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The CVT (continuously variable transmission) is an automatic transmission that fills the demands of modern motor vehicles
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The CVT system is increasing in application to automobiles |
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As global environmental concerns becoming more critical
than ever, the demands for clean exhaust gas and fuel economy
are growing steadily even in the world of motorcycles. Also,
to enhancement the quality of riding, voices requesting a
decrease in noise are increasing. Unfortunately, those demands
are factors that require compromising of the driving performance.
What Honda engineers chose was the development of a transmission
that transmits the engine power more efficiently to the road
via the tire.
The CVT, which is recently drawing more attention in the world
of automobiles, is a system that continuously varies the reduction
ratio by changing the pulley ratio in the input side and in
the output side. Compared to the conventional transmission
that uses a fixed gear ratio, the CVT allows easy presetting
of the shifting characteristics to best-match the characteristics
of the engine used in the vehicle including factors such as
the power output, emissions, etc., thereby allowing use of
the cleanest zone and the most powerful zone when running.
While a metal belt is usually used in automotive transmission
systems, in Honda S Matic, a rubber belt is applied because
of its potential to reduce weight at a low cost.
 Exhaust
emission level in D mode |
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The conventional belt-type CVT system |
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In motorcycles, the belt-type CVT, which excels in the balance of weight, performance and cost, has been used for a long
time predominantly in scooters for the purpose of easy driving. In conventional belt-type CVT, the centrifugal force of the
weight rollers in the drive pulley located on the crankshaft acts on the ramps and presses the moveable drive face against
the drive belt in the axial direction. The belt-pitch diameter on each pulley changes depending on the balance between the
above-mentioned side force in the drive pulley and the side force in the driven pulley that occurs from the spring load and
the torque cam that detects the driving force of the rear wheel causing the reduction ratio to change. However, as the shift
characteristics are determined solely by mechanical factors, it is difficult to liberally adjust the reduction ratio for each
level of throttle opening to attain the best balance of clean exhaust gas, fuel economy, quietness and driving performance.
Also seen is such a phenomenon that as the belt wears over time, the pitch diameter becomes smaller in the drive side and
larger in the driven side, resulting in a loss of maximum speed due to a change in the reduction ratio. |
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