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Development of Deviceless Tumble Enhancement Method for Small Motorcycles

Article of Honda R&D Technical Review Vol.32 No.2


Using the CFD and targeting at small motorcycles, we have pursued a technology that can enhance the tumble flow in the cylinder only in a low load range of the engine without the need to use any intake path switching mechanisms. In a throttle body with a butterfly valve, a reverse flow occurs after the intake air has passed the throttle valve when the throttle valve opening is small. We have confirmed that installing a flow separator behind the throttle valve that vertically divides the intake port flow can successfully capture the reverse flow into one of the two flow paths. Furthermore, we confirmed that optimizing the separator position can capture most of the intake air into one path, thereby gaining the required amount of flow that can generate tumble in the combustion chamber. Through the analysis of combustion pressure of an actual engine, we have confirmed that the combustion period in the low load range is shorter in the new design than in the conventional port design, which proves that the target tumble effect has been achieved. With the new design applied, the emission norms of EURO5 and India’s BS-VI are satisfied as well as improving the fuel economy of the motorcycle by 1.7% in the WMTC mode. For mass production, the separator is created as an integral part of the inlet pipe casting by incorporating a slit in the port core. This enables application of the new tumble port design without adding extra parts or modifying existing production equipment.


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Author (organization or company)

Makoto FUJIKUBO(Honda Motor Co., Ltd.)、Yohei NAKAMURA(Innovative Research Excellence Power Unit & Energy)、Yosuke INOUE(Innovative Research Excellence Power Unit & Energy)、Keigo KAMEDA(Honda Motor Co., Ltd.)、Hazuki HIDAKA(Honda Motor Co., Ltd.)、Hironobu OIKAWA(Honda Motor Co., Ltd.)