DE10038458A1 - Device for purifying IC engine exhaust gas comprises control device arranged in branch of exhaust gas pipe to distribute exhaust gas stream onto nitrogen oxides storage catalysts - Google Patents

Abstract

A device for purifying IC engine exhaust gas comprises a control device arranged in a branch of the exhaust gas pipe to distribute the exhaust gas stream onto NOx storage catalysts. An Independent claim is also included for a process for purifying IC engine exhaust gas. Preferred Features: The control device is a flap. Sensors are connected to storage catalysts and the control device is controlled by information obtained from the sensors. The sensors are lambda sensors or NOx sensors. An oxidation catalyst, preferably a 3-way catalyst, is arranged between the engine and the branch.

Description

The invention relates to a device and a method for exhaust gas purification according to the General terms of the independent claims.

From EP 580 389 A1 and EP 0585 900 A1, so-called NO _x storage catalysts for use in the exhaust gas flow of lean-burn internal combustion engines are known. The lean operation of internal combustion engines has the advantage that fuel consumption can be significantly reduced, but the disadvantage is that a relatively large amount of nitrogen oxides (NO _x ) is present in the raw exhaust gas during lean operation. In order to solve this problem, it is known to arrange a NO _x storage catalytic converter in the exhaust gas flow of the internal combustion engine, on the surface of which the nitrogen oxides are deposited and chemically bound, for example according to the following reaction:

2BaO + O ₂ + 4NO ₂ → 2Ba (NO ₃ ) ₂

This significantly reduces the amount of nitrogen oxides in the exhaust gas flow from the catalyst. Such a storage catalytic converter must be regenerated at certain intervals since its storage capacity is exhausted. This happens because the internal combustion engine is operated rich for a certain period of time, so that unburned hydrocarbons and carbon monoxide are located in the exhaust gas stream downstream of the NO _x catalyst. The storage catalytic converter is regenerated by means of these reducing agents, the nitrogen oxides or the corresponding nitrates being reduced to nitrogen by the reducing agents present, for example with the following reaction:

Ba (NO ₃ ) ₂ + 5CO → BaO + N ₂ + 5CO ₂

Ideally, these reducing agents are fully implemented, so that in the Final exhaust gas neither nitrogen oxides nor unburned during the regeneration phase Hydrocarbons or carbon monoxide.  

NOx storage catalytic converters are mainly used in direct injection systems, the significant fuel savings possible in the so-called stratified charge mode do. This ensures safe combustion of extremely lean mixtures at idle and part load range with fuel savings of <40% at idle and approx. 15% possible over the entire Eurotest cycle MVEG. The fuel is over electromagnetic nozzle valves injected directly into the combustion chamber. The Engine operated with the throttle valve almost completely open, which additionally Loss of gas exchange can be avoided. Only after a certain requested The engine must return to conventional operation, in which the Throttle valve position determines the amount of air / fuel mixture drawn in, operate. During stratified charging, the NOx storage catalytic converter operated in absorption mode. In contrast, in homogeneous operation of the engine stoichiometric or a rich one for the regeneration of the NOx storage catalytic converter Air / fuel mixture supplied.

A 3-way catalytic converter is usually connected upstream of the NO _x storage catalytic converter, so that the entire exhaust gas purification system consists of two catalytic converters connected in series.

For packaging reasons, the use of a single NOx storage catalytic converter is not possible, an exhaust line is split behind the oxidation catalytic converter and the exhaust gas two NOx storage catalytic converters connected in parallel.

Such a solution is used for example in all-wheel drive vehicles which the cardan shaft the arrangement of a single cylindrical NOx catalyst makes impossible. On the other hand, with turbocharged engines with a single Turbocharger the arrangement of two completely self-sufficient exhaust lines from two Pre-catalytic converters and two NOx storage catalytic converters not possible.

If more than one NOx storage catalytic converter is used, its uniformity can be achieved Exposure to NOx cannot be assumed, since function and efficiency are one NOx storage catalytic converters are dependent on a large number of influencing factors. however is a detection of the operating state, for example the NOx loading state or the end of the NOx regeneration of the individual NOx storage catalysts sensor means arranged in the mixed exhaust gas behind the NOx storage catalytic converters,  for example, a downstream NOx sensor or a lambda probe possible.

It is therefore more favorable to arrange sensor means downstream of each NOx Storage catalyst. This is the case when controlling NOx regeneration Problem of setting the end time of the regeneration mode on the condition that the NOx regeneration by the exhaust gas with several NOx Storage catalytic converters happen at the same time. In particular, here be avoided that one or more of the catalysts permanently only be partially regenerated, which increasingly limits their NOx storage capacity would.

On the other hand, there is a risk that one relative to the other NOx Storage catalysts quickly regenerated catalyst Reducing agent breakthrough, resulting in the release of Hydrocarbons into the environment.

The object of the invention is therefore to provide a method and Device for exhaust gas purification in an internal combustion engine with at least two Arranged parallel downstream of a branch of an exhaust line regenerable NOx storage catalytic converters that allow for complete regeneration of all NOx storage catalytic converters enable and at the same time a high degree of Perform exhaust gas cleaning.

This object is achieved with a device with the features of claims 1 and solved by a method with the features of claim 8.

The basic idea of the invention is to provide a control means in the branch which divides the exhaust gas flow, by means of which the distribution of the exhaust gas flow over the two NO _x storage catalytic converters can be influenced. It can thus be achieved that both catalysts at least approximately exhaust their maximum NO _x storage capacity and that both catalysts are completely or at least almost completely eliminated in the regeneration phase. This has the advantage that the length of the lean phases can be maximized and that both catalysts can be emptied in the regeneration phase without reducing agent breakthroughs.

According to claim 3, a sensor is preferably mounted behind the two NO _x storage catalysts. The control means is controlled by means of the signals generated by this sensor. The setting of the control means is thus influenced by the actual states of the catalysts.

According to claim 9, the behavior of the control means of the control Catalysts in one or more previous lean and / or fat phases considered. This creates a feedback control loop with which very good Results regarding the best possible use of the existing catalysts can be achieved and a good adaptation to the current conditions of the Catalysts is achieved.

The invention will now be described using exemplary embodiments with reference to FIG Illustrations explained in more detail. Show it:

Fig. 1 is a schematic diagram of the inventive arrangements,

Fig. 2: a schematic diagram of the junction with a built-in flap.

In Figs. 1 and 2, the device according to the invention is shown schematically. The raw exhaust gases coming from an internal combustion engine 10 are fed to a pre-catalytic converter 20 by means of a first exhaust section 11 . This pre-catalyst 20 is usually a 3-way catalyst. The exhaust gases pre-cleaned by the pre-catalytic converter 20 pass via the second exhaust section 22 to the branch 25 , which divides the exhaust section into the third exhaust section 33 and the fourth exhaust section 34 . Arranged in the branch 25 is a finely or continuously adjustable flap, by means of which the distribution of the exhaust gas flow between the third exhaust gas section 33 and the fourth exhaust gas section 34 can be controlled. The first NO _x storage catalytic converter 41 is arranged in the third exhaust gas section 33 . The first sensor 51 is arranged downstream of it. It can be either a lambda sensor, in particular a step response lambda sensor, or a NO _x sensor. The second NO _x storage catalytic converter 42 is located in the fourth exhaust gas section 34 . The second sensor 51 is located downstream of the second NOX storage catalytic converter. It too is either a lambda sensor, in particular a step response lambda sensor, or a NO _x sensor. The signals from the two sensors 51 , 52 are fed to the control unit 60 . This in turn controls the flap 27 , which is arranged in the branch 25 and serves as control means, and on the other hand forwards signals to the engine control 70 . Control device 60 and engine control 70 can of course also be integrated in a single device.

The type of control of the flap 27 can take place according to various schemes. Three such schemes are presented below. Which of these options is chosen in individual cases depends on the respective technical framework. The three options shown are particularly preferred, but not exhaustive.

First embodiment

Here, the two sensors 51 , 52 are step response lambda sensors. In this exemplary embodiment, the flap 27 is controlled relatively simply: in the lean phases it is observed in which the NO _x storage catalytic converter is the first to experience a NOX breakthrough. In the next lean phase, the flap 27 is then adjusted in such a way that the exhaust gas flow in the NO _x storage catalytic converter which has broken through first is reduced. The flap 27 can be adjusted, for example, by a fixed amount. The adjustment of the plate 27 in the grease is carried out in an analogous manner. During regeneration, it is observed in which of the two NO _x storage catalysts a reductant breakthrough first occurs, that is, behind which NO _x storage catalyst the lambda value drops first. In the subsequent regeneration phase, the flap in 27 is then adjusted so that less exhaust gas flows to the NO _x storage catalytic converter which broke through first.

In this simple exemplary embodiment, the influencing of the flap 27 with respect to the lean and rich phases is completely decoupled. The influencing only occurs with regard to the immediately preceding lean or fat phase.

Second embodiment

Here, too, the two sensors 51 , 52 are step response lambda sensors. In contrast to the first exemplary embodiment described above, however, only the reductant breakthroughs in the regeneration phases are observed. However, the behavior of the last and penultimate regeneration phases is required. In detail, the flap 27 is controlled according to the following matrix:

Here, “flap in direction A” means that the flap 27 is adjusted so that less exhaust gas flows to the first NO _x storage catalytic converter 41 . Accordingly, “flap in direction B” means that the flap is adjusted such that more exhaust gas flows to the first NOx storage catalytic converter 41 .

This type of control takes into account the storage capacity of the catalysts. Possible damage to the catalyst is also taken into account which, in a known manner, allows reducing agent breakthroughs to occur prior to complete NO _x regeneration.

Third embodiment

In this exemplary embodiment, the sensors 51 , 52 are NO _x sensors. The NO _x breakthrough behavior in lean operation and the reducing agent breakthrough behavior in rich operation during the last cycle are considered. The flap 27 is then controlled according to the following matrix:

The definition of the direction of the valve movements corresponds to that given above Definition.

Other sensor arrangements or control schemes are also conceivable. In particular, it is conceivable that one of the two sensors is a NO _x sensor and the other sensor is a lambda sensor.

In all exemplary embodiments, the signals in the sensors 51 , 52 are also passed on indirectly or directly to the engine control 70 . In particular, the information about the reductant breakthroughs at the end of the regeneration phases is required for the engine control. As with previous systems, the engine returns to lean operation as soon as a reducing agent breakthrough on one of the two NO _x storage catalytic converters has been determined, since otherwise there would be unnecessary environmental pollution with carbon monoxide and incompletely burned hydrocarbons.

It is conceivable in all exemplary embodiments that the deflection of the flap 27 is limited to maximum values, provided that a complete shutoff of an exhaust gas duct with a severely damaged NOx catalytic converter is undesirable. Furthermore, status information can be sent to the diagnostic devices if the flap 27 has a constantly strong deflection in one direction or very different positions in the lean or rich mode. These operating conditions indicate a severely damaged catalytic converter.

The proposed devices and the proposed method are furthermore suitable for compensating for the constructional and / or production-related uneven loading of the two NO _x storage catalytic converters as well as differences in performance of the catalysts within the series distribution.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

11

first exhaust section

20

precatalyzer

22

second exhaust section

25

diversion

27

flap

33

third exhaust route

34

fourth exhaust system

41

first NO _x

storage catalyst

42

second NO _x

storage catalyst

51

first sensor

52

second sensor

60

control unit

70

motor control

Claims (11)

1. Device for exhaust gas purification for an internal combustion engine ( 10 ) with at least two NO _x storage catalysts ( 41 , 42 ) arranged in parallel, the exhaust gas stream coming from the internal combustion engine ( 10 ) via a branch ( 25 ) arranged in the exhaust line to the NO _x storage catalysts ( 41 , 42 ), characterized in that a control means is arranged in the branch ( 25 ), by means of which the distribution of the exhaust gas flow to the NO _x storage catalytic converters ( 41 , 42 ) can be controlled. 2. Device according to claim 1, characterized in that the control means is a flap ( 27 ). 3. Device according to claim 1 or 2, characterized in that at least one sensor ( 51 , 52 ) is connected downstream of the NO _x storage catalytic converters ( 41 , 42 ), and that the control means is obtained by means of the information obtained from these sensors ( 51 , 52 ) is controlled. 4. The device according to claim 3, characterized in that the sensors ( 51 , 52 ) are lambda sensors. 5. The device according to claim 3, characterized in that the sensors ( 51 , 52 ) are NO _x sensors. 6. Device according to one of the preceding claims, characterized in that an oxidation catalyst ( 20 ) is arranged between the internal combustion engine ( 10 ) and the branch ( 25 ). 7. The device according to claim 6, characterized in that the oxidation catalyst ( 20 ) is a 3-way catalyst. 8. Method for exhaust gas purification in an internal combustion engine ( 10 ) with at least two NO _x storage catalysts ( 41 , 42 ) arranged in parallel in the exhaust gas flow of an alternately lean and rich operated internal combustion engine ( 10 ), the two NO _x storage catalysts ( 41 , 42 ) are arranged in the exhaust gas stream behind a branch ( 25 ) having control means and a sensor ( 51 , 52 ) is arranged behind each of the two NO _x storage catalytic converters ( 41 , 42 ), characterized in that the control of the control means taking into account that of the Signals ( 51 , 52 ) generated signals. 9. The method according to claim 8, characterized in that the control of the control means depends on the NO _x storage catalytic converter in which one or more of the preceding lean phases a NO _x breakthrough first occurred and / or the NO _x storage catalytic converter a reductant breakthrough first occurred in one or more of the previous fat phases. 10. The method according to claim 9, characterized in that in each case only the last Lean and rich phase is taken into account when controlling the control means. 11. The method according to claim 9, characterized in that in each case the last and penultimate fat phase is taken into account when controlling the control means.