Wheel-rail Adhesion Research Articles

Experimental investigation of wheel rail adhesion under leaf contamination conditions

Experimental investigation of wheel rail adhesion under leaf contamination conditions

Mechanism of Wheel-Rail Adhesion Recovery during Large Sliding processes under Water Lubrication condition

The challenge of low adhesion between the wheel and rail constrains the advancement of train braking technologies, resulting in sliding during braking, increased braking distances, and even operational safety incidents. Low adhesion arises from the contamination of the rail surface by a third body, such as water or oil, significantly reducing adhesion. However, experimental studies have found that wheel-rail adhesion coefficient under water lubrication conditions possesses a recovery capability: In scenarios characterized by low adhesion in water lubrication conditions, a secondary rise in adhesion occurs when substantial wheel-rail sliding is present. This paper focuses on numerically modeling the unique phenomenon of adhesion recovery during large-sliding processes under water lubrication conditions. Considering the notable differences in frictional heating during wheel sliding, as opposed to pure rolling conditions, we construct a wheel-rail contact model under mixed lubrication conditions that incorporates the solid-liquid coupled heat transfer effect. This model achieves stable solutions for the wheel-rail contact relationship and the temperature at the wheel-rail interface. The impacts of velocity, axle load, water temperature, and slide ratio on the adhesion recovery phenomenon are discussed, revealing the underlying mechanism of adhesion recovery during large sliding processes. Finally, brake adhesion tests under water lubrication conditions are conducted on a scaled test rig to validate the proposed theoretical model.

A comprehensive wheel–rail contact model incorporating sand fragments and its application in vehicle braking simulation

Increasing the wheel–rail adhesion coefficient by spreading sand grains to the wheel–rail interface is a common approach to improve the traction and braking efficiency of trains. To simulate this process accurately, two highlights are presented in this paper. Firstly, this paper proposes a wheel–rail contact model considering sand fragments, a third body, based on the non-Hertzian theory, which includes a random sand-grain generator and a sand crushing model. The proposed wheel–rail model is used to analyze the wheel–rail adhesion state after sand grains enter the wheel–rail contact interface. How sand particles change the distribution of normal force and tangential force to affect the wheel–rail adhesion is clarified and, in addition, the influence of the parameters of sand fragments on the wheel–rail adhesion coefficient is given. Secondly, a vehicle system dynamics model considering sanding and wheel slip protection (WSP) control is developed to analyze the effect of sanding on braking distance and wheel slip during braking processes. The wheel–rail contact model and the vehicle system dynamics model presented in this paper can support the study of more effective sanding and adhesion enhancement devices.

DEVELOPMENT OF A MATHEMATICAL MODEL FOR DETERMINING TRACTION AND ENERGY PERFORMANCE INDICATORS OF A MANEUVERING LOCOMOTIVE

Fuel consumption for traction significantly depends on the locomotive's operating mode, and by selecting a rational mode during station maneuvers or transit, it is possible to reduce fuel consumption. Previous works on this topic do not provide sufficient analysis of locomotive motion with varying numbers of connected engines. To optimize energy resource consumption, a combination of methods for the rational use of the locomotive is necessary. The traction and energy performance indicators for the maneuvering work of the ČME3 locomotive are calculated by performing traction calculations. In this paper, a mathematical model has been developed to determine these indicators when operating with 4 and 2 parallel-connected traction electric motors. Graphs were constructed to illustrate the relationship between traction force and locomotive speed, the time required to cover a given distance, fuel consumption for a specified distance, and the temperature rise above ambient conditions concerning 6 parallel-connected traction electric motors for the 3rd, 4th, and 5th positions of the engineer's controller. The locomotives were compared while covering the same stretch of track with the same train weight, considering wheel-rail adhesion constraints.Analyzing the obtained dependencies allows the conclusion that using different configurations of connected engines can result in fuel savings of up to 15 % during maneuvering operations, depending on operational conditions. Furthermore, the engine temperature remains within acceptable limits for insulation class F, based on the results of approximating existing locomotive characteristics and deriving analytical expressions (6, 7, 8, 24). Mathematical models of the motion of the ЧМЕ3 locomotive were created for various engine connection scenarios using the obtained mathematical formulas (9, 10, 11, 13, 20, 21, 22, 23, 24).

The Two-Parameter Bifurcation and Evolution of Hunting Motion for a Bogie System

The complex service environment of railway vehicles leads to changes in the wheel–rail adhesion coefficient, and the decrease in critical speed may lead to hunting instability. This paper aims to reveal the diversity of periodic hunting motion patterns and the internal correlation relationship with wheel–rail impact velocities after the hunting instability of a bogie system. A nonlinear, non-smooth lateral dynamic model of a bogie system with 7 degrees of freedom is constructed. The wheel–rail contact relations and the piecewise smooth flange forces are the main nonlinear, non-smooth factors in the system. Based on Poincaré mapping and the two-parameter co-simulation theory, hunting motion modes and existence regions are obtained in the parameter plane consisting of running speed v and the wheel–rail adhesion coefficient μ. Three-dimensional cloud maps of the maximum lateral wheel–rail impact velocity are obtained, and the correlation with the hunting motion pattern is analyzed. The coexistence of periodic hunting motions is further revealed based on combined bifurcation diagrams and multi-initial value phase diagrams. The results show that grazing bifurcation causes the number of wheel–rail impacts to increase at a low-speed range. Periodic hunting motion with period number n = 1 has smaller lateral wheel–rail impact velocities, whereas chaotic motion induces more severe wheel–rail impacts. Subharmonic periodic hunting motion windows within the speed range of chaotic motion, pitchfork bifurcation, and jump bifurcation are the primary forms that induce the coexistence of periodic motion.

Research on the Identification of Nonlinear Wheel–Rail Adhesion Characteristics Model Parameters in Electric Traction System Based on the Improved TLBO Algorithm

The wheel–rail adhesion is one of the key factors limiting the traction performance of railway vehicles. To meet the adhesion optimization needs and rapidly obtain wheel–rail creep characteristics under specific operating conditions, an engineering identification method for wheel–rail adhesion characteristics based on a nonlinear model is proposed. The proposed method, built upon the traditional Teaching-Learning-Based Optimization (TLBO) algorithm, has been adapted to the specific nature of nonlinear wheel–rail adhesion model parameters identification, enhancing both the search speed in the early stages and the search accuracy in the later stages of the algorithm. The proposed identification algorithm is validated using experimental data from the South African 22E dual-flow locomotive. The validation results demonstrate that the proposed identification algorithm can obtain a nonlinear wheel–rail adhesion characteristics model with an average adhesion coefficient error of around 0.01 within 50 iteration steps. These validation results indicate promising prospects for the engineering practice of the proposed algorithm.

Multi-objective optimisation of wheel-rail adhesion for high-speed trains with aerodynamic lift wings

A high-speed train with aerodynamic lift wings (aero-wings) is designed to improve train speed and mitigate energy consumption. Nevertheless, the impact of aero-wings on wheel-rail adhesion and safety remains uncertain. In this examination, a multi-body dynamics (MBD) model of a high-speed train integrated with aero-wings was first created. The influences of train speed, wheel-rail contact conditions, and aerodynamic lift on the wheel-rail adhesion, wheel wear, and dynamics performance were briefly investigated, indicating that aerodynamic lift degrades wheel-rail adhesion and dynamics performance but reduced wheel wear. Then, the multi-parameters matching optimisation design for sufficient wheel-rail adhesion and minimal wheel wear was conducted. The results indicate that, under dry contact and traction conditions, the minimum wear and optimal wheel-rail adhesion can be achieved when the train speed is about 440.62 km/h, the aerodynamic lift is about 24.48% of the vehicle weight, and the wheel wear optimisation rate is 25.38%. While the train speed of 549.54 km/h and an aerodynamic lift of 12.39% corresponds to the optimal results with wear reduction of 11.62%, under wet and braking conditions. This study provides valuable insights for determining aerodynamic load limits and formulating traction/braking control strategies for high-speed trains with aero-wings.

Analysis of wheel-rail adhesion redundancy considering the third-body medium on the rail surface

PurposeIn response to the problem of insufficient traction/braking adhesion force caused by the existence of the third-body medium on the rail surface, this study aims to analyze the utilization of wheel-rail adhesion coefficient under different medium conditions and propose relevant measures for reasonable and optimized utilization of adhesion to ensure the traction/braking performance and operation safety of trains.Design/methodology/approachBased on the PLS-160 wheel-rail adhesion simulation test rig, the study investigates the variation patterns of maximum utilized adhesion characteristics on the rail surface under different conditions of small creepage and large slip. Through statistical analysis of multiple sets of experimental data, the statistical distribution patterns of maximum utilized adhesion on the rail surface are obtained, and a method for analyzing wheel-rail adhesion redundancy based on normal distribution is proposed. The study analyzes the utilization of traction/braking adhesion, as well as adhesion redundancy, for different medium under small creepage and large slip conditions. Based on these findings, relevant measures for the reasonable and optimized utilization of adhesion are derived.FindingsWhen the third-body medium exists on the rail surface, the train should adopt the low-level service braking to avoid the braking skidding by extending the braking distance. Compared with the current adhesion control strategy of small creepage, adopting appropriate strategies to control the train’s adhesion coefficient near the second peak point of the adhesion coefficient-slip ratio curve in large slip can effectively improve the traction/braking adhesion redundancy and the upper limit of adhesion utilization, thereby ensuring the traction/braking performance and operation safety of the train.Originality/valueMost existing studies focus on the wheel-rail adhesion coefficient values and variation patterns under different medium conditions, without considering whether the rail surface with different medium can provide sufficient traction/braking utilized adhesion coefficient for the train. Therefore, there is a risk of traction overspeeding/braking skidding. This study analyzes whether the rail surface with different medium can provide sufficient traction/braking utilized adhesion coefficient for the train and whether there is redundancy. Based on these findings, relevant measures for the reasonable and optimized utilization of adhesion are derived to further ensure operation safety of the train.

Study on the wheel/rail adhesion characteristic under water and oil conditions by using mixed lubrication model

During train operation, water, oil, or oil-water mixtures may adhere to the wheel/rail contact interface, thereby altering the adhesion between the wheel and the rail. In order to study the adhesion characteristics of wheel/rail under wet conditions, a deterministic mixed lubrication model considering surface roughness and transient state is established in this paper, in which the quasi-system numerical and finite difference method are used for numerical solution. The results show that the influence of speed on the wheel-rail adhesion characteristics is more obvious, with the increase of train speed, the fluid dynamic pressure effect between the wheel-rail contact interface is enhanced, the contact pressure of the wheel-rail carried by the fluid film increases, the wheel-rail contact area accounts for the direct contact area of the proportion of the wheel-rail contact area continues to decrease, the thickness of the fluid film between the wheel-railcontinues to increase, and the coefficient of the wheel-rail adhesion decreases. Under the same working condition, with the increase of axle weight, the wheel-rail attachment coefficient increases, and when the axle weight reaches 22t, the attachment coefficient becomes obviously smaller; with the increase of creep-slip rate, the wheel-rail attachment coefficient increases obviously, and then stays relatively stable; with the increase of the wheel-rail surface roughness, the wheel-rail attachment coefficient also increases. Different wetting conditions between wheel/rail interfaces have more obvious effects on wheel/rail adhesion characteristics. In particular, under the same working conditions, the film thickness between the wheel/rail is the largest and the wheel/rail adhesion coefficient is the smallest when the wheel/rail interface is lubricated by oil. It is worth noting that when oil lubrication occurs on the surface of the wheel -rail, the thickness of the fluid film between the wheel-rail is the largest, and the coefficient of adhesion of the wheel-rail is the smallest, which brings safety hazards to the train operation. Therefore, it is necessary to regularly check and clean up the wheel-rail surface, especially the oil contaminants.

Review of various influencing factors and improvement measures on wheel-rail adhesion

The Wheel-rail adhesion is essential for safe and stable vehicle operation. Since the beginning of railway construction, many railway researchers and engineers have been actively involved in the study of this railway-specific issue. Most studies to date have focused on the various factors influencing the adhesion characteristics and quantifying the extent of their influence. This paper gives an overview of experimental and theoretical studies on evaluating wheel-rail adhesion characteristics under conditions where different third-body materials are interposed between wheel and rail and describes further challenges and research directions in the field of adhesion for the future.

Tribological and rheological performance of friction modifiers with different viscosities

Friction modifier (FM) in the rail/wheel applications is a special lubrication material that could be applied between the top of rail and the tread of wheel. The application of FM brings many benefits to the wheel-rail interface such as reducing noise, alleviating wheel-rail wear and mitigating corrugation. Viscosity is an important parameter to reflect fluid properties of FM materials. In this study, FM samples with different viscosities were prepared by changing the content of sodium carboxymethyl cellulose (CMC). The tribological and rheological performance of these FM samples were explored using the twin-disc testing machine and rotational rheometer. Furthermore, the relationship between the tribological and rheological results were tried to establish. The results showed that the increase in the content of CMC could increase the viscosity of FM and enhance the solid-like characteristic of FM, which could help FM reduce coefficient of adhesion (COA) level and wheel-rail damage. For the FM material developed in this study, the rational applying amount and the range of viscosity were about 15 μL/time and 200 Pa s to 400 Pa s, respectively, considering the factors of wheel-rail adhesion, wear, potential waste and pumping process in the practical application.

A transient three-dimensional wheel-rail adhesion model under wet condition considering starvation and surface roughness

The objective of this paper is to propose a new three-dimensional wheel-rail adhesion model under wet condition which considers insufficient water supply, the measured surface roughness and dynamic effect of the vehicle and track coupling system. Firstly, a longitudinal vehicle/track coupling dynamic model (LVTDM) was developed to obtain the dynamic parameters and contact points trace in curved track. Then, an improved numerical method was used to solve the transient general starved Reynolds equations, utilizing the input dynamic parameters acquired from the LVTDM. The numerical model was validated under the starved steady condition for the smooth surface and subsequently applied to investigate wheel and rail contact behaviors under wet condition. The results show that the effect of starvation on the wheel-rail rolling contact behaviours becomes significant when the inlet film thickness is less than 1000 nm for smooth surface. The numerical results were also compared with experimental results conducted by a high-speed tribology facility. In addition, the time-dependent characteristics of the wheel-rail rolling contact were obtained at different time instants. The transient wheel-rail adhesion characteristics under wet condition for different train speeds were obtained. The transient wheel-rail adhesion modeling results shows that the train speed has a significant effect on the adhesion ability.

Experimental investigation of high-speed wheel-rail adhesion characteristics under large creepage and water conditions

With the increase of train operational speed, the wheel-rail adhesion will behave differently. This behavior will directly affect the utilization of wheel-rail adhesion during traction and braking. Typical rainy and snowy weather will cause the wheel-rail low adhesion problem. Correspondingly, the wheel sliding can happen and causes wheel burns on both the wheel and rail contact surfaces. Besides, the braking distance will exceed the limit, which endangers driving safety. The engineering application of brake adhesion of high-speed EMUs mainly utilizes the second peak of braking force coefficient (it refers to the instantaneous adhesion force coefficient during the braking process.) under large creepage through anti-skid braking system, where the braking force coefficient reaches its maximum value at this second peak [11]. However, this wheel-rail adhesion behavior and the underlying mechanism are complexed especially under the high speed, which restricts its effective use for high-speed trains. In this paper, an innovative full-scale high-speed wheel-rail test rig is used to investigate the high-speed wheel-rail adhesion characteristics under large creepage and water conditions. The influence of different test speeds of 100–400 km/h is considered. Based on the test, it is found that the braking force coefficient is influenced by the test speed. Therefore, the optimal “beneficial zone” where the braking force coefficient has the maximum value and, in the meantime, guarantees the wheel-rail contact in stability varies with speed. The test results provide a fundamental basis for improving the utilization of EMU braking adhesion.

Introducing wheel-rail adhesion control into longitudinal train dynamics

Introducing wheel-rail adhesion control into longitudinal train dynamics

Dynamic characteristics of rack vehicle-track coupled system on large slope line: theoretical modelling and experimental validation

Rack railway is a rail transportation that utilizes the gear-rack engagement to supply the traction forces on large-slope lines, primarily employed in mountainous regions where the conventional trains cannot operate due to the wheel-rail adhesion limitations. However, there is limited research on this system dynamics and further analysis is required to understand the interaction mechanism between the rack vehicle and track. Based on the typical vehicle-track coupled dynamics theory, the rack vehicle-track spatially coupled dynamics model is developed in this paper to evaluate the dynamic behaviours of the rack vehicle and the track system running on large-slope line with a detailed modeling of the longitudinal motion for the rack and sleeper, where the time-varying gear-rack mesh stiffness and the rail geometrical irregularity are incorporated. The excellent agreement observed between simulated and field-test results serves as strong validation for developed dynamics model. The results demonstrate that the vibration responses of the wheelset and the rack are dominated by the gear-rack mesh excitations. It should be noticed that the wheel loads are reduced by the presence of the gear-rack engagement. Furthermore, the vibration of the sleeper can explicitly reflect the gear-rack mesh characteristics through the transfer of the rack fastener.

Numerical study of wheel–rail adhesion performance of new-concept high-speed trains with aerodynamic wings

Numerical study of wheel–rail adhesion performance of new-concept high-speed trains with aerodynamic wings

Numerical investigation on wheel-rail adhesion under water-lubricated condition during braking

PurposeThe purpose of this study is to develop a 3D wheel-rail adhesion model under wet condition, which considers the generated surface roughness topography and the traditional braking procedure for high-speed trains.Design/methodology/approachWheel-rail adhesion has an important effect on the braking ability of railway vehicle. Based on the deterministic mixed lubrication approach, the model was solved to get the adhesion characteristics of the train during braking. The elastic deformation was calculated with the discrete convolution and fast Fourier transform method. The simulation results of adhesion coefficient were compared with the experimental values. The wheel-rail adhesion characteristics of train braking at several different initial speeds were investigated. The effects of the time-step length and roughness orientation on the contact load ratio were also discussed.FindingsThe results show that the adhesion coefficient of the numerical model is in good agreement with the experimental results. At the instant of braking, the adhesion coefficient drops to a lower adhesion level, the value of adhesion coefficient is lower than 0.06, especially at a higher speed (200, 300 and 400 km/h).Originality/valueIt can provide a better understanding of the low adhesion phenomenon of train braking under wet condition.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2023-0040/

Influence of different solid particles in friction modifier on wheel-rail adhesion and damage behaviours

Friction modifier (FM) is widely used in the curve section to suppress the damage and noise between the wheel and rail. This paper compared typical third body materials, including water, oil and FM to explore their influencing mechanism on wheel-rail adhesion and damage. Furthermore, FM samples containing different solid particles were prepared. The tribological performance of these FM samples, water and oil were tested with a twin-disc testing apparatus and a hand-push tribometer. The results indicated that the shear strength of the third body material plays a vital role in the friction. The hardness of solid particles in FM greatly influences the friction control performance of FM. The change in the hardness of the solid particles makes the FM exhibit either “lack of lubrication” or “over lubrication”, that both are detrimental to the wheel and rail interface. For FM material, it is necessary to select solid particles according to the adhesion and damage comprehensively. The most suitable particle in this paper was kaolin.

Calculation and Characterization of Braking Performance for Rail Eddy Current Brake With AC Excited Ring-Winding Armature

With the continuous increases of the train speed, the braking device that relies on the wheel-rail adhesion has approached its acceptable speed limit. Compared with traditional friction brakes, eddy current brakes (ECBs) have the advantages of non-wheel-rail contact, fast response, low noise, wide application range, and no pollution. This study describes an ECB with AC excitation based on Faraday's law. The two-dimensional analytical model of ECB is established by the sub-domain method. Then, the experiment system of rail ECB is designed and built to test the braking characteristics. The authenticity of mathematical model is verified by experimental results. The research indicated that braking force increased at first and reached a maximum value, then slowly decreased with the increase of speed, while normal attractive force was always reduced. This characteristic matches the requirements of high-speed trains with large braking force and low normal force, which makes it a great option for auxiliary braking mechanism in the high-speed trains.

Study on Creepage Control for PLS-160 Wheel-Rail Adhesion Test Rig Based on LADRC.

Aiming at the problem of low control accuracy caused by nonlinear disturbances in the operation of the PLS-160 wheel-rail adhesion test rig, a linear active disturbance rejection controller (LADRC) suitable for the wheel-rail adhesion test rig was designed. The influence of nonlinear disturbances during the operation of the test rig on the control accuracy was analyzed based on SIMPACK. The SIMAT co-simulation platform was established to verify the control performance of the LADRC designed in this paper. The simulation results show that the speed and creepage errors of the test rig under the control of the LADRC met the adhesion test technical indicators under four different conditions. Compared with the traditional PID controller, the creepage overshoot and response time with the LADRC were reduced by 1.27% and 60%, respectively, under the constant creepage condition, and the stability recovery time was shorter under the condition of a sudden decrease in the adhesion coefficient. The LADRC designed in this paper shows better dynamic and anti-interference performance; therefore, it is more suitable for a follow-up study of the PLS-160 wheel-rail adhesion test rig.