[b], but, by about 11 seconds, the ATO
realises it needs to increase the brake
rate if the target stopping distance is to
be achieved and the slope of the white
line becomes steeper than the yellow
line [c].
This situation is quite complicated
to simulate just for one car, but all this
interaction is being simulated for each of
the seven or eight cars individually. And,
whilst target speed remains a constant
factor, the brake effort contribution for
each of the 28 or 32 axles has to be
integrated to calculate the actual train
velocity. Moreover, the impact of sander
operation on all axles behind them has
to be assessed - all being calculated in
real time. A very complex simulation!
The ATO test has been a vital part in
developing the case for ATO running in
the London Underground Metropolitan,District, Circle and Hammersmith and
City lines, without having to specify
excessively low brake rates. Stuart
acknowledged the partnership with
Gilbert Rowe, London Underground’s
brakes engineer, who has been in the
vanguard over the last 20 years of safely
and reliably delivering comparatively
high brake rates of around 0.7 m/s^2 for
ATO operation, even under adverse
adhesion conditions.
Sanders were a late addition to LU’s S
Stock design and there was insufficient
space for large sand hoppers, so it
was particularly important to minimise
sand consumption whilst achieving the
required performance. The delivery
of the Sanding and ATO modules on
WSPER were part of this work, which was
validated with extensive testing at RIDC
Melton.In discussion, Gilbert Rowe highlighted
the challenge presented by ATP systems
using two tachometers on adjacent
axles. In poor adhesion conditions,
the two axles may end up rotating at
different speeds or decelerate at a rate
above the value the ATP considers to
be feasible. The ATP may then trigger
an emergency stop, demanding the
highest brake demand, usually in low
adhesion conditions, and sometimes
leading to flatted wheels.
Could WSP be altered to help and
be evaluated by WSPER, Rail Engineer
mused?
Stuart advised that this is something
that could be considered for the future.
This led to a further discussion about
using WSPER to evaluate trains where
the ATP tachometer(s) are fitted to an
unbraked axle, as is increasingly being
specified.
Perhaps the last word should go
to Stuart Brown, who probably
won’t thank me for calling him Mr
WSPER: “We are proud to be able to
provide our customers with a more
comprehensive WSPER package.
WSPER has a 30-year pedigree and we
are developing the system to meet the
future needs of our customers, ensuring
that it is the system of choice for the
next 30 years.”Figure 3 - Four plots from the same test. (top left) driving car with no sander, (top right) 2nd car car with one sander,
(bottom left) 3rd car car with one sander, (bottom right) 4th car car with no sander positioned after the two sander cars.a bc
Figure 4 - Enlargement of the
bottom right plot from figure 3 with
three areas highlighted.1414 FE ATURE