EP0623739A1 - Manifold - Google Patents

Abstract

The invention relates to a manifold (double manifold 1) for internal combustion engines with a tubular body (2, 3) produced by a metal forming process. Its open end can be connected to apertures (4 to 7) of a flange (8) on the engine-side. The wall of the tubular body has a collecting aperture, which faces a flange (11) on the exhaust side. In order to increase the fatigue strength of manifolds of this type, it is proposed to manufacture their tubular bodies (2, 3) in one part with different wall thickness by means of internal high pressure metal forming. At the same time, a pipe union leading from the collecting aperture to the aperture of the flange (9, 10) on the exhaust side is directly formed on. <IMAGE>

Description

The invention relates to a pipe bend according to the preamble of patent claim 1.

A generic pipe elbow has become known from EP-0321869-A1 (F01N7 / 10). This shows an arcuate tubular body, which is produced from a cylindrical tube piece by a forming process, not described in detail. With its open ends, this tubular body is connected to the outlet openings of an internal combustion engine via flange bodies. A collection opening is provided on a side of the pipe jacket facing away from the engine, to which a pipe socket leading to an exhaust-side flange is welded. Compared to the pipe elbows known up to now in the prior art, this construction is particularly advantageous because the weld seams required for the assembly of the pipe elbow have been relocated to low-stress areas.

The invention has for its object to further optimize a generic elbow with regard to its fatigue strength.

This object is achieved by the characterizing features of patent claim 1. The subclaims contain particularly expedient developments of the invention.

According to the invention, the pipe bend is made in one piece by internal high-pressure forming, including pipe sockets, and has walls whose wall thicknesses correspond to the respective flanges on the motor or. Increase exhaust side towards each. The one-piece design of the tubular body means that welding processes are no longer required. This not only simplifies production, but also significantly increases the fatigue strength. The hydroforming process, also known as hydroforming, also allows highly reproducible fine tolerances and ensures high fatigue strength because no longitudinal stresses occur in the component itself and, depending on the process control, the material structure can be strengthened and a stiffening effect can be achieved. It should also be emphasized that wrinkle-free tubular bodies can be produced, in the walls of which the fiber course is undisturbed.

Internal hydroforming is generally known, for example, from the magazine "Blech, Rohr, Profile" (see in particular the 1988 vintage, pages 175 to 180, and the 1981 vintage, pages 54 to 57). There, however, only basic application possibilities for hydroforming are shown using the example of simple pipe geometries. The reference to the manufacture of exhaust pipes in the summary of the last article also indicates in connection with the chapter "Application aspects" in the first article that so far only the production of relatively simple rotationally and axially symmetrical pipe part shapes has been considered. However, references to complicated geometries, such as are common with pipe elbows, cannot be found in these publications.

Of particular importance for the invention is the setting of different wall thicknesses along the tube body. The increase in wall thickness towards the flanges means that more material is placed in the ends of the tubular body. As a result, the wall thickness transitions on the flange are reduced, which is particularly important for heat management during welding. The compared to that However, thinner wall thicknesses in the middle regions of the tubular body also cause it to become more elastic and thus to better compensate for relative movements between the internal combustion engine and the exhaust system, which are generally subject to strong periodic fluctuations.

A further development according to the invention deserves special attention, according to which, starting from a circular cross section at the ends of the tubular bodies, the central regions have an approximately elliptical cross section. The smaller of the ellipse axes runs approximately perpendicular to the bending axis of the tubular body. In this way, for example, the pre-deformation of the tubular body before the application of hydraulic medium can be made considerably easier. The circular ends allow use in flanges, the openings of which can be made by simple drilling operations.

In a development of the invention according to claim 4, a tulip plate is arranged between the molded pipe socket and the opening of the exhaust-side flange, which is frictionally connected to one of the aforementioned components and can thus compensate for relative movements generated by thermal stresses or mechanical fluctuations. The method steps specified in claims 5 to 7 not only enable the pipe bend according to the invention to be shaped in a manner which is particularly stress-resistant, but also provide information on the most rational possible production thereof.

Figur 1:

einen erfindungsgemäßen Rohrkrümmer mit einer Draufsicht auf einen motorseitigen Flansch,

Figur 2:

den Querschnitt durch Rohre des Rohrkrümmers gemäß den Schnitten II-II in Figur 1,

Figur 3:

einen erfindungsgemäßen Rohrkrümmer mit einer Draufsicht auf einen auspuffseitigen Flansch,

Figur 4:

einen vorgebogenen Rohrrohling in einem Werkzeug zur Innenhochdruckumformung.

A particularly advantageous embodiment of the invention is shown in the drawing. It shows

Figure 1:

a pipe elbow according to the invention with a plan view of a motor-side flange,

Figure 2:

the cross section through pipes of the pipe bend according to the sections II-II in Figure 1,

Figure 3:

a pipe bend according to the invention with a plan view of an exhaust side flange,

Figure 4:

a pre-bent pipe blank in a tool for hydroforming.

The same components are numbered the same in all figures.

One can see in FIG. 1 a double pipe bend 1, which here essentially has two pipe bodies 2, 3 which protrude with openings 2.1, 2.2 or 3.1, 3.2 into openings 4 to 7 of a motor-side flange 8. On the tubular body 2, 3 molded pipe sockets 2.3 and 3.3 protrude into openings 9, 10 of an exhaust-side flange 11. Also of importance here are tulip plates 12 and 13, which are attached to their edges at the edges by means of a weld, not shown, on the tubular bodies 2 and 3 and the pipe sockets 2.3 and 3.3 are held in a frictionally locking manner in the openings 9 and 10. The open ends 2.1, 2.2 or 3.1, 3.2 are connected to the motor-side flange 8 by means of circumferential sealing welds on the end face of the pipe ends.

The construction of the double pipe elbow shown in FIG. 1 is essentially comparable to that of DE-29 35 926-A1 (F01N7 / 08). In the case of a four-cylinder in-line engine, this design is particularly expedient with an ignition sequence of 1, 3, 4, 2 or 1, 2, 4, 3 and also enables a space-saving design.

In Figure 2 it is shown that the originally circular cross sections of the tubular body 2 and 3 at the open ends 2.1, 2.2. or 3.1, 3.2 gradually change into elliptical cross-sections. In this way, the elasticity of the pipe bend and the production of pre-bent pipe bend blanks are favored over long areas. The smooth transitions from circular to elliptical cross-sections also allow a particularly streamlined design of the tubular body 2, 3. Relative to the entire pipe elbow construction In particular, the wide range of design options, particularly in the case of internal high-pressure molding, enables flow-efficient exhaust gas routing, as was previously only known from cast manifolds.

FIG. 3 shows another view of how the open ends 2.1, 2.2 or 3.1, 3.2 protrude into the openings 4 to 7 of the motor-side flange 8.

For the manufacture of the previously described tubular bodies 2, 3, two tool stages are required in an inner tube pressure forming machine. First, a cylindrical tube blank is pre-bent or pre-crimped and then annealed to remove the strain hardening. This is followed by a first forming process, in which the pipe is given its final shape except for the pipe socket 9 or 10 leading to the exhaust-side flange. At the same time, material is pressed into the outer radius from the inside of the pipe body in the area of the molding point for the pipe socket. A second annealing process then takes place. According to a special development of the method proposed according to the invention, the material flow is regulated in a tool 14 so that the tubular body 2 is not destroyed by increased friction in a critical area 15 on the tool edges. This is done by an electronically controlled piston 16, which supports the pipe socket 2.3 when it is pressed out and periodically lifts it off from the edges and tool walls (see FIG. 4). This allows material from a wide area to flow around the area to be reshaped. In this way, the wall thickness can also be varied at certain points. This is done by means of a corresponding pre-deformation of the tube blank, as a result of which the outer walls bear partially against the tool 14, so that the material flow is impeded there due to the friction that is then present. At other points in the pipe, material can flow in from thicker points via pistons by deliberately lifting the blank from the tool wall.

A pressure of up to 6000 bar is usually generated for the previously described forming processes via locking cylinders 17, 18. Such a method allows an initial Form a wall thickness of 1.75 mm from an approximately 10 mm long socket from a semicircular tubular body. With an increase in the outside diameter from originally 42 mm in the area of the engine-side flange 8 to 50 mm in the area of the exhaust-side flange 11, a wall thickness of 1.3 mm is not undershot here. Particularly good results are achieved for austenitic materials with ferritic properties. Such metastable austenitic steels can be, for example, an X15CrNiSi 20 12, X2CrNiMo 17 13 3 or X2CrNiMoN 17 13 5. In the latter case, the ferrite content ensures good ductility. Austenite significantly reduces the tendency towards scaling and embrittlement, especially during and after welding processes.

The use of pipe blanks with an elliptical cross-section enables a reduction of critical stresses in particularly vulnerable areas by approx. 40% with an axial ratio for the outside diameter of 32 mm to 55 mm compared to circular pipes with a comparable cross-sectional area.

It should be emphasized that the use of hydroforming in particular opens up a wide range of applications. The invention is therefore not limited to pipe elbows for four-cylinder in-line engines. Embodiments of tubular bodies are also conceivable which can protrude with three or four open ends into openings in flanges on the motor side.

Claims (7)

Pipe elbow (double pipe elbow 1) for internal combustion engines with a tubular body (2, 3) produced by a forming process, the open ends (2.1, 2.2 or 3.1, 3.2) of which are designed for connection to openings (4 to 7) of a motor-side flange (8) , and the jacket wall of which has at least one collecting opening facing an exhaust-side flange (11),
characterized in that
the tubular body (2, 3) is made in one piece with different wall thicknesses by internal high pressure forming, and has a molded pipe socket (2.3 or 3.3) on the collecting opening for connection to an opening (9 or 10) of the exhaust-side flange (11). Pipe elbow according to claim 1, characterized in that the walls of the tubular body (2, 3) have increased wall thicknesses towards the flanges (8, 11). Pipe elbow according to claim 1, characterized in that an approximately elliptical cross section is provided on the pipe bodies (2, 3) starting from circular cross sections in the area of the motor-side flange (8) towards the collecting opening, the smaller of the ellipse axes being approximately perpendicular to the bending axis of the tubular body (2, 3). Pipe elbow according to claim 1, characterized in that a tulip plate (12 or 13) between the molded pipe socket (2.3 or 3.3) of the pipe body (2 or 3) and the opening (9 or 10) of the exhaust-side flange (11) is arranged, which is frictionally connected to the flange (11) or the tubular body (2 or 3). A process for producing a pipe bend according to claim 1, characterized by the process steps: a) pre-bending or pre-crimping a pipe blank, b) heating the tube blank to a stress-relieved state, c) inserting the pipe blank heated according to b) into an engraving of a tool (14) of a hydroforming machine, d) loading the pre-bent pipe blank with high hydraulic pressure, e) Removal of the partially or completely deformed tube blank. A method according to claim 5, characterized in that for forming the pipe socket, the already partially finished blank is reheated to produce a stress-relieved state and then deformed to the finished size. Method according to claim 5, characterized in that the pressure exerted on the pipe socket is varied periodically by means of an electronically controlled pressure piston.

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