FR3102210A1 - PROCESS FOR ACTIVATING A POST-TREATMENT SYSTEM FOR AN INTERNAL COMBUSTION ENGINE AND ASSOCIATED DEVICE - Google Patents

Abstract

The invention proposes a method for activating a post-treatment system of an internal combustion engine of a motor vehicle, the engine being associated with at least one electric compressor or with electric assistance, with a partial recirculation circuit. high pressure of the exhaust gases at the intake, and to heating means mounted in said system and / or in another post-treatment system mounted upstream. The main characteristic of the method according to the invention is that in the event of detection of a high probability of an imminent starting of the engine, if the temperature of said system is lower than an activation threshold, said heating means are actuated. , and air is circulated from the exhaust to said system by the recirculation circuit, by activating the electric or electrically assisted compressor and by opening a valve of the recirculation circuit.

Description

PROCEDURE FOR STARTING AN INTERNAL COMBUSTION ENGINE AFTER-TREATMENT SYSTEM AND ASSOCIATED DEVICE

Technical field of the invention

The present invention relates to a method for activating a post-treatment system for the polluting emissions of an internal combustion engine. By actuation, we mean bringing such a post-treatment system to a temperature sufficient for it to have a predetermined minimum treatment efficiency.

The invention also relates to an actuation device capable of implementing the method. It finds a particularly advantageous application in motor vehicle engines.

State of the art

Modern combustion engines, more particularly those of motor vehicles which are subject to increasingly stringent anti-pollution standards, are equipped with various post-treatment systems for the polluting molecules emitted in the combustion gases of said engines, in order to limit the release of harmful species into the outside atmosphere.

On compression ignition (diesel) type engines, which usually run on a lean burn, we know in particular oxidation catalysts, which are able to oxidize carbon monoxide (CO) and unburnt hydrocarbons (HC); particulate filters, which are able to store and then burn, during regeneration phases, fine particles (PM); nitrogen oxide traps, which are able to store and then reduce, during regeneration phases, nitrogen oxides (NOx); and catalysts for the selective reduction of nitrogen oxides, which are capable of continuously reducing nitrogen oxides under the action of urea-based reducers (Adblue®).

On spark-ignition type engines (operating in particular on gasoline), three-way catalysts are known in particular, which are able to treat the HC, CO and NOx emitted in the combustion gases of the engine. On the other hand, like diesel engines, more and more use is made of additional pollution control systems such as the nitrogen oxide trap and the particulate filter.

It is known that the efficiency of an after-treatment system depends on its temperature. By efficiency, we mean the proportion of polluting molecules of a given type that enter the system, that the said system manages to treat. Efficiency is generally very low at low temperatures, which makes motor vehicles particularly polluting during cold starts. There is a need to quickly bring the temperature of such after-treatment systems to a temperature threshold at which they have a minimum acceptable efficiency in order to comply with vehicle pollution control standards.

On the other hand, in the particular case of the catalyst for the selective reduction of nitrogen oxides, also called SCR catalyst (English acronym for: Selective Catalytic Reduction), it is necessary to reach a minimum temperature, typically of the order of 180°C, to allow the injection of urea-based reducers (Adblue®) upstream of said SCR catalyst. It is known that urea decomposes into ammonia (NH ₃ ) inside the SCR catalyst and enables NOx to be reduced into dinitrogen N ₂ and water H ₂ O. Part of the ammonia is also stored in the SCR catalyst. It is known that the NOx treatment efficiency depends on the value of the ammonia stock,

As long as the minimum temperature is not reached, it is impossible to proceed with any injection, and the efficiency of NOx treatment is almost zero, with the exception of a small proportion of NOx which can be treated thanks to with ammonia previously stored in the catalyst.

As part of the tightening of the standards regulating nitrogen oxide emissions from vehicles, there is a need to quickly bring the temperature of SCR catalysts to a threshold temperature for the injection of reducing agents.

Several processes are known from the state of the art which aim to fulfill such objectives. For example, publication US8756924 discloses a hybrid vehicle comprising a heat engine and an electric machine. The thermal engine comprises an electrically heated catalyst. The rise in temperature of the engine post-treatment system is ensured, before starting the engine, by the combination of electric heating and the supply of an air flow to the exhaust by the engine which is driven at vacuum by electric machine. Such a process can only be used on a hybrid vehicle.

In the publication US5814283, the activation of electric heating means of a catalyst is combined with the supply of an air flow to the exhaust which is supplied by an air pump. Such a process takes place after starting the engine. A similar method is also known from publication FR2778206 which is implemented before starting the engine. These processes require the presence of an air pump.

Presentation of the invention

The present invention aims to remedy the shortcomings of the known methods of activating post-treatment systems, in the case where the engine has at least one electric supercharger and a partial high-pressure recirculation circuit of the exhaust gases at the intake, which is a frequent case. It makes it possible to dispense with one or more additional dedicated components for the implementation of the actuation of said systems.

For this, it proposes a method for activating a post-treatment system mounted on the exhaust of a motor vehicle internal combustion engine, said engine being associated with at least one electric or electrically assisted compressor capable of to compress air from an intake circuit of the engine, and to at least one high-pressure partial recirculation circuit connecting the exhaust circuit of the engine to a point of the intake circuit located downstream of said compressor, said method comprising:

-a step of detecting a high probability of an imminent engine start;

-a step of measuring the temperature of said post-treatment system;

-a step of comparing said temperature with a temperature threshold; And,

-as long as said temperature is below said threshold, steps of actuating electric heating means at the exhaust of the engine and of injecting air upstream of said electric heating means, suitable for circulating heated air through said post-processing system.

The main characteristic of the process according to the invention is that to ensure the injection of heated air upstream of the post-treatment system, it comprises:

- a step of opening a valve of the high pressure partial recirculation circuit; And,

- a stage for activating the electric or electric-assisted compressor.

Brief description of figures

Other characteristics and advantages of the invention will appear on reading the following description of a non-limiting embodiment of the invention, in support of the appended figures, in which:

is a schematic view of a drive device capable of implementing the method according to the invention.

is a flowchart of the steps of an embodiment of the method according to the invention.

Detailed description of figures

In the following description, identical reference numerals designate identical parts or parts having similar functions.

In Figure 1, there is shown a drive device suitable for implementing the method according to the invention. The device comprises an internal combustion engine 1 which here is of the compression ignition (diesel) type, for example with direct injection. In another mode not shown, it could be an engine of the controlled ignition type (running in particular on gasoline).

The engine 1 is associated with an air intake circuit 2 and an exhaust circuit 3. The fresh air taken from the outside atmosphere enters the intake circuit 2 in the direction of the arrow E, in an air inlet pipe 4. It can pass through components not shown in the figure such as an air filter and a flow meter. According to the invention, the engine 1 comprises at least one compressor which can be actuated electrically, independently of the circulation of exhaust gases through a turbine.

In the non-limiting example of Figure 1, the air first passes through an electric compressor 5, which is driven by an electric motor 6, then a compressor 7 of a turbocharger 8 of the engine.

In a first variant, not shown, the electric compressor 5 can be located downstream of the compressor 7 of the turbocharger 8, and it can be associated with a bypass line fitted with a flow rate adjustment valve. In this variant, all of the incoming air first passes through compressor 7 of the electric turbocharger, then adjusting the degree of opening of the bypass valve makes it possible to adjust the proportion of air that passes through the electric compressor. For example, if the valve is completely closed, all the air passes through the electric compressor.

In a second variant, not shown, the engine may be devoid of the turbocharger 8 and only include the electric compressor 5.

In a third variant, not shown, the engine may be devoid of the electric compressor 5 but include an electrically assisted turbocharger 8, in which the compressor can not only be driven by the energy coming from the turbine 12 thanks to the expansion of the gases d engine exhaust, but also, independently of this gas expansion or in combination therewith, by a supply of electrical energy.

Other variants are still possible without affecting the generality of the invention.

The air then enters an intake manifold 9, or distributor 9 of the engine, from where it enters the combustion chambers of the engine. An air intake valve 10 is placed at the inlet of the distributor 9 to regulate the flow of gases entering the engine. The intake circuit may also have other characteristics not shown in the figure, for example a supercharged air cooler located downstream of the compressor 7, without affecting the generality of the invention.

The combustion gases from the engine are discharged into an exhaust manifold 11 of the engine. Then they cross, from upstream to downstream in their direction of circulation: a first post-treatment system 13, which here takes the form of an electric oxidation catalyst 13, that is to say a catalyst comprising electrical heating means 14, for example an electrical resistor 14 which is in the form of a heating grid 14. In the example of FIG. 1, the heating grid 14 is located at the entrance to the first post-processing system.

The combustion gases then pass through a second post-treatment system 15, which here comprises in the same metal casing (known as the English term "canning") a particulate filter 17 and a catalyst for the selective reduction of nitrogen oxides 18 , or SCR catalyst 18. Finally, the combustion gases are evacuated into the outside atmosphere through an exhaust pipe 16, in the direction of the arrow E.

Of course, the exhaust circuit may include additional post-processing systems, or other types of processing systems than those shown in Figure 1, without affecting the generality of the invention. For example, a nitrogen oxide trap can be provided in addition to or instead of the SCR catalyst. For example, if the engine is of the spark ignition type, there may be one or more three-way catalysts at the engine exhaust, in particular a close catalyst (pre-catalyst) and/or an underbody catalyst. You can also find a nitrogen oxide trap and/or a particulate filter.

Here, the SCR catalyst 18 of the second pollution control system 15 is supplied with urea-based reducers (Adblue®) via a urea injector 19 which is installed in the exhaust circuit 3 upstream of the second post-treatment system 15. The reducers generally come from a liquid solution which is stored in a tank 20 and which is conveyed to the urea injector 19 by means of a pump 21.

For the implementation of the method according to the invention, at least one post-processing system 13,15 is associated with means for measuring its temperature. In the example of FIG. 1, it is an SCR catalyst temperature sensor 22 which is mounted in the exhaust circuit 3 upstream of the second post-treatment system 15 and which makes it possible to determine a value representative of the temperature of the SCR catalyst 15. Of course, other variants are possible without harming the generality of the invention. It is for example possible to provide a temperature sensor close to the reducer injector 19 to determine an injector temperature value T. It is also possible to provide a sensor at the inlet and/or at the outlet of the first post system. -processing 13 so as to determine its temperature T, etc.;

In addition, the exhaust circuit comprises at least one high pressure partial recirculation circuit 23 of the exhaust gases at the engine intake, also known as the EGR HP circuit (acronym for: Exhaust Gas Recycling – High Pressure). This circuit originates at a point of the exhaust circuit located upstream of the turbine 12 and its other end emerges at a point of the intake circuit located downstream of the compressor 7.

In the case not shown of the aforementioned first variant where the electric compressor 5 is located downstream of the compressor 7 of the turbocharger, the exhaust gases recycled to the intake are reintroduced downstream of said electric compressor 5. In the case not shown of the aforementioned second variant where the engine has no turbocharger 8 and only comprises an electric compressor 5, the exhaust gases recycled to the intake are reintroduced downstream of said electric compressor 5. In the case not shown of the third variant mentioned above where the engine has only one electrically assisted turbocharger 8, the exhaust gases recycled to the intake are reintroduced downstream of the compressor of said electrically assisted turbocharger. In other words, in all cases, the exhaust gases recycled to the intake are reintroduced downstream of all the compressors present.

The HP EGR circuit is fitted with a valve, called the EGR 24 valve, which adjusts the flow of exhaust gases recycled to the engine intake. As this is a diesel engine, the advantage of such an EGR circuit is to make it possible to reduce the engine's NOx emissions. In the case of a spark-ignition engine, the advantage is to cool the load thanks to the supply of exhaust gases and to repel knocking, which in particular makes it possible to reduce fuel consumption. This is the reason why more and more motor vehicle internal combustion engines are equipped with such an HP EGR circuit.

According to the invention, the HP EGR circuit is also used for another purpose, which is to supply air into the exhaust circuit, before the engine is started, by virtue of the actuation of the electric compressor 5, by combination with the heating of the grid 14 of the first post-treatment system 13. By using an already pre-existing component of the engine, it is freed from having to install a specific dedicated component, such as an air pump. It is advantageously possible to use the means for determining the temperature T to stop the heating and the circulation of air and allow the engine to start at the exact moment when this temperature is greater than a threshold Ts for the injection temperature of reducers in the SCR 18 catalyst and/or when it is greater than a threshold for activating a post-treatment system. In a simplified mode, it is also possible to actuate the heating means and the compressor for a predetermined duration before starting the engine, said duration being sufficient to reach the desired temperature threshold, without it being necessary to determine the value of the temperature. Said duration can be determined by preliminary tests.

The exhaust circuit may have other additional characteristics without affecting the generality of the invention. For example, the HP EGR circuit may include a cooler. For example, the exhaust circuit may also include a low-pressure partial exhaust gas recirculation circuit at the intake, etc.

The operation of the engine is placed under the supervision of an electronic computer (not shown), which determines a certain number of engine operating parameters from a plurality of sensors and which controls a plurality of actuators of the engine.

Among the sensors, mention may be made in particular of a vehicle accelerator pedal and an engine speed sensor N, from which the computer establishes an engine torque setpoint corresponding to a desire to obtain a given acceleration from the driver. The torque setpoint is then translated in particular into an air flow setpoint Qair, an EGR gas flow setpoint Qegr and a fuel flow setpoint Qcarb. Of course, other setpoint parameters can be determined, such as a fuel injection phasing setpoint, an ignition advance setpoint in the case of a spark-ignition engine, etc.

Among the actuators, mention may be made in particular of the air intake valve 10, which makes it possible to adjust the total flow of air and of recycled gases entering the engine, the EGR valve which makes it possible to adjust the flow of only the recycled gases Qegr, and the fuel injectors which adjust the Qcarb flow and fuel injection phasing.

In the context of the invention, at least one additional sensor is provided in the form of the SCR catalyst temperature sensor 22. At least two additional actuators are provided, in the form of a part of the heating grid 14 of the catalyst oxidizer 13 and at least one electric compressor 5 or an electrically assisted compressor 7.

In Figure 2, there is shown a flowchart of the different steps of the method, according to a non-limiting embodiment thereof. The method begins with a step 100 during which the engine computer determines that a start of the vehicle is probable within an imminent time. For example, it can recognize the proximity of a vehicle start card to the vehicle; operation of a vehicle door; increasing load on the driver's seat, or switching on the engine.

The method continues with a step 200 during which the computer determines a value T of the temperature of the second post-processing system 15, for example thanks to the sensor 22. Then it continues with a test step 300, during of which said temperature T is compared with a temperature threshold Ts. For example, the temperature threshold Ts corresponds to a temperature of the SCR catalyst itself, or to a temperature for authorization of injection by the reducer injector 19.

According to the invention, if said temperature T is lower than said threshold Ts, the method directs to an activation step 400 of the heating grid 14 of the first post-processing system 13; then, by a step 500 of opening the EGR valve 500, preferably completely; then, by a step 600 of activation of the electric compressor 5 by its motor 6. It is also possible, but not essential, to close the air intake valve 10. The method then resumes, iteratively, at the step 200 for measuring the temperature.

Otherwise, the method directs to a step 700 of deactivating the electrical resistor 14 (which is a non-activation step if just after the step of detecting 100 the probability of a start, the temperature is immediately greater than said threshold, this case typically corresponding to a warm restart). Then the method continues with a step of starting the engine 800, under the action of the driver, and, conventionally, with a step 900 of determining a value of engine torque C and engine speed N, of which the computer deduced from the airflow Qair, recycled gas Qegr and fuel Qcarb setpoints as indicated above. The method further comprises a step 1000 during which the position of various actuators of the motor is adjusted so as to reach these setpoint values. In particular, the angular position of the EGR valve is adjusted to obtain the set recycled gas flow rate, and the angular position of the air intake valve 10 and/or the electric compressor 5 and/or the turbocharger 8 is adjusted to get the total intake gas flow into the engine.

Of course, the method according to the invention is not limited to the particular embodiment which has just been described. For example, it is possible to invert the steps of activating the resistance 400, of opening the EGR valve 500 and of activating the electric compressor 600. It is also possible to invert the steps of deactivating the resistance electric 700 and engine start 800, so that the heating continues after the engine has started to complete the actuation of the emission control systems.

Also for example, it is possible for the electric heating means 14 to be associated with the same post-processing system as that on which the temperature T is determined, or with a distinct post-processing system and of a different type from the systems shown in Figure 1 (i.e.: oxidation catalyst and SCR catalyst). However, it will be noted that if the post-processing system provided with electric heating means is separate from the post-processing system provided with the means for determining the temperature which it is desired to activate, it is necessary that the latter went up downstream of that one.

Claims (10)

Method for activating a post-treatment system (15) mounted on the exhaust of an internal combustion engine (1) of a motor vehicle, said engine being associated with at least one electric or electric-assisted compressor ( 5.7) suitable for compressing air from an engine intake circuit (2) and at least one high-pressure partial recirculation circuit (23) connecting the exhaust circuit (3) of the engine to a point of the intake circuit (2) located downstream of said compressor (5,7), said method comprising:
-A detection step (100) of a high probability of an imminent start of the engine;
-A measurement step (200) of the temperature (T) of said post-treatment system (15);
-A comparison step (300) of said temperature (T) with a temperature threshold (Ts); And,
-As long as said temperature (T) is lower than said threshold (Ts), steps of actuating (400) electric heating means (14) at the exhaust of the engine and of injecting air upstream of said means of electric heaters (14), suitable for circulating heated air through said post-treatment system,
CHARACTERIZED IN THAT
To ensure the injection of air to the exhaust upstream of the post-treatment system (15), the method comprises:
-A step of opening (500) a valve (24) of the high pressure partial recirculation circuit (23); And,
-An activation step (600) of the electric or electric-assisted compressor (5,7). Method according to Claim 1, characterized in that the opening of the said valve (24) is complete. Process according to any one of the preceding claims, characterized in that the post-treatment system (15) comprises a catalyst for the selective reduction of nitrogen oxides (18) associated with an injector (19) for the injection of reducing agents upstream of said selective reduction catalyst. Process according to Claim 4, characterized in that the temperature (T) is, respectively, the temperature of the catalyst for the selective reduction of nitrogen oxides (18) proper or the temperature of the reducing agent injector (19). Process according to claim 5, characterized in that the temperature threshold is, respectively, a minimum efficiency threshold of said catalyst (18) or a threshold for authorization of injection by the reducer injector (19). Method according to any one of the preceding claims, characterized in that the electric heating means (14) are located at least partially in another after-treatment system (13) of the engine, mounted upstream of said after-treatment system (15). Method according to any one of the preceding claims, characterized in that the electric heating means (14) are located at least partially in the said post-treatment system (15). Method according to any one of the preceding claims, characterized in that it also comprises a step of closing an admission valve (10) for the admission gases into the engine. Device for activating a post-treatment system (15) of an internal combustion engine (1) of a motor vehicle, said engine being associated with at least one electric compressor (5) or with electric assistance (7) for the compression of engine intake gases, at least one partial recirculation circuit (23) at high pressure of the exhaust gases of the engine connecting the exhaust circuit of the engine (3) to a point of the circuit of exhaust (2) located downstream of said compressor, and to electric heating means (14) mounted in the exhaust circuit (3) of said engine,
CHARACTERIZED IN THAT it further comprises:
-means for determining a strong probability of an imminent start of the engine;
-means for measuring a value of the temperature (T) of said system (15), and means for comparing said temperature (T) with an actuation temperature threshold (Ts);
- means for actuating said electric heating means (14), means for opening a valve (24) of said recirculation circuit (23), and means for actuating said compressor, (5,7), capable of circulating heated air in said depollution system (15) when said temperature (T) is below said threshold (Ts) when a high probability of starting is detected. Device according to the preceding claim, characterized in that the electric heating means (14) are mounted on another engine post-treatment system (13) mounted upstream of said post-treatment system (15) and/or on said system (15). -