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Development of Positive Crankcase Ventilation System of Four-stroke Engine for Small Motorcycles

Article of Honda R&D Technical Review Vol.16 No.2


In motorcycle engines, blow-by gas is generally introduced into intake system including air cleaner to decrease blow-by emission inside crankcase. There was concern in the previous system that some running conditions might shorten an interval of oil change. Those phenomena were caused by mixing of water or gasoline in the blow-by gas into engine oil. In order to control the phenomena, a new positive ventilation system of the crankcase was developed. In the new system, fresh air was introduced into the crankcase by pressure fluctuation in the crankcase. The fresh air ventilates the crankcase. Comparing to the previous system, the developed Positive Crankcase Ventilation system has decreased the density of the water and the gasoline contained in the engine oil: water by 73% and gasoline by 42%.


(1) Ishikawa, M.: The Crankcase Emission Control System of Automotive Engine, ENGINE THECHNOLOGY, Vol. 3, No. 6 (in Japanese)
(2) Murakami, H., Aihara, H.: Analysis of Mechanism Intermixing Combustion Products in Engine Oil, Transactions of The Japan Society of Mechanical Engineers (Edition B), Vol. 55, No. 519 (1989)
(3) Schwartz, S.E., Smolenski, D.J.: Development of an Automatic Engine Oil-Change Indicator System, SAE Paper 870403 (1987)

Author (organization or company)

Ryuji MORIYAMA(Asaka R&D Center)、Yuki MURAOKA(Asaka R&D Center)、Kazuo FUJIHARA(Asaka R&D Center)

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