Patent Application
20050020366
The invention relates to a convoluted boot for sealing an annular gap between two parts which are connected to one another in a rotationally fast way, which can be articulated relative to one another and which are axially displaceable relative to one another, especially of a constant velocity plunging joint, consisting of a low-strain hard polymer material, having a first larger collar to be secured to a first component, a second smaller collar to be secured to a second component and a plurality of annular fold units which extend between the first collar and the second collar and which, in the form of outer folds consisting of two annular flanks, form a fold peak between two fold valleys.
Because requirements become more and more stringent, convoluted boots of said type are produced from hard polymer materials to an increasing extent. As compared to soft resilient materials used earlier, said hard polymer materials feature an improved resistance in mechanical and chemical respects, and in view of higher speeds and the need for a longer service life, it is inevitable that they are used. One concern is their reduced flexibility which can be a problem at low temperatures. In the case of constant velocity fixed joints which effect articulation only between two rotating components, convoluted boots made of said materials, even today, do meet the respective requirements in their entirety. In the case of constant velocity plunging joints which, in addition to the angular movement, effect an axial displacement between the two rotating components, this means that the sealing convoluted boots are subject to friction contact between the annular flanks on the inside of the angle when the joint is in a telescoped and articulated condition and, when the joint is in the extended and articulated condition, the individual annular folds open up excessively widely on the outside of the angle, causing a collapsing of the annular folds or other irregularities. At high speeds, in particular, this can result in the elasticity limit of the convoluted boot being exceeded and it can lead to boot damage.
It is therefore the object of the present invention to provide a convoluted boot of said type which is able to meet more stringent requirements in operation without suffering any damage and which is therefore particularly suitable for constant velocity plunging joints. The objective is achieved by providing a convoluted boot of the initially mentioned type with the following characteristics:
By providing two special groups of folds, the deformation of the convoluted boot when articulation and changes in axial length occur is allocated to said two groups in such a way that, in the first group consisting of folds of a decreasing size, deformation largely takes place in the form of articulation, whereas the second group consisting of at least one fold with a small diameter largely accommodates the change in axial length by being extended. Convoluted boots with two different groups of folds are known from DE 33 09 386 C1, DE 43 23 686 C2, DE 196 01 096 A1 and DE 198 06 173 C1 for example. However, in these cases, between the two groups of folds, there exists a region which is in constant contact with the inserted shaft. From DE 38 73 496 T2, there is known a convoluted boot of said type with two different functional regions, having folds whose flanks extend parallel relative to one another and, on the outside, are connected to one another by a rounded annular bead. The annular folds according to the present invention, however, when the two collars are coaxially aligned relative to one another in the fitted condition, are contact-free relative to the inserted shaft and the annular folds each, approximately, comprise the shape of a double cone.
The first group of folds can comprise up to five annular folds and the second group of folds can comprise up to eight annular folds. The number of folds depends on the respective requirement profile. It is obvious that with an increased number of annular folds, the need for a longer boot length also increases, but the angle work to be carried out by the individual folds generally decreases during articulation. However, this does not affect the possibility of varying the shape of the individual folds within certain ranges, i.e. that it is possible to provide more pointed and wider folds, but in principle, the folds of the first group are wider (have a larger volume) and the folds of the second group are more pointed (narrower).
According to a preferred embodiment it is proposed that the two annular flanks of each of the annular folds of the first group form opposed angles with a radial plane, wherein a smaller angle β is formed by the annular flank pointing towards the second collar and wherein a larger angle α with ≧(β+25°) is formed by the annular flank pointing towards the first collar. Furthermore, it is proposed that the annular flanks of each of the annular folds of the second group form opposed angles with a radial plane, wherein the annular flank pointing towards the second collar forms an angle β and wherein the annular flank pointing towards the first collar forms an angle α which is defined by (β+5°)
As the approximately conical annular flanks, in particular the annular flanks of the first group which point towards the first collar, can be curved so as to comprise a convex outside, it is specified hereby that the reference for the angle values has to be the conical face between the outer line of a fold valley and the outer line of a fold peak and that, if viewed in a longitudinal section, it has to be the straight line between the smallest outer radius of a fold valley and the greatest outer radius of a fold peak.
According to a further embodiment it is proposed that between the annular folds of the first group and the annular folds of the second group, there is provided a transition fold whose diameters at the fold valleys deviate from one another, wherein the diameter of the annular flank pointing towards the first collar is greater than the diameter of the annular flank pointing towards the second collar. In particular, it is proposed that the annular flanks of the transition fold form opposed angles with a radial plane, wherein the annular flank pointing towards the second collar forms an angle β and that the annular flank pointing towards the first collar forms an angle α which is defined by (β+25°)≧α≧(β+5°). Said transition fold is thus similar to the annular folds of the first group in that the diameter of the fold valleys decreases towards the second collar; however, as far as the angle configuration of the annular flanks is concerned, said transition fold is similar to the annular folds of the second group. The purpose is to ensure that even at larger angular movements of the convoluted boot, there is preferably no friction contact between the fold valleys and the inserted shaft.
A preferred material for the convoluted boot is a thermoplastic elastomer (TPE); in particular, there are proposed materials based on polyurethane (TPU), on polyester (TPEE), in particular a polyether ester or a polyester ester, materials based on polyamide (TPA) or on polyolefin, in particular polypropylene or polyethylene.
A preferred embodiment of the convoluted boot in accordance with the invention will be described below with reference to the drawings wherein
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 10144576.8 | Sep 2001 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP01/11111 | 9/26/2001 | WO |
