Method for operating a drive unit for a motor vehicle, corresponding drive unit for a motor vehicle and computer program product

Abstract

The invention relates to a method for operating a drive unit (2) for a motor vehicle, wherein the drive unit (2) has a traction battery (1) comprising several cell modules (3) and a drive unit designed as an electric traction machine, which is electrically connected to electrical terminals (4, 5) of the traction battery (1) via an inverter, wherein the cell modules (3) can be electrically connected differently between the terminals (4, 5).The invention provides that the cell modules (3) are divided into battery modules (6), each containing the same number of electrically parallel-connected cell modules (3) and electrically connected in series between the terminals (4, 5), wherein a number of the battery modules (6) are adjusted during operation of the drive unit (2) such that an electrical voltage applied to the terminals (4, 5) corresponds to at least one operating voltage of the traction motor. The invention further relates to a drive unit (2) for a motor vehicle and a computer program product.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, wherein the drive unit comprises a traction battery with several cell modules and a drive unit designed as an electric traction machine, which is electrically connected to the electrical terminals of the traction battery via an inverter, wherein the cell modules can be electrically connected differently between the terminals. The invention further relates to a drive unit for a motor vehicle and a computer program product.

[0002] For example, the prior art is known in the publication DE 10 2019 212 860 A1.This describes a battery system for a motor vehicle, wherein a switching unit is provided for each battery component of the battery system, which is configured to determine, depending on its respective switching state, one of several possible mutual interconnections of the battery components to each other, wherein a processor device is configured to switch the respective switching state of the switching unit of at least one of the battery components to a predetermined target state, for this purpose setting a predetermined enable level at a flip-flop output of a shift register assigned to this battery component by means of an enable signal, and setting a predetermined block level at each other flip-flop output, and generating the selection signal for the target state in at least one common selection line.

[0003] Furthermore, the publication DE 10 2021 119 607 A1 discloses an energy storage device, comprising at least one connection for connecting the energy storage device to an electrical network, as well as battery cells for storing energy and a cell contacting device which is designed to connect the battery cells to the at least one connection.The cell contacting device is designed as a multi-layer cell contacting device, wherein the multi-layer cell contacting device has at least one layer system for a respective voltage level, wherein the at least one layer system comprises at least one respective conductor layer to connect the battery cells to the at least one terminal of the energy storage device, the multi-layer cell contacting device has a switching device comprising a control unit and several controllable switching units, wherein the control unit is configured to connect the battery cells to the respective layer system according to one of at least two predetermined circuit configurations of the switching units in order to provide the respective voltage level in the at least one layer system.

[0004] The object of the invention is to propose a method for operating a drive direction for a motor vehicle which has advantages over known methods, in particular enabling the provision of a consistently high drive power of the drive device.

[0005] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that the cell modules are divided into battery modules, each containing the same number of electrically parallel-connected cell modules and connected electrically in series between the terminals, wherein a number of the battery modules are adjusted during operation of the drive unit such that an electrical voltage applied to the terminals corresponds to at least one operating voltage of the traction motor.

[0006] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0007] The method serves to operate the drive unit. The drive unit is designed and configured to propel the motor vehicle, i.e., to provide drive torque directed toward propelling the motor vehicle. To provide this drive torque, the drive unit comprises the drive assembly, which is an electric traction motor. The drive unit is preferably an integral part of the motor vehicle, but can, of course, exist separately from it, particularly until the drive unit is mounted on or in the motor vehicle.

[0008] The electric traction motor is electrically connected to the traction battery via the inverter. The traction motor is operated, at least intermittently, with electrical energy drawn from the traction battery. Conversely, it may be possible to store electrical energy, provided by the electric traction motor, in the traction battery, at least intermittently. The inverter converts the direct current supplied by the traction battery into alternating current for the traction motor, or conversely, converts the alternating current supplied by the traction motor into direct current, which is fed back to the traction battery. The inverter is preferably designed as a pulse inverter.

[0009] The traction battery has several cell modules which are electrically interconnected between the electrical terminals of the traction battery.

[0010] Cell modules are elements of the traction battery, each comprising at least one battery cell of the traction battery. Each cell module thus contains at least one battery cell from among the multiple battery cells that make up the traction battery. Preferably, each cell module contains multiple battery cells, and in particular, each cell module contains the same number of battery cells. For example, the battery cells of each cell module are electrically connected in series. Preferably, each cell module comprises at least 10, at least 30, or at least 50 battery cells, especially those connected in series.

[0011] The cell modules can be electrically connected in different ways between the terminals of the traction battery. For example, some of the cell modules can be connected in series and others in parallel between the terminals. This different connection of the cell modules between the terminals allows for different voltages to be provided at each terminal. A higher voltage is achieved with a series connection of the cell modules than with a parallel connection.

[0012] The traction motor's drive power depends significantly on the electrical voltage supplied by the traction battery at its electrical terminals. This voltage can also be referred to as battery voltage. The battery voltage, in turn, depends on the voltages of the individual cell modules or individual battery cells. Since the voltages of the cell modules, and consequently the battery voltage, change with the traction battery's state of charge, the available drive power for propelling the vehicle via the traction motor also changes. In particular, the drive power decreases considerably as the traction battery's state of charge decreases.

[0013] Typically, the cell modules between the terminals are electrically connected in such a way that the battery voltage, when the traction battery is fully charged (i.e., at approximately or exactly 100%), corresponds to the nominal voltage of the traction motor. Starting from the nominal power available at nominal voltage, the traction motor's drive power decreases as the charge level decreases, for example, to a maximum of 50%, 40%, or 30% of the nominal power. This is perceived as annoying by a vehicle user.

[0014] For this reason, the invention provides that the cell modules are divided into battery modules. Each cell module is thus assigned to one of the battery modules, so that each battery module ultimately contains at least one cell module. The use of the term "battery modules" in the plural does not imply a quantification of the battery modules; rather, any number of cell modules can be present, for example, a single cell module or several cell modules. The term "battery modules" is therefore used to represent at least one battery module, preferably several battery modules.

[0015] The cell modules are distributed among the battery modules such that each battery module contains the same number of cell modules. The cell modules within each battery module are electrically connected in parallel. The battery modules themselves, however, are electrically connected in series between their terminals, so that the battery voltage equals the sum of the individual voltages of the battery modules. This distribution of the cell modules among the battery modules and their corresponding interconnection between the terminals occurs during operation of the drive unit. Therefore, it is designed that the cell modules are electrically interconnected between the terminals in different ways during operation of the drive unit, resulting in a temporary first interconnection and a temporary second interconnection of the cell modules.

[0016] The cell modules are distributed among the battery modules in such a way that the cell modules within the battery modules and the battery modules themselves are interconnected, resulting in an electrical voltage at the terminals that is at least equal to the operating voltage of the traction motor, i.e., exactly equal to or greater than the operating voltage. The operating voltage of the traction motor is understood to be the electrical voltage currently used, or intended to be used, to operate the traction motor. For example, the operating voltage is specified by a control unit of the drive system.

[0017] Particularly preferably, the cell modules are distributed among the battery modules and electrically interconnected in such a way that the battery voltage corresponds at least to the nominal voltage of the traction motor, especially regardless of the charge level of the traction battery. This means that during operation of the drive system, the cell modules are distributed among the battery modules depending on the charge level, namely in such a way that the resulting voltage at the terminals corresponds at least to the nominal voltage of the traction motor.

[0018] Before the cell modules are divided into battery modules, the number of battery modules is determined. The number of battery modules is chosen to ensure the desired voltage at the terminals is achieved, for example, that the voltage corresponds at least to the operating voltage of the traction motor or at least to the nominal voltage of the traction motor. This procedure ensures, at least partially, that high drive power can be provided using the traction motor, independent of the traction battery's state of charge.

[0019] A further development of the invention provides that the number of battery modules is selected such that the electrical voltage applied to the terminals lies within a voltage range encompassing the operating voltage, wherein the voltage range is limited towards lower voltages by a first threshold and towards higher voltages by a second threshold. The voltage range encompasses the operating voltage of the traction motor and is limited on one side by the first threshold and on the other by the second threshold. For example, the operating voltage lies midway within the voltage range, i.e., midway between the first and second thresholds. Instead of the operating voltage, the voltage range can also encompass the nominal voltage of the traction motor.

[0020] The number of battery modules, into which the cell modules are distributed, is determined such that the electrical voltage provided at the terminals, i.e., the battery voltage, lies within the specified voltage range. Preferably, the voltage range is constant during operation of the drive unit, meaning that the two threshold values ​​also remain constant. It is preferably provided that, as long as the battery voltage is within the specified voltage range, the connection of the traction battery is not changed and the number of battery modules remains the same. If the battery voltage falls below the first threshold value, the number of battery modules is adjusted or changed, specifically in such a way that the battery voltage increases.

[0021] The number of battery modules is selected and the cell modules distributed across the modules in such a way as to increase the battery voltage. Specifically, the number of battery modules is chosen so that the battery voltage is higher than the first threshold but lower than the second. Ultimately, changing the number of battery modules results in the battery voltage falling within the specified voltage range. For example, the voltage range encompasses a voltage difference that is at least 30%, at least 40%, or at least 50% and / or at most 70%, at most 60%, or at most 50% of the nominal voltage of the traction motor. Using this voltage range allows for flexible selection of the number of battery modules and ensures that a sufficient voltage is achieved to operate the traction motor.

[0022] A further development of the invention provides that, to adjust the number of battery modules, a connection is selected from several connection configurations of the battery modules and set on the traction battery, wherein in a first of the connection configurations the number of battery modules corresponds to a first number of battery modules and the number of cell modules per battery module corresponds to a first number of cell modules, and in a second of the connection configurations the number of battery modules corresponds to a second number of battery modules different from the first number of battery modules and the number of cell modules per battery module corresponds to a second number of cell modules different from the first number of cell modules.

[0023] The wiring configurations correspond to different electrical connections of the battery modules between the terminals of the traction battery and, consequently, to different numbers of battery modules. In the first configuration, the battery modules have the first number of modules, and each cell module has the first number of cells. In the second configuration, the second number of modules has the second number of modules, and each cell module has the second number of cells. The total number of cells always remains the same, such that the product of the first number of modules and the first number of cells equals the product of the second number of modules and the second number of cells. Due to the different numbers of battery modules, different voltages are achieved between the terminals for a given state of charge.

[0024] A further development of the invention provides that a third configuration is used as one of the possible configurations. In this third configuration, the number of battery modules corresponds to a third number of battery modules, and the number of cell modules per battery module corresponds to a third number of cell modules. The third number of battery modules differs from both the first and second number of battery modules, and the third number of cell modules differs from both the first and second number of cell modules. Thus, at least three different configurations are available, from which the desired configuration is selected and configured on the traction battery. The traction battery is therefore operated sometimes with the first configuration, sometimes with the second configuration, and sometimes with the third configuration. This results in particularly high flexibility and ensures reliable achievement of the desired battery voltage.

[0025] A further development of the invention provides that the number of battery modules is determined as a function of the charge level of the traction battery and / or the discharge current of the traction battery. It has already been explained that the voltage between the terminals depends primarily on the charge level. However, it can also depend on the discharge current. In particular, the voltage is lower the higher the discharge current with which the traction battery is discharged to operate the traction motor. By determining the number of battery modules as a function of the charge level and / or the discharge current, it is ensured that the electrical voltage at the terminals corresponds at least to the operating voltage of the traction motor.

[0026] A further development of the invention provides that the first connection is selected when the charge level is in a first charge level range and the second connection is selected when the charge level is in a second charge level range adjacent to the first charge level range, wherein the electrical voltage in the first connection and at a charge level corresponding to a region boundary of the first charge level range facing the second charge level range and the electrical voltage in the second connection and at a charge level corresponding to a region boundary of the first charge level range facing the first charge level range are in a ratio to each other which corresponds to a ratio of the first number of battery modules and the second number of battery modules.

[0027] The two charge level areas, i.e., the first charge level area and the second charge level area, are directly adjacent to each other, such that the (first) boundary of the first charge level area facing the second charge level area is directly adjacent to the (second) boundary of the second charge level area, which limits it on its side facing the first charge level area. When the charge level is present in the first charge level area, the first circuit is used, and when the charge level is present in the second charge level area, the second circuit is used.

[0028] At a charge level corresponding to the first range limit, a first battery voltage is present, and at a charge level corresponding to the second range limit, a second battery voltage is present. The two circuits are configured such that the first and second voltages are in a ratio to each other that corresponds to the ratio of the number of battery modules in the first battery and the number of battery modules in the second battery. Therefore, the circuits do not result in a significant jump in the voltage applied to the terminals; rather, the voltage is provided according to the described principle. This ensures reliable operation of the drive system.

[0029] A further development of the invention provides that the number of battery modules is selected, at least temporarily, such that the electrical voltage applied to the terminals is greater than the nominal voltage of the traction motor, and the inverter is controlled in such a way that the inverter's output voltage corresponds at most to the nominal voltage. This means that the battery voltage provided by the traction battery, which represents an input voltage of the inverter, is reduced, at least temporarily, by using the inverter, namely at least to the nominal voltage of the traction motor.

[0030] For example, it is intended that the number of battery modules is selected, at least temporarily, such that the battery voltage is at least 30%, at least 40%, or at least 50% higher than the nominal voltage. Preferably, the number of battery modules in different configurations is selected such that the battery voltage is higher than the nominal voltage, in particular by one of the aforementioned percentages.

[0031] Nevertheless, the inverter ensures that the traction machine can be operated reliably within its specifications, so that the voltages resulting from the different interconnections of the cell modules guarantee a sufficiently high drive power regardless of the charge level of the traction battery.

[0032] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the descriptions in this document, wherein the drive device has a traction machine comprising several cell modules and a drive unit designed as an electric traction machine, which is electrically connected to electrical terminals of the traction battery via an inverter, wherein the cell modules can be electrically connected differently between the terminals.

[0033] The drive unit is designed and configured to divide the cell modules into battery modules, each containing the same number of electrically parallel connected cell modules and electrically connected in series between the terminals, whereby a number of the battery modules are adjusted during operation of the drive unit such that an electrical voltage applied to the terminals corresponds to at least one operating voltage of the traction machine.

[0034] The advantages of such a procedure or such a design of the drive system have already been mentioned. Both the drive system for a motor vehicle and the method for operating it can be further developed as explained in this description, and reference is made to these explanations in this respect.

[0035] Furthermore, the invention relates to a computer program product comprising commands that cause the drive device to execute the described method as described herein. For the advantages and possible advantageous embodiments, reference is made to the description in its entirety.

[0036] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0037] The invention is explained below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The only embodiment shown is... Fig. 1 a schematic representation of an area of ​​a drive direction for a motor vehicle, namely a traction battery, for three different interconnections of cell modules.

[0038] The Fig.Figure 1 shows a highly schematic representation of a traction battery 1, which is a component of a drive system 2 of a motor vehicle. The traction battery 1 is shown here with three different configurations of cell modules 3: a first configuration on the far left, a second configuration in the middle, and a third configuration on the far right. Also shown only in a highly schematic way are the electrical connections 4 and 5 of the traction battery, between which an electrical voltage is supplied by means of the cell modules 3.

[0039] The cell modules are distributed across battery modules 6. For illustrative purposes, the first configuration consists of two battery modules, the second of three, and the third of four. A total of twelve cell modules 3 are shown, all of which are distributed across the battery modules 6 such that each battery module 6 contains the same number of cell modules 3. The cell modules 3 of each battery module 6 are connected electrically in parallel. The battery modules 6, however, are connected in series between terminals 4 and 5. Consequently, with a constant voltage across the cell modules 3, the traction battery 1 will have different voltages between terminals 4 and 5.

[0040] The different circuit configurations are used at different charge levels of the traction battery in order to achieve a battery voltage sufficient to supply a traction motor of the drive unit 2 with a sufficiently high operating voltage, despite the different charge levels and the resulting different voltages of the cell modules 3. Overall, this procedure, only roughly outlined here, ensures that similar voltages are always available for operating the traction motor, despite different charge levels. REFERENCE MARK LIST: 1 traction battery 2 Drive unit 3-cell module 4 connection 5 connection 6 battery module QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 212 860 A1

[0002] DE 10 2021 119 607 A1

[0003]

Claims

[1] Method for operating a drive unit (2) for a motor vehicle, wherein the drive unit (2) has a traction battery (1) comprising several cell modules (3) and a drive unit designed as an electric traction machine, which is electrically connected to electrical terminals (4, 5) of the traction battery (1) via an inverter, wherein the cell modules (3) can be electrically connected differently between the terminals (4, 5), characterized by , that the cell modules (3) are divided into battery modules (6), each containing the same number of electrically parallel connected cell modules (3) and electrically connected in series between the terminals (4, 5), wherein a number of the battery modules (6) are adjusted during operation of the drive device (2) such that an electrical voltage applied to the terminals (4, 5) corresponds to at least one operating voltage of the traction machine. [2] Method according to claim 1, characterized by , that the number of battery modules (6) is chosen such that the electrical voltage applied to the terminals (4, 5) lies within a voltage range that accommodates the operating voltage, the voltage range being limited in the direction of lower voltages by a first threshold and in the direction of higher voltages by a second threshold. [3] Method according to any one of the preceding claims, characterized by, that to adjust the number of battery modules (6) from several battery module configurations (6) one configuration is selected and set on the traction battery (1), wherein in a first of the configurations the number of battery modules (6) corresponds to a first number of battery modules and the number of cell modules (3) per battery module (6) corresponds to a first number of cell modules, and in a second of the configurations the number of battery modules (6) corresponds to a second number of battery modules different from the first number of battery modules and the number of cell modules (3) per battery module (6) corresponds to a second number of cell modules different from the first number of cell modules. [4] Method according to any one of the preceding claims, characterized by, that as one of the interconnections a third interconnection is used in which the number of battery modules corresponds to a third number of battery modules and the number of cell modules per battery module (6) corresponds to a third number of cell modules, wherein the third number of battery modules is different from both the first number of battery modules and the second number of battery modules and the third number of cell modules is different from both the first number of cell modules and the second number of cell modules. [5] Method according to any one of the preceding claims, characterized by , that the number of battery modules (6) is determined depending on a charge level of the traction battery (1) and / or a discharge current of the traction battery (1). [6] Method according to any one of the preceding claims, characterized by, that the first connection is chosen when the charge level is in a first charge level range and the second connection is chosen when the charge level is in a second charge level range adjacent to the first charge level range, wherein the electrical voltage in the first connection and at a charge level corresponding to a range boundary of the first charge level range facing the second charge level range and the electrical voltage in the second connection and at a charge level corresponding to a range boundary of the second charge level range facing the first charge level range are in a ratio to each other which corresponds to a ratio of the first number of battery modules and the second number of battery modules. [7] Method according to any one of the preceding claims, characterized by, that the number of battery modules (6) is selected at least temporarily such that the electrical voltage applied to the terminals (4, 5) is greater than a nominal voltage of the traction machine, and the inverter is controlled in such a way that an output voltage of the inverter corresponds at most to the nominal voltage. [8] Method according to any one of the preceding claims, characterized by , that a sodium-ion battery is used as the traction battery (1). [9] Drive unit (2) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit (2) has a traction battery (1) having several cell modules (3) and a drive unit designed as an electric traction machine, which is electrically connected to electrical terminals (4, 5) of the traction battery (1) via an inverter, wherein the cell modules (3) can be electrically connected differently between the terminals (4, 5), characterized by, that the drive device (2) is designed and configured to divide the cell modules (3) into battery modules (6), each containing the same number of electrically parallel connected cell modules (3) and electrically connected in series between the terminals (4, 5), wherein a number of the battery modules (6) are adjusted during operation of the drive device (2) such that an electrical voltage applied to the terminals (4, 5) corresponds to at least one operating voltage of the traction machine. [10] Computer program product comprising instructions that cause the drive device (2) according to claim 9 to execute the method according to one or more of claims 1 to 8.

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