A hydraulic control system for use in machine tools, construction machines, hoists and the like, with a driven unit the hydraulic circuit of which is controlled by one or more electromagnetically positioned slide valves, and with an arrangement for automatically regulating the velocity of the hydraulic drive unit regardless of fluctuations in the pressure of the oil supply and similar disturbances. The regulating arrangement includes a potentiometer mechanically controlled by a flow meter interposed in the hydraulic circuit; and an electric comparator the inputs of which are connected to the potentiometer and to a desired-flow-value selector, respectively, and the output of which controls the valve electromagnet(s). In this manner the difference signal developed by the comparator is used to change the setting of the valve in a correcting sense. Several implementations for this regulating circuit and for the design of the flow meter and the valves are disclosed.
A bi-directional fluid flow transducer includes a hollow cylindrical housing which slidably receives a movable hollow cylindrical core which coaxially receives a fixed rod or valve member. A pair of springs are biased to urge the core to a neutral position. The core is displaced from its neutral position in the direction of fluid flow by an amount linearly proportional to the rate of fluid flow. An LVDT coil and circuit generate an output signal which represents the amount and direction of core displacement.
A fluid flow sensor includes a housing defining a flow path for fluid flow therethrough. A valve member slidably engages the housing and moves with respect to a fixed cylindrical metering member in response to fluid flow through the flow path. A spring biases the valve member to a no-flow position. A portion of the valve member engages a seat to prevent reverse fluid flow. The metering member receives one end of the valve member while a reluctive displacement transducer is received by a bore extending into the valve member from the other end.
A marine speedometer system is disclosed which utilizes a short pitot tube or air column. The speedometer system includes an inlet having a short air column, a transducer, a control circuit, and a display. The electric signal from the transducer is representative of the pressure in the short air column. The control circuit preferably utilizes a microprocessor and a look-up table to generate a display signal in response to an electric signal from the transducer. The look-up table includes T-Buoy values and count values. The count values are used to drive a frequency signal for an air core meter. The display provides a needle and a metered background which is easy to read. The microprocessor is coupled to receive calibrate up and calibrate down signals. The microprocessor causes the needle to jump when it receives a signal to provide feedback to the driver. The microprocessor includes an auto zero subroutine which automatically calibrates the speedometer at start up.
An apparatus, according to the invention, detects the relative speed of the apparatus with respect to the fluid into which it extends. The apparatus includes a streamlined body portion having an upper end, a lower end, a front edge, a back edge, and a pair of sides. A conduit extends through the body portion and is exposed to the fluid at an orifice located beneath the fluid line. The other end of the conduit is coupled to a pressure transducer which produces an output proportional to the pressure acting on the orifice and thus proportional to the speed of the apparatus relative to the fluid. This apparatus can be connected to an appropriate speedometer and is particularly useful for measuring the speed of a watercraft to which the apparatus is mounted.
