AN ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 719 



plunger toward that coil. If an equal current is flowing in the other coil 

 the forces are balanced and the valve remains centered and closed. If 

 the currents in the two coils are not equal, the valve plunger is moved 

 until the differential magnetic force is balanced by the force in the 

 spring. In this manner the amount of oil flow can be regulated by vary- 

 ing the difference of the currents in the two coils. 



The coil housing is attached to the valve body by means of a non- 

 magnetic stainless steel adapter, N. The adapter isolates the steel 

 plunger and inserts from the magnetic flux. Because of the close fit 

 between these parts the presence of flux would cause sticking. A push 

 rod attached to the armature drives an aluminum piston, R, in a cylin- 

 der, Q. The small radial clearance between these parts is filled with a 

 viscous fluid so that a damping force is produced that is proportional to 

 armature velocity. 



Fig. 4 shows the complete assembly with manifolds attached, while 

 Fig. 5 gives an exploded view of the valve proper with all details in 

 their correct relative positions. Other views of the valve parts are 

 shown in Figs. 6 and 7. Fig. 8 is a view looking into the bore of the hy- 

 draulic assembly. This is the hole that is normally occupied by the 

 plunger. The ports formed by the internal shapes of the inserts are 

 clearly visible. 



CHARACTERISTICS OP THE ACTUATING MECHANISM 



The J-7 valve is designed to be driven by a push-pull dc amplifier. 

 When the amplifier has no input signal, the output current in each side 

 is 10 ma. When a signal is applied, the current in one side is increased 

 and that in the other is decreased; at maximum signal, the current in one 

 coil reaches 19 ma and zero in the other. The dissipation in each coil for 

 (luiescent current is about 0.4 watt, and the full signal power is 1.5 watts. 



The requirements that the frequency response must extend to dc and 

 that the control power consumption be held to a minimum suggest the 

 use of a dc push-pull output stage. The cjuiescent dc plate current is 

 used as the magnetizing current for the solenoids instead of providing 

 the field by a permanent magnet or separate coil. In spite of the small 

 output current available from the amplifier, relatively large forces and 

 a high resonant frequency are realized. This is accomplished by an effi- 

 (!ient magnetic circuit and low armature mass. The opposing solenoid 

 configuration described makes these features ])ossible. 



The magnetic circuit used in the J-7 valve has very low reluctance 

 for a sliding armature type actuator. This low reluctance is accom- 

 plished by providing ample thickness in the iron parts and employing 



