Abstract: A gas spring 20 having a piston 23 slidably disposed within a cylinder 21 sealed with air 25, with one end of the cylinder closed, having a rod 22 fixed to the piston 23, having cylinder grooves 29 extending in an axial direction of the cylinder formed on the inner periphery of the cylinder so that an extension side damping force is generated in an extension process in the cylinder grooves, and having one end of the cylinder and the rod fitted to a vehicle body with the other end fitted to a rear door pivoted on the body, wherein the cylinder grooves are formed in both-side movable areas X and Z excluding a locking area Y in a stroke area of the piston.

Abstract: There is provided a gas spring 20 in which: a cylinder groove 29 is formed on an inner surface of a cylinder 21 with a piston 23 therein, the piston 23 being fixed at one end of a rod 22 and the cylinder groove 29 extending in an axial direction of the cylinder throughout the range of piston stroke except an area near a stopper 30; and an airlock chamber is definable nearby the stopper of the cylinder so that damping operation can be performed when being fully extended at the end of the extending phases, the piston being formed of a porous material to communicate air between chambers provided at both sides of the piston.

Abstract: There is provided a gas spring 20 in which: a cylinder groove 29 is formed on an inner surface of a cylinder 21 slidably arranging a piston 23 therein, the piston 23 being fixed at one end of a rod 22 and the cylinder groove 29 extending in an axial direction of the cylinder throughout the range of piston stroke except an area nearby a stopper 30; and an airlock chamber is definable nearby the stopper of the cylinder so that damping operation can be performed when being fully extended at the end of the extending process, characterized in that the cylinder groove is a square groove having a substantially square cross section with a constant groove width W and a groove depth H gradually reduced toward an area nearby the stopper.