Abstract: A light commercial vehicle experienced a cracking fault at the suspension installation position on the transmission shell during the durability test of the vehicle structure. Through the analysis and research of fracture, metallography, chemical composition and design check, it is determined that the root cause of shell fracture is insufficient safety factor of shell strength design, which may lead to shell cracking under extreme working conditions. The load boundary of the finite element analysis (FEA) model of shell strength is updated by measuring the load spectrum of mounting point. The optimized FEA analysis results show that the stress state of the suspension installation position is improved significantly, and meet the latest stress acceptance standards, and the transmission passes smoothly the vehicle structure durability test.

Key words: Transmission; Shell; Strength; Fracture

摘要： 某轻型商用车在整车结构耐久试验过程中出现变速器壳体上的悬置安装点开裂故障， 通过断口、金相、化学成分、设计校核等方面的分析研究，确定了壳体断裂的根本原因为壳 体强度设计安全系数不足，在极端工况下可能导致壳体开裂。经过实测悬置安装点载荷谱， 更新了壳体强度有限元分析（FEA）模型的受力边界。壳体结构优化后的 FEA 分析结果显示， 悬置安装点的应力状态得到明显改善，满足最新的应力接受标准，变速器顺利通过整车结构 耐久试验。

关键词: 变速器；壳体；强度；开裂