EP1543229A1

EP1543229A1 - Exhaust-gas purification installation for an internal combustion engine

Info

Publication number: EP1543229A1
Application number: EP03779789A
Authority: EP
Inventors: Peter Müller; Stefan Detterbeck; Stephan Ramatschi; Florian Preuss; Matthew Keenan
Original assignee: Bayerische Motoren Werke AG
Current assignee: Bayerische Motoren Werke AG
Priority date: 2002-09-23
Filing date: 2003-09-17
Publication date: 2005-06-22
Anticipated expiration: 2023-09-17
Also published as: WO2004029439A1; JP2006515910A; JP4505330B2; DE10244137A1; EP1543229B1

Abstract

The invention relates to an exhaust-gas purification installation (1) for an internal combustion engine (2), comprising an NOX adsorbtion unit containing a first exhaust-gas conduit (3) equipped with a first catalytic purification device (4) and a second exhaust-gas conduit (3') equipped with a second catalytic purification device (4'), which lead into a common exhaust-gas conduit (6) downstream of the first and the second catalytic purification device (4, 4'). A respective first sensor (7, 7') is allocated upstream of each catalytic purification device (4, 4') in the respective exhaust-gas conduit (3, 3'). Said catalytic purification devices (4, 4') are NOX adsorbers and a common third sensor (8) is provided in the common exhaust-gas conduit (6), at least for the regeneration of the catalytic purification devices (4, 4'). The inventive exhaust-gas purification installation only requires three sensors for the regeneration of the NOX adsorbtion unit system and the related method for the regeneration of the NOX adsorbers.

Description

Emission control system for an internal combustion engine

The invention relates to an exhaust gas cleaning system for an internal combustion engine according to the features in the preamble of patent claim 1, and to methods for regenerating the first and second catalytic converters of an exhaust gas cleaning system according to the features in the preambles of patent claims 6 and 8.

The invention is based on the German patent application DE 100 12 839 A1. This describes a multi-flow exhaust system of a multi-cylinder internal combustion engine for motor vehicles with two exhaust lines, into which one or more cylinders each open. In each exhaust line there is a catalytic converter with one sensor upstream and one downstream. Downstream of the sensors, the two exhaust gas lines open into a common exhaust line, in which a NO _x adsorber is integrated. Another sensor is integrated into the common exhaust pipe behind the NO _x adsorber. Furthermore, a method for controlling regeneration fuel that is supplied to the internal combustion engine that works with a lean fuel-air mixture is described. The aim is to create optimal emissions control with minimal fuel consumption. The method monitors the exhaust gases that flow out of the NO _x adsorber during the regeneration event to detect when a fuel-air mixture for the internal combustion engine is in an excessively lean or rich range. If the detected exhaust gases contain an excessively lean fuel-air mixture, the amount of fuel for the engine is increased. The amount of fuel is reduced if the detected exhaust gases contain an excessively rich fuel-air mixture. The amount of fuel can be increased or decreased by adjusting the duration or the air-fuel ratio of the regeneration event.

A disadvantage of the described design of the exhaust gas cleaning system is that when the NO _x adsorber is regenerated, all cylinders of the internal combustion engine must be operated with a rich mixture.

The object of the present invention is to show an exhaust gas purification system with which cylinder-group-selective regeneration of NO _x adsorbers is possible, at the same time the number of sensors required being minimal.

This object is achieved by the feature in the characterizing part of patent claim 1.

The construction of the exhaust gas cleaning system according to the invention enables cylinder group-selective regeneration of NO _x adsorbents. Furthermore, the required number of sensors required for regeneration of the NO _x adsorbers is minimal. In addition, the arrangement of the NO _x adsorbers close to the engine advantageously leads to faster starting and thus to an early storage of pollutants after a cold start of the internal combustion engine.

According to claims 2 and 3, an inexpensive common parts principle is used for the sensors, with an optimal desulfation strategy, regeneration of the NO _x , depending on the design of the sensors, NO _x sensor or O ₂ sensor, in a linear or step response design Adsorber, is possible.

Since control by a control unit is customary for modern internal combustion engines, it makes sense, according to claim 4, to also include the desulfation of NO _x adsorbents in the control strategy of the control unit. This integration saves separate control units or components and thus reduces manufacturing costs.

Since NO _x adsorbers do not remove all pollutants from the exhaust gas, it makes sense according to claim 5, at least one further catalytic purifier. integration device in the exhaust gas cleaning system. This can be a 3-way catalytic converter, for example.

The method for the regeneration of NO _x adsorbents according to claim 6 is characterized above all by its simple control strategy. Here, as in the cited prior art, the entire internal combustion engine is operated uniformly with the same fuel / air mixture, but only three sensors are required to regulate the regeneration. The same regeneration start applies to all cylinder groups, with the determination of the regeneration duration being detected by means of the probe signal using a linear sensor. The regeneration cycle is either ended when the measured exhaust gas component, such as. B. O ₂ or NO _x , approaching a limit value, or if the exhaust gas component converges within a tolerance limit for all three sensors.

In the method for regeneration of the NO _x adsorbers according to claims 8 and 9, a cylinder-group-selective control is used, which makes it possible to detect the loading state of the individual NO _x adsorbers and to carry out the control in a catalyst-selective manner. When using this method, the amount of residual pollutants is reduced again compared to the first method from patent claims 6 and 7, since the fuel / air mixture control is more precise at the end of the regeneration cycle. In this method too, the regeneration start for the two NO _x adsorbers is simultaneous, the regeneration duration being determined via the sensor signal and the sensors being linear sensors. The estimated regeneration duration, which is always shorter than the actual regeneration duration of the NO _x adsorbers, is either calculated from the raw emissions of the internal combustion engine or read from a map in the control unit. The estimated regeneration duration thus divides the actual regeneration duration into at least two individual phases, which makes it possible to determine the loading of the individual NO _x adsorbers separately and to selectively determine the duration of a regeneration cycle for cylinder groups.

The method for regeneration of the NO _x adsorbers according to claims 10 and 11 is again characterized by a very simple control strategy. A step response sensor is used for this procedure. advises a digital signal. With this method, the regeneration starts for each cylinder group at a different time. The start for the regeneration cycle for the first cylinder group serves as a delayed start signal for the regeneration cycle of the second cylinder group. Basically, the process steps are the same as in the process according to claims 6 and 7, but separately for each cylinder group. Thus, the simplicity of the control strategy according to claims 6 and 7 is retained, but each cylinder group, viewed individually, successively goes through its regeneration cycle. The start of the regeneration cycle for the second cylinder group begins before the end of the regeneration cycle for the first cylinder group, but at the latest when the first regeneration cycle ends.

The method for the regeneration of the NO _x adsorbers according to claim 12 largely corresponds with its advantages to the method according to claims 10 and 11. In contrast to the aforementioned method, a linear probe is used here with which tolerance ranges can be better defined and adhered to.

The estimated regeneration times are in a time range in which a regeneration cycle can be carried out in a meaningful manner without affecting the operation of the internal combustion engine or the driver receiving feedback about the internal combustion engine.

The definition of the first and second regeneration times t- *, t ₂ to values according to claim 14 are also useful periods for practical driving, which allow a regeneration cycle without influencing the operating properties of the internal combustion engine.

The determination of the estimated regeneration period t according to claims 15 and 16 allows internal engine changes in the operation of the internal combustion engine to be determined with respect to the emission formation over the life of the internal combustion engine and corrected accordingly. The determination of the estimated regeneration time t according to claims 15 and 17 is a simple and inexpensive method to carry out a simple and within narrow tolerance limits with regard to the exhaust gas emissions to keep exhaust gas cleaning for the entire life of the internal combustion engine.

In the following, a preferred exemplary embodiment of an exhaust gas purification system according to the invention is explained in more detail in a single figure.

1 shows a schematically illustrated exhaust gas purification system 1 on a schematically illustrated internal combustion engine 2.

An intake system 10, consisting of a first intake manifold group 10 ′ and a second intake manifold group 10 ″, is attached to an internal combustion engine 2. Only one intake manifold is depicted for each intake manifold group 10 ′, 10 ″. The first intake manifold group 10 'opens into a first combustion chamber group 5, the second intake manifold group 10 "opens into a second combustion chamber group 5'. Similarly, each combustion chamber group is represented by only one combustion chamber. The first combustion chamber group 5 is gas-carrying with a first exhaust pipe 3 and the second combustion chamber group 5 'is connected to a second exhaust line 3' in a manner guiding the exhaust gas. In the first exhaust line 3 there is a first catalytic cleaning device 4, a NO _x adsorber, and in the second exhaust line 3 'there is a second catalytic cleaning device 4', also a NO _x adsorber, preferably the NO _x adsorbers are NO _x storage catalytic converters Catalytic cleaning device 9, here a 3-way catalytic converter, is integrated upstream of the first catalytic cleaning device ng 4 is a first sensor 7 and upstream of the second catalytic cleaning device 4 'a second sensor 7' is arranged in the exhaust pipes 3, 3 '. A third sensor 8 is arranged in the common exhaust line 6 upstream of the third catalytic cleaning device 9. The sensor-active elements of the sensors 7 and 8 are in contact with the exhaust gas. All three sensors 7, 7 'and 8 are oxygen sensors, but can also be NO _x sensors. In the present case, these are linear sensors, but they can also be step response sensors for other regeneration methods of the NO _x adsorber. All three sensors 7, 7 ', 8, are electrically connected to a control unit 2', which is also the control unit for the internal combustion engine. Separate control units for the exhaust gas cleaning system 1 and the internal combustion engine 2 are also possible. In further exemplary embodiments, at least one further catalytic cleaning device can be provided downstream of the first and second sensors 7, 7 ′ and / or downstream of the third sensor 8.

The following are four preferred methods for regeneration of the first and second catalytic cleaning devices 4, 4 '. in the exhaust gas cleaning system 1 explained in more detail.

It is common for all four methods that the internal combustion engine 1 has at least two combustion chamber groups 5, 5 'and each combustion chamber group 5, 5' is connected to an exhaust gas line 3, 3 'in a gas-carrying manner. A separate mixture control, different lambda values λ for each combustion chamber group 5, 5 ', is also possible. The lambda value λ for the mixture of the first combustion chamber group 5 is designated λ _z * ι and for the second combustion chamber group 5 'λzz. The λ _N κ is the lambda value in the common exhaust pipe. A stoichiometric mixture means λ = 1, a rich mixture (excess fuel) is in the range 0.5 <λ <1 and a lean mixture (excess air) is in the range 30>λ> 1. Depending on the sensor used, 7, 7 are present in the exhaust gas 'and 8, NO _x sensor or O ₂ sensor, various exhaust gas components, such as NO _x or O ₂ or HC, measured. The start of a regeneration cycle is the beginning of rich operation of at least one combustion chamber group 5, 5 '. The regeneration cycle is necessary when the NO _x absorption capacity of the catalytic cleaning devices 4, 4 ', the NO _x adsorbers, has dropped below a tolerable limit value. A regeneration cycle is understood to mean the time period within which all NO _x adsorbers are regenerated; a regeneration period relates to a NO _x adsorber.

In the first method, each sensor 7, 7 ', 8 is a linear sensor, and the two combustion chamber groups 5, 5' are fed the same mixture in this method. The following process steps are carried out after the start of the regeneration cycle: - Operating the internal combustion engine, ie the first and second cylinder groups 5, 5 'together, with the same rich mixture λ = (λ _z1 = λ _Z2 ), preferably 0.7 <λ <95 and continuously determining λ _z1 with the first Sensor 7, λ _Z2 with the second sensor 7 'and λ _N κ with the third sensor 8, - When a limit value is reached within given tolerances for λ _NK , the regeneration cycle ends. Alternatively, the lambda values can λ ι _z *, λ _Z2 and λ _NK by the control unit 2 'are compared to λ _z1 = λ _z2 = λ _NK, is when the three measuring points have the same values, end of the regeneration cycle, ^ie,' re- Operation of the internal combustion engine with a lean mixture.

In the second method, each sensor 7, 7 ', 8 is a linear sensor, the start of the regeneration cycle is simultaneous for each combustion chamber group 5, 5'. The following method steps are carried out after the start of the regeneration cycle: - Operation of the first and second cylinder groups 5, 5 'with a rich mixture λ _Z ι = λ _F ι and λ _Z2 = λ _F1 , with λ _F1 = λ _F2 after the start of the regeneration _cycle preferably 0.5 <λ <0.95, and continuously measuring λ _z1 with the first sensor 7, λ _Z2 with the second sensor 7 'and λ _NK with the third sensor 8, and determining an estimated regeneration time t by the control device 2 'by calculation or removal from a map;

- Before the end of an estimated regeneration period t, the first cylinder group 5 is operated with an air ratio λ _z1 = (λ _Fi + _x ) <1 and the second cylinder group 5 'with an air ratio λ _Z2 = (λ _F2 - _x ) <λ _Z ι and

- Continuously checked by the control unit 2 'whether a first condition, λ _NK = ((λ _F1 + _x ) ^* mi + λ _reg ^* m ₂ )) / (m-, + m ₂ ), or a second condition, λNK = ((λ _F2 - _x ) ^* m ₂ + λ _z1 ^* m * ι)) / (m * ι + m ₂ ) is fulfilled;

- If the first condition is met, the first combustion chamber group 5 is operated with a stoichiometric mixture λ _z -ι = 1 and the mixture of the second combustion chamber group 5 'λ _F2 for the next regeneration cycle by the control. device 2 'on λ _F2πe u <λ _F2 ;

- If the second condition is met, the second combustion chamber group 5 'is operated with a stoichiometric mixture λ ∑ = 1 and the mixture of the first Combustion chamber group 5 λ _F1 for the next regeneration _cycle by control unit 2 'to λ _F1n eu <λ _F1 ; subsequently

- Continuous checking by the control unit 2 'whether (λ _Z ι + λ _Ω ) / 2 = λ _N κ;

- If the condition λ _N «= (λ _z1 + λ _Z2 ) / 2 is fulfilled, the regeneration cycle is ended.

In the third method, each sensor (7, 7 ', 8) is a step response sensor, the start of the regeneration cycle is offset in time for the combustion chamber groups 5, 5. The following process steps are carried out after the start of the regeneration cycle:

- Operating the first cylinder group 5 with a rich mixture (λ _z1 = λ _F1 ) <1, preferably 0.7 <λ <0.95, and the second cylinder group 5 'with a stoichiometric or lean air ratio λ _Z2 > 1 and starting one Time measurement for determining an elapsed first regeneration period t- and determining a total regeneration period t by the control unit 2 ';

- Before the determined total regeneration period t, operating the second cylinder group 5 'with a rich mixture (λ ^ = λ _F2 ) <1, preferably 0.7 <λ <0.95;

- then continuous measurement of λ _N) until NK exceeds a threshold value, then stop the time measurement of the first regeneration period t **

- Operating the first cylinder group 5 with a stoichiometric mixture λ _z1 = 1 and further operating the second cylinder group 5 'with the rich mixture λ ₂₂ = λ _F2 and starting a second time measurement for a second regeneration period t ₂ , and - Continuous measurement of λ _NK until a threshold is exceeded;

- If the threshold value is exceeded, the regeneration cycle is ended and the duration of the second regeneration period t _{2 is} recorded.

For the next regeneration cycle, the rich mixture for λ _F1 and λ _F2 can be adjusted as a function of the measured first and second regeneration times t, and t ₂ . The following applies: if t ₂ > t-, change from λ _F2 by control unit 2 'to λ _F2neu <λ _F2 and if t ₂ <t- *, change from λ _F1 by control unit 2' to λ _F1neu <λ _F ι, for the next regeneration cycle. In the fourth method, each sensor 7, 7 ', 8 is a linear sensor, the start of the regeneration cycle is offset in time for the combustion chamber groups 5, 5. It is characterized by the following process steps after the start of regeneration:

- Operating the first cylinder group 5 with a first rich mixture λ ₂₁ <1, preferably 0.7 <λ <0.95 and the second cylinder group 5 'with a second mixture λ _Z2 >1;

- Continuous measurement of λ _N κ until λ _NK = (λ * ^ ^* m ₂ + λ _z1 ^* m * ι) / (m ** + m ₂ ), then

- Operation of the first cylinder group 5 'with a lean mixture λ _z1 > 1, and the second cylinder group 5' with a rich mixture λ _Z2 <1, preferably 0.7 <λ <0.95, and

- Continuous measurement from λ _NK> to λ _N κ = (λzi ^* m * - + λ _Ω ^* m ₂ ) / (m ** + m ₂ );

- If λ _NK = (λ _z1 ^* m ₁ + λz- * ^* m ₂ ) / (m-, + m ₂ ), end the regeneration cycle.

For all processes it applies that the total regeneration time t lasts at least 0.2 seconds. The total regeneration duration t is determined by the control unit, either by calculation from the raw NO _x emission of the internal combustion engine or by reading from a map stored in control unit 2 '. The first and second regeneration times t **, t ₂ are between 0.5 times and 0.99 times the total regeneration time t.

LIST OF REFERENCE NUMERALS

1 emission control system

2 internal combustion engine

2 'control unit

3 First exhaust pipe 'Second exhaust pipe

First catalytic cleaning device 'Second catalytic cleaning device

First combustion chamber group 'Second combustion chamber group

Common exhaust pipe

First sensor 'Second sensor

Third sensor

Third catalytic cleaning device 0 suction system 0 'first suction pipe group 0 "second suction pipe group

Claims

claims

1. Exhaust gas cleaning system (1) for an internal combustion engine (2) with a NO _x adsorbing device with a first exhaust line (3) with a first catalytic cleaning device (4) and a second exhaust line (3 ') with a second catalytic cleaning device (4') , which flow downstream of the first and the second catalytic cleaning device (4, 4 ') into a common exhaust pipe (6), each catalytic cleaning device (4, 4') in the respective exhaust pipe (3, 3 ') upstream is assigned to the first sensor (7, 7 '), characterized in that the catalytic cleaning devices (4, 4') are NO _x adsorbers and in the common exhaust line (6) a common third sensor (8) at least for regeneration of the catalytic Cleaning devices (4, 4 ') is provided.

2. Emission control system according to claim 1, characterized in that each of the three sensors (7, 7 ', 8) has a NO _x -

Sensor and / or an O ₂ sensor.

3. exhaust gas cleaning system according to claim 1 or 2, characterized in that each of the three sensors (7, 7 ', 8) is a linear sensor and / or a step response sensor.

4. Exhaust gas cleaning system according to one of the aforementioned claims, wherein each sensor emits an electrical signal, characterized in that the signals can be evaluated by a control device (2 ').

5. Exhaust gas cleaning system according to one of the aforementioned claims, characterized in that downstream of the first and the second sensor

(7, 7 ') and / or at least one further catalytic cleaning device (9) is arranged downstream of the third sensor (8).

6. A method for the regeneration of the first and the second catalytic cleaning device (4, 4 ') of an exhaust gas cleaning system (1) according to at least one of the claims 1 to 5, characterized by the following method steps after the start of a regeneration cycle:

- Operating the internal combustion engine (2) with an excess of fuel, - Continuous measurement of a proportion of an exhaust gas component in the common exhaust pipe (6),

- End of the regeneration cycle when the proportion of the exhaust gas component approaches a limit.

7. The method according to claim 6, characterized by the following process steps:

- Continuous measurement of a proportion of the exhaust gas component in the first, the second and the common exhaust gas line (3, 3 ', 6),

- End the regeneration cycle if the same proportion of the exhaust gas component is measured within a tolerance limit in the first, the second and the common exhaust gas line (3, 3 ', 6).

8. A method for the regeneration of the first and the second catalytic cleaning device (4, 4 ') of an exhaust gas cleaning system (1) after at least one According to claims 1 to 5, the internal combustion engine has at least two combustion chamber groups (5, 5 ') and each exhaust pipe (3, 3') is connected to a combustion chamber group (5, 5 ') in a gas-carrying manner and a separate mixture control for each combustion chamber group (5 , 5 '), characterized by the following method steps after a start of a

Regeneration cycle:

Operating the internal combustion engine (2) with a first excess fuel,

- Continuous measurement of a proportion of an exhaust gas component in the first, the second and the common exhaust gas line (3, 3 ', 6),

Operating the first combustion chamber group (5) with a second excess fuel and operating the second combustion chamber group (5 ') with a third excess fuel before an estimated regeneration period t has expired,

- Determining a loading condition for each catalytic cleaning device (4, 4 ') and adjusting the excess fuel for each combustion chamber group (5, 5'),

- End the regeneration cycle when the proportion of the exhaust gas component in the common exhaust pipe (6) approaches a limit value.

9. The method according to claim 8, characterized by the following process step:

- End the regeneration cycle if the same proportion of the exhaust gas component is measured within a tolerance limit in the common exhaust gas line (6) as on the average of the first and second exhaust gas lines (3, 3 ').

10. A method for the regeneration of the first and the second catalytic cleaning device (4, 4 ') of an exhaust gas cleaning system (1) according to at least one of the claims 1 to 5, wherein the internal combustion engine has at least two combustion chamber groups (5, 5') and each exhaust line (3 , 3 ') is connected to a combustion chamber group (5, 5') in a gas-carrying manner and a separate mixture control is carried out for each combustion chamber group (5, 5 '), characterized by the following method steps after the start of a regeneration cycle: - Operating the first combustion chamber group (5) with an excess fuel and operating the second combustion chamber group with a stoichiometric mixture and starting a measurement for a first regeneration time t * ,,

Operating the second combustion chamber group (5 ') with an excess of fuel and starting a measurement for a second regeneration time t ₂ before the end of an estimated regeneration period t,

- Operate the first combustion chamber group. (5) with a stoichiometric mixture and determining the first regeneration time t ** when the proportion of the exhaust gas component in the common exhaust gas line (6) approaches a limit value,

- Determining the second regeneration time t ₂ , and ending the regeneration cycle when the proportion of the exhaust gas component in the common exhaust pipe (6) approaches a limit value.

11. The method according to claim 10, characterized by the following process steps:

- Changing the mixture for the second combustion chamber group (5 ') for the next regeneration cycle to more fuel excess, if the second regeneration time t _{2 is} greater than the first regeneration time t *, - Changing the mixture for the first combustion chamber group (5) for the next regeneration cycle to more fuel excess if the second regeneration time t _{2 is} less than the first regeneration time t-.

12. A method for the regeneration of the first and the second catalytic cleaning device (4, 4 ') of an exhaust gas cleaning system (1) according to at least one of claims 1 to 5, wherein the internal combustion engine has at least two combustion chamber groups (5, 5') and each exhaust pipe (3, 3 ') is connected to a combustion chamber group (5, 5') in a gas-carrying manner and a separate one

Mixture control for each combustion chamber group (5, 5 ') takes place, characterized by the following process steps after the start of a regeneration cycle: Operating the first combustion chamber group (5) with an excess fuel and the second combustion chamber group (5 ') with a stoichiometric air / fuel mixture or with an excess air,

- Operating the first combustion chamber (5) with a stoichiometric air / fuel mixture or an excess of air and the second combustion chamber (5 ') with an excess of fuel if the proportion of the exhaust gas component in the common exhaust line (6) is an averaged proportion of the exhaust gas. gas components from the first and second exhaust pipes (3, 3 ') are reached within a tolerance range,

- End of the regeneration cycle when the proportion of the exhaust gas component in the common exhaust gas line (6) reaches the average proportion of the exhaust gas components from the first and the second exhaust gas line (3, 3 ') within a tolerance range.

13. The method according to any one of claims 8 to 11, characterized in that the estimated regeneration time t lasts at least 0.2 seconds.

14. The method according to any one of claims 10 or 11, characterized in that the first regeneration time t ** and the second regeneration time t ₂ between 0.5 times and 0.99 times the total regeneration duration.

15. The method according to any one of claims 8 to 11, characterized in that the estimated regeneration time t is determined by the control unit (2 ').

16. The method according to claim 15, characterized in that the estimated regeneration time t is calculated by the control unit (2 ').

17. The method according to claim 15, characterized in that the estimated regeneration period t is taken by the control unit (2 ') from a characteristic diagram.