The Design Of Valve Train For T-GDI Engine

In an engine,the valve train is a very important components.The most important part of the valve train is the valve cam.The valve cam determines the movement of the valve and controls the intake and exhaust,which influence the performance,bsfc,emission and durability of the engine,etc.This paper firstly studied the development and trend of the valve train home and abroad.Based on the design theory of the valve train,a set of complete and practical design theory of the valve train is presented.An example is given to develop a valve train with a 1.5L displacement of GDI,turbocharged,and DVVT.Firstly,this paper analyzed the characteristics of various kinds of valve train.DOHC is used according to the aim engine performance requirement and working environment.The cam profile of the opening duration is equal velocity –equal acceleration equation and the working duration is high –order polynomial equation.The mathematical model is established according to the type of the selected line.And the mathematical model is created with software matlab.The engine performance simulation model is established by the software GT-Power,valve train dynamics simulation model is established by the software AVL-TYCON,which lay the foundation for subsequent design.Then,according to the performance requirements of the whole machine,through the comparison and analysis of the database,combined with the characteristics of the function,the initial input parameters are determined.The initial input parameters should be put into the matlab program design in order to design first-edition profile.The first-edition profile should be put in the AVL-TYCON simulation model to check power performance.At the same time,the valve timing phase of the first edition should be designed according to the database.First-edition profile is usually not the most optimal,so it needs further optimization.The optimization of the general type line is to optimize the four parameters of the working angle of the intake,the maximum of the intake air,the working angle of the exhaust gas and the maximum lift of the exhaust gas.In this paper,each parameter is obtained by taking the following five schemes.Due to too much combinations and test work,this paper creatively introduces the method of orthogonal experimental design of DOE.25 combinations are selected according to the orthogonal table and their results are analyzed.The influence °ree of every parameter on the performance of the engine is summarized and the parameters of the three type line alternative scheme are selected.Through the control of discovery and orthogonal table based on orthogonal DOE analysis,the three alternative schemes are not in the test which has been completed in 25 combinations,so the three alternative schemes need more detailed additional test.By comparing the test results,the parameters of the profile are determined,and the final cam profile is designed according to the final parameters.Timing is the key parameter that affects the performance of the engine.For the different performance requirements of high speed and low speed engine,the optimal timing is different.In this paper,a continuous intake & exhaust variable timing mechanism,namely DVVT,that is used to adjust the most reasonable gas distribution in different working conditions.Usually,the timing of DVVT is determined by the DVVT scanning test of the engine,but there are too much working conditions points need to be scanned which will take a lot of effort.In addition,the initial phase of the valve is to refer to the database for the preset,whether it is reasonable need further verification.In this pager,put the certain cam profile into the GT-POWER model,scanned the intake and exhaust timing phase in a wide range over actual sample,select the appropriate timing angle for the characteristics of working conditions,and determine the initial valve timing phase according to the selected timing angle range,and into the adjustment range exhaust VVT.Finally,this paper introduces the design of other parts in the valve train.Make sample part for all the design confirmed parts;assemble the sample part to the engine;put the engine on bench to test the performance.The performance test result meets the target performance of the engine.