EHAs in Mobile Machinery: Simulative Evaluation of a Control Scheme Including Load-holding Capability Using Active Hysteresis and Throttle Control
DOI:
https://doi.org/10.13052/ijfp1439-9776.2714Keywords:
EHA, 4Q-operation, electrification, active throttling, hysteresis control, recuperationAbstract
In recent years, the electrification of mobile machinery has advanced. One crucial issue is that the energy density of the associated storage solutions is lower, requiring more space on the machines or more frequent recharging. To compensate for this the hydraulic system must be more efficient and sustainable. In this context, the use of decentralized electro-hydrostatic actuators (EHA) shows high potential. However, they are not yet widely used. The reasons for this are likely higher initial component costs, worse dampening, and the high cost of implementing necessary control software.
This paper presents a simulation-based evaluation of an electro-hydrostatic actuator with a hydraulic high-speed unit intended for use in mobile machinery. The circuit layout was selected based on cost considerations and incorporates load-holding capability. Furthermore, the load-holding valves are a key aspect of the control scheme. They are used to introduce a small amount of active throttling on the outflow side of the cylinder while energy is supplied to it. This extends the load pressure range in which the hydraulic unit is pumping and enables full operational coverage of all working conditions, which would otherwise be impossible. The developed controller synchronizes the valves’ switching times with motor speed to enhance system performance and prevent excitation.
The controller is linked with a lumped parameter model of the hydraulic circuit and validated based on test cases that focus specifically on the quadrant switches, as well as on a measured dig and dump cycle. The results qualitatively demonstrate the excellent performance of the EHA, with mostly brief and minor velocity deviations during quadrant switching. The combination of the developed EHA and corresponding controller achieves good position tracking during the load cycle once drift due to inherent control delays is compensated for by a simple P-controller, representing the machine operator adjusting to the system response. This reduces the maximum RMSE of position deviation from 163 mm to 42 mm.
In conclusion, the results demonstrate the functionality of the developed EHA and encourage further investigation, particularly experimental validation, to confirm the findings.
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References
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