DE102012011840A1 - Electrical system for motor vehicle e.g. electric vehicle, has low-voltage energy storage device that is formed of lithium-based and/or lithium compound storage element - Google Patents

Abstract

The system (1) has a high-voltage network (3) that is provided with a high-voltage energy storage device (5). A low-voltage network (4) is provided with a low-voltage energy storage device (6). The high-voltage and low-voltage energy storage devices are connected in electrical conversion devices (12, 13) for converting the first electrical voltage of the high-voltage network into the second electrical voltage of the low voltage network and vice versa. The low-voltage energy storage device is formed of lithium-based and/or lithium compound storage element (8). An independent claim is included for a motor vehicle.

Description

The invention relates to a vehicle 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 electric-powered electric motor vehicles, for driving at least one, in particular designed as an electric motor, electric drive unit is provided, or partially or temporarily electrically powered hybrid motor vehicles, for their drive at least one, in particular designed as an electric motor , Electric drive unit and a, in particular designed as an internal combustion engine, further drive unit is provided, regularly have a divided into two areas wiring system.

The sections of the vehicle electrical system differ essentially in the voltage applied to each of these, so that a corresponding vehicle electrical system usually designed for a first electrical voltage high-voltage network in which, for example, an electrical voltage greater than or equal to 200 volts (V) is applied and a designed for a lower than the first voltage of the high voltage network second electrical voltage low-voltage network in which, for example, an electrical voltage of about 12 volts (V) is applied (12-volt low-voltage network) includes. Both the high-voltage network and the low-voltage network comprises at least one corresponding energy store. At the Hochvoltenergiespeicher associated with the high-voltage network are corresponding high-voltage consumers, in particular the electrically powered drive unit of the motor vehicle, and at the low-voltage network associated Niedervoltenergiespeicher corresponding low-voltage consumers, in particular a part of the illumination device of the motor vehicle connected.

It is also known, between the respective networks forming the electrical system, that is the high-voltage network and the low-voltage network to switch electrical Wandlervorrichtungen, each for converting the first electrical voltage of the high-voltage network in the second electrical voltage of the low-voltage network, and vice versa, are formed. In this way, the low-voltage energy storage associated with the low-voltage network can be compensated for in comparison to the high-voltage energy storage associated with the high-voltage network, such that an energy flow from the high-voltage network-side highvoltage energy storage into the lowvoltage network-side lowvoltage energy storage is possible.

However, conventional types of corresponding low-voltage network-side low-energy energy storage represent technical restrictions on the potential performance of a corresponding electrical system.

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

The problem is solved by an electrical system according to the invention, which comprises at least one designed for a first electrical voltage high-voltage network, the high-voltage network comprises at least one high-voltage energy storage, at least one for a lower compared to the first voltage of the high voltage network second electrical voltage low-voltage network, said Low-voltage network comprises at least one low-energy energy storage, at least a first and at least one second connected between the high-voltage energy storage and the low-energy energy storage electrical conversion device, which in each case for converting the first electrical voltage of the high-voltage network in the second electrical voltage of the low-voltage network, and vice versa, is formed, wherein Low-energy storage is formed from at least one based on lithium and / or a lithium compound storage element.

The present invention is based on the idea of designing the low-energy storage device associated with the low-voltage network of a corresponding vehicle electrical system such that it comprises 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.

Within the scope of the present invention, various different configurations of the low-voltage energy storage device associated with the low-voltage network are therefore conceivable, which have in common that they each have at least one storage element based on lithium and / or a lithium compound. Any further memory elements forming the low-energy energy storage device may or may not, however, be formed as it were based on lithium and / or a lithium compound. Under a corresponding memory elements is generally to be understood as an electrochemical cell as part of a battery.

The formation of the low-voltage energy storage device associated with the low-voltage network from at least one storage element based on lithium and / or a lithium compound, that is to say substantially as a rechargeable lithium accumulator or lithium battery, is in particular Therefore, advantageous because lithium accumulators have a higher power or energy density compared to conventional low energy energy storage devices formed in particular from memory elements based on lead or lead compounds. Likewise, corresponding low energy storage devices formed from memory elements based on lithium and / or lithium compounds are advantageous in comparison to conventional low energy energy storage devices (with comparable electrical properties) in terms of their weight, being significantly lighter, so that corresponding motor vehicles equipped with the vehicle electrical system according to the invention are also lighter basically has a positive effect on energy consumption.

A further advantage of the vehicle electrical system according to the invention is that by the use of at least two corresponding electrical converter devices, which are designed in particular as a DC-DC converter or DC / DC converter, even in case of failure of an electrical converter device still at least one further functional electrical converter device is given , via which various to the electrical system, d. H. connected to the high-voltage network or the low-voltage network consumers can be supplied with electrical energy. It is particularly advantageous that, in particular for the operation of the motor vehicle equipped with the vehicle electrical system according to the invention safety-related consumers can continue to operate, so that the motor vehicle can be turned off at least still safe in such cases of failure of an electrical converter device.

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

Therefore, it is preferable that the low-energy storage is composed of three storage elements based on lithium and a lithium titanate storage element, or three lithium-based storage elements and two nickel metal hydride compound storage elements, or three lithium titanate based storage elements and two storage elements based on a lithium iron-phosphate compound, or four storage elements based on lithium titanate and a storage element based on lithium, or four storage elements based on lithium titanate and a storage element based on a lithium-cobalt-manganese-nickel compound ( so-called NMC memory elements or NMC cells), or six storage elements based on lithium titanate, or a storage element based on lithium titanate and three storage elements based on a lithium-cobalt-manganese-nickel compound, or three storage elements based on a lithium Cobalt-manganese-nickel compound and a storage element based on lithium titanate, or four storage elements is formed based on a lithium-iron-phosphate compound.

The concrete number of memory elements forming the low-energy energy storage device can be used to specifically control its internal resistance, the principle being that a smaller number of memory elements leads to a lower internal resistance of the low-energy energy storage compared to a higher number of memory elements , Likewise, a smaller number of memory elements forming the low-energy energy storage device may also be advantageous with regard to cost aspects. The memory elements forming the low-voltage energy storage are usually connected in series.

In the aforementioned configurations of the low-voltage energy storage device or the storage elements forming the low-energy energy storage device, it is assumed that a 12-volt low-voltage network forms part of the vehicle electrical system according to the invention. In the case of a design of the low-voltage network as a 24 volt low-voltage network, the respective number of the above-mentioned, the low-energy storage memory forming memory elements doubled, the combination options of the different storage element types remain the same.

The high-voltage energy storage device is likewise formed from a number of storage elements, in particular connected in series. In this case, the memory elements forming the high-voltage energy storage device can, for. B. based on lithium or lithium compounds.

The memory elements forming the highvoltage energy storage device may be referred to as first memory elements, and the memory elements forming the lowvoltage energy storage device may be referred to as second memory elements.

It is possible for the low-energy energy storage device to comprise, in addition to the plurality of memory elements, at least one capacitor, in particular a double-layer capacitor. 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 opposite polarity collect at the electrodes. It forms a charge carrier layer of immobile charge carriers. Behave the electrodes with the charge carrier layer as a dielectric like two capacitors connected in series across the electrolyte. They store the energy electrostatically in contrast to electrochemical energy storage. Double-layer capacitors generally have small internal resistances and a large number of possible charging or discharging cycles. Thus, the property profile of the low-energy energy storage, in particular with regard to a low internal resistance, can be improved in this way.

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

According to a preferred embodiment of a low-energy storage device, this can consist of three memory elements each based on a lithium-manganese-nickel compound and a double-layer capacitor connected in series therewith, and one of the three each on a lithium-cobalt-manganese-nickel compound based memory elements as well as this in series downstream double-layer capacitor further double-layer capacitor may be formed. The low-energy energy storage device according to this embodiment can accordingly be divided into two parts connected in parallel, a first part being formed by the three storage elements each based on a lithium-cobalt-manganese-nickel compound and the double-layer capacitor connected in series this parallel connected part is formed by the further double-layer capacitor.

It is possible that the first electrical conversion device has a higher output than the second electric conversion device. In principle, the electric traveling devices forming respective components of the vehicle electrical system according to the invention are advantageously DC-DC converters, ie devices or electrical circuit arrangements which are designed to convert an electrical input voltage (input direct voltage) into an electrical output voltage (DC output voltage) with higher, lower or inverted voltage level to convert. In the context of the present invention, therefore, a high input voltage of the high-voltage network, that is about an applied voltage in the high-voltage network of greater than or equal to 200 volts, in a comparison lower output voltage of the low-voltage network, that is about a voltage applied in the low-voltage network electrical Voltage of 12 volts, to be converted. A reverse conversion of the voltage applied in the low-voltage network electrical voltage as an input voltage in an applied voltage in the high-voltage network voltage as an output voltage is possible.

As mentioned, the power consumption of the two electrical conversion devices is advantageously different, wherein the power consumption of the first electrical conversion device is higher than the power consumption of the second electrical conversion device. This is therefore possible because of the first electrical converter device, in particular electrical high-power consumers, such. B. as a drive unit serving electric motors or starters, are supplied with electrical energy, whereas via the second electrical converter device, in particular in the context of energy flow between the high-voltage network side high-voltage energy storage and the low-voltage network low-energy storage, a certain amount of electrical energy to the low-voltage network or the low-energy energy storage contained therein is deliverable or is discharged.

In this case, 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, for example, a power in the range of only 1-10 watts (W), in particular 2 watts (W), has or is designed for this.

As already mentioned, the second electrical converter device advantageously serves at least temporarily to enable an electrical energy flow (current flow) from the high-voltage network into the low-voltage network 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-energy storage. As appropriate low-voltage consumers, for example, a motor vehicle side lighting device, in particular a parking light, various driver assistance systems, including in particular safety-related driver assistance systems, such. As brake or steering assistance systems, but also acoustic and / or visual motor vehicle-side multimedia devices such. As radios, television or communication equipment for telephone, Internet, etc., are to be understood.

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

As a corresponding boundary condition, the existence of which is verifiable in particular via the control device, for example, a certain minimum amount of energy or maximum energy and / or a certain minimum voltage or maximum voltage in the low-energy energy storage and / or the low-voltage network in question, wherein the control device for controlling the energy flow between the high-voltage energy storage and the Niedervoltenergiespeicher is designed such that in the low-energy energy storage a certain minimum amount of energy and / or minimum voltage is not exceeded or a certain maximum energy and / or maximum voltage is not exceeded, and / or at least one operating state of the vehicle electrical system comprehensive into consideration.

Accordingly, the control device or a communicating with this verification device, such. B. a suitable comparator circuit, continuously or discontinuously at certain times determine the existing amount of electrical energy and / or voltage applied in the low-voltage energy storage and / or the low-voltage network and this with a predetermined or predetermined minimum electrical energy or maximum energy and / or a predetermined or specifiable electrical Compare minimum voltage or maximum voltage in the low-voltage energy storage or the low-voltage network in terms of an actual value-target-value comparison. If the current value of the electrical energy quantity or voltage present in the low-energy energy store or low-voltage network exceeds or falls below a corresponding upper or lower limit value in the sense of corresponding threshold values, the control device conditions an energy flow via the electrical converter devices, in particular via the second electrical converter device the high-voltage network or the high-voltage energy storage and the low-voltage network or the Niedervoltenergiespeicher such that in the low-energy energy storage and / or the low-voltage network a certain minimum amount of energy and / or minimum voltage is not exceeded or a certain maximum energy and / or maximum voltage is not exceeded. A corresponding energy flow between the high-voltage network or the high-voltage energy storage and the low-voltage network or low-energy storage can already take place when the current value of the local electrical energy or the voltage applied there approaches the respective minimum or maximum value, whereby the underflow or excess corresponding limit values can be prevented even safer.

Of course, the control device communicates for this purpose with suitable detection means, 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 storage. 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 storage.

For example, a corresponding low-voltage network side or low energy energy storage side minimum energy amount in the form of a certain serving as a boundary condition quiescent current, which quiescent current in the low-voltage network low-energy storage is always vorzuhalten to ensure the operation of certain low-voltage network connected consumers in all circumstances. This is borne by the consumer, such as B. corresponding driver assistance systems, such as brake or steering assistance systems, or a parking light, are safety-relevant for the operation of the motor vehicle equipped with the electrical system according to the invention, to significant safety advantages.

It is also conceivable that a corresponding boundary condition concerns at least one operating state of the motor vehicle comprising the vehicle electrical system. Under operating condition of the motor vehicle, for example, a driving or stationary operation to understand. Sonach, it is particularly advantageous if the vehicle equipped with the vehicle electrical system according to the invention is or is parked, which z. B. over certain operating parameters of the motor vehicle, such as. B. vehicle speed, ignition, etc., can be determined, the aforementioned quiescent current in the low-voltage network or the Niedervoltenergiespeicher via an optionally necessary energy flow between the to ensure high-voltage network-side high-voltage energy storage and the low-voltage network low-energy storage.

Advantageously, the or a control device for controlling at least one of the electrical converter devices, in particular the second electrical converter device is formed. Again, depending on the presence of certain boundary conditions is thus a control, which in particular a switching on or off of the electrical conversion device (s), possible. As appropriate boundary conditions, the above-mentioned, the electrical energy amount and / or electrical voltage in the low-voltage network and / or the low-voltage energy storage boundary conditions can be used. For example, it is therefore possible to switch on the second electrical converter device if 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, for. B. 12 volts, below. Conversely, the second electrical conversion device can be turned off when the electrical voltage in the low-voltage network a predetermined or predetermined maximum electrical voltage in the sense of an upper limit or threshold value, for. B. 14 volts, exceeds.

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

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

Further advantages, features and details of the invention will become apparent from the embodiments described below and with reference to the drawings, wherein

1 a schematic diagram of a vehicle electrical system of a motor vehicle according to a first exemplary embodiment of the invention;

2 a schematic diagram of a vehicle electrical system of a motor vehicle according to a second exemplary embodiment of the invention; and

3 a schematic diagram of a vehicle electrical system of a motor vehicle according to a third exemplary embodiment of the invention shows.

1 shows a schematic diagram of a vehicle electrical system 1 of a motor vehicle 2 according to a first exemplary embodiment of the invention. The car 2 is an electric motor vehicle, ie it is purely electrically via one or more, each serving as a drive units electric motors 9 driven.

The wiring system is obvious 1 in a high-voltage network 3 and a low voltage network 4 divided. The high voltage network 3 has a voltage level of about 250 volts, the low-voltage network 4 has a voltage level of about 12 volts. Both in the high voltage network 3 as well as in the low-voltage network 4 are arranged corresponding rechargeable energy storage. Accordingly, the high-voltage network includes 3 a high-voltage energy storage 5 and the low voltage network 4 a low energy energy storage 6 ,

Here is the high-voltage energy storage 5 from several series-connected, each based on lithium storage elements 7 , which may also be referred to as cells, formed. The low energy energy storage 6 is also made up of several series-connected, lithium-based storage elements 8th educated.

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

To the high voltage network 3 are corresponding high-voltage consumers or high-power consumers, such. B. the drive unit of the motor vehicle 2 forming electric motor 9 , connected, which via the high-voltage network 3 and thus the high-voltage energy storage 5 is supplied with electrical energy. The electrical connection between the high-voltage energy storage 5 and the high power consumers is via the operation, ie opening and closing, electrical switching means 11 separable and recoverable. It can be such z. B. be prevented that even outside the driving of the motor vehicle 2 a high voltage, ie in particular the respective voltage of the high-voltage network 3 , on the electric motor 9 is applied.

To the low voltage network 4 are corresponding low-voltage consumers 10 , such as B. in the form of designed as a brake or steering assistance systems driver assistance systems, a lighting device of the motor vehicle 2 , ie in particular the parking light of the motor vehicle 2 , various multimedia devices, such. As radio, television, etc., connected via the low-voltage network 4 and thus on the Niedervoltenergiespeicher 6 be supplied with electrical energy (electricity).

Visibly includes the electrical system 1 two parallel connected, each designed as a DC-DC converter or DC / DC converter electrical converter devices 12 . 13 , The electrical converter device 12 is hereinafter referred to as the first electrical converter device, the electrical converter device 13 hereinafter referred to as a second electrical converter device.

The electrical converter devices 12 . 13 are in the high-voltage network 3 arranged. In particular, the electrical conversion device 13 including the highvoltage energy storage 5 in a common housing part 14 made of an electrically insulating material, ie plastic arranged. Consequently, the high-voltage energy storage 5 and the electrical conversion device 13 integrated into a common unit.

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

The electrical system 1 is also a control device 15 associated or assigned. The control device 15 is in particular for controlling an electrical energy flow in the sense of an exchange of certain amounts of electrical energy between the high-voltage network side high-voltage energy storage 5 and the low-voltage grid side low-energy storage 6 , and conversely, trained. As part of the control of the energy flow between the high-voltage energy storage 5 and the low energy energy storage 6 can the controller 15 take into account certain boundary conditions, ie, make the control of the energy flow as a function of the presence or absence of corresponding boundary conditions.

A corresponding boundary condition may, for example, a certain minimum amount of energy or maximum energy and / or a certain minimum voltage or maximum voltage in the low-voltage energy storage 6 affect. Here, the control device 15 for controlling the flow of energy between the high-voltage energy storage 5 and the low energy energy storage 6 is formed such that in the low-energy energy storage 6 a certain minimum amount of energy and / or minimum voltage is not exceeded or a certain maximum 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 the control device 15 as appropriate limits and are on the part of the controller 15 as setpoint values with the currently given amounts of energy or electrical voltages in the low-voltage network to be considered as actual values 4 or the low-energy energy storage 6 compared. In this case, a control of the electrical converter devices takes place 12 . 13 especially if the part of the control device 15 carried out actual value setpoint comparison results in a lower or exceeding a corresponding actual value with a corresponding setpoint.

In particular, it is possible on the part of the low-voltage network 4 or in the low-energy energy storage 6 always to be kept quiescent current, which is the basic operation of the low-voltage network 4 connected consumers 10 allows to ensure. The quiescent current, which with a certain minimum amount of energy in the low-energy energy storage 6 can therefore also by a flow of energy from the high-voltage energy storage 5 in the low energy energy storage 6 be guaranteed.

Determines z. B. the controller 15 in that in the low energy energy storage 6 an underrun of the amount of energy required for the quiescent current is given, this can be the electrical converter device 13 control and so a needs-based amount of energy from the high-voltage energy storage 5 to the low energy energy storage 6 be transmitted. For the exchange of appropriate amounts of energy between the high-voltage network-side high-voltage energy storage 5 and the low-voltage grid side low-energy storage 6 Advantageously comes exclusively the second electrical converter device 13 for use. Of course, the control device includes or communicates 15 this with suitable detection means for detecting the in the high-voltage network 3 , the low voltage network 4 , the high-voltage energy storage 5 as well as the Low-voltage energy storage 6 currently applied or existing electrical voltages or electrical energy quantities.

As appropriate of the control device 16 Considerable boundary condition can also, ie alternatively or additionally, an operating state of the electrical system 1 comprehensive motor vehicle 2 be used. Thus, the control device 15 a control of the electrical converter device 13 z. B. only allow if the motor vehicle 1 stands or is turned off. For this purpose, the control device 15 z. B. with motor vehicle side detection means for detecting the vehicle speed, the operating state of the electric motors, the ignition, etc. communicate, so that these clearly the current operating state of the motor vehicle 2 can determine. For example, it is possible that when the control device 15 determines that the motor vehicle 2 was turned off, the above quiescent current in the low-voltage network 4 or in addition to the low-energy energy storage 6 vorzuhaltende electrical energy from the high-voltage network 3 or the high-voltage energy storage 5 provide.

The control device 15 is for controlling at least one of the electrical conversion devices 12 . 13 , in particular the second electrical converter device 13 , educated. Thus, the control device 15 the electrical converter devices 12 . 13 into different operating states, ie in particular turn on and off. It is therefore possible, in particular the second electrical converter device 13 only to turn on at certain times and thus an energy flow between the high-voltage network 3 and the low voltage network 4 respectively the high-voltage energy storage arranged therein 5 and low energy storage 6 to enable. Taking into account the existence of a corresponding boundary condition, such. B. currently in the low-voltage network 4 or the low-energy energy storage 6 adjacent electrical voltage can therefore a switching on the second electrical conversion device 13 done when in the low voltage network 4 and / or the Niedervoltenergiespeicher 6 a drop below a minimum voltage, z. B. 12 volts is displayed. The same applies if an exceeding of a maximum voltage, z. B. 14 volts, in the low-voltage network 4 and / or the Niedervoltenergiespeicher 6 was recorded.

It should be noted that when the vehicle is parked 2 an energy flow for the purpose of charging or recharging the low-energy storage 6 over the second electrical conversion device 13 regularly is not appropriate, since in this case there is a risk that outside the high-voltage network 3 a correspondingly high voltage is applied, which is to be prevented for safety-related aspects. Similarly, the efficiency of a corresponding charging process is insufficiently high, so that corresponding charging operations are generally inefficient.

2 shows a schematic diagram of a vehicle electrical system 1 of a motor vehicle 2 according to a second exemplary embodiment of the invention. The main difference to the in 1 shown embodiment of the electrical system according to the invention 1 consists in the execution of low-voltage grid side low-voltage energy storage 6 , which is not based solely on lithium or lithium compounds based storage elements 8th is formed, but in addition several double-layer capacitors 16 includes.

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

The low energy energy storage 6 is therefore to ensure the operation of the low-voltage network 4 connected consumers 10 intended. The double-layer capacitors 16 can be required, ie, about failure of the first electrical converter device 12 , be switched on, possibly occurring voltage peaks, especially in the low-voltage network 4 to compensate.

3 shows a schematic diagram of a vehicle electrical system 1 of a motor vehicle 2 according to a third exemplary embodiment of the invention. The main difference to those in the 1 . 2 shown embodiments, in turn, in the configuration of the low-energy energy storage 6 , The in 3 shown low-energy storage 6 is through three storage elements 8th based on a lithium-cobalt-manganese-nickel compound, which in series a double-layer capacitor 16 downstream and one of the three based on a lithium-cobalt-manganese-nickel compound storage elements 8th and this in series downstream double-layer capacitor 16 connected in parallel another double-layer capacitor 16 educated. The low energy energy storage 6 can therefore be mentally divided into two parts connected in parallel, the first part by the three based on a lithium-cobalt-manganese-nickel compound storage elements 8th in series with a double-layer capacitor 16 and the second part through the parallel connected another double-layer capacitor 16 is formed.

With the principle according to the invention, it is basically possible to have a corresponding vehicle electrical system 1 lighter in weight, which is due to the fact that the potential energy flow between the high-voltage network-side high-voltage energy storage 5 and the low-voltage grid side low-energy storage 6 the low energy energy storage 6 can be sized smaller in its capacity. Thus, for example, a corresponding low-energy storage 6 with a capacity in the range of 1-6 amp hours (Ah), in particular only about 2 amp hours (Ah), and a maximum current of about 150 amps (A) are used, whereas conventional low-energy storage at least a capacity of about 44 amp hours must have. Due to the smaller dimensions of the low-energy energy storage 6 This results in weight savings of up to 70% (considering a weight of a conventional low-energy storage of about 14 kilograms (kg) and a weight of a usable according to the invention low-energy storage 6 of about 4 kilograms).

Claims (12)

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 designed for a first electrical voltage ( 3 ), the high-voltage network ( 3 ) at least one high-voltage energy storage ( 5 ), at least one for one compared to the first voltage of the high-voltage network ( 3 ) lower second electrical voltage designed low-voltage network ( 4 ), the low-voltage network ( 4 ) at least one low-energy energy storage device ( 6 ), at least one first and at least one second between the high-voltage energy storage ( 5 ) and the low-voltage energy storage ( 6 ) switched electrical converter device ( 12 . 13 ), each for converting the first electrical voltage of the high-voltage network ( 3 ) in the second electrical voltage of the low-voltage network ( 4 ), and vice versa, is formed, wherein the low-energy energy storage ( 6 ) of at least one lithium and / or lithium compound based memory element ( 8th ) is formed. Vehicle electrical system according to claim 1, characterized in that the low-energy energy storage ( 6 ) from: - three memory elements ( 8th ) based on lithium and a memory element ( 8th ) based on lithium titanate, or - three memory elements ( 8th ) based on lithium and two memory elements ( 8th ) based on a nickel-metal hydride compound, or - three memory elements ( 8th ) based on lithium titanate and two memory elements ( 8th ) based on a lithium-iron-phosphate compound, or - four memory elements ( 8th ) based on a lithium-iron-phosphate compound, or - four memory elements ( 8th ) based on lithium titanate and a memory element ( 8th ) based on lithium, or - four memory elements ( 8th ) based on lithium titanate and a memory element ( 8th ) based on a lithium-cobalt-manganese-nickel compound, or - six memory elements ( 8th ) based on lithium titanate, or - a memory element ( 8th ) based on lithium titanate and three memory elements ( 8th ) is formed based on a lithium-cobalt-manganese-nickel compound. Vehicle electrical system according to claim 1 or 2, characterized in that the Niedervoltenergiespeicher ( 6 ) forming memory elements ( 8th ) are connected in series. Vehicle electrical system according to one of the preceding claims, characterized in that the low-energy energy storage device ( 6 ) additionally at least one capacitor, in particular a double-layer capacitor ( 16 ). Vehicle electrical system according to claim 4, characterized in that the capacitor in parallel or in series with the low-voltage energy storage ( 6 ) is switched. Vehicle electrical system according to claim 4 or 5, characterized in that the low-voltage energy storage ( 6 ) of three storage elements each based on a lithium-cobalt-manganese-nickel compound ( 8th ) and a series-connected double-layer capacitor ( 16 ) and one to the three each on a lithium-cobalt-manganese-nickel compound based memory elements ( 8th ) and the series-connected double-layer capacitor ( 16 ) another double-layer capacitor ( 16 ) is formed. Vehicle electrical system according to one of the preceding claims, characterized in that the first electrical converter device ( 12 ) higher power than the second electrical conversion device ( 13 ) having. Vehicle electrical system according to one of the preceding claims, characterized by a control device ( 15 ), which are used to control an energy flow between the high-voltage energy storage ( 5 ) and the Low energy energy storage ( 6 ), and vice versa, the control device ( 15 ) for controlling the flow of energy between the high-voltage energy storage ( 5 ) and the low-voltage energy storage ( 6 ), and vice versa, taking into account at least one boundary condition is formed. Vehicle electrical system according to claim 8, characterized in that the boundary condition 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 ( 6 ), wherein the control device ( 15 ) for controlling the flow of energy between the high-voltage energy storage ( 5 ) and the low-voltage energy storage ( 6 ) is designed such that in the low-voltage energy storage ( 6 ) 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, and / or the boundary condition at least one operating state of the vehicle electrical system ( 1 ) comprehensive motor vehicle ( 2 ). Vehicle electrical system according to one of the preceding claims, characterized in that the or a control device ( 15 ) for controlling at least one of the electrical conversion devices ( 12 . 13 ), in particular the second electrical conversion device ( 13 ), is trained. Vehicle electrical system according to one of the preceding claims, characterized in that the high-voltage energy storage ( 5 ) with at least one electrical converter device ( 12 . 13 ) in a common housing ( 14 ) is arranged. Motor vehicle ( 2 ), comprising a vehicle electrical system ( 1 ) according to one of the preceding claims.

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