Cylinder apparatus

1. A cylinder apparatus comprising:

a cylinder body including

a seal groove provided in a cylinder bore,

a cup seal fitted into the seal groove, and

a piston slidably inserted into the cylinder bore, wherein

the cup seal includes

a base portion having a base end surface opposing an opening-side-surface of the seal groove,

an inner circumferential lip portion having an inner circumferential surface slidably abutting against an outer circumferential surface of the piston,

an outer circumferential lip portion having an outer circumferential surface abutting against a bottom surface of the seal groove,

an abutment portion provided on the base end surface of the base portion of the cup seal, and

a contact pressure adjustment portion provided on the base end surface of the base portion, and

the contact pressure adjustment portion does not contact with an inner circumferential side of the opening-side-surface of the seal groove in a state where the cylinder apparatus is in a non-operational state, and contacts with the inner circumferential side of the opening-side-surface in a state where the cylinder apparatus is in an operational state.

2. The cylinder apparatus of claim 1 , wherein

the seal groove has a seal groove opening opened to a piston side,

the seal groove opening is closer to an inner circumference than the abutment portion on the base end surface, and

the contact pressure adjustment portion is provided on a seal groove opening side to extend across an entire circumference of the cup seal.

3. The cylinder apparatus of claim 1 , wherein

the seal groove includes

the seal groove bottom surface positioned between a bottom-side-surface and the opening-side-surface, and

a seal groove opening opened to a piston side.

4. The cylinder apparatus of claim 3 , wherein

the seal groove bottom surface extends in a circumferential direction,

the bottom-side-surface is on a cylinder bore bottom portion side, and

the opening-side-surface is on a cylinder bore opening portion side.

5. The cylinder apparatus of claim 4 , wherein the base portion is disposed on the cylinder bore opening portion side of the seal groove.

6. The cylinder apparatus of claim 1 , wherein the outer circumferential lip portion extends from an outer circumferential side of the base portion toward a bottom portion of the cylinder bore.

7. The cylinder apparatus of claim 1 , wherein the abutment portion is protruded from the base end surface of the base portion of the cup seal toward a cylinder bore opening portion so that a protruded end thereof abuts with the opening-side-surface of the seal groove.

8. The cylinder apparatus of claim 7 , wherein the contact pressure adjustment portion is provided on the base end surface of the base portion of the cup seal at a position closer to an inner circumference than the abutment portion.

9. The cylinder apparatus of claim 8 , wherein the abutment portion is provided at a position closer to an outer circumference than an extended base end portion of the inner circumferential lip portion.

10. The cylinder apparatus of claim 1 , wherein the contact pressure adjustment portion is a surface in which a distance between the surface and the opening-side-surface of the seal groove gradually becomes large toward an inner circumferential side from the abutment portion.

11. The cylinder apparatus of claim 1 , wherein the contact pressure adjustment portion is a conical surface which intersects a cylindrical surface of the cylinder bore at an acute angle.

12. The cylinder apparatus of claim 1 , wherein the abutment portion has an abutment surface brought into surface contact with an outer circumferential side of the opening-side-surface.