I don't think this
can be regarded a true articulation, as found on Mallet or
Beyer-Garratt locos. It is more a system to give a bit
more flexibility and side-ways movement to the outer
I beg to differ.
These type of "bogies" (Krauss-Helmholtz, etc.) actually
consist of a linkage between the pony-trucks and their
adjacent coupled axles to push the driving axles a bit
sideways and so ease its passage through sharp curves.
They were often used on long-wheelbase, coupled locos in
Europe, although I don't think they were much used here or
the rest of the "English-speaking" world. The Germans also
tried out various types of "flexible-wheelbase" locos,
such a Luttermoller and Klein-Lindner, in which the end
axles did actually pivot a bit on curves; there was no
actual axle-pivoting in the Krauss-Helmholtz system.
There is no actual "hinge" between two groups of coupled
wheels, to allow them to take up an angle to each other,
as in true articulated locos.