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The world’s first,* electronically controlled steering damper “HESD” automatically controls the damping force depending on the vehicle speed and the acceleration.For more exciting riding, higher performance and more comfort, Honda has developed the world’s first electronically controlled hydraulic steering damper called “HESD (Honda Electronic Steering Damper)”. To constantly obtain an optimum damping force, Honda has employed the world’s first electronic control system based on the rotary-type hydraulic damper applied to the RC211V MotoGP machine. Using race tracks to improve the design, a steering damper that enhances “sure-footed” feeling at high speeds while maintaining the light-effort handling at low speeds was developed. Such steering damper characteristics are not attainable from conventional mechanical-type steering dampers.
The HESD controls the damping force at an optimum level by means of the electronic control system depending on the vehicle speed and the acceleration. With the sensors detecting vehicle speed and acceleration, and the ECU controlling the damper, the HESD allows light-effort handling at low speeds, while at high speeds, it reduces front end shake triggered by a kickback from the road, thus realizing confidence-inspiring handling characteristics. The system has reached to such a level that the functioning of HESD is so natural that the presence of the steering damper is almost unnoticeable for the rider. The HESD ensures good handling not only in sporty riding, but also in a variety of riding conditions, and contributes to the reduction of rider fatigue after a high-speed, long distance run, etc. Honda has applied the HESD to the new super-sport motorcycle CBR1000RR, which inherits the DNA of the RC211V.

HESD : Honda Electronic Steering Damperaaa*According to Honda’s research

System and damper configuration

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.

Internal construction of HESD

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.Main valve: Alters flow resistance depending on the valve opening. Check valve: Allows flow of fluid only in one direction into the main valve. Relief valve: Located in the fluid passage parallel to the main valve, this valve restricts the maximum damping force. Accumulator: For stabilization of hydraulic pressure in the damper when the fluid volume changes due to temperatures.

Control of damping force

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.

Electronic control system

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.

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