WO2014037661A1

WO2014037661A1 - Hydraulic stop for the limit braking of a piston and damper provided with such a stop

Info

Publication number: WO2014037661A1
Application number: PCT/FR2013/052022
Authority: WO
Inventors: Benjamin Talon; Yan CHABRERIE; Frédéric IZEMBART
Original assignee: Soben
Priority date: 2012-09-05
Filing date: 2013-09-03
Publication date: 2014-03-13
Also published as: FR2995048B1; FR2995048A1

Abstract

The invention concerns a hydraulic stop (10) for the limit braking of a main piston (5) comprising: · a cylindrical stop body (11) closed at one end, · a stop piston (12) that is axially movable in the stop body, · a return spring (23) for returning the stop piston to the extended position of same and · means for limiting the travel of the stop piston in the extended position of same, the stop piston (12) being designed to enter into contact and to be driven in the direction of the compressed position of same by said main piston (5) when said main piston reaches a predefined position in the vicinity of the limit of same, the stop piston comprising an axial orifice (16) designed to be plugged by a plug (9) integral with the main piston when said main piston comes into contact with the stop piston and to compress a fluid occupying the compression volume. The invention also concerns a damper or a hydraulic ram provided with such a hydraulic stop.

Description

HYDRAULIC STOP FOR BRAKING AT THE END OF THE RACE OF A PISTON AND SHOCK ABSORBER WITH SUCH A ROCKET

The invention relates to a hydraulic stop for braking at the end of stroke, in compression or relaxation, the piston of a piston machine such as a damper or a cylinder. The invention also extends to a damper (or cylinder) equipped with such a stop.

In the present text, the term "hydraulic" is used in its broadest sense, that is, operating with an incompressible fluid, whether oil or any other liquid. "Incompressible fluid" is understood to mean incompressible or quasi-incompressible fluids, that is to say fluids capable of containing an emulsion of a compressible fluid (gas) with an incompressible fluid and therefore having a small variation in volume with the pressure. The hydraulic stop according to the invention is intended to equip a piston machine, that is to say a machine having at least one cylindrical tube inside and in the axis of which moves a piston. The description of the hydraulic stop according to the invention is made in connection with its use in a damper of a suspension device of a motor vehicle, and more particularly a two-tube damper, without this being limiting as to its use which can extend to single tube dampers, tri tube or hydraulic cylinders. Similarly, terms such as "upper" and "lower" and their derivatives are used with respect to the usual position of a damper mounted on a motor vehicle, that is to say substantially vertical, the rod of the damper being placed above the body thereof, without this being limiting to the use of the damper (or cylinder) in other positions, for example horizontal or downward rod.

In known manner, a twin-tube damper comprises a tubular body consisting of two concentric tubes, an inner tube inside which can move a piston extended by a rod, and an outer tube. The tubular body is closed on both sides by yokes, the upper yoke being traversed by the rod. The inner tube is filled with an incompressible fluid, general oil, whose rolling by the piston can dissipate the kinetic energy. The volume of oil occupied by the piston rod is absorbed in / restored by a compensation chamber formed between the inner tube and the outer tube, passing through passages in the lower yoke.

One of the problems frequently encountered with hydraulic dampers is the problem of tailgating when the piston reaches the end of the stroke in the body of the damper, particularly at the end of compression stroke. To overcome this problem, it is known to dispose in the vicinity of the ends of the body of the damper hydraulic stops to brake the piston when it reaches the end of the race to avoid shock and, where appropriate, the Damage of the cylinder heads in the event of "tailgating" of the piston.

Document FR 1 522 498 discloses for example a damper comprising an auxiliary piston connected to the rod passing through the main piston and of a diameter smaller than that of the main piston, penetrating into an auxiliary cylinder placed at the appropriate end of the main cylinder. at the end of the shock stroke. The volume of oil enclosed between the auxiliary piston and its cylinder then escapes through a leakage passage whose cross section gradually decreases as the auxiliary piston enters further in its wake. Such a device, however, suffers from the difficulty of aligning the cylinder and the auxiliary piston when they are disengaged from one another and therefore requires expensive and difficult machining.

Document FR 1 361 239 also discloses a pneumatic cylinder comprising limit stops, fixed at the ends of the body of the jack. These abutments comprise a stop body in which slides a stop piston in the side wall of which is arranged a main air passage. The stop piston is pushed into the extended position by a spring and held in this position by locking collars formed in the body and the stop piston. When the main piston, in the vicinity of its end of travel, docks the stop piston, it sinks into the stop body which then closes the main air passage. The braking of the main piston is then effected by the compression of the air under the main piston. This type of stop is however unsuitable in the case where the fluid used is incompressible and where the main piston has fluid passages as is the case in a damper.

The present invention therefore aims a hydraulic stop for the braking end of stroke of a piston that does not have the disadvantages of the prior art. In particular, the invention aims to provide such a stop that is simple to manufacture and does not exhibit complex machining.

The invention also aims to provide such a stop whose assembly and mounting in the damper is simplified.

The invention also aims to provide such a stop which is adaptable to a two-tube damper, a single tube damper, and a hydraulic cylinder without requiring significant changes.

The invention also aims to provide such a stop which makes it possible to provide a braking function of the piston to an existing shock absorber or cylinder which is not provided with original without causing major modifications.

The invention also aims at providing such a stop which makes it possible to provide a complementary static support function making it possible, when fitted to a damper, to dispense with the elastomeric stops used for this purpose.

The invention also aims to provide such a stop which does not require modification of the damper and allows several possible braking laws.

The invention also aims to provide such a stop that allows the realization of an inexpensive damper, using materials and economic processes.

The invention also aims to provide such a stop whose operation does not cause audible noise.

To do this, the invention relates to a hydraulic stop for the end of stroke braking of a main piston, said stop comprising:

A body, said stop body, cylindrical closed at one end, • a piston, called stop piston,

moving axially in the abutment body between a first position, said compressed position and a second position, said extended position, defining between these positions a compression volume, adapted to come into contact and be driven towards its compressed position by the main piston when it reaches a predetermined position in the vicinity of its end position,

- Having an axial orifice, adapted to be plugged by a plug secured to the main piston when it comes into contact with the stop piston and compress a fluid occupying the compression volume,

• elastic return means of the stop piston in its extended position and

• stroke limiting means adapted to stop the stop piston in its extended position,

characterized in that the stop piston has an outer diameter ring fitted to the inner diameter of the stop body and having a radial flange extending inwardly of the ring and a substantially cylindrical ferrule having the axial orifice to the one of its ends and whose other end is adapted to be fixed by snapping on the radial flange of the ring.

Thanks to the stop piston remaining permanently in the abutment body, there is no longer any risk of the abutment piston engaging in the abutment body due to offsets under the effect of lateral bending forces. Chamfers or conical guides that increase the inactive length of the stop are no longer needed. As the stop piston is approached by the main piston by simple plane-to-plane contact, it is no longer necessary to perform machining operations requiring precise tolerances, in particular for the concentricity and coaxiality of the piston. rod / main piston assembly with the stop. Thanks to the elastic return means, the stop piston is naturally in the extended position until the main piston comes into contact with it and closes the axial orifice. Therefore, the volume of fluid contained within the stop is compressed and can escape only by leaks around the stop piston, causing braking of the main piston. When the movement of the main piston changes direction, the axial orifice is disengaged, the fluid inside the damper tube can then enter the compression volume without significant loss of load and the stop piston returns to its position extended without the need for special means to fill the compression volume. The hydraulic stop instantly regains its braking capacity of the main piston. In addition, by making the piston by a ring, which acts as a piston itself in the stop body, and by extending it by a cylindrical nozzle extending towards the main piston, the stop piston is protruding relative to the abutment body and the height of the cylindrical end piece makes it possible to adjust the stroke depth of the hydraulic abutment. In addition, the tip is advantageously made of synthetic material, preferably injected or molded, which allows an economic realization of the stop piston, with a detent device by crown or resilient tongues coming to recover on the radial rim of the Ring. The use of a tip made of synthetic material, where appropriate comprising at least one elastomer zone, also makes it possible to improve the contact between the main piston (or its nut) and the tip of the stop piston, avoiding shocks metal on metal and improving the seal around the axial orifice in the tip.

Advantageously and according to the invention, the plug is a nut for fixing said main piston. The tightness to be provided around the axial orifice being a dynamic type of sealing, it is not necessary to provide a plug ensuring complete sealing of this orifice. Therefore, it is sufficient to provide a nut for fixing the main piston on the piston rod whose diameter is greater than that of the axial orifice so that the cap function is completely provided without additional parts.

Advantageously and according to the invention, the ring is made of reduced friction coefficient material and preferably brass. The ring can also be made of sintered steel so that its coefficient of expansion is compatible with that of the stop body.

Advantageously and according to the invention, the endpiece comprises a central recess adapted to receive and guide a spiral spring forming the elastic return means of the stop piston in its extended position. In this way, the elastic return means are centered relative to the tip and therefore to the stop piston and guided relative to the stop body.

Advantageously and according to the invention, the tip has a circular groove adapted to receive an elastomeric O-ring opposite the plug. Thanks to this elastomer seal, the impact between the piston nut and the end piece is even better cushioned, allowing for quiet operation and improved sealing.

Advantageously and according to the invention, the spiral spring has a stiffness adapted to generate a complementary static force when the stop piston tends to its compressed position. By choosing a sufficiently high stiffness for the elastic return spring of the stop piston, it is possible to improve the roll maintenance of a vehicle using a damper provided with the abutment according to the invention. More particularly, a progressive stiffness spring, with a very low preload and a low attack stiffness allows a docking without perceptible shock when the piston nut comes into contact with the tip, then increasing stiffness towards a high value allows to develop a static support force in addition to the dynamic force generated by the hydraulic portion of the abutment, to dispense at least partially elastomeric stops generally used in conventional dampers.

Advantageously and according to the invention, the abutment body has on its inner side wall at least one longitudinal groove opening at the open end of the abutment body, adapted to allow a predetermined leakage rate of the fluid occupying the compression volume. By thus forming a groove parallel to the axis, of predetermined section, it is possible to provide a predetermined leakage rate of the fluid occupying the volume of compression when the stop piston sinks under the force exerted by the main piston. The leakage rate makes it possible to determine the driving speed of the stop piston for a constant force applied to it or the braking force exerted on the main piston at constant driving speed.

Advantageously and according to the invention, the stop body comprises a plurality of stepped length grooves, angularly distributed on the inner side wall of the stop body so as to allow a decreasing leakage flow when the stop piston moves from the position extended to the compressed position. Thus, by providing a plurality of grooves opening on to the open end of the stop body and extending over distinct and increasing lengths, the leakage rate between the stop piston and the stop body depends on the position of the piston. stopper, in this case the number and the section of the grooves extending on either side of the ring of the stop piston and can be adjusted by varying the number and length of the grooves. Advantageously, the grooves being formed in the stop body, it is sufficient to change the stop body to change the piston braking law.

Advantageously and according to a variant of the invention, the abutment body comprises at least one groove of variable cross section as a function of the desired leakage flow rate, decreasing from the open end of the abutment body towards the bottom thereof. Many embodiments can be envisaged, for example a groove of semi-conical shape or in the form of stepped half-cylinders, etc.

Advantageously and according to the invention, each groove is made by stamping the side wall of the stop body. This allows an economic realization of the stop body by avoiding complex machining. In addition, the embossing of the grooves is repetitive and makes it possible to obtain high precision economically.

Advantageously and according to the invention, in the case where the outside of the side wall of the abutment body is in contact with the fluid occupying the space under the main piston, the grooves can be replaced by openings in the side wall of the stop body, having a decreasing section approximating the closed end of the stop body. In this way, a variable leakage flow is established through these holes which are masked by the ring of the stop piston as it sinks into the stop body.

Advantageously and according to the invention, the means for limiting the stroke of the stop piston are substantially radial pins, formed by stamping on an edge of the abutment body opposite the closed end thereof. By thus forming two to four (or more) pins angularly distributed on the edges of the open end of the stop body, extending sufficiently inwardly of the cylinder, the axial output of the ring of the stop piston is blocked by simple way. Advantageously, the minimum diameter determined by the end of the lugs is greater than the diameter of the tip of the stop piston, to insert it into the stop body and fix it on the ring after making the lugs.

The invention also extends to a hydraulic damper, comprising at least one tube closed at both ends, at least partially filled with an incompressible fluid, in which a piston provided with a rod passing through one of the ends, characterized in that it comprises at least one hydraulic stop according to the invention comprising at least one of the characteristics stated above.

Advantageously and according to the invention, in one embodiment of a damper comprising a hydraulic stop adapted to operate in compression in a twin-tube damper, the stop body has ducts between the stop body and the inner tube of the damper adapted to allow a passage of the fluid of the damper of the inner tube to a compensation chamber. The abutment body is thus formed so as to provide one or more fluid conduits around the abutment body to allow the fluid of the damper to join the lower yoke and thus pass to the compensation chamber of the damper. Advantageously and according to the invention, the abutment body has an outside diameter substantially smaller than the inside diameter of the inner tube and has reliefs protruding outwardly from the abutment body, regularly distributed over the periphery thereof in the vicinity of the abutment body. edge opposite the closed end, said reliefs forming angular sectors of a cylinder of diameter substantially equal to the inner diameter of the inner tube of the damper. These protruding reliefs can be arranged by stamping, at the same time as the realization of the grooves. In addition, the outer diameter they determine depends on the stamping tool and can be obtained with precise tolerances. Between these protruding reliefs, the space existing between the outer surface of the stop body and the inner tube of the damper makes it possible to arrange fluid ducts from the damper to the lower yoke.

Advantageously and according to the invention, the abutment body is attached to the inner tube of the damper by resistance welds made in said reliefs. The abutment body, centered by protrusions protruding into the inner tube of the damper can thus be economically fixed thereto.

Advantageously and according to the invention, in one embodiment of a damper comprising a hydraulic stop adapted to operate in expansion in a twin-tube damper, the stop body comprises sealing means for fixing on the inner tube of the damper in the vicinity the upper yoke and a passage in its closed end for the passage of the rod of the damper. In this embodiment of the hydraulic stop according to the invention, it is not necessary to provide ducts around the stop body. This can be fixed directly between the upper part of the inner tube of the damper and the upper yoke.

The invention also relates to a piston and end-stop machine of said piston characterized in that it is equipped with a hydraulic stop according to the invention having all or part of the features set out above. The invention also relates to a hydraulic stop, a piston machine and a shock absorber according to the invention characterized in combination by all or some of the characteristics mentioned above or below.

The invention also relates to a vehicle suspension device comprising at least one damper according to the invention.

Other objects, features and advantages of the invention will become apparent from the following description and the accompanying drawings showing an embodiment given solely by way of example, in which:

- Figure 1 shows a partial longitudinal section of a twin-tube damper equipped with a hydraulic stop according to the invention;

- Figure 2 shows a longitudinal section of a hydraulic stop according to the invention;

FIG. 3 represents a perspective view of the abutment body of a hydraulic abutment according to the invention; and

- Figure 4 is a graph illustrating the braking force applied to a damper piston by a hydraulic stop according to the invention.

FIG. 1 represents a longitudinal section passing through the axis of the lower part of a twin-tube damper 1 equipped with a hydraulic stop according to the invention. The damper 1 comprises an inner tube 2 inside which slides a main piston 5 fixed to the lower end of a rod 6. The inner tube 2 is completely filled with a fluid, in this case the oil, above and below the main piston 5. An outer tube 3 is mounted coaxially with the inner tube 2 and the space between the two tubes forms a compensation volume 4 to compensate the volume of the rod 6 when the it sinks into the inner tube 2. The inner tube 2 and the outer tube 3 are held and closed at their lower end by a lower yoke 7 and at their upper end by an upper yoke (not shown) allowing the passage of the stem 6. The hydraulic stop is placed in the immediate vicinity of the bottom yoke 7, or even in contact therewith, and extends towards the main piston 5. In the example shown in FIG. 1, the main piston 5 is in contact the stop 10, for example at a time when the main piston descends into the inner tube 2, just before the braking of the main piston by the hydraulic stop.

The hydraulic stop has a stop body 11 in which a stop piston 12 slides. The abutment body 11 is substantially cylindrical, preferably made of steel, and closed at its lower end by a crimped base 19 (FIG. 2).

The stop piston 12 comprises a cylindrical ring 13 of outer diameter fitted to the inner diameter of the abutment body 11 so as to be axially slidable therein by minimizing peripheral leakage. For example, the preferential adjustment is of the H8 / f7 type, thus providing a clearance by means of the order of 5/100 of a millimeter between the stop body and the ring. The cylindrical ring 13 has, at its upper edge, a rim 14 extending towards the inside of the ring. The ring 13 is preferably made of brass or sintered steel.

The stop piston 12 also comprises a cylindrical nozzle 15 of synthetic material, for example made of PTFE or any other polymer compatible with the fluid used and its operating temperature. The tip 15 may also be made of elastomer or be bi-material injection molded, having one end towards the main piston 5 of elastomer and an opposite end of a non-malleable polymer such as a polyamide for example. Alternatively, the tip 15 may also comprise on its outer face facing the nut of the main piston 5 a circular groove 27 adapted to receive an O-ring 28 of elastomer whose average diameter is greater than that of the axial orifice 16 and less than the outside diameter of the nut 9 of the main piston 5.

The cylindrical end 15 comprises, at its end closest to the bottom 19 of the abutment body 11, latching means, in this case a deformable ring or tongues 18 distributed around the periphery of the nozzle, having a hook profile adapted to cooperate with the flange 14 of the ring 13, so as to insert the lower end of the nozzle 15 into the ring 13 until the resilience of the ring or tongues 18 locks the tip on the ring. At its opposite end to the latching means, the end piece 15 is closed by a bottom pierced with an axial orifice 16. The end piece 15 also comprises a cylindrical recess 17 adapted to receive and guide a spring 23 extending between the bottom 19 of the abutment body and the bottom of the end piece 15 so as to return the abutment piston 12 in extended position relative to the abutment body 11.

Figures 2 and 3 show in more detail the shape of the abutment body 11. As seen above, the abutment body 11 has a substantially cylindrical shape, the upper end is open and the lower end closed by a bottom 19 The bottom 19 can be fitted and crimped into the cylindrical wall of the abutment body 11 or be welded to it or can be obtained integrally therewith by a deep drawing process. The inner peripheral wall of the abutment body 11 is hollowed out with at least one longitudinal groove 20 extending from the open end towards the bottom of the abutment body so as to provide a calibrated leak between the abutment body and the ring 13. The abutment body 11 preferably comprises three grooves 20 of stepped lengths distributed angularly around the perimeter of the inner peripheral wall of the abutment body. Alternatively, the abutment body 11 may be provided with one or more grooves of variable cross-section decreasing towards the bottom of the abutment body, the groove section being determined as a function of the desired leak rate for each position of the abutment piston. .

The grooves 20 are preferably made by plastic deformation of the side wall of the abutment body 11, for example by stamping.

In an exemplary embodiment of a stop body 11 particularly adapted to the realization of a hydraulic abutment in compression of a two-tube damper, as shown in Figures 1 to 3 of the drawing, the diameter outside the abutment body 11 is substantially smaller than the inner diameter of the inner tube 2 of the damper 1. The abutment body 11 has in the vicinity of its open upper end reliefs 22 projecting outwardly of the abutment body whose depth is adapted to compensate for the difference in diameter between the abutment body and the inner tube 2. Preferably, these reliefs 22 extend longitudinally over a length less than the height of the ring 13 of the abutment piston 12 in order not to not generate additional leakage between the ring and the inner peripheral wall of the stop body. Similarly, these reliefs 22 extend over angular sectors regularly distributed on the peripheral wall of the abutment body, for example on four angular sectors of 20 ° each, making it possible to arrange between the reliefs 22 conduits 26 ensuring the passage of the fluid of the damper around the abutment body 11, between the underside of the main piston 5 and the lower yoke 7.

In the case where the outside of the side wall of the abutment body is in contact with the fluid occupying the space under the main piston, the grooves may be replaced by orifices provided in the lateral wall of the abutment body, having a decreasing section by approaching the closed end of the stop body. In this way, a variable leakage flow is established through these holes which are masked by the ring of the stop piston as it sinks into the stop body. These holes may also be made by punching in the peripheral wall of the stop body.

The abutment body 11 also has, on its upper edge, lugs 21 folded towards the inside of the abutment body intended to limit displacement and prevent the exit of the ring 13 from the abutment body. These lugs 21 are also made by plastic deformation of the open edge of the abutment body 11.

The mounting of the hydraulic stop in the damper 1 is as follows:

The abutment body 11 is made by stamping with the exception of the lugs 21. The cylindrical ring 13 is inserted into the abutment body 11, flange 14 up. The lugs 21 are then folded so as to prevent the ring 13 from coming out of the stop body.

The abutment body 11 provided with the ring 13 is then inserted into the inner tube 2, for example by sliding it from the end corresponding to the lower yoke 7 to a position adapted to allow the subsequent installation of the cylinder head . The abutment body 11 is then fixed on the inner tube 2 by resistance welds (spot welds) made inside the reliefs 22 (FIG. 1). Alternatively, the abutment body 11 could be fixed on the lower yoke 7 and inserted and fixed at the same time as the latter.

The end piece 15, provided with the spring 23, is then inserted by the open end of the abutment body 11 is depressed until the tabs 18 snap onto the flange 14 of the ring 13, thereby securing the mouthpiece and the ring. When releasing the pressure on the tip 15, the stop piston 12 rises under the effect of the spring 23 until the ring 13 is stopped by the lugs 21 or until the spring 23 is completely closed. deployed. Of course, the outer diameter of the tip 15 must be such that it can pass between the lugs 21.

The hydraulic stop is then installed in the damper 1 as a compression stop thereof.

The hydraulic stop works in the following manner.

The entire inner tube 2 is filled with an incompressible fluid, in this case oil, including the inner part of the abutment 10 in the extended position forming the compression volume 24. When the main piston 5 descends into the inner tube 2, the oil below the main piston is partially discharged into the upper chamber above the main piston via the main piston of the main piston. The volume of oil corresponding to the volume of the rod 6 circulates around the hydraulic stop, via the ducts 26 formed between the reliefs 22 to reach the lower yoke 7 and be discharged to the compensation volume 4 via passages 8 formed in the lower cylinder 7. When the nut 9 of the main piston 5 comes into contact with the nozzle 15, it closes the axial orifice 16 and closes the compression volume 24. Under the effect of the movement of the main piston downwards, the stop piston 12 sinks into the stop body, the compression volume 24 decreases and the oil enclosed in the compression volume 24 escapes through the grooves 20 around the ring 13. The leakage rate of the oil through grooves 20 varies according to the depression of the stop piston 12, when the ring 13 masks the end of one of the grooves 20. The resistant force exerted by the stop piston 12 against the displacement of the main piston 5 thus increases in proportion to the reduction of the leakage flow through grooves 20 and thus provides progressive braking to the shaft assembly 6 and main piston 5 as it progresses towards the end of its stroke in the inner tube 2 of the shock absorber.

When the movement of the rod and the piston is reversed, the nut 9 of the main piston no longer exerts force on the tip 15. Under the effect of the spring 23, the stop piston 12 tends to resume its extended position relative to the abutment body 11. For this, the volume of oil necessary to fill the increasing compression volume 24 penetrates through the axial orifice 16 thus allowing the stop piston 12 to resume its position almost instantaneously and to be immediately available for a new compression stroke.

Advantageously, the spring 23 may be a spring of variable stiffness or a combination of two springs of different stiffness, then to complete the dynamic braking operated by the hydraulic circuit of the abutment 10 by adding a static force when the stop piston 12 sinks towards its compression position. The spring 23 thus has, in the first part of its compression stroke, a few millimeters, a first stiffness of a relatively low value of the order of 20 × 10 ³ N / m with a preload (spring tension when the piston of stop is in its extended position) minimum to allow an almost imperceptible docking and a maximum of progressiveness in the first part of the race. The stiffness of the spring 23 then increases very rapidly to reach values of the order of 150 × 10 ³ N / m at the end of a 25 mm stroke so as to develop a static force of the order of 1000 to 2000 N. Of course, the spring 23 can be made in the form of two coaxial springs, the first of low stiffness and greater length than the second, of greater stiffness. Thanks to the static force developed by the stop 10 when the main piston 5 is at the end of the compression stroke, it is possible to improve the rolling resistance of a vehicle equipped with shock absorbers provided with a stop according to the invention. do without elastomeric stops used especially for this purpose.

FIG. 4 represents a graph of the resistant force F (ordinate) exerted by the hydraulic stop on the main piston as a function of the stroke d of the stop piston, for speeds of movement of the main piston of the order of 500 mm / s and 2000 mm / s. The origin of the stroke d is chosen when the stop piston is in its extended position, at the time of contact of the main piston on the stop piston. As soon as the nut of the main piston closes the axial orifice 16 of the stop piston, the resistant force F increases to a first level corresponding to the leakage flow conjugate of all the grooves 20. After a stroke L1 corresponding to the length of the shortest groove 20, the ring 13 closes this groove and the leakage rate is decreased, causing an increase in the resisting force to a second bearing. When the ring 13 closes a second groove of length L2, the resistant force increases to a third bearing. The same phenomenon is reproduced throughout the stroke of the stop piston 12, the braking force developed by the hydraulic stop 10 increasing each time the ring 13 closes an additional groove. The resistant force F depending on the sum of the sections of the grooves allowing the leakage rate and the flow rate itself of the piston insertion speed, for each bearing, the resistant force is increasing as a function of the speed of the piston. depression of the piston.

When the compression stroke of the main piston stops and the movement of the main piston is reversed, the resisting force F instantly vanishes and the return of the stop piston to its maximum extension position is effected with effort substantially zero. The abutment described above is a compression stop of a two-tube damper. It is however possible to adapt the hydraulic stop according to the invention to an expansion stop of a damper.

In this case, the stop body is fixed on the inner tube of the damper in the vicinity of the upper yoke. It is not necessary to provide ducts similar to the conduits 26 of the compression stop because of the absence of oil circulation around the stop. The stop body then forms a cylinder of outside diameter substantially equal to the inside diameter of the inner tube 2. The bottom of the abutment body then comprises a passage allowing the main piston rod to circulate. This passage may or may not have a peripheral seal around the stem. Similarly, the fixing of the abutment body on the inner tube 2 may be made in a sealed manner or not, the sealing of the inner tube 2 and around the rod can be performed by the upper yoke.

In the case of the detent stop, the rod 6 must circulate inside the stop piston. Therefore, it is adapted to allow this circulation, for example by enlarging the axial orifice to a diameter greater than that of the rod and providing it with an element such as a collar adapted to seal the annular space of the axial orifice around the rod. Similarly, the axial recess of the nozzle is adapted to receive a spring whose inner diameter allows the passage of the rod 6.

Of course, this description is given by way of illustrative example only and the person skilled in the art will be able to make numerous modifications without departing from the scope of the invention, such as for example modifying the fixing of the end piece on the ring. replace the snap with a bayonet attachment, or choose any material adapted to the function of the parts made.

Similarly, the adaptation of this hydraulic stop for use in a hydraulic cylinder is within the reach of the skilled person who will use a stop of the compression abutment type having side ducts if the supply / discharge port the cylinder chamber is on the opposite side to the main piston with respect to the stop or a stop similar to the stop of if the inlet / outlet port of the cylinder chamber is between the main piston and the hydraulic stop.

Claims

1 / - Hydraulic stop (10) for the end-of-stroke braking of a main piston (5), said stop comprising:

A body, said stop body (11), cylindrical closed at one end,

"A piston, called stop piston (12),

moving axially in the abutment body between a first position, said compressed position and a second position, said extended position, defining between these positions a compression volume (24);

- adapted to come into contact and be driven towards its compressed position by the main piston (5) when it reaches a predetermined position in the vicinity of its end of stroke,

- Having an axial orifice (16), adapted to be plugged by a plug (9) integral with the main piston when it comes into contact with the stop piston and compress a fluid occupying the compression volume,

• elastic return means (23) of the stop piston in its extended position and

• stroke limiting means (21) adapted to stop the stop piston in its extended position,

characterized in that the stop piston (12) has a ring (13) of outer diameter fitted to the inner diameter of the stop body (11) and having a radial flange (14) extending inwardly of the ring and a substantially cylindrical nozzle (15) having the axial orifice (16) at one of its ends and whose other end is adapted to be fixed by snapping on the radial flange (14) of the ring (13).

21 - Stopper according to claim 1, characterized in that the plug is a nut (9) for fixing said main piston.

3 / - Stop according to one of claims 1 or 2, characterized in that the ring (13) is made of reduced friction coefficient material and preferably brass. 4 / - Stop according to any one of claims 1 to 3, characterized in that the tip (15) has a recess (17) central adapted to receive and guide a spring (23) spiral forming the elastic return means of the thrust piston in its extended position.

5 / - Stop according to any one of claims 1 to 4, characterized in that the tip (15) has a groove (27) circular adapted to receive an O-ring (28) of elastomer facing the plug (9) .

6 / - Stop according to any one of claims 4 or 5, characterized in that the spring (23) hairspring has a stiffness adapted to generate a complementary static force when the stop piston (12) tends to its compressed position.

II - Stop according to any one of claims 1 to 6, characterized in that the stop body (11) has on its inner side wall at least one longitudinal groove (20) opening at the open end of the stop body, adapted to allow a predetermined leakage rate of the fluid occupying the compression volume (24).

8 / - Stopper according to claim 7, characterized in that the abutment body (11) comprises at least one groove of variable cross-section as a function of the desired leakage flow, decreasing from the open end of the abutment body towards the bottom of it.

91 - Stopper according to claim 7, characterized in that the abutment body (11) comprises a plurality of grooves (20) of staggered length angularly distributed on the inner side wall of the abutment body (11) so as to allow a decreasing leakage rate when the stop piston (12) moves from the extended position to the compressed position.

10 / - Stop according to any one of claims 7 to 9, characterized in that each groove (20) is formed by stamping the side wall of the stop body (11).

11 / - Stop according to any one of claims 1 to 10, characterized in that the means for limiting the stroke of the stop piston are substantially radial lugs (21) formed by stamping on an edge of the abutment body (11) opposite to the closed end thereof.

12 / - Hydraulic damper, comprising at least one closed tube at both ends, at least partially filled with an incompressible fluid, in which a piston is provided provided with a rod passing through one of the ends, characterized in that it comprises at least one hydraulic stop (10) according to any one of claims 1 to 11.

13 / - Damper according to claim 12, comprising a stop (10) hydraulic adapted to operate in compression in a two-tube damper, characterized in that the stop body (11) has ducts (26) between the stop body (11). ) and the inner tube (2) of the damper adapted to allow a passage of the fluid of the damper of the inner tube to a compensation chamber (4).

14 / - Damper according to one of claims 12 or 13, characterized in that the abutment body (11) has an outer diameter substantially smaller than the inner diameter of the inner tube (2) and has protrusions (22) projecting towards the outside of the stop body, regularly distributed on the periphery of the latter in the vicinity of the edge opposite the closed end, said reliefs (22) forming angular sectors of a cylinder of diameter substantially equal to the inside diameter of the tube internal shock absorber.

15 / - Damper according to claim 14, characterized in that the stop body (11) is fixed to the inner tube (2) of the damper by welds (25) by resistance formed in said reliefs (22).

16 / - Damper according to claim 12, comprising a stop (10) hydraulic adapted to operate in expansion in a two-tube damper, characterized in that the stop body comprises fastening means on the inner tube of the damper in the vicinity of the upper yoke and a passage in its closed end for the passage of the damper rod.