Technical field

The invention relates to the field of internal combustion engine arrangements with exhaust gas recirculation installations and processes for the control thereof, Such can engine arrangements may be used for example in vehicles, in construction equipment machines or as stationary arrangements.

Background art

It is known to provide internal combustion engine arrangements with exhaust gas recirculation (EGR) installations whereby a portion of the exhaust gases produced by the combustion inside the engine are recirculated to the engine rather than being released the atmosphere. The EGR gases which are fed to the engine, generally through an EGR line connecting an exhaust line to an intake line of the engine, allow modifying the temperature and the composition of the gases inside the combustion chambers of the engine, thus modifying the conditions of the combustion. Depending on the engine operating conditions and on the EGR recirculation rate, it is possible, amongst other things, to alter the production of noxious emissions in the exhaust gases, especially nitrogen oxides (NQx), to reduce fuel consumption and/or to alter exhaust gases temperatures.

More and more engine arrangements are now also charged air engine arrangements where the intake gases provided to the engine for the combustion are compressed, to increase efficiency. Although air charging can be performed by compressors driven electrically or driven mechanically by the engine crankshaft, most charged air engines are equipped with a turbo-compressor system having at least one turbine driven by exhaust gases flowing In the exhaust line and at least one compressor for compressing gases flowing in the intake line. One compressor of a given turbo-compressor is driven by the corresponding turbine through a mechanical connection. Turbo-compressor systems may comprise several turbo- compressors, with different possible arrangements. The turbines and/or the compressors can be arranged In series and/or in parallel respectively in the exhaust line and In the intake line.

In turbocharged engines arrangements, various EGR installations have been proposed where an EGR line can be connected to the exhaust line either upstream or downstream of the turbine(s), or even between turbines In the case of several serially arranged turbines. In such installations various combinations have been proposed where the EGR line can be connected to the intake line either upstream or downstream of the compressor^), or even between compressors in the case of several serially arranged compressors.

Installations where the. EGR line is. connected to the exhaust line downstream of at least one turbine have the advantage of providing cooler EGR gases, which is generally favorable for reducing the production of NOx during the combustion.

Document US-2011/000470 describes an internal combustion engine arrangement equipped with a complex exhaust gas recirculation installation which would allow at least theoretically different EGR recirculation schemes. Such installation is very complex, thus costly, both in terms of the hardware installation and in terms of the process for controlling the arrangement.

Summary

According to a first aspect of the invention, it may be provided an internal combustion engine arrangement comprising

-an internal combustion engine

- an intake line for conveying fresh air from the atmosphere to the engine,

- an exhaust line for conveying exhaust gases out of the engine to the atmosphere, - a turbo-compressor system having at least one turbine driven by exhaust gases flowing in the exhaust line and at least one compressor for compressing gases flowing in the intake line,

- at least one exhaust gas recirculation (EGR) line fiuidically connected to the exhaust line at a low pressure branch-out location located in the exhaust line downstream of said at least one turbine of the turbo-compressor system, and fiuidically connected to the intake line at a branch-In location for conveying recirculated exhaust gases from the exhaust line to the intake line,

- a turbine bypass line which is fiuidically connected to the exhaust line at a high pressure branch-out location located in the exhaust line upstream of said at least one turbine of the turbo-compressor system, and fiuidically connected to the EGR line at an EGR junction location,

^■ wherein the EGR line comprises an EGR valve for controlling the flow of EGR gases from the low pressure branch-out location to the branch-in location,

characterized in that the EGR junction location Is located in the EGR line between the low pressure branch-out location and the EGR valve.

As such the EGR valve can control the flow of EGR gases whatever their source, upstream or downstream of the turbine.

According to further optional features of the invention:

- The turbine by-pass line may have a turbine by-pass valve distinct from the

EGR valve and the turbine by-pass valve and the EGR valve may be arranged in series for the flow of EGR gases conveyed through the turbine by-pass towards the intake line. The bypass valve may be used to control the flow of high pressure EGR gases, depending however on the mount of gases allowed by the EGR gases.

- A non-return valve may be provided in the EGR line between the branch-out location and the EGR junction location. This may prevent or limit any flow of high pressure EGR gases, coming from the turbine by-pass, directly back to the exhaust line.

- The EGR valve may be a single two-way proportional valve, thereby being relatively cheap and easy to control. - A particle filter may be arranged in the EGR line downstream of the EGR junction location, thereby allowing the same filter to filter all EGR gases,

- The branch-in location of the EGR line on the Intake line is located upstream of at least one compressor. This can assist in having a favorable pressure difference across the EGR line to allow EGR flow over a vast range of engine operating conditions.

- The arrangement may comprise at least two turbines in series in the exhaust line, and the branch-out location of the EG R line in the exhaust line may be located downstream of an upstream turbine and upstream of a downstream turbine, This can assist in having a favorable pressure difference across the EG R line to allow EGR flow over a vast range of engine operating conditions.

- The arrangement may comprise at least two compressors in series in the intake Jitte,_.and_theJ5ranehrJn Qcation^

located upstream of said at least two compressors.

- The branch-out location of the EGR line in the exhaust line may be located upstream of a device which is located in the exhaust li ne and which generates a resistance to the flow of exhaust gases. This can assist in having a favorable pressure difference across the EGR line to allow EGR flow over a vast range of engine operating conditions. Such device may comprise at least one of

- an exhaust after-treatment device (oxidation catalyst, particle filter, reduction catalyst, three-way catalyst, NOX absorbers, a muffler;

- an exhaust throttle

- The at least one turbine which Is bypassed by the turbine bypass line may be a variable geometry turbine, to adjust the operation of the turbin e to the limited flow of gases it receives when the by-pass in open. This m ay help in recovering enough energy from this limited flow of exhaust gases at the turbine to drive th e compressor in such a way for it to be effective in compressing gases in the intake line, According to another aspect of the invention, it may be proposed a process for controlling an internal combustion engine arrangement according to above, characterized in that it comprises:

- determining the actual pressure of compressed gases delivered to the engine by the Intake line downstream of the turbo- compressor system ;

- determining the actual pressure of exhaust gases out of the engine upstream of the turbo-compressor system ;

controlling the flow in the turbine by pass line with a target pressure difference between the pressure of exhaust gases out of the engine and the pressure of compressed gases delivered to the engine by the intake line is maintained below a threshold value. Such a control process will allow minimizing the pumping losses at_the . engine,, at least for certain operating ranges where such process can be performed,

According to further optional features of the process:

- The flow in the turbine by-pass line may be stopped if the actual pressure of compressed gases delivered to the engine by the intake line downstream of the turbo-compressor system is below a minimum value.

The minimum value of the actual pressure of compressed gases delivered to the engine may be set depending on the operating point of the engine.

- The at least one turbine which is bypassed by the turbine bypass line may be a variable geometry turbine, so that, when the bypass valve is opened, the geometry of the turbine may be controlled in view of maximizing the pressure delivered by a compressor driven by said turbine.

According to still another aspect of the Invention, it may be provided a process for operating an internal combustion engine arrangement comprising:

- conveying fresh air from the atmosphere to the engine through an intake line;

- conveying exhaust gases out of the engine to the atmosphere through an exhaust line;

- recovering energy from the exhaust gases in an expander; - controlling a low pressure exhaust gas recirculation (EGR) flow of gases which are taken from the exhaust line at a low pressure branch-out location located in the exhaust line downstream of the expander and conveying the low pressure exhaust gas recirculation flow to the intake line;

- controlling a high pressure exhaust gas recirculation (EGR) flow which are taken from the exhaust line at a high pressure branch-out location located in the exhaust line upstream of the expander, and conveying the high pressure exhaust gas recirculation flow to the intake line;

- determining the actual pressure of compressed gases delivered to the engine by the intake line,

- determining the actual pressure of exhaust gases out of the engine, characterized in that the process involves controlling the high pressure exhaust gas recirculation (EGR) flow with a target that a pressure difference between the pressure of exhaust gases out of the engine and the pressure of compressed gases delivered to the engine by the intake line is maintained below a threshold value,

According to further optional features of the invention:

- The process may involve

-setting a minimum value for the pressure of compressed gases delivered to the engine by the intake line;

- stopping the flow of high pressure exhaust gas recirculation flow If the actual pressure of compressed gases delivered to the engine by the intake line is determined to be lower than said minimum value.

- The threshold value for the pressure difference between the pressure of exhaust gases out of the engine and the pressure of compressed gases delivered to the engine by the intake line may be a constant, or it may be set depending on the operating point of the engine,

According to a further aspect of the invention, it may be provided a controller for an interna) combustion engine arrangement, wherein the controller is programmed to perform a process as set forth above. Description of figures

- Figure 1 is a schematic view of a first embodiment of an arrangement according to the invention;

- Figure 2 is a schematic view of a second embodiment of an arrangement according to the invention

Detailed description

On Figures 1 and 2 are shown some of the elements of an Internal combustion arrangement 10.

The arrangement 10 comprises an internal combustion engine 12. The engine 12 is for example a multi-cylinder reciprocating piston engine, which is here shown as an in-line engine having six cylinders 14 which provides mechanical output power through a crankshaft 16. The engine can be a compression-ignition engine, such as a Diesel engine, but could be a spark ignited engine.

The arrangement further comprises an intake line 18 for conveying fresh air from the atmosphere to the engine. The Intake line comprises at least one gas conduit 20 which draws fresh air from the atmosphere, and may comprise an air filter 21. The intake line typically also comprises an intake manifold 22 which is connected to the engine 12 and which distributes intake gases to the cylinder(s) 14 of the engine 12. In some engine arrangements, the intake line could comprise an intake throttle and/or a fuel Injection apparatus for injecting fuel in the Intake line before the intake gases are delivered to the engine 12,

The arrangement further comprises an exhaust line 24 for conveying exhaust gases out of the engine to the atmosphere. The exhaust line 24 typically comprises an exhaust manifold 26 which Is connected to the engine 12 and which collects the exhaust gases resulting from the combustion in the cylinders. It comprises at least one exhaust conduit 27 which conveys the gases towards the atmosphere. In the exhaust line can be provided one or several exhaust after-treatment devices 28 which remove at least part of the noxious substances from the exhaust gases. Such exhaust after-treatment devices 28 may comprise one or several of a particle filter (which may be catalytically coated), an oxidation catalyst, a reduction catalyst (such as a so called SCR catalyst), a NOx trap, a SOx trap, a three-way catalyst, etc.... The exhaust line 24 may also comprise a muffler 30 for reducing the noise generated by the exhaust gases. The exhaust line could also comprise an exhaust throttle.

The engine arrangement 12 is a charged air engine arrangement in which the Intake gases which participate in the combustion are compressed in the intake line 18, before being delivered to the engine 12, to a level above atmospheric pressure. Preferably, the energy required by such compression is provided by energy which is recovered from the exhaust gases, preferably via an expander located in the exhaust line.24,. most prefer.ably.by. on.e or severaLturblnes located in the exhaust line 24.

Therefore, the engine arrangement preferably comprises a turbo-compressor system 32 having at least one turbine driven by exhaust gases flowing In the exhaust line and at least one compressor for compressing gases flowing in the intake line. In the embodiment of Figure 1, the compressor system 32 comprises a single turbo- compressor having a turbine 34 In the exhaust line 24 and a rotary compressor 36 In the intake line 28, the compressor 36 being mechanically driven by the turbine 34. In such a system, the turbine Is used as an expander for recovering energy from the exhaust gases, and said recovered energy is used for compressing gases flowing in the intake line thanks to the compressor.

The turbo-compressor system 32 could comprise several turbo-compressors. A common layout is then to have two turbo-compressors, with the turbines being arranged in series in the exhaust line and with the corresponding compressors arranged in series in the intake line, as shown in Figure 2 with a high pressure turbine 34' being arranged upstream of low pressure turbine 34", The high pressure turbine 34' drives a high pressure compressor 36' which is located downstream in the intake line of a low pressure compressor 36" driven by the low pressure turbine 34'. Nevertheless, other layouts are possible, for example with the turbines in parallel in the exhaust line and/or with the compressors In parallel In the i ntake line. The engine arrangement could also comprise an electrically driven compressor in the Intake line and/or a compressor driven mechanically by the engine cran kshaft through an appropriate mechanical transmission.

The engine arrangement may comprise, in the intake line 18, one or several

"charge air coolers" for cooling the intake gases before they are delivered to the engine 12. Such charge air coolers are provided downstream of at least one compressor of the compressor system 32. One such charge air cooler 37 Is shown on Figures 1 and 2 in the intake line between the compressor 36 and the engine 12.

The engine arrangement further comprises an exhaust gas recirculation (EGR) installation. which is external. to the engine itself. Preferably,, the EGR . installation comprises at least one "low pressure" exhaust gas recirculation (EGR) line 38 fl uidically connected to the exhaust line 24 at a low pressure branch-out location BOLP located in the exhaust line 24 downstream of at least one turbine of the turbo-compressor system, and fluidically connected to the intake line IS at a branch-in location Bl for conveying recirculated exhaust gases from the exhaust line to the Intake line, The recirculated exhaust gases, or EGR gases, are a portion of the exh aust gases coming out of the engine cylinders which are recirculated at least on ce through the engine cylinders for participating in a further combustion event. In the shown embodiments, it is clear that this recirculation is achieved via the EG R installation which is external to the engine itself. Such "low pressure" EGR line forms a "low pressure" EGR circuit inasmuch as the EGR gases circulating in that circuit are taken from the exhaust line downstream of at least one expander (in th is case a turbine of a turbo-compressor) a nd that they are therefore at a lower pressure than if they had been taken upstream of said at least one expander.

In the case of a single turbo-compressor, the low pressure branch-out location BOLP for the EGR line 38 is therefore located in the exhaust line 24 downstream of the sole turbine 34. In the embodiment of Figure 2, in the case where the turbo-compressing system comprises several turbines 34' 34" In series in the exhaust line, I.e. with a downstream or low pressure turbine 34" receiving at its input exhaust gases coming from the output of an upstream or high pressure turbine 34', the low pressure branch out location BOLP where the "low pressure" EGR line 38 Is connected to the exhaust line 24 could be located downstream of all turbines, or cou ld be located between an upstream turbine 34' and a downstream turbine 34", such as shown in Figure 2.

The branch-out location BOLP, where the low pressure EGR line 38 is connected to the exhaust line 24, is preferably located upstream of at least one of:

- an exhaust after-treatment device 28;

- a muffler;

- an exhaust throttle

Indeed, any of such devices located in the exhaust line would generate a resistance to the flow of exh aust gases, and therefore create a counter pressure at the low pressure branch-out BOLP location which would faci litate the circulation of EGR gases through the EGR line from the exhaust line towards the Intake line. Nevertheless, any of such devices could also be located upstream of the branch-out location BOLP.

In the embodiment of Figure 1, the branch-tn location Bl at which EGR line 38 is connected to the intake line is located upstream the sole compressor 36. In the case where there would be several compressors 36' 36" in series, the branch-in location could advantageously be located upstream of a ll compressors in the intake line, as is shown in figure 2, although other locations could be considered, such as in between two compressors arranged In series.

In an embodiment, the branch-in location could be formed in a Venturi system where the flow, of gases in the intake line would generate a lower pressure zone to facilitate the circulation of EGR gases through the EGR line from the exhaust line towards the intake line.

The engine arrangement further comprises, in the EGR line 38, an EGR valve 39 for controlling the flow of EGR gases from the low pressure branch-out location BOLP of the EGR line 38 to the branch-in location B|, The EGR valve 39 is preferably a proportional valve. In a preferred embodiment, the EGR valve 39 can be a single two-way proportional EGR valve, rather than a multi-way valve or a combination of several valves.

The EGR valve can be controlled in a conventional way through a controller 48, such as an electronic control unit, which can be a dedicated controller or which can be shared with other elements of the engine arrangement. The controller can be formed of several units operatively connected one to the other, Preferably, the controller 48 has access to one or several operating parameters of the engine arrangement, for example through a digital communication network such as a CAN- bus.

The controller 48 for the EGR valve can include a PID controller. The controller can for example have as an input a target EGR rate (whlcb_ma\Lb^^xp.rje.s..s.e Las_a_ percentage of EGR gases in the total amount of Intake gases fed to the engine by the intake line - this rate may be expressed as a function, a map, or a table depending on engine arrangement operating conditions such as engine torque and speed, external temperature, coolant temperature, oil temperature, .,.), and the flow of EGR gases in the EGR line 28. The flow of EGR gases may be determined in various ways, for example using a flow rate sensor 54 in the EGR line, possibly in combination with a temperature sensor 56.

The engine arrangement further comprises a turbine bypass line 40 which is fluldically connected to the exhaust line at a high pressure branch-out location BOHP located in the exhaust line upstream of said at least one turbine of the turbo- compressor system, and fluidically connected to the EGR line 38 at an EGR junction location J.

Preferably, the high pressure branch-out location BOHP for the turbine bypass line 40 is located in the exhaust line 24 as close as possible to the engine 12, i.e. where the pressure is the highest In the exhaust line 24, for example located at or near the exhaust manifold 26, in the exhaust conduit 27 upstream of the sole or most upstream turbine 34, 34', or at the entry of the sole or most upstream turbine 34, 34\ N evertheless, in an engine arrangement having several turbines in series in the exhaust line, the high pressure branch-out location BOH P for the turbine bypass line 40 could be located in the exhaust line 24 between an upstream and a downstream turbine, provided that there would be at least one turbine between the high pressure branch-out location BOH P for the turbine bypass line 40 and the low pressure branch-out location BQLP for the EGR line 38.

The terms "high pressure" and "low pressure" used in connection with the branch-out locations for the bypass line and the EGR line respectively are used to indicate the relative pressure levels between these two locations, not necessarily implying specific absolute pressure levels, nor necessarily implying that they are respectively the highest or the lowest pressure levels in the exhaust line.

For the sake of clarity, the EGR junction location J is located in the EGR line 38 upstream of the branch-In location Bl, i.e. at a location in the EGR Installation where EGR gases are not yet mixed with fresh air coming the atmosphere. Also, the EGR junction location J Is located in the EGR line 38 downstream of the low pressure branch out location BOLP where the EGR line 38 is connected to the exhaust line 34, i.e. at a location In the EGR installation where the gas flow is recirculated towards the engine and not to the atmosphere.

I n the engine arrangement, the EGR junction location J is located in the EGR line 38 between th e low pressure branch-out location BOLP for the EGR line 38 and the EGR valve 39. As such, the EGR valve 39, while potentially being a mere 2 way valve, may be used to control the amount of EGR gases irrespective of whether they have been taken out of the exh aust line from upstream or downstream of the turbine 34.

In a preferred embodiment of the arrangement, the turbine by-pass line 40 has a turbine by-pass valve 42 distinct from the EGR valve 39 and the turbine by-pass valve 42 and the EGR valve 39 are arranged in series for the flow of EGR gases conveyed through the turbine by-pass 40 towards the intake line 34, with the bypass valve 42 being upstream of the EGR va lve. The bypass valve may be closed to block any flow of exh aust gases through the turbine bypass line 40. The bypass valve may be opened to a llow a flow of exh aust gases through the tu rbine bypass line 40, depending also on the opening of the EGR valve 39.

As shown in the Figures, the turbine by-pass valve 42 may be located upstream of the EGR junction location J.

The EGR installation is p referably provided with a non-return valve 44 In the

EGR line between the low pressure branch-out location BOLP and the EGR junction location J. Such non-return valve 44 may he a passive valve, controlled only by the pressure difference In the EGR line on the opposite sides of the valve 44. The nonreturn valve 44 ensures that gases taken from the exhaust line 24 at the branch-out point BOHP for the turbine bypass lin e 40 do not return to the exhaust line 34 (and thereby to the atmosphere) by flowing back through the low pressure branch-out location BOLP of the EGR line which Is by definition at a lower pressure level than the branch out I.ocation_BOHP_for„the_tur.b.in.e_b.ypass.-line- 40....The. non-return, valve may be biased or non-biased towards its closed position. It could be a ball check valve, a flap check valve, etc.... Alternatively, the non-return valve could be a controlled valve, for example similar to the bypass valve 42 or to the EGR valve 39

Alternatively, the turbine bypass valve could be a three way valve installed at the EGR junction location J. Such three-way valve could then also play th e role of the non-retu rn valve.

With the above arrangement, it will be seen that it is possible to easily control both the total flow rate of EGR gases recirculated to the engine and to control the pressure of exhaust gases in the exhaust line.

The turbine bypass valve 42 can be an electrically controlled valve {as shown on the figures) controlled in a conventional way, for example through a dedicated controller, which could be of any form as described above for the controller 48 of the EGR valve, but preferably through the same controller 48 as the EGR valve 39.

Nevertheless, the tu rbine by-pass valve could be a pne um atically controlled valve, where the opening and closing of the valve could be controlled for example by the combined action of a pressure at the intake manifold and of a pressure at the exhaust m anifold. In a preferred embodiment, the turbine 34, 34 ^J which is bypassed by the bypass line 40 is a variable geometry turbine. This may allow to optimize the turbine operating point when the bypass valve is opened, by controlling the geometry of the turbine, especially in view of maximizing the pressure delivered by the compressor attached to said turbine despite the lower flow and pressure received by said turbine. This may involve restricting the available section of flow for the gases through the variable geometry turbine.

As shown in the Figures 1 and 2, a cooler 46 may be provided in the EGR line 38 between the EGR Junction location J and the branch-in location Bl, for cooling the EGR gases before they are introduced in the intake line 18. Thereby, a same EGR cooler may be used to cool down the EGR gases irrespective of whether they have been taken out of the exhaust line from upstream or downstream of the turbine 34. The cooler 46 may be arranged downstream of the EGR valve 39.

As shown in the Figures 1 and 2, a particle filter 50 may be arranged In the EGR line 38. It is preferably located downstream of the EGR junction location J. The filter could be catalytically coated filter and /or it could be associated with a Diesel oxidation catalyst arranged upstream of the filter. Thereby, a same filter 50 may be used to remove particles from the EGR gases irrespective of whether they have been taken out of the exhaust line from upstream or downstream of the turbine 34. Such location of the filter would also be favorable at periods where it necessary to regenerate the filter, because high temperature gases coming from the branch-out location BOHP for the turbine bypass line 40 can be directed to the filter to ease this regeneration.

The particle filter 50 may for example be arranged between the EGR junction location J and the EGR valve, in which case the valve is better protected from particles. Such a particle filter 50 is preferably also located upstream of the cooler 46, to protect the cooler from particles.

An arrangement as described above makes it possible to implement an innovative process for controlling the internal combustion engine arrangement, An objective of such process is to reduce the pumping losses in the engine due possibly to too high pressures in the exhaust manifold, at least on certain operating points of the engine arrangement.

Such a process would typically involve determining the actual pressure P2 of compressed gases delivered to the engine by the intake line downstream of the turbo-compressor system 32 and determining the actual pressure P3 of exhaust gases out of the engine, in the exhaust line upstream of the turbo-compressor system 32.

Such pressures can be determined by the means of pressure sensors, such as those shown on the Figures, where It can be seen that an intake pressure sensor 50 is shown to be installed In the intake manifold and exhaust pressure sensor 52 is shown to be installed in the exhaust manifold. The intake pressure sensor 50 could be installed elsewhere in the intake line 18, downstream of the compressor system 32. The exhaust pressure sensor 52 cou!d_beJnstalled. else be

24, upstream of the compressor system 32. Nevertheless, rather than being actually measured by such sensors, these pressures could be determined indirectly, with the use of determination algorithms, for example based on pressures measured at other locations in the arrangement and/or based on maps/tables allowing the determination of the relevant pressures as a function of a set of parameters defining the operating point of the engine arrangement (engine speed, engine torque, temperature of gases, etc..)

According to a process for controlling the engine arrangement described above, it is proposed to control the flow of gases in the turbine by pass line 40 with a target that a pressure difference DeltaP between the pressure P3 of exhaust gases out of the engine and the pressure P2 of compressed gases delivered to the engine by the intake line (i.e. DeltaP = P3 - P2) is maintained below a threshold value DeltaPmax. Typically, the bypass control valve 42 is opened when the pressure difference approaches or reaches the threshold value, so as to cause a pressure reduction in the exhaust manifold due to the fact that the flow of exhaust gases out of the engine will not anymore be restricted by the turbine which is by-passed. If the by-pass valve 42 Is proportional, this valve opening can be progressive and the amount of opening may be linked to the actual value of the pressure difference. Preferably, the flow of exhaust gases in the turbine by-pass line 40 may be stopped if the actual pressure P2 of compressed gases delivered to the engine by the intake line downstream of the turbo-compressor system is below a minimum value P2min which may be set depending on the operating point of the engine. Such feature would give priority to a goal of having the pressure of the intake gases delivered to the engine remaining above a certain level, even if that then induces an increase in pumping losses.

More generally, an aspect of the invention is to be found in a process for operating an internal combustion engine arrangement, the process comprising:

- conveying fresh air from the atmosphere to the engine through an intake line;

- conveying exhaust gases out of the engine to the atmosphere throug an exhaust line;

- recovering energy from the exhaust gases in an expander. The expander is preferably located in the exhaust line, and it can comprise for example a turbine 34, 34' of turbo-compressor system 32, with a view of expanding the exhaust gases in the expander which will in return provide mechanical energy. The said recovered energy can be used for compressing gases flowing in the intake line, for example through the rotary compressor 36 located in the intake line and mechanically driven by the turbine 34. Other uses of the recovered energy could be considered,

Such a process encompasses controlling a low pressure exhaust gas recirculation (EGR) flow of gases which are taken from the exhaust line at a branch- out location located in the exhaust line downstream of the expander and conveying the low pressure exhaust gas recirculation (EGR) flow to the intake line. In the shown examples, this is done for example by controlling the EGR valve 39 in the low pressure EGR line 38.

Such process further comprises controlling a high pressure exhaust gas recirculation (EGR) flow which are taken from the exhaust line (24) at a branch-out location located in the exhaust line upstream of the expander, and conveying the high pressure exhaust gas recirculation (EGR) flow to the intake line. In the shown embodiments, this can be achieved by controlling the flow in the turbine bypass line 40. Nevertheless, this could be done with a different EGR installation, for example with a dedicated high pressure EGR line which would not be connected to the low pressure EGR line, but would instead be connected directly to the intake line. It could be particularly advantageous that the dedicated high pressure EGR line has a branch-in location in the intake line which is located upstream of a compressor driven by the said expander.

Such a dedicated high pressure EGR line would typically have a dedicated HP EGR valve and may also comprise a dedicated cooler and /or a dedicated HP EGR particle filter and/or a dedicated Diesel oxidation catalyst.

Even in the case of two separate high pressure and low pressure EGR lines, a common particle filter could be installed in the main exhaust line upstream of both the branch-out location of the high pressure EGR line and of the branch-out location of the low pressure EGR line.

Such process would Involve determining the actual pressure P2 of compressed gases delivered to the engine by the intake line, and determining the actual pressure P3 of exhaust gases out of the engine, for example as explained above.

Similarly to the particular example described above in connection to the embodiments shown above, this more general process involves controlling the high pressure exhaust gas recirculation (EGR) flow with a target that a pressure difference DeltaP between the pressure P3 of exhaust gases out of the engine and the pressure P2 of compressed gases delivered to the engine by the intake line is maintained below a threshold value DeltaPmax. This process would therefore contribute in minimizing pumping loses at the engine which could be attributed to pressure In the exhaust line compared to the pressure in the intake line as seen by the engine.

On the other hand, such a process could include, similarly to what has been described above, setting a minimum value P2min for the pressure of compressed gases delivered to the engine by the intake line. The minimum value P2min for the pressure of compressed gases delivered to the engine by the intake line may depend on the operating point of the engine. The process may further comprise stopping the flow of high pressure exhaust gas recirculation (EGR) flow if the actual pressure P2 of compressed gases delivered to the engine by the intake line is determined to be lower than said minimum value P2min, giving priority to a goal of having the pressure of the Intake gases delivered to the engine remaining above a certain level, even if that then induces an increase in pumping losses.

In all cases, the threshold value DeltaPmax can be positive or negative, or null. If it is positive, then the pressure P3 at the exhaust may become superior to the pressure P2 at the intake, but only up to the maximum limit determined by DeltaPmax. For example, a DeltaPmax value can be determined to be 100 millibar, In which case, the engine arrangement will be controlled so that the pressure at the exhaust of the engine does not exceed the pressure at the intake by more than 100 millibar. If threshold value DeltaPmax is negative, then , the pressure P3 at the exhaust will remain below the pressure P2 at the intake, at least by that limit determined by DeltaPmax.

The threshold value can be a fixed value, independent of the engine arrangement operating conditions. Nevertheless, the threshold value can also be a variable value which may for example vary depending on the operating point of the engine (engine speed, engine torque, engine temperature, etc..)

In the embodiments of the arrangement where a turbine bypass line is fluidically connected to low pressure EGR line at an EGR junction location J located in the EGR line between the branch-out location and the EGR valve, it will be advantageous to have an EGR flow determining device, such as the flow sensor 54, and potentially the temperature sensor 56, in the EGR line downstream of the EGR junction J. Thereby, a same EGR flow determining device may be used to determine the flow of EGR gases irrespective of whether they have been taken out of the exhaust line from upstream or downstream of the turbine 34. The EGR flow determining device can be located in the low pressure EGR line 38 downstream of the EGR valve 39. In the shown embodiments, it is shown to be located downstream of the EGR cooler 46.