Gas spring comprising a safety device

The present invention relates to a compressible fluid device, type having a compression chamber intended to be filled by a compressible fluid and a piston in the chamber to compress the fluid therein.

Such a device is known from EP-A-0427468.

The fluid which is compressed by the piston exerts on the latter a return force and when the fluid used is a gas, such a device is also called a gas spring.

The piston includes a rod which slides in a bore of a guide piece also called cartridge and the rod is provided at its end situated in the chamber Compression of a collar which at rest abuts against the guide piece.

Accidental stroke of the piston beyond its nominal running, collar is likely to hit the bottom of the pressure chamber and break, in which case it no longer performs its function of retaining the stem and the latter is then violently thrown out of the spring by the pressure of gas in the chamber compression, likely to cause property damage and / or injury.

The invention aims to remedy this problem.

This is achieved in that the compressible fluid device comprises a safety member arranged to be struck by the piston in the event of travel of the last greater by a predetermined value than its nominal stroke and in that this safety member is arranged to cause purging of the compression chamber when struck by the piston.

Thanks to the invention it is avoided that in case of shock of the piston against the bottom of the compression chamber and damage to the piston rod is expelled violently out of the device.

The safety member according to the invention is different from a limit valve for hydraulic cylinder, as described in the Engineering Techniques, 1976 edition, Chapter "Hydraulic cylinders" and more particularly in Figure 49.

The safety device according to the invention does not in fact intended to limit travel but to avoid the risk of accidental starting of the piston rod, as explained above.

Additionally, after actuation of the safety member according to the invention, the spring is off, which is not the case in a limit device for cylinders.

In a particular embodiment of the invention, the safety member has a portion whose breaking strength is predetermined.

Still in a particular embodiment, the safety member protrudes in the bottom of the compression chamber, preferably of at least 3mm.

It may be advantageous to ensure that the safety member is integral with a plug screwed into the body of the spring and operable to test the resistance of the spring to the pressure and empty the compression chamber at the end of the use of the spring.

When the piston comprises a rod whose lower end is provided with a collar, the safety member is advantageously arranged to be struck by the collar at a location closer to the axis of the rod than its periphery.

Preferably, the piston stroke from which the security organ is hit and causes the purge the compression chamber is greater than 2mm least at the rated race.

The invention will be better understood on reading the detailed description which monitor, one non-limiting embodiment, and on examining the attached drawing in which:<ul><li>Figure 1 is a schematic sectional view of a gas spring according to the invention, the piston being shown at the end of nominal stroke,</li><li>Figure 2 is a view similar to Figure 1, the piston being shown in abutment in the bottom of the compression chamber, and</li><li>3 illustrates an alternative embodiment of the safety member.</li></ul>

The gas spring 1 shown in the figures comprises a metal casing 2 in hollow cylindrical shape formed at its lower end and open at its end upper, defining a compression chamber 3 inside which there can move a one-piece piston rod 4 which, of longitudinal axis X, slides in a bore in a guide part 5 inserted in the opening of the casing 2.

The piston rod 4 has at its lower end a collar 6 which, in rest, abuts against the guide part 5 for retaining the piston 4 in the gas spring.

The guide member 5 is retained in the housing 2 by an annular metal ring 8, which bears on the one hand in an annular recess 7 of the guide part 5 and on the other hand in an annular groove 9 made in the vicinity of the upper end of housing 2.

guide segments 10 and 11 and successive sealing elements 12 and 13 are known manner accommodated in the guide piece and are applied to the rod piston.

The sealing elements 12 and 13 can be constituted for example by composite seals and between them define an annular chamber 15 for lubrication, filled with a lubricant.

A wiper seal 16 is accommodated in the upper part of the guide part 5.

Two O-rings 17 and 18 are interposed sealingly between the workpiece guide 5 and the casing 2.

An axial recess 20, whose depth is greater than that of the groove housing the seal 17 adjacent the compression chamber 3, allows the latter to deform when the pressure in the assembly clearance between the guide part 5 and the casing 2 between the joints 17 and 18 is greater than pressure prevailing in the chamber compression.

A radial bore 19 opening at one end into the lubrication chamber 15 and at the other end to the periphery of the guide member between the joints 17 and 18 allows, at the end of the use of the spring, and when the compression chamber is evacuated, to achieve automatic purge the lubrication chamber 15 due to the fact that the O-ring 17 ceases to be sealed when it engages in the axial recess 20 supra.

According to the invention, a safety member 21 is arranged to be struck by the piston 4 when the latter stroke exceeds a value predetermined nominal race.

In the example described, the safety member 21 has a central peg 25 forming 3mm projection in the bottom of the compression chamber and an annular thinned portion 22 connecting the peg 25 in a hollow screw cap 23 in a bore 24 of the casing 2.

The unscrewing of the cap 23 to purge the compression chamber.

The mechanical strength of the annular thin portion 22 is selected such so that the latter breaks when the pin 25 is struck by the piston 4.

In case of stroke of piston 4 sufficient so that the latter comes to bear in the bottom of the compression chamber 3, as shown in Figure 2, the flange 6 strikes a point relatively close to the axis X the pin 25 and pushes the inside of the plug 23 after breaking the annular thinned portion 22.

The pin 25 is then expelled through the hollow plug 23 and the chamber 3 compression can empty.

This avoids in case of breakage of the flange 6 under the effect of fatigue metal reign sufficient pressure in the compression chamber to expel 3 the rod 4 out of the spring.

In the example, it was assumed that the spring was based on a S frame so that the pin 25 is projected against it.

Where this is not the case, can be fixed by bolting for example the lower end of the casing 2 a plate against which the pin 25 is projected.

This plate ensures protection screen function vis-a-vis the expulsion the pin 25 through the plug 23.

Of course, the invention is not limited to the example embodiment just described.

the form may especially modify and / or the nature of the security organ and other spring elements within the scope of the present invention.

Is shown in Figure 3 an alternative embodiment of the safety member.

The safety member 21 'shown in Figure 3 differs from that shown in Figure 1 in that the central peg 25 'is frusto-conical instead of being cylindrical revolution.

Thanks to the slight taper of the pin 25 'inwardly of the spring, the expulsion of pin through the plug 23 is facilitated.

In a variant not shown, the safety member is constituted by a solid plug fastened in a bore of the spring body, the plug being e.g. threaded and screwed into said bore and having an inner end arranged to be struck by the piston when the travel of the latter exceeds a predetermined value its nominal stroke. The cap is arranged to release the drill when it is hit by the piston, by destruction of the threads of the plug and the bore of the housing, these threads having a predetermined breaking effort.