Active bogies, chassis levelling and transmission efficiency for a vehicle operating in rough terrain

Abstract

There is a growing interest in developing systems that allow the mobility of vehicles in rugged terrain, as in forestry areas, where conventional wheeled vehicles have limitations. Four axle vehicles with bogies can adapt the position of the wheels to follow irregularities in the terrain, having an obstacle surpassing ability far greater than conventional 2-axle vehicles. Still, the ability to overcome discrete obstacles on a steep slope is very different depending on the wheel that is facing the obstacle. A possible solution to diminish this variation can be found if the vehicle is able to actively redistribute the load on each wheel. One strategy is to design the suspension mechanism so it can adjust chassis’ height, being able to level it. Also, an active torque on the pin join between the bogie and the chassis can be applied achieving a redistribution of the load, adopting a system of active bogies. This study examines the longitudinal motion of a vehicle along ascending ramps, with different slope, at the time that one of its wheels is facing an obstacle. Results for different vehicle’s configurations are presented, and the efficiency of the proposed driveline is calculated in different situations. Results show that the use of active bogies provides improved capacity to overcome obstacles, active chassis levelling can also provide an improvement in the obstacle surmounting ability. However, the wheels of the front bogie are negatively affected by the height regulation, so implementing a permanent chassis levelling is not the best solution. The driveline efficiency results are considerably lower than the combination of the maximum efficiency values of each of the components because they all never work simultaneously at their maximum efficiency working point. In addition, the overall driveline efficiency is highly dependant on the operating conditions of each of the elements and their operation mode.