Heavy equipment: Electrohydraulic flow matching increases hydraulic system dynamics

Rexroth says Electrohydraulic Flow Matching (EFM) is next generation of flow-sharing controls.
By Control Engineering Staff July 24, 2008

Bethlehem, PA —In conventional flow-sharing (LUDV) systems, the pump controls the supply pressure of the valve control via a hydraulic-mechanical mode. Consequently, the pump reacts to every change of pressure made by consumers. Bosch Rexroth says its electrohydraulic flow matching (EFM) system replaces this pressure control loop with a new kind of control. The EFM control generates the adjusting signals for the pump at the same time the valves are controlled, thereby ensuring that adequate flow is made available. The company says this system makes hydraulics react a lot faster to the user’s commands, making controls easier to operate.
EFM, the company says, also improves the extent to which energy is used, specifically in machine operating states where hydraulic consumers’ demand for flow is smaller than the pump’s maximum flow capacity. As long as demand stays below the implement hydraulics’ maximum capacity, the EFM saves energy by up to 10%, depending on the operating point. The company says savings are based on the fact that pressure losses between pump and valve adjust themselves according to the operating point. They are therefore smaller than losses created by hydraulic-mechanical flow-sharing (LUDV) solutions due to rigidly adjusted pressure surpluses.
The system also achieves an improved toughness in closed loop technology, the company continues. Particularly in critical operating points such as fast changes in set-point values or serious changes in load pressure, this toughness has a positive effect due to a decreased vibration tendency. It achieves this advantage because the pump is no longer operated in the pressure control loop, but instead in as an electro-proportional variable pump an open control chain. Consequently, fewer breakdowns and mutual influences occur.
The EFM system is based on Rexroth components that include a variable pump with an electrohydraulic pilot control, such as the A10VO, an electronic joystick (such as the company’s THE series), an electrohydraulic load-sensing valve (SX14NGE or M7), as well as a Bodas controller (for instance the RC36-20) with the expanded Bodas Vac (valve control) software to which the specific EFM function has been added.
— Edited by C.G. Masi , senior editor
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