GB1344373A - Electrohydraulic control of a hydraulic actuator - Google Patents

Abstract

1344373 Fluid-pressure servomotor systems MESSERSCHMITT-BOLKOW-BLOHM GmbH 29 July 1971 [21 Aug 1970] 35818/71 Heading G3P A hydraulic actuator is controlled by a spool valve 2, Fig.1, having one end subjected to pressure from a motive fluid supply 8 and the other end connected by a common line 4 to two or more servovalves 1 which also supply signals to an error monitoring system. The servovalves are operated by solenoids 16 and have their outputs from ports 12 connected to a comparator 13 which connects a pressure port 20 through an orifice 25 to a drain 23 when the pressures from the ports 12 are unequal. The change in pressure operates a warning device or a safety circuit. The circuit shown in Fig. 1 may be duplicated and the outputs from the two comparators fed to an AND gate so that the system continues to operate if only one circuit develops a fault. A further modification is shown in Fig.3 in which the outputs from three comparators 59 are fed to an AND gate 60 so that no safety switching operation occurs until two spurious servovalve output signals are produced. The warning device shown in Fig. 4 may be interposed between each comparator and the AND gate when the circuit of Fig. 1 is duplicated and has outlets 67 and 68 connected to the comparator and the AND gate, respectively, while a third outlet 69 supplies the servovalves from a pressure source 65. When the comparator reduces the pressure in outlet 67, a spool 71 is moved to the left by the supply pressure so that the servovalves are connected to a drain 66. An orifice 72 prevents pressure fluid flowing to drain through the comparator. The spool 71 is returned by the spring 73 when a solenoid valve 70 is de-energized for a brief period. The supply to the servovalves may alternatively be discontinued by de-energization of the solenoid valve 70. In modified forms of the warning device, the spool is first displaced by flow through a restrictor, the solenoid valve is replaced by a pair of valves or by a valve which can be energized to move to either side of a neutral position. In the last modification, a delay valve is also provided to isolate the line 67 from direct connection with the pressure medium inlet while the spool is re-set. The line 67 is recharged through a restrictor and the spool is retained in the re-set position only when the outlet pressures from the servovalves are again uniform. The lines 68 from the warning devices may be connected as shown to the duplicated AND gate of Fig.17 in which failure of pressure in either the upper or lower pair of lines 68 causes loss of pressure in the other pair through lines 131 so that springs 126 operate safety switches 128 through plungers 122...125.