Two-tube telescopic hydraulic shock absorbers

Claim 1

A two-tube hydraulic shock absorber comprising coaxial inner and outer tubes or cylinders which define an interspace therebetween, wherein a piston is slidable in the inner cylinder and includes a rod which projects from an upper end of the shock absorber through an annular head common to both cylinders, the head having an annular radial lower shoulder which engages axially a rim at the upper end of the inner cylinder, wherein the head includes a bushing in which the rod is slidable and the head is formed with an annular reservoir overlying the bushing for receiving hydraulic fluid which is drawn between the rod and the bushing from the chamber of the internal cylinder, radial passages interconnecting the reservoir and the upper part of the interspace, and wherein the interspace contains gas under pressure, one-way sealing means being provided to prevent the gas under pressure from reaching the passages and at the same time to allow oil to descend into the interspace through the passages, wherein said sealing means comprises an annular gasket (48; 148; 248) of elastomeric or similar material which has an inverted U- or V-shaped cross section and is arranged in the upper part of the interspace (44) so as to form a channel (50) which opens downwardly and is defined by two annular lips (52, 54; 252, 254) engaged with the inner cylinder (12) and the outer cylinder (10) respectively, one (52; 252) of which deforms elastically to separate from the respective cylinder and enable the oil to descend into the interspace (44), the deformable lip (52; 252) engaging the respective cylinder in an annular zone below the rim at the upper end (24) of the inner cylinder (12), wherein the deformable lip (52; 252) has an external face with a longitudinal profile which diverges upwardly relative to the respective cylinder so as to define, between the lip and the cylinder, an annular passage (56; 256) normally closed at its lower end by the contact between the lip and the cylinder, wherein an upper reinforcing washer (58; 158; 258) is connected to the gasket (48; 148; 248), wherein the radial shoulder (22) of the head (14) projects radially outwards relative to the inner cylinder (12), wherein the washer has a radially internal flat annular edge which engages the projecting part of the shoulder (22), and wherein said washer includes at least one notch which exposes at least a part of the upper mouth of said annular passage (56; 256).