Patent GB-1401626-A (GB)
Title: Electro hydraulic actuator arrangement
IPC: F15B9/09
Filed: 1971-11-13
Abstract: 1401626 Fluid-pressure servomotor systems LUCAS INDUSTRIES Ltd 9 Nov 1972 [13 Nov 1971] 52818/71 Heading G3P In a fluid-pressure servomotor system, a hydraulic ram 10, 11 is isolated by a lock valve 37 when the difference between two input signals 62, 63 or between a feedback signal from the ram and a signal proportional to a calculated position of the ram exceeds a predetermined amount. The valve 37, which is normally held open by supply pressure in a line 36 acting on a plunger 51, is spring-loaded so that it is also moved to the closed position to isolate the ram if the supply pressure fails. A solenoid valve 54 is de-energized by a switch 56 operated by closure of the valve 37 so that when supply pressure is restored in the line 36 it is applied to both ends of valve 37 which thus remains closed until a manual switch 55 again energizes the valve 54. De-energization of the valve 54 also occurs in response to a signal either from a comparator for the signals 62, 63 or from a discriminator 72 which receives the feedback signal from the ram and a signal from an analog model circuit 71 of the ram control. The signals 62, 63, which may be command and reference signals respectively, are fed through rate limiting circuits 64, 65, the signal 62 being additionally fed to the model 71 and to a summing junction 69 which also receives the ram feedback signal. The junction 69 is connected through an amplifier 70 to a torque motor 32 for a pivoted jet 31 controlling a relay valve 30. When the valve 37 is closed, a valve 57 may be energized by a switch 58 to allow fluid to leak through a restriction 59 to an exhaust line 38 from the left hand side of the ram so that the ram piston 10 is gradually displaced to the left, for example under the influence of aerodynamic forces from the air intake ramps of a gas turbine. At the end of the stroke, spring fingers 18 are engaged by a clamp 21 to hold the piston, the clamp being automatically released when fluid under pressure is admitted to the left hand end of the ram. During the leftward movement of the piston, fluid flows from the exhaust line 38 through a non- return valve 61 to prevent cavitation in the right hand end of the ram cylinder. Summing junctions may be provided in the two inputs to discriminator 72 to compare the signal from circuit 64 with the feedback from the ram and with the signal from the model 71. Reduction of differences between the time constants of the latter and the ram control system may be reduced by providing a further analog model circuit (75), Fig. 4 (not shown) responsive to the output of circuit (64) and connected to a multiplying junction (82) through threshold and rectifier circuits (77, 78), a summing junction (79) receiving a reference voltage (80) and an amplifier (81) having a limited output. The gain of the loop (83) for the ram feedback signal may be set so that it is always less than that of the loop which includes the circuit (75). Alternatively, it may be set by the voltage on line (80) to have a medium value approximate to that of the loop for the circuit (75).