An Electrohydraulic Load Sensing System based on flow/pressure switched control for mobile machinery

In mobile machinery, the existing load sensing system is featured by low response and oscillation tendency. As a promising alternative, the Electrohydraulic Flow Matching (EFM) system has the controllability advantages of fast response and good damping, but suffers from the flow mismatch problem leading to pressure impacts and low efficiency. To retain the controllability advantages and reduce flow mismatches of the EFM system, this paper proposes an Electrohydraulic Load Sensing (ELS) system via flow/pressure switched control, in which the pump displacement is controlled by the smaller output of the flow controller and the pressure controller. The actual flow requirement is calculated by the flow feedforward controller, while the pressure margin is kept as a desired value by the pressure feedback controller. The system linearization model is firstly established, and then the theoretical analysis was carried out to investigate the stability performance in the flow or pressure control mode. More importantly, the stability is analyzed under the condition of switching between flow/pressure controls. Using a converted hydraulic excavator, a test rig was constructed to verify the effectiveness of the switched controller. The performance of the existing EFM controller is studied as a comparison The result indicates that the pressure impacts caused by flow mismatches were avoided, and then the energy consumption was reduced. Meanwhile, the velocity performance is consistent with the EFM controller without loss of controllability.