Abstract
The objective proposed by the EU to drastically reduce vehicular CO2 emission for the years up to 2030 requires an increase of propulsion systems’ efficiency, and accordingly, the improvement their technology. Hybrid electric vehicles could have a chance of achieving this, by recovering energy during braking phases, running in pure electric mode and allowing the internal combustion engine to operate under better efficiency conditions, while maintaining traditionally expected vehicle performances (mileage, weight, available on-board volume, etc.). The energy storage systems for hybrid electric vehicles (HEVs) have different requirements than those designed for Battery Electric Vehicles (BEVs); high specific power is normally the most critical issue. Using Li-ion Batteries (LiBs) in the designing of on-board Energy Storage Systems (ESS) based only on power specifications gives an ESS with an energy capacity which is sufficient for vehicle requirements. The highest specific power LiBs are therefore chosen among those technologically available. All this leads to an ESS design that is strongly stressed over time, because current output is very high and very rapidly varies, during both traction and regeneration phases. The resulting efficiency of the ESS is correspondingly lowered, and LiBs lifetime can be relevantly affected. Such a problem can be overcome by adopting hybrid storage systems, coupling LiBs and UltraCapacitors (UCs); by properly dimensioning and controlling the ESS’ components, in fact, the current output of the batteries can be reduced and smoothed, using UCs during transients. In this paper, a simulation model, calibrated and validated on an engine testbed, has been used to evaluate the performances of a hybrid storage HEV microcar under different operative conditions (driving cycles, environment temperature and ESS State of Charge). Results show that the hybridization of the powertrain may reduce fuel consumption by up to 27%, while LiBs lifetime may be more than doubled.
Highlights
Mobility in modern metropolitan cities, especially within historical city centers, is affected by overcrowding, congestion, low transit speed, fuel consumption, air pollution and parking problems.Among the causes of these phenomena, there is the diffusion of vehicles of excessive size with respect to their use, and the low occupancy rate of vehicles
Results show that the hybridization of the powertrain may reduce fuel consumption by up to 27%, while Li-ion Batteries (LiBs) lifetime may be more than doubled
Energy Storage Systems (ESS) for hybrid electric vehicles (HEVs) have different requirements than those designed for battery electric vehicles (BEVs), and high specific power is normally the most critical issue
Summary
Mobility in modern metropolitan cities, especially within historical city centers, is affected by overcrowding, congestion, low transit speed, fuel consumption, air pollution and parking problems. Energy Storage Systems (ESS) for HEVs have different requirements than those designed for battery electric vehicles (BEVs), and high specific power is normally the most critical issue. The present work starts from a previous experimentation, performed at the ENEA Research better efficiency than connecting them with the pre-existing on-board alternator (connected to the Centre, on the existing chassis of a quadricycle called ERAD SPAZIA (born as a Lead Acid BEV), ICE crankshaft via a dedicated belt, with a global efficiency of about 60%). This resulted in both a which was converted to a parallel HEV by installing a Hybrid Powertrain Pack (HPP). DC/DC converter has been used, as in [8,10,19]
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