Shihui Luo

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.

Coupler jackknifing and derailments of locomotives on tangent track

A number of derailments occurred in recent years due to coupler jackknifing, some of them were reported on tangent tracks where conventionally thought to be the safer sections. This article studied coupler jackknifing behaviour and its implications for locomotive safety on tangent tracks from the experience of China heavy haul. Three types of coupler systems were modelled and simulated regarding coupler jackknifing behaviour. Two typical locomotive derailments occurred on tangent tracks were analysed. From the derailment experience, coupler angle self-lock behaviour was introduced and simulated. An approach to determine coupler angles in the jackknifed position was derived and validated with a self-coded program and SIMPACK. Methods to prevent coupler jackknifing were also evaluated with regard to locomotive stability.

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.

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 locomotives 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 locomotives coupler system and its effect on the dynamic behaviour of such a trains 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 couplers rotation behaviour differs between the tangent and curved tracks, significantly affecting the locomotives running performance under the braking condition. A larger coupler rotation angle generates a larger lateral component, which increases the wheelsets lateral force and the derailment coefficient. Decreasing the maximum coupler free angle can improve the locomotives operational performance and safety. Based on these results, the recommended maximum coupler free angle is 4°.

Modelling Polymer Draft Gears

ABSTRACT 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.

Comparisons of draft gear damping mechanisms

ABSTRACT This paper compared three types of draft gears with different damping mechanisms: friction, polymer and friction–polymer. Impact characteristics, frequency responses, in-train characteristics and fatigue damage for these draft gears were compared. Wagon impact simulations show that the friction draft gear, polymer draft gear and the friction–polymer draft gear can withstand impact speeds of 9, 12 and 11 km/h, respectively. Comparisons of frequency responses show that the friction draft gear has higher stiffness at lower working velocities, while the polymer draft gear has lower stiffness at lower working velocities. The response of the friction–polymer draft gear is less sensitive to the working velocities as it blends the friction and polymer damping mechanisms and offsets their influences on draft gear forces. Train dynamics simulations show that the in-train characteristics of friction draft gears and polymer draft gears are similar to their static characteristics and very different from their impact characteristics. The in-train characteristics of the polymer draft gears have lower stiffness and lower damping abilities than the other two types of draft gears. The friction–polymer draft gears achieved better vehicle acceleration performance than the friction draft gears. The polymer draft gears achieved similar maximum accelerations throughout the train and the maximum accelerations were significantly lower than that of the other two types of draft gears. The polymer draft gears achieved 23.4% less fatigue damage than the friction draft gears; the fatigue damage of the friction–polymer case is only half that of the friction case.

An overview: modern techniques for railway vehicle on-board health monitoring systems

ABSTRACT Health monitoring systems with low-cost sensor networks and smart algorithms are always needed in both passenger trains and heavy haul trains due to the increasing need for reliability and safety in the railway industry. This paper focuses on an overview of existing approaches applied for railway vehicle on-board health monitoring systems. The approaches applied in the data measurement systems and the data analysis systems in railway on-board health monitoring systems are presented in this paper, including methodologies, theories and applications. The pros and cons of the various approaches are analysed to determine appropriate benchmarks for an effective and efficient railway vehicle on-board health monitoring system. According to this review, inertial sensors are the most popular due to their advantages of low cost, robustness and low power consumption. Linearisation methods are required for the model-based methods which would inevitably introduce error to the estimation results, and it is time-consuming to include all possible conditions in the pre-built database required for signal-based methods. Based on this review, future development trends in the design of new low-cost health monitoring systems for railway vehicles are discussed.

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.

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 locomotives 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 locomotives lateral clearance of the secondary stopper are important in decreasing the wheelset lateral forces of the locomotive. It is advised that a smaller locomotives 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 couplers 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.

An analysis of resonance effects in locomotive drive systems experiencing wheel/rail saturation adhesion

This study investigates the dynamic response of a locomotive drive system experiencing wheel/rail saturation adhesion. A dynamic locomotive model is created and then integrated with electromechanical and control systems to simulate the vibration in the component parts of the drive system. The model is used to investigate the drive system’s sensitivity to resonance effects. The obtained results show that the wheel/rail stick-slip state can experience both longitudinal vibrations and self-excited vibrations in the drive system. Different parts of the drive system are excited by the two types of vibrations; however, in both cases the main frequencies are multiples of the natural frequency vibration of the drive system. It is necessary to select an appropriate value for the motor suspension rubber stiffness if structural resonances of the drive system under wheel/rail saturated adhesion are to be avoided.