In this paper, the operational conditions of a new hydraulic/pneumatic system conception for medium and heavy-duty vehicles are evaluated. The design comprises a hydraulic system, coupled to a pneumatic system, with ability to recover braking energy in driving cycles characterized by frequent stop-and-go, and also on highways with small inclinations. In order to evaluate the potential of the hybrid system, the vehicle is subjected to a driving cycle, whose route is comprised in part by a road in the horizontal plane, and in part by a road with slope. A heuristic control strategy is presented, whose approach is based on a mathematical model built in platform-MATLAB/SIMULINK and supported by maps of performance and efficiency and physical parameters of the components. The control strategy provides five operating modes for the vehicle in order to meet the different traffic conditions, in accordance with the driving cycle analyzed. As the trip occurs, is required the hybrid system supply the pneumatic auxiliaries of the vehicle employing the regenerated energy stored in the accumulators preferably, or the power generated from internal combustion engine when the accumulators are empty. The simulating results prove the effectiveness of the control strategy to command the hybrid system properly, as well as the ability of the vehicle to achieve the requirements of performance and maintaining a high overall efficiency of the engine.

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