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Abstract:
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Fuel consumption in passenger vehicles has become more important due to the
significant increase of fuel cost and the awareness of the environmental impact.
Thus finding optimal speed profiles and gear shift strategies to cover a distance in
order to decrease fuel consumption is an important issue.
The optimization problem is presented and solved by means of dynamic programming
and using a quasistatic vehicle model approach. Different models are
presented in order to solve the problem with different assumptions. For one model
it is assumed an instantaneous gear shift maneuver and for another model the
gear shift maneuver requires a certain time to be done. For this second model, the
influence of taking into account a realistic way to compute the losses during a gear
shift maneuver is also developed and studied. Comparing the results provided by
the two models, this method to compute the gear shift losses in the optimization
problem has influence in the optimal speed profiles compared to the models that
do not take into account losses during the gear shift.
There are two engine models used in this project, a Willans approximation
engine model and a map based engine model. The differences between the results
from each engine model are explained and illustrated. Moreover, the influence of
the trip length is studied, stating that without a time constraint it has no influence
on the results. This investigation highlights the importance of selecting a suitable
discretization. A smart choice of the discretization is explained in order to have
the coasting solution achievable in the deceleration phase.
In order to study the results in different road situations, the optimization
problem is solved by changing the road topology. It is stated like in previous
research papers that keeping constant speed to drive through a hill is optimal, if
no braking is required to maintain constant speed. Finally some vehicle parameters
are changed in order to observe its sensitivity on the optimization results. Results
for several vehicle masses and engine sizes are illustrated and compared between
them. Regarding the engine size it is shown that it has a significant influence on
the fuel consumption as well as on the driving mission. |
