Internal Name: Quick Landing Solenoid
What’s New: To land quickly without high impact, a valve actuation solenoid must maintain a high rate of deceleration until nearly closed, then increase the magnetic attraction force rapidly on final approach to closure, overcoming the decelerating spring force and latching without re-opening. This quick increase in magnetic force normally calls for a correspondingly rapid increase in magnetic flux, demanding an impractically high drive voltage to the solenoid windings. This invention causes a rapid change in magnetic force, as a function of armature position, in a manner that simultaneously creates passive electromagnetic damping.
Status: Issued U.S. May 18, 2004
Why: While most magnetic valve actuation technology is focused on efficiency, soft landing, and high armature speed in the middle of transitions, practical actuators spend much of their transit time approaching landing and pulling away from release. Where quick transitions are needed from valve-open to valve-closed or vice versa, rapid changes in acceleration are required, for example, from rapid deceleration on approach to landing to greatly reduced deceleration approaching a force balance at landing. If an armature is rapidly decelerating when it lands, that second derivative of motion will inevitably continue long enough to cause the solenoid to re-open. The practical speed with which magnetic flux can be raised to latch and hold the armature is limited by coil drive voltage limits. Putting this in perspective, there is typically some natural increase in magnetic attraction, even at constant flux linkage, as the poleface gap approaches zero and fringing flux concentrates progressively into the attraction area between the pole faces. This natural change in force presents difficulties and advantages: difficulties because the force change is destabilizing and thus demands better servo control of motion; and advantages because the change hastens the transition from rapid deceleration to force balance at landing. Using techniques of this invention, the natural change of magnetic force with gap width is increased as a controllable function of gap, while undesired destabilizing force changes are damped by passive electromagnetic means that actually enhance active electromagnetic motion control.
How: To give a more rapid increase in magnetic attraction at constant flux linkage on approach to pole face closure, part of the pole face area is recessed slightly so that flux concentrates into a reduced area just before that smaller area closes into mating contact. A given total flux causes more attraction force when concentrated into a reduced area. This passive redistribution of flux can take place much more rapidly than changes in the total flux than links the drive windings. Passive shorted windings are used to slow the gap-dependent redistribution of flux, thus causing electromagnetic damping without introducing wear-prone mechanical damping components. By configuring the shorted windings in a figure-8 topology, this electromagnetic damping is created without causing the shorted-turn effect that would otherwise interfere with the active magnetic control process. Thus, the active and passive aspects of control work in a complementary fashion.
Download: A Solenoid for Efficient Pull-In and Quick Landing, U.S. 6,737,946 Seale, Bergstrom
Magnesense LLC Gorham,ME (207) 839-8637
©2009 Joseph Seale