Convoluted boot

A convoluted boot made of a thin-walled thermoplastic elastomer with at least one collar region which, on its inside, has an internal annular bead engaging a flat annular groove of a universal joint with a rectangular or trapezoidal cross-section, where at least the one collar region, on its outside, has an annular groove with a rectangular or trapezoidal cross-section for tensioning element, which annular groove is provided with a substantially flat bottom part resting against the tensioning element and is wider than the internal annular bead, and the collar region, within the flat annular groove in the region of the internal annular bead, has at least one recess-like annular gap with a rectangular or trapezoidal cross-section whose cross-sectional depth is greater than its width.

BACKGROUND OF THE INVENTION 
The invention relates to a convoluted boot made of a thin-walled 
thermoplastic elastomer with at least one collar region which, on its 
inside, comprises an internal annular bead engaging a flat annular groove 
of a universal joint with a rectangular or trapezoidal cross-section. 
Such convoluted boots made of a material such as Hytrel (.RTM. Dupont) or 
Santoprene (.RTM. Monsanto) have a considerably higher modulus of 
elasticity than previously used rubber-elastic materials, which means that 
holding the collar regions on the respective universal joint components or 
the like constitutes a problem. The tensioning elements used have to meet 
more stringent requirements because higher pretensioning forces have to be 
applied. 
To reduce the necessary forces it is proposed in JP 62-16541 Y 2, for 
example, to provide the outer groove with a projecting central web so that 
deformation by the tensioning element remains limited to this central web, 
the disadvantage of this design being that the material of the radially 
loaded web may flow into the large-volume annular spaces underneath the 
tensioning element, thereby loosening the connection. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to design a convoluted boot in the 
region of its collar in such a way that it is possible to use conventional 
tensioning elements, i.e., tensioning strips of standard strength while at 
the same time ensuring a firm fit of the collar region. The boot is to be 
produced by blow molding. 
In accordance with the invention, the objective is achieved in that at 
least the one collar region, on its outside, comprises an annular groove 
with a rectangular or trapezoidal cross-section for a tensioning element, 
which annular groove is provided with a substantially flat bottom part 
resting against the tensioning element and is wider than the internal 
annular. The collar region, within the flat annular groove in the region 
of the internal annular bead, comprises at least one recess-like annular 
gap with a rectangular or trapezoidal cross-section whose cross-sectional 
depth is greater than its width. 
Such a boot ensures a secure form-fitting engagement between the internal 
bead and the respective annular groove, which engagement, because of the 
large area of contact between the tensioning strip and the outer groove, 
cannot be released. The internal bead is preferably slightly wider than 
the corresponding groove in the joint component or the like so that full 
sealing is ensured, especially in the flank regions. 
As there are no large-volume spaces underneath the tensioning strip, the 
internal bead cannot be lifted out of the annular groove. 
Because of the recess-like annular gap in the externally positioned annular 
groove, it is possible to produce the boot by the blow molding method 
which uses hose material of a uniform wall thickness. Without the deep 
annular gaps proposed by the invention, which result in material 
displacement during the blowing process, the internal annular bead could 
only be produced while simultaneously creating large-volume hollow spaces 
underneath the tensioning strip on the outside, which would again cause 
the disadvantages as described above. 
In a preferred embodiment, the ratio of depth to width of the recess-like 
annular gap amounts to approximately 3, with the depth of the annular gap 
approximately corresponding to the thickness of the collar region in the 
annular groove adjoining the internal annular bead and amounting to 
between 1.2 and 2 mm in order to achieve satisfactory strength conditions. 
Preferably, two such annular gaps are provided and it is possible to 
arrange them asymmetrically relative to the external annular groove. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a boot 1 with a first collar region 2 and a second collar 
region 3, partially in section, and it can be seen that the collar regions 
2, 3 each comprise a flat circumferential groove 4, 5, the groove 4 having 
internal annular gaps 8, 9, whereas the annular groove 5 is provided with 
a single deep annular gap 10 in the region of the internal annular bead 7. 
FIG. 2 shows a collar region 2 in the form of a detail showing the annular 
groove 4 having a width a within which there is positioned an internal 
bead 6 having a considerably smaller width b and a radial depth c. In the 
region of the annular bead 6 there are provided the two annular gaps 8, 9 
for forming the internal annular bead 6, which annular gaps, as compared 
to the width a of the annular groove 4, have a very small width d, e and 
great depth f which corresponds to the thickness of the collar region 2 
laterally adjoining the internal annular bead 6. 
While the invention has been illustrated and described as embodied in a 
convoluted boot, it is not intended to be limited to the details shown, 
since various modifications and structural changes may be made without 
departing in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.