Method for operating an electric drive system for a motor vehicle and motor vehicle

Abstract

The invention relates to a method for operating an electric drive system (10) for a motor vehicle, in which the drive system (10) has a first electric machine (12) which has a first rotor (14). A second electric machine (18) is provided which has a second rotor (20) arranged coaxially to the first rotor (14). A first vehicle wheel (28) is provided which is permanently coupled to the first rotor (14) in a torque-transmitting manner and can thus be driven by the first rotor (14) and is assigned to the first electric machine (12). A second vehicle wheel (30) is provided which is permanently coupled to the second rotor (20) in a torque-transmitting manner and can thus be driven by the second rotor (20) and is assigned to the second electric machine (18).A friction clutch (34) is provided which is designed to connect the first rotor (14) to the second rotor (20) in a rotationally fixed manner, the friction clutch (34) being the only means for coupling the two rotors (14, 20).

Description

The invention relates to a method for operating an electric drive system for a motor vehicle. The invention also relates to a motor vehicle having such an electric drive system.DE 10 2018 221 601 A1 discloses a drive axle of an electrically drivable vehicle, wherein the drive axle has an electric drive system with two drivable vehicle wheels, two electric machines and a multi-gear transmission system. A shift method for the multi-speed transmission system is presented.It is an object of the present invention to provide a method for operating an electric drive system for a motor vehicle and a motor vehicle having such an electric drive system, so that particularly advantageous operation and a particularly compact and light construction of the drive system can be realized.This object is achieved by a method having the features of patent claim 1 and by a motor vehicle having the features of patent claim 10. Advantageous embodiments with expedient developments of the invention are specified in the other claims.A first aspect of the invention relates to a method for operating an electric drive system, also referred to as a drive device or designed as a drive device, for a motor vehicle, also referred to simply as a vehicle. This means that the motor vehicle, which is preferably designed as a motor vehicle, in particular as a passenger car, has the electric drive system in a completely produced state and can be driven, in particular purely electrically, by means of the electric drive system. In the method, the electric drive system has a first electric machine which has a first rotor. In particular, the first electric machine has a first stator, by means of which the first rotor can be driven and can thereby be rotated about a first machine rotational axis relative to the first stator. In the method, the electric drive system has a second electric machine, which has a second rotor. In particular, the second electric machine has a second stator, by means of which the second rotor can be driven and can thereby be rotated about a second machine rotational axis relative to the second stator. The rotors and thus the electric machines are arranged coaxially with respect to each other, so that the machine rotation axes coincide. In the method, the drive system has a first vehicle wheel which is permanently coupled to the first rotor in a torque-transmitting manner and is thereby drivable by the first rotor and is assigned to the first electric machine. This means that the first vehicle wheel is assigned to the first electric machine which is assigned to the first vehicle wheel. In the method, the drive system has a second vehicle wheel which is permanently coupled to the second rotor in a torque-transmitting manner and is thereby drivable by the second rotor and assigned to the second electric machine. This means that the second vehicle wheel is associated with the second electric machine which is associated with the second vehicle wheel. In particular, the first vehicle wheel can be driven by the first rotor, bypassing the second vehicle wheel. This is to be understood as meaning, in particular, the following: The first electric machine can provide, via its first rotor, first drive torques for, in particular purely electric, driving of the first vehicle wheel. With respect to a first torque final flow, along which the respective first drive torque can be transmitted or is transmitted from the first rotor to the first vehicle wheel, in particular in order thereby to drive the first vehicle wheel, the second vehicle wheel is not arranged in the first torque flow downstream of the first rotor and upstream of the first vehicle wheel. Furthermore, it is preferably provided that the second vehicle wheel can be driven by the second rotor, bypassing the first vehicle wheel. This is to be understood as meaning, in particular, the following: The second electric machine can provide, via its second rotor, second drive torques for, in particular purely electric, driving of the second vehicle wheel. With respect to a second torque end flow, along which the respective second drive torque can be transmitted or is transmitted from the second rotor to the second vehicle wheel, in particular in order to be driven here by the second vehicle, the first vehicle wheel is not arranged in the second torque end flow downstream of the second rotor and upstream of the second vehicle wheel. The electric drive system is thus designed as a dual drive.The expression that a second element is driven by a first element by bypassing a third element means that the third element is not arranged between the first element and the second element with respect to a torque flow originating from the first element and directed toward the second element.In the method, the electric drive system has a friction clutch, which is designed, for example, as a multiplate clutch and is designed to connect the first rotor to the second rotor in a rotationally fixed manner. In other words, the rotors can be connected to one another in a rotationally fixed manner by means of the friction clutch. The friction clutch can thus be switched over, for example, between a coupling state and a decoupling state. In the coupled state, the rotors are connected to one another in a rotationally fixed manner by means of the friction clutch. In the decoupling state, the friction clutch releases the rotors for a relative rotation between the rotors, which occurs in particular about the respective machine rotational axis, in particular in such a way that in the decoupling state no torques can be transmitted via the friction clutch between rotors, so that, for example, in the decoupling state the rotors are completely decoupled from one another. It is in particular conceivable for the friction clutch to be switchable into at least one or more intermediate states. In the intermediate state, for example, the rotors are coupled to one another in a torque-transmitting manner via the friction clutch, but are rotatable relative to one another about the respective machine rotational axis, so that, for example, in the intermediate state, the friction clutch is operated in a slipping manner. In the intermediate state, for example, a torque can be transmitted between the rotors via the friction clutch, which is greater than 0 in terms of amount. In other words, for example, the following is provided: in the coupled state of the friction clutch, at most a first torque can be transmitted between the rotors via the friction clutch, which is also referred to as the first clutch torque and is greater than 0 in terms of amount. In the intermediate state, for example, at most a second torque can be transmitted between the rotors via the friction clutch, which is also referred to as the second clutch torque and is greater than 0 and less than the first torque in terms of absolute value. In the decoupling state, for example, no torque can be transmitted between rotors via the friction clutch. In particular, it is conceivable that the friction clutch can be operated or is operated in a slipping manner in the intermediate state, so that a torque is transmitted between the rotors via the friction clutch, but the rotors rotate relative to one another, in particular about the respective machine rotational axis. Thus, in particular in the coupled state, the rotors are connected to one another in a rotationally fixed manner by means of the friction clutch. In the decoupling state, the rotors are decoupled from one another, in particular completely. In the intermediate state, the rotors are connected to one another via the friction clutch in a torque-transmitting manner, but are rotatable relative to one another about the respective machine rotational axis.In the method, the friction clutch is the only means for torque-transmitting coupling of the two rotors. This means that there is no further clutch, no further coupling transmission or no differential transmission and also no other coupling device by means of which the two rotors could be coupled to one another directly or indirectly in a torque-transmitting manner. As a result, the number of parts and thus the installation space requirement, the costs and the weight of the drive system can be kept within a particularly small scope. In other words, a particularly slender construction of the drive system can be realized as a result, wherein a particularly advantageous operation of the drive system can be simultaneously realized. The term "means" is therefore understood here to mean a vehicle-mounted means. Of course, it is additionally the case that the vehicle wheels are coupled to one another to a certain extent via the road or via the underlying surface on / on which the motor vehicle travels, as a result of which the two rotors are also coupled to one another via the roads or the underlying surface.In the method, the drive system is operated in a single-engine mode when the motor vehicle is cornering. Cornering of the motor vehicle is to be understood to mean that the motor vehicle is passing through a curve which is designed, for example, as a left-hand curve or right-hand curve. The motor vehicle has, for example, at least one vehicle axle. In particular, the motor vehicle in its completely manufactured state has at least or exactly two vehicle axles, namely the aforementioned vehicle axle as a first vehicle axle and a second vehicle axle. If the term is used above and below as referring to the vehicle axle, this is to be understood as meaning the first vehicle axle unless otherwise stated. Preferably, the vehicle axle includes the first vehicle wheel and the second vehicle wheel, such that the first vehicle wheel and the second vehicle wheel are preferably vehicle wheels of the same first vehicle axle. When reference is made above and below to the vehicle wheels, unless otherwise stated, this is to be understood as meaning the first vehicle wheel and the second vehicle wheel. The vehicle wheels are ground contact elements, by means of which the motor vehicle can be or is supported on a ground in the vertical direction of the motor vehicle downwards. If the motor vehicle is driven along the ground while the motor vehicle is supported on the ground via the ground contact elements in the vertical direction of the motor vehicle downwards, the ground contact elements roll off the ground, in particular directly. In particular, the vehicle wheels are steerable vehicle wheels, to which a steering system of the motor vehicle is assigned. By means of the steering system, the vehicle wheels can be pivoted relative to a superstructure of the motor vehicle and thus steered. By steering the vehicle wheels, it is possible, for example, to bring about lane changes, i.e. lane changes, changes in direction and cornering of the motor vehicle, so that, for example, during the aforementioned cornering, the vehicle wheels are pivoted out of a straight-ahead position, in particular relative to the superstructure, in order thereby to carry out the cornering, and therefore in order thereby to drive the motor vehicle through the curve. The straight-ahead position of the vehicle wheels is provided to bring about a straight-ahead travel of the motor vehicle, wherein cornering of the motor vehicle is prevented during the straight-ahead travel of the motor vehicle. The feature that the vehicle wheels are pivoted out of the straight-ahead position during cornering is to be understood to mean that, during cornering, the vehicle wheels are pivoted with respect to the straight-ahead position, and therefore assume a respective first pivot position which differs from a respective second pivot position, wherein the vehicle wheels are in the respective second pivot position during straight-ahead travel or in the straight-ahead position.Single-engine operation is to be understood to mean that in or during single-engine operation only one of the electric machines is driven with respect to the electric machines, so that with respect to the electric machines only the one electric machine drives exactly one of the vehicle wheels or both vehicle wheels, while the other electric machine does not drive exactly one of the vehicle wheels or both vehicle wheels, and therefore while the other electric machine does not drive any of the vehicle wheels and in particular does not provide any torque, i.e. outputs it via its rotor. In the single-motor mode, the other electric machine is dragged by the one electric machine, for example, or operated in a zero-torque control.In the method according to the invention, in or during single-engine operation and when the motor vehicle is cornering, only the electric machine to which the vehicle wheel which is on the outside of the curve during cornering is operated in a driving manner, while driving of exactly one of the vehicle wheels or both vehicle wheels by the other electric machine to which the vehicle wheel which is on the inside of the curve during cornering is prevented. In addition, in the method according to the invention, it is provided that, during or during single-engine operation and when the motor vehicle is cornering, the friction clutch is closed up to a degree of closure which is selected such that a specific, and therefore predefined, drive torque distribution takes place from the electric machine, to which the vehicle wheel which is on the outside of the curve during cornering, to the two vehicle wheels. In particular, the degree of closure is selected such that in or during single-engine operation and during cornering, the friction clutch is operated in slipping fashion, and therefore the friction clutch is in the intermediate state. The following is to be understood in particular by the said drive torque distribution: during single-engine operation and during cornering, the electric machine which is operated in a driving manner provides via its rotor at least one of the aforementioned drive torques which is transmitted at or through the drive torque distribution starting from the rotor of the electric machine to which the vehicle wheel which is on the outside of the curve during cornering is assigned to the two vehicle wheels, such that a first wheel torque and a second wheel torque result from the at least one drive torque, such that the first wheel torque is transmitted to the first vehicle wheel and the second wheel torque is transmitted to the second vehicle wheel, wherein, for example, the first vehicle wheel is driven by means of the first wheel torque and the second vehicle wheel is driven by means of the second wheel torque. Preferably, the respective wheel torque is greater than 0 in terms of absolute value.The electric machine to which the vehicle wheel that is on the outside of the curve during cornering is also referred to as an electric machine that is on the outside of the curve, and the electric machine to which the vehicle wheel that is on the inside of the curve during cornering is also referred to as an electric machine that is on the inside of the curve. The wheel torques can be equal in terms of amount, or the wheel torques can differ from one another in terms of amount, as a result of which a particularly advantageous drive can be produced. The invention is based in particular on the following findings and considerations:Dual drives having two electric machines are generally less efficient than individual drives, that is to say than drives having only one electric machine for driving both vehicle wheels, if these dual drives can only be operated in a dual mode in which both electric machines are operated simultaneously in a driving manner and thus drive the vehicle wheels. In order to operate a dual drive, such as the electric drive system of the method according to the invention, efficiently, it is advantageous to implement a so-called single mode, also referred to as single mode, in which, with respect to the electric machines, only one electric machine is operated in a driving or driving manner, while the other electric machine does not drive any of the vehicle wheels. Usually, however, several clutches and possibly additional differential transmissions are required for this purpose. A changeover from the dual mode to the single mode can often not take place without delay. A torque vectoring intervention is also frequently not possible without delay. The aforementioned problems and disadvantages can now be avoided by the invention. In the invention, the friction clutch is used as a single clutch between the rotors and as a lock-up clutch, and a torque capacity of the friction clutch may be advantageously small. For example, the torque distribution is set as a function of a steering angle, that is to say as a function of a value by which the respective vehicle wheel is pivoted with respect to the straight-ahead position during cornering. In particular depending on a relative rotational speed difference at the friction clutch and depending on one side of the active, thus driving or motively operated electric machine, a torque of the motively operated electric machine can be transmitted to the opposite vehicle wheel, whereby a particularly advantageous drive can be provided. In addition, the invention enables always and immediately available torque vectoring capabilities without undue dwell times, adverse mode transitions, or other adverse constraints. Furthermore, the realization of different efficiency modes, which are available in at least almost all driving situations, makes it possible, however, to use a mechanical separating unit between the electric machines. In addition, the number of mechanical components can be kept low, as a result of which a particularly space-saving design of the drive system can be produced.The term torque vectoring means an operating mode in which the two vehicle wheels of the vehicle axle are driven with individually adjustable different torques. In a mode of operation without torque vectoring, both vehicle wheels of an axle are driven with the same torque.The invention enables the drive system to be designed as a slender system, which is therefore inexpensive, weight-efficient and space-saving, although different advantageous operating modes can be realized at the same time. A first of the operating modes is single-motor operation, which can be, for example, the aforementioned single mode or a first single mode. In this case, for example, the friction clutch can be realized or function as a type of differential gear, in particular in that the friction clutch is operated in a slipping manner. A second of the operating modes is a dual-motor operation, also referred to as dual operation, which can be the aforementioned dual mode, for example. In two-motor operation, for example, the electric machines are operated simultaneously in a driving manner, with the result that the electric machines simultaneously drive the vehicle wheels, in particular in such a way that the first electric machine drives the first vehicle wheel via its first rotor, in particular bypassing the second vehicle wheel, and that the second electric machine simultaneously drives the second vehicle wheel via its second rotor, in particular bypassing the first vehicle wheel. In addition, torque vectoring can be carried out in a particularly advantageous manner, in particular as a third operating mode of the operating modes.Within the scope of the present disclosure, the feature that two rotatably mounted components are connected to one another in a rotationally fixed manner is understood to mean that the components connected to one another in a rotationally fixed manner are arranged coaxially with respect to one another and, in particular when the components are driven, rotate together or simultaneously about a component rotation axis common to the components, which is for example the respective machine rotation axis, at the same winding speed, in particular relative to a reference element such as for example a housing of the drive system. In other words, two rotatably mounted elements are connected to one another in a rotationally fixed manner if they are arranged coaxially with respect to one another, with respect to their component rotational axis or with respect to a rotational symmetry axis, and if they are connected to one another in such a way that they rotate at the same angular speed. An element is connected to the housing in a rotationally fixed manner if it cannot be rotated with respect to, that is to say relative to, the housing.The feature that two components, such as the rotors, are connected or coupled to one another in a torque-transmitting manner is to be understood to mean that the components are coupled or connected to one another in such a way that torques can be transmitted between the components, wherein, if the components are connected or coupled to one another in a rotationally fixed manner, the components are also connected or coupled to one another in a torque-transmitting manner. Two torque-transmittingly connected components can thus be connected to one another in a rotationally fixed manner. It is furthermore conceivable that two torque-transmittingly connected components are connected to one another via an interposed transmission unit and / or coupling unit, such as the friction clutch, in a torque-transmitting manner, so that torques can be transmitted between the components via the transmission unit or coupling unit, while the components are connected to one another in a torque-transmitting manner, wherein the components can, however, be rotatable relative to one another, in particular about the component axis of rotation.The feature that two components are permanently connected or coupled to one another in a torque-transmitting manner is to be understood to mean that there is not, for example, a shift element which can be switched between a coupling state which connects or couples the components to one another in a torque-transmitting manner and a decoupling state in which no torques can be transmitted between the structural torques via the shift element, but rather the components are always or always and thus permanently connected or coupled to one another in a torque-transmitting manner, that is to say in such a way that a torque can be transmitted between the components. Thus, for example, one of the components can be driven by the respective other component or vice versa.In particular, the feature that two components are permanently connected or coupled to one another in a rotationally fixed manner is to be understood to mean that a shifting element is not provided, for example, which is switchable between a coupling state which connects or couples the components to one another in a rotationally fixed manner and a decoupling state in which the components are decoupled from one another and are rotatable relative to one another, such that no torques can be transmitted between the components via the shifting element, but rather the components are always or always, therefore permanently, connected or coupled to one another in a rotationally fixed manner.Furthermore, the feature that two components which can be connected or coupled to one another in a rotationally fixed manner is to be understood as meaning that the components are assigned a changeover element which can be changed over between at least one coupling state and at least one decoupling state. In the coupled state, the components are connected or coupled to one another in a rotationally fixed manner by means of the changeover element. In the decoupling state, the components are decoupled from one another, so that in the decoupling state the components are rotatable relative to one another about the component rotation axis and so that in particular no torques can be transmitted between the components via the changeover element. The same applies to the feature that two components can be connected or coupled to one another in a torque-transmitting manner. Thus, for example, the feature that two components can be connected or coupled to one another in a torque-transmitting manner is understood to mean that a switching element is assigned to the components, wherein the switching element can be switched over between at least one connection state and at least one release state. In the connected state, the components are coupled or connected to one another in a torque-transmitting manner by means of the shift element, such that torques can be transmitted between the components, in particular via the shift element. In the release state, the components are decoupled from one another, so that in the release state no torque can be transmitted between the components via the shift element.Preferably, the friction clutch is a wet multiplate clutch. This is to be understood in particular as meaning that the multi-plate clutch has friction plates which, at least during operation of the drive system, are lubricated by means of a liquid which is embodied, for example, as an oil and in the process come in particular into direct contact with the liquid, wherein, for example, the friction plates run in a sump formed by the liquid. By means of the friction clutch, the rotors can be connected to one another in a frictionally fixed manner.In order to realize particularly advantageous operation in a particularly space-saving, weight-saving and cost-effective manner, it is provided in one embodiment of the invention that torque vectoring is carried out during single-engine operation by selecting the degree of closure in such a way that the vehicle wheel on the outside of the curve receives more drive torque than the vehicle wheel on the inside of the curve. Thus, the wheel torque transmitted to the vehicle wheel on the outside of the curve to thereby drive the vehicle wheel on the outside of the curve is larger than the wheel torque transmitted to the vehicle wheel on the inside of the curve to thereby drive the vehicle wheel on the inside of the curve. In this case, both wheel torques are preferably greater than zero in terms of absolute value.A further embodiment is distinguished in that torque vectoring is omitted during single-engine operation, in that both vehicle wheels receive the same drive torque. That is, the wheel torque transmitted to the vehicle wheel on the outside of the curve to thereby drive the vehicle wheel on the outside of the curve and the wheel torque transmitted to the vehicle wheel on the inside of the curve to thereby drive the vehicle wheel on the inside of the curve are equal in magnitude.Preferably, when torque vectoring is performed and torque vectoring is omitted, the wheel torques are greater than zero in terms of absolute value.In order to be able to realize a particularly slender construction of the drive system, it is provided in a further embodiment of the invention that the rotors are arranged at least substantially coaxially with respect to the vehicle wheels. This is understood to mean that the rotors are either arranged strictly coaxially with respect to the vehicle wheels, or the rotors are arranged with a slight axial offset with respect to the vehicle wheels, wherein, for example, the axial offset is effected by a respective interposed articulated shaft. It is thus conceivable, for example, for the first rotor to be coupled to the first vehicle wheel via a first articulated shaft and the second rotor to be coupled to the second vehicle wheel via a second articulated shaft in a permanently torque-transmitting manner, wherein the respective articulated shaft brings about a respective axial offset, with or under which the first rotor is arranged with respect to the first vehicle wheel and the second rotor is arranged with respect to the second vehicle wheel. This produces a particularly slender construction.In order to be able to realize a particularly slender construction of the drive system and a particularly advantageous drive of the vehicle wheels, it is provided in a further embodiment of the invention that exactly one first transmission device is arranged between the first vehicle wheel and the first rotor, via which transmission device the first vehicle wheel is permanently coupled to the first rotor in a torque-transmitting manner. In addition, in this case, exactly one second transmission device is arranged between the second vehicle wheel and the second rotor, via which transmission device the second vehicle wheel is permanently coupled to the second rotor in a torque-transmitting manner.It has proven particularly advantageous if the first transmission device is designed as a first planetary gear set and the second transmission device is designed as a second planetary gear set, whereby the installation space requirement, the weight and the costs of the drive system can be kept within a particularly small scope.In order to be able to realize a particularly slender construction of the drive system, it is provided in a further embodiment of the invention that the respective planetary gear set is designed as a respective simple planetary gear set.In order to be able to realize a particularly weight-, cost- and space-saving construction of the drive system, it is provided in a further embodiment of the invention that a first sun gear of the first planetary gear set is permanently connected to the first rotor in a torque-transmitting manner, in particular permanently in a rotationally fixed manner, that a first ring gear of the first planetary gear set is permanently connected to the housing of the drive system in a rotationally fixed manner, and that a first planetary carrier of the first planetary gear set is permanently connected to the first vehicle wheel in a torque-transmitting manner, in particular permanently in a rotationally fixed manner. It has proven particularly advantageous here if a second sun gear of the second planetary gear set is permanently connected to the second rotor in a torque-transmitting manner, in particular permanently in a rotationally fixed manner, if a second ring gear of the second planetary gear set is permanently connected to the housing of the drive system in a rotationally fixed manner, and if a second planetary carrier of the second planetary gear set is permanently connected to the second vehicle wheel in a torque-transmitting manner, in particular permanently in a rotationally fixed manner.Finally, for the realization of a particularly slender construction of the drive system, it has been shown to be particularly advantageous if the respective electric machine is designed as a respective axial flow machine (AFM), which is also referred to as an axial flow motor.A second aspect of the invention relates to a motor vehicle which is also referred to simply as a vehicle and is preferably designed as a motor vehicle, in particular as a passenger car, and which has an electric drive system and can be driven, in particular purely electrically, by means of the electric drive system, wherein the electric drive system of the motor vehicle according to the second aspect of the invention is designed to carry out a method according to the first aspect of the invention. Advantages and advantageous configurations of the first aspect of the invention are to be regarded as advantages and advantageous configurations of the second aspect of the invention and vice versa.Further advantages, features and details of the invention will become apparent from the following description of a preferred exemplary embodiment and with reference to the drawing.The drawing shows in: FIG. 1 shows a schematic illustration of an electric drive system for a motor vehicle; FIG. 2 shows a schematic illustration for illustrating a method for operating the electric drive system; and FIG. 3 shows a further schematic illustration for further illustrating the method.In the figures, identical or functionally identical elements are provided with identical reference symbols.FIG. 1 shows a schematic illustration of an electric drive system 10 for a motor vehicle, also referred to simply as a vehicle, which, in its completely produced state, has the electric drive system 10 and can be driven by means of the electric drive system 10, in particular purely electrically. The electric drive system 10 includes a first electric machine 12 that includes a first rotor 14 and a first stator 16. Via its rotor 14, the electric machine 12 may provide first drive torques for propelling the motor vehicle. The electric drive system 10 has a second electric machine 18 which has a second rotor 20 and a second stator 22. Via its second rotor 20, the second electric machine 18 can provide second drive torques for driving the motor vehicle. The drive system 10 also includes a housing 24. For example, the respective electric machine 12, 18 is arranged at least partially in the housing 24. In particular, the respective stator 16, 22 is connected to the housing 24 in a rotationally fixed manner, in particular permanently. In the exemplary embodiment shown in FIG. 1, the respective electric machine 12, 18 is designed as a respective axial flow machine (AFM).The motor vehicle has at least or exactly two vehicle axles, namely a first vehicle axle and a second vehicle axle. The vehicle axles are also arranged in succession in the longitudinal direction of the vehicle and thus one behind the other. The first vehicle axle can be seen in FIG. 1 and is denoted by 26. The first vehicle axle 26 has at least or exactly two vehicle wheels, namely a first vehicle wheel 28 and a second vehicle wheel 30. thus, the vehicle wheels 28 and 30 are vehicle wheels of the same first vehicle axle 26. In the present case, the drive system 10 has the vehicle wheels 28 and 30. The vehicle wheels 28 and 30 are arranged on opposite sides of the motor vehicle in the vehicle transverse direction of the motor vehicle. The vehicle transverse direction is illustrated by a double arrow 32. The electric drive system 10 includes the first vehicle wheel 28 and the second vehicle wheel 30.The first vehicle wheel 28 is permanently coupled to the first rotor 14 in a torque-transmitting manner, by means of which the first vehicle wheel 28 can be driven, in particular bypassing the second vehicle wheel 30. Thus, the first vehicle wheel 28 is associated with the first electric machine 12 and vice versa. The second vehicle wheel 30 is permanently connected to the second rotor 20 in a torque-transmitting manner, by means of which the second vehicle wheel 30 can be driven, in particular bypassing the first vehicle wheel 28. The second vehicle wheel 30 is associated with the second electric machine 18, and vice versa.The drive system 10 also has a friction clutch 34, which is designed, for example, as a multiplate clutch and is designed to connect the rotors 14 and 20 to one another in a rotationally fixed manner. The friction clutch 34 is the only means for torque-transmitting coupling of the two rotors 14 and 20.In the exemplary embodiment shown in FIG. 1, exactly one transmission device, namely a first transmission device 36, is arranged between the first vehicle wheel 28 and the first rotor 14, via which transmission device the first vehicle wheel 28 is permanently coupled to the first rotor 14 in a torque-transmitting manner. This means that, with respect to a first torque flow along which the respective first drive torque can be transmitted from the first rotor 14 to the first vehicle wheel 28, in particular bypassing the second vehicle wheel 30, the first transmission device 36 is arranged downstream of the rotor 14 and upstream of the vehicle wheel 28 in the first torque flow.Arranged between the second vehicle wheel 30 and the second rotor 20 is exactly one second transmission device 38 via which the second vehicle wheel 30 is permanently coupled to the second rotor 20 in a torque-transmitting manner. This means that, with respect to a second torque flow along which the respective second drive torque can be transmitted and is transmitted from the second rotor 20 to the second vehicle wheel 30, the second transmission device 38 is arranged in the second torque flow downstream of the second rotor 20 and upstream of the second vehicle wheel 30.In the exemplary embodiment shown in FIG. 1, the respective transmission device 36, 38 is designed as a respective, simple planetary gear set, namely a first planetary gear set 40 and a second planetary gear set 42. The first planetary gear set 40 has a first sun gear 44 permanently connected in a rotationally fixed manner to the first rotor 14 and a first ring gear 46 permanently connected in a rotationally fixed manner to the housing 24. The first planetary gear set 40 has a first planetary carrier 48 which is rotatable about a main axis of rotation 50 relative to the housing 24. The first sun gear 44 and the respective rotor 14, 20 are also rotatable about the main axis of rotation 50 relative to the housing 24. The first planetary gear set 40 also includes first planet gears 52 rotatably supported on the first planet carrier 48. The respective first planetary gear 52 meshes on the one hand with the first ring gear 46 and on the other hand with the first sun gear 44, wherein a meshing of the first sun gear 44 with the first ring gear 46 is omitted.The first transmission device 36 and the second transmission device 38 are non-shiftable transmission devices 36, 38 each having a fixed transmission ratio.The second planetary gear set 42 has a second sun gear 54 permanently connected in a rotationally fixed manner to the second rotor 20 and a second ring gear 56 permanently connected in a rotationally fixed manner to the housing 24. The second planetary gear set 42 includes a second planet carrier 58 which, like the first planet carrier 48, is rotatable about the main axis of rotation 50 relative to the housing 24. The second sun gear 54 is also rotatable about the main axis of rotation 50 relative to the housing 24. The second planetary gear set 42 has second planetary gears 60 rotatably supported on the second planetary carrier 58. The respective second planetary gear 60 meshes on the one hand with the second ring gear 56 and on the other hand with the second sun gear 54, wherein a meshing of the second sun gear 54 with the second ring gear 56 is omitted. The planetary gear sets 40 and 42 are arranged coaxially with each other. It can also be seen from FIG. 1 that the rotors 14 and 20 and thus the electric machines 12 and 18 are arranged coaxially with respect to one another. The first planet carrier 48 is permanently torque-transmittingly connected to the first vehicle wheel 28, and the second planet carrier 58 is permanently torque-transmittingly connected to the second vehicle wheel 30.The electric drive system 10 can be operated in different operating modes. A method for operating the electric drive system 10 is described below.A first operating mode of the operating modes is, for example, a dual mode in which the first electric machine 12 drives the first vehicle wheel 28 and at the same time the second electric machine 18 drives the second vehicle wheel 30, in particular while the friction clutch 34 is, in particular, completely, open, so that the friction clutch 34 is in its decoupling state, in which no torques can be transmitted via the friction clutch 34 between the rotors 14 and 20. Torque vectoring is possible in or in the first operating mode by the first electric machine 12 and the second electric machine 18 providing different torques.The aforementioned dual mode, which is designed as a first operating mode, is also referred to as a first dual mode, wherein, in or in the first dual mode, the friction clutch 34, which is also referred to as a multiplate clutch or is designed as a multiplate clutch, is opened, in particular completely, and is therefore in the decoupling state.In the first operating mode, torque vectoring is also possible by means of the friction clutch 34.The friction clutch 34 can basically be switched between the mentioned decoupling state and a coupling state. In the coupled state, the rotors 14 and 20 are connected to one another in a rotationally fixed manner by means of the friction clutch 34, with the result that, for example, in the coupled state of the friction clutch 34, a first torque can be transmitted between the rotors 14 and 20 via the friction clutch 34. The first torque is greater than 0 in terms of absolute value. The friction clutch 34 can also be shifted, for example, into at least one intermediate state, preferably a plurality of intermediate states, so that the friction clutch 34 can preferably be operated in the decoupling state, the coupling state and the respective intermediate state. In the respective intermediate state, for example, a second torque can be transmitted between the rotors 14 and 20 via the friction clutch 34, wherein the second torque is greater than 0 and less than the first torque in terms of amount. In particular, the intermediate state is slipping operation of the friction clutch 34, so that the friction clutch 34 is slippingly operated in its intermediate state. This means that, if the friction clutch 34 is operated in a slipping manner, that is to say in the intermediate state, a torque, also referred to as transmission torque and greater in terms of amount with respect to zero, can be transmitted or is transmitted between the rotors 14 and 20 via the friction clutch 34, while, however, the friction clutch 34 allows relative rotations between the rotors 14 and 20 which take place about the main axis of rotation 50, that is to say while the rotors 14 and 20 are rotatable relative to one another about the main axis of rotation 50 or rotate relative to one another about the main axis of rotation 50. In this case, the transmission torque is greater than 0 in terms of absolute value and in particular less than the first torque.A second operating mode of the operating modes is a second dual mode, in or in which the first electric machine 12 drives the first vehicle wheel 28 and at the same time the second electric machine 18 drives the second vehicle wheel 30, while the friction clutch 34 is fully closed, and therefore while the friction clutch 34 is in its coupled state, such that the rotors 14 and 20 are connected to one another in a rotationally fixed manner by means of the friction clutch 34. As a result, the friction clutch 34 functions as a differential lock.A third operating mode of the operating modes is a first individual operation, which is also referred to as a first single operation. In the third operating mode, with respect to electric machines 12 and 18, only one of electric machines 12 and 18 drives vehicle wheels 28 and 30, while the other electric machine 18, 12 does not drive either of vehicle wheels 28 and 30. In or in the third operating mode, the friction clutch 34 is closed, in particular completely, so that the friction clutch 34 is in its coupling state and the rotors 14 and 20 are connected to one another in a rotationally fixed manner. The third operating mode is a first efficiency operation with the differential lock activated, since in the third operating mode the friction clutch 34 functions as a differential lock.A fourth operating mode of the operating modes is a second single mode, which is also referred to as a second single mode. In or in the fourth operating mode, the friction clutch 34 is operated slippingly and thus in particular in the intermediate state, wherein torque vectoring and thus unequal distribution of torque to the vehicle wheels do not occur in the fourth operating mode. As in the first single operation, it is provided in the second single operation that, with respect to the electric machines 12 and 18, only one of the electric machines 12 and 18 drives the vehicle wheels 28 and 30, while the respective other electric machine 18, 12 does not drive any of the vehicle wheels 28 and 30. Thus, for example, the fourth operating mode is a second efficiency operation.A fifth of the operating modes is a third individual operation, which is also referred to as a third single operation. Torque vectoring is omitted in or in the fourth operating mode, wherein torque vectoring is carried out in or in the fifth operating mode. The fifth operating mode is a third efficiency mode, since in the fifth operating mode, only one of the electric machines 12 and 18 drives the vehicle wheels 28 and 30, while the respective other electric machine 18, 12 does not drive any of the vehicle wheels 28 and 30.The fourth mode of operation is illustrated in FIG. 2 and the fifth mode of operation is illustrated in FIG. 3. For example, in the method, the respective operating mode is carried out during a respective time phase of the method. For example, the fourth operating mode is carried out during normal cornering of the motor vehicle. For example, the fifth operating mode is carried out during a sport cornering of the motor vehicle. During the cited cornering, the motor vehicle travels through a curve designed, for example, as a left-hand curve or right-hand curve. In cornering, in particular, depending on whether the curve is a right curve or a left curve, one of the vehicle wheels 28 and 30 is a vehicle wheel on the outside of the curve, while the other vehicle wheel 30, 28 is a vehicle wheel on the inside of the curve. The respective individual operation is also referred to as single-motor operation.A sport cornering is to be understood, for example, as cornering with a particularly high vehicle speed and / or a particularly high vehicle acceleration in the curve.In an upper part T 1 of FIG. 2, the fourth operating mode is shown during a first cornering of the motor vehicle, which during or during the first cornering drives through a curve designed as a left-hand curve. Here, for example, the vehicle wheel 30 is the vehicle wheel on the outside of the curve and the vehicle wheel 28 is the vehicle wheel on the inside of the curve. During the first cornering, only the second electric machine 18, to which the second vehicle wheel 30 that is on the outside of the curve during the first cornering, is assigned, is driven with respect to the electric machines 12 and 18, so that, with respect to the electric machines 12 and 18, only the electric machine 18 drives the vehicle wheels 28 and 30, while the first electric machine 12 does not drive any of the vehicle wheels 28 and 30. During the first cornering, the friction clutch 34 is closed to a degree of closure which is selected such that a uniform drive torque distribution takes place starting from the second electric machine 18, to which the first vehicle wheel 28 which is on the outside of the curve during the first cornering, to the two vehicle wheels 28 and 30 and the friction clutch 34 is operated in a slipping manner. FIG. 2 schematically shows a steering handle 62 of the motor vehicle, which is designed as a steering wheel. As is shown in the first part T 1, the first part T 1 illustrates the first cornering, and therefore a travel of the motor vehicle through the said left-hand curve. A bar B 1 illustrates a torque acting on the friction clutch 34, which is transmitted via the friction clutch 34. A bar B 2 illustrates torque applied to (but not provided by) the first electric machine 12 and a bar B 3 illustrates torque provided by the second electric machine 18. A bar B 4 illustrates a torque, also referred to as a first wheel torque or first wheel torque, acting on the first vehicle wheel 28, and a bar B 5 illustrates a torque, also referred to as a second wheel torque or second wheel torque, acting on the second vehicle wheel 30. It can be seen in particular from the bars B 2 and B 3 that during the first cornering, the second electric machine 18 drives the vehicle wheels 28 and 30, while the first electric machine 12 does not drive any of the vehicle wheels 28, 30 and in particular does not provide any torque via its first rotor 14. It can also be seen from the bars B 4 and B 5 that the torques transmitted to the vehicle wheels 28 and 30 in particular simultaneously and also referred to as wheel torques or wheel torques are of the same magnitude, so that the vehicle wheel on the outside of the curve and the vehicle wheel on the inside of the curve receive the same wheel torque also referred to as drive torque, wherein the respective vehicle wheel 28, 30 is driven by means of the respective wheel torque which is transmitted to the respective vehicle wheel 28, 30. Torque vectoring with unequal torque distribution to the vehicle wheels 28, 30 is thus omitted. A bar B 6 illustrates a rotational speed of the first vehicle wheel 28 and a bar B 7 illustrates a rotational speed of the second vehicle wheel 30, It can be seen that during the first cornering the second vehicle wheel 30 is the vehicle wheel on the outside of the curve and thus rotates at a greater rotational speed than the first vehicle wheel 28 on the inside of the curve.In a second part T 2 of FIG. 2, driving travel of the motor vehicle is illustrated by a right turn. In other words, the part T 2 illustrates a second cornering of the motor vehicle which, during the second cornering, travels through a right turn. During the first cornering, the fourth operating mode is carried out, that is to say the drive system 10 is operated in the fourth operating mode. During the second cornering, the drive system 10 is operated in the fourth operating mode, in which the multiplate clutch (friction clutch 34) is operated in a slipping manner and torque vectoring is omitted. During the second cornering, the first vehicle wheel 28 is the vehicle wheel on the outside of the curve and the second vehicle wheel 30 is the vehicle wheel on the inside of the curve, so that during the second cornering, the first vehicle wheel 28 rotates at a greater rotational speed than the second vehicle wheel 30 on the inside of the curve. Also during the second cornering, the friction clutch 34 is closed to a degree of closure which is selected such that a specific drive torque distribution takes place starting from the first electric machine 12, to which the first vehicle wheel 28 which is on the outside of the curve during the second cornering, to the two vehicle wheels 28 and 30, and the friction clutch 34 is operated in a slipping manner in the process. Torque vectoring is also omitted during the second cornering, so that the wheel torques transmitted to the vehicle wheels 28 and 30 for driving the vehicle wheels 28 and 30 are the same. In other words, vehicle wheels 28 and 30 receive the same drive torque, also referred to as drive torque, during both first cornering and second cornering.In a third part T 3 of FIG. 2, a first straight-ahead travel of the motor vehicle is illustrated. During the first straight-ahead travel, the drive system 10 is operated in the fourth operating mode, in which the friction clutch 34 is operated in a slipping manner and torque vectoring is omitted. During the first straight-ahead travel, only one of the electric machines 12 and 18, in the present case for example the second electric machine 18, is operated in a driving manner with respect to the electric machines 12 and 18, with the result that the second electric machine 18 drives the vehicle wheels 28 and 30, while the first electric machine 12 does not drive any of the vehicle wheels 28 and 30 and in particular does not provide any driving torque. It can be seen from the bars B 6 and B 7 that during the first straight-ahead travel, the vehicle wheels 28 and 30 rotate at the same rotational speed. The first cornering is a first driving cornering and the second cornering is a second driving cornering. The first straight-ahead travel is a first driving straight-ahead travel. If, for example, a deceleration takes place during a travel of the motor vehicle through a left turn, and therefore, for example, a decelerating cornering of the motor vehicle takes place through a left turn, then, for example, a deceleration of the motor vehicle with respect to the electric machines 12 and 18 is effected exclusively by means of the first electric machine 12 to which the vehicle wheel 28 on the inside of the turn is assigned, while a deceleration by means of the second electric machine 18 to which the second vehicle wheel 30 on the outside of the turn is assigned is omitted. If, for example, a decelerating cornering is carried out by a right-hand curve, then, for example, a deceleration of the motor vehicle with respect to the electric machines 12 and 18 is effected exclusively by means of the second electric machine 18 to which the second vehicle wheel 30 on the inside of the curve is assigned, while a deceleration by the first electric machine 12 to which the first vehicle wheel 28 on the outside of the curve is assigned is omitted. In the fourth operating mode, for example, the friction clutch 34 is operated in a slipping manner in such a way that a slip of the friction clutch 34 is set in such a way that the respective vehicle wheel 28, 30 on the inside of the curve receives half the respective drive torque.A third cornering of the motor vehicle is illustrated in a first part T 4 of FIG. 3, which cornering runs through a left turn during the third cornering. A second part 5 of FIG. 3 illustrates a fourth cornering of the motor vehicle, which, during the fourth cornering, drives through a right-hand turn. During the third cornering and during the fourth cornering, the drive system 10 is operated in the fifth operating mode, which corresponds basically to the fourth operating mode, with the difference, however, that torque vectoring and thus unequal distribution of drive torque to the vehicle wheels 28, 30 is carried out in the fifth operating mode. Such torque vectoring is omitted in the fourth operating mode. Torque vectoring of the fifth operating mode is to be understood as meaning that the respective vehicle wheel 28, 30 on the outside of the curve receives more, that is to say a greater drive torque, than the vehicle wheel 30, 28 on the inside of the curve.Since, during the third cornering through the left curve, the second vehicle wheel 30 is the vehicle wheel on the outside of the curve, the wheel torque for driving the second vehicle wheel 30 transmitted to the outside of the curve is greater than the wheel torque for driving the first vehicle wheel 28 transmitted to the first vehicle wheel 28 on the inside of the curve, so that the second vehicle wheel 30 on the outside of the curve receives more drive torque than the first vehicle wheel 28 on the inside of the curve. The different wheel torques or drive torques of the vehicle wheels 28 and 30 can be seen on the bars B 4 and B 5.Since, during the fourth cornering through the right turn, the first vehicle wheel 28 is the vehicle wheel on the outside of the turn and the second vehicle 30 is the vehicle wheel on the inside of the turn, the first vehicle wheel 28 on the outside of the turn receives more drive torques than the second vehicle wheel 30 on the inside of the turn, so that the wheel torque transmitted to the first vehicle wheel 28 for driving the first vehicle wheel 28 is greater than the wheel torque transmitted to the second vehicle wheel 30 for driving the second vehicle wheel 30. This can be seen again with reference to the bars B 4 and B 5. The wheel torque transmitted to the respective vehicle wheel on the inside of the curve can be 0 or can be greater than 0 in terms of absolute value. The wheel torque transmitted to the respective vehicle wheel on the outside of the curve is preferably greater than 0 in terms of absolute value.In a third part T 6 of FIG. 3, a second straight-ahead travel of the motor vehicle is illustrated, which travels straight-ahead during the second straight-ahead travel. During the second straight-ahead travel, the drive system 10 is operated in the fifth operating mode or else in the fourth operating mode, as has already been described with reference to the part T 3. The highest possible torque that can be transmitted between the rotors 14 and 20 via the friction clutch 34 is also referred to as clutch torque. Via the clutch torque, a drive torque distribution between the vehicle wheels 28 and 30 corresponding to the transverse dynamic requirement can be set with only one active electric machine 12, 18. For this purpose, it is advantageous to switch from one electric machine to the other electric machine if the electric machine assigned to the vehicle wheel on the inside of the curve is preselected. When using position signals, which are embodied, for example, as GPS signals and characterize an in particular current position of the motor vehicle on the earth and are determined, for example, by satellite, and map data can be switched over, for example, in a predictive manner. However, the aim is to realize an imperceptible switchover independently of this. A changeover from one drive machine to the other is virtually neutral in terms of energy.List of reference characters10 Electric drive system 12 First electric machine 14 First rotor 16 First stator 18 Second electric machine 20 Second rotor 22 Second stator 24 Housing 26 Vehicle axle 28 First vehicle wheel 30 Second vehicle wheel 32 Double arrow 34 Friction clutch 36 First transmission device 38 Second transmission device 40 First planetary gear set 42 Second planetary gear set 44 First sun gear 46 First ring gear 48 First planetary carrier 50 Main axis of rotation 52 Planetary gear 54 Second sun gear 56 Second ring gear 58 Second planetary carrier 60 Planetary gear 62 Steering handle B 1 Beam B 2 Beam B 3 Beam B 4 Beam B 6 Beam B 7 Beam T 1 Part T 2 Part T 3 Part T 4 Part T 5 Part T 6 PartReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2018 221 601 A1

[0002]

Claims

Method for operating an electric drive system (10) for a motor vehicle, in which the drive system (10) has: - a first electric machine (12), which has a first rotor (14); - a second electric machine (18), which has a second rotor (20) arranged coaxially with respect to the first rotor (14); - a first vehicle wheel (28), which is permanently coupled in a torque-transmitting manner to the first rotor (14) and is thereby drivable by the first rotor (14) and is assigned to the first electric machine (12); - a second vehicle wheel (30), which is permanently coupled in a torque-transmitting manner to the second rotor (20) and is thereby drivable by the second rotor (20) and is assigned to the second electric machine (18); and - a friction clutch (34) which is designed to connect the first rotor (14) to the second rotor (20) in a rotationally fixed manner, wherein the friction clutch (34) is the only means for coupling the two rotors (14, 20); wherein, in single-engine operation during cornering of the motor vehicle: o, with respect to the electric machines (28, 30), only the electric machine (12, 18) to which the vehicle wheel (28, 30) on the outside of the curve is assigned is operated in a driving manner; and o, the friction clutch (34) is closed up to a degree of closure which is selected such that a specific drive torque distribution takes place starting from the electric machine (12, 18) to which the vehicle wheel (28, 30) on the outside of the curve is assigned, to the two vehicle wheels (28, 30).Method according to Claim 1, characterized in that torque vectoring is carried out during the single-engine operation by selecting the degree of closure in such a way that the vehicle wheel (28, 30) on the outside of the curve receives more drive torque than the vehicle wheel (28, 30) on the inside of the curve.Method according to Claim 1, characterized in that torque vectoring is omitted during the single-engine operation, in that both vehicle wheels (28, 30) receive the same drive torque.Method according to one of the preceding claims, characterized in that the rotors (14, 20) are arranged at least substantially coaxially with respect to the vehicle wheels (28, 30).Method according to one of the preceding claims, characterized in that: - exactly one first transmission device (36) is arranged between the first vehicle wheel (28) and the first rotor (14), via which transmission device the first vehicle wheel (28) is permanently coupled to the first rotor (14) in a torque-transmitting manner; and - exactly one second transmission device (38) is arranged between the second vehicle wheel (30) and the second rotor (20), via which transmission device the second vehicle wheel (30) is permanently coupled to the second rotor (20) in a torque-transmitting manner.Method according to Claim 5, characterized in that: - the first transmission device (36) is designed as a first planetary gear set (40); and - the second transmission device (38) is designed as a second planetary gear set (42).Method according to Claim 6, characterized in that the respective planetary gear set (40, 42) is designed as a respective simple planetary gear set (40, 42).Method according to Claim 6 or 7, characterized in that: - a first sun wheel (44) of the first planetary gear set (40) is connected to the first rotor (14) in a permanently torque-transmitting, in particular permanently rotationally fixed manner; - a first ring wheel (46) of the first planetary gear set (40) is connected to a housing (24) of the drive system (10) in a permanently rotationally fixed manner; - a first planetary carrier (48) of the first planetary gear set (40) is connected to the first vehicle wheel (28) in a permanently torque-transmitting, in particular permanently rotationally fixed manner; - a second sun wheel (54) of the second planetary gear set (42) is connected to the second rotor (20) in a permanently torque-transmitting, in particular permanently rotationally fixed manner; - a second ring wheel (56) of the second planetary gear set (42) is connected to the housing (24) of the drive system (10) in a permanently rotationally fixed manner; and - a second planet carrier (58) of the second planetary gear set (42) is permanently connected to the second vehicle wheel (30) in a torque-transmitting manner, in particular permanently in a rotationally fixed manner.Method according to one of the preceding claims, characterized in that the respective electric machine (12, 18) is designed as a respective axial flow machine.Motor vehicle, having an electric drive system (10) which is designed to carry out a method according to one of the preceding claims.

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