Page 39 - 360.revista de Alta Velocidad - Nº 5

Technological, economic and sociological factors on the maximum design speed of high speed trains

to, is a linear function of the train speed divided by the wavelength. These two relationships
together constitute the following effect: as regards a specific frequency under consideration,
the wheels are excited by larger amplitudes, if the train runs faster on the same, non-ideal
track. In turn, the vibration comfort will be compromised and higher dynamic contact wheel
-rail forces will stress wheels and rails for higher train speeds.
However, passenger railway vehicles use two levels of suspensions and it is a matter of concept
and design tuning to organize a comfortable train ride and keep the dynamic forces at the wheel-
rail interface within acceptable limits. There is a large, so far unexploited potential to deploy
active or semi-active components which allow for online adaption of suspension characteristics
to the train speed and the track quality is a tuning parameter as well. In summary, train speeds
up to the range of the TGV record seem to be feasible even in daily operation concerning
vertical dynamics.
As regards b., the lateral dynamics of railway vehicles is strongly related to the so-called
hunting motion : lateral track irregularities initiate lateral oscillations of the wheel-sets that
1
are intended to be damped out in order to fulfill the guidance task. However, the stability of
this hunting motion depends on the vehicle speed, which defines a requirement for vehicle
design. Measures such as low equivalent conicities of the wheel-rail contact geometry [16],
[9], adjusted stiffnesses of the primary suspensions [10], additional yaw dampers [11], [12],
long wheel-bases [10] among others increase the stability region or the maximum speed a
vehicle is capable of running safely, respectively. It can be concluded that a proper mechanical
design provides a stable running of a railway running gear even at very high speeds. As Delfosse
mentioned in [13], the simulation of the modified TGV unit, which set the former speed record
of 515.3 km/h, showed that the critical speed of the train was above 700 km/h.

Figure 3: Exemplary estimation of wheel wear as a function of vehicle speed

1 Streaktly speaking, this applies to the vast majority of railway vehicles that use wheel-sets, only.

International Congress on High-speed Rail: Technologies and Long Term Impacts - Ciudad Real (Spain) - 25th anniversary Madrid-Sevilla corridor 37