孙小伟1，2，胡洪涛1，2，申景倩1，2，刘刚1，2，韩玉伟1，2

（1、长城汽车股份有限公司技术中心，河北 保定 071000；2、河北省汽车工程技术研究中心，河北保定 071000）

摘要：针对涡轮增压汽油机冷热循环试验中排气歧管螺母松动进行仿真分析,计算出不同工况下的变形和排气歧管垫片密封情况。结果表明排气歧管膨胀后与螺母产生相对变形,相对变形导致排气歧管螺母安装面受力不均匀。排气歧管螺母安装面在高温条件下,局部受力过大产生塑性变形,造成排气歧管螺母与排气歧管接触面产生间隙(接触面张开量),加上排气歧管冷热变化条件下会与排气歧管螺母产生相对滑动,进而导致螺母松动问题出现。本文还对比了不同螺柱轴力下排气歧管螺母安装面的塑性变形量和接触面的张开量,在减小螺柱轴力后,排气歧管螺母安装面的塑性变形量和接触面的张开量明显减小。为了验证分析结果,在保持螺母拧紧力矩不变的条件下通过改变螺母和螺柱表面处理方式来减小螺柱轴力,经过试验验证,没有再出现螺母松动问题。

关键词：排气歧管；排气歧管螺母；冷热循环试验；塑性变形；张开量

Abstract: Exhaust manifold nuts of a turbocharged gasoline engine were loosened in the cold-hot cycle test. In order to solve this problem, the simulation is conducted, calculating the deformation of relevant parts and the sealing effect of the exhaust manifold gasket. The simulation result shows that relative deformation between the exhaust manifold and nuts leads to an uneven load on the installation area of nuts. Plastic deformation happens in the nut installation area of the exhaust manifold under the hot work conditions, causing a gap in the contact surface between the nut and the exhaust manifold. Because the exhaust manifold expands as it heats up and contracts as it cools down, while the contact surface opens, nuts become loosen. When the bolt force is reduced, the plastic deformation of the exhaust manifold nut in the installation area is reduced, and the contact surface opening amount is smaller. To verify the simulation result, the surface treatment of the bolt and the nut is changed while nuts are tightened under a same torque, reducing the bolt axial force. The problem that the bolt nuts are loosened does not happen any more.

Keywords: Exhaust Manifold; Exhaust Manifold Nut; Cold and Hot Cycle Test; Plastic Deformation; Contact Surface Opening Amount