Uncoupling element for uncoupling vibrations

An uncoupling element is proposed for uncoupling vibrations in an exhaust gas conduit of an internal combustion engine, having a screw thread-shaped or annular waved, metal corrugated hose, which is inserted between a first conduit element arranged upstream and a second conduit element arranged downstream. In order to combine a good uncoupling action with ease of installation and repair friendliness, the uncoupling element is configured such that the first conduit element arranged upstream is provided with an annular bulge in the region of its end to be connected to the corrugated hose, that the first conduit element, downstream from the annular bulge, continues into a flame pipe reaching into the corrugated hose, without touching the inner waves of the corrugated hose, that in the transition region between annular bulge and flame pipe a centering surface is provided, and that the corrugated hose is separably connected with the first conduit element on the annular bulge via a clamp connection, while it lies against the centering surface.

BACKGROUND OF THE INVENTION
 The invention relates to an uncoupling element for uncoupling vibrations in
 an exhaust gas conduit of an internal combustion engine, having a screw
 thread-shaped or annular waved, metallic corrugated hose, which is
 installed between a first conduit element arranged upstream and a second
 conduit element arranged downstream.
 With exhaust gas conduits of motor vehicles, it is known to install a
 flexible conduit element in the form of waved, corrugated hose as an
 intermediate part, in order to absorb motions and vibrations and to
 uncouple transmission to adjacent components. Such motions and vibrations
 result on the part of the elastically mounted drive mechanism as a
 consequence of load shifting reactions in normal driving operation or also
 as temperature-conditioned changes in length within the exhaust gas
 conduit. Transmission of these motions and vibrations to the vehicle
 should be prevented as far as possible, in order to increase the lifetime
 of the exhaust gas facility and to prevent undesirable transmission of
 body noise, as well as the emission of air noise.
 An example of such a flexible conduit element for exhaust gas conduits of
 motor vehicles may be taken from German utility model DE 296 09 293 U1.
 The conduit element described there is firmly connected with the conduit
 elements lying upstream and downstream, usually by means of a welding
 connection. For bracing in the axial direction, the corrugated hose is
 enclosed by a knit hose fastened on both ends of the corrugated hose. In
 the cited utility model, it is moreover proposed to additionally enclose
 the knit hose with a netting hose.
 Such a known uncoupling element is indeed gas-tight and internally stable,
 but the installation of this conduit element in the exhaust gas facility
 by the motor vehicle manufacturer must be conducted very carefully.
 Fastening of the connection ends of the corrugated hose may be undertaken
 only within narrow tolerances. Even the replacement of a corrugated hose,
 which has possibly become harmful, requires exact processing by the
 workshop entrusted with it, as well as good capabilities in metalworking.
 As an alternative to permanent installation of a conduit element just
 mentioned, it is known according to the prior art, for example from German
 published patent application DE 35 42 684 A1, to separably connect the
 exhaust manifold of a motor vehicle engine with a following corrugated
 hose. In this publication, the connection is undertaken by means of a
 sealing ring of slightly pre-stressed material, such as metal wires or
 metal shavings, which is arranged on the cylindrical running-out tube end
 and on which a bent collar of the corrugated hose is laid, wherein a
 profile clamp braces the collar together with the sealing ring on the tube
 end. It has become apparent though, that the uncoupling action of such a
 separable construction is capable of improvement. Also, a corrugated hose
 with good uncoupling action can hardly be joined in this manner with the
 tube end of a conduit element of an exhaust gas facility close to the
 engine.
 SUMMARY OF THE INVENTION
 Underlying the present invention is therefore the object of proposing an
 uncoupling element for uncoupling vibrations in an exhaust gas conduit of
 an internal combustion engine having a screw thread-shaped or annular
 waved metal corrugated hose, which combines a good uncoupling action with
 easy installation and repair friendliness.
 In accordance with the invention, an uncoupling element of the type
 mentioned at the beginning is configured such that the first conduit
 element, arranged upstream in the region of its end to be connected with
 the corrugated hose, is provided with an annular bulge, that the first
 conduit element, downstream of the annular bulge, continues into a flame
 pipe which reaches into the corrugated hose without touching the inner
 waves of the corrugated hose, that in the transition region between the
 annular bulge and the flame pipe a centering surface is provided, and that
 the corrugated hose is separably connected with the first conduit element
 on the annular bulge by means of a clamp connection, while it lies against
 the centering surface.
 The annular bulge on the first conduit element makes possible a very easy
 installation of the uncoupling element, wherein the fitter need not pay
 attention to the exact position of the clamp connection, since this is
 pre-determined by the annular bulge, and also ensures later an easy
 separability for repair purposes.
 Downstream of the annular bulge, the first conduit element continues into a
 flame pipe which reaches into the corrugated hose and to this extent
 serves as a heat shield for the corrugated hose and, since the wave form
 of the corrugated hose could lead to flow disturbances, serves for better
 flow guidance. Moreover, the flame pipe has an external diameter
 dimensioned such that it does not touch the interior waves of the of the
 corrugated hose, and indeed not even when angular motions occur, owing to
 relative motions within the exhaust gas facility. After the flame pipe is
 constructed as a continuation of the first conduit element arranged
 upstream, its position relative to the first conduit element is
 unalterable, so that the corrugated hose can simply be put on over the
 flame pipe and fastened on the clamp connection. Moreover, the centering
 surface provided in accordance with the invention guarantees therein, in
 any case, an exact and nonetheless easy installation, wherein the spacing
 between the flame pipe and the internal waves of the corrugated hose,
 necessary for avoiding rattling noises, can be automatically maintained.
 The centering surface finally forces, in interaction with the annular
 bulge, a centering of the corrugated hose relative to the first conduit
 element in all three spatial directions. Errors owing to inexact
 processing in the installation are thus largely ruled out per se.
 Preferably, the flame pipe is formed in one piece on the first conduit
 element, wherein, as a rule, it will have an outer radius diminished in
 relation to the first conduit element.
 The clamp connection of the corrugated hose on the first conduit element
 can be undertaken in usual manner by means of an installable profile clamp
 adapted to the annular bulge. Expediently, the annular bulge is here
 constructed as a V-shaped rim and the profile clamp as a V-shaped clamp.
 The clamp connection can then be made gas-tight in a simple manner, in
 that the corrugated hose is provided on its end facing the first conduit
 element with an annular flanged, outwardly conical-shaped collar, wherein
 the annular bulge of the first conduit element has a mating conical
 seating surface for the collar, and the collar is thus braceable with the
 annular bulge by placing on and tightening the profile clamp.
 The conical seating surface of a thus-configured clamp surface can serve as
 part of the centering surface, for the seating of the flanged collar of
 the corrugated hose end on such a conical surface inherently insures the
 desired centering according to the invention in all three directions.
 In order to facilitate the installation of the uncoupling element and to
 increase its accuracy, the centering surface preferably includes a
 cylindrical shoulder arranged between the annular bulge and the flame
 pipe.
 To diminish the inherent ability of the corrugated hose to vibrate, the
 corrugated hose can be constructed with multiple walls, preferably with
 three wall layers. The friction between the individual wall layers, in
 connection with vibratory motions of the corrugated hose, provides for the
 internal damping of these motions.
 The invention displays particular advantages when the corrugated hose has a
 high internal rigidity, and indeed such that its internal frequency lies
 higher than the excitation frequency of the internal combustion engine
 and/or of its auxiliary units. Especially because the danger of resonance
 vibrations is hereby eliminated, an additional damping of the corrugated
 hose by a knit jacket or a knit hose is dispensable. This makes it
 possible for the overall construction--when the corrugated hose itself is
 so manufactured that it has a substantially linear vibration behavior--to
 manifest a linear vibration behavior: Even the connection of the
 corrugated hose to the first conduit element lying upstream, using the
 clamp connection of the invention arranged on the annular bulge, generates
 no non-linearities of any kind, since the transition from the first
 conduit element to the annular bulge and from the annular bulge to the
 corrugated hose is not encumbered with an internal damping.
 In contrast, with conduit elements according to the prior art mentioned at
 the outset, non-linearities have not been avoidable up until now, either
 by the knit hose enclosing the corrugated hose or by the clamping taking
 place by an elastic ring, so that the known uncoupling elements or pipe
 connection elements have generally always had up until now a
 non-negligible, non-linear vibration behavior.
 Since the motor vehicle industry, in particular, strives to shorten the
 development times for new products and for this purpose to undertake as
 many development steps as possible by means of computer simulation, a
 linear vibration behavior of the vehicle parts, in particular of the
 exhaust gas facility as well, can be desirable. For only then can a result
 be reached through computer simulation, which to a sufficient extent
 corresponds to reality.
 The particularly advantageous configuration of the invention obviously does
 not rule out that it can be expedient for particular applications to
 enclose the corrugated hose with a weave and/or a knit in known manner.

DETAILED DESCRIPTION OF THE INVENTION
 Between a first conduit element 1 lying upstream and a second conduit
 element 2 lying downstream in an exhaust gas facility of a motor vehicle
 combustion engine, a ring-waved corrugated hose 3 is inserted, in order to
 uncouple vibrations and to compensate for relative motions of the two
 conduit elements 1 and 2. The flow direction of the exhaust gases is
 designated with the reference numeral 4. The corrugated hose 3 is provided
 downstream with a cylindrical connection end 5 formed in one piece, which
 is slid onto the second conduit element 2 and fastened to this by means of
 a welding seam 6.
 The first conduit element 1 is deformed into a V-shaped annular bulge 7 in
 the region of its end to be connected to the corrugated hose 3, and then
 continues downstream over a cylindrical shoulder 8 into a flame pipe 9
 with a diminished outer radius. The flame pipe 9 extends into the interior
 of the corrugated hose 3 and thus protects it against the hot exhaust
 gases. Furthermore, the flame pipe 9 improves the through flow of the
 uncoupling element, in that the gas flow is surrounded with a smooth
 interior pipe wall. The flame pipe 9 is so dimensioned that, between its
 end and the second conduit element 2 as well as between its outer wall and
 the inner waves of the corrugated hose 3, respectively, a clear space
 remains which guarantees, with all usually occurring relative motions of
 the two conduit elements 1 and 2, that the flame pipe 9 does not strike
 against the inner waves of the corrugated hose 3 or against the second
 conduit element 2.
 The connection of the corrugated hose 3 to the first conduit element 1
 takes place via a separable clamp connection. This is formed such that the
 corrugated hose 3 also has on its upstream-lying end a hollow cylindrical
 connection piece 10 formed in one piece, which is provided on its end with
 a conically flanged annular collar 11. Toward the corrugated hose 3 the
 annular bulge 7 has a mating conical seating surface 12 for the collar 11,
 against which the collar 11 is placed. By means of a V-shaped profile
 clamp 13, which is placed upon the annular bulge, the collar 11 of the
 corrugated hose 3 is braced gas-tight with the annular bulge 7 of the
 first conduit element 1.
 As can be well recognized in the drawing, the cylindrical shoulder 8 of the
 first conduit element 1 and the seating surface 12 of the annular bulge 7
 together form a centering surface 14 for the corrugated hose 3, which in
 the shown, fully-installed state lies with its connection piece 10 and its
 flanged collar 11 against the centering surface 14, and is thereby
 centered in all three spatial dimensions.
 It can be recognized how simply and nonetheless precisely the installation
 of the uncoupling element according to the invention takes place: The
 corrugated hose 3, which is already welded with the second conduit element
 2, is placed over the flame pipe 9, wherein the flanged collar 11 of the
 upstream-lying connection piece 10 of the corrugated hose 3 optionally
 serves as a catch incline. The flame pipe 9 then broadens into the
 cylindrical shoulder 8, on which the connection piece 10 is slid, until
 its flanged collar 11 comes to lie against the seating surface 12 of the
 annular bulge 7. In this way, the flame pipe 9 is centered by itself into
 the correct installation position inside the corrugated hose 3. Finally,
 it is only left to set the profile clamp 13 on the annular bulge 7 and to
 brace it there, in order to complete the installation.