Electrification of Load Handling Hydraulic Systems : With a Focus on Loader Cranes

Abstract: The work of this thesis is focused on creating the base for developing new hydraulic systems for mobile machinery tailored for an electric drive system. The loader crane is used as the principal application. With batteries being costly to invest in and having a much lower energy density than diesel fuel, the new systems must significantly reduce the energy consumption compared to the conventional system while keeping the performance in order to enable an electric drive. Exactly how much more energy efficient a new system must be will differ with the use case of the application, and with time, as components and the market develop. The aim is therefore to present a large number of new system concepts with different levels of energy reducing capabilities and complexity rather than proposing a single solution. In order to be able to evaluate and compare different system solutions, a drive cycle for the working envelope of the loader crane is developed. The drive cycle includes as much variance of the movement as possible in a short time, which is of practical use when testing prototypes. The task of finding new energy efficient solutions is started by performing a loss analysis on the reference crane. The analysis shows that losses due to simultaneously operated functions are significant, and consequently that multi-pump systems are of interest. A concept study that looks deeper into multi-pump systems as well as other loss-reducing concepts is carried out, and a large number of new system solutions with different energy reducing potential are presented. A promising concept is the two-pump system with open flow control, which is investigated in more detail by building and testing a prototype. The results from operation of the prototype highlight the challenge of achieving smooth control, but also that the efficiency is indeed improved compared to the refer-ence system. As this work is part of a larger research project, studies have been conducted on other interesting concepts as well, but with different applications. Results from these that are relevant to the loader crane case are discussed together with the results from the studies included in this thesis, in order to give a broad view on how a suitable system can be selected for the intended application.