自由活塞发动机活塞环-气缸套的润滑及摩擦特性

The friction load of the cylinder and the piston for a free piston engine(FPE)is different from a traditional crank engine(CE).To study the lubrication and friction characteristics of piston ring of the FPE, a numerical model based on hydrodynamic lubrication equations and asperity contacting equations was established.The simulation model was certificated by the experiment of a FPE prototype.Further, the differences of minimum oil film thickness, friction force and friction power loss between the FPE ring and the CE ring were analyzed, and the influences of different tribology parameters on lubrication performances for the FPE ring were conducted.Results show that, near the top dead center(TDC), the minimum oil film thickness of the FPE ring is greater than that of the CE ring and its boundary lubrication duration is shorter.Compared with the CE ring, the peak friction force and the friction loss of the FPE ring are relatively smaller, but its peak friction power is significantly higher.When the tubbish height of the FPE ring increases from 2μm to 4μm, the minimum film thickness near the TDC decreases by 47%, the peak friction force increases by 20% and the friction loss decreases by 4.6%.When the tubbish offset of the FPE ring increases from -50μm to 50μm, the peak friction force and its duration decrease, the peak friction power decreases by 32% and the friction loss decreases by 5.2%.