| 摘要 |
998, 304. Fluid-pressure servomotor systems. BRAKESHOE INTERNATIONAL S.A. Oct. 18,1961 [Oct. 19, 1960], No. 37399/61. Heading G3P. [Also in Divisions H1 and H2] A pilot-controlled main-valve which is identical with that described in Specification 979,015 has the adjustable electromagnetic loading of the pilot valve effected by both direct and alternating current, the period of the A.C. being less than the response time of the valve. The pilot-valve solenoid 43 is connected in series with the thermistor 44 having a parallel resistor R T which provides a combined temperature-constant resistance. The D.C. supply at terminals 90, 91 is obtained from an A.C. source 94,95 through a rectifier arrangement comprising oppositely connected diodes D 1 , D 2 ; condensers C 1 , C 2 , a resistor R 1 and a further diode D 3 . The A.C. supply to the solenoid 43 is obtained from the source 94, 95 via leads 103,104 the former being connected to a variable resistor R 2 the adjustable tap 107 of which leads to the primary of a transformer T having the other primary terminal connected to the lead 104. The D.C. terminals 90, 91 are each connected to a variable resistor R 3 , R 4 , the taps 108, 110 of which are connected to one side of the solenoid 43; the tap 110 is also joined by a condenser C 4 to one side of the transformer secondary the other side of which is connected to the resistor R T . The taps 107,108, 110 may be ganged as shown whereby the A.C. voltage is reduced as the D.C.voltage is increased. The superimposition of the A.C. voltage on the D.C. D.C. voltage in the solenoid establishes a fluctuating flux so minimising the hysteresis of the core material. In a modification, the solenoid is energized through any of a number of fixed resistors of different values instead of the variable resistors R 2 , R 3 , R 4 . |
