A non-contacting sealing concept is presented which employs an elasto-hydrodynamic principle to reduce an initially large gap between seal and counter-surface to a small value for tolerable leakage. The seal is a circular ring, made of polymeric material to enable the intended radial deformation. It has basically rectangular cross section but two slightly conical surfaces: The outer girthed area in order to get a hydrostatic feedback from the pressure field in the sealing gap; and the lower pressure sided front face to limit the radial ring deflection. An analytical model based on a perfect geometry assumption demonstrates the function principle and analysis the role of main design parameters. An FEM model which can take complex ring deformation and partial contact of seal with its counter-surface into account shows a deeper insight to effects not covered by the analytical model and shows a reasonable agreement with experimental investigations made with a prototype.

For the realization of compact and lightweight digital hydraulic cylinder drives for exoskeleton actuation the hydraulic binary counter concept was proposed. This counter principle is based on hydraulically piloted switching valves which feature a hysteretic response with respect to the pilot pressure. In first prototypes of that counter bistable mechanical buckling beams realized the hysteretic response. Their performance suffered from high friction in the hinges and high local stresses. Furthermore, they require tight manufacturing tolerances not only of themselves but also of their bearing structure. In this paper, the usage of a permanent magnet concept to realize the hysteresis function in an alternative way is studied. The valve spool is made of a ferromagnetic material and is attracted or repelled by a permanent magnet made of a Neodymium-Iron-Bor. The expected benefits are lower friction, lower demands on manufacturing tolerances, and an easier assembly of the valve. To find an advantageous embodiment of this functioning principle ring or disc shaped magnets of different sizes are analyzed. The magnetic forces exhibited by these different magnetic circuit designs are simulated with the Magnetic Finite Element code ‘FEMM’. The quasi-static magnetic forces at different spool positions are computed. Magnetic saturation and remanence are considered in this analysis. The aim is to achieve the required force on the piston and, thus, ensure the valve’s functionality. At the same time, however, the valve should be designed as compact and light as possible. The Finite element simulations are compared with an analytical model which provides a compact understanding of the influence of the design parameters on the functional and non functional performance criteria.

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This paper presents a novel elastohydrodynamic sealing concept for the contactless sealing of spool valves. The basic goal is that the spool and the sleeve can be manufactured with standard mechanical engineering precision. High initial gaps are compensated for the elastic deformation of an elastomer seal driven by a self-regulating hydrodynamic effect. The final gap reveals a small leakage within the range normal for precisely manufactured spool valves and also features a low friction since a direct, solid contact between the seal and the sleeve is prevented. This sought-after behavior in ideal conditions is compared with imperfect situations by means of a simulation study and experiments. The simulation uses a Finite Element model which takes the seal‘s elastic deformation, the mechanical contact, the sealing gap pressure and the surface roughness into account. A simple prototype of the sealing system was produced to test its functionality in real conditions. Leakages of QLeak <= 18 ml/min @180 bar were recorded. However, an unexpectedly high friction occurred indicating an actual contact between the seal and the sleeve. The component roughness was identified as the cause of this behavior.