THE KNOWLEDGE
Self propelled or not
Why are there pull type and self propelled
transporters? It used to be that the
ever-increasing loads to be moved were
initially still pulled by a prime mover.
It started, however, to pose serious
limitation on the manoeuvrability and
accuracy of the transport. For starters,
the turning radius (especially in existing
congested infrastructure areas) was
often a challenge. A separate push and
pull prime mover was often used to
overcome the turning limitations. These
kinds of exercises however slowed down
the transport and added to the risk of
handling heavy loads. The turning radius
of a self propelled transporter, on the
other hand, given its physical dimensions,
is smaller than its pulled counterpart.
Another limitation of a pull type
transporter is the accuracy of final
positioning over, for example, anchor
bolts. With a self propelled transporter,
which is electronically controlled,
accuracies of a few millimetres are
achievable. Not necessarily impossible with
pull type transporters but definitely much
harder to achieve.
Axles and axle lines
An over the road type trailer has wheel
sets that attach to an axle shaft that
runs across the full width of the trailer.
Transporters, on the other hand, have
pendulum axles. A pendulum axle is not
attached to such a shaft; a shaft is simply
not present on a transporter. Instead there
are two independent axle assemblies, one
on the left and one on the right side of the
transporter. Each assembly is mounted
on a turntable against the underside of
the transporter deck (see C in the figure).
Each pendulum axle can rotate in the
horizontal plane.
The turntable holds the upper leg of
the axle, which is fixed. The turntable and
the upper leg are bound to make the same
motion. The upper leg ends in a knee joint
(see A in the figure) that joins the upper
leg to the lower leg, the lower leg in turn
connects to the wheel assembly. The knee
joint allows the lower leg to pivot in respect
to the upper leg. This pivoting motion is
A pull type transport with prime mover
and drawbar
A goose neck type
trailer mounting with
fifth wheel coupling
initiated by the hydraulic axle cylinder (see
B in the figure). It is these hydraulic axle
cylinders that can be plumbed into groups
that form the hydraulic suspension for
which transporters are so well known.
The pendulum design brings with it
a possible clash in terminology. When
talking about trailer axles, an axle really
means one axle. When talking about
pendulum axles, however, one axle in
reality means two axles. For this reason the
term “axle lines” was introduced. One axle
line includes the pendulum axles between
the left and the right sides of a transporter.
Taking turns
The steering of the pull type transporter
is effected by physically connecting every
axle to the next axle by means of steering
rods. A plate is horizontally connected
to the side of the axle, just below the
turntable. The plate contains a hole pattern
to which steering rods are connected from
one plate to the next. Which hole is used
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MODULAR TRAILERS AND SELF-PROPELLED VEHICLES
INDUSTRIE COMETTO S.p.A.
12011 Borgo San Dalmazzo CUNEO (Italy) - Tel. +39 0171 263300
building for the heaviest duties
