Abstract
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 and having the energy storage unit empty at the start of the driving cycle, 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%, start with the energy storage unit full, 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 brake mean effective pressure x speed map points in addition to the thermal engine energy supply reduction by the 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.
KEYWORDS – environmentally friendly vehicles, lightweight materials, kinetic energy recovery systems, small high power density engines