In certain applications such as vehicle exhaust systems it is desired to provide a pipe joint with high pull-apart strength and with a good fluid seal between the pipes. It has become increasingly important, especially in connection with vehicle exhaust systems, to achieve greater reliability and uniformity in providing pipe couplings with a good fluid seal.
In the prior art, a pipe coupling which provides high strength and a good fluid seal has been provided by a pipe lap joint having a collapsible sealing zone and a band clamp as disclosed and claimed in Cassel U.S. Pat. No. 4,629,226 granted Dec. 16, 1986. In the lap joint of that patent, a collapsible sealing zone is provided in the outer pipe by at least one pair of intersecting end-to-end slots which afford 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. The clamping band is tightened around the outside pipe to clamp the pipes together and to collapse the sealing zone of the outer pipe into close fitting engagement with the inner pipe and thereby cause sealing engagement of the outer pipe with the inner pipe and with the band. The intersecting slots comprise an outboard slot and an inboard slot. The outboard slot has sidewalls extending inwardly from the end of the outside pipe and terminating in a transverse inner end wall within the overlap region of the pipes. The inboard slot is circumferentially offset from the outboard slot with sidewalls extending axially inwardly from an outer end wall. The adjacent sidewalls of the slots are in substantial alignment with each other and the end walls are in substantial alignment with each other. When the overlap region of the outer pipe is collapsed into close fitting engagement with the inner pipe, the end walls of the slots are moved into engagement with each other and thereby isolate the slots from each other and provide a seal.
The lap joint of the aforementioned U.S. Pat. No. 4,629,226 utilizes a pair of slots which intersect each other at adjacent corners with the outer pipe in an uncollapsed state. The inner pipe and outer pipe walls are telescoped together in a loose fit to form the lap joint. The manufacturing tolerances of the pipe diameters result in a large percentage of the mated pipes having a sufficiently loose fit that the outer pipe is collapsed sufficiently by the band clamp that the end walls of the slots are moved into engagement with each other to isolate the inboard and outboard slots. However, there is some small percentage of mating pipes in which the initial fit is so close that tightening of the band clamp causes very little collapse of the outer pipe before it is in close fitting engagement with the inner pipe and there is insufficient displacement to cause the edge-to-edge engagement of the end walls of the slots which is necessary to provide isolation between the two slots. This may lead to undesirable leakage in some of the pipe joints.
In the earlier prior art, it was known to use a collapsible sealing zone at the free end of the outer pipe which is collapsed into sealing engagement with the inner pipe by a clamping band. A pipe lap joint of this type is disclosed in Wagner et al. U.S. Pat. No. 4,113,289 granted Sep. 12, 1978. The collapsible sealing zone in the Wagner et al. patent comprises several sets of slots which are disposed circumferentially around the end of the outer pipe. In each set of slots there is an open slot which extends inwardly from the end of the pipe and an adjacent closed slot, i.e. one which does not extend to the end of the pipe. The difficulty with this sealing zone is that the slot structure exhibits a high resistance to collapsing and accommodates a relatively small amount of reduction in the circumference of the pipe at each set of slots.
A lap joint of the type using a collapsible sealing zone is also disclosed in Cassel U.S. Pat. No. 4,056,273. In the joint of this patent, a collapsible sealing ring forms an extension of the outer pipe but is separate from it. The sealing ring is split so as to form a tongue on each free end with the tongues having complementary ramp surfaces in engagement with each other and which slide relative to each other when the ring is contracted or collapsed. This sealing ring provides a good seal but the structure is not adapted to a sealing ring which is integral with the pipe end.
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.