GB2376571A

GB2376571A - Magnetic flux control device

Info

Publication number: GB2376571A
Application number: GB0114772A
Authority: GB
Inventors: Gilbert Brian Edlin
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-06-16
Filing date: 2001-06-16
Publication date: 2002-12-18
Also published as: GB0114772D0

Abstract

A magnetic flux control device for use in a magnetic loop 2 includes a chamber 8 defining a gap 6 in the loop. Magnetic fluid 10 stored in bores 12 communicating with the chamber 8 can be driven out of the bores 12 in response to energisation of a drive coil 14, by gravity upon inversion, or by a fluid pump, to fill the chamber 8 and so reduce the magnetic reluctance of the loop. The control device can thus be used in various applications as a magnetic flux switch.

Description

MAGNETIC FLUX CONTROL DEVICES The present invention relates to magnetic flux control devices.

The level of magnetic flux in any circuit can be increased or decreased by varying the magnetic reluctance in a section of the circuit. This is usually achieved by varying the disposition of a magnetic and magnetisable component in the circuit. The magnetic or magnetisable component takes the form of a solid member which is displaced in response to a mechanical force to control or vary the flux in the circuit of which it forms part.

It is an object of the invention to provide an improved magnetic flux control device.

According to the present invention there is provided a magnetic flux control device for insertion in series with a magnetic circuit, the device comprising a chamber separating two magnetisable components of the circuit, a reservoir for containing a magnetic fluid, said reservoir communicating with said chamber, and means for driving said magnetic fluid into said chamber to bridge the two magnetisable components and for driving said magnetisable fluid from the chamber to break said bridge.

Magnetic flux control devices embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a front elevation of a magnetic circuit incorporating a flux control device in an inactive mode;

Figure 2 is a front elevation of a magnetic circuit of Figure 1 with the flux control device activated; Figure 3 is a cross-section along the line 3-3 of Figure 1; Figure 4 is a front elevation of a magnetic circuit incorporating two magnetic flux switches; Figure 5 is a front elevation of another flux switch embodying the invention; and Figure 6 is a front elevation of yet another flux switch embodying the invention.

As shown in Figures 1 and 2, the magnetic circuit is in the form of a rectangular frame 2 of generally square cross-section ferromagnetic material. One arm 2A contains a permanent magnet 4 with north and south poles at opposite ends within the circuit. The opposite arm 2B includes a gap 6 defined by a closed chamber 8 containing a magnetisable fluid 10. One face of the gap is provided with an array of bores 12 of generally circular section to allow the magnetisable fluid to drain from the chamber 8 into the bores 12 and vice versa. The magnetisable fluid may comprise a fluid such as is used in conventional ferromagnetic clutches or may be a suspension of magnetisable particles in a liquid such as silicone oil or in any other form (eg powder) which is magnetisable and will flow in response to magnetic forces.

An electric coil 14 extends around the region of the gap 6. Another electric coil extends around another arm 2C of the frame in the region spaced from magnet 4 and the bores 12.

In operation, with the magnetic fluid 10 being mostly located in the bores 12, the gap is filled mostly with air (see Figure 1). When the coil 14 is energised with a DC current of one polarity, the magnetic flux it creates will drive the magnetic fluid out of the bores 12 to fill the gap (see Figure 2). This changes the reluctance of the circuit and causes an increase in the magnetic flux density around the circuit.

The change in magnetic flux density in the circuit is detected by the coil 16 which will then generate an electrical output.

It will be appreciated that the polarity of the DC current energising the coil 14 will determine the direction in which the magnetic fluid is driven either to fill or empty the chamber 8.

The movement of magnetic fluid into and out of the gap can also be effected in other ways for example by gravity-the magnetic circuit can be inverted, by centrifugal force, or even with the aid of a fluid pump which communicates with the bases of the bores 12.

The magnetic flux control device defined by the gap 8, the magnetic flux 10 and the coil 14 are in effect a flux switch.

In the magnetic circuit shown in Figure 4, a rectangular member 22 of magnetisable ferromagnetic material has a central transverse arm consisting of an elongate permanent

magnet 20 so as to provide two auxiliary magnetic circuits fed by the common permanent magnet 20. Each auxiliary magnetic circuit incorporates, respectively, a magnetic flux switch 24 and 26, each substantially as described in Figure 1. Each auxiliary magnetic circuit includes a respective output coil 28 and 30 to provide an electrical output in response to flux changes in the magnetic circuit.

The flux switches 24 and 26 are operated so that when one switch is ON the other switch is OFF and vice versa. In this way, the magnetic flux generated by the permanent magnet 20 is effectively switched from one auxiliary circuit to the other. The emf generated as a result by the two output coils 28 and 30 may be used to control the energisation of the flux switches, with the coil 28 controlling the flux switch 26 and the coil 30 controlling the flux switch 24. In this way a continuous cycling of flux from one auxiliary magnetic circuit to the other occurs with the flux density remaining the same and merely the path it takes changing.

It will be appreciated that the permanent magnet can be coupled to three or more auxiliary magnetic circuits each with its own flux switch and output coil winding. In the case of three auxiliary circuits, the output coil windings can be connected to the flux switches so that the flux is switched in succession around the three auxiliary circuits. In this way, the outputs of the three coil windings, when connected in a star or delta configuration, would provide a three phase voltage supply.

The flux switches can be used in many different situations to control and switch

magnetic flux as required.

When magnetic flux is switched from one magnetic circuit to the other, a progressive switching operation between circuits may be preferred. The flux switch shown in Figure 5 allows this.

As shown, core 40 of the two facing surfaces of the gap is inclined to the other 42 so that when the magnetic fluid is driven out of the bores 12 in response to energisation of the coil, its contact with the surface 40 increases progressively to progressively change the magnetic reluctance of the switch. Similarly, when the coil 14 is energised in the opposite sense, its contact with the surface 40 decreases progressively. The inclination of the two facing surfaces with respect to each other may be in excess of 30 .

It will be appreciated that the bores 12 in the magnetic switch may extend fairly deeply into the magnetic circuit so as not to decrease the density of the magnetic circuit in that region. Also, for example as shown in Figure 6, the bores 12 may terminate in bulbous reservoirs 44 located at different depths in the magnetic circuit.

Claims

CLAIMS 1. A magnetic flux control device for insertion in series with a magnetic circuit, the device comprising a chamber separating two magnetisable components of the circuit, a reservoir for containing a magnetic fluid, said reservoir communicating with said chamber, and means for driving said magnetic fluid into said chamber to bridge the two magnetisable components and for driving said magnetisable fluid from the chamber to break said bridge.
2. A device according to Claim 1, wherein said reservoir comprises one or more recesses in at least one of said two magnetisable components.
3. A device according to Claim 1, wherein said reservoir comprises an array of bores in that surface of one of said magnetisable components which faces said chamber.
4. A device according to Claim 3, wherein at least some of said bores end in a bulbous storage volume.
5. A device according to any preceding claim, wherein the adjacent surfaces of the magnetisable components face each other on opposite sides of the chamber and extend substantially parallel to one another.
6. A device according to any preceding claim, wherein the adjacent surfaces of the two magnetisable components face each other on opposite sides of the chamber and are inclined

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relative to each other.
7. A device according to Claim 6, wherein the two facing surfaces of the magnetisable components are inclined with respect to each other at an angle of greater than 30 .
8. A device according to any preceding claim, wherein the drive means comprises drive coil encircling the magnetic fluid to magnetise the fluid in one sense or the other in response to the energising polarity of the current supplied to the coil.
9. A device according to any one of Claims I to 7, wherein the drive means comprises a fluid pump.
10. A device according to any one of Claims 1 to 7, wherein the drive means comprises means for inverting the chamber.
11. A magnetic flux circuit comprising a loop of magnetisable material having in series therewith a permanent magnet and said magnetic flux control device according to any preceding claim and an output coil encircling a serial portion of the loop of magnetised material at a location spaced from said device and from said permanent magnetic and operable to generate an emf in response to flux changes taking place in the loop.
12. A magnetic flux circuit comprising a permanent magnet sharing a common circuit with two loops of magnetisable material, a device according to Claim 8, in series with each

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loop, a respective output coil coupling a serial portion of each loop, and control means responsive to the outputs of the two output coils to energise the drive coils of the two loops in a manner to cause the devices to repetitive switch in opposite directions to each other.
13. A magnetic flux control device substantially as hereinbefore described, with reference to Figures 1 to 3 or 5 or 6.
14. A magnetic flux circuit substantially as hereinbefore described, with reference to Figure 4.