Design Of Hydraulic Variable Compression Ratio Mechanism

The variable compression ratio technology is a cutting-edge technology research in the field of engine which can improve the dynamic performance of the engine under low load and avoid knocking under heavy load.Through the comparison of domestic and foreign technical schemes,this paper chooses to change the relative height of piston to realize the technical solution of variable compression ratio.The concrete implementation method is to install the swing hydraulic motor inside the piston and through the transmission of the double helix structure to realize the compression ratio change.The variable compression ratio piston designed in this paper is based on the piston of a single cylinder diesel,ZS1100.The VCR piston was designed by using Proe software.The basic size of the VCR piston was determined,the variation range of compression ratio was obtained from 17.5 ~ 14.3,The dynamic analysis of VCR piston mechanism was carried out by Adams,obtained the relationship between the acceleration,speed,displacement and crankshaft angle of piston in the engine speed of 200r/min,800r/min,1800r/min.The acceleration of the piston at 1800r/min was 2610m/s2.Then the finite element analysis is carried out to analyze the static stress and deformation of the piston through the cylinder pressure,inertia force,gravity,support force,hydraulic pressure,acting on the VCR piston.It is concluded that the stress and strain value of the piston combustor are maximal,the maximum stress is 243 Mpa and the maximum strain is 0.21 Mpa.Finally,the mechanical load on the piston is combined with the piston temperature field to determine the stress and strain values of the piston in thermo-mechanical coupling analysis.In order to verify the feasibility of the hydraulic VCR piston mechanism,this paper determines the basic dimensions and leaf number of swing hydraulic cylinder,thus obtaining the geometrical displacement of the hydraulic motor is 38640mm3/rad and the theoretical torque is 9.66N·m.Then we simulated the hydraulic driving process of piston,and obtained the response characteristics of piston under different pressure.In this paper,the height of cylinder head,cylinder head bolt and tappet are lengthened to compensate for the interference caused by the height of the piston.The oil circuit of diesel engine was modified,and the assembled VCR piston was placed into diesel engine for static experimental verification.The paper summarized and analyzed the reasons for the leakage of hydraulic system in the experiment,improved the research scheme,and drawn the improved mechanical drawing.