Extended range proportional valve

Abstract

An extended range proportional valve which can control rates of mass flow over continuous low, intermediate and high ranges has a pilot member mounted on an armature of a solenoid which can be dithered onto and off of a pilot opening in a main valve member which seals a main valve opening to control mass flow rates over the low range by varying the duty cycle and/or frequency of a pulse width modulated current in the solenoid coil. Intermediate and high flow rates are achieved by dithering the pilot valve member with a duty cycle and/or frequency sufficient to raise the main valve member relatively short and relatively long respective distances from the main valve seat.

What is claimed is:  
     
         1 . A proportional flow valve for selectively controlling the rate of flow of fluid over an intermediate range of mass flow rates between a contiguous low range of mass flow rates and a contiguous high range of mass flow rates, comprising: 
 a valve body including an inlet port, an outlet port, and a main valve seat mounted in said body and having an inlet side exposed to said inlet port and an outlet side exposed to said outlet port,    a main valve member movably mounted within said valve body into and out of engagement with the main valve seat to close and open the valve, said main valve unit having a pilot opening extending therethrough and a pilot seat surrounding said pilot opening,    a pilot valve member movably mounted within said valve body into engagement with the pilot seat for sealing the pilot opening thereby preventing fluid flow from said inlet port to said outlet port through said pilot opening and out of engagement with the pilot seat for exposing the pilot opening thereby permitting fluid flow from said inlet port to said outlet port through said pilot opening,    a solenoid actuator having an armature on which said pilot valve member is mounted for movement therewith, and a coil for producing a flux as a function of an electrical current flowing therein, said armature being movable in response to said flux,    and alternating current electrical energizer means operatively connected to said coil for selectively inducing therein an alternating current having a characteristic with a magnitude selectable from a range of magnitudes for disengaging said pilot valve member from said pilot valve seat for a time long enough to cause sufficient flow of said fluid through said pilot opening for creating a differential pressure across said main valve member sufficient to disengage said main valve member from said main valve seat by a distance equal to a fraction of a diameter of said main valve opening for causing flow of said fluid through said pilot opening at a mass flow rate in said intermediate range of flow rates.