An integrated draft gear model with the consideration of wagon body structural characteristics

With the increase of railway wagon axle load and the growth of marshalling quantity, the problem caused by impact and vibration of vehicles is increasingly serious, which leads to the damage of vehicle structures and the components. In order to improve the reliability of longitudinal connection model for vehicle impact tests, a new railway wagon longitudinal connection model was developed to simulate and analyse vehicle impact tests. The new model is based on characteristics of longitudinal force transmission for vehicles and parts. In this model, carbodies and bogies were simplified to a particle system that can vibrate in the longitudinal direction, which corresponded to a stiffness-damping vibration system. The model consists of three sub-models, that is, coupler and draft gear sub-model, centre plate sub-model and carbody structure sub-model. Compared with conventional draft gear models, the new model was proposed with geometrical and mechanical relations of friction draft gears considered and with behaviours of sticking, sliding and impact between centre plate and centre bowl added. Besides, virtual springs between discrete carbodies were built to describe the structural deformation of carbody. A computation program for longitudinal dynamics based on vehicle impact tests was accomplished to simulate. Comparisons and analyses regarding the train dynamics outputs and vehicle impact tests were conducted. Simulation results indicate that the new wagon longitudinal connection model can provide a practical application environment for wagons, and the outputs of vehicle impact tests agree with those of field tests. The new model can also be used to study on longitudinal vibrations of different vehicles, of carbody and bogie, and of carbody itself.     

Locomotive dynamic performance under traction/braking conditions considering effect of gear transmissions

Traction or braking operations are usually applied to trains or locomotives for acceleration, speed adjustment, and stopping. During these operations, gear transmission equipment plays a very significant role in the delivery of traction or electrical braking power. Failures of the gear transmissions are likely to cause power loses and even threaten the operation safety of the train. Its dynamic performance is closely related to the normal operation and service safety of the entire train, especially under some emergency braking conditions. In this paper, a locomotive–track coupled vertical–longitudinal dynamics model is employed with considering the dynamic action from the gear transmissions. This dynamics model enables the detailed analysis and more practical simulation on the characteristics of power transmission path, namely motor–gear transmission–wheelset–longitudinal motion of locomotive, especially for traction or braking conditions. Multi-excitation sources, such as time-varying mesh stiffness and nonlinear wheel–rail contact excitations, are considered in this study. This dynamics model is then validated by comparing the simulated results with the experimental test results under braking conditions. The calculated results indicate that involvement of gear transmission could reveal the load reduction of the wheelset due to transmitted forces. Vibrations of the wheelset and the motor are dominated by variation of the gear dynamic mesh forces in the low speed range and by rail geometric irregularity in the higher speed range. Rail vertical geometric irregularity could also cause wheelset longitudinal vibrations, and do modulations to the gear dynamic mesh forces. Besides, the hauling weight has little effect on the locomotive vibrations and the dynamic mesh forces of the gear transmissions for both traction and braking conditions under the same running speed.     

Dynamics of railway wagons subjected to braking/traction torque

Braking or traction torque is regarded as an important source of wheelset skid and a potential source of derailment risk that adversely affects the safety levels of train operations; therefore, this research examines the effect of braking/traction torque to the longitudinal and lateral dynamics of wagons. This paper reports how train operations safety could be adversely affected due to various braking strategies. Sensitivity of wagon dynamics to braking severity is illustrated through numerical examples. The influence of wheel/rail interface friction coefficient and the effects of two types of track geometry defects on wheel unloading ratio and wagon pitch are also discussed in the paper.     

Longitudinal train dynamics: an overview

This paper discusses the evolution of longitudinal train dynamics (LTD) simulations, which covers numerical solvers, vehicle connection systems, air brake systems, wagon dumper systems and locomotives, resistance forces and gravitational components, vehicle in-train instabilities, and computing schemes. A number of potential research topics are suggested, such as modelling of friction, polymer, and transition characteristics for vehicle connection simulations, studies of wagon dumping operations, proper modelling of vehicle in-train instabilities, and computing schemes for LTD simulations. Evidence shows that LTD simulations have evolved with computing capabilities. Currently, advanced component models that directly describe the working principles of the operation of air brake systems, vehicle connection systems, and traction systems are available. Parallel computing is a good solution to combine and simulate all these advanced models. Parallel computing can also be used to conduct three-dimensional long train dynamics simulations.     

Establishment and verification of three-dimensional dynamic model for heavy-haul train–track coupled system

For the long heavy-haul train, the basic principles of the inter-vehicle interaction and train–track dynamic interaction are analysed firstly. Based on the theories of train longitudinal dynamics and vehicle–track coupled dynamics, a three-dimensional (3-D) dynamic model of the heavy-haul train–track coupled system is established through a modularised method. Specifically, this model includes the subsystems such as the train control, the vehicle, the wheel–rail relation and the line geometries. And for the calculation of the wheel–rail interaction force under the driving or braking conditions, the large creep phenomenon that may occur within the wheel–rail contact patch is considered. For the coupler and draft gear system, the coupler forces in three directions and the coupler lateral tilt angles in curves are calculated. Then, according to the characteristics of the long heavy-haul train, an efficient solving method is developed to improve the computational efficiency for such a large system. Some basic principles which should be followed in order to meet the requirement of calculation accuracy are determined. Finally, the 3-D train–track coupled model is verified by comparing the calculated results with the running test results. It is indicated that the proposed dynamic model could simulate the dynamic performance of the heavy-haul train well.     

The stability and mechanical characteristics of heavy haul couplers with restoring bumpstop

To investigate the stability and mechanical characteristics of a type of heavy haul coupler with restoring bumpstop, the geometry and force states of couplers were analysed at different yaw angles and the longitudinal forces. The structural characteristics of this coupler were summarised. To aid in the investigation, a multi-body dynamics model with four heavy haul locomotives and three detailed couplers was established to simulate the process of emergency braking. In addition, the coupler yaw instability and lateral forces were tested in order to investigate the effect of relevant parameters on the locomotive's wheelset lateral forces. The results show that only when the bumpstop force exceeds half of the coupler longitudinal compression force, can the follower be rotated and the yaw angle of the coupler increase. The bumpstop preload is the most important stabilising factor. The coupler lateral force is constant when the coupler longitudinal force is smaller than the critical values of 2000, 1400 and 1150 kN at coupler free angles of 7°, 8° and 9°, respectively, for operation on straight track. The coupler free angle and the locomotive's lateral clearance of the secondary stopper are important in decreasing the wheelset lateral forces of the locomotive. It is advised that a smaller locomotive's secondary lateral suspension stiffness, a free clearance of 35 mm and an elastic clearance of 15 mm from the secondary lateral stopper be selected. If the coupler's free angle is less than the self-stabilising angle which is 5.5° for operation on straight track, the coupler is stable no matter how great the longitudinal force is. The wheelset lateral forces are allowed at the coupler longitudinal force of 2500 kN when the free angle is 6°. These studies establish meaningful improvements for the stability of couplers and match the heavy haul locomotive with its suspension parameters.     

Simulation of longitudinal dynamics of a freight train operating through a car dumper

A heavy haul train and car dumper model was created to analyse train longitudinal dynamics during dumping. Influence of such factors as performance curve of draft gears, total free slack in couplers, operating mode of train positioner and braking of last two cars of train on the in-train forces was considered.     

Coupler rotation behaviour and its effect on heavy haul trains

When a locomotive coupler rotates at an angle, the lateral component of the coupler force has an adverse effect on the locomotive's safety, particularly in heavy haul trains. In this paper, a model of a head-mid configuration, a 20,000-t heavy haul train is developed to analyse the rotation behaviour of the locomotive's coupler system and its effect on the dynamic behaviour of such a train's middle locomotive when operating on tangent and curved tracks. The train model includes detailed coupler and draft gear with which to consider the hysteretic characteristics of the rubber draft gear model, the friction characteristics of the coupler knuckles, and the alignment-control characteristics of the coupler shoulder. The results indicate that the coupler's rotation behaviour differs between the tangent and curved tracks, significantly affecting the locomotive's running performance under the braking condition. A larger coupler rotation angle generates a larger lateral component, which increases the wheelset's lateral force and the derailment coefficient. Decreasing the maximum coupler free angle can improve the locomotive's operational performance and safety. Based on these results, the recommended maximum coupler free angle is 4°.     

Analysis of the car body stability performance after coupler jack-knifing during braking

This paper aims to improve car body stability performance by optimising locomotive parameters when coupler jack-knifing occurs during braking. In order to prevent car body instability behaviour caused by coupler jack-knifing, a multi-locomotive simulation model and a series of field braking tests are developed to analyse the influence of the secondary suspension and the secondary lateral stopper on the car body stability performance during braking. According to simulation and test results, increasing secondary lateral stiffness contributes to limit car body yaw angle during braking. However, it seriously affects the dynamic performance of the locomotive. For the secondary lateral stopper, its lateral stiffness and free clearance have a significant influence on improving the car body stability capacity, and have less effect on the dynamic performance of the locomotive. An optimised measure was proposed and adopted on the test locomotive. For the optimised locomotive, the lateral stiffness of secondary lateral stopper is increased to 7875?kN/m, while its free clearance is decreased to 10?mm. The optimised locomotive has excellent dynamic and safety performance. Comparing with the original locomotive, the maximum car body yaw angle and coupler rotation angle of the optimised locomotive were reduced by 59.25% and 53.19%, respectively, according to the practical application. The maximum derailment coefficient was 0.32, and the maximum wheelset lateral force was 39.5?kN. Hence, reasonable parameters of secondary lateral stopper can improve the car body stability capacity and the running safety of the heavy haul locomotive.     

A review of dynamics modelling of friction draft gear

Longer and heavier trains mean larger in-train forces and more complicated force patterns. Practical experience indicates that the development of fatigue failure of coupling systems in long heavy trains may differ from conventional understanding. The friction-type draft gears are the most widely used draft gears. The ever developing heavy haul transport environment requires further or new understanding of friction draft gear behaviour and its implications for train dynamics as well as fatigue damage of rolling stock. However, modelling of friction draft gears is a highly nonlinear question. Especially the poor predictability, repeatability and the discontinuity of friction make this task more challenging. This article reviews current techniques in dynamics modelling of friction draft gears to provide a starting point that can be used to improve existing or develop new models to achieve more accurate force amplitude and pattern predictions.     

Influence of train length on in-train longitudinal forces during brake application

It needs some seconds for a signal, which is created from brake application, to travel from the first part of the train system (locomotive) to the end part of it (last wagon). Delay in time of all parts of the system (train) brake is seen which might deteriorate the longitudinal dynamic interaction of the long trains. For instance, this results in running of the rear cars to the front ones and hence producing large in-train forces at the buffers and couplers. Major parts of the rolling stock in railway system repair are known for relative compression and tension forces, which are applied to the whole train system and cause huge expenses for the industry. For trains with long lengths, operating in safe area is another important relation with train forces along the system. By using MATLAB simulation in this study, we investigated the length's effect on train dynamic along the system mainly for freight trains. We did our research on the trains which are currently used in Railways of Islamic Republic of Iran, RIRI. Four diverse cases were under our simulation, in each of which, trains consist of 52, 32, 20 and 12 cars, respectively. Two different forces (tension and compression) are displayed here as of the outcome of the research. Simulations show different forms of interplays in dynamics along the system. Then we compared the graphs to each other to find out detailed influences of length of the whole system (train including different number of wagons and locomotive) on dynamics of system along it while braking is applied.     

Dynamic performances of an innovative coupler used in heavy haul trains

An innovative structure for a heavy haul coupler with an arc surface contact and restoring bumpstop is proposed. This coupler has a small lateral force at a small yaw angle and a limitable yaw angle to ensure an allowable coupler lateral force under intense compressive force. The main structural characteristic of the combined contact coupler is a lateral movable follower with an appropriate friction coefficient of 0.06–0.08 and a slide block with a single freedom of longitudinal movement. In order to verify and simulate the performances, a multi-body dynamics model with four heavy haul locomotives and three detailed couplers was established to simulate the process of emergency braking. In addition, the coupler yaw instability and wheel set lateral forces were tested in order to investigate the effect of relevant parameters on the coupler performances. The combined contact coupler is suitable for heavy haul train for a good dynamic performance.     

The stability mechanism and its application to heavy-haul couplers with arc surface contact

To investigate the stability mechanism of a type of heavy-haul coupler with arc surface contact, the force states of coupler were analysed at different yaw angles according to the friction circle theory and the structural characteristics of this coupler were summarised. A multi-body dynamics model with four heavy-haul locomotives and three detailed couplers was established to simulate the process of emergency braking. In addition, the coupler yaw instability was tested in order to investigate the effect of relevant parameters on the coupler stability. The results show that this coupler exhibits the self-stabilisation and less lateral force at a small yaw angle. The yaw angle of force line is less than the actual coupler yaw angle which reduces the lateral force and the critical instability. An increase in the friction coefficient of the arc contact surfaces can improve the stability of couplers. The friction coefficient needs to be increased with the increase in the maximum coupler longitudinal compressive force. The stability of couplers is significantly enhanced by increasing the secondary suspension stiffness and reducing the clearance of the lateral stopper of the locomotives. When the maximum coupler compressive force reaches 2500 kN, the required friction coefficient reduces from 0.6 to 0.35, which notably lowers the derailment risk caused by the coupler. The critical instability angle of the coupler mainly depends on the arc contact friction coefficient. When the friction coefficient is 0.3, the critical instability angle was 4–4.5°. The simulation results are consistent with the locomotive line tests. These studies establish meaningful improvements for the stability of couplers and match the heavy-haul locomotive with its suspension parameters.     

Simulation of curving at low speed under high traction for passive steering hauling locomotives

The traction control in modern electric and diesel electric locomotives has allowed rail operators to utilise high traction adhesion levels without undue risk of damage from uncontrolled wheel spin. At the same time, some locomotive manufacturers have developed passive steering locomotive bogies to reduce wheel rail wear and further improve locomotive adhesion performance on curves. High locomotive traction loads in curving are known to cause the loss of steering performance in passive steering bogies. At present there are few publications on the curving performance of locomotive steering with linkage bogies. The most extreme traction curving cases of low speed and high adhesion for hauling locomotives have not been fully investigated, with effects of coupler forces and cant excess being generally ignored. This paper presents a simulation study for three axle bogie locomotives in pusher and pulling train positions on tight curves. The simulation study uses moderate and high traction adhesion levels of 16.6% and 37% for various rail friction conditions. Curving performance is assessed, showing forced steering bogies to have considerable advantages over self steering bogies. Likewise it is shown that self steering bogies are significantly better than yaw relaxation bogies at improving steering under traction. As the required traction adhesion approaches the rail friction coefficient, steering performance of all bogies degrades and yaw of the bogie frame relative to the track increases. Operation with excess cant and tensile coupler forces are both found to be detrimental to the wear performance of all locomotive bogies, increasing the bogie frame yaw angles. Bogie frame pitching is also found to have significant effect on steering, causing increased performance differences between bogie designs.     

Simulation analysis on the coupler behaviour and its influence on the braking safety of locomotive

In order to simulate the runtime behaviour of coupler and buffer systems accurately, the dynamic model was improved by adopting the polygonal contact model. And the reliability of the friction phenomenon in flat-pin coupler’s tail and the connecting constraint between coupler heads were verified. Then the detailed model which fully considered the dynamic characteristics of middle locomotive and its adjacent wagons was incorporated into the simplified longitudinal dynamic model of combined heavy-haul train. The dynamic response of coupler and its influence on the running safety of locomotive under flat straight line emergency braking condition and long steep grade cycle braking condition were simulated respectively. According to the simulation results, the following suggestions were proposed: flat-pin coupler is more suitable for heavy-haul locomotive, but the inspection work on the friction surface of coupler tail needs to be strengthened; and the vertical anti-off stopping device should be added to avoid the occurrence of decoupling accidents.     

Coupler dynamic performance analysis of heavy haul locomotives

In this paper, a train dynamic model was developed to study the dynamic performance of heavy haul locomotives, taking into account the use of different coupler and buffer systems under conditions of severe longitudinal coupler compressive forces. The model consists of four locomotives each having 38 independent degrees of freedom and one dummy freight vehicle connected to each other by couplers and buffers. Simulation results showed that the longitudinal coupler compressive forces withstood by large rotation angle couplers with coupler shoulders were larger than those withstood by small rotation angle couplers. The results obtained for the large rotation angle coupler model showed that it had higher safety curve negotiation speeds. Due to the smaller static impedance, it was found that large capacity elastic clay (or cement) buffers cannot satisfy the requirement of heavy haul locomotives during cycle braking in long heavy downgraded tracks; the use of friction clay buffers can solve this problem.     

Modelling polymer draft gears

This paper developed a new and simple approach to model polymer draft gears. Two types of polymer draft gears were modelled and compared with experimental data. Impact characteristics, in-train characteristics and frequency responses of these polymer draft gears were studied and compared with those of a friction draft gear. The impact simulations show that polymer draft gears can withstand higher impact speeds than the friction draft gear. Longitudinal train dynamics simulations show that polymer draft gears have significantly longer deflections than friction draft gears in normal train operations. The maximum draft gear working velocities are lower than 0.2?m/s, which are significantly lower than the impact velocities during shunting operations. Draft gears’ in-train characteristics are similar to their static characteristics but are very different from their impact characteristics; this conclusion has also been reached from frequency response simulations. An analysis of gangway bridge plate failures was also conducted and it was found that they were caused by coupler angling behaviour and long draft gear deflections.     

Real-time implementation of a traction control algorithm on a scaled roller rig

Traction control is a very important aspect in railway vehicle dynamics. Its optimisation allows improvement of the performance of a locomotive by working close to the limit of adhesion. On the other hand, in case the adhesion limit is surpassed, the wheels are subjected to heavy wear and there is also a big risk that vibrations in the traction occur. Similar considerations can be made in the case of braking. The development and optimisation of a traction/braking control algorithm is a complex activity, because it is usually performed on a real vehicle on the track, where many uncertainties are present due to environmental conditions and vehicle characteristics. This work shows the use of a scaled roller rig to develop and optimise a traction control algorithm on a single wheelset. Measurements performed on the wheelset are used to estimate the optimal adhesion forces by means of a wheel/rail contact algorithm executed in real time. This allows application of the optimal adhesion force.     

Longitudinal force distribution using quadratically constrained linear programming

In this paper, a new method is presented for the optimisation of force distribution for combined traction/braking and cornering. In order to provide a general, simple and flexible problem formulation, the optimisation is addressed as a quadratically constrained linear programming (QCLP) problem. Apart from fast numerical solutions, different driveline configurations can be included in the QCLP problem in a very straightforward fashion. The optimisation of the distribution of the individual wheel forces using the quasi-steady-state assumption is known to be useful for the study of the influence of particular driveline configurations on the combined lateral and longitudinal grip envelope of a particular vehicle–driveline configuration. The addition of the QCLP problem formulation makes another powerful tool available to the vehicle dynamics analyst to perform such studies.     

Simplified and advanced modelling of traction control systems of heavy-haul locomotives

Improving tractive effort is a very complex task in locomotive design. It requires the development of not only mechanical systems but also power systems, traction machines and traction algorithms. At the initial design stage, traction algorithms can be verified by means of a simulation approach. A simple single wheelset simulation approach is not sufficient because all locomotive dynamics are not fully taken into consideration. Given that many traction control strategies exist, the best solution is to use more advanced approaches for such studies. This paper describes the modelling of a locomotive with a bogie traction control strategy based on a co-simulation approach in order to deliver more accurate results. The simplified and advanced modelling approaches of a locomotive electric power system are compared in this paper in order to answer a fundamental question. What level of modelling complexity is necessary for the investigation of the dynamic behaviours of a heavy-haul locomotive running under traction? The simulation results obtained provide some recommendations on simulation processes and the further implementation of advanced and simplified modelling approaches.