Method and device for regenerating a particle filter in a motor vehicle with a hybrid drive

Description

[0001] The invention relates to a method and a device for regenerating a particle filter in the exhaust duct of a motor vehicle with a hybrid drive.

[0002] The continuous tightening of emissions legislation places high demands on vehicle manufacturers, which are met through appropriate measures to reduce engine-out emissions and through appropriate exhaust aftertreatment. With the introduction of the EU6 legislative level, a limit for the number of particles is prescribed for gasoline engines or vehicles with hybrid drive, which in many cases requires the use of a particulate filter. During operation, such a particulate filter becomes loaded with soot. To prevent exhaust backpressure from increasing too sharply, this particulate filter must be regenerated continuously or periodically. In order to carry out thermal oxidation of the soot trapped in the particulate filter with oxygen, a sufficiently high temperature level in conjunction with the simultaneous presence of oxygen in the exhaust system of the combustion engine is necessary.Since modern gasoline engines are normally operated without excess oxygen and with a stoichiometric combustion air ratio (λ=1), additional measures are required. One option for regenerating the particulate filter is to introduce oxygen into the exhaust duct during the engine's overrun phases, i.e., phases in which no fuel is injected and thus an excess of oxygen is present in the exhaust gas. However, such overrun phases do not always occur according to plan in an internal combustion engine, but rather randomly and uncontrollably, so the regeneration phase is triggered more frequently than necessary to avoid the risk of excessive loading of the particulate filter and the associated risk of thermal damage to the particulate filter due to uncontrolled soot burnoff.In the worst case scenario, such uncontrolled soot burn-off could lead to the particulate filter burning through and thus to its destruction.

[0003] From DE 103 40 934 B4 a method for controlling an internal combustion engine is known, wherein a distinction is made between normal operation and regeneration operation of the internal combustion engine, wherein in normal operation the air mass supplied to the internal combustion engine is controlled by an exhaust gas recirculation valve and a throttle valve, and in regeneration the exhaust gas recirculation valve is closed and the air mass supplied to the internal combustion engine is controlled exclusively via the throttle valve.

[0004] From DE 10 2016 101 105 A1 a method for regenerating a particulate filter in an overrun operation of an internal combustion engine is known, wherein the duration of an overrun phase in which no fuel is injected into the combustion chambers of the internal combustion engine is controlled as a function of the temperature of the particulate filter.

[0005] WO2011 / 104459 A1 discloses a method for regenerating a particulate filter of an internal combustion engine in a hybrid vehicle. The inlet temperature of the particulate filter is continuously measured and compared with a first threshold value. Stopping the internal combustion engine is prevented if the temperature at the inlet of the particulate filter is below this first threshold value. Stopping the internal combustion engine is prevented until the temperature at the inlet of the particulate filter is above a second threshold temperature, above which stopping the internal combustion engine is permitted.

[0006] EP 1 197 642 A2 discloses a method for regenerating a particulate filter in a hybrid vehicle. The exhaust gas temperature is increased by increasing the load on the combustion engine, which charges the battery of the hybrid vehicle's electric motor in addition to driving the vehicle.

[0007] From FR 2 982 317 A1 a method for regenerating a particulate filter in the exhaust system of an internal combustion engine is known, wherein the internal combustion engine is towed by an electric motor to regenerate the particulate filter and pumps air into the exhaust system.

[0008] DE 10 2015 015 794 A1 discloses a method for heating an exhaust aftertreatment component in a hybrid vehicle, wherein combustion in the combustion chambers is deactivated by suppressing fuel injection. The combustion engine pumps an air stream into the exhaust system, which is heated by an electric heating element to supply the exhaust aftertreatment component with this heated air stream.

[0009] DE 10 2013 202 142 A1 discloses a method for regenerating a particulate filter in the exhaust system of an internal combustion engine, wherein the temperature is raised to an ignition temperature to start regeneration. The method provides that regeneration takes place at least partially with the internal combustion engine switched off through a controlled supply of fresh air without additional heating measures. The method provides that a temperature of approximately 600°C is reached to start regeneration. It is provided that fresh air continues to be supplied while regeneration is ongoing and the internal combustion engine is stopped in order to continue regeneration through a controlled supply of fresh air to the particulate filter.

[0010] DE 10 2012 022 153 A1 discloses a method and a control device for regenerating a particulate filter in the exhaust system of a gasoline engine. The temperature of the particulate filter is determined, and the temperature of the exhaust gas flow of the internal combustion engine is increased by internal heating measures until the exhaust gas temperature reaches a regeneration temperature of the particulate filter. Once the temperature of the particulate filter has reached the regeneration temperature, a throttle valve in the air supply system of the internal combustion engine is opened to ensure the oxygen surplus in the exhaust system necessary for regeneration of the particulate filter.

[0011] The disadvantage of these solutions, however, is that it is still necessary to wait for the combustion engine to overrun in order to regenerate the particulate filter and the particulate filter continues to be regenerated more frequently than actually necessary.

[0012] The invention is based on the object of enabling the fastest possible regeneration of a particulate filter in a hybrid vehicle with a hybrid drive consisting of an internal combustion engine and an electric motor and, after successful regeneration of the particulate filter, of enabling a smooth resumption of combustion in the internal combustion engine.

[0013] According to the invention, the object is achieved by a method for regenerating the particulate filter in the exhaust duct of a motor vehicle with a hybrid drive consisting of an electric motor and an internal combustion engine, which method comprises the following steps: Operating the motor vehicle in hybrid mode, wherein during operation of the internal combustion engine the exhaust gas of the internal combustion engine is passed through the particulate filter, determining a loading state of the particulate filter, initiating a regeneration of the particulate filter when the loading state of the particulate filter has reached a defined maximum loading state, carrying out a regeneration process of the particulate filter, wherein the internal combustion engine and the electric motor are coupled during the regeneration and the electric motor tows the internal combustion engine, wherein the internal combustion engine supplies air into the exhaust duct in order to oxidize the soot particles retained in the particulate filter, and wherein a throttle valve of the air supply of the internal combustion engine is controlled during the regeneration of the particulate filter independently of a torque request from the driver to the hybrid drive.

[0014] This enables efficient overrun phases of the combustion engine, which can be actively shaped by the torque of the electric motor. This means that it is not necessary to wait for an overrun phase required by a driving situation to initiate regeneration, meaning that less frequent regeneration processes of the particulate filter are necessary. In a vehicle with a hybrid drive, a regeneration phase of the particulate filter can therefore be initiated when the particulate filter has reached a defined maximum load state. In this context, an overrun phase is understood to be an operating state in which no fuel is injected into one of the combustion chambers of the combustion engine and the combustion engine does not deliver any drive torque to the crankshaft. In this context, overrun of the combustion engine is understood to be an operating state in which the electric motor must generate torque to rotate the combustion engine.The combustion engine is rotated at a speed of greater than 100 rpm, preferably at least 600 rpm, and fuel injection into the combustion chambers of the combustion engine is preferably completely suppressed. Since the combustion engine is driven by the electric motor during regeneration of the particulate filter, the combustion engine serves to supply the oxygen required for regeneration of the particulate filter into the exhaust duct. By controlling the throttle valve independently of the load requirement, the throttle valve can thus supply the particulate filter with the amount of oxygen required for optimal regeneration.By opening the throttle valve widely, rapid regeneration of the particulate filter can be achieved. Closing the throttle valve reduces the air supply and prevents uncontrolled soot burn-off on the particulate filter, which can lead to its destruction. This allows for significantly faster and more effective regeneration of the particulate filter compared to uncontrolled regeneration with a closed throttle valve. This shortens the electric motor's drag phase and allows the vehicle to return to normal operation more quickly.

[0015] The measures specified in the dependent claims enable advantageous improvements and further developments of the method for regenerating the particulate filter specified in the independent claim.

[0016] According to the invention, the throttle valve is closed at the end of the particulate filter regeneration process. Closing the throttle valve at the end of the regeneration process creates a vacuum in the intake tract of the combustion engine, enabling the combustion engine to restart at low power output. This allows for a particularly smooth coupling of the combustion engine, thereby increasing the driving comfort of the vehicle.

[0017] In a preferred embodiment of the invention, the throttle valve is moved to a defined position at the beginning of regeneration. To initiate a defined regeneration process of the particulate filter, it is advantageous if the throttle valve is moved to a defined position at the beginning of regeneration, i.e., if the opening angle of the throttle valve is fixed at the beginning of regeneration.

[0018] It is particularly preferred if the throttle valve opening angle at the beginning of the particulate filter regeneration is between 30° and 70°. To enable rapid regeneration of the particulate filter without the risk of uncontrolled soot burn-off and thermal destruction of the particulate filter, it is advantageous to begin the regeneration process with the throttle valve partially open. Opening angles between 30° and 70° have proven particularly useful, as they represent a good compromise between sufficiently rapid regeneration and limiting the oxygen supply to the particulate filter.

[0019] According to an advantageous embodiment of the method, the throttle valve is closed in discrete steps. One possibility for implementing the method according to the invention is to transition the throttle valve in discrete steps from an at least partially closed initial state to a substantially closed final state. The steps can be selected depending on the progress of the regeneration of the particulate filter or depending on the temperature prevailing at the particulate filter.

[0020] In a further advantageous embodiment of the method, the opening angle of the throttle valve is continuously and steadily reduced from the start of regeneration to the end of the regeneration of the particulate filter. By constantly closing the throttle valve, a comparatively large amount of oxygen is initially supplied to the particulate filter at the start of regeneration, resulting in rapid soot burn-off on the particulate filter. An uncontrolled temperature increase above a critical temperature can be prevented by closing the throttle valve. In addition, closing the throttle valve before the combustion engine is restarted creates a vacuum in the intake tract of the combustion engine, which enables a smooth restart of the combustion engine and a corresponding power coupling of the combustion engine's drive power into the drive train of the hybrid vehicle.This prevents the combustion engine from suddenly restarting, thereby increasing driving comfort and the durability of the drive train.

[0021] It is particularly preferred if the throttle valve closes during regeneration of the particulate filter depending on the temperature and / or the soot load of the particulate filter. By changing the opening angle of the throttle valve depending on the temperature and / or the load of the particulate filter, particularly rapid regeneration of the particulate filter can be achieved without the risk of thermal damage to the particulate filter.

[0022] In a preferred embodiment of the invention, the regeneration process is preceded by a heating process in which the particulate filter is heated to a temperature range necessary for the oxidation of the soot. Since overrun operation is generally associated with a reduction in temperature in the exhaust duct, it may be necessary to heat the exhaust duct and thus the particulate filter to a regeneration temperature before initiating regeneration. Since both a sufficiently high temperature level and an excess of oxygen in the exhaust duct are necessary for the regeneration of the particulate filter, such a heating phase is a simple and effective means of achieving the temperature level. The excess oxygen is achieved, as shown, by the overrun operation of the internal combustion engine, whereby the internal combustion engine supplies air into the exhaust duct.

[0023] It is particularly preferred if the regeneration of the particulate filter takes place in several steps, alternating between a heating phase and a regeneration phase. If complete regeneration of the particulate filter is not possible in a coasting phase, in particular because the exhaust gas temperature falls below the lower threshold value, a multi-stage regeneration of the particulate filter is provided, alternating between a heating phase and a regeneration phase of the particulate filter. The combustion engine is connected to the drive train of the motor vehicle both in the heating phase and in the regeneration phase. During the heating phases, the combustion engine rotates of its own accord; during the regeneration phases, the combustion engine is driven by the electric motor and thus rotated.This prevents engine shutdown and decoupling of the combustion engine from the electric motor throughout the entire regeneration phase. Complete regeneration of the particulate filter can be achieved through multiple regeneration steps.

[0024] According to an advantageous further development of the method, the internal combustion engine is operated with a stoichiometric air-to-fuel ratio during the heating phase. A stoichiometric air-to-fuel ratio enables particularly effective conversion of pollutants on a three-way catalyst upstream of the particulate filter. Furthermore, a stoichiometric air-to-fuel ratio of the internal combustion engine is particularly well suited to heating the exhaust gas, since a lean air-to-fuel ratio is generally associated with a decrease in engine performance, and a rich air-to-fuel ratio generally leads to cooling of the exhaust gas by the unburned fuel.

[0025] In a preferred embodiment of the method, a load point of the internal combustion engine is shifted during the heating phase such that the internal combustion engine must additionally apply a greater load by charging the battery. Thus, the load is increased during the heating phase without the drive torque having a propulsive effect. As a result, the exhaust gas and thus the particulate filter are heated more quickly, under otherwise identical conditions (such as vehicle speed, engine speed), than in a motor vehicle that has and is powered exclusively by an internal combustion engine.

[0026] In a further preferred embodiment of the invention, it is provided that the throttle valve is used to throttle the internal combustion engine and transfer it from drag mode to drive mode, even when regeneration of the particulate filter is currently underway but still incomplete, if the load demand on the hybrid drive exceeds a certain threshold, in particular the rated power of the electric motor. If a load is requested during regeneration that lies above the rated load of the electric motor, the regeneration process of the particulate filter can be interrupted in order to provide the maximum system power from the internal combustion engine and electric motor. Regeneration of the particulate filter is thereby inhibited until the system power is again below the threshold and the necessary drive torque and drag torque of the internal combustion engine can be generated by the electric motor.The multi-stage regeneration of the particulate filter makes it possible to make the entire system performance available in the short term without having to fear damage to the particulate filter due to overloading and thus subsequent uncontrolled soot burn-off.

[0027] In a preferred embodiment, the load point of the electric motor is shifted during the regeneration of the particulate filter such that the electric motor provides the driver's desired torque and additionally tows the combustion engine. This allows additional power to be provided by the electric motor during the regeneration of the particulate filter, allowing the regeneration process to take place without compromising the driving experience.

[0028] It is particularly preferred if the regeneration of the particulate filter occurs in a torque-neutral manner for the propulsive drive torque of the vehicle, i.e., if the electric motor provides exactly as much additional torque during the regeneration of the particulate filter as is necessary to tow the combustion engine. This allows the regeneration phases to be carried out particularly comfortably and virtually unnoticed by the driver. The drag torque introduced into the drivetrain by the frictional power of the unfired combustion engine is fully compensated.

[0029] In a further preferred embodiment of the invention, the method is carried out in a spark-ignition internal combustion engine. The proposed method is, in principle, feasible in hybrid vehicles with a self-ignition internal combustion engine as well as in a spark-ignition internal combustion engine. However, since self-ignition internal combustion engines based on the diesel process are generally operated with a corresponding excess of oxygen, the provision of oxygen for regenerating the particulate filter in a diesel hybrid represents little challenge. In a gasoline hybrid, which is generally operated with a stoichiometric combustion air ratio, additional measures for introducing oxygen into the exhaust duct are necessary to regenerate the particulate filter.Since a spark-ignition combustion engine cannot be operated with a lean combustion air ratio without restrictions in performance, exhaust emission characteristics and / or comfort, the proposed method offers the advantage that regeneration is possible, especially at medium and lower partial loads, such as those that occur during operation in urban traffic.

[0030] The invention further proposes a control unit for a motor vehicle with a hybrid drive, with which such a method can be implemented. Such a control unit can easily control the power distribution between the electric motor and the combustion engine, thus creating the prerequisites for implementing such a method.

[0031] The invention further proposes a motor vehicle with a hybrid drive, comprising an electric motor and an internal combustion engine, wherein a particulate filter is arranged in the exhaust duct of the internal combustion engine and which has a control unit for controlling the internal combustion engine and the electric motor. The electric motor tows the internal combustion engine during regeneration of the particulate filter, and the internal combustion engine supplies air into the exhaust duct to oxidize the soot particles retained in the particulate filter. In such a motor vehicle, a particularly rapid and efficient regeneration of the particulate filter is possible without this regeneration being associated with a noticeable loss of comfort or performance for the driver.

[0032] Further preferred embodiments of the invention result from the remaining features mentioned in the subclaims.

[0033] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless stated otherwise in the individual case.

[0034] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show: Figure 1 shows a first exemplary embodiment of a motor vehicle according to the invention with a hybrid drive comprising an internal combustion engine and an electric motor; Figure 2 shows a further exemplary embodiment of a motor vehicle according to the invention with a hybrid drive; Figure 3 shows a first flowchart of a method according to the invention for regenerating a particulate filter in a motor vehicle with a hybrid drive; and Figure 4 shows a further flowchart of a method according to the invention for regenerating a particulate filter in a motor vehicle with a hybrid drive.

[0035] Figure 1shows a schematic representation of a motor vehicle 1 with a hybrid drive 2. The hybrid drive 2 comprises an internal combustion engine 10 and an electric motor 20, which can both be operatively connected to a common transmission 46 via a drive train 26. The internal combustion engine 10 is connected to an air supply 30 on the inlet side. The air supply 30 has an air filter 32 in the direction of flow of fresh air, an air mass meter 38 downstream of the air filter 32, further downstream a compressor 36 of a turbocharger 40 and a throttle valve 34. The internal combustion engine 10 is connected to an exhaust duct 12 on the outlet side, in which a turbine 18 is arranged in the direction of flow of an exhaust gas, which turbine is connected to the compressor 36 of the turbocharger 40 via a shaft. Downstream of the turbine 18 is a catalytic converter 14 and further downstream a particulate filter 16.The transmission 46 is connectable to the internal combustion engine 10 via a first clutch 48 and to the electric motor 20 via a second clutch 50. The internal combustion engine 10 and the electric motor 20 can drive the motor vehicle 1 either individually or together. For this purpose, the internal combustion engine 10 is connected to a first drive axle of the motor vehicle 1 via the transmission 46, and the electric motor 20 is connected to a second drive axle 44 of the motor vehicle 1. The electric motor 20 is connected to a battery 22, which supplies the electric motor 20 with power. The electric motor 20 and the internal combustion engine are connected via signal lines 28 to a control unit 10 of the hybrid drive 2, which transmits the driver's power requirements to the two drive motors 10, 20. Alternatively, the hybrid drive 2 can also be designed with a naturally aspirated engine, in which case the turbocharger 40 with the compressor 36 and the turbine 18 is omitted.

[0036] In Figure 2 1 shows a further exemplary embodiment of a motor vehicle 1 according to the invention with a hybrid drive 2. The internal combustion engine 10 and the electric motor 20 are preferably arranged transversely to the direction of travel of the motor vehicle 1 in an engine compartment in the front of the motor vehicle. Alternatively, the internal combustion engine 10 and the electric motor 20 can also be arranged longitudinally to the direction of travel. A first clutch 48 is arranged between the internal combustion engine 10 and the transmission 46, via which the internal combustion engine 10 can be mechanically connected to the transmission 46. This first clutch 48 can be designed either as a simple shift clutch or as a, preferably automated, double clutch. A further clutch 50 is provided between the transmission 46 and the electric motor 20, which enables the electric motor 20 to be coupled or uncoupled.

[0037] A tank for the combustion engine 10 and a battery 22 for the electric motor 20 are arranged at the rear of the vehicle to achieve a uniform weight distribution between the first drive axle 42, preferably the front axle of the motor vehicle 1, and the second axle, preferably the rear axle. Alternatively, the tank and / or the battery 22 can also be arranged at other positions on the motor vehicle 1.

[0038] The internal combustion engine 10 has an air supply 30, in which an air filter 32 and an air mass meter 38 are arranged in the direction of flow of the fresh air. Alternatively, the air mass meter 38, in particular a hot-film air mass meter, can also be integrated into the air filter 32. Downstream of the air mass meter 38 is a throttle valve 34, with which the air supply to the combustion chambers of the internal combustion engine 10 can be controlled.

[0039] The electric motor 20 and the combustion engine 10 are connectable to one another via a common drive train 26, wherein the connection can be established or interrupted by the clutches 48 and 50. By engaging only one of the clutches 48 or 50, the motor vehicle 1 can be operated either exclusively electrically, by the electric motor 20, or exclusively with the combustion engine 10. If both clutches 48 and 50 are engaged, boost operation with both drive units 10, 20, recuperation (i.e., charging the battery 22 of the electric motor 20), or electric braking can be performed. The transmission 46 is connected to a differential, which drives the wheels of the first drive axle 42, in particular the front axle, via drive shafts.

[0040] The internal combustion engine 10 has an exhaust duct 12 in which a three-way catalytic converter 14 and a particulate filter 16 are arranged. A control unit 24 is provided to control the internal combustion engine 10 and the electric motor 20. The control unit 24 is connected to the internal combustion engine 10 via first signal lines 28 and to the electric motor 20 via second signal lines 28.

[0041] During normal operation, the motor vehicle 1 is operated in a hybrid mode in which the driver's desired torque is passed on to the internal combustion engine 10, the electric motor 20, or both motors 10, 20 by the control unit 24 after a specific drive motor 10, 20. The operating strategy of the hybrid drive 2 stored in the control unit 24 specifies how the driver's request is fulfilled. The drive torque can either be provided entirely by the electric motor 20, by being split between the electric motor 20 and the internal combustion engine 10, or entirely by the internal combustion engine 10. During hybrid operation, it is also possible for the internal combustion engine 10 to generate more torque than is necessary to drive the motor vehicle, with the additional torque being used by coupling the electric motor 20 via the clutch 50 to charge the battery 22 of the electric motor 20.

[0042] While the internal combustion engine 10 is active, the exhaust gas of the internal combustion engine is passed through the particulate filter 16 in the exhaust duct 12. During hybrid operation, the particulate filter 16 is loaded with soot particles until a maximum permissible loading state of the particulate filter 16 is reached.

[0043] In Figure 3A flow chart for the regeneration of the particulate filter 16 is shown. In a first phase I, the motor vehicle is operated in hybrid mode I until the particulate filter 16 has reached a maximum permissible load state. The opening angle α of the throttle valve 34 can be changed between 0% and 100% and depends on the power requirement of the internal combustion engine 10. The maximum permissible load state can be determined by a differential pressure measurement across the particulate filter 16 or by modeling the soot entry and the soot discharge from the particulate filter 16 using a calculation model stored in the control unit 24. If the need for regeneration of the particulate filter 16 is determined, in a second phase II the particulate filter 16 is heated to a temperature required for regeneration. The heating phase II of the particulate filter 16 is followed by the regeneration phase III of the particulate filter 16.The regeneration phase III of the particulate filter 16 can be carried out as in . Figure 4 shown in several steps III 1 to III 5 or as in Figure 3 shown continuously. In Figure 4a regeneration with five regeneration steps is shown, but regenerations with more or fewer regeneration steps are also possible. In addition, heating phase II can be omitted if the particulate filter 16 already has a temperature necessary for oxidizing the soot retained in the particulate filter 16 when regeneration phase III is initiated. In heating phase II, the internal combustion engine 10 is operated under load until an upper threshold temperature T SO is reached. This upper threshold temperature is, for example, 750°C, which creates ideal conditions for oxidizing the soot retained in the particulate filter 16. Heating phase II can, for example, comprise adjusting the ignition timing towards retardation and / or an additional load on the internal combustion engine 10 by operating the electric motor 10 as a generator. The internal combustion engine 10 is preferably operated with a stoichiometric combustion air ratio.If the upper threshold temperature T SO is reached, the fuel injection into the combustion chambers of the internal combustion engine 10 is stopped and the internal combustion engine 10 is overrun by the electric motor 20. In this regeneration phase III, the internal combustion engine 10 is rotated by the electric motor 20, with the internal combustion engine 10 supplying air into the exhaust duct 12. During regeneration phase III, which represents an overrun phase for the internal combustion engine 10, the soot in the particulate filter 16 is oxidized, with the exhaust gas temperature dropping due to the lack of combustion in the combustion chambers of the internal combustion engine 10. Alternatively, the injection of fuel into individual or all cylinders of the internal combustion engine 10 can be suppressed. During regeneration phase III, the internal combustion engine 10 does not deliver any drive torque, so that the entire drive torque must be generated by the electric motor 20.The opening angle α of the throttle valve 34 is set to a fixed value, for example 50%, at the start of the regeneration of the particulate filter 16. During the regeneration of the particulate filter 16, the throttle valve 34 is continuously closed until the opening angle α of the throttle valve 34 reaches 0% at the end of the regeneration, i.e., a maximum throttling of the fresh air quantity is reached. Regeneration phase 3 is maintained until the temperature at the particulate filter 16 reaches a lower threshold value T SU of approximately 600°C. Below this temperature, no further oxidation of the soot is possible, so that a heating phase II must be initiated again. To regenerate the particulate filter 16, it is possible to alternate between heating phase II and regeneration phase III 3.This alternating change between heating phase II and regeneration phase III is repeated until the particulate filter 16 can be considered regenerated, which can be done by measuring the differential pressure across the particulate filter 16 or by modeling the load state using a calculation model. By closing the throttle valve 34 at the end of regeneration III, a negative pressure is created in the intake port of the internal combustion engine 10, which enables a particularly gentle resumption of combustion in the combustion chambers of the internal combustion engine 10.

[0044] After successful regeneration of the particulate filter 16, the motor vehicle is again operated in hybrid mode I and the particulate filter 16 is again loaded with soot particles.

[0045] In Figure 4 Another scheme for regenerating the particulate filter 16 is shown. With essentially the same procedure as in Figure 3As described, the closing of the throttle valve 34 takes place here in discrete steps, for example by 10% per step. At the beginning of regeneration III 1 of the particulate filter 16, the throttle valve 34 is open with a defined, fixed opening angle α of, for example, 60%, with each further step III 2 to III 5 further closing the throttle valve 34 by a defined amount until, at the end of the regeneration of the particulate filter 16, it is at least substantially closed and has a maximum residual opening of 10%.

[0046] If, during the regeneration of the particulate filter 16, a load demand is placed on the hybrid drive 2 that exceeds the power of the electric motor 20, the throttle valve 34 is closed to facilitate the start-up of the combustion engine 10. Regeneration phase III of the particulate filter 16 is interrupted until suitable conditions for regeneration of the particulate filter 16 are present again.

[0047] The method according to the invention creates a particularly efficient mechanism for burning off soot particles on the particulate filter 16. Due to the overrunning of the internal combustion engine 10 by the electric motor 20, the introduction of oxygen into the exhaust duct 12 can be controlled largely independently of the load point of the hybrid drive 2. The torque required to overrun the internal combustion engine 10 is generated by the electric motor 20, so that the regeneration of the particulate filter 16 is imperceptible to the driver of the motor vehicle 1 and is particularly comfortable.

[0048] To optimize regeneration, both the load point of the combustion engine 10 (particularly in heating phase II) and the load point of the electric motor 20 during the overrun phase can be shifted, as described. The combustion engine 10 is not disconnected from the drive train of the motor vehicle 1 with hybrid drive 2 during regeneration. This results in a significantly simpler regeneration option for the particulate filter 16. List of reference symbols

[0049] 1Motor vehicle 2Hybrid drive 10Combustion engine 12Exhaust duct 14Catalyst 16Particulate filter 18Turbine 20Electric motor 22Battery 24Control unit 26Drive train 28Signal line 30Air supply 32Air filter 34Throttle valve 36Compressor 38Air mass meter 40Turbocharger 42First drive axle 44Second drive axle 46Gearbox 48First clutch 50Second clutch SSoot loading of the particulate filter PProgress of particulate filter regeneration tTime αOpening angle of the throttle valve α FIX Opening angle during regeneration specified by process IHybrid operation IIHeating phase of the particulate filter IIIRegeneration phase of the particulate filter III 1 First regeneration step III 2 Second regeneration step III 3 Third regeneration step III 4 Fourth regeneration step III 5 Fifth regeneration step

Claims

1. Method for regenerating a particulate filter (16) in the exhaust duct (12) of a motor vehicle having a hybrid drive comprised of an electric motor (20) and an internal combustion engine (10), comprising the following steps: - operating the motor vehicle in hybrid mode, wherein, during operation of the internal combustion engine (10), the exhaust gas from the internal combustion engine (10) is passed through the particulate filter (16), - determining a load state of the particulate filter (16), - initiating a regeneration of the particulate filter (16) when the load state of the particulate filter (16) has reached a defined maximum load state, - carrying out a regeneration process of the particulate filter (16), wherein the internal combustion engine (10) and the electric motor (20) are coupled during the regeneration and the electric motor (20) lugs the internal combustion engine (10), wherein - the internal combustion engine (10) feeds air into the exhaust duct (12) in order to oxidize the soot particles retained in the particulate filter (16), characterized in that - during the regeneration of the particulate filter (16), a throttle valve (34) of the air supply of the internal combustion engine (10) is controlled independently of a torque request from the driver to the hybrid drive, and - the throttle valve (34) is closed at the end of the regeneration of the particulate filter.

2. Method according to claim 1, characterized in that the throttle valve (34) is brought into a defined position at the beginning of the regeneration of the particulate filter (16).

3. Method according to claim 2, characterized in that the opening angle of the throttle valve (34) at the beginning of the regeneration represents a significantly dethrottled operating point, preferably an opening angle between 30° and 70°.

4. Method according to any of claims 1 to 3, characterized in that the opening angle of the throttle valve (34) is continuously and steadily reduced from the beginning of the regeneration to the end of the regeneration.

5. Method according to claim 4, characterized in that the reduction of the opening angle of the throttle valve (34) during the regeneration of the particulate filter (16) takes place on the basis of a temperature and / or a load state of the particulate filter (16).

6. Method according to any of claims 1 to 5, characterized in that the regeneration process is preceded by a heating process in which the particulate filter (16) is heated to a temperature range necessary for the oxidation of the soot.

7. Method according to claim 6, characterized in that the internal combustion engine (10) is operated with a stoichiometric air-fuel equivalence ratio during the heating phase.

8. Method according to any of claims 6 or 7, characterized in that a load point of the internal combustion engine (10) is shifted in the heating phase in such a way that, owing to a charging process of the battery (22), the internal combustion engine (10) has to apply additional load counter to the work of the electric motor (20).

9. Method according to any of claims 1 to 8, characterized in that, if the load requirement on the hybrid drive exceeds a certain threshold value, the throttle valve (34) is closed and the internal combustion engine (10) is started, even if the regeneration of the particulate filter (16) is incomplete.

10. Method according to any of claims 1 to 8, characterized in that a load point of the electric motor (20) is shifted during the regeneration of the particulate filter (16) in such a way that solely the electric motor (20) provides the driver's desired torque for the motor vehicle (1) and additionally lugs the internal combustion engine (10).

11. Method according to claim 10, characterized in that the regeneration of the particulate filter (16) is torque-neutral for the propulsive drive torque of the motor vehicle (1).

12. Method according to any of claims 1 to 11, characterized in that the method is carried out on an external-ignition internal combustion engine (10).

13. Control unit (24) for a motor vehicle (1) having a hybrid drive (2) comprised of an internal combustion engine (10) and an electric motor (20), which control unit is configured to carry out a method according to any of claims 1 to 12.

14. Motor vehicle (1) having a hybrid drive (2), comprising an electric motor (20) and an internal combustion engine (10), wherein a particulate filter (16) is arranged in an exhaust duct (12) of the internal combustion engine (10), and which motor vehicle also has a control unit (24) according to claim 13.