FR2844854A1 - Gas spring without or with reduced volume lubrication chamber has piston designed to disperse lubricant in compression chamber to lubricate rod - Google Patents

Abstract

Gas spring (1) consists of body (2), guide assembly (7) forming compression chamber (4) with body that contains gas (G) and lubricant (L), and piston (5) with rod (6) that slides in the guide assembly so that the gas exercises return force on it. The guide assembly is without a lubrication chamber or has one of reduced volume, and the piston is designed to disperse lubricant in compression chamber to lubricate rod when piston moves. The gas spring (1) consists of a body (2), a guide assembly (7) forming a compression chamber (4) with the body that contains a gas (G) and a lubricant (L), and a piston (5) with a rod (6) that slides in the guide assembly so that the gas exercises a return force on it. The guide assembly is without a lubrication chamber or has one of reduced volume, and the piston is designed to disperse lubricant in the compression chamber to lubricate the rod when the piston moves. The piston has a collar (8) to limit its stroke and an agitator (21) of a different material round the collar to disperse lubricant in the compression chamber. The guide assembly has two annular grooves with seals (15, 16), the one nearest the compression chamber being asymmetrical to favor the return of lubricant.

Description

The present invention relates to gas springs comprising a chamber

  compression filled by a gas and a piston movable in this chamber to compress the gas therein and generate an elastic restoring force. Such springs are used on

presses, for example.

  European patent EP 0 959 263 discloses a gas spring comprising a metal casing open at one end and a compression chamber inside which is movable a piston whose rod slides in a bore produced in a guide piece inserted into the opening of the housing. The guide piece has an annular lubrication chamber filled with a lubricant. Due to the presence of this lubrication chamber 10, the guide piece can have a relatively large length,

  which affects the axial size of the spring.

  Other springs are known, which include a guide segment

  self-lubricating with a fairly high axial dimension.

  There is a need to have a spring having a reduced axial size compared to known springs, for the same return force.

  The present invention meets this need thanks to a gas spring comprising: - a body, - a guide assembly defining with the body a compression chamber intended to contain a gas and a lubricant, a piston being able to slide in the assembly guiding so that the gas can exert a restoring force on the piston,

  this spring can be characterized by the fact that the guide assembly does not have a lubrication chamber or comprises a lubrication chamber of reduced volume, and by the fact that the piston is configured to disperse the lubricant in the compression chamber in order to allow lubrication of the rod when the piston moves.

  The term "reduced" volume lubrication chamber means a chamber of volume less than 1800 mm3, better 500 mm3, for springs of force less than or equal to 500 daN, less than 4400 mm3, better 1000 mm, for springs of force between 500 and 750 daN inclusive, less than 8800 mm3, better 3000 mm3, for springs of force between 750 and 1500 daN inclusive and with force less than

  20,000 mm3, better 10,000 mm3 for springs with a force greater than 1,500 daN.

  The piston can be made, in order to obtain the desired dispersion, so that the ratio of the section of the rod to the section of the largest passage for the gas formed between the piston and the wall of the chamber is greater than 2 , 1 for springs with a force less than 1500 daN and more than 1.5 for springs with a force greater than or equal to 1500 daN. This ratio can advantageously be greater than 2.5 for springs with a force greater than or equal to 750 daN and less than 1500 daN. The ratio can be greater than 2, or even 2.6, for springs with a force greater than or equal to 1500 daN and less than or equal

at 3000 daN.

  The desired dispersion of the lubricant can still be obtained without the ratio of

  sections defined above, by attaching to the piston rod a drill bit or a spring dipping 10 in the lubricant.

  The piston, during its movements, disperses in the gas at least a fraction of the lubricant contained in the compression chamber and allows it to effectively lubricate the rod. Thus, the guide assembly can be produced with a relatively short length, in particular without a lubrication chamber or with a reduced chamber, without however the piston being insufficiently lubricated, which makes it possible to reduce

the axial size of the spring.

  In an exemplary implementation of the invention, the piston comprises a collar making it possible to limit the stroke of the piston in the opposite direction from its depression and a stirring member secured to the collar. The latter has sufficient mechanical strength to retain the piston in the compression chamber, abutting against the guide assembly when the volume of the compression chamber is maximum and the spring is at rest. The collar can be made in one piece

  with the piston rod, in steel for example.

  In an exemplary implementation of the invention, the stirring member is attached to the collar. The stirring member can extend, for example, all around the collar. In an exemplary implementation of the invention, the stirring member is made of a material different from that of the collar. The stirring member may in particular comprise a washer fixed to the flange, this washer being for example made of spring steel. When attached to the flange, this washer can

  have main frustoconical faces slightly inclined in the direction of the guide assembly with respect to a plane perpendicular to the longitudinal axis of the piston.

  This washer may have a substantially flat shape before it is fixed to the flange and take its frustoconical shape only when it is fixed to the flange, from the

  made of the appearance of internal constraints.

  The stirring member can be fixed to the flange by any means, for example by snap-fastening, gluing, crimping, shrinking, welding or screwing. In an exemplary implementation of the invention, the collar comprises a

  annular groove in which the stirring member can engage, at least partially.

  Such a configuration of the collar is advantageous in particular when the stirring member comprises a washer snapped onto the collar. Such a washer can make it possible to save material compared to the use of a flange.

  which would have the same outside diameter.

  In one implementation of the invention, the flange is configured to come to bear, at rest, against a radially inner region of the guide assembly, which is advantageous in terms of internal stresses because a support of the flange on a radially outer region could, in the case of a relatively short length of the guide assembly, generate a torque at the piston rod and therefore

significant internal constraints.

  The piston can be devoid of a stirring member separate from the flange, in which case the latter can be configured not only to serve as a stop at the end of the piston stroke but also to stir the gas in the compression chamber,

  so as to disperse the lubricant therein.

  The guide assembly may include two annular grooves housing

  seals, the groove closest to the compression chamber possibly containing a seal having an asymmetrical profile favoring the return of the lubricant present on the rod 25 towards the compression chamber during the piston driving movements.

  The aforementioned seal can be a TURCONe STEPSEAL K seal. The present invention also relates, according to another of its aspects, to a gas spring comprising: - a body, - a guide assembly defining with the body a compression chamber intended to contain a gas and a lubricant, - a piston which can slide in the guide assembly so that the gas can exert on the piston a restoring force, the piston comprising a rod comprising, when the spring is at rest, a first portion emerging from the compression chamber and a second portion surrounded by the guide assembly, the spring being characterized by the fact that the length of the first portion is greater than that of the second portion and by the fact that the piston is configured so as to disperse, during its movements in the compression chamber, the lubricant

  contained in the compression chamber.

  Another subject of the present invention, independently of the above, according to another of its aspects, is a gas spring comprising: a body, - a guide assembly defining with the body a compression chamber intended to contain a gas and a lubricant, - a piston which can slide in the guide assembly so that the gas can exert on the piston a restoring force, the piston comprising a flange 15 making it possible to limit the stroke of the piston in the opposite direction of its depression ,

  the spring being characterized in that the piston includes a stirring member attached to the flange. Such a member can make it possible to create, during movements of the piston, turbulence within the gas sufficient to disperse in the gas the lubricant contained in the compression chamber. The use of such an attached stirring member makes it possible to save material.

  The invention will be better understood on reading the detailed description

  which follows, non-limiting examples of implementation thereof, and on examining the appended drawing, in which: - Figure 1 shows schematically and partially, in axial section, a gas spring according to the invention, - Figures 2 to 5 show schematically and partially, in axial section, the gas spring of Figure 1, respectively in four successive stages of its operation, - Figure 6 is a detail view, schematic of the guide assembly of the gas spring of FIG. 1, and FIG. 7 schematically and partially represents a piston conforming

  to a variant implementation of the invention.

  FIG. 1 shows a gas spring 1 comprising a metal casing 2 in the form of a hollow cylinder of axis X, provided with a bottom wall 3, open at its upper end and defining a compression chamber 4 to l inside

  which can move a monobloc piston 5, metallic.

  The compression chamber 4 has a tubular inner wall 18 opposite which the piston 5 moves. This wall 18 has an upper part 18a of internal diameter dl and a lower part i8b of internal diameter d2 greater than dl.

  The bottom wall 3 is equipped with a valve 9, known in itself, for filling the compression chamber 4 with a gas G such as nitrogen, for example.

  Lubricant L, such as conventional hydraulic oil, coats the

  bottom of the chamber 4 when the piston 5 is at rest.

  The piston 5 comprises a rod 6 of longitudinal axis X, made of steel, of section

  circular of diameter d5, sliding in a bore made in a guide assembly 7 15 inserted in the upper opening of the casing 2.

  The rod 6 is connected at its lower end to a flange 8 of external diameter d4, which has sufficient mechanical strength to retain the piston 5 when the latter comes to rest in abutment, under the effect of the pressure of the gas G contained in

  the compression chamber 4, against the guide assembly 7.

  The latter comprises a guide piece 10 retained in the casing 2 by a metal rod 11, which comes to bear, on the one hand, in an annular recess 12 of the guide piece 10 and, on the other hand, in a groove annular 13 made in the casing 2, at

  near its upper end.

  As illustrated in FIG. 6, the guide piece 10 comprises, in the upper part, a first annular groove 15 at the bottom of which is disposed an O-ring intended to apply a seal 26 also housed in the groove 15 against the

piston rod 6.

  In the example described, the seal 26 is a seal sold under the

  name TURCONe GLYD RING ', in polyethylene.

  The guide piece 10 comprises, below the groove 15, a second annular groove receiving a guide segment 14, which is applied against the rod

piston 6.

  A third annular groove 16 of the guide piece 10 located under the guide segment 14 houses an O-ring 27 and a seal 28, the latter being in abutment against the seal 27 and the piston rod 6, which seal 28 is a seal sold

  under the name TURCONO STEPSEALC K, in PTFE loaded with bronze.

  The shape of the seal 28 facilitates the return of the oil present on the rod 6 to the

  compression chamber during piston driving movements.

  An O-ring 17 is sealingly interposed between the guide piece 10 and

the housing 2.

  The guide piece 10 has at its lower end an annular surface 19 perpendicular to the axis X. At rest, the flange 8 comes to bear against an annular region radially

inside the surface 19.

  In the example of Figure 1, the flange 8 has an upper part 8a

  cylindrical of revolution extended below by a slightly frustoconical part 15 8b converging towards the bottom of the compression chamber 4.

  In a variant implementation of the invention, as illustrated in the figure

  7, the flange 8 may have at its periphery a frustoconical upper part 30 converging in the direction of the rod 6 so as to present a reduced bearing surface against the surface 19 of the guide piece, close to the radially inner edge of the 20 guide piece.

  The collar 8 may also have in its lower part an annular clearance 31 in order to avoid contact of the collar with the bottom of the chamber 4, in particular when the bottom wall of the latter is relatively thick and

  has a roundness at its periphery.

  The flange 8 has an annular groove 20 allowing it to snap-fasten therein a stirring member 21 of external diameter d3, constituted in the example

  considered by a washer 21, the latter being made, for example, of spring steel.

  It is not beyond the scope of the present invention when the stirring member

  21 is fixed to the flange 8 by another means, for example by crimping.

  As can be seen in FIG. 1, the washer 21 has main frustoconical faces 22 slightly inclined in the direction of the guide assembly 7, with respect to a plane perpendicular to the axis X. The washer 21 has before it is fixed on the flange 8 a substantially planar shape and takes the frustoconical shape after its

  attachment to the flange 8, due to the appearance of internal stresses.

  The following table gives some examples of section reports for

  springs according to the invention and known springs.

  The force of the spring is that exerted by the gas on the piston when the latter is at rest, in the configuration of FIG. 1, the flange 8 coming into abutment against the

  underside of the guide assembly 7.

  In the table above, e designates the maximum width of the passage for air between the piston and the wall of the chamber, that is to say (d2-d3) / 2 for the spring according to the invention illustrated .

  Spring force daN Rod section (MM2) St = 7t d2 / 4 Section (min2) of the gas passage between the piston and the wall of the chamber 5p = f (d2-d3) / 4 Section ratio R = St / Sp Spring according to 750 490.9 186.1 2.64 the invention 1500 1017.9 370.7 2.75

3000 1963.5 725.7 2.71

  Spring according to 750 490.9 245 2 the condition of the 1500 1017.9 716.3 1.42 technical 3000 1963.5 1500.9 1.31 The higher the ratio R, the higher the speed of the gas circulating between the piston and the

  wall of the chamber is high, for the same depression of the piston rod.

  Gas springs with a ratio R> 2.1, preferably greater than 2.5

  approximately allow a gas flow with a higher speed, therefore capable of creating turbulence making it possible to efficiently disperse the lubricant in the chamber 20 to bring it into contact with the rod.

  At rest, in the example illustrated, the length 12 of the portion of the rod 6 surrounded by the guide assembly 7 is less than the length Il of the portion of the rod 6 emerging from the spring. The length 12 can be slightly greater than the nominal stroke of the piston, which can be around 50 mm for example. It could be otherwise without departing from the scope of the present invention, and the length It could in particular be less than the length 12. During the operation of the spring 1, when the piston 5 is depressed in order to reduce the volume of the compression chamber 4, the flange 8 and the stirring member 21 generate a pressure difference on either side of the stirring member 21 and turbulence within the gas G, as illustrated in FIG. 2. The pressure upstream of the stirring member 21 becomes higher than that prevailing downstream thereof, having regard to the

  direction of piston movement. As the piston 5 is depressed, the turbulence created by the stirring member 21 becomes large enough to transport lubricant dispersed during the previous cycle in the compression chamber 4 to the rod 6 to lubricate it, as illustrated in FIG. 3. This prevents damage to the seals 15 and 16 by dry friction and heating against the rod 6.

  When the piston 5 rises under the effect of the restoring force exerted by the gas G, the stirring member 21 generates turbulence contributing to dispersing in the gas

  G the lubricant L contained in the bottom of the compression chamber 4.

  Thus, the piston 5 can be satisfactorily lubricated during the operation of the spring, despite the absence of a lubrication chamber between the seals 15

and 16.

  In the example described, the guide assembly is devoid of a

  lubrication, which is satisfactory for a spring with a force of 500 or 750 daN.

  Without departing from the scope of the invention, for a spring of greater force, for example of 1500 or 3000 daN, it is possible to provide a lubrication chamber having a

reduced volume.

  The following table gives two examples of chamber volume.

  lubrication for springs in accordance with the invention and known springs.

  Spring force Spring according to Spring according to the state in the invention of the technique 1500 2780 mm3 8874 mm3 3000 8034 mm '22030 mm3 Of course the invention is not limited to the examples of implementation which

have just been described.

  The piston 5 can in particular be devoid of an added stirring member and the collar have at its periphery a diameter sufficient to allow it to serve as a stirring member. The collar is advantageously made in one piece with the stem of the

  piston but, alternatively, the collar could be attached to the piston rod.

  Throughout the description, including the claims, the expression

  "comprising a" should be understood as being synonymous with "comprising at least 10 one", unless otherwise specified.

Claims (12)

  1. Gas spring (1) comprising: - a body (2), - a guide assembly (7) fixed relative to the body (2) and defining with the body (2) a compression chamber (4), this compression chamber being intended to contain a gas (G) and a lubricant (L), - a piston comprising a rod (6) which can slide in the guide assembly so that the gas can exert on the piston a force of reminder, characterized in that the guide assembly does not have a lubrication chamber or comprises a lubrication chamber of reduced volume and in that the piston is configured to disperse the lubricant in the compression chamber in order to   allow the rod to be lubricated when the piston moves.   2. Spring according to claim 1, characterized in that the guide assembly has no lubrication chamber.   3. Spring according to claim 1, characterized in that the ratio   (R = St / Sp) from the section (St) of the rod (6) to the section (Sp) of the largest passage for the gas formed between the piston and the wall (18b) of the chamber is greater than 2, 1 for springs with a force less than 1500 daN and greater than 1.5 for springs with a force greater than or equal to 1500 daN.   4. Spring according to one of the preceding claims, characterized in that   that the piston has a collar (8) configured to limit the stroke of the piston and a stirring member (21) integral with the collar, allowing the lubricant (L) to be stirred in the compression chamber.   5. Spring according to the preceding claim, characterized in that   the stirring member (21) is attached to the collar (8).   6. Spring according to one of claims 4 or 5, characterized in that   the stirring member (21) extends around the flange (8).   7. Spring according to any one of claims 4 to 6, characterized in that the stirring member (21) is made of a material different from that of the collar (8).   8. Spring according to any one of claims 4 to 7, characterized by the 1l   fact that the stirring member (21) comprises a washer fixed to the flange (8).   9. Spring according to any one of the preceding claims, characterized   by the fact that the collar is configured to come to bear, at rest, against a region   radially inner of the guide assembly.   10. Spring according to any one of the preceding claims, characterized   by the fact that the gas consists of nitrogen.   11. Spring according to any one of the preceding claims, characterized   by the fact that the guide assembly comprises two annular grooves housing seals and by the fact that the groove closest to the compression chamber 10 contains a seal (28) having an asymmetrical profile promoting the return of the lubricant present on the rod towards the compression chamber when the piston is pushed in. 12. Spring according to claim 11, characterized in that the seal (28) is a TURCONe STEPSEAL8 K seal.