Drive system and drive device for a hybrid vehicle

Abstract

Drive device for a hybrid vehicle (1) comprising a first (VA) and a second driven axle (HA), comprising: a first motor / generator unit (EVA) which is connected to the first driven axle (VA); an internal combustion engine unit (ICE) which is rotationally fixed to a differential / gearbox unit (DCU) which is connected to the second driven axle (RA) designed as a rear axle; a second motor / generator unit (EHA) which is connected in parallel to the internal combustion engine unit (VKM) and is non-rotatably connected to the differential / transmission unit (PDK); a drive clutch unit (FC) designed to disconnect and connect a power flow between the differential / transmission unit (PDK) and the second driven axle (HA); and a control unit (SE) which controls the drive clutch unit (FK), the internal combustion engine unit (VKM), the first engine / generator unit (EVA) and the second engine / generator unit (EHA) depending on predefined operating conditions; wherein the first motor / generator unit (EVA) comprises two electric machines (EM1, EM2) each connected to wheels (21, 22) of the first driven axle (VA), and / or the drive clutch unit (FK) is designed as a friction-locking switching clutch which can be switched by the control unit (SE).

Description

[0001] The present invention relates to a drive method and a drive device for a hybrid vehicle.

[0002] Hybrid drives have different structural variants regarding the transmission of combustion engine-generated power and electric motor-generated power to the drive wheels of a hybrid vehicle.

[0003] US Patent 2009 / 0093336 A1 describes an automatic clutch for a hybrid vehicle. The described automatic clutch is used in the powertrain of a hybrid vehicle, which includes a crankshaft, a motor-generator unit, a transmission unit, and a clutch unit. The hybrid vehicle also includes a traction battery and an internal combustion engine. Furthermore, the vehicle clutch control system includes several powertrain operating modes.

[0004] DE 100 12 221 A1 describes a hybrid drive system for motor vehicles, which has a main drive train between a main engine and a main transmission with a variable gear ratio and which is connected or connectable to a first vehicle axle. In the described hybrid drive system for motor vehicles, a first electric machine is also connected or connectable to the main drive train and a second electric machine is connected or connectable to a second vehicle axle.

[0005] DE 102 32 312 A1 describes a drive system for a motor vehicle with at least one electric motor / generator connected to an electric accumulator and connected to a drive axle, furthermore with a first piston internal combustion engine and at least one further piston internal combustion engine, as well as with a transmission gearbox connecting the piston internal combustion engines, which can be connected to a drive axle via a switchable main clutch, and with a shift clutch arranged between the further piston internal combustion engine and the transmission gearbox.

[0006] DE 10 2010 038 086 A1 discloses a drive device for a hybrid vehicle having a first and a second driven axle, comprising: a first motor / generator unit connected to the first driven axle; an internal combustion engine unit non-rotatably connected to a differential / gearbox unit connected to the rear axle; a second motor / generator unit connected to the differential / gearbox unit; and a control unit which controls the drive clutch unit, the internal combustion engine unit, the first motor / generator unit and the second motor / generator unit depending on predetermined operating conditions.

[0007] One object of the present invention is therefore to provide an improved drive device and an improved drive method for a hybrid vehicle, enabling good adaptation of the operating states according to a predetermined operating strategy.

[0008] Accordingly, a drive device for a hybrid vehicle with the features of claim 1 and a drive method for a hybrid vehicle according to the features of claims 3 and 11 are provided according to the invention.

[0009] The drive method and drive device according to the invention have the advantage that they enable the operating states of the hybrid vehicle to be adapted according to an operating strategy with a simplified design of the drive device.

[0010] The idea underlying the present invention is that an electric motor / generator unit is connected to the internal combustion engine unit of the hybrid vehicle in a rotationally fixed manner and, in particular, is connected to an input shaft of a differential / transmission unit in a non-disconnectable manner.

[0011] The dependent claims contain advantageous further developments and improvements of the respective subject matter of the invention.

[0012] According to a further preferred embodiment, the first motor / generator unit and the second motor / generator unit can each be controlled by the control unit in either motor or generator mode.

[0013] The drive system has operating states which are called up by the control unit, wherein in a first operating state, with the internal combustion engine unit switched on, the first motor / generator unit and the second motor / generator unit are operated as motors, wherein in a second operating state, with the internal combustion engine unit switched on, the first motor / generator unit is operated as a generator and the second motor / generator unit is operated as a generator or as a motor, wherein in a third operating state, with the internal combustion engine unit switched off, the first motor / generator unit is operated as a motor and the second motor / generator unit as a generator, wherein in a fourth operating state, with the internal combustion engine unit switched on, the first motor / generator unit is operated as a motor and the second motor / generator unit as a generator.

[0014] According to a further preferred embodiment of the drive method, the drive method has a further operating state, which is called up by the control unit, wherein, with the internal combustion engine unit switched off, the first motor generator unit and the second motor generator unit are operated as generators.

[0015] According to a further preferred embodiment of the drive method, the drive method has a further operating state which is called up by the control unit, wherein the first motor / generator unit is operated by motor when the internal combustion engine unit is switched off.

[0016] According to a further preferred embodiment of the drive method, the drive method has a further operating state which is called up by the control unit, wherein when the internal combustion engine unit is started, the first motor / generator unit and the second motor / generator unit are operated by motors.

[0017] According to a further preferred embodiment of the drive method, the drive method has a further operating state which is called up by the control unit, wherein, with the internal combustion engine unit switched on, the first motor / generator unit is operated as a motor and the second motor / generator unit is operated as a motor or generator.

[0018] According to a further preferred embodiment of the drive method, the drive method has a first operating state change, which enables a change from an operating state with a switched-off internal combustion engine unit to an operating state with a switched-on internal combustion engine unit by means of motor operation of the second motor / generator unit.

[0019] According to a further preferred embodiment of the drive method, the drive method has a second operating state change, which enables a change from an operating state with a switched-off internal combustion engine unit to an operating state with a switched-on internal combustion engine unit by dragging the internal combustion engine unit along.

[0020] Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description.

[0021] They show: Fig. 1 an exemplary representation of a hybrid vehicle with a drive device according to a first embodiment of the present invention; Fig. 2 an exemplary representation of a drive device for a hybrid vehicle according to a further embodiment of the present invention; Fig. 3 an operating table of the drive device to explain an embodiment of the method according to the invention for a hybrid vehicle; Fig. 4 an operating table of the drive device to explain a further embodiment of the method according to the invention for a drive device; Fig. 5 an operating table of the drive device to explain a further embodiment of the method according to the invention for a drive device; Fig. 6 a speed characteristic curve of an internal combustion engine unit to illustrate a change of operating state according to a further embodiment of the present invention; Fig. 7 a diagram of the respective torques of individual components of the drive device to illustrate a further embodiment of the method according to the invention; Fig. 8 a speed characteristic curve of an internal combustion engine unit to illustrate a change of operating state according to a further embodiment of the present invention; and Fig. 9 a diagram of the respective torques of individual components of the drive device to illustrate an embodiment of the method according to the invention.

[0022] In the figures, the same reference symbols denote identical or functionally equivalent elements - unless otherwise stated.

[0023] In the Fig. Reference numeral 1 denotes a hybrid vehicle which has a drive system. The drive system comprises a first motor / generator unit EVA, which is connected to a first driven axle VA (front axle). Furthermore, the drive system comprises an internal combustion engine unit VKM, which is connected via a differential / transmission unit PDK to a second driven axle HA (rear axle).

[0024] Furthermore, the drive device has a second motor / generator unit EHA, which is connected in parallel to the internal combustion engine unit VKM via the differential / gearbox unit PDK to the second driven axle HA, and a drive clutch unit FK, which is designed to disconnect and connect a power flow between the differential / gearbox unit PDK and the second driven axle HA.

[0025] Furthermore, the drive device includes a control unit SE, which controls the drive clutch unit FK, the internal combustion engine unit VKM, the first motor / generator unit EVA and the second motor / generator unit EHA depending on predetermined operating conditions.

[0026] In this example, wheel 21 and wheel 22 are connected to the first driven axle VA. Wheel 23 and wheel 24 are connected to the second driven axle HA. The second motor / generator unit EHA is connected to the internal combustion engine unit VKM via a first transmission element 50, a second transmission element 45, and a third transmission element 40.

[0027] Furthermore, the third transmission element 40 connects the internal combustion engine unit VKM to the differential / transmission unit PDK. The differential / transmission unit PDK is designed, for example, as a dual-clutch transmission or as an automated manual transmission that enables fully automatic gear changes without interruption of traction by means of two sub-transmissions, and also includes the drive clutch unit FK.

[0028] The control unit SE is connected to the first motor / generator unit EVA via the first control line 61. Furthermore, the control unit SE is connected to the second motor / generator unit EHA via a second control line 62, to the internal combustion engine unit VKM via a third control line 63, and to the differential / transmission unit PDK via a fourth control line 64.

[0029] Fig. Figure 2 shows a hybrid vehicle 1 with a drive device according to a further embodiment of the present invention. In contrast to the Fig. 1 is in Fig. Figure 2 shows how a first motor / generator unit EVA is designed with two separate electric machines EM1 and EM2. The first electric machine EM1 is connected to wheel 21 via the first driven axle VA. Furthermore, the second electric machine EM2 is connected to wheel 22 via the first driven axle VA. The reference numerals not mentioned in the Fig. 2 are in the character description of the Fig. 1 explained.

[0030] Fig. Figure 3 shows an operating table of the drive device of the method according to the invention, comprising an operating strategy, wherein the recall of the individual operating states of the hybrid vehicle 1 is controlled by the control unit SE. The control unit SE controls a change between the individual operating states of the hybrid vehicle 1 according to a predetermined operating strategy. Criteria of the predetermined operating strategy can be, for example, a reduced fuel consumption of the hybrid vehicle 1 or an increase in the range of the hybrid vehicle 1. Furthermore, criteria of the predetermined operating strategy can also include avoiding cooling of a vehicle catalyst or an exhaust aftertreatment system of the hybrid vehicle, or reducing material stress on rotating drive motors or drivetrain components such as the internal combustion engine unit (ICU).For example, the operating strategy, taking into account driving condition variables and other data from the hybrid vehicle or the outside temperature, can achieve a desired driving dynamics of the hybrid vehicle by avoiding or favoring certain operating conditions.

[0031] The operating states are characterized by different modes of the first motor-generator unit EVA, the second motor-generator unit EHA, and the internal combustion engine unit VKM, whereby the first motor-generator unit EVA and the second motor-generator unit EHA can be operated as motors or generators, or can be switched off. The internal combustion engine unit VKM can be switched on or off.

[0032] The respective modes of the first motor-generator unit EVA, the second motor-generator unit EHA, and the internal combustion engine unit VKM are listed in the operating table of the Fig. Figure 3 shows the first, second, third and fourth operating states of the hybrid vehicle 1.

[0033] The first operating state BST comprises a motor-driven (M) first motor / generator unit, a motor-driven (M) second motor / generator unit, and an engaged (E) internal combustion engine VKM. The first operating state BST is implemented, for example, as an electronic boost of the hybrid vehicle 1, whereby the hybrid vehicle 1 is accelerated by positive drive torques from both the internal combustion engine VKM and the electric motor / generator units EHA and EVA.

[0034] The second operating state, LPV, comprises a first engine / generator unit operated as a generator (G) and a second engine / generator unit, EHA, which can be operated as a motor or generator (G / M), with the internal combustion engine unit (VKM) switched on (E). The second operating state, LPV, is designed, for example, as a load point shift of the internal combustion engine unit (VKM), allowing the VKM to be operated under operating parameters most favorable for fuel consumption.

[0035] The third operating state, REK, comprises a motor-driven (M) first motor / generator unit, a generator-driven (G) second motor / generator unit, and a switched-off (A) internal combustion engine unit (VKM). The third operating state, REK, is used, for example, for recuperation during braking of the hybrid vehicle 1 or for energy recovery by the second motor / generator unit (EHA).

[0036] The fourth operating state REX further comprises a first motor / generator unit EVA, which is operated as a motor (M), as well as a second motor / generator unit EHA, which is operated as a generator (G), and an engaged (E) internal combustion engine unit VKM. The fourth operating state REX is designed as a mode to increase the range of the hybrid vehicle 1.

[0037] The Fig. Figure 4 shows an operating table of the drive device to explain a further embodiment of the drive method according to the invention for a drive device.

[0038] Another operating state, LSP, features a first motor / generator unit operating in generator mode (G), a second motor / generator unit operating in generator mode (G), and a switched-off internal combustion engine (VKM). The LSP operating state is designed, for example, as an operating state with long overrun phases for sporty driving.

[0039] Another operating state, RWF, comprises a motor-driven (M) first motor / generator unit and a switched-off (A) second motor / generator unit, EHA, with the internal combustion engine unit VKM switched off (A). The operating state RWF is, for example, implemented as an operating state for the electric reversing of the hybrid vehicle 1.

[0040] In another operating state, AMP, the first motor / generator unit is operated (M) and the second motor / generator unit is operated (M), with the internal combustion engine unit (VKM) being started by an ignition process (Z). The operating state AMP is implemented, for example, as an operating state for starting the hybrid vehicle 1 at a traffic light.

[0041] Another operating state ELAL further comprises a first motor / generator unit EVA, which is operated as a motor (M), as well as a second motor / generator unit EHA, which is operated as a motor or generator (M / G), and an activated (E) internal combustion engine unit VKM. The operating state ELAL is, for example, implemented as an operating state for an electric all-wheel drive of the hybrid vehicle 1.

[0042] The Fig. Figure 5 shows an operating table of the drive device to explain a further embodiment of the drive method according to the invention for a drive device.

[0043] Another operating state, EU20, features a motor-driven (M) first motor / generator unit EVA, a switched-off (A) second motor / generator unit EHA, and a switched-off (A) internal combustion engine VKM. Operating state EU20 is designed, for example, for preparing hybrid vehicle 1 for a new European driving cycle at an outside temperature of 20 °C.

[0044] Another operating state, EU7, comprises a motor-driven (M) first motor / generator unit EVA and a motor-driven (M) second motor / generator unit EHA, with the internal combustion engine unit VKM switched off (A). In the case of a prevailing battery temperature below 15 °C, the first motor / generator unit EVA and the second motor / generator unit EHA are operated in motor or generator mode (G / M), and the internal combustion engine unit VKM is switched on (E). Operating state EU7 is designed, for example, for preparing the hybrid vehicle 1 for a new European driving cycle at an outside temperature of 7 °C.

[0045] In another operating state, FTP20, the first motor / generator unit EVA is operated (M), while the second motor / generator unit EHA and the internal combustion engine unit VKM are switched off (A). Operating state FTP20 is designed, for example, for preparing hybrid vehicle 1 for use in an American driving cycle at an outside temperature of 20 °C.

[0046] Another operating state, HGW, further comprises a first motor / generator unit EVA, which is motor-driven (M), while the second motor / generator unit EHA and the internal combustion engine unit VKM are switched off (A). The operating state HGW is designed, for example, to prepare the hybrid vehicle 1 for a further driving cycle.

[0047] Another operating state, USFTP, features a motor-driven (M) first motor / generator unit EVA, a motor-driven (M) second motor / generator unit EHA, and a switched-off (A) internal combustion engine VKM. The USFTP operating state is designed, for example, to prepare the hybrid vehicle 1 for a further driving cycle that simulates a real-world drive.

[0048] Another operating state, SC03, comprises a motor-driven (M) first motor / generator unit EVA and a switched-off (A) second motor / generator unit EHA, with the internal combustion engine unit VKM switched off (A). Operating state SC03 is designed, for example, to prepare hybrid vehicle 1 for a further driving cycle.

[0049] In another operating state FTP7, the first motor / generator unit EVA is operated as a motor (M) and the second motor / generator unit EHA is operated as a motor (M), with the internal combustion engine unit VKM being started by an ignition process, wherein in the case of a prevailing battery temperature of less than 15 °C the first motor / generator unit EVA and the second motor / generator unit EHA are operated as motors or generators (G / M) and the internal combustion engine unit VKM is switched on (E).

[0050] The operating state FTP7 is designed, for example, for preparing the hybrid vehicle 1 according to an American driving cycle at an outside temperature of 7 °C.

[0051] Another operating state, JC08, further comprises a first motor / generator unit EVA, which is motor-driven (M), while the second motor / generator unit EHA and the internal combustion engine unit VKM are switched off (A). Operating state JC08 is designed, for example, to prepare hybrid vehicle 1 for another driving cycle.

[0052] Fig. Figure 6 shows a diagram of the time course of the rotational speed n of the internal combustion engine unit during a first operating state change, designated as ANL. The first operating state change ANL involves a restart of the internal combustion engine unit VKM, whereby the second engine / generator unit EHA is driven and the internal combustion engine unit VKM, which is rigidly connected to it, begins to rotate at the speed NVKM and can be started at time t1.

[0053] The rotational speed n of the internal combustion engine (VKM) is represented as a characteristic curve (NVKM) in a speed-time diagram. At the time of ignition, the rotational speed of the internal combustion engine (VKM) initially increases linearly, before asymptotically approaching a predetermined target value.

[0054] Fig. Figure 7 shows a torque diagram illustrating the time course of the torques M of the individual components of the drive system. During the first operating state change ANL, the torque of the first electric motor / generator unit MEHA shows a sudden increase at the time of ignition of the internal combustion engine unit VKM. After restarting the internal combustion engine unit VKM, the torque of the first electric motor / generator unit MEHA drops back to zero. The torque of the internal combustion engine MVKM initially exhibits negative values, which is due to the mechanical resistance of the internal combustion engine unit VKM while it is being towed. Only after ignition at time t1 does the internal combustion engine unit VKM transmit the torque MVKM it generates to the drive system.At a later point, the torque delivered by the differential / transmission unit MPDK increases due to a clutch engagement process, thereby accelerating the hybrid vehicle 1.

[0055] Fig. Figure 8 shows the time course of the rotational speed n of the internal combustion engine unit during a second operating state change, designated ANS. The second operating state change ANS can be initiated by the control unit SE if the hybrid vehicle 1 has reached a certain minimum speed. The second operating state change ANS involves restarting the internal combustion engine unit VKM, whereby a frictional connection is established between the second driven axle HA and the internal combustion engine unit VKM by the drive clutch unit FK. Since, in this example, the hybrid vehicle 1 has reached a certain speed, the internal combustion engine unit VKM begins to rotate at speed NVKM after the drive clutch unit FK engages and can therefore be started by the control unit SE. Ignition of the internal combustion engine unit VKM occurs at time t1.

[0056] Fig.Figure 9 shows the time course of the torques M of the individual components of the drive device according to a further embodiment of the present invention. The torque of the internal combustion engine unit MVKM increases linearly after ignition of the internal combustion engine unit VKM and reaches a predetermined setpoint. The torque of the electric machine MEHA decreases from a first value to a second value after ignition at time t1 of the internal combustion engine unit VKM. The torque of the internal combustion engine MVKM initially exhibits negative values, which is due to the mechanical resistance of the internal combustion engine unit VKM during its initial rotation.

Claims

[1] Drive device for a hybrid vehicle (1) comprising a first (FA) and a second driven axle (RA), comprising: a first motor / generator unit (EVA) which is connected to the first driven axle (VA); an internal combustion engine unit (ICE) which is rotationally fixed to a differential / gearbox unit (DCU) which is connected to the second driven axle (RA) designed as a rear axle; a second motor / generator unit (EHA) which is connected in parallel to the internal combustion engine unit (VKM) and is non-rotatably connected to the differential / transmission unit (PDK); a drive clutch unit (FC) designed to disconnect and connect a power flow between the differential / transmission unit (PDK) and the second driven axle (HA); and a control unit (SE) which controls the drive clutch unit (FK), the internal combustion engine unit (VKM), the first engine / generator unit (EVA) and the second engine / generator unit (EHA) depending on predefined operating conditions; wherein the first motor / generator unit (EVA) comprises two electric machines (EM1, EM2) each connected to wheels (21, 22) of the first driven axle (VA), and / or the drive clutch unit (FK) is designed as a friction-locking switching clutch which can be switched by the control unit (SE). [2] Drive device according to claim 1, wherein the first motor / generator unit (EVA) and the second motor / generator unit (EHA) can each be controlled by the control unit (SE) in motor or generator mode. [3] Propulsion method for a hybrid vehicle (1) comprising a first (VA) and a second driven axle (HA), a first motor / generator unit (EVA) connected to the first driven axle (VA) and a differential / transmission unit (PDK) connected to the second driven axle (HA), which is connected to an internal combustion engine unit (VKM) and a second motor / generator unit (EHA); wherein the second motor / generator unit (EHA) is connected in parallel to the internal combustion engine unit (VKM) via the differential / transmission unit (PDK) to the second driven axle (HA); wherein a drive clutch unit (FK) is used to disconnect and connect a power flow between the differential / transmission unit (PDK) and the second driven axle (HA); wherein the first motor / generator unit (EVA) comprises two electric machines (EM1, EM2) each connected to wheels (21, 22) of the first driven axle (VA), and / or the drive clutch unit (FK) is designed as a friction-fit clutch which can be switched by the control unit (SE); and wherein a control unit (SE) controls the drive clutch unit (FK), the internal combustion engine unit (VKM), the first motor / generator unit (EVA) and the second motor / generator unit (EHA) depending on predefined operating conditions. [4] Drive method according to claim 3, wherein operating states of the drive device are called up by the control unit (SE), wherein in a first operating state (BST) with the internal combustion engine unit (VKM) switched on, the first engine / generator unit (EVA) and the second engine / generator unit (EHA) are operated by motors; wherein in a second operating state (LPV) with the internal combustion engine unit (VKM) switched on, the first motor / generator unit (EVA) is operated as a generator and the second motor / generator unit (EHA) is operated as a generator or as a motor; wherein in a third operating state (REK) with the internal combustion engine unit (VKM) switched off, the first motor / generator unit (EVA) is operated as a motor and the second motor / generator unit (EHA) as a generator; in a fourth operating state (REX) with the internal combustion engine unit (VKM) switched on, the first motor / generator unit (EVA) is operated as a motor and the second motor / generator unit (EHA) as a generator. [5] Drive method according to claim 3 or 4, wherein the drive method has a further operating state (LSP) which is called by the control unit (SE), wherein when the internal combustion engine unit (VKM) is switched off, the first motor / generator unit (EVA) and the second motor / generator unit (EHA) are operated as generators. [6] Drive method according to any of the preceding claims 3 to 5, wherein the drive method has a further operating state (RWF) which is called by the control unit (SE), wherein the first motor / generator unit (EVA) is operated in motor mode when the internal combustion engine unit (VKM) is switched off. [7] Drive method according to any one of the preceding claims 3 to 6, wherein the drive method has a further operating state (AMP) which is called by the control unit (SE), wherein when the internal combustion engine unit (ICE) is started the first motor / generator unit (EVA) and the second motor / generator unit (EHA) are motor-driven. [8] Drive method according to any of the preceding claims 3 to 7, wherein the drive method has a further operating state (ELAL) which is called by the control unit (SE), wherein when the internal combustion engine unit (ICE) is switched on the first motor / generator unit (EVA) is operated as a motor and the second motor / generator unit (EVA) is operated as a motor or generator. [9] Drive method according to any one of the preceding claims 3 to 8, wherein the drive method has a first operating state change (ANL) which enables a change from an operating state with an internal combustion engine unit (ICE) switched off to an operating state with an internal combustion engine unit (ICE) switched on by motor operation of the second engine / generator unit (ECU). [10] Drive method according to any one of the preceding claims 3 to 8, wherein the drive method has a second operating state change (ANS) which enables a change from an operating state with an internal combustion engine unit (ICE) switched off to an operating state with an internal combustion engine unit (ICE) switched on by dragging the internal combustion engine unit. [11] Drive system for a hybrid vehicle (1) comprising a first (VA) and a second driven axle (HA), a first motor / generator unit (EVA) connected to the first driven axle (VA) and a differential / transmission unit (PDK) connected to the second driven axle (HA), which is connected to an internal combustion engine unit (VKM) and a second motor / generator unit (EHA); wherein the second motor / generator unit (EHA) is connected in parallel to the internal combustion engine unit (VKM) via the differential / transmission unit (PDK) to the second driven axle (HA); wherein a drive clutch unit (FC) is used to disconnect and connect a power flow between the differential / transmission unit (PDK) and the second driven axle (HA); and wherein a control unit (SE) controls the drive clutch unit (FK), the internal combustion engine unit (VKM), the first motor / generator unit (EVA) and the second motor / generator unit (EHA) depending on predefined operating states such that operating states of the drive device are called up by the control unit (SE), wherein in a first operating state (BST) with the internal combustion engine unit (VKM) switched on, the first engine / generator unit (EVA) and the second engine / generator unit (EHA) are operated by motors; wherein in a second operating state (LPV) with the internal combustion engine unit (VKM) switched on, the first motor / generator unit (EVA) is operated as a generator and the second motor / generator unit (EHA) is operated as a generator or as a motor; wherein in a third operating state (REK) with the internal combustion engine unit (VKM) switched off, the first motor / generator unit (EVA) is operated as a motor and the second motor / generator unit (EHA) as a generator; in a fourth operating state (REX) with the internal combustion engine unit (VKM) switched on, the first motor / generator unit (EVA) is operated as a motor and the second motor / generator unit (EHA) as a generator.

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