Method for heating a catalytic converter and exhaust gas aftertreatment system

Abstract

A method for heating a catalytic converter in an exhaust system of an internal combustion engine, in which an exhaust gas burner for heating the catalytic converter is arranged, upstream of the catalytic converter. A lambda probe for controlling the combustion air ratio of the exhaust gas burner is arranged immediately downstream of the exhaust gas burner and upstream of the catalytic converter. The method includes operating the internal combustion engine with a stoichiometric combustion air ratio (λ.sub.E=1), activating the exhaust gas burner, which is operated alternately with a substoichiometric combustion air ratio (λ.sub.B<1) and a superstoichiometric combustion air ratio (λ.sub.B>1), wherein from the substoichiometric combustion air ratio (λ.sub.B<1) to the superstoichiometric combustion air ratio (λ.sub.B>1) as soon as a rich breakthrough is detected by the second lambda probe (34), and wherein a switchover from the superstoichiometric combustion air ratio (λ.sub.B>1) to the substoichiometric combustion air ratio (λ.sub.B<1) takes place as soon as a lean breakthrough is detected by the second lambda probe.

Claims

1. A method for heating a catalytic converter in an exhaust system of an internal combustion engine with at least one combustion chamber, wherein an exhaust gas burner is arranged in the exhaust system upstream of the catalytic converter for heating the catalytic converter, wherein a first lambda probe for controlling the combustion air ratio of the internal combustion engine is arranged downstream of an outlet the internal combustion engine and upstream of the exhaust gas burner, and wherein a second lambda probe for controlling the combustion air ratio of the exhaust gas burner is arranged immediately downstream of the exhaust gas burner and upstream of the catalytic converter, said method comprising the following steps: operating the internal combustion engine with a stoichiometric combustion air ratio (λ.sub.E=1), activating the exhaust gas burner, wherein the exhaust gas burner is operated alternately with a substoichiometric combustion air ratio (λ.sub.B<1) and a superstoichiometric combustion air ratio (λ.sub.B>1), wherein a switchover from the substoichiometric combustion air ratio (λ.sub.B<1) to the superstoichiometric combustion air ratio (λ.sub.B>1) takes place as soon as a rich breakthrough is detected by the second lambda probe, wherein a switchover from the superstoichiometric combustion air ratio (λ.sub.B<1) to the substoichiometric combustion air ratio (λ.sub.B>1) takes place as soon as a lean breakthrough is detected by the second lambda probe, and wherein a frequency of the alternating change between the substoichiometric combustion air ratio and the superstoichiometric combustion air ratio is greater than one Hertz.

2. The method for heating a catalytic converter according to claim 1, wherein a third lambda probe, by which a stoichiometric exhaust gas is set downstream of the catalytic converter, is arranged downstream of the catalytic converter.

3. The method for heating a catalytic converter according to claim 1, wherein the combustion air ratio (λ.sub.B) of the exhaust gas burner is adjusted by an adjustment of the quantity of fuel in the exhaust gas burner.

4. The method for heating a catalytic converter according to claim 1, wherein the combustion air ratio (λ.sub.B) of the exhaust gas burner is set by an adjustment of the quantity of air in the exhaust gas burner or by an adjustment of the quantity of fuel and the quantity of air.

5. The method for heating a catalytic converter according to claim 1, wherein the superstoichiometric combustion air ratio is set in the range 1.02<λ.sub.B<1.1.

6. The method for heating a catalytic converter according to claim 1, wherein the substoichiometric combustion air ratio is set in the range 0.9<λ.sub.B<0.98.

7. The method for heating a catalytic converter according to claim 1, wherein the method is initiated immediately after a cold start of the internal combustion engine.

8. An exhaust gas aftertreatment system for an internal combustion engine with at least one combustion chamber, wherein the exhaust gas aftertreatment system comprises: an exhaust system in which an exhaust gas burner for heating a catalytic converter is arranged in a flow direction of an exhaust gas in the internal combustion engine and in which the catalytic converter is arranged downstream of the exhaust gas burner, wherein a first lambda probe for controlling the combustion air ratio of the internal combustion engine is located downstream of an outlet of the internal combustion engine and upstream of the exhaust gas burner, and wherein a second lambda probe, by which a combustion air ratio (λ.sub.B) of the exhaust gas burner can be regulated, is arranged immediately downstream of the exhaust gas burner, and a control unit which is set up to implement a method according to claim 1 when a machine-readable program code is executed by the control unit.

9. The exhaust gas aftertreatment system according to claim 8, wherein the catalytic converter is designed as a three-way catalytic converter or as a four-way catalytic converter.

10. The exhaust gas aftertreatment system according to claim 8, wherein the catalytic converter is arranged as a first emission-reducing exhaust gas aftertreatment component in the flow direction of an exhaust gas of the internal combustion engine through the exhaust system.

11. The exhaust gas aftertreatment system according to claim 8, wherein the catalytic converter is arranged in an underbody position of a motor vehicle.

12. The exhaust gas aftertreatment system according to claim 8, wherein the second lambda probe is designed as a jump probe.

13. The exhaust gas aftertreatment system according to claim 8, wherein the second lambda probe is designed as a broadband probe.

14. The exhaust aftertreatment system according to claim 8, wherein a further catalytic converter is arranged downstream of the catalytic converter, wherein a third lambda probe is arranged downstream of the catalytic converter and upstream of the further catalytic converter, and wherein the further lambda probe is set up to regulate the combustion air ratio (λ.sub.E) of the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The same components or components having the same function are identified in the different figures with the same reference numerals. In the drawings:

(2) FIG. 1 shows a preferred exemplary embodiment of an internal combustion engine with an exhaust gas aftertreatment system;

(3) FIG. 2 shows a further exemplary embodiment of an internal combustion engine with an exhaust gas aftertreatment system for carrying out a method according to the invention for heating a catalytic converter;

(4) FIG. 3 shows time profiles of various parameters during the implementation of a method according to the invention for heating a catalytic converter in the exhaust system of an internal combustion engine; and

(5) FIG. 4 shows a further exemplary embodiment of an internal combustion engine with an exhaust gas aftertreatment system for carrying out a method according to the invention for heating a catalytic converter.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows a schematic illustration of an internal combustion engine 10, the outlet 18 of which is connected to an exhaust system 20 of an exhaust gas aftertreatment system according to the invention for exhaust gas aftertreatment of an exhaust gas stream from the internal combustion engine 10. The internal combustion engine 10 is designed as a gasoline engine, which is spark-ignited by means of external ignition means, in particular by means of spark plugs 16. The internal combustion engine 10 has a plurality of combustion chambers 12, in which a fuel-air mixture is burned. For this purpose, a fuel injector 14 is provided in each case at the combustion chambers 12 in order to inject a fuel into the combustion chambers 12. The internal combustion engine 10 is preferably designed as an internal combustion engine 10 charged by means of an exhaust gas turbocharger 24, wherein a turbine 26 of the exhaust gas turbocharger 24 is arranged downstream of the outlet 18 and upstream of a three-way catalytic converter 30 close to the engine. The exhaust system 20 comprises an exhaust gas duct 22, in which a second catalytic converter 38, 40 is arranged in the direction of flow of an exhaust gas through the exhaust gas duct 22 downstream of the three-way catalytic converter 30 close to the engine in an underbody position of a motor vehicle. The second catalytic converter 38, 40 is preferably designed as a four-way catalytic converter 40 and combines a three-way catalytic function with a particulate reduction function. Alternatively, the second catalytic converter 38, 40 can also be designed as a further three-way catalytic converter 38.

(7) Downstream of the turbine 26 of the exhaust gas turbocharger 24 and upstream of the three-way catalytic converter 30 close to the engine, an inlet point 32 for an exhaust gas burner 28 is provided, at which a hot burner exhaust gas of the exhaust gas burner 28 for heating the three-way catalytic converter 30 can be introduced into the exhaust gas duct 22. A first lambda probe 60 for controlling the combustion air ratio of the internal combustion engine 10 is arranged downstream of the outlet 18 of the internal combustion engine and upstream of the inlet point 32, in particular downstream of the turbine 26 of the exhaust gas turbocharger 24 and upstream of the inlet point 32. The first lambda probe 60 is preferably designed as a broadband probe 44. A second lambda probe 34, in particular a jump probe 42, is arranged downstream of the inlet point 32 and upstream of the three-way catalytic converter 30 in order to regulate the combustion air ratio λ.sub.B of the exhaust gas burner 28. A third lambda probe 36, which can be designed as a jump probe 42 or as a broadband probe 44, is arranged downstream of the three-way catalytic converter 30 and upstream of the second catalytic converter 38, 40. Alternatively, the second lambda probe 34 can also be designed as a broadband probe 44.

(8) The exhaust gas burner 28 has a secondary air supply 46 and a fuel supply 48, via which the combustion air ratio λ.sub.B of the exhaust gas burner 28 can be set. The secondary air supply 46 preferably comprises a secondary air pump 52 and a secondary air valve 54, wherein the secondary air valve 54 is arranged in a secondary air line 56 which connects the secondary air pump 52 to the exhaust gas burner 28. The fuel supply 48 comprises in particular a fuel injector 58 which is connected to a fuel supply system which supplies the fuel injectors 14 of the internal combustion engine 10 with fuel. The three-way catalytic converter 30 close to the engine can thus be heated up with the exhaust gas burner 28.

(9) The internal combustion engine 10 and the exhaust gas burner 28 are connected to a control unit 50, which controls the fuel injection through the fuel injectors 14, 58 at the combustion chambers 12 of the internal combustion engine 10 and at the combustion chamber of the exhaust gas burner 28.

(10) According to the invention, a method is proposed which is designed to heat up a three-way catalytic converter 30, 38 or a four-way catalytic converter 40 of a gasoline engine as quickly as possible to the light-off temperature required for a high conversion rate. During this active heating phase, the lambda control is carried out in such a way that the gaseous emissions are as low as possible until the light-off temperature is reached. Such a method is shown in FIG. 3.

(11) The time profile of the exhaust gas air ratio λ.sub.nK downstream of the three-way catalytic converter 30, the time profile of the electrical voltage U at the jump probe 42, and the fuel mass flow {dot over (m)} of the exhaust gas burner 28 during implementation of a method according to the invention for heating the catalytic converter 30, are shown in FIG. 3. Based on the exemplary embodiment according to FIG. 4, FIG. 3 shows the time profile of the exhaust gas air ratio λ.sub.nK downstream of the further catalytic converter 38, 40.

(12) In order to represent the lowest possible gaseous emissions in the active heating phase of the catalytic converter 30, 38, 40, it is necessary to regulate the mixed lambda from the combustion air ratio λ.sub.E of the internal combustion engine 10 and the combustion air ratio of the exhaust gas burner 28 to a stoichiometric ratio. A jump probe 42 is preferably used for this purpose. The combustion air ratio λ.sub.E of the internal combustion engine 10 is controlled to a stoichiometric combustion air ratio. The exhaust gas burner 28 is subjected to a forced amplitude in a pilot-controlled manner. The manipulated variable is preferably the fuel. This is carried out, for example, with an increase/decrease in a stoichiometric combustion air ratio of +/−5%. As soon as the second lambda probe 34 detects the rich mixture of engine exhaust gas and burner exhaust gas during the rich phase, the forced amplitude is adjusted to ˜5% lean. After the lean exhaust gas of the exhaust gas burner 28 has been mixed with that of the internal combustion engine 10 and the gas running time, the probe detects a lean jump, and the forced amplitude is changed again. This method is repeated periodically during the entire heating phase, so that there is an alternating change between a substoichiometric combustion air ratio λ.sub.B<1 and a superstoichiometric combustion air ratio λ.sub.B>1. Due to the lack of oxygen storage capacity between the exhaust gas burner 28 as the actuator of this control and the second lambda probe 34, 42 as the measuring element, the lean and rich periods are very short in accordance with the gas running time and thus the frequency of the switchover is high. As a result, no long lean and rich phases are formed which could lead, for example, to increased particulate emissions from the exhaust gas burner 28.

(13) This means that combustion air control can be implemented in a very cost-effective and simple manner in interaction with the exhaust gas burner. The combustion air ratio AB of the exhaust gas burner 28 is pilot-controlled via the blown-in secondary air and the activation period of the fuel injector 58.

(14) FIG. 2 shows a particularly simple exemplary embodiment of an internal combustion engine 10 with an exhaust gas aftertreatment system for carrying out a method according to the invention for heating a three-way catalytic converter 30. The internal combustion engine 10 is designed as a gasoline engine. The internal combustion engine 10 can be designed as a naturally aspirated engine. An exhaust gas burner 28 is provided downstream of an outlet 18 of the internal combustion engine 10 and upstream of a three-way catalytic converter 30, and by means of this exhaust gas burner hot burner exhaust gas can be introduced into the exhaust gas duct 22 at an inlet point 32 upstream of the three-way catalytic converter 30 in order to heat up the three-way catalytic converter 30.

(15) FIG. 4 shows a further, preferred exemplary embodiment of an internal combustion engine 10 with an exhaust system 20. With substantially the same structure as shown in FIG. 1, in this exemplary embodiment the inlet point 32 of the exhaust gas burner 28 is formed downstream of a first three-way catalytic converter 30 close to the engine and upstream of a further three-way catalytic converter 38, 40. The further catalytic converter 38, 40 is preferably arranged in an underbody position of a motor vehicle. In order to enable the further catalytic converter 38, 40 to heat up quickly to its light-off temperature, the hot exhaust gases of the exhaust gas burner 28 are introduced into the exhaust gas duct 22 at the inlet point 32, so that the exhaust gas flow of the internal combustion engine 10 is mixed with the exhaust gases of the exhaust gas burner 28 and ensures a uniform heating of the further catalytic converter 38, 40 over the cross section of the exhaust gas duct 22.

LIST OF REFERENCE NUMERALS

(16) 10 internal combustion engine 12 combustion chamber 14 fuel injector 16 spark plug 18 outlet 20 exhaust system 22 exhaust gas duct 24 exhaust gas turbocharger 26 turbine 28 exhaust gas burner 30 three-way catalytic converter 32 inlet point 34 second lambda probe 36 third lambda probe 38 second three-way catalytic converter 40 four-way catalytic converter 42 jump probe 44 broadband probe 46 secondary air supply 48 fuel supply 50 control unit 52 secondary air pump 54 secondary air valve 56 secondary air line 58 fuel injector 60 first lambda probe