Shock absorber

1. A shock absorber comprising:

a shock absorber body composed of an outer tube and an inner tube going into and out of the outer tube, the shock absorber body being interposed between a vehicle body on a vehicle body side and a wheel on a wheel side;

a cylinder connected to the wheel side and standing in a shaft center portion of the shock absorber body;

a liquid chamber formed in the cylinder and filled with an operating liquid, the liquid chamber including first and second sides in which the first side is disposed closer to the vehicle body side than the second side;

an annular rod guide fixed to the cylinder and closing the first side of the liquid chamber;

a piston rod connected to the vehicle body side, penetrating a shaft center portion of the rod guide, and going into and out of the cylinder;

an annular seal member held on an inner periphery of the rod guide and in sliding contact with an outer peripheral surface of the piston rod;

an upper-side relief portion formed on an outer periphery of the piston rod and forming a gap between the piston rod and the seal member when the piston rod retreats from the cylinder by a predetermined amount;

a free piston in sliding contact with a portion, on a side opposite to a piston rod side, of an inner peripheral surface of the cylinder, the free piston closing the second side of the liquid chamber;

an urging means adapted to urge the free piston to a side of the liquid chamber;

an extension-side damping valve provided between the piston rod and the free piston;

a compression-side damping valve provided between the piston rod and the free piston; and

a lower-side relief portion formed on an inner periphery of the cylinder and forming a gap between the free piston and the cylinder when the free piston moves to the wheel side by a predetermined amount.

2. The shock absorber according to claim 1 , wherein the upper-side relief portion includes a slope portion having a diameter gradually reduced toward the wheel side in an axial direction of the piston rod.

3. The shock absorber according to claim 1 , wherein the upper-side relief portion is set to form the gap when only a vehicle body load is applied.

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

an annular bush fitted in an inner periphery of the rod guide and in sliding contact with the outer peripheral surface of the piston rod, wherein

the bush is arranged in series with the seal member from a side opposite to a cylinder side; and

in the rod guide, a lateral hole opened on an outer side of the cylinder and opened between the seal member and the bush is formed.

5. The shock absorber according to claim 4 , wherein

the rod guide includes an insertion portion inserted into the cylinder and a protrusion portion continuing to the insertion portion and protruding from the cylinder; and

the lateral hole is formed along a radial direction of the protrusion portion.

6. The shock absorber according to claim 1 , wherein in the cylinder, a communication hole penetrating the lower-side relief portion is formed.

7. The shock absorber according to claim 1 , wherein the lower-side relief portion is a large inner-diameter portion formed such that an inner diameter of the large inner-diameter portion is larger than an inner diameter of another portion of the cylinder.

8. The shock absorber according to claim 1 , wherein the extension-side damping valve is an extension-side check valve.