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Longitudinal Train Dynamics 271
“emergency” application. Emergency applications result in the maximum pressures in brake
cylinders being applied. In Australia this is slightly greater than full service pressure due to valving
design. In the North American system, asecond reservoir ofair is released during an emergency
application giving asignificantly higher cylinder pressure for emergency brake applications. Due
to the slightly differing designs of the brake system and the policies of rail operators, driver braking
practices will vary between countries and rail systems. The following practices are noted:
† Minimum applications without application of locomotive brakes.
† Minimum applications with application of locomotive brakes.
† Minimum applications with locomotive power applied application (power braking).
† Service applications without application of locomotive brakes.
† Service applications with application of locomotive brakes.
† Emergency applications.
† Penalty applications (automatic emergency in response to vigilance systems).
† Requirement to make alarge service reduction after several minimum applications to
ensure on-wagon valves are all operating correctly.
† Requirement to maintain any reduction for atime period.
The use of minimum applications to either stretch the train or the use of minimum with power
applied as afirst stage of braking can reduce wagon accelerations and therefore improve in-train
stability, Figure 9.44.
The most recent innovation in train braking is the development of electro-pneumatic (ECP)
braking, although take up by freight operators has been slow.
The capability of the system to apply all brake cylinders simultaneously will reduce coupler
impacts during brake applications and improve vehicle stability. Driving practices required to
ensure the correct operation of the triple valves would also be expected to disappear.
3. Application of Traction and Dynamic Braking
The improved control systems for both tractive effort and dynamic braking has greatly improved
locomotive performance inrecent years with higher adhesion levels and greater ranges ofspeed
where dynamic braking is effective. Significant improvement totraction systems can be found in
slip controls and steering bogies. In practice, ground radar based slip controls give slightly better
results than systems based on minimum locomotive drive axle speed. For train systems where the
majority of running speeds fall within the flat region of dynamic brake response, driving strategies
have been developed to predominantly use dynamic braking.Animportant practice is to ensurethat
drivers allow aperiod of time between the end of athrottle application and the beginning of a
dynamic brake application or viceversa .Thistime period allowsinter-wagon states to slowlymove
Wagon Accelerations,
m/s/s
8
4
0
- 4
- 8
Normal Full Service
Application
- 12
40 60 80 100
Time, s
Wagon Accelerations,
m/s/s
FIGURE 9.44 Wagon accelerations compared —different braking strategies.
© 2006 by Taylor & Francis Group, LLC
8
4
0
- 4
- 8
Minimum Applied 20 Seconds Before
Full Service Application
- 12
40 60 80 100
Time,s