Patent GB-612804-A (GB)
Title: Improvements in or relating to electro-hydraulic control systems
IPC: G05D1/02
Filed: 1941-12-10
Abstract: 612,804. Fluid-pressure servomotor-control systems. HILLIER, A. (Sperry Gyroscope Co., Inc.). Dec. 10, 1941, No. 15929. [Class 135] [Also in Groups XXXIII, XXXV and XXXVIII] In a system for controlling aircraft elevators, ailerons, &c., the valve of a hydraulic system of the kind described in Specification 538,526 is operated by the receiver of an electric signalling system, the control signal comprising a component proportional to the displacement of a control handle or to the difference between the displacements of such a handle and the control surface and a component depending on the rate of change or acceleration or higher time derivative of such displacement or difference. The displacement signal may be obtained from the receiver of a selsyn system operating as described in Specification 417,995, [Group XXXVIII]. The invention is applicable to a system in which power assisted manual control can be substituted for automatic pilot control. First arrangement, Fig. 1. The control handle 1 unbalances a bridge supplied from two of the phases of a three-phase source and supplying a pair of tubes 10, 10<1> fed from the same phases. A battery 12 in conjunction with a condenser 11 provides an additional signal proportional to the speed of the handle. The signal is passed on to another pair of tubes 15, 15<1> fed from another pair of phases with the aid of condensers 17, 171. The size of these condensers and of grid resistances 18, 18<1> may be chosen so that the A.C. displacement signal is passed freely and the D.C. signal corresponding to the speed is passed in part and in part produces a signal proportional to acceleration. The output of these tubes is taken to the windings of a receiver comprising windings 21, 21<1> which are connected so that the flux due to both of them flows in the same direction through a pivoted armature 22 shaped in relation to the poles so that the air-gap does not vary as the armature rotates. This armature is coupled to the valve of a hydraulic servomotor arranged as described in Specification 538,526, so that the force exerted by the motor is proportional to the force exerted on the valve. The iron of the receiver is arranged to, be magnetized normally to the middle, of the straight part of the magnetization curve so that the torque is proportional to the difference in current in the two windings. As an alternative to the bridge arrangement, use may be made of the pick-up device described in connection with a gyro compass in Specification 480,] 15, [Group XXXVIII]. Second arrangement, Fig. 2. In this case, a gyro 31 unbalances one bridge and the control surface 46 unbalances another, the difference between the outputs being applied to a pair of rectifier tubes 40, 40<1> via transformer windings 39, 39<1> in series with direct voltages developed across resistances 43, 43<1> by a differentiating circuit comprising a pair of tubes 38, 38<1> having their plate circuits shunted by condensers 41, 411 which eliminate the A.C. displacement signal component. Voltages develop across resistances 43, 43<1> proportional to the rate of change of the displacement signal. The anodes of the rectifier tubes 40, 40<1> are directly connected to the grids of a pair of balanced output tubes 44, 44<1> fed from the same A.C. source as the tubes 40, 40<1> for the control of a receiver like that described in the preceding paragraph. Power assisted control. In a further arrangement, Fig. 3 (not shown), and Fig. 4, the systems such as those previously described are controlled by means of a " bank and climb " gyro or, on the operation of a change-over switch, by means of a control stick 58, Fig. 4, in which is mounted a hand wheel 57. The wheel is rigidly connected to a cross-shaped armature 71 coupling a normally excited, centrally arranged primary winding differentially to four secondary windings 69, 69<1>, 70, 70<1>, Fig. 6, for providing the control signals. These windings are carried bv a sleeve 65 mounted in ball bearings on the control stick and carrying the pulley 66 of the aileron control. The hand wheel is coupled to the sleeve 65 and control. stick by means of a sleeve 63 which provides a small torsional " give " and a diaphragm 64 which provides a small axial " give " when the controls are actuated so as to provide the necessary relative motion between the armature and coils of the pick-up device to control the servo system without interfering with full manual control in an emergency. Similar arrangements may be provided for giving power assisted rudder control. Specifications 416,813, [Group XXXIII], 612,810, 612,897, [Group XXXVIII], and 612,898, [Group XL (c)], also are referred to.