Gearless Track-Friendly Metro with Guided Independently Rotating Wheels

Track–vehicle severe interaction on track with small curve radius results in rail wear and corrugation, and wheel polygonization, which drain considerable resources for rail grinding and wheels re-profiling in metro lines. To reduce the damage caused by track-vehicle severe interaction, the paper analyzes the reasons leading to rail wear and then proposes an architecture of a metro vehicle with independently rotating wheels driven directly by permanent magnet synchronous motors. The architecture is axle guidance, offered by passive linkages, which ensures that all axles are oriented radially, while control strategy was kept as simple as possible, identifying only two basic traction conditions. The concept is first discussed and then validated through a comprehensive set of running dynamics simulation performed with a multibody software to evaluate rail wear and rolling contact fatigue in traction/braking, coasting with different cant deficiency/excess conditions. The multibody dynamics simulation shows that the proposed architecture is virtually capable of avoiding both wear and rolling contact fatigue damages, and achieves the highest possible track friendliness. The concept of the proposed architecture is a track-fiendly metro architecture and could be a good reference for reducing rail-track interaction damages and maintainace cost.

Mechanical Wear Contact between the Wheel and Rail on a Turnout with Variable Stiffness

The operation and maintenance of railroad turnouts for rail vehicle traffic moving at speeds from 200 km/h to 350 km/h significantly differ from the processes of track operation without turnouts, curves, and crossings. Intensive wear of the railroad turnout components (switch blade, retaining rods, rails, and cross-brace) occurs. The movement of a rail vehicle on a switch causes high-dynamic impact, including vertical, normal, and lateral forces. This causes intensive rail and wheel wear. This paper presents the wear of rails and of the needle in a railroad turnout on a straight track. Geometrical irregularities of the track and the generation of vertical and normal forces occurring at the point of contact of the wheel with turnout elements are additionally considered in this study. To analyse the causes of rail wear in turnouts, selected technical–operational parameters were assumed, such as the type of rail vehicle, the type of turnout, and the maximum allowable axle load. The wear process of turnout elements (along its length) and wheel wear is presented. An important element, considering the occurrence of large vertical and normal forces affecting wear and tear, was the adoption of variable track stiffness along the switch. This stiffness is assumed according to the results of measurements on the real track. The wear processes were determined by using the work of Kalker and Chudzikiewicz as a basis. This paper presents results from simulation studies of wear and wear coefficients for different speeds. Wear results were compared with nominal rail and wheel shapes. Finally, conclusions from the tests are formulated.

Design method of worn rail grinding profile based on Frechet distance method

Due to the large volume and high running density of railway freight lines, rail deterioration occur frequently. Thus, it is necessary to grind the rail in time to improve the wheel-rail relationship. The profile data of the worn rail were measured at different measuring points in a section, and the Frechet distance method was adopted to analyze the data. The representative profile reflecting the overall condition of rail wear in this section is obtained. Combined with NURBS curve theory, a fitting algorithm in which the rail profile with certain discrete points was established. Taking the reduction of the amount of grinding material removed as the objective function, setting wheel-rail matching characteristics, and the reduction of rail wear as the constraint conditions, a calculation model for rail grinding profile was established. The dynamic characteristics of standard profile CN75 and g grinding profile OP75 were analyzed by the vehicle track dynamics model. The results showed that compared with the standard profile CN75, the amount of grinding material removed of the grinding profile OP75 is reduced by 44.7%, and the height reduction of the rail top is reduced by 0.39 mm. After [Formula: see text] km of running, the wear amounts of grinding profile OP75 is about 36.1%–36.5% less than that of standard profile CN75.In the small curve section, the derailment coefficient of grinding profile OP75 is reduced by 11.7% compared with that of standard profile CN75. The dynamic performance is improved. The grinding target profile has better dynamic characteristics and is beneficial to reduce wheel-rail wear.

Study on Gage Widening Methods for Small-Radius Curves

Existing gage widening standards and the influence of gage widening on the curve passing performance of trains and rail wear were examined. The existing gage widening theory can determine the minimum curve radius that needs to be widened, the widening value required by curves with different radii, and whether multiaxle locomotives can pass small-radius curves. However, it does not quantify the influence of the gage widening value on the curve passing performance and track maintenance workload. The range of the minimum curve radius that needs to be widened is 220–350 m, whereas some countries adopt a radius of 600 m; the maximum gage widening range is 15–20 mm, and few countries adopt gage widening values exceeding 30 mm. When the gage widening value increases from 0 to 10 mm, the lateral force of the curved wheel or rail with a radius less than 300 m is reduced by 16–20%, and that with a radius exceeding 300 m is reduced by 10–15%. The results of this study reveal that using proper gage widening values can reduce the lateral force of the wheel or rail and improve the curve passing performance. In the rail lifecycle, the implementation of the current gage widening standard requires only one gage adjustment operation, whereas the implementation of the original gage widening standard requires doubling gage adjustment operations.

An Experimental Study of the Influence of the Amount of Top-Of-Rail Friction Modifiers on Traction

This study presents an experimental study of the effect of Top-of-Rail Friction Modifiers (TORFM) in quantities ranging from a small to a large amount on the progression of wheel-rail wear, using the Virginia Tech-FRA (VT-FRA) roller rig. TORFM behaves as a third body layer in between the wheel and rail and is applied to reduce wheel and rail wear while preserving a stable traction condition. An added benefit of TORFM is that it is estimated that it can reduce fuel consumption by controlling friction, although we are not aware of any proven data in support of this. Although widely used by the U.S. Class I railroads, there exists no proven method for determining, qualitatively or quantitatively, how the amount of TORFM and rail/wheel wear are related. Simply put, would increasing TORFM amount by a factor of two reduce wheel/rail wear and damage by one-half? How would such doubling effect traction or the longevity of TORFM on the wheel/rail surface? In this study, the VT-FRA roller rig is used to perform a series of tests under highly controlled conditions to shed more light on answering these questions. A series of controlled experiments are designed and performed in order to investigate the potential factors that may influence the traction performance. The wheel surface profile is measured by a high-precision, 3D, laser profiler to measure the progression of wheel wear for the duration of the experiments. The results indicate that it takes as much longer time for the traction force (traction coefficient) to reach a condition that is the same as the unlubricated rail, when compared between lightly-, moderately-, and heavily-lubricated conditions. The results further indicate that wear generation is delayed significantly among all lubrication conditions — even, the lightly-lubricated — when compared with the unlubricated conditions. A further evaluation of the results and additional tests are needed to provide further insight into some of the preliminary results that we have observed thus far.

Application of methods for analysing combinations of wheelset sizes and switch elements to determine the size of gutters of check-rail assemblies

The paper considers methods for analysis of size combinations of wheelsets and elements of switches that are used at determination of dimensions of gutters for check-rail assemblies. The method of limit combinations, from the one side, doesn’t guarantee a reliable train operation on crossing assemblies in real operation, but, from the other side, it makes unreasonably strict demands to the design of the assembly. In order to eliminate the contradictions the paper proposes to use a method of probable compositions that allows not only solving an issue of limited safe dimensions of gauge and gutters, but also determining repeatability of impacts on check-rails in the most loaded cross sections and repeatability of motion paths of wheels on crossing. However, while using this method the authors have revealed a number of contradictions between calculated results and real operation. They show that it is possible to avoid the contradictions by the use of conditional probabilities method that allows calculating probabilities of phenomena for specific size combinations of gauge and gutters. As a result, the authors have concluded that it is the most accurate method of determination of permissible dimensions for gauge and gutters on switches. With the use of the method the authors have determined the maximal values of check-rail wear for straight track made of SP special profiles in conditions of nonexceedance of «impact effect» in bent part of the check-rail for switches with various angles.