U.S. patent application number 11/945876 was filed with the patent office on 2008-11-27 for powder-metallurgically produced piston body comprising support webs.
This patent application is currently assigned to GKN Sinter Metals GmbH. Invention is credited to Ewald May, Rainer Schmitt.
Application Number | 20080289491 11/945876 |
Document ID | / |
Family ID | 31984220 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080289491 |
Kind Code |
A1 |
May; Ewald ; et al. |
November 27, 2008 |
Powder-Metallurgically Produced Piston Body Comprising Support
Webs
Abstract
A powder-metallurgically produced piston body for a
piston-cylinder arrangement, in particular a shock absorber piston,
has a one-part piston body, a revolving or circumferential web that
protrudes radially outwardly from outer surface of the piston body,
longitudinal webs, and at least one traverse groove. A
collar-shaped seal, made of thermally deformable material, is
formed onto the piston body such that the revolving or
circumferential web and the support webs are formed into the seal
over at least a part of their heights.
Inventors: |
May; Ewald; (Bonn, DE)
; Schmitt; Rainer; (Wachtbeg, DE) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
CIRA CENTRE, 12TH FLOOR, 2929 ARCH STREET
PHILADELPHIA
PA
19104-2891
US
|
Assignee: |
GKN Sinter Metals GmbH
Radevormwald
DE
|
Family ID: |
31984220 |
Appl. No.: |
11/945876 |
Filed: |
November 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11091246 |
Mar 28, 2005 |
7310876 |
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11945876 |
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PCT/EP03/09670 |
Aug 30, 2003 |
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11091246 |
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Current U.S.
Class: |
92/248 |
Current CPC
Class: |
F16F 9/3481 20130101;
B22F 2998/00 20130101; Y10T 29/49249 20150115; F16F 9/3214
20130101; F16F 9/348 20130101; F16F 2226/00 20130101; B22F 2998/00
20130101; B22F 5/02 20130101; F16F 9/368 20130101 |
Class at
Publication: |
92/248 |
International
Class: |
F16J 1/00 20060101
F16J001/00; F16J 15/18 20060101 F16J015/18; F16J 9/28 20060101
F16J009/28 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2002 |
DE |
102 45 404.3 |
Claims
1. A powder-metallurgically produced piston body for a
piston-cylinder arrangement, in particular a shock absorber piston,
having a one-part piston body that is provided on its peripheral
surface in an area adjacent to a terminal piston area, with a
revolving web that protrudes beyond the peripheral surface, to
which longitudinal support webs are adjacent that extend to the
other terminal piston area and that are disposed parallel to and at
a distance from each other, at least a part of said support webs
being provided with at least one transverse groove between the two
terminal piston areas, each pair of adjacent support webs
delimiting a groove-shaped recess, the ends opposite the revolving
web of said recesses being open in the longitudinal direction, a
collar-shaped seal made of a thermally deformable sealing material
being able to be formed onto the piston body in such a way that
both the revolving web and also the support webs are formed into
the material of the collar-shaped seal at least over a part of
their vertical direction.
2. The piston body according to claim 1, wherein the depth of the
groove-shaped recesses is less at an area adjacent to the revolving
web than in the area of the final area opposite the revolving
web.
3. The piston body according to claim 1, wherein at least two
transverse grooves are provided.
4. The piston body according to claim 1, wherein the at least one
transverse groove has a depth less than that of the groove-shaped
recess.
5. The piston body according to claim 1, wherein a collar-shaped
seal made of a thermally deformable plastic, preferably PTFE, is
formed onto the piston body by means of thermal deformation in such
a way that the seal does not completely fill the groove-shaped
recess and does completely fill the transverse grooves.
6. A shock-absorber comprising: a one-part piston body having
through openings formed therein and including: an outer surface
that includes a first terminal portion and an opposing second
terminal portion; a circumferential web, adjacent to the first
terminal portion, protruding radially beyond the outer surface;
longitudinal support webs, adjacent the circumferential web,
extending between the first and second terminal portions, the
support webs delimiting recesses that are open on their ends
opposite the support web; at least a portion of the support webs
providing at least one transverse groove disposed between the first
and second terminal portions a collar-shaped seal formed of a
thermally deformable sealing material, the seal being formed to a
portion of the piston body such that a least a portion of the
circumferential web and at least a portion of the support webs are
impressed into the seal; and a cylinder in which the piston body is
moveably disposed.
7. The shock absorber according to claim 6, wherein the support
webs are mutually spaced apart and disposed mutually parallel, and
each pair of adjacent support webs delimit a recess.
8. The shock absorber according to claim 7 wherein the recesses are
groove-shaped.
9. The shock absorber according to claim 8, wherein depths of the
groove-shaped recesses are less adjacent to the circumferential web
than near the second terminal portion.
10. The shock absorber according to claim 8, wherein the at least
one transverse groove has a depth less than a depth of the
groove-shaped recess.
11. The shock absorber according to claim 6, wherein the support
webs provide least two of said transverse grooves.
12. The shock absorber according to claim 6, wherein the
collar-shaped seal is formed of a thermally deformable plastic,
said seal being formed onto the piston body by thermal deformation
such that the seal does not completely fill the groove-shaped
recesses and does completely fill the transverse grooves.
13. The shock absorber according to claim 12, wherein the plastic
is PTFE.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a Divisional of U.S. patent
application Ser. No. 11/091,246, filed Mar. 28, 2005, which is a
Continuation of PCT Application No. PCT/EP2003/009670, filed Aug.
30, 2003, which claims priority to German Application No. 102 45
404.3 filed Sep. 28, 2002, the contents of which are hereby
incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates to pistons and methods of forming
same, and more particularly, to shock absorber pistons formed by
powder metallurgy and related processing.
BACKGROUND
[0003] From EP-A-0 658 611, a shock absorber piston is known that
is provided with a revolving web on its peripheral surface, a
multiplicity of webs that run in the axial direction being adjacent
to or connected to one side of this revolving web. Using an
injection molding method, a thermoplastic plastic seal is sprayed
onto this piston body, and in particular the webs extending in the
axial direction act, with their intermediate grooves filled with
sealing material, to reliably anchor the sealing material and to
guide the piston. The sealing applied in the injection molding
enables a narrow tolerance in order to avoid what is known as
"blow-by" and thus to effect a reliable sealing of the mutually
associated cylinder chambers. The method for manufacturing seals
that are injection-molded in this way is relatively expensive.
[0004] From U.S. Pat. No. 3,212,411, a piston-cylinder arrangement
is known whose piston body has a multiplicity of revolving grooves
on its peripheral surface. In order to apply the seal, a cup-shaped
preform made of PTFE (polytetrafluorethylene) is provided that is
first placed loosely on the piston body. The piston body prepared
in this way is subsequently first pressed into a highly heated
shaping and calibrating cylinder, where the PTFE material is
pressed into the grooves on the peripheral surface of the piston
body under the influence of heat. Subsequently, the piston body
with the pressed-on seal is cooled in a correspondingly fashioned
cooling cylinder. The grooves are filled completely with the
sealing material, in order to bring about a positive, fixed
connection of the seal with the peripheral surface of the piston
body. For use as a shock absorber piston, the base surface of the
preform, still covering the final piston area or end surface of the
piston body on one side, must subsequently be removed.
[0005] From EP-A-682 190, a shock absorber piston is known that
differs in its manufacture from the above-described method
essentially only in that a stamped annular disc is used to apply
the seal, instead of a cup-shaped preform. This annular disc is
placed on one end of the piston body. The piston body prepared in
this way is again pressed into a heated shaping and calibration
cylinder, and the annular disc is placed around the peripheral
surface of the piston body as a band and is subsequently pressed
into the grooves running in the peripheral direction of the piston
body under the influence of heat. Subsequently, the piston, with
its pressed-on seal, is guided through a cooling tube. Here as
well, the sealing material fills the grooves practically
completely, so that the sealing is connected in positive, fixed
fashion with the peripheral surface of the piston body.
[0006] The two methods described above have the disadvantage that
considerable pressure can be required for the deforming and the
complete pressing of the sealing material into the grooves on the
peripheral surface of the piston body, and that the sealing
material that forms the seal is subjected to strong deformations
that disadvantageously influence the structure of the sealing
material.
[0007] From DE-A-198 47 342, a piston is known for a
piston-cylinder arrangement, in particular a shock absorber piston,
having a piston body that is provided, on its peripheral surface in
an area adjacent to one end of the piston, with a revolving web
that protrudes beyond the peripheral surface, to which longitudinal
support webs are adjacent that run in the direction towards the
other end of the piston, disposed in parallel to one another and at
a distance from one another, each pair of adjacent support webs
delimiting a groove-shaped recess that is open at its ends opposite
the revolving web in the longitudinal direction, and having a
collar-shaped seal made of a thermally deformable sealing material
that is formed onto the piston body in such a way that both the
revolving web and the support webs are formed into the material of
the seal only over a part of their vertical direction or
height.
[0008] This known solution has shown that for a good sealing
between the collar-shaped seal of the piston on the one hand and
the external contour of the piston body on the other hand, it is
not required for the seal to lie tightly against the piston body
over the full periphery. For many cases of application, it is
sufficient if the sealing collar lies tightly only on the
relatively narrow revolving web in the peripheral direction. In
addition, it has turned out, surprisingly, that for a problem-free
and reliable connection between the seal and the piston body it is
not required that the groove-shaped recesses between the
longitudinal support webs be filled completely by the sealing
material. In this way, there remains a sufficient open space into
which the sealing material can escape in case of expansion due to
increases in temperature, while the piston is nonetheless guided in
a problem-free manner via the longitudinal support webs.
[0009] In some circumstances, the provision of only one revolving
web protruding from the peripheral surface for the fixing of the
collar-shaped seal may not be sufficient, so that it is desirable
to provide two revolving webs, one at each end, that are connected
by the longitudinal support webs that run parallel to one another
and at a distance from one another. However, the
powder-metallurgical production of such a piston body by pressing a
green compact from a sinterable metal powder, with subsequent
sintering, presents significant forming problems, so that in
DE-A-101 08 246 it was proposed to divide the piston body into two
sub-bodies, each having at one end a revolving web from which the
longitudinal support webs situated at a distance from one another
emanate. The two sub-bodies can be formed without great difficulty
from a sinterable metal powder as green compacts, and then
sintered. The complete piston is then assembled from the two
finally sintered parts in such a way that the revolving webs are
each situated at an end of the piston facing away from the dividing
plane. By beveling the support webs at their end facing the
dividing plane, it is then possible to provide an additional
transverse groove. The disadvantage of this design is that the
joining process for the two sub-bodies is expensive, if these have
to be joined with a defined position to one another. This is for
example the case for piston bodies for shock absorber pistons,
because here the partial channels present in the two sub-bodies
must be precisely aligned with one another.
[0010] The present invention is based on the object of creating a
piston that is simple to manufacture, in particular a shock
absorber piston.
SUMMARY
[0011] According to the present invention, this object is achieved
by a one-part piston body that is provided on its peripheral
surface in an area adjacent to a final or terminal piston area,
with a revolving web that protrudes beyond the peripheral surface,
to which longitudinal support webs are adjacent that extend to the
other final piston area and that are disposed parallel to and at a
distance from each other. At least a part of the support webs are
provided with at least one transverse groove, and preferably two
transverse grooves, between the two final or terminal piston areas.
Each pair of adjacent support webs delimit a groove-shaped recess.
The ends opposite the revolving web of the recesses are open in the
longitudinal direction. A collar-shaped seal made of a thermally
deformable sealing material is able to be formed onto the piston
body in such a way that both the revolving web and also the support
webs are formed into the material of the collar-shaped seal at
least over a part of their vertical direction. Preferably, the
piston body is powder-metallurgically produced for a
piston-cylinder arrangement, in particular a shock absorber
piston.
[0012] Further constructions of the present invention are indicated
in the following description of exemplary embodiments and in the
subclaims.
BRIEF DESCRIPTION OF THE FIGURES
[0013] The present invention is explained in more detail on the
basis of schematic drawings of an exemplary embodiment.
[0014] FIG. 1 shows a partial section in the axial direction
through a piston-cylinder arrangement for a shock absorber.
[0015] FIG. 2 shows a side view in partial section of a finally
sintered blank for a shock absorber.
[0016] FIG. 3 shows a schematic horizontal section through the
blank along the line III-III in FIG. 2, without the sealing
collar.
[0017] FIG. 4 shows a side view of a finally shaped piston body in
partial section with the applied sealing collar,
[0018] FIG. 5 shows a partial section according to FIG. 4 in an
enlarged view,
[0019] FIG. 6 shows a device for forming transverse grooves and for
calibrating a piston body blank as a step of the manufacturing
method,
[0020] FIG. 7 shows the device according to FIG. 6 during the
forming and calibration step,
[0021] FIG. 8 shows the device according to FIG. 6 at the end of
the forming and calibration step,
[0022] FIG. 9 shows a vertical section through the forming station
of the tool according to FIG. 6 with the inserted blank during the
forming process,
[0023] FIG. 10 shows an enlarged view of the construction of the
stamping tool,
[0024] FIG. 11 shows a view of the forming station according to
FIG. 9, with an arrangement of the stamping tools.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] FIG. 1 shows, as a functional schematic diagram, an axial
section through a shock absorber that connects two parts with one
another that can be moved relative to one another, for example a
vehicle axle and a vehicle frame. The shock absorber has a cylinder
part 1 that is connected to one of the two parts that can be moved
relative to one another. In cylinder 1 a piston 2 is guided that is
fastened to a piston rod 3, whose free end is set on the other part
of the two parts that can be moved relative to one another. Here,
cylinder 1 is closed at both sides and is filled with a hydraulic
fluid, so that the piston-cylinder arrangement is designed to be
double-acting, and the piston separates two cylinder chambers 4, 5
from one another.
[0026] Piston body 6 of piston 2 comprises a plurality of
pass-through channels 7, 8 that run alongside one another.
Pass-through channels 7, 8 are each covered at their exit side
(whose function is still to be explained) with a throttle valve 7.1
or 8.1. The arrangement is made here in such a way that a plurality
of pass-through channels 7 and a plurality of pass-through channels
8 are provided so as to be arranged about the cylinder axis in
alternating fashion.
[0027] The peripheral surface of piston 2 is provided with a
collar-shaped seal 9 that seals cylinder chamber 4 against cylinder
chamber 5. When piston 2 moves into cylinder chamber 4, the fluid
is pressed through pass-through channels 7 against the reset force
of throttle valves 7.1. Pass-through openings 8 are here kept
closed by the pressure of fluid chamber 4 acting on throttle valves
8.1. When there is movement in the opposite direction, pass-through
channels 7 are closed by throttle valves 7.1, while the fluid can
flow from cylinder chamber 5 through channels 8 back into cylinder
chamber 4.
[0028] Because a piston body of the type indicated above moves back
and forth, and when there is a high load collar-shaped seal 9 is
also correspondingly loaded during the reverse motion, a revolving
web at one end of the piston body is no longer sufficient in some
circumstances to reliably fix the collar-shaped seal against
loading in the axial direction. In order to permit a piston body of
this type to be manufactured in a one-part construction in such a
way that additional transverse grooves are present for fixing the
collar-shaped seal, first a green compact is pressed from
sinterable metal powder, in the shape shown in FIG. 2 and explained
in more detail below, and is subsequently finally sintered to form
a blank 6.1.
[0029] Blank 6.1 is provided on its peripheral surface with a
multiplicity of longitudinal support webs 10 that delimit
corresponding groove-shaped recesses 11 and that extend from final
piston area 4.1, to which a revolving web 12 is allocated, to the
other end of blank 6.1 in the area adjacent to final piston area
5.1. Revolving web 12 and longitudinal support webs 10, which form
an external surface of piston body 6, are at grade with one
another. In order to achieve a better representation, this external
surface is hatched. Support webs 10, and, correspondingly, grooves
11, run axially parallel to one another.
[0030] In FIG. 3, piston body 6 is shown in a horizontal section
along the line III-III in FIG. 2, so that the structure of support
webs 10 and grooves 11 can be seen.
[0031] In FIG. 4, piston body 6 is shown partially in section and
in a side view without seal 9, in its final form after transverse
grooves 11.1 have been made on the surface of longitudinal webs 10.
Transverse grooves 11.1 are made in sintered blank 6.1 by a
stamping method to be explained in more detail below, and after
this stamping the blank is again calibrated. Seal 9 is then made on
finally calibrated piston body 6.
[0032] Collar-shaped seal 9 situated on the periphery of piston
body 6 is made of a thermally deformable plastic, preferably PTFE.
In the exemplary embodiment shown here, collar-shaped seal 9 is
formed onto piston body 6 by thermal deformation.
[0033] In the thermal deformation of the sealing material, which
can be a pre-manufactured annular disc or a pre-manufactured tube
piece, support webs 10 and revolving web 12 are formed into the
material of collar-shaped seal 9 only over a part of their vertical
direction, so that a certain amount of open space remains between
the material of seal 9 and the floor of groove-shaped recesses 11,
so that during the forming of seal 9 the sealing material can flow
into groove 11 freely and without being forced. In this deformation
process, the cylindrical external surface 13 of seal 9 is
simultaneously calibrated, so that the desired tolerances to the
inner diameter of cylinder 1 can be maintained. Because, in
particular given the use of such a piston-cylinder arrangement as a
shock absorber, during operation a heating of the overall system
occurs, this remaining open space in the base of the groove also
permits the sealing material to expand into the groove within
certain limits, so that the wearing of the seal at the cylindrical
peripheral surface of seal 9, adjacent to the edges, is reduced.
Piston 2 is supported as a whole in practically tip-free fashion
over its vertical direction. Seal 9 is supported on the one groove
end on the inside of revolving web 12.
[0034] In FIG. 5, the positioning of seal 9 is shown, in a greatly
reduced scale, in a partial section corresponding to FIG. 4. Seal 9
is made here of a homogenous material that during the
above-described thermal deformation is partly formed into
longitudinal grooves 11 and transverse grooves 11.1, while on the
other hand longitudinal support webs 10 and revolving web 12 are
correspondingly formed into the material. To illustrate this, the
material formed into longitudinal groove 11 is provided with a
cross-hatching, in order to make it clear that longitudinal grooves
11 are not completely filled.
[0035] In order to avoid excessive stressing or loading, during the
thermal deformation, of the material of seal 9 in longitudinal
groove 11 in area of transition B to revolving web 12, it is
provided that longitudinal groove 11 comprises in this area a depth
that decreases, i.e., is reduced, in the direction towards
revolving web 12. The reduction of the axial support surface
brought about in this way for the sealing material on revolving web
12 is compensated by the additional support surfaces of transverse
groove 11.1 acting in the axial direction, and the advantage is
gained that in this area, which is highly stressed in later
operation, the structure of the material will be less stressed by
the thermal deformation, thus having a higher degree of
stability.
[0036] On the basis of FIGS. 6, 7, and 8, the method according to
the present invention for producing a piston body in the form shown
in FIG. 4 is now explained in more detail. In a first step, a green
compact corresponding to FIG. 2 is pressed from a sinterable
metallurgical powder, and is subsequently finally sintered to form
a blank 6.1. After this, as is shown in FIG. 6, a blank 6.1a is
removed from a supply S1 of blanks 6.1, and is supplied to a
pressing device P that comprises a first press location I and a
second press location II.
[0037] In addition to the standard upper stamp 15.1 and lower stamp
16, first press location I is provided with radially disposed
stamping tools 14 with which transverse grooves 11.1 are made in
support webs 10, as is explained in more detail below.
[0038] Blank 6.1b, which was provided with transverse grooves in
the preceding stamping step at press location I, is then supplied
to second press location II, in which blank 6.1b prepared in this
way is calibrated both in relation to the piston end surfaces and
also in relation to the outer periphery of the revolving web and of
the support webs, corresponding to a finished piston body 6. This
process is shown in FIG. 7.
[0039] At press location II, a lower stamp 16.2 is allocated to
upper stamp 15.2; the forming surface of this lower stamp
corresponds to the forming surface of blank 6.1a or 6.1b that is to
be inserted. In first press location I, practically speaking blank
6.1a is merely held between movable stamp 15.1 and stationary
counterstamp 16.1, while in second press location II press stamp
15.2 is subjected to pressure such a way that a calibrating final
formation of inserted blank 6.1b takes place, so as to form
finished piston body 6.
[0040] As is shown in FIG. 8, press stamp 15 is subsequently drawn
back, and an ejection tool 17 at both press locations is used to
push blank 6.1b, now provided with transverse grooves, and finally
calibrated piston body 6 out of the press form, so that blank 6.1b
can be transported to press location II and finished piston body 6
can be stored in a storage area S2, from which the finished piston
body can then be removed for the application of collar-shaped seal
9.
[0041] FIG. 9 shows, in a vertical section through first press
location I, the arrangement with blank 6.1a in place. Drawn-in
upper stamp 15.1 is not shown here. Stamping tools 14 are pressed
into the material of support webs 10, and transverse grooves 11.1
are formed. This can be seen in the enlarged view in FIG. 10.
[0042] Radially adjustable stamping tools 14 are fashioned as
slides, and, as can be seen from FIGS. 6, 7, 10, and 11, can be
adjusted radially against blank 6.1a. In the specific embodiment
shown here, three stamping tools 14 are provided, situated at the
same angular distance from one another. Depending on the size of
the system, more than three stamping tools may be provided. The
provision of only two stamping tools situated diametrally opposite
one another is also possible in principle.
[0043] As can be seen from the enlarged view according to FIG. 10,
for the formation of two transverse grooves 11.1 in support webs 10
of a blank 6.1 each stamping tool 14 has two parallel blade-type
stamping edges 18, which are used to displace material when
pressure is applied by stamping tools 14, with cold deformation of
the sintered material corresponding to FIG. 7, forming transverse
grooves 11.1. As can be seen from FIG. 10, this cold deformation
takes place only over a part of the overall vertical direction of
support web 10, so that transverse grooves 11.1 result, having a
smaller depth than grooves 11.
[0044] The forming and calibrating process can also be carried out
using only one press location whose design is essentially that of
press location I. Only the upper stamp and the lower stamp are
formed corresponding to upper stamp 15.2 and to lower stamp 16.2.
Correspondingly, in the first step blank 6.1a is merely held by the
upper stamp and the lower stamp, so that transverse grooves 11.1
can be formed in it. Subsequently, stamping tools 14 are drawn back
and the pressure on the upper stamp and the lower stamp is
increased, and the blank is calibrated; only then is the form
removed as a finished piston body.
* * * * *