CNG发动机活塞热-机耦合应力分析
Thermo-mechanical Coupling Stress Analysis of CNG Engine Piston

随着CNG发动机不断地向着高速化、大功率的方向发展，使得活塞销座由于应力集中而引起疲劳裂纹。为此，设计了一种新型弧面衬套活塞销座，对衬套进行了运动分析和装配条件分析。通过有限元方法分析了活塞在机械载荷、热-机耦合载荷条件下的应力分布状态。研究结果表明：在机械载荷作用下，新型活塞-衬套的Mises应力比原活塞降低了25.3%，新型活塞销座最大Mises应力比原活塞降低了27.9%，新型活塞销座的接触应力比原活塞降低了35.4%。活塞在热-机耦合载荷作用下的应力状态与在机械载荷作用下的结果相似，活塞应力状态都有很大改善。装配有衬套的活塞销座的应力分布更加的均匀，更容易形成润滑油膜。因此，该结构具有降低活塞销座应力、提高润滑能力和提高活塞销座的疲劳寿命的优点。
As the compressed natural gas (CNG) engine moves toward the direction of high speed and high power development, the piston pin hole stress is greater, causing fatigue crack on the piston pin hole. Therefore, we design the new structure of an arc surface bush piston pin hole. Such piston bush is derived from the movement analysis and assembly conditions analysis. The stress distribution state of the piston under different load conditions of mechanical load and thermo-mechanical coupling load were analyzed with the finite element method. Simulation results show that the Mises stress of the new structured piston bush decreases by 25.3%, that the Mises stress of the new structured piston pin hole decreases by 27.9% compared with the original structured piston and that its contact stress decreases by 35.4% under the mechanical load. The analysis results on the piston stress state of the thermo-mechanical coupled load are similar to those on the mechanical load. In addition, the piston's stress state has been greatly improved. The stress distribution of the piston pin hole with an arc surface bush is more homogeneous; it is easier to form oil film on the arc surface bush. Therefore, the new structure of the piston pin hole with arc surface bush has strong capability of decreasing stress and increasing the lubricity and anti-wear ability