CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Application of PCT International Application No. PCT/EP2018/068509, International Filing Date Jul. 9, 2018, claiming priority of German Patent Application No. 10 2017 115 408.6, filed Jul. 10, 2017, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a system and method for the exhaust gas aftertreatment of an internal combustion engine in accordance with the definition of the species set forth in the independent claims.

BACKGROUND OF THE INVENTION

Rigorous demands are placed on vehicle manufacturers by the increased tightening of emission-control legislation. These are met by appropriate measures for reducing untreated engine emissions and by providing a suitable exhaust gas aftertreatment. With the introduction of the EU6 stage legislation for spark-ignition engines, a limit value for a particle count is required that, in many cases, necessitates the use of a gasoline particulate filter. Such soot particles form, in particular following a cold start of the internal combustion engine due to an incomplete combustion in combination with a leaner than stoichiometric air/fuel ratio, and due to cold cylinder walls during the cold start. The cold-start phase is, therefore, relevant to compliance with the legally required particulate matter limits. Such a gasoline particulate filter also becomes further saturated with soot during vehicle operation. Preventing a sharp increase in the exhaust gas back pressure requires continuously or periodically regenerating such a gasoline particulate filter. The rise in the exhaust back pressure can lead to an excess consumption by the internal combustion engine, a power loss, a degradation of running smoothness, and even to misfires. Thermally oxidizing the soot trapped in the gasoline particulate filter requires a high enough temperature level in conjunction with the simultaneous presence of oxygen in the exhaust system of the spark-ignition engine. Since today's spark-ignition engines are normally operated without excess oxygen at a stoichiometric air/fuel ratio of (λ=1), additional measures are needed. These include, for example, increasing the temperature by adjusting the ignition timing, temporarily adjusting the spark-ignition engine toward lean, injecting secondary air into the exhaust system, or a combination thereof. Until now, an ignition-timing retard has preferably been used in combination with a lean adjustment of the spark-ignition engine, since such a method does not require additional components, and a sufficient quantity of oxygen is able to be supplied in most operating points of the spark-ignition engine. Due to the good efficiencies of the spark-ignition engine, it is not possible to regenerate a particulate filter in the underbody position in certain operating situations, so that regenerating a particulate filter in the underbody position requires special driving cycles. A close-coupled, i.e., near to the engine, positioning of the particulate filter is beneficial since this results in higher exhaust gas temperatures at the particulate filter and facilitates the heating to a regeneration temperature. Another problem of three-way catalytic converters having a three way catalytically active coating, what are generally referred to as four-way catalytic converters, is the fact that the coating can exhibit pronounced ageing effects, so that converting the gaseous pollutants can require an additional three-way catalytic converter in a close-coupled position.

The German Patent Application DE 10 2008 036 127 A1 discusses a method for the exhaust gas aftertreatment of an internal combustion engine in whose exhaust duct are located a particulate filter and a three-way catalytic converter. As the first component of the exhaust gas aftertreatment, the particulate filter is thereby configured downstream of an exhaust of the internal combustion engine. A three-way catalytic converter is disposed downstream of the particulate filter. The oxygen content in the exhaust gas is thereby increased to regenerate the particulate filter by a lambda control of the three-way catalytic converter.

The German Patent Application DE 10 2010 046 747 A1 discusses an exhaust gas aftertreatment system for a spark-ignition engine, as well as an exhaust gas aftertreatment method. A particulate filter is thereby configured downstream of a three-way catalytic converter; to regenerate the soot particles trapped in the particulate filter, it being possible to provide a secondary air system that blows fresh air into the exhaust system downstream of the three-way catalytic converter and upstream of the particulate filter.

In addition, the German Patent Application DE 10 2012 204 779 A1 describes an exhaust gas aftertreatment system for an internal combustion engine, where an electrically heatable three-way catalytic converter and, downstream thereof, another three-way catalytic converter are located in an exhaust system. In this context, secondary air can be introduced into the exhaust system to reduce emissions.

SUMMARY OF THE INVENTION

It is an object of the present invention to ensure that a regeneration temperature of the particulate filter is reached in all driving cycles to improve the ageing behavior of the exhaust gas aftertreatment system, and to overcome the disadvantages known from the related art.

This objective is achieved in accordance with the present invention by an exhaust gas aftertreatment system for an internal combustion engine having an exhaust system that is coupled 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 the first emission-reducing component, in a close-coupled position; downstream thereof, likewise in a close-coupled position, an electrically heatable three-way catalytic converter; and downstream of the electrically heatable catalytic converter, another three-way catalytic converter. In this connection, a close-coupled configuration of the particulate filter and of the electrically heatable three-way catalytic converter is understood to be a configuration of the exhaust gas aftertreatment components having an exhaust gas flow length of less than 80 cm, in particular of less than 50 cm, especially of less than 35 cm from an exhaust of the internal combustion engine. This permits an accelerated heating of the particulate filter and of the electrically heatable three-way catalytic converter, in particular following a cold start of the internal combustion engine. Due to the close-coupled position of the particulate filter, less waste heat is lost via the walls of the exhaust duct, so that, in comparison to a particulate filter in the underbody position of the internal combustion engine; on the particulate filter, it is easier to reach an oxidation temperature of soot particles trapped in the particulate filter required to regenerate the particulate filter.

Advantageous improvements to and refinements of the exhaust gas aftertreatment system according to the present invention for an internal combustion engine are made possible by the features delineated in the dependent claims.

A preferred and advantageous specific embodiment of the present invention provides that the internal combustion engine have 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. The secondary air is thereby injected into the hot exhaust ducts of the internal combustion engine, the unburned exhaust components reacting exothermally with the secondary air still in the exhaust duct and thus ensuring a heating of the exhaust gas. It is thus possible to further reduce the time it takes for the electrically heatable three-way catalytic converter to reach the light-off temperature thereof. In addition, the secondary air system may be utilized for regenerating the particulate filter and for introducing the oxygen required for the regeneration into the exhaust duct upstream of the particulate filter. The operating state of the internal combustion engine may thereby be suitably adapted in the case of a regeneration of the particulate filter, eliminating the need for operating the internal combustion engine at a leaner than stoichiometric air/fuel ratio to permit a regeneration of the particulate filter.

An advantageous enhancement of the present invention provides that the electrically heatable three-way catalytic converter include an electrical heating element, in particular an electrical heating disk, and a metallic substrate structure. An electrical heating element may be readily heated by an electrical heating resistor independently of the exhaust-gas flow from the internal combustion engine; a heating of the electrical heating element is also thereby possible when the internal combustion engine is switched off, in particular immediately before a start thereof. The metallic substrate element makes possible an especially efficient heat transfer, so that the heat produced in the electrical heating element may be transferred to the metallic substrate element without significant losses. Moreover, a metallic substrate structure permits a correspondingly thin-walled construction of the electrically heatable three-way catalytic converter, making it possible to reduce the flow resistance and thus the exhaust back pressure.

It is thereby especially preferred that a pin connection be used to attach the electrical heating element to the metallic substrate structure of the electrically heatable three-way catalytic converter. A pin connection allows the heating disk to be stably supported on the metallic substrate structure of the electrically heatable three-way catalytic converter, avoiding mechanical rigidity of the electrically heatable three-way catalytic converter, as well as vibrations caused by the use of a loose, vibrating heating disk.

Alternatively, an advantageous design variant of the present invention provides that the electrically heatable three-way catalytic converter have a directly electrically heatable substrate. A directly electrically heatable substrate generates the heat directly in the substrate, making it possible for the substrate to be heated, in particular following a cold start of the internal combustion engine, without any further heat transfer from the heating disk to the exhaust gas and from the exhaust gas to the catalytic converter.

A preferred specific embodiment of the present invention provides that a first lambda probe be disposed upstream of the particulate filter, and that a second lambda probe in the exhaust duct be disposed downstream of the electrically heatable catalytic converter and upstream of the further three-way catalytic converter. In this way, one lambda probe pair may be used to both perform the lambda control of the internal combustion engine, as well as the on-board diagnosis of the electrically heatable three-way catalytic converter since the uncoated particulate filter does not affect the lambda control. The first lambda probe is thereby preferably designed as a wide band lambda probe to make possible a quantitative statement about the oxygen content in the exhaust gas. The second lambda probe may be designed as a two-step lambda probe to reduce the costs and thus provide a qualitative statement about the excess oxygen in the exhaust gas.

An advantageous specific embodiment of the present invention provides that the particulate filter be uncoated and free of an oxygen accumulator. The particulate filter thereby lacks both a three-way catalytic coating, as well as a coating for the selective catalytic reduction of nitrogen oxides. It is thereby especially preferred that the particulate filter be designed to be essentially free of an oxygen accumulator and not have any oxygen storage capacity. In this way, an ageing-induced change in the properties of the particulate filter may be thereby prevented, so that the particulate filter has essentially the same performance characteristics over the service life thereof. Moreover, in this way, a shared lambda probe pair may thereby monitor the functioning of the particulate filter and of the electrically heatable three-way catalytic converter, the first lambda probe being disposed upstream of the particulate filter, and the second lambda probe downstream of the electrically heatable three-way catalytic converter. Since, as the first exhaust gas aftertreatment component, the particulate filter is disposed downstream of the exhaust of the internal combustion engine, high exhaust gas temperatures act thereon, in particular in a full-load operation of the internal combustion engine, which otherwise lead to an increased thermal ageing of a catalytic coating. Moreover, by omitting a coating, the particulate filter may be designed to have fewer cells, thereby reducing the thermal mass of the particulate filter and promoting a heating of the particulate filter. Moreover, the exhaust gas back pressure is additionally reduced, whereby the flow losses in the exhaust system may be reduced, and thus the power efficiency of the internal combustion engine enhanced. This may be utilized to achieve greater power output or a decreased consumption, even when working with otherwise unchanged boundary conditions.

In accordance with the present invention, a method for the exhaust gas aftertreatment of an internal combustion engine using an inventive exhaust gas aftertreatment system is provided that includes 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 beginning from a start of the internal combustion engine;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; andregenerating the particulate filter; the particulate filter being heated to a regeneration temperature by the exhaust gas from the internal combustion engine.

A method according to the present invention makes it possible for at least one pollutant-reducing exhaust gas aftertreatment component, in particular the electrically heatable three-way catalytic converter, to be heated to a light-off temperature shortly after a cold start of the internal combustion engine, making it possible to efficiently convert the harmful gaseous exhaust components. Moreover, the durability of the catalytic coating may be enhanced since the electrically heatable three-way catalytic converter in a full-load operation of the internal combustion engine does not become as hot as the particulate filter disposed in the first position downstream of the exhaust.

A preferred specific embodiment of the exhaust gas aftertreatment method provides that secondary air be 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. Injecting secondary air may enhance the transfer of heat from the electrical heating element of the electrically heatable three-way catalytic converter to the substrate element, and prevent electrical heating element-induced local overheating since the generated heat is convectively transferred by the secondary air to the rest of the catalytic converter.

Unless indicated otherwise in the individual case, the various specific embodiments of the present invention mentioned in this Application may be advantageously combined with one another.

