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Force, MN
2.5
2
1.5
1
0.5
Unit 1 Unit 2
0
0 20 40 60 80
Deflection, mm
FIGURE 9.8 Typical manufacturer’s draft gear response data.
ways. In early driver training simulators when computing power was limited, it was common
practice to further reduce the complexity of the dynamic system by lumping vehicle masses
together and deriving equivalent connection models. As adequate computational capacities are now
available it is normal practice to model each wagon in detail. 9,10 It would seem reasonable in the
first instance to base models on the hysteresis published for the drop hammer tests of draft gear
units. Typical draft gear response curves are shown inFigure 9.8.
The first thing to remember is that the published data, asshown inFigure 9.9, represents the
extreme operating behaviour simulated by adrop hammer test. The drop hammer of12.27 tonne
(27,000 lb) impacts the draft gear at avelocity of 3.3 m/sec, this simulating an inter-wagon impact
with arelative velocity between wagons of 6.6 m/sec, (23.8 km/h). In normal train operation it
would be hoped that such conditionsare quite rare. Data recording of in-train forces of unit trains in
both iron ore and coal haulage systems inAustralia revealed that draft gear stiffness in normal
operation could be very different from that predicted by drop hammer test data. 1,9 The approach
taken by Duncan and Webb 1 was to fit amodeltothe experimental model, as showninFigure9.10,
using piecewise linear functions.
It will be noted that the model proposed by Duncan and Webb includes the locked stiffness, as
discussedearlier. Asignificant outcome from the train test data reflected in the modelinFigure9.10
was that unloading and loading couldoccur along the locked curve whenever the draftgear unit was
locked. This cyclic loading and unloading could occur at any extension. Data from this program, 1
and later by Cole, 9 confirmed that the draft gear unit would remain locked until the force level
reduced to apoint closetothe relaxation or unloading line. Due to individual friction characteristics,
there is considerable uncertainty about where unlocking occurs. In some cases unlocking was
observed below the unloading curve.
Stiffness, MN/m
200
150
100
50
Unit 1 Unit 2
0
0 20 40 60 80
Deflection, mm
FIGURE 9.9 Draft gear package stiffness–drop hammer tests.
© 2006 by Taylor & Francis Group, LLC
Handbook of Railway Vehicle Dynamics