Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Fluid-power cylinder provided with a cushioninq device
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a fluid-power cylinder provided
with a cushioning device for cu~hioning the movements of the
piston in the cylinder.
Prior Art:
Fluid-power cylinders often require a cushioning device
which retards the piston at one or both ends of its stroke within
the cylinder. In most cushioning devices, a residual volume of
fluid trapped in a cushioning compartment is allowed to escape
from the cushioning compartment only through a restricted dis-
charge passage in order to retard the movement of the piston
during the final portion of its stroke.
A problem which is present in many prior art cushioning
devices is that the cushioning effect is dependent on the dimen-
sional accuracy of components which move relative to one another
and de~ine the restricted discharge passage between them. Wear of
these components also affects the cushioning effect which may
therefore be gradually r~duced in the course of time.
Another problem which is present in many prior art
cushioning devices is that it is difficult to adjust the
cushioning effect such that the desired cushioning is achieved for
both end positions or stroke ends.
SUMMARY OF THE INVENTION
An object of this invention is to provide a fluid-power
cylinder provided with a cushioning device which is improv~d in
respect of the above-mentioned problems.
According to the invention, there is provided a fluid-power
3n cylinder comprising a power cylinder member, a power piston
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member, which includes a power piston body reciprocable in the
power cylinder member between opposed end positions and a piston
rod secured to the power piston body and projecting from one end
of the power cylinder member, and a device for cushioning the
relative movements oE the power cylinder member and the power
piston msmber at the end positions, which device comprises for
each end position a c~shioning piston on one of the power cylinder
and power piston member; and a cushioning cylinder on the other
member, the cushioning cylinder defining a cushioning compartment
having a closed inner e:nd and an open outer end in which the
cushioning piston is receivable when it approaches the end posi-
tion, and a cushioning fluid reservoir in constant fluid flow
communication with both cushioning compartments, a restricted
discharge passage providing the sole path for sscape of cushioning
fluid from the associated cushioning compartment to the cushioning
fluid reservoir when the cushioning piston is received in the
cushioning cylinder.
A preferred embodiment of the invention, which is particu-
larly useful in a pneumatic fluid-power cylinder having a hydrau-
lic cushioning device, has the following features:
- the piston rod of the power piston member is hollow, its
interior being in constant unrestricted communication with the
cushioning fluid reservoir,
- the cushioning cylinders are located within the piston rod
of the power piston member and axially spaced apart, adjacent
cylinder ends being open to define the open outer ends of the
cushioning compartments,
: - the cushioning pistons are stationary with respect to the
power cylinder member,
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- each cushioning piston is provided exteriorly with a fluid
seal adapted to sealingly engage the interior wall of the associa-
ted cushioning cylinder when the cushioning piston i5 moving in
the cushioning cylinder towards the inner end of the cushioning
compartment and to permit substantially unrestricted fluid flow
between the cushioning piston and the interior wall of the
cushioning cylinder when the cushioning piston is moving in the
cushioning cylinder towards the outer end of the cushioning com-
partment, and
- the discharge passage is a passage which is provided in
the cushioning piston and bypasses the fluid seal.
Other objects, features and advantages of the invention will
become apparent from the following description of a preferred
embodiment with reference to the drawing.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a longitudinal sectional view of a fluid-power
cylinder embodying the invention:
Fig. 2 is an enlarged longitudinal sectional view of a
portion o~ the fluid-power cylinder of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawing, the invention is embodied in a
; double-acting pneumatic cylinder provided with a hydraulic device
for cushioning the stroke of the power piston member of the
cylinder at both end positions or stroke ends. Two separate
cushioning cylinders are provided within a tubular piston rod of
the power piston member and reciprocate therewith, and a dual
cushioning piston is stationary with respect to the power cylinder
member in which the power piston member is reciprocable. It is to
be understood, however, that the invention may be embodied in
other types of fl~lid-power cylinders, e.g. single-acting cylin-
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ders, cylinders in which cushioning is effected only at one endposition or stroke end, and cylinders in which the same kind of
fluid is used both as working fluid and cushioning fluid.
The illustrated fluid-power cylinder comprises a power
cylinder member generally designated by 11 and a power piston
member 12 which is reciprocable in the power cylinder member. It
also comprises a hydraulic cushioning device including a pair of
cushioning cylinders 13, a dual cushioning piston 14 with an
associated support tube 15 and a cushioning liquid reservoir 16.
Main components of the power cylinder member 11 are a cy-
lindrical tube 20 of circular cross-section and front and rear end
walls ~1 and 22, respectively, which sealingly close the ends of
the tube and are provided with connectors 23 and 24, respectively,
through which the working fluid, namely compressed air, is
supplied and discharged. The rear end wall 22 is made integral
with the cushioning liquid reservoir 16. Mounted on the reservoir
16 are a pair of aligned pivot pins 25 by which the power cylinder
member 11 may be pivotally mounted on a bracket (not shown).
The power piston member 12 comprises a power piston body 26
which sealingly engages the inner wall of the cylinder tube 20 and
divide~ the cylinder space between the end walls into front and
rear cylinder compartments 27 and 28, respectively, which communi-
- cate with respectively the front air connector 23 and the rear air
connector 24, and a tubular piston rod 29, one end of which, the
rear end, is secured to the power piston body and projects for-
wardly through a sliding seal in the front end wall 21 of the
power cylinder member 11. Secured to the front end of the piston
rod 29 is an eye bolt 30, through which the power piston member 12
may be connected to a part to be actuated, such as a door or the
like.
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The end positions of the reciprocating movements of the
power piston member 12 in the power cylinder member 11 are defined
by a pair of abutments which are provided on the cylinder end
walls 23 and 24 and are adapted to be engaged by the power piston
body 26.
The cushioning cylinders 13 of the cushioning device are
formed by front and rear cylindrical sleeves which are secured in
the hollow piston rod 29 adjacent respectively the front and the
rear end thereof. The adjacent ends of the two sleeves are intern-
ally bevelled or widened. Together with the front part of thepiston rod 29 and the power piston body 26 the sleeves 13 define a
pair of cushioning compartments 31A, 31B, which are open towards
the interior 32 of the piston rod at their outer, adjacent ~nds
but are otherwise closed.
The dual cushioning piston 14 is secured to the front end of
the support tube 15 which in turn has its rear end secured to the
cylinder end wall 22 and is in constant open communication with a
cushioning liquid compartment 33 in the cushioning liquid reser-
voir 16. The support tube 15 extends through a sliding seal 34 in
the power piston body 26 and through the rear cushioning cylinder
sleeve 13.
: The cushioning piston 14 comprises a front piston section
14A and a rear piston section 14B. When the power piston member 12
is moved inwardly to its inner end position in the power cylinder
member 11 as shown in the drawing, the front cushioning piston
: section 14A is moved inwardly in the front cushioning cylinder
compartment 3lA to the vicinity of the inner end or bottom of the
compartment. Similarly, in the outer end position of the power
piston member 12, the rear cushioning piston section 14B is moved
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inwardly in the rear cushioning cylinder compartment 31B to the
vicinity of the inner end or bottom thereof.
The dual cushioning piston 14 comprises a dumbbell-shaped
metal body, the enlarged end portions of which form the front and
rear cushioning piston sections 14A, 14B and have a diameter
slightly smaller than the inner diameter of the cushioning cylin-
der sleeves 13. The difference in diameters is sufficient to
permit a substantially unrestricted liquid flow through the gap
between each cushioning cylinder sleeve 13 and the associated
cushioning piston section 14A, 14B received therein.
Each cushioning piston section 14A, 14B is provided with an
external circumferential groove 35A, 35B, which accommodates a
frusto-conical sealing ring 36A, 36B of relatively soft material.
The sealing rings are opposed such that their larger ends, which
are adapted to engage sealingly the interior wall of the cushion-
ing cylinder sleeves 13, are directed away from one another, i.e.
towards the inner ends of the cushioning compartments.
Extending through entire cushioning piston 14 is a central
axial passage 37 which is in constant open communication with the
interior of the support tube 15 and thus with the cushioning
liquid compartment 33. Inserted in the front end of ~his passage
is a calibrated restrictor 38. By way of a transverse passage 39
the central portion of the passage 37 is in constant unrestricted
communication with the space around the cushioning piston.
From the rear end face of the rear piston section 14B ex-
tends an axial passage 40, which is in constant unrestricted
communication with the pis~on rod space 32 and is in constant but
restricted communication with the space around the cushioning
piston, the last-mentioned communication being by way of a cali-
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brated restriction 41 located between the two sealing rings asmall distance from the sealing ring 36B.
The piston rod space 32 and the spaces communicating with it
are always filled with the cushioning liquid. When the power
piston 12 moves outwardly relativa to the power cylinder member 11
from the illustrated inner end position under action of compressed
air supplied to the rear power cylinder compartment 28, the front
cushioning cylinder compartment 31A defined in fxont of the front
cushioning piston section 14A expands. During this movement, the
cushioning compartment 31A is successively filled with cushioning
liquid which flows against very little resistance into the com-
partment past the sealing ring 36A because this sealing ring is
pressed into its groove 35A. Thus, the sealing ring 36A acts as a
valve (one-way valve) which opens automatically to permit liquid
flow into the front cushioning cylinder compartment 31A.
When the power piston member 12 approaches its outer end
position, the rear cushioning piston section 14B is received in
the rear cushioning cylinder sleeve 13. The rear sealing ring 36B,
because of its frusto-conical shape, is caused to engage sealingly
the inner wall of the sleeve (one-way valve action). The only path
through which the cushioning liquid trapped in the rear cushioning
cylinder compartment 31B can escape is therefore formed by the
passage 40 containing the calibrated restriction 41. By virtue o~
its cross sectional area, this restriction determines the rate at
which the power piston member 12 continues its movement to the
outar end position.
Similarly, during the retraction of the power piston member
12 to its inner end position, the calibrated restrictor 38 in the
: front cushioning piston section 14A determines the rate at which
the ~inal portion of this retraction takes place.
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In use, there is no wear of those elements, namely the
restrictors 38 and 41, of the cushioning device which determine
the speed at which the power piston member 12 moves near the end
positions, assuming that the forces acting on the power piston
member 12 are given. These elements therefore do not undergo any
change in respect of their predetermined cross-sectional flow area
during the use~ul life of the cushioning device. Moreover, because
it is also easy to design the restrictors with the desired cross-
sectional flow area and to ensure that the cushioning liquid
trapped in the cushioning cylinder compartments cannot escape
except through the restrictors, the cushioning device can be
designed to provide the desired cushioning effect. Moreover, it is
easy to ensure that any wear that takes place does not cause the
cushioning effect to change over the time in a way that is diffi-
cult to compensate. I~ the cushioning effect of the device should
be reduced because of wear of the sealing rings of the cushioning
pistons, the desired cushioning effect can readily be restored by
replacement of the sealing ringsO
I~ the illustrated embodiment the calibrated restrictors are
fixed, but it is of course within the scope of the invention to
make them adjustable.
The cushioning liquid xeservoir 16, the main body of which
is made integral with the rear cylinder end wall 22, has a sub-
stantially circular cylindrical exterior shape and is sealingly
clo~ed at its rear end by means of a screw-threaded cover 42.
The two aligned pivot pins 25 are secured to a circular
clamp 43 which is held in position about the cushioning liquid
reservoir 16 by means of a bolt 44 which is passed through a pair
of outwardly bent flanges 45 of the clamp. The clamp 43 is secured
axially in its position, and possibly also against rotation, on
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the cushioning liqu.id reservoir by a ridge 46 on the inner side of
the clamp or by any other suitable projection which engages a
corresponding groove or recess 47 on the outer side of the
cushioning liquid rsservoir 16.
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