INTEGRATED ENERGY EMISSION MANAGEMENT FOR HYBRID ELECTRIC VEHICLES

摘要

The powertrain of hybrid electric vehicles offers opportunities to increase the energy efficiency as well as to reduce hazardous tailpipe emissions. The concept of model-based Integrated Powertrain Control (IPC) is proposed to come to a well balanced trade-off between energy management and emission management. Requirements on tailpipe emissions from type approval are included as hard constraints, whereas the remaining freedom is used to minimize the operational cost which is important for creating customer value. A case study is presented for a heavy duty hybrid electric vehicle with an SCR-deNO_x aftertreatment system. As long as the temperature of the aftertreatment system is low, IPC focuses on emission management. When the aftertreatment system is sufficiently hot, the main objective of IPC becomes energy management. Simulation results demonstrate how IPC optimizes the trade-off between operational costs (comprising fuel use and AdBlue dosing) versus NO_x emissions. TECHNICAL PAPER - Hybrid electric vehicles (HEVs) are typically associated with a green image through their reduced fuel consumption and accompanying CO_2 emission reduction. The required control strategies take care of the power-split between the internal combustion engine (ICE) and the electric machine. The main focus of these control strategies is energy efficiency, i.e. minimization of the primary fuel consumption. Nevertheless, an HEV is also an enabler to reduce harmful emissions such as hydrocarbons (HC), nitrogen oxides (NO_x) and particulate matter (PM). These requirements typically emerge from legislation on tailpipe emissions for type approval. It is generally known that the catalytic converters in the aftertreatment system suffer from a poor conversion efficiency below light-off temperature. Therefore, a fast catalyst light-off strategy is desirable during the cold-start period. To reach early light-off temperature, a hybrid vehicle is in the position to deliver additional heat to the exhaust gas by changing the engine calibration in combination with its operating point. Simultaneously, the electric machine guarantees sufficient torque reserve to satisfy the power request from the driver. Altogether, the benefits for emission reduction will improve the return on investment for a hybrid powertrain. This work presents a novel Integrated Powertrain Control (IPC) strategy incorporating both energy and emission management. During the cold-start period this strategy is dominated by emission management, whereas the focus changes to energy management when the aftertreatment system reaches light-off temperature. The IPC concept is generally valid for both gasoline and diesel engines but to keep the length of this paper limited, the main part has been written from a diesel perspective. As a case-study, the IPC strategy is evaluated on a heavy duty HEV. This vehicle is equipped with a diesel engine and Selective Catalyst Reduction (SCR) in the exhaust system to lower NO_x emissions. After developing the IPC strategy, simulations will demonstrate how this strategy realizes a well-defined trade-off between CO_2 emissions and NO_x emissions.