K.J. Rustamov
Tashkent State Transport University, Tashkent, Uzbekistan

Abstract: Optimization of the parameters of an excavator hydraulic drive-in order to minimize energy losses: this study proposes an integrated dynamic mathematical model. The proposed approach takes into account the interaction between mechanical dynamics, hydraulic processes and changing external loads, different from a regular quasi-static method. The model accounts for fluid compressibility, leakage, friction and hysteresis mechanisms of nonlinear soil resistance, as a set of coupled nonlinear differential equations. We present a multi-criteria optimization framework to enhance energy efficiency and the stability of such systems. The approach is validated by numerical simulations and experimental results, with a reduction of total energy losses by 20–25% and better system efficiency. The results verify that dynamic modeling is a dependable basis to design energy-efficient hydraulic systems in construction machinery

Keywords: hydraulic drive, excavator, dynamic modeling, energy efficiency, optimization, energy losses, nonlinear systems, MATLAB/Simulink, hydraulic cylinder, system dynamics.

Introduction: 
    Hydraulic drives are by far the most common power transmission systems in modern excavators due to their high-power density, flexibility, and adaptability to variable load conditions. Excavators operate in fast time-varying regions (i.e. variable soil interaction, operator control and working conditions leading to a variability of load) as they interact with the soil. This kind of variability results in complex transient processes that significantly affect system efficiency and reliability [1–3].

    The design methodology used for conventional hydraulic systems is mainly built on quasistatic paradigms. These approaches calculate forces and pressures under conditions of steadystate, and ignore transient phenomena such as pressure oscillations in the case where blood flow fluctuates or where dynamic load redistribution occurs. Although these simplifications lead to a reduction in calculation time, they usually incur loss of performance and energy losses within the system.

    This means in hydraulic systems the energy losses can be as high as 20–30% of total input power. This loss is mainly due to throttling in valves, internal leaks, viscous friction and the parameter selection of hydraulic components. It is a necessity in modern engineering to reduce these losses as we have entered into the dominion of energy efficiency [3].

    Recent work has focused on dynamic modeling. Dynamic models incorporate time and give a realistic view of actual system behavior. These models provide engineers with the ability to study how pressure pulsations and flow fields evolve through and between components in the system, under actual operating conditions.

    The second thing, the interaction of the excavator working equipment and soil. Soil resistance is non-linear and relies on parameters such as cohesion, density, cutting depth and velocity. Ignoring this interaction gives rise to erroneous load predictions and ultimately a suboptimal system design [16].

    Due to the interconnected nature of hydraulic systems, there is a requirement for integrated modeling. When mechanical, hydraulic, and control subsystems are considered separable components for study purposes, important information about the system behavior is lost. This calls for a consistent modeling framework which can account these interactions.

    The objective of this study is to create a coupled dynamic model of an excavator hydraulic drive. The model is built upon a common framework of mechanical dynamics, hydraulic flow equations and energy balance relationships. An optimization strategy is proposed on the basis of this model, to minimize energy losses without compromising required performance

    The uniqueness of the research is that several physical processes are incorporated within a single model and jointly optimized using an energy based optimization criterion. Results: The results help designing the methodology of hydraulic systems and provide practical tools to improve energy efficiency.