Abstract:
A multi-piece exhaust manifold includes a ring seal between separate portions. The separate portions have generally cylindrical sealing surfaces formed thereon to mate with the ring seal. The ring seal may include a metal sheath filled with graphite or other sealing material.

Description:
TECHNICAL FIELD 
     The present invention relates to gaskets for interconnecting components that may experience relative movement and in particular to gaskets for interconnecting multi-piece exhaust manifolds. 
     BACKGROUND 
     In multi-cylinder internal combustion engines, exhaust manifolds are typically in fluid communication with exhaust ports. In a typical in-line 6 cylinder engine, the exhaust manifold includes 6 ports connected to the exhaust ports and one exit passage connected to a turbo charger or exhaust pipe. For larger engines, the exhaust manifold may need to be greater than three feet in length. The heat differential and resulting thermal expansion experienced by a longer exhaust manifold generally prohibits a single piece manifold as the internal stresses and resulting stresses placed on the cylinder head connections exceed desired levels. 
     In a turbocharged application, generally the exhaust gasses are desirably routed from the cylinder head exhaust ports to the intake of the turbine with minimal loss of power. This requires that the exhaust gasses reach the turbine by following the shortest path. Multi-piece manifolds, therefore, have been developed for larger engines to route exhaust gasses to a turbocharger turbine, while allowing for thermal expansion of the exhaust manifold. Typically, a multi-piece exhaust manifold includes one or more connections that allow for relative movement of the connecting portions of the exhaust manifold sub-assembly portions. 
     In order to adequately seal between the exhaust manifold sub-assembly portions, the end connections are typically annular in form with one end of one sub-assembly interposed within another end of another sub-assembly, and the axis of each end generally aligned with the length of the exhaust manifold such that thermal expansion of the exhaust manifold sub-assemblies will result in relative axial movement between the ends. A ring seal can then be disposed between the ends to provide a seal that allows for the relative axial movement. 
     For lower heat applications, many polymers may be used to seal between the ends of the multi-piece exhaust manifold. With the advent of engines with higher operational temperatures to increase efficiency, polymers have been found to be undesirable and unable to provide the required sealing properties and material properties. Indeed polymers have been found to degrade with increase in temperature. 
     Referring to  FIG. 1 , a partial view of a prior art manifold  20  is illustrated. Manifold  20  includes a first portion  22  and a second portion  24 . First portion  22  includes a generally hollow body  30  defining an annular connection end  32 . Annular end connection  32  is defined in part by a cylindrical sealing surface  36 . Second portion  24  includes a generally hollow body  40  defining an annular connection end  42 . Annular end connection  42  is defined in part by a cylindrical sealing surface  46  that may be separated into three grooves  48 . Each groove  48  accommodates a split ring (not shown) which is similar to a piston ring. Typically, the split rings are made of precisely machined Inconel™ alloy to provide a tight fit between the split rings and cylindrical sealing surfaces  36 ,  38 . 
     When installed, both first portion  22  and second portion  24  are connected to a cylinder head (not shown) and are in fluid communication with at least one exhaust port of the cylinder head. Importantly, first portion  22  and second portion  24  are not in contact, with the split rings sealing therebetween and allowing for relative axial movement. 
     An advantage of the Inconel™ alloy split ring is that the material retains its desired sealing properties at increased operating temperatures. However, the split ring connection does not provide a positive seal as exhaust gasses may escape between the splits in the split rings. Another disadvantage of the split ring connection is that both the Inconel™ and the required machining are relatively costly. What is needed, therefore, is a seal between ends of a multi-piece exhaust manifold that provides a positive seal while reducing associated costs. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides an multi-piece manifold that includes a first portion having a first generally cylindrical sealing surface and a second portion having a second generally cylindrical sealing surface. The manifold also includes a metallic, continuous sealing ring interposed between the first generally cylindrical sealing surface and the second generally cylindrical sealing surface. 
     Another embodiment of the present invention provides a sealing system for providing a seal between at least two components. The sealing system includes a first component having a first generally cylindrical surface and a second component having a second generally cylindrical sealing surface. At least a portion of the first generally cylindrical surface and at least a portion of the second generally cylindrical surface are generally coaxial. A metallic, continuous sealing ring is interposed between the first generally cylindrical sealing surface and the second generally cylindrical sealing surface. The ring has a metal wrap at least partially enclosing a core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a partial sectional view of a prior art manifold. 
         FIG. 2  is a partially exploded perspective view of a manifold in accordance with an embodiment of the present invention. 
         FIG. 3  is a partial sectional view of the manifold of  FIG. 2 , taken along line  3 - 3 . 
         FIG. 3A  is an enlarged view of region  3 A of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 2 and 3 , an embodiment of a multi-piece manifold  60  is illustrated. Manifold  60  includes a first portion  62 , a second portion  64  and a third portion  66 . First portion  62  includes a generally hollow body  70  defining a first annular connection end  72 . First annular connection end  72  is defined in part by a first generally cylindrical sealing surface  76 . Second portion  64  includes a generally hollow body  80  defining a pair of second annular connection ends  82 . Each second annular connection end  82  is defined in part by a second generally cylindrical sealing surface  86 . Third portion  66  includes a generally hollow body  90  defining a third annular connection end  92 . Third annular connection end  92  is defined in part by a third generally cylindrical sealing surface  96 . 
     With specific reference to  FIG. 3 , a ring seal  100  is interposed between the first cylindrical sealing surface  76  and the second cylindrical sealing surface  86 . As shown in  FIG. 3A , ring seal  100  is preferably constructed of an outer metal wrap  102  with a heat resistant and resilient core  104 . Outer metal wrap preferably includes a circular edge  106  and an overlapping edge  108 . As illustrated, first portion  62  and second portion  64  are not in direct contact. Preferably, first portion  62  and second portion  64  never contact once secured to the cylinder head, since contact during thermal expansion, contraction or vibrations would result in undesirable induced stresses. 
     Ring seal  100  may be interposed between the first cylindrical sealing surface  76  and the second cylindrical sealing surface  86  in a press fit fashion where some force is used to assemble manifold  60 . Preferably, outer metal wrap  102  is constructed of a conformable metal in order to form a metallic ring seal  100  that can bindingly seat on the cylindrical sealing surfaces  76 ,  86 ,  96 . 
     To assemble the manifold  60 , ring seal  100  is superposed on second sealing surfaces  86 . First portion  62  may then be coupled to second portion  64  by interposing second end  82  into first end  72  as ring seal  100  contacts first sealing surface  76 . Third portion  66  is coupled to second portion  64  in similar fashion. 
     In some applications, relative movement between the first annular connection end  72  and the second annular connection end  82  may be in excess of 3 mm of relative axial displacement due to thermal expansion. Thus, ring seal  100  may slide along at least one of the first cylindrical sealing surface  76  and the second cylindrical sealing surface  86  as the temperature of manifold  60  changes. Also, some amount of misalignment between the axes of the first cylindrical sealing surface  76  and the second cylindrical sealing surface  86  can be permitted as ring seal  100  provides a seal therebetween. Therefore, ring seal  100  seals the connection between the first annular end  72  and the second annular end  82  while accommodating relative movement. This sealing system allows the ring seal  100  to flex while maintaining a seal, while the prior art sealing systems that incorporate rigid split rings cannot flex to the same degree. 
     Similar ring seals are disclosed in commonly owned U.S. Pat. No. 6,517,086, the disclosure of which is hereby incorporated by reference in its entirety. The core  104  of ring seal  100  may be graphite, mica, mica based inorganic filler, metallic, or other materials that promote a seal. Preferably, the core  104  can withstand a temperature of 1500° F. without significant degradation of its resilient characteristics. An example of a favorable material for the core  104  is an expandable graphite, which includes unexpanded or un-exfoliated graphite flakes. Upon heating, the un-exfoliated graphite flakes may separate and expand to several times their original thickness, causing the ring seal  100  to expand and bias the wrap  102  against the first cylindrical sealing surface  76  and the second cylindrical sealing surface  86 . Ring seal  100  is preferably somewhat deformable to allow a press fit onto second generally cylindrical sealing surface  86 . Also preferable, outer metal wrap  102  is stamped from a sheet of metal stock into a torrid shape and deformed, or wrapped to contain core  104  to provide a ring seal  100  that is formed as a continuous ring with no gap or split. 
     While surfaces  76 ,  86 ,  96  are described and depicted herein as generally cylindrical and generally parallel, surfaces  76 ,  86 ,  96  may be slightly conical and/or deviate from a parallel orientation while ring seal  100  provides an adequate sealing pressure therebetween. While manifold  60  has been described as an exhaust manifold, other components may benefit from the sealing system described herein. 
     It is to be understood that the above description is intended to be illustrative and not limiting. Many embodiments will be apparent to those of skill in the art upon reading the above description. Therefore, the scope of the invention should be determined, not with reference to the above description, but instead with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications are incorporated herein by reference for all purposes.