Performances analysis of a novel load-sensing hydraulic system with overriding differential pressure control

Abstract

The traditional load-sensing hydraulic system is an energy-saving fluid power transmission, which supply ''on-demand'' flow at a prescribed pressure margin greater than the highest load pressure of the system. In this paper, a novel loadsensing system that has a variable pressure margin through overriding differential pressure control via integrating an electro-proportional three-way type pressure reducing valve into the hydro-mechanical load-sensing valve is proposed. Also, a bond graph model taking into account the dynamic characteristics of load-sensing valve and load-sensing path is constructed, and three group experiments are performed to verify the validation of the model. Based on the bond graph model, a series of theoretical simulations are carried out to prove that the proposed Load-Sensing system enables a satisfactory balance between energy efficiency and rapid dynamic response over a wide range of operating conditions. In addition, due to overriding differential pressure control, mode selection and power limit regulation can also be achieved.

Energy-saving design of variable-displacement bi-directional pump-controlled electrohydraulic system

“…A compensator in a VDP establishes flow matching by adjusting the pump stroking through a swash mechanism, whose inclination λ is guided by the piston in the stroking cylinder and a spring-loaded bias cylinder. 27–29 These cylinders are shown in Figure 1 as SC and BC, respectively. The change in inclination from λ max to λ min causes the stroking to vary from the maximum for the rated pump flow at a cut-in pressure to near zero at the cut-off pressure yielding no outflow from the pump.…”

“…The electrohydraulic arrangement has an additional solenoid-operated pressure reducing valve (SOPRV), meant for active control. 29 High and low cut-in delivery pressures are set in the COV and the LSV, respectively, by manually adjusting a screw in each to vary the pre-compression of a spring sitting on one flat face of the respective spool. Each of these valves has a pilot line from the pump delivery up to the opposite face of the spool as well as to an open port at the valve periphery.…”

“…Although adequate margin is accepted as necessary for non-oscillatory good actuation dynamics, a high margin degrades the energy efficiency. 21,29 Seeking an optimum balance between these conflicting needs remain a major challenge in configuring an LS pump with the controller integrated with either the motor 29 or the pump. 24…”

“…In a novel compensator design with SOPRV for electrohydraulic load sensing (EHLS), the pressure margin was varied dynamically. 29 Figure 1 shows the SOPRV to feed what is called a pressure override on an additional area of the spool of the LSV on the opposite of the spring side. Since the override thrust opposes the pre-compression force on the LSV spool from the spring, this design ensures a variable pressure margin.…”

“…27,28 In some EHLS designs, the power limiting option is also integrated to the controller on the basis of the sensor feedback of the pump speed for handling a situation of possible power saturation. 29 Such saturation could arise in a mobile system, if the installed power capacity of the pump falls below the total demand to all the serving actuators over some period. Many upcoming requirements indeed call for exploring electrohydraulic compensators.…”