Flexible pipe element

Details Flexible pipe element Flexible pipe element

2002-07-18

2003-09-02

Brinson, Patrick (Department: 3752)

Pipes and tubular conduits

Flexible

C138S121000, C138S114000, C138S148000, C138S123000

Reexamination Certificate

active

06612342

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention concerns a flexible pipe element, in particular for exhaust pipes of combustion engines of motor vehicles.
Flexible pipe elements of this type generally comprise a helical-shaped or corrugated bellows and a strip wound hose which is helically wound or which comprises several annular segments and which is coaxially adjacent to the bellows, wherein the helical winding or the annular segments of the strip wound hose have a substantially S-shaped cross-section by means of which axially neighboring elements of the helical winding or axially neighboring annular segments of the strip wound hose engage one another. They are installed as intermediate pieces in the motor vehicle exhaust pipe which is usually fixed to the vehicle floor, optionally using flexible support parts to accept movement and vibration produced by the elastically suspended engine and by changes in length due to temperature etc. and to prevent same from being passed on to neighboring structural components.
Particularly disadvantageous thereby is the limited freedom of motion of the pipe element caused by the strip wound hose. This deteriorates the decoupling properties of the pipe element when the strip wound hose has reached its maximum possible axial length and leads to transfer of load changes in the engine to the exhaust system causing unpleasant noise. The limited mobility of these pipe elements also usually requires an exhaust system which is displaceably suspended from the underbody of the motor vehicle which can accept extreme motion leading to blocking of the pipe element.
Known pipe elements (EP 0 903 528 A1, EP 0 709 558 A1, DE 296 09 293 U1) furthermore mostly comprise a metal braid disposed on the outside to protect the bellows from exterior mechanical influence and excessive lengthening. Disadvantageously, such a braid is radially extended or retracted when the pipe element becomes longer or shorter. When the braid adjoins e.g. the bordering bellows, the pipe element is additionally blocked from further axial extension and also clearly hardened against lateral and angular motions such that oscillating motions are transferred to the exhaust pipe of the motor vehicle when the pipe element is in this state. If the braid is radially separated from the neighboring bellows, it could strike the bellows and/or neighboring vehicle parts in response to transmitted engine vibrations to produce unpleasant noise.
EP 0 681 096 A1 describes a flexible pipe element comprising a bellows wherein the outer metal braid is replaced by knitted fabrics, thereby preventing the metal braid from generating disturbing striking noises. The knitted fabric can also softly support axial motion of the bellows since the mesh can be displaced in both tension and compression directions within limits which are relatively soft. However, in particular the bellows of such a pipe element may fail prematurely since the knitted fabric alone provides insufficient support. An inner pipe is preferably provided to protect the bellows and is coaxially surrounded by the bellows. This considerably limits the motion of the pipe element, in particular with respect to angular deflection.
DE 296 09 293 U1 describes a flexible pipe element comprising a bellows and a knitted fabric directly surrounding same and an outwardly disposed metal braid. This device shares the above mentioned disadvantages.
DE 198 48 451 A1 describes a flexible pipe element wherein spacers are disposed between the bellows and at least one additional element such as e.g. a strip wound hose or a metal braid to effectively damp the bellows. This pipe element has insufficient mobility for many applications.
It is the underlying purpose of the invention to propose a flexible pipe element which has increased mobility thereby preventing premature failure of the bellows, and at the same time good decoupling properties in the high and low frequency ranges, in particular for small amplitude oscillations and large amplitude load change oscillations of the engine.
SUMMARY OF THE INVENTION
This object is achieved in accordance with the invention with a flexible pipe element, in particular for exhaust pipes of combustion engines of motor vehicles with a helical or corrugated bellows, at least one strip wound hose which is helically wound or has several annular segments and which coaxially adjoins the bellows, at least one spacer locally disposed between the bellows and the strip wound hose and an outwardly disposed tube of knitted fabric, wherein the pipe element has a total stiffness of not more than 5 N/mm.
In the inventive design, the bellows is sufficiently supported by the strip wound hose in the axial and radial directions such that premature failure thereof is safely prevented. Moreover, the total maximum stiffness of the inventive pipe element of 5 N/mm advantageously permits a fixed arrangement of the exhaust system on the underbody of the motor vehicle. This is desired by the automobile industry since thermally or mechanically produced distance and angle changes between the engine and exhaust system are reliably accommodated.
The spacers locally disposed between the bellows and the strip wound hose prevent contact between the bellows and the strip wound hose due to oscillating motion of the motor vehicle and the resulting noise caused thereby as known per se from DE 198 48 451 A1. The local spacers reliably prevent the bellows and the adjacent strip wound hose from striking each other to prevent noise, in particular at resonance frequencies, due to direct collision of these components.
The tube of knitted fabric disposed on the outside protects the flexible pipe element from external influences, such as mechanical loading during assembly and hurled stones during operation, without impairing its motion. A highly flexible tube of knitted fabric of this type abuts the inside adjoining element, e.g. at least on the outer crests of the bellow corrugations and across its entire length such that generation of undesired noise due to oscillating motions is reliably prevented.
As mentioned above, the helical windings or annular segments of the strip wound hose have a substantially S-shaped cross-section by means of which axially neighboring elements of the helical winding or axially neighboring annular segments of the strip wound hose each engage one another. In a preferred embodiment, the substantially S-shaped cross-sectional profile of the helical winding or of the annular segments of the strip wound hose has a central section each end of which has an adjacent bar extending substantially in the axial direction with each bar being joined by an end bar extending towards the central section and disposed substantially in an axial direction, wherein the radial separation between the bars is larger than the radial thickness of the end bars and the axial separation between the central section and the bridges is greater than the axial length of the end bars. This embodiment forms a soft stop between each helical winding or between each of the annular segments of the strip wound hose in an axial and also radial direction to prevent distortion of the bellows due to bending, stretching or compression, etc. On the other hand, the overall length of the pipe element ensures increased mobility in the axial and radial directions since axially neighboring elements or segments of the strip wound hose can move relative to another. In particular angular motion is also possible having a maximum value which depends on the ratio between the radial separation of the bars and the radial thickness of the end bars and on the ratio between the axial separation between the central section and the bridges and the axial length of the end bars of the substantially S-shaped cross-sectional profile. Engagement of the axially neighboring elements of the helical winding or the axially neighboring annular segments of the strip wound hose with axial and radial play also guarantees a considerably increased freedom of motion with respect to axial, radial and angular movements of the pipe e

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