Development of Effective Exhaust Gas Heat Recovery System for a Hybrid Electric Vehicle 2011-01-1171

The success of improved fuel economy is the proper integration of thermal management components which are appropriately performed to reduce friction and wasted energy. The thermal management systems of vehicle are able to balance the multiple needs such as heating, cooling, or appropriate operation within specified temperature ranges of propulsion systems. Since the propulsion systems of vehicle have changed from a single energy source based on conventional internal combustion engine to hybrid system including more electrical system such as full type of hybrid electric vehicle or plug-in hybrid electric vehicles, a new transition associated with vehicle thermal management arises. More efficient thermal management systems are required to improve the fuel economy in the hybrid electric vehicles because of the driving of electric traction motor and the increase of engine off time. The decrease of engine operation time may not sustain the proper temperature ranges of engine and gearbox. As an engine starts at low ambient temperature, heat from the wasted heat of exhausted gas can be supplied not only to cabin heater, but also to engine and gearbox at initial warm-up.

To practically apply recent thermal management technologies in commercial use, improved performance for the low energy density per cost in a viable vehicle package is necessary in general. This research describes the one of cost effective thermal management solutions recovering exhaust gas heat exchanging system with coolant and gear box oil simultaneously. The previous type of recovering the exhaust heat is to exchange the heat between the coolant and the exhaust gas to increase the temperature of the engine coolant, thereby reducing the friction and improving the fuel efficiency. However, the reduction in engine friction loss and improvement of fuel economy remains low due to the short period of exchanging heat between exhaust gas and coolant. It is more advantageous to increase the temperature of the engine oil or gear box oil rather than to increase the coolant temperature. Accordingly, the developed exhaust heat recovery device which performs integral heat exchange of the exhaust gas heat of engine increases the temperature of the coolant and the gear box oil, thereby reducing friction loss and improving fuel economy. The experimental result of this system improved 2.5% of fuel economy at UDDS drive cycles.