Abstract
Keywords- Hybrid electric vehicle, Mechanical brake, Retarder, Regenerative braking, City bus.
The Regenerative Braking System (RBS) employs the electric motor, providing negative torque to the driven wheels and converting kinetic energy to electrical energy recharging the battery. In Hybrid Electric Vehicles (HEVs) the dissipation of kinetic energy during braking can be recovered advantageously by controlling power electronics. The recovered energy can be retuned to the battery for future use.
An HEV combines an Electric Vehicle power-train system with conventional power-train components, such as an Internal Combustion Engine (ICE). Combining an auxiliary powerplant, such as an ICE/Generator combination, with an Electric Vehicle power-train, not only the vehicle performance and fuel economy of an HEV can be extended but also the emission is reduced in comparison with a conventional ICE power-train. Most of the HEVs employ both a conventional braking system and a regenerative one. The conventional braking system typically includes frictional drum or disc braking assemblies selectively actuated by a hydraulic or pneumatic system. Auxiliary brake systems such as hydraulic retarders can provide significant brake retardation levels that take some load off the service brake system. Through the hybridization of a conventional city bus the gearbox and its hydraulic retarder may completely be removed. Therefore, the retarder should be replaced in such a way that no extra load is exerted on the service brake in hybrid bus comparing with the conventional one.
In this paper, the retarder braking performance of one of the Iran-Khodro city buses, O457, is compared with the regenerative braking performance of the developing series hybrid electric bus in Vehicle, Fuel, and Environment Research Institute of University of Tehran, employing AVL/CRUISE vehicle simulation.