制动过程中闸片材料与制动盘温度关系试验研究

为探讨碳/陶制动盘与不同闸片材料的匹配性,对碳/陶制动盘分别与碳/陶复合闸片、铜基粉末冶金闸片和铁基粉末冶金闸片组成的摩擦副进行制动试验,研究了在制动过程中盘面各点瞬时温度、最高温度、闸片温度与制动工况的关系。结果表明：碳/陶制动盘与碳/陶复合闸片摩擦副温度及温度梯度均高于其他2种摩擦副,其温度梯度在低速制动时随压力的增加而明显增加,当制动速度较高时,温度梯度并没有随压力的增加而增加;对于碳/陶制动盘与铜基和铁基粉末冶金闸片摩擦副,随制动速度和压力的提高,盘面温度梯度变化不明显。原因在于材料导热性和起始摩擦因数决定了盘面的散热能力和制动功率,碳/陶制动盘与碳/陶复合闸片摩擦副因较高的起始摩擦因数以及较低的导热性,其制动功率高和散热能力低,导致盘面温度持续升高。     

Investigation of disc/pad interface temperatures in friction braking

Maintaining appropriate levels of friction interface temperature is important for the overall operating effectiveness of modern friction brakes, and implicitly the safety of the vehicle. Measurement and prediction of the distribution and magnitude of brake friction interface temperatures are difficult. A thermocouple method with an exposed hot junction configuration was used for interface temperature measurement, and the magnitude and distribution of the friction interface temperature were investigated in this study. Using a designed experiment approach, the factors affecting the interface temperature, including the number of braking applications, sliding speed, braking load and type of friction material were studied. It was found that the number of braking applications had the strongest effect on the friction interface temperature. The real contact area between the disc and pad, i.e. pad regions where the bulk of the kinetic energy is dissipated via friction, had a significant effect on the braking interface temperature. For understanding the effect of real contact area on local interface temperatures and friction coefficient, finite element analysis (FEA) was conducted, and it was found that the maximum temperature at the friction interface does not increase linearly with decreasing contact area ratio. This finding is potentially significant in optimising the design and formulation of friction materials for stable friction and wear performance.     

摩擦副组合对摩擦磨损性能的影响

在1：1惯性力矩制动试验台上研究了两种不同石墨形态的铸铁制动盘与两种混杂纤维增强的酚醛基制动闸片配副时的摩擦磨损性能。结果表明，对于某一配方的制动闸片，使用灰口铸铁盘的摩擦副具有较高的摩擦系数，但制动盘表面温度较高，闸片磨损量较大；对于某一种制动盘，使用B配方制动闸片时，制动盘表面的温度较高，但闸片的磨损量较小；在所有四种组合中，B配方制动闸片与灰口铸铁盘配副的瞬时摩擦系数能够完全满足有关技术要求。     

动态摩擦因数对蝶式制动器温度场影响的试验和模拟研究

针对蝶式制动器制动过程中温度场研究的需要,利用相似原理研制定速制动试验台,用以模拟摩托车匀速下长坡时的制动工况。制动试验台用车床的三爪卡盘控制固定在旋转轴上的制动盘做定速旋转运动,内外摩擦片通过液压力夹紧制动盘,使制动盘与摩擦片发生摩擦运动,通过热电偶、拉压力传感器、压力表、热成像仪分别测出定速制动50 s的摩擦片上固定点的温度变化、制动扭矩(经计算得出)的动态变化、制动力的均值、制动盘摩擦区域的温度场变化,实时显示并记录下来。定速制动摩擦试验机能实现不同转速、不同制动力等条件下,制动过程中的各变量的动态测量。试验还选取热成像仪测得的最大的温度为变量,研究摩擦因数随温度的变化。在试验的基础上,用ABAQUS对制动盘与摩擦片的相互作用做了一些仿真和分析。仿照实际模型1∶1建模,加载与边界条件与实际模型相同,将测得的摩擦因数随温度变化的数据输入接触条件,仿真得到制动盘与摩擦片温度场的变化。仿真与试验的结果对比表明摩擦因数动态变化的接触模型能很好的模拟制动的实际工况。     

摩擦块形状对制动盘摩擦温度及热应力分布的影响

列车制动产生的摩擦热在制动盘表面的分布与闸片结构密切相关,并影响到制动盘的耐热疲劳程度.基于实际应用的圆形、六边形、三角形3种形状摩擦块的制动闸片,利用有限元分析软件ABAQUS,模拟制动时制动盘的温度及热应力分布情况.结果显示:制动盘摩擦表面温度及热应力呈环形带状分布,沿周向变化不明显,在径向上分布的均匀程度差异较大;其变化程度与摩擦块形状和位置有关,摩擦块为圆形时,盘面的温差和热应力最小,摩擦块为三角形时,盘面的温差和热应力最大;摩擦块的位置分布影响到摩擦副接触弧长度,接触弧长度增加,对应的摩擦环带温度升高;各环带对应的接触弧长度偏差越小,制动盘温度越低,分布也越均匀.     

Thermal behavior of full and ventilated disc brakes of vehicles

Braking is a process which converts a vehicle’s kinetic energy into mechanical energy which must be dissipated in the form of heat. During the braking phase, the frictional heat generated at the interface of the disc and pads can lead to high temperatures. This phenomenon is even more important than the tangential stress. The relative sliding speeds during contact are also important. The prediction of surface temperature for a brake rotor is regarded as an important step in studying brake system performance. The frictional heat generated on the rotor surface can influence excessive temperature rise which, in turn, leads to undesirable effects such as thermal elastic instability (TEI), premature wear, brake fluid vaporization (BFV) and thermally excited vibrations (TEV). The objective of this study is to analyze the thermal behavior of the full and ventilated brake discs of the vehicles using computing code ANSYS. The modeling of the temperature distribution in the disc brake is used to identify all the factors and the entering parameters concerned at the time of the braking operation, such as the type of braking, the geometric design of the disc and the material used. The results obtained by the simulation are satisfactory compared to those of the specialized literature.     

基于ANSYS Workbench的盘式制动器热-机耦合分析

为进一步研究盘式制动器在制动过程中的行为,在建立盘式制动器热-机耦合简化计算模型的基础上,考虑温度变化对材料物理性能和摩擦因数的影响,运用ANSYS Workbench模拟分析不同制动初速度与不同制动压力下制动盘的热-机耦合特性,并从制动盘径向、周向、轴向等维度对其温度场与应力场进行了研究。结果表明：盘式制动器在紧急制动过程中,温度和应力的最大值与制动初速度和制动压力成正相关;制动初速度和制动压力对制动盘温度场和应力场有较大的影响,其中制动压力对制动盘温度和应力最大值的影响比制动初速度更加明显;制动盘温度与等效应力在圆周上都呈环带状分布,二者具有一致性,制动盘达到温度最大值早于达到应力最大值,二者之间具有耦合特性;制动盘温度在径向和轴向上存在较大的温度梯度,从而引起较大的应力变化。研究结果为探索制动盘温度场、应力场分布规律和制动盘在不同工作状态下的热-机耦合特性提供了参考。     

风电制动器的热—结构耦合分析

针对制动器紧急制动时制动盘的旋转运动规律,根据风电制动器的实际结构和热传导的基本理论,建立了制动盘的温度场的数值模型,提出了循环迭代的计算方法,并用ANSYS有限元软件模拟了制动盘的温度场。将温度场中的热单元转化成结构单元实现热-结构的间接耦合,采用184单元刚性梁特性来带动制动盘转动,从而来模拟制动盘的减速运动,在充分考虑温度场和应力场的耦合关系的情况下,提出了分步加载的方法来计算制动盘的应力场。模拟结果表明:制动盘摩擦区域的点的等效应力分布与其温度场的分布基本一致。     

Neural network prediction of disc brake performance

An automotive brake's performance results from the complex interrelated phenomena occurring at the contact of the friction pair. These complex braking phenomena are mostly affected by the tribochemical properties of the friction material's ingredients, the brake disc properties, and the brake's operating regimes. In this paper, the synergistic effects of the friction material's properties, defined by its composition and manufacturing conditions, and the brake's operating regimes on the disc brake factor C variation have been modelled by means of artificial neural networks. The influences of 26 input parameters, determined by the friction material composition (18 ingredients), its manufacturing conditions (5 parameters), and the brake's operating regimes (3 parameters) on the brake factor C variation, have been predicted. The neural model of the disc brake cold performance has been developed by training 18 different neural network architectures with the five different learning algorithms. The optimal neural model of disc brake operation has been shown to be valid for predicting the brake factor C variation of the cold disc brake over a wide range of brake's operating regimes and for different types of friction material.     

Frictional Properties and Mechanisms of an Organic–Metal Brake Pair Braking Repeatedly in Magnetic Field

With the aim to investigate repeated braking of organic–metal brake pairs, tribological and scanning electron microscopy (SEM) experiments were performed to reveal the influence of a magnetic field on the tribological performance of brakes. A nonasbestos copper-based brake pad and gray cast iron brake disc were selected as the brake pair. The X-DM pad-on-disc friction tester was improved to set up a tribological tester under a magnetic field. The worn surfaces were observed by SEM to reveal the friction mechanisms. It was found that a magnetic field can ameliorate the dynamic friction and wear. In addition, the global mean friction coefficient increases and the wear resistance of brake materials improves. A magnetic field promotes surface oxidation and aggravates the surface heat emission condition. As a result, the mean temperature on the friction surface increases obviously. An appropriate magnetic field can improve the dynamic temperature rise and decrease the global temperature rise on the friction surface. It is considered that a magnetic field has important influences on tribological performance in repeated braking. Therefore, this research could provide theoretical references for studying the tribological performance in repeated braking and/or under a magnetic field.     

Monitoring of Transient Phenomena in Sliding Contact Application to Friction Brakes

This work focuses on the study of transient phenomena, in particular the non-uniformity and space–time variation of friction forces and surface temperature of a brake disc during stop-braking. Friction tests were conducted on a braking tribometer. The friction forces in the contact were measured using a 3D piezoelectric sensor, while the disc surface temperature was investigated by means of a high frequency fibre-optic two-colour pyrometer. An optical lap-top device was used to keep track of disc revolutions, and an original programme was written to plot the space–time variations of the measured parameters. This new original approach helps better understand the coupling between thermal and tribological phenomena occurring during braking.     

车联网环境下考虑前方车辆驾驶人意图的汽车主动预警防撞模型

前方车辆驾驶人意图信息对后方车辆预警防撞模型危险判断至关重要,针对传统防撞模型误警率高、制动不及时等问题,设计了一种考虑前方车辆驾驶人意图的汽车主动预警防撞模型。首先,选择BP神经网络（Back-propagation neural network,BPNN）和隐马尔可夫模型（Hidden Markov model,HMM）作为驾驶行为层与驾驶意图层的主体模型,并利用驾驶模拟器采集的前车制动踏板、加速踏板和车速等意图观测数据作为输入构建意图识别模型,从而实现对前车驾驶人加速驾驶、匀速驾驶、正常制动和紧急制动意图的识别;其次,利用车联网将前车驾驶人意图识别结果与路面附着信息传递给后方车辆,建立考虑前车驾驶人意图的汽车主动预警防撞模型,动态判断碰撞危险并调整预警及制动执行逻辑;最后,为验证所提出的意图识别模型准确性和主动预警防撞模型的有效性,搭建基于Simulink、Carsim及PreScan的联合仿真平台,并进行多工况试验测试。结果表明,所提出的BP-HMM模型对前车驾驶人意图的平均识别准确率为94.17%,优于传统BP或HMM识别模型;主动预警防撞模型在预警测试中的平均正警率为93.43%,与TTC、Mazda及考虑后车驾驶人意图的三种模型相比,平均误警率分别降低了16.12%、23.43%和26.67%,且在自动紧急制动测试工况中均能成功避免碰撞,两车最短相对距离大多保持在2～8 m范围内,平均值为3.698 m,具有更高的安全性和稳定性。     

盘式制动衬片力学模型的特性分析

通过对盘式制动衬片的受力分析 ,建立盘式制动衬片表面受力的力学模型 ,并计算出总摩擦力的作用中心。通过对底板与摩擦材料之间的受力分析 ,说明在各种应力作用下 ,在制动过程中有可能出现制动不稳定状态 ,为了避免这一现象 ,应合理设计衬片的几何尺寸。同时对如何设计底板上抗剪力孔的位置进行简单的分析。定性的说明了由于摩擦热而引起底板的弯曲变形 ,对摩擦面受力情况的影响。     

Increase in the coefficient of friction of the rolling stock disc brake via fluid cooling of its friction elements

The paper presents the results of theoretical and experimental investigations in the effect of a partial heat energy removal in the friction contact zone upon the disc brake coefficient of friction during braking. A fluid cooling system for the disc brake friction elements has been proposed based on a recuperative liquidpneumatic heat-exchange apparatus.     

摩擦副结构与制动盘温度关系的试验与模拟研究

摩擦副结构是影响制动盘温度分布的重要因素之一。针对闸片形状为圆形、三角形和六边形三种结构的摩擦副,采用制动试验台进行了速度为50～250 km/h的制动试验,并利用ABAQUS软件数值模拟了三种摩擦副不同工况条件下制动盘温度场的变化过程。结果表明：数值模拟温度场与试验测试结果具有良好的相似性。摩擦副结构对盘面温度分布的影响程度与制动条件密切相关,其结构形式对制动盘面温度的影响程度在制动初期最为明显,且随制动初速度和制动压力的增加而增加。这缘于闸片结构的不同导致了摩擦面摩擦弧长分布的不同,随制动速度升高和压力增加,摩擦弧长的差异起到了放大能量差别的作用,从而表现制动盘温度分布对闸片结构的敏感程度增加。     

Numerical simulation of operation heat modes of multidisc oil-cooled vehicle brake. Part 1. Heat problem solution

The paper considers the operating heat modes of multidisc oil-cooled vehicle brakes under single and multiple braking, as well as under deceleration over a long downgrade. The initially boundary-value heat problem for the given operating modes of the brake is formulated and solved by the finite-element method. The regularities of formation of nonstationary temperature fields both on the contact surfaces and in the bulk of the brake friction elements are obtained for preset braking modes. The dependences are obtained for the maximal contact surface temperature on the metal counterbody and frictional material vs. the load and velocity parameters of vehicle motion. A method for forecasting the critical operating regimes of multidisc oil-cooled brakes is proposed for the given operation conditions of the vehicle.     

汽车风冷盘式制动器摩擦学特性试验研究

为得出制动参数对汽车风冷盘式制动器摩擦学特性的影响机理,考虑空气流动和车辆惯性因素,基于噪声、振动与声振粗糙度（NVH,Noise Vibration and Harshness）台架试验机精确模拟制动工况,研究摩擦副表面在不同制动压力（1.0~3.0 MPa）、行驶速度（5~30 m/s）以及温度（100~350  ℃）条件下平均摩擦系数与摩擦稳定系数的变化规律。试验结果表明：制动压力增大时,摩擦力矩并非一定随之增大,尤其是较高行驶速度条件;当制动盘表面温度超过300 ℃时,低速条件下的平均摩擦系数和摩擦稳定系数急剧减小。     

High thermal diffusivity materials for railway brakediscs

Two high thermal diffusivity brake discs have been worn againsta metallic pad, a composite pad and a new ceramic pad. Thesediscs are composed of a friction track made of molybdenum orCu-2.5% Be alloy. Molybdenum was used in the form of a coatingsprayed on an aluminum-based disc or as a thin solid disc mechanically clamped onto an aluminum-based stand disc. Coatingadherence, friction coefficient, surface temperature and wearthickness loss were determined for a set of reduced-scale steelbrake discs during a continuous braking simulation. It is shownthat the solid molybdenum disc tested against the composite padinduces significant surface temperature decreases as opposed tosliding against the bare steel disc. The friction coefficient isstable and wear damage acceptable. However, the molydenumcoating performs unsatisfactorily as the large difference inthermal expansion coefficient between molybdenum and aluminuminduces disbonding and crazing of the coating. The aluminumtitanate pad/Cu-2.5Be disc brake system has demonstrated remarkable tribological performance, with a steady frictioncoefficient, a pad surface temperature about 60°C lower thanthat of a steel disc and low pad wear.     

重型车辆织构化刹车系统热力学行为与摩擦学性能研究

重型车辆刹车系统受瞬态高温和雨水异常侵入的影响,易引起热力学行为与摩擦性能退化。为研究表面织构对刹车系统热力学行为和摩擦学特性的影响,基于有限元法开展刹车系统热力学分析,考虑大量雨水侵入的液体润滑极端情况,提出一种动压润滑与织构集成模型的摩擦学性能分析方法。结果表明：水平凹槽织构可使制动盘温度场及应力场分布较均匀,进而避免接触区域局部瞬态高温引起的车辆制动失效;随着凹槽织构倾斜角度增大,承载力增大,摩擦因数减小;不同组合型织构中,圆柱与椭球组合型织构表面承载力最大、摩擦因数最小,圆锥与椭球组合型织构表面承载力最小、摩擦因数最大。研究发现重型车辆刹车系统表面构筑合适倾斜角度凹槽织构和组合型织构有助于提升其工作性能。     

基于接触压力分布和非均匀热流密度的列车制动盘热机耦合分析

针对铁路列车制动闸片摩擦块排布方式对制动盘热机耦合响应状态影响显著的问题,提出了一种考虑接触压力分布和非均匀热流密度的热机耦合仿真分析方法。通过在轨道车辆制动性能试验台上进行的制动台架试验,从温度的角度验证了所提方法的正确性。在此基础上,建立了列车全尺寸盘型制动系统有限元仿真分析模型,对现有铁路列车制动闸片摩擦块的排布方式进行了优化分析。结果表明,合理的制动闸片摩擦块排布方式可以显著降低制动盘面的温度和应力峰值,在改善制动盘面温度和应力分布的同时,提供较为优异的制动性能。研究成果可为铁路列车盘型制动系统热机耦合分析提供一种快速有效的仿真分析方法,同时可为铁路列车制动闸片摩擦块的排布优化提供指导方向。