FR3069886B1 - METHOD FOR DIAGNOSING THE FAILURE OF A PARTICLE FILTER AND EXHAUST GAS POST-PROCESSING SYSTEM - Google Patents

Abstract

The method is implemented in an aftertreatment system (1) of the exhaust gas (EG) of a heat engine, the exhaust gas aftertreatment system comprising a particulate filter (31) and a catalyst (4) disposed downstream of the particulate filter in a gas exhaust line (LE). According to the invention, the diagnosis of the particle filter failure is made from a measurement of a differential pressure (dP) between an inlet and an outlet of the catalyst.

Description

METHOD FOR DIAGNOSING THE FAILURE OF AN APARTICLE FILTER AND EXHAUST GAS POST-TREATMENT SYSTEM

[001] The invention generally relates to the depollution of the exhaust gas emitted by the engine of a vehicle. More particularly, the invention relates to a method for diagnosing the failure of a particulate filter. The invention also relates to an exhaust gas aftertreatment system including a particulate filter, in which the above-mentioned method is implemented.

[002] In motor vehicles, exhaust gas after-treatment systems have become indispensable today for compliance with environmental standards. Regulated pollutant emissions include carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx) and soot particles.

[003] For the removal of soot particles in the exhaust gas, it is well known to equip exhaust aftertreatment systems with a particulate filter. Particle filters are very present in vehicles with a Diesel engine type and are also widespread in engine type engines, especially with the entry into force of the European environmental standard "Euro 6.3".

[004] The particulate filter is effective to reduce particulate pollution.However, the progressive accumulation of soot particles retained in the porous layers of the filter causes a pressure drop in the gas exhaust line thermal engine. Periodic regeneration at high temperatures is required to burn off the accumulated soot particles. During the life of the vehicle, particle filter failures may occur with respect to particle emission, for example, following a particularly severe regeneration phase resulting in filter cracking, tampering or other causes. Filter deficiency results in particulate emissions that exceed the maximum threshold set by the regulations.

[005] In accordance with the regulations, the "particle filter failure" event must be detected by the on-board diagnostic system, known as OBD for "OnBoard Diagnostics" in English. This event must also be reported to the vehicle user by activating a light on the dashboard, such as the MIL light for Malfunction Indicator Lamp, to inform him that a vehicle repair is required. necessary.

[006] In the state of the art, it is known to evaluate the loss of filtration efficiency from a measurement of the differential pressure, called backpressure, between the inlet and the outlet of the particulate filter. This method of evaluating the efficiency of the particulate filter is sufficient to control its regeneration phases, but could be further improved. The addition of a soot sensor to measure the amount of soot in the filter would improve the accuracy of the evaluation of its efficiency, but such a sensor has implementation difficulties and leads to a significant increase in cost .

[007] Patent documents KR20070062309 and FR2950108 disclose particulate filter diagnostic devices employing a detection filter implanted downstream of the particulate filter in the exhaust gas line of a heat engine. Differential pressure between the inlet and the outlet of the detection filter is measured to detect a particle filter failure from a level of fouling of the detection filter. In KR20070062309, the detection filter is a second particulate filter that is mounted in the gas exhaust line. In FR2950108, the detection filter is placed in a bypass line of the main exhaust pipe. These diagnostic devices have the disadvantage of requiring an additional particle filtering means which is dedicated to the diagnosis of particulate filter failure and impacts the cost.

[008] There is therefore a need for a reliable and accurate method of diagnosing the defectiveness of a particulate filter which does not have the abovementioned disadvantages of the prior art.

According to a first aspect, the invention relates to a method of diagnosing the defectiveness of a particulate filter in an exhaust gas after-treatment system of a heat engine, the gas post-treatment system. exhaust comprising a particulate filter and a catalyst disposed downstream of the particulate filter in a gas exhaust line. According to the invention, the diagnosis of the particle filter failure is made from a measurement of differential pressure between an inlet and an outlet of the catalyst.

According to a particular characteristic, the method is implemented by executing program code instructions in an electronic unit for controlling the exhaust gas aftertreatment system.

According to another aspect, the invention also relates to an exhaust gas aftertreatment system of a vehicle engine comprising a device for treating emissions of nitrogen oxides, an electronic control unit, a particulate filter and an ammonia conversion catalyst disposed downstream of the particulate filter in a gas exhaust line. In accordance with the invention, the system includes a differential pressure sensor device mounted between an inlet and outlet of the ammonia conversion catalyst, the differential pressure sensing device having the function of providing a measurement of the differential pressure between an inlet and an outlet of the ammonia conversion catalyst, the differential pressure measurement being intended for a fault diagnosis of the particulate filter.

According to a particular embodiment, the device for treating nitrogen oxide emissions comprises a catalyst of selective catalytic reduction type.

According to another particular embodiment, the selective catalytic reduction type catalyst and the particulate filter are included in one and the same compact device.

According to another particular embodiment, the device for treating nitrogen oxide emissions also comprises a passive accumulator of nitrogen oxides contained in an oxidation catalyst.

According to yet another particular embodiment, the nitrogen oxides emission treatment device comprises a nitrogen oxide trap.

The invention also relates to a vehicle equipped with the system briefly described above for a post-treatment of the exhaust gas emitted by the engine of the vehicle.

Other advantages and features of the present invention will appear more clearly on reading the detailed description below of several embodiments of the invention, with reference to the accompanying drawings, in which: Fig.1 is seen of a particular embodiment of an exhaust gas aftertreatment system embodying the method according to the invention; Figs.2A and 2B are curves showing negative and positive detections of particle filter failure, respectively, in the method according to the invention.

A particular embodiment 1 of an exhaust gas after-treatment system in which is implemented the method according to the invention for the diagnosis of the failure of the particulate filter is now described with reference to Figs. 1 and 2A, 2B.

The exhaust gas after-treatment system 1 described here is intended for the post-treatment of the exhaust gas EG of a diesel engine in a vehicle.

As shown in FIG. 1, the exhaust gas after-treatment system 1 essentially comprises a LE gas exhaust line and an electronic control unit 5. The gas exhaust line LE here comprises a oxidation catalyst 2, a compact device 3 for selective catalytic reduction and filtering of soot particles and an ammonia conversion catalyst 4.

The oxidation catalyst 2 is typically a type of oxidation catalyst DOC (for "Diesel Oxidation Catalyst" in English) incorporating here a passive accumulator NOx (not shown), said PNA for "Passive NOx Adsorber" in English .

[0022] The compact device 3 comprises a catalytic selective reduction (SCR) catalyst 30 and a particulate filter 31. The SCR catalyst 30 and the particulate filter31 are shown in Fig. 1 as two separate components. Note however that the compact device 3 may advantageously be of the type called "CompactLiquid System" and integrate the catalytic layer SCR, called "washcoat", in a formimpregnated in the particulate filter. The SCR catalyst destroys NOx by reacting it with ammonia (NH3) as a reducing agent. The NH 3 is contained in an aqueous solution of urea, such as AdBlue (registered trademark), introduced into the LE gas escape line by the injector 300. NOx sensors 20 and 301 are provided in the LE gas exhaust line. at the inlet of the catalyst 20 and at the outlet of the compact device 3, for controlling the catalyst SCR 30 and an EGR valve (not shown). The particulate filter 31 is conventionally equipped with a differential pressure sensor device (not shown) used in particular for controlling the regeneration phases of the filter 31.

In the gas exhaust line architecture of FIG. 1, the accumulator PNA contained in the oxidation catalyst 2 and the catalyst SCR 30 form a nitrogen oxidation treatment device.

The invention may also be implemented in an architecture of gas escape line not comprising SCR catalyst, but a NOx trap, called LNT for "Lean NOx Trap" in English, which is associated with a catalyst ASC disposed downstream of the particulate filter. In such a case, the gas exhaust line will not include a PNA accumulator and the nitrogen oxide treatment device will be formed only from the NOx trap.

The invention may also be implemented in a gas exhaust gas architecture comprising a SCR catalyst and a NOx trap which are associated with an ASC catalyst disposed downstream of the particulate filter. In such a case, the gas exhaust line will not comprise a PNA accumulator and the nitrogen oxide treatment device will be formed of the SCR catalyst and the NOx trap.

The ammonia conversion catalyst 4, said ASC for "Ammonia SlipConverter" in English, has the function of reducing the amount of NH3 rejection, NH3 release resulting from the injection of urea associated with SCR catalyst 30 in the architecture of FIG. 1 and / or generation of NH3 in the purge phase of the NOx trap in the aforementioned NOx trap architectures.

According to the invention, the catalyst ASC 4 is equipped with a differential pressure sensor device 40 which measures a differential pressure between the inlet and the outlet of the catalyst ASC 4. The sensor device 40 comprises pressure sensors 400 and 401 at the inlet and outlet of the ASC 4 catalyst and delivers the differential pressure measurement signal dP.

It will be noted that various other sensors and components equip the system 1 and are not described here, not being necessary for the understanding of the invention.

The differential pressure dP, like other measurement signals of the system sensors 1, is supplied to an input / output port 50 of the electronic control unit 5.

According to the invention, the differential pressure dP measured between the inlet and outlet of the catalyst ASC 4 is used for the diagnosis of failure of the particulate filter 31.

The electronic control unit 5 is typically the engine control unit of the vehicle. The unit 5 comprises in particular an input / output port 50, as indicated above, through which transit the various signals necessary for the control of the functional components of the exhaust gas after-treatment system 1 and a communication port 51 with a CAN network of the vehicle. A dedicated software module estimablanté in the unit 5 for the implementation of the particulate filter defect diagnosis method according to the invention, by the execution of program code instructions by a processor of the unit 5.

The inventive entity has found that the differential pressure between the inlet and outlet of a catalyst is lower, by design, than that obtained at the terminals of a particulate filter (by a factor of about four). As a result, the differential pressure of a catalyst increases rapidly from the moment when its front surface begins to be obstructed by soot particles. A large gradient therefore exists between the clogged state and the unobstructed state of a catalyst, as compared to a particulate filter. It will be appreciated that a catalyst having a high density of the number of channels in its ceramic stratum will generate a greater gradient. high. Moreover, in the diesel engines, the presence of fatty soot particles due to a lower exhaust gas temperature than that existing in petrol engines participates disadvantageously in obtaining a high gradient.

The above findings of the inventive entity have been used in the method according to the invention to improve the accuracy of the diagnosis of failure of a particulate filter in a gas exhaust line, using not the differential pressure. dP between the inlet and the outlet of the particle filter subject of the diagnosis, but that of a catalyst located downstream of the particulate filter.

Thus, in the architecture of FIG. 1, the differential pressure dP between the inlet and outlet of the catalyst ASC 4 is measured by means of the differential pressure sensor device 40 and is used to develop the diagnosis of filter failure. 31. When the particulate filter 31 fails, a proportion of soot ensured by the filter 31 is captured by the downstream catalyst ASC 4 and affects the differential pressure dP, which thus indirectly provides information on the state of the particulate filter 31. .

In this embodiment, the decision on the faulty state or not of the particle filter 31 is established by a direct comparison of measurements of the differential pressure dP at a threshold. Alternatively, it will be possible to use an integration of the measurements of the successive differential pressures dP to make the decision on the defectiveness of the particulate filter from a storage level of the soot particles.

As shown in FIGS. 2A and 2B, a TH threshold curve is used which, as a function of the flow rate D of the exhaust gas EG in the catalyst ASC 4, provides the characteristic differential pressure dP measured at the terminals of the catalyst ASC. 4 when that is loaded with the soot particles of a defective particulate filter 31. Typically, this threshold curve TH is obtained by performing tests on a plurality of exhaust lines LE.

FIG. 2A shows the case of a negative decision on the fault diagnosis of the particulate filter 31. The measurements carried out MP of the differential pressure dP for different flow rates D of the exhaust gases remain below the corresponding threshold values of the TH curve. The particulate filter 31 operates normally and no failure is to be reported.

FIG. 2B shows the case of a positive decision on the diagnosis of failure of the particulate filter 31. The measurements carried out MP of the differential pressure dP for different flow rates D of the exhaust gases are greater than the corresponding threshold values of the TH curve. The particulate filter 31 is faulty.

Although the invention has been described here in the context of applications for vehicles equipped with a diesel engine, it should be noted that the invention will also find applications in vehicles equipped with a petrol engine.

The invention is not limited to the particular embodiments which have been described here by way of example. Those skilled in the art, according to the applications of the invention, may make various modifications and variations within the scope of the appended claims.

Claims (7)

1. A method of diagnosing the failure of a particulate filter (31) in an aftertreatment system (1) of the exhaust gas (EG) of a thermal engine, said aftertreatment system (1) of the gases exhaust system (EG) comprising a particulate filter (31) and a catalyst (4) disposed downstream of said particulate filter (31) in a gas exhaust line (LE), characterized in that said diagnosis of the failure of the particulate filter (31) is made from a measurement of a differential pressure (dP) between an inlet and an outlet of saidcatalyst (4). 2.Aftertreatment system (1) of the exhaust gas (EG) of a vehicle thermal engine comprising a nitrogen oxide emission treatment device (30), an electronic control unit (5), a particle filter (31) and an ammonia conversion catalyst (4) disposed in a particulate filter (31) in a gas exhaust line (LE), characterized in that it comprises a differential pressure sensor device ( 40, 400, 401) mounted between an inlet and an outlet of said ammonia conversion catalyst (4), said differential pressure sensor device (40, 400, 401) having the function of providing a differential pressure measurement (dP) between an inlet and an outlet of said ammonia conversion catalyst (4), said differential pressure measurement (dP) being for a failure diagnosis of said particulate filter (31). 3. System according to claim 2, characterized in that said device for treating nitrogen oxide emissions comprises a catalytic selective catalytic reduction catalyst (30). 4. System according to claim 3, characterized in that said selective catalytic reduction type catalyst (30) and said particulate filter (31) are included in a same compact device (3). 5. System according to claim 3 or 4, characterized in that said device for treating the emissions of nitrogen oxides also comprises a passive accumulator of nitrogen oxides contained in an oxidation catalyst (2). 6. System according to any one of claims 3 to 5, characterized inThat said nitrogen oxide emission treatment device comprises a trap nitrogen oxides. 7. Vehicle comprising a heat engine, characterized in that it comprisesa system (1) according to any one of claims 3 to 6 for a post-treatment of the exhaust gas emitted by said engine.