EP3011571B1 - Self-holding magnet with a particularly low electric trigger voltage - Google Patents

Description

The invention relates to the field of electromagnetic actuators.

So-called self-holding magnets are generally known and used (see e.g. E. Kallenbach, R. Eick, P. Quendt, T. Ströhla, K. Feindt, M. Kallenbach: Elektromagnete (2008), chap. 9.2 Polarized magnets, p. 298 ).

These are permanently polarized, switchable electromagnets: With the help of permanent magnets, self-holding magnets can hold a (magnetic) armature stable in at least one position, with a counter-excitation that can be generated by means of a coil ("release coil"), which makes the permanent magnet generated field is compensated so far that the anchor position is no longer stable. It is known to provide a magnetic shunt in self-holding magnets. With regard to the permanent magnetically generated flux, the shunt is connected in parallel with the working air gap or gaps of the armature. However, they are connected in series with regard to the flux generated by the coil. The shunt reduces on the one hand the electrical power required to compensate for the field generated by permanent magnets; on the other hand, the permanent magnet or magnets are protected from demagnetization. Often times, self-holding magnets are combined with springs and together with these they form electrically triggered spring accumulators. The spring thus acts on the armature in order to open the working air gap or gaps. The self-holding magnet is designed in such a way that if the air gap falls below a certain minimum, a residual air gap remains to hold the spring in the tensioned state.

By energizing the trip coil, counter-excitation can be generated in such a way that the magnetic holding force is less than the spring force and the armature starts moving, whereby the elastic energy previously stored in the spring can be used to perform work. Such "magnetic spring accumulators" are used, for example, as a trigger, in particular residual current releases, used in electrical switching devices, for example circuit breakers. It is also generally known to be used as a residual current release in residual current circuit breakers. In addition, they are used in locking units ("locking magnets"), whereby the tensioning can take place mechanically or by reverse excitation of the magnet with the aid of the coil (excitation instead of counter-excitation as when triggering). In order to facilitate the magnetic clamping, use can be made of influencing the characteristic curve, which can result in much higher force constants when the working air gap is fully open.

A self-holding magnet according to the preamble of claim 1 is from WO 99/33078 known. Further self-holding magnets are off DE 10 2011 014192 A1 , DE 943 479 C , U.S. 6,130,594 A , GB 765 411 A , U.S. 3,444,490 A and U.S. 2,130,870 A known.

A low trip current is particularly desirable in battery operated locking units. The same applies to the releases of electrical switching devices, in particular for residual current releases of self-supplied low and medium voltage switching devices. Trip devices, especially residual current trip devices, should also react as quickly as possible, that is to say have short dead times. Such triggers must also be designed in such a way that excessive counter-excitation does not inadvertently prevent or slow down the triggering inadmissibly: An overcompensation of the permanent magnetically generated field and thus the associated holding force can namely cause a holding force to develop as a result of the Result in a linked flux tripping current, so that the self-holding magnet triggers delayed or not at all. Trigger magnets must of course be quite insensitive to vibrations, unintentional triggering as a result of blows or other vibrations should be made very difficult, which is why the desired high electrical sensitivity - i.e. the desired low trigger currents or outputs - cannot be easily achieved by magnetic holding force and spring force are aligned as closely as possible.

The inventive task is thus set: self-holding magnet with spring ("magnetic spring accumulator") which, compared to known types, has a particularly low electrical release power.
According to the invention, this object is achieved by a self-retaining magnet according to claim 1. Preferred embodiments of the present invention are the subject of the subclaims.

The invention is based on a self-holding magnet with a spring, the self-holding magnet having a stop for the armature and a magnetic shunt. In the tensioned state, the armature of the self-holding magnet is held permanently magnetically against the spring force, the working air gap (or the working air gap, if an armature with several pole faces is used) is closed except for a (working) residual air gap given by the stop, whereby the frame of the self-holding magnet (as an anchor counterpart) itself can serve as a stop, if necessary with an anti-adhesive film or similar.

The shunt has a particularly low reluctance: According to the invention, the shunt is to be dimensioned so that its reluctance in the clamped state is of the same order of magnitude and as large as possible as the reluctance of the (working) residual air gap (or the sum of the reluctances of the remaining working air gaps, provided that several working air gaps are connected in series; this is the case, for example, with pole plates where two poles act on the same surface).

With regard to the permanent magnetically generated flux, the working air gap (s) and shunt are magnetically connected in parallel. However, they are connected in series with regard to the flux that can be generated by the coil. As mentioned, the reluctance of the shunt is of the same order of magnitude as the reluctance of the (working) residual air gap and, if possible, the same size as this. Flux-carrying parasitic residual air gaps must also be taken into account according to their arrangement. In any case, an electrical counter-excitation of the self-holding magnet leads to the flux density in the Working air gap (s) is reduced while the flux density in the shunt increases.

The shunt partial circuit can also be designed with regard to the flux-carrying cross-sections occurring in it so that due to magnetic saturation the reluctance of the iron circuit "seen" by the coil increases with increasing counter-excitation so that even a comparatively strong counter-excitation does not hold the armature against the spring force able (because the flux density in the shunt increases with increasing counter-excitation). For this purpose, the shunt pitch circle can have the smallest effective cross section possible over a certain (minimum) length. The shunt can be defined geometrically; however, it can also be formed from a soft magnetic material with a comparatively low (macroscopic) permeability, in particular a sintered material with a distributed air gap, which can simplify production.

In contrast to known self-holding magnets, a self-holding magnet according to the invention also has a resilient stop.

In conventional self-holding magnets with springs ("storage springs"), the stop can be regarded as rigid to a good approximation. In these drives, the armature only starts to move when, as a result of the electrical counter-excitation, the magnetic holding force falls below the acting (releasing) spring force of the storage spring. This is not the case if the stop is able to compress itself. However, in order to meet the requirement for low tripping capacities with sufficient insensitivity to vibrations, the residual air gap produced with the help of the stop should be small. Accordingly, the resilient stop should be of suitable rigidity: On the one hand, the stop should be much stiffer than the "first" spring of the self-holding magnet ("storage spring") serving for elastic energy storage. On the other hand, the resilient stop should be far less stiff than a solid stop (made of an iron material) would be. According to the invention, the stop is 100 bis 10,000 times stiffer than the "first" spring (accumulator spring). The stop should in no way have a linear characteristic, but can also be degressive, for example, and be built up with the help of spiral springs, in particular a disc spring. The resilient stop can also be preloaded. Furthermore, the stop can be configured to be adjustable, for example with a fine thread, so that its preload and / or rest position can be adjusted in order to match the triggering characteristics. In summary, the "first" spring (storage spring) and the "second" spring, namely the resilient stop, together form a combined spring with a highly progressive characteristic curve, based on their effect on the armature. The resilient stop allows a very small counter-excitation to cause a certain (small) movement of the armature. Since, however, according to the invention, the shunt has a very small reluctance, even very small deflections of the armature from its (closed, tensioned) initial stroke position result in the flow over the shunt increasing considerably and the flow over the working air gap (s) decreases noticeably, with the associated magnetic holding force naturally developing proportionally to the square of the flux density in the working air gap. The small deflection of the armature, which is caused by a small counter-excitation as a result of the resilient stop, thus leads to a considerable reduction in the magnetic holding force on the armature due to the changing distribution of the flux between the working air gap and the shunt. When designing and setting the resilient downstop, it must be taken into account that the system remains sufficiently insensitive to vibrations (insensitivity to accidental triggering). In order to improve the insensitivity to accidental triggering processes due to vibrations or to counter-excitations induced by interference fields, an additional electrical excitation can be used. For this purpose, the trip coil can be used and energized against the direction that is needed for the trip. But an additional winding can also be used.

The self-holding magnet according to the present invention can further be a have the following configurations:

1. Variable shunt by design as a reversing stroke magnet

The reversing solenoid can have a variably designed shunt. This means that when the armature is detached - i.e. while the working air gap is still of the order of magnitude of its remaining air gap - a movement of the armature which increases the working air gap results in a reduction in the reluctance of the shunt. For this purpose, the invention can be designed as a reversing stroke magnet, one end face of the armature forming the working air gap of the self-holding magnet together with the frame. The opposite end of the armature can form the shunt, the shunt being designed as an armature-armature counterpart system, which is preferably designed so that the highest "force constant" occurs at the start of the stroke (i.e. in the position in which the working air gap except for one Residual air gap is closed; the "tensioned" position). Consequently, in this embodiment of the invention, the armature is supplied with a permanent magnetically generated magnetic flux, which is distributed to the working air gap (without influencing the characteristic curve) and shunt (with influencing the characteristic curve, acts to open the working air gap) according to the associated reluctances. The counter-excitation with the help of the associated coil then causes an increase in the reluctance force acting on the armature at the shunt and a decrease in the reluctance force at the "holding surface", ie at the working air gap. The shunt and accumulator spring exert force on the armature in the same direction (to open the working air gap).

2. Useful work from reducing the reluctance of the variable shunt with the help of a second armature

A reduction in the flux-carrying shunt air gap (decrease in its reluctance) can also take place with the aid of a second armature ("shunt armature"). This anchor is movably arranged that it is able to close the shunt air gap, which is small anyway, except for a residual air gap. The reluctance force acting on the shunt armature can be transmitted to the armature via a mechanical or hydraulic device with or without transmission to open the working air gap (the force on the "shunt armature" should therefore be applied in the same direction to the (working) ) Anchors of the self-holding magnet act like the force of the accumulator spring). A simple plunger is suitable for power transmission. In the tensioned state of the drive, the shunt armature is in a position in which the reluctance of the shunt is as equal as possible to the series reluctance of the (working) residual air gap (s). If a counter-excitation is now generated, the force acting on the shunt armature increases and is transferred to the (working) armature in the direction of the (storage) spring force acting on the (working) armature, i.e. it acts to remove it from its initial stroke position to solve. At the same time, the magnetic holding force is reduced by the counter-excitation. Movement of the armature and shunt armature ultimately causes a decrease in the reluctance of the shunt and an increase in the reluctance of the working air gap.

• geringe Totzeit, d.h. kurze Zeit zwischen Bestromungsbeginn und einsetzender Ankerbewegung
• kein Versagen auch bei, verglichen mit üblichen Selbsthaltemagneten, hohen Gegenerregungen.

The magnetic spring accumulator according to the present invention can, if necessary, have the following additional features:

• short dead time, ie short time between the start of current application and the onset of armature movement
• no failure even with high counter-excitations compared to conventional self-holding magnets.

Fig. 1a

einen Längsschnitt durch einen Selbsthaltemagneten gemäß dem ersten Beispiel der vorliegenden Erfindung; und

Fig. 1b

einen Querschnitt durch einen Selbsthaltemagneten gemäß dem ersten Beispiel der vorliegenden Erfindung.

The invention is explained in more detail below using the examples shown in the figures. The illustrations are not necessarily true to scale and the invention is not limited to the aspects shown. Rather, emphasis is placed on illustrating the principles on which the invention is based. In the pictures shows:

Fig. 1a

a longitudinal section through a self-holding magnet according to the first example of the present invention; and

Figure 1b

a cross section through a self-holding magnet according to the first example of the present invention.

In the figures, the same reference symbols designate the same or similar components, each with the same or similar meaning.

In Fig. 1a and Figure 1b . shows an exemplary embodiment for a self-holding magnet according to the invention with a spring, which has a shunt armature. A resilient stop is not shown, but can advantageously be added. Fig. 1a shows a section through the approximately rotationally symmetrical drive. The drawing is not to scale, but offers the developer a good basis for FEM optimization. The exemplary embodiment serves only for explanation and is in no way to be seen as a restriction.

• 10 Stößel, mit dem Arbeitsanker verschweißt, Austenitischer Edelstahl (NiCr)
• 11 Arbeitsanker, Silizium-Eisen (FeSi)
• 20 Mitnehmer, mit dem Nebenschlussanker verschweißt, (NiCr)
• 21 Nebenschluss-Anker (FeSi)
• 30 äußeres Rahmenteil (FeSi)
• 31 inneres Rahmenteil (FeSi)
• 32 weiteres äußeres Rahmenteil (FeSi)
• 40 Ankerführung (Messing)
• 41 Flussrückführung (FeSi)
• 42 Nebenschlussanker-Anschlag (NiCr)
• 50 Feder (Federstahl, kann vorteilhaft als Wellringfeder ausgeführt werden)
• 60 Widerlager für Feder und Gleitlager(buchse) für Stößel (Bronze)
• 70 Spule, gewickelt in die Nut des Rahmenteils (Kupfer-Lackdraht)
• 80 Permanentmagnet (insb. NdFeB)

The individual illustrated components of the drive can consist of the following materials:

• 10 plungers, welded to the working anchor, austenitic stainless steel (NiCr)
• 11 working anchor, silicon iron (FeSi)
• 20 drivers, welded to the shunt armature, (NiCr)
• 21 shunt armature (FeSi)
• 30 outer frame part (FeSi)
• 31 inner frame part (FeSi)
• 32 further outer frame part (FeSi)
• 40 anchor guide (brass)
• 41 Flux return (FeSi)
• 42 shunt anchor stop (NiCr)
• 50 spring (spring steel, can advantageously be designed as a corrugated ring spring)
• 60 abutment for spring and slide bearing (bushing) for plunger (bronze)
• 70 coil, wound in the groove of the frame part (enamelled copper wire)
• 80 permanent magnet (esp. NdFeB)

A coil body can be dispensed with if, for example, the groove in which the coil lies is coated with an insulating coating.

δ10 and δ11 are the working air gaps (connected in series) in the tensioned stroke start position and are therefore closed except for residual air gaps (not shown). δ20 is the shunt air gap that is used by the shunt armature 21 to do work. The inner frame part 31 is chamfered in the area of the working air gap δ10.

Figure 1b shows a top view of the drive with removed armature guide and removed working armature and ram. The permanent magnets made up of radially polarized circular segments can be seen, which are located in recesses in the (soft magnetic) frame. 33 are structural magnetic shunts, the magnets being dimensioned in such a way that these structural magnetic shunts 33 saturate, so that a magnetic tension occurs between the inner frame part 31 and the outer area with the outer frame part 30, 32 and flux return 41. The construction with radially polarized circular segments, constructive (saturated) shunts, etc. is comparatively complex, but enables a particularly high dimensional accuracy and thus meets the basic requirement for small residual air gaps.

Functionality:

Secondary air gap δ20 is in the illustrated stroke start position (panned state) of the same reluctance as possible as the series connection δ10, δ11 (but with a larger cross section). From the point of view of the coil, this can result in a polarized (sic!) Magnetic circuit with low reluctance, which enables large force constants (N / A). The shunt anchor 21 acts via the driver 20 on the plunger 10 welded to the working anchor and thus additionally helps to maintain the holding force which is imparted via δ10 and δ11 overcome and accelerate the working anchor. As a result of the series connection (sic!) Of δ10 and δ11, opening these residual air gaps by a given (small) length causes their series reluctance to increase approximately twice as much as would be the case with a simple (small) working air gap. At the same time, the shunt armature 21 starts moving and not only helps to move the working armature by means of drivers 20, but also removes flow from the working air gaps δ10, δ11, since a closing movement of the shunt armature leads to a reduction in the reluctance of the shunt and this is connected in parallel with the working air gaps with respect to the permanent magnetically generated flux. As mentioned, the (electrical) sensitivity of this drive can be further increased by equipping it with a resilient stop of suitable rigidity. This stop (not shown) can, for example, make use of a plate spring and act on the plunger 10. Pre-tensioning the disc spring or changing its rest position, whereby the fine adjustment can be carried out by means of screws with fine threads, then enables the electrical sensitivity of the drive to be adjusted. It can be advantageous to connect the drive according to the invention in series with a diode and to connect a varistor in parallel to the drive, because during opening a voltage is induced in the coil which is opposite to the trigger voltage. Such an external circuit can shorten the tripping time considerably. When using a resilient stop, triggering proceeds as follows:
Electrical counter-excitation reduces the flow through working air gaps δ10, δ11 and increases that through the shunt air gap δ20. As a result of the resilient stop, even a minimal supply of current leads to a certain amount of rebound. As a result of this rebound, δ10 and δ11 increase, while δ20 decreases accordingly (since the shunt armature 21, accelerated by reluctance force, follows the plunger 10). Because the air gaps mentioned are all small, this small deflection of the system - the rebound - leads to a markedly different distribution of the permanent magnetically generated flux: The flow through the working air gaps δ10, δ11 decreases, that through the shunt increases. The rapid increase in the force acting on the shunt armature 21 contributes to the triggering of the self-holding magnet and also enables a considerable shortening due to the additional force transmitted to the working armature 11 via the driver 20 and plunger 10 and the magnetic "short-circuiting" of the working air gaps δ10, δ11 the achievable actuating times, because in the vicinity of the stroke start position only small forces from the difference between the spring force and the reluctance force to accelerate the armature are available with conventional self-holding magnets, at least with low release powers. In the exemplary embodiment, however, the reluctance force inhibiting the armature movement is short-circuited with the associated flux as a result of the movement of the shunt armature, while the working armature 11 is driven by the reluctance force acting on the shunt armature 21 in addition to the spring force).

Claims (13)

1. A self-holding magnet, comprising:

   - a magnetic circuit comprising a stator and a first armature (11);

   - a stop;

   - a stroke starting position defined by the stop, in which between stator and first armature one or more working residual air gaps are present;

   - at least one spring (50) which exerts a spring force which urges the first armature away from the stop;

   - a magnetic shunt (33; 31, δ20, 21, 32);

   - one or more permanent magnets (80) for the excitation of the magnetic circuit;

   - one or more trigger coils (70) for the counter-excitation of the magnetic circuit,

   wherein the magnetic circuit is dimensioned such that it is able to magnetically hold its first armature in the stroke starting position against the spring force, wherein in the stroke starting position the magnetic shunt has a reluctance which is of the same order of magnitude as the reluctance of the working residual air gap or in the case of a series connection of a plurality of working residual air gaps as the series reluctance of the working residual air gaps, wherein working air gap(s) (δ10, δ11) and shunt (33; 31, δ20, 21, 32) are magnetically connected in parallel with respect to the permanent-magnetically generated flux, but are connected in series with respect to the flux generated by the trigger coil(s),
   wherein the trigger coil(s) are energized such that the magnetic flux in the working air gap(s) is attenuated and the magnetic flux in the shunt is increased, which leads to the relaxation of the spring when the amount of the magnetic holding force falls below the spring force;
   characterized in
   that the stop is designed as a resilient stop, wherein the stop itself has spring properties and is 100 to 10,000 times stiffer than the at least one spring.
2. The self-holding magnet according to claim 1, wherein the magnetic shunt is configured such that a movement of the first armature away from the stroke starting position results in a reduction of the reluctance of the shunt, so that the permanent-magnetically generated flux increasingly commutates onto the shunt with the onset of movement of the first armature.
3. The self-holding magnet according to claim 2, wherein commutating of the permanent-magnetically generated flux onto the shunt is achieved in that:
   the shunt comprises a second armature (21) which transmits the reluctance force acting on the same to the first armature for example by means of a tappet (10), so that a counter-excitation by the trigger coil(s) leads to the fact that the flux in the working air gap(s) of the first armature decreases, but the flux in the working air gap(s) of the second armature increases.
4. The self-holding magnet according to claim 2, wherein commutating of the permanent-magnetically generated flux onto the shunt is achieved in that:
   the self-holding magnet is configured as a reversing stroke magnet, wherein an end face of the armature together with a frame forms the working air gap of the self-holding magnet, wherein the opposite end of the armature forms the shunt, and wherein the shunt is configured as a system of armature and armature counterpart, which is designed such that the highest force constant occurs in the stroke starting position.
5. The self-holding magnet according to claim 1, wherein the resilient stop is 100 to 1000 times stiffer than the at least one spring.
6. The self-holding magnet according to claim 1, characterized in that the resilient stop is adjustable in terms of its pretension and/or position, preferably by means of threads.
7. The self-holding magnet according to claim 1, characterized in that the shunt is not configured as a geometrically specified air gap, but by means of a material with a distributed air gap.
8. The self-holding magnet according to claim 1, characterized in that the shunt or the associated flux guidance is dimensioned and shaped such that the reluctance of the iron circuit seen by the coil can rise as a result of saturation to the effect that even with a comparatively high counter-excitation an inadvertent retention of the armature in its stroke starting position or an inadmissibly delayed triggering is avoided.
9. The self-holding magnet according to claim 1, characterized in that it is equipped with a rectifier and a varistor, wherein the rectifier is connected in series with the self-holding magnet, but the varistor is connected in parallel, namely such that in the case of a change of the current direction in the coil of the self-holding magnet the current no longer flows over the rectifier, but freely runs over the varistor.
10. The self-holding magnet according to claim 1, characterized in that the spring used is a corrugated annular spring.
11. The self-holding magnet according to claim 1 or 3, characterized in that at least the armature or the armatures is/are of round design and that slots are incorporated into the armature(s) and/or into frame parts of the armature, and that these slots are filled with a bearing material of poor electrical conductivity, which protrudes to such an extent that it can serve as part of a plain bearing.
12. The self-holding magnet according to claim 1, characterized in that the spring used is a disk spring or a disk spring pack which has such a degressive characteristic that the spring force first increases on relaxation of the spring.
13. The self-holding magnet according to claim 1, characterized in that the resilient stop is constructed by means of at least one bending spring, in particular a disk spring.

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