EP0726584B1 - Control device for an electromagnet - Google Patents

Abstract

The magnetically influenced switch device (5) contains a sensor coil (22) with at least one winding coupled to at least part of the electromagnet's magnetic field at least when an air gap is open. The sensor coil is switched over to a controlled semiconductor (11) connected in series with a pull-in coil (1) of the electromagnet, which also has a hold-in coil, by a voltage peak which occurs at the instant of air gap closure. The sensor coil is changed over by an electronic switching device. It takes the form of at least one winding mounted at any point around the core and/or the armature. It can be mounted near the air gap and core and/or the armature and is coupled to the stray field of the electromagnet about the air gap.

Description

The present invention relates to a device for controlling an electromagnet with a fixed core, with a temporary after switching on current-carrying pull-in winding, with one in the operating state current-carrying holding winding, with a relative to the core below Change an air gap movable armature, and with one with the pull-in winding series-connected, magnetically influenceable switching device which Power supply to the pull-in winding is interrupted when the air gap disappears.

DE-A1-1921232 describes a device for controlling an electromagnet of the type mentioned above. The electromagnet is with one Tightening winding and provided with a holding winding. To switch off the Tightening winding after the air gap between the core and the Anchors use a magnetically influenceable switching device, which Power supply to the pull-in winding is interrupted when the electromagnet is tightened. The magnetically influenceable switching device absorbs the stray flux by the presence of an air gap between the core and the armature of the electromagnet is created. The switching device contains tongue contacts Made of a magnetic material, at least one of which is compliant and is suitable to be attracted to the other tongue contact when a magnetic flux surrounding the contacts. This electromagnet points at Switch on a non-negligible switch-on delay, because the on the Terminals permanently connected and when the electromagnet is switched on immediately holding current flows through the magnetic first Stray field must build up in order to respond to the magnetic stray field To close the switching device and thereby the pick-up winding on the supply voltage to connect. The switching device responsive to the stray magnetic field is also particularly sensitive to external magnetic fields. Such external fields can come from an adjacent electromagnet Contactor or from neighboring lines through which short-circuit current flows. An external field can be the switching device responsive to a magnetic field close and unintentionally turn on the suit coil, which will result in the worst In the event that the suit coil can burn. In the further this switching device responsive to a magnetic field is required proportionately lots of space, which increases and increases the cost of the entire electromagnet leads. In addition, the mechanical contacts have one Contact burn-up, relatively short lifespan.

In FR-A1-2290009 there is also a device for controlling an electromagnet described with a pull-in winding and with a holding winding. An electronic circuit arrangement is connected in parallel to the holding winding, which controls the power supply to the pull-in winding by attracted, closed magnetic circuit whose power supply interrupts. The electronic circuit arrangement is the in the closing moment of Electromagnets induced in the holding winding induced overvoltage interrupt the power supply to the pull-in winding. The holding winding is not only during the electromagnet's tightening process, but connected to the mains during the entire operating period. That is why terminal voltage supplied to the electronic circuit arrangement with im Network existing interference voltages contaminated. Because that's the electronic circuitry feeding signal with interference voltages originating from the network is contaminated and not only by the holding winding at the closing moment of the Electromagnet induced overvoltage, the holding winding must Time lag associated with cost can be added to the effect to make the interference voltages ineffective. This time delay of the switch-on time is dependent on the phase of the voltage at the moment of switch-on, ie not constant. Furthermore, the electronic provided here needs Circuit arrangement also an external power supply, the additional cost means. In order to allow the switch-off delay of the electromagnet Keeping limits is an additional switch in this circuit arrangement intended. The envisaged electronic switch of the pull-in winding is because of the difficulty in deleting a controlled semiconductor Direct current unsuitable for direct current supply. In summary it can be stated be that this device for controlling an electromagnet not only complicated and relatively expensive, but also susceptible to interference voltage and is unsuitable for direct current supply.

DE-C2-2128651 is a further device for controlling a Electromagnets with a pull-in winding and a holding winding are known. In this device, switching electronics are provided, which after expiration turns off the pull-in winding for a predetermined time. This facility fails at least if the electromagnet for some reason remains blocked, or the voltage applied to the windings from the provided deviates significantly.

DE-A1-3637133 describes a further device for controlling a Electromagnets. This electromagnet has only one winding. An electronic switching arrangement reduces the current through the only one Winding with the electromagnet's air gap closed. To the switching arrangement to control is a Hall effect sensor near the air gap attached, which is connected to the electronic switching arrangement via cable is. The Hall effect sensor delivers from the moment it is switched on until it closes a tension in the air gap. To control the electronic circuitry The voltage output is strongly dependent on the installation location of the Hall effect sensor. therefore, the Hall effect sensor must be in relation to the core and the Anchor must be positioned exactly. Furthermore, a Hall effect sensor is through Magnetic external fields can be strongly influenced. So can an external magnetic field reduce the current flowing through the winding of the electromagnet or enlarge, the holding force of the electromagnet to the unwanted Separation of the anchor from the core can decrease. Another disadvantage is this arrangement that the electronic switching arrangement is a relative emits high power dissipation because the operationally flowing through the winding Holding current constantly flow through the electronic switching arrangement got to. The necessary supply of the Hall effect sensor also has an adverse effect out.

The object of the present invention is to provide a device at the outset to develop the above-mentioned type for controlling an electromagnet, the one has a relatively long service life in an electromagnetic Switchgear can be accommodated in a space-saving manner with all occurring Operating conditions work reliably, on external magnetic fields is largely insensitive, gives off a relatively small power loss and is economically advantageous.

The task is solved in that the magnetically influenceable Switching device with at least one open air gap Part of the magnetic field of the electromagnet coupled, at least one turn having sensor coil, and a controllable semiconductor connected in series with the pull-up winding via an electronic switching arrangement, the sensor coil with the one in the moment of Air gap closure induced voltage spike the controllable Semiconductor switches with high resistance. This device has no mechanically moved Parts on, the lifespan is therefore relatively long. The order is also space-saving because both the sensor coil and the controllable one Semiconductors with the associated additional circuit elements are proportionate are small. The magnetically influenceable switching device is magnetic Foreign fields are also largely insensitive because they are not sensitive to that Disappearance in the air gap area until the electromagnet closes existing magnetic stray field, but on the closing of the Very steep change in the magnetic flux in the air gap Electromagnets and at that moment induced in the sensor coil clear voltage spike. This magnetically controllable switching device takes advantage of the fact that at the closing moment of the air gap one Electromagnets a very steep change in the magnetic flux occurs. The voltage spike induced in the sensor coil at this moment is essential higher than that from a possible AC excitation or by a other foreign field induced voltage. This switching device works also in all operating conditions, such as too low or coil voltage applied too high, because it is only in the actual closing torque of the electromagnet responds. After the circuit of the pull coil is switched to high resistance when the electromagnet is energized Power loss of the switching device is also negligibly small. The out of proportion few circuit elements formed device for control an electromagnet is also economically advantageous.

The sensor coil can consist of at least one at any point around the Core and / or winding formed around the anchor. While closing the air gap between the core and the anchor is in the at one any point of the core and / or the armature Spike induces the switching of the controllable semiconductor the high-resistance position with certainty and thus the shutdown of the Ensures tightening winding.

The sensor coil is advantageously in the area of the air gap next to the Core and / or the armature arranged and with the stray field of the electromagnet coupled around the air gap. The stray field of the electromagnet in the The sensor coil attached to the area of the air gap gives an induced voltage peak at the moment the air gap closes. This clear spike brings the controllable semiconductor clearly into the high-resistance Position. The pull-in winding receives the semiconductor, which has become high impedance practically no more current, after which only the holding winding supplies power and remains effective.

The magnetically influenceable switching device is advantageously in one piece Unity trained. This solution is particularly advantageous because the one-piece unit very easily housed, especially in the air gap area and this unit can be connected in series with the pull-in coil contains both sensor and circuit elements. Without any positioning work This arrangement ensures a safe high-resistance circuit of the controllable Semiconductor. This magnetically influenceable switching device is included Advantage in the air gap flange of the bobbin of the pull-in and holding windings built-in. The accommodation of the magnetically influenceable switching device with the sensor coil in the air gap-side flange of the coil body the tightening and holding windings is a particularly advantageous solution because the air gap set flange of the coil body usually directly in the air gap area lies, so that the sensor coil detecting the stray field around the air gap no special positioning measures are required.

The switching device which can be influenced magnetically can have a tightening time limit effecting switching arrangement to be equipped with the non-operational Behavior of the armature after the power supply to the pull-in winding Interruption of a predetermined limit time. At the tightening time E.g. limit even with the electromagnet blocked in the open position, this circuit arrangement is provided, any combustion of the Tightening winding is prevented.

The magnetically influenceable switching device can be the pull-in winding on and off semiconductor switching element controlling flip-flop included, which is controlled directly by the sensor coil. The simply constructed Tilting stage offers an advantageous solution for controlling the controllable Semiconductor.

Fig.1

das Schaltschema einer Halte- und Anzugswicklung mit einer magnetisch beeinflussbaren Schalteinrichtung,

Fig.2

das Schaltschema der magnetisch beeinflussbaren Schalteinrichtung mit der Anzugswicklung,

Fig.3

eine schematische Darstellung einer Sensorspule um den Eisenkern,

Fig.4

eine schematische Darstellung einer im Bereich des Luftspaltes eines Elektromagneten untergebrachten Sensorspule und

Fig.5

einen schematischen Querschnitt des Elektromagneten mit Wicklungen und Spulenkörper.

In the following an embodiment of the invention will be described with reference to the accompanying drawings. Show it:

Fig. 1

the circuit diagram of a holding and pull-in winding with a magnetically influenced switching device,

Fig. 2

the circuit diagram of the magnetically influenceable switching device with the pull-in winding,

Fig. 3

a schematic representation of a sensor coil around the iron core,

Fig. 4

a schematic representation of a sensor coil housed in the area of the air gap of an electromagnet and

Fig. 5

a schematic cross section of the electromagnet with windings and coil former.

As shown in FIG. 1, a pull-in winding 1 and a holding winding 2 are one Electromagnetic switching device, not shown, on the coil connection terminals 3, 4 connected in parallel. Is between terminals 4 and 6 a magnetically influenceable connected in series with the starting winding 1 Switching device 5 for controlling the power supply of the pull-in winding 1. The electromagnet excitable by the pull-in and holding windings 1, 2 contains a stationary core 7 (Fig. 3, 4 and 5) and one relative to the core 7 armature 8, changing the air gap therebetween.

2 shows the circuit diagram of the terminals 4 shown in FIG. 1 and 6 existing, magnetically influenceable switching device 5 can be seen. Between terminals 4 and 6 is a Transil 9 as overvoltage protection available. Behind the input terminal 6 is a diode 10 as protection against polarity reversal provided for the DC variant of the switching device 5 shown here. Between terminals 4 and 6, which are in series with pull-in winding 1 are a controllable semi-conductor, in this exemplary embodiment a MOS-FET 11, a supply capacitor 13 connected via a diode 12, and a via a charging resistor 14 connected blocking capacitor 15 connected in parallel. At the terminals of the supply capacitor 13 are a switch-on resistor 16 the gate terminal 17 and the source terminal 18 of the MOS-FET 11, a gate-source capacitor 19, a zener diode 20 and an npn transistor 21 connected in parallel. A sensor coil 22 is connected via a diode 23 the base of the NPN transistor 21 connected. The base of the NPN transistor 21 is on the one hand with a load resistor 24 determined for the sensor coil 22 the emitter of this transistor 21 and on the other hand with a resistor 25 the terminal of the blocking capacitor 15 connected.

This switching device 5, which can be influenced magnetically and is shown in FIG. 2 using the circuit diagram, functions as follows. When the contactor is switched on, the coil voltage is applied to the coil connection terminals 3, 4. The full coil voltage appears at the open terminals 4, 6 of the switching device 5. The supply capacitor 13 is charged to the full voltage via the diode 12 with a time constant of T _s . The gate-source capacitor 19 is charged via the switch-on resistor 16 with a switch-on time constant T _e . After at least one switch-on time constant T _{e has} expired, the MOS-FET 11 switches through and becomes low-resistance. At this moment, the current flows via the MOS-FET 11 to the pull-in winding 1, the contactor magnet is excited, the armature 8 moves towards the core 7, reducing the air gap. At the time the armature 8 hits the core 7, the one in between disappears Air gap. This leads to a very steep change in the magnetic flux in the core 7 and in the armature 8, so that a sensor voltage is induced in a sensor coil 22 (FIG. 3) attached to the core 7. The sensor coil 22 does not have to be wound around the core 7, it can also lie in the region of the air gap, next to the core 7 and the armature 8, as is schematically indicated in FIG. When the stray flux disappears very rapidly in the air gap region, a tip-shaped sensor voltage with very steep flanks is induced in the sensor coil 22. The sensor voltage is supplied via the diode 23 to the base of the npn transistor 21, as a result of which a base current occurs in the npn transistor 21. Via the resistor 25, the blocking capacitor 15 is also at least partially charged by the sensor voltage, so that after the sensor voltage has disappeared, the npn transistor 21 remains conductive until the blocking capacitor 15 has been further charged via the charging resistor 14. The npn transistor 21 thus becomes conductive as soon as the sensor voltage is supplied to the base and discharges the gate-source capacitor 19, whereupon the MOS-FET 11 becomes high-resistance. Thus, the current through the pull-in winding 1 is interrupted, the contactor magnet is only held in the drawn position by the holding winding 2 directly connected to the coil connection terminals 3, 4.

As soon as the MOS-FET 11 has become high-resistance, the blocking capacitor 15 is charged via the charging resistor 14 with a time constant of T _v , after which the npn transistor 21 continues to be supplied with base current via the resistor 25. The npn transistor 21 thus remains conductive after the sensor voltage has disappeared and prevents the MOS FET 11 from becoming low-resistance again. The time constant T _v given by the resistor 14 and the blocking capacitor 15 is chosen to be substantially larger than the switch-on time constant T _e given by the switch-on charging resistor 16 and the gate-source capacitor 19, which prevents the npn transistor 21 from being switched on during the switch-on time becomes a leader.

If the armature 8 of the electromagnetic switching device is blocked for some reason and immovable, so that the device cannot be switched on, the switching on proceeds as previously described until the sensor coil 22 should emit a sensor voltage due to the disappearance of the air gap. Because the armature 8 is blocked in this case, the air gap cannot disappear despite the energized pull-in coil 1. In this case, the gate-source capacitor 19 is partially discharged via the zener diode 20, via the npn transistor 21 and via the MOS-FET 11 by leakage currents with a time constant of T _n . As soon as the voltage at the gate terminal 17 of the MOS-FET 11 has dropped below the threshold value, the MOS-FET 11 becomes high-resistance again, after which the current supply to the pull-in winding 1 is interrupted. Due to the voltage increase at the drain terminal 26 of the MOS-FET 11, the blocking capacitor 15 is charged via the charging resistor 14. As a result, the npn transistor 21 is supplied with base current via the resistor 25 and becomes conductive. The gate-source capacitor 19 discharges completely via the npn transistor 21 which has become conductive.

When the contactor is switched off, the voltage at the coil connection terminals 3, 4 interrupted. The charge of the feed capacitor 13 overflows the switch-on resistor 16 and via the npn transistor 21. While At this time, the NPN transistor 21 receives the base current from the blocking capacitor 15 through the resistor 25 so that it is used for the discharge of the feed capacitor 13 remains conductive.

The exemplary embodiment described above was one DC excited electromagnet. With AC excitation one closes advantageously one before the terminals 4 and 6 of the switching device 5 Rectifier. The sensor coil 22 is in this arrangement after Switching on the electromagnet corresponding to the frequency of the alternating current induced AC voltage. This is induced AC voltage but much smaller than that due to the closing of the air gap the steep flow change induced voltage spike so that before closing of the air gap induced AC voltage neglected as "noise" can be. The base current caused by the induced AC voltage is not sufficient to make the npn transistor 21 conductive.

The magnetically influenceable switching device 5 with the sensor coil 22 is advantageously as a one-piece unit, in the form of a printed circuit board 26 trained. This circuit board 26 is, as Fig.5 shows, in the air gap side Flange of the bobbin 27 of the pull-in and holding windings 1, 2 built-in. The sensor coil 22 integrated in the circuit board 26 lies in this way automatically in the air gap area and detects the leakage flow there.

Claims (7)

1. A device for controlling an electromagnet with a fixed core (7), a pickup winding (1) temporarily traversed by current after switch-on, a holding winding (2) traversed by current in the operating state, an armature (8) moveable relative to the core thereby changing an air gap, and a magnetically influenceable switching device (5) which is connected in series with the pickup winding and which interrupts the current supply to the pickup winding (1) upon the disappearance of the air gap, characterised in that the magnetically influenceable switching device (5) contains a sensor coil (22) which, at least when the air gap is open, is coupled to at least a part of the magnetic field of the electromagnet, is arranged separate from the pickup- and holding windings (1, 2) and has at least one turn, and a controllable semiconductor (11) which is connected in series with the pickup winding (1) via an electronic switching arrangement, where said sensor coil (22), with the voltage peak induced therein at the instant of the air gap closure, switches the controllable semiconductor (11) into the high-ohmic state.
2. A device according to Claim 1, characterised in that the sensor coil (22) is formed by at least one turn positioned around the core (7) and/or the armature (8) at an arbitrary position.
3. A device according to Claim 1, characterised in that the sensor coil (22) is arranged in the region of the air gap beside the core (7) and/or the armature (8) and is coupled to the stray field of the electromagnet around the air gap.
4. A device according to one of Claims 1 to 3, characterised in that the magnetically influenceable switching device (5) is formed as an integral unit.
5. A device according to Claim 4, characterised in that the magnetically influenceable switching device (5) is installed in the flange, arranged on the air gap side, of the coil body (27) of the pickup- and holding windings (1, 2).
6. A device according to one of Claims 1 to 5, characterised in that the magnetically influenceable switching device (5) is equipped with a switching arrangement (11, 19, 20, 21) which limits the pickup time and which, in the non-operational mode of the armature (8), interrupts the current supply to the pickup winding (1) after the expiration of a predetermined limitation time.
7. A device according to one of Claims 1 to 6, characterised in that the magnetically influenceable switching device (5) contains a trigger stage (19, 21) which controls the semiconductor switching element (11) which switches the pickup winding (1) on and off, which trigger stage (19, 21) is directly controlled by the sensor coil (22).

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