EP0172080A1 - Polarised electromagnet with three positions and control circuit - Google Patents

Abstract

The electromagnet comprises a fixed assembly (1) surrounded by a coil (5) and a movable assembly (7). Each crew consists of a permanent magnet (2; 14) fitted with pole pieces (3, 4; 12, 13). The ends of the pole pieces are arched towards each other to define four air gaps (E1 to E4) allowing movement of the crew (7) between two extreme positions. One end of the pole piece belongs to only one air gap and the faces of the air gaps are connected to polar faces of permanent magnets of the same polarity, so as to cancel the flows in the closed air gaps in the absence of excitation and to allow a return to a stable central position. Use in reversing contractors for two-way motor, with time delay in the event of a sudden reversal command.

Description

The present invention relates to a three-state electromagnet.

The present invention also relates to a circuit for its control.

Three-state electromagnets are useful, for example, for controlling a device between a rest state and two different operating states. For example, such an electromagnet can be mounted in a contactor making it possible to put a three-phase motor in forward, in reverse or in standstill. Such a contactor comprises contacts of the reversing type capable of also taking an intermediate position between the two extreme positions. To avoid a short circuit of the source during the duration of the electric arcs on the contacts, it is necessary to avoid that the inversion of the contacts is too fast.

We know from DE A1 31 38 265 and FR - A - 2 532 107 a polarized contactor with three stable positions, comprising a bistable electromagnet with permanent magnet and a return spring whose effect is zero in the central position of the armature with a sudden variation as soon as the armature deviates from its central position. The permanent magnet ensures the stability of each of the extreme positions despite the opposite effect of the spring.

Thus, this known contactor is tristable. However, the uses with monostable contactors are more frequent. In addition, to leave an extreme position, it is necessary to excite the coil in a direction opposite to that which served for the preceding excitation. However, at this stage, the reinforcement risks exceeding the stable central position and going up to the other extreme position, Instead of stopping, the controlled motor will turn in the opposite direction, which can be very dangerous. We know in fact that it is difficult to dose amperes, because of the voltage and resistance differences due to heating. In addition, the strength of the magnets varies with temperature and the strength of the contact springs decreases with contact wear.

To remedy this defect, the prior document proposes to simultaneously excite the windings in the opposite direction. Their total effect is then only that resulting from leaks due to the different positions of the windings, which leads to poor efficiency. In addition, the switching of the windings is difficult to implement. In addition, the creation of a stable central position by a spring is difficult to obtain and requires costly implementation precautions. See for example the book "La Télégraphie et le Télex" by D. FAUGERAS, Ed. Eyrolles 1962, page 194 - three-position relay.

It is indeed proposed in one of the cited documents a means of making the contactor monostable but this means is insufficient in practice.

We also know from EP -A 86 121 an electromagnet having two equipments provided with permanent magnets and movable relative to each other by defining between them four air gaps. The permanent magnets are in series with each other at one of the extreme positions which is therefore stable, and in opposition with each other at the other extreme position which is therefore unstable. Such an electromagnet is monostable without artifice but if it is used in a contactor, it can only put the power contacts in two different positions, not three.

FR - 2 554 957 (not published on the date priority of the present application) describes an electromagnet of the same type (two positions, two permanent magnets), but bistable.

Also known from US-A-2 872 546 is a three-position monostable electromagnet in which a permanent rotating magnet is mounted between two fixed magnets connected by their middle each to one end of a fixed yoke. In the absence of excitation, the mobile magnet takes an intermediate position in which its North pole is equidistant from the North poles of the fixed magnets and its South pole equidistant from the South poles of the fixed magnets. Depending on the direction of excitation of a coil surrounding the cylinder head, the movable magnet pivots in one direction or the other. However, this electromagnet is not very effective because the coils act practically only to suppress certain repulsion forces and to let others remain.

Now we know that the forces of repulsion are weaker than forces of attraction in closed air gaps.

The object of the invention is thus to propose a three-position monostable electromagnet, which develops significant magnetic forces in the "working" positions and which is not likely to pass from one extreme position to the other when it has only been ordered to return to the central or intermediate position, and which, without costly modification such as an increase in the travel or the inertia of the moving assembly, is not likely to pass too quickly from an extreme position to the other by creating a short circuit risk.

The invention thus relates to a polarized electromagnet comprising a magnetic circuit and at least one excitation coil surrounding part of the magnetic circuit; the latter is constituted by two crews each comprising at least one permanent magnet provided on its pole faces with pole pieces, the crews being movable relative to each other between two extreme positions; the pole pieces of one crew form with the pole pieces of the other crew two opposing pairs of variable air gaps, the air gaps of one pair closing when the air gaps of the other pair open due to the relative movement of the crews whose direction is determined by the state of excitation of the coil.

In one of the pairs of air gaps, each air gap has facing faces connected to the polar faces of permanent magnets of the same magnetic polarity.

According to the invention, in the other pair of air gaps, each air gap has facing faces connected to polar faces of permanent magnets of the same magnetic polarity and the sizes of the permanent magnets are chosen to cancel substantially, in the absence of excitation of the coil, the flow which passes in a closed air gap, thus making it possible to bring the position of the crews to an intermediate position between the two extreme positions, and on the other hand to ensure in the presence of the excitation an attraction towards one or the other of the extreme positions according to the direction of the excitation of the coil.

In a preferred embodiment of the invention, the air gaps are formed by ends of the pole pieces and each of these ends belongs to only one air gap.

In this way, when the crews are in an extreme position relative to each other and that the supply is cut, the electromagnetic force of attraction is removed and repulsion forces appear as in the "working" position of the contactor described in EP -A - 86121. If the force of the permanent magnets has been chosen sufficient by compared to a possible remanence in the closed air gaps, these repulsive forces bring the two crews back into their intermediate rolling position. It is also possible to choose weaker magnets in connection with elastic return means, for example the elasticity of the power contacts if the electromagnet is used in a contactor. It should be understood that the return means envisaged here as a possible only have a supporting role bringing into play low forces compared to the electromagnetic forces and possibly ensuring better resistance to vibrations in the intermediate position, the essential being to remove the electromagnetic force of attraction. They are therefore not recall means providing significant efforts that more than counterbalance the force of the permanent magnet, at the risk of remanance.

Once taken off from their extreme relative position, the crews cannot exceed their intermediate relative position because beyond that, symmetrical restoring forces appear. The intermediate position is therefore stable. It is in this position that each magnet "sees" the lowest reluctance of the magnetic circuit which is imposed on it.

When an excitation of a given direction is applied, one of the crews moves relative to the other towards an extreme position, under the effect of forces similar to those generated in the contactor according to EP - A - 86121. The differences between two magnet forces being stable over time and indifferent to the temperature, the intermediate position is precisely defined. It can be adjusted by selective demagnetization.

According to another aspect of the invention, the control circuit for the above electromagnet is characterized in that it comprises, for at least one of the windings of the coil, an assembly comprising a pluggable capacitor in parallel with the winding, a resistor connected in series with this winding, a discharge resistor connectable in parallel with the capacitor, and a movable switching means between a first position in which a supply line of the winding and the capacitor are connected to a source terminal while the discharge resistance is disconnected, and a second position in which the capacitor is in series with the discharge resistance while the winding supply line is open.

Thus, in order to pass the armature from one extreme position to the other, one begins by cutting the supply of the winding in service and the winding equipped with the above-mentioned assembly is energized; the moving part is thus recalled to the intermediate position. But at first, it cannot go beyond this position. Indeed, the voltage across the winding in question increases with the charge of the capacitor and it is only after a certain delay or stop time that said voltage is enough to push the moving element to another extreme position. With such a control circuit, a contactor according to the invention allows for example a motor to change the direction of rotation without abruptness or risk of short circuit between phases. When this other winding is put back into service, the capacitor discharges into the discharge resistance. The two windings can each be equipped with an aforementioned assembly, in which case the operation described above takes place each time that the excitation is passed from one winding to the other.

Other features and advantages of the invention will emerge from the description below.

• - la figure 1 est une vue en coupe suivant l'axe de la bobine d'un électro-aimant selon l'invention ;
• - la figure 2 est une vue en coupe de l'électro-aimant de la figure 1, perpendiculairement à l'axe de la bobine ;
• - la figure 3 est une vue en perspective et en coupe d'un autre agencement d'un électro-aimant suivant l'invention ;
• - la figure 4 est un schéma de montage de l'électro-aimant des figures 1 à 3 dans un contacteur pour la commande avant-arrière-arrêt d'un moteur triphasé ; et
• - les figures 5 et 6 montrent le contacteur des figures 1 à 3 respectivement associé à deux circuits de commande selon l'invention, pour la commande avant-arrière-arrêt d'un moteur triphasé.

In the accompanying drawings, given by way of nonlimiting examples ₁

• - Figure 1 is a sectional view along the axis of the coil of an electromagnet according to the invention;
• - Figure 2 is a sectional view of the electromagnet of Figure 1, perpendicular to the axis of the coil;
• - Figure 3 is a perspective view in section of another arrangement of an electromagnet according to the invention;
• - Figure 4 is a mounting diagram of the electromagnet of Figures 1 to 3 in a contactor for the front-rear-stop control of a three-phase motor; and
• - Figures 5 and 6 show the contactor of Figures 1 to 3 respectively associated with two control circuits according to the invention, for the front-rear-stop control of a three-phase motor.

In the embodiment of FIGS. 1 and 2, the electromagnet comprises a fixed element 1 and a mobile element 7. The fixed element 1 comprises a permanent magnet 2 whose pole faces (N, S) are respectively provided with pole pieces 3 and 4. A coil 5, wound on a coil carcass 6, surrounds the crew 1 in its central region where the magnet 2 is located, so that the field of the coil along an axis YY 'is perpendicular to the magnetization axis XX 'of the permanent magnet 2.

The moving element 7 also includes a permanent magnet 14 whose magnetization axis is parallel to XX 'and whose pole faces (N, S) are provided with pole pieces 12 and 13 respectively.

The pole piece 3 has two ends 15, 16 emerging from the coil 5 and bent at right angles along the cheeks of the coil carcass 6.

The pole piece 12 has two ends 8, 9 bent at right angles so that they are parallel to the ends 15 and 16 and outside the latter. A variable air gap El between the ends 15 and B and a variable air gap E2 between the ends 16 and 9 is thus determined between the crews.

The pole piece 13 has two ends 10, 11 bent at right angles so that they are parallel and outside the ends 8 and 9.

Finally, the pole piece 4 has two ends 17, 18 emerging from the coil 5 and bent at right angles so that they are parallel to the ends 10 and 11 and outside the latter. A variable air gap E3 between the ends 10 and 17 and a variable air gap E4 between the ends 11 and 18 is thus determined between the crews.

In a preferred version of the invention, the movable element 7 can move by translation in a direction parallel to the axis of the coil. It can be seen in FIG. 2 that this crew is guided by notches in the cheeks of the coil carcass 6.

For a first extreme position of the mobile assembly 7, the air gaps El and E4 are closed by bringing their opposite faces together while the E2 and E3 air gaps are open. For the other extreme position, the air gaps E2 and E3 are closed, El and E4 being open.

The two pairs of air gaps E1-E4 and E2-E3 therefore have antagonistic effects.

According to the invention, the polarities of the permanent magnets 2 and 14 are chosen so that the facing faces of each air gap are connected to polar faces of permanent magnet of the same polarity, namely the polarity N for the air gaps El and E2 and the polarity S for the air gaps E3 and E4.

This arrangement is made possible by the fact that each end of the pole piece belongs to only one air gap, while for example in EP - A - 86121, certain ends of the pole pieces (9a and 9b) belong to two air gaps antagonists.

According to the invention also the sizes of the permanent magnets (mainly their surfaces) are chosen so that no magnetic flux crosses a closed air gap in the absence of excitation of the coil 5. This avoids that the extreme positions are stable positions. It is even possible for the permanent magnets to see lower external reluctances when the moving element 7 is in an intermediate position substantially at the halfway point of the extreme positions, as in FIG. 1. For this, it can @ it is advantageous to add permanent magnets near the air gaps, for example between the parallel ends 8 and 10 as well as 9 and 11.

But the sizes of the magnets (mainly their thickness) must also be chosen according to the invention according to the amps of the coil so that the latter reinforce a sense of passage of the flux of the permanent magnet 2, bypassing the permanent magnet 14 and ensuring a sufficient "working" force in the pair of closed air gaps, according to the direction of excitation of the coil.

Practically, taking into account the asymmetries between the two air gaps of a pair of air gaps, it is difficult to obtain a sufficient repelling force, and the central position can be ensured in a conventional manner by opposing springs acting as soon as the movable assembly 7 deviates, in one direction or the other, from its central position, improving the impact resistance.

To increase the "working" force, it may be advantageous to increase the power of the permanent magnet 2, even if this means having a low flux in the closed air gaps after cutting the coil, the corresponding residual force being easily compensated by a spring. bandaged at the end of the stroke, this force may result in part from the contact compression force.

The operation of this electromagnet is therefore of the monostable type from a stable central position. The direction of movement of the moving element towards one of the extreme positions depends on the direction of excitation of the coil, and the cutting of the latter causes the suppression of the electromagnetic working forces, at least in their major part, the return in the central position being possibly assisted by springs. The labor forces can be significant because the entire flux of the permanent magnet 2 is directed by the coil 5 in closed air gaps, while for example that in US - A - 2 872 546, the coils act practically only to suppress certain forces of repulsion and to let others remain.

In addition, by adding parts polar, the invention makes it possible to have sufficient labor forces, without however having residual forces.

Of course, the invention is not limited to the structure described above and many modifications can be made to the embodiment without departing from the scope of the invention.

Thus one can swap the fixed and movable parts by sliding the crew 1 in the coil carcass 6 whose cheeks are close together. It is also possible to remove certain arched ends of pole pieces, such as 15 and 16 in order to have a bearing end of the pole piece.

It is also possible to rotate the moving element 7 by 90 ° around the axis passing through the air gaps, possibly placing two moving elements on either side of the coil 5.

Instead of arching the ends of the pole pieces 3 and 4 on the same side of the axis YY 'of the coil 5, they can be arched on either side of this axis, as shown in FIG. 3 In this figure, it is the crew 1 which is movable by sliding in the carcass of the coil 6 and the crew 7 is split on either side of the coil 5. (Only the permanent magnet 14a with its pole pieces 12a-13a is visible).

Instead of being bent at a right angle, the ends of the pole pieces can also be flat or bent into a bayonet, as in FIG. 6 of FR - A - 2 554 957, while respecting the near magnetic polarities.

Finally, instead of having air gap closings by bringing together two faces of constant surface, it is possible to have air gaps with constant air gap, which close by varying the overlapping area of two opposite faces. To make such an arrangement, it suffices to provide in FIG. 1 that the mobile epipage 7 can pivot around the axis XX ′, the air gaps El to E4 having cylindrical surfaces suitably angularly offset.

FIG. 4 shows the electromagnet 21 of FIGS. 1 and 2, the moving assembly of which is fixed to the moving part 22 of three power contacts 23 of the reversing type, that is to say that the part mobile 22 of each contact 23 connects two pairs of distinct fixed contacts according to the extreme position occupied by the mobile assembly 7.

In the situation shown, the crew 7 is in the intermediate position and the moving parts 22 are also in an intermediate position in which no contact is made.

The contacts 23 are mounted between the terminals RST of a three-phase source and the terminals of a three-phase motor M according to a conventional arrangement such that the motor turns in one direction or the other depending on whether the contacts 23 are in a position or in the other.

The coil 5 comprises two coils 5a, 5b (shown diagrammatically) wound to generate flows of opposite directions when they are supplied and having a common end A3 connected to the negative terminal of a direct current source by means of an emergency stop button A.

The other two ends Aa, Ab of the coils 5a, 5b can be connected as desired to the positive terminal of said source by a supply line 24a, 24b respectively.

Line 24a associated with winding 5a carries the working contacts of a monostable manual switch Pa whose rest contacts are on the line 24b. It also carries the working contacts of another monostable manual switch Pb.

At rest, none of the windings 5a, 5b is supplied, and the motor M remains stopped.

Depending on whether a button or the other Pa or Pb is pressed, the motor M rotates in one direction or the other. As soon as the button is released, the engine stops.

The assembly of FIG. 5 constitutes an improvement on that of FIG. 4, associated with a contactor similar to that of FIG. 4 except that it comprises an additional change-over contact, referenced 23a, whose moving part 22 is integral with the moving parts. 22 of the contacts 23. The input terminal of each fixed contact of the contact 23a is connected to the positive terminal of the source. Each of the output terminals is connected to a respective line 26a or 26b. Line 26a is connected to line 24a which passes through a rest contact of an inverter 27b of the switch Pb. Likewise line 26b is connected to line 24b passing through a rest contact of an inverter 27a of the switch Pa. As can be checked from the arrows a and b respectively showing in which direction the windings 5a and 3b stress the moving parts 22, the arrangement is such that the self-supply line 26a or 26b which is closed by the contact 23a is always that which supplies the winding 5a or Sb, the action of which keeps the moving parts 22 in the position they occupy.

In addition, in parallel with the contact 23a, the lines 24a and 24b are connected to the positive terminal of the source via a working contact of the inverters 27a and 27b respectively.

Each coil 5a or 5b is associated with an assembly comprising a capacitor Ca or Cb mounted between point A3 and the positive terminal of the source, in series with a working contact of a second inverter 28a or 28b of the inverter Pa or Pb respectively. In parallel with each capacitor Ca or Cb, a discharge resistor ra or rb is mounted in series with a rest contact of the second inverter 28a or 28b. A resistor R3 common to the two assemblies is mounted between the pint A3 and the stop button A.

• Le moteur étant supposé en marche dans le sens déterminé par le bobinage 5a, l'équipage mobile du contacteur est en position extrême vers la droite (flèche a) et le bobinage 5a est auto-alimenté via le vontact 23a et la ligne 26a, les boutons des commutateurs Pa ou Pb étant relâchés. Chaque condensateur Ca ou Cb est en circuit fermé sur sa résistance de décharge ra ou rb et n'a donc pas d'effet sur la commande.

The operation is as follows:

• The motor being assumed to be running in the direction determined by the winding 5a, the moving element of the contactor is in the extreme position to the right (arrow a) and the winding 5a is self-powered via the vaact 23a and the line 26a, Pa or Pb switch buttons being released. Each capacitor Ca or Cb is in a closed circuit on its discharge resistance ra or rb and therefore has no effect on the control.

To change the direction of rotation, press the Pb button. This has several effects. On the one hand, the inverter 27b opens the self-supply circuit of the winding 5a. The same inverter closes the direct link between line 24b and the positive terminal of the source. At the same time, the inverter 28b puts the capacitor Cb in parallel with the winding 5b and switches off the resistor rb.

As soon as its self-supply circuit is interrupted, the winding 5a ceases its action and allows the mobile assembly to return to the intermediate position. At first, the mobile team does not go beyond. In fact, the other winding 5b having been connected in parallel with the capacitor Cb and in series with the resistor R3, its voltage rise takes place with the time constant R3, Cb, for example 1s, preferably more than 0 , 2s. It is only after a certain delay that the the magnetic force generated by the winding Sb is sufficient to move the moving element to its other extreme position, to the left, allowing the engine to start in the other direction.

The example of FIG. 6 is analogous to that of FIG. 5 except that, to take advantage of the presence of the capacitors by allowing supply by alternating current, a half-wave rectifier diode da has been inserted between point A3 and resistance R3. In addition, each winding 5a or 5b is mounted in parallel with a freewheeling diode da or db with which the winding 5a or 5b forms a closed circuit when the winding is disconnected, the diode then having for direction passing the normal direction. through the winding, as permitted by the diode d.

The resistor R3 avoids the use of winding wires that are too fine for a 220 V alternating voltage and the low power required to control the electromagnet avoids having a large resistor R3.

The ra, rb, Ca, Cb and R3 components and any diodes can easily be housed in a housing with the same profile as that of the contactor (snap-on bar, similar terminals, etc.) - or in a housing snapped onto the body of the contactor as a classic additive.

In the case of automatic control, the pushbuttons Pa and Pb can be replaced by a single set of change-over contacts, with or without self-supply, but retaining the time delay for reversing the directions of rotation of the controlled motor.

The electromagnet described can also be used in a 3-way solenoid valve.

Claims (10)

1. Polarized electromagnet comprising at least one excitation coil (5) and a magnetic circuit constituted by two crews (1, 7) each comprising at least one permanent magnet (2, 14) provided on its pole faces with pole pieces (3, 4; 12, 13), the coil (5) surrounding one of the crews in a region comprising the permanent magnet, the crews (1, 7) being movable relative to one another between two extreme positions, the pole pieces (3, 4) of a crew (1) forming with the pole pieces (12, 13) of the other crew (7) two antagonistic pairs of variable air gaps (El, E4; E2, E3), the air gaps of one pair closing when the air gaps of the other pair open due to the relative movement of the crews, the direction of which is determined by the state of excitation of the coil (5). a pair of air gaps (E1, E4) having facing faces connected to polar faces of permanent magnets of the same magnetic polarity, characterized in that the other pair of air gaps (E2, E3) has faces opposite related to the polar faces of permanent magnets of the same magnetic polarity, and in that the sizes of the permanent magnets (2, 14) are chosen to, on the one hand, cancel substantially, in the absence of the excitation from the coil (5), the flow which passes through a closed air gap, thus making it possible to bring the crews into a relative intermediate position between the two extreme positions and, on the other hand, to ensure, in the presence of the excitation of the coil ( 5), an attraction towards one or the other of the extreme positions according to the direction of the excitation of the coil (5). 2. Electro-aissant according to claim 1, characterized in that the air gaps (E1, E2, E3, E4) are formed by ends (8, 9, 10, 11, 15, 16, 17, 18) of the pole pieces (3, 4, 12, 13) and in that each end of the pole piece belongs to only one air gap (El, E2, E3, E4). 3. Electromagnet according to claim 2, characterized in that the ends (8, 9, 10, 11, 15, 16, 17, 18) of pole pieces (3, 4, 12, 13) are bent at right angles to be parallel to each other. 4. Electromagnet according to claim 3, characterized in that the closing of the air gaps (El, E2, E3, E4) is obtained by bringing together the facing air gap surfaces, these being transverse to the axis (YY ') of the coil (5) so that the relative movement of the equipment (1, 7) is a translation in a direction parallel to the axis (YY') of the coil (5). 5. Electromagnet according to any one of claims 1 to 4, characterized in that it comprises elastic return means. 6. Contactor comprising an electromagnet according to claim 5, and power contacts (23) of the reversing type, the state of which is determined by the relative position of the equipments of the electromagnet, characterized in that the means of recall include the elasticity of the power contacts (23). 7. Control circuit for an electromagnet according to one of claims 5 or 6 in which the coil (5) comprises two windings (5a, Sb) wound to generate flows of opposite directions, characterized in that it comprises, for at least one of the windings, an assembly comprising a capacitor (Ca, Cb) connectable in parallel with the winding, a resistor (R3) connected in series with this winding, a discharge resistance (ra, rb) connectable in parallel with the capacitor (Ca, Cb) and a switching means (Pa, Pb) movable between a first position in which a supply line (24a, 24b) of the winding (5a, 5b) and the capacitor are connected to a source terminal while the discharge resistance is disconnected, and a second position in which the capacitor is in series with the discharge resistance while the winding supply line is open. B. Control circuit according to claim 7, characterized in that it comprises an aforementioned assembly for each winding, the first position of each switching means being unstable and the second position stable. 9. Control circuit according to claim 8, characterized in that it comprises means for connecting the windings to the source via an inverter type contact (23a) controlled by the relative position of the crews and via, for each winding ( 5a, Sb), a contact closed at rest (27a, 27b) of the switching means (Pb, Pa) assigned to the other winding (5b, 5a), so as to produce a self-supply type control. 10. Control circuit according to one of claims 7 to 9, which can be connected to an alternative source, characterized in that a single-wave rectifier diode (d1) is connected in series with the two windings (5a, Sb) and in that each winding (5a, Sb) is mounted in parallel with a freewheeling diode (d2, d3).

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