Method for controlling the state of charge of a low-voltage battery of a motor vehicle, computer program product, vehicle electrical system and motor vehicle

Abstract

A method for controlling the state of charge of a low-voltage battery of a motor vehicle is described, wherein the state of charge of the low-voltage battery and a battery temperature of the low-voltage battery are measured, wherein the low-voltage battery is charged at a state of charge lower than a limit state of charge, and wherein the limit state of charge is raised at a battery temperature below a limit temperature.

Description

[0001] The text describes a method for controlling the state of charge of a low-voltage battery in a motor vehicle, a computer program product, an on-board network, and a motor vehicle.

[0002] Methods for controlling the state of charge of a low-voltage battery of a motor vehicle, computer program products, on-board networks and motor vehicles of the type mentioned above are known in the prior art.

[0003] The state of charge of a vehicle's on-board battery, or low-voltage battery, can be regulated by a variety of methods tailored to the requirements of modern vehicles and their electronic systems. These batteries are increasingly subject to higher demands, as they no longer just power the starter motor, but also numerous electrical consumers and systems such as start-stop functions and regenerative braking.

[0004] The goals of such a system are to ensure a consistently stable energy supply, maximize efficiency, and extend battery life. Early systems were based on relatively simple concepts, while today's methods employ intelligent sensors and often algorithm-controlled energy management systems (EMS) to precisely monitor and control the state of charge. The energy management system can control the charging process not only based on the battery's current state of charge but also respond to specific driving modes. For example, energy consumption is minimized in Eco mode, while more energy is allocated to dynamic driving demands in Sport mode. This adaptive control helps to increase the overall system efficiency and thus optimize energy consumption.

[0005] Traditional state-of-charge (SOC) control methods rely on the use of a charge controller in conjunction with an alternator. The charge controller monitors the battery voltage and adjusts the alternator voltage accordingly. As soon as the battery voltage falls below a defined threshold, the alternator is activated to charge the battery. Conversely, the alternator output is reduced or stopped when a maximum charging voltage is reached. This method fulfills basic requirements, such as preventing deep discharge or overcharging. However, it only indirectly considers the actual state of charge of the battery and often operates inefficiently, as the alternator also supplies power when no immediate recharging is required.

[0006] Modern vehicles often use intelligent battery sensors (IBS) that measure temperature in addition to voltage and current. Temperature has a significant impact on battery performance, lifespan, and safety. Low temperatures increase internal resistance and reduce charging capacity, while high temperatures accelerate battery aging and, in extreme cases, can cause thermal damage. Continuous temperature monitoring helps keep the battery within its optimal operating range and prevents damage from overloading or adverse temperature conditions.

[0007] The IBS measurements enable a more precise determination of the state of charge and remaining capacity, as the battery's resting and charging voltages are highly temperature-dependent. This allows the charging strategy to be dynamically adjusted. At low temperatures, the charging current is limited to prevent damage, while at high temperatures, the charging power is reduced or a generator is switched off to prevent overheating. Additionally, temperature monitoring allows for the early diagnosis of problems, such as abnormalities in temperature behavior that indicate aging or malfunction.

[0008] An IBS can be used to record not only the state of charge (SoC) but also the remaining capacity (State of Health, SoH) and other battery condition parameters.

[0009] From DE 198 24 448 A1, a discharge protection device for electric batteries, particularly in motor vehicles, is known, with automatic shutdown of at least one electrical consumer in case of danger of excessive battery discharge, wherein a monitoring unit that detects both battery voltage and ambient temperature is coupled with a switch arranged in the electrical current path between the battery and the consumer and opens this switch when the actual value pair of battery voltage and ambient temperature is outside a predetermined setpoint field for sufficient battery charge.

[0010] In conventional low-voltage battery systems for motor vehicles, the low-voltage battery must be designed to meet all requirements. However, since the capacity decreases at low ambient temperatures and the performance of the low-voltage battery diminishes, either some vehicle systems may not be supported at low temperatures, or larger, heavier, and more expensive low-voltage batteries must be used.

[0011] The task therefore is to further develop methods for controlling the state of charge of a low-voltage battery of a motor vehicle, computer program products, vehicle electrical systems and motor vehicles of the type mentioned above in such a way that the vehicle electrical system of a motor vehicle can be operated with a compact low-voltage battery even at low temperatures.

[0012] The problem is solved by a method for controlling the state of charge of a low-voltage battery of a motor vehicle according to claim 1, a computer program product according to dependent claim 6, an on-board power supply according to dependent claim 7, and a motor vehicle according to dependent claim 8. Further embodiments and developments are the subject of the dependent claims.

[0013] A method for controlling the state of charge of a low-voltage battery of a motor vehicle is described, wherein the state of charge of the low-voltage battery and a battery temperature of the low-voltage battery are measured, wherein the low-voltage battery is charged at a state of charge lower than a limit state of charge, and wherein the limit state of charge is raised at a battery temperature below a limit temperature.

[0014] A low-voltage battery in motor vehicles is an electrical energy storage component with a nominal voltage typically of 12 volts (occasionally 24 volts in commercial vehicles) that powers the low-voltage electrical system. It is responsible for supplying essential vehicle functions, including starting, lighting, infotainment systems, and other electrical consumers. The most common technologies are lead-acid, AGM (absorbent glass mat), and increasingly, lithium-ion batteries.

[0015] By raising the threshold state of charge at temperatures below a certain limit temperature, it is possible for the low-voltage battery to continue charging at such temperatures and consequently provide more current at the same voltage.

[0016] However, this also prevents the charge level from remaining permanently elevated, which would reduce the usable charging range for discharge processes. Furthermore, at higher temperatures and with a higher charge level, energy consumption would increase due to the higher voltage. Additionally, a higher charge level generally has a negative impact on the aging of the low-voltage battery.

[0017] By raising the charge level of the low-voltage battery only at lower temperatures, it is therefore possible to largely prevent these undesirable side effects or to accept them only when necessary due to the temperatures.

[0018] In a first further development, it is provided that the limiting state of charge is lowered when the battery temperature exceeds a limit temperature.

[0019] Lowering and raising the state-of-charge threshold depending on the battery temperature can be implemented, for example, using a parameter table or a corresponding function. In one case, a discrete number of threshold temperatures are defined, to which corresponding state-of-charge thresholds are assigned. In the other case, the state-of-charge threshold can be continuously adjusted.

[0020] In a further, more advanced embodiment, it is provided that the low-voltage battery is charged by a high-voltage battery using a DCDC converter.

[0021] This is particularly useful for hybrid or electric vehicles. High-voltage batteries are typically used as traction batteries.

[0022] In a further, more advanced embodiment, it is provided that the limiting state of charge is adjusted by a control unit of an on-board network.

[0023] In a further, more advanced embodiment, it is provided that the limiting state of charge is adjusted depending on the condition of the motor vehicle.

[0024] This allows different driving programs to be taken into account, e.g. an economical mode or a sport mode.

[0025] A first independent subject matter relates to a computer program product comprising a computer-readable storage medium on which instructions are embedded which, when executed by at least one computing unit, cause that at least one computing unit to be equipped to execute the procedure of the aforementioned type.

[0026] The process can be executed on one or more computing units, so that certain process steps are executed on one computing unit and other process steps on at least one other computing unit, whereby calculated data can be transmitted between the computing units if necessary.

[0027] Another independent item relates to the electrical system of a motor vehicle, comprising a low-voltage battery, a temperature sensor for measuring battery temperature, and a control unit connected to the low-voltage battery and the temperature sensor, the control unit comprising the computer program of the type described above.

[0028] Another independent item concerns a motor vehicle with an on-board electrical system of the type described above.

[0029] In a first further development, it is provided that the vehicle electrical system has at least one high-voltage battery which can be connected to the low-voltage battery for charging the low-voltage battery via a DCDC converter.

[0030] Further advantages, features, and details will become apparent from the following description, in which – possibly with reference to the drawing – at least one embodiment is described in detail. Identical, similar, and / or functionally equivalent parts are identified by the same reference numerals.

[0031] The single figure schematically depicts a motor vehicle 2 with an on-board electrical system 3.

[0032] The vehicle electrical system 3 includes a low-voltage battery 4 and a high-voltage battery 6. The low-voltage battery 4 can be charged by the high-voltage battery 6 using a DC-DC converter 8, for which a corresponding switch 10 must be closed.

[0033] Furthermore, the high-voltage battery 6 serves to operate a high-voltage consumer 12, such as a drive motor.

[0034] The low-voltage battery 4 serves to supply consumers 14 to 20, for example a steering system, an audio system, lighting, cameras and the like.

[0035] The state of charge (SoC) of the low-voltage battery 4 is controlled by means of a control unit 22, which has a computing unit 24 with a memory 26 in which a computer program product 28 is stored, which, when loaded and executed by the computing unit 24, implements the procedure described here.

[0036] Furthermore, memory 26 contains a limit state of charge curve 30, which represents a limit state of charge SoCg as a function of a battery temperature T.

[0037] Alternatively, a limit temperature Tg can be defined at which the limit state of charge SoCg is adjusted.

[0038] The battery temperature T is measured using a temperature sensor 32, which is arranged on the low-voltage battery 24. In this way, the computer program 28 can determine a limit state of charge SoCg based on the input data of the temperature sensor 32 and, if necessary, increase the state of charge SoC of the low-voltage battery 4 by charging the low-voltage battery 4 from the high-voltage battery 6.

[0039] Although the invention has been further illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned as examples are truly only examples and are not to be understood in any way as limiting, for example, the scope of protection, the possible applications, or the configuration of the invention.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without leaving the scope of protection defined by the claims and their legal equivalents, such as a further explanation in the description. Reference symbol list 2 motor vehicles 3 On-board electrical system 4 low-voltage batteries 6 high-voltage batteries 8 DC-DC voltage converters 10 switches 12 high-voltage consumers 14 - 20 consumers 22 Control unit 24 computing units 26 storage 28 Computer program product 30 Limit state of charge curve 32 Temperature sensor SoC state of charge SoCg limit charge state Battery temperature Tg limit temperature QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 198 24 448 A1

[0009]

Claims

[1] Method for controlling the state of charge (SoC) of a low-voltage battery (4) of a motor vehicle (2), wherein the state of charge (SoC) of the low-voltage battery (4) and the battery temperature (T) of the low-voltage battery (4) are measured, wherein the low-voltage battery (4) is charged at a state of charge (SoC) lower than a limit state of charge (SoCg), characterized by , that the limiting state of charge (SoCg) is raised when the battery temperature (T) is below a limiting temperature (Tg). [2] Method according to claim 1, characterized by , that the limiting state of charge is lowered at a battery temperature (T) above a limit temperature (Tg). [3] Method according to claim 1 or 2, characterized by , that the low-voltage battery (4) is charged by a high-voltage battery (6) using a DCDC converter (8). [4] Method according to any of the preceding claims, characterized by, that the limiting state of charge (SoCg) is adjusted by a control unit (22) of an on-board network (3). [5] Method according to any of the preceding claims, characterized by , that the limiting state of charge (SoCg) is adjusted depending on a state of the motor vehicle (2). [6] Computer program product (28), comprising a computer-readable storage medium (26) on which instructions are embedded which, when executed by at least one computing unit (24), cause the at least computing unit (24) to be configured to execute the method according to one of the preceding claims. [7] On-board electrical system (3) of a motor vehicle (2), comprising a low-voltage battery (4), a temperature sensor (32) for measuring a battery temperature (T) and a control unit (22) connected to the low-voltage battery (4) and the temperature sensor (32), characterized by , that the control unit (22) comprises the computer program product (28) according to claim 6. [8] Motor vehicle (2) with an on-board electrical system according to claim 7. [9] Motor vehicle (2) according to claim 8, characterized by , that the vehicle electrical system (3) has at least one high-voltage battery (6) which can be connected to the low-voltage battery (4) for charging the low-voltage battery (4) via a DCDC converter (8).

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