Self-holding magnet with a particularly low electric trigger voltage

Abstract

A self-holding magnet has a spring (accumulator spring) and a first armature. The self-holding magnet is capable of holding the first magnet armature against the spring force in a lift position which is determined by a stop. The stop determines a remaining air gap of a working air gap. The magnetic circuit of the self-holding magnet has a magnetic shunt with particularly low reluctance of the same order of magnitude as a series reluctance of the remaining working air gap(s). The working air gap(s) and the shunt are magnetically connected in parallel with the flow generated by a permanent magnet but in series with the flow generated by the trigger coil. The self-holding magnet additionally has at least one positive feedback device such as a compressible resilient stop or a shunt.

Claims

1. A self-holding magnet, comprising: a magnetic circuit having a stator and a first armature; a stop; said stop defining a first stroke end position, in which between said stator and said first armature one or more working residual air gaps are present, which have a series reluctance; at least one spring disposed to exert a spring force urging said first armature away from said stop; a magnetic shunt of particularly low reluctance; one or more permanent magnets for exciting the magnetic circuit and one or more coils for counter-exciting the magnetic circuit; wherein: the magnetic circuit is dimensioned such that the magnetic circuit is able to magnetically hold said first armature in the first stroke end position against the spring force; said magnetic shunt has a reluctance which is of the same order of magnitude as the series reluctance of the working residual air gap(s); working air gap(s) and said shunt 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 said trigger coil(s); said 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, leading to a relaxation of the spring when a amount of the magnetic holding force falls below the spring force; one or more positive feedback devices selected from the following group of devices: (1) said stop, being a resilient stop, said resilient stop having spring properties and being very much stiffer than said at least one spring and much less stiff than a solid stop of iron; and (2) design of the magnetic shunt such that a movement of said first armature results in a reduction of the reluctance of said magnetic shunt, so that a permanent-magnetically generated flux increasingly commutates onto said shunt with an onset of a movement of said first armature.

2. The self-holding magnet according to claim 1, wherein commutating of the permanent-magnetically generated flux onto said shunt is achieved in that: the shunt comprises a shunt armature configured to transmits a reluctance force acting on the same to the first armature, so that a counter-excitation by said coil(s) leads to a decrease in a flux in the working air gap(s) of said first armature and an increase of a flux in one or more shunt working air gap(s) of said shunt armature; as soon as an amount of a total reluctance force acting on said first armature and shunt armature together falls below the spring force, said shunt armature also starts to move along with said first armature, in order to close the shunt working air gap(s), which results in a reduction of the reluctance of a flux path leading over said shunt armature.

3. The self-holding magnet according to claim 1, wherein commutating of the permanent-magnetically generated flux onto said shunt is achieved in that: the self-holding magnet is configured as a permanently excited reversing stroke magnet, wherein the armature has a first side having no geometric influence on the characteristic with the stator, so that a magnetic holding force as high as possible is generated against the spring force, while on the opposite side of the armature, where the armature is subject to a reluctance force in direction of a spring force generated by the compression of the spring, said armature comprises the shunt, with the shunt and said stator having a geometric influence on the characteristic.

4. A self-holding magnet, comprising: at least one spring and an armature, wherein said armature is configured to be held in a stroke position against a spring force, said stroke position being determined by a stop; said stop determining at least a residual air gap of a working air gap; a magnetic circuit of the self-holding magnet having a magnetic shunt with a particularly low reluctance that is of a same order of magnitude as a series reluctance of the working residual air gap or gaps; with respect to a permanent-magnetically generated flux, the working air gap or air gaps and said shunt are magnetically connected in parallel; with respect to a flux generated by a coil, the working air gap or air gaps and said shunt are connected in series; and at least one of the three following positive feedback devices: said stop being a resilient stop that is much stiffer than said at least one spring but much less stiff than a solid stop of iron; said shunt being configured such that a movement of said armature leads to a reduction of a reluctance of said shunt, in that the self-holding magnet is configured as a reversing stroke magnet, wherein a holding force which can keep the accumulator spring tensioned is generated, and said shunt is formed as armature-armature counterpart system; said shunt being configured such that a movement of said armature leads to a reduction of the reluctance of said shunt, in that said shunt is provided with a shunt armature that is able to close a small air gap of said shunt except for a certain (still smaller) residual air gap, wherein a force acting on said shunt armature is transmitted to the armature of the self-holding magnet such that it acts thereon in a same direction as a force of said accumulator spring.

5. The self-holding magnet according to claim 4, wherein the resilient stop is adjustably mounted with respect to a pretension and/or a position thereof, allowing a sensitivity of the self-holding magnet to be adjusted.

6. The self-holding magnet according to claim 4, wherein said shunt is not configured as a geometrically determined air gap but by way of a material with distributed air gap.

7. The self-holding magnet according to claim 4, wherein said shunt or an associated flux guide is dimensioned and shaped such that, as a result of saturation, the reluctance of an iron circuit seen by the coil can increase to the effect that even with a comparatively high counter-excitation an inadvertent retention of the armature in its stroke starting position or inadmissibly delayed triggering is avoided.

8. The self-holding magnet according to claim 4, wherein said at least one spring is a corrugated annular spring.

9. The self-holding magnet according to claim 4, wherein one or more armatures are round.

10. The self-holding magnet according to claim 4, wherein said at least one spring has such a degressive characteristic that a spring force initially increases on relaxation of the spring.

11. The self-holding magnet according to claim 4, wherein said resilient stop is between 100 and 1000 times stiffer than said at least one spring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in detail below with reference to examples illustrated in the drawings. The representations are not necessarily true to scale and the invention is not only limited to the illustrated aspects. Rather, importance is placed on representing the principles underlying the invention. In the drawings:

(2) FIG. 1A shows a longitudinal section through a self-holding magnet according to the first example of the present invention;

(3) FIG. 1B shows a cross-section through a self-holding magnet according to the first example of the present invention;

(4) FIG. 2A shows a longitudinal section through a self-holding magnet in a half opened position; and

(5) FIG. 2B shows a longitudinal section through a self-holding magnet in a fully opened position.

(6) In the Figures, identical reference numerals designate identical or similar components each with the same or a similar meaning.

DESCRIPTION OF THE INVENTION

(7) FIG. 1A and FIG. 1A show an exemplary embodiment for a self-holding magnet 100 according to the invention with spring, which includes a shunt armature and a resilient stop 90. FIG. 1A shows a section through the approximately rotationally symmetrical drive. The drawing is not true to scale, but for the developer offers a good basis for FEM optimizations. The exemplary embodiment only serves for explanation and by no means is to be regarded as limitation.

(8) The individual depicted components of the drive can be made of the following materials: 10 tappet to which the working armature is welded, austenitic stainless steel (NiCr) 11 working armature, silicon iron (FeSi) 20 carrier to which the shunt armature is welded (NiCr) 21 shunt armature (FeSi) 30 outer frame part (FeSi) 31 inner frame part (FeSi) 32 further outer frame part (FeSi) 40 armature guide (brass) 41 flux recirculation (FeSi) 42 shunt armature stop (NiCr) 50 spring (spring steel, can advantageously be designed as corrugated annular spring) 60 abutment for spring and plain bearing (bush) for tappet (bronze) 70 coil, wound into the groove of the frame part (enameled copper wire) 80 permanent magnet (in particular NdFeB)

(9) A coil body can be omitted, when e.g. the groove in which the coil lies has an insulating coating.

(10) 10 and 11 are the (series-connected) working air gaps in the tensioned stroke starting position and therefore closed except for the (non-illustrated) residual air gaps. 20 is the shunt air gap which is utilized by the shunt armature 21 to perform work. The inner frame part 31 is chamfered in the region of the working air gap 10.

(11) FIG. 1b shows a top view of the drive with removed armature guide and removed working armature and tappet. There are shown the permanent magnets consisting of radially polarized circular segments, which are located in cutouts of the (soft magnetic) frame. Reference numeral 33 designates constructive magnetic shunts, wherein the magnets are to be dimensioned such that these constructive magnetic shunts 33 saturate, so that a magnetic tension occurs between the inner frame part 31 and the outer region with outer frame part 30, 32 and flux recirculation 41. The construction with radially polarized circular segments, constructive (saturated) shunts etc. is comparatively expensive, but provides for a particularly high dimensional accuracy and thus very well satisfies the basic requirement of small residual air gaps.

(12) Mode of Operation:

(13) In the illustrated stroke starting position (tensioned condition), the shunt air gap 20 possibly has the same reluctance as the series connection 10, 11 (but a larger cross-section). From the point of view of the coil, this can lead to a polarized (sic!) magnetic circuit of low reluctance, which provides for large force constants (N/A). Via the carrier 20, the shunt armature 21 acts on the tappet 10 welded to the working armature and thus additionally helps to overcome the holding force, which is conveyed via 10 and 11, and to accelerate the working armature. As a result of the series connection (sic!) of 10 and 11, opening of these residual air gaps by a given (small) length approximately effects an increase of their series reluctance twice as high as would be the case with a simple (small) working air gap. The shunt armature 21 starts to move, so to speak, and helps to move the working armature not only by means of the carrier 20, but additionally withdraws flux from the working air gaps 10, 11, since a closing movement of the shunt armature leads to a reduction of the reluctance of the shunt and the same is connected in parallel with the working air gaps with respect to the permanent-magnetically generated flux. As mentioned, the (electric) sensitivity of this drive can be increased further, in that it is equipped with a resilient stop of suitable stiffness. This stop (not shown) for example can make use of a disk spring and act on the tappet 10. Pretensioning the disk spring or changing its rest position, wherein the fine adjustment can be effected by means of screws with fine threads, then provides for an adjustment of the electric sensitivity of the drive. It can be advantageous to connect the drive according to the invention in series with a diode and to connect a varistor in parallel with the drive, as during opening a voltage is induced in the coil which is opposite to the triggering voltage. Such external wiring can considerably shorten the triggering time. By using a resilient stop, triggering proceeds as follows:

(14) Electric counter-excitation reduces the flux through working air gaps 10, 11 and increases the one through the shunt air gap 20. Due to the resilient stop, a minimal energization already leads to a certain decompression. As a result of this decompression, 10 and 11 are increased, while 20 decreases correspondingly (since the shunt armature 21, accelerated by reluctance force, follows the tappet 10). Because said air gaps all are small, this small deflection of the systemthe decompressionleads to a markedly different distribution of the permanent-magnetically generated flux: The flux through the working air gaps 10, 11 decreases, the one through the shunt increases. The rapid increase of the force acting on the shunt armature 21 contributes to triggering of the self-holding magnet and because of the force additionally transmitted to the working armature 11 via carrier 20 and tappet 21 and the magnetic short-circuiting of the working air gaps 10, 11 also provides for a considerable shortening of the achievable actuating times, as in conventional self-holding magnets, in any case at low triggering powers, only small forces from the difference of the spring force and the reluctance force are available for the acceleration of the armature in the surroundings of the stroke starting position. In the exemplary embodiment on the other hand 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.