Folded and Brazed Tube for Heat Exchanger and Heat Exchanger Including Such Tubes

The present invention concerns a folded and brazed tube for heat exchangers such as a motor vehicle engine cooling radiator, for example.

The invention is more particularly concerned with a tube of the above kind comprising a metal band folded on itself to form two parallel channels separated by a cross-piece, the cross-piece being formed by at least one margin of the band folded locally from the surface of the tube towards the interior of the tube.

A tube of the above type that has a flat section is already known in itself. A tube of the above kind has large, flat or curved faces against which are brazed or welded undulating spacers forming heat exchange fins with a view to constituting a bundle formed of a multiplicity of tubes and spacers.

A depression is formed on the surface of the tube, at the place where the margin is folded inwards, the depression corresponding to the fact that the fold is not a right-angled fold but a circular arc. This depression must be filled in, on the one hand to assure continuity of each of the large faces of the tube in the regions near the cross-piece and, on the other hand, to assure a sealed connection between the tubes and the header plates of the heat exchanger.

The problem is to fill the brazing opening properly during fabrication of the tube.

The aim of the invention is to overcome this drawback and more particularly to obtain a tube in which the depressions due to folding are smaller and therefore easier to fill during brazing.

To this end the invention consists in a folded and brazed tube for heat exchangers, in particular for motor vehicles, comprising a metal band folded on itself to form two parallel channels separated by a cross-piece, the cross-piece being formed by at least one margin of the band folded locally from the surface of the tube towards the interior of the tube.

According to the invention the tube comprises at least one sheet pressed against the exterior of the cross-piece and having an edge flush with the surface of the tube adjacent the fold area of the margin.

The advantage of a sheet whose edge is flush with the surface of the tube is that the sheet clearly delimits the volume to be filled during brazing, between itself and the rounded exterior of the local fold in the sheet.

More particularly, if two opposite margins of the band are folded face-to-face to form a cross-piece, the sheet is disposed between the two margins and therefore divides in two the generally triangular shaped space between the two circular arcs. It is therefore easier to fill these two half-spaces with brazing metal than the original complete space.

In one particular embodiment of the invention the sheet is formed by a marginal area of the margin folded 180.degree. on itself.

In another embodiment the sheet is formed by the other margin of the band, opposite the aforementioned margin, folded onto the cross-piece.

More particularly, the sheet can have at least one depression in its thickness within which an exterior part of the local fold in the margin is accommodated.

This depression, which can be formed by pressing or knurling, for example, has a two-fold advantage. On the one hand, it further reduces the volume to be filled with brazing metal. On the other hand, it immobilizes the sheet relative to the cross-piece, assuring that the edge of the sheet is flush with the surface of the tube.

In another aspect the invention concerns a heat exchanger including a bundle of tubes and cooling fins in which the tubes are as defined hereinabove.

Particular embodiments of the invention will now be described by way of non-limiting example and with reference to the accompanying diagrammatic drawings.

FIG. 1 is an exploded perspective view of a prior art eat exchanger.

FIG. 2 is a view of the same heat exchanger when assembled.

FIG. 3 is an end view of a tube from the heat exchanger shown in FIGS. 1 and 2.

FIG. 4 is a view to a larger scale of the detail IV from FIG. 3.

FIG. 5 is a view similar to FIG. 3 of a tube in accordance with the invention.

FIG. 6 is a view to a larger scale of the detail VI from FIG. 5.

FIG. 7 is an exploded perspective view of a heat exchanger made from tubes constituting a different embodiment of the invention.

FIG. 8 is a view of the heat exchanger from FIG. 7 after assembly.

FIG. 9 is an end view of a tube from the heat exchanger shown in FIGS. 7 and 8.

FIG. 10 is a view to a larger scale of the detail X from FIG. 9.

FIG. 11 is a view to a larger scale of a detail of a tube constituting a further embodiment of the invention.

FIG. 1 shows some of the component parts of a prior art heat exchanger, for example a motor vehicle engine cooling radiator.

The radiator is built up from flat tubes 1 made from folded and brazed sheet metal. Each tube 1 comprises a metal band folded to form the envelope of two parallel channels 2 and 3. The channels 2 and 3 are separated by a cross-piece 4 obtained by folding two opposite margins 4a and 4b of the metal band 90.degree. from the surface of the tube 1 towards its interior. The facing surfaces of the margins 4a and 4b are brazed together to seal the tube 1. The ends of the tubes 1 are engaged in slots 5 in two header plates 6 (only one of which is shown here), on which the header boxes at the ends of the heat exchanger are mounted. During assembly cooling fins 7 made from sheet metal folded to an undulating shape are inserted between the tubes 1.

FIG. 4 shows that the embodiment just described for the tubes 1 leads to the formation of a substantially triangular section volume 8 that must be filled in with brazing metal, at least at the ends of the tubes 1, in order to seal them after they are assembled to a header plates 6.

The volume 8 is in fact delimited by the plane 9 of the outside surface of a tube 1 and by the two quarter-cylinders 10 comprising the outside surface of folds in the sheet metal of the tube 1 forming the two half-cross-pieces 4a and 4b. The aim of the invention is to divide up the volume 8 so that it is easier to fill during brazing.

FIGS. 5 and 6 show a tube 11 in accordance with the invention.

This tube is made substantially as previously, by folding a metal band. The two opposite margins of the band are folded from the surface of the tube towards its interior to form a cross-piece 12. As before, the cross-piece is formed firstly by a margin 13a of the band folded 90.degree.. The cross-piece 12 also comprises the opposite margin 13b of the band, but here its marginal area is folded 180.degree. outwards on itself to form a sheet 14, an edge 15 of which is flush with an outside surface 16 of the tube 11.

The sheet 14 is folded outwards relative to the part of cross-piece 13b, i.e. convex side of a fold 17 producing that half-cross-piece. The sheet 14 is therefore disposed between the half-cross-pieces 13a and 13b.

The edge of the sheet 14 divides the prior art triangular section space into two half-spaces 18a and 18b with half the volume. They are therefore much easier to fill in when brazing the tube.

Here only the half-cross-piece 13b has been folded 180.degree. to form a sheet 14. In an alternative embodiment it would obviously be possible also to fold the marginal area of the half-cross-piece 13a to form two sheets equivalent to the sheet 14.

FIGS. 7 through 10 show an embodiment of the invention applied to long tubes.

Here each tube is formed of two separate half-tubes 21a and 21b made as previously from folded sheet metal and brazed to header plates 22.

Cooling fins 23 in the form of an undulating strip are disposed as previously between the flat tubes each comprising two half-tubes 21a and 21b joined together.

Each half-tube 21a, 21b is made from a folded metal band, a middle area 24 of which forms the body of the tube. A first margin of the metal band is folded from the surface of the tube 21a towards its interior to form a first cross-piece 25a coming into contact with the inside surface of the tube opposite the fold area.

In accordance with the invention, the other margin of the band, opposite the first margin, is folded from the surface of a tube outwards, immediately after the edge 27a of the cross-piece 25a, to form a sheet 26a. The edge 28a of an sheet 26a is flush with the outside surface of the tube.

The other half-tube 21b is made in the same way with the result that its cross-piece 25b is inside the half-tube and its sheet 26b is on the outside. The half-tubes 21a and 21b are folded in opposite directions with the result that the edge 28b of the sheet 26b is on the opposite side of the flat tube to the edge 28a of the sheet 26a. The assembly is such that, starting from the left in FIGS. 9 and 10, the cross-piece 25a and the sheet 26a of the half-tube 21a and the sheet 26b and the cross-piece 25b of the half-tube 21b are pressed successively against each other.

There are therefore two opposite volumes of each tube to be filled in during brazing. FIG. 10 shows one of these volumes, whose substantially triangular section is defined by a surface 29 of the tube and by two quarter-cylinders 30a and 30b formed by the outside surface of the fold of the cross-piece 25a, on the one hand, and the sheet 26b, on the other hand. Here this volume is divided into two equal parts by the edge of the sheet 26a.

Similarly, the edge of the sheet 26b divides in two the volume formed on the other side of the tube by the fold of the sheet 26a and that of the cross-piece 25b.

In the FIG. 11 embodiment, which is similar to that of FIGS. 5 and 6, a single margin 31 of the metal band is folded from the surface of the tube towards its interior to form a cross-piece, coming into contact with the opposite face of the tube. The other margin 32 is folded only to enable it to be brazed.

The marginal area of the margin 31 is folded substantially 180.degree. outwardly of the cross-piece to form a sheet 33 whose edge 34 is flush with a surface 35 of the tube.

Here the cross-piece 31 is folded to an angle slightly less than 90.degree. to form a projection 36 facing a projection 37 formed by the fold of the margin 32. The sheet 33 has two depressions 38 and 39 in its thickness, here formed by crushing, for example using a press or by knurling. The depressions 38 and 39 receive the respective projections 36 and 37 so that volumes 40 and 41 to be filled in during brazing are smaller and a flat outside surface of the tube is assured by virtue of rigorous positioning of the edges of the band relative to the edge 34 of the sheet 33.