Exhaust Gas Aftertreatment System and Exhaust Gas Cleaning Method

Abstract

An exhaust gas aftertreatment system, and a method for exhaust gas purification, has a first oxidation catalyst device, a NOx catalyst device for removing nitrogen from the exhaust gas, a device for actively increasing an exhaust gas temperature with at least one second oxidation catalyst device, and a device for removing particles. The devices are arranged one behind the other in the flow direction of the exhaust gas of an internal combustion engine, so that the exhaust gas flows through them. A respective operating temperature of the NOx catalyst device and of the device for removing particles can be set independently of an exhaust gas temperature at an outlet of the internal combustion engine.

Description

RELATED APPLICATIONS

This application is a National Phase Entry under 35 U.S.C. § 371 of international application number PCT/EP2007/001742, filed Mar. 1, 2007, which claims priority under 35 U.S.C. § 120 to German patent application number 10 2006 009 934.6, filed Mar. 3, 2006. The disclosures of each of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an exhaust-gas aftertreatment system and a method for exhaust-gas purification in an exhaust-gas aftertreatment system, having, arranged in series in the flow direction of exhaust gas of an internal combustion engine, and traversed by exhaust gas, a first oxidation catalytic converter device, a NOx catalytic converter device for the denitrogenization of the exhaust gas, a device for actively raising an exhaust-gas temperature with at least one second oxidation catalytic converter device, and a device for particle removal.

Exhaust-gas aftertreatment serves to convert and retain statutorily limited pollutant components in the exhaust gas of internal combustion engines.

U.S. Pat. No. 6,467,257 B1 discloses an exhaust-gas aftertreatment system having, arranged downstream of a catalytic converter for the selective catalytic reduction (SCR) of nitrogen oxides (NOx), a particle filter for removing soot particles in the exhaust gas.

EP 1 469 173 A1 discloses an exhaust-gas aftertreatment system in which an oxidation catalytic converter is arranged upstream of an SCR catalytic converter and a subsequent particle filter. Arranged between the oxidation catalytic converter and the SCR catalytic converter is a heat exchanger. Exhaust gas can be cooled therein or can bypass the heat exchanger. A separate burner supplies the particle filter with thermal energy in order to regenerate the particle filter by burning off the accumulated soot.

DE 103 47 133 A1 discloses an exhaust-gas aftertreatment system in which an oxidation catalytic converter with a fuel metering apparatus is arranged downstream of an SCR catalytic converter. The oxidation catalytic converter is followed by a particle filter. A further oxidation catalytic converter is arranged upstream of the SCR catalytic converter.

One object of the invention is to specify an exhaust-gas aftertreatment system and a method for exhaust-gas purification by means of which functionally optimized operation of the components is possible.

The exhaust-gas aftertreatment system according to the invention is designed such that a respective operating temperature of the NOx catalytic converter device and of the device for particle removal can be set independently of an exhaust-gas temperature at an outlet of the internal combustion engine. The functionally optimized arrangement of the NOx catalytic converter device, which preferably comprises at least one SCR catalytic converter, and of the device for particle removal, differs from known exhaust-gas aftertreatment systems, which arrangement is substantially dependent on the components by means of which the respective operating temperature can be set. Said components are preferably a unit for generating a heat tone at the inlet side of the NOx catalytic converter device and of the device for actively raising the exhaust-gas temperature at the inlet of the device for particle removal.

A unit for generating a heat tone to control the temperature of a NOx catalytic converter device is preferably also up, in addition to the device for actively raising an exhaust-gas temperature, upstream of a device for particle removal, wherein the NOx catalytic converter device can be decoupled from the exhaust-gas temperature of the internal combustion engine. Both the device for particle removal and also the NOx catalytic converter device can be operated in a functionally optimized manner. The unit for generating a heat tone permits optimized operation of the preferred SCR catalytic converter with regard to its conversion of nitrogen oxides (NOx). For this purpose, the temperature of the SCR catalytic converter can be regulated. In addition, the temperature of the second oxidation catalytic converter can be set so as to permit the use of a fuel metering apparatus. The functionalities of the NOx catalytic converter device and of the device for particle removal are therefore no longer coupled to the exhaust-gas temperatures of the internal combustion engine. The exhaust-gas aftertreatment system can consequently be operated in a manner decoupled from the internal combustion engine.

The unit for generating a heat tone is preferably arranged upstream of the NOx catalytic converter device and downstream of the first oxidation catalytic converter device.

Alternatively, the unit for generating a heat tone can also be arranged upstream of the first oxidation catalytic converter unit.

Furthermore, the device for actively raising an exhaust-gas temperature can comprise at least one fuel metering apparatus in addition to a second oxidation catalytic converter device with at least one oxidation catalytic converter. Here, the oxidation catalytic converter device can be of single-strand or twin-strand design, wherein the fuel metering apparatus can be provided separately for each oxidation catalytic converter. Alternatively, a single fuel metering apparatus can be provided for commonly supplying all of the oxidation catalytic converters of the device for actively raising an exhaust-gas temperature.

The NOx catalytic converter device can likewise be of single-strand or twin-strand design.

Furthermore, the device for particle removal can have at least one particle filter, wherein the device for particle removal can be of single-strand or twin-strand design.

It is possible for a third oxidation catalytic converter device to be provided downstream of the device for particle removal.

Here, the third oxidation catalytic converter device can be of single-strand or twin-strand design.

The second and/or third oxidation catalytic converter unit can be dispensed with if the device for particle removal has a suitable catalytic coating of the particle filter, or the particle filters.

At least one temperature sensor can be provided upstream of the first oxidation catalytic converter unit and/or downstream of the unit for generating a heat tone and/or upstream of the NOx catalytic converter device and/or downstream of the NOx catalytic converter device and/or upstream of the second oxidation catalytic converter device and/or upstream of the device for particle removal and/or downstream of the device for particle removal.

An ammonia sensor can expediently be provided downstream of the NOx catalytic converter device, by means of which ammonia sensor it is possible to provide improved regulation of the addition of reducing agent, in particular aqueous urea solution, to the NOx catalytic converter device.

A NOx sensor can advantageously be provided downstream of the NOx catalytic converter device and/or upstream of the first oxidation catalytic converter unit. The arrangement downstream of the NOx catalytic converter device permits improved regulation of the addition of the reducing agent and/or of any on-board diagnosis (OBD). On-board diagnosis means the monitoring of exhaust-gas-relevant components and systems during driving, detecting malfunctions and for example displaying said malfunctions by means of a warning lamp and transferring said malfunctions to a scanning tool in the workshop. Furthermore, it is intended to protect vulnerable components such as catalytic converters. The arrangement upstream of the first oxidation catalytic converter device can serve for quantifying untreated emissions and the resulting demands on the NOx catalytic converter device.

In each case one pressure sensor can be provided upstream and downstream of the device for particle removal. It is thereby possible to provide an estimation of the soot and/or ash content in the device for particle removal and therefore to control the fuel metering apparatus.

The method according to the invention for exhaust-gas purification provides that, in addition to the device for particle removal, the NOx catalytic converter device can, according to demand, be operated independently of the exhaust-gas temperature of the internal combustion engine.

The unit for generating a heat tone to control the temperature of the NOx catalytic converter device can preferably be activated if regulated operation of a metering of reducing agent into the NOx catalytic converter device and/or regulated operation of the device for actively raising an exhaust-gas temperature is required and the NOx catalytic converter device and/or one or more oxidation catalytic converter(s) of the device for actively raising an exhaust-gas temperature are/is outside a respective preferred temperature range.

Furthermore, regulated operation of the device for actively raising an exhaust-gas temperature takes place if the device for particle removal exceeds a pressure loss increase and/or a temperature to be expected in the device for particle removal when the device for raising the exhaust-gas temperature is active exceeds a limit value, and/or a loading of the device for particle removal exceeds an admissible limit value.

When the device for raising an exhaust-gas temperature is active, a mean temperature of the device for particle removal can expediently be between 550° C. and 850° C., preferably between 600° C. and 800° C.

In regulated operation of the device for raising an exhaust-gas temperature, the temperature of its oxidation catalytic converter device can advantageously be higher than 250° C., preferably higher than 300° C.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, in which:

FIG. 1 is a first embodiment of the exhaust-gas aftertreatment system with single-strand exhaust-gas guidance,

FIG. 2 is a further embodiment of the exhaust-gas aftertreatment system with single-strand exhaust-gas guidance,

FIG. 3 is a further embodiment of the exhaust-gas aftertreatment system with partially twin-strand exhaust-gas guidance,

FIG. 4 is a further embodiment of the exhaust-gas aftertreatment system with partially twin-strand exhaust-gas guidance,

FIG. 5 is a first embodiment of a preferred exhaust-gas aftertreatment system with partially twin-strand exhaust-gas guidance and a single-strand outlet-side oxidation catalytic converter.

DETAILED DESCRIPTION OF THE DRAWINGS

In the figures, functionally equivalent components are denoted by the same reference symbols.

A first embodiment of the invention is shown in FIG. 1. In a first embodiment, a preferred exhaust-gas aftertreatment system 10 of an internal combustion engine (not illustrated) has, in series in the flow direction 70 of the exhaust gas, firstly a first oxidation catalytic converter device 20, a NOx catalytic converter device 30 for the denitrogenization of the exhaust gas, a device 40 for actively raising an exhaust-gas temperature, a device 50 for particle removal, and a third oxidation catalytic converter device 60.

Between the two first components, the first oxidation catalytic converter device 20 and the NOx catalytic converter device 30 for the denitrogenization of the exhaust gas, an infusive unit 22 for generating a heat tone to control the temperature of the NOx catalytic converter device 30 introduces heat. The energy input by the infusive unit 22 can take place by means of the combustion of a liquid and/or gaseous substance, and/or by radiation and/or by means of electrical energy and/or by means of a heat exchanger and/or by means of a hot gas flow. The unit 22 serves to set a temperature expedient for the NOx reduction in the NOx catalytic converter device 30 and to provide a temperature, which is suitable for an active regeneration of the unit 50 for particle removal, of the device 40 for actively raising the exhaust-gas temperature with the oxidation catalytic converter 42.

A further infusive unit 36 conducts a reducing agent, for example a precursor of a reducing agent, for example an aqueous urea solution, hydrocarbon or the like, to the SCR catalytic converter 32. In the first oxidation catalytic converter 20, unburned hydrocarbons, carbon monoxide and particles are oxidized as completely as possible to form nitrogen monoxide (NO) and partially to form nitrogen dioxide (NO2). The unit 36 sprays the reducing agent, for example urea solution, into the hot exhaust-gas flow whose temperature is suitably controlled by means of the unit 22, where said reducing agent is hydrolyzed to form ammonia (NH3) and carbon dioxide (CO2). In the selective reduction itself, the NH3 then reacts with the NO/NO2 mixture to form nitrogen and water. The reaction takes place on a catalyst which is conventionally composed of transition metal compounds on a ceramic substrate. Unused NH3 proportions can be converted in a downstream second oxidation catalytic converter 42 of a unit 40 for actively raising an exhaust-gas temperature.

The unit 40 for actively raising the exhaust-gas temperature comprises, in addition to the oxidation catalytic converter 42, a fuel metering apparatus 46, by means of which fuel can be metered according to demand into the exhaust-gas duct in order to set a suitable temperature in the oxidation catalytic converter 42 by means of the oxidation of said fuel. The resulting heat tone can be utilized for the active, regulated regeneration of the particle filter 52 of the subsequent, downstream device 50 for particle removal, without it being necessary for the internal combustion engine to be adapted in terms of its present operating conditions for a regeneration phase of said type. The oxidation catalytic converter 42 can be replaced or supplemented by a suitable catalytic coating of the particle filter 52.

The particle filter 52 is preferably composed of a unit for retaining the soot particles contained in the exhaust gas, which soot particles can be burned off by means of the unit 40 in the event of a corresponding exhaust-gas temperature increase. The particle filter 52 can be formed with or without a catalytic converter coating.

The third oxidation catalytic converter device 60 with its oxidation catalytic converter 62 serves to oxidize components in the exhaust gas which are not fully oxidized during operation of the unit 40 for actively increasing an exhaust-gas temperature. The oxidation catalytic converter device 60 can be replaced or supplemented by a suitable catalytic converter coating of the particle filter 52.

Not illustrated are any present, suitably positioned temperature sensors, ammonia sensors, NOx sensors, pressure sensors.

It is thus possible for at least one temperature sensor to be provided upstream of the first oxidation catalytic converter unit 20 and/or downstream of the unit 22 for generating a heat tone and/or upstream of the NOx catalytic converter device 30 and/or downstream of the NOx catalytic converter device 30 and/or upstream of the device 40 for actively raising the exhaust-gas temperature and/or upstream of the device 50 for particle removal and/or downstream of the device 50 for particle removal. The placement upstream of the first oxidation catalytic converter unit 20 permits an estimation of the NO2 proportion in the exhaust gas at the outlet of the oxidation catalytic converter unit 20. By means of the placement downstream of the unit 22 for generating a heat tone, it is possible to check the functionality of the latter, and if appropriate detect a malfunction. The placement upstream of the NOx catalytic converter device 30 and/or downstream of the NOx catalytic converter device 30 permits regulation of the addition of the reducing agent by means of the unit 36.

The placement of an ammonia sensor downstream of the NOx catalytic converter device 30 permits improved regulation of the addition of the reducing agent by means of the unit 36.

The placement of a NOx sensor downstream of the NOx catalytic converter device 30 permits improved regulation of the addition of the reducing agent by means of the unit 36 and/or improved diagnosis (on-board diagnosis). The placement upstream of the first oxidation catalytic converter device 20 permits quantification of untreated emissions, and of the resulting demands on the subsystem of the NOx catalytic converter device 30.

By placing in each case one pressure sensor upstream and downstream of the device 50 for particle removal, it is possible for an estimation of the soot or ash content in the particle filter 52, and therefore a regulation of the fuel metering apparatus 46, to take place.

Also provided is a control unit (not illustrated in the drawing) which is connected to sensors and which serves for regulating the unit 22 for generating a heat tone, the unit 36 for metering a reducing agent, and the fuel metering apparatus 46, and for communicating with a conventional engine control unit which controls the internal combustion engine.

FIG. 2 shows an alternative embodiment of the exhaust-gas aftertreatment system 10 in FIG. 1, in which the unit 22 for generating a heat tone is arranged upstream of the first oxidation catalytic converter device 20. The arrangement of the components is otherwise identical. The unit 22 can, in the following exemplary embodiments, be arranged upstream or downstream of the first oxidation catalytic converter device 20.

The exemplary embodiment of FIG. 3 illustrates a further preferred variant of the exhaust-gas aftertreatment system 10, in which the NOx catalytic converter device 30, the unit 40 for actively raising the exhaust-gas temperature, the device 50 for particle removal and the third oxidation catalytic converter device 60 are each of twin-strand design. The functionalities, embodiments and alternatives explained for the single-strand embodiment of the individual components apply analogously to the components of the twin-strand designs.

The first oxidation catalytic converter device 20 is arranged, in a single-strand design, upstream of the strand division. The unit 36, by means of which the reducing agent is metered, is common to the two SCR catalytic converters 32, 34.

Here, the NOx catalytic converter device 30 comprises two SCR catalytic converters 32, 34 which are connected in parallel in terms of flow. The device 40 for actively raising the exhaust-gas temperature comprises two oxidation catalytic converters 42, 44 which are connected in parallel in terms of flow, the device 50 for particle removal comprises two particle filters 52, 54 which are connected in parallel in terms of flow, and the oxidation catalytic converter device 60 comprises two oxidation catalytic converters 62, 64 which are connected in parallel in terms of flow.

Arranged at the inlet of the first oxidation catalytic converter device 20, as in the exemplary embodiment of FIG. 2, is the infusive unit 22 for supplying a heat tone, and the unit 36 for supplying reducing agent for the SCR catalytic converters 32, 34 of the NOx catalytic converter device 30 is arranged between the first oxidation catalytic converter device 20 and upstream of a strand division 72 upstream of the NOx catalytic converter device 30.

The fuel metering apparatus 46 for the two oxidation catalytic converters 42, 44 of the unit 40 for actively raising the exhaust-gas temperature is arranged in the strand confluence 74 downstream of the NOx catalytic converter device 30.

Downstream of the third oxidation catalytic converter device 60, the twin-strand exhaust-gas guidance of the NOx catalytic converter device 30, of the unit 40 for actively raising the exhaust-gas temperature and of the third oxidation catalytic converter device 60 opens out into a strand confluence 76.

FIG. 4 shows an embodiment of the exhaust-gas aftertreatment system 10 corresponding to FIG. 3, with the difference that the fuel metering apparatus 46 is provided separately in each strand for the respective oxidation catalytic converter 42, 44 of the unit 40 for actively raising the exhaust-gas temperature. Said twin design of the fuel metering apparatus 46 permits regulation of the temperature downstream of the strand confluence 74.

FIG. 5 shows a further variant of the exhaust-gas aftertreatment system 10 according to the invention, which corresponds largely to the twin-strand design in FIG. 4. In the embodiment shown, however, the third oxidation catalytic converter unit 60 is now of single-strand design downstream of a strand confluence 76.

For all of the twin-strand arrangements shown in the exemplary embodiments, it is also possible to dispense with a strand confluence 76 downstream of the third oxidation catalytic converter unit 60; if appropriate, it is also possible to dispense with a strand confluence 74 downstream of the NOx catalytic converter unit 30.

For regulated operation of the unit 36 for supplying reducing agent, an SCR catalytic converter temperature of at least 150° C., preferably at least 200° C. and a maximum of 500° C., preferably the maximum of 500° C., is preferable. The unit 36 is active when the untreated NOx emissions of the internal combustion engine are higher than the statutorily demanded limit value.

For the operation of the NOx reduction arrangement, a temperature of the first oxidation catalytic converter device 20 of at least 120° C., preferably of at least 150° C., and an SCR catalytic converter temperature of at least 180° C., preferably at least 200° C., are preferable.

For the regulated operation of the fuel metering apparatus 46, a temperature of the second oxidation catalytic converter 42 or of the second oxidation catalytic converters 42, 44 of over 280° C., preferably over 300° C. is preferable. The fuel metering apparatus is active if the loading of the unit 50 for particle removal with soot and/or ash exceeds a threshold value of the resulting pressure loss increase across the particle filter(s) 52, 54, for example in the range from 50 to 200 mbar, and/or if the temperature to be expected in the particle filter(s) 52, 54 exceeds a certain threshold value, for example in the range from 700° C. to 800° C. and/or if the loading of the particle filter(s) 52, 54 exceeds a certain threshold value, for example 2 g/l to 15 g/l.

During operation of the fuel metering apparatus 46, a mean temperature of the particle filter(s) 52, 54 of at least 550° C., preferably of at least 600° C., and a maximum of 850° C., preferably a maximum of 800° C., is preferable.

The unit 22 for generating a heat tone is expediently designed so as to permit operation over the entire state space of the engine system variables. The unit 22 is activated if regulated operation of the unit 36 for metering reducing agent and/or regulated operation of the fuel metering apparatus 46 is required, and the SCR catalytic converter temperature or the temperature of the oxidation catalytic converter 42 or of the oxidation catalytic converters 42, 44 are not in the respective preferred range.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims

1-24. (canceled)

25. An exhaust-gas aftertreatment system having, arranged in series in the flow direction of exhaust gas of an internal combustion engine, and traversed by exhaust gas, a first oxidation catalytic converter device, a NOx catalytic converter device for the denitrogenization of the exhaust gas, a device for actively raising an exhaust-gas temperature with at least one second oxidation catalytic converter device, and a device for particle removal, wherein a respective operating temperature of the NOx catalytic converter device and of the device for particle removal can be set independently of an exhaust-gas temperature at an outlet of the internal combustion engine.

26. The exhaust-gas aftertreatment system of claim 25, further comprising a unit for generating a heat tone to control the temperature of the NOx catalytic converter device.

27. The exhaust-gas aftertreatment system of claim 26, wherein the unit for generating a heat tone is arranged upstream of the NOx catalytic converter device and downstream of the first oxidation catalytic converter device.

28. The exhaust-gas aftertreatment system of claim 26, wherein the unit for generating a heat tone is arranged upstream of the first oxidation catalytic converter device.

29. The exhaust-gas aftertreatment system of claim 25, wherein the device for actively raising an exhaust-gas temperature comprises at least one fuel metering apparatus upstream of the second oxidation catalytic converter device.

30. The exhaust-gas aftertreatment system of claim 29, wherein the oxidation catalytic converter device has a twin-strand configuration.

31. The exhaust-gas aftertreatment system of claim 30, wherein a fuel metering apparatus is provided separately for each oxidation catalytic converter.

32. The exhaust-gas aftertreatment system of claim 30, wherein a single fuel metering apparatus supplies all of the oxidation catalytic converters of the device for actively raising an exhaust-gas temperature together.

33. The exhaust-gas aftertreatment system of claim 25, wherein the NOx catalytic converter device has a twin-strand configuration.

34. The exhaust-gas aftertreatment system of claim 25, wherein the device for particle removal has at least one particle filter.

35. The exhaust-gas aftertreatment system of claim 34, wherein the device for particle removal has a twin-strand configuration.

36. The exhaust-gas aftertreatment system of claim 35, wherein the oxidation catalytic converter of the device for actively raising the exhaust-gas temperature or the first oxidation catalytic converter is integrated into the device for particle removal.

37. The exhaust-gas aftertreatment system of claim 36, wherein a third oxidation catalytic converter device is provided downstream of the device for particle removal.

38. The exhaust-gas aftertreatment device of claim 37, wherein the third oxidation catalytic converter device has a single-strand configuration.

39. The exhaust-gas aftertreatment device of claim 37, wherein the third oxidation catalytic converter device has a twin-strand configuration.

40. The exhaust-gas aftertreatment device of claim 25 wherein at least one temperature sensor is provided upstream of the first oxidation catalytic converter unit or downstream of the unit for generating a heat tone or upstream of the NOx catalytic converter device or downstream of the NOx catalytic converter device or upstream of the device for actively raising the exhaust-gas temperature or upstream of the device for particle removal or downstream of the device for particle removal.

41. The exhaust-gas aftertreatment device of claim 25, wherein an ammonia sensor is provided downstream of the NOx catalytic converter device.

42. The exhaust-gas aftertreatment device of claim 25, wherein a NOx sensor is provided downstream of the NOx catalytic converter device or upstream of the first oxidation catalytic converter unit.

43. The exhaust-gas aftertreatment device of claim 25, wherein one pressure sensor is arranged upstream and downstream of the device for particle removal.

44. A method for exhaust-gas purification in an exhaust-gas aftertreatment system having, arranged in series in the flow direction of exhaust gas of an internal combustion engine, a first oxidation catalytic converter device, a NOx catalytic converter device for the denitrogenization of the exhaust gas, a device for actively raising an exhaust-gas temperature with at least one second oxidation catalytic converter device, and a device for particle removal, said method comprising the steps of:

operating the NOx catalytic converter device and the device for particle removal independently of the exhaust-gas temperature at an outlet of the internal combustion engine and according to demand.

45. The method of claim 44, further comprising the steps of activating the unit for generating a heat tone to control the temperature of the NOx catalytic converter device if regulated operation of a metering of reducing agent into the NOx catalytic converter device or regulated operation of the device for actively raising an exhaust-gas temperature is required and the NOx catalytic converter device or one or more oxidation catalytic converters of the device for actively raising an exhaust-gas temperature are outside a respective preferred temperature range.

46. The method as claimed in claim 44, further comprising activating a regulated operation of the device for actively raising an exhaust-gas temperature if the device for particle removal exceeds a pressure loss increase or a temperature to be expected in the device for particle removal when the device for raising the exhaust-gas temperature is active exceeds a limit value, or if a loading of the device for particle removal exceeds an admissible limit value.

47. The method as claimed in claim 45, further comprising activating regulated operation of the device for actively raising an exhaust-gas temperature if the device for particle removal exceeds a pressure loss increase or a temperature to be expected in the device for particle removal when the device for raising the exhaust-gas temperature is active exceeds a limit value, or a loading of the device for particle removal exceeds an admissible limit value.

48. The method as claimed in claim 44, further comprising

activating the unit for generating a heat tone to control the temperature of the NOx catalytic converter device if regulated operation of a metering of reducing agent into the NOx catalytic converter device or regulated operation of the device for actively raising an exhaust-gas temperature is required and the NOx catalytic converter device or one or more oxidation catalytic converters of the device for actively raising an exhaust-gas temperature are outside a respective preferred temperature range;

and activating regulated operation of the device for actively raising an exhaust-gas temperature if the device for particle removal exceeds a pressure loss increase or a temperature to be expected in the device for particle removal when the device for raising the exhaust-gas temperature is active exceeds a limit value, or a loading of the device for particle removal exceeds an admissible limit value;

wherein when the device for raising an exhaust-gas temperature is active, a mean temperature of the device for particle removal is between 550° C. and 850° C., preferably between 600° C. and 800° C.

49. The method as claimed in claim 44, wherein in regulated operation of the device for raising an exhaust-gas temperature, the temperature of its oxidation catalytic converter device is higher than 250° C., preferably higher than 300° C.