FR2925937A1 - Particulate filter regenerating method for internal combustion engine e.g. supercharged oil engine, of motor vehicle, involves injecting exhaust gas enriched with unburned hydrocarbon in exhaust line - Google Patents

Abstract

The method involves estimating a quantity of trapped particle in a particulate filter, and triggering a regeneration phase of the filter for given quantity i.e. regeneration value, of the estimated particle during burning the trapped particles. A quantity of trapped unburned hydrocarbon in the filter is estimated, and the estimated quantity of hydrocarbon is compared with predetermined set value. Exhaust gas enriched, with unburned hydrocarbon, is injected in an exhaust line when the estimated quantity of hydrocarbon is lower than the set value. An independent claim is also included for a device for regenerating a particulate filter of an exhaust line of an internal combustion engine comprising an electronic control unit.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention generally relates to the depollution of internal combustion engines of motor vehicles. It relates more particularly to a method for regenerating a particulate filter of an exhaust line of an internal combustion engine, which comprises the following steps: a) the quantity of particles trapped in the particulate filter is estimated, b) for a given quantity, called the regeneration value, of trapped particles estimated at step a), a regeneration phase of the particle filter during which said trapped particles are burned. TECHNOLOGICAL BACKGROUND Diesel internal combustion engines emit in their exhaust gases unburnt hydrocarbons, soot particles and pollutant nitrogen oxide molecules. In order to limit these pollutant emissions, pollution control devices are located on the exhaust line downstream of the combustion chamber. These depollution devices generally comprise a nitrogen oxide trap placed upstream of a particulate filter. These devices each operate in two alternating operating phases: in a first phase, known as normal operation, the nitrogen oxide trap traps the nitrogen oxide molecules and the particulate filter traps the soot particles and the unburned hydrocarbons. In a second phase, called purge for the nitrogen oxide trap or regeneration for the particulate filter, they treat these pollutants and release them in the exhaust gas sent to the outside of the engine in a non-polluting form . To regenerate the particulate filter, the trapped particles are burned inside the filter by raising its temperature sharply. Thus, the temperature at the inlet of the particle filter reaches a value of between 600 and 700 ° C., approximately equal to 650 ° C. For this purpose, it is planned to modify the injection of the fuel into the combustion chamber (for example, by increasing the number of injection per engine cycle or the duration of the injections, or the moment of injection into the cycle) to raise the temperature of the exhaust gas passing through the particulate filter. For example, a post-injection is carried out, that is to say an additional injection of fuel into the combustion chamber after the usual main fuel injection. The combustion of the fuel injected late during the engine cycle raises the temperature of the exhaust gases and produces a lot of unburned hydrocarbons. It is also known to carry out a second post-fuel injection in order to trigger a specific exothermic operating mode of the nitrogen oxide trap in which a high temperature rise of this trap occurs, which contributes to heating the gases. exhaust system to bring the particulate filter to its regeneration temperature. However, this method of regeneration of the high temperature particle filter has the drawback of considerably accelerating the aging of the nitrogen oxide trap. Indeed, in order for the inlet temperature of the particle filter to reach a value close to 650 ° C., the temperature of the nitrogen oxide trap more often exceeds a threshold temperature of about 700 ° C., beyond which the aging Nitrogen oxide trap is very fast. Thus, a very short time spent at a temperature above the threshold temperature results in a very significant aging of this trap, whereas a long operation at temperatures below this threshold (for example between 600 and 650 ° C.) does not lead to that a weak aging of the trap with oxides of nitrogen. The high temperature regeneration phases of the particulate filter thus have the effect of reducing the depollution performance of the nitrogen oxide trap because of its accelerated aging. In order to limit this accelerated aging of the nitrogen oxide trap, it is known to bring the nitrogen oxide trap of the particle filter as close as possible to the exhaust line. Since heat losses are thus limited between the nitrogen oxide trap and the particulate filter, the temperature to be reached in the nitrogen oxide trap is reduced to ensure an adequate regeneration temperature in the particulate filter. However, these conditions may not be sufficient for the temperature reached in the nitrogen oxide trap to be lower than the threshold temperature. It is also known to provide an additional fuel injection nozzle on the exhaust line between the nitrogen oxide trap and the particulate filter. Fuel injection directly into the exhaust line between the nitrogen oxide trap and the particulate filter makes it possible to increase the temperature of the exhaust gas downstream of the nitrogen oxide trap, and to maintain the temperature of it below the threshold temperature. However, the addition of an additional injection nozzle on the exhaust line is very expensive. OBJECT OF THE INVENTION In order to solve the disadvantages of the state of the art mentioned above, it is proposed according to the invention a new regeneration method of the particle filter at low temperatures, to ensure the maintenance of the oxide trap. nitrogen at a temperature below the aging threshold, without additional production costs. For this purpose, it is proposed according to the invention a regeneration process as defined in the introduction, comprising the following additional steps: c) the quantity of unburned hydrocarbons trapped in the particulate filter is estimated, d) the estimated quantity is compared in step c) at a predetermined target value and if the quantity estimated in step c) is lower than this predetermined setpoint value, e) hydrocarbon-enriched exhaust gases are injected into the exhaust line; unburned. The unburned hydrocarbons trapped in the particulate filter lower the combustion temperature of the trapped particles. The regeneration of the particulate filter can therefore take place at temperatures lower than those used in the known regeneration processes at high temperatures. The process according to the invention advantageously makes it possible to control the amount of unburned hydrocarbons trapped in the particulate filter, by making it tend towards a predetermined set value. The setpoints are predetermined to ensure that the amount of unburned hydrocarbons trapped in the particulate filter at the time of its regeneration is sufficient to lower the combustion temperature of the particles so that the nitrogen oxide trap is not removed. not heated beyond its threshold temperature. If the quantity of trapped unburned hydrocarbons estimated in step c) is less than the set value, the injection of unburned hydrocarbon enriched exhaust gas makes it possible to increase this quantity to make it tend towards the setpoint value. . The aging of the nitrogen oxide trap is then considerably slowed down.

According to a first advantageous characteristic of the process, in step e), a fuel / air rich mixture is mixed into the combustion chamber, that is to say containing an excess of fuel.

When an excess of fuel is introduced into the combustion chamber, the fuel is not completely consumed during the combustion reaction and a large amount of unburned hydrocarbons is produced. These unburned hydrocarbons thus enrich the exhaust gases emitted and are partially trapped by the particulate filter. According to another advantageous characteristic of the process, step c) is carried out if the quantity of particles trapped in the particulate filter estimated in step a) exceeds a threshold value called pre-regeneration value. Step c) and the subsequent steps of the process are thus performed only when the quantity of particles trapped in the filter approaches the given amount at which the regeneration is triggered. According to another advantageous characteristic of the method, step c) is carried out at regular time intervals. By regular time intervals are meant time intervals of fixed duration or whose duration gradually decreases. Advantageously, the time intervals decrease when the quantity of particles trapped in the particulate filter estimated in step a) is close to the regeneration value. In particular, the duration of the time interval between two steps c) is reduced when the initiation of step b) approaches, for quantities of particles estimated in step a) between the value of pre-regeneration and the regeneration value. According to another advantageous characteristic of the process, exhaust gas enriched with unburned hydrocarbons is injected into the exhaust line before carrying out step b). Thus, regardless of the amount of unburned hydrocarbons trapped in the filter, this amount is increased before triggering the regeneration of the particulate filter. According to another advantageous characteristic of the method, in step d) a set value is used determined as a function of the quantity of particles trapped in the particulate filter estimated in step a). Advantageously then, the setpoint increases with the quantity of particles trapped in the particulate filter estimated in step a). According to another advantageous characteristic of the method, it is realized. step a) at regular time intervals during operation of the engine. According to the invention, a device for implementing the previously mentioned method is also proposed, comprising an electronic control unit in which said setpoint values are recorded, and said pre-regeneration and regeneration values, to which are provided estimates of the quantities of particles and unburned hydrocarbons trapped in the particulate filter, and which - compares the amount of unburned hydrocarbons trapped in the particulate filter to the predetermined setpoint and - depending on the result of this comparison, controls the injection into the exhaust line of the exhaust gas enriched in unburned hydrocarbons, and - triggers for a quantity of trapped particles estimated equal to the regeneration value a regeneration phase of the particulate filter. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description, with reference to the appended drawings, given by way of non-limiting example, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: FIG. 1 is a schematic view of the various components of an internal combustion engine comprising a nitrogen oxide trap and a particulate filter on the exhaust line; and FIGS. 2A, 2B and 2C diagrammatically show the evolution of the quantity of Qpart particles trapped in the particle filter as a function of time (FIG. 2A), of the quantity of QHC unburned hydrocarbons trapped in this particulate filter. time function (solid line) as well as predetermined set values for trapping unburned hydrocarbons (dashed line) according to the invention (Figure 2B). It also schematically shows the evolution of the fuel / air ratio of the quantities of fuel and air introduced into the combustion chamber of the engine as a function of time according to the invention (FIG. 2C). - Figure 3 is a schematic representation of an embodiment of the method according to the invention. FIG. 1 shows a supercharged diesel engine comprising a combustion chamber 23 supplied with fresh air via an intake line 300 and opening downstream on an exhaust line 400. The intake line 300 comprises a pipe intake 4 in which circulates fresh air. The fresh air flow rate is measured at the inlet of the intake pipe 4 by an air flow meter 1. The engine comprises a turbocharger 14 comprising two turbines 2, 9. The driving turbine 9 is placed in an exhaust pipe 16 and drives the driven turbine 2 placed in the intake pipe 4 to compress the fresh air flowing there. As this compression has the effect of heating up the air, an air cooler 3 is provided on the path of the intake duct 3 which cools the air leaving the turbocharger 14. The intake duct 4 opens into a manifold 6. It comprises upstream of this manifold 6 an intake flap 5. The orientation of the intake flap 5 relative to the axis of the intake duct 4 controls the flow of fresh air entering the manifold 6. The manifold 6 is connected to an intake valve 21 of a cylinder 20 of the engine. The compressed air enters via this intake valve 21 into a combustion chamber 23 of the cylinder 20 and an injector 8 is provided which injects the fuel into this combustion chamber 23.

The motor advantageously comprises an electronic control unit 30 which controls the quantity of fuel injected by the injector 8 into the combustion chamber 23 as well as the moment when this injection is made. After the combustion, the residual exhaust gases are expelled from the combustion chamber 23 by an exhaust valve 22 in the exhaust line 16 of the exhaust line 400. Part of this exhaust gas is taken by a recirculation circuit 17 which brings them, after passing through an air cooler 15, to the collector 6 where they mix with the fresh air arriving from the intake pipe 4.

The supply of exhaust gas into the manifold 6 is regulated by a valve 13 called EGR (Exhaust Gas Recirculation). The electronic control unit 30 also controls the actuation of the intake flap 5 and the EGR valve 13 to regulate the flow of air into the manifold 6 and therefore the amount of air introduced into the combustion chamber 23.

The electronic control unit 30 thus regulates the ratio of the quantities of air and fuel introduced into the combustion chamber 23. The exhaust gases that are not directed in the recirculation line 17 flow in the exhaust pipe 16 to arrive at the driving turbine 9 of the turbocharger 14. They then pass through a nitrogen oxide trap 11 and a particulate filter 12 of the exhaust line 400 before being released into the atmosphere. Advantageously, the regeneration of the particulate filter 12 is carried out according to a regeneration process, the steps of which are shown diagrammatically in FIG. 3. It is estimated at a given instant T, during a step a), the quantity Qpart of particles trapped in the particle filter 12, and in a step f) this quantity Qpart is compared to a value S min of pre-regeneration. This value Smin corresponds to a quantity of particles trapped slightly lower, for example, 3% lower, the maximum amount of particles that can be trapped in the particulate filter 12 before the regeneration thereof, called regeneration value Smax. This Smax value is for example between 5 and 7 grams per liter. Step a) is performed at regular intervals of time throughout the operation of the engine. It is performed for example once a second. As shown in FIG. 2A, the Qpart amount of particles trapped in the particulate filter 12 increases progressively over time. It reaches the value Smin of pre-regeneration at time Ti, then the value Smax of regeneration at time T2. As long as the quantity Qpart of trapped particles remains below the value Smin of pre-regeneration, step a) is repeated. When the quantity Qpart estimated in step a) becomes equal to or greater than the value S min of pre-regeneration, this quantity Qpart is compared with the value Smax of regeneration during a step g). If the quantity Qpart estimated in step a) is greater than or equal to the value Smax of regeneration, regeneration of the particle filter 12 is initiated in a step b). As shown in FIG. 2A, after the initiation of the regeneration at time T2, the quantity of particles trapped in the particulate filter 12 decreases: the particulate filter is emptied. If the quantity Qpart estimated in step a) is lower than the value Smax of regeneration, it is estimated, during a step c), the amount of QHC unburned hydrocarbons trapped in the particulate filter 12, and compared, in a step d), the quantity QHC to a predetermined set value. Step c) is preferably performed at regular time intervals when the Qpart amount of particles trapped in the particulate filter 12 exceeds the pre-regeneration value Smin. This step c) is for example performed once per second.

The set values are shown in dashed lines in Figure 2B. These values are preferably predetermined as a function of the quantity Qpart of particles trapped in the particulate filter 12, and increase progressively when the quantity Qpart approaches the value Smax of regeneration. The set values are predetermined so that the amount of QHC unburned hydrocarbons, shown in solid lines in Figure 2B, reaches a target value when the quantity Qpart is equal to the regeneration value Smax. This target value is predetermined so that the combustion temperature of the particles trapped in the particulate filter 12 is lowered. Thus, the regeneration of the particulate filter 12 can be carried out at a temperature not exceeding the accelerated aging threshold temperature of the nitrogen oxide trap 11. This target value is limited to allow controlled combustion of the particles in the particulate filter 12 during regeneration. In practice, the combustion temperature of the trapped particles is lowered by about 50 to 100 ° C.

The setpoints are preferably predetermined empirically. Alternatively, they can be predetermined by a calculation. These setpoints are preferably predetermined for Qpart quantities of particles trapped in the particle filter 12 between the pre-regeneration Smin and regeneration Smin values, as shown in FIG. 2B. If the quantity QHC estimated in step c) is greater than the set value, the operation of the motor is not modified. If the quantity QHC estimated in step c) is less than the set value, exhaust gas enriched with unburned hydrocarbons is injected into the exhaust line 400 during a step e). The carrying out of step c) automatically entails that of step d), and possibly that of step e), according to the result obtained in step d). To carry out step e), the operation of the motor is transiently modified. Indeed, in so-called normal operation, the engine operates with a fuel / air mixture lean, that is to say with a fuel fault with respect to the amount of air introduced into the combustion chamber 23 of the engine. The fuel / air ratio is then less than 1, as shown in FIG. 2C.

In order to inject exhaust gases enriched with unburned hydrocarbons into the exhaust line 400, a rich mixture engine operating phase is initiated, that is to say one or more successive engine cycles in which the fuel / air mixture injected has an excess of fuel. The fuel / air ratio is then greater than 1, as shown in FIG. 2C. It is also possible to trigger several engine operating phases in a rich mixture, or to lengthen the duration of this operating phase as a function of the difference between the quantity of unburned hydrocarbons estimated in step c) and the setpoint value. In practice, the method is implemented in the engine described previously by the electronic control unit 30. This electronic control unit 30 regulates the quantities of air and fuel introduced into the combustion chamber 23. It controls the tripping of an operating phase of the engine with a rich fuel / air mixture, particularly as a function of the state of the nitrogen oxide trap 11: when this nitrogen oxide trap 11 is saturated, an operating phase is provided engine fuel / rich air mixture to allow its purge. This is in fact carried out by a reduction reaction of the nitrogen oxides by the unburnt hydrocarbons produced during the phases of operation in rich mixture of the engine. This reduction reaction is also favored by the high temperature of the exhaust gases during these phases of operation. According to the method according to the invention, it is provided that the electronic control unit 30 triggers operating phases in a rich fuel / air mixture as a function of the quantity Qpart of particles trapped in the particulate filter 12, and in function the amount of QHC unburnt hydrocarbons trapped in this particulate filter 12. The regeneration Smax values and Smin of pre-regeneration of the particulate filter 12 and the set values are recorded in the electronic control unit 30. Qpart, QHC quantities of particles and unburned hydrocarbons trapped in the particulate filter 12 are estimated in steps a) and c) by the electronic control unit 30. This electronic control unit 30 also performs the comparison of the quantity Qpart Smin values of pre-regeneration and Smax regeneration in steps f) and g).

If the quantity Qpart estimated in step a) is lower than the value S min of pre-regeneration, or if the quantity QHC estimated in step c) is greater than the set value, the operation of the engine remains unchanged, and the electronic control unit 30 triggers the operating phases in a rich fuel / air mixture depending on the state of the nitrogen oxide trap 11, independently of the quantities Qpart, QHC of particles and unburned hydrocarbons estimated. The fuel / rich air mixture operating phases visible in FIG. 2C at times less than Ti thus correspond to the purges of the nitrogen oxide trap 11. If the quantity Qpart estimated in step a) is greater than the value Smin pre-regeneration and lower than the regeneration value Smax, and if the quantity QHC estimated in step c) is less than or equal to said corresponding reference value, the electronic control unit 30 triggers additional phases of operation of the engine in rich mixture to increase the amount of unburned hydrocarbons trapped. Under these conditions, the engine operating phases in a rich mixture are more frequent or longer durations than when the electronic control unit 30 triggers the operating phases fuel mixture / rich air only depending on the state of the trap to Nitrogen oxides 11. This is visible in FIG. 2C by comparing the operating phases in a rich fuel / air mixture that are triggered close to T2 times to the corresponding phases triggered at times shorter than Ti.

If the Qpart quantity estimated in step a) is greater than or equal to the regeneration value Smax, the electronic control unit 30 triggers step b). The electronic control unit 30 controls the regeneration of the particulate filter 12 by triggering a rise in temperature of the exhaust gas and the nitrogen oxide trap 11 through several post-injections.

The combustion of particles trapped in the particulate filter 12 in the presence of unburned hydrocarbons occurring at temperatures of 50 to 100 ° C below the combustion temperatures of the unburned hydrocarbon-free particles, the combustion temperature is lowered to a value of between 550 ° C. and 600 ° C.

Since the temperatures to be achieved in the particulate filter 12 are lower, the amount of fuel injected during the post-injection is decreased so that the temperatures of the exhaust gas and the nitrogen oxide trap 11 during the regeneration decrease. The nitrogen oxide trap 11 is then heated to temperatures preferably below the threshold temperature of this trap.

The lifetime of the nitrogen oxide trap 11 and its depollution performance are therefore advantageously increased. Since the quantity of fuel injected post-injection into the combustion chamber 23 is reduced, the fuel consumption of the vehicle is advantageously reduced. Moreover, the fuel efficiency of the fuel injected during the post-injections is low, a portion of the fuel injected post-injection is not burned, resulting in a significant dilution of fuel in the engine oil. Reducing the amount of fuel injected post-injection therefore reduces the dilution of fuel in the oil and allows the user to space the oil changes. Finally, the depollution performance of the nitrogen oxide trap 11 being improved, it is longer resistant to sulfur poisoning. Indeed, the nitrogen oxide trap 11 also traps sulfur compounds which limit, by their accumulation, storage capacity of nitrogen oxides 11. Purges of these sulfur compounds, or desulfurization of the nitrogen oxide trap 11, are then performed. Desulfurization also causes a dilution of fuel in the engine oil. Here, the desulphurations are spaced apart, and this dilution decreases, which helps to space the oil changes of the engine. The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant consistent with his mind.

For example, it is conceivable to carry out step c) with increasing frequency when the quantity Qpart approaches the value Smax of regeneration. Alternatively, step c) is performed at regular intervals regardless of the amount of Qpart particles trapped in the particulate filter.

It is also conceivable that the set values are predetermined for all Qpart quantities and zero for Qpart quantities less than the pre-regeneration value Smin. Alternatively, the set values are predetermined for any quantity Qpart.

According to another variant of the process described above, the regeneration step of the particulate filter is preceded by purging the nitrogen oxide trap or a simple engine operating phase in a fuel / air rich mixture.

Claims (10)

A method of regenerating a particulate filter (12) of an exhaust line (400) of an internal combustion engine, which comprises the steps of: a) estimating the amount of particles trapped in the filter with particles (12), b) for a given quantity of trapped particles estimated in step a), called the regeneration value, a regeneration phase of the particulate filter (12) during which said trapped particles are burned is ignited; , characterized in that it further comprises the following steps: c) the quantity of unburned hydrocarbons trapped in the particulate filter (12) is estimated, d) the quantity estimated in step c) is compared with a value predetermined setpoint and if the quantity estimated in step c) is less than this predetermined setpoint, e) is injected into the exhaust line (400) of the exhaust gas enriched unburned hydrocarbons. 2. A method of regenerating a particulate filter (12) according to the preceding claim, wherein, in step e), is injected into the combustion chamber (23) a rich fuellair mixture, that is to say say containing excess fuel. 3. Process for regenerating a particulate filter (12) according to one of the preceding claims, wherein step c) is carried out if the quantity of particles trapped in the particulate filter (12) estimated at step a) exceeds a threshold value called pre-regeneration value. 4. Process for regeneration of a particulate filter (12) according to the preceding claim, wherein step c) is carried out at regular time intervals. 5. A method of regenerating a particulate filter (12) according to claim 3, wherein step c) is carried out at time intervals whose duration gradually decreases when the amount of particles trapped in the particulate filter (12). ) estimated in step a) is close to the regeneration value. 6. A method of regenerating a particulate filter (12) according to one of the preceding claims, wherein is injected in the exhaust line of the exhaust gas enriched unburned hydrocarbons before performing step b). 7. A method of regenerating a particulate filter (12) according to one of the preceding claims, wherein is used in step d) a set value determined according to the amount of particles trapped in the particulate filter (12) estimated in step a). 8. A method of regenerating a particulate filter (12) according to the preceding claim, wherein the set value increases with the amount of particles trapped in the particulate filter (12) estimated in step a). 9. A method of regenerating a particulate filter (12) according to one of the preceding claims, wherein step a) is carried out at regular intervals of time during operation of the engine. 10. Device for implementing the method according to one of the preceding claims, comprising an electronic control unit (30) in which are recorded said set values, and said values of pre-regeneration and regeneration, which are provided estimates of the quantities of particulates and unburnt hydrocarbons trapped in the particulate filter (12), and which compares the amount of unburned hydrocarbons trapped in the particulate filter (12) to the predetermined setpoint and - in depending on the result of this comparison, controls the injection into the exhaust line of the exhaust gas enriched with unburned hydrocarbons, - triggers for a quantity of trapped particles estimated equal to the regeneration value a regeneration phase of the particulate filter (12) .25