Browse Publications Technical Papers 2019-32-0523
2020-01-24

Optimum Design of an Assist Mechanism for a Motorcycle Multi-Plate Clutch 2019-32-0523

In recent years, the popularity of leisure-motivated large motorcycles has increased as the demand for high-added value motorcycles is growing. Therefore, large motorcycle engines have become more powerful. Due to this trend, the capacity of the clutch is also required to increase. Contrary to the demand for high engine power and high clutch capacity, reductions in weight, space, operational load, and shock at deceleration are permanent issues of motorcycle development. The consideration of all these issues are required during development of a clutch for large motorcycles. Considering the above issues, a clutch with an assist cam and slipper cam mechanism is effective for cost and performance. The assist cam mechanism allows the clutch to have a larger transmittable torque without an increase of the clutch lever load. The slipper cam mechanism can automatically reduce the transmitted torque when shock from sudden engine braking happens during downshifting. Therefore, the installation of the clutch with cam mechanism on large motorcycles is becoming standard in the motorcycle industry. Regarding smaller motorcycles, the reduction of the number of clutch discs can be realized by adopting an assist mechanism, which enables reductions in weight, space, and the operational amount of the clutch lever. On the other hand, the riding experience while operating a clutch with assist mechanism is considered to be unfavorable compared with a conventional non-assist clutch mechanism; a phenomenon which is anticipated to occur based on the assist mechanism structure and confirmed with our evaluations. This paper focuses on the clutch assist mechanism, specifically the development of the basic theory of a cam to make it applicable for a motorcycle assist clutch and prove the validity of the theoretical formula with test results. The results clarified an efficient setting range of the cam shape of the assist mechanism for the clutch. Furthermore, the practical range of the cam shape was determined to ensure proper operator comfort. From this research, we achieved the optimum design of the assist clutch, which enables comparable riding experience to the conventional non-assist clutch but with all the benefits that the assist mechanism brings.

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