Damping force adjustable shock absorber

1. A damping force adjustable shock absorber comprising:

a cylinder sealingly containing hydraulic fluid therein;

a piston slidably and fittedly mounted inside the cylinder and partitioning an inside of the cylinder into two chambers, a one-side chamber and an opposite-side chamber;

a piston rod having one end coupled with the piston and an opposite end protruding out of the cylinder;

a first passage and a second passage establishing communication between the two chambers in the cylinder;

a first main valve configured to generate a damping force against a flow of the fluid in the first passage that is generated when the piston in the cylinder moves to one side;

a second main valve configured to generate a damping force against a flow of the fluid in the second passage that is generated when the piston in the cylinder moves to an opposite side; and

a control valve configured to be driven by a solenoid and control the damping force that is generated when the piston in the cylinder moves to the one side and the opposite side,

wherein the first main valve includes

a damping valve configured to generate the damping force by restricting the flow of the hydraulic fluid flowing via the first passage when the piston moves to the one side,

a back-pressure chamber configured to apply an inner pressure to the damping valve in a valve-closing direction, and

a back-pressure chamber introduction passage configured to introduce the hydraulic fluid from a chamber on an upstream side toward a back-pressure chamber side,

wherein the control valve includes

a tubular case member slidably containing a plunger configured to be driven by the solenoid therein, the tubular case member being opened on one end side thereof,

a valve seat member including an annular valve seat provided on a side facing the opening, the valve seat having an inner peripheral side in communication with the one-side chamber and the back-pressure chamber introduction passage and an outer peripheral side in communication with the opposite-side chamber,

an orifice passage provided between the outer peripheral side of the valve seat and the opposite-side chamber,

a unidirectional valve permitting a flow of the hydraulic fluid from the outer peripheral side of the valve seat to the opposite-side chamber,

the first main valve slidably provided in the case member and configured to control the flow of the hydraulic fluid by being separated from or contacting the valve seat, and

a valve body configured to be seated on an inner valve seat provided between an orifice passage at a bottom portion of the first main valve inside the case member and the one-side chamber, the valve body being configured to move according to the movement of the plunger,

wherein the damping adjustable shock absorber further includes

a tubular case member in which at least a part of the back-pressure chamber introduction passage is formed, the case member being provided on an outer peripheral side of the piston rod,

a deflectable annular disk disposed with the piston rod extending therethrough in the case member, the disk being supported on an inner peripheral side or an outer peripheral side thereof, the disk being provided with an annular elastic seal member sealing between the disk and the case member or between the disk and the piston rod, and

two chambers in the case member that are provided by being defined by the disk,

wherein the disk blocks at least a unidirectional flow through the second passage.