发动机活塞系摩擦功多耦合因素影响机制及多学科鲁棒优化研究

Energy and environmental problems have urged governments all over the world to propose more and more stringent emission regulations. Design optimization of low-friction engines has become a critical issue for both the automobile industry and society. The friction pair of piston and cylinder liner is exposed at terrible working conditions and contributes to the most friction loss of an engine. Multiple factors, including those from the working conditions and the components of the engine, may affect the friction loss significantly. Nevertheless, those multiple factors can be dependent with each other. As a result, the mechanism of how these multiple coupled factors affect the friction loss cannot be directly or easily obtained, which however, is quite necessary and will shed light on the optimal design of low-friction engines. The proposed research will develop analysis techniques to address how those multiple coupled factors affect the friction loss based on a friction model concerning these factors, and then perform multi-disciplinary robust optimization for the development of low-friction engines. The major tasks of the proposed research will include: 1) to establish a structured friction model taking into consideration of multiple coupled factors; 2) to investigate and analyze the mechanism of how each factor affects the friction loss in the context of factor couplings, and to determine critical and non-critical factors; and 3) to formulate the multi-disciplinary problem with the objective of reducing friction loss and meanwhile improving the engine performance consistency, and to propose a multi-disciplinary robust optimization algorithm to obtain optimal solutions.

在当前能源与环境问题愈发严峻的形势下，低摩擦发动机设计优化已成为汽车行业发展的前沿关键议题。活塞系是发动机摩擦损失的最关键部位，影响活塞系摩擦功的因素众多，且因素间具有复杂耦合关系，深入研究各因素对摩擦功的作用机制并进行相关优化对节能减排极为关键。本研究在考虑影响活塞系摩擦功的热、固、流、力及活塞系结构尺寸、公差等各因素复杂耦合及不确定性的基础上建立摩擦功模型，并分析各因素对摩擦功的影响机理，进而设计优化。具体工作包括：1）建立多耦合因素考量的活塞系摩擦功模型；2）探究各影响因素间的复杂耦合关系，明晰各因素对发动机摩擦功的影响机理，并区分关键因素和非关键因素；3）提出并解决考虑多耦合因素及不确定性参数的活塞系摩擦功多学科鲁棒优化问题，对非关键因素研究其在后续优化过程中可降低问题维度的有效处理方法，对关键因素进行设计优化，获得降低摩擦功及其波动的设计优化方案。

发动机作为汽车的动力核心，零部件工序多，工艺复杂，且制造精度要求高。发动机摩擦功是评定发动机性能的重要指标之一，对发动机的扭矩输出和燃油消耗等关键性能有直接影响。提高发动机制造性能一致性并进行低摩擦发动机设计优化是汽车行业发展的重要议题。影响摩擦功的因素众多，包括热固流力等外界因素及发动机自身的尺寸公差。基于弹性流体润滑理论，考虑到润滑、动力学、温度场等，针对一款1.2L发动机建立了考虑多因素耦合作用的曲轴系和活塞系的摩擦功仿真模型，并设计了发动机摩擦功拆解实验，根据发动机台架实验结果对于仿真模型进行了标定及验证。基于建立的仿真模型，分别对影响发动机曲轴系和活塞系摩擦功的长度尺寸、形位公差及部分尺寸之间的耦合作用进行了系统的分析，利用单因素分析方法研究了尺寸公差对摩擦功影响的趋势，利用多水平正交实验研究了公差耦合作用对摩擦功波动的影响，并确定了影响轴系和活塞系摩擦功的关键尺寸。在此基础上，基于Kriging差值理论建立了关键尺寸公差与摩擦功波动的关系模型，并利用提出的多目标优化算法，对于尺寸的公差区间进行了优化。研究表明优化后的区间公差，相比原公差区间，曲轴系摩擦功波动降低了44.67%，活塞系摩擦功波动降低了33.91%。研究为公差分配及发动机精密制造提供了科学合理的依据。