EP1249587B1 - Exhaust manifold for engine - Google Patents

Description

The present invention relates to a combustion gas exhaust device of an internal combustion engine, including a motor vehicle. It concerns more precisely the exhaust manifold, which is the part of the exhaust system attached to the cylinder head of the engine and intended to collect the exhaust gases leaving the different ducts of the cylinder head to transport them, at the outlet of the manifold, in a single conduit.

These exhaust manifolds are conventionally obtained by molding, or possibly by mechanical welding.

For example, there is shown in Figure 1 a molded exhaust manifold, as known from the state of the art.

This manifold comprises a main tube 1, one end has a flange 4 for connecting the exhaust system located downstream. A plurality of ducts 2, intended to communicate respectively with each exhaust duct of the cylinder head, are connected to the main tube 1. The ducts 2 are held on the cylinder head by a clamping system formed of a flange 3 intended to be fixed on the engine cylinder head by screws, directly screwed into threaded holes of the cylinder head, or by studs, implanted in the cylinder head, and nuts screwed on said studs. In a conventional manner, a seal is interposed between the flange 3 and the cylinder head.

The space available in the engine compartment of a car, taking into account in particular the requirements of general shape of the vehicle, requires to make parts of the exhaust system in a form increasingly compact. For example, it will be noted in FIG. 1 that the counterbores 5 for supporting the screw heads or nuts have a flat half-ring. This particular embodiment is intended to simultaneously ensure the clamping of the exhaust manifold flange and intake manifold flange, which fit into one another, each screw or nut simultaneously bearing on a 5 of the exhaust manifold and on a counter 6 of the intake manifold, placed vis-a-vis, as shown in dashed lines on the left side of the drawing.

From this research of great compactness, it results, in the parts concerned, thermal and vibratory stresses more and more important, which can lead to cracks and even breaks in these parts, during operation, especially under the effect differential expansion stresses between the various parts assembled, or within the same room.

In the current exhaust manifolds, such as that shown in FIG. 1, in order to attenuate these stresses in the ducts or to their connection with the flange, one carries out in the latter one or more saw cuts 7 which allow a relative mobility of the flange elements thus separated, and has the direct effect of releasing the existing stresses in said ducts, particularly at the level of the connection zones between the tubes or ducts, in the elbows, the ribs, etc. This greatly reduces the risk of cracking in these relatively fragile areas.

But the realization of this kerf has several disadvantages. In the first place, it is not possible to achieve this separation of the flange in several elements before performing the other machining, such as the planing of the bearing face against the cylinder head or countersinks. Indeed, it would then be almost impossible to maintain sufficiently rigid the various elements of a previously cut flange, during these machining operations, or the complexity of the clamping means of the workpiece on the machining machine. would be such that the cost of machining would be prohibitive.

Moreover, the sawing operation alone generates a significant additional cost for machining operations.

In addition, the sawing performed after the planing of the seal face, can release internal stresses originally existing in the room in the case of collectors cast iron or cast steel, or resulting from the assembly of its constituent elements in the case of a mechanically welded construction. The release of these internal constraints can lead to the original flatness of the said bearing face is destroyed after sawing, or that the fixing centers are modified. Now the flatness of said support face is necessary to avoid leakage problems between the cylinder head and collector, and the precise spacing of the fixing points is required to avoid creating genes during factory assembly.

The present invention aims to solve these problems and aims in particular to provide an exhaust manifold with minimal risk of cracking, and without burdening the cost.

With these objectives in view, the invention relates to an exhaust manifold for an internal combustion engine, comprising a flange for securing the manifold to the cylinder head of the engine, characterized in that the flange has a continuity of material along its length and comprises at least one predetermined location area which has a substantial weakening, also predetermined value, relative to the other parts of the flange.

This area of lower resistance relative to the surrounding areas of the flange is determined so as to ensure a rigid connection between the different parts of the flange, but to break naturally during the first minutes or first hours of operation of the engine, under the effect of the thermal and vibratory stresses generated by the operation.

The break is thus somehow guided, and located precisely at the desired location, predetermined to ensure the best conditions of subsequent differential expansions, that is to say to allow the collector to expand and accept vibratory stresses in current operation of the engine, without risk of uncontrolled cracking in areas where it would be unacceptable for the reliability of the collector.

On the other hand, before this break occurs, the collector flange remains an integral part element, ensuring the geometry required for optimum flatness of the support face of the flange and for the correct positioning of the manifold on the breech when fixing.

Preferably, said weakening is obtained by a reduction of the section of the flange, it itself preferably obtained by a transverse notch leaving a section of material with a tensile strength of resistance within a predetermined range. In practice, the breaking strength of the material remaining at the notch must of course be less than that of the neighboring zones, so that the desired break is achieved well at the desired location and not elsewhere in an uncontrolled manner. It must also be greater than a predetermined minimum threshold, so that the rupture can not occur before fixing the collector on the cylinder head. In particular, the resistance of the weakened zone must be sufficient to withstand, without breaking the stresses generated during manufacturing operations or machining of the collector.

According to a still preferred arrangement, the notch is formed on the side of the bearing face of the collector. The situation of the notch on this side of the flange is particularly favorable to facilitate breakage, especially when the notch is made at a fastener, the tightening locally causes a bending effect of the flange, clean to open the notch.

According to another preferred arrangement, the notch has a "V" section, the bottom of which accordingly has a relatively sharp edge, constituting a clear incipient fracture for the desired break.

In a first embodiment of the notch, the section reduction is obtained during the molding of the collector. This particularly advantageous production method makes it possible to avoid any specific operation for obtaining the notch, and therefore does not create any additional cost.

Alternatively, the section reduction can be carried out, for example in the form of a simple fracture primer, by a specific tool adapted, such as a blade or punch cut performed at the end of the finishing or deburring operation. of the part after demolding.

Other features and benefits will appear in the description that will be made an embodiment of an exhaust manifold according to the invention, comprising four ducts connected to a main tube.

• la figure 1 est une vue de face d'un collecteur selon l'art antérieur, déjà décrit au début de ce mémoire,
• la figure 2 est une vue en perspective d'un collecteur d'échappement conforme à l'invention,
• la figure 3 est une vue de dessus de ce collecteur.

Reference is made to the accompanying drawings in which:

• FIG. 1 is a front view of a collector according to the prior art, already described at the beginning of this memorandum,
• FIG. 2 is a perspective view of an exhaust manifold according to the invention,
• Figure 3 is a top view of this collector.

The manifold according to the invention, shown in Figures 1 and 2 comprises a main tube 1 on which are connected four ducts 2. The flange 3 for fixing the manifold on the cylinder head, not shown, of an internal combustion engine, comprises four clamping elements 31, made in one-piece casting with the conduits 2 and the main tube 1. Each clamping element comprises, in a conventional manner, a communication orifice with a respective conduit 2.

In the case of a welded construction, the flange 3 is formed by cutting a thick plate, on which the ducts 2 are then welded.

The fixing of the collector on the cylinder head is ensured conventionally by studs and nuts, or by screws. The flange 3 has several holes 32 or notches 33 of semi-cylindrical shape for the passage of the rods of said studs or screws. The notches 33 of half-cylindrical shape are intended to cooperate with similar notches, made on an intake manifold and located in correspondence during the assembly of said collectors to form cylindrical holes together. Furthermore, at each of these holes or indentations, a counterbore 5 is made for service surface support at the head of the screw or the fixing nut.

A notch 37 is formed in the flange at the notch 33 located towards the middle thereof. This notch, formed during the molding, opens on the side of the support face 35 of the flange and a section of general shape in "V", as can be seen in FIG. 3. The section of material 38 remaining at this point is substantially reduced, and especially as the notch is formed just at the notch of the screw passage and corresponding counterbore. This gives the attenuation according to the invention, conducive to breaking during the subsequent operation of the motor, as indicated above.

The invention is not limited to the embodiment which has just been described. In particular, other similar cuts could be made on the flange, at other holes or notches, or at other points in the flange that are suitable for developing a break that could reduce thermal or vibration stresses in the other parts. of the collector. The shape and orientation of the notch could also be modified, depending on the specific shapes of the collectors.

Claims (7)

1. An exhaust manifold for an internal combustion engine comprising a flange (3) intended to ensure fixing of the manifold to the cylinder head of the engine,
   the flange having a continuity of material over its length and comprising at least one predetermined localisation zone (38) which has a perceptible weakening of a value which is also predetermined with respect to the other parts of the flange,
   characterised in that the reduction in section is obtained by a transverse notch (37) which leaves a section (38) of material affording a tensile breaking strength within a predetermined range.
2. An exhaust manifold according to claim 1 characterised in that said weakening (38) is obtained by a localised reduction in the section of the flange.
3. An exhaust manifold according to claim 1 or claim 2 characterised in that the notch (37) is provided at the side of the support face (35) of the manifold.
4. An exhaust manifold according to claim 1, claim 2 or claim 3 characterised in that the notch (37) is of a V-shaped section.
5. An exhaust manifold according to one of claims 1 and 4 characterised in that the weakening (38) is implemented in a zone (33) provided for receiving means for fixing the manifold to the cylinder head.
6. An exhaust manifold according to one of claims 2 to 5 characterised in that the reduction in section is obtained when casting the manifold.
7. An exhaust manifold according to one of claims 2 to 6 characterised in that the reduction in section is implemented by a suitable tooling in the operations of finishing the component after removal from the mould.

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