【作者】 陈超；

【导师】 田春；

【作者基本信息】 同济大学 ， 载运工具运用工程， 2023， 博士

【摘要】 轮轨接触是轨道车辆的一个重要边界条件,是轨道车辆区别于其他交通工具的最大特征之一。通常,轨道车辆依靠轮轨接触进行承载、导向、牵引和制动。由于车轮和轨道不是完全刚性的,在轮轨接触界面处存在蠕滑率,进而产生蠕滑力。这种状态称为轮轨黏着。当轨道表面被水、油或树叶污染时,车轮与轨道之间的黏着降低,导致制动力的损失以及停车距离延长,威胁行车安全。研究发现,除了撒砂方式外,车轮和轨道之间的大滑移还可以改变接触界面状态,恢复较低的黏着力。为了进一步开展大滑移条件下黏着改善的理论和试验研究,有必要开发一种专用于多种轨面条件下轮轨黏着模拟试验的新型试验台。通过创新试验台的结构型式,还原第三介质污染物的实际分布状态。为轨道车辆新型制动控制和防滑系统的设计提供试验数据支撑,切实提高轨道交通运输系统的安全和效率,具有重要的意义。本文简述了经典黏着理论的发展和局限性,回顾了黏着改善现象的发现和大滑移工况黏着特性的研究历程,对国内外现有的轮轨接触模拟试验台进行了分类评估,包括轮/轮型式试验台、轮/轨型式试验台和轮/环型式试验台。轮/环型式试验台可在有限场地内进行较高速度的轮轨黏着模拟试验,且能够保证第三介质处于静止不动的轨道表面,与车辆实际运行工况接近。故优选该型式的试验台,能够满足轨面第三介质条件下制动大滑移工况轮轨黏着模拟研究需求。为了能通过试验台研究实车轮轨黏着特性,故开展不同型式试验台轮轨黏着模拟研究。首先分析了实车轮轨黏着状态,根据滚动接触理论求解出实车三向蠕滑率、三向蠕滑力。其次基于轮轨法向力相似性原理,要求试验台接触斑椭圆长半轴和短半轴的比值、接触斑上最大法向接触应力与实车相等。分析计算试验台接触几何误差、比例、垂向力、功率。轮/轮型式的试验台由于轨道的纵向曲率半径有限,造成了法向接触误差。试验台的比例决定了车轮直径、加载垂向力以及试验台所需的功率。最后开展轮/环型式试验台切向力相似性研究,建立实车和试验台纵向蠕滑率等效关系。根据实车踏面等效锥度计算出试验台回转半径范围为525 mm至2100 mm。当回转半径为1 m时,试验台接触斑纵向切应力误差小于8%。随后讨论试验台自旋蠕滑率带来的横向蠕滑力的影响。当回转半径为1 m,纵向蠕滑率大于5%时,横向蠕滑力与纵向蠕滑力的比值小于0.5%,不会由于横向力的存在占用纵向力,影响制动力的模拟。考虑到实验室中的功率限制和工程因素,选择试验台比例为1:4,回转直径为2 m。根据车辆动力学相似比例分析,确认了试验台的缩比策略合理、自洽。在此基础上阐述了试验台自解耦设计思想,进行试验台传动系统设计,列写试验台动力学方程,通过确立试验台的结构参数与传动参数相等的自解耦条件,实现了车速电机和轮速电机的功率分流,黏着力的变化不影响车速。试验台运行过程中受到轮轨间黏着力、齿轮啮合振动、结构件变形和风阻力等非线性因素的影响。通过SIMPACK建立了考虑上述因素的试验台非线性动力学模型,研究试验台动力学响应。仿真分析发现试验台在初始时刻会出现滑移率的波动,且在2至5 s内收敛到目标值。应用PID控制算法的试验台双闭环控制系统可以保证滑移率的控制精度。SIMAT联合仿真结果表明其误差小于1%,据此提出试验台设计指标。PID控制算法可作为试验台工程实践中滑移率精确控制的解决方案。本文完成了制动工况轮轨黏着模拟试验台的搭建和验证。试验台由车轮、转臂、环形轨道、齿轮箱、机架、电机和流体喷洒装置等组成。滑移率通过制动轮和纯滚轮的转速计算得到,而黏着系数根据扭矩仪和压力传感器计算得到。试验台落成后,开展了验证性试验,试验结果表明试验台能够实现自解耦的设计预期,车速、滑移率的控制效果能够达到提出的精度指标,试验台可以复现制动大滑移条件下的黏着改善现象。对试验台的黏着系数和滑移率进行了误差分析,发现车轮半径带来的误差约为回转半径误差的10倍,需要根据磨耗状态及时更换车轮才能满足试验台技术指标,车轮半径的磨耗到限量为1 mm。通过独特的轮/环结构型式,试验台还原了第三介质污染物的实际分布状态,且具备探索不同轨面条件下黏着改善现象的能力和精确性。最后,基于试验台开展制动大滑移工况轮轨黏着模拟试验研究。对不同速度、轴重、滑移模式、水量水温、轨面介质进行了轮轨黏着试验。得到水工况下黏着改善与速度差平方正相关,与轴重负相关。试验结果还表明滑移周期对黏着改善基本没有影响,说明黏着改善与时间的累积作用无关;黏着改善是大滑移工况下的特殊现象,滑移率较低时不出现。洒水流量增大,轨面初始水膜厚度增加,黏着改善越困难,洒水流量存在饱和值;洒水温度增大,黏着改善量逐渐减小。对于减摩液工况,黏着改善在较高车速下才能出现。油脂和树叶污染物一般不会发生黏着改善。利用试验台获得的试验数据,提出了水工况下黏着改善的经验公式,能够较好地描述大滑移过程中黏着系数随速度差、轴重的变化规律。更多还原

【Abstract】 Wheel-rail contact is an important boundary factor for rail vehicles,which is one of the biggest characteristics different from other transportation.Ordinarily,rail vehicles rely on wheel-rail contact for loading and guiding,traction and braking.Since the wheel and rail are not completely rigid,creep occurs at the wheel-rail contact interface,which generates creep force.This condition is called wheel-rail adhesion.When the rail surface is contaminated by water,oil or leaves,the adhesion between wheel and rail will be reduced,resulting in the loss of braking force and extended stopping distances,threatening the driving safety.It has been found that large slip between wheel and rail can alter contact interface state and recover poor adhesion,besides the method of sanding.In order to further theoretical and experimental research on adhesion recovery under large slip conditions,it is necessary to develop a new test-rig for wheel-rail contact experiments under various surface conditions,and restore the actual distribution status of contaminants on the rail surface by innovating the structural form of the test-rig.It is of great significance to provide test data for the design of new braking control and anti-skid system of rail vehicles,and effectively improve the safety and efficiency of rail transportation.This article briefly describes the development and limitations of classical adhesion theory,reviews the discovery of adhesion recovery and the research process of adhesion characteristics under large slip conditions,then classifies and evaluates the existing wheel-rail contact simulation devices at home and abroad,including wheel/wheel test-rigs,wheel/rail test-rigs,and wheel/ring test-rigs.The wheel/ring test-rig can conduct wheel-rail adhesion simulation tests with high speed in a limited field,and can ensure that the third medium is on a stationary rail surface,which is similar to the actual operating conditions of the vehicle.Therefore,this type of test-rig is selected to meet the research needs of wheel-rail adhesion simulation under large slip conditions in the third medium condition of the rail surface.In order to study the wheel-rail adhesion characteristics of actual vehicle through a test-rig,wheel-rail adhesion simulation on different types of test-rigs was carried out.Firstly,the adhesion state of the actual wheel-rail vehicle was analyzed,and the three-dimensional creepages and forces of the actual vehicle were calculated based on the rolling contact theory.Secondly,with the similarity principle of wheel-rail normal force,the ratio of the long and short half axles as well as the maximum normal stress of the contact spot on the test-rig be equal to the actual vehicle is required.Analyze and calculate the contact error,scale,vertical force,and power of the test-rig.The wheel/wheel test-rig results in normal contact error due to the limited longitudinal radius of rail.The scale of the test-rig determines the wheel diameter,loading vertical force,and the power required for the test-rig.Finally,study on the similarity of tangential force between wheel/ring test-rig and actual vehicle is conducted,and the equivalent relationship with the longitudinal creepages is established.The radius of the test-rig is calculated to be 525 mm to 2100 mm according to the equivalent taper of the real vehicle tread.When the radius is 1 m,the longitudinal stress error of the test-rig contact spot is less than 8%.Subsequently,the impact of the lateral creep force caused by the spin creepage of the test-rig is discussed.When the radius is 1 m and the longitudinal creepage is greater than 5%,the ratio of the lateral creep force to the longitudinal creep force is less than 0.5%.The existence of the lateral force will not occupy the longitudinal force,affecting the simulation of braking force.Considering the power limitations and engineering factors in the laboratory,the scale of 1:4 and the rotating diameter of 2 m of the test-rig were selected.According to the similarity analysis of vehicle dynamics,it is confirmed that the scaling strategy of the test-rig is reasonable and self-consistent.On this basis,the self-decoupling design concept of the test-rig was elaborated,then the transmission system of the test-rig was designed and the dynamic equations of the test-rig were written.By establishing the self-decoupling condition that the structural parameter is equal to the transmission parameter of the test-rig,the power split between the vehicle speed motor and the wheel speed motor is achieved,and the change in adhesion will not affect the vehicle speed.The test-rig is affected by nonlinear factors such as wheel-rail adhesion,gear meshing vibration,structural deformation,and wind resistance during operation.A nonlinear dynamic model of the test-rig considering the above factors was established through SIMPACK to study the dynamic response of the test-rig.Simulation analysis found that the test-rig experienced fluctuations in slip rate at the initial moment and converged to the target value within 2 to 5 seconds.The double closed-loop control system of the test-rig using PID control algorithm can ensure the control accuracy of slip rate.The SIMAT joint simulation results show that the error is less than 1%.Based on this,the design indicators of the test-rig are proposed.The PID control algorithm can be used as a solution for precise control of slip rate in the test-rig engineering.This article completes the construction and verification of the test-rig for wheel-rail adhesion simulation under braking conditions.The test-rig is composed of wheels,rotating arm,ring track,gearbox,frame,motors,and fluid spraying device.The slip rate is calculated by the rotational speed of the braking wheel and the pure rolling wheel,while the adhesion coefficient is calculated by the torque meter and pressure sensor.Validation tests were conducted on the test-rig and the results showed that the test-rig can achieve the expected design of self-decoupling,and the control effect of vehicle speed and slip rate can achieve the proposed accuracy indicators.The test-rig can reproduce the adhesion recovery under large slip conditions.The error analysis of the adhesion coefficient and slip rate of the test-rig shows that the error caused by the wheel radius is about 10 times the error of the radius of test-rig.The wheel should be replaced in time according to the wear status to meet the technical indicators of the test-rig.The maximum wear amount of the wheel is limited to 1 mm.Through a unique wheel/ring structure,the test-rig restores the actual distribution of contaminants and shows the capability and accuracy to explore adhesion recovery under various surface conditions.Finally,experimental investigations of wheel-rail adhesion simulation under large slip conditions were conducted on the test-rig.Wheel-rail adhesion experiments were carried out on different running speeds,axle loads,slip modes,water volume,water temperature,and rail surface contaminants.The adhesion recovery under water conditions is positively correlated with the square of the velocity difference,and is negative correlated with the axle load.The experimental results also indicate that the slip period has little effect on adhesion recovery,suggesting that adhesion recovery is not related to the cumulative effect of time;Adhesion recovery is a special phenomenon under large slip conditions,which does not occur on small creepage.The increase in sprinkler flow results in an increase in the initial water film thickness on the rail surface,making it more difficult to improve adhesion.The sprinkler flow has a saturation value;As the watering temperature increases,the amount of adhesion recovery gradually decreases.For antifriction fluid conditions,adhesion recovery can only occur at higher vehicle speeds.Oil and leaf contaminants generally do not improve adhesion.Using the experimental data obtained from the test-rig,an empirical formula for adhesion recovery has been proposed,which can better describe the variation of adhesion coefficient with speed difference and axle load during large slip processes.更多还原