Design Of Variable Compression Ratio Mechanism Based On Electrically Driven Variable Length Connecting Rod

Variable Compression Ratio(VCR)technology is a cutting-edge technology that improves engine power,economy,and emissions.Through the study of domestic and foreign variable compression ratio mechanism,this paper chooses engine connecting rod as the research object,and the variable compression ratio is realized by changing the length of connecting rod.The variable compression ratio mechanism design is proposed in this paper is based on a single cylinder diesel engine,ZS1100,and the invention patent "A variable length connecting rod driven by built-in motor".The plan puts the motor inside the connecting rod,making full use of the small space inside the cylinder;there are only four main transmission parts of the VCR connecting rod,the structure is simple and easy to process;and in order to realize the change of length,the connecting rod cleverly utilizes the function of thread transmitting motion to convert the rotary motion into up and down movement.This paper selected two drive motors,N20 gear motor and JGA20-180 B DC gear motor,and then determine the basic dimensions of the VCR connecting rod parts according to the selected motor and the structural parameters of the original machine connecting rod,the overall size of the VCR connecting rod parts driven by the N20 geared motor is larger than the VCR connecting rod driven by the JGA20-180 B DC geared motor.Through the CATIA software,the 3D model of the VCR connecting rod was designed.The paper calculated the range of compression ratio,also analyzed the relationship between the compression ratio and the length of the VCR connecting rod.this paper used ADAMS perform the kinematics analysis of VCR mechanism,and compared the effects of different compression ratios on the displacement,velocity and acceleration of VCR mechanism,it was found that the stroke of the piston is constant and the velocity and acceleration change little under different compression ratio.In the paper,the static analysis of VCR connecting rod was carried out through the ANSYS Workbench,and the static stress and static strain of VCR connecting rod under the maximum compression condition and the maximum tension condition was analyzed,we obtained the stress and strain distribution nephogram of VCR connecting rod under the two limit conditions,the simulation analysis showed that,with the exception of the transmission shaft,for other parts,the maximum stress and strain of the VCR connecting rod driven by N20 geared motor is smaller than that ofthe VCR connecting rod driven by JGA20-180 B DC geared motor,but the stress and strain of the two VCR connecting rods meet the design requirementsIn order to further verify the feasibility of the variable compression ratio mechanism,a VCR engine test bench was set up and the trailing experiment was performed.the trailing experiment shows that although the VCR connecting rod driven by N20 geared motor can achieve the change of compression ratio,the compression ratio no longer changes when the length of the connecting rod reaches a certain position,while the VCR connecting rod driven by the JGA20-180 B DC geared motor can achieve the stable change of compression ratio,and both VCR connecting rods respond slowly to changes in compression ratio.