Look Ahead Control - Consequences of a Non-Linear Fuel Map on Truck Fuel Consumption
Consequences of non-linearities in specific fuel consumption (SFC) of
a heavy truck combustion engine are studied with focus on such small
road gradients that a constant speed is optimal if the engine torque
has an affine relation to fuelling. A quasi-static analysis gives
valuable insights into the intrinsic properties of minimization of
fuel consumption. Two objective functions are shown to give different
optimal velocity trajectories on a constant road gradient, when the
non-linearity in SFC is significant, a notation which is
quantified. For a significant non-linearity, when a constraint is set
to keep a final time, switching between two characteristic speeds is
optimal. Alternatively, if consumed time, in addition to fuel
consumption, is part of the objective function, then keeping to one
constant speed is optimal also for significant
non-linearities. However, the different optimal solutions still show
similarities, since for a certain significant non-linearity a specific
speed range determined by the characteristic velocities is shown to be
unobtainable for both optimality criteria. Similar results are
obtained for a full dynamic model including a realistic fuel map and
other realistic constraints.
Maria Ivarsson, Jan Åslund and Lars Nielsen
Proceedings of the Institution of Mechanical Engineers, Part D, Journal of Automobile Engineering,
2009
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