Optimal Control of Wheel Loader Operation in the Short Loading Cycle Using Two Braking Alternatives
Abstract—The optimal control of wheel loader operation is
used in order to investigate the potentials for fuel cost and
cycle time minimization during the short loading cycle. The
wheel loader is modeled as a nonlinear system with three control
inputs and four state variables where a diesel engine generates
the power utilized for lifting and traction. The lifting system is
modeled considering the limitations in the hydraulics and also
the structural constraints. A torque converter is included in the
driveline model which introduces nonlinearities into the system
and operates in different modes affecting the fuel consumption.
The gear shifts during the loading cycle impose a discrete variable
into the system and this is taken care of by representing the
loading cycle as a multi-phase optimal control problem with
constant gearbox gear ratio in each phase. Minimum fuel and
minimum time system transients are calculated and analyzed
for two alternative cases one where the torque converter is
used to stop the vehicle before reaching the reversing point
and another where the service brakes are utilized. The optimal
control problem is iteratively solved in order to obtain the tradeoff
between fuel consumption and cycle time for both braking
alternatives. It is shown that although the engine operates at
lower speeds when the torque converter is used for braking, the
fuel consumption increases as higher torques are demanded from
the engine during braking. The increase in fuel consumption
is higher in faster cycle operations as the vehicle travels at
higher speeds and larger torques are required to stop the vehicle.
Wheel loader operators tend to use torque converter braking
alternative as it is more convenient; however, it accompanies
higher fuel consumption which highlights the importance of
developing intelligent and easy to use braking systems.
Vaheed Nezhadali and Lars Eriksson
2013
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Senast uppdaterad: 2021-11-10
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