Pipe joints or couplings – Flexible joint – rigid members – Bellows
Reexamination Certificate
1999-05-28
2001-11-13
Luu, Teri Pham (Department: 3627)
Pipe joints or couplings
Flexible joint, rigid members
Bellows
C285S226000
Reexamination Certificate
active
06315332
ABSTRACT:
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 of motor vehicles.
2. Description of the Prior Art
Flexible line elements arc e.g. incorporated as adaptors into the exhaust pipe of a motor vehicle, which is installed on the vehicle floor, in order to absorb movements and vibrations and prevent the transfer thereof to adjacent components, such as arise due to elastically mounted driving engines, vehicle faults, temperature-caused length changes, etc. They generally comprise a helically or annularly corrugated metal bellows, together with further elements, such as line and/or support elements, together with additional elements for supporting and/or increasing stability, e.g. metal gauze, or damping elements, so that if vibrations are excited in the resonant frequency range of the bellows movement increases of the latter are prevented, because they could lead to a reduction of the service life and to interaction with other components for noise production purposes.
In many cases flexible line elements of this type are exposed to torsional stresses. If the bellows of such line elements has a torsion-stiff construction, such as e.g. a parallel bellows, although such torsional stresses do not lead to its failure, they are transferred in undesired manner to adjacent components. If the bellows is torsion-soft, it is suitable for the decoupling of adjacent components, but in particular dynamic torsional stresses can lead to its failure. It is stressed in this connection that in the case of dynamic stressing a metallic material is subject to earlier fatigue than with static stressing, the stresses to which a line element in the exhaust pipe of a vehicle is exposed being more particularly of a dynamic nature.
Thus, on the basis of a line element of the aforementioned type, one object of the invention is to provide a line element that is compact and especially may have short axial extension. A further object of the invention is to provide the line element on the one hand to be torsion-soft, so that it does not transfer torsional stresses to adjacent components, but on the other that the line element does not fail when high torsional stresses occur.
SUMMARY OF THE INVENTION
According to the invention, the problem of the prior art is solved in the case of a line element of the aforementioned type in that there are at least two interconnected metal bellows provided with cylindrical joining ends and at least one of the bellows is a helically corrugated bellows and/or the bellows are telescoped and the two bellows are connected at only one of their joining ends. One joining end of a first bellows is firmly connected to one joining end of the other bellows and the other joining end of the first bellows is firmly connected to one end of a substantially rigid pipe element, the other end of the pipe element serving as one cylindrical joining end of the line element and the other joining end of the outer bellows serving as the other cylindrical joining end of the line element.
The twistability of the inventively designed line element is based on the physical similarity of a helically corrugated metal bellows and a coil spring. If a coil spring is lengthened or shortened, it is subject to a restoring force F, which is proportional to the deflection s, the proportionality factor D being the spring strength;
F=D×s
In the case of a deflection s the coil spring starts to twist about its median longitudinal axis, the twisting about the latter being proportional to the deflection. Conversely a coil spring is able to transform a torsional stress into a length change, the restoring which is proportional to the deflection, consequently being proportional to the twisting about the coil spring's median longitudinal axis. Thus, if several coil springs are combined with one another, the individual springs can transform torsional movements into axially directed, translatory movements, the combination of coil springs being able to compensate torsion-induced, translatory movements.
As has already been stated, a helically corrugated bellows behaves in a similar way. In the case of torsional stressing, it transforms the twisting about its median longitudinal axis into a length change and it is subject to a restoring force proportional to the length change. If further axially flexible bellows are combined with a helically corrugated bellows, then there is a decoupling of torsional movements and translatory movements and it is in most cases sufficient to only combine two bellows. At least one bellows must be helically corrugated for transforming the torsion into a length change, whereas the second bellows can either be helically or annularly corrugated for compensating for the length change.
The torsion-softness of the inventive line element can be adjusted via the geometry of the threads of the helically corrugated bellow or bellows. The torsion-softness increases with an increasing number of threads, for a constant thread pitch. In addition, the torsion softness increases with increasing thread pitch for a constant number of threads. If a particularly torsion-soft line element is to be provided, it should consequently have at least one helically corrugated bellows with a large number of threads with a high thread pitch.
In a preferred embodiment, the line element according to the invention has successively arranged bellows, whose diameters are roughly identical and which are interconnected, e.g. by welding at in each case one of the cylindrical joining end there of. As two bellows are generally sufficient for decoupling torsional stresses occurring in the exhaust-pipe of a motor vehicle (namely a helically corrugated bellows for transforming the torsion into a length change and a further helically or annularly corrugated bellows for compensating the length change), it is preferred for cost reasons to use only two bellows as basic components of the line element.
As has already been suggested, according to a variant a helically corrugated bellows is combined with a further helically corrugated bellows. In another variant a helically corrugated bellows is combined with an annularly corrugated bellows. In both cases a torsional deflection at one of the two ends of the arrangement leads to a translatory displacement of the connection point between the bellows due to the transformation of a rotary movement into an axial movement of a helically corrugated bellows, the end of the arrangement opposite to the introduction of the torsional movement remains idle. In order to e.g. compensate the torsion-induced length increase of a helically corrugated bellows by means of the length reduction of a further, series-arranged, helically corrugated bellows, it is particularly appropriate to combine helically corrugated bellows with opposing thread pitch, but the same pitch height in succession so as to form a line element. Thus, e.g. a torsion-induced shortening of one helically corrugated bellows is compensated by the lengthening of the second bellows and a torsional stress acting on a bellows is not transferred in undesired manner in the form of a translatory stress.
According to another preferred embodiment of the inventive line element, there is a parallel arrangement of telescoped bellows, whereof at least one is helically corrugated and are interconnected, preferably in the vicinity of in each case one of their joining ends, e.g. by welding. Thus, a joining end of the inner bellows arranged internally of the line element is firmly connected to one end of the pipe element, whereas the other end of the pipe element arranged internally o f the inner bellows serves as a cylindrical joining end of the line element. In much the same way as for the consecutive arrangement of the bellows, a torsional deflection at one of the two ends of the parallel arrangement leads to a translatory displacement of the connection point between the bellows due to the transformation of the rotary movement into an axial m
Aschoff Wolfgang
Salzer Georg
Antonelli Terry Stout & Kraus LLP
IWK Regler und Kompensatoren GmbH
Luu Teri Pham
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