DAILY MCA2014 4x4 ‒ BODYBUILDER INSTRUCTIONS
CHASSIS INTERVENTIONS
2.6 INSTALLING THE TOW HOOK
15
– Printed 603.95.994 – 1 Ed. - Base 05/2015
Drawbar couplings for centre axle trailers
Centre axle trailers are defined as those that have the drawbar rigidly connected to the frame and the axle (or more close axles)
placed at half the length of the same chassis.
Compared to the articulated drawbars, the rigid drawbar acts on the drawbar coupling with the increase of the static vertical loads
and, in the braking phase or in the oscillations caused by the road surface, the increase of the dynamic vertical loads. By means of
the hook, these loads lead to increases in the torsion of the rear crossbar of the vehicle, as well as push-ups on the overhang.
The use of centre axle trailers therefore requires the use of suitable towing hooks.
The values of the towed weights and vertical loads allowed are listed on the technical documents of the drawbar coupling manufac-
turer and on the part manufacture plate (see DIN 74051 and 74052).
For mechanical coupling devices for trailers with a central axle, refer to the following formulas:
● D
C
= g (T • C) / (T + C)
● V = a • C (X
2
/ L
2
)
D
C
= representative value of drawbar class [kN]. This is defined as the determination of the theoretical reference value for hori-
zontal load between tractor
g = acceleration of gravity [m/s
2
]
T = maximum weight of the towing vehicle [kg]
R = maximum weight of the trailer [kg]
S = value of vertical static load that, in static conditions, is transmitted to the coupling point. S must be ≤ 0.1 x R and, in any case,
less than 1000 kg
C = sum of maximum axial loads of the centre axle trailer at full load. It is equal to the maximum mass of the trailer decreased by
the vertical static load (C = R - S)
V = value of the theoretical dynamic vertical load [kN]
a = vertical acceleration in the area of the drawbar coupling/hook. in function of the rear tractor suspension, use the following
values:
● a = 1.8 m/s
2
of air suspensions
● a = 2.4 m/s
2
for other types of suspensions
X = length of the load bed [m], (see Figure 5)
L = theoretical drawbar length, distance between the centre of the drawbar eye and the centre line of the trailer axles [m], (see
Figure 5)
X
2
/ L
2
≥ 1 if the result is less than the unit, use the value 1
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