WO2010123411A1

WO2010123411A1 - Method and arrangement for recirculation of exhaust gases of a combustion engine

Info

Publication number: WO2010123411A1
Application number: PCT/SE2009/000210
Authority: WO
Inventors: Andreas Hinz; Bert-Inge Bertilsson
Original assignee: Volvo Lastvagnar Ab
Priority date: 2009-04-23
Filing date: 2009-04-23
Publication date: 2010-10-28

Abstract

The invention relates to a method and an arrangement for keeping an internal surface of an exhaust recirculation (EGR) cooler of a turbo charged combustion engine substantially free from residuals. A return line (3) is connected with the exhaust line (2) upstream of the turbine (54). In the return line a first valve means (S1) is arranged upstream of a first cooler (82). A bypass line (4) connects a second valve means (S2) in the inlet line (1) with the return line (3) between the first cooler (82) and the first valve means (S1). The actual operation condition of the combustion engine (10) for switching the first valve means (S1) and/or the second valve means (S2) is determined by monitoring an efficiency level of the recirculation of exhaust gases and an exhaust gas after treatment system (30), placed downstream of the turbine (54), in regard to NO_x and particular reduction in given engine map points.

Description

D E S C R I P T I O N

Method and Arrangement for Recirculation of Exhaust Gases of a Combustion Engine

TECHNICAL FIELD

The invention relates to a method for recirculation of exhaust gases of a combustion engine with a turbocharger and an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger according to the preambles of the independent claims.

BACKGROUND OF THE INVENTION

The recent years have shown a trend towards stricter legislation concerning emission levels from vehicles. For gasoline powered vehicles, the three-way catalyst has made it possible to run an engine practically without unwanted emissions.

For diesel powered vehicles or compression ignition (Cl) engines, the emission problems are, however, far from solved. Cl engines have inherent high emission levels for nitric oxides NOx, such as NO and NO₂, and particulate matter, such as soot, whereas the emission levels of carbon monoxide (CO) and hydrocarbons (HC) are low. Moreover, it is fairly easy to reduce the already low emission of HC and CO from a Cl engine.

One other inherent feature of Cl engines is the low fuel consumption. There is, however, a well-known trade-off between fuel consumption and emissions: an engine tuned for maximum fuel economy will emit large amounts of NOx and small amounts of particulates, whereas an engine tuned for low emissions of NOx will get high fuel consumption and high emissions of particulates.

Another well known phenomenon is the connection between engine speed and particulate emissions. Lowering of the engine speed usually leads to a reduction of the particulate emissions, simply due to the fact that there will be more time to combust the particulates in the combustion chamber. Today, it is more or less an industry standard to provide the engine exhaust system with some kind of Exhaust gas After Treatment System (EATS), e.g. a particulate filter, a three-way catalyst (for gasoline engines), a SCR (SCR = Selective Catalytic Reduction) catalyst or a lean NOx trap catalyst.

A common method to improve the performance and fuel consumption of a Cl engine is to provide the engine with a turbocharger. The function of the turbocharger is to recover some of the energy present in the exhaust gases in a turbine connected to a compressor used to compress air to be let into the engine cylinders. This leads to more air being inducted into the cylinders during the intake stroke, which in turn leads to the engine being able to provide more power per swept engine volume.

Moreover, particulate emissions depend heavily on injection pressure, i.e. the pressure with which the diesel fuel is injected into the combustion chambers. The higher the injection pressure, the lower the particulate emissions.

Another known technique to reduce the content of NOx in the exhaust gases is known as EGR (exhaust gas recirculation). In an EGR system part of the exhaust gases from the combustion process in a combustion engine are lead back via a return line to an inlet for supplying air to the combustion engine. A mixture of air and exhaust gases is thus applied via the inlet line to the engine's cylinders in which the combustion takes place. Adding exhaust gases to the air causes a lower combustion temperature which results in a reduced content of NOx in the exhaust gases. This technique can be used for both Otto engines and diesel engines.

WO 2004/067945 A1 describes a method and an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle. The described arrangement comprises an EGR system with a return line, an EGR valve and an exhaust gas cooler used to lower the temperature of the exhaust gases prior to lead them back from an exhaust line towards cylinders of the combustion engine in order to reduce NOx emissions. The EGR valve is settable to provide a desired amount of EGR via the return line. An electrical control unit is adapted to control the EGR valve on basis of information concerning a load of the combustion engine. In case of supercharged combustion engines, the exhaust gases are mixed with air of an inlet line which is at a relative high pressure. When a rapid increase in engine load is required, the EGR valve is closed to increase the flow of fresh air to the engine so that the required engine load can be reached quickly without any increase in soot emissions. A rapid reduction in engine load also requires closure of the EGR valve. The EGR valve closes to maintain a charge pressure of the air as long as possible so that it can be used for any possible subsequent rapid increase in engine load. In course of time, soot deposits from the exhaust gases inevitably build up on inside surfaces of the EGR cooler, thereby impairing the heat transfer capacity of the EGR cooler and at the same time increasing a resistance to the flow of exhaust gases through the EGR cooler. Insufficient cooling of the exhaust gases leads to impaired engine performance. Therefore in the described arrangement the EGR valve is kept open on at least some occasions of situations in which the exhaust gases form the combustion engine are at a pressure which is lower than the pressure in the inlet line. With the EGR valve open, the difference in pressure between the compressed air and the exhaust gases results in a flow of fresh air from the inlet line being led back to the return line. This flow of fresh air also passes through the EGR cooler and cleans soot deposits off the internal surfaces of the EGR cooler. But the pressure difference is often relatively limited, resulting in a relatively small air flow which is not sufficient to clean the EGR cooler effectively.

WO 2007/011299 A1 describes a method and an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle. The described arrangement comprises an EGR system with a return line, an EGR valve and an exhaust gas cooler used to lower the temperature of the exhaust gases prior to lead them back from an exhaust line towards cylinders of the combustion engine in order to reduce NOx emissions. The EGR valve is arranged in the return line upstream of the EGR cooler with respect to the intended direction of exhaust gas flow in the return line. Additionally the arrangement comprises a valve means arranged in the inlet line and a bypass line extending from the valve means to a connection point to the return line, which connection point is situated upstream from the EGR cooler with respect to the intended direction of exhaust gas flow in the return line. A control unit is adapted to place the valve means in certain situations in a cleaning position so that at least part of the compressed air in an inlet line is led via the valve means and the bypass line to the return line, whereby the air is led in such direction that it flows through the EGR cooler before it is led to the intake of the combustion engine. The described arrangement makes the cleaning independent from the pressure ration between the inlet line and the exhaust gas pressure but the accumulated residuals in the EGR cooler, which may contain e.g. sulphates, soot, particulates and sludge, are led through the combustion engine.

WO 2007/011300 A1 describes a method and an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle. The described arrangement comprises an EGR system with a return line, a valve device and an exhaust gas cooler used to lower the temperature of the exhaust gases prior to lead them back from an exhaust line towards cylinders of the combustion engine in order to reduce NOx emissions. The valve device is arranged in the return line upstream of the EGR cooler with respect to the intended direction of exhaust gas flow in the return line. A control unit is adapted to place the valve device in certain situations in a cleaning position in which a portion of the return line which comprises the EGR cooler is connected to surrounding air, so that compressed air from the inlet line flows through the portion of the return line and the EGR cooler before it is led to surrounding air by means of the valve device. The described arrangement makes the cleaning independent from the pressure ration between the inlet line and the exhaust gas pressure but is not emission neutral considering that the accumulated residuals in the EGR cooler may contain e.g. sulphates, soot, particulates and sludge.

WO 2007/062682 A1 describes a method and an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle. The described arrangement comprises an EGR system with a return line, an EGR valve and an exhaust gas cooler used to lower the temperature of the exhaust gases prior to lead them back from an exhaust line towards cylinders of the combustion engine in order to reduce NOx emissions. The EGR valve is arranged in the return line upstream of the EGR cooler with respect to the intended direction of exhaust gas flow in the return line. Additionally the arrangement comprises a fresh air injection line connecting the EGR cooler with a source of fresh air under pressure. A valve means arranged in the fresh air injection line can be placed in certain situations in a cleaning position so that fresh air is led from the source of fresh air under pressure via the valve means and the injection line to the return line, whereby the air is led in such direction that it flows through the EGR cooler before it is led to the intake of the combustion engine. The described arrangement makes the cleaning also independent from the pressure ration between the inlet line and the exhaust gas pressure but the accumulated residuals in the EGR cooler, which may contain e.g. sulphates, soot, particulates and sludge, are led through the combustion engine.

WO 2007/120126 A2 describes an engine with emissions control and a method of controlling engine emissions. The described engine with an emissions control arrangement includes an engine including an intake and an exhaust system, an EGR system comprising a conduit between the exhaust system and the intake and an EGR controller between the exhaust system and the conduit. The EGR controller is adapted to control EGR flow from the exhaust system to the intake. A reduction agent introduction system is adapted to introduce a reduction agent into the exhaust system. A controller is arranged to adjust the EGR flow and the reduction agent introduction as function of each other.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved method for recirculation of exhaust gases of a combustion engine with a turbocharger wherein an internal surface of an exhaust gas recirculation cooler is kept substantially free from residuals of the exhaust gases of the combustion engine in an emission neutral manner. Another object is to provide an improved arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger.

The objects are achieved by the features of the independent claims. The other claims and the description disclose advantageous embodiments of the invention.

According to a first aspect of the invention a method is proposed for recirculation of exhaust gases (EGR) of a combustion engine with a turbocharger, wherein the combustion engine comprises a turbine placed in an exhaust line and adapted to be driven by exhaust gases from the combustion engine, a compressor adapted to be driven by the turbine in order to supply compressed air to an inlet line, which is adapted to lead compressed air to an intake of the combustion engine, a return line adapted to recirculate exhaust gases from the exhaust line connected with an exhaust outlet of the combustion engine to the inlet line, wherein the return line is connected with the exhaust line upstream of the turbine of the turbocharger unit with respect to the intended direction of the exhaust gas flow in the exhaust line, a first cooler arranged in the return line in order to cool the exhaust gases, a first valve means arranged in the return line upstream of the first cooler with respect to the intended direction of exhaust gas flow in the return line, a second valve means arranged in the inlet line, and a bypass line connecting the second valve means with the return line upstream of the first cooler and downstream of the first valve means with respect to the intended direction of the exhaust gas flow in the return line, wherein the first valve means and/or the second valve means are switched to given positions in accordance with an actual operation condition of the combustion engine, wherein the first valve means allows a fluid flow in either way between the inlet line and the exhaust line passing the first cooler in an open position and prevents such a fluid flow in a closed position, and wherein the second valve means allows at least part of the compressed air flow in the inlet line to be passed to the return line in an open position and prevents such a compressed air flow in a closed position. An exhaust gas aftertreatment system comprising a NOx reduction catalytic converter and a particulate filter is used for reducing emissions of the internal combustion engine and arranged in the exhaust line downstream of the turbine of the turbocharger with respect to the intended direction of exhaust gas flow in the exhaust line, wherein the actual operation condition of the combustion engine for switching the first valve means and/or the second valve means is determined by monitoring an efficiency level of the recirculation of exhaust gases and the exhaust gas aftertreatment system in regard to NOx and particular emission reduction in given engine map points.

During operation of the engine equipped with an EGR (exhaust gas recirculation) the first cooler needs to be frequently cleaned due to contamination of the cooler with soot, sludge, etc. decreasing the heat transfer efficiency of the first cooler and thus impacting detrimental on the engine performance. The cleaning procedure can be performed emission neutral with high efficiency in regard to fuel consumption and required duration by using the SCR exhaust gas aftertreatment system and by monitoring the efficiency level of the recirculation of exhaust gases and the SCR exhaust gas aftertreatment system to recognize at least one operation condition at which the cleaning of the first cooler can be performed emission neutral. At the least one operation condition the NOx emission is within the legislation limit. If there are any increased soot and/or particulate emission levels in the exhaust gas due to the cleaning process of the first cooler it will be taken care of in the particulate filter comprised in the exhaust gas aftertreatment system. Thus, the cleaning procedure of the first cooler is performed in case of sufficient and/or optimum SCR exhaust gas aftertreatment system operation efficiency securing NOx control in a tailpipe position. Compared to known cleaning processes, where the first cooler is cleaned at engine transients and which are not very effective due to their extreme short duration time, embodiments of the invention offer a highly effective and efficient cleaning procedure for the first cooler. For example, transients do not exist if the vehicle is running at constant speed on a highway with 80 km/h, so there is no chance in previous methods to clean the first cooler if a loss in performance or an in emission compliance is occurring. Transients during gear change can be very frequent, but are not longer in duration as 10^th of a second or at most a second, which is not sufficient to clean the first cooler. Furthermore, the invention can be used to control the temperature of the exhaust gases especially during particulate filter regeneration events, prohibiting a temperature increase above a desired temperature level, which could increase ageing of the components comprised in the exhaust gas aftertreatment system. Favourably, in an operation mode where the EGR is used the first valve means is switched to an open position, in which at least part of the exhaust gases of the exhaust line are led through the return line and the first cooler to a mixer unit, in which the recirculated exhaust gases are mixed with compressed air of the inlet line, wherein the mixture is led to the intake of the combustion engine, and the second valve means to the position in which all of the compressed air in the inlet line is led to a second cooler arranged in the inlet line upstream of the mixer unit with respect to the intended direction of the compressed air flow in the inlet line in a first operation condition of the combustion engine. During operation of the engine, sensors controlling the EGR and the exhaust gas aftertreatment system diagnose the efficiency level of the EGR and exhaust gas aftertreatment system in regard to NOx and particulate emission reduction in a given engine map point as well as the EGR-system efficiency in terms of heat transfer.

Preferably the first valve means is switched to the closed position, in which no exhaust gases of the exhaust line are recirculated to the inlet line, and the second valve means is switched to the position, in which at least part of the compressed air from the inlet line is led through the first cooler to clean a heat exchange area inside the first cooler in a at least one operation condition of the combustion engine, wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine, and soot and/or particulate emissions passing the combustion chamber of the engine are reduced to lower emission levels in the exhaust gas aftertreatment system.

Additionally or alternatively a source of fresh air under pressure is connected with the return line upstream of the first cooler and downstream of the first valve means with respect of the exhaust gas flow in the return line using a purge line and a third valve means arranged in the purge line, wherein the third valve means in an open position allows an air flow in the purge line and prevents such an air flow in a closed position. The first valve means is switched to the closed position, in which no exhaust gases of the exhaust line are recirculated to the inlet line, and the third valve means is switched to the position, in which fresh air under pressure from the purge line is led through the first cooler to clean a heat exchange area inside the first cooler in a at least one operation condition of the combustion engine, wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine, and soot and/or particulate emissions passing the combustion chamber of the engine are reduced to lower emission levels in the exhaust gas aftertreatment system. The somewhat higher inlet air temperature caused by the bypass air not passing the second cooler and its detrimental effect on engine performance is off-set by the non-EGR modus the engine is operated in, because it is known that non-EGR engines are more efficient in performance than EGR engines. This enables the first cooler to be cleaned frequently and with sufficient duration of the cleaning event and independently from engine operation and emission compliance, which is achieved by the emission conversion efficiency of the exhaust gas aftertreatment system. Thus, the first cooler cleaning event is not any longer limited to transients, e.g. gearshifts, that impact on driveability or emergency first cooler cleaning events that impact on NOx emission compliance. Preferably the at least one operation condition to clean the first cooler is recognized, when the SCR exhaust gas aftertreatment system is working with high efficiency for NOx conversion. The NOx conversion is determined as function of temperature and/or exhaust mass flow and/or NOx content in the exhaust gas, for example.

In an embodiment of the method an exhaust gas temperature is determined at an inlet of the SCR exhaust gas aftertreatment system, wherein a first operation condition to clean the first cooler is recognized, when the exhaust gas temperature at the inlet of the SCR exhaust gas aftertreatment system lies in a given temperature range. The given temperature ranges between about 150⁰C to about 45O⁰C, for example.

In a further embodiment of the method the nitric oxides (NOx) emission level is determined at an outlet of the SCR exhaust gas aftertreatment system, and the value of the nitric oxides (NOx) emission level is compared to a map value, wherein a second operation condition to clean the first cooler is recognized, when the determined value of the nitric oxides (NOx) emission level is below a corresponding first threshold value in the map.

In yet a further embodiment of the method the nitric oxides (NOx) emission level at the outlet of the engine and at the outlet of the exhaust gas aftertreatment system are determined, and the nitric oxides (NOx) emission conversion over the exhaust gas aftertreatment system is calculated, wherein a third operation condition to clean the first cooler is recognized, when the determined nitric oxides (NOx) emission conversion value is above a corresponding second threshold value. The second threshold value for the nitric oxides emission conversion is at least 70%, for example.

Preferably, the cleaning procedure of the first cooler is started, when a measured contamination of the first cooler exceeds a given third threshold value. In a further embodiment of the method the second valve means is switched to the position, in which at least part of the compressed air from the inlet line is led to return line, and the first valve means is switched to an open position, in which at least part of the compressed air in the return line is led to the exhaust line, in an operation condition of the combustion engine, where the compressed air from the return line is mixed with the exhaust gases in the exhaust line. Additionally or alternatively the third valve means is switched to the position, in which fresh air under pressure from the source is led through the purge line to the return line, and the first valve means is switched to an open position, in which at least part of the air under pressure in the return line is led to the exhaust line, in the operation condition of the combustion engine, where the compressed air from the return line is mixed with the exhaust gases in the exhaust line. This operation condition is used to cool the exhaust gases to prevent ageing of the components comprised in the exhaust gas aftertreatment system due to high temperature of the exhaust gases. The fourth operating condition of the combustion engine is recognized, for example, when the determined exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system exceeds a given fourth threshold value. The fourth threshold value of the temperature is about 580⁰C, for example. Similar, the fourth operating condition of the combustion engine is also recognized, for example, when the determined exhaust gas temperature at an inlet of the particular trap exhaust gas aftertreatment system exceeds a given fifth threshold value. The fifth threshold value of the temperature is about 700⁰C, for example.

According to another aspect of the invention an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle for performing the above described method, comprises a turbine placed in an exhaust line and adapted to be driven by exhaust gases from the combustion engine, a compressor adapted to be driven by the turbine in order to supply compressed air to an inlet line, which is adapted to lead compressed air to an intake of the combustion engine, a return line adapted to recirculate exhaust gases from the exhaust line connected with an exhaust outlet of the combustion engine to the inlet line, wherein the return line is connected with the exhaust line upstream of the turbine of the turbocharger unit with respect to the intended direction of the exhaust gas flow in the exhaust line, a first cooler arranged in the return line in order to cool the exhaust gases, a first valve means arranged in the return line upstream of the first cooler with respect to the intended direction of exhaust gas flow in the return line, a second valve means arranged in the inlet line, a bypass line connecting the second valve means with the return line upstream of the first cooler and downstream of the first valve means with respect to the intended direction of the exhaust gas flow in the return line, and a control unit, which is adapted to switch the first valve means and/or the second valve means to given positions in accordance with an actual operation condition of the combustion engine, wherein the first valve means allows a fluid flow in either way between the inlet line and the exhaust line passing the first cooler in an open position and prevents such a fluid flow in a closed position, and wherein the second valve means allows at least part of the compressed air flow in the inlet line to be passed to the return line in an open position, and prevents such a compressed air flow in a closed position. An exhaust gas aftertreatment system for reducing emissions of the internal combustion engine is arranged in the exhaust line downstream of the turbine of the turbocharger with respect to the intended direction of exhaust gas flow in the exhaust line, wherein the control unit is determining the actual operation condition of the combustion engine for switching the first valve means and/or the second valve means by monitoring an efficiency level of the recirculation of exhaust gases and the exhaust gas aftertreatment system in regard to NOx and particular emission reduction in given engine map points.

Favourably, the control unit is switching the first valve means to an open position, in which at least part of the exhaust gases of the exhaust line are led through the return line and the first cooler to a mixer unit, in which the recirculated exhaust gases are mixed with compressed air of the inlet line, wherein the mixture is led to the intake of the combustion engine, and the second valve means to the position in which all of the compressed air in the inlet line is led to a second cooler arranged in the inlet line upstream of the mixer unit with respect to the intended direction of the compressed air flow in the inlet line in a first operation condition of the combustion engine. During operation of the engine, sensors controlling the EGR and the exhaust gas aftertreatment system diagnose the efficiency level of the EGR and exhaust gas aftertreatment system in regard to NOx and particulate emission reduction in a given engine map point as well as the EGR-system efficiency in terms of heat transfer.

Preferably, the control unit is switching the first valve means to the closed position, in which no exhaust gases of the exhaust line are recirculated to the inlet line, and the second valve means to the position, in which at least part of the compressed air from the inlet line is led through the first cooler to clean a heat exchange area inside the first cooler in at least one operation condition of the combustion engine, wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine, and soot and/or particulate emissions passing the combustion chamber of the engine are reduced to lower emission levels in the exhaust gas aftertreatment system. Additionally or alternatively a source of fresh air under pressure is connected with the return line upstream of the first cooler and downstream of the first valve means with respect of the exhaust gas flow in the return line using a purge line, and a third valve means is arranged in the purge line, wherein the third valve means in an open position allows an air flow in the purge line and prevents such an air flow in a closed position. The control unit is switching the first valve means to the closed position, in which no exhaust gases of the exhaust line are recirculated to the inlet line, and the third valve means to the position, in which fresh air under pressure from the purge line is led through the first cooler to clean a heat exchange area inside the first cooler in at least one operation condition of the combustion engine, wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine, and soot and/or particulate emissions passing the combustion chamber of the engine are reduced to lower emission levels in the exhaust gas aftertreatment system.

Favourably, the control unit is recognizing the at least one operation condition to clean the first cooler, when the SCR exhaust gas aftertreatment system is working with high efficiency for NOx conversion. Additionally the control unit is determining the NOx conversion as a function of temperature and/or exhaust mass flow and/or NOx content in the exhaust gas, for example.

In an embodiment of the arrangement the control unit is determining an exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system, wherein the control unit recognizes a first operation condition to clean the first cooler, when the exhaust gas temperature at the inlet of the SCR exhaust gas aftertreatment system lies in a given temperature range. The given temperature ranges between about 15O⁰C to about 450⁰C, for example.

In a further embodiment of the arrangement the nitric oxides (NOx) emission level is determined at an outlet of the SCR exhaust gas aftertreatment system, and the value of the nitric oxides (NOx) emission level is compared to a map value, wherein a second operation condition to clean the first cooler is recognized, when the determined value of the nitric oxides (NOx) emission level is below a corresponding first threshold value in the map.

In yet a further embodiment of the arrangement the nitric oxides (NOx) emission level at the outlet of the engine and at the outlet of the exhaust gas aftertreatment system are determined, and the nitric oxides (NOx) emission conversion over the exhaust gas aftertreatment system is calculated, wherein a third operation condition to clean the first cooler is recognized, when the determined nitric oxides (NOx) emission conversion value is above a corresponding second threshold value. The second threshold value for the nitric oxides emission conversion is at least 70%, for example.

Preferably, the control unit is starting the cleaning procedure of the first cooler, when a measured contamination of the first cooler exceeds a given third threshold value.

In a further embodiment of the arrangement the control unit is switching the second valve means to the position, in which at least part of the compressed air from the inlet line is led to the return line, and the first valve means to an open position, in which at least part of the compressed air in the return line is led to the exhaust line, in an operation condition of the combustion engine, where the compressed air from the return line is mixed with the exhaust gases in the exhaust line. Additionally or alternatively the control unit is switching the third valve means to the position, in which fresh air under pressure from the source is led through the purge line to the return line, and the first valve means to an open position, in which at least part of the air under pressure in the return line is led to the exhaust line, in the operation condition of the combustion engine, where the compressed air from the return line is mixed with the exhaust gases in the exhaust line. This operation condition is used to cool the exhaust gases to prevent ageing of the components comprised in the exhaust gas aftertreatment system due to high temperature of the exhaust gases. The control unit recognizes this operating condition of the combustion engine, when the determined exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system exceeds a given fourth threshold value. The fourth threshold value of the temperature is about 580⁰C, for example. Similar, the fourth operating condition of the combustion engine is also recognized, for example, when the determined exhaust gas temperature at an inlet of the particular trap exhaust gas aftertreatment system exceeds a given fifth threshold value. The fifth threshold value of the temperature is about 700⁰C₁ for example.

In a further embodiment of the arrangement the exhaust aftertreatment system comprises a device for reducing a content of particulates in the exhaust gas, preferably a particulate filter and/or a device for reducing a content of nitrogen oxides (NOx) in the exhaust gas, preferably a SCR catalyst. The device for reducing a content of particulates in the exhaust gas is arranged upstream or downstream of the device for reducing a content of nitrogen oxides (NOx) in the exhaust gas. In yet a further embodiment of the arrangement the combustion engine is a diesel engine.

All together, embodiments of the invention control the EGR system and the exhaust gas aftertreatment system during operation and diagnose the efficiency level of the EGR system and the exhaust gas aftertreatment system in regard to NOx and particulate reduction in a given engine map point as well as the EGR system in terms of heat transfer. Additionally embodiments of the invention are able to clean the first cooler more frequently with sufficient duration of the cleaning process by using the above described different operation conditions to clean the first cooler. Thus the cleaning process of the first cooler is no longer limited to transients, e.g. gearshifts that impact on driveability or emergency cleaning processes of the first cooler that impact on NOx emission compliance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but not restricted to the embodiments, wherein is shown schematically:

Fig. 1 an embodiment of an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle according to the invention in a first operation condition;

Fig. 2 the embodiment of an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle according to the invention of Fig. 1 in a second operation condition;

Fig. 3 the embodiment of an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle according to the invention of Fig. 1 in a third operation condition, Fig. 4 the embodiment of an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle according to the invention of Fig. 1 in a forth operation condition, and Fig. 5 the embodiment of an arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger in a vehicle according to the invention of Fig. 1 in a fifth operation condition. In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 to 5 schematically illustrates an arrangement according to the present invention, which can be utilised particularly for a combustion engine of the diesel type.

According to a preferred embodiment, the diesel engine 10 is intended for use in a load- carrying vehicle, and comprises e.g. six cylinders 11 (only one is denoted with a reference numeral). The invention is however not limited to any specific number of cylinders or any specific cylinder configuration. The diesel engine 10 can also be used for stationary engines for electrical power generation etc.

In a way as such previously known, the engine 10 is equipped with an inlet manifold 14, to which air is fed from the atmosphere via an intake conduit 100 and an inlet line 1. The input air is then divided between the various cylinders 11. Furthermore, fuel is supplied to the cylinders 11 by a corresponding number of fuel injection devices (not shown) that are each connected to a central control unit 40 via an electrical connection (not shown). The control unit 40, which is preferably computer based, is in a known manner operative to control each fuel injection device so as to supply, in each instant, an appropriate fuel/air mixture to the engine 10.

During operation of the engine 10, the control unit 40 is operative to control the respective injection device in such a way that the fuel/air mixture supplied to the engine 10 will be adapted, in each instant, to the current operating conditions. The fuel supply is hereby obtained in a generally known manner, i.e. in dependence of a multitude of parameters representative of the operating conditions of the engine 10 and the vehicle in question. For example, the control can be performed depending on the present power demand (also called "throttle position", and the rotational speed and load of the engine 10. Each cylinder 11 is provided with an exhaust outlet. Together, the exhaust outlets converge into an exhaust manifold 12, continuing into an exhaust line 2. This exhaust line 2 runs via a turbocharger unit 50, which as such is substantially conventional. Thus, the turbocharger unit 50 comprises a compressor 52 and an energy absorbing unit 54 for absorbing energy from the exhaust gases in the form of a turbine, which is arranged in the exhaust line 2 and is being rotated by the exhaust gases flowing through the exhaust line 2 and which drives the compressor 52. As an alternative to the embodiment shown in the figure, which is designed in such a way that the exhaust outlets join into a single exhaust line 2 (known as a "single inlet"), the exhaust outlets may be grouped into two groups, making the exhaust duct consist of two lines leading to the turbine 54 (known as a "twin inlet").

The turbine 54 is arranged on a shaft 56, on which the compressor 52 is likewise arranged. The energy absorbed from the exhaust flow by the turbine 54 is in this way transferred to the compressor 52, which functions to compress the in-flowing air in the air conduit 100 to the inlet conduit 14 of the engine 10. In this manner, an increased fuel amount may be fed to the engine 10, whereby its power output can be increased.

The engine 10 is further equipped with an arrangement for recirculation of a certain amount of exhaust gases to the intake side of the engine 10. According to what was discussed in the introduction, an EGR system 80 ("Exhaust Gas Recirculation") is as such previously known. According to the embodiment, a return line 3 is therefore connected to the exhaust line 2, at a point upstream of the turbine 54 with respect to the intended direction of the exhaust gas flow in the exhaust line 2. The return line 3 is connected with the inlet line 1 , which is connected with the inlet manifold 14 via a mixer unit 84, at a point upstream of the inlet manifold 14 of the engine 10. The mixer unit 84 mixes the recirculating exhaust gases with the compressed air in the inlet line 1. The mixer unit 84 is a venturi, for example. Along the return line 3, a controllable first valve means S1 is arranged, connected to the control unit 40 via a further connection, which is represented by a dashed line. The control unit 40 is operative, in dependence of the present operating conditions, to adjust the first valve means S1 to a closed, open or partially open position. Depending on the position of the first valve means S1 , a corresponding amount of exhaust gases will thus be recirculate to the inlet manifold 14 via the return line 3. Through the recirculation of these EGR gases to the intake manifold 12, a temperature reduction during the combustion is achieved in the respective cylinder 11 , whereby the NOx generation in the cylinder 11 is reduced. The NOx generation in the respective cylinder 11 is temperature-dependent and for this reason it is desirable to lower, as far as possible, the temperature of the gases (i.e. including air and recirculated EGR gases) coming in to the engine 10. For this reason, the return line 3 is provided with a first cooler 82 functioning to cool the EGR gases recirculated to the inlet manifold 14. To this end the first cooler 82 includes a loop through which a suitable coolant is circulated. Preferably, this coolant is the ordinary coolant for the engine 10, but air may also be used for this cooling. By means of this first cooler 82, the EGR gases can be cooled, which further contributes to reducing the generated amount of NOx compounds.

The inlet line 1 is equipped with another cooler 20, also known as an "intercooler", which is used for cooling the compressed air supplied by the compressor 52. This also contributes to a reduction of the amount of NOx compounds generated in the engine 10. The second cooler 20 is preferably arranged for cooling by air.

In the shown embodiment a second valve means S2 is arranged in the inlet line 1 and is also controlled by the control unit 40 via a further connection, which is represented by a dashed line. A bypass line 4 is connecting the second valve means S2 with the return line upstream of the first cooler 82 and downstream of the first valve means S1 with respect of the exhaust gas flow in the return line 3. The control unit 40 is operative, in dependence of the present operating conditions, to adjust the second valve means S2 to a closed, open or partially open position. Depending on the position of the second valve means S2, a corresponding amount of compressed air will thus be led to the return line 3 via the second bypass line 4. Furthermore a purge line 5 is connecting the return line 3 with a source 70 of fresh air under pressure and a third valve means S3 is arranged in the purge line 5. The third valve means S3 is also controlled by the control unit 40 via a further connection, which is represented by a dashed line, wherein the third valve means S3 in an open position allows an air flow in the purge line 5 and prevents such an air flow in a closed position.

According to the invention an exhaust gas aftertreatment system 30 for reducing emissions of the internal combustion engine 10 is arranged in the exhaust line 2 downstream of the turbine 54 of the turbocharger 50 with respect to the intended direction of exhaust gas flow in the exhaust line 2, wherein the control unit 40 is determining the actual operation condition of the combustion engine 10 for switching the first valve means S1 and/or the second valve means S2 by monitoring an efficiency level of the recirculation of exhaust gases and the exhaust gas aftertreatment system 30 in regard to NOx and particular reduction in given engine map points. The exhaust gas aftertreatment system 30 favourably comprises at least one of a unit 32 for reducing particulate matter in the exhaust gas or a unit 34 for converting NOx, particularly a SCR catalyst. The NOx converting unit 34 can be arranged upstream or downstream of the unit 32. The unit 32 can be a particulate filter which holds back soot particles and/or an oxidation catalyst for oxidizing unburned carbon.

Fig. 1 shows the embodiment of the arrangement for recirculation of exhaust gases of a combustion engine with a turbocharger 50 in a vehicle according to the invention in a first operation condition. In the first operating condition the first valve means S1 is settable to provide a desired amount of EGR via the return line 3. The third valve means S3 is set in the closed position and the second valve means S2 is set in a position where no compressed air from the inlet line 1 is led to the return line 3. The control unit 40 is adapted to control the valve means S1 , S2, and S3 on basis of information concerning a load of the combustion engine 10, an efficiency level of the EGR and the exhaust aftertreatment system 30 for example. The exhaust gases of the exhaust line 2 are led ^• through the return line 3 and the first cooler 82 to a mixer unit 84. The mixer unit 84 is mixing the exhaust gases of the return line 3 with the compressed air of the inlet line 1 which is at a relative high pressure. In course of time, soot deposits from the exhaust gases inevitably build up on inside surfaces of the first cooler 82, thereby impairing the heat transfer capacity of the first cooler 82 and at the same time increasing a resistance to the flow of exhaust gases through the first cooler 82. Insufficient cooling of the exhaust gases leads to impaired engine performance. In case of an indication, that the first cooler 82 has to be cleaned in the shown embodiment of the invention different operation conditions to clean the first cooler 82 can be recognized by the control unit 40.

Therefore in a second operation condition of the combustion engine 10 for cleaning the first cooler 82 shown in Fig. 2, the control unit 40 switches the first valve means S1 to a closed position, in which no exhaust gases of the exhaust line 2 are recirculated to the inlet line 1 , and the second valve means S2 to a position, in which at least part of the compressed air from the inlet line 1 is led through the bypass line 4 to the return line 3 and the first cooler 82 to clean a heat exchange area inside the first cooler 82. During the cleaning process soot and/or particulates coming loose are led from the first cooler 82 into a combustion chamber of the engine 10, and soot and/or particulate emissions passing the combustion chamber of the engine 10 are reduced to lower emission levels in the exhaust gas aftertreatment system 30. In a third operation condition of the combustion engine 10 for cleaning the first cooler 82 shown in Fig. 3, the control unit 40 switches the first valve means S1 to the closed position, in which no exhaust gases of the exhaust line 2 are recirculated to the inlet line 1, and the third valve means S3 to the position, in which fresh air under pressure from source 70 is led through the purge line 5 to the return line 3 and the first cooler 82 to clean the heat exchange area inside the first cooler 82. During the cleaning process soot and/or particulates coming loose are led from the first cooler into a combustion chamber of the engine 10, and soot and/or particulate emissions passing the combustion chamber of the engine 10 are reduced to lower emission levels in the exhaust gas aftertreatment system 30.

The control unit 40 is recognizing the operation conditions to clean the first cooler 82, shown in Fig. 2 or 3, when the SCR exhaust gas aftertreatment system 34 is working with high efficiency for NOx conversion, wherein the control unit 40 is determining the NOx conversion as a function of temperature and/or exhaust mass flow and/or NOx content in the exhaust gas. For example, the control unit 40 is determining an exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system 34. In this case the control unit 40 recognizes an operation condition to clean the first cooler 82, when the exhaust gas temperature at the inlet of the SCR exhaust aftertreatment system 30 lies in a given temperature range, preferably when the temperature ranges between about 150⁰C to about 450⁰C.

Additionally or alternatively the control unit 40 is determining the nitric oxides (NOx) emission level at an outlet of the SCR exhaust gas aftertreatment system 34 and compares the value of the determined nitric oxides (NOx) emission level to a map value. In this case the control unit 40 recognizes an operation condition to clean the first cooler 82, when the determined nitric oxides (NOx) emission value is below a corresponding first threshold value in the map.

Additionally or alternatively the control unit 40 is determining the nitric oxides (NOx) emission level at the outlet 12 of the engine 10 and at the outlet of the exhaust gas aftertreatment system 30, and calculates the nitric oxides (NOx) emission conversion. In this case the control unit 40 recognizes an operation condition to clean the first cooler 82, when the determined nitric oxides (NOx) emission conversion value is above a corresponding second threshold value, preferably higher than 70%. The control unit 40 may start the cleaning procedure of the first cooler 82, when a measured contamination of the first cooler 82 exceeds a given third threshold value. During operation of the engine 10, the control unit 40 is determines the different values by using corresponding sensors to measure temperature and/or the nitric oxides (NOx) emission of the exhaust gases.

In a forth operation condition shown in Fig. 4 the control unit 40 is switching the second valve means S2 to the position, in which at least part of the compressed air from the inlet line 1 is led to return line 3, and the first valve means S1 to an open position, in which at least part of the compressed air in the return line 3 is led to the exhaust line 2. In this operation condition of the combustion engine 10 the compressed air from the return line 3 is mixed with the exhaust gases in the exhaust line 2. Therefore the bypass line 4 can be used to control the temperature for a better regeneration of the particulate filter (DPF) 32 of the exhaust gas aftertreatment system 30. Such a controlling is active in case that temperature sensors (not shown) monitoring the exhaust gas aftertreatment system 30 indicate an undesired deviation in temperature of the exhaust gas aftertreatment system 30 towards higher temperatures.

In a fifth operation condition shown in Fig. 5 the control unit 40 is switching the third valve means S3 to the position, in which fresh air under pressure from the source 70 is led through the purge line 5 to the return line 3, and the first valve means S1 to an open position, in which at least part of the air under pressure in the return line 3 is led to the exhaust line 2. In this operation condition the air under pressure from the return line 3 is mixed with the exhaust gases in the exhaust line 2. Therefore the purge line 6 can be used to control the temperature for a better regeneration of the particulate filter (DPF) 32 of the exhaust aftertreatment system 30. Such a controlling is active in case that temperature sensors (not shown) monitoring the exhaust gas aftertreatment system 30 indicate an undesired deviation in temperature of the exhaust gas aftertreatment system 30 towards higher temperatures.

The control unit 40 recognizes the operating conditions of the combustion engine 10 shown in Fig 4 or 5, when the determined exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system 34 exceeds a given fourth threshold value. The fourth threshold value of the temperature is about 58O⁰C, for example.

Additional the control unit 40 recognizes the operating conditions of the combustion engine 10 shown in Fig 4 or 5, when the determined exhaust gas temperature at an inlet of the particulate trap exhaust gas aftertreatment system 32 exceeds a given fifth threshold value. The fifth threshold value of the temperature is about 700⁰C, for example.

Not shown, but similar applicable are embodiments of the invention if the order within the exhaust gas system 30 has changed, i.e. the SCR catalyst 34 upstream the diesel particulate filter 32.

Not shown, but similar applicable are embodiments with 2-step and/or 2-stage EGR systems, where different coolers are using different coolant media like ambient air, engine coolant etc. or the same coolant medium.

Claims

C L A I M S

1. A method for recirculation of exhaust gases of a combustion engine (10) with a turbocharger (50), wherein the combustion engine (10) comprises a turbine (54) placed in an exhaust line (2) and adapted to be driven by exhaust gases from the combustion engine (10), a compressor (52) adapted to be driven by the turbine (54) in order to supply compressed air to an inlet line (1), which is adapted to lead compressed air to an intake (14) of the combustion engine (10), a return line (3) adapted to recirculate exhaust gases from the exhaust line (2) connected with an exhaust outlet (12) of the combustion engine (10) to the inlet line (1), wherein the return line (3) is connected with the exhaust line (2) upstream of the turbine (54) of the turbocharger unit (50) with respect to the intended direction of the exhaust gas flow in the exhaust line (2), a first cooler (82) arranged in the return line (3) in order to cool the exhaust gases, a first valve means (S1) arranged in the return line (3) upstream of the first cooler (82) with respect to the intended direction of exhaust gas flow in the return line (3), a second valve means (S2) arranged in the inlet line (1), and a bypass line (4) connecting the second valve means (S2) with the return line (3) upstream of the first cooler (82) and downstream of the first valve means (S1) with respect to the intended direction of the exhaust gas flow in the return line (3), wherein the first valve means (S1) and/or the second valve means (S2) are switched to given positions in accordance with an actual operation condition of the combustion engine (10), wherein the first valve means (S1) allows a fluid flow in either way between the inlet line (1) and the exhaust line (2) passing the first cooler (82) in an open position and prevents such a fluid flow in a closed position, and wherein the second valve means (S2) allows at least part of the compressed air flow in the inlet line (1) to be passed to the return line (3) in an open position and prevents such a compressed air flow in a closed position, characterized by

- using an exhaust gas aftertreatment system (30) for reducing emissions of the internal combustion engine (10) arranged in the exhaust line (2) downstream of the turbine (54) of the turbocharger (50) with respect to the intended direction of exhaust gas flow in the exhaust line (2),

- determining the actual operation condition of the combustion engine (10) for switching the first valve means (S1) and/or the second valve means (S2) by monitoring an efficiency level of the recirculation of exhaust gases and the exhaust gas aftertreatment system (30) in regard to NOx and particular emission reduction in given engine map points.

2. The method according to claim 1, characterized by switching the first valve means (S1) to an open position, in which at least part of the exhaust gases of the exhaust line (2) are led through the return line (3) and the first cooler (82) to a mixer unit (84), in which the recirculated exhaust gases are mixed with compressed air of the inlet line (1), wherein the mixture is led to the intake (14) of the combustion engine

(10), and the second valve means (S2) to the position in which all of the compressed air in the inlet line (1) is led to a second cooler (20) arranged in the inlet line (1) upstream of the mixer unit (84) with respect to the intended direction of the compressed air flow in the inlet line (1) in a first operation condition of the combustion engine (10).

3. The method according to claims 1 or 2, characterized by switching the first valve means (S1) to the closed position, in which no exhaust gases of the exhaust line (2) are recirculated to the inlet line (1), and the second valve means (S2) to the position, in which at least part of the compressed air from the inlet line (1) is led through the first cooler (82) to clean a heat exchange area inside the first cooler ■ (82) in a at least one operation condition of the combustion engine (10), wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine (10), and soot and/or particulates emissions passing the combustion chamber of the engine (10) are reduced to lower emission levels in the exhaust gas aftertreatment system (30).

4. The method according to any preceding claim, characterized by connecting a source (70) of fresh air under pressure with the return line (3) upstream of the first cooler (82) and downstream of the first valve means (S 1) with respect of the exhaust gas flow in the return line (3) using a purge line (5) and a third valve means (S3) arranged in the purge line (5), wherein the third valve means (S3) in an open position allows an air flow in the purge line (5) and prevents such an air flow in a closed position.

5. The method according to claim 4, characterized by switching the first valve means (S1) to the closed position, in which no exhaust gases of the exhaust line (2) are recirculated to the inlet line (1), and the third valve means (S3) to the position, in which fresh air under pressure from the purge line (5) is led through the first cooler (82) to clean a heat exchange area inside the first cooler (82) in a at least one operation condition of the combustion engine (10), wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine (10), and soot and/or particulate emission passing the combustion chamber of the engine (10) are reduced in the exhaust gas aftertreatment system (30).

6. The method according to any preceding claim, characterized by recognizing the at least one operation condition to clean the first cooler (82), when a SCR exhaust gas aftertreatment system (34) is working with high efficiency for NOx conversion.

7. The method according to claim 6, characterized by determining the NOx conversion as a function of temperature and/or exhaust mass flow and/or NOx content in the exhaust gas.

8. The method according to claims 6 or 7, characterized by determining an exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system (34), wherein a first operation condition to clean the first cooler (82) is recognized, when the exhaust gas temperature at the inlet of the SCR exhaust gas aftertreatment system (34) lies in a given temperature range.

9. The method according to claim 8, characterized in that the given temperature ranges between about 150⁰C to about 450⁰C.

10. The method according to anyone of the claims 6 to 9, characterized by determining the level of nitric oxides (NOx) emission at an outlet of the exhaust gas aftertreatment system (30) and comparing the values of the nitric oxides (NOx) emission to a map value, wherein a second operation condition to clean the first cooler (82) is recognized, when the determined value of the nitric oxides (NOx) emission level is below a corresponding first threshold value in the map.

11. The method according to anyone of the claims 6 to 10, characterized by determining the level of nitric oxides (NOx) emission at the outlet (12) of the engine (10) and at the outlet of the exhaust gas aftertreatment system (30) and calculating the nitric oxides (NOx) emission conversion, wherein a third operation condition to clean the first cooler (82) is recognized, when the determined nitric oxides (NOx) emission conversion value is above a corresponding second threshold value.

12. The method according to claim 11 , characterized in that the second threshold value for the nitric oxides emission conversion is at least 70%.

13. The method according to anyone of the claims 6 to 12, characterized by starting the cleaning procedure of the first cooler (82) when a measured contamination of the first cooler (82) exceeds a given third threshold value.

14. The method according to any preceding claim, characterized by switching the second valve means (S2) to the position, in which at least part of the compressed air from the inlet line (1) is led to return line (3) and the first valve means (S1) to an open position, in which at least part of the compressed air in the return line (3) is led to the exhaust line (2), in a forth operation condition of the combustion engine (10), where the compressed air from the return line (3) is mixed with the exhaust gases in the exhaust line (2).

15. The method according to any preceding claim, characterized by switching the third valve means (S3) to the position, in which fresh air under pressure from the source (70) is led through the purge line (5) to the return line (3), and the first valve means (S 1) to an open position, in which at least part of the air under pressure in the return line (3) is led to the exhaust line (2), in the forth operation condition of the combustion engine (10), where the compressed air from the return line (3) is mixed with the exhaust gases in the exhaust line (2).

16. The method according to claims 14 or 15, characterized in that the fourth operating condition of the combustion engine (10) is recognized, when the determined exhaust gas temperature at an inlet of the SCR exhaust gas aftertreatment system (34) exceeds a given fourth threshold value.

17. The method according to, claim 16 characterized in that the fourth threshold value of the temperature is about 580°C.

18. The method according to anyone of the claims 14 to 17, characterized in that the fourth operating condition of the combustion engine (10) is recognized, when the determined exhaust gas temperature at an inlet of a particulate trap exhaust gas aftertreatment system (32) exceeds a given fifth threshold value.

19. The method according to, claim 18 characterized in that the fifth threshold value of the temperature is about 700⁰C.

20. An arrangement for recirculation of exhaust gases of a combustion engine (10) with a turbocharger (50) for performing the method according to anyone of the preceding claims, wherein the arrangement comprises a turbine (54) placed in an exhaust line (2) and adapted to be driven by exhaust gases from the combustion engine (10), a compressor (52) adapted to be driven by the turbine (54) in order to supply compressed air to an inlet line (1), which is adapted to lead compressed air to an intake (14) of the combustion engine (10), a return line (3) adapted to recirculate exhaust gases from the exhaust line (2) connected with an exhaust outlet (12) of the combustion engine (10) to the inlet line (1), wherein the return line (3) is connected with the exhaust line (2) upstream of the turbine (54) of the turbocharger unit (50) with respect to the intended direction of the exhaust gas flow in the exhaust line (2), a first cooler (82) arranged in the return line (3) in order to cool the exhaust gases, a first valve means (S1) arranged in the return line (3) upstream of the first cooler (82) with respect to the intended direction of exhaust gas flow in the return line (3), a second valve means (S2) arranged in the inlet line (1), a bypass line (4) connecting the second valve means (S2) with the return line (3) upstream of the first cooler (82) and downstream of the first valve means (S 1 ) with respect to the intended direction of the exhaust gas flow in the return line (3), and a control unit (40), which is adapted to switch the first valve means (S1) and/or the second valve means (S2) to given positions in accordance with an actual operation condition of the combustion engine (10), wherein the first valve means (S1) allows a fluid flow in either way between the inlet line (1) and the exhaust line

(2) passing the first cooler (82) in an open position and prevents such a fluid flow in a closed position, and wherein the second valve means (S2) allows at least part of the compressed air flow in the inlet line (1) to be passed to the return line (3) in an open position, and prevents such a compressed air flow in a closed position, characterized by an exhaust gas aftertreatment system (30) for reducing emissions of the internal combustion engine (10) arranged in the exhaust line (2) downstream of the turbine (54) of the turbocharger (50) with respect to the intended direction of exhaust gas flow in the exhaust line (2), wherein the control unit (40) is provided for determining the actual operation condition of the combustion engine (10) for switching the first valve means (S1) and/or the second valve means (S2) by monitoring an efficiency level of the recirculation of exhaust gases and the exhaust gas aftertreatment system (30) with regard to NOx and particular emission reduction in given engine map points.

21. The arrangement according to claim 20, characterized in that the control unit (40) is switching the first valve means (S1) to an open position, in which at least part of the exhaust gases of the exhaust line (2) are led through the return line (3) and the first cooler (82) to a mixer unit (84), in which the recirculated exhaust gases are mixed with compressed air of the inlet line (1), wherein the mixture is led to the intake (14) of the combustion engine (10), and the second valve means (S2) to the position, in which all of the compressed air in the inlet line (1) is led to a second cooler (20) arranged in the inlet line (1) upstream of the mixer unit (84) with respect to the intended direction of the compressed air flow in the inlet line (1) in a first operation condition of the combustion engine (10).

22. The arrangement according to claims 20 or 21 , characterized in that the control unit (40) is switching the first valve means (S1) to the closed position, in which no exhaust gases of the exhaust line (2) are recirculated to the inlet line (1), and the second valve means (S2) to the position, in which at least part of the compressed air from the inlet line (1) is led through the first cooler (82) to clean a heat exchange area inside the first cooler (82) in a at least one operation condition of the combustion engine (10), wherein soot and/or particulates coming loose during the cleaning are going into a combustion chamber of the engine (10), and soot and/or particulate emissions passing the combustion chamber of the engine (10) are reduced to lower emission levels in the exhaust gas aftertreatment system (30).

23. The arrangement according to anyone of the claims 20 to 22 characterized by a source (70) of fresh air under pressure connected with the return line (3) upstream of the first cooler (82) and downstream of the first valve means (S 1 ) with respect of the exhaust gas flow in the return line (3) using a purge line (5), and a third valve means (S3) arranged in the purge line (5), wherein the third valve means (S3) in an open position allows an air flow in the purge line (5) and prevents such an air flow in a closed position.

24. The arrangement according to claim 23, characterized in that the control unit (40) is switching the first valve means (S1) to the closed position, in which no exhaust gases of the exhaust line (2) are recirculated to the inlet line (1), and the third valve means (S3) to the position, in which fresh air under pressure from the purge line (5) is led through the first cooler (82) to clean a heat exchange area inside the first cooler (82) in a at least one operation condition of the combustion engine (10), wherein soot and/or particulates coming loose during the cleaning are going into a 5 combustion chamber of the engine (10), and soot and/or particulate emissions passing the combustion chamber of the engine (10) are reduced to lower emission levels in the exhaust gas aftertreatment system (30).

25. The arrangement according to anyone of the claims 22 to 24, characterized in that 10 the control unit (40) is recognizing the at least one operation condition to clean the first cooler (82), when a SCR exhaust gas aftertreatment system (34) is working with high efficiency for NOx conversion.

26. The arrangement according to claim 25, characterized in that the control unit (40) 15 is determining the NOx conversion as function of temperature and/or exhaust mass flow and/or NOx content in the exhaust gas.

27. The arrangement according to claims 25 or 26, characterized in that the control unit (40) is determining an exhaust gas temperature at an inlet of the SCR exhaust

20. gas aftertreatment system (34), wherein the control unit (40) recognizes a first operation condition to clean the first cooler (82), when the exhaust gas temperature at the inlet of the SCR exhaust gas aftertreatment system (34) lies in a given temperature range.

25 28. The arrangement according to claim 27, characterized in that the given temperature ranges between about 15O⁰C to about 45O⁰C.

29. The arrangement according to anyone of the claims 25 to 28, characterized by determining the level of nitric oxides (NOx) emission at an outlet of the exhaust 30 gas aftertreatment system (30) and comparing the values of the nitric oxides (NOx) emission level to a map value, wherein a second operation condition to clean the first cooler (82) is recognized, when the determined value of the nitric oxides (NOx) emission level is below a corresponding first threshold value in the map.

35 30. The arrangement according to anyone of the claims 25 to 29, characterized by determining the level of nitric oxides (NOx) emission at the outlet (12) of the engine (10) and at the outlet of the exhaust gas aftertreatment system (30) and calculating the nitric oxides (NOx) emission conversion, wherein a third operation condition to clean the first cooler (82) is recognized, when the determined nitric oxides (NOx) emission conversion value is above a corresponding second threshold value.

31. The arrangement according to claim 30, characterized in that the second threshold value for the nitric oxides emission conversion is at least 70%.

32. The arrangement according to anyone of the claims 25 to 31 , characterized in that the control unit (40) is starting the cleaning procedure of the first cooler (82), when a measured contamination of the first cooler (82) exceeds a given third threshold value.

33. The arrangement according to anyone of the claims 29 to 32, characterized in that the control unit (40) is switching the second valve means (S2) to the position, in which at least part of the compressed air from the inlet line (1) is led to return line (3), and the first valve means (S1) to an open position, in which at least part of the compressed air in the return line (3) is led to the exhaust line (2), in a forth operation condition of the combustion engine (10), where the compressed air from the return line (3) is mixed with the exhaust gases in the exhaust line (2).

34. The arrangement according to anyone of the claims 20 to 33, characterized in that the control unit (40) is switching the third valve means (S3) to the position, in which fresh air under pressure from the source (70) is led through the purge line (5) to the return line (3), and the first valve means (S1) to an open position, in which at least part of the air under pressure in the return line (3) is led to the exhaust line (2), in the forth operation condition of the combustion engine (10), where the compressed air from the return line (3) is mixed with the exhaust gases in the exhaust line (2).

35. The arrangement according to claims 33 or 34, characterized in that the control unit (40) recognizes the fourth operating condition of the combustion engine (10), when the determined exhaust gas temperature at an inlet of the SCR exhaust aftertreatment system (34) exceeds a given fourth threshold value.

36. The arrangement according to, claim 35 characterized in that the fourth threshold value of the temperature is about 580⁰C.

37. The arrangement according to anyone of the claims 33 to 36, characterized in that the control unit (40) recognizes the fourth operating condition of the combustion engine (10), when the determined exhaust gas temperature at an inlet of a particulate trap exhaust gas aftertreatment system (32) exceeds a given fifth threshold value.

38. The arrangement according to, claim 37 characterized in that the fifth threshold value of the temperature is about 700⁰C.

39. The arrangement according to one of the claims 20 to 38, characterized in that the exhaust aftertreatment system (30) comprises a device (32) for reducing a content of particulates in the exhaust gas and/or a device (34) for reducing a content of nitrogen oxides (NOx) in the exhaust gas.

40. The arrangement according to claim 39, characterized in that the device (32) for reducing a content of particulates in the exhaust gas is arranged upstream or downstream of the device (34) for reducing a content of nitrogen oxides (NOx) in the exhaust gas.

41. The arrangement according to one of the claims 20 to 40, characterized in that the combustion engine (10) is a diesel engine.