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BOGIES
the wheel/rail friction coefficient. The
equivalent conicity is applied as a
simplified parameter in order to describe
the wheel/rail contact geometry. The
equivalent conicity can vary to a large
degree and plays a significant role in the
running behaviour of the vehicle. Whereas
a very low conicity in modern vehicles
sometimes leads to a deterioration of
running behaviour in lateral direction as
well as ride comfort degradation (see
Figure 3 opposite) without exceeding the
safety criteria, the high conicity limits the
maximum permissible speed with respect
to running safety. The range of equivalent
conicities to be complied with during the
vehicle acceptance tests is certainly defined
Figure 2: Typical dynamics analyses applied during railway vehicle engineering
in the European standard EN 14363
3
.
However, the individual track maintenance
Typical dynamics analyses related to the The conditions for the testing of the specifications often do not reflect these
mentioned tasks together with the aim and safety against derailment are certainly conditions with the consequence that the
suitable methods are listed in Figure 2. defined within the scope of the stationary real conditions often widely diverge from
tests in the European standard EN 14363
3
the conditions defined in EN 14363.
Eigenbehaviour and stationary tests concerning the testing for the acceptance On the one hand, more and more
The assessment of the eigenbehaviour is of running characteristics of railway alternative rail profiles are applied during
one of the first calculations to be done vehicles. However, some scope for rail grinding, leading to a lower conicity.
following the model building. This application and interpretation is still open. On the other hand, very high conicity is
investigation is carried out primarily for For instance, purely the range between the often referenced in the vehicle
in-house requirements – it serves as a minimum and maximum wheel/rail specification, in order to cover all present
plausibility check and the first parameter friction coefficient levels which must be track conditions occasionally containing
optimisation. Quasi-static calculations of maintained during the test influences the track sections that are narrow-to-gauge or
carbody roll coefficient and safety against result decisively and can determine contain heavily worn rails.
derailment in twisted track constitute one whether a particular vehicle will be These contradictory tendencies
of the trade-offs of bogie development. approved or not. Our specialists in increasingly extend the range of the
The roll coefficient limit is prescribed in dynamics analyse the individual methods equivalent conicities with which the
continental vehicle specifications and must and influencing parameters, as well as vehicle has to comply with. In addition to
be complied with in relation to the vehicle support activities of UNIFE directed this, even the specification of an
gauging and the pantograph lateral towards improving the assessment of equivalent conicity is insufficient to
movements. This requirement then limits safety against derailment. provide the exact wheel/rail contact
the minimum vertical stiffness levels for conditions necessary for stability
the primary and secondary suspensions as Running stability assessment. Namely, the same equivalent
well as the anti-roll device characteristics. A further safety relevant criterion concerns conicity value can represent various
In contrast, the requirements of safety stability. In the case of rail vehicles contact geometries and, according to the
against derailment on twisted track possessing conventional wheelsets, starting chosen method of analysis, each can lead
necessitate rather low stiffness. This trade- from a specific speed, self-excited to differing critical speeds as can be seen
off becomes more critical in vehicles with oscillations called instability can arise. in the comparison of the simulation
deflated air suspension and constitutes one These vibrations not only lead to a results in Figure 4 on page 80. More
of the major challenges during bogie deterioration of running characteristics, the detailed description of the examinations
engineering. In order to avoid complex emergence of high lateral forces between related to the stability assessments by
design of the (rarely used) emergency wheelset and track can also cause lateral computer simulations can be found in
4
.
suspension, it is imperative that the track shift and thus precipitate derailment. Friction value between wheel and rail also
margin of the safety against derailment The decisive influencing parameters are, plays an important role (see Figure 5 on
is exploited in the case of vehicles with apart from the vehicle parameters, the page 80), which presents friction values of
deflated air suspension running on contact geometry between wheel and rail 0.3 to 0.6, all of them representing dry
twisted track. or more precisely wheelset and track and conditions, but nevertheless leading to
78 EUROPEAN RAILWAY REVIEW
l
ISSUE 3
l
2008
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