Study On Single Overhead Camshaft Engine VVT Institutions

As one of the important parts of the car engine valve mechanism plays a decisive role in the work cycle of the engine. The valve timing of the traditional valve mechanism can’t be changed, which is used in all kinds of working conditions and selected from various experiments of valve timing and is compromise proposal of engine performance. In order to keep the engine inlet performance under various speed, the design of the valve mechanism has become one of the core of the engine design technology at home and abroad. Motorcycle engine’s speed range is much bigger than the car’s. For high speed and low speed conditions, Its differences of requirements is much larger than the car engine’s, so the use of fixed valve timing in the entire speed range of the engine exposes some disadvantages. Compared with the car engine, there is more pressing need variable valve technology to improve the comprehensive performance. Traditional variable valve system adopts hydraulic drive way, but there are no applications of VVT mechanism in motorcycle engines in virtue of the restriction of manufacture cost and structure complication.Jinan Qingqi K157model motorcycle engine is used for the research object, a moving rocker shaft Variable valve mechanism is developed. By moving Rocker arm shaft, It is to achieve high low-speed rocker meshing and separating, And then To realize working cam’s conversion between high speed cam and low speed cam, In order to meet the needs of the engine under different conditions. Realize the best Vale Timing in various conditions. Improve power and economy and emissions performance. Finally promote the pace of application of VVT technology in the Small-medium Displacement Single Over Head Cam (SOHC) Motorcycle Engine. The completed works as follows:Firstly, complete the design work of VVT mechanism. The paper emphasis on introducing the overall layout and the role of main components and working prinking of the moving rocker shaft variable valve mechanism. By the means of the description of the relevant issues in the high and low speed rocker meshing process and the meshing time calculation, the feasibility of the moving rocker shaft variable valve mechanism is verified theoretically. From the following three aspects:the air intake rocker arm shaft can move smoothly, high low-speed rocker would be able to mesh and high speed rocker can cling to high speed cam, the feasibility of the moving rocker shaft variable valve mechanism is verified theoretically.Secondly, one dimensional flow simulation model of K157engine is set up with the BOOST according to the basic theory of internal combustion engine cycle simulation and the structure characteristics of K157engine. K157engine model parameters are set up. The results of torque, power and fuel consumption rate through the simulation calculation under throttle ajar condition compare with measured data of the original machine, in order to verify the correctness and reliability of the simulation model.Thirdly, VVT engine BOOST model is established on the basis of the original engine model. By the simulation calculation result of the model under different valve timing, the best valve motion law of the VVT engine model is determined. By the comparison of torque, power and fuel consumption rate of VVT engine through the simulation calculation and the measured values of the original engine, power Performance and fuel economy of VVT engine are improved in the entire speed range of the engine. Especially under the medium and low speed conditions that engines commonly used, the improvement of the engine power and economy Performance is particularly evident. The use of the VVT mechanism achieves the desired effects.Finally, do meshing performance and intake performance experimental research on VVT engine. It is to verify high low-speed rocker arm can mesh and separate smoothly within appropriate crank angle and measure charging efficiency of the VVT engine under various working conditions. Compare the charging efficiency of VVT engine with the original engine’s. Results show charging efficiency of VVT engine are improved within the high-low speed compared with the original machine and increase obviously under medium and low speed conditions.