A team from the University of Palermo and ICAR has developed an electric kinetic energy recovery system (e-KERS) for internal combustion engine vehicle (ICEVs) based on the use of a supercapacitor as energy storage, interfaced to a brushless machine through a power converter.

In a paper in the Journal of Power Sources, they report energy savings of the order of 20%, with a slight increase in vehicle weight (+2%) and with an overall commercial cost that would be compensated in 5 years due to the fuel economy improvement, to which corresponds an equal reduction of CO₂ emissions.

The researchers suggest that the low complexity of the system—never proposed for ICEV—the moderate weight of its components, and their availability on the market, make the solution ready for the introduction in current vehicle production.

The only kind of electric KERS currently studied and developed for internal combustion engine vehicles is represented by alternator-control KERS, which has been already introduced in the market by some car manufacturer (e.g., BMW Efficient Dynamics): with this kind of systems, the alternator output is increased during braking phases, thus transferring part of the vehicle kinetic energy to the battery, whose energy is employed to supply electrical consumers of the vehicle, reducing the power absorbed by the alternator during vehicle positive traction phases. The advantage of this system relies on its immediate applicability to current ICEV production, but, being realized with components not dedicated or optimized for KERS application, the fuel economy improvement is limited, ranging from 1% to 5%.

In the present paper, the authors propose an electric KERS (e-KERS) for internal combustion engine vehicles composed of a supercapacitors bank (SC), used as electric energy storage system, a motor-generator unit (MGU) to convert vehicle kinetic energy into electric energy and vice versa, and a power converter (PC), whose task is to manage the power transfer between SC and MGU. The system was conceived to recover the vehicle kinetic energy during braking phases by charging the supercapacitor, whose stored energy is employed by the MGU for the successive vehicle acceleration.

… Differently from any other electric KERS proposed for ICEV, the system proposed in this paper allows to use the recovered energy for vehicle acceleration, rather than for electric users supply, thus substantially increasing the amount of recycled energy.… Furthermore, differently from Formula 1 application, where the sizing of the KERS aims to maximize propulsion power, the guidelines followed in the present work aim to optimize the overall vehicle cost without causing a marked weight increase, thus allowing the power to be optimally managed during braking and acceleration phases.

—Pipitone and Vitale (2019a)

The supercapacitors bank is electrically interfaced, by means of an expressly designed power converter (PC), to a motor-generator unit (MGU). The MGU is mechanically connected to the drive shaft via a fixed gear ratio and converts the vehicle kinetic energy into electric energy and vice versa.

Drivetrain layout of the vehicle with KERS.

Resources

• E. Pipitone, G. Vitale (2019a) “A regenerative braking system for internal combustion engine vehicles based on supercapacitors - Part 1: system analysis and modelling,” submitted for publication to Journal of Power Sources

• Emiliano Pipitone, Gianpaolo Vitale (2019b) “A regenerative braking system for internal combustion engine vehicles using supercapacitors as energy storage elements - Part 2: Simulation results,” Journal of Power Sources doi: 10.1016/j.jpowsour.2019.227258

• Pipitone, E., Vitale, G., Lanzafame, R., Brusca, S. et al. (2019) “A Feasibility Analysis of an Electric KERS for Internal Combustion Engine Vehicles,” SAE Technical Paper 2019-24-0241 doi: 10.4271/2019-24-0241.