DE102012011840B4 - Electrical system for a motor vehicle - Google Patents

Abstract

Vehicle electrical system (1) for a motor vehicle (2), in particular for an electric motor vehicle or a hybrid motor vehicle, comprising:
- at least one high-voltage network (3) designed for a first electrical voltage, the high-voltage network (3) comprising at least one high-voltage energy store (5),
- at least one low-voltage network (4) designed for a second electrical voltage that is lower than the first voltage of the high-voltage network (3), the low-voltage network (4) comprising at least one low-voltage energy store (6),
- At least one first and at least one second electrical converter device (12, 13) connected between the high-voltage energy storage device (5) and the low-voltage energy storage device (6), which are each used to convert the first electrical voltage of the high-voltage network (3) into the second electrical voltage of the low-voltage network ( 4) and vice versa, wherein the low-voltage energy store (6) is formed from at least one storage element (8) based on lithium and/or a lithium compound and additionally comprises at least one capacitor connected in series with the storage element (8).

Description

The invention relates to an electrical system for a motor vehicle, in particular for an electric motor vehicle or a hybrid motor vehicle.

It is known that modern motor vehicles, such as in particular purely electrically powered electric motor vehicles, are provided to drive at least one electric drive unit, in particular designed as an electric motor, or partially or temporarily electrically driven hybrid motor vehicles, to drive at least one electric drive unit, in particular designed as an electric motor , electric drive unit and a further drive unit, in particular designed as an internal combustion engine, are provided, usually have a vehicle electrical system divided into two areas.

The sections of the vehicle electrical system differ essentially in the electrical voltage applied to them, so that a corresponding vehicle electrical system is usually a high-voltage system designed for a first electrical voltage, in which, for example, an electrical voltage greater than or equal to 200 volts (V) is present, and a low-voltage network designed for a second electrical voltage that is lower than the first voltage of the high-voltage network, in which, for example, an electrical voltage of approximately 12 volts (V) is present (12-volt low-voltage network). Both the high-voltage network and the low-voltage network include at least one corresponding energy store. Corresponding high-voltage consumers, such as in particular the electrically operated drive unit of the motor vehicle, are connected to the high-voltage energy storage device associated with the high-voltage network, and corresponding low-voltage consumers, such as in particular part of the lighting device of the motor vehicle, are connected to the low-voltage energy storage device belonging to the low-voltage network.

It is also known to connect electrical converter devices between the respective networks forming the vehicle electrical system, i.e. the high-voltage network and the low-voltage network, which are each designed to convert the first electrical voltage of the high-voltage network into the second electrical voltage of the low-voltage network, and vice versa. In this way, the capacity or performance of the low-voltage energy store associated with the low-voltage network, which is lower than that of the high-voltage network associated with the high-voltage network, can be compensated for in such a way that energy can flow from the high-voltage network-side high-voltage energy store into the low-voltage network-side low-voltage energy store.

However, the usual types of corresponding low-voltage network-side low-voltage energy storage represent technical limitations of the possible performance of a corresponding vehicle electrical system.

Out of DE 10 2010 046 616 A1 a vehicle with a two-voltage vehicle electrical system is known, which includes a low-voltage vehicle electrical system and a high-voltage vehicle electrical system. Two voltage converters are provided for transferring electrical power from the high-voltage vehicle electrical system to the low-voltage system. The low-voltage electrical system includes a lead-acid battery as an energy store, which can have supercapacitors connected in parallel.

DE 10 2007 001 673 A1 discloses a vehicle electrical system for a motor vehicle, comprising a high-voltage energy store with a high-voltage energy store and a low-voltage vehicle electrical system with a low-voltage energy store. The low-voltage vehicle electrical system is coupled to the high-voltage vehicle electrical system via two converter devices connected in parallel.

Out of DE 10 2009 000 121 A1 and U.S. 2006/0 125 319 A1 a concept for an on-board network of a motor vehicle is known, in which a converter device is provided.

In the conference paper Miller, John M.: "Trends in Vehicle Energy Storage Systems: Batteries and Ultracapacitors to Unite", IEEE Vehicle Power and Propulsion Conference (VPPC), September 3-5, 2008, Harbin, China, concepts for improving energy storage systems are discussed discussed for electric vehicles, wherein in particular circuits including batteries and capacitors are described.

The present invention is based on the problem of specifying an improved vehicle electrical system.

The problem is solved according to the invention by an on-board electrical system which comprises at least one high-voltage network designed for a first electrical voltage, the high-voltage network comprising at least one high-voltage energy store, at least one low-voltage network designed for a second electrical voltage which is lower than the first voltage of the high-voltage network, the Low-voltage network comprises at least one low-voltage energy store, at least one first and at least one second electrical converter device connected between the high-voltage energy store and the low-voltage energy store, each of which is used to convert the first electrical voltage of the high-voltage network into the second electrical voltage of the low-voltage network, and vice versa reverse, is formed, wherein the low-voltage energy storage device is formed from at least one storage element based on lithium and/or a lithium compound and additionally comprises at least one capacitor connected in series with the storage element.

The present invention is based on the idea of constructing the low-voltage energy storage device associated with the low-voltage network of a corresponding vehicle electrical system in such a way that it is made up of at least one storage element based on lithium and/or a lithium compound or comprises at least one storage element based on lithium and/or a lithium compound or having.

Various different configurations of the low-voltage energy store associated with the low-voltage network are therefore conceivable within the scope of the present invention, which have in common that they each have at least one storage element based on lithium and/or a lithium compound. Any other storage elements forming the low-voltage energy storage device can, but do not have to be based on lithium and/or a lithium compound. A corresponding storage element is generally understood to mean an electrochemical cell as part of a battery.

The design of the low-voltage energy storage associated with the low-voltage network from at least one storage element based on lithium and/or a lithium compound, i.e. essentially as a rechargeable lithium accumulator or lithium battery, is particularly advantageous because lithium accumulators, compared to conventional ones, are particularly Low-voltage energy storage devices formed from storage elements based on lead or lead compounds have a higher power or energy density. Equally, corresponding low-voltage energy stores formed from storage elements based on lithium and/or lithium compounds are advantageous in comparison to conventional low-voltage energy stores (with comparable electrical properties) in terms of their weight, since they are significantly lighter, so that corresponding motor vehicles equipped with the vehicle electrical system according to the invention are also lighter, what basically has a positive effect on energy consumption.

A further advantage of the vehicle electrical system according to the invention is that the use of at least two corresponding electrical converter devices, which are designed in particular as direct current converters or DC/DC converters, means that there is still at least one additional functional electrical converter device even if one electrical converter device fails , via which various to the vehicle electrical system, d. H. consumers connected to the high-voltage network or the low-voltage network can be supplied with electrical energy. It is of particular advantage that safety-relevant consumers can continue to be operated, especially for the operation of the motor vehicle equipped with the on-board electrical system according to the invention, so that the motor vehicle can at least still be parked safely even in such cases of a failure of an electrical converter device.

Possible preferred configurations of the low-voltage energy store associated with the low-voltage network are listed below in a non-exhaustive manner.

It is therefore preferred that the low-voltage energy storage device consists of three storage elements based on lithium and one storage element based on lithium titanate, or three storage elements based on lithium and two storage elements based on a nickel metal hydride compound, or three storage elements based on lithium titanate and two storage elements based on a lithium iron phosphate compound, or four storage elements based on lithium titanate and one storage element based on lithium, or four storage elements based on lithium titanate and one storage element based on a lithium cobalt manganese nickel compound ( so-called NMC memory elements or NMC cells), or six memory elements based on lithium titanate, or one memory element based on lithium titanate and three memory elements based on a lithium-cobalt-manganese-nickel compound, or three memory elements based on a lithium Cobalt-manganese-nickel compound and a memory element based on lithium titanate, or four memory elements based on a lithium iron phosphate compound is formed.

The specific number of storage elements forming the low-voltage energy storage device can influence its internal resistance, i.e. its internal resistance can be set in a targeted manner, the principle applying that a smaller number of storage elements compared to a higher number of storage elements leads to a lower internal resistance of the low-voltage energy storage device . Equally, a smaller number of storage elements forming the low-voltage energy storage device can also be advantageous with regard to cost aspects. The storage elements forming the low-voltage energy store are usually connected in series.

In the aforementioned configurations of the low-voltage energy store or the storage elements forming the low-voltage energy store, a 12-volt low-voltage network is assumed to be part of the vehicle electrical system according to the invention. If the low-voltage network is designed as a 24-volt low-voltage network, the respective number of storage elements forming the low-voltage energy storage device specified above is doubled, with the possible combinations of the different storage element types remaining the same.

The high-voltage energy store is formed equally from a number of storage elements, in particular those connected in series. In this case, the storage elements forming the high-voltage energy storage device, e.g. B. based on lithium or lithium compounds.

The storage elements forming the high-voltage energy store can be referred to as first storage elements, and the storage elements forming the low-voltage energy store can be referred to as second storage elements.

According to the invention, it is provided that the low-voltage energy storage device comprises at least one capacitor connected in series with the storage element in addition to the at least one storage element. It is possible for the low-voltage energy storage device to include the at least one capacitor, which is in particular a double-layer capacitor, in addition to the multiple storage elements. Double-layer capacitors typically have two electrodes between which there is an electrically conductive electrolyte. After applying an electrical voltage, ions of the electrolyte of reversed polarity collect on the electrodes. A charge carrier layer is formed from immobile charge carriers. The electrodes with the charge carrier layer as a dielectric behave like two capacitors which are connected in series across the electrolyte. In contrast to electrochemical energy storage devices, they store the energy electrostatically. Double-layer capacitors usually have low internal resistances and a large number of possible charging and discharging cycles. Consequently, the property profile of the low-voltage energy store can be improved in this way, in particular with regard to a low internal resistance.

In the sense of a further storage element, the capacitor is advantageously connected in series with the storage elements forming the low-voltage energy storage device. In this way, the nominal voltage of the low-voltage energy store can be further increased. Of course, it is also conceivable to connect more than one capacitor connected in series and/or parallel to the storage elements forming the low-voltage energy storage device.

According to a preferred embodiment of a low-voltage energy store, this can consist of three storage elements based on a lithium-cobalt-manganese-nickel compound and a double-layer capacitor connected in series and one of the three each based on a lithium-cobalt-manganese-nickel compound based memory elements as well as the further double-layer capacitor connected in series downstream of these. The low-voltage energy storage device according to this embodiment can therefore (mentally) be divided into two parts connected in parallel, with a first part consisting of the three storage elements each based on a lithium-cobalt-manganese-nickel compound and the double-layer capacitor connected in series and the second part part connected in parallel thereto is formed by the further double-layer capacitor.

It is possible for the first electrical converter device to have a higher output than the second electrical converter device. In principle, the electrical traveling devices forming components of the vehicle electrical system according to the invention are advantageously direct voltage converters (DC/DC converters), i.e. devices or electrical circuit arrangements which are designed to convert an electrical input voltage (input direct current voltage) into an electrical output voltage (DC output voltage) with a higher, lower or inverted voltage level. Within the scope of the present invention, a high input voltage of the high-voltage network, i.e. an electrical voltage present in the high-voltage network of greater than or equal to 200 volts, can therefore be converted via the electrical converter devices into a comparatively lower output voltage of the low-voltage network, i.e. an electrical voltage present in the low-voltage network voltage of 12 volts. A reverse conversion of the electrical voltage present in the low-voltage network as input voltage into an electrical voltage present in the high-voltage network as output voltage is also possible.

As mentioned, the power or power consumption of the two electrical converter devices are advantageously different, with the power or power consumption of the first electrical converter device being higher than the power or power consumption of the second electrical converter device. This is possible because of the first electrical converter device in particular high-power electrical consumers, such as e.g. E.g. electric motors or starters serving as a drive unit, are supplied with electrical energy, whereas via the second electrical converter device, in particular as part of the energy flow between the high-voltage network-side high-voltage energy storage device and the low-voltage network-side low-voltage energy storage device, a certain amount of electrical energy is sent to the low-voltage network or the low-voltage energy storage device contained therein is or will be handed over.

The first electrical converter device has, for example, a power in the range of 1-3 kilowatts (kW), in particular 2 kilowatts (kW) or is designed for this, whereas the second electrical converter device has a power in the range of only 1-10 watts, for example (W), in particular 2 watts (W), or is designed for this.

As already mentioned, the second electrical converter device is advantageously used to allow electrical energy to flow (current flow) from the high-voltage network into the low-voltage network at least temporarily, and thus to ensure the supply of certain low-voltage consumers connected to the low-voltage network with electrical energy via the low-voltage network-side low-voltage energy store. Corresponding low-voltage consumers are, for example, a lighting device on the motor vehicle, in particular a parking light, various driver assistance systems, including in particular safety-related driver assistance systems, such as B. braking or steering assistance systems, but also acoustic and / or visual vehicle-side multimedia devices such. As radios, televisions or communication devices for telephone, Internet, etc., are to be understood.

In an expedient development of the invention, a control device, which is designed to control an electrical energy flow between the high-voltage energy storage device and the low-voltage energy storage device, and vice versa, can be provided, the control device for controlling the energy flow between the high-voltage energy storage device and the low-voltage energy storage device, and vice versa, taking into account at least one boundary condition is formed. Consequently, all energy flows taking place via the two electrical converter devices between the high-voltage network-side high-voltage energy store and the low-voltage network-side low-voltage energy store can be controlled via the control device, which z. B. includes suitable control algorithms. Accordingly, the control device expediently communicates with the two electrical converter devices, in particular in order to exchange corresponding control commands with them. As mentioned, an energy flow can be possible both from the high-voltage network-side high-voltage energy store in the direction of the low-voltage network-side low-voltage energy store, but also vice versa.

A certain minimum amount of energy or maximum amount of energy and/or a certain minimum voltage or maximum voltage in the low-voltage energy storage device and/or the low-voltage network can be considered as a corresponding boundary condition, the existence of which can be checked in particular via the control device, with the control device for controlling the energy flow between the high-voltage energy storage device and the low-voltage energy store is designed in such a way that the low-voltage energy store does not fall below a specific minimum amount of energy and/or minimum voltage or does not exceed a specific maximum amount of energy and/or maximum voltage, and/or at least one operating state of the motor vehicle that includes the on-board electrical system.

Accordingly, the control device or a checking device that communicates with it, e.g. B. a suitable comparator circuit, continuously or discontinuously at certain points in time determine the existing amount of electrical energy and / or electrical voltage present in the low-voltage energy storage device and / or the low-voltage network and this with a predetermined or specifiable minimum amount of electrical energy or maximum amount of energy and / or a predetermined or specifiable electrical Compare the minimum voltage or maximum voltage in the low-voltage energy storage device or the low-voltage network in the sense of an actual value/target value comparison. If the current value of the amount of electrical energy or electrical voltage present in the low-voltage energy store or low-voltage network falls below or exceeds a corresponding upper or lower limit value in the sense of corresponding threshold values, the control device causes an energy flow between the electrical converter devices, in particular via the second electrical converter device the high-voltage network or the high-voltage energy store and the low-voltage network or the low-voltage energy store in such a way that the low-voltage energy store and/or the low-voltage network does not fall below a certain minimum amount of energy and/or minimum voltage or a certain maximum amount of energy and/or maximum voltage is not exceeded. A corresponding flow of energy between the high-voltage network or the high-voltage energy store and the low-voltage network or low-voltage energy store can already take place when the current value of the electrical energy quantity there or that is present there brings the electrical voltage closer to the respective minimum or maximum value, which means that the corresponding limit values can be prevented even more reliably.

Of course, the control device communicates with suitable detection means for this purpose, which is designed for the continuous or discontinuous detection of various electrical parameters, in particular of the low-voltage network or the low-voltage energy store. Corresponding parameters relate in particular to the amount of electrical energy and/or the electrical voltage in the low-voltage network or the low-voltage energy store.

For example, a corresponding minimum amount of energy on the low-voltage network side or low-voltage energy storage device side can be present in the form of a specific quiescent current serving as a boundary condition, which quiescent current must always be maintained in the low-voltage network-related low-voltage energy storage device in order to ensure the operation of certain low-voltage network-connected consumers under all circumstances. This contributes if consumers, such as B. corresponding driver assistance systems, such as braking or steering assistance systems, or a parking light, for the operation of equipped with the vehicle electrical system according to the invention are relevant to safety, to significant safety advantages.

It is also conceivable that a corresponding boundary condition relates to at least one operating state of the motor vehicle that includes the vehicle electrical system. The operating state of the motor vehicle is to be understood, for example, as driving or stationary operation. It is therefore possible with particular advantage if the motor vehicle equipped with the vehicle electrical system according to the invention is stationary or parked, which z. B. on certain operating parameters of the motor vehicle, such. B. vehicle speed, ignition, etc., can be determined to ensure the aforementioned quiescent current in the low-voltage network or the low-voltage energy storage device via an energy flow that may be necessary between the high-voltage network-side high-voltage energy storage device and the low-voltage network-side low-voltage energy storage device.

The or a control device is advantageously designed to control at least one of the electrical converter devices, in particular the second electrical converter device. Again depending on the presence of certain boundary conditions, activation is thus possible, which in particular relates to switching the electrical converter device(s) on or off. The boundary conditions mentioned above, which relate to the amount of electrical energy and/or electrical voltage in the low-voltage network and/or the low-voltage energy store, can be used as corresponding boundary conditions. For example, it is therefore possible to switch on the second electrical converter device when the electrical voltage in the low-voltage network is a predetermined or specifiable minimum electrical voltage in the sense of a lower limit or threshold value, e.g. B. falls below 12 volts. Conversely, the second electrical converter device can be switched off when the electrical voltage in the low-voltage network is a predeterminable or predetermined maximum electrical voltage in the sense of an upper limit or threshold value, e.g. B. 14 volts exceeds.

In an expedient development of the invention, the high-voltage energy store can be arranged with the electrical converter devices in a common housing. Consequently, the high-voltage energy store and the electrical converter devices are structurally integrated in one housing and represent a particularly highly integrated and compact unit of the vehicle electrical system according to the invention, ie they also contribute to a more compact design of the vehicle electrical system according to the invention. The housing can be made of an electrically insulating material, such as. B. plastic, be formed, which is to be regularly guaranteed with regard to safety aspects such. B. the safety against electric shock is advantageous.

In addition, the present invention relates to a motor vehicle which includes an on-board network as described above. The motor vehicle is in particular an electric motor vehicle or a hybrid electric motor vehicle. The above statements regarding the vehicle electrical system according to the invention therefore apply analogously to the motor vehicle according to the invention.

• 1 eine Prinzipdarstellung eines Bordnetzes eines Kraftfahrzeugs gemäß einer ersten beispielhaften, nicht-erfindungsgemäßen Ausführungsform;
• 2 eine Prinzipdarstellung eines Bordnetzes eines Kraftfahrzeugs gemäß einer zweiten beispielhaften, nicht-erfindungsgemäßen Ausführungsform; und
• 3 eine Prinzipdarstellung eines Bordnetzes eines Kraftfahrzeugs gemäß einer dritten beispielhaften, erfindungsgemäßen Ausführungsform zeigt.

Further advantages, features and details of the invention result from the exemplary embodiments described below and from the drawings, in which:

• 1 a schematic representation of a vehicle electrical system of a motor vehicle according to a first exemplary embodiment, not according to the invention;
• 2 a schematic representation of a vehicle electrical system of a motor vehicle according to a second exemplary embodiment, not according to the invention; and
• 3 shows a schematic representation of a vehicle electrical system of a motor vehicle according to a third exemplary embodiment of the invention.

1 shows a schematic representation of an on-board network 1 of a motor vehicle 2 according to a first exemplary embodiment not according to the invention. The motor vehicle 2 is an electric motor vehicle, ie it is driven purely electrically by one or more electric motors 9 each serving as a drive unit.

The vehicle electrical system 1 is divided into a high-voltage network 3 and a low-voltage network 4 . The high-voltage network 3 has a voltage level of approximately 250 volts, and the low-voltage network 4 has a voltage level of approximately 12 volts. Appropriate rechargeable energy stores are arranged both in the high-voltage network 3 and in the low-voltage network 4 . Correspondingly, the high-voltage network 3 includes a high-voltage energy store 5 and the low-voltage network 4 includes a low-voltage energy store 6.

In this case, the high-voltage energy store 5 is formed from a plurality of series-connected storage elements 7, each based on lithium, which can also be referred to as cells. The low-voltage energy store 6 is also formed from a plurality of storage elements 8 connected in series and each based on lithium.

A preferred configuration of the low-voltage energy store 6 is the embodiment of three storage elements 8 based on a lithium-cobalt-manganese-nickel compound (so-called NMC storage elements or NMC cells) and one storage element 8 based on lithium titanate. Alternative possible configurations of the low-voltage energy store 6 have already been mentioned above.

Corresponding high-voltage consumers or high-power consumers, such as e.g. B. the electric motor 9 forming the drive unit of the motor vehicle 2, which is supplied with electrical energy via the high-voltage network 3 and thus via the high-voltage energy store 5. The electrical connection between the high-voltage energy storage 5 and the high-power consumers is about the operation, d. H. Opening and closing, electrical switching means 11 can be separated and restored. Such it can z. B. can be prevented that outside of the driving operation of the motor vehicle 2, a high voltage, d. H. in particular the respective voltage of the high-voltage network 3 to which the electric motor 9 is applied.

Corresponding low-voltage consumers 10, such as e.g. B. in the form of driver assistance systems designed as braking or steering assistance systems, a lighting device of motor vehicle 2, d. H. in particular the parking lights of the motor vehicle 2, various multimedia devices such. As radio, television, etc., which are supplied via the low-voltage network 4 and thus via the low-voltage energy storage device 6 with electrical energy (current).

As can be seen, the vehicle electrical system 1 comprises two parallel-connected electrical converter devices 12, 13, each designed as a direct current converter or DC/DC converter. The electrical converter device 12 is referred to below as the first electrical converter device, and the electrical converter device 13 is referred to below as the second electrical converter device.

The electrical converter devices 12, 13 are arranged in the high-voltage network 3. In particular, the electrical converter device 13 together with the high-voltage energy store 5 is in a common housing part 14 made of an electrically insulating material, d. H. plastic, arranged. Consequently, the high-voltage energy store 5 and the electrical converter device 13 are integrated into a common structural unit.

The electrical converter devices 12 , 13 differ in their power or power consumption, with the first electrical converter device 12 generally having a higher power or power consumption than the second electrical converter device 13 . The power or power consumption of the first electrical converter device 12 is z. B. about 2 kilowatts (kW), the power or power consumption of the second electrical converter device 13 is z. B. only about 10 watts (W).

A control device 15 is also associated with or assigned to vehicle electrical system 1 . The control device 15 is designed in particular to control an electrical energy flow in terms of an exchange of specific amounts of electrical energy between the high-voltage network-side high-voltage energy store 5 and the low-voltage network-side low-voltage energy store 6 and vice versa. As part of the control of the energy flow between the high-voltage energy store 5 and the low-voltage energy store 6, the control device 15 can take certain boundary conditions into account, i. H. carry out the control of the energy flow depending on the presence or absence of corresponding boundary conditions.

A corresponding boundary condition can relate, for example, to a specific minimum amount of energy or maximum amount of energy and/or a specific minimum voltage or maximum voltage in the low-voltage energy store 6 . This is the control device 15 for controlling the energy flow between the high-voltage energy store 5 and the low-voltage energy store 6 is designed in such a way that in the low-voltage energy store 6 a specific minimum amount of energy and/or minimum voltage is not fallen below or a specific maximum amount of energy and/or maximum voltage is not exceeded. The minimum amount of energy or maximum amount of energy as well as the minimum voltage or the maximum voltage are available to the control device 15 as corresponding limit values and are processed by the control device 15 as setpoint values with the currently given amounts of energy or electrical voltages in the low-voltage network 4 or electrical voltages to be considered as actual values Low-voltage energy storage 6 compared. In this case, the electrical converter devices 12, 13 are actuated in particular when the comparison of the actual value and the target value carried out by the control device 15 results in a corresponding actual value being undershot or exceeded with a corresponding target value.

In particular, it is possible to ensure the quiescent current that is always to be provided by the low-voltage network 4 or in the low-voltage energy store 6 and which enables the basic operation of the consumers 10 connected to the low-voltage network 4 . The quiescent current, which is linked to a certain minimum amount of energy in the low-voltage energy store 6 , can therefore also be ensured by an energy flow from the high-voltage energy store 5 into the low-voltage energy store 6 .

determined e.g. B. the control device 15 that in the low-voltage energy storage device 6 there is a drop below the amount of energy required for the quiescent current, it can control the electrical converter device 13 and thus a required amount of energy can be transferred from the high-voltage energy storage device 5 to the low-voltage energy storage device 6. For the exchange of corresponding amounts of energy between the high-voltage network-side high-voltage energy store 5 and the low-voltage network-side low-voltage energy store 6, only the second electrical converter device 13 is advantageously used. Of course, the control device 15 includes or communicates with suitable detection means for detecting the electrical voltages or amounts of electrical energy currently present or present in the high-voltage network 3 , the low-voltage network 4 , the high-voltage energy storage device 5 and the low-voltage energy storage device 6 .

Furthermore, as a corresponding boundary condition which can be taken into account by the control device 15, i.e. H. alternatively or additionally, an operating state of motor vehicle 2 comprising vehicle electrical system 1 can also be used. Consequently, the control device 15 can control the electrical converter device 13 z. B. only allow when the motor vehicle 1 is or is parked. For this purpose, the control device 15 z. B. communicate with vehicle-side detection means for detecting the vehicle speed, the operating state of the electric motors, the ignition, etc., so that they can clearly determine the current operating state of the motor vehicle 2. For example, if control device 15 determines that motor vehicle 2 has been parked, it is possible to provide the above-mentioned quiescent current in low-voltage network 4 or the amount of electrical energy to be kept available in low-voltage energy store 6 from high-voltage network 3 or high-voltage energy store 5.

The control device 15 is designed to control at least one of the electrical converter devices 12, 13, in particular the second electrical converter device 13. Consequently, the control device 15 can put the electrical converter devices 12, 13 into different operating states, i. H. especially turning on and off. It is therefore possible, in particular, to switch on the second electrical converter device 13 only at specific points in time and thus to enable an energy flow between the high-voltage network 3 and the low-voltage network 4 or the high-voltage energy store 5 and low-voltage energy store 6 arranged therein. Taking into account the existence of a corresponding boundary condition, such as g. the electrical voltage currently present in the low-voltage network 4 or the low-voltage energy store 6, the second electrical converter device 13 can therefore be switched on if the voltage in the low-voltage network 4 and/or the low-voltage energy store 6 falls below a minimum voltage of z. B. 12 volts, is displayed. The same applies if exceeding a maximum voltage of z. B. 14 volts, was detected in the low-voltage network 4 and / or the low-voltage energy storage 6.

It should be noted that when the motor vehicle 2 is parked, an energy flow for the purpose of charging or recharging the low-voltage energy storage device 6 via the second electrical converter device 13 is generally not expedient, since in this case there is a risk that a correspondingly high electrical voltage will be generated outside the high-voltage network 3 is present, which is to be prevented for safety reasons. Equally, the efficiency of a corresponding charging process is not sufficiently high, so that corresponding charging processes are generally inefficient.

2 shows a schematic representation of an on-board network 1 of a motor vehicle 2 according to a second exemplary embodiment not according to the invention. The main difference to the in 1 shown embodiment of the invention The vehicle electrical system 1 according to the invention consists in the design of the low-voltage network-side low-voltage energy store 6 , which here is not formed solely from storage elements 8 based on lithium or lithium compounds, but also includes a number of double-layer capacitors 16 .

The low-voltage energy store 6 is therefore preferably formed from three storage elements 8 based on a lithium-cobalt-manganese-nickel compound and one storage element 8 based on lithium titanate, which storage elements 8 are connected in parallel with six double-layer capacitors 16 connected in series.

The low-voltage energy store 6 is therefore provided to ensure the operation of the consumers 10 connected to the low-voltage network 4 . The double layer capacitors 16 can be used as needed, i. H. be switched on, for example in the event of failure of the first electrical converter device 12, in order to compensate for any voltage peaks that may occur, in particular in the low-voltage network 4.

3 shows a schematic diagram of an on-board network 1 of a motor vehicle 2 according to a third exemplary embodiment of the invention. The main difference to those in the 1 , 2 Embodiments shown in turn consists in the configuration of the low-voltage energy storage 6. The in 3 The low-voltage energy storage device 6 shown is composed of three storage elements 8 based on a lithium-cobalt-manganese-nickel compound, which are connected in series to a double-layer capacitor 16 and one to the three storage elements 8 based on a lithium-cobalt-manganese-nickel compound and the this further double-layer capacitor 16 connected in parallel in series downstream double-layer capacitor 16 is formed. The low-voltage energy storage device 6 can therefore be divided into two parts connected in parallel, the first part being connected in series with a double-layer capacitor 16 by the three storage elements 8 based on a lithium-cobalt-manganese-nickel compound, and the second part being connected in parallel with it connected further double-layer capacitor 16 is formed.

With the principle according to the invention, it is basically possible to construct a corresponding vehicle electrical system 1 in terms of weight that is lighter, which is due to the fact that the capacity of the low-voltage energy store 6 can be dimensioned smaller due to the possible energy flow between the high-voltage network-side high-voltage energy store 5 and the low-voltage network-side low-voltage energy store 6. For example, a corresponding low-voltage energy storage device 6 with a capacity in the range of 1-6 ampere hours (Ah), in particular only approx. 2 ampere hours (Ah), and a maximum current of approx. 150 ampere (A) can be used, whereas conventional low-voltage energy storage devices can be used at least have a capacity of approx. 44 ampere hours. The smaller dimensioning of the low-voltage energy store 6 results in weight savings of up to 70% (considering a weight of a conventional low-voltage energy store of approximately 14 kilograms (kg) and a weight of a low-voltage energy store 6 that can be used according to the invention of approximately 4 kilograms).

Claims (12)

Vehicle electrical system (1) for a motor vehicle (2), in particular for an electric motor vehicle or a hybrid motor vehicle, comprising: - at least one high-voltage network (3) designed for a first electrical voltage, the high-voltage network (3) comprising at least one high-voltage energy store (5), - at least one low-voltage network (4) designed for a second electrical voltage that is lower than the first voltage of the high-voltage network (3), the low-voltage network (4) comprising at least one low-voltage energy store (6), - At least one first and at least one second electrical converter device (12, 13) connected between the high-voltage energy storage device (5) and the low-voltage energy storage device (6), which are each used to convert the first electrical voltage of the high-voltage network (3) into the second electrical voltage of the low-voltage network ( 4) and vice versa, wherein the low-voltage energy store (6) is formed from at least one storage element (8) based on lithium and/or a lithium compound and additionally comprises at least one capacitor connected in series with the storage element (8). on-board network claim 1 , characterized in that the low-voltage energy store (6) consists of: - three storage elements (8) based on lithium and one storage element (8) based on lithium titanate, or - three storage elements (8) based on lithium and two storage elements (8) based on a nickel metal hydride compound, or - three storage elements (8) based on lithium titanate and two storage elements (8) based on a lithium iron phosphate compound, or - four storage elements (8) based on a lithium iron phosphate - compound, or - four storage elements (8) based on lithium titanate and one storage element (8) based on lithium, or - four storage elements (8) based on lithium titanate and one storage element (8) based on a lithium-cobalt-manganese-nickel compound, or - six storage elements (8) based on lithium titanate, or - one storage element (8) is formed based on lithium titanate and three storage elements (8) based on a lithium-cobalt-manganese-nickel compound. on-board network claim 1 or 2 , characterized in that the storage elements (8) forming the low-voltage energy storage device (6) are connected in series. Vehicle electrical system according to one of the preceding claims, characterized in that the at least one capacitor is a double-layer capacitor (16). Vehicle electrical system according to one of the preceding claims, characterized in that the low-voltage energy store (6) comprises a plurality of capacitors, at least one of which is connected in parallel with the storage element (8). Vehicle electrical system according to one of the preceding claims, characterized in that the low-voltage energy store (6) consists of three storage elements (8), each based on a lithium-cobalt-manganese-nickel compound, and a double-layer capacitor (16) connected in series with them and one for the three each based on a lithium-cobalt-manganese-nickel compound storage elements (8) and the double-layer capacitor (16) connected downstream of these in series further double-layer capacitor (16). Vehicle electrical system according to one of the preceding claims, characterized in that the first electrical converter device (12) has a higher output than the second electrical converter device (13). Vehicle electrical system according to one of the preceding claims, characterized by a control device (15) which is designed to control an energy flow between the high-voltage energy store (5) and the low-voltage energy store (6) and vice versa, the control device (15) for controlling the energy flow between the high-voltage energy store (5) and the low-voltage energy store (6), and vice versa, is formed taking into account at least one boundary condition. on-board network claim 8 , characterized in that the boundary condition relates to a specific minimum amount of energy or maximum amount of energy and/or a specific minimum voltage or maximum voltage in the low-voltage energy store (6), the control device (15) for controlling the energy flow between the high-voltage energy store (5) and the low-voltage energy store (6) is designed in such a way that in the low-voltage energy store (6) a certain minimum amount of energy and/or minimum voltage is not fallen below or a certain maximum amount of energy and/or maximum voltage is not exceeded, and/or the boundary condition includes at least one operating state of a motor vehicle comprising the vehicle electrical system (1) ( 2) concerns. Vehicle electrical system according to one of the preceding claims, characterized in that the or a control device (15) is designed to control at least one of the electrical converter devices (12, 13), in particular the second electrical converter device (13). Vehicle electrical system according to one of the preceding claims, characterized in that the high-voltage energy store (5) is arranged with at least one electrical converter device (12, 13) in a common housing (14). Motor vehicle (2) comprising an on-board network (1) according to one of the preceding claims.

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