On-board electrical system arrangement for a mild hybrid vehicle and mild hybrid vehicle with such an on-board electrical system arrangement, as well as methods for operating the on-board electrical system arrangement

Abstract

The invention relates to an on-board electrical system (2) for a mild hybrid vehicle (1), comprising, according to the invention: a powertrain on-board electrical system (4), two consumer on-board electrical systems (7, 9), a 48V battery (3) with two battery banks (3.1, 3.2) and a switching device (10) with two switching arrangements (10.1, 10.2) electrically connected in series, two disconnect switches (S5, S6), a DC-DC converter (11), two transfer switches (S7, S8), wherein the two battery banks (3.1, 3.2) can be connected in parallel via the switching device (10), and wherein the powertrain on-board electrical system (4) is connected to the first battery bank (3.1) via the DC-DC converter (11) and the first switching arrangement (10.1) and to the second battery bank via the DC-DC converter (11) and the second switching arrangement (10.2). (3.2) connectable or connected,- wherein the respective consumer electrical system (7, 9) is connected to the one battery bank (3.1, 3.3) via the respective disconnect switch (S5, S6).2) and can be connected or is connected to the other battery bank (3.2, 3.1) via the respective disconnect switch (S5, S6) and the switch assembly (10), - wherein the powertrain electrical system (4) can be connected or is connected to the first battery bank (3.1) via the first transfer switch (S7) and to the second battery bank (3.2) via the second transfer switch (S8).

Description

The invention relates to an on-board electrical system arrangement for a mild hybrid vehicle, a mild hybrid vehicle and a method for operating the on-board electrical system arrangement. A vehicle electrical system arrangement is known from the prior art, as described in DE 10 2023 001 735 A1. The invention is based on the objective of providing an improved on-board electrical system arrangement for a mild hybrid vehicle compared to the prior art, a mild hybrid vehicle improved compared to the prior art, and a method for operating the on-board electrical system arrangement improved compared to the prior art. The object is solved according to the invention by an on-board power supply arrangement for a mild hybrid vehicle with the features of claim 1, a mild hybrid vehicle with the features of claim 6 and a method for operating the on-board power supply arrangement with the features of claim 7. Advantageous embodiments of the invention are the subject of the dependent claims. An on-board electrical system arrangement according to the invention for a mild hybrid vehicle comprises a powertrain on-board electrical system with an integrated starter generator and powertrain components, a first consumer on-board electrical system with electrical consumers, a second consumer on-board electrical system with electrical consumers, a 48V battery, two disconnect switches, a DC voltage converter and two transfer switches. The first transfer switch and / or the second transfer switch are / are advantageously located in the 48V battery, i.e. the 48V battery has the first transfer switch and / or the second transfer switch. The DC-DC converter is specifically designed as a bidirectional DC-DC converter. The 48V battery comprises a first battery bank, in particular a 48V battery bank, a second battery bank, in particular a 48V battery bank, and a switching device with two electrically connected switch arrangements in series. The two battery banks can be electrically connected in parallel to each other via the switch device. The powertrain electrical system can be connected to the first battery bank via the DC / DC converter and the first switch arrangement, and to the second battery bank via the DC / DC converter and the second switch arrangement. The first consumer electrical system can be connected to the first battery bank via the first disconnect switch and to the second battery bank via the first disconnect switch and the switch assembly. The second consumer electrical system can be connected to the second battery bank via the second disconnect switch and to the first battery bank via the second disconnect switch and the switch assembly. The first switch arrangement comprises, from the direction of the first battery bank, a first parallel circuit consisting of a first discharge switch and a first diode forward-biased to the first battery bank, and a second parallel circuit consisting of a first charge switch and a second diode reverse-biased to the first battery bank. The first and second parallel circuits are electrically connected in series. The second switch arrangement features, from the direction of the second battery bank, a third parallel circuit consisting of a second discharge switch and a third diode forward-biased to the second battery bank, and a fourth parallel circuit consisting of a second charge switch and a fourth diode reverse-biased to the second battery bank. The third and fourth parallel circuits are electrically connected in series. The powertrain electrical system can be connected to the first battery bank via the first transfer switch and to the second battery bank via the second transfer switch. Each battery bank of the 48V battery has, in particular, a plurality of battery cells connected electrically in series and / or in parallel. A mild hybrid vehicle according to the invention has the following on-board electrical system arrangement. In a method according to the invention for operating the on-board electrical system, in particular in a mild hybrid vehicle, the charging switches, discharging switches and disconnect switches are or are closed in a normal operating state, the transfer switches are or are opened, the consumer on-board electrical systems are supplied with electrical energy by the 48V battery and the integrated starter generator charges the 48V battery via the DC voltage converter and supplies the powertrain on-board electrical system, in particular the powertrain components of the powertrain on-board electrical system, with electrical energy. It is specifically designed that, under normal operating conditions, if there is an electrical energy demand in the powertrain electrical system that cannot be met by the integrated starter generator, particularly due to dynamic processes within the powertrain electrical system, the system will be supplied with electrical energy from the 48V battery via the DC-DC converter. It is therefore specifically designed that, in such a case, particularly during dynamic processes within the powertrain electrical system, the DC-DC converter will switch rapidly from buck mode to boost mode and support the powertrain electrical system with electrical energy and thus electrical power. In this case, the 48V battery will no longer be charged by the integrated starter generator via the DC-DC converter. Starting from normal operating conditions, in the event of a fault in the first electrical system, for example a short circuit, undervoltage, or overvoltage, the first electrical system is electrically isolated from the second electrical system by opening the first disconnect switch. Alternatively or additionally, particularly as a backup, the first discharge switch and the first charge switch are opened to electrically isolate the first electrical system from the second electrical system. This prevents disruption to the second electrical system and ensures the continued electrical power supply to both the second electrical system and the powertrain electrical system. However, with the first discharge switch and first charge switch open, the power is supplied with reduced performance, solely by the second battery bank. Starting from normal operating conditions, in the event of a fault in the second electrical system, for example a short circuit, undervoltage, or overvoltage, the second electrical system is electrically isolated from the first electrical system by opening the second disconnect switch. Alternatively or additionally, particularly as a backup, the second discharge switch and the second charge switch are opened to electrically isolate the second electrical system from the first. This prevents disruption to the first electrical system and ensures the continued electrical power supply to both the first electrical system and the powertrain. However, with the second discharge switch and the second charge switch open, the power is supplied with reduced performance, solely by the first battery bank. Starting from normal operating conditions, in the event of a fault in the first battery bank, for example, a short circuit, undervoltage, or overvoltage, at least the first discharge switch and the first charge switch are opened. For example, the second discharge switch and the second charge switch are also opened, particularly as a backup. This ensures that the second battery bank is not affected. The electrical power supply to the powertrain components in the powertrain electrical system remains available, albeit with reduced performance, since only the second battery bank is available for this power supply if at least the second discharge switch remains closed. The electrical power supply to the second consumer electrical system also remains available, but again with reduced performance, since only the second battery bank is available for this power supply. Starting from normal operating conditions, in the event of a fault in the second battery bank, for example, a short circuit, undervoltage, or overvoltage, at least the second discharge switch and the second charge switch will open. Additionally, the first discharge switch and the first charge switch may also open, particularly as a backup. This ensures that the first battery bank is not affected. The electrical power supply to the powertrain components in the powertrain electrical system remains available, albeit with reduced performance, as only the first battery bank is available for this power supply if at least the first discharge switch remains closed. The electrical power supply to the first consumer electrical system also remains available, but again with reduced performance, as only the first battery bank is available for this power supply. Specifically, starting from normal operating conditions, in the event of a short circuit in a supply line to the powertrain electrical system between the switchgear and the DC / DC converter, both discharge switches are opened. This prevents disruption to the two electrical systems, which continue to be supplied with power by the 48V battery. The powertrain components within the electrical system can then be supplied with power by the internal starter generator and thus continue to operate (albeit with reduced performance). Starting from normal operating conditions, in the event of a fault in the powertrain electrical system, such as a short circuit, undervoltage, or overvoltage, the powertrain electrical system is electrically isolated from at least the two auxiliary electrical systems by means of the DC-DC converter. The DC-DC converter incorporates the necessary circuitry for this purpose. This isolates the fault via the DC-DC converter, preventing disruption to the auxiliary electrical systems, which continue to be supplied with electrical power by the 48V battery. Depending on the specific fault, the powertrain components within the powertrain electrical system can, for example, still be supplied with electrical power by the internal starter generator and thus continue to operate (albeit with reduced performance). If the two battery banks are separated from each other by the open discharge switches and / or charge switches, for example due to previously occurring faults, due to the opening of the discharge switches and / or charge switches in a parked state of the mild hybrid vehicle or due to other events, it is advantageous to equalize the charge states of the two battery banks in order to avoid high equalization currents. To equalize the charge levels of the two battery banks, if the first battery bank has the lower charge level, the second discharge switch and the first charge switch are closed, starting from at least the open second discharge switch, the open first charge switch, and the open transfer switches. The charge levels of the two battery banks are then equalized by charging the first battery bank with the second battery bank via the DC-DC converter. Afterwards, the first charge switch is closed, the first transfer switch is opened, and the first discharge switch is closed if it is not already closed. Finally, the second charge switch is closed if it is not already closed. This prevents a high equalization current. If the second battery bank has a lower state of charge, the following steps are taken to equalize the states of charge of the two battery banks: starting from at least the open first discharge switch, the open second charge switch, and the open transfer switches, the first discharge switch and the second transfer switch are closed, the states of charge of the two battery banks are equalized by charging the second battery bank using the first battery bank via the DC-DC converter, and then the second charge switch is closed, the second transfer switch is opened, and the second discharge switch is closed if it is not already closed, and the first charge switch is closed if it is not already closed. This prevents a high equalization current. This charging circuit makes it possible to carry out the described charging process of the battery banks to equalize their charge levels completely without using the integrated starter generator and therefore without starting the combustion engine of the mild hybrid vehicle. This allows the charging process to be carried out even when the mild hybrid vehicle is parked. The equalization of the charge states of the two battery banks is coordinated, for example, by a battery management system and / or on-board network management system and / or by another unit, in particular by another software unit. The opening of the respective discharge switch and / or the respective charging switch and / or the respective disconnect switch and / or the electrical isolation of the powertrain electrical system by means of the DC voltage converter, at least with respect to the two consumer electrical systems, is carried out in particular within a specified, in particular short, in particular very short, fault tolerance time. The powertrain electrical system has a voltage level of 48V. The first consumer electrical system has a voltage level of 48V. The second consumer electrical system has a voltage level of 48V. For example, it is intended that several electrical consumers are each connected to at least one of the two consumer vehicle electrical systems. For example, it is stipulated that safety-relevant electrical consumers are connected to both electrical systems. Safety-relevant consumers include, for example, a steering system and / or a braking system and / or an emergency call system and / or systems for carrying out automated, in particular highly automated, or autonomous driving operation and / or sensors, in particular environmental sensors and / or sensors for carrying out automated, in particular highly automated, or autonomous driving operation. Alternatively, it may be provided, for example, that the safety-relevant electrical consumers are each supplied with energy via redundant components, or that the safety-relevant electrical consumers, or at least one or more of the safety-relevant electrical consumers, are each connected to only one of the two consumer on-board networks. Electrical comfort features, such as seat heating and / or seat ventilation, can be connected to both electrical systems or to only one. For example, the electrical comfort features are distributed between the two electrical systems. It is specifically intended that the electrical consumers are connected to the respective vehicle electrical system via power distribution units. Each power distribution unit includes semiconductor switches and / or electronic fuses (eFuse) and a microcontroller for their control, and may also include, for example, additional or alternative fuses. Alternatively, the fuses can be located outside the power distribution units. These electrical power distribution units are also referred to as intelligent power distribution units. Advantageously, the respective vehicle electrical system has several such power distribution units through which the electrical consumers are connected. A power distribution unit that only includes fuses is also referred to as a fuse distribution unit. The respective disconnect switch is specifically designed as a semiconductor switch. The two disconnect switches are specifically designed to protect the battery cells in the event of short circuits or similar incidents in one of the two electrical systems. Each disconnect switch can be integrated, for example, into the 48V battery, one of the power distribution units, or several or all of the power distribution units in the respective electrical system. The electrical consumers in the respective consumer vehicle electrical system exhibit, in particular, ASIL-B(D) integrity. The entire electrical system arrangement, or at least the combined electrical system consisting of the two consumer electrical systems, advantageously meets overall integrity requirements of ASIL D and redundancy requirements, for example ADAS >= L3 and steer-by-wire (ADAS = Advanced Driver Assistance Systems). The 48V battery in the vehicle electrical system configuration has an ASIL D rating for energy availability. This ASIL rating can be internally broken down into the two 48V battery banks, each with an ASIL B(D). The two battery banks of the 48V battery can be separated in predefined fault cases, in particular to maintain independence between the two consumer electrical systems, especially by means of the charging and discharging switches. The two transfer switches serve, particularly in specific applications, to equalize the charge levels of the battery banks without having to use the integrated starter generator, as described above. Specifically, it is intended that each transfer switch is only closed for this purpose, as described above, and is otherwise open. The integrated starter generator and the powertrain components of the electrical system do not inherit the ASIL rating due to the isolation provided by the DC-DC converter. In the event of a fault, such as an impermissible overvoltage or undervoltage, or other fault conditions, the powertrain components of the electrical system can be isolated via the DC-DC converter. The DC-DC converter primarily serves to separate the powertrain electrical system from the two auxiliary electrical systems. This means that the auxiliary electrical systems are exempt from VDA320 testing; only the powertrain electrical system is subject to this requirement. The DC-DC converter is designed to be highly dynamic and capable of covering the full voltage range of the integrated starter generator. As mentioned above, the DC-DC converter is bidirectional, particularly due to the charging circuit described above and the resulting balancing of the battery bank charge levels, as well as the need to start the integrated starter generator and / or the combustion engine. The first consumer electrical system serves in particular to supply electrical power to all static and dynamic loads in the first consumer electrical system with an energy availability of ASIL B(D) through the 48V battery. The second consumer electrical system serves in particular to supply electrical power to all static and dynamic loads in the second consumer electrical system with an energy availability of ASIL B(D) through the 48V battery. At least one, several, or all of the switches in the 48V battery's switching assembly, and for example, at least one or both of the disconnect switches, can be implemented or are implemented with an ASIL rating of ASIL B(D). In the "non-conductive / open" operating state of the respective switch(es) or all of the switches in the switching assembly, and for example, at least one or both of the disconnect switches, the following tasks are performed in particular: In the event of faults, such as short circuits, or under- or overvoltage events in the supply line to the powertrain's electrical system or within the 48V battery, the switches in the switching assembly and / or one or both of the disconnect switches isolate the two electrical systems from each other within the specified fault tolerance time (which is particularly short and depends on the functional safety concept).This ensures the independence of the two electrical systems by maintaining a "non-conducting" state at predefined undervoltage and / or overvoltage thresholds, and / or at a predefined overcurrent, and / or at other predefined events. The fault tolerance time is defined, in particular, based on a functional safety concept. The described solution provides a redundant on-board network architecture with a DC / DC converter and a charging circuit for a mild hybrid vehicle. The solution described differs in particular from previously considered solutions for battery electric vehicles and mild hybrid vehicles. In considered solutions for battery electric vehicles with a high-voltage and a low-voltage electrical system, the low-voltage system has power supply safety requirements with a maximum ASIL D. To achieve overall integrity of ASIL D and meet redundancy requirements, the power supply requirements with ASIL D are decomposed into two ASIL B(D) components and allocated to two independent power supply channels of the low-voltage electrical system. All power supply channels must be independent of each other according to ISO 26262-9:2018 with ASIL D; a fault in one power supply channel must not affect the other. By using highly available and highly dynamic DC-DC converters with direct connection to a high-voltage battery, the low-voltage power supply channels can be implemented "battery-free," meaning no low-voltage battery is required.Due to the overall integrity of ASIL D, the high-voltage battery must also have ASIL D, which can be achieved by dividing it into two separate high-voltage banks. In the solutions under consideration for mild hybrid vehicles, the low-voltage electrical system has safety requirements for the power supply with a maximum ASIL D. For this purpose, the low-voltage electrical system is divided into three sub-systems, each with different voltage levels: the powertrain electrical system with the integrated starter generator and powertrain components at 48V, a first sub-system with low-voltage consumers at 12V, and a second sub-system with redundant low-voltage consumers at 12V. Each of these 12V sub-systems requires a DC / DC converter to supply the static loads and a 12V battery to supply the dynamic loads, with each 12V battery having an energy availability of ASIL B(D). The problem with this proposed solution for mild hybrid vehicles, which differs from the one described here, is that for the on-board networks with ASIL-D classification in mild hybrid vehicles, two DC voltage converters and three low-voltage batteries (two 12V batteries and one 48V battery) must be installed, resulting in significant cost, weight and installation space disadvantages. The solution described here solves this problem through the described redundant mild hybrid vehicle electrical system architecture using only one battery, namely the 48V battery, and one DC voltage converter, while complying with all ASIL-D requirements. The solution described here offers the following advantages: It eliminates the need for additional low-voltage batteries and a DC / DC converter, as only a single 48V battery and one DC / DC converter are required. The 48V battery powers both the propulsion system and the electrical systems for other components, including safety-related equipment. This results in significant cost, weight, and space savings. ASIL-D requirements are met with just one 48V battery and one DC-DC converter. Additional low-voltage batteries or DC-DC converters are not required. A high level of power reliability is ensured. The described solution advantageously allows the use of modular components in the consumer electrical systems, since the DC / DC converter advantageously regulates the voltage of the two consumer electrical systems to standard voltage ranges (for example, VDA320). Separating the electrical systems for electrical consumers from the powertrain electrical system via the DC / DC converter advantageously allows for the reuse of electrical systems from battery-electric vehicles, thus reducing variance. Furthermore, there is no need to comply with VDA 320 requirements for the electrical systems for electrical consumers, resulting in cost reductions for their electrical consumers and / or ECUs (electronic control units). VDA 320 requirements can arise from desired behavior of the powertrain components, such as a start pulse. ASIL-D independence is not allocated to the integrated starter generator because it is separated via the DC-DC converter. Each switch / switch pair consisting of a discharge switch and a charge switch has an ASIL B(D) rating, not a pure ASIL D rating. The described configuration of the 48V battery with two electrically parallel connected or switchable battery banks, also known as the 2P battery configuration, is also required for performance reasons of the powertrain and is therefore advantageously already provided for. The charging process when the two battery banks have unequal charge levels, i.e., to equalize the charge levels of the battery banks, can be implemented via the DC voltage converter and the respective charging switch, and thus without the integrated starter generator, i.e., without starting it or without starting the combustion engine using the integrated starter generator. The term "voltage level" used in this application text refers in particular to a nominal voltage of the respective vehicle electrical system. The abbreviation ASIL used in this application text stands for Automotive Safety Integrity Level and is in particular a safety requirement level specified by ISO 26262, especially ISO-26262-9:2018, for safety-related systems in motor vehicles. The mild hybrid vehicle mentioned in this application is a motor vehicle, in particular a motor vehicle with at least one internal combustion engine as a drive engine in a drive train of the motor vehicle and with the starter generator, in particular the starter generator integrated into the drive train, which is designed, set up and arranged in the motor vehicle to be used for driving the motor vehicle, for recuperating electrical energy and in particular also for starting the internal combustion engine. Exemplary embodiments of the invention are explained in more detail below with reference to drawings. Figure 1 schematically shows a mild hybrid vehicle with an exemplary embodiment of an on-board electrical system arrangement; Figure 2 schematically shows the mild hybrid vehicle with the embodiment of the on-board electrical system arrangement according to Figure 1 in the event of a fault in a first consumer on-board electrical system of the on-board electrical system arrangement; Figure 3 schematically shows the mild hybrid vehicle with the embodiment of the on-board electrical system arrangement according to Figure 1 in the event of a fault in a first battery bank of a 48V battery of the on-board electrical system arrangement; Figure 4 schematically shows the mild hybrid vehicle with the embodiment of the on-board electrical system arrangement according to Figure 1 in the event of a fault in an access point to a powertrain on-board electrical system of the on-board electrical system arrangement; Figure 5 schematically shows the mild hybrid vehicle with the embodiment of the on-board electrical system arrangement according to Figure 1 in the event of a fault in the powertrain on-board electrical system of the on-board electrical system arrangement; and Figure 6 schematically shows the mild hybrid vehicle with the embodiment of the on-board electrical system arrangement according to Figure 1.1 when equalizing the charge levels of battery banks of the 48V battery of the on-board electrical system. Corresponding parts are marked with the same reference symbols in all figures. With reference to Figures 1, 2, 3, 4, 5 to 6, a mild hybrid vehicle 1 with an electrical system 2 and a method for operating the electrical system 2 are described below. The electrical system 2 is shown in Figure 1 in a normal operating state, in Figures 2, 3, 4 to 5 under various fault conditions, and in Figure 6 during the equalization of charge states of battery banks 3.1, 3.2 of a 48V battery 3 of the electrical system 2. The on-board electrical system 2 comprises a powertrain on-board electrical system 4 with an integrated starter generator 5 and powertrain components 6, a first consumer on-board electrical system 7 with electrical consumers 8, a second consumer on-board electrical system 9 with electrical consumers 8, the 48V battery 3, two disconnect switches S5, S6, a DC voltage converter 11 and two transfer switches S7, S8. The respective disconnect switch S5, S6 is designed in particular as a semiconductor switch. In the illustrated embodiment, the two transfer switches S7, S8 are arranged in the 48V battery 3. The DC voltage converter 11 is designed as a bidirectional DC voltage converter 11. The powertrain electrical system 4 has a voltage of 48V. The first consumer electrical system 7 has a voltage of 48V. The second consumer electrical system 9 has a voltage of 48V. For example, it is provided that several electrical consumers 8 are each connected to at least one of the two consumer on-board networks 7, 9. For example, it is provided that safety-relevant electrical consumers 8 are each connected to both consumer on-board networks 7, 9. Safety-relevant consumers 8 include, for example, the steering device and / or the braking device and / or the emergency call device and / or systems for carrying out automated, in particular highly automated, or autonomous driving operation and / or sensors, in particular environmental detection sensors and / or sensors for carrying out automated, in particular highly automated, or autonomous driving operation. Alternatively, it may be provided, for example, that the safety-relevant electrical consumers 8 are each supplied with energy via redundant components, or that the safety-relevant electrical consumers 8, or at least one or more of the safety-relevant electrical consumers 8, are each connected to only one of the two consumer on-board networks 7, 9. Electrical consumers 8 designed as electrical comfort consumers, for example seat heaters and / or seat ventilated seats, can, for example, be connected to both electrical systems 7, 9 or to only one of the two electrical systems 7, 9. For example, the electrical consumers 8 designed as electrical comfort consumers are distributed between the two electrical systems 7, 9. It is specifically provided that the electrical loads 8 are connected to the respective electrical system 7, 9 via power distribution units (not shown), wherein each power distribution unit comprises semiconductor switches and / or electronic fuses (eFuse) and a microcontroller for their control, and, for example, additionally or alternatively, fuse links. Alternatively, the fuse links can also be located outside the power distribution units. These electrical power distribution units are also referred to as intelligent power distribution units. Advantageously, each electrical system 7, 9 has several such power distribution units, via which the electrical loads 8 are connected to the respective electrical system 7, 9. A power distribution unit that only has fuse links is also referred to as a fuse link distributor. The 48V battery 3 comprises the first battery bank 3.1, configured as a 48V battery bank, the second battery bank 3.2, configured as a 48V battery bank, and a switching device 10 with two electrically connected switch arrangements 10.1, 10.2 in series. The two battery banks 3.1, 3.2 can be electrically connected in parallel to each other via the switching device 10. The powertrain electrical system 4 can be connected or is connected to the first battery bank 3.1 via the DC voltage converter 11 and the first switch arrangement 10.1 and to the second battery bank 3.2 via the DC voltage converter 11 and the second switch arrangement 10.2. The first consumer electrical system 7 can be connected to the first battery bank 3.1 via the first disconnect switch S5 and to the second battery bank 3.2 via the first disconnect switch S5 and the switch assembly 10. The second consumer electrical system 9 can be connected to the second battery bank 3.2 via the second disconnect switch S6 and to the first battery bank 3.1 via the second disconnect switch S6 and the switch assembly 10. The first switch arrangement 10.1, from the direction of the first battery bank 3.1, has the first parallel circuit consisting of the first discharge switch S1 and the first diode D1, forward-biased towards the first battery bank 3.1, and the second parallel circuit consisting of the first charge switch S3 and the second diode D2, reverse-biased towards the first battery bank 3.1. The first and second parallel circuits are electrically connected in series. The second switch arrangement 10.2, from the direction of the second battery bank 3.2, has the third parallel circuit consisting of the second discharge switch S2 and the third diode D3, forward-biased to the second battery bank 3.2, and the fourth parallel circuit consisting of the second charge switch S4 and the fourth diode D4, reverse-biased to the second battery bank 3.2. The third and fourth parallel circuits are electrically connected in series. The powertrain electrical system 4 can be connected to the first battery bank 3.1 via the first transfer switch S7 and to the second battery bank 3.2 via the second transfer switch S8. The two disconnect switches S5, S6 are specifically designed to protect battery cells of battery banks 3.1, 3.2 of the 48V battery 3 in the event of short circuits or similar incidents in one of the two electrical systems 7, 9. The respective disconnect switch S5, S6 can be integrated, for example, into the 48V battery 3, as in the embodiment shown here, or into one of the power distribution units, or into several or all of the power distribution units of the respective electrical system 7, 9. In the method for operating the on-board electrical system 2, in the normal operating state, as shown in Fig. 1, the charging switches S3, S4, discharging switches S1, S2 and disconnect switches S5, S6 are or will be closed, the transfer switches S7, S8 are or will be opened, the consumer on-board electrical systems 7, 9 are supplied with electrical energy by the 48V battery 3 and the integrated starter generator 5 charges the 48V battery 3 via the DC voltage converter 11 and supplies the powertrain on-board electrical system 4, in particular the powertrain components 6 of the powertrain on-board electrical system 4, with electrical energy. It is specifically designed that, under normal operating conditions, if there is an electrical energy demand in the powertrain electrical system 4 that cannot be met by the integrated starter generator 5, particularly if this demand arises due to dynamic processes within the powertrain electrical system 4, the powertrain electrical system 4 will be supplied with electrical energy from the 48V battery 3 via the DC-DC converter 11. It is therefore specifically designed that, in such a case, particularly during dynamic processes within the powertrain electrical system 4, the DC-DC converter 11 will quickly switch from buck mode to boost mode and support the powertrain electrical system 4 with electrical energy and thus electrical power. In this case, the 48V battery 3 will no longer be charged by the integrated starter generator 5 via the DC-DC converter 11. In the event of a fault in the first electrical system 7, schematically represented by a fault symbol F in Fig. 2, for example a short circuit, undervoltage or overvoltage, the first electrical system 7 is electrically isolated from at least the second electrical system 9 within a predetermined fault tolerance time by opening the first disconnect switch S5. Alternatively or additionally, particularly as a fallback, the first discharge switch S1 and the first charge switch S3 are opened, for example, to electrically isolate the first electrical system 7 from at least the second electrical system 9 within the predetermined fault tolerance time.This ensures that the second consumer electrical system 9 is not disturbed and the electrical power supply of the second consumer electrical system 9 and the powertrain electrical system 4 remains ensured, although with the first discharge switch S1 and first charge switch S3 open, the power is supplied with reduced performance only by the second battery bank 3.2. In the event of a fault in the second electrical system 9, for example a short circuit, undervoltage, or overvoltage, the second electrical system 9 is electrically isolated from the first electrical system 7 within the specified fault tolerance time by opening the second disconnect switch S6. Alternatively or additionally, particularly as a fallback, the second discharge switch S2 and the second charge switch S4 are opened to electrically isolate the second electrical system 9 from the first electrical system 7 within the specified fault tolerance time. This prevents disruption to the first electrical system 7 and ensures the continued electrical power supply to the first electrical system 7 and the powertrain electrical system 4. However, with the second discharge switch S2 and second charge switch S4 open, the power supply is reduced and provided solely by the first battery bank 3.1.In the event of a fault in the first battery bank 3.1, schematically represented by a fault symbol F in Fig. 3, for example a short circuit, undervoltage or overvoltage, at least the first discharge switch S1 and the first charge switch S3 are opened within the specified fault tolerance time. For example, within the specified fault tolerance time, the second discharge switch S2 and the second charge switch S4 are also opened, particularly as a fallback. This ensures that the second battery bank 3.2 is not affected. The electrical power supply to the powertrain components 6 in the powertrain electrical system 4 then remains, albeit with reduced performance, since only the second battery bank 3.2 is available.2 is available for this electrical power supply if at least the second discharge switch S2 remains closed, and the electrical power supply in the second consumer on-board network 9, but here also with reduced performance, since only the second battery bank 3.2 is available for this electrical power supply. In the event of a fault in the second battery bank 3.2, for example a short circuit, undervoltage, or overvoltage, at least the second discharge switch S2 and the second charge switch S4 will open within the specified fault tolerance time. For example, within the specified fault tolerance time, the first discharge switch S1 and the first charge switch S3 will also open, particularly as a fallback. This ensures that the first battery bank 3.1 is not affected. The electrical power supply to the powertrain components 6 in the powertrain electrical system 4 will then remain available, albeit with reduced performance, since only the first battery bank 3.1 is available for this power supply if at least the first discharge switch S1 remains closed. The electrical power supply in the first consumer electrical system 7 will also remain available, but again with reduced performance, since only the first battery bank 3.1 is available.1 is available for this electrical power supply. In the event of a fault, schematically represented by fault symbol F in Fig. 4, caused by a short circuit in an access line 12 to the powertrain electrical system 4 between the switch assembly 10 and the DC-DC converter 11, both discharge switches S1 and S2 are opened within the specified fault tolerance time. This prevents disruption to the two consumer electrical systems 7 and 9, which continue to be supplied with electrical energy by the 48V battery 3. The powertrain components 6 in the powertrain electrical system 4 can be supplied with electrical energy by the internal starter generator 5 and thus continue to operate. In the event of a fault in the powertrain electrical system 4, schematically represented by a fault symbol F in Fig. 5, for example a short circuit, undervoltage, or overvoltage, the powertrain electrical system 4 is electrically isolated from at least the two consumer electrical systems 7 and 9 by means of the DC-DC converter 11, advantageously within the specified fault tolerance time. This isolates the fault via the DC-DC converter 11, preventing disruption to the consumer electrical systems 7 and 9, which then continue to be supplied with electrical energy by the 48V battery 3. Depending on the specific fault, the powertrain components 6 in the powertrain electrical system 4 can, for example, still be supplied with electrical energy by the internal starter generator 5 and thus continue to operate. If the two battery banks 3.1, 3.2 are separated from each other by the open discharge switches S1, S2 and charge switches S3, S4, for example due to previously occurring faults, due to the opening of the discharge switches S1, S2 and charge switches S3, S4 in a parked state of the mild hybrid vehicle 1 or due to other events, it is advantageous to equalize the charge states of the two battery banks 3.1, 3.2 in order to avoid high equalization currents. To equalize the charge states of the two battery banks 3.1, 3.2, if, as shown in Fig. 6, the first battery bank 3.1 has the lower charge state, the second discharge switch S2 and the first charge switch S7 are closed, starting from at least the open second discharge switch S2, the open first charge switch S3, and the open transfer switches S7, S8. The charge states of the two battery banks 3.1, 3.2 are then equalized by charging the first battery bank 3.1 with the second battery bank 3.2 via the DC-DC converter 11. Afterwards, the first charge switch S3 is closed, the first transfer switch S7 is opened, and the first discharge switch S1 is closed if it is not already closed, and the second charge switch S4 is closed if it is not already closed. This prevents a high equalization current. If the second battery bank 3.2 has a lower state of charge, the following steps are taken to equalize the states of charge of the two battery banks 3.1 and 3.2: Starting from at least the open first discharge switch S1, the open second charge switch S4, and the open transfer switches S7 and S8, the first discharge switch S1 and the second transfer switch S8 are closed. The states of charge of the two battery banks 3.1 and 3.2 are then equalized by charging the second battery bank 3.2 using the first battery bank 3.1 via the DC-DC converter 11. Afterward, the second charge switch S4 is closed, the second transfer switch S8 is opened, and the second discharge switch S2 is closed if it is not already closed, and the first charge switch S3 is closed if it is not already closed. This prevents a high equalization current. This charging circuit makes it possible to carry out the described charging process of battery banks 3.1 and 3.2 to equalize their charge states completely without using the integrated starter generator 5 and therefore without starting the combustion engine of the mild hybrid vehicle 1. This allows the charging process to be carried out even when the mild hybrid vehicle 1 is parked. The two transfer switches S7 and S8 thus serve, particularly in specific applications, to equalize the charge states of battery banks 3.1 and 3.2 without having to use the integrated starter generator 5. It is specifically intended that the respective transfer switch S7 or S8 is only closed for this purpose and otherwise remains open. The equalization of the charge states of the two battery banks 3.1, 3.2 is coordinated, for example, by a battery management system and / or on-board network management system and / or by another unit, in particular by another software unit. Reference symbol list 1 Mild hybrid vehicle 2 On-board electrical system layout 3 48V battery 3.1 First battery bank 3.2 Second battery bank 4 Powertrain electrical system 5 Starter generator 6 Powertrain component 7 First consumer electrical system 8 Consumers 9 Second consumer electrical system 10 Switching arrangement 10.1 First switch arrangement 10.2 Second switch arrangement 11 DC / DC converter 12 Access line D1 First diode D2 Second diode D3 Third diode D4 Fourth diode F Fault symbol S1 First discharge switch S2 Second discharge switch S3 First charge switch S4 Second charge switch S5 First disconnect switch S6 Second disconnect switch S7 First transfer switch S8 Second transfer switch

Claims

On-board electrical system arrangement (2) for a mild hybrid vehicle (1), characterized by: - ​​a powertrain on-board electrical system (4) with an integrated starter generator (5) and powertrain components (6), - a first consumer on-board electrical system (7) with electrical consumers (8), - a second consumer on-board electrical system (9) with electrical consumers (8), - a 48V battery (3) comprising a first battery bank (3.1), a second battery bank (3.2) and a switching device (10) with two switching arrangements (10.1, 10.2) electrically connected in series, - two disconnect switches (S5, S6), - a DC-DC converter (11), and - two transfer switches (S7, S8), - wherein the two battery banks (3.1, 3.2) can be electrically connected in parallel to each other via the switching device (10), - wherein the powertrain on-board electrical system (4) is connected via the DC-DC converter (11) and the first switching arrangement (10.1) with the first battery bank (3rd1) and is connectable or connected to the second battery bank (3.2) via the DC-DC converter (11) and the second switch arrangement (10.2),- wherein the first consumer electrical system (7) is connectable or connected to the first battery bank (3.1) via the first disconnect switch (S5) and to the second battery bank (3.2) via the first disconnect switch (S5) and the switch arrangement (10),- wherein the second consumer electrical system (9) is connectable or connected to the second battery bank (3.2) via the second disconnect switch (S6) and to the first battery bank (3.1) via the second disconnect switch (S6) and the switch arrangement (10),- wherein the first switch arrangement (10.1) provides a first parallel circuit from the direction of the first battery bank (3.1) consisting of a first discharge switch (S1) and a first diode (D1) with forward bias towards the first battery bank (3.1) and a second parallel circuit comprising a first charging switch (S3) and a second diode (D2) with reverse bias towards the first battery bank (3.1), wherein the first and second parallel circuits are electrically connected in series,- wherein the second switch arrangement (10.2) from the direction of the second battery bank (3.2) comprises a third parallel circuit comprising a second discharge switch (S2) and a third diode (D3) with forward bias towards the second battery bank (3.2) and a fourth parallel circuit comprising a second charging switch (S4) and a fourth diode (D4) with reverse bias towards the second battery bank (3.2), wherein the third and fourth parallel circuits are electrically connected in series, and- wherein the powertrain electrical system (4) can be connected to or is connected to the first battery bank (3.1) via the first transfer switch (S7) and can be connected to or is connected to the second battery bank (3.2) via the second transfer switch (S8). On-board electrical system arrangement (2) according to claim 1, characterized in that the first transfer switch (S7) and / or the second transfer switch (S8) are arranged in the 48V battery (3). On-board electrical system arrangement (2) according to one of the preceding claims, characterized in that the DC voltage converter (11) is designed as a bidirectional DC voltage converter (11). On-board network arrangement (2) according to one of the preceding claims, characterized in that safety-relevant electrical consumers (8) are each connected to both consumer on-board networks (7, 9). On-board network arrangement (2) according to one of the preceding claims, characterized in that the electrical consumers (8) are connected to the respective consumer on-board network (7, 9) via power distributors, wherein the respective power distributor has semiconductor switches and a microcontroller for controlling them. Mild hybrid vehicle (1) comprising an on-board electrical system arrangement (2) according to one of the preceding claims. Method for operating an on-board electrical system arrangement (2) according to any one of claims 1 to 5, in particular in a mild hybrid vehicle (1) according to claim 6, wherein: - in a normal operating state the charging switches (S3, S4), discharging switches (S1, S2) and disconnect switches (S5, S6) are closed or become closed, the transfer switches (S7, S8) are open or become open, the consumer on-board electrical systems (7, 9) are supplied with electrical energy by the 48V battery (3) and the integrated starter generator (5) charges the 48V battery (3) via the DC-DC converter (11) and supplies the powertrain on-board electrical system (4) with electrical energy, - in the event of a fault in the first consumer on-board electrical system (7), the first consumer on-board electrical system (7) is electrically isolated from at least the second consumer on-board electrical system (9) by opening the first disconnect switch (S5),- in the event of a fault in the second consumer electrical system (9), the second consumer electrical system (9) is electrically isolated from the first consumer electrical system (7) by opening the second disconnect switch (S6), - in the event of a fault in the first battery bank (3.1), at least the first discharge switch (S1) and the first charge switch (S3) are opened, - in the event of a fault in the second battery bank (3.2), at least the second discharge switch (S2) and the second charge switch (S4) are opened, - in the event of a fault due to a short circuit in an access line (12) to the powertrain electrical system (4) between the switch assembly (10) and the DC-DC converter (11), both discharge switches (S1, S2) are opened, - in the event of a fault in the powertrain electrical system (4), the powertrain electrical system (4) is electrically isolated from the two consumer electrical systems (7, 9) by means of the DC-DC converter (11), and - to equalize the charge states of the two battery banks (3.1,3.2) to each other, if the first battery bank (3.1) has the lower state of charge, starting from at least the open second discharge switch (S2), the open first charge switch (S3) and the open transfer switches (S7, S8), the second discharge switch (S2) and the first transfer switch (S7) are closed, the states of charge of the two battery banks (3.1, 3.2) are equalized by charging the first battery bank (3.1) using the second battery bank (3.2) via the DC-DC converter (11), and then the first charge switch (S3) is closed, the first transfer switch (S7) is opened, the first discharge switch (S1) is closed if it is not already closed, and the second charge switch (S4) is closed if it is not already closed, and if the second battery bank (3.2) has the lower state of charge, starting from at least the open first discharge switch (S1),From the open second charging switch (S4) and from the open transfer switches (S7, S8), the first discharge switch (S1) and the second transfer switch (S8) are closed, the charge states of the two battery banks (3.1, 3.2) are equalized by charging the second battery bank (3.2) using the first battery bank (3.1) via the DC-DC converter (11), and then the second charging switch (S4) is closed, the second transfer switch (S8) is opened, the second discharge switch (S2) is closed if it is not already closed, and the first charging switch (S3) is closed if it is not already closed. Method according to claim 7, characterized in that, in the normal operating state, when there is an electrical energy demand in the powertrain on-board network (4) which cannot be met by the integrated starter generator (5), the powertrain on-board network (4) is supplied with electrical energy from the 48V battery (3) via the DC voltage converter (11). Method according to claim 7 or 8, characterized in that the equalization of the charge states of the two battery banks (3.1, 3.2) is coordinated by a battery management system and / or vehicle electrical system management system. Method according to one of claims 7 to 9, characterized in that the opening of the respective discharge switch (S1, S2) and / or the respective charging switch (S3, S4) and / or the respective disconnect switch (S5, S6) and / or the electrical isolation of the powertrain on-board network (4) by means of the DC voltage converter (11) is carried out at least with respect to the two consumer on-board networks (7, 9) within a predetermined fault tolerance time.

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