The ECU in the control system determines the level of control current to apply to the linear solenoid incorporated in the damper, using inputs from the vehicle speed sensor. The linear solenoid is attached to the main valve, and alters the pressing force depending on the level of the control current determined by the ECU. The linear solenoid has been chosen because of its operation responsiveness during hard acceleration and deceleration, and for realization of linear damping characteristics in relation to changes to the current.

Construction
The damper body composes of the fluid chamber in that the vane splits the cavity and the hydraulic fluid passage filled with hydraulic fluid. The damper body is retained on the vehicle frame body, and the vane in the fluid chamber is linked to the steering system.

Operation
The steering stem and the vane have a common axis and turns at 1:1 ratio. As the vane turns, a flow of fluid from a side to another occurs, and the flow resistance at that time serves as a damping torque around the steering axis.

Hydraulic passage
To make the system compact and light in weight, the hydraulic passage is created three-dimensionally, with the main valve, check valve, relief valve and accumulator incorporated in the system.

The flow resistance changes depending on the angular velocity of the vane and the opening of the main valve. The opening of the main valve depends on the balance of two forces, i.e., the pressing force from the linear solenoid and the counter-acting force from the hydraulic pressure in the main valve.

Damping characteristics when no current (valve fully open)
When no current is applied, the spring in the valve keeps the main valve at the fully opened condition to ensure the targeted minimum damping force. The flow resistance of hydraulic fluid occurs mainly in the main valve, and increases depending on the steering angular velocity.
Damping characteristics when current occurs (valve fully closed)	Click the illustration to view an enlarged picture.
In the low steering angular velocity zone, as the counter-acting force from the hydraulic pressure is smaller than the pressing force of the linear solenoid, the main valve maintains the fully closed condition.

To realize fine and responsive damper control, the electronic control system has been employed. The ECU computes vehicle speed and acceleration by the signals from the vehicle speed sensor, and determines a linear solenoid control current using the three dimensional control map. The damping force is infinitely variable depending on the increase or decrease of control current.

Control map
At a low speed, the linear solenoid control current is lowered. The control current is increased depending on the increase of vehicle speed. When acceleration, the control current is increased depending on the acceleration rate, and when deceleration, the control current is set at the same level as in a constant speed.

3 major accomplishments through the development of HESD