FR2920824A1 - METHOD FOR MANAGING THE OPERATION OF AT LEAST ONE CATALYTIC CONVERTER FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The present invention relates to a method for managing the operation of at least one catalytic converter (7) fitted to an exhaust line (3) of an internal combustion engine (1), said catalytic converter (7) being purged according to determined criteria such as when a threshold value is reached for example, said method is remarkable in that it comprises at least the following stages of: - estimation of the dilution during rolling, - comparison of the estimated dilution with a determined critical threshold modifying the sulfur and nitrogen oxide purge occurrence of the catalytic converter (7) when the estimated dilution is greater than the determined critical threshold.Another subject of the invention concerns a system for managing the operation of the catalytic converter (7). at least one catalytic converter (7) fitted to the exhaust line (3) implementing the method according to the invention.

Description

The present invention relates to a method for managing the operation of a combustion engine exhaust system of the type comprising at least one catalytic converter. In the automotive field, it is well known to use particulate filters and catalytic converters in an exhaust line of a diesel or gasoline engine that generates particulates, nitrogen oxides and sulfur so to trap the particles, treat the oxides of nitrogen and sulfur and thus meet the standards in force. The particulate filters are inserted into the exhaust line of the combustion engine and are adapted to trap the soot particles contained in the exhaust gas. Controlled regeneration devices make it possible to periodically burn the particles trapped in the filters and avoid clogging them. In order to heat the exhaust gases at a temperature of the order of 550 to 600 ° C to burn the particles accumulated in the particle filter, various systems have been proposed such as heating resistors or means for injecting a fuel. additional amount of fuel in at least one of the combustion chambers of the engine in the form of a post-injection for example, these systems being controlled by an electronic control system.

Catalytic converters also known as nitrogen oxide or Noxtrap traps operate in two distinct modes, a lean mode and a rich mode in which the converter is purged. In lean mode, the catalytic converter stores oxides of nitrogen in different compartments. It will be noted that catalytic converters have a storage capacity which decreases over time. When the catalytic converter has reached its storage capacity, it must be purged. The purge occurs in rich mode, i.e. when there is an oxygen deficiency with respect to the stoichiometry. During this purge, reducing agents, usually unburned hydrocarbons and carbon monoxide, pass into the converter and reduce the nitrogen oxides to release them into the atmosphere as di-nitrogen N2 and carbon dioxide CO2 .

Moreover, the absorption capacity of these converters is reduced by the presence of sulfur in the fuel and in the oil. Sulfur attaches to catalytic zones to trap nitrogen oxides and thereby reduces their effectiveness. Thus, it is known to purge the sulfur of the Noxtrap, that is to say to release the sulfur fixed in the nitrogen oxide trap. For this purpose, it is necessary to raise the temperature in the Noxtrap to a temperature of about 650 ° C and switch to rich mode. Such a process of purging the Noxtrap requires a large amount of additional energy to heat the Noxtrap to the purge temperature as well as an increase in the amount of fuel to run in rich mode. To overcome this drawback, it is well known to arrange a second catalyst called Soxtrap or sulfur oxide trap on the exhaust line upstream of the nitrogen oxide trap. Such a catalyst makes it possible to trap the sulfur contained in the exhaust gas when it operates in lean mode.

The storage capacity of the sulfur oxide trap is limited and it is necessary to carry out periodic purges so as to release the sulfur. This purge is to increase the temperature of the exhaust gas and to go into rich mode by controlling by means of sensors, the composition of the exhaust gases so that they are reducing.

For a diesel engine whose exhaust line includes a particulate filter and a nitrogen oxide trap, purges of nitrogen oxides and sulfur and regeneration of particulate filters contribute to the increase of the dilution . Dilution means the presence of fuel in the engine oil which is harmful to the proper mechanical operation. Under severe driving conditions, such as an urban cycle for the particulate filter or an urban / road cycle for an exhaust line comprising a particulate filter and a nitrogen oxide trap, a means of limiting the dilution is to limit purges of nitrogen oxide and sulfur providing a direct impact on the emissions of nitrogen oxides on a cycle such as on a NEDC cycle according to the English acronym New European Driving Cycle of European standards .

According to the systems of the prior art, purges of nitrogen oxides and sulfur are cut beyond a calibrated dilution threshold, for vehicles with a severe rolling dilution, so that the impact regeneration of particulate filters and evaporation are sufficient to reduce dilution and converge towards the emptying interval objective. However, it is common for the interruption of nitrogen oxides and sulfur purges to no longer allow, by an absence of control of the mass of sulfur and nitrogen oxides, to comply with the limits for the pollution control of oxides. in the legislation in force.

One of the aims of the invention is therefore to remedy all these drawbacks by proposing a method and a system for managing the operation of a particle filter and catalytic converters for a combustion engine of robust, reliable and inexpensive design , allowing to respect the thresholds of depollution. For this purpose and in accordance with the invention, there is provided a method for managing the operation of at least one catalytic converter fitted to an exhaust line of an internal combustion engine, said catalytic converter being purged according to determined criteria such as only when a threshold value is reached for example; said method is remarkable in that it comprises at least the following stages of estimation of the dilution during rolling, comparison of the estimated dilution with a determined critical threshold, and modification of the occurrence of purges of sulfur oxides and nitrogen of the catalytic converter when the estimated dilution is above the determined critical threshold. The occurrence of the sulfur oxide purges of the catalytic converter is modified by modifying the trigger threshold mass of the sulfur oxide purge of said catalytic converter and / or the occurrence of the nitrogen purges of the catalytic converter is modified by modifying the trigger threshold mass of the nitrogen oxide purge of said catalytic converter. Furthermore, the critical threshold is determined according to the driving conditions, a critical threshold being determined for the driving in urban cycle and / or road cycle and / or highway cycle taken separately or in combination.

In addition, the purge of the catalytic converter is obtained by increasing the temperature in said catalytic converter to a temperature of about 650 ° C and by operation in rich mode. Another subject of the invention concerns a system for managing the operation of at least one catalytic converter fitted to an exhaust line of an internal combustion engine, said catalytic converter being purged according to determined criteria and being driven by a unit electronic control system which comprises management means for controlling purges of sulfur oxides and nitrogen; said system is remarkable in that said management means are arranged to estimate the dilution during rolling, then compare the estimated dilution with a determined critical threshold and modify the occurrence of sulfur and nitrogen oxide purges of the catalytic converter when the estimated dilution is greater than the determined critical threshold. According to an essential characteristic of the system according to the invention, the management means are arranged to modify the occurrence of sulfur oxide purges of the catalytic converter by modifying the trigger threshold mass of the sulfur oxide purge of said catalytic converter and / or by modifying the trigger threshold mass of the purge nitrogen oxides of said catalytic converter. Moreover, the management means are arranged to determine the critical threshold as a function of the driving conditions, a critical threshold being determined for driving in urban cycle and / or road cycle and / or highway cycle taken separately or in combination. Incidentally; the exhaust line has a particulate filter. Other advantages and features will become more apparent from the following description of several alternative embodiments, given by way of non-limiting examples, of the method and the system for managing the operation of at least one catalytic converter for a combustion engine. according to the invention, from the appended drawings in which: - Figure 1 is a schematic representation of an engine according to a preferred embodiment of the invention; - Figure 2 is a flowchart of the steps of the method according to the invention; . Referring to Figure 1, there is shown a motor 1 according to a preferred embodiment of the invention.

Said engine 1 conventionally comprises a motor unit 2, an exhaust line 3 in which circulates an exhaust gas emitted by the engine block 2, and control means for controlling the performance of the engine. Said engine block 2 comprises in particular an intake manifold 4 and 10 exhaust 5. The exhaust line 3 is composed in particular on the one hand of a turbocharger 6 provided with a turbine 6a capable of driving a compressor 6b and on the other hand, a catalytic converter 7. The turbine 6a of the turbocharger 6 receives the exhaust gas leaving the exhaust manifold 5 and the compressor 6b receives fresh air to compress and supercharge the collector intake 4. Said fresh air passes through a flow meter 8 and an air filter not shown in Figure 1. It is obvious that the exhaust line 3 may include an exhaust gas recirculation system commonly called EGR according to the acronym 20 Anglo-Saxon Exhaust Gas Recirculation without departing from the scope of the invention. The catalytic converter 7 is fed by the outlet of the turbine 6a of the turbocharger 6 so that it receives the exhaust gas exiting the turbine 6a after driving it in rotation. This catalytic converter 7 has the function of trapping nitrogen oxides (NOx) and sulfur oxides (SOx) present in the exhaust gas. Said catalytic converter 7 is conventionally constituted by channels made in a monolith with a porous structure impregnated with a catalytic phase and having a large contact area with the exhaust gas. The exhaust line 3 may also comprise a particulate filter or an oxidation catalyst coupling the post-treatment of the gas by reduction of NOx nitrogen oxides to a post-treatment of unburnt hydrocarbon particles and carbon monoxide oxides. carbon. Furthermore, the engine 1 comprises an upstream probe 02 positioned on the exhaust line 3 upstream of the catalytic converter 7, that is to say between the turbine 6a and the catalytic converter 7, and preferably at the input of said converter 7, and delivering a measurement of the oxygen content in the exhaust gas located upstream of said converter 7. The engine 1 also comprises a downstream 02 probe 10 positioned on the exhaust line 3 downstream of the catalytic converter 7, that is to say between said catalytic converter 7 and the outlet of the exhaust gas, and preferably at the outlet of said converter 7, and delivering a measurement of the oxygen content in the exhaust gas located in downstream of said converter 7. The upstream 9 and downstream probes 10 may be probes of the proportional or binary type, that is to say probes delivering a signal of the all-or-nothing type depending on the oxygen content that is in contact with the sensitive element of the probe, without departing from the scope of the invention. All or nothing means that the signal delivered by the probe generally takes two perfectly distinguishable values such as 0 and 1 for example. Said upstream 9 and downstream probes 10 are connected to an electronic control unit 11 called ECU possibly coupled to a computer not shown in FIG. 1. This electronic control unit 11 is also connected to the flow meter 8 and controls the motor 1 so as to well known per se by implementing a suitable control method.

Said electronic control unit 11 also comprises means for managing the operation of the exhaust line 3 and more precisely means for controlling the purges of sulfur and nitrogen oxides as a function of the dilution during severe rolling. . Said means are arranged to estimate the dilution as a function of the rolling conditions and means for increasing the tripping periods of the purges of nitrogen oxides (NOx) and / or sulfur (SOx) when the estimated dilution is greater than one. critical threshold. Said means comprise several critical thresholds which depend on the estimated dilution and / or the rolling conditions of the vehicle. Furthermore, said means comprise means for varying the mass threshold of sulfur oxides (SOx) with respect to a mass reference sulfur oxide (SOx) threshold corresponding to a normal situation. Thus, with reference to FIG. 2, the dilution is in a first estimated step 100 and then, in a step 110, it is compared with a critical threshold. Assuming that the estimated dilution is greater than the critical threshold (step 120), the mass of sulfur oxide and / or the mass of nitrogen oxides to trigger purges of nitrogen oxide and sulfur in the catalytic converter 7 are increased relative to the mass of sulfur oxide and / or the mass of standard nitrogen oxides (step 130). Assuming that the estimated dilution is below the critical threshold (step 140), the mass of sulfur oxide and / or the mass of nitrogen oxides to trigger purges of sulfur oxide and / or nitrogen in the catalytic converter 7 are unchanged with respect to the mass of sulfur oxide and / or the mass of standard nitrogen oxides (step 150). For example, the standard sulfur oxide (SOx) mass for triggering purge of sulfur oxides (SOx) in the catalytic converter 7 is 3 g in the urban cycle, 1.3 g in the road cycle and 1 g in the motorway cycle. . The mass of nitrogen oxides (NOx) standard for triggering the purge of nitrogen oxides (NOx) in the catalytic converter 7 is 0.6 g regardless of the cycle, thus, when the estimated dilution is below the critical threshold (Step 110), the average occurrence of nitrogen oxide purges in the catalytic converter 7 is about every 5 km and the average sulfur sulfur purge occurrence in the catalytic converter 7 is about every 1500 km. Assuming that the estimated dilution is greater than the critical threshold (step 120), the sulfur oxide (SOx) mass increased to trigger purge sulfur oxides (SOx) in the catalytic converter 7 is 7g cycle urban, 5g in the road cycle and 3g in the motorway cycle. The mass of nitrogen oxides (NOx) increased to trigger the purge of nitrogen oxides (NOx) in the catalytic converter 7 is 1.2g regardless of the cycle. Thus, when the estimated dilution is greater than the critical threshold (step 120), the average occurrence of nitrogen oxide purges in the catalytic converter 7 is then approximately every 10 km and the average occurrence of the purges of the sulfur oxides in the catalytic converter 7 is approximately every 4500 km. In this way, the dilution cost due to the catalytic converter 7 is reduced at the expense of emissions of nitrogen oxides at the exhaust while complying with the European regulations in force. When the estimated dilution exceeds the critical threshold, it is clear that only sulfur dioxide (SOx) purges that are not diluting, ie purges of sulfur oxides (SOx) triggered by cycle, are allowed with a mass of sulfur oxides increased compared to the standard mass to trigger the purges, and secondly that the frequencies of the purges of oxides of nitrogen (NOx) are adapted by increasing the threshold triggering to reduce dilution while controlling emissions on the NDEC cycle. In addition, when the mass of sulfur oxides (SOx) increases progressively, sulfur diluent purge (SOx) purges are allowed. It goes without saying that the purge of the catalytic converter (7) is obtained, as is well known to those skilled in the art, by increasing the temperature in said catalytic converter (7) to a temperature of approximately 650 ° C. and by operation in rich mode or by any other equivalent means. It will be observed that the exhaust line described above comprises only a single catalytic converter; However, it goes without saying that the exhaust line may include several catalytic converters such as a Noxtrap and a Soxtrap and possibly a particle filter without departing from the scope of the invention. Finally, it is obvious that the examples that have just been given are only particular illustrations in no way limiting as to the fields of application of the invention.

Claims (12)

1 - Method for managing the operation of at least one catalytic converter (7) fitted to an exhaust line (3) of an internal combustion engine (1), said catalytic converter (7) being purged according to determined criteria such as when a threshold value is reached for example, characterized in that it comprises at least the following stages of: - estimation of the dilution during rolling, - comparison of the estimated dilution with a determined critical threshold, - modification of the sulfur and nitrogen oxide purges of the catalytic converter (7) occur when the estimated dilution is above the determined critical threshold. 2 - Process according to claim 1 characterized in that the occurrence of purges of sulfur oxides of the catalytic converter (7) is modified by modifying the trigger threshold mass of purge sulfur oxides of said catalytic converter (7). 3 - Process according to any one of claims 1 or 2 characterized in that the occurrence of purges of nitrogen oxides of the catalytic converter (7) is modified by changing the trigger threshold mass of the purge of oxides of nitrogen of said catalytic converter (7). 4 - Process according to any one of claims 1 to 3 characterized in that the critical threshold is determined according to the driving conditions. 5 - Process according to claim 4 characterized in that a critical threshold is determined for driving in urban cycle and / or road cycle and / or highway cycle taken separately or in combination. 6 - Process according to any one of claims 1 to 5 characterized in that the purge of the catalytic converter (7) is obtained by increasing the temperature in said catalytic converter (7) to a temperature of about 650 ° C and by operating in rich mode. 7 - System for managing the operation of at least one catalytic converter (7) fitted to an exhaust line (3) of an internal combustion engine 2920824 i0 (1), said catalytic converter (7) being purged according to criteria determined and being controlled by an electronic control unit (11) which comprises management means for controlling purges of sulfur oxides and nitrogen, characterized in that said management means are arranged to estimate the dilution during the rolling, then compare the estimated dilution with a determined critical threshold and change the occurrence of purges sulfur oxides and nitrogen of the catalytic converter (7) when the estimated dilution is greater than the determined critical threshold. 8 - System according to claim 7, characterized in that the management means are arranged to modify the occurrence of the sulfur oxide purges of the catalytic converter (7) by modifying the trigger threshold mass of the purge of sulfur oxides. said catalytic converter (7). 9 - System according to any one of claims 7 or 8 characterized in that the management means are arranged to change the occurrence of nitrogen oxide purges 15 of the catalytic converter (7) by modifying the trigger threshold mass purging nitrogen oxides of said catalytic converter (7). 10 - System according to any one of claims 7 to 9 characterized in that the management means are arranged to determine the critical threshold as a function of driving conditions. 20 11 - System according to claim 10 characterized in that a critical threshold is determined for driving in urban cycle and / or road cycle and / or highway cycle taken separately or in combination. 12 - System according to any one of claims 7 to 11 characterized in that the exhaust line (3) comprises a particle filter.