Method for determining a load current and battery sensor

Abstract

Method for determining a load current (Iload) which comprises the following steps: - Passing the load current (Iload) through a first branch of a measuring resistor group and simultaneously through a second branch of the measuring resistor group parallel to the first branch, wherein the first branch has a first measuring resistor (R1) and a second measuring resistor (R2) in series with it, and the second branch has a third measuring resistor (R3) and a fourth measuring resistor (R4) in series with it, - simultaneous measurement of a first voltage (Utot) and a second voltage (Uy) across the entire measuring resistor group with only a load current (Iload) flowing through it, and - Calculating a correction value (a) based on the first voltage (Utot) and the second voltage (Uy), - the procedure consists of the following steps exclusively during the respective calibration periods: - Introducing a calibration current (Iref) with a known current strength into the measuring resistor group at a first point (P1) which is located between the first measuring resistor (R1) and the second measuring resistor (R2), and - Measuring a third voltage (Uy) between the first point (P1) and a second point (P2), wherein the second point (P2) is located between the third measuring resistor (R3) and the fourth measuring resistor (R4), while the calibration current (Iref) flows through it, - where the load current (Iload) is calculated based on the first voltage (Utot), the third voltage (Uy), the current of the calibration current (Iref) and the correction value (a).

Description

[0001] The invention relates to a method for determining a load current and an associated battery sensor, which in particular can perform such a method.

[0002] Battery sensors are typically used to monitor the condition of a battery, such as a vehicle battery. This can particularly refer to an accumulator.

[0003] In known designs, a measuring resistor, also known as a shunt resistor, is used, which is typically temperature- and long-term stable. For this purpose, it can be made, for example, of a copper-nickel-manganese alloy, especially manganin.

[0004] The measurement accuracy is essentially based on two factors: firstly, the accuracy with which the electrical resistance of the measuring resistor is known at all times, and secondly, the accuracy with which the voltage caused by the current to be measured across the shunt can be measured.

[0005] From DE 10 2011 078 334 A1, a measuring resistor with two measuring terminals for applying a measuring current is known, which flows through the measuring resistor along a main current direction. The measuring resistor has slotted structures which divide the measuring resistor along the main current direction into two side current sections and one main current section. Furthermore, two calibration terminals are provided, which are connected to the side current sections. A reference current or a reference voltage can be applied to the two calibration terminals via a calibration device, and a calibration voltage can be determined as a function of a voltage drop across the two calibration terminals.Furthermore, a correction circuit is provided which is connected to the calibration device and a detection circuit for detecting a measuring current flowing through the measuring resistor, and which is designed to correct a measurement signal generated by the detection circuit depending on the detected calibration voltage.

[0006] However, a disadvantage of state-of-the-art designs is that the material required for the measuring resistor is expensive and difficult to process.

[0007] It is therefore an object of the invention to provide a method for determining a load current which, compared to known methods, can be implemented alternatively, for example without a measuring resistor made of a correspondingly expensive material. It is further an object of the invention to provide an associated battery sensor.

[0008] This is achieved according to the invention by a method according to claim 1 and a battery sensor according to claim 14. Advantageous embodiments can be found, for example, in the respective dependent claims. The content of the claims is incorporated into the description by express reference.

[0009] The invention relates to a method for determining a load current, which comprises the following steps: - Passing the load current through a first branch of a measuring resistor group and simultaneously through a second branch of the measuring resistor group parallel to the first branch, wherein the first branch has a first measuring resistor and a second measuring resistor connected in series with it, and the second branch has a third measuring resistor and a fourth measuring resistor connected in series with it, - simultaneous measurement of a first voltage and a second voltage across the entire measuring resistor group with only a load current flowing through it, and - Calculating a correction value based on the first voltage and the second voltage, - the procedure consists of the following steps exclusively during the respective calibration periods: - Introducing a calibration current of known current strength into the measuring resistor group at a first point, which is arranged between the first measuring resistor and the second measuring resistor, and - Measuring a third voltage between the first point and a second point, the second point being located between the third and fourth measuring resistors, while the calibration current flows through it, - where the load current is calculated based on the first voltage, the third voltage, the current of the calibration current and the correction value.

[0010] The method according to the invention allows for an advantageous determination of a load current, taking into account the fact that, in the case of a measuring resistor that is not temperature- and / or long-term stable, its resistance value continuously changes, particularly under the conditions found in automobiles, which are characterized by rapidly changing currents and potentially high power losses and thus heating. The method according to the invention makes it particularly advantageous to significantly reduce the overall expected error, which will be discussed in more detail below.

[0011] The load current can be, in particular, a current flowing from a vehicle battery through vehicle consumers and finally through a battery sensor where the process is carried out. It can vary considerably in value; for example, it can be very high when the starter motor is engaged.

[0012] The measuring resistor group can be designed in particular in the form of a Wheatstone bridge, with each branch having two measuring resistors and the third voltage being measured in the middle.

[0013] Ideally, all voltmeters and circuits should have identical readings. Therefore, any deviation between these two readings can provide information about errors. Such errors can be reflected, in particular, in the correction value.

[0014] The connection point between the first measuring resistor and the second measuring resistor can be identical to the first point.

[0015] According to a preferred embodiment, the measuring resistors have identical or at least nearly identical resistance values. This simplifies calculations and evaluations.

[0016] Preferably, both the second and third voltages are measured with a single voltmeter. This single voltmeter can then be calibrated, for example, by comparing the readings of the second and first voltages, and the information obtained can also be used to measure the third voltage.

[0017] It should be noted that "common voltage meter" is simply a chosen term for a specific type of voltage meter. This could also be referred to as a central voltage meter, for example.

[0018] When measuring the first and second voltages, the combined voltmeter can advantageously be decoupled from the first point and also from the second point. This allows for dedicated measurement of the first and second voltages.

[0019] When measuring the third voltage, the common voltmeter can be decoupled from the external terminals of the measuring resistor group and connected to both the first and second points. Decoupling from external terminals prevents interference with the measurement.

[0020] The calibration current can be determined, in particular, by measuring the voltage across a reference resistor, especially one that is temperature- and / or long-term stable. Specifically, this can be done by dividing the voltage drop across the reference resistor by its resistance value. This method has proven effective in practice; however, it should be noted that other approaches are also possible. In particular, a sufficiently stable reference current source can be used, thus eliminating the need to measure the reference current.

[0021] According to one interpretation, outside of the calibration periods, the load current is calculated by dividing the current first voltage by the correction value and by the third voltage measured during the last calibration period, and multiplying by the current of the calibration current of the last calibration period.

[0022] According to one interpretation, during a calibration period the load current is calculated by dividing the current first voltage by the correction value and by the current third voltage, and multiplying by the current strength of the calibration current.

[0023] The two calculation methods just mentioned result in a significantly lower error rate for calculating the load current compared to alternative methods. This will be discussed in more detail below.

[0024] Advantageously, calibration periods begin every 10 ms or at intervals between 8 ms and 12 ms. According to a preferred embodiment, each calibration period lasts at least 100 µs, preferably 200 µs or 300 µs. The duration of the calibration periods can, for example, be 1% of the time between calibration periods. This has proven advantageous in practice.

[0025] The first and / or the second measuring resistor can advantageously each have a value between 50 µΩ and 150 µΩ. In particular, they can each have a value of 100 µΩ. Such values ​​have proven advantageous.

[0026] The third voltage is preferably measured over the entire calibration period. In particular, averaging can be used. Thus, a large number of values ​​can be recorded and averaged to calculate the third voltage. This third voltage is then preferably used in the same way until the next calibration period.

[0027] The third voltage is preferably measured over the entire calibration period and also immediately before and / or immediately after each calibration period. In particular, this can be done for a period of 10 µs, 100 µs, 200 µs, 300 µs or even longer.

[0028] It should be noted that the third voltage is typically not zero even in the absence of the calibration current, but depends on the ratios of the resistances of the first to the second measuring resistor and of the fourth to the third measuring resistor. These resistances are typically not all exactly equal, but only approximately equal. By measuring before and after applying the calibration current, the resulting offset of the third voltage can be obtained, for example, by averaging the third voltage over the period before the calibration current was applied, averaging the third voltage over the period after the calibration current was applied, and then averaging the two averaging values.

[0029] Preferably, the correction value is calculated by dividing the second voltage by the first voltage and / or by linear regression of the second voltage relative to the first voltage. This allows the relationship between the first and second voltages to be captured in the correction value, which in turn allows conclusions to be drawn about the error present in the system.

[0030] The invention further relates to a battery sensor. The battery sensor comprises a measuring resistor group with a first branch and a second branch parallel thereto, wherein the first branch has a first measuring resistor and a second measuring resistor connected in series thereto, and the second branch has a third measuring resistor and a fourth measuring resistor connected in series thereto. The battery sensor includes a total voltage meter configured to measure a first voltage drop across the measuring resistor group.

[0031] The battery resistor further includes a common voltmeter, which is connected via a first switch to a first point between the first measuring resistor and the second measuring resistor, via a second switch to a second point between the third measuring resistor and the fourth measuring resistor, via a third switch to a first external connection point of the measuring resistor group, and via a fourth switch to a second external connection point of the measuring resistor group.

[0032] The battery sensor has a calibration current source which is configured to introduce a calibration current with a switchable current strength into the first point.

[0033] Furthermore, the battery sensor has an electronic control device configured to execute a method according to the invention. All described embodiments and variants can be used for this purpose.

[0034] The battery sensor according to the invention makes it particularly advantageous to carry out the method according to the invention. As mentioned, a suitable measuring resistor group is provided for this purpose. Furthermore, suitable measuring instruments, in particular a total voltage meter and a common voltage meter, as well as a calibration current source and a control device for evaluation, are provided.

[0035] According to a preferred embodiment, the battery sensor further comprises a reference resistor and a reference voltmeter, wherein the reference voltmeter is configured to measure a voltage drop across the reference resistor, and wherein the reference resistor is connected between the calibration current source and the measuring resistor group, such that the calibration current flows through the measuring resistor.

[0036] This advantageously allows for the measurement of the calibration current or its current intensity. However, it should be noted that other measurement methods can also be used for the calibration current, or that the calibration current can also be obtained from a sufficiently accurate calibration current source.

[0037] Further features and advantages will be apparent to those skilled in the art from the exemplary embodiment described below with reference to the accompanying drawing. These show: Fig. 1: a battery sensor, and Fig. 2: a battery sensor according to an embodiment of the invention.

[0038] Before we continue below Fig. 1 and Fig. Before we describe section 2 in more detail, let us first give some general remarks on the background of the invention.

[0039] As mentioned above, it is state of the art to use high-precision measuring resistors or shunt resistors made of special resistance alloys, which are optimized, among other things, for minimal deviations of their resistance from the initial value over temperature and lifetime. To keep the electrical power dissipated in the measuring resistor as low as possible, the resistance is set to very small values, typically 0.1 mΩ, through material selection and geometric dimensions. Accordingly, when measuring currents in the range of 1 mA to 2000 A, voltages across the measuring resistor in the range of approximately 0.1 µV to 200 mV occur. To measure these voltages, the measurement chain usually includes a high-gain amplifier and an analog-to-digital converter.Amplifiers and analog-to-digital converters are usually included in an integrated circuit together with a microcontroller for evaluating the measured signals and other measurement channels, for example for temperature and other battery voltages.

[0040] If one now considers the error of the current measurement of such a measuring chain, one can see that it is composed of the error of the measuring resistor, the error of the amplifier and the error of the analog-to-digital converter.

[0041] For some time now, there have been approaches to replace the precision resistor as a measuring resistor with more cost-effective components, especially in conjunction with a method to recalibrate the measuring resistor repeatedly over the lifetime of the current sensor.

[0042] However, it has been found that it is difficult to perform continuous recalibration even during the simultaneous measurement of the high and highly variable currents occurring in the motor vehicle under the prevailing boundary conditions such as low current consumption of the sensor, since the reference current to be applied for calibration should be chosen to be small and should only be present for a short time.

[0043] It would now be desirable to be able to determine a physical quantity that is proportional to the electrical resistance of the measuring resistor on the one hand, and can be determined independently of the applied load current, i.e., the battery current to be measured.

[0044] Such considerations lead to the execution according to Fig. 1. It should be noted that this embodiment can represent an independent aspect of the invention. It uses a group of four measuring resistors, namely a first measuring resistor R1, a second measuring resistor R2, a third measuring resistor R3, and a fourth measuring resistor R4. As shown, the first measuring resistor R1 and the second measuring resistor R2 are connected in series. Likewise, the third measuring resistor R3 and the fourth measuring resistor R4 are connected in series. The first measuring resistor R1 and the second measuring resistor R2 form a first branch, and the third measuring resistor R3 and the fourth measuring resistor R4 together form a second branch. The two branches are connected in parallel to each other, as shown.

[0045] The in Fig. The battery sensor shown is designed to be connected to a vehicle battery via a load. The connection point to the vehicle battery is designated Vbat. The load is generally referred to as Load, which encompasses various consumers that can be found in a motor vehicle. These can include, for example, vehicle lighting, electronic control units, or a starter motor. A load current Iload flows through this load and is then introduced into the measuring resistor group at a first connection point A1. This first connection point A1 is defined at a location that is directly connected to the respective terminals of the second measuring resistor R2 and the third measuring resistor R3.

[0046] A second, opposite connection point A2 is defined at a location connected to the respective poles of the first measuring resistor R1 and the fourth measuring resistor R4. This connection point is connected to a ground, which is labeled GND.

[0047] A first point P1 is defined between the first measuring resistor R1 and the second measuring resistor R2. Similarly, a second point P2 is defined between the third measuring resistor R3 and the fourth measuring resistor R4. A common voltmeter Uy is connected between these two points P1 and P2. This allows it to measure the voltage occurring centrally within the measuring resistor group. Furthermore, a total voltage meter Utot is connected between the two terminals A1 and A2, which thus measures the total voltage drop across the measuring resistor group.

[0048] Furthermore, means are provided to introduce a calibration current Iref into the measuring resistor group. For this purpose, a series resistor Rlim is first provided, which is connected directly to the vehicle battery. From there, a switch S1 is connected, which in turn is connected to a reference resistor Rref. This reference resistor Rref is then connected to the first point P1, thus introducing a calibration current Iref, which can be switched by means of switch S1, into the measuring resistor group. A voltmeter Uref is connected across the reference resistor Rref to measure the voltage drop across it, which allows conclusions to be drawn about the current of the calibration current Iref.

[0049] Furthermore, there is a difference between the in Fig. A capacitor C is connected to the left pole of switch S1 and to the second point P2 as a current source for the calibration current Iref.

[0050] The in Fig. The device shown in Figure 1 enables, in particular, the measurement of an electrical resistance in a direction orthogonal to the load current Iload. A known current with a component orthogonal to the load current Iload, i.e., perpendicular to the load current Iload, is applied, and the resulting voltage drop in the perpendicular direction to the load current is determined. This voltage drop in the perpendicular direction depends primarily on the calibration current Iref and, due to deviations from ideal behavior, only to a small extent on the load current Iload. This allows for a largely load-independent determination of the voltage drop across the measuring resistor group generated by the calibration current Iref.

[0051] Furthermore, a microcontroller MK is provided to perform calculations and control the switch S1, which is connected to the voltage meters Utot, Uy, Uref and to the switch S1.

[0052] Next, the accuracy of current measurement achievable with such a device will be considered. For the time being, inaccuracies arising from a possible spatially asymmetrical distribution of the system's partial resistances will be disregarded. Investigations of the invention have shown that these inaccuracies only cause relatively small errors under real-world conditions.

[0053] The basic objective is to measure the load current Iload of all loads, collectively referred to as the load load, from the measured voltage Utot across the group of measuring resistors consisting of the four measuring resistors R1, R2, R3, and R4. The resistance values ​​of these resistors are unknown, but can be assumed to be essentially the same. For the measurement, a reference current Iref is briefly applied by discharging capacitor C through the closing of switch S1. This generates a voltage Uy, which is calculated using the following formula: Uy=Iref*(R2+R3)*(R1+R4)R1+R2+R3+R4

[0054] The load current Iload induces a voltage Utot at the measuring resistor group, which is calculated according to the following formula: Utot=Iload*(R1+R2)*(R3+R4)R1+R2+R3+R4

[0055] Provided that the resistances of the measuring resistors R1, R2, R3, R4 are essentially the same, the following applies: (R1+R2)*(R3+R4)R1+R2+R3+R4=(R2+R3)*(R1+R4)R1+R2+R3+R4

[0056] Thus, folate Iload=Utot*IrefUy

[0057] The calibration current Iref does not necessarily need to be known initially, but can be determined as follows: Iref=UrefRref

[0058] The reference resistor Rref is a correspondingly precise resistor and, unlike the measuring resistors R1, R2, R3, and R4, exhibits low temperature dependence and a low current-carrying capacity. It can be made, for example, from a copper-nickel-manganese alloy, particularly manganin. Due to its small size and low current-carrying capacity, it is inexpensive, readily available, and easily mounted on a printed circuit board.

[0059] The calculation method for the load current Iload to be measured at time t, using the results Uy(t0) and Uref(t0) of a reference current measurement carried out at an earlier time t0 and with a known reference resistance Rref, is thus: Iload(t)=Utot(t)*Iref(t0)Uy(t0)*Rref

[0060] The voltage meters for Uref, Utot, and Uy typically have an error-prone gain g and an absolute error z, especially neglecting noise, which can be easily eliminated for accuracy considerations by appropriate filtering. The absolute error z can be eliminated, if necessary, by using a chopper.

[0061] Thus, in the error analysis, the relative errors of the three measuring instruments or voltmeters for Uref, Utot, and Uy remain, with their relative errors Δg1 (as the error of the voltmeter for Uref), Δg2 (as the error of the voltmeter for Utot), and Δg3 (as the error of the voltmeter for Uy). To clarify that it is not the voltages Uref, Utot, and Uy themselves that are subject to error, but rather their measured values, the error-prone quantities g1, g2, and g3 are explicitly included in the calculation formula for Iload, even though this is actually superfluous due to their nominal value of 1. g1, g2, and g3 denote the respective gain of the measuring instruments for Utot, Uy, and Uref, which is nominally 1 but contains errors.

[0062] The following formula therefore results for the load current Iload at a time t: Iload(t)=g1*Utot(t)*g3*Uref(t0)g2*Uy(t0)*Rref

[0063] According to the known formula for the maximum total errors of a function y consisting of independent, error-prone variables x Δy=∑i|∂y∂xiΔxi| The maximum error ΔIload(t) of the current calculated from the measurements can now be specified: ΔI^load(t)= =|Utot(t)*g3Uref(t0)g2Uy(t0)*Rref*Δg1|+|g1Utot(t)*Uref(t0)g2Uy(t0)*Rref*Δg3|+ +|g1Utot(t)*g3Uref(t0)g22Uy(t0)*Rref*Δg2|+|g1Utot(t)*g3Uref(t0)g2Uy(t0)*Rref2*ΔRref|

[0064] The deltas in equation 9 are still the absolute errors of the quantities subject to error. The transition to relative errors is achieved via the following equations, where the snakes denote the relative errors.

[0065] One can also immediately equate g with 1. Δg1=Δg˜1*g1=Δg˜1*1 Δg2=Δg˜2*g2=Δg˜2*1 Δg3=Δg˜3*g3=Δg˜3*1 ΔRref=ΔR˜ref*Rref

[0066] Substituting these quantities yields equation 10. In particular, the g and the squares of Rref and g2 vanish in the denominator of the respective fractions. ΔIload(t)=|Utot(t)*Uref(t0)Uy(t0)*Rref|*(|Δg˜1|+|Δg˜2|+|Δg˜3|+|ΔR˜ref|)

[0067] It is immediately apparent that the total error of Iload contains the sum of two terms (|Δg̃1| + |Δg̃2|) that are each proportional to the error of the measurement of Utot and Uy respectively, i.e. the errors of the voltage measurements of Utot and Uy add up in the total error.

[0068] Fig. Figure 2 shows a battery sensor according to an embodiment of the invention, with which a method according to the invention can be carried out. The differences to the embodiment of [the invention] are discussed below. Fig. 1. addressed, while regarding the elements not specifically mentioned, reference is made to the description at Fig. 1 is referred to.

[0069] In contrast to the execution of Fig. 1 indicates the execution of Fig. 2. Additionally, a first switch S2a, a second switch S2b, a third switch S3a, and a fourth switch S3b are installed. The first switch S2a is located between the first point P1 and the middle voltmeter Uy. The second switch S2b is located between the first terminal A1 and the middle voltmeter Uy. The third switch S3a is located between the second point P2 and the middle voltmeter Uy. The fourth switch S3b is located between the second terminal A2 and the middle voltmeter Uy. This allows precise selection of the points or terminals between which the middle voltmeter Uy should measure.

[0070] The first switch S2a and the third switch S3a should only be closed when a measurement of the voltage caused by the calibration current Iref is to be taken, which was referred to above as the third voltage. At the same time, the second switch S2b and the fourth switch S3b should be open. Thus, there is no longer a connection between the middle voltmeter Uy and the two terminals A1 and A2.

[0071] As mentioned above, this is relatively rare, since the duration and frequency of calibration current measurements should be kept as short as possible to minimize power consumption. For example, the calibration current can be applied every 10 ms for a duration of 10 µs, 100 µs, or even several hundred µs. A measurement of the third voltage, Uy, is then useful for a duration of 30 µs, 300 µs, or even longer. Specifically, the respective voltage Uy can be measured for a duration before the calibration current pulse, for an approximately equal duration during the calibration current pulse, and again for an approximately equal duration after the calibration current pulse.

[0072] During the remaining time, i.e., outside of calibration periods, the first switch S2a and the third switch S3a should be open, and the second switch S2b and the fourth switch S3b should be closed. Ideally, the measurement of Uy should yield the same result as the measurement of Utot, except for the deviations or errors in the measurement chains of Utot and Uy. A continuum from the measurement points Utot and Uy across the entire measurement range of Utot and Uy is achieved by considering the expected fluctuations of Iload during vehicle operation. The MK microcontroller can store pairs of values ​​of Utot and Uy at various operating points Iload for a predefined period and perform a linear regression of the stored value pairs Utot, Uy.

[0073] In this way, a fixed relationship between the measured values ​​of Utot and Uy can be derived over the respective time period, for example as long as the temperature of the integrated circuit does not change within specified limits: g2*Uy=a*g1*Utot

[0074] The factor a is a parameter that corresponds to the correction value mentioned above.

[0075] Since the real values ​​of Utot and Uy are the same when the second and fourth switches S2b, S3b are closed and the first and third switches S2a, S3a are open, it follows that: g2=a*g1

[0076] If the fixed relationship between the measured values ​​of Uy and Utot determined according to the invention is inserted into the formula for calculating Iload, one obtains: Iload(t)=g1*Utot(t)a*g1*Uy(t0)*g3*Uref(t0)Rref

[0077] It is immediately apparent that an erroneous quantity, g2, is now replaced in the formula by a*g1, where g1 can in turn be eliminated from the calculation by cancellation. In other words, according to the invention, the actual gains of the measuring instruments Utot and Uy, and thus their relative errors, no longer play a role in determining Iload. The proportionality factor a was determined with sufficient accuracy according to the invention by comparing the measured voltages Uy and Utot with the second and fourth switches S2b and S3b closed, as well as with the first and third switches S2a and S3a open.

[0078] To calculate the load current Iload at a time t, the formula given above can be used, in particular, by assuming the gain factors g are 1, their nominal value, and using Uy and Uref from the last calibration period or during a calibration period, respectively, with their current values. The reference resistance Rref is known and constant, and the voltage Utot is used with its current value.

[0079] The total error is therefore reduced according to the formula above to: ΔIload(t)=|Utot(t)*Uref(t0)a*Uy(t0)*Rref|*(|Δg3|+|ΔRref|)

[0080] Since the reference resistor Rref is significantly larger than the measuring resistors R1, R2, R3, and R4, the voltage Uref across the reference resistor Rref can be measured with a much smaller error than the voltages across the measuring resistors R1, R2, R3, and R4. The measurement of the reference voltage Uref can advantageously be performed without an amplifier, whereas the voltmeters Utot and Uy are typically equipped with a high-sensitivity amplifier with a high gain. It is precisely these amplifiers with high gain that cause a comparatively high relative measurement error in the measuring instruments for Utot and Uy, which, however, can be compensated for in the final result by the design according to the invention.

[0081] It should be noted that this application uses designations for both elements and associated values ​​or parameters. In particular, the designations R1, R2, R3, R4, and Rref can be used to refer both to the respective resistors as components and to their respective resistance values. Similarly, the designations Utot, Uref, and Uy can be used to refer to both the respective voltage meters and their respective voltages.

[0082] It should also be mentioned that the designation Uy here refers to voltages which, although typically measured by the same voltmeter, are measured in different contexts: once with a reference current Iref flowing (first and third switches S2a, S3a closed, second and fourth switches S2b, S3b open), and once without a reference current Iref to measure a comparative value to Utot (first and third switches S2a, S3a open, second and fourth switches S2b, S3b closed). The first case corresponds in particular to the second voltage mentioned above, and the second case corresponds in particular to the third voltage mentioned above.

[0083] The MK microcontroller can be used particularly when executed according to Fig. 2 be configured to carry out a method according to the invention. For this purpose, it is in particular not only equipped with the already mentioned with reference to Fig.1 described elements, but also connected to the first, second, third and fourth switches S2a, S2b, S3a, S3b to control them.

[0084] The steps of the method according to the invention can be carried out in the specified order. However, they can also be carried out in a different order. The method according to the invention can be carried out in one embodiment, for example with a specific combination of steps, in such a way that no further steps are performed. However, further steps can also be carried out in principle, including those not mentioned.

[0085] The claims relating to the application do not constitute a waiver of the right to obtain further protection.

[0086] If, during the course of the proceedings, it becomes apparent that a feature or group of features is not strictly necessary, the applicant is already seeking to formulate at least one independent claim that no longer includes the feature or group of features. This could, for example, involve a subcombination of a claim filed on the filing date or a subcombination of a claim filed on the filing date that is further restricted by additional features. Such newly formulated claims or combinations of features are to be understood as being covered by the disclosure of this application.

[0087] It should further be noted that embodiments, features, and variants of the invention, which are described in the various embodiments or exemplary embodiments and / or shown in the figures, can be combined with one another as desired. Individual or multiple features are freely interchangeable. Any resulting combinations of features are to be understood as being covered by the disclosure of this application.

[0088] References in dependent claims are not to be understood as a waiver of the right to obtain independent, substantive protection for the features of the referenced dependent claims. These features can also be combined with other features as desired.

[0089] Features that are only disclosed in the description, or features that are only disclosed in the description or in a claim in conjunction with other features, can in principle be of independent, essential importance to the invention. They can therefore also be included individually in claims to distinguish the invention from the prior art.

Claims

[1] Method for determining a load current (Iload) comprising the following steps: - Passing the load current (Iload) through a first branch of a measuring resistor group and simultaneously through a second branch of the measuring resistor group parallel to the first branch, wherein the first branch has a first measuring resistor (R1) and a second measuring resistor (R2) in series with it, and the second branch has a third measuring resistor (R3) and a fourth measuring resistor (R4) in series with it, - simultaneous measurement of a first voltage (Utot) and a second voltage (Uy) across the entire measuring resistor group with only a load current (Iload) flowing through it, and - Calculating a correction value (a) based on the first voltage (Utot) and the second voltage (Uy), - the procedure consists of the following steps exclusively during the respective calibration periods: - Introducing a calibration current (Iref) with a known current strength into the measuring resistor group at a first point (P1) which is located between the first measuring resistor (R1) and the second measuring resistor (R2), and - Measuring a third voltage (Uy) between the first point (P1) and a second point (P2), wherein the second point (P2) is located between the third measuring resistor (R3) and the fourth measuring resistor (R4), while the calibration current (Iref) flows through it, - where the load current (Iload) is calculated based on the first voltage (Utot), the third voltage (Uy), the current of the calibration current (Iref) and the correction value (a). [2] Method according to claim 1, - where the measuring resistors (R1, R2, R3, R4) have identical or at least nearly identical resistance values. [3] Method according to any one of the preceding claims, - where both the second voltage (Uy) and the third voltage (Uy) are measured with a common voltmeter. [4] Method according to claim 3, - wherein when measuring the first voltage (Utot) and the second voltage (Uy) the common voltage meter is decoupled from the first point (P1) and decoupled from the second point (P2). [5] Method according to one of claims 3 or 4, - wherein when measuring the third voltage (Uy) the common voltage meter is decoupled from external connection points (A1, A2) of the measuring resistor group, and is connected to the first point (P1) and the second point (P2). [6] Method according to any one of the preceding claims, - wherein the current strength of the calibration current (Iref) is determined by voltage measurement across a reference resistor (Rref), in particular a temperature- and / or long-term stable reference resistor (Rref), in particular by dividing the voltage drop (Uref) across the reference resistor (Rref) by the resistance value of the reference resistor (Rref). [7] Method according to any one of the preceding claims, - where outside the calibration periods the load current (Iload) is calculated by dividing the current first voltage (Utot) by the correction value (a) and by the third voltage (Uy) measured during the last calibration period and multiplying by the current of the calibration current (Iref) of the last calibration period. [8] Method according to any one of the preceding claims, - where during a calibration period the load current (Iload) is calculated by dividing the current first voltage (Utot) by the correction value (a) and by the current third voltage (Uy) and multiplying by the current strength of the calibration current (Iref). [9] Method according to any one of the preceding claims, - wherein each calibration period begins every 10 ms, and / or wherein each calibration period lasts at least 100 ms, and / or wherein the duration of the calibration periods is 1% of the time between the calibration periods. [10] Method according to any one of the preceding claims, - wherein the first measuring resistor (Rref) and / or the second measuring resistor (Rref) each has a resistance value between 50 mOhm and 150 mOhm, in particular 100 mOhm. [11] Method according to any one of the preceding claims, - where the third voltage (Uy) is measured over the entire calibration period, in particular averaged. [12] Method according to any one of the preceding claims, - wherein the third voltage (Uy) is measured immediately before and / or immediately after a respective calibration period, in particular for a respective period of 10 ms. [13] Method according to any one of the preceding claims, - wherein the correction value (a) is calculated by dividing the second stress (Uy) by the first stress (Utot), and / or by linear regression of the second stress (Uy) relative to the first stress (Utot). [14] Battery sensor, which has the following features: - a measuring resistor group with a first branch and a second branch parallel to it, wherein the first branch has a first measuring resistor (R1) and a second measuring resistor (R2) in series with it, and the second branch has a third measuring resistor (R3) and a fourth measuring resistor (R4) in series with it, - a total voltage meter (Utot) configured to measure a first voltage drop (Utot) across the measuring resistor group, - a common voltage meter (Uy) which is connected via a first switch (S2a) to a first point (P1) between the first measuring resistor (R1) and the second measuring resistor (R2), via a second switch (S2b) to a second point (P2) between the third measuring resistor (R3) and the fourth measuring resistor (R4), via a third switch (S3a) to a first external connection point (A1) of the measuring resistor group and via a fourth switch (S3b) to a second external connection point (A2) of the measuring resistor group, - a calibration current source configured to introduce a calibration current (Iref) with a switchable current intensity into the first point (P1), and - an electronic control device (MC) configured to perform a method according to any of the preceding claims. [15] Battery sensor according to claim 14, - which furthermore includes a reference resistor (Rref) and a reference voltage meter (Uref), - wherein the reference voltage meter (Uref) is configured to measure a voltage drop (Uref) across the reference resistor (Rref), and - wherein the reference resistor (Rref) is connected between the calibration current source and the measuring resistor group, so that the calibration current (Iref) flows through the measuring resistor (Rref).

Images