Fluid operated damper unit

A fluid operated damper unit comprising a cylinder member having an axis, two cylinder ends and a cavity within said cylinder member, a piston rod unit being axially movable with respect to said cylinder member and extending sealingly through at least one of said two cylinder ends, damping means being provided on said piston rod unit, a damping fluid being contained within said cavity, said piston rod unit being movable along a predetermined path along said axis, movement of said piston rod unit being subject to variable damping resistance in response to the location of said piston rod unit along said path of movement, said piston rod unit being provided with two axially spaced piston units within said cavity, both of said piston units having respective annular sealing engagement members mounted thereon for substantially common axial movement with the respective piston units along the total length of said predetermined path and cooperating with an internal cylindrical face of said cylinder member, said annular sealing engagement members having a substantially constant axial distance between them, at least one by-pass passage means being provided along an intermediate part of the axial length of said cylinder member, said bypass passage means having respective axial ends spaced apart axially from the cylinder ends, said by-pass passage means having an axial extent at least substantially equal to said axial distance, said by-pass passage means providing a fluid connection between fluid spaces on both sides of a respective piston unit when the sealing engagement zone of the respective piston unit is positioned within the axial extent of said by-pass passage means, each of said piston units being movable beyond said by-pass passage means toward a respective cylinder end nearer to the respective piston unit, throttled flow path passage means being provided across each of said piston units, said throttled flow path passage means of each respective piston unit providing a damping resistance for said piston rod unit in response to axial movement thereof when the respective piston unit moves beyond a respective end of the axial extent of said by-pass passage means toward the respective axial cylinder end nearer to the respective piston unit, said throttled flow passage means of each of said piston units being such as to provide a larger fluid flow resistance when the respective piston unit moves beyond said axial extent of said by-pass passage means toward the respective axial cylinder end nearer to said piston unit and a smaller fluid flow resistance when the respective piston unit moves from the respective nearer cylinder end toward and beyond the beginning of said by-pass passage means, said by-pass passage means having such length and being located within said predetermined path of movement such that in a terminal position of both of said piston units adjacent a respective cylinder end nearer to said respective piston unit the respective other piston unit is located with its respective sealing engagement member within the axial extent of said by-pass passage means.