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 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.
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.
To estimate the safety against flange-climb derailments the safety measures based on Nadal's formula have been used in the world. These measures are effective, but the safety margin against ...flange-climb cannot be estimated quantitively because the actual friction condition between rail and wheel flange cannot be measured by conventional methods. In this paper, the authors propose a new method for the estimation of the friction condition between rail and wheel flange, and using the estimated value of the friction coefficients, a safety measure, the “flange-climb index” (FCI), is proposed. The value of FCI can evaluate the margin for the safety against flange-climb occurrences quantitatively according to the friction conditions.
•Y/Q in Nadal's formula cannot examine the margin against flange-climb occurrence quantitatively.•The authors propose a new safety measure index FCI against flange-climb derailments.•FCI can quantitatively estimate the margin against flange-climb occurrences.•FCI is calculated considering the friction coefficient between wheel flange and rail.•The friction coefficient can be estimated by look-up tables created by MBD simulations.
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 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.
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.
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