Development of a closed crankcase system engine for motorcycles

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Development of a closed crankcase system engine for motorcycles

Kudo, O. / Shimura, Y. / Terada, K. / Inumaru, N.

A large-displacement single cylinder engine requires a large-volume breather chamber to assure the breather performance. The authors developed a new engine with a bulkhead separating the crank chamber and the transmission chamber. The pressure fluctuations in the crankcase that are caused by the reciprocating motion of the piston are accomodated within the crankchamber by using a bulkhead between the crank chamber and transmission chamber. In this paper the construction and action of the closed crankcase system are outlined: - construction, - oil discharge action, - verification of pumping loss, - verification of reduced pressure fluctuations in the transmission chamber. The effects of the closed crankcase system engine were studied by using a conventional engine without the bulkhead between the crank chamber and transmission chamber, and also by comparison test of the pressure fluctuation. The following effects were obtained: 1. By reducing the pressure fluctuation, the breather chamber volume was reduced by 80 % and breathing performance was enhanced. A dry sump lubrication system could be applied and scavenging performance was enhanced. 2. By stabilizing the oil level in the crankcase, the friction loss of oil was reduced, and the pumping loss was reduced compared with a conventional crankcase.