FR3053404B1 - EXHAUST GAS CIRCULATION ASSEMBLY OF A THERMAL ENGINE - Google Patents

Abstract

An exhaust gas circulation assembly of a heat engine comprises an exhaust gas recirculation circuit (22) receiving exhaust gas from the engine. The exhaust gas recirculation circuit (22) includes a turbine (28) for energy recovery. According to the invention, the assembly comprises a device for diverting (30) the exhaust gas formed downstream of the energy recovery turbine (28) and configured to evacuate all or part of the exhaust gas from the exhaust gas circuit. exhaust gas recirculation (22) after passing through the energy recovery turbine (28).

Description

The invention relates to the field of thermal engines of a motor vehicle, and it relates more particularly to engines equipped with an exhaust gas recirculation circuit.

A motor can conventionally be equipped with a turbocharger comprising a supercharger and a turbine, connected by a common shaft. The turbine, disposed across an exhaust gas exhaust system from the engine after combustion, is rotated under the effect of the exhaust gas therethrough, and this movement is transmitted to the compressor which allows the supplying the engine with fresh air at a pressure higher than the atmospheric pressure at which air is drawn in an intake circuit. The turbocharger is intended in particular to increase the amount of air admitted into the engine cylinders.

A heat exchanger may be placed between the compressor and an engine intake manifold to cool the compressed air at the outlet of the compressor. Indeed, it is understood that when the intake air of the engine is compressed, its temperature rises. Hot air occupies a larger volume than cold air, it is intended, in order not to reduce the desired effect of the turbocharger, to cool the temperature of the air brought to penetrate the engine block.

In the case of a combustion engine, in particular a diesel engine, nitrogen oxides and particles are released into the exhaust gas. As pollution control standards are becoming more stringent, exhaust gas treatment devices are placed in the exhaust line and may include a particulate filter, a catalyst and other devices that make it possible to oxidize the reducers. present at the engine outlet, such as unburned hydrocarbons and carbon monoxide.

To further reduce nitrogen oxide emissions, it is known to set up a flue gas recirculation circuit at the output of the engine block, also known by the acronym EGR for "Exbaust Gas Recirculation". The EGR circuit is stung on the. exhaust circuit and a valve associated with this EGR circuit is configured to direct the exhaust in the opposite direction, from the output of the engine block to the admission thereof. The EGR valve is used to modulate the amount of recycled exhaust gas in the intake manifold.

Such an exhaust gas recirculation has the effect on the one hand of lowering the oxygen content in the gases admitted to the heat engine, which has the effect of reducing the rate of combustion, and on the other hand of reducing the gas temperature during combustion. This in particular makes it possible to reduce the emissions of nitrogen oxides.

In a manner similar to that described above for the cooling of the fresh air in the intake circuit, and always with the aim of increasing the efficiency of the engine, it is possible for the recirculated exhaust gases to be cooled before mixing with fresh air in the intake circuit. The recirculation circuit may then comprise a heat exchanger commonly known by the acronym EGRC for "Exhaust Gas Recirculation Cooler".

The exhaust gas recirculation circuit is thus configured in the prior art so that the portion of the exhaust gas taken from the exhaust circuit is reinjected, in full into the intake of the engine block, the EGR valve. to control the amount of gas withdrawn.

A turbine, additional in that it is separate from the turbine of the turbocharger, can be provided on the exhaust gas recirculation circuit, to be rotated by the passage of the exhaust gas circulating in this recirculation circuit . This rotation is used to assist the operation of the vehicle, for example by relieving the alternator in the production of electricity and / or by providing mechanical assistance to the engine or to elements of the engine architecture such as the turbocharger. example. This additional energy recovery turbine may for example be mechanically coupled to an electric machine, capable of generating electrical energy. The electrical energy thus produced can be redistributed elsewhere or stored in an energy storage system.

In this context, the present invention aims to propose an improvement to existing engines, comprising an exhaust gas recirculation circuit, which allows a plurality of distinct modes of operation.

Lin exhaust gas circulation assembly of a heat engine according to the invention comprises an exhaust gas recirculation circuit receiving the exhaust gas of the engine and which comprises an energy recovery turbine. According to the invention, the assembly further comprises an exhaust gas diversion device arranged downstream of the energy recovery turbine and configured to evacuate all or part of the exhaust gases from the gas recirculation circuit. exhaust after their passage through the energy recovery turbine.

Such a circulation assembly may in particular be implanted in a heat engine, optionally a turbocharger, comprising an intake circuit and an exhaust circuit, the exhaust gas recirculation circuit extending from the exhaust circuit. exhaust to the intake circuit.

The arrangement of the exhaust gas bypass device is downstream of the energy recovery turbine with respect to the recirculation direction of the exhaust gas in the recirculation circuit.

Thus, the exhaust gases circulating in the recirculation circuit are allowed to cooperate with the turbine without necessarily having to recirculate towards the engine intake circuit, but instead be redirected towards the outlet of the exhaust circuit.

It is then possible to operate the heat engine according to several modes of operation among which a standard exhaust gas recirculation mode in which energy recovery is carried out in the EGR circuit and other modes of operation in which it facilitates the recovery of energy in the deceleration phase or during very high loads of the engine.

According to a characteristic of the invention, the bypass device comprises at least one bypass element and a bypass circuit configured to be connected to an exhaust circuit of the heat engine.

According to other characteristics of the invention, taken alone or in combination, provision may be made for: the exhaust gas bypass element is disposed on the recirculation circuit while being configured to distribute the exhaust gases between the recirculation circuit and the bypass circuit; - The bypass circuit is arranged to lead to the exhaust circuit downstream of a turbine of a turbocharger of the engine; - The bypass circuit opens on the exhaust circuit upstream, with respect to the flow of exhaust gas in the exhaust circuit, an exhaust gas treatment device; the recirculation circuit comprises a downstream heat exchanger, with respect to the circulation of the exhaust gases in the recirculation circuit, of the exhaust gas bypass device; - The recirculation circuit comprises a valve regulating the passage of exhaust gas in the recirculation circuit arranged downstream, with respect to the direction of recirculation of the exhaust gas, the exhaust gas bypass device; - The control valve and the exhaust gas bypass device are controlled according to the amount of exhaust gas to be fed back into an intake circuit of the engine; - The gas bypass element is a three-way valve, and may in particular be a rotary valve valve, a valve valve, it being understood that the choice of technology to achieve this bypass element is not limiting to the the invention, since it allows the distribution of the exhaust gas between the recirculation circuit and the bypass circuit; the energy recovery turbine is coupled to an electric machine; - the engine is a diesel engine. The invention also relates to a motor vehicle equipped with a heat engine as just presented. The invention furthermore relates to a method of implementing an exhaust gas recirculation of a heat engine, during which the exhaust gases, taken from an exhaust system of the heat engine, are passed through. in an energy recovery turbine arranged in a recirculation circuit, before selectively directing these exhaust gases in the continuity of the recirculation circuit or in a bypass circuit bringing the exhaust gases back to the exhaust circuit of the engine. Other features and advantages of the present invention will become more apparent from the description and the single figure, which is an illustration of an engine architecture according to one embodiment of the invention.

In the following description, the terms upstream and downstream will be used, in particular to qualify the position of this or that element of the recirculation circuit. These terms will be understood according to the flow direction of the gases in the corresponding circuit. Thus, when it will be specified that a first element of the recirculation circuit is upstream of a second element of the recirculation circuit, it will be understood that the gases flowing in this recirculation circuit pass through the first element before the recirculation circuit. cross the second element.

A heat engine 1 comprises a motor block 2 defining combustion chambers 3 provided with pistons which rotate a shaft output. The combustion chambers of the engine block 2 are connected to an intake circuit 4 of fresh air taken from the outside of the vehicle, and to an exhaust system 6 of the flue gases during combustion, or gas of combustion. 'exhaust.

The engine 1 comprises for example a turbocharger formed by the cooperation of a compressor 8, arranged on the intake circuit 4, and a turbine 10, placed on the exhaust circuit 6 so as to recover a portion of the fuel. Exhaust gas energy and rotate the compressor 8. In particular, the compressor 8 and the turbine 10 can be mounted on a common shaft, not shown here.

The intake circuit 4 comprises, upstream of the compressor 8, an air filter 12, and may comprise an exchanger, not shown here, for cooling the supply air of the combustion chambers of the engine block 2. It is understood that that without departing from the context of the invention, one could provide to equip the intake circuit of any type of filter and any type of exchanger. Furthermore, the intake circuit 4 has, downstream of the compressor 8, a first control valve 14 controlled to control the supply of fresh air to the combustion chambers of the engine block 2.

The exhaust circuit 6 comprises, downstream of the turbine 10, a device 16 for treating the pollutants of the exhaust gases, which may notably consist, for example, of a catalyst and / or a particulate filter.

The exhaust system comprises in particular two elements for regulating the flow of the exhaust gases, one 18 upstream and the other 20 downstream of the processing device 16, forming a downstream exhaust-pressure device the turbocharger on the exhaust circuit 6. A first regulating element 18, directly downstream of the turbocharger turbine 10, is controlled to determine the quantity of exhaust gas allowed to pass through the turbine, and the second regulating element 20, arranged downstream of the treatment device, manages the pressure conditions to allow the passage of recirculated exhaust gas through the treatment device, as will be described in more detail below.

The engine according to the invention further comprises a recirculation circuit 22 of the exhaust gas, which allows to reinject a portion of the exhaust gas into the inlet, in particular to the combustion chambers. This contributes to the cooling of the combustion in the cylinders and the reduction of the oxygen content, which makes it possible to reduce the amount of nitrogen oxides (NOx) in the exhaust gases by combustion in the engine block, harmful nitrogen oxide being mainly developed at high temperatures and at high pressures.

The recirculation circuit 22 is here a high pressure circuit in that it is connected, at a first end 24, to the exhaust circuit 6 upstream of the turbine 10 and, at the opposite end 26, or second end at the intake circuit 4 downstream of the compressor 8.

We will now describe in more detail the recirculation circuit 22 and the various elements that compose it, and in particular their specific arrangement according to the invention.

From the first end 24 to the second end 26, the gases recirculated from the exhaust circuit 6 to the intake circuit 4 successively meet a turbine 28 for energy recovery of the recirculated gases, a device for diverting the recirculated gases. , an additional heat exchanger 32 and a regulating valve 34.

The energy recovery turbine 28 is rotated by the passage of the exhaust gas circulating in the recirculation circuit 22, and this rotation is used to assist the operation of the vehicle, for example by relieving the alternator in the production of electricity and / or by providing mechanical assistance to the engine or to elements of the engine architecture such as the turbocharger for example. In the illustrated example, the energy recovery turbine is mechanically coupled to an electric machine 36, capable of generating electrical energy. The electrical energy thus produced can be redistributed elsewhere or stored in an energy storage system. It is in particular according to the examples detailed above that the turbine 28 is qualified exhaust energy recuperator.

The exhaust gas bypass device 30 comprises a bypass element 31, disposed on the recirculation circuit, and a bypass circuit 38. The bypass device 30, and in particular the bypass element 31, is driven to take at least a first position in which it allows the flow of exhaust gases along the recirculation circuit 22 or a second position in which it allows the derivation of these exhaust gases to the branch circuit 38 which will be detailed below. after. The branch element 31 may consist of a three-way valve. In the illustrated example, it takes the form of a valve valve as defined in the patent application filed by the applicant under the reference WO 2012/001282, but it is understood that this three-way valve can take any other type as long as it includes at least one entrance and at least two exits.

Of course, the bypass element 31 is able to take any intermediate positions between the first position and the second position mentioned above, thus allowing a shared flow of exhaust gases between the branch circuit 38 and a portion of the recirculation circuit 22 connecting the bypass element 31 of the exhaust gas 30 to the inlet of the engine. The EGR heat exchanger 32 is disposed on the recirculation circuit for cooling the recirculated exhaust gas before mixing with fresh air in the intake circuit 4. The additional heat exchanger 32 may comprise a heat exchanger air-to-air type or air-water type, especially depending on space constraints.

The regulating valve 34 is arranged directly upstream of the connection point, called the second end 26, with the intake circuit 4 and it allows, in particular in combination with the first control valve 14 placed on the intake circuit 4, to controlling the percentage of exhaust gas in the air admitted into the combustion chamber of the engine block 2. In the example shown, the regulating valve 34 comprises a flap movable between an open position in which the flap passes the recirculated gas to the intake circuit and a closed position in which the flap blocks the passage of recirculated exhaust gas, and any intermediate positions between this open position and this closed position.

It is understood that, in the foregoing, each element, device or control valve may be associated with a control means configured to control the passage of air or gas depending on the desired operating characteristics of the engine.

Depending on the configuration of the recirculated gas diversion device 30, and especially the bypass element 31, downstream of the energy recovery turbine 28, the bypass circuit 38 makes it possible to evacuate all or part of the gases exhaust system circulating in the recirculation circuit 22, towards the exhaust circuit 6, downstream of the turbine 10. The branch circuit 38 extends from the branch element 31 to a connecting end 39 6. In the illustrated example, this connecting end 39 is stitched on the exhaust circuit between the first flow control element 18 of the exhaust back pressure device and the gas treatment device. In this way, it can be ascertained that all the exhaust gases, both those having passed through the turbine disposed on the exhaust system and those having It has been derived, is treated by the particle filter or the catalyst arranged on this exhaust system.

In this context, it is possible in particular to identify a first mode of operation in which the device for bypassing the recirculated gases 30, and in particular the bypass element 31, is configured so that the gases flowing in the recirculation circuit 22, after being passed through the energy recovery turbine 28, go completely to the second end 26 of the recirculation circuit 22 and thus to the admission of the engine. As described above, the branch element 31 is then in a first position. Here we find ourselves in a standard operating mode of recirculation of the gases, in which the part of the gases taken downstream of the engine block 2 is reinjected into the engine block 2 to optimize the internal combustion, while also rotating a recovery turbine. energy.

The recirculated gas diversion device 30, and in particular the bypass element 3L, may alternatively be controlled to take a second position so as to allow, in a second mode of operation, a total or partial discharge, according to the configuration of the device. bypass, gas recirculated by the bypass circuit 38. This second mode of operation can in particular be useful when the engine operates at a very high load and too much energy is exerted on the turbocharger. It is then intended that a portion of the exhaust gas does not pass through the turbocharger turbine 10, and for this purpose, the part of the gases flowing in the recirculation circuit 22 passes into the energy recovery turbine 28 before This is because of the configuration of the recirculated gas diversion device 30, the recirculated gases are directed downstream of the turbocharger turbine 10, and upstream of the pollutant treatment device 16. exhaust gas. The amount of gas initially intended to pass through this treatment device has thus been split between a first part passing through the turbine 10 and a second part derived via the recirculation circuit 22 and the bypass circuit 38, this second part allowing no not to overload the turbine of the turbocharger, however, being useful for starting up the energy recovery turbine 28. The arrangement of the elements of the recirculation circuit according to one aspect of the invention also allows a third mode of operation implemented during a deceleration of the engine, mode in which the fuel injection is cut. The exhaust back pressure device, and in particular the position of each of the flow control elements 18 and 20, is then controlled to block the passage of exhaust gas by the turbine 10, and all of these gases circulates. then in the recirculation line 22, through the energy recovery turbine 28 to recover the deceleration energy and convert it into electrical energy, then by the branch circuit 38 to be directed to the processing device 16 exhaust pollutants.

It is understood from the above that the bypass element 31 here acts as a three-way valve, controlled so as to deflect the gases coming upstream of the gas recirculation circuit, either to the branch circuit 38, either to the downstream part of the recirculation circuit 22, or to both.

The provision of this bypass element, which can take the form of a three-way valve, and the bypass circuit downstream of the energy recovery turbine 28 can recover energy almost all the time the engine thermal is in action, allowing recirculation of exhaust gas alternately to the intake or to the exhaust. This arrangement makes it possible in particular to deflect the burnt gases in order to avoid excessive loading of the turbine of the turbocharger, while implementing the energy recovery turbine 28 so as not to let escape of exhaust gas without derive energy for the overall operation of the vehicle.

Of course, various modifications may be made by those skilled in the art to the exhaust gas circulation assembly without departing from the context of the invention, it being understood that the invention can not be limited to the embodiment specifically described. in this document, and that it extends in particular to all equivalent means and any technically operating combination of these means, since a bypass device is disposed downstream, in the direction of flow of the exhaust gas. in the recirculation circuit, an energy recovery turbine also disposed on this exhaust gas recirculation circuit.

Claims (14)

CLAIMS! Exhaust gas circulation assembly of a heat engine comprising: - an exhaust gas recirculation circuit (22) receiving the exhaust gas of the engine, wherein the exhaust gas recirculation circuit ( 22) comprises a turbine (28) for energy recovery, - a treatment device (16) for exhaust gas pollutants, characterized in that the assembly comprises: - a bypass device (30) for the exhaust gases; exhaust arranged downstream of the energy recovery turbine (28) and configured to exhaust all or part of the exhaust gases of the exhaust gas recirculation circuit (22) after passing through the recovery turbine of energy (28) and - an exhaust gas flow control element (20) downstream of the treatment device (16). Exhaust gas circulation assembly according to claim 1, characterized in that the bypass device (30) comprises at least one bypass element (31) and a bypass circuit (38) configured to be connected to a exhaust circuit (6) of the engine, 3- exhaust gas circulation assembly according to claim 2, characterized in that the exhaust gas bypass element (31) is arranged on the recirculation circuit (22) being configured to distribute the exhaust gases. exhaust between the recirculation circuit (22) and the bypass circuit (38). Exhaust gas circulation assembly according to claim 2 or 3, characterized in that the bypass circuit (38) is arranged to open onto the exhaust circuit (6) downstream of a turbine (10). a turbocharger of the engine, 5- exhaust gas circulation assembly according to one of claims 2 to 4, characterized in that the bypass circuit (38) opens on the exhaust circuit (6) upstream of a device for processing the exhaust gas. exhaust gas (16). 6. Exhaust gas circulation assembly according to one of the preceding claims, characterized in that the recirculation circuit (22) comprises a heat exchanger. (32) downstream of the exhaust gas diversion device (30). Exhaust gas circulation assembly according to one of the preceding claims, characterized in that the recirculation circuit (22) comprises a regulating valve (34) of the exhaust gas passage in the recirculation circuit, arranged downstream of the exhaust gas diversion device (30). 8. Exhaust gas circulation assembly according to the preceding claim, characterized in that b regulating valve (34) and the bypass device (30) of the exhaust gas are controlled according to the amount of exhaust gas. to be reinjected into an intake circuit (4) of the engine. 9- exhaust gas circulation assembly according to one of the preceding claims, in combination with claim 2, characterized in that the gas branching element (31) is a three-way valve. 10. exhaust gas circulation assembly according to one of the preceding claims, characterized in that the energy recovery turbine (28) is coupled to an electric machine (36). 11. Heat engine comprising a gas circulation assembly according to one of the preceding claims. 12. Heat engine according toa preceding claim, characterized in that it is a diesel engine. 13. Motor vehicle equipped with a heat engine according to one of claims 11 or 12. 14- A method for implementing an exhaust gas recirculation of a heat engine, during which the exhaust gas, taken from an exhaust circuit (6) of the heat engine, is passed through a energy recovery turbine (28) arranged in a recirculation circuit (22), before selectively directing these exhaust gases in the continuity of the recirculation circuit or in a bypass circuit (38) reducing the gases of exhaust on the exhaust system of the engine.