Although Hybrid Electric Vehicles (HEVs) represent one of the key technologies to reduce CO 2 emissions, their effective potential in real world driving conditions strongly depends on the performance of their Energy Management System (EMS) and on its capability to maximize the efficiency of the powertrain in real life as well as during Type Approval (TA) tests. Attempting to close the gap between TA and real world CO 2 emissions, the European Commission has decided to introduce from September 2017 the Worldwide Harmonized Light duty Test Procedure (WLTP), replacing the previous procedure based on the New European Driving Cycle (NEDC). The aim of this work is the analysis of the impact of different driving cycles and operating conditions on CO 2 emissions and on energy management strategies of a Euro-6 HEV through the limited number of information available from the chassis dyno tests. The vehicle was tested considering different initial battery State of Charge (SOC), ranging from 40% to 65%, and engine coolant temperatures, from −7 • C to 70 • C. The change of test conditions from NEDC to WLTP was shown to lead to a significant reduction of the electric drive and to about a 30% increase of CO 2 emissions. However, since the specific energy demand of WLTP is about 50% higher than that of NEDC, these results demonstrate that the EMS strategies of the tested vehicle can achieve, in test conditions closer to real life, even higher efficiency levels than those that are currently evaluated on the NEDC, and prove the effectiveness of HEV technology to reduce CO 2 emissions.
A plug-in hybrid electric powertrain, as one of the most promising solutions to increase the fuel economy and to meet the stringent requirements of low emissions urban zones, has been investigated and developed for a light duty commercial vehicle application in this work. The plug-in hybrid electric powertrain combines an advanced small diesel internal combustion engine with a high energy battery pack, capable to assure an extended range in pure electric mode for specific areas, like the low/zero emissions urban zones. Since the right size of the powertrain components is essential to fully exploit the benefits of the hybridization, an advanced methodology has been proposed to optimize the design of the plug-in hybrid powertrain at an early phase. This methodology is based on the genetic algorithm approach for the choice of the powertrain component characteristics, combined with a quasi-optimal energy management strategy that is the Equivalent fuel Consumption Management Strategy (ECMS). The performance of the hybrid electric powertrain which was designed through the proposed methodology were then assessed and analyzed over the Worldwide Harmonized Light Duty Driving Cycle (WLTC) by means of a simulation model, thus demonstrating its effectiveness in addressing the issue of the powertrain components sizing from the early stage of the design process.
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