Note: Descriptions are shown in the official language in which they were submitted.
~0~65
The present invention relates a cylinder-piston
combination, and more particularly to a cylinder-piston
structural arrangement for high-pressure, hydraulic
application to control positioning of heavy loads, remote
- control positioning, remote control locating, servo
positioning, and the like. Combination of dual piston-
or double-acting
cylinder arrangements can provide push-pull/effects.
Specifically, the present invention is directed to the
structural arrangement which provides for sealing of the
fluid, preferably hydraulic fluid within a working space,
that is, within a c~inder chamber by means of a flexible
elastic sealing tube, p~erably made of an elastomer which
is attached with its respective ends to the piston,and
cylinder, respectively, to form a leakproof, sealed, tight
connection for the working fluid which may be under very
high pressure, for example in the order of 100 at gauge.
Piston-cylinder arrangements for high-pressure
application provided with leakproof seals are difficult to
use in continuous high-power applications in which high
operating frequencies, high operating speeds, and high
pressures arise. The low mechanical strength of the
sealing tubes has heretofore inhibited such applications
because, to provide a leakproof, tight seal, the sealing
tube must be locally clamped and has been terminated by an
abrupt transition on the respective support element, that is,
the piston or the cyllnder, depending on the end of the tube
~: '
--2--
-
Qk65
under consideration. These termination resulted in high-
stress gradients in radial direction at localized points or
zones of the sealing tube. These hlgh stresses greatly
reduced the durability of the sealing tubes. If sliding or
movable seals are used between a relatively movable piston
and cylinder, using elastic substance, then high coefficients
-of friction inhibit rapid and efficient operation; the high
frictional forces can be reduced only by special
arrangements. Heat due to friction, as well as
the frictional force itself, cause rapid deterioration of the
elastic portions of the seal, typically of elastomer material.
It is an object of the present invention to provide
a cylinder-piston positioning or drive arrangement which is
so constructed that it permits high power or force transfer
with high efficiency and at high speed in continuous
operation without losing its leakprooF seal.
~ S~bject matter of the present invention: Briefly,
a sealing tube is provided which is slidable with respect to
one part. A transition zone is connected to the sealing
tube and to the other part extending in the dlrection of
movement, the sealing tube and at least the transition zone
being supported in or retained on a durable or regenerating
sliding bearing surf~ce.
In accordance with a preferred embodiment of the
invention, the transition zone is formed with an elastically
deformable surface extending over at least a portion of its
length and is supported on the sliding bearing surface, loaded
by the pressure of the workïng medium, by an arrangement
which provides for decreasing application pressure from the
side of the working medium, which may be uniformly decreasing
S pressure or a decrease occurring in steps.
The sliding, bearing surface may be a fixed coating
or cover on the support walls for the sealing tube or part of
the surface of the support walls. Tlle sliding surface on the
sealing tube is extendable or stretchable and bonded or secured
to or is part of the surface thereof. The sliding surface may,
however, also be a fluid surface such as a lubricating filling
which is sealed towards the outside. The low-friction sliding
surface may also be a lubricant introduced between the flexible,
resilient sealing tube and the inner surface of the cylinder,
whereby the slippery, sliding bearing surface is formed as a
hydrostatic bearing. The lubricant flow is conducted over a
choke after passing the gap between the sealing tube and the
cylinder wall. The choke maintains the pressure balance between
the luhricant and the working medium before the lubricant can
be relieved of pressure and escape, for recycling and re-use.
The choke may be formed by a portion oE the transition zone, the
surface of which is so constructed that in unloaded state it has
some radial play; upon loading, a choke-type gap is formed, the
` size of which depends on the pressure of the working medium as
well as the pressure of the lubricant and lubricant flow, so
that the gap
--4--
s
will be self-adjusting. The lubricant may be branched off
from the working pressure fluid,if this fluid is a liquid
with lubricating properties.
The transition zone is preferably formed of a plurality
of parts, particularly at least two parts which are
constructed of mater~ls of different stiffness, adhered
together at a junction surface. The separate elements in
the transition zone can be arranged in various ways; it is
preferred,however, that at least one of the elements of lower
stiffness than another, or others,forms at ieast a portion
of the surface of the transition zone. The transition zone
is usually loaded by the working medium at working
medium pressure, most commonly at the end or side of the
sealing medium. ~ deformation will result in the transition
zone which depends on the pressure of the working medium but
which changes over the length of the transition zone,
decreasing at the median thereof, the deformation depending,
in general, on the particular shape or form of the separate
elements as well as on the shape and form of the junction
. surfaces between the various elements.
In a preferred form7 the lubricant flow for the
hydrostatic bearing is independent of lubricant pressure.
The invention will be described by way of example
with reference to the accompanying drawings, wherein:
Fig. 1 is a longitudinal sectional view of a piston-
cylinder apparatus in which a resilient sealing tube is
-
loaded internally by the working fluid;
~34~(~ti 5
- Fig. 2 is a transverse section along line II-II,with
the interior elements of the arrangement omitted;
Fig. 3 is an enlarged Eragmentary view of the region
circled in Fig. 1 and identified at III;
Fig. 4 is a longitudinal sectional schematic view of
a piston-cylinder arrangement in which the working pressure
fluid is applied to the outside of the sealing tube;
Fig. 5 is a fragmentary cross-sectiopal area of one
form of the sealing tube at the fixed, non-movable end
thereof;
Fig. 6 is a fragmentary transverse section of a portion
of the cylinder-piston arrangement illustrating a portion of
the piston and the transition zone of the sealing tube with
two elements;
Fig. 7 is a view similar to Fig. 6, having a transition
zone with three elements;
Fig. 8 is a transverse section similar to Fig. 6,
showing a transition zone having four pa~ialelements with
junction surfaces below the top surface of ~ e transition
zone;
Figs. 10 and 11 are transverse sections of a
transition zone having six partial elements;
Fig~ 11 is a transverse section of a transition
zone having seven partial elements, in which one partial
element surrounds the other like a sleeve;
~U4~ S
Fig. 12 is a fragmentary sectional view of a
transition zone having three partial elements joined to an
elastic, flexible metal tube; and
Fig. 13 is a transverse sectional view of a transition
zone having two partial elements.
The cylinder-piston combination - see Fig. l - has
- a cylinder element l, of approximately square or rectangular
outer cross section (see Fig. 2) with a bore 2. The
cylinder is closed off at one end by a cylinder end cover 3
secured thereto , for example, by means of bolts (not shown).
The junction surface between the cylinder body l itself and
the cover 3 is sealed by an O-ring 5 located in a groove 4
o the cylinder l.
A piston 6, which is essentially cylindrical or
slightly conical, is located in bore 2 and guided therein
by means of a piston rod 7. The piston rod 7 is slidable
in a sleeve 8 which, in turn, is secured to a holder or
clamp 9. The holder 9 extends through a bore lo formed in
the cover 3 of the cylinder and is secured therein by means
of a nut 3. The holder 9 is formed with a longitudinal
duct l2, extending lengthwise thereof, and terminating in
mouths l3. The pressure working medium which may, for
example, be a pressurized gas, hydraulic fluid or the like,
may enter and leave through the duct 9 and the openings l3
thereof. The holder 9 is formed with a thickened region
l4 in the vicinity of the mouths l3. The thickened region
--7--
14 has ridges 15 thereon. The thickened 14 is used to
clamp the flxed end 16 of an elastic sealing tube 17 between
the inner wall of the bore 2 of the cylinder and the outer
surface of the holder 9. The tube is clamped tight to be
leakproof. The other end 18 of tube 17 is connected to a
transition zone A extending in the direction of movement of
the piston 6. The transition zone mer~es into the piston
6 itself. This transition zone A is formed of two partial
elements 60, 70. The partial elements 60, 70 have
different stiffness; the partial element 60 may be made of the
same material as the sealing tube 17 and has a lower
sti.ffness than the partial element 70 which merges into the
piston 6. As ~ result, the deormation of the transition
zone A is greatest at the side thereof where the sealing
tube 17 is located, and decreases in axial direction towards
the piston. The two partial elements 60, 70 are secured
together at theirjunction surface 62. The attachment at the
junction surface may be by means of adhesive or chemical
bonding. The junction surface 62 does not pass through the
surface of the transition zone A and,therefore,deformation
of the transition zone decreases continuously even if
the thickness of material of the partial element 60 is
constant over its entire length. At the side of the sealing
. tube, a thickened region 61 is provided in the transition
zone to influence the deformation of the transition zone A
and, further, to increase the junction surface 62.
l~oa6~ '
The outside of the sealing tube 17 has a durable
sliding or low-friction surface 21 applied thereto.
Surface 21, which may be in form of a thin layer, is
securely adhered to the tube 17. It is important -that the
surfaces between the tube 17 and the inner wall of the
cylinder 1 be of low friction; thus, the sliding surface may
also be applied to the interior wall of the cylinder 1,
and, ifdesired, sliding low-friction s~rface layers can
be applied to both the tube 17 and the inner wall of the
bore 2 of the cylinder 1.
~ ring groove 19 is located at the transition or
junction between the cylinder 1 and the cover 3. The groove
19 i9 connected by means of a gap 20 with the bore 2 of the
cylinder. The groove 19 communicates with a duct 22 (Fig. 2)
formed in the wall of the cylinder 1. Duct 22 is in
communication with a connecting line 23 which is connected
to the cylinder 1 by means of a pipe thread coupling. A
stream of lubricant is applied through duct 23, preferably
independent o~ pressure. ~s a result, the pressure in the
groove 19 and the duct 20 will adjust itself to correspond
to the pressure of the working fluid. The lubricant
escapes through the groove 19 and the gap 20 between the
sealing tube 17 and the wall of the bore 2 of the cylinder.
It will spreadat the outer circumference o~ the sealing
tube 17 and can escape at the piston end of the cylinder-
piston combination. The deformation of the transition zone
~)40~65
A depends on the pressure of the working fluid and on the
pressure of the lubricant stream. At the surface of the
transition zone A, the~fore, due to the deformation, a
self-adjusting throttling region will be formed acting as
a hydraulic choke wlth respect to the lubricant which will
achieve a pressure balance with the pressure of the working
fluid or medium. Asfar as the sealing tube 17 is
concerned, therefore, the forces acting thereon will be in
balance: The sealing tube, the inside of which is loaded
by the pressure of the working fluid, is supported throughout
its outer circumference by a thin hydrostatic film of
lubricant in pressure-balance with the pressure of the
working 1uid. ThUs, the sealing tube is supported from
the inner wall of the bore 2 of the cylinder without,
however, touching the wall o the cylinder, so that the
tube can slide freely with respect thereto. The resulting
coefficient of friction is extremely low.
The lubricant which escapes at the piston-end of the
combination is collected and re-cycled. A collecting
bellows 25 is located at the piston-end of the cyllnder 1.
Bellows 25 is secured in the groove 26 and may be held at
the outside by a clamp ring, if needed. The bellows is
not stressed by fluid pressures and thus no specially
devised or constructed holding arrangement is needed. The
bellows 25 is centrally secured to piston 6 by means of a
bolt 27 and clamped between a cover 28 and an internal
--10--
G5
shield 29. Shield 29 itself is held by a sleeve 30
supported on a shoulder 31 formed in the piston 6.
The lubricant collected with1n the bellows 25 is
removed by means of ducts 32, 33 (Fig. 2) formed in the
cylinder 1 and connected to a removal line 34. The ducts
32, 33 can be arranged in any suitable configuration and
it is only necessary to so locate them that lubricant can
be removed from the bellows 25. They may, for example, be
secured in fluid-tight connection through a small opening
formed in the bellows 25 itself and, since the fluid
therefrom will not be under pressure, can be removed by
a flexible, for example plastic tubing.
Fig. 4 illustrates an arrangement in which the
sealing tube 35 is loaded by pressure fluid at the outside
thereo~. The sealing tube 35 is engaged by a smooth piston
36, the end of which is rounded. The end portion 16 of
the sealing tube 35 is clamped by means of a clamp element
37 which is secured to piston 36 by bolt 38. The
cylindrical portion 37' of the clamp 37 is extended to form
a piston guide portion for the piston 36. The clamp element
37 is formed with through-bores 39 which conduct the
working pressure fluid to the outside of the sealing tube
35. The other end 418 of the sealing tube 35 merges into
the transition zone A which, similar to the arrangement of
Fig. l, includes the partial elements 460, 470, secured
together at their junction surface 462. In the description
--11--
~:~4V065
that follows, similar parts have been given similar
reference numerals, incremented by hundred numeral
corresponding to the respective drawing. The transition
zone ~ facing the sealing tube is formed with a thickened
portion 461 which, however, in contrast to the zone 61 of
Fig. 1, is located at the outside of sealing tube 35. The
- part-element 470 is, actually, a portion of the end 40 of
the cylinder itself. In this embodiment as well, the
thickness of the partial element 460 decreases towards the
outside within the transition zone A so that, as in the
embodiment of Fig. 1, the localized stiffness and form
stability of the transition zone increase looked at from
the side oE the working pressure fluid.
A bore 43 in piston 36 provides working pressure
fluid which can be applied to the piston by a suitable
connection screwed into the coupling bore of a coupling
bolt 42. Bolt 42 also secures the holding end 44 to the
piston 36. The holding end 44 has threaded bores 45, 46
for connection of supply,and drain lines, respectively,
for lubricant; and a bore 47 with a ring groove 48 sealed
by means of 0-rings 50 located in grooves 49. A
longitudinal bore 51 communicates with groove 48 and
conducts lubricant ~ the end 416 of tube 35. A small ring
groove or gap 54 is formed between a head portion 53
and the piston 36 itself, sealed by an 0-ring 52. The
ring groove is similar to ring groove 19 (Fig. 3) to permit
--12--
1~40(~65
escape of lubricant between the piston 36 and the sealing
tube 35 and allow spreading of the lubricant to escape at
the other end 418 of the tube 35. The region beneath the
end 418, that is, in the transition zone A, forms a
hydraulic choke of-variable cross section, controlled by
.
the pressure of the working pressùre fluid. A sealing
bellows 425 is provlded to collect lubricant for removal
through duct 55.
The bolt 38 has a bore extending therethrough to
permit working pressure fluid to enter the cylinder chamber
and to cause relative movement between the piston and the
cylinder. The working pressure fluid is applied to the
outside of the sealing tube 35 through the bores 39. The
clamping bolt 38 holds the clamp element 37 which, in turn,
is secured to the end 416 of the sealing tube 35 and
further holds the head portion 53 to the piston 36 itself.
The cylinder chamber is closed off by an outer cover 56
sealed by an O-ring 57. Lubrication is effected similar
to that explained in connection with Fig. l,
and the same low coefficients of friction will obtain
herein.
The structure of Fig. 1 may require a larger
passage 12 than that shown and described in connection
therewith. If a larger duct is required, the end 516 of the
sealing tube 517 (Fig. 5) can be constructed to have an
externally extending lip, as seen in Fig. 5. The other
--13--
104~ 65
reference numerals in Fig. 5 correspond to those of
Fig. l. The end portion 516 is held in the wall of the
bore 2 of the cylinder and by a preformed collar portion
3' of the bottom cover plate 503 of the cylinder for
secure and sealed connection.
The transition zone A may have various shapes and
arrangements with respect to the partial elements thereof,
as shown, for example, in Figs. 6 to 13.
Fig. 6: The transition zone A has two partial
elements 660, 670 of different stiffness. The elements
are attached or secured together for example by adhesives,
or by ch~?mical bonding. The partial element 660 is an
extension of the end 618 of the sealing tube which is
formed with a thickened region 661. It has lesser stiffness
~han the partial el~m ent 670 which is formed as a portion
of the piston 666. Again, deformation of the surface of
the transition zone A is obtained, in decreasing direction
looked at from the side of -the working pressure fluid
medium towards the piston.
Flg. 7: The transition zone A of the end 718 of
the sealing tube includes three partial elements 760, 763,
770 having two junction surfaces 762, 762'. The junction
surface between partial elements 760, 753 extends at an
inclination from the side of the working pressure fluid
and passes through the surface of the transition zone A.
--14--
~i~4~ui~i
The piston is shown at 766, forming one of the partial
elements.
Fig. 8 shows the end 818 of the tube in the
transition zone A,and four partial elements 860, 864, 865,
870. The two partial elements 864, 865 are formed as closed
tubes or sleeves and are located between the partial
elements 860, 870. The relative stiffness of all the
partial elements is different, decreasing in the direction
towards partial element 860 from the stiffest element 870.
All junction surfaces 862 are within the transition zone
A. The piston 866 forms one of the elements 870. The end
818 of the tube is formed with a thickened region 861.
Fig.9:The end 918 of the tube is located in a transition
zone A. :Eormed of six partial elements. A thickened region
961 has a partial element 960 of lowest stiffness applied
thereto; four disk-shaped partial elements 965 of
increasing stiffness are joined to the partial element 960
and the last one is the piston 966, having a disk end,
and forming the partial element 970 of highest stiffness.
The intermediate junction surfaces 962 include at least
one secured bonded connection. Due to the larger number of
partial elem.ents, with increasing stiffness, the pressure
with respect to the support wall does not increase in
excessively great steps even if, as in this embodiment, the
junction surfaces of the disk-shaped partial elements
penetrate the surface of the transition zone A. Not all
~)4~ S
.
the junction surfaces have to be adhered together if the
piston 966 is constantly loaded by a counteracting force, for
example by a spring, holding the elements together.
Fig. lO: The arrangement is similar to Fig. 9;
the -transition zone A has seven partial elements. The partial
element 1065 is joined to a sleeve-like partial element 1063.
The junction surfaces are shown at 1062; the piston 1066
forms one of the partial elements, namely the stiffest partial
element 1070.
Fig. ll: The end 111 8 of the sealing tube is within
the transition zone A and merges into partial element 1160
which has a decreasing thickness looked at from the side of
the working pressure fluid. Five partial elements 1165 are
located within the partial element 1160, as is the partial
element l170 of hi~hest stiffness which, itself, may be the
piston or part thereof. A thickened portion of the end 111 8
of the tube is shown at 1161. If the number of partial
elements of increasing stiffness is increased and the
thickness of the partial elements is decreased then, in a
limiting condition, a transition zone in which the stiffness
changes continuously with respect to lengt~' will result.
Such a transition zone can be made of suitable plastic, for
examply polyurethane, and can be so constructed that the
piston forms an integral part thereof.
Fig. 12 A metal tube 1217 has an end 1218 which
is joined to the transition zone A consisting of the partial
--16--
~ .. . . ... . .. ~ . . , ............. .... . . . . ~1
~ elements 1267, 1268, 1270. Although the partial elements
may all consist of the same material, deformation of the
transition zone is non-uniform. The partial element 1268
has a wall thickness which increases towards the piston 1266.
Preferably, the working pressure fluid is applied from the
inside against the partial element 1268. The partial element
1268 forms the throttling region or choke for the hydrostatic
pressure lubr-ication, and provides/self-adjusting choking
passage therefor. Partial elem~ ts 1267, 1270 are provided
for guidance. They may be formed with grooves at the outside
thereof to permit passage of lubricant, as schematically
shown at 1269, 1269'.
Fig. 13: The choke or throttling of the lubricant,
as controlled by the pressure of the working pressure fluid,
is located within the transition zone A. The transition
zone, joined to the end 1318 of the flexible tube, includes
the partial elemenk 1360 with the thickening 1361 and a
stiff, non-deformable partial element 1370 merging into the
piston 1366. The partial element 1370 has a partial zone
1371 at the side of the sealing tube, which zone 1371 is
relative
formed of reduced diameter / to the adjacent zone 1372.
The zone 1372 has a diameter which has just slight play
with re~pect to the wall of the cylinder.
The choke is formed by a piston 1376 held by means
of a spring 1374 against a stop or abutment 1375. A bore
1373 is in communication with the working pressure fluid.
- - -
6S
The lubricant passes along the zone 1371 and in the gap formed
by the reduced diameter thereof and then through a passage
1377 towards the face of the piston 1376 which is opposed to
the face against which the working pressure fluid is applied.
The lubricant forces the piston towards the left (Fig. 13)
and is relieved of pressure and drains off through drain
line 1378 which terminates in the ring duct selectively
opened by leftward movement of the choke piston 1376.
A minor portion of the lubricant flows through the
10 gap formed by the enlarged zone 1372 of the partial element
i370 and the inner wall of the cylinder. This gap may,
if desired, by sealed, for example by an O-ring. The
lubricant pressure is held in balance with the working fluid
pressure also in the arrangement of Fig. 13. Movement of
15 ~e choke piston 1376 can be damped by suitable damping
arrangements, not shown, and well known.
Parl~ial elements inform of thin metallic disks
located between othex partial elements of lower stiffness
may be used. Also, partial elements of substantial stiffness
20 which have surface coatings, or surface layers of materials
of lesser stiffness, can be used.
The transition zone A should be so arranged that
in the first partial region thereof it deforms, corresponding
to the pressure of the working pressure fluid. It is
25 supported at its support wall with in the mean or average
decreasing pressure; the first partial zone merges into a
--18--
V~65
second partial zone in which the deformation decreases and
the transition region no lon~er is supported by the support
wall, that is, is self-supporting. The transition zones may
include level or bowed disk-shaped partial elements of
differential stiffness and with junction surfaces passing
through the outside surface thereof. Such partial elements
have stepped characteristics which are effective up to the
outer surface of the tra~sition zone regarding locallzed
deformation. Thus,~the decrease of pressure on the support
wall occurs in steps within the transition zone A or within
a partial region thereof. Continously decreasing pressure
agai.nst the support wall can be obtained by a transition zone
which has either a continuously variable stiffness or a
finite number of partial elements which are so arranged that
the junction surfaces are located beneath the surface of
the transition zone and are continuous. The least stiff (or
most flexible) partial element then covers the entire surface
of the transition zone, as shown in Figs. 1, 4, 8 and 11 for
example. Lookec~ at from the working pressure fluid, the stability
of shape of the transition zone is progressively increasing.
The length of the transition zone A is indicated by
the respective arrows in the respective Figures, and extends
from an end 18 (and 418, 518...1318) of the sealing tube, that
is, from that point at which the thickness of material of the
-- lg
~4~5
~ sealing tube begins to vary, up to the partial element formed
by a portion of the piston 6, 36, 666...1366. The embodiments
6 13
descnbed in connection with Figs.j may be applied to the
arrangement shown in Fig. 4 or in Fig. 5, and are not
restricted to the specific embodiment shown, which is
illustrated in connection with the structure specifically
described in connection with Fig. 1.
The working pressure of the piston-cylinder
combination may be high, for example 100 at-gauge, and higher.
The sealing tube 17,/ may have good characteristics regarding
elasticity, due to its support on the wall of the cylinder,
so that the force necessary to merely move the piston, that
is, to overcome friction only, is low. The coefficient of
friction can be so low that, when utilizing pressure
lubrication, the coeficient of friction may be less than
0.001. This particularly low friction can be obtained.by the
hydrostatic bearing obtained between the sealing tube and
the adjacent inner surface of the support wall, since the
sealing tube surface and the inner surface of the support wall
are not in physical engagement with each other, due to the
interposed film of lubricant.
_ . If the working fluid is
practically incompressible under high pressure operating
conditions the displacement of the piston-cylinder
combination is effectively directly proportional to the
-
quantity of working .luid supplied. The combination
-20-
~4V()6S
~ may be used for leakproof piston pumps, for servo positioning
systems and the like. Placing tWo piston-cylinder combinations
in paired arrangement and connecting the two pistons(or
cylinders respectively) together results in the double-
acting combination.
The pressure lubrication results in extremely low
-coefficients or friction. Low friction i5 also obtainable
without pressure lubrication, however, if slippery sliding
surfaces 21 are applied to the sealing tube, and/or to the
engaging movable surface. Such sliding surface may be elastic
or flexible mesh or net systems made, for exa~ple, of smooth
or textured man-made fibers or yarns, such as nylon,
~o o /,y 7~e f rq ~ oro e 7~y/c~
A ~ or the like. Threads, yarn, or woven or knit
fabric macle of such material may be applied to the sealing
tubes, if necessary, with an intermediate layer of other
adhesive or adhering yarn or thread made, for example, of
elastic material, various types of elastomers, nylon, cotton,
or the like.
Various changes and modifications may be made and
features described in connection with any one of the embodi-
ments may be used with any of -the others, within the scope
of the inventive concept.
-21-
