WO2017006025A1

WO2017006025A1 - Exhaust gas recirculation circuit for a spark-ignition heat engine

Info

Publication number: WO2017006025A1
Application number: PCT/FR2016/051640
Authority: WO
Inventors: Hua Su; Sylvain FAVELIER; Florent David
Original assignee: Valeo Systemes De Controle Moteur
Priority date: 2015-07-09
Filing date: 2016-06-30
Publication date: 2017-01-12
Also published as: FR3038661A1; FR3038661B1

Abstract

The invention relates to an exhaust gas recirculation circuit (22) for a petrol engine (10) comprising: a heat exchanger (50) arranged so as to cool the exhaust gases that pass therethrough, and a heat exchanger bypass channel (60) for selectively guiding the exhaust gases towards the engine (10) without passing through the heat exchanger (50).

Description

EXHAUST GAS RECIRCULATION CIRCUIT

FOR A THERMAL ENGINE WITH IGNITION CONTROL

The present invention relates to an exhaust gas recirculation circuit for a spark ignition engine.

The principle is known to recirculate at intake a portion of the exhaust gas of a spark ignition engine. Exhaust gas recirculation is generally referred to as EGR, as the abbreviation of the English term "Exhaust Gas Recirculation". Thereafter, we will speak of EGR circuit for an exhaust gas recirculation circuit.

Diluting the air admitted into the engine by exhaust gas changes the course of combustion of the fuel mixture. Thus, the presence of the exhaust gases, which are chemically inert, and which have a high heat capacity, makes it possible to reduce the combustion temperature. In addition, the tendency to auto-ignite the mixture is reduced, which decreases the tendency to rattle. In general, the use of exhaust gas recirculation on a spark ignition engine makes it possible to reduce fuel consumption, which makes it a very interesting technology, particularly when it is applied to a supercharged engine. Supercharged means that the intake air of the engine is compressed by a supercharging device before being admitted into the engine. It is well known to those skilled in the art to perform a "low pressure" type exhaust gas recirculation, in which a part of the exhaust gas is returned to the intake circuit, upstream of the device. of overeating. The flow of recirculated gas is controlled by a metering valve located on the low pressure recirculation circuit, called the EGR valve.

Depending on its operating point, the EGR circuit reduces fuel consumption and improves engine knock resistance. Nevertheless, the use of such an EGR circuit at low temperatures generates condensates as well as combustion stability problems.

The invention proposes to improve the operation of such an exhaust gas recirculation circuit especially during cold starts of the engine. For this purpose, the subject of the present invention is an exhaust gas recirculation circuit for a spark ignition engine comprising:

a heat exchanger arranged to cool the exhaust gases flowing through it, and

a bypass duct of said heat exchanger for selectively directing the exhaust gases towards the engine without passing through the heat exchanger.

Advantageously, during cold starts, the gases are recirculated but not cooled thus allowing a temperature rise of the engine faster.

The exhaust gas recirculation circuit according to the invention may also comprise one or more of the following characteristics, considered individually or in any technically possible combination:

the EGR circuit comprises a selection means arranged to send the exhaust gas selectively to the heat exchanger or in the recirculation circuit downstream of the exchanger;

the selection means is a three-way type valve configured to be actuated by an electric motor and to be driven by a control circuit according to operating parameters of the spark ignition engine;

the selection means 62 is a three-way valve configured to be actuated by a pneumatic actuator;

the EGR circuit comprises a control valve arranged to regulate the recirculation flow of the exhaust gas of the spark ignition engine;

the control valve is mounted downstream of the heat exchanger;

the control valve is mounted upstream of the heat exchanger;

the valve is of rotary shutter type;

the EGR circuit comprises a main recirculation duct on which are mounted the heat exchanger and the control valve, and wherein the branch duct opens into the main recirculation duct between the heat exchanger and the control valve; the heat exchanger is configured to allow heat exchange between the exhaust gases passing therethrough and a cooling fluid; the EGR circuit comprises a thermal valve arranged to regulate the flow rate of the cooling fluid as a function of the temperature of the cooling fluid with respect to a predefined setpoint temperature;

the thermal valve is configured to retain a majority of the cooling fluid in the heat exchanger as long as the temperature of the cooling fluid is lower than a predefined setpoint temperature;

the thermal valve is configured to guarantee a minimum leakage flow rate of the cooling fluid;

the thermal valve is configured to pass, when the temperature of the coolant is higher than the set temperature, cooling fluid with a maximum flow rate that is greater than the maximum flow rate when the temperature of the coolant is below the temperature set point, the ratio between these two maximum rates being greater than 20, in particular 50, advantageously 100;

the thermal valve is electrically controlled;

the thermal valve comprises a wax capsule, the opening of the valve being conditioned by the temperature at which the wax capsule is subjected; the preset set temperature is substantially between 40 ° C and 80 ° C;

the thermal valve is mounted on an outlet duct of the cooling fluid of the heat exchanger;

the circulation circuit of the exchanger communicates with the main cooling circuit of the engine;

the cooling fluid is a liquid, in particular water added with glycol;

the EGR circuit is a low pressure EGR circuit.

The invention also relates to an air intake system for a spark ignition engine comprising: an EGR circuit according to the invention, and

an intake line connected to the EGR circuit comprising:

• an intake duct directing the air towards the engine,

A cooler mounted on the intake duct and intended to allow a heat exchange between the air passing therethrough and a heat-transfer fluid, and

A bypass duct of said cooler for selectively directing air into the intake duct downstream of the cooler.

Advantageously, such an arrangement makes it possible not to cool the gases heading towards the intake distributor of the engine thus allowing a faster temperature rise during cold starts.

The air intake system for a spark ignition engine according to the invention may also comprise one or more of the following characteristics, considered individually or in any technically possible combination:

the bypass duct of said cooler directly connects the intake duct upstream of the cooler;

the air intake system comprises a selection means mounted at the intersection of the intake duct and the bypass duct for supplying air either to the cooler or to the inlet duct downstream of the cooler;

the selection means is a three-way valve configured to be actuated by a pneumatic actuator and to be driven by a control circuit according to operating parameters of the motor;

the cooler is of the air / air type;

the cooler is of the air / water type;

the circulation circuit of the cooler communicates with the main cooling circuit of the engine. Other characteristics and advantages of the invention will appear on reading the detailed description of an embodiment given by way of non-limiting example and illustrated, accompanied by FIG. 1 schematically illustrating the architecture of a exhaust gas recirculation system of the engine according to the invention.

In the figure, similar elements are designated by identical references. In addition, the various elements are not necessarily represented on the scale in order to present a view making it easier to understand the invention.

Referring to Figure 1, a spark ignition engine 10 comprises a combustion chamber 12 having a plurality of cylinders, in this case four in number, and intended to receive a mixture of oxidant and fuel, here the gasoline, whose combustion in the cylinders generates the work of the engine 10.

The operation of the engine 10 is conventional: the gases are admitted into the combustion chamber 12, are compressed, burned and expelled in the form of exhaust gas; these are the four classic times of a combustion engine (intake, compression, combustion and exhaust).

The invention relates to an air intake system 20 for such a spark ignition engine, comprising an exhaust gas recirculation circuit, said EGR circuit 22, and an intake line 24 connected to the EGR circuit 22. .

The gas inlet line 24 in the engine 10 comprises a supply air intake duct 30 or fresh air (whose flow is represented by the arrow Fl), a compressor 32 of the supply gases, which is in this case a turbocharger, and a heat exchanger 34 for cooling the gases from the compressor 32.

The heat exchanger 34 is mounted on the intake circuit 20 and intended to allow a heat exchange between the air passing therethrough and a heat transfer fluid. This heat exchanger 34 is commonly designated by those skilled in the art by its acronym "RAS", which means "charge air cooler"; its function is indeed to cool the intake gas and in particular the air, which is said to be supercharged since it is compressed.

The RAS, placed at the output of the turbocharger, lowers the temperature of the gases that pass through it before sending them to the intake of the engine, so that it can operate in optimal conditions.

At the outlet of the RAS 34, the gases open into an inlet distributor 36 of the gases in the combustion chamber 12 of the engine 10, the distributor 36 forming a gas inlet box in the cylinder head of the engine 10.

According to the invention, the intake circuit 20 further comprises a bypass duct 37 of the channel containing the RAS 34 for selectively directing the air into the intake duct downstream of the cooler.

Preferably, the bypass duct 37 of said RAS directly connects the intake duct 30 upstream of the cooler 34.

Advantageously, the air intake system 20 comprises a selection means 38 mounted at the intersection of the intake duct 30 and the bypass duct 37 to send air either to the cooler 34 or to the duct. intake 30 downstream of the cooler 34 to direct them to the inlet manifold 36 of the engine 10. This selection means 38 regulates the gas between the cooled track and the uncooled track 37.

For example, the selection means 38 is a three-way type valve configured to be actuated by an electric motor and to be driven by a control circuit according to operating parameters of the spark ignition engine.

In another embodiment, not shown, the selection means 38 is actuated by a pneumatic actuator.

Advantageously, the cooler can be of the air / water type, and in particular the circulation circuit of the cooler can communicate with the main cooling circuit of the engine.

Of course, the cooler can be of the air / air type according to an alternative. Upstream of the gas inlet manifold 36 in the engine 10, the intake circuit may also comprise a valve (not shown) comprising a butterfly valve whose function is to regulate the gas flow to adjust the level of torque supplied by the engine. This butterfly valve can then be controlled by a motor control unit (typically designated by the acronym ECU which stands for Engine Control Unit in English), and well known to those skilled in the art.

At the outlet of the combustion chamber 12 of the engine 10, a gas exhaust circuit 40 comprises an exhaust gas manifold 42 connected to an exhaust channel or channel 44 of the gases.

The exhaust circuit 40 further comprises a turbine 46, integral in rotation with the compressor 32 of the inlet gas and forming with it a turbocharger. The turbine 46 is driven by the exhaust gas of the exhaust path 44, whose flow is shown schematically by the arrow F2.

After expansion in the turbine 46, the exhaust gas passes through at least one after-treatment device 47, comprising a catalyst that catalyzes the chemical reactions of oxidation and reduction of the pollutants found in the exhaust gases, these pollutants especially from incomplete combustion.

Finally, the exhaust circuit 40 is connected to the exhaust gas recirculation circuit 22 comprising a main exhaust gas recirculation duct 48, called "EGR gas", arranged to take exhaust gases from the circuit exhaust 40, and reintroduce them into the intake circuit 20, in this case upstream of the compressor 32. Such exhaust gas recirculation is called low pressure, since it is made on exhaust gas at the outlet of the exhaust circuit 40, downstream of the turbine 46.

The gases that are not recirculated form the exhaust gas of the vehicle, whose flow is designated by arrow F3 and are released into the atmosphere. In the embodiment illustrated in FIG. 1, two depollution devices 47A, 47B are mounted in the exhaust circuit 40. The recirculation circuit 22 is connected to the exhaust circuit between the two depollution devices 47A, 47B. The two depollution devices combine the role of catalyst and particulate filter. Since the entry point of the EGR circuit is located downstream of the pollution control device 47 A, the recirculated gases are thus freed of most pollutants and particles. The second pollution control device 47B makes it possible to further reduce the pollutants found in the exhaust gases and not being recirculated. By connecting the entry point of the EGR circuit between the two pollution control devices, the pressure of the gases is higher than that of the second pollution control device, which allows a higher flow rate for a given passage section. The EGR circuit 22 according to the invention will now be described in more detail.

The EGR circuit comprises a heat exchanger 50 arranged to cool the exhaust gas flowing therethrough, thereby increasing their beneficial effect on fuel economy gains, in particular by reducing the engine's rattling tendency.

Thanks to Γ heat exchanger which thus allows to cool the recirculated exhaust gas, the efficiency of EGR gas recirculation to reduce fuel consumption is increased.

The heat exchanger 50 is mounted on the main recirculation duct 48 of the EGR gas and is configured to allow a heat exchange between the exhaust gases passing through it and a cooling fluid, such as a liquid, in particular the water with added glycol. The efficiency of a liquid-cooled exchanger is better compared to a gas / gas exchanger.

In addition and advantageously, the circulation circuit of the cooling fluid of the exchanger communicates with the main cooling circuit of the engine, for example by a bypass thereof, thus allowing a smaller footprint of the heat exchanger. In this case and as shown in FIG. 1, the cooling liquid which is nothing other than the engine coolant used elsewhere in another water / air heat exchanger for heating the passenger compartment of the vehicle, enters the exchanger via an inlet duct 52 and exits through an outlet duct 54. In addition, the EGR circuit advantageously comprises a thermal valve 56 arranged to regulate the flow rate of the cooling fluid as a function of the temperature of the cooling fluid relative to a predefined setpoint temperature. In particular, the thermal valve 56 is configured to retain a majority quantity of the cooling fluid in the heat exchanger as long as the temperature of the cooling fluid is lower than the predetermined set temperature.

Preferably, the preset set temperature is substantially between 20 ° C and 80 ° C.

In addition, the thermal valve 56 may be configured to ensure a minimum leakage rate of the coolant to allow minimal circulation of the coolant and thereby allow the heated water to heat the heat valve 56 itself.

According to a preferred embodiment, the thermal valve 56 is configured to pass, when the temperature of the cooling fluid is higher than the set temperature, cooling fluid with a maximum flow rate that is greater than the maximum flow rate when the temperature of the cooling fluid is below the set temperature, the ratio between these two maximum flows being greater than 20, in particular 50, advantageously 100.

Advantageously, the valve or thermal actuator 56 is mounted on the outlet duct 54 of the cooling fluid of the heat exchanger 50.

The thermal valve can be controlled electrically, in particular by the engine control unit (ECU).

According to another embodiment, not shown, the thermal valve comprises a wax capsule, the opening of the valve being conditioned by the temperature at which the wax capsule is subjected;

The EGR circuit 22 further comprises a bypass duct 60 of the heat exchanger 50 for selectively directing the EGR gas to the engine 10 without passing through the heat exchanger.

For this purpose, the EGR circuit advantageously comprises a selection means

62 arranged to send the exhaust gas selectively to the heat exchanger 50 or in the recirculation circuit downstream of the exchanger. For example, the selection means 62 is a three-way type valve configured to be actuated by an electric motor and to be driven by a control circuit according to operating parameters of the spark ignition engine.

In another embodiment, not shown, the selection means 62 is actuated by a pneumatic actuator.

Advantageously, the bypass duct 60 opens into the main recirculation duct 48 between the heat exchanger 50 and a control valve 64 arranged to regulate the recirculation flow rate of the exhaust gas of the spark ignition engine, which is will subsequently name EGR valve. This EGR valve adjusts the flow of fresh air entering the engine.

In this case, the EGR valve 64 is mounted downstream of the heat exchanger 50 at the level where the exhaust gases taken from the exhaust circuit 40 are reintroduced into the intake circuit 20 upstream of the compressor 32. .

According to one variant, the control valve of the exhaust gas recirculation flow rate of the spark ignition engine can be mounted on the EGR gas guide pipe 48 upstream of the heat exchanger 50.

For example, the EGR valve is of the rotary shutter type. This type of valve generates low pressure losses and allows high flow rates.

In the case of a cold start, a first mode of operation consists in leaving the selection means 62 closed so that the recirculated gases take the bypass 60 allowing a faster temperature rise of the gases with a view to their admission into the engine. Similarly, the selection means 38 is closed so that the gases for admission into the engine take the bypass duct 37 so that they are not cooled by the RAS 34. This operating mode makes it possible to obtain more favorable combustion conditions at low temperatures.

A second mode of operation is to leave the selection means 62 partially or completely open so that the recirculated gases pass through the heat exchanger 50 to be cooled. The heat valve 56 is first closed so that the circulation of the coolant is limited as long as the temperature thereof is lower than a preset setpoint temperature and the circulation is free above this setpoint temperature. This limitation of the circulation of the coolant allows the temperature to rise quickly in the heat exchanger 50 and thus to have hot exhaust gases for their reintroduction into the intake circuit of the engine. engine.

The heat recovered from the exhaust gases in the heat exchanger via the coolant thus makes it possible firstly to accelerate the warm-up of the engine and then to heat the passenger compartment.

The two modes of operation can be used separately, one after the other or alternatively.

The EGR circuit according to the invention thus makes it possible to obtain hotter gases during the engine heating phase and at cold temperatures.

One advantage is to be able to reduce the icing conditions of the low pressure EGR circuit and the compressor when the ambient temperatures are negative. Thus, the risks of using the EGR circuit at low temperature are reduced.

Another advantage is the recovery of the heat of the exhaust gas cold, by transferring it into the coolant, thus accelerating the temperature rise of the engine and the passenger compartment of the vehicle. The fuel consumption of the vehicle is thus reduced and the thermal comfort improved.

Claims

An exhaust gas recirculation circuit (22) for a spark ignition engine (10) comprising:

a heat exchanger (50) arranged to cool the exhaust gases flowing through it, and

- a bypass duct (60) of said heat exchanger for selectively directing the exhaust gas to the engine (10) without passing through the heat exchanger (50).

2. EGR circuit according to claim 1, comprising a selection means (62) arranged to send the exhaust gas selectively to the heat exchanger (50) or in the recirculation circuit downstream of the exchanger (50), the selection means (62) being a three-way type valve configured to be actuated by an electric motor and to be driven by a control circuit according to operating parameters of the spark ignition engine (10).

3. EGR circuit according to one of the preceding claims, wherein the heat exchanger (50) is configured to allow a heat exchange between the exhaust gas therethrough and a cooling fluid.

4. EGR circuit according to the preceding claim, comprising a thermal valve (56) arranged to regulate the flow rate of the cooling fluid as a function of the temperature of the coolant relative to a preset target temperature.

5. EGR circuit according to the preceding claim, wherein the thermal valve (56) is configured to retain a majority of the cooling fluid in the heat exchanger as the temperature of the coolant is less than a preset target temperature.

6. EGR circuit according to one of claims 4 or 5, wherein the thermal valve (56) is configured to pass, when the temperature of the cooling fluid is greater than the set temperature, the cooling fluid with a flow rate maximum which is greater than the maximum flow rate when the temperature of the cooling fluid is lower than the set temperature, the ratio between these two maximum flow rates being greater than 20, in particular 50, advantageously 100.

7. EGR circuit according to any one of claims 4 to 6, wherein the thermal valve (56) is electrically controlled.

8. EGR circuit according to one of claims 4 to 7, wherein the thermal valve (56) is mounted on an outlet duct (54) of the cooling fluid of the heat exchanger.

9. EGR circuit according to the preceding claim, wherein a circulation circuit of the exchanger (50) communicates with a main cooling circuit of the engine (10).

EGR circuit according to one of the preceding claims, wherein the EGR circuit (22) is a low pressure EGR circuit.

An air intake system (20) for a spark ignition engine (10) comprising:

an EGR circuit (22) according to any one of the preceding claims, and

an intake line (24) connected to the EGR circuit comprising:

An intake duct (30) directing the air towards the engine, a cooler (34) mounted on the intake duct (30) and intended to allow a heat exchange between the air passing therethrough and a fluid coolant, and a bypass duct (37) of said cooler (34) for selectively directing air into the intake duct (30) downstream of the cooler (34).