This paper concerns a novel moving coil actuator integrated with a high-performance seat valve for use in Digital Displacement Machines (DDM), which is an emerging fluid power technology that sets strict actuator requirements in order to get a high energy conversion efficiency. Hence, the mechanical switching time must be in the millisecond range and the actuator power consumption must be in range of few tens of watts. The objectives are twofold: (i) to establish a proof-of-concept for the integrated actuator/valve that relies on several principles and mechanisms new or uncommon in fluid power applications and (ii) to formulate and validate a transient numerical model describing the actuator/valve. A coupled simulation model is established to predict the switching performance: transient electromagnetic finite-element-analysis with dynamic re-meshing is coupled to a set of ordinary differential equations describing the motion dynamics. In this way, the movement induced hydro-mechanical fluid forces caused by rapid acceleration of the valve plunger is coupled with the electromagnetic dynamics. The proposed model is compared rigorously against measurements obtained from a series of experiments based on a fully operational valve prototype. Comparisons of e.g. transient flux density, current, and plunger position show that the model describes both the actuator and the valve motion very well. Finally, results are presented when testing the prototype valve in fully operational DDM to establish proof-of-concept for the proposed valve concept. The actuator/valve is shown to be capable of rapid switching in less than 4 ms while only consuming approximately 45 W corresponding to 0.7% of the machine output power.

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The efficiency of digital hydraulic machines is strongly dependent on the valve switching time. Recently, fast switching have been achieved by using a direct electromagnetic moving coil actuator as the force producing element in fast switching hydraulic valves suitable for digital hydraulic machines. Mathematical models of the valve switching, targeted for design optimisation of the moving coil actuator, are developed. A detailed analytical model is derived and presented and its accuracy is evaluated against transient electromagnetic finite element simulations. The model includes an estimation of the eddy currents generated in the actuator yoke upon current rise, as they may have significant influence on the coil current response. The analytical model facilitates fast simulation of the transient actuator response opposed to the transient electro-magnetic finite element model which is computationally expensive. Fast simulation of the problem is crucial for optimising the switching valves, especially when using several design variables in an optimisation algorithm.

In this paper, a method is developed to estimate the parameters and motion of a moving coil actuator in the digital valves of Digital Displacement machines. The parameter estimation is carried out using three simple distinctive schemes from which certain electrical and magnetic parameters may be estimated. The parameter estimation method uses simple adaptation laws to update the moving coil actuator parameters used to estimate the valve plunger motion in an observer. The observer estimates the velocity using the back electro-motive force (back-emf) induced when moving the coil based on current and voltage measurements, but without any mechanical sensors. The valve movement of digital valves is confined by mechanical end-stops enabling estimating the valve position through integration of the estimated velocity relatively accurate. The observer depends on precise knowledge of the electrical dynamics to accurately estimate the valve motion. When the parameters are converged through adaptation the observer proves to be capable of tracking the valve motion relatively accurate, however some deviation occur at the mechanical end-stops of the valve. The parameter estimation method and the observer is implemented and tested off-line when using experimental data obtained from a newly developed digi-valve prototype which uses a moving coil actuator as the force producing element.