考虑时变速度的盘式制动系统的颤振特性研究

制动过程中的黏滑与颤振是一个与摩擦密切相关的复杂动力学问题.为了研究制动盘与摩擦片的黏滑与颤振现象,建立了制动系统考虑制动盘旋转自由度的五自由度非线性动力学模型.利用数值仿真方法,通过改变制动过程中的制动压力和初速度,研究速度时变的动力学特性,从而探索其黏滑与颤振现象产生的相关原因.研究结果表明:制动盘和摩擦片的切向振幅随着制动初速度的增加,呈先增大后减小的趋势;低速时制动盘和摩擦片切向将产生明显的黏滑颤振,随着制动初速度的增加,黏滑颤振逐渐减小;随着制动压力的增加,切向和法向的振动有增强趋势,系统由纯滑动逐渐进入黏滑运动并产生颤振.     

表面空气对制动力矩的影响

研究了摩擦表面流动的空气对摩擦力的影响。通过制动模拟试验，对4种不同表面形状衬片的制动力矩-时间曲线的波动幅度进行了比较分析，根据摩擦表面中流动空气的不同工作特性，建立了相应的简图进行了详细的说明：试验结果表明：在摩擦热的作用下，表面空气的温度升高，气压增加，从而削弱了工作载荷对表面的作用力，使摩擦力矩产生波动。随着制动速度的下降，热空气对摩擦力矩波动的影响减小。制动时，摩擦盘带入表面的空气越多，空气对摩擦力矩的影响就越大；摩擦表面存留的热空气越多，热空气对摩擦力矩的影响就越大。     

汽车制动颤振瞬态特性与关键因素试验研究

在常规平路起步和坡道空档起步工况下开展汽车制动颤振整车道路试验,分析制动颤振的瞬态动力学特性。设计汽车制动颤振关键因素试验,研究动力总成、制动器总成、悬架总成对制动颤振的影响。研究表明,汽车制动颤振包括两种典型的运动模式,一是具有持续时间短、宽频带特征的冲击振动,没有明确的极限环;二是具有持续时间长、多倍频特征的周期谐波振动,它属于一种典型的粘滑振动,具有明显的极限环。制动压力是汽车制动颤振发生的关键触发条件,制动压力以较大斜率下降至特定范围时,往往触发冲击振动为主的制动颤振;反之,则容易触发周期谐波振动为主的制动颤振。汽车动力总成驱动力和发动机转速波动是制动颤振的关键影响因素,合理设计发动机从低温到常温的加浓控制策略和起步时的动力总成控制策略,可有效地抑制制动颤振。制动器动、静摩擦因数差值是制动颤振重要的影响因素,制动块背板与保持架的连接刚度、制动钳质量也是关键因素。通过制动器总成结构参数设计改变颤振时制动器的振动模式,改善制动中的悬架弓形效应,为控制制动颤振提供了新思路。     

基于颤振补偿的电子液压制动系统液压力优化控制

集成式电子液压制动系统满足了车辆智能化和电动化的发展需求,已经成为制动系统的发展趋势。针对集成式电子液压制动系统液压力控制中摩擦力给系统带来的振荡和低速爬行现象,采用颤振补偿方法对系统进行液压力控制。试验表明,叠加颤振信号后的系统控制精度高,系统性能得到改善。在跟踪正弦信号时,相对于无颤振补偿的系统其误差方均根减小了79.7%。针对颤振补偿,基于试验分析,对比不同的颤振补偿信号的响应,从而优化了低频和高频液压力控制工况下叠加的颤振信号。试验证明,颤振补偿能够减轻集成式电子液压制动系统液压力控制中摩擦力所带来的振荡和低速爬行现象。此外,经过优化的颤振信号能够进一步地提高系统的液压力控制品质。     

高速制动啸叫主要影响因素的仿真与实验研究

基于高速盘式制动器的简化有限元模型,利用Abaqus进行复特征值仿真分析,对引起制动啸叫的主要影响因素进行研究。仿真结果表明:低速、高压、摩擦因数-速度曲线负斜率和高摩擦因数情况下,发生制动啸叫的可能性较大。通过不同制动速度和压力的制动实验验证了仿真研究结果的正确性。研究将对有效预防和控制制动啸叫具有指导意义。     

直线电机牵引颤振研究

建立了由直线电机定子和吊杆等组成系统的有限元模型,利用ABAQUS软件对该直线电机系统牵引颤振进行瞬态动力学仿真,研究直线电机牵引颤振发生的条件和横向拉杆对直线电机振动的影响。仿真结果显示,电磁牵引力-滑动速度的负斜率引起直线电机发生颤振,直线电机在惰行情况下不发生颤振;横向拉杆能够较大的减小直线电机的横向和垂向振动,对直线电机的纵向振动影响不大;直线电机横向和垂向之间存在耦合振动。     

制动初速度对制动盘峰值温度和温差的影响*

为改进制动盘的使用寿命,研究车辆速度改变时制动盘峰值温度、最大温差以及单位时间温度增量在不同制动时刻的瞬时温差。利用ADINA软件,针对盘形制动,基于热-机耦合模型模拟计算制动压力0.5 MPa、制动初速度140、160和180 km/h工况下制动盘温度场的变化。结果表明:随制动初速度的增加,盘面峰值温度和最大温差增加,3种速度条件下盘面峰值温度分别为151、167、200℃,最大温差分别为85、91和112℃;盘面温差主要缘于摩擦弧的分布形态,制动初速度的增加放大了摩擦弧的作用;制动初速度对制动盘单位时间温度增量的影响主要体现在制动初始阶段,在制动后期,温度的变化主要由冷却条件和热传导所控制;盘轴向最大温差依赖于盘的导热性能,对制动初速度不敏感。     

盘式制动系统参数对制动颤振的影响分析

为了研究盘式制动系统参数对制动颤振的影响,建立了二自由度的动力学模型,利用Matlab进行数值仿真,分别研究了制动初速度、制动压力、阻尼和刚度等因素对制动系统动力学特性的影响。根据得到的位移曲线和相图可以看出:随着制动初速度的增大,系统黏滞阶段持续时间减少,并逐渐进入稳定运动状态;制动压力相对较小时,制动系统处于稳定状态,随着制动压力的增大,摩擦片和制动盘的振动幅值也随之增大,振动强度变大;在阻尼增大的过程中,摩擦片和制动盘均由起初的纯滑动运动状态进入稳定运动状态,且达到稳定运动状态的时间也逐渐缩短;摩擦片在相对较小的制动刚度下即可达到稳定状态,而制动盘则需要有较大的刚度才能达到稳定状态。     

利用粘滑机理分析铁道车辆盘形制动颤振

以往的盘形制动颤振模型都把制动盘看成不动的刚体,这是不太合理的.在分析盘形制动颤振现象之后,建立一个并联的两自由度颤振模型.通过数值仿真,主要探讨不同制动速度、不同制动压力以及不同阻尼对颤振的影响,得出一系列对制动颤振控制有意义的结论.     

应用多体动力学制动器盘片间多柔体建模分析

盘式制动器制动过程分析时,难点在于建立制动盘和摩擦片之间柔性体接触摩擦力,影响制动器性能和可靠性重要因素。根据制动器结构和功能特点,分析制动过程中车轮和制动器的受力情况,结合制动盘片之间正压力和摩擦力实现方法,分析制动器盘片之间柔性体接触摩擦力,采用多体动力学理论建立多柔体分析模型。利用模型对制动过程进行分析,对动摩擦因数、安装误差等影响因素对制动过程对制动性能和振动特性影响,获得制动过程中减速度和角减速度傅里叶变换等参数随时间变化趋势。进行盘式制动器样车测试,并将模型分析结果与试车测试结果进行对比分析,可知模型分析与试车试验结果基本一致,为制动器问题深入研究提供一种可行研究手段和方法。     

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。     

Influence of Thermal Fatigue on the Wear Behavior of Brake Discs Sliding against Organic and Semimetallic Friction Materials

ABSTRACT

In this article, brake discs are exposed to high thermal stress, causing thermal fatigue damage. The aim of this work is to study the evolution of the wear behavior of brake disc materials, such as cast iron, chromium steel, and metal matrix composites, under the influence of thermal fatigue. The brake disc specimens are heated and then cooled rapidly. Then, wear tests are carried out using a pin-on-disc-type tribometer. Organic and semimetallic friction materials are used for all wear tests. The results show that thermal fatigue affects the structure of the contact surfaces of all of the disc specimens by increasing their roughness. Furthermore, the wear rate of the friction materials increased, except a reduction of the wear rate is noted for the semimetallic friction material rubbing against cast iron. Moreover, thermal fatigue has no significant influence on the coefficient of friction. The worn surface of the metal matrix composite sliding against semimetallic friction material is characterized by abrasive and adhesive wear mechanisms.     

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。     

On the nature of tribological contact in automotive brakes

The tribological contact in automotive brakes involves dry sliding contact at high speeds and high contact forces. The commonly used organic binder-type brake pad friction materials are extremely inhomogeneous and exhibit very low bulk strengths. Despite the low strength, the specific contact surfaces that form during the use render the pads very good friction and wear characteristics. This paper gives a general view of the contact situation of organic binder brake friction materials against cast iron discs, with special emphasis on many mechanisms for contact surface variations and the corresponding variations of the coefficient of friction.     

On the dry and wet sliding performance of potentially new frictional brake pad materials for automotive industry

In this work, dry and wet continuous sliding performances of newly developed four different non-commercial frictional brake pad materials (NF1, NF2, NF4, and NF5) were evaluated and compared with other two chosen commercial brake pad materials (CMA and CMB) using a small-scale tribo-tester of pad-on-disc type.Results showed that under dry continuous braking, friction coefficients for all non-commercial brake pad materials including the CMB were insensitive to the type of brake pad materials. In addition, all brake pad materials showed a slight increase in the friction coefficients (5–19%) with increasing pressure or speed. Meanwhile, the wear rates were substantially dependent on the type or ingredient of brake pad materials and the pressure. Conversely, under wet sliding condition, the friction coefficients were decreased by a factor of 2. Moreover, no evidence of HD water film could be evidenced as the measured friction coefficient values were in the order of dry friction. Thus, the wet results suggested that the friction behaviour was influenced by factors other than HD film, and the values of friction coefficient were in the range of dry friction, mixed and boundary lubrication friction. Qualitative assessment of the SEM morphologies of brake pad surfaces showed that tribofilms were easily formed in dry braking and hardly formed in wet braking. Besides, all brake pad rubbing surfaces showed contact plateaus “patches” and disintegrations of various sizes and locations depending on the braking condition. Furthermore, the removal of material was associated with either mechanical crushing action performed by entrapped wear debris or due to disintegration of plateaus which were accelerated by spraying the water.     

Comparison of Chase and inertial brake Dynamometer testing of automotive friction materials

For effective and safe automotive brake system applications, friction materials must meet certain minimum requirements for performance, noise and durability. To ensure this, friction materials are subjected to a series of vehicle tests on a test track or on the road before they are released as commercial products.While vehicle tests are expensive, time consuming and subject to road conditions and weather variability, brake dynamometer testing in the laboratory is faster and less costly to screen or verify friction material characteristics. Furthermore, because of the capability to control test conditions precisely, a brake dynamometer serves as an excellent tool for the research and development of friction materials.In the U.S.A. two major types of brake dynamometers are commonly used: the inertial dynamometer which evaluates a full size brake or a brake system and simulates vehicle braking well, but is time consuming and expensive, or a smaller Chase dynamometer that features low capital expenditure and shorter test time using a small friction material sample against a large drum. The Chase dynamometer does not simulate brake conditions as well as the inertial dynamometer, and therefore is used primarily for rapid screening and/or for quality control only.The correlation, or the lack of it, between these two brake dynamometers is discussed in this paper. Friction and wear data from both test systems on several friction pairs under various temperature, sliding speed and load conditions are compared and discussed. The materials used were (a) non-asbestos organic disc pads against cast iron rotors, (b) semimetallic disc pads against cast iron rotors and (c) non-asbestos organic disc pads against copper rotors.     

Tribological surfaces of organic brake pads

Despite the enormous amount of testing and development of automotive brakes and brake pad materials, rather little is known about their tribological contact situation on a microscopic level. The sliding of an organic brake pad against a grey cast iron rotor is very different from most tribological systems. When worn against the rotor, the complex structure and very inhomogeneous composition of the pads results in a particular surface structure, with large contact plateaus rising a few micrometers above the rest of the surface [Wear 232 (1999) 163; Wear 2000 (submitted for publication); Proceedings of the Nordtrib 2000, vol. 2 (2000), 358]. The present investigation involves a more comprehensive study of the formation, mechanical properties and composition of the tribological surfaces of such pads, using high resolution scanning electron microscopy, nanoindentation, energy dispersive X-ray analysis and three-dimensional profilometry using white light optical interferometry. The observations are discussed and correlated to observed friction phenomena.     

Fundamental studies on the brake friction of resin-based friction materials

The effects of various factors on brake friction were studied on the braking of a cast iron disk by small brake specimens made of resin, resin-asbestos composites and three-component composites. When the disk temperature rises, the resin-based composites containing asbestos and high melting point additive exhibit considerably lower friction during braking following high friction in the initial braking stage. The initial high friction is attributed to the deformation resistance of the resin in the composite. Low friction is attributed to the lubricating action of resin decomposition products in the neighbourhood of the filler raised to a high temperature by frictional heating. Increase of friction toward the end of braking is mainly due to increase of the true contact area as the frictional speed decreases. Variation of the average frictional coefficient during braking with load and the initial speed is generally small. There is no correlation between the mechanical properties and the brake frictional behaviour of resin-based composites.     

Advanced Friction–Wear Behavior of Organic Brake Pads Using a Newly Developed System

The objective of this study was to investigate the influence of an advanced performance system on the tribological behavior of brake pad material using a specially designed brake pad tester system following standard SAE J-661. The tribological behavior and friction and wear characteristics of the organic brake pad samples were evaluated. During braking tests, the samples, in contact with a cast iron disk, were studied at different disc speeds, temperatures, and braking cycles under a constant pressure. In order to understand the friction and wear behavior, the unworn surfaces, worn surfaces, and wear debris were characterized by means of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). Furthermore, the surface characteristics and differences in the wear modes of the brake pad samples were examined. Wear debris was permitted to deform the brake pad surfaces, leading to friction layers and enabling the estimation of the friction behavior of the brake pads. The results showed that the best friction–wear behavior was obtained with lower braking cycles at low speeds and temperature. Thus, the newly developed brake pad tester system proved very effective in evaluating the performance of the brake pad samples.     

Effect of convective cooling on temperature and thermal stresses in disk during repeated intermittent braking

A numerical solution of the heat-friction problem for a brake pad–brake disk system during repeated intermittent braking has been obtained using the finite-element method. The obtained temperature field has been used to study the thermal stress state of the disk. A numerical analysis has been carried out for a metal-ceramic pad–cast iron disk friction pair during ten intermittent brakings. The effect of the coefficient of the coefficient of heat transfer on the temperature, the stress tensor components, and the Huber–Mises–Henky stresses on the working surface of the disk has been investigated.