FR2853255A1 - Exhaust gas filtration structure for use in exhaust gas pollution control system, has two filtration blocks, each equipped with two faces that are arranged with respect to one another and joined by linking joint - Google Patents

Abstract

The structure has two filtration blocks (15A, 15B), each with two faces arranged with respect to one another and joined by a linking joint (17). Each face has strong adherence and weak adherence regions (33A,33B,and 35A,35B) with strong and weak adherence with the joint, respectively. The corresponding regions of the faces are arranged with respect to one another.

Description

i

  The present invention relates to a filtration structure, in particular a particle filter for the exhaust gases of an internal combustion engine, of the type comprising: - at least first and second filtration members respectively provided with a first and a second face arranged opposite one another; and - a connection joint of said faces, extending between said faces.

  Such structures are used in particular in devices for cleaning up exhaust gases from internal combustion engines. These 10 devices include an exhaust pipe comprising in series a catalytic purification device and a particle filter. The catalytic purification device is adapted for the treatment of polluting emissions in the gas phase, while the particle filter is adapted to retain the soot particles emitted by the engine.

  In known structures of the aforementioned type (see for example EP-A1 142 619), the filtration members comprise a set of adjacent conduits with parallel axes, separated by porous filtration walls.

  These conduits extend between an inlet face for the exhaust gases to be filtered and an outlet face for the filtered exhaust gases. These 20 conduits are moreover closed at one or the other of their ends in order to delimit inlet chambers opening onto the intake face and outlet chambers opening along the discharge face.

  These structures operate according to a succession of filtration and regeneration phases. During the filtration phases, the soot particles emitted by the engine are deposited on the walls of the inlet chambers. The pressure drop across the filter gradually increases.

  Beyond a predetermined value of this pressure drop, a regeneration phase is carried out.

  During the regeneration phase, the soot particles, composed essentially of carbon, are burnt on the walls of the inlet chambers in order to restore the structure to its original properties.

  However, the soot particles do not accumulate homogeneously in the filtration devices. Thus, the soot preferably accumulates in the center of the filtration structure and towards the face for discharging the exhaust gases. During the regeneration phases, the combustion of soot causes a rise in temperature in the preferential accumulation zones, greater than the rise in temperature observed in the other zones of the structure.

  The temperature gradients within the filtration structure generate local expansions of different amplitudes, and consequently, longitudinal and transverse stresses in and / or between the different filtration members.

  These high thermomechanical stresses cause cracks in the filtration elements and / or in the connection joints between these filtration elements.

  To limit the risk of these cracks appearing, patent application EP-A-1,142,619 proposes to use connection joints whose thickness 15 is chosen in the range from 0.3 to 3 mm and whose thermal conductivity is between 0.1 and 10 W / mK

  The current structures are not entirely satisfactory. Indeed, beyond a certain number of regeneration phases, cracks may appear in the connection joint. These cracks are accompanied by a total loss of cohesion in the filtration structure. This loss of cohesion leads to leaks and the structure must be replaced.

  The main object of the invention is to remedy this drawback, that is to say to provide a porous filtration structure for a particle filter allowing prolonged use of the filter.

  To this end, the subject of the invention is a filtration structure of the aforementioned type, characterized in that the first face comprises at least one first zone of strong adhesion with said seal and at least one zone of weak or zero adhesion with this joint, said zones respectively comprising a first region of strong adhesion with said joint and a region of weak or zero adhesion with this joint, said regions being disposed respectively opposite a first region of weak or zero adhesion of the second face with said seal, and a region of strong adhesion of the second face with said seal.

  The filtration structure according to the invention may include one or more of the following characteristics, taken in isolation or according to any technically possible combination: - the first face also comprises a second strong adhesion zone 5 with said seal comprising a second region of strong adhesion with said seal disposed opposite a second region of weak or no adhesion of the second face with said seal; in at least one section of the filtration structure, the region of weak or zero adhesion with said seal on the first face is disposed between the first and second regions of strong adhesion with said seal on this first face; - Said section is a longitudinal section; - Said section is a cross section; a filtration member is a prismatic brick, each of the 15 lateral faces of which is opposite a lateral face of an associated filtration member, a connection joint of said faces extending between said faces; and each of the side faces of the brick comprises at least one zone of strong adhesion of this face of the brick with said joint and at least one zone of weak or zero adhesion of this face with said joint, said zones respectively comprising a region of strong adhesion of this face of the brick with said joint and a region of weak or zero adhesion of this face with said joint, said regions being arranged respectively opposite a region of weak or zero adhesion with said joint seal of the face opposite the associated filter member and a region of strong adhesion with said seal of the face opposite the associated filter member; - The region of strong adhesion with said joint of the first face of the brick is arranged opposite a region of weak or zero adhesion with said joint of a second face of the same brick; and each of the zones of weak or zero adhesion to said joint is covered with a non-stick coating, at least before the structure is put into service.

  The term "prismatic brick" designates an assembly comprising an entry face, an exit face and at least three lateral faces which connect the entry face to the exit face. Examples of implementation of the invention will now be described with reference to the accompanying drawings in which: - Figure 1 is a perspective view of a first filtration structure according to the invention; - Figure 2 is a partial sectional view along line 11-II of the filtration structure of Figure 1; - Figure 3 is a partial exploded perspective view of the filtration structure of Figure 1; - Figure 4 is a view similar to Figure 2, after several regeneration cycles of the filtration structure; - Figure 5 is a view similar to Figure 3 of a variant of the first filtration structure according to the invention; and - Figure 6 is a view similar to Figure 2 of a second filtration structure according to the invention.

  The particulate filter 11 shown in Figure 1 is arranged in a gas exhaust line 13 of a diesel engine of a mobile auto20 vehicle, shown partially.

  This exhaust line 13 extends beyond the ends of the particle filter 11 and delimits a passage for circulation of the exhaust gases.

  The particulate filter 11 extends in a direction X-X 'longitudi25 nal exhaust gas circulation. It comprises a plurality of filtration blocks 15 connected to each other by connection seals 17.

  Each filtration block 15 is of substantially rectangular parallelepipedal shape elongated in the longitudinal direction XX ′.

  As illustrated in FIG. 2, each filtration block 15A, 15B 30 comprises a porous filtration structure 19, a face 21 for admitting the exhaust gases to be filtered, a face 23 for discharging the filtered exhaust gases, and at least four side faces 24.

  The porous filtration structure 19 is made of a filtration material consisting of a monolithic structure, in particular ceramic (cordierite or silicon carbide).

  This structure 19 has sufficient porosity to allow the passage of exhaust gases. However, as known per se, the diameter of the pores is chosen to be small enough to ensure retention of the soot particles.

  The porous structure 19 comprises a set of adjacent conduits with an axis parallel to the longitudinal direction XX ′. These conduits are separated 10 by porous filtration walls 25. In the example illustrated in FIG. 1, these walls 25 are of constant thickness and extend longitudinally in the filtration structure 19, from the inlet face 21 to the outlet face 23.

  The conduits are divided into a first group of inlet conduits 27 and a second group of outlet conduits 29. The inlet conduits 27 and the outlet conduits 29 are arranged head to tail.

  The inlet conduits 27 are closed at the discharge face 23 of the filter unit 15A, 15B and are open at their other end.

  On the contrary, the outlet conduits 29 are closed at the inlet face 21 of the filter unit 15A, 15B and open out along its discharge face 23.

  In the example illustrated in Figure 1, the inlet 27 and outlet 29 conduits have constant sections along their entire length.

  As shown in Figure 1, the side faces 24 of the filter unit located opposite another filter unit are flat. The lateral faces 31 situated opposite the exhaust line 13 are of a shape adapted to ensure contact with the cylindrical inner wall of this line 13.

  As illustrated in FIGS. 2 and 3, each of the planar faces 24 situated opposite another filtration unit comprises at least one zone 33 firmly secured to the seal 17, and at least one zone 35, which during the manufacture of the structure 19, is covered with a non-stick coating. This coating is for example based on paper, polytetrafluoroethylene, or boron nitride.

  Thus, the zone 33 constitutes a region of strong adhesion with the joint 17, while the zone 35 constitutes a region of weak or zero adhesion with the joint 17.

  The adhesion between the connection joint 17 and the flat faces 24 of the filter blocks 15 in the zones 33 of strong adhesion is at least 10 times greater than that of the zones 35 of weak or zero adhesion, this adhesion being between 0 and 50 MPa.

  For example, the arrangement of zones 33 and zones 35 on the flat faces 24 of the filter blocks 15 is illustrated in FIGS. 2 and 3.

  As shown in FIG. 2, the first planar face 24A of the first filtration block 15A successively comprises, in the longitudinal direction X-X ', a first zone 33A of strong adhesion with the seal 15 17, a zone 35A of adhesion weak or zero with the seal 17 and a second zone 33C of strong adhesion with the seal 17.

  The second filtration block 15B comprises a second face 24B, facing the first face 24A.

  This second face 24B successively comprises in the direction XX ′, a first zone 35B of weak or no adhesion opposite the first zone 33A of strong adhesion of the first face 24A, a zone 33B of strong adhesion, opposite of the zone 35B of weak or zero adhesion of the first face 24A, and a second zone 35C of weak or zero adhesion opposite the second zone 33C of strong adhesion of the first face 24A.

  In the example illustrated in FIG. 3, this relative arrangement of the zones 33 of strong adhesion and of the zones 35 of weak or zero adhesion is common to all the flat faces 24 of the same filtration block 15.

  The connection joint 17 is disposed between the planar faces 24 of the filtration blocks 30. This connection joint 17 is made on the basis of ceramic cement, generally consisting of silica and / or silicon carbide and / or nitride of aluminum. After sintering, this cement has a modulus of elasticity of around 5000 MPa. This cement fixes the filter blocks together.

  For the mounting of the structure 19, a first filtration stage is formed by assembling two by two along vertical surfaces of the filtration blocks 15 using the connection joint 17.

  A second filtration stage is then carried out according to the same process.

  In the case where the connecting joint consists of a very rigid cement, and whatever the arrangement of the zones 33 and 35 on the various faces of the blocks 15, before the first and second filtration stages are assembled together along horizontal surfaces, protections (for example cardboard boxes) are arranged between the horizontal surfaces of the bricks to cover the edges adjacent to zones of weak or zero adhesion of the vertical surfaces. Thus, the formation by the connecting joint of horizontal bridges of strong adhesion between the zones of weak or zero adhesion of the vertical surfaces is avoided.

  The operation of the first filtration structure according to the invention will now be described.

  During a filtration phase (Figure 1), the exhaust gas loaded with particles is guided to the inlet faces 21 of the filter blocks 15 by the exhaust line 13. As indicated by arrows 20 on Figure 2, they then enter the inlet conduits 27, and pass through the walls 25 of the porous structure 19. During this passage, the soot is deposited on the walls 25 of the inlet conduit 27. These soot are preferably deposited in the center of the particle filter 11 and towards the discharge face 23 of the filter blocks 15 (on the right in the drawing).

  The filtered exhaust gases escape through the exhaust pipes 29 and are guided towards the outlet of the exhaust pipe.

  When the vehicle has traveled approximately 500 km, the pressure drop across the filter 11 increases significantly. A regeneration phase is then carried out.

  In this phase, the soot is oxidized by raising the temperature of the filter 11. This oxidation is exothermic. The inhomogeneous distribution of the soot in the filter 11 causes a temperature gradient between the zones of strong accumulation of soot and zones of weak accumulation of soot.

  In addition, the filter blocks and the seals expand under the effect of temperature. The local magnitude of this expansion depends on the temperature.

  These variations in expansion amplitude, under the effect of temperature gradients, generate strong thermomechanical stresses. We believe that the system according to the present invention can, thanks to the presence of zones of weak or zero adhesion, release the stresses without creating cracks in a filtering member or in the connection joint.

  Furthermore, the zones of weak or zero adhesion and those of strong adhesion are arranged in such a way that, if the thermomechanical stresses are too strong for the structure, cracking takes place in privileged zones 41.

  Thus, as illustrated in FIG. 4, the propagation of the cracks 41 in the seals 17 is guided along the zones 35 of weak or no adhesion of the seal 17 on the flat faces 24 of the filtration blocks 15. Thus, the cracks 41 between the first filtration block 15A and the second filtration block 15B are located according to the first zone 35B of weak or no adhesion of the second face 24B, then between the right end of this zone 35B and the left end of the zone 35A of weak or zero adhesion of the first face and following this latter zone 35A of weak or zero adhesion.

  Even if the seal 17 is completely cracked in these areas 35A and 35B, a first portion 43A of the seal 17 remains integral with the first filtration block 15A following the first area 33A of strong adhesion of the first face 24A. A second portion 43B of seal 17 of shape complementary to the first portion 43A remains integral with the second filtration block 15B along the strong adhesion zone 33B of the second face 24B.

  The cooperation between these first and second portions 43A and 43B of seal 17 prevents the relative longitudinal movement of the first filter block 15A relative to the second filter block 15B towards the discharge faces 23 of the filter blocks 15A and 15B.

  Furthermore, the propagation of the cracks 41 is guided between the right end of the area 35A of weak or no adhesion of the first face 24A to the left end of the second area 35C of weak or zero adhesion of the second face 24B and following this second zone 35C.

  Even if the seal is completely cracked in these areas 35B and 35C, the first filtration block 15A remains integral with a third portion 43C of seal 17 opposite the second area 33C of strong adhesion of the first face 24A. This third portion 43C is of complementary shape to the second portion 43B of seal 17.

  This third portion 43C cooperates with the second portion 43B to prevent the relative displacement of the first block 15A relative to the second block 15B in the longitudinal direction X-X 'towards the intake faces 21 of the filtration blocks 15A and 15B.

  In this particle filter, the relaxation of the thermomechanical stresses is therefore ensured, according to their intensity, by the structure itself (in the presence of zones of zero adhesion), and by the formation of cracks 41 whose propagation is control.

  Furthermore, the propagation of these cracks 41 in the seals 17 is guided to prevent the relative displacement of the filter blocks 15 relative to each other and thus preserve the seal of the particle filter 11 relative to the soot.

  In the variant illustrated in FIG. 5, unlike the structure illustrated in FIG. 3, zones 33 of strong adhesion with the joint 17 and zones 35 of weak or zero adhesion with the joint 17, on each 25 planar faces 24 of the filter blocks 15, are arranged successively alternately along, on the one hand, directions parallel to the longitudinal direction XX 'and, on the other hand, directions parallel to the transverse directions YY' and ZZ 'perpendicular to the longitudinal direction XX '. The zones 33 and the zones 35 thus form a checkerboard structure on each face 24 of each block 15.

  Furthermore, the zones 33 of strong adhesion with the seal 17 and the zones 35 of weak or zero adhesion with the seal 17 of a face 24 of a block 15 are located respectively opposite zones 35 of weak adhesion or zero with the seal 17 and zones 33 of strong adhesion with the seal 17 of a face 24 of another block 15.

  In this structure, the relative displacement of the blocks on the one hand, in the longitudinal direction X-X 'and on the other hand, in the transverse directions Y-Y' and Z-Z 'is thus avoided.

  In the variant illustrated in FIG. 6, the central filtration block 15C successively comprises, in the direction X-X ', on a first face 24D, a single zone 33D of strong adhesion with the seal 17 and a single zone 35D of weak adhesion with the gasket 17. It also comprises, 10 on a second face 24E opposite the first face 24D, a second zone 35E of weak or zero adhesion opposite the first zone 33D of strong adhesion with the seal 17, and a second zone 33E of strong adhesion with the seal 17 opposite the first zone 35D of weak or zero adhesion with the seal 17. The filter blocks 15D and 15E located opposite 15 of the first and second faces 24D and 24E comprise zones of strong adhesion and zones of weak adhesion opposite, respectively, zones of weak adhesion 35D, 35E and zones of strong adhesion 33D, 33E of the first and second faces 24D and 24E of the central filter block 15C.

  In this example, if the seal 17 cracks, the relative longitudinal displacement of the central filter block 15C towards the discharge faces 23 is prevented by the relative arrangement of the zones of strong adhesion and zones of weak adhesion on its first face 24E. Likewise, the relative longitudinal movement of this block 15C towards the intake faces 21 is prevented by the distribution of the areas of strong adhesion and of the areas of weak or zero adhesion on its second face 24E.

  As a variant, part of a zone of strong adhesion of one face of a block can be arranged facing a part of a zone of strong adhesion of a block opposite. Likewise, a part of a zone of weak or zero adhesion of one face of a block can be arranged facing a part of a zone of weak or zero adhesion of a block opposite.

  Thanks to the invention which has just been described, it is possible to have a filtration structure which can endure a multitude of re-generation phases while preserving its mechanical cohesion and its tightness with respect to soot.

Claims (8)

  1. Filtration structure, in particular a particulate filter for the exhaust gases of an internal combustion engine, of the type comprising: - at least first and second filtration members (15A, 15B) 5 provided with a first respectively and a second face (24A, 24B) arranged opposite one another; and - a joint (17) connecting said faces, extending between said faces (24A, 24B); characterized in that the first face (24A) comprises at least a first zone (33A) of strong adhesion with said joint (17) and at least one zone (35A) of weak or zero adhesion with this joint (17) , said zones (33A, 35A) respectively comprising a first region of strong adhesion with said joint (17) and a region of weak or zero adhesion with this joint (17), said regions being respectively disposed opposite a 15 first region (35B) of weak or no adhesion of the second face (24B) with said seal (17), and of a region (33B) of strong adhesion of the second face (24B) with said seal (17) .   2. Structure according to claim 1, characterized in that the first face (24A) further comprises a second zone (33C) of strong adhesion with said seal (17) comprising a second region of strong adhesion with said seal ( 17) disposed opposite a second region (35C) of weak or no adhesion of the second face (24B) with said seal (17).   3. Structure according to claim 2, characterized in that, in at least one section of the filtration structure, the region (35A) of weak or zero adhesion with said seal (17) of the first face (24A) is disposed between the first and second regions (33A, 35C) of strong adhesion with said seal (17) of this first face (24A).   4. Structure according to claim 3, characterized in that said section is a longitudinal section.   5. Structure according to claim 3, characterized in that said section is a cross section.   6. Structure according to one of claims 1 to 5, characterized in that at least one filtration member (15) is a prismatic brick, each of the side faces (24) facing a side face (24) an associated filter member (15), a connecting joint (17) of said faces extending between said faces (24); and in that each of the side faces (24) of the brick comprises at least one zone (33) of strong adhesion of this face of the brick with said joint (17) and at least one zone (35) of adhesion weak or zero of this face (24) with said joint (17), said zones respectively comprising a region (33) of strong adhesion of this face of the brick with said joint (17) and a region (35) of adhesion weak or zero of this face (24) with said seal (17), said regions being available respectively opposite a region (35) of weak or zero adhesion with said seal (17) of face (24) facing the associated filter member (15) and a region (33) of strong adhesion with said seal (17) of the face (24) facing the associated filter member (15).   7. Structure according to claim 6, characterized in that the region 15 (33D) of strong adhesion with said joint (17) of the first face (24D) of the brick (15C) is arranged opposite to a region (35E) of weak or no adhesion with said joint (17) of a second face (24E) of the same brick (1 5C).   8. Structure according to one of claims 1 to 7, characterized in that each of the zones (35) of weak or zero adhesion with said seal is covered with a non-stick coating, at least before the commissioning of the structure.