Method for operating an electric powertrain of a motor vehicle and motor vehicle

Abstract

The invention relates to a method for operating an electric drive train (10) of a motor vehicle, wherein the electric drive train (10) comprises a first electric machine (20) and a coupling device (58) comprising a first friction clutch (60) and a second friction clutch (62); wherein a first output element (64) of the first friction clutch (60) is coupled or can be coupled to a first vehicle wheel (14) in a torque-transmitting manner; wherein a second output element (66) of the second friction clutch (62) is coupled or can be coupled to a second vehicle wheel (16) in a torque-transmitting manner; wherein a first input element (68) of the first friction clutch (60) and a second input element (70) of the second friction clutch (62) are rotationally fixed to a common input shaft (72); wherein a first rotor (22) of the electric machine (20) is coupled or can be coupled to the common input shaft (72) in a torque-transmitting manner;wherein, during a braking process to decelerate the vehicle wheels (14, 16), if a braking power demand is greater than a first threshold and less than a second threshold, the first electric machine (20) is operated in recuperative mode, while the first friction clutch (60) and the second friction clutch (62) are operated in slipping mode, such that a first rotor speed of the first electric machine (20) is lower than a first speed of the first output element (64).

Description

[0001] The invention relates to a method for operating an electric drive train of a motor vehicle according to the preamble of claim 1. Furthermore, the invention relates to a motor vehicle.

[0002] DE 10 2021 006 124 B3 discloses an electric axle drive for a motor vehicle that is at least partially electrically powered.

[0003] DE 10 2022 209 064 A1 and DE 10 2021 122 043 A1 each show possible operating modes of an electric drive train in which an input shaft driven by an electric machine can be coupled to a vehicle wheel via a friction clutch.

[0004] The object of the present invention is to provide a method for operating an electric drive train of a motor vehicle and such a motor vehicle, in such a way that the motor vehicle can be braked particularly advantageously.

[0005] This problem is solved by a method with the features of claim 1 and by a motor vehicle with the features of claim 4. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0006] A first aspect of the invention relates to a method for operating an electric drive train, also referred to as an electric drive unit, electric drive device, or electric drive system, of a motor vehicle, which is preferably a motor car, and in particular a passenger car. In this method, the electric drive train comprises a first electric machine, which has a first rotor. For example, the first electric machine has a first stator, by means of which, for example, the first rotor can be driven and thereby rotated about a first axis of rotation relative to the first stator. In particular, the first electric machine can, for example, provide first drive torques via its first rotor for the, in particular, purely electric propulsion of the motor vehicle.In particular, the first rotor is rotatable around the first machine axis of rotation at a first rotational speed, also simply called rotational speed, so that the first rotational speed is also referred to as the first rotational speed of the first electric machine or the first rotor speed. When rotational speed is mentioned before and below, unless otherwise specified, this refers to the rotational speed of the first rotor, and thus the rotational speed of the first electric machine. In particular, the rotational speed can be varied. This means that the rotational speed can assume different values. For example, one of the values ​​is zero, so that the rotational speed is then zero. When the rotational speed is zero, the first rotor does not rotate around the first machine axis of rotation relative to the first stator. It is conceivable that the electric drive train includes a second electric machine, which, for example, has a second rotor.For example, the second electric machine has a second stator, by means of which, for instance, the second rotor can be driven and thus rotated about a second axis of rotation relative to the second stator. In particular, the second rotor can be rotated about the second axis of rotation relative to the second stator at a second speed, whereby the preceding and following explanations regarding the first speed can readily be applied to the second speed and vice versa. For example, the electric machine can provide second drive torques via its second rotor for, in particular, purely electric propulsion of the motor vehicle. It is conceivable that the electric machines are arranged coaxially to each other, so that their axes of rotation coincide.

[0007] The electric drive train, whose axial direction coincides with a main axis of rotation of the electric drive train, also includes a coupling device comprising a first friction clutch and a second friction clutch. Where the axial direction is mentioned before and below, unless otherwise specified, this refers to the axial direction of the electric drive train, whose radial direction is perpendicular to the axial direction of the electric drive train and thus perpendicular to the main axis of rotation. Where the radial direction is mentioned before and below, unless otherwise specified, this refers to the radial direction of the electric drive train.In particular, it is provided that the main axis of rotation coincides with the first machine axis of rotation and / or with the second machine axis of rotation, or that the main axis of rotation runs parallel to the first machine axis of rotation and / or parallel to the second machine axis of rotation. Preferably, the respective electric machine is a high-voltage component whose electrical voltage, in particular its operating and / or rated voltage, is preferably greater than 50 volts, particularly greater than 60 volts, and most preferably several hundred volts. For example, the first rotor is rotatable about the first machine axis of rotation relative to a housing of the drive train. For example, the second rotor is rotatable about the second machine axis of rotation relative to the housing.It is conceivable that the first friction clutch and / or the second friction clutch and / or the first rotor and / or the second rotor and / or the first stator and / or the second stator are each at least partially arranged in the housing.

[0008] The term "radial" refers to the radial direction. In other words, "radial" means the radial direction. The term "axial" refers to the axial direction. In other words, "axial" means the axial direction. Put another way, "axial" refers to the axial direction, and "radial" refers to the radial direction of the electric drivetrain.

[0009] For example, the electric powertrain has a vehicle axle, also simply referred to as an axle, which is also referred to as the first axle. Whenever the vehicle axle or axle is mentioned before or after, it refers to the first axle unless otherwise specified. For example, the fully manufactured vehicle has at least or exactly two vehicle axles, namely the aforementioned first axle and a second axle. For example, the axles are arranged consecutively in the longitudinal direction of the vehicle. Each axle has at least or exactly two wheels.The vehicle wheels are ground contact elements of the vehicle, which, in the vehicle's vertical direction, can be supported downwards by these ground contact elements against the ground or, particularly during operation, is supported. If the vehicle is driven along the ground while supported downwards by these ground contact elements, the ground contact elements roll along the ground, especially directly. The respective vehicle wheels of each axle are arranged on opposite sides of the vehicle in the transverse direction.In this context, for example, the vehicle wheels of at least or exactly one of the vehicle axles can be driven by means of the electric drivetrain, in particular by means of the first rotor and thus by means of the first electric machine, such that, for example, the vehicle wheels of the first vehicle axle can be driven electrically, in particular purely, by means of the electric drivetrain, in particular by means of the first electric machine and in particular by means of the rotor, in particular such that, with respect to the vehicle wheels of the vehicle axles, only the vehicle wheels of the first axle can be driven by means of the electric drivetrain, that is, by means of the first electric machine and thus by means of the first rotor, in particular bypassing the vehicle wheels of the second vehicle axle. The vehicle wheels that can be driven by means of the electric drivetrain are also referred to as drive wheels.When the vehicle wheels are mentioned below, unless otherwise specified, this refers to the drive wheels, which are in particular the wheels of the first axle. The respective friction clutch is designed, for example, as a multi-plate clutch.

[0010] In the electric drive train, a first output element of the first friction clutch is, in particular, permanently, torque-transmitting, and in particular rotationally fixed, coupled or connectable to a first of the vehicle wheels. A second output element of the second friction clutch is, in particular, permanently, torque-transmitting, and in particular rotationally fixed, coupled or connectable to a second of the vehicle wheels.

[0011] The electric drivetrain, particularly in a first embodiment, may include a differential gear, also simply referred to as a differential, which, for example, may be omitted in a second embodiment. The differential gear comprises, for example, a differential input shaft, a first differential output shaft, and a second differential output shaft. The differential input shaft is rotatable about the main axis of rotation relative to the housing of the electric drivetrain. For example, the first machine axis of rotation and / or the second machine axis of rotation may coincide with the main axis of rotation. It is conceivable that the differential gear is at least partially arranged within the housing.The differential input shaft, the first differential output shaft, and the second differential output shaft are preferably all arranged coaxially with each other, so that, for example, the first differential output shaft and the second differential output shaft are also rotatable about the main axis of rotation relative to the housing. It is conceivable that the first electric machine and / or the second electric machine are arranged coaxially with the differential gear, so that, for example, the first machine axis of rotation and / or the second machine axis of rotation coincides with the main axis of rotation. In this configuration, for example, the vehicle wheels can be driven via the differential gear by the first rotor and thus by the first electric machine. Furthermore, for example, the drive wheels can be driven via the differential gear by the second rotor and thus by the second electric machine.For example, the first vehicle wheel can be driven by the first differential output shaft, bypassing the second vehicle wheel and the second differential output shaft, and for example, the second vehicle wheel can be driven by the second differential output shaft, bypassing the first vehicle wheel and the first differential output shaft. For example, the first differential output shaft can be driven by the differential input shaft, bypassing the second vehicle wheel and the second differential output shaft, and for example, the second differential output shaft can be driven by the differential input shaft, bypassing the first vehicle wheel and the first differential output shaft.For example, the input torque resulting from the respective first drive torque and, if applicable, the respective second drive torque can be transmitted to the differential input shaft, thereby driving the differential input shaft. By driving the differential input shaft, the respective differential output shaft can be driven by the differential input shaft. The input torque can be transmitted to the respective differential output shaft via the differential gear or via the differential input shaft, thereby driving the respective differential output shaft.In particular, the differential gear has the function, which is well known from the general state of the art, of transmitting the respective input torque to the respective differential output shaft and thus to the respective vehicle wheel, and, for example, allowing different rotational speeds of the differential output shafts and thus of the vehicle wheels, i.e., the drive wheels, when the vehicle is cornering, in particular such that the outer vehicle wheel rotates or can rotate at a higher rotational speed than the inner vehicle wheel or drive wheel.

[0012] For example, when a differential gear is provided, the first output element of the first friction clutch is, in particular, permanently and non-rotatably connected to the first differential output shaft, preferably bypassing the second differential output shaft. Similarly, the second output element of the second friction clutch is, in particular, permanently and non-rotatably connected to the second differential output shaft, again bypassing the first differential output shaft. Each output element is, for example, designed as a shaft.

[0013] In this method, a first input element of the first friction clutch and a second input element of the second friction clutch are connected, in particular permanently and in a rotationally fixed manner, to an input shaft common to both input elements and thus to both friction clutches. The respective input element is, for example, a shaft. For example, the first output element is a first plate carrier of the first friction clutch. For example, the first input element is a second plate carrier of the first friction clutch. For example, the second output element is a third plate carrier of the second friction clutch. For example, the second input element is a fourth plate carrier of the second friction clutch. Each friction clutch has, for example, friction elements, which are in particular designed as friction plates. The friction plates are also simply referred to as plates.For example, the first friction plates of the first friction clutch are supported on the first plate carrier in a torque-transmitting manner, and in particular in a rotationally fixed manner. For example, the second friction plates of the first friction clutch are supported on the second plate carrier in a torque-transmitting manner, and in particular in a rotationally fixed manner. For example, the third friction plates of the second friction clutch are supported on the third plate carrier in a torque-transmitting manner, and in particular in a rotationally fixed manner. And for example, the fourth friction plates of the second friction clutch are supported on the fourth plate carrier in a torque-transmitting manner, and in particular in a rotationally fixed manner. By pressing the first and second friction plates together, particularly in the axial direction of the first friction clutch, the first plate carrier and the second plate carrier can be connected to each other in a rotationally fixed manner.By compressing the third and fourth friction plates, particularly in the axial direction of the second friction clutch, the third and fourth plate carriers can be connected to each other in a rotationally fixed manner. This means, for example, that the first friction clutch can be switched between a first open state and a first closed state. In the first open state, the first and second plate carriers are rotatable relative to each other, and in the first closed state, the first and second plate carriers are connected to each other in a rotationally fixed manner, particularly because the first and second friction plates are compressed together in the first closed state, and especially more tightly than in the first open state.The second friction clutch can, for example, be switched between a second open state and a second closed state. In the second open state, the third and fourth friction plate carriers are rotatable relative to each other. In the second closed state, for example, the third and fourth friction plate carriers are rotationally fixed to each other, in particular because, in the second closed state, the third and fourth friction plates are pressed together, especially more tightly than in the second open state. Each friction clutch is open in its respective open state, and each friction clutch is closed in its respective closed state. It is conceivable that the first friction clutch could be in the first closed state while the second friction clutch is in the second open state.Furthermore, it is conceivable that the second friction clutch is in the second closed state, while the first friction clutch is in the first open state.

[0014] With regard to a first torque flow emanating from the first rotor and thus from the first electric machine, along which or via which, for example, the respective first drive torque can be transmitted from the first rotor to the first vehicle wheel, the first rotor, the common input shaft, the first output element and the first vehicle wheel are arranged in the aforementioned order, that is, in the order in which they are named, one after the other in the first torque flow, so that with regard to the first torque flow the first rotor, the common input shaft, the first output element and the first vehicle wheel are arranged in the following order, one after the other and thus consecutively, in the first torque flow: the first rotor - the common input shaft - the first output element - the first vehicle wheel.In other words, with respect to the first torque flow, the input shaft is located downstream of the first rotor, the first output element is located downstream of the input shaft, and the first vehicle wheel is located downstream of the first output element. Regarding a second torque flow originating from the first rotor and thus from the first electric machine, along which the respective first drive torque can be transmitted from the first rotor to the second vehicle wheel, the first rotor, the common input shaft, the second output element, and the second vehicle wheel are arranged in the aforementioned order, that is, in the order they are listed, one after the other and thus consecutively in the second torque flow.In other words, with regard to the second torque flow, the first rotor, the common input shaft, the second output element, and the second vehicle wheel are arranged sequentially in the following order: the first rotor – the common input shaft – the second output element – ​​the second vehicle wheel. Thus, in the second torque flow, the common input shaft is located downstream of the first rotor, the second output element is located downstream of the common input shaft, and the second vehicle wheel is located downstream of the second output element.

[0015] In order to brake the vehicle wheels and thus the motor vehicle, i.e., to be able to slow down, the method provides, in a manner known per se, that if, during a braking process intended to slow down the vehicle wheels, a braking power requirement is greater than a first threshold and less than a second threshold that is greater than the first threshold, the first electric machine is operated in recuperation mode, i.e., in its recuperation mode, while the first friction clutch is operated in slipping mode and the second friction clutch is operated in slipping mode, such that the first rotor speed of the first electric machine is less than the first speed of the first output element, which is also referred to as the first output element speed.

[0016] The first rotor is not rotatable at a first rotational speed, but rather at a first rotor speed around the first machine axis of rotation relative to the stator! The previous statements regarding rotational speed refer to the first rotor speed, whereby the second rotor is rotatable at a second rotor speed (!) around the second machine axis of rotation relative to the second stator!

[0017] In other words, if the braking process, which is designed or intended for braking the vehicle wheels, is carried out during the process, and if the braking power requirement during the braking process is greater than the first threshold and less than the second threshold, then the first electric machine operates in recuperation mode, while the first friction clutch operates in slip mode, and while the second friction clutch operates in slip mode, such that the first rotor speed is lower than the first speed of the first output element. This allows for a reduction in the first rotor speed, which can increase the braking torque provided or available from the first electric machine in its recuperation mode and designed or intended for braking the vehicle wheels.Furthermore, due to the slipping operation of the friction clutches, which are also simply referred to as clutches, a high frictional power can be achieved, thereby enabling a particularly high braking torque for slowing the vehicle wheels. The braking torque provided or made available by the first electric machine in its recuperation mode and intended or designed for braking, i.e., for slowing the vehicle wheels, is also referred to as the first recuperation torque of the first electric machine. The invention is based in particular on the finding that the first recuperation torque increases when the first rotor speed is slightly reduced. In other words, a slightly lower initial value of the first rotor speed results in a greater value of the first recuperation torque than a slightly higher subsequent value of the first rotor speed.In order to slightly reduce the initial rotor speed compared to the open states of the friction clutches, and thus slightly increase the recuperation torque, the friction clutches are operated with a slight slippage. Advantageously, the friction clutches are adjusted, i.e., operated with such a slight slippage, that the same braking torque resulting from the recuperation torque acts on both differential output shafts.

[0018] According to the invention, when the braking power requirement is greater than the second threshold, the first electric machine is operated in a driving mode such that an input shaft rotation direction of the common input shaft, which rotates about an input shaft rotation axis in the first input shaft rotation direction, particularly relative to the housing, has a opposite sign to an output element rotation direction of the first output element, which rotates, for example, in the output element rotation direction at the first speed, particularly relative to the housing, while the first friction clutch is operated in a slipping manner and the second friction clutch is operated in a slipping manner.The characteristic that the input shaft rotation direction has a different sign than the output element rotation direction means that a rotation of the input shaft in the input shaft direction, caused by the first electric machine being driven, opposes a rotation of the first output element in the output element direction. For example, in order to drive a motor vehicle by means of the electric machine in such a way that the vehicle is driven forward in its longitudinal direction, and thus propelled forward movement, the electric machine is driven in such a way that the input shaft is rotated, in particular about its axis of rotation and relative to the housing, in the direction of the input shaft rotation.For example, in order to drive the motor vehicle by means of the first electric machine in such a way that the motor vehicle is driven backwards in the longitudinal direction of the fan, along the ground, thus effecting a reverse movement of the motor vehicle, the electric machine is operated in such a driving manner that the input shaft is rotated in particular about the input shaft axis of rotation and relative to the housing in a second shaft direction of rotation opposite to the first shaft direction of rotation.If, during the process, the motor vehicle rolls or drives forward and the braking power requirement during the braking process is greater than the first threshold and greater than the second threshold, the first electric machine is operated in such a driving manner that the input shaft is rotated, in particular about the input shaft axis of rotation and relative to the housing, in the second shaft direction of rotation, so that the input shaft direction of rotation corresponds to the second shaft direction of rotation.For example, if the vehicle is rolling or driving backwards during the process and the braking power requirement during braking exceeds both the first and second thresholds, the first electric machine is preferably operated in such a way that the common input shaft is rotated in the input shaft direction, particularly around the input shaft axis and relative to the housing, so that the input shaft direction corresponds to the first shaft direction. This allows the vehicle to be braked particularly strongly.

[0019] In order to brake the vehicle wheels and the motor vehicle particularly effectively, one embodiment of the invention provides that the first friction clutch and the second friction clutch are operated in a slipping manner such that the first rotational speed of the first output element is equal to a second rotational speed of the second output element, also referred to as the second output element speed. This results in the vehicle wheels, in particular the differential output shafts and, via these, the vehicle wheels, being braked to the same degree, thus enabling particularly effective braking of the motor vehicle.

[0020] Furthermore, it has proven particularly advantageous if the electric drive train comprises the aforementioned second electric machine with the second rotor, as well as the aforementioned differential gear with the differential input shaft, the first differential output shaft, and the second differential output shaft. The second rotor is coupled, particularly permanently, to the differential input shaft, particularly in a torque-transmitting or rotationally fixed manner, such that first torques emanating from the second rotor can be introduced into the differential gear at the differential input shaft. The first output element is connected, particularly permanently, to the first differential output shaft in a rotationally fixed manner. The second output element is connected, particularly permanently, to the second differential output shaft in a rotationally fixed manner.If the braking power demand during the braking process exceeds the second threshold, the electric motor operates in recuperation mode. This allows the vehicle wheels, and therefore the vehicle itself, to be braked particularly strongly.

[0021] A second aspect of the invention relates to a motor vehicle, also referred to simply as a vehicle, and preferably a motor car, in particular a passenger car, which is configured to carry out a method according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention and vice versa.

[0022] The term "braking power requirement" refers to a required or requested braking power that must be provided, for example, by the motor vehicle, in particular by the electric powertrain, in order to brake the motor vehicle, for example, when it is moving forward or backward, i.e., to at least reduce its speed.

[0023] The braking power to be provided can be adjusted, for example, by actuating a control element of the motor vehicle, such as a brake pedal, so that the braking power requirement depends, for example, on the position of the control element, which can be moved, in particular pivoted, into that position by actuating the control element. The control element is, for example, a control element that can be actuated by a person, in particular with their foot, whereby the person can, for example, be the driver of the motor vehicle.

[0024] The housing is, for example, a gearbox housing and / or a housing of the first electric machine or the second electric machine.

[0025] Within the scope of this disclosure, the feature "radially overlapping" is to be understood as follows: Two elements, in particular those that are essentially rotationally symmetrical, are arranged, in particular with respect to a common axis, for example extending in the radial direction, and / or in a radially overlapping manner, especially with respect to each other, if they are each arranged at least partially in a region of the same radial coordinates, in particular with the same angular coordinates. The feature "axially overlapping" is to be understood as follows: Two elements are arranged with respect to a common axis, in particular extending in the axial direction, and / or in an axially overlapping manner, especially with respect to each other, if they are each arranged at least partially in a region of the same axial coordinates.Within the scope of the present disclosure, the feature that a first component is arranged radially inside a second component is also understood to mean that the first component is arranged in a region of smaller radii than the second component, particularly with respect to the main axis of rotation, such that the respective radii are perpendicular to the main axis of rotation or extend along an axis perpendicular to the main axis of rotation. Accordingly, the feature that a first component is arranged radially outside a second component is also understood to mean that the first component is arranged in a region of larger radii than the second component, particularly with respect to the main axis of rotation, such that the respective radii are perpendicular to the main axis of rotation or extend along an axis perpendicular to the main axis of rotation.In other words, the characteristic that a first component is arranged radially within a second component means that the first component is arranged in an area of ​​larger radial coordinates than the second component, in particular with respect to equal angular coordinates.

[0026] For example, the respective input element and the respective output element of the respective friction coupling is or comprises a respective coupling half, which is, for example, a shaft connected, in particular permanently, to the respective coupling half in a rotationally fixed manner and which is rotatably mounted, such that the respective input element of the respective friction coupling is arranged upstream of the respective output element of the respective friction coupling in the respective torque flow that passes through the respective friction coupling, and the respective output element of the respective coupling is arranged downstream of the respective input element of the respective coupling in the respective torque flow that passes through the respective friction coupling.

[0027] Within the scope of the present disclosure, the feature that two components are rotationally fixed to one another is understood to mean that the components connected in a rotationally fixed manner are arranged coaxially to one another and, in particular when the components are driven, rotate together or simultaneously about a component rotation axis common to the components, such as the main axis of rotation, at the same angular velocity, especially relative to a reference element such as the housing. In other words, two components, which are in particular rotatably mounted, are rotationally fixed to one another if they are arranged coaxially to one another, especially with respect to their component rotation axis and / or with respect to a rotational symmetry axis, and if they are connected to one another in such a way that they rotate, in particular always, at the same angular velocity.An element is fixed to the housing if it cannot be rotated opposite, that is, relative to the housing.

[0028] The characteristic that two components are connected or coupled in a torque-transmitting manner means that the components are coupled or connected in such a way that torques can be transmitted between them. If the components are connected or coupled in a rotationally fixed manner, they are also connected or coupled in a torque-transmitting manner. Two components connected in a torque-transmitting manner can thus be connected in a rotationally fixed manner. Furthermore, it is conceivable that two components connected in a torque-transmitting manner are connected via an intermediate transmission unit, such that torques can be transmitted between the components via the transmission unit while the components are connected in a torque-transmitting manner, although the components may be rotatable relative to each other.The characteristic that two components are permanently connected or coupled in a torque-transmitting manner means that there is no switching element that can be toggled between a coupling state in which the components are connected or coupled in a torque-transmitting manner and a decoupling state in which no torque can be transmitted between the components via the switching element. Rather, the components are always and therefore permanently torque-transmitting, meaning they are connected or coupled in such a way that torque can be transmitted between them. Thus, for example, one component can be driven by the other, and vice versa.

[0029] The characteristic that two elements are permanently connected or coupled to each other in a rotationally fixed manner means that a switching element is not provided which can be switched between a coupling state in which the components are rotationally fixed to each other and a decoupling state in which the components are decoupled from each other and rotatable relative to each other, so that no torques can be transmitted between the components via the switching element. Rather, the components are always permanently connected or coupled to each other in a rotationally fixed manner. Furthermore, the characteristic that two components can be connected or coupled to each other in a rotationally fixed manner means that the components are assigned a switching element which can be switched between at least one coupling state and at least one decoupling state.In the coupled state, the components are rotationally fixed to one another by means of the switching element. In the decoupled state, the components are decoupled from each other, so that in the decoupled state the components can rotate relative to each other about the component axis of rotation and no torque can be transmitted between the components via the switching element. The same applies to the feature that two components can be connected or coupled to one another in a torque-transmitting manner. Thus, the feature that two components can be connected or coupled to one another in a torque-transmitting manner means that a switching element is assigned to the components, wherein the switching element can be switched between at least one connected state and at least one enabled state.In the connected state, the components are coupled or connected to each other via the switching element, thus transmitting torque between them. In the enabled state, the components are decoupled, so that no torque can be transmitted between them via the switching element.

[0030] The drawing shows in: Fig. 1 a schematic representation of a first embodiment of an electric powertrain of a motor vehicle; Fig. 2 a schematic representation of a second embodiment of the electric drive train; and Fig. 3. A flowchart to illustrate a procedure for operating the electric drive train.

[0031] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0032] Fig. Figure 1 shows a schematic representation of a first embodiment of an electric drive train 10 of a motor vehicle, also referred to simply as a vehicle, which is preferably designed as a car, in particular as a passenger car. The motor vehicle, in its fully manufactured state, has exactly two axles arranged consecutively in the longitudinal direction of the motor vehicle, namely a first axle and a second axle. Each axle has exactly two wheels, the wheels of each axle being arranged on opposite sides of the motor vehicle in the transverse direction. The wheels of the motor vehicle are the ground contact elements of the motor vehicle. The drive train 10 comprises, in particular with regard to the axles, only the first axle, which is located in Fig. 1 is labelled with 12. The vehicle wheels of vehicle axle 12 are in Fig. Figure 1 is shown schematically and labeled 14 and 16. As will be explained in more detail below, the vehicle wheels 14 and 16 can be driven electrically, in particular purely, by means of the electric drive train 10, thus making the motor vehicle, in particular purely, electrically propellable. The vehicle's transverse direction is illustrated by a double arrow 18. Since the vehicle wheels 14 and 16 can be driven electrically, in particular purely, by means of the electric drive train 10, the vehicle wheels 14 and 16 are also referred to as drive wheels.

[0033] The electric drive train 10 comprises an electric machine 20, which has a first rotor 22 and a first stator 24. In the first embodiment, the electric drive train 10 comprises exactly one electric machine, namely the first electric machine 20 for electrically driving the vehicle wheels 14 and 16.

[0034] Fig. Figure 2 shows a second embodiment of the electric drive train 10. In the second embodiment, the electric drive train 10 comprises, in particular, two electric machines: the first electric machine 20 and a second electric machine 26 provided in addition to the first electric machine 20. The electric machine 26 has a second rotor 28 and a second stator 30. In both the first and second embodiments, the respective electric machines 20 and 26 are designed as axial flux machines, also known as axial flux motors (AFMs). The respective electric machines 20 and 26 can provide drive torques via their respective rotors 22 and 28 for, in particular, purely electric, driving of the vehicle wheels 14 and 16, and thus of the motor vehicle.

[0035] The rotor 22 can be driven by means of the stator 24 and is thereby rotatable about a first machine axis of rotation of the first electric machine 20 relative to the stator 24. Accordingly, the second rotor 28 can be driven by means of the second stator 30 and is thereby rotatable about a second machine axis of rotation of the second electric machine 26 relative to the second stator 30. In the second embodiment, the electric machines 20 and 26 are arranged coaxially to each other, so that the machine axes of rotation coincide. The first rotor 22 can rotate at a first rotor speed and at the first machine axis of rotation relative to the stator 24. The second rotor 28 can rotate at a second rotor speed about the second machine axis of rotation relative to the second stator 30.

[0036] The electric drive train 10, whose axial direction coincides with a main axis of rotation of the electric drive train 10, has, in the second embodiment, a differential gear 32, also referred to simply as a differential, through which the vehicle wheels 14 and 16 can be driven by the respective rotors 22 and 28, and thus by the respective electric machines 20 and 26. The differential gear 32 is omitted in the first embodiment. This means that the differential gear 32 is not provided in the first embodiment. In the first embodiment, and also in the present second embodiment, the first machine axis of rotation coincides with the main axis of rotation. In the second embodiment, the second machine axis of rotation also coincides with the main axis of rotation. Furthermore, it would be conceivable that the first machine axis of rotation runs parallel to the main axis of rotation and is, for example, spaced apart from the main axis of rotation.Furthermore, it would be conceivable that the second machine axis of rotation runs parallel to the main axis of rotation and is, for example, spaced apart from the main axis of rotation. When the axial direction is mentioned before and below, this refers, unless otherwise specified, to the axial direction of the electrical drive train 10, whose radial direction is perpendicular to the axial direction and thus perpendicular to the main axis of rotation.

[0037] In the second embodiment, the differential gear 32 is designed as a planetary differential gear, also referred to as a planetary gear differential or planetary differential, and thus comprises, in particular, a planetary gear 34. The planetary gear 34 comprises a sun gear 36, a ring gear 38, and a planet carrier 40. Furthermore, the planetary gear 34 comprises first planet gears, one of which, designated 42, is located in Fig. 2 is recognizable. Furthermore, the planetary gear has 34 second planet gears, one of which is in Fig. The second planet gear, designated 44, is identifiable. The first and second planet gears are rotatably mounted on the planet carrier 40. The respective first planet gear 42 meshes with the sun gear 36, without meshing with the ring gear 38. The respective second planet gear 44 meshes with the ring gear 38, without meshing with the sun gear 36. Exactly one of the second planet gears 44 is assigned to each first planet gear 42, so that each first planet gear 42 and the respective second planet gear 44 assigned to it form a planet gear pair.The respective planet gears 42 and 44 of the respective planet gear pair mesh with each other in such a way that the respective first planet gear 42 of the respective planet gear pair meshes with the respective, assigned second planet gear 44 of the respective planet gear pair and with no other second planet gears 44, and that the respective second planet gear 44 of the respective planet gear pair meshes with the respective, assigned first planet gear 42 of the respective planet gear pair and with no other first planet gears 42.

[0038] The differential gear 32 has a first differential output shaft 46, which is, in particular, permanently and non-rotatably connected to the planet carrier 40. Furthermore, the differential gear 32 has a second differential output shaft 48, which is, in particular, permanently and non-rotatably connected to the sun gear 36. The differential gear 32 also has a differential input shaft 50, which is, in particular, permanently and non-rotatably connected to the ring gear 38. In addition, the differential input shaft 50 can be connected to the rotor 28 in a torque-transmitting manner, in particular non-rotatably, wherein, for example, the differential input shaft 50 is, in particular, permanently and non-rotatably connected to the rotor 28.

[0039] The differential input shaft 50 and also the differential output shafts 46 and 48 are rotatable about the main axis of rotation relative to a housing 52 of the drive train 10, such that the electric drive train 10 comprises the housing 52. It can be seen that the differential input shaft 50 can be driven by means of the rotor 28 and is therefore rotatable about the main axis of rotation relative to the housing 52. By driving the differential input shaft, the differential output shaft 46 can be driven by the differential input shaft 50, particularly bypassing the differential output shaft 48, and vice versa.By driving the differential output shaft 46, the vehicle wheel 14 can be driven by the differential output shaft 46, bypassing the differential output shaft 48 and the vehicle wheel 16. Conversely, by driving the differential output shaft 48, the vehicle wheel 16 can be driven by the differential output shaft 48, bypassing the differential output shaft 46 and the vehicle wheel 14. It can be seen that the vehicle wheel 14 can be driven by the differential output shaft 46, for example, via a first final drive unit 54, and the vehicle wheel 16 can be driven by the differential output shaft 48, for example, via a second final drive unit 56. The respective final drive unit 54, 56 is or comprises, for example, at least or exactly one gear pair, designed, for example, as a spur gear pair, and thus as a spur gear stage.

[0040] Since the differential gear 32 is not provided in the first embodiment, the drive train 10 in the first embodiment has a first output shaft 47 and a second output shaft 49, whereby the output shaft 47 essentially takes on the role of the differential output shaft 46 and the output shaft 49 takes on the role of the differential output shaft 48. Thus, by driving the output shaft 47, the vehicle wheel 14 can be driven by the output shaft 47, bypassing the output shaft 49 and the vehicle wheel 16, and by driving the output shaft 49, the vehicle wheel 16 can be driven by the output shaft 49, bypassing the output shaft 47 and the vehicle wheel 14. The vehicle wheel 14 can be driven by the output shaft 47 via the final drive unit 54, and the vehicle wheel 16 can be driven by the output shaft 49 via the final drive unit 56.The output shafts 47 and 49 are driven by the rotor 22 and thus by the electric machine 20. Each output shaft 47, 49 is rotatable about the main axis of rotation relative to the housing 52.

[0041] In the second embodiment, the differential gear 32 can also be driven by the rotor 28 and thus by the electric machine 26, so that the vehicle wheels 14 and 16 can also be driven by the rotor 28 and thus by the electric machine 26 via the differential gear 32. Since in the first embodiment only the electric machine 20 is provided for driving the vehicle wheels 14 and 16, in the first embodiment the vehicle wheels 14 and 16 can be driven by the rotor 22 and thus by the electric machine 20. Furthermore, in the second embodiment, the differential gear 32 can be driven by the rotor 22 and thus by the electric machine 20, so that the vehicle wheels 14 and 16 can be driven by the rotor 22 and thus by the electric machine 20 via the differential gear 32.

[0042] In the second embodiment, the electric drive train 10 can be operated in at least or exactly two operating modes, namely a first operating mode and a second operating mode. In the first operating mode, the vehicle wheels 14 and 16 are driven exclusively by the electric machine 26, i.e., by the rotor 28, with respect to the electric machines 20 and 26, while the electric machine 20 does not drive the vehicle wheels 14 and 16, and in particular, it does not drive the differential gear 32, especially because the rotor 22 and the electric machine 20 are decoupled from the differential gear 32 in the first operating mode.In the second operating mode, the vehicle wheels 14 and 16 can be driven or are driven by both electric machines 20 and 26, that is, by both rotors 22 and 28, in particular simultaneously, since in the second operating mode the differential 32 can be driven or is driven by both the electric machine 26, that is, by both rotor 28 and the electric machine 20, that is, by rotor 22. Thus, for example, in the second operating mode, the electric machine 20, that is, rotor 22, is coupled to the differential 32 for torque transmission. In the first embodiment and in the second embodiment, the electric drive train 10 has a coupling device 58, which has a first friction clutch 60 and a second friction clutch 62. The friction clutches 60 and 62 are also simply referred to as clutches.

[0043] In the first embodiment, a first output element 64 of the first friction clutch 60 is coupled or can be coupled to the first vehicle wheel 14 in a torque-transmitting manner, in particular in a rotationally fixed manner. Specifically, in the first embodiment, it is provided that the first output element 64 is coupled to the vehicle wheel 14 in a torque-transmitting manner, in particular permanently. In the first embodiment, a second output element 66 of the second friction clutch 62 is coupled or can be coupled to the second vehicle wheel 16 in a torque-transmitting manner, in particular in a rotationally fixed manner. Specifically, in the first embodiment, it is provided that the second output element 66 is coupled to the second vehicle wheel 16 in a torque-transmitting manner, in particular permanently.A first input element 68 of the first friction clutch 60 and a second input element 70 of the second friction clutch 62 are, in particular permanently, rotationally fixed to an input shaft 72 of the electric drive train 10, which is common to the input elements 68 and 70 and thus to the friction clutches 60 and 62. In the first embodiment, the rotor 22 is torque-transmitting, in particular rotationally fixed, to the input shaft 72 or can be coupled, specifically in the case of the following: Fig. In the first embodiment shown in Figure 1, it is provided that the input shaft 72 is permanently connected to the first rotor 22 in a rotationally fixed manner.

[0044] In the second embodiment, the first output element 64 is, in particular, permanently and non-rotatably connected to the first differential output shaft 46, and the second output element 66 is, in particular, permanently and non-rotatably connected to the second differential output shaft 48. Also in the second embodiment, the input elements 68 and 70 are, in particular, permanently and non-rotatably connected to the common input shaft 72 of the drive train 10, the axial direction of which coincides with the main axis of rotation.

[0045] The input shaft 72 of the electric drive train 10, whose radial direction is perpendicular to the axial direction of the electric drive train 10 and thus perpendicular to the main axis of rotation, is rotatable about an input shaft axis of rotation relative to the housing 52, the input shaft axis of rotation coinciding with the main axis of rotation in the embodiments. Where the axial direction is mentioned before and below, this refers, unless otherwise specified, to the axial direction of the electric drive train 10. Where the radial direction is mentioned before and below, this refers, unless otherwise specified, to the radial direction of the electric drive train 10. "Axial" means the axial direction, and "radial" means the radial direction.In the second embodiment, the rotor 22 is also torque-transmitting, in particular rotationally fixed, and can be coupled or coupled to the common input shaft 72.

[0046] In the first embodiment and in the second embodiment, with respect to a first torque flow emanating from the first rotor 22, along which the respective drive torque provided or make available by the first rotor 22 for driving the vehicle wheels 14 and 16 can be transmitted from the first rotor 22 to the first vehicle wheel 14, the first rotor 22, the input shaft 72, the first input element 68, the first output element 64 and the first vehicle wheel 14 are arranged in the following sequence, that is, consecutively in the first torque flow: the first rotor 22 - the common input shaft 72 - the first input element 68 - the first output element 64 - the first vehicle wheel 14.

[0047] With regard to a second torque flow emanating from the first rotor 22, along which or via which the respective drive torque provided or made available by the first rotor 22 for driving the vehicle wheels 14 and 16 can be transmitted from the rotor 22 to the second vehicle wheel 16, the first rotor 22, the common input shaft 72, the second input element 70, the second output element 66 and the second vehicle wheel 16 are arranged in the following order, that is, successively, in the second torque flow: the first rotor 22 - the common input shaft 72 - the second input element 70 - the second output element 66 - the second vehicle wheel 16.In the first embodiment, the output shaft 47 is arranged in the first torque flow downstream of the output element 64 and upstream of the vehicle wheel 14, thus between the output element 64 and the vehicle wheel 14, and the output shaft 49 is arranged in the second torque flow downstream of the output element 66 and upstream of the vehicle wheel 16, thus between the output element 66 and the vehicle wheel 16. Accordingly, in the second embodiment, the differential output shaft 76 is arranged in the first torque flow downstream of the output element 64 and upstream of the vehicle wheel 14, thus between the output element 64 and the vehicle wheel 14, and the differential output shaft 48 is arranged in the second torque flow downstream of the output element 66 and upstream of the vehicle wheel 16, thus between the output element 66 and the vehicle wheel 16.

[0048] The following describes a method for operating the electric drive train 10. It shows Fig.Figure 3 shows a flowchart to illustrate the procedure. The procedure includes, for example, a start step ST, in which it is checked whether a braking power request exists, specifically whether a braking power request is being made to the drivetrain 10. The braking power request characterizes the braking power to be provided by the drivetrain 10 to decelerate the vehicle wheels 14 and 16, and thus the vehicle itself. If it is determined in the start step ST that no braking power request is being made to the drivetrain 10, the procedure continues from the start step ST. If it is determined in the start step ST that a braking power request exists, specifically that a braking power request is being made to the drivetrain 10, a test step PS is performed.In test step PS, a comparison is performed in which the braking power requirement is compared with a first threshold and with a second threshold that is higher than the first. Preferably, the first threshold, and in particular its magnitude, is greater than zero; preferably, the second threshold, and in particular its magnitude, is greater than zero. If the comparison, i.e., test step PS, determines that the braking power requirement is lower than both the first and second thresholds, a first braking step BS1 is initiated. In the first braking step BS1, the vehicle wheels 14 and 16, and thus the vehicle itself, are braked by operating the electric machine 20 in its normal recuperation mode – in the first embodiment.Regarding the second embodiment, during the first braking step BS1, the vehicle wheels 14 and 16, and thus the vehicle, are decelerated by operating the electric machine 20 and / or the electric machine 26 in their normal recuperation mode. In the respective recuperation mode, the respective electric machine 20, 26 provides a recuperation torque, which results in a braking torque by means of which the vehicle wheels 14 and 16, and thus the vehicle, are braked. In particular, it is provided that during the first braking step BS1, slippage of both friction clutches 60 and 62 is prevented, specifically such that during the first braking step BS1 both friction clutches 60 and 62 are closed, and in particular completely closed, both simultaneously.

[0049] If the comparison, i.e., the test step PS, shows that the braking power requirement is greater than the first threshold and less than the second threshold, then, in particular instead of the first braking step BS1, a second braking step BS2 is performed. In the second braking step BS2, with regard to the second embodiment, the first electric machine 20 is operated in recuperative mode, i.e., in its recuperative mode, while the first friction clutch 60 is operated in slipping mode, and the second friction clutch 62 is operated in slipping mode, such that the first rotor speed of the first electric machine 20 is lower than a first speed of the first output element 64, which, for example, rotates at the first speed about a first output element axis of rotation relative to the housing 52.With regard to the second embodiment, during the second braking step BS2, the first electric machine 20 and / or the second electric machine 28 are operated in recuperative mode, i.e., in their recuperative mode, while the friction clutches 60 and 62 are operated, in particular, simultaneously in slipping mode, such that the first rotor speed is lower than the first speed of the first output element 64 and / or a second rotor speed of the second electric machine 26 is lower than a second speed of the second output element 66, which rotates at the second speed about a second output element axis of rotation relative to the housing 52. The second rotor 28 rotates at the second rotor speed about the second torque requirement relative to the second stator 30.Thus, during the second braking step BS2, the first rotor speed and / or the second rotor speed is reduced compared to the first speed or the second speed, respectively, while the electric machine 20 and / or the electric machine 26 is operating in its recuperation mode. This allows the respective electric machine 20, 26 to provide an advantageously high recuperation torque through its recuperation operation, resulting in an advantageously high braking torque for decelerating the vehicle wheels 14 and 16.

[0050] If the comparison, i.e., the test step PS, shows that the braking power requirement is greater than the first threshold and also greater than the second threshold, then a third braking step BS3 is performed, in particular instead of the first braking step BS1 and instead of the second braking step BS2. With regard to the first embodiment, in the third braking step BS3 the electric machine 20 is operated in such a way that the direction of rotation of the common input shaft, which rotates about its axis of rotation relative to the housing 52 in the direction of rotation of the input shaft, has the opposite sign to the direction of rotation of the first output element 64, which rotates about its axis of rotation relative to the housing 52 in the direction of rotation of the first output element, while the first friction clutch 60 and the second friction clutch 62 are operated in a slipping manner.With regard to the second embodiment, during the third braking step BS3, the first electric machine 20 is operated in a driving mode such that the direction of rotation of the common input shaft 72 has the opposite sign to the direction of rotation of the output element, while the friction clutches 60 and 62 are operated in a slipping mode and the second electric machine 26 is operated in its normal recuperation mode, i.e., in a recuperating mode. This allows the vehicle to be braked particularly strongly.

[0051] It can be seen that the first vehicle wheel 14 is assigned a first wheel brake 8 in addition to the friction clutches 60 and 62, and the vehicle wheel 16 is assigned a second wheel brake 82 in addition to the friction clutches 60 and 62 and in addition to the wheel brake 80. The wheel brakes 80 and 82 are designed as friction brakes, in particular as disc brakes.It can be seen that a vehicle friction brake device can be represented within the electric drive train 10 by means of the friction clutches 60 and 62, which are designed, for example, as lamellar clutches, in order to be able to brake the vehicle wheels 14 and 16 and thus the motor vehicle in a special way, for example when the aforementioned braking performance requirement is present, with the help of the friction clutches 60 and 62 and in particular without having to actuate or excessively actuate the respective friction brake 80, 82 assigned to the respective vehicle wheel 14 and 16 and which is designed in particular as a friction brake. Reference symbol list 10 electric powertrain 12 vehicle axle 14 first vehicle wheel 16 second vehicle wheel 18 Double Arrow 20 first electric machine 22 first rotor 24 first stator 26 second electric machine 28 second rotor 30 second stator 32 Differential gears 34 planetary gears 36 Sun wheel 38 Ring gear 40 planetary carriers 42 first planetary gear 44 second planetary gear 46 first differential output shaft 47 first output wave 48 second differential output shaft 49 second output wave 50 Differential input shaft 52 cases 54 Final translation unit 56 Final translation unit 58 Coupling device 60 first friction clutch 62 second friction clutch 64 first starting element 66 second starting element 68 first input element 70 second entrance element 72 Input wave 80 first wheel brake 82 second wheel brake BS1 first braking step BS2 second braking step BS3 third braking step PS Exam step ST Starting step

Claims

[1] Method for operating an electric powertrain (10) of a motor vehicle, wherein: - the electric powertrain (10) features: ◯ a first electric machine (20) comprising a first rotor (22); and ◯ a coupling device (58) comprising a first friction clutch (60) and a second friction clutch (62); - a first output element (64) of the first friction clutch (60) is coupled or can be coupled to a first vehicle wheel (14) in a torque-transmitting manner; - a second output element (66) of the second friction clutch (62) is coupled or can be coupled to a second vehicle wheel (16) in a torque-transmitting manner; - a first input element (68) of the first friction clutch (60) and a second input element (70) of the second friction clutch (62) are connected to a common input shaft (72) in a rotationally fixed manner; - the first rotor (22) is coupled or can be coupled to the common input shaft (72) in a torque-transmitting manner; - with respect to a first torque flow emanating from the first rotor (22), the first rotor (22), the common input shaft (72), the first output element (64) and the first vehicle wheel (14) are arranged in the following order in the first torque flow: the first rotor (22) - the common input shaft (72) - the first output element (64) - the first vehicle wheel (14); and - with regard to a second torque flow emanating from the first rotor (22), the first rotor (22), the common input shaft (72), the second output element (66) and the second vehicle wheel (16) are arranged in the following order in the second torque flow: the first rotor (22) - the common input shaft (72) - the second output element (66) - the second vehicle wheel (16); wherein, during a braking operation to decelerate the vehicle wheels (14, 16), if a braking power demand is greater than a first threshold and less than a second threshold, the first electric machine (20) is operated in recuperative mode, while the first friction clutch (60) and the second friction clutch (62) are operated in slipping mode, such that a first rotor speed of the first electric machine (20) is less than a first speed of the first output element (64), characterized by , that If the braking power requirement is greater than the second threshold, the first electric machine (20) is operated in driving mode, such that an input shaft rotation direction of the common input shaft (72) has a opposite sign to an output element rotation direction of the first output element (64), while the first friction clutch (60) is operated in slipping mode and the second friction clutch (62) is operated in slipping mode. [2] Method according to claim 1, characterized by , that the first friction clutch (60) and the second friction clutch (62) are operated in such a slipping manner that the first speed of the first output element (64) is equal to a second speed of the second output element (66). [3] Method according to claim 1 or 2, characterized by , that: - the electric powertrain (10) features: ◯ a second electric machine (26) which has a second rotor (28); and ◯ a differential gear (32) comprising a differential input shaft (50), a first differential output shaft (46) and a second differential output shaft (48); - the second rotor (28) is coupled to the differential input shaft (50) in such a way that first torques emanating from the second rotor (28) can be introduced into the differential gear (32) at the differential input shaft (50); - the first output element (64) is connected to the first differential output shaft (46) in a rotationally fixed manner; - the second output element (66) is rotationally fixed to the second differential output shaft (48); and - if the braking power requirement is greater than the second threshold, the second electric machine (26) is operated in recuperative mode. [4] Motor vehicle designed to carry out a method according to any of the preceding claims.

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