Control strategy for NOx-accumulator

The invention relates to a method for operating a NOx accumulator for an internal combustion engine according to the main patent DE 196 53 756th

DE 196 53 756 relates to a control device for operating a NOx accumulator for an Internal combustion engine, wherein the control device controls the metering of the regeneration agent on the determined based on individual working cycles of the internal combustion engine.

In contrast, it is an object of the invention to provide a method for operating a NOx accumulator for to improve an internal combustion engine with regard to the metering of the regeneration agent.

For this purpose, it is provided for determining the number of necessary for regeneration Working cycles, corresponding to a metering of fuel as a regenerating agent, further, a Delay time between the metering of the regeneration agent and its effect in NOx storage to consider influencing parameters. Thus, it is considered that the to Regeneration fuel supplied first not is available for regeneration, but rather build a fuel wall film in an intake passage for the internal combustion engine and degradation of the O₂-Vorrates, The catalysts in the upstream of the NOx trap as well as optionally NOx storage itself is bound, is required. It is therefore proposed that these parameters (Fuel wall film, amount of bound O₂) When determining the number of the regeneration necessary working games considered. Alternatively, it is possible to use in the inventive control device the fuel by means of a direct fuel injection in the supplying combustion chamber, and thus not even build a fuel wall film. Alternatively or in addition thereto, it is proposed in the use of the control device according to the invention Control device to use a catalyst located upstream of the NOx trap, whereby the Catalyst in terms of storable in the catalyst O₂Quantity is minimized; the best Case is not O₂Storage capacity available.

The invention is suitable both for diesel internal combustion engines as well as spark ignition internal combustion engines applicable.

The invention is described with reference to the embodiment shown in the single figure explained in more detail.

An internal combustion engine 1 having four cylinders 2 to 5 has an intake system 6 with a Air mass sensor 7 and a throttle sensor 8 on. are before the individual cylinders 2 to 5 Injectors 9 to 12 arranged for fuel metering. To the internal combustion engine 1 is further a crankshaft sensor 13 is provided.

Exhaust side, the internal combustion engine 1, an exhaust system 14, in the first of the cylinder 2 a separate exhaust passage 15 is provided. The separate exhaust passage 15 opens with the other part of the exhaust system 14 in a NOx trap 16. In the inlet area of ​​the NOx trap 16 is a probe 17 which determines the oxygen excess in the exhaust gas. the NOx trap 16 is finally a catalyst downstream of 18th

A control unit 19 receives the signals from the air mass sensor 6, the Drosseklappengebers 7, the Crankshaft sensor 13 and the probe 17. The control unit 19 controls via the Einspitzdüsen 9-12 individual cylinder fuel metering to the engine. 1

In operation, ie at operating temperature engine 1 and normal operation outside the Maximum conditions such as idling or full load, the fuel metering is effected via the control unit 19 in such a manner that the internal combustion engine 1 is operated with excess air. In this first Mode decreases the NOx storage 16 from the exhaust gas NOx.

The control unit 19 detects for controlling the loading of the NOx storage catalyst 16, the number of Work games, here the number of combustion cycles of the internal combustion engine 1. In a revolution the crank shaft not shown of the engine 1 are two combustion cycles finished, so counted two working cycles. Each eighth operating cycle, wherein is counted over all the cylinders 2 to 5, the control device 19 increases to the first cylinder 2 supplied fuel quantity, so that with here at the next operating cycle of the first cylinder 2 Excess fuel works and unburned fuel is passed into the separate exhaust gas routing 15th This exhaust gas volume flows through the separate exhaust passage 15 unmixed for NOx trap 16, the now the stored NOx gives a result of the change in concentration of exhaust gas components. The such released NOx reaches below together with the unburned fuel in the Catalyst 18 and is reduced here.

The control unit 19 detects a signal of an engine temperature sensor 20, which at the Internal combustion engine 1 is arranged. Using this temperature signal, and other Operating parameters of the internal combustion engine 1, the control device 19 in a known manner, the Forming a fuel film on a wall of the intake system 6 in the region downstream of the Injectors 9 determine to 12th In the present case this is primarily a first Cylinder 2 leading intake pipe 21 of concern, the first on the injector 9 of the above Excess fuel described is introduced. This fuel is additionally introduced However, partly used to build the above-described fuel wall film. That's why controls the control unit 19, the fuel injector 9 in the manner that the regeneration of the NOx trap 16 required amount of fuel even when considering the structure of the Fuel wall film used share always reaches a sufficient size in the flue 15th In place of a change in the zugefühten amount of fuel can also alternatively or additionally a change in the number of working cycles until the next increase of the supplied Amount of fuel occur. So corresponds to a reduction in the number of working cycles increase the supplied amount of fuel.

The exhaust system 14 comprises upstream of the NOx trap 16 to a start catalyst 22; for the separate exhaust passage 15 is provided a separate precatalyzer 23rd In particular, the second Pre-catalyst 23 is so designed that its O₂Storage capacity is as low as possible, since otherwise the second pre-catalyst 23 stored O₂ to an additional reduction of the would separate exhaust passage 15 directed unburned fuel. Also one O₂Storage capacity of the NOx trap 16 is to minimize, if the coating of the NOx trap 16 in addition to the adsorbing properties, catalytic properties having. Since the unburned fuel exclusively through the separate exhaust passage 15 for NOx trap 16 passes, is the O₂Storage capacity of the first pre-catalyst 22 in the present Example irrelevant.

As far as the O₂Storage capacity of the second pre-catalyst 23 on the scale required can be suppressed, it may be alternatively or additionally provided for this purpose that the Control unit 19 in metering the amount of additional fuel through the first fuel injector 9 or the number of working cycles takes into account the amount of fuel that is needed to the in Precatalyzer 23 stored O₂ reduce, so a sufficient amount of unburned to allow to enter the fuel NOx storage 16th