EXHAUST AFTERTREATMENT SYSTEM AND METHOD FOR REGENERATING A PARTICULATE FILTER

Abstract

The invention relates to an exhaust aftertreatment system for an internal combustion engine (10). The exhaust aftertreatment system comprises an exhaust system (20) having at least one three-way catalyst (22, 24) near the engine, wherein a particulate filter (28) is arranged downstream from the three-way catalyst, preferably in an underbody installation in a motor vehicle. A heated catalyst (26), which has at least one heating stage (62, 66, 68) that can be heated by means of an electric heating element (72, 74, 76, 78), is provided upstream from the at least one three-way catalyst (22, 24) and downstream from the particulate filter (28). It is provided that the at least one electrically heatable heating stage (62, 66, 68) is supplied with electric power directly from a generator (46) that is operatively connected to the internal combustion engine (10), so that heating of the heated catalyst (26) takes place essentially independently of the charge status of the vehicle battery (44). The invention also relates to a method for regeneration of a particulate filter (28) in the exhaust system (20) of an internal combustion engine (10) by means of such an exhaust aftertreatment system.

Claims

1. An exhaust aftertreatment system for an internal combustion engine (10) having an exhaust system (20) comprising a three-way catalyst (22, 24) near the engine and a particulate filter (28) arranged downstream from the three-way catalyst (22, 24) near the engine, characterized in that a heated catalyst (26) having at least one electric heating element (72, 74, 76, 78) is arranged downstream from the three-way catalyst (22, 24) and upstream from the particulate filter (28), wherein the electric heating element (72, 74, 76, 78) is connected to a generator (46) of the internal combustion engine (10) so that heating of the at least one electric heating element (72, 74, 76, 78) is possible directly by the electric power generated by the generator (46).

2. The exhaust aftertreatment system according to claim 1, characterized in that the heated catalyst (26) comprises a plurality of electric heating elements (72, 74, 76, 78).

3. The exhaust aftertreatment system according to claim 2, characterized in that the heated catalyst (26) comprises a plurality of heating stages (62, 66, 68) arranged in sequence, wherein a support catalyst ((64) downstream from each heating stage (62, 66, 68).

4. The exhaust aftertreatment system according to any one of claims 1 to 3, characterized in that the electric heating elements (72, 76, 78) are designed as electric heating disks (74).

5. The exhaust aftertreatment system according to any one of claims 1 to 4, characterized in that the particulate filter (28) is designed to be free of a catalytic coating.

6. The exhaust aftertreatment system according to any one of claims 1 to 5, a second three-way catalyst (24) is arranged in the in the exhaust system (20) downstream from the first three-way catalyst (22) and upstream from the heated catalyst (26), wherein a first lambda probe (34) is arranged in the exhaust system (20) upstream from the first three-way catalyst (22) and a second lambda probe (36) is arranged downstream from the first three-way catalyst (22) and upstream from the second three-way catalyst (24).

7. The exhaust aftertreatment system according to claim 6, characterized in that an inlet point (60) for introducing secondary air into the exhaust system (20) is provided downstream from a second three-way catalyst (24) and upstream from the heated catalyst (26).

8. A method for exhaust aftertreatment of an internal combustion engine (10) having an exhaust aftertreatment system according to any one of claims 1 to 7, comprising the following steps: determining the charge status of the particulate filter (28) determining the component temperature of the particulate filter (28) heating the particulate filter (28) to a regeneration temperature (T.sub.reg) required for oxidation of the carbon black retained in the particulate filter (28) if regeneration of the particulate filter (28) is required, wherein the electric heating element (72, 74, 76, 78) of the heated catalyst (26) is supplied with electric power directly from the generator (46).

9. The method according to claim 8, characterized in that an additional load is generated on detection of a regeneration requirement of the particulate filter (28) by the generator (46), so that an operating point (P.sub.1) of the internal combustion engine (10) is shifted in the direction of a higher engine torque at the same rotational speed (n.sub.1=n.sub.2) so that a higher exhaust temperature (T.sub.EG) is established at the same rotational speed (n).

10. The method according to claim 8 or 9, characterized in that the internal combustion engine (10) is operated with a sub-stoichiometric or stoichiometric combustion air ratio during regeneration of the particulate filter (28), wherein secondary air is injected into the exhaust system (20) downstream from the last three-way catalyst (22, 24), such that a super-stoichiometric exhaust gas with an exhaust air ration of 1.05<<1.2 is established at the entrance to the particulate filter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will now be explained in greater detail below on the basis of exemplary embodiments as illustrated in the respective drawings, in which:

[0028] FIG. 1 shows a first embodiment of an internal combustion engine having an exhaust aftertreatment system according to the invention;

[0029] FIG. 2 shows an alternative embodiment of an internal combustion engine having a generator and an exhaust aftertreatment system in which a secondary air system is additionally provided for injecting fresh air into the exhaust channel of the exhaust system;

[0030] FIG. 3 shows a preferred embodiment of a heated catalyst for an exhaust aftertreatment system according to the invention; and

[0031] FIG. 4 shows a diagram for visualization of a load point shift because of an increased load due to the generator in a method according to the invention for regeneration of a particulate filter.

DETAILED DESCRIPTION OF THE INVENTION

[0032] FIG. 1 shows an internal combustion engine 10 with spark ignition by means of sparkplugs 16. The internal combustion engine has a plurality of combustion chambers 12. The internal combustion engine 10 is connected to an exhaust system 20 at its outlet 14. Furthermore, an output shaft 18 which drives a generator 46 via a drive element 48 is provided on the internal combustion engine. The drive element may be embodied in particular as a belts or a chain. The exhaust system 20 comprises an exhaust channel 58 in which (listed in the direction of flow of the exhaust through the exhaust channel 58) the exhaust channel 58 has a turbine 32 of an exhaust turbocharger 30; downstream from the turbine 32, it has a first three-way catalyst 22 near the motor; and downstream from the first three-way catalyst 22, it has another three-way catalyst 24. Downstream from the second three-way catalyst 24, there is a heated catalyst 26 by means of which an exhaust stream of the internal combustion engine 10 can be heated before entering into a particulate filter 28 arranged downstream from the heated catalyst 26. The particulate filter 28 is preferably designed to be free of a catalytic coating. Alternatively, the particulate filter 28 may also be embodied as a so-called four-way catalyst, i.e., as a particulate filter 28 with a three-way catalytically active coating. Downstream from the outlet 14 and upstream from the first three-way catalyst 22, preferably downstream from the turbine 32 of the exhaust turbocharger 30 and upstream from the first three-way catalyst 22, a first lambda probe 34, preferably a broadband lambda probe, is arranged in the exhaust channel 58. Downstream from the first three-way catalyst 22 and upstream from the second three-way catalyst 24, a second lambda probe, in particular a lambda probe trim 36 is arranged in the exhaust channel 58. Downstream from the heated catalyst 26 and upstream from the particulate filter 28, a first pressure sensor 40 is provided in the exhaust channel 58. A second pressure sensor 42 is provided downstream from the particulate filter 28, so that a differential pressure measurement can be carried out across the particulate filter 28. Furthermore, at least one temperature sensor 38 may be provided in the exhaust system 58 in order to determine an exhaust temperature and/or at least one component temperature of an exhaust aftertreatment component 22, 24, 26, 28, in particular the temperature of the particulate filter 28 or the temperature of the four-way catalyst 29.

[0033] FIG. 3 shows an electric heated catalyst 26 of an exhaust aftertreatment system according to the invention in a schematic sectional diagram. In this embodiment, the heated catalyst 26 has three heating stages 62, 66, 68, wherein each heating stage 62, 66, 68 is connected directly to a support catalyst 64 for stability reasons. Due to the use of a plurality of heating stages 62, 66, 68, the electric heating power can be multiplied, and thus the temperature that can be reached in the particulate filter can be increased. The heating stages 62, 66, 68 each have an electric heating element 72, 76, 78, preferably in the form of an electric heating disk 74. Furthermore, a control unit 70 is provided for controlling the internal combustion engine 10 and the generator 46, which is connected to the lambda probes 34, 36 and to the sensors 38, 40, 42 of the exhaust system 20 via appropriate signal lines.

[0034] The generator 46 is connected by a first electric line 50 to the positive pole of a battery 44. The generator 46 is connected to the negative pole of the battery 44 by a second electric line 52. The positive pole is connected to at least one electric heating stage 62, 66, 68 of the heated catalyst 26 by a third electric line 54. The exhaust channel 58 is connected to the negative pole of the battery 44 by a fourth electric line 56 (ground line). Therefore, there is a direction connection between the generator 46 and the electric heating elements 72, 74, 76, 78 of the heated catalyst 26 via the electric lines 50, 54 and 52, 56. The electric power required for heating the heating stages 62, 66, 68 is taken directly from the generator 46, which preferably supplies a 48-volt vehicle electric system with electric power during the heating phase and the regeneration of the particulate filter 28.

[0035] FIG. 2 shows another embodiment of an internal combustion engine 10 having an exhaust aftertreatment system according to the invention. In this embodiment, a secondary air system with which secondary air can be injected downstream from the second three-way catalyst 24 and upstream from the heated catalyst 26 into the exhaust channel 58 of the exhaust system 20 is additionally provided with essentially the same design as that described for FIG. 1. The inlet point 60 for the secondary air is as far upstream from the heated catalyst 26 and thus as far upstream from the particulate filter 28 or the four-way catalyst 29 as possible in order to permit the best possible mixing of the secondary air supplied via the inlet point 60 and the exhaust up to the point of entrance into the particulate filter 28 or into the four-way catalyst.

[0036] The gaseous pollutants are converted exclusively via the two three-way catalysts 22, 24 near the engine. The particulate filter 28 and the heated catalyst 26 are preferably embodied without a coating. This has the advantage that the particulate filter 28 can be monitored with respect to the on-board diagnostics by means of only the differential pressure sensors 40, 42 to prevent a total failure. One additional lambda probe for diagnosis or another three-way catalyst downstream from the particulate filter 28 may thus be omitted.

[0037] During engine operation of the internal combustion engine 10, the exhaust of the internal combustion engine 10 is cleaned by the three-way catalysts 22, 24 and the particulate filter 28. If the particulate filter 28 has reached a load level that can be determined by means of the differential pressure sensors 40, 42 or by means of a load model, regeneration of the particulate filter 28 is initiated. To achieve the temperature required for regeneration even in a particulate filter 28 in an underbody installation of a motor vehicle, the heating stages 62, 66, 68 of the heated catalyst 26 are energized electrically and heated accordingly.

[0038] At the same time there is a load point shift in the internal combustion engine 10 due to the added load of the generator 46 at the same rotational speed resulting in a higher torque and thus a greater power which additionally results in an increase in the exhaust temperature. Such a shift in load point during the heating of the heated catalyst 26 and/or regeneration of the particulate filter 28 is illustrated in FIG. 4.

[0039] Different load points and isotherms are shown in the engine characteristics map of the internal combustion engine 10 as a function of the rotational speed n and the torque M. At the output level, the internal combustion engine 10 is operated at a rotational speed n.sub.1, torque M.sub.1, exhaust mass flow mi and power P.sub.1. By turning on the generator 46 and/or increasing the load for the generator 46, there is a shift toward a higher power P.sub.2 with a greater torque M.sub.2 at a constant rotational speed n.sub.2=n.sub.1 so that the exhaust temperature and the exhaust mass flow M.sub.2 also increase. The additional power level thereby achieved is introduced into the heated catalyst 26 via the generator 46, thereby resulting in a further temperature increase in the exhaust before entering the particulate filter 28. After conclusion of regeneration of the particulate filter, the generator power is reduced again so that the internal combustion engine 10 is operated again at a lower power P.sub.1 and a lower exhaust temperature.

[0040] The oxygen required for regeneration of the particulate filter 28 can thus be supplied by a coasting phase of the internal combustion engine, for example. Alternatively, oxygen can also be supplied by means of a lean setting of the internal combustion engine 10. If a secondary air system is present, as in the embodiment according to FIG. 2, then the oxygen required to oxidize the carbon black is supplied by a secondary air injection into the exhaust channel 58 downstream from the second three-way catalyst 24. The required secondary air can be supplied via a secondary air pump, a compressor or by tapping fresh air from the intake system downstream from the compressor of the exhaust turbocharger 30. The mixing ratio of exhaust gas and secondary air is ideally adjusted, so that a mixed lambda of 1.05<.sub.M<1.2 is established at the inlet to the particulate filter 28. Then enough oxygen is being supplied for regeneration and the risk of an uncontrolled carbon burn-off in the particulate filter 28 is avoided.

LIST OF REFERENCE NUMERALS

[0041] 10 internal combustion engine [0042] 12 combustion chamber [0043] 14 outlet [0044] 16 sparkplug [0045] 18 output shaft [0046] 20 exhaust system [0047] 22 first three-way catalyst [0048] 24 second three-way catalyst [0049] 26 heated catalyst [0050] 28 particulate filter [0051] 30 exhaust turbocharger [0052] 32 turbine [0053] 34 first lambda probe [0054] 36 second lambda probe [0055] 38 temperature sensor [0056] 40 first pressure sensor [0057] 42 second pressure sensor [0058] 44 battery [0059] 46 generator [0060] 48 drive element [0061] 50 first electric line [0062] 52 second electric line [0063] 54 third electric line [0064] 56 fourth electric line [0065] 58 exhaust channel [0066] 60 inlet point [0067] 61 first heating stage [0068] 64 support catalyst [0069] 66 second heating stage [0070] 68 third heating stage [0071] 70 control unit [0072] 72 first electric heating element [0073] 74 heating disk [0074] 76 second electric heating element [0075] 78 third electric heating element [0076] .sub.E combustion air ratio [0077] M torque [0078] n rotational speed [0079] P efficiency [0080] T temperature