Optimal Speed Profiles for Passenger Cars with Gear Shifting
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
the gear shifts are assumed to be instantaneous, and for another model
used the gear shift maneuver requires a certain time. For the 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 of the driving mission, the
time constraint 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. Regarding the engine size it is shown that it has a
significant influence on the fuel consumption as well as on the
optimal speed profile.
Xavier Llamas
2012
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Senast uppdaterad: 2021-11-10
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