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.
A Parametric Approach for Evaluating the Stability of Agricultural Tractors Using Implements during Side-Slope Activities
A methodological approach for evaluating a priori the stability of agricultural vehicles equipped with different mounted implements and operating on sloping hillsides is shown here. It uses a Matlab simulator in its first phase and, subsequently, the Response Surface Modelling (RSM) to evaluate the coefficients of a set of regression equations able to account for the Type-I and Type-II stability of the whole vehicle (tractor + implement with known dimensions and mass). The regression equations can give reliable punctual numeric estimations of the minimum value of the Roll Stability Index (RSI) and can verify the existence of a Type-I equilibrium without the need of using the simulator or knowing any detail about the model implemented in it. The same equations can also be used to generate many intuitive graphs (“equilibrium maps”) useful to verify quickly the possible overturning of the vehicle. A case-study concerning a 4-wheel drive articulated tractor is then presented to show the potential of the approach and how using its tools. The tractor has been studied in three scenarios, differing on where the implement has to be connected to the tractor (1: frontally; 2: frontally-laterally; 3: in the back). After performing a series of simulations, a set of polynomial models (with 6 independent variables) has been created and verified. Then, these models were used, together with the related equilibrium maps, to predict the stability of 8 implements for scenario 1, 7 implements for scenario 2, and 3 implements for scenario 3, evidencing in particular the danger of using a lateral shredder with a mass greater than 245 kg. The proposed approach and its main outcomes (i.e., the regression equations and the equilibrium maps) can give an effective contribution to the preventive safety of the tractor driver, so it could be useful to integrate it in the homologation procedures for every agricultural vehicle and to include the resulting documentation within the tractor logbook.
LATERAL DYNAMICS OF COMMERCIAL VEHICLE COMBINATIONS. A LITERATURE SURVEY
SUMMARY This paper presents a review of theoretical and experimental works relative to the handling performance of commercial vehicle combinations. A commercial vehicle combination (road train) is defined as a tractor unit and an arbitrary number of trailers. The review contains literature corresponding the most widely used types of trains: tractor-semitrailer, truck-trailer and tractor-semitrailer-semitrailer (doubles). The vehicle dynamic performance has been investigated taking into consideration the following features: directional performance, roll dynamics, braking performance and combined braking and directional performance. With the aim of evaluating the present state of research activities in the field of lateral dynamics of articulated commercial vehicles, the author has compiled some 250 references.