A series-parallel hybrid electric powertrain for industrial vehicles

In the last years there is a growing interest in electric and hybrid electric propulsions due to environmental concerns. In particular industrial vehicles are a promising field of application for their duty cycles characterized by low velocities, frequent start and stop jobs, long periods of idling and material-handling tool power peaks. In this paper a series-parallel hybrid electric powertrain for wheel loaders is investigated with the goal to reduce the fuel consumption. The developed architecture exploits the benefits of a series hybrid electric powertrain at low traction requirements and progressively takes advantage from the typical power coupling of a parallel hybrid drivetrain at increasing power demands, according to the ordinary employment of a loader. In the drivetrain, a planetary gear unit and the electrical subsystem (generator/motor and battery) decouple the wheels from the engine operating point. Therefore the supervisory regulator can control the engine in its high efficiency regions. The drivetrain is modeled and a control algorithm is derived. Simulation results confirm the attractiveness of the proposed series-parallel hybrid electric powertrain for loaders.