Methods for exhaust aftertreatment of an internal combustion engine in a hybrid vehicle and hybrid vehicles with an exhaust aftertreatment system

Abstract

Method for exhaust aftertreatment of an internal combustion engine (10) in a motor vehicle with a hybrid drive consisting of an electric motor (60) and an internal combustion engine (10), wherein the internal combustion engine (10) is connected with its outlet (18) to an exhaust system (22), wherein an electrically heated three-way catalyst (34) is arranged in the exhaust system (22), and wherein the internal combustion engine (10) has a cylinder deactivation actuator (64), comprising the following steps: - Operating the motor vehicle in hybrid mode, whereby the motor vehicle is driven exclusively by the electric motor (60), - electrical heating of an electric heating element (36) in the exhaust duct (32) upstream of a catalytically active structure (38) of the electrically heated three-way catalyst (34), - Introducing secondary air into the exhaust duct (32) upstream of the electric heating element (36) to form a carrier mass flow which enables convective heat transfer from the electric heating element (36) to the catalytically active structure (38) of the electrically heated catalyst (34), wherein - the combustion engine (10) is towed by the electric motor (60) and, during towing operation, supplies fresh air as secondary air to the exhaust system (22), and - the cylinder deactivation actuator (64) is used to reduce the carrier mass flow during towing by not using all cylinders of the internal combustion engine (10) to pump fresh air into the exhaust port (32), and - Switching on the combustion engine (10) when the catalytically active structure (38) of the electrically heated three-way catalyst (34) reaches its light-off temperature (T LO ) has reached.

Description

[0001] The invention relates to a method for exhaust aftertreatment of an internal combustion engine in a hybrid vehicle with an internal combustion engine and an electric drive motor, as well as a hybrid vehicle with an exhaust aftertreatment system.

[0002] The continuously tightening of emissions regulations places high demands on vehicle manufacturers, which are met through appropriate measures to reduce raw engine emissions and through suitable exhaust aftertreatment. To effectively convert the unavoidable raw emissions into emissions after the engine, catalytic converters coated with precious metals are installed in the exhaust system of the combustion engine. For these catalytic converters to convert the pollutants, a minimum temperature level of the exhaust gas and the catalytic converter is necessary. To bring the catalytic converter up to operating temperature as quickly as possible after a cold start of the combustion engine, engine heating measures are used, such as retarding the ignition timing or operating the combustion engine at substoichiometric temperatures while simultaneously introducing secondary air.To introduce even more heat energy into the exhaust system, the catalyst can be electrically heated. This allows emissions to be significantly reduced even during the catalyst's heating phase. Heating resistors are typically used, positioned upstream of the actual catalyst in the exhaust system, in the direction of gas flow. When heating the catalyst, it is essential to warm as large an area of ​​the catalytically active coating as possible, ensuring a large surface area is available for converting the pollutants contained in the exhaust gas.

[0003] Typically, in a hybrid vehicle, the combustion engine is deactivated after the vehicle is ready to drive, so the electric motor initially provides the sole propulsion. When the electric energy source runs low, the combustion engine usually has to be started. To convert the gaseous emissions as efficiently as possible, the catalytic converter must reach its operating temperature as quickly as possible. Because the combustion engine is not rotating during purely electric driving, there is no heat transfer fluid flow during electric driving to transport the heat introduced into the exhaust manifold by an electric heating element to the catalytically active surface of the catalyst. If the heat from the heating element cannot be dissipated, it can also overheat and suffer thermal damage.

[0004] German patent application DE 10 2016 014 254 A1 discloses a method for heating an exhaust aftertreatment system of a hybrid vehicle with a diesel engine and an electric drive motor, wherein an electric heating element is arranged in the exhaust system of the diesel engine and a particulate filter with a coating for the selective catalytic reduction of nitrogen oxides is arranged downstream of the electric heating element. The electric motor is designed to pull the combustion engine and supply air to the exhaust system to heat the particulate filter. The air is heated by the electric heating element upstream of the particulate filter and convectively transferred to the particulate filter, so that the SCR coating of the particulate filter reaches a temperature necessary for the conversion of the nitrogen oxides.

[0005] From DE 10 2011 101 676 A1, a catalyst heating device for an exhaust aftertreatment system of a hybrid vehicle is known, wherein the exhaust aftertreatment system comprises an electrically heated catalyst, wherein an electric heating element is energized to heat the catalyst and secondary air is simultaneously blown into the exhaust channel upstream of the electrically heated catalyst in order to heat the electrically heated catalyst to its operating temperature before the combustion engine is switched on.

[0006] From EP 1 197 642 A2, a method for regenerating a particulate filter in a hybrid vehicle is known. In this method, the temperature of the exhaust gas is increased by increasing the load on the combustion engine, by having the combustion engine charge the battery of the electric motor of the hybrid vehicle in addition to propelling the vehicle.

[0007] DE 10 2008 063 449 A1 describes a method for operating a hybrid drive with an internal combustion engine and an electric motor, which can be coupled to the internal combustion engine for drive purposes, and with a heated catalyst through which exhaust gas from the internal combustion engine flows. To improve the cleaning effect of the catalyst, particularly when starting the internal combustion engine after a standstill, the internal combustion engine is driven by the electric motor during a catalyst cold phase, in which the catalyst has not yet reached a desired operating temperature and is being heated. This is done to pump a flow of heating medium through the heated catalyst for heating purposes before the internal combustion engine is started.

[0008] From DE 10 2009 020 809 A1, a control system is known comprising an air pump control module that controls an air pump and an internal combustion engine start module that starts an internal combustion engine. The air pump control module activates the air pump based on the temperature of a catalyst in order to supply oxygen to the catalyst. The internal combustion engine start module starts the internal combustion engine based on the temperature of the catalyst.

[0009] Furthermore, DE 10 2015 015 794 A1 discloses a method for heating at least one exhaust aftertreatment device arranged in an exhaust tract of a motor vehicle comprising an internal combustion engine and driven by the internal combustion engine, in particular a hybrid vehicle, wherein, during combustion of fuel in the internal combustion engine, an airflow is effected which flows at least through the exhaust aftertreatment device and which is heated by means of at least one electric heating element.

[0010] DE 10 2005 001 046 A1 describes a method for operating a hybrid vehicle as well as a hybrid vehicle with a multi-cylinder combustion engine coupled to an electric machine.

[0011] Furthermore, a combustion engine with a mechanically fully variable valve train and cylinder deactivation is known from the publication: FIERL, Rudolf: MECHANICALLY FULLY VARIABLE VALVE DRIVE AND CYLINDER DEACTIVATION ; Motorentechnische Zeitung, issue 04 / 2013, page 334ff.

[0012] The invention is based on the objective of enabling the fastest and most efficient heating of the three-way catalytic converter in a hybrid vehicle with a gasoline engine and an electric motor, and of enabling efficient exhaust aftertreatment for starting the combustion engine.

[0013] According to the invention, the problem is solved by a method for exhaust aftertreatment of an internal combustion engine in a motor vehicle with a hybrid drive consisting of an electric motor and an internal combustion engine, wherein the internal combustion engine is connected to an exhaust system via its exhaust outlet. An electrically heated three-way catalytic converter is arranged in the exhaust system of the internal combustion engine. The internal combustion engine has a cylinder deactivation actuator. The method comprises the following steps: - Operating the motor vehicle in hybrid mode, whereby the motor vehicle is driven exclusively by the electric motor, - electrical heating of an electric heating element in the exhaust duct upstream of a catalytically active structure of the electrically heated three-way catalyst, - Introducing secondary air into the exhaust duct upstream of the electric heating element to create a carrier mass flow which enables convective heat transfer from the electric heating element to the catalytically active structure of the electrically heated catalyst, wherein - the combustion engine is towed by the electric motor and, during towing operation, fresh air is supplied as secondary air to the exhaust system, and - the cylinder deactivation actuator is used to reduce the carrier mass flow during towing by not using all cylinders of the internal combustion engine to pump fresh air into the exhaust manifold, and - Switching on the combustion engine when the catalytically active structure of the electrically heated three-way catalyst has reached its light-off temperature.

[0014] A method according to the invention makes it possible to heat the catalytically active structure of the three-way catalyst to such an extent before the combustion engine is started that efficient conversion of harmful exhaust gas components from the combustion engine is possible from the moment the engine starts. Furthermore, the carrier mass flow achieves faster heating of the catalytically active structure and reduces the risk of thermal damage to the electrical heating element, since the carrier mass flow acts as a cooling airflow on the electrical heating element. Thus, in a hybrid vehicle, emissions can be reduced not only in purely electric mode, but also when the combustion engine is running, particularly during a cold start phase.

[0015] In a preferred embodiment of the method, it is provided that at least one further component for exhaust aftertreatment of an internal combustion engine, in particular another three-way catalyst, a four-way catalyst, a gasoline particulate filter or an HC adsorber, is arranged downstream of the electrically heated three-way catalyst.

[0016] According to the invention, the combustion engine is towed by the electric motor, with the combustion engine supplying fresh air to the exhaust system during towing operation. In this context, towing operation of the combustion engine is understood to mean an operating condition in which the electric motor must provide torque to rotate the combustion engine. During this operation, the combustion engine is rotated at a speed greater than 100 rpm, preferably at least 600 rpm, and the injection of fuel into the combustion chambers of the combustion engine is completely disabled. Since the combustion engine is towed by the electric motor during the heating phase of the catalytically active structure of the electrically heated three-way catalyst, the combustion engine serves during regeneration to supply the air necessary for the carrier mass flow into the exhaust manifold.Furthermore, with such a solution, a secondary air pump for providing a carrier mass flow can be omitted.

[0017] The features specified in the dependent claims enable advantageous improvements and further developments of the exhaust aftertreatment method for a hybrid vehicle specified in the independent claim.

[0018] It is particularly advantageous to vary the opening angle α of the throttle valve in the intake manifold of the combustion engine to regulate the carrier mass flow. Opening the throttle valve wide increases the carrier mass flow, thereby dissipating more heat from the electric heating element. Closing the throttle valve reduces the air supply, thus decreasing the flow velocity of the carrier mass flow in the exhaust manifold. This allows the carrier mass flow to be adjusted for optimal convective heat transfer. Furthermore, it prevents the electric heating element from burning out due to thermal overload. Compared to an uncontrolled carrier mass flow, this results in significantly faster and more effective heating of the catalytically active structure, thus shortening the drag phase of the electric motor.Since a mechanical oil pump driven by the combustion engine is also activated during the coasting phase, the combustion engine is adequately lubricated during this phase to prevent increased wear. Furthermore, coasting can have beneficial effects on oil and fuel pressure, resulting in favorable operating conditions for an extremely controlled and smooth engine start. Closing the throttle valve at the end of the warm-up phase creates a vacuum in the combustion engine's intake manifold, enabling a restart at low power output. This allows for a particularly smooth engagement of the combustion engine, thereby increasing the vehicle's driving comfort.

[0019] Alternatively or additionally, it is advantageous to modify the valve opening times of the internal combustion engine to regulate the airflow. A camshaft adjuster can adapt the valve opening times, thereby adjusting the amount of air supplied to the exhaust manifold. In particular, valve overlap—that is, the simultaneous opening of the intake and exhaust valves of the internal combustion engine—can be used to increase the amount of air supplied to the exhaust manifold at the same engine speed or to prevent pulsations.

[0020] According to another preferred alternative, it is proposed that an exhaust flap be provided in the exhaust system, the position of which regulates the carrier mass flow. The position of the exhaust flap can alter the exhaust back pressure in the exhaust duct. This can additionally lead to an increase in the exhaust temperature, which promotes the heating of the catalytically active structure of the electrically heated three-way catalyst.

[0021] In an embodiment not part of the invention, a disconnect clutch is arranged between the internal combustion engine and the electric motor. This disconnect clutch may have a slippage that allows the internal combustion engine to rotate at a reduced speed compared to a transmission input shaft connected to the electric motor. This reduces the carrier flow, thus minimizing cooling of the exhaust duct due to excessive fresh air flow. Combining two or more of the aforementioned measures enables improved control of the carrier mass flow. For example, the amount of air in the carrier mass flow can be pre-controlled via the rotational speed of the internal combustion engine, while fine control is achieved by opening and closing the throttle valve and / or the exhaust flap.

[0022] In an internal combustion engine with cylinder deactivation actuators, these actuators can be used to reduce the carrier mass flow during towing operation by not using all cylinders of the internal combustion engine to pump fresh air into the exhaust channel, but by reducing, in particular halving, the "pump power" of the towed internal combustion engine.

[0023] Furthermore, additional parameters such as ambient air pressure or the position of any tumble damper that may be present can be used to control or regulate the carrier mass flow.

[0024] In a further improvement of the method, the hybrid drive is provided to include at least one control unit with which a carrier mass flow rate necessary for maximum efficient heating of the catalytically active structure of the electrically heated three-way catalyst is calculated. Preferably, in addition to the control unit for the combustion engine, a further control unit is provided that manages the interaction between the combustion engine and the electric motor. Alternatively, the functions can also be implemented in a single control unit.In at least one of the control units, a control algorithm or a characteristic map for heating the catalytically active structure of the three-way catalyst is stored in order to achieve the best possible heating result and to avoid overheating of the electrical heating element, in particular a heating disc directly upstream of the catalytically active structure of the electrically heated three-way catalyst.

[0025] In a further improvement of the method, it is provided that at least one control unit detects an imminent start-up of the combustion engine and initiates the method according to the invention when such a start-up of the combustion engine is imminent. This can be achieved in particular by monitoring the state of charge (SOC) of the electric motor's battery.

[0026] In an embodiment not belonging to the invention, the internal combustion engine is designed as a turbocharged internal combustion engine, wherein the supplied carrier mass flow is introduced upstream of the turbine, and the carrier mass flow is regulated by the position of a wastegate valve or an adjustable guide geometry of the turbine of the exhaust gas turbocharger. Particularly when secondary air is supplied by a secondary air pump, adjusting the guide geometry and / or via the wastegate valve provides a further possibility of regulating the carrier mass flow through the electric heating element.

[0027] It is particularly preferred if the introduction of the carrier mass flow is torque-neutral with respect to the propulsive drive torque of the vehicle, that is, if the electric motor provides precisely the amount of additional torque during the heating phase required to pull the combustion engine. This allows the heating phase to be performed particularly comfortably and virtually imperceptibly for the driver. Preferably, this results in complete compensation of the drag torque introduced into the drivetrain by the frictional power of the unpowered combustion engine.

[0028] The invention further proposes a control unit for a motor vehicle with a hybrid drive consisting of an internal combustion engine and an electric motor, with which such a method can be carried out. The power distribution between the electric motor and the internal combustion engine can be controlled in a simple manner via such a control unit, thus creating the prerequisites for carrying out a method according to the invention.

[0029] The invention further proposes a motor vehicle with a hybrid drive, comprising an electric motor and an internal combustion engine as well as a cylinder deactivation actuator, wherein an electrically heated catalyst with an electric heating element and a catalytically active structure is arranged in an exhaust system of the internal combustion engine. The motor vehicle has at least one control unit for controlling the internal combustion engine, the control unit being configured to control a method for exhaust aftertreatment of an internal combustion engine as described in the preceding sections. In such a motor vehicle, particularly rapid and efficient heating of the three-way catalyst is possible, so that the emissions of the internal combustion engine can be efficiently converted from the moment the engine is started.

[0030] In a preferred embodiment of the vehicle, a further exhaust aftertreatment component is arranged downstream of the electrically heated three-way catalytic converter in the exhaust system of the combustion engine. The further components can, in particular, be another three-way catalytic converter, an HC adsorber, a four-way catalytic converter, or an uncoated particulate filter. In the case of a four-way catalytic converter or an uncoated particulate filter, the method can be used to supply the oxygen necessary for the regeneration of the particulate filter or four-way catalytic converter by carrying out the regeneration in a phase during which the combustion engine is towed by the electric motor.

[0031] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0032] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 an embodiment of a powertrain of a motor vehicle according to the invention with a hybrid drive consisting of an internal combustion engine and an electric motor; Fig. 2 an internal combustion engine and the exhaust system connected to the internal combustion engine of a motor vehicle according to the invention with a hybrid drive; and Fig. 3 a flowchart for carrying out a method according to the invention for the exhaust aftertreatment of a motor vehicle with a hybrid drive consisting of an internal combustion engine and an electric motor.

[0033] Fig. Figure 1 shows a schematic representation of a powertrain of a motor vehicle according to the invention with a hybrid drive. The hybrid drive comprises an internal combustion engine 10 and an electric motor 60, which can both be operatively connected to a transmission 70 via a common powertrain. A disconnect clutch 20 is provided between the internal combustion engine 10 and the electric motor 60, by which the electric motor 60 can be decoupled from the internal combustion engine 10. The electric motor 60 is connected to the main battery 62 of the hybrid vehicle via a corresponding electrical connection. The electric motor 60 is also connected to a transmission 70 of the hybrid vehicle via a transmission input shaft 66. The transmission 70 transmits a drive torque to at least one drive wheel 80 of the hybrid vehicle.The combustion engine 10 is assigned an engine control unit 52, which connects the engine control unit 52 to the combustion engine 10 via a signal line 54. The hybrid vehicle also has a main control unit 56, which is connected to the engine control unit 52 and the electric motor 60 via signal lines 58 and controls the coordination of the electric motor 60 and the combustion engine 10.

[0034] In Fig. Figure 2 shows an internal combustion engine 10 of a hybrid vehicle according to the invention. The internal combustion engine 10 is designed as a spark-ignition engine and has several combustion chambers 14, each of which has at least one spark plug 16. The internal combustion engine 10 is connected to an air supply system (not shown) via its inlet 12. The internal combustion engine 10 is connected to an exhaust system 22 via its outlet 18. The exhaust system 22 comprises an exhaust duct 32 in which, in the direction of exhaust gas flow, the turbine 30 of an exhaust gas turbocharger 28, an electrically heated three-way catalytic converter 34 downstream of the turbine 30, and a four-way catalytic converter 40 further downstream are arranged. Furthermore, an exhaust flap 42 is provided in the exhaust duct 32 downstream of the four-way catalytic converter 40, with which the exhaust duct 32 can be at least partially closed.

[0035] The electrically heated three-way catalyst 34 comprises a housing in which an electric heating element 36, in particular a heating disc, and a catalytically active structure 38 of the three-way catalyst 34 are arranged downstream of the electric heating element 36. Alternatively, the electric heating element 36 can also be arranged upstream of the catalyst housing of the electrically heated three-way catalyst 34 in the exhaust gas channel 32. A first lambda sensor 44, preferably a wideband lambda sensor, is arranged in the exhaust gas channel 32 downstream of the turbine 30 and upstream of the electrically heated three-way catalyst 34. A second lambda sensor 46, preferably a switching sensor, is arranged downstream of the electrically heated three-way catalyst 34 and upstream of the four-way catalyst 40.A temperature sensor 48, 50 is provided upstream and downstream of the four-way catalytic converter 40, respectively. The lambda sensors 44, 46 and the temperature sensors 48, 50 are each connected to the engine control unit 52 via signal lines 54. Furthermore, a secondary air pump 24 can be provided on the exhaust system 22, with which secondary air can be injected into the exhaust channel 32 downstream of the outlet 18 of the internal combustion engine 10 and upstream of the electric heating element 36, preferably upstream of the turbine 30 of the exhaust gas turbocharger 28. For this purpose, the secondary air pump 24 is connected to the exhaust channel 32 via a secondary air line 26. A secondary air valve (not shown) can also be arranged in the secondary air line 26, by which the amount of secondary air can be controlled.

[0036] In normal operation, the vehicle operates in a hybrid mode, in which the driver's requested torque is transmitted by the control units 52, 56 to the combustion engine 10, the electric motor 60, or both engines 10, 60. The operating strategy of the hybrid drive, stored in the control unit 56, determines how the driver's request is fulfilled. The drive torque can be provided entirely by the electric motor 60, shared between the electric motor 60 and the combustion engine 10, or provided entirely by the combustion engine 10. In hybrid operation, it is also possible for the combustion engine 10 to generate more torque than is required to propel the vehicle. This additional torque is used to charge the electric motor 60's battery 62 by engaging the electric motor 60 via the clutch 20.

[0037] While the combustion engine 10 is active, the pollutants contained in the exhaust gas of the combustion engine 10 must be converted or retained. For this purpose, the exhaust gas of the combustion engine 10 is passed through the electrically heated three-way catalytic converter 34 and the four-way catalytic converter 40. During hybrid operation, the four-way catalytic converter 40 becomes loaded with soot particles until a maximum permissible loading state of the four-way catalytic converter 40 is reached and it must be regenerated.

[0038] In Fig. Figure 3 shows a flowchart for the operating strategy of the hybrid drive. This is shown in the diagram. Fig.Figure 3 shows the temperature T of the catalytically active structure 38 of the electrically heated three-way catalyst 34 over time t. In a first phase I, the vehicle operates in hybrid mode I, in which propulsion is provided solely by the electric motor 60. If the control unit 56 detects that the combustion engine 10 will soon be engaged, which occurs particularly due to a low state of charge of the battery 62, the electric heating element 36 is energized in a phase II, and a carrier mass flow is generated. This flow convectively transfers the heat generated at the electric heating element 36 to the catalytically active structure 38 of the electrically heated three-way catalyst 34. For this purpose, the combustion engine 10 is driven by the electric motor 60, causing the combustion engine 10 to draw fresh air into the exhaust port 32 of the combustion engine 10.This fresh air serves as a carrier mass flow to enable convective heating of the catalytically active structure 38 of the three-way catalyst 34 and to prevent overheating of the electric heating element 36. The carrier mass flow is reduced by an actuator for cylinder deactivation 64 and can additionally be influenced by the rotational speed n of the internal combustion engine 10, the position of a throttle valve in the intake manifold of the internal combustion engine 10, camshaft adjustment and the associated change in valve opening times, tumble flap control, and exhaust flap control. Based on these and other parameters, such as the ambient air pressure p, UThe carrier mass flow rate can be modeled so that it can be controlled to achieve optimal heating of the catalytically active structure 38. The calculation of the ideal carrier mass flow rate also takes into account the heat capacity of the turbine 30 and the exhaust aftertreatment components 34, 40.

[0039] Has the catalytically active structure 38 of the electrically heated three-way catalyst 34 reached its light-off temperature T LOOnce the required temperature is reached, the combustion engine 10 is activated in a third phase III, whereby efficient conversion of the pollutants contained in the exhaust gas by the catalytically active structure 38 is possible from the start S of the combustion engine 10. In this third phase III, the catalytic structure 38 is heated in parallel by the electric heating element 36 and by the exothermic reaction during the conversion of the pollutants. With the start of the combustion engine 10, the secondary air injection is discontinued, since from the start of the combustion engine 10 the exhaust gas mass flow serves as the carrier mass flow and an additional introduction of secondary air is not necessary.Alternatively, the secondary air injection can also remain active, especially if the combustion engine 10 is operated with a substoichiometric combustion air ratio during the cold start phase and the unburned hydrocarbons are reacted exothermically with the additional oxygen of the secondary air injection on the catalytically active structure 38 of the electrically heated three-way catalyst 34.

[0040] Once the catalytically active structure 38 of the electrically heated three-way catalyst 34 has reached its operating temperature, the electrical heating element 36 is deactivated in a fourth phase IV and the three-way catalyst 34 is kept at this temperature exclusively by the exhaust gas of the combustion engine 10 and the exothermic process taking place on its catalytically active structure. Reference symbol list 10 Internal combustion engine 12 Admission 14 Combustion chamber 16 Spark plug 18 Outlet 20 Disconnect coupling 22 Exhaust system 24 secondary air blowers 26 Secondary air line 28 exhaust gas turbochargers 30 Turbine 32 Exhaust duct 34 electrically heated three-way catalytic converter 36 electric heating element 38 catalytically active structures 40 Four-way catalytic converter 42 Exhaust flap 44 first lambda sensor 46 second lambda sensor 48 first temperature sensor 50 second temperature sensor 52 Engine control unit 54 Signal line 56 Hybrid control unit 58 Signal line 60 electric motor 62 Battery 64 cylinder deactivation actuator 66 Gearbox input shaft 70 gearboxes 80 drive wheel n Engine speed p U Ambient air pressure t time α Throttle valve opening angle E End of the electric heating phase S Starting the combustion engine Temperature T LO Light-off temperature of the three-way catalytic converter I Hybrid operation II Heating phase of the electrically heated three-way catalyst III. Parallel electrical and chemical heating of the three-way catalyst IV Normal operation of the internal combustion engine

Claims

[1] Method for exhaust aftertreatment of an internal combustion engine (10) in a motor vehicle with a hybrid drive consisting of an electric motor (60) and an internal combustion engine (10), wherein the internal combustion engine (10) is connected with its exhaust outlet (18) to an exhaust system (22), wherein an electrically heated three-way catalyst (34) is arranged in the exhaust system (22), and wherein the internal combustion engine (10) has a cylinder deactivation actuator (64), comprising the following steps: - Operating the motor vehicle in hybrid mode, whereby the motor vehicle is driven exclusively by the electric motor (60), - electrical heating of an electric heating element (36) in the exhaust duct (32) upstream of a catalytically active structure (38) of the electrically heated three-way catalyst (34), - Introducing secondary air into the exhaust duct (32) upstream of the electric heating element (36) to form a carrier mass flow which enables convective heat transfer from the electric heating element (36) to the catalytically active structure (38) of the electrically heated catalyst (34), wherein - the combustion engine (10) is towed by the electric motor (60) and, during towing operation, supplies fresh air as secondary air to the exhaust system (22), and - the cylinder deactivation actuator (64) is used to reduce the carrier mass flow during towing by not using all cylinders of the internal combustion engine (10) to pump fresh air into the exhaust port (32), and - Switching on the combustion engine (10) when the catalytically active structure (38) of the electrically heated three-way catalyst (34) reaches its light-off temperature (T LO ) has reached. [2] Method according to claim 1, characterized by , that the opening angle α of a throttle valve in the intake manifold of the internal combustion engine (10) is varied to control the carrier mass flow. [3] Method according to one of claims 1 or 2, characterized by , that the opening times of the valves of the internal combustion engine (10) are changed in order to regulate the carrier mass flow. [4] Method according to any one of claims 1 to 3, characterized by , that an exhaust flap (42) is provided in the exhaust system (22), whereby the carrier mass flow is regulated via the position of the exhaust flap (42). [5] Method according to any one of claims 1 to 4, characterized by , that a control unit (52, 56) is provided with which a carrier mass flow rate necessary for a maximum efficient heating of the catalytically active structure (38) of the electrically heated three-way catalyst (34) is calculated. [6] Motor vehicle with a hybrid drive comprising an electric motor (60) and an internal combustion engine (10) as well as a cylinder deactivation actuator (64), wherein an electrically heated catalyst (34) with an electric heating element (36) and a catalytically active structure (38) is arranged in an exhaust system (22) of the internal combustion engine (10), as well as with at least one control unit (52, 56) which is configured to control a method according to one of claims 1 to 5.

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