The vibration amplitude of the front combination lamp bracket of a heavy-duty truck was overlarge when the engine was operating at idle speed. The finite element model of the front combination lamp bracket was established. The modal analysis showed that the first-order modal of the model was similar to the realistic vehicle vibration modal, and the first order modal frequency was close to the excitation frequency when the engine was at the idle speed. Then, the rigid-flexible coupling dynamic model of the vibration system was established. The simulation results verified the phenomenon of beat vibration under the excitation frequency when the engine was at the idle speed, and the first-order modal participation factor played a dominant role in the system vibration. Finally, an auxiliary bracket was designed for the truck based on the modal analysis theory in order that the first-order frequency of the system could avoid from the excitation frequencies when the engine was at the idle speed and at commonly used speed. Through the simulation analysis and real vehicle test again, it was confirmed that the vibration amplitude of the system was controlled within a reasonable range.%为解决某重型汽车前组合灯在发动机怠速时振幅过大的实际问题,建立前组合灯支架的有限元模型,通过模态分析发现其1阶振型与实车振型相似,1阶模态频率与发动机怠速时的激励频率相近.建立振动系统的刚柔耦合动力学模型,仿真结果验证在发动机怠速时的激励频率输入下振动系统在开始阶段发生近似拍振现象,而且1阶模态参与因子在系统振动中的贡献率最大.根据模态分析理论设计前组合灯辅助支架,使系统基频避开发动机怠速和常用转速时的激振频率,经过再次仿真分析和实车试验验证,系统振幅控制在合理的范围内.
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