Gas spring comprising a safety device

2778956 The present invention relates to a compressible fluid device, of the type comprising a compression chamber intended to be filled with a compressible fluid and a piston movable in this chamber to compress the fluid therein.

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

The piston comprises a rod which slides in a bore of a guide part also called a cartridge and the rod is provided at its end situated in the compression chamber with a collar which at rest bears against the guide part.

In the event of accidental stroke of the piston beyond its nominal stroke, the collar is liable to strike the bottom of the compression chamber and break, in which case it no longer performs its function of retaining the rod and the latter is then thrown violently out of the spring by the pressure of the gas present in the compression chamber, risking material damage and / or bodily injury.

The invention aims to remedy this problem.

It achieves this by the fact that the compressible fluid device comprises a safety member arranged so as to be struck by the piston in the event of the latter's stroke greater by a predetermined value than its nominal stroke and by the fact that this member safety device is arranged to cause the bleeding of the compression chamber when it is struck by the piston.

Thanks to the invention, it is avoided that in the event of impact of the piston against the bottom of the compression chamber and damage to the piston, the rod is not forced out of the device.

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

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

It may be advantageous to arrange for the safety member to be integral with a plug screwed into the body of the spring and which can be used to test the resistance of the spring to pressure and to empty the compression chamber at the end of the process. use of the spring.

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

Preferably, the stroke of the piston from which the safety member is impacted and causes the bleeding of the compression chamber is at least 2mm greater than its nominal stroke.

The invention will be better understood on reading the detailed description which follows, of a non-limiting exemplary embodiment, and on examining the appended drawing in which:

- Figure 1 is a schematic sectional view of a gas spring according to the invention, the piston being shown at the nominal end of travel and,

- Figure 2 is a view similar to Figure 1, the piston being shown in abutment in the bottom of the compression chamber.

The gas spring 1 shown in the figures comprises a metal casing 2 in the form of a hollow cylinder formed at its lower end and open at its upper end, defining a compression chamber 3 inside which a monobloc piston 4 is movable. the rod, of longitudinal axis X, slides in a bore made in a guide part 5 introduced into the opening of the housing 2.

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

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

Guide segments 10 and 11 and successive sealing elements 12 and 13 are in a manner known per se housed in the guide piece and apply to the piston rod.

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

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

Two O-rings 17 and 18 are interposed in a sealed manner between the guide part 5 and the housing 2.

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

A radial bore 19 opening at one end into the lubrication chamber 15 and at the other end at the periphery of the guide piece between the seals 17 and 18 allows, at the end of the use of the spring, and when the chamber compression is emptied, to perform an automatic purge of the lubrication chamber 15 thanks to the fact that the O-ring 17 ceases to be sealed when it engages in the aforementioned axial recess 20.

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

In the example described, the safety member 21 comprises a central pin 25 forming a 3mm projection in the bottom of the compression chamber and a thinned annular portion 22 connecting this pin 25 to a hollow plug 23 screwed into a bore 24 of the housing 2.

Unscrewing the plug 23 allows the compression chamber to be purged.

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

In the event of sufficient piston stroke 4 for the latter to come to rest against the bottom of the compression chamber 3, as shown in FIG. 2, the collar 6 strikes at a point relatively close to the X axis the pin 25 and pushes it back inside the plug 23, after rupture of the thinned annular portion 22.

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

In the event of rupture of the collar 6 under the effect of metal fatigue, this prevents sufficient pressure to prevail in the compression chamber 3 to expel the rod 4 from the spring.

In the example considered, it is assumed that the spring rests on a frame S so that the pin 25 is thrown against it.

When this is not the case, it is possible to fix by bolting, for example on the lower end of the casing 2, a plate against which the pin 25 is projected.

This plate thus performs the function of a protective screen against the expulsion of the pin 25 through the plug 23.

Of course, the invention is not limited to the exemplary embodiment which has just been described.

It is in particular possible to modify the shape and / or the nature of the safety member and of the other elements of the spring without departing from the scope of the present invention.