FR2963641A1 - METHOD AND DEVICE FOR REGENERATING A PARTICLE FILTER - Google Patents

Abstract

A method and apparatus for specifically launching the regeneration of a particulate filter (15) in the exhaust gas line (12) of an internal combustion engine (10) having a downstream catalyst (17, 18) particulate filter (15). Regeneration of the particulate filter (15) is by oxidation combustion of the particles during the regeneration phase. For a combustion engine (10), hot, but not yet at a temperature sufficient for the regeneration of the particulate filter (15), periodically intervenes to increase the temperature of the exhaust gas upstream of the filter to particles (15) or in it.

Description

FIELD OF THE INVENTION The present invention relates to a method for specifically launching the regeneration of a particulate filter installed in the exhaust gas duct of an internal combustion engine having a catalyst downstream of the filter. particulate filter according to the direction of passage of the exhaust gas, wherein the regeneration of the particulate filter is by oxidation combustion of the particles during the regeneration phase. The invention also relates to a device for specifically launching, monitoring and regulating the regeneration of a particulate filter installed in the exhaust gas duct of an internal combustion engine, having a catalyst downstream of the filter particles according to the direction of passage of the exhaust gas, - the regeneration of the particulate filter being carried out by the oxidative combustion of the particles during a regeneration phase, and - the launching, the control and the monitoring of the regeneration of the particulate filter, by means of a control unit, by using the signals of a first Lambda probe installed upstream of the particle filter in the direction of passage of the exhaust gases, signals of a second Lambda probe installed downstream of the particulate filter or behind the catalyst in the direction of passage of the exhaust gas and / or the signals of at least one temperature sensor. State of the art In order to reduce particle emissions from diesel engines and, in the future, even more significantly from gasoline engines (limit value set according to the EU6 standard from 2014), particle filters are used in the exhaust gas ducting of internal combustion engines. The exhaust gases pass through the particulate filter and the solid particles that charge the exhaust gas, settle and remain in the filter. The masses of particles or black smoke thus accumulated in the filter, gradually cause clogging of the particulate filter, which results in an increase of the opposing pressure opposite the exhaust gas with an effect

2 negative on engine efficiency and fuel consumption. For this reason, it is necessary from time to time to eliminate the mass of black smoke thus stored. This regeneration of the filter takes place during particular regeneration phases by an oxidation combustion of the particles in the form of an autonomous exothermic reaction insofar as the temperature of the exhaust gas is at least 580 ° C and with a sufficient concentration of oxygen in the exhaust gas. By the composition of the exhaust gases and their temperature, the progress of the regeneration is controlled.

In addition to the particulate filter, aftertreatment of exhaust gases by internal combustion engines requires other components. Thus, in the case of petrol engines operating in homogeneous mode, pollutants such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO.) Are converted by a catalytic converter. three way. In the case of lean combustion, there is generally a downstream nitrogen oxide storage catalyst. The regulation of the Lambda coefficient makes it possible to achieve the lowest emissions of pollutants. By this Lambda control of combustion, the fuel-air mixture feeding the internal combustion engine is regulated as a function of the oxygen concentration in the exhaust gas. The oxygen content of the exhaust gas is described by the value of the Lambda coefficient. For stoichiometric combustion, the Lambda coefficient has a value of 1; in the case of an excess of oxygen, the Lambda coefficient has a value> 1 and in the case of a lack of oxygen, the Lambda coefficient has a value <1. The Lambda coefficient is measured with the aid of Lambda sensors installed in the exhaust pipe. In general, regeneration of the particulate filter is as indicated above, when exceeding the limit value of the counterpressure opposing the exhaust gas. This situation can be detected using an appropriate model and compensating for a difference in pressure. The oxidation of the black smoke and thus the regeneration of the filter are mainly influenced by the temperature of the exhaust gases and the residual oxygen content.

3 exhaust gases. Since the combustion of the particles requires an excess of oxygen in the exhaust gas, it is not possible to freely choose the composition of the mixture supplying the internal combustion engine for this phase, in accordance with the otherwise requirements of the driving mode. Therefore, it is desirable to determine the end of the regeneration to switch back to a normal operating mode. DE 10 2009 028237.8 discloses a method for monitoring and regulating the regeneration of a particulate filter installed in the exhaust gas duct of an internal combustion engine. According to this method, the regeneration of the particulate filter is done by oxidative combustion of the particles during a regeneration phase. It is intended to operate the internal combustion engine at least during the regeneration phase of the particulate filter in lean mode or by oscillating the mixture around a lean operating point. Regeneration of the particle filter is monitored according to the chronological evolution of a second signal of a second Lambda probe installed downstream of the particulate filter in the direction of passage of the exhaust gas or a second characteristic quantity which is deduced from this, by comparison with the chronological evolution of a first signal provided by a first Lambda probe installed upstream of the particle filter in the direction of passage of the exhaust gases or from a first characteristic quantity which in is deduced, we monitor the operating phases in lean mode or during the oscillation of the mixture. The disadvantage of this solution is that the regeneration takes place during a lean phase during which the other pollutant components of the gases can not be eliminated optimally.

In addition, since it is not certain that the engine is regularly in an operating state in which the regeneration of the particulate filter can take place automatically, it must also be possible to force the regeneration.

OBJECT OF THE INVENTION The object of the present invention is therefore to develop a method for forcing regeneration and allowing regulation and reliable monitoring of the regeneration of the particulate filter. The invention also aims to develop a device for implementing such a method. DESCRIPTION AND ADVANTAGES OF THE INVENTION For this purpose, the present invention relates to a process of the type defined above, characterized in that for a combustion engine, hot, but which is not yet at a temperature sufficient to the regeneration of the particulate filter is periodically intervened to increase the temperature of the exhaust gas upstream of the particulate filter or in it. The invention also relates to a device of the type defined above, characterized in that by means of a routine implemented in the control unit, it performs limited interventions to increase the temperature in a targeted manner. upstream of the particulate filter or in it. For the regeneration of a particulate filter, the temperature of the exhaust gas must be in a range that allows regeneration and the regeneration is carried out automatically while respecting the conversion of the other polluting components, since the exhaust gases uncleaned, always contain some residual oxygen (between 0.5 and 0.7%). In addition, under the appropriate conditions, it is also possible to have a regeneration by a heterogeneous equilibrium reaction of the hydrogen defined below:

C + H2O <-4 CO + H2 It is used for this fact that in case of lack of oxygen, the kinetics of the regeneration reaction of the particulate filter changes. For this, no additional oxygen is needed in the exhaust. Water is always present in the exhaust gases from combustion. But this reaction is only at high temperatures, that is to say higher than 800 ° C. The need to regenerate the particulate filter can be deduced from an appropriate model or given by corresponding sensors such as a pressure difference measurement; to start the regeneration, it is first necessary to check the other environmental conditions, such as for example the exhaust gas temperature and the current operating mode. The method and the device according to the invention make it possible to regenerate the particle filter even in operating states of the internal combustion engine in which the surrounding conditions are not optimal conditions for the regeneration. This is for example the internal combustion engine that has operated for a long time under partial load or low load as is often the case for urban traffic. In addition, during this phase, it is necessary to ensure a sufficient conversion of all other pollutant components of the exhaust gas, which must also be achieved by the process. One possibility is to damage the output in a targeted manner with the aim of increasing the temperature of the exhaust gas. Strategies that are usually used to heat the catalyst when the engine is still cold can be applied for this purpose. A preferred variant of the process is characterized in that to target the regeneration of the particulate filter in a targeted manner, the ignition angle must be offset in the direction of an ignition delay and thus shift the exothermic reaction of more and more in the exhaust manifold, which results in an increase in the temperature of the exhaust gas and allows as described above, to automatically start the regeneration of the particulate filter. To compensate for the deterioration of the yield and the resulting loss of torque, it is expected that during the shift of the ignition angle, the internal combustion engine is throttled. As furthermore, the regulation is effected according to the stoichiometric air ratio, this strategy is neutral with regard to the exhaust gases, that is to say that a sufficient conversion of all the components is ensured. exhaust pollutants. This deterioration in output

6 at the cost of some additional consumption during the regeneration phase. Besides the simple offset in the direction of the delay, it is also possible to use another variant of the method in addition to the offset in the direction of the delay of the ignition angle, namely the divided homogeneous mode (HSP mode). This mode of operation is used for example to raise the temperature of the catalyst after the startup phase, that is to say when the engine is still cold, as quickly as possible to its operating temperature. For this purpose, a second injection is used during the compression phase, which acts in the stabilization direction to retard the ignition in an extreme manner, and for a large part of the combustion energy to be used to increase the enthalpy of the heat. exhaust gas ; in the application of the process according to the invention, the particle filter is thus heated very rapidly (in less than a few seconds) to the operating temperature necessary for the regeneration. This second injection and if necessary other injections, give a great ignition security. In addition, having a rich mixture near the spark plug increases the stability of the combustion.

Another possibility for initiating the regeneration in an active manner is to increase the exothermic reaction in the three-way catalyst. For this, it is planned to regulate the operating mode to go from a Lambda value equal to 1, for a limited period to Lambda value> 1 (lean mode) and thus fill the oxygen accumulator of the catalyst and then, once the oxygen accumulator is filled, it is previously ordered on a Lambda value <1; the oxygen storage tank of the catalyst will be emptied. The process, which is thus generally highly exothermic, results in heating of the exhaust gas system and since the Lambda-sum coefficient is equal to 1, the process is practically neutral for the components of the exhaust gases. This alternation of the Lambda coefficient control mode can be done in a particularly efficient manner, by this mode of operation which, until then, was used to heat the

7 catalyst or to remove the sulfur of an NOS nitrogen oxide storage catalyst, if the particulate filter is made as a combination of a particulate filter and a catalyst with a catalytic coating. This measurement allows a particularly efficient heating of the particulate filter. For all active measurements, the regeneration must be monitored. Therefore, it is planned to use the temperature of the particulate filter; as a control variable for initiating the regeneration and for monitoring the regeneration, this temperature is measured by means of at least one temperature sensor installed in or on the particulate filter and which directly gives the temperature or is derived from signals supplied by Lambda probes installed in the exhaust gas line upstream or downstream of the particulate filter and the catalyst, these probes serving for the regulation of the Lambda coefficient; it is also possible to deduce the temperature in a modeled way from a model of temperature of the exhaust gases. This allows to influence in a targeted way the intensity and the duration of the heating phase. A variant of the device thus provides for implementing an exhaust gas temperature model in the control unit and the regulation quantity used for the regeneration of the particulate filter, is a modelized temperature of the particulate filter deduced from this model. . This ensures continuous monitoring. A preferred application of the method described in these variants consists in using, for regeneration, a particulate filter close to the engine in the exhaust gas duct of an internal combustion engine which is a gasoline engine with injection into the tubing intake or direct injection. It is advantageous under these conditions to use existing Lambda probes or existing sensor concepts, since the gasoline engine exhaust pipe is already equipped with Lambda probes for regulating the Lambda coefficient, so that signals from these probes, can be used to initiate, control and regulate the regeneration of the particulate filter, so that the process will apply in a

8 particularly economical in the case of future gasoline engines equipped with particulate filters. Drawings The present invention will be described in more detail below with the aid of an exemplary method of starting the regeneration of a particulate filter and a device for carrying out this process shown in FIGS. attached drawings in which: - Figure 1 shows an internal combustion engine whose exhaust gas pipe is equipped with a particulate filter and also a downstream precatalyst and a main catalyst or a Catalyst LNT / SCR, and - Figure 2 shows the internal combustion engine equipped with a catalyst / combined particulate filter and downstream main catalyst or a catalyst LNT / SCR. DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION FIG. 1 shows an internal combustion engine 10 equipped with an air supply 11 and a particulate filter 15 installed in the exhaust pipe 12 as well as a pre-catalyst 17 downstream and a main catalyst 18 in the form of a three-way catalyst. The exhaust gases of the internal combustion engine 10, cleaned in the particulate filter 15 and in the catalysts 17, 18, are supplied to the exhaust 20 of the exhaust system. The Lambda coefficient of the exhaust gas in the exhaust gas duct 12 directly downstream of the internal combustion engine 10 is determined by means of a first Lambda probe 13. In addition, this zone the temperature of the exhaust gas using a temperature sensor 14. During the operation of the internal combustion engine 10, particles accumulate in the particulate filter 15. This deposit increases the counterpressure that opposes exhaust gas. Therefore, if necessary, remove the particulate filter 15 by burning the particles and thus regenerating the filter. Regeneration may occur if the temperature of the exhaust gas exceeds about 580 ° C; this can be seen using the temperature sensor 14. In addition, it is necessary to

9 have enough oxygen for combustion. This is observed using the first Lambda probe 13. Downstream of the particulate filter 15 and the precatalyst 17, the exhaust gas channel 12 comprises a second Lambda 16 probe. For the regulation of the Lambda coefficient downstream of the catalyst, the probe can only be installed downstream of the main catalyst 18. From the difference between the output signals of the first Lambda probe 13 and those of the second Lambda probe 16, it is determined to what extent the combustion of particles in the particulate filter 15 consumes oxygen. If there is no difference between the signals, it means that the combustion is complete. The signals of the first Lambda probe 13 and those of the second Lambda probe 16 as well as the output signal of the temperature sensor 14 are applied to a control unit 21.

Control unit 21 applies a program to compare signals and initiate, control and monitor regeneration. The signals of the first Lambda probe 13, those of the second Lambda probe 16 and / or the signals of the temperature sensor 14, are used as critical control variables; the program implemented in the control unit 21 will be able to perform time-limited measurements to specifically increase the temperature upstream of the particle filter 15 or therein. According to another exemplary embodiment, an exhaust gas temperature model is implemented in the control unit 21.

As regulating variable of the regeneration of the particulate filter 15, there is the modeled temperature of the particulate filter. The control unit 21 can be integrated in the control of the internal combustion engine 10 which usually implements the Lambda control.

This basic structure is presented for a variant of operation for which the regulation is done on a Lambda value equal to 1. For the lean mode of operation with a Lambda value such that> 1, one can alternatively provide a catalyst LNT / SCR 19 instead of the main catalyst 18.

The abbreviation LNT represents the terms "lean NO. Trap"; it is

10 nitrogen oxides traps NO. lean. This reference applies to a catalyst whose surface is impregnated with barium salts and platinum or other noble metals to adsorb nitrogen oxides. The expression SCR corresponds to the selective catalytic reduction and denotes a selective catalytic reduction of the nitrogen oxides contained in the exhaust gases. The chemical reaction carried out on the SCR catalyst is selective, since it preferably reduces the nitrogen oxides while avoiding undesirable side reactions, such as, for example, the oxidation of sulfur dioxide to sulfur trioxide. Nitrogen oxides, which are typically NO and NO2 oxides, can accumulate on the surface of the catalyst. When such a catalyst is periodically exposed to a rich fuel-air mixture, the nitrogen oxides will be converted to nitrogen, carbon dioxide and water.

FIG. 2 schematically shows a modification of the assembly of FIG. 1. Unlike FIG. 1, the particulate filter 15 and the precatalyst 17 are combined into a combined assembly uniting the particulate filter and the catalyst. The particulate filter may include a catalytic coating. In this case also, the regulation is made for an operating variant on a Lambda coefficient equal to 1 and a main catalyst 18 is used. For the lean mode of operation with a Lambda coefficient> 1, it will be possible, as shown in FIG. 1, replace the main catalyst 18 with a catalyst LNT / SCR 19. 30 NOMENCLATURE OF THE MAIN ELEMENTS

10 internal combustion engine 11 air supply 12 exhaust pipe 13 first Lambda probe 14 temperature sensor 15 particle filter 16 second Lambda probe 17 precatalyst 18 main catalyst / three-way catalyst 20 exhaust 21 control unit

Claims (1)

CLAIMS 1 °) A method for specifically launching the regeneration of a particulate filter (15) installed in the exhaust gas duct (12) of an internal combustion engine (10) having a catalyst (17, 18) downstream of the particulate filter (15) in the direction of passage of the exhaust gas, - the regeneration of the particulate filter (15) is carried out by oxidation combustion of the particles during the regeneration phase, characterized in that that for a combustion engine (10), hot, but not yet at a temperature sufficient for the regeneration of the particulate filter (15), periodically intervenes to increase the temperature of the exhaust gas upstream of the filter with particles (15) or in it. 2) Method according to claim 1, characterized in that to launch the regeneration of the particulate filter (15) in a targeted manner, the ignition angle is shifted in the direction of an ignition delay. 3) Method according to claims 1 or 2, characterized in that during the shift of the ignition angle, it throttles the internal combustion engine. 4) Method according to one of claims 1 to 3, characterized in that in addition to the setting in the direction of the delay of the ignition angle, the operating mode homogeneous / divided. 5 °) Method according to claim 1, characterized in that one passes from the Lambda coefficient control mode around a Lambda value equal to 1, limited to a Lambda value> 1 and thus charges an oxygen accumulator of the catalyst (17, 18), then 13 once the charged oxygen accumulator, a Lambda value <1. 6 °). The method according to claim 5, characterized in that the change of the Lambda control mode s is applied to a particulate filter (15) which is formed as a combination of a particulate filter and a catalyst and which has a catalytic coating. Method according to Claim 1, characterized in that the regulation quantity for initiating the regeneration and for monitoring the regeneration is the temperature of the particulate filter (15), this temperature being measured by means of minus a temperature sensor (14) installed in or on the particulate filter (15), which directly determines the temperature or is derived from Lambda sensor signals (13, 16) installed in the exhaust gas channel (12) upstream or downstream of the particulate filter (15) and the catalyst (17, 18) and used for Lambda control, or determined in a modeled manner from an exhaust gas temperature model. 8 °) Application of the method according to one of claims 1 to 7 to the regeneration of a particulate filter (15) installed in the exhaust pipe (12) of an internal combustion engine (10) under form of gasoline engine. 9 °) Apparatus for purposefully launching, monitoring and regulating the regeneration of a particulate filter (15) installed in the exhaust pipe (12) of an internal combustion engine (10) having a catalyst (17, 18) downstream of the particulate filter (15) in the direction of passage of the exhaust gas, 14 - the regeneration of the particulate filter (15) is carried out by the oxidative combustion of the particles during a regeneration phase, and - the launch, control and monitoring of the regeneration of the particulate filter (15), being performed by a control unit (21), using the signals of a first Lambda sensor (13) installed upstream of the particulate filter (15) in the direction of passage of the exhaust gas, signals of a second Lambda probe (16) installed downstream of the particulate filter (15) or behind the catalyst (17, 18) in the direction of passage of the exhaust gases and / or the signals of at least one sensor ur of temperature (14), characterized in that by means of a routine implemented in the control unit (21), it performs limited interventions to increase in a targeted manner the temperature upstream of the particulate filter (15) or in it. Device according to Claim 9, characterized in that an exhaust gas temperature model is implemented in the control unit (21) and the control quantity for the regeneration of the particulate filter (15) is a modeled temperature of the particulate filter (15) derived therefrom. A method for specifically initiating the regeneration of a particulate filter (15) installed in the exhaust gas line (12) of an internal combustion engine (10) having a catalyst (17). , 18) downstream of the particulate filter (15) in the direction of passage of the exhaust gas, - the regeneration of the particulate filter (15) by oxidation combustion of the particles during the regeneration phase, characterized in that for a combustion engine (10), hot, but not yet at a sufficient temperature for the regeneration of the particulate filter (15), periodically intervening to increase the temperature of the exhaust gas upstream of the particulate filter (15) or in it. 2) Method according to claim 1, characterized in that to launch the regeneration of the particulate filter (15) in a targeted manner, the ignition angle is shifted in the direction of an ignition delay. 3) Method according to claims 1 or 2, characterized in that during the shift of the ignition angle, it throttles the internal combustion engine. 4) Method according to one of claims 1 to 3, characterized in that in addition to the setting in the direction of the delay of the ignition angle, the operating mode homogeneous / divided. 5 °) Method according to claim 1, characterized in that one passes from the Lambda coefficient control mode around a Lambda value equal to 1, limited to a Lambda value> 1 and thus charges an oxygen accumulator of the catalyst (17, 18), then 13 once the charged oxygen accumulator, a Lambda value <1. 6 °). The method according to claim 5, characterized in that the change of the Lambda control mode s is applied to a particulate filter (15) which is formed as a combination of a particulate filter and a catalyst and which has a catalytic coating. Method according to Claim 1, characterized in that the regulation quantity for initiating the regeneration and for monitoring the regeneration is the temperature of the particulate filter (15), this temperature being measured by means of minus a temperature sensor (14) installed in or on the particulate filter (15), which directly determines the temperature or is derived from Lambda sensor signals (13, 16) installed in the exhaust gas channel (12) upstream or downstream of the particulate filter (15) and the catalyst (17, 18) and used for Lambda control, or determined in a modeled manner from an exhaust gas temperature model. 8 °) Application of the method according to one of claims 1 to 7 to the regeneration of a particulate filter (15) installed in the exhaust pipe (12) of an internal combustion engine (10) under form of gasoline engine. 9 °) Apparatus for purposefully launching, monitoring and regulating the regeneration of a particulate filter (15) installed in the exhaust pipe (12) of an internal combustion engine (10) having a catalyst (17, 18) downstream of the particulate filter (15) in the direction of passage of the exhaust gas, 14 - the regeneration of the particulate filter (15) is carried out by the oxidative combustion of the particles during a regeneration phase, and - the launch, control and monitoring of the regeneration of the particulate filter (15), being performed by a control unit (21), using the signals of a first Lambda sensor (13) installed upstream of the particulate filter (15) in the direction of passage of the exhaust gas, signals of a second Lambda probe (16) installed downstream of the particulate filter (15) or behind the catalyst (17, 18) in the direction of passage of the exhaust gases and / or the signals of at least one sensor ur of temperature (14), characterized in that by means of a routine implemented in the control unit (21), it performs limited interventions to increase in a targeted manner the temperature upstream of the particulate filter (15) or in it. Device according to Claim 9, characterized in that an exhaust gas temperature model is implemented in the control unit (21) and the control quantity for the regeneration of the particulate filter (15) is a modeled temperature of the particulate filter (15) derived therefrom. 30