CN108087070B

CN108087070B - Method for heating a catalytic converter and motor vehicle having a catalytic converter

Info

Publication number: CN108087070B
Application number: CN201711164942.3A
Authority: CN
Inventors: L.施吕特; F-C.B.冯科伊默恩-林登斯杰纳; S.保克纳
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2016-11-21
Filing date: 2017-11-21
Publication date: 2020-06-09
Anticipated expiration: 2037-11-21
Also published as: CN108087070A; DE102016122304A1

Abstract

The invention relates to a method for heating an electrically heatable catalytic converter in an exhaust gas duct of a motor vehicle having an internal combustion engine. In order to heat the catalytic converter before the internal combustion engine is started, it is provided that the catalytic converter is electrically heated before the motor of the internal combustion engine is started and that an effective exhaust gas aftertreatment is carried out in connection with the motor start. In this case, after the electric preheating phase after the start of the motor, a further heating of the catalytic converter is achieved by a combination of electric heating and chemical heating by the exothermic conversion of the unburned fuel components on the catalytically active surface of the electrically heatable catalytic converter. The invention further relates to a motor vehicle having an internal combustion engine and an exhaust system, in which the method according to the invention is carried out.

Description

Method for heating a catalytic converter and motor vehicle having a catalytic converter

Technical Field

The invention relates to a method for heating a catalytic converter in an exhaust gas system of a motor vehicle and to a motor vehicle having a catalytic converter arranged in an exhaust gas system.

Background

Increasingly stringent exhaust gas regulations place high demands on vehicle manufacturers, which are achieved by corresponding measures for reducing untreated emissions of the engine and by corresponding exhaust gas aftertreatment. In order to be able to effectively convert untreated emissions which cannot be completely avoided after the engine, noble metal-coated catalysts are installed in the exhaust system of internal combustion engines. In order for the catalyst to convert harmful substances, a minimum temperature level of the exhaust gas and the catalyst is required. In order to bring the catalytic converter to operating temperature as quickly as possible after a cold start of the internal combustion engine, thermal measures are used in the engine, for example, adjusting the ignition angle in the "late" direction, or substoichiometric operation of the internal combustion engine with simultaneous entrainment of secondary air is used. In order to deliberately introduce still more thermal energy into the exhaust system, it is possible to electrically heat the catalytic converter. Thereby, already in the heating-up phase of the catalyst, the emissions can be significantly reduced.

Furthermore, with the introduction of the legislation level EU6 for gasoline engines, limit values for the quantity of particles are specified, which in many cases necessitate the use of a gasoline particulate filter. During driving operation, such a gasoline particle filter is loaded with soot. In order for the exhaust gas back pressure not to increase excessively, the gasoline particulate filter must be continuously or periodically regenerated. In order to carry out the thermal oxidation of the soot remaining in the gasoline particulate filter with oxygen, a sufficiently high temperature level is required in combination with the simultaneous presence of oxygen in the exhaust gas system of a gasoline engine. Since modern gasoline engines are usually operated without excess oxygen with stoichiometric combustion air ratios (λ =1), additional measures are required for this purpose. For this purpose, measures such as, for example, briefly lean-regulating the gasoline engine by increasing the temperature as a function of the ignition angle, blowing secondary air into the exhaust system or combinations of these measures are conceivable. It is preferable to use a combination of late-oriented ignition angle regulation and lean regulation of the gasoline engine up to now, since this method can be implemented without additional components and a sufficient oxygen quantity can be provided in the majority of operating points of the gasoline engine.

DE 102010014332 a1 discloses a method for the thermal management of an exhaust system of a motor vehicle having a hybrid drive composed of an internal combustion engine and an electric motor. In this case, the catalyst is first electrically preheated by means of an electrically heatable catalyst and air injection, and then the catalyst is heated chemically by injecting air into the exhaust gas duct in combination with the rich regulation of the internal combustion engine. However, this method has the disadvantage of separating the electrically heated catalyst from another catalyst which is to be heated and which is to be decisively responsible for the conversion of the pollutant. Furthermore, in the known method a secondary air supply of the exhaust gas channel is required in order to blow in the required air before the catalyst.

From document US 2009/0293450 a1, a method is known for heating a catalytic converter in an exhaust gas duct of an internal combustion engine, in which the catalytic converter is already heated to a first temperature by electrical heating before the internal combustion engine is started, and after reaching this first temperature, heating is continued to an ignition temperature of the catalytic converter by a rich regulation of the combustion mixture and simultaneously bringing secondary air into the exhaust gas duct, wherein the electrical heating of the catalytic converter is deactivated when the ignition temperature of the catalytic converter is reached. However, this method has the disadvantage that it requires a secondary air system and can therefore only be carried out on motor vehicles with an internal combustion engine and a secondary air system.

From document US 2008/0282673 a1, a method is known for heating a catalytic converter in an exhaust gas duct of a motor vehicle having a hybrid drive composed of an internal combustion engine and an electric motor. In this case, the temperature of the catalytic converter is determined by the engine controller before the internal combustion engine is started, and the catalytic converter is electrically heated below a threshold temperature, in particular during a cold start of the internal combustion engine, and the start of the internal combustion engine is delayed until the catalytic converter is heated to a defined temperature. In this case, after the first electrical heating, the catalyst can be heated in parallel by electrical heating and measures in the engine, for example an adjustment of the ignition angle to the "late" direction, in order to further heat the catalyst or to keep the temperature of the catalyst above a defined temperature for effective exhaust gas aftertreatment after the electrical heating has been switched off. However, this method has the disadvantage that the internal combustion engine can only be started with hysteresis and the vehicle can be operated only by the electric motor of the hybrid drive in the first few seconds until the catalyst is effectively heated by electric heating, or that there is no effective, thermally operated catalyst yet in the case of a direct start of the internal combustion engine.

Disclosure of Invention

It is now an object of the present invention to provide a method for heating a catalytic converter in an exhaust gas duct of an internal combustion engine, which overcomes the disadvantages known from the prior art and makes it possible to quickly heat the catalytic converter to an operating temperature.

According to the invention, this object is achieved by a method for heating an electrically heatable catalytic converter in an exhaust gas system of an internal combustion engine, wherein the electrically heatable catalytic converter has an electrical heating element and a catalytically active surface, in particular a catalytically active coating, and wherein the electrical heating element is controllable via a controller, comprising the following steps:

-electrically heating the electrically heatable catalyst before starting the internal combustion engine,

heating the electrically heatable catalytic converter by electrical heating and simultaneously by measures in the engine interior of the internal combustion engine in parallel, wherein unburned or partially burned fuel components are converted exothermically on the catalytically active surface of the electrically heatable catalytic converter,

the electric heating element is switched off and the electrically heatable catalytic converter is further heated by measures internal to the engine, oxygen required for the exothermic conversion of unburned and/or partially burned fuel components being fed into the exhaust gas system via the combustion chamber of the internal combustion engine.

By means of the method according to the invention, it is achieved that a catalyst in an exhaust system of an internal combustion engine is heated to a temperature at which a significant change in pollutants by the catalyst has already taken place, wherein the exhaust system does not require secondary air supply and can therefore be designed relatively simply and cost-effectively. In this case, the catalytic converter is already electrically heated before the motor to a temperature at which the catalytically active surface requires a chemical reaction of the unburned or partially burned fuel components. The combination of electrical heating of the catalyst and chemical heating of the catalyst by measures inside the engine makes it possible to generate heat directly in the catalyst. In this way, uniform heating of the entire exhaust system upstream of the catalyst, for example the turbine of an exhaust gas turbocharger, can be reduced, thereby additionally accelerating the heating of the catalyst. In this way, the ignition temperature of the catalytic converter can be achieved more quickly and the heating phase of the catalytic converter can be shortened. Here, the fuel overconsumption can be reduced and cold start emissions can be avoided by the shortened chemical heating phase. In this connection, the chemical heating phase of the catalytic converter is understood to be a measure in which heat is generated as a result of an exothermic chemical reaction, in particular the conversion of unburned or partially burned fuel components with oxygen on the catalytically active surface of the electrically heatable catalytic converter.

The features set forth in the invention make possible advantageous improvements and improvements of the method for heating a catalytic converter set forth in the invention.

In a preferred embodiment of the invention, it is provided that the measures within the engine include a combustion-chamber-specific oxygen control, wherein a first group of the combustion chambers of the internal combustion engine is operated with a super-stoichiometric combustion air ratio and a second group of the combustion chambers of the internal combustion engine is operated with a sub-stoichiometric combustion air ratio. The combustion chamber-specific oxygen regulation is achieved by simultaneously supplying unburned or partially burned fuel components and oxygen into the exhaust gas duct. By means of the already electrically preheated catalytic converter, unburned or partially burned fuel components can then be converted exothermically on the catalytically active surface of the catalytic converter, whereby the catalytic converter can be heated rapidly to the ignition temperature. The light-off temperature is the temperature at which the catalytic converter converts 50% of the exhaust gas constituents entering the catalytic converter. In this case, the conversion of the unburned or partially burned fuel components takes place directly on the surface of the catalytic converter, so that the other components of the exhaust system are heated in a time-staggered manner. In this way, it is not necessary to heat the components in the exhaust gas system upstream of the catalytic converter at least immediately after a cold start of the internal combustion engine, in comparison with the adjustment of the ignition angle in the late direction. These components can be heated at staggered times in order to achieve full purification power of the exhaust gas aftertreatment system. Furthermore, no secondary air system is required, so that no additional components are required. This provides a cost-effective and very efficient embodiment for heating the electrically heatable catalytic converter.

In this case, it is particularly preferred that a stoichiometric exhaust gas is present in the exhaust gas duct of the exhaust gas system downstream of the output of the internal combustion engine, wherein the unburned or partially burned fuel components of the exhaust gas are exothermically converted together with the residual oxygen present in the exhaust gas on the catalytically active coating of the electrically heatable catalyst. With the stoichiometric exhaust gas in the heating phase, the end pipe emissions can already be greatly reduced during the chemical heating, that is to say during the heating by an exothermic chemical reaction on the catalytically active surface of the catalyst.

In a further preferred embodiment of the method, it is provided that the internal combustion engine is operated with a super-stoichiometric, lean combustion air ratio in the heating phase of the electrically heatable catalyst and that fuel is introduced into the exhaust gas duct of the exhaust gas system upstream of the electrically heatable catalyst. In particular in internal combustion engines which operate with excess air, for example diesel engines, or in gasoline engines which operate with lean operation, the oxygen for the exothermic reaction can alternatively be provided via an excess of air of the combustion mixture. The fuel can be supplied either by injecting the fuel later (for example, significantly after top dead center of the piston) into at least one of the combustion chambers of the internal combustion engine or by directly dosing the fuel into the exhaust gas duct.

In a further preferred embodiment of the method, it is provided that all combustion chambers of the internal combustion engine are periodically operated alternately with a super-stoichiometric and a sub-stoichiometric combustion air ratio during a heating phase of the electrically heatable catalyst, wherein in the case of super-stoichiometric operation of the internal combustion engine the oxygen reservoir of the electrically heatable catalyst is filled with oxygen and in the case of sub-stoichiometric operation of the internal combustion engine the unburned or partially burned fuel components react exothermically with the oxygen stored in the electrically heatable catalyst. In this way, an exothermic conversion of the unburned or partially burned fuel components on the catalytically active surface of the catalyst is likewise achieved, in order to continue heating the catalyst starting from the temperature achieved by the electrical heating.

In a preferred development of the method, it is provided that the electrical heating of the electrically heatable catalytic converter is initiated by a door contact switch, a receiver for a keyless locking system, a receiver for a central locking part or a belt lock contact. Usually, the driver enters the motor vehicle before the internal combustion engine is started cold and the driver fastens a safety belt. Sensors already present on the motor vehicle can be used by means of a door contact switch, a receiver for a transmitter or central locking part of a keyless locking system (keyless entry system), or a belt contact switch, in order to start the electrical heating already before the internal combustion engine is started in time. In this case, the door contact switch and the receiver for the signal of the locking system are particularly preferred, since the time interval between opening or opening the door and starting the internal combustion engine is relatively long, and thus an effective heating of the electrically heatable catalytic converter is achieved in this time interval.

In automatically or semi-automatically operated vehicles, the electric heating can also be initiated by a request of a driving command, wherein the internal combustion engine is started only when the electrically heatable catalytic converter has reached a first threshold temperature.

According to a preferred embodiment of the invention, provision is made for the heating measure to be initiated inside the engine when the electrically heatable catalytic converter reaches the first limit temperature by electrical heating. In order to achieve as efficient a heating of the electrically heatable catalytic converter as possible, it is advantageous if the measures for chemically heating the engine interior of the catalytic converter are only started when the electrically heatable catalytic converter has reached the first limit temperature by electrical heating. If the measures inside the engine are started before the catalyst has reached this first threshold temperature, this can lead to cooling of the catalyst due to unburned fuel and the higher emissions associated therewith.

According to a further advantageous development of the method, the internal combustion engine is operated with a stoichiometric combustion air ratio after the second threshold temperature has been reached, and the heating measure is terminated. If the electrically heatable catalyst reaches a second threshold temperature, which is preferably above the ignition temperature of the catalyst, the chemical, engine-internal heating measures of the internal combustion engine are adjusted and the internal combustion engine is preferably operated with a stoichiometric combustion air ratio in normal operation. Thereby, the untreated emissions and the fuel consumption of the internal combustion engine are reduced.

According to a further embodiment of the method, it is provided that the electrically heatable catalytic converter is heated to operating temperature when the battery of the electric drive is discharged to such an extent that the hybrid drive is switched over to being driven by the internal combustion engine in a predictable time, in particular within the following minutes.

According to the invention, a motor vehicle is proposed with an internal combustion engine, preferably with a hybrid drive comprising an internal combustion engine and an electric motor, and an exhaust gas system in which at least one electrically heatable catalytic converter is arranged, wherein the motor vehicle, preferably the internal combustion engine, has a control unit which is designed to carry out the method according to the invention.

In a preferred embodiment of the invention, it is provided that the current source for heating the electrically heatable catalytic converter, preferably the electrically heatable three-way catalytic converter, is a 48V onboard power system of a motor vehicle or a battery for driving an electric drive motor of a hybrid vehicle. Although heating the electric catalyst with a 12V on-board electrical system is relatively difficult and time consuming due to the low voltage, the heating of the electrically heatable catalyst can be performed relatively simply and quickly with a 48V on-board electrical system. Alternatively, in a hybrid vehicle with an internal combustion engine and an electric motor, the battery for the electric motor can also be used as a voltage source for heating the electrically heatable catalytic converter.

The different embodiments of the invention described in this application document can be combined with one another advantageously if not specifically stated in a specific case.

Drawings

The invention is elucidated below in an embodiment with reference to the drawing. Wherein:

figure 1 shows a preferred embodiment variant of the drive system of a motor vehicle according to the invention,

figure 2 shows another view of a motor vehicle according to the invention,

figure 3 shows a temperature profile in the case of a conventional heating of a catalyst in the exhaust system of an internal combustion engine,

figure 4 shows a flow chart of a method according to the invention for heating a catalyst in an exhaust system of an internal combustion engine,

figure 5 shows the temperature profile in the catalyst in the method according to the invention for heating an electrically heatable catalyst,

figure 6 shows another temperature profile in the exhaust gas channel in the method according to the invention for heating the catalyst in the exhaust gas channel at three measuring points,

figure 7 shows an alternative embodiment of the drive system of a motor vehicle according to the invention,

figure 8 shows a further alternative embodiment of the drive system of a motor vehicle according to the invention,

figure 9 shows a further alternative embodiment of the drive system of a motor vehicle according to the invention,

fig. 10 shows a further alternative embodiment of the drive system of a motor vehicle according to the invention, and

fig. 11 shows a further alternative embodiment of the drive system of a motor vehicle according to the invention.

List of reference numerals

1 Motor vehicle

10 internal combustion engine

12 combustion chamber

14 spark plug

16 first group of combustion chambers

18 second group of combustion chambers

20 exhaust system

22 exhaust gas channel

24 turbine

26 electrically heatable catalytic converter

28 electric heating element

30 three-way catalyst capable of being electrically heated

32 second catalytic converter

34 second three-way catalyst

36 particle filter

38 four-element catalyst

40 electrically heatable quaternary catalyst

42 controller

44 door contact switch

46 receiver

48 belt lock sensor

50 catalytic surface

52 output unit

54 cell

56 electric drive motor

58 sensor for recognizing the occupancy of a seat

60 third three-way catalyst

T temperature

T₁Temperature before turbine

T₂Temperature before three-way catalyst

T₃Temperature in three-way catalyst

T₄First threshold temperature

T₅Second threshold temperature

Starting of S internal combustion engine

time t

λ_ARatio of exhaust gas to air

λ_ECombustion air ratio

λ_E16Combustion air ratio of first group of combustion chambers

λ_E18Combustion air ratio of the second group of combustion chambers

Electrically heated start-up of an O-catalyst

I first stage

II second stage

III third stage

Electrical heating of IV catalyst

Chemical heating of V-catalyst

Parallel electrical and chemical heating of the VI catalyst.

Detailed Description

Fig. 1 shows a first exemplary embodiment of a motor vehicle 1 according to the invention with an internal combustion engine 10 and an exhaust gas system 20. The motor vehicle 1 according to the invention is preferably designed as a hybrid vehicle with an internal combustion engine 10 and an electric motor 56, particularly preferably with a gasoline engine which is ignited externally by means of a spark plug 14. The internal combustion engine 10 has at least one combustion chamber 12, preferably four combustion chambers 12 as shown in fig. 1, the combustion chambers 12 being connected to the exhaust gas duct 22 of the exhaust gas system 20 via a common outlet 52. The exhaust system 20 has a turbine 24 of an exhaust gas turbocharger in the flow direction of the exhaust gas through an exhaust gas passage 22 of the exhaust system. Downstream of the turbine 24, an electrically heatable catalytic converter 26 is arranged in the exhaust gas duct 22, the catalytic converter 26 having an electrical heating element 28 and a catalytically active surface 50, preferably a catalytically active coating. The electrically heatable catalytic converter 26 is preferably designed as an electrically conductive three-way catalytic converter 30, wherein the catalytic converter 26 itself acts as a thermal resistor and thus as an electrical heating element 28 when a voltage is applied. Downstream of the electrically heatable catalytic converter 26, a further catalytic converter 32, preferably a further three-way catalytic converter 34, is arranged in the exhaust gas duct 22. The electric heating element 28 of the electrically heatable catalytic converter 26 can be controlled via a controller 42, preferably via an engine controller of the internal combustion engine 10 or a power controller of a hybrid vehicle. An electric drive motor 56 of the hybrid vehicle is powered via a battery 54, which battery 54 may also be used to heat the electric heating element 28. The combustion chambers 12 of the internal combustion engine 10 can be divided into a first group of combustion chambers 16 and a second group of combustion chambers 18, wherein both

groups

16,18 preferably have as many combustion chambers 12. In the internal combustion engine 10 shown in fig. 1, the two

groups

16,18 each have two combustion chambers 12. The internal combustion engine 10 is preferably configured as a reciprocating piston engine, but may also be configured as a rotary piston engine. The internal combustion engine 10 is preferably designed as an internal combustion engine 10 which is acted upon by means of an exhaust gas turbocharger, but may alternatively also be designed as a self-priming engine.

Fig. 2 shows a further illustration of a motor vehicle 1 according to the invention. The motor vehicle 1 has an internal combustion engine 10 with an exhaust system 20. In the exhaust system 20, in the flow direction of the exhaust gas of the internal combustion engine 10 through the exhaust gas duct 22, an electrically heatable catalyst 26 with an electrical heating element 28 is arranged, and downstream of the electrically heatable catalyst 26, a second catalyst 32 is arranged, which is in the form of a three-way catalyst 34. The motor vehicle 1 has a plurality of

sensors

44,46,48 which transmit signals to a control unit 42 of the motor vehicle 1. Thus, in FIG. 2, there is shown a door contact switch 44, a receiver for a keyless locking system of a motor vehicle 46, and a belt lock sensor 48. Alternatively or additionally, however, a further sensor may also be provided, for example a receiver for the transmitter of the central locking part or a sensor 58 for detecting the seat occupancy of the seat.

As illustrated in fig. 4, the procedure of the method according to the invention for heating the electrically heatable catalyst 26 can be described as follows: at time O, the internal combustion engine 10 obtains a signal that an engine start S of the internal combustion engine 10 is about to start. In a first phase I, the electrically heatable catalyst 26 is heated to a first threshold temperature T by the electric heating element 28₄The above. In this first phase, the electrically heatable catalytic converter 26 is heated only by the electrical heating IV of the catalytic converter 26. In this case, the electrical heating IV is activated by a signal from one of the

sensors

44,46,48,58, in particular by the door contact switch 44, so that the heating of the catalytic converter 26 can be carried out significantly before the motor of the internal combustion engine 10 is started S. Alternatively, the electric preheating is carried out in a phase in which the hybrid vehicle is driven solely by the electric drive motor 56 and no torque is available from the internal combustion engine 10. After a motor start S of the internal combustion engine 10, the electrically heatable catalytic converter 26 is brought to a second threshold temperature T in a second phase II₅Preferably the operating temperature of the catalyst 26 and above the light-off temperature of the catalyst 26. In this second phase II, a parallel heating VI is first carried out by the electrical heating IV and the chemical heating V of the catalytic converter 26 in order to avoid cooling the electrically heatable catalytic converter 26 directly after the motor start S of the internal combustion engine 10. In this way, unburned or partially burned exhaust gas components are supplied together with the required air to the preheated, electrically heatable catalyst 26. In this case, the unburned exhaust gas constituents, in particular unburned carbohydrates HC, and the partially burned exhaust gas constituents, in particular carbon monoxide CO, react exothermically together with oxygen at the preheated, catalytically active surface 50 of the electrically heatable catalyst 26. Thus, a combination of chemical and electrical heating by the electrically heatable catalytic converter 26 occurs. In this case, the first group 16 of combustion chambers 12 utilizes a superstoichiometric combustion air ratio λ for chemically heating the electrically heatable catalytic converter 26_E16> 1, and the second group 18 of combustion chambers 12 utilizes a substoichiometric combustion air ratio λ_E16Runs < 1. After that, in the third stage III,using stoichiometric combustion air ratio lambda in all combustion chambers 12_E=1 running the internal combustion engine 10 and disabling the heating measures IV, V. Fig. 6 shows the combustion air ratio λ of the internal combustion engine 10 in the case of heating the electrically heatable catalytic converter 26 according to the invention_E。

In conventional catalyst heating strategies, for example by adjusting the ignition angle of the internal combustion engine 10 in the "late" direction or by blowing secondary air into the exhaust gas duct 22, the necessary heat upstream of the turbine 24 of the turbocharger is generated directly at the output 52 of the internal combustion engine 10 and supplied to the exhaust gas duct 22. In this case, heat is extracted from the exhaust gas on the way to the catalytic converter 26 by two operating principles. On the one hand, the cold components upstream of the catalytic converter 26 are heated according to their heat capacity. On the other hand, the generated heat is given off to the environment via the surfaces of these components. This leads to heat losses up to the catalyst 26 to be heated and thus to disadvantages in terms of time and energy. With the proposed combined method, the chemical heating V of the catalytic converter 26 can be carried out directly on the catalytically active surface 50 of the electrically heatable catalytic converter 26 by means of the electric heating element 28.

Since the temperature of the electrically heatable catalytic converter 26 is ideally already at the first threshold temperature T at the time of the motor start S₄Above, low exhaust emissions are contemplated herein. By means of the method according to the invention, a significant pollutant conversion can be carried out significantly earlier in time, since in the conventional method the catalytic converter has an ambient temperature in the case of a motor start S of the internal combustion engine 10.

In fig. 3, in the case of a conventional heating of a catalytic converter 26, for example an electrically heatable catalytic converter 26, and in the case of a switching off of an electrical heating element 28, three measuring points T are shown in the exhaust gas duct 22 of the internal combustion engine 10₁、T₂And T₃The temperature profile of (a). The first measuring point is upstream of the turbine 24 of the exhaust-gas turbocharger, and the second measuring point T is₂Upstream of catalyst 26, and the third measurement point is in catalyst 26.

In fig. 5, the case is shown where an electrically heatable catalyst 26 is heated according to the inventionIn this case, the measurement points T are shown at the same three measurement points₁,T₂And T₃The temperature profile of (a).

Fig. 7 to 11 show alternative embodiments of the motor vehicle 1 shown in fig. 1. In this case, in essentially the same construction, only the internal combustion engine 10 and the exhaust system 20 of the internal combustion engine 10 are shown in each case.

In the exhaust system shown in fig. 7, an electrically heatable catalyst 26 is arranged downstream of the second catalyst 32, in the case of an otherwise identical construction as shown in fig. 1. Since the second catalytic converter 32 is still cold at the start S of the motor, the unburned or partially burned exhaust gas constituents flow through the second catalytic converter as far as possible without chemical reaction and are only converted exothermically on the catalytically active surfaces of the preheated catalytic converter 26.

In the embodiment shown in fig. 8, a particle filter 36 is additionally arranged in the exhaust system 20 downstream of the electrically heatable catalyst 26 and upstream of the second catalyst 32, in a configuration which is otherwise identical to that shown in fig. 1. Alternatively, an additional particle filter 36 may also be arranged downstream of the second catalytic converter 32, as shown in fig. 9. Alternatively, the functionalities of the second three-way catalyst 34 and the particle filter 36 may also be combined in one component, and as the second catalyst 32, as shown in fig. 10, a four-way catalyst 38 may be arranged in the exhaust gas duct 22 downstream of the electrically heatable catalyst 26.

Fig. 11 shows a further exemplary embodiment of an exhaust system 20 of a motor vehicle 1 according to the invention. In this case, the exhaust gas of the internal combustion engine 10 first flows through the second catalytic converter 32, in particular the second three-way catalytic converter 34, then through the third catalytic converter 60 and finally through the electrically heatable catalytic converter 26, wherein the electrically heatable catalytic converter 26 is configured as an electrically heatable four-way catalytic converter 40. The electric heating element 28 can be used here not only to heat the electrically heatable quaternary catalyst 40 to operating temperature using the method according to the invention, but also to assist the electrically heatable quaternary catalyst 40 in the event of the burning-off of soot remaining in the electrically heatable quaternary catalyst 40.

Claims

1. A method for heating an electrically heatable catalyst (26) in an exhaust gas system (20) of an internal combustion engine (10), wherein the electrically heatable catalyst (26) has an electrical heating element (28) and a catalytically active surface (50), and wherein the electrical heating element (28) is controllable via a controller (42), the method comprising the steps of:

-electrically warming the electrically heatable catalyst (26) in advance before the internal combustion engine (10) is started,

-heating the electrically heatable catalytic converter (26) in parallel by electrical heating and simultaneously by measures inside the internal combustion engine (10), wherein unburned or partially burned fuel components are exothermically converted on a catalytically active surface (50) of the electrically heatable catalytic converter (26),

-switching off the electric heating element (28) and further heating the electrically heatable catalyst (28) by means internal to the engine, wherein oxygen required for the exothermic conversion of the unburned or partially burned fuel components is conveyed into the exhaust gas system (20) via a combustion chamber (12) of the internal combustion engine (10).

2. The method according to claim 1, characterized in that the measures inside the engine comprise combustion chamber specific oxygen regulation, wherein a first group (16) of combustion chambers (12) of the internal combustion engine (10) utilizes a super-stoichiometric combustion air ratio (λ)_E> 1), and a second group (18) of combustion chambers (12) of the internal combustion engine (10) utilizes a substoichiometric combustion air ratio (lambda)_E< 1) to run.

3. Method according to claim 2, characterized in that stoichiometric exhaust gas (λ) occurs in the exhaust gas channel (22) downstream of the output (52) of the internal combustion engine (10)_A=1), wherein the catalytic action of the unburned or partially burned fuel component of the exhaust gas together with the residual oxygen present in the exhaust gas at the electrically heatable catalyst (26)Is exothermically converted on the surface (50).

4. Method according to claim 1, characterized in that the internal combustion engine (10) utilizes a superstoichiometric, leaned combustion air ratio (λ) in the heating phase of the electrically heatable catalyst (26)_E> 1) and entrains fuel into an exhaust gas channel (22) of the exhaust gas system (20) upstream of the electrically heatable catalyst (26).

5. Method according to claim 1, characterized in that all combustion chambers (12) of the internal combustion engine (10) periodically utilize an over-stoichiometric combustion air ratio (λ) alternately during the heating phase of the electrically heatable catalyst (26)_E> 1) and substoichiometric combustion air ratio (lambda)_E< 1), wherein, when the internal combustion engine (10) is operated superstoichiometrically, the Oxygen Storage (OSC) of the electrically heatable catalyst (26) is filled with oxygen, and, when the internal combustion engine (10) is operated substoichiometrically, the unburned or partially burned fuel components react exothermically with the oxygen stored in the electrically heatable catalyst (26).

6. Method according to one of claims 1 to 5, characterized in that the electrical heating of the electrically heatable catalytic converter (26) is started by means of a door contact switch (44), a receiver (46) for a signal of a keyless locking system or a central locking part, or a belt lock contact (48), or the electrical heating of the electrically heatable catalytic converter (26) is started when a battery (54) of an electric drive motor (56) of the hybrid drive is discharged to such an extent that a switch over to the internal combustion engine is imminent.

7. Method according to any one of claims 1 to 5, when the electrically heatable catalyst (26) has reached the first threshold temperature (T) by electrical heating₄) When this happens, measures inside the engine are started.

8. The method according to claim 7, characterized in that the internal combustion engine (10) is reaching a second threshold temperature (T;)₅) Thereafter using stoichiometric combustion air ratio (lambda)_E=1), and the measures inside the engine are ended.

9. Motor vehicle (1) having an internal combustion engine (10) and an exhaust gas system (20), in which exhaust gas system (20) at least one electrically heatable catalyst (26) is arranged, and having a control unit (42) which is designed to carry out the method according to one of claims 1 to 8.

10. Motor vehicle (1) according to claim 9, characterized in that the current source for heating the electrically heatable catalyst (26) is the 48V onboard network of the motor vehicle (1) or a battery for supplying an electric drive motor (56) of the motor vehicle (1).