When railway vehicles run on sharp curves, the coefficient of friction (COF) between the outer rail and the leading-outside wheel flange of a bogie is an important value related to problems such as ...wheel/rail severe wear, squeak noise arising from wheel/rail contact, and running safety against flange-climb derailment. In general, it is difficult to grasp the actual state of COF, which changes from moment to moment during commercial operations. From the viewpoint of running safety and maintenance, it is desirable to detect curved tracks with relatively high COF from the entire service line. The monitoring bogie, which can measure wheel/rail contact forces during commercial operations, has realized a long-term observation of wheel/rail contact forces. For further applications of the monitoring bogie, the simulation-based estimation method of COF at the wheel flange have been proposed in the author’s previous paper. Furthermore, an investigation based on roller-rig tests have been conducted. However, the probability of the flange wear progress cannot be determined only by COF at the wheel flange, and other factors should be involved. The wear number is used to assess rolling contact fatigue and wheel/rail wear progress. In the present paper, on the basis of a multi-body dynamics simulation model of the roller-rig equipment, the difference of the wear number among four lubrication conditions on the bogie is clarified. The estimation method of COF is extended to estimate the wear number simultaneously. The extended method is applied to the roller-rig test and the wear number is estimated. The estimated wear number shows qualitative agreement with the amount of wear debris, which is observed in the roller-rig test conducted in previous research.
The authors researched and developed a new measurement method that can continuously measure the contact forces and derailment coefficients at all curves of commercial lines. This new method can ...determine the derailment coefficients, which change according to the friction coefficients and other factors, using the measuring system on in-service trains. In this paper, the analysis results for actual curve data collected on commercial subway lines are introduced. Additionally, parameters that are influential on the changes of the derailment coefficients, such as “friction” and “track irregularity,” are discussed using the regression analysis on the accumulated data with the newly developed system.
•We developed a new measurement method that can continuously measure the contact forces.•The method can grasp rail/wheel interface conditions every time using service trains.•We are collecting huge data on commercial lines by the developed method.•We analyzed the mechanism of increase of L/V (i.e. Y/Q) in sharp curves.•Increases of L/V by friction change and track irregularities are verified.
Measurement of wheel–rail contact forces is very important, but it is not executed so often because of its difficulties. A new measuring method introduced in this paper can measure such contact ...forces without special wheelsets equipped with strain gauges and slip rings or telemeters. In this method the lateral contact force is measured from the lateral distortion of wheel measured directly by several non-contact gap sensors. Normal and longitudinal contact forces are also measured from the deflection of spring or the strain of parts of the bogies except wheelsets. According to the results of full-size bogie stand tests and train running tests, it is verified that the new method has sufficient practicability of monitoring the contact forces on commercial lines.
The derailment coefficient, which is calculated based on the wheel-rail contact forces, indicates the running safety of a railway vehicle with respect to flange climb derailment. The value of the ...derailment coefficient changes constantly due to numerous factors associated with the vehicle and track conditions while the vehicle runs on a service line. Therefore, it is desirable to monitor the state of the wheel/rail contact in order to ensure the running safety. Recently, a new monitoring bogie, which can measure the derailment coefficient during commercial operations, has been developed and introduced into some service lines. Large-scale data have been collected by this monitoring bogie. In this paper, the temporal subtraction analysis is carried out for preparing appropriate plan for reducing the derailment coefficient based on these data. In the analysis, the vehicle running position is important for accurate calculation of the difference between two waveforms. However, the vehicle running position contains errors because of the accumulated error of integral calculation of the vehicle velocity. The present paper proposes a method which modifies the running position along track so that the two waveforms are well matched. The proposed method is based on DP matching, and the waveforms of the track irregularity of twist estimated by the monitoring bogie are used in the method. After DP matching, an example of temporal subtraction analysis of the derailment coefficient between two periods is performed. Finally, by using the long-term measurements acquired by the monitoring bogie, the monthly variation of the derailment coefficient for a certain spot on the track is shown as a practical example.
The coefficient of friction (COF) between the outer rail and the leading-outside wheel flange of a railway bogie running on sharp curved track is an important parameter for the progress of wheel/rail ...wear and running safety. Therefore, it is desired to grasp the actual state of COF of wheels especially at the leading-outside wheel flange. In the author’s previous studies, a roller-rig experiment was conducted with changing lubrication condition of each wheel of the bogie to figure out relationship between lubrication conditions and wheel/rail contact forces such as tangential, lateral and vertical directions. In this paper, a method to estimate the value of COF of leading-outside wheel with look-up tables built by repetitive numerical simulations is explained. In the construction of the look-up tables, friction coefficients for each wheel in the numerical simulation model are changed while collecting calculated wheel/rail contact forces. A railway bogie running on roller-rig test is considered for both numerical simulations and experiment with different lubrication condition, therefore look-up tables are built with a half-vehicle model running on the roller-rig. By inputting the wheel/rail contact forces measured in roller-rig test into the look-up tables built by simulations, and the COF of leading-outside wheel flange is estimated. The result shows that the lubrication condition of leading-outside wheel flange can be estimated by the proposed method especially when the value of COF is large and is useful for the detection of high COF condition.
By using non-contact gap sensors equipped on non-rotating parts of a bogie, a new measuring method of wheel/rail contact forces has been developed. The developed system has been verified to have ...sufficient durability for continuous measurement on in-service trains and sufficient practical accuracy after various stand tests and train running tests. After a long-period of continuous measurement on a commercial subway line, some important characteristics of wheel/rail contact mechanics were found by the analysis of measured data. Numerical simulations of curving with a full vehicle model using multi-body dynamics software were carried out, and according to the comparison with measured data, simulation results agree well with measured data in the steady-state values of derailment coefficients considering friction coefficient.
The purpose of this study is to demonstrate the friction control between wheel and rail can solve wheel/rail contact problems, such as wheel-slipping, rail corrugation, squeak noises, wheel/rail wear ...and so on. Firstly, fundamental tests with two-roller-rigs were carried out to evaluate the friction performances of several types of friction modifiers. Then, for the purpose of realizing the friction control with them, authors developed an on-board system, which sprayed friction modifier from a bogie to the top of rail accurately. This method is very advantageous to control friction between wheel and rail. As a result of track tests, it was found that one type of friction modifier, which had proper coefficient of friction (COF) and positive creep characteristics, was very effective to reduce the lateral force and the squeak noises.
From full-scale stand tests, commercial line experiments and numerical simulation, we found that corrugation of rail in curve section of track is formatted by stick–slip vibration between wheel and ...rail, which is caused by the large creepage and vertical force fluctuation on wheel/rail contact surface. On the basis of this theory, we analyzed the growing process of corrugation by numerical simulation.
The derailment coefficient is calculated from wheel-rail contact forces and it indicates the running safety of the railway vehicle especially in sharp curves. The derailment coefficient is affected ...by many factors such as the track irregularities, the vehicle parameters and the friction characteristics between wheel and rail. Therefore, monitoring of the derailment coefficient is desired to evaluate the running safety of the vehicle. Recently, a new monitoring bogie which can collect time series data of the derailment coefficient during commercial operation has been developed, and a large scale data is collected. However, there was no way to use such a data efficiently because an efficient method and an analysis tool have not been developed. In this research, a new analysis tool which can easily handle a large scale data and assist analysis of the derailment coefficient has been designed using MATLAB. In addition to measuring the derailment coefficient, the wheel load reduction and the track irregularity of twist are also measured. The tool can extract points where the derailment coefficient increases from a large scale data, and quickly show detailed information. On the basis of the information displayed on the user-interface, the data analyst can identify factors that increase the derailment coefficient. Not only analysis focused on a particular curve, but also the tool has the function for comparison of some curves. Analysis of the time change of the derailment coefficient is also possible. This paper shows the basic design of the analysis tool and gives some examples of analysis using this tool.
It is important to secure running safety of railway vehicles against wheel-climb derailment accidents. The safety is often discussed according to the value of derailment coefficients for the leading ...outside wheel of a railway bogie running on sharp curves. Therefore, the detailed force induced mechanism which influences the value of derailment coefficients should be clarified. One of the most dominant factors affecting the value of derailment coefficients is magnitudes of the coefficient of friction (COF) between wheel and rail. Since the gauge corner of the outer rail and the top of the inner rail are lubricated at some sharp curves, COF of wheels of a bogie are different from each other and show complicated variation. In this study, the effect of lubrication for the running safety of the railway bogie is investigated while considering the detailed force induced mechanism of the derailment coefficient increase utilizing both multibody dynamics simulations and experiments. Experiments and simulations are conducted with a roller-rig test equipment under various conditions of wheel/rail lubrication. In this research, a method to identify whether the bogie is in suitably lubricated condition in terms of running safety is discussed. The proposed method making use of the longitudinal force measurement with mono-link type axle supporting device is mentioned.
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