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1. (WO2017001675) ÉLÉMENT D'ARRÊT DE COMPRESSION HYDRAULIQUE DESTINÉ À UN AMORTISSEUR HYDRAULIQUE POUR SUSPENSION DE VÉHICULE DOTÉE D'UN LIMITEUR DE PRESSION
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CLAIMS

1. Hydraulic stop member (30) for hydraulic shock-absorbers (10), in particular for twin-tube hydraulic shock-absorbers for vehicle suspensions, the hydraulic stop member (30) being designed to operate during the compression stroke of the shock-absorber (10) to hydraulically dissipate kinetic energy when the shock-absorber (10) is close to an end-of-travel position of the compression stroke,

wherein the hydraulic stop member (30) comprises

a cup-shaped body (32) which is configured to be mounted in a compression cham-ber (24) of the shock-absorber (10), enclosed by an inner cylindrical tube (14) of the shock-absorber (10), so as to be arranged coaxially to said inner cylindrical tube (14), a piston (34) which is configured to be mounted at an end of a rod (18) of the shock-absorber (10), coaxially thereto, so as to slide in the cup-shaped body (32) when the shock-absorber (10) is close to the end-of-travel position of the compression stroke, wherein the cup-shaped body (32) comprises a side wall (36) separate from said inner cylindrical tube (14) and a bottom wall (38), the side wall (36) and the bottom wall (38) defining, along with the piston (34), a working chamber (46) in which a damping fluid of the shock-absorber (10) is compressed by the piston (34) when the latter slides in the working chamber (46) towards the bottom wall (38) of the cup-shaped body (32), and

a seal ring (54) which is mounted around the piston (34) to close the working chamber (46) at the upper and thereof when the piston (34) slides in the working chamber (46) towards the bottom wall (38) of the cup-shaped body (32),

the hydraulic stop member (30) being characterized

in that it has a bypass conduit (76, 84, 90) configured to connect the working chamber (46) with a portion of the compression chamber (24) placed above the seal ring (54), and in that it further comprises a pressure relief valve (74) configured to keep the bypass conduit (76, 84, 90) closed as long as the pressure in the working chamber (46) remains below a given threshold value and to open the bypass conduit (76, 84, 90), thereby allowing discharge of the damping fluid from the working chamber (46) to the compression chamber (24) through the bypass conduit (76, 84, 90), when the pressure in the working chamber

(46) exceeds said threshold value.

2. Hydraulic stop member according to claim 1, wherein the bypass conduit (76, 84, 90) and the pressure relief valve (74) are located inside the piston (34).

3. Hydraulic stop member according to claim 2, wherein the bypass conduit (76, 84, 90) comprises

an axial cavity (76) which is provided in the piston (34) and is closed at its bottom end by a plug (78),

at least one first hole (84) which extends through the plug (78) and is configured to connect the axial cavity (76) with the working chamber (46), and

at least one second hole (90) which extends through the piston (34) and is configured to connect the axial cavity (76) with the compression chamber (24) above the seal ring (54).

4. Hydraulic stop member according to claim 3, wherein the plug (78) has, on a face thereof facing towards the inside of the axial cavity (76), a valve seat (82) connected with said first hole (84) and wherein the pressure relief valve (74) comprises a closure member (86) configured to cooperate with the valve seat (82) and elastic means (88) configured to urge the closure member (86) against the valve seat (82) to normally keep the bypass conduit (76, 84, 90) closed.

5. Hydraulic stop member according to any of the preceding claims, wherein the inner surface of the side wall (36) of the cup-shaped body (32) has axial channels (44) which extend parallel to a longitudinal axis (z) of the cup- shaped body (32) and are configured to allow the damping fluid to flow axially out of the working chamber (46) when the piston (34) slides in the working chamber (46) towards the bottom wall (38) of the cup-shaped body (32), said axial channels (44) having a cross-section whose area decreases continuously along the longitudinal axis (z) towards the bottom wall (38) of the cup-shaped body (32).

6. Hydraulic stop member according to any of the preceding claims, wherein the piston (34) comprises a cylindrical body (50), which is configured to be attached to the rod (18) of the shock-absorber (10) and around which the seal ring (54) is axially slidably

mounted, and first and second ring-shaped abutment elements (56, 58), which are axially restrained onto the cylindrical body (50) and are configured to axially limit, in either direction, the axial sliding movement of the seal ring (54) along the cylindrical body (50), the seal ring (54), the first abutment element (56) and the second abutment element (58) being configured such that when the seal ring (54) slides along the inner surface of the cup-shaped body (32) during the compression stroke of the shock-absorber (10) the seal ring (54) is in abutment against the first abutment element (56) and there is no flow of damping fluid from one side of the seal ring (54) to the other, while during the extension stroke of the shock-absorber (10) the seal ring (54) is in abutment against the second abutment ele-ment (58) and the damping fluid is allowed to flow from one side of the seal ring (54) to the other.

7. Hydraulic stop member according to any of the preceding claims, wherein a plurality of passages (48) are provided in the bottom wall (38) of the cup-shaped body (32) and/or a gauged ring gap (54a) is provided in the seal ring (54) of the piston (34) to allow leakage of the damping fluid from the working chamber (46) of the cup- shaped body (32).

8. Twin-tube hydraulic shock-absorber (10) for vehicle suspensions, comprising a hydraulic stop member (30) according to any of the preceding claims, the hydraulic stop member (30) being mounted in a compression chamber (24) of the shock-absorber (10) enclosed by an inner cylindrical tube (14) of the shock-absorber (10).