汽车盘制动器优化设计热和机械特性的研究(二)

由于热量集中于制动盘的表面造成热弹不稳定性(TEI)而引起热变形.这样可能发生大家知道的低频强烈振动.因为在盘和衬块的接触面间的摩擦系数变化,在摩擦衬块发生尖叫声.通过对热聚集和尖叫现象的联合分析,对高热和机械特性可设计一最佳的盘和摩擦衬块.本文同时考虑了热和机械不稳定性按照盘的厚度,卡钳的加压方式,衬片弧长进行了数值...     

汽车盘制动器优化设计热和机械特性的研究(一)

由于热量集中于制动盘的表面造成热弹不稳定性(TEI)而引起热变形.这样可能发生大家知道的低频强烈振动.因为在盘和衬块的接触面间的摩擦系数变化,在摩擦衬决发生尖叫声.通过对热聚集和尖叫现象的联合分析,对高热和机械特性可设计一最佳的盘和摩擦衬块.本文同时考虑了热和机械不稳定性按照盘的厚度,卡钳的加压方式,衬片弧长进行了数值和实验分析.采用有限元分析法(FEA)计算了热变形和压力分布.采用汽车底盘测功器和高速红外摄像仪进行实验评估TEI性能,结果用FEA修正.采用FEA估计机械不稳定性进行复杂固有值分析,按照转子和摩擦衬盘的形状对于一固有值问题应用修正仿真结果分析接合形式.在热聚集和尖叫问题期间,讨论因考虑盘制动器性能盘和摩擦衬块的设计.     

盘式制动器中热问题的研究概况

摩擦热是影响摩擦副材料性能变化的最直接因素。过高的摩擦热不仅使摩擦副材料的摩擦学性能发生变化,而且导致热弹性不稳定性（TEI）、局部过热点现象等发生,制动盘发生热变形。目前研究认为,热弹性不稳定性是制动器发生热颤振和噪声的主要来源,最终可能导致制动器过早失效。本文针对这些方面的研究进行了综述,最后进行总结并对未来研究工作提出了展望与建议。     

干式摩擦元件的热弹不稳定性分析

针对干式摩擦元件热弹性失稳问题,通过理论和仿真计算相结合的方法,将系统扰动因素和系统结构因素相统一,从扰动频率对临界速度影响的角度,开展制动器干式摩擦元件的热弹不稳定分析。研究发现,系统失稳与扰动频率有关,造成系统失稳的临界速度存在一个极小值点,在该点系统最容易产生失稳;摩擦副局部热应力过大是造成系统失稳的主要原因,摩擦副整体温度的高低与系统失稳之间不存在必然的联系。提出的基于热固耦合扰动边界的干式摩擦元件热弹不稳定性分析方法,其计算结果可以直接用来指导摩擦片热弹性失稳的结构设计。     

摩擦引起的模态耦合不稳定性分析

模态耦合是摩擦系统振动不稳定性的重要机理之一,它会受到系统摩擦副的结构阻抗特性和摩擦接触特性的显著影响。针对一类由一个摩擦副部件的不同方向模态导致耦合不稳定性的现象,建立2自由度摩擦振动动力学模型,推导在摩擦副部件机械阻抗特性相差极大的条件下,系统摩擦耦合模态不稳定性及其对摩擦力方向的依赖性,以及研究了不稳定区域对摩擦副结构和摩擦接触特性参数的敏感性;同时,也分析摩擦副部件的自身约束模态频率和系统接触模态频率对系统摩擦耦合模态区域和频率的影响。这为指导以避免模态耦合的摩擦振动系统的结构参数和摩擦接触参数匹配,以及识别摩擦振动不稳定的摩擦副模态来源提供了理论依据。     

摩擦材料特性对离合器热弹性不稳定性的影响

针对车辆换挡离合器,应用热弹性不稳定性(Thermoelastic instability,TEI)理论研究其接合过程中的温度场非均匀分布问题。建立离合器接合过程的二维理论模型,采用扰动法求解系统发生TEI的临界条件。通过试验验证TEI理论对离合器温度场分布研究的适用性和临界速度的存在性。研究表明当离合器接合速度超过临界速度时,系统由于摩擦热、热应力和弹性应力等因素耦合作用而失稳,摩擦副表面温度场出现强烈的非均匀性。热点数小于5时,铜基材料临界速度小于纸基材料;热点数大于5时,铜基材料临界速度大于纸基材料。减小摩擦材料弹性模量、增大热导率以及减小对偶材料热膨胀系数,可以提高系统稳定性。     

制动工况下圆盘/摩擦衬块接触面间动态压力中心的测量(一)

本文阐明了活塞尾端或内侧,摩擦衬块在制动产生听觉可分辨的噪声方面的影响。采用独特的技术测量常态制动工况下摩擦衬块/圆盘接触面间的动态中心压力(Cop)。该新技术采用一个在摩擦衬块内嵌入压力感敏膜。本文还提出了摩擦衬块/卡钳接触区的共面分析,以及它对圆盘/摩擦衬块Cop位置的影响。该分析表明,活塞尾端情况,影响Cop位置,并进一步说明该中心的移动类似于摩擦衬块支架振动与支架反向。本文包含用12个活塞对立卡钳的附加研究,初始Cop位置可以沿摩擦衬块和径向两个方向变化。结果表明,Cop的运动很明确使制动压力增大。     

盘式制动器的制动效能和接触应力分析

研究汽车制动性能的影响因素,分析盘式制动器的制动效能。计算摩擦衬块产生的最大制动力矩、制动效能因素及摩擦衬块对制动盘的压紧力等。以摩擦衬块、制动盘为研究对象,研究轿车在低速、中速、高速和最高时速制动时,制动盘和摩擦衬块上的应力分布规律,给出速度对应力分布的影响规律。应力分布影响制动器的制动转矩容量、热容、磨损等,摩擦衬块与制动盘之间既不是完全接触更不是均匀分布的接触压力,接触表面的应力分布一直是工程界和学术界关注的热点之一。     

火箭橇滑块摩擦热的结构耦合场分析

利用ANSYS软件建立火箭橇试验中滑块与轨道的滑动摩擦热-结构耦合场模型,研究特定载荷和运行工况下滑块的温度场和应力场。结果表明:滑块材料的热参数和滑块轨道间的摩擦因数对接触面温度有很大影响,接触面温度随摩擦因数增大而增大;分析指定路径上的应力分布可知,摩擦热影响区和热应力集中区域约为从接触面开始至向上6 mm范围内,滑块在运行中的破坏发生在该区域。     

基于分形理论的接触式机械密封端面摩擦热模拟计算

通过模拟计算,分析工作参数和端面形貌分形参数对接触式机械密封端面摩擦热的影响。基于机械密封端面接触分形模型,考虑密封端面摩擦热、摩擦系数、端面温度之间相互影响的关系,提出了密封端面摩擦热的耦合计算方法。对内流式部分平衡型机械密封端面摩擦热的影响因素进行了计算分析。结果表明,随着弹簧比压或密封流体压力的增大,密封端面摩擦热线性增大;随着转速的增大,密封端面摩擦热近似线性增大,且密封端面越光滑,摩擦热的增量越大;随着端面分形维数的增大或特征尺度系数的减小,密封端面摩擦热非性线增大,且随着密封端面趋于光滑,摩擦热的增幅变大。     

Surface modification of brake discs to reduce squeal problems

Noise and squeal from brakes is a problem in the automotive industry and large efforts are made to reduce the squeal tendencies. The approach taken is mainly to improve the design of the caliper, to fine-tune the brake pad material and finally to trim by introducing shims on the backside of the pads. Despite these efforts still no general solutions exist. To advance the situation, a deeper understanding of the actual source of excitation of the sound in the friction interface is needed.Earlier investigations by the present authors have made it clear that grit blasting of a disc lowers the coefficient of friction between disc and pad and may have a strong influence on the squeal propensity. Depending on the pattern of the grit blasted area the noise can be either promoted or reduced.In the present investigation, a spiral shaped modification of the brake disc surface topography has been tested with respect to the noise reduction properties. All tests have been made in a brake test equipment consisting of a complete front wheel corner of a car.The treatment has resulted in a significant reduction of the generation of noise. Unfortunately, due to wear the silencing effect has a limited life-time, here around 3000 long brakings.     

A study on squeal noise reduction considering the pad shape of the disc brake system for urban railway vehicles

Journal of Mechanical Science and Technology - In this paper, to help reduce the squeal noise produced during the braking of urban railway vehicles, the shape of the disc brake pad was investigated...     

Analytical formulation of mode-coupling instability in disc-pad coupled system

This paper describes the mode-coupling-type squeal mechanism in a disc brake system. The mode shapes of a disc and a brake pad (an annular sector plate) are obtained using the component eigenvalue analysis and the Rayleigh-Ritz method, respectively. The disc-pad coupled system subject to friction-couple is discretized by the truncated set of system component modes. Mode-coupling instability is determined in closed form resulting from a reduced-order friction-coupling model, which subsequently defines the modal stability index. The proposed index parameter determines the necessary condition for flutter instability without solving system complex eigenvalues. The numerical investigation shows that the disc-pad modal interaction has a strong squeal tendency when two pads are not identical.     

闸片沟槽织构对盘式制动尖叫的影响

为研究制动闸片沟槽织构对盘式制动系统制动尖叫的影响,基于摩擦自激振动理论,建立盘式制动系统普通闸片和沟槽闸片有限元模型,采用复特征值分析法研究该盘式制动系统的摩擦自激振动特性。利用该有限元模型开展沟槽的宽度和深度的参数化分析,获得其对制动尖叫的影响规律。结果表明：制动闸片与制动盘间的摩擦自激振动是导致制动尖叫发生的主要原因,沟槽型闸片对抑制制动尖叫具有明显效果;当闸片沟槽深度在5~20 mm区间内,盘式制动系统的稳定性随沟槽深度的增大而呈现逐渐降低的趋势,表明沟槽深度越小,发生摩擦自激振动的可能性越小;在沟槽宽度5~20 mm范围内,随沟槽宽度的增大,盘式制动系统的稳定性先增大后降低,在沟槽宽度为10 mm时,系统发生制动噪声的可能达到最大。     

基于盘／销装置的摩擦尖叫噪声研究

为了研究摩擦尖叫的产生机理,利用汽车制动盘、摩擦材料及铝合金圆销设计了一种长度可调的盘／销摩擦试验装置,进行了不同销长的摩擦尖叫试验。基于盘／销零件的约束模态试验结果,建立了装置的有限元模型。利用复特征值分析方法研究了销长、摩擦因数、载荷、速度和材料特性等因素对摩擦尖叫噪声的影响。结果表明：当圆销和制动盘间弯曲模态频率相近时会形成模态耦合,系统不稳定,产生摩擦尖叫噪声;通过改进系统结构、适当降低摩擦因数和调整材料特性可以减轻或消除摩擦尖叫。     

Finite element modeling for stick-slip pattern of squeal modes in disc brake

This paper provides the finite element modeling for describing the nonlinear stick-slip response of squealing modes in a disc brake system. The analytical nonlinear contact kinematics is applied to each contact node of the finite element disc and pads. Numerical results show that a portion of the contact area can undergo the stick-slip oscillation. Depending on the size of the stick-slip zone, the corresponding squeal vibration can be either the pure harmonic or periodic oscillation. Particularly, the squeal mode arising from the pad rigid mode generates the periodic stick-slip limit cycle in its steady-squealing response, as opposed that the disc squeal modes become the pure harmonic response.     

约束对盘形制动摩擦噪声影响的有限元研究

建立了铁路车辆盘形制动装置的三维实体有限元模型，分别为该模型中的制动盘、闸片和夹钳等部件设置了不同的材料特性。利用线性弹簧力模拟制动摩擦面间的法向力，摩擦力取为线性弹簧力与摩擦因数的乘积。通过对系统有限元运动方程进行复特征值分析，根据复特征根实部为正值判断系统发生失稳的模态，这也是可能产生摩擦噪声的模态。仿真结果显示，系统的约束条件对摩擦噪声的形成有显著的影响。改变模型的约束条件，可以抑制制动系统的摩擦噪声发生趋势，说明通过优化设置约束条件来提高摩擦系统的运动稳定性从而抑制摩擦噪声的发生是可行的。     

Disc brake squeal characterization through simplified test rigs

This paper presents a review of recent investigations on brake squeal noise carried out on simplified experimental rigs. The common theme of these works is that of approaching the study of squeal noise on experimental set-ups that are much simpler than commercial disc brakes, providing the possibility of repeatable measurements of squeal occurrence. As a consequence, it is possible to build consistent and robust models of the experimental apparatus to simulate the squeal events and to understand the physics behind squeal instabilities.     

Improvements for reduction of the brake squeal noise at Seoul metro rolling stock on tracks

Experimental and theoretical methods were applied to find and understand the phenomenon of brake squeal noise of the Seoul Metro rolling stock on tracks. Generally, it is well known that brake squeal noise is strongly related to stick and slip between brake pad and disk. In most cases for rolling stock on tracks, trailer cars needed more particular attention through the tests, because they were the major sources of brake noise due to frictional braking. There are two types of rolling stocks in Seoul Metro: chopper and VVVF. Both types of rolling stocks for lines 1 and 3 in the Seoul Metro were used for experimental analyses. To study brake squeal noise under various braking conditions, dynamometer tests were performed at the S&T Brake, Co., which is one of major manufacturers of brake pads for rolling stock on tracks. For measuring brake squeal noise, acoustic tests were performed with a microphone in the Gunja depot. And modal tests for brake parts, which consisted of brake lining, brake lining pad, and back plates, were executed to obtain the natural frequencies related to the brake squeal noise. Also, modal tests of the whole brake assembly and lining block were performed at the heavy maintenance shop of the Gunja depot. The mode analysis using an ANSYS was simulated to determine the relations between the mechanisms of brake squeal noise. As the results of the tests and the simulations, it was found that specific natural frequencies of the brake parts affected squeal noise, and also, the reason to create squeal noise. Finally, improvements for reducing squeal noise were proposed, and applied to lines 2 and 3 at Seoul Metro rolling stock on tracks. This paper was recommended for publication in revised form by Associate Editor Yeon June Kang Seong Keol Kim received his B.S. in Mechanical Design and Production Engineering from Seoul National University, Korea, in 1986. He then received his M.S. and Ph.D. degrees from Seoul National University in 1988 and 1994, respectively. Dr. Kim is currently an Assistant Professor at the School of Mechanical Design and Automation Engineering at Seoul National University of Technology in Seoul, Korea. Also, he works as an Executive Director of R&BD division of Seoul Technopark. Dr. Kim’s research interests include reliability of Micro System Packaging and mechanical vibration.