Piston assembly for a shock absorber

Claim 1

A piston assembly for a direct acting hydraulic shock absorber including a reciprocal piston rod and a cylinder containing damping fluid, said assembly comprising a piston member formed with a plurality of circumferentially spaced, axially extending flow ports and an annular cavity communicable with said ports and defined by inner and outer circular walls, said inner wall defined by a generally cylindrical body portion concentric with and surrounding the piston rod, said outer wall including an annular shoulder extending axially of said piston rod and defining a first flat, radially extending seating surface, said surface being forMed with a first plurality of circumferentially spaced bleed openings extending axially downwardly from said surface and extending radially entirely through said shoulder, a flat annular spacer member arranged concentric with said piston rod and said cylindrical body portion and carried in fixed relation thereto and spaced axially from said cylindrical body portion, the side of said spacer member facing said first seating surface defining a second radially extending seating surface, a thin resilient valve disc positioned across said cavity and having its radially outer marginal portion seated against said first seating surface and adapted for movement in a first axial direction away from said shoulder, the radially inner marginal portion of said valve disc being seated against said second seating surface and adapted for movement away from said second surface in a second axial direction, the outer diameter of said spacer member being greater than the diameter of said body portion and greater than the inner diameter of said valve disc, a flat disc-shaped metering element positioned axially between said spacer member and said cylindrical body portion, said element lying in the same general radial plane as said valve disc and having an outer diameter less than the outer diameter of said spacer member and approximately equal to the inside diameter of said valve member, with said spacer member and metering element being independently interchangeable in order to vary the axial spacing between said seating surfaces, said metering element providing a second plurality of bleed opening which are formed by circumferentially spaced, radially inwardly extending recesses arranged around the outer periphery of said element, the outer diameter of said metering element being smaller than the outer diameter of said spacer member, with one axial end of each of said second plurality of bleed openings being covered by the adjacent side of said spacer member, whereby fluid flow through said second plurality of bleed openings is prevented when said second seating surface is engaged by the adjacent side of said valve member, with a substantially uniform controlled amount of fluid flow through said second plurality of openings being permitted when the inner peripheral portion of said valve member is deflected axially away from said second seating surface any distance less than the axial thickness of said metering element, and a fluid flow substantially greater than said uniform controlled amount thereof is permitted when said inner peripheral portion of said valve member is deflected axially away from said second seating surface a distance greater than the axial thickness of said metering member, said uniform controlled amount of fluid flow being determined solely by the cross-sectional size of said second plurality of bleed openings and being substantially independent of the position of said inner peripheral portion of said valve member during the time said portion is deflected an axial distance less than said axial thickness of said metering member.