Heat Exchanger Tube, Heat Exchanger And Corresponding Production Method

Abstract

The invention relates to a method for producing a heat exchanger tube (1) by bending a metal strip (11), said tube (1) having an internal partition (19) formed by joining the ends of opposing edges (11a, 11b), said partition facing a projection (50) that extends into the heat exchanger tube (1) at a joining zone (22). The method comprises the following steps: locally stamping the metal strip (11) in order to produce a projection at the joining zone (22); and bending the metal strip (11) in order to form said heat exchanger tube (1), such that the projection extends into the tube (1). The invention also relates to such a tube (1) and to a heat exchanger (3) comprising a bundle of said tubes (1).

Description

The invention relates to a method for producing a heat exchanger tube, in particular for motor vehicles, to a heat exchanger tube and to a heat exchanger comprising a core of heat exchanger tubes of this type.

Generally, the heat exchangers comprise a core having parallel heat exchanger tubes and two collectors having openings, to which the corresponding ends of the heat exchanger tubes are connected by brazing. The collectors are each equipped with an inlet and an outlet for a fluid, for example a coolant, which flows through the heat exchanger. The fluid therefore penetrates the heat exchanger tubes by means of the collectors.

Several types of technology are used to manufacture said tubes, and in this case, heat exchanger tubes produced using bending technology are discussed.

Generally, heat exchanger tubes of this type are produced from a reel of metal sheeting which, once unrolled to form a strip, is progressively shaped to the desired cross section using specific bending tools. After the bending, the longitudinal edges of the sheeting are joined to create one or more compartments in the heat exchanger tube. The heat exchanger tube can then be cut to the desired length, into portions corresponding to the final heat exchanger tubes.

The tubes can for example have a B-shaped cross section, having two substantially planar large parallel faces connected by two small curved faces.

A parameter to be taken into account when dimensioning the heat exchanger tubes is the mechanical stress during operation. Indeed, the heat exchanger tubes are subject in particular to the pressure of the circuit of which they are part.

A solution for increasing the mechanical strength of the heat exchanger tube is that of forming a spacer between the two large parallel faces. For example, the metal strip can be folded on itself by joining two opposing edges to form an internal partition. The internal partition separates the tube into two fluid circulation ducts. The internal partition abuts an opposing planar face common to the two ducts.

Another parameter to be taken into account when dimensioning the tubes is the efficiency of the desired exchange of heat.

In order to increase the efficiency of the exchange of heat, an internal divider may for example be arranged inside the tubes. Said internal divider, which is for example corrugated, disrupts the flow of the fluid in the tubes by increasing the exchange surface area. Said internal divider is also used to modify the internal pressure of the tubes. In order to arrange the internal divider in the heat exchanger tube, it may for example be provided that a gap is left between the internal partition and the opposing planar face. The internal divider thus passes through the two ducts of the tube.

However, the designer may want to use two internal dividers, that is to say one per circulation duct, or may not want to use any internal dividers. In this case, the gap between the internal partition and the opposing planar face is not filled, and the tube loses mechanical strength.

If the gap between the internal partition and the opposing face is greater than the brazing limit, that is to say greater than 100 μm, a solution consists in increasing the height of the internal partition in order to fill this gap. Drawbacks of this method are that it is time-consuming and requires specific tools.

The method set out in the following overcomes these drawbacks at least in part by putting in place a simple and cost-effective solution allowing the gap between the internal partition and the opposing planar face of the tube to be reduced without having to adapt the height of the internal partition.

For this purpose, the invention relates to a method for producing a heat exchanger tube having two fluid circulation ducts separated by an internal partition formed by joining opposing edges of a metal strip, said opposing edges each having an end opposite an inner wall of the tube at a joining zone, said method comprising the steps of:

• • locally stamping the metal strip to produce a projection at the joining zone,
  • bending the metal strip to form said heat exchanger tube having two fluid circulation ducts by joining the ends of the opposing edges at the stamped inner wall so that the projection is directed towards the inside of the heat exchanger tube.

According to another aspect of the method, the projection is positioned so as to be in contact with the ends of the opposing edges.

According to another aspect of the method, during an additional step:

• • the metal strip is dimensioned so as to create a gap between the ends of the opposing edges and the inner wall of the tube at the joining zone, and in which
  • the metal strip is stamped to produce a projection having a height that is less than or equal to the gap.

According to another aspect of the method, the gap is between 30 μm and 200 μm, preferably between 50 μm and 70 μm.

According to another aspect of the method, if the height of the projection is less than the gap, the height of the projection is selected such that the distance between the projection and the ends is less than 100 μm.

According to another aspect of the method, the ends and the projection are brazed together.

The invention also relates to a heat exchanger tube having two fluid circulation ducts separated by an internal partition formed by joining opposing edges of a metal strip, said opposing edges each having an end opposite an inner wall of the tube at a joining zone, the inner wall having a projection directed towards the inside of the heat exchanger tube at the joining zone.

According to another aspect of the tube, the inner wall of the projection is in contact with the ends.

According to another aspect of the tube, the thickness of the metal strip is between 0.15 mm and 0.35 mm, preferably between 0.20 mm and 0.27 mm.

The invention also relates to a heat exchanger, in particular for a motor vehicle, comprising a core of heat exchanger tubes.

The main advantage of the invention is that it allows the shape of a heat exchanger tube to be adapted to fill the space between the internal partition and the opposing face of the tube without having to modify the height of the internal partition thereof. The method described is simple and cost-effective, and allows the tube to maintain good mechanical strength.

Other features and advantages of the invention will emerge more clearly upon reading the following description, which is given as an illustrative and non-limiting example, and from the accompanying drawings, in which:

FIG. 1 is a schematic partial view of a heat exchanger,

FIG. 2 is a perspective view of the heat exchanger tube produced by the above-described method,

FIG. 3 is a flow diagram showing the steps of the method for manufacturing the heat exchanger tube,

FIG. 4 a is a schematic view of a metal strip which is used to form the heat exchanger tube, FIG. 4a not being representative of the dimensions of the strip for forming the heat exchanger tube,

FIG. 4 b is a schematic partial cross section of an exchanger tube, in which an internal divider is represented by dashes,

FIG. 4 c is a schematic view of the metal strip from FIG. 4a after having been stamped.

In these drawings, substantially like elements have the same reference numerals.

As partially shown in FIG. 1, a heat exchanger 3 conventionally comprises a core of heat exchanger tubes 1 (FIG. 1) in which a first fluid circulates by means of collectors 5 having openings 2 for receiving the ends of said tubes 1.

The heat exchanger 3 is substantially parallelepipedal, a longitudinal axis L is defined along the length of the heat exchanger 3 and a transverse axis T is defined over the width of the heat exchanger 3.

The heat exchanger tubes 1 may be separated from one another by external dividers 9, for example dividers which are corrugated in the direction of the axis L. A second fluid passes through said external dividers 9 so as to exchange heat with the first fluid.

The disruption produced by the presence of the external dividers 9 allows exchanges of heat between the two fluids to be made easier.

One of the objects of the method is that of producing a heat exchanger tube 1 (FIG. 2) having a height h_t, a length L_t and a width l_t. The height h_t of the tube 1 is for example between 1.0 mm and 2.0 mm, preferably between 1.2 mm and 1.6 mm. The dimensions of the tube 1 shown in FIG. 2 are not to scale.

The tube 1 is formed by bending a metal strip 11. The tube 1 has an outer wall 13 and an inner wall 15. The tube 1 has a substantially B-shaped cross section having a large face 43 and a second large face 44 which are in parallel and are interconnected by two small curved faces. The tube 1 also has an internal partition 19 positioned substantially in the middle of the parallel large faces 43, 44. Said internal partition 19 originates from the first large face 43 and is opposite a projection 50 positioned on the internal wall 15 of the second large face 44. The internal partition 19 forms the central bar of the B and divides the tube 1 into two fluid circulation ducts 17a, 17b which form the two loops of the B. The internal partition 19 forms a spacer between the first large face 43 and the second large face 44. The internal partition 19 has a height h_c.

The internal partition 19 is for example formed by opposing edges 11a, 11b of the metal strip 11 which are folded substantially at 90°. Said folded opposing edges 11a, 11b rest against each other to together form the partition 19. The outer walls 13 of the opposing edges 11a, 11b are in contact. Said opposing edges 11a, 11b each have an end 12a, 12b. Said ends 12a, 12b are opposite the inner wall of the projection 50 of the second large face 44 at the joining zone 22.

Said projection 50 has a height h_s, said height h_s being defined as how far the projection 50 goes inside the tube 1. Said height h_s is for example between 30 μm and 200 μm, preferably 50 μm to 100 μm, preferably 50 μm to 70 μm.

The height h_s of the projection 50 is preferably selected such that once the tube 1 is bent, the ends 12a, 12b are in contact with the projection 50. Alternatively, the ends 12a, 12b and the inner wall 15 of the projection 50 are separated by a distance. Said distance is less than 100 μm, that is to say the brazing limit. The ends 12a, 12b and the inner wall 15 of the projection 50 may be easily brazed. A good mechanical strength is thus achieved.

Reference is now made to FIG. 3, which shows the steps for producing a heat exchanger tube, as well as to FIGS. 4a, 4b, 4c and 2, which illustrate some of these steps.

With reference to FIG. 3, the method for producing a heat exchanger tube 1 of this type is described.

The method may comprise a preliminary step 100 for dimensioning the tube 1.

Said tube 1 is produced from a metal strip 11. The metal strip 11 is preferably made of aluminium or aluminium alloy. The strip 11 is shown schematically and by way of illustration in FIG. 4a. To aid understanding, the drawings are not to scale.

The strip 11 is for example of a rectangular general shape and comprises a first wall, referred to as an outer wall 13, and a second wall, referred to as an inner wall 15, in parallel with and opposite the outer wall 13. The terms “inner” and “outer” are defined with respect to the inside and the outside of the bent tube 1. Thus, once the strip 11 is bent, the outer wall 13 of the strip 11 forms the outer wall 13 of the heat exchanger tube 1 thus formed, and the inner wall 15 of the strip 11 forms the inner wall 15 of the heat exchanger tube 1 thus formed (see FIG. 2).

The strip 11 (FIG. 4a) has a length L_b, a width l_b and a thickness e_b. The thickness e_b is for example between 0.15 mm and 0.35 mm, preferably between 0.20 mm and 0.30 mm, preferably between 0.20 and 0.27 mm.

The strip 11 has opposing longitudinal edges 11a, 11b. The edges 11a, 11b each have an end 12a and 12b.

The length l_b of the strip 11 is selected so that once bent, the edges 11a, 11b rest against each other to together form the internal partition 19. The ends 12a, 12b are opposite the internal wall 15 of the second large face 44 of the tube 1, without touching said face. The height h_c of the internal partition 19 is defined such that the ends 12a, 12b are separated from the inner wall 15 of the second large face 44 by a gap h_e (FIG. 4b). This gap h_e allows an internal divider 7, if used, represented by dashes and having a thickness e_i, to be arranged in the tube 1. The value of the gap h_e corresponds substantially to the thickness e_i of the internal divider 7. This thickness e_i is between 30 μm and 200 μm, preferably 50 μm to 100 μm, preferably 50 μm to 70 μm.

When an internal divider 7 is to be used through the ducts 17a, 17b, or when internal dividers 7 are not to be used, the gap h_e is no longer necessary. Said gap therefore needs to be filled so that the tube 1 has good mechanical strength. For this purpose, it is provided that the strip 11 is deformed.

A plurality of portions of the strip 11 can be delimited in order to determine where the deformation will be positioned (FIG. 4a).

First portions 31a, 31b, represented by dots, and a second portion 32 are defined according to the cross section that the tube 1 is to be given. In the present example, a B-shaped cross section is to be produced.

The second portion 32 is positioned at the joining zone 22 between the ends 12a, 12b and the inner wall 15 of the tube 1. According to the example shown, the joining zone 22 is defined substantially in the centre of the width l_b of the strip 11, and the two first portions 31a, 31b are on either side of the joining zone 22.

It is provided that the strip is deformed at the second portion 32 of the strip 11.

During the step 101 (FIG. 3), the outer wall 13 of the tube 1 is stamped. According to the example described, the outer wall 13 of the portion 32 is stamped (FIG. 4c). A first wheel is engaged on the outer wall 13 of the strip 11. A projection 50 is thus produced at the joining zone 22.

According to a first variant, the height h_s of the projection 50 is selected so that said projection 50 is in contact with the ends 12a, 12b once the strip 11 is bent. In this case, the height h_s of the projection 50 is equal to the gap h_e, that is to say is between 30 μm and 200 μm.

According to a second variant, the height h_s of the projection 50 is less than the gap h_e. In this case, the height h_s of the projection 50 is selected so that the distance between the projection 50 and the ends 12a, 12b is less than 100 μm, that is to say the brazing limit, once the strip 11 is bent.

By way of example, if the gap h_e is equal to 200 μm, the height h_s of the projection 50 is equal to 100 μm.

Preferably, the height h_s of the projection 50 is between 50 μm and 70 μm. In all cases, the difference between the gap h_e and the height h_s of the projection 50 is less than or equal to 100 μm, that is to say the brazing limit.

In addition to this step, localised stamping can be provided together with global stamping of the metal strip 11. In this case, second wheels are used to produce bosses on the entire strip 11. The bosses thus formed will disrupt the flow of the fluid in the fluid circulation ducts 17a, 17b and will improve the exchanges of heat.

During a step 102, the metal strip 11 is bent to form the two fluid circulation ducts 17a, 17b (FIG. 2) by joining the opposing edges 11a, 11b at the joining zone 22. For example, the opposing edges 11a, 11b can be bent to substantially 90° and two portions of the strip 11 which will form the two small curved faces of the tube 1 can be curved over.

It is therefore conceivable to insert one or more internal dividers 7 into each duct 17a, 17b of the bent tube 1.

Finally, the opposing edges 11a, 11b are folded down so as to rest against each other. The tube 1 is thus closed and the internal partition 19 of the heat exchanger tube 1 is thus formed.

The internal divider 7, if used, may therefore be inserted during bending, before the strip 11 is completely folded up.

If the height h_s of the projection 50 is equal to the gap h_e, then the ends 12a, 12b are in contact with the inner wall 15 of the projection 50.

If the height h_s of the projection 50 is less than the gap h_e, the distance between the ends 12a, 12b and the inner wall 15 of the projection 50 has to be less than 100 μm in order to allow brazing. This distance is less than 100 μm (that is to say less than the brazing limit).

The bent strip 11 has the height h_t, the width l_t and the length L_B. The general shape of the bent strip 11, and consequently of the tube 1, is not affected by the projection 50. The tube 1 may therefore be easily inserted into the openings 2 in the collectors 5 of the heat exchanger 3.

Once the bending is complete, during a step 103, the strip 11 of length L_b in which the internal divider(s) 7 are optionally arranged may be cut to form heat exchanger tubes 1 of length L_t.

According to a variant, the metal strip 11 of length L_b is cut to the desired length L_t of the tube 1 before the internal divider(s) 7 are inserted, if being used.

Finally, during a step 104, the ends 12a, 12b, the internal divider(s) 7, if used, and the inner wall 15 of the tube 1 can be connected by being brazed together.

It is therefore understood that this method allows the shape of a heat exchanger tube 1 to be easily adapted, depending on whether or not it is intended to contain an internal divider 7. This method allows good mechanical strength to be conferred on the tube 1 without the height hc of the internal partition having to be changed and without changing the general shape of the tube 1.

Claims

1. A method for producing a heat exchanger tube (1) having two fluid circulation ducts (17a, 17b) separated by an internal partition (19) formed by joining opposing edges (11a, 11b) of a metal strip (11), said opposing edges (11a, 11b) each having an end (12a, 12b) opposite an inner wall (15) of the tube (1) at a joining zone (22), said method comprising the steps of: locally stamping the metal strip (11) to produce a projection (50) at the joining zone (22); andbending the metal strip (11) to form said heat exchanger tube (1) having two fluid circulation ducts (17a, 17b) by joining the ends (12a, 12b) of the opposing edges (11a, 11b) at the stamped inner wall (15) so that the projection (50) is directed towards the inside of the heat exchanger tube (1).

2. The method for producing a heat exchanger tube (1) according to claim 1, wherein, during the bending step, the projection (50) is positioned so as to be in contact with the ends (12a, 12b) of the opposing edges (11a, 11b).

3. The method for producing a heat exchanger tube (1) according to claim 1, wherein the method comprises: a preliminary step, during which the metal strip is dimensioned so as to create a gap he between the ends (12a, 12b) of the opposing edges (11a, 11b) and the inner wall (15) of the tube (1) at the joining zone (22), and in whichthe metal strip (11) is stamped to produce a projection (50) having a height hs that is less than or equal to the gap he.

4. The method for producing a heat exchanger tube (1) according to claim 3, wherein the gap he is between 30 μm and 200 μm.

5. The method for producing a heat exchanger tube (1) according to claim 3, wherein, if the height hs of the projection (50) is less than the gap he, the height hs of the projection (50) is selected such that the distance between the projection (50) and the ends (12a, 12b) is less than 100 μm.

6. The method for producing a heat exchanger tube (1) according to claim 1, wherein the faces of the end (12a, 12b) and the projection (50) are brazed together.

7. A heat exchanger tube (1) having two fluid circulation ducts (17a, 17b) separated by an internal partition (19) formed by joining opposing edges (11a, 11b) of a metal strip (11), said opposing edges (11a, 11b) each having an end (12a, 12b) opposite an inner wall (15) of the tube at a joining zone (22), wherein the inner wall (15) has a projection (50) directed towards the inside of the heat exchanger tube (1) at the joining zone (22).

8. The heat exchanger tube (1) according to claim 7, wherein the inner wall (15) of the projection (50) is in contact with the ends (12a, 12b).

9. The heat exchanger tube (1) according to claim 7, wherein the thickness of the metal strip (11) is between 0.15 mm and 0.35 mm, preferably between 0.20 mm and 0.27 mm.

10. A heat exchanger for a motor vehicle, comprising a core of heat exchanger tubes (1) according to claim 7.

11. The method for producing a heat exchanger tube (1) according to claim 2, wherein the method comprises: a preliminary step, during which the metal strip is dimensioned so as to create a gap he between the ends (12a, 12b) of the opposing edges (11a, 11b) and the inner wall (15) of the tube (1) at the joining zone (22), and in which the metal strip (11) is stamped to produce a projection (50) having a height hs that is less than or equal to the gap he.

12. The method for producing a heat exchanger tube (1) according to claim 3, wherein the gap he is between 50 μm and 70 μm.

13. The method for producing a heat exchanger tube (1) according to claim 11, wherein the gap he is between 30 μm and 200 μm.

14. The method for producing a heat exchanger tube (1) according to claim 11, wherein the gap he is between 50 μm and 70 μm.