GB2505336A

GB2505336A - Charging device with safety shutdown

Info

Publication number: GB2505336A
Application number: GB1317821.5A
Authority: GB
Inventors: Juergen Mack
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-03-11
Filing date: 2012-02-01
Publication date: 2014-02-26
Anticipated expiration: 2032-02-01
Also published as: GB2505336B; CN103415978B; GB201317821D0; DE102011005414A1; WO2012123180A1; CN103415978A

Abstract

A charging device for charging an electrical energy store comprises a current source and a switching device for connecting the energy store to the current source depending on a control signal. In this case, the switching device comprises a magnetically closable switching element, a magnet for closing the switching element, and an electric heater for the magnet.

Description

Description Title

Chargin device with safety shutdown The invention relates to a charging device for charging an electrical energy store, wherein the charging device comprises a shutdown device.

Prior art

Chargeable electrical energy stores, for example lithium ion batteries, lead batteries or nickel metal hydride batteries, can be charged by means of an electric charging device so that they are then capable of supplying electrical energy to a consumer. Electrical energy stores of this type are used for example in small electrical appliances such as lamps, electric drills or electric screwdrivers. When charging the electrical energy store, there is the fundamental problem that an incorrect charging current can result, in Øamage both to the electrical energy store and the charging device. Lithium ion batteries are particularly sensitiveand can rupture if overcharged which, in unfavourable circumstances, can be linked to an explosion or fire. . To protect the charging device and the electrical energy store, a switch device is normally provided between the charging device and the energy, store, which is designed to interrupt a charging current when a critical situation arises during charging. The switch device here should be small and economical and should shut down reliably, particularly in the event of too high a charging current.

It is further desirable for the switch device to be reversible so that, after the shutdown procedure, it readily enables a user to continue the charging procedure at a later point in time. Moreover, the shutdown should preferably be exteinallV controllable so that the shutdo'wn can also take place as a result of a critical charging situation with is otherwise determined.

The object on which the invention is based is therefore to provide a switch device which fulfils as many of the above-mentioned requirements as possible.

The invention achieves this object by means of a charging device having the features of Claim 1. Dependent claims represent preferred embodiments.

Disclosure of the invention

A charging device according to the invention for charging an electrical energy store comprises a current source and a switch devd.ce for connecting the energy store tq the current source depending on a control signal. Here, the switch device comprises a magnetically closable switch element, a magnet for closing the switch eLement and an electric heating device for the magnet.

On the basis of the control signal, the electric heating device can be activated to heat the magnet. If the magnet reaches a predetermined temperature, the so-called Curie temperature, it loses a substantial proportion of its magnetic effect so that the switch element is no longer activated and a charging current between the charging device and the electrical energy store is interrupted.

A certain amount of time in which the electric heating device heats the magnet is usually necessary until this reaches its Cu±ie temperature. Conversely, it takesa certain amount of time for the4 heated magnet to drop back below the Curie temperature after the electric heating device has been switched off: A shutdown delay and a start-4 up delay of the switch element can therefore be influenced by a suitable design of the magnet, the switch element and the heating device and their relative positions.and spacings. A brief disturbance or a control signal which is only briefly activated can therefore not cause a shutdown of the switch element, for example.

In one embodiment, the charging device further comprises a monitoring device for determining a charging situation of the charging device, wherein the monitoring device is designed to control the heating device depending on the particular charging situation in order to open the switch element.

The monitoring device can scan one or more currents, voltages, temperatures and other physical parameters in the region of the charging device and/or the electrical energy store and, on the basis of the scanned values, determine whether a critical situation has arisen. If this is the case, the mon.itozing device can control the heating device so that the electrical energy store is ultimately electrically, separated from the current source. The switch device according to the invention can thus be used for shutdown on the basis of a plurality of parameters.

In a further embodiment, the electric heating device is connected in series to the switch element so that a current flowing between the current source and the energy store flows through the heating device.

This'enables a simple and robust overcurrnt shutdown of the energy store to be implemented by the current source.

In *this case, the switch device can be triggered without an auxiliary voltage or an auxiliary current to enable very rcbustand failsafe operation. As described above, the switch device can enable further operation of the charging device at a later point in time, namely when the magnet has cooled back down below its Curie temperature, without the need for any intervention on the part of a user. Unlike a fuse, for example, the described switch device operates non-destructively so that the reliability of the switch device can also be tested non-destructively, for example within a quality control procedure.

Tn one embodiment, the charging device comprises a further heating device and a monitoring device for determining a charging situation of the charging device, wherein the monitoring device is designed to control the further heating device depending on the determined charging situation in order to open the switch element. This enables the advantages of the described switch element with the heating device through which the charging current flows to be combined with the universal actuabililty of a separately controlled heating device. In one variant, the two heating devices can be completely or partially identical to one another.

The magnet can be constructed in the form of a hollow cylinder and the switch element can be arranged in the cavity of the magnet. Here, the poles of the magnet are conventionally arranged at the ends of the hollow cylinder.

The magnetic field cf the magnet can be particularly strong in the regicn of the cavity here,. sc that a relatively weak magnet can be sufficient for reliable closure of the switch element. The maget can therefore have a relatively lbw mass so that a thermal capacity of the magnet can be lowered, which can result in a shorter shutdown and start-up delay. The switch element is conventionally enclosed in a glass tube sq that the hollow cylindrical magnet can serve at the same time for mechanical protection of the glass tube.

The heating device can comprise a winding encircling the magnet. This enables a low-loss introduction of the heat generated by the heating device into the magnet.

The winding can be orientated so that a magnetic field created by the winding with the current flowing through it counteracts the magnetic field of the magnet. This enables more rapid shutdown. The thermal inertia of the magnet can nevertheless be sufficient to keep the open switch element initially open, even when the current flowing through the heating device is shut off as a result of the switch element opening.

The monitoring device can be designed to connect the above-j mentioned.heating device or the further heating device in parallel to the energy store-Chargeable energy stores are usually capable of delivering a relatively high final charging current: This enables the heating device or the further heating device to realise a high thermal output to heat the magnet quickly and bring about rapid shutdown. The energy store is advantageously discharged at the same time within the shutdown procedure, which can be helpful in the event of an irnminent overcharging of the energy store.

A casing can be provided to thermally insulate the magnet and the heating device from the surrounding environment.

Thermal influence of the heating device on the sur±ounding environment, in particular in the region of electronic components of the charging device and/or the energy store, can thereby be reduced. Moreover., a large proportion of the thermal energy released by the electric heating device can be introduced into the maqnet so that it is possible to minimise the energy costs for shutdown by means of the switch device.

Brief description of the Figures

The invention is now described in more detail with reference to the accompanying Figures, which show: Figure 1 a charging device for charging an electrical energy store; Figure 2 a variant of part of the charging device of Figure 1; and Figure 3 a switch device for use in the charging *device of Figure 1 or. 2. .

Precise description of exemplary embodiments. 30. .

Figure 1 shows a charging device 100 for charging an electrical energy store 105. The charging device 100 comprises a current source 110 and a switch device 115. The switch device 115 comprises a reed contact 120, a magnet.

and an electric heating element 130. The charging device 100 further comprises a first monitoring.device 135.

li-i the illustration of Figure 1, the el1ectrical energy store 105 is part of a battery pack 140 which moreover comprises a second monitoring device 145. The second monitoring device 145 is preferably connected to individual cells of the energy store 105 and designed to scan one or more parameters in the region of the battery pack 140 in order to control a charging procedure of the electrical energy store 105.

The battery pack 140 is connected to the charging device by means of three contacts 150, 155 and 160. The contacts 150 and l60 represent a positive and a negative connection for a charging current for charging the energy store 105. The second monitoring device 145 is connected to the first monitoring device 135 by way of the contact 155 in order to transmit measured values and/or control information. In an alternative embodiment, it is also possible to dispense with the contact 155 and/or the second monitoring device 145.

The current source 110 is connected to two connections 165, 170 at which a charging voltage or charging current is supplied. The first connection 165 is connected to the contact 150 for the battery pack 140 by means of the reed contact 120. The second connection 170 is connected directly to the contact 160 for the battery pack 140. So long as the reed contact 120 is closed, a charging current can flow between the current source 110 and the energy store 105 so that the energy store 105 is charged. The reed contact 120 can be magnetically actuated. In particular, the reed contact 120 is designed to close when the reed contact 120 is within range of a sufficiently strong magnetic field. At a short distance from the reed contact 120, the magnet 125 is arranged: and aligned such that its magnetic fiela closes the reed contact 120. The manet 115 can be heated by means of the electric heating element 130, which can be activated by the first monitoring device 135.

If the first monitoring device 135 determines a critical charging situation in the region of the charging device 100 and/or the battery pack 140, it effects a current.through the electric heating element 130 so that the electric heating element 130 heats the magnet 125 until the magnet exceeds a Curie temperature associated with it, whereupon its magnetic field substantially collapses. The reed contact 120 is therefore not actuated, so that the reed contact 120 separates the first connection 165 electrically from the contact 150. The.charging current flowing through the electrical energy store 105 is therefore shut down.

In the illustration of Figure 1, the first monitoring, device 135 is electrically connected to the oontacts 150 and 160 in order to draw the current required to operate the electric heating element 130 completely or partially from the electrical energy store 105. This current can be maintained after the reed contact 120 has separated the first connection 165 from the contact 150. In another embodiment, the first monitoring device 135 is electrically connected to the first connection 365 instead of to the contact 150 so that, after the reed contact 120 has opened, the electric heating element 130 can only be operated by the current supplied by the current source 110.

In a further embodiment, contrary to the illustration of Figure 1, the switch device 115 can also be constructed on the side of the battery pack 140. In the illustration of Figure 1, the contacts 150 and 160 are dispensed with in this case and an electrical connection of the battery pack and the current source 110 takes place in the region of the connections 165 and 170. The monitoring devices 135 and can then be integrated in a common monitoring device.

Figure 2 shows a variant of part of the charging device 100 fztm Figure 1. This illustrates the section shown between the connections 165, 170 and the contacts 150 to 160 in Figure 1.

In that embodiment of the charging device 100 which is shown in Figure 2, the electric heating element 130 is connected in series to the reed contact 120 so that the current flowing from the first connection 165 firstly passes through the reed contact 120 and then the electric heating element 130 before it reaches the contact 150. The heating of the magnet 125 by the heating device 130 is therefore dependent on the charging current flowing between the. first connection 165 and the contact 150. In one embodiment, no further option is provided for triggering the switch device 115 by means of the first monitoring device 135, which mean,s that it is possible to dispense with the first monitoring device 135.

In the embodiment shown in Figure 2, however, the first monitoring device 135 is connected to a further electric heating element 205 which, like the heating.elemert 130, is designed to heat the magnet 125. In addition to the above-described triggering of the switch device 115 on the basis of the charging current, it is therefore also possible to effect an independent triggering of the switch element 115 on the basis of other parameters by means of the first monitoring device 135.

In a futher embodiment, the electriè heatin elements 130 and 205 can be formed by a single heating element. The heating elements 130 and 205 can also be formed for example by a èingle conductor with different taps.

Figure 3 shows a switch device 115 for use in the charging device 100 of Figures 1 and 2.

The reed contact 120 comprises two contact elements 305 and 310 which are partially fused into a glass tube 315. The contact elements 305 and 310 are connected to the first connection 165 and the contact 150 respectively in the arrangement of Figure 1. The magnet 125 of Figure 3 is formed as a hollow cylinder, wherein the reed contact, 120 is repeived in the cavity of the magnet 125. A north pole of the magnet 125 is shown on the left by way of example in the illustration of Figure 3, a south pole is shown on the right. The heating element 13Q is formed by a wire with windings 320. The windings 320 encircle the hollow cylindrical magnet 125 on its outer side. Ends of the wires form a positive heating connection 325 and a negative heating connection 330. In one embodiment, the polarity of the heating connections 325, 30 is selected such that a magnetic field established in the region of the windings 320 of the heating element 130 when a current flows through the heating element 130 counteracts the magnetic field of the magnet 125. This enables the magnetic field of the magnet 125 to already be weakened before it reaches its Curie temperature in all regions, so that a shutdown behaviour of the switch device 115 can be altogether accelerated.

In one embodiment, the switèh device 115 is surrounded by a casing 335 which provides thermal insulation with respect to a sürroünding environment of the switch deicd 115. Ends of the, contact elements 305, 310 and the heating connections 325, 330 are guided outwards through the cathing 335.

The construction of the switch device 115 of Figure 3 is exemplary in nature. In other embodiments, it is also possible for example to use a rod-shaped magnet 125 in a suitable arrangement and at *a suitable spacing from the reed contact 120. In general, the force of the magnetic field of the magnet 125 which acts to close the reed contact 120 is influenced by the alignment and spacing. The effective force can also be influenced by the size, shape and material of the magnet 125. The magnet 125 is preferably configured together with the reed contact 120 so that the reed contact 120 is reliably closed so long as the magnet 125 has a temperature below its Curie temperature.

To influence a time delay between activation of the. heating element 130 and shutdown of the reed contact 120, it is in particular possible to influence the Curie point of the magnet 125 through the appropriate selection of the material of the material of the magnet 125 and a heating capacity of the electric heating element'130.

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