Method and apparatus for operating a lean-burn internal combustion engine

The invention relates to a method and apparatus for Operation of operating with excess air engine according to the preambles of the independent claims.

The reduction of nitrogen oxide emission of air excess operated internal combustion engine, especially a diesel engine can with an ammonia-containing reducing agent at a selectively operating catalyst (SCR catalyst) to N₂ and H₂O done (SCR Selective Catalytic Reduction). The reducing agents used either gaseous Ammonia (NH₃), Ammonia in aqueous solution or urea used in aqueous solution. When using urea as a reducing agent, the urea before a hydrolysis injected into the exhaust system, there by means of Hydrolysis to ammonia converted, which then in turn in the actual SCR catalytic converter reduces nitrogen oxides. At a such a method results in faster load increase the internal combustion engine a particularly large NO_x-Emission.

Main reason for this is that with increasing load the NO_x-Rohemission the internal combustion engine increases by leaps and bounds. simultaneously is the Adsorbtionsvermögen of the SCR catalyst with the case rising temperature of the exhaust catalyst and lower.

An additional problem arises in the warm-up when the Catalyst has not yet reached its operating temperature. In that case, no conversion of the nitrogen oxides instead of. For a better NO_x-Absenkung In the two aforementioned Operating conditions could the average conversion in the exhaust gas test increased significantly.

In WO 94/04258 is a method for the catalytic conversion of the contained in the exhaust of an internal combustion engine Nitrogen oxides is known in which a conventional Denoxverfahren with Addition of reducing agents with a NO_xcombined adsorber is. It makes the NO_x Adsorbent in lowering of NO_x the main task, charged in the each of the adsorber and the exhaust gas produced by desorption of the adsorber a Denoxkatalysator is supplied. Such a process has the disadvantage that the SCR catalyst on only insufficiently each bout of flue gas with a high NO_x -Concentration is set. In addition, have a previous adsorber unsatisfactory service time. This applies in particular in connection with fuels containing sulfur.

Other methods with the simultaneous use of NO_x adsorbers and Denoxsystemen are in German Offenlegungsschriften DE 196 26 835, DE 196 26 836, DE 196 26 837 and European Patent Application EP 0702134.

The exhaust system described in DE 196 26 835 has two by a flap alternatively releasable exhaust lines, where in one a NO_xStoring catalyst and in the other an oxidation catalyst are provided. the NO_x storage catalyst is a fuel injection, upstream, controlled over a downstream of the NO_x storage catalyst arranged lambda probe takes place. After merging the two exhaust lines is an oxidation catalyst provided. In overrun and idling operation of the diesel engine the valve closes the exhaust line with the NO_xStorage catalyst from the exhaust gas stream so that only a minimum flow through the NO_xStoring catalyst takes place. Simultaneously, by fuel injection, in the Minimum flow, a lambda <1 generated so that a regeneration of NO_xStoring catalyst takes place.

The invention has for its object, the NO_x-Emission in transient operation, particularly for the increase and to reduce the warm-up of the internal combustion engine more than it is possible with the conventional SCR systems. In addition to the adjusted life of the overall system of the vehicle life be, that is the loading of the adsorber with Exhaust gas to be limited to a minimum time period.

This object is according to the features of the independent claims dissolved.

By involving a bypass to the exhaust line by means an electrically controllable exhaust flap, the exhaust gas stream in certain operating states of the internal combustion engine, especially during fast load increase or the Warm-up partially or completely over a generally then relatively cool adsorber are passed, wherein the exhaust gas contained in NO_x especially favorably is adsorbed.

The dependent claims relate to advantageous developments and embodiments of the following reference to the single Drawing figure described invention. Here, in the described Embodiment shown only those parts which are necessary for understanding the invention.

In one of the outlet side of a non-illustrated internal combustion engine joined main exhaust pipe 4 is an SCR or a DeNOx catalytic converter 1 with an upstream hydrolysis 2 is arranged. In front of the hydrolysis catalyst 2 a metering valve 3 for a reducing agent, e.g. Urea provided. The hydrolysis thereby has the Task of the metered aqueous solution of urea generating the reducing agent is ammonia. In NO_x-Reduktionsteil, namely, the SCR catalyst, is then combined with the aid of the Ammonia, the nitric oxide in the non-hazardous components Nitrogen, carbon dioxide and water is converted. additionally the SCR catalyst also acts as an oxidation catalyst for Hydrocarbons.

The reducing agent is by means of a pump from a reservoir (Not shown) and conveyed via a reducing-agent line 18 the metering valve 3 supplied.

Temperature sensors 11, 12 detect the temperature of the exhaust gas upstream and downstream of the SCR catalyst.

In the main exhaust line 4 is, via an actuator 9 is provided pivotable exhaust valve 6 so that the passage cross section the main exhaust line 4 can be changed. Upstream of the exhaust flap 6 branches off from the main exhaust line 4, a bypass line 5 from, in the further course a Adsorber 7 with a hydrolysis catalyst vorgeschaltenem 8 is arranged. The bypass pipe 5 to discharges a location upstream of the hydrolysis catalytic again 2 in the main exhaust line. 4

To determine the load state of the adsorber 7 is a downstream of the adsorber 7 arranged NO_xSensor 13. Alternatively, the loading state the adsorber 7 by means of a mathematical model are determined.

Moreover, downstream of the adsorption catalyst 7 a Exhaust gas sensor 15 is arranged whose signal is a regulator 16 which is and by means of which a desired air ratio and so that an adjusted quantity of fuel, for example. Diesel fuel via a fuel line 17, or alternatively, a reducing agent, For example, urea via the aforementioned reducing agent line 18 the system hydrolysis / adsorber 7,8 supplied and thereby the stored NO_x desorbed becomes.

An electronic control device 10 assumes the Control of the exhaust aftertreatment system. For this purpose, In addition to the signals of the sensors mentioned further, for the Operation of the internal combustion engine necessary signals, such as Speed, control path, boost pressure, charge air temperature etc. of the control device 10 is fed. This can advantageously take place via a CAN bus. On the output side the control device 10 described above unspecified Lines to the controller 16, the metering valve 3, the injector 14 and the actuator 9 for the exhaust flap 6 connected. It also controls the pump for the reducing agent at evaluates signals of a level sensor for the reducing agent and controls a heater for the Reducing agent tank to.

With rapid increase in load and / or in the warm-up of the internal combustion engine the actuator 9 is controlled such that the exhaust flap 6 the exhaust gas flow partially or completely passes in the bypass line. 5 Particularly in fast Last raising the exhaust gas through the generally cool Adsorber 7 steered, wherein said contained in the exhaust NO_x is adsorbed in a particularly favorable manner.

The adjustment of the exhaust flap 6 by means of the actuator 9 takes place in dependence on various operating parameters, such as. Accelerator pedal position and its temporal changes, Fuel injection quantity of the internal combustion engine or its temporal change, the exhaust gas temperature before and after the SCR catalyst or temperature of the SCR catalyst itself.

For rapid heating and for maintaining a high Temperature of the SCR catalyst 1, in loading of the Adsorbtionskatalysators 7 the latter and the SCR catalyst in connected series, so the exhaust stream closed due to the Exhaust flap 6 via the bypass line. 5

After the adsorber 7 with NO_x loaded, carried desorption by short supply of fuel or reductant via the injection nozzle 14. On the signal the exhaust gas sensor 15 and the controller 16, a desired Air ratio and thus the adjusted amount to be supplied Fuel or reducing agent is adjusted so that the stored Nox is desorbed. For precise control of the adsorption / Desorptionszustandes the adsorber 7 is this monitored by means of the NOx sensor.

In the desorption process, the exhaust flap is 6 in a accommodated position in which a part of the exhaust gas flow through the Bypass line 5 and thus through the adsorber 7 flows, in order to ensure a sufficiently high temperature.

The invention has been explained using an example in which Urea in aqueous solution prior to hydrolysis is supplied. When using fuel or ammonia as a reducing agent is not a hydrolysis catalyst such necessary, the reducing agent is then directly to the adsorber supplied.