WO2020201648A1

WO2020201648A1 - Method for diagnosing the presence of frost in the tapping of a differential pressure sensor

Info

Publication number: WO2020201648A1
Application number: PCT/FR2020/050478
Authority: WO
Inventors: Javier Furio Vizcaino; Julie DILLENSCHNEIDER; Yassine Benryan
Original assignee: Psa Automobiles Sa
Priority date: 2019-04-03
Filing date: 2020-03-09
Publication date: 2020-10-08
Also published as: FR3094752B1; FR3094752A1

Abstract

The invention relates to a method for diagnosing the presence of frost in the tapping of a differential pressure sensor, referred to as a backpressure sensor, comprising: - a step of defining a time interval (I), - a step of calculating a reference value (dPdV_ref) of a gradient of a backpressure of the particulate filter returned by the backpressure sensor depending on a volume flow rate of the exhaust gases upstream of the particulate filter, and - a step of analysing an evolution, over the time interval (I), of an instantaneous value (dPdVJnst) of the gradient of the backpressure of the particulate filter returned by the backpressure sensor depending on the volume flow rate of the exhaust gases upstream of the particulate filter compared to the reference value (dPdV_ref) previously calculated to deduce the presence or absence of frost in the tapping of the backpressure sensor.

Description

DESCRIPTION

Title of the invention: PROCESS FOR DIAGNOSING THE PRESENCE OF GEL IN A PITCH OF A DIFFERENTIAL PRESSURE SENSOR

The present invention claims the priority of French application 1903564 filed April 3, 2019, the content of which (text, drawings and claims) is incorporated here by reference.

The present invention is in the field of the pollution control of the exhaust gases of a heat engine. More specifically, the invention relates to a method for diagnosing the presence of gel in a tap of a differential pressure sensor at the terminals of a particulate filter. The invention finds a particularly advantageous, but not exclusive, application with internal combustion compression or spark ignition engines equipped with a particulate filter associated with a differential pressure sensor.

[0003] During the combustion of a mixture of air and fuel in a heat engine, solid or liquid particles consisting essentially of carbon-based soot and / or oil droplets may be emitted. These particles typically have a size of between a few nanometers and one micrometer. To trap them, one can advantageously provide particle filters, usually made of a mineral matrix, of ceramic type, of honeycomb structure, defining channels arranged substantially parallel to the general direction of flow of the exhaust gases in the filter. , and alternately closed on the side of the gas inlet face of the filter and on the side of the gas outlet face of the filter, as described in document EP2426326.

The exhaust line is also provided with a differential pressure measurement sensor, said back pressure sensor, to measure the pressure difference between an upstream connection and a downstream connection of the particulate filter from which it is possible to deduce a mass of accumulated soot. To this end, a map is used which establishes a correlation between the measurement of the pressure difference and the mass of soot in the particulate filter. [0005] The back pressure sensor is thus used to carry out the necessary diagnostics of the state of the particulate filter and required by regulations (called "OBD" for "On Board Diagnostic" in English) as well as safety diagnostics. Its information is therefore essential to guarantee the proper functioning of the heat engine. However, when the outside conditions are cold, the presence of frost in the sensor connections can falsify the information acquired by the sensor and therefore the interpretation of it by the engine ECU.

The invention aims to effectively remedy this drawback by providing a method for diagnosing the presence of gel in a tap of a differential pressure sensor, called back pressure sensor, connected upstream and downstream of a filter. particles intended to filter the exhaust gases of a heat engine, said method comprising:

- a step of defining a time interval,

a step of calculating a reference value of a gradient of a backpressure of the particulate filter returned by the backpressure sensor as a function of a volume flow rate of the exhaust gases upstream of the particulate filter, and

a step of analyzing an evolution, over the time interval, of an instantaneous value of the gradient of the backpressure of the particle filter returned by the backpressure sensor as a function of the volume flow rate of the upstream exhaust gases of the particulate filter with respect to the previously calculated reference value in order to deduce therefrom the presence or absence of gel in a tap of the backpressure sensor.

[0007] The invention thus makes it possible to reduce the false detections of the diagnostics of the state of the particulate filter which are based on the backpressure information and which would be produced because of the formation of gel in the nozzles of the sensor caused by cold outdoor conditions. This translates into economic gain for the driver and the manufacturer if the vehicle is still within the warranty period by reducing the number of after-sales service interventions due to false detections.

[0008] According to one implementation, the analysis step comprises:

- a step of calculating a ratio between the instantaneous value of the gradient of the backpressure and the previously calculated reference value, - a step of comparing the calculated ratio with a maximum threshold and a minimum threshold, and

a step of determining the presence of gel or not in a stitching as a function of a result of the comparison carried out previously.

[0009] According to one implementation, the reference value is calculated at the start of the time interval.

[0010] According to one implementation, a method for calculating the gradient of the backpressure of the particulate filter as a function of the volume flow rate of the exhaust gas upstream of the particulate filter consists in taking a sample of points of size N, each point being a pair of measurements comprising a measurement of back pressure returned by the sensor and a measurement of the volume flow rate upstream of the particulate filter, and in calculating a linear regression on these points.

[001 1] According to one implementation, said method comprises the step of retaining only the backpressure and volume flow measurements which have been obtained under conditions of stable operation of the heat engine.

According to one implementation, the back pressure and volume flow measurements are considered to have been obtained under conditions of stable operation of the heat engine when a derivative of the volume flow rate of the exhaust gases upstream of the filter. particles is less than a maximum bound.

[0013] According to one implementation, the time interval is between 2 and 3 minutes.

[0014] According to one implementation, said method is implemented only if an outside temperature is less than 0 ° C.

[0015] According to one implementation, following a fault linked to detection of the presence of gel in a stitching, said diagnostic process will be rehabilitated when the ratio returns to a value situated between the minimum threshold and the maximum threshold. [0016] The subject of the invention is also a computer comprising a memory storing software instructions for implementing the method as defined above.

[0017] The invention will be better understood from reading the description which follows and from examining the accompanying figures. These figures are given only by way of illustration but in no way limit the invention.

[0018] [Fig. 1] FIG. 1 is a schematic representation of an exhaust line of a heat engine comprising a particulate filter and a computer allowing the implementation of the method according to the invention;

[0019] [Fig. 2] FIG. 2 is a diagram of the different steps of the method according to the invention for detecting the presence of gel in a tap of a back pressure sensor;

[0020] [Fig. 3] FIG. 3 is a graphic representation of differential pressure measurements returned by the backpressure sensor as a function of measurements of the exhaust gas flow rate of the heat engine;

[0021] [Fig. 4] FIG. 4 is a representation of temporal diagrams of the evolution of signals illustrating a detection of a gel plug in a tap of a backpressure sensor during an implementation of the method according to the invention.

FIG. 1 shows a heat engine 10 in particular intended to equip a motor vehicle. The heat engine 10 may be compression or controlled ignition. The heat engine 10 is connected to an exhaust line 11 for the evacuation of the burnt gases produced by the operation of the heat engine 10.

The exhaust line 1 1 comprises a pollution control member 12 of gaseous pollutant, for example an oxidation catalyst or a three-way catalyst. The three-way catalyst 12 makes it possible in particular to reduce the oxides of nitrogen to nitrogen and to carbon dioxide, to oxidize the carbon monoxides to carbon dioxide, and the unburnt hydrocarbons to carbon dioxide and to water. The exhaust line 1 1 further comprises a particulate filter 13 for filtering soot particles in the exhaust gases of the heat engine 10. The particulate filter 13 is suitable for filtering soot particles from fuel combustion.

In the particulate filter 13, the exhaust gases pass through the material making up the particulate filter 13. Thus, when the particulate filter 13 is formed of channels, each of these channels comprises a plugged end, so that the exhaust gases flowing in the particle filter 13 pass from channel to channel, passing through the walls of the various channels of the particle filter 13 to exit the particle filter 13. The particle filter 13 may be based on 'a porous ceramic matrix, for example of cordierite, mullite, aluminum titanate or silicon carbide. If necessary, the depollution unit 12 and the particulate filter 13 may be located inside the same envelope 15.

The exhaust line 1 1 is also provided with a sensor 16, said back pressure sensor, for the differential pressure measurement between the upstream and downstream of the particulate filter 13 from which it is possible to deduce a mass of accumulated soot. To this end, the sensor 16 is connected upstream and downstream of the particulate filter 13 respectively by means of an upstream connection 16.1 and a downstream connection 16.2. A map makes it possible to establish a correlation between the differential pressure measurement and the mass of soot in the particulate filter 13.

A computer 17, for example the engine computer or a dedicated computer comprises a memory storing software instructions for the implementation of the method according to the invention for diagnosing the presence of frost in a tap 16.1, 16.2 of the sensor of back pressure 16.

To this end, the computer 17 receives as input a measurement of the back pressure dP across the filter 13 returned by the sensor 16, an estimate of the volume flow Qvol of the exhaust gases upstream of the particulate filter 13, as well than an outside temperature because the diagnostic is preferably activated only for temperatures below 0 ° Q to exclude false detection which would be due to fouling other than freezing. Calculator 17 is able to generate at output a fault signal F_def in state 1 in the event of detection of the presence of frost in a tap 16.1, 16.2.

[0029] The various steps of the diagnostic process according to the invention are described below with reference to FIG. 2.

In a step 101, the computer 17 calculates a gradient dPdV of the back pressure dP returned by the back pressure sensor 16 as a function of the volume flow Qvol of the exhaust gases upstream of the particulate filter 13 expressed in KPa / (m ³ / s).

The relationship between these two physical quantities (backpressure dP and volume flow Qvol) can be approximated by a polynomial of order 2 or quadratic, but there is a range PJin of volume flow in which the relationship can be considered as linear, with acceptable errors, as shown in Figure 3.

The dPdV gradient calculation method consists in taking a sample of points of size N, calibratable for example between 800 and 1000. Each point is a couple of measurements: a measurement of back pressure dP expressed in mbar and a flow measurement volume Qvol upstream of the particle filter 13 expressed in m ³ / s. A linear regression is then calculated on these points, in particular by the least squares method.

Preferably, all the measurements of back pressure dP and volume flow rate Qvol are not used for the calculation of the gradient dPdV. A criterion is applied in order to take into account only the measurements which are obtained under stabilized operating conditions of the heat engine. By "stabilized operating conditions" is meant the operating conditions of the thermal engine for which the flow rate of the exhaust gases Qvol does not vary abruptly, in other words, in the absence of sudden acceleration or braking.

This criterion is verified by calculating the derivative of the volume flow Qvol of the exhaust gases upstream of the filter 13 which indicates the rate of change of this flow as a function of time, and by ensuring that this value is less than a maximum limit, for example of the order of 0.05 m ³ / s ² . By "of the order of" is meant a variation of plus or minus 10% around this value. Thanks to this criterion, it is possible to improve the precision of the calculation of the dPdV gradient. In FIG. 3, the stabilized points which are retained for the calculation are represented by crosses; while the transient points which are not retained for the calculation are represented by circles.

During a step 102, a time interval I is defined in which the behavior of the calculation of the gradient dPdV is observed. This time interval I, also referred to as the observation window, is provided sufficiently short to exclude a false detection which would be due to a fouling other than by freezing. In fact, fouling other than by freezing, for example by soot or ash, causes a slow change in the backpressure gradient. A faster evolution of this backpressure gradient during this time interval I is indicative of the appearance of gel in the nozzle. This time interval I is for example between two and three minutes.

During a step 103, a reference value of the gradient dPdV_ref is stored at the start of each interval I and maintained throughout the interval I. During the time interval I, the computer 17 also calculates current (or instantaneous) gradient values dPdVJnst. The computer 17 therefore performs two different calculations, namely the calculation of the current gradient dPdVJnst and the reference gradient dPdV_ref frozen at the start of the time interval I.

During a step 104, the computer 17 calculates the ratio R_dPdV between the current gradient dPdVJnst and the reference gradient dPdV_ref, ie R_dPdV = d Pd V J nst / d Pd V_ref.

During a step 105, the ratio R_dPdV is compared with a minimum threshold Smin and a maximum threshold Smax. The minimum threshold Smin is for example equal to 0.5 while the maximum threshold Smax is for example equal to 2.

[0039] The result of this comparison determines the result of the diagnosis. Indeed, in the case where the ratio is between the minimum threshold Smin and the maximum threshold Smax, then we deduce that there is no presence of gel in the nozzles 16.1, 16.2 of the backpressure sensor 16. If the ratio is not between the minimum threshold Smin and the maximum threshold Smax, then we deduce that there is has a presence of gel in a nozzle 16.1, 16.2 of the backpressure sensor 16.

Figure 4 shows a temporal evolution of the signals obtained during an implementation of the method according to the invention for detecting the presence of gel in a tap 16.1, 16.2 of the backpressure sensor 16. We distinguish the temporal evolution the current gradient dPdVJnst, the reference gradient dPdV_ref, the R_dPdV ratio, as well as the state variable F_def ("flag") taking the value 1 in the event of a fault. The points P indicate the instants at the start of time interval I at which the reference gradient dPdV_ref is calculated.

During the first two time intervals I, the ratio R_dPdV is between the minimum threshold Smin and the maximum threshold Smax. During the third time interval I, a strong change in the R_dPdV ratio is observed, which exceeds the maximum authorized Smax threshold. This indicates an anomaly in the measurement of the back pressure of the particulate filter 13, probably caused by the presence of a gel plug in a nozzle 16.1, 16.2. The fault signal F_def then changes to state 1.

[0042] In fact, the dPdVJnst parameter is not supposed to change rapidly under normal operating conditions, that is to say without disturbing the back pressure measurement. The dPdVJnst parameter changes with the storage of particles in the filter 13 in a slow manner due to the relatively low speed of production of particles by the heat engine 10.

For example, for a spark ignition engine, to double its value (R_dPdV = 2) it would take between 2 and 4 hours considering that we are in critical conditions vis-à-vis the production of polluting particles. A faster development than this necessarily indicates an anomaly in the acquisition of the differential pressure between the upstream and downstream terminals, typical of the presence of a gel plug in a tap 16.1, 16.2.

When the R_dPdV ratio returns to a value situated between the minimum threshold Smin and the maximum threshold Smax, it is considered to be in the "acceptable" range and the diagnosis is rehabilitated. It is possible to provide a confirmation period Te of removal of the fault before returning the fault signal F_def to state 0 and again observing the development of the R_dPdV ratio.

As a variant, it is possible to analyze the evolution, over the time interval I, of the instantaneous value dPdVJnst relative to the reference value dPdV_ref in another way than by calculating a ratio R_dPdV. As a variant, the calculated ratio is the inverse ratio of that previously indicated.

Claims

1. Method for diagnosing the presence of frost in a tap (16.1, 16.2) of a differential pressure sensor (16), called a backpressure sensor, connected upstream and downstream of a particle filter (13) intended to filter exhaust gas from a heat engine, characterized in that said method comprises:

- a step of defining a time interval (I),

- a step of calculating a reference value (dPdV_ref) of a gradient of a backpressure (dP) of the particle filter (13) returned by the backpressure sensor (16) as a function of a volume flow (Qvol ) exhaust gases upstream of the particulate filter (13), and

- a step of analyzing an evolution, over the time interval (I), of an instantaneous value (dPdVJnst) of the backpressure gradient (dP) of the particulate filter (13) returned by the backpressure sensor (16) as a function of the volume flow rate (Qvol) of the exhaust gases upstream of the particulate filter (13) compared to the reference value (dPdV_ref) previously calculated to deduce the presence or absence of gel in a nozzle ( 16.1, 16.2) of the backpressure sensor (16).

2. Method according to claim 1, characterized in that the analysis step comprises:

- a step of calculating a ratio (R_dPdV) between the instantaneous value (dPdVJnst) of the backpressure gradient and the reference value (dPdV_ref) previously calculated,

- a step of comparing the ratio (R_dPdV) calculated with a maximum threshold (Smax) and a minimum threshold (Smin), and

- a step of determining the presence of gel or not in a stitching (16.1, 16.2) as a function of a result of the comparison carried out previously.

3. Method according to claim 1 or 2, characterized in that the reference value (dPdV_ref) is calculated at the start of the time interval (I).

4. Method according to any one of claims 1 to 3, characterized in that a method of calculating the gradient of the backpressure (dP) of the particulate filter (13) as a function of the volume flow (Qvol) of the gases of exhaust upstream of the particulate filter (13) consists in taking a sample of points of size N, each point being a pair of measurements comprising a back pressure measurement (dP) returned by the sensor (16) and a volume flow measurement (Qvol ) upstream of the particulate filter (13), and to calculate a linear regression on these points.

5. Method according to claim 4, characterized in that it comprises the step of retaining only the back pressure (dP) and volume flow (Qvol) measurements which were obtained under conditions of stable operation of the heat engine.

6. Method according to claim 5, characterized in that the back pressure (dP) and volume flow (Qvol) measurements are considered to have been obtained under conditions of operating stability of the heat engine (10) when a derivative of the volume flow rate (Qvol) of the exhaust gases upstream of the particulate filter (13) is less than a maximum limit.

7. Method according to any one of claims 1 to 6, characterized in that the time interval (I) is between 2 and 3 minutes.

8. Method according to any one of claims 1 to 7, characterized in that it is implemented only if an outside temperature is below 0 ° C.

9. The method of claim 2, characterized in that following a fault linked to a detection of the presence of gel in a nozzle (16.1, 16.2), said diagnostic method will be rehabilitated when the ratio (R_dPdV) returns to a value. located between the minimum threshold (Smin) and the maximum threshold (Smax).

10. Computer (17) comprising a memory storing software instructions for implementing the method as defined in any one of the preceding claims /