Apparatus and method for increasing the range of an electric vehicle

Abstract

The invention relates to a device and a method for increasing the range of a vehicle driven by an electric motor and a high-voltage battery, comprising an electronic control unit which is in particular programmed such that a corresponding residual range is displayed to the driver as a function of an always newly updated estimated state of charge of the high-voltage battery; a lower state of charge limit is defined which is assigned to a displayed residual range of zero when the state of charge is estimated without error; a defined minimum permissible first battery cell voltage limit is assigned to the lower state of charge limit; it is monitored during the driving operation whether a greater range is displayed as a result of an estimation error than the range which is callable on the basis of the current state of charge; the display is not corrected by the estimation error difference; and an emergency mode is automatically activated when an estimation error is identified, in which emergency mode the battery cell voltage is permitted to fall below the first battery cell voltage limit.

Description

TECHNICAL FIELD

[0001] The present application relates to a device for increasing the range of an electrically operated vehicle and a corresponding method. BACKGROUND

[0002] Vehicles having an electric drive (i.e. having an electric motor for driving the vehicle) usually comprise an energy store (also referred to as high-voltage energy accumulator or traction battery) which is designed to store electrical energy for operating the electric motor. The electrical energy for driving the vehicle (also referred to as traction energy) is usually stored in the energy store in an electrochemical manner. Exemplary energy stores comprise a large number of lithium-ion-based storage cells.

[0003] The electrical energy store comprises a limited capacity for storing traction energy. Here, the currently achievable vehicle range with the limited capacity is relatively small compared to the achievable vehicle range with vehicles having an internal combustion engine. Furthermore, the number of public charging stations for electrically operated vehicles is currently relatively limited. As a result, there is an increasing risk in electrically operated vehicles that the electrically operated vehicle cannot reach a desired destination of travel with the available electrical energy and that the electrically operated vehicle can "remain stationary".

[0004] For example, DE 10 2015 203 491 A1 relates to the technical task of effectively reducing the risk that an electrically operated vehicle does not have enough electrical energy to reach a desired destination of travel. In particular, it is intended to enable the driver of the electrically operated vehicle to effectively increase the range of the electrically operated vehicle when required.

[0005] According to this document, a method for increasing the range of a vehicle is described, which comprises the step of reserving a filling level of an energy store of the vehicle for operating the electric motor.

[0006] The energy store is designed for storing electrical energy, wherein the amount of electrical energy in the energy store is usually represented by the filling level (also referred to as state of charge SOC) of the energy store. The energy store is usually operated in a standard operating mode in which the energy store is not fully charged and / or not fully discharged in order to achieve as long a service life (i.e. as large a number of storage cycles) of the energy store as possible. For example, in the standard operating mode, the energy store can be discharged all the way to a minimum permissible filling level (hereinafter also referred to as lower state of charge limit) (wherein the minimum permissible filling level is greater than 0%) and / or can be charged all the way to a maximum permissible filling level (wherein the maximum permissible filling level is less than 100%). In other words, in the standard operating mode, the energy store can be operated within a filling level range which is set for the energy store in principle. Here, the set filling level range can be limited downwards by the minimum permissible filling level and / or upwards by the maximum permissible filling level.

[0007] The filling level reserve lies outside the set filling level range provided for the energy storage. For example, the filling level reserve can comprise a lower filling level reserve, in the case of which the filling level of the energy storage is below a minimum permissible filling level (possibly down to a minimum possible filling level of, for example, 0%). Alternatively or additionally, the filling level reserve can comprise an upper filling level reserve, in the case of which the filling level of the energy storage is above a maximum permissible filling level (possibly up to a maximum possible filling level of, for example, 100%).

[0008] In general, the service life of the energy storage is statistically less reduced when the energy storage is operated within the set filling level range than when the energy storage is operated within the filling level reserve. It is therefore generally advantageous (for the service life of the energy storage) for the energy storage to be operated in compliance with the standard in the standard operating mode, i.e. within the set filling level range. The filling level reserve of the energy storage, on the other hand, is only used in exceptional cases, since the use of the filling level reserve of the energy storage generally statistically leads to a reduction in the service life of the energy storage (compared to use only within the set filling level range).

[0009] The method therefore comprises the taking of a decision (exceptionally) to use the filling level reserve of the energy storage for operating the electric motor of the vehicle. This operating mode of the energy storage can be referred to as a capacity-extended operating mode of the energy storage. It is therefore possible to take the decision to activate the capacity-extended operating mode of the energy storage, in which not only the set filling level range but also the filling level reserve of the energy storage is used to operate the electric motor for driving the vehicle.

[0010] The method further comprises, in response to the taking of the decision to activate the capacity-extended operating mode of the energy storage, using the electrical energy from the filling level reserve of the energy storage for operating the electric motor of the vehicle, i.e. for driving the vehicle. The use of the filling level reserve of the energy storage can be limited to a predefined number of charging cycles of the energy storage, for example one unique charging cycle. That is to say, the method can further comprise limiting the use of the filling level reserve of the energy storage to a predefined, limited number of charging cycles. After the limited number of charging cycles, the energy storage can automatically switch from the capacity-extended operating mode to the standard operating mode.

[0011] According to the prior art, the capacity-extended operating mode can in principle only be activated by an explicit request or input by the user. The taking of the decision to use the filling level reserve of the energy storage therefore comprises detecting an input by the user of the vehicle via an input / output unit of the vehicle. By requiring an explicit input by the user of the vehicle and by optionally coupling the use of the filling level reserve of the energy storage to one or more conditions, damage to the energy storage as a result of excessive use of the filling level reserve can be limited. Furthermore, the use of the filling level reserve can be offered to the user as a value-added function (if necessary, payment addition) of the vehicle.

[0012] The method can further comprise activating one or more measures by which the consumption of electrical energy by the vehicle is reduced during the use of the electrical energy from the filling level reserve for operating the electric motor. It can be assumed that when the user activates the capacity expansion operating mode of the energy store, the user of the vehicle wishes to maximize the range of the vehicle. It is therefore advantageous if one or more consumption reduction measures (for example, deactivation of the air conditioning system and / or limitation of the vehicle travel speed) are automatically carried out if necessary when the capacity expansion operating mode of the energy store is activated. This can further increase the range of the vehicle.

[0013] A lower filling level reserve can be provided during travel of the vehicle in order to increase the range of the vehicle (for example, for reaching a destination). In particular, it can be provided during travel of the vehicle that the lower filling level reserve is to be used. The vehicle can therefore be provided with a so-called "LIMP HOME" function, also known as "Turtle Mode". In the system described in DE 10 2015 203 491 A1, with the so-called "LIMP HOME" function, the filling level reserve of the high-voltage energy store is only provided on manual request by the driver. If the filling level reserve is activated, the range is not displayed to the driver here, for example "0 km" or "---". SUMMARY

[0014] It is an object of the application to increase the range of an electric vehicle without increasing the burden on the driver by required manual interventions.

[0015] To this end, the application proposes a device for increasing the range of a vehicle, which is driven by an electric motor and a high-voltage battery, comprising an electronic control unit, which is designed to:

[0016] - display a corresponding residual range RRW to the driver as a function of an always newly updated estimated state of charge SOC of the high-voltage battery,

[0017] - define a lower state of charge limit SOCmin, which is assigned a residual range RRW to be displayed of zero when the state of charge SOC is estimated without error, wherein, in a standard operating mode, the lower state of charge limit is not undershot,

[0018] - assign the lower state of charge limit SOCmin a defined minimum permissible first battery cell voltage limit,

[0019] - monitor during travel operation whether a greater range is displayed than is available on the basis of the current state of charge as a result of an estimation error,

[0020] - the display can be corrected without an estimation error difference, and

[0021] - automatically activating an emergency mode in which the cell voltage can be lowered below the first cell voltage limit, in which emergency mode the cell voltage is lowered such that the displayed remaining range RRW can be actually reached, upon recognition that a range is displayed which is greater than the range which is callable on the basis of the current state of charge as a result of an estimation error.

[0022] The application also proposes a method for increasing the range of a vehicle driven by an electric motor and a high-voltage battery by means of an electronic control unit, wherein

[0023] - a corresponding remaining range RRW is displayed to the driver as a function of the continuously repeatedly updated estimated state of charge SOC of the high-voltage battery,

[0024] - a lower state of charge limit SOCmin is defined, which lower state of charge limit is assigned to a displayed remaining range RRW of zero when the state of charge SOC is estimated without error, wherein in the standard operating mode, the lower state of charge limit is not undershot,

[0025] - the defined minimum permissible first cell voltage limit is assigned to the lower state of charge limit SOCmin,

[0026] - it is monitored during the driving operation whether a range is displayed which is greater than the range which is callable on the basis of the current state of charge as a result of an estimation error,

[0027] - the display is not corrected for the estimation error discrepancy; and

[0028] - an emergency mode is automatically activated in which the cell voltage is allowed to be lowered below the first cell voltage limit, in which emergency mode the cell voltage is lowered such that the displayed remaining range RRW can be actually reached, upon recognition that a range is displayed which is greater than the range which is callable on the basis of the current state of charge as a result of an estimation error.

[0029] The application relates to a device and a method for increasing the range of a vehicle driven by an electric motor and a high-voltage battery, having an electronic control unit which is programmed in particular such that

[0030] - a corresponding remaining range RRW is displayed to the driver as a function of the continuously repeatedly updated estimated state of charge SOC of the high-voltage battery,

[0031] - a lower state of charge limit is defined, which lower state of charge limit is assigned to a displayed remaining range RRW of zero when the state of charge is estimated without error,

[0032] - a defined minimum allowable first cell voltage limit is provided for the lower state of charge limit,

[0033] - during the driving operation, it is monitored whether a range greater than the range that is callable on the basis of the current state of charge is displayed as a result of the estimation error,

[0034] - the display is not corrected (in a jump) by the estimation error difference; and

[0035] - an emergency mode is automatically activated upon recognition of the estimation error, in which emergency mode the cell voltage is allowed to fall below the first cell voltage limit.

[0036] Preferably, in the emergency mode the cell voltage is lowered such that the displayed remaining range is actually achievable. However, the lowered cell voltage is only allowed temporarily, for example until the next charging process or until a lowered second cell voltage limit is reached.

[0037] The invention comprises the following advantageous extensions:

[0038] - the emergency mode is preferably preset in a state of charge range directly below the defined estimation margin.

[0039] - the defined estimation margin is preset directly below the lower state of charge limit.

[0040] - the emergency mode can be blocked in the presence of defined conditions, wherein the conditions for blocking the emergency mode can be, for example, below the second cell voltage limit or the aging limit.

[0041] - in a driving operation in which the emergency mode is blocked, the lower state of charge limit can be specified to be higher than in a driving operation in which the emergency mode is allowed.

[0042] - in a driving operation in which the emergency mode is blocked, additionally or alternatively, the state of charge range of the estimation margin can be greater than in a driving operation in which the emergency mode is allowed.

[0043] The invention is based on the following considerations:

[0044] In the field of development of high-voltage accumulators for electric vehicles, within the framework of SOC (state of charge) algorithm development and when designing the available energy content, there is a constant attempt to, first, reduce the estimation margin in order to be able to provide the vehicle with a greater available range, and second, to reduce or at least not increase the number of cases in which the remaining range is displayed as 0 km, although there is still a greater remaining range in reality ("standing still with remaining range").

[0045] In each electric vehicle, the state of charge of the battery is only estimated, as a practical measurement is technically not possible. In a vehicle operated electrically, it should always be ensured that the driver does not "stay stationary" due to an actually empty battery when the displayed remaining range is used. To ensure this, an algorithm is used to estimate the state of charge as accurately as possible. Since this estimation has only a limited accuracy, a so-called "estimation margin" is defined, which in normal cases does not provide as range and thus in principle reduces the available energy or electric range.

[0046] Despite the high estimation margin, a stay stationary with remaining range cannot be ruled out in all cases. A compromise between reducing the "stay stationary" risk and optimizing the electric range must always be found.

[0047] If an estimation error is identified which means that the range or power displayed to the driver is greater than the range or power which is available from the state of charge of the battery (for example, according to constant driving at 80 km / h), an emergency mode is preferably activated according to the invention which is added to the estimation margin to ensure the remaining range ("ReSi" mode). In this emergency mode, the conventional cell voltage limit is temporarily reduced to release energy which is not available in normal cases. The operating range of the battery is so-called temporarily expanded, even by more than one estimation margin.

[0048] Due to aging, the cell voltage limit cannot be permanently reduced, as the cells age relatively strongly in this low voltage range. However, since this emergency mode only occurs in a few cases (SOC estimation error and driver fully utilizing the displayed range), a reduction of the cell voltage limit is acceptable in these time-limited cases.

[0049] According to the invention, a relatively small estimation margin can also be defined by means of an emergency mode which depends on the estimation error. Thus, a continuously increasing range is also obtained.

[0050] According to an embodiment of the method:

[0051] If the electronic control unit required for the implementation of the invention recognizes an estimation error, in particular because: the cell voltage of the individual cells of the high-voltage accumulator is already at the cell voltage limit of the standard operating mode (e.g. 2.8 V); the range in the standard operating mode is 0 km taking into account the estimated state of charge (SOC); but the range displayed to the driver still exceeds 0 km, the emergency mode is automatically activated according to the invention. For this purpose, the cell voltage limit is reduced (e.g. from 2.8 V (normal operation) to 2.1 V) to release the energy reserve. In principle, this requires a voltage monitoring of all cells.

[0052] The emergency mode will be returned when the vehicle is charging.

[0053] The estimated margin, which is usually assumed to be 5% estimation error, can be reduced for all vehicles, because for a few "critical" cases there is now an emergency mode according to the invention to avoid staying stationary with remaining range.

[0054] The manually triggerable fill level reserve in the prior art is thus replaced according to the invention in two stages by the (preferably reduced) estimated margin and the automatically triggered emergency mode according to the estimation error identification. BRIEF DESCRIPTION OF DRAWINGS

[0055] In the following, the invention is described in more detail with reference to embodiments. Herein, in the drawings

[0056] Figure 1 a schematic diagram showing possible components of an electric vehicle with an emergency mode according to the invention,

[0057] Figure 2 a first aspect of the invention, compared to the status quo, for ensuring the remaining range when the SOC estimation error is greater than a prescribed estimation margin,

[0058] Figure 3 a second aspect of the invention, compared to the status quo, for ensuring the remaining range when the SOC estimation margin is reduced, but when the SOC estimation error is zero,

[0059] Figure 4 a diagram showing defined different voltage thresholds for the battery cells,

[0060] Figure 5 an emergency mode according to the invention when the estimation margin is simultaneously reduced, and

[0061] Fig. 6 shows an estimation margin according to the prior art. DETAILED DESCRIPTION

[0062] Figure 1 a block diagram showing example components of an electric vehicle 100. In particular, the electric vehicle 100 comprises an energy store 102, in particular a high-voltage energy accumulator, which is designed to provide electrical energy for operating an electric motor of the vehicle 100. The energy store 102 is designed to determine its fill level, also referred to as state of charge, SOC, or charge state, and to provide it to an electronic control unit 101. The control unit 101 can be designed to determine the remaining range of the vehicle 100 from the fill level, the SOC, of the energy store 102. But alternatively, the control unit 101 can also determine, in particular estimate, the state of charge and the resulting remaining range itself from the signal of the energy store 102.

[0063] The vehicle 100 can also comprise a navigation unit 104 designed to determine the position of the vehicle 100 and / or a planned driving route for the vehicle 100. The control unit 101 can be designed to determine whether the vehicle 100 can drive the planned driving route to completion in view of the remaining range.

[0064] In order to increase the service life of the energy store 102, in particular of an electrochemical energy store, for example a lithium-ion-based energy store, the energy store 102 is usually operated in a fill level range in which the effective available capacity of the energy store 102 is reduced compared to the maximum capacity of the energy store 102 (standard operating mode). In particular, in the standard operating mode, the lower state of charge limit is not undershot in principle.

[0065] Furthermore, the input / output unit 103 of the vehicle 100 can be provided for detecting an input by a user of the vehicle 100.

[0066] Furthermore, the control unit 101 can be designed to cause one or more controllers 105 of the vehicle 100 to switch into an energy-saving operating mode when it is identified that the minimum SOC value of the standard operating mode is reached. For example, the air conditioning system of the vehicle 100 can be deactivated and / or the driving speed and / or the acceleration of the vehicle 100 can be limited. In other words, the control unit 101 can be designed to take measures which reduce the energy consumption of the vehicle 100, thereby further increasing the range of the vehicle 100.

[0067] These components are in principle state of the art. An important component of the present application is the electronic control unit 101, which is in particular programmed accordingly (computer program product in the controller) in order to implement the emergency mode according to the present application.

[0068] According to Figure 2 and the first case the first aspect of the present application is explained:

[0069] Figure 2 Left: state of the art (status quo)

[0070] Case 1 : The drivable limit (= lower SOC value of the estimated reserve) is reached, but the remaining range RRW > 0 km is displayed to the driver, since a maximum estimation error of only 5% was assumed when specifying the estimation reserve, but this has actually been exceeded here.

[0071] The lower limit of the defined (first) cell voltage (the cell voltage limit has not been reduced) is reached.

[0072] • In a few "worst" cases (in particular after aging), the SOC estimation error can also be greater than 5%.

[0073] • In this case, if the driver drives his vehicle completely "empty", it can happen that the "standstill" is displayed when the remaining range is greater than 0 km.

[0074] Figure 2 Right: the application in the same case 1 ("robustness measure")

[0075] - the drivable limit is reduced in emergency mode so that the displayed range reaches 0 km; i.e. the driver can drive electrically to the display "0 km" or "—".

[0076] - for this purpose, preferably or as required, the lower battery cell voltage limit is reduced so that the energy reserve required for emergency mode is available in a short time.

[0077] • Thus, if in case 1 above, with an energy forecast > 0 kWh, the power drops below the defined drivable level (e.g. only constant driving 80 km / h is possible), an estimation error is recognized according to the application and the lower battery cell voltage limit is temporarily reduced.

[0078] • In the ideal case, the driver can still go to the charging column "to recover", but at least the driver can still continue to drive until the display "— " (RRW = 0 km).

[0079] • Due to the inventor's insight in tests on battery cell aging, it is unproblematic to temporarily reduce the lower battery cell voltage limit (e.g. from 2.8 V to 2.1 V) only in special cases, i.e. at a low state of charge (SOC) with a range greater than 0 km based on the recognized high estimation error.

[0080] • But the reduced battery cell voltage limit, like 2.1 V, is to be preferred to continue to be above the limit required for functional safety, like 1.7 V.

[0081] Reference Figure 3 Explanation of the second aspect of the application:

[0082] Figure 3 Left: prior art (status quo)

[0083] - Case 2: The lower state of charge limit in the standard operating mode is relatively high, "below" would lead to an advance use of the estimation margin in the sense of a filling level reserve.

[0084] - reduced to "normal" also relatively high drivable limit as lower limit of the estimation margin (limp home range, so-called "turtle mode"): 5% estimation margin is not displayed to the driver as available range and can only be used as estimation margin in "turtle mode".

[0085] • The 5% SOC estimation margin is considered in the energy design.

[0086] • In many use cases the actually feasible range is not released because for the special case of "higher estimation error" a margin has to be kept.

[0087] Figure 3 Right: the invention ("robustness measure") in the same case 2.

[0088] - A part of the estimation margin according to the status quo (e.g. 2%) is here displayed to the driver as available range.

[0089] - Lowering the "normal" drivable limit: driving limit "ReSi" (= assurance of remaining range = emergency mode): if the estimation error > 3% in the low SOC range, the emergency mode is activated.

[0090] • In the energy design the estimation margin can be lowered according to the invention (e.g. from 5% to 3%). The estimation error does not change due to the emergency mode.

[0091] • In the now more often occurring case of "estimation error and displayed remaining range" the emergency mode (ReSi) is activated and for this the battery cell voltage limit is lowered. The result is at least no increased risk of "staying still" compared to the prior art.

[0092] Figure 4 Different voltage thresholds defined for the battery cell are shown. According to the invention it is possible to define in the electronic control unit 101 that the estimation margin is chosen up to a first upper voltage threshold S1 (e.g. 2.8 V). If the emergency mode is activated, the battery cell voltage limit can be lowered to a lower second threshold S2 (e.g. 2.1 V), which can also be variably set depending on parameters such as temperature and aging.

[0093] In Figure 5 , the invention is again shown differently compared to the prior art according to Fig. 6. Here, Fig. 6 corresponds to the left side (status quo) of Figure 2 . Figure 5 Corresponds to the right side (robustness measure) of Figure 3 .

[0094] In Figure 5 and Fig. 6 the Gaussian curve of the estimation error is recorded in view of the prescribed lower state of charge limit and the drivable limit, respectively.

[0095] Fig. 6 (according to the prior art) defines a relatively high lower state of charge limit and a drivable limit (normal) of -5% estimation margin.

[0096] For example, at the operating point B1 with an estimated margin of 5%: here the state of charge SOC is falsely estimated, since the estimation error is depicted as being greater than 5%. Then, for example, the display screen can falsely display a remaining range (RRW) of 6 km, but if the driver continues to drive, the vehicle can remain stationary with a displayed remaining range (RRW) of 4 km. For reasons of reliability, a jump correction from 6 km to 4 km should be prevented.

[0097] In Figure 5 , the operating point B1'is recorded as an example in a reduced estimation margin of 3% compared to the prior art (the estimation margin can also remain at 5%, but the present application allows a reduced estimation margin): since an estimation error greater than 3% occurs and this is also identified in accordance with the present application, the state of charge SOC is falsely estimated. If the displayed remaining range (RRW > 0 km) is greater than the remaining range actually achievable by the current estimated state of charge and should not exceed the minimum cell voltage limit set in principle (for example 2.8 V), an increased estimation error is identified. In accordance with the present application, an emergency mode is now activated in such a way that it is allowed to fall below the "normal" drivable limit. This is achieved by temporarily releasing a lower minimum cell voltage limit (for example 2.1 V, also see Figure 4 ). Preferably, the cell voltage limit is temporarily reduced to such an extent that the remaining range actually achievable thereby coincides with the displayed remaining range. Charging takes place at a remaining range of 0 km, whereby the emergency mode is automatically switched off.

[0098] By means of this temporary and estimation error-dependent automatic emergency mode, it is possible to reduce the estimation margin and / or to reduce the lower state of charge limit. This can be seen by comparing the SOC threshold in Figure 5 with the SOC-threshold in Figure 4 .

[0099] The present application is not limited to the embodiments shown. In particular, it is noted that the description and the drawings only apply to illustrate the principles of the proposed method, device and system.

Claims

1. Device for increasing the range of a vehicle (100) driven by an electric motor and a high-voltage battery (102), comprising an electronic control unit (101), which causes: - a corresponding residual range RRW to be displayed to the driver as a function of an always newly updated estimated state of charge SOC of the high-voltage battery (102), - defining a lower state of charge limit SOCmin, which is assigned to a residual range to be displayed RRW of zero when the state of charge SOC is estimated without error, wherein - in a standard operating mode, not below a lower state of charge limit, - a defined minimum permissible first battery cell voltage limit S1 to be assigned to the lower state of charge limit SOCmin, - during a driving operation, it can be monitored whether a range is displayed which, due to an estimation error, is greater than the range which can be called up on the basis of the current state of charge, - the display can be corrected without an estimation error discrepancy, and - an emergency mode ReSi can be activated automatically when it is identified that a range is displayed which, due to an estimation error, is greater than the range which can be called up on the basis of the current state of charge, in which emergency mode ReSi the battery cell voltage U_Z can be reduced below the first battery cell voltage limit S1, in which emergency mode ReSi the battery cell voltage U_Z is reduced such that the displayed residual range RRW can be actually reached.

2. The apparatus of claim 1, wherein, The temporarily permissible reduced battery cell voltage U_Z is reduced until the next charging process or until a reduced second battery cell voltage limit S2 is reached, which is lower than the first battery cell voltage limit S1.

3. The apparatus of claim 1 or 2, wherein, The emergency mode is preset in a state of charge range directly below a defined estimation margin.

4. The apparatus of claim 1 or 2, wherein, The defined estimation margin is preset directly below the lower state of charge limit.

5. The apparatus of claim 1 or 2, wherein, The emergency mode can be prevented when defined conditions are present.

6. The apparatus of claim 1 or 2, wherein, The condition for preventing the emergency mode is: below the second battery cell voltage limit S2.

7. The apparatus of claim 1 or 2, wherein, The lower state of charge limit in a driving operation in which the emergency mode is prevented is specified to be higher than the lower state of charge limit in a driving operation in which the emergency mode is permitted.

8. The apparatus of claim 1 or 2, wherein, The state of charge range of the estimation margin in a driving operation in which the emergency mode is prevented is greater than the state of charge range of the estimation margin in a driving operation in which the emergency mode is permitted.

9. Method for increasing the range of a vehicle (100) driven by an electric motor and a high-voltage battery (102) by means of an electronic control unit (101), wherein - a corresponding residual range RRW is displayed to the driver as a function of an always newly updated estimated state of charge SOC of the high-voltage battery (102), - a lower state of charge limit SOCmin is defined, which is assigned to a residual range RRW to be displayed of zero when the state of charge SOC is estimated without error, wherein, in a standard operating mode, not below the lower state of charge limit, - a defined minimum permissible first battery cell voltage limit S1 is assigned to the lower state of charge limit SOCmin, - during a driving operation, it is monitored whether a range is displayed which, due to an estimation error, is greater than the range which can be called up on the basis of the current state of charge, - the display is not corrected without an estimation error discrepancy; and - an emergency mode ReSi is activated automatically when it is identified that a range is displayed which, due to an estimation error, is greater than the range which can be called up on the basis of the current state of charge, in which emergency mode ReSi the battery cell voltage U_Z is reduced below the first battery cell voltage limit S1, in which emergency mode ReSi the battery cell voltage U_Z is reduced such that the displayed residual range RRW can be actually reached. - automatically activating an emergency mode ReSi in which the battery cell voltage U_Z is allowed to drop below a first battery cell voltage limit S1, in which emergency mode ReSi the battery cell voltage U_Z is lowered such that the displayed range to empty RRW can be actually reached, upon recognition that a range to empty is displayed which is greater than the range to empty which is callable based on the current state of charge due to an estimation error. - automatically activating an emergency mode ReSi in which the battery cell voltage U_Z is allowed to drop below a first battery cell voltage limit S1, in which emergency mode ReSi the battery cell voltage U_Z is lowered such that the displayed range to empty RRW can be actually reached, upon recognition that a range to empty is displayed which is greater than the range to empty which is callable based on the current state of charge due to an estimation error.

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