Hydraulic shock absorber

A hydraulic shock absorber comprising:

• a cylinder;
• a first support member at a first end portion of the cylinder;
• a cover member that closes a second end portion of the cylinder;
• a main piston rod slidably extending through the first support member;
• a sub piston rod positioned on a same axis as that of the main piston rod, and connected to a first end portion of the main piston rod which is positioned inside the cylinder;
• a pipe arranged in the cylinder in a state in which the pipe is positioned on the same axis as that of the main piston rod and the sub piston rod, and including a first end portion fixed to the cover member and a second end portion into which a distal end portion of the sub piston rod is inserted;
• a second support member fixed to the second end portion of the pipe, and including an outer circumferential portion having a diameter larger than a diameter of the pipe, fitted on an inner circumferential surface of the cylinder, and further including an inner circumferential portion which slidably supports the distal end portion of the sub piston rod;
• a piston slidably fitted in the cylinder in a state in which the piston is fixed between the main piston rod and the sub piston rod, and defining a first oil chamber between the piston and the first support member and a second oil chamber between the piston and the second support member;
• a free piston slidably fitted between the pipe and the cylinder such that the pipe extends through the free piston, and defining a third oil chamber between the free piston and the second support member and a gas chamber between the free piston and the cover member;
• a first hydraulic oil passage that communicates the first oil chamber with the second oil chamber;
• a valve in the first hydraulic oil passage;
• and
• a second hydraulic oil passage in the second support member such that hydraulic oil is able to freely pass, and communicates the second oil chamber with the third oil chamber;
• wherein
• the first oil chamber, the second oil chamber, and the third oil chamber are filled with the hydraulic oil;
• the gas chamber is filled with a gas having a pressure which pushes the free piston toward the second support member;
• a closed space in the pipe;
• an outer diameter of a sliding portion of the main piston rod differs from an outer diameter of a sliding portion of the sub piston rod;
• and
• a total cross-sectional area of the second hydraulic oil passage is not less than a difference between a cross-sectional area of the sliding portion of the main piston rod and a cross-sectional area of the sliding portion of the sub piston rod.