Abstract: The present invention is directed to an electro hydraulic control system wherein electric current output of the control is applied to an electric force motor to position a valve spool which in turn modulates fluid flow to a device to be controlled. The valve spool, either to accommodate manufacturing tolerance or to assure zero output flow, in the neutral position, has a flow dead zone which requires a substantial valve spool travel to initiate fluid flow through the valve. In the preferred device the manual control handle modulates the current output of the electric circuit which in turn proportionately modulates the position of the valve spool. The electric circuit is provided with resistance means which are selectively inserted into the circuit to assure that sufficient output current is provided to the force motor to move the valve spool that amount necessary to initiate fluid flow upon a small movement of the control handle to compensate for the fluid flow dead zone in said valve.

Abstract: In the preferred form, the invention disclosed herein provides a single servo control valve to modulate the flow of control fluid to a servo mechanism of a variable displacement pump wherein the single valve is provided with both a manual primary input and an electro-hydraulic secondary input which modulates the primary input. The servo valve is spring biased toward a neutral position with the manual input displacement command being applied to such servo valve through a resilient linkage. Also applied to the servo valve is a hydraulic signal which is electrically controlled to modify the displacement of the servo valve relative to the yieldably applied manual input.

Abstract: A capacitive differential pressure transducer for sensing the difference in pressure between at least two fluids includes first and second halves of a housing separated by a diaphragm which acts as a common capacitive plate to the capacitive differential pressure transducer with each housing half being identical and containing an interior chamber which is filled with a force transmitting fluid, a sensing capacitive plate located within the chamber and cooperating with the common capacitive plate, a fastening mechanism for holding the sensing capacitive plate tight against its housing half, sealing devices for sealing in the force transmitting fluid and terminals for connecting the common capacitive plate and the sensing capacitive plate to a sensing circuit.

Abstract: A fluidic servovalve is disclosed comprising a pilot stage valve having a pilot output for supplying a control fluid dependent upon a movable element, a boost valve responsive to the control fluid for supplying an output fluid, and a fluidic mechanical feedback connected from the output of the boost valve to the pilot stage valve, the fluid mechanical feedback having a ball-type motor responsive to the output fluid acting against it for positioning the movable element.

Abstract: A pilot stage for use in pilot pressure control applications includes a magnetic torque motor having an output torque in response to an input current, a flapper operated by the magnetic torque motor and responsive to the output torque, the magnetic torque motor being arranged to apply a resultant spring rate to the flapper, and first and second nozzles responsive to the output torque applied to the flapper for providing a differential output pressure proportional to input current, the first and second nozzles having a size sufficiently large to swamp out the resultant spring rate applied to the flapper so that the first and second nozzles apply a feedback force to the flapper sufficient by itself to substantially balance motor torque.

Abstract: A protection circuit for a semiconductor device such as a field effect transistor is disclosed having an oscillator which is connected to both the gate turn on circuitry and to the drain-source circuit of the field effect transistor for sensing the voltage of the drain-source circuit and for turning off cyclically the field effect transistor upon the simultaneous occurrence of a gate turn on signal to the gate of the transistor and high drain-source voltage.

Abstract: A gear pump having a pair of intermeshing gears which operate in a housing and which are supported by a pair of bearing blocks which are biased towards the side faces of the gears for effecting a seal. There is interposed, between each bearing block and the adjacent side faces of the gears, a flexible plate which on its outer side is pressure-loaded by pump-delivery pressure admitted to an area of the plate confined by a linear seal element that includes part-circular portions extending around the gear axes at a radial distance appreciably smaller than the radius of the root circle of the gear teeth.