Abstract
The paper presents the CFD model of a load sensing directional control valve. The model was validated experimentally in terms of pressure drop and flow force at different positions of the spool. The spool position was imposed manually by means of a micrometric screw and a load cell was used for measuring the flow force. The CFD model was developed with the CAD-embedded tool FloEFD®. The model has been proved to be very reliable in estimating the pressure drop, moreover quite good results were obtained also in the evaluation of the flow force. The CFD simulations were used to tune the coefficients of a lumped parameter model of the valve, so that such a model can be efficiently used for the simulation of an entire hydraulic circuit. Moreover, the CFD model has been used as design tool for attenuating the detrimental effect of the flow force. In particular, the width of the land upstream of the metering edge has an influence on the resultant force on the spool. If was found that it is possible to significantly reduce the flow force at maximum opening with a relatively small increment of the pressure drop across the valve.
Highlights
In mobile hydraulic systems used in many off-road vehicles, such as excavators, telehandlers or agricultural machines, the proportional directional control valves are the control elements for deciding the direction and the velocity of the actuators
The experimental tests were aimed at determining the pressure drop across the valve and the flow force acting on the main spool
The drawback is the increment of the inlet pressure due to the reduced flow area, it is possible to observe that a reduction of the land distance of a couple of millimeters allows a reduction of the flow force of more than 20% with an increment of the pressure drop of just 5%
Summary
In mobile hydraulic systems used in many off-road vehicles, such as excavators, telehandlers or agricultural machines, the proportional directional control valves are the control elements for deciding the direction and the velocity of the actuators. Despite in the recent years the trend is to move towards valveless systems [1, 2], most of the current machines still use a centralized hydraulic circuit with the load sensing principle [3,4,5]. Such a layout includes a variable displacement pump with a differential pressure control and a proportional valve with local compensator for each actuator. In this paper a CFD model developed with FloEFD of a load sensing valve is presented Both the pressure drop and the flow force have been simulated and measured in different operating conditions. A modification of the spool has been proposed for reducing the flow force with an acceptable increment of the pressure drop
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