metal, which can be adapted for high temperature applications and can provide additional packing against leakage. 
     X. Eighth Alternative Embodiment Bellows  802 . 
     The bellows  802  is similar to the bellows  702  described above, except that reduced-diameter corrugations  809 ,  819  are provided in inner and outer sections  806 ,  812  respectively. 
     XI. Ninth Alternative Embodiment Bellows  902 . 
       FIGS. 10 and 10   a  show a ninth alternative embodiment bellows  902  with inner and outer section  906 ,  912  respectively. The inner section  906  is elongated and terminates at a downstream end  910   b  located just downstream of a corrugated length  918  of the outer section  912 . The inner and outer section  906 ,  912  include reduced-diameter corrugations  909 ,  919  respectively at the upstream end of the corrugated length  918 . Additionally, the outer section  912  includes a reduced-diameter corrugation  919  located at the downstream end of the corrugated length  918 . 
     XII. Tenth Alternative Embodiment Bellows  1002 . 
       FIGS. 11 and 11   a  show a bellows  1002  comprising a tenth alternative embodiment of the present invention. The bellows  1002  includes an inner section  1006  and an outer section  1012 . The bellows  1002  is substantially similar to the bellows  902 , except that the outer section  1012  does not include a reduced-diameter corrugation  1019  at its downstream end, but does include such a corrugation at its upstream end which cooperates with and overlies a reduced-diameter corrugation of the inner section  1006 . 
     XIII. Eleventh Alternative Embodiment Bellows  1102 . 
       FIGS. 12 and 12   a  show a bellows  1102  comprising an eleventh alternative embodiment of the present invention. The bellows  1102  is similar to the bellows  402  described above, except that an inner section  1106  thereof is relatively long and extends for substantially the entire length of a corrugated length  1118  of the outer section  1112 . 
     XIV. Twelfth Alternative Embodiment Bellows  1202 . 
     A bellows  1202  comprising the eleventh alternative embodiment is shown in  FIGS. 13 and 13   a . The bellows  1202  is similar to the bellows  502  described above, except that the inner section  1206  thereof is elongated and terminates at a downstream end  1210   b  located just downstream of a corrugated length  1218  of an outer section  1212 . 
     XV. Thirteenth Alternative Embodiment Bellows  1302 . 
       FIGS. 14 and 14   a  show a thirteenth alternative embodiment bellows  1302  including an inner section  1306  and an outer section  1312 . The bellows  1302  is similar to the bellows  1202  described above, except that the inner and outer sections  1306 ,  1312  respectively include only single annular protrusions  1307  and  1313  respectively. 
     XVI. Fourteenth Alternative Embodiment Bellows  1402 . 
       FIGS. 15 and 15   a  show a bellows  1402  comprising a fourteenth alternative embodiment of the present invention. The bellows  1402  is similar to the bellows  702  described above, except that an inner section  1406  thereof is elongated with a downstream end  1410   b  located just downstream of a corrugated length  1418  of an outer section  1412 . 
     XVII. Fifteenth Alternative Embodiment Bellows  1502 . 
       FIGS. 16 and 16   a  show a bellows  1502  comprising a fifteenth alternative embodiment of the present invention. The bellows  1502  is similar to the bellows  802  described above except that an inner section  1506  thereof includes a downstream end  1510  located downstream from a corrugated length  1518  of an outer section  1512 . 
     XVIII. Sixteenth Alternative Embodiment Bellows  1602 . 
       FIGS. 17 and 17   a  show a bellows  1602  comprising a sixteenth alternative embodiment of the present invention. The bellows  1602  is similar to the bellows  1502  described above, except that all of the corrugations  1611  and  1621  of inner and outer sections  1606 ,  1612  respectively are of substantially uniform diameter. 
     XIX. Seventeenth Alternative Embodiment Bellows  1702   
       FIGS. 18 and 18   a  show a bellows  1702  comprising a seventeenth alternative embodiment of the present invention. The bellows  1702  includes an outer ply  1704  with generally cylindrical end sections  1706 ,  1708  and a bellows section  1710  therebetween. The bellows section  1710  includes a tapered end  1712 . 
     An inner ply  1714  is positioned generally within the outer ply  1704  and includes generally cylindrical end sections  1715 ,  1716  with an intermediate section extending therebetween and located generally within the outer ply bellows section. The inner ply intermediate section includes an extended cylindrical section  1713  and a tapered bellows end section  1717  generally conforming to the configuration of the outer ply  1704 . A rigid sealing ring  1718  is mounted on one end of the inner ply  1714 . The opposite end of the outer ply  1704  receives another rigid sealing ring  1720 . The rings may be applied to both ends, neither end, or one of the ends of the assembly as desired. 
     The inner ply bellows section can be conformed to the configuration of the outer ply bellows section by means of a hydroforming or mechanical manufacturing process performed with or without a layer of lubricant between the plies. The tapered bellows portion of the inner ply can extend for any desired length and include any desired number of corrugations within the outer ply bellows section. 
     The inner and outer plies  1704 ,  1712  can comprise any suitable material. For example, dissimilar materials can be used to avoid a galling interaction which can occur with two similar metals. Examples of suitable metals include stainless steel alloys designated 316, 316TI (Titanium), 316L (low carbon), 321 and 304. The stainless steel alloys with high number designations generally provide greater corrosion resistance, whereas lower numbers tend to be less expensive. Metals chosen for the inner and out ply constructions can have suitable properties of resistance to galvanic action. 
     XX. Eighteenth Alternative Embodiment Bellows  1802   
       FIGS. 19 and 19   a  show a bellows  1802  comprising an eighteenth alternative embodiment of the present invention. The bellows  1802  is similar to the bellows  1702  described above, with a multiple ply material comprising the inner ply and/or the outer ply. As discussed above, the materials, proportions and dimensions of the bellows can vary considerably within the scope of the present invention. 
     XXI. Nineteenth Alternative Embodiment Bellows  2002   
       FIGS. 20 and 20   a  show a bellows  2002  comprising a nineteenth alternative embodiment of the present invention. The bellows  2002  includes an outer ply  2012  with corrugated, tapered bellows sections at both ends. First and second inner plies  2006  extend partway into the outer ply bellows section  2012  and terminate at inner ply ends which are positioned in spaced-apart relation. 
     In operation, the tapered bellows at both ends facilitate damping dynamic stresses. By providing a gap between the inner ply sections, torsional stress control is enhanced by facilitating slippage between the independent inner plies and outer ply. Still further, by providing connections between the inner and outer plies which are substantially fluid-tight, leakage can be controlled or at least greatly reduced. The end sections receive rings  2020  similar to rings  1720 . 
     XXII. Twentieth Alternative Embodiment Bellows  2102   
       FIGS. 21 and 21   a  show a bellows  2102  comprising a twentieth alternative embodiment of the present invention. The bellows  2102  is similar to the bellows  2002  described above, except that the inner ply sections extend considerably further into the outer ply. Moreover, the inner ply sections terminate at ends  2106   a  which are only slightly spaced from each other. Rings  2120  are on the outer ends of the inner ply section  2106 . Operationally, the bellows  2102  functions in a manner similar to the bellows  2002  described above, with a few operational differences resulting from the extended end sections. For example, extended portions of the extended ply section resist deflection by the extended lengths of inner ply captured within the outer ply. 
     XXIII. Twenty-First Alternative Embodiment Bellows  2202   
       FIGS. 22 and 22A  show a bellows  2202  comprising a twenty-first alternative embodiment of the present invention. The bellows  2202  is essentially identical to the bellows  2  shown in  FIGS. 1 and 1   a , except that the inner ply  2206  and the outer ply  2212  overlap at only a single corrugation identified at  2207  in  FIG. 22   a.    
     XXIV. Twenty-Second Alternative Embodiment Bellows  2302   
       FIGS. 23 and 23   a  show a bellows  2302  comprising a twenty-second alternative embodiment of the present invention. The bellows  2302  includes an outer ply  2312  with generally cylindrical end sections  2312   a  and  2312   b  and an intermediate corrugated bellows section located therebetween. An inner ply  2306  is located generally within one end of the outer ply  2312  and includes a single corrugation  2307  which closely matches the configuration of the corresponding outer ply corrugation. The inner ply terminates at an inner end  2306   a  located within the outer ply bellows section  2312  and an outer free end  2306   b.    
     XXV. Twenty-Third Alternative Embodiment Bellows  2402   
       FIGS. 24 and 24   a  show a bellows  2402  comprising a twenty-third alternative embodiment of the present invention. The bellows  2402  is similar to the bellows  2302  described above, with the addition of an intermediate ply  2405  comprising a layer of brass or some other suitable material located between the outer and inner plies,  2412  and  2406 , respectively. The material of the intermediate ply  2405  is preferably chosen for inertness and lack of interaction with the materials (generally metal) comprising the outer and inner plies. The intermediate ply  2405  extends generally from a first end  2412   a  of the outer ply downstream to a location immediately downstream of the first corrugation  2407 . The intermediate ply  2405  facilitates the “slip plane” effect by maintaining a relative low coefficient of friction between the outer and inner plies whereby the aforementioned torsional loads can effectively be resisted throughout the life of the bellows. The intermediate ply  2405  can extend for any desired length between the outer and inner plies, and can be adapted to any configuration thereof, including, but not limited to, the outer/inner ply configurations described herein. In the  FIG. 24  embodiment, only a single corrugation  2407  overlaps between the inner and outer plies and the intermediate ply  2405 . 
     XXVI. Twenty-Fourth Alternative Embodiment Bellows  2502   
       FIG. 25  shows a bellows  2502  comprising a twenty-fourth alternative embodiment of the present invention. The bellows  2502  includes first and second bellows sections  2502   a  and  2502   b  each having inner and outer bellows section ends  2550  and  2552 , respectively. The outer section bellows ends include four regularly-spaced slots  2554  which facilitate constricting the diameters of the bellows outer sections when mounting same on an exhaust system component. 
     An interlock  2556  comprising helical windings has first (upstream) and second (downstream) ends  2556   a  and  2556   b,  respectively, received in bellows section inboard ends  2550 . First and second rings  2558  and  2560  are mounted in overlying relation over the bellows section ends  2550  and the interlocking section ends  2556   a  and  2556   b.  The rings  2558  and  2560  are secured in place by any suitable means, including clamping, adhesives and welding. For example, the rings can be seam welded, spot welded, TIG welded, etc. 
     XXVII. Twenty-Fifth Alternative Embodiment Bellows  2602   
       FIG. 26  shows a bellows  2602  comprising a twenty-fifth alternative embodiment of the invention. The bellows  2602  is similar to bellows  2502  except that bellows  2602  includes only a single bellows section  2602   a  which is relatively long and includes an inner ply  2606  and an interlocking yet relatively rotatable outer ply  2612 . An interlock  2656  comprising spiral workings has its upstream end received in the downstream end of the bellows section  2602   a . A ring  2660  is mounted to extend around the overlapping ends of section  2602   a  and the interlock  2656  and can be secured in place by any suitable means. 
     Preferably the construction of the multi-ply bellows facilitates slippage between the plies by forming a “slip plane” therebetween. The effectiveness of the slip plane can be enhanced by lowering the coefficient of friction between the plies, and by minimizing interactions between the materials over the course of time which would otherwise cause them to bond with each other. In addition to choice of ply materials, various lubricants can be applied between the plies to minimize frictional engagement therebetween. Such lubricants include graphite pastes, liquid lubricants, spray-on lubricants, Boron Nitride and Microblue lubricant. 
     In operation the hydroformed or mechanically formed inner ply facilitates a tight-fitting engagement with the outer ply for sealing and minimizing or eliminating leakage, with the seal between the inner and outer plies being maintained during relative rotation between them. Torsional loads between the exhaust system components are thereby resisted through the relative slippage between the plies. Moreover, the function of the bellows is to accommodate displacement between the exhaust system components particularly in the form of axial loads tending to expand and compress the bellows. Other loads include displacements along the axes of the exhaust system components, which can be accommodated by the bellows sections and by the slip planes. The end rings  1718  and  1720  add to the stiffness of the end sections of the construction. 
     Embodiments that include an extended liner result in a relatively smooth bore which has a number of advantages, including noise reduction and a reduction in static losses.