CN107084023B

CN107084023B - Method and device for exhaust gas aftertreatment of an internal combustion engine

Info

Publication number: CN107084023B
Application number: CN201710084244.6A
Authority: CN
Inventors: F.青克
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2016-02-16
Filing date: 2017-02-16
Publication date: 2021-01-15
Anticipated expiration: 2037-02-16
Also published as: DE102016202349A1; CN107084023A

Abstract

The invention relates to a method and a device for exhaust gas aftertreatment of an internal combustion engine having an exhaust gas channel, a catalytic converter, a Lambda probe and a particle filter, comprising the following steps: -determining the load state of the particulate filter, -determining the exhaust gas temperature in the exhaust gas channel by measuring the internal resistance of the first Lambda probe, -determining the oxygen content in the exhaust gas by the first Lambda probe, -introducing a regeneration of the particulate filter when the respective load state, the combustion air ratio of the internal combustion engine and the temperature in the exhaust gas channel are within predetermined ranges for the regeneration of the particulate filter are reached, -avoiding the introduction of a regeneration by a respective engine measure when the temperature in the exhaust gas channel and/or the oxygen content in the exhaust gas are above certain, defined limits, -adjusting the particulate filter for regeneration by introducing the respective engine measure when the temperature in the exhaust gas channel is below a defined threshold value.

Description

Method and device for exhaust gas aftertreatment of an internal combustion engine

Technical Field

The invention relates to a method and a device for exhaust gas aftertreatment of an internal combustion engine.

Background

The continuous increase in exhaust gas legislation has placed high demands on vehicle manufacturers, which are achieved by corresponding measures for reducing untreated emissions from the engine and by corresponding exhaust gas aftertreatment. With the introduction of the next legislation level EU6, limit values for the number of particles are specified for gasoline engines. This may result in the use of an ottomartikelfilter (Ottopartikelfilter) being possible in some vehicle models. Such otto particle filters are loaded with soot during driving operation. In order not to raise the exhaust gas back pressure too strongly, the otto particulate filter has to be regenerated continuously or periodically. In order to carry out the thermal oxidation of the soot remaining in the otto filter with oxygen, a sufficiently high temperature level is required in connection with the simultaneous presence of oxygen in the exhaust gas system of a gasoline engine. Since modern gasoline engines are typically operated inStoichiometric combustion air ratio (lambda) without excess oxygen_E=1), for which additional measures are required. Measures for this are, for example, temperature increase by adjusting the ignition angle, temporary lean setting (magervestellung) of the gasoline engine, blowing in secondary air into the exhaust system, or a combination of these measures. Regeneration of particulate filters is known, for example, from DE 102013220899 a 1. In this case, Lambda regulation is provided for the gasoline engine, wherein the combustion air ratio is adjusted for the regeneration of the particle filter from the stoichiometric combustion air ratio in the direction of the stoichiometric combustion air ratio, and the regeneration of the particle filter is effected by oxidation of the soot with excess oxygen. However, under certain, unfavorable operating conditions (i.e. if high temperatures and an excess of oxygen are present at the same time in the exhaust gas duct), an uncontrolled burn-up of soot on the particle filter and thus damage to the components can result.

For Lambda regulation of internal combustion engines, Lambda probes are used, which can be heated by means of heating elements in order to increase the measurement accuracy, in order to bring the Lambda probe to a predetermined temperature. Such a temperature regulation of the Lambda probe can be effected, for example, by means of a temperature sensor in the exhaust gas duct. However, such temperature sensors are associated with additional costs as additional components. Solutions have therefore been proposed in the past in which the exhaust gas temperature is determined from the resistance or the change in resistance of the Lambda probe.

DE 102008011833 a1 discloses a method for controlling a Lambda-regulated exhaust system of an internal combustion engine, wherein the exhaust system has at least one catalytic converter and at least one heating element for heating a Lambda probe to an operating temperature. It is provided that the operating efficiency of the heating element is determined and at least one corrected control parameter controlled by the heating element is used for the controlled heating of the heating element.

Disclosure of Invention

The invention now aims to facilitate the regeneration of the particle filter and to avoid damage to components of the components used for exhaust gas aftertreatment, in particular to the particle filter.

According to the invention, this object is achieved by a method for exhaust gas aftertreatment of an internal combustion engine having an exhaust gas channel, a catalyst arranged in the exhaust gas channel, a first Lambda probe arranged in the exhaust gas channel, which can be heated by means of a heating element, and having a particle filter, comprising the following steps:

-determining the loading state of the particle filter,

determining the exhaust gas temperature in the exhaust gas channel of the internal combustion engine by measuring the internal resistance of the Lambda probe,

determining the oxygen content in the exhaust gas by means of a Lambda probe,

-introducing a regeneration of the particulate filter when the respective load condition, the combustion air ratio of the internal combustion engine and the temperature in the exhaust gas channel are reached in the ranges predetermined for the regeneration of the particulate filter,

avoiding the introduction of regeneration by corresponding engine measures when the temperature in the exhaust gas channel and/or the oxygen content in the exhaust gas lies above certain, defined limits,

-adjusting (konditioinierung) the particle filter for regeneration by introducing a corresponding engine measure when the temperature in the exhaust gas channel is below a defined threshold value.

In this way, a combined measurement of the exhaust gas temperature and the oxygen content in the exhaust gas duct can be achieved in an advantageous manner, so that both parameters are determined by means of a component. The reliability of the measurement can thereby be improved and the method for the regeneration of the particle filter can thereby be introduced more simply. Furthermore, the parallel measurement of the oxygen content and the temperature provides increased component protection of components in the exhaust gas channel of the internal combustion engine, since unfavorable operating conditions are identified which can lead to an uncontrolled increase in the exhaust gas temperature. In this case, an additional temperature sensor in the exhaust gas duct can be dispensed with, which reduces costs.

According to a preferred embodiment of the method, coasting (Schubbetrieb) of the internal combustion engine is prevented if the temperature in the exhaust gas duct is above a threshold value. This prevents fresh air from being pumped into the exhaust gas channel via the cylinder block of the internal combustion engine and thus prevents sufficient oxygen from being available to cause uncontrolled burning of soot on the particle filter. In this way, an undesirable excess of oxygen in the exhaust gas channel, which promotes uncontrolled soot burnup (Russabbrand), can be avoided.

In a preferred embodiment of the method according to the invention, it is provided that the ignition angle of the internal combustion engine is adjusted in the "early" direction in the event of an excessively high temperature in the exhaust gas duct. By adjusting the ignition angle to the "early" direction, combustion of the fuel may begin earlier and have substantially ended when the exhaust valve is opened. As a result, the temperature in the exhaust gas duct of the internal combustion engine is reduced, as a result of which the temperature can be reduced again to a range that is advantageous for the regeneration of the particle filter and thermal damage to the particle filter is avoided.

According to an alternative embodiment of the method according to the invention, the exhaust gas temperature is raised by adjusting the ignition angle of the internal combustion engine in the late direction. By adjusting the ignition angle in the "late" direction, the combustion starts later and does not yet end when the exhaust valve opens, so that the temperature in the exhaust gas channel increases.

According to a preferred development of the method, the heating element of the Lambda probe is deactivated during the regeneration of the particle filter. This allows a simplified measurement of the internal resistance of the Lambda probe and a calculation of the exhaust gas temperature during the regeneration of the particle filter based thereon.

For effective regeneration of the particle filter without the risk of thermal damage to the components, the regeneration of the particle filter is carried out in a temperature range between 600 ℃ and 700 ℃ and at a combustion air ratio lambda of the internal combustion engine_EIt is advantageous when this is achieved in the case between 1.1 and 1.3. In order to enable an efficient oxidation of the soot remaining in the particulate filter and thus a regeneration of the particulate filter, the temperature at the inlet into the particulate filter should be at least 600 ℃ to achieve a significant conversion rate of the soot. Furthermore, the oxidation should be carried out with a slight excess of oxygen in the exhaust gas duct, in order to provide sufficient oxygen for the oxidation of soot particles, on the one hand, while avoiding a higher excess of oxygen and thus uncontrolledThe risk of soot burn-up.

According to the invention, an arrangement for the exhaust gas aftertreatment of an internal combustion engine is proposed, comprising an exhaust gas channel, a catalytic converter arranged in the exhaust gas channel, a particulate filter arranged in the exhaust gas channel, and a control unit, wherein a first Lambda probe is arranged downstream of the catalytic converter and upstream of the particulate filter in the flow direction of the exhaust gas, wherein the oxygen content in the exhaust gas can be measured by means of the first Lambda probe, wherein the first Lambda probe can be heated by means of a heating element, wherein a temperature in the exhaust gas channel, preferably just before the inlet into the particulate filter, can be determined by means of the internal resistance of the first Lambda probe, and wherein, depending on this information, a regeneration of the particulate filter can be prevented in order to prevent an uncontrolled soot burn-up on the particulate filter.

In a preferred embodiment, a first catalytic converter, preferably a front catalytic converter close to the engine, and a second catalytic converter are arranged in the exhaust gas duct, wherein the second catalytic converter is designed as a so-called quaternary catalytic converter, i.e. as a three-way catalytic converter with an additional particle filter function, in particular as a particle filter with a three-way effective catalytic coating. In a preferred embodiment, a second Lambda probe, in particular a broad-band Lambda probe, is arranged upstream of the first catalytic converter and a first Lambda probe is arranged upstream of the quaternary catalytic converter, wherein the first Lambda probe is designed as a step probe (sprangsonde). At least the first Lambda probe is heatable. The particulate filter with the three-way active catalytic coating is again more thermally loaded during regeneration than the uncoated particulate filter, since here the exothermic reaction of soot burn-up and the exothermic catalytic reaction of the three-way catalyst are superimposed. The device according to the invention for exhaust gas aftertreatment is therefore particularly preferably arranged in an exhaust gas system with a quaternary catalyst.

According to a preferred embodiment, it is provided that the catalyst comprises a pre-catalyst and a main catalyst, wherein the Lambda probe is arranged downstream of the pre-catalyst or upstream of the post-catalyst. By arranging the Lambda probe between the front and rear catalyst, the Lambda probe is used for correction of the total Lambda regulation in the exhaust gas channel. The post-catalyst is a so-called quaternary catalyst and is used for filtering solid pollutants in addition to the conversion of gaseous pollutants.

Preferably, the particle filter is arranged in a floor layer (Unterbodenlage) of the motor vehicle. The particulate filter may be arranged in the floor layer away from the engine such that the particulate filter is not loaded as strongly thermally. In addition, the improved radiation and convection heat dissipation at the particle filter is achieved by the floor layer in relation to installation in the engine compartment. An arrangement away from the engine is in this connection understood to be an arrangement at least 80cm, preferably at least 100cm, downstream of the outlet of the internal combustion engine. The risk of thermal damage can be reduced, in particular during regeneration of the particle filter, by improved heat dissipation at the particle filter.

Further preferred embodiments of the invention result from the remaining features.

The different embodiments of the invention mentioned in this application can advantageously be combined with one another if not implemented separately.

Drawings

The invention is explained below in an exemplary embodiment with reference to the attached drawings. Wherein:

figure 1 shows an internal combustion engine with a device for exhaust gas aftertreatment according to the invention,

figure 2 shows a flow chart of a method for carrying out the exhaust gas aftertreatment for an internal combustion engine according to the invention,

fig. 3 shows an alternative embodiment of the device according to the invention for exhaust gas aftertreatment of an internal combustion engine.

List of reference numerals

10 internal combustion engine

12 exhaust gas channel

14 catalytic converter

16 heating element

18 particle filter

20 first Lambda Probe (before particle Filter)

22 controller

24 front catalytic converter

26 particulate filter with integrated after-catalyst

28 rear catalytic converter

30 second Lambda Probe (before front catalyst)

λ_ECombustion air ratio

T_ATemperature of exhaust gas

T_SOUpper threshold value

T_SUA lower threshold value.

Detailed Description

Fig. 1 shows a device according to the invention for exhaust gas aftertreatment of an internal combustion engine 10. The device comprises an exhaust gas duct 12 connected to the internal combustion engine 10, in which a second Lambda probe 30, a front catalytic converter 24, a first Lambda probe 20 and a rear catalytic converter 28 in the form of a particle filter 26 with a three-way effective catalytic coating are arranged in the flow direction of the exhaust gases of the internal combustion engine 10 through the exhaust gas duct 12. The front catalytic converter 24 is designed as a three-way catalytic converter, and the rear catalytic converter 28 is designed as a four-way catalytic converter, i.e. as a particle filter 26 with a three-way effective catalytic coating. Alternatively, an uncoated particle filter 18 can also be used as shown in fig. 3. The internal combustion engine 10 and the Lambda probes 20, 30 are each connected via a signal line to a control unit 22 for controlling the internal combustion engine 10. A heating element 16 is arranged on the first Lambda probe 20, with which heating element the first Lambda probe 20 can be brought to operating temperature. For this purpose, a heating regulator, not shown, is provided, which can be integrated into the control unit 22, for example, and by means of which the temperature of the Lambda probe 20 can be set to a predetermined operating temperature.

The temperature measurement in the exhaust gas duct 12 provides important information on the state of the exhaust gas system. This can be done, for example, by the internal combustion engine 10 as a function of the temperature T in the exhaust gas duct 12_AThe corresponding control takes protective measures against overheating of the exhaust gas aftertreatment components, in particular of the catalytic converter 14 or of the particle filters 18, 26.

In an exhaust system with two catalytic converters 14 (in particular with a front catalytic converter 24 close to the engine and a rear catalytic converter 26 arranged in the floor layer of the motor vehicle), a first Lambda probe 20 (which is designed as a step-Lambda probe) is used for correcting the overall Lambda regulation in the exhaust gas duct 12. The first Lambda probe 20 is downstream of the front catalyst 24 and upstream of the rear catalyst 28. The probe temperature of the first Lambda probe 20 can be controlled or regulated by the controller 22. The internal resistance of the first Lambda probe 20 can be used here together with the applied heating voltage and possibly further parameters (for example the measured ambient conditions) to establish a correlation with the exhaust gas temperature. The second catalytic converter 28 and/or the

particle filter

18,26 downstream of the first Lambda probe 20 can be protected from overheating by this measure.

During operation of the internal combustion engine 10, the particle filters 18,26 are loaded with soot particles, so that the flow resistance in the exhaust gas duct 12 increases with the load. The

particulate filter

18,26 must be periodically regenerated. In order to use the

particle filter

18,26 in the floor layer of a motor vehicle in the exhaust gas duct 12 of an externally ignited internal combustion engine 10, high demands are made on the protection of the components of the

particle filter

18,26, in particular during the regeneration of the

particle filter

18, 26. Temperature T of exhaust gas_AA certain threshold value is not allowed to be exceeded during regeneration, so that the

particle filter

18,26 is not subjected to thermal damage and the

particle filter

18,26 is not destroyed by the exothermic burn-up reaction of soot on the

particle filter

18, 26.

By using the first Lambda probe 20 upstream of the

particle filter

18,26, which is preferably installed in the floor layer of the motor vehicle, the monitoring of the internal resistance and the heating output of the first Lambda probe 20 can be used to determine the temperature of the exhaust gas as it enters the

particle filter

18,26 and to influence the operation of the internal combustion engine 10, if necessary by means of the controller 22, in such a way that the

particle filter

18,26 is protected from overheating.

Here, the internal resistance of the first Lambda probe 20 is proportional to the temperature of the first Lambda probe 20. The higher the temperature of the first Lambda probe 20, the lower its internal resistance. During operation of the internal combustion engine 10, the first Lambda probe 20 is heated both by the hot exhaust gas of the internal combustion engine 10 and by the heating element 16, which is preferably designed as a heating resistor, in particular as a heating wire integrated into the first Lambda probe 20. The operating temperature of the first Lambda probe 20 is precisely defined and is applied to all occurring exhaust gas temperatures by control or regulation. The more heat that is emitted by the exhaust gas to the first Lambda probe 20, the less heating power is introduced by the heating element 16.

In the case of regeneration requirements of the

particle filter

18,26, higher exhaust gas temperatures in the range >600 ℃ are required in order to burn up the soot remaining in the

particle filter

18, 26. By means of this oxidation reaction, an exothermic reaction starts in the

particle filter

18,26, which in turn causes a temperature increase at the

particle filter

18, 26. This is particularly critical for a particle filter 26 with a three-way effective catalytic coating, since here the exothermic reactions of the three-way effective catalytic coating and soot burn-up are superimposed. This temperature increase may detrimentally affect the

particulate filter

18,26 when it exceeds a defined limit. Therefore, the initial enthalpy (eingangsententhipe), i.e. the temperature at the inlet into the

particle filter

18,26, is not allowed to exceed a certain threshold value.

For the regeneration of the particle filters 18,26 and for the burning of soot, the heating element 16 can now be deactivated in order to heat the first Lambda probe 20 exclusively by the exhaust gases of the internal combustion engine 10. The internal resistance of the first Lambda probe 20 is measured and the exhaust gas temperature in the exhaust gas duct 12 is inferred from the internal resistance of the first Lambda probe 20. Based on this measurement, measures for component protection of the

particle filter

18,26 can then be introduced by the controller 22. For example, an adjustment of the ignition angle of the internal combustion engine 10 to the "early" direction and/or a matching of the injection point or injection quantity of the fuel injection is suitable as a measure.

In this case, Lambda probes 20, 30 are not only provided with regard to the temperature T in exhaust gas duct 12_ABut also provides information about the oxygen content in the exhaust gas and the composition of the exhaust gas. For the regeneration of the particle filters 18,26, the amount of residual oxygen in the exhaust gas is also relevant in addition to the temperature. The supply of a large amount of fresh air into the

hot particle filter

18,26 can, like an excessively high temperature, lead to damage to the components of the

particle filter

18,26, since in this case uncontrolled burning of soot on the

particle filter

18,26 can result. As further protective measures controlled by means of Lambda probes 20, 30, for exampleSuch as a thrust cut-off (schubabcchaltung) that prevents the internal combustion engine 10.

Fig. 2 shows a flow chart of a method according to the invention for exhaust gas aftertreatment of an internal combustion engine 10.

In a first method step<100>The loading state of the

particle filter

18,26 is determined, which can be achieved, for example, by differential pressure measurement on the

particle filter

18,26 or by modeling of the soot discharge and soot entry from the

particle filter

18, 26. In a further method step<110>By measuring the internal resistance of the first Lambda probe 20 to determine the temperature T in the exhaust gas channel 12 of the internal combustion engine 10_A. In a further method step<120>By at least one of the Lambda probes 20, 30, the oxygen content in the exhaust gas channel 12 is determined. Therein, the method step<100>、<110>And<120>may be implemented in parallel or in any order.

According to the method steps<100>、<110>And<120>when the respective load state of the

particle filter

18,26 is reached and the temperature T in the exhaust gas duct 12 is reached_AAnd when the oxygen concentration in the exhaust gas channel 12 is in a predetermined range for the regeneration of the

particle filter

18,26, in the following method step<140>Which introduces regeneration of the

particulate filter

18, 26.

If the temperature T in the exhaust gas channel 12_ABelow this predetermined range, in particular below a defined threshold value T_SUIn the preceding method step<130>By introducing corresponding engine measures to pre-condition the

particle filter

18,26 and to raise the exhaust gas temperature to the range necessary for the regeneration of the

particle filter

18, 26.

If the temperature 12 in the exhaust gas duct is above a certain defined limit, in particular above a threshold value T_SOAt the method step<150>Regeneration of the

particle filter

18,26 is avoided by introducing corresponding engine measures in order to avoid thermal damage of the

particle filter

18, 26.

Fig. 3 shows an alternative embodiment of the device according to the invention for exhaust gas aftertreatment of an internal combustion engine 10. In the same way as in the exemplary embodiment according to fig. 1, an uncoated particle filter 18 is used instead of a particle filter 26 with a three-way catalytically effective coating. The first catalyst 14 is configured here as a three-way catalyst close to the engine.

Claims

1. A method for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust gas channel (12), a catalyst (14) arranged in the exhaust gas channel (12), a first Lambda probe (20) arranged in the exhaust gas channel (12) which can be heated by means of a heating element (16), and with a particle filter (18,26), comprising the steps of:

-determining the loading state of the particle filter (18,26),

-by measuring the internal resistance R of the first Lambda probe (20)_iTo determine the exhaust gas temperature in an exhaust gas channel (12) of the internal combustion engine (10),

-determining the oxygen content in the exhaust gas by means of the first Lambda probe (20),

-a combustion air ratio (λ) of the internal combustion engine (10) when a corresponding load state is reached_E) And the temperature (T) in the exhaust gas channel (12)_A) Introducing a regeneration of the particulate filter (18,26) when in a predetermined range for the regeneration of the particulate filter (18,26),

-temperature (T) as in the exhaust gas channel (12)_A) And/or, when the oxygen content in the exhaust gas lies above a certain, defined limit, the introduction of regeneration is avoided by corresponding engine measures,

-adjusting the particulate filter (18,26) for regeneration by introducing a corresponding engine measure when the temperature in the exhaust gas channel (12) is below a defined threshold value.

2. Method according to claim 1, characterized in that the temperature (T) in the exhaust gas channel (12)_A) Above a threshold value, coasting of the internal combustion engine (10) is prevented.

3. The method of claim 1 or 2Method, characterized by the temperature (T) in the exhaust gas channel (12)_A) In the event of an excessive increase, the ignition angle of the internal combustion engine (10) is adjusted in the early direction.

4. Method according to any one of claims 1 to 2, characterized in that the heating element (16) of the first Lambda probe (20) is deactivated during regeneration of the particle filter (18, 26).

5. Method according to any of claims 1-2, characterized in that the exhaust gas temperature (T;) is_A) The lift of (2) is achieved by adjusting the ignition angle in the "late" direction.

6. The method according to any one of claims 1 to 2, characterized in that the regeneration of the particulate filter (18,26) is in the temperature range of 600 ° to 700 ° and at the combustion air ratio (λ) of the internal combustion engine (10)_E) In the range 1.1<λ_E<1.3.

7. An arrangement for the exhaust gas aftertreatment of an internal combustion engine (10) having an exhaust gas channel (12), a catalyst (14) arranged in the exhaust gas channel (12), a particle filter (18,26) arranged in the exhaust gas channel (12), having a combustion air ratio (λ) heatable by means of a heating element (16) for adjusting the internal combustion engine (10)_E) And with a controller (22), characterized in that the controller (22) is set up to carry out the method according to any one of claims 1 to 6.

8. The device for the exhaust-gas aftertreatment of an internal combustion engine (10) according to claim 7, characterized in that the particle filter (18) is configured as a catalytically effective coated particle filter (26).

9. Arrangement for exhaust gas aftertreatment of an internal combustion engine (10) according to one of the claims 7 to 8, characterized in that the catalyst (14) comprises a front catalyst (24) and a rear catalyst (28), wherein the first Lambda probe (20) is arranged downstream of the front catalyst (24) and upstream of the particle filter (26).

10. The device for exhaust gas aftertreatment of an internal combustion engine (10) according to claim 9, characterized in that a second Lambda probe is arranged upstream of the pre-catalyst (24).