Design, simulation, and validation of a bond graph model and controller to switch between pump and motor operation using four on/off valves with a hydraulic axial piston pump/motor

Bond graphs model the power flow in a system and the state equations are formulated directly from this graphical representation. As the paper demonstrates, bond graphs can quickly and accurately model and simulate the dynamics in electrohydraulic systems. Many applications use a hydraulic motor intermittently as a pump for dynamic braking, commonly through the use of directional control valves or pump/motor units capable of over-center operation. To reduce costs, improve efficiency, and decrease switching times, research has been completed performing dynamic switches between pump and motor operation using four high-speed on-off poppet valves (Lumkes and Hartzell, 1995). The bond graph model and simulation results are used to design appropriate control methods, which are then implemented in the lab. It was determined that an electronic variable delay circuit could be used to cycle the valves. This was constructed in the lab and the simulation and experimental results compared. Both methods demonstrate the possibility of efficient switches between pump and motor operations with switching times less then 150 ms. The controller delays are critical for efficiency and pressure spikes while also being highly dependent on system operating conditions. Thus an adaptive controller is required for satisfactory operation at all conditions.