Method for adjusting the air-fuel ratio in the exhaust gas of a direct injection internal combustion engine for NOx storage catalytic converter regeneration

Abstract

Method for adjusting the air-fuel ratio in the exhaust gas of a direct injection internal combustion engine, wherein the combusting fuel injection is divided into a plurality of individual injections, and wherein the air-fuel ratio in the exhaust gas of the internal combustion engine for a given load (PMI) is predictively adjusted by at least one model, by adjusting the position of the centroid of heat release conversion rates and the injection amount of the total combusting fuel injection, to a value that is necessary for the regeneration of an NOx storage catalytic converter in the exhaust system of the internal combustion engine.

Claims

1. A method for adjusting the air-fuel ratio in the exhaust gas of a direct injection internal combustion engine, comprising: dividing, by an electronic control unit, combusting fuel injection into a plurality of individual injections; and predictively adjusting, by the electronic control unit, an air-fuel ratio in the exhaust gas of the internal combustion engine for a given load to a value that is necessary for regeneration of an NOx storage catalytic converter in the exhaust system of the internal combustion engine by adjusting a position of a centroid of heat release conversion rates and an injection amount of a total combusting fuel injection using at least one model.

2. The method according to claim 1, wherein the injection amount of the total combusting fuel injection and the number, the start and the end of the individual injections are adjusted to adjust the position of centroid of heat release conversion rates.

3. The method according to claim 1, wherein the combusting fuel injection is divided into a main injection and a post-injection.

4. The method according to claim 1, the injection amount of the total combusting fuel injection is calculated on the basis of a target value of the air-fuel ratio in the exhaust gas and a determined amount of oxygen in the induction air of the internal combustion engine.

5. The method according to claim 1, the position of the centroid of heat release conversion rates is determined using a model and based on a target value of the indicated average pressure and the injection amount of the total combusting fuel injection.

6. The method according to claim 1, wherein a necessary difference is determined from a predetermined target value of the indicated average pressure and a measured actual value of the indicated average pressure and a correction value for the position of the centroid of heat release conversion rates is determined from this by means of a higher level regulator.

7. The method according to claim 6, wherein a corrected target value for the centroid of heat release conversion rates is determined from the correction value for the centroid of heat release conversion rates and a target value for the centroid of heat release conversion rates.

8. The method according to claim 7, wherein a difference value for the centroid of heat release conversion rates is determined from the corrected target value for centroid of heat release conversion rates and an actual value for the centroid of heat release conversion rates and based on said difference value, positions of the individual injections and/or the distribution of the injection amounts of the total injection amount among the individual injections are regulated by a regulator.

9. The method according to claim 7, wherein the target value for the centroid of heat release conversion rates is determined based on a characteristic field.

10. The method according to claim 8, wherein the actual value for the centroid of heat release conversion rates is determined by a combustion model or from measured pressure profiles of the combustion chamber pressure.

11. The method according to claim 1, wherein an actual value of the air-fuel ratio in the exhaust gas of the internal combustion engine is measured by a sensor.

12. The method according to claim 1, wherein a necessary difference is determined from a target value of the air-fuel ratio in the exhaust gas and an actual value of the air-fuel ratio, and from this the injection amount of the total combusting fuel injection is regulated by a higher level regulator.

13. The method according to claim 1, a model for calculating the energy conversion and the combustion profile is used for adjusting the position of the centroid of heat release conversion rates.

14. The method according to claim 1, wherein positions of the individual predictively determined injections are adjusted by a higher level combustion position regulator.

15. A direct injection internal combustion engine system comprising: a direct injection internal combustion engine; an exhaust system; a NOx storage catalytic converter; and an electronic control unit configured to: divide combustion fuel injection into a plurality of individual injections, predictively adjust an air-fuel ratio in the exhaust gas of the internal combustion engine for a given load to a value that is necessary for regeneration of the NOx storage catalytic converter in the exhaust system of the internal combustion engine by adjusting a position of a centroid of heat release conversion rates and an injection amount of a total combusting fuel injection using at least one model.

16. The direct injection internal combustion engine system according to claim 15, wherein at least one combustion chamber pressure sensor for combustion position regulation is provided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features and details of the present specification can be found in the following description in which exemplary embodiments of the present specification are described in detail with reference to the drawings. In the drawings, in each case in a schematic form:

(2) FIG. 1 shows a schematic representation of an internal combustion engine with an exhaust system; and

(3) FIG. 2 shows a schematic representation of a process flow.

DETAILED DESCRIPTION

(4) FIG. 1 shows schematically the design of a diesel internal combustion engine 2 with an exhaust system 1. The diesel internal combustion engine 2 is connected to a first exhaust pipe 3 leading to a turbine 4 of a turbocharger. The first exhaust pipe 3 can contain one or a plurality of exhaust manifolds, in which the exhaust gas flows of different combustion chambers or cylinders of the diesel internal combustion engine 2 are combined. In addition, further components can be provided here, such as AGR valves and branches for example.

(5) The turbine 4 is connected to an exhaust retreatment device by a second exhaust pipe 5. The exhaust retreatment device includes an oxidation catalytic converter 6 and a particle filter 7. A third exhaust pipe 8 is connected thereto and leads to a NOx storage catalytic converter 9 that opens into a fourth exhaust pipe 10 as an end piece. Further components can be provided in the individual exhaust pipes 3, 5, 8, 10.

(6) The air-fuel ratio in the exhaust gas of the diesel internal combustion engine 2 is particularly important for the regeneration of the NOx storage catalytic converter 9. If the absorption capacity of the NOx storage catalytic converter 9 is exhausted, a rich, reducing exhaust gas mixture is briefly set by an electronic control unit (ECU) 16 that are not shown here. In the rich cycle, the oxides of nitrogen temporarily stored in the NOx storage catalytic converter 9 are reduced to nitrogen and the NOx storage catalytic converter 9 is regenerated and thereby prepared for the next storage cycle.

(7) It is necessary for this purpose to adjust the air-fuel ratio .sub.actual in the exhaust gas of the diesel internal combustion engine 2 such that the oxides of nitrogen temporarily stored in the NOx storage catalytic converter 9 can be reduced to nitrogen. This is carried out according to the process flow shown in FIG. 2, executed by the ECU 16, using a target value for the air-fuel ratio .sub.target and the amount of oxygen m.sub.oxygen in the induction air of the diesel internal combustion engine 2.

(8) In step 11 of the process, initially the injection amount q.sub.total total of the total combusting fuel injection is determined in order to adjust the air-fuel ratio .sub.actual.

(9) In step 12 of the process, a target value of the indicated average pressure PMI.sub.HD, target for the demanded load based on the ambient conditions UB is necessary, and the determined injection amount q.sub.total of the total combusting fuel injection determines the position of the centroid of heat release conversion rates .sub.Q50, Des. For this purpose, in step 12 of the process an energy conversion and the combustion profile model can be used for the calculation of the energy conversion and the combustion profile. The energy conversion and the combustion profile model is stored in memory of the ECU 16 and executed by the ECU 16.

(10) The division of the injection amount q.sub.total of the total combusting fuel injection among the individual injections in individual injection amounts q.sub.HE, q.sub.NE is carried out in step 13 of the process from the position of the centroid of heat release conversion rates .sub.Q50, Des and predefined values for the number, the start .sub.HE, .sub.NE and end of the individual injections.

(11) In order to enhance the response times of the system, regulators 14,15 can be placed in control of process step 11 for determining the injection amount q.sub.total of the total combusting fuel injection and/or process step 12 for determining the position of the centroid of heat release conversion rates .sub.Q50, Des.

(12) Thus for example a regulator 14 is provided for determining the injection amount q.sub.total of the total combusting fuel injection. Initially the actual air-fuel ratio .sub.actual in the exhaust gas of the diesel internal combustion engine 2 is determined by an air-fuel ratio sensor 17 in the exhaust gas system 1. The ECU 16 is configured to calculate a difference value is from this and from the target value for the air-fuel ratio .sub.actual and is fed to the regulator 14. The regulator 14 then determines a difference value for the injection amount q.sub.total of the total combusting fuel injection which, together with the injection amount q.sub.total of the total combusting fuel injection determined in process step 11, is fed to process step 12 for determining the position of the centroid of heat release conversion rates and to process step 13 for determining the injection amounts q.sub.HE, q.sub.NE of the individual fuel injections.

(13) Further, a higher level regulator 15 is likewise provided for determining the position of the centroid of heat release conversion rates .sub.Q50, Des. The actual indicated average pressure PMI.sub.HD, actual is initially determined by means of a combustion chamber pressure sensor 18 in at least one of the cylinders of the diesel internal combustion engine 2. From said actual indicated average pressure and the target value for the indicated average pressure PMI.sub.HD, target, a difference value is formed that is fed to the regulator 15. The regulator 15 then determines a difference value for the position of the centroid of heat release conversion rates .sub.Q50, Des, which is fed, together with the position of the centroid of heat release conversion rates .sub.Q50, Des determined in process step 12, to process step 13 for determining the injection amounts of the individual fuel injections.

(14) The explanation above of the embodiments describes in the present specification exclusively within the scope of examples. Of course, individual features of the embodiments can also, where technically appropriate, be free to combine with one another without departing from the scope of the present specification.

REFERENCE CHARACTER LIST

(15) 1 Exhaust system

(16) 2 Diesel internal combustion engine

(17) 3 Exhaust pipe

(18) 4 Turbine

(19) 5 Exhaust pipe

(20) 6 Oxidation catalytic converter

(21) 7 Particle filter

(22) 8 Exhaust pipe

(23) 9 NOx storage catalytic converter

(24) 10 Exhaust pipe

(25) 11 Process step for determining the injection amount of the total combusting fuel injection

(26) 12 Process step for determining the position of the centroid of heat release conversion rates

(27) 13 Process step for determining the injection amounts for the individual fuel injections

(28) 14 Regulator

(29) 15 Regulator

(30) 16 Electronic control unit

(31) 17 Air-fuel ratio sensor

(32) 18 Combustion chamber pressure sensor

(33) m.sub.oxygen Amount of oxygen

(34) PMI.sub.HD,actual Actual value for the indicated average pressure

(35) PMI.sub.HD,target Target value for the indicated average pressure

(36) q.sub.total Injection amount for the total combusting fuel injection

(37) q.sub.HE Injection amount of the main injection

(38) q.sub.NE Injection amount of the secondary injection

(39) UB Ambient conditions

(40) Aq50, Des Centroid of heat release conversion rates

(41) .sub.actual Actual value of the air-fuel ratio

(42) .sub.target Target value of the air-fuel ratio

(43) .sub.HE Start of the main injection

(44) .sub.NE End of the main injection