DE102017222197B4 - Method for controlling an electrical system of an electrically driven motor vehicle and charge state control device for a motor vehicle - Google Patents

Abstract

Method for controlling an electrical system (10) of an electrically driven motor vehicle, wherein the electrical system comprises an on-board network with at least one lithium battery (12) and at least one electrical machine (14), wherein at least one electrical consumer (16; 18) is coupled to the on-board network; comprising the following steps:a) specifying a lower (USW) and an upper threshold value (OSWnorm) for a target state of charge range of the lithium battery (12) (step 100);b) determining an electrical base load (GL) of the on-board network (step 120);c) modifying the upper threshold value (OSW) for the target state of charge range of the at least one lithium battery (12) depending on the electrical base load (GL) of the on-board network determined in step b) (step 180); andd) when the motor vehicle is being driven: setting a state of charge of the lithium battery (12) between the lower (USW) and the modified upper threshold value (OSW) for the target state of charge range of the lithium battery (12) (step 200); characterized in that in step c) the upper threshold value (OSW) is selected to be greater the greater the electrical base load (GL) of the vehicle electrical system determined in step b).

Description

The present invention relates to a method for controlling an electrical system of an electrically driven motor vehicle, wherein the electrical system comprises an on-board network with at least one lithium battery and at least one electrical machine, wherein at least one electrical consumer is coupled to the on-board network. The method comprises the following steps: a) specifying a lower and an upper threshold value for a target state of charge range of the lithium battery; b) determining a basic electrical load of the on-board network; c) modifying the upper threshold value for the target state of charge range of the at least one lithium battery depending on the basic electrical load of the on-board network determined in step b); and d) When the motor vehicle is driving: setting a state of charge of the lithium battery between the lower and the modified upper threshold value for the target state of charge range of the lithium battery. It further relates to a charge state control device for a motor vehicle for controlling a charging of at least one lithium battery of the motor vehicle, wherein the charge state control device is designed to set the charge state of the at least one lithium battery between a lower and an upper threshold value for a target charge state range of the lithium battery when the motor vehicle is being driven, wherein the charge state control device is further designed to modify the upper threshold value for the target charge state range of the at least one lithium battery depending on a basic electrical load of the on-board network.

1 shows in this context an electrical system 10 of an electrically driven motor vehicle known from the prior art. The electrical system 10 comprises an on-board network with at least one lithium battery 12, an electrical machine 14 and electrical consumers 16, 18 shown as examples. The electrical machine 14 is designed as a belt starter generator and takes on the functions of a starter, a generator, a drive, in particular a boost, or a load point shift. In the present exemplary embodiment, the voltage level of the on-board network is approximately 12 V. The invention can also be used without further ado in electrical systems whose on-board network has, for example, two different voltage levels, in particular a low voltage range of approximately 12 V and a high voltage range of approximately 48 V, the two voltage ranges being coupled to one another, for example via a DC/DC converter. The lithium battery 12 is assigned a battery monitoring module 20 which comprises a voltage measuring device 22 and a current measuring device 24. The electrical machine 14 is assigned a monitoring module 26, which also includes a voltage measuring device 28 and a current measuring device 30. If a current measuring device is integrated in the electrical machine 14, the current measuring device 30 can be omitted.

As part of climate protection, the _CO2 requirements for motor vehicles are becoming increasingly stricter. To take this into account, there are on-board network concepts with more powerful energy storage devices than lead batteries or on-board network concepts with more than one energy storage device. By using recuperation devices, such as belt starter generators, it is possible to recuperate more energy, for example during braking phases, and also to carry out a load point reduction during traction phases in order to relieve the load on the motor vehicle's drive, for example an internal combustion engine. By reducing the load point, the internal combustion engine delivers a torque that is not sufficient to meet the driver's desired torque. The difference can, as mentioned, be provided, for example, by a belt starter generator, which draws electrical energy from an energy storage device. This means that the internal combustion engine can be operated in an optimal range in terms of efficiency. In this way, fuel can be saved.

The optimum operating range of the internal combustion engine can also be greater than the driver's desired torque. In this case, the belt starter generator can be controlled accordingly and the energy for generating the differential torque can be converted into electrical energy. Since the internal combustion engine is working at an optimum operating point in this case, the electrical energy is generated efficiently. This is a controlled load point increase.

Such on-board networks require energy storage devices that can absorb and absorb more energy and power than a conventional on-board network with a 12V lead battery. It has been found that the use of a lithium battery is particularly advantageous. A lithium battery is a cycle-resistant energy storage device that is particularly suitable for recuperation.

Due to technological constraints, particularly the lifetime design, the usable SOC (State of Charge) range of a lithium battery is typically between between a lower threshold of about 20% and an upper threshold of about 80%.

• Aus der DE 10 2016 005 125 A1 ist ein Verfahren zum Steuern einer Energiespeichereinrichtung eines Mild-Hybrid-Kraftfahrzeugs sowie eine Ladezustandssteuereinrichtung bekannt, bei dem/ bei der während mindestens einer Fahrt mindestens ein Lade- und ein Entladevorgang mit Bezug auf mit der Energiespeichereinrichtung ausgetauschte Energiemengen überwacht und daraus mit einer vorgebbaren Wahrscheinlichkeit zu erwartende Energiemengen für zukünftige Lade- und Entladevorgänge ermittelt werden. Basierend auf diesen Ermittlungen werden der obere und der untere Schwellenwert für einen Zielladezustandsbereich der Energiespeichereinrichtung festgelegt.

Various new on-board network concepts are known from the state of the art:

• From the EN 10 2016 005 125 A1 A method for controlling an energy storage device of a mild hybrid motor vehicle and a charge state control device are known in which at least one charging and discharging process are monitored during at least one journey with reference to the amounts of energy exchanged with the energy storage device and from this, expected amounts of energy for future charging and discharging processes are determined with a predeterminable probability. Based on these determinations, the upper and lower threshold values for a target charge state range of the energy storage device are determined.

From the EN 10 2016 007 505 A1 A method for controlling an electrical system of an electrically driven motor vehicle is known, wherein a first electrical direct voltage is provided by means of a first electrical energy store of a first on-board network and a second electrical direct voltage is provided by means of a second electrical energy store of a second on-board network, wherein the two on-board networks are electrically coupled to one another by means of a DC/DC converter, wherein the motor vehicle is driven in a normal driving mode by means of an electrical machine connected to the first on-board network and coupleable to an internal combustion engine, wherein a charge state of the first electrical energy store is controlled by means of a charge state control unit in accordance with a predictive driving mode of the motor vehicle. The first and the second electrical energy store provide the same storage capacity for electrical charge, wherein the electrical coupling of the DC/DC converter is controlled by a control signal of the charge state control unit and a charge state of the second electrical energy store is controlled by means of the charge state control unit in accordance with the predictive driving mode of the motor vehicle, in that the charge state control unit controls the DC/DC converter accordingly by means of the control signal. The target charge level range is set by controlling the target torque on the belt starter generator. This publication mentions that, with regard to predictive charge level control, an accumulator of a first on-board network, to which the drive device is also connected, can be controlled using a charge level control unit provided for this purpose. The charge level control unit uses a wide variety of information to control the charge level of the accumulator of this on-board network, such as environmental data, driver behavior, navigation data, and the like. The charge level control unit thus makes it possible to take this into account in the charge level control if sufficient information is available about a route to be traveled. If, for example, a route is planned that involves driving over a mountain pass, the charge level control unit can be used to control the charge level of the electrical energy storage device in the vehicle's electrical system in such a way that the electrical energy storage device has the lowest possible charge level when the top of the pass is reached, so that during a subsequent downhill journey, electrical energy gained through overrun and/or braking recuperation by the drive device can be fed into the electrical energy storage device. In this respect, predictive charge level control can not only record any energy recovery, but also plan a predicted energy requirement. If, for example, the route is also planned to run through a traffic-calmed zone at reduced speed, the charge level control can be used to control the electrical energy storage device in such a way that any roll stabilization or even an electric drive of a turbo compressor does not need to be planned.

From the EN 10 2011 116 132 A1 A method for operating a vehicle with a hybrid drive is known. It describes a load point increase in operating mode B6 and a load point reduction in operating mode B7.

From the EN 10 2013 215 519 A1 A method for operating a motor vehicle is known in which additional electric motor drive power is made available when a battery is fully charged and a route ahead includes sections with high recuperation. This prevents the load point of an internal combustion engine from having to be raised.

The EN 10 2011 085 454 A1 describes a method for controlling a hybrid drive with an internal combustion engine, an electric motor and an electrical energy storage device, in particular for a rail vehicle. The method selects a preferred operating mode based on route and battery data. For example, the energy storage device can be emptied as far as possible before known and predictively usable braking processes using predictive operating control of the energy storage device. The electrical energy storage device can also be fully charged in advance as part of an example of predictive operating control for a "boost" drive profile.

Finally, the EN 10 2007 038 585 A1 a method for shifting the load point in hybrid operation in a parallel hybrid vehicle is known. The method measures a charge state of a battery and lowers a load point of an internal combustion engine when the battery is fully charged.

In the EN 10 2014 009 448 A1 a battery management system for predictive charge level control in an electrically powered motor vehicle is disclosed. In the cited publication, predictive route data from navigation data is used to predict the energy requirement of a device in an on-board power supply and, based on the predicted energy requirement, to regulate an energy reserve of the energy storage device on a particular route section in such a way that no unnecessary energy reserve is kept for a device in an on-board power supply of the motor vehicle on the route section if this device is not expected to be used on the route section. The expected driving situation can, for example, include a course of the route section, such as a serpentine. Furthermore, a traffic situation on the route section, speed limits or a traffic situation can be taken into account.

The EN 10 2016 005 115 B3 relates to a method for controlling an energy storage device of a mild hybrid motor vehicle, wherein the energy storage device has a total capacity. A charge state control device of the energy storage device sets a charge state of the energy storage device between an upper and a lower threshold value for a target charge state range of the energy storage device according to a first operating state. If, due to the fulfillment of at least one predefinable condition, it is determined that at least one climate control device of the motor vehicle is to be activated or remains activated for at least a predefinable period of time, the upper and lower threshold values for the target charge state range are set at least for the predefinable period of time according to a second operating state. This publication was used to formulate the preambles of the independent claims.

From the EN 10 2014 222 007 A1 A PHEV energy management controller with trip-oriented energy consumption pre-planning is developed. A driving pattern-based plug-in hybrid electric vehicle energy consumption pre-planning process enables a PHEV's trip-oriented energy management controller to use scalable levels of available driving prior knowledge to optimize the use of on-board energy. The pre-planning process generates an optimal battery state of charge depletion profile for a given route to be driven by a PHEV.

The EN 10 2012 001 820 A1 relates to a system and method for controlling a state of charge of a vehicle battery used by a hybrid electric vehicle to power the vehicle so that the SOC is maintained within a desired SOC range that is temperature dependent.

The object of the present invention is to further develop a generic method and a generic charge state control device in such a way that it enables the operation of a motor vehicle to be as resource-efficient as possible.

This object is achieved by a method having the features of patent claim 1 and by a charge state control device having the features of patent claim 10.

The present invention is based on the finding that fuel can be saved and thus a particularly resource-saving operation of the motor vehicle is made possible if a target charge level range of the lithium battery, which is defined by a lower and an upper threshold value, is adapted to the base load of the vehicle electrical system by appropriately modifying the upper threshold value of the target charge level range. As explained below, this enables a particularly energy-efficient distribution and use of recuperated energy.

On the one hand, the aim is to release the energy stored in the lithium battery as quickly as possible so that energy can be absorbed again in a recuperation phase. However, if there is no more energy available in the lithium battery during a long phase without recuperation, energy must be generated again via the generator, i.e. the electric machine, to supply the base load, which can lead to higher fuel consumption. If one looks at the efficiency of generating energy on the one hand and boosting energy on the other, this results in high losses. A particularly efficient use of energy is achieved by using the energy in the state in which it is available. It is therefore less efficient to convert electrical energy back into mechanical energy to drive the vehicle. It is much more efficient to provide electrical energy to the electrical base load consumers of the vehicle. Adapting the charging strategy for the lithium battery depending on a base load determined for the vehicle's base load consumers therefore leads to an optimized efficiency of the vehicle. Fuel consumption can be significantly reduced.

According to the invention, an electrical base load of the vehicle electrical system is therefore determined in a step b). The upper threshold value for the target charge level range of the at least one lithium battery is then modified or selected depending on the electrical base load of the vehicle electrical system determined in step b). When the motor vehicle is being driven, the charge level of the lithium battery is then set between the lower and the modified upper threshold value for a target charge level range of the lithium battery.

If, for example, a high base load is detected because the seat heating, interior heating, rear window heating and exterior mirror heating are in operation during winter operation of the vehicle at low outside temperatures, the upper threshold is raised accordingly. This means that more energy gained through recuperation is stored in the lithium battery in order to make it available to the vehicle electrical system to feed the electrical consumers mentioned, instead of using this energy for boosting, for example. Conversely, if a low base load of the vehicle electrical system is detected, the upper threshold can be lowered accordingly. This means that more energy can be drawn from the lithium battery more often and more often.

As mentioned, in step d) when the motor vehicle is being driven, a state of charge of the lithium battery is set between the lower and the upper threshold value for a target state of charge range. This means that the target state of charge range is between the lower and the upper threshold value. As described below with reference to 2 As will be explained in more detail below, charging above the upper threshold can nevertheless occur if there is no suitable recipient for the excess energy at that time. However, an attempt will then be made to release this amount of energy stored above the upper threshold when the opportunity arises, so that the energy content of the lithium battery is again between the lower and the modified upper threshold for the target state of charge range.

For example, by lowering the upper threshold value in view of the base load of the vehicle, the load point of the combustion engine can be reduced more frequently.

The base load can change depending on summer and winter. The higher the base load, the more energy must be stored in the lithium battery. The upper threshold value for the target charge level range of the lithium battery must be set accordingly.

A particularly preferred embodiment is characterized by the following additional steps: e) determining a typical value for a period of time between two consecutive overrun phases of the motor vehicle; and f) wherein in step c) the upper threshold value for the target state of charge range of the at least one lithium battery is modified depending on a combination of the base load determined in step b) and the typical value determined in step e) for a period of time between two consecutive overrun phases of the motor vehicle. In particular, during overrun phases of the motor vehicle, energy can be obtained by recuperation to charge the lithium battery. As will be discussed in more detail below, typical, reliable values can be determined for a period of time between two consecutive overrun phases of the vehicle. In this way, it is possible to approximately estimate the regularity with which energy can be expected to be obtained through recuperation. The longer the typical period of time between two consecutive overrun phases, the higher the energy to be kept in the lithium battery. If, however, the typical value for a period between two consecutive overrun phases is short, an inflow of energy gained through recuperation into the lithium battery can be expected with a correspondingly higher frequency. The upper threshold value can then be set lower accordingly.

According to the invention, the electrical base load of the vehicle electrical system and the typical value for a time period between two consecutive overrun phases can therefore be combined to set an optimal upper threshold value for a target state of charge range of the lithium battery.

Preferably, the typical value for a period of time between two consecutive overrun phases is determined by evaluating an operating parameter of the charge state control device that is assigned to the at least one lithium battery. In this way, without extensive recordings and measurements, with sufficient accuracy for many applications, ity, a typical value for a time period between two consecutive overrun phases can be determined. The operating parameter of the charge state control device can in this context be derived from a standardized operating cycle of the motor vehicle, in particular a typical customer profile or NEDC (New European Driving Cycle) or WLTP (Worldwide Harmonized Light Duty Test Procedure). For NEDC, the time period between two consecutive overrun phases is 3 min 40 s and for WLTP it is 3 min 20 s. If the same charge state control device is installed in different vehicle types from one manufacturer, a different typical value for a time period between two consecutive overrun phases can be assigned depending on the installation. If the charge state control device is installed in a coupe, a smaller typical value for the time period between two consecutive overrun phases is assigned than if the charge state control device had been installed in an SUV. This takes into account the different customer profiles of coupe drivers and SUV drivers. A finer gradation can be achieved by taking into account the engine size of the respective motor vehicle, whereby a higher engine size is associated with a smaller typical value for the time period between two consecutive overrun phases and vice versa.

Alternatively or additionally, according to an embodiment of the method according to the invention for controlling an electrical system of an electrically driven motor vehicle, a step g) can also be provided: setting a driving mode from a plurality of driving modes by the driver of the motor vehicle or by a control device of the motor vehicle, each driving mode being assigned a typical value for a period of time between two consecutive overrun phases of the motor vehicle. According to a subsequent step h), in step f), the value assigned to the respective driving mode is used for a period of time between two consecutive overrun phases of the motor vehicle. If, for example, the driver selects a "sporty" or "dynamic" driving mode, the associated typical value for a period of time between two consecutive overrun phases is significantly shorter than if the driver selects a "comfort" or "eco" driving mode. Different driving modes are therefore associated with different typical values for a period of time between two consecutive overrun phases. In this way, a particularly precise setting of the upper threshold value for the charge state of the lithium battery can be achieved.

Alternatively or additionally, the following steps can be carried out to determine a typical value for a period of time between two consecutive overrun phases: i) monitoring the driver activities during a predeterminable period of time; j) determining a typical value for a period of time between two consecutive overrun phases of the motor vehicle from the driver activities monitored in step i); and k) in step f): using the typical value determined in step j) for a period of time between two consecutive overrun phases of the motor vehicle. For example, the time intervals between two consecutive overrun phases can be determined for a period of time and an average value derived from this, which is used as a typical value for a period of time between two consecutive overrun phases of the motor vehicle. This allows the upper threshold value for the state of charge of the at least one lithium battery to be adapted particularly precisely to a respective driver of a motor vehicle. The fuel savings that can be achieved in this way are therefore even higher than with the aforementioned variants.

Preferably, in step b), the electrical base load of the vehicle electrical system is determined by evaluating the voltage of the vehicle electrical system and the current flowing in the vehicle electrical system over a predeterminable period of time. Preferably, the current flowing in the vehicle electrical system is the currents flowing in and out of a respective battery of the vehicle electrical system, as well as the currents flowing in and out of a respective electrical machine, in particular a belt starter generator, of the vehicle electrical system. The base load current of the electrical consumers connected to the vehicle electrical system can be determined from the currents mentioned. In a typical application, the currents are measured every 1 ms and filtered to calculate the base load of the vehicle electrical system. If the vehicle electrical system contains a DC/DC converter, the current flowing through the DC/DC converter is measured via a measuring shunt and also taken into account.

In a further preferred embodiment, the temperature of the at least one lithium battery is measured in a step I), wherein in a subsequent step m) the modification of the upper threshold value for the target state of charge range of the lithium battery according to step c) continues to take place depending on the temperature of the at least one lithium battery measured in step I). The lower the temperature of the lithium battery, the higher the upper threshold value for the state of charge of the lithium battery should be selected. In this way, it is taken into account that a battery can store less energy at a low temperature level than at a higher temperature.

Further preferred embodiments emerge from the subclaims.

The preferred embodiments presented with reference to the method according to the invention and their advantages apply accordingly, as far as applicable, to a charge state control device according to the invention for a motor vehicle for controlling a charging of at least one lithium battery of the motor vehicle.

• 1 eine schematische Darstellung einer aus dem Stand der Technik bekannten elektrischen Anlage eines elektrisch antreibbaren Kraftfahrzeugs;
• 2 eine schematische Darstellung zur Erläuterung eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens zum Steuern einer elektrischen Anlage eines elektrisch antreibbaren Kraftfahrzeugs;
• 3 ein Geschwindigkeits-Zeit-Diagramm (3a) zur Ableitung eines typischen Werts für den Abstand zwischen zwei aufeinanderfolgenden Schubphasen des Kraftfahrzeugs (3b);
• 4 die in der Lithium-Batterie vorzuhaltende Energie in Abhängigkeit der elektrischen Grundlast des Bordnetzes sowie unterschiedlicher typischer Werte T_m1, T_m2, T_m3 der Zeitdauer zwischen zwei aufeinanderfolgenden Schubphasen des Kraftfahrzeugs; und
• 5 in schematischer Darstellung einen Signalflussgraphen zur Erläuterung eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

In the following, embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. These show:

• 1 a schematic representation of an electrical system of an electrically driven motor vehicle known from the prior art;
• 2 a schematic representation to explain an embodiment of a method according to the invention for controlling an electrical system of an electrically driven motor vehicle;
• 3 a speed-time diagram ( 3a) for deriving a typical value for the distance between two consecutive overrun phases of the motor vehicle ( 3b) ;
• 4 the energy to be stored in the lithium battery depending on the electrical base load of the vehicle electrical system and different typical values T _m1 , T _m2 , T _m3 of the time between two consecutive overrun phases of the motor vehicle; and
• 5 in schematic representation a signal flow graph for explaining an embodiment of the method according to the invention.

The information relating to 1 The reference symbols introduced will continue to be used for identical and equivalent components.

2 shows a schematic representation to explain an inventive strategy for controlling charging of a lithium battery 12. On the left side, the state of charge SOC (State Of Charge) of the lithium battery 12 is indicated. The state of charge is given as a percentage of the fully charged state of the lithium battery.

Also shown is a charge state control device 32 for the lithium battery 12, which is coupled to the battery monitoring module 20 for the lithium battery 12 and the monitoring module 26 for the electric machine 14. The charge state control device 32 is designed to control the charging and discharging of the lithium battery 12.

The normally permitted range of charge states is designated 34. Above this range there is a range 35 which may not be used due to technological constraints. A lower range 37 may not be used because an energy reserve must be kept in case the motor vehicle is parked for a long period of time. Within range 34 a target charge state range is designated 39. The range 42 located between ranges 39 and 35 serves as a reserve for energy recovery systems, for example overrun and brake recuperation systems. As indicated by arrow 44, starting from the target charge state range 39, charging into range 42 can take place by energy recovery, with kinetic energy of the motor vehicle being considered as the energy source in particular. This energy range 42 is discharged, as indicated by arrow 46, by lowering the load point, in particular with the aim of saving fuel.

The energy range 48 located between the ranges 37 and 39 provides the necessary energy for various other fuel-saving measures, such as extended start-stop and freewheeling engine off. As shown by the arrow 50, this range is discharged by the other fuel-saving measures mentioned with the aim of saving fuel. The arrow 52 indicates that this range must be charged by increasing the load point, using fuel as the energy source. When the lower limit is reached, the lithium battery 12 must be charged - as efficiently as possible by optimally increasing the load point - in order to ensure the availability of the other fuel-saving measures.

The boundary between the ranges 39 and 48 is defined by a lower threshold USW, and that between the ranges 39 and 42 by an upper threshold OSW. Typically, the lower threshold USW is about 20% of the total capacity of the lithium battery 12, and the upper threshold OSW is about 80%.

According to the invention, an electrical base load of the electrical consumers of the on-board network of the electrical system 10 is determined from the current and voltage values provided by the battery monitoring module 20 and the monitoring module 26, and the upper threshold value OSW is modified as a function of this, as indicated by the arrow 36, within a range limited by a minimum upper threshold value OSW _min and a maximum upper threshold value OSW _max , starting from a standard value OSW _norm . The modification can, for example, be carried out according to a linear dependency between the minimum value OSW _min corresponding to a minimum determined base load and the maximum value OSW _max can be changed in accordance with a maximum determined base load. However, a storage device can also be provided in the state of charge control device 32 in which corresponding values for the upper threshold value OSW are assigned to certain determined values of the base load. Instead of a linear relationship, other relationships between base load and upper threshold value OSW can also be used if this has proven to be advantageous.

The charge state control device 32 is also coupled to a device 38 for determining a typical value for a period of time between two consecutive overrun phases of the motor vehicle and to a device 40 for determining the temperature of the lithium battery. The values determined by the devices 38 and 40 can also be used, i.e. in combination with the determined electrical base load of the vehicle electrical system, to determine an optimal value for the upper threshold value OSW.

However, in this context, we first want to 3 reference may be made. 3a shows the temporal progression of the speed of a motor vehicle during an exemplary period of time. As can be seen, the speed increases from time t ₀ to time t ₁ .

Between times t ₁ and t ₂ the speed is reduced and then increased again during the period t ₂ to t _3. Between times t ₃ and t ₄ the vehicle is braked to a standstill and then between t ₄ and t ₅ its speed is increased again. Between times t ₅ and t ₆ the vehicle is braked again to a standstill.

In the presentation of 3b the corresponding traction and thrust phases of the motor vehicle are shown. Accordingly, traction phases occur between times t ₀ and t ₁ , times t ₂ and t ₃ and between times t ₄ and t ₅ . Thrust phases occur between times t ₁ and t ₂ , times t ₃ and t ₄ and times t ₅ and t ₆ .

Δt ₁ refers to the time period between a first thrust phase, which occurs between times t ₁ and t ₂ , and a subsequent thrust phase, which occurs between times t ₃ and t _4. Δt ₂ refers to the time period between the thrust phase, which occurs between times t ₃ and t ₄ , and the subsequent thrust phase, which occurs between times t ₅ and t _6. A typical value for a time period T _M between two consecutive thrust phases of the motor vehicle can therefore be determined, for example, as an average as follows: $$\left(\Delta {\text{t}}_1+\Delta {\text{t}}_2\right)/2={\text{T}}_{\text{M}}.$$

This typical value for a time period T _M between two consecutive overrun phases of the motor vehicle can be taken into account via the device 38 in addition to the determined electrical base load when modifying the upper threshold value OSW for the target state of charge range of the lithium battery 12. The greater the determined typical value for a time period between two consecutive overrun phases, the higher the upper threshold value OSW should be selected, since energy can then be obtained less frequently to supply the electrical base load of the vehicle's electrical system. The smaller the typical value for a time period between two consecutive overrun phases, the more often energy can be collected through recuperation and the lower the upper threshold value OSW can therefore be selected.

Coming back to 2 As mentioned, the upper threshold value OSW can be further modified depending on the temperature of the lithium battery 12 detected by the device 40. The lower the detected temperature, the higher the upper threshold value OSW should be selected.

4 For the sake of simplicity, the dependency of the upper threshold value OSW only on a combination of base load and determined typical value for a period of time between two consecutive overrun phases of the vehicle is shown. The graph shows three characteristic curves for different typical values of the period of time between two consecutive overrun phases. The following applies: T _M1 >T _M2 >T _M3 .

As can be seen from the graph, the higher the base load determined and the higher the typical value determined for a period between two consecutive thrust phases, the higher the upper threshold value OSW should be. The temperature can be increased by expanding the representation of 4 into a characteristic field. These dependencies can be used as an algorithm or as a lookup table in the state of charge control device 32, see 2 , must be saved.

5 shows a signal flow graph to explain an embodiment of the method according to the invention.

First, in step 100, a lower threshold USW and a standard value OSW _norm for the upper threshold value OSW for a target state of charge range of the lithium battery 12. In step 120, an electrical base load of the vehicle electrical system is determined. In step 140, a typical value for a period of time between two consecutive overrun phases of the motor vehicle is determined. In step 160, a temperature of the lithium battery 12 is determined. In step 180, the upper threshold value OSW for the state of charge of the lithium battery 12 is modified depending on the base load determined in step 120, the typical value determined in step 140 for a period of time between two consecutive overrun phases and the temperature determined in step 160.

In step 200, while the motor vehicle is being driven, a charge level of the lithium battery 12 is set between the lower and the modified upper threshold value USW, OSW for the target charge level range. In step 220, the terminal 15 signal of the motor vehicle is evaluated, i.e. it is checked whether the motor vehicle has been turned off. If the terminal 15 signal is off, the method is ended in step 240. However, if the combustion engine is still on, i.e. the terminal 15 signal is "on", the method branches back to step 120 in order to continuously - in particular continuously or at predeterminable time intervals - set an optimal upper threshold value OSW for the target charge level range of the lithium battery 12.

Claims (10)

Method for controlling an electrical system (10) of an electrically driven motor vehicle, wherein the electrical system comprises an on-board network with at least one lithium battery (12) and at least one electrical machine (14), wherein at least one electrical consumer (16; 18) is coupled to the on-board network; comprising the following steps: a) specifying a lower (USW) and an upper threshold value (OSW _norm ) for a target state of charge range of the lithium battery (12) (step 100); b) determining an electrical base load (GL) of the on-board network (step 120); c) modifying the upper threshold value (OSW) for the target state of charge range of the at least one lithium battery (12) depending on the electrical base load (GL) of the on-board network determined in step b) (step 180); and d) when the motor vehicle is being driven: setting a state of charge of the lithium battery (12) between the lower (USW) and the modified upper threshold value (OSW) for the target state of charge range of the lithium battery (12) (step 200); characterized in that in step c) the upper threshold value (OSW) is selected to be greater the greater the electrical base load (GL) of the vehicle electrical system determined in step b). Procedure according to Claim 1 , characterized by the following further steps: e) determining a typical value for a time period (T _M ) between two consecutive coasting phases of the motor vehicle (step 140); f) wherein in step c) the upper threshold value (OSW) for the target state of charge range of the at least one lithium battery (12) is modified depending on a combination of the base load (GL) determined in step c) and the typical value determined in step e) for a time period (T _M ) between two consecutive coasting phases of the motor vehicle. Procedure according to Claim 2 , characterized in that the typical value for a time period (T _M ) between two successive overrun phases is determined by evaluating an operating parameter of the charge state control device (32) which is assigned to the at least one lithium battery (12). Procedure according to Claim 3 , characterized in that the operating parameter of the charge state control device (32) is derived from a standardized operating cycle of the motor vehicle, in particular a typical customer profile, NEDC or WLTP. Procedure according to one of the Claims 2 until 4 , characterized by the following further steps: g) setting a driving mode from a plurality of driving modes by the driver of the motor vehicle or by a control device of the motor vehicle, each driving mode being assigned a typical value for a time period (T _M ) between two consecutive coasting phases of the motor vehicle; h) in step f): using the value assigned to the respective driving mode for a time period (T _M ) between two consecutive coasting phases of the motor vehicle. Procedure according to one of the Claims 2 until 5 , characterized by the following steps: i) monitoring the driver activities during a predeterminable period of time (t ₀ ,...t ₆ ); j) determining a typical value for a period of time (T _M ) between two consecutive coasting phases of the motor vehicle from the driver activities monitored in step i); and k) in step f): using the typical value determined in step j) for a period of time (T _M ) between two consecutive coasting phases of the motor vehicle. Method according to one of the preceding claims, characterized in that in step b) the electrical base load (GL) of the on-board network is determined by evaluating the voltage of the on-board network and the current flowing in the on-board network during the predeterminable period of time. Procedure according to Claim 7 , characterized in that the currents flowing in and out of a respective battery of the on-board network and the currents flowing in and out of a respective electrical machine (14), in particular a belt starter generator, of the on-board network are evaluated as the current flowing in the on-board network. Method according to one of the preceding claims, characterized by the following further steps: I) measuring a temperature of the at least one lithium battery (12); m) wherein in step c) the upper threshold value (OSW) for the target state of charge range of the lithium battery (12) is further modified depending on the temperature of the at least one lithium battery (12) measured in step I) (step 160). State of charge control device (32) for a motor vehicle for controlling charging of at least one lithium battery (12) of the motor vehicle, wherein the state of charge control device (32) is designed to set the state of charge of the at least one lithium battery (12) between a lower (USW) and an upper threshold value (OSW) for a target state of charge range of the lithium battery (12) when the motor vehicle is being driven; wherein the state of charge control device (32) is further designed to modify the upper threshold value (OSW) for the target state of charge range of the at least one lithium battery (12) depending on an electrical base load (GL) of the on-board network, characterized in that the state of charge control device (32) is designed to select the upper threshold value (OSW) to be greater the greater the electrical base load (GL) of the on-board network.

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