U.S. patent application number 09/834322 was filed with the patent office on 2002-04-25 for piston for a piston-cylinder arrangement, in particular a shock absorber piston.
Invention is credited to Casellas, Antonio, May, Ewald.
Application Number | 20020046651 09/834322 |
Document ID | / |
Family ID | 7884434 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020046651 |
Kind Code |
A1 |
Casellas, Antonio ; et
al. |
April 25, 2002 |
Piston for a piston-cylinder arrangement, in particular a shock
absorber piston
Abstract
The invention relates to a piston for a piston-cylinder
arrangement, especially a shock absorber piston, comprising a
piston body (6) that is fitted with at least one peripheral web
(10) on its peripheral surface, wherein a collar-shaped sealing
element (9) made of thermoformable plastic material is also formed
on the peripheral surface of the piston body (6) in such a way that
the web (10) is only formed in part of the height of the material
of the collar-shaped sealing element (9).
Inventors: |
Casellas, Antonio;
(Siegburg, DE) ; May, Ewald; (Bonn, DE) |
Correspondence
Address: |
Woodcock Washburn Kurtz
Mackiewicz & Norris LLP
One Liberty Place - 46th Floor
Philadelphia
PA
19103
US
|
Family ID: |
7884434 |
Appl. No.: |
09/834322 |
Filed: |
April 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09834322 |
Apr 13, 2001 |
|
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PCT/EP99/07642 |
Oct 12, 1999 |
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Current U.S.
Class: |
92/248 |
Current CPC
Class: |
Y10T 29/49261 20150115;
Y10T 29/49252 20150115; Y10T 29/49256 20150115; F16J 15/164
20130101; F16F 9/368 20130101 |
Class at
Publication: |
92/248 |
International
Class: |
F16J 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 1998 |
DE |
198 47 341 9 |
Claims
1. A piston for a piston-cylinder arrangement, in particular a
shock absorber piston, with a piston body (6) that is provided with
at least one peripheral web (10) on its peripheral, and with a
collar-shaped seal (9) made of a thermoplastic sealing material
that is formed onto the peripheral surface of the piston body (6)
in such a way that the web (10) presses into the material of the
collar-shaped seal (9) over only a portion of its height.
2. A piston according to claim 1, characterized in that at least
two peripheral webs (10) are arranged on the peripheral surface
that border a notch (11).
3. A piston according to claims 1 or 2, characterized in that each
of the edges (9.1, 9.2) of the collar-shaped seal (9) extends
beyond the end surface (4.1, 5.1) of the piston body (6) associated
with it.
4. A piston according to one of claims 1 through 3, characterized
in that at least one web (10) is located in an area adjacent to an
end surface (4.1, 5.1) of the piston body (6).
5. A piston according to one of claims 1 through 4, characterized
in that the piston body (6) is assembled from at least two element
sections (6.1, 6.2) that each have a plane of separation running
perpendicular to the piston axis.
6. A piston according to one of claims 1 through 5, characterized
in that each element section (6.1, 6.2) of the piston body (6) has
a peripheral web (10).
7. A piston according to one of claims 1 through 5, characterized
in that the piston body (6) is manufactured using powder
metallurgy.
8. A piston according to one of claims 1 through 7, characterized
in that the collar-shaped seal (9) consists of PTFE as a
thermoplastic synthetic.
9. A piston according to one of claims 1 through 8, characterized
in that the collar-shaped seal (9) is pressed on, calibrating its
exterior surface (12) at least in its area overlapping the webs
(10).
Description
DESCRIPTION
[0001] There is a shock absorber piston known from EP-A-0 658 611
that has a piston body that is provided with a peripheral web at
its peripheral surface. A number of webs running in the axial
direction attach to this peripheral web on one side of it. A seal
made of thermoplastic synthetic is sprayed onto this piston body in
an injection molding process. The webs extending in the axial
direction and the notches between them, which are filled in with
sealing material, serve to reliably anchor the sealing material.
The seal applied by injection molding enables close tolerancing,
which prevents "blow-by" and thus provides a reliable seal of the
cylindrical spaces facing one another. The process to produce these
types of injection-molded seals is relatively expensive.
[0002] There is a piston-cylinder arrangement known from U.S. Pat.
No. 3,212,411 whose piston body has a number of peripheral grooves
on its peripheral surface. To apply the seal, a cup-shaped
preliminary mold made of PTFE (polytetrafluoroethylene) is provided
that is first placed on the piston body loosely. The piston body so
prepared is then pressed into a forming and calibrating cylinder
that is heated to a high temperature. Under the influence of the
heat, the PTFE material is pressed into the grooves on the
peripheral surface of the piston body. Then, the piston body with
the pressed-on seal is cooled in an appropriately designed cooling
cylinder. The grooves are completely filled with the sealant
material so as to provide a form-locked solid connection of the
seal to the peripheral surface of the piston body. When used as a
shock absorber piston, the bottom surface of the preliminary mold
that still overlaps the end surface of the piston body on one side
must then be removed.
[0003] There is a shock absorber piston known from EP-A-682 190
whose only essential difference from the processes described above
in its manufacture is in that to apply the seal, instead of a
cup-shaped preliminary mold, a stamped circular sleeve is used.
This circular sleeve is placed on one end of the piston body. The
piston body prepared thusly is then pressed into a heated forming
and calibrating cylinder, wherein the circular sleeve is placed
around the peripheral surface of the piston body as a strip and
then pressed into the grooves running in the peripheral direction
of the piston body under the influence of heat. Then, the piston
with its pressed-on seal is guided through a cooling tube. Here, as
well, the sealant material fills the grooves practically completely
so that the seal is solidly connected to the peripheral surface of
the piston body in form-locked fashion.
[0004] The two processes described above have the disadvantage in
that considerable pressures are required to shape and to press the
sealant material into the grooves on the peripheral surface of the
piston body. Also, the sealant material forming the seal is subject
to strong shaping forces that disadvantageously influence the
structure of the sealant material.
[0005] The objective of this invention is to produce a piston, in
particular a shock absorber piston, in which the disadvantages
described above are avoided.
[0006] This objective is met according to the invention by a piston
for a piston-cylinder arrangement, in particular a shock absorber
piston, with a piston body that is provided with at least one
peripherally running web on its peripheral surface. Furthermore, in
this piston arrangement, a collar-shaped seal made of a
thermoformable plastic material is formed onto the peripheral
surface of the piston body such that the web presses into the
material of the seal only along a portion of its height.
Surprisingly, it has been shown that, in order to get a good seal
between the seal and the piston, it is not necessary to arrange a
multitude of grooves on the peripheral surface of the piston body.
A minimum of one peripheral web is sufficient here, onto which the
collar-shaped seal is formed in the manner described in
EP-A-682-190. It has also been shown, surprisingly, that it is
sufficient for the web to press into the material of the seal only
along a portion of its height. On one hand, this results in an
acceptable form-lock between the collar-shaped seal and the piston
body, and on the other hand, only moderate shaping forces result on
the plastic material so that not only do less pressure forces have
to be applied, but material flow is also kept to a very minimum
during the deformation, thus preventing a disadvantageous influence
on the material structure for practical purposes. The web is then
located near one end surface of the piston body, preferably the end
surface with the higher load.
[0007] At higher loads during operation, a useful embodiment of the
invention provides that at least two peripheral webs are located on
the peripheral surface, the peripheral webs being located on both
sides of a notch. This results in a reliable form-locked connection
even at higher working pressures. An arrangement with one, or even
two peripheral webs can still be produced cost-effectively through
machining.
[0008] In another advantageous embodiment of the invention, it is
provided that each of the edges of the collar-shaped seal extends
beyond the end surface of the piston body associated with it. Since
the collar-shaped seal is produced according to a known process
from a circular sleeve, the phenomenon of "back memory" of the
sealant material described in EP-A-0 682 190 can be used to cause
the edge around the inner diameter of the circular sleeve to pull
inward after it is applied to the piston body, and to cause the
edge of the collar-shaped seal produced from the external edge of
the circular sleeve to move back outward and in this way to
protrude above the rest of the peripheral surface of the
collar-shaped seal as a lip seal. If the piston body is installed
such that, when used as a shock absorber piston, the piston surface
provided with the lip-shaped edge extending outward faces the
pressurized side, i.e. the side subjected to the high load, and if
the piston surface with the edge that springs back inward is
located on the so-called suction side, this results in an improved
seal of the piston in the shock absorber cylinder during a pressure
load since the hydraulic fluid in the lip-shaped edge presses
against the cylinder wall. When it springs back, i.e. for suction
loads, the hydraulic fluid can then enter the intermediate space
between the piston wall and the cylinder wall to some degree as a
result of the minimal play between the two. The fluid can thus find
its way up to the edge where the lip-shaped edge of the
collar-shaped seal sits against the cylinder wall for the purposes
of lubrication. Thus, acceptable lubrication is provided,
preventing wear of the seal. Since the flow resistance due to this
minimum gap between the sealing surface of the piston and the
cylinder wall is considerably higher than the flow resistance
through the flow channels in the piston body, practically no drop
in performance results.
[0009] In an especially advantageous embodiment of the invention,
it is provided that at least one web is located in an area adjacent
to one end surface of the piston body. In particular, in this
geometry, it is useful to provide only two webs, which then sit on
both sides of only one notch in the peripheral surface of the
piston body lying in between. The webs can be dimensioned to be
relatively wide; the notch laterally bordered by the webs can then
be twice to three times as wide as the width of a web. This
simplifies the contour of the peripheral surface of the piston body
considerably.
[0010] In an especially advantageous embodiment of the invention,
the piston body is pieced together from at least two element
sections, each of which has a plane of separation that runs
perpendicular to the piston axis. This type of piston body design
is suited for manufacture using a powder-metallurgy process, i.e.
as a sintered metal part. The form of the two element sections is
particularly favorable if each element section has only one
peripheral web so that the mirror-imaged element sections pieced
together border a notch with their webs. This allows cost-effective
manufacture of an [undercut] notch since machining work is not
necessary.
[0011] The invention is explained in more detail with the help of
schematic drawings of an embodiment example. Shown are:
[0012] FIG. 1 a partial section in the axial direction through a
piston-cylinder arrangement for a shock absorber,
[0013] FIG. 2 an enlarged partial section through the piston of the
arrangement according to FIG. 1,
[0014] FIG. 3 an enlarged partial section through a piston with one
web.
[0015] FIG. 1 shows an axial section through a shock absorber that
connects two parts that are movable relative to one another, for
example a vehicle axis and a vehicle frame. The shock absorber has
a cylindrical part 1 that is connected to one of the two parts that
are movable with respect to one another. A piston 2 is guided
inside cylinder 1 that is fastened to a piston rod 3 whose free end
is fixed to the other part of the parts moving relative to one
another. The cylinder 1 is closed on both sides and is filled with
a hydraulic fluid so that the piston-cylinder arrangement is
designed to be dual-acting, with the piston separating two cylinder
spaces 4, 5 from one another.
[0016] The piston body 6 of the piston 2 has a number of
penetration channels 7, 8 running alongside one another. A throttle
valve 7.1 and 8.1 covers the exit side of each of the penetration
channels 7, 8. The function of these exits is yet to be explained.
This arrangement is designed such that, for example, three
penetration channels 7 and three penetration channels 8 are
arranged in the shape of a star in alternating fashion around the
cylinder axis.
[0017] The peripheral surface of the piston 2 is provided with a
collar-shaped seal 9 that seals off cylinder space 4 against
cylinder space 5. When the piston 2 moves toward cylinder space 4,
the fluid is pushed through the penetration channels 7 against the
return force of the throttle valve 7.1. The penetration openings 8
are held shut by the pressure of the fluid space 4 acting on the
throttle valve 8.1. When it moves in the reverse direction, the
penetration channels 7 are closed by throttle valve 7. 1, with the
fluid now able to flow back through the flowing channels 8 out of
cylinder space 5 into cylinder space 4.
[0018] FIG. 2 shows a piston 2 in an enlarged representation
without the arrangement of the throttle valves 7.1 and 8.1. The
piston body 6 is provided with two webs 10 on its peripheral
surface, which are arranged in the embodiment example shown here
such that they also contain a portion of the respective end surface
4.1 or 5.1 of the piston body 6. The two webs border a notch 11 on
the peripheral surface of the piston body 6. The arrangement can
also be designed such that at least one of the webs 10 is set back
somewhat with respect to its associated end surface 4.1 and/or
5.1.
[0019] The collar-shaped seal 9 arranged on the peripheral surface
of the piston body 6 consists of a thermoplastic synthetic
material, preferably PTFE. In the embodiment example shown here,
the collar-shaped seal 9 was formed onto the peripheral surface of
the piston body 6 by heat forming a circular sleeve, with edge 9.1
of the seal 9 being formed by the inner edge of the circular sleeve
and edge 9.2 being formed by the outer edge of the circular sleeve.
The width of the circular sleeve was dimensioned such that it was
wider than the thickness of the piston body 6 in the axial
direction. By doing so, edge 9.1 produced by the inner edge of the
circular sleeve is pulled inward after it deforms, whereas edge 9.2
produced by the outer edge of the circular sleeve is bent outward,
thus forming a functioning lip seal.
[0020] In heat forming the circular sleeve, the webs 10 press into
the material of the collar-shaped seal 9 over only a portion of
their height so that a certain amount of free space remains between
the material of the seal 9 and the bottom of the notch 11. This
allows the sealing material to freely flow into the notch 11
without being squeezed when the seal 9 is formed. In this shaping
process, the cylindrical exterior surface 13 of the seal 9 is
simultaneously calibrated so that the desired tolerances to the
inner diameter of the cylinder 1 can be maintained. Since the
overall system heats up during operation, especially when these
piston-cylinder arrangements are used as shock absorbers, this
remaining free space in the base of the notch also allows the
sealing material to expand into the notch within certain limits so
that the wear of the seal on the peripheral surface of the seal 9
adjacent to the edges is reduced.
[0021] As can be seen in FIG. 1 and FIG. 2, the piston body 6 is
produced from two element sections 6.1 and 6.2. The shape of the
contours of the penetration channels 7 and 8 in one section is
identical with that in the other section in the embodiment example
shown so that regardless of the arrangement of a bushing 6.3 on
element section 6.1 and a corresponding recess 6.4 in element
section 6.2, both element sections have the identical external form
and are designed without back tapering [undercutting], which
hinders the press process. This makes it possible to form this kind
of a piston body 6 from two element sections produced through
powder metallurgy, said sections being pressed as element sections
from a sinterable metallurgical powder. The pressed element
sections are then put together in an assembly operation and then
sintered. This is just the kind of manufacturing process that
allows the element sections to be produced such that the
penetration channels can be formed differently depending on the
different flow conditions for suction and pressure loads.
[0022] Depending on the manufacturing process, it is also possible
to provide more than two webs so that two respective adjacent webs
border a notch, resulting in a higher number of notches
accordingly.
[0023] In FIG. 3, an embodiment form is shown differing in
comparison to FIG. 2. The same references apply to the same
elements so that reference can be made to FIG. 2 accordingly.
[0024] The embodiment form shown in FIG. 3 is provided for cases of
minimal suction-pressure load so that the piston body 6 is provided
with only one peripheral web 10. In this event, the end surface 4.1
of the piston body 6 is subjected to the higher pressure so that
the web 10 is located close to this end surface in this case.
[0025] The collar-shaped seal 9 is formed onto the piston body 6 in
the manner described above, wherein here, as well, the peripheral
web 10 presses into the material of the collar-shaped seal 9 only
over a portion of its height.
[0026] Due to the "back memory ability" of the plastic material as
described above, it inevitably sits against the piston body 6 in
the transition region 13 leading to end surface 5.1. In the area
near the web 10, at least, a free space or cavity 11.1 remains.
This makes it possible that, here as well, the material of the
collar-shaped seal 9 can expand into this free space 11.1 under the
influence of temperature.
[0027] Although it is especially favorable to produce the piston
body described here using powder metallurgy, the embodiment
according to the invention with only one web, or two webs bordering
a notch, can also still be manufactured at reasonable expense by
machining.
* * * * *