Valve structure of shock absorber

1. A valve structure of a shock absorber which includes a piston dividing an interior of a cylinder filled with a fluid into a compression chamber and a rebound chamber in a state of being coupled to one end of a piston rod, and having main channels and compression channels formed outside the main channels, the valve structure comprising:

an upper disc valve which is in close contact with an upper surface of the piston and is opened by pressure of a fluid discharged to an outlet side of the compression channels during a compression stroke to generate a damping force;

a lower disc valve which is in close contact with a lower surface of the piston and is opened by pressure of a fluid discharged to an outlet side of the main channels during a rebound stroke to generate a damping force; and

an auxiliary disc valve which is in close contact with a lower portion of the lower disc valve and is opened sequentially when the lower disc valve is opened, to generate a damping force,

wherein a rebound-side stepped portion continuously protrudes along the outside of the main channels on the upper surface of the piston to support an edge of the upper disc valve,

a compression-side inner stepped portion continuously protrudes along the outside of the main channels on the lower surface of the piston to support the lower disc valve, and

a compression-side outer stepped portion continuously protrudes along a space between the compression-side inner stepped portion and the compression channels on the lower surface of the piston to support the auxiliary disc valve, and

the compression-side outer stepped portion is arranged radially inward of an exit port of the compression channels.

2. The valve structure of claim 1 , wherein the compression-side outer stepped portion protrudes downward so as to be longer than the compression-side inner stepped portion.

3. The valve structure of claim 1 , wherein each of the compression channels consists of a long hole so as to have a length in a circumferential direction of the piston.

4. The valve structure of claim 1 , wherein rebound-side support protrusions protrude at set intervals along a space between the rebound-side stepped portion and the compression channels on the upper surface of the piston, and support the edge of the upper disc valve in a state of being spaced apart from each other.

5. The valve structure of claim 4 , wherein each of the rebound-side support protrusions protrudes in a circular shape such that an edge thereof forms a circumference.

6. The valve structure of claim 4 , wherein each of the rebound-side support protrusions protrudes in a tapered shape such that a diameter thereof is gradually decreased toward an upper portion thereof.

7. The valve structure of claim 4 , wherein, when the edge of the upper disc valve deviates from the rebound-side stepped portion by a set length or more, the rebound-side support protrusions support the edge of the upper disc valve.

8. The valve structure of claim 4 , wherein the upper disc valve includes an intake disc of which an edge is supported by the rebound-side stepped portion and the rebound-side support protrusions, and which has a plurality of first through-holes such that a fluid of the rebound chamber is moved to an inlet side of the main channels during the rebound stroke,

a rebound-side retainer which is in close contact with an upper surface of the intake disc,

an intake spring which is in close contact with an upper surface of the retainer and has a plurality of support portions protruding along an edge thereof and elastically and downwardly supporting the intake disc, and

a rebound-side washer which is in close contact with an upper surface of the intake spring and has second through-holes such that the fluid of the rebound chamber is moved to an inlet side of the first through-holes.

9. The valve structure of claim 1 , wherein the lower disc valve includes a first lower disc which is in close contact with the lower surface of the piston and has a plurality of slits formed along an edge thereof,

at least one second lower disc which is in close contact with a lower surface of the first lower disc, and

a first compression-side retainer which is in close contact with a lower surface of the second lower disc, and

wherein the auxiliary disc valve includes a first main disc which has a diameter greater than that of the first lower disc, is in close contact with a lower surface of the compression-side retainer and of which an edge is supported by the compression-side outer stepped portion,

at least one second main disc which is in close contact with a lower surface of the first main disc,

at least one sub disc which is in close contact with a lower surface of the second main disc,

a second compression-side retainer which is in close contact with a lower surface of the sub disc, and

a compression-side washer which is in close contact with a lower surface of the second compression-side retainer.

10. The valve structure of claim 1 , wherein each of the rebound-side stepped portion, the compression-side inner stepped portion, and the compression-side outer stepped portion protrudes in a tapered shape such that a diameter thereof is gradually decreased toward an upper portion thereof.