METHOD FOR OPERATING A HYBRID DRIVE SYSTEM OF A MOTOR VEHICLE, HYBRID DRIVE SYSTEM AND MOTOR VEHICLE

Description

[0001] The present invention relates to a method for operating a hybrid drive system of a motor vehicle. Furthermore, the invention relates to a hybrid drive system for a motor vehicle and a motor vehicle with a hybrid drive system.

[0002] Motor vehicles with hybrid drive systems are known, in which the hybrid drive system comprises an internal combustion engine, a transmission, a drive train generator, an exhaust tract for the internal combustion engine, and a control device. A first clutch is arranged between the internal combustion engine and an output of the hybrid drive system. A second clutch is arranged between the drive train generator and the output. A generic drive system is known, for example, from documents US 2015 / 0239463 A1 and JP 2009-292246 A1. The drive train generator is arranged in series with the internal combustion engine, so that when the second clutch is disengaged, the drive train generator, together with the internal combustion engine, is decoupled from the output. Further drive systems are known from documents US 2021 / 381446 A1 and US 2004 / 025835 A1.

[0003] Furthermore, hybrid drive systems are known that, in addition to a drive train generator, also have a belt starter generator, which is coupled to the internal combustion engine directly or indirectly, for example, via a transmission. The belt starter generator, together with the internal combustion engine, can be decoupled from the output and thus also from the drive train generator by means of the first clutch.

[0004] Furthermore, hybrid drive systems often have a gasoline engine as the internal combustion engine, as well as a three-way catalytic converter for cleaning the gasoline engine's exhaust gases, and often also a particulate filter. Modern hybrid drive systems have two three-way catalytic converters, a first located near the internal combustion engine and a second located under the vehicle's floor.

[0005] Known hybrid drive systems have the disadvantage that, in an operating state in which the internal combustion engine is not providing thrust and is being dragged by the downforce, air is drawn in by the internal combustion engine and fed into the exhaust tract. This causes oxygen to build up in the three-way catalysts, which leads to increased emissions, particularly NOx emissions, when the internal combustion engine is started up. Until now, this problem has been solved by deliberately burning out the oxygen from the three-way catalysts. This, in turn, leads to increased fuel consumption in the hybrid drive system.

[0006] It is therefore an object of the present invention to eliminate, or at least partially eliminate, the disadvantages described above in a hybrid drive system. In particular, the object of the present invention is to provide a method for operating a hybrid drive system, a hybrid drive system, and a motor vehicle that prevent oxygen deposition in the three-way catalyst in a simple and cost-effective manner.

[0007] The above object is achieved by the patent claims. Accordingly, the object is achieved by a method for operating a hybrid drive system of a motor vehicle having the features of independent claim 1, by a hybrid drive system for a motor vehicle having the features of the independent claim 9, and by a motor vehicle having the features of the independent claim 10. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the hybrid drive system according to the invention and the motor vehicle according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is and can always be made to each other.

[0008] According to a first aspect of the invention, the object is achieved by a method for operating a hybrid drive system of a motor vehicle. The hybrid drive system comprises an internal combustion engine with a belt starter generator coupled thereto, a transmission, a drive train generator, an exhaust tract for the internal combustion engine, a control device, and an output. A first clutch is arranged between the internal combustion engine and the transmission. An optional second clutch can be arranged between the drive train generator and the output. The method comprises: Driving the motor vehicle to a first speed by controlling the internal combustion engine and / or the drive train generator by the control device, causing an operating state of the hybrid drive system by the control device in which the first clutch is open, switching off the internal combustion engine by the control device, detecting a braking request to brake the motor vehicle by the control device, closing the first clutch to tow the internal combustion engine and to operate the belt starter generator in a recuperation mode by the control device, and configuring the internal combustion engine by the control device such that only intake valves of the internal combustion engine remain closed during rotation of a crankshaft of the internal combustion engine.

[0009] The hybrid drive system with which the method according to the invention is carried out has the internal combustion engine with the belt starter generator coupled thereto. The internal combustion engine is designed to drive the motor vehicle. The internal combustion engine is preferably designed as a gasoline engine. The belt starter generator is preferably mechanically coupled to the crankshaft of the internal combustion engine via a transmission, such as a single-stage gear transmission, a belt drive, or the like. According to the invention, an intermediate clutch for mechanically decoupling the belt starter generator from the crankshaft can be provided in the torque flow between the belt starter generator and the internal combustion engine. The belt starter generator is an electric motor designed to operate in both motor mode and generator mode.The belt starter generator is designed to convert electrical energy into rotational energy during motor operation. This provides additional torque to assist the internal combustion engine in driving the motor vehicle. Furthermore, the belt starter generator is designed to convert rotational energy into electrical energy during generator operation. This provides electrical energy for storage in a battery of the motor vehicle or for operating the drive train generator.

[0010] The internal combustion engine is mechanically coupled to the output of the hybrid drive system via the first clutch and the transmission. When the first clutch is engaged, torque can be transmitted from the crankshaft of the internal combustion engine to the output via the transmission. When the first clutch is disengaged, the transmission of torque is interrupted. In this state, the internal combustion engine can be switched off, for example, or is configured to operate the belt starter generator in generator mode. Furthermore, the internal combustion engine is configured such that the intake valves and / or exhaust valves of the internal combustion engine can be switched decoupled from the rotation of the crankshaft. Thus, the intake valves or exhaust valves can be closed, for example, when the crankshaft is rotating, over several revolutions of the crankshaft or over an extended period of time.This prevents the deactivated combustion engine from pumping air into the exhaust tract of the internal combustion engine of the hybrid drive system when the engine is in a towed state. The internal combustion engine is preferably designed such that at least the intake valves can be closed independently of the rotation of the crankshaft.

[0011] The exhaust tract is fluidly coupled to a combustion gas outlet of the internal combustion engine. Combustion gases from cylinders of the internal combustion engine can be discharged to the environment of the motor vehicle via the exhaust tract. The exhaust tract preferably has a particulate filter, such as a gasoline particulate filter, and a catalytic converter, such as a three-way catalytic converter. According to the invention, the exhaust tract can have multiple particulate filters and / or multiple catalytic converters or further devices for cleaning the exhaust gas. The exhaust tract preferably has a first three-way catalytic converter close to the engine and a second three-way catalytic converter arranged adjacent to a vehicle floor. In this case, it is preferred that the particulate filter, which is preferably designed as a gasoline particulate filter, is arranged between the first three-way catalytic converter and the second three-way catalytic converter in the flow direction of the exhaust gas.

[0012] The drivetrain generator is mechanically coupled, for example, directly or via an optional second clutch, to the output of the hybrid drive system. The drivetrain generator transmits torque for driving the motor vehicle to the output. The drivetrain generator is preferably arranged between a transmission output of the transmission and the optional second clutch. Alternatively, the drivetrain generator can also be arranged between the first clutch and a transmission input of the transmission. In this case, it is preferred that the transmission be arranged between the drivetrain generator and the optional second clutch.In an alternative embodiment of the invention, the drivetrain generator and the optional second clutch are mechanically coupled to the output such that when the second clutch is open, the drivetrain generator is decoupled from the output, and when the first clutch is simultaneously closed, the internal combustion engine is coupled to the output. In this configuration, a third clutch is preferably provided, by means of which the internal combustion engine with belt starter generator, the first clutch, the second clutch, the transmission, and the drivetrain generator can be decoupled from the output.

[0013] The control device is designed to operate the hybrid drive system. Thus, the implementation of the method according to the invention can be coordinated by means of the control device. This means that, by means of the control device, commands can be generated and preferably also transmitted to components of the hybrid drive system, such as an injection pump for injecting fuel into the cylinders of the internal combustion engine, the transmission for setting a selected gear, the first clutch, the optional second clutch, the intake valves, the exhaust valves, the drive train generator, or the belt starter generator, for implementing individual aspects of the method according to the invention.Furthermore, the control device is configured to receive commands for operating the hybrid drive system, such as a speed command from an accelerator pedal, a limiting device for complying with legal speed limits, an input interface of a cruise control device, or the like, as well as a braking command from a brake pedal, the limiting device, the input interface of the cruise control device, or the like. Furthermore, the control device is preferably configured to monitor the hybrid drive system, such as rotational speeds, temperatures, configurations, or the like of individual or multiple components of the hybrid drive system.

[0014] First, the motor vehicle is driven to the first speed. This is preferably done by accelerating the motor vehicle from a lower speed to the first speed. In this case, the control device preferably controls the internal combustion engine and / or the drive train generator accordingly. Likewise, driving to the first speed can be done by decelerating the motor vehicle from a higher speed to the first speed. In this case, the control device preferably controls a conventional braking device of the motor vehicle for braking the motor vehicle, such as a disc brake device, a drum brake device, or the like. As an alternative to braking, the first speed can also be reached by letting the motor vehicle coast.The first speed is preferably higher than 50 km / h and more preferably higher than 100 km / h.

[0015] At the first speed, the control device brings about the operating state of the hybrid drive system in which the first clutch is open. This can be done, for example, by deliberately opening the first clutch. An optional second clutch is also open in this operating state. This can be done, for example, by deliberately opening the second clutch. Alternatively, the first clutch can already be opened. In the context of the invention, an open clutch is understood to mean a decoupling position of the clutch such that torque flow through the clutch is interrupted. In the context of the invention, a closed clutch is understood to mean a coupling position of the clutch such that torque flow through the clutch is established.

[0016] The internal combustion engine is shut down by means of the control device. This can occur, for example, before or after the first clutch is disengaged. Preferably, the internal combustion engine is shut down after the first clutch is disengaged. Within the context of the invention, shutting down the internal combustion engine means that the internal combustion engine is no longer operating in combustion engine mode, so that the internal combustion engine—apart from the moment of inertia of the still rotating crankshaft—provides no torque to drive the belt starter generator or the motor vehicle.

[0017] If a braking request is generated to decelerate the motor vehicle, this is detected by the control device. The braking request can be initiated, for example, by a driver pressing the brake pedal, a manual input at the cruise control device's input interface, the limiting device for complying with legal speed limits, or similar. The control device analyzes the braking request and implements measures to decelerate the motor vehicle in accordance with the braking request.

[0018] One measure carried out in this context is the closing of the first clutch by the control device so that the crankshaft of the internal combustion engine is mechanically coupled to the output of the hybrid drive system for torque transmission.

[0019] Depending on the design of the hybrid drive system, closing the optional second clutch may also be necessary to establish this operating state. The internal combustion engine is thus in towing mode and is driven via the output. The belt starter generator, which is mechanically coupled to the internal combustion engine, is thus operated in recuperation mode and converts rotational energy into electrical energy. In this case, the internal combustion engine and the belt starter generator provide a braking torque to brake the motor vehicle. In addition, an additional conventional braking device, such as a disc brake, a drum brake, or the like, can be actuated to brake the motor vehicle if the provided braking torque is insufficient to meet the braking requirement.

[0020] A further measure implemented in this context includes configuring the internal combustion engine by the control device such that only the intake valves of the internal combustion engine remain closed during rotation of the crankshaft of the internal combustion engine. For this purpose, the intake valves or the exhaust valves are designed, for example, to be specifically electrically controllable, so that there is no mechanical forced coupling between the rotation of the crankshaft and the intake valves or the exhaust valves. Alternatively, the intake valves or the exhaust valves can also be designed to be decoupled from a camshaft of the internal combustion engine. Thus, a valve position of the intake valves or the exhaust valves remains closed even during rotation of the crankshaft.

[0021] This means that no air is sucked in by the internal combustion engine and pumped into the exhaust system while the engine is towing.

[0022] A method according to the invention for operating a hybrid drive system of a motor vehicle has the advantage over conventional methods that the belt starter generator can be operated in recuperation mode using simple means and in a cost-effective manner. The targeted configuration of the intake and / or exhaust valves of the internal combustion engine prevents the conveyance of air into the exhaust system. This prevents the accumulation of oxygen in exhaust treatment devices of the exhaust system, such as catalytic converters, and avoids the costly and fuel-consuming burnout of oxygen.

[0023] According to a preferred further development of the invention, a method can be provided in which the control device specifically configures the towed internal combustion engine such that the intake and exhaust valves convey a predefined air flow into the exhaust tract of the motor vehicle. This configuration preferably takes place shortly before starting the internal combustion engine. More preferably, this configuration takes place at a vehicle speed at which this configuration can be carried out particularly gently and with low wear. This has the advantage that the starting process of the internal combustion engine in a rolling motor vehicle can be improved using simple means and in a cost-effective manner. Furthermore, combustion gas residues can thus be diverted from the cylinders.

[0024] According to the invention, it is preferred that the control device actuates a fuel injection device for the targeted injection of fuel into one or more cylinders of the towed internal combustion engine. The internal combustion engine is in towing mode, at least at the beginning of the targeted injection, so that the fuel-air mixture in the cylinders does not ignite. This preferably also occurs shortly before the internal combustion engine is started. This has the advantage that the starting process of the internal combustion engine in a moving motor vehicle can be improved using simple means and in a cost-effective manner. Furthermore, a targeted burnout of oxygen from exhaust gas treatment devices in the exhaust tract, such as catalytic converters, particulate filters, or the like, can thus be effected.

[0025] Further preferably, the drive train generator can be mechanically coupled to the output of the hybrid drive system via a second clutch, wherein the control device closes the second clutch to operate the drive train generator in the recuperation mode for braking the motor vehicle. In a hybrid drive system in which the first clutch and the second clutch are arranged in the torque flow between the internal combustion engine and the output, the second clutch must be closed before the first clutch, since in this configuration both the first clutch and the second clutch must be closed to transmit drive torque from the internal combustion engine to the output. By closing the second clutch, the drive train generator provides a braking torque and in the process generates electrical energy.After the first clutch is subsequently engaged, the internal combustion engine and the belt starter generator provide additional braking torque, thus providing a higher total braking torque. In a hybrid drive system in which the first clutch is arranged in the torque flow between the internal combustion engine and the output, and the second clutch is arranged parallel to the first clutch in the torque flow between the drive train generator and the output, the engagement of the second clutch can, according to the invention, occur independently of the time at which the first clutch is engaged, for example, before, after, or during engagement. This has the advantage that recuperation power for braking the motor vehicle can be maximized using simple means and in a cost-effective manner.

[0026] In a particularly preferred embodiment of the invention, a method can be provided that the second clutch is engaged before the first clutch to brake the motor vehicle. Thus, a braking torque is initially provided by the drive train generator. By subsequently engaging the first clutch, an additional braking torque can be provided by the internal combustion engine and the belt starter generator. This has the advantage of ensuring particularly smooth braking and particularly efficient recuperation using simple means and in a cost-effective manner, especially when braking requirements are relatively low.

[0027] The first clutch is preferably opened again when the motor vehicle reaches a second speed, wherein the second speed is lower than the first speed. The second speed is preferably between 15 km / h and 30 km / h, particularly preferably between 20 km / h and 25 km / h. Below such a speed, efficient recuperation by the belt starter generator is no longer guaranteed. By opening the first clutch, recuperation takes place solely by the drive train generator. Any additional braking torque that may be required can be generated by a braking device, such as a disc brake, a drum brake or the like. This has the advantage that particularly gentle braking and particularly efficient recuperation are guaranteed using simple means and in a cost-effective manner.

[0028] According to a preferred embodiment of the invention, the configuration of the internal combustion engine by the control device comprises switching a camshaft to zero cams. Such switchable cams are already known in drive systems for motor vehicles, which can be operated with a reduced number of cylinders to reduce fuel consumption and exhaust emissions. The cams of the cylinders to be deactivated can be decoupled from the camshaft, so that the intake valves and / or exhaust valves of the deactivated cylinders remain in their position, for example, a closed position, when the camshaft rotates. The deactivated cylinders can be reactivated when there is an increased power requirement, such as a kickdown, by coupling the respective cams to the camshaft.This has the advantage that particularly reliable closing of the intake and exhaust valves is ensured using simple means and in a cost-effective manner.

[0029] Particularly preferably, air is evacuated from the exhaust tract using an evacuation device of the hybrid drive system. Alternatively or additionally, an oxygen-free or oxygen-reduced gas is preferably introduced into the exhaust tract using a gassing device of the hybrid drive system to displace the oxygen present in the exhaust tract. The evacuation device preferably has a vacuum chamber for receiving the air. The evacuation device is preferably designed to evacuate the vacuum chamber again during combustion engine operation of the internal combustion engine. The gassing device preferably has a pressure chamber in which the gas can be stored.The gassing device is preferably designed to fill the pressure chamber with exhaust gas from the internal combustion engine during engine operation, preferably at a pressure higher than atmospheric pressure, in particular several times higher. This has the advantage that oxygen residues can be removed from the exhaust tract using simple means and in a cost-effective manner.

[0030] According to a second aspect of the invention, the object is achieved by a hybrid drive system for a motor vehicle. The hybrid drive system has an internal combustion engine with a belt starter generator coupled thereto, a transmission, a drive train generator, an exhaust tract for the internal combustion engine, and a control device. A first clutch is arranged between the internal combustion engine and an output of the hybrid drive system. An optional second clutch can be arranged between the drive train generator and the output. According to the invention, the hybrid drive system according to the invention is designed to carry out a method according to the first aspect of the invention. The individual components of the hybrid drive system have already been sufficiently described in connection with the method according to the invention.

[0031] The hybrid drive system according to the invention provides all the advantages already described for a method for operating a hybrid drive system of a motor vehicle according to the first aspect of the invention. Accordingly, the hybrid drive system according to the invention has the advantage over conventional hybrid drive systems that the belt starter generator can be operated in recuperation mode using simple means and in a cost-effective manner, wherein the targeted configurability of the intake valves and / or exhaust valves of the internal combustion engine prevents the conveyance of air into the exhaust tract. Thus, an accumulation of oxygen in exhaust treatment devices of the exhaust tract, such as catalytic converters, can be prevented, and the complex and fuel-consuming burnout of oxygen can be avoided.

[0032] According to a third aspect of the invention, the object is achieved by a motor vehicle. According to the invention, the motor vehicle has a hybrid drive system according to the second aspect of the invention. The hybrid drive system accordingly has an internal combustion engine with a belt starter generator coupled thereto, a transmission, a drive train generator, an exhaust tract for the internal combustion engine, and a control device. A first clutch is arranged between the internal combustion engine and an output of the hybrid drive system. A second clutch is arranged between the drive train generator and the output. According to the invention, the hybrid drive system is designed to carry out a method according to the first aspect of the invention.

[0033] The motor vehicle according to the invention provides all the advantages already described for a method for operating a hybrid drive system of a motor vehicle according to the first aspect of the invention and for a hybrid drive system for a motor vehicle according to the second aspect of the invention. Accordingly, the motor vehicle according to the invention has the advantage over conventional motor vehicles that the belt starter generator can be operated in recuperation mode using simple means and in a cost-effective manner, wherein the targeted configurability of the intake valves and / or exhaust valves of the internal combustion engine prevents air from being pumped into the exhaust tract. Thus, an accumulation of oxygen in exhaust gas treatment devices of the exhaust tract, such as catalytic converters, can be prevented, and complex and fuel-consuming burnout of the oxygen can be avoided.

[0034] A method according to the invention, a hybrid drive system according to the invention, and a motor vehicle according to the invention are explained in more detail below with reference to the drawings. They show schematically: Figure 1 shows a flow diagram of a preferred embodiment of a method according to the invention for operating a hybrid drive system of a motor vehicle, Figure 2 shows a schematic diagram of a preferred first embodiment of a hybrid drive system according to the invention, Figure 3 shows a schematic diagram of a preferred second embodiment of a hybrid drive system according to the invention, Figure 4 shows a schematic diagram of a preferred third embodiment of a hybrid drive system according to the invention, Figure 5 shows a schematic diagram of a preferred fourth embodiment of a hybrid drive system according to the invention, and Figure 6 shows a side view of a preferred embodiment of a motor vehicle according to the invention.

[0035] Elements with the same function and mode of action are listed in the Figures 1 to 6 each provided with the same reference numerals.

[0036] In Fig. 1 is a preferred embodiment of a method according to the invention for operating a hybrid drive system 1 (cf. Fig. 2 ) of a motor vehicle 2 (cf. Fig. 6 ) is shown schematically in a flow chart. Within the scope of a first method action 100, the hybrid drive system 1 is controlled by means of a control device 8 (cf. Fig. 2) of the hybrid drive system 1 is controlled such that the motor vehicle 2 is brought to a first speed. This is preferably done by accelerating the motor vehicle 2. According to a second method action 200, an operating state of the hybrid drive system 1 is brought about by the control device 8 in which a first clutch 10 of the hybrid drive system 1 is opened. This can be done, for example, by opening the first clutch 10. Alternatively, the first clutch 10 can already be opened and thus remains in the open position. According to a third method action 300, the internal combustion engine 3 is switched off by means of the control device 8.

[0037] According to a fourth method action 400, a braking request for braking the motor vehicle 2 is detected by the control device 8. According to a fifth method action 500, the first clutch 10 is closed by the control device 8, so that the switched-off internal combustion engine 3 is operated in a towed state. A belt starter generator 4 mechanically coupled to the internal combustion engine 3 (see Fig. 2) is also towed and thus operated in a generator mode to generate electrical energy. Thus, the internal combustion engine 3 and the belt starter generator 4 provide a braking torque for braking the motor vehicle 2. According to a sixth method action 600, an internal combustion engine 3 of the hybrid drive system 1 is configured by means of the control device 8 such that intake valves and / or exhaust valves of the internal combustion engine 3 are opened during a rotation of a crankshaft 12 (cf. Fig. 2 ) of the internal combustion engine 3 remain closed. This is done, for example, by decoupling the intake valves and / or exhaust valves from a camshaft of the internal combustion engine 3. The sixth method action 600 is preferably carried out directly or immediately after the fifth method action 500 in order to minimize the amount of air delivered.

[0038] Fig. 2shows a preferred first embodiment of a hybrid drive system 1 according to the invention schematically in a schematic diagram. The hybrid drive system 1 has an internal combustion engine 3, which is mechanically coupled to a belt starter generator 4 via a belt drive 16. The internal combustion engine 3 has a fuel injection device 13 for injecting fuel into cylinders of the internal combustion engine 3. An exhaust tract 7 of the hybrid drive system 1 is arranged on the internal combustion engine 3 for discharging the combustion gases. A crankshaft 12 of the internal combustion engine 3 can be mechanically coupled to and decoupled from a transmission input 5a of a transmission 5 via a first clutch 10. A drive train generator 6 is arranged at a transmission output 5b of the transmission 5.The drive train generator 6 can be mechanically coupled to and decoupled from an output 9 of the hybrid drive system 1 via an optional second clutch 11. To control the components of the hybrid drive system 1, the hybrid drive system 1 has a control device 8. An alternative embodiment of the invention differs from the first embodiment in that no second clutch 11 is present.

[0039] In Fig. 3A preferred second embodiment of a hybrid drive system 1 according to the invention is shown schematically in a schematic diagram. The second embodiment differs from the first embodiment in the arrangement of the drive train generator 6. The drive train generator 6 is arranged in the torque flow between the first clutch 10 and the transmission input 5a. An alternative embodiment of the invention differs from the second embodiment in that no second clutch 11 is present.

[0040] Fig. 4shows a preferred third embodiment of a hybrid drive system 1 according to the invention schematically in a principle sketch. The third embodiment differs from the first embodiment in a third clutch 17, which is arranged in the torque flow between the transmission output 5b and the drive train generator 6. The transmission 5 can be decoupled from the drive train generator 6 and the output 9 via the third clutch 17. Furthermore, the hybrid drive system 1 has an optional evacuation device 14 for evacuating air from the exhaust tract 7. An alternative embodiment of the invention differs from the third embodiment in that no second clutch 11 is present.

[0041] In Fig. 5A preferred fourth embodiment of a hybrid drive system 1 according to the invention is shown schematically in a principle sketch. The fourth embodiment differs from the first embodiment in an arrangement of the drive train generator 6 with the second clutch 11 parallel to the torque flow of the internal combustion engine 3 with the belt starter generator 4 and the transmission 5. In this arrangement, when the second clutch 11 is open, the drive train generator 6 is mechanically decoupled from the output 9, with the transmission 5 still being mechanically coupled to the output 9. Furthermore, the hybrid drive system 1 has an optional gassing device 15. The gassing device 15 is designed to store combustion gases generated during operation of the internal combustion engine 3 under excess pressure to the atmosphere.Furthermore, the gassing device 15 is designed to discharge the stored exhaust gases into the exhaust tract 7 when the internal combustion engine 3 is switched off. In this way, air can be displaced from the exhaust tract 7. An alternative embodiment of the invention differs from the fourth embodiment in that no second clutch 11 is present.

[0042] Fig. 6 shows a preferred embodiment of a motor vehicle 2 according to the invention schematically in a side view. The motor vehicle 2 has a hybrid drive system 1 according to the invention with a battery 18. List of reference symbols

[0043] 1 hybrid drive system 2 motor vehicle 3 internal combustion engine 4 belt starter generator 5 transmission 5a transmission input 5b transmission output 6 drive train generator 7 exhaust tract 8 control device 9 output 10 first clutch 11 second clutch 12 crankshaft 13 fuel injection device 14 evacuation device 15 gassing device 16 belt drive 17 third clutch 18 battery 100first procedural action 200second procedural action 300third procedural action 400fourth procedural action 500fifth procedural action 600sixth procedural action

Claims

1. Method for operating a hybrid drive system (1) of a motor vehicle (2), wherein the hybrid drive system (1) comprises an internal combustion engine (3) having a belt starter generator (4) coupled thereto, a transmission (5), a powertrain generator (6), an exhaust gas tract (7) for the internal combustion engine (3), a control device (8) and an output (9), wherein a first clutch (10) is arranged between the internal combustion engine (3) and the transmission (5), the method comprising: - bringing the motor vehicle (2) to a first speed by controlling the hybrid drive system (1) by means of the control device (8), - bringing about an operating state of the hybrid drive system (1), in which the first clutch (10) is opened, by means of the control device (8), - switching off the internal combustion engine (3) by means of the control device (8), - detecting, by means of the control device (8), a braking request for braking the motor vehicle (2), - closing the first clutch (10) by means of the control device (8) for overrunning the internal combustion engine (3) and for operating the belt starter generator (4) in a recuperation mode, and - configuring the internal combustion engine (3) by means of the control device (8) such that only inlet valves of the internal combustion engine (3) remain closed during a rotation of a crankshaft (12) of the internal combustion engine (3).

2. Method according to claim 1, characterized in that the control device (8) configures the overrun internal combustion engine (3) in a targeted manner such that the inlet valves and outlet valves convey a predefined air flow into the exhaust gas tract (7) of the motor vehicle (2).

3. Method according to claim 2, characterized in that the control device (8) controls a fuel injection device (13) for the targeted injection of fuel into one or more cylinders of the overrun internal combustion engine (3).

4. Method according to any of the preceding claims, characterized in that the powertrain generator can be mechanically coupled to the output of the hybrid drive system via a second clutch (11), the control device (8) closing the second clutch (11) in order to operate the powertrain generator (6) in the recuperation mode for braking the motor vehicle (2).

5. Method according to claim 4, characterized in that the second clutch (11) is closed before the first clutch (10) in order to brake the motor vehicle (2).

6. Method according to any of the preceding claims, characterized in that the first clutch (10) is opened again when the motor vehicle (2) reaches a second speed, the second speed being lower than the first speed.

7. Method according to any of the preceding claims, characterized in that the configuration of the internal combustion engine (3) by means of the control device (8) comprises switching a camshaft to null cams.

8. Method according to any of the preceding claims, characterized in that air is evacuated from the exhaust gas tract (7) using an evacuation device (14) of the hybrid drive system (1), and / or in that an oxygen-free or oxygen-reduced gas is introduced into the exhaust gas tract (7) by means of a gassing device (15) of the hybrid drive system (1), in order to displace the oxygen situated in the exhaust gas tract (7).

9. Hybrid drive system (1) for a motor vehicle (2), comprising an internal combustion engine (3) having a belt starter generator (4) coupled thereto, a transmission (5), a powertrain generator (6), an exhaust gas tract (7) for the internal combustion engine (3), and a control device (8), a first clutch (10) being arranged between the internal combustion engine (3) and an output (9) of the hybrid drive system (1), characterized in that the hybrid drive system (1) is designed to carry out a method according to any of the preceding claims.

10. Motor vehicle (2), characterized in that the motor vehicle (2) comprises a hybrid drive system (1) according to claim 9.