Wheel loader optimal transients in the short loading cycle

A nonlinear wheel loader model with nine states and four control inputs is utilized to study the fuel and time efficient optimal control of wheel loader operation in the short loading cycle. The wheel loader model consists of lifting, steering and powertrain subsystems where the nonlinearity originates from the torque converter in the drivetrain. The short loading cycle, from loading point to a load receiver and back to the loading point, for a fork lifting application is described in terms of boundary conditions of the optimization problem while the operation is divided into several phases with constant gearbox gear ratios in order to avoid discontinuities due to discrete gear ratios. The effect of load receiver standing orientation on the wheel loader trajectory, fuel consumption and cycle time is studied showing that a small deviation from the optimal orientation (≈ 20 [deg]) results in up to 18 % higher fuel consumption in the minimum time cycles. Also, an alternative lifting strategy where for operation safety load is lifted only when wheel loaders moves forward is studied showing that this increases the fuel consumption of a typical 25 [sec] cycle only less than 2 %. The wheel loader path between loading point and load receiver is also calculated by optimization and analyzed for different cases. It is shown that when the load receiver orientation is not optimized and is set manually, the time or fuel optimal paths will differ from the shortest distance path, however when the load receiver orientation is calculated by optimization the fuel, time and shortest distance paths become identical.