Thermal fatigue and wear of compacted graphite iron brake discs with various thermomechanical properties

The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.

Sustainable Biocomposites Materials for Automotive Brake Pad Application:An Overview

Research into converting waste into viable eco-friendly products has gained global concern.Using natural fibres and pulverized metallic waste becomes necessary to reduce noxious environmental emissions due to indiscriminately occupying the land.This study reviews the literature in the broad area of green composites in search of materials that can be used in automotive brake pads.Materials made by biocomposite,rather than fossil fuels,will be favoured.A database containing the tribo-mechanical performance of numerous potential components for the future green composite was established using the technical details of bio-polymers and natural reinforcements.The development of materials with diverse compositions and varying proportions is now conceivable,and these materials can be permanently connected in fully regulated processes.This explanation demonstrates that all of these variables affect friction coefficient,resistance to wear from friction and high temperatures,and the operating life of brake pads to varying degrees.In this study,renewable materials for the matrix and reinforcement are screened to determine which have sufficient strength,coefficient of friction,wear resistance properties,and reasonable costs,making them a feasible option for a green composite.The most significant,intriguing,and unusual materials used in manufacturing brake pads are gathered in this review,which also analyzes how they affect the tribological characteristics of the pads.

Numerical and Experimental Analysis of the Aerodynamic Torque for Axle-Mounted Train Brake Discs

As the velocity of a train increases,the corresponding air pumping power consumption of the brake discs increases proportionally.In the present experimental study,a standard axle-mounted brake disc with circumferential pillars was analyzed using a 1:1 scale model and a test rig in a wind tunnel.In particular,three upstream velocities were selected on the basis of earlier investigations of trains operating at 160,250,and 400 km/h,respectively.Moreover,3D steady computational fluid dynamics(CFD)simulations of the flow field were conducted to compare with the wind tunnel test outcomes.The results for a 3-car train at 180 km/h demonstrated:(1)good agreement between the air resistance torques obtained from the wind tunnel tests and the related numerical results,with differences ranging from 0.95%to 5.88%;(2)discrepancies ranging from 3.2 to 3.8 N·m;(3)cooling ribs contributing more than 60%of the air resistance torque;(4)the fast rotation of brake discs causing a significantly different flow field near the bogie area,resulting in 25 times more air pumping power loss than that obtained in the stationary brake-disc case.

Brake Discs Surface Defect Detection Using the IGD-IHT Algorithm and the PIQEDS-ISSA-NESN Algorithm

As one of the core parts, the brake discs directly impact the braking and safety performance of vehicles. Traditional surface detection methods of the brake disc have poor robustness due to their reliance on manual feature extraction. A detection instrument was designed to focus on the detection. The features were extracted using the improved Gaussian difference algorithm and Hough transform algorithm(IGD-IHT). An identification method for brake disc surface defects was designed in this paper based on the Perception-based Image Quality Evaluator and Dempster rule-improved sparrow search algorithm-Nonlinear echo state network(PIQEDS-ISSA-NESN) to better identify. It was shown in the experiment that the accuracy was more than 97%, the false alarm rate was less than 1.5%, and the false alarm rate was less than 1.5%.

Sepiolite:A new component suitable for 380 km/h high-speed rail brake pads

To enhance the high-temperature adaptability of copper-based composite materials and C–C/SiC discs,this article innovatively introduces a method of replacing graphite with sepiolite,resulting in the successful fabrication of samples with exceptional mechanical and friction properties.The results reveal that moderate incorporation(less 6%)of sepiolite provides a particle reinforcement effect,resulting in an improvement of mechanical properties.Interestingly,the addition of sepiolite causes a change in the traditional saddle-shaped friction curve due to high temperature lubrication.Meanwhile,the primary advantage of sepiolite lies in its superior abrasion resistance,evident in the increased friction coefficient and altered wear mechanisms with higher sepiolite content.The wear resistance is optimal at 200 Km/h(400℃).Particularly,the unique composition of the friction layer(outermost layer:a composite film consisting of B2O3,sepiolite,graphite,and metal oxide films;intermediate layer:metal oxide films)plays a pivotal role in improving friction stability.Finally,there are significant optimizations in the GA algorithm,especially GA-GB model has the best prediction effect on the maximum friction temperature.

轮毂电动机驱动车辆并联式复合制动策略

基于并联式轮毂电动机驱动实车构型,分析影响制动能量回收效率的主要因素,采用联邦卡尔曼滤波纵向车速估计算法,提出了三层式复合制动控制策略.该策略中的制动决策层根据踏板输入信号和行驶状态来识别制动工况,并进入相应的制动模式.制动控制层根据制动决策层的指令,在常规制动工况下通过粒子群优化(PSO)算法优化前、后轮电制动力矩分配,实现电池有效回收效率最大化;紧急制动工况下,通过模糊自整定PID算法实现车辆在不同附着路面上各轮滑移率的安全有效控制,优化了制动防抱死控制的鲁棒性,提高制动安全性.制动执行层响应制动控制层的指令,设计了电制动补偿机制,以迅速补偿调节各轮轮缸的压力误差,提高车辆制动稳定性.最后实车验证了该复合控制策略的有效性.

电动汽车多参数模型预测制动能量跟踪策略

针对电机制动能量回收率低和直流母线电压波动大的问题,提出了考虑电机功率、双向DC/DC变换器效率、超级电容电压等多个参数实时调整超级电容电流参考值的制动能量跟踪策略。采用储能单元的离散状态空间模型预测超级电容的电流和电压,并结合系统中多个参数计算超级电容的电流参考值。使用基于比例积分(PI)的电流环控制超级电容电流实时跟踪参考值,实现超级电容对电机能量的跟踪。通过仿真分析和对比试验,结果表明:所提出的策略能够将制动能量的回收效率由55.93%提升至86.76%,直流母线的电压波动范围抑制在0.9%以内。

Thermal analysis for brake disks of SiC/6061 Al alloy co-continuous composite for CRH3 during emergency braking considering airflow cooling

The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk during emergency braking at a speed of 300 km/h considering airflow cooling were investigated using finite element （FE） and computational fluid dynamics （CFD） methods. All three modes of heat transfer （conduction, convection and radiation） were analyzed along with the design features of the brake assembly and their interfaces. The results suggested that the higher convection coefficients achieved with airflow cooling will not only reduce the maximum temperature in the braking but also reduce the thermal gradients, since heat will be removed faster from hotter parts of the disk. Airflow cooling should be effective to reduce the risk of hot spot formation and disc thermal distortion. The highest temperature after emergency braking was 461 °C and 359 °C without and with considering airflow cooling, respectively. The equivalent stress could reach 269 MPa and 164 MPa without and with considering airflow cooling, respectively. However, the maximum surface stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk without cooling. The simulation results are consistent with the experimental results well.

全自动运行列车制动电阻液压风机自动控制方法研究

全自动运行列车制动电阻液压风机是一种利用液压技术驱动的设备,在列车运行过程中,其性能受到多个因素影响,容易导致输出气流或气压不稳定问题,因此研究全自动运行列车制动电阻液压风机的自动控制技术具有重要意义。在列车与轨道间作用力的基础上,构建列车制动模型,获取制动力矩,将相对扭转角作为基础,计算自旋蠕滑力矩,根据瞬时蠕滑速度,计算出列车车轮与轨道间的粘着力矩;构建列车驱动模型,建立制动力矩主动分配目标函数,利用Park变换和Clarke变换,获取电阻液压风机电磁转矩,通过转子磁链与控制频率实现电阻液压风机的自动控制。实验结果表明:该控制方法在列车制动控制过程中,其风机效率及恒速占比均值分别为5.26 s和99.77%,控制电阻后的风机电压与理想电压基本一致,能够高效恒定的实现制动电阻液压风机控制,提高列车的安全性。

Distribution and Dissipation of Braking Power of Wet Multidisc Brake

To study the distribution and dissipation of braking power of wet multidisc brake and determine thermal load and thermal flux distribution between mated discs, the concept of distributing brake power four times was put forward. The third and the fourth distribution of brake power were calculated by using finite element(FE) software ANSYS. The third and the fourth distribution of wet multidisc brake are mainly related to material characteristics of discs during emergency braking, while most of the braking power is carried off during continuous braking. Basis is provided for further analysis of disc failure and applicability of different friction materials.

基于剩余碰撞时间的线控制动分层控制策略

针对不同制动工况需求的制动策略存在差异的情况,提出一种线控制动分层控制策略.在该分层策略的上层,利用二阶TTC安全碰撞时间模型计算出车辆与前车的剩余碰撞时间,以此作为依据进行制动策略的选取,并建立了汽车二自由度模型、车身法向受力模型和Burckhardt轮胎模型;在该分层策略的下层,进行了制动力在轮间的分配,使用序列二次规划(SQP)方法,分别在一般制动、紧急制动、失稳制动3种工况下,以轮胎滑移率为对象建立优化函数,对车辆制动力进行了优化分配.使用MATLAB/Simulink和Carsim进行了联合仿真,对所提出3种工况下的制动分配策略进行了有效性验证.结果表明:在一般制动工况下,采用该策略时相比对照工况制动距离减少18.08%,制动时间减少25.12%;在紧急制动工况下,采用该策略时相比对照工况制动距离减少19.17%,制动时间减少12.79%;在失稳制动工况下,该策略可通过轮胎差扭来提升车辆的横向稳定性.采用文中制动策略显著提升了车辆的制动效能.

星形超曲面上Hamilton系统Brake轨道的多重存在性

研究Hamilton系统具有固定能量的brake轨道的个数问题.在适当条件下,证明了R2n中紧星 形超曲面∑上brake轨道的几个多重存在性定理,结果包含了Szulkin的已有结论.

正定型超曲面上Hamilton系统Brake轨道的存在性

结合Rabinowitz和Szulkin关于Brake轨道的存在性与多重性的结论,利用部分对称泛函的临界点理论研究Hamilton系统在更广泛的能量面上Brake轨道的存在性问题.在适当条件下,证明了R2n中正定型超曲面Σ上存在Hamilton系统的Brake轨道.由于星型超曲面是正定型超曲面的特殊情形,该研究包含了Rabinowitz的相应结论.

考虑可变俯仰角的垂直轴风力机翼型优化设计方法

针对设计垂直轴风力机翼型时普遍将俯仰角(θ_(p))设定为固定值,导致不能很好地发挥翼型的气动性能的问题,文章首先提出了一种考虑可变θ_(p)的垂直轴风力机设计方法,并将其应用于翼型优化;然后,基于制动圆柱理论不断迭代计算其功率系数(C_p),以极大功率系数直接作为目标函数,利用遗传算法耦合RFOIL软件优化翼型廓线与θ_(p)分布;最后,优化得到垂直轴风力机新翼型VAWT250。与参考翼型AIR001相比,无论是光滑条件,还是粗糙条件,新翼型的气动性能具有明显提升,尤其是粗糙条件,其最大升力系数与升阻比分别提升了16.1%和17.1%;在粗糙条件下,考虑俯仰角时,风力机的最大C_(p)提高了6.81%。该结果对垂直轴风力机翼型的优化设计具有一定的指导意义。

基于BP神经网络的EHB主缸液压力估计

电子液压制动(EHB)系统主缸液压力估计对降低EHB的传感器依赖性至关重要,基于BP神经网络进行主缸液压力估计。首先开展了实车道路试验,并采集车速、主缸活塞位移、主缸活塞速度和主缸液压力等数据。然后,以主缸活塞位移和主缸活塞速度为特征输入、以实际主缸液压力为目标输出建立BP神经网络,并采用训练集数据及梯度下降算法对BP神经网络进行训练。最后,利用测试集数据对液压力估计效果进行验证。结果表明,所提算法比基于动态位移压力模型和基于LSTM的估计算法估计误差分别减小38%和15%。

自动扶梯制动系统多体动力学建模与分析

自动扶梯作为现代城市公共交通的重要组成部分,其安全性直接关系到乘客的生命财产安全。附加制动器作为自动扶梯的关键安全装置,能够在自动扶梯发生超速、逆转、主驱动链断链等故障时迅速制停扶梯,确保乘客安全。通过建立整梯数值仿真模型,施加制动载荷和制动力矩,模拟了制动过程并进行了分析。对比仿真模型与现场试验的结果显示,仿真模型在制动过程中的梯级振动参数与现场试验结果一致,验证了仿真模型的有效性。

高性能驱动系统在复杂工况下下运带式输送机的实现

下运带式输送机在复杂工况下需要具备稳定的运行性能和承载能力,能够适应各种突发情况并确保安全可靠的输送作业。对下运带式输送机上可控启动传输装置(CST)的应用进行了深入研究,通过项目验证高性能驱动系统的稳定性和可靠性,降低了能耗,为相关领域的研究提供了重要的理论和实践参考。

基于模糊控制的纯电动汽车再生能量回收技术

针对车辆低速行驶的制动能量回收率低,频繁充放电影响动力电池寿命的问题,提出以电池荷电状态(state of charge,SOC)、制动强度、车速和制动间隔时间为输入,再生制动力分配系数为输出的纯电动汽车模糊控制再生制动策略。同时,采用遗传算法对控制参数进行优化。在Simulink中搭建控制策略模型,并在不同测试工况下与CarSim联合进行仿真,结果表明,相比于仅以电池SOC、制动强度和车速为输入的模糊控制再生制动策略,所提策略减少了制动能量回收次数,提高了制动能量回收率。该策略不仅可以改善对动力电池的损害情况,而且可以获得更多的制动能量。

汽车制动抖动问题的机理及控制措施研究综述

为了减少汽车制动抖动的售后抱怨,降低索赔成本,提升用户满意度,文章对制动抖动问题的国内外研究成果进行了归纳和总结。首先对制动抖动问题的特征及类型进行了阐述,然后分析了产生机理及影响因素,最后有针对性的提出了控制措施。结果表明,制动抖动的直接原因为制动力矩波动和传递路径的放大作用,制动力矩波动的根本原因为制动盘周向厚度差及制动盘端面跳动。最终明确了制动抖动问题的控制措施为控制振源和降低传递路径的放大作用。文章的研究结果可以为解决汽车制动抖动问题的售后分析人员提供参考,也可以为制动系统的前期开发人员提供经验借鉴。

指标理论及星形Hamiltonian系统多个次brake轨道的存在性

利用Ｚｐ指标理论定义了一种相对Ｚｐ指标，并应用它研究了星形能量面上Ｈａｍｉｌｔｏｎｉａｎ系统多个次闸轨道的存在性，从而改进了Ｓｚｕｌｋｉｎ的结果。