EP3137744A1

EP3137744A1 - Device for diagnosing a particle filter

Info

Publication number: EP3137744A1
Application number: EP10754486.8A
Authority: EP
Inventors: Saïd ZIDAT
Original assignee: Individual
Current assignee: ZIDAT, SAID; Katcon Global SA de CV
Priority date: 2009-09-15
Filing date: 2010-09-14
Publication date: 2017-03-08
Also published as: WO2011032933A1; US20130047841A1

Abstract

The invention relates to a novel device for diagnosing a particle filter attached onto a main exhaust line (13) of an internal combustion engine, wherein said diagnosis device includes, downstream from the first particle filter, a detection filter (14) and a means (15) for measuring an output parameter of the detection filter. The detection filter (14) is arranged in a secondary exhaust line (16) through which a first portion of the gases from the particle filter passes, wherein a second portion of the gases from the particle filter follows the main exhaust line. The invention can be used for diagnosing particle filters for an automobile having a heat combustion engine.

Description

DEVICE FOR DIAGNOSING A PARTICLE FILTER

Technical field and state of the art

The invention relates to a device for the diagnosis of a particulate filter attached to a main exhaust line of an internal combustion engine, a diagnostic device of the type comprising, downstream of the first particle filter, a detection filter. and means for measuring an output parameter of the detection filter.

To limit the pollution of motor vehicles with internal combustion engine, it is known to install in the main exhaust line of the engine gas a particulate filter capable of limiting the amount of particles in the flow of gas leaving below a tolerated threshold value.

The most commonly used particulate filters are composed of a set of channels with filtering walls and plugged alternately at the inlet or the outlet (Figure 1). The exhaust gases enter one channel and exit through another after passing through at least one filter wall. In filters made of silicon carbide (SiC), the channels are grouped into segments interconnected by a seal that compensates for the significant expansion of silicon carbide during thermal transients.

Particle filters now installed on almost all motor vehicles in Europe are highly efficient and can limit particle emissions to less than 5 mg / km traveled, the maximum level allowed by the Euro 5 standard which will come into effect in 2010 and measured following the standard NEUDC driving cycle. Standards for other diesel applications or more generally with thermal engines (trucks, agricultural machinery, constructions) in Europe as well as in other countries like the United States and Japan impose similar limits.

Even though particulate filters are known to be robust and suitably perform their function throughout the life of the vehicles on which they are installed, some filters may fail, for example because of a manufacturing defect, or they may fail. following severe operating conditions for example. The most well-known failures result in cracking of a filter wall, a seal connecting several segments and / or a plug closing a or more channels. These failures result in a particle emission higher than the threshold tolerated by the legislation.

The current OBD (On Board Diagnostic) standard requires the establishment of means for detecting a component failure (in particular the particulate filter) that could lead to pollutant emissions exceeding the threshold set by legislation. . These detection means must send a visible signal to the driver of the vehicle to signal the need to control pollutant emissions.

Several types of detection means are being evaluated or developed:

· Resistive sensors: a metal plate positioned in the flow coming out of the particle filter increases its resistance when particles stick to it. The soot deposition mechanisms on the resistive element are very complex; dependent on parameters that are difficult to control. In addition, low-intensity electrical signals require expensive processing electronics. · Electric discharge sensors: two electrodes are arranged in the flow of gases leaving the particle filter and, when a predefined high voltage is applied between these electrodes, an electric discharge occurs if the quantity of particles in the gas flow is greater than a threshold value. These sensors, however, require complex electronic devices to produce a voltage sufficient to create an electric shock.

Optical sensors: an optical signal passing through the flow of gases leaving the particle filter makes it possible to determine the quantity of particles present in the stream. These sensors, however, are difficult to maintain in good operating condition in a difficult environment such as exhaust.

All these techniques are complex to implement and lack robustness. It is therefore not yet envisaged to use them on production vehicles.

Another technique envisaged in document Dl (KR20070062309) consists in putting a detection filter downstream of the particulate filter and detecting the pressure difference between the input and the output of the detection filter. A pressure difference close to zero means that the detection filter does not stop particles, that is to say that the particles present in the exhaust gas leaving the engine have been properly filtered in the particulate filter. Conversely, an increasing pressure difference means that the detection filter is fouled with particles that are not filtered by the particulate filter, ie the particulate filter fails. The main disadvantage of the solution proposed in D1 is that, in normal operation, the detection filter generates a significant counter-pressure in the exhaust duct, especially at the points of operation of the engine where the gas flow is important. Such back pressure causes overconsumption of fuel and a decrease in engine performance. Moreover, in case of failure of the particulate filter, the detection filter clogs up and quickly turns into a plug on the exhaust line so that the vehicle must be immediately immobilized at the risk of damaging the engine.

WO 03/091553 discloses a defect detection device for a particulate filter. The device is in the form of a chamber installed in the exhaust duct of an engine, downstream of the particulate filter. The chamber comprises a filter wall, facing the flow of exhaust gas, and a gas outlet port in the opposite wall. The device uses two oxygen sensors, one placed in the chamber and the other in the conduit.

Description of the invention

The invention proposes a new diagnostic device, not having the disadvantages of the prior devices described above.

More precisely, the invention proposes a device for diagnosing a particulate filter fixed on a main exhaust line of an internal combustion engine, the diagnostic device comprising, downstream of the first particulate filter, a filter of detection and means for measuring an output parameter of the detection filter representative of an operating state of the particulate filter. According to the invention, the detection filter is traversed by a first portion of the gases from the particulate filter, a second part of the gases from the particulate filter along the main exhaust line.

Thus, in normal operation of the vehicle, there is no back pressure in the main exhaust line. Moreover, in the event of particle filter failure and fouling of the detection filter, the exhaust gases may continue to flow into the unobstructed main exhaust line. It is therefore possible to continue using the vehicle.

The portion of the gas passing through the detection filter is preferably small relative to the total amount of gas exiting the particulate filter, for example between 0.1 and 70%. Preferably, in order to limit the influence of the detection filter on the operation of the exhaust line, the quantity of gas passing through the detection filter is limited to the amount necessary and sufficient to allow the measurement of the output parameter of the filter. detection with the desired accuracy. Thus, the portion of the gas passing through the detection filter is preferably limited to 0.1 to 15% of the total quantity of gas leaving the particulate filter, more preferably 0.1 to 10%, and even 0.1 to 5%. With a fraction of the exhaust gas as low, it is possible to use a small detection filter. This makes it possible to limit the bulk while allowing accurate measurement.

According to the invention, the detection filter is installed in a secondary exhaust line which divides the flow of the main line downstream of the particle filter and extends outside the main line (at least in part). To do this, the secondary line comprises a gas inlet connected to the main exhaust line downstream of the particulate filter. Different possibilities exist for the connection of the output of the secondary exhaust line; it can in particular be connected downstream downstream, be in the open air, or connected to the air intake line of the engine.

The use of a secondary line distinct from the main line (and external to it) is particularly advantageous when working on the basis of temperature variations generated by the clogging of the detection filter, because this avoids a warming by the main line. The secondary line may of course include an inlet section placed in the main line to deflect a portion of the gases, and, where appropriate, an outlet section may be positioned in the main line.

Preferably, the means for measuring an output parameter of the detection filter then comprises a sensor placed in the secondary line portion out of the line. main, which can be used alone or in combination with an upstream sensor as discussed below.

The detection filter can be placed in the secondary line (out of the main line) or in the input section of the secondary line, so in the main line. This latter configuration is advantageous for regenerating the detection filter via heating caused by the regeneration of the particulate filter.

According to variants also, the measuring means can be:

A temperature, flow rate, flow velocity or oxygen concentration sensor of the gases, positioned at the output of the detection filter, or

A differential measuring means able to establish a difference (gradient) between the input and the output of the detection filter. It may be for example a means for measuring differential pressure or differential temperature, comprising a first pressure sensor, respectively a temperature sensor, upstream of the detection filter, a second pressure sensor, respectively a temperature sensor, downstream of the detection filter and a comparator able to determine a difference in pressure, respectively temperature, between the input and the output (upstream / downstream difference) of the detection filter.

Thus, with the invention, it is possible to use known, simple and robust measurement sensors.

The diagnostic device according to the invention may also comprise an alerting means for producing an alert signal if a profile of the output parameter of the detection filter is different from a reference profile.

The device according to the invention is particularly useful for equipping motor vehicles, such as cars, trucks, tractors, etc. But it can also be used more generally for the diagnosis of any particulate filter associated with a heat engine, such as for example engines on fixed installations, boats, construction equipment, etc.

Preferred embodiments of the present invention are set forth in dependent claims 2 to 17. In another aspect, the present invention relates to a method of diagnosing a particulate filter according to claim 18. Preferred embodiments are set forth in dependent claims 19 to 22.

Brief description of the figures

The invention will be better understood, and other characteristics and advantages of the invention will emerge in the light of the following description of diagnostic examples of a particulate filter, according to the invention. These examples are given in a non-limiting manner. The description is to be read in conjunction with the appended drawings in which:

FIG. 1 is a block diagram of a diagnostic device according to one embodiment of the invention;

FIGS. 2 to 5, 11 and 12 show variants of the device of FIG. 1;

• Figure 6 is a graph illustrating the speed of the exhaust gas according to the operating state of the particulate filter;

FIGS. 7, 8 and 10 show illustrations of the signals measured by the sensors to be used by the electronic controller of the motor;

• Figure 9 illustrates the principle of calibration and detection of the present device.

Detailed description of several embodiments of the invention

In FIG. 1 is shown a known particulate filter comprising an inlet 11 for connection to an exhaust outlet of a heat engine. An outlet 12 of the particulate filter 10 is connected to a main exhaust line 13 in which the exhaust gas has a total flow rate Qt when the engine is operating normally. In the exhaust line, at a given section of the said exhaust line, the total pressure Ptotal is given by the relation: Ptotal = Pstatic + Pdynamic.

The dynamic pressure is a function of the velocity V of displacement of the gases: Pdynamic = l / 2 * rho * V * V, rho being the density of the exhaust gases.

The diagnostic device according to the invention comprises, downstream of the particle filter 10, a detection filter 14 and a measurement means 15. The detection filter 14 is positioned so as to receive only a part of the flow of the gases leaving the particle filter, and the detection means 15 is preferably fixed at the output of the detection filter (downstream, after this). One can also consider the use of two sensors: one placed in front of (upstream) the detection filter and the other at the outlet (downstream) which makes it possible to measure a difference in temperature or a pressure difference as it is will see later, (the terms "entry" and "upstream", as well as "exit" and "downstream", are here used interchangeably as synonyms)

The detection filter preferably has filtering properties similar to those of a particulate filter. The most widely used particle filters today are those of silicon carbide or cordierite but with different filter properties such as porosity, pore size and the number of channels per flow passage section. Preferably, the detection filter employed is designed to allow a low pressure drop when the detection filter is not loaded with soot and then clog quickly even with very low levels of soot emissions. Other filters such as metal foams or woven metal sheets can be used when they have such a filtering behavior.

In a first variant, the detection filter 14 is placed in a bypass duct or secondary exhaust line 16. The secondary line is dimensioned (section, shape, etc.) so that only 0.1 to 70% of the total of the gases The exhaust system is diverted to the secondary line and the detection filter. Preferably, the section is limited so that only 0.1 to 15%, more preferably 0.1 to 10% or 0.1 to 5%, of the total of the exhaust gases is drifted to the secondary line. and the detection filter, to limit at best the consequences on the operation of the engine of a fouling of the detection filter 14 during a failure of the particulate filter 10.

An inlet 17 of the secondary line is connected to the main line 13 downstream of the particle filter 10 so that said inlet 17 is subjected to the total pressure Ptotal gases. According to a variant, an output of the secondary line is connected to the main exhaust line so that, at the outlet of the secondary line, the gases are only subjected to the static pressure. An output of the secondary line is made such that, at the output of the secondary line, the gases are subjected to a pressure less than or equal to the static pressure Pstatic. Thus, the pressure difference between the inlet and the outlet of the secondary line is greater than or equal to the dynamic pressure and a fraction of the gases is naturally driven towards the secondary line and the detection filter. According to a variant, the output of the secondary line is connected to the main line, the gases are thus output at the static pressure and the pressure difference between the input and the output of the secondary line is equal to Pdynamique = Ptotale - Pstatic. According to another variant, the output of the secondary line is left in the open air, the gases are thus subjected to the output at the only atmospheric pressure (less than the static pressure) and the pressure difference between the inlet and the outlet of the secondary line is greater than the dynamic pressure.

The flow of gases in the secondary line is a function notably of:

· The pressure difference between the inlet and the outlet of the secondary line,

• pressure losses in the secondary line due to the detection filter and the secondary line (shape, section, length, wall roughness, etc.)

The shape, the dimensions, and the connection on the main line of the secondary line are therefore dimensioned so that the secondary flow rate of the gases is sufficient to allow a detection of a parameter of the gases by the detection means 14. If necessary, several solutions can be considered to increase the secondary flow.

The secondary exhaust line thus realizes a deflection of a portion of the exhaust gas and constitutes a distinct line of the main duct extending out of it. For its connection to the main line, it may simply be connected to the main conduit, or include an inlet section (or primer) within the main line to facilitate gas deflection. The inlet section is preferably substantially parallel to the gas flow.

It is possible to locally reduce the section of the main line to the vicinity (upstream or downstream) of the input of the secondary line Figure 2, narrowing 19. Thus, the speed of the gases, and therefore also the dynamic pressure, increase locally. . The secondary flow, function of the dynamic pressure, increases accordingly. The other possibility is to place this restriction in the main line between the input 17 and the output 18 of the secondary line 16 so as to force a part of the flow to pass through the detection filter 14. This restriction is preferably limited to the minimum necessary to ensure sufficient gas flow to the detection filter to ensure accurate measurement (Figure 2bis). The restriction can be a grid (19a) placed around the inlet section 17 of the secondary line or a simple restriction (19b) or any other means that can increase the pressure drop in the main exhaust line behind the section d entry 17.

It is also possible to put a valve on the main line in the vicinity of the input of the secondary line (in place of the narrowing 19 - not shown in the figure), which allows to adjust the secondary flow at will. But the installation of such a valve is generally delicate and expensive to implement.

It is also possible, in the case of a main line comprising in series a particle filter 10 and an additional element (such as a silencer 20 or a resonator), to position the input of the secondary line between the output of the particle filter 10 and the inlet of the additional element. The secondary line is thus in derivation with respect to the main line. As the pressure losses in the main line are increased by the presence of the additional element, the flow of gas in the secondary line parallel to the main line is increased.

The outlet 18 of the secondary line can be left open (Figure 1), so that the exhaust gases are discharged in the open air, as well as the gases flowing in the main line. The outlet 18 can also be connected to the main line downstream of the inlet 17 (FIGS. 2, 3). The outlet 18 can still be connected to the main line downstream of the additional element if there is one (FIG. 4). It can also be connected to any point of the exhaust line or engine air intake (not shown) may have a pressure differential sufficient to ensure a flow derived from a suitable flow. In this context, it will be possible to connect the output 18 to the engine air intake line, in particular to a low pressure section (for example between the throttle valve and the compressor, if applicable). The secondary line 16 can be installed inside a muffler 20 to save space (FIG. 5).

The detection filter 14 has filtering properties similar to those of a particulate filter:

If the particulate filter 10 is operating normally, the detection filter passes all the particles passed through the particulate filter (i.e. the smallest particles or soot and in a very small residual amount); the detection filter is thus quasi-transparent for the flow of gas that passes through it,

If the particulate filter 10 is faulty, the detection filter blocks all particles that the particulate filter should have filtered if it had functioned properly. As the detection filter has detection capabilities (in terms of volume and number of particles that it is able to absorb), the detection filter gradually clogs up to almost no longer allow the gas to pass.

It follows that:

• If the particle filter 10 is working properly, the parameters of the gas stream at the output of the detection filter follow in time a similar evolution to that of the gas flow parameters leaving the particle filter (Figure 6, dotted line). For an operating point of the motor the flow to the detection filter will remain stable over time (Figure 7 - without soot leakage).

• If the particulate filter 10 is faulty, it will let pass a certain amount of soot more or less important depending on the size of the failure. This soot leakage will gradually seal the detection filter 14 thus increasing its resistance to flow. The variations over time of the parameters of the gas stream at the output of the detection filter 14 no longer then follow the variations of the corresponding parameters of the flow at the outlet of the particulate filter and the deflected flow will progressively tend towards zero (FIG. 6, line curve). full).

This reduction of the gas flow towards the detection filter takes place more or less rapidly depending on the amount of soot leaking from the faulty main filter (Figure 7 - light and important soot leakage). Indeed the detection filter will clog all the more quickly that the soot leak is important which will cause a decrease fast flow of deviated gases. The evolution of the deviated gas flow can be measured using known sensors such as temperature or pressure sensors or any other sensor. Figure 8 shows the example of the evolution of the deviated gas flow followed by a temperature sensor placed at the output of the detection filter.

When operating on a vehicle or on an engine, it is sufficient to:

1- Record the evolution of the parameter measured at the output or the input / output gradient of the detection filter as a function of the soot level fleeing from the particle filter and the distance traveled or the operating time (Figure 9). These data will be considered as specific reference to the application.

2- define the level of soot not to be exceeded (10 mg / km in the example of the figure

9) which will also determine the distance traveled (or the operating time) at which the output parameter or the input / output gradient of the detection filter will have reached a certain value - intersection of the horizontal line with the line 10 mg / km in Figure 9. We can consider this value of the parameter as a threshold to associate with 10mg / km of soot leakage.

3- If during the use of the vehicle the reading of the parameter at the output of the detection filter is greater than this threshold, before reaching the distance to be traveled indicated on the graph of FIG. 9 (stored in the controller and based on the calibrated data), then we can consider that the critical level of soot is exceeded and that it is necessary to send a warning signal.

The amount of soot leaking from the main filter can be determined by measuring the gas temperature gradient between the inlet and the outlet of the detection filter. Indeed, when the flow rate of the deflected gases towards the detection filter decreases because of the clogging of the latter, the temperature loss through the detection filter will tend to increase as shown in FIG. 10. While without soot leakage of the main filter, the temperature gradient between the input and the output of the detection filter remains constant. The increase in the temperature gradient is directly related to the level of soot leakage. It is therefore sufficient to characterize the temperature gradient through the detection filter over time as a function of the deviated gas flow and the level of soot emissions, to store these reference data in the engine control unit for the engine. then use them during operation of the vehicle or the engine to give the warning signal as soon as a temperature gradient corresponding to the maximum soot level tolerated is reached or exceeded. One can also consider following the same methodology but using other sensors such as gas flow sensors, pressure or other.

The evolution of the parameters of the flow towards the detection filter will of course depend on the nature and the size of the element 14. For some applications it will be advantageous to reduce its size to ensure a low resistance to flow. and thus increase the flow of the derived gases. But by reducing its size it is then possible that the evolution of the temperature after the detection filter, during its progressive clogging, is not sufficiently significant, which will reduce the accuracy of detection of the soot level fleeing the main filter 10 In order to overcome this problem, one solution consists in placing behind the detection filter 14 a dissipater element 14bis having a small pressure drop but a large capacity to absorb or exchange heat with the ambient air, FIG. to observe the evolution of temperature existing with the large detection filter but without the disadvantage of a significant loss of load.

The detection filter can be made according to the same principle and with the same materials as the particulate filter. But any other type of filter can be used, as long as it has the above properties.

It is recalled that in normal operation of the particulate filter, the parameters of the gas flow at the outlet of the particulate filter vary enormously in amplitude, as a function of the engine speed, the type of engine, etc.

This is checked for gas flow parameters such as temperature, pressure, flow rate, flow rate, oxygen concentration, etc. placed at the output and / or at the input of the detection filter. It is therefore possible to use as a measuring means at the output of the detection filter a single sensor (FIGS. 1, 2, 4, 5) such as a temperature, pressure, flowmeter, anemometer, probe or oxygen, etc. All these sensors are widely known, they have the advantage of being robust, efficient even in a difficult environment such as exhaust and do not require complex control electronics. It is also possible to use a differential measuring means, for example pressure or differential temperature (see Figure 3), comprising a first pressure sensor (or temperature) 24 upstream of the detection filter 14, a second pressure sensor (or temperature sensor) 25 downstream of the detection filter and a comparator 26 adapted to determine a pressure difference (or temperature) between the upstream and downstream of the detection filter.

To be effective, the particulate filter is regenerated regularly when the engine is running. In order to regenerate the particulate filter, the temperature of the exhaust gas is raised significantly to burn the soot absorbed by the particulate filter. As a portion of the exhaust gas exiting the particulate filter passes through the detection filter, the latter may be automatically regenerated each time the particulate filter is regenerated.

In some cases, the particulate filter is regenerated from time to time even if it fails. In this case, the detection filter must be dimensioned to clog quickly in case of failure of the particulate filter, so that it can be detected before the regeneration of the particulate filter. In such a case, a small detection filter is used.

It is also possible to improve the regeneration of the detection filter by placing it in the inlet section of the secondary line, that is to say the part of the bypass surrounded by the main flow from the particle filter, figure 12. This will take advantage of all the energy available in the gas stream to regenerate it.

Regeneration can alternatively be envisaged using a power supply using the vehicle's electrical network (not shown in the figure). This solution is however less recommended knowing that it leads to overconsumption of fuel. The present diagnostic device advantageously also comprises an alert means (not shown), for monitoring the variations in time of the parameter measured by the measuring means and producing an alert signal if the profile of the measured signal is different from a reference profile.

In one embodiment, the alerting means is a comparator, which compares the amplitude of the output parameter with a reference threshold and produces the alert signal when the magnitude of the output parameter is below the reference threshold. .

In another embodiment, the alert means comprises a memory and a comparator. In the memory is stored a reference profile corresponding to the evolution of the detected parameter as a function of time in the case of normal operation of the particulate filter. The reference profile is for example obtained by testing the vehicle in which a diagnostic device is installed, before it is put on the market. During operation of the thermal engine, the comparator continuously compares the signal supplied by the measuring means with the reference profile, and provides the alert signal when the measured signal deviates more than X% from the reference profile. X is a percentage whose value is to be adjusted according to properties desired for the diagnostic device (speed of detection of a particle filter failure, guarantee that an alert corresponds to a failure of the particulate filter, etc.). ).

Claims

1. Device for the diagnosis of a particulate filter attached to a main line of exhaust of an internal combustion engine, the diagnostic device comprising, downstream of the first particulate filter, a detection filter and a means of measuring an output parameter of the detection filter,

the detection filter being traversed by a first portion of the gases from the particulate filter, a second part of the gases from the particulate filter following the main exhaust line.

characterized in that the detection filter is placed in a secondary exhaust line extending at least partially out of the main line, the secondary exhaust line having a gas inlet and a gas outlet, the inlet of gas being connected to the main exhaust line downstream of the particulate filter.

2. Device according to claim 1, wherein the first part of the gases corresponds to 0.1 to 70% of the gases from the particulate filter.

3. Device according to claim 2, wherein the first portion of the gases corresponds to 0.1 to 5%, 10 or 15%, gases from the particulate filter.

4. Device according to any one of the preceding claims, adapted for a main exhaust line comprising an additional element such as a silencer or a resonator downstream of the particle filter, wherein the gas inlet of the secondary line. exhaust is connected to the main line downstream of the additional element.

5. Device according to any one of claims 1 to 3, adapted for a main exhaust line comprising an additional element such as a silencer or a resonator downstream of the particle filter, wherein the input of the line secondary exhaust is connected to the main line between the particulate filter and the additional element.

6. Device according to any one of the preceding claims, wherein the output of the secondary line is connected to the main line downstream of the detection filter or to an air intake line of the engine, or is left to the 'outdoors.

7. Device according to claim 4 or 5, wherein the secondary line, the input of the secondary line and the output of the secondary line are located inside the additional element.

8. Device according to any one of the preceding claims, wherein the output of the secondary line is connected to the main line downstream of the input of the secondary line.

9. Device according to one of claims 1 to 8, wherein the input of the secondary line and optionally the output of the secondary line are connected to the main line so that the pressure difference between the inlet and the outlet of the secondary line is greater than a dynamic pressure of the gases in the main exhaust line.

10. Device according to one of claims 1 to 9, wherein a section of the main line has a narrowing in the vicinity of the input of the secondary line.

11. Device according to one of claims 1 to 10, wherein the gas inlet of the secondary line is defined by an inlet section placed in the main line.

12. Diagnostic device according to any one of the preceding claims, wherein the detection filter has filtration properties such that the detection filter is clogged when the rate of particles contained in the gases from the first filter is greater than one. alert threshold.

13. Diagnostic device according to any one of the preceding claims, comprising a heat sink element (14a) having a low pressure drop placed downstream of the detection filter.

The diagnostic device of claim 1, wherein the secondary exhaust line has a gas inlet section, and wherein: the gas inlet section is positioned in the main exhaust line downstream of the particulate filter, the detection filter is arranged in the gas inlet section, and a heat sink element (14a) having a low loss charge is placed downstream of the detection filter in the section of the secondary line out of the main line.

Device according to any one of the preceding claims, wherein the measuring means is:

A temperature, flow rate, flow velocity or oxygen concentration sensor for the exhaust gas, positioned at the output of the detection filter; or

A differential measuring means, comprising a first sensor upstream of the detection filter, a second sensor downstream of the detection filter and a comparator able to determine a pressure difference between an input and an output of the detection filter.

16. Apparatus according to any one of the preceding claims, wherein the measuring means comprises a sensor downstream of the detection filter in a portion of the secondary line out of the main line.

17. A diagnostic device according to any one of the preceding claims, also comprising an alert means, for producing an alert signal if a profile of the output parameter of the detection filter is different from a reference profile.

18. A method of diagnosis of a particulate filter in a main line of exhaust of an internal combustion engine, the diagnostic device comprising, downstream of the first particle filter, a detection filter and a measuring means of an output parameter of the detection filter, the detection filter being arranged so that only a predetermined portion of the total flow of exhaust gas can pass therethrough, in which method the evolution of the output parameter is monitored the detection filter; and it is concluded that the particle filter has failed when the output parameter deviates from a calibrated reference value.

19. The method of claim 18, wherein one concludes a failure of the particulate filter when the output parameter deviates from the calibrated reference value in a monitoring period whose duration is less than a calibrated duration.

20. The method of claim 19, wherein said calibrated duration is representative of a duration of time use or mileage traveled.

The method of any of claims 18 to 20, wherein the output parameter is indicative of a measured or estimated value or a gradient of measured or estimated values.

22. A method according to any one of claims 18 to 21, wherein the detection filter is placed in a secondary exhaust line, the secondary exhaust line having a gas inlet and a gas outlet, the gas inlet being connected to the main exhaust line downstream of the particulate filter.

23. Internal combustion engine comprising a main exhaust line equipped with a diagnostic device according to any one of claims 1 to 17.