FR3041034A1 - EXHAUST GAS RECIRCULATION SYSTEM COMPRISING A CYCLONE FILTER - Google Patents

Abstract

The invention relates to an engine assembly comprising a heat engine (2) with an air intake line at its inlet (1), an exhaust line (7, 8) at its outlet (3) and a fuel system. recirculating (5, 6, 9, 11) exhaust gases having a stitching on the exhaust line (7, 8) bypassing a downstream portion (8). The system comprises a cyclonic filter (5) having an inlet downstream of the stitching, a first outlet connected to the downstream portion (8) of the line (7, 8) and a second outlet connected to the inlet (1) of the motor separating the gases into a filtered stream exiting through the first outlet and a stream containing the heavier particles of the gases exiting through the second outlet, a bypass valve (4) being provided in the system at the stitching to at least prohibit in a position the gas inlet in the system.

Description

EXHAUST GAS RECIRCULATION SYSTEM COMPRISING A

CYCLONE FILTER

The invention relates to a system for recirculating the exhaust gas to the air intake of a heat engine, the system comprising a cyclonic filter. This recirculation system is part of an engine assembly comprising a heat engine with its auxiliary elements such as, for example, an air intake line, an exhaust line and, where appropriate, at least one turbocharger.

To reduce the emission of polluting substances from a motor vehicle with a combustion engine, it is known to equip motor vehicles with a circulation of exhaust gas in order to recover the engine exhaust and exhaust gases. inject them back into the engine inlet at the air intake. This exhaust gas circulation is commonly called the EGR system, the abbreviation EGR means exhaust gas recirculation, this system is also known as the Anglo-Saxon EGR.

In what follows, it will be used indifferently exhaust gas recirculation system or EGR system for the designation of such a system.

The polluting substances emitted by a motor vehicle are mainly oxides and especially nitrogen oxides, also called abbreviations NOx, formed by the high temperature reaction of oxygen with nitrogen. The exhaust gases, already used by the engine, are relatively low in oxygen and the fact of recirculating them in the admission of the engine in the place of the fresh air supplying the engine decreases the quantity of oxygen available and therefore the formation of NOx.

The EGR system may either be provided with a loop or there may be two exhaust gas circulation loops in an EGR system for a turbo-compressed engine, the first loop being the low pressure loop and the second the high pressure loop. The present invention applies equally to these two EGR systems or to a combination of these two systems.

The loop of a system EGR both high pressure and low pressure has a stitching on an exhaust line from an exhaust manifold at the output of the engine for the exhaust gas leaving the engine. engine. The exhaust line may comprise a turbine, in the case of a turbocharged heat engine, as well as various elements for the selective removal of exhaust gases, for example a particulate filter, these particles being mainly soots and one or more catalysts, especially an oxidation catalyst mainly for hydrocarbons. The presence in the exhaust line of a selective catalytic reduction system or SCR system, also known by the acronym SCR, is also possible.

The loop of a high pressure EGR system has its stitching at the entrance of the exhaust line just at the outlet of the exhaust manifold of the engine and therefore before the turbine in the case of a turbocharged engine. The loop of a low-pressure EGR system has its tapping further downstream on the exhaust line than for a high-pressure EGR system, advantageously downstream of one or more elements of depollution that comprise the exhaust line.

[0008] The high and / or low pressure EGR mouth (s) join a fresh air intake pipe upstream of an air intake manifold that the heat engine comprises, where appropriate when the engine is a motor. turbocharged engine through a compressor after joining the fresh air intake line.

An EGR exhaust gas circulation system generally comprises a heat exchanger for cooling the exhaust gas burned and at least one valve, commonly called EGR valve, which adjusts the flow of burnt gas to a collector. admission to an air intake to the engine, this for any type of EGR loop.

This valve is controlled by the computer of a motor control control in charge of the proper operation of the engine. There is thus a heat exchanger, preferably water, and at least one EGR valve for each of the two loops described above. It is known that the EGR valve is liable to become fouled and to then have an altered operation due to the particles present in the recirculated exhaust gas.

Particles and hydrocarbons present in the exhaust gas recirculated by the EGR system to be reintroduced to the air intake of the engine are mostly burned or burnt in the combustion chamber of the engine.

However, the amount of gas recirculated by the EGR system is relatively low, the majority of the particles and hydrocarbons leaving the engine must be treated by the pollution control elements present in the exhaust line.

The more the gases are charged in particles and more it is necessary to increase the regeneration frequency of the pollution control elements, which has a negative impact on the engine fuel consumption and emissions. The unburned hydrocarbons present in the exhaust gases can be considered as causing a loss of energy, whereas it would be desirable to recirculate them to the intake of the engine in larger quantities than a conventional EGR system allows. .

DE-A-2 833 431 discloses a motor with a bypass on the exhaust line of the engine for the return of a portion of the exhaust gas at the engine inlet. This part of the exhaust gas may have been enriched in very heavy particles by passing through a cyclonic filter.

This document is prior to the use of an exhaust gas recirculation system and the derivation shown in this document is not comparable to a typical recirculation system with recirculation valve and heat exchanger. In addition, this document does not mention any depollution element present in the exhaust line and therefore does not address the problem of decreasing the regeneration frequency of any depollution element.

EP-A-2 078 832 discloses an engine assembly with an exhaust gas recirculation system at the engine inlet. The system includes a cyclonic filter enriching heavy particles of pollutant recirculated gas but it is expected treatment of recirculated gases before their arrival at the engine inlet for the removal of particles. This document thus illustrates a strong prejudice of the state of the art considering as disadvantageous the renewal of pollutants at the engine inlet, these pollutants being supposed to have a fouling effect on the system and the engine inlet.

Therefore, the problem underlying the present invention is to perform a better recovery of hydrocarbons and certain pollutants present in the exhaust gas which according to the state of the art are treated in at least one depollution element integrated in the exhaust line of a combustion engine of a motor vehicle in particular to slow down the pollutant filling of this element or to ensure operation of the engine with less emission of pollutants.

To achieve this objective, there is provided according to the invention an engine assembly comprising a heat engine, an air intake line to an engine air inlet and an exhaust line to an engine outlet , the assembly also comprising an exhaust gas recirculation system at the engine air intake having a stitching on the exhaust line in a bypass of a downstream portion of the line, characterized in that the system recirculation circuit comprises a cyclonic filter having an inlet downstream of the stitching, a first outlet connected to the downstream portion of the line and a second outlet connected to the engine air inlet, the cyclonic filter separating the exhaust gases the passing through a first filtered stream exiting through the first outlet and a second stream containing the heavier particles of the gases exiting through the second outlet, a bypass valve being disposed in the sys recirculation system at the stitching to at least prohibit in a closed position the entry of exhaust gas into the system.

The technical effect obtained is the filtering of the exhaust gas and the separation of the exhaust gas into two streams, one of which is heavily loaded with heavy particles, such as condensates, hydrocarbons or soot-type particles. The highly charged flow can be directed to the admission of air to the heat engine via the recirculation system, this when it is decided to protect or not to overload pollutants or elements of pollution in the portion downstream of the exhaust line or when an increase in engine temperature and / or better recovery of hydrocarbons are desired.

In this case, the water contained in the recirculated condensate part of the heavier particles allows an increase in the heat capacity of the intake air in the engine. This recirculation of water with the condensates makes it possible to reduce the emissions of nitrogen oxides because of the significant heat capacity of the water and the resulting increase in the combustion temperature in the engine.

Hydrocarbons are also contained in the heavier particles and can be burned again in the engine, which represents a recovery of energy.

In addition, the first flow grouping the heavier particles of the gas is discharged to the engine air inlet in the gas recirculation system, which allows to reduce the emissions of particles and particulates by withdrawing. hydrocarbons present in the exhaust line before their treatment. This can favorably reduce the regeneration frequency of a pollution control element of a pollutant belonging to the heavier particles, for example particles of soot to be retained in the particulate filter. The overall efficiency of the engine is therefore improved.

It has been found that the possible fouling of the recirculation system that could induce such a passage of the first flow in the recirculation system, contrary to the existing prejudice against the implementation of the present invention, was to be minimized given the significant progress made in controlling particulate emissions at the source by better fuel combustion achieved in the engine.

Advantageously, the gas recirculation system comprises a recirculation valve and a heat exchanger downstream of the cyclonic filter.

Advantageously, the downstream portion of the exhaust line comprises at least one selective depollution element for the depollution of the exhaust gas and, where appropriate, at least a portion of the heavy particles of the first stream.

Advantageously, the first output of the cyclonic filter is connected to the downstream portion of the line by an intermediate pipe.

Advantageously, the recirculation system comprises an upstream recirculation pipe between the valve and the cyclonic filter and a downstream recirculation pipe at the outlet of the cyclonic filter, the downstream recirculation pipe opening into a fresh air inlet pipe. upstream of the engine air intake.

Advantageously, the engine is a supercharged engine comprising at least one turbocharger having a turbine in the exhaust line and a compressor at the air inlet of the engine, the compressor being traversed by fresh air and exhaust gas from the recirculation system supplying an air intake manifold as the engine air inlet.

Advantageously, the recirculation system is a high pressure system collecting the exhaust gas directly at the outlet of an exhaust manifold of the engine, the first output of the cyclonic filter being connected to the downstream portion of the line by a intermediate pipe upstream of the turbine.

Advantageously, the bypass valve is a one-way valve, a multi-way valve, a valve having only a full open position and a complete closed position or a proportional valve with opening and closing positions. as well as a plurality of intermediate open and closed positions. The bypass valve influences the flow rate of the gases that pass through the cyclonic filter and therefore the pressure drop of this cyclonic filter but also its efficiency.

A multiple-channel bypass valve and adjustable opening allows flow control both in the downstream portion of the exhaust line in the system RGE. Thus, the bypass valve is preferably a proportional valve controlled by a motor control control in charge of the operation of the motor assembly.

The invention also relates to a method of controlling such a motor assembly with a controlled bypass valve, in which it is carried out a control of the bypass valve opening to the recirculation system: - according to the a request for reduction of the production of nitrogen oxides emitted by the engine and / or a request for recovery of hydrocarbons in the exhaust gas, the increase of the amount of condensate containing water and the amount of hydrocarbons as the heaviest particles in the outgoing flow by the second output of the cyclonic filter to respectively meet these demands, and, - when the downstream portion of the exhaust line comprises at minus one selective abatement element for the exhaust gas depollution and that this abatement element reaches its filling limit.

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the accompanying drawings given by way of non-limiting examples and in which: - Figure 1 is a schematic representation of a motor vehicle engine assembly according to the present invention, this assembly comprising a heat engine equipped with an EGR system incorporating a cyclonic filter, the valve associated with the system allowing at least partial passage of exhaust gas in the engine. Figure 2 is a schematic representation of the motor assembly of Figure 1, the valve associated with the system closing the at least partial passage of exhaust gas in the system and the filter being inactive in this figure.

It is to be borne in mind that the figures are given by way of examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular, the dimensions of the various elements illustrated are not representative of reality.

By engine assembly, it is considered the engine with all its auxiliary elements for example its fresh air intake line, its exhaust line and a low pressure RGE system and / or high pressure, if necessary l assembly comprising at least one turbo compressor with a compressor in the air intake line and a turbine in the exhaust line. The present invention also extends to an engine assembly with several turbo-compressors.

Figures 1 and 2 show a heat engine 1 equipped with an RGE system with a high pressure loop. It should be borne in mind that the present invention can be adapted to a single loop EGR system whether it is high or low pressure or two loops although its adaptation to a high pressure loop is preferred.

In the case of a two-loop EGR system, a circulation loop is said low-pressure EGR loop and performs an exhaust gas sampling downstream of a pollution control element of the vehicle exhaust line. automobile, for example a particulate filter. These relatively clean exhaust gases, after cooling in a water exchanger, can be injected by the first loop into the intake air supplying the engine.

The advantage of the first so-called low pressure EGR loop is to use relatively clean exhaust and allow a sharp decrease in temperature and better homogenization of the mixture of air and recirculated exhaust gas low pressure at the engine inlet. The first so-called low pressure EGR loop is used in normal operation of the motor vehicle until full load. An EGR valve is provided for each of the two low pressure and high pressure loops.

As illustrated in FIGS. 1 and 2, the so-called EGR high-pressure loop of an RGE system 5, 6, 9 and 11 carries out an exhaust gas sampling at the outlet of the engine 2, the if necessary upstream of the turbine of the turbocharger when the latter is present, this advantageously just after the exhaust manifold 3 of a heat engine 2. There is provided an EGR valve 6 for the operation of said loop.

When the engine 2 is a supercharged engine it comprises at least one turbocharger having a turbine in the line 7, 8 exhaust and a compressor to the air inlet 1 of the engine 2, the compressor being traversed by de fresh air and exhaust gases from the recirculation system 5, 6, 9, 11 supplying an air intake manifold as air intake 1 of the engine 2.

The exhaust gas, after a cooling in a water heat exchanger, is injected by the high-pressure RGE loop into the fresh intake air supplying the heat engine 2, advantageously passing through the exhaust manifold. intake 1 of engine air as engine inlet. The fresh air follows the path shown by the arrow F1 and the fresh air plus the recirculated gases by the EGR system follows the path of the arrow F2.

A high pressure loop of an EGR system is disposed closer to the engine 2 in its exhaust line 7 than the low pressure loop and the exhaust gas passing through said high pressure loop is hotter than those passing through. the low pressure loop. The high-pressure loop can recover more calories than the low-pressure loop, but the recirculated gases in the high-pressure loop are dirtier than those in the low-pressure loop, which are frequently cleaned up by passing through one or more of the depollution elements. located in the exhaust line 7, this or these elements not being illustrated in Figures 1 and 2.

The engine assembly according to the present invention conventionally comprises a thermal engine 2, turbo-compressed or not, an air intake line to an air inlet 1 of the engine 2, to the figures an intake manifold 1 of fresh air and recirculated gas and a line 7, 8 exhaust to an output 3 of the engine 2, figures an exhaust manifold 3 of the flue gases in the engine 2.

The assembly also comprises an EGR system or recirculation system 5, 6, 9, 11 of the exhaust gas at the inlet 1 of the engine 2. This system has a stitching on the line 7, 8 exhaust pipe at the outlet of the exhaust manifold 3 of the engine 2. There is therefore a downstream portion 8 of the exhaust line 7, 8 continuing the exhaust line being in bypass with the recirculation system 5, 6, 9, 11. This downstream portion 8 may carry one or various selective decontamination elements of the exhaust gas therethrough, examples of pollution abatement elements having been previously mentioned.

According to the present invention, the recirculating RGE system 5, 6, 9, 11 comprises a cyclonic filter 5 having an inlet downstream of the stitching and a first outlet connected to the downstream portion 8 of the line 7, 8. there can therefore be a return of the exhaust gas passing through the filter 5 in the exhaust line 7, 8, more precisely in its downstream portion 8.

The cyclonic filter 5 has a second outlet opening into the rest of the RGE system 5, 6, 9, 11 connected to the air intake 1 of the engine 2 in particular by a downstream recirculation pipe RGE 11 which comprises a valve EGR 6 downstream of the filter 5. This cyclonic filter 5 can be both simple and multi-cyclonic.

The cyclonic filter 5 separates the exhaust gas passing through it into a first filtered stream leaving the first outlet and a second stream containing the heaviest particles of the gases leaving the second outlet. A bypass valve 4 is arranged in the recirculation system 5, 6, 9, 11 at the stitching to at least prohibit in a closed position the exhaust gas inlet in the system 5, 6, 9, 11 This is shown in Figure 2.

In Figure 1, the bypass valve 4 allows the passage of exhaust gas in the system RGE 5, 6, 9, 11 according to the arrow F3. Part of these gases returns to the exhaust line 7, 8 via the downstream portion 8 of the line 7, 8 according to the arrow F4 by the first output of the cyclonic filter 5 while the rest of the exhaust gas continues its course in the EGR system 5, 6, 9, 11 to the input 1 of the engine 2, this path being illustrated by the arrow F5.

Thus in the mode shown in Figure 1, when the thermal engine 2 operates with recirculation of the exhaust gas, the particles, condensate and hydrocarbons are concentrated to the recirculation valve 6 RGE. The gases towards the downstream portion 8 of the exhaust line 7, 8 are then less loaded with particles, hydrocarbons and condensates.

In Figure 2, the cyclonic filter 5 is disabled. The bypass valve 4 does not allow the passage of the exhaust gas in the EGR system 5, 6, 9, 11 via the cyclone filter 5 and the exhaust gases pass into the rest of the exhaust line 7, 8 according to the arrow F3a. It is possible, but not always effective, for some of these gases to leave the exhaust line 7, 8 to return to the RGE system 5, 6, 9, 11 via the first output of the cyclonic filter 5 then inactive while taking the route. opposite that shown in Figure 1 by the arrow F4.

The exhaust gas and recirculated are not filtered and follow the path indicated by the arrow F5a, similar course to that of the arrow F5. It is of course still possible to recirculate exhaust gas to the inlet if desired. This can be done by the motor control control of the motor vehicle equipped with the motor assembly according to the present invention.

The examples illustrated in Figures 1 and 2 are in no way limiting. Indeed, if the bypass valve 4 can be a one-way valve, all-or-nothing type, with only a full open position and a complete closed position, this bypass valve 4 can be a proportional channel valve, a multi-way valve advantageously proportional by having complete open and closed positions as well as a plurality of intermediate open and closed positions. The flow rates of the gases in the EGR system 5, 6, 9, 11 and in the exhaust line 7, 8 can thus be controlled.

The bypass valve 4 may be advantageously but not only a proportional solenoid valve with an opening proportional to the electric current or the voltage of its power supply. This type of solenoid valve is generally controlled via a command, preferably by an engine control control having all the parameters to perform this command.

The bypass valve 4 allows a regulation of the flow rate of the gases that pass through the cyclonic filter 5 and therefore has an influence on the pressure drop of the filter 5 but also the efficiency of the filter 5. The flow of gases leaving the engine and the flow of recirculated gas being highly variable, it is clear that once the size and geometry of the filter 5 chosen, the bypass valve 4 can be used to adjust the flow to have the best compromise between pressure drop and efficiency filtering.

The first output of the cyclonic filter 5 can be connected to the downstream portion 8 of the line 7, 8 by an intermediate pipe 10. The recirculation system RGE 5, 6, 9, 11 may comprise an upstream pipe 9 recirculation between the valve 4 and the cyclone filter 5 and a downstream pipe 11 for recirculation at the outlet of the cyclone filter 5, the downstream pipe 11 for recirculation opening into a fresh air intake pipe upstream of the air inlet 1 of the engine 2.

In the preferred embodiment of the present invention, the first flow comprising the heavier particles of the gases is discharged to the air inlet 1 of the engine 2 in the recirculation system 5, 6, 9, 11 of the gases . The heavy particles may contain water in condensates, hydrocarbons and / or particles, including soot present in the exhaust gas.

This mode is intended to protect or allow proper operation of the element or the pollution control elements present in the downstream portion 8 of the exhaust line with respect to the quilting in addition to performing a recovery of energy at engine, by recovery of previously unburned hydrocarbons and increase of the engine temperature by the presence of recycled water, this water being present in the heavier particles.

According to this first embodiment, the heavier particles, for example soot, hydrocarbons and condensates, present in the exhaust gas are extracted by the cyclonic filter 5 and entrained in the recirculated gases at the inlet of the air or engine air intake 2.

The first effect obtained is to reduce the amount of particles and hydrocarbons emitted via the combustion of the fuel in the engine 2. The favoring of the recirculation of water which has a high heat capacity can contribute to reducing the emission of nitrogen oxides or NOx for the same flow of the EGR system.

For a system RGE 5, 6, 9, 11 high pressure, the system is tapped at the beginning of the exhaust line 7, 8, preferably near the exhaust manifold 3. In this case and for a turbo-compressed engine the downstream portion 8 at the stitching of the exhaust line 7, 8 houses the turbine of the turbo-compressor. The exhaust gases collected at the outlet 3 of the engine are sent to the inlet of the cyclonic filter 5 or to the turbine according to the position of the bypass valve 4 located at the tap of the RGE system 5, 6, 9, 11.

When the engine 2 operates with a recirculation of the exhaust gas, that is to say with a recirculation valve or valve EGR 6 exhaust gas not closed and the bypass valve 4 at the level of stitching is in the open position towards the filter 5, a portion of the exhaust gas passes into the cyclonic filter 5 before passing into the turbine or into the rest of the EGR system, mainly a recirculation pipe 11 downstream of the filter 5.

Thus, the gases leaving the cyclonic filter 5 by its first outlet to go to the turbine disposed in the downstream portion 8 of the exhaust line 7, 8 are freed of a portion of the particles, hydrocarbons and condensates then that the recirculated gases leaving the cyclonic filter 5 at its second outlet are enriched with the latter.

As previously mentioned, the downstream portion 8 of the exhaust line 7, 8 comprises one or more depollution elements which are filled with a respective pollutant or with several pollutants such as an additive particulate filter. If, for example, one of the depollution elements is close to a complete filling, the unfiltered flow of gas containing the heavier particles of the gases may contain the pollutant to be treated by the depollution element.

In this case, the pollutant, part of the heavier particles, is sent into the remaining portion of the RGE system 5, 6, 9, 11 to the engine inlet and the pollution control element dedicated to depollution of this pollutant no longer has to treat this pollutant.

For a turbocharged engine, when the recirculation RGE valve 6 is closed or for a particular need, the bypass valve 4 upstream of the cyclonic filter 5 at the stitching of the system RGE 5, 6, 9, 11 can be open to the turbine to minimize the pressure drop or not to reduce the amount of unburned hydrocarbons, which for example is particularly appropriate during the regeneration of a particulate filter as a pollution control element in the portion downstream of the exhaust line or any other depollution element requiring an increase in temperature for its regeneration. The cyclonic filter 5 does not operate then.

The present invention is preferably applied to an engine assembly having a recirculating system 5, 6, 9, 11 high pressure collecting the exhaust gas directly at the outlet of an exhaust manifold 3 as a output of the engine 2, the first output of the cyclonic filter 5 being connected to the downstream portion 8 of the line 7, 8 by an intermediate pipe 10 upstream of the turbine.

However, it is possible to adapt the present invention to an engine assembly with a recirculation system 5, 6, 9, 11 low pressure, the nozzle of the recirculation system being preferably upstream of the element or elements of depollution present in the exhaust line to maintain the protective benefits of the abovementioned elements or abatement elements.

According to another aspect of the invention, it relates to a control method of a motor assembly for which the bypass valve 4 is a controlled valve, preferably by the control of the motor, in charge of optimal operation of the motor. The engine control unit receives information from several sensors, including temperature sensors, sensors of the oxygen sensor type or pressure sensors that allow it to monitor, by measure or estimate, the operation of the engine, for example the amount of unburned hydrocarbons or pollutants in the exhaust line of the vehicle as well as the filling of one or pollution abatement elements.

In this method, it is carried out a control of the bypass valve 4 opening to the recirculation system 5, 6, 9, 11. This control can, for example, be done according to a reduction request. the production of nitrogen oxides emitted by the engine and / or a request for recovery of hydrocarbons in the exhaust gas. It is advantageously the control command of the engine that is in charge of managing these requests.

In these cases, increasing the amount of condensate containing water and the amount of hydrocarbons as the heaviest particles in the outflow by the second output of the cyclonic filter 5 can respectively respond respectively. to these requests. The presence of water increases the operating temperature of the engine and reduces the emission of nitrogen oxides at the outlet of the engine, which relieves the element or the elements of depollution specifically dedicated to the capture or elimination of oxides nitrogen.

In addition, when the downstream portion 8 of the exhaust line 7, 8 comprises at least one selective pollution control element for the exhaust gas depollution, which is almost always the case, and that this element of clearance reaches its filling limit, an increase in very heavy particles recirculated to the engine air inlet can relieve this or these depollution elements of an increase in their load and for example, space their regeneration.

For example, without this being limiting, regenerating a particulate filter during a journey in the city may be disadvantageous for the good performance of the regeneration, this path may be short and interrupt the regeneration . The control command may have information on the type of conduct of the driver and suspend a regeneration by recirculating the soot particles to fill the particle filter to the engine inlet by the EGR system until the vehicle performs a course more conducive to regeneration. There is therefore in this case an overload of the soot particle filter.

The invention is not limited to the described and illustrated embodiments which have been given only as examples.

Claims (10)

Claims: An engine assembly comprising a heat engine (2), an air intake line at an engine air inlet (1) (2) and an exhaust line (7, 8) at an outlet (3). ) of the engine (2), the assembly also comprising a recirculation system (5, 6, 9, 11) of the exhaust gas at the inlet (1) of the engine air (2) having a stitching on the line (7, 8) of exhaust from a downstream portion (8) of the line (7, 8), characterized in that the recirculation system (5, 6, 9, 11) comprises a cyclonic filter ( 5) having an inlet downstream of the stitching, a first outlet connected to the downstream portion (8) of the line (7, 8) and a second outlet connected to the air inlet (1) of the motor (2), the cyclonic filter (5) separating the exhaust gas passing through it into a first filtered stream exiting through the first outlet and a second stream containing the heavier particles of the gases exiting through the second outlet, a diverter valve; rivet (4) being disposed in the recirculation system (5, 6, 9, 11) at the stitching to at least prohibit in a closed position the exhaust gas inlet in the system (5, 6, 9). , 11). 2. Engine assembly according to claim 1, wherein the gas recirculation system (5, 6, 9, 11) comprises a recirculation valve (6) and a heat exchanger downstream of the cyclonic filter (5). 3. Engine assembly according to claim 1 or 2, wherein the downstream portion (8) of the exhaust line (7, 8) comprises at least one selective pollution control element for the exhaust gas depollution. 4. Engine assembly according to any one of the preceding claims, wherein the first output of the cyclone filter (5) is connected to the downstream portion (8) of the line (7, 8) by an intermediate pipe (10). Motor unit according to one of the preceding claims, in which the recirculation system (5, 6, 9, 11) comprises a recirculation upstream line (9) between the bypass valve (4) and the cyclonic filter ( 5) and a downstream duct (11) for recirculation at the outlet of the cyclone filter (5), the downstream duct (11) for recirculation opening into a fresh air intake pipe upstream of the inlet (1) of engine air (2). 6. Engine assembly according to any one of the preceding claims, wherein the engine (2) is a supercharged engine comprising at least one turbocharger having a turbine in the line (7, 8) exhaust and a compressor at the inlet (1) of the engine air (2), the compressor being traversed by fresh air and exhaust gases from the recirculation system (5, 6, 9, 11) supplying an intake manifold ( 1) of air as engine air inlet (2). 7. The engine assembly of claim 6, wherein the recirculation system (5, 6, 9, 11) is a high pressure system collecting the exhaust gas directly at the outlet of an exhaust manifold (3) as a the output of the engine (2), the first output of the cyclonic filter (5) being connected to the downstream portion (8) of the line (7, 8) upstream of the turbine. 8. Engine assembly according to any one of the preceding claims, wherein the bypass valve (4) is a one-way valve, a multi-way valve, a valve having only a fully open position and a complete closed position or a proportional valve with full open and closed positions as well as a plurality of intermediate open and closed positions. 9. Engine assembly according to claim 8, wherein the bypass valve (4) is a proportional valve controlled by a motor control control in charge of the operation of the motor assembly. 10. A method of controlling an engine assembly according to claim 9, wherein it is carried out a control of the bypass valve (4) opening to the recirculation system (5, 6, 9, 11): - in based on a request to reduce the production of nitrogen oxides emitted by the engine and / or a request for recovery of hydrocarbons in the exhaust gas, the increase in the amount of condensate containing water and the quantity of hydrocarbons as heavier particles in the flow leaving by the second outlet of the cyclonic filter (5) making it possible respectively to respond to these requests, and, - when the downstream portion (8) the exhaust line (7, 8) comprises at least one selective abatement element for the exhaust gas depollution and that this abatement element reaches its filling limit.