Porportional pressure control valve

Abstract

A proportional pressure control valve has a metering spool which selectively meters flow between an axial first port and radial second ports. The spool is axially reciprocable with a larger face toward the first port and a smaller face opposite from the first port, with a pressure equalization bore through the spool. A first spring extends between the smaller face of the spool and an armature and the armature is biased to a normal position by a second spring and also has a pressure equalization bore through it. Radial orifices are formed in the end of the armature facing the smaller face of the spool, and the end of the armature seats in the main bore in which the spool is seated. Passageways extend from the orifices to the second ports, and two selectively and variably energizable electromagnetic coils coaxially encircle the armature, one to draw the armature to one side of the normal position and the other to draw the armature to the opposite side. The normal position of the armature preferably biases the spool to an intermediate setting so that energizing the coil which is toward the closed position of the spool stiffens the response to the valve and energizing the coil which is away from the closed position of the spool softens the response of the valve. Energizing one or the other coil also varies the exposed area of the orifices to change the slope of the pressure-flow rate curve at the particular energization level for low flow rates.