Proportional flow control valve

Claim 1

A proportional flow control valve including a main flow control portion having a plunger slidably inserted into a valve body, said plunger being biased in one direction by a spring acting on one end thereof and a pressure of a chamber housing said spring and responsive to a pressure of an inlet port of said valve body acting on the other end thereof against said biasing force to regulate an opening of a passage from said inlet port to an outlet port of said valve body, and a restriction passage formed across said plunger, a pilot operation portion having a proportion solenoid fixedly secured to said valve body for producing a pushing force acting on a push rod, said pushing force being proportional to an input current to said solenoid and a pilot spool slidably inserted into said valve body and biased in one direction by a spring acting on one end thereof, the other end being urged to said push rod by said spring biasing, said pilot operation portion forming a variable orifice whose opening depends upon a deviation of said pilot spool, a pilot passage connecting a space in the spring side of said plunger to one side of said opening of said variable orifice and a drain passage connecting the other side of said opening of said variable orifice to a drain, in which a flow rate of fluid flowing said restriction passage and hence a pressure difference across said restriction passage is varied by varying said input current, to vary a position of said plunger to thereby control the flow rate, wherein said pilot spool is slidably inserted into a sleeve inserted into and secured to a valve bore of said valve body and said one end of said pilot spool is formed with a poppet portion which is able to contact with a valve seat formed in one end of said sleeve, a restriction passage is connected across said pilot spool, said drain passage is provided between a chamber in which said push rod is arranged and said drain, said poppet portion is in intimate contact with said valve seat when a pushing force of said proportion solenoid is zero, said pilot passage is connected through said variable orifice and said poppet portion to a spring chamber when said pilot spool is pushed by said push rod, and said pilot spool is formed, in a region between an annular groove formed thereon and connected to said pilot passage and a chamber connected to said drain passage, with a long land which is in contact with an inner surface of said sleeve.