Hydraulic shock absorber

1. A hydraulic shock absorber comprising:

a piston rod attached to one of a vehicle body side and an axle side, the piston rod being inserted into an oil chamber of a cylinder which is attached to the other of the vehicle body side and the axle side;

the oil chamber of the cylinder being comparted into a piston side oil chamber and a rod side oil chamber by a piston provided in a leading end portion of the piston rod; and

an oil reservoir chamber for compensating a volumetric capacity of the piston rod moving forward and backward with respect to the oil chamber of the cylinder, the oil reservoir chamber being in communication with the oil chamber of the cylinder,

wherein a damping force generating device is provided between the piston side oil chamber and the rod side oil chamber of the cylinder, including a bypass flow path communicating the piston side chamber of the cylinder directly with the oil reservoir chamber while bypassing the compression side damping valve and a damping force adjusting valve that is externally operated in the bypass flow path, in a valve piece that is fixed to the cylinder;

wherein a center plate is provided in the center along an axial direction of an outer periphery of the valve piece, and

wherein the compression side damping valve and the extension side check valve are provided on one side in the axial direction with respect to the center plate in the outer periphery of the valve piece, the extension side damping valve and the compression side check valve are provided on the other side, and a set of the compression side damping valve and the extension side check valve and a set of the extension side damping valve and the compression side check valve are arranged line-symmetric with respect to the center plate;

wherein in a compression stroke, a compression side flow path for circulating oil in the piston side oil chamber of the cylinder through only an outside flow path of the cylinder toward the rod side oil chamber is provided in the damping force generating device, a compression side damping valve is provided in an upstream side of the compression side flow path, a compression side check valve is provided in a downstream side thereof, and an intermediate portion between the compression side damping valve and the compression side check valve in the compression side flow path communicates directly with the oil reservoir chamber, and

wherein in an extension stroke, an extension side flow path for circulating oil in the rod side oil chamber of the cylinder through only the outside flow path of the cylinder toward the piston side oil chamber is provided in the damping force generating device, an extension side damping valve is provided in an upstream side of the extension side flow path, an extension side check valve is provided in a downstream side thereof, and an intermediate portion between the extension side damping valve and the extension side check valve in the extension side flow path communicates directly with the oil reservoir chamber;

wherein the damping force generating device utilizes a compression side laminated disc valve as the compression side check valve provided in a downstream side of the compression side flow path, the compression side laminated disc valve provided with a compression side damping force generating means.

2. The hydraulic shock absorber according to claim 1 , wherein the damping force generating device utilizes an extension side laminated disc valve as the extension side check valve, the extension side laminated disc valve provided in a downstream side of the extension side flow path provided with an extension side damping force generating means.

3. The hydraulic shock absorber according to claim 1 , wherein the damping force generating device includes an extension side damping force generating means provided by the extension side check valve in the downstream side of the extension side flow path.