DE102004022814B4 - Method for operating a lean-running internal combustion engine of a vehicle, in particular of a motor vehicle - Google Patents

Abstract

Method for operating a lean-running internal combustion engine of a vehicle, in particular of a motor vehicle,
with a lean operating range in which nitrogen oxides produced by the internal combustion engine are stored in a nitrogen oxide storage which is part of a catalytic converter connected downstream of the internal combustion engine in the exhaust gas line and in which oxygen contained in the exhaust gas flow is stored in an oxygen storage of the catalytic converter, and
with a regeneration operating region in which the nitrogen oxides stored in the nitrogen oxide storage and the oxygen stored in the oxygen storage are expelled by adding a regeneration agent,
wherein the switching from the lean operating region into the regeneration operating region is predetermined for a predefinable regeneration operating time by means of a control device when an exhaust gas flow leaving the catalyst device and thus the nitrogen oxide storage exceeds a predetermined nitrogen oxide emission limit, and wherein the end of the regeneration operating time by the nitrogen oxides for and the oxygen required for the regeneration of the nitrogen oxide storage and the oxygen storage time is given,
characterized,
that by the control device during the regeneration operating time ...

Description

The The invention relates to a method for operating a lean-running internal combustion engine Vehicle, in particular a motor vehicle according to the preamble of claim 1.

It It is generally known that in lean-running internal combustion engines due the exhaust gas composition during the lean operating areas in which the internal combustion engine with an excess of air is operated in the exhaust system in conjunction with a catalyst device a nitric oxide storage needed is going to be the more prevalent there Store or buffer nitrogen oxides. simultaneously be during such Lean operating phases of an internal combustion engine, the existing oxygen storage a catalyst device loaded with oxygen. As soon as the Nitrogen oxide storage of the catalyst device is loaded so far, that a catalyst device and thus the nitrogen oxide storage leaving exhaust gas flow exceeds a predetermined nitrogen oxide emission limit, can be concluded that no further storage of nitric oxide in the nitrogen oxide storage is more possible or the nitrogen oxide storage already a high degree of filling has, so then by means of a control device, preferably a motor control device from the lean operating region into a so-called regeneration operating area is switched, in the for one predetermined regeneration operating time a regeneration of the stick oxide storage and the oxygen storage by adding fuel as a regenerant he follows. That is, by this addition of a regenerant the stored in the nitrogen oxide storage nitrogen oxides and the Oxygen stored in the oxygen storage are re-stored. Once the nitric oxide storage and the oxygen storage accordingly a predetermined degree of implementation are discharged, if possible Completely In turn, it will be discharged from the regeneration operating phase to another phase of operation, such. B. the lean operating phase switched.

One Problem in connection with such operation of an internal combustion engine is, however, that although here, z. B. by the use of a nitrogen oxide storage Downstream nitrogen oxide sensor ensures that it is too no overrun the predetermined nitrogen oxide emission limit values can come, wherein however, it is not possible at a previous detected To reach the nitrogen oxide emission limit to distinguish whether this early Reaching a deterioration of the nitrogen oxide storage, d. H. of the nitrogen oxide catalyst or an increase in the level of raw nitrogen oxide emissions, d. H. the nitrogen oxide raw mass flow of the internal combustion engine is based, d. h. that in both cases an early one Reaching the specified nitrogen oxide emission limit as premature nitrogen oxide slip is recognized, but no distinction between these two make is possible, as desirable would.

A method for controlling a NOx storage catalyst is already out of DE 102 21 568 A1 known. With this method, in addition to the lowest possible emission of reducing agent, too high a saturation and thus a poor regenerability of the NOx storage catalyst should be avoided. Concretely, at the beginning of the regeneration, the current catalyst behavior with regard to oxygen depletion of the oxygen-containing components in the catalyst coating is evaluated on the basis of the catalyst temperature. In order to avoid saturation of the NOx storage catalytic converter, it is further proposed to initiate regeneration earlier than would actually be required, depending on a predetermined NOx threshold value.

task The invention is therefore a method for operating a lean-running internal combustion engine a vehicle, in particular a motor vehicle available with which when a nitrogen oxide emission limit is reached ahead of time as nitrogen oxide slip a distinction between a deterioration of the Nitric oxide storage and an increase the nitrogen oxide raw emissions possible is.

These Task is solved with the features of claim 1. According to claim 1 is by the control device the while the regeneration operating time required nitrogen oxide regenerant amount for the Regeneration of the nitrogen oxide storage determined, taking into account while each regeneration operating phase constant oxygen storage regenerant amount, the for the regeneration of the fully loaded at the end of the lean operating phase Oxygen storage required being, while the the previous lean operating phase in the exhaust gas mass flow existing Nitrogen oxide as nitrogen oxide raw mass flow in dependence from the needed Nitrogen oxide regeneration agent quantity is determined.

Due to this proportionality between the nitrogen oxide regeneration agent quantity and the nitrogen oxide raw mass flow, ie the raw nitrogen oxide emissions, a statement about the actual nitrogen oxide raw mass flow during the preceding lean operation phase is advantageously possible in a simple manner, so that a differentiated statement can be made as to whether premature nitrogen oxide slip on deterioration of the nitrogen oxide storage, ie aging of the sticko xid storage catalyst or on a z. B. motor-related increase in nitrogen oxide raw emissions is based.

In order to becomes a possibility in a simple way the detection of the nitrogen oxide raw emission changes possible.

According to claim 2, it is provided that the nitrogen oxide regeneration agent with is compared to a comparison regenerant amount, which in dependence from a certain amount of nitrogen oxide present in the exhaust gas mass flow is specified as nitrogen oxide Rohmassenstrom, with a deviation the actual required Nitrogen oxide regenerant amount from the comparison regenerant amount a measure of the actual Nitrogen oxide raw mass flow during the previous lean operating phase represents. Preference is given here according to claim 3, provided that the comparative regeneration agent quantity is based on a new engine, so that each Engine-related deterioration of raw nitrogen oxide emissions can be detected in a simple way. Possibly. can in the course of operation the internal combustion engine also an adaptation of the comparison regenerant quantity done, z. B. by acquisition the last detected nitrogen oxide regenerant amount as a comparison Regenerationsmittelmenge.

alternative and possibly also in addition is provided according to claim 4, that the dependence between the nitrogen oxide Rohmassenstrom and the nitrogen oxide regenerant requirement is stored in a map of the engine control device.

According to one another preferred method it is envisaged that fuel is added as a regeneration agent becomes.

The The invention will be explained in more detail with reference to a drawing.

It demonstrate:

1 the schematic structure of an internal combustion engine downstream exhaust system according to the prior art, and

2 schematically the need for regeneration over time.

In 1 schematically is the structure of one of the internal combustion engine 1 Downstream exhaust system 2 shown a 3-way catalytic converter close to the engine 3 and a downstream of this nitrogen oxide storage catalyst 4 having as nitrogen oxide absorber or memory. In the area of the 3-way catalyst 3 is upstream and downstream of an oxygen sensor 5 . 6 provided during the nitrogen oxide storage catalyst 4 a temperature sensor 7 upstream and a nitrogen oxide sensor 8th is downstream. The 3-way catalyst 3 and the nitrogen oxide storage catalyst 4 together form a catalyst device 9 which may also comprise more than one of the two catalysts mentioned, as is well known.

In the 2 is now schematically the need for regeneration means during a regeneration operating range of the internal combustion engine for the regeneration of the oxygen storage and the nitrogen oxide storage of the catalyst device 9 applied as a function of the lean time. This diagram shows that due to the fast and early complete loading of the oxygen storage device during the lean operating region in the subsequent regeneration operating region, approximately the same amount of regeneration agent is always needed to regenerate the oxygen storage device. This is in the 2 through the bend 10 shown. Like this the diagram of 2 based on the curves 11a . 11b and 11c can be seen, however, changes with the nitrogen oxide Rohmassenstrom the need for regeneration of the regeneration of the nitrogen oxide storage, so that, as the cumulative curves 12a to 12c show at high nitrogen oxide raw emissions according to curve 12a higher quantities of regenerants are required than with lower levels of raw nitrogen oxide emissions according to the curves 12b and 12c the case is. The curve 12b can do it as well as the curve 11b serve as a comparison regenerant quantity curve, which is compared with a nitrogen oxide regeneration agent quantity actually required during operation of the internal combustion engine, with a deviation upward in the direction of the curve 11a respectively. 12a A measure of a higher nitrogen oxide raw mass flow is a deviation in the direction of curves 11c respectively. 12c is a measure of a lower nitrogen oxide raw mass flow.

Claims (5)

Method for operating a lean-running internal combustion engine of a vehicle, in particular a motor vehicle, with a lean operating range, in which nitrogen oxides produced by the internal combustion engine in a nitrogen oxide, which is part of one of the internal combustion engine in the exhaust system catalytic converter is stored, and in the oxygen contained in the exhaust stream in a Oxygen storage of the catalyst device is stored, and with a regeneration operating range in which are stored by adding a regeneration agent stored in the nitrogen oxide storage nitrogen oxides and stored in the oxygen storage oxygen, wherein the switching from the lean operating region into the regeneration operating region is predetermined for a predefinable regeneration operating time by means of a control device when an exhaust gas flow leaving the catalyst device and thus the nitrogen oxide storage exceeds a predetermined nitrogen oxide emission limit, and wherein the end of the regeneration operating time by the nitrogen oxides for and the time required for the regeneration of the nitrogen oxide storage and the oxygen storage is specified, characterized in that the control device, the required during the regeneration operating time nitrogen oxide regeneration agent quantity for the regeneration of the nitrogen oxide storage is determined, taking into account during each regeneration operating phase constant oxygen storage regeneration medium amount for the regeneration of the fully loaded at the end of the lean phase oxygen storage be is required, and that the amount of nitrogen oxide present in the exhaust gas mass flow during the previous lean operating phase is determined as nitrogen oxide raw mass flow as a function of the required amount of nitrogen oxide regeneration agent. Method according to claim 1, characterized in that in that the amount of nitrogen oxide regeneration agent is compared with a comparison amount of regenerant is compared, depending on from a certain amount of nitrogen oxide present in the exhaust gas mass flow is specified as nitrogen oxide Rohmassenstrom, with a deviation the actual required Nitrogen oxide regenerant amount from the comparison regenerant amount a measure of the actual Nitrogen oxide raw mass flow during represents the previous lean operating phase. Method according to claim 2, characterized in that that the comparison amount of regenerant to a new Internal combustion engine and optionally adapted during operation of the internal combustion engine is. Method according to claim 1, characterized in that that dependence between the nitrogen oxide raw mass flow and the nitrogen oxide regeneration agent requirement is stored in a map of the engine control device. Method according to one of claims 1 to 4, characterized that fuel is added as regeneration agent.