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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