Wheel-rail Adhesion Research Articles

Effect and mechanism of wheel–rail adhesion on torsional vibration and stability of the braking system

A high-speed train braking system with the disc–pad sliding friction pair and the wheel–rail rolling friction pair is a classic torsional system. By adopting a developed braking system torsional dynamics model, the influences of dry and wet rail surface conditions on system dynamic responses were investigated. Further, the system stability under different disc–pad friction and wheel–rail adhesion characteristics was explored and the interaction mechanism between the disc–pad and the wheel–rail sub-systems was revealed. The results indicated that the wheel–disc torsional vibration was more complicated under the wet rail surface condition. Moreover, the braking system had worse stability when the negative slope characteristics of disc–pad friction and wheel–rail adhesion were interacted.

Design and validation of a wheel-rail adhesion simulator in PLS-Circulator

A 1:4 scaled test rig called 'PLS-Circulator' is introduced for wheel-rail contact research under large slip conditions, which is composed of two wheel assemblies, 2 m diameter ring track with sprinklers surrounded, gearbox and two servo motors. On this basis, a wheel-rail adhesion simulator was designed to generate and measure the wheel-rail contact force. The slip ratio is the specific value of two motor speeds, which brings convenience to precisely control. SIMPACK simulation results showed that the slip ratio converged to the target value after the initial time in consideration of gear meshing vibration. The validation of the adhesion recovery was carried out utilizing PLS-Circulator under large slip conditions. Experimental results showed that in both steady and dynamic slip ratio experiments the adhesion coefficient could increase up to 26% from a lower adhesion caused by wet wheel-rail interface at the vehicle velocity of 20 km/h.

Research Progress of High-Speed Wheel–Rail Relationship

The research on wheel–rail relationship includes the basic theoretical models and corresponding numerical methods of wheel–rail in rolling contact, geometric parameter matching and material matching of them, friction and wear, wheel–rail rolling contact fatigue, wheel–rail adhesion and noise. They are also key theoretical and technical problems of the high-speed train/track coupling system. The basic theoretical models of wheel–rail in rolling contact and the corresponding numerical methods are the basis and one of the basic means for solving other wheel–rail relationship problems. The other is the experimental means. Moreover, the modeling and analysis of coupling behavior of the train and track can only be realized by means of the wheel–rail rolling contact mechanics model and its corresponding numerical method. This paper mainly discusses some research work and achievements on high-speed wheel–rail relationship problems since China opened a high-speed railway system on a large scale. The discussions in this paper include the classic wheel–rail rolling contact theoretical models (analytical forms) and the modern wheel–rail rolling contact theories (numerical methods), their advantages and disadvantages, their application and future development direction of them. The reviewed research progress on the other wheel–rail relationships mainly expounds the thorny problems of the wheel–rail relationship encountered in the operation of China’s high-speed railway, how to adopt new theoretical analysis methods, test means and take effective measures to solve these problems. It also includes research results of similar important reference values performed by international peer experts in related fields. Challenging and unsolved problems in high-speed wheel–rail relationship research are also reviewed in the full text.

An experimental study on the effects of friction modifiers on wheel–rail dynamic interactions with various angles of attack

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel–rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive; stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick–slip; the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Numerical study of wheel/rail dynamic interactions for high-speed rail vehicles under low adhesion conditions during traction

The evolution of wheel-rail dynamic interaction of a high-speed railway vehicle is essential for the simulation of wheel-rail rolling contact damage under low adhesion conditions. The main objective of this study is to reproduce the dynamic wheel-rail interaction behaviour under various interfacial contaminations by experimental and numerical modelling methodology. Firstly, the wheel-rail adhesion characteristics under different interfacial contaminations were obtained. Subsequently, a simplified numerical methodology was proposed to extract the parameters from the high-speed adhesion tests to modify the simplified theory of Kalker (FASTSIM). The initial slop reduction factor and the slip-velocity-dependent coefficient of friction (COF) were introduced based on the high-speed experimental curves. Furthermore, the modified wheel-rail rolling contact model was incorporated into a longitudinal vehicle-track coupled dynamic model. The wheel-rail dynamic interaction behaviours under different operational conditions were attained. Finally, the wheel-rail wear performances were primarily investigated for typical traction coefficients under wet conditions. Results show that the wheel-rail creep force drops dramatically when the wheel enters the low adhesion zone (LAZ). There is a sudden increase in the creep force when the adhesion recovers. In addition, the wheelsets begin to slide and have severe wear at LAZ when the traction coefficient is larger than 0.1 at high speed.

Freight train air brake models

ABSTRACT This paper is an outcome of an international collaborative research initiative. Researchers from 24 institutions across 12 countries were invited to discuss the state-of-the-art in railway train air brake modelling with an emphasis on freight trains. Discussed models are classified as empirical, fluid dynamics and fluid-empirical dynamics models. Empirical models are widely used, and advanced versions have been used for train dynamics simulations. Fluid dynamics models are better models to study brake system behaviour but are more complex and slower in computation. Fluid-empirical dynamics models combine fluid dynamics brake pipe models and empirical brake valve models. They are a balance of model fidelity and computational speeds. Depending on research objectives, detailed models of brake rigging, friction blocks and wheel-rail adhesion are also available. To spark new ideas and more research in this field, the challenges and research gaps in air brake modelling are discussed.

Coupled dynamic behaviours of the brake system considering wheel–rail interactions

ABSTRACT During vehicle operation, the brake system is influenced by wheel–rail interactions. To investigate the dynamic behaviours of the brake system, we propose a novel dynamic model of the brake system by considering the coupling effects between the disc–pad and the wheel–rail subsystems. Using the established model, the nonlinear coupled dynamic behaviours including wheel–rail adhesion characteristics, wheel–disc torsional vibrations and disc–pad stick–slip vibrations were comprehensively explored. The results showed that braking conditions remarkably influenced the longitudinal slip rate. The wheelset and brake units affect each other, and the wheels on one wheelset influence each other when they are asynchronous. The brake system is stable in the wheel–rail stick state, but becomes unstable in the wheel–rail stick–slip state or slip state. The limit cycle analysis showed that the brake pad stick–slip vibrations were easier to occur at a large slip rate.

Prescribed Performance Active Braking Control with Reference Adaptation for High-Speed Trains

Active braking control systems are vital for the safety of high-speed trains by leading the train operation at its maximum adhesion state. The train adhesion is a nonlinear function of the slip ratio and varies with the uncertain wheel-rail contact conditions. A nonlinear active braking control with rapid and accurate tracking performance is highly required for train braking systems. This paper proposes a novel prescribed performance active braking control with reference adaptation to obtain the maximum adhesion force. The developed feedback linearization controller employs a prescribed performance function that specifies the convergence rate, steady-state error, and maximum overshoot to ensure the transient and steady-state control performance. Furthermore, in the designed control approach, a continuous-time unscented Kalman filter is introduced to estimate the uncertainty of wheel-rail adhesion. The estimation is utilized to represent uncertainty and compensate for the prescribed performance control law. Finally, based on the estimated wheel-rail adhesion, an on-line optimal slip ratio generation algorithm is proposed for the adaptation of the reference wheel slip. The stability of the system is provided, and experiment results validate the effectiveness of the proposed method.

Experimental Study of Effects of the Third Medium on the Maximum Friction Coefficient between Wheel and Rail for High-Speed Trains

The changes of the friction coefficient between wheel and rail affect the wheel-rail adhesion characteristics of high-speed trains. The adhesion state in the wheel-rail contact area could be distinguished by the maximum friction coefficient between wheel and rail. The wheel-rail adhesion is of great significance for high-speed train traction. In order to study the influence of water, oil, fallen leaves, quartz sand, or their mixtures on the maximum friction coefficient between high-speed wheel and rail, a wheel-rail contact test bed is built to carry out the wheel-rail contact test and wheel-rail friction contact test. The comparative analysis of the test results shows that the axle load has little influence on the maximum friction coefficient between wheel and rail. Water, oil, and fallen leaves would reduce the maximum friction coefficient. Quartz sand could increase the maximum friction coefficient in a short time, while the excessive static friction coefficient would damage the wheel and rail. Besides, the maximum friction coefficient of water, oil, and fallen leaves mixing in pairs is lower than each of them existing alone. Both water and oil could increase the adhesion of quartz sand, and the effect of water is better. Therefore, when the sand still could not meet enough traction, it could be considered to add some water to increase the wheel-rail adhesion.

Experiment validation of the brake control of railway vehicle based on the wheel-rail adhesion characteristics

Experiment validation of the brake control of railway vehicle based on the wheel-rail adhesion characteristics

Experimental investigation on wheel–rail adhesion characteristics under water and large sliding conditions

Purpose The purpose of this study is to investigate the adhesion characteristics of the wheel–rail under water and large sliding conditions. This is carried out by conducting a series of tests on a full-scale roller rig. The measured data provides an experimental base for conducting further theoretical research. Design/methodology/approach The influence of the slip ratio, rolling speed and the axle load on the adhesion coefficient between the wheel and the rail is analyzed under wet conditions using a full-scale roller rig. Findings From the research, it is found that the adhesion coefficient–slip ratio curve varies from the traditional theoretical description under water and large sliding conditions. Moreover, it is also observed that after the adhesion coefficient reaches the saturation point, the adhesion coefficient does not decrease, but continues to increase as the slip ratio increases. Originality/value The adhesion improvement phenomenon in this paper may provide new ideas for designing anti-skid control and braking system mechanisms for trains. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0236/

Adaptive slip ratio estimation for active braking control of high-speed trains

Active braking control systems in high-speed trains are vital to ensure safety and are intended to reduce brake distances and prevent the wheels from locking. The slip ratio, which represents the relative difference between the wheel speed and vehicle velocity, is crucial to the design and successful implementation of active braking control systems. Slip ratio estimation and active braking control are challenging owing to the uncertainties of wheel–rail adhesion and system nonlinearities. Therefore, this paper proposes a novel adaptive slip ratio estimation approach for the active braking control based on an improved extended state observer. The extended state observer is developed through the augmentation of the system state-space to estimate the unmeasured train states as well as the model uncertainty. The accurate slip ratio is estimated using the observed extended states. Furthermore, the adaptability of the observer is improved by introducing the beetle antennae search algorithm to determine the optimal observer parameters. Finally, a feedback linearization braking control law is established to stabilize the closed-loop system due to its potential in coping with nonlinearities, which benefits the proven theoretical bounded stability. Experimental results validate the effectiveness of the proposed method.

Research on Traction Load Characteristics of Sichuan-Tibet Railway Under Different Weather

The Sichuan-Tibet Railway faces severe challenges such as changeable weather and long ramps. In order to reduce the ramp stop accidents of locomotive, the traction characteristic curve and braking characteristic curve of the locomotive are revised considering the wheel-rail adhesion limit under different weather conditions. Then the traction quality of dry rail, wet rail and ice rail is given. The modified characteristic curves and traction quality are used to simulate the traction load of Sichuan-Tibet Railway under different rail surface conditions. The results show that under dry rail conditions, the traction quality is 2500 tons and the driving power and regenerative braking power are extremely large, respectively 20MW and 16MW. Under wet rail and ice rail conditions, traction quality and regenerative braking power are significantly limited by adhesion. When ice rail, the traction quality is only 1200 tons; the driving power and the regenerative braking power are only respectively 14MW and 9 MW. At the same time, the running interval when growing uphill is 7 minutes longer than that under dry rail conditions. It provides a reference for the layout of the train operation diagrams and the design of the traction power supply system.

Real-time multibody modeling and simulation of a scaled bogie test rig

In wheel–rail adhesion studies, most of the test rigs used are simplified designs such as a single wheel or wheelset, but the results may not be accurate. Alternatively, representing the complex system by using a full vehicle model provides accurate results but may incur complexity in design. To trade off accuracy over complexity, a bogie model can be the optimum selection. Furthermore, only a real-time model can replicate its physical counterpart in the time domain. Developing such a model requires broad expertise and appropriate software and hardware. A few published works are available which deal with real-time modeling. However, the influence of the control system has not been included in those works. To address these issues, a real-time scaled bogie test rig including the control system is essential. Therefore, a 1:4 scaled bogie roller rig is developed to study the adhesion between wheel and roller contact. To compare the performances obtained from the scaled bogie test rig and to expand the test applications, a numerical simulation model of that scaled bogie test rig is developed using Gensys multibody software. This model is the complete model of the test rig which delivers more precise results. To exactly represent the physical counterpart system in the time domain, a real-time scaled bogie test rig (RT-SBTR) is developed after four consecutive stages. Then, to simulate the RT-SBTR to solve the internal state equations and functions representing the physical counterpart system in equal or less than actual time, the real-time simulation environment is prepared in two stages. To such end, the computational time improved from 4 times slower than real time to 2 times faster than real time. Finally, the real-time scaled bogie model is also incorporated with the braking control system which slightly reduces the computational performances without affecting real-time capability.

Experimental study of train sanding

Train sanders are ubiquitous in remediating low wheel–rail adhesion. Sanders operate by taking sand stored in a hopper, pneumatically conveying it through a nozzle, then spraying it into the wheel–rail interface. In this research, the wheel–rail–sander system was simulated experimentally in a laboratory. The system was optically accessible, and Particle Tracking Velocimetry was used to observe the trajectory of sand particles approaching the nip. The percentage of sand conveyed through the nozzle that makes it to the wheel–rail nip – the deposition efficiency – was measured gravimetrically. The maximum efficiency was found to be 91% for 1.15 mm mean diameter silica sand with a proprietary coating, and the minimum efficiency was 59% for uncoated aluminum oxide with a 0.91 mm mean diameter, both at a simulated train speed of 18 km/h. Irregular particles were found to be less efficient when compared to spherical particles with a similar size and composition. Increasing the size of silica sand from 0.18 mm to 1.05 mm in diameter slightly decreased the sanding efficiency from 67% to 60%. There was no statistically significant dependence of the efficiency on the particle coefficient of restitution. The single parameter most closely correlated with the deposition efficiency is the expansion of the particle-laden jet downstream of the nozzle. Larger, round particles typically had the smallest jet expansion and the highest efficiency, whereas rough particles with large diameters were found to have a large jet expansion and lowest efficiency. Finally, the effect of train speed on deposition efficiency was studied. The deposition efficiency was found to be very low at low train speeds and asymptotically approaches a fixed value at higher speeds. A simple physical model is proposed that explains the low efficiency at low speeds.

An Online Super-Twisting Sliding Mode Anti-Slip Control Strategy

The variability of rail surfaces can result in wheel–rail slippage, which reduces the accuracy of subway braking systems, or even endangers the operation safety. It is necessary to conduct optimal anti-slip control with the estimation of the wheel–rail adhesion state. In this paper, an online super-twisting sliding mode anti-slip control strategy is proposed for subway vehicles. Firstly, real-time wheel–rail adhesion state estimation is performed by utilizing the recursive least squares algorithm under complex and variable rail surface conditions. Then, the differential evolution algorithm is adopted to search the current optimal slip velocity based on the wheel–rail adhesion state. The super-twisting sliding mode controller is designed to implement the optimal sliding velocity tracking. The controller exploits the high-order derivatives of the sliding mode to eliminate chatter vibration and avoid the effect of disturbance, improving the anti-slip control performance. Finally, the effectiveness of the proposed anti-slip strategy is verified by experimental results.

Wheel–rail adhesion during torsional vibration of driven railway wheelsets

Stability verification of railway wheelsets in Germany can currently become a process difficult to plan. Besides standardised calculations, expensive and often time-consuming test ride measurements have to be conducted. In particular, determining the maximum dynamic torsional stresses resulting from torsional vibration of wheelsets is a frequently discussed topic. Neither an analytical nor an empirical model has been found yet to predict the named stresses. Actually, they are determined experimentally and the representativeness of the recorded maximum dynamic torque is assured statistically. However, statistical evaluation only deals with axle stresses (torque and bending) itself. The origin of torsional vibration, which is the wheel–rail contact point, is not considered for evaluation. Its conditions are typically described by wheel–rail adhesion characteristics, but normally the necessary quantities describing these characteristics are not measured or not measured in sufficient precision. Therefore, this article analyses high-resolution wheel–rail adhesion data that have been recorded additionally on regular test ride measurements. The analysis of these measurement data leads to the following two correlations: (1) Torsional vibration events occur at a certain ratio of adhesion change and slippage change. (2) Dynamic torque swings up within a characteristic time span.

Simultaneous Estimation of Wheel-Rail Adhesion and Brake Friction Behaviour

In the field of longitudinal train dynamics the brake process is not only a safety critical aspect but it also determines the capacity of the rail network. Therefore, a reduction of the brake distance increases the safety level and the network capacity at the same time. However, to implement an advanced brake control set-up, the knowledge of the wheel-rail adhesion and the brake pad-disc friction is usually necessary. Since the direct measurement of these determining parameters is not reasonable due to technical and economic reasons, the present work presents an estimator framework for their online identification. To ensure a robust and reliable performance of the estimator, a generic wagon model is designed and the observability of the nonlinear system is evaluated. Furthermore, a reasonable synthesis of an extended Kalman filter is discussed that takes account of the system characteristics. In the end, the test results from a roller rig verify the accurate and robust performance of the developed estimator and confirm the great potential of such a concept in the context of mechatronic railway systems.

An experimental study of high speed wheel-rail adhesion characteristics in wet condition on full scale roller rig

Adhesion at the wheel-rail interface is a key factor determining stable running conditions and safety during train traction and braking. The wheel-rail abrasion of EMUs often occurs when the adhesion force is insufficient. This paper presents experiments performed on a high-speed full-scale roller rig of wheel-rail interface to simulate the low adhesion problem of high-speed railway in wet condition. Tests were conducted to study the adhesion characteristics at high speed under water lubrication. The influential factors on the high-speed wheel-rail adhesion coefficient are investigated, which include water spray amount, roughness of wheel-rail contact surface, running speed, water temperature and axle load. In the adhesion tests, water was sprayed on the wheel-rail contact interface at 0–250 ml/min, the roughness of the wheel-rail contact surface Ra was set within 0.30 to 1.1 μm, the test running speed range was 40 to 400 km/h, the temperature of water changed from 0 to 60 °C to simulate the effect of temperature on the adhesion coefficient and the axle load ranged from 8 to 16t. The law of influence on wheel-rail adhesion characteristic curves at high speed was revealed and explained based on the test results, which can be helpful to the design and optimization of the anti-slip control device in brake and the rotation/slip control device of the traction wheel of EMUs.

An Intelligent Wheelset Spinning Detection System in a Direct Current Traction Drive

A spinning detection method of a locomotive wheelset in a dc traction drive and its implementation on the basis of intelligent processing of measuring data of the drive control system is considered. An increase in the amplitudes of the low-frequency harmonics of the voltage sensor output signal on the locomotive power circuit elements is used as a sign of loss of motion stability of the wheelset due to reaching the threshold wheel–rail adhesion. For automatic multilevel identification of spinning modes, a random forest algorithm-based classifier is used. The results of the analysis of the control power circuit parameters preindicated by experts show the high sensitivity and accuracy of the proposed intelligent spinning detection system.