WO2017216440A1

WO2017216440A1 - Process for correcting diagnosis of a catalyst taking into account a regeneration of a particle filter in an exhaust line

Info

Publication number: WO2017216440A1
Application number: PCT/FR2017/051246
Authority: WO
Inventors: Vincent Chassefeyre
Original assignee: Psa Automobiles S.A.
Priority date: 2016-06-16
Filing date: 2017-05-22
Publication date: 2017-12-21
Also published as: FR3052808B1; FR3052808A1

Abstract

The invention relates to a process for correcting a diagnosis of functionality of a catalyst (4) present in an exhaust line (1) of an internal combustion engine (2) of a motor vehicle that also comprises a particle filter (3), the diagnosis of the catalyst (4) being carried out according to measurements of two oxygen probes (5, 5a) respectively upstream of the catalyst (4) and downstream of the catalyst (4) and of the particle filter (3), the upstream and downstream pressures at the ends of the particle filter (3) being detected and a differential pressure between the upstream and downstream pressures being calculated at different moments. During a diagnosis of the catalyst (4), it is checked that the differential pressure at the end of the diagnosis is not lower than the differential pressure at the start of the diagnosis, in which case no correction of the diagnosis is carried out, and if this is not so a correction of the diagnosis is performed.

Description

METHOD FOR CORRECTING DIAGNOSIS OF A CATALYST TAKING INTO ACCOUNT OF REGENERATION OF A FILTER

PARTICLES IN AN EXHAUST LINE

The invention relates to a method for correcting the diagnostic functionality of a catalyst taking into account a regeneration of a particulate filter in an exhaust line of an internal combustion engine taking place during the diagnosis. .

Preferably, but not limited to, the exhaust line concerned by the present invention is an exhaust line of an internal combustion engine gasoline motor vehicle.

In a nonlimiting manner, in Figure 1, which shows an exhaust line 1 for a gasoline engine, the exhaust line 1 is equipped with a gasoline particulate filter 3 and a catalyst three channels 4 Other depollution elements may however be present in this line 1, for example but not only selective catalytic reduction elements. In Figure 1, the three-way catalyst 4 and the gasoline particle filter 3 are grouped in the same system, which is not mandatory. The particulate filter 3 is advantageously positioned downstream of the three-way catalyst 4.

Conventionally, it can be provided at least one oxygen sensor or lambda probe, in Figure 1 two oxygen probes 5, 5a. A 5a of these two probes 5, 5a lambda can be placed in the exhaust line 1 between the exhaust manifold of the engine 2 and the catalyst 4. Its measurements can be transmitted to an injection computer provided in a control- control of the engine 2 to provide the possibility of determining the proportion of air-fuel mixture for which the efficiency of the engine 2 is optimal.

This keeps a low level of pollutants and positively influences a reduction in fuel consumption. The oxygen probes 5, 5a may be stoichiometric or linear.

The other oxygen sensor 5 may be provided downstream of the catalyst 4 and the particulate filter 3 in the exhaust line 1. The main function of this oxygen sensor 5 downstream of the particulate filter 3 is, for a last generation engine control, in addition to the oxygen sensor 5a disposed upstream of the particulate filter 3, to make it possible to evaluate the efficiency of the particulate filter 3 and the three-way catalyst 4 permanently. Each oxygen sensor 5, 5a delivers wealth information through a potential difference provided by the sensing element that composes it.

In summary, the oxygen sensor 5a disposed upstream of the catalyst 4 measures the output richness of the engine, the three-way catalyst 4 oxidizes the gaseous agents and the oxygen sensor 5 disposed downstream of the catalyst 4 verifies the functionality of the catalyst 4.

As regards FIGS. 2 and 3 with reference to FIG. 1 for some of the references, U (A) is the voltage in millivolt of an oxygen probe, t (s) is the time in seconds, the succession of R and P denotes the rich phases and the fuel-poor phases alternating, samc the signal of the oxygen probe upstream of the catalyst 4 and the particulate filter 3, therefore the upstream probe 5a, the signal samc being in full line and savc the signal of the oxygen probe downstream of the catalyst 4 and the particulate filter, so the downstream probe 5, the signal savc being dashed. In Figure 2, with a functional catalyst 4, there is an oscillation of the signal of the upstream oxygen sensor 5a reflecting the regulation of the wealth on the engine. The signal from the downstream oxygen sensor 5 hardly changes because the catalyst 4 oxidizes the gaseous agents.

In Figure 3, with a catalyst out of service, there is an oscillation of the signal of the upstream sensor 5a reflecting the regulation of the wealth on the engine. The signal of the downstream probe 5 evolves almost like the upstream probe 5 because the catalyst 4 no longer oxidizes the gaseous agents.

It is known to make a diagnosis of functionality of a catalyst according to measurements of the two oxygen probes respectively upstream and downstream of the catalyst.

It is known that a particulate filter is filled with particles and must be emptied at regular intervals. The particle filter is then regenerated during which the particles are burned. It is then desired a sharp increase in temperature in the exhaust system near the particle filter. The heating then continues until the regeneration is detected as complete. A particle filter thus performs its regeneration passively in the presence of a high rate of oxygen where self-combustion of the particles takes place. An example of regeneration for a particulate filter is given in EP-A-1 281 843.

When such a regeneration occurs during a diagnosis of functionality of a catalyst, it can distort the diagnosis by consuming oxygen and lowering a value of oxygen storage capacity of the catalyst that suggests that the catalyst is out of order while it may still be in working order.

The object of the invention is to optimize the diagnosis of the catalyst in the presence of a particulate filter, taking into account for the development of such a diagnosis of a possible course of regeneration during the diagnosis. , regeneration that can distort the diagnosis by consuming oxygen.

To achieve this objective, it is provided according to the invention a method for correcting a diagnosis of functionality of a catalyst present in an exhaust line of an internal combustion engine of a motor vehicle also comprising a particle filter, the diagnosis of the catalyst being made according to measurements of two oxygen probes respectively upstream of the catalyst and downstream of the catalyst and the particulate filter, the upstream and downstream pressures at the terminals of the particulate filter being detected and a differential pressure between the upstream and downstream pressures being calculated at different times, characterized in that, during a diagnosis of the catalyst, it is checked whether the differential pressure at the end of the diagnosis is not less than the differential pressure at the beginning of the diagnosis in which case no correction of the diagnosis is carried out and, in the opposite case, a correction of the diagnosis is carried out.

The technical effect is to take into account a possible course of a regeneration of a particulate filter during the diagnosis of the catalyst, such a regeneration distorting the established diagnosis. Indeed, during the rolling of the vehicle, if a supply of oxygen arrives upstream of the particulate filter in sufficient amount, so in poor richness, a regeneration of the particulate filter begins. It is accompanied by an oxygen consumption and a temperature rise in the regeneration phase. Since the particulate filter will consume oxygen during this phase, the calculation of the oxygen storage capacity of the catalyst and thus its diagnosis is degraded because the tilting of the downstream probe can be advanced. According to the invention, it is decided on the possible holding of a regeneration of the particulate filter to deduce a duration related to the oxygen consumption caused by the regeneration of the particulate filter.

A possible regeneration is detected by the differential pressure at the terminals of the particulate filter which quantifies the pressure drop between the upstream and downstream to estimate the soot rate stored in the particulate filter. The amount of soot stored will increase the pressure drop of the particulate filter because a back pressure will appear upstream of the particulate filter. Conversely, during a regeneration of the particulate filter, the differential pressure drops because the soot is burned. The present invention therefore proposes to monitor the differential pressure in the diagnostic phase of the catalyst to detect whether a possible regeneration is in progress simultaneously with the taking of the diagnosis. If the pressure differential of the particulate filter has not changed, it is considered that the particle filter regeneration has not taken place and therefore the diagnosis has not been distorted. Such regeneration is indeed not systematic during a poor rich phase suitable for the development of a diagnosis of the catalyst.

If the particle filter pressure differential has evolved, it is considered that the regeneration of the particulate filter has taken place and therefore the diagnosis has been distorted. The diagnosis of the catalyst is then corrected by applying a compensation of the oxygen consumed by the particulate filter.

Advantageously, for the diagnosis of the catalyst, it is calculated an oxygen storage capacity of the catalyst, the catalyst being diagnosed non-functional when its oxygen storage capacity is less than a predetermined threshold. This oxygen storage capacity is the best parameter for the diagnosis of a catalyst, the oxygen storage capacity decreasing with aging of the catalyst until it becomes insufficient for an out of service catalyst.

Advantageously, the exhaust line is associated with an internal combustion engine operating at several successive intervals of richness, including a poor richness interval, the oxygen storage capacity of the catalyst being calculated in the lean phase by integration of the catalyst. a signal from the downstream oxygen sensor between an instant of a zero value of the signal of the upstream oxygen sensor and an instant of a zero value of the signal of the downstream oxygen sensor. A poor rich phase is thus created upstream of the catalyst, causing a tilting of the downstream probe a certain time after the switchover of the upstream probe. The duration is measured between the moment of tilting of the upstream probe and that of the downstream probe. We integrate the result by calculation and thus obtain the oxygen storage capacity of the catalyst. The oxygen storage capacity of the catalyst is the ability of the catalyst to store oxygen. The longer the catalyst ages, the more the storage capacity of oxygen drops over time. From a certain value, the non-functional catalyst is considered because the storage capacity of the oxygen is too low. Without correction by the method according to the invention, a catalyst can be considered non-functional although in perfect working order due to a low oxygen storage capacity, which is due to a calculation biased by the progress of a regeneration of the particulate filter simultaneously with a diagnosis, the regeneration consuming oxygen which is then subtracted in the calculation of the oxygen storage capacity of the catalyst and leads to a false measure of this ability.

Advantageously, the signals of the downstream and upstream oxygen probes are filtered before integration of the signal of the downstream oxygen probe. These signals can indeed oscillate according to the pulsations of the motor. It may also be possible to average oxygen storage capacities taken during successive poor wealth.

Advantageously, for the correction of the diagnosis, it is carried out a correction of the oxygen storage capacity calculated by adding to it a correction of oxygen storage capacity estimated according to a map giving, as a function of the pressure. differential, the amount of oxygen consumed by the particulate filter regenerating during the lean phase during which the calculation of the storage capacity of oxygen is performed.

This cartography, advantageously in two dimensions, relates the pressure differential of the particulate filter consumed during the oxygen storage capacity phase to the oxygen content consumed for the regeneration. Depending on the pressure differential across the particle filter, an oxygen level consumed by the particulate filter is estimated. The oxygen content consumed by the particulate filter can then be injected into the calculation by integration of oxygen for a readjustment of the storage capacity of the oxygen. Advantageously, the mapping is established during a characterization phase of the particulate filter during the development of an internal combustion engine associated with the exhaust line.

Advantageously, the catalyst is purged at the beginning of the process.

The invention also relates to a set of an internal combustion engine exhaust line in a motor vehicle and a control system of the depollution in the exhaust line, the exhaust line comprising a particulate filter with respectively upstream and downstream pressure sensors with respect to the particulate filter and a flow of exhaust gases and oxygen sensors disposed respectively upstream and downstream of a catalyst, characterized in that the Depot control control system includes a catalyst functionality diagnostic supervisor for the implementation of such a method.

Advantageously, the supervisor comprises means for calculating an oxygen storage capacity of the catalyst, means for calculating a differential pressure at the terminals of the particulate filter and means for correcting the storage capacity. catalyst oxygen when the differential pressure has decreased during the catalyst functionality diagnostic.

Advantageously, the catalyst is a three-way catalyst and the particulate filter is a particulate filter for gasoline engine. Other features, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the accompanying drawings given by way of non-limiting examples and in which:

FIG. 1 is a schematic representation of an engine and part of an exhaust line of a motor vehicle according to the state of the art,

FIGS. 2 and 3 are diagrammatic representations of two time voltage curves respectively for the upstream oxygen sensor and the downstream oxygen sensor for an exhaust line comprising at least one particle filter and a respectively functional or out of service catalyst. during a succession of richness equal to one and of poor richness, a portion of the exhaust line showing the positioning of the oxygen probes in the line being shown in FIG. 2 above the curves, FIG. 4 is a diagrammatic representation of two voltage curves for respectively the upstream oxygen sensor and the oxygen sensor downstream of the catalyst being functional, these two curves being associated with a motor richness curve, a portion of the curve illustrating the progress of a diagnosis during a rich phase by calculating a storage capacity of the oxygen of the catalyst, this calculation being able to be distorted by the progress of a regeneration of the particulate filter during the diagnosis the diagnosis can then be corrected according to a method according to the invention,

FIG. 5 shows a map giving a differential pressure at the terminals of a particulate filter as a function of a consumed oxygen level, such mapping serving to establish a correction of the oxygen storage capacity of the catalyst according to to a correction method according to the present invention.

It is to be borne in mind that the figures are given by way of examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular, the dimensions of the various elements illustrated are not representative of reality.

In what follows, it is referred to all the figures taken in combination. When reference is made to one or more specific figures, these figures are to be taken in combination with the other figures for the recognition of the designated reference numerals. In what follows, the terms upstream and downstream are to be taken in the direction of gas flow in the exhaust line. For simplicity, the oxygen probes respectively upstream and downstream of the catalyst will be referred to respectively upstream or downstream oxygen sensor. Referring to all the figures and more particularly to Figures 1 to 3, the present invention relates to a method for correcting a diagnostic of functionality of a catalyst 4 present in an exhaust line 1 of an engine 2 to an internal combustion engine of a motor vehicle which also comprises a particulate filter. The exhaust line 1 may comprise, for a selective pollutant, other depollution elements than the particulate filter 3 and the catalyst 4, for example other oxidation or three-way catalysts, a selective catalytic reduction system or a nitrogen oxide trap system.

The particle filter 3 can also be of several types, such as for example a diesel particulate filter 3 also known by the name of FAP or a particulate filter 3 for gasoline engine also known as FPE for particulate filter gasoline 3, which corresponds to the English name of GPF for "gasoline particle filter" previously mentioned.

In a known manner, the thermal combustion engine 2 operates according to several richness values R, P a poor richness P, an average value of oxygen concentration being established for each of these richness values R, P. This has been shown in particular in Figures 2 and 3.

The diagnosis of the catalyst 4 is made according to measurements of two oxygen probes 5a, respectively upstream of the catalyst 4 and downstream of both the catalyst 4 and the particulate filter. The upstream and downstream pressures at the terminals of the particle filter 3 are detected and a differential pressure, referenced ΔΡ in FIG. 5, between the upstream and downstream pressures is calculated at different times. This differential pressure is representative of the particulate load of the particulate filter, a very high differential pressure according to the standards of the particulate filter 3 being synonymous with a very high particulate load and an obligation to perform a regeneration of the filter with particles 3.

According to the invention, during a diagnosis of the catalyst 4, it is checked whether the differential pressure at the end of the diagnosis is not less than the differential pressure at the beginning of the diagnosis in which case no correction of the diagnosis is made. performed. Otherwise, the diagnosis is corrected.

To establish a diagnosis of the catalyst 4, it can be calculated an oxygen storage capacity of the catalyst 4, the catalyst 4 being diagnosed non-functional when its oxygen storage capacity is less than a predetermined threshold. This threshold is determined during the design of catalyst 4 for each type of catalyst. The exhaust line 1 is associated with an internal combustion engine 2 operating at several successive intervals of richness R, P including a poor richness interval P. The oxygen storage capacity of the catalyst 4 is calculated in accordance with FIG. lean phase by integrating a signal from the downstream oxygen probe 5 between a moment of obtaining a zero value of the signal of the upstream oxygen sensor 5a and a moment of obtaining a zero value of the signal of the downstream oxygen sensor 5.

This is shown in Figure 4 while referring to Figure 1 for some of the references. The curve with sinusoids illustrates a curve of the oxygen probe upstream 5a and the other curve illustrates a curve of the downstream oxygen sensor 5. It is known that an oxygen sensor delivers a voltage inversely proportional to the oxygen concentration present in the exhaust gas. A wealth curve occurring under a succession of slots is also shown, a positive slot corresponding to a richness greater than 1 and referenced R and a negative slot corresponding to a poor richness and referenced P.

Without this being limiting, for a binary oxygen probe, the equilibrium point for a probe in natural respiration is 450 mV point to lambda equal to about 1. The range generally ranges from 50 to 800 mV. In the presence of a working catalyst, the range of the downstream probe can range from about 400 to about 500 mV. The equilibrium point is at 450 mV but the performance of the motor 2 can shift this average slightly. The regeneration of the particulate filter 3 results in additional oxygen consumption, which can be quantified as a percentage of additional oxygen or% O 2. The offset may be a few tens of millivolts at the signal of the probe 5a relative to the previously obtained or expected average signal, previously referenced savc in Figures 2 and 3.

The frequency of regulation of a probe that characterizes its ability to move from a rich / poor / rich R, P, R is about 3Hz to 4Hz. It may be wise to consider several failovers to average them. As a result, the acquisition of the average value previously obtained or expected can be a few seconds. The supervisor can compare acquisition periods of a few seconds to identify the phase in the presence of an offset. The signals of the probes can also be filtered.

In richness greater than 1 referenced R, the two curves rise to the maximum, the curve of the next downstream oxygen probe 5 with a slight lag delay the curve of the upstream oxygen sensor 5a which rises to its maximum almost immediately. . In richness greater than 1 referenced R, it can be carried out purging the catalyst, which is referenced 6 and then maintaining the purge, which is referenced 7.

During the transition to poor richness P, the curve of the upstream oxygen sensor 5a follows almost immediately this passage while the curve of the downstream oxygen probe 5a decreases only very slowly. The integration of the oxygen flow rate is done during the interval 8 between the time of passage to a zero value (equivalent to 450mV) of the signal of the upstream oxygen sensor 5a and the time of passage to a zero value (equivalent to 450mV) of the downstream oxygen sensor signal 5, the duration between these two respective dwell times for upstream and downstream oxygen sensors 5a being referenced 8.

It is found that this diagnostic time for the calculation of an oxygen storage capacity of the catalyst 4 by integration is also a possible duration for the implementation of a regeneration of the particulate filter 3. such regeneration consumes oxygen and can distort the calculation of the oxygen storage capacity of the catalyst 4.

According to a preferred embodiment of the present invention, for the correction of the diagnosis, it can be carried out a correction of the oxygen storage capacity calculated by adding a corrective storage capacity of oxygen. This correction of oxygen storage capacity can be estimated according to a map giving, as a function of the differential pressure, the amount of oxygen consumed by the particulate filter 3 regenerating during the poor phase P during which is carried out the calculation of the storage capacity of oxygen. Such a mapping is illustrated in Figure 5. The relationship between the differential pressure ΔΡ and the amount of oxygen% 02 consumed can be linear. This mapping can be established during a characterization phase of the particulate filter 3 during the development of an internal combustion engine 2 associated with the exhaust line 1. Referring to all the figures and in particular to Figures 1 and 5, the invention also relates to a set of a line 1 of internal combustion engine exhaust 2 in a motor vehicle and a control system control of the depollution in the line 1 of exhaust. The exhaust line 1 comprises a particle filter 3 and a catalyst 4. The exhaust line 1 comprises pressure sensors respectively upstream and downstream relative to the particle filter 3 and to a gas flow of exhaust and oxygen probes 5, 5a disposed respectively upstream and downstream of the catalyst 4.

The exhaust line 1 may also include other pollution control elements that a particulate filter 3 and a catalyst 4. The pollution control control system that can start the regeneration includes, as previously mentioned, a catalyst 4 functionality diagnostic supervisor for the implementation of the method as previously described.

The supervisor may comprise means for calculating an oxygen storage capacity of the catalyst 4, means for calculating a differential pressure ΔΡ at the terminals of the particulate filter 3 and means for correcting the capacity Oxygen storage of the catalyst 4 when the differential pressure ΔΡ has decreased during the diagnosis of catalyst functionality 4.

In a preferred but non-limiting application of the present invention, the catalyst 4 is a three-way catalyst. The particulate filter 3 may be a particulate filter for gasoline engine 2.

The invention is not limited to the described and illustrated embodiments which have been given only as examples.

Claims

Method for correcting a functionality diagnosis of a catalyst (4) present in an exhaust line (1) of an engine

(2) internal combustion of a motor vehicle also comprising a particle filter (3), the diagnosis of the catalyst (4) being carried out according to measurements of two oxygen probes (5, 5a) respectively upstream of the catalyst (4). ) and downstream of the catalyst (4) and the particle filter (3), the upstream and downstream pressures at the terminals of the particle filter

(3) being detected and a differential pressure (ΔΡ) between the upstream and downstream pressures being calculated at different times, characterized in that, during a diagnosis of the catalyst (4), it is checked whether the differential pressure (ΔΡ ) at the end of the diagnosis is not lower than the differential pressure (ΔΡ) at the start of the diagnosis in which case no correction of the diagnosis is made and, otherwise, a correction of the diagnosis is made.

Method according to claim 1, in which, for the diagnosis of the catalyst (4), an oxygen storage capacity of the catalyst (4) is calculated, the catalyst (4) being diagnosed non-functional when its storage capacity of oxygen is below a predetermined threshold.

Method according to claim 2, in which the exhaust line (1) is associated with an internal combustion engine (2) operating in several successive richness intervals (R, P) including a lean richness interval (P), the oxygen storage capacity of the catalyst

(4) being calculated in the lean phase by integration of a signal from the downstream oxygen probe (5) between an instant of zero value of the signal from the upstream oxygen probe (5a) and an instant of zero value of the signal from the downstream oxygen sensor (5).

Method according to claim 3, in which the signals from the downstream and upstream oxygen probes (5, 5a) are filtered before integrating the signal from the downstream oxygen probe

(5).

Method according to claim 3 or claim 4, in which, for the correction of the diagnosis, a correction of the calculated oxygen storage capacity is carried out by adding to it an oxygen storage capacity correction estimated according to a map giving, as a function of the differential pressure (ΔΡ), the quantity of oxygen consumed by the particle filter (3) regenerating during the phase poor during which the calculation of the oxygen storage capacity is carried out.

6. Method according to claim 5, in which the mapping is established during a phase of characterization of the particle filter (3) during the development of an internal combustion engine (2) associated with the exhaust line (1).

7. Method according to any one of the preceding claims, in which a purge (6, 7) of the catalyst (4) is carried out at the start of the process.

8. Assembly of an exhaust line (1) from an internal combustion engine (2) in a motor vehicle and a control system for depollution in the exhaust line (1), the line (1) ) exhaust comprising a particle filter (3) with pressure sensors respectively upstream and downstream relative to the particle filter (3) and to a flow of exhaust gases and oxygen probes (5, 5a) arranged respectively upstream and downstream of a catalyst (4), characterized in that the depollution control system comprises a supervisor for diagnosing the functionality of the catalyst (4) for implementing the process according to any one of the preceding claims.

9. Assembly according to the preceding claim, in which the supervisor comprises means for calculating an oxygen storage capacity of the catalyst (4), means for calculating a differential pressure (ΔΡ) across the terminals of the filter. particles (3) and means for correcting the oxygen storage capacity of the catalyst (4) when the differential pressure (ΔΡ) has fallen during the functionality diagnosis of the catalyst (4).

10. Assembly according to claim 8 or claim 9, in which the catalyst (4) is a three-way catalyst and the particle filter (3) is a particle filter for a gasoline engine.