A fun-to-drive, economical and environmentally-friendly mobility solution

Alberto A. Boretti


Kinetic energy recovery systems (KERS) placed on the rear non-motored axle of a small, lightweight, forward drive passenger car with a turbocharged direct injection (TDI) internal combustion engine (ICE) is possibly the best solution presently available to dramatically improve the fuel economy of today’s passenger cars within today’s constraints of budget, weight, packaging, simple construction, easy operation and best life cycle environmental friendliness. The vehicle may be built by using different KERS designs, from the purely mechanical M-KERS based on a continuously variable transmission and a flywheel permitting round trip regenerative braking efficiencies above 80% but requesting additional research and development, to purely electric E-KERS systems based on an electric motor/generator and a battery with off the shelf components permitting round trip regenerative braking efficiencies above 70% but having however the traction battery as the weak part of the design, to mixed mechanical-electric systems EM-KERS adopting an electromechanical flywheel replacing the traction battery for intermediate advantages and downfalls. The engine is small displacement, small number of cylinders, high power density, turbocharged, direct injection. The TDI ICE may be gasoline or diesel, with higher power density but lower fuel conversion efficiency or vice-versa, with or without start-stop capability, to deliver high part load efficiencies over the reduced off idle operating points of a driving cycle. Downsizing, down speeding and KERS assistance permits to reduce the operation of the thermal engine over non-efficient BMEP x speed map points in addition to the thermal engine energy supply reduction by regenerative braking. The front wheel drive vehicle behaves as a four wheel drive during the driving characterized by accelerations and decelerations, with the thermal engine torque boosted by the KERS.
The proposed vehicles may have fuel economy figures well below 2.5 litres/100 km covering a modified NEDC where the unrealistic sharp deceleration from 120 km/h to rest at the end of the extra urban sector is followed by another urban sector as the first four ones.


vehicles, powertrains, internal combustion engines, kinetic energy recovery systems

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