Hitch / Drawbar eye / calculation
1. Tractor weight - In the absence of the D-value:
The admissible total vehicle combination weight (currently 40 t) minus the admissible total weight of tractor is the towed load.
2. Vertical load - Static vertical load
- Vertical load from the central axle trailer at the hitch point.
- The maximum possible static vertical load depends on the size of the hitch andamounts to 10 % of the total weight of the trailer or 1000 kg (which ever isless). Higher values are possible.
- The static vertical load should be at least 4% of the trailer weight in order toavoid a damaging negative vertical load.
- The level of the vertical load also depends on the speed.
Central axle trailer (C):
- Use admissible in principle:
- Size of the central axle trailer depends on the characteristics of the drawbareye and the tractor unit.
D-value (not in all hitches)
Theoretical horizontal force between towing vehicle and trailer, comparative mathematical value of forces between two moving masses.
The D-value can only be calculated from the admissible total weight of both masses (towing vehicle and trailer).
Calculation of the D-value in (kN):
T: total weight of the towing vehicle in t
R: total weight of the turntable trailer in t
g: gravitational acceleration (9.81 m/s2)
The calculated D-value can be equal to or less than the D-value of the hitch (type plate) or the weakest link in the overall rig.
Where use of the hitch is permitted for the trailer:
R1: total weight of the trailer on which the coupling is mounted in t;
R1 ≥ R2
Hitches and drawbar eyes for road traffic which are tested pursuant to the European standard 94/20 also have specialcharacteristic values established for use with the central axle trailer, the Dc-value and the V-value.
Towing vehicle and central-axle trailer: The Dc-value