Valve and Manifold considerations for Efficient Digital Hydraulic Machines

This paper seeks to shed light on the topic of design and sizing of switching valves and connecting manifolds found in large digital hydraulic motors, also known commercially as Digital Displacement Motors. These motors promise very high operation efficiencies with broad operation ranges, which set strict requirements to the switching valves and the overall manifold design. To investigate this topic, the largest known digital motor (3.5 megawatt) is studied using models and optimization. Based on the limited information available about this motor, a detailed reconstruction of the motor architecture is developed in CAD. This
reconstruction is used to estimate the manifold flow losses of the complete motor with a quasi-static model, where all pressure chambers are simulated simultaneously. The pressure losses for the low and high pressure manifold are found to be small compared to the manifold pressure levels. A simplified flow model of the manifolds is established, and this result is carried on to the second study of the paper. In this second study, focus is turned towards switching valve sizing and actuator requirements. A single chamber model is developed, suitable for optimization of the switching valves when considering also the manifold flow losses.
A global optimization is conducted by use of the generalized differential evolution 3 algorithm, where the valve diameters, valve stroke lengths, actuator force capabilities and actuator timing signals are used as design variables. The results of this optimization confirms that high efficiencies in a broad operation range is possible, and gives the optimum valve sizes and actuator specifications for the reconstructed 3.5 MW motor simulated. Comment are made on these findings in relation to valve implementation.