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1. A hydraulic shock absorber comprising:
a cylinder attached to one of a vehicle body side and an axle side; a piston rod attached to the other of the vehicle body side and the axe side and inserted into an oil chamber of the cylinder; a piston which is provided in a leading end portion of the piston rod and divides the oil chamber of the cylinder into a piston side oil chamber and a rod side oil chamber; and an oil reservoir chamber compensating a volumetric capacity of the piston rod moving forward and backward to the oil chamber of the cylinder, the oil reservoir chamber being communicated 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, the damping force generating device is provided with a compression side flow path which circulates the oil in the piston side oil chamber of the cylinder from an outer flow path of the cylinder toward the rod side oil chamber in a compression side stroke, 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, and an intermediate portion between the compression side damping valve and the compression side check valve in the compression side flow path is communicated with the oil reservoir chamber, the damping force generating device is provided with an extension side flow path which circulates the oil in the rod side oil chamber of the cylinder from the outer flow path of the cylinder toward the piston side oil chamber in an extension side stroke, 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, and an intermediate portion between the extension side damping valve and the extension side check valve in the extension side flow path is communicated with the oil reservoir chamber, and the damping force generating device is provided with a through-hole which communicates the piston side oil chamber of the cylinder with the rod side oil chamber of the cylinder via the outer flow path of the cylinder, a leading end portion of the piston rod is provided with a needle capable of coming in and out of the through-hole of the damping force generating device, and an opening degree of the through-hole is variable by the needle according to a forward and backward position of the piston rod with respect to the oil chamber of the cylinder, the damping force generating device is fixedly provided with first and second base pistons around a bolt, the first base piston is provided with a compression side flow path which is opened and closed by the compression side damping valve, and an extension side flow path which is opened and closed by the extension side check valve, the second base piston is provided with a compression side flow path which is opened and closed by the compression side check valve, and an extension side flow path which is opened and closed by the extension side damping valve, and the bolt is provided with the through-hole, wherein the cylinder consists of an outer tube and an inner tube, and
the damping force generating device is embedded by being inserted and attached into an inner periphery of each of lower ends of the outer tube and the inner tube of the cylinder, to form a valve unit in which the first and second base pistons are fixedly provided around the bolt. |
