The CVT (continuously variable transmission) is an automatic transmission that fills the demands of modern motor vehicles

The CVT system is increasing in application to automobiles

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
 Exhaust emission level in D mode

The conventional belt-type CVT system
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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