Drive system for a hybrid vehicle and methods for operating such a drive system

Abstract

Drive system for a hybrid vehicle, with an internal combustion engine (12) which has an internal combustion engine shaft (14) and can drive, a vehicle transmission (16) which has a transmission shaft (18) arranged coaxially to the combustion engine shaft (14) on the drive side, a flywheel drive unit (20) which is arranged between the internal combustion engine (12) and the vehicle transmission (16) and has an intermediate shaft (22) arranged coaxially to the internal combustion engine shaft (14), a first clutch (24) for coupling or uncoupling the internal combustion engine shaft (14) and the intermediate shaft (22), a second clutch (26) for coupling or decoupling the intermediate shaft (22) and the transmission shaft (18), an electric machine (28) which has an electric machine shaft (30) and can drive it in a motor operation, as well as a transverse drive module (32) that couples the electric machine shaft (30) with the intermediate shaft (22), wherein at least one working machine (34, 36) is provided and is connected to the electric machine shaft (30) for drive purposes, and wherein the electric machine (28) is also designed as a generator and is configured so that when a vehicle brake (62) is applied, a desired vehicle deceleration is first generated by an electric braking torque adjustable via the resistance of the electric machine (28), and only when a maximum electric braking torque is reached is a friction brake (64) of the vehicle engaged.

Description

[0001] The invention relates to a drive system for a hybrid vehicle and a method for operating such a drive system.

[0002] To propel hybrid vehicles in an energy-efficient manner, it is known from the prior art to disengage the power transmission in the drivetrain while the combustion engine is running when the accelerator pedal is not depressed, i.e., when no active vehicle acceleration is desired, thus entering a state of so-called "idling coasting". Furthermore, it is also known to switch off the combustion engine with the power transmission in the drivetrain engaged when the accelerator pedal is not depressed, resulting in mechanical coasting.

[0003] However, a particularly energy-saving shutdown of the combustion engine is currently rare and only occurs for short periods, as the combustion engine must ensure the power supply to the vehicle's electrical system. This system is usually heavily loaded due to the numerous electrical consumers in the vehicle's now extensive electronics. Furthermore, the electrical system typically needs to be able to provide a high starting current when the combustion engine is restarted.

[0004] DE 199 41 705 A1 shows a drive train comprising a drive unit with a drive shaft, an output unit and an electric machine operatively connected to these.

[0005] A drive system is known from DE 195 49 259 A1. The drive system comprises an internal combustion engine, an electric machine, and a traction control system. The electric machine is designed such that traction slip reduction can be achieved using the electric machine.

[0006] US Patent 6,668,953 B1 discloses a powertrain comprising an internal combustion engine, a transmission, and an energy converter located between the engine and the transmission. A first clutch is located between the engine and the energy converter, and a second clutch is located between the transmission and the energy converter. The energy converter is driven by at least one accessory to power the accessory using energy derived either from the rotary motion of the engine crankshaft or from the rotary motion transmitted from the vehicle's drive wheels through the transmission.

[0007] Therefore, the object of the invention is to create a drive system for a hybrid vehicle and a method for operating the drive system that enables a particularly frequent and long-lasting operating state with the combustion engine switched off, so that a particularly energy-efficient drive of the hybrid vehicle can be realized.

[0008] This problem is solved according to the invention by a drive system for a hybrid vehicle, comprising an internal combustion engine which has and can drive an internal combustion engine shaft, a vehicle transmission which has a transmission shaft arranged coaxially to the internal combustion engine shaft on the drive side, a flywheel drive unit which is arranged between the internal combustion engine and the vehicle transmission and which has an intermediate shaft arranged coaxially to the internal combustion engine shaft, a first clutch for coupling or decoupling the internal combustion engine shaft and the intermediate shaft, a second clutch for coupling or decoupling the intermediate shaft and the transmission shaft, an electric machine which has an electric machine shaft and can drive it in motor operation, and a transverse drive module which couples the electric machine shaft to the intermediate shaft, wherein at least one driven machine is provided and is connected to the electric machine shaft in a drive manner.wherein the electric machine is also designed as a generator and is designed such that when a vehicle brake is applied, a desired vehicle deceleration is first generated by an electric braking torque adjustable via the resistance of the electric machine, and only when a maximum electric braking torque is reached is a friction brake of the vehicle engaged.

[0009] Since the function of at least one working machine is thus ensured, if necessary, by the electric machine, the combustion engine can also be switched off for a longer period of time.

[0010] Furthermore, no electric starter is required to restart the combustion engine because the flywheel drive unit and the first clutch enable a mechanical drag start of the switched-off combustion engine when the vehicle is stationary or rolling. Consequently, the combustion engine can be switched off even under high load on the electrical system, as the system does not need to supply starter current when restarting the combustion engine. The drag recuperation described above is further supplemented by regenerative braking to convert as much of the vehicle's kinetic energy as possible into electrical energy. Only when the maximum electric braking torque is reached is the friction brake engaged, which converts the vehicle's kinetic energy into heat energy.

[0011] In one embodiment of the drive system, the at least one driven machine comprises a coolant compressor for a vehicle air conditioning system. Since the coolant compressor is driven by the electric motor when needed, the combustion engine can remain switched off for extended periods without affecting the vehicle's air conditioning. In general, the at least one driven machine can perform comfort-, function-, or safety-related tasks in the hybrid vehicle. Apart from the coolant compressor, other driven machines, such as a transmission oil pump or a water pump, can be mounted on the electric motor shaft.

[0012] Preferably, the flywheel drive unit is designed as a torque converter or dual-mass flywheel. The flywheel drive unit acts as an energy storage device and is in any case designed so that the internal combustion engine can be started via a rotating flywheel of the flywheel drive unit. To achieve or maintain a minimum rotational speed of the flywheel required for this purpose, the flywheel drive unit may be driven by the electric motor.

[0013] According to another embodiment of the drive system, an electrical on-board network is provided, which feeds electrical energy into the on-board network in generator mode.

[0014] Specifically, only a low-voltage electrical system with an operating voltage of less than 60 V is permitted. Designing the system as a low-voltage electrical system reduces the cost of the drive system. This is primarily because the lower electrical voltage in the system reduces the risk of damage, making the electrical system's protection simpler and more cost-effective. Specifically, the low-voltage electrical system is either a 12-volt and / or a 48-volt system.

[0015] Furthermore, in this embodiment of the drive system, a regenerative on-board energy storage device connected to the electric motor is preferably provided. Specifically, lithium-ion batteries, for example, can be used as regenerative on-board energy storage devices.

[0016] According to a preferred embodiment of the drive system for a hybrid vehicle, the vehicle transmission is an automatic transmission.

[0017] The above-mentioned task is also solved by a method for operating the drive system described above, which includes an electrical control unit for controlling the combustion engine and the electric machine, wherein the method comprises the following steps: a) The electrical control unit determines a first control variable to enable or prevent vehicle coasting operation and a second control variable to enable or prevent combustion engine shutdown; b) If both the vehicle coasting mode and the combustion engine shutdown are enabled by the two control variables, the electrical control unit switches to an operating state in which the combustion engine is switched off, the first clutch is open and the second clutch is closed, whereby the electric machine in step b) is switched to generator mode and generates electrical energy, and whereby when a vehicle brake is applied, a desired vehicle deceleration is initially generated by an electric braking torque adjustable via the resistance of the electric machine and only when a maximum electric braking torque is reached is a friction brake of the vehicle engaged.

[0018] In this context, vehicle coasting refers to an operating state of the hybrid vehicle in which the combustion engine is decoupled from the vehicle transmission. Within vehicle coasting, a further distinction is made between "idle coasting" (with the combustion engine running) and "engine-off coasting" (with the combustion engine off).

[0019] In this operating state, the electric machine and at least one working machine are driven via the transmission shaft, the transverse drive module and the electric machine shaft.

[0020] This generator operation, in which the electric machine converts the vehicle's kinetic energy into electrical energy, is also known as recuperation.

[0021] Preferably, a resistance is set on the electric machine in generator mode that essentially corresponds to the mechanical drag torque of the combustion engine. This so-called drag recuperation in the "engine-off coasting" operating state thus simulates a conventional, mechanical coasting operation of the vehicle, in which the power transmission in the drivetrain is engaged and the accelerator pedal is not depressed, so that the combustion engine is dragged along. Subjectively, the driver therefore perceives "engine-off coasting" with drag recuperation exactly like the usual mechanical coasting operation of the vehicle, whereby electrical energy is advantageously recovered via recuperation.

[0022] The electrical energy generated by the electric machine in generator mode can initially be fed into the vehicle's electrical system and, if the electrical system's energy demand exceeds a certain threshold, charge an on-board energy storage device. Preferably, the second clutch is opened when the intermediate shaft's speed falls below a minimum threshold, and the electric machine switches to motor mode. This minimum speed is specifically set so that the energy of the flywheel in the flywheel drive unit is just sufficient to start the switched-off combustion engine. If the predetermined minimum speed of the intermediate shaft is reached, the electric machine prevents a further decrease in speed by switching to motor mode and driving the flywheel drive unit.If the vehicle transmission is designed as an automated manual transmission, a shift to a lower gear can be performed alternatively or additionally to increase the speed when the minimum speed of the intermediate shaft is reached, using a preset shifting strategy.

[0023] According to another method variant, in step a), the electronic control unit receives a signal for vehicle coasting mode and for combustion engine shutdown from function-, safety-, and / or comfort-relevant vehicle components. The electronic control unit only enables vehicle coasting mode if all corresponding signals are enable signals, and it only enables combustion engine shutdown if all corresponding signals are enable signals. The signals from the respective vehicle components are either enable signals or prevent signals. A signal to prevent combustion engine shutdown is generated, for example, by pressing the accelerator pedal, by an excessively low coolant temperature in the engine cooling circuit, or by a low battery charge level.Examples of signals to prevent vehicle coasting include pressing the accelerator pedal, detecting a vehicle driving close ahead, an excessive incline or decline, or activated special equipment such as driving in sport mode.

[0024] Preferably, the electrical control unit switches to an operating state in which the internal combustion engine is fired, the first clutch is open and the second clutch is closed, if the vehicle's coasting operation is enabled by the first control variable and the internal combustion engine shutdown is prevented by the second control variable.

[0025] Furthermore, the electrical control unit preferentially switches to an operating state in which the combustion engine is switched off, the first clutch is closed and the second clutch is also closed, if the first control variable prevents the vehicle from coasting and the second control variable enables the combustion engine to be switched off.

[0026] Finally, the electrical control unit preferably switches to an operating state in which the internal combustion engine is fired, the first clutch is closed and the second clutch is also closed, if the first control variable prevents the vehicle from coasting and the second control variable also prevents the internal combustion engine from shutting down.

[0027] Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawing, wherein the single figure shows a schematic sketch of a drive system 10 according to the invention for a hybrid vehicle.

[0028] The drive system 10 comprises an internal combustion engine 12, which has and can drive an internal combustion engine shaft 14, a vehicle transmission 16, which has a transmission shaft 18 arranged coaxially to the internal combustion engine shaft 14 on the drive side, a flywheel drive unit 20, which is arranged between the internal combustion engine 12 and the vehicle transmission 16 and has an intermediate shaft 22 arranged coaxially to the internal combustion engine shaft 14, a first clutch 24 for coupling or decoupling the internal combustion engine shaft 14 and the intermediate shaft 22, a second clutch 26 for coupling or decoupling the intermediate shaft 22 and the transmission shaft 18, an electric machine 28, which has an electric machine shaft 30 and can drive this in a motor operation of the electric machine 28, and a transverse drive module 32, which couples the electric machine shaft 30 with the parallel, non-coaxial intermediate shaft 22.

[0029] The transverse drive module 32 is a fixed gear ratio between the electric machine shaft 30 and the parallel, non-coaxial intermediate shaft 22, on which the flywheel drive unit 20 is located.

[0030] According to the figure, the second clutch 26 is a separate clutch located upstream of the vehicle transmission 16. Alternatively, the second clutch 26 can also be a transmission clutch integrated into the vehicle transmission 16, in which case the vehicle transmission 16 is in particular an automatic transmission.

[0031] Furthermore, the drive system 10 of the hybrid vehicle comprises working machines 34, 36, which are connected to the electric motor shaft 30 for drive purposes. In the present embodiment, the working machine 34 is a coolant compressor of a vehicle air conditioning system, while the working machine 36 is a pump, in particular a transmission oil pump or water pump of the hybrid vehicle.

[0032] In the present embodiment, the drive motors 34, 36 are fixedly mounted on the electric motor shaft 30. Alternatively, however, it is also conceivable that the drive motors 34, 36 have their own auxiliary shafts which are permanently fixed to the electric motor shaft 30.

[0033] By having the drive machines 34, 36 driven by the electric machine 28 in motor operation, the working machines 34, 36 no longer need to be dragged along via a belt drive of the internal combustion engine, so that according to a particularly preferred embodiment a beltless internal combustion engine 12 can be realized.

[0034] Although the figure shows two working machines 34, 36 as examples, it is clear that either just one working machine 34, 36 or more than two working machines 34, 36 can be mounted non-rotatably on the electric machine shaft 30 and driven by the electric machine 28. If the working machines 34, 36 operate in different speed ranges, a suitable gear ratio may need to be provided.

[0035] The flywheel drive unit 20 forms an energy storage device and is specifically designed as a torque converter. Alternatively, a dual-mass flywheel can also be used as the flywheel drive unit 20.

[0036] Regardless of the specific design of the flywheel drive unit 20, its flywheel mass, together with the first clutch 24, enables a mechanical drag start of the switched-off internal combustion engine 12 when the vehicle is stationary or rolling. Consequently, an electric starting device for the internal combustion engine 12 is not required.

[0037] Preferably, the second clutch 26 is (briefly) open during the tow start to avoid an unwanted vehicle jerk when coupling the internal combustion engine 12.

[0038] According to the figure, an electrical on-board network 38 is also provided, wherein the electric machine 28 is also designed as a generator and feeds electrical energy into the electrical on-board network 38 in generator mode.

[0039] In the present embodiment, only a low-voltage electrical system 38 with an operating voltage of less than 60 V is provided. Specifically, the electrical system 38 is a dual-voltage system comprising a 48 V electrical system storage device 40 and a conventional 12 V electrical system storage device 42, wherein the two electrical system storage devices 40, 42 are coupled by a DC / DC converter 44.

[0040] In this case, at least the 48 V on-board power storage device 40 connected to the electric machine 28 is a recuperation-capable on-board power storage device that can be charged when the electric machine 28 is operating as a generator. In the present embodiment, lithium-ion batteries are used as recuperation-capable on-board power storage devices 40 and 42.

[0041] The vehicle transmission 16 shown in the figure is, in particular, an automatic transmission due to the complex control of the drive system 10. Furthermore, automatic transmissions enable extremely efficient recuperation, whereas energy recovery in manual transmissions is limited by the interruption of traction during downshifting. In principle, however, the drive system 10 shown is also suitable for manual transmissions.

[0042] According to the figure, an electrical control unit 46 is also provided for controlling the internal combustion engine 12, the electric machine 28 and the vehicle transmission 16 designed as an automatic transmission, wherein the electrical control unit 46 in the present case has, by way of example, three separate control units 48, 50, 52, which are, however, connected to each other.

[0043] The control unit 48 for transmission control is connected to the vehicle transmission 16, which is designed as an automatic transmission, and to an actuator 54 for actuating the second clutch 26.

[0044] The control unit 50 for controlling the internal combustion engine 12 is connected to the internal combustion engine 12 and to an actuator 56 for actuating the first clutch 24. Furthermore, an accelerator pedal 58 and a brake pedal 60 of a vehicle brake 62 are indicated in the figure. These are coupled to the control unit 50 in such a way that the electrical control unit 46 can detect actuation of the accelerator pedal 58 or the brake pedal 60. In particular, the electrical control unit 46 can even detect an actuation force and / or an actuation distance of the accelerator pedal 58 and / or the brake pedal 60.

[0045] The control unit 52 for controlling the electric machine 28 is connected on the one hand to the electric machine 28 and on the other hand to the electrical on-board network 38 and can switch the electric machine 28, for example, from motor operation to generator operation, or vice versa.

[0046] The following section describes the procedure for operating the drive system 10 described above for a hybrid vehicle, with reference to the figure.

[0047] In a first process step a), the electrical control unit 46 determines a first control variable to enable or prevent vehicle coasting operation and a second control variable to enable or prevent combustion engine shutdown.

[0048] If both the vehicle's coasting mode and the combustion engine shutdown are enabled by the two control variables, the electrical control unit 46 switches the drive system 10 to an operating state in a subsequent process step b) in which the combustion engine 12 is switched off, the first clutch 24 is open, and the second clutch 26 is closed. In this sequence, the first clutch 24 is opened first, followed by the combustion engine 12 being switched off and the second clutch 26 being closed.

[0049] In this operating state, also known as "engine-off coasting", the internal combustion engine 12 is switched off, i.e., unpowered (i.e., switched off) and decoupled from the vehicle transmission 16. The electric motor 28 and the driven motors 34, 36, on the other hand, are essentially rotationally fixed to the intermediate shaft 22 via the electric motor shaft 30 and the transverse drive module 32, and also to the transmission shaft 18 of the vehicle transmission 16 via the closed second clutch 26, so that they are dragged along when the vehicle moves.

[0050] Furthermore, the flywheel drive unit 20, which is located on the intermediate shaft 22, is also coupled to the transmission shaft 18 via the closed second clutch 26.

[0051] The electric machine 28 is switched to generator operation by the electrical control unit 46 in process step b) and generates electrical energy.

[0052] In this process, an electrical drag torque, acting as resistance, is applied to the electric machine 28 in generator mode. With the brake pedal 60 not depressed, this torque essentially corresponds to a mechanical drag torque of the internal combustion engine 12. This operating state of the drive system 10 is also referred to as "engine-off coasting with drag recuperation" and simulates a conventional, mechanical drag operation of the internal combustion engine 12, in which the switched-off, unfired internal combustion engine 12 is dragged along by a closed frictional connection in the drive train.

[0053] This has a positive effect on the driving experience, as the driver subjectively perceives no change from the usual mechanical towing operation when "engine-off coasting with towing recuperation".

[0054] However, during engine-off coasting with towing recuperation, electrical current is generated via the generator operation of the electric machine 28, which can be fed into the electrical system 38 or charge an on-board energy storage device 40, 42 of the electrical system 38. Consequently, engine-off coasting with towing recuperation is significantly more energy-efficient than the mechanical towing operation of the drive system 10.

[0055] When the brake pedal 60 of a vehicle brake 62 is pressed, the desired vehicle deceleration is initially generated by an electric braking torque, which is higher than the electric drag torque and is adjustable via the resistance of the electric motor 28. Only when a maximum electric braking torque is reached is a friction brake 64 of the vehicle engaged. This so-called brake recuperation can be set for both mechanical drag operation and engine-off coasting with drag recuperation in the case of desired vehicle deceleration and contributes to a further increase in the energy efficiency of the drive system 10.

[0056] Only when the desired vehicle deceleration can no longer be generated by the electric braking torque adjustable via the resistance of the electric machine 28, is the conventional friction brake 64 switched on, which converts the kinetic energy of the vehicle into heat energy.

[0057] The electrical energy generated by the electric machine 28 in generator mode is initially fed into the vehicle's electrical system 38. Only when the energy demand of the vehicle's electrical system 38 is exceeded is the electrical energy generated by the electric machine 28 in generator mode used to charge the vehicle's electrical storage system 40, 42.

[0058] If the speed of the intermediate shaft 22 falls below a minimum threshold, the second clutch 26 is opened by the electrical control unit 46 and the electric machine 28 is switched to motor operation. The minimum speed of the intermediate shaft 22, which is rigidly connected to the flywheel of the flywheel drive unit 20, is selected such that the speed of the flywheel, or the energy stored in the flywheel drive unit 20, is just sufficient to restart the unfired, i.e., switched-off, combustion engine 12.

[0059] If the specified minimum speed of the intermediate shaft 22 is undershot, the second clutch 26 opens to decouple the flywheel drive unit 20 from the transmission shaft 18. The electric motor 28 switches to motor mode and, via the transverse drive module 32, drives the flywheel of the flywheel drive unit 20 as required, such that the speed of the flywheel or the energy stored in the flywheel drive unit 20 is sufficient to start the internal combustion engine 12.

[0060] In this case, the working machines 34 and 36 are also driven by the electric machine 28.

[0061] Even during a cold start of the hybrid vehicle, the flywheel drive unit 20 is driven and accelerated by the electric motor 28 when the first clutch 24 and the second clutch 26 are open, until the energy of the flywheel drive unit 20 is sufficient to start the combustion engine 12 by closing the first clutch 24. Thus, an electric starter device for the combustion engine 12 is completely unnecessary. To then accelerate from a standstill, the second clutch 26 must be closed again.

[0062] In the method for operating the drive system 10, the electrical control unit 46 receives in step a) from function-, safety- and / or comfort-relevant vehicle components a signal each for vehicle coasting operation and for combustion engine shutdown, wherein the electrical control unit 46 only enables vehicle coasting operation if all corresponding signals are enable signals, and wherein the electrical control unit 46 only enables combustion engine shutdown if all corresponding signals are enable signals.

[0063] The signals from the respective vehicle components are either enable signals or prevent signals. A signal to prevent the combustion engine from shutting down is generated, for example, by pressing the accelerator pedal, by an excessively low coolant temperature in the engine cooling circuit, or by a low battery charge level. Signals to prevent the vehicle from coasting are generated, for example, by pressing the accelerator pedal, by a sensor detecting a vehicle traveling too close ahead, by an excessively steep incline or decline, or by activated optional equipment such as driving in Sport mode.

[0064] In this context, a release signal can also be generated by interrupting a prevention signal in order to accelerate signal processing and system response.

[0065] According to a preferred method variant, for example, each vehicle component relevant to function, safety, and / or comfort generates a prevent signal for the combustion engine shutdown and / or vehicle coasting mode for as long as this is necessary for the desired functionality, safety, or comfort of the hybrid vehicle. As soon as enabling the combustion engine shutdown or vehicle coasting mode is possible, the respective vehicle component then simply interrupts the prevent signal, with this signal interruption being equivalent to an enable signal.

[0066] If at least one signal to prevent the combustion engine from shutting down is present, the electrical control unit 46 prevents the combustion engine 12 from shutting down or initiates the starting of the already shut-down combustion engine 12. Similarly, the electrical control unit 46 prevents vehicle coasting or initiates a coupling between the combustion engine 12 and the vehicle transmission 16, provided at least one signal to prevent vehicle coasting is present.

[0067] If the first control variable enables the vehicle's coasting mode and the second control variable prevents the combustion engine from shutting down, the electrical control unit 46 switches to an operating state in which the combustion engine 12 is firing, the first clutch 24 is open, and the second clutch 26 is closed. This operating state is also referred to as idling coasting.

[0068] If the first control variable prevents the vehicle from coasting and the second control variable enables the combustion engine to shut down, the electrical control unit 46 switches to an operating state in which the combustion engine 12 is unfired, i.e., switched off, and the first clutch 24 and the second clutch 26 are closed. This operating state corresponds to the mechanical towing operation already mentioned above.

[0069] If, finally, the first control variable prevents the vehicle from sailing and the second control variable also prevents the combustion engine from shutting down, the electrical control unit 46 switches to an operating state in which the combustion engine 12 is fired, the first clutch 24 is closed and the second clutch 26 is also closed.

[0070] To transition from engine-off coasting to this operating state, the second clutch 26 is first opened to prevent an unwanted vehicle jerk when engaging the internal combustion engine 12. A drag start of the internal combustion engine 12 is then performed, whereby the first clutch 24 is engaged to increase the engine speed and the internal combustion engine 12 is fired up. Finally, the second clutch 26 is engaged again, synchronizing the speeds of the internal combustion engine shaft 14 and the transmission shaft 18 and restoring the power transmission in the drivetrain.

[0071] This operating state is selected, for example, when the driver indicates by pressing the accelerator pedal 58 that he wishes to actively accelerate the vehicle or actively keep the vehicle speed constant.

Claims

[1] Drive system for a hybrid vehicle, with an internal combustion engine (12) which has an internal combustion engine shaft (14) and can drive, a vehicle transmission (16) which has a transmission shaft (18) arranged coaxially to the combustion engine shaft (14) on the drive side, a flywheel drive unit (20) which is arranged between the internal combustion engine (12) and the vehicle transmission (16) and has an intermediate shaft (22) arranged coaxially to the internal combustion engine shaft (14), a first clutch (24) for coupling or uncoupling the internal combustion engine shaft (14) and the intermediate shaft (22), a second clutch (26) for coupling or uncoupling the intermediate shaft (22) and the transmission shaft (18), an electric machine (28) which has an electric machine shaft (30) and can drive it in a motor operation, as well as a transverse drive module (32) that couples the electric machine shaft (30) with the intermediate shaft (22), wherein at least one working machine (34, 36) is provided and is connected to the electric machine shaft (30) for drive purposes, and wherein the electric machine (28) is also designed as a generator and is configured so that when a vehicle brake (62) is applied, a desired vehicle deceleration is first generated by an electric braking torque adjustable via the resistance of the electric machine (28), and only when a maximum electric braking torque is reached is a friction brake (64) of the vehicle engaged. [2] Drive system according to claim 1, characterized by , that at least one working machine (34) includes a coolant compressor of a vehicle air conditioning system. [3] Drive system according to claim 1 or 2, characterized by , that the flywheel drive unit (20) is designed as a dual-mass flywheel or converter. [4] Drive system according to one of the preceding claims, characterized by , that an electrical on-board network (38) is provided, wherein in generator operation electrical energy is fed into the electrical on-board network (38). [5] Drive system according to claim 4, characterized by , that only a low-voltage electrical system (38) with an operating voltage of less than 60 V is provided. [6] Drive system according to claim 4 or 5, characterized by , that a recuperation-capable on-board power supply storage device (40, 42) connected to the electric machine (28) is provided. [7] Drive system according to any one of the preceding claims, characterized by , that the vehicle transmission (16) is an automatic transmission. [8] Method for operating a drive system according to one of the preceding claims, comprising an electrical control unit (46) for controlling the internal combustion engine (12) and the electric machine (28), the method comprising the following steps: a) the electrical control unit (46) determines a first control variable to enable or prevent vehicle coasting operation and a second control variable to enable or prevent combustion engine shutdown; b) if both the vehicle coasting mode and the combustion engine shutdown are enabled by the two control variables, the electrical control unit (46) switches to an operating state in which the combustion engine (12) is switched off, the first clutch (24) is open and the second clutch (26) is closed, the electric machine (28) is switched to generator mode in step b) and generates electrical energy, and when a vehicle brake (62) is applied, a desired vehicle deceleration is initially generated by an electric braking torque adjustable via the resistance of the electric machine (28) and only when a maximum electric braking torque is reached is a friction brake (64) of the vehicle engaged. [9] Method according to claim 8, characterized by, that a resistance is set on the electric machine (28) in generator operation which essentially corresponds to a mechanical drag torque of the internal combustion engine (12). [10] Method according to claim 8 or 9, characterized by , that the electrical energy generated by the electric machine (28) in generator operation is first fed into an electrical on-board network (38) and, if the energy demand of the electrical on-board network (38) is exceeded, charges an on-board network storage device (40, 42). [11] Method according to any one of claims 8 to 10, characterized by , that the second clutch (26) is opened when the intermediate shaft (22) falls below a minimum speed and the electric machine (28) is switched to motor operation. [12] Method according to any one of claims 8 to 11, characterized by, that the electrical control unit (46) in step a) receives a signal for vehicle coasting operation and for combustion engine shutdown from function-, safety- and / or comfort-relevant vehicle components, releases vehicle coasting operation only if all corresponding signals are release signals, and releases combustion engine shutdown only if all corresponding signals are release signals. [13] Method according to any one of claims 8 to 12, characterized by , that the electrical control unit (46) switches to an operating state in which the internal combustion engine (12) is fired, the first clutch (24) is open and the second clutch (26) is closed, if the vehicle's coasting operation is enabled by the first control variable and the internal combustion engine is prevented from being shut down by the second control variable. [14] Method according to any one of claims 8 to 13, characterized by, that the electrical control unit (46) switches to an operating state in which the internal combustion engine (12) is switched off, the first clutch (24) is closed and the second clutch (26) is also closed, if the first control variable prevents the vehicle from sailing and the second control variable enables the internal combustion engine to be switched off. [15] Method according to any one of claims 8 to 14, characterized by , that the electrical control unit (46) switches to an operating state in which the internal combustion engine (12) is fired, the first clutch (24) is closed and the second clutch (26) is also closed, if the first control variable prevents the vehicle from sailing and the second control variable also prevents the internal combustion engine from being switched off.

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