Patent GB-513624-A (GB)
Title: Improvements in magnetic compasses
IPC: G01C17/36
Filed: 1937-12-01
Abstract: 513,624. Fluid - pressure servomotor - control systems. HILLIER, A. (Sperry Gyroscope Co., Inc.). Dec. 1, 1937. Nos. 33210 and 33211. [Class 135] [Also in Groups XXXIV and XXXV] In a gyro-magnetic compass combination for craft, an air jet issuing from the directional element 27 of the magnetic compass controls a servomotor according to the angular relationship between the said element and the follow-up element therefor, which may comprise the craft itself, and the follow-up element is controlled at least in part from the gyroscope. The tendency of the gyroscope to wander is corrected by the compass without imparting the rapid oscillations of the compass thereto. The gyroscope may also have a follow-up member and the compass and the gyroscope then each act to adjust the reference member of the other as well as its own reference member. The invention is shown applied to an automatic pilot similar to that in Specification 416,813, [Group XXXIII], in which the rotor 1 of a directional gyroscope influences by means of a control or "pick off" disc 5 and an associated ported member 7, the differential pressure on a diaphragm unit 20 which controls a relay valve 21 in turn controlling a servomotor by operating a rudder 23. The output of the motive fluid supply pump 22 is controlled by a valve 17 with additional handles 17", 17<111> to adjust the supply to the elevator and aileron servomotors. A follow-up connection between the servomotor 9 and the member 7 comprises belt gearing 10, 11, worm gearing 14, 15, Fig. 4, differential gearing 13 and spur gearing (not shown). The third element of the differential gearing 13 is connected through worm gearing 75, 76 and spur gearing 72, 73 with two oppositely acting turbine wheels G7, 67', and is the means by which the compass adjusts the reference member 7 of the gyroscope The compass 24, Fig. 8, comprises a directional element 27 carrying permanent magnets 28 which may be arranged to pivot about a horizontal axis and provided with a hemispherical convex base 31 which is airborne by means of air rising in passages 30 in a pedestal member 26 with a corresponding hemispherical bearing surface. The bearing surfaces are maintained in proper relations by a screw 34 carried by an arm 35 on the pedestal 26 and having a jewel thrust bearing at the centre of curvature of the spherical bearing surfaces. A pin 36 co-operating with the jewel bearing 34a limits the angle of tilt. The jewel bearing may be replaced by a second air film bearing. The element 27 has a radial nozzle 38 supplied with air through a central passage 37 and normally directing an air jet between two spring-urged pivoted vanes 39. The latter have arms 41 adapted to close ports 42, 42' respectively communicating with annular channels 59, 59' in the pedestal 26. The channels 59, 59<1> are in permanent communication with pipes 32, 32' leading to a course-changing unit 58, Fig. 5, having a rotary cylindrical valve 62 operated through bevel gearing 64 by a handle 63. The valve 62 connects the pipes 32, 32' with pipes 65, 65' leading to turbine nozzles 66, 66', and can thus be used to suspend the compass control during turns. The element 27 carries an annular card 44 which moves between a bezel 48 secured below the transparent cover 49 and a disc 50 fixed to the bracket 35, the card, bezel and disc all having an index mark. Course-changing is effected by rotation of the pedestal 26 by worm gearing operated through a flexible shaft 55 by a knob 57 on the unit 58. The shaft 56 carrying the knob 57 operates through bevel and worm gearing 83, 82, 81 a compass card 77 co-operating with a fixed mark. The shaft 56 also operates through gearing 85, 86, 87 a vernier dial 84 also co-operating with a fixed mark, the two scales being visible through a cover 78. Relative movement between the element 26, 27 is limited by the arm 35. Such movement causes depression of one of the arms 41 and the difference in air pressure is communicated through pipes 32, 32<1>, 65, 65' to the turbine nozzles 66, 66' so that through the turbines and the gearing 72, 73, 75, 76, 13 the follow-up or reference member 7 of the gyroscope is adjusted and consequently the rudder 23 is moved to bring the craft back to the course set by the compass in which the members 26, 27 occupy their previous relative positions. The course may also be adjusted at the gyroscope by a knob 90. Air is exhausted from the gyroscope casing and hence also by means of the nozzles 66, 66' and pipes 65, 65', 32, 32' from the compass casing 24 by means of a passage 71. The air inlet of the compass casing has a filter 29. The two pipes 32, 32<1> may alternatively lead to the opposite sides of a diaphragm the displacement of which controls a servomotor, or the jet issuing from the member 27 may co-operate with one of two displaceable blades operating electric contacts which control an electric servomotor directly or through a relay. Flexible shafting cables, selsyns, or the like may be used to transmit the movements due to the gyroscope servomotor to the reference member of the magnetic compass. Specification 466,864, [Group XXXIV], also is referred to. According to the first Provisional Specification the magnetic compass may control its own follow-up member directly without the use of a gyroscope. Also if a double pivoted directional element is used, the compass casing may be gyroscopically stabilised. Further the relation between the gyroscope and its reference member may be adjusted by applying torques to precess the former in known manner. According to the second Provisional Specification the servomotor controlled by the gyroscope may be an air turbine. The reference member of the gyroscope may be used merely as a compass without provision for automatic steering.