汽油机排气门碰撞活塞失效分析及优化
马京卫1，2，常雪嵩1，2，于鹏飞1，2，王晨曦1，2，刘鲁平1，2，王晋林1，2
1.长城汽车股份有限公司，河北 保定 071000；2.河北省车用发动机技术创新中心，河北 保定 071000
摘要：为解决某出口发动机运行中排气门碰撞活塞导致的发动机失火故障，通过对气门导管和排气门杆的化学成分及金相组织、气门弹簧受力、整车排温、驾驶习惯对发动机热负荷的影响等进行多维分析，确定故障原因为发动机出现急加速与急减速等激烈工况且持续时间较长，气门导管热负荷增大，气门导管间隙减小，造成气门卡滞撞击活塞，导致发动机失火。采用增大气门导管包裹面积的方案进行优化，仿真结果表明：优化后导管最高温度由245.3 ℃降为208.5 ℃，气门导管最大收缩量由0.026 1 mm减小为0.014 3 mm。将气门导管下端杆径由5.948 mm减小为5.943 mm，对优化后的发动机进行300 h急加速与急减速台架试验，发动机正常运行,未出现气门撞击活塞故障。
关键词：汽油发动机；排气门；热负荷；气门导管；活塞
Analysis of gasoline engine failure by exhaust valve-piston collision and its optimization
MA Jingwei1,2, CHANG Xuesong1,2, YU Pengfei1,2, WANG Chenxi1,2，LIU Luping1,2, WANG Jinlin1,2
1. Great Wall Motors Co., Ltd., Baoding 071000, China;
2. Hebei Automotive Engine Technology Innovation Center, Baoding 071000, China
Abstract: In order to solve the export engine misfire fault caused by the collision of the exhaust valve with the piston during the operation of an engine, the chemical composition, metallographic structure, valve spring force, vehicle exhaust temperature, and driving habits of the valve guide and exhaust valve stem are analyzed, and the influence of the vehicle exhaust temperature and driving habits on the engine thermal load is determined. The cause of the fault is that the engine is prone to intense working conditions such as sudden acceleration and deceleration during operation, which lasts for a long time. The thermal load of the valve guide is increased, and the clearance of the valve guide is decreased, causing the valve to jam and impact the piston, resulting in engine misfire. The optimization is carried out by increasing the wrapping area of the valve guide. The simulation results show that the maximum temperature of the optimized guide is decreased from 245.3 ℃ to 208.5 ℃, and the maximum contraction of the valve guide is decreased from 0.026 1 mm to 0.014 3 mm. At the same time, the lower end diameter of the valve guide is reduced from 5.948 mm to 5.943 mm. A 300 hours rapid acceleration and deceleration test is conducted on the optimized engine, and no valve impact piston failure occurs, indicating normal engine operation.
Keywords: gasoline engine; exhaust valve; heat load; valve guide; piston
