Abstract: The pre-charging system of new energy electric vehicles is crucial to vehicle safety. In order to furtherly improve the reliability of the pre-charging system and to propose practical and reliable control measures, this paper analyzes in depth the reasons for the functional failure of the pre-charging system. Through the systematic troubleshooting method, it is found that the abnormally high surface resistance of the contacts of the pre-charging relay is the direct cause of the pre-charging failure. Suction test, computed tomography (CT), microscope inspection, and scanning electron microscope analysis are conducted. The results show that some parts in the battery management system (BMS) have free monomeric phosphorus and volatile silicone, and material migration occurs during high-voltage operation, and the elements of silicon and phosphorus migrate to the surface of the relay contacts, resulting in an abnormally high contact resistance, which ultimately triggers the pre-charging functional failure. The application of this paper concludes that the red phosphorus and siloxane content of BMS system parts needs to be controlled during the design and mass production stage to ensure the reliability of the pre-charging system. The research has strong practical application and reference value.

Key words: Pre-charging relay; Red phosphorus; Silicone; Contact resistance

摘要： 新能源电动车的预充系统对车辆安全至关重要。为了进一步提升预充系统的可靠性并 提出切实可靠的控制措施，文章深入地分析了预充系统功能失效的原因。通过系统排查方法， 发现了预充继电器的触片表面电阻异常增高是导致预充故障的直接原因。进一步对预充继电 器进行吸合测试、计算机断层扫描（CT）、拆解后显微镜检测、扫描电镜分析，结果表明， 电池管理系统（BMS）的部分零件存在游离单质磷和可挥发的硅氧烷，在高压工作过程中发 生了材料迁移，硅和磷元素迁移至继电器触片表面，导致接触电阻异常增高，最终引发了预 充功能失效。文章的应用结论是在设计和批量生产阶段，需要对 BMS 系统零件的红磷和硅氧 烷含量进行控制，以保证预充系统的可靠性。该研究具有较强的实际应用和参考价值。

关键词: 预充继电器；红磷；硅氧烷；接触电阻