WO1999024993A2 - Electromagnet - Google Patents

Abstract

Electromagnet comprising a moveable part, i.e. a 'plunger', shaped as a flap (5) which closes a magnetic circuit when a current flows through a coil (1) enclosing at least a portion of the circuit, i.e. the 'core' (3), which is arranged on a base surface (4). The magnetic circuit comprises contact means (3, 8) shaped as tongues or the like, which are stamped out in the flap (5) and the base surface (4) respectively. The shape of the tongues may differ for different applications. The electromagnet may preferably be designed for blocking or locking functions.

Description

Electromagnet

Technical Ωeld

The invention relates to an electromagnet comprising a moving part that closes a magnetic circuit when a current is flowing through a coil that encloses at least a portion of the circuit.

Prior art

A known type of electromagnet, a so-called solenoid, see figure 1, consists of a magnet core arranged inside a bobbin with an enclosing current coil. Inside the bobbin there is also a moveable plunger. When current flows through the coil a magnetic force is obtained and if the plunger at that moment is located at a distance from the core, thus with an air gap A between the plunger and the core, the force "strives" to increase the air gap. The force will thus cause an attraction between plunger and core that reduces the air gap. The bobbin with core and plunger is arranged in connection to a magnetic feedback yoke for closing of the magnetic circuit, consisting of core, plunger and yoke.

Between yoke and plunger there is however always a small air gap B that will cause a loss of the magnetic flow, which will cause a decrease of the magnetic attracting force. This is a disadvantage with those known electromagnets.

A further disadvantage is caused by dust and dirt entering between plunger and bobbin, and affecting the friction of the movement of the plunger.

If the electromagnet mentioned above is to be used as a blocking element, i.e. if the plunger is to be used to block a lock cylinder or other object, the plunger will be laterally biased which results in a seizing thereof. This is yet another disadvantage with the above mentioned electromagnets. The object of the invention is to provide an electromagnet without the above mentioned disadvantages.

Brief description of the invention According to the invention the electromagnet comprises a moveable part that closes a magnetic circuit when a current is passing through a coil that encloses at least a portion of the circuit. The magnetic circuit comprises a supporting surface, or base, in which is arranged a magnetic contact means for co-operation with a magnetic contact means at the moveable part. The moveable part consists of a flap device pivotally arranged to at least one wall that is connected to the mentioned base. The mentioned contact means can be compared or equivalent to plunger and core according to the known technique. The electromagnet is characterised by that the contact means are formed as tongues or the like that are stamped out in the base and in the flap respectively.

The electromagnet according to the invention present low friction when moving the moveable part, irrespective of the direction and magnitude of the load, even when the details included have relatively large manufacturing tolerances.

A further advantage with an electromagnet according to the invention is that it presents very high mechanical strength and that it, for example as a blocking element, may be exposed to a heavy mechanical load with maintained low friction. The electromagnet according to the invention presents the advantage of cheap and simple manufacturing, and it is reliable and easy to modify for different applications.

Further features with the electromagnet according to the invention will be seen from the accompanying claims.

Description of drawings The electromagnet according to the invention will be described in greater details below with reference to the accompanying drawings, in which: figure 1 shows an electromagnet according to prior art, figures 2 a, b, c schematically show an embodiment according to the invention, figures 3 a, b schematically show a pivotally arranged attachment device for attaching the flap to the wall, figures 4 a - e show different embodiments of magnetic contact means, figure 5 a, b, c shows an embodiment of the invention that includes several flaps.

Description of embodiments In figure 1, 1 indicates a winding or current coil, which encloses a coil former, i.e. a bobbin 2. Inside the bobbin 2 a core of magnetic material 3 is located, which core at its outer end is attached to a yoke 4 of magnetic material. Inside the bobbin 2 there is also a plunger 5 movable along the axis of the bobbin. Between the core 3 and the plunger 5 a maximum air gap A can be found. The plunger 5 extends through an opening or the like in the other end of the yoke 4 and by that there is a little air gap B between plunger 5 and yoke 4. The plunger 5 travels inside the bobbin 2 with a little free space between plunger and bobbin. When current flows through the coil a magnetic force trying to close the magnetic circuit consisting of core 3, plunger 5 and yoke 4 occurs, which will pull the plunger towards the core causing the air gap to cease.

The electromagnet shown in figure 1 is generally known even though its design may vary.

The electromagnet according to the invention shown in figure 2 is specially adapted for use related to blocking or locking functions, for example in electrical locks for a filler cap, for blocking in-gear level housings and similar applications in vehicles. The invention is however not limited to these applications. Figures 2 a, b, c thus shows an electromagnet according to the invention, where details with the same function as those in figure 1 have the same reference numbers. In a housing, or a box 4 or other construction, of magnetic material, a magnetic contact means 3, a "magnet core", is arranged, enclosed by a bobbin 2 with current coil 1. A flap device 5, or other pivotally arranged moveable device, a "plunger", is arranged at a wall, or at two opposite walls, of the box 4 by means of a pivot arrangement, for example of hinge type. Conveniently, protruding parts 6 are arranged at opposite sides of the flap 5, for cooperating with the inside of corresponding recesses 7 in at least one wall of the box, so that the flap 5 may swing up and down on this "hinge" . Other types of attachment objects for the flap is possible. Likewise other types of coil arrangements are possible. The moveable part, or flap, 4 is meant to work completely or partly between the walls of the box to create the magnetic feedback normally needed in magnetic circuits.

To limit the motion of the moving part 5 upwardly a sound-absorbing abutment device 9 is conveniently arranged at the upper edge of the box 4. The "stroke" of the moving part (see arrows shown in figure 2a) in the shown embodiment ranges between the abutment device 9 and the upper part of the bobbin 2.

Conveniently, a return spring is attached to the moving part 5 (not shown) to revert the moving part to its open state when current no longer flows through the coil.

In the present embodiment the flap 5 constitute a "cover" to the box 4, or a portion of a cover, in which cover a tongue 8 is stamped out. This tongue, the "plunger", is bent downwardly to be magnetised when current flows through the coil, and be attracted towards a corresponding tongue 3, the "core", which is formed in the bottom of the box and then bent upwards. The tongue 3 at the bottom of the box extends into the bobbin 2 with the current coil 1. The tongues may be arc-shaped (see figure 4b) or be designed with an angled contact edge (see figure 4c). There could also be arranged contact devices with U-shape (see figure 4d) or with co-operating M and V-shape (see figure 4e) or in some other way where two surfaces are able to close contact with each other. By bending of the material or by adding further material in wanted configurations greater and smaller magnetic flows can be obtained. By differently shaping of the magnetic contact parts different magnetic characteristics may be obtained. The stamping out of tongues is a cheap method resulting in many magnetical variations.

In figure 2b are illustrated typical forces C and D which bias the flap when used as a blocking element or the like.

Figures 3a and b show the protruding portions 6 of the yoke 5 co-operating with the recesses 7 in the wall. In figure 3a the yoke 5 is most loaded in the direction shown by the arrow, the flap turns around centre of rotation X. In figure 3b the yoke is most loaded in the opposite direction, the yoke is turned around the centre of rotation Y. By different loads in the direction of the arrows C and D (see figure 2b) or combinations of those directions a function in the "hinge" is obtained according to figures 3a and 3b. Irrespective of the combination of loads biasing the flap, the flap will "tip" towards either of the walls of the recess 7. This means that the friction at the centre of rotation of the flap will be low even at heavy loads and irrespective of the direction of the load and also in case at relatively large manufacturing tolerances at the details 6 and 7 are allowed. Consequently, the electromagnet according to the invention does not have the problem with seizing of the moving part when loaded laterally.

Figure 5 schematically shows the same technique used to obtain magnetic devices with several coils (not shown). Figure 5 shows a type of bistable magnetic device where the holding function in each state obtains by permanent magnets 10. As an alternative, flaps 5 may be provided with holding springs or else could pressure springs (not shown) be arranged associated to the ends of the flap.

Claims

Patent claims

1. Electromagnet including a moveable part (5) for closing a magnetic circuit (3, 4, 5) when a current flows through a coil (1) that enclosing at least a portion of the circuit, the magnetic circuit comprising a supporting surface or base, provided with a magnetic contact means (3) adapted to co-operate with a magnetic contact means (8) at the moveable part (5), which including a flap means pivotally arranged (6, 7) at at least one wall connected to said base, characterised in that the contact means is essentially tongue shaped or the like and are stamped or cut out and preferably bent towards each other, at the base and such flap.

2. Electromagnet according to claim 1, characterised by the contact means (8, 3) being arc-shaped, or designed with an angled contact edge, or co-operating M- and V-shape respectively. (See fig. 4 a-e)

3. Electromagnet according to any of the claims 1-2, characterised by the flap (5) having two protruding portions (6) for co-operation with recesses (7) in the walls of the box to constitute hinge.

4. Electromagnet according to any of claims 1-3, characterised by the magnetic circuit (3, 4, 5) comprising a box-like device, on the base of which a bobbin (2) with a current coil (1) is arranged, in which bobbin (2) said contact means extends and, in order to have a closed magnetic circuit, contact with the contact means (8) of the flap (5), by means of the hinge devices (6, 7) being attached to one or two of the boxes walls.

5. Electromagnet according to claim 4, characterised by the movement of the flap (5) from the contact part 3 in the base being limited by means of a noise-absorbing abutment device (9) arranged at a wall of the box.

6. Electromagnet according to any of the preceding claims, characterised in that two opposite directed flaps (5) with magnetic contact parts, which are pivotally arranged in a hinge device (6,7), constitute a bistable magnetic device when a current alternately flows through at least two coils comprising magnetic contact parts (3) and the two magnetic circuits are closed alternately.