IE48247B1 - Electromagnet - Google Patents

Abstract

This contactor comprises a fixed circuit with three branches (5, 6, 7) cooperating with an armature (12) and energised by a coil supplied with DC, a housing (1) and a contact unit (2). At least one part of the cooperating pole surfaces (21, 21', 23, 23' - 22, 22', 24, 24') is inclined with respect to the axis of the central branch (7), whilst the outer limbs (5, 6) of the fixed circuit each have a lateral rim which bears on a corresponding stop (25, 25') placed in the vicinity of the bearing surface (11) of the housing (1) receiving the contact unit (2). Such a contactor is easy to assemble and the use of auxiliary contacts is possible, even for low values of the coil's supply voltage, without calling upon a bulky magnetic circuit and without requiring a number of ampere turns liable to cause excessive heating up of the coil.

Description

This invention relates to an electromagnet having a magnetic coil excited in particular by means of direct current, said coil being wound on a housing, the electromagnet having a three-limbed magnetic circuit consisting of a fixed E-shaped core and a movable armature, likewise E-shaped, said circuit being provided, on all the limbs, with fitted pole surfaces symmetrically inclined with respect to the central axis of displacement of the armature, and in which the armature is guided in its displacement stroke by means of guiding devices.

A magnet of this type is known from the publication Niederspannungs-Schaltgeraete of the firm Calor-Emag. Each of the inclined pole surfaces on the outer limbs of the armature points to the exterior of the magnetic circuit, and the guide devices are made from sheet metal strips of tin bronze disposed along the central axis of displacement, said strips projecting above the middle limb of the armature and sliding in corresponding grooves of the middle limb of the core even when the armature has been lifted off.

In another magnet (DE-AS 12 46 857), this time an AC magnet, a coil body is provided having guide grooves disposed along the central axes of displacement, and armature and core of the magnetic circuit are fitted on both sides with elongated sliding strips, which are slidably received in the guide grooves and are pressed into perforations of the magnet components by securing pieces which stand out perpendicularly.

For fitting such magnets into a housing it is known (DE-GM 18 92 298) to produce or extend the planar outer pole surfaces on the outer limbs of the core further than corresponds to the counter-surfaces of the armature, and to press them against abutments in the housing by means of a spring inserted between the housing base and the under-surface of the core.

The problem which the invention seeks to solve, is to design a magnet of the type described above in such a way that, while assembly remains simple, there is achieved a well centered lift movement of the armature, which produces a reduction of the thermal stress of the magnet or, as the case may be, an increased attractive force with constant thermal stress.

It is an object of the present invention to overcome the aforementioned problem.

Accordingly, the invention provides an electromagnet which comprises a magnetic coil excited in particular by means of direct current, said coil being wound on a housing, the electromagnet having a three-limbed magnetic circuit consisting of a fixed E-shaped core and a movable armature, likewise E-shaped, said circuit being provided, on all the limbs, with fitted pole surfaces symmetrically inclined with respect to the central axis of displacement of the armature, and in which the armature is guided in its displacement stroke by means of guiding devices, said guiding devices being made up of guide grooves on the interior of the coil housing extending along the central axis of displacement, and of guide rods projecting transversely of the middle limb of the movable armature and slidably housed in said guide grooves, and central perpendiculars erected on the pole surfaces of the outer limbs of the movable armature which intersect in the region of the guide rod.

In the electromagnet according to the invention, the guide rods can be the projecting heads of assembly rivets in the case of a laminated magnetic circuit or rods pressed into normal through bores in the case of a magnetic circuit consisting of solid material.

The special design of the outer circuit with, in this case, inclined pole surfaces inwardly turned in the outer limbs of the armature produces no unbalancing moment with respect to the guide rod even if the armature is somewhat irregularly lifted, so that the simplified guide device is sufficient to prevent unbalancing of the armature and to make it easily movable. A reduction of the connecting current necessary for lifting is made possible as against comparable electromagnets, and the relatively difficult assembly of the sliding guide strip becomes unnecessary.

In an advantageous further embodiment according to the invention the acute angle between the pole surfaces on the middle limbs of core and armature and the central axis of displacement is smaller than the corresponding acute angle between the pole surfaces of the outer limbs and the central axis of displacement. This embodiment produces a greater proportion of the attractive force by means of the middle limb as against the outer limbs, so that the centering of the lift movement is further improved.

In an advantageous further embodiment according to the invention outwardly directed projections are provided on the outer sides of the outer limbs of the fixed core, which projections have abutment surfaces which cooperate with openings in elastic side walls of an outer magnet casing, the abutment surfaces being loaated as close as possible to a support surface of the casing on which support surface the respective contact housing for the contacts influenced by the movable armature rests.

In this embodiment alongside the easier assembly and the abolition of the base spring, there is a still further improved centering of the core position and thus a further improvement in the guiding for the armature.

Exemplary embodiments of the invention are described in more detail as follows with reference to the drawing, in which Fig 1 shows two axial sections, each of which is through one half of an embodiment of the magnet, once in the lifted and once in the closed condition, Fig 2 shows details of tne securing devices of the magnet core, and Fig 3 shows a further embodiment of the magnet, which permits limitation of the strength of the lateral attractive forces between the core and the armature.

The magnet of Fig 1 is built into a hollow housing 1, which is closed by a contact block 2 which forms the cover of the housing.

A fixed, E-shaped magnetic core is disposed in the housing 1, and has a middle limb 7 and two side limbs 5 and 6, arranged mutually parallel and connected together by a common bridge 8. This core is held in the housing at three points, namely an elastic device 10 presses on the under surface 27 of the bridge 8 and thereby urges the core upwardly as shown in the drawing, said core coming to rest by means of two projections 26, 26' (see also Fig 2) against abutments 25, 25' on the side walls 19, 19' of the housing 1.

The elastic device can be formed of the elastic base 9 of the housing itself, while the abutments are advantageously formed of the upper edges of openings 20, 20' in the walls 19, 19’{Fig 2); at the same time the walls are executed with sufficent elasticity to be pushed apart from one another transversely, to permit introduction of the core into the interior of the housing 1 by the application of force. Thus the core is held to the side walls of the housing, the latter being moulded in one piece from a suitable materi al.

The core can also be held in a direction perpendicular to the plane of the drawing by means of other edges of the openings 20, 20' and by means of cheeks 29 which are likewise formed integrally with the base 9 of the housing 1.

A coil 4 surrounds the middle limb 7 of the core and serves for excitation of the electromagnet. The inner surface of the coil housing possesses grooves 28 which extend parallel to the middle axis X-X and cooperate with a transverse rod 23 through the core for aligning the latter.

The housing 1 terminates upwardly in a plane surface 11. This surface 11 serves as a mounting surface for an under-surface 31 of a contact block 2 which is secured to the housing with the help of clamping devices (not shown).

This contact block contains all moving parts of the device, namely a movable armature 12, likewise of E-shaped design, a contact carrier 16, on which the movable contacts 17 are arranged and cooperate with fixed contacts 18, and a return spring 13 which is mounted during assembly on a fixed part of the housing or on the coil, and which biases the surface 14 of the armature against an abutment surface 15 of the contact block 2. The middle limb 32 of the armature possesses a transverse rod 13, the ends of which enter the said grooves 28.

In the lifted or resting condition of the magnet shown in the left half of Fig 1, the armature is pressed against the surface 15 which accordingly serves as a reference surface.

If the coil is energized by means of a sufficient direct current, the armature executes a lift movement with amplitude L and thereby causes the pole surfaces 22, 22' of the armature outer limbs to contact the pole surfaces 21, 21' of the core outer limbs. in this closed condition of the magnetic circuit a residual gap £ (Fig 1 and Z) exists between the pole surface 24 and 23 of the central limbs 32 and 7 of the armature and of the core respectively.

As shown in Fig 1, the pole surfaces 21, 22, 23 and 24 of the outer and middle limbs are inclined to the axis X-X' of the magnet. For a given lift L of the armature, therefore, there is produced a smaller air gap and a greater pole surface and thereby a smaller air-gap magnetic resistance for the magnetic circuit. Tne residual gap _e on the middle limbs reduces the influence of the remanence of the iron circuit and thus prevents adhesion of the magnet.

The pole surfaces 23 and 24 on the middle limbs 7 and 32 have a symmetrical V-shape with respect to the axis X-X * of the coil, said axis representing at the same time the central axis of displacement of the armature. The angles which these surfaces make with the axis X-X' are kept smaller than the angles which the surfaces 21, 22 of the outer limbs make with this axis, so that the attractive force arising between the middle limbs 7 and 32 is higher than the attractive force between the outer limbs.

This ensures better stability of the lift movement of the armature; but there may still exist a lateral disequilibrium of the attractive forces. This disequilibrium is nevertheless restricted, firstly by the fact that the outer pole surfaces are also symmetrically inclined to the central axis of displacement X-X‘, and by the disposition of the rod 30 in such a way that the perpendiculars N through the mid-points of the pole surfaces 21, 21' of the outer limbs pass through that region of the middle limb in which the guide rod 30 is located.

In order that the abutments 25, 25' constituted by the upper limit of the opening 20, 20’ may not have a too great displacement from the limiting surface 11 which serves as a support, the surfaces 21, 21' of the outer limbs 5, 6 of the magnetic core are outwardly directed. In this arrangement the pole surfaces 23 and 24 of the middle limb are disposed approximately in the middle between the upper bridge of the armature 12 and the lower bridge 8 of the armature, when the iron core is closed. This provision also serves to improve the stability of the magnetic system which acquires a significant increase in the initial attractive force with the armature lifted, as a result of the totality of the provisions described. In order that the armature may in fact De pulled, the lift distance L may not exceed certain limits. This distance is therefore determined with whatever precision the manufacturing tolerances will permit.

In the magnetic circuit illustrated, the distance between the common plane of the surfaces 11 and 31 and the support surface 13 for the armature is designated dp the distance between this common plane and the plane through the abutments 25 and 25', against which the projections 26 and 26' rest, is designated d?, and the distance between the plane of these abutments and the lower surface 27 of the core against which the elastic device 10 acts, is designated d^.

Since the parts 1 and 2 are plastics mouldings, the danger exists that alterations in the lengths of these parts may contribute to an excessive enlargement of the lift L. The influence of this alteration resulting from the manufacturing tolerances is reduced, however, if the sum of the distances dj and d? is kept as small as possible.

Since an extension of the outer limbs of the core to the height of the surface 15 would lead to laterally directed magnetic force and disturbing effects, and at the same time to an enlargement of the transverse dimensions (by increase of the space necessary for the coil windings), the surface defined by the abutments 25, 25' is arranged as close as possible to the plane of the surface 11. By this arrangement there is simultaneously achieved an efficient securing and exact alignment of the core supported at its three points, and assembly is facilitated.

In the embodiment shown in Fig 3, which is otherwise designed as described with respect to Figs 1 and 2, the symmetry of the transverse magnetic forces is improved by forming each of the fixed core and the armature from two half circles of iron 40, 41 and 46, 47, which are designed symmetrically about a plane through the central axis of displacement X-X1 and perpendicular to the plane of the drawing, and which are fitted together by means of lateral strips so as to form a central air gap 50, 51.

If, in this embodiment, there is a mutual approach of the two surfaces 42, 44 and 43, 45 which belong to two poles of the outer limb and two poles of the middle limb respectively, by reason of magnetic asymmetry or by the lateral effect P of gravity (when the magnetic circuit lies horizontally) then the magnetic resistance produced in the magnetic circuit R by the air gap 50 and 51 will limit the attractive force which can develop between the said surfaces, and thereby the laterally directed components of the total attraction between armature and core is likewise 1imited.

Claims (4)

1. CLAIMS:1. An electromagnet which comprises a magnetic coil excited in particular by means of direct current, said coil being wound on a housing, the electromagnet having 5 a three-limbed magnetic circuit consisting of a fixed E-shaped core and a movable armature, likewise E-shaped, said circuit being provided, on all the limbs, with fitted pole surfaces symmetrically inclined with respect to the central axis of displacement of the armature, and in 10 which the armature is guided in its displacement stroke by means of guiding devices, said guiding devices being made up of guide grooves on the interior of the coil housing extending along the central axis of displacement, and of guide rods projecting transversely of the middle limb of 15 the movable armature and slidably housed in said guide grooves, and central perpendiculars erected on the pole surfaces of the outer limbs of the movable armature which intersect in the region of the guide rod.

2. An electromagnet according to Claim 1, wherein 20 the acute angle between the pole surfaces on the middle limbs of core and armature and the central axis of displace ment is smaller than the corresponding acute angle between the pole surfaces of the outer limbs and the central axis of displacement. 25

3. An electromagnet according to Claim 1 or 2, wherein outwardly directed projections are provided on the outer sides of the outer limbs of the fixed core, which projections have abutment surfaces which cooperate with openings in elastic side walls of an outer magnet 30 casing, the abutment surfaces being located as close as possible to a support surface of the casing on which support surface the respective contact housing for the contacts influenced by the movable armature rests.

4. An electromagnet according to Claim 1, substantially as hereinbefore described with reference to and as illustrated in 1 - 3 of the accompanying drawings.