FR2917457A1 - SYSTEM AND METHOD FOR REGENERATING DEPOLLUTION MEANS OF A MOTOR VEHICLE. - Google Patents

Abstract

The present invention relates to a regeneration system of means (12) for filter media decontamination arranged in an exhaust line (14) of a motor vehicle, said system (10) comprising means (18, 20, 22, 24) of generating an exotherm at the inlet of the depollution means (12) for raising the internal temperature thereof.According to the invention, the means (18, 20, 22, 24) for generating the exotherm are capable of generating the latter according to a temperature profile comprising a first phase of rapidly increasing the temperature at the inlet of the means (12) of depollution to a first predetermined temperature followed by a second phase of slow increase of the inlet temperature means (12) of depollution to a second predetermined temperature.

Description

-1- SYSTEM AND METHOD FOR REGENERATING DEPOLLUTION MEANS

  The present invention relates to a system and a method for regenerating filter media depollution means arranged in a motor vehicle exhaust line. More particularly, the present invention relates to the regeneration of the depollution means by generating an exotherm at the inlet thereof to raise their internal temperature. A particulate filter, or FAP, arranged in an exhaust line of a motor vehicle engine needs to be regularly regenerated to burn the soot it contains. Conventionally, there is provided upstream thereof an oxidation catalyst coupled to means for post-injection of fuel into the engine cylinders, the post-injection having the effect of increasing the amount of unburned hydrocarbons present in the exhaust. These unburned hydrocarbons, or HC, which are reducing agents of an oxidation reaction carried out by the catalyst, are thus catalyzed by the latter, thereby producing an exotherm at the outlet of the latter.

  The quantity of HC introduced into the exhaust gas is controlled so that the exotherm produced by the catalyst has the effect of increasing the internal temperature of the FAP to a predefined soot combustion temperature of the order of 600 to 700 C. However, if the conditions of the regeneration of the FAP are poorly controlled, and particularly the conditions of elevation of the internal temperature of the FAP, a runaway of the soot combustion reaction can then occur. This leads to a thermal shock and thus to irreversible damage to the filter media of the FAP (melting of the material, cracking, etc.), a phenomenon which is all the more noticeable if this filtering medium comprises cordierite.

  To limit the risks of runaway of a soot combustion reaction in a FAP, a strategy generally implemented is to control the production of the exotherm so that the input temperature of the FAP does not exceed a target temperature whose value depends on the mass of soot present in it. Thus, for a predefined target temperature, the regeneration of the FAP will have to be carried out before the mass of stored soot -2- reaches a limit value better known under the name of SML (acronym for Soot Mass Limit). The problem with this type of strategy is that the mass of soot that can be stored by the FAP without risk of runaway is reduced. A frequent regeneration of the FAP is then necessary, thus leading to an overconsumption of fuel and accelerated aging thereof. The object of the present invention is to propose a system and a method for regeneration of filter media depollution means which limit the risk of a regeneration reaction of these being rushed, thus allowing an increase in the mass of pollutants that can be stored in them. For this purpose, the subject of the invention is a system for regenerating filter media depollution means arranged in a motor vehicle exhaust line, said system comprising means for generating an exotherm at the inlet of the depollution means for to raise the internal temperature thereof, characterized in that the means for generating the exotherm are able to generate it according to a temperature profile comprising a first phase of rapidly increasing the temperature at the inlet of the depollution means to a first predetermined temperature followed by a second phase of slow increase of the inlet temperature of the pollution control means to a second predetermined temperature.

  Indeed, the inventors have found that the slow increase in temperature to reach the target temperature has the effect of significantly limiting the risk of runaway regeneration reactions. According to particular embodiments of the invention, the system comprises one or more of the following characteristics: the means for generating the exotherm comprise gear oxidation means arranged upstream of the depollution means and means injecting into the exhaust gases of reducing agents upstream of the oxidation means; the means for generating exotherm include means for measuring the temperature at the inlet of the pollution control means and means for regulating the temperature at the inlet on the temperature profile by controlling the quantity of reducers injected upstream of the means of generation of the exotherm; the gearbox injection means comprise means for injecting fuel into the engine cylinder of the vehicle according to at least one main injection and a fuel injection post-injection; The first temperature corresponds to a reduced risk of runaway of a regeneration reaction of the depollution means; the second temperature corresponds to a regeneration temperature of the depollution means.

  The subject of the invention is also a method for regenerating filter media depollution means arranged in a motor vehicle exhaust line, said method comprising a step of generating an exotherm at the inlet of the depollution means for raising the temperature. internal of these, characterized in that the exotherm generation step comprises a first step of rapidly increasing the inlet temperature of the pollution control means to a first predetermined temperature followed by a second step of slow increase of the inlet temperature of the pollution control means to a second predetermined temperature.

  The subject of the invention is also a motor vehicle line comprising filter media depollution means and a regeneration system of the aforementioned type. According to the invention, the depollution means comprise a particulate filter.

  The present invention will be better understood on reading the following description, given solely by way of example, and with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of an exhaust line; a motor vehicle engine provided with a FAP and a regeneration system according to the invention; FIG. 2 is a flowchart of a regeneration method implemented by the system of FIG. 1; FIG. 3 is a graph of input temperature time profiles of the FAP according to the state of the art and according to the invention; FIG. 4 is a graph of internal temperature time profiles of the FAP according to the state of the art and according to the invention at different positions in the FAP; and FIG. 5 is a graph of temporal profiles of a thermal gradient reached in the FAP according to the state of the art and according to the invention. In FIG. 1, a regeneration system 10 of a FAP 12, arranged in an exhaust line 14 of a diesel engine 16 of a motor vehicle equipped with means 18 for injecting fuel into the cylinders of the engine. with common feed ramp, comprises an oxidation catalyst 20 arranged in the exhaust line 14 upstream of the FAP 12 and capable of producing an exotherm output by reduction of unburned hydrocarbons present in the exhaust gases, means 22 for driving the injection means 18 for the latter to deliver a fuel post-injection into the cylinders of the engine 16 and a temperature sensor 24 arranged in the exhaust line 14 at the inlet of the FAP 12 and connected to the 22 piloting means.

  The regeneration system 10 implements a regeneration method of the FAP 12 illustrated in FIG. 2. In a first step 30, the regeneration of the FAP 12 is triggered. In a next step 32, the control means 22 then control the injection means 18 so that they inject into the cylinders of the engine 16 a post-injection according to a first predetermined strategy of post-injection. This first strategy is determined so that the amount of HC introduced into the exhaust line 14 causes the catalyst 20 to produce FAP 12 input a rapid increase in temperature, about 5 degrees Celsius per second. In a step 34, a test is carried out by the control means 22 to know if the temperature measured at the input of the FAP 12 by the sensor 24 is substantially equal to a predetermined first temperature Trisque. The Trisque temperature is a temperature below which there is substantially no risk of runaway of the FAP regeneration reaction. If the result of the test implemented at 34 is negative, step 34 loops back to step 32 and the first post-injection strategy continues. According to one embodiment, the control means 22 implement a regulation of the increase of the temperature measured by the sensor 24 on a predetermined reference value AT1 C / min, for example by means of a control law of the integral proportional type, or PI law. The temperature increase is thus precisely controlled and the risks of runaway reduced to a greater extent. If the result of this test is positive, the control means 22 then control at 36 the post-injection of fuel according to a second predetermined strategy of post-injection. This second strategy is determined so that the amount of HC introduced into the exhaust line 14 causes the catalyst 20 to produce at the input of the FAP 12 a slow increase in temperature, of about 1 degree Celsius per second. A test is then implemented at 38 by the control means 22 to know if the temperature measured at the input of the FAP 12 by the sensor 24 is substantially equal to a second predetermined target temperature T. The second temperature Tcible is the temperature to be reached for the combustion of the soot stored in FAP 12 to take place. If the result of this test is negative, step 38 loops back to step 36 and the second post-injection strategy continues. According to one embodiment of the invention, the control means 22 implement a regulation, for example PI, of the increase of the temperature measured by the sensor 22 to a predetermined reference value AT2 C / min. The increase in temperature is thus precisely controlled and the risks of runaway reduced in an increased manner. If the result of this test is positive, that is to say if the inlet temperature of the FAP 12 has reached the second temperature Tcible, the control means 22 then controls the means for these to inject into the cylinders of the engine a post-injection according to a third predetermined strategy of post-injection for example to maintain the inlet temperature of the FAP substantially close to the Tcible temperature to complete the regeneration thereof.

  A test is then implemented at 42 by the control means 22 to know if the regeneration of the FAP 12 is complete. If this is not the case, step 42 loops to step 40 for further regeneration. Otherwise, the regeneration ends and the control means 22 control the injection means 18 to stop the post-injection. In FIG. 3, curves of the input temperature of the FAP 12 as a function of time illustrate the temperature increases at the input of the FAP 12 according to the state of the art and according to the invention. A first dashed line curve corresponds to the state of the art in which the rise in the input temperature of the FAP 12 is performed in a single phase to reach the Tcible temperature.

  A second continuous line curve corresponds to a rise in temperature according to the invention. As can be seen, the rise in temperature is carried out in two phases. The first phase consists of a rapid increase in temperature up to the Trisque temperature, for example at the same rate as that of the state of the art. The second phase, triggered once the temperature has been reached, consists of a slower increase in the input temperature of the FAP 12 than that of the state of the art up to the target temperature. Figures 4 and 5 illustrate the effects on the internal temperature of the FAP of the implementation of such a strategy.

  In FIG. 4, a first and a second dotted line curve illustrate the temporal evolution of the temperature in two different internal positions P1 and P2 of the FAP, by applying the prior art elevation strategy illustrated in FIG. FIG. 3. Likewise, a third and a fourth continuous line curve illustrate the temporal evolution of the temperature at the same positions P1 and P2 respectively by applying the elevation strategy according to the invention illustrated in FIG. As can be seen from the application of the strategy according to the invention, the maximum temperatures reached in these two positions are respectively 200 C and 300 C below those found in the state of the art, thus limiting sensitive way the thermal shock suffered by FAP 12.

  In FIG. 5, the time evolution curves of the thermal gradient reached in FAP 12, that is to say the temperature difference between the two positions P1 and P2 of FAP 12, are illustrated. The curve in dashed line corresponds to the application of the strategy of the state of the art and the continuous line curve corresponds to the application of the strategy of the invention, illustrated in FIG.

  As it is also possible to note, the maximum gradient obtained by the invention is lower than that obtained by the state of the art of nearly 230 C / cm. The thermal shock is therefore lower by application of the strategy according to the invention. In addition, temperatures within FAP 12 are more homogeneous, thereby increasing the efficiency of regeneration in FAP.

  As previously stated, the typically selected temperature is determined according to a predetermined mass of stored soot to prevent runaway. As can be seen, the invention makes it possible to obtain temperatures and maximum gradients in FAP 12 that are substantially lower than those found in the state of the art. It is therefore possible, for the same target temperature, to increase the mass of soot stored in the FAP until the temperature and gradient levels of the state of the art and without risking runaway. It is also possible to keep the same mass values as those foreseen in the state of the art in order to increase the life of the FAP which is subjected to lower thermal stresses with the application of the strategy according to the invention. 'invention. The invention therefore makes it possible to manage the regeneration of the FAP much more flexibly. Although a regeneration system of a particulate filter has been described, it will be understood that such a system also applies to any type of filter media depollution means such as a NOx trap for example. Indeed, a NOx trap also requires a regeneration requiring an increase in the inlet temperature thereof, for example during a desulfation phase, and is subject to the same risk of runaway if this temperature is not controlled adequately. Similarly, although it has been described a regeneration system using a post-fuel injection, it will be understood that other types of injections can be used, such as for example a phase out of the main injection of fuel for qu a part of it takes place after the top dead center of the cylinder cycle, or a fuel injection not performed by the engine but by a dedicated injection system such as an injector or an additional vaporizer in the line d 'exhaust.

Claims (9)

  1. Regeneration system means (12) filter media pollution control arranged in an exhaust line (14) of a motor vehicle, said system (10) comprising means (18, 20, 22, 24) for generating an exotherm at the inlet of the depollution means (12) for raising the internal temperature thereof, characterized in that the means (18, 20, 22, 24) for generating the exotherm are capable of generating the latter according to a temperature profile comprising a first phase of rapidly increasing the temperature at the inlet of the pollution control means (12) to a first predetermined temperature followed by a second phase of slow increase of the inlet temperature of the means (12). ) depollution to a second predetermined temperature.   2. System according to claim 1, characterized in that the means (18, 20, 22, 24) for generating the exotherm comprises means (20) for reducing oxidation, arranged upstream of the means (12) of depollution, and injection means (18) in the exhaust gas of reducing agents upstream of the means (18) of oxidation.   3. System according to claim 2, characterized in that the means (18, 20, 22, 24) for generating exotherm comprises means (24) for measuring the temperature at the inlet of the means (12) of depollution and means (22) for regulating the inlet temperature on the temperature profile by controlling the quantity of reducers injected upstream of the means for generating the exotherm.   4. System according to claim 2 or 3, characterized in that the means (18) for injecting reducers comprise means for injecting fuel into the engine cylinder of the vehicle according to at least one main injection and a post-injection fuel.   5. System according to any one of the preceding claims, characterized in that the first temperature corresponds to a reduced risk of runaway of a regeneration reaction of the depollution means.   6. System according to any one of the preceding claims, characterized in that the second temperature corresponds to a regeneration temperature of the pollution control means.   7. A method of regeneration means (12) for pollution control filter media arranged in a motor vehicle exhaust line, said method comprising a step (32,36) for generating an exotherm at the input of the means (12) of depollution for raising the internal temperature thereof, characterized in that the step (32, 36) for generating the exotherm comprises a first step (32) for rapidly increasing the temperature at the inlet of the depollution means up to at a first predetermined temperature followed by a second step (36) of slowly increasing the inlet temperature of the depollution means to a second predetermined temperature.   Exhaust line (14) of a motor vehicle comprising means (12) for decontamination with a filter medium and a regeneration system thereof according to any one of claims 1 to 6.   9. Exhaust line according to claim 8, characterized in that the pollution control means comprise a particulate filter.