WO2023180582A1

WO2023180582A1 - Power circuit and method for increasing the release forces when switching a relay, a relay, a charging device and a control unit

Info

Publication number: WO2023180582A1
Application number: PCT/EP2023/057836
Authority: WO
Inventors: Rudolf Haeussermann; Robert Ruef
Original assignee: Webasto SE
Priority date: 2022-03-25
Filing date: 2023-03-27
Publication date: 2023-09-28
Also published as: DE102022107181B3

Abstract

The present invention relates to a power circuit for increasing the release forces when switching a mechanical relay (3) in a charging device (1) or in a charging cable (4) for a motor vehicle (5). The relay (3) comprises a spring-biased armature (10) for establishing or breaking an electrical connection (11) in a primary current circuit (2) for charging the motor vehicle (5), the armature (10) being moved by a control unit (7) using an exciter coil (8). The control unit (7) of the relay (3) is designed to apply the switching voltage of the exciter coil in synchronisation with a switching time point (tout) in order to break the electrical connection with a periodic excitation voltage (UA) at an excitation frequency which corresponds to a characteristic frequency of the spring-mass system of the armature (10) of the relay (3). The excitation voltage (UA) causes the armature (10) to vibrate, releasing, due to the dynamic force, the armature (10) from the contact (9) if the armature (10) is adhering to the contact (9) because of a bonding during operation.

Description

Power circuit and method for increasing the release forces when switching a relay, as well as a relay, a charger and a control unit

Technical area

The present invention relates to a power circuit and a method for increasing the release forces when switching a mechanical relay controlled with a mechanical excitation coil, as well as a relay, a charger and a control unit.

State of the art

AC chargers for electric vehicles, which are provided in a wallbox or a cordset, for example, switch the power path between the power grid and the electric vehicle using electromagnetic relays. These relays have special requirements regarding the welding resistance of the contacts. For example, significant inrush currents arise when charging the input filter of electric vehicles. Switching off under load can lead to arcing and contact wear. In some cases, these effects are limited by the relevant specifications. However, it can happen that these specifications are exceeded under real conditions. The relays therefore have to be significantly oversized in terms of welding resistance.

When closing under voltage, an arc forms between the contacts, which locally melts the contact surface and thus leads to the contacts being “welded”. This is a normal process that occurs every time a switching relay closes, although it may be more pronounced with more load. This bond must be released again when the relay drops out using the return spring. In order to make a relay more weld-resistant, this release force is increased through design measures. This can be done through a stronger design of the return spring or through designs that exert a tangential release force on the contact. Other, more exotic contact materials are also possible, which reduce the strength of the weld but increase the cost of the relay. A method for repairing an “adhesive” contact bridge is known from DE 10 2012 011 251 A1, whereby the control frequency of a pulse sequence is adapted to the mechanical resonance of the armature with the contact bridge.

In DE 102012 222 129 A1, the course of the control voltage is selected so that the contact means is excited to oscillate with a natural frequency of the contact means and a mechanical “shaking” is achieved on the contact means.

From DE 102015 016 992 A1 a method for releasing the contact bridge from a contact is known, in which the electrical contacts are vibrated at their natural frequency.

From WO 2005/069330 A1 a method for using a lower voltage for pull-in of the contact plates is known, the voltage being applied to electrodes with a resonance frequency of the structure.

From DE 102015 016 992 A1 an excitation of mechanical vibrations of an electrical contact by applying an electrical waveform with the natural frequency of the electrical contact is known.

From DE 102011 052 173 B3 an electromagnetic actuator for holding and releasing moving parts in motor vehicles is known.

Presentation of the invention

Based on the known prior art, it is an object of the present invention to increase a switching force of a contact means for establishing or separating an electrical connection in a power circuit.

The task is solved by a device with the features of claim 1. Advantageous further developments result from the subclaims, the description and the figures.

Accordingly, a power circuit for increasing the release forces of a mechanical relay controlled with an excitation coil, preferably in an AC (alternating current) charger for a motor vehicle, is proposed, the relay comprising a spring-loaded armature. The power circuit includes a control unit that can be connected to the excitation coil of the relay and is designed and set up to apply a switching voltage to the excitation coil of the relay at a predetermined switching time for switching the relay. In other words, the armature can be released from an electrical contact by means of a return spring to disconnect an electrical connection between the armature and the contact. To establish the electrical connection between the armature and the contact in a primary circuit, the armature is pressed onto the contact by a magnetic force from the excitation coil due to the switching voltage, which counteracts the return spring. Alternatively, this can also be the other way around.

The switching voltage in the excitation coil to generate the switching force that presses or releases the armature onto the contact can have a constant average value. The switching voltage can be generated by a control device at the time of switching. For this purpose, the switching time can be received by the control device by means of an input signal, for example from a timer or a battery control device of a motor vehicle, comprising the switching time for starting or ending charging and/or stored in a memory. When the switching point is reached, the control unit can control the excitation coil with the switching voltage to establish, i.e. armature is on the contact, or disconnect, i.e. armature is released from the contact, the electrical connection.

When making and breaking the electrical connection, a welded connection can arise between the armature and the contact due to flashover voltages, which can result in the armature no longer being able to be released from the contact by the return spring or by a switching force of the excitation coil. The anchor can therefore adhere or stick to the contact.

The power circuit is characterized in that the control unit is designed and set up to apply, in addition to the switching voltage of the excitation coil of the relay, an excitation voltage that is synchronized with the switching time (in a time interval before and/or simultaneously and/or in a time interval after) and periodically to provide additional dynamic switching force.

In other words, synchronous can mean that the excitation voltage can be impressed on the switching voltage by the control device in a time interval before or after the switching time or at the same time as the switching time. By means of its periodic course, the excitation voltage can cause a fluctuating magnetic force of the excitation coil on the armature and thus cause the armature to vibrate, in particular to mechanically shake. The vibration can create additional dynamic switching force in addition to the restoring force the return spring or the excitation coil through the switching voltage to disconnect the electrical connection and cause the armature to be released from the contact, in particular the welded connection.

Since the switching time for disconnecting the electrical connection can already be known in advance, the control unit can apply the excitation voltage to the switching voltage before the switching time and stimulate the contact to vibrate before the switching process in order to prevent the armature from sticking to the contact before switching solve.

In order to be able to apply the excitation voltage before the actual switching time and accordingly apply an additional dynamic switching force, the switching time can also be delayed based on an external switching command by the excitation time interval desired before the switching time.

Additionally or alternatively, the control device can apply the excitation voltage to the switching voltage simultaneously with the switching process or after the switching process and thus increase the switching force of the restoring force or the excitation coil by means of vibration. This results in the advantage that the switching force for releasing the armature from the contact can be increased solely on an electronic basis and existing mechanical and electrical components can be designed to be smaller and therefore more space and energy-saving.

One embodiment provides that the control unit is designed and set up to provide the excitation voltage at an excitation frequency which is in the range of the natural frequency of the spring-mass system comprising the spring-loaded armature, in particular in the range of the natural frequency of the armature. In other words, the dynamic force can be optimized in that the excitation frequency in the excitation coil causes a magnetic force on the armature, which oscillates at the natural frequency of the spring-mass system comprising the armature and the return spring and generates a resonance. Additionally or alternatively, the excitation frequency can also assume the natural frequency of the armature, so that a connection between the armature and the contact can be released by the resonance. The anchor and contact can be made of different materials. For example, the anchor can be made of iron and the contact can be made of a silver alloy or can include these materials. Alternatively, the anchor and the contact can also be made of the same material. This has the advantage that the energy required to release the armature from the contact is optimized by exploiting mechanical resonance and the force to release the armature from the contact, which is caused by the resonance, enables a smaller design of the spring and coil.

One embodiment provides that the control unit is designed and set up to vary (wobble) the excitation frequency over a predefined period of time, in particular to adjust the excitation frequency to a changed natural frequency of the spring-mass system or the armature by means of the variation. In other words, the natural frequency of the spring-mass system or the armature can change due to at least a mechanical tolerance and/or a temperature fluctuation and must therefore be determined again. This can be determined heuristically by varying the excitation frequency. While the excitation voltage is being applied, the control device can increase or decrease the excitation frequency in a frequency band, for example depending on the temperature. If the armature separates from the contact when the excitation frequency is reached, a resonance may occur. The excitation frequency reached can be saved as a new resonance frequency. This makes it easy to determine a changing resonance frequency. This has the advantage that changing environmental conditions can be taken into account by the control unit.

One embodiment provides that the control unit is designed and set up to modulate the excitation voltage by means of pulse width modulation, in particular with an asymmetrical duty cycle, i.e. not equal to (0.5) half the period duration. In other words, if the armature is made of a non-permanent magnetic material such as iron, the armature can only be attracted and not repelled by the excitation coil. In order to still provide an alternating pressing or pulling of the armature from the contact, i.e. vibration or shaking, the armature can be alternately pressed or pulled away from the contact by means of a sum of a spring force of the return spring and the tightening force of the excitation coil. The attraction force of the excitation coil can be zero for as long as possible or the excitation voltage can be zero by means of pulse width modulation until the armature swings back due to the restoring force of the restoring spring.

The duration over which the attraction force of the excitation coil acts on the armature and the duration over which the armature swings back due to the return spring can be of different lengths. The excitation voltage required for the attraction force of the excitation coil can be generated by the control unit using pulse width modulation, in particular with an asymmetrical duty cycle. By choosing the duty cycle of the pulse width modulation, In particular, if it is not equal to half the period (0.5) of the excitation frequency, the excitation voltage can be set to a mechanical time constant of the return spring, in particular to the duration of the armature swinging back.

Additionally or alternatively, the armature can consist of a permanent magnetic material, so that the armature is alternately electrically pulled away or pressed against the contact by the periodic course of the excitation voltage. For example, by filtering the periods of the excitation frequency by the control unit, which presses the armature, which is to be released from the contact, onto the contact, the vibration can be converted into a rhythmic pulling away without pressing. This can further improve vibration efficiency. For example, if the excitation voltage follows a sine function with a period T, where the negative voltage values of the excitation voltage cause the armature to be pressed against the contact and the positive voltage values of the excitation voltage cause the armature to be released from the contact, the period halves can have the negative voltage values can be used as the excitation voltage and/or the odd multiples of the period half with the negative voltage values. Alternatively, depending on the design of the relay, this can also be the other way around.

The mere vibration as a back and forth movement can thus be given a direction. This has the advantage that, in addition to the use of a resonance frequency, the energy requirement can also be optimized and the time it takes for the armature to be released from the contact can be reduced.

One embodiment provides that the control unit is set up to impose the excitation voltage on the switching voltage over the predefined period of time, which in particular includes a duration for reducing and / or building up a magnetic field of the excitation coil. In other words, the predefined period of time for applying the excitation voltage can take into account the time required to build up or reduce the magnetic field of the excitation coil, which can cause the force that presses the armature onto the contact. The duration of the reduction of the magnetic field of the excitation coil can be longer or shorter than the duration of the build-up of the magnetic field, for example due to the use of freewheeling diodes in the power circuit. The time it takes to build up and break down the magnetic field of the excitation coil is therefore asymmetrical. For example, in a first case where the armature is pressed onto the contact by means of the magnetic force of the excitation coil, the duration for the reduction of the magnetic field can be at least partially equal to the period in which the excitation voltage is applied are added, whereas at least partially the duration for building up the magnetic field is added to the period where the excitation voltage is zero and the return spring acts on the armature. In a second case, in an alternative design of the relay, where the armature is pulled away from the contact by means of the magnetic force of the excitation coil, the duration for building up the magnetic field can be at least partially added to the period of time for the excitation voltage to be applied, whereas at least partially the duration can be added Reduction of the magnetic field is added to the period where the excitation voltage is zero. The timing of the application of the excitation voltage can thus be adapted to the oscillation behavior of the spring-mass system, in particular by modulating the excitation voltage using pulse width modulation with an asymmetrical duty cycle in order to meet the resonance frequency of the spring-mass system. This has the advantage that the timing of the application of the excitation voltage can be adapted to the oscillation behavior of the spring-mass system.

One embodiment provides that the control unit is designed and set up to measure a voltage in a primary circuit, which the armature opens or closes, by means of a measuring device, in particular after the switching time. In other words, the voltage in the primary circuit can be measured by the control unit. This allows the control unit to recognize that the relay is closed when the measured voltage reaches a threshold and that the relay is open when the measured voltage is 0V. The threshold value can be at least partially the value of the operating voltage of the primary circuit. Alternatively, the control unit can determine the switching state of the relay by using an auxiliary contact (monitor contact) in the relay.

Additionally or alternatively, the control unit can be set up to measure the current, in particular a rate of current rise, in the secondary circuit for determining the switching state of the relay. Opening or closing the relay can change an inductance of the excitation coil by changing the position of the armature with respect to the excitation coil. For example, with a closed relay, a larger portion of the armature may be in the field coil than with an open relay. The change in inductance due to a change in the switching state of the relay causes a change in the rate of rise of the current in the secondary circuit. The control unit can determine the respective switching state of the relay by measuring the rate of current rise in the secondary circuit. In particular, by measuring the current and/or The speed of current rise in the secondary circuit can be checked for plausibility by the control unit.

Preferably, the control unit can check the plausibility of whether the armature is still resting on the contact or has been released from the contact by monitoring, in particular by means of at least two different methods for determining the switching state. In this way, in addition or alternatively, a changing resonance frequency can be determined by monitoring the current in the primary circuit by the control unit and a natural frequency of the mass-spring system or the armature that changes due to environmental influences. While the excitation voltage is being applied to release the armature from the contact, the excitation frequency can be varied by the control unit, for example increased or decreased. The excitation frequency at which the measured current in the secondary circuit reaches a minimum and the armature is released from the contact due to a resonance effect can be stored as a new natural frequency or resonance frequency by the control unit. With a welded relay, the resonance frequency can shift from the original resonance frequency of the spring-mass system. The resonance frequency may increase in this case, and this can be recognized by the control unit when the measured current reaches the minimum. This results in the advantage that by monitoring the current in the secondary circuit, switching reliability can be increased and an additional means for determining a new natural frequency can be provided when environmental conditions change.

One embodiment provides that the control unit is set up to apply the excitation voltage to the switching voltage when the measured voltage reaches a threshold value after the switching time and/or to apply the excitation voltage to the switching voltage until the measured voltage in the primary circuit is essentially zero . In other words, in addition to or as an alternative to the blanket imposition of the excitation voltage by the control unit when the electrical connection is disconnected, the imposition of the excitation voltage can be made dependent on the condition as to whether the armature has actually detached from the contact after the switching time for disconnecting the electrical connection . This can be determined by the control unit by measuring the voltage in the primary circuit and/or by measuring the rate of current rise in the secondary circuit or alternatively by measuring the voltage with respect to an auxiliary contact (monitor contact). When the measured voltage in the primary circuit has reached the threshold value, the control unit can detect sticking or detachment of the armature from the Recognize contact. Additionally or alternatively, the control unit can detect and/or check the plausibility of whether the relay is open or closed by measuring the current in the primary circuit. The threshold value can be different from zero and can be at least partially the value of the operating voltage of the primary circuit.

If the voltage measured by the control unit after the switching time for disconnecting the electrical connection reaches the threshold value, the control unit can detect that the armature is sticking to the contact and can apply the excitation voltage to the switching voltage for disconnecting the electrical connection, so that the armature is fed through the excitation coil to the contact Vibration is caused and comes away from contact. The control unit can align the duration of the application of the excitation voltage according to the predetermined period of time, in particular the duration for the build-up or reduction of the magnetic field of the excitation coil, or, additionally or alternatively, apply the excitation voltage to the switching voltage until the measured voltage after the switching time for disconnecting the electrical connection is essentially zero, i.e. the relay is open, and/or the measured current in the primary circuit is essentially zero. This has the advantage that the safety of the relay is improved.

Furthermore, a relay is also proposed which includes at least one of the power circuits described herein.

Furthermore, a charger or charging cable is proposed, which includes at least one of the power circuits described herein and/or the relay described herein.

Furthermore, a method for increasing the release forces of a mechanical relay controlled by an excitation coil with a spring-loaded armature, preferably in an AC charger for a motor vehicle, is proposed, the method comprising the following steps:

Receiving and/or storing an input signal comprising a predetermined switching time when the relay should be opened,

Impressing a switching voltage on the excitation coil at the time of switching by means of a control unit which is connected to the excitation coil, - imposing an excitation voltage with an excitation frequency on the switching voltage synchronously (before, after, at the same time) at the switching time by means of the control unit over a predefined period of time, in particular over a period of time to reduce or build up a magnetic field of the excitation coil,

Ending the application of the excitation voltage after the predefined period of time has elapsed.

In other words, the control unit can use an excitation voltage to control an excitation coil in the power circuit, which establishes or separates an electrical connection between at least two contacts of a primary circuit by means of a contact means at a switching time. A periodic course of the excitation voltage that is synchronous with the switching time (in a time interval before and/or at the same time and/or in a time interval after) can cause the contact means to vibrate, with the vibration increasing a switching force of the contact means for separating or establishing the electrical connection .

Further developments of the method according to the invention are described which have features as have already been described in connection with the developments of the power circuit described herein. For this reason, the corresponding further developments of the proposed method are not described again here.

Furthermore, a control unit for operating the power circuit, in particular a relay, is proposed, wherein the control unit comprises at least one processor and/or at least one memory, wherein program instructions are stored in the memory, which cause the at least one processor to carry out the method. In other words, the control unit can have a data processing device or at least a processor device that is set up to carry out an embodiment of the method according to the invention.

For this purpose, the processor device can have at least one microprocessor and/or at least one microcontroller and/or at least one FPGA (Field Programmable Gate Array) and/or at least one DSP (Digital Signal Processor). Furthermore, the processor device can have program code that is designed to carry out the embodiment of the method according to the invention when executed by the processor device. The program code can be stored in a data memory or processor device.

Short description of the characters Preferred further embodiments of the invention are explained in more detail by the following description of the figures. Show:

Figure 1 shows a schematic representation of the electrical circuit that is installed in a charging station or in a charging cable for an electric vehicle;

Figure 2 shows an exemplary course of the control voltage, taking into account the duty cycle of a pulse width modulation, and

Figure 3 shows a schematic progression of the method for increasing the release force in the electrical circuit.

Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, the described components of the embodiment each represent individual features of the invention that can be viewed independently of one another, which also develop the invention independently of one another and are therefore also to be viewed as part of the invention individually or in a combination other than that shown. Furthermore, the described embodiment can also be supplemented by further features already described. The same, similar or identical elements in the different figures are given identical reference numbers, and a repeated description of these elements is partly omitted in order to avoid redundancies.

1 schematically shows a charger 1, such as a charging station or a wallbox, for charging an electrically powered motor vehicle 5. The charger 1 is connected to an electrical network, which forms the primary circuit 2, and charges the motor vehicle 5 via a relay 3. Additionally or alternatively, the relay 3 can also be integrated in a control unit of the charging cable 4. The relay 3 establishes an electrical connection between the primary circuit 2 and the motor vehicle 5 over the charging period by closing the relay 3 for charging and opening it to end charging. Furthermore, a detailed schematic representation of the relay 3 is shown, which is connected, for example, to a phase L1 of the primary circuit 2 and, by means of the armature 10, establishes or separates an electrical connection 11 between the contacts 9 and 9 'by opening or closing the armature 10. Alternatively, relay 3 can be a contactor.

When the electrical connection 11 is separated, due to the current flow in the primary circuit 2, a flashover voltage can form between the contact 9 and the armature 10 when the armature 10 is detached from the contact 9, which can lead to the armature 10 sticking or sticking to the contact 9. As a rule, this is counteracted by a correspondingly strong design of a return spring 15, which releases the armature 10 from the contact 9. To establish or disconnect the electrical connection 11 from the excitation coil 8 via the power circuit 6, the armature 10 is controlled by the control unit 7 using an excitation voltage UA. The excitation coil 8 thus moves and/or vibrates the armature 10 to establish or disconnect the electrical connection 11. To support the release of the armature 10 from the contact 9, the excitation voltage UA can be applied to the switching voltage synchronously with the switching time tout to disconnect the electrical connection 11 . The excitation voltage UA can have a periodic course comprising at least one excitation frequency. The excitation voltage UA is generated by the control unit 7 and causes a vibration, in particular a shaking, of the armature 10, which increases the switching force for releasing the armature 10 from the contact 9, so that the switching force can overcome the adhesion of the armature 10 to the contact 9. The excitation voltage UA can be activated by the control unit 7 before or simultaneously or after the switching time tout to disconnect the electrical connection 11 from the control unit 7. The period of time as long as the control unit 7 activates the excitation voltage UA or applies it to the switching voltage can be a predetermined duration, such as 0.5, 1 or 1.5 s seconds or the duration for building up or reducing a magnetic field of the excitation coil 8 depending on a design of the relay must be set, i.e. whether an average value of the switching voltage is not equal to 0 V or equal to 0 V to disconnect the electrical connection 11.

Additionally or alternatively, the control unit 7 can measure a voltage in the primary circuit 2 synchronously with the switching time tout by means of a measuring device 12, which is essentially 0 V after the electrical connection 11 has been disconnected after the switching time tout. If the voltage measured by the control unit 7 exceeds a threshold value after the switching time tout, the control unit 7 can control the excitation coil 8 with the excitation voltage UA, so that the excitation coil 8 causes the contact means 10 to vibrate, which causes the Armature 10 shakes away from contact 9. The threshold value can, for example, be at least partially the operating voltage of the primary circuit, for example 20 V. In addition, the control unit 7 can effect the duration of activating the excitation voltage UA until the measured voltage in the primary circuit after the switching time tout is 0 V.

In particular, the excitation voltage can be modulated asymmetrically by the control unit, so that the different duration for building up or reducing the magnetic field of the excitation coil 8 and the duration as long as the return spring 15 resets the armature 10 can be taken into account. In addition, the vibration of the armature 10 in two directions or only in one direction can be caused by the excitation coil 8 by a course of the excitation voltage UA predetermined by the control unit 7. If the armature 10 vibrates in only one direction, this corresponds to a rhythmic pulling on the armature 10 away from the contact 9. This can be effected by the control unit 7 in that the control unit 7 modulates the excitation voltage UA by means of pulse width modulation with an asymmetrical duty cycle and provides the excitation voltage UA modulated in this way to the excitation coil 8.

2 shows an example of how the excitation voltage UA in III can be generated based on an information signal 14 with the period T in I by means of a pulse width modulation 13 according to II. The information signal 14 can be a sine signal and, additionally or alternatively, also a periodic square wave or a triangle or a sawtooth signal or a combination of the previously mentioned signal forms. The excitation voltage UA can be generated by the control unit 7 from the information signal 14 by means of a pulse width modulation 13 with a duty cycle of, for example, 0.5 of the period T to II. This creates the excitation voltage UA to III, which is applied to the excitation coil 8. The excitation voltage UA includes the odd multiples 17 of at least one period T of the sinusoid of the information signal 14, here only the antinodes with negative voltage values. Depending on the design of the relay, these can also be the positive voltage values.

If the armature 10 is made of a non-permanent magnetic material, such as iron, the armature 10 can only be attracted and not repelled by the excitation coil 8. A vibration or shaking can therefore be generated by alternately tightening the armature 10 to the contact 9 by the excitation coil 8 and pulling the armature 10 away from the contact 9 by the return spring 15. Due to the course of the excitation voltage UA to III on the excitation coil 8, the armature 10 can be pressed in a direction towards the contact 9 by the negative voltage values of the excitation voltage UA, while the Return spring 15 pulls the armature 10 away from contact 9 when the excitation voltage UA to III is 0 V. Between the multiples 17 of the negative voltage values in III, the excitation voltage UA is essentially 0 V, so that the return spring 15 can pull the armature 10 away from the contact 9. The excitation voltage UA according to III is therefore alternately switched on and off by means of the pulse width modulation 13 according to II, so that a vibration or shaking of the armature 10 occurs in order to release the armature 10 from the contact 9 during welding.

The period of time as long as the excitation voltage UA is different from 0 V can be set according to II using the duty cycle of the pulse width modulation 13. An asymmetrical duty cycle is set in II. The duration as long as the attraction force of the excitation coil 8 acts on the armature 10 and the duration as long as the armature 10 swings back due to the return spring 15 can be different. The excitation voltage UA required for the attraction force of the excitation coil 8 can be generated by the control unit 7 by means of the pulse width modulation 13 with the asymmetric duty cycle according to II in order to generate a vibration or shaking of the armature 10. By selecting the duty cycle of the pulse width modulation 13, the excitation voltage UA can be set to a mechanical time constant of the return spring 15, in particular to the duration of the armature's swing back.

In addition, by generating the excitation voltage UA from the information signal 14 using the pulse width modulation 13 from II, the duration for the build-up and/or breakdown of the magnetic field of the excitation coil 8 can be taken into account. The excitation voltage UA in III can be 0 V until the magnetic field of the excitation coil has subsided and the return spring 15 pulls the armature 10 away from the contact 9. In contrast, the excitation voltage UA in III can have the negative voltage values until the magnetic field of the excitation coil 8 has built up and pushes the armature 10 in the direction of the contact 9. The duration of the build-up and breakdown of the magnetic field can be different, so that the excitation voltage UA during the period T is 0 V for different lengths of time and, on the other hand, has the non-zero voltage values, here the negative voltage values of the multiples 17 in III. The control unit 7 can generate the excitation voltage UA according to III by adjusting the duty cycle of the pulse width modulation 13 according to II, an asymmetrical duty cycle, from the information signal 14. The control device 7 can additionally set or change the duty cycle of the pulse width modulation 13 so that the excitation voltage UA and thus a vibration pattern of the armature 10 varies over a period of time or is adapted to changing environmental conditions of the spring-mass system.

In addition or alternatively, the positive and negative voltage values in the case of a permanent magnetic armature 10 can alternately cause the armature 10 to be pulled off (positive) and pushed forward (negatively) from or to the contact 9. This can be undesirable because the armature 10, which is pressed against the contact 9 again after the switching time tout to disconnect the electrical connection 11. The alternating withdrawal can be effected by means of the odd-numbered multiples 17 of the periods with the negative voltage values in the excitation voltage UA. Alternatively, depending on the design, the positive and negative voltage values can be swapped.

Figure 3 shows a course of the method for increasing the release forces of a mechanical relay 3 controlled with the excitation coil 8. In a first step S1, an input signal 16 is received from the control unit 7, which comes, for example, a signal from a timer or a battery control unit and includes a switching time tout to end the charging process. The control unit 7 stores the switching time tout in a memory. In a second step S2, the control unit 7 applies a switching voltage to the excitation coil 8, so that the armature 10 is released from the contact 9 to disconnect the electrical connection 11. For example, a return spring can release the armature 10 from the contact 9. To prevent the armature 10 from sticking or sticking to the contact 9 due to a breakdown voltage when the electrical connection 11 is disconnected, the control unit 7 applies an excitation voltage UA to the switching voltage in a third step S3 synchronously with the switching time tout. The excitation voltage UA can be impressed within a time interval before or after the switching time tout or at the same time as the switching time tout.

Additionally or alternatively, the control unit 7 can measure a voltage in the primary circuit 2 after the switching time tout by means of a measuring device 12 and if the measured voltage after the switching time tout essentially reaches a threshold value, the control unit 7 can detect that the armature 10 is sticking to the contact 9 and impress the excitation voltage UA onto the switching voltage. The threshold value can at least partially be the operating voltage of the primary circuit. The excitation coil 8 is controlled by the excitation voltage UA in such a way that it causes the armature 10 to vibrate and the armature 10 is released from the contact 9 due to the dynamic force of the vibration. In a fifth step S5, the control unit 7 deactivates the excitation voltage UA after a predetermined period of time has elapsed. The Period can be, for example, 0.5, 1 to 10 seconds. Alternatively, the period can correspond to a multiple of the time until the magnetic field of the excitation coil 8 is built up or reduced. Additionally or alternatively, the control unit can deactivate the excitation voltage UA if the voltage measured in the primary circuit 2 by means of the measuring device 12 is essentially 0 V. Alternatively, the voltage can be measured using an auxiliary contact (monitor contact).

The aim is to increase the release forces without changing the design of the relay. The return spring, together with the armature, forms a spring-mass system. By appropriately stimulating this mechanically oscillatory system, a dynamic force can be generated in addition to the spring force. The excitation occurs by periodically energizing the excitation coil with the mechanical natural frequency. The control is carried out by a controller, which is usually already present on the system anyway. For precise control, the current can also be regulated using, for example, PWM (pulse width modulation). In the simplest case, the required on and off times of the coil are determined experimentally. In this case, it is necessary to vary the excitation frequency over time (wobble) in order to reach the resonance point even if the resonance frequency differs (tolerances, temperature).

When switching off, the spring force acts on the system; when switching on, the electromagnet minus the spring force acts on the system. In addition, when the coil is switched off, the reduction of the magnetic field in the coil is delayed by any protective circuitry. The switch-on and switch-off forces are therefore regularly different. Therefore, asymmetrical control (duty cycle != 0.5) is required.

Furthermore, the resonance point can also be set and/or controlled by monitoring the coil current. The activation of the excitation frequency can either be carried out across the board with every switch-off process or only when necessary, i.e. the relay has not yet released despite the coil voltage being switched off. The excitation frequency is applied either for a predefined time or until the contact is released. This control can be done either by monitoring the switched voltages or by using an auxiliary contact set or again by monitoring the field coil current.

This makes it possible to use purely electrical measures to increase the release force

Increase relay contact. This means that special mechanical measures can be used

Increase in dissolving force can be dispensed with or kept lower. Overall, this makes possible a smaller, cheaper and more energy efficient version of the relay compared to the current state of the art. Special contact materials are expensive and have other disadvantages, in particular a higher contact resistance, which leads to losses and increased temperature stress. Stronger hollow return springs in turn require a stronger design of the exciter coil, which leads to additional costs, increased power consumption and heating. Special designs for generating differently directed release forces require more installation space. Larger excitation coils also require more installation space.

Accordingly, an active increase in release force for relay contacts is provided in this way.

To the extent applicable, all individual features shown in the exemplary embodiments can be combined and/or exchanged with one another without departing from the scope of the invention.

Reference character list

1 charger

2 primary circuit

3 relays

4 charging cables

5 motor vehicle

6 power circuit

7 control unit

8 excitation coil

9, 9' contact

10 anchors

11 electrical connection

12 measuring device

UA excitation voltage

13 pulse width modulation

14 information signal

T period duration tout switching time

15 return spring

16 input signal

17 multiples

51 Step 1

52 Step 2

53 Step 3

54 Step 4

Claims

Power circuit (6) for increasing the release forces when switching a mechanical relay (3) controlled by an excitation coil (8) with a spring-loaded armature (10), preferably in an AC charger (1) for a motor vehicle (5), comprising one with the Excitation coil (8) of the relay (3) connectable control unit (7), which is designed and set up to apply a switching voltage to the excitation coil (8) of the relay (3) at a predetermined switching time (tout) for switching the relay (3), characterized in that the control unit (7) is designed and set up to apply, in addition to the switching voltage of the excitation coil (8) of the relay (3), an excitation voltage (UA) which is synchronized with the switching time (tout) and runs periodically in order to achieve an additional dynamic To provide switching force. Power circuit (6) according to claim 1, characterized in that the control unit (7) is designed and set up to provide the excitation voltage (UA) at an excitation frequency which is in the range of the natural frequency of the spring-mass system comprising the spring-loaded armature (10 ), particularly in the range of the natural frequency of the armature (10). Power circuit (6) according to claim 1 or 2, characterized in that the control unit (7) is designed and set up to vary (wobble) the excitation frequency over a predefined period of time, in particular the excitation frequency to a changed natural frequency of the spring-mass system or the anchor (10) by varying. Power circuit (6) according to one of the preceding claims, characterized in that the control unit (7) is designed and set up to modulate the excitation voltage (UA) by means of pulse width modulation (13), in particular with an asymmetrical duty cycle. Power circuit (6) according to one of the preceding claims, characterized in that the control unit (7) is set up to reduce the excitation voltage (UA) over the predefined period of time, which in particular is a duration and/or building up a magnetic field of the excitation coil (8) to be impressed on the switching voltage. Power circuit (6) according to one of the preceding claims, characterized in that the control unit (7) is designed and set up to measure a voltage in a primary circuit (2), which the armature (10) opens or closes, by means of a measuring device (12). to be measured, especially after the switching time (tout). Power circuit (6) according to claim 6, characterized in that the control unit (7) is set up to impose the excitation voltage (UA) on the switching voltage if, after the switching time (tout), the measured voltage reaches a threshold value and / or the excitation voltage ( UA) to be applied to the switching voltage until the measured voltage in the primary circuit

(2) is essentially zero. Relay (3) comprising at least one power circuit (6) according to one of claims 1 to 7. Charger (1) or charging cable (4) comprising at least one power circuit (6) according to one of claims 1 to 7 and / or a relay (3) according to claim 8. Method for increasing the release forces of a mechanical relay (3) controlled with an excitation coil (8) with a spring-loaded armature (10), preferably in an AC charger (1) for a motor vehicle (5), comprising the steps:

Receiving and/or storing an input signal (16) comprising a predetermined switching time (tout) when the relay (3) should be opened,

- imposing a switching voltage on the excitation coil (8) at the switching time (tout) by means of a control unit (7) which is connected to the excitation coil (8),

- Impressing an excitation voltage (UA) with an excitation frequency onto the switching voltage synchronously (in a time interval before and/or in a time interval after and/or at the same time) at the switching time (tout) by means of the control unit (7) over a predefined period of time, in particular over a period of time for reducing or building up a magnetic field of the excitation coil (8),

Ending the application of the excitation voltage (UA) after the predefined period has expired. 11. Control unit (7) for operating a power circuit (6), in particular a relay

(3), wherein the control unit (7) comprises at least one processor and/or at least one memory, wherein program instructions are stored in the memory which cause the at least one processor to carry out a method according to claim 10.