Patent ID: 8418723

Claim:
An electromagnetic proportional flow rate control valve, comprising: a valve body; a valve member; a movable core fixed to the valve member and guided so as to slide freely within the valve body; a spring configured to drive the valve member in a valve opening direction; and a solenoid coil configured to directly drive the movable core, and hence drive the valve member, in a valve closing direction in accordance with an increase in a driving current of the solenoid coil against a spring force of the spring, wherein a solenoid driving force itself is set such that an amount of change in a displacement of the valve member in the valve closing direction is reduced with respect to a unit change in the driving current in a region where a stroke of the valve member is short, and a cavity portion for magnetic field regulation, having an annular shape, is formed in an inner circumferential surface of the valve body, an inner diameter of the cavity portion is larger than an inner diameter of the inner circumferential surface of the valve body, which provides a magnetic circuit around the movable core, and the cavity portion is formed in a position extending to an inner circumferential step portion in the inner circumferential surface with which the movable core makes contact at a valve stroke end, wherein the cavity portion is configured to regulate the magnetic circuit generated by the solenoid coil for driving the movable core and to alter the solenoid driving force versus solenoid driving current curve, so as to reduce an amount of change of the solenoid driving force with respect to a unit change in the driving current in a region where a stroke of the valve member is short.