The invention relates to a device for forming a sealed screw connection for connecting a pipe to an outlet for a flow medium which thermally loads the device, in particular for connecting an exhaust manifold to the exhaust outlet of an internal combustion engine, with holes provided in a fixing flange of the pipe for the respective threaded bolts and a sealing arrangement located between the flange and the outlet.
Of course, thermal loads as occur in hot flow media, in particular in the exhaust gases of internal combustion engines, can lead to major mutual distortions of the components in line connections with fixed screw connections. Differences in the amount of thermal expansion of the flange of exhaust manifolds relative to the colder cylinder head of a pertinent internal combustion engine can be, for example, in the millimeter range. This leads to a series of adverse effects such as deformation of the manifold, lengthening of the threaded bolts/stud bolts, damage to the bolt thread, damage to the cylinder head, loosening of the seal combination with the corresponding sealing problems, component wear, etc. The increase of the temperature level in the exhaust gas region, which is currently being observed, leads to further exacerbation of these problems.
To remedy this, attempts are currently underway to reduce the mutual adverse effects on the components by reduced tightening torque of the screw connection. As a result of this measure, deformation of the manifold is reduced, at the same time, however, cyclic changes in length of the manifold occur to an intensified degree. This can lead in turn to damage of the threaded bolts as a result of the entraining effect on the screw head or the nut of the threaded bolt due to friction against the flange of the manifold. As a result the threaded bolts can be moved cyclically back and forth, the bolt thread is damaged, the sealing combination is loosened, and leaks occur.
With respect to these problems, the object of the invention is to make available a device which ensures reliable connection of a pipe, in particular an exhaust manifold, even in operating conditions with high thermal loading.
According to the invention, this object is achieved by a device which has the features of claim 1 in its entirety.
According to the characterizing part of claim 1, the invention provides for an enclosure part for the flange of the pipe. While oblong holes, which are located in the flange of the pipe, allow a displacement motion of the flange relative to the threaded bolts, the enclosure part is essentially fixed by a suitable diameter of at least one hole and the associated threaded bolt against thermally induced displacement motions. Accordingly, the threaded bolts, which penetrate the enclosure part, are decoupled from the displacement motions of the flange. Displacement motions of the flange take place on its side facing the outlet relative to the adjoining seal element of the sealing arrangement, which element is also encompassed by the enclosure part, and on the opposite upper side of the flange relative to the inside of the enclosure part and therefore not in frictional contact against the screw head (nut) of the screw connection. Thermally induced movements of the flange therefore do not cause any flexural loads of the threaded bolts. In this respect, it is also possible for the exhaust manifold to move relative to the entire seal or for the exhaust manifold, including associatable seal parts, to be shifted relative to other seal parts.
In advantageous embodiments, the flange on the two longitudinal edges that extend along the displacement direction, which is dictated by the oblong holes, has a sequence of oblong holes, the enclosure part on its side facing the outlet forming a bottom which continues essentially from longitudinal edge to longitudinal edge of the flange, and which is provided with passages for the medium and with holes that are matched to the diameters of the threaded bolts. This yields between the enclosure part and the facing surface of the flange on the bottom of the enclosure part a continuous sealing surface for the sealing element of the sealing arrangement, which element is located on the inside of the bottom of the enclosure part.
In especially advantageous embodiments the enclosure part is made integral with the side walls that are angled off from the bottom and that extend along the longitudinal edges of the flange, and with cover parts which extend in the region of the longitudinal edges of the flange on its upper side which faces away from the outlet. In this cage-like configuration of the enclosure part the installation process is especially simple in the production of a junction, because the enclosure part which surrounds the flange in the form of a cage can be slipped onto the flange beforehand, where it advantageously remains by self-retention in the installation position, in which both the holes in the enclosure part as well as the oblong holes in the flange can be penetrated by the threaded bolts when the junction is produced.
The arrangement can be such that the cover parts, which contain a sequence of holes for the threaded bolts, extend over the entire length of the enclosure part. In such embodiments it can be advantageous in regions, which are located between successive holes, to provide the cover parts with convexities which each form an intermediate space between the upper side of the flange and the cover part. These intermediate spaces, which reduce the size of the contact surface between the flange and the enclosure part, reduce the heat transfer to the enclosure part.
Alternatively, the arrangement can be such that the cover parts are divided into separate cover sections which are separated by intermediate spaces, the holes for the threaded bolts being provided in the cover sections. In this respect as well, heat transfer is reduced by the intermediate spaces present between the cover sections.
As indicated in the foregoing, in the invention relative movement between the flange and enclosure part can take place due to thermal expansion. More precisely, sliding zones are formed between the upper side of the flange and the cover parts of the enclosure part and between the bottom and the facing side of the flange, here displacement taking place on one or both sealing surfaces of the sealing element of the sealing arrangement. In this respect, it can be advantageous to make the sealing element, which is provided between the bottom of the enclosure part and the facing surface of the flange, to be friction-reducing and/or to provide it with friction-reducing means. Furthermore, displacement can also occur between the laminar sealing parts themselves.
Analogously, it is advantageous for there to be friction-reducing configurations and/or friction-reducing means between the upper side of the flange and the cover parts of the enclosure part.
In cases, in which the flange is part of an exhaust manifold which, in order to form a common connection for several exhaust outlets distributed in the longitudinal direction, has elongated longitudinal edges that contain oblong holes and shorter side edges that connect the longitudinal edges on the end side, the enclosure part extends preferably over the entire sequence of oblong holes of the flange. In this configuration it is also possible to decouple the entire screw connection which can have at least one pair of threaded bolts each in a multi-cylinder engine for the exhaust outlet of each cylinder by means of a single enclosure part relative to the displacement motions of the flange.
The invention is detailed below using embodiments shown in the drawings.
The invention is explained below using the example of a screw connection for connecting an exhaust manifold to the cylinder head of a multi-cylinder internal combustion engine. It goes without saying that the invention can be advantageously used equally well in screw connections for connecting different types of pipes through which hot media, which can be gaseous or liquid, flow.
In the drawings, of a multi-cylinder internal combustion engine only
Distributed along its elongated longitudinal edges 9, the flange 7 has a sequence of oblong holes 13 through which threaded bolts can extend which can be stud bolts 15 that are anchored in the cylinder head 1 in the embodiment. As
Of the enclosure part which is designated as a whole as 19 in
As can likewise be most clearly seen from
As is apparent from
As is apparent, the screw heads of the screw connection are formed by nuts 43 which sit on the stud bolts. The tightened nuts 43 press on the cover parts 27 or optionally the cover sections 29, that is, on contact surfaces on the enclosure part 19 which does not execute any thermally induced displacement motions. In displacements of the flange 7 there is therefore no frictionally induced entrainment of the nuts 43, as would be the case if the nuts 43 were supported on the flange 7. Rather, relative movement takes place on the upper side 41 of the flange in a displacement zone 45 (
Number | Date | Country | Kind |
---|---|---|---|
10 2006 033 357.8 | Jul 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP2007/005148 | 6/12/2007 | WO | 00 | 9/3/2009 |