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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the bolster and the side-frames and provides a proper lateral suspension at that point. Moreover, if
controlled flexibility is provided, by means of an elastomeric pad mounted between the side frames
and bearing adaptors, for example, then, in conjunction with cross-bracing, specified suspension
stiffnesses can be provided, enabling optimisation of the design. Reduced bending stiffness between
the wheelsets improves curving, and the improvement of the primary and secondary lateral suspension
enhances ride quality and reduces loads. Crossed-braced three-piece bogies were produced in
the 1970s, notably by Scheffel [160] in South Africa, by Pollard [161] in Britain and by List [162] in
North America, though more widespread application has been retarded by the increment in first cost.
2.14.6 Independently Rotating Wheels
As mentioned previously, independently rotating wheels have been frequently proposed, as they
eliminate the classical hunting problem. The guidance is provided by the lateral component of the
gravitational stiffness (reduced by the lateral force due to spin creep), which becomes the flange
force when the flangeway clearance is taken up. In the early days, as lateral oscillations were experienced
frequently, and as there was concern about large flange forces in curves, various alternatives
to the conventional form of wheelset were proposed. Even Robert Stephenson, who was concerned
about reducing friction in curves, invented schemes with independently rotating wheels [163,164].
The matter was discussed by the Gauge Commission as early as 1845. Cubitt gave evidence and, in
a reply to a question about independently rotating wheels, said that [165] ‘I am not sure that we are
perfectly right yet about wheels and rails and flanges, we have adopted the old coal railway system
designs without trying sufficient experiments’.
Then followed considerable discussion about various combinations of conventional wheelsets
and independently rotating wheelsets applicable to locomotives [166], but experiments with them
invariably resulted in an unsatisfactory outcome. For example, Nicholas Wood described experience
with wheelsets fitted with one loose wheel and said ‘the carriages were very liable to get off
the road and we had several instances where they had’ [167]. Some engineers, such as Crampton
and Haswell, believed that wheelsets with cylindrical treads were superior. However, by this time,
the coned wheelset had been firmly established as the norm. Nevertheless, experiments with independently
rotating wheels have occurred repeatedly over the years, and all have proved nugatory.
More recently, Frederich [168] has surveyed some of the possibilities. Though the kinematic
oscillation is eliminated, the self-centring action is slow. Extensive experimental experience has
shown that indeed the kinematic oscillation is absent but that one or other of the wheels tends to run
in continuous flange contact [169]. Good agreement between calculation and experiment is demonstrated
in [170–172].
Elkins [172] and Suda [153,154] showed both by calculation and by experiment that a configuration
of bogie, with the trailing axle having independently rotating wheels and the leading axle conventional,
significantly improved stability and curving performance and reduced rolling resistance. This provides
the possibility of a re-configurable design, as the wheelsets could be provided with a lock that
is released on the trailing wheelset (allowing free rotation of the wheels) and locked on the leading
wheelset (providing a solid axle). The lock would be switched depending on the direction of motion.
A proposal to incline substantially from the horizontal the axis of rotation of the wheel that
would increase the effect of the lateral resultant gravitational force but reduce the amount of spin
was put forward by Wiesinger [173]. Jaschinski and Netter [174] studied a generic wheelset model,
including the effect of modest amounts of camber.
2.14.7 Articulated Trains
The need to improve curving performance; maximise the use of the clearance gauge; minimise
axle loads; and reduce mass, aerodynamic drag and cost has led to many designs in which there is
articulation of the car bodies of a vehicle or train, so that the connections between vehicles form