English - Nooteboom Giants on the Road Magazine English - Nr. 6 - 2019 | Page 52

GIANTS ON THE ROAD
History
HYDRAULIC
SUSPENSION
A LARGE PART OF NOOTEBOOM TRAILERS ARE EQUIPPED WITH HYDRAULIC
SUSPENSION AS STANDARD. THIS USED TO BE DIFFERENT, BECAUSE UNTIL THE
LATE SEVENTIES MOST TRAILERS WERE STILL FITTED WITH LEAF SPRINGS. THE
MANDATORY LOAD-DEPENDENT BRAKING FORCE DIRECTIVES, INTRODUCED
IN 1976, CHANGED THIS.
In just a few years, advanced air suspension and hydraulic
suspension systems were developed and the trailers with leaf spring
suspension disappeared from the European roads. Nooteboom
delivered the first trailer with hydraulic suspension in 1975 and
improved the system time and time again during the past decades.
Many Nooteboom customers opt for hydraulic suspension because
the stability – particularly with a load that has a high centre of
gravity – is better than other suspension systems.
BACK IN TIME
Around 1970 nearly every trailer had robust leaf spring assemblies
that functioned very well, even if the trailer was significantly
overloaded. The regulation of the braking force was done via a
simple valve: empty, half empty or full. In the EEG there were
already regulations in force in 1971 to improve the braking of
trucks and trailers. In October 1976 the directive 75/524/EEG was
introduced. The most important task for the trailer manufacturers:
the brake power balance must from now on adjust automatically
to the load of the trailer. On trailers with leaf spring suspension
the braking power is regulated via the spring deflection of the
leaf spring assembly. This method is not very exact because old-
fashioned trailers have a very short suspension stroke, sometimes
no more than a few centimetres. Moreover, after some time the leaf
springs tend to ‘settle’, so that the brake pressure regulator ‘thinks’
that the trailer is always loaded. Air suspension and hydraulic
suspension give a much better signal. But it still took more than
ten years before the coordination between the tractor and trailer
functioned properly. Hydraulic suspension was a huge step
forward, not only because of the effective brake pressure regulator,
but also because the old trailers with leaf spring suspension were
notorious for their bumpy rides.
52
PRINCIPLE AND OPERATION
With hydraulic suspension a hydraulic cylinder is placed between
the axle and chassis. The cylinder itself does not provide the
suspension, but it is connected to an expansion tank which is
partly filled with nitrogen gas, the accumulator. By compressing
the gas in the accumulator the axle can move up and down.
The cylinders of the suspension on either side of the trailer are
connected, so that the hydraulic pressure in the cylinders and the
pressure on each wheel is more or less the same. The hydraulic
circuit of the suspension can also be connected to a hydraulic
adjustable gooseneck.
THE CLEVER SOLUTIONS OF NOOTEBOOM
The axle housing at the front has two short parabolic springs.
The short, wedged-in springs act as a stabiliser that increases the
rolling resistance when the trailer is cornering. The cylinder of
the suspension is secured in a particular way on both sides. On
the axle there is a removable ball joint that prevents the hydraulic
cylinder from bending, which can cause it to leak. On the chassis
side there is a spherical bearing that also allows the cylinder to
move in transverse direction. Both the ball joint and spherical
bearing are essential constructive elements for a long lifespan.
THE ACCUMULATOR
The accumulator, which is partly filled with nitrogen gas, takes
care of the suspension. By combining various accumulators the
trailer will have a comfortable suspension, whether fully loaded or
empty. The first accumulator (from 15 bar) comes into action with
an empty trailer and the other one (from 60 bar) with a loaded
trailer. An additional advantage of hydraulic suspension is that no
shock absorbers are required.