EP2340099A1

EP2340099A1 - Particle filter devices

Info

Publication number: EP2340099A1
Application number: EP09755965A
Authority: EP
Inventors: Philippe Auroy; Anthony Briot; David Pinturaud
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2008-10-10
Filing date: 2009-10-05
Publication date: 2011-07-06
Also published as: KR20110066931A; FR2936956A1; FR2936956B1; US20110167806A1; JP2012505339A; WO2010040941A1

Abstract

The invention relates to a decontamination device for an internal-combustion engine, comprising an assembly of monolithic honeycomb elements connected by cement, each element incorporating a series of adjacent channels with mutually parallel axes, separated by porous walls, which channels are closed by plugs at either one of their ends to define inlet chambers which are open on a gas admission face and outlet chambers which are open on a gas exit face, in such a way that the gas to be filtered passes through the porous walls, said assembly being inserted in a metal jacket by means of a compacted fibrous mat. The device is such that: the cement has a three point modulus of bending rupture of between 0.5 and 6 MPa, the cement has a dynamic Young's modulus of less than or equal to 17 GPa, the mat has an average density in the compacted state of between 0.30 and 0.54, and the average thickness of the mat in the compacted state is between 2 and 8 mm.

Description

PARTICLE FILTRATION DEVICES

The present invention relates to the field of particle filtration devices from an internal combustion engine, possibly comprising a catalytic component, in particular installed in an exhaust line of a diesel engine for the removal of soot produced by combustion. fuel. Diesel engines are known to produce a large amount of soot. This results from hydrocarbon pyrolysis phenomena in the absence of oxygen even within the combustion flame and the insufficiency of the temperature within the combustion chamber to burn all the soot particles thus produced. . These soot, when emitted outside the vehicle, serve as seeds on which unburned hydrocarbons condense, thus constituting solid particles that can be inhaled and whose small size allows progression to the pulmonary alveoli.

To limit the emission of soot to the outside of the vehicle and to comply with increasingly stringent environmental standards, it is known to dispose on the exhaust line of filtration devices, possibly associated with catalytic devices, the latter having as their object the transformation of pollutant gaseous emissions into inert gases. Pollutant gaseous emissions include unburned hydrocarbons and nitrogen oxides (NO _x ) or carbon monoxide (CO).

Soot filtration devices include "particulate filters" which generally consist of a porous ceramic filter media. This support generally has a honeycomb structure, one of the faces of said structure allowing the admission of the exhaust gas to be filtered and the other side the evacuation of the filtered exhaust gas. Between these faces, the filtering structure has a set of longitudinal and parallel channels between them separated by porous walls, said channels being closed at one of their ends in order to force the exhaust gas to pass through said porous walls. For a good seal of the whole, the part Peripheral structure is surrounded by a cement called coating cement. The filter is also surrounded by a cladding, frequently called "canning" and consists of a fibrous mat and a metal shell. To provide better resistance to thermal shocks, the filters sometimes consist of an assembly of monolithic and parallelepipedic elements having a honeycomb structure, said elements being assembled using a material, called "material jointing ".

The ceramics most often used are cordierite (Mg ₂ Al ₄ Si ₂ O 8) or silicon carbide (SiC), the latter being preferred for its properties of thermal conductivity and corrosion resistance. The silicon carbide filters are preferably obtained by sintering, for example sintered silicon-bonded SiC filters or those obtained by recrystallization (R-SiC). Examples of filters are for example described in patent applications EP 816,065, EP 1 142 619, EP 1 455 923 or WO 2004/065088 which will be referred to for more details on their structure or their method of synthesis.

During engine operation, the particulate filter is loaded with soot particles, which are deposited on the porous walls. In the same way as in the combustion chamber arises the problem of the minimum temperature necessary to allow the combustion of soot. The soot being retained in the filter, the kinetics of combustion can be slower than in the combustion chamber, which allows to lower the soot combustion temperature to about 600 ⁰ C. This gain is however insufficient to ensure combustion soot within the filter over the entire operating range of the engine. It is therefore necessary to provide, following a filtration cycle, a regeneration cycle, during which the soot is burned.

The particulate filter therefore operates according to the following modes: filtration and almost simultaneous combustion of soot when the temperature of the exhaust gas permits, retention and accumulation of soot particles in the filter when the exhaust gas temperature is too high low, regeneration of the filter before the losses due to the accumulation of soot become unacceptable.

The progressive clogging of the filter during the soot retention phase in fact causes an increase in the pressure drop resulting in an increase in the consumption of the engine, or even an overpressure which can deteriorate the combustion system.

The regeneration step is done by raising the temperature of the exhaust gas using a post injection, which is to inject late into the engine cycle of the fuel that will burn in the exhaust line. During the regeneration, and because of the exothermic combustion of the soot, the filter undergoes high temperatures, and moreover inhomogeneous within the material because the soot particles are deposited preferentially in the central part of the filter as well as in its downstream part. . The filter is therefore subjected to intense radial and tangential thermomechanical stresses, capable of generating within the material micro-cracks resulting in a partial or total loss of its filtration capacity.

In general, the improvement of the filters results in obtaining a better possible compromise between the following properties for equivalent engine speeds. In particular the invention aims to provide a filtration device formed by the assembly of monolithic elements having all at once: a low pressure loss caused by a filtering structure in operation, that is to say typically when it is in the exhaust line of an internal combustion engine, both when said structure is free of soot and when it is loaded with particles, a soot storage volume high so as to reduce the frequency regeneration, a mass of the most suitable filter to ensure sufficient thermal mass to minimize the maximum regeneration temperature and gradients experienced by the filter, a strong thermomechanical resistance that is to say, allowing a longer life of the filtration device. The performance of the filtering devices comprising a filter inserted into a metal envelope by means of a fibrous mat is characterized by the following properties: the mechanical integrity of the device: the monolithic unitary elements of the filter, the fibrous mat and the metal shell must remain solid after the device has been subjected to vibration, in particular vibrations representative of those experienced by such a device in an exhaust line of an engine. Insufficient mechanical integrity can be manifested by a separation of the fibrous mat and the filter or the mat from the metal shell, or by a separation of one or more monolithic elements of an assembled filter. the sealing of the hot gases to be filtered: the soot passages through the mat, between the mat and the filter or between the mat and the metal casing must be avoided. It appears important to be able to obtain a device for solving all of the previously discussed problems, in particular a device having improved thermomechanical resistance and mechanical integrity.

The inventors have highlighted the key parameters necessary and sufficient to obtain such a device.

In its most general form, the present invention relates to a device for the depollution of an internal combustion engine, comprising an assembly of monolithic elements of the honeycomb type bonded by a grouting material, each element incorporating a set of adjacent channels of axes parallel to each other separated by porous walls, which channels are closed by plugs at one or other of their ends to define inlet chambers opening along an admission face gases and outlet chambers opening on a gas evacuation face, such that the gas to be filtered passes through the porous walls, said assembly being inserted into a metal shell by means of a compacted fibrous mat. The device according to the invention is characterized in that: the grouting material has a modulus of rupture in three-point bending between 0.5 and 6 MPa, preferably between 1 and 5 MPa, in particular between 2 and 4 MPa, the grouting material has a dynamic Young modulus less than or equal to at 17G Pa, preferably less than or equal to 10 GPa, the mat has an average density in the compacted state of between 0.30 and 0.54, preferably less than or equal to 0.50, the average thickness of the matte in the compacted state is between 2 and 8 mm. It is indeed thanks to a judicious combination between these different parameters that the filtration device according to the invention makes it possible to solve the various problems mentioned above.

The porous walls are preferably made of a ceramic material, typically cordierite (Mg ₂ Al ₄ Si ₂ O 8), aluminum titanate or silicon carbide (SiC), the latter being preferred for its thermal conductivity properties. and corrosion resistance. For the purposes of the present description, SiC-based material is understood to mean that said material comprises at least 30% by weight SiC, preferably at least 70% by weight.

SiC en masse and very preferably at least 98% SiC en masse. The material constituting the walls preferably has an open porosity of between 35 and 65%, and even more preferably between

40% and 60%. Especially in the particle filter application, too low porosity leads to a too high pressure drop. Too high a porosity, however, leads to a level of mechanical resistance that is too low. The median diameter d.sub.50, by volume, of the pores constituting the porosity of the material is preferably between 5 and 25 microns, especially between 10 and 30 microns. In general, in the targeted applications, it is generally accepted that a too small pore diameter leads to excessive pressure loss, while too large median pore diameter leads to poor filtration efficiency.

In general, the section of a monolithic element constituting the assembled structure is square, the width of the element being between 30 mm and 50 mm. Advantageously, the thickness of the walls is between 200 and 500 μm. The number of channels in the filter elements is preferably between 7.75 and 62 per cm ² , said channels having a section of about 0.5 to 9 mm ² . The channels can have various forms. They can be of identical or different shapes and dimensions, in particular of square, hexagonal, octagonal, triangular shape. The channels may for example be all square and of identical size. They may also, for example, be alternately square and hexagonal or square and octagonal. The channels may also have more complex shapes related to a corrugation of the walls, as for example described in application WO 05/016491.

The filters are preferably such that the total volume of the inlet chambers opening along the gas intake face is greater than the total volume of the outlet chambers opening on the gas evacuation face. For example, the input channels may be more numerous than the output channels (especially if the input and output channels all have the same cross-sectional area) and / or the input channels may have a surface in cross section higher than that of the output channels (especially if the number of input channels is equal to the number of output channels). Input channels, respectively output channels, means open channels in front of admission, respectively in front of discharge, gases. Such filters, known as asymmetric filters, have the advantage of being able to store a greater quantity of soot, which makes it possible to increase the time between two successive regenerations and to reduce the increase in pressure drop during the soot loading. The implementation of the invention has proved particularly advantageous in the case of these filters because the inventors have been able to demonstrate that such filters were more likely to be subjected to higher thermomechanical stresses than standard filters.

The average thickness of the grouting material is preferably between 0.5 and 4 mm, in particular at least 1 mm. For small thicknesses, the mechanical strength of the filter is low and the flatness dispersion of the monolithic elements can then generate local thermomechanical stresses and reduce stress relaxation by the grouting material. If the thickness is too high, the pressure loss of the filter becomes too strong, especially since the monolithic elements are numerous, that is to say that the number of joints in the filter section perpendicular to the axis of the filter is high.

The grouting material is understood here as a moldable composition formed by a particulate and / or fibrous mix, dry or wet, capable of setting in mass and having a sufficient mechanical strength at ambient temperature or after drying and / or heat treatment of which the temperature will not exceed the softening or subsiding temperature which defines the refracting material (s) constituting the monolithic elements. Mouldable means a composition capable of plastic deformation necessary for the display on the joint face of the monolithic elements and having a sufficient adhesion with respect to these elements so as to make them integral or to allow the manipulation of the filter assembled immediately after the grouting operation, or if necessary after heat or chemical treatment or other treatment such as ultraviolet irradiation.

The grouting material preferably comprises particles and / or fibers of ceramic or of refractory material, chosen from non-oxides, such as SiC, aluminum and / or silicon nitride, aluminum oxynitride, or from oxides, especially comprising Al ₂ O 3, SiO ₂ , Cr ₂ O 3, MgO, ZrO ₂ , or any of their mixtures.

Preferably the composition comprises at least 20% SiC. In order to promote its hardening, the grouting material preferably comprises a thermosetting resin, in an amount of at least 0.05%, and at most 5% by weight relative to the mineral filler. A setting catalyst agent for accelerating caking of the resin, preferably also in powder form, may be added to the mixture. The grouting material may include clay to promote plasticity and moldability. The grouting material may also include inorganic fibers and organic and / or inorganic binders. By organic binder is meant in particular temporary binders such as cellulose derivatives or lignin, such as carboxymethylcelluloses, dextrin or polyvinyl alcohols. Inorganic binder is understood to mean in particular chemicals such as phosphoric acid, aluminum monophosphate or sols based on silica and / or alumina and / or zirconia or optionally sintering promoters such as titanium dioxide or magnesium hydroxide or even shaping agents such as calcium stearate or magnesium stearate. The grouting material is preferably a ceramic and / or refractory cement.

Preferably, the monolithic filter elements are based on SiC and are joined by a jointing material whose thermal conductivity is greater than or equal to 0.1 W / mK for any temperature between 20 and 800 ^° C. High thermal conductivity grouting material advantageously makes it possible to homogenize the heat transfers in the filter while a low thermal conductivity, especially less than 0.1 W / mK (measurement typically performed at a temperature of 600 ^° C.) contributes to increasing the thermal gradients and thermomechanical stresses in the seal and within the filter.

The monolithic elements are preferably assembled by partial bonding, in the sense that the space between the monolithic elements may not be completely filled by the grouting material, so as to relax the thermomechanical stresses on the filter, as is for example described in applications EP 1 726 800 or FR 2 833 857. Jointing material configurations as described in WO 2005/084782 or WO2004 / 090294, which involve areas of weak or no adhesion between the material of grouting and the filter element and areas of strong adhesion between the grouting material and the filter element are also conceivable.

The assembled filter preferably has a coating cement integral with the assembled filter, in particular of the same mineral composition as the grouting material in order to reduce the thermomechanical stresses.

The pollution control device may further comprise a catalytic coating for the treatment of CO or HC and / or NOx type polluting gases.

The fibrous mat is preferably formed of inorganic fibers to impart the thermal insulation properties required by the application. The inorganic fibers are preferably ceramic fibers, such as fibers of alumina, mullite, zirconia, titanium oxide, silica, silicon carbide or nitride, or glass fibers, such as glass R. These fibers can be obtained by fiber drawing from a bath of molten oxides, or from a solution of organometallic precursors (sol-gel process). The fibrous mat is preferably non-intumescent. It is advantageously in the form of a needle felt.

The density in the compacted state of the mat depends in particular on the density of the material constituting this mat before compaction and the thickness of the mat after compaction. Mats likely to have densities in the compacted state required are for example marketed by Saffil Ltd under references 1600, 1250 or 2400 or by the company Ibiden Co., Ltd, under the references N4-1515 or N4- 1253.

In particular for non-circular section filters, the density in the compacted state and / or the thickness of the mat is advantageously non-uniform, in the sense that it can vary according to the zone of the space formed between the filter and the metal envelope. During regenerations, this type of filter is indeed likely to have a temperature heterogeneity at its periphery. The difference between the temperature of certain zones of the periphery of the filter and the temperature at the center of the filter may thus be 20% or more greater than the average difference between the peripheral temperature and the temperature in the center of the filter, and this heterogeneity temperature is likely to result in high concentrations of highly localized stresses in these areas. In order to favorably distribute the thermomechanical stresses, the density of the mat is therefore preferably lower than the average density and / or the thickness of the mat is preferably higher than the average thickness in contact with the areas where the stresses can be concentrated. thermomechanical during the regeneration phases. In order to optimally optimize the overall thermomechanical resistance of the filtration device according to the invention, the thickness of the mat in the compacted state at the peripheral zones of the filter subjected to the highest thermomechanical stresses is preferably at least 20%, in particular at least 50% and even at least 100% higher than the thickness of the mat at the peripheral zones subjected to the lowest thermomechanical stresses. Alternatively or cumulatively, the density compacted at the level of the peripheral zones of the filter subjected to the lowest stresses is preferably at least 20%, especially at least 50% and even at least 100% higher than the density in the areas subject to the most strong constraints. The "shrinking" method (by contraction of the metal envelope around the mat) makes it possible to modulate the density and / or the thickness of the mat, by creating zones of lower density and / or of greater thickness in these areas. areas likely to be the most affected by this concentration of constraints. In the case of an ellipsoidal or substantially ellipsoidal filter, it is particularly preferable that the density of the mat be lower and / or the thickness of the mat higher at the ends of the small and long axes of the ellipse, these ends being the most subject to thermomechanical stresses during regeneration.

In the case where the density in the compacted state is not uniform, the measurement made corresponds to an average value. The average thickness of fibrous mat, in the compacted state, is determined on the filter placed in its metal envelope, by calculating the average of 4 thickness measurements made in a plane perpendicular to the filter axis in 4 segments. two straight lines perpendicular to each other and passing to the geometric center of the filter. The density of the mat in the compacted state can be measured in the following way: the filter surrounded by its mat is taken out of its metallic envelope then unrolled so as to be able to measure its surface, and weighed in order to measure its surface density in g / cm ² . The density in the compacted state is obtained by dividing the surface density determined previously by the average mat thickness in cm.

The insertion into the metal casing can be done according to various methods known to those skilled in the art. We can cite the so-called "tourniquet" methods, shrinking, the "clamshell" method or the "stuffing" method. The fracture modulus of the grouting material is measured at room temperature on a specimen of dimensions 150 ^* 25 ^* 25 mm ³ . The 3-point flexural mounting according to the NF B41-104 standard is achieved with a distance of 120 mm between the two lower supports and the speed of descent of the punch is equal to 0.5 mm / min. The value is an average resulting from three successive measurements.

The dynamic Young's modulus is measured, in accordance with the ASTM C1259-01 standard, on test pieces of the same dimensions as above with an apparatus marketed under the reference Grindosonic MK5 by J.W. Lemmens. The dynamic Young's modulus is determined by measuring the natural bending vibration frequency at the ambient temperature of a sample of the "dynamic" mode seal material. The test specimen is placed on two rubber-like supports so as not to interact with the vibration mode of the sample to be tested. The supports are placed symmetrically with respect to the center at mid-length of the test piece. The distance between supports is 100mm. The test piece is excited by a mechanical pulse as close as possible to its center on its upper face opposite the bearing surface on the supports, for example by means of a stick or a pencil or a small hammer supplied with the device, because the necessary energy of excitation is weak. This excitation induces a vibration within the material of the specimen. A piezoelectric detector placed in contact with the specimen then records this vibration and converts it into an electrical signal from which the natural vibration frequency is displayed.

The dynamic Young's modulus E (in GPa) is then calculated as a function of the mass m (in g) of the specimen and the bending resonance frequency f (in Hz) according to the following formula:

E = 9,1584.10 ^"9 xmx / ² All measurements (density, thickness, modulus of rupture and

Young) are performed at room temperature.

For module measurements, the grouting material specimen is prepared by molding the composition, and then undergoes the same treatment (eg heat treatment) as that experienced by the grouting material when used to assemble the elements. monolithic between them, and finally drying at 110 ⁰ C before cooling to room temperature.

The invention and its advantages will be better understood on reading the examples which follow. It is understood that these examples should only be considered, in any of the aspects described, as limiting the present invention.

Figures 1 and 2 show diagrammatically non-circular filters 1, formed from a plurality of elements 2. The hatched areas 3 represent the peripheral areas for which the temperature difference with the temperature in the center of the filter is likely, during a regeneration, to be 20% or more greater than the average difference between the peripheral temperature and the temperature at the center of the filter. This heterogeneity of temperature is likely to lead to high concentrations of highly localized stresses in these areas. It is therefore interesting that the density of the mat is lower near this area, or the thickness of the larger mat.

Examples of realization

In the examples which follow, was synthesized a series of filtering devices according to the invention and illustrating its advantages over another series of devices given for a comparative purpose and do not meet the criteria of the invention.

All the monolithic filtering elements were synthesized according to the following method. In a kneader, silicon carbide powders, a polyethylene blowing agent and an organic methylcellulose binder were first blended. Water is added and kneaded to obtain a homogeneous paste whose plasticity allows the extrusion through a die of monolithic honeycomb structures of square section whose dimensional characteristics are given in Table 1.

The green microwaves are then dried for a time sufficient to bring the water content not chemically bound to less than 1% by weight.

The channels of each face of the blocks are alternately plugged according to well-known techniques, for example described in application WO 2004/065088. The elements are then cooked according to a rise in temperature of 20 ° C./hour until a temperature of the order of 2200 ^° C. is reached which is maintained for 2 hours.

Finally, we obtain a series of monolithic filtering elements in silicon carbide whose microstructural characteristics are substantially identical.

Table 1

In accordance with the teaching of patent application EP 816 065,

16 monolithic filter elements are then assembled together by gluing using a ceramic grouting material and then machined to form filters of appropriate diameter. The thickness of the grouting material is 1 mm.

In the case of comparative examples C1 to C3 and of the example according to the invention 1, the grouting material is prepared by mixing the composition J1:

81% by weight of a SiC powder having a particle size of between 10 and 200 μm,

4% by weight of a calcined alumina powder whose median diameter is approximately 5 microns, marketed by Almatis, - 8% by weight of a reactive alumina powder having a median diameter of approximately 3 micrometers marketed by Almatis, 6% silica fume of the Elkem 971 type

0.8% by weight of a temporary binder and plasticizer of the cellulose type,

0.2% by weight of a deflocculant of the TPPNa type (sodium tripolyphosphate). An amount of water corresponding to approximately 15% of the weight of this mixture is added to obtain a paste of adequate viscosity.

After machining the filter, a coating cement of the same mineral composition as that of the grouting material is applied to the cylindrical and volume filters of the order of 2.48 liters. The assembled filter is then subjected to a heat treatment under air at 750 ⁰ C with maintaining the maximum temperature for 2 hours. In the case of Comparative Example C3, the heat treatment was carried out at a temperature of 950 ^° C. instead of 750 ° C., which has the effect of increasing the fracture and Young moduli of the grouting material. In the case of comparative example C4 and examples according to the invention 2 and 3, the grouting material is prepared by mixing the following composition J2:

67% by weight of a SiC powder of particle size between 10 and

200 microns, - 3% by weight of a reactive alumina powder marketed by Almatis, whose median diameter is about 3 micrometers.

24% of hollow spheres marketed by Enviro-spheres under the name "e-spheres", which have a typical chemical composition comprising 60% SiO 2 and 40% Al 2 O 3 and a median diameter of the order of 100 μm,

6% silica fume of the Elkem 971 type,

0.8% by weight of a temporary binder and plasticizer of the cellulose type,

After machining the filter, a coating cement of the same mineral composition as that of the grouting material is applied to the filters of cylindrical shape and volume of the order of 2.48 liters. The assembled filter is then subjected to heat treatment in air at 950 ^° C. with the maximum temperature maintained for 2 hours.

The filters are then coated with different fibrous mats and then inserted into their metal casings in accordance with the teaching associated with FIG. 5 of patent application EP 1 382 374 (so-called "tourniquet" method) in order to obtain densities at 1 compacted state and compacted matte thicknesses reported in Table 2.

The metal casing consists of two parts formed from sheets of 13% chromium refractory stainless steel 1.5 mm thick.

The devices thus obtained were subjected to the following characterization tests.

A) Thermomechanical resistance control

The devices are mounted on an exhaust line of a direct injection diesel 2.0 L engine running at full power (4000 rpm) for 30 minutes and then disassembled and weighed to determine their initial mass. The devices are then reassembled on the engine bench with a speed of 3000 rpm and a torque of 50 Nm for different times to obtain a soot load of 8 g / liter (by volume of the filter). The devices thus loaded are reassembled on the line to undergo a severe regeneration thus defined: after stabilization at an engine speed of 1700 revolutions / minute for a torque of 95 Nm for 2 minutes, a post-injection is performed with 70 ° phasing for a post-injection flow rate of 18mm ³ / stroke. Once the soot combustion initiated, more precisely when the pressure drop decreases for at least 4 seconds, the engine speed is lowered to 1050 revolutions / minute for a torque of 40 Nm for 5 minutes to accelerate the combustion of soot . The devices are then subjected to an engine speed of 4000 rpm for 30 minutes to remove the remaining soot.

The regenerated filters are inspected after cutting to reveal the possible presence of cracks visible to the naked eye. Resistance Thermomechanical filter is appreciated in view of the number of cracks, a small number of cracks reflecting a thermomechanical resistance acceptable for use as a particulate filter.

As reported in Table 2, the following scores were assigned to each of the filters:

+++: presence of numerous fissures, ++: presence of numerous cracks, +: presence of some cracks,

: no cracks or rare cracks. The severe regeneration is characterized by particularly extreme conditions, the presence of some cracks (note "+") is acceptable. The notes "++" and "+++" are however representative of a bad thermomechanical resistance.

B) Integrity control method

The device comprising the filter with its metal envelope and its fibrous mat is placed on an electrodynamic bench equipped with accelerometers placed at different locations. A first accelerometer is placed in contact with the filter in the center of one of its flat faces, a second accelerometer being placed on the metal casing of the cladding. These two at least bi-axis accelerometers make it possible to measure the vibration in the direction of the axis of the filter as well as the radial vibrations and any decoupling between the filter and its cladding and to control the stability of the fixation of the filter sheathed on the bench. electrodynamics. The filter is subjected to a vibration cycle at a frequency of 185 Hz comprising successive stages of 15 minutes each corresponding to a given acceleration. The first stage corresponds to an acceleration of 5G, the second to an acceleration of 10G, the acceleration then being increased in steps of 10G for each successive stage. This vibration test can be carried out on an electrodynamic bench marketed by LDS Test and Measurement LLC, with a capacity of 35KN and equipped with a hydraulic ram of maximum effort 10KN, working in the frequency range 0-500 Hz and a hydraulic plant with 200 bars and flow rate 21 L / min. The device is then subjected to a filtration efficiency test. The filtering efficiency of the filter device after vibration test is determined by measuring the amount of smoke emitted at the outlet of the filter relative to the input quantity. To do this, a smoke meter is placed upstream and downstream of the filter device, the latter being disposed on an exhaust line of a diesel engine. The smoke meter is used to determine the amount of soot particles emitted through a measurement of blackening due to smoke. When measuring, the motor is preferably placed at its operating point corresponding to its maximum power. If the filter device has the characteristics of sufficient integrity, the filtration efficiency index must remain above 85%.

Table 2 below shows, for the comparative examples C1 to C4 and the examples according to the invention 1 to 3 the following properties: the nature of the grouting material (J1 or J2, according to the codes given above), the temperature (in ⁰ C) and the duration (in hours) of the heat treatment after assembly, the modulus of rupture, called "MOR", measured according to the method described above, and expressed in MPa, - the dynamic Young's modulus, called "MOE", measured according to the method described above, and expressed in GPa, the density of the mat in the compacted state, measured according to the method described above, the average thickness of the mat in the compacted state, measured according to the method described above, and expressed in mm, the results of the thermomechanical resistance test, the results of the integrity check test after vibration; the symbol "X" means that the integrity of the filter has not been affected by the test, the abbreviation "0" signifying the opposite, - the efficiency of the filter after integrity control test, expressed in%.

Table 2

The various examples and comparative examples illustrate the fact that the four essential characteristics of the invention must be respected simultaneously, therefore in combination, in order to solve all of the aforementioned technical problems. The choice of a mat density in the compacted state that is too high (example C1) results in a very low thermomechanical resistance, illustrated by the presence of numerous cracks after severe regeneration, despite the choice of a low modulus grouting material. Breakup and Young. It is the same when the matte thickness in the compacted state is too low (example C2), despite the choice of an adequate density. Conversely, too low a density (example C4) is detrimental to obtaining good integrity: the filter obtained is not resistant to strong vibrations, which leads to a separation of the various elements of the device and a significant decrease in filtration efficiency. Finally, the choice of a suitable thickness and mat density does not make the filter acceptable in terms of thermomechanical resistance if, moreover, the fracture and Young moduli of the grouting material are too high (example C3). As illustrated by the examples according to the invention 1 to 3, it is indeed the combination, on the one hand, of a mat having an adequate density and thickness, and, on the other hand, of a jointing material having modules Young and suitable break that allow to obtain a really powerful filtration device.

The preceding description makes it possible to illustrate a few possible embodiments of the invention. It is understood that this description is however not limiting and that the skilled person is able to achieve other variants of the invention without departing from its scope.

Claims

1. A device for the depollution of an internal combustion engine, comprising an assembly of monolithic elements of the honeycomb type bonded by a grouting material, each element incorporating a set of adjacent channels of axes parallel to each other separated by porous walls, which channels are closed by plugs at one or other of their ends to define inlet chambers opening along a gas inlet face and outlet chambers opening on a gas evacuation face, such that the gas to be filtered passes through the porous walls, said assembly being inserted into a metal casing by means of a compacted fibrous mat, characterized in that: the grouting material has a modulus of three-point bending fracture between 0.5 and 6 MPa, the grouting material has a dynamic Young's modulus less than or equal to 17G Pa, the mat has an average density the compacted state of between 0.30 and 0.54, - the mat average thickness in compacted state is between 2 and 8 mm.

2. Device according to claim 1, such that the modulus of rupture is between 1 and 5 MPa, in particular between 2 and 4 MPa.

3. Device according to one of the preceding claims, such that the dynamic Young's modulus is less than or equal to 10 GPa.

4. Device according to one of the preceding claims, such that the average density in the compacted state is less than or equal to 0.50.

5. Device according to one of the preceding claims, such that the porous walls are made of a ceramic material based on silicon carbide (SiC).

6. Device according to the preceding claim, such that the thermal conductivity of the grouting material is greater than or equal to 0.1 W / mK between 20 and 800 ⁰ C.

7. Device according to one of the preceding claims, such that the average thickness of the grouting material is between 0.5 and 4 mm.

8. Device according to one of the preceding claims, such that the monolithic elements are assembled by partial gluing.

9. Device according to one of the preceding claims, such that the density in the compacted state and / or the thickness of the mat is non-uniform, especially such that the density of the mat is lower than the average density and / or the The thickness of the mat is higher than the average thickness in contact with the zones where the thermomechanical stresses can be concentrated during the regeneration phases.

10. Device according to the preceding claim, such that the thickness of the mat in the compacted state at the peripheral zones of the filter subjected to the highest thermomechanical stresses is at least 20%, especially at least 50% and even at least 100%. higher than the thickness of the mat at the peripheral zones subjected to the lowest thermomechanical stresses and / or the density of the mat in the compacted state at the peripheral zones of the filter subjected to the lowest stresses is at least 20%, in particular at least 50% and even at least 100% higher than the density in the areas with the highest stress.

11. Device according to one of the preceding claims, further comprising a catalytic coating for the treatment of pollutants of CO or HC and / or NOx type.