This invention relates to magnetic flux-shifting fluid valves. In valves of this description the shifting of a magnetic flux causes the movable valve element to move from one of its limit positions to the other of its limit positions.
The oldest type of magnetic flux-shifting fluid valves called for two magnetizing windings to effect required flux-shift and were bulky for this reason.
A flux-shifting fluid valve was suggested that required but one magnetizing winding, and furthermore had the advantage that moving the valve element from one of its limit positions to the other of its limit positions was effected by a magnetic pulse, and the valve element was thereafter held in its respective limit position by the latching action of a permanent magnet. This magnetic flux-shifting valve suffered, however, from the drawback of being unstable, i.e. mechanical vibrations or shock moved the valve element toward the permanent magnet and caused the valve element to stay close to the permanent magnet, while it was supposed to stay in a position remote from the permanent magnet.
An improvement of the above referred-to magnetic flux-shifting valve was suggested in U.S. Pat. No. 3,458,769; 07/29/67 to Harald Stampfli for "ELECTRICALLY CONTROLLED VALVE". To move the valve element upwardly, Stampfli applies a first d-c magnet winding having just sufficient ampere-turns to attract the valve element, or plunger, and magnetize the permanent magnet enough to hold the plunger, after removal of the attracting ampere-turns of the first magnet winding. A second d-c pulse in the same magnet coil is needed to get the permanent magnet sufficiently strong to keep the valve element safe in position. Releasing the plunger and/or avoidance of false closure is effected by demagnetizing the permanent magnet. This is accomplished by applying by means of an additional magnet winding ampere-turns of opposite direction, or opposite polarity, and of such lesser magnitude as to make it impossible to attract the armature, or plunger, and/or to remagnetize the permanent magnet in opposite polarity.
Stampfli thus discloses a magnetic flux-shifting valve that is potentially free from susceptibility to failure by mechanical shock, vibrations, and pressure transients at the price of introducing a susceptibility to failure when electrical parameters vary.
Other pertinent prior art is disclosed in U.S. Pat. No. 3,203,447; 08/31/65 to W. C. Bremer et al for "MAGNETICALLY OPERATED VALVE" and in U.S. Pat. No. 3,368,788; 02/13/68 to L. D. Padula for "MAGNETIC LATCH VALVE".
The first mentioned valve shows an over center toggle response which is the result of a movable permanently magnetized armature, or plunger, system whose limit positions couple attractively to either of two sections of an electromagnet with two equal limbs forming separate flux return paths, of which either one can complete the circuit if the armature is brought close thereto. This design can be made to work efficiently, but if a shock or transient fluid pressure peak in the absence of any holding current in the coil accidentally moves the armature or plunger to the opposite limit position, or even past center in that direction, the armature will then proceed to and remain at the wrong limit position.
The second mentioned valve, no less than that of Stampfli, provides reasonably secure freedom from false positioning due to shock or transient pressures. It, however, achieves this as a result of providing two permanent magnetic elements, one operationally unalterable and the other remagnetized in opposite polarity each time the valve position is changed. These two magnetic elements are required to be "chosen so they both establish the same flux levels in their remanent states". It is this equality of flux levels which purports to eliminate any holding flux in the armature and working air gap under the operating conditions calling for armature release. While such an equality of two fluxes can be achieved experimentally, it is practically compromised in in many ways, including, but not limited to, the following: manufacturing variations in the constituent magnetic properties of two totally different magnetic materials; dimensional variations in any part of the two magnetic circuits which include the said magnets, and particularly in any air gaps at joints; variations in temperature effects on the strength of the two different permanent magnets; the effect of stray magnetic fields or of proximate ferro-magnetic structures or machine parts, whose effect in modifying the field strengths of the two magnets may differ. If as a consequence of an accumulation of perturbation of the desired equality of flux levels some armature flux remains in the air gap, its attractive force will reduce the effectiveness of the return spring in returning the armature against the resistance either of fluid pressure or accidental friction. In extreme cases such undesired armature-air gap flux might even prevent release completely.
Besides the above susceptibility to operating difficulties, the structure of U.S. Pat. No. 3,368,788 has the further disadvantage of requiring for efficient operation a second coil surrounding the armature and air gap, in addition to the one for remagnetizing the appropriate permanent magnet.
Objects of the present invention accordingly include the following:
1. To provide an improved magnetic latch valve;
2. To provide magnetic latch valves which are free from the disadvantages and/or drawbacks of the prior art latch valves;
3. To provide a flux-shifting fluid valve which, when inadvertently moved from a desired state to a second state, will not remain in the second state, but will spontaneously return to the desired state, even when operating current is absent from the flux shifting winding;
4. To achieve said freedom from inadvertent perturbability without requiring precise mechanical or magnetic dimensions or quantities;
5. To achieve the foregoing with only a single winding location;
6. To achieve magnetically efficient operation such that the valve may be operated with momentary current pulses or may be left energized for long periods with voltages at the high limits of any particular coil rating without undue temperature rise;
7. To provide an integral valve structure performing both the function of controlling the flow of fluids and of being operated magnetically by flux-shift rather than a composite valve comprising a magnetic drive for valve means controlling the flow of fluids;
8. To provide a valve that includes two permanent magnets, one having a relatively high coercive force and the other having a relatively low coercive force, and of changing the magnetization of the latter in such a way that the fluxes of the two magnets are either in series across the working air gap, or in parallel through a diverting shunt path, but that the permanent magnet having the relatively low coercive force is never left demagnetized.