Electrically operable drive train of motor vehicle

Abstract

The invention relates to an electrically operable drive train (1) of a motor vehicle (2), comprising an electric machine (3) for driving the motor vehicle (2), and a first rechargeable vehicle battery (4) permanently mounted in the motor vehicle (2) for powering the electric machine (3), the drive train (1) has a second rechargeable vehicle battery (5) which can be detached from the motor vehicle (2) and is used to supply the electric machine (3), the storage capacity of the first vehicle battery (4) being greater than the storage capacity of the second vehicle battery (5).

Description

Field of the Invention

[0001] The present invention relates to an electrically operable driveline for a motor vehicle, the driveline including an electric machine for driving the motor vehicle and a first rechargeable vehicle battery permanently installed in the motor vehicle and configured to supply power to the electric machine. Background Art

[0002] Electric motors are increasingly being used to drive motor vehicles as an alternative to internal combustion engines that require fossil fuels. Considerable efforts have been made to improve the suitability of electric drives for everyday use and to also be able to provide the driving comfort to which users are accustomed. For example, a detailed description of an electric drive can be found in the article titled "Hochintegrativ und Flexibel Elektrische Antriebseinheit fnt E-Fahrzeuge [Highly Integrative and Flexible Electric Drive Unit for E-Vehicles]" published by Erik Schneider, Frank Fickl, Bernd Cebulski, and Jens Liebold in the German automotive magazine ATZ, Vol. 113, May 2011, pages 360 to 365. The article describes a drive unit for an axle of a vehicle, the drive unit including an electric motor arranged coaxially with a bevel gear differential.

[0003] In vehicles with an electric drive unit of this type, the heating and cooling system for the passenger compartment is the largest auxiliary energy consumer because, in a fully electric drive concept, an internal combustion engine is generally not used as a heat provider. There are also additional temperature control requirements for drive components such as batteries, power electronics, and the electric drive unit itself.

[0004] In particular, ambient temperature limitations can lead to a significant loss of driving range for vehicles with an electric drive unit. In addition to heating the passenger compartment, preconditioning the battery by heating - which is necessary for an upcoming rapid charging phase - is also one of the most energy-intensive thermal management functions. An example of such a thermal management system can be found in DE102012208992A1.

[0005] In order to charge the battery as gently as possible and achieve the lowest possible charging losses, it is recommended to charge the vehicle battery as gently as possible, i.e., slowly. Slow charging reduces the internal resistance of the battery and makes it almost negligible. However, in the case of so-called fast charging with a high current, this resistance increases significantly. This process damages the battery and, in the long run, leads to a shortening of the battery life and a rapid decrease in the amount of energy that can be stored in the battery.

[0006] When operating the vehicle, there is also the challenge of using recuperation, i.e., charging the vehicle battery as effectively and battery-friendly as possible during the generator operation of the electric motor. Currently, typical recuperation outputs are usually between approximately 100 kW and 300 kW. This also applies to the recuperation process: the colder the battery, the higher the internal resistance and the lower the maximum possible charging power.

[0007] Therefore, the object of the present invention is to provide an electrically operable powertrain for a motor vehicle that avoids or at least alleviates the problems known in the prior art and uses the energy available in the powertrain as effectively as possible. Summary of the Invention

[0008] This object is achieved by an electrically operable powertrain for a motor vehicle, which powertrain includes an electric motor for driving the motor vehicle and a first rechargeable vehicle battery permanently installed in the motor vehicle and used to supply power to the electric motor, wherein the powertrain has a second rechargeable vehicle battery that can be detached from the motor vehicle and used to supply power to the electric motor, and wherein the storage capacity of the first vehicle battery is greater than the storage capacity of the second vehicle battery.

[0009] Therefore, the powertrain has an architecture in which at least two different vehicle batteries are installed, and these batteries are preferably significantly different in their "size" as measured by the storage capacity. The present invention is based on the idea that the storage capacity also determines the physical size and weight of the corresponding vehicle battery. In other words, a vehicle battery with a higher storage capacity is larger and heavier than a vehicle battery with a smaller storage capacity. In this regard, the smaller of the two vehicle batteries is provided as a replaceable unit, while the larger vehicle battery is preferably installed as an integral part of the motor vehicle.

[0010] In this regard, the second vehicle battery, i.e., the smaller vehicle battery, is preferably used for recuperation and / or fast charging and is also preferably used to handle larger charging currents, while the first vehicle battery, i.e., the larger integral vehicle battery, is reserved for optimal constant charging and smaller charging currents.

[0011] A vehicle battery is a storage battery mainly intended to supply electrical energy to an electric motor that provides propulsion in an electric vehicle. For the purposes of the present application, the term vehicle battery also includes buffer batteries in fuel cell vehicles and hybrid drives. A vehicle battery is sometimes also referred to as a high-voltage battery, traction battery or cycle battery.

[0012] Preferably, the nominal voltage of the vehicle battery is greater than or equal to 400 V, highly preferably greater than or equal to 600 V, and particularly preferably greater than or equal to 800 V.

[0013] The vehicle battery can preferably be selected from the group of lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, sodium-ion batteries and / or thermal batteries.

[0014] The electric motor within the meaning of the present application is used to convert electrical energy into mechanical energy and / or convert mechanical energy into electrical energy, and generally includes a fixed part called a stator or stationary armature, and a part called a rotor or moving armature that is arranged movably relative to the fixed part. In the context of the present invention, the electric motor can be specifically designed as a rotating machine. In the case of such an electric rotating machine, a distinction is made in particular between a radial-flux machine and an axial-flux machine. A radial-flux machine is characterized in that the magnetic field lines extend in the radial direction in the air gap formed between the rotor and the stator, while in the case of an axial-flux machine, the magnetic field lines extend in the axial direction in the air gap formed between the rotor and the stator. In the context of the present invention, the electric motor is specifically arranged for use within the driveline of a hybrid motor vehicle or a fully electric motor vehicle. In particular, the electric motor is dimensioned such that a vehicle speed of more than 50 km / h, preferably more than 80 km / h, and particularly more than 100 km / h can be achieved. The electric motor particularly preferably has an output of more than 30 kW, preferably more than 50 kW, and particularly more than 70 kW. In addition, it is preferred that the electric motor provides a speed of more than 5000 rpm, particularly preferably more than 10,000 rpm, and very particularly preferably more than 12,500 rpm.

[0015] The electric machine may have a housing, also referred to as a motor housing. The motor housing encloses the electric machine. The motor housing may also accommodate control electronics and power electronics, and preferably may also accommodate at least a part of the braking system. In addition, the motor housing may be part of a cooling system for the electric machine and may be designed such that cooling fluid is supplied to the electric machine via the motor housing and / or heat may be dissipated to the outside via the motor housing surface. Additionally, the motor housing protects the electric machine and any electronics that may be present from external mechanical and / or chemical influences. In particular, the motor housing of the electric machine may be formed of a metallic material. Advantageously, the motor housing may be formed of a metal casting material such as gray cast iron or cast steel. In principle, it is also conceivable for the motor housing to be formed entirely or partially of plastic. The motor housing of the electric machine may also be designed as a single part or multiple parts.

[0016] The rotor is the rotating (swirling) part of the electric machine. In particular, the rotor includes a rotor shaft and one or more rotor bodies formed by a laminated rotor core that are arranged on the rotor shaft in a non-rotatable manner. The rotor shaft may be hollow, which on the one hand results in weight reduction and on the other hand allows the supply of lubricant or coolant to the rotor body. In particular, the rotor shaft may be coupled to the brake shaft of the braking system.

[0017] According to an advantageous embodiment of the invention, the electric machine may have a motor cooling circuit for removing heat from or supplying heat to the electric machine, wherein a hydraulic control unit acts on the motor cooling circuit by means of at least one hydraulic switching element in order to influence the volume flow in the motor cooling circuit.

[0018] Advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims may be combined with one another in a technically meaningful way and may define further embodiments of the invention. Additionally, the features indicated in the claims are specified and explained in more detail in the description, wherein further preferred embodiments of the invention are shown.

[0019] According to an advantageous embodiment of the invention, the storage capacity of the first vehicle battery may be at least twice, preferably three times, the storage capacity of the second vehicle battery. This allows the concept of a "small fast-charging" vehicle battery and a "large slow-charging" vehicle battery to be further optimized.

[0020] According to a further preferred refinement of the invention, the drive train can have a control device to which at least a first vehicle battery, a second vehicle battery and an electric machine are connected, and the control device controls the power flow between these components. Furthermore, according to an equally advantageous embodiment of the invention, a charging device for an electrical energy source located outside the vehicle can be connected to the control device, whereby an optimized charging control can be achieved both during the driving operation and during the stationary charging of the vehicle battery.

[0021] According to a further particularly preferred embodiment of the invention, the first vehicle battery can have a first hydraulic battery cooling circuit by means of which heat can be removed from and / or supplied to the first vehicle battery under the control of the control device. Furthermore, the invention can be further refined such that the second vehicle battery has a second hydraulic battery cooling circuit by means of which heat can be removed from and / or supplied to the second vehicle battery under the control of the control device.

[0022] In this regard, according to an advantageous embodiment of the invention, a vehicle battery can have a battery cooling circuit for removing heat from or supplying heat to the vehicle battery, wherein a hydraulic control unit for influencing the volume flow in the corresponding battery cooling circuit acts on the battery cooling circuit by means of at least one hydraulic switching element.

[0023] For example, this makes it possible to first heat a small battery to a predetermined charging temperature and charge the small battery in a recuperative or stationary manner, since the size of the small battery allows it to be heated to the predetermined charging temperature faster than the larger and thermally more cumbersome vehicle battery.

[0024] Thus, in an equally preferred embodiment of the invention, the control device can also be configured such that when a predetermined first temperature is present, the second vehicle battery is first charged by the electric machine operating in generator operation. It can also be advantageous to further refine the invention such that the control device is configured such that when a predetermined second temperature is reached, the second vehicle battery is first charged via the charging device.

[0025] According to a further preferred embodiment of the subject matter of the invention, the drive train has a thermal management system which includes an electric machine for driving a motor vehicle, a first battery cooling circuit, a second battery cooling circuit and a hydraulic control system for influencing the volume flow in the cooling circuits, wherein the control device is coupled to the hydraulic control system for controlling the hydraulic control system.

[0026] In the context of the present invention, the term "thermal management" means: demand-oriented and effective control of the heat flow in an electric vehicle, in particular a battery-powered vehicle, depending on the current operating or charging state.

[0027] According to an advantageous embodiment of the invention, the electric machine can have a motor cooling circuit for removing heat from or supplying heat to the electric machine, wherein the hydraulic control unit acts on the motor cooling circuit by means of at least one hydraulic switching element in order to influence the volume flow in the motor cooling circuit.

[0028] Finally, the invention can also be advantageously embodied such that the thermal management system includes a brake having a brake cooling circuit which is connected to the hydraulic control system and is used for removing heat from or supplying heat to the brake.

[0029] According to an advantageous embodiment of the invention, the brake can have a brake cooling circuit for removing heat from or supplying heat to the brake, wherein the hydraulic control unit acts on the brake cooling circuit by means of at least one hydraulic switching element in order to influence the volume flow in the brake cooling circuit.

[0030] The hydraulic control system guides the volume flow within the thermal management system of the motor vehicle by means of switching elements which act hydraulically on the fluid, such as valves, slides, pumps, etc. For example, for this purpose, the hydraulic control system can throttle the volume flow completely or partially and / or distribute the volume flow to relevant heat sources and radiators in sub-circuits of the thermal management system of the motor vehicle. For this purpose, the hydraulic switching elements are preferably controlled and switched by an electronic control unit.

[0031] The hydraulic switching element can be a hydraulic pump, a switching valve, a controllable throttle valve, etc. The hydraulic switching element is preferably electrically controllable. In addition, the hydraulic switching element preferably has at least two different switchable operating states, in which the hydraulic switching element acts on the corresponding fluid in the circuit in different ways.

[0032] The brake of the thermal management system has, for example, the function of braking the shaft to be braked by means of a frictional connection. In particular, the brake can be based on the functional principle of a dry multi-disc brake or a wet multi-disc brake, a disc brake or a drum brake.

[0033] The brake is preferably arranged in a brake housing. The brake housing encloses the brake. The brake housing can also accommodate one or more brake actuators. In addition, the brake housing can be part of a cooling system and is designed such that cooling fluid is supplied to the braking system via the brake housing and / or heat can be removed to the outside via the housing surface. The brake housing also protects the brake from external mechanical and / or chemical influences. In particular, the brake housing can be formed from a metallic material. Advantageously, the brake housing can be formed from a metallic casting material such as gray cast iron or cast steel. In principle, it is also conceivable to form the brake housing completely or partially from plastic. The brake housing can also be designed as a single part or multiple parts. The brake housing can also be designed, in whole or in part, as a component of the motor housing of an electric motor or as a component of a transmission housing of a transmission coupled to the electric motor. Preferably, the brake housing and the motor housing or the transmission housing form a single structural unit. For example, the brake housing can be bolted to the motor housing or the transmission housing. The brake housing is preferably designed such that wear generated during braking cannot escape from the brake housing. This prevents unnecessary pollution of the environment due to brake wear. By encapsulating the braking system in this way, noise pollution due to braking noise can also be reduced. Another advantageous aspect of this encapsulation is that the braking performance of the braking system is not affected by weather conditions outside the motor vehicle.

[0034] Therefore, in summary, it can be summarized again that by cleverly dividing the battery system into "small replaceable" vehicle batteries and "large fixed" vehicle batteries and cleverly integrating the "small replaceable" vehicle batteries and the "large fixed" vehicle batteries into the thermal management system of the vehicle, a favorable operating state of the charging process can be achieved and reached more quickly, thereby improving the overall efficiency, charging efficiency and recovery capacity of the motor vehicle. At the same time, with the help of an optimized charging strategy, the replaceable small vehicle batteries ensure higher sustainability and extend the service life of the integrated large vehicle battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be explained in more detail below with reference to the drawings without limiting the general concept of the present invention.

[0036] In the drawings:

[0037] Figure 1 A motor vehicle with an electric drive train is shown in a schematic block diagram,

[0038] Figure 2 An embodiment of a thermal management system for an electric motor vehicle is shown in a schematic hydraulic circuit diagram. DETAILED DESCRIPTION

[0039] Figure 1 Shows an electrically operable powertrain 1 of a motor vehicle 2, which powertrain includes an electric motor 3 for driving the motor vehicle 2, and a first rechargeable vehicle battery 4 permanently installed in the motor vehicle 2 and for supplying power to the electric motor 3.

[0040] The powertrain 1 also has a second rechargeable vehicle battery 5 that can be detached from the motor vehicle 2 and for supplying power to the electric motor 3, wherein the storage capacity of the first vehicle battery 4 is greater than the storage capacity of the second vehicle battery 5, which is also indicated by Figure 1 the size of the rectangles characterizing the vehicle batteries 4, 5.

[0041] Generally, the two vehicle batteries 4, 5 are capable of directly operating the drive of the motor vehicle 2 via the electric motor 3 and without any other voltage conversion except for the voltage conversion provided by the inverter 15. However, as already mentioned above, the second vehicle battery 5 is designed to be significantly smaller than the first vehicle battery 4 such that the maneuverability and weight of the second vehicle battery 5 are significantly optimized, i.e., reduced.

[0042] Figure 1 It is also clearly shown that the powertrain 1 has a control device 6 to which the first vehicle battery 4, the second vehicle battery 5, and the electric motor 3 are connected, and which controls the power flow between these components. A charging device 7 for an electrical energy source 8 located outside the vehicle is also connected to the control device 6.

[0043] As can be seen in Figure 2 the first vehicle battery 4 has a first hydraulic battery cooling circuit 9 by means of which heat can be removed from and / or supplied to the first vehicle battery 4 under the control of the control device 6. The second vehicle battery 5 also has a second hydraulic battery cooling circuit 10 by means of which heat can be removed from and / or supplied to the second vehicle battery 5 under the control of the control device 6. The control device 6 is configured such that when a predetermined first temperature is reached, the second vehicle battery 5 is first charged by the electric motor 3 operating in generator mode. When the motor vehicle 2 is being charged at the stationary energy source 8, the control device 6 can also be configured such that when a predetermined second temperature is reached, the second vehicle battery 5 is first charged via the charging device 7.

[0044] This has the great advantage that the small vehicle battery 5 can reach the operating temperature faster than the large vehicle battery 4 - this is solely due to its smaller weight. This means that, especially in cold environments and after starting a journey, the drive components and the small vehicle battery 5 preferably reach the expected operating temperature first, and then the large vehicle battery 4 reaches the expected operating temperature.

[0045] This means that, for example, vehicle 2 can acquire the recuperation ability more quickly at low temperatures because the small vehicle battery 5 already has a lower internal resistance than the large vehicle battery 4. This distribution is also advantageous for conventional charging via the charging device 7 at the fixed energy source 8. Here, for example, the small vehicle battery 5 is also preheated first before it can be charged quickly. Thus, this arrangement allows the small vehicle battery 5 to be heated quickly, supplied with a larger charging current, and then charge the large vehicle battery 4 quickly with a certain time delay.

[0046] Therefore, during the driving operation, the small vehicle battery 5 is preferably used to recuperate the braking energy from the electric machine 3 operating as a generator. This avoids the charging cycles for the large vehicle battery 4, thereby significantly increasing the service life and the wear rate of the large vehicle battery. Although the small vehicle battery 5 may be worn out more quickly due to the higher charging load or cycling load, it can also be easily replaced and updated.

[0047] This also makes it possible to replace the small vehicle battery 5 with a better / faster or more efficient form of available vehicle battery 5 after the end of the service life of the small vehicle battery. The replaceable small vehicle battery 5 can also be replaced with a fully charged module at a special exchange station intended for "turbocharging". Although only the energy from the small vehicle battery 5 can be transmitted in this way, this can be done within a few minutes and is not affected by the external temperature. The preheated small vehicle battery 5 can also be installed in the vehicle 2, especially in winter, thus significantly improving the efficiency of the corresponding motor vehicle 2. Currently, battery-powered electric vehicles 2 lose approximately 30% of their energy in winter, not due to the driving operation, but in order to keep the drive components and the interior at a suitable temperature. Since current batteries are becoming larger and heavier, for example, it will become apparent how much energy is required to heat a 600 kg battery by 20 K.

[0048] To heat the vehicle batteries 4, 5, the powertrain 1 has a thermal management system 11, which includes the electric machine 3 for driving the motor vehicle 2, a first battery cooling circuit 9, a second battery cooling circuit 10, and a hydraulic control system 12 for influencing the volume flow in the cooling circuits 9, 10, wherein the control device 6 is coupled to the hydraulic control system 12 for controlling the hydraulic control system. The thermal management system 11 also has a brake 13 with a brake cooling circuit 14, which is connected to the hydraulic control system 12 and is used to remove heat from or supply heat to the brake 13.

[0049] Figure 2An embodiment of the thermal management system 11 is shown, in which a brake cooling circuit 14 and a motor cooling circuit 16 are formed together such that the brake 13 and the electric machine 3 are arranged in a common cooling circuit. A hydraulic switching element 17 designed as a hydraulic pump 18 is provided, which is used to supply a volumetric flow of coolant in the common cooling circuit. After the switching element 17 designed as a hydraulic pump 18, the volumetric flow of the coolant is distributed - the brake 13 and the electric machine 3 are arranged in parallel. The volumetric flow of the coolant can be opened or closed via the hydraulic switching element 17 of the hydraulic control system, which is designed as a switching valve 19. The heat exchange in the inverter cooling circuit 23 is carried out by means of a heat exchanger 20. This requires the use of a coolant in the common cooling circuit, the material composition of which also meets the requirements of the brake 13 and the electric machine 3.

[0050] The hydraulic control system 12 is designed as a distribution device to which the battery cooling circuits 9, 10 and the inverter cooling circuit 23 are connected, wherein the distribution device is configured such that at least these cooling circuits 9, 10, 23 are connected to each other.

[0051] In addition, the thermal management system 11 also has an inverter 15 and an inverter cooling circuit 23 for removing heat from or supplying heat to the inverter 15, wherein the hydraulic control system 12 acts on the inverter cooling circuit 23 by means of at least one hydraulic switching element 17 in order to influence the volumetric flow in the inverter cooling circuit 15. In the inverter cooling circuit 23, the hydraulic switching element 17 is also designed as a hydraulic pump 22.

[0052] Furthermore, a charging device 7 - also referred to as an on-board charger - and the inverter 15 are connected in series in the inverter cooling circuit 23. The heat exchanger 20 of the separate motor cooling circuit 16 of the electric machine 3 is arranged downstream of the inverter cooling circuit 23 in the same sub-circuit of the thermal management system 11.

[0053] The heat exchanger 25 supplied by the hydraulic pump 21 allows heat exchange between the battery cooling circuits 9, 10 and the passenger compartment air conditioning circuit 26. Here, the passenger compartment air conditioning circuit 26 and the battery cooling circuits 9, 10 at the third heat exchanger 25 are connected in a switchable manner. This enables the vehicle batteries 4, 5 intended to supply power to the electric machine 3 to be heated and cooled. An ambient heat transfer unit 24 is also arranged in the inverter cooling circuit 23, which allows heat to be dissipated into the environment. Thus, this provides two ways to reduce the temperature of the inverter cooling circuit 15, namely via the ambient heat transfer unit 24 and via the third heat exchanger 25 and by means of the passenger compartment air conditioning circuit 26 to reduce the temperature of the inverter cooling circuit.

[0054] The present invention is not limited to the embodiments shown in the drawings. Therefore, the above description should not be considered restrictive, but rather illustrative. The appended claims should be understood to mean that the stated features are present in at least one embodiment of the present invention. This does not exclude the presence of other features. When the claims and the above description define a "first" feature and a "second" feature, such naming is used to distinguish between two features of the same type and does not define a priority order.

[0055] List of Reference Numerals

[0056] 1 Powertrain

[0057] 2 Motor Vehicle

[0058] 3 Electric Machine

[0059] 4 Vehicle Battery

[0060] 5 Vehicle Battery

[0061] 6 Control Device

[0062] 7 Charging Device

[0063] 8 Energy Source

[0064] 9 Battery Cooling Circuit

[0065] 10 Battery Cooling Circuit

[0066] 11 Thermal Management System

[0067] 12 Hydraulic Control System

[0068] 13 Brake

[0069] 14 Brake Cooling Circuit

[0070] 15 Inverter

[0071] 16 Motor Cooling Circuit

[0072] 17 Hydraulic Switching Element

[0073] 18 Hydraulic Pump

[0074] 19 Valve

[0075] 20 Heat Exchanger

[0076] 21 Hydraulic Pump

[0077] 22 Hydraulic Pump

[0078] 23 Inverter Cooling Circuit

[0079] 24 Ambient Heat Transfer Unit

[0080] 25 Heat exchanger

[0081] 26 Passenger compartment air conditioning circuit

Claims

1. An electrically operable driveline (1) of a motor vehicle (2), said driveline comprising: an electric machine (3) for driving the motor vehicle (2); and a first rechargeable vehicle battery (4) permanently installed in the motor vehicle (2) and for supplying power to the electric machine (3), characterized in that the powertrain (1) has a second rechargeable vehicle battery (5) which is detachable from the motor vehicle (2) and for supplying power to the electric machine (3), wherein the storage capacity of the first vehicle battery (4) is greater than the storage capacity of the second vehicle battery (5).

2. The powertrain (1) according to claim 1, characterized in that the storage capacity of the first vehicle battery (4) is at least twice, preferably three times, the storage capacity of the second vehicle battery (5).

3. The powertrain (1) according to claim 1 or 2, characterized in that the powertrain (1) has a control device (6) to which at least the first vehicle battery (4), the second vehicle battery (5) and the electric machine (3) are connected, and the control device controls the power flow between these components.

4. The powertrain (1) according to claim 3, characterized in that a charging device (7) for an electrical energy source (8) located outside the vehicle is connected to the control device (6).

5. The powertrain (1) according to any one of the preceding claims, characterized in that the first vehicle battery (4) has a first hydraulic battery cooling circuit (9) by means of which heat can be removed from and / or supplied to the first vehicle battery (4) under the control of the control device (6).

6. The powertrain (1) according to any one of the preceding claims, characterized in that the second vehicle battery (5) has a second hydraulic battery cooling circuit (10) by means of which heat can be removed from and / or supplied to the second vehicle battery (5) under the control of the control device (6).

7. The powertrain (1) according to any one of claims 3 to 6, characterized in that the control device (6) is configured such that when a predetermined first temperature is reached, the second vehicle battery (5) is first charged by the electric machine (3) operating in generator mode.

8. The powertrain (1) according to any one of claims 3 to 7, characterized in that the control device (6) is configured such that when a predetermined second temperature is reached, the second vehicle battery (5) is first charged via the charging device (7).

9. The powertrain (1) according to any one of the preceding claims, characterized in that The drive train (1) has a thermal management system (11), which includes the electric machine (3) for driving the motor vehicle (2), the first battery cooling circuit (9), the second battery cooling circuit (10), and a hydraulic control system (12) for influencing the volume flow in the cooling circuits (9, 10), wherein the control device (6) is coupled to the hydraulic control system (12) for controlling the hydraulic control system.

10. The drive train (1) according to claim 9, characterized in that the thermal management system (11) includes a brake (13) having a brake cooling circuit (14), the brake cooling circuit being connected to the hydraulic control system (12) and being used to remove heat from or supply heat to the brake (13).

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