METHOD FOR OPERATING A BATTERY SENSOR AND BATTERY SENSOR

Description

[0001] The invention relates to a method for operating a battery sensor according to the preamble of claim 1 and to a battery sensor according to the preamble of claim 11.

[0002] Such battery sensors contain, in particular, devices for measuring the battery voltage, the current drawn or delivered by the battery, and the ambient temperature of the battery. The battery sensor typically also includes a microcontroller that temporarily stores and filters this measurement data and uses it to calculate other battery parameters, such as the state of charge or the battery's internal resistance.

[0003] To measure the load current, state-of-the-art designs use high-precision resistors or sensors for measuring the magnetic field strength. A disadvantage of these designs is the high cost, particularly for the production of resistor materials, which exhibit more or less constant resistance values ​​over a typical temperature range of -40°C to 105°C. One example of such a material is a copper-nickel-manganese alloy.

[0004] For some time now, there have been attempts to replace a high-precision resistor used as a measuring resistor, also known as a shunt resistor, with more cost-effective components. One possibility is to repeatedly recalibrate a shunt resistor over the lifetime of the battery sensor.

[0005] The document EP 1378757 A2 proposes to connect a reference resistor in parallel to the measuring resistor and to evaluate the electrical quantity occurring at the measuring resistor and the reference resistor.

[0006] The document WO 2016 / 041658 A1 discloses a calibration method of a battery sensor by injecting a known reference current into a measuring resistor and detecting a calibration voltage drop.

[0007] DE 10 2016 202 501 A1 discloses a battery sensor with two measuring resistors connected in series, wherein in addition to the load current, a calibration current is passed through at least one measuring resistor and a calibration current pulse is calculated based on the measured voltage pulses.

[0008] However, it has been found that continuous recalibration, even during the simultaneous measurement of the high and temporally highly variable currents occurring in the motor vehicle, is difficult under the prevailing boundary conditions, in particular a desired low power consumption of the sensor, since the reference current to be applied for calibration should be selected to be small and should only be applied for a short time.

[0009] The object of the invention is to provide a method for operating a battery sensor which, compared to known embodiments, can be carried out with little effort or with a simpler structure of the battery sensor, as well as a battery sensor for carrying out this method, wherein the battery sensor has a simpler and more cost-effective structure.

[0010] This object is achieved according to the invention by a method according to claim 1 and a battery sensor according to claim 11. Advantageous embodiments can be found, for example, in the respective subclaims. The content of the claims is incorporated into the content of the description by express reference.

[0011] To achieve the object, a method for operating a battery sensor is provided, wherein the battery sensor comprises at least a first battery sensor terminal and a second battery sensor terminal, as well as a load current terminal, a current measuring device for detecting a load current, with a first measuring resistance element and a second measuring resistance element, wherein the first and the second measuring resistance element are connected in series between the load current terminal and the second battery sensor terminal, and a reference current circuit with at least one reference resistor, wherein the reference resistor is in contact with the first battery sensor terminal and a contact point provided between the measuring resistance elements.

[0012] The electrical resistance of the first measuring resistance element is determined by Connecting a reference current and detecting the respective resulting voltage drops across the first and second measuring resistance elements as well as the battery voltage, determining the reference current from the quotient of the battery voltage and the electrical resistance of the reference resistance, and determining the electrical resistance of the first measuring resistance element from the detected voltage drops, the reference current and at least one correction factor which characterizes the relationship between the electrical resistance of the first measuring resistance element and the electrical resistance of the second measuring resistance element.

[0013] To achieve the object, a battery sensor is further provided for determining a battery state of a battery, in particular a vehicle battery, comprising at least a first battery sensor connection and a second battery sensor connection, as well as a load current connection, a voltage measuring device for detecting the electrical voltage at the first battery sensor connection, a current measuring device for detecting the load current, with a first measuring resistance element and a second measuring resistance element, wherein the first and the second measuring resistance element are connected in series between the load current connection and the second battery sensor connection, and wherein a first and a second voltage measuring device are provided for detecting the voltage drop across the first and the second measuring resistance element, a reference current circuit with at least one reference resistor,wherein the reference resistor is contacted with the first battery sensor terminal and a contact point provided between the measuring resistance elements, and a controller for determining the load current and the battery state, using the method according to the invention.

[0014] The load current and / or the battery state are determined using the method described above and explained in detail below.

[0015] Typically, a controller or evaluation unit requires one input each for the battery voltage, the two voltage drops across the measuring resistor elements, a temperature sensor, and for determining the magnitude of the reference current. Therefore, at least five inputs are preferably required to capture all battery parameters necessary to determine the battery condition.

[0016] Conveniently, only three signals are required at a time, with the signals alternating for defined periods or measurement intervals. The controller thus requires only three inputs. This is particularly advantageous if the signals are to be digitized for further processing or for determining battery parameters, as it also reduces the number of required analog-to-digital converters to three.

[0017] During normal operation, the load current is preferably determined by measuring the voltage drops across the measuring resistor elements. Using the ohmic principle, the load current can be determined using the known electrical resistances of the measuring resistor elements. For this purpose, the signals from the first and, optionally, the signals from the second voltage measuring device are output to the controller.

[0018] To conveniently calibrate the measuring resistance elements, the reference current is applied to the contact point between the first and second measuring resistance elements, with the reference current being essentially driven by the first measuring resistance element. The exact electrical resistance of the first measuring resistance element can be determined by changing the measured voltage drops across the measuring resistance elements or by measuring the voltage drop across the first measuring resistance element and a known or previously determined proportionality between the electrical resistances of the measuring resistance elements. The electrical resistance of the second measuring resistance element can also be determined using the known proportionality. The proportionality between the measuring resistance elements is represented, for example, by correction factors, where: U1 = U2*α+β.

[0019] Typically, or by way of example, the reference current is provided with high precision, or the magnitude of the measurement current is measured, which requires an additional measuring device and an additional analog-to-digital converter. According to the method described above, the measurement current is preferably determined from the quotient of the simultaneously measured battery current and the known electrical resistance of the reference resistor.

[0020] At the same time, the battery voltage is preferably continuously measured via the voltage measuring device. The reference current circuit is directly connected to the battery sensor terminal, where the battery voltage is also measured. This means that the reference current or the voltage drop across the reference resistor is directly dependent on the battery voltage, in particular, proportional to it. Since the battery voltage is continuously measured, no separate voltage measurement at the reference resistor is required. The reference current corresponds to the quotient of the battery voltage and the electrical resistance of the reference resistor.

[0021] To determine the reference current and thus the precise electrical resistance of the first resistance element, no separate detection device or separate input for the controller is required. The reference current and the precise electrical resistance of the first resistance element are determined from the three signals applied to the controller.

[0022] Advantageously, no additional switching elements, in particular no additional analog / digital converters, are required.

[0023] Furthermore, preferably no switching elements are required to regulate the reference current, since this is determined using the method described above. Therefore, no switching elements, especially for regulating the reference current, are provided between the battery sensor terminal and the reference current circuit. Only a switch is required to turn the reference current on and off.

[0024] The reference current circuit is preferably designed such that it does not include a current regulator or no additional electrical component is provided between the battery sensor connection and the reference current circuit.

[0025] It should be noted that the electrical resistance of the reference resistor is preferably many times greater than the electrical resistances of the measuring resistor elements, preferably at least by a factor of 1000. The voltage drop of the reference current across the measuring resistor elements is therefore significantly lower than the voltage drop of the reference current across the reference resistor, so that it can be neglected for the calculation of the reference current.

[0026] In principle, a plurality of first and a plurality of second measuring resistance elements can also be provided, wherein the first and the second voltage measuring devices can either each detect the voltage drops across all first and all second measuring resistance elements and / or a separate voltage measuring device can be provided for each measuring resistance element.

[0027] Using the method described above, the load current and battery voltage can be determined using, conveniently, only three analog-to-digital converters. The load current measurement is highly precise due to the continuous recalibration of the measuring resistor. This is particularly advantageous since available integrated circuits for use in battery sensors typically contain a maximum of three analog-to-digital converters.

[0028] The load current is preferably determined by switching off the reference current and detecting the voltage drop across the first resistance element. In principle, the voltage drops across both resistance elements can be used for load current measurement. Using the method described above, the electrical resistances of both resistance elements are precisely determined, allowing for a very accurate current measurement. However, a reliable and accurate current measurement is also possible if only one voltage drop and the precisely determined electrical resistance of the corresponding resistance element are known. The controller input used to detect the other voltage drop can instead be used to detect another battery parameter.This allows for continuous current measurement, continuous battery voltage detection, and the acquisition of additional battery parameters, while requiring only three inputs on the controller. This allows for a reduction in the number of analog-to-digital converters, particularly if the signals are to be digitized before being acquired by the controller. Only three analog-to-digital converters are required at or before the three inputs of the controller. Preferably, the load current is determined continuously, i.e., without interruption, via the voltage drop across the first measuring resistor element.

[0029] Preferably, at the same time as determining the load current via the voltage drop across the first resistance element, a battery state is determined by detecting the battery voltage, determining the load current from the voltage drop across the first measuring resistance element, and detecting a battery parameter with a sensor, in particular detecting a temperature with a temperature sensor.

[0030] As explained above, only three inputs on the controller are preferably required to determine the battery state and to accurately determine the electrical resistances of the measuring resistance elements, ie, regardless of which function is currently being performed, only three signals need to be acquired and processed by the controller.

[0031] The at least one correction factor is determined, for example, from the respective voltage drops and / or the curves of the voltage drops of the load current across the first and second measuring resistance elements when the reference current is switched off. This means that only the load current is applied to the measuring resistance elements, and the voltage drops across the first and second measuring resistance elements are respectively detected by the first and second voltage measuring devices. The at least one correction factor can be determined from the detected voltage drops. The correction factor can, for example, represent a linear relationship between measured voltage drops or offset. Using the at least one correction factor, the voltage drop across the other measuring resistance element or the electrical resistance of the other measuring resistor can be calculated from a detected voltage drop or the determined electrical resistance of one measuring resistance element.

[0032] In order to fully record the battery condition, three steps or three measuring intervals are preferably required. First, the correction factors are determined in a first time interval, whereby a load current can also be determined from the measured voltage drops. In a second time interval, the exact electrical resistances of the measuring resistance elements or at least the exact electrical resistance of the first measuring resistance element are determined. Subsequently, in a third time interval, the exact load current is determined and / or the battery condition is determined. The three steps of determining the electrical resistance of the first measuring resistance element, determining the load current, determining the battery condition and / or recording the battery parameter with the sensor are preferably repeated alternately, in particular periodically.

[0033] The repetition frequency of the individual time intervals can be varied. For example, determining a temperature, i.e., a battery parameter, or determining correction factors needs to be performed less frequently, as these change only slowly.

[0034] The length of the individual time intervals can also vary, depending on how quickly and / or accurately the individual parameters can or should be determined.

[0035] Preferably, the reference resistor is very precise or exhibits only a very small change in electrical resistance due to temperature or aging. Using the battery voltage and the very precise electrical resistance, a very precise determination of the reference current and thus the electrical resistance of the first and second measuring resistor elements is possible.

[0036] The reference resistor can also consist of multiple reference resistors, whereby only one of them needs to be highly accurate. For example, a high-precision reference resistor with a low electrical resistance is connected in series with another reference resistor with a lower accuracy and higher resistance. This reduces the cost of the high-precision reference resistor because the high-precision reference resistor does not have to be designed to accommodate the entire voltage drop across the reference resistor.In a method described above, the reference resistor therefore has at least a first reference sub-resistor and a second reference sub-resistor, and the reference resistance is determined by connecting the reference current to the measuring resistor group comprising at least a first reference sub-resistor and a second reference sub-resistor, detecting a voltage at a voltage tapping point between the reference sub-resistors, detecting the battery voltage, determining the divider ratio from the detected voltage and the detected battery voltage, and determining the electrical resistance of the second reference sub-resistor from the divider ratio and the known electrical resistance of the first reference sub-resistor.

[0037] This means that the known – relatively small – electrical resistance of the high-precision reference resistor is preferably used to determine the – larger – electrical resistance of the second reference resistor, and thus the electrical resistance of the reference resistor. It is not necessary for the entire voltage drop across the reference resistor to occur across a high-precision resistor.

[0038] This step can also be repeated periodically in another measurement interval. It should be noted again that only three signals are required for the calibration of the reference resistor.

[0039] The detection of the voltages, the voltage drops and the detection of the battery parameters is preferably carried out using three analog / digital converters, wherein a first analog / digital converter is provided for detecting the voltage drop across the first measuring resistance element, a second analog / digital converter is provided for selectively detecting the voltage drop across the second measuring resistance element or the battery parameter of one sensor and a third analog / digital converter is provided for detecting the battery voltage.

[0040] Typically, or by way of example, a separate analog / digital converter is required to record each voltage drop, the voltage drops across the measuring resistor elements, and the reference resistor. Additionally, an analog / digital converter is required to record the battery voltage and other sensor data, such as a temperature sensor. This is particularly necessary to ensure uninterrupted current measurement of the load current and uninterrupted recording of the battery voltage. This is required to ensure constant and therefore reliable determination of the battery status. Using the method described above, all data can be recorded and the battery status determined using just three analog / digital converters. One analog / digital converter is used to record the battery voltage, and at least one digital converter is used to record the load current.The second analog-to-digital converter is used alternately to determine the correction factors, to measure the load current, or to measure another signal, such as a temperature signal. Furthermore, the signals are used multiple times. For example, the measured battery current is also used to determine the reference current or to calibrate the reference resistance.

[0041] Optionally, the same input signals can preferably be applied to two analog-to-digital converters for calibration or adjustment. For example, a calibration factor of the second or third analog-to-digital converter can be determined by applying the same battery voltage, the same voltage drop, and / or the same sensor parameter to the second and third analog-to-digital converters.

[0042] For example, the battery voltage is measured simultaneously using the second and third analog-to-digital converters. The values ​​can be compared, and a calibration factor can be determined for the second or third analog-to-digital converter. If necessary, a voltage divider can be provided to divide the battery voltage. The advantage of this calibration method is that the battery voltage measurement can be continued without interruption and the method can also be implemented using the three existing signal inputs.

[0043] Alternatively, or preferably additionally, the second and third analog-to-digital converters can each detect a voltage present at a voltage tap point between the first reference resistor and the second reference resistor of the reference resistor in order to determine at least one calibration factor. For example, no voltage divider is required for this, allowing calibration using simple means without additional electronic components.

[0044] The voltage measuring device and / or the first and second voltage measuring devices preferably comprise an analog-to-digital converter.

[0045] At least one sensor can be provided for detecting a battery parameter, and the second voltage measuring device can be assigned a switch, in particular a multiplexer, for switching between a signal from the second voltage measuring device and a signal from the sensor, wherein the switch is provided in particular upstream of an analog-to-digital converter of the second voltage measuring device. The switch enables the analog / digital converter to detect several different signals, so that multiple use of the analog / digital converter is possible. Thus, in particular when carrying out the method described above, the number of analog / digital converters can be reduced to three. The battery sensor preferably has a total of only three analog / digital converters.

[0046] A switch, in particular a multiplexer, is understood to mean in particular a selection circuit with which one of a number of input signals can be selected and switched through to the output.

[0047] The reference current circuit has, for example, a switch element arranged in series with the reference resistor in order to be able to switch the reference current on or off.

[0048] The reference resistor can preferably comprise at least two reference sub-resistors arranged in series, with a voltage tapping point provided between the reference sub-resistors. A changeover switch for selectively detecting the battery voltage or the voltage present at the voltage tapping point can be assigned to the voltage measuring device, with the changeover switch being provided in particular upstream of an analog-to-digital converter of the voltage measuring device. Alternatively or additionally, a changeover switch for selectively detecting the voltage drop across the second measuring resistance element and the voltage present at the voltage tapping point can be assigned to the second voltage measuring device, with the changeover switch being provided in particular upstream of an analog-to-digital converter of the second voltage measuring device. Preferably, the first or the second reference sub-resistor is a high-precision resistor.This arrangement allows, as described above, the reference resistance to be determined if a reference partial resistance is known. Furthermore, at least one calibration factor of the second and / or third analog-to-digital converter can be determined.

[0049] The switches are preferably multiplexers located upstream of the respective analog / digital converter. The switch can also be designed for more than two input signals, for example, a voltage drop signal and several sensor signals, such as temperature signals. Regardless of the number of sensors, no more than three analog / digital converters are required, or the entire battery status determination can be performed with three analog / digital converters.

[0050] In order to be able to expediently detect the battery voltage with the second and the third analog / digital converter, for example to determine a calibration factor, a voltage divider for the battery voltage can be provided and the second voltage measuring device is assigned a changeover switch for selectively detecting the voltage drop at the second measuring resistance element and the battery voltage present at the first battery sensor connection, wherein the changeover switch is provided in particular upstream of an analog / digital converter of the second voltage measuring device.

[0051] The first and the second measuring resistance element can each be designed as parts, in particular as measuring zones and / or measuring sections, of a one-piece load resistance unit.

[0052] Since the electrical resistances of the measuring resistors can be determined very precisely using the above-described preferred method or the above-described preferred battery sensor, it is not necessary to use a material with only a low temperature dependence and / or low aging behavior. The electrical resistances are continuously adjusted during operation, ensuring a very precise load current measurement regardless of the material of the measuring resistors.

[0053] The load resistance unit, preferably consisting of the one-piece load resistance unit, as well as the battery terminal and the ground connection, can also be formed in one piece, in particular as a stamped and bent part.

[0054] The measured voltage drops, voltages, and signals can also be amplified, for example. For this purpose, amplifier circuits can be provided, in particular, upstream of the analog / digital converter and / or the switch. The amplifiers or the amplification factors are preferably designed such that the magnitude of the input signals for the switch and / or the analog / digital converter, or the signals for the control system, are in a similar range. Optionally, an error value for the load current can be calculated based on the reference current to estimate the reliability of the determined load current.

[0055] The controller may in particular comprise processor means and memory means, wherein program code is stored in the memory means, upon execution of which the processor means execute a method according to the invention or behave accordingly.

[0056] Further features and advantages will become apparent to those skilled in the art from the exemplary embodiments described below with reference to the accompanying drawings, which schematically show: Figure 1 shows a battery sensor from the prior art; Figure 2 shows a battery sensor according to a first embodiment of the invention; Figure 3 shows a battery sensor according to a second embodiment of the invention; and Figure 4 shows a battery sensor according to a third embodiment of the invention.

[0057] Further explanations of the invention are given below, which serve to explain its function.

[0058] For this purpose, first Figur 1 Reference is made.

[0059] Figur 1 shows a state-of-the-art battery sensor that can be used to perform a calibration procedure. However, it requires three A / D converters U1, U2, and Uref, none of which allows for uninterrupted measurement of Vbat.

[0060] The measuring resistor group comprises a first measuring resistor element R1 and a second measuring resistor element R2, through which a time-varying load current Iload is conducted. This load current Iload originates initially from a battery, which has a voltage Vbat in Figur 1 The load current Iload also flows through a load generally referred to as load, which is shown here only schematically and can include typical electrical components of a motor vehicle such as a starter motor, a vehicle light or electronic components as well as a generator.

[0061] A first voltmeter U1 is arranged above the first measuring resistor element R1. A second voltmeter U2 is arranged above the second measuring resistor element R2. These are designed to measure the respective voltage drops across the two measuring resistors R1, R2 when currents I1, I2 flow through them. Since the resistor elements R1, R2 are arranged in series, I1, I2 each correspond to the load current Iload.

[0062] A first capacitor C1 and a second capacitor C2 serve as current sources for a reference current Iref, which are charged directly from the vehicle battery via a series resistor Rlim. The load current Iload is generated from the battery Vbat via the load, which flows to ground GND via the resistor network of measuring resistors R1 and R2.

[0063] The two capacitors C1 and C2 are connected via a switch S1 and a reference resistor Rref to a point between the first measuring resistor and the second measuring resistor. The two voltmeters U1 and U2 are also connected to this point. A further voltmeter Uref is arranged above the reference resistor Rref, which measures the voltage drop across the reference resistor Rref when the reference current Iref flows through it.

[0064] By closing switch S1, in addition to the load current Iload, a reference current Iref is fed into the resistor network consisting of the measuring resistors R1, R2, whereby the first capacitor C1 discharges essentially via the first measuring resistor R1, and the second capacitor C2 discharges essentially via the second measuring resistor R2. This consequently creates two calibration partial currents, namely a first calibration partial current Iref,1 and a second calibration partial current Iref,2, whereby the first calibration partial current Iref,1 flows through the first measuring resistor R1 and the second calibration partial current Iref,2 flows through the second measuring resistor R2. The two calibration partial currents Iref,1 and Iref,2 have opposite signs across the two measuring resistors R1, R2, while their sum Iref flows through the reference resistor Rref and can be measured via a voltage measurement as already described.

[0065] The voltmeters U1, U2 for measuring the voltages dropped across the two measuring resistors R1, R2 are not described in further detail here. The voltmeters U1, U2 typically each have at least one amplifier, usually with a variable gain, and one analog-to-digital converter.

[0066] In Figur 1 Not shown is an arithmetic unit, for example an electronic control device, which can be designed, for example, as a microcontroller. Such an electronic control device can, for example, have processor means and memory means, wherein program code is stored in the memory means, the execution of which causes the processor means to carry out a method according to the invention. In particular, the processor means can calculate the load current Iload according to the formulas stated below. The arithmetic unit or the electronic control device can preferably also have an interface for reading the voltages U1, U2, Uref, as well as an interface for controlling the switch S1.

[0067] It should be noted that any other type of power source can be used instead of capacitors C1 and C2. For example, DC / DC converters, a direct connection to the positive terminal of a battery (with or without a series resistor Rlim), series regulators, regulated precision current sources (especially those that eliminate the Iref measurement via Rref), or other suitable designs can be used.

[0068] When switch S1 is closed, i.e. when the reference current is applied, the following solvable system of equations results for the voltages at the measuring resistance elements R1, R2: U m = I load , i + I ref , m * R m * g m U n = I load , i + I ref , n * R n * g n

[0069] These include U m , U n are the measured voltage drops across each of the measuring resistance elements, where m is 1 and n 2, R m , R n are the (unknown) electrical resistances of the measuring resistance elements across which the voltage drops U m , U n are measured. The measuring resistor elements can in turn consist of further measuring resistors connected in series or parallel, gm , gn the (erroneous) amplification factors of the measuring instruments for the voltages U m , U n , I load,i the load current to be measured or a part of this load current which flows through the measuring resistors of the measuring resistor group via which the calibration voltages U m , U n are measured, I ref,m and I ref,n applied calibration partial currents which flow through the measuring resistors R m , R n of the measuring resistor group via which the calibration voltages U m , U n are measured, where I ref,m and I ref,n flow in different directions, relative to I load,i.

[0070] In particular, the reference currents or the reference current are applied periodically, for example, with a period between 10 ms and 100 ms for a duration of between 10 µs and 100 ps. This results in times in which reference currents or parts thereof flow through the measuring resistor elements of the measuring resistor group, i.e., periods, and times in which no reference currents flow through the measuring resistor group. At these times, i.e., outside of calibration periods, at least some of the equations of the system of equations simplify to U m = I load , i * R m * g m U n = I load , i * R n * g n

[0071] U m , U n are the voltage drops of the load current across the measuring resistance elements R1, R2.

[0072] Alternatively, time-varying reference currents can be applied at the times when reference currents flow, i.e. within calibration periods.

[0073] At times when no calibration currents flow through the network, it is advantageous to determine the proportionality of individual equations of the system of equations (or between measured voltages U i ), for example, in a microcontroller, which may be part of a current measuring device or connected to it. For this purpose, a correction factor α is determined, where: U m = α mn * U n or U m = α mn * I Load , i * R n * g n

[0074] For example, voltage pairs U n (t), U m (t) measured at the same time t can be stored. These stored pairs can be evaluated in the microcontroller using linear regression to determine the correction factors m, o.

[0075] Advantageously, with calibration currents switched on, by measuring the voltages U m , U n U m = α mn * I load , i + I ref , m * R n * g n + o U n = I Load , i + I ref , n * R n * g n the part of the load current to be measured can be determined as follows: U m α mn * R n * g n = I load , i + I ref , m U n R n * g n = I load , i + I ref , n U n R n * g n − U m α mn * R n * g n = I ref , n − I ref , m U n I ref , n − I ref , m − U m α mn * I ref , n − I ref , m = R n * g n I load , i = U n R n * g n − I ref , n

[0076] The penultimate formula provides a calculation rule for the second operating parameter.

[0077] At times when no reference current is applied, I ref,m = 0 and I ref,n = 0 and the last equation can be used to determine the load current I load to be measured.

[0078] With known R n , gn , α, β the following equation can be advantageously used to determine I load: I load , i = 1 2 * U m R m * g m + U n R n * g n − I ref , m − I ref , n

[0079] From the sum of both equations, I load can also be approximately calculated for the times when the reference current is switched on: I load , i = 1 2 * U m R m * g m + U n R n * g n − I ref , m − I ref , n = 1 2 * U m R m * g m + U n R n * g n ± I ref , m − I ref , n

[0080] An error occurs particularly when the currents I ref,m and I ref,n differ significantly.

[0081] The value I ref,m -I ref,n is known; it corresponds to the reference current, i.e., the sum of the calibration currents. The different signs are taken into account.

[0082] To determine the load current, the following requirements must be met: First: The relationship α mn of two products each R n * g n , R m * g m The relationship between the measuring resistors R n and R m and the gain factors gn and gm should be essentially stable over a certain period of time. This period of time should be significantly longer than the period with which the periodically applied calibration currents are switched on and off or periodically changed. Second, the value of the reference current I ref = I ref,n - I ref,m =| I ref,n |+ | I ref,m | should at least one time when U n and U m measured with a reference current applied must be known exactly.

[0083] It should now be noted that 1) the voltage drop in one measuring resistor is increased, the other is reduced, and 2) the resistance is calculated from the difference between the two measuring voltages.

[0084] This allows for real-time measurement of the resistance. Therefore, it doesn't have to remain constant over time. More cost-effective materials can be used.

[0085] The described arrangement and method make it possible to determine the load current with virtually no prior knowledge of the resistor network or measuring resistor group and the relative accuracy of the measuring devices used to measure the voltages. This allows for even higher current measurement accuracy than with prior art designs, despite the lower-cost materials. Previously, both the tolerance of the resistance value of the measuring resistor and the tolerance of the voltage measuring device for the voltage drop were essentially included in the tolerance of the measured current value.

[0086] With the device or arrangement described, typically only precise knowledge of I ref at a given point in time is required. Furthermore, practically no requirements are placed on the quality of the current source for I ref. Only an accurate measurement of I ref is typically necessary. This can be easily achieved, for example, with a sufficiently accurate reference resistor R ref and an accurate measurement of the voltage drop across R ref. Unlike the measuring resistor for the load current, R ref can have a high resistance of, for example, 1 ohm, which only needs to be designed for small reference currents and not for high load currents. By choosing an appropriately high value for R ref, the voltage drop I ref * R ref can also be conveniently measured, since, for example, no complex amplifier is required.

[0087] Not shown here is that the battery voltage Vbat is also recorded.

[0088] The battery condition can be determined from the battery voltage Vbat, the load current Iload and optionally a recorded battery temperature.

[0089] However, to determine the electrical resistances of the resistance elements R1, R2, the measurement of the load current Iload is interrupted. For example, the measured value of Iload for the calibration time can be calculated from the average values ​​of the measured values ​​before and after the calibration time. Alternatively, a decision can be made as to whether the erroneous measured value is used or a substitute value is calculated. The decision can be made, for example, based on a current value of the "symmetry factor" m compared to previous values ​​of m. However, the decision can also be made dependent on the ratio of the error to the applied load current.

[0090] However, for a reliable determination of the battery condition, uninterrupted current measurement is required in order to always obtain accurate values ​​of the load current Iload.

[0091] Figur 2 shows a battery sensor according to the invention.

[0092] The battery sensor has a current measuring device, a voltage measuring device, a reference current circuit and a controller pC.

[0093] The voltage measuring device includes an analog-to-digital converter (V-ADC), which is connected to a first battery sensor terminal (Vbat+), which in this case is formed by the positive terminal of the battery. Furthermore, the analog-to-digital converter (V-ADC) is connected to the controller microcontroller (µC).

[0094] The current measuring device has a first and a second measuring resistor element R1, R2, each of which is assigned a voltage measuring device. The first voltage measuring device has an amplifier PGA and a first analog / digital converter I-ADC, while the second voltage measuring device has an amplifier Ext. and a second analog / digital converter T-ADC. The analog / digital converters I-ADC and T-ADC are each connected to an input of a controller µC. The measuring resistor elements R1, R2 are connected in series between a load current terminal and a second battery sensor terminal Vbat-.

[0095] A switch (T-MUX) is provided between the amplifier (Ext.) and the second analog-to-digital converter (T-ADC). A temperature sensor (Tint) is connected to the switch in addition to the amplifier (Ext.). The switch can be used to output either the signal from the amplifier (Ext.) or the signal from the temperature sensor to the second analog-to-digital converter.

[0096] Furthermore, a reference current circuit is provided, which has a switch S1 and a reference resistor Rref. The switch S1 is arranged in series with the reference resistor. The reference current circuit is directly connected to a first battery sensor terminal Vbat+. The reference current Iref is therefore directly dependent on the battery voltage. Furthermore, the reference current circuit is connected to a contact point between the two series-arranged measuring resistor elements R1, R2.

[0097] Between the contact point and the measuring resistance elements, additional resistances Rp2 and Rp1 are shown, which can be formed, for example, by line resistances.

[0098] By closing the switch S1, which is controlled, for example, by the controller µC, the reference current Iref is fed into the resistance elements R1, R2 in addition to the load current Iload, whereby the current I1 flowing through the first resistor R1 is essentially composed of the current I2 flowing through the second resistor R2 and the reference current Iref.

[0099] The method for operating or using the current sensor preferably comprises three measuring intervals, the order, frequency and duration of which can be changed as desired, as explained below.

[0100] In a first measurement interval, the ratio of the measuring resistors, i.e., the correction factors α, β, is determined. During this measurement interval, switch S1 is open. The first analog-to-digital converter (I-ADC) determines the voltage drop U1=R1*I1 across the first measuring resistor element R1, amplified by the first amplifier (PGA), and the second analog-to-digital converter (T-ADC) determines the voltage drop U2=R2*I2 across the second measuring resistor element R2, amplified by the second amplifier (Ext).

[0101] At the same time, the battery voltage Vbat+ is determined by the third analog-to-digital converter V-ADC.

[0102] The battery voltage Vbat+ and the load current Iload determined from the voltage drops U1 and U2 are used in the control system to determine the battery status.

[0103] During this first measurement interval, the microcontroller also calculates the ratio between the first amplified measurement voltage U1 and the second amplified measurement voltage U2 from at least one measurement pair, for example using linear regression. For example, a ratio α or preferably a ratio α and an offset β are determined according to the following equation: U1 = α 12 *U2 + β 12 . A measurement pair consists, in particular, of the measurement of the first amplified measurement voltage and the second amplified measurement voltage.

[0104] In a second measurement interval, switch S1 is closed, and a reference current Iref flows through the reference resistor Rref. During this measurement interval, the first analog-to-digital converter I-ADC measures the voltage drop U1 amplified by the first amplifier PGA, and the second analog-to-digital converter T-ADC measures the voltage drop U2 amplified by the second amplifier Ext.

[0105] At the same time, the battery voltage Vbat is determined by the third analog-to-digital converter V-ADC.

[0106] Based on the determined first operating parameter and the measured amplified voltage U2, the amplified voltage U1 can be estimated, for example, using the following equation: U1est = α 12 * U 2 + β 12 .

[0107] A difference between the measured voltage U1 and the estimated voltage U1 can then be determined from: Udiff = U 1 − U1est .

[0108] In addition, the reference current can be determined using the known resistance value Rref and the measured battery voltage Vbat, for example, using the following equation: Iref = Vbat / Rref .

[0109] It should be noted again that the electrical resistances of R1 and Rp1, as well as Rp2 and R2, are significantly smaller than the electrical resistance of Rref. The electrical resistances of R1, Rp1, R2, and Rp2 are in the range of 0.05 to 0.1 mOhm. The electrical resistance of Rref is in the range of 10 ohms to 100 ohms, in order to keep the calibration current within a range of approximately 1 A. This makes R1 and Rp1 negligible compared to Rref (<0.1%), so that the electrical resistances of R1 and rp1 can be neglected for the calculation of the reference current Iref.

[0110] Based on the difference between the measured voltage U1 and the estimate of the voltage U1 as well as the reference current, the exact electrical resistance of R1 can be determined, and from this, as well as the determined correction factors, the electrical resistance of R2, according to the formulas: R1 = Udiff / Iref ; und R22 = Cal1 * α 12 + β .

[0111] The electrical resistances can then be used to determine the load current from I1=U1 / R1 or I2=U2 / R2.

[0112] The following is a derivation for the above formulas. For the meaning of the individual variables, please refer to the description above. I ref , 1 + I ref , 2 = I ref I 1 = I load + I ref , 1 I 2 = I load − I ref , 2 U 1 = R 1 * g 1 * I load + I ref , 1 U 2 = R 2 * g 2 * I load + I ref , 2 α * R 1 * g 1 = R 2 * g 2 U 2 = α * R 1 * g 1 * I load − I ref , 2 U 1 − 1 α * U 2 = R 1 * g 1 * I ref , 1 + I ref , 2 R 1 * g 1 = U 1 − 1 α * U 2 I ref R 2 * g 2 = α * R 1 * g 1

[0113] Since the battery voltage Vbat+ is still determined via the third analog / digital converter V-ADC and the load current Iload via the voltage drops at R1 and R2, an uninterrupted battery status determination continues.

[0114] In a third measurement interval, the second analog-to-digital converter T-ADC determines the voltage of the internal temperature sensor Tint via a corresponding position of the first multiplexer T-MUX. During the third measurement interval, switch S1 is advantageously open, as this ensures that no reference current Iref flows and, accordingly, no measurement of Iref is necessary.

[0115] During this measurement interval, the first analog-to-digital converter I-ADC continues to record the voltage drop across R1, from which the current I1, which corresponds to the load current Iload, can be determined.

[0116] Therefore, the battery voltage Vbat+ continues to be measured continuously via the third analog-to-digital converter (V-ADC) and the load current Iload via the first analog-to-digital converter. In addition, the temperature is measured via the second analog-to-digital converter.

[0117] The temperature changes relatively slowly. The correction factors α and β also change slowly. Therefore, the first and third measurement intervals can be performed less frequently or, if necessary, shorter than the second measurement interval.

[0118] However, in each measuring interval, the load current Iload and the battery voltage Vbat+ are determined without interruption.

[0119] Figur 3 shows a measuring resistor group with a measuring circuit according to a second embodiment, in which the first multiplexer T-MUX has a third input. The third input can be used to select an analog temperature signal from, for example, an additional external temperature sensor.

[0120] Figur 4shows a measuring resistor group with a measuring circuit according to a third exemplary embodiment, in which the reference resistor has a first reference sub-resistor Rref 1 and a second reference sub-resistor Rref 2. A voltage at a voltage tapping point between the first reference sub-resistor Rref 1 and the second reference sub-resistor Rref 2 is supplied to a fourth input of the second multiplexer T-ADC and to a further input of the third multiplexer V-MUX, which is connected upstream of the third analog-to-digital converter V-ADC.

[0121] Preferably, only one of the reference resistors Rref1 and Rref2, namely the reference resistor Rref1, is a high-precision resistor with low temperature dependence and low aging-related drift. Furthermore, the electrical resistance of Rref1 is significantly lower than that of Rref2, so the high-precision resistor is significantly smaller and thus more cost-effective.

[0122] In this embodiment, however, it is necessary to determine the exact electrical resistance of Rref2. This is done in a fourth measurement interval by determining the voltage at the voltage tap point between Rref1 and Rref2 using the second analog-to-digital converter T-ADC via a corresponding setting of the second multiplexer T-MUX. During the fourth measurement interval, switch S1 is closed.

[0123] Furthermore, the battery voltage Vbat+ is determined via the third analog-to-digital converter V-ADC and the battery current via the first analog-to-digital converter I-ADC and the second analog-to-digital converter T-ADC via a corresponding position of the multiplexer V-MUX.

[0124] The microcontroller calculates the divider ratio between Rref1 and the sum of Rref1 and Rref2 based on the ratio of the voltage potentials determined by the third analog-to-digital converter V-ADC and the second analog-to-digital converter T-ADC and fed to the microcontroller.

[0125] From the determined divider ratio and from the known electrical resistance of the first reference resistor Rref1, an exact total resistance value for the entire reference resistor (Rref1 + Rref2) can be determined.

[0126] With this value, a more precise determination of the reference current and thus a more precise determination of the electrical resistance of the first measuring resistance element R1 can be carried out in a subsequent second measuring interval.

[0127] In a fifth measuring interval, a mutual calibration of the first, second and third analog-to-digital converters can be carried out by at least two analog-to-digital converters determining the same physical measurement quantity and at least one calibration factor being determined based on the deviation of the determined physical measurement quantity.

[0128] For example, when switch S1 is closed, i.e., when the reference current Iref is applied, the third multiplexer V-MUX and the second multiplexer T-MUX are switched so that the third analog-to-digital converter V-ADC and the second analog-to-digital converter T-ADC each determine the voltage at the voltage tap point between the reference resistor Rref1 and the reference resistor Rref2. Based on the respective measured voltages, a calibration factor is determined for the second analog-to-digital converter T-ADC.

[0129] Alternatively, in a fifth measuring interval in which switch S1 is open, the third multiplexer V-MUX and the second multiplexer T-MUX are switched such that the third analog-to-digital converter V-ADC and the second analog-to-digital converter T-ADC each measure the voltage potential of the battery Vbat+. Preferably, a voltage divider divides the voltage potential of the battery Vbat+ using a known divider ratio in order to adapt the voltage potential of the battery Vbat+ to the measuring range of the analog-to-digital converter T-ADC. Based on the respectively determined voltage potential Vbat, a calibration factor for the second analog-to-digital converter T-ADC is determined. In this alternative advantageous embodiment, the measurement of the voltage potential of the battery does not have to be interrupted.

[0130] The steps of the method described above can be performed in the specified order. However, they can also be performed in a different order. The method according to the invention can be carried out in one of its embodiments, for example, with a specific combination of steps, in such a way that no further steps are performed. However, in principle, further steps can also be carried out, even those not mentioned.

[0131] Any subset of the circuits shown can, for example, be mounted discretely on a circuit board or integrated into a semiconductor component. Additionally, the discrete circuit or semiconductor component can contain additional devices, such as temperature sensors, particularly for temperature measurement, at least one of the resistors Rref, R1, R2,..., Rn, voltage sensors, in particular for measuring battery voltages, communication interfaces, devices for regulating the current sources C1, C2, further current sources, clock generators, volatile and / or non-volatile data memories, in particular for storing calibration data of the current measuring device, for example a value of Rref determined in the final production test or a temperature coefficient of Rref, microprocessors, in particular for calculating physical quantities of the battery or for calculating temperature models, in particular for calculating the battery temperature, the ambient temperature of the device or for calculating a temperature of one or more of the resistors Rref, R1,..., Rz used.

[0132] The entire assembly or any subset of the device can, for example, be installed in a plastic or metal housing with or without an integrated connector, or can be overmolded with a plastic.

[0133] The entire arrangement or any subset of the devices mentioned, in particular the measuring resistors or shunt resistors R1,..., Rz, can be integrated into a battery terminal, a cable lug, a battery cable or a battery.

[0134] The measuring resistance elements R1, R2 can be part of a one-piece load resistance unit, for example zones on a load resistor.

[0135] The load resistance unit consisting of the one-piece load resistance, as well as the battery terminal and the ground connection can also be designed in one piece, in particular as a stamped and bent part.

[0136] The circuit may also contain one or more choppers for the voltages tapped at the resistors Rref, R1,..., Rz.

[0137] The circuit may further include one or more sample-and-hold elements or other analog buffers for voltages tapped at the resistors Rref, R1,..., Rz or voltages tapped or amplified there.

[0138] The claims included in the application do not constitute a waiver of the right to obtain further protection.

[0139] If it becomes apparent during the proceedings that a feature or group of features is no longer absolutely necessary, the applicant will now endeavor to formulate at least one independent claim that no longer includes the feature or group of features. This may, for example, be a subcombination of a claim existing on the filing date or a subcombination of a claim existing on the filing date that is limited by additional features. Such newly formulated claims or combinations of features are to be understood as being covered by the disclosure of this application.

[0140] For the sake of better readability, some reference symbols are abbreviated in the claims. For example, the first operating parameter is designated α.

Claims

1. Method for operating a battery sensor, comprising at least - a first battery sensor connection (Vbat+) and a second battery sensor connection (Vbat-), - a current measurement device for recording a load current (Iload), with a first measuring resistor element (R1) and a second measuring resistor element (R2), wherein the first and the second measuring resistor element (R1, R2) are connected in series between a load current connection and the second battery sensor connection (Vbat-), - a reference current circuit with at least one reference resistor (Rref, Rref1, Rref2), wherein the reference resistor (Rref, Rref1, Rref2) is in contact with the first battery sensor connection (Vbat+) and a contact point provided between the measuring resistor elements (R1, R2), wherein the electrical resistance of the first measuring resistor element (R1) is determined by - switching on a reference current (Iref) and recording the respective resulting voltage drops (U1, U2) across the first and the second measuring resistor element (R1, R2) and the battery voltage (Vbat+), - determining the reference current (Iref) from the quotient of the battery voltage (Vbat+) and the electrical resistance of the reference resistor (Rref), characterized by - determining the electrical resistance of the first measuring resistor element (R1) from the recorded voltage drops (U1, U2), the reference current (Iref) and at least one correction factor (α, β) that characterizes the relationship between the electrical resistance of the first measuring resistor element (R1) and the electrical resistance of the second measuring resistor element (R2).

2. Method according to Claim 1, characterized in that the load current (Iload) is determined by - switching off the reference current (Iref), - recording at least the voltage drop (U1) across the first measuring resistor element (R1).

3. Method according to Claim 2, characterized in that a battery state is ascertained by - recording the battery voltage (Vbat+) - determining the load current (Iload) from the voltage drop (U1) across the first measuring resistor element (R1), and - recording a battery parameter using a sensor (Tint, Text), in particular recording a temperature using a temperature sensor.

4. Method according to one of Claims 1 to 3, characterized in that the at least one correction factor (α, β) is determined from the respective voltage drops (U1, U2) and / or the profiles of the voltage drops (U1, U2) of the load current (Iload) across the first and the second measuring resistor element (R1, R2) when the reference current (Iref) is switched off.

5. Method according to Claim 3, characterized in that - determining the electrical resistance of the first measuring resistor element (R1), - determining the load current (Iload), - ascertaining the battery state and / or - recording the battery parameter using the sensor (Tint, Text) are repeated alternately, in particular periodically.

6. Method according to either of Claims 1 and 2, characterized in that the reference resistor (Rref) has at least a first reference sub-resistor (Rref 1) and a second reference sub-resistor (Rref 2), and the reference resistance (Rref) is determined by - switching the reference current (Iref) into the measuring resistor group consisting of at least the first reference sub-resistor (Rref 1) and the second reference sub-resistor (Rref 2), - recording a voltage at a voltage tapping point between the reference sub-resistors (Rref 1, Rref 2), - recording the battery voltage (Vbat+), - determining the division ratio from the recorded voltage and the recorded battery voltage (Vbat+), - determining the electrical resistance of the second reference sub-resistor (Rref 2) from the division ratio and the known electrical resistance of the first reference sub-resistor (Rref 1).

7. Method according to either of Claims 3 and 5, characterized in that the voltage (Vbat+), the voltage drops (U1, U2) and the battery parameter are recorded using three analogue-to-digital converters, wherein a first analogue-to-digital converter (I-ADC) for recording the voltage drop (U1) across the first measuring resistor element (R1), a second analogue-to-digital converter (T-ADC) for selectively recording the voltage drop (U2) across the second measuring resistor element (R2) or the battery parameter of the one sensor (Tint, Text) and a third analogue-to-digital converter (V-ADC) for recording the battery voltage (Vbat+) are provided.

8. Method according to Claim 7, characterized in that a calibration factor of the second or the third analogue-to-digital converter is temporarily determined by applying the same battery voltage (Vbat+), the same voltage drop and / or the same parameter of a sensor to the second and the third analogue-to-digital converter.

9. Method according to Claim 8, characterized in that the battery voltage (Vbat+) is recorded simultaneously using the second analogue-to-digital converter (T-ADC) and the third analogue-to-digital converter (V-ADC).

10. Method according to Claim 8, characterized in that a respective voltage present at a voltage tapping point between a first reference sub-resistor (Rref 1) and a second reference sub-resistor (Rref 2) of the reference resistor (Rref) is recorded using the second analogue-to-digital converter (T-ADC) and the third analogue-to-digital converter (V-ADC).

11. Battery sensor for determining a battery state of a battery, in particular a vehicle battery, comprising at least - a first battery sensor connection (Vbat+) and a second battery sensor connection (Vbat-), - a voltage measurement device for recording the electrical voltage (Vbat+) at the first battery sensor connection, - a current measurement device for recording the load current (Iload), with a first measuring resistor element (R1) and a second measuring resistor element (R2), wherein the first and the second measuring resistor element (R1, R2) are connected in series between the load current connection and the second battery sensor connection (Vbat-), and wherein a first and a second voltage measurement apparatus for recording the respective voltage drop (U1, U2) across the first and the second measuring resistor element (R1, R2) are provided, - a reference current circuit with at least one reference resistor (Rref, Rref1, Rref2), wherein the reference resistor (Rref, Rref1, Rref2) is in contact with the first battery sensor connection (Vbat+) and a contact point provided between the measuring resistor elements (R1, R2), characterized by - a controller (µC) for ascertaining the load current (Iload) and the battery state by way of a method according to one of the preceding claims.

12. Battery sensor according to Claim 11, characterized in that the voltage measurement device and / or the first and the second voltage measurement apparatuses have an analogue-to-digital converter (V-ADC, T-ADC, I-ADC).

13. Battery sensor according to either of Claims 11 and 12, characterized in that at least one sensor (Tint, Text) for recording a battery parameter is provided and in that a changeover switch, in particular a multiplexer (T-MUX), for switching between a signal of the second voltage measurement apparatus and a signal of the sensor (Tint, Text) is assigned to the second voltage measurement apparatus, wherein the changeover switch is in particular provided upstream of an analogue-to-digital converter (T-ADC) of the second voltage measurement apparatus.

14. Battery sensor according to either of Claims 11 and 12, characterized in that the reference resistor (Rref) has at least two reference sub-resistors (Rref1, Rref2) arranged in series, wherein a voltage tapping point is provided between the reference sub-resistors (Rref1, Rref2), wherein the voltage measurement device is assigned a changeover switch (V-Mux) for selectively recording the battery voltage (Vbat+) or the voltage present at the voltage tapping point, wherein the changeover switch is in particular provided upstream of an analogue-to-digital converter (V-ADC) of the voltage measurement device and / or wherein the second voltage measurement apparatus is assigned a changeover switch (T-MUX) for selectively recording the voltage drop (U2) across the second measuring resistor element (R2) and the voltage present at the voltage tapping point, wherein the changeover switch (T-MUX) is in particular provided upstream of an analogue-to-digital converter (T-ADC) of the second voltage measurement apparatus.

15. Battery sensor according to either of Claims 11 and 12, characterized in that a voltage divider for the battery voltage (Vbat+) is provided and the second voltage measurement apparatus is assigned a changeover switch (T-MUX) for selectively recording the voltage drop (U2) across the second measuring resistor element (R2) and the battery voltage (Vbat+) present at the first battery sensor connection, wherein the changeover switch (T-MUX) is in particular provided upstream of an analogue-to-digital converter (T-ADC) of the second voltage measurement apparatus.