Torque Control of a Hydrostatic Transmission Applied to a Wheel Loader

A hydrostatic transmission enables continuous, bidirectional transfer of torque. Thereby, no friction clutch is required, which makes it ideal for construction machines with high torques and many stop and go movements. However, the controller design is challenging mainly because of the inherent nonlinearities and the hard system constraints. Furthermore, the systems overactuation has to be exploited to avoid operating states with bad efficiencies. In this paper, an optimization-based control concept for real-time application on a commercial electronic control unit (ECU) is presented. Based on a reduced-order mathematical model, an optimisation-based feedforward control and a flatness based feedback control with a nonlinear compensation is derived. The concept is successfully evaluated for a wheel loader on a test track where the desired driving torque is followed and simultaneously the overall efficiency is maximised.