Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Damper in the form of a shock absorber
The invention relates to a damper in the form of a shock
absorber consisting of an absorber sleeve of plastics
material and a piston co-operating therewith, wherein the
piston (1, 21) is arranged inside the absorber sleeve (2,
22) and has as least one expansion bead (10, 30; 31), of
which the external diameter is greater than the internal
diameter of the undeformed absorber sleeve.
Dampers in the form of shock absorbers which absorb high
energy over a short distance, in particular during collisions
between vehicles, are known. They are used for vehicle
seats, bumpers and the like, but, if suitably dimensioned,
can also be used universally.
It is normal to use hydraulic dampers. Although they
are very effective, they are also very expensive, are
designed fox many thousands of load cycles and are relatively
heavy.
As a less expensive solution (DE-OS-29 18 280), attempts
have already been made to insert a lid-like piston against an
absorber sleeve of~duroplastic material (epoxide resin) with
a wound glass fibre inlay. HowevE:r, such a shock absorber
can only be loaded once as the sleeve is desirably destroyed
due to the high stress occurring. Moreover, it can only be
loaded in one direction.
A buffer gear on railway vehicles is known from DE-AS 1
079 618, which consists of a buffer with a piston-like end
penetrating into the end of a tubular, i.e, sleeve-like
pressure-transmitting member. This pressure-transmitting
member extends from one carriage end face to the other and
widens under impact due to the piston-like end of the buffer
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CA 02024917 2000-O1-06
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penetrating more deeply. A buffex is only effective in one
direction in each case.
Dampers are also known in which a piston with an expansion
bead is immersed into a metal sleeve provided with an internal
liner of rubber or plastics material (GB-PS 1 039 300) or into
a sleeve of rubber alone, wherein the expansion bead, as
described at the outset, has a greater external diameter than
the internal diameter of the sleeve or of the internal liner.
Dampers of this type are designed as bearing elements for
vibrating machines or machine parts, such as washing machines
or vehicle engines. They are not suitable as shock absorbers.
The object is also to design dampers of this type such
that they can also be used as shock absorbers and, in
particular, allow repeated stressing, more specifically in both
directions.
The object is to provide an inexpensive damper for shock
absorption which is adapted to the stress frequency, can be
stressed several times and, in particular, is operative in both
directions.
The invention provides damper in the form of a shock
absorber comprising an annular absorber sleeve of plastics
material and a piston cooperating therewith arranged inside
the absorber sleeve for shock absorbing motions in to and fro
directions, the piston having at least one expansion bead the
external diameter of which is greater than the internal
diameter of the undeformed absorber sleeve, the absorber sleeve
comprising a thermoplastic material having a tensile strength
~R of at least 40 MPa, an elongation at break eR of at least
60$, a tensile stress at yield 6S of at least MPa and an
elongation at yield es of at, least 3.5~ (according to ISO/R
527 or DIN 53 455 in each case), and a support housing for the
sleeve spaced outwardly away from the undeformed and deformed
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surfaces of the sleeve said support housing having end portions
mounting opposite ends of the sleeve therein.
Thermoplastic materials having these physical properties
guarantee optimum behaviour during appropriate stressing, in
particular with respect to the contraction of the absorber
sleeve to its original external diameter after stressing.
Thermoplastic materials with values below this can also be
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used, but sometimes experience undesirable plastic
deformation which could limit the capacity for repeated
stressing.
Particularly good results can be achieved with plastics
materials having a tensile strength ~R of about 50 MPa and an
elongation at break ~ R of about 85~ as well as a tensile
stress at yield oS of about 55 MPa and an elongation ~ S of
about 5.5~. The elongation modulus E~ should be about 2200
MPa.
A thermoplastic blend of polycarbonate and
acrylonitrile-butadiene-styrene-copolymers of the type
described in DE-OS-22 59 565 and DE-OS-23 53 428 (both
corresponding to US-PS-3 988 389) is particularly suitable.
A blend of polycarbonate and polybutylene terephthalate,
described in DE-OS-31 18 526 (corresponding to US-PS-4 482
672) is also particularly preferred as material for the
absorber sleeve.
Such mixtures are distinguished by the particular
stability to ageing of the rubber contents.
The novel damper is distinguished by its compactness
with high energy absorption as well as low weight. It is
operative in both directions of its axis. These properties
allow use of the new damper for shock absorption on vehicle
seats in the event of rear end collisions. The thermoplastic
material of the absorber sleeve has the property that it
"flows" so to speak over the expansion bead by elastic
deformation when stressed, the absorber sleeve subsequently
resuming its original diameter.
The piston is introduced into the absorber sleeve in
basically the same way as during the actual stress, but
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considerably more slowly in order reliably to prevent
permanent overstretching of the absorber sleeve. In other
words, the piston is pressed slowly into the absorber sleeve.
The piston and piston rod are of steel or of a suitable
plastics material such as polyamide, optionally reinforced
with glass fibres. Depending on the application, the piston
rod and the absorber sleeve are provided with corresponding
connections; the end of the piston rod, for example, to a
head for pushing through a screw and the absorber sleeve, for
example, tc~ an abutment which also has a head or flange for
fining purposes. The piston rod should be mounted ~t least
in one slideway, advantageously more desirably in two
slideways, that is preferably at the ends of an abutment in
which the absorber sleeve is fixed. However, the piston rod
and abutment can also have flanges for fixing purposes. If
necessary, at least one flange can be arranged at an angle to
the axis of the absorber sleeve and piston rod if the
constructional parameters necessitate this. It is important
merely that the absorber sleeve has sufficient external
clearance round it in the radial direction always to leave
space from other components as it is deformed by the piston
or expansion bead.
The cross-sectional geometry of the piston or of the
expansion bead and of the absorber sleeve will generally be
round, simply for reasons of prodL~ction. However, an
elliptical or polygonal cross-sectional shape is certainly
also feasible.
If the piston has several expansion beads, higher energy
can be absorbed. The distance between expansion beads has an
effect. The greater this distance, the more the absorber
sleeve can contract again between them. If necessary, the
external diameter of the expansion beads can be selected
differently. Depending on the stress direction, if the
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thicker expansion bead is stressed first, more energy is
absorbed in a shorter distance than in the opposite direction
in which the thinner expansion bead reacts,first. This
embodiment is advantageous whenever faster energy absorption
is to be achieved in one direction than in the opposite
direction.
If the expansion bead is constructed in the longitudinal
section, there is the alternative between a continuous
external contour and a discontinuous external contour.
A sinusoidal external contour should be offered most
frequently, but any other continuous curvature can offer its
advantages in special cases. The contour generally extends
outwardly in the form of a hollow groove from the piston,
then passes into the opposite curvature and, after reaching
the maximum diameter, preferably passes in a mirror image to
the course just described back into the piston rod or the
piston. Bevels which enclose an angle preferably of 30° to
60° with the central axis of the piston or expansion bead are
provided for the discontinuous course of the external
contour. The greater this angle, the stronger the
absorption. Starting from the piston, a bevel with a greater
angle which then kinks into a bevel, of smaller angle will
generally be selected. A cylindrical portion of maximum
diameter then follows. The expansion bead can also be
pravided with bevels having a different angle on the other
side. It goes without saying that curved portions can be
combined with bevels.
If the absorber sleeve has a wall thickness which
increases in at least one stress direction, a desired damping
characteristic is achieved. If the wall thickness increases,
then the damping also increases if there is a stress in this
direction; it decreases in a similar manner if the wall
thickness decreases. The change in the wall thickness can
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also be achieved by external ribs or, in extreme cases,
internal grooves in the longitudinal direction. Peripheral
beads provided externally on the absorber sleeve or annular
grooves provided internally also produce similar properties
to several expansion beads.
Two embodiments of the novel damper are shown purely
schematically in section in the drawings and are described in
more detail below.
Figure 1 shows a first embodiment of the damper.
Figure 2 shows a second embodiment.
In Figure 1, the damper consists of a piston i, an
absorber sleeve 2 and an abutment 3 for the absorber sleeve
2. The piston 1 is arranged on a piston rod 4 which has a
connecting flange 5 at one end and is mounted on both sides
in the abutment 3 in slideways 6. Piston 1, piston rod 4 and
connecting flange 5 are produced from steel. The abutment 3
consists of two forged metallic bearing bushes 7 and 8, of
which the bearing bush 7 can be fixed on a foundation and the
bearing bush 8, as a lid, is screwed to the bearing bush 7 so
that the absorber sleeve 2 is clamped in centering means 9.
The piston 1 has an expansion bead. 10 of which the maximum
external diameter is greater than the internal diameter of
the absorber sleeve 2. From left to right in the drawing,
the piston 1 or the expansion bead 10 has the following
geometry: a 5 mm wide cylindrical portion and an external
diameter corresponding to the internal diameter of the
absorber sleeve 2, a 5 mm wide portion (bevel) widening
sonically at an angle ~.of 45°, a 5 mm wide cylindrical
portion of maximum diameter, a 2 mm wide portion tapering
sonically at an angle ~ of 30°, a further 3 mm wide portion
tapering sonically but at an angle's of 45o and a portion
corresponding to the first portion in diameter and width. The
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absorber sleeve 2 has an internal diameter of 47 mm in the
undeformed region and of 50 mm in the region which is
deformed to a maximum. Its wall thickness in the undeformed
region is 1.5 mm. It consists of a blend of polycarbonate
and acrylonitrile-butadiene-styrene-copolymer having a
tensile strength cYR of 50 MPa, an elongation at break ~.R of
85~, a tensile stress at yield crs of 55 MPa, an elongation ES
of 5.5~ and an elongation modulus ~2 of 2200 MPa (commercial
product ~ayblend T 85 MN made by Bayer AG, heverkusen,
Federal Republic of Germany, according to Code of Practice,
Order No. KU 46151, edition 8.84, D4-838/845319).
In Figure 2, the damper consists of a piston 21, an
absorber sleeve 22 and an abutment 23 for the absorber sleeve
22. The piston 21 is arranged on a piston rod 24 which has a
connecting head 25 at one end and is mounted in slideways 26
on both sides. The piston 21 and the piston rod 24 are
produced from glass fibre reinforced epoxide resin. The
abutment 23 also produced from glass fibre reinforced epoxide
resin consists of a sleeve 27 and a lid 28 which are screwed
together and clamp the absorber sleeve 22 in centering means
29. The piston 21 is provided with two expansion beads 30,
31 which pass into one another. The piston 21 and the
expansion beads 30 and 31 have the following geometry in the
illustration, from left to right: a 6 mm wide cylindrical
portion and a diameter corresponding to the internal diameter
of the absorber sleeve 22, a 10 mm wide portion which widens
conically at an angle of of 30°, passes into a sine curve and
xeaches the maximum diameter, a 10 mm wide portion until a
minimum diameter which is smaller than the internal diameter
of the absorber sleeve 22 is reached, a portion with a
sinusoidal shape increasing again to a second, but smaller
maximum diameter, which is greater than the internal diameter
of the absorber sleeve 22, and finally a 6 mm wide portion in
which the sinusoidal shape decreases again and passes into
the cylindrical shape corresponding to the internal diameter
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of the absorber sleeve 22. At the point at which the piston
21 is placed after insertion, the absorber sleeve 22 has a
wall thickness of 3 mm in the undeformed state. The internal
diameter is 30 mm in the undeformed state. In the
illustration, the wall thickness increases continuously to 4
mm going out in both directions from the position of the
piston 21. To the right, the absorber sleeve 22 has an
external bead 32 having an external diameter of 40 mm. It
consists of a blend of polycarbonate and polybutylene
terephthalate having a tensile strength dR of 57 MPa and an
elongation at break of 120 as well as a tensile stress at
yield css of 55 MPa and an elongation of 4~ a d an elongation
modules EZ of 2200 MPa. (Commercial product ~akroblend PR 5i
produced by Bayer AG, Leverkusen, Federal Republic of
Germany, according to Code of Practice KU 47.404 dated
15.f.1987).
T.o n 77 1 Oz
