Patent Application
20110057751
This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/EP2008/003628 which has an International filing date of May 6, 2008, which designates the United States of America, the entire contents of which are hereby incorporated herein by reference.
At least one embodiment of the invention generally relates to a switching device with a movable contact for closing and opening a circuit and with a magnetic shape memory alloy, by which the position of the movable contact can be changed.
A switching device is known from WO 2007/057030 A1, in which the tripping armature of the drive for tripping in the event of short-circuit currents comprises a ferromagnetic shape memory alloy.
Secondly, it is known that certain shape memory alloys are magnetically sensitive and are subject to a change in length when a magnetic field passes through them. The force generated in the event of a change in length can in principle be used as a drive force. The known magnetic shape memory alloys display a technically usable response in terms of change in length only in strong magnetic fields of at least 0.5 tesla. In technical applications such as the switching device proposed here, high drive currents with a correspondingly high energy consumption need to be avoided.
In at least one embodiment of the invention, a switching device includes a magnetic shape memory alloy, sensitive to magnetic fields, which only requires a small current consumption for inducing a magnetic field in the shape memory alloy for the holding mode.
In at least one embodiment, a movably mounted magnet is provided, it being possible to change a magnetic field acting on the magnetic shape memory alloy for closing and opening the circuit by virtue of changing the position of said magnet. This makes it possible in a simple manner to control the drive force emanating from the shape memory alloy and acting on the movable contact.
Advantageous developments of the invention are given in the dependent claims.
It is particularly advantageous if the magnet is the form of a ferromagnet.
It is furthermore advantageous if a drive is provided, by which the position of the magnet can be changed.
In addition, it is advantageous if a plate is provided which passes on the drive force of the shape memory alloy to the movable contact.
If the plate has a high modulus of elasticity, it is ensured that a low pressure is applied uniformly to the shape memory alloy.
Advantageously, a plate-shaped component part which has a low thermal conductivity and a low radiation absorption is provided between the movable contact and the shape memory alloy, which brings about thermal protection with respect to switching energy converted into heat.
Example embodiments will be explained in more detail below with reference to a drawing, in which:
The controlling magnetic field 10 in the shape memory alloy 4 is induced with the aid of a technical device 11. By virtue of the controlling magnetic field in the shape memory alloy 4, the shape memory alloy 4 experiences an extension of length and therefore causes the movable contact 2 to close with the fixed contact 3. This takes place via the spring 8, which ensures the required contact force for guiding the current.
In order to make full use of the drive with the magnetic shape memory alloy 4, the magnetic field needs to pass through said shape memory alloy as homogeneously as possible with at the same time a high field strength. This can be achieved by a suitable arrangement of ferromagnetic component parts between the technical device 11 for inducing the magnetic excitation and the magnetic shape memory alloy 4.
No coil with an iron core is provided which is used for exclusively inducing the magnetic field at the level which is required for the necessary change in length of the shape memory alloy 4 in order thus to bring about the holding mode. For this purpose, permanently high currents would be required which would result in an unacceptably high current consumption, which is intended to be avoided by an embodiment of the present invention.
Instead, in the example embodiment below shown in
In the OFF contact position shown in
As a result, the shape memory alloy 4 is magnetized by the entire magnetic field of the permanent magnet and causes the movable contact 2 to close with the fixed contacts 3 shown in
The arrangement explained in the example embodiments make it possible to decrease the physical size of a contactor drive. Owing to the relatively high mechanical prestress, it is no longer necessary to reserve a large proportion of the attraction path for a safety gap for ensuring vibration and shock resistance, as is the case at present in conventional relays and contactors. This keeps the physical volume of the shape memory alloy 4 low. A parallelepiped of a shape memory alloy 4 with a basic area of 2 cm2 and a height of 8 cm is sufficient, with a high degree of reliability, for ensuring a switching path of 4 mm with a force of 100 N applied. The high force of the shape memory alloy makes it possible to further enlarge the displacement path via levers.
The technical solution given in the example embodiment for inducing the controlling magnetic field likewise has smaller dimensions than a conventional reluctance drive with comparable power.
Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/003628 | 5/6/2008 | WO | 00 | 11/5/2010 |
