Fuel optimal controller for hydrostatic drives and real-world experiments on a wheel loader

In this study, we design a fuel optimal controller for hydrostatic drive transmissions (HSD) that significantly improves their fuel economy. Contrary to great proportion of the literature, efficacy of the controller is demonstrated by real machine implementation equipped with online fuel consumption measurement system. The main control objective of the devised controller is to minimise consumed fuel per travelled distance. Control commands are determined utilizing steady-state equations of the system, which facilitates real-time implementation. Dynamic situations are addressed with auxiliary functions running at higher frequency than the fuel economy part of the controller. The machine is a 5-ton wheel loader with pure HSD and no energy storage devices installed. In addition, all the components are commercially available. Thus, structure of the HSD and presented improvements in fuel economy are comparable to commercial machines and retrofitting existing drive-by-wire machinery with proposed controller will require little cost. The optimal controller is compared to a rule-based alternative that is based on a control method utilized in commercial wheel loaders. In autonomously driven drive cycles, measured total fuel consumption reduced up to 16.6% with the devised controller. In addition, the functionality of the controller is proven in extreme hill climbing tests.