EP1638798A1

EP1638798A1 - Hybrid vehicle and method for operating a hybrid vehicle

Info

Publication number: EP1638798A1
Application number: EP04740384A
Authority: EP
Inventors: Ekkehard Pott
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2003-06-30
Filing date: 2004-06-28
Publication date: 2006-03-29
Also published as: US7395659B2; US20060156710A1; JP2009513402A; WO2005000617A1

Abstract

The invention relates to a hybrid vehicle comprising an internal combustion engine (20) and an electric motor (10), which can respectively produce a torque, in particular to drive a vehicle wheel. An exhaust gas system (50) is associated with the internal combustion engine (20), said system having a catalytic converter system (60, 70), whose conversion activity is dependent on predefined activity parameters. According to the invention, the value of the conversion activity is determined in a predefined time interval T_Kat. To achieve a predefined conversion threshold value for the conversion activity of the catalytic converter system (60, 70) the torque produced by the electric motor (10) is preferably increased according to requirements and the torque produced by the internal combustion engine (20) is reduced, if the value of the conversion activity lies below the aforementioned threshold value. To this end, a device (90a) is provided to control the torque produced by the internal combustion engine (20) and the electric motor (10). The invention also relates to a method for operating a hybrid vehicle.

Description

Hybrid vehicle and method for operating a hybrid vehicle

The invention relates to a hybrid vehicle and a method for operating a

Hybrid vehicle according to the preambles of the independent claims.

Vehicles with parallel hybrid drives have an internal combustion engine and at least one electric motor that drives at least one vehicle wheel via the same or a different drive train of the internal combustion engine. Insofar as the electric motor can also be operated as a generator, motor support or additional generator loading by the electric motor and a certain decoupling from internal combustion engine operation is possible in almost every point of the vehicle operating map.

This is accompanied by a change in the exhaust gas quality, in particular with regard to the exhaust gas mass flow, the exhaust gas temperature and the pollutant composition. Such a change in the exhaust gas quality has effects on the function and efficiency of a catalytic converter system connected downstream of the internal combustion engine. From EP 1 182 074 A2 it is known to increase the load of the internal combustion engine at a catalytic converter temperature below a characteristic light-off temperature by regenerative operation of the electric motor and thus to increase the exhaust gas temperature and accelerate the catalytic converter system after a cold start to reach. In addition, it is proposed to relieve the load on the internal combustion engine when the engine or the catalyst system is at operating temperature by operating the electric motor.

This mode of operation is designed in a very one-sided manner to shorten the light-off phase, since it is not taken into account that with the load of the internal combustion engine, the raw emissions, in particular the raw emissions of hydrocarbons, also increase significantly. The reduction in pollutant emissions, in particular in hydrocarbons, by shortening the light-off phase of the catalyst system can therefore be more than compensated for by an increase in raw emissions and, under certain circumstances, can lead to an overall increase in total emissions downstream of the catalyst system (tail pipe emissions).

BESTATIGUNGSKOPIE A hybrid vehicle is also known from DE 100 41 535 A1, in which a generator generates electrical energy when the catalytic converter is not activated and thus increases the load on the internal combustion engine. The temperature of the machine, the temperature of the exhaust gas emitted by the internal combustion engine or the temperature of the cooling water of the internal combustion engine are thus accelerated

Activation of the catalyst increased.

The object of the present invention is to create a hybrid vehicle and a method for operating a hybrid vehicle in which an optimized torque output from the internal combustion engine and the electric motor

Conversion activity of a catalyst system assigned to the internal combustion engine can be influenced in order to achieve a predetermined conversion threshold value.

This object is achieved by the independent claims.

In the hybrid vehicle according to the invention, a device for controlling the torque output of the internal combustion engine and the electric motor is provided according to the invention, by means of which the value of the conversion activity of the

Catalyst system determined and depending on this value for a predetermined time interval T_Kat, the torque output of the electric motor is increased and the torque output of the internal combustion engine is reduced compared to operating the hybrid vehicle without providing torque by the electric motor. This control is preferably carried out as required in relation to a torque specification.

By reducing the torque output of the internal combustion engine, a raw emission, in particular of hydrocarbons, can be reduced for the predetermined time interval, while at the same time the conversion activity of the catalyst system is favorably influenced in order to achieve the predetermined conversion threshold value. The method according to the invention permits an optimized use of the torque output from the internal combustion engine and the electric motor with a view to achieving a predetermined conversion threshold. An embodiment of the invention is particularly preferred in which an exhaust gas emission is determined downstream of the catalyst system and the increase or decrease in the torque output of the internal combustion engine or of the electric motor is carried out in such a way that the emission value falls below a predetermined value downstream of the catalyst system. This aims to overcome the one-sided design of the operating mode of a hybrid vehicle and to shorten a light-off phase and takes into account the interrelation between raw emissions and conversion activity when limiting the exhaust gas emissions actually released into the environment.

An increase in the catalyst temperature by moving the ignition angle late is particularly expedient. In a further preferred embodiment, an efficiency deterioration of the

Internal combustion engine, especially due to a shift in the ignition angle late, by operating with a higher air filling. With this the

Exhaust gas mass flow can be increased simultaneously with an increase in the catalyst temperature.

In order to achieve a noticeable relief of a typical internal combustion engine, it is preferred if the electric motor has a maximum output of at least 2

KW, preferably 3.5, particularly preferably 5 KW, each per ton of vehicle empty weight, preferably in a speed range of 700-1500, optimally 1,000 / min to 1,500 / min. Particularly high exhaust gas purification performances can be achieved with a catalytic converter which comprises at least one pre-catalytic converter close to the engine and at least one main catalytic converter arranged downstream of the pre-catalytic converter. According to the invention, in particular the conversion activity of the pre-catalyst is increased quickly and effectively.

Further embodiments and advantages of the invention can also be found independently of their summary in the claims of the following description and the drawings. The drawings show in FIG. 1 a hybrid drive with a control system for a hybrid vehicle according to the invention 2 shows a time profile of engine torques and driving speed for a cold start according to the prior art without electrical support. FIG. 3 shows a time profile of engine torques and driving speed for a cold start according to the prior art with additional electrical generator load. FIG. 4 shows a time profile of engine torques and driving speed 5 shows a time course of the accumulated hydrocarbon emissions after a pre-catalytic converter close to the engine in different cold start operating modes.

Figure 1 shows a schematic representation of a hybrid drive 1 for an otherwise not shown hybrid vehicle. An electric motor 10 and an internal combustion engine 20 are coupled to a transmission 30, which is coupled to at least one vehicle wheel (not shown in FIG. 1). An arrangement of the electric motor 10 between a crankshaft output of the internal combustion engine 20 and a transmission input is preferred. The electric motor 10 is electrically coupled to an electrical energy storage device, for example a rechargeable battery or the like. The internal combustion engine 20 is an exhaust system

50 associated with a pre-catalytic converter 60 near the engine and a main catalytic converter 70 arranged downstream. An engine control unit 90 receives from control sensors 80, for example the accelerator pedal module or an anti-lock braking system, control signals and from sensors 100 values of operating parameters of the hybrid vehicle, in particular of the electric motor 10, of the

Internal combustion engine 20, exhaust system 50 and other vehicle components.

In a preferred embodiment of the invention, the internal combustion engine 20 is a lean-running, direct-injection gasoline engine. A stratified direct-injection gasoline engine is particularly preferred, since considerable savings in fuel consumption compared to a conventional gasoline engine can be achieved in the lower load speed ranges. In particular in the case of these embodiments of the invention, it is expedient to design the catalyst system in such a way that the pre-catalyst 60 is a 3-way catalyst and the main catalyst 70 is a NOx storage catalyst. The pre-catalyst 60 is preferably used to purify a stoichiometric exhaust gas, to convert hydrocarbons (HC) in the case of lean exhaust gas and to improve the Exhaust gas cleaning during a cold start. In particular, in order to enable rapid heating of the pre-catalytic converter, it is provided that pre-catalytic converter 60 is arranged at a distance of less than 500 mm, optionally less than 400 mm, particularly preferably less than 300 mm, of the average exhaust gas run length of the cylinder head flange in exhaust system 50. The NOx storage catalytic converter 70 is preferably designed to store nitrogen oxides (NOx) when the exhaust gas is lean. Depending on the loading with NOx and possibly other boundary conditions, regeneration of the NOx storage catalytic converter with a stoichiometric to rich exhaust gas is necessary.

The conversion activity of the catalyst system or its components pre-catalyst 60 and NOx storage catalyst 70 is dependent on activity parameters, in particular the catalyst temperature. The conversion rate only exceeds a limit of 50% from a minimum temperature, the so-called light-off temperature. In general, the light-off temperature of a catalyst is different for different pollutant components such as HC or NOx.

Further activity parameters of the catalyst system are values of an exhaust gas mass flow, the raw emission of exhaust gas components and the loading with NOx and / or sulfur oxides (SOx). The values of these activity parameters are determined as a function of the operating parameters of the internal combustion engine, possibly using a model of the catalyst system with the aid of signals from sensors 100, and evaluated in control unit 90.

In a preferred embodiment, the control device 90 contains one or more microprocessors, data memories and interfaces as well as a device 90a by means of which, depending on the control signals of the sensors 80, the total torque is determined, which is supplied by the electric motor 10 and the internal combustion engine 20 and at least partially by the transmission 30 is made available. The coupling between the electric motor 10 and the internal combustion engine 20 enables both negative and positive torque transmission between these two components. The sensors 100, not shown in detail in FIG. 1, comprise sensors for measuring or determining operating parameters, preferably the storage device 40, the electric motor 10, the internal combustion engine 20 and the Exhaust system 50. In particular, lambda probes can be arranged in the exhaust system 50 upstream of the pre-catalytic converter 60, downstream of the pre-catalytic converter 60, upstream of the main catalytic converter 70 or downstream of the main catalytic converter 70. Furthermore, NOx, SOx or hydrocarbon sensors can be arranged at various points in the exhaust systems. To measure the

The temperature of the exhaust gas or the catalyst system can be provided at different installation locations.

The method according to the invention aims to deliver the torque of the internal combustion engine and the electric motor in order to achieve a predetermined one

To optimize the conversion threshold and the conversion activity of the catalyst system 60, 70. Such an optimization is preferably provided in a time interval Temp_K after a cold start of the vehicle, but can, if necessary, also take place in other operating phases of the internal combustion engine 20. After a cold start, the temperature of the catalyst system is initially below the light-off temperature. In this case, the conversion activity is below a light-off value of 50% or 80% and must therefore be increased in order for the internal combustion engine 20 to operate in an environmentally friendly manner.

In the following, procedures with a cold start that are already known from the prior art are first described with reference to FIGS. 2 and 3.

FIG. 2 shows the time course of an engine torque M of a conventional internal combustion engine during a cold start process. The moment M includes in particular the moments required for starting the engine, friction, operating auxiliary units and propulsion. F denotes the driving speed as a function of time.

In the starting process shown, after an idling phase from the time T_A, a starting process begins with an acceleration and a corresponding increase in the torque M. After a relatively short time after the start, the internal combustion engine thus has a maximum realizable torque reserve M_Max, which in itself can be used to heat the catalyst , After a stationary driving phase, the driving speed is reduced to zero again at time T_S. Accordingly, the engine load drops. In the cold start process shown in FIG. 2, the temperature of the catalyst system is initially below the light-off temperature, so that considerable parts of the raw emission of the internal combustion engine are released into the environment. Only when the engine or the exhaust gas heats up does the catalytic converter system also heat up, unless a separate catalytic converter heater is provided.

The operating mode during cold start shown in more detail in FIG. 3 and known from the prior art aims to make the currently available torque reserve usable for heating the catalyst system. In

FIG. 3 shows a cold start process with additional electrical generator load for the same driving curve F as in FIG. 2, it being assumed that the catalyst temperature is below a light-off temperature. In the time interval between the times T_A and T_B, in order to achieve particularly short catalyst heating times, the engine, which is still cold, is usually filled up to

Limits of stable engine running increased. The load torque of the internal combustion engine is thus brought up to the maximum realizable torque reserve. However, the raw emissions, especially for hydrocarbons, usually increase significantly with the engine load of the internal combustion engine. The emissions reduced by shortening the light-off phase can therefore be more than compensated for by an increase in raw emissions and lead to an overall increase in tail pipe emissions.

If, as in EP 1 182 074, the ignition angle is retarded, the temperature of the exhaust gas can be increased. However, another takes place

Load request, for example by a start-up process, the air filling of the internal combustion engine is not reduced. Rather, the ignition angle is shifted so far in the direction that the required load can be provided by the associated improvement in efficiency. This energy component is then not available for heating the catalyst system. Therefore, if the load of the internal combustion engine is increased even further by generator operation of the electric motor, the power available for heating the catalytic converter can be reduced. FIG. 4 shows the course over time of a torque M and a driving speed F during a cold start operation according to the invention. It is assumed that the catalyst system has a temperature below a light-off Has temperature and therefore its conversion activity is below a conversion threshold. After the internal combustion engine has started, it first emits an idling torque M_L, which is made available in particular for carrying out the engine start, overcoming friction, supplying auxiliary units. M_L is preferably selected so that an acceptable value of raw emissions is not exceeded in the relevant point of the operating map.

At time T_A, a torque request is made to carry out a starting process. At the time T_B the start-up process is finished and there is a

Constant travel at a constant driving speed until time T_S. In the time interval T_A to T_B there is an electromotive

Support of the internal combustion engine 2 | 0 by the electric motor 10 is provided.

In the said time interval, therefore, only part of the total torque output required for the starting process is generated by the internal combustion engine 20

Provided while the rest of the required effort of torque is performed by the electric motor 10. The prerequisite for this is that the electrical power available through the electrical storage device 40 allows this. At the time T_S, the driving curve F shows a reduction in the driving speed, which leads to a transition from an idling to a later one

Time leads. At this point at the latest, the momentary delivery of the

Internal combustion engine 20 returned to the value M_L.

According to the invention, such an optimization of the torque output of the electric motor 10 and the internal combustion engine 20 can be carried out within a time interval

T_Kat take place, which is necessary to bring the catalyst system into a state in which the conversion threshold has been reached or exceeded. This state is usually characterized by a catalyst temperature which is above the light-off temperature for hydrocarbon.

In a preferred embodiment of the invention, the torque output of the internal combustion engine 20 is limited to the value M_L during the time interval T_Kat, so that any additional torque request going beyond this is served by the electric motor 10. It is also preferably provided that within T_Kat at least 60%, preferably at least 80%, ideally at least 90% of a torque request is served by the electric motor 10. Within the time interval T_Kat, according to the invention, the combustion efficiency of the internal combustion engine 20 is deliberately deteriorated to increase an exhaust gas temperature. Such a deterioration in efficiency is used to increase the exhaust gas temperature. A possible method for

Degradation in efficiency is a shift in the ignition angle late. This means that a higher proportion of the fuel energy converted in the combustion chamber reaches the exhaust gas. Part of the efficiency reduction of the engine can be compensated for by an operation with a higher filling, in that the engine is operated with an increased air mass flow. This creates a higher exhaust gas mass flow, which further accelerates the heating of the catalytic converter.

As is known per se, lower hydrocarbon concentrations occur upstream of the catalyst system when the ignition angle is shifted late due to the increased exhaust gas temperature. In addition to a higher energy input into the exhaust system and the catalyst system, the method according to the invention therefore has the advantage of lower raw emissions.

The higher energy input into the exhaust system makes it faster

Heating of at least one part of the catalyst system, in particular close to the engine, is made possible. The heating of the catalyst system can thus be reduced. A reduction in the additional chemical-thermal energy input into the exhaust system generated for heating the catalyst system is preferred according to the invention. Additionally or alternatively, the time interval

T_Kat more than 10%, preferably 25%, particularly preferably 40% can be reduced compared to conventional heating of the catalyst system.

Since in most countries of the world the cleaning effect of the exhaust system is prescribed by statutory regulations for exhaust emission limit values, the method according to the invention and the hybrid vehicle according to the invention are preferably designed such that the legally prescribed limit values are reached or undershot. In the EU countries, the New European Driving Cycle (NEDC) specifies a speed profile that should correspond to typical urban and interurban traffic. The design mentioned is therefore carried out in such a way that in the NEDC the emissions with the electrical support according to the invention reach the level in a conventional one At least not exceed the operating mode of the same internal combustion engine or hybrid vehicle.

In Figure 5, the time course of cumulative hydrocarbon emissions downstream of a pre-catalyst is shown schematically. One is shown in each case

Cold start process with the same driving curve labeled F. The emission curve labeled A denotes a conventional catalyst heating process as was shown in FIG. 2. Curve B denotes a catalyst heating method in which a negative torque is applied in the cold start phase, while curve C is an operation according to the invention

Process called. The arrow placed on the top of each of the curves A to C denotes the point in time at which an 80% HC conversion rate on the pre-catalyst is exceeded. As the illustration in FIG. 5 shows, the mode of operation according to the invention enables a lower cumulative hydrocarbon emission and an earlier achievement of an 80% hydrocarbon conversion rate on the pre-catalyst.

Since the invention makes it easier to achieve a light-off value for the catalyst system or at least one of its components, the noble metal content of the catalysts used in such a hybrid vehicle can be reduced. This applies in particular to vehicles with a direct-injection and / or stratified gasoline engine. In the prior art, for direct-injection and / or stratified-charge gasoline engines, such as in the NEDC, with thermally undamaged catalyst systems that operate at a time

Shifts in operation of at least 250 seconds achieve a hydrocarbon emission of 0.07 g / km and a NOx emission of> 0.05 g / km, catalysts with a noble metal content of <110 g / km / ft ³ (3.95 g / dm ³ ) or even <130 g / ft ³ (4.76 g / dm ³ ). In this case, the catalyst system consists of a pre-catalyst close to the engine and at least one downstream NOx storage catalyst with a stored sulfur mass of> 0.2 grams / per liter of catalyst volume.

According to the invention, the noble metal content of at least one or more of the precatalysts is reduced to less than 100 g / ft ³ (3.59 g / dm ³ ), in particular to> 80 g / ft ³ (2.87 g / dm ³ ). A reduction to less than 60 g / ft ³ (2.16 g / dm ³ ) is preferred. This makes it possible that even after oven aging of the at least one Pre-catalyst with reduced precious metal content for four hours at 1,100 degrees Celsius in an atmosphere of 2% O2 and 10% H2O and a NOx storage catalyst with reduced precious metal content for four hours at 850 degrees Celsius in an atmosphere of 2% O2 and 10% H2O at otherwise same vehicle by using the method according to the invention in the NEDC

Hydrocarbon emission of no more than 0.1 g / km and a NOx emission of 0.08 g / km is achieved. I The electric motor 20 has a maximum output of at least 2 KW, preferably 3.5 KW, particularly preferably 5 KW per ton of vehicle empty weight. A speed range of 700-1,500, ideally 1,000 rpm to 1,500, is preferred

1 / min.

REFERENCE SIGN LIST Hybrid vehicle and method for operating a hybrid vehicle

Hybrid drive with control system Electric motor Internal combustion engine Battery Exhaust system Pre-catalytic converter Main catalytic converter Sensors Engine control unit Device for controlling the torque output 0 sensors

Claims

PAT EN TAN SPR Ü CHE Hybrid vehicle and method for operating a hybrid vehicle

1. Method for operating a hybrid vehicle with an internal combustion engine and at least one electric motor, each for delivering a torque, in particular in order to be able to drive at least one vehicle wheel, the combustion engine being assigned an exhaust system with a catalyst system for at least one exhaust gas component, the conversion activity of which depends on predetermined activity parameters is dependent, characterized in that in order to achieve a predetermined conversion threshold value of the conversion activity for at least one exhaust gas component in a predetermined time interval T_Kat, the value of the conversion activity is determined and if this value is below said threshold value, the torque output of the electric motor, preferably depending on demand, is increased and the Torque output of the internal combustion engine is reduced compared to operation of the hybrid vehicle without the provision of torque by the electric motor.

2. The method according to claim 1, characterized in that an exhaust gas emission is determined downstream of the catalytic converter system and the increase or decrease in the torque output of the internal combustion engine or the electric motor is carried out in such a way that a predetermined emission limit value is undershot downstream of the catalytic converter system.

3. The method according to claim 1 or 2, characterized in that the activity parameters include at least a catalyst temperature or an exhaust gas mass flow.

4. Method according to at least one of the preceding claims, characterized in that T_Kat follows a cold start.

Method according to at least one of the preceding claims, characterized in that within _Kat a torque requirement of at least 60%, preferably at least 80%, particularly preferably at least 90%, is served by the electric motor.

Method according to at least one of the preceding claims, characterized in that within T_Kat the combustion efficiency of the internal combustion engine is specifically deteriorated in order to increase an exhaust gas temperature and an exhaust gas mass flow.

7. The method according to at least one of the preceding claims, characterized in that the ignition angle is moved later in order to increase the catalyst temperature.

8. Method according to claim 6 or 7| characterized in that to at least partially compensate for a deterioration in the efficiency of the internal combustion engine, in particular due to a retarded ignition angle, the internal combustion engine is operated with a higher air charge.

9. The method according to at least one of the preceding claims, characterized in that catalyst heating is provided with a chemical-thermal energy input into the exhaust system that is reduced by at least 10%, 25% or preferably 40% compared to operation without the provision of torque by the electric motor.

10. The method according to at least one of the preceding claims, characterized in that catalyst heating is provided with a value that is reduced in time by at least 10%, 25% or 40% compared to operation without the provision of torque by the electric motor.

11. The method according to at least one of the preceding claims, characterized in that the electric motor provides a maximum power of at least 2 KW, preferably 3.5 KW, particularly preferably 5 KW, in each case per tonne of empty vehicle weight, preferably in a speed range of 700-1.55, ideally 1,000 rpm to 1,500 rpm. ι

12. The method according to at least one of the preceding claims, characterized in that the electric motor is arranged between a crankshaft output of the internal combustion engine and a transmission input.

13. The method according to at least one of the preceding claims, characterized in that the catalyst system comprises at least one pre-catalyst close to the engine and at least one main catalytic converter arranged downstream of the pre-catalyst.

14. The method according to claim 13, characterized in that the pre-catalyst close to the engine is arranged at a distance of less than 500 mm, optionally less than 400 mm, particularly preferably less than 300 mm average exhaust gas run length from the cylinder head flange.

15. The method according to at least one of the preceding claims, characterized in that the conversion threshold value is a light-off value for at least one of the exhaust gas components hydrocarbon, carbon monoxide or nitrogen oxide of the primary and main catalyst.

16. The method according to at least one of the preceding claims, characterized in that the internal combustion engine is a preferably lean-burn, direct-injection gasoline engine.

17. The method according to at least one of the preceding claims, characterized in that the internal combustion engine is a preferably lean-burn, direct-injection, stratified-charge Otto engine.

18. The method according to claim 17, characterized in that the internal combustion engine in the New European driving cycle with a thermally undamaged catalytic converter system, which has at least one pre-catalyst close to the engine and at least one NOx storage catalytic converter arranged downstream, at least one of the catalytic converters having a noble metal content of > 110 g / ft ³ and in a shift operation portion of at least 250 seconds. a hydrocarbon emission of <0.07 g/km and a nitrogen oxide emission of <0.05 g/km are achieved without the provision of torque by the electric motor and with the provision of torque by the electric motor and a precious metal content of the pre-catalyst of <100 g/ft ³

1.6

preferably, <80 g/ft ³ , particularly preferably <60 g/ft ³ , a hydrocarbon emission of less than 0.1 g/km and a nitrogen oxide emission of less than 0.08 g/km are achieved in the New European Driving Cycle.

19. The method according to claim 18, characterized in that the pre-catalyst with reduced precious metal content undergoes oven aging for 4 hours at 1100 ° C in an atmosphere of 2% O ₂ and 10% H ₂ O and the NOx storage catalyst with reduced precious metal content for 4 hours 850°C in an atmosphere of 2% O ₂ and 10% H ₂ O.

20. Hybrid vehicle with an internal combustion engine and at least one electric motor, each of which can deliver a torque, in particular to drive at least one vehicle wheel, with the combustion engine being assigned an exhaust system with a catalytic converter system! is, the conversion activity of which is dependent on predetermined activity parameters, characterized in that a device for controlling the torque output of the internal combustion engine and the electric motor is provided, by means of which to achieve a predetermined conversion threshold of the conversion activity of the catalytic converter system for at least one exhaust gas component in a predetermined time interval T_Kat The value of the conversion activity is determined and if this value is below the said threshold value, the torque output of the electric motor, preferably! Depending on demand, increased and the torque output of the internal combustion engine is reduced compared to operation of the hybrid vehicle without the provision of torque by the electric motor.

21. Hybrid vehicle according to claim 20, characterized in that the internal combustion engine in the New European driving cycle with a thermally undamaged catalytic converter system, which has at least one pre-catalyst close to the engine and at least one NOx storage catalytic converter arranged downstream, whereby at least one of the catalytic converters has a noble metal content of > 110 g/ft ³ and in a time shift operation share of at least 250I sec. a hydrocarbon emission of ι < 0.07 g / km and a nitrogen oxide emission of < 0.05 g / km without providing one Torque achieved by the electric motor and when torque is provided by the electric motor and a precious metal content of the pre-catalyst of <100 g/ft ³ , preferably <80 g/ft ³ , particularly preferably <60 g/ft ³ in the New European Driving Cycle, a hydrocarbon emission of less than 0.1 g/km and a nitrogen oxide emission of less than 0.08 g/km.