Shock absorber including thermostatically controlled fluid flow passage

Claim 1

A hydraulic shock absorber, comprising a cylindrical casing having an inner diameter enclosing a working chamber containing a hydraulic fluid, and a piston adapted to reciprocate in said working chamber, said piston including a piston rod and a cylindrical piston head connected to said rod, the hydraulic fluid being adapted to pass between opposite sides of said piston head during the reciprocation, a non-metallic ring surrounding the peripheral wall of said piston head, said ring comprising a material selected from the group consisting of a flourine-based resin, an acetal resin or a polyamide, said piston head being devoid of any permanent flow passages within the area delimited by said peripheral wall, said head comprising a material having a first coefficient of expansion, and said ring material having a coefficient of expansion higher than said first coefficient of expansion, circular flanges at said opposite sides of said piston head extending radially outwardly of said peripheral wall and having outer diameters slightly less than said inner diameter, said ring being discontinuous by having at least one pair of opposed free ends having parallel related walls extending in the direction of the longitudinal axis of said casing and being spaced a predetermined distance apart, said ring throughout its entire length extending radially outwardly of said flanges, said ring having an outer diameter which is slightly less than said inner diameter of said casing for solely insuring smooth reciprocating movement of said piston without defining any annular passage through which the fluid may pass between said opposite sides of said piston, at least one permanent open passage being located outwardly of said peripheral wall of said piston head through which fluid solely passes in permanent flow relation between said opposite ends of said piston to thereby control the dampening effect during reciprocation of said piston, said passage being delimited by said parallel walls, said outer diameters of said flanges, and said inner wall of said casing, and the space between said parallel walls varying with change in temperature of said ring to thereby solely change the size of said passage and to control the dampening effect.