Claims

[Claim 1] Device for cooling a turbine ring (1),

including:

- at least one annular flange (33, 34) configured to be fixed to an annular radial flange (32) of a ring support structure (3) by being arranged upstream of the turbine ring (1), and comprising at least one cooling air circulation channel (33a, 34a),

- a diffuser (40) configured to be fixed to said annular radial flange (32) downstream of the annular flange (33, 34) and comprising at least one inlet channel (40a) in fluid communication with the circulation channel (33a , 34a) of the annular flange (33, 34), and comprising an injection cavity (41) comprising a plurality of injection holes (421) and being configured to inject onto a radially outer face (12b) of the ring (10), via the injection holes (421), cooling air coming from the intake channel (40a),

- a particulate filter (50) disposed on an inlet section (E) of the circulation channel (33a, 34a) of the annular flange (33, 34), the particulate filter (50) comprising a plurality of orifices ( 50a), the diameter of these orifices (50a) being smaller than the diameter of the injection holes (421) of the diffuser (40).

[Claim 2] Device according to claim 1, comprising a cooling circuit, the cooling circuit comprising the inlet section (E), the circulation channel (33a, 34a), the inlet channel (40a) and the injection cavity (41), said circuit having a variable section and comprising a section for calibrating the flow rate of cooling air, the calibration section being a section of minimum diameter of the cooling circuit.

[Claim 3] Device according to claim 1 or 2, in which a total passage section of all the orifices (50a) of the particulate filter (50) is between 1.5 and 5 times greater than the calibration section.

[Claim 4] Device according to any one of claims 1 to 3, in which the annular flange is a first flange (34), and the circulation channel is a first channel (34a), the device further comprising at least one second annular flange (33) configured to be fixed to the first flange (34) and to an upstream radial attachment flange (14) of the ring (10) by being interposed between said first flange (34) and said radial flange d upstream attachment (14), the second annular flange (33) comprising a second circulation channel (33a) for cooling fluid in

fluid communication with the first channel (34a) and the inlet channel (40a) of the diffuser (40).

[Claim 5] Device according to claim 4, in which the diameter of the second circulation channel (33a) is smaller than the diameter of the first circulation channel (34a) and defines the calibration section.

[Claim 6] Device according to any one of Claims 1 to 5, in which the particulate filter (50) has a round shape.

[Claim 7] Device according to any one of Claims 1 to 6, in which the particulate filter (50) comprises an attachment portion (51) fixed to the annular flange (33a, 34a) around the inlet section ( E), and a filter portion (52) comprising the plurality of orifices (50a).

[Claim 8] Device according to claim 7, in which the fixing portion (51) has a flat shape, and the filtering portion (52) has a convex shape, the convexity being directed towards the outside of the circulation channel ( 33a, 34a).

[Claim 9] Device according to any one of Claims 1 to 8, in which the axis of the orifices (50a) of the filter (50) is inclined with respect to a central axis (A) of the filter (50).

[Claim 10] An assembly comprising a turbine ring (1) extending about a central axis, a ring support structure (3), and a cooling device according to any preceding claim, the turbine ring (1) comprising an annular base (12) having a radially inner face (12a), defining an air flow path (F), a radially outer face (12b), and two radial attachment flanges (14, 16) arranged at the upstream and downstream ends, along the central axis, of the annular base (12).

[Claim 11] Turbine comprising the assembly according to

claim 10.

Title of Invention: Improved Aircraft Turbine Ring Cooling Device

Technical area

[1 ] This presentation concerns the field of turbomachine turbines,

in particular a turbine ring sector cooling device made of ceramic matrix composite material, as well as a turbine comprising such a device.

Prior technique

[2] In turbomachine turbines, in particular high pressure turbines, but also low pressure turbines, comprising entirely metallic elements, it is necessary to cool all the elements and in particular the high or low pressure turbine ring which is subjected to the hottest flows. In particular, this cooling can be carried out by means of a cooling circuit comprising a diffuser making it possible to cool the ring and to limit the thermal gradients, by impact of a jet of cooling air on the radially external wall. of this ring. This injection of cooling air into a cavity external to the hot air flow passage also makes it possible to pressurize this cavity, thus limiting the risk of reintroduction of hot air coming from the passage.

[3] This cooling has a significant impact on engine performance since the cooling flow used is taken from the main flow of the engine, for example in a high pressure compressor stage. Furthermore, the use of metal for the turbine ring limits the possibilities of increasing the temperature at the level of the turbine, and therefore limits the possibilities of improving the performance of the engine.

[4] In an attempt to solve these problems, it was envisaged to carry out

turbine ring sectors made of ceramic matrix composite material (CMC)

replacing the use of metallic material. CMC materials have good mechanical properties making them suitable for forming structural elements and advantageously retain their properties at high temperatures. The use of CMC materials has advantageously made it possible to reduce the cooling flow to be imposed during operation and therefore to increase the performance of the turbomachines. In addition, the use of CMC materials advantageously makes it possible to reduce the mass of the turbomachines and to reduce the hot expansion effect encountered with the metal parts.

[5] In order to nevertheless maintain sufficient cooling of the CMC ring, while limiting the quantity of cooling air necessary, the diameter of the injection holes present in the diffuser and allowing the injection of cooling air by air jet impact on the wall of the ring, can be reduced. The reduction of this diameter makes it possible, at a given flow rate, to increase the speed of impact of the air on the ring and thus to improve the efficiency of the heat exchanges and therefore of the cooling of the CMC ring.

[6] However, having injection holes of smaller diameters

increases the risk of clogging these holes with particles, such as grains of sand. In such a situation of obstruction of the injection holes, the CMC ring could no longer be sufficiently cooled. The cavity external to the hot air flow stream could no longer be sufficiently pressurized, consequently increasing the risk of reintroduction of hot air coming from said stream, and the risk of significant thermal stresses.

These phenomena could cause damage to the ring, the turbine and, by extension, the engine.

[7] In this context, there is therefore a need for a device allowing

to improve the cooling of turbine parts subject to significant temperature gradients, such as high or low pressure turbine rings, without reducing engine performance.

Disclosure of Invention

[8] In order to at least partly solve the drawbacks mentioned above, this presentation relates to a turbine ring cooling device,

including:

- at least one annular flange configured to be fixed to an annular radial flange of a ring support structure by being arranged upstream, with respect to a direction of circulation of an air flow, of the ring of turbine, and comprising at least one cooling air circulation channel,

- a diffuser configured to be fixed to said annular radial flange downstream of the annular flange and comprising at least one inlet channel

fluid communication with the circulation channel of the annular flange, and comprising an injection cavity comprising a plurality of injection holes and being configured to inject on a radially outer face of the ring, via the injection holes, cooling air from the intake channel,

- a particulate filter arranged on an inlet section of the circulation channel of the annular flange, the particulate filter comprising a plurality of orifices, the diameter of these orifices being smaller than the diameter of the injection holes of the diffuser.

[9] In this presentation, the terms "upstream" and "downstream" are defined in relation to the direction of circulation of the air flow within the turbine, this air flow being in particular a flow of hot air flowing in the air stream delimited by the radially inner face of the turbine ring, inside which the rotor blade is arranged. Furthermore, the terms "radially internal" and "radially external" are defined with respect to the radial direction of the ring,

perpendicular to the central axis of the ring.

[10] The turbine ring may comprise a plurality of ring sectors, preferably comprising a ceramic matrix composite (CMC), and assembled together to form the turbine ring. The annular flange is a separate part of the ring, fixed to an annular radial flange of a ring support structure, this structure itself serving to support the ring. More specifically, the annular flange is an upstream flange dedicated to taking up the force of the high pressure distributor (DHP). The annular flange upstream of the turbine ring is free from any contact with the ring and configured to transmit a maximum of axial force induced by the DBH directly into the ring support structure without passing through the ring CMC.

[1 1 ] The cooling air can be taken from upstream of the turbine, by

example at the bottom of the combustion chamber, in particular a cavity bypassing the chamber, in a region where the air is cooler than the air flowing in the hot air flow path, defined by the wall radially inner of the turbine ring. This cooling air is then routed to the inlet section of the circulation channel of the flange, via, for example, a pipe extending between the sampling region and said inlet section, arranged at the upstream end of said flange. In particular, the high air pressure in this bypass cavity makes it possible to circulate the air in the pipe and to convey it to the inlet section of the flange.

[12] By “in fluidic communication”, we understand that the air of

Cooling entering through the inlet section of the annular flange circulation channel flows along the circulation channel of the flange, then along the inlet channel of the diffuser, to the injection holes. It is further understood that the injection cavity of the diffuser comprises a wall comprising the injection holes, this wall being opposite the radially outer face of the ring, so that the air present in the injection cavity of the diffuser can be injected onto the radially outer face of the ring. The impact of the cooling air on said radially outer face thus makes it possible to limit the increase in temperature of the ring, caused by the hot air circulating in the hot air stream, along the radially inner face. of the ring.

[13] The presence of the particulate filter on the inlet section of the flange allows on the one hand, thanks to the presence of the holes, to allow the air to

cooling to enter the circulation channel of the annular flange and to be routed to the injection holes. On the other hand, given the fact that the particulate filter orifices have a smaller diameter than the diameter of the injection holes, particles can be blocked by the particulate filter before they can reach the diffuser, thus preventing these particles from blocking the injection holes. The fact that this filter is arranged on a flange upstream of the ring facilitates maintenance operations, during which the filters are cleaned, their arrangement being more accessible than the injection holes located inside the diffuser .

[14] In certain embodiments, the device comprises a cooling circuit, the cooling circuit comprising the inlet section, the circulation channel, the intake channel and the injection cavity, said circuit having a section variable and comprising a section for calibrating the flow rate of cooling air, the calibration section being a section of minimum diameter of the cooling circuit.

[15] At a given cooling air flow velocity, the cooling air flow is determined by the passage section of the channel in which this cooling air flows. Consequently, the flow section of the cooling circuit being variable, the flow rate is therefore calibrated by the section of the circuit having the lowest value. The presence of the calibration section, by choosing the value of the minimum diameter section, thus makes it possible to set a desired flow rate, depending on the cooling needs of the turbine ring.

[16] In certain embodiments, a total passage section of all the orifices of the particulate filter is between 1.5 and 5 times greater than the calibration section.

[17] “Total passage section” means the sum of the passage sections of each orifice of the particulate filter. It is thus possible to have a total passage section through the filter sufficiently greater than the calibration section, and the total section of the injection holes of the diffuser, so as not to restrict the cooling flow of the ring, while having filter orifices of a diameter slightly smaller than that of the injection holes of the diffuser. Thus, between two cleanings of the particle filter, a sufficient flow of cooling air can be maintained, even if some

particulate filter holes are blocked. These particles stuck in the filter can be removed during engine cleaning.

[18] In some embodiments, the annular flange is a first flange, and the circulation channel is a first channel, the device further comprising at least one second annular flange configured to be attached to the first flange and to a radial flange for attachment upstream of the ring, being interposed between said first flange and said radial attachment flange, the second annular flange comprising a second cooling fluid circulation channel in fluid communication with the first channel and the inlet channel of the diffuser.

[19] In other words, the cooling circuit includes the section

inlet, the first circulation channel of the first flange, the second circulation channel of the second flange, the inlet channel of the diffuser, then the injection cavity. Preferably, the second flange is also fixed to the annular radial flange of the ring support structure, being interposed between the first flange and said flange. Thus, the second flange is fixed both to the annular radial flange of the ring support structure, and to the radial attachment flange upstream of the ring. The second annular flange makes it possible in particular to provide axial sealing between the CMC sectorized turbine ring and the annular casing of the support structure.

[20] In some embodiments, the diameter of the second circulation channel is smaller than the diameter of the first circulation channel and defines the calibration section.

[21] In other words, the first circulation channel of the first flange, having a larger diameter, serves as a flowing orifice making it possible to process a maximum of particles upstream via the particulate filter. Conversely, the second circulation channel of the second flange, having a smaller diameter, serves as a calibration orifice, making it possible to calibrate the flow of cooling air injected downstream via the injection holes of the diffuser. The calibration and filtration functions are thus performed by separate parts of the ring and of the ring support structure, without having to modify the structure of the ring support or of the ring.

[22] In some embodiments, the length of the second channel is shorter than the length of the first channel. In other words, the length of the calibrating hole is shorter than the length of the output hole. This makes it possible to limit the head losses occurring in the second circulation channel, defining the flow rate.

[23] In some embodiments, the filter is welded or brazed to the inlet section of the flow channel.

[24] In some embodiments, the filter has a round shape.

[25] The cooling fluid flow channels preferably being of circular section, the use of a filter having a round shape similar to that of the channels, facilitates the manufacture of this filter.

[26] In some embodiments, the filter includes an attachment portion attached to the annular flange around the inlet section, and a filter portion including the plurality of orifices.

[27] Preferably, the fixing portion does not have an orifice. The fixing portion makes it possible to hold the filter against the upstream wall of the annular flange, in particular of the first annular flange. In other words, the fixing portion is fixed, by being welded or brazed, to the upstream wall of the flange, the fixing surface between the fixing portion and the flange surrounding the inlet section so that the filtering portion comprising the orifices either facing said inlet portion. This improves the efficiency of particle filtering.

[28] In some embodiments, the fixing portion has a planar shape, and the filtering portion has a convex shape, the convexity being directed towards the outside of the circulation channel.

[29] The flat surface of the fixing portion makes it possible to increase the contact surface between said fixing portion and the wall of the flange, thus improving the holding of the filter against the flange. Furthermore, the convex or domed shape of the filtering portion of the filter makes it possible to limit the risk of the particles pressing against the filter and remaining blocked in its orifices. Indeed, the slope of the surface of the filter, in particular of the filtering portion, makes it possible to cause the particles to slide along this surface, then along the flange.

[30] In some embodiments, the axis of the filter orifices is inclined with respect to a central axis of the filter.

[31 ] When the filter has a circular shape, the central axis of the filter is the axis passing through the center of the circle. When the filter is attached to the inlet section, the central axis of the filter is coaxial with the central axis of the first circulation channel. Preferably, the axis of the orifices is inclined so as to present a direction opposite to the direction of gyration of the flow of the air in this zone of the engine. This makes it possible to limit the risk that the orifices of this filter will become clogged.

[32] In some embodiments, the diffuser injection holes

have a diameter of less than 1 mm.

[33] The injection holes may for example have a diameter equal to 0.5 mm. These values ​​make it possible to obtain a high air impact velocity on the radially outer wall of the ring, thus increasing the heat exchanges and therefore the cooling efficiency of the CMC ring.

[34] This presentation also relates to a set comprising a

a turbine ring extending around a central axis, a ring support structure, and a cooling device according to any of the preceding embodiments, the turbine ring comprising an annular base having a face radially internal, defining an air flow vein, a radially outer face, and two radial attachment flanges arranged at the upstream and downstream ends, along the central axis, of the annular base.

[35] The turbine ring is preferably made of CMC.

[36] This presentation also relates to a turbine comprising

the assembly according to the present disclosure, the turbine possibly being a high or low pressure turbine.

[37] This presentation also relates to a turbomachine comprising the turbine according to this presentation.

Brief description of the drawings

[38] The invention and its advantages will be better understood on reading the

detailed description given below of various embodiments of the invention given by way of non-limiting examples. This description refers to the pages of appended figures, on which:

[39] [Fig. 1] Figure 1 is a perspective view of a turbine ring assembly according to the present disclosure;

[40] [Fig. 2] Figure 2 shows an exploded sectional view of a turbine ring cooling device according to the present disclosure;

[41] [Fig. 3A-3B] Figure 3A shows a perspective view of a

diffuser, and FIG. 3B represents a view of the diffuser of FIG. 3A according to the direction INB;

[42] [Fig. 4] Figure 4 shows an enlarged perspective view of

the ring assembly of Figure 1, in particular the first annular flange, without a particle filter;

[43] [Fig. 5] Figure 5 shows an enlarged perspective view of

the ring assembly of Figure 1, in particular the first annular flange, with a particle filter;

[44] [Fig. 6A-6C] Figure 6A shows a perspective view of a particle filter according to a first embodiment, Figure 6B shows a perspective view of a particle filter according to a second embodiment, Figure 6C shows a perspective view of a particle filter according to a third embodiment;

[45] [Fig. 7] Figure 7 shows a sectional view, along the section plane

VII-VII, of the particle filter of FIG. 6B;

[46] [Fig. 8] Figure 8 shows a sectional view, along the section plane

VIII-VIII, of the particulate filter of FIG. 6C.

Description of embodiments

[47] The remainder of the description refers to a high pressure turbine.

Nevertheless, this example is not limiting, the invention being able in particular

apply to a low pressure turbine. Figure 1 shows a high pressure turbine ring assembly comprising a turbine ring 1 made of ceramic matrix composite (CMC) material and a metallic ring support structure 3. The turbine ring 1 surrounds a set of blades rotary (not shown). The turbine ring 1 is formed of a plurality of ring sectors 10, only one of which is visible in FIG. 1. The arrow D A indicates the axial direction of the turbine ring 1 while the arrow D R indicates the radial direction of the turbine ring 1. For reasons of presentation simplification, FIG. 1 is a partial view of the turbine ring 1 which is in reality a complete ring.

[48] ​​Each ring sector 10 has, according to a plan defined by the

axial D A and radial D R directions , a section substantially in the shape of the inverted Greek letter p. The section indeed comprises an annular base 12 and flanges, or annular radial attachment tabs upstream and downstream, respectively 14 and 16. The terms "upstream" and "downstream" are used here in reference to the flow direction of the flow gas in the turbine represented by the arrow F in FIG. 1. The legs of the ring sector could have another shape, the section of the ring sector having a shape other than p, such as for example a K shape or a O.

[49] The annular base 12 comprises, in the radial direction D R of the ring 1, an internal face 12a and an external face 12b opposite to each other. The inner face 12a of the annular base 12 is coated with a layer 13 of abradable material to define a gas stream flow path in the turbine.

The terms "internal" and "external" are used here in reference to the radial direction D R in the turbine.

[50] The radial attachment flanges upstream and downstream 14 and 16 extend projecting, in the direction D R , from the outer face 12b of the annular base 12 at a distance from the upstream and downstream ends 121 and 122 of the annular base 12. The radial attachment flanges upstream and downstream 14 and 16 extend over the entire width of the ring sector 10, that is to say over the entire arc of a circle described by the sector d ring 10, or over the entire circumferential length of the ring sector.

[51] As illustrated in Figure 1, the ring support structure 3, which is integral with a turbine housing, comprises a central shroud 31, extending in the axial direction D A , and having a axis of revolution coinciding with the axis of revolution of the turbine ring 1 when they are fixed together, as well as a first annular radial flange 32 and a second annular radial flange 36, the first annular radial flange 32 being positioned in upstream of the second annular radial flange 36.

[52] The second annular radial flange 36 extends in the direction

circumferential of the ring 1 and, in the radial direction DR, from the central shroud 31 towards the center of the ring 1. The second annular radial flange 36 is in contact with the downstream radial attachment flange 16 and is fixed to this one.

[53] The first annular radial flange 32 extends in the direction

circumferential of the ring 1 and, in the radial direction DR, from the central shroud 31 towards the center of the ring 1.

[54] The turbine ring 1 comprises a first annular flange 34 and a second annular flange 33, the two annular flanges 33 and 34 being removably fixed on the first annular radial flange 32. The first and second annular flanges 33 and 34 are arranged upstream of the turbine ring 1 with respect to the direction F of flow of the gas stream in the turbine.

[55] The second annular flange 33 is disposed downstream of the first annular flange 34. The first annular flange 34 and the second annular flange 33 can be sectorized into a plurality of ring sectors or be in one piece.

[56] A portion of the second flange 33 rests on the radial flange

upstream attachment 14 of the ring sector 10 and fixed to this flange. The two flanges 33 and 34 are removably fixed to the upstream annular radial flange 32 by means of fixing screws 60 and nuts 61, the screws 60 passing through holes provided respectively in the two upstream flanges 33 and 34 thus than in the upstream annular radial flange 32.

[57] The first annular flange 34 allows the resumption of the effort of the high pressure distributor (DHP) on the ring assembly by passing this effort to the casing line which is mechanically more robust, that is to say say towards the line of the ring support structure 3.

[58] The outer face 12b and the flanges 14, 16 form a cavity outside the vein, in other words a cavity external to the hot air flow vein F. Due to the presence of air at high temperature on the vein side, the wall 12 is subjected to significant thermal gradients. Furthermore, the high pressures existing in the hot air flow path F increase the risk of hot air leaking, in particular at the level of the junctions between the ring sectors 10. The injection of cooling air in the cavity outside the vein thus makes it possible to cool the wall 12 of the ring and reduce the thermal gradients therein, and also to increase the pressure in the cavity outside the vein, thus limiting the risk of hot air leaking F flowing in the vein.

[59] To do this, the assembly comprises a cooling device, itself comprising in particular the first and the second flange 33, 34, and a diffuser 40 disposed in the cavity outside the vein. In particular, in addition to the orifices allowing the fixing of the flanges 33, 34 and the passage of the screws 60, the flanges 33, 34 also comprise orifices defining a cooling air flow channel.

[60] More specifically, the first annular flange 34 comprises a first circulation channel 34a, and the second annular flange 33 comprises a second circulation channel 33a. The first and the second channel 34a, 33a are coaxial with each other. Preferably, the diameter of the second channel 33a is smaller than the diameter of the first channel 34a.

[61] The diffuser 40 includes an inlet channel 40a in fluid communication with an injection cavity 41. Figure 3A shows a perspective view of a diffuser 40. In this example, the diffuser 40 includes two orifices 40b of fixing, making it possible to fix the diffuser 40 to the upstream annular radial flange 32, by means of the screws 60 also serving for fixing the flanges 33, 34, or directly on the second flange 33, passing through a passage formed in the upstream annular radial flange 32 along the circumference of the ring support 3. In this example, the diffuser 40 comprises two intake channels 40a, each coaxial with a second

channel 33a of the second flange 33 and in fluid communication therewith.

The injection cavity 41 is delimited by an envelope 42 of the shape

substantially curved in the circumferential direction, so as to match the shape of the outer face 12b of the ring 12. More specifically, a wall 42a, arranged under the diffuser 40 in the radial direction, faces the outer face 12b, and extends circumferentially substantially parallel to this outer face 12b.

[62] Figure 3B shows a bottom view of the diffuser 40 of Figure 3A.

The wall 42a comprises a plurality of injection holes 421. In this example, these injection holes 421 have a diameter of between 0.1 and 1 mm, for example 0.5 mm. The air present in the injection cavity 41 is thus injected by air jet impact against the external face 12b, via these injection holes 421.

[63] More specifically, the cooling air is taken from upstream in the engine, for example at the bottom of the combustion chamber, and is routed to the inlet section E of the first channel(s) 34a (cf. arrow in figure 2). It then flows along the first channel(s) 34a, along the second channel(s) 33a, along the intake channel(s) 40a, then into the injection cavity 41 of the diffuser 40. The pressure existing in the injection cavity 41 then allows the injection of cooling air via the injection holes 421.

[64] Figure 4 shows an enlarged view of the inlet section E of a

first circulation channel 34a of the first flange 34. FIG. 4 shows a configuration in which the inlet section E does not include a filter. For the sake of simplification, only the first flange 34, and part of the second flange 33 visible through the first circulation channel 34a are represented, the other elements of the assembly being concealed. The upstream face of the first flange 34 comprises a shoulder 341 around the inlet section E and delimiting the latter.

[65] Figure 5 shows a configuration in which a particle filter 50 is arranged on the inlet section E. More specifically, the particle filter 50 can be a circular plate of a diameter allowing it to be inserted into

the shoulder 341, and fixed by being welded or brazed on the upstream face of the first flange 34, by being inserted into said shoulder 341.

[66] Furthermore, the particulate filter 50 comprises a plurality of orifices 50a.

The number and section of these orifices are determined so as to control an air flow allowing cooling of the external face 12b, in

preventing the particles whose dimensions are greater than the diameter of the injection holes 421, from penetrating into the first channel 34a, and therefore from being routed to the injection cavity 41. More precisely, the air flow of cooling passing through the flow calibration section, that is to say the section of the second circulation channel 33a, must remain controlled between two maintenance operations of the device, during which the filter is cleaned.

[67] Figure 6A shows a first embodiment in which the filter 50 is flat. Figure 6B shows a second embodiment of the particulate filter 50 of this disclosure. In this second embodiment, the filter 50 comprises a fixing portion 51 of flat shape, allowing the fixing of the filter 50 on the upstream face of the first flange 34, in particular at the bottom of the shoulder 341. The filter 50 further comprises a filtration portion 52 comprising the orifices 50a. The filtration portion 52 has a convex or curved shape, making it possible to limit the risk of the particles pressing against the filter 50, by promoting the sliding of the particles along this curved surface, then along the first flange 34. FIG. 7 presents a sectional view of the particle filter 50 of this second embodiment. According to this embodiment, the axis of the orifices 50a is substantially parallel to the central axis A of the filter 50, in other words to the axis of the first channel 34a.

[68] Figure 6C shows a third embodiment of the particulate filter 50 of this disclosure. The filter 50 of this third embodiment is similar to the filter 50a of the second embodiment, but differs from the latter in that the axis of the orifices 50a is inclined with respect to the central axis A of the filter 50, as is visible in FIG. 8. Preferably, the axis of the orifices 50a is oriented in a direction opposite to the gyration of the air in this zone of the engine, so as to limit the obstruction of the orifices 50a. Alternatively, this third embodiment can be combined with the

characteristics of the first embodiment. In other words, the filter 50 can have a flat shape, the orifices 50a being inclined with respect to the central axis A.

[69] Although the present invention has been described with reference to

specific embodiments, it is obvious that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual characteristics of the different embodiments

illustrated/mentioned may be combined in additional embodiments. Accordingly, the description and the drawings should be considered in an illustrative rather than restrictive sense.