Drive train for a vehicle, in particular a motor vehicle

Abstract

A drive train (10) for a vehicle, in particular for a motor vehicle, comprising at least one electric machine (18) operable in generator mode for supplying an on-board power supply with electric current, and comprising a dual-clutch transmission (20) having at least one first shaft (42), at least one second shaft (32), a first clutch (36) associated with the first shaft (42), a second clutch (38) associated with the second shaft (32), and at least one input element (40) common to the clutches (36, 38) and coupleable to a drive unit (12), which input element can be coupled to the first shaft (42) via the first clutch (36) and to the second shaft (32) via the second clutch (38), wherein a switching device (50) is provided which can be switched between a first switching state (1), in which the electric machine (18) is coupled to the input element (40), and a second switching state (2),in which the electrical machine (18) is coupled to one of the shafts (32, 42), characterized in that the switching device (50) can be switched into a third switching state (3) in which the electrical machine (18) is coupled to the other shaft (32), wherein the electrical machine (18) is decoupled from the shafts (32, 42) in the first switching state, from the input element (40) and from the other shaft (32) in the second switching state, and from the input element (40) and from one shaft (42) in the third switching state.

Description

[0001] The invention relates to a drive train for a vehicle, in particular a motor vehicle, according to the preamble of patent claim 1.

[0002] Such drive trains for vehicles, in particular motor vehicles such as passenger cars, are already sufficiently known from the general prior art. Such a drive train comprises at least one electric machine which can be operated in generator mode. The electric machine is thus designed at least as a generator by means of which an on-board electrical system of the vehicle can be supplied with electrical current. Electrical consumers of the vehicle can then be supplied with electrical current via the on-board electrical system. Alternatively or additionally, the electrical current fed into the on-board electrical system by the electric machine or generator can be stored in an electrical storage device such as a battery.

[0003] The drive train further comprises a dual-clutch transmission having at least a first shaft and at least one second shaft. The dual-clutch transmission further comprises a first clutch associated with the first shaft, a second clutch associated with the second shaft, and at least one input element common to the clutches that can be coupled to a drive unit. The input element can be coupled to the first shaft via the first clutch and to the second shaft via the second clutch.

[0004] For example, at least one of the shafts is a transmission input shaft. Furthermore, it can be provided that at least one of the shafts is designed as a countershaft. The clutches form a so-called double clutch, wherein the clutches can each be selectively opened and closed. For example, in the finished state of the vehicle, the input element is coupled to the at least one drive unit, so that the torque provided by the drive unit is transmitted to the input element. For example, the input element is a clutch bell housing common to the clutches or a so-called clutch basket, which can be driven by the drive unit. As a result, torques provided by the drive unit can be introduced into the double clutch via the input element.

[0005] To couple the input element to the first shaft, the first clutch is closed, while the second clutch is preferably open. This transfers the torque transmitted to the input element to the first shaft via the closed first clutch. To couple the input element to the second shaft, the second clutch is closed, while the first clutch is preferably open. This transfers the torque transmitted to the input element to the second shaft via the closed second clutch.

[0006] If the shafts are designed as transmission input shafts, the dual clutch transmission can comprise at least one countershaft which can be driven by at least one of the transmission input shafts and on which gear wheels for respective gears of the dual clutch transmission are arranged. By means of the dual clutch transmission it is thus possible in the sufficiently known manner to drive the vehicle via an engaged first gear of the dual clutch transmission, while a second gear of the dual clutch transmission, different from the first gear, is already engaged. In this case, for example, the first clutch is initially engaged, while the second clutch is disengaged. In order to realize a particularly fast change from first gear to second gear, the first clutch is disengaged and the second clutch is engaged, so that the vehicle is then driven via the engaged second gear.In this way, it is possible to avoid or minimize interruptions in traction when shifting or changing gears.

[0007] Furthermore, drive trains are known from the general state of the art in which a starter, in particular in the form of a so-called pinion starter, and a separate generator are provided. The starter is used for starting, i.e. for starting or activating the drive unit designed as an internal combustion engine, wherein the generator can be driven by the internal combustion engine in order to feed electrical current provided by the generator into the on-board electrical system. Alternatively, it is possible to use a so-called starter-generator instead of the starter and the separate generator, which is coupled to the internal combustion engine, for example via a traction drive such as a belt drive. Alternatively, it is possible to couple the starter-generator to the internal combustion engine via a gearing, for example directly on the crankshaft.The starter generator can be used to start the internal combustion engine. It can also be driven by the internal combustion engine and thus convert mechanical energy into electrical energy, or electric current, which can then be fed into the vehicle's electrical system.

[0008] Furthermore, a so-called coasting operation is known from the general state of the art, in which vehicles, in particular motor vehicles, can be operated. Such coasting operation is usually also referred to as sailing mode and is described, for example, in DE 10 2008 029 453 A1, DE 10 2011 005 284 A1, DE 10 2011 005 320 A1, DE 10 2012 008 632 A1 and DE 10 2012 105 307 A1. To implement coasting operation, for example, a clutch is opened to decouple the internal combustion engine from the drive train. This allows the vehicle to roll and thus move due to its kinetic energy, without this rolling or movement being impaired by the drag torque of the internal combustion engine, i.e., the so-called engine drag torque.Furthermore, to implement coasting, it is possible to shift a transmission in the drivetrain to neutral, or idle, so that no gear is engaged. This decouples the vehicle's wheels, over which the vehicle rolls along a roadway, from the activated internal combustion engine, so that the vehicle's movement or rolling is not affected by the drag torque of the internal combustion engine (so-called coasting).

[0009] In addition, the combustion engine can be deactivated or switched off during coasting (so-called engine start-stop coasting) in order to keep the vehicle's energy consumption or fuel consumption particularly low.

[0010] During coasting, the problem typically arises of feeding electrical power into the vehicle's electrical system via the generator or electric motor. Since the internal combustion engine is decoupled from the drivetrain and deactivated during coasting or sailing, and especially during engine start-stop sailing (corresponding to a "disconnected" state), the generator cannot be driven either by the internal combustion engine itself or by the vehicle's wheels via the internal combustion engine. Activating the deactivated internal combustion engine to use the generator to supply the vehicle's electrical system would lead to undesirable fuel consumption.This means that with a conventional connection of the generator to the drive train or the internal combustion engine, it is not possible to supply the vehicle electrical system with electrical power without rotating or dragging the internal combustion engine, which results in undesirable drag losses. Thus, the generator cannot supply the vehicle electrical system with electrical power during engine start-stop coasting, i.e., when the internal combustion engine is switched off.

[0011] Therefore, it is usually provided that the on-board electrical system is supplied with electrical energy from at least one electrical energy storage device, such as a battery and / or so-called supercapacitors, when coasting. These energy storage devices are charged, for example, during deceleration phases by recuperating the vehicle's kinetic energy. If the on-board electrical system is supplied with electrical power from at least one such electrical energy storage device when coasting, it is expedient to use a particularly powerful and therefore large and weight-intensive energy storage device in order to meet the requirements regarding the supply of electrical energy to the on-board electrical system when the combustion engine is deactivated.However, it has been shown that coasting increases the load on the electrical energy storage device, especially in the form of a battery, due to frequent charging and discharging cycles, which can negatively impact the service life of the energy storage device. The use of a large and weight-intensive energy storage device leads to space and packaging problems, as well as high costs and a high weight of the powertrain and thus of the vehicle as a whole.

[0012] DE 102 09 514 A1 discloses a drive train. EP 2 383 139 A1 discloses a hybrid vehicle.

[0013] The object of the present invention is therefore to provide a drive train of the type mentioned at the outset in which the electric machine can be driven particularly efficiently, in particular during sailing operation of the vehicle.

[0014] This object is achieved by a drive train having the features of patent claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims. In order to further develop a drive train of the type specified in the preamble of patent claim 1 such that the electric machine can be driven particularly efficiently, in particular during coasting operation, in particular during idle coasting, of the vehicle in order to thereby, for example, be able to supply the vehicle's on-board network with electrical power particularly efficiently even during coasting operation, a switching device is provided according to the invention which can be switched between a first switching state and a second switching state. In the first switching state, the electric machine is coupled to the input element.This makes it possible, for example, to drive the electric machine in its generator mode via the input element by means of the activated drive unit, which is designed, for example, as an internal combustion engine, so that, for example, mechanical energy provided by the drive unit can be transferred to the electric machine via the input element and converted into electrical energy or electrical current by means of the electric machine, whereby the electrical current can then be fed into the vehicle electrical system.

[0015] In the second switching state, the electric motor is coupled to one of the shafts. This makes it possible, for example, to drive the electric motor in generator mode via the shaft, e.g., designed as a countershaft, and thus, for example, via the vehicle's wheels, which roll along a roadway when the vehicle is moving. Both clutches are open, so that, for example, the drive unit is decoupled from the drivetrain during coasting, and the internal combustion engine can be deactivated.In other words, in the second switching state of the switching device, it is possible to drive the electric machine in its generator mode via the shaft using kinetic energy from the moving vehicle rolling along a roadway via its wheels, while the drive unit, which is designed, for example, as an internal combustion engine, is decoupled from the drive train and deactivated, i.e., is switched off. Kinetic energy from the vehicle can be transferred via the shaft to the electric machine, which, in its generator mode, converts at least part of the provided kinetic energy into electrical energy or electrical current, which can then be fed into the vehicle electrical system.

[0016] The aforementioned coasting mode means that the internal combustion engine is decoupled from the drive train. The internal combustion engine can be deactivated, so that coasting mode is designed as what is known as engine start-stop coasting mode. If the internal combustion engine is decoupled from the drive train during coasting mode and activated at the same time, i.e. if the internal combustion engine is running during coasting mode, then the coasting mode is what is known as idle coasting mode. This is set, for example, to be able to respond quickly to a driver's input regarding load requirements. In both cases, i.e. in engine start-stop coasting mode and idle coasting mode, the internal combustion engine consumes less fuel than if the electric motor also had to be driven.

[0017] The described decoupling and possible deactivation of the drive unit is provided, for example, during coasting mode of the vehicle, in which the on-board electrical system can be supplied with electrical power via the electric motor. However, since the drive unit is decoupled from the drive train by disengaging both clutches, the described movement or rolling of the vehicle is not affected by the drag torque of the drive unit.

[0018] Since the electric motor can be driven via the shaft even when the vehicle is coasting, the on-board electrical system can be supplied with electrical power by the electric motor during coasting. Thus, it is neither intended nor necessary to supply the on-board electrical system exclusively with power stored in an electrical energy storage device such as a battery or supercapacitor. As a result, it is possible to use electrical energy storage devices with small external dimensions and low weight, thus keeping the costs, weight, and installation space requirements of the drive train particularly low.

[0019] The switching device is designed, for example, as a transmission through which the electric machine is connected to the drive train. The transmission comprises, for example, switchable gear stages, in particular spur gear stages, to enable the described switchability of the switching device between the switching states. This also makes it possible, for example, to drive the electric machine at particularly advantageous speeds in the respective switching states, thus achieving particularly efficient or high-efficiency operation of the electric machine.

[0020] In the invention, the switching device can be switched into a third switching state in which the electric machine is coupled to the other shaft. This allows the electric machine to be driven and consequently provide electrical energy or electrical current and feed it into the vehicle electrical system even when both clutches are open and consequently the input element and thus the drive unit are decoupled from the drive train. Furthermore, particularly efficient operation of the electric machine can be achieved because the electric machine can, for example, be driven optionally via one shaft or the other shaft. This allows the electric machine to be operated at the respective speeds as required, so that particularly efficient operation of the electric machine and thus of the drive train as a whole can be achieved.

[0021] In the invention, the electric machine is decoupled from the shafts in the first switching state, from the input element and the other shaft in the second switching state, and from the input element and one shaft in the third switching state. This allows unfavorable and undesirable impairments to the operation of the electric machine to be avoided.

[0022] In an advantageous embodiment of the invention, the electric machine is decoupled from one shaft in the first switching state and from the input element in the second switching state of the switching device, thereby enabling particularly efficient operation of the electric machine. This makes it possible for the operation of the electric machine to be unaffected by the shaft in the first switching state and unaffected by the input element in the second switching state.

[0023] It has also proven particularly advantageous if one shaft is a countershaft, on which gear wheels for the respective gears of the dual-clutch transmission are located. This allows the electric motor to be connected to the drivetrain in a particularly space-efficient manner.

[0024] The other shaft is, for example, a first transmission input shaft of the dual-clutch transmission, which, for example, has a second transmission input shaft, wherein the countershaft is drivable via at least one of the transmission input shafts. The dual-clutch transmission can have a second countershaft drivable by the other transmission input shaft, on which additional gear sensors for respective additional gears of the dual-clutch transmission are arranged. This makes it possible, for example, to minimize the axial space requirement of the dual-clutch transmission and thus of the drive train as a whole.

[0025] In a particularly advantageous embodiment of the invention, it is provided that the other shaft is a transmission input shaft of the dual-clutch transmission.

[0026] It has also proven particularly advantageous if the electric machine can be operated in motor mode. In generator mode, the electric machine acts as a generator, by means of which mechanical energy, which is transmitted to the generator, for example, via one of the shafts or the input element, is converted into electrical energy. In motor mode, the electric machine acts as a motor or electric motor, by means of which, for example, the drive unit designed as an internal combustion engine can be started, i.e. started or activated. Furthermore, hybridization of the drive train is conceivable in this case, since, for example, wheels of the vehicle can be driven via one of the shafts or the input element by means of the electric machine in its motor mode. In this case, the wheels can be driven purely electrically, for example.Alternatively or additionally, the electric machine can, in its motor operation, electrically support the driving of the wheels caused by the internal combustion engine, so that, for example, an electric boost operation or a load point shift can be realized, so that a particularly efficient operation of the drive unit designed as an internal combustion engine with only low energy consumption or fuel consumption can be realized.

[0027] The invention also includes a vehicle, in particular a motor vehicle such as a passenger car, with a drive train according to the invention. Advantageous embodiments of the drive train according to the invention are to be regarded as advantageous embodiments of the vehicle according to the invention, and vice versa.

[0028] Also disclosed is a method for operating a drive train according to the invention, which is not part of the invention. Advantageous embodiments of the drive train according to the invention are to be regarded as advantageous embodiments of the method according to the invention, and vice versa.

[0029] It has proven particularly advantageous if the vehicle is operated in coasting mode, in which both clutches are open and the second switching state or the third switching state of the switching device is selected. This makes it possible to decouple the input element and thus the drive unit from the drive train, as both clutches are open. To achieve only low energy consumption, the drive unit is preferably deactivated, i.e. put away. In coasting mode, the vehicle's kinetic energy can be used, so that the vehicle can roll or move without this rolling or moving being affected by the drag torque of the drive unit. Nevertheless, in coasting mode, the vehicle's on-board electrical system can be supplied with electrical power by the electric machine in its generator mode, since the electric machine is driven via one shaft or the other.

[0030] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figure, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0031] The drawing shows in the only figure a schematic representation of a drive train for a vehicle in the form of a motor vehicle, in particular a passenger car.

[0032] The figure shows a schematic representation of a drive train, designated overall by 10, for a vehicle in the form of a motor vehicle, in particular a passenger car. The drive train 10 comprises a drive unit in the form of an internal combustion engine 12, which is, for example, a three-cylinder in-line engine and has a cylinder housing 14. Three combustion chambers in the form of cylinders 16 are formed by the cylinder housing 14. Respective pistons in the form of cylinders 16 are accommodated in the cylinders 16 for translational movement, which pistons are articulatedly coupled via respective connecting rods to an output shaft in the form of a crankshaft of the internal combustion engine 12. Alternatively, it is possible for the internal combustion engine 12 to be designed as a rotary piston engine.When the internal combustion engine 12 is activated, fuel and air are introduced into the cylinders 16 during firing operation, forming a respective fuel-air mixture in the cylinders 16. This fuel-air mixture is combusted. The expansion resulting from the combustion drives the pistons and, as a result, the crankshaft.

[0033] The drive train 10 further comprises an electric machine 18, which can be operated at least in generator mode and thus as a generator. Preferably, the electric machine 18 can also be operated in motor mode and thus as an electric motor.

[0034] The drive train 10 further comprises a dual-clutch transmission, designated as a whole by 20. Finally, the drive train 10 comprises at least one axle 22 of the passenger car, wherein the axle 22 is, for example, a rear axle of the passenger car. The axle 22 comprises wheels 24, which are driven wheels. This means that the passenger car as a whole can be driven via the wheels 24. For this purpose, the wheels 24 are coupled via respective drive shafts 26 to an axle transmission 28, which is, for example, a rear axle transmission (HAG). The wheels 24 and thus the passenger car as a whole can thus be driven via the axle transmission 28 and the drive shafts 26.

[0035] The dual-clutch transmission 20 comprises a first shaft in the form of a first transmission input shaft 30 and a second shaft in the form of a second transmission input shaft 32, which is designed as a hollow shaft. The first transmission input shaft 30 extends through said hollow shaft. Furthermore, the dual-clutch transmission 20 comprises a dual clutch, designated overall by 34, with a first clutch 36 assigned to the first transmission input shaft 30 and a second clutch 38 assigned to the second transmission input shaft 32. The dual clutch 34 further comprises an input element common to the clutches 36 and 38, in this case in the form of a clutch basket 40, which is coupled to the crankshaft of the internal combustion engine 12 in a torque-transmitting manner.As a result, torques provided by the internal combustion engine 12 via its crankshaft are transmitted to the clutch basket 40, so that the clutch basket 40 is driven when the internal combustion engine 12 is activated and operating in its fired mode. The transmission input shafts 30 and 32 are so-called clutch output shafts of the dual clutch 34!.

[0036] The clutch basket 40 can be coupled to the first transmission input shaft 30 via the first clutch 36 in a torque-transmitting manner by engaging the first clutch 36. During this time, the second clutch 38 is preferably disengaged. Furthermore, the clutch basket 40 can be coupled to the second transmission input shaft 32 via the second clutch 38 in a torque-transmitting manner by engaging the second clutch 38, while preferably the first clutch 36 is disengaged. In other words, if, for example, the first clutch 36 is engaged while the second clutch 38 is disengaged, the clutch basket 40 and, via it, the internal combustion engine 12 are coupled to the first transmission input shaft 30 via the first clutch 36 in a torque-transmitting manner and are decoupled from the second transmission input shaft 32.

[0037] If, for example, the second clutch 38 is closed while the first clutch 36 is open, the clutch basket 40 and, via it, the internal combustion engine 12, in particular the crankshaft, are coupled to the second transmission input shaft 32 in a torque-transmitting manner and are decoupled from the first transmission input shaft 30. The torque-transmitting coupling means that torques can be transmitted between the internal combustion engine 12, in particular its crankshaft, and the respective transmission input shaft 30 or 32. The transmission input shaft 32 or 30, decoupled from the crankshaft, can then rotate relative to the crankshaft.

[0038] The dual-clutch transmission 20 further comprises a third shaft in the form of a first countershaft 42, on which first gear wheels for respective gears of the dual-clutch transmission 20 are arranged. The first countershaft 42 is coupled to the first transmission input shaft 30 and can thus be driven by the first transmission input shaft 30. Furthermore, the dual-clutch transmission 20 comprises a fourth shaft in the form of a second countershaft 44, on which further gear wheels for respective further gears of the dual-clutch transmission 20 are arranged. The second countershaft 44 is coupled to the second transmission input shaft 32 and can therefore be driven by the second transmission input shaft 32. Furthermore, the dual-clutch transmission 20 comprises an output common to the countershafts 42 and 44 in the form of a gear 46, on which both countershafts 42 and 44 act. The gear 46 is non-rotatably coupled to a shaft 48.Shaft 48 is a transmission input shaft with respect to axle drive 28, since torques provided by the respective countershaft 42 or 44 can be transmitted to gear 46 and via this to shaft 48 and introduced via shaft 48 into axle drive 28. Via axle drive 28, the provided or introduced torques are transmitted to the cardan shafts 26 and via these in turn to the wheels 24, so that - when one of the clutches 36 or 38 is closed - the wheels 24 can be driven by the internal combustion engine 12 or vice versa.

[0039] For example, the gear wheels of odd-numbered gears of the dual-clutch transmission 20 are arranged on the first countershaft 42. This means that, for example, the gear wheels of a first gear, a third gear, a fifth gear, and a seventh gear of the dual-clutch transmission 20 are arranged on the countershaft 42. The gear wheels of so-called even-numbered gears of the dual-clutch transmission 20 are arranged on the countershaft 44. This means, for example, that the gear wheels of a second gear, a fourth gear, and a sixth gear of the dual-clutch transmission 20 are arranged on the countershaft 44. It is understood that the dual-clutch transmission 20 can alternatively have just one countershaft. The function of such a dual-clutch transmission is well known and will not be explained in more detail below.

[0040] Within the scope of a method for operating the drive train 10, the drive train 10 or the passenger car can be operated in coasting mode. If the drive train 10 or the passenger car is operated in coasting mode, both clutches 36 and 38 are opened, so that the clutch basket 40 and thus the internal combustion engine 12 are decoupled from the drive train 10. Thus, the clutch basket 40 and the internal combustion engine 12 cannot be driven by the wheels 24 when the passenger car is moving and the wheels 24 are rolling on a roadway. Conversely, however, this also means that this movement or rolling of the moving passenger car is not impaired by the drag torque of the internal combustion engine 12. As a result, the passenger car can roll a particularly long distance without having to be powered by the internal combustion engine 12.This allows fuel consumption to be kept particularly low. If the coasting mode is performed as engine start-stop coasting mode, the internal combustion engine 12 is decoupled from the drive train 10 and deactivated during the coasting mode. If the coasting mode is performed as idle coasting mode, the internal combustion engine 12 is decoupled from the drive train 10 and activated during the coasting mode, i.e., the internal combustion engine 12 runs during the coasting mode.

[0041] However, in order to feed electrical energy or electrical current into the on-board network via the electrical machine 18 even during sailing operation and to achieve particularly efficient drive or operation of the electrical machine 18, the drive train 10 comprises a switching device 50 which can be switched between three switching states 1, 2 and 3. The switching device 50 is designed, for example, as a gearbox and comprises three gears 52, 54 and 56, which are designed, for example, as spur gears. Furthermore, the switching device 50 comprises a shaft 58 on which the gears 52, 54 and 56 are arranged. The shaft 58 is, for example, rotationally fixedly coupled to a shaft of a rotor of the electrical machine 18 or can be coupled or is designed as this shaft of the rotor of the electrical machine 18.This means that it can be provided that the shaft 58 can be coupled to the shaft of the rotor in a rotationally fixed manner, for example by means of a coupling device, and can be decoupled or uncoupled from the shaft of the rotor. The gears 52, 54 and 56 are, for example, loose wheels which, although arranged on the shaft 58, are fundamentally rotatable relative to the shaft 58. In order to couple the gears 52, 54 and 56 in a rotationally fixed manner to the shaft 58 as required, corresponding coupling elements can be provided, for example in the form of shift sleeves or sliding sleeves. This makes it possible, for example, to couple the gear 52 in a rotationally fixed manner to the shaft 58, while the gears 54 and 56 are decoupled from the shaft 58 and are therefore rotatable relative to the shaft 58.The same can be applied to gears 54 and 56, so that, for example, gear 54 is non-rotatably coupled to shaft 58, while the other gears 52 and 56 are decoupled from shaft 58 and are therefore rotatable relative to shaft 58. Furthermore, it is possible to non-rotatably couple gear 56 to shaft 58, while the remaining gears 52 and 54 are decoupled from shaft 58 and are therefore rotatable relative to shaft 58.

[0042] In the first switching state 1, the electric machine 18 is coupled to the clutch basket 40 via the switching device 50, in particular the gear 52, and is decoupled from the countershaft 42 and the transmission input shaft 32. It is preferably provided that the gear 52 is coupled to the shaft 58 in the first switching state, so that the electric machine 18 can be driven by the clutch basket 40 via the shaft 58 and the gear 52, or vice versa.

[0043] In the second switching state, the electric machine 18 is coupled to the first countershaft 42 and thus to the transmission input shaft 30 via the switching device 50, in particular the gear 56, and is decoupled from the transmission input shaft 30 or the second countershaft 44 and from the clutch basket 40. The gear 56 is coupled to the shaft 58. This makes it possible in the second switching state for the electric machine 18 to be driven by the countershaft 42 via the shaft 58 and the gear 56, or vice versa. Finally, in the third switching state, it is provided that the electric machine 18 is coupled to the second transmission input shaft 32 and thus to the countershaft 44 via the switching device 50, in particular the gear 54, and is decoupled from the clutch basket 40 and the first countershaft 42 or the transmission input shaft 30.

[0044] Preferably, the gear 54 is coupled to the shaft 58 in the third switching state 3. In the third switching state, the electric machine 18 can be driven by the transmission input shaft 32 via the shaft 58 and the gear 54, or vice versa.

[0045] Overall, it can be seen that in the first switching position 1, the electric machine 18 is connected to the internal combustion engine 12 via the clutch basket 40. The first switching state 1 is selected, for example, when the passenger car is stationary and the internal combustion engine 12 is running, i.e., activated, whereby the speed of the electric machine 18 can correspond to the speed of the crankshaft. In this case, the electric machine 18 is preferably operated in its generator mode, so that the mechanical energy provided by the internal combustion engine 12 can be converted into electrical energy.

[0046] In the second switching state 2 and the third switching state 3, it is possible to couple the electric machine 18 to the drive train 10, particularly in generator mode, at different speeds while maintaining the same driving speed of the passenger vehicle. The second switching state 2 or the third switching state 3 is set, for example, when the internal combustion engine 12 is switched off, i.e., in coasting mode. Depending on the current driving speed, one of the switching states 2 and 3 is selected so that the electric machine 18 can be operated in an at least substantially optimal speed operating range and thus with particularly favorable efficiency.The second switching state 2 represents a mechanical connection of the electric machine 18 to the odd gears or the countershaft 42, wherein the third switching state 3 establishes a mechanical connection of the electric machine 18 to the even gears or, via the transmission input shaft 32, to the countershaft 44. All three switching states enable the operation of the electric machine 18 as a generator while the passenger car is powered by the internal combustion engine 12. Switching states 1, 2, and 3 differ in terms of their gear ratios, via which the electric machine 18 is connected to the drive train 10. This enables at least almost optimal operation of the electric machine 18 in generator mode, since the electric machine 18 can be operated in an at least almost optimal speed range and thus with at least almost optimal efficiencies.

[0047] In addition, switching states 2 and 3 enable the operation of the electric machine 18 when the internal combustion engine 12 is switched off, i.e. when it is decoupled and deactivated from the drive train 10 by opening the clutches 36 and 38, so that during coasting operation and during recuperation of the kinetic energy of the passenger car, the on-board electrical system can continue to be supplied with electrical current via the electric machine 18 in its generator mode.

[0048] Furthermore, it is possible to start, i.e., to activate, the internal combustion engine 12 in its motor mode by means of the electric machine 18. For this purpose, the first switching state 1 is set, so that torques provided by the electric machine 18 in its motor mode are transmitted via the shaft 58 and the gear 52 to the clutch basket 40 and finally to the crankshaft. This makes it possible to activate the internal combustion engine 12 in its motor mode by means of the electric machine 18 when the passenger car is stationary and also when the passenger car is moving, i.e., when the passenger car has a driving speed greater than 0.

[0049] Overall, it is possible to connect the electric motor 18 to the drive train 10 particularly easily and cost-effectively, while also achieving particularly efficient and high-efficiency operation during coasting. In other words, it is possible to enable energy-efficient coasting of the passenger car with the internal combustion engine 12 deactivated and decoupled from the drive train 10, to realize an efficient supply of electrical power to the vehicle electrical system via the electric motor 18 during coasting, and to enable particularly high energy recovery efficiency during recuperation.It is possible to use particularly lightweight and cost-effective electrical energy storage devices, such as batteries with only small external dimensions, and to keep the number of such electrical energy storage devices particularly low, so that overall the costs, weight and installation space requirements of the drive train 10 can be kept low.

Claims

[1] Drive train (10) for a vehicle, in particular for a motor vehicle, with at least one electric machine (18) operable in generator mode for supplying an on-board power supply with electric current, and with a dual-clutch transmission (20) which has at least one first shaft (42), at least one second shaft (32), a first clutch (36) associated with the first shaft (42), a second clutch (38) associated with the second shaft (32), and at least one input element (40) common to the clutches (36, 38) and which can be coupled to a drive unit (12), which can be coupled to the first shaft (42) via the first clutch (36) and to the second shaft (32) via the second clutch (38), wherein a switching device (50) is provided which can be switched between a first switching state (1), in which the electric machine (18) is coupled to the input element (40), and a second switching state (2),in which the electric machine (18) is coupled to one of the shafts (32, 42), characterized by that the switching device (50) can be switched into a third switching state (3) in which the electrical machine (18) is coupled to the other shaft (32), wherein the electrical machine (18) is decoupled from the shafts (32, 42) in the first switching state, from the input element (40) and from the other shaft (32) in the second switching state, and from the input element (40) and from the one shaft (42) in the third switching state. [2] Drive train (10) according to claim 1, characterized by that the electrical machine (18) is decoupled from one shaft (42) in the first switching state (1) and from the input element (40) in the second switching state (2) of the switching device (50). [3] Drive train (10) according to one of claims 1 or 2, characterized bythat one shaft (42) is a countershaft (42) on which gear wheels for respective gears of the dual clutch transmission (20) are arranged. [4] Drive train (10) according to one of the preceding claims, characterized by that the other shaft (32) is a transmission input shaft (32) of the dual clutch transmission (20). [5] Drive train (10) according to one of the preceding claims, characterized by that the electric machine (18) can be operated in a motor mode. [6] Vehicle, in particular motor vehicle, with a drive train (10) according to one of the preceding claims.

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