Electronic Flow Control Valve (EFCV) with Pressure Compensation Capability
A new concept for an Electronic Flow Control Valve (EFCV) with pressure compensation capability is introduced. Based on its embedded sensors and micro controller, the EFCV can provide flow control without the need of load/displacement/speed information from the power elements, like hydraulic cylinders or hydraulic motors.
The flow controller inside the EFCV estimates the actual flow rate by the quasi-steady flow rate equation. Experimental studies show that the analytical model is not accurate enough to cover all operating conditions. Therefore, an experiment-based calibration method is suggested so that the electronic flow controller can provide accurate flow control across the working pressure and flow range. Finally, an innovative application of the EFCV, a self-sensing cylinder, is also presented.
Flow control is one of the most critical functionalities in the hydraulic industry. Traditionally, flow control is implemented via a proportional or servo valve. The principle of proportional and servo valves is briefly reviewed in the following. When current is applied into the coil of a solenoid (proportional valve) or a torque motor (servo valve), a corresponding electromagnetic force is generated. These forces could either directly stroke the spool (single stage configuration) or indirectly move the main stage spool via regulating the hydraulic pressures on the each end of the main stage spool (multiple stage configuration). The motion of the main stage spool leads to the variation of the orifice area. With a given pressure drop, the orifice area is directly associated with the flow rate. Modeling and control of proportional and servo valves is very rich in literature /Mer67/Jel03/Eat99/. However, most proportional and servo valves on the market are incapable of providing accurate flow rate control without feedback from the power elements or without the addition of mechanical pressure compensators. For example, consider a double-ended hydraulic cylinder with the piston area equal to 1 [unit]. If the required speed is 1 [unit], then the required flow rate is actually 1 [unit]. Without knowing the displacement/speed information from the hydraulic cylinder, neither the servo valve nor the proportional valve can correctly provide the desired flow. The reason for this is because the flow rate is related not only to the spool displacement (orifice area) but also to the pressure drop across the orifice. Therefore, feedback from the power elements is often required to achieve accurate flow control.