Structural Optimization And Experimental Verification Of Variable Length Connecting Rod And Variable Compression Ratio Mechanism

Variable Compression Ratio(VCR)technology can use a higher compression ratio to improve the low thermal efficiency and poor overall performance of the engine under small load conditions,and reduce the compression ratio to adapt to the working conditions at high load and full load.,Prevent the engine from producing abnormal conditions,and achieve a good unification of the economy,power and emissions of the internal combustion engine.In this paper,based on the existing research in this direction in the laboratory,the engine connecting rod is designed to change its length to change the engine compression ratio.This article uses the Changchai ZS1100 engine connecting rod as a test prototype,and proposes a variable-length connecting rod mechanism scheme.Compared with the previous scheme in the laboratory,the scheme in this article cleverly uses a doublethreaded drive shaft as the transmission mechanism.The upper and lower reverse threads can achieve more up and down.The double-stage reverse thread structure design can realize more rapid change of the connecting rod length,and realize the rapid change of the connecting rod length by changing the compression ratio.This paper selects the more reliable ZGX17 RU planetary DC geared motor as the power source of the mechanism.According to the size of the motor,the size of the original machine connecting rod and the crankshaft,the size of each part of the variable-length connecting rod is designed,and the change in the length of the connecting rod and the compression ratio are calculated theoretically.Use CATIA to model the variable-length connecting rods in three dimensions.This paper uses ANSYS Workbench finite element simulation platform to carry out static strength analysis and transient dynamics analysis of variable length connecting rods.Through static strength analysis,the stress and stress of variable length connecting rods under maximum compression conditions and maximum tension conditions are analyzed through static strength analysis.For deformation,optimize the plan based on the simulation results.After the optimization,the stress and deformation of the simulation results meet the design requirements for further verification.The crank-connecting rod mechanism model is established,and the transient dynamics analysis method is applied to analyze the length of the two cycles.For the change of connecting rod stress,the time when the maximum stress occurs in the second cycle is selected for analysis,and the variable-length connecting rod scheme meets the strength requirements.The stress change of the angle-variable-length connecting rod near the top dead center of the work stroke is analyzed to verify the accuracy of the simulation calculation results.In order to further verify the feasibility of the variable length mechanism,a variable compression ratio engine test bench was built,and the ignition test and the reverse towing test were carried out.The towing test data showed that the program was indeed more responsive than the previous mechanism in the laboratory.But it did not reach the theoretical double;the ignition test verified that the variable-length connecting rod did indeed change the length of the connecting rod to achieve a change in the compression ratio when the pressure in the ignition cylinder increased dramatically.