Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Plural magnets or flux sources
Reexamination Certificate
2001-03-13
2002-07-23
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Plural magnets or flux sources
C335S078000, C335S080000, C335S083000, C335S084000, C335S179000, C335S186000, C335S190000, C335S227000, C335S234000, C335S279000, C335S281000
Reexamination Certificate
active
06424244
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a magnetic switch having a cup-shaped yoke, a core, a coil, an armature and a fixed contact and a movable contact.
DESCRIPTION OF THE PRIOR ART
Magnetic switches of this kind are known, for example, from EP 0 442 311 A2, which discloses a magnetic switch in which a non-magnetic armature is moved by a permanent magnet fixedly connected thereto. During this, in the direction of movement of the armature, only an operational air gap between the permanent magnet and the core brings about the effect. Furthermore, the known magnetic switch has a small coupling surface between the permanent magnet and the core, which extends only over the inner region of the cup-shaped yoke.
The known magnetic switch has the disadvantage that the coupling surface between the permanent magnet and the core, and thus the holding force of the magnet system, is only very small relative to the structural volume of the magnetic switch. This means that the known magnetic switch is not suitable for use as a battery disconnecting switch in a motor vehicle, where on the one hand large currents of a few thousand amps have to be switched, and where on the other hand vibrations and jolts act on the magnetic switch. To achieve a greater holding force, it would be possible for special magnetic materials which generate a very strong magnetic field to be used. These have the disadvantage that they are expensive to procure and complicated to process.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a magnetic switch which presses the movable contact onto the fixed contact with a high holding force while having a small structural volume.
This object is achieved by a magnetic switch having a yoke that has the shape of a cup with an axis of symmetry. The cup has a base and a wall and is open to one side. Arranged in the cup is a core which has a radial core flange at its end facing the base. This radial core flange forms with the wall of the cup a marginal air gap with a width of H
R
. This marginal air gap has a magnetic resistance of W
R
. Furthermore, the cup contains a plate-shaped permanent magnet which is magnetised parallel to the axis of symmetry of the cup. The permanent magnet is arranged between the core flange and the base and is magnetically coupled thereto. Moreover, arranged in the cup is a coil whereof the coil axis is the axis of symmetry of the cup. The cup is covered by a plate-shaped armature which forms with the yoke a yoke air gap with a width of H
J
and forms with the air gaps together form, connected serially one behind the other, the operational air gap, which has a magnetic resistance of W
A
. Moreover, there is arranged on the magnetic switch a means for lifting the armature axially away from the cup. In the closed condition of the magnetic switch, the following applies: W
A
<W
R
.
As a result of the construction of the magnetic switch, in accordance with the invention, a magnetic switch is produced which is shielded from the outside extremely well and has only extremely low scattering losses for the magnetic fields. Because the armature forms an operational air gap with the core and the cup-shaped yoke, a coupling surface which is as large as possible is formed with a particular predetermined structural volume. The large coupling surface between the armature and the yoke and the core respectively results in a large holding force of the magnetic switch in the closed condition. Because the magnetic resistance of the operational air gap is smaller than the magnetic resistance of the marginal air gap, it is ensured that the majority of the magnetic flux of the permanent magnet is conducted through the armature in the closed condition. The system polarised by the permanent magnet moreover has the advantage that only a short switch pulse has to be sent through the coil in order to close the switch, and the coil current can be returned to zero in the closed condition. This means, in particular, that low-power operation of the magnetic switch is possible.
In order to achieve the maximum holding force of the armature, it would be desirable for the ratio W
R
/W
A
to be as large as possible. This would ensure that all of the magnetic flux of the permanent magnet is guided through the armature without losses being produced by way of the marginal air gap. A very large ratio W
R
/W
A
would, however, mean that a high counter-excitation of the coil would be required to open the switch, in order to displace the magnetic field of the permanent magnet out of the core and guide it through the marginal air gap and the wall of the cup, back onto the underside of the permanent magnet. Consequently, for the magnetic switch to have a high sensitivity to switching off, it would be desirable for the ratio W
R
/W
A
to be in the order of magnitude of one. Thus, it is particularly advantageous to set the ratio W
R
/W
A
such that both the holding force of the armature and the sensitivity of the magnetic switch to switching off are in a reasonable range. Tests have shown that this is the case if the ratio W
R
/W
A
is selected to be between 1 and 100. A ratio W
R
/W
A
=50 has been shown to be particularly advantageous.
A magnetic switch according to the invention may for example readily be produced with the following dimensions: for the cup, a radial extent of between 10 mm and 50 mm is chosen. With a size such as this, a compact construction is possible for the magnetic switch, as is specifically necessary for its use as a battery disconnecting switch in a motor vehicle. For the width of the yoke and core air gaps, purely for reasons of the superficial roughness of the underside of the armature or of the surfaces of the cup wall and the core, the following range can readily be set: 0.005 mm<H
J
<0.05 mm and 0.005 mm<H
K
<0.05 mm. If a wall thickness of the cup of approximately 1 mm is chosen, moreover, then a surface for the yoke air gap with a size of approximately 100 mm
2
is obtained. If the core air gap or the marginal air gap is constructed to have approximately the same order of magnitude as regards their surfaces, then to fulfil the relation mentioned above between the magnetic resistances of the operational and the marginal air gaps, the following apply: 1 mm>H
R
>0.1 mm. The said dimensions of the core and yoke air gaps relate to the closed condition of the switch. With a magnetic switch constructed in accordance with these example dimensions, a holding force of approximately 30 N can be achieved. The axial extent of the switch corresponds approximately to the radial extent. A magnetic switch of this type can be switched at a switching capacity of approximately 0.7 W.
Particularly advantageous is a magnetic switch in which the yoke, permanent magnet, core, coil and armature are arranged rotationally symmetrically about the axis of symmetry. As a result of the rotationally symmetrical arrangement according to the invention of the elements of the magnetic switch about the axis of symmetry, an optimum flux concentration is achieved in the interior of the switch without magnetic field losses occurring at corners or edges. Moreover, a magnetic switch with rotational symmetry is easy to produce.
Furthermore, particularly advantageous is a magnetic switch in which the permanent magnet is of a material containing barium ferrite. Barium ferrite is a readily available, inexpensive material for a permanent magnet, which greatly simplifies production of the magnetic switch. Because of the high holding force of the magnetic switch according to the invention, expensive highly magnetised special materials for the permanent magnet can be dispensed with.
Furthermore, particularly advantageous is a magnetic switch in which the yoke and/or the core are of a material which contains magnetically soft iron. Magnetically soft iron can very readily be demagnetised, which simplifies the displacement of the flux of the permanent magnet out of the core when the magnetic switch is opened. Furthermore, magnetically soft iro
Barrera Ramon M.
Tyco Electronics Amp GmbH
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