1. Technical Field
The present invention relates to a damping force adjustable shock absorber mounted on, for example, a suspension apparatus of a vehicle such as an automobile.
2. Description of the Related Art
Generally, in a damping force adjustable shock absorber mounted on a suspension apparatus of an automobile, a piston coupled to a piston rod is slidably fitted in a cylinder sealingly containing oil, whereby the inside of the cylinder is divided into two chambers, and a damping force is generated by controlling an oil flow generated by a sliding movement of the piston in the cylinder with use of a damping force generating mechanism comprising an orifice, a disk valve and others. In addition, the damping force is adjusted by changing flow resistance of the damping force generating mechanism with use of, for example, a flow control valve or a pressure control valve.
As this kind of damping force adjustable shock absorber, for example, Japanese Patent Public Disclosure No. 2001-12534 discloses a shock absorber in which a back-pressure chamber is formed behind a disk valve serving as a damping force generating mechanism. In this invention, the back-pressure chamber is in communication with an upstream-side cylinder chamber through a fixed orifice, and also is in communication with a downstream-side cylinder chamber through a pressure control valve (solenoid valve).
Due to this configuration, it is possible to directly adjust flow resistance against an oil flow with use of the pressure control valve, and also possible to adjust a valve-opening pressure of the disk valve by adjusting the inner pressure of the back-pressure chamber, whereby it is possible to broaden the adjustable range of the damping force characteristics.
However, the damping force adjustable shock absorber as disclosed in Japanese Patent Public Disclosure No. 2001-12534 has the following drawbacks. For example, if the damping force adjustable shock absorber is mounted on a suspension control apparatus of a vehicle such as an automobile, and performs a damping force control by receiving a control signal from a controller according to a running condition of the vehicle, response delay may occur due to, for example, the inertia of the plunger of the pressure control valve (solenoid valve), leading to overshoot in the damping force control. In addition, abnormal noises may be generated due to self-excited vibration of the valve body of the pressure control valve.