Design Theory And Critical Technical Research On Variable Load Rate Reciprocating Internal Combustion Engine

The integration and collaboration of various technologies gradually become the inevitable trendfor vehicle reciprocating internal combustion engine(engine for short) development. If the engine loadrate is adjusted dynamically by using advanced engine technology according to specific workingcondition, it can stay in the range of optimum load rate, and the engine over-all performance at allspeed working conditions is expected to enhance. Based on the concept of variable load rate, the worldfamous auto companies have developed the engines with variable compression ratio, variabledisplacement and variable cycle etc. separately, which are unanimously approved by the industry andthe market. However, the domestic research on such area is almost blank, so research in this area haspractical and broad prospect. This paper designed a engine platform which combines both two-strokeand four-stroke working cycle, mainly focus on operating principle, design theory, parameteroptimization and feasibility test verification, which also lay a theoretical and experimental basis forself-developed high-tech advanced vehicle engine. The main research contents are as follows:A variable load rate engine(VLRE) which can combine the variable valve, variable compressionratio, variable displacement, variable cycle and HCCI combustion technology simultaneity is proposed.The VLRE working principle of different work cycle mode, variable compression ratio and variabledisplacement by applying thermodynamic cycle theory are analyzed, and finally determined the bestmode switch timing is near the compression top dead center. Based on the engine cycle powerfrequency and effective compression ratio concept respectively, the diversity of cycle power frequencyand the interdependence characteristics between VLRE variable compression ratio and variabledisplacement technology are analyzed. According to the ventilation theory for two-stroke engine,VLRE’s two-stroke mode (VLRE-T) top intake-side exhaust ventilation program is determined. Finally,the feasibility advantage of developing VLRE is analyzed.Based on the prototype Honda WH125-6, VLRE’s four-stroke mode (VLRE-F) performancesimulation model is built, and the best valve timing for VLRE-F in maximum torque speed is obtainedby using orthogonal test simulation. Using only seven engine parameters, a programmablemathematical model for getting the closed-form solution of two-stroke engine port parameters and valve timing is established. After initially identifying the cylinder exhaust port parameters and valvetiming of VLRE-T mode in design maximum power speed by programmable mathematical model, theparameters of cylinder exhaust port and valve timing are optimized again by using VLRE-T modeperformance simulation model.Based on different drive functions of each VLRE valve cam, the kinematics and dynamics modelsof VLRE distribution device are built up according to the dual mass equivalent model and cam valvedesign theory by using Excite_TD. During the cam profile optimization and design process, a programis written for the cam parameters calculation and indicators inspection in order to improve theefficiency of the access and adjustment of calculated parameters. Each VLRE cam profile is optimizeddesign base on the kinematics and dynamics models of distribution device.Variable distribution device overall design plan of VLRE is proposed, and the structural featuresand working principle of variable cam profile mechanism are analyzed. Using numerical transformationmodeling, the VLRE-T intake cam bimodal profile is worked out. Then the method of determining therelative position of multiple mounted cam each hump is studied base on the valve timing of VLRE, andthe driving forces of multiple mounted cam is analyzed during the mode switching process. By buildingthe three-dimensional virtual prototype of variable cam profile mechanism and carrying out multi-bodydynamics analysis, further validate the correctness and reasonableness of cam profile design.Based on the functional requirements of the VLRE camshaft drive mechanism, a drive mechanismscheme that the double-planetary gear train structure are used to realize the phase and speed ratiochanging at the same time is proposed. In order to identify the different configurations quickly andoptimize the reasonable VLRE camshaft drive mechanism program, the rough set theory and clusteranalysis were applied to do the type synthesis and classification research on mechanism schemes withthe target of realize the function, so as to find out those mechanism schemes which can meet theapplication requirements of VLRE.In order to achieve the best over-all performance at all speed, so as to optimize the designparameters of VLRE, the composite performance coefficient is proposed and constructed. Thestructural characteristics of the composite performance coefficient and the rating valuenon-dimensional method determined the parameter weight and non-dimensional results have noessential impact on effect of the evaluation, and its reasonableness is verified with examples calculationand the method of fuzzy matter element. Compared with the traditional engine over-all performance evaluation method, the method is not only computationally efficient, but also can evaluate and comparethe over-all performance at all speed under different engine types or different mode. Based on theCampbell diagram of composite performance coefficient, the valve timing of VLRE-T mode at allspeed are optimized, and the optimum shape, size dimension and position parameters of VLRE cylinderexhaust port are determined. Base on the optimal principle of composite performance coefficient andload rate, the two switching strategy of "over-all performance mode" and "economy mode" for VLRE’stwo operating mode are established respectively.According to the specific structure and layout characteristics of the prototype, VLRE bench testplatform is built up, and the testing program about VLRE distribution device is designed, theprocessing position of the cylinder exhaust port and the supercharger drive scheme are determined. Amethod for rapidly adjusting the valve timing of VLRE-T mode is found out based on the practice, andthe exhaust piping system with exhaust buffer function is designed, which can solve problems ofsmall-displacement engine exhaust back pressure is too high when bench test. Finally, the bench test ofWH125-6, VLRE-F mode and VLRE-T mode is carried out, the analysis result of test datademonstrated the feasibility of VLRE design idea.