起落架系统刹车走步动力学特性研究

Gear walk dynamical characteristics study of braking landing gear systems

起落架碳陶刹车系统的刹车力矩在角速度快速变化时,随着机轮转速的减小而增大,刹车力矩和机轮转速曲线的负斜率与起落架刹车走步振动有较大的关系。本文建立了一个三自由度起落架刹车走步动力学模型,对水陆两栖飞机主起落架刹车振动进行了分析,重点研究刹车力矩负斜率对起落架刹车振动的影响,计算的加速度响应、频率与起落架外场滑跑刹车试验测试结果一致。研究了初始刹车力矩、负斜率、起落架航向刚度与阻尼、支柱等效高度等参数对起落架动力学系统的影响,给出了初始刹车力矩与刹车力矩负斜率在高速刹车状态下的双参数振动收敛边界。通过Hopf分岔分析得到了起落架刹车系统的刹车力矩负斜率与初始速度的双参数分岔图。通过分析得出,起落架刹车低频振动发散可能由刹车力矩负斜率超过一定范围或刹车压力大导致刹车力矩过大,滑移率超过限值两种原因导致。相对于高速刹车,刹车力矩负斜率对低速刹车稳定性影响更大。在分析结果的基础上给出了抑制起落架刹车走步的方法与建议。

The braking torque of the carbon ceramic braking system of the landing gear increases with the reduction of wheel speed under the condition of rapid change of angular speed.The negative slope of the braking torque and wheel speed curve has a great relationship with the landing gear walking vibration.Focusing on the impact of the negative slope of the braking torque on the landing gear brake vibration,a three degree of freedom landing gear brake walking model is established,and the main landing gear brake vibration of amphibious aircraft is analyzed.The calculated acceleration response and frequency are consistent with the test results of the landing gear field skid brake test.The effects of initial braking torque,negative slope,landing gear heading stiffness and damping,strut equivalent height and other parameters on the landing gear dynamic system are studied,and the dual parameter vibration convergence boundary of initial braking torque and negative slope of braking torque under high speed braking is given.By means of Hopper bifurcation analysis,the two parameter stability boundary of the negative slope of braking torque and velocity under the global state of the landing gear system is given.Through analysis,it is concluded that the gear walk may be caused by two reasons:the negative slope of the braking torque exceeds a certain range,or the braking torque is too large due to large braking pressure,and the slip ratio exceeds the limit.Compared with high speed braking,the negative slope of braking torque has greater influence on the stability of low speed braking.Finally,based on the analysis results,the methods and suggestions to improve the gear walking vibration of landing gear are given.