Shock absorber

A shock absorber, comprising:

• a cylinder;
• a piston slidably inserted into the cylinder, the piston defining an expansion side chamber and an pressure side chamber inside the cylinder;
• a reservoir;
• a suction passage that allows only a flow of liquid from the reservoir toward the pressure side chamber;
• a rectifying passage that allows only a flow of liquid from the pressure side chamber toward the expansion side chamber;
• a damping force adjusting unit that allows only a flow of liquid from the expansion side chamber toward the reservoir, the damping force adjusting unit being configured to change resistance provided to the flow of liquid;
• a housing that includes a pressure chamber including a small-cross-sectional-area portion and a large-cross-sectional-area portion;
• a free piston that includes:
• a small-piston portion slidably inserted into the small-cross-sectional-area portion of the pressure chamber;
• and a large-piston portion slidably inserted into the large-cross-sectional-area portion of the pressure chamber, the free piston defining a small chamber inside the small-cross-sectional-area portion using the small-piston portion, the free piston defining an outer peripheral chamber in an outer periphery of the small-piston portion inside the large-cross-sectional-area portion, the free piston defining a large chamber inside the large-cross-sectional-area portion using the large-piston portion;
• a spring element configured to position the free piston in a center position of the pressure chamber, the spring element being configured to generate a biasing force to reduce displacement of the free piston from the center position;
• an expansion side passage that causes one of the small chamber and the outer peripheral chamber to communicate with the expansion side chamber;
• a pressure-side first passage and a pressure-side second passage that communicate between the large chamber and the pressure side chamber;
• a first valve disposed in the pressure-side first passage, the first valve being configured to allow only a flow of liquid from the large chamber toward the pressure side chamber while providing resistance to the flow;
• and
• a second valve disposed in the pressure-side second passage, the second valve being configured to allow only a flow of liquid from the pressure side chamber toward the large chamber while providing resistance of the flow.