DE102022213760B3 - Method for detecting foreign bodies in a battery for a motor vehicle, measuring device and a motor vehicle - Google Patents

Abstract

A method for detecting foreign bodies in a battery (10) for a motor vehicle (20) is proposed, wherein the vehicle has a measuring device (100), a measuring circuit (11) and a high-voltage system (HV system) (13) and that HV system (13) has a first y-capacity (C1) and a second y-capacity (C2). The method has the following steps:a) actuating the measuring circuit (11) to alternately reload the first y-capacitance (C1) and the second y-capacitance (C2) of the HV system (13);b) determining a y-capacity Total capacity from recharging the first y-capacity (C1) and the second y-capacity (C2);c) comparing the y-total capacity with a y-capacity reference value;d) detecting a foreign body in the battery (10) by detecting a deviation when comparing the total y-capacity from reloading the first y-capacity (C1) and the second y-capacity (C2) with the y-capacity reference value; ande) based on the detection of a foreign body, initiate a protective measure.

Description

The invention generally relates to the field of monitoring operating states of batteries, in particular high-voltage batteries. In particular, the invention relates to a method for detecting foreign bodies in a battery for a motor vehicle, a measuring device and a motor vehicle.

For safe operation of a battery, such as a traction battery of a motor vehicle, and/or a high-voltage battery, monitoring of its condition is necessary. It should always be avoided that foreign bodies, such as liquid, enter the battery or the battery system. Because if this happens, it can lead to an undesirable condition, such as a thermal reaction, such as corrosion in the battery. Monitoring the condition of the battery can therefore include, among other things, the detection of foreign bodies inside the battery system. This can be carried out, for example, using moisture sensors or comparable sensors. However, installing sensors in battery systems can require space and require regular repairs. The use of special sensors to detect foreign bodies in battery systems generally requires the use of an additional component. This entails both costs and new potential vulnerabilities for leaks.

Batteries are used, for example, in motor vehicles. In particular, high-voltage batteries for electric vehicles, i.e. H. Motor vehicles that are at least partially powered by electrical energy are used. In the latter example, as well as in other exemplary uses of batteries and high-voltage batteries, it must be possible to ensure that in no case, i.e. H. not even if an error occurs that endangers the user. Against such a safety background, in addition to monitoring the battery condition, it may be necessary to monitor the insulation resistance and the y-capacity of the battery system.

From the DE 10 2013 216 972 A1 A method for determining a foreign body in a battery is disclosed, wherein a change in an electrical quantity is measured using an equivalent circuit made up of capacitances and ohmic resistances and based on the change a foreign body can be recognized.

From the DE 10 2011 116 968 A1 a method for detecting a loss of coolant in a battery system is known, wherein a first and a second capacity of a discharge current are measured and a loss of coolant can be detected by comparing the first and the second capacity.

It is the object of the present invention to at least partially eliminate the disadvantages described above. In particular, it is the object of the present invention to enable the detection of foreign bodies in a battery for a motor vehicle without special sensors. At the same time, it is the object of the present invention to utilize an existing insulation resistance monitoring for monitoring the y-capacitance in order to enable foreign body detection from the monitoring of the y-capacitance. In particular, it is the object of the present invention to increase the safety of the operation of a battery for a motor vehicle, in particular a high-voltage battery for a motor vehicle.

The above object is achieved by a method with the features of claim 1, by a measuring device with the features of claim 9, by a vehicle with the features of claim 10, by a computer program product with the features of claim 11 and by a computer-readable medium the features of claim 12. Further features and details of the invention result from the subclaims, the description and the drawings. Features and details that are described in connection with the method according to the invention naturally also apply in connection with the vehicle according to the invention, the computer program product and/or the computer-readable medium and vice versa, so that reference is always made to each other with regard to the disclosure of the individual aspects of the invention or can be.

Embodiments of the invention can advantageously provide an improved method for detecting foreign bodies in a battery for a motor vehicle. With such a method, the safety of the operation of a battery for a motor vehicle, in particular a high-voltage battery for a motor vehicle, can be increased.

1. a) Betätigen der Messschaltung, um wechselweise die erste y-Kapazität und die zweite y-Kapazität des HV-Systems umzuladen;
2. b) Bestimmen einer y-Gesamtkapazität aus dem Umladen der ersten y-Kapazität und der zweiten y-Kapazität;
3. c) Vergleichen der y-Gesamtkapazität mit einem y-Kapazitätsreferenzwert;
4. d) Erkennen eines Fremdkörpers in der Batterie durch Feststellen einer Abweichung beim Vergleich der y-Gesamtkapazität aus dem Umladen der ersten y-Kapazität und der zweiten y-Kapazität mit dem y-Kapazitätsreferenzwert; und
5. e) basierend auf dem Erkennen eines Fremdkörpers, Einleiten einer Schutzmaßnahme.

One aspect of the present invention relates to a method for detecting foreign bodies in a battery for a motor vehicle, wherein a measuring device has a measuring circuit and a high-voltage system (HV system), and the HV system has a first y-capacity and a second y-capacity. The procedure has the following steps:

1. a) actuating the measuring circuit to alternately charge the first y-capacitance and the second y-capacitance of the HV system;
2. b) determining a total y capacity from reloading the first y capacity and the second y capacity;
3. c) comparing the y-total capacity with a y-capacity reference value;
4. d) detecting a foreign body in the battery by detecting a deviation when comparing the total y capacity from recharging the first y capacity and the second y capacity with the y capacity reference value; and
5. e) based on the detection of a foreign body, initiate a protective measure.

In other words, the method can provide for the use of monitoring of the y-capacity to detect foreign bodies, in particular liquids, in the battery by changing the overall y-capacity. Because the y-capacity and thus the y-total capacity depend on the electrical permittivity. A change in the electrical permittivity can affect the value of the y-total capacitance. A change in the y-total capacity can be determined by comparing the y-total capacity with a y-capacity reference value.

It should be noted that the term foreign body detection in the battery is to be understood broadly in the context of the present disclosure. This can mean foreign body detection in a battery system. In principle, this can involve the detection of disruptive foreign bodies in the battery. The term battery is to be understood just as broadly in this case. This can be a high-voltage battery, a battery module, a battery system or the like. In particular, the battery can have several cells and a battery housing.

The measuring device can have a first high-voltage potential, a second high-voltage potential and a vehicle ground, which are electrically connected to both the measuring circuit and the HV system. The first high-voltage potential can be a positive pole, e.g. B. be electrically connected to an anode of the battery. The second high-voltage potential can be a negative pole, e.g. B. be electrically connected to a cathode of the battery. It should be noted that the measuring device may include the battery. Alternatively, the measuring device can be electrically connected to the battery and not include the battery.

The measuring circuit can have two switches. A first switch can be arranged between the first high-voltage potential and the vehicle ground. A second switch can be arranged between the second high-voltage potential and the vehicle ground. The measuring circuit can also have a defined resistance.

The HV system can have two y-capacitances and two insulation resistances. The first y-capacitance and a first insulation resistance in the HV system can be arranged between the first high-voltage potential and the vehicle mass. The second y-capacitance and the second insulation resistance can be arranged between the second high-voltage potential and the vehicle mass.

In a first method step, the measuring circuit can be actuated in such a way that the first y-capacitance and the second y-capacity of the HV system are reloaded. In other words, the first and second y-capacitances can be periodically charged and discharged again. This can be achieved by actuating the measuring circuit between a first state and a second state.

It should be noted that the first y-capacity and the second y-capacity can each denote the total y-capacity of the system, but in each case the y-capacity, which can be measured by a first and correspondingly a second measurement. The y-capacities mentioned refer in particular to the total y-capacities in the corresponding part of the electrical system. The separate designation of the first y-capacity and the second y-capacity may have computational reasons. The terms “first” and “second” should not be understood to mean two different physical capacities.

In the first state, the second switch can be opened and the first switch can be actuated. In a second state, the first switch can be opened and the second switch can be actuated. By reloading the two y-capacities alternately, the total y-capacity can be determined. The total y capacity includes the first y capacity and the second y capacity.

It should be noted that to determine the total y-capacity from the reloading of the two y-capacities, a mathematical optimization method such as curve fitting, approximation method, parameter estimation and/or adjustment calculation can be used.

After the total y capacity has been determined, it can be compared to a y capacity reference value. When comparing the y-total capacity with the y-capacity reference value, a deviation from the y-capacity reference value can in particular be determined. The y-capacity reference value can correspond to the y-total capacity in the event of a negative foreign body detection. In other words, the y-capacity reference value can correspond to the y-total capacity without foreign bodies, that is, correspond to a safe operating state of the battery.

It may turn out to be necessary that the dependence of the parasitic y-capacitance, i.e. H. the y-total capacity must be filtered out from the other dependencies, such as the battery charge level and/or temperature. The penetration of a foreign body can also have an influence on the insulation resistance, which can be determined in the same measurement and can be used as an additional parameter.

If a deviation is found in the comparison explained above and below, the presence of a foreign body in the battery can be determined. The deviation can in particular correspond to an increase.

It should be noted that a y-capacitance usually denotes the capacity of a y-capacitor. A large area with separate potentials can arise between the cells and the battery housing of the battery. This can be particularly the case with high-voltage batteries. These can be simplified as a large plate capacitor, which contains a dielectric in its gap.

wobei A die Fläche der Platten ist, d der Abstand zwischen zwei Flächen des Kondensatoren und ε₀ die elektrische Feldkonstante (Permittivität des Vakuums). In einem sicheren Betriebszustand der Batterie soll in der Regel die elektrische Permittivität ε_r des Dielektrikums jener der Luft entsprechen. Eine Erhöhung der y-Kapazität kann somit auf eine Erhöhung der Permittivität des Dielektrikums hindeuten. Eine Erhöhung der Permittivität des Dielektrikums kann wiederrum auf die Anwesenheit eines Fremdkörpers hindeuten, denn nur die Permittivität des Vakuums kann bei gleicher Temperatur niedriger als die der Luft sein. Die Permittivität ε_r beträgt für eine Temperatur von ca. 18°C z. B. für Wasser ε_r ≈ 80,1, für Glas ε_r ≈ 6, und für Methanol ε_r ≈ 32. Es sei bemerkt, dass die Primitivität von zahlreichen Faktoren, wie z.B. Temperatur und Messfrequenz, abhängen kann, sodass die voranstehend genannten Werte je nach Messung, bzw. Messprozedere und/oder Messkonditionen, leicht variieren können.The y-capacitance C depends on the relative electrical permittivity ε _r of the dielectric (hereinafter referred to as electrical permittivity) between two plates of a plate capacitor as follows $$C={\epsilon }_0{\epsilon }_r\frac{A}{d},$$

where A is the area of the plates, d is the distance between two surfaces of the capacitor and ε ₀ is the electric field constant (permittivity of the vacuum). In a safe operating state of the battery, the electrical permittivity ε _r of the dielectric should generally correspond to that of the air. An increase in the y-capacitance can therefore indicate an increase in the permittivity of the dielectric. An increase in the permittivity of the dielectric can in turn indicate the presence of a foreign body, because only the permittivity of the vacuum can be lower than that of air at the same temperature. The permittivity ε _r is z. for a temperature of approx. 18°C. E.g. for water ε _r ≈ 80.1, for glass ε _r ≈ 6, and for methanol ε _r ≈ 32. It should be noted that the primitiveness can depend on numerous factors, such as temperature and measurement frequency, so that the above mentioned Values may vary slightly depending on the measurement, or measurement procedure and/or measurement conditions.

If the determined y-total capacity is greater than the y-capacity reference value, it can be determined that the battery not only contains air, but also an undesirable foreign body.

It should be noted that not every deviation when comparing the y-total capacity with the y-capacity reference value can confirm the detection of a foreign body in the battery. Rather, in the context of the present disclosure, the term deviation is to be understood broadly, or in its technical sense. When defining the deviation, an error tolerance or an error margin should generally be taken into account. When defining the deviation, a permissible error range should be taken into account. Such an error range can, for example, be stored in the measuring device or can also be determined statistically when evaluating the measurement(s) or the determination(s) of the y (total) capacity.

In a final step of the process, one or more protective measures can be initiated if a foreign body has been detected in the battery. The term protective measure is to be understood broadly in the context of the present disclosure. A protective measure can in particular include aborting a charging process for the battery or switching off the battery using a charging device. A protective measure can alternatively or additionally include sending a signal, such as a warning signal.

The method described above and below can therefore provide safe operation of a battery for a motor vehicle. The method can provide reliable foreign body detection in a battery for a motor vehicle. The process can also offer great potential for savings compared to using special sensors. Necessary additional resources can be saved because existing measurements or procedures, e.g. B. Methods for monitoring the y-capacity can be exploited. The process described above and below means that no further constructive measures on the battery are necessary, so that the emergence of new weak points can be reduced or even eliminated.

The method described above and below can enable early detection of liquids in a high-voltage battery and thus prevent events, corrosion and unwanted conditions.

According to one embodiment of the method, the y-capacity reference value is determined by calibrating the HV system. Alternatively or additionally, it is stored in a storage medium of the motor vehicle.

The y-capacitance reference value can be determined using a calibration process. A calibration process can basically have the process steps a) and b). Alternatively or additionally, a calibration process or calibration can consist of calculating or estimating the y-capacity reference value. The y-capacity reference value can correspond to the y-total capacity of the measuring device in an operating state in which no foreign body is present. In other words, the y-capacity reference value may correspond to a target value. In other words, the y-capacity reference value can correspond to a y-total capacity that can be measured or calculated when the battery is in a safe operating state.

The calibration of the HV system can correspond to a calibration of the measuring device. The calibration of the HV system can be carried out by the manufacturer. By calibrating the HV system, the reliability of foreign body detection in a battery can be further increased.

The y-capacity reference value can also be stored in a storage medium of the motor vehicle. The measuring device can thus, for example, retrieve the y-capacity reference value during the comparison process step. In principle, it is conceivable that the y-capacity reference value can be called up by the measuring device at any time. This can further increase the reliability of foreign body detection in a battery.

• f) Speichern in einem Speichermedium des Kraftfahrzeugs von der bestimmten y-Gesamtkapazität als y-Kapazitätsreferenzwert; und
• g) iteratives Wiederholen der Schritte a) - e)

According to one embodiment of the method, the method further comprises one of the following steps:

• f) storing the determined y-total capacity in a storage medium of the motor vehicle as a y-capacity reference value; and
• g) iterative repetition of steps a) - e)

In other words, it is conceivable that the y-capacity reference value corresponds to the y-total capacity of a previous measurement, provided that no foreign body or deviation has been detected up to that point. In other words, storing the determined y-total capacity as a y-capacity reference value can be understood to mean that a time course of the y-capacity reference value can be saved. It is therefore conceivable that in the comparison process step, i.e. H. c) the determined total y-capacity is compared with y-capacity reference values, such as the two, three or four last stored y-capacity reference values. In method step c), the y-total capacity can be compared with a time course of the y-capacity reference value.

The y-total capacity determined in method step b) can be stored as a y-capacity reference value as long as the fluctuations in the determined y-total capacity do not exceed a certain error margin or a certain permitted deviation from one or more previous measurements of the y-total capacity do not exceed.

This can prove to be advantageous because a time course of the determined y-total capacity can be saved and the reliability of foreign body detection in a battery can be increased. This allows, for example, systematic errors or random errors when measuring the y-total capacity to be determined and, if necessary, taken into account. The accuracy of the foreign body detection and thus the safety of operating the battery for a motor vehicle can be increased.

Process steps a) to e) can be repeated iteratively. In particular, the process steps can be carried out continuously or periodically, i.e. at certain time intervals.

• h) Vergleichen der y-Gesamtkapazität mit einem Grenzwert für die y-Gesamtkapazität;
• i) basierend auf dem Vergleich der y-Gesamtkapazität mit dem Grenzwert, Einleiten einer Schutzmaßnahme.

According to one embodiment of the method, the method further comprises one of the following steps:

• h) comparing the y-total capacity with a limit for the y-total capacity;
• i) based on the comparison of the y-total capacity with the limit value, initiate a protective measure.

The insulation resistance usually needs to be monitored. However, it may prove advantageous to monitor the total y capacitance in addition to the insulation resistance of the measuring device.

It should be noted that the higher the voltage of the system, the stricter the requirement for the maximum capacity that can be achieved be system. In other words, at higher voltage levels, the overall budget of the y-capacities of a vehicle can become smaller.

In addition to the capacitors with a defined capacity provided in the motor vehicle, the effective y-capacitances can also include parasitic components, e.g. B. in the HV battery, and y-capacitors in a charging infrastructure for DC charging, e.g. B. in charging stations external to the vehicle. The currently effective y-capacity depends, for example, on environmental influences, on an operating state (in particular due to the influence of a charging infrastructure) or on aging. This means that safety reserves must be maintained when designing the capacitors for radio interference suppression in motor vehicles and the influence of parasitic effects must be taken into account, so that under no circumstances can energies that are dangerous to people be released from y-capacitors in the first case of a fault ( DE 102020102658 A1 ).

For example, the total y capacity must not exceed a prescribed limit, i.e. H. a total energy content of z. B. cannot reach 0.2 joules. The limit value for the y total capacity can therefore be stored in a storage medium of the motor vehicle. The limit value for the y-total capacity can be regulated or standardized.

Protective measures can be initiated as soon as the limit for the y-total capacity is reached. The protective measures may be similar or the same as the protective measures that can be taken when a foreign object is detected in the battery. Alternatively, the protective measures that are initiated when the limit value for the y-total capacity is reached may differ from the protective measure(s) of method step e). The protective measure can, for example, include an electrical discharge of at least part of the y-capacitances. This means that the limit value for the y-total capacity can be fallen below as quickly as possible.

Method steps h) and i) can have the advantage that the y-capacity or the y-total capacity of the battery and/or the measuring device can also be monitored at the same time as the foreign body detection. This further increases the safety of the battery's operation.

According to one embodiment of the method, an electrical permittivity in the battery is further estimated in step b).

wobei die Parameter τ, K und U₀ mittels Kurvenanpassung ermittelt werden können. Beim Ermitteln der Parameter, insbesondere des Parameters τ können die Isolationswiderstände verwendet werden. Der Parameter τ setzt sich wie folgt zusammen $$\tau =C_y\cdot R_T,$$

wobei C_y die y-Gesamtkapazität und R_T der Gesamtisolationswiderstand ist. Vorausgesetzt die Geometrie der Batterie bzw. des Batteriesystems ist bekannt, kann aus $$C_y={\epsilon }_0{\epsilon }_r\frac{A}{d},$$

die elektrische Permittivität ε_r zumindest abgeschätzt werden, da R_T aus dem ersten und dem zweiten Isolationswiderstand und dem definierten Widerstand bestimmt werden kann. Dies kann in vorteilhafter Weise die Zuverlässigkeit der Fremdkörpererkennung weiter erhöhen.From the reloading of the first y-capacitance and the second y-capacitance, parameters from the course of the corresponding voltages can be determined using curve fitting. The following function can be used as a curve fitting function $$U\left(t\right)=K\left(1-e^{\frac{-t}{\tau }}\right)+U_0,$$

where the parameters τ, K and U ₀ can be determined by curve fitting. When determining the parameters, in particular the parameter τ, the insulation resistances can be used. The parameter τ is composed as follows $$\tau =C_y\cdot R_T,$$

where C _y is the y total capacitance and R _T is the total insulation resistance. Provided the geometry of the battery or battery system is known, this can be done $$C_y={\epsilon }_0{\epsilon }_r\frac{A}{d},$$

the electrical permittivity ε _r can at least be estimated, since R _T can be determined from the first and second insulation resistance and the defined resistance. This can advantageously further increase the reliability of foreign body detection.

This can prove to be advantageous in that it can be estimated which foreign body or liquid is present in the battery.

According to one embodiment of the method, the y total capacity is determined continuously.

In the context of the present disclosure, the term continuous is to be understood broadly. Continuous can be understood to mean that the y-total capacity is determined at regular, periodic or irregular time intervals. This means that the safety of the battery's operation can be continuously guaranteed in a reliable manner.

According to one embodiment of the method, in step b), the y total capacity is determined by curve fitting a time profile of a voltage between at least one high-voltage potential and a vehicle mass.

The y-total capacity can be determined quickly and accurately using curve fitting. The measured curves of the voltages when recharging the first y-capacitance and the two th y-capacity are approximated by an equation and function. This allows parameters such as parameters K, U ₀ and τ of the approximation to be determined.

According to an embodiment of the method, initiating a protective measure includes issuing on a user interface.

In other words, the user of a battery and/or a motor vehicle with such a battery can be informed that the battery is not in a safe operating state and/or that a foreign body has been detected in the battery. The user interface can be, for example, a radio interface, a remote device and/or an operating device of the motor vehicle.

The user of the battery and/or the motor vehicle can be informed about what protective measures have been taken. For example, the user of the vehicle can be informed that the charging process of the battery of the motor vehicle has been stopped or stopped. Outputting to a user interface can therefore involve sending a signal e.g. B. via radio to a user device.

This can advantageously further increase the safety of the battery's operation.

A third aspect of the present disclosure relates to a measuring device having a measuring circuit, a battery and a high-voltage system (HV system), wherein the HV system has a first y-capacity and a second y-capacity. The measuring device can be coupled to a control unit, the control unit being set up to control the measuring circuit, to initiate a protective measure and to carry out a method as described above and below.

The control unit can be arranged inside or outside the vehicle. The control unit can control the measuring circuit via wire or alternatively via radio. The control unit can also be set up to order the initiation of a protective measure. The control unit can also transmit via a radio interface the parameters and/or physical variables measured and/or estimated during the method, such as. B. the y-capacity, to an external storage medium, whereby the external storage medium can be a storage medium outside the vehicle, such as an online memory.

With such a measuring device, early detection of liquids in a high-voltage battery can be made possible and events, corrosion and unwanted conditions can thus be prevented.

A fourth aspect of the present disclosure relates to a motor vehicle comprising a battery, a measuring circuit, a high-voltage system (HV system), a drive and a control unit. The HV system is set up to operate the battery and the drive of the motor vehicle. The control unit is set up to control the measuring circuit, to initiate a protective measure and to carry out a method as described above and below.

A fifth aspect of the present disclosure relates to a computer program product comprising instructions which, when executed by a computer unit of the control unit of the motor vehicle, as described above and below, cause the computer unit to execute a method as described above and below.

A final aspect of the present disclosure relates to a computer-readable medium on which the computer program product is stored as described above.

All disclosures described above and below with respect to one aspect of the present disclosure apply equally to all other aspects of the present disclosure.

• 1 eine schematische Darstellung einer Batterie gemäß einem Ausführungsbeispiel,
• 2 eine schematische Darstellung einer Messvorrichtung gemäß einem Ausführungsbeispiel,
• 3 ein Flussdiagram eines Verfahrens gemäß einem Ausführungsbeispiel,
• 4 ein Diagramm mit zwei Spannungsverläufen in einer betriebenen Messvorrichtung,
• 5 eine schematische Darstellung eines Kraftfahrzeugs gemäß einem Ausführungsbeispiel.

Exemplary embodiments of the invention are described below with reference to the figures. Show it:

• 1 a schematic representation of a battery according to an exemplary embodiment,
• 2 a schematic representation of a measuring device according to an exemplary embodiment,
• 3 a flowchart of a method according to an exemplary embodiment,
• 4 a diagram with two voltage curves in an operated measuring device,
• 5 a schematic representation of a motor vehicle according to an exemplary embodiment.

Similar, similar-acting, identical or identically acting elements are provided with the same reference numerals in the figures. The figures are only shown schematically and not to scale.

1 shows a schematic representation of a battery 10 according to an exemplary embodiment. In particular shows 1 a side view of a battery 10. The battery 10 of the 1 represents in particular a battery module and has seven cells. Such a battery module can, for example, be installed in a battery system in many ways. The cells of the battery 10 or the battery module 1 are arranged on a first layer 16. The first layer can in particular be an insulator. For example, a polypropylene film (PP film) can be used as insulators or separating layer. However, such a layer is optional.

Furthermore, the battery 10 or the battery module has the 1 , at each longitudinal end there is a second layer 14, which can be designed, for example, as a spacer. The second layer 14 can be made of PET, for example. The second layer 14 can electrically and thermally insulate the cells of the battery 10. Finally, an aluminum plate 18 can be provided, which forms a measuring area 12 together with the first layer 16 or the second layer 14. The aluminum plate 18 can correspond to the mass of the measuring device 100 (see 2 ). The first layer 16 and the second layer 14 are each optional. However, there should generally be an installation space which forms a measuring area 12 that can accommodate air. The measuring area 12 can generally designate an installation space into which a foreign body may/could possibly be forced. The measuring area 12 is usually filled with air. It should be noted that the measuring range 12 can refer to the entire battery 10, ie to a battery with several battery modules. In 1 only a battery module is shown.

The HV system 13 and the measuring circuit 11 are electrically connected to the cells of the battery 10. In particular, the switches or the measuring circuit 11 can be arranged in the battery system, but not between the cells of the battery.

If the measuring range fills up, for example B. with liquid, the specific y-total capacity will change.

The monitoring of the insulation resistance and/or the y-capacitance can be modified in such a way that liquids, e.g. B. water, in the battery system or in the battery can be detected. Monitoring the y-capacitance can involve monitoring the entire capacity of parasitic effects and installed capacitors throughout the entire connected system. It can therefore be provided that with an open HV switching element (not shown here), which can be arranged between the battery and the HV system, the pure y-capacitance, which is caused by parasitic effects between the surfaces of the housing of the battery 10 and the cells, or between an aluminum plate 18 and the cells, is measured. Due to the dependence of the electrical capacity on the electrical permittivity, it may be possible to detect liquids in the measuring area 12 with otherwise unchanged distances and areas.

2 shows a schematic representation of a measuring device 100 according to an exemplary embodiment. The measuring device 100 the 2 has a battery 10, a measuring circuit 11 and an HV system 13. It should be noted that the measuring device 100 may only have a measuring circuit 11 and an HV system 13 and can be or is connected to a battery 10 in an electrically conductive manner.

The HV system 13 has a first high-voltage potential 15, a second high-voltage potential 17 and a vehicle mass M. The HV system 13 has a first y-capacitance C1 and a first insulation resistance R1 between the first high-voltage potential 15 and the vehicle mass M. The HV system 13 has a second y-capacitance C2 and a second insulation resistance R2 between the second high-voltage potential 17 and the vehicle mass M. The measuring circuit 11, like the HV system 13, has the same high-voltage potentials 15 and 17 and the vehicle ground. The measuring circuit has a first switch S1 between the first high-voltage potential 15 and the vehicle ground and a second switch S2 between the second high-voltage potential 17 and the vehicle ground. The measuring circuit 11 further comprises a defined resistance Rm. The defined resistance Rm usually denotes a resistor with a known resistance value.

The first high-voltage potential 15 is electrically connected to an anode of the battery 10. The vehicle mass M is neutral. The second high-voltage potential 17 is electrically connected to a cathode of the battery 10.

In a first method step a), the measuring circuit 11 is activated (see 3 ). This enables successive operation of the measuring circuit 11 in a first state with an open second switch S2, whereby the second switch S2 is actuated, and in a second state with an opened first switch S1, whereby the second switch S2 is actuated. As a result, the first and second y-capacitances C1, C2 are alternately reloaded.

In the HV system 13 there is a voltage across the y-capacitances C1, C2, the level of which is both from the system voltage U0, also referred to as the voltage of the battery, and the ratio of the insulation resistances R1, R2 of the high-voltage potentials 15, 17. The monitoring of the insulation resistance R1, R2 in motor vehicles can be achieved by arranging the defined resistance Rm between the high-voltage potentials 15, 17 and the vehicle mass M.

3 shows a flowchart of a method according to an exemplary embodiment. In a first method step a), the measuring circuit 11 is actuated to alternately reload the first y-capacitance C1 and the second y-capacity of the HV system 13. Actuating the measuring circuit 11 therefore includes alternately actuating the two switches S1, S2. During step a), a time course of a first voltage U1 between the first high-voltage potential 15 and the vehicle mass M can be measured. The insulation resistances R1, R2 and thus the y-capacitances C1, C2 can be determined from the time profile of the first voltage U1. Preferably, stationary values of the voltage U1, U2 can be used to determine the insulation resistances R1, R2 and thus the y-capacitances C1, C2. If the corresponding voltage curve has reached a stationary state, the time curve of the voltage can become superfluous. For example, it is possible to wait for the respective voltage to reach a stationary state in order to record or retrieve or record the corresponding voltage value.

The time course of the first voltage U1 can be determined in a first state of the measuring circuit 11. Analogously, the second voltage U2 can be determined in a second state of the measuring circuit 11. From the time course of the two voltages U1, U2, parameters can be determined by means of curve fitting that are used to determine the insulation resistances and thus to determine the y-capacitances C1, C2. In a second method step b), the y total capacity is determined. This is done by reloading the y-capacitances C1, C2 using approximation methods.

In a third method step c), the y total capacity is compared with a y capacity reference value. The y-capacity reference value can be stored in a storage medium of the motor vehicle or the measuring device. The y-capacity reference value can be viewed as a setpoint. If a deviation is found when comparing the y-total capacity with the y-capacity reference value, a foreign body is detected in the battery in step d). For example, liquid, such as water, is detected in the battery when the total y capacity is greater than the y capacity reference value. When determining a deviation, fluctuations and a permissible margin of error are taken into account. A deviation or increase of 5% or 10% or 20% or 30% of the total y capacity may indicate the presence of liquid in the battery.

If a foreign body has been detected in the battery, one or more protective measures can be initiated in a further process step e). A protective measure can consist of issuing a warning message or an error message to the user of the motor vehicle, for example via a user interface.

4 shows a diagram with two voltage curves U1, U2 of the two insulation resistances R1, R2 in an operated measuring device. T1 corresponds to the time from which the second state changes to the first state. T2 corresponds to the time from which the measuring circuit 11 is in the first state. Curve fitting can be applied to a specific portion of the voltage timing, such as between T1 and T2. The time period between T1 and T2 can represent a charging curve of the corresponding insulation resistance R1, R2.

können die Parameter K, U₀ und τ bestimmt werden, wobei durch $$\tau =C_y\cdot R_T$$

gegeben ist, durch C_y die y-Kapazität und durch R_T der Gesamtisolationswiderstand. Der Gesamtisolationswiderstand kann dabei unter anderem durch Bestimmen des Parameters K ermittelt werden.. Es sei angemerkt, dass die Zeit t auf die Startzeit zentriert sein kann, d. h. t=t_Messung - t_start.By means of a curve fitting in which the following function is used $$U\left(t\right)=K\left(1-e^{\frac{-t}{\tau }}\right)+U_0,$$

the parameters K, U ₀ and τ can be determined, where by $$\tau =C_y\cdot R_T$$

is given by C _y the y-capacitance and by R _T the total insulation resistance. The total insulation resistance can be determined, among other things, by determining the parameter K. It should be noted that the time t can be centered on the start time, ie t=t _measurement - t _start .

5 shows a schematic representation of a motor vehicle 20 according to an exemplary embodiment. The motor vehicle 20 has a battery 10 and a drive 21 that can be driven at least partially by electrical energy stored in the battery. The battery can be part of a measuring device 100 of the motor vehicle 20. Alternatively, the measuring device 100 can only be connected to the battery of the motor vehicle 20 in an electrically conductive manner. The HV system 13 the measuring device Device 100 can be set up to operate the battery 10 and the drive of the motor vehicle 20. The motor vehicle 20 further comprises a control unit which is set up to control the measuring circuit, to initiate one or more protective measures and to carry out a method as described above and below.

In addition, it should be noted that the terms “comprising” and “having” do not exclude other elements and the indefinite articles “a” or “an” do not exclude a plurality. Furthermore, it should be noted that features and steps described with reference to one of the above embodiments can also be used in combination with other features and steps of other embodiments described above. Reference symbols in the claims are not to be regarded as limitations.

Reference symbol list

100

Measuring device

10

battery

11

Measuring circuit

12

Measuring range

13

HV system

14

second layer

15

first high voltage potential

16

first layer

17

second high voltage potential

18

Aluminum plate

20

motor vehicle

21

Drive of the vehicle

C1

first y-capacity

C2

second y-capacity

Rm

defined resistance

R1

first insulation resistance

R2

second insulation resistance

U1

Voltage at the first high-voltage potential

U2

Voltage at the second high-voltage potential

M

Vehicle mass

U0

System voltage

S1

first switch

S2

second switch

t1

Time after the second state

t2

Time before the first state

t3

point in time during the first state

Claims (12)

Method for detecting foreign bodies in a battery (10) for a motor vehicle, wherein a measuring device (100) has a measuring circuit (11) and a high-voltage system (HV system) and the HV system (13) has a first y-capacity (C1 ) and a second y-capacitance (C2); the procedure has the following steps: a) actuating the measuring circuit (11) to alternately reload the first y-capacitance (C1) and the second y-capacitance (C2) of the HV system (13); b) determining a total y-capacity from the reloading of the first y-capacity (C1) and the second y-capacity (C2); c) comparing the y-total capacity with a y-capacity reference value; d) detecting a foreign body in the battery (10) by detecting a deviation when comparing the y-total capacity from the recharging of the first y-capacity (C1) and the second y-capacity (C2) with the y-capacity reference value; and e) based on the detection of a foreign body, initiate a protective measure. Procedure according to Claim 1 , characterized in that the y-capacity reference value is determined by calibrating the HV system (13) and/or is stored in a storage medium of the motor vehicle. Procedure according to Claim 1 or 2 , characterized in that the method further comprises the following steps: f) storing the determined y-total capacity in a storage medium of the motor vehicle as a y-capacity reference value; and g) iteratively repeating steps a) to e) Method according to one of the preceding Claims 1 until 3 , characterized in that the method further comprises the following steps: h) comparing the y-total capacity with a limit value for the y-total capacity; i) based on the comparison of the y-total capacity with the limit value, initiate a protective measure. Method according to one of the preceding Claims 1 until 4 , characterized in that in step b) an electrical permittivity in the battery is further estimated. Method according to one of the preceding Claims 1 until 5 , characterized , that the y-total capacity is determined continuously. Method according to one of the preceding Claims 1 until 6 , characterized in that in step b) the y-total capacity is determined by curve fitting a time profile of a voltage between at least one high-voltage potential and a vehicle mass (M). Method according to one of the preceding Claims 1 until 7 , characterized in that initiating a protective measure includes issuing on a user interface. Measuring device (100), comprising a battery (10), a measuring circuit (11) and a high-voltage system (HV system), wherein the HV system (13) has a first y-capacity (C1) and a second y-capacity (C2); and wherein the measuring device (100) can be coupled to a control unit, the control unit for controlling the measuring circuit (11), for initiating a protective measure and for carrying out a method according to one of the preceding Claims 1 until 8th is set up. Motor vehicle (20), comprising a battery (10), a measuring circuit (11), a high-voltage system (HV system) (13), a drive (21) and a control unit, the HV system (13) being used for operation the battery (10) and the drive (21) of the motor vehicle (20) are set up; and wherein the control unit is used to control the measuring circuit (11), to initiate a protective measure and to carry out a method according to one of the preceding Claims 1 until 8th is set up. Computer program product, comprising commands that, when executed by a computer unit, follow the control unit of the motor vehicle (20). Claim 10 cause the computer unit to use a method according to one of the Claims 1 until 8th to carry out. Computer-readable medium on which the computer program product is based Claim 11 is stored.

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