Metal working – Method of mechanical manufacture – Muffler – manifold or exhaust pipe making
Reexamination Certificate
1998-11-30
2002-02-26
Cuda Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Muffler, manifold or exhaust pipe making
C060S323000
Reexamination Certificate
active
06349468
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to an air gap insulated exhaust pipe with branch pipe stub and method of manufacturing same.
A method for manufacturing an exhaust pipe is known from German patent document DE 195 11 514 C1, corresponding to U.S. Pat. No. 5,682,741. This document teaches the manufacture of an exhaust pipe, insulated by an air gap, and provided with a branch stub in conjunction with a combination of several exhaust pipes to form an exhaust manifold with the outer jacket of the branched exhaust pipe consisting of two half-shells connected with one another being a common component of all the exhaust pipes of the exhaust manifold. Thus, the inner tubes of the exhaust pipes are initially pushed onto one another with a push fit and provided in a costly fashion with special spacing rings which later evaporate after assembly during the operation of the exhaust system. The plug connection is then inserted into a lower shell of the outer jacket and positioned in an awkward fashion. Since the individual tubes which are subject to manufacturing tolerances are displaceable with respect to one another and have different insertion lengths from one plug-in connection to the next plug-in connection because of the assembly work, and the spacing rings are themselves subject to manufacturing tolerances and also, because of their design relative to the shape of the lower shells, rarely abut the latter circumferentially, the manufacture of the entire exhaust manifold is subject to tolerances due to these factors alone. There is no such thing as exact reproducibility.
It is important to observe during assembly that a certain minimum insertion length is maintained so that the individual internal tubes do not slide apart. This retention requires visual estimation and hence considerable effort. During the transfer of the parts to the welding station, vibrations and centrifugal forces can likewise occur that can lead to additional displacement of the individual inner tubes with respect to one another and with respect to the lower shell of the outer jacket, which can lead to the plug-in connection coming apart. The transposition of the troublesome positioning of the inner tubes in the lower shell of the outer jacket by means of the spacing rings and the tolerances resulting from manufacturing technology in the design of the inner tubes as well as the different associated relative positions of the inner tube inside and outside the outer jacket to the outer jacket, an individual branched inner tube with an outer jacket consisting of two half-shells can be produced in simple fashion. The inner tube with the branched stub with the stated manufacturing tolerances is never located inside the outer jacket with the desired defined circumferential air gap.
Due to the delayed rebound of the two sheet-metal half-shells following deep drawing, the two half-shells do not abut one another continuously tightly and thus gap-free. Therefore, in the welding station, the upper shell of the outer jacket is placed on the lower shell and pressed against the latter. In this situation as well, there are vibrations of the plug-in connection and/or displacement of the relative position of the branched inner tube in the outer jacket. Finally, the shells of the outer jacket are laser-welded to one another. After the pressure is relieved, because of the nonuniformity of the contact surfaces of the half-shells, considerable tensile forces act on the welded seam, which reduces the long-term load-carrying capacity of the assembly, especially of the outer jacket, and can result in failure of the part during operation of the exhaust line.
In addition, the welding of the half-shells to form a crimped seam is relatively awkward, especially since at the transition to the cutout in the outer jacket for the branch stub of the inner tube, because of the edge radii, a triangular gore results which must be welded for processing safety, which in practice logically takes place only with the assistance of an additional material. In addition, the crimped seam can also be subjected only to limited mechanical loading due to its design. To secure the inner tube to the outer jacket, a weld is also required that forms a round seam, in other words, a circumferential hollow weld in the end area of the branch stub, with the end of the inner tube of the stub being slightly recessed relative to the opening of the outer jacket. The outer jacket is also designed to project considerably into space because of the branched exhaust pipe, which, during the manufacture of the half-shells by deep-drawing, cannot achieve branching and thus is not suitable for a defined formation of an outer jacket relative to the design of the inner tube. However, this requires considerable space and increases the weight of the branched exhaust pipe. In addition, the design of a defined, uniformly constant air gap with a branched exhaust pipe cannot be achieved by this design.
A goal of the invention is to improve on a method of manufacturing an exhaust pipe that an air-gap-insulated exhaust pipe with a branch stub can be manufactured exactly reproducibly in simple fashion, and which can easily be built up without adversely affecting the dimensional accuracy of the width of the air gap and the position of the inner tube relative to the outer jacket.
This and other goals have been achieved according to the present invention by providing a method for producing an air-gap-insulated exhaust pipe with a branch stub for a vehicle exhaust line having an inner tube with a branch for carrying exhaust surrounded at a distance by an outer jacket to form an insulating air gap, said method comprising: providing two tubes having a corresponding shape, inserting said tubes into one another with limited play to form a double tube, placing said double tube in a first internal high-pressure shaping tool having a first engraving including a branch, sealing off both ends of said double tube to be tight to a high-pressure fluid, closing the first shaping tool and introducing a pressure fluid into an interior of the inner tube of the double tube such that the double tube expands to match the contours of the first engraving to form a shaped double tube including a double-walled branch stub blown out of the double tube into the branch, relieving the pressure fluid in the first shaping tool, removing the shaped double tube from the first shaping tool, placing the shaped double tube in a second internal high-pressure shaping tool having a second engraving which holds the shaped double tube at axial end areas in a fit with play, the second engraving being spaced apart from the shaped double tube between the axial end areas including the branch stub to define an expansion chamber, closing the second shaping tool and introducing a pressure fluid between the two tubes that form the shaped double tube and simultaneously into the interior of the inner tube, such that the outer tube expands into said expansion chamber and engages said second engraving of the second shaping tool to define an insulating air gap between the outer tube and the inner tube, an end of the branch stub facing away from the rest of the double tube being externally supported without yielding via a second tool counterpunch located in a branch of said second engraving, relieving the pressure fluid in the second shaping tool, removing the finished double tube from the second shaping tool, and cutting off a cap area at the end of the branch stub to form a through opening between the interior of the inner tube and the outside of the air-gap-insulated exhaust pipe.
This and other goals have been achieved according to the present invention by providing a method for producing an air-gap-insulated exhaust pipe with a branch by internal high-pressure forming, said method comprising: placing an inner tube inside of an outer tube to form a double tube; placing said double tube in a first internal high-pressure shaping tool having a first engraving including a branch; forming an intermediate shaped double tube by
Bonny Pierre
Huelsberg Thomas
Crowell & Moring LLP
Cuda Rosenbaum I
Daimler-Chrysler AG
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