Control of a Fast Switching Valve for Digital Hydraulics

Student thesis: Doctoral ThesisPhD


Fluid power control is dominated by the throttling orifice. This is an inherently inefficient methodology that is responsible for low system efficiencies. The field of digital fluid power seeks to replace the throttling orifice with on-off valves and in the process greatly improve the efficiency of fluid power systems. One implementation of these on-off valves is the Switched Inertance Hydraulic System (SIHS) which operates in a similar way to Switched Mode Power Supplies (SMPS) in power electronics. In order to realise SIHS it is necessary to have valves that can switch large flow rates between high and low pressure supplies quickly. This report details the development of such a valve. It is demonstrated empirically that by using multiple grooves on a single spool a flow rate of 55L/min (at 10bar pressure drop) can be achieved whilst switching in <1ms. This is achieved through cascading a State Variable Feedback (SVF) controller with Iterative Learning Control (ILC) feedforward. The addition of novel stop learning conditions to the simple proportional lag compensated ILC scheme allow the valve to be tested to the limit of its abilities giving a minimum switching time of 0.5ms, where the limitation proved to be the range of the accelerometer used. Using the valve in a SIHS yielded promising initial results with efficiencies above 80\% being achieved across a range of switching ratios.
Date of Award8 Jun 2015
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorNigel Johnston (Supervisor), Andrew Plummer (Supervisor) & Andrew Hillis (Supervisor)

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