Internal Name: Single-Winding Solenoid
What’s New: Valve control solenoids that latch in both valve-open and valve-closed positions have required two windings and two sets of drive circuitry. Sagem has patented a solenoid using just one coil, but the dual latching function is achieved by a very inefficient routing of magnetic flux, making the solenoid considerably larger and much less efficient. Our system starts with a conventional yoke and winding topology but then wires the two windings is series and connects the series-pair to a single drive circuit. This approach may sound inefficient, but in the final analysis it is almost as efficient as the old approach and considerably cheaper.
Status: Issued in U.S. on April 20, 2004
Why: Electromagnetic engine valves have required two sets of everything but the armature: two magnetic yokes, two windings, two drive circuits. Elimination of one drive circuit represents a considerable cost saving.
How: Engine valve solenoids operate against unsymmetrical gas-force loads, so optimum design calls for restoring the armature with springs toward an off-center rest position. Suppose that two opposite yokes are energized in series from a common drive circuit. An armature resting off-center will initially be attracted toward the nearer of the two energized yokes. By rhythmically applying and removing the yoke excitation, the armature can be vibrated at resonance until it latches on one side. A reduction in the drive current will then cause the armature to release, with the spring pulling it toward the opposite side, where an increasing drive current will again latch the armature. Because the attraction force has a strong inverse dependence on distance from yoke to armature, there will be minimal force cancellation from the yoke on the far side.
Our patented approach is simply to connect the two windings of a conventional solenoid in series and drive them together. This obviously doubles the net winding resistance, but in the final analysis, this doubling has little effect on overall power consumption. In a practical system, the DC resistance for each winding is less than 0.2 ohms, so the problem is not with reducing coil ohms but with keeping circuit board and transistor resistances down to a level comparable with the winding resistance. By wiring the two windings in series and cutting the drive circuitry in half, a little extra investment in the remaining drive transistors partly offsets the higher coil resistance. Under dynamic conditions, the predominant losses are not resistive anyway, but come from a combination of magnetic hysteresis and eddy currents, so that overall system efficiency is almost the same with series-wound coils as with separately-driven coils.
Our methods as described in the “Sensorless Position Measurement” patent and the “State Space Controller” patent are expected to be applicable, in engineering practice, to this “Single Winding Solenoid.” This combination would offer major improvements in cost, performance, endurance, quiet operation, and reliability, as compared with other approaches.
Download: Single-Winding Dual-Latching Valve Actuation Solenoid U.S. 6,724,606 Seale, Bergstrom
Magnesense LLC Gorham,ME (207) 839-8637
©2009 Joseph Seale