鼓式制动器制动不稳定时变特性分析

由于工作环境复杂多变，制动器工作不稳定而导致振动和噪声，鼓式制动器制动时的温度变化对制动不稳定性影响较大，研究制动不稳定性影响因素及其制动不稳定时变特性具有实际工程意义。基于鼓式制动器四自由度接触模型，分别在Hypermesh和ABAQUS中建立鼓式制动器制动鼓和制动蹄总成模型与摩擦制动接触模型并进行试验验证；通过热机耦合动态分析，研究制动鼓温度对制动应力的影响；分析弹性模量和热膨胀系数对鼓式制动器制动不稳定时变特性的影响。分析表明：制动不稳定性是摩擦力耦合所致；制动过程中制动鼓温度与应力相互作用且均先快速上升后缓慢下降；鼓式制动器制动不稳定时变特性主要体现在不稳定模态个数及不稳定倾向系数（tendency of instability, TOI）值的变化，制动温度变化导致弹性模量变化，引起不稳定模态个数和TOI值略有变化，弹性模量对鼓式制动器制动不稳定时变特性影响较小；制动温度变化导致热膨胀系数变化，引起不稳定模态个数和TOI值先大幅降低后略有升高，热膨胀系数对鼓式制动器制动不稳定时变特性影响较大。研究结果对改善汽车制动声品质具有一定指导意义。

Analysis of time-varying characteristics of braking instability of drum brake

The brake works unsteadily and causes vibration and noise, because of the complex and changeable working environment, and the temperature change of drum brake has a great influence on the brake instability. It is of practical engineering significance to study the influence factors and time-varying characteristics of braking instability. Based on the four-degree-of-freedom contact model of drum brake, the model of brake drum and brake shoe assembly of drum brake and the contact model of friction brake were established respectively in Hypermesh and ABAQUS and tested and verified. The influence of brake drum temperature on brake stress was studied through the dynamic analysis of thermal-mechanical coupling. The effects of elastic modulus and thermal expansion coefficient on the time-varying characteristics of braking instability of drum brake were analyzed. The results showed that the braking instability was caused by friction coupling. During the braking process, the temperature and stress of the brake drum interacted with each other and rose rapidly first and then fell slowly. The time-varying characteristics of braking instability of drum brake were mainly reflected in the number of unstable modes and the change of tendency of instability (TOI) value. The braking temperature change led to the change of elastic modulus, which caused a slight change in the number of unstable modes and the TOI value. The elastic modulus had little influence on the time-varying characteristics of braking instability of drum brake. The braking temperature change led to the change of the thermal expansion coefficient, which caused the number of unstable modes and TOI value to decrease at first and then slightly increase, and the thermal expansion coefficient had a great influence on the time-varying characteristics of braking instability of drum brake. The results of this study have some guiding significance for improving the braking sound quality of automobile.