Hydraulic shock absorber

A hydraulic shock absorber comprising:

• a cylinder;
• a piston slidably inserted into the cylinder to partition the inside of the cylinder into an expansion-side chamber and a contraction-side chamber;
• an expansion-side passage and a contraction-side passage that connect the expansion-side chamber with the contraction-side chamber;
• an expansion-side valve body configured to open or close the expansion-side passage;
• a contraction-side valve body configured to open or close the contraction-side passage;
• an expansion-side back-pressure chamber configured to press an expansion-side spool abutting on the expansion-side valve body by virtue of an internal pressure, the expansion-side back-pressure chamber being configured to bias the expansion-side valve body to close the expansion-side passage;
• a contraction-side back-pressure chamber configured to press a contraction-side spool abutting on the contraction-side valve body by virtue of an internal pressure, the contraction-side back-pressure chamber being configured to bias the contraction-side valve body to close the contraction-side passage;
• a communicating channel that communicates with the expansion-side back-pressure chamber through an expansion-side resistance element configured to generate resistance to a passing liquid flow, the communicating channel communicating with the contraction-side back-pressure chamber through a contraction-side resistance element configured to generate resistance to a passing liquid flow;
• an expansion-side pressure introduction passage configured to permit only a liquid flow directed from the expansion-side chamber to the contraction-side back-pressure chamber;
• a contraction-side pressure introduction passage configured to permit only a liquid flow directed from the contraction-side chamber to the expansion-side back-pressure chamber;
• a regulating passage connected to the communicating channel;
• a contraction-side discharge passage that connects the downstream of the regulating passage with the expansion-side chamber, the contraction-side discharge passage being configured to permit only a liquid flow directed from the regulating passage to the expansion-side chamber;
• an expansion-side discharge passage that connects the downstream of the regulating passage with the contraction-side chamber, the expansion-side discharge passage being configured to permit only a liquid flow directed from the regulating passage to the contraction-side chamber;
• and
• a solenoid pressure control valve provided in the regulating passage to control a pressure in the upstream of the regulating passage,
• wherein, when a pressure of the expansion-side back-pressure chamber is equal to a pressure of the contraction-side back-pressure chamber, an expansion-side load for biasing the expansion-side valve body by virtue of the pressure of the expansion-side back-pressure chamber is larger than a contraction-side load for biasing the contraction-side valve body by virtue of the pressure of the contraction-side back-pressure chamber.