DE102010029788B4 - Vehicle electrical system and method and device for operating the vehicle electrical system - Google Patents

Abstract

Vehicle electrical system for a motor vehicle comprising- a first vehicle electrical system branch (BN1), which has:- a first energy store (ES1) with a first connection (KN1_BN1) and a second connection (KN2_BN1), the second connection (KN2_BN1) being connected to a reference potential (GND ) is electrically coupled, - a generator (G), which is coupled to the first connection (KN1_BN1) of the first energy store (ES1), - at least one first consumer (V1), which is connected to the first connection (KN1_BN1) of the first energy store ( ES1) can be electrically coupled, and- at least one second vehicle electrical system branch (BN2), which has:- a second energy store (ES2) with a first connection (KN1_BN2) and a second connection (KN2_BN2), the second connection (KN2_BN2) of the second Energy store (ES2) is electrically coupled to the reference potential (GND),- at least one second consumer (A) connected to the first connection (KN1_BN2) of the second energy store (ES2) and/or to the first connection (KN1_BN1) of the first energy store (ES1) can be electrically coupled, and- an energy flow controller (DCW) with a first connection (T1) and a second connection (T2), the second connection (T2) of the energy flow controller (DCW) being electrically coupled to the first connection (KN1_BN2 ) of the second energy store (ES2) and the first connection (T1) of the energy flow controller (DCW) can be electrically coupled to the first connection (KN1_BN1) of the first energy store (ES1)- a switching element (S2) is designed and arranged in such a way that- in a first switching position of the switching element (S2), the first connection (KN1_BN2) of the second energy storage device (ES2) and the first connection (KN1_BN1) of the first energy storage device (ES1) are electrically coupled and- in a second switching position of the switching element (S2) the first connection ( KN1_BN2) of the second energy store (ES2) and the first connection (KN1_BN1) of the first energy store (ES1) are electrically decoupled,- at least one third vehicle electrical system branch (BN3), which has:- a third energy store (ES3) with a first connection (KN1_BN3 ) and a second connection (KN2_BN3), the second connection (KN2_BN3) of the third energy store (ES3) being electrically coupled to the reference potential (GND) and the first connection (KN1_BN3) of the third energy store (ES3) being electrically coupled to the first Connection (T1) of the energy flow controller (DCW) and can be electrically coupled to the first connection (KN1_BN1) of the first energy store (ES1), - a further switching element (S3) is designed and arranged in such a way that - in a first switching position of the further switching element (S3 ) the first connection (KN1_BN1) of the first energy store (ES1) is electrically coupled to the first connection (KN1_BN3) of the third energy store (ES3) and the first connection (T1) of the energy flow controller (DCW) of the second vehicle electrical system (BN2) and-in a second switching position of the further switching element (S3) the first connection (KN1_BN1) of the first energy store (ES1) is electrically decoupled from the first connection (KN1_BN3) of the third energy store (ES3) and the first connection (KN1_BN3) of the third energy store (ES3) is electrically coupled to the first connection (T1) of the energy flow controller (DCW) of the second vehicle electrical system (BN2).

Description

The invention relates to an electrical system for a motor vehicle and a method and a device for operating the electrical system.

In modern motor vehicles, high demands are placed on an on-board electrical system with an electrical energy store, particularly in motor vehicles that have an automatic start-stop system, for example. Starting the engine requires a lot of power, which has to be provided by the vehicle electrical system.

The document DE10322875A1 relates to an arrangement for supplying power to a number of consumers, in particular for a vehicle. The arrangement has at least two energy stores on board network, of which a first energy store is connected in a starter sub-circuit with a starter for starting an engine, and of which a second energy store is connected in a consumer sub-circuit with the consumers. The starter pitch circuit is connected to the consumer pitch circuit via a coupling element, with a number of consumers classified as safety-relevant being able to be connected to the starter pitch circuit via an additional coupling element.

The document DE10305357A1 relates to a device for supplying energy to an on-board network with a starter generator mechanically coupled to an internal combustion engine, with an AC/DC converter connected downstream, the DC connection of which is connected via a first switch to a first accumulator, which supplies energy to a first on-board network and its loads, is connected, is connected via a second switch to a double-layer capacitor, and in the case of a two-voltage vehicle electrical system is additionally connected via a bidirectional DC/DC converter to a second accumulator, which supplies a second vehicle electrical system and its loads with energy.

The document DE102005051433A1 relates to a method for controlling a generator in a two-voltage vehicle electrical system of a motor vehicle, with a first voltage circuit to which the generator is assigned and whose voltage level is variably controlled within a voltage interval depending on the operating conditions of the vehicle, and with a second voltage circuit whose voltage level is is the lower limit of the voltage interval, with a capacitor that is assigned to the first voltage circuit and with a vehicle battery that is assigned to the second voltage circuit, with a coupling device via which the two voltage circuits are coupled and which has a linear regulator and a DC voltage converter, and with a recuperation device for recovering braking energy, in which a charging control is provided which controls a charging process of the capacitor and in which a discharging control is provided which controls a discharging process of the capacitor.

The document DE102007037937A1 relates to a vehicle electrical system with a first vehicle electrical system branch or vehicle electrical system area, which contains a first, in particular "critical", electrical consumer and a voltage source connected in parallel thereto, and a second vehicle electrical system branch or vehicle electrical system area, which contains a second, in particular "sensitive" consumer and a third consumer contains. In addition, a particularly unidirectional DC-DC converter is provided, through which the first vehicle electrical system branch can be coupled to the second vehicle electrical system branch, in particular in order to supply the second vehicle electrical system branch with a voltage that is more stable than the voltage in the first vehicle electrical system branch. The second load can be coupled to the first or the second vehicle electrical system branch by a first switching device. The third load can be coupled to the first or the second vehicle electrical system branch by a second switching device.

The object on which the invention is based is to create an on-board power supply system of a motor vehicle and a method and a corresponding device for operating the on-board power supply system, which enables consumers to be operated reliably.

The object is solved by the features of the independent patent claim. Advantageous developments of the invention are characterized in the dependent claims.

According to a first aspect, the invention is characterized by an on-board network for a motor vehicle, which includes a first on-board network branch, a second on-board network branch and at least a third on-board network branch. The first vehicle electrical system branch has a first energy store with a first connection and a second connection, the second connection being electrically coupled to a reference potential. Furthermore, the first vehicle electrical system branch has a generator which is coupled to the first connection of the first energy store. Furthermore, the first vehicle electrical system branch has at least one first consumer, which can be electrically coupled to the first connection of the first energy store. The second vehicle electrical system branch has a second energy store with a first connection and a second connection, the second connection of the second energy store being electrically coupled to the reference potential. Furthermore, the second vehicle electrical system branch on at least one second consumer, which can be electrically coupled to the first connection of the second energy store and/or to the first connection of the first energy store. Furthermore, the second vehicle electrical system branch has an energy flow controller with a first connection and a second connection, the second connection of the energy flow controller being electrically coupled to the first connection of the second energy store and the first connection of the energy flow controller being electrically coupled to the first connection of the first energy store. Furthermore, the second branch of the vehicle electrical system has a switching element which is designed and arranged in such a way that in a first switching position of the switching element the first connection of the second energy store and the first connection of the first energy store are electrically coupled and in a second switching position of the switching element the first connection of the second energy store and the first connection of the first energy store are electrically decoupled. The third branch of the vehicle electrical system has a third energy store with a first connection and a second connection, the second connection of the third energy store being electrically coupled to the reference potential and the first connection of the third energy store being electrically coupled to the first connection of the energy flow controller and being able to be electrically coupled to the first connection of the first energy store. Furthermore, the third branch of the vehicle electrical system has a further switching element, which is designed and arranged in such a way that in a first switching position of the further switching element, the first connection of the first energy storage device is electrically coupled to the first connection of the third energy storage device and the first connection of the energy flow controller of the second vehicle electrical system and in a second switching position of the further switching element, the first connection of the first energy store is electrically decoupled from the first connection of the third energy store and the first connection of the third energy store is electrically coupled to the first connection of the energy flow controller of the second vehicle electrical system.

The energy flow controller can, for example, be directly electrically coupled to the first connection of the first energy storage device or can be electrically coupled to the first connection of the first energy storage device, for example by means of a switch. Advantageously, at least two energy storage devices are available, the first energy storage device being coupled to the second energy storage device by means of the energy flow controller in such a way that, depending on requirements, energy can be fed in from the second vehicle electrical system branch into the first vehicle electrical system branch or from the first vehicle electrical system branch into the second vehicle electrical system branch and on the other hand, it is prevented that, for example in the case of high power consumption by one or more electrical consumers in the second branch of the vehicle electrical system, the voltage in the first branch of the vehicle electrical system falls below a predetermined minimum. This can advantageously be used for an automatic start-stop system.

The switching element of the second vehicle electrical system branch makes it possible to electrically couple or decouple the second vehicle electrical system branch and the first vehicle electrical system branch as required, for example depending on an operating state of the motor vehicle. This makes it possible to electrically couple the first and/or the second consumer to the first and second energy store, as a result of which more electrical power can be made available. This can be used advantageously when, for example, ambient conditions of the motor vehicle, for example a very low outside temperature of the motor vehicle, require an electrical load to consume a very high amount of power, for example when the motor vehicle is started cold.

The vehicle electrical system advantageously has an additional power source through the third vehicle electrical system branch, which can be used to supply, for example, high-power consumers with high peak consumption, for example an electric steering system and/or a rolling system. This additional power source can advantageously be used for automatic start-stop operation of the motor vehicle.

The further switching element of the third on-board branch makes it possible to electrically couple or decouple the third on-board branch and the first on-board branch as required, for example depending on the operating state of the motor vehicle.

According to an advantageous embodiment, the energy flow controller is designed as a DC voltage converter.

According to a further advantageous embodiment, the energy flow controller is designed as a bidirectional DC voltage converter. Advantageously, the bidirectional DC-DC converter is suitably designed to allow energy to be fed in from the second vehicle electrical system branch into the first vehicle electrical system branch and/or from the first vehicle electrical system branch into the second vehicle electrical system branch and/or to prevent a predetermined minimum voltage in the first vehicle electrical system branch being undershot.

According to a further advantageous embodiment, the second consumer is designed as a Starter for a motor vehicle internal combustion engine. By separating the starter in the second branch of the vehicle electrical system, it can be prevented that the voltage in the first branch of the vehicle electrical system falls below a predetermined minimum value when the internal combustion engine is started and that safety-related functions, for example a steering system and/or a roll system, are functional if they are electrically coupled to the first branch of the vehicle electrical system remain.

This is particularly important when starting the combustion engine at a higher vehicle speed. This enables an automatic start-stop system to also be used for higher speeds.

According to a further advantageous embodiment, the third energy store is designed as a double-layer capacitor. Compared to other types of capacitors, double-layer capacitors have a very high energy density and are therefore more suitable than other types of capacitors for buffering an accumulator and/or an electric generator in the motor vehicle.

According to a further advantageous refinement, the third vehicle electrical system branch has at least one third consumer which can be electrically coupled to the first connection of the third energy store.

According to a second and third aspect, the invention is characterized by a method and a corresponding device for operating the vehicle electrical system according to the first aspect. An operating state of the motor vehicle is determined and the shift position of the shifting element and/or the further shifting element is controlled depending on the determined operating state of the motor vehicle. Advantageous refinements of the first aspect also relate to the second and third aspect. This advantageously makes it possible to electrically couple or decouple the respective energy stores, depending on the determined operating state and a resulting requirement for one or more energy stores.

According to an advantageous embodiment, the switching position of the switching element and/or the further switching element is controlled depending on a predefined assignment of at least one predefined electrical load to one of the vehicle electrical systems.

According to a further advantageous refinement, one or more operating variables are recorded and the switching position of the switching element and/or the further switching element is controlled as a function of the recorded operating variable or the recorded operating variables. This makes it possible, for example, to discharge the double-layer capacitor down to a predefined minimum voltage when the vehicle is deactivated and to charge the double-layer capacitor to a predefined target voltage when the vehicle is activated. The operating variable can also be a state of charge of an energy store, for example.

According to a further advantageous refinement, this takes place as a function of at least one specified requirement
at least one energy store and/or at least one consumer and/or at least one further circuit component of the vehicle electrical system controls the switching position of the switching element and/or the further switching element. A specified requirement can be, for example, that an energy store, which is designed as a double-layer capacitor, for example, is discharged when it is not being used in order to increase the service life of the capacitor.

According to an advantageous embodiment, it is detected whether the vehicle has a first and/or second and/or third operating state, with the first operating state representing an active operating state of the vehicle, the second operating state representing a deactivation of the vehicle, and the third operating state representing an activation of the vehicle represents. If it is recognized that the vehicle is in the first operating state, the switching element is switched to the second switching position and the further switching element is switched to the first switching position. If it is recognized that the vehicle is in the second operating state, the switching element is moved to the first and/or the second switching position and the further switching element is moved to the second switching position. If it is recognized that the vehicle is in the third operating state, the switching element is switched to the first or the second switching position and the further switching element is switched to the second switching position. In addition, it is checked whether a detected voltage of the third energy store has a predefined second voltage value, and if the detected voltage has the predefined second voltage value, the further switching element is switched to the first switching position.

According to a further advantageous embodiment, when it is recognized that the vehicle is in the second operating state, the switching element is switched to the first switching position and the further switching element is switched to the second switching position. Furthermore, it is checked whether a detected voltage of the third energy store a predetermined first Voltage falls below. If the detected voltage falls below the predetermined first voltage value, the switching element is switched to the second switching position.

According to a further advantageous embodiment, if it is detected that the vehicle is in the third operating state, it is checked whether a detected temperature that is representative of an operating temperature of the vehicle and/or an operating temperature of the first and/or the second and/or the third energy store and / or an ambient temperature of the vehicle, falls below a predetermined limit and / or it is checked whether an estimated starting time exceeds a predetermined time limit. If it is recognized that the detected temperature falls below the limit value and/or the estimated starting time exceeds the predetermined time limit value, the switching element is switched to the first switching position. If it is recognized that the detected temperature exceeds the limit value and/or the estimated starting time falls below the predetermined time limit value, the switching element is switched to the second switching position.

The starting time period characterizes a time period when starting the drive motor, for example until the ignition process was successful and/or a minimum speed of the drive motor is reached. The estimated starting time can be determined, for example, as a function of a state of charge of the second energy store.

• 1 ein erstes Ausführungsbeispiel eines Bordnetzes,
• 2 ein zweites Ausführungsbeispiel des Bordnetzes,
• 3 ein drittes Ausführungsbeispiel des Bordnetzes,
• 4 ein viertes Ausführungsbeispiel des Bordnetzes,
• 5 ein Ablaufdiagramm für ein erstes Programm zum Betreiben des Bordnetzes und
• 6 ein Ablaufdiagramm für ein zweites Programm zum Betreiben des Bordnetzes.

Exemplary embodiments of the invention are explained in more detail below with reference to the schematic drawings. Show it:

• 1 a first exemplary embodiment of a vehicle electrical system,
• 2 a second embodiment of the electrical system,
• 3 a third exemplary embodiment of the vehicle electrical system,
• 4 a fourth exemplary embodiment of the vehicle electrical system,
• 5 a flowchart for a first program for operating the vehicle electrical system and
• 6 a flowchart for a second program for operating the vehicle electrical system.

Elements of the same construction or function are provided with the same reference symbols across the figures.

1 shows a schematic representation of a first exemplary embodiment of a vehicle electrical system for a motor vehicle. The vehicle electrical system includes a first vehicle electrical system branch BN1, a second vehicle electrical system branch BN2 and a third vehicle electrical system branch BN3.

The first branch of the vehicle electrical system BN1 has a generator G, which is used, for example, as an alternator in the motor vehicle. The generator G is preferably operated at least partially during operation of the motor vehicle and is designed to provide a source voltage, for example 12 V, during its operation.

The first vehicle electrical system branch BN1 also includes a first energy store ES1, which is embodied as a lead-acid battery, for example. The first energy store ES1 has a first connection KN1_BN1, for example a positive pole, and a second connection KN2_BN1, for example a negative pole. The second connection KN2_BN1 is electrically coupled to a reference potential GND, for example. The first energy store ES1 is electrically coupled to the generator G with its first connection KN1_BN1, for example.

The first vehicle electrical system branch BN1 includes at least one first electrical consumer V1, which can be switched on and off at least partially. The first electrical load V1 is arranged in parallel with the first energy store ES1 so that it can be electrically coupled. Several first electrical loads V1 can also be provided.

The third vehicle electrical system branch BN3 has a third energy store ES3, which is embodied as a double-layer capacitor, for example. The third energy store ES3 has a first connection KN1_BN3, for example a positive pole, and a second connection KN2_BN3, for example a negative pole. The second connection KN2_BN3 of the third energy store ES3 is electrically coupled to the reference potential GND.

Furthermore, the third vehicle electrical system BN3 has, for example, a further switching element S3. The additional switching element S3 is designed and arranged, for example, such that when the additional switching element S3 is in a first switching position, the first connection KN1_BN1 of the first energy storage device ES1 is electrically coupled to the first connection KN1_BN3 of the third energy storage device ES3.

The second vehicle electrical system branch BN2 has a second energy store ES2, which is embodied as a lead-acid battery, for example. The second energy store ES2 has a first connection KN1_BN2, for example a positive pole, and a second connection KN2_BN2, for example a negative pole. The second connection KN2_BN2 of the second energy store ES2 is electrically coupled to the reference potential GND.

The second vehicle electrical system branch BN2 also has an energy flow controller DCW, which is designed, for example, as a DC-DC converter, in particular as a bidirectional DC-DC converter. The energy flow controller DCW has a first connection T1 and a second connection T2, the second connection T2 of the energy flow controller DCW being electrically coupled to the first connection KN1_BN2 of the second energy store ES2 and the first connection T1 of the energy flow controller DCW being electrically coupled to the first connection KN1_BN3 of the third energy store ES3 and can be electrically coupled to the first connection KN1_BN1 of the first energy store ES1.

Furthermore, the second vehicle electrical system branch BN2 has at least one second electrical consumer A, which is designed, for example, as a starter for an internal combustion engine. It is also possible that the second vehicle electrical system branch BN2 has additional second electrical loads V2 (see 4 ) having. The second electrical load A can be electrically coupled to the first connection KN1_BN2 of the second energy store ES2, for example.

Furthermore, the second vehicle electrical system branch BN2 has a switching element S2, for example. The switching element S2 is designed and arranged, for example, such that in a first switching position of the switching element S2 the first connection KN1_BN2 of the second energy storage device ES2 and the first connection KN1_BN1 of the first energy storage device ES1 are electrically coupled and in a second switching position of the switching element S2 the first connection KN1_BN2 of the second energy store ES2 and the first connection KN1_BN1 of the first energy store ES1 are electrically decoupled.

2 shows a second exemplary embodiment of the vehicle electrical system. Compared to the in 1 shown on-board network has the in 2 On-board network shown only a first on-board branch BN1 and a second on-board branch BN2. The switching element S2, by means of which the first energy store ES1 and the second energy store ES2 can be connected in parallel, is also not present, for example.

3 shows a third exemplary embodiment of the vehicle electrical system. Compared to the in 1 In the exemplary embodiment shown, the switching element S2 is designed and arranged in such a way that in a first switching position of the switching element S2 the second consumer A can be electrically coupled to the first connection KN1_BN1 of the first energy store ES1 and in a second switching position of the switching element S2 the second consumer A can be electrically coupled with the first connection KN1_BN2 of the second energy store ES2 and the second connection T2 of the energy flow plate DCW.

4 shows a fourth exemplary embodiment of the vehicle electrical system, in which the first vehicle electrical system branch BN1 has at least one further first consumer HLV1 and/or the second vehicle electrical system branch BN2 has at least one further second consumer V2 and/or the third vehicle electrical system branch BN3 has at least one third consumer V3. The respective loads HLV1, V2, V3 can be designed as high-power loads and/or as a load that requires less power, for example a radio.

In 5 the program for operating the vehicle electrical system is shown as a flow chart. The program is executed in an energy management unit of the motor vehicle, for example. The energy management unit can also be referred to as a device for operating the vehicle electrical system.

The program is started in a step S_00. In a step S_02, an operating state of the motor vehicle is determined in such a way that it is detected whether the motor vehicle has a first or a second or a third operating state, with the first operating state representing an active operating state of the vehicle, for example, and the second operating state representing a deactivation of the vehicle and the third operating state represents activating the vehicle. In the active operating state, the motor vehicle is operated by a driver; the engine can be switched on or off, for example at traffic lights. In the first operating state, the vehicle can have both a moving and a stationary operating state. The deactivation of the vehicle can be characterized, for example, in that at the beginning of a rest phase of the motor vehicle, the motor vehicle is parked and the engine is switched off and the vehicle driver optionally leaves the vehicle. The activation of the vehicle can be characterized, for example, by a vehicle driver entering the motor vehicle at the end of a rest phase of the motor vehicle.

If it is recognized in step S_02 that the motor vehicle is in the first operating state, in step S_11 the switching element S2 is switched to controlled the second switching position and the other switching element S3 in the first switching position.

If, for example, the generator is in an active operating state and the motor vehicle is in a moving operating state, if the output of the generator G is not sufficient to supply the specified consumers of the first branch of the vehicle electrical system BN1, power can be supplied by means of the first energy store ES1 and the third energy store ES3 .

If the switching element S2 is in the second switching position, energy is fed from the second vehicle electrical system branch BN2 into the first vehicle electrical system branch BN1 and/or the third vehicle electrical system branch BN3, for example by means of the energy flow controller DCW. As a result, an energy throughput of the first energy store ES1 is reduced, for example. This has the advantage that, for example, the service life of the first energy store ES1 can be extended.

In the operating state in which the generator G is in an active operating state and the motor vehicle is in a moving operating state, the switch element S2 can also be switched to the first switch position and/or the further switch element S3 can be switched to the first switch position, at least for a short time. In the event that the vehicle electrical system only has the first vehicle electrical system branch BN1 and the second vehicle electrical system branch BN2 and the switching element S2 is not present or has the second switching position, energy can be fed from the second vehicle electrical system branch BN2 into the first vehicle electrical system branch BN1 by means of the energy flow controller DCW.

If, for example, the generator G is in an inactive operating state, the power can be supplied to the specified consumers of the first on-board network branch BN1 and the third on-board network branch BN3 by means of the first energy store both when the motor vehicle is in the driving and stationary operating state and the further switching element S3 is in the first switching state ES1 and the third energy store ES3 take place. A lack of generator output can thus be compensated for, for example, by means of the third energy store ES3.

When the motor vehicle is in the first operating state, when the engine is started while the motor vehicle is moving and/or stationary, the power can be supplied to the first consumer V1 or to the first consumer V1 and/or to the third consumer V3 or to the third consumer V3 by means of the first energy store ES1 and/or the third energy store ES3. The second consumer A, which is designed as a starter, for example, can be supplied by means of the second energy store ES2. The energy flow controller DCW can prevent a predetermined minimum voltage in the first vehicle electrical system branch BN1 and/or the third vehicle electrical system branch BN3 from falling below a predetermined minimum voltage in the second vehicle electrical system branch BN2 when there is high power consumption, for example by the starter.

If it is recognized in step S_02 that the motor vehicle is in the second operating state, in step S_22 the switching element S2 is switched to the first switching position and the further switching element S3 is switched to the second switching position. Furthermore, in a step S_24 it is checked whether a detected voltage U_ES3 of the third energy store ES3 falls below a predetermined first voltage value U1, and if the detected voltage U_ES3 falls below the predetermined first voltage value U1, in a step S_26 the further switching element S3 and the switching element S2 controlled in the second switching position. This makes it possible, for example when the vehicle is deactivated, to discharge the third energy store ES3, which is in the form of a double-layer capacitor, for example, down to a predetermined minimum voltage. In this case, for example, the third energy store ES3 is discharged via the energy flow controller DCW into the second energy store ES2 and into the first energy store ES1. Alternatively, it is also possible for the switching element S2 to be controlled into the second switching position independently of the detected voltage U_ES3 of the third energy store ES3. In this case, the third energy store ES3 is discharged into the second energy store ES2 via the energy flow controller DCW. After the deactivation of the vehicle has ended, when the motor vehicle is in the idle state, the switching element S2 and the further switching element S3 are in the second switching position.

If it is recognized in step S_02 that the motor vehicle is in the third operating state, in step S_33 the switching element S2 and the further switching element S3 are moved to the second switching position. Furthermore, in a step S35 it is checked whether a detected voltage U_ES3 of the third energy store ES3 approximately has a predetermined second voltage value U2. If the detected voltage U_ES3 approximately has the predefined second voltage value U2, the further switching element S3 is switched to the first switching position in a step S_37.

This makes it possible, for example, for the second energy store ES2 to feed energy into the third vehicle electrical system BN3 by means of the energy flow controller DCW when the vehicle is activated. At the occasion sen of the engine, the starter is supplied, for example, only via the second energy store ES2.

Depending on a load distribution in the first BN1 and/or second BN2 and/or third vehicle electrical system BN3 by connecting one or more consumers and/or high-performance consumers, a more precise subdivision of the operating state of the motor vehicle can be advantageous, for example that the active operating state is divided into several operating states is divided in order to control the switching element S2 and/or the further switching element S3 and the associated electrical coupling of the first energy store ES1 and/or the second energy store ES2 and/or the third energy store ES3 depending on the operating state determined.

6 shows the flowchart for a second program for operating the vehicle electrical system. The second program is different from the one in 5 shown first program in that a step S_31 checks whether a detected temperature T, which is representative of an operating temperature of the vehicle, for example, falls below a specified limit value T_limit and/or an estimated starting time t exceeds a specified time limit value t_limit. If the recorded temperature T falls below the specified limit value T_limit and/or the estimated starting time t exceeds the specified time limit value t_limit, in step S_34 the switching element S2 is switched to the first switching position and the further switching element S3 is switched to the second switching position. If the detected temperature T exceeds the limit value T_limit and/or if the estimated starting time t falls below the specified time limit value t_limit, in a step S_33 the switching element S2 is switched to the second switching position and the further switching element S3 is switched to the second switching position.

This is used, for example, to be able to design the second energy store ES2 to be smaller in terms of its performance. For example, in such a way that the performance is sufficient for starting the engine at higher temperatures, for example with a so-called warm start, but the performance is not sufficient for starting the engine at low temperatures, for example with a so-called cold start. For this reason, in the event of a cold start and/or a first start problem, for example, all of the energy stores in the vehicle electrical system are coupled. For example, it is also possible for only some of the energy stores ES1, ES2, ES3 to be electrically coupled, so that the further switching element S3, for example, remains open.

Reference List

A

second consumer

BN1

first on-board branch

BN2

second on-board branch

BN3

third on-board branch

DCW

energy flow controller

ES1

first energy storage

ES2

second energy storage

ES3

third energy storage

G

generator

GND

reference potential

KN1_BN1

first connection of the first energy store

KN1_BN2

first connection of the second energy store

KN1_BN3

first connection of the third energy storage device

KN2_BN1

second connection of the first energy store

KN2_BN2

second connection of the second energy storage device

KN2_BN3

second connection of the third energy storage device

S2

switching element

S3

another switching element

t

estimated boot time

t_limit

time limit

T

detected temperature

T_limit

limit

T1

first connection of the energy flow controller

T2

second connection of the energy flow controller

U1

first tension

U2

second tension

U_ES3

detected voltage of the third energy store

V1

first consumer

v2

another second consumer

V3

third consumer

Claims (14)

Vehicle electrical system for a motor vehicle comprising - a first vehicle electrical system branch (BN1), which has: - a first energy store (ES1) with a first connection (KN1_BN1) and a second connection (KN2_BN1), the second connection (KN2_BN1) being electrically coupled to a reference potential (GND), - a generator (G) which is connected to the first Connection (KN1_BN1) of the first energy store (ES1) is coupled, - at least one first consumer (V1) which can be electrically coupled to the first connection (KN1_BN1) of the first energy store (ES1), and - at least one second vehicle electrical system branch (BN2), which has: - a second energy store (ES2) with a first connection (KN1_BN2) and a second connection (KN2_BN2), the second connection (KN2_BN2) of the second energy store (ES2) being electrically coupled to the reference potential (GND), - at least a second consumer (A), which can be electrically coupled to the first connection (KN1_BN2) of the second energy store (ES2) and/or to the first connection (KN1_BN1) of the first energy store (ES1), and - an energy flow controller (DCW) with a first connection (T1) and a second connection (T2), the second connection (T2) of the energy flow controller (DCW) being electrically coupled to the first connection (KN1_BN2) of the second energy store (ES2) and the first connection (T1) of the energy flow controller (DCW) can be electrically coupled to the first connection (KN1_BN1) of the first energy storage device (ES1) - a switching element (S2) is designed and arranged in such a way that - in a first switching position of the switching element (S2), the first connection (KN1_BN2) of the second energy storage device (ES2) and the first connection (KN1_BN1) of the first energy store (ES1) are electrically coupled and - in a second switching position of the switching element (S2) the first connection (KN1_BN2) of the second energy store (ES2) and the first connection (KN1_BN1) of the first energy store (ES1) are electrically decoupled, - at least one third vehicle electrical system branch (BN3), which has: - a third energy store (ES3) with a first connection (KN1_BN3) and a second connection (KN2_BN3), the second connection (KN2_BN3) of the third energy store (ES3) is electrically coupled to the reference potential (GND) and the first connection (KN1_BN3) of the third energy store (ES3) is electrically coupled to the first connection (T1) of the energy flow controller (DCW) and can be electrically coupled to the first Connection (KN1_BN1) of the first energy storage device (ES1), - a further switching element (S3) designed and arranged in such a way that - in a first switching position of the further switching element (S3), the first connection (KN1_BN1) of the first energy storage device (ES1) is electrically coupled with the first connection (KN1_BN3) of the third energy store (ES3) and the first connection (T1) of the energy flow controller (DCW) of the second vehicle electrical system (BN2) and - in a second switching position of the further switching element (S3) the first connection (KN1_BN1) of first energy store (ES1) is electrically decoupled from the first connection (KN1_BN3) of the third energy store (ES3) and the first connection (KN1_BN3) of the third energy store (ES3) is electrically coupled to the first connection (T1) of the energy flow controller (DCW) of second vehicle electrical system (BN2). on-board network claim 1 , In which the energy flow controller (DCW) is designed as a DC voltage converter. on-board network claim 1 or 2 , In which the energy flow controller (DCW) is designed as a bidirectional DC-DC converter. Vehicle electrical system according to one of the preceding claims, in which the second consumer (A) is designed as a starter for an internal combustion engine of the motor vehicle. Vehicle electrical system according to one of the preceding claims, in which the third energy store (ES3) is designed as a double-layer capacitor. Vehicle electrical system according to one of the preceding claims, in which the third vehicle electrical system branch (BN3) has at least one third consumer (V3) which can be electrically coupled to the first connection (KN1_BN3) of the third energy store (ES3). Method for operating a vehicle electrical system according to one of the preceding claims, in which - An operating state of the motor vehicle is determined and - Depending on the determined operating state of the motor vehicle, the switching position of the switching element (S2) and/or the further switching element (S3) is controlled. procedure after claim 7 , in which the switching position of the switching element (S2) and/or the further switching element (S3) is controlled depending on a predetermined assignment of at least one predetermined electrical consumer to one of the vehicle electrical systems (BN1, BN2, BN3). procedure after claim 7 or 8th , in which one or more operating variables are recorded and, depending on the recorded operating variable or the recorded operating variables, the controller the switching position of the switching element (S2) and/or the further switching element (S3). Procedure according to one of Claims 7 until 9 , in which, depending on at least one predetermined requirement, at least one energy store (ES1, ES2, ES3) and/or at least one consumer (A, V1, V2, V3) and/or at least one further circuit component of the vehicle electrical system controls the switching position of the switching element ( S2) and/or the further switching element (S3). Procedure according to one of Claims 7 until 10 with an electrical system according to one of the Claims 1 until 6 , in which - it is detected whether the vehicle has a first and/or second and/or third operating state, the first operating state representing an active operating state of the vehicle, the second operating state representing a deactivation of the vehicle, and the third operating state representing an activation of the represents the vehicle - if it is detected that the vehicle is in the first operating state, the switching element (S2) is controlled into the second switching position and the further switching element (S3) is controlled into the first switching position, - if it is detected that the vehicle is in the has the second operating state, the switching element (S2) is moved to the first and/or the second switching position and the further switching element (S3) is moved to the second switching position, and - if it is recognized that the vehicle is in the third operating state, the switching element (S2 ) is controlled into the first or the second switching position and the further switching element (S3) into the second switching position and - it is checked whether a detected voltage (U_ES3) of the third energy store (ES3) has a predetermined second voltage value (U2), and - if the detected voltage (U_ES3) has the predetermined second voltage value (U2), the further switching element (S3) is controlled into the first switching position. procedure after claim 11 , in which - if it is recognized that the vehicle is in the second operating state, the switching element (S2) is switched to the first switching position and the further switching element (S3) is switched to the second switching position, and it is checked whether the detected voltage (U_ES3) of the third energy store (ES3) falls below a predetermined first voltage value (U1), and - if the detected voltage (U_ES3) falls below the predetermined first voltage value (U1), the switching element (S2) is controlled into the second switching position. Procedure according to one of Claims 11 or 12 in which - if it is recognized that the vehicle has the third operating state, it is checked whether a detected temperature (T) that is representative of an operating temperature of the vehicle and/or an operating temperature of the first (ES1) and/or the second (ES2) and/or the third energy store (ES3) and/or an ambient temperature of the vehicle falls below a specified limit value T_limit and/or it is checked whether an estimated start time duration (t) exceeds a specified time limit value (t_limit), - if the recorded temperature (T) falls below the limit value (T_limit) and/or the estimated starting time (t) exceeds the specified time limit value (t_limit), the switching element (S2) is controlled into the first switching position and - if the detected temperature (T) exceeds the limit value ( T_limit) and/or the estimated starting time (t) falls below the predetermined time limit (t_limit), the switching element (S2) is controlled into the second switching position. Device for operating an on-board network according to one of the above Claims 1 until 6 which is designed - to determine an operating state of the motor vehicle and - to control the switching position of the switching element (S2) and/or the further switching element (S3) depending on the operating state of the motor vehicle determined.

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