Heat Exchanger With Stacked Plates

Abstract

A heat exchanger (1) comprises a plurality of stacked plates (4, 12, 14) inside a box (5). The plurality of stacked plates (4, 12, 14) enable an exchange of heat between a first and a second fluid (C, G) circulating in contact with the plurality of stacked plates (4, 12, 14). The plurality of stacked plates (4, 12, 14) comprise a stress area (70) intended to withstand heat variations that may cause mechanical stress. The heat exchanger (1) further comprises a reinforcement (71) that is in contact with the stress area (70) and the box (5).

Description

The present invention relates to a stacked plate heat exchanger.

The invention applies to any type of heat exchanger, notably for a motor vehicle, for example exchangers intended to be mounted in the engine compartment of the vehicle such as charger air coolers (CACs) or engine exhaust gas recirculation coolers, also known as EGR exchangers (or EGRCs).

In this field, heat exchangers comprising a heat exchange core bundle comprising a series of plates stacked parallel on top of one another are known. The stack of plates forms heat exchange surfaces between which a fluid that is to be cooled and a cooling fluid circulate, in alternate layers, through fluid passage circuits, it being possible for spacers to be provided to improve the exchange of heat between the fluid that is to be cooled and the cooling fluid. The stack of plates is thus configured to define two different circuits: that of the fluid that is to be cooled and that of the cooling fluid.

In these exchangers, the plates are provided with punctured pressed pockets that allow the cooling fluid to circulate perpendicular to the plane of the plate so that said cooling liquid can pass from one cooling liquid circulation layer to the other without communicating with the circulation layer for fluid that is to be cooled that is situated between them.

Specific mechanical stresses occur at these pressed pockets that define the cooling fluid circuit, notably during thermal shock testing. What happens is that the temperature of the cooling liquid entering and leaving the exchanger at these pockets varies enormously and over a very short period of time causing phenomena of differential thermal expansion in the exchanger. There is therefore a risk of the bursting of connections at the pressed pockets of two adjacent plates and this may cause cooling liquid to leak in the exchanger.

This set of problems is all the more sensitive when the plates have to withstand external corrosion phenomena (in the case of EGR gases) and/or internal corrosion phenomena (in the case of the cooling fluid circuit) entailing the use of special materials that have inferior mechanical properties.

One known solution for alleviating this problem is to increase the thicknesses of the plates, but this has an unfavorable impact on cost and packaging.

The invention seeks to improve the situation.

To this end it proposes a stacked plate heat exchanger comprising a box inside which there is a plurality of stacked plates which plurality is intended to allow exchange of heat between a first and a second fluid circulating in contact with said plates, said plates comprising a zone intended to experience thermal variations liable to create mechanical stresses, referred to as the stress zone.

According to the invention, said exchanger comprises a reinforcement in contact with said stress zone and the box.

Thus the reinforcement stiffens the stress zone thereby limiting the risks of rupture that may occur at this point.

According to one aspect of the invention, the plates are arranged in pairs, each pair of plates defining a circulation layer for the first fluid, each plate comprising a zone referred to as the pressed zone that is provided with pressed pockets for the passage of the first fluid from one circulation layer for the first fluid to another layer, said stress zone corresponding to said pressed zone. The reinforcement therefore allows that zone of the plates where the pressed pockets are situated to be reinforced. The pockets are, for example, punctured at right angles to the planes in which the plates extend.

According to another aspect of the invention, said exchanger comprises a heat exchange zone intended to encourage the exchange of heat between the first and the second fluid, and what is referred to as a bypass zone able to allow the second fluid to bypass the heat exchange zone, said bypass zone corresponding to said stress zone, said reinforcement allowing the second fluid to circulate freely over the entire exchange zone. Thus, the reinforcement covers only the stress zone, i.e. the bypass zone or even the pressed zone, without extending into the heat exchange zone so as to reinforce the stress zone without disrupting the entry of the second fluid into the exchange zone.

According to one embodiment, the plates comprise, at the stress zone, a bent-over edge extending in a plane perpendicular to a plane in which the plates extend so that contact between the reinforcement and the stress zone is at least via the bent-over edge. The bent-over edges thus allow contact between the reinforcement and the plates to be flat to flat. They improve the mechanical retention of the reinforcement on the plates which is achieved notably by brazing.

According to another embodiment, said box comprises two lateral walls facing a peripheral edge of the plates, a lower wall and/or an upper wall which are situated at the top and at the bottom of the plurality of stacked plates. More specifically, the box may for example comprise four walls referred to as the upper, right-hand, lower and left-hand walls, said walls being joined together to form an internal volume in which the plurality of plates is situated.

Advantageously, the reinforcement is in contact with one of the lateral walls of the box, which wall is situated in the proximity of the stress zone. It is notably the left-hand wall of the box which is situated in proximity to the stress zone. Proximity here refers to a distance of between 0 and 30 mm.

According to one embodiment, the reinforcement is in contact with the upper wall and/or the lower wall. The reinforcement may also be in contact with the left-hand wall, the upper wall and the lower wall of the box so as to increase the stiffening it affords to the stress zone.

Advantageously, the reinforcement is continuous from an upper edge to a lower edge of said reinforcement so that it is in contact with all said plates.

According to one aspect of the invention, the upper wall of the box comprises a first housing accommodating said reinforcement. The upper wall of the box in particular accommodates the upper edge of the reinforcement. Advantageously, the lateral wall of the box in contact with said reinforcement comprises a second housing accommodating said reinforcement. In addition to improving the mechanical retention of the reinforcement on the box, this first housing and/or this second housing allow the reinforcement to be pre-positioned on the box before it is secured to the latter, for example by brazing.

According to another aspect of the invention, an upper end and/or a lower end of the reinforcement comprises a first flange, extending in a plane parallel to the plane in which the upper and lower walls of the box extend so that contact between the reinforcement and the upper wall and/or between the reinforcement and the lower wall is flat-to-flat. Advantageously, a lateral end of the reinforcement comprises a second flange, extending in a plane parallel to the plane in which the lateral wall of the box in contact with said reinforcement extends, so that contact between the reinforcement and the wall of the box in contact with said reinforcement is flat-to-flat. Thus, the first and/or second flanges improve the mechanical retention of the reinforcement on the box via the wall of the box in contact with said reinforcement, its upper wall and/or its lower wall, by increasing the surface area of reinforcement and box that are to be brazed together.

According to one embodiment, a top of the reinforcement comprises a protrusion espousing an upper part of the lateral wall of the box in contact with said reinforcement.

According to another embodiment, the reinforcement comprises at least one clip which clips onto the box. The clips are clipped, for example, to the left-hand wall, the upper wall and/or the lower wall. They thus make it easier for the reinforcement to be pre-positioned on the box while at the same time improving the mechanical retention of the reinforcement on the box.

According to one aspect of the invention, the reinforcement is a component separate from the box.

According to another aspect of the invention, the reinforcement is a component formed as an integral part of the box. The reinforcement is, for example, formed as one with the left-hand wall, the upper wall and/or the lower wall of the box.

The invention also relates to an air intake module for a motor vehicle engine comprising an exchanger as described hereinabove.

To make the features explained hereinabove easier to describe, drawings have been attached which depict, schematically and solely by way of nonlimiting example, practical embodiments of the stacked plate heat exchanger of the invention. In these drawings:

FIG. 1 is a perspective view illustrating, in exploded form, a heat exchanger according to the invention;

FIG. 2 is a perspective view of a lateral part of the box and of the associated plates;

FIG. 3 is a perspective view of a lower or upper part of the box and of the associated plates, with the reinforcement not having been depicted;

FIG. 4 is a view similar to FIG. 2 depicting an alternative form of embodiment;

FIG. 5 is a perspective view of a lateral edge of the exchanger, and

FIG. 6 is a perspective view of part of a lateral edge of the exchanger illustrating an alternative form of FIG. 5.

As illustrated in FIG. 1, the invention relates to a heat exchanger 1 allowing an exchange of heat between a first fluid, notably a liquid coolant C, and a second fluid that will be referred to as the fluid that is to be cooled G, for example a gas. It may be a charge air cooler, in which a stream of compressed air, intended to be supplied to a combustion engine, for example a motor vehicle engine, is cooled by a liquid coolant, notably a mixture of water and glycol.

The exchanger 1 comprises a heat exchange core bundle 2 comprising a stack of plates 4 which stack is intended to allow an exchange of heat between the liquid coolant C and the fluid to be cooled G circulating in contact with the plates 4. The plates 4 between them delimit alternating circuits 6, 8 for the fluid that is to be cooled G and for the liquid coolant C. The core bundle 2 is of parallelepipedal overall shape here and has an inlet face 10 and an opposite outlet face, not visible, for the fluid that is to be cooled G. On either side of the stack it ends in a plate 12 referred to as the top plate and a plate 14 referred to as the bottom plate.

The exchanger 1 comprises a box 5 in which the core bundle 2 is situated. It guides the fluid that is to be cooled G between the plates 4 from the inlet face 10 to the outlet face of the core bundle 2. Here it comprises four walls referred to as the top wall 23, right-hand wall 19, bottom wall 22 and left-hand wall 18, which are joined together to form an internal volume inside which the plurality of plates 4 is situated. The left-hand wall 18 comes into contact with a first peripheral edge 16 of the plates 4, 12, 14, the right-hand wall 19 comes into contact with a second peripheral edge 16′ of the plates 4, 12, 14, the top wall 23 situated at the top of the stack of plates comes into contact with the top plate 12 and the bottom wall 22 situated at the base of the stack of plates comes into contact with the bottom plate 14. The top wall 23 may be provided with orifices 24, 26 allowing the liquid coolant C to enter and leave the core bundle 2.

The exchanger 1 may also comprise outlet and/or inlet nozzles 28, 30 for the liquid coolant C, these communicating with orifices 24, 26 made in the box 5.

The various components of the exchanger are, for example, made of aluminum or aluminum alloy. They are notably brazed together.

Each plate 4, 12, 14 comprises, for example, a substantially flat bottom 31, surrounded by a peripheral border 32 ending in a flat 34 allowing the plates to be brazed together. The circuit 8 for the liquid coolant C is defined, firstly, by the peripheral border 32, and secondly, by one or more of the borders 60, 60′, for example formed integrally with the bottom 31 of the plate.

The plates 4, 12, 14 are grouped in pairs and assembled by their flats 34 and/or the borders 60, 60′. Thus, the circuit of the top plate and of the bottom plate of a pair of plates combine to constitute a circulation canal for the liquid coolant C. Each pair of plates thus defines a circulation layer for the first fluid C. The circuits 6 for the circulation of the fluid that is to be cooled are provided between two opposing plates 4 of two adjacent pairs of plates 4.

In the example illustrated, the top 12 and bottom 14 plates are assembled with the top 23 and bottom 22 walls of the box to define a circulation canal for the liquid coolant C.

The plates 4 for example have the overall shape of an elongate rectangle having two long sides and two short sides, each plate comprising two pressed pockets 38, a first of these pockets having an inlet 40 to the circuit 8 for the circulation of the liquid coolant C and the other of the pockets having an outlet 42 of the circuit 8 for the circulation of the liquid coolant C.

The pockets 38 are in this instance pierced with an orifice 50 for the passage of the cooling liquid, which orifice is oriented perpendicular to the bottom 31 of the plates and which pockets are intended to come into contact on the pockets 38 of an adjacent plate 4 to form respectively an inlet header, not visible, and an outlet header 44, not visible, for the cooling fluid. The pockets 38 thus allow the first fluid to pass from one layer to another, i.e. from one pair of plates to another. The inlet header opens, for example, into the inlet nozzle 28 via the inlet orifice 24 of the box and/or the outlet header opens, for example, into the outlet nozzle 20 via the outlet orifice 26 of the box 5.

Thus, the cooling fluid enters the core bundle 2 via the inlet nozzle 28 and is then distributed between the plates 4 through the circuits 8 for the circulation of the liquid coolant C by the inlet header. It flows through the circuits 8 for the circulation of the liquid coolant C from their inlets 40 to their outlets 42 where it enters the outlet header 44. It then leaves the exchanger 1 via the outlet nozzle 30.

The pockets 38 are situated along one and the same short side of the plates 4, 12, 14 situated to the left in FIG. 1, i.e. in proximity to the first peripheral edge 16 of the plates 4, 12, 14. The pockets 38 of two pairs of plates 4 between them determine the height of the circuits 6 for the circulation of the fluid G that is to be cooled.

The exchanger 1 therefore comprises a heat exchange zone that facilitates the exchange of heat between the liquid coolant C and the fluid that is to be cooled G, and which extends between the pockets 38 and the second peripheral edge 16′ of the plates 4. The zone in which the pockets 38 are situated, i.e. the zone in proximity to the first peripheral edge of the plates, referred to as the pressed zone, is a zone likely to allow the second fluid to bypass the heat exchange zone.

An inlet header tank and an outlet header tank (neither depicted) may be fitted to the periphery of the box to supply and remove the fluid that is to be cooled.

The exchanger may also comprise secondary heat exchange surfaces, for example corrugated inserts (referenced 55 in FIG. 5) attached between the plates 4 in the circuits 6 for the circulation of the fluid G that is to be cooled. These inserts disrupt the flow of the fluid G that is to be cooled so as to improve the exchange of heat between the two fluids.

Each plate 4, 12, 14 for example comprises corrugations 52 arranged in the circuits 8 for the circulation of the liquid coolant C. These corrugations 52 extend between the pockets 38 constituting the inlet header and the outlet header 44 of the liquid coolant C and the second peripheral edge 16′ of the plates 4, 12, 14. The corrugations 52 are, for example, derived from material from the bottom 31 of the plates 4, 12, 14, notably by the pressing of the plates 4, 12, 14.

The circuit 8 for the circulation of the liquid coolant, which circuit is defined by the plates 4, 12, 14, guides the liquid coolant in a number n of successive passes, in this instance four passes, in which the liquid circulates between the inlet 40 and the outlet 42 of said circuit. Two adjacent passes are separated, for example, by the borders 60, 60′ of the plates 4, 12, 14.

The passes are arranged parallel to one another in a direction of extension, in this instance the long side of the plates 4, 12, 14. They could be provided in series, one after the other.

The borders 60, 60′ are thus oriented along the long side of the plates 4 to define a serpentine path along which the liquid coolant C circulates in each of the passes of each of the circuits 8 for the circulation of the liquid coolant C. Some 60 of the borders extend from the first peripheral edge 16 of the plates 4, 12, 14 toward the second peripheral edge 16′ of the plates 4, 12, 14 while leaving a passage so that fluid can flow from the pass on one side of the border 60 to the other pass. They alternate with borders 60′ extending from the second peripheral edge 16′ of the plates 4, 12, 14 toward the first peripheral edge 16 of the plates 4, 12, 14, leaving a passage so that the fluid can flow from the pass on one side of the border 60′ to the other.

The fluid G that is to be cooled circulates through the circuits 6 for the circulation of the fluid that is to be cooled in a direction that is on the whole perpendicular to the direction of flow of the liquid coolant C, i.e. from the front face of the core bundle 2 toward the rear face thereof.

The zone of the exchanger in which the pockets 38 are situated is liable to be subjected to steep thermal variations because the temperature of the liquid coolant entering or leaving it may vary considerably and over a short space of time depending on the desired use of the heat exchanger. These sharp thermal variations are likely to create stresses above and beyond the stresses experienced by the rest of the exchanger. This pressed zone of the exchanger where the pockets 38 are situated and which suffers high stresses is also referred to as the stress zone 70. The stress zone 70 is therefore situated near the first peripheral edge 16 of the plates 4, 12, 14, i.e. at a distance of between 0 and 30 mm away.

According to the invention, the exchanger comprises a reinforcement 71 in contact with the stress zone 70 and the box 5. The reinforcement 71 here takes the form of a wall extending in a plane perpendicular to the planes in which the left-hand wall 18 and the top wall 23 of the box 5 extend. The reinforcement 71 is, for example, in contact with the entire stress zone 70. It is in contact with the box 5 notably via the left-hand wall 18 and the top wall 23 and/or the bottom wall 22. The reinforcement 71 in this instance is a component separate from the box 5 but could also be formed as an integral part of the box 5, for example with the left-hand wall 18, the bottom wall 22 and/or the top wall 23.

The reinforcement 71 of the invention is illustrated in greater detail in FIG. 2. The reinforcement 71 here adopts the shape of an L-shaped wall. Specifically, a left-hand lateral end 61 of the reinforcement 71 comprises a flange 72 extending in a plane parallel to the plane in which the left-hand wall 18 of the box 5 extends. In this way, contact between the reinforcement 71 and the left-hand wall 18 of the box 5 is flat to flat contact which notably makes brazing the reinforcement 71 and the box 5 together easier.

In order to expand the area of contact between the reinforcement 71 and the top wall and/or between the reinforcement 71 and the bottom wall, it is also possible to provide at least one flange at a top 62 and/or bottom end of the reinforcement 71.

FIG. 3 illustrates another aspect of the invention whereby the plates 4, 12, 14 comprise bent-over edges 75 in the region of the stress zone 70. The bent-over edges 75 begin in the proximity of the first peripheral edge 16 of the plates 4, 12, 14 at a lateral end 65 of the plates 4, 12, 14 that is situated on the same side as the inlet face for the fluid that is to be cooled. They run parallel to the pressed pockets 38, i.e. in a plane perpendicular to the plane in which the bottom of the plates 4, 12, 14 extends, i.e. a plane parallel to the plane in which the reinforcement extends. The bent-over edges 75 begin in particular in the region of the flats 34 of the peripheral borders of the plates 4, 12, 41. Thus contact between the reinforcement and the stress zone 70 is at least via the bent-over edges 75. At least part of the contact between the reinforcement and the contact zone 70 is therefore flat to flat contact.

The top wall 23 of the box 5 comprises, for example, a first housing 76 accommodating the upper end of the reinforcement. This first housing 76 takes the form of a groove starting from one end of the top wall 23 in contact with the left-hand wall, directed toward the core bundle and extending over the stress zone 70. This first housing 76 allows the reinforcement to be prepositioned on the box 5 and held in a correct position so that the brazing operation can be performed. An identical housing may also be provided on the left-hand wall (referred to as the second housing), and/or on the bottom wall and performing the same function as the first housing 76 namely that of allowing the reinforcement to be prepositioned on the box 5 and held in a correct position so that the brazing operation can be carried out.

FIG. 4 depicts the reinforcement 71 in an embodiment in which it comprises a protrusion 80 situated at the top end 62 of the reinforcement 71 and projecting from the left-hand lateral end 61 of the reinforcement 71 in contact with the left-hand wall 18 of the box 5. The protrusion 80 here espouses an upper part 81 of the left-hand wall 18 of the box 5. In the example depicted, the protrusion 80 has a curved portion espousing the upper part 81 of the left-hand wall 18 which is likewise curved. This protrusion 80 notably makes it possible to limit the ingress of the fluid that is to be cooled into the bypass zone, i.e. the stress zone of the exchanger.

FIG. 5 shows one embodiment in which the reinforcement 71 is continuous from an upper edge to a lower edge of the reinforcement, i.e. from the top wall 23 to the bottom wall 22 of the box 5. The reinforcement 71 is thus in contact with all the plates 4, 12, 14. It therefore allows the entire stress zone of the exchanger 1 to be strengthened.

It may also be noticed from this figure that the reinforcement 71 leaves the fluid that is to be cooled free to circulate over the entire heat exchange zone. The reinforcement 71 is thus in contact at its left-hand lateral end with the left-hand wall 18 of the box 5 and continues toward the inside of the core bundle 2, its right-hand lateral end 63 stopping at the boundary between the bypass zone and the heat exchange zone without protruding into the heat exchange zone, i.e. stopping at the boundary between the stress zone and the rest of the exchanger.

The reinforcement 71 may also comprise, as illustrated in FIGS. 5 and 6, clips 85. These clips 85 are, for example, situated at the left-hand lateral end 61 of the reinforcement 71 (FIG. 5) so as to clip onto the left-hand wall of the box 5. They are notably situated on the upper end of the reinforcement 71 (FIG. 6) so as to clip onto the top wall 23 of the box 5.

The clips 85 clip onto the left-hand wall 18, onto the bottom wall 22 and/or onto the top wall 23 of the box 5 at notches 86 that the box has. The clips 85 thus enter the notches 86 and have a bent-over part 87 in contact with an opposite face of the left-hand wall 18 to the face of the left-hand wall 18 with which the reinforcement 71 is in contact, so as to clamp the left-hand wall 18.

These clips 85 serve the purpose of mechanically retaining the reinforcement 71 on the box 5 in order notably to optimize the process of brazing these two elements together.

Claims

1. A stacked plate heat exchanger (1) comprises a plurality of stacked plates (4, 12, 14) inside a box (5), said plurality of stacked plates (4, 12, 14) is intended to allow exchange of heat between a first and a second fluid (C, G) circulating in contact with said plurality of stacked plates (4, 12, 14), said plurality of stacked plates (4, 12, 14) comprising a stress zone (70) intended to experience thermal variations liable to create mechanical stresses, with a reinforcement (71) in contact with said stress zone (70) and said box (5).

2. The exchanger (1) as claimed in claim 1, wherein said plurality of stacked plates (4, 12, 14) are arranged in pairs, each pair of plates defining a circulation layer for the first fluid (C), each plate (4, 12, 14) comprising a pressed zone having pressed pockets (38) for the passage of the first fluid (C) from one circulation layer to another circulation layer, with said stress zone (70) corresponding to said pressed zone.

3. The exchanger (1) as claimed in claim 1, further comprising a heat exchange zone intended to encourage exchange of heat between the first and the second fluid (C, G), and a bypass zone able to allow the second fluid (G) to bypass said heat exchange zone, said bypass zone corresponding to said stress zone (70), said reinforcement (71) allowing the second fluid (G) to circulate freely over an entire exchange zone.

4. The exchanger (1) as claimed in claim 1, wherein said plurality of stacked plates (4, 12, 14) comprise, at said stress zone (70), a bent-over edge (75) extending in a plane perpendicular to a plane in which said plurality of stacked plates (4, 12, 14) extend so that contact between said reinforcement (71) and said stress zone (70) is at least via said bent-over edge (75).

5. The exchanger (1) as claimed in claim 1, wherein said box (5) comprises two lateral walls (18, 19) facing a peripheral edge of said plurality of stacked plates (4, 12, 14), and a lower wall (22) and/or an upper wall (23) which is/are situated at the top and at the bottom of said plurality of stacked plates (4, 12, 14).

6. The exchanger (1) as claimed in claim 5, wherein said reinforcement (71) is in contact with one of said lateral walls (18) of said box (5), with said lateral wall (18) situated in the proximity of said stress zone (70).

7. The exchanger (1) as claimed in claim 5, wherein said reinforcement (71) is in contact with said upper wall (23) and/or with said lower wall (22).

8. The exchanger (1) as claimed in claim 5, wherein said upper wall (23) of said box (5) comprises a first housing (76) accommodating said reinforcement (71).

9. The exchanger (1) as claimed in claim 7, wherein said lateral wall (18) of said box (5) in contact with said reinforcement (71) comprises a second housing accommodating said reinforcement (71).

10. The exchanger (1) as claimed in claim 5, wherein an upper end (62) and/or a lower end of said reinforcement (71) comprises a first flange, extending in a plane parallel to the plane in which said upper and lower walls (22, 23) of said box (5) extend so that contact between said reinforcement (71) and said upper wall (23) and/or between said reinforcement (71) and said lower wall (22) is flat-to-flat.

11. The exchanger (1) as claimed in claim 6, wherein a top of said reinforcement (71) comprises a protrusion (80) espousing an upper part (81) of said lateral wall (18) of said box (5) in contact with said reinforcement (71).

12. The exchanger (1) as claimed in claim 6, wherein a lateral end (61) of said reinforcement (71) comprises a second flange (72), extending in a plane parallel to the plane in which said lateral wall (18) of said box (5) in contact with said reinforcement (71), referred to as left-hand wall (18), extends, so that contact between said reinforcement (71) and said left-hand wall (18) of said box (5) is flat-to-flat.

13. The exchanger (1) as claimed in claim 1, wherein said reinforcement (71) comprises at least one clip (85) which clips onto said box (5).

14. The exchanger (1) as claimed in claim 1, in which said reinforcement (71) is continuous from an upper edge to a lower edge of said reinforcement (71) so that said reinforcement (71) is in contact with all of said plurality of stacked plates (4, 12, 14).

15. An air intake module for a motor vehicle engine comprising an exchanger (1) as claimed in claim 1.

16. The exchanger (1) as claimed in claim 2, further comprising a heat exchange zone intended to encourage exchange of heat between the first and the second fluid (C, G), and a bypass zone able to allow the second fluid (G) to bypass said heat exchange zone, said bypass zone corresponding to said stress zone (70), said reinforcement (71) allowing the second fluid (G) to circulate freely over an entire exchange zone.

17. The exchanger (1) as claimed in claim 6, wherein said reinforcement (71) is in contact with said upper wall (23) and/or with said lower wall (22).