عنوان مقاله [English]
An articulated heavy vehicle, in typical form, consists of two units that include a tractor and a semi-trailer. The tractor unit is controlled by the driver, and the trailer unit used to carry heavy freight is connected to the tractor unit through a mechanical coupling point called the fifth wheel. The commonly used performance measure that reflects the maneuverability capabilities of the articulated vehicle is called off tracking. It refers to the phenomenon where the rear end of the trailer unit does not closely follow the path of the tractor unit. It is important to note that the poor
path-following ability increases safety concerns for the surrounding vehicle and destruction of road infrastructures. In this paper, a new method is presented to eliminate off-tracking, leading to the maneuverability improvement of the articulated heavy vehicle. A reference model generating a desired articulation angle is derived based on geometric and kinematic analysis. The tracking of the desired value ensures that the rear end of the semi-trailer unit follows the path of the fifth wheel. The inputs to the reference model are the yaw rate and the longitudinal and lateral velocity of the tractor unit, while the output is the desired articulation angle. A fuzzy controller is designed to adjust the articulation angle. The proposed controller makes the articulation angle follow the desired value by active semi-trailer steering.
Furthermore, a controller is designed to adjust the tractor yaw rate through active steering of the tractor front wheels.
A fourteen-degree of freedom vehicle model is developed in order to evaluate the proposed method. Computer simulations, including different maneuvers, show the significant effects of the proposed method on improving the maneuverability and stability of the articulated vehicle. Furthermore, the sensitivity of the method against errors in the input variables of the reference model is evaluated. The sensitivity analysis revealed that the proposed method is not so sensitive to errors in the variables. In low speed turning, the large error in tractor yaw rate has a major effect on system performance. However, yaw rate can be accurately measured by a typical sensor. Furthermore, the impact of different sizes of time increment on system performance is also evaluated.