Measurement of the disc-pad friction coefficient for mechanical brakes using direct and indirect methods

It is necessary to guarantee the proper brake force to stop a train safely in a limited distance and o adjust its speed. Currently, most trains are run by electrical power and have a combined electrical and mechanical (friction) braking system. The mechanical brake force is determined by many parameters, such as the friction coefficient of the brake disc and pad, the pressure in the brake cylinder, the brake cylinder’s cross sectional area and the brake linkage ratio. In general, the friction coefficient data of the brake disc and pad have been taken through a dynamo-test in a laboratory, but these data might not be well matched with real data under operating conditions because of the difference in data acquisition conditions. The present study examined two methodologies that can measure the friction coefficient of the brake pad and disc based on a train’s real operating conditions. The first method was the direct method, which measured the brake force and clamping force applied on the mechanical brake by using strain gauges installed on the brake to calculate the friction coefficient. The second was an indirect method that obtained the friction coefficient by using the weight of the train and the equivalent brake force. Those variables were calculated from the longitudinal dynamic characteristics, such as resistance to motion, gradient resistance and curved resistance. These two methodologies were used to obtain the disc-pad friction coefficient for the mechanical brakes of a Korean high-speed train (HSR350x).     

Analysis of automotive disc brake squeal considering damping and design modifications for pads and a disc

The squeal noise occurring from the disc brakes of passenger cars has been analyzed by using the complex eigenvalue method numerically. The contact between a disc and two pads was analytically modeled as many linear springs and dampers in an effort to develop the improved equation of motion derived on the basis of Lagrange’s equation and the assumed mode method. The finite element modal analysis results for disc brake components constitute an eigenvalue matrix in the analytical equation of motion. The complex eigenvalue analyses based on the equations of motion are able to examine the dynamic instability of a brake system, which is an onset of squeal, by considering the disc rotational effect. Numerical analyses showed that the modes unstable in an undamped analysis became stable in a damped case, which illustrates the important effect of damping on the squeal instability in a brake squeal simulation. Then several modified brake models were suggested and investigated how effectively they suppressed the occurrence of squeal noise. The brake parts such as a pad chamfer and a disc vane were modified and the influence of pad chamfer and vane shapes on squeal occurrence was proved to be significant. The numerical results showed that proper structural modification of a disc brake system can suppress the brake squeal to some extent.     

盘式制动器制动尖叫的有限元分析与试验

建立了产生制动尖叫的钳盘式制动器各主要零件的有限元模型,并通过集成构建了制动器总成的接触摩擦耦合有限元模型,计算了制动器振动系统的复特征值分布和模态,分析了可能产生制动尖叫的不稳定模态,并与制动噪声台架试验统计结果进行了对比,结果表明所建模型能够较好地预测出制动器发生制动尖叫的倾向;分析了各零件的振动模态对产生制动尖叫不稳定模态的贡献大小,揭示出有尖叫倾向的不稳定模态是由子结构未耦合时的多阶振动模态叠加而成;分析讨论了摩擦因数、摩擦片结构及其背板阻尼对制动尖叫的影响,为控制制动尖叫提供了途径。     

Improvement of drivability and fuel economy with a hybrid antiskid braking system in hybrid electric vehicles

When braking on wet roads, Antilock Braking System (ABS) control can be triggered because the available brake torque is not sufficient. When the ABS system is active, for a hybrid electric vehicle, the regenerative brake is switched off to safeguard the normal ABS function. When the ABS control is terminated, it would be favorable to reactivate the regenerative brake. However, recurring cycles from ABS to motor regenerative braking could occur. This condition is felt to be unpleasant by the driver and has adverse effects on driving stability. In this paper, a novel hybrid antiskid braking system using fuzzy logic is proposed for a hybrid electric vehicle that has a regenerative braking system operatively connected to an electric traction motor and a separate hydraulic braking system. This control strategy and the method for coordination between regenerative and hydraulic braking are developed. The motor regenerative braking controller is designed. Control of regenerative and hydraulic braking force distribution is investigated. The simulation and experimental results show that vehicle braking performance and fuel economy can be improved and the proposed control strategy and method are effective and robust.     

Load and Load Dependent Friction Identification and Compensation of Electronic Non-Circular Gear Brake System

Control of the electronic non-circular gear brake (ENGB) involves challenges, including the non-linear variation of loads and the effect of friction, which is dependent upon load. The controller must be designed based on modelling information in order to enhance control performance. This study performed model identification of the ENGB system using a DOB-based model identification method. By employing the nearest neighbor search method, the even-odd disturbance was separated without the influence of hysteresis even in situations with low control precision. The accuracy of the resulting ENGB system model was validated through experiments. The self-energizing effect due to friction between the brake disc and pad within the mechanical system was also validated.     

FSC赛车制动系统设计

本文提出了一套适用于FSC赛车制动系统的设计方法。选用简单液压盘式制动系统，并且加装平衡杆以调节制动器制动力分配系数。计算和分析表明，该制动系统能够满足比赛时动态测试的要求。     

Analysis of disc brake instability due to friction-induced vibration using a distributed parameter model

This paper deals with friction-induced vibration of a disc brake system with a constant friction coefficient. A linear, lumped, and distributed parameter model to represent the floating caliper disc brake system is proposed. The complex eigenvalues are used to investigate the dynamic stability, and, in order to verify simulations which are based on the theoretical model, an experimental modal test and dynamometer test are performed. The comparison of experimental and theoretical results shows good agreement, and the analysis indicates that modal coupling due to friction forces is responsible for disc brake squeal. Also, squeal type instability is investigated, using a parametric analysis. This indicates which parameters have influence on the propensity of brake squealing. This is helpful for validating the analysis model and establishing confidence in the experimental results of the modified system. These results may also be useful during system development or diagnostic analysis.     

Prediction of the cooling factors of a vehicle brake disc and its influence on the results of a thermal numerical simulation

In the process of developing the brake disc, it is necessary that we predict the suitability of the design. In this manner, we can affirm that even the first prototype will satisfy all of the customer homologation requests. Usually those comprise different sequential braking tests in which the maximal achieved temperature is the criterion that governs brake disc suitability. The knowledge of how to predict the behavior of a brake disc in the early pretesting phase has a significant impact on development costs and time. The common method that is used for predicting the temperatures in the brake disc during braking is numerical simulation analysis. With the help of Computational Fluid Dynamics, the flow through a vehicle ventilated brake disc of known geometry was determined, and the wall heat transfer coefficients for all vehicle speeds and brake disc temperatures were calculated. The results were then imported into a thermal numerical simulation of a sequential-braking vehicle test. The results showed that the consideration of cooling factors has a significant impact on temperature courses. To obtain accurate results from the numerical simulation and to simulate the vehicle test precisely, the proper wall heat transfer coefficients must be considered. The proposed method produces more accurate numerical results and enables the development engineer to develop suitable brake disc geometry in the early pretesting phase.     

Stress analysis of ventilated brake discs using the finite element method

One of the most common problems related to ventilated brake discs are crack formations, particularly under high brake loads or from the associated stresses during braking. In this study, three different ventilated brake discs, the crossdrilled disc, the cross-slotted disc, and the cross-slotted with a side groove disc, were manufactured, and their braking force performances were investigated experimentally together with a solid disc. Stress analyses were subsequently performed by the finite element method. Analyses results showed that the maximum stress generations were formed on the ventilated discs in comparison to the solid disc. However, these comparisons indicate that the application of varying force distributions along brake pads reduces the stresses on ventilated discs by 8.8% to 19.1%.     

盘式制动器在我国中重卡上应用的可行性分析

随着汽车技术的不断发展,盘式制动器相较于鼓式制动器而言优势明显,已在欧洲等市场得到了广泛应用.尽管多年前国内主要中重卡生产企业就已开始对盘式制动器的应用进行探索,做了大量的推广工作;但是直到2012上半年,除了个别汽车生产企业在前桥上有一些批量使用外,其他主流企业均未形成有效的批量应用.     

汽车气压盘式制动器的结构特点与性能分析

介绍了几种国内外重型汽车气压盘式制动器的结构及其特点,从左右轮制动力差异,制动器的效能因数与摩擦系数的关系及迟滞量等方面对盘式制动器与鼓式制动器进行性能对比分析,说明盘式制动器在制动效能、制动效能的稳定性以及制动时汽车的方向稳定性上比鼓式制动器具有明显的优势,理论和试验表明盘式制动器与ABS、ASR、EBS等系统匹配时可简化系统结构、优化系统性能,并对重型汽车装用盘式制动器带来的制动系统的相关问题进行了探讨.     

气制动大客车制动力矩计算分析

介绍气制动大客车制动力以及制动力矩的计算方式,并通过实际气制动客车制动力矩的计算和数据对比.为今后在客车制动系统设计当中,提供有效理论依据.     

智能可变轮胎附着力系统的设计与应用

通过检测车轮速度及踩踏制动踏板的急缓程度,由电控单元判断,若是在紧急制动的情况下,控制电磁线圈通电,电磁作用使安装在轮辋上的泄气电磁阀动作,轮胎泄压,瞬间增大轮胎与地面的附着力,从而缩短制动距离;若是在冰雪、泥泞等特殊路面上,由电控单元通过电磁线圈控制泄气电磁阀,使轮胎泄半压,增大轮胎与地面的附着力,提高车辆的加速和制动性能,保持方向稳定。当紧急制动或特殊路面的情况消失之后,安装在轮辋上的充气阀将自动充气到轮胎的正常气压,并自动停止。     

Model-based control of an electropneumatic brake system for commercial vehicles

A properly functioning brake system is critical for ensuring the safe operation of any vehicle on roadways. Commercial vehicles such as trucks, tractors-trailers and buses are equipped with an air brake system that uses compressed air as the energy transmitting medium. This paper presents a model-based control scheme for an electropneumatic brake system for use in commercial vehicles. A mathematical model for an electropneumatic brake system was developed and corroborated with experimental data. A control scheme was developed based on this model and was used to regulate the pressure of air inside the brake chamber according to a desired pressure trajectory. This control scheme was implemented on an experimental test bench, and its performance was studied for various values of the controller parameter. The control scheme was tested for various desired pressure trajectories reflecting actual brake operation.     

基于混杂理论的电磁与摩擦集成制动方法

鉴于传统电子液压制动系统连续制动易产生"热衰退"现象，结构缺陷导致的制动响应慢，制动系统与电控系统衔接差等缺点，提出了一种基于混杂自动机模型的电磁与摩擦集成制动方法。首先分析集成制动器制动时的工作特点以及不同情况下对应的工作模式（纯电磁制动、纯摩擦制动以及集成制动），并确定3种制动模式的切换条件，通过逻辑门限算法将其实现。根据制动时车辆既具有连续运动状态又有离散状态的混杂特性，使用MATLAB/Stateflow建立基于制动模式切换系统的推广自动机模型，并根据制动模式切换控制策略，对3种制动模式切换进行试验，验证制动模式切换控制策略的合理性。最后选取车辆制动初速度为28 m·s^-1的直线制动工况，分别在高附着系数（0.85）以及低附着系数（0.3）的路面条件下，通过试验平台对控制算法和制动系统性能进行试验验证。研究结果表明：所提出的汽车混杂理论模型以及优化方法在在低附着系数（0.3）路面条件下，集成制动方法较传统液压制动系统缩短5.12%的制动距离，缩短制动时间0.3 s；在高附着系数（0.85）路面条件下，集成制动方法较传统液压制动系统缩短5.66%的制动距离，缩短制动时间0.2 s，能有效提高制动效能。     

汽车液压感载比例阀

感载比例阀能改变前后制动器制动力的比值,使汽车制动时方向稳定并有足够的制动减速度、文章介绍了汽车液压感载比例阀的原理、输入压力和输出压力的比例关系,阐述了变比值制动力分配汽车的利用附着系数和路面附着系数利用率的计算方法,表明虽然该方法比固定比值制动力分配汽车的计算分析方法复杂,但利用该计算方法得到的带比例阀汽车的利用附着系数完全满足M1类车辆的制动法规的要求,并且利用附着系数和制动强度之间的关系曲线与路面附着系数利用率曲线完全吻合,指出使用该计算方法匹配感载比例阀完全正确。     

气压盘式制动器在大客车上的应用

与传统的鼓式制动器相比,气压盘式制动器无论在性能还是可靠性方面都表现出极大的优势。通过简要介绍气压盘式制动器的结构、特点及应用状况,提出了一种气压盘式制动器制动力矩的计算方法,并对气压盘式制动器在应用设计中应注意的一些问题作了初步的探讨。     

沥青路面抗滑性能研究现状与展望

作为未来道路交通荷载的主流形式,车辆的行驶稳定性与路面抗滑性能存在着直接关系,而且随着时间变化,沥青路面的抗滑性能受各种不确定性因素的影响。为了明确国内外沥青路面抗滑性能的研究现状,对胎-路接触力学模型和路面附着特性、动摩擦因数的计算方法、不确定性影响因素、抗滑性能评价指标和衰变模型以及抗滑性能在无人驾驶车辆安全性中的应用等热点问题研究进展进行了综述与总结,对比分析了现有沥青路面与橡胶轮胎的接触力学模型,探讨了设计、施工及运营阶段中的不确定性因素,归纳了现有沥青路面抗滑性能评价指标及衰变模型,最后论述了沥青路面抗滑性能的发展方向。分析结果表明：基于路表分形理论的Persson迟滞摩擦理论更适用于沥青路面动摩擦因数的计算要求,计入了橡胶对表面粗糙度的有关尺度变形响应及滑动摩擦的温度依存性;考虑路表峰值附着系数时变性的摩擦因数-滑移率（μ-s）曲线附着系数估算方法更能反映路面实际附着特性;当前沥青路面抗滑性能研究在胎-路相互作用机理、评价指标、衰变模型等方面研究不足,需要从时变性、统一性及车辆抗滑需求感应参数等方面进一步深入研究。推行基于时间效应的抗滑评价指标是沥青路面抗滑层设计与抗滑性能评价发展的必然趋势,也是提高中国沥青路面全寿命周期内服役水平的重要方法。     

Hot judder simulation of a ventilated disc and design of an improved disc using sensitivity analysis

In a disc brake system, thermal expansion of the material is caused by friction energy that is generated by the sliding contact between a disc and pad during braking. This phenomenon, thermo-elastic instability, can lead to hot spots on the disc surface and a hot judder phenomenon. Transient finite element analysis has been used to simulate this phenomenon. Three dimensional finite element models of a disc, pad, and cylinder were created. Each part was connected by a joint. Contact condition was applied to the disc and pad with a friction coefficient (μ) of 0.4. A convective heat transfer coefficient was set as 40 W/m²K. Using a commercial program SAMCEF, the simulation of the thermo-mechanically coupled system was performed. In order to find the sensitive parameters of brake judder, sensitivity analysis was carried out with consideration for disc design parameters. As a result, the hot spot phenomenon was confirmed and hot judder was predicted. Moreover, the more sensitive parameters of the hot judder phenomenon were presented. Finally, an improved disc model and an analysis technique were verified by comparison to dynamo test results.     

轿车制动性能的控制方法

针对目前轿车开发以逆向开发为主体,对整车制动性能控制能力较弱的实际问题,文章提出了一套制动性能控制方法,即以整车设计参数、制动强制性法规适应性及制动系统零部件尺寸系列化等为制动性能控制的输入约束条件,在设计初期预测新开发轿车的9项主要制动性能,经过多辆轿车制动系统的开发实践验证,此性能控制方法不仅可保证制动系统设计质量,而且缩短了轿车制动系统的设计周期。