| 摘要 |
A valve construction wherein the rotor shaft of a reversible electric motor is axially displaceable between axially spaced elements of a differential-screw system for driven displacement of a valve member. Each of these spaced elements is preferably a ball screw, independently co-operative with upper and lower regions of the rotor shaft, i.e., at the respective upper and lower sides of the rotor carried by the shaft. The valve of the invention and its control and drive system are contained within a housing which fixedly mounts (a) the ball-screw nut of the upper element of the differential-screw system and (b) the stator of the motor, so that motor-driven rotation results in axial displacement of the rotor and its shaft, pursuant to the helical advance lead or pitch of the upper ball-screw nut. The ball-screw nut of the lower element of the differential-screw system is (a) engaged to the shaft and (b) axially displaceable yet effectively keyed against rotation with respect to the housing; and this lower ball-screw nut is adapted to provide axial displacement control of a poppet-valve member with respect to its coacting seat, in a valve-body passage between inlet and outlet ports of the valve. Great mechanical advantage is achieved for relatively low motor-torque delivery, when the helical leads (or pitches) of the respective ball screws are in the same direction but are slightly different.
|
