In conventional vehicles the entire power is derived from the IC engine, so it is obligatory to size the engine larger than necessary for its cruising speed. The engine must be designed to account for peak power requirements like acceleration. This oversizing of the engine shifts the operating point from its efficient zone and this adversely affects the fuel economy and emissions. The idea of hybridization is that a part of the total power required can be replaced by an auxiliary power source, generally a motor powered by batteries. Hence, the IC engine can be designed for average load and can be operated with better fuel efficiency. A simulation tool called ADVISOR (Advanced Vehicular Simulator) is used for this study. The software takes the vehicle input and the drive cycle from the user, simulates the vehicle drive and gives fuel economy, acceleration performance and emissions. In this study, each of the three vehicle platforms (average SUV, full size SUV and heavy truck) is selected and a reasonable power level for that vehicle platform is taken from the data of the current conventional vehicle type. The powertrain is then hybridized by replacing part of the total power by an equivalent motor power and a set of simulations are run in ADVISOR at three different battery charge capacities to understand the effect of on-board charge. A weighted combination of performance and fuel economy results is recorded for each run, and the simulations are then repeated at a higher level of hybridization. The results for a range of “percent hybridization” levels are then evaluated to determine the optimum level. A cost optimization is also done by adding weighted factors based on cost effect of the motor, batteries, and the projected lifetime fuel costs. The penalty due to the weight of the batteries is reflected in the simulated performance and fuel economy of the vehicle, and the space effect of the batteries is also considered. The results of this thesis support the conclusion that parallel hybridization of the drive train could help SUVs and heavy trucks to improve fuel efficiency. Depending on the assumptions made for replacement battery costs and total mileage over the lifetime of the vehicle, the increased initial cost of a hybrid SUV can be justified by the operating cost savings; the benefits of hybridization are even more pronounced for heavy trucks. The “optimum” hybridization percentages are reported for each platform, with and without cost considerations.
Enhancing the fuel economy of a plug-in series hybrid vehicle system