Gas spring with two-stage damping

Claim 1

In a gas spring which includes a gas-tight cylinder containing a gas under pressure and a body of oil, a piston rod movable through a main seal adjacent one end of the cylinder, a piston on the rod subdividing the cylinder into variable volume tube and rod chambers, and a flow-restricting bypass passage communicating the tube chamber to the rod chamber through an opening at a location on the rod spaced axially from the rod side of the piston, the improvement comprising an annular oil cushion seal adjacent the seal end of the cylinder interposed between the cylinder and rod and spaced axially from the main seal to define with the main seal an oil cushion chamber, and a flow-restricting passage through the oil cushion seal communicating the rod chamber with the oil cushion chamber for permitting controlled flow of gas and oil from the rod chamber to the oil cushion chamber as the rod nears the fully extended position, thus to afford a second damping stage near the end of an operating stroke when the bypass passage opens to the oil cushion chamber and communication from the rod chamber to the tube chamber is via the oil cushion chamber and both flow-restricting passages in series.