ABSTRACT
Hybrid electric vehicles (HEVs), as the name stands for, have two types of power sources. An electric power source is added to the conventional internal combustion engine (ICE), which helps to improve the fuel economy through load sharing and regenerative braking. Note that ICEs have the optimum fuel efficiency in the middle speed and high torque range. However, the efficiency is low in the low speed/low torque region. Therefore, the ICEs have relatively poor performance in urban driving where there are many stop-go situations. On the other hand, electric motors generate high torque naturally in the low speed range and have a pretty high efficiency in overall operating region. When the vehicle is driven by a motor in a low speed region, the overall fuel economy will be improved significantly. In addition, the motor can force the engine to operate in an optimal condition independently of the road load. The motor also enables the regenerative braking, i.e., vehicle’s kinetic energy can be recovered in the battery when the vehicle is decelerating. But, the ICE’s power is sustainable over a long driving period and have the advantage of short refueling times.
