Heat-expandable multi-passage pipe having parts for intended breakage

A heat-expandable tube-like component includes a tubular wall having a length dimension and defining an inner space; and a septum attached to the tubular wall and dividing the inner space into separate, longitudinally extending passages. The septum has a weakened portion which includes first and second groove-like recesses in opposite faces of the septum. The first recess extends substantially parallel to the length dimension (axial dimension) of the tubular wall. The second groove-like recess extends slightly offset from and parallel to the first groove-like recess. Further, portions of the septum flanked by the first and second recesses are sufficiently weak to break under the effect of forces derived from heat-caused expansion of the component. Also, the recesses are so arranged with respect to one another that upon breakage of the septum portions flanked by the recesses the septum halves obtained by the breakage are adapted to glide past one another.

BACKGROUND OF THE INVENTION 
This invention relates to a tubular structural component which is thermally 
stressed in service and which, by means of a septum, is separated into 
several flow passages or the like. Such a component may find application 
particularly in the outlet zone of an exhaust manifold which forms part of 
the exhaust system of an internal combustion engine. 
In order to improve the engine performance of internal combustion engines, 
it is conventional to use multi-passage pipes (that is, pipes which have 
exhaust channels separated from one another) in the exhaust system, at 
least in the zone adjacent the exhaust manifold. The outlet portion of the 
exhaust manifold itself is, in such cases, designed as a multi-channel 
component; the septum in the exhaust manifold and the septum in the 
adjoining exhaust pipe are in alignment with one another. Frequently, the 
connection between the exhaust manifold and the exhaust pipe is designed 
as an articulated joint, wherein the exhaust manifold is provided with a 
cylindrical sealing flange to which the exhaust pipe is secured by means 
of a bowl-shaped terminus with the interposition of a heat-resistant 
sealing ring. By virtue of this coupling structure oscillations and 
vibrations occurring during operation may be taken up. 
During the operation of the internal combustion engine the exhaust manifold 
and the exhaust pipe are exposed to hot exhaust gases whose temperature 
may reach approximately 900.degree. C. The septum of the exhaust manifold 
which is exposed to the hot exhaust gases on both sides is heated to a 
substantially greater extent than the outer wall of the exhaust manifold 
which, in addition, is better cooled, particularly by air streams 
generated during vehicle travel. Thus, the septum which expands to a 
greater extent due to heating, risks to deform the originally circular 
sealing flange of the exhaust manifold, that is, it may exert such a 
pressure on the flange that the latter assumes a cross-sectionally oval 
configuration. As a result of this occurrence a satisfactory sealing 
effect between the sealing flange and the sealing ring can no longer be 
ensured. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved tubular structural 
component of the aboveoutlined type in which deformations or uncontrolled 
breakages caused by thermal stresses are prevented while its basic 
functions are retained. 
This object and others to become apparent as the specification progresses, 
are accomplished by the invention, according to which, briefly stated, the 
septum of the tubular component includes at least one intended location of 
breakage (weakened portion) which extends in the length dimension of the 
component and which becomes effective during thermal stresses that 
normally occur during operation. The intended location of breakage is 
formed of a longitudinally extending first groove-like recess arranged on 
the one side of the septum and a second groove-like recess extending on 
the other side of the septum parallel to and at a small distance from the 
first recess. The depth, shape and position of the recesses are so 
selected that after breakage of the septum portion flanked by the two 
recesses, the two wall halves may slide past one another in an overlapping 
relationship. 
By providing for an intended location of breakage in the septum it is 
ensured that an appreciable deformation of the tubular component which 
would adversely affect the operation thereof is prevented because the 
septum, prior to exerting the critical deforming forces on the component, 
is interrupted in continuity at the intended location of breakage, so that 
the wall halves situated at either side of the location of breakage may, 
upon further thermal expansion, move past one another into the inside of 
the structural component. The separating effect of the septum is thus not 
appreciably affected, if at all, because the two wall halves lie sealingly 
on one another. A disadvantageous effect on the engine performance thus 
does not occur. 
The above-outlined problem of deformation and uncontrollable breakage could 
have been theoretically resolved to initially include in the septum an 
obliquely extending slot as an expansion groove which could be expected to 
prevent a deformation of the tubular structural component. Such a 
solution, however, would be disadvantageous in that a slot, from the point 
of view of casting technology cannot be provided in the original cast; it 
could only be subsequently provided by means of mechanical machining such 
as sawing or grinding. Further, such a relatively wide separating slot 
would cause an undesirable circulatory short circuit between the flow 
passages that are separated by the septum. Further, the wall portions 
extending with sharp edges in the zone of such a separating slot would be 
exposed to heat-caused corrosion which would result in wear. All these 
disadvantages do not appear in the tubular component structured according 
to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the Figures, there will be described a preferred embodiment 
of the invention, with several variants, finding an advantageous 
application in the exhaust system of an internal combustion engine. 
Turning now particularly to FIGS. 1 and 2, during the operation of the 
internal combustion engine (not shown) a cast exhaust manifold 1 carries 
hot exhaust gases in the direction of the arrows A. From the exhaust 
manifold 1, the gases enter an exhaust pipe 3 connected with the exhaust 
manifold 1. 
Turning now in particular to FIG. 2, an outlet portion of the exhaust 
manifold 1 is divided by a septum 2 into two separated flow passages 1a 
and 1b. A similar--not illustrated--division of the flow passage cross 
section is also provided in the exhaust pipe 3; the septum of the exhaust 
manifold, on the one hand and that of the exhaust pipe, on the other hand 
are in alignment with one another. Such a division of the exhaust gases 
along at least one part of their traveling path is advantageous for 
reasons of engine performance. 
That end of the exhaust manifold 1 which is oriented towards the exhaust 
pipe 3 is formed as a cylindrical sealing flange 4. The septum 2 is cast 
together with the exhaust manifold 1 and thus constitutes an integral 
component of the exhaust manifold. The exhaust pipe 3 is secured to the 
exhaust manifold 1 with the interposition of a heat-resistant intermediate 
sealing ring 5. Further details of this joint connection are not shown. 
The outer contour of the sealing ring 5 as well as the contour of the pipe 
portion engaging the sealing ring 5 are so designed that a ball joint-like 
connection is obtained whereby oscillations, vibrations as well as 
mounting tolerances may be compensated for or may be taken up. 
The hot exhaust gases, as they pass through the channels of the exhaust 
manifold, substantially heat particularly the septum 2 which is exposed to 
the exhaust gases on both sides. In contradistinction, the outer tubular 
wall including the cylindrical sealing flange 4 is heated to a somewhat 
lesser extent, since the conditions for cooling are more favorable there. 
Due to these thermal conditions, the septum 2 undergoes, from one pipe 
wall to the other, a greater heat-caused expansion than the heat-caused 
increase of the diameter of the sealing flange 4. Without particular 
measures, such an occurrence would cause the circular cross section of 
sealing flange 4 to be necessarily deformed to assume, for example, an 
oval shape. This, however, would result in a marked deterioration of the 
seal between the exhaust pipe 3 and the sealing flange 4. Further, 
non-controllable breakages may also occur. 
In order to prevent the above-outlined disadvantageous results, in the mid 
zone of the septum 2 there is provided an intended location of breakage 6. 
This location is formed of a first groove-like recess 6' which extends on 
the one face of the septum 2 in the longitudinal dimension of the tubular 
component and a second groove-like recess 6" which, in turn extends on the 
other face of the septum 2, parallel to and at a small distance from the 
recess 6'. The depth, the configuration, as well as the position of the 
two recesses 6', 6" are so selected that between the two recesses there 
remains only a thin residual connecting portion 2' of the septum 2. 
Upon reaching a predetermined thermal stress, the septum portion 2' breaks 
under the effect of sheering stresses. In the course of continued 
heat-caused expansion of the septum 2, the two wall halves to the right 
and to the left of the location of breakage may move past one another 
towards the middle of the pipe so that no deforming forces will be exerted 
on the sealing flange 4. The separating groove obtained during these 
occurrences is of such a small dimension that a flow dynamic communication 
between the two passages 1a and 1b on the two sides of the septum 2 
practically does not occur. 
The groove-like recesses 6' and 6" extending in the longitudinal direction 
of the structural component, that is the exhaust manifold 1, may 
advantageously be cast together with the septum 2, so that no subsequent 
mechanical machining (boring, sawing, milling etc.) is necessary. The 
shape of the groove-like recesses may, in principle, be arbitrarily 
selected. Thus, the recesses may have an angular, pointed, oval or round 
cross-sectional shape. Examples of such groove shapes are shown 
schematically in FIGS. 3a, 3b and 3c. From the point of view of casting 
technology, it is, however, of advantage to utilize rounded contours as 
shown, for example, in FIG. 2 or in FIGS. 3a and 3b. In order to ensure 
that the groove-like recesses perform their function fully and reliably, 
they have to be of such a length that the critical zone (concerning the 
deformation of the structural component) is well overlapped. Thus in the 
case of the described embodiment, the intended location of breakage 6 
should be sufficiently longer than the axial length of the sealing flange 
4, as it may be observed in FIG. 1. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.