Abstract:
A pipe lap joint is disclosed with an improved sealing zone structure in the overlap region of the pipes. The sealing zone comprises a slot extending from the end of the outer pipe to an inner end wall of the slot. The joint comprises a band clamp with a clamping band which covers the sealing zone including the inner end of the slot. The slot has a bridge extending between the sidewalls and dividing the slot into an outboard slot segment and an inboard slot segment. The bridge has an axial dimension which is substantially smaller than the axial length of either of the slot segments. When the band clamp is tightened, the sealing zone is collapsed by collapse of the slot and consequent deformation of the bridge such that it obstructs fluid flow between the slot segments.

Description:
This Application claims the benefit of Provisional Application 60/088,094 filed Jun. 5, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to pipe couplings and, more particularly, to a pipe lap joint especially adapted for use in vehicle exhaust systems. 
     INVENTION BACKGROUND 
     In vehicle exhaust systems it is desirable for pipe joints to have high pull-apart strength and to provide a good fluid seal between the pipes. It is becoming increasingly important to provide exhaust pipe couplings that achieve greater reliability and uniformity in providing a good fluid seal. 
     In U.S. Pat. No. 4,629,226, granted Dec. 16, 1986 to Cassel, a pipe lap joint is disclosed which provides a collapsible sealing zone in the outer pipe. The sealing zone is formed by providing a pair of intersecting end-to-end slots in the outer pipe which provide relief for circumferential contraction of the sealing zone within an overlap region where the pipe ends overlap. A clamping band is disposed around the outside pipe and covers the inboard slot. When the clamping band is tightened around the outside pipe the sealing zone of the outer pipe is collapsed into close fitting engagement with the inner pipe. The intersecting outboard and inboard slots are circumferentially offset. Adjacent sidewalls of the slots are in substantial alignment with each other. The inner end wall of the outboard slot is in substantial alignment with the outer end wall of the inboard slot. With this alignment and with the sidewalls and end walls of the slots being rectilinear, an inner corner of the outboard slot makes a point-to-point intersection with an outer corner of the inboard slot. With this structure, only a very small amount of collapse of the outer pipe is necessary to cause a sealing engagement between the inner end wall of the outboard slot and the outer end wall of the inboard slot. 
     The Cassel et al. U.S. Pat. No. 5,588,680 discloses a pipe lap joint for vehicle exhaust system in which a pair of non-intersecting end-to-end slots are provided to afford relief for circumferential contraction of a sealing zone within an overlap region of two overlapped pipe ends. With this construction, precise location of the adjacent corners of the slots is required and the sidewalls and end walls that form the corners are rectilinear. In this pipe joint, a fluid seal is obtained upon tightening of the clamp on the outer pipe even though there is no substantial contraction of the sealing zone by collapse of the slots because a frangible bridging segment of the pipe wall extends between adjacent corners of the slots. Thus, the slots are isolated from each other when the frangible bridging element is either only slightly deformed or when it is completely fractured by collapse of the overlap region of the outer pipe. 
     A general object of this invention is to overcome certain disadvantages of the prior art and to provide a pipe lap joint with an improved sealing zone. 
     INVENTION SUMMARY 
     In accordance with this invention, a pipe lap joint is provided that exhibits good fluid sealing and pull-apart strength and that can be manufactured at low cost. 
     Further, in accordance with this invention, a pipe lap joint is provided in which an overlap region of an outside pipe over an inside pipe comprises a collapsible sealing zone with at least one slot extending from the end of the outer pipe to an inner end wall of the slot. The slot has an open end at the end of the outer pipe and terminates in a closed end within the overlap region of the pipe ends. The slot also has two generally parallel sidewalls that extend from the open end to the closed end, the closed end being defined by an end wall. 
     Further, in accordance with the invention, an integral bridge integrally extends from each sidewall and spans the slot adjacent the open end. The bridge is configured to collapse as the sidewalls of the slot move toward each other in response to the application of inward clamping pressure around the lap joint. The bridge collapses into a position that provides a fluid seal or sealing zone across the slot and between the inner and outer pipes. 
     Further in accordance with the invention, the bridge of the pipe wall is configured to seal off the slot by blocking axial fluid flow through the slot. The bridge seals off the slot whether or not the diametrical gap between the outer pipe and the inner pipe is large enough to require that the outer pipe be collapsed around the inner pipe to fit tightly around the inner pipe. In other words, a fluid seal is obtained upon tightening of the clamp on the outer pipe even though there is no contraction of the sealing zone by collapse of the slot because the bridge of the pipe wall extends across the slot adjacent the open end. Thus, the bridge isolates an axial inner portion of the slot from an outer portion of the slot whether or not the bridge is deformed at all by collapse of the overlap region of the outer pipe. 
     Still further in accordance with the invention, the bridge is configured so that the collapse of the outer pipe will not distort the bridge in such a way as to permit any significant leakage past or through the slot. This is because, for each embodiment, the bridge is configured to collapse without creating a gap between the bridge and the outer pipe  12  or between the bridge and the inner pipe  14 . In other words, the bridge is a continuous unbroken structure from one sidewall to the other in both its collapsed and uncollapsed configuration. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a lap joint constructed according to the invention with the parts in assembled relation but before the clamp is tightened; 
     FIG. 2 is a fragmentary cross-sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional end view taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a magnified view of a slot in the lap joint of FIG. 1 before an outer pipe of the lap joint is collapsed around an inner pipe of the lap joint; 
     FIG. 5 is a magnified view of the slot of FIG. 4 after the outer pipe is collapsed; 
     FIG. 6 is a magnified view of a lap joint slot constructed according to a second embodiment of the present invention; 
     FIG. 7 is a magnified view of the lap joint slot of FIG. 6 after the outer pipe is collapsed; 
     FIG. 8 is a magnified view of a lap joint slot constructed according to a third embodiment of the present invention; and 
     FIG. 9 is a magnified view of the lap joint slot of FIG. 8 after the outer pipe is collapsed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A lap joint constructed according to a first illustrative embodiment of the present invention is generally indicated at  10  in FIGS. 1-5. A pipe lap joint constructed according to a second embodiment of the invention is generally indicated at  10 ′ in FIGS. 6 and 7 and a pipe lap joint constructed according to a third embodiment is generally indicated at  10 ″ in FIGS. 8 and 9. Reference numerals with the designation prime (′) in FIGS. 6 and 7 and the designation double-prime (″) in FIGS. 8 and 9 indicate alternative configurations of elements that also appear in the first or second embodiment. Unless indicated otherwise, where a portion of the following description uses a reference numeral to refer to the figures, I intend that portion of the description to apply equally to elements designated by primed and double-primed numerals in FIGS. 6-9. 
     As shown in FIGS. 1-3, the pipe lap joint  10  comprises, in general, inside and outside pipes  12  and  14 , respectively, in a telescoping relationship. The lap joint  10  also includes a band clamp  16  for holding the pipes together and causing the inside and outside pipes  12 ,  14  to engage each other in a fluid sealing relationship. The outside pipe  14  has a lap portion which extends over the inside pipe to provide an overlap region  18  of the pipes  12 ,  14  as shown in FIG.  2 . To provide a fluid seal between the pipes, a radially collapsible sealing zone  22  is provided on the outside pipe  14  in the overlap region. 
     The sealing zone  22  comprises a ring-shaped portion of a free end of the outside pipe  14 . The sealing zone  22  is configured to be contracted or collapsed in a radial direction by the clamp  16  so that the sealing zone  22  is in close fitting engagement with the inside pipe  12 . To facilitate the collapse or contraction of the sealing zone  22 , an end portion of the outside pipe  14  is provided with a slot  24 . In the illustrative embodiment, only a single slot  24  is used. However, in other embodiments, it may be desirable to use two or more slots  24  spaced circumferentially around the pipe  14 . 
     The slot  24  is shown in the assembly view of FIG.  1  and is shown in more detail in FIGS. 4 and 5. The slot  24  has an open end at the end of the outer pipe  14 . The slot  24  extends generally in the axial direction of the pipe to a closed end that is disposed within the sealing zone  22  on the outside pipe  14 . The slot  24  is bounded by a pair of generally parallel sidewalls  32 ,  34  and an arcuate end wall  36 . The slot  24  extends from the end wall  36  to the open end of the slot  24  at the end of the outside pipe  14 . A bridge  26  extends across the slot  24 . 
     The bridge  26 , formed by the wall of the outside pipe  14 , integrally extends into the slot  24  from a juncture zone  28  at each sidewall  32 ,  34  and spans the slot  24  adjacent the open end. The bridge  26  divides the slot into an outboard slot segment  31  and an inboard slot segment  33  and blocks fluid flow therebetween. The bridge  26  is oriented diagonally or obliquely across the slot in relation to the sidewalls  32 ,  34 . The diagonal orientation of the bridge  26  facilitates its collapse as the sidewalls  32 ,  34  of the slot  24  move toward each other in response to the application of inward clamping pressure around the lap joint  10 . The collapse may include a gentle bending of the bridge along its length into a general S-shape and/or a more acute bending of the bridge at the juncture zones as shown in FIG.  5 . In any event, the bridge  26  collapses into a position that provides a fluid seal or sealing zone across the slot  24 . 
     As shown in FIG. 6, the bridge  26 ′ of the second embodiment is of arcuate or quarter-moon shape across the slot  24 ′ with a convex edge adjacent the open end of the slot  24 ′. As with the diagonal orientation of the bridge  26  in the first embodiment, the arcuate shape of the bridge  26 ′ facilitates its collapse as the sidewalls  32 ′,  34 ′ of the slot  24 ′ move toward each other in response to the application of inward clamping pressure around the lap joint  10 ′. The collapse generally includes a gentle bending of the bridge  26 ′ along its length into a more acute convex configuration as shown in FIG.  7 . In this more acute convex configuration, the bridge  26 ′ continues to provide a fluid seal across the slot  24 ′. While the bridge in the illustrative embodiment has a convex edge adjacent the open end of the slot other embodiments may have a concave edge adjacent the open end of the slot. 
     As shown in FIG. 8, the bridge  26 ″ of the third embodiment is of doughnut shape and comprises a thick-walled generally cylindrical plug. Juncture zones  28 ″ are disposed at diametrically opposite sides of the plug where the bridge  26 ″ merges with or integrally extends from the opposing sidewalls  32 ″,  34 ″. The cylindrical shape of the bridge  26 ″ facilitates its collapse as the sidewalls  32 ″,  34 ″ of the slot  24 ″ move toward each other in response to the application of inward clamping pressure around the lap joint  10 ″. More specifically, an axial through-hole  30  that defines the center of the cylindrical shape of the bridge  26 ″ provides a space for the cylindrical bridge  26 ″ to collapse inward. The collapse may include a deformation of the circular cylindrical shape of the bridge  26 ″ into an oblong or oval cylindrical shape as shown in FIG.  9 . As with the first and second embodiments, the bridge  26 ″ collapses into a position that maintains a fluid seal or sealing zone across the slot  24 ″. 
     As shown at  16  in FIGS. 1,  2  and  3 , the preferred clamp  16  for use with the invention comprises a clamping band  72  that is disposed around the outer pipe  14  over the sealing zone  22 . The clamping band  72 , for sealing purposes, must cover the inboard end of the slot  24  and cover the bridge  26 . The clamping band  72  is provided with a tightening means  74 . The clamping band  72  is, for the most part, circular or roundish in cross-section. It has a roundish sector  76  adapted to fit around the sealing zone  22  on the pipe  14  and a channel-shaped sector  78  that comprises a pair of sidewalls  82 ,  84 . The sidewalls  82 ,  84  extend radially outwardly from the roundish sector. The clamping band  72  is made of a single piece of sheet metal and each free end of the band  72  is folded back on itself to form a double layer. Thus, the sidewalls  82 ,  84  are of double thickness and terminate at their outer ends in respective loops or bights  86 ,  88 . The bights  86 ,  88  serve as retaining members for holding the sidewalls  82 ,  84  in place when the tightening means  74  is tightened. 
     The tightening means  74  tightens the clamping band  72  around the pipe  14 . The tightening means comprises a reaction member or spline  92  that is disposed within a channel-shaped sector  78 . The spline  92  is adapted to seat upon the outer surface of the sealing zone  22  of pipe  14 . For this purpose, the spline has an arcuate inner surface that conforms to the pipe  14 . The spline  92  is provided with a pair of oppositely facing concave surfaces  94  and  96 . The tightening means includes a bolt  98  and a nut  102 . It also includes a spacer  104  disposed outside the sidewall  82  and having a convex surface disposed opposite the concave surface  94  of the spline  92 . The bolt  98  has a head  101  with a convex surface that is disposed outside the sidewall  84  opposite the concave surface  96  on the spline  92 . The bolt extends through holes in the sidewalls  94  and  96 , the spline  92  and the spacer  104 . 
     When the pipe joint  10  is assembled and the nut  102  is tightened on the bolt  98 , the relationship of the parts is as shown in FIGS. 1 and 3. Before the nut and bolt are tightened, the sidewalls  82  and  84  of the channel-shaped sector  58  are not seated against the spline  92 . When the nut  102  is tightened, the bolt head  101  and the spacer  104  are drawn together and press the sidewalls  82  and  84  into seating engagement with the spline  92 . Because of this tightening action, the roundish sector  76  is stretched around the sealing zone  22  of the pipe  14  in tight engagement therewith. This tightening action of the clamp  16  exerts sufficient force on the sealing zone  22  to compress the slot  24  and deform or distort the bridge  26 . 
     Although the description of this invention has been given with reference to particular embodiments, it is not to be construed in a limiting sense. Many variations and modifications will now occur to those skilled in the art. For a definition of the invention, reference is made to the appended claims.