Abstract: The factors of affecting crankshaft torsional fatigue strength and the causes of various torsional failure were analyzed by torsional fatigures test of crankshafts， and the corresponding improvement measures were put forward. It was pointed out that with the increase of engine explosion pressure， the torque of crankshafts increases accordingly， which leads to the increase of crankshaft torsional fatigue failures. The main torsional failure locations include pin journal oil hole， crank arm and pin journal bottom center of the crankshafts. The causes of failure are related to structural design， raw materials， machining， heat treatment and so on. The oil holes of pin journal are the most common part of torsional fatigue failures， and the crack sources are generally about 8～10 mm from the inner walls of oil holes to the journal surfaces. The torsional fatigue strength of crankshafts is more affected by induction hardening on the journal surfaces. The torsional fatigue strength of crankshaft reduces about 30% by surface induction hardening. The torsional fatigue strength of surface hardening crankshafts is increased more than 25% by polishing the internal surfaces of the oil holes. 

Key words:  , crankshaft, torsional fatigue strength, failure model, induction hardening

摘要： 通过对内燃机曲轴进行扭转疲劳试验研究，分析了影响曲轴扭转疲劳强度的因素以及导致曲轴扭转失效的原因，并提出了相应的改进措施。分析指出，随内燃机爆发压力的提高，曲轴所承受的扭矩会相应增大，由此导致的曲轴扭转疲劳失效不断增加。曲轴扭转失效位置主要在连杆颈油孔、曲柄臂和连杆颈下止点，失效原因涉及结构设计、原材料、机加工、热处理等多个因素。连杆颈油孔是扭转疲劳失效最常见部位，裂纹源一般在油孔内壁距轴颈表面约8～10 mm位置，轴颈表面感应淬火对扭转疲劳强度影响较大，表面感应淬火使曲轴的扭转疲劳强度降低约30%，油孔内壁抛磨可使轴颈表面淬火曲轴的扭转疲劳强度提高25%以上。

关键词: 曲轴, 扭转疲劳强度, 失效形式, 感应淬火