WO2017097963A1

WO2017097963A1 - Hydraulic control device

Info

Publication number: WO2017097963A1
Application number: PCT/EP2016/080401
Authority: WO
Inventors: Christophe Mollier; Roberto Canale; Sandro Bonardo; Massimo CIMA
Original assignee: Valeo Embrayages
Priority date: 2015-12-11
Filing date: 2016-12-09
Publication date: 2017-06-15
Also published as: FR3045114B1; CN108474394B; CN108474394A; FR3045114A1

Abstract

The invention relates to a hydraulic control device (1) comprising: a cylinder body (2) provided with a borehole (3) defining a hydraulic chamber (5), and a piston assembly (4) mounted such that it slides in an axial direction (X) in the borehole of the cylinder body in order to modify a volume of the hydraulic chamber (5). The piston assembly comprises: a rigid piston body (15) having a front end portion facing the hydraulic chamber, an annular magnet (16) carried by the piston body so as to allow a magnetic detection of the axial position of the piston assembly in the borehole of the cylinder body, and an elastic body (18) arranged in a deformed state against an axial end surface and/or a radially inner surface of the annular magnet (16) in such a way as to exert an axially and/or radially oriented elastic load over the entire circumference of the annular magnet.

Description

HYDRAULIC CONTROL DEVICE Technical field

The invention relates to the field of hydraulic control devices comprising a cylinder body provided with a bore defining a hydraulic chamber and a piston assembly mounted in the bore of the cylinder body to modify a volume of the hydraulic chamber, particularly for the control of a motor vehicle clutch. More particularly, the invention relates to devices of this type in which magnetic detection of the position of the piston assembly in the bore of the cylinder body is performed.

Technological background

The use of a magnetic sensor for detecting the position of a piston in the bore of a cylinder body is known. In this context, various techniques have been proposed for fixing an annular magnet on a front end portion of the piston.

DE-A-10323797 employs a fixing ring which comprises both locking lugs oriented radially inwards and axially forward and resilient lugs oriented radially inwards and axially towards the rear. The locking tabs serve to retain the attachment ring on an axial projection of the piston engaging a groove, while the resilient tabs support the annular magnet against a reference axial surface of the piston. Such a fixing ring has disadvantages as to its manufacture which is not easy and as to its use. Indeed, in use, the elastic tabs are likely to produce localized stresses on the magnet that may affect its life. In addition, given the high number of locking tabs and elastic tabs may have slightly different inclinations from each other resulting from manufacturing inaccuracies, misalignment is likely to occur, which would adversely affect the stability of the magnet in time.

summary

An idea underlying the invention is to provide a hydraulic control device in which an annular magnet is reliably attached to the piston. In particular, this reliable attachment must satisfy as much as possible the following constraints:

- Absence of play to avoid the sound of the position signal by vibrations generated in the environment of the hydraulic control device, especially in a vehicle, and therefore recovery of the dimensional tolerances of the magnet and the piston body,

- Limitation and balanced distribution of the stresses exerted on the magnet to avoid the risks of fatigue and rupture of the magnet,

- Compatibility with the chemical nature, pressure and temperature of the piston environment.

For this, according to one embodiment, the invention provides a hydraulic control device comprising:

a cylinder body having a bore defining a hydraulic chamber, and a piston assembly slidably mounted in an axial direction in the bore of the cylinder body for changing a volume of the hydraulic chamber, wherein the piston assembly comprises :

a rigid piston body having a front end portion facing the hydraulic chamber,

an annular magnet carried by the piston body to enable magnetic detection of the axial position of the piston assembly in the bore of the cylinder body, the annular magnet having a symmetry of revolution with respect to the axial direction and being mounted on a cylindrical bearing secured to the front end portion of the piston body and parallel to the axial direction, and

an elastic body having a symmetry of revolution with respect to the axial direction, the elastic body being arranged in a deformed state against an axial end surface and / or a radially inner surface of the annular magnet so as to exert an elastically oriented load axially and / or radially over the entire circumference of the axial end surface and / or the radially inner surface of the annular magnet,

so that the annular magnet is immobilized on the front end of the piston body by the rotationally symmetrical elastic body in the deformed state. Thanks to these features, the elastic body can be made in a relatively simple manner and distribute relatively uniformly its elastic force over the entire circumference of the annular magnet.

According to advantageous embodiments, such a device may have one or more of the following characteristics:

In one embodiment, the annular magnet and the rotationally symmetrical elastic body are juxtaposed in the axial direction on the cylindrical bearing surface, the end portion of the piston body having a radially oriented surface facing towards the front forming a rear stop surface, the cylindrical bearing surface extending in front of the rear stop surface and being adjacent to the rear stop surface, so that one of the annular magnet and the rotationally symmetrical elastic body is axially abutting against the rear stop surface.

In such an arrangement, the elastic body may be disposed at the front or rear of the annular magnet, or both sides thereof (in which case a second elastic body is added).

In some embodiments, the elastic body (s) may be sufficient to achieve the attachment of the magnet to the piston body.

In other embodiments, the device further comprises a mounting piece fastened to the front end portion of the rigid piston body, the mounting piece having a radial portion having a radially facing surface rearwardly forming a forward stop surface arranged at a forward end of the cylindrical seat, the cylindrical seat extending behind the forward abutment surface between the forward abutment surface and the rear abutment surface.

In one embodiment, the other one of the annular magnet and the rotationally symmetrical elastic body is axially abutting against the front abutment surface. Thanks to these features, the elastic body axially stabilizes the annular magnet against the front or rear stop surface.

The cylindrical scope on which the annular magnet is mounted may be formed completely by the cylinder body or totally by the mounting piece or partially by each of them. For this, in one embodiment, the piece mounting device further comprises a cylindrical axial portion arranged against the front face of the piston body, the cylindrical axial portion of the mounting part forming all or part of the cylindrical surface on which the annular magnet and the symmetrical elastic body of revolution. are juxtaposed, the radial portion of the mounting piece being constituted by a radial flange projecting radially outside the cylindrical axial portion, the radial flange being arranged at a front end of the cylindrical axial portion of the mounting piece .

In one embodiment, the cylindrical axial portion of the mounting piece forms the entire cylindrical surface, the front end portion of the piston body having a larger diameter than the cylindrical axial portion of the mounting piece, the front face piston body forming the rear stop surface.

In another embodiment, the front end portion of the piston body has a cylindrical axial portion coaxial with and substantially of the same diameter as the cylindrical axial portion of the mounting piece, so that the cylindrical axial portion of the piece and the cylindrical axial portion of the piston body together form the cylindrical surface on which the annular magnet and the symmetrical elastic body of revolution are juxtaposed.

The mounting piece can be attached to the piston body by various means. A glueless mechanical assembly is preferred to avoid chemical contamination of the hydraulic fluid. In one embodiment, the mounting member has a rearwardly-facing attachment pin axially engaged in a bore of a front face of the piston body and secured in said bore by force fit.

In one embodiment, the cylindrical surface is formed on the end portion of the piston body, the radial portion of the mounting piece being constituted by a radial flange projecting radially outwardly of the fixing rod, the radial flange being arranged at a front end of the fastening rod against the front face of the piston body.

In one embodiment, the mounting piece has a rearwardly facing attachment bushing, larger in diameter than the cylindrical bearing surface on which the annular magnet and the rotationally symmetrical elastic body are juxtaposed, the fastening bush extending axially along the span cylindrical so as to house the cylindrical surface, the annular magnet and the rotationally symmetrical elastic body in the interior space of the fixing sleeve, the radial portion of the mounting part consisting of a radially projecting radial flange inside the attachment sleeve at a front end of the attachment sleeve, a rear end of the attachment sleeve being attached to the piston body.

The attachment of the fixing sleeve to the piston body can be achieved by snapping, screwing or otherwise, preferably without gluing.

In one embodiment, the cylindrical seat is formed on the end portion of the piston body, a peripheral groove being formed in the cylindrical seat at the front end of the cylindrical seat, the mounting piece having a fixed elastic ring. in the peripheral groove and protruding radially around the cylindrical bearing.

In one embodiment, the cylindrical surface is formed on the end portion of the piston body, a peripheral groove being formed in the cylindrical surface at the front end of the cylindrical surface, the symmetrical elastic body being housed in the circumferential groove in an elastically stretched state in the circumferential direction, so as to be stabilized in the groove by its own elastic tension, the rotationally symmetrical elastic body projecting radially around the cylindrical bearing surface, the annular magnet being disposed between the rotationally symmetrical elastic body and the rear stop surface, so that the rotationally symmetrical elastic body in the elastically stretched state bears against a front end surface of the annular magnet.

Thanks to these characteristics, the elastic body can be sufficient to achieve the fixing of the magnet on the piston body without an additional mounting piece is necessary.

In one embodiment, the elastic body is interposed axially between the rear abutment surface and a rear end surface of the annular magnet, so that the annular magnet compresses said elastic body against the rear abutment surface. In one embodiment, it is a second elastic body which is interposed axially between the rear abutment surface and a rear end surface of the annular magnet, so that the annular magnet compresses said second elastic body against the rear abutment surface.

In one embodiment, the elastic body or second elastic body is partially housed in a circumferential groove axially hollowed in the rear abutment surface.

In one embodiment, the cylindrical surface is formed on the end portion of the piston body, a peripheral groove being formed in the cylindrical surface, the symmetrically symmetrical elastic body or a second symmetrical elastic body being housed. in the peripheral groove and having a thickness at rest greater than the depth of the groove, the annular magnet being mounted on the cylindrical seat in line with the groove so as to span the groove and maintain said elastic body or second elastic body in an elastically compressed state in the groove, said elastic body or second elastic body exerting a radial pressure on the radially inner surface of the annular magnet by reaction.

Thanks to these characteristics, the elastic body can be sufficient to achieve the fixing of the magnet on the piston body without an additional mounting piece is necessary. A mounting piece as described above may, however, be combined with this embodiment to enhance the axial stability of the magnet.

The or each rotationally symmetrical elastic body may be made in different ways, in particular elastomer, but also in metallic or synthetic elastic material. Embodiments of the rotationally symmetrical elastic bodies include an elastomeric O-ring, an elastomeric lip seal, and a conically shaped elastic metal washer.

In one embodiment, the forward end portion of the piston body has the cylindrical bearing surface and a radially forwardly facing surface forming a rear abutment surface, the cylindrical bearing surface extending on the piston body from a front face of the piston body to the rear stop surface, the device further comprising a mounting piece attached to the forward end portion of the piston body, the mounting piece having a fixing rod facing the rear, engaged axially in a bore of the front face of the piston body and fixed in said bore, the mounting piece having a resilient radial portion extending radially outwardly about the fixing rod in front of the front face of the piston body and constituting said rotationally symmetrical elastic body, the elastic radial portion bearing against the front surface of the piston annular magnet, so that the annular magnet holds the elastic radial portion in a conical bending state and is held axially abutting against the rear abutment surface by the elastic reaction of the elastic radial portion.

In an alternative embodiment, the elastic radial portion with symmetry of revolution can be replaced by a set of discrete elastic portions distributed around the longitudinal axis with a symmetry of order N, where N is an integer greater than 1. However, in this case, the benefits resulting from the symmetry of revolution are lost, especially in terms of uniform distribution of stresses.

In one embodiment, the bore of the piston body in which the fastening rod is engaged is a blind bore, and wherein the fastening rod comprises an internal channel for putting in fluid communication a bottom portion of the bore. blind with the outside of the piston body.

Thanks to these characteristics, it is avoided to imprison air under pressure in the blind bore when force-fitting the fastening rod, namely when the contact between the fastening rod and the wall of the bore is sealed due to compression of the material. The mounting of the fixing rod is thus facilitated and made more reliable. Such a communication channel putting in fluid communication a bottom portion of the blind bore with the outside of the piston body may also be formed in the wall of the blind bore, for example in the form of a channel parallel to the fixing rod locally bypassing the surface of the fixing rod.

Brief description of the figures

The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly in the course of the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes. with reference to the accompanying drawings.

FIG. 1 is a partial view in axial section of a hydraulic control device according to one embodiment of the invention, FIG. 2 is an enlarged view of zone II of FIG.

- Figure 3 to Figure 18 are views similar to Figure 2 showing other embodiments. Detailed description of embodiments

Figure 1 schematically shows a transmitter cylinder 1 for controlling a motor vehicle clutch. The emitter cylinder 1 comprises a generally tubular body 2 which extends axially along a main axis X of longitudinal orientation. The body 2 has an internal bore 3 in which a piston assembly 4 slides axially, respectively forwardly or rearwardly along the main axis X, between at least one extreme forward position, called an actuation position, and an extreme position. back, called rest.

The internal bore 3 of the emitter cylinder 1 defines, at the front, a hydraulic chamber 5 of variable volume which is delimited axially from front to back by the bottom (not shown) of the body 2 and a front portion 6 of the piston assembly 4. The emitter cylinder 1 comprises sealing means 7, 8 which are interposed radially between the body 2 of the cylinder and the piston assembly 4 and a control rod (not shown) which is connected in movement to the piston. piston assembly 4.

The emitter cylinder 1 comprises a connector 9 arranged centrally and intended to allow the connection of the hydraulic chamber 5 of the emitter cylinder 1 in particular to a fluid supply reservoir not shown. In use, the replenishment tank is generally mounted outside the emitter cylinder 1 and is connected to the upper free end of the connector 9.

The connector 9 comprises a channel 10 which passes through the lateral wall of the body 2 to open radially inside the central portion of the internal bore 3. The sealing of the hydraulic chamber 5 with respect to the outside is ensured by sealing means which comprise at least one front seal 8 and a rear seal 7.

In operation, the front seal 8 seals between the hydraulic chamber 5 and the feed channel 10 which opens axially between the seals 8 and 7, while the rear seal 7 seals between the piston assembly 4 and the rear portion 12 of the bore 3 behind the channel 10. However, if the rear seal 7 seals permanently regardless of the position of the piston assembly 4, this is not the case of the front seal 8 which must allow the fluid supply of the chamber 5 by the channel 10 when the piston assembly 4 is in its extreme rear position of rest.

With reference to FIGS. 1 and 2, the front portion 6 of the piston assembly 4 comprises a generally cylindrical piston body 15 made of a rigid material, for example a plastic material, preferably a thermosetting material, on the front of which An annular magnet 16, which has a square section, is mounted by means of a mounting nail 17 and an O-ring 18 of elastic material. Since these elements all have a symmetry of revolution about the X axis, the enlarged half-view of Figure 2 is sufficient to understand their geometry.

The piston body 15 has a smaller diameter front stage defining a cylindrical surface 20 and a larger diameter rear stage separated from the front stage by a radial shoulder 21 defining a stop surface at a rear end of the cylindrical surface. 20.

The mounting nail 17 comprises a toothed rod 22, which is forced into a blind bore 23 of the piston body 15, a cylindrical intermediate portion 24 of the same diameter as the cylindrical surface 20, which is separated from the toothed rod 22 by a radial shoulder surface 25, and a wide head 26. In the assembled state as shown, the radial shoulder surface 25 abuts the end face of the piston body 15, so that the peripheral surface 27 of the cylindrical intermediate portion 24 extends the cylindrical surface 20 substantially continuously. The wide head 26 forms a radial surface 28 which protrudes beyond the peripheral surface 27 and thus defines an abutment surface at a front end of the peripheral surface 27.

Thus, the cylindrical surface 20 of the piston body 15 and the peripheral surface 27 of the mounting nail 17 together form a cylindrical surface delimited between the radial shoulder 21 at the rear and the radial surface 28 at the front and on which the Annular magnet 16 and O-ring 18 are connected in series. The distance between the radial shoulder 21 and the radial surface 28 is sized to be slightly smaller than the sum of the nominal axial lengths of the annular magnet 16 and the O-ring 18, so that the seal O-ring 18 is in a compressed state in the mounted state as shown. This results in an axial load exerted elastically against the front surface of the annular magnet 16, uniformly over the entire periphery of the latter and which firmly plates it against the radial shoulder 21. Any mounting set of the annular magnet 16 is removed. The axial positions of the annular magnet 16 and the O-ring 18 can be swapped without changing this operation.

In an alternative embodiment, the diameter of the cylindrical intermediate portion 24 is slightly smaller than that of the cylindrical surface 20. The operation is essentially the same.

With reference to FIGS. 3 to 18, other embodiments of the front portion 6 of the piston assembly 4 will now be described. The same reference numerals are used in all the figures to denote identical or similar elements.

In FIG. 3, the cylindrical surface is formed exclusively by the peripheral surface 27 of the mounting nail 17 which is longer. The abutment surface at the rear end of the cylindrical seat is formed directly by the end face 30 of the piston body 15. For the remainder, the operation is identical to FIG. 2.

In FIG. 4, the wide head 26 of the mounting nail 17 carries a protective sleeve 31 which extends axially rearwards to protect the annular magnet 16 and the O-ring 18. The protective sleeve 31 covers the surface radial outer 32 of the annular magnet 16. For the rest, the operation is identical to Figure 2.

In FIG. 5, the cylindrical surface is formed exclusively by the cylindrical surface 20 of the piston body 15 and the mounting nail 17 is replaced by a mounting sleeve 35 which extends axially parallel to the cylindrical surface 20 to protect the annular magnet 16 and the O-ring 18. It carries at the front an internal radial rim 36 which defines the abutment surface at the front of the cylindrical seat and at the rear a rod 37 which snaps into a groove 38 of the piston body 15. For the rest, the operation is identical to FIG.

In FIG. 6, the axial positions of the annular magnet 16 and the O-ring 18 are exchanged with respect to FIG. 2. Moreover, the O-ring 18 is partially housed in a circular groove 33 hollowed out axially in the radial shoulder 21. This makes it possible to slightly shorten the cylindrical surface 20 to limit the bulk. This results in an axial load exerted elastically against the rear surface of the annular magnet 16, uniformly over the entire periphery thereof and which firmly plates it against the wide head 26. For the rest, the operation is identical to Figure 2.

In Figure 8, two O-rings 18 are respectively placed in front of and behind the annular magnet 16, as in Figures 2 and 6 taken in combination. The two O-rings 18 are compressed axially due to the sizing of the cylindrical seat. For the rest, the operation is identical to FIG.

In FIG. 7, the cylindrical surface is formed exclusively by the cylindrical surface 20 of the piston body 15 and the mounting nail 17 is replaced by a mounting ring 34 mounted in a groove 39 of the piston body 15, for example a ring split metal or circlips. The mounting ring 34 defines the abutment surface at the front of the cylindrical seat. Furthermore, the O-ring 18 is partially housed in a circular groove 33 hollowed axially in the radial shoulder 21. For the rest, the operation is identical to FIG.

In FIG. 9, the cylindrical surface is formed exclusively by the cylindrical surface 20 of the piston body 15 and the mounting nail 17 has only the notched rod 22, and the wide head 26 without an intermediate portion. The wide head 26 abuts against the end face 30 of the piston body 15. In addition, a groove 41 is hollowed radially in the cylindrical surface 20 and accommodates an elastic O-ring 40, which protrudes radially out of the groove 41 at rest, and which is compressed in the groove 41 by the annular magnet 16 mounted above it. In the compressed state, the elastic O-ring 40 exerts pressure against the inner radial surface 42 of the annular magnet 16 uniformly over the entire periphery thereof, thereby firmly immobilizing the annular magnet 16 on the piston body 15. Any mounting set of the annular magnet 16 is therefore removed. Alternatively or in combination with the O-ring 40, an O-ring 18 could be mounted on the cylindrical seat 20 as in the previous embodiments, to exert an axial load on the annular magnet 16. Figure 10 illustrates such a combination of O-ring 40 exerting a radial load and an O-ring 18 exerting axial load. The mounting nail 17 is here produced as in FIG.

Figure 1 1 is similar to Figure 10 and shows another implementation of symmetrical elastic bodies of revolution, here in the form of lip seals 1 18 and 140, for example rubber.

Figure 12 is similar to Figure 2 and shows another implementation of symmetrical elastic bodies of revolution, here in the form of a conical metal washer 218, also known as the Belleville washer.

In FIG. 13, the cylindrical bearing surface is formed exclusively by the cylindrical surface 20 of the piston body 15 and the mounting nail 17 comprises a toothed rod 122 and an elastic head 126. The slightly conical shape facing towards the rear of the elastic head 126 allows to exert an axial pressure on the front surface of the annular magnet 16. The elastic head 126 also carries a protective ring 44 which covers the outer radial surface 32 of the annular magnet 16. For the rest, the operation is identical to FIG.

In FIG. 17, the cylindrical bearing surface is formed exclusively by the cylindrical surface 20 of the piston body 15 and the mounting nail 217 comprises the toothed rod 22 and a narrow head 226. A resilient disc blade 45 projects radially around the head narrow 226 and has a cylindrical flange 46 facing rearwardly which allows to exert an axial pressure on the front surface of the annular magnet 16. For the rest, the operation is identical to Figure 2.

In a variant, the disc resilient lamella 45 is replaced by a plurality of resilient tabs distributed around the narrow head 226.

In Fig. 14, the cylindrical seat is formed exclusively by the cylindrical surface 20 of the piston body 15 and the mounting nail 17 is removed. The O-ring 18 is immobilized on the cylindrical surface 20 by means of a groove 39. The distance between the groove 39 and the radial shoulder 21 is dimensioned so that the O-ring 18 exerts an axial load against the front surface of the groove. annular magnet 16 under the effect of its own elastic tension. A second O-ring could be added on the other side of the annular magnet 16 as in FIG. 8. For the rest, the operation is identical to FIG. Figure 15 illustrates a combination of O-ring 18 of Figure 14 exerting axial load and O-ring 40 exerting radial load. A third O-ring could be added on the other side of the annular magnet 16 as in FIG.

Figures 16 and 17 illustrate two embodiments of the mounting nail 17 further comprising an internal channel 50 for exhausting air. In FIG. 16, the internal channel 50 extends centrally along the axis X. In FIG. 17, it extends on the edge of the notched rod 22.

The use of the verb "to include", "to understand" or "to include" and its conjugated forms does not exclude the presence of other elements or steps other than those set out in a claim. The use of the indefinite article "a" or "an" for an element or a step does not exclude, unless otherwise stated, the presence of a plurality of such elements or steps.

In the claims, any reference sign in parentheses can not be interpreted as a limitation of the claim.

Claims

1. Hydraulic control device (1) comprising:

a cylinder body (2) provided with a bore (3) defining a hydraulic chamber (5), and a piston assembly (4) slidably mounted in an axial direction (X) in the bore of the cylinder body for modifying a volume of the hydraulic chamber (5), in which the piston assembly comprises:

a rigid piston body (15) having a front end portion facing the hydraulic chamber,

an annular magnet (16) carried by the piston body to allow magnetic detection of the axial position of the piston assembly in the bore of the cylinder body, the annular magnet having a symmetry of revolution with respect to the axial direction and being mounted on a cylindrical seat (20, 27) integral with the front end portion of the piston body and parallel to the axial direction, and an elastic body (18, 1 18, 218, 40, 126, 45) to symmetry of revolution with respect to the axial direction, the elastic body being arranged in a deformed state against an axial end surface and / or a radially inner surface of the annular magnet (16) so as to exert an axially oriented elastic load and / or radially on the entire circumference of the axial end surface and / or the radially inner surface of the annular magnet,

so that the annular magnet (16) is immobilized on the front end of the piston body (15) by the rotationally symmetrical elastic body (18, 18, 218, 40, 126, 45) in the state deformed.

2. Device according to claim 1, wherein the annular magnet (16) and the rotationally symmetrical elastic body (18, 1 18, 218) are juxtaposed in the axial direction on the cylindrical bearing surface (20, 27), the end portion of the piston body having a radially forwardly directed surface forming a rear abutment surface (21, 30), the cylindrical surface extending in front of the rear abutment surface and being adjacent to the abutment surface rearwardly, so that one of the annular magnet (16) and the rotationally symmetrical elastic body (18, 18, 218) is axially abutting against the rear abutment surface (21, 30).

3. Device according to claim 2, further comprising a mounting piece (17, 34, 35) fixed on the front end portion of the piston body. rigid member (15), the mounting piece having a radial portion (26, 34, 36) having a radially rearward facing surface forming a forward stop surface arranged at a front end of the cylindrical bearing surface (20, 27) the cylindrical span extending behind the front abutment surface between the forward abutment surface and the rear abutment surface (21, 30).

4. Device according to claim 3, wherein the other of the annular magnet (16) and the symmetrical elastic body of revolution (18, 1 18, 218) is axially abutting against the front abutment surface.

5. Device according to claim 3 or 4, wherein the mounting piece (17) further comprises a cylindrical axial portion (27) arranged against the front face (30) of the piston body, the cylindrical axial portion (27) of the mounting part forming all or part of the cylindrical surface on which the annular magnet (16) and the symmetrical elastic body of revolution (18, 1 18, 218) are juxtaposed, the radial portion of the mounting piece being constituted a radial flange (26) projecting radially outwardly from the cylindrical axial portion, the radial flange being arranged at a front end of the cylindrical axial portion (27) of the mounting piece.

6. Device according to claim 5, wherein the cylindrical axial portion (27) of the mounting part forms the entire cylindrical surface, the front end portion of the piston body (15) having a larger diameter than the axial portion. cylindrical part of the mounting piece, the front face (30) of the piston body forming the rear stop surface.

7. Device according to claim 5, wherein the front end portion of the piston body (15) comprises a cylindrical axial portion (20) coaxial with the cylindrical axial portion (27) and of substantially the same diameter as the cylindrical axial portion. (27) of the mounting piece (17) so that the cylindrical axial portion (27) of the mounting piece and the cylindrical axial portion (20) of the piston body together form the cylindrical seat on which the annular magnet (16) and the rotationally symmetrical elastic body (18, 18, 218) are juxtaposed.

8. Device according to one of claims 3 to 7, wherein the mounting piece (17) comprises a fastening rod (22) facing rearward, engaged axially in a bore (23) of a front face of the piston body (15) and fixed in said bore by press fit.

9. Device according to claim 8, wherein the cylindrical seat (20) is formed on the end portion of the piston body (15), the radial portion of the mounting part being constituted by a radial flange (26). protruding radially outwardly from the fixing rod (22), the radial flange being arranged at a front end of the fixing rod against the front face (30) of the piston body.

10. Device according to one of claims 3 to 7, wherein the mounting part comprises a rearward-facing fixing bushing (35) of larger diameter than the cylindrical surface on which the annular magnet (16). and the rotationally symmetrical elastic body (18, 18, 218) are juxtaposed, the fixing sleeve (35) extending axially along the cylindrical bearing surface to accommodate the cylindrical bearing surface, the annular magnet and the elastic body with symmetry of revolution in the interior space of the fixing sleeve, the radial portion of the mounting piece consisting of a radial flange (36) protruding radially inside the fixing sleeve at one end before the fixing sleeve, a rear end (37) of the fixing sleeve being attached to the piston body.

1 1. Device according to Claim 3, in which the cylindrical bearing surface (20) is formed on the end portion of the piston body (15), a peripheral groove (39) being formed in the cylindrical bearing surface at the front end of the bearing cylindrical, the mounting piece having an elastic ring (34) fixed in the peripheral groove and projecting radially around the cylindrical seat (20).

12. Device according to claim 2, wherein the cylindrical seat (20) is formed on the end portion of the piston body (15), a peripheral groove (39) being formed in the cylindrical seat (20) to the front end of the cylindrical bearing surface, the rotationally symmetrical elastic body (18) being housed in the circumferential groove (39) in an elastically stretched state in the circumferential direction, so as to be stabilized in the groove by its own elastic tension, the rotationally symmetrical elastic body (18) protruding radially around the cylindrical bearing surface (20), the annular magnet (16) being disposed between the rotationally symmetrical elastic body and the rear stop surface (21) so that the rotationally symmetrical elastic body in the elastically stretched state bears against a front end surface of the annular magnet.

13. Device according to any one of claims 2 to 12, wherein said elastic body (18, 1 18, 218) or a second elastic body (18, 1 18, 218) is interposed axially between the rear abutment surface ( 21) and a rear end surface of the annular magnet (16) so that the annular magnet compresses said elastic body or second elastic body against the rear stop surface (21).

14. Device according to claim 13, wherein said elastic body (18, 1 18) or second elastic body (18, 1 18) is partially housed in a circumferential groove (33) axially hollowed in the rear abutment surface (21). .

15. Device according to any one of claims 1 to 12, wherein the cylindrical seat (20) is formed on the end portion of the piston body (15), a peripheral groove (41) being formed in the cylindrical seat the rotationally symmetrical elastic body (40) or a second rotationally symmetrical elastic body (40) being accommodated in the circumferential groove (41) and having a resting thickness greater than the depth of the groove, the magnet annular (16) being mounted on the cylindrical seat in line with the groove so as to straddle the groove (41) and to maintain said elastic body or second elastic body in an elastically compressed state in the groove, said elastic body (40) or second elastic body (40) exerting a radial pressure on the radially inner surface of the annular magnet (16) by reaction.

16. Device according to any one of claims 1 to 15, wherein the or each symmetrical elastic body is selected from the group consisting of an O-ring (18) elastomer, a lip seal (1 18). elastomer and a resilient metal washer (218) of conical shape.

Device according to claim 1, wherein the front end portion of the piston body (15) has the cylindrical bearing surface (20) and a radially forwardly directed surface forming a rear stop surface (21), the cylindrical bearing surface extending on the piston body from a face front (30) of the piston body to the rear stop surface (21), the device further comprising a mounting piece (17, 217) attached to the front end portion of the piston body (15) the mounting piece having a rearward-facing attachment pin (22, 122) axially engaged in a bore (23) in the front face of the piston body and fixed in said bore, the mounting piece having a portion resilient radial member (126, 45) extending radially outwardly about the fixation rod in front of the front face (30) of the piston body and constituting said rotationally symmetrical elastic body, the radial elastic portion (126, 45 ) resting on the front end surface of the annular magnet (16), so that the annular magnet holds the elastic radial portion in a conical bending state and is held axially abutting against the rear abutment surface (21) by the elastic reaction of the elastic radial portion.

18. Device according to any one of claims 8, 9 and 17, wherein the bore (23) of the piston body (15) in which is engaged the fixing rod is a blind bore, and wherein the rod of fastener (22) includes an inner channel (50) for fluidically connecting a bottom portion of the blind bore to the exterior of the piston body.