EP0919704B1 - Method for manufacturing an air gap insulated exhaust pipe junction - Google Patents

Description

The invention relates to a method for producing a an air gap insulated exhaust pipe provided with a branch pipe according to the preamble of claim 1.

A generic method is known from DE 195 11 514 C1. This includes the manufacture of an air-gap insulated exhaust pipe with a branch pipe in connection with a Assembly of several exhaust pipes to form an exhaust manifold, the one consisting of two interconnected half shells existing outer jacket of the branched exhaust pipe common Part of all exhaust pipes of the exhaust manifold is. So the inner pipes of the exhaust pipes are first fitted with a sliding seat put on top of each other and in a complex way with special Spacer rings, which later in the operation after assembly evaporate from the exhaust system. The plug-in will then placed in a lower shell of the outer casing and in more elaborate Positioned way. Because, on the one hand, those with manufacturing tolerances afflicted individual tubes are displaceable against each other and due to the assembly work from connector to connector have different insertion lengths and on the other hand the Spacers, on the one hand, are subject to manufacturing tolerances and because of their design, they are relative to training the lower shell rarely fits all around it, the production of the entire exhaust manifold is already under subject to tolerances. Exact reproducibility there is no such thing. This is during assembly to ensure that a certain minimum insertion length is observed so that the individual inner tubes do not slide apart. This compliance requires a sense of proportion and therefore considerable Expenditure. When transferring parts to the welding station vibrations and centrifugal forces also occur, the one to another shift of the individual inner tubes to each other and to the lower shell of the outer jacket, this even can lead to the disassembly of the connector. The transposition the complex positioning of the inner tubes in the lower shell of the outer jacket by means of the spacer rings and the manufacturing-related tolerances in the inner tube formation as well as the associated from assembly to assembly different relative positions of the inner ear in each and outside of the outer shell to the outer shell can be without further on a single branched inner tube with one out Execute two outer shells. The inner tube with the branch pipe is within the stated manufacturing tolerances practically never with the desired defined revolving Air gap inside the outer jacket. Because of the springback delay of the two sheet metal half-shells after deep drawing the two half-shells are not continuous on their own full and therefore gap-free. In the welding station is therefore the upper shell of the outer shell on the lower shell set and pressed against this. This also causes vibrations the plug connection or the displacement of the relative position of the shown inner tube in the outer jacket. Finally the shells of the outer jacket are laser welded together. After releasing the contact then act the non-uniformity of the contact surfaces of the half-shells the weld seam has considerable tensile forces, which makes it durable assembly, especially the outer jacket and even failure of the component during operation of the exhaust line can lead. Also the welding of the half shells to form a flared seam relatively expensive, in particular, because at the transition to the cutout of the outer jacket for the branch connector of the inner tube due to edge radii Triangular gusset is created, which is welded closed for process reliability must be what in practice only makes sense with the help of a filler material. The flared seam is also also limited mechanical strength due to their design. For the fixing of the inner tube on the outer jacket is additional a weld to form a circular seam, i.e. one all-round fillet weld required in the end area of the branch connector, the end of the inner tube of the nozzle opposite the opening of the outer casing is set back somewhat. The outer jacket is just because of the branched exhaust pipe spatially very expansive, which in the manufacture the half-shells did not branch out by deep drawing can be and thus for a contoured training of a Outer jacket with regard to the design of the inner tube is not is suitable. However, this requires considerable space and increases the weight of the branched exhaust pipe. In addition, this is the formation of a defined uniformly uniform Air gap cannot be reached in the branched exhaust pipe.

WO 95/31635 A1 describes the production of an exhaust manifold known, which is bent from a tube end, the curved ends serve as inlets that are at the outlets of the Cylinder head are attached. The straight pipe blank becomes by means of fluidic internal high pressure in a corresponding Tool formed a branch that the outlet of the exhaust manifold represents and is connected to the further exhaust line. During the molding process, tube material ends up in the forming area of the branch additionally pushed axially.

Finally, US 5,363,544 shows the production of a curved one Exhaust pipe from a double pipe, being in a two-stage Process by means of internal high pressure the outer pipe of the double pipe is expanded to form an air gap.

The invention has for its object a generic To further develop methods in a simple manner an air gap-insulated exhaust pipe with a branch connector exactly can be produced reproducibly, which is easy to install is without affecting the dimensional accuracy with regard to Air gap width and the relative position of the inner tube to the outer jacket.

The task is according to the invention by the features of the claim 1 solved.

Thanks to the invention is a simple manufacture of the branched Exhaust pipe made of two nested welded or drawn and, if necessary, pre-bent double tubes cut to length from the rod possible. A complex deep drawing of half-shells, that form the outer jacket, as well as the very complicated welding of the two half shells, especially in the transition of the Flare seam to the circular seam in the area of the branch connector, in which Transition occurs due to edge radii a gusset to ensure the durability of the weld can only be welded with filler material. Of there is also no faulty and tolerance-prone assembly Assembly of the exhaust pipe necessary, rather that Relative position of the two nested pipes to each other after the first deformation due to the clamping at the end of the pipes fixed to each other. Can on spacer rings to be dispensed with, since the air insulation gap does not a suitable installation of the inner tube in the outer jacket, but due to the second forming of the double tube from comes about itself. As a result of the fixed non-movable Relative position of the two tubes after the first forming to each other and the dependencies of the air insulation gap width only from the engraving design and completeness the forming, both of which are easily controllable ensures a constant gap width in a simple manner. Because of the fact that the branch pipe from a double-walled from inner tube and outer tube - the later outer jacket - existing pipe during the first hydroforming process is formed, the outer tube arises due to the process conform to the inner tube. As a result, the branched exhaust pipe and thus across the entire exhaust line of deep-drawn half-shells construction space, material and weight saved. Due to the contour of the outer tube can measure the length of the branch connector relatively short be so that when connecting the branched exhaust pipe further exhaust line components in the area of the branch connector one Compacting, i.e. gaining space for this assembly can be achieved. The branched according to the invention is also Exhaust pipe more durable than the conventional solutions because the exhaust pipe only at the connection points to others Components of the exhaust system during the welding process receives which in a simple manner in the form of revolving mechanically highly resilient fillet welds can be formed. The failure-prone flared seams in the well-known exhaust pipe omitted. Finally, due to the process the freedom from tolerance associated with hydroforming enables exact reproducibility of the branched exhaust pipe and thus automation of exhaust pipe production relieved without touching up. Because of the clamp the single pipe walls on both exhaust pipe ends can do that Exhaust pipe can be easily coupled to other components there, without the relative position of the inner tube to the outer tube and the The gap width changes. At the end of the branch connector, this can be done Inner tube - if desired - in a simple way to another Inner pipe of another air-gap insulated exhaust pipe be plugged in and remain there in the sliding seat, while the outer pipes of the two exhaust pipes are easier to form circumferential fillet welds are welded together. The exhaust pipe according to the invention is therefore due to its space advantages and its hassle-free and safe or fast to enable connection to other components of the exhaust system easy to install.

Fig. 1 in einer seitlichen Ansicht einen ersten Schritt des erfindungsgemäßen Verfahrens beim Ineinanderstecken zweier Rohre, wobei das innere Rohr gelocht ist,

Fig. 2 in einem seitlichen Längsschnitt den Steckverbund aus Fig .1 in einem ersten Innenhochdruck-Umformwerkzeug eingelegt, wobei das Doppelrohr und die Lochung des Innenrohres abgedichtet ist, vor der Umformung im entspannten Druckzustand des in das Innenrohr eingeleiteten Druckfluides,

Fig. 3 in einem seitlichen Längsschnitt das Doppelrohr im Umformwerkzeug aus Fig. 2, an dem unter Innenhochdruck ein Abzweigstutzen mit flaschenhalsförmigem Ende ausgeformt ist,

Fig. 4 in einem seitlichen Längsschnitt das umgeformte Doppelrohr aus Fig. 3 in einem zweiten Innenhochdruck-Umformwerkzeug nach einer zweiten Umformung unter Innenhochdruck, wobei die Lochung des Innenrohres unabgedichtet bleibt und zwischen dem Innen- und Außenrohr des Doppelrohres ein Luftspalt ausgebildet ist, der sich bis zum Flaschenhals des Abzweigstutzens erstreckt,

Fig. 5 in einer perspektivischen Ansicht einen Endabschnitt des Doppelrohres aus Fig. 4 mit Beschnittstreifen des Außenrohres nach Durchtrennung des Innenrohres,

Fig. 6 in einem seitlichen Längsschnitt das gemäß den Verfahrensschritten aus den Fig. 1-5 fertighergestellte luftspaltisolierte Abgasrohr mit Abzweigstutzen nach einem Kappenbeschnitt des Abzweigstutzens.

Expedient embodiments of the invention can be found in the subclaims; otherwise the invention is explained in more detail below with reference to an embodiment shown in the drawings; shows:

1 is a side view of a first step of the method according to the invention when two tubes are inserted into one another, the inner tube being perforated,

2 in a lateral longitudinal section, the plug-in assembly from FIG. 1 is inserted in a first internal high-pressure forming tool, the double tube and the perforation of the inner tube being sealed, before the deformation in the relaxed pressure state of the pressure fluid introduced into the inner tube,

3 in a lateral longitudinal section the double tube in the forming tool from FIG. 2, on which a branch connector with a bottle neck-shaped end is formed under high internal pressure,

Fig. 4 in a lateral longitudinal section, the formed double tube from Fig. 3 in a second hydroforming tool after a second forming under internal high pressure, the perforation of the inner tube remains unsealed and an air gap is formed between the inner and outer tube of the double tube extends to the bottle neck of the branch connector,

5 shows a perspective view of an end section of the double tube from FIG. 4 with trimming strips of the outer tube after severing the inner tube,

Fig. 6 in a lateral longitudinal section, the air gap-insulated exhaust pipe with the branch connector, which is produced according to the method steps from Figs. 1-5, after a cap trimming of the branch connector.

In Fig. 1 are two straight tubes of equal length shown with an approximately circular cross-section, the one tube, the inner tube 1, in the other tube, the outer tube 2, with complete coverage of the inner tube 1 with little Game in the direction of the arrow. The inner tube 1 has at both ends 3.4 over the circumference evenly each distributes a ring of holes 5 with through holes 6. The two tubes 1 and 2 can also be bent and one of the Circular cross-section have a different cross-section, however they must be pluggable.

After the formation of a plug-in connection of the two pipes 1 and 2, they become a double tube in the engraving 7 of a first internal high-pressure forming tool 8 inserted according to FIG. 2. This has a radial branch 9 from the engraving 7, in which a Counterstamp 10 is performed. The face 11 of the counter-stamp 10, which has a pocket 12 in the middle, lies flush with Engraving 7 and before the first forming of the double pipe on this true to the contour. The double tube is used for forming at both ends by means of two sealing heads 13 which are in the ends of the double pipe be pushed in and each with an axial punch are rigidly connected, sealed. The sealing head protrudes 13 with a conically tapering in the direction of insertion Section 14 so far into the double tube that the Perforated ring 5 of the inner tube 1 is covered. The conical section 14 of the sealing head 13 carries on branch facing Side of the rim 5 a radially expandable sealing element 15, for example an elastic O-ring used for sealing with high force fluid high pressure sealing on the inside 16 of the inner tube 1 is pressed. On branch facing away Side of the rim 5 is the circumference of the conical section 14 dimensioned larger than the inner circumference of the inner tube 1, so that the double pipe there when inserting the sealing head 13 to form a radially acting metallic seal is squeezed radially for the double tube. At the same time thereby the inner tube 1 with the outer tube 2 their relative position clamped to each other or pressed together. The sealing head 13 points at the end of the conical section facing away from the branch 14 an annular collar 17, in the use position of the sealing head 13 on the end face 18 of the double pipe abuts, creating an axial seal for the double tube becomes.

After closing the first hydroforming tool 8 is a pressure fluid over one in the axial punch and the associated Sealing head 13 extending pressure fluid channel 19 in the Interior 20 of the inner tube 1 initiated and under high pressure set. According to Fig. 3, the double tube expands, which double-walled tube material in the pocket 12 of the counter stamp 10 is pushed into it. Simultaneously or subsequently gives way the first counter-punch 10 by means of a controllable hydraulic cylinder checked out in branch 9, whereby by means of the internal high pressure from the double pipe a double wall Branch connector 21 is blown out, which end is supported by the counter-punch 10 and laterally on the Wall of the branch 9 hugs the shape. Through the counter stamp 10 is a reliable blowout of the branch connector 21 guaranteed, due to the high pressure counteracting pent-up force of the counter stamp 10 the pipe material of the double pipe to the branch wall is pressed, resulting in a corresponding to the first engraving 7 true-to-shape shaping of the branch connector 21 with high outer contour quality leads. This results in a defined reproducibility Connection to other components of the exhaust system.

Because of the central pocket formed in the counter stamp 10 12 becomes the end face 22 of the double-walled branch connector 21 bulging like a bottle neck due to the internal high pressure. As a result this bulge 31 of the end face 22 is a radial clamping the walls of inner tube 1 and outer tube 2 also there, namely reached at the end of branch connector 21, after which despite later trimming of the cap area 23 of the end face 22 of the branch connector 21 by the clamping the positioning of the inner tube 1 to the outer tube 2 is fixed, even if the Ends of the double tube are already trimmed. With that the Uniformity of the gap width of the air insulation gap created later secured. If there is a fixed connection of the branch connector 21 reached with another component of the exhaust system should favor the formation of the end face 22nd After trimming, a simple assembly of the air gap insulated Exhaust pipe through the flushness of the adjacent pipe walls.

The process reliability during the first forming process becomes significant promoted by sufficient supply of pipe material. By Introduction of an axial force on the pipe ends of the double pipe by means of the axial ram over the on the front side 18 of the Double pipe ring collar 17 of the sealing heads 13 can Pipe material of the double pipe to branch 9, i.e. the location of the greatest degree of deformation are pushed. With the variable The amount of pushing force to be set can be adjusted as required the blow-out length changes reliably within certain limits be, whereby a high adaptability of the exhaust pipe to the each different available space conditions achieved can be. It is done safely by pushing no noticeable thinning of the wall thickness, which makes good Installation conditions when connecting to another component is guaranteed. If the pipe material is not added, so it is definitely in the interest of process security, in particular the tightness of the forming device is essential, that the axial punch with the sealing heads according the shortening resulting from the shaping of the branch connector 21 of the double pipe must be tracked.

After the double-walled branch connector 21 has been formed the originally unbranched double pipe through the first hydroforming process the pressure fluid is released and out led out of the branched double pipe, after which the first forming tool 8 is opened and the branched double tube is removed becomes.

Then it is engraved 24 of a second hydroforming tool 25 inserted. The engraving 24 is such trained that the double tube at its end portions of the Engraving 24 held in a game fit and between the two Ends all around and consistently of one cylindrical expansion coaxial to the double tube 26 surrounded is. The branch connector 21 is located in a branch 27 of the engraving 24, which corresponds to the expansion space 26 by approximately the same Dimension surrounds the branch connector 21. Branch 27 is a second counter-stamp 28 arranged, in its end face 29 corresponding to the counter punch 10 of the first forming tool 8 trained pocket 34 the bottle neck-like Bulge 31 of the branch connector 21 added with little play is.

The now following second forming process according to FIG. 4 is the forming tool 25 closed and the double pipe on again both ends through sealing heads 30 of axial punches forming a metallic seal and crushing the Sealed pipe ends, but in such a way that the ring of holes 5 one Internal high pressure remains freely accessible. about Pressurized fluid channels 32 are now in the interior 20 of the inner tube 1 a pressure fluid is introduced and placed under high pressure.

Due to the free perforated ring 5, the outer tube 2 is direct pressurized, causing it to expand into the expansion space 26 is expanded into and engages in the engraving 24 of the forming tool 25 and the wall of the branch 27 in line with the contour invests. The counter-punch 28 is relentlessly supported on the outside and thus remains unchanged during the expansion its support position without evading radially outwards, whereby the not bulged area of the end face 22 of the branch connector 21 on the facing end face 29 of the counter-stamp 28 creates.

The second deformation of the exhaust pipe results in the lifting the outer tube 2 from the inner tube 1 this one evenly between the pinched ends all around surrounding gap, the So-called air insulation gap 33, which is in its Width is dimensioned completely constant, being in its course the contour of the inner tube 1 follows exactly. The inner tube 1 remains between its interior due to the pressure equalization 20 and the gap 33 undeformed during the second forming.

It is also conceivable to design the inner tube 1 without a rim 5 and the pressure fluid in the joint between inner tube 1 and Outer tube 2 over the play gap or especially for this on the inner tube 1 trained columns in the parting line. However, an upstream pressure chamber is necessary for this, what space and a more complicated sealing of the double pipe requires. Through the rim 5, however, in most advantageously an easy to manufacture and immediate relatively large-area exposure to the outer tube 2 achieved by high pressure. Furthermore, the end areas experience of the double pipe no deformation in the event of any Introducing the pressure fluid into the joint of the two pipes 1 and 2 from the outside, so that the dimensional accuracy of the double pipe both ends is preserved, which is particularly beneficial for a connection with other components affects. Finally is the pressure compensation for the inner tube 1 by a simple achieved in the formation of the rim 5 fluid guidance.

After the second forming, the pressure fluid is released from the almost finished air gap insulated exhaust pipe led out, after which the second forming tool 25 is opened and the exhaust pipe is removed. After that, in a tool clamping of the deformed exhaust pipe, the cap region 23 of the branch connector 21 to form a through opening 35, the interior 20 of the inner tube 1 with the external environment of the air-gap insulated exhaust pipe connects, for example cut off by sawing or laser cutting. by virtue of the bottle neck-like design of the end face 22 then remains a short cylindrical portion 36 in which a clamping of the tube walls is still present, so that too after trimming, no change in the relative position of the inner tube 1 to the outer tube 2 can be done.

Finally, the ends of the double pipe are optionally in the Clamping separated. This happens when there is a minimization of thermal bridges in the connection area with other exhaust pipes is desired and this with respect to the outer tube 2 a simple all-round fillet weld and with respect to the inner tube 1 by means of a sliding seat to compensate for axial thermal expansion and vibrations in the operation of the exhaust system shall be. This connection can be done in a most advantageous manner to assemble an air-gap-insulated exhaust system with other air-gap insulated exhaust pipes by simply plugging them together the diameter of which is matched to one another at the end Pipes are used. In particular, the Formation of the branched exhaust pipe produced according to the invention with its end trim (Fig. 6) for the first time a modular design for air-gap-insulated exhaust manifolds, wherein the branched tube forms part of the exhaust manifold. The remaining clamp of the cylindrical portion 36 the end face 22 holds the tubes 1 and 2 to each other in the previous spaced apart position, whereby at the Mounting tolerances and gap non-uniformities be avoided. This can also be achieved if the End face 22 no bulge 31, i.e. after trimming none cylindrical section 36 and thus no clamping of the walls of tubes 1 and 2. However, this must be done after trimming the cap area 23 of the branch connector 21 with respect Inner tube 1 and outer tube 2 by connecting the exhaust pipe at the end of branch 21 with another Component of the exhaust system, for example by welding of the outer tube 2 with the outer tube of the connecting component and Sliding seat formation of the inner tube 1 with its inner tube be set radially, after which the exposed end areas of the exhaust pipe with the walls clamped together there the inner tube 1 and the outer tube 2 cut off become.

To cut the pipe ends, these are on the outer pipe 2 branch-facing side of the rim 5 by means of a Beam cutting process, preferably by a cutting laser applied. The cutting laser cuts the outer tube Formation of a slot axially on two circumferentially diametrically opposed Hire. Then the outer tube 2 by means of the irradiation of the cutting laser two spaced apart Performed circumferential cuts, each by a of the end points of the axial slots. The result protruding semicircular metal strips 37 of the outer tube 2 are detached, making the inner tube 1 freely accessible becomes. The inner tube 1 can now - if necessary flush with the cutting edge 38 of the outer tube 2 - by sawing or also by a beam cutting process, for example laser or electron beam are severed (Fig. 5). Beam cutting of the outer tube 2 advantageously provides a total true-to-shape separation of the ends of the double pipe.

Of course, it is conceivable that after the cap trim of the branch connector 21 outer tube 2 and inner tube 1 are open, wherein the ends of the double tube remain jammed together, so that the centering of the inner tube by the clamping there 1 in the outer tube 2 is guaranteed. Another connection with Exhaust pipes at the ends are made by welding to the Double wall of the branched pipe.

Claims (6)

1. Method of manufacturing an air gap insulated exhaust pipe provided with a branch connection in the exhaust train of a motor vehicle wherein an exhaust gas guiding inner pipe formed with a branch is surrounded at a distance around it with an outer shell with the formation of an air insulation column which together with the outer shell forms the exhaust pipe including branch conenctor
   characterised in that
   for the purpose of forming the exhaust pipe two pipes ( 1, 2) having the same shape are placed inside each other with little clearance with the formation of a double pipe, that the thus formed double pipe is brought into a first inner high pressure shaping tool 8), is at both ends fluid high pressure sealed and after closure of the first shaping tool (8) and introduction of a pressure fluid into the inner area (20) of the inner pipe (1) of the double pipe is impacted with inner high pressure via the introduced pressure fluid in such a way that the double pipe widens corresponding to the contour of the engraving (7) of the first shaping tool (8) wherein due to a branch (9) of the engraving (7) by means of the inner high pressure from the double pipe a double walled branch connection (21) is blown out and wherein due to a concentric pocket (12) formed in the counterpunch (10) the front side (22) of the double walled branch connection (21) is bulged like the neck of a bottle through the inner high pressure, that after the production of the branch connection (21) the pressure fluid relaxes and is fed out of the inner area (20 of the inner pipe (1) and thereafter the first shaping tool (8) is opened and the shaped double pipe is removed and brought into a second inner high pressure shaping tool (25) wherein the double pipe at the end areas of the engraving (24) of the second shaping tool (25) is held in a clearance fit and running between the two ends including the branch connection (21) and through corresponding formation of the engraving (24) is surround by a widening area (26), that after the closure of the shaping tool (25) and sealing of the double pipe formed with a branch connection under high pressure a pressure fluid is passed on the one hand between the two pipes (1, 2) forming the double pipe and is on the other hand simultaneously fed into the inner area (20) of the inner pipe (1) wherein the outer pipe (2) is widened in an inner high pressure impacted way until contour positioned against the engraving (24) of the second shaping tool (25) into the widening area, that upon widening the front side of the branch connection (21) guiding from the double pipe by means of a second counterpunch (28) arranged in the branch (27) of the engraving (24) is outwardly supported in an unyielding way, and that after the widening of the double pipe, relaxing and removal of the pressure fluid out of the double pipe which due to the two reshapings is provided with a branch connection (21) and an air column isolation, as well as opening of the second shaping tool (25) and removal of the finished shaped double pipe wherein the outer shell is formed by the outer pipe (2) which the cap area (23) of the branch connection (21) containing the front side (22) ... with the formation of a through passage (35) between the inner area (20) of the inner pipe (1) and the outer surroundings of the air column isolating exhaust gas pipe.
2. Method according to claim 1
   characterised in that
   after a radial fixing of inner pipe (1) and outer pipe (2) based upon the connection of the exhaust pipe at the end of the branch connection (21) with a further component of the exhaust train the free-lying end areas of the exhaust gas pipes are cut off with the walls of the inner pipe (1) and the outer pipe (2) pressing against each other in a pressed way.
3. Method according to claim 2
   characterised in that for the purpose of cutting off the end areas of the exhaust pipe on the outer pipe (2) around the entire perimeter perimeter strips (37) are cut out by means of beam cutting and that afterwards the inner pipe (1) is separated in the area made free after removal of the strips (37) through sawing or beam cutting.
4. Method according to claim 1
   characterised in that for the purpose of forming the air isolating column (33) the pressure fluid is guided from the inner area (20) of the inner pipe (1) through at least one passage hole (6) formed in the wall of the inner pipe (1) between the pipes (1, 2) forming the double pipe wherein the respective hole (6) in the widening of the double piepe is sealed in the first inner high pressure shaping tool (8).
5. Method according to claim 1
   characterised in that during the first shaping process the double walled branch connection (21) is supported on the front side by means of a first counterpunch (10) giving way outwards and guided in a displaceable way in the branch (9) of the engraving (7) of the first inner high pressure shaping tool (8).
6. Method according to claim 1
   characterised in that during the first shaping process for blowing out the branch connection (21) pipe material is pushed by means of at least one axial punch impacting one end of the double pipe to the formation point of the branch connection (21).

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