Overview of Problematic Aspects of Passenger Car Hybrid Technologies

Abstract

Hybrid electric vehicles (HEV) with Atkinson cycle engines typically use variable valve timing (VVT) technology that reduces fuel consumption up to 30% due to the delay in closing intake valve. Engine thermal efficiency can be raised even up to 40%, however it is necessary to reduce heat loss through the cooling system and to avoid knocking combustion. Electric Vehicle (EV) mode operates at very low loads and the traction force is generated only by the electric motor, while internal combustion engine (ICE) is off to avoid an inefficient zone. Parallel Hybrid (PH) mode operates at higher loads, ICE is on and depending on accelerator pedal and on the State of Charge (SOC) of high voltage batteries, the powertrain can operate in Smart Charge (SC) and Electric Boost (E-Boost). HEVs emission profile is not always improved due to cold start events. NOx, HC, CO and particle number (PN) increase significantly after cold start. Moreover, the amount of emissions depends on SOC of batteries. At high SOC fuel consumption, CO and NOx emissions are reduced, while at low SOC emissions are increased significantly enough. Analysis show that cold start CO2 emissions along the New European Driving Cycle (NEDC) and Worldwide Light duty vehicle Test Procedure (WLTP) procedures have differences even up to 30%.