Novel solutions for tracked crane electrification

Nowadays regulators, industry and academy are pushing toward electrification to reduce air pollution and energy consumption in a variety of sectors, including non-road mobile machinery. All-electric heavy-duty equipment is already available, not just due to lower energy consumption and emissions, but as there is a demand for equipment that can operate in noise-sensitive locations and indoors. Often electrification of these machines is achieved just substituting the internal combustion engine with an electric motor, which is not optimal. This work aims to propose novel solutions for a better exploitation of the advantages offered by electric motors. Some novel solutions to address the energy efficiency issue typical of traditional fluid power systems were identified in literature, but there is still a lack of proposals for mobile cranes. The suitability for mobile cranes of the identified solutions was evaluated and two of them, decentralization and electronic load sensing, were selected for a deeper study. Decentralization is realized splitting the centralized hydraulic system in separated subsystems, for which electric-driven pumps are the most practical solution. In the first part of this work, a simulation model for fast energetic analyses of centralized and decentralized system was developed. Following experimental tests conducted on a prototype crane, the developed model was used to compare energy consumption of the two concepts through some operating cycles. The study highlighted that savings offered by decentralization are strongly-dependent on the considered operating conditions and on the low-speed operation ability of the pumps. Moving to a decentralized system, thus, must be carefully evaluated, due to the higher initial cost. As for electronic load sensing, an algorithm based on accurate control of fixed-displacement pump speed to achieve pressure control is proposed. Controllability offered by electric drives is exploited to realize a behavior similar to the one achieved with more complex variable-displacement pumps, which often are not adopted on small-size, low-cost machines. The proposed pressure controller is tuned relying on an purpose-built analytical model that takes into account the dynamics of the speed control loop. Compared to the traditional fixed-speed, fixed-displacement concept adopted on small-size machines, which makes use of unloading valves to control pump pressure, the proposed approach saves approximately 10% energy, without introducing costly components.