Shock absorber

A shock absorber comprising:

• a cylinder in which a working fluid is sealed;
• a piston slidably provided in the cylinder and configured to divide a chamber in the cylinder into a first chamber and a second chamber;
• a piston rod connected to the piston and extending toward an outside of the cylinder;
• a first passage through which the working fluid flows out from the first chamber to the second chamber or from the second chamber to the first chamber, due to a movement of the piston;
• a first damping force generating mechanism provided in the first passage and configured to generate a damping force;
• a second passage provided separately from the first passage, and communicating with the second chamber;
• a second damping force generating mechanism provided in the second passage and opened to generate a damping force when a piston speed is lower than a piston speed at a time when the first damping force generating mechanism generates the damping force;
• a third passage provided separately from the second passage, and communicating with the second chamber;
• a fourth passage provided in the third passage, and communicating with the third passage;
• and
• a volume variable mechanism including
• a flexible disk which is operated by the working fluid flowing from the third passage, and
• a relief mechanism which opens after the flexible disk is operated and the second damping force generating mechanism is opened, and communicates between the third passage and the fourth passage, wherein:
• the flexible disk
• is bendable,
• is deformed before the second damping force generating mechanism is opened, and
• is formed with a communication hole configured to allow communication between the upstream side and the downstream side, at a position from an inner circumferential end portion to an outer circumferential end portion or at a position from the inner circumferential end portion to an outer diameter of the piston rod;
• the volume variable mechanism includes a biasing member configured to abut an end surface of the flexible disk and bias the flexible disk;
• and
• the relief mechanism is configured to open and close the communication hole of the flexible disk in accordance with a deflection amount of the flexible disk.