Research And Development Of VVT Mechanism For Small-medium Displacement Motorcycle Engine

In China, large proportion of motorcycle engine displacement is narrow in the range of Small-medium displacement(50ml～250ml), and much of motorcycle engine valve train structure is Single Over Head Cam (SOHC) structure. Fuel efficiency and power output and emission of an internal combustion engine can be significantly improved by VVT technology that has been widely used in motor engine. But there are no applications of VVT mechanism in small-medium displacement motorcycle engines base on SOHC valve train structure in virtue of the restriction of manufacture cost and structure complication. Variable valve timing (VVT) mechanism of switching cam profile was developed for the small-medium displacement motorcycle engines. The VVT mechanism which designs two intake cams, two intake rocker arms and a switching mechanism is able to make the engines set two series of valve timing parameters by switching cam profile according to the engine rotation speed and engine load. It has been proved by using the mechanism in JH125 motorcycle engine that the VVT mechanism is simple in structure, requiring less modification for the engines, having low cost for manufacture, and effectively realizing the variable control for valve timing to improve the engine performance. All of these make it possible to use the original mechanism for small-medium displacement motorcycle engine, and this mechanism has been applied practicality patent. The process is described through using the mechanism in JH125 motorcycle engine. Including the presentation of the general layout of VVT mechanism, structure features, design difficulties of typical parts, technological characteristic and material selection. And then, a new oil circuit extensional switch system and automatic switch control system according to motorcycle engine oil circuit system is put forward. Another is optimum design of cam profile, finite element analysis (FEA) of high-speed and low-speed rocker arm and multi-mass dynamic model simulation analysis that are carried out on valve train of VVT mechanism. The performance test of JH125 engine and function validation test of VVT mechanism are finished at engine test bench. The test result that has been obtained is proved to succeed. The design of VVT mechanism can guarantee both the preferable performance of whole engine and function property of general VVT mechanism.