REGENERATION AIR SYSTEM FOR AN EXHAUST AFTERTREATMENT SYSTEM OF AN INTERNAL COMBUSTION ENGINE, AND METHOD FOR EXHAUST AFTERTREATMENT

Abstract

The invention relates to a regeneration air system for an exhaust aftertreatment system of an internal combustion engine and to such an exhaust aftertreatment system. The regeneration air system comprises a regeneration air delivery element, a regeneration air duct, and a regeneration air valve. A sensor system is provided in the regeneration air duct with which a regeneration air mass flow {dot over (m)}.sub.SL can be determined exactly. The exhaust aftertreatment system comprises an exhaust system with an exhaust duct in which, in the direction of flow of an exhaust gas through the exhaust duct, a three-way catalytic converter is arranged underhood and a four-way catalytic converter is arranged downstream. A provision is made that an intake point for the regeneration air from the regeneration air system is formed on the exhaust duct downstream from the underhood three-way catalytic converter and upstream from the four-way catalytic converter.

Claims

1. A regeneration air system for an exhaust aftertreatment system of an internal combustion engine, the regeneration air system comprising: a regeneration air delivery element, a regeneration air duct, a regeneration air valve, and a sensor system for determining a regeneration air mass flow {dot over (m)}.sub.SL arranged in the regeneration air duct.

2. The regeneration air system as set forth in claim 1, wherein the sensor system for determining the regeneration air mass flow {dot over (m)}.sub.SL comprises an air mass meter, in particular a hot-film air mass meter (60).

3. The regeneration air system as set forth in claim 1, wherein the sensor system comprises at least one differential pressure sensor for determining a pressure difference over the regeneration air delivery element.

4. The regeneration air system as set forth in claim 1, further comprising a controller that regulates the flow rate of the regeneration air delivery element by means of the sensor system.

5. An exhaust aftertreatment system for an internal combustion engine, with an exhaust system that can be connected to an outlet of an internal combustion engine, the exhaust system having an exhaust duct in which, in the direction of flow of an exhaust gas of the internal combustion engine through the exhaust duct, a three-way catalytic converter is arranged underhood and a particulate filter with a catalytically active coating is arranged downstream from the underhood three-way catalytic converter, wherein the exhaust aftertreatment system has a regeneration air system as set forth in claim 1, an intake point for the regeneration air of the regeneration air system being formed at the exhaust duct downstream from the underhood three-way catalytic converter and upstream from the particulate filter.

6. The exhaust aftertreatment system as set forth in claim 5, further comprising a turbine of an exhaust gas turbocharger arranged in the exhaust duct downstream from an outlet of the internal combustion engine and upstream from the underhood three-way catalytic converter.

7. The exhaust aftertreatment system as set forth in claim 5, further comprising a first lambda sensor arranged in the exhaust duct upstream from the underhood three-way catalytic converter, and a second lambda sensor arranged downstream from the intake point for the regeneration air and upstream from the particulate filter with the catalytically active coating.

8. The exhaust aftertreatment system as set forth in claim 5, further comprising a differential pressure sensor provided in the exhaust system with which a pressure difference can be measured via the particulate filter with the catalytically active coating.

9. A method for exhaust aftertreatment of an internal combustion engine, with an exhaust system that can be connected to an outlet of an internal combustion engine, the exhaust system having an exhaust duct in which, in the direction of flow of an exhaust gas of the internal combustion engine through the exhaust duct, a three-way catalytic converter is arranged underhood and a particulate filter with a catalytically active coating is arranged downstream from the underhood three-way catalytic converter, as well as with an exhaust aftertreatment system a regeneration air system as set forth in claim 1, an intake point for the regeneration air of the regeneration air system being formed at the exhaust duct downstream from the underhood three-way catalytic converter and upstream from the particulate filter, comprising the following steps: determining an exhaust gas temperature (T.sub.EG) or a component temperature (T.sub.OPF) of the particulate filter with the catalytically active coating, heating the particulate filter when the determined exhaust gas temperature (T.sub.EG) or the component temperature (T.sub.OPF) of the particulate filter is below a regeneration temperature (T.sub.reg) required for the regeneration of the particulate filter, with the internal combustion engine being operated with a substoichiometric combustion air ratio (<1), with fresh air being blown into the exhaust duct by the regeneration air system with which the unburned exhaust gas components on the catalytically active coating of the particulate filter are reacted exothermically, and with the metering and regulation of the regeneration air mass flow {dot over (m)}.sub.SL being performed in such a way that a stoichiometric or superstoichiometric exhaust gas is established downstream from an intake point of the regeneration air system into the exhaust duct.

10. The method for exhaust aftertreatment of an internal combustion engine as set forth in claim 9, further comprising determining an actual mass flow and comparing it with a target mass flow, the regeneration air delivery element being regulated appropriately by a controller if the actual mass flow deviates from the target mass flow.

11. The method for exhaust aftertreatment of an internal combustion engine as set forth in claim 9, wherein the exhaust gas temperature (T.sub.EG) of the internal combustion engine is determined and compared with a threshold temperature (T.sub.S), with internal engine heating measures being initiated if the exhaust gas temperature (T.sub.EG) is below the threshold temperature (T.sub.S).

12. The method for exhaust aftertreatment of an internal combustion engine as set forth in claim 9, wherein the regeneration air system has an air mass meter, the regeneration air mass flow {dot over (m)}.sub.SL being inferred from a change in the current or in the resistance of the air mass meter.

13. The method as set forth in claim 9, wherein a pressure difference p is determined via the regeneration air delivery element, the regeneration air mass flow {dot over (m)}.sub.SL being calculated from the pressure difference p and the rotational speed {dot over (m)}.sub.SL of the regeneration air delivery element.

14. The method as set forth in claim 9, further comprising determining a combustion air ratio (.sub.1) at the first lambda sensor, and the regeneration air mass flow {dot over (m)}.sub.SL is regulated in such a way that a stoichiometric exhaust gas results downstream from the intake point.

15. The method as set forth in claim 9, further comprising determining an exhaust gas temperature (T.sub.EG) upstream and/or downstream from the particulate filter, the regeneration air mass flow {dot over (m)}.sub.SL being regulated in such a way that thermal damage to the particulate filter is avoided and/or a drop in the temperature (T.sub.OPF) of the particulate filter below its regeneration temperature (T.sub.reg) is prevented.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will be explained below in exemplary embodiments with reference to the accompanying drawing. Same components or components with the same function are identified in the drawings with the same reference numerals. In the drawing:

[0034] FIG. 1 shows a first embodiment for an internal combustion engine with an exhaust aftertreatment system according to the invention;

[0035] FIG. 2 shows another embodiment for an internal combustion engine with an exhaust aftertreatment system according to the invention;

[0036] FIG. 3 shows an operating state of the internal combustion engine in which the particulate filter is heated to its light-off temperature by internal engine measures;

[0037] FIG. 4 shows a second operating state of the internal combustion engine, in which regeneration air is blown in for the purpose of further heating the particulate filter through an exothermic conversion of the unburned exhaust gas components with the regeneration air; and

[0038] FIG. 5 shows a third operating state of the internal combustion engine, in which the particulate filter is regenerated after its regeneration temperature has been reached, the regeneration air system supplying the oxygen required to oxidize the soot retained in the particulate filter.

DETAILED DESCRIPTION OF THE INVENTION

[0039] FIG. 1 shows the schematic representation of an internal combustion engine 10 that is connected with its outlet 18 to an exhaust system 20. In this exemplary embodiment, the internal combustion engine 10 is a direct-injection gasoline engine and has a plurality of combustion chambers 12. A spark plug 14 and a fuel injector 16 for injecting a fuel into the respective combustion chamber 12 are arranged at the combustion chambers 12. Intake valves and exhaust valves are arranged at the combustion chambers with which a fluid connection from the air intake system to the combustion chambers 12 or from the combustion chambers 12 to the exhaust system 20 can be opened or closed. The exhaust system 20 comprises an exhaust duct 22 in which are arranged, in the direction of flow of an exhaust gas of the internal combustion engine 10 through the exhaust duct 22, a turbine 26 of an exhaust gas turbocharger 24 and, downstream from the turbine 26, a three-way catalytic converter 28. A particulate filter 30 with a three-way catalytically active coating 32, which is also referred to as a four-way catalytic converter, is arranged downstream from the underhood three-way catalytic converter 28 in an underbody position of a motor vehicle. The exhaust aftertreatment system further comprises a regeneration air system 50 by means of which regeneration air can be blown into the exhaust duct 22 downstream from the underhood three-way catalytic converter 28 and upstream from the particulate filter 30 at an intake point 48.

[0040] The regeneration air system 50 comprises a regeneration air delivery element 52 and a regeneration air duct 54, which connects the regeneration air delivery element 52 to the intake point 48 at the exhaust duct 22. A regeneration air valve 56 is arranged in the regeneration air duct 54 with which the regeneration air supply to the exhaust duct 22 can be released or blocked. Furthermore, the regeneration air valve 56 prevents exhaust gas from flowing out of the exhaust duct in the direction of the regeneration air system 50. An air mass meter 58, particularly a hot-film air mass meter 60, is arranged in the regeneration air duct 54 upstream from the regeneration air delivery element 52. Furthermore, a regulator 68 is provided on the regeneration air system 50 with which the speed of the regeneration air delivery element 52 can be regulated.

[0041] A first lambda sensor 34, which is embodied as a wideband lambda sensor, is arranged downstream from the turbine 26 of the exhaust gas turbocharger 24 and upstream from the underhood three-way catalytic converter 28. A second lambda sensor 36, which is preferably embodied as a two-step sensor, is arranged downstream from the intake point 48 and upstream from the particulate filter 30. Furthermore, a differential pressure sensor 38 is provided in the exhaust duct 22 with which a pressure difference can be determined via the particulate filter 30. Furthermore, a respective temperature sensor 40, 42 is provided upstream and downstream from the particulate filter 30 in order to detect the exhaust gas temperatures upstream and downstream from the particulate filter 30. A mixing section 44 is formed between the intake point 48 and an inlet of the particulate filter 30 in which the exhaust gas of the internal combustion engine 10 mixes with the fresh air from the regeneration air system 50.

[0042] A regulation of the regeneration air mass flow {dot over (m)}.sub.SL by the second lambda sensor 36 cannot be achieved with sufficient accuracy, since with an under-stoichiometric combustion air ratio, hydrogen in an unknown amount is formed on the underhood three-way catalytic converter 28 and falsifies the sensor signal of the second lambda sensor 36.

[0043] The internal combustion engine 10 is connected to an engine control unit 46 with which the fuel injection quantity, the ignition timing, and the regeneration air quantity, among other things, are regulated.

[0044] The invention therefore makes a provision for the hot-film air mass meter 60 to be used for the precise air metering in the regeneration air duct 54. The combustion air ratio in the combustion chambers 12 of the internal combustion engine 10 can be set very precisely through the adaptation of the mixture. The air mass flow supplied to the internal combustion engine 10 and the exhaust gas mass flow resulting therefrom can likewise be determined exactly by the engine control unit 46. With these two variables, the regeneration air mass flow {dot over (m)}.sub.SL that is required in order to achieve the target combustion air ratio upstream from the particulate filter 30 can be calculated and passed on as a controlled variable to the controller 68 of the regeneration air delivery element 52.

[0045] FIG. 2 shows another exemplary embodiment of an exhaust aftertreatment system according to the invention for an internal combustion engine 10. With essentially the same construction as that shown in FIG. 1, the amount of regeneration air in the regeneration air system 50 is not determined by a hot-film air mass meter 60, but by pressure sensors 62, 64, which, as differential pressure sensors 66, determine a pressure difference p via the regeneration air delivery element 52. The regeneration air mass flow {dot over (m)}.sub.SL can be used in an alternative manner to determine this pressure difference p and the speed {dot over (m)}.sub.SL of the regeneration air delivery element 52.

[0046] During operation of the internal combustion engine 10, the particulate filter 30 is loaded with soot particulates from the exhaust gas of the internal combustion engine 10. Since regeneration of the particulate filter 30 requires a temperature of greater than 600 C., such a temperature cannot be achieved or can only be achieved with extreme difficulty by internal engine heating measures during low-load operation. Therefore, the particulate filter 30 is provided with a catalytically active coating 32, which enables exothermic conversion of unburned exhaust gas componentsin particular unburned hydrocarbons, carbon monoxide, and hydrogenwhile heating the particulate filter 30. For this purpose, the internal combustion engine 10 is operated with a substoichiometric combustion air ratio <1, and regeneration air is blown into the exhaust duct 22 at the same time. Such heating of the particulate filter 30 is also referred to as chemical heating. As a result of this possibility, the particulate filter 30 only has to be heated to the light-off temperature of the catalytically active coating 32 for regeneration. After the regeneration temperature has been reached, the amount of regeneration air can be increased while maintaining the chemical heating via the regeneration air system 50, so that an over-stoichiometric exhaust gas is established downstream from the intake point 48. With the excess of oxygen in the exhaust gas, the soot retained in the particulate filter 30 can thus be oxidized and the particulate filter 30 regenerated. For a fast and low-emission regeneration of the particulate filter, it is necessary to know the regeneration air mass flow {dot over (m)}.sub.SL with maximum possible accuracy.

[0047] During the heating phase, the substoichiometric operation of the internal combustion engine 10 on the underhood three-way catalytic converter forms ammonia, which would be converted into nitrogen oxide in the particulate filter 30 if the excess air were too high. An excessively low air supply would lead to the emission of hydrocarbons, carbon monoxide, and ammonia.

[0048] During the regeneration phase of the particulate filter, an excessively high regeneration air mass flow {dot over (m)}.sub.SL can unintentionally reduce the temperature in the particulate filter 30, thereby interrupting the regeneration, or in case of an excessive soot load of the particulate filter, cause thermal damage to the particulate filter 30 due to excessive exothermicity. If the regeneration air mass flow {dot over (m)}.sub.SL is too low, the regeneration will take place too slowly and therefore not be completed within a reasonable time interval.

[0049] FIG. 3 shows a first operating state of the internal combustion engine 10, in which the particulate filter 30 is heated up exclusively by means of internal engine measures, such as an adjustment of the ignition angle in the late direction. The internal combustion engine 10 is operated with a stoichiometric combustion air ratio in order to enable efficient conversion by the underhood three-way catalytic converter 10 of the pollutants in the exhaust gas of the internal combustion engine 10. The regeneration air system 50 is deactivated, and the regeneration air valve 56 is closed. This operating state is maintained as long as the catalytically active coating 32 of the particulate filter 30 has not yet reached its light-off temperature.

[0050] Once the three-way catalytically active coating 32 of the particulate filter 30 has reached its light-off temperature of approximately 300 C., from which an efficient conversion of the pollutants in the exhaust gas of the internal combustion engine with release of heat is possible, the internal combustion engine 10 is operated in the operating state shown in FIG. 4. The internal combustion engine 10 is operated with a substoichiometric combustion air ratio and, at the same time, regeneration air is blown into the exhaust duct 22 at the intake point 48, so that a stoichiometric exhaust gas is produced at the inlet of the particulate filter 30. The unburned exhaust gas components are reacted with the regeneration air exothermically on the catalytically active surface 32 of the particulate filter 32 until the latter has reached its regeneration temperature of approximately 600 C.

[0051] Subsequently, as shown in FIG. 5, the amount of regeneration air is increased, so that a superstoichiometric exhaust gas occurs downstream from the intake point 48. The soot particles retained in the particulate filter 30 are oxidized with the residual oxygen in the exhaust gas, thereby regenerating the particulate filter 30. The internal combustion engine 10 preferably continues to be operated with a substoichiometric combustion air ratio in order to maintain the chemical heating of the particulate filter 30 during the regeneration and to prevent the particulate filter 30 from cooling below its regeneration temperature.

LIST OF REFERENCE SYMBOLS

[0052] 10 combustion engine [0053] 12 combustion chamber [0054] 14 spark plug [0055] 16 fuel injector [0056] 18 outlet [0057] 20 exhaust system [0058] 22 exhaust duct [0059] 24 exhaust gas turbocharger [0060] 26 turbine [0061] 28 three-way catalytic converter [0062] 30 particulate filter [0063] 32 catalytically active coating [0064] 34 first lambda sensor/wideband lambda sensor [0065] 36 second lambda sensor/two-step sensor [0066] 38 differential pressure sensor [0067] 40 first temperature sensor [0068] 42 second temperature sensor [0069] 44 mixing section [0070] 46 engine control unit [0071] 48 intake point [0072] 50 regeneration air system [0073] 52 regeneration air delivery element [0074] 54 regeneration air duct [0075] 56 regeneration air valve [0076] 58 air mass meter [0077] 60 hot-film air mass meter [0078] 62 first pressure sensor [0079] 64 second pressure sensor [0080] 66 differential pressure sensor [0081] 68 regulator