A coupling device particularly adapted for use in steering apparatus in aircraft to give a displacement of a driven member in accordance with the displacement and rate of displacement of a driving member comprises a resilient mechanical connecting means and a superimposed hydraulic connecting means with an open but adjustable valve for modifying the controlling effect in accordance with the speed of the driving member. Further orifices adapted to be masked at times by a system of sleeves or the like and fitted with spring loaded valves or equivalent devices' limit the effect of the superposed hydraulic connecting means. In the form shown, a slidable driving member 2 is adapted to act on a slidable driven member 3 through a pile of Belleville spring washers 5 in each direction of movement. The member 1 is provided with a central piston 24 slidable in a fixed casing 25 and at each end is hollowed out to form cylinders 19, 20 housing pistons 14, 15 on the member 3. These pistons are held against shoulders 19, 17 on the members 3 by nuts 13, 18. The central part of the member 2 is formed with passages 21, 22 adapted to establish communication between the inner ends of the cylinders 19, 20 and the chambers 32, 33 on either side of the piston 24, the outer ends of the cylinders being open to atmosphere through ports 40, 41. The central part also had symmetrical passages 23 provided with spring loaded ball valves 50 adapted under certain circumstances to connect the two sides of the piston 24. The outlet ports from these valves may be masked during part of the travel of the member 2 by sleeves 28, 29 supported by the casing 25. The chambers on the two sides of the piston 24 are connected through a conduit 36 fitted with an adjustable throttle 37 and a connection 38 fitted with a non‐return valve 39 is provided to connect the device to a source of fluid under pressure. A movement of the driving member away from the neutral or mid‐position tensions the spring washers either by removing the washer 6 away from the fitting 17 or by sliding the sleeve 11 along the rod 9. At the same time hydraulic pressure is generated in one of the chambers 32, 33 and is communicated through passage 21 or 22 to chamber 19 or 20 to act on piston 14 or 15. Should this pressure exceed that corresponding to the loading of the valves 50, 54 fluid passes through one of the valves from one chamber to the other, otherwise fluid passes at a restricted rate from one chamber to the other through the pipe connection 36 and adjustable throttle 37. During the return movement to the neutral position the valve 50 or 54 which otherwise would be operative is prevented from operating by sleeve 28 or 29 closing the associated valve discharge port.
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