No abstract

No abstract

One of the key components of a hybrid electric vehicle (HEV) drive train is its secondary energy storage device. The automotive industry is still in the process of debating on the fact, as to which device provides the best option in HEVs, for the purpose of load leveling. This paper aims at providing a fair idea with regards to the selection of secondary energy sources, based on vehicle performance characteristics and overall drive train efficiency. The performances of lead-acid (PBA), lithium-ion (Li-Ion), nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), and nickel-zinc (Ni-Zn) batteries, as well as ultra-capacitors (UC) are investigated over city and highway driving schedules for a heavy-duty diesel-parallel hybrid transit bus application.Based on the simulation studies for the above-mentioned storage devices, the Ni-MH, PBA, and the ultra-capacitor technologies demonstrate best results in terms of fuel economy and percentage drive train efficiency. On the other hand, the Ni-Zn and Li-Ion batteries show much promise, but still demand a great deal of research and development work, before they become a viable option for HEV applications. Finally, the paper compares and summarizes critical performance characteristics for the energy storage devices under investigation.

Alternative electric motor geometry with potentially increased efficiency is being considered for hybrid electric vehicle applications. An axial flux motor with a dynamically adjustable air gap (i.e., mechanical field weakening) has been tested, analyzed, and modeled for use in a vehicle simulation tool at Argonne National Laboratory. The advantage of adjusting the flux is that the motor torque-speed characteristics can better match the vehicle load. The challenge in implementing an electric machine with these qualities is to develop a control strategy that takes advantage of the available efficiency improvements without using excessive energy to mechanically adjust the air gap and thus reduce the potential energy savings. Motor efficiency was mapped in terms of speed, torque, supply voltage, and rotor-tostator air gap. Maps of optimal gap versus efficiency were used to develop a motor model and control strategy, which were incorporated into the PNGV Systems Analysis Toolkit vehicle modeling software.