Stability of very long trailers

Summarising , the Lusaro caravan shows better safety properties than the conventional centre axle caravan, and may be considered a promising step towards a new type of caravan which matches low-speed manoeuvrability with high-speed safety and stability.

Teletrailers

The transportation of very long loads such as pipes, rotor blades or concrete bridge structures is pushing the trailer manufacturers to build semi-trailers that can be extended to ever increasing lengths. Nooteboom Trailers offers special flatbed trailers that can be extended in up to 46 meters in length. These teletrailers® consist of a front part linked to the fifth wheel of the tractor, the rear part including steerable axles, and a beam in between that can be extended to over 27 meters.

Due to the flexibility of this beam, any sudden change in steering of the front wheels of the tractor will lead to a delay in the order of seconds   in the response of the rear part of the semi-trailer, resulting in lateral displacements at the rear axles which may pose a safety risk on the road in case of high speeds.

This phenomenon has been investigated, based on simulation analysis, for stationary behaviour, as well as under dynamic performance for several steering inputs including single and double lane change, step steer, and random steer. The model included lateral, yaw and roll behaviour of the vehicle, with the compliance of the fifth wheel incorporated and with distinction between sprung and unsprung mass. The compliance in lateral direction, yaw and roll of the interconnecting beam has been accounted for, as well as its inertia effects.

Different payload configurations and semi-trailer lengths have been analysed, with specific emphasis on the interaction between the front and rear part of the semi-trailer when the load is applied. The model has been validated against experiments for different payload configurations, including steady state tests and lane change manoeuvres. The experiments showed a good correspondence to the simulation results, both in a qualitative and a quantitative sense.

Semi-trailer flexibility

The investigations demonstrated that even under extreme steering input and high speeds, the lateral performance of the tractor semi-trailer combination remains within limits that can be regarded as safe. Due to the flexibility of the semi-trailer, the delay in response of the rear part of the semi-trailer counteracts the steering effect of the rear axles (hydraulically connected to the fifth wheel), stabilising the rearward lateral displacements.  

Reference

J.P. Pauwelussen, S. Bijker, J. Broeze, G. v.d. Vlist.: The Behaviour of Very Long Semi-trailers. Int. J. Veh. Syst. Mod. & Testing, Vol.1,no 4, page 253 - 277 (2006)