FR3069886A1 - 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

PARTICLES AND EXHAUST GAS AFTER-TREATMENT SYSTEM [001] The invention relates generally to the depollution of exhaust gases emitted by the thermal 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 after-treatment system including a particulate filter, in which the above-mentioned process is implemented.

In motor vehicles, exhaust gas aftertreatment systems have today become essential for compliance with environmental standards. Regulated polluting emissions include carbon monoxide (CO), unburnt hydrocarbons (HC), nitrogen oxides (NOx) and soot particles.

For the removal of soot particles in exhaust gases, it is well known to equip exhaust after-treatment systems with a particle filter. Particulate filters are very present in vehicles with a Diesel type engine and are also becoming widespread in petrol type engines, especially with the entry into force of the European environmental standard known as "Euro 6.3".

The particle filter is effective in reducing particulate pollution. However, the progressive accumulation of soot particles retained in the porous layers of the filter causes a pressure drop in the exhaust line of gas from the heat engine. Periodic regenerations at high temperature are necessary to remove the accumulated soot particles by combustion. During the life of the vehicle, failures of the particle filter may occur with regard to the emission of particles, for example, following a particularly severe regeneration phase causing cracking of the filter, handling malicious or other causes. The filter failure results in particulate emissions that exceed the maximum threshold set by regulations.

In accordance with the regulations, the event "particle filter failure" must be detected by the on-board diagnostic system, called OBD for "On Board Diagnostic" in English. This event must also be reported to the vehicle user by activating a warning light on the dashboard, such as the MIL warning light for “Malfunction Indicator Lamp” in English, to inform them that a repair of the vehicle is necessary.

In the prior art, it is known to evaluate the loss of filtration efficiency from a measurement of the differential pressure, called back pressure, between the inlet and the outlet of the particle filter. . This method of assessing the loss of efficiency of the particulate filter is sufficient for controlling its regeneration phases, but could still be 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 loss of efficiency, but such a sensor presents installation difficulties and leads to an increase. cost sensitive.

By patent documents KR20070062309 and FR2950108, it is known to particulate filter diagnostic devices using a detection filter implanted downstream of the particulate filter in the exhaust gas line of a heat engine . The differential pressure between the inlet and the outlet of the detection filter is measured to detect a failure of the particulate filter from a fouling level of the detection filter. In KR20070062309, the detection filter is a second particulate filter which is mounted in the gas exhaust line. In FR2950108, the detection filter is placed in a pipe bypassing the main exhaust pipe. These diagnostic devices have the disadvantage of requiring an additional particle filtering means which is dedicated to the diagnosis of particle filter failure and impacts the cost.

There is therefore a need for a reliable and precise diagnostic method for the failure of a particulate filter which does not have the abovementioned drawbacks of the prior art.

According to a first aspect, the invention relates to a method for diagnosing the failure of a particulate filter in an aftertreatment system for the exhaust gases of a heat engine, the aftertreatment system for exhaust gas comprising a particulate filter and a catalyst arranged downstream of the particulate filter in a gas exhaust line. In accordance with the invention, the diagnosis of the particle filter failure is carried out by measuring a differential pressure between an inlet and an outlet of the catalyst.

According to a particular characteristic, the method is implemented by the execution of program code instructions in an electronic control unit of the exhaust gas aftertreatment system.

According to another aspect, the invention also relates to a system for post-treating the exhaust gases of a vehicle heat engine comprising a device for treating nitrogen oxide emissions, an electronic control unit , a particulate filter and an ammonia conversion catalyst disposed downstream of the particulate filter in a gas exhaust line. According to the invention, the system comprises a differential pressure sensor device mounted between an inlet and an outlet of the ammonia conversion catalyst, the differential pressure sensor device having the function of providing a measurement of the differential pressure between an inlet and an outlet for the ammonia conversion catalyst, the differential pressure measurement being intended for diagnosing a failure of the particulate filter.

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

According to another particular embodiment, the catalyst of the selective catalytic reduction type and the particle filter are included in 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 device for treating nitrogen oxide emissions comprises a nitrogen oxide trap.

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

Other advantages and characteristics of the present invention will appear more clearly on reading the detailed description below of several particular embodiments of the invention, with reference to the accompanying drawings, in which:

Fig. 1 is an overview of a particular embodiment of an exhaust gas post-treatment system implementing the method according to the invention;

Figs.2A and 2B are curves showing negative and positive detections of the failure of a particulate filter, respectively, in the method according to the invention.

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

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

As shown in FIG. 1, the exhaust gas post-treatment system 1 essentially comprises an LE gas exhaust line and an electronic control unit 5. The LE gas exhaust line here comprises an 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 DOC type oxidation catalyst (for “Diesel Oxidation Catalyst” in English) incorporating here a passive NOx accumulator (not shown), called PNA for Passive NOx Adsorber in English .

The compact device 3 comprises a catalyst of the selective catalytic reduction (SCR) type 30 and a particle filter 31. The SCR catalyst 30 and the particle filter 31 are shown in FIG. 1 as two separate components. Note however that the compact device 3 may advantageously be of the type called "Compact Liquid System" and integrate the catalytic layer SCR, called "washcoat", in an impregnated form in the particle filter. The SCR 30 catalyst destroys the Nox by reacting them with ammonia (NH3) as a reducing agent. NH3 is contained in an aqueous urea solution, such as AdBlue (registered trademark), introduced into the LE gas exhaust line by the injector 300. NOx sensors 20 and 301 are provided in line d 'LE gas exhaust, at the inlet of the catalyst 20 and at the outlet of the compact device 3, for controlling the SCR catalyst 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 PNA accumulator contained in the oxidation catalyst 2 and the SCR catalyst 30 form a device for treating nitrogen oxides.

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

The ammonia conversion catalyst 4, called ASC for "Ammonia Slip Converter" in English, has the function of reducing the amount of NH3 rejection, NH3 rejection which results from the injection of urea associated with SCR 30 catalyst in the architecture of Fig. 1 and / or generation of NH3 in the purge phase of the NOx trap in the architectures with NOx trap mentioned above.

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 dP differential pressure measurement signal.

It will be noted that various other sensors and components are fitted to the system 1 and are not described here, since they are not necessary for understanding the invention.

The differential pressure dP, like other measurement signals from the sensors of the system 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 the 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 vehicle engine control unit. The unit 5 comprises in particular an input / output port 50, as indicated above, through which the various signals necessary for controlling the functional components of the exhaust gas aftertreatment system 1 pass through and a port for communication 51 with a CAN network of the vehicle. A dedicated software module is installed in unit 5 for the implementation of the particulate filter failure diagnostic method according to the invention, by the execution of program code instructions by a processor of unit 5 .

The inventive entity has found that the differential pressure between the inlet and the outlet of a catalyst is lower, by design, than that obtained across a particle filter (by a factor of approximately four ). As a result, the differential pressure of a catalyst increases rapidly from the moment its front inlet surface begins to be blocked by soot particles. A significant gradient therefore exists between the obstructed state and the unobstructed state of a catalyst, compared to a particle filter. It will be noted that a catalyst having a high density of the number of channels in its ceramic substrate will generate a higher gradient. In addition, in diesel engines, the presence of fatty soot particles due to a lower exhaust gas temperature than that existing in petrol engines contributes favorably to obtaining a high gradient.

The above findings of the inventive entity were 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 outlet of the particulate filter being diagnosed, 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 the outlet of the catalyst ASC 4 is measured by means of the differential pressure sensor device 40 and is used to develop the fault diagnosis of the particle filter 31. When the particle filter 31 is faulty, a proportion of the soot leaving the filter 31 is captured by the catalyst ASC 4 located downstream and affects the differential pressure dP, which therefore indirectly provides information on the particle filter condition 31.

In this embodiment, the decision on whether the particle filter 31 has failed or not is established by a direct comparison of measurements of the differential pressure dP at a threshold. Alternatively, an integration of successive differential pressure measurements dP may be used to make the decision on the failure of the particulate filter from a soot particle storage level.

As shown in Figs.2A and 2B, a threshold curve TH is used which provides, as a function of the flow rate D of the exhaust gases EG in the catalyst ASC 4, the characteristic differential pressure dP noted at the terminals of the catalyst ASC 4 when the one is loaded with soot particles from a faulty particle filter 31. Typically, this threshold curve TH is obtained by carrying out tests on a plurality of LE exhaust lines.

Fig.2A shows the case of a negative decision on the diagnosis of failure of the particulate filter 31. The measurements made MdP of the differential pressure dP for different flow rates D of the exhaust gases remain below the threshold values corresponding to the TH curve. The particulate filter 31 operates normally and there are no faults to report.

Fig.2B shows the case of a positive decision on the diagnosis of failure of the particulate filter 31. The measurements made MdP of the differential pressure dP for different flow rates D of the exhaust gases are greater than the threshold values corresponding to the TH curve. The particle filter 31 has failed.

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

The invention is not limited to the particular embodiments which have been described here by way of example. A person skilled in the art, depending on the applications of the invention, can make various modifications and variants which fall within the scope of the appended claims.

Claims (7)

1. Method for diagnosing the failure of a particulate filter (31) in an aftertreatment system (1) of the exhaust gases (EG) of a heat engine, said aftertreatment system (1) exhaust gas (EG) 5 comprising a particle filter (31) and a catalyst (4) arranged downstream of said particle filter (31) in a gas exhaust line (LE), characterized in that said diagnosis of the failure of the particle filter (31) is carried out from a measurement of a differential pressure (dP) between an inlet and an outlet of said catalyst (4). 10 2. Post-treatment system (1) for the exhaust gases (EG) of a vehicle heat engine comprising a device for treating nitrogen oxide emissions (30), an electronic control unit (5) , a particle filter (31) and an ammonia conversion catalyst (4) disposed downstream of said particle filter (31) in a gas exhaust line (LE), characterized 15 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 measurement of the differential pressure (dP) between an inlet and an outlet of said ammonia conversion catalyst (4), said measurement of 20 differential pressure (dP) being intended for a diagnosis of failure of said particle filter (31). 3. System according to claim 2, characterized in that said device for treating nitrogen oxide emissions comprises a catalyst of the selective catalytic reduction type (30). 25 4. System according to claim 3, characterized in that said catalyst of the selective catalytic reduction type (30) and said particle filter (31) are included in the same compact device (3). 5. System according to claim 3 or 4, characterized in that said device for treating nitrogen oxide emissions also comprises an accumulator 30 passive nitrogen oxides contained in an oxidation catalyst (2). 6. System according to any one of claims 3 to 5, characterized in that said device for treating nitrogen oxide emissions comprises a nitrogen oxide trap. 7. Vehicle comprising a heat engine, characterized in that it comprises a 5 system (1) according to any one of claims 3 to 6 for an aftertreatment of the exhaust gases emitted by said heat engine.