|Assessment and analysis by actual test run|
The development team started a challenge to indicate in numbers the light-effort handling (steering effort) and the front end shake from kickback. Analyzing the handling characteristics at low speeds and the front end shake from kickback at high speeds, the development team then determined target damping characteristics. What the damping force should be for light-effort handling? What the damping force should be to reduce front end shake from kickback? The answer is the development of an unprecedented steering damper that allows altering of the damping force by an electronic control system depending on the running conditions.
|Need of a control system|
|After repeating various tests, it was clarified
that the damping force of a steering damper has to be altered
depending on the requirements. While some conventional steering
dampers permit damping force adjustment by a manual operation,
the development team set the goal at realization of an optimum
damping force in any running conditions. To accomplish the goal,
a new challenge began toward the world’s first system
having an automatic control system employing electronic control.
Target minimum damping force
The light-effort handling is attainable by choosing a small damping force from the hydraulic steering damper. The development team increased the damping force of the steering damper step by step, tested and analyzed the results, and determined the damper characteristics
Target maximum damping force
To reduce front end shake from kickback at high speeds, a steering damper that offers a large damping force is required. The development team increased the damping force of the steering damper step by step, tested and analyzed the results, and determined the damper characteristics for effective reduction of front end shake from kickback. As the damping force is increased, the front end shake decreased. It is found more effective to apply a large damping force from where the steering angle and the steering angular velocity are low.
If the damping force is increased in accordance with the increase of steering angular velocity with the target maximum damping force maintained constant, the pressure in the damper will become high, resulting in a large-size equipment. It is, however, clarified that if an appropriate damping force can be provided from the low steering angular velocity zone, the front end shake from kickback can be adequately reduced even with a small damping force. Accordingly, by incorporating the relief valve that permits controlling of the relief pressure, and relieving the pressure above the prescribed level, the optimum size and specifications of the damper unit has been attained.
|When a steering damper is equipped, the rider feels that the steering is heavy, more noticeably at low speeds. It is because when the speed is low, the rider has to use more positive steering inputs. Consequently, the steering angular velocity increases. On the other hand, the front end shake from kick back tends to occur more often at a high speed or during acceleration. Such a phenomenon occurs because the higher the speed, the more load is applied to the steering system in the direction of travel, and the load on the front tire is low during acceleration. Considering these factors, the development team applied such principles into the control map that “reduce damping force at low speeds for light-effort steering”, “increase damping force to reduce front end shake at high speeds or during acceleration”, using the vehicle speed and the acceleration as the control parameters of the damping characteristics.|