Method for controlling a drive train

Abstract

Method for controlling a drive train having an electric drive (EA), an electrical energy storage device (ES) connected thereto, and an internal combustion engine drive (VA), comprising the steps: - Determining a total target torque to be generated by the drive train (AS), - Determining a cost quotient that corresponds to a ratio of a change in fuel consumption from a current load point to a new load point to a corresponding change in the energy content of the electrical storage (ES); and - Changing a load point of the electric drive (EA) from the current load point to the new load point by increasing the generator power of the electric drive (EA) when the cost quotient falls below a first charging threshold; and / or by increasing a motor power of the electric drive (EA) if the cost quotient exceeds a first motor threshold; where the threshold values have different values for different charging states of the electrical energy storage (ES) and for different power parameters which characterise a future electrical power to be generated or obtained by the electric drive (EA), the threshold values have different values, the method further comprising the step of: - Changing a load point of the electric drive (EA) by reducing the generator power of the electric drive (EA) if the cost quotient exceeds a second charging threshold; and / or by reducing the motor power of the electric drive (EA) when the cost quotient falls below a second motor threshold.

Description

[0001] The invention relates to a method for controlling a drive train.

[0002] It is known to equip vehicles with a hybrid drivetrain that combines an electric drive with a combustion engine. The electric drive is powered by an energy storage unit, and in recuperation mode, the electric drive acts as a generator and can charge the electric energy storage unit. For this purpose, the vehicle's kinetic energy or potential energy is converted by the electric drive, acting as a generator, into electrical energy, which is then stored in the energy storage unit.

[0003] Since a hybrid powertrain features two different drive systems whose operating parameters can be adjusted independently, it is possible to separate the contribution made by the electric drive from that made by the combustion engine. These variable operating points are associated with different costs.

[0004] In section 7.2 of the textbook “Optimal Control of Hybrid Vehicles” by Bram de Jager, Thijs van Keulen and John Kessels (Springer 2010), a case study is used to describe how an electric truck with a hybrid drive can be operated using an optimal power split strategy between the electric drive and the combustion engine.

[0005] DE 10 2009 008 474 A1 discloses a method for operating a hybrid system. Based on the current state of charge of an energy storage device of an electric machine, a cost threshold and a savings threshold are determined. Based on a current operating point, a potential specific cost value is determined from a cost map, which is compared with the cost threshold. If the cost threshold is undershot or equal to the cost threshold, the potential specific cost value is considered as the specific cost value. Based on the current operating point, a potential specific savings value is determined from a savings map, which is compared with the savings threshold. If the savings threshold is exceeded or equal to the cost threshold, the potential savings value is considered as the specific savings value.If a specific cost value and / or a specific savings value is available, a future operating mode of the hybrid system is selected based on this.

[0006] From DE 10 2017 208 654 A1, a method for controlling a drive device of a hybrid vehicle is known, which comprises an internal combustion engine, a first electric machine, a second electric machine and a battery, wherein the drive device for driving the hybrid vehicle is operable in several operating modes and the operating modes include: a first electrical operating mode in which the second electric machine, in electromotive operation, produces a drive torque while the internal combustion engine is stationary; a second electrical operating mode in which a wheel torque acts on the second electric machine and, in generator operation, generates current for charging the battery while the internal combustion engine is stationary; a serial operating mode in which the internal combustion engine drives the first electric machine to generate electrical energy, which drives the second electric machine, which produces a drive torque and;a parallel operating mode in which the internal combustion engine generates a propulsion torque. The method comprises: controlling the drive device by means of a first switching logic to set an operating mode; determining a serial savings function and a parallel savings function, each based on the relationship between a required fuel output and a required battery discharge power at an operating point; determining a savings limit based on a consumption criterion for a speed profile in an operating period; comparing the serial savings function, the parallel savings function, and the savings limit at an operating point; selecting one of the operating modes based on a comparison result; setting the selected operating mode.

[0007] It is an object of the invention to show a possibility by which a hybrid drive train can be operated cost-effectively.

[0008] This object is achieved by the method according to claim 1. Further properties, features, embodiments and aspects result from the subclaims, the description and the figure.

[0009] It was recognized that the cost of fuel consumption does not behave linearly with the power of the combustion engine drive and that when changing the load point, not only the current costs but also the energy requirement for the load point change should be taken into account, which in turn depends on a future (positive or negative) power of the electric drive.

[0010] A method for controlling a drive train is proposed, wherein the drive train comprises an electric drive, a connected electrical energy storage device, and an internal combustion engine drive. The drive train can thus also be referred to as a hybrid drive train. The drive train combines the power of the electric drive and the internal combustion engine drive. The electric drive can be a starter generator, in particular a belt starter generator. The electric drive can have a nominal voltage of more than 40 V, for example, substantially 48 V. Alternatively, the electric drive can be a high-voltage drive with a nominal voltage of more than 60 V, in particular of at least 400 V, 600 V, or 800 V.The operating voltage of the energy storage device can be more than 40 V, for example 48 V, or can be a high-voltage storage device, in particular with a nominal voltage of more than 60 V, for example of substantially 400 V or 800 V. The energy storage device can be provided as an accumulator, in particular as a lithium-ion accumulator, or can be provided as a capacitor bank.

[0011] The method involves recording a total target torque. This total target torque is to be generated by the drive train. The total target torque can be specified by a control system.

[0012] A cost quotient is determined which corresponds to the ratio of a change in fuel consumption from a current load point to a new load point to a corresponding change in the energy content of the electrical storage device. Preferably, several cost quotients are determined, in particular at different new load points, in order to be able to determine which new load point results in the best (lowest) cost quotient in relation to the corresponding change in energy content. The cost quotient therefore has a numerator which corresponds to a difference between a first fuel consumption and a second fuel consumption. The first fuel consumption relates to the current load point and the second fuel consumption relates to a new load point. The fuel consumption can be represented as a fuel flow rate, as a time-related fuel injection quantity or as an energy rate. The denominator of the cost quotient orThe ratio corresponds to the corresponding energy content change rate of the electrical storage device. The energy content change rate corresponds to the additional rate of change of the energy content at the new load point compared to the rate of change at the current load point. Preferably, at the current load point, the energy content change rate of the electrical storage device is zero (neither charging nor discharging the energy storage device). The energy content change can be defined as an amount of energy or as a proportion of a capacity of the energy storage device, or as an energy content change rate in terms of power or similar.

[0013] The load point of the electric drive is changed from the current load point to the new load point if this is associated with a favorable cost ratio. Threshold values are used to achieve this.

[0014] The load point is changed by increasing the generator power of the electric drive. The case should preferably be considered here where neither the generator nor the motor power of the electric drive is effective at the current load point. This is carried out when the cost quotient falls below a first charging threshold. The charging threshold therefore indicates how necessary charging is and which relative costs for generating electrical energy are accordingly acceptable. The lower the state of charge, the more likely unfavorable cost quotients are taken into account and the more likely the generator power is increased. The generator power of the electric drive is increased when the cost quotient falls below a first charging threshold. By using a charging threshold, the necessity of charging is taken into account orthe state of charge of the energy storage device is taken into account, since in addition to cost minimization, the management of the energy storage device must also be considered. These two aspects can be taken into account alternatively or additionally during motor operation of the electric drive. Alternatively or in addition to increasing the generator power, it can be provided that the motor power of the electric drive is increased when the cost quotient exceeds a first motor threshold. In this case, the cost quotient describes the relative saving of fuel energy through the use of stored electrical energy. The first charging threshold relates to a threshold for the cost quotient for the generator case or charging case. The motor threshold forms a threshold for the cost quotient when the electric drive is in drive mode or the electric drive is used as a motor.

[0015] As mentioned, in order to take the energy management of the energy storage system into account, the threshold values (i.e., the charging threshold and the motor threshold) have different values for different states of charge of the electrical energy storage system. This also takes into account the requirement for a minimum state of charge of the energy storage system. However, not only the energy present in the energy storage system must be considered, but also other forms of energy in the vehicle that can be recovered and (after conversion) stored in the energy storage system. Likewise, consideration should be given to which other forms of energy can still be generated using the energy from the energy storage system, for example, kinetic energy and / or potential energy of the electric vehicle.The threshold values thus depend not only on the charge states, but also on performance parameters that characterize the future electrical power to be generated or recovered by the electric drive. The performance parameters thus characterize the power or energy that still needs to be generated by the drive, for example, to increase other types of energy (of the vehicle), such as kinetic energy or potential energy, or the electrical power that still needs to be recovered, whereby this particularly refers to the recuperation power or recuperation energy that is expected in the future.

[0016] For different performance parameters that characterize future electrical power to be generated or obtained by the electric drive, the thresholds (ie the charging threshold and the motor threshold) have different values.

[0017] This not only reflects the current state of the vehicle, but also takes into account which electrical power or energy content needs to be generated or can be generated (and stored) through recuperation. This allows a complete picture of the vehicle's energy gain or energy generation to be presented, thus actually achieving the lowest costs, taking into account the future route or driving style.

[0018] For example, if the two drives are set to optimize costs based solely on the current state of charge, this fails to take into account the fact that a high amount of recuperation energy may be expected in the future, by which the amount of energy to be generated would have to be reduced. Without such a reduction in the actual energy demand, the drivetrain's cost-driven control would be incorrect, since the calculations are not based on the actual energy still to be generated.

[0019] The load point of the electric drive can be changed by reducing the electric drive's generator power when the cost quotient exceeds a second charging threshold. Since the first charging threshold, which determines the power increase, differs from the second charging threshold, which determines the generator power decrease, a hysteresis effect occurs. This effect prevents the increase and decrease steps from alternating very frequently.

[0020] Alternatively, or in combination with this, the load point of the electric drive can be changed by reducing the motor power of the electric drive when the cost quotient falls below a second motor threshold. Since the second motor threshold, which is decisive for reducing the motor power, differs from the first motor threshold, which in turn is decisive for increasing the motor power, a hysteresis effect also arises here for the control of the motor power (i.e., the control of the electric drive during motor operation).

[0021] Preferably, the first charging threshold is lower than the second charging threshold. It is also preferable for the first motor threshold to be higher than the second charging threshold.

[0022] One embodiment provides that, in the context of determining whether the cost quotient exceeds one of the threshold values (i.e., one of the charging threshold values or engine threshold values) or falls below this relevant threshold value, the old load point and the new load point are adapted to an operating state of the combustion engine. This adaptation is carried out, in particular, by changing the level of the old load point and the new load point for which the cost quotient is determined. Furthermore, in the context of determining whether the cost quotient exceeds one of the aforementioned threshold values or falls below it, the cost quotient can be adapted to an operating state of the combustion engine. For different operating states, the cost quotient is changed to different degrees during the adaptation.The operating state of the combustion engine is characterized in particular by the operating temperature of the combustion engine, by the running time since the last start or by the running time since the last cold start, or by the level of engine torque loss (also known as drag torque) that must be expended to drag the combustion engine without combustion at the corresponding speed. A first operating state can be the start-up phase or the warm-up phase, while another operating state, which is different from this, can be the operation of the combustion engine at a standard operating temperature interval. Furthermore, it can be provided that the level of the old load point and the new load point is changed more the more the operating temperature of the combustion engine deviates from a standard operating temperature interval. The standard operating temperature interval can be, for example, 70°C to 95°C.The change in the amount can be done by raising the load points or by adjusting the cost quotient by increasing or decreasing it.

[0023] This increase is all the greater the more additional losses in the combustion engine that result from low operating temperatures have to be taken into account. The change is all the more pronounced the greater the losses due to, for example, the viscosity of the lubricant in the combustion engine. The background to this is that the cost quotient is heavily dependent on the level of torque that the combustion engine generates from the combustion of fuel (so-called indicated torque), since the effectiveness of the conversion of additional fuel energy into additional mechanical energy depends heavily on the level of this torque from combustion. High losses in the combustion engine lead to a higher indicated torque for the same torque required by the driver, just as would be the case with a higher torque required by the driver, which must be taken into account when determining the cost quotient.As mentioned, the operating state of the combustion engine can correspond to an actual temperature of the combustion engine. This actual temperature is, in particular, the temperature of a cooling circuit of the combustion engine, for example, the cooling water temperature.

[0024] It can be provided that, when determining whether the cost quotient exceeds or falls below one of the threshold values, the old load point and the new load point are adjusted to the operating status of the auxiliary units. This adjustment is preferably carried out by changing the level of the old load point and the new load point for which the cost quotient is determined. The change is carried out in particular by increasing the load points. The load points are increased or changed more the greater the power of the mechanical auxiliary units with which they are operated. In particular, auxiliary units that consume mechanical power are taken into account here. These include, in particular, the air conditioning compressor, any additional alternator provided, or pumps for a hydraulic power steering system.The background to this is that increased mechanical power consumption of such auxiliary units leads to an increase in the indicated torque, just as would be the case with an increased torque required by the driver.

[0025] The performance parameters can reflect the vehicle speed of the vehicle driven by the powertrain. Alternatively, or in combination with this, the performance parameters can reflect the electrical power of an on-board electrical system, whereby this on-board electrical system is connected to the powertrain's energy storage device. This includes, in particular, the on-board electrical system in which electrical ancillary units are provided, especially electrical consumers such as lighting or similar.

[0026] In combination with this or alternatively, the performance parameters can represent gradient information or a gradient-related potential energy amount of a section of road ahead. The gradient information or amount can also refer to the current section of road. The gradient information can, for example, be given as a percentage of an incline or as a percentage of a decline. The gradient information can therefore represent a section of road with an incline or a decline. This gradient information is directly linked to the additional energy required to be generated (due to the incline) or to an amount of energy that is generated due to the incline and therefore does not have to be provided by the drive. Alternatively, the performance parameter directly represents the energy that can be generated through recuperation, in particular the amount that results from the potential energy and thus from the incline.The power parameter can correspond to an amount of energy that results from the potential energy and thus from the gradient or decline.

[0027] A gradient-related potential energy amount can thus correspond to the power parameters, whereby on an incline the power parameter indicates a future electrical power to be generated by the electric drive, and on a downhill section of road ahead the power parameter indicates an electrical power to be obtained. Alternatively, or in combination with this, the power parameter can also represent a payload, such as the mass of a payload in the vehicle and / or the mass of a coupled trailer. For example, if a trailer is detected, a different performance parameter with a different height can be used than when detecting a free trailer hitch. The payload can be determined in particular by the tire pressure, so that different performance parameters are applied for different tire pressures.In particular, at higher tire pressure the value of the performance parameter is higher than at lower tire pressure.

[0028] Changing the load point can be achieved by changing the power or torque of the electric drive. The rate of change is preferably limited according to a maximum rate of change. This can improve driving comfort, since simultaneous, opposing changes in the load point of the combustion engine and the torque of the electric drive can result in a temporary deviation from the driver's desired torque due to dynamic processes. By limiting the rate of change, this temporary deviation can be significantly reduced. In addition, changing the load point of the combustion engine, in particular, can lead to a change in the acoustic behavior, which is perceived as less disturbing by the vehicle occupants at a lower rate of change. The maximum rate of change can be predetermined and can be constant or variable.In particular, the maximum rate of change depends on the gear ratio of the drive, the speed of the vehicle or the gradient of the current route.

[0029] Furthermore, it can be provided that the load point is changed according to a predetermined change curve. The change curve can be the time curve of the load point (i.e., the time curve of the power or torque). Different change curves are provided for different gear ratios, in particular of a transmission in the drive train, or also for different vehicle speeds. Several change curves can be stored, for example in a memory, which are provided for different gear ratios or for different vehicle speeds. The relevant change curve can then be retrieved and executed for the corresponding gear ratio or the relevant vehicle speed.

[0030] The method may further comprise executing a passive driving state when the load point is not changed. The passive driving state can be executed by operating the electric drive train with a substantially constant power or with a substantially constant torque of the electric drive. The power or torque of the electric drive is preferably only changed when the state of charge of the electrical energy storage device leaves a predetermined interval or is outside the interval. In particular, the power or torque of the electric drive is only changed when the state of charge of the electrical energy storage device falls below a lower limit or exceeds an upper limit. If both limits are used to trigger the change in power or torque, the interval can be defined by the upper limit and the lower limit.

[0031] This passive driving state can be used in particular to operate the electric drive neither in generator mode nor in motor mode when the charge level of the electrical energy storage device is sufficiently high and, based on the cost quotient, neither the generation of additional electrical energy nor the consumption of stored electrical energy is advantageous for propulsion of the vehicle. The electrical energy storage device is then continuously discharged by the consumption of the on-board electrical system. If the charge level of the electrical energy storage device falls below a threshold, a low torque or a low electrical power of the electric drive can initially be activated in generator mode to counteract the decrease in the charge level of the electrical energy storage device, which increases increasingly as the charge level decreases.Since this change in the state of charge generally occurs slowly, the electric drive essentially produces a constant torque or a constant electrical power for a given speed. If the operation of the electric drive is specified in the form of a torque, this torque can depend not only on the state of charge of the electrical energy storage device but also on the speed of the electric drive, since the electrical power generated by the electric drive depends primarily on its torque and speed.The torque or power of the electric drive in passive mode can also advantageously be determined by a controller, for example a PI controller, which increases the generator torque or generator power at a relatively low rate depending on the amount by which the energy storage device's charge level falls below a threshold, so that the torque or power of the electric drive remains essentially constant compared to the dynamic operation of the vehicle drive. In all of the cases mentioned, the rate of change of the torque or power of the electric drive is considerably lower than the rate of change when the generator torque increases when the cost quotient falls below a threshold.

[0032] The interval, or the upper and / or lower limits, can depend on the level of the performance parameter. In particular, the interval can be defined by different limit values for different performance parameters. This takes into account that different performance parameters also have different requirements for the energy storage system, and thus the execution of the passive driving mode can depend on the performance parameters.

[0033] The electric drive can be put into an energy-saving mode when the power at which the electric drive is operated is zero. This particularly applies to driving situations in which the charge level of the electrical energy storage device is neither particularly low nor particularly high. In the energy-saving mode, at least parts of a control system for the electric drive are in an inactive state. If the target torque of the electric drive or the target power of the electric drive changes from zero to a value that is different from zero, these parts of the control system or the control system itself are put into an active state. In the then intended active state, the drive is controlled to operate with the target torque or the target power.By alternating between phases with increased load of the combustion engine and electric drive in generator mode to generate the required electrical energy, if the cost quotient is favorable, as well as phases with electric drive in energy-saving mode, the overall result is a particularly low fuel consumption to generate the required electrical energy.

[0034] Changing the load point can depend on one or more prerequisites. If one or more of these prerequisites are not met, the load point will not be changed. One of these prerequisites can be that when the total target torque is increased, the difference to be generated by the combustion engine drive between the total target torque and the new load point of the electric drive is not greater than an emissions torque threshold. This emissions torque threshold is linked to an emissions limit for the combustion engine exhaust gas. This ensures that when the target torque of the combustion engine drive is increased (i.e. when the target power of the combustion engine drive increases), this increase is only realized if it is certain that this will not result in an emissions limit being exceeded. If the emissions limit is exceeded, this increase is not realized.The relevant emission limit is linked to an emission torque threshold, above which the combustion engine exhibits emissions that exceed the emission limit. The emission limit can be a limit for a soot concentration or for a gas concentration in the exhaust gas, for example, a nitrogen oxide concentration. The emission limit can be constant or depend on the location of the vehicle. This can, for example, protect areas with a high population density or where a special (particularly low) emission limit applies from excessive emissions. The target torque or target power of the combustion engine drive can be specified by a control system and thus directly or indirectly by a driver's request.

[0035] There may be one prerequisite for changing the load point, in particular one of several prerequisites. If the prerequisite is not met, the load point is not changed. If the prerequisite is met (if there is one prerequisite in total) or if all of the several prerequisites are met, then the load point is changed. The prerequisite for changing the load point can be that the previous load point, in particular corresponding to the current load point, and / or the changed load point (corresponding to the new load point) of the combustion engine exceeds an immediately implementable torque (i.e. maximum torque that can be set at the current operating point) by no more than a predetermined amount. This limits the gap between a desired torque and a torque that cannot be fully achieved; if the desired torque is too far removed from the implementable torque, then the change is not carried out orThe planned load point change is not carried out. This can prevent the driver from failing to achieve the torque desired, or a sudden change in the generated torque occurring without driver action. For example, a reduction in the total generated torque could occur if the combustion engine load is increased beyond the immediately convertible torque with electric drive in generator mode, or if operation of the electric drive in motor mode is deactivated when the combustion engine load is limited by the convertible torque.

[0036] When changing the load point, the rate of change of the power or torque of the electric drive can be selected to be lower or reduced if a previous load point (or a current load point) and / or the changed load point (corresponding to the new load point) of the combustion engine exceeds the immediately convertible torque by a predetermined amount. In this case, a change in the load point can cause a change in the total torque generated, but due to the low rate of change, this is perceived by the driver as little disturbing or not even noticed at all. In these cases with a limited rate of change, it is also possible for the immediately convertible torque to follow the required load point of the combustion engine with greater accuracy.

[0037] As mentioned, the method can be implemented depending on emission limits. One embodiment is that the immediately implementable torque is determined depending on the exhaust emissions. Different (specified) emission limits result in different levels of implementable torque being determined. The implementable torque can therefore depend not only on the technically possible maximum (currently achievable) torque, but can also additionally depend on emission limits. In other words, the technically possible maximum (currently achievable) torque can be corrected depending on the specified emission limits before the thus corrected torque is used to change the load point.

[0038] The method can be carried out by means of a drive train comprising the electric drive, the electrical energy storage device connected thereto, and the combustion engine drive, and further comprising a control device connected to the two drives in a controlling manner. This control device is configured to carry out the method for controlling the drive train as mentioned here. For this purpose, the control device can, in particular, comprise a memory in which different threshold values are stored for different performance parameters (and possibly for different charge states of the energy storage device). Fig. 1 shows a symbolic representation of components of a vehicle to explain the procedure described here in more detail.

[0039] The Fig.1 shows a vehicle F with a drive train AS. This drive train AS contains an electric drive EA, which has a control system ST. The drive train further comprises an internal combustion engine VA. This is supplied with fuel from a tank T. A control device, which contains a storage device S, is connected in a controlling manner to the electric drive EA and the internal combustion engine drive VA. The control device C is thus configured to adjust the load point of the drives EA, VA. An electrical energy storage device ES is connected to the electric drive EA such that the electric drive EA can be fed from the electrical energy storage device ES (for example, in a motor mode), and such that the electric drive EA can supply energy to the energy storage device ES in a generator mode.

[0040] This is represented by the arrow pointing in both directions between the energy storage unit ES and the electric drive unit EA. The electric energy storage unit ES also supplies an on-board electrical system BN.

[0041] As symbolically shown, the electric drive train AS comprises a transmission G, via which the power of the combustion engine drive VA and the electric drive EA can be delivered to an output AT of the vehicle, whereby this output AT is connected downstream of the drive train. The power flow to the drive train AT is shown, i.e. in an operating state in which the drive train delivers energy to the output AT, although it can also be provided that energy can be transferred from the drive train AT to the electric drive EA in a recuperation state. In addition, mechanical energy can be transferred from the combustion engine drive VA to the electric drive EA so that it generates electrical energy in generator mode, which is stored in the energy storage device.In the same way, during recuperation, the output AT can store energy in electrical form in the electrical energy storage ES via the electric drive EA, which works as a generator.

[0042] A memory S is provided in the control device C, in particular a semiconductor memory, for example a non-volatile memory. Different threshold values are stored in this memory for different performance parameters of the electric drive, which trigger the change in the load point of the electric drive EA. The control device C is configured to use different threshold values for different performance parameters of the electric drive EA and to increase the generator power if a cost quotient falls below a first charging threshold. The threshold values thus indicate what the cost quotient is based on in order to decide, based on the comparison, whether the load point of the electric drive EA should be changed or not. Furthermore, different threshold values are also stored in the memory S for different charging states.These charge levels refer to the electrical energy storage device ES, which is why the energy storage device ES is connected to the control device C for signal transmission. This allows the control device C to detect the charge level of the energy storage device ES to execute the method and provide different threshold values (for different charge levels) accordingly. A multidimensional characteristic map is thus stored in the memory S, which assigns threshold values to different charge levels and different performance parameters. Retrieving a threshold value is therefore dependent on two values; the memory indicates that the threshold values are a function of the charge level and the performance parameter (vehicle speed, electrical power of the on-board electrical system, etc.).

Claims

[1] Method for controlling a drive train having an electric drive (EA), an electrical energy storage device (ES) connected thereto, and an internal combustion engine drive (VA), comprising the steps: - Determining a total target torque to be generated by the drive train (AS), - Determining a cost quotient that corresponds to a ratio of a change in fuel consumption from a current load point to a new load point to a corresponding change in the energy content of the electrical storage (ES); and - Changing a load point of the electric drive (EA) from the current load point to the new load point by increasing the generator power of the electric drive (EA) when the cost quotient falls below a first charging threshold; and / or by increasing a motor power of the electric drive (EA) if the cost quotient exceeds a first motor threshold; where the threshold values have different values for different charging states of the electrical energy storage (ES) and for different power parameters which characterise a future electrical power to be generated or obtained by the electric drive (EA), the threshold values have different values, the method further comprising the step of: - Changing a load point of the electric drive (EA) by reducing the generator power of the electric drive (EA) if the cost quotient exceeds a second charging threshold; and / or by reducing the motor power of the electric drive (EA) when the cost quotient falls below a second motor threshold. [2] The method of claim 1, wherein the first charging threshold is lower than the second charging threshold and / or the first motor threshold is higher than the second charging threshold. [3] Method according to one of the preceding claims, wherein, in the course of determining whether the cost quotient exceeds or falls below one of the threshold values, the old load point and the new load point are adapted to an operating state of the combustion engine by changing the level of the old load point and the new load point for which the cost quotient is determined, or, in the course of determining whether the cost quotient exceeds or falls below one of the threshold values, the cost quotient is adapted to an operating state of the combustion engine, wherein, in different operating states, the cost quotient is changed to different degrees during the adaptation. [4] Method according to claim 3, wherein the operating state of the combustion engine corresponds to an actual temperature of the combustion engine. [5] Method according to one of the preceding claims, wherein, in the course of determining whether the cost quotient exceeds or falls below one of the threshold values, the old load point and the new load point are adapted to the operating state of auxiliary units by changing the level of the old load point and the new load point for which the cost quotient is determined. [6] Method according to one of the preceding claims, wherein the performance parameters - represent a vehicle speed of a vehicle (F) driven by the drive train (AS), and / or - represent the electrical power of an on-board network (BN) connected to the energy storage device (ES) of the drive train (AS), and / or - provide gradient information or a gradient-related potential energy amount of a section of track ahead. [7] Method according to one of the preceding claims, wherein changing the load point is carried out by changing the power or torque of the electric drive (EA), the amount of the rate of change being limited according to a maximum rate of change. [8] Method according to one of the preceding claims, wherein the changing of the load point is carried out according to a predetermined change profile, wherein different change profiles are provided for different gear ratios or driving speeds of the vehicle (F). [9] A method according to any one of the preceding claims, wherein the method further comprises: executing a passive driving state when the load point is not changed, wherein executing the passive driving state comprises: Operating the electric drive (EA) with a substantially constant power or a substantially constant torque of the electric drive (EA), wherein the power or torque of the electric drive (EA) is only changed when the state of charge of the electrical energy storage device leaves a predetermined interval or is outside the interval. [10] Method according to claim 9, wherein the interval is defined by different limit value pairs for different performance parameters. [11] Method according to one of the preceding claims, wherein the electric drive (EA) is put into an energy-saving mode when the power with which the electric drive (EA) is operated is equal to zero, wherein in the energy-saving mode at least parts of a control (ST) of the electric drive (EA) are provided in an inactive state, and when the electric drive target torque changes from zero to a value which is different from zero, these parts of the control (ST) or the control (ST) itself is put into an active state. [12] Method according to one of the preceding claims, wherein one of several prerequisites for changing the load point is that a previous load point and / or a new load point of the internal combustion engine exceeds an immediately convertible torque by at most a predetermined amount. [13] Method according to one of the preceding claims, wherein when changing the load point, the amount of the rate of change of the power or the torque of the electric drive is selected to be lower if the preceding load point and / or the changed load point of the internal combustion engine exceeds an immediately convertible torque by a predetermined amount. [14] Method according to claim 12 or 13, wherein the immediately convertible torque is determined as a function of the exhaust emissions.

Images