GB2031653A - Electromagnetic actuating device for high-speed switch elements - Google Patents

Abstract

The invention discloses an electromagnetic actuating device for high-speed switch elements, particularly for controlling hydraulic or pneumatic valves. The device includes an armature in the form of a cylindrical core 2 having at least one reactive part 3 and two one-turn coils 4, 5 fixed in the device housing, one on each side of the reactive part 3. The core 2 consists of electrically nonconductive or less highly conductive material and the reactive part is formed of highly electrically conductive material. In another embodiment, a plurality of reactive parts are formed on the core 2 whilst in yet another embodiment the reactive part is in the form of a spiral the ends of which are electrically connected together, the coil or coils also being in the form of a spiral or spirals. <IMAGE>

Description

SPECIFICATION Electromagnetic actuating device for high-speed switch elements The invention relates to an electromagnetic actuating device for high-speed switch elements, particularly but not exclusively, for controlling hydraulic and pneumatic valves, with a coil and with an armature movable coaxially relative to the coil axis.

Known switching devices, e.g. electromagnetically actuated valves, have physically dictated switching time limits of around 0.5 millisecond. This however, is too slow for many practical applications.

The invention seeks to produce a switching device operating at substantially higher speed, which is nevertheless simple in its construction and costs and can be produced cheaply.

According to the invention there is provided an electromagnetic actuating device for high-speed switch elements including a coil fixed in a housing and an armature constituted buy a cylindrical ortubu- lar core with at least one reactive part coaxial to the coil and movable axially relative to the coil, the arrangement being such that current impulses or alternating currents fed to the coil produce a magnetic field which generates eddy currents in the reactive part which eddy currents generate a force in the direction of the coil axis directed away from the coil.

With such a switching device the switching time limit can be reduced to below 0.1 millisecond. The physical principles which are utilized by the invention, and are applied e.g., to the magnetic moulding process for deforming cylindrical metal objects (ETZ-A, Vol. 88 (1967) No. 9, P 217 ff and No. 19, P.475 et seq.) have been known for a long time.

When cylindrical metallic objects are compressed a powerful magnetic field with an induction of several hundred thousand Gauss is built up for a short time in the space between the solenoid and the workpiece. The skin effect generated by the pulsatory pattern of the magnetic field leaves the interior of the workpiece virtually field-free. A reciprocal magnetic compression of up to several thousand kilopond per square centimentre is therefore produced, which results in a permanent deformation of the workpiece. The present invention is based on a modification of this process for the actuation of high-speed switching elements.

In orderto acheivethe greatest possible acceleration of the armature, it should have the smallest possible weight. Therefore the core of the armature may be constituted by electrically nonconductive or less highly conductive material and the reactive part of electrically highly conductive material. The purpose mentioned may also be served by a tubular construction of the armature core.

If the force effect of the switch element is required to act in more than one direction, then it is provided that for an actuation of the armature in the counterdirection a second coil is fixed in the housing so that the reactive part with the desired movement space is located between the two coils.

For a summation of forces a plurality of reactive parts may be arranged on the core of the armature and the corresponding coils in the housing. Alternatively a device may be constructed in such a way that the reactive part wraps the core of the armature spirally, the start and end of the coil being connected electrically highly condutively together, and the associated coil or coils is or are likewise arranged spirally in the housing.

For the sake of simplified construction each coil may have only a single turn. In orderto further increase the forces and acceleration the coil may be attached to a field concentrator made of electrically highly conductive material, sectioned, and known per se, from which it is electrically insulated, the cross-section of which tapers towards the associated reactive part. If desired the armature may be biassed to a definite rest position mechanically, e.g., by springs.

Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows an embodiment with one reactive part and two coils, Figure 2 shows an embodiment with two reactive parts, Figure 3 shows an embodiment with field concentrators and Figure 4 shows an embodiment with triply spiralled reactive part.

Figure 1 illustrates a simple actuating element with two coils and an armature located in a cylindrical housing 1. The armature comprises an electrically nonconductive cylindrical core 2 and an electrically highly conductive annular reaction part 3, and is mounted coaxially with the housing axis and displaceably in both directions of said axis. Both ends of the armature core 2 project out of the housing. The displacement of the armature in the axial direction is limited by stop surfaces in the interior of the housing co-operable with the reactive part 3. On each of the two sides of the reactive part 3, outside its range of movement space there is present respective coils 4 and 5, which each comprise a single turn fixed coaxially to the armature in the housing. The start and end of each coil are passed upwards out of the housing. The housing parts are screwed together.The ends of the armature core 2 protruding out of the housing act on one or on both sides upon actuating members of valves, not shown.

When the coil 4 is subjected to an alternating current or current impulses of great intensity and steep rising flank, the magnetic field built up round the coil generates eddy currents in the annular reactive part, which in accordance with Lenz's law generate an elecromotive force - directed away from the coil upon the armature in the direction +F. For an appropriate current intensity and rising flank the armature then undergoes an acceleration which can lead to switching times of below 0.1 millisecond. In analogous manner, a current in the coil 5 produces a movement of the armature in the direction -F.

Figure 2 shows in a similar manner to Figure 1 an actuating element, but with two reactive parts 3 and 3' on an armature core 2 with corresponding coils 4 and 5 or 4' and 5'. This arrangement produces an intensification of the force or acceleration when cur rent flows simultaneously in the coils 4 and 4' or 5 and 5'. It will be appreciated that more than two reactive parts and corresponding coils may be provided.

Figure 3 shows an embodiment similar to Figure 1, but with the difference that the coils 4 and 5 have a field concentrator 6 or 7 respectively on their sides confronting the reactive part 3. It is constituted by a sectional ring of electrically highly conductive material tapering in cross-section towards the reactive part, which ring is insulated electrically from the associated coil by an insulating layer 8 or 9. When a current flows through the coil, eddy currents are likewise generated in the field concentrator, which displace the magnetic field into the gap between field concentrator and reactive part and thereby intensify the compression effect and the acceleration of the armature.

Figure 4 shows lastly an embidiment wherein in contrast to the multiple reactive parts of the embodiment according to Figure 2, the reactive part 3' ' and colis 4'' and 5'' are arranged in the form of a spiral in order to intensify the acceleration of the armature.

In this case an electrically conductive connection 10 is necessary between the start and end of the spiralled reactive part in order to permit the flow of the eddy currents.

In all the embodiments described the armature is either exposed to the forces generated or left to itself, i.e., it is not maintained in a specific rest position by any additional members - e.g., springs. This has the advantage that no additional energy is required in order to overcome return forces.

However, such additional members can obviously be provided if necessary.

Claims (9)

1. An electromagnetic actuating device for highspeed switch elements including a coil fixed in a housing and an armature constituted by a cylindrical or tubular core with at least one reactive part coaxial to the coil and movable axially relative to the coil, the arrangement being such that current impulses or alternating currents fed to the coil produce a magnetic field which generates eddy currents in the reactive part which eddy currents generate a force in the direction of the coil axis directed away from the coil.

2. A device according to Claim 1, wherein the core of the armature consists of electrically nonconductive or less highly conductive material and the reactive part of highly electrically conductive material.

3. A device according to Claim 1 or 2, wherein for actuation of the armature in a counter-direction a second coil is fixed in the housing so that the reactive part with a desired movement space is located between the two coils.

4. A device according to any one of the preceding Claims, wherein a plurality of reactive parts are arranged on the core of the armature and corresponding coils are fixed in the housing, one on each side of each reactive part.

5. A device according to any one of Claims 1 to 3, wherein forthe summation of forces the reactive part is in the form of a spiral which wraps round the core of the armature, the start and end of the spiral being joined together highly electrically conductively and wherein the associated coil or coils is or are likewise arranged spirally in the housing.

6. A device according to any one of Claims 1 to 4, wherein the or each coil has a single turn.

7. A device according to any one of the preceding Claims, wherein the coil is attached to a field concentrator made of electrically highly conductive material sectioned in the axial direction from which it is electrically insulated, the cross-section of which concentrator tapers towards the associated reactive part.

8. A device according to any one of the preceding Claims, wherein the armature is biassed mechanically in a predetermined rest position.

9. An electromagnetic actuating device for highspeed switch elements substantially as described herein with reference to and as illustrated in Figure 1, 2,3 or 4 of the accompanying drawings.