This paper presents the results of a simulation study regarding the energy consumption of a load-sensing excavator hydraulic system and discusses the possible energy savings by eliminating the directional control valves. The energy consumption of the excavator hydraulic system has been studied for typical working cycles. For this purpose a coupled multi-body dynamics and hydraulic system model was developed in the Matlab Simulink environment, including a precise measurement-based loss model of the variable displacement pump. Power transmission and dissipation was calculated for each component and subsystem, including pumps, motors, valves, cylinders, transmission lines, and others. The simulation results show the amount of dissipated energy, indicating the major loss sources during various operations. Furthermore, the potential recoverable energy in the cycle is calculated, highlighting the prospective advantages of equipping the existing machine with new pump-controlled actuator technology.
In this paper a hydraulic hybrid system architecture for multi-actuator displacement controlled systems is analyzed. In particular the problem of optimal control for a hybrid excavator with four actuators is solved. The system states and controls are identified and classified into those which are cycle defined and those which are free to vary during the duty cycle. A state space model is derived for the hybrid system using the free states and controls and an outline of the algorithm used to apply dynamic programming to the system is described. The optimal controls and states for an aggressive truck loading cycle of the excavator are compared with suboptimal controls and states obtained using a rule based control strategy. Finally a comparison is made for the simulated fuel consumption of the system using optimal and suboptimal controls. A comparison is also made between the fuel consumption of the hybrid and non-hybrid excavators.
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