农用柴油发动机变压缩比机构设计及主要部件仿真

摘要

A kind of variable compression ratio mechanism of agricultural diesel engine was designed and it could make the compression ratio of hydraulic pressure control adjust to different working condition change automatically.The range of compression ratio was from 15 to 19.The compression ratio was 19 under the working condition of cold-start and medium-small load.The compression ratio was 15 under the working condition of large load.The stress and strain nephograms under different compression ratio and working conditions were obtained through simulation of gear,rack and piston assembly carried out by ANSYS finite element software.The simulation results showed that：The maximum stress point of piston assembly was at the pit position of piston superface,and its value was 0.053 522 MPa.The maximum stress point of gear and rack was at the meshing position of gear,rack and drive rack,and its value was 0.198 445 MPa.The maximum strain point of piston assembly was at the contact position of piston and piston rod,and its value was 0.000 863 mm.The maximum strain point of gear and rack was at the meshing teeth root position of gear,rack and drive rack,and its value was 0.003 326 mm.The designed variable compression ratio mechanism could satisfy the working requirement of engine.%增大发动机压缩比可提高发动机的动力性,但又会影响其工作的可靠性及寿命,为解决此矛盾,设计了一种农用柴油发动机的变压缩比机构,在发动机不同工况下实现了液压控制的压缩比自动调节,压缩比的变化范围为15～19;在发动机冷启动及中小负荷时压缩比为19,在发动机大负荷时压缩比为15。通过ANSYS有限元软件对活塞组及齿轮齿条进行了仿真,得到了不同压缩比、不同工况下的应力、应变云图。仿真结果表明：活塞组的最大应力出现在活塞顶面凹坑位置,其数值为0.0535 22MPa;齿轮齿条的最大应力出现在齿轮齿条与传动齿条的啮合位置,其数值为0.198 445MPa;活塞组的最大应变出现在活塞与活塞杆的连接部位,其数值为0.000 863mm,齿轮齿条的最大应变出现齿轮齿条与传动齿条啮合齿的根部,其数值为0.003 326mm,所设计的变压缩比机构能够满足发动机工作要求。