Simon Iwnicki (Editor)_ Maksym Spiryagin (Editor)_ Colin Cole (Editor)_ Tim McSweeney (Editor) - Handbook of Railway Vehicle Dynamics, Second Edition-CRC Press (2019)

A History of Railway Vehicle Dynamics
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FIGURE 2.13 A generic bogie configuration. (From Kar, A.K. and Wormley, D.N., Generic properties
and performance characteristics of passenger rail vehicles, In Wickens, A.H. (Ed.), Proceedings 7th IAVSD
Symposium held at Cambridge University, 7–11 September 1981, Swets and Zeitlinger, Lisse, the Netherlands,
pp. 329–341, 1982; With kind permission from CRC Press: Handbook of Railway Vehicle Dynamics, CRC
Press, Boca Raton, FL, 2006, Iwnicki, S. [ed.].)
radial steering but would result in dynamic instability at low speeds. The design of a two-axle
vehicle with a purely elastic suspension therefore requires a compromise between stability and
curving. It was also shown by Boocock that for conventional vehicles in which there are primary
longitudinal and lateral springs connecting the wheelsets to a frame, there is a limit to the shear
stiffness for a given bending stiffness, and therefore, the stability/curving trade-off is constrained.
This limitation is removed if the wheelsets are connected directly by diagonal elastic elements or
cross-bracing, or interconnections, which are structurally equivalent. This is termed a self-steering
bogie. Superficially, it is similar to the systems of articulation between axles by means of rigid
linkages discussed in Section 2.5, but the significant difference is the computed elasticity of the
linkages. Self-steering bogies have been applied to locomotives (with benefits to the maximum
exploitation of adhesion), passenger vehicles and freight vehicles [124].
Inter-wheelset connections can be provided by means other than elastic elements. For example,
the equivalent of cross-bracing can be provided by means of a passive hydrostatic circuit, which
has a number of potential design advantages [125]. Hobbs [126] showed that the use of yaw relaxation
dampers could provide sufficient flexibility at low frequencies in curves and sufficient elastic
restraint at high frequencies to prevent instability, and this was demonstrated on the research vehicle
HSFV-1 [127]. Other possibilities were revealed by consideration of generic two-axle vehicles or
bogies [128–133], and an example is shown in Figure 2.13, but the added complexity has prevented
practical application.
2.14.2 Forced Steering
An alternative to providing self-steering by means of elastic or rigid linkages directly between
wheelsets is to use a linkage system that allows the wheelsets to take up a radial position but provides
stabilising elastic restraint from the vehicle body. This is the so-called forced steering, as it
can be considered that the vehicle body imposes a radial position on the wheelsets. Liechty’s work
on the earlier equivalent of body steering embodying rigid linkages has already been discussed in
Section 2.5, and his later work is discussed in [134,135]. The first analytical studies of forced steered
bogie vehicles, taking account of the elasticity of the linkages, were carried out in 1981 by Bell and
Hedrick [136] and Gilmore [137], who identified various instabilities, which were promoted by low
conicities and reduced creep coefficients. A considerable body of work by Anderson and Smith and
colleagues is reported in [138–143], covering the analysis of a vehicle with bogies having separately