METHOD FOR MAKING A HEAT EXCHANGER FOR GASES AND EXCHANGER FOR GASES MADE BY SAID METHOD

Technical field

A first aspect of the present invention relates in general to a method for making a heat exchanger for gases, which comprises fixing a structural member to one end of a housing using a laser welding process, and more particularly to a method that comprises directing a laser beam onto surfaces to be welded from a point above a side wall of the housing.

A second aspect of the present invention relates to a heat exchanger made by the method of the first aspect.

The invention applies in particular to exchangers for recirculation of exhaust gases from an engine ("Exhaust Gas Recirculation Coolers" or EGRC) ) .

Prior art

Methods are known in the prior art for making a heat exchanger for gases, in particular for exhaust gases from an engine, that have the features of the introductory clause of Claim 1 of the present invention, i.e. for which the heat exchanger comprises:

- a housing with the shape of a hollow elongated body that extends along a longitudinal axis, and that is open at its respective opposite ends; - a first fluid circuit for the circulation of gases and a second fluid circuit for the circulation of a cooling fluid, in which the first and second fluid circuits are arranged within said housing for heat exchange between said gases and said cooling fluid; and - at least two structural members, each joined to a respective end of said opposite ends of the housing. These methods known in the prior art comprise fixing at least one of the aforementioned two structural members to the respective end of the housing using a laser welding process, for the purpose of providing various types of welded joints.

Some of these known methods are described in the following patent documents: ES2269569T3, EP1518043B1 and DE19907163A1. The welding processes described in said documents are carried out from positions that are rather disadvantageous (generally frontal, i.e. from points that are not included in a volume that surrounds the housing between its opposite ends), and/or include some structural requirements (end supporting plates with doubled end portions) , dimensional requirements (ratio of thicknesses) and requirements relating to assembly of the parts to be joined, with the aim that the welded joints meet minimum strength requirements, meaning that the welding processes cannot be carried out quickly, automatically and by sequences of simple movements, as well as a high cost of material because the parts must be of a considerable thickness. It therefore seems necessary to offer an alternative to the prior art that provides a method for making a heat exchanger, and the heat exchanger obtained, that does not have the drawbacks of those known in the prior art, allowing a considerable increase in the speed of the laser welding process of the parts thereof and therefore making it possible to reduce the thickness of the parts to be welded. Explanation of the invention

For this purpose, in a first aspect, the present invention relates to a method for making a heat exchanger for gases, in particular for exhaust gases from an engine, in which the heat exchanger comprises:

- a housing with the shape of a hollow elongated body that extends along a longitudinal axis, and that is open at its respective opposite ends;

- a first fluid circuit for the circulation of gases and a second fluid circuit for the circulation of a cooling fluid, in which the first and second fluid circuits are arranged within said housing for heat exchange between said gases and said cooling fluid; and

- at least two structural members, each joined to a respective end of said opposite ends of the housing.

The method comprises, in a manner known per se, fixing at least one of the aforementioned two structural members to the respective end of the housing using a laser welding process.

In contrast to the methods known in the prior art, in that proposed by the first aspect of the present invention, at least one of the two structural members (preferably both) has a projecting portion that extends outwards with respect to the housing and transversely with respect to said longitudinal axis, and the method comprises carrying out the laser welding process by directing a laser beam so that it impinges on respective surfaces to be welded, both of the housing and of said projecting portion of the structural member, so that the laser beam follows a straight path that comes from a point located within a volume that surrounds the housing between its opposite ends, i.e. from a point located above a side wall of the housing.

For a preferred embodiment example, the method of the first aspect of the present invention comprises directing the laser beam, during the laser welding process, in such a way that the aforementioned straight path is inclined with respect to the longitudinal axis.

Advantageously, the method comprises directing the laser beam, during the laser welding process, in such a way that the straight path is inclined with respect to the longitudinal axis at an angle of between 20 and 75°, preferably of substantially 45°. According to one embodiment example, the surface of the housing to be welded is located in a region of a wall of the housing adjacent to the edge of the corresponding end thereof, and the method comprises controlling the energy and the time of application of the laser beam so that a weld bead is created that penetrates both into said wall of the housing and into said projecting portion to predetermined depths, without going all the way through them. According to one implementation of said embodiment example, the aforementioned structural member is an end supporting plate that has a flat perimeter portion, and the method comprises supporting the housing, by the edge of its respective end, transversely against the flat perimeter portion of the end supporting plate, so that a part of the flat perimeter portion defines the aforementioned projecting portion, and then carrying out the welding process. According to a variant of said implementation, the method of the first aspect of the invention comprises supporting the housing, by the edge of its respective end, orthogonally against the flat perimeter portion of the end supporting plate and then carrying out the welding process, in order to provide a T joint.

Advantageously, the thickness of said wall of the housing, in the aforementioned region, and that of the flat perimeter portion of the end supporting plate are related by a thickness ratio of substantially 1:1, always taking into account some tolerance, of for example ± 25%.

According to another embodiment example, the surface of the housing to be welded is located in a zone of a wall of the housing adjacent to an end portion thereof that includes one of its opposite ends, the method comprising controlling the energy and the time of application of the laser beam so that a weld bead is created that penetrates both into said wall of the housing and into said projecting portion to predetermined depths, without going all the way through them.

According to one implementation of said embodiment example, the aforementioned structural member is a flange member that has a through-hole, in which a perimeter portion that surrounds said through-hole defines the previously designated projecting portion, the method comprising introducing said end portion of the housing with a tight fit in the aforementioned through-hole, and then carrying out the welding process.

Advantageously, the thickness of the perimeter portion of the flange member and that of the wall of the housing, in said zone, are related by a thickness ratio within a range of thickness ratios from substantially 1:1 to substantially 2:1.

The positioning of the aforementioned projecting portion compensates the phenomenon known as "shrinkage" (contraction) that affects some structural members after undergoing one or more welding processes. In particular, when the structural member is the aforementioned end supporting plate, and this is the plate on which the ends of some pipes of the first fluid circuit for the circulation of gases are welded, welding of these pipe ends causes the aforementioned phenomenon of "shrinkage", therefore the fact that the end supporting plate includes the aforementioned projecting portion, defined by a respective flat perimeter portion (on the whole of its periphery), i.e. its transverse dimension is greater than that of the housing, means that even if the transverse dimension of the plate shrinks a little on account of this phenomenon, said shrinkage is not harmful either structurally or for the various welded joints, so that the phenomenon of "shrinkage" is compensated. According to one embodiment example of the method of the first aspect of the present invention, the structural member is an end supporting plate that has a flat perimeter portion, and the method further comprises joining said end supporting plate to a gas tank by means of an additional laser welding process, said method comprising arranging said flat perimeter portion of the end supporting plate against a flat perimeter portion of said gas tank, superimposing them on one another, and then carrying out the additional laser welding process.

According to a first variant, the aforementioned additional laser welding process comprises directing a laser beam so that it follows a straight path that comes from a point located within a volume that surrounds the housing between its opposite ends, to impinge firstly on a surface of the flat perimeter portion of the end supporting plate, and then, by controlling the energy and the time of application of the laser beam, create a weld bead that goes all the way through the flat perimeter portion of the end supporting plate and penetrates into the flat perimeter portion of the gas tank to a predetermined depth.

According to a second variant, the additional laser welding process comprises directing a laser beam so that it follows a straight path orthogonal to the aforementioned longitudinal axis and that comes from a point located above a limit area of contact between the flat perimeter portions, of the end supporting plate and of the gas tank, to impinge simultaneously on respective edges of said flat perimeter portions, and then, by controlling the energy and the time of application of the laser beam, create a weld bead that penetrates into both flat perimeter portions, to predetermined depths, without going all the way through them.

For a third variant, part of the flat perimeter portion of the end supporting plate extends beyond the superposed flat perimeter portion of the gas tank, and the additional laser welding process comprises directing a laser beam so that it follows a straight path inclined with respect to said longitudinal axis and that comes from a point located within a volume contiguous with the aforementioned volume that surrounds the housing between its opposite ends, to impinge simultaneously on an edge of the flat perimeter portion of the gas tank and on said part of the flat perimeter portion of the end supporting plate, and then, by controlling the energy and the time of application of the laser beam, create a weld bead that penetrates into both flat perimeter portions, to predetermined depths, without going all the way through them. Advantageously, in relation to said third variant, the method of the first aspect of the present invention comprises directing the laser beam, during the additional laser welding process, so that said straight path is inclined with respect to the longitudinal axis at an angle of between 20 and 75°, preferably of substantially 45°.

Preferably, the parts to be welded together are made of the same material (or of very similar materials) , at least the housing and the structural member.

Advantageously, said material is stainless steel, for example austenitic or ferritic.

For the purpose of carrying out complete welding of the parts to be welded, the method of the first aspect of the present invention comprises carrying out the welding process by laser and/or the additional laser welding process with relative movement of the corresponding laser beam in relation to the respective parts to be welded, preferably automatically, to weld them with a continuous weld bead (i.e. that defines a closed circuit) , maintaining the orientation and length of the respective straight path of the laser beam with respect to the surfaces to be welded during the aforementioned movement.

Each of these movements is associated with a working cycle that is really rapid compared to the prior art, which reduces the cost of manufacture both through the reduction in the working cycle time and through the amount of material required for making the parts to be welded, as these are generally of smaller thickness than those used in the prior art, as well as providing stronger joints than those obtained in the prior art.

Regarding the point mentioned above from which the laser beam comes, depending on the embodiment example this coincides directly with the position of the laser light source (for example, a laser head) or with that of a unit directing the laser beam in an optical path that starts from the laser source, such as a prism or a mirror of a galvanometric system.

Moreover, the present invention also proposes, for one embodiment example, for the welding process described above and/or for the additional welding process, carrying out monitoring of the respective weld bead that is being created (for example, with a remote camera system combined with image recognition techniques) , for the purpose of establishing closed- loop control of the laser beam, which allows greater precision in directing it so as to absorb small variations in the position of the parts to be welded.

A second aspect of the present invention relates to a heat exchanger for gases, in particular for exhaust gases from an engine, which comprises, in a manner known per se:

- a housing with the shape of a hollow elongated body that extends along a longitudinal axis, and that is open at its respective opposite ends;

- a first fluid circuit for the circulation of gases and a second fluid circuit for the circulation of a cooling fluid, in which the first and second fluid circuits are arranged within said housing for heat exchange between said gases and said cooling fluid; and

- at least two structural members, each joined to a respective end of said opposite ends of the housing.

In contrast to the heat exchangers known in the prior art, in that proposed by the second aspect of the present invention, at least one (preferably both) of the at least two structural members has a projecting portion that extends outwards with respect to the housing and transversely with respect to the aforementioned longitudinal axis, and the heat exchanger has been made by the method of the first aspect of the present invention.

According to one embodiment example, the heat exchanger of the second aspect of the invention has been made according to the embodiment example described above of the method of the first aspect for which the laser beam was moved relative to the respective parts to be welded, in order to weld them with a continuous weld bead, the exchanger comprising, for a first implementation, a welded joint between the housing and the structural member that is formed by the aforementioned continuous weld bead, and, for a second implementation, for which the structural member is an end supporting plate, a welded joint between the end supporting plate and the gas tank that is formed by the aforementioned continuous weld bead.

Brief description of the drawings

The foregoing and other advantages and features will be understood more fully from the following detailed description of some embodiment examples with reference to the appended drawings, which are given for purposes of illustration and are non-limiting, in which:

Fig. 1 is an exploded perspective view that shows the heat exchanger proposed by the second aspect of the invention, for one embodiment example;

Fig. 2 illustrates the exchanger of Fig. 1, once assembled; Fig. 3 is a plan view of the exchanger illustrated in Fig. 2;

Fig. 4 is a side view of a cross-section of the exchanger of Fig. 3, taken through a cutting plane as indicated by the cutting line A-A in Fig. 3;

Fig. 5 corresponds to an enlarged view of the detail indicated as D in Fig. 4, illustrating the joint between the housing and the end supporting plate;

Fig. 6 corresponds to an enlarged view of the detail indicated as E in Fig. 4, illustrating the joint between the housing and the flange member;

Figs. 7a, 7b and 7c are respective enlarged views of the detail indicated as H in Fig. 4, illustrating the joint between the end supporting plate and the gas tank, for three corresponding alternative embodiment examples of the present invention.

Detailed description of some embodiment examples

Figs. 1 to 4 show the heat exchanger for gases proposed by the second aspect of the invention, made according to the method of the first aspect, for one embodiment example, for which it comprises:

- a housing B in the shape of a hollow elongated body that extends along a longitudinal axis, and that is open at its respective opposite ends Ba, Bb;

- a first fluid circuit for the circulation of gases (illustrated in Fig. 4, for an embodiment for which it is formed by a tube bundle T) and a second fluid circuit for the circulation of a cooling fluid, which enters via the inlet pipe Rl and leaves via the outlet pipe R2, in which the first and second fluid circuits are arranged within the housing B for heat exchange between the gases and the cooling fluid; two end supporting plates P, each joined to a respective end of the opposite ends Ba, Bb of the housing B;

- a gas tank G joined to one of the end supporting plates P; and

- a flange member F joined to an end portion of the housing B that includes the end Bb .

Fig. 5 shows, enlarged, the detail indicated as D in Fig. 4, showing the joint between the housing B and one of the end supporting plates P by means of a laser welding process.

In particular, Fig. 5 shows how the end supporting plate P has a flat perimeter portion Pc, part of which defines a projecting portion, against which the edge C of the end Ba of the housing B is supported, according to the method of the first aspect of the invention, in this case orthogonally, after which the laser welding process was carried out by directing a laser beam so that it impinges on respective surfaces to be welded, both of the housing B, in particular in a region of a wall of the housing B adjacent to the edge of the end Ba, and of the projecting portion of the end supporting plate P, by controlling the energy and the time of application of the laser beam so that the weld bead SI illustrated is created, which penetrates both into the wall of the housing B and into the projecting portion defined by the flat perimeter portion Pc of the end supporting plate P to predetermined depths, without going all the way through them.

The end supporting plate P includes, for some embodiment examples (as can be seen in Figs. 5, 7a, 7b and 7c) , one or more ribs Z (one continuous or several discontinuous, in both cases along the entire periphery of the plate P) that is/are fitted into the respective end of the housing B, in this case of the end Bl, for the purpose of facilitating the orthogonal positioning of the housing B against the end supporting plate P, and both pieces of which are not separated prior to and during execution of the welding process.

Figs. 3 and 4 show schematically a laser head LI positioned at a point located within a volume that surrounds the housing B between its opposite ends Ba, Bb, and is responsible for generating the laser beam used for performing the welding in Fig. 5, following a straight path inclined with respect to the aforementioned longitudinal axis, in the direction indicated by the arrow coming from the laser head LI, with an inclination Y of between 20 and 75°, preferably of substantially 45°.

The orientation and length of the respective straight path of the laser beam with respect to the surfaces to be welded are not only maintained for the two positions illustrated in Figs. 3 and 4, but throughout relative movement of the laser beam in relation to the respective parts to be welded (whether moving the head LI or the parts to be welded) , to weld them with a continuous weld bead SI.

For the embodiment illustrated in Fig. 5, the wall thickness of the housing B, in the aforementioned region, and that of the flat perimeter portion Pc of the end supporting plate P are related by a thickness ratio of substantially 1:1, as indicated by the dimensions in said figure (for arbitrary units) , both being made of the same material (or of very similar materials) , and the width of the bead SI is at least equal to each of said thicknesses.

Fig. 6 shows, enlarged, the detail indicated as E in Fig. 4, relating to the joint between the housing B and the flange member F.

As shown in Fig. 1, the flange member F has a through- hole Fo in which a perimeter portion Fc that surrounds the through-hole Fo defines a projecting portion, the method of the first aspect of the invention comprising introducing said end portion of the housing B into the through-hole Fo with a tight fit, and then carrying out the laser welding process, in which the surface to be welded of the housing B is located in a zone of a wall of the housing B adjacent to the aforementioned end portion thereof.

In relation to said welding process of the housing B to the flange member F, Figs. 3 and 4 also show schematically a laser head L2 positioned at a point located within a volume that surrounds the housing B between its opposite ends Ba, Bb, and is responsible for generating the laser beam used for performing the welding in Fig. 6, which also follows a straight path inclined with respect to the aforementioned longitudinal axis, in the direction indicated by the arrow that comes from the laser head L2, with an inclination X of between 20 and 75°, preferably of substantially 45°.

For welding the housing B to the flange member F, the energy and the time of application of the incident laser beam that leaves the head L2 are controlled, so that a weld bead S2 is created that penetrates both into the wall of the housing B and into the perimeter portion Fc that defines the projecting portion, to predetermined depths, without going all the way through them, as shown in Fig. 6. In this case, both the width and the depth of the bead S2 are at least equal to the wall thickness of the housing B, and the thickness of the perimeter portion Fc and that of the wall of the housing B, in the aforementioned zone, are related by a thickness ratio within a range of thickness ratios from substantially 1:1 to substantially 2:1, both being made of the same material (or of very similar materials) .

In the same way as for welding the housing B to the end supporting plate P, for welding the housing B to the flange member F, there is relative movement of the laser beam, in this case that emitted by the head L2, in relation to the respective parts to be welded, to weld them with a continuous weld bead S2, maintaining the orientation and length of the respective straight path of the laser beam with respect to the surfaces to be welded during the aforementioned movement.

Finally, Figs. 7a, 7b and 7c illustrate some alternative embodiment examples of the welding of the end supporting plate P to the gas tank G, in respective enlarged views of the detail indicated as H in Fig. 4.

For the three embodiment examples illustrated in Figs. 7a, 7b and 7c, the method of the first aspect of the invention comprises disposing the flat perimeter portion Pc of the end supporting plate P against a flat perimeter portion Gc of the gas tank G, superimposing them on one another, and then carrying out an additional laser welding process.

The thicknesses of the flat perimeter portions Pc and Gc are related by a thickness ratio of substantially 1:1, as indicated by the dimensions in said figure (for arbitrary units) , both being portions of the same material (or of very similar materials) .

For the embodiment in Fig. 7a, the aforementioned additional laser welding process comprises directing a laser beam so that it follows a straight path that comes from a point located within a volume that surrounds the housing B between its opposite ends Ba, Bb (and which in this case follows a path parallel to the aforementioned longitudinal axis of the housing B) , to impinge firstly on a surface of the flat perimeter portion Pc of the end supporting plate P, and then, by controlling the energy and the time of application of the laser beam, creating a weld bead S3 that goes right through the flat perimeter portion Pc of the end supporting plate P and penetrates into the flat perimeter portion Gc of the gas tank G to a predetermined depth, which in this case includes at least 80% of the thickness thereof (as indicated by the arbitrary unit 1.8 relating to the minimum depth of S3) .

As indicated in Fig. 7a, the width of the bead S3 is at least equal to double each of the thicknesses of the flat perimeter portions Pc and Gc .

For the embodiment example in Fig. 7b, the additional laser welding process comprises directing a laser beam so that it follows a straight path orthogonal to the longitudinal axis of the housing B and that comes from a point located above a limit area of contact between the flat perimeter portions Pc, Gc of the end supporting plate P and of the gas tank G, to impinge simultaneously on respective edges of the flat perimeter portions Pc, Gc, and then, by controlling the energy and the time of application of the laser beam, creating a weld bead S4 that penetrates into both flat perimeter portions Pc, Gc to predetermined depths, without going all the way through them. In this case, both the width and the depth of the bead S4 are equal to at least each of the thicknesses of the flat perimeter portions Pc and Gc . Regarding the embodiment example in Fig. 7c, for this, part of the flat perimeter portion Pc of the end supporting plate P extends beyond the superposed flat perimeter portion Gc of the gas tank G, and the additional laser welding process comprises directing a laser beam so that it follows a straight path inclined with respect to the longitudinal axis of the housing B (at an angle of between 20 and 75°, preferably of substantially 45°) and that comes from a point located within a volume contiguous with the aforementioned volume that surrounds the housing B between its opposite ends (i.e. from the side of the gas tank G) , to impinge simultaneously on an edge of the flat perimeter portion Gc of the gas tank G and on the aforementioned part of the flat perimeter portion Pc of the end supporting plate P, and then, by controlling the energy and the time of application of the laser beam, creating a weld bead S5 that penetrates into both flat perimeter portions Pc, Gc to predetermined depths, without going all the way through them.

In this case, both the width and the depth of the bead S5 are equal to at least each of the thicknesses of the flat perimeter portions Pc and Gc .

In the same way as has been explained with reference to the weld beads SI and S2, for producing the beads S3, S4 and S5 there is also relative movement of respective laser heads (not shown) with respect to the parts to be welded, so that said beads S3, S4, S5 are continuous, i.e. define respective closed circuits, the orientation and length of the respective straight paths of the laser beams relative to the surfaces to be welded being maintained during said movements.

A person skilled in the art would be able to make changes and modifications in the embodiment examples described while remaining within the scope of the invention as defined in the appended claims.