FR2672355A1 - Self-contained (autonomous) pneumatic spring - Google Patents

Abstract

The pneumatic spring (101) comprises a casing defining a closed chamber (103) of variable volume, delimited by a movable wall (104), this chamber (103) containing a neutral gas (5) under pressure capable of exerting an elastic force on the said movable wall. The spring includes a push rod (106) mounted slidingly in a bore (107) of the chamber, this rod projecting to the outside of the casing and being capable of transmitting or of receiving mechanical loads. The rod (106) is equipped with a head (110) capable of sliding in the said bore, to which head is applied, by a fluid (L), a pressure equal to that of the gas. The passage cross-sections offered to the fluid (L) acting on the head of the rod have flow characteristics which are identical in both directions, and the ratio of the maximum volume displaced by the head, during the movements of the rod, to the volume of the chamber (103) containing the gas is at most equal to 1/8. The spring (101) constitutes an autonomous device.

Description

SELF-CONTAINED PNEUMATIC SPRING.

 The invention relates to a pneumatic spring of the kind which comprises an envelope defining a closed chamber, of variable volume, delimited by a movable wall, this chamber containing a neutral gas under pressure suitable for exerting an elastic force on said movable wall. .

 The object of the invention is, above all, to provide a pneumatic spring which can easily replace a helical spring while having a reduced bulk, improved elastic characteristics and easier adjustment possibilities.

 I1 is also desirable that the establishment and / or replacement of such an air spring is simpler to perform than in the case of a helical spring.

 According to the invention, an air spring comprising an envelope defining a closed chamber, of variable volume, delimited by a movable wall, this chamber containing a neutral gas under pressure suitable for exerting an elastic force on said movable wall is characterized by the fact that it comprises a push rod slidingly mounted in a bore of the casing whose diameter is less than the diameter of the chamber, this rod protruding outside the casing and being suitable for transmitting or receiving forces mechanical, this rod being provided with a clean slide to slide in said bore, head on which is applied, by a fluid, a pressure equal to that of the gas, the passage sections offered to the fluid acting on the head having characteristics d identical flow in one direction and in the other, and the ratio of the maximum volume displaced by the head, during displacements of the rod, to the volume of the chamber containing the gas being at most equal to 1/8, the spring constituting an autonomous device.

 The aforesaid fluid can be constituted by the neutral gas itself, in which case the head of the push rod is directly subjected to the action of the gas contained in the chamber and constitutes the aforesaid movable wall. The seal between the head of the rod and the surface of the bore can be obtained using a cup of self-lubricating material, in particular polytetrafluoroethylene, covering the head, and an elastic annular seal arranged in a groove of the head inside, in the radial direction, of said cup.

 Advantageously, the fluid acting on the head of the rod is a liquid, in particular oil, disposed between the head of the rod and the aforesaid movable wall limiting the chamber containing the gas, the liquid being subjected to no constriction or rolling regardless of the direction of flow.

 The movable wall, limiting the chamber containing the gas, can be constituted by a piston capable of sliding in the chamber and provided with a seal on its periphery.

 According to another possibility, this movable wall is constituted by a deformable membrane whose periphery is fixed to the envelope, which is advantageously formed by two assembled half-shells, the periphery of the membrane being clamped between these two half-shells.

 The head of the rod can extend towards the chamber containing the gas and include means for lubricating the rod, in order to reduce sliding friction.

 The rod can be self-lubricated and comprise a reservoir of liquid lubricant communicating, by radial passages, with an annular chamber located in the bore of the envelope and comprised between two seals, the lubricant of the reservoir being subjected to the action of a piston forming a movable cover mounted to slide in leaktight manner in the tank, this piston itself being subjected to the action of gas under pressure.

 According to another possibility, the rod has two axially spaced shoulders located in the bore of the envelope, and delimiting between them an annular chamber forming a reserve of lubricant, this chamber communicating by a radial passage provided in the wall of the envelope. with a valve allowing an injection of lubricant.

 The air spring advantageously comprises an inflation valve, preferably provided in the bottom opposite to the rod.

 To facilitate mounting and dismounting of the spring, fixing means are provided on the casing, for fixing on a support, these means being advantageously formed by a threaded sleeve surrounding the rod.

 Preferably, the ratio v / V of the volume displaced by the piston head to the volume of the chamber containing the gas is between 1/20 and 1/10.

 The invention consists, apart from the arrangements set out above, of a certain number of other arrangements which will be more explicitly discussed in connection with exemplary embodiments described with reference to the appended drawings, but which are by no means limiting.

 Figure 1 of these drawings is an axial section of a pneumatic spring according to the invention.

 Figure 2 is an axial section of an alternative embodiment of the air spring.

 Figure 3 is an axial section of another alternative embodiment.

 Figure 4 is an axial section of another alternative embodiment.

 Figure 5, finally, is a partial axial section of a last alternative embodiment.

 Referring to Figure 1, we can see a pneumatic spring 1 comprising a casing 2 of cylindrical shape of revolution, defining a closed chamber 3, of variable volume, limited by a movable wall 4. This chamber 3 contains a neutral gas 5 (air or nitrogen for example) under pressure, capable of exerting an elastic force on said movable wall 4.

 The spring 1 comprises a shouldered push rod 6 slidably mounted in a bore 7 of the casing whose diameter d is less than the diameter D of the chamber. The rod 6 projects outside the envelope, coaxially, and is capable of transmitting or receiving mechanical forces. The bore 7 is provided in a portion of smaller section 8, forming a sort of projecting appendage on one end 'of the portion of larger diameter of the envelope 2. The bore 7 extends internally, according to the axial direction, in chamber 3, being limited by a kind of inner jacket 9.

 The rod 6 is provided with a head 10 whose diameter is equal to the diameter d of the bore 7, apart from the sliding clearance. The shoulder 11, formed at the connection of the tette 10 and the portion of smaller diameter of the rod 6, is pushed into abutment against a corresponding shoulder 12 of the casing 2 located at the connection of the bore 7 and a passage 13 for the rod 6. When the shoulders 11 and 12 are in contact, the rod 6 projects over a length C equal to the stroke of the spring 1.

 The head is provided, on the side facing the chamber 3, with sealing means E arranged to ensure good gas / gas tightness (that is to say between the gas of chamber 3 and the air of the atmosphere) while introducing as little friction as possible.

 The sealing means E advantageously comprise a cup 14 of self-lubricating material, in particular of polytetrafluoroethylene, covering an extension 15, of smaller diameter, from the head 10 towards the chamber 3. The cup 14 is in axial support against the face end of this extension 15 and it can be considered that the movable wall 4 formed by the transverse surface of the cup 14, facing the chamber 3, belongs to the head 10. The cylindrical edge of the cup 14 surrounds the extension 15. This extension comprises a peripheral groove 16 in which is mounted an elastomer ring 17 capped by the cylindrical skirt of the cup 14.

 The distance 1 between the movable wall 4, when the rod 6 is extended at the end, and the lower end of the bore 7, is at least equal to the stroke C.

 The dimensions of the various parts of the spring 1 are determined so that the ratio of the maximum volume displaced by the tette 10 during the movements of the rod 6, to the volume of the chamber 3 is at most equal to 1/8. This ratio is preferably between 1/20 and 1/10.

 A spring is thus obtained, the flexibility of which is much greater than that of conventional helical springs. The effort delivered is practically constant.

 The passage sections offered to the fluid acting on the head 10 and the wall 4 have identical flow characteristics in one direction or the other. Indeed, the communication between the bore 7 and the chamber 3 takes place along the entire section of this bore 7 both when the gas pushes the rod 6 outwards as when the gas is expelled from the bore 7 towards chamber 3. It follows that the device behaves like a pure spring, - without any damping function.

The spring 1 has fixing means
F on a support S schematically represented. These fixing means are advantageously formed by a threaded sleeve 18 provided at the end of appendix 8 and suitable for being screwed into a tapped hole in the support.
S .. To facilitate screwing, the appendix 8 comprises, between the sleeve 18 and the part of larger diameter of the casing 2, a part with an external surface 19 prismatic with hexagon allowing the use of a key.

 The envelope 2 is closed, at its end remote from the rod 6, by a bottom or cap 20 fixed for example by screwing, and equipped on its internal cylindrical wall with an annular groove provided with an elastomeric sealing ring 21 . In its central part, the bottom 20 is provided with an inflation valve 22 comprising for example a ball 23, movable in a cavity 24 closed on the side of the chamber 3 by a screwed washer 24a, provided with passage holes for the gas . The ball 23 is applied by the pressure of the gas 5 against a frustoconical seat provided in the bottom 20.

An axial duct 25 connects the cavity 24 to a connector 26 allowing communication with the outside. A removable plug 27 crushing a seal 28 is provided to close this connector 26 in normal use of the spring 1.

 By removing the plug 27 and connecting a source of pressurized gas to the connector 26, it is possible to inflate the chamber 3 to a predetermined pressure. It is thus possible to recharge the spring 1 with gas after a certain time of use. The characteristics of the spring 1 can also be modified by modifying the pressure in the chamber 3.

 That said, the installation and operation of the air spring 1 immediately result from the foregoing explanations.

 The installation of the spring 1 is obtained by screwing the threaded sleeve 18 into the threaded hole of the support S, the external end of the rod 6 coming to bear against a stop (not shown) with which it is intended to cooperate. The head 10 thus deviates from the shoulder 12 which allows it to perform deflections in both directions in response to the stresses exerted on the rod 6 and to the reaction caused by the gas under pressure from the chamber 3.

 If a spring 1 in place must be replaced by another spring 1, for example with different characteristics, it suffices to unscrew the first spring from the support S by action on the hexagon formed by the area 19. As disassembly takes place of this spring, the rod 6 comes out of the casing 2 to come to its extreme position corresponding to the stop of the head 10 against the shoulder 12. There is therefore no fear of having, during this disassembly, screws vis-à-vis a possible projection of the rod 6, comparable to the relaxation of a helical spring kept compressed.

 Referring now to Figure 2 which illustrates an alternative embodiment of the air spring according to the invention, variant in which a liquid L is disposed between the head 110 of the rod 106 and the movable wall 104 limiting the chamber 103 containing the gas .

 The different elements of the spring 101 of FIG. 2 which are identical or playing roles analogous to elements already described with respect to FIG. 1 are designated by the same reference numerals or, where appropriate, by a numerical reference having the same unit digit. and tens but having the number 1 for the hundreds. The description of these elements will not be repeated or will be done only briefly.

 The movable wall 104 is formed by the transverse surface of a piston 28 slidably mounted in the large diameter portion of the casing 102. The piston 28 is provided on its cylindrical surface with an annular groove equipped with a ring sealing 29 made of elastomeric material for sealing between the liquid L, generally consisting of oil, located on the side of the rod 106, and the gas 5 located on the other side of the piston.

The volume of liquid L is sufficient to completely fill the bore 107 and part of the large diameter space of the casing 102 where the piston 28 is placed, while the head 110 is in abutment against the shoulder 112. t
The groove 116 of the head 110 is equipped with an elastomeric ring 117 bearing, in the external radial direction, against the surface of the bore 107.

 This ring 117 is intended to provide a seal between the liquid L and the atmosphere. In practice, the two gas / liquid seals of the embodiment of FIG. 2 are easier to produce than the only gas / gas seal of the embodiment of FIG. 1.

 FIG. 3 illustrates an alternative embodiment in which the piston of FIG. 2 is replaced by a deformable membrane 30, the periphery of which consists of a bead 31 is fixed to the casing 202.

 The elements of the air spring 201 of FIG. 3 which are identical or play roles analogous to elements already described in connection with FIG. 1 are designated by the same reference numerals, the tens digit of which is possibly preceded by a hundreds digit equal to 2 The description of these elements will not be repeated or will be made only succinctly.

 The envelope 202 is constituted by two half-shells 202a, 202b in the form of cylindrical or hemispherical pots turning their concavity towards one another.

 The lower half-shell 202b has a planar transverse surface 32 at its end adjacent to the shell 202a, the surface against which the periphery of the membrane 30 is applied.

The adjacent end of the half-shell 202a has a groove 33 suitable for receiving the bead 31.

Maintaining the two shells 202a, 202b tight against each other is carried out using a sleeve 34 whose lower end has an internal edge 35 suitable for being hooked under a shoulder 36 provided on the outer surface of the half-shell 202b. The sleeve 34 has, towards its other end, a thread 37 suitable for receiving a thread provided on the outer surface of the lower cylindrical end of the half-shell 202a. It should be noted that the external radial edge of this half-shell 202a, during tightening, after crushing the bead 31, comes to bear against the face 32. The groove 33 is limited, radially inwards, by a wall slightly set back from this face 32 so as not to shear the membrane 30 during tightening.

 In the position shown in FIG. 3, the membrane 30 has the shape of a dome turning its convexity towards the head 210.

 According to the two embodiments of Figures 2 and 3, the pneumatic spring operates without any rolling of the hydraulic fluid in a preferential direction, unlike an oscillation damper.

 The liquid transmits the driving force between the pressurized gas and the head of the rod, forming a push piston, in one direction or the other, and plays the role of lubricant of the rod and its head. The hydraulic fluid lubricates the sliding surfaces and minimizes the parasitic friction of the device.

Finally, this liquid serves as a power reserve, in the event of minimal leakage to the outside, thus extending the operational life of the spring.

 The isolation of the working gas from the buffer liquid L could be carried out, instead of the piston 28 in FIG. 2 and the membrane 30 in FIG. 3, by a thin-walled metal bellows (not shown ).

 All the isolation members (piston 28, elastic membrane 30, metal bellows) work in equilibrium between the gas and the liquid and do not pose any major production problems.

 In the embodiments of Figures 4 and 5, the hydraulic fluid does not participate in the transmission of the force between the gas and the pusher, but only assumes the role of lubricant.

 Referring to Figure 4, we can see an alternative embodiment according to which the head 310 of the rod extends towards the chamber 303 and comprises lubrication means G in order to reduce sliding friction.

 Identical elements or playing roles analogous to elements already described with respect to FIG. 1 are designated by the same numerical references, possibly preceded by a number of hundreds equal to 3. Their description will not be repeated or will be made only succinctly.

 The extension 38 of the head 310 projects into the chamber 303 while the head 310 abuts against the shoulder 312. The extension 38 comprises a cylindrical internal cavity 39, forming a reservoir, opening at the lower end into the chamber 303. A piston 40, forming a movable cover, is slidably mounted in a sealed manner in the reservoir 39, at the bottom of the latter. This piston 40 is stopped, on the side opposite to the rod 306, by a split ring 41 anchored in a groove in the surface of the reservoir 39.

 This reservoir is filled with liquid lubricant L situated on the side of the piston 40 opposite to the gas in the chamber 303. At its end close to the rod 306, the reservoir 39 has a portion of smaller diameter which communicates by radial passages 42 with a annular chamber 43, located in the bore 307, and included between the seal 317, adjacent to the shoulder 311 and another seal 44, advantageously formed by an elastomer ring, located on the side of the piston 40, relative to the passages 42. The assembly is such that the seals 317 and 44 remain permanently inside the bore 307, even when the rod 306 is pushed as far as possible into the casing 302.

 The installation and operation of the air spring of Figure 4 immediately result from the preceding explanations.

 The gas acts on the rod 306, directly at the level of the annular part surrounding the cavity 39 and, indirectly, by the liquid L, at a section corresponding to that of the cavity 39, to generate the force. The gas permanently compresses the liquid reserve L located in the cavity 39. This liquid L supplies the annular space located between the seals 317, 44. It follows that the friction surface is permanently lubricated, a very favorable both for sealing the system outwards and for reducing the parasitic friction force. The liquid reservoir 39 constitutes a power reserve in the event of minimal leakage to the outside.

 Referring to Figure 5, we can see an alternative embodiment also comprising lubrication means G of the sliding of the rod 406. The head 410 of this rod has two shoulders 410a, 410b axially spaced, located in the bore 407 and delimiting between them an annular chamber 45 forming a reserve of lubricant L. Each shoulder 410a, 410b has a peripheral groove in which is disposed a sealing ring made of elastomeric material 417, 46 respectively. A split metal ring 47 is anchored in a groove provided towards the end of the bore 407 remote from the rod 406 to retain the shoulder 410b inside this bore 407 in case the gas pressure drops in the chamber 403.

 The chamber 410 communicates by a radial passage 48, provided in the wall of the nose 408, with a valve 49 allowing an injection of lubricant L (oil or grease) from the outside towards the chamber 410. The valve 49 opposes the lubricant outlet.

 It is possible to maintain the operability of the spring by programmed lubricant injections. The passage 48 is located in the vicinity of the shoulder 410b, when the shoulder 410a is in abutment against the shoulder 412.

 The operation of the air spring of Figure 5 immediately results from the previous explanations.

 The lubrication of the rod 406 makes it possible to reduce the parasitic friction which, during the retraction of the rod 406, is added to the resistance opposed by the gas of the chamber 403 and, in the direction of the exit of the rod 406 , brake this rod, against the thrust of the gas.

 The valve 49 makes it possible to complete the filling of the chamber 410 with lubricant, after a certain time of use, to compensate for possible leaks.

 Whatever the embodiment adopted, an air spring according to the invention makes it possible to advantageously replace a helical spring, in particular when the strokes of the spring are relatively small.

 An advantageous application of such an air spring lies in its use as a return spring of a valve control device.

 The air springs according to the invention have many advantages.

 Their extremely small footprint and mass make it possible to obtain a very compact architecture for a device equipped with such springs.

 Their elastic characteristic is excellent and would practically correspond to that of a helical spring of infinite length.

 The penalty due to a variable force delivered by a spring is minimized to the extreme.

 In self-contained air springs, the free length and the length in place are substantially identical, which radically eliminates all the assembly disadvantages inherent in helical springs, when they have to be installed precompressed in a mechanical system.

 The adjustment range (inflation) can commonly reach the ratio 3 for the effort.

 The self-contained air springs can be removed and replaced in service. This operation, very easy and very fast, can be carried out at the end of the high or low stroke. The effort delivered can thus be radically modified, if the need arises.

 The independent air springs are mounted on the pneumatic actuator by a standardized thread.

 They can be easily stored and identified securely, unlike what happens with coil springs. Their calibration can be checked at any time by simple tools.

 It is also possible to inflate the autonomous pneumatic spring, between two force limit values, and thus to modify at any time the functional characteristics of devices in service. This operation is normally done by inflating spare springs in the workshop then by removing the springs mounted on a device and replacing them with the new springs.

 A simple portable inflation tool could make it possible to modify the calibration of the springs "in situ", on a device in service previously placed in neutral position.

 In general, the solutions of the various embodiments ensure minimal friction of the seals equipping the displaceable piston or pistons. There is thus an optimization of the device by minimizing the parasitic friction force responsible for the operating hysteresis which affects the compression / extension cycle of the spring.

Claims (11)

 1. A pneumatic spring comprising an envelope defining a closed chamber, of variable volume, delimited by a movable wall, this chamber containing a neutral gas under pressure capable of exerting an elastic force on said movable wall, characterized in that it comprises a push rod (6, ... 406), slidingly mounted in a bore (7, ... 407) of the chamber, this rod projecting outside the envelope and being suitable for transmitting or receiving mechanical forces, this rod being provided with a head (10, ... 410) capable of sliding in said bore, head on which is applied by a fluid a pressure equal to that of the gas, the passage sections offered to the fluid acting on the head of the rod having identical flow characteristics in one direction and in the other, and the ratio of the maximum volume displaced by the head, during movements of the rod, to the volume of the chamber (3 ,. ..403) containing the gas as at most equal to 1/8, the spring (1 ... 401) constituting an autonomous device.  2. Spring according to claim 1, characterized in that the fluid consists of the neutral gas (5) itself, the head (10) of the rod (6) being directly subjected to the action of the gas, l sealing between the head (10) and the surface of the bore (7) being obtained by means of a cup (14) made of self-lubricating material, and of an elastic annular seal (17), covering the head ( 6).  3. Spring according to claim 1, characterized in that the fluid acting on the head of the rod is a liquid (L), in particular oil, disposed between the head (110, 210) of the rod and the above movable wall (104, 204) limiting the chamber (103, 203) containing the gas, the liquid being subjected to no constriction whatever the direction of flow.  4. Spring according to claim 3, characterized in that the movable wall (104), limiting the chamber containing the gas, is constituted by a piston (28) capable of sliding in the chamber (103) and provided with a seal sealing around its periphery.  5. Spring according to claim 3, characterized in that the movable wall (204) is constituted by a deformable membrane (30) whose periphery is fixed on the envelope (202), which is formed by two half-shells ( 202a, 202b) assembled, the periphery of the membrane (30) being clamped between these two half-shells.  6. Spring according to claim 1, characterized in that the head of the rod (310, 410) has an extension towards the chamber containing the gas and lubrication means (G) of the rod, in order to reduce friction sliding.  7. Spring according to claim 6, characterized in that the rod is self-lubricated and comprises a reservoir (39) of liquid lubricant communicating, by radial passages (42), with an annular chamber (43) located in the envelope bore and between two seals (317, 44), the lubricant of the reservoir (39) being subjected to the action of a piston (40) forming a movable cover mounted to slide in leaktight manner in the reservoir , this piston itself being subjected to the action of gas under pressure.  8. Spring according to claim 6, characterized in that the rod has two shoulders (410a, 410b) spaced axially, located in the bore of the envelope, and delimiting between them an annular chamber (45) forming a reserve of lubricant , this chamber communicating by a radial passage (48) provided in the wall of the envelope with a valve (49) allowing an injection of lubricant.  9. Spring according to one of the preceding claims, characterized in that it comprises an inflation valve (22), provided in the bottom opposite to the rod.  10. Spring according to one of the preceding claims, characterized in that fixing means (F) are provided on the casing for fixing on a support (S), these means being in particular formed by a threaded sleeve ( 18, ... 418) surrounding the base of the stem.  11. Spring according to one of the preceding claims, characterized in that the ratio of the volume displaced by the piston head (10, ... 410) to the volume of the chamber (3, ... 403) containing the gas is between 1/20 and 1/10.