FR2576995A1 - GAS SPRING - Google Patents

Abstract

IN A CYLINDRICAL TANK 2 SLIDES A PISTON 4, THE ROD 33 OF THE PISTON THROUGH AN END OF THE CYLINDER PROVIDED WITH GUIDING AND SEALING MEANS 5, 6. AN ANNULAR SEPARATOR PISTON7 IS IN WATERTIGHT CONTACT WITH THE PISTON ROD 4 AND THE SURFACE INTERNAL OF THE TANK 2. A SEALING LIQUID IS CONTAINED INSIDE AN ANNULAR SEALING CHAMBER11 LOCATED AXIALLY BETWEEN THE GUIDING AND SEALING MEANS 5, 6 on the one hand and the SEPARATOR PISTON 7 on the other hand GO. A VOLUME OF GAS UNDER PRESSURE IS PROVIDED ON THE OTHER SIDE OF THE SEPARATOR PISTON 7. THE GAS UNDER PRESSURE ACTS ON THE SEPARATOR PISTON 7 SO AS TO CREATE A PRESSURE ON THE SEALING LIQUID INSIDE THE SEALING CHAMBER 11. A SPRING 12 IS PROVIDED TO ACT ON SEPARATOR PISTON 7 IN PARALLEL WITH THE GAS UNDER PRESSURE, SO AS TO INCREASE THE PRESSURE ON THE SEALING LIQUID BEYOND THE PRESSURE OF THE GAS UNDER PRESSURE.

Description

i "Gas spring" The present invention relates to a device

pneumatic,

  kind of those known under the name of "gas springs".

  It is known to provide in gas springs a liquid

  sheath placed inside the cylinder, near guide means

  and sealing of the piston rod, to improve the sealing properties

  cheity of the piston rod guide and sealing means.

  To seal the piston rod of a gas spring, it is known from the German utility model I 971 284 to seal the chamber filled with gas, which is subjected to high pressure and placed in a tank, at using a sealing liquid. For this purpose, a chamber filled with liquid is provided against a seal of the piston rod, so that this seal of the piston rod is effective essentially as a liquid seal. Any slight loss of liquid in this chamber results in the formation of a gas cushion in this chamber filled with liquid, which escapes through the gasket

  the piston rod significantly faster than the liquid. A concen-

  increased gas ration in the liquid filled chamber is not only-

  harmful to lubrication between the piston rod and the piston rod seal and tends to increase friction and wear on the piston rod seal, but also causes a gradual reduction in the pressure in the tank, this which causes the spring force to decrease after prolonged use. It is also proposed, by French patent application N 84 06009, to seal the chamber filled with liquid with respect to the chamber of the spring filled with gas,

  which is subjected to high pressure by means of a separating piston.

  This separating piston is provided with sealing elements which cooperate in a sealed manner on the one hand with the piston rod and on the other hand with the internal surface of the reservoir. Thus, friction forces appear between the separator piston and the internal surface of the reservoir and the external surface of the piston rod, which means that, caused by the actuation of the gas spring and / or by temperature fluctuations ambient pressure may drop between the gas filled chamber and the liquid filled chamber. Due to different diffusion effects such as permeabilization and dependence on temperature, pressure and time, it is not possible under ordinary operating conditions to avoid the formation of small amounts of gas in the liquid-filled chamber, which causes the disadvantages

  described may also appear, although in a more reduced form.

  you. The arrangement of the gas spring according to one embodiment of the aforementioned French patent application N 84 06009 produces a greater pressure drop between the chamber filled with gas subjected to high pressure and the chamber filled with liquid subjected to pressure lower, which means that the disadvantages described above

  are not eliminated but strengthened.

  The object of the present invention is to provide a gas spring i0 avoiding the drawbacks of known designs and guaranteeing satisfactory sealing for an extended period of time, without loss of the gaseous working fluid, or at least without appreciable loss.

of it.

  To this end, the gas spring object of the invention comprises means defining a reservoir, said reservoir having an internal surface. A piston rod enters this reservoir through means for guiding and sealing the piston rod. This piston rod has an axis and an external surface, and can move in the direction of

  the axis in and out of the tank. A partition wall

  annular tion is in leaktight contact both with the outer surface of the piston rod and with the inner surface of the reservoir. This annular partition wall is capable of effecting an axial movement with respect to both the external surface of the piston rod and the internal surface of the reservoir. An annular sealing chamber is defined

  by the external surface of the piston rod and the internal surface of the reservoir

  see, axially between the rod guide and sealing means

  piston and the annular partition wall. A volume of liquid

  content is contained within the annular sealing chamber.

  A working chamber is defined inside the tank on the side of the annular partition wall which is distant from the means for guiding and sealing the piston rod. A volume of pressurized gas is contained inside the working chamber. Spring means

  separate from the volume of gas under pressure are provided and act directly

  axially on the annular partition wall so as to increase the pressure of the sealing liquid inside the sealing chamber

  annular above a pressure resulting from the volume of gas under pressure.

  The aim defined above is therefore achieved by establishing, under conditions

  non-functioning, in the annular sealing chamber replaced

  folds of a liquid sealing fluid, a pressure lower than the pressure prevailing in the working chamber, so that the diffusion effects

  undesirable between the working chamber and the annular sealing chamber

  the area filled with the liquid sealing fluid is minimized. In addition, the relative pressure fluctuation at the level of the piston rod seal, for a given fluctuation of the internal pressure, is reduced, which facilitates the design of the seal of the piston rod guide and sealing means, which is most often made optimal only for a specific pressure drop for which the seal can be

  used with favorable sealing effects.

  The principle of the invention is also advantageous for use cases where a negative pressure, at least temporary, can appear in the working chamber near the partition wall

annular.

  Compression spring means can be used to obtain a particularly simple construction assembly. These spring means

  compression can be supported on a support surface provided inside

  laughing of the working chamber by the means defining the reservoir.

  Preferably, it is a helical compression spring, but it is also possible to use tension springs or secondary gas cushions to obtain the desired pressure increase in

  the annular sealing chamber.

  The additional spring means are preferably arranged so as to act on the annular partition wall in parallel with the action of the volume of gas under pressure. These spring means must

  be preloaded such as the pressure of the sealant

  inside the annular sealing chamber exceeds the pressure

  pressure of the volume of gas under pressure, this under practically all operating conditions, and preferably under all operating conditions. So the migration of gas from the working chamber

  towards the annular sealing chamber is reduced significantly.

  When using a gas spring, it can happen that the gas pressure near the annular partition wall is reduced andi: 35 ... i. nrci in prs'ion z-amosph-rique ambient. This p and cause: -: - in er sixn of L :. pressure weaving at the anointed part

  :, yen oe> '_ idy_' and d'-t Cc.heit ie pi3ton rod.

  According to another characteristic of the present invention, avoiding this drawback, the spring means are subjected to a prestressing such that the pressure of the sealing liquid inside the annular sealing chamber is higher than the atmospheric pressure surrounding the gas spring, this practically in all operating conditions-

  nement, and preferably under all operating conditions.

  Thus, the drop in pressure at the seal of the piston rod guide and sealing means is always in the same direction, which makes it possible to use a seal of simplified design and in particular

  use a seal provided for reduced friction.

  As certain friction forces always act on the partition wall in the axial direction, due to the sealed contact with the external surface of the piston rod and with the internal surface of the reservoir, the preload exerted by the spring means must be

  as it overcomes these friction forces.

  A very simple construction of the annular separating wall is obtained by producing an annular separating piston in one piece.

  with the annular sealing elements.

  The gas spring may further include a working piston which is connected to the piston rod inside the working chamber, and which divides the working chamber into two parts, in which case the two parts of the chamber are put in communication by means of passage. These passage means can be throttled. In that case,

  it is possible that reduced pressure in the nearby working chamber

  the annular partition wall may appear, and the principle of the present invention is therefore particularly advantageous for this

  widely used type of gas spring.

  In any case, the invention will be better understood using

  the description which follows, with reference to the appended schematic drawing representing

  feeling, by way of nonlimiting examples, two embodiments of this gas spring FIG. 1 represents a gas spring according to the invention, seen in longitudinal section, and FIG. 2 represents, still in longitudinal section. a

: 35 variant of this gas spring.

  The gas spring 1 shown in Figure I comprises a cylindrical reservoir 2, one end of which is closed by a bottom provided with a connecting eyelet for attachment to another element. A working piston 4 connected to a piston rod 3 slides on the internal surface of the reservoir 2, while the piston rod 3 is guided by a piston rod guide, and made watertight with respect to the outside by a seal. piston rod 6. An annular sealing chamber filled with a liquid 11 is separated from a chamber filled with pressurized gas 10 by a separating piston 7, constituted by a support washer 8 and by a separating piston seal 9 % The separating piston 7 is biased by a helical spring 12 which bears against a support face 13 located in the chamber 10, this support face 3 preferably being constituted by an internal rib arranged in the reservoir 2. The spring 12, produced in the form of a compression spring, has an elastic force greater than the friction force acting on the separator piston seal 9, due to

  friction on the internal surface of the tank 2 and on the external surface

  ne of the piston rod 3. Thus, one obtains this result that the pressure in the annular chamber filled with liquidell is greater than the pressure prevailing in the chamber filled with gas 10, in all the operating conditions of the gas spring. The consequence is also that

  diffusion of the gas out of the chamber filled with gas 10 and towards the chamber

  annular bre filled with liquid It is made minimal. A return in

  position of the separator piston seal 9 is guaranteed under all conditions

  operating conditions, so that changes in temperature and changes in pressure caused by the use of the gas spring cause no transfer of even very small amounts of gas to the annular chamber filled with liquid 11. The pressure force additional force exerted by the spring 12 on the separating piston 7 can be made sufficiently large so that, even in unfavorable cases, there still prevails in the annular chamber filled with liquid There is greater pressure than on the other side of the rod seal piston 6. Consequently, even in such use cases, the seal 6 of the piston rod can be produced in the form of a simple seal, since it is stressed only in one direction of drop

pressure.

  The embodiment according to FIG. 2 differs from that of FIG. I essentially by the fact that the separating piston 7 is constituted by a lining 14. This lining 14 separates the chamber

  ring filled with liquid II from the chamber filled with gas under pressure

  if we. The spring 12 supported on the support face 13 and located in the chamber filled with gas 10 acts by means of a support washer on the lining 14, and acts in parallel with the force exerted by the

  pressure of the gas in chamber 10 on the separator piston 7.

  Instead of the spring produced in the form of a helical compression spring, it is naturally possible to use mechanical or pneumatic elastic elements of any desired configuration, which exert on the separating piston 7 an elastic force acting in parallel with the pressure of the chamber filled with gas 10. It is even possible to replace the helical compression spring with a secondary annular chamber filled with gas, defined by the separating piston 7 on the one hand and by another separating piston adjacent to the face d 'support

13 on the other hand.

  Of course, the invention is not limited to only modes of

  realization of this gas spring which have been described above, by way of example

  ples; it embraces, on the contrary, all the variants respecting

the same principles.

Claims (13)

I. Gas spring comprising:   means defining a reservoir (2), said reservoir (2) pre-   feeling an internal surface; a piston rod (3) entering the reservoir (2) by means of guide and sealing of the piston rod (5,6), the piston rod (3) having an axis and an external surface and being movable   in the direction of its axis inward and outward from the reservoir   see (2); an annular partition wall (7) in leaktight contact both with the external surface of the piston rod (3) and with the internal surface of the reservoir (2), this annular partition wall (7) being capable of performing a axial movement with respect to both the external surface of the piston rod (3) and the internal surface of the reservoir (2) an annular sealing chamber (11) being defined by the external surface of the piston rod (3 ) and the internal surface of the reservoir (2) axially between the means for guiding and sealing the piston rod (5,6) and the annular partition wall (7); a volume of sealing liquid inside the annular sealing chamber (11); a working chamber (10) inside the tank (2) on the side of the annular partition wall (7) which is distant from the piston rod guide and sealing means (5,6) a volume pressurized gas in the working chamber (10);   spring means (12) separate from this volume of gas under   pressure and acting in an axial direction on the annular partition wall   laire (7), characterized in that said spring means are provided so as to increase the pressure applied to the sealing liquid   in the annular sealing chamber (1!) above a resulting pressure   both the volume of gas under pressure.   2. Gas spring according to claim 1, characterized in that   that said spring means (12) are compression spring means   sion (i2u et sonr aopuî y su '' re support face (13), this support lace. '' irie - of working room (l) by the '2 _ s.r.oixr _ O 3. Gas spring according to claim 1 or 2, characterized in that said spring means comprise a helical spring compression (12).   4. Gas spring according to any one of the claims   1 to 3, characterized in that said spring means (12) act on the annular partition wall (7) in parallel with the action of the volume gas under pressure.   5. Gas spring according to any one of claims   1 to 4, characterized in that said spring means (12) are subjected   to a prestress such as the pressure of the sealing liquid inside   of the annular sealing chamber (11) exceeds the pressure of the volume of gas under pressure, this under practically all conditions Operating.   6. Gas spring according to claim 5, characterized in that said spring means (12) are subjected to a prestressing such   that the pressure of the sealing liquid inside the sealing chamber   ring gasket (i 1) exceeds the pressure of the volume of gas under pressure   under all operating conditions.   7. Gas spring according to any one of the claims   ! 6, characterized in that said spring means (12) are subjected   to a prestress such that the pressure of the sealing liquid at lPinté-   of the annular sealing chamber (11) exceeds the atmospheric pressure   ring around the gas spring (1), this practically in all the operating conditions.   8. Gas spring according to claim 7, characterized in that said spring means (12) are subjected to a prestressing such   that the pressure of the sealing liquid inside the sealing chamber   annularity (11) exceeds the atmospheric pressure surrounding the   gas spring (1) in all operating conditions.   9. Gas spring according to any one of claims   1 to 8, characterized in that said spring means (12) are subjected to a prestress making it possible to overcome friction forces acting on the annular partition wall (7) in the axial direction, and resulting from the sealed contact with the external surface of the rod   piston (3) and the internal surface of the tank (2).   10. Gas spring according to any one of claims   I to 9, charac * erized in that the annular separation wall (7) comprises an annular separator piston (8) and annular sealing elements (9) provided on this annular separator piston (8) to come into contact with the outer surface of the piston rod (3), and with the inner surface of the tank (2).   11. Gas spring according to claim 10, characterized in that the annular separating piston (14) is made in one piece   with the annular sealing elements.   12. Gas spring according to any one of claims   1 to I 1, characterized in that the piston rod (3) is connected to a working piston (4) inside the working chamber (10), the working piston (4) dividing the working chamber work (10) in two parts, passage means being provided for switching these two parts. 13. Gas spring according to claim 12, characterized in   what the passage means include throttling means.