Pipe lap joint with improved collapsible slot

A pipe lap joint is disclosed with an improved sealing zone structure in the overlap region of the pipes. The sealing zone comprises a serpentine 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. One sidewall of the slot defines an inwardly protruding tooth and the other sidewall defines another inwardly protruding tooth with a narrow passage between the teeth which is provided by rounded corners on the teeth. The slot also includes a bulbous end-wall which facilitates uniform collapse of the sealing zone. When the band clamp is tightened, the sealing zone is collapsed such that the two teeth engage each other and seal the serpentine slot against leakage.

FIELD OF THE INVENTION 
This invention relates to pipe couplings; more particularly, it relates to 
a pipe lap joint especially adapted for use in vehicle exhaust systems. 
BACKGROUND OF THE INVENTION 
In vehicle exhaust systems, it is desirable to provide a pipe joint with 
high pull-apart strength and with a good fluid seal between the pipes. It 
is becoming increasingly important to achieve greater reliability and 
uniformity in providing exhaust pipe couplings with a good fluid seal. 
In the Cassel U.S. Pat. No. 4,629,226, granted Dec. 16, 1986, a pipe lap 
joint is disclosed which provides a collapsible sealing zone in the outer 
pipe. This is achieved 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 the overlap region of the pipe 
ends. 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 with the adjacent sidewalls in 
substantial alignment with each other and with the inner end wall of the 
outboard slot 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 granted Dec. 31, 1996 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 the sealing zone within the overlap region 
of the pipe ends. With this construction, precise location of the adjacent 
corners of the slots is required and the sidewalls and end walls which 
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. 
In the prior art discussed above reliable and uniform fluid sealing is 
achieved in such joints. However, the production tooling requires punch 
and die sets which are subject to relatively short life due to the 
rectangular or acute angles of the corners of the slots in both the 
intersecting and non-intersecting slot designs. This results in 
undesirably high cost in punching the pipe ends to form the slots. 
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. 
SUMMARY OF THE INVENTION 
In accordance with this invention, a pipe lap joint is provided which 
exhibits good fluid sealing and pull-apart strength and which can be 
manufactured at low cost. 
Further, in accordance with this invention, a pipe lap joint is provided in 
which the overlap region of the outside pipe comprises a collapsible 
sealing zone with at least one serpentine slot extending from the end of 
the outer pipe to an inner end wall of the slot. The serpentine slot is 
open-ended at the end of the outer pipe and terminates in a closed end 
within the overlap region of the pipe ends. Further, in accordance with 
the invention, the serpentine slot terminates in a bulbous inner end. 
Preferably, in accordance with the invention, the slot has first and second 
sidewalls extending along the length of said outside pipe to an endwall, 
the first sidewall defines a first tooth protruding part way across said 
slot and the first tooth has a first side edge, a second side edge and a 
top edge, the second sidewall defines a second tooth protruding part way 
across said slot, and the second tooth having a first side edge, a second 
side edge and a top edge, the first side edge of the first tooth and the 
first side edge of the second tooth are substantially aligned and 
substantially parallel with each other, and the first side edge of the 
first tooth and the top edge of the first tooth are joined by a rounded 
corner, the first side edge of the second tooth and the top edge of the 
second tooth are joined by a rounded corner, whereby the first side edge 
of the first tooth and the first side edge of the second tooth are 
disposed in edge-to-edge engagement with each other when the overlap 
region of the outside pipe is collapsed into close fitting engagement with 
the inside pipe by clamping the band around said outside pipe. 
A complete understanding of this invention will be obtained from the 
detailed description that follows.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, there is shown an illustrative embodiment of 
the invention in a pipe lap joint which is especially adapted for use in 
vehicle exhaust systems. It will be appreciated as the description 
proceeds that the invention is useful in other embodiments and other 
applications. 
As shown in the drawings, the pipe joint 10 of this invention comprises, in 
general, inside and outside pipes 12 and 14, respectively, in a 
telescoping relationship and with a band clamp 16 for holding the pipes 
together and causing engagement thereof 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 as shown in FIG. 3. In order 
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 
collapsible sealing zone will be described presently. 
The sealing zone 22 comprises a ring-shaped portion of the free end of the 
outside pipe 14. It is adapted 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, an end portion of the outside pipe 14 is 
provided with a serpentine sealing slot 24. In the illustrative 
embodiment, only a single slot is used; however, in certain embodiments it 
may be desirable to use two or more slots spaced circumferentially around 
the pipe. 
The serpentine slot 24 is shown in the perspective view of FIG. 1 before 
the sealing zone is collapsed and in FIG. 2 after it is collapsed. The 
slot is shown in more detail in FIGS. 4 and 5. The serpentine slot has an 
open end at the end of the outer pipe 14 and it extends generally in the 
axial direction of the pipe to a closed end which is disposed within the 
sealing zone 22 on the outside pipe 14. The serpentine slot 24 is bounded 
by a pair of sidewalls 32 and 34 and a bulbous end wall 36. The serpentine 
slot 24 defines a sinuous passage from the bulbous end wall 36 to the open 
end of the slot at the end of the pipe. The sinuous passage is formed by a 
tooth 42 in the configuration of sidewall 34 and a tooth 44 in the 
configuration of the sidewall 32. The tooth 42 has an inboard edge 46 
which extends substantially perpendicularly to the axis of the pipe 14. 
The tooth 44 has an outboard edge 48 which extends substantially 
perpendicularly to the axis of pipe 14 and in alignment with edge 46 of 
tooth 42. The teeth 42 and 44 have free or end edges 52 and 54, 
respectively, which extend axially in substantial alignment with each 
other. The tooth 42 is provided with an outboard edge 56 which extends 
obliquely at an acute angle from the edge 52 to a juncture with an axially 
extending portion 62 of the sidewall 34 of the slot. The inboard edge 46 
of the tooth 42 forms a juncture with an axial portion 62' of the sidewall 
34. Tooth 44 is provided with an inboard edge 58 which extends obliquely 
at an acute angle from the end edge 54 to a juncture with an axially 
extending portion 64' of the sidewall 32 of the slot. 
The serpentine slot 24 is shaped to provide teeth 42 and 44 in a 
configuration which has no angular corners formed by straight lines 
meeting at a point; instead, each change of direction of the sidewalls 32 
and 34 is curvilinear to form the teeth. Such corners are referred to 
herein as "rounded" corners. Preferably, the rounded corners have a radius 
of about one-half millimeter or greater. The use of rounded corners on 
teeth 42 and 44, as opposed to angular corners, is effective to reduce the 
wear of the punch and die tooling so that a significant increase in the 
number of operating cycles is realized. 
It is noted that the rounded corners 66 and 68 on the teeth 42 and 44, 
respectively, form a narrow passage which will provide a fluid leakage 
path unless it is substantially closed by tightening the clamp 16, as will 
be described subsequently. 
The bulbous end wall 36 of the slot 24 facilitates the collapse of the 
sealing zone 18 under the force exerted by the clamp 16. The clearance 
provided by the bulbous end wall 36 allows the slot to close together 
uniformly along its length and thereby provides improved sealing. 
FIG. 5 shows a magnified view of the teeth 42 and 44 before the outer pipe 
is collapsed. FIG. 6 shows a magnified view of the teeth 44 with the outer 
pipe collapsed radially in tight engagement with the inner pipe 12 by the 
tightening of clamp 16. In this condition, the teeth 42 and 44 are in 
engagement with each other which seals the serpentine slot against 
significant leakage. 
Because of manufacturing tolerances on the sizes of the pipes 12 and 14, 
the clearance between two randomly selected pipes when the end of one is 
inserted into the end of the other will vary between a theoretical minimum 
and maximum. The amount of collapsing of the outer pipe by tightening the 
clamp 16 will thus vary from joint-to-joint. The dimensions of the slot 24 
are such that with pipes 12 and 14 having the tightest allowable fit 
within manufacturing tolerances, the radial contraction of the outside 
pipe 14 by tightening clamp 16 will be sufficient to close the slot by 
engagement of the teeth 42 and 44 with each other. It has been discovered 
that if the pipes can be manually telescoped together there will be a 
sufficient collapse of the outer pipe to displace the teeth 42 and 44 into 
engagement so that there will be no significant leakage. This occurs 
because a pair of pipes having the tightest allowable fit within the 
specified manufacturing tolerances cannot, as a practical matter, be 
telescoped together due to such factors as out-of-roundness or other 
irregularities in the shape or surfaces of the pipes. Thus, the sealing 
slot 24 will provide a good fluid seal between such pipes provided that 
the two pipes can be telescoped together by hand. In the case of pipes 12 
and 14 having the loosest allowable fit within manufacturing tolerances, 
sliding engagement of the teeth 42 and 44 with each other during radial 
contraction of pipe 14 will be allowed by the slot dimensions until the 
clamp 16 is fully tightened so that the outside pipe 14 is in tight 
engagement with the inside pipe 12. Thus the sealing slot 24 will provide 
a good fluid seal between two pipes having the loosest allowable fit. 
The preferred clamp for use with the invention will be described with 
reference to FIGS. 1, 2 and 3. The clamp 16 comprises a clamping band 72 
which 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 juncture of the teeth 42 and 44. 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 which comprises a pair of sidewalls 82 and 84 
extending radially outwardly from the roundish sector. The clamping band 
72 is made of a single piece of sheet metal and each free end thereof is 
folded back on itself to form a double layer. Thus, the sidewalls 82 and 
84 are of double thickness and terminate at their outer ends in respective 
loops or bights 86 and 88. The bights 86 and 88 serve as retaining members 
for holding the sidewalls in place when the tightening means 74 is 
tightened, as will be described subsequently. 
The clamping band 72 is tightened around the pipe 14 by the tightening 
means 74. The tightening means comprises a reaction member or spline 92 
which is disposed within the channel-shaped sector 78 and which is adapted 
to seat upon the outer surface of the sealing zone 22 of pipe 14. For this 
purpose, the spline has an inner surface of arcuate configuration 
conforming 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 which is opposite the 
concave surface 94 of the spline 92. The bolt 98 has a head 101 with a 
convex surface which 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. 2 and 4. It 
will be understood that, before the nut and bolt are tightened, the 
sidewalls 82 and 84 of the channel-shaped sector 78 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. As a result 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 collapse the 
sealing zone and thereby move the teeth 42 and 44 into engagement to seal 
the slot 24. 
Although the description of this invention has been given with reference to 
a particular embodiment it is not to be construed in a limiting sense. 
Many variations and modifications will now occur to those skilled in the 
art.