Modelling of the Warm-up of a Spark Ignition Engine: Application to Hybrid Vehicles 2011-01-1747

One of the main advantage of a hybrid thermal-electric vehicle is that the internal combustion engine (ICE) can be shut down when not needed anymore (Stop&Start system, propulsion with full-electric mode), thus reducing fuel consumption. But this use of the ICE impacts its thermal behavior because of a lack of heat source and thermal losses. Furthermore, the ICE is sometimes used with higher load in order to charge the batteries that increases the total heating power produced by the combustion. Therefore, the simulation of hybrid vehicles becomes really interesting to evaluate the effect of different control strategies (energy repartition between the engine and the electric motor) on the fuel consumption. However, in most of actual hybrid vehicles simulation tools, for calculation speed reasons, the thermal phenomena are either not taken into account, or their calculation is not based on physical equations (empirical formulas). Their predictive capability is then limited.

The global aim of this study is the development of a simulation tool (using the Amesim® software) for hybrid electric vehicle which takes into account most of the thermal phenomena occurring in the various components and between them without increasing the calculation time. In this paper, we first focus on thermal phenomena occurring in the spark ignition ICE. The coupling of a combustion model with a thermal model of the engine cooling system and its metal parts allows a simulation of its warm-up after a cold start. The thermal transfers between the different thermal inertia are computed and their dependence with different parameters like speed or load is evaluated. Research about the heating speed of the cooling water and the lubricating oil (due to the viscous friction and dependent of the global thermal state of the ICE) are interesting in order to find the best use of the ICE and therefore reducing the fuel consumption. Finally, the model of the engine including the thermal transfers is integrated in a simulation of the whole vehicle.

The thermal behavior of two vehicles (a conventional and a parallel hybrid electric) using the same spark ignition engine is finally presented. The first results show that the thermal phenomena have a significant impact on the final consumption of the vehicles.