Method for early detection of an imminent overheating of at least one battery cell of a battery, detection device, and motor vehicle

Abstract

A method for detecting an imminent overheating of at least one battery cell of a battery, preferably for a motor vehicle. The imminent overheating is detected as a function of at least one determined first variable relating to the at least one battery cell. A temperature gradient over time of a temperature sensed in a predetermined proximity to the at least one battery cell and/or a voltage of the at least one battery cell is determined as the at least one first variable.

Claims

1. A method for detecting an imminent overheating of at least one battery cell of a battery, comprising: detecting a plurality of temperatures sensed in predetermined proximities to the at least one battery cell, calculating a temperature gradient over time for each of the plurality of temperatures, calculating a mean adjusted temperature gradient based on the plurality of temperature gradients, and normalizing the plurality of temperature gradients based on the mean adjusted temperature gradient, wherein the imminent overheating is detected when one or more of the plurality of temperature gradients so normalized exceed a predetermined gradient limit.

2. The method according to claim 1, further comprising extrapolating, based on one or more of the plurality of temperature gradients, a duration required for one or more of the at least one battery cell to exceed a critical temperature limit, wherein, when the at least one battery cell are below the critical temperature limit, the imminent overheating is detected when the duration so extrapolated falls below a predetermined duration limit.

3. The method according to claim 1, wherein the predetermined gradient limit is based on one or more of the plurality of temperature gradients prevailing at other locations in the battery.

4. A detection device for a motor vehicle for detecting an imminent overheating of at least one battery cell of a battery, the detection device comprising circuitry configured to execute the method according to claim 1.

5. The method according to claim 1, wherein the predetermined gradient limit is based on one or more of the plurality of temperatures, such that the predetermined gradient limit is reduced as one or more of the plurality of temperatures approaches a critical temperature limit.

6. The method according to claim 5, further comprising extrapolating, based on one or more of the plurality of temperature gradients, a duration required for one or more of the at least one battery cell to exceed a critical temperature limit, wherein, when the at least one battery cell are below the critical temperature limit, the imminent overheating is detected when the duration so extrapolated falls below a predetermined duration limit.

7. The method according to claim 5, further comprising detecting a voltage of one or more of the at least one battery cell, wherein the imminent overheating is detected when the voltage exceeds and/or falls below a predetermined voltage limit.

8. The method according to claim 7, wherein a parallel connection of the one or more of the at least one battery cell are temporarily separated to measure the voltage.

9. The method according to claim 1, further comprising detecting a voltage of one or more of the at least one battery cell, wherein the imminent overheating is detected when the voltage exceeds or falls below a predetermined voltage limit.

10. The method according to claim 9, wherein a parallel connection of the one or more of the at least one battery cell are temporarily separated to measure the voltage.

11. The method according to claim 10, wherein the parallel connection is separated via a switch.

12. The method according to claim 1, wherein one or more of the plurality of temperature gradients are calculated based on a specification of one or more of the at least one battery cell such that the one or more of the plurality of temperature gradients calculated differs from that which is measured.

13. The method according to claim 12, further comprising extrapolating, based on one or more of the plurality of temperature gradients, a duration required for one or more of the at least one battery cell to exceed a critical temperature limit, wherein, when the at least one battery cell are below the critical temperature limit, the imminent overheating is detected when the duration so extrapolated falls below a predetermined duration limit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, exemplary embodiments of the invention will be described. Concerning these embodiments:

(2) FIG. 1 shows a schematic diagram of a battery having a detection device for detecting an imminent overheating of at least one battery cell of the battery, according to one exemplary embodiment of the invention; and

(3) FIG. 2 shows a flowchart illustrating a method for detecting an imminent overheating of at least one battery cell of a battery according to one exemplary embodiment of the invention.

DETAILED DESCRIPTION

(4) The exemplary embodiments described in the following are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be viewed independently of one another and that further refine the invention independently of one another. The disclosure is therefore also intended to include combinations of the features of the embodiments other than those described. The described embodiments can also be enhanced by other features of the invention that have already been described.

(5) In the figures, the same reference signs are used to denote elements that have the same function.

(6) FIG. 1 shows a schematic diagram of a battery 10, in particular a high-voltage battery for a motor vehicle, having a detection device 12 for detecting an imminent overheating of at least one battery cell 14 of the battery 10 according to an exemplary embodiment of the invention. The battery 10 can in particular comprise a plurality of battery modules, not explicitly depicted here, which can in turn have a plurality of battery cells 14. In the present example, only a small number of battery cells 14 are shown. These battery cells 14 can generally be arranged in any series and/or parallel connection to one another. The battery 10, in particular the detection device 12, further has a plurality of sensors. In this example, these include a plurality of temperature sensors 16, which sense the temperature Ti at various positions within the battery 10, in particular each in predetermined proximity to the relevant battery cells 14, in particular continually, for example intermittently at specifiable measuring time intervals, or continuously. The number of temperature sensors 16 need not necessarily match the number of battery cells 14. In particular, either more or fewer temperature sensors 16 than battery cells 14 may be provided. The detection device 12 further has a plurality of voltage sensors 18. A respective voltage sensor 18 is assigned to a respective battery cell 14 and senses the respective individual cell voltage Ui of the relevant, assigned battery cell 14, in particular likewise continuously or intermittently at predetermined measuring time intervals. The measurements sensed by the respective sensors 16, 18 are correspondingly transmitted intermittently to a control unit 20 of the detection device 12. Said control unit analyzes the transmitted measurements and, on the basis of this analysis, determines whether a possible overheating of at least one of the battery cells 14 is imminent or whether a spread of such a possible overheating has already begun. This verification or detection of the imminent overheating will be explained in greater detail below in reference to FIG. 2. If the control unit 20 determines accordingly that an overheating of at least one of the battery cells 14 is imminent, the control unit 20 can initiate further measures that will likewise be described in greater detail below. One of these measures, for example, is to disable the battery system 10 or to decouple the battery 10 from the remainder of the motor vehicle's electrical system, which can be done by opening the main battery contactor 22. These main contactors 22 can therefore likewise be actuated by the control unit 20 as such a measure to detect an imminent overheating, and can be opened accordingly. Before the battery system is disabled, however, a timely warning is preferably issued to the driver of the motor vehicle to allow him sufficient time, for example, to bring the motor vehicle to a stop in a position on the shoulder. However, this requires the earliest possible detection of an imminent overheating, as is advantageously made possible by the invention and the embodiments thereof, and as will now be described in greater detail in reference to FIG. 2.

(7) FIG. 2 shows a flowchart illustrating a method for detecting an imminent overheating of at least one of the battery cells 14 according to an exemplary embodiment of the invention. The method described below can be carried out in particular by means of the detection device 12, in particular by means of the control unit 20 of the detection device 12.

(8) The method begins in step S10, in which the current sensor measurements, specifically the sensed temperatures Ti, along with the current individual cell voltages Ui are provided to the control unit 20. Using these provided measured variables as a basis, additional monitoring variables can then advantageously be derived or determined in step S12. A particularly advantageous one of these monitoring variables is the temperature gradient (ΔT/Δt)i. This variable represents, in particular, the change in the temperature ΔT within a given time interval Δt, for example the time interval Δt between two measuring steps at which the temperature Ti is sensed by a respective temperature sensor 16. To determine the temperature gradient (ΔT/Δt)i, at least two temperature values Ti recorded in succession for a relevant position are required. Since the temperature values Ti are continuously or intermittently sensed by a respective temperature sensor 16, as has already been described in reference to FIG. 1, the temperature gradient (ΔT/Δt)i can be determined in a simple manner, factoring in the temperature value Ti recorded immediately previously, for example.

(9) Another particularly advantageous monitoring variable is the predicted duration ΔZi until a specified critical temperature GT2 is reached, as will be described in greater detail later in reference to step S16. This predicted duration ΔZi can likewise be determined as a function of a determined current temperature value Ti and the temperature gradient (ΔT/Δt)i associated with this position. If this critical temperature limit GT2 is 120 degrees Celsius, for example, and if a current temperature Ti of 80 degrees Celsius is measured at a specific position, and if a current positive temperature gradient (ΔT/Δt)i of 10 degrees Celsius per minute, for example, is determined for the same position, then assuming a linear further temperature increase according to the determined temperature gradient (ΔT/Δt)i, the stated duration ΔZi can be determined as four minutes, in particular according to the formula:
(GT2−Ti)/(ΔT/Δt)i=(120° C.-80° C.)/(10° C./1 min)=4 min.

(10) In this way, it can be estimated, for example, how long it will take until a specified critical temperature GT2 is reached.

(11) A further suitable monitoring variable is the difference between a current temperature value Ti and the mean value T, which is formed from all the temperature values Ti currently sensed at a respective time increment. Based on the measured variables Ti, Ui sensed directly in step S10 and based on the variables derived therefrom in step S12, early detection of a possible overheating of at least one of the battery cells 14 can now be detected particularly advantageously. For this purpose, the relevant values can be compared with corresponding limits, as will be described in greater detail below.

(12) For example, in step S14 a check can first be made to determine whether the current temperature Ti is greater than a predetermined first temperature limit GT1. This check can be carried out in particular for all of the respective sensed temperature values Ti. If at least one of these temperature values Ti is above said first limit GT1, a further check can be carried out in step S16 to determine whether the relevant temperature value(s) Ti is/are also above a second predetermined temperature limit GT2, the critical temperature limit, for example 120 degrees or 130 degrees Celsius. This second temperature limit GT2 is greater than the aforementioned first temperature limit GT1. If at least one of the currently sensed temperatures Ti is above this second temperature limit GT2, a corresponding measure, in particular a disabling of the battery system, for example by opening the main contactor 22, can then be carried out immediately in step S18. This is the last possible measure to prevent a supercritical situation, in particular a battery fire. If possible, however, additional measures should be initiated much earlier so that such a disablement does not have to occur at all or at least so that a timely warning can be issued to the driver. This can now be accomplished as follows:

(13) Usually, in order for a chain reaction to be triggered at all the temperature Ti at the relevant battery cell 14 or at a position in a predetermined proximity to such a battery cell 14 must first increase gradually from a significantly lower value, in particular below the first limit GT1. In other words, before such a spread of overheating begins, the sensed temperature values Ti are still below the first limit GT1. Therefore, in step S14 the process can first proceed to step S20, in which a check is first made to determine whether the voltage values Ui sensed for the respective battery cells 14 at a respective time increment either exceed a predetermined first limit GU1 or at least one of the sensed voltages Ui, or whether at least one of the sensed voltage values Ui is below a predetermined second voltage limit GU2. In this way, voltage anomalies can be detected, which can likewise be used as an indication of an imminent overheating. For example, if such an overvoltage or undervoltage is detected in step S20, at least for one of the aforementioned battery cells 14, an imminent overheating can be considered to be detected and accordingly, an appropriate early measure can be initiated in step S22, for example a warning can be issued to the driver and/or for example the power to the motor vehicle can be limited. Monitoring can then begin again in step S10 for the next time increment. However, if no voltage anomaly is found in step S20, a further check can be made in step S24 to determine whether at least one of the determined temperature gradients (ΔT/Δt)i exceeds a predetermined gradient limit GG. If that is the case, the process can likewise return to step S22 and an early measure can be initiated. Otherwise, in step S26 a further check can be made to determine whether at least one of the determined temperature differences between a respective current temperature Ti and the temperature mean value T is greater than a certain third temperature limit GT3. This third temperature limit GT3 is likewise lower than the previously described second temperature limit GT2 and in particular is also lower than the first temperature limit GT1 mentioned. If that is the case, the process moves back to step S22; otherwise, in step S28 a check is made to determine whether a respective predicted duration ΔZi is shorter than a predetermined duration limit Δt.sub.crit. Such a predicted duration ΔZi can also be determined separately for the respective positions where the temperature sensors 16 are arranged, and accordingly a comparison such as is carried out in step S28 can be carried out for a respective duration ΔZi predicted in this manner. If at least one of the predicted durations determined in this way is shorter than the aforementioned duration limit Δt.sub.crit, an early measure can in turn be initiated in step S22. Otherwise, the method starts at the beginning again in step S10 for the next time increment.

(14) Early identification of an imminent overheating can thus be provided overall on the basis of numerous advantageous monitoring variables. This enables appropriate measures to be initiated at a particularly early stage, in particular before the high-voltage system or the high-voltage battery 10 has to be disabled completely. In this way, for example, the driver of the motor vehicle can be made aware of such a possible imminent overheating at a particularly early stage, and can be warned accordingly, giving him significantly more time to find a suitable parking space or some other position where the motor vehicle can be parked safely before the battery 10 is disabled and in particular before the further spread of overheating can lead to more serious consequences. This also allows the driver to leave the motor vehicle in good time, even if an overheating of the battery 10 and more serious consequences, such as a battery fire, can no longer be prevented. Based on these advantageous monitoring variables, in particular the temperature gradient and/or the additionally observed individual cell voltages, safety can thus be significantly increased.

(15) Taken together, the examples demonstrate how the invention can be used to identify the start of the spread of overheating in a high-voltage battery, in which, by the observation, in particular the additional observation, of the temperature gradient over time and/or the individual cell voltage, a significant increase in safety is made possible.