Control of Hybrid Electric Vehicles with Diesel Engines
Abstract: This thesis is an approach to improve electric hybrid vehicles with respect to fuel consumption and to fulfil the future intended NOX emission regulations. It is based upon the conclusions made in the licentiate thesis Analysing Hybrid Drive System Topologies (Jonasson, 2002). The study in this thesis is restricted to a parallel hybrid vehicle equipped with a diesel engine, two electric machines and electrical energy storage and a model thereof is presented in the thesis. The choice to focus on the diesel engine is related to the high efficiency of this engine that also is the reason for the in later years increased market for diesel engines in conventional vehicles. Since one of the disadvantages, related to the diesel engine, are the nitrogen oxides (NOX) emissions, efforts is concentrated on reducing them, by means of the advantages of hybridisation. The reference vehicle in the simulations presented in this thesis is a Toyota Prius, an electric hybrid passenger car, which is available on the market today. As input for the combustion engine model, engine data from a diesel engine considered as state of the art 2004, has been used. The engine data is scaled to correspond to the engine size used in the Prius. It should be mentioned that the engine in the Toyota Prius is run on petrol. There are many possible parameters in the simulation model, which are adjustable; vehicle chassis parameters, engine, electric machine(s) and battery size and types, losses models, charging strategies and driver behaviour etc. A number of key parameters have been selected in this study: control strategy, NOX control by means of EGR (exhaust gas recirculation) and SCR (selective catalytic reduction), gear ratios and gearshift strategies and finally cylinder deactivation. The accuracy of the simulation model is ratified by means of measured data on the engine used in the simulation. Fuel consumption and NOX are determined by using look-up-tables based on measured data. The engine temperature, needed to determine the NOX conversion by means of SCR, is also received from a look-up-table. The simulation model is evaluated in the driving cycle ECE+EUDC. The results presented are chosen to illustrate the impact each individual parameter has on the behaviour of the hybrid vehicle, the fuel consumption and the emissions. The results from the simulations show that it is possible to pass the expected limit of the future Euro 5 NOX regulations, if NOX emission treatment with EGR and SCR is implemented. The price to pay for this action is to sacrifice some of the fuel savings that the hybridization brings. The result is nevertheless a vehicle with decreased fuel consumption compared with a conventional diesel powered vehicle, and a vehicle that passes the intended emission regulation.
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