SYSTEM AND METHOD FOR EXHAUST GAS AFTERTREATMENT OF AN INTERNAL COMBUSTION ENGINE

Abstract

The invention relates to an exhaust gas aftertreatment system for an internal combustion engine (10), in particular for an internal combustion engine (10) which is charged by means of a turbocharger (30) and spark-ignited by means of spark plugs (16). A particulate filter (24) and an electrically heatable three-way catalytic converter (26) downstream of the particulate filter (24) are arranged in a position close to the engine in an exhaust gas system (20) connected to an outlet (12) of the internal combustion engine (10). A further three-way catalytic converter (28) is arranged in the underbody position of the motor vehicle downstream of the electrically heatable catalytic converter (26). According to the invention, the electrically heatable three-way catalytic converter (26) is heated electrically after engine start, and the particulate filter (24), the electrically heatable three-way catalytic converter (26) and the further three-way catalytic converter are additionally heated by the exhaust gas flow from the internal combustion engine (10). The electric heating of the electrically heatable three-way catalytic converter (26) is switched off when the electrically heatable three-way catalytic converter (26) has reached its light-off temperature.

Claims

1. An exhaust gas aftertreatment system for an internal combustion engine comprising: an exhaust system that is couplable to an exhaust of the internal combustion engine the exhaust system including an exhaust duct, in which are disposed in the flow direction of an exhaust gas of the internal combustion engine through the exhaust duct: a particulate filter, as a first emission-reducing component, in a close-coupled configuration; downstream of the particulate filter, likewise in a close-coupled position, an electrically heatable three-way catalytic converter; and downstream of the electrically heatable catalytic converter, a further three-way catalytic converter.

2. The exhaust gas aftertreatment system as recited in claim 1, further comprising a turbine of an exhaust-gas turbocharger is configured in the exhaust duct downstream of the exhaust and upstream of the particulate filter.

3. The exhaust gas aftertreatment system as recited in claim 1, wherein the internal combustion engine has a secondary air system for introducing secondary air into the exhaust duct, a feed point of the secondary air system being located at the exhaust of the internal combustion engine or downstream thereof and upstream of the particulate filter.

4. The exhaust gas aftertreatment system as recited in claim 1, wherein the electrically heatable three-way catalytic converter has an electrical heating element and a metallic substrate structure.

5. The exhaust gas aftertreatment system as recited in claim 4, wherein a pin connection attaches the heating disk to the metallic substrate structure of the electrically heatable three-way catalytic converter.

6. The exhaust gas aftertreatment system as recited in claim 1, wherein the electrically heatable three-way catalytic converter has an electrically directly heatable substrate.

7. The exhaust gas aftertreatment system as recited in claim 1, further comprising a first lambda probe disposed upstream of the particulate filter, and a second lambda probe in the exhaust duct is disposed downstream of the electrically heatable catalytic converter and upstream of the further three-way catalytic converter.

8. The exhaust gas aftertreatment system as recited in claim 1, wherein the particulate filter is uncoated and is free of an oxygen accumulator.

9. A method for the exhaust gas aftertreatment of an internal combustion engine using an exhaust gas aftertreatment system according to claim 1, comprising the following steps: electrically heating the electrically heatable three-way catalytic converter to a light-off temperature of the electrically heatable three-way catalytic converter at the start of the internal combustion engine; and heating the particulate filter, the electrically heatable three-way catalytic converter and the further three-way catalytic converter using the exhaust-gas flow from the internal combustion engine, beginning from the start of the internal combustion engine.

10. The method for the exhaust gas aftertreatment as recited in claim 9, wherein secondary air is introduced into the exhaust-side cylinder head or into the exhaust duct downstream of the exhaust and upstream of the particulate filter in a heating phase of one of the three-way catalytic converters or of the particulate filter, to promote the heating of the catalytic converters or of the particulate filter by an exothermic reaction of unburned fuel components.

Description

[0022] The present invention will be explained in the following in exemplary embodiments with reference to the accompanying drawings. The same reference numerals in the various figures thereby denote identical components or components having the same function, where:

[0023] FIG. 1 shows a first exemplary embodiment of an internal combustion engine having an exhaust gas aftertreatment system according to the present invention;

[0024] FIG. 2 shows another exemplary embodiment of an internal combustion engine having an exhaust gas aftertreatment system according to the present invention, the exhaust gas aftertreatment system additionally having a secondary air system for introducing fresh air into the exhaust system; and

[0025] FIG. 3 is a diagram showing the temperature profile in the exhaust system upon implementation of an exhaust gas aftertreatment method according to the present invention.

[0026] FIG. 1 is a schematic representation of an internal combustion engine 10 whose exhaust 12 is coupled to an exhaust system 20. Internal combustion engine 10 is a spark ignition engine that is spark ignited by spark plugs 16 and has a plurality of combustion chambers 14. Internal combustion engine 10 is preferably designed to be charged by an exhaust-gas turbocharger 30, a turbine 32 of exhaust-gas turbocharger 30 being configured downstream of exhaust 12 and upstream of the first emission-reducing exhaust gas aftertreatment component, in particular upstream of a particulate filter 24. Exhaust system 20 includes an exhaust duct 22, in which are disposed in the direction of flow of an exhaust gas through exhaust duct 22: a particulate filter 24; downstream thereof, an electrically heatable three-way catalytic converter 26; and, further downstream, another three-way catalytic converter 28. Particulate filter 24 and electrically heatable three-way catalytic converter 26 are preferably each in a close-coupled position, i.e., disposed at a distance of less than 80 cm exhaust gas flow length, in particular of less than 50 cm exhaust gas flow length from exhaust 12 of internal combustion engine 10. Other three-way catalytic converter 28 is preferably disposed in the underbody position of a motor vehicle and thus in a remote-coupled position, i.e., at a distance of more than 100 cm exhaust gas flow length from exhaust 12 of the internal combustion engine.

[0027] Additionally disposed in exhaust system 20, there may be further catalytic converters, in particular a further three-way catalytic converter, a NOx storage catalytic converter or a catalytic converter for selectively catalytically reducing nitrogen oxides. Located upstream of particulate filter 24 in exhaust duct 22 is a first lambda probe 50 for determining oxygen content Xi of the exhaust gas downstream of exhaust 12 and upstream of the first exhaust gas aftertreatment component, thus of particulate filter 24. Disposed in exhaust duct 22 downstream of electrically heatable three-way catalytic converter 26 and upstream of further three-way catalytic converter 28 is a second lambda probe 52, which may be used for determining oxygen content .sub.2 in exhaust duct 28 downstream of electrically heatable three-way catalytic converter 26 and upstream of further three-way catalytic converter 28. First lambda probe 50 is preferably in the form of a broadband lambda probe and communicates via a first signal line 58 with a control unit 56 of internal combustion engine 10. Second lambda probe 52 is preferably in the form of a step change probe and communicates via a second signal line 60 with control unit 56. First lambda probe 50 and second lambda probe 52 thereby form a sensor assembly for regulating air/fuel ratio k of internal combustion engine 10. In addition, the sensor assembly may perform an on-board diagnosis of electrically heatable catalytic converter 26.

[0028] Electrically heatable three-way catalytic converter 26 has an electrical heating element 34, in particular an electrical heating disk, as well as a metallic substrate structure 36. A pin connection 38 is used to attach electrical heating element 34 to the metallic substrate structure, making it possible to permanently mechanically fix electrical heating element 34. Alternatively, electrically heatable three-way catalytic converter 26, as shown in FIG. 2, may also feature an electrically heatable substrate 54. Also provided upstream and downstream of particulate filter 24 are pressure sensors, which may be used to perform a differential pressure measurement via particulate filter 24 to determine the saturation condition of particulate filter 24. Moreover, the pressure sensors may be used to perform an on-board diagnosis of particulate filter 24.

[0029] FIG. 2 shows another exemplary embodiment of an internal combustion engine having an exhaust gas aftertreatment system. The exhaust gas aftertreatment system additionally has a secondary air system 40 in essentially the same design as in FIG. 1. Secondary air system 40 includes a secondary air pump 46, a secondary air conduit 44, as well as a secondary air valve 48 located in secondary air conduit 44 downstream of secondary air pump 46 and upstream of a feed point 42. Feed point 42 is formed in an exhaust-side cylinder head 18 of internal combustion engine 10 to be able to introduce secondary air into a hottest possible exhaust gas and thus promote exothermic reactions with unburned fuel components. Alternatively, feed point 42 may also be configured at locations upstream of particulate filter 24, making it possible for particulate filter 24 and three-way catalytic converters 26, 28 disposed downstream of particulate filter 24 to be supplied with secondary air. Electrically heatable three-way catalytic converter 26 features an electrically heatable substrate, which may be used to generate heat directly at the catalytically active structure of electrically heatable catalytic converter 26. Alternatively, as illustrated in FIG. 1, electrically heatable catalytic converter 26 may also feature an electrical heating element 34 and a metallic substrate structure 36.

[0030] During operation of internal combustion engine 10, the exhaust gas from the internal combustion engine is directed through particulate filter 24, electrically heatable three-way catalytic converter 26, as well as through further three-way catalytic converter 28; the soot particles contained in the exhaust gas being filtered out of the exhaust-gas flow, and the harmful exhaust-gas components being converted into harmless exhaust-gas components. The close-coupled configuration of particulate filter 24 and of electrically heatable three-way catalytic converter 26 allows an especially rapid heating to a light-off temperature following a cold start of internal combustion engine 10 to make possible a rapid, efficient conversion of the gaseous pollutants following the cold start. In this context, particulate filter 24 is preferably uncoated, in particular does not have a coating having an oxygen storage capacity. This makes it possible to use lambda probes 50, 52 to diagnose electrically heatable catalytic converter 26. By configuring particulate filter 24 as the first component of the exhaust gas aftertreatment, electrically heatable catalytic converter 26 is loaded to a lesser extent during a full-load operation of the internal combustion engine, thereby making it possible to reduce the ageing of the catalytic coating.

[0031] FIG. 3 illustrates the temperature profile at a plurality of locations of exhaust system 20 during execution of an exhaust gas aftertreatment method according to the present invention. In a first curve I, temperature T1 is thereby shown directly downstream of particulate filter 24. In second curve II, temperature T2 in electrically heatable three-way catalytic converter 26 is shown in the case of activated electrical heating element 34. To that end, temperature T2 at the component middle of electrically heatable three-way catalytic converter component 26 is determined. Internal combustion engine 10 is thereby started at a starting instant S, and electrical heating element 34 simultaneously begins to be electrically heated. In a first phase <100>, particulate filter 24 and electrically heatable catalytic converter 26 are traversed by the flow of the exhaust gas from internal combustion engine 10 and heated by the same. In parallel thereto, electrically heatable catalytic converter 26 is heated by electrical heating element 34, the heat being essentially convectively transferred by the exhaust-gas flow of internal combustion engine 10 from heating element 34 to metallic substrate structure 36. If electrically heatable catalytic converter 26 has reached light-off temperature T.sub.LO thereof, electrically heatable three-way catalytic converter 26 undergoes a combined heating, an electrical heating and a chemical heating, in a second phase <110>, since, from this point in time on, the unburned exhaust components may be converted exothermally on the catalytic surface of electrically heatable three-way catalytic converter 26. If electrically heatable three-way catalytic converter 26 has reached the operating temperature thereof, electrical heating element 34 is switched off. In a third phase <120>, the electrical heating of electrically heatable three-way catalytic converter component 26 is stopped, and the temperature is maintained by the exothermic reactions of the unburned fuel components on the catalytically active surface of electrically heatable three-way catalytic converter 26. In a fourth operating phase <130>, both electrically heatable three-way catalytic converter 26 and particulate filter 24 have reached a temperature at which no further heating measures are needed. As a comparison, temperature T3 of electrically heatable three-way catalytic converter 26 is shown in the third curve when electrical heating element 34 is not activated in any of phases <100>, <110> or <120>.

[0032] A substrate flow for heat transfer may be produced by a secondary air system 40, whereby heating of electrically heatable three-way catalytic converter 24 may already be begun in a pre-start phase <90>, enabling light-off temperature T.sub.LO to be reached even faster following start S of internal combustion engine 10.

REFERENCE NUMERAL LIST

[0033] 10 internal combustion engine

[0034] 12 exhaust

[0035] 14 combustion chamber

[0036] 16 spark plug

[0037] 18 cylinder head [0038] 20 exhaust system

[0039] 22 exhaust duct

[0040] 24 particulate filter

[0041] 26 electrically heatable three-way catalytic converter

[0042] 28 three-way catalytic converter

[0043] 30 exhaust-gas turbocharger

[0044] 32 turbine

[0045] 34 electrical heating element/electrical heating disk

[0046] 36 metallic substrate structure

[0047] 38 pin connection

[0048] 40 secondary air system

[0049] 42 feed point

[0050] 44 secondary air conduit

[0051] 46 secondary air pump

[0052] 48 secondary air valve

[0053] 50 first lambda probe/wide band lambda probe

[0054] 52 second lambda probe/step change probe

[0055] 54 electrically heatable substrate

[0056] 56 control unit

[0057] 58 signal line

[0058] 60 signal line

[0059] <90> pre-start phase

[0060] <100> start phase of the internal combustion engine

[0061] <110> second phase

[0062] <120> third phase

[0063] <130> fourth phase

[0064] S start of the internal combustion engine

[0065] T temperature

[0066] T1 temperature

[0067] T2 temperature of the electrically heatable three-way catalytic converter in the case of an active heating element

[0068] T3 temperature of the electrically heatable three-way catalytic converter in the case of a deactivated heating element

[0069] T.sub.LO light-off temperature of electrically heatable catalytic converter

[0070] T.sub.REG regeneration temperature of the particulate filter