Battery pack with current limiting

Abstract

Battery pack (2) for an electrical device (1) with at least one accumulator cell (6), wherein - the battery pack (2) has a sensor (10, 14, 15) which is configured to generate a sensor signal depending on an electrical or thermal measurement quantity, wherein the electrical or thermal measurement quantity relates to a temperature of the at least one accumulator cell (6); - the battery pack (2) has a control circuit (12) configured to control or regulate a discharge current of the at least one accumulator cell (6) such that the discharge current is less than a maximum current which depends on the sensor signal; and - the control circuit (12) is configured to set the maximum current to a predetermined first value depending on the sensor signal; - the control circuit (12) is configured to determine whether the discharge current lies between a predetermined second value and the first value for a predetermined maximum time period after the maximum current has been set to the first value, where the second value is less than the first value and where both the first and second values ​​are greater than zero; and - the control circuit (12) is configured to reduce the maximum current from the first value to the second value as soon as the discharge current for the maximum duration lies between the second value and the first value.

Description

[0001] The present invention relates to a battery pack for an electrical device comprising at least one accumulator cell and a method for operating an electrical device.

[0002] Battery cells, such as lithium-ion batteries used in battery packs for power tools or other electrical devices like garden equipment or household appliances, typically contain components whose temperature must be limited to prevent damage. Failure to do so could potentially destroy the battery cell and the entire battery pack, posing a risk to people. Such temperature-sensitive components might include a battery cell separator that separates the cathode and anode, or a solid electrolyte interface (SEI) layer.

[0003] Since the temperature inside the battery cell, and thus directly at the temperature-sensitive components, cannot be measured directly, monitoring and limiting the temperature outside the battery cell can be achieved at another location within the battery pack, for example, using a temperature sensor mounted on a circuit board that also houses the battery pack's management system. However, due to the spatial distance of the temperature sensor from the actual temperature-sensitive components and the resulting uncertainties in the measured temperature value, as well as the time lag with which a temperature change in the battery cell becomes noticeable at the temperature sensor, this method only allows for relatively imprecise monitoring.

[0004] This leads to the corresponding temperature thresholds being chosen more pessimistically, i.e., lower, than would actually be possible. This limits the potential power output of the battery pack and therefore restricts its use for high-power electrical devices, meaning that larger and / or multiple battery packs may be necessary.

[0005] Document DE 10 2013 210 305 A1 describes a battery pack for a hand-held power tool with an energy storage device and a circuit for controlling the charging and / or discharging process of the energy storage device. The control device is connected to a temperature sensor for detecting the temperature of the energy storage device. The temperature sensor provides the control device with a temperature signal that correlates with the temperature of the electrical energy storage device. The control device is designed to control the charging and / or discharging process based on this temperature signal.

[0006] It is an object of the present invention to increase the possible power output by a battery pack for an electrical device without increasing the risk of thermal overload of the battery cells.

[0007] This problem is solved by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

[0008] The invention is based on the idea of ​​defining a maximum current for the discharge current depending on an electrical or thermal measurement parameter relating to the temperature of a battery cell of a battery pack.

[0009] According to one aspect of the invention, a battery pack for an electrical device, in particular a power tool, is provided. The battery pack comprises at least one accumulator cell and a sensor. The sensor is arranged and configured to generate a sensor signal depending on a thermal or electrical measurement, wherein the electrical or thermal measurement relates to the temperature of the at least one accumulator cell. The battery pack comprises a control circuit configured to control or regulate a discharge current of the at least one accumulator cell such that the discharge current is always less than a maximum current, wherein the maximum current depends on the sensor signal. The control circuit is configured to set the maximum current to a predetermined first value depending on the sensor signal.

[0010] The control circuit, for example a timer circuit, is configured to determine whether the discharge current lies between a predetermined second value and the first value for a specified maximum duration, when or after the maximum current has been set to the first value. The second value is less than the first value. The control circuit is configured to reduce the maximum current from the first value to the second value if the discharge current lies between the second and first values ​​for the maximum duration, specifically as soon as the discharge current lies or has been between the second and first values ​​for the maximum duration.

[0011] The at least one accumulator cell is specifically designed as at least one lithium-ion accumulator cell, but can also be designed as at least one accumulator cell of another type or based on a different electrochemical system.

[0012] If the battery pack is connected to the electrical device, the battery pack can supply the electrical device with the discharge current and thus with electrical energy, in particular to drive a motor of the electrical device.

[0013] The battery pack can be detachably, and in particular non-destructively, connected to the housing of the electrical device, for example via a snap-fit ​​connection, a plug connection, and / or a clamp connection. In particular, the mechanical connection of the battery pack to the housing of the electrical device can be designed as a positive-locking and / or force-locking connection without a material bond. In other words, the mechanical connection of the battery pack to the housing of the electrical device can be released without having to break a material bond. Preferably, the mechanical connection can be released manually as intended, without the use of any other tools. In other words, the battery pack is designed as a replaceable battery pack, in particular a system battery pack. The housings of the battery pack and the electrical device can have respective interfaces for electrical and mechanical connection.

[0014] An electrical connection between at least one battery cell and the electrical device, in particular a motor of the electrical device, can be made, for example, via one or more detachable electrical contacts, such as clamp contacts or plug contacts, in particular so-called tulip contacts or sword contacts. For example, compatible plugs or sockets or receptacles or the like can be provided at the interfaces of the corresponding housings to achieve the electrical connection of the battery pack to the electrical device.

[0015] The discharge current of at least one battery cell can only flow if the battery pack is electrically connected to the electrical device or a corresponding housing of the electrical device and thus to the motor of the electrical device.

[0016] The temperature of the at least one accumulator cell can, for example, be the temperature directly at a surface of the at least one accumulator cell, such as at a surface of a cell casing of the at least one accumulator cell. In particular, the temperature can be the temperature at a pole or at a location on the at least one accumulator cell that corresponds to a pole of the at least one accumulator cell.

[0017] A measured quantity relates to the temperature of at least one battery cell, particularly if the temperature can be derived or estimated directly or indirectly from the value of the measured quantity. For this purpose, models, especially battery models, can be used that take into account several measured quantities, such as temperature, discharge current, output voltage, and / or output power.

[0018] The electrical or thermal quantity measured can be the temperature of the at least one battery cell itself. In this case, the sensor is specifically designed as a temperature sensor, which is arranged at the corresponding location on the at least one battery cell. However, the electrical or thermal quantity measured can also be the discharge current, an output voltage or terminal voltage of the battery pack or the at least one battery cell, or an output power of the battery pack or the at least one battery cell. In this case, the sensor can, for example, be designed as a current and / or voltage sensor. Since discharge current, output voltage, and output power influence the temperature of the at least one battery cell, and vice versa, these quantities also relate to temperature in the aforementioned sense.

[0019] The first and second values ​​for the maximum current are greater than zero. This means, in particular, that the reduction of the maximum current from the first value to the second value does not correspond to a reduction of the maximum current to zero, which would be equivalent to an interruption of the discharge current.

[0020] To determine whether the discharge current lies between the second and first values ​​for the specified maximum duration, the timer circuit can, for example, define a time period during which the current lies between the second and first values ​​and compare this period to the specified maximum duration. Alternatively, the timer circuit can be configured to start a timer or similar device as soon as the current lies between the second and first values, particularly as soon as the current exceeds the second value. Alternatively, the timer circuit can generate a current or voltage signal that depends on the duration for which the current lies between the second and first values ​​and perform the determination accordingly based on this signal.

[0021] The control circuit can, for example, correspond to or constitute part of the battery management system of the battery pack. The control circuit or the battery management system can be located, for example, on a circuit carrier, particularly a circuit board, of the battery pack. The control circuit can include, for example, one or more microcontrollers, application-specific integrated circuits, ASICs, central processing units, CPUs, field-programmable gate arrays, FPGAs, systems-on-a-chip, SoCs, or other integrated circuits or computing units. The control circuit can also include analog or digital discrete circuits.

[0022] In particular, the battery pack contains a switching element that can be controlled by the control circuit to control or regulate the discharge current. The control circuit can, in particular, open the switching element to interrupt the discharge current. The switching element can, for example, contain one or more transistors, such as field-effect transistors and / or bipolar transistors, especially power transistors, such as power MOSFETs, IGBTs, and so on.

[0023] The minimum one accumulator cell can, for example, consist of exactly one accumulator cell. Alternatively, the minimum one accumulator cell can, for example, consist of two or more accumulator cells connected in series.

[0024] In a battery pack according to the invention, the sensor provides direct or indirect temperature monitoring of the at least one battery cell, and at least two values ​​for the maximum discharge current, different from each other and from zero, are specified. Depending on the sensor signal, and thus depending on the temperature of the at least one battery cell, the higher second value for the maximum current can be permitted for a limited time. By reducing the maximum current to the first value after the maximum time period has expired, excessive heating of temperature-sensitive components of the at least one battery cell can still be avoided.

[0025] This allows the battery pack according to the invention to handle a short-term increase in current or power demand from the motor of the electrical device without the risk of overheating or overloading the at least one battery cell. This enables the handling of short-term current spikes or similar demands, particularly in electrical devices with short-term, exceptionally high power consumption. Ultimately, this extends the applicability of the battery pack to such electrical devices without requiring, for example, multiple or larger battery packs, or a parallel connection of several battery cells or multiple strings of battery cells, to increase the output power while maintaining a constant output voltage. This allows the use of battery packs with fewer battery cells overall, resulting in a smaller size, lower weight, and lower cost.

[0026] This is advantageous because even in power-intensive applications, i.e., when using electrical appliances with relatively high power consumption, such as chainsaws, hammer drills, and so on, the actual current peaks are only required for a relatively short time, on the order of a few seconds, roughly between 1 and 20 seconds or so. Therefore, when using the electrical appliance as intended, a user does not have to expect the discharge current to be interrupted during a brief period of high power demand, and consequently, the motor of the electrical appliance to stop. The invention thus improves user comfort as well as saving time when performing power-intensive tasks with the electrical appliance.

[0027] According to at least one embodiment of the battery pack, the sensor is designed as a temperature sensor and is arranged on or in the immediate vicinity of the at least one accumulator cell, wherein the electrical or thermal measurement corresponds to the temperature of the at least one accumulator cell.

[0028] In other words, the temperature sensor is arranged directly on a cell housing of the at least one accumulator cell, i.e., it is in mechanical contact with the cell housing, or it is arranged in the immediate vicinity of the at least one accumulator cell in such a way that there are no other components or parts of the battery pack between the temperature sensor and the cell housing of the at least one accumulator cell.

[0029] In such embodiments, the temperature of at least one accumulator cell corresponds to the temperature at the location of the temperature sensor.

[0030] The temperature sensor can be designed, for example, as a temperature-dependent resistor or with a temperature-dependent resistor, for example as or with an NTC resistor.

[0031] In this way, direct monitoring of the temperature of at least one battery cell can be achieved, allowing for lower tolerances in determining the maximum current depending on the sensor signal and consequently achieving higher performance of the battery pack.

[0032] According to at least one embodiment, the battery pack is designed as a single-row battery pack. A single-row battery pack can be understood to mean a battery pack containing exactly one accumulator cell, or two or more accumulator cells connected in series, and no further accumulator cells. In other words, all accumulator cells of the battery pack are connected exclusively in series with each other.

[0033] The term "single-row battery pack" can be understood in particular in contrast to a multi-row battery pack. A multi-row battery pack contains two or more accumulator cells connected in parallel. For example, a multi-row battery pack can contain two or more first accumulator cells connected in series, as well as two or more second accumulator cells, also connected in series. The first and second accumulator cells are, for example, connected in parallel or partially in parallel with the first accumulator cells.

[0034] Multi-row battery cells offer the advantage of providing a higher overall output current and, consequently, higher output power for a given output voltage. A corresponding disadvantage of multi-row battery packs is the larger number of cells required, resulting in greater weight and a larger pack size.

[0035] Accordingly, the invention is particularly advantageous for single-row battery packs, since the available output power or the maximum discharge current represents an even greater limiting factor in the applicability of the battery pack than in multi-row battery packs. However, the invention is also fundamentally applicable to multi-row battery packs, where the available power can also be temporarily increased further.

[0036] According to at least one embodiment, the temperature sensor is arranged at one pole of the at least one accumulator cell.

[0037] For example, each accumulator cell of at least one accumulator cell can have a cell casing. The electrodes of each accumulator cell can then be electrically contacted at two points on the respective cell casing. These points can be called terminals. Alternatively, the at least one accumulator cell can have a common cell casing with two points where the series-connected electrodes of at least one accumulator cell can be contacted.

[0038] The cell casing can be designed as rigid, for example in the case of cylindrical or prismatic accumulator cells, or as a flexible casing, for example in the case of pouch accumulator cells.

[0039] Positioning the temperature sensor at the pole is particularly advantageous because the poles of at least one battery cell tend to be the areas with the highest temperature both within the battery pack and outside the battery cells themselves. Furthermore, a temperature change inside the at least one battery cell is most quickly felt at the poles outside the battery cells.

[0040] According to at least one embodiment, the sensor is designed as a current sensor, which is arranged accordingly and configured to generate the sensor signal depending on the current strength of the discharge current.

[0041] The discharge current, particularly in combination with other electrical or thermal measurements, such as the output voltage, can, via a battery model, allow for estimations of the temperature of at least one battery cell. In such embodiments, the control circuit can set and / or change the maximum current, for example, depending on the sensor signal and one or more additional sensor signals generated by corresponding sensors based on these additional measurements. This can be done, in particular, by reducing the maximum current. For example, corresponding value ranges for the sensor signal and the additional sensor signal(s) are stored, which, according to the battery model, correspond to the desired temperature ranges.

[0042] According to at least one embodiment, the sensor is designed as a voltage sensor, which is set up and arranged to generate the sensor signal depending on an output voltage of the at least one accumulator cell.

[0043] The output voltage, particularly in combination with other electrical or thermal measurements, such as the discharge current, can enable estimations of the temperature of at least one battery cell via a battery model. In such embodiments, the control circuit can set and / or change the maximum current, for example, depending on the sensor signal and one or more additional sensor signals generated by corresponding sensors based on these additional measurements. This can be done, in particular, by reducing the maximum current. For example, corresponding value ranges for the sensor signal and the additional sensor signal(s) are stored, which, according to the battery model, correspond to the desired temperature ranges.

[0044] According to at least one embodiment, the control circuit is configured to set the maximum current to the first value only if the temperature of the at least one accumulator cell, according to the sensor signal, is lower than a predetermined first maximum temperature.

[0045] The first maximum temperature is selected and coordinated with the maximum duration in such a way that damage to at least one accumulator cell can be ruled out with high reliability if the current for the maximum duration lies between the first and second values, provided that the temperature is lower than the first maximum temperature.

[0046] Depending on the design of the battery cell, the electrochemical system, and the positioning or type of sensor, the first maximum temperature can, for example, be in a range between 60 °C and 90 °C. In one exemplary embodiment, the first maximum temperature is 75 °C or approximately 75 °C.

[0047] According to at least one embodiment, the control circuit is configured to set the maximum current to the first value at a first time point in time when the temperature of the at least one accumulator cell, according to the sensor signal, is lower than the first maximum temperature. The control circuit is configured to set the maximum current to the second value at a second time point in time, which is after the first time point and, in addition, the temperature of the at least one accumulator cell, according to the sensor signal, is greater than or equal to the first maximum temperature.

[0048] In particular, the temperature is initially lower than the first maximum temperature, and after the maximum current has been set to the first value accordingly, the temperature rises above the first maximum temperature, so that the control circuit reduces the maximum current to the second value.

[0049] The timer circuit is configured to determine whether at least a predetermined cooling time has elapsed between the second time point and a third time point located after the second time point. The control circuit is configured to reset the maximum current at the third time point from the second value back to the first value only if at least the cooling time has elapsed between the second and third time points and the temperature of at least one accumulator cell, according to the sensor signal at the third time point, is lower than the first maximum temperature.

[0050] In other words, the cooling period can be considered a recovery period. If the temperature has exceeded the initial maximum temperature, the maximum current will not return to its initial value until at least the cooling period has elapsed. Additionally, the temperature must have dropped below the initial maximum temperature.

[0051] This ensures sufficient recovery of the electrochemical system of at least one battery cell after exceeding the initial maximum temperature. It prevents the initial maximum temperature from being repeatedly exceeded due to high discharge currents at too short intervals. This further increases the safety and / or lifespan of at least one battery cell.

[0052] According to at least one embodiment, the control circuit is configured to interrupt the discharge current, i.e., to set the maximum current to zero, when the temperature of the at least one accumulator cell, according to the sensor signal, is greater than or equal to a predetermined second maximum temperature that is greater than the first maximum temperature.

[0053] The second maximum temperature can be, for example, 10 K to 30 K, or approximately 15 K, higher than the first maximum temperature. If the first maximum temperature is 75 °C, then in a specific embodiment, the second maximum temperature could be, for example, 90 °C.

[0054] In this way, overheating or overloading of at least one battery cell, for example at correspondingly high outside temperatures, can be avoided.

[0055] According to at least one embodiment, the control circuit is configured to terminate the interruption of the discharge current only if, and in particular to restore the maximum current to the first or second value after the interruption, the temperature of the at least one accumulator cell according to the sensor signal is lower than a predetermined third maximum temperature, wherein the third maximum temperature is in particular lower than the first and lower than the second maximum temperature.

[0056] For example, the third maximum temperature can be 20 K to 40 K lower than the second maximum temperature, for example 25 K lower.

[0057] According to at least one embodiment, the battery pack has a further temperature sensor which is configured and arranged to generate a further sensor signal depending on a further temperature of the at least one battery cell. The control circuit is configured to interrupt the discharge current if the further temperature of the at least one battery cell, according to the further sensor signal, is greater than or equal to a predetermined fourth maximum temperature.

[0058] The temperature of at least one accumulator cell is generally different from the temperature of the other accumulator cell. If the sensor is a temperature sensor, then the temperature sensor and the other temperature sensor are arranged at different positions within the battery pack. In particular, the other temperature sensor is not arranged directly on a cell casing of the at least one accumulator cell. For example, the other temperature sensor can be arranged on the circuit carrier, for example on a side of the circuit carrier facing away from the at least one accumulator cell.

[0059] In particular, a temperature change inside at least one accumulator cell affects the temperature of that cell more quickly than the temperature of the other cells. Accordingly, the fourth maximum temperature can, for example, be lower than the first maximum temperature.

[0060] This allows for an additional level of safety. In particular, not only the discharge current but also the ambient temperature of the battery pack can be relevant to the internal temperature of at least one battery cell. A very high ambient temperature can therefore be taken into account, for example, by additional monitoring using the extra temperature sensor.

[0061] According to at least one embodiment, the control circuit is configured to terminate the interruption of the discharge current, in particular the interruption when the further temperature is greater than or equal to the fourth maximum temperature, only when the further temperature of the at least one accumulator cell according to the further sensor signal is less than a predetermined fifth maximum temperature.

[0062] According to a further aspect of the invention, an electrical device, in particular a power tool, is also provided with a battery pack according to the invention. The electrical device, in particular a motor of the electrical device, can be operated by means of the discharge current of the at least one battery cell.

[0063] The individual cells of at least one battery cell can, for example, be designed to continuously deliver an electrical power output in the range of 70 W to 110 W. Depending on the number and connection of the battery cells, the maximum continuous power consumption of the electrical device or the maximum continuous power output of the battery can be calculated.

[0064] The electrical power output of 70 W to 110 W per battery cell can be delivered, for example, when the maximum current is set to the second value. According to the invention, this power output can be exceeded, particularly for short periods, for example, when the maximum current is set to the first value.

[0065] For example, the electrical device can be designed as a chainsaw, a hammer drill, a miter saw, a circular saw, in particular as a table circular saw or hand-held circular saw, a plunge saw or a tile cutting machine.

[0066] As explained above, the use of a battery pack according to the invention in such electrical devices is particularly advantageous due to the high power consumption, at least for short periods.

[0067] According to a further aspect of the invention, a method for operating an electrical device is also described. A discharge current from the at least one accumulator cell is supplied to the electrical device, in particular to the motor of the electrical device, by means of a battery pack of the electrical device, wherein the battery pack comprises at least one accumulator cell. Depending on an electrical or thermal measurement, a sensor signal is generated, in particular by means of a sensor of the battery pack, wherein the electrical or thermal measurement relates to the temperature of the at least one accumulator cell. The discharge current of the at least one accumulator cell is controlled or regulated, in particular by means of a control circuit of the battery pack, such that the discharge current is always less than a maximum current, wherein the maximum current depends on the sensor signal.The maximum current is set to a predetermined first value, particularly by means of the control circuit, depending on the sensor signal.

[0068] It is determined, in particular by means of a timer circuit in the battery pack, for example the control circuit, whether the discharge current lies between a predetermined second value and the first value for a specified maximum duration, where the second value is less than the first value. The maximum current is reduced from the first value to the second value, in particular by means of the control circuit, if the discharge current lies between the second value and the first value for the maximum duration.

[0069] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures, may be encompassed by the invention not only in the combinations specified, but also in other combinations. In particular, the invention also encompasses embodiments and combinations of features that do not have all the features of an originally formulated claim. Furthermore, the invention also encompasses embodiments and combinations of features that go beyond or deviate from the combinations of features set out in the cross-references to the claims.

[0070] The invention is explained in more detail below with reference to specific embodiments and associated schematic drawings. In the figures, identical or functionally equivalent elements may be designated with the same reference numerals. The description of identical or functionally equivalent elements is not necessarily repeated with respect to different figures.

[0071] The figures show Fig. 1 schematically an exemplary embodiment of an electrical device according to the invention; Fig. 2 schematically an exemplary embodiment of a battery pack according to the invention; Fig. 3 a block diagram of a further exemplary embodiment of a battery pack according to the invention; and Fig. 4 schematically exemplary temperature profiles at different positions within a battery pack.

[0072] In Fig. Figure 1 schematically depicts an electrical device 1 according to the invention, which is designed purely by way of example as a battery-operated chainsaw. The electrical device 1 has a battery pack according to the invention.

[0073] In Fig. 2 shows a battery pack according to the invention schematically in an exploded view, as is the case, for example, for an electrical device 1 made of Fig. 1 can be used.

[0074] The battery pack 2 comprises several accumulator cells 6 connected in series, which may, for example, be arranged in a cell holder 7. The battery pack 2 also comprises, for example, a lower shell 3 and an upper shell 4, which can be connected to each other by plug or clamp connections and form an interior space in which the at least one accumulator cell 6 can be arranged with the cell holder 7. The upper shell 4 has a contact area 5 to mechanically connect the housing formed by the upper and lower shells 3 and 4 to a corresponding further housing of the electrical device 1. An electrical connection of the electrical device 1 also takes place via the contact area or via contacts 13 located in the interior, which are brought to the outside via the contact area 5. The contacts 13 are connected to the at least one accumulator cell 6.

[0075] The battery pack 2 also has a circuit carrier 8, on which, for example, the contacts 13 can be arranged. Furthermore, a control circuit 12 is arranged on the circuit carrier 8, which can, for example, function as a battery management system. The control circuit 12 is configured to regulate or control a discharge current of the at least one accumulator cell 6 and accordingly deliver it to the electrical device via the contacts 13 when the battery pack 2 is attached to the electrical device 1. The battery pack 2 has a switching element 9, for example, a power MOSFET, which is arranged between one of the contacts 13 and the at least one accumulator cell 6. The control circuit 12 can activate the switching element 9 to interrupt the discharge current or to terminate the interruption of the discharge current.

[0076] In the example shown, battery pack 2 exhibits the Fig. 2. A temperature sensor 10 is located at one terminal of one of the accumulator cells 6 and connected to the control circuit 12. The temperature sensor 10 can, for example, be designed as an NTC resistor.

[0077] Optionally, the battery pack includes an additional temperature sensor 11, which is located on the upper side, i.e., the side facing away from the battery cells 6, of the circuit carrier 8. This additional temperature sensor 11 can, for example, be designed as an NTC resistor.

[0078] In Fig. Figure 3 shows a block diagram of battery pack 2. Fig. Figure 3 shows an optional current sensor 14 between one of the contacts 13 and the at least one accumulator cell 6, and an optional voltage sensor 15 between the two contacts 13. The current sensor 14 is connected to the control circuit 12, so that the control circuit 12 can determine the discharge current via the current sensor 14. Similarly, the optional voltage sensor 15 is connected to the control circuit 12, so that the control circuit 12 can determine the output voltage between the contacts 13, if necessary.

[0079] The temperature sensor 10 generates a temperature sensor signal depending on the temperature of at least one accumulator cell and transmits it to the control circuit 12. The control circuit 12 can then control or regulate the discharge current such that the discharge current is always less than a maximum current, whereby the control circuit 12 can set the maximum current depending on the temperature sensor signal. In particular, the control circuit 12 can open the switching element 9 to interrupt the discharge current when the discharge current reaches the maximum current.

[0080] Here, two different and non-zero values ​​for the maximum current are specified. In this specific embodiment, the first value can be, for example, 50 A and the second value, for example, 40 A. Depending on the application, however, other non-zero values ​​are of course possible. In any case, the second value is lower than the first value. Depending on the temperature sensor signal, the control circuit 12 sets the maximum current to the first value. In particular, the control circuit 12 only sets the maximum current to the first value if, according to the temperature sensor signal, the temperature at the at least one accumulator cell 6 is lower than a predefined first maximum temperature, for example, 75 °C.In this case, the control circuit allows a discharge current of 12 A for a predetermined maximum duration, for example 10 s, that is greater than the second value, i.e. greater than 40 A, and less than the first value, i.e. less than 50 A. If the discharge current for the maximum duration lies between the second and the first value, the control circuit reduces the maximum current to the first value to prevent excessive heating of at least one battery cell 6 due to the high discharge current.

[0081] However, if the temperature according to the temperature sensor signal is greater than the first maximum temperature, the control circuit 12 only allows a discharge current with a current strength that is smaller than the second value.

[0082] For example, an absolute upper limit for the temperature can also be specified according to the temperature sensor signal. In particular, the control circuit 12 can interrupt the discharge current by opening the switching element 9 if the temperature according to the temperature sensor signal is greater than a specified second maximum temperature, for example 90 °C.

[0083] If such an interruption occurs, the control circuit 12 can only lift the interruption, for example, if the temperature has fallen below a third maximum temperature, for example 65 °C, according to the temperature sensor signal.

[0084] In embodiments in which the battery pack 2 contains the additional temperature sensor 11, the control circuit 12 can also take into account the additional temperature according to the additional temperature sensor signal, which the additional temperature sensor can generate accordingly, when controlling or regulating the discharge current.

[0085] Since in the example of the Fig. 2. If the temperature sensor 10 is arranged directly on the at least one accumulator cell 6, for example at one pole of the accumulator cell 6, while the other temperature sensor 11 is located further away from it, in particular on the top side of the circuit carrier 8, a temperature change inside the at least one accumulator cell 6 becomes noticeable in the temperature sensor signal more quickly than in the other temperature sensor signal. This is due to the fact that... Fig. Figure 4 schematically shows the time course of the temperatures T and T' at the respective positions of temperature sensor 10 and the further temperature sensor 11 at a constant discharge current. The temperature T according to the temperature sensor signal rises significantly faster than the temperature T' according to the further temperature sensor signal.

[0086] Accordingly, the control circuit 12 can also interrupt the discharge current, for example by opening the switching element 9, if the further temperature according to the further temperature sensor signal is greater than a fourth maximum temperature, for example 70 °C.

[0087] If such an interruption occurs, the control circuit 12 can only lift the interruption, for example, if the temperature has fallen below a fifth maximum temperature, for example 60 °C, according to the temperature sensor signal.

[0088] Alternatively or additionally to the temperature sensor 11, the control circuit can use a current sensor signal from current sensor 14 and / or a voltage sensor signal from voltage sensor 15 to determine the respective value for the maximum current. The output voltage, which represents the voltage sensor signal, or the discharge current, can provide temperature estimates for at or within at least one battery cell via a suitable battery model. Accordingly, the first or second value can also be determined depending on these measured values.

[0089] Furthermore, it is noted that setting the respective maximum current does not necessarily have to be linked to exceeding certain absolute values ​​for the temperature of at least one accumulator cell. Rather, temperature differences between the temperature according to the temperature sensor signal and the other temperature sensor signal can also be used to determine the maximum current. Alternatively or additionally, setting the maximum current based on a time-dependent temperature profile or a time-dependent temperature difference profile, and so on, can also be implemented.

[0090] As explained, particularly with regard to the figures, the invention makes it possible to increase the current or power output of a battery pack for an electrical device. If the temperature at a critical point of the at least one battery cell is sufficiently low, the limitation of the maximum current to the second value can be removed and replaced by a limitation to the first value. This prevents the discharge current from being interrupted by the electrical device during short-term high power demands, even though the temperature of the at least one battery cell is still within an acceptable range. In preferred embodiments, the increase in the maximum current can be reversed after the maximum duration has elapsed.

[0091] During operation of the battery pack or the electrical device, the internal battery cells heat up. Furthermore, other components of the battery pack or the battery cells, such as linkers, contacts, fuses, and so on, can also heat up. This additional heat can also be transferred to the battery cells and cause a further temperature increase. Both types of heat input can be taken into account in appropriate embodiments of the invention. REFERENCE MARK LIST: 1 electrical appliance 2 battery packs 3 Bottom tray 4 Upper shell 5 Contact area 6 accumulator cells 7 cell holders 8 circuit carriers 9 Switching element 10 Temperature sensor 11 Temperature sensor 12 Control circuit 13 contacts 14 Current sensor 15 Voltage sensor

Claims

[1] Battery pack (2) for an electrical device (1) comprising at least one accumulator cell (6), wherein - the battery pack (2) has a sensor (10, 14, 15) which is configured to generate a sensor signal depending on an electrical or thermal measurement quantity, wherein the electrical or thermal measurement quantity relates to a temperature of the at least one accumulator cell (6); - the battery pack (2) has a control circuit (12) configured to control or regulate a discharge current of the at least one accumulator cell (6) such that the discharge current is less than a maximum current which depends on the sensor signal; and - the control circuit (12) is configured to set the maximum current to a predetermined first value depending on the sensor signal; - the control circuit (12) is configured to determine whether the discharge current lies between a predetermined second value and the first value for a predetermined maximum time period after the maximum current has been set to the first value, where the second value is less than the first value and where both the first and second values ​​are greater than zero; and - the control circuit (12) is configured to reduce the maximum current from the first value to the second value as soon as the discharge current for the maximum duration lies between the second value and the first value. [2] Battery pack (2) according to claim 1, wherein the sensor (10, 14, 15) is configured as a temperature sensor (10) and is arranged on or in the immediate vicinity of the at least one accumulator cell (6), wherein the electrical or thermal measurement quantity corresponds to the temperature of the at least one accumulator cell (6). [3] Battery pack (2) according to claim 2, wherein the temperature sensor (10) is arranged at one pole of the at least one accumulator cell (6). [4] Battery pack (2) according to claim 1, wherein - the sensor (10, 14, 15) is designed as a current sensor (14) which is configured to generate the sensor signal depending on the current strength of the discharge current; or - the sensor (10, 14, 15) is designed as a voltage sensor (15) which is configured to generate the sensor signal depending on an output voltage of the at least one accumulator cell (6). [5] Battery pack according to one of the preceding claims, wherein the control circuit (12) is configured to set the maximum current to the first value only when the temperature of the at least one accumulator cell (6) according to the sensor signal is less than a predetermined first maximum temperature. [6] Battery pack (2) according to claim 5, wherein the control circuit (12) is configured to set the maximum current to the second value when the temperature of the at least one accumulator cell (6) according to the sensor signal is greater than or equal to the first maximum temperature. [7] Battery pack (2) according to claim 6, wherein - the control circuit (12) is configured to set the maximum current to the first value at a first time when the temperature of the at least one accumulator cell (6) according to the sensor signal is less than the first maximum temperature; - the control circuit (12) is configured to set the maximum current to the second value at a second time point which is after the first time point and at which the temperature of the at least one accumulator cell (6) according to the sensor signal is greater than or equal to the first maximum temperature; - the control circuit (12) is configured to determine whether at least a predetermined cooling time has elapsed between the second time point and a third time point that lies after the second time point; and - the control circuit (12) is configured to set the maximum current at the third time from the second value to the first value only if at least the cooling time has elapsed between the second time and the third time and the temperature of the at least one accumulator cell (6) according to the sensor signal at the third time is less than the first maximum temperature. [8] Battery pack (2) according to one of the preceding claims, wherein the control circuit (12) is configured to interrupt the discharge current when the temperature of the at least one accumulator cell (6) according to the sensor signal is greater than or equal to a predetermined second maximum temperature which is greater than the first maximum temperature. [9] Battery pack (2) according to claim 8, wherein the control circuit (12) is configured to terminate the interruption of the discharge current only when the temperature of the at least one accumulator cell (6) according to the sensor signal is less than a predetermined third maximum temperature. [10] Battery pack (2) according to any of the preceding claims, wherein - the battery pack (2) has a further temperature sensor (11) which is configured to generate a further sensor signal depending on a further temperature of the at least one accumulator cell (6); - the control circuit (12) is configured to interrupt the discharge current when the further temperature of the at least one accumulator cell (6) according to the further sensor signal is greater than or equal to a predetermined fourth maximum temperature. [11] Battery pack (2) according to claim 10, wherein the control circuit (12) is configured to terminate the interruption of the discharge current only when the further temperature of the at least one accumulator cell (6) according to the further sensor signal is less than a predetermined fifth maximum temperature. [12] Battery pack (2) according to one of the preceding claims, wherein the battery pack (2) is configured as a single-row or multi-row battery pack (2). [13] Electrical device (1) with a battery pack (2) according to one of the preceding claims, wherein the electrical device (1) can be operated by means of the discharge current. [14] Method for operating an electrical appliance (1) wherein - by means of a battery pack (2) comprising at least one accumulator cell (6), a discharge current of the at least one accumulator cell (6) is delivered to the electrical device (1); - a sensor signal is generated depending on an electrical or thermal measurement quantity, wherein the electrical or thermal measurement quantity relates to the temperature of at least one accumulator cell (6); - the discharge current of at least one accumulator cell (6) is controlled or regulated such that the discharge current is less than a maximum current which depends on the sensor signal; and - the maximum current is set to a predetermined first value depending on the sensor signal; - determines whether the discharge current lies between a given second value and the first value for a given maximum duration after the maximum current has been set to the first value, where the second value is less than the first value and where both the first and second values ​​are greater than zero; and - the maximum current is reduced from the first value to the second value as soon as the discharge current lies between the second value and the first value for the maximum duration.

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