Lateral stability analysis of the tractor/full trailer combination vehicle
This paper presents a linear dynamics model of tractor/full trailer with six degrees of freedom, and a series of simulations are performed on obstacle avoidance manoeuvers in which the combination vehicle moves at a constant forward speed. It is found that the ratio of the peak lateral acceleration of the full trailer's center of gravity (CG) to that of the tractor is 2.3, meanwhile, the articulated angle of the trailer is larger than that of the dolly. This phenomena, defined as the ‘rearward amplification ratio’(RWA), leads vehicle to rollover easily. A larger wheelbase of trailer would be useful to improve the lateral stability of the combination vehicle but it is limited by width of the road. Acting a resistive torque on the turntable can be absolutely effective in improving the dynamics stability of the tractor/full trailer combination vehicle but if acted at hitch point it has little improvement.
On the feedback control of hitch angle through torque-vectoring
This paper describes a torque-vectoring (TV) algorithm for the control of the hitch angle of an articulated vehicle. The hitch angle control function prevents trailer oscillations and instability during extreme cornering maneuvers. The proposed control variable is a weighted combination of terms accounting for the yaw rate, sideslip angle and hitch angle of the articulated vehicle. The novel control variable formulation results in a single-input single-output (SISO) feedback controller. In the specific application a simple proportional integral (PI) controller with gain scheduling on vehicle velocity is developed. The TV system is implemented and experimentally tested on a fully electric vehicle with four on-board drivetrains, towing a single-axle passive trailer. Sinusoidal steer test results show that the proposed algorithm significantly improves the behavior of the articulated vehicle, and justify further research on the topic of hitch angle control through TV.
BIFURCATION THEORY AND VEHICLE DYNAMICS - WITH APPLICATION TO THE TRACTOR - SEMITRAILER
For a tractor-semitrailer system with four degrees of freedom the influence of variations of parameters on the driving behavior for steady state and braking motions is investigated. As parameters the driving speed (for steady state motion), the steering angle, nonsymmetric loading and the braking force distribution are considered. The goal of the paper is not only to give stability boundaries but also to obtain at least qualitative information about the behavior of the system after the transition from the stable to the unstable regime. To achieve this goal a nonlinear mechanical model must be used, the nonlinearity of which is mainly due to the relationship between the tire side force and the tire slip angle. Results obtained in bifurcation theory during the last decade are used to give a complete description and classification of the driving behavior if the parameter values pass through critical values. For the steady state motion for practically important cases divergence bifurcation occurred, which is extensively discussed for a symmetric and a nonsymmetric model. In the motion during braking besides divergence bifurcation also Hopf-bifurcation was found. This means that an oscillatory motion sets in after the parameter values pass through a critical value. Which type of bifurcation is found is heavily dependent on the braking force distribution to the different axles and also the arrangement of the loading on the trailer. For the covering abstract of the conference see TRIS 378303. (Author/TRRL)