Modelling of steered and lifted axles on long combination vehicles for performance based measures

Abstract

High Capacity transport (HCT) vehicles are much more transport efficient compared to conventional heavy goods vehicles. They also contribute to increased energy efficiency and reduction of CO2 emission. In a recent study by Ghandriz et al., it is shown that long heavy vehicle combinations which are run in heterogeneous fleet results in around 53% reduction in total cost of ownership (TCO) when compared to rigid trucks in homogeneous fleet. [26] Long combination vehicles (LCVs) can be difficult to operate on city limits because of the tight corners and roundabouts that the vehicle needs to go through. One possible way to evaluate these vehicles is a PBS (Performance Based Standard) based approach in which certain measures with its associated required performance levels are used for assessment of a vehicle combination. The target for this thesis work is to add low speed steered and lifted axles to the existing models in OpenPBS tool and support the main research project "Performance Based Standards II", by further development of this tool. Two different methods namely friction-zero side-slip and algorithm-based command steering methods and three different vehicle combinations (Nordic,A-double and Tractor-semitrailer) were considered with semi-trailer axles steered at low speeds. Low speed swept path (LSSP) is considered as the main performance measure of the vehicle to evaluate the effect of steered and lifted axles on semi-trailer at low speeds. Friction-zero side-slip and algorithm-based command steering methods were implemented and compared. The results show that both methods provide similar percentage improvement of LSSP for all three different vehicle combination. It can be concluded that friction-zero side-slip steering method is a conservative representation of algorithm based command steering method and hence a simple friction-zero side-slip steering method is good enough for representing semi-trailer steered axles in OpenPBS. For tractor semi-trailer with the last two axles of the semi-trailer steered at low speed, the percentage improvement in the LSSP is 6 % in 90 degree and 8 % in 180 degree turn respectively. For nordic combination with the last two axles of the semi-trailer steered at low speed, the percentage improvement in the LSSP is 10 % in 90 degree and 15 % for 180 degree turn respectively. v For A-double combination vehicle the percentage improvement in the LSSP with first semi-trailer steered is 13 % and with second semitrailer steered is 7 % in 90 degree turn. The improvement in the LSSP with first semi-trailer steered is 18 % and with second semitrailer steered is 12 % in 180 degree turn. Temporarily retractable axles were also investigated and it was shown that lifting the second semi-trailer axle improves the percentage of the LSSP by 6 % compared to non-lifted case. Keywords: