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Assessment and analysis by actual test run |
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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. |
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Need of a control system |
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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.
Relief
valve
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. |
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Control parameters |
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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. |
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