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In every driving condition powertrain and vehicle dynamics deeply influence each other. The main role of powertrain influence is played by the differential, which transmit the driving torque with respect to wheel kinematics. Many different solutions have been historically developed from pure mechanical devices (as open, self-locking, torque sensitive and speed sensitive) to semi-active and full-active differentials. The recently developed controlled differentials underlined the importance of a good project and tuning of this component to achieve a good performance of the vehicle, in terms of traction, stability, and, more over, drive “feeling”. This paper tries to cover the lack of present literature to provide analysis tools to be used in the preliminary phase of vehicle project in order to evaluate differential influence on vehicle performance.

The flow-field around a “common” European heavy truck, equipped with several different trailer devices, is investigated using steady and unsteady simulations. This work demonstrates how with simple devices added on the trailer it is possible to strongly decrease the aerodynamic drag over 10%, with an increase of overall dimensions below 1% without any change to the load capacity of the trailer. Several devices, installed on the trailer, are tested on a target vehicle and the shape of the “airbag”, the “fin”, the “boat tail” and the “front-rear trailer device” has been optimized to achieve the maximum in drag reduction in front wind. The performance of the optimized devices are tested also in cross wind conditions with the yaw angle varying from 0° to 30°. The truck equipped with the front-rear trailer device is also investigated using time variant simulation with yaw angle of 0°, 5°, 10°.