الفهرس 
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Abstract
Due to the significant decrease in energy resources and increasing its cost in recent
years, governments and institutions concerned with the provision of energy saving
researches in various fields and in every possible ways to get energy saving by
simplest and least expensive means and tlJa1 what has been studied ia tius research.
In the present study, a small model of hydraulic system was designed to study using
new means to save energy consumed in the circuit by adding a frequency inverter to
control the rotating speed of AC motor, which drives the hydraulic circuit pump. So,
the pump discharge can be controlled. Also, a helical spring was used to act on the
hydraulic cylinder piston resulting a variable load with piston displacement.
A mathematical model of hydraulic circuit components was built to study the
different cases of saving energy consumption in the circuit theoretically by using
computer software for simulation (Simulink) included in program (Matlab).
In the theoretical model, the piston speed was decreased with the load increasing by
measuring the hydraulic cylinder pressure to control the frequency inverter which
decreases the pump discharge instead of opening of the relief valve. This behavior is
required in many practical applications such as in excavators and loaders arms, when
it raises the load to reach its unloading position on the trucks. Also, it is required in
the fork of electrical lifting cranes inside the stores and robot handling arms inside the
factories where” its moving speed is reduced gradually before reaching to the stroke
end to reduce the moment of inertia and to obtain high accuracy in reaching to the
desired location.
The theoretical cases were applied experimentally. The theoretical results were
compared with the experimental results. It was found that the theoretical and the
experimental results are convergent, which proves the effectiveness of the theoretical
simulation model.
The theoretical simulation model was utilized to eliminate the measuring of the
hydraulic cylinder pressure by calculating the values of hydraulic cylinder pressure
during the piston stroke and calculating the corresponding values of pump discharge.
These values were saved in the computer to control the frequency inverter. So, the
cost and problems of measurement were eliminated.
The simulation model by computer with the frequency inverter were utilized also, to
calculate the required values of pump discharge to achieve the desired values of piston speed during its stroke with the values of the force acting on the piston to
maintain the reliefvalve closed and it does not open during the piston stroke.
The calculated values of pump discharge were saved in the computer to control the
frequency inverter and thus, the resulting losses are due to friction and leakage only
and the maximum possible efficiency is obtained