WO2011128543A1

WO2011128543A1 - Method for regenerating a particle filter

Info

Publication number: WO2011128543A1
Application number: PCT/FR2011/050581
Authority: WO
Inventors: Thomas Bernichon; Jean-Florent Genies; Arnold Singer
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2010-04-14
Filing date: 2011-03-21
Publication date: 2011-10-20
Also published as: FR2958969B1; FR2958969A1

Abstract

The invention relates to a method and system for regenerating a particle filter. According to the invention, the method comprises the following steps: identifying a severe regeneration risk on the basis of the amount of soot in the particle filter and on the basis of the temperature upstream from the filter; when a severe risk is identified, determining the limits (25) of an engine operation area (22, 24) for which the regeneration of the filter is stifled; triggering an engine operation mode that enables stifling of the filter regeneration when the engine operation point is located within said area (22, 24); stopping said engine operation mode when the severe regeneration conditions have disappeared and passing to routine regeneration mode (26); and repeating the preceding steps until said engine operation area (22, 24) is very small.

Description

METHOD FOR REGENERATING A PARTICLE FILTER

The present invention claims the priority of the French application 1052847 filed April 14, 2010 whose content (text, drawings and claims) is here incorporated by reference.

The present invention relates to a method and system for regenerating a particulate filter placed in an exhaust line of a heat engine of a vehicle.

[ooo3] Vehicles equipped with a combustion engine are increasingly equipped with antipollution devices that may include a set of catalysts transforming the toxic constituents of exhaust gases (carbon monoxide, unburned hydrocarbons, nitrogen oxides) in less toxic elements (water and C0 ₂ ). These antipollution devices also include, particularly for diesel engines, a particulate filter that traps the carbon particles from the combustion in the cylinders. A particulate filter generally has a cylindrical shape and is made of ceramic. The filter is composed of a multitude of parallel channels, small diameters, which trap the particles. These accumulate in the filter and it is periodically necessary to regenerate the filter by eliminating the trapped particles to avoid excessive pressure drop in the exhaust line. For this, the temperature of the filter is increased until a temperature at which the carbon particles burn. Several methods can be used to raise the temperature. For example, a heating resistor can be inserted into the filter. However the most common method is to increase the temperature of the exhaust gas that will pass through the filter. For this purpose, it is possible, for example, to inject an additional quantity of fuel into at least one of the cylinders in the form of post-injection. This fuel ignites by producing an increase in the temperature of the exhaust gas. Another solution, which can be combined with post-injection, is to delay the main fuel injection. [ooo4] The need for regeneration of the filter can be detected by the measurement of the pressure drop, that is to say by measuring with a sensor the pressure difference between the inlet and the outlet of the filter. filtered. The need for regeneration can also be estimated according to the number of kilometers traveled and the conditions of use of the vehicle. The regeneration of the filter is triggered automatically and usually happens without the driver's knowledge.

[ooo5] As the combustion propagates in the filter, it results in a temperature gradient inside the filter which, if it is too important, can seriously damage the filter causing cracks. In addition, a generally too high temperature (generally above 1000 ° C) can lead to the destruction of the filter. It is therefore important to control the combustion of the trapped particles so as not to cause irreversible damage to the filter. [ooo6] Several solutions have already been proposed and described in patent applications. For example, the patent application FR 2 830 274 proposes a regeneration process for improving the efficiency of the regeneration by a post-injection and / or the shift of the main injection.

[ooo7] The patent application FR 2 862 704 describes a system comprising means for analyzing the running conditions of the vehicle and comparing them to threshold values, to drive the engine in a first operating mode to lean mixture for rolling conditions greater than the threshold values or in a second operating mode implementing engine operating sequences alternating lean-mix and high-mix operating phases for conditions below the threshold values.

[Ooo8] The patent application FR 2 927 362 describes a process for the regeneration of an exhaust gas aftertreatment device according to which each regeneration phase is divided into a succession of fractional periods in which the temperature of the gases exhaust is alternatively warmer for a rich period and colder for a poor period. The duration of these periods is determined so that the surplus of energy brought by a rich period is compensated by a defect of energy in a poor period so that the average energy brought to the device allows the temperature leaving the post device. -treatment to stay close to an optimal setpoint temperature. The variation of the temperature of the exhaust gas is obtained by a variation of the mode of combustion of the engine, as by the variation of the richness in fuel.

[0oo9] The methods described in these patent applications do not take into account all the parameters for effectively controlling the regeneration of the particulate filter, including the runaway combustion when the filter contains a large amount of soot.

The present invention provides a method and system for regenerating a particulate filter to prevent runaway combustion of soot particles trapped in the filter. The invention is particularly well suited to the case where the regeneration is severe, that is to say when there is a risk of runaway combustion of soot. According to the invention, this risk exists when a large amount of soot is present in the filter and when the temperature of the exhaust gas is high enough to cause the combustion of soot in the filter. By large amount of soot means less than the amount that would completely clog the filter but large enough so that the combustion of soot is a risk of runaway. In other words, the pressure loss measured between the inlet and the outlet of the filter is between an upper threshold, corresponding to a clogged filter, and a lower threshold corresponding to a dirty filter.

[Ooi i] More specifically, the invention relates to a method of regenerating a particulate filter placed in the line of the exhaust gas of a heat engine of a vehicle, comprising the following steps: • identification of a risk of severe regeneration depending on the amount of soot in the particulate filter and the temperature upstream of the filter,

• when a serious risk is identified, determination of the limits of an engine operating zone for which the regeneration of the filter is suppressed,

• triggering an engine operating mode to suppress the regeneration of the filter when the engine operating point is in that zone, · stopping the engine operating mode when the severe regeneration conditions have disappeared and switching to regeneration mode current,

Repeating the preceding steps until said engine operating zone is reduced to such an end that it practically no longer exists.

According to the invention:

said risk of severe regeneration is identified when:

The quantity of soot in said filter is greater than a predetermined threshold, and the temperature of the exhaust gas at the inlet of the filter is sufficient to cause the combustion of said soot.

According to one embodiment, the amount of soot in the filter is determined by a pressure difference measurement between the inlet and the outlet of the filter.

[Ooi 4] According to another embodiment, the amount of soot in the filter is estimated.

According to the invention: Said engine operating zone is characterized by the engine torque as a function of the engine speed and the upper limit of said zone is a function of the quantity of soot in the filter and the vehicle running conditions; · Said engine operating mode for quenching the regeneration of the filter depends on the value of the engine torque.

[Ooi 6] Advantageously, when said engine torque is negative, said engine operating mode to quench the regeneration of the filter is a zero air flow mode and, when the vehicle is equipped with a metering valve and a EGR valve, said operating mode comprises closing the metering valve and opening the EGR valve.

When the engine torque is positive, said engine operating mode for quenching the regeneration of the filter is advantageously a rich mode according to which the gases entering the filter have a low oxygen content, which may be close to 0%. or even 0%.

When an oxidation catalyst is present in the exhaust line upstream of the particulate filter, the low oxygen content can be obtained through substantially stoichiometric conditions of fuel and oxygen at the catalyst inlet oxidation. Said stoichiometric conditions can be obtained by adding late post combustion into the engine operating cycle.

The invention also relates to a system for controlling the regeneration of a particle filter intended to be placed in an exhaust line of the combustion gases of a heat engine, the device comprising a controller adapted to set the regeneration process as defined above.

Other advantages and features of the invention will become apparent from the following description of an embodiment of the invention, given by way of non-limiting example, with reference to the accompanying drawings and in which: ό

• Figure 1 shows schematically an architecture of exhaust gas line;

FIG. 2 illustrates the principle of the method of the invention;

• Figure 3 illustrates a way to quench the regeneration of the particulate filter;

FIGS. 4 and 5 are schematic diagrams illustrating the operating mode of a "normal" and "zero air flow" respectively.

The accompanying drawings may not only serve to complete the invention, but also contribute to its definition, if any.

Preferably and in a summarized manner, the strategy of the invention can be applied when:

The amount of soot in the filter is greater than a threshold corresponding to an established risk of severe regeneration and less than a predetermined threshold which may correspond to the triggering of an alarm indicating that the filter is clogged; and

• the temperature upstream of the filter is greater than a threshold corresponding to a risk of initiation of combustion of soot.

The amount of soot in the filter and the rolling conditions used to define an initial "rich zone".

During travel, the vehicle will pass successively by engine operating points located in the "rich zone" where the regeneration is quenched and in a "current mode zone" where the regeneration is activated. Thus the mass of soot in the filter will gradually decrease. A smaller "rich area" will then be determined and the previous process will begin again. The strategy of the invention is deactivated when:

• The amount of soot in the filter is below a threshold corresponding to an established risk of severe regeneration, or

• The temperature upstream of the filter remains below a threshold corresponding to a risk of initiation of combustion of soot for a sufficient duration.

The implementation of the method of the invention may be based on an exhaust line architecture illustrated in FIG. 1. In this figure, the exhaust line 10 comprises, successively and in the direction of the flow of the exhaust gas, a turbine 1 1 of a turbocharger, a temperature probe 12 and oxygen, a diesel oxidation catalyst 13 (usually referred to as DOC for Diesel Oxydation Catalyst), a temperature probe 14, a particulate filter 15 and an oxygen sensor 16. The probes 12, 14 and 16 are connected to a data collection device 17 which communicates with a controller 18 which may be the engine operating controller or a controller dedicated to the regeneration of the particulate filter. The controller 18 includes in a memory the different steps for implementing the method of the invention. The method of the invention is based on the principle of activation and smothering of the combustion of soot particles trapped in the filter. Choking occurs depending on the driving conditions when these conditions do not allow the evacuation of the heat released by the combustion and the control of the temperature of the filter. For example, when driving on a highway at high speed, the air flow in the exhaust line is generally sufficient to remove the calories released by the combustion of soot. On the other hand, the situation is probably different when driving in the city at low speed. In this case, it may occur a runaway combustion in the filter and an increase in the overall temperature of the filter and / or too large temperature gradients that can lead to crack the filter. It is then necessary to quench the combustion of soot, for example by decreasing the oxygen level at the inlet of the filter. For this purpose, it is possible, for example, to cut the gas flow by raising the foot or to drive the engine in rich mode.

In Figure 2, there is shown the different operating zone of the engine according to the engine speed (in revolutions per minute) and the effective torque in Nm This figure illustrates how to proceed. We begin by determining the maximum allowable torque that can be achieved for each engine speed point. The set of maximum allowable torques is represented by the curve 21 in FIG. 2 which shows the effective average pressure or MSY (in bar) as a function of the engine speed R (from 0 to 5000 revolutions / minute). The PME pressure is a value proportional to the engine torque. The different possible values of the engine torque are located inside a space 20 delimited by the curve 21, by the minimum (around 800 t min) and maximum (around 4500 rpm) values of the engine speed R and by the SME minimum value _mir , of PME (this value is negative, equal to approximately -30 bars, knowing that the torque can be negative for example during a foot-lift during a deceleration phase, the motor then being driven by the vehicle). Within the space 20, a zone 22 corresponding to the negative torque values (zone delimited by the axis 23, the minimum value of PME, PME _mir "and the minimum values (approximately 800 t / min) and maximum (approximately 4500 rpm) of engine speed For all engine operating points within zone 22, the engine is operated at "zero air flow" (Figure 5). in order to quench the combustion of soot in the particulate filter In the interior of the space 20, a zone 24 of positive torque, called the "rich zone" defined by a curve 25, is also defined by the minimum and maximum values of the engine speed and the axis 23. For all the engine operating points located inside the rich zone 24, the combustion of the soot is suppressed by operating the engine in rich mode. consists in increasing the quantity of fuel injected into the cylinders so as to obtain an input concentration of the filter close to zero%, and if possible 0%. The combustion is thus stifled in the filter for lack of oxidizer. The size of the rich zone 24 depends on the soot load of the filter and the driving conditions. The greater the amount of soot, the larger the size of the rich zone 24. The size of the rich zone 24 therefore decreases as the soot is burned in the filter. The shape and position of the curve 25 are adapted according to the running conditions of the vehicle and the amount of soot remaining in the filter.

Inside the space 20, there is also defined a zone 26 called "current mode" and delimited by the curves 21 and 25. For the engine operating points located in this zone 26, the combustion is left is conducted according to the normal regeneration process.

During a car journey, the vehicle will alternately encounter operations corresponding to the zones "zero air flow" 22, rich 24 and current mode 26. So we will have a succession of combustion soot according to the current mode and smothering soot. The amount of soot present in the filter will therefore decrease as and when: this results in a gradual decrease in the size of the rich zone 24 and the zone "zero air flow" 22. The regeneration process continues as long as soot remains in the filter and so that the sizes of the zones 22 and 24 are not reduced to practically zero.

The smothering strategy of the combustion requires the calibration of the engine in a rich mode on a motor load zone (that is to say a torque area requested by the driver) very extensive motor field. For this purpose, specific mappings can be defined for the following quantities:

• Feed Injection Driver 2.

• Injection Pilot Quantity 2.

• Feed Injection Driver 1.

• Injection Pilot Quantity 1. · Main Injection Advance. • Advance Post Injection 1.

• Post Injection Quantity 1.

• Advance Post Injection 2.

• Post Injection Quantity 2. · Rail Pressure.

• Position Air Dispenser Shutter.

• Position EGR valve.

Figures 1 or 2 for, for example, pilot 1 or injection 2, represent the position of the injections or the order of injections relative to the top dead center. These parameters are those that make it possible to run the engine in rich mode (a method well known to motorists).

When the exhaust line comprises an oxygen catalyst (such as catalyst 13 of FIG. 1), late afterburner can be added to at least one cylinder so as to reach stoichiometric conditions at the inlet of the catalyst. between the fuel to be burned and the oxygen that remains after combustion in the cylinders. This deprives the oxygen filter so as to quench the combustion of soot. This is illustrated in FIG. 3 which schematically represents a Diesel Oxidation Catalyst (DOC) followed by a particulate filter 31. Air 32 and fuel 33 impregnated in the cylinders enter the inlet 34 of the catalyst. By varying the injection times and the quantities of fuel injected into the cylinders, it is possible to obtain stoichiometric fuel / oxygen conditions contained in the air at the inlet 34 of the filter 31. As a result, the oxygen concentration in the exhaust gas at the outlet of the catalyst is very low, close to 0% or even equal to 0% .This procedure makes it possible to deprive oxygen of the particulate filter 31 and therefore to smother the combustion of soot.

Figures 4 and 5 illustrate the principle of the operating mode "zero air flow", Figure 4 for a "normal" foot lift of the driver (lifting the foot of the accelerator pedal: it is so a phase deceleration), while Figure 5 relates to a foot lift of the type "zero air flow".

In Figures 4 and 5, the vehicle is provided with a compressor 40 and a turbine 41 of a turbocharger, the compressor is followed by a heat exchanger 42 and a metering valve 43. The compressed and cooled air is injected into the cylinders of the engine 44. The vehicle also comprises an exhaust gas recirculation loop (EGR loop) which comprises an EGR valve 45 followed by a heat exchanger 46. The exhaust gas from the cylinders pass in the turbine 41, then in catalysts 47 and 48 and in a particulate filter 49.

For a normal foot lift (Figure 4), the metering valve 43 is open and the EGR valve 45 is closed. The intake air then flows as indicated by the arrows 50, 51 and 52 and the exhaust gas then flows directly to the exhaust line (arrow 53) and passes through the catalysts 47 and 48 and the filter 49 (arrow 54). For a foot lift type zero airflow (Figure 5), the metering valve 43 is closed and the EGR valve 45 open. The engine then rotates on the EGR loop: when leaving the engine 44, the exhaust gases pass through the EGR valve 45 and the exchanger 46, as indicated by the arrows 55, 56 and 57. The particulate filter 49 is thus deprived of gas and the combustion of soot in the filter can thus be smothered.

The adaptation of the rich zone 24 to the rolling conditions and the amount of soot remaining in the filter allows the control of the regeneration of the filter for soot loads to reach the threshold causing an alarm indicating that the filter is clogged. This must make it possible to:

• contain the filter cracks and thus ensure compliance with the emission standards in mass and number, and avoid the risk of aggravated heating of the filter; to size just the filter substrate and • to choose less expensive filter substrates since they are less constrained to high thermal levels.

Other embodiments than those described and shown may be designed by those skilled in the art without departing from the scope of the present invention.

Claims

1. A method of regenerating a particulate filter (15) placed in the line of the exhaust gas (10) of a thermal engine of a vehicle, characterized in that it comprises the following steps: · identification of a risk of severe regeneration depending on the amount of soot in the particulate filter and the temperature upstream of the filter,

• when a serious risk is identified, determining the limits (25) of a motor operating zone (22, 24) for which the regeneration of the filter is suppressed,

• triggering an engine operating mode to suppress the regeneration of the filter when the engine operating point is located in said zone (22, 24),

Stopping said motor operating mode when the severe regeneration conditions have disappeared and switching to the current regeneration mode (26),

Repeating the preceding steps until said engine operating zone (22, 24) is reduced to such an end that it practically no longer exists.

2. Method according to claim 1 characterized in that said risk of severe regeneration is identified when:

The quantity of soot in said filter is greater than a predetermined threshold, and

The temperature of the exhaust gas at the inlet of the filter is sufficient to cause the combustion of said soot.

3. Method according to one of the preceding claims characterized in that the amount of soot in the filter is determined by a pressure difference measurement between the inlet and the outlet of the filter.

4. Method according to one of claims 1 and 2 characterized in that the amount of soot in the filter is estimated.

5. Method according to one of the preceding claims characterized in that said engine operating zone is characterized by a parameter (21) characteristic of the engine torque as a function of the engine speed (R) and in that the upper limit (25) of said zone is a function of the amount of soot in the filter and the running conditions of the vehicle.

6. Method according to one of the preceding claims characterized in that said engine operating mode for quenching the regeneration of the filter depends on the value of a parameter (21) characteristic of the engine torque.

7. The method of claim 6 characterized in that, when said engine torque is negative, said engine operating mode for quenching the regeneration of the filter is a zero air flow mode (22).

8. A method according to claim 7 characterized in that, when the vehicle is provided with a metering valve and an EGR valve, said operating mode comprises the closing of the metering valve and the opening of the EGR valve.

9. Method according to one of the preceding claims characterized in that, when the engine torque is positive, said engine operating mode for quenching the regeneration of the filter is a rich mode (24) according to which the gases entering the filter have a low oxygen content.

10. The method of claim 9 characterized in that said content is close to 0% or equal to 0%.

11. Method according to one of claims 9 and 1 0 characterized in that, when an oxidation catalyst (30) is present in the exhaust line upstream of the particulate filter (31), the low oxygen content is obtained by substantially stoichiometric conditions of fuel (33) and oxygen (32) at the inlet of the oxidation catalyst (30).

12. The method of claim 1 1 characterized in that said stoichiometric conditions are obtained by adding late post combustion in the operating cycle of the engine.

13. System for controlling the regeneration of a particle filter intended to be placed in an exhaust line of the combustion gases of a heat engine, the device being characterized in that it comprises a controller (1 8) adapted to implement the regeneration method according to one of the preceding claims.