Design and analysis of a parallel hydraulic – pneumatic regenerative braking system for heavy-duty hybrid vehicles

• Published in: Applied energy 2018-09, Vol.225, p.60-77
• Main Authors: Bravo, Rafael Rivelino Silva, De Negri, Victor Juliano, Oliveira, Amir Antonio Martins
• Format: Article
• Language: English
• Subjects: Heavy-duty hybrid vehicles; Hybrid commercial vehicles; Hydraulic-pneumatic hybrid drive train; Vehicular energy efficiency
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2018.04.102

[Display omitted] •A new concept of hydraulic-pneumatic regenerative system for heavy vehicles is presented.•It was designed to store braking energy in both urban and highway conditions.•The stored energy is used for propulsion and to power auxiliary systems.•A dynamic simulation using data from commercial components was applied to a 19 tonnes bus.•The system recovers 69% of the available energy during full stop and 14% in a long downward slope. Hydraulic-pneumatic hybrid powertrains provide an opportunity for combined high power and high energy regenerative braking systems for heavy duty vehicles that need to transpose both highway and urban areas. The challenge in designing these systems resides in the proper sizing, integration, and control of the components to exploit with high efficiency the different energy and power range available in these applications. In the novel concept proposed here, braking energy is recovered by a hydraulic system and stored in a hydraulic accumulator and in an air reservoir. While the hydraulic system shares the vehicle propulsion in parallel to the internal combustion engine, the compressed air is used to power auxiliaries in power-assist mode. The conception, modeling, sizing, and system integration are presented, relying on commercially available components. The lumped parameter simulation model written in MATLAB/Simulink is first validated by comparing measurements and predictions for a laboratory system. Then, two conditions of braking energy recovery for a 19 tonnes bus are analyzed: a full stop, typical of urban driving, and a downward road slope, typical of highway driving. Results indicate that the system proposed is able to store 69% of the available energy during full stop and 14% in the highway downward slope. However, although the storage efficiency is smaller in the downward slope, the total energy recovered is 2.8 times larger than the energy recovered after full stop. Also, while the pneumatic energy stored is only 20% of the energy stored in the hydraulic accumulators after full stop, it is more than twice for the road slope. These results indicate an opportunity for significantly improving the overall energy efficiency of delivery trucks and buses.