冷启动条件下铝合金活塞裙部智能复合涂层体系构筑及磨损机理研究

Friction power consumption is one of the main obstacles in the process of engine energy saving and emission reduction, it account for nearly half of the energy loss of engine. As a friction pair with the most friction loss in the engine, the piston-cylinder system is very important to improve fuel efficiency and reliability. However, due to poor working conditions and deep inside the equipment, it is difficult to study the tribological properties and wear characteristics. In this paper, aiming at the cold start stage with severe wear, the preparation and wear mechanism of smart composite coatings on the aluminum alloy piston skirt was studied: prepare composite coatings contains piezoelectric BaTiO3 layer and wear resistant graphite layer, observe the microscopic morphology and phase structure, test the mechanical properties and bonding strength, then evaluate and optimize the coating forming quality; according to the hydrodynamic lubrication theory to determine the formation condition of the oil film, establish the secondary motion model of piston under cold start condition, and reflect the contact characteristics through the cumulative wear load, the friction power loss, etc.; receive electrical signal from coatings, plot the relationship curve between load-signal-coatings damage, combine with the wear morphology to determine the main wear types and the evolution characteristics, confirm the weight of wear under cold start condition, reveal the effects of the starting temperature and velocity on the friction and wear behavior of the skirt coatings. The intercross and coalescence among the multi disciplines will be conducted in this project. The aforementioned investigations will give the basic support for the application of smart coatings under complex loading conditions.

摩擦功耗占据着发动机近半的能量损耗，是车辆节能减排征程中的主要阻碍之一。活塞-气缸系统作为发动机中摩擦损失最大的摩擦副，对提高燃油效率和结构可靠性至关重要，但由于工作条件恶劣且深处设备内部，其摩擦特性及磨损表征研究困难。本项目针对磨损程度严重的冷启动阶段，以铝合金活塞裙部智能复合涂层为对象研究其构筑及磨损机理：制备包含压电层和耐磨层的复合涂层，观察微观形貌及物相结构，测试力学性能及结合强度，评定涂层的成形质量并进行优化；根据流体动压润滑理论确定油膜的形成条件，建立冷启动条件下活塞的二阶运动模型，并通过累积磨损载荷、摩擦功率损失等反映接触特征；接收涂层电信号，绘制载荷-信号-涂层损伤关系曲线，结合涂层磨损形貌判定主要磨损类型及演变特征，确定冷启动磨损权重，揭示启动温度、速度等对裙部涂层摩擦磨损行为的影响规律。本项目体现了多学科的交叉融合，为复杂载荷下智能涂层的应用奠定了理论基础。

针对冷启动工况、标准工况等条件下内燃机活塞裙部摩擦功过高、易发生磨损失效的问题，从涂层成形质量、摩擦副接触特征以及减磨耐磨机理等方面展开了系统研究。采用等离子喷涂在活塞裙部制备了BaTiO3压电陶瓷涂层（传感涂层）并极化处理，采用高致密丝网印刷制备了石墨涂层（服役涂层），形成复合涂层结构，通过形貌观察、物相分析、性能测试等确定了涂层成形质量，并从基体质量、喷涂工艺、印刷工艺三方面进行了优化，另外在活塞内腔布置了传感装置，为带有智能涂层的活塞实时传输压力信号奠定了基础；搭建了活塞运动可视化平台、内冷打靶试验平台，通过温度场测试、润滑油膜观察、动力学数值模拟等量化出接触压力、敲击动能、累积磨损载荷、摩擦功率损失等信息，确定了活塞裙-缸壁的接触状态；通过单项试验、摩擦模拟试验、发动机台架试验等系统分析了启动温度、销孔偏心、裙部型线等对裙部涂层摩擦磨损行为的影响规律，建立了边界润滑条件下的裙部磨损模型，确定了冷启动磨损权重，并结合磨损形貌判定出主要磨损类型及演变特征。研究表明：冷启动条件下活塞裙部涂层可使裙部接触压力降低约40%，摩擦功率损失降低约50%，刀纹磨损量则降低约60%，定量分析出裙部涂层提高活塞润滑及抗磨损性能的效力；结构方面，销孔偏心是改善活塞运动平稳性、降低发动机噪声和摩擦损失较为有效的方法，且柴油机活塞接触压力对偏心量的敏感程度要高于汽油机活塞，销孔越偏向主推力侧，摩擦功损失则越大，但有些发动机可能会在某个销孔偏心量上出现拐点；外圆型线设置的理想状态是保持尽可能小的运转间隙，通过增加大点高度和最大直径区域的宽度，可有效提高磨损载荷的均匀性。本项目的研究成果为科学设计内燃机活塞涂层体系提供了参考依据，同时，磨损机制方面的研究内容对于活塞服役安全性和可靠性提升也具有明显的推动作用，系列研究成果可直接应用于裙部磨损评价和预测。