Engineering Studies of The Control Structure of Electro-Hydraulic Pumps And Variable Axial Pistons

Pumps are often used in both industrial applications and mobile hydraulic machinery. In variable displacement pumps, the flow rate is dictated by the system requirements. The electro-hydraulic pump is a new integrated product, which comprise the combination of a pump and motor as a unit replacing the traditional connection with a shaft coupling. The pump is actuated without a rotating shaft utilizing a piston pump embedded in the motor. This brings with it some added advantages such as easy installation, reduction of noise in the system and decrease in power loss. In operation, the piston pump body is placed in the motor rotor, the air gap between the rotor and motor stator is filled with hydraulic oil, the rotor is directly rotated in the hydraulic oil and the control of the pressure and flow is achieved by means of the mechanical adjustment at the pressure valve. Electro-hydraulic systems with volumetric control offer a lot of advantages for pumping, due to the use of axial pistons with variable displacements possibilities. Several researchers have tried to describe the performance structure of these pumps in relation to efficiency; energy loss etc. without needed success. Previous studies have shown that using single loop suppress the steady state vibration, causes relatively good valve performance and reduces the impact on the control piston at the ends of a system’s strokes. The use of single feedback control loop reduces the pump production cost whilst maintaining reasonable performance useful for many different and acceptable commercial applications. In our research work we carried out some engineering studies of the control structures of these systems by investigating the characteristics, the convenience and dependence on control scheme and power operation. This paper focuses particularly on the automation of the control systems of these pumps. A system that enhanced the control of flow, pressure and hydraulic power without modifying the structure of the pump was designed, fabricated, tested and is hereby presented. We report on the relationship and dependence of control scheme on power operation and conclude that the use of either single or double feedback loop scheme is largely dependent of the demand and need to protect the pump drive motor.