Shock absorber

1. A shock absorber, comprising:

a cylinder filled with a fluid;

a piston valve dividing the cylinder into a rebound chamber and a compression chamber;

a piston rod extending to the outside of the cylinder, and connected to the piston valve;

a free piston which

divides the rebound chamber into an upper chamber and a lower chamber, wherein the piston rod is configured to vertically pass through the free piston, and

forms a vertical passage, wherein the upper chamber and the lower chamber are connected to each other through the vertical passage; and

a support which

is disposed below the free piston,

is connected to the piston rod,

has a larger diameter than the piston rod,

is configured to increase a pressure of the upper chamber by approaching to the free piston from below during a rebound stroke of the piston rod, and

forms a horizontal passage connected to the vertical passage,

wherein the piston rod includes a locking groove disposed along a horizontal direction of the piston rod,

wherein the free piston includes a locking portion configured to move downward together with the locking groove during only compression stroke of the piston rod, and

wherein, when the locking portion moves downward, the locking portion is locked to and supported by the locking groove.

2. The shock absorber according to claim 1 , wherein the free piston further includes:

a hollow portion which vertically penetrates the free piston, wherein the hollow portion is connected to the piston rod;

an installation groove which is disposed inside the free piston, wherein the locking portion is positioned in the installation groove, wherein the installation groove is opened toward the hollow portion, and wherein the installation groove is locked to and supported by the locking groove; and

an orifice groove which has a concave shape, is disposed in a bottom surface of the free piston, and forms the horizontal passage while locally tightly contacting the support.

3. The shock absorber according to claim 2 , wherein the locking portion includes:

a locking member which is installed inside the installation groove, the locking member protruding toward the hollow portion, and having a protruding front end configured to be inserted into the locking groove; and

an elastic member configured to apply an elastic compression force between the locking member and the installation groove.

4. The shock absorber according to claim 3 , further comprising:

a guide protrusion which is disposed on an inner top surface of the installation groove, wherein the guide protrusion protrudes toward the hollow portion; and

a guide groove which is disposed in a top surface of the locking member, wherein the guide groove is paired with the guide protrusion for guiding the guide protrusion in a protruding and inserting direction.

5. The shock absorber according to claim 3 , wherein the locking groove and the front end of the locking member have flat top surfaces, and bottom surfaces inclined in opposite directions.

6. The shock absorber according to claim 1 ,

wherein the free piston and the support are configured to move upward, when the free piston and the support are contacted with each other during the rebound stroke of the piston rod, and

wherein the free piston and the support are configured to move downward, when the free piston and the support are separated from each other during a compression stroke of the piston rod.

7. The shock absorber according to claim 1 , further comprising:

a first stopper which is disposed at an upper end of the free piston, and

a second stopper which is disposed at a lower end of the support,

wherein the stoppers are configured to absorb shock at the time of collision.