Braking Conditions Research Articles

Influence of Wheel/Rail Dynamic Interaction Induced by Polygonal Wheels under Braking Condition

Influence of Wheel/Rail Dynamic Interaction Induced by Polygonal Wheels under Braking Condition

Development of the chemical composition and modes of heat treatment of steel for railway wheels with increased wear resistance at high axle loads

One of the directions of the development of railway transport is increasing the load on the axle, while it is necessary to create new, more wear-resistant materials to increase the durability of railway wheels. At the same time, in many cases, a high level of hardness and strength must be combined with no less high values of plasticity and viscosity indicators. Purpose: to investigate the effect of the developed chemical composition and processing modes on the mechanical properties of laboratory-produced steels for railway wheels with increased wear resistance, which work in light braking conditions with high axleloads. Material and methodology. Research was carried out on steels of the experimental composition of the laboratory manufacturing method. Metallographic studies of experimental and industrial steels were performed on a light microscope "Neophot 32" and "Axiovert 200 M MAT" of the company "Carl Zeiss". Grinds were made mechanically. The microstructure was revealed by etching in a 2—3 % alcoholic solution of nitric acid (HNO3). Mechanical tensile tests at room temperature were carried out according to standard methods. Results. Based on the results of analytical studies and calculation models that allow predicting the mechanical properties of steels depending on the content of chemical elements in the steel, the chemical composition of small-volume experimental ingots for smelting in laboratory conditions was developed. Smelting of experimental melts has been completed. The possibility of obtaining a full set of mechanical properties and microstructure, standardized by the requirements of AAR M-107/M-208 for railway wheels of class D from developed steel, has been established.

Adaptive inverse optimal backstepping control strategy for longitudinal vibration of high-speed elevator system based on fuzzy observer

To effectively suppress the longitudinal vibration of the car under the conditions of high-speed operation and emergency braking, and improve the ride comfort of the car system, this paper proposes an adaptive fuzzy inverse optimal output feedback control strategy. Firstly, the dynamic model of the high-speed elevator system is established and the nonlinear dynamic model is approximated by the fuzzy logic system, and the auxiliary system model is established. Fuzzy state observer is designed to estimate the unmeasurable state. Furthermore, an adaptive inverse optimal output feedback controller based on fuzzy observer is designed by using adaptive backstepping technology and inverse optimal control principle. The stability analysis shows that the proposed adaptive fuzzy inverse optimal output feedback control strategy not only ensures the stability of the car attitude of high-speed elevator but also realizes the inverse optimization of the target cost function. Finally, the acceleration time–frequency response analysis of the two typical stages of high-speed elevator uniform running and emergency braking is carried out, and the numerical results are compared with the linear quadratic controller optimized by stepping quantum genetic algorithm (GA-LQR) and controller based on the state-dependent Ricatti equation (SDRE). The analysis verifies the effectiveness of the controller.

Material Wear Calculation of Braking Surface under High-Power Braking Conditions

The wear phenomenon of the braking surface of a high-power disc brake under emergency braking conditions is analyzed in this paper. Considering the classical Archard wear model, including the influence of the braking load, speed, and friction coefficient on the braking surface, the wear model of the brake disc surface is established to obtain the wear depth and distribution. It is essential to investigate the wear mechanism of the brake disc surface, and the evolution of wear laws is revealed under different braking parameters. The results have shown that the brake disc surface wear is constantly accumulating. The large load, the high speed, and the large friction coefficient would aggravate the surface wear area. It is expected that the wear study of the brake disc surface can guide the design of the disc brake.

Evolution mechanism of water column separation in pump turbine: Model experiment and occurrence criterion

Whether the superposition of pressure pulsation and water hammer pressure caused by the fast closing of guide vanes causes water column separation in draft tube inlets is a hot topic in engineering and academic fields. It is also not known whether the bridging of water column separation endangers the operation of the units. This study uses a model pumped storage power station platform with two units to perform water column separation. Data on the pressure pulsation at different measurement points, discharges, and speeds are collected by an acquisition system, whereas the development process of water column separation is characterized by a high-speed camera. The measured pressure is decomposed into the water hammer pressure, which migrates with the unit operation point and pressure pulsation. The test results reveal that the pressure in the inlet section of the draft tube below the vaporization pressure that lasts for several seconds is a sufficient and necessary condition for water column separation to occur. The water hammer pressure has a significant influence on the water column separation, while low-frequency pressure pulsation has less influence. Water column separation is divided into four stages: starting, improvement, separation, and bridging. The main frequency of the pressure pulsation in the water column separation process is the frequency of the water hammer caused by load rejection and has a value of 0.47f/fn. Cavity bridging generates a frequency of 0.30f/fn. The flow-speed curve remains in the braking condition of turbine for 1.25 s. The separation and part of the bridging stage occur under the braking condition of turbine.

Effect of the Addition of Waste Generated during the Plasma Cutting of Aluminum Products on the Friction and Emission Properties of a Commercial Friction Material Formulation

With recycling and reuse in mind, this study explores the possibility of the utilization of waste generated during the plasma cutting operations to produce aluminum products in a commercial friction material formulation for car braking applications. The as-received waste, analyzed in the form of a powder, was subjected to various characterization techniques to obtain its composition and phase constituents. The friction, wear, and emission analyses were organized in two ways: the first part focused on the selection of the most suitable waste content in the friction material formulation—10, 15, and 20 wt.%—tested in the form of pins, using a pin-on-disc tribometer. The second part evaluated the most suitable content in the formulation in the form of coupons on a subscale dynamometer to comprehend its friction and emission characteristics in a more complex scenario. Through the pin-on-disc analysis, it was seen that the 10 wt.% of waste in the formulation provided permissible friction and wear behavior, and similar emission magnitude and secondary plateau characteristics were seen, as compared to the reference composition. Similar results were recorded on the subscale dynamometer at mild braking conditions. At ‘severe’ testing conditions, a different trend was observed. Through this analysis, the possibility of the addition of this kind of waste in friction material composition has been evaluated deeply, paving a path for further analysis and possible implementation.

An approach for simulating the air brake system of long freight trains based on fluid dynamics

Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air brake systems based on fluid dynamics theory was proposed. The structures and working mechanisms of locomotive and wagon air brakes are introduced, and mathematical models of the pipes, brake valves, reservoirs or chambers, cylinders, etc., are presented. Besides, the dynamic motions of parts in the main valve are considered. The simulation model of the whole air brake system is then formulated, and the solving method based on the finite-difference method is used. New efficient pipe boundary conditions without iterations are developed for brake pipes and branch pipes, which can achieve higher computational efficiency. The proposed approach for simulating the air brake system is validated by comparing with published measured data. Simulation results of different train formations indicate that models that consider the dynamic behavior of brake pipes are recommended for predicting the characteristics of long trains under service braking conditions.

Emergency Braking Evoked Brain Activities during Distracted Driving

Electroencephalogram (EEG) was used to analyze the mechanisms and differences in brain neural activity of drivers in visual, auditory, and cognitive distracted vs. normal driving emergency braking conditions. A pedestrian intrusion emergency braking stimulus module and three distraction subtasks were designed in a simulated experiment, and 30 subjects participated in the study. The common activated brain regions during emergency braking in different distracted driving states included the inferior temporal gyrus, associated with visual information processing and attention; the left dorsolateral superior frontal gyrus, related to cognitive decision-making; and the postcentral gyrus, supplementary motor area, and paracentral lobule associated with motor control and coordination. When performing emergency braking under different driving distraction states, the brain regions were activated in accordance with the need to process the specific distraction task. Furthermore, the extent and degree of activation of cognitive function-related prefrontal regions increased accordingly with the increasing task complexity. All distractions caused a lag in emergency braking reaction time, with 107.22, 67.15, and 126.38 ms for visual, auditory, and cognitive distractions, respectively. Auditory distraction had the least effect and cognitive distraction the greatest effect on the lag.

Intelligent prediction of wear life of automobile brake pad based on braking conditions

PurposeTo avoid braking accidents caused by excessive wear of brake pad, this study aims to achieve online prediction of brake pad wear life (BPWL).Design/methodology/approachA simulated braking test bench for automobile disc brake was used. The correlation and mechanism between the three braking condition parameters of initial braking speed, braking pressure and initial braking temperature and the tribological performance were analyzed. The different artificial neural network (ANN) models of wear loss were discussed. Genetic algorithm was used to optimize the ANN model. The structure scheme of the online prediction system of BPWL was discussed and completed.FindingsThe results showed that the braking conditions were positively correlated with the wear loss, but negatively correlated with the friction coefficient. The prediction accuracy of back propagation (BP) ANN model was higher. The model was optimized by genetic algorithm, and the average deviation of prediction results was 4.67%. By constructing the online monitoring system of automobile braking conditions, the online prediction of BPWL based on the ANN model could be realized.Originality/valueThe research results not only have important theoretical significance for the study of BPWL but also have practical value for guiding the maintenance and replacement of automobile brake pads and avoiding the occurrence of braking accidents.

Research progress on friction and wear properties of powder metallurgy brake pad

The terrain of China is relatively complex, which leads to the complex and changeable working conditions of high-speed trains during braking. Studying the influence under different braking conditions on the performance of train brake pads is a problem worthy of in-depth discussion. In order to explore the performance changes of powder metallurgy brake pads during train braking, this paper summarizes the friction and wear properties and wear mechanism of powder metallurgy brake pads under different braking conditions; combined with the research status of powder metallurgy brake pad materials, it provides directions for the research of new powder metallurgy materials. Provide reference for the improvement of brake pads of high-speed train in the future.

Research on fuzzy control strategy of PMSM electric braking considering state constraints

The PMSM drive system is widely used in new energy vehicles, and the rational design of the electric braking control strategy can maximize the recovery of energy during the braking process of the vehicle and improve the energy utilization rate of the vehicle. This paper firstly analyzes the energy system architecture of PMSM driving electric vehicle. Then the braking range, braking intensity and vehicle speed are classified and the braking intention is accurately identified based on the fuzzy control strategy. And, the braking strategy is modified by considering the braking constraints of the PMSM and the state constraints of the power battery. Finally, a test platform is built to verify the designed control strategy under six typical braking conditions.

A reliability‐based robust optimization design for the drum brake using adaptive Kriging surrogate model

AbstractTo decrease random parameters’ influence on the drum brake reliability, the reliability‐based robust optimization design (RBROD) of the electric vehicle brake is proposed. Based on the assumption that the maximum temperature of the brake cannot exceed the allowable temperature, a performance function model of thermal–mechanical coupling reliability of drum brakes is established by the adaptive Kriging method, and the analysis of reliability sensitivity and RBROD are conducted. The accuracy of the proposed model is verified by temperature measurement experiment under emergency braking condition. The robust optimization design improves the drum brake reliability to 0.99998 and reduce the influence of the design parameters on the reliability, with the absolute values of the reliability sensitivity and the weight of the drum brake are significantly smaller. Therefore, the objectives of reliability design, robustness design, and optimization design are simultaneously achieved by the proposed methods. Besides, the relative error of the proposed method is 0.373%, the number of function evaluations is 39, and the comparison with four meta‐model methods show that the proposed method holds high‐accuracy and high‐efficiency. This study provides a high‐precision theoretical explanation for the robust optimization design of drum brake.

Research on friction performance and wear rate prediction of high-speed train brake pads

As we know, the wear of high-speed trains cannot be avoided, otherwise it cannot brake and stop. But its operating environments are complex and changeable, leading to insufficient research on friction performance of copper (Cu)-based powder metallurgy (PM) brake pads and difficult prediction of the wear rate. Therefore, we explore the variation trend of the friction performance of the brake pad with different multi-factors coupling braking conditions, and predict the wear rate of Cu-based PM brake pad based on Atom Search Optimization-Back Propagation (ASO-BP) neural network. The Cu-based PM brake pad regarded as the research object whose friction coefficient, friction temperature, braking distance, wear rate, and change mechanism are discussed with multi-factors coupling braking conditions, and wear rate is predicted based on ASO-BP neural network that can obtained by optimizing the weights and thresholds of the Back Propagation (BP) neural network with Atom Search Optimization (ASO) method. The results show that braking speed and braking pressure are main contributors to braking ability, the average coefficient of friction of the Cu-based PM brake pads varied nearly between 0.35 and 0.45 with different braking conditions, the maximum of temperature, braking distance, braking time and the wear rate of the brake pad are 473 °C, 3506 m, 138s and 0.14 cm3/MJ, respectively. And the prediction accuracy of brake pad wear rate based on ASO-BP neural network can reach 97.3%.

Numerical simulation of mechanical response analysis of asphalt pavement under dynamic loads with non-uniform tire-pavement contact stresses

The selection of accurate input design parameters is important for understanding the dynamic response of an asphalt pavement structure. The transverse and longitudinal shear stresses that affect the dynamic response of asphalt pavement are not considered in traditional asphalt pavement design. To this end, this study utilizes the finite element method (FEM) to analyze the mechanical response of asphalt pavement under dynamic loads with non-uniform tire-pavement contact stresses. For this purpose, firstly a three-dimensional (3D) finite element (FE) model of a rubber tire is developed. Secondly, the predicted and laboratory measured stresses are compared to develop a 3D FE model of the contact stresses. Finally, a 3D FE model of the tire–pavement contact is analyzed to investigate the influence of shear stresses on the response of the asphalt pavement and the superposition effect of the mechanical response. The results show that the distribution and magnitude of the vertical contact pressure under the free-rolling state are the same as those under the static state, and the traction and braking conditions could change the symmetry of tire-pavement interactions. In addition, the shear stress at the tire-pavement interface affects the peak response of the surface layer, indicating that shear stress plays a considerable role in controlling the development of rutting and longitudinal cracks. Considering the viscoelasticity of the asphalt material, it is observed that the superposition effect of the mechanical response is a comprehensive result of the space–time domains. In conclusion, this study analyzes the influence of tire-pavement contact on the mechanical response of asphalt pavement and proposes input design parameters for improving the design of asphalt pavement.

Electrothermal Multicriteria Comparative Analysis of Two Competitive Powertrains Applied to a Two Front Wheel Driven Electric Vehicle during Extreme Regenerative Braking Operations

The powertrain performance in an electric vehicle is fully dependent on the electrical and thermal constraints of the static converters ensuring the power transfer taking place between the energy storage systems and the electromechanical machines. These constraints depend on the architectures of the power converters, and their control strategies. Particularly, the maximal limits are reached in maneuvers such as hard regenerative braking circumstances. Indeed, braking recovery is a critical phase in the vehicle’s operation, and its duration and intensity may strongly impact the vehicle’s battery behavior or integrated hybrid storage system. The innovative objective of the paper is to propose an electrothermal multicriteria comparative study based on electrical and thermal criteria for two competitive powertrains. These semi-active power configurations (a 3-level DC/DC converter-based, and a Z-source converter-based) are implemented in a two-front wheel driven electric vehicle during extreme regenerative braking conditions. Open-loop and closed-loop controls were implemented in the Z-source using the maximal constant boost control with 3rd harmonic injection modulation technique. We considered two paralleled IGBT modules instead of the single shoot-through structure. Our approach is based on simulation during an extreme braking maneuver leading to heavy repercussions on the overall powertrain system. The aim is to investigate the challenging structure of the Z-source. Results showed that the proposed 3-level DC/DC-based topology has better performances in terms of power losses, efficiency, thermal behavior, and electromagnetic interference.

Study on the wear performance of high-speed railway brake materials at low temperatures under continuous braking conditions

A simulated test was completed using pin-on-disc friction and wear test machine to simulate the wear performance of the high-speed railway braking disc and braking pad materials at different temperatures (20, 0, −10, −20, −30 °C) under continuous braking conditions. The results show that the low temperature has a significant effect on the wear characteristics of the brake material under continuous braking conditions. At the initial stage of continuous braking, the instantaneous coefficient of friction at low temperature reaches its maximum value at approximately 500 s, which is almost one half of the time of that at room temperature (20 °C). At each temperature, the instantaneous friction coefficient shows a trend of increasing firstly and then decreasing, and with the decrease in temperature, the average friction coefficient of brake disc material tends to increase at the stable stage of instantaneous friction coefficient. As the continuous braking time increases, the average coefficient of friction at low ambient temperatures is greater than that at room temperature (20 °C). As the temperature decreases, the wear rate of the brake material shows a trend of increasing and then decreasing. With the fall of temperature, the damage form of brake pad material changes from adhesion damage to abscission damage, while the brake disc damage changes from abrasive wear and adhesion wear to damage mixture of abrasive wear, adhesion wear and crack.

Influence of thin water film on asphalt pavement skid resistance: from indoor to in-situ test

ABSTRACT Pavements skid resistance, especially in wet states, is an essential indicators of traffic safety. However, the existing testers cannot reflect actual road friction situations and oversimplify water’s effect on texture and skid resistance. Therefore, this study compared a traditional British pendulum tester (BPT) with actual vehicle braking. A simplified water coverage simulation programme was proposed, and the BPT characterised the influence of different thin water films on skid resistance in the laboratory. Besides, several freshly constructed road sections (AC-13, SMA-13, and PAC-13) were tested with both BPT and vehicle braking during rainfall. The results showed that water film, even thin, is unfavourable for pavement skid resistance. The BPT results were inconsistent with that of the vehicle braking. Because the tribological properties characterised by BPT are provided by micro-texture and partly macro-texture within the rubber-texture interaction depth (0.1 mm). Larger texture depth and more tortuous and connected pores will offer pavements larger water capacity and higher water permeability, which is beneficial for alleviating braking distance reduction during rainfall. In general, an ideal skid resistance tester should consider characteristics within the rubber-texture contact depth and should consider braking conditions such as speed, water film thickness, drainage method, and slip rate.

A novel coordinated control strategy of regenerative braking and anti-lock system for electric vehicles

Regenerative braking is one of the core technologies to improve the economy of pure electric vehicles. To realize the improvement of the energy recovery effect under conventional braking conditions and the coordinated control between regenerative braking and anti-lock system under emergency braking conditions of pure electric vehicles, this paper studies a front and rear axle braking force distribution method with the actual road adhesion coefficient and braking strength as the premise, while using fuzzy control to distribute the front axle electromechanical braking force. The sliding mode controller with double power convergence law is designed to enhance the stability of the anti-lock system. Finally, the braking coordination control strategy is proposed by combining the designed regenerative braking and anti-lock control. Through simulations and experiment, it has been proved that the control strategy is effective and can effectively improve the economy of pure electric vehicles.

Brake Instability Dynamic Model and Active Control Strategy for a Multiunit Articulated Rubber-Wheel Autonomous Rail Rapid Transit System

Due to the particularity of the structure, the dynamic properties of multiunit articulated rubber-wheel autonomous rail rapid transit system are very complex, which increases the difficulty of studying its braking stability. In this paper, a dynamic analysis model for the emergency braking of a multiunit articulated rubber-wheel autonomous rail rapid transit system is established by introducing the axle load transfer, suspension deformation compatibility equation, articulation force relationship equations, etc. Based on an in-depth analysis of the risks of the lateral swing instability and their formation mechanisms, an active control strategy for the multiunit articulated rubber-wheel autonomous rail rapid transit system under emergency braking conditions is innovatively proposed to ensure the stability of the vehicle, with the shortest braking distance as the optimization goal. Through simulation and experimentation, the established dynamic model is confirmed to approach the real vehicle well, and the feasibility of the active control strategy is proved.

A Numerical Study on the Thermal Behavior of Various Brake Disc Designs

The performance of a braking system is a fundamental requirement in both the railway and automotive vehicles. The brake disc is the main component of the braking system; it is considered one of the most critical parts for safety in modern vehicles. The braking performance and the vehicle safety are strongly dependent on the brake disc design ensuring the conversion of the kinetic energy of a moving vehicle into thermal energy dissipated in form of heat. In this work, a complete thermal analysis is proposed in order to identify the behavior of three different designs of brake discs under coupled mechanical and thermal loads. By simulating the condition of normal braking, the temperature distribution and variation are obtained using the numerical simulation for each brake disc. A comparison of simulation results is exposed to evaluate the effect of ventilation system design on the thermal behavior of the studied brake discs.