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274 Coupler Force locomotives be positioned in proportion to wagon tonnages, i.e., “two trains connected”. Parker’s diagrams are redrawn in Figure 9.48 to Figure 9.50. The position and movement during operation of the point of zero coupler force, or “node,” was discussed in the paper at some length. Particular problemswere notedwith the two trains connected configuration in that if the lead locomotive units slow down relative to the remoteunits, the node moves forward. Underthe resulting increased load the remote units will then slow down allowing the node to travel backward. Of interest was the author’s note that the relative speedsoflead and remotelocomotive groups coulddiffer by as much as 8km/h. If the dynamic action in the train is severeenough, the front half of the train will attempt to accelerate the remotelocomotive. This can result in large coupler force peaks or coupler failure. The movement of the units either forward orbackward, Figure 9.49 and Figure 9.50, is recommended. It will be noticed that the units on the abscissa in Figure 9.50are inconsistent with previous figures. This is consistent with Parker’s paper. 22 Parker 22 also details several incidents of coupler failure due to the combination of track grade conditions and incorrect train control techniques. These are summarised briefly as follows: 1. Starting atrain on acrest: inthis case the coupler behind the remote locomotive failed. The locomotives, both lead and remote, were powered equally using multiple unit Coupler Force 3Lead Units 3000 tons 2Remote Units 3Lead Units 2Remote Units 2000 tons FIGURE 9.48 Two trains connected configuration. 22 Source: From Parker, C. W., Rail. Eng. J., January, 1974. With permission. 3000 tons 3000 tons FIGURE 9.49 Remote locomotives placed ahead of abalanced operation node. 22 Source:Parker, C. W., Rail. Eng. J ., January, 1974. With permission. F 3Lead Units Balanced Operation Node between wagons 156 and 157 2Remote Units 175 wagons 85 wagons Handbook of Railway Vehicle Dynamics FIGURE 9.50 Remote locomotives placed behind abalanced operation node. 22 Source: Parker, C. W., Rail. Eng. J ., January, 1974. With permission. © 2006 by Taylor & Francis Group, LLC
Longitudinal Train Dynamics 275 operation. Thefailure occurred because the forceapplied by the lead locomotives was not required to haul the lead portion of wagons as they were located on adown hill grade.The force was therefore transferred through to the rear wagon group. The highest force was therefore generated behind the remote locomotives. The train could have been started successfully by powering the remote locomotives alone. 2. Wheel slip on aheavy grade: inthis case the train was on asteep grade of greater than 2% and atrain separation occurred near the front of the train. The failure occurred due to slippage or amomentary power loss that developed in the lead. The remote units then took up the slack and pushed the wagons in the front wagon rake. The lead locomotive then regained adhesion and accelerated forward causing severe coupler impacts and the failure of acoupler in awagon near the front of the train. The problem can be solved by aslight reduction in the lead locomotive power setting. This requirement led to the incorporation of adevice termed the “lead unit power reduction feature” into the multiple unit system. 3. Effect of changes ofgrade: the author noted several cases of short descents encountered after ascending agrade. In such cases the problem was the same as when starting atrain on acrest. Excess traction force was transferred to the remote wagon rake resulting in separation behind the remote locomotives. Again, the reduction of lead locomotive power usingindependent control could have been used to prevent the problem. However, control strategies can become quite complicated if descents are short and followed by another grade. Power reductions that are too large could result in the remote units being stalled or slipping. Thedriver must therefore attempt to balance power settings and keep locomotive speeds the same. 4. Braking under power: the author 22 notes acase where separation occurred near the lead locomotives due to braking under power with the tail of the train on aslight grade. The traction force ofthe remote locomotive, combined with the grade, bunched the wagons in the front half of the train to compress the draft gears in that region. The compressed draft gears then forced the front locomotives forward causing aseparation. The problem could have been prevented by reducing the remote locomotives to idle before the brakes were applied. While the case studies by Parker 22 are not exhaustive, they are illustrative of the typesofissues that arise in long train distributed poweroperation. It can be seen that driving strategies appropriate to the track topography are required. Simulation of train dynamics is akey tool in gaining an understanding of the train dynamics that could occur on aparticular route. In such cases, attention to representative modelling ofwagon connection elements, locomotive traction, adhesion, and braking characteristics are of utmost importance. VII. CONCLUSIONS Detailed nonlinear models with stick–slip features for the simulation and study oflongitudinal train dynamics have been developed, allowing increased understanding of long train dynamics. There still remains scope for further modelling and validation of models of existing draft gear packages. Further research should also be directed to new draft gear package designs. The area of the interaction of train–wagon dynamics is an emerging area of research where train operators are operating longer trains on infrastructures with tighter curves. Advances in locomotive controls and bogie design in recent years warrant the development of improved and more detailed traction and dynamic braking models. The adoption of electro-pneumatic controlled brakes infreight train systems will improve wagon stability during braking and add anew variation to train management and driving practice. © 2006 by Taylor & Francis Group, LLC
Page 1 and 2: 9 CONTENTS Longitudinal Train Dynam
Page 3 and 4: Longitudinal Train Dynamics 241 ass
Page 5 and 6: Longitudinal Train Dynamics 243 By
Page 7 and 8: Longitudinal Train Dynamics 245 Pol
Page 9 and 10: Longitudinal Train Dynamics 247 For
Page 11 and 12: Longitudinal Train Dynamics 249 If
Page 13 and 14: Longitudinal Train Dynamics 251 var
Page 15 and 16: Longitudinal Train Dynamics 253 For
Page 17 and 18: Longitudinal Train Dynamics 255 Com
Page 19 and 20: Longitudinal Train Dynamics 257 Tra
Page 21 and 22: Longitudinal Train Dynamics 259 Bra
Page 23 and 24: Longitudinal Train Dynamics 261 The
Page 25 and 26: Longitudinal Train Dynamics 263 G .
Page 27 and 28: Longitudinal Train Dynamics 265 Lon
Page 29 and 30: Longitudinal Train Dynamics 267 FIG
Page 31 and 32: Longitudinal Train Dynamics 269 tak
Page 33 and 34: Longitudinal Train Dynamics 271 “
Page 35: Longitudinal Train Dynamics 273 Res
Page 39: Longitudinal Train Dynamics 277 V f

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