Line element with damping, particularly for exhaust pipes of internal combustion engines in motor vehicles

A flexible line element, particularly for exhaust pipes of internal combustion engines of motor vehicles, is disclosed having a screw thread-like or annularly corrugated bellows provided with cylindrical connection ends and a metal netting directly surrounding the bellows. The metal netting is inherently stable and has at least one plastic deformation for acoustic or mechanical damping of the bellows. Consequently, the metal netting has both a protective and a damping function.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to a flexible line element, particularly for exhaust
 pipes of internal combustion engines for motor vehicles, with a screw
 thread-like or annularly corrugated bellows provided with cylindrical
 connection ends, and a metal netting or braid arranged coaxially to and in
 contact with the bellows.
 2. Description of the Prior Art
 Such line elements are introduced in the form of adaptors into the exhaust
 pipe, which is normally installed in fixed manner on the vehicle floor,
 optionally accompanied by the interposing of flexible support parts, in
 order to absorb movements and vibrations and prevent the transfer thereof
 to adjacent components, such as occur through the elastically mounted
 engine, vehicle faults, temperature-caused length changes, etc. If there
 is a lack of bellows damping, in the resonant range of the free bellows
 increased movements occur thereto, leading to a reduction in the service
 life and interact with other components for producing noise.
 EP 681 096 A1 describes a flexible line element, in which the bellows is
 surrounded by a knitted fabric tube fixed at both bellows ends. The
 knitted fabric tube supports the bellows axially in both directions,
 because the meshes can be moved in both the tension and pressure
 directions and there are limits to the movement thereof in both
 directions. However, it is disadvantageous that the line element is
 relatively unprotected to the outside, because it is possible for
 impurities or particles, e.g. gravel or loose stones, to be fixed in the
 mesh gaps, so that the mobility of the knitted fabric is impaired in such
 a way that the axial mobility of the line element overall is reduced and
 consequently so is its decoupling action. Moreover, the knitted fabric is
 not only flat, but also has a finite, compressible height, so that the
 knitted fabric can also be compressed, accompanied by a lose of its
 action.
 German utility model 296 09 293.2 discloses a flexible line element with a
 knitted fabric tube directly surrounding the bellows and which
 additionally has a braided tube completely externally surrounding the
 knitted fabric hose and positioned coaxially to the line element. The
 braided tube is fixed to the connection ends of the line element, so that
 the knitted fabric hose surrounding the bellows is protected against
 pollution and dirt applied from the outside. This construction is
 relatively expensive, because the line element is formed from three
 different types of tubes and the damping function and protective function
 are fulfilled by different components.
 SUMMARY OF THE INVENTION
 According to the invention, the problem of the prior art is solved by a
 line element of the aforementioned type, in that the metal netting has
 plastic deformations for the acoustic and/or mechanical damping of the
 bellows.
 Therefore, the problem solved by the invention, based on a line element of
 the aforementioned type, is to equip it in such a way that on the one hand
 the decoupling action is still maintained for loose stones and dirt
 applied from the outside to the line element and, on the other hand, the
 damping function and protective function are fulfilled by a single line
 element component.
 The damping principle of the constructed line element of the invention is
 based on the plastic deformations of the dimensionally stable metal
 netting, which are imparted thereto in an appropriate structure and
 arrangement and in particular bring about a sound absorption. Thus, the
 damping principle according to the invention is characterized by a
 complete departure from conventional damping actions, where the damping is
 brought about by a wide-mesh knitted fabric tube, which has a height
 significantly exceeding the thickness of the wire filament forming it and
 whose meshes, which must be protected for maintaining the damping function
 against penetrating dirt, such as loose stones, can be moved in the
 tension and compression directions. According to a preferred development,
 the metal netting of the invention can comprise one or more wire coils and
 completely surround the bellows, so that the latter is protected against
 dirt. The inherently stable metal braiding provided with plastic
 deformations maintains its characteristics even under dirt exposure and
 also contributes to the axial support of the ends of the line element
 relative to one another, because it engages directly on the bellows and
 consequently acts as a stop member, particularly in the tension direction,
 which is important with suddenly occurring inertia forces. Thus, an
 excessive elongation of the bellows is reliably prevented.
 The metal netting can be in monofilament or multifilament form and for a
 multifilament construction it preferably has metal bands or strips of
 differing thickness and consequently differing fundamental frequencies, so
 that the resonance case occurs when there is no vibrational excitation of
 the netting. The metal netting can e.g. be built up from a basic netting
 of stronger or thicker metal filaments, in which are introduced less
 strong or thinner metal filaments, e.g. by weaving therein.
 The plastic deformations imparted to the metal netting are provided as
 shaped profiles facing and/or remote from the bellows and in the simplest
 case are in the form of circular depressions or elevations. However, as a
 function of the damping requirement, the plastic deformations can also
 have any other random profiling, e.g. oval or polygonal and can be
 distributed either over the entire circumference of the wire netting or in
 planned manner at particularly vibration-sensitive areas. According to a
 preferred variant, elongated depressions or elevations extend
 longitudinally or helically or crosswise around the bellows surface.
 Whereas in one application of the line element of the invention, namely for
 exhaust pipes of internal combustion engines for motor vehicles, the metal
 netting is preferably applied to the outside of the bellows and
 consequently has a protective function in addition to the damping
 function, particularly when high damping requirements exist and additional
 netting can be applied to the inside of the bellows. If there is no need
 for a protection against external effects, the netting can also be
 exclusively applied to the inside of the bellows.
 In order to create a reliable fixing of the metal netting and the bellows
 to the connection ends of the line element and consequently an effective
 longitudinal support, preferably the metal netting is held on the ends of
 the bellows by cylindrical rings. The rings which are preferably
 externally mounted on the bellows with the metal netting ensure that the
 netting reliably directly engages on the bellows, so that a release of the
 metal netting and consequently a loss of its damping characteristics is
 prevented.
 According to a further development an inliner is provided. It is a
 medium-conducting, optionally of sound-absorbing element, such as a woven
 fabric tube or the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The flexible line element 1 shown in FIG. 1 has an annularly corrugated
 bellows 2, to whose outside is applied a sectionally represented metal
 netting 3 directly surrounding the same. The line element 1 has at its
 cylindrical connection ends a cylindrical rings 8 for fixing the line
 element 1 in an exhaust pipe and for the reliable fixing of the metal
 netting 3 to the bellows 2.
 FIGS. 2 and 3 show the metal netting 3 of a line element 1 with plastic
 deformations 5, facing an annularly corrugated bellows 2, imparted on the
 metal netting 3. The deformations 5 can be located both at the contact
 points 7 of the bellows 2 with the metal netting 3 (FIG. 2) and also
 between the contact points 7 (FIG. 3). To bring about an optimum damping
 of the bellows 2, according to a preferred development the plastic
 deformations 5 of a metal netting 3 are located both at and also between
 the contact points 7 of a bellows 2.
 FIGS. 4 to 9 show very varied plastic deformations 5 of a sectionally
 represented metal netting 3. The deformation 5 in the form of a depression
 shown in FIG. 4 extends in screw thread-like manner around the
 circumferential surface of the cylindrical line element. FIGS. 5 and 6
 show radial (FIG. 5) or longitudinal directed (FIG. 6) deformations 5,
 which have different profiles in FIG. 5. Whereas FIGS. 7 and 8 show
 symmetrical (FIG. 7) or asymmetrical (FIG. 8) punctiform deformations,
 FIG. 9 shows elongated hole-like deformations 5 in the longitudinal
 direction of the line element. Obviously not only the embodiments of the
 plastic deformations shown in FIGS. 4 to 9 can be varied in random number
 and combination, but the deformations 5 imparted to a metal netting 3 of a
 line element 1 can be of random form and the represented embodiments are
 merely to be looked upon as a selection of possible variants.
 Finally, FIG. 10 shows different shaped profiles 6 of the plastic
 deformations in a metal netting, which can be round, oval or polygonal
 and, as shown in the upper row 6a, can have different heights or depths.
 In the manufacture of a line element according to the invention, either the
 metal netting can be prefabricated, the plastic deformations imparted and
 the metal netting subsequently placed on the inside or outside of a
 corresponding bellows, or the metal netting and bellows are prefitted and
 subsequently the plastic deformations are imparted to the metal netting.