Patent Application
20170067694
The present invention relates to the technical field of motor vehicle heat exchangers and relates more specifically to a tube for a heat exchanger of this kind.
The exchanger tubes concerned are so-called “flat” tubes intended to pass through the openings in a plurality of fins of the heat exchanger. The tubes are shaped in the heat exchanger by expansion, so that they are pressed against the edges of the openings in the fins.
A tube of the kind referred to is already known from document FR 2 722 563, said tube exhibiting an oblong cross section which is substantially equivalent to that of an opening in a fin.
A tube of this kind comprises two longitudinal walls facing one another which are curved and exhibit a concave portion (in other words, a portion having a convexity turned towards the inside of the tube), even though the tube has a restricted outer width in a region in which the longitudinal walls are closest one to the other. This kind of particularly flat tube is therefore adapted to be located in a small-size heat exchanger.
However, once a tube of this kind has been shaped in an exchanger, cohesion problems have been noticed between the longitudinal walls of the tube and the openings in the fins. Tubes of this kind are subject to an elastic spring back of their walls after shaping in the openings of the fins. This elastic springback of the walls of the tube creates play between the walls and the openings in the fins which results in a reduction in heat conductance between the tube and the fins. These kinds of deficiencies therefore have a negative impact on the overall thermal efficiency of the exchanger.
The particular aim of the present invention is to overcome the aforementioned problems by proposing a heat exchanger tube, the thermal efficiency of which is improved.
To this end, the object of the invention is a tube for a motor vehicle heat exchanger exhibiting a cross section comprising two opposite longitudinal walls, each wall being provided with at least two concave portions.
Hence, a particularly flat tube is proposed which exhibits dimensions adapted to be fitted in a small-size heat exchanger, while eliminating the cohesion problems between the walls of the tube and the opening in the fin. Surprisingly, the inventors have noticed that this particular tube shape allows an elastic springback of the walls of the tube to be avoided following its shaping by expansion. In fact, following the shaping of a tube, the sides of the tube remain pressed against the edges of the opening and prevent the problem of play emerging between the openings in the fins and the walls of the tube. The conductance of heat between the fins and the tube is therefore optimized, which thereby improves the thermal efficiency of the exchanger.
The tube as defined above may, moreover, comprise one or more of the following characteristics, either alone or in combination.
According to the invention, the two concave portions are separated by a convex portion. A shape of this kind should be understood in the broadest sense, in other words without the convex portion having to have a particular shape.
The convex portion is of such a size that the internal perimeter of the section has a value that is at least 2% greater than the section of a tube in which the walls are straight. Hence, the convex portion allows the internal perimeter of the tube, also referred to as the wetted perimeter, to be increased by a value of 2% in respect of a tube that does not exhibit any convexity, the result of this being an increase in the tube's heat exchange performance.
For example, the walls of the tube are connected to one another by sections which are substantially circular or even oval in shape.
It can be envisaged that, according to the cross section of the tube, a length LTube denotes the greatest distance between the sections with a substantially circular shape on the outside of the tube, a width ITube denotes the smallest distance between the two walls of the tube on the outside of the tube and a flatness ratio Tf of the tube is defined by the relationship:
where the flatness coefficient Tf is strictly lower than 0.20 to ±0.01.
Another object of the invention is a fin comprising at least one substantially oblong opening which comprises an edge provided with two opposite longitudinal walls, each one provided with at least two convex portions. The specific shape of a fin of this kind is particularly appropriate for avoiding an elastic springback of the walls of the tube following shaping in an opening in the fin.
The invention will be easier to understand on reading the attached figures, which are provided by way of example and are in no way limiting in nature, in which:
With reference to
The two longitudinal walls 12 are connected to one another by two end sections 16 which are circular in shape. In the example, a convex portion 18 is arranged between the two concave portions 14 of each longitudinal wall 12. Hence, viewed from the outside, each wall 12 of the tube exhibits a raised section arranged between the two hollow shapes 14.
The tube 10 is produced from a metal alloy adapted to be easily deformed and has a wall with a substantially constant thickness e.
Along the cross section, the tube has a length LTube denoting the greatest distance separating the two end sections 16 which are substantially circular in shape on the outside of the tube and a width ITube denoting the shortest distance between the two walls 12 of the tube on the outside of the tube. A flatness ratio Tf of the tube can be defined by the relationship:
where the flatness coefficient Tf is strictly smaller than 0.20 to ±0.01.
With reference to
Each opening 22 exhibits a cross section which is substantially oblong in shape, comprising two longitudinal edges 26 facing one another, each edge 26 being provided with at least two convex portions 28. The two convex portions 28 of an edge 26 of the opening 22 are separated by a concave portion 30. Viewed from the inside of the opening, each longitudinal edge exhibits one hollow section and two raised sections.
Each opening 22 in a fin 20 therefore has a shape that is substantially identical to that of a tube 10, but its dimensions are smaller, in order to allow the tube to be threaded inside the opening 22 prior to shaping. Hence, each opening is configured to receive a tube as previously described, in such a manner that an assembly formed by an opening provided with a tube exhibits play J between the tube and the receiving opening that matches it.
There follows a description of a method of shaping a tube 10 according to the invention in a plurality of fins 20 of a heat exchanger. In a first stage, the tube 10 is positioned in an opening 22 of at least one fin 20, in such a manner that the tube 10 is positioned to create play J between the tube and the opening, said play J not having a consistent value over the entire periphery of the tube. The tube is then made to press against the inside of the opening 22 in the fin due to the expansion of its walls.
The tube and the fin that are presented are not limited to the embodiment described above and other embodiments will appear clearly to the person skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1454043 | May 2014 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/059867 | 5/5/2015 | WO | 00 |
