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.