Abstract
Full hybrid electric vehicles have proven to be a midterm viable solution to fulfil stricter regulations, such as those regarding carbon dioxide abatement. Although fuel economy directly benefits from hybridization, the use of the electric machine for propulsion may hinder an appropriate warming of the aftertreatment system, whose temperature is directly related to the emissions conversion efficiency. The present work evaluates the efficacy of a supervisory energy management strategy based on Equivalent Minimization Consumption Strategy (ECMS) which incorporates a temperature-based control for the thermal management of the Three-Way Catalyst (TWC). The impact of using only the midspan temperature of TWC is compared against the case where temperature at three different sampling points along the TWC length are used. Moreover, a penalty term based on TWC temperature has been introduced in the cost functional of the ECMS to allow the control of the TWC temperature operating window. In fact, beyond a certain threshold, the increase of the engine load, requested to speed up TWC warming, does not translate into a better catalyst efficiency, because the TWC gets close to its highest conversion rate. A gasoline P2 parallel full hybrid powertrain has been considered as test case. Results show that the effects of the different calibrations strategies are negligible on the TWC thermal management, as they do not provide any improvements in the fuel economy nor in the emissions abatement of the hybrid powertrain. This effect can be explained by the fact that the charge sustaining condition has a greater weight on the energy management strategy than the effects deriving from the addition of the soft constraints to control the TWC thermal management. These results hence encourage the use of simple setups to deal with the control of the TWC in supervisory control strategies for full hybrid electric vehicles.
Highlights
The share of hybrid and electric vehicles in the worldwide market has increased in recent years to meet the stringent regulations concerning vehicle pollution [1], thanks to the decrease of the their total cost of ownership [2]
The control code was paired to GT-Suite as represented in Fig. 1: all the control signals which result from the on-line optimization process carried out by the Equivalent Minimization Consumption Strategy (ECMS)-based algorithm are sent to GT-Suite powertrain model, which sends back to the control strategy the powertrain components state signals, such as the battery state of charge (SoC), the internal combustion engine (ICE) actual output torque and the Three-Way Catalyst (TWC) temperature at the used sampling points
It is important to note that the control strategy was calibrated every time so to have a maximum deviation of the final battery SoC value from the target value SoCref equal to −+1%: this enables a fair comparison between different calibration setups in terms of fuel consumption and emissions, since the net battery energy balance is almost null
Summary
The share of hybrid and electric vehicles in the worldwide market has increased in recent years to meet the stringent regulations concerning vehicle pollution [1], thanks to the decrease of the their total cost of ownership [2]. There exist different powertrain architectures, such as the series, the parallel and the series-parallel ( called power-split) that allow to change the number of degrees of freedom to operate the vehicle by using the internal combustion engine (ICE) and the electric machine/s (EM) at the same time [5]. PHEV powertrains have a greater capability to operate using the electrical energy, even though they require a higher level of electrification with respect to full-hybrid vehicles (FHEV). Supervisory energy management control relies on sophisticated algorithms which manage the power split between the internal combustion engine (ICE) and the electric machine/s (EM) and at the same time guarantee the best energy use to ensure the minimum fuel consumption
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