Development and Analysis of Power Supply Systems Based on Common Pressure Rail Architectures in Hybrid Excavators

Construction machines, particularly excavators, contribute in a non-negligible percentage to CO2 emissions, which are considered one of the main causes of global warming. The excavators currently on the market have hydraulic architectures that are highly reliable from an operational standpoint but exhibit low energy efficiency, as only a small percentage of fuel is converted into useful net work for the actuators. The causes of energy losses are distributed among various components of the excavator hydraulic circuit, but the greatest contribution can be attributed to hydraulic distributors. For this reason, in recent decades, new types of systems have been studied with the aim of reducing energy dissipation during the excavator's operating cycle, and among these, the Common Pressure Rail (CPR) architecture has proven to be very advantageous in terms of fuel consumption. This thesis aimed to develop a model of a hybrid hydraulic excavator using the CPR system, with a primary focus on the design and optimization of its power supply. The study began by analyzing a Load Sensing hydraulic model of a 9-ton excavator, which was subsequently modified to obtain the innovative CPR architecture. To achieve system hybridization, gas accumulators were added and carefully sized. Furthermore, a control system was designed to maintain quasi-constant pressure levels within the accumulators, ensuring continuous operation while minimizing throttling losses. Subsequently, a CPR architecture based on a dual power supply system was studied, with the aim of investigating whether splitting the circuit could lead to further improvements in terms of fuel consumption and energy efficiency.  CPR architectures show significant limitations when operating at pressures very close to the system's maximum pressure; for this reason, two possible solutions were analyzed: the resizing of the accumulators and the introduction of a pressure intensifier. In conclusion, well-designed CPR architectures demonstrate their viability as effective alternatives to conventional hydraulic systems in excavators, showing significant fuel savings, mainly due to their inherent energy efficiency and ability to recover energy that is typically wasted in traditional systems.