Simulation Based Design and Optimization of Digital Pump/Motors

Abstract

Current state of the art variable displacement pump/motors have high efficiencies when operating at high displacements. However, as the displacement of the pump/motor is reduced, the efficiency significantly decreases. Digital pump/motors aim to increase the efficiency and range of operation of the fluid power system by minimizing leakages, friction losses and compressibility losses. It is based on the concept of actively controlling high speed on/off valves connected to each piston cylinder displacement chamber. This work involves the development of a coupled dynamic model of a digital hydraulic pump/motor that is crucial for understanding the design tradeoffs and operating characteristics of the digital pump/motor. This simulation model can be used to characterize and predict the efficiency, define the dynamic response and flow requirements of on/off valves required to provide significant improvements in efficiency and dynamic response over traditional pump/motors, and perform design optimization studies. The model can analyze different operating strategies (flow limiting and flow diverting) and characterize the effects on pump/motor efficiency and flow ripple. The simulation analysis shows that the sequential flow limiting strategy yields the lowest power loss in both pumping and motoring and that small variances in the valve response would cause a significant loss of power.

Data-driven Adaptive Thresholding Model for Real-time Valve Delay Estimation in Digital Pump/Motors

“…To investigate the significance of valve timing on the performance of digital pump/motors, Merrill et al (2013) developed a multi-domain simulation model using MATLAB based Simscape. The simulation model was for a three and seven piston in-line pump.…”

“…By controlling the states of the valves at different shaft locations, pumping or motoring could be achieved, along with the ability to vary the displacement with the use of unique operating strategies. Several digital pump/motor operating strategies have been proposed in literature (Nieling et al, 2005) and four of them have been experimentally implemented, partial flow-diverting, partial flow-limiting, sequential flow-diverting, and sequential flow-limiting (Merrill et al, 2013). All the experiments and data presented in this paper were conducted using the partial flow-diverting operating strategy, so the interest of this paper, only this method will be described (others are described in Merrill, 2012).…”

Engineering research in fluid power: a review

“…This technique enables innovative solutions for mobile equipment systems (Wadsley, 2011). The piston digital pump/motors research has also been investigated in Purdue University recently (Merrill and Lumkes, 2010;Merrill et al, 2013). The advantages and disadvantages of the different operating strategies and the design trade-offs for digital pump/ motors were studied.…”

Control of a fast switching valve for digital hydraulics

“…The same architecture was used to extract power from a tidal current generator, allowing for a peak efficiency of 94.8% and average efficiency above 80%, over a year's operation [12]. Further work on digital pumps has also been carried out by [13], [14], [15] and [16].…”