排气制动工况下摇臂轴断裂问题的分析与试验研究

Research and analysis of rocker arm shaft fracture at exhaust braking test

某四缸柴油机在电力测功机台架上采用倒拖方法进行排气制动工况模拟试验时,功率突然下降,拆机检查发现摇臂轴断裂且排气门与活塞有碰撞痕迹。本文借助有限元计算、断口分析和理化检验等手段对故障件进行分析,同时在试验台架上测量活塞与排气门的运动间隙。经分析和试验研究发现在制动工况下排气门出现反跳导致活塞与排气门碰撞是摇臂轴断裂的主要原因。

Some type of four cylinder diesel engine simulated the exhaust braking test in power dynamometer bench with the method of reversal dragging,then the power fell down suddenly. Inspecting all parts after disassembly,we found the fracture of rocker arm shaft and collision traces between exhaust valves and pistons. The disabled parts are analyzed by means of finite element analysis,fracture analysis and physicochemical examination. At the same time we measure the moving clearance of piston and exhaust valve in the test bench. Through analysis and experiment,the study found that the exhaust valves＇ rebound in the braking condition causes the final collision is the main reason for the rocker arm shaft fracture.