Particle filter diagnostics

Abstract

The invention provides a device for diagnosing a particle filter, the device being suitable for: - determining a measured pressure time profile (100) and a theoretical pressure time profile (200) upstream of the filter, - carrying out for each profile (100, 200): o performing a second low-pass filtering (132, 232) on a first filtered time profile (130, 230), o performing a second low-pass filtering (142, 242) on the first filtered time profile to obtain a second filtered time profile (140, 240), o calculating (152, 252) a difference between the second filtered time profile and the first filtered time profile, o obtaining an absolute value (160, 260) of the calculated difference (150, 250), and o calculating (172, 272) an integral (170, 270) of the absolute value, and, based on a comparison (410) between the two integrals, establishing a diagnosis of the particle filter.

Description

Technical Field

[0001] The present application relates to a diagnostic device for a particle filter of an internal combustion engine, and a diagnostic method performed by such a device. Background Art

[0002] Regulations regarding emissions from vehicles with internal combustion engines are becoming increasingly stringent, setting lower and lower emission limits. In order to meet these requirements, various exhaust gas reduction strategies must be applied simultaneously using a variety of components.

[0003] In particular, today's exhaust circuits are usually provided with a catalytic converter making it possible to limit the emissions of carbon monoxide CO, nitrogen oxides NOx and unburned hydrocarbons HC. The exhaust circuit also comprises a particle filter making it possible to reduce the emissions of fine particles.

[0004] Particle filters for diesel engines have been used for a long time. Gasoline internal combustion engines and especially direct fuel injection engines (in which fuel is introduced directly into the combustion chamber under high pressure and atomized very finely) also produce fine particles, which are less in number by mass but larger in number at the engine outlet. For these engines, increasingly stringent anti-pollution standards have also promoted the large-scale deployment of particle filters.

[0005] A particle filter generally comprises a housing and a monolith inserted into the housing, the composition of which makes it possible to capture particles, such as soot particles.

[0006] It may happen that the particle filter is removed after installation to reduce vehicle repair costs, or that the particle filter breaks. However, since the particle filter represents an important component in limiting particle emissions, current standards require the ability to reliably detect the absence of a particle filter or its malfunction.

[0007] Several methods have been proposed to implement this type of diagnosis, some of which are based on evaluating the temperature variation over time of the exhaust gases upstream and downstream of the particle filter, involving positioning one thermocouple upstream of the particle filter and one downstream in the exhaust circuit.

[0008] Several methods are also known, such as for example the method described in document FR 3121356, which are based on detecting the removal of a particle filter by exploiting the pressure difference between the inlet and the outlet of the particle filter. This type of solution involves the use of an exhaust gas pressure sensor upstream of the particle filter and another pressure sensor downstream of the particle filter.

[0009] Also known from document US 2005091970 is a diagnostic method based on the use of a pressure difference determined from a pressure measurement carried out by an upstream pressure sensor and a pressure drop model, making it possible to infer therefrom the pressure value downstream of the particle filter.

[0010] In all cases, these known methods involve either having two sensors or using a sensor with a downstream pressure estimate. In the first case, the use of more sensors increases the risk of sensor clogging, dispersion, ageing, water infiltration or any other phenomenon that degrades the correct operation of the sensor. In addition, this represents an additional cost of the equipment, increases the complexity of the system and requires more calibration work. In the second case, the diagnosis made is less precise because it is based on a downstream pressure estimate. Summary of the invention

[0011] The object of the present invention is to propose a particle filter diagnostic device which does not have the disadvantages of the prior art.

[0012] In particular, it is an object of the invention to make it possible to determine the removal of a particle filter without requiring two sensors which are arranged upstream and downstream of the particle filter, respectively.

[0013] In this respect, the invention proposes a device for diagnosing a particle filter of an exhaust circuit of an internal combustion engine, the exhaust circuit comprising a particle filter and a pressure sensor suitable for measuring the exhaust gas pressure upstream of the particle filter, the device comprising a computer suitable for:

[0014] - determine the measured pressure time profile (profil) upstream of the particle filter from the pressure sensor,

[0015] - determine the theoretical pressure-time profile upstream of the particle filter,

[0016] - performing a processing on each of the measured pressure-time distribution and the theoretical pressure-time distribution, the processing comprising:

[0017] * low pass filtering the time distribution to obtain a first filtered time distribution,

[0018] * performing a second low pass filtering on the first filtered time distribution to obtain a second filtered time distribution,

[0019] * calculating the difference between the second filtered time distribution and the first filtered time distribution,

[0020] * get the absolute value of the calculated difference, and

[0021] * calculating an integral of the absolute value, wherein the integral calculation step is performed if the difference or the absolute value obtained from the theoretical pressure-time profile exceeds a first threshold value and if the first filtered theoretical pressure-time profile exceeds a second threshold value, and

[0022] - Based on the comparison between the two calculated integrals, a diagnosis of the particle filter is established.

[0023] In one embodiment, the computer is configured to determine a theoretical pressure-time profile upstream of the particle filter from the exhaust gas flow rate in the exhaust circuit.

[0024] In one embodiment, the device further comprises a memory, and the computer is further configured to determine a theoretical pressure-time profile upstream of the particle filter from a polynomial function of the exhaust gas flow rate in the exhaust circuit, said function being stored in the memory.

[0025] In one embodiment, the computer is configured to implement the step of calculating the integral of the differences obtained from each time profile over a predetermined time period.

[0026] In one embodiment, the computer is configured to stop the step of calculating the integral of the differences obtained from each time profile if the absolute value obtained from the theoretical pressure time profile upstream of the particle filter exceeds a predetermined third threshold value.

[0027] In one embodiment, the computer is configured to compare the integrals obtained from the measured pressure-time profile and the integral obtained from the theoretical pressure-time profile by calculating a ratio between the integrals.

[0028] The computer may then be configured to: compare the ratio to a fourth threshold; and determine that the particulate filter is properly installed if the ratio exceeds the fourth threshold.

[0029] The fourth threshold may be between 0.8 and 1.1.

[0030] The invention also relates to a method for diagnosing a particle filter in an exhaust circuit of an internal combustion engine, the exhaust circuit comprising a particle filter and a pressure sensor suitable for measuring the exhaust gas pressure upstream of the particle filter, the method being implemented by a computer and comprising the implementation of the following steps:

[0031] - determine the measured pressure time profile upstream of the particle filter from the pressure sensor,

[0032] - determine the theoretical pressure-time profile upstream of the particle filter,

[0033] - performing a processing on each of the measured pressure-time distribution and the theoretical pressure-time distribution, the processing comprising:

[0034] * low pass filtering the time distribution to obtain a first filtered time distribution,

[0035] * performing a second low pass filtering on the first filtered time distribution to obtain a second filtered time distribution,

[0036] * calculating the difference between the second filtered time distribution and the first filtered time distribution,

[0037] * get the absolute value of the calculated difference, and

[0038] * calculating an integral of the absolute value, wherein the integral calculation step is performed if the difference or the absolute value obtained from the theoretical pressure-time profile exceeds a first threshold value and if the first filtered theoretical pressure-time profile exceeds a second threshold value, and

[0039] - Based on the comparison between the two calculated integrals, a diagnosis of the particle filter is established.

[0040] The invention also relates to a computer program product comprising code instructions for implementing the method according to the preceding description when executed by a computer.

[0041] Finally, the invention relates to an exhaust circuit of an internal combustion engine, comprising a catalytic converter, a particle filter arranged downstream of the catalytic converter, a single pressure sensor arranged upstream of the particle filter, and a device according to the preceding description.

[0042] The proposed invention goes against the established prejudice, according to which the exhaust gas pressure upstream of the particle filter itself makes it possible to diagnose this filter.

[0043] It is thus possible to establish a diagnosis without having to have recourse to a pressure difference, whether this is calculated from two pressure measurements upstream and downstream of the particle filter, or whether this is assessed from a measurement of the upstream pressure and an estimate of the downstream pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other features, details and advantages will become apparent upon reading the following detailed description and analyzing the accompanying drawings, in which:

[0045] Figure 1 [ Figure 1 ] schematically represents an internal combustion engine including a diagnostic device.

[0046] Figure 2 [ Figure 2 ] schematically represents an example of the processing performed to diagnose a particulate filter.

[0047] Figure 3 [ Figure 3 ] indicates that according to Figure 2 The process represented in shows the ratio distributions calculated for an empty particle filter and a missing particle filter, respectively. DETAILED DESCRIPTION

[0048] Reference now Figure 1 , which schematically shows an internal combustion engine 10 and an exhaust circuit 20. The exhaust circuit is used to discharge and treat exhaust gases 37 from the combustion chambers of the internal combustion engine. The exhaust circuit comprises: an exhaust gas catalytic converter 21, for example a three-way catalytic converter; and a particle filter 22, which is arranged downstream of the exhaust gas catalytic converter. In the following, the terms "upstream" and "downstream" are considered to be relative to the flow direction of the exhaust gases, that is, from the internal combustion engine to the catalytic converter and then to the particle filter.

[0049] The exhaust circuit 20 also comprises a first exhaust gas sensor 23, which is arranged upstream of the catalytic converter 21, and a second exhaust gas sensor 24, which is arranged downstream of the catalytic converter 21. The first sensor 23 and the second sensor 24 are suitable for determining the properties of the exhaust gases upstream and downstream of the catalytic converter 21, respectively, and in particular the amount of oxygen present in these exhaust gases.

[0050] The exhaust circuit 20 also includes a single pressure sensor 25, which is arranged upstream of the particle filter 22 and is suitable for measuring the pressure of the exhaust gas 2 upstream of the particle filter. The pressure measurement can be carried out discretely, at predefined time intervals or continuously within a certain period of time. In all cases, the pressure sensor 25 is suitable for measuring the time distribution of the pressure upstream of the particle filter 22 within a determined period of time. In the case of the pressure measurement being carried out in a discrete manner, the time distribution corresponds to a series of measurements carried out within the period of time.

[0051] exist Figure 1 Also represented is an engine control unit ECU, which comprises a device 30 for diagnosing a particle filter, the device comprising a computer 31 and a memory 32. The computer 31 is configured to implement the diagnostic method described below on the basis of code instructions and parameters described later, which are stored in the memory. The vehicle comprising the engine 10 and the exhaust circuit 20 advantageously also comprises an error display 34, which is connected to the engine control unit ECU and is suitable for signaling a particle filter failure or a particle filter missing detected by the engine control unit ECU. The display 34 can be, for example, a warning light, which is illuminated if a particle filter is not detected. It can also be a screen, which displays an error message if a particle filter is not detected.

[0052] The computer 31 of the control unit ECU is configured to implement the following reference Figure 2 The described diagnostic method checks for the presence of the particulate filter 22 .

[0053] The computer determines a pressure time profile 100 from the measurement of the pressure upstream of the particle filter by the pressure sensor 25 over a certain period of time.

[0054] The measured pressure time profile 100 is then filtered 130 by a low pass filter 132. The filtered time profile 130 is then filtered again by a second low pass filter 142 to obtain a second filtered time profile 140 of the pressure measured upstream of the particle filter. The computer 31 then calculates the difference 150 between the first filtered time profile 130 and the second time profile 140, which has been filtered twice. The block representing the subtraction operation is indicated as 152, and the result of this operation is referred to as the difference 150 obtained from the measured pressure time profile.

[0055] The computer then determines the absolute value 160 of the difference 150, the corresponding block being denoted 162 in the figure. The computer 31 then calculates the integral 170 of the absolute value 160 previously obtained, the corresponding block being denoted 172.

[0056] Furthermore, the computer 31 is configured to determine a theoretical pressure-time profile 200 upstream of the particle filter. This theoretical pressure-time profile is determined during step 50 from the volume flow rate of the exhaust gas in the exhaust circuit upstream of the particle filter. This volume flow rate of the exhaust gas can be calculated from the mass flow rate of the exhaust gas leaving the engine, and the temperature and pressure of the exhaust gas upstream of the filter. The mass flow rate of the exhaust gas is itself determined by the engine control according to the operating conditions of the engine.

[0057] In one embodiment, the theoretical pressure-time profile may be determined by means of a polynomial function of the volume flow rate of the exhaust gas (the polynomial function being stored in the memory 32), which may be of the following form:

[0058]

[0059] in is the volume flow rate of exhaust gas upstream of the particulate filter, P th is the theoretical pressure upstream of the particulate filter (as a function of time), and β1 and β2 are two parameters also stored in the memory 32 , which are determined for a given engine and particulate filter configuration.

[0060] The computer 31 is further configured to perform the same processing on the theoretical pressure-time profile 200 upstream of the particle filter as described above and performed on the measured pressure-time profile 100 upstream of the particle filter. Thus, the computer 31 performs a first low-pass filtering 232 on the profile 200 to obtain a first filtered theoretical pressure-time profile 230, and then it performs a second low-pass filtering 242 on the first filtered profile to obtain a second filtered profile 240.

[0061] The computer 31 then calculates during a step 252 (block 252) the difference between the first filtered profile 230 and the second filtered profile 240 obtained from the theoretical pressure-time profile and determines during a step 262 (block 262) the absolute value 260 of this difference. This result 260 is also denoted as difference obtained from the theoretical pressure-time profile.

[0062] The computer 31 then calculates, during a step 272 (block 272 ), an integral 270 of the difference 260 obtained.

[0063] In one embodiment, the computer 31 starts calculating the integrals 170 and 270 only if the difference 260 obtained from the theoretical pressure-time profile 200 is greater than a first threshold 302 and if the first filtered profile 230 obtained from the theoretical pressure-time profile 200 is greater than a second threshold 304. Since the quantities 260 and 230 compared with these thresholds are functions of time, obtained over a determined period of time, the comparison is performed for each value taken by the functions 260 and 230 over a determined period of time. The first threshold 302 and the second threshold 304 can be stored in the memory 32.

[0064] This additional condition established by the previous calibration makes it possible to ensure that the volume flow rate and the pressure are within a sufficiently high value range to allow a diagnosis of the particle filter to be carried out in a sufficiently robust manner.

[0065] In one embodiment, the calculation of the integrals 170 and 270 is stopped if the time integral of the difference 260 obtained from the theoretical pressure time profile 200 is greater than a third threshold value determined by calibration. The third threshold value may also be stored in the memory.

[0066] As a variant, the calculation of the integrals 170 and 270 is stopped after a time period (determined by calibration) has elapsed since the start of the integration. Figure 2 ) can be implemented simultaneously so that the integration stops when the first of these two conditions is met.

[0067] Once the two integrals 170 and 270 have been calculated from the measured pressure-time profile and the theoretical pressure-time profile upstream of the particle filter, respectively, the computer 31 performs a comparison 410 of these integrals to establish a diagnosis of the particle filter. In one embodiment, the comparison 410 is a calculation of the ratio 400 between the integral 170 obtained from the measured pressure-time profile and the integral 270 obtained from the theoretical pressure-time profile.

[0068] refer to Figure 3 , a bar graph of the values ​​of the ratio 400 has been represented, where the particle filter is missing as "FAP ABS" and where the particle filter is unloaded as "FAP OK", the bar graph being the result of a Monte Carlo simulation to study the results of the method as a function of the dispersion of the upstream pressure. The study was carried out for 100 samplings with a random dispersion of the upstream pressure values ​​between plus or minus 10 hPa. Unloaded means that the particle filter contains no soot or ash, i.e. it is new or has just been regenerated. Figure 3 As can be seen in FIG. 4 , the calculated ratio is sufficiently disjoint between the case where the particle filter is missing and the case where the particle filter is unloaded to enable a threshold to be set, thereby making it possible to establish a diagnosis. For example, the computer 31 can compare the calculated ratio 400 with a fourth threshold value (which can be between 0.8 and 1.1) to establish a diagnosis. If the ratio is below the fourth threshold value, the computer 31 determines that the particle filter is missing, and if the ratio is higher, the computer 31 determines that the particle filter is present. The fourth threshold value can be stored in a memory, and all threshold values ​​can be determined by previous calibration.

[0069] If the computer 31 determines that the particulate filter is missing, it may generate an alarm, for example by activating a warning light or an error message displayed via the display 34 .

[0070] It can thus be seen that, despite the established prejudices in the art, it is not necessary to acquire a pressure value downstream of the particle filter in order to be able to carry out a diagnosis of the presence or absence of the filter, since the processing presented of the upstream pressure alone makes it possible to distinguish with sufficient robustness the case of a present or absent particle filter.

Claims

1. A device (30) for diagnosing a particle filter of an exhaust circuit (20) of an internal combustion engine (10), the exhaust circuit comprising a particle filter (22) and a pressure sensor (25) adapted to measure the exhaust gas pressure upstream of the particle filter, the device comprising a computer (31) adapted to: - determining a measured pressure time profile (100) upstream of the particle filter from the pressure sensor (25), - determining a theoretical pressure-time profile upstream of the particle filter (200), - performing a processing on each of the measured pressure-time distribution and the theoretical pressure-time distribution (100, 200), the processing comprising: o low pass filtering (132, 232) the time distribution to obtain a first filtered time distribution (130, 230), o performing a second low pass filtering (142, 242) on the first filtered time distribution to obtain a second filtered time distribution (140, 240), o calculating (152, 252) a difference between the second filtered time distribution and the first filtered time distribution, o obtain the absolute value of the calculated difference (150, 250), and o calculating (172, 272) the integral (170, 270) of the absolute value, wherein the integral calculation step is performed if the difference (250) or the absolute value (260) obtained from the theoretical pressure-time profile exceeds a first threshold value (302) and if the first filtered theoretical pressure-time profile (230) exceeds a second threshold value (304), and - Based on the comparison between the two calculated integrals ( 410 ), a diagnosis of the particle filter is established.

2. The device (30) according to claim 1, wherein the computer (31) is configured to determine the theoretical pressure-time profile (200) upstream of the particle filter from the exhaust gas flow rate in the exhaust circuit.

3. The device (30) according to claim 1 or 2, further comprising a memory (32), the computer being further configured to determine the theoretical pressure-time distribution upstream of the particulate filter from a polynomial function of the exhaust gas flow rate in the exhaust circuit, the function being stored in the memory (32).

4. The device (30) according to claim 1 or 2, wherein the computer (31) is configured to implement the step of calculating the integral (170, 270) of the differences obtained from each time distribution within a predetermined time period.

5. The device (30) according to claim 1 or 2, wherein the computer (31) is configured to stop the step of calculating the integral (170, 270) of the difference obtained from each time distribution if the absolute value obtained from the theoretical pressure-time distribution upstream of the particle filter exceeds a predetermined third threshold value.

6. An apparatus (30) according to claim 1 or 2, wherein the computer (31) is configured to compare (410) the integral by calculating a ratio (400) between the integral (170) obtained from the measured pressure-time distribution and the integral (270) obtained from the theoretical pressure-time distribution.

7. The apparatus of claim 6, wherein the computer (31) is configured to: compare the ratio (400) with a fourth threshold; and determine that the particulate filter is properly installed if the ratio exceeds the fourth threshold.

8. The device (30) according to claim 7, wherein the fourth threshold value is between 0.8 and 1.

1.

9. A method for diagnosing a particle filter in an exhaust circuit (20) of an internal combustion engine (10), the exhaust circuit comprising a particle filter (22) and a pressure sensor (25) suitable for measuring the exhaust gas pressure upstream of the particle filter, the method being implemented by a computer (31) and comprising the implementation of the following steps: - determining a measured pressure time profile (100) upstream of the particle filter from the pressure sensor (25), - determining a theoretical pressure-time profile upstream of the particle filter (200), - performing a process on each of the measured pressure-time distribution and the theoretical pressure-time distribution, the process comprising: o low pass filtering (132, 232) the time distribution to obtain a first filtered time distribution (130, 230), o performing a second low pass filtering (142, 242) on the first filtered time distribution to obtain a second filtered time distribution (140, 240), o calculating (152, 252) a difference (150, 250) between the second filtered time distribution and the first filtered time distribution, o obtain the absolute value of the difference calculated by (162, 262), and o calculating (172, 272) the integral (170, 270) of the absolute value, wherein the integral calculation step is performed if the difference (250) or the absolute value (260) obtained from the theoretical pressure-time profile (200) exceeds a first threshold value (302) and if the first filtered theoretical pressure-time profile (230) exceeds a second threshold value (304), and - Based on the comparison between the two calculated integrals ( 410 ), a diagnosis of the particle filter is established.

10. A computer program product comprising code instructions for implementing the method according to claim 9 when executed by a computer (31).

11. An exhaust circuit (20) of an internal combustion engine, the exhaust circuit comprising: Catalytic converter (21); A particle filter (22) arranged downstream of the catalytic converter; a single pressure sensor (25) arranged upstream of the particle filter (22); and a device (30) according to any one of claims 1 to 8.

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