Thermal analysis of a novel retarder by using the nanofluid cooling system: Numerical and experimental approaches

To solve the problem of braking torque decline or even brake failure of vehicle retarders caused by high temperature due to long-time or high-power braking, the nanofluid with high thermal conductivity is introduced into the previously proposed novel retarder. To evaluate the nanofluid cooling capabilities, a model depicting the vertical fluid flow in the retarder is formulated. Adopting similarity transformations and a shooting method coupled with Runge–Kutta iterative technology, the model boundary value problem is tackled numerically. The cooling capabilities of three typical ethylene glycol (EG)-based nanofluids: Cu–EG, Al₂O₃–EG, and TiO₂–EG are investigated and compared. Finally, an experimental test is carried out to examine the temperature rise and the variation of braking torque for the retarder. It is demonstrated that Al₂O₃–EG nanofluid has the highest Nusselt number (rate of heat transfer), and more importantly, the braking torque of the proposed retarder decreases by only 8.2% under high-power braking condition.     

Temperature and thermal stresses in a pad/disc during braking

A two-element model of braking process for a tribosystem consisting of the pad (the strip) sliding with the time-dependent velocity (braking at uniform retardation) on a surface of the disc (the semi-space) is studied. The dependences of temperature and thermal stresses on the boundary conditions on upper surface of the ceramic–metal strip were investigated. It was proved that there is a possibility of applying the obtained results to modelling of a thermal cracking of the frictional elements during braking.     

Influence of the Pad's Material Properties on the Thermal Stresses during Braking

A three-element model of a braking process for a tribosystem consisting of semi-space, sliding with the time-dependent velocity (braking at uniform retardation) on a surface of a strip deposited on a semi-infinite foundation is considered. The dependencies of temperature and thermal stresses on thermophysical properties of the materials, the time of braking, and the strip thickness were studied. It was proved that there is a possibility of applying the obtained results to modeling of a thermal cracking of frictional elements during braking.     

3D investigation of thermal stresses in a locomotive ventilated brake disc based on a conjugate thermo-fluid coupling boundary conditions

The frictional heat generated during braking application can cause several negative effects on the brake system such as brake fade, premature wear, thermal cracks and disk thickness variation. It is then important to determine with precision, the temperature field and thermal stresses of the brake disc. In this study, thermal stress analyses on a ventilated locomotive wheel-mounted brake disc R920K with a three-dimensional model for two cases (the first case considers braking to a standstill; the second case considers braking on a hill and maintaining a constant speed) were investigated. The rate of braking heat generation is calculated using the assumption of uniform pressure distribution at the contact area. Then, thermal stress analyses for each case were performed. Finally, we have found that the maximum thermal stresses occur in the case with an emergency braking in the beginning of the braking process.     

Measurements of brake disc surface temperature and emissivity by two-color pyrometry

A fiber optic two-color pyrometer was developed for brake disc surface temperature and emissivity measurements. The two-color pyrometer consists of a fluoride glass optical fiber, two HgCdTe detectors equipped with bandwidth filters and a data conditioning and acquisition device. The two-color pyrometer measures the brake disc temperature in the 200–800 °C range with a time resolution of 8 μs. The calibration formula for the signals obtained using a blackbody of known temperature is used to compute the true temperature. The uncertainty estimation for temperature and emissivity was obtained from the calibration results. Tests were carried out on known temperature target and a good correlation was found between results obtained with our two-color pyrometer and those obtained with a commercial two-color pyrometer. Hold braking and deceleration braking tests performed on a braking test bench enabled us to reach the brake disc surface temperature and emissivity during braking. Experimental results show a significant variation of emissivity during braking. Direct measurement of emissivity was carried out on the brake disc after braking and shows the emissivity dependence with the surface quality.     

发动机辅助制动作用及其对汽车制动性能的影响

本文分析了发动机辅助制动作用的产生机理，建立了发动机辅助制动作用的数学模型，作为应用，对一台排量为1．8L的四缸四冲程汽油机进行了仿真计算，还就发动机辅助制动作用对整车制动性能的影响进行了分析。     

风电机组偏航制动器制动稳定性分析

针对风电机组偏航制动器制动不稳定问题，基于ABAQUS软件开展偏航制动器制动稳定性分析。运用复特征值分析法和不稳定倾向系数TOI值，分析制动压力、摩擦系数、偏航速度、弹性模量以及开槽方式等对制动稳定性的影响。基于全因子试验及Design-expert软件建立不稳定倾向系数TOI值响应面模型，并开展相关参数优化。研究表明：对制动稳定性具有显著影响的因素是摩擦系数、偏航制动缸弹性模量、摩擦片弹性模量；开双槽的摩擦片对制动稳定性影响显著，开单槽影响较小；制动稳定性受制动压力与偏航速度影响很小；参数优化后的偏航制动器制动不稳定系数降低73.7%。该研究结论可为偏航制动器设计、开发提供理论指导。     

Determination of the maximum temperature at single braking from the FE solution of heat dynamics of friction and wear system of equations

A system of equations of heat dynamics of friction and wear (HDFW) for a pad–disc tribosystem during a single braking has been formulated. It takes into account the coefficient of friction dependent on the maximum temperature, which is the sum of the mean temperature of the nominal contact region (the macro contact) and the flash temperature on the real contact area (the micro contact), temperature-dependent properties of materials and wear. Numerical solution of the initial problem of motion and the nonlinear boundary-value heat conduction problem was obtained. Computations were performed using the axisymmetric FE contact model for the metal ceramic pad and the cast-iron disc.     

Temperature in thermally nonlinear pad–disk brake system

The influence of the thermal sensitivity of pad and disk materials on temperature at braking is under investigation. A mathematical model of process of frictional heating in a pad–disk brake system, which takes into account the temperature-sensitive materials, is proposed. The basic element of this model is the thermal problem of friction—a one-dimensional boundary-value heat conduction problem with temperature-dependent thermal conductivity and specific heat. Contrary to the prior studies of authors, where a simple nonlinearity was considered, in this article the arbitrary nonlinearity of the thermophysical properties of materials is studied. The solution of a nonlinear boundary-value heat conduction problem is obtained by the method of successive approximations. The numerical analysis of temperature is executed for some materials of a pad and a disk with and without taking into account their thermal sensitivity.     

Influence of thermal sensitivity of the pad and disk materials on the temperature during braking

The transient frictional heating of pad–disk tribosystem at single braking is under consideration. To determine the average friction surface temperature, the one-dimensional thermal problem of friction at braking has been formulated. The linear dependence of the thermophysical properties of the disk and pad materials on the temperature has been taken into account. Model of materials with a simple nonlinearity has been adopted, i.e. materials in which coefficients of heat conduction and specific heat depend on the temperature, and their ratio – coefficient of thermal diffusivity – is constant. Linearization of the corresponding boundary-value heat conduction problem by the Kirchhoff transformation and linearizing parameter method has been performed. The numerical–analytical solution to the problem has been found by using the integral Laplace transform and the Newton–Raphson methods. The influence of the thermosensitive materials of titanium pad, sliding over the surface of the disk made of steel, aluminum alloy or gray cast iron, on the temperature has been studied.     

Dynamic thermal behavior of a brake system

A mathematical model is presented to describe the thermal behavior of a brake system that consists of shoe and drum. The model is solved analytically using Green's function method for any type of the stopping braking action. In terms of the obtained solutions, the transient temperature distribution of the brake is described. The thermal behavior is investigated for three specified braking actions that are the impulse, unit step and trigonometric stopping actions.     

全液压制动系统双回路制动阀仿真与实验研究

分析了双回路制动阀的动态工作过程,探讨了双回路制动阀上、下阀芯对其前、后桥输出口的遮盖量对动态工作特性的影响.基于AMESim液压/机械多场耦合仿真平台建立了双回路制动阀的仿真模型,研究了遮盖量变化对制动压力输出特性的影响规律以及单回路制动安全性能.搭建了全液压制动系统的实验台架,对具有不同遮盖量的制动阀样品的制动性能进行了实验对比测试.实测结果表明:遮盖量与制动空行程成正相关,与前、后桥的最大制动压力成负相关;双回路制动阀的前、后回路相互独立,当其中一条回路失效时,另一条回路仍能正常工作.实验结果与仿真结果具有良好的一致性,验证了该仿真模型的有效性.     

3D FE model of frictional heating and wear with a mutual influence of the sliding velocity and temperature in a disc brake

Numerical simulation of frictional heating in a disc brake of a typical passenger vehicle based on the equation of motion and the boundary-value problem of heat conduction was carried out. An influence of temperature-dependent coefficient of friction on the sliding velocity, braking time, braking distance and the thermomechanical wear was studied. Two materials of the pad combined with the cast-iron brake disc were examined. The dependencies of the coefficient of friction and wear rate on the temperature and contact pressure were derived from experimental measurements and implemented to the computational model of the brake. Comparisons of temperature for validation purposes calculated using the contact model developed in this study were made with the model introducing an approach based on the heat partition adopted from other studies.     

机车制动系统流量传感器的研究

对应用于机车制动系统的“V”型内锥式流量传感器进行了理论分析和试验研究。利用流体动力学分析软件,对其进行建模和数字仿真。仿真结果和试验数据对比表明,该流量传感器能够较准确地测出制动系统流量,可满足对列车制动系统工作的安全性和可靠性的流量检测要求。     

Axisymmetric FEA of temperature in a pad/disc brake system at temperature-dependent coefficients of friction and wear

Robust braking results in heat generation whose effects may have considerable impact on the parameters of the process such as wear rate and coefficient of friction. Fluctuations of the latter disagree with essential operational and braking requirements. Finite element analysis (FEA) of a single braking process for axisymmetric heat conduction problem of friction in a pad/disc brake system in the present article was carried out. Two materials of the pad FC-16L (retinax A) and FMC-11 (metal ceramic) and one material of the disc ChNMKh (cast iron) were analysed. Experimental dependencies of the coefficient of friction and wear rate on the temperature under specified contact pressures for these two friction pairs were approximated and applied to FE contact model. The temperature and wear evolutions on the contact surface of the pad/disc brake system obtained for constant and temperature-dependent abovementioned coefficients were confronted and compared. Mutual correlations of the obtained results with the studied materials were discussed.     

Three-dimensional transient temperature field of brake shoe during hoist’s emergency braking

In order to exactly master the change rules of brake shoe’s temperature field during hoist’s emergency braking, the theoretical model of three-dimensional (3-D) transient temperature field was established according to the theory of heat conduction, the law of energy transformation and distribution, and the operating condition of mining hoist’s emergency braking. An analytic solution of temperature field was deduced by adopting integral-transform method. Furthermore, simulation experiments of temperature field were carried out and the variation regularities of temperature field and internal temperature gradient were obtained. At the same time, by simulating hoist’s emergency braking condition, the experiments for measuring brake shoe’s temperature were also conducted. It is found, by comparing simulation results with experimental data, that the 3-D transient temperature field model of brake shoe is valid and practical, and analytic solution solved by integral-transform method is correct.     

电制动技术在乌溪江水电厂的应用

阐述了乌溪江水电厂50 Mw水轮发电机组电气制动技术系统的设计原理、结构、控制回路及设备选型.现场试验运行结果表明,该系统结构简单、稳定可靠,满足了"少人值班、无人值守"及系统调峰要求,是一种较理想的制动方式,可为电气制动停机技术的应用提供借鉴.     

提升机恒减速制动系统优化分析

提升机是煤矿井下生产作业中不可缺少的关键性设备,其运行质量对矿井生产作业效率有着直接影响。以此为着手点,对提升机恒减速制动系统优化开展探究。在对提升机控制系统进行概述的基础上,对提升机恒减速制动要求和恒减速制动系统的优化进行了探究,并对优化后的提升机恒减速制动系统进行了分析,希望能够为其他矿井相似工作的开展提供帮助。     

High-power lead–acid batteries for different applications

High-power lead–acid batteries have been used for a rather long time in various applications, especially for uninterruptible power supplies (UPSs) and starting of automobiles. Future automotive service requires, in addition to cold-cranking performance, the combination of high-power capability, a very good charge-acceptance, and an excellent cycle-life. Such applications include stop–start, regenerative braking, and soft, mild and full hybrid vehicles. For UPS, there has been a clear tendency to shorter discharge times and higher discharge rates. During the past decades, the specific power of lead–acid batteries has been raised steadily and there is still, room for further improvement. This paper gives an overview of the progress made in the development of high-power lead–acid batteries and focuses on stationary and automotive applications.     

论电梯制动性能试验的影响因素

本文针对目前电梯制动系统试验的实际状况，分析了电梯曳引条件与曳引机制动能力对电梯制动性能的影响，阐述了制动系统试验的评价方法。通过算例，分别讨论了曳引条件变化、机械制动器制动力变化与制动试验滑移距离的关系；并揭示了曳引条件与机械制动力综合作用时对制动性能的影响规律。