Battery monitoring system and method for monitoring the state of a battery

Abstract

The proposal relates to a battery monitoring system (1) for monitoring the state of a battery (2), in particular a traction battery of a vehicle (10), wherein the battery monitoring system (1) is designed to monitor the operating state of the battery (2) by evaluating sensor signals from at least two sensors (3) which detect different physical measurement variables. Depending on the detected, currently existing operating situation P; C; D of the battery (2), the battery monitoring system (1) assigns the sensors to different hierarchy levels with staggered priorities L1; L2; L3 and identifies a critical state of the battery (2) by evaluating the signals from sensors of the hierarchy level with the highest priority L1. The proposal also relates to a method for monitoring the state of a battery.

Description

[0001] Description

[0002] title

[0003] Battery monitoring system and method for monitoring the condition of a battery

[0004] State of the art

[0005] Battery-based drive systems that use relatively large batteries are gaining importance. Large electric batteries carry the risk of triggering a highly exothermic chemical reaction in the event of a failure. If a local short circuit of the internal electrodes occurs in a lithium-ion cell due to mechanical, electrical, and / or thermal stress, for example due to contamination or damage, a short-circuit current can heat the area surrounding the damage to such an extent that the surrounding areas are affected. This causes the energy stored in the cell to be released in a short time. This process is also known as thermal runaway. The thermal runaway of a single lithium-ion cell typically lasts between 20 and 60 seconds.Due to the thermal coupling of individual battery cells, neighboring cells can also thermally break down, dramatically increasing heat generation and potentially destroying the entire battery in a matter of minutes. Therefore, battery monitoring systems are used to ensure the functional safety of battery operation and detect critical battery conditions, especially damage, in a timely manner. They initiate countermeasures such as the decoupling of individual cells, emergency cooling, or a driver alarm.

[0006] From DE 102013 218681 A1, a battery monitoring system is known which is designed to monitor the operating state of the battery by evaluating sensor signals from at least two sensors which record different physical measurement variables, whereby pressure sensors, temperature sensors, voltage sensors and current sensors are used here.

[0007] Disclosure of the invention

[0008] The invention relates to a battery monitoring system for monitoring the condition of a battery, in particular a traction battery of a vehicle. The battery monitoring system is designed to monitor the operating condition of the battery by evaluating sensor signals from at least two sensors that detect different physical variables. According to the invention, the battery monitoring system comprises at least the following means:

[0009] - detection means which detect the current operating situation of the battery,

[0010] - allocation means which allocate the sensors to at least two different hierarchy levels, wherein the hierarchy levels are assigned staggered priorities from a highest priority to a lowest priority, wherein the allocation of the sensors to the hierarchy levels is at least dependent on the currently existing operating situation of the battery as recorded by the recording means,

[0011] - Detection means which determine in a first detection step whether the battery is in a critical state from the sensors assigned to a hierarchy level with the highest priority and

[0012] - Execution means which execute a safety measure if the detection means detect that a critical condition of the battery exists.

[0013] Furthermore, the invention relates to a method for monitoring the condition of a battery, in particular a traction battery of a vehicle, wherein the operating condition of the battery is monitored by evaluating sensor signals from at least two sensors that record different physical measurement variables. According to the invention, it is provided that

[0014] - will record the current operating situation of the battery,

[0015] - the sensors are assigned to at least two different hierarchy levels, with the hierarchy levels being assigned staggered priorities from a highest priority to a lowest priority, with the sensors being assigned to the hierarchy levels at least depending on the detected, currently existing operating situation of the battery,

[0016] - in a first detection step, the sensors assigned to a hierarchy level with the highest priority are used to determine whether the battery is in a critical condition,

[0017] - and a safety measure is carried out if it is detected that the battery is in a critical condition.

[0018] Effective battery monitoring is a very important function, especially in electric, battery-powered, or hybrid vehicles, as it can enable timely detection of critical conditions or damage to a vehicle's traction battery. Battery monitoring is also increasingly required by law in many countries.

[0019] The battery monitoring system can, for example, be integrated into a battery management system (BMS) that is used to control the charging and discharging processes of the battery, or it can be designed as a separate system with a power supply and data processing that is independent of the battery management system and which can, for example, also be retrofitted in a vehicle.

[0020] In principle, the battery monitoring system can use sensor data from different sensors, with the sensors being selected in particular from a group of the following sensor types: temperature sensors for determining temperature, sensors for determining electrical parameters of the battery, pressure sensors, gas sensors, and particle sensors. The battery monitoring system can have multiple sensors of each of the aforementioned sensor types. Regardless of this, at least two sensors should record different physical measured variables. A battery monitoring system that has at least three sensors that record different measured variables is particularly preferred.With three sensors, it is advantageous if at least one of the sensors detects an electrical parameter of the battery, another sensor detects the temperature in or on the battery, and a third sensor detects the pressure or a gas component or gas composition in the battery's environment. The sensors can be designed as separate sensors or as sensors that are partially installed together in a sensor module.

[0021] The temperature sensors can, for example, measure a cell temperature of the battery, a temperature of a coolant of the battery or a module temperature of a battery module.

[0022] The sensors for determining the battery's electrical parameters can measure, for example, cell impedance, cell voltage, or the current supplied by the battery. These interdependent electrical parameters can be measured directly at the cell (individual cell voltage, cell impedance), directly at the module (cell-specific charging or discharging current), and at the pack level (load current).

[0023] The pressure sensors can, for example, be installed on the housing wall of a battery cell, on or in a battery module, or at pack level. Pressure waves caused by the opening of safety valves or the explosion of individual cells that propagate through a battery module or the entire battery pack can be very effectively detected using a dynamic low-pressure sensor. If the pressure wave is detected, it is an early indication of an irregular condition of the battery. In sealed modules, however, an opening cell can also lead to a prolonged, gradual pressure increase within a module before a safety valve opens. In this case, a pressure sensor could detect this pressure increase in addition to or alternatively to a propagating pressure wave.This means that both pressure waves and static pressure increases or pressure drops within a sealed battery module or battery pack can be recorded.

[0024] The gas sensors can be designed to detect the concentration of a gas component (e.g., H2, CO, CO2) in a gas, which is caused by electrolyte leakage or by thermal decomposition of the electrolyte material or other cell components, or the changes in the gas composition in a gas. Gas components that enter the ambient air of a battery module or battery pack through evaporation, decomposition, and / or partial oxidation of electrolytes or other battery components from mechanically damaged and / or overheated cells can be detected with a gas sensor. For NMC cells (NMC: nickel-magnesite-cobalt is the cathode material of a typical lithium-ion battery) with standard electrolytes such asDimethyl carbonate (DMC) is suitable for the detection of hydrogen in the environment ("ambient air") of the battery (for example by means of a hydrogen sensor, which can be designed as a threshold sensor with 10 ppm H2 as the trigger threshold), but gas sensors for the detection of other leading components can also be used, such as undecomposed electrolyte, carbon dioxide, and / or carbon monoxide.

[0025] The particle sensors can detect particles in the battery's gas mixture, whereby smoke sensors can preferably be used to detect smoke particles.

[0026] In the context of the present application, a battery status is understood to be a state of the battery, which may include an assessment of the current electrical performance, the battery's function, and / or a forecast of the development of the performance or the future course of the battery's functionality. Battery status detection enables a statement about the expected proper operation of the battery in the current mode, as well as the detection of a critical condition or damage to the battery. Without being limited to this, this may include, in particular, a continuous or periodic assessment of the battery's state of charge (SoC) or state of health (SoH).

[0027] In the context of the present application, a battery operating situation refers to a state, mode, or operating type in which the battery is generally operated, for example, a charge state under load, a state during charging, or a state when an electrical consumer connected to the battery is switched off. In the case of a traction battery of a battery-powered electric vehicle (BEV), the battery operating situations generally depend on the type of use of the vehicle and can initially be roughly divided into: situation with the vehicle moving (D: Drive), situation with the vehicle parked (P: Park) without charging, and situation when the battery is charging (C: Charge). However, further differentiations are of course also possible. For example, a distinction can be made between rapid charging and normal charging when charging.When driving, for example, a distinction can be made between a driving condition under partial load and a driving condition under full load. When parking, for example, a distinction can be made between a situation in which the vehicle's battery management system is running on, and a long-term parking situation. The battery monitoring system can detect the operating situation directly, for example, using data transmitted by an ECU, or corresponding signals from a battery management system.

[0028] A safety measure is defined as a measure initiated by the battery monitoring system when a critical battery condition or a battery failure is detected, in order to prevent an accident, property damage, or harm to vehicle occupants or persons who may be in the vicinity of the battery. The measure can be initiated directly by the battery monitoring system or indirectly by the battery monitoring system initiating the measure via a vehicle control unit. The battery monitoring system can initiate the measure preferably via the battery management system (BMS) or the vehicle control unit (ECU).The measure may, in particular, consist of activating emergency cooling of the battery, reducing the electrical power consumption from the battery, deactivating individual cells of the battery, disconnecting the battery from a charging station, issuing an alarm to a driver, initiating an emergency stop of a vehicle or similar.

[0029] Advantages of the invention

[0030] The battery monitoring system presented here, or rather the method for monitoring the condition of a battery, advantageously enables dynamic prioritization of the sensors used for monitoring, resulting in significant improvements over the known state of the art. The reliability of battery condition monitoring is greatly improved through situation-dependent prioritization of different sensors which record different physical parameters, as well as possible data redundancy. This possible data redundancy can be advantageously used for improved functions for checking the plausibility of the battery condition. The sensors can be installed in or on the battery or in the space surrounding the battery. In particular, it is easier to avoid no reaction at all to a critical battery condition (“no alarm” orThis can lead to a false negative alarm, or a critical condition being incorrectly detected ("false alarm" or false positive alarm). Depending on the battery's operating situation, only a subset of the total number of available sensors can be used in individual cases. For example, low-power measurement principles can be advantageously used to reduce energy consumption in operating situations such as when the vehicle is parked.

[0031] Advantageous embodiments and further developments of the invention are made possible by the features contained in the dependent claims.

[0032] For example, if the detection means detect a critical battery condition in the first detection step, they can evaluate the sensor signals from sensors assigned to a lower priority hierarchy level in a second detection step to quantify the critical battery condition. Quantification refers to recording the individual extent or specific dynamics of a critical condition. This makes it possible, for example, not only to detect a critical battery condition but also to better assess the exact type and extent of the condition in order to adapt the security measure accordingly. This makes it easier to differentiate, for example, between a minor malfunction and a condition that requires immediate action.

[0033] Furthermore, if it cannot be ruled out in the first detection step that the battery is in a critical condition, it is possible to evaluate the sensor signals from sensors assigned to a hierarchy level with a lower priority in a second detection step in order to more easily identify whether the battery is in a critical condition. In this way, false positive and false negative alarms can be better avoided. For example, the sensors assigned to the highest hierarchy level can be used to detect battery conditions where there is a certain suspicion that a critical condition may exist, or where it cannot be ruled out that a critical condition exists or will soon occur. The evaluation of the sensor signals from sensors at a lower hierarchy level, which are only switched on in case of doubt, can provide clarity in this case.

[0034] Particularly advantageous for conserving battery consumption is the ability of the battery monitoring system to continuously activate sensors assigned to a hierarchy level with the highest priority or to activate them regularly at specified time intervals, while only activating sensors assigned to a hierarchy level with a lower priority if the detection means detect in the first detection step that the battery is in a critical condition or if the detection means cannot rule out the existence of a critical condition in the first detection step. In this way, the energy consumption of the battery monitoring system can be optimized. For example, in the "parking" operating situation, the continuous measurement of all cell voltages and temperatures at the module level could be associated with a significant negative energy consumption.Furthermore, these sensors are usually connected via the central control unit of the battery management system, which usually has to actively request the measurements. Therefore, this unit itself would have to be regularly activated from a potential energy-saving mode. In this operating situation, it is therefore advantageous to give higher priority to sensors that, on the one hand, monitor the battery and, on the other hand, are characterized by particularly energy-saving operation. For example, a pressure sensor or gas sensor can be assigned to the hierarchy level with the highest priority, thus detecting a change in the pressure or gas composition in the atmosphere of the battery module or pack when parked. If a critical condition is detected, the electrical and thermal sensors can then be activated as Level 2 sensors to verify the malfunction.

[0035] Advantageously, a predefined assignment of sensors to hierarchy levels can be stored in a memory for different operating situations of the battery. As soon as the detection devices have detected an operating situation, the corresponding assignment of the sensors to the hierarchy levels is read from the memory and implemented accordingly by the assignment devices.

[0036] Advantageously, the sensors can also be assigned to at least two different hierarchy levels depending on a predefined battery type (where the battery type is defined by the cell chemistry and the battery design). Different battery types can result in different processes in the event of a malfunction.

[0037] By taking the battery type into account, monitoring can be optimally adapted to the battery type.

[0038] Short description of the drawings

[0039] Possible embodiments of the invention are explained below with reference to the accompanying figures. The drawings show:

[0040] Figure 1 is a schematic view of an electrically battery-powered vehicle with a battery monitoring system according to the invention,

[0041] Figure 2 shows three different operating situations of the battery of an electric battery-powered vehicle,

[0042] Figure 3 shows an example of the assignment of different sensors in hierarchy levels with three different priority levels,

[0043] Figure 4 is a flowchart of a method according to the invention for monitoring the condition of a battery.

[0044] Embodiments of the invention

[0045] Figure 1 shows a schematic view of an electrically battery-powered vehicle 10 with a battery monitoring system 1 according to the invention. The battery monitoring system can be an integral component of the battery management system, where the sensor evaluation also takes place. The battery monitoring system 1 comprises, for example, an electronic circuit and sensors 3. The vehicle further comprises a battery 2. The battery 2 consists, for example, of a battery pack having numerous cells that can be combined in modules. This battery can be the traction battery or drive battery of the vehicle 10, which supplies the energy required for the vehicle drive. The vehicle 10 can also have a control unit 44, which is required, among other things, for the driving functionality. In addition, the vehicle 10 can have a battery management system (not shown).

[0046] In Figure 1, reference numeral 31 denotes a pressure sensor, which is arranged, for example, on a housing wall of the battery 2. Furthermore, the vehicle 10 has a gas sensor 37, which can detect a concentration of a gas component (e.g., H2, CO, CO2) or changes in the gas composition in one or more battery modules of the battery 2. Furthermore, a further gas sensor 34 can detect the concentration of a gas component in the environment of the battery 2. A temperature sensor 35 can, for example, detect a temperature of the battery module. Another temperature sensor 36 can, for example, detect the coolant temperature of the battery 2. The sensors 32 and 33 detect electrical parameters of the battery 2, such as the cell impedance, the cell voltage, and / or the current of the battery 2. The sensor 38 is designed as a particle sensor. All sensors 3 can be installed in or on the battery 2 or the battery pack.

[0047] As further illustrated in Figure 1, the battery monitoring system 1 comprises detection means 11, which detect a currently existing operating situation of the battery 2, which, in the illustrated embodiment, correlates with the driving situation of the vehicle 10. Figure 2 illustrates three basic operating situations of the vehicle 10.

[0048] Examples of operating situations include: the situation with the vehicle moving (D: Drive), the situation with the vehicle parked (P: Park) without charging, and the situation with the battery charging (C: Charge). In addition, as described above, further differentiations are of course also possible, which are not shown here. The detection means 11 can detect the current operating situation P; C; D automatically by evaluating vehicle data or by receiving corresponding information, for example, from the vehicle control unit 44.

[0049] Furthermore, the battery monitoring system 1 comprises allocation means 12, which assigns all sensors 3 connected to the battery monitoring system 1 to different hierarchy levels. In the exemplary embodiment shown here, for example, there are three hierarchy levels with staggered priorities L1 to L3, where L1 is the highest priority level and L3 is the lowest priority level. Of course, there can also be more than three priority levels or just two. The allocations can be stored, for example, in a retrievable memory 15, which the allocation means 12 can access. One possible allocation is shown for one exemplary embodiment in Figure 3. This allocation can be predetermined depending on the battery type. A different allocation table can be stored for a different battery type.In the example shown, for example, in the operating situation P for parking, the sensor signals of pressure sensor 31 are assigned to a hierarchy level L1 with the highest priority, while the gas sensors and the particle sensor are assigned to a medium priority L2, and the remaining sensors 32, 33 and 35, 36 are assigned to a lower hierarchy level L3. In the operating situation D for driving, however, the sensors 32, 33 for detecting the electrical parameters are assigned to the highest hierarchy level L1, while the pressure sensor 31 and the gas sensors are assigned to a hierarchy level L2 with a lower priority.

[0050] The battery monitoring system 1 further comprises detection means 13, which determine from the sensors 3, each assigned to a hierarchy level with the highest priority L1 depending on the operating situation D; C; P, whether a critical condition of the battery 2 exists. If this is the case, execution means 14 initiate a safety measure 105.

[0051] The method performed by the battery monitoring system 1 for monitoring the condition of the battery is examined in more detail with reference to Figure 4. In block 101, the current operating situation P, C or D is recorded and transmitted to block 102. In block 102, the assignment table corresponding to the battery type T is loaded and, in a further method step, the sensors 3 are assigned to the corresponding different hierarchy levels depending on the recorded, currently existing operating situation P, C or D, whereby only two are shown here for the sake of simplicity. For example, the assignment for operating situation D is such that sensors 32, 33 and 35, 36 are assigned to the hierarchy level with the highest priority L1 and sensors 31 and 34, 37, 38 are assigned to a hierarchy level with a lower priority L2.

[0052] In block 103 in Figure 4, a first detection step 103a is performed, in which it is determined from the sensors assigned to the hierarchy level with the highest priority L1 whether a critical condition of battery 2 exists. If this is not the case, detection step 103a can be repeated. If a critical condition is detected in the first detection step 103a, the sensor signals from sensors 3 assigned to a hierarchy level with the lower priority L2 (in the example, the pressure sensor 31 and the gas sensors 34, 37) are used in a second detection step 103b to quantify the critical condition of battery 2 in a second detection step 103b.

[0053] Then, in the final block 104, one or more safety measures 105 are executed. Depending on the signal from block 103b, a safety measure may, in particular, consist of activating emergency cooling of the battery, reducing the electrical power consumption from the battery, bridging and / or decoupling individual cells or modules of the battery, disconnecting the battery from a charging station, issuing an alarm to a vehicle driver, initiating an emergency stop of a vehicle, or similar.

[0054] The above illustrations show that there are a multitude of different design options.

[0055] In the above exemplary embodiment, for example, if the operating situation "Driving" is present, the electrical parameters of the battery system (e.g., measured cell-individual voltages and impedances as well as the module current) are assigned, together with the sensor signals from the temperature sensors 35; 36, to a hierarchy level with the highest priority L1 and processed as Level 1 sensor data or as primary sensors. Therefore, the continuous battery condition assessment while the vehicle is driving, in particular the continuous determination of SoC and SoH, is carried out on the basis of this Level 1 sensor data. Critical temperature, current, and / or cell voltage data provide indications of an impending or already occurring overheating condition in a battery partition.In the Driving D operating situation, the primary task of the battery monitoring system can be to warn the vehicle occupants in the event of thermal runaway of one or more cells within the battery pack. To avoid false-positive detection, several sensor signals are integrated in hierarchical priority into the evaluation of a thermal event. In the Driving D operating situation, the sensors 32; 33 for recording the electrical data, e.g. load current and cell voltages, as well as the temperature sensors 35, 36 for monitoring coolant and module temperatures can therefore be permanently active in order to determine the charge and health status of the battery or battery pack while driving. These are therefore ideally also used to detect thermal runaway within battery 2.

[0056] The pressure sensor 31 and the gas sensors 34, 37 and the particle sensor 38, which register, for example, dynamic pressure changes on a battery module and changes in the gas composition in the air surrounding the battery or smoke particles, can be assigned to a hierarchy level with a lower priority L2 in the driving D operating situation and are therefore processed as level 2 sensor data. The pressure sensor 31 and / or gas sensors 34; 37 are therefore used with a lower evaluation priority than the level 1 sensors. In order to detect a pressure threshold that arises when a cell is opened due to the internal overpressure during a thermal runaway of the battery, it is recommended to also operate the pressure sensor permanently in this operating mode. Sampling rates of 10 to 100 Hz, for example, are conceivable in order to detect the characteristic pressure increase.A gas sensor, on the other hand, could, for example, only be activated as a Level 2 sensor after the Level 1 sensors (electrical sensors, temperature) have been triggered, or as a Level 3 sensor with priority L3 after the pressure sensor has detected an increase in pressure. Therefore, in a slightly modified embodiment, the gas sensors 34; 37 could also be assigned to the hierarchy level with priority L3, unlike what is shown in Figure 3. In an embodiment not shown in the figures, however, it is also conceivable to evaluate the pressure sensor 31 and / or the gas sensors 34, 37 at the hierarchy level with the highest priority L1 and, for example, to use the electrical data of the sensors 32, 33 only for confirmation. This is particularly advantageous for cell types in which a pressure-induced cell membrane or cell valve opening occurs before the thermal runaway can be detected in the electrical data.As described above, the sensors can be assigned to the different hierarchy levels depending on a predefined battery type T. For example, gas sensors can be prioritized for pouch cells, since trace gases such as hydrogen diffuse through the cell housing at the onset of a thermal runaway before pressure-related destruction of the cell housing and can be detected in the battery 2 using a sensitive gas sensor 34; 37. The vehicle can then be put into emergency mode, which allows the driver to park the vehicle safely. By prioritizing pressure sensors and / or gas sensors, a time advantage can be achieved for this battery type compared to the embodiment described above with primary monitoring using electrical sensors.

[0057] In the first exemplary embodiment, in the charging C operating situation, both the electrical sensors 32; 33 and the temperature sensors 35; 36 can be actively used to detect the charging progress and the operating temperature of the battery pack. In contrast to the driving mode, for example, in the charging C operating situation, the pressure sensor 31 and the gas sensors 34; 37 can also be evaluated at the hierarchy level with the highest priority L1, since critical conditions often occur during charging for many battery types. If a critical condition is detected, in addition to a warning message, an interruption of the charging process can be initiated as a safety measure in order to reduce the additional risk posed by the energy introduced if an (impending) thermal runaway is detected.

[0058] As already explained above, in the Parking P operating situation, it must be noted that the continuous measurement of all cell voltages and temperatures at the module level can be associated with significant energy consumption. Furthermore, in practice, such sensors are often connected via the central control unit of the battery management system, which must actively request the measurements. Thus, the central control unit of the battery management system would also have to regularly wake up from a potential "low power" mode. In the Parking P operating situation, however, it is necessary to achieve the lowest possible energy consumption in order to enable a long operating time with the supply battery. In this case, it is therefore advisable to give higher priority to additional sensors that autonomously monitor the battery and / or are characterized by particularly energy-efficient operation.For example, in the embodiment of Figure 3, pressure sensor 31 is used with the highest priority L1 to detect the opening of a cell as a result of thermal runaway. The sampling rate of pressure sensor 31 could, for example, be in the range of 1 to 20 Hz. Gas sensors 34; 37 and particle sensor 38 can be used with a lower priority L2 if the pressure sensor detects a critical condition. If a characteristic pressure change is detected and subsequently a change in the gas composition is detected by the gas sensors, the battery monitoring system can, for example, use a "wake-up" signal to wake up the battery management system in sleep mode, so that the sensor data from electrical sensors 32, 33 and temperature sensors 35, 36 become available and can be used as Level 3 sensor data.

[0059] In a further embodiment, not shown in Figure 3, a gas sensor can be used instead of the pressure sensor or in addition to the pressure sensor. This gas sensor, as a Level 1 sensor, can detect a change in the gas composition in the atmosphere of the battery module or pack. Upon detection of such a condition, the electrical and thermal sensors can then be activated as Level 2 sensors for verification after the battery management system has been alerted.

Claims

Claims 1 . Battery monitoring system (1) for monitoring the state of a battery (2), in particular a traction battery of a vehicle (10), wherein the battery monitoring system (1) is designed to monitor the operating state of the battery (2) by evaluating sensor signals from at least two sensors (3) detecting different physical measurement variables, characterized in that the battery monitoring system (1) comprises at least the following means: Detection means (11) which detect a currently existing operating situation (P; C; D) of the battery (2), allocation means (12) which assign the sensors (3) to at least two different hierarchy levels, wherein staggered priorities (L1; L2; L3) from a highest priority (L1) to a lowest priority (L3) are assigned to the hierarchy levels, wherein the assignment of the sensors (3) to the hierarchy levels takes place at least depending on the currently existing operating situation (P; C; D) of the battery (2) detected by the detection means (11), detection means (13) which, in a first detection step (103a), determine from the sensors (3) assigned to a hierarchy level with the highest priority (L1) whether a critical state of the battery (2) exists and - Execution means (14) which execute a safety measure (105) if the detection means (13) detect that a critical state of the battery (2) exists.

2. Battery monitoring system according to claim 1, characterized in that the detection means (13), if it is detected in the first detection step (103a) that a critical state of the battery (2) exists, in a second detection step (103b) evaluate the sensor signals from sensors (3) assigned to a hierarchy level with a lower priority (L2; L3) in order to quantify the critical state of the battery (2), or if it cannot be ruled out in the first detection step (103a) that a critical condition of the battery exists, in a second detection step (103b) the sensor signals from sensors assigned to a hierarchy level with a lower priority (L2; L3) are evaluated in order to detect whether a critical condition of the battery (2) exists.Battery monitoring system according to one of claims 1 or 2, characterized in that the battery monitoring system (1) continuously activates the sensors (3) assigned to a hierarchy level with the highest priority (L1) or regularly activates them at predetermined time intervals, and only activates sensors (3) assigned to a hierarchy level with a lower priority (L2; L3) if the detection means detect in the first detection step (103a) that a critical condition of the battery (2) exists, or if the detection means cannot rule out in the first detection step (103a) that a critical condition of the battery (2) exists. Battery monitoring system according to one of the preceding claims, characterized in that for different operating situations (P; C; D) of the battery (2), a predetermined assignment of the sensors (3) to the hierarchy levels is stored in a memory (15).Battery monitoring system according to one of the preceding claims, characterized in that the allocation means (12) allocate the sensors (3) to the at least two different hierarchy levels depending on a predeterminable battery type (T). Battery monitoring system according to one of the preceding claims, characterized in that the battery (2) is a traction battery of an electric, battery-operated vehicle (10), and in that the detection means (11) detect at least three different operating situations (P; C; D) of the battery when the vehicle is moving (D), the vehicle is parked (P), and the vehicle is charging (C) the battery (2). Battery monitoring system according to one of the preceding claims, characterized in that the sensors (3) are selected from a group of the following sensor types: Temperature sensors (35; 36) for determining a temperature, in particular a cell temperature of the battery, a coolant temperature of the battery or a module temperature of the battery (2), Sensors (32; 33) for determining electrical parameters of the battery, in particular the cell impedance, the cell voltage, or a current intensity, pressure sensors (31), in particular pressure sensors, which are installed on a housing wall of a cell of the battery (2) or on or in a module of the battery, Gas sensors (34; 37) which are designed to detect the concentration of a gas component in a gas or the changes in the gas composition in a gas, Particle sensors (38), in particular smoke sensors, which detect particles in the gas mixture of the battery. Battery monitoring system according to claim 7, characterized in that the battery monitoring system (1) has at least one sensor (32; 33) for determining electrical parameters of the battery (2), at least one temperature sensor (35; 36), and at least one further sensor designed as a pressure sensor (31) and / or gas sensor (34; 37). Method for monitoring the condition of a battery (2), in particular a traction battery of a vehicle (10), wherein the operating condition of the battery is monitored by evaluating sensor signals from at least two sensors (3) detecting different physical measurement variables, characterized in that a currently existing operating situation (P; C;D) of the battery (2), the sensors (3) are assigned to at least two different hierarchy levels, wherein the hierarchy levels are assigned staggered priorities (L1; L2; L3) from a highest priority (L1) to a lowest priority (L3), wherein the assignment of the sensors (3) to the hierarchy levels takes place at least as a function of the detected, currently existing operating situation (P; C; D) of the battery (2), from the sensors assigned to a hierarchy level with the highest priority (L1) it is determined in a first detection step (103a) whether a critical state of the battery (2) exists; a safety measure (105) is carried out if it is detected that a critical condition of the battery (2) exists. Method according to claim 9, characterized in that the sensors (3) assigned to a hierarchy level with the highest priority (L1) are constantly activated or regularly activated at predetermined time intervals, and sensors (3) assigned to a hierarchy level with a lower priority (L2; L3) are only activated if it is detected in the first detection step (103a) that a critical condition of the battery exists, or if it cannot be ruled out in the first detection step (103a) that a critical condition of the battery (2) exists. Method according to one of claims 9 or 10, characterized in that for different operating situations (P; C; D) of the battery (2), a predetermined assignment of the sensors (3) to the hierarchy levels is used in each case.Method according to one of claims 9 to 11, characterized in that the sensors (2) are assigned to the at least two different hierarchy levels depending on a predeterminable battery type (T). Method according to one of claims 9 to 12, characterized in that the battery (2) is a traction battery of an electric, battery-operated vehicle (10), and in that at least three different operating situations (P; C; D) of the battery (2) are detected: when the vehicle is moving (D), when the vehicle is parked (P), and when the vehicle is charging the battery (C).

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