Heat exchanger

Abstract

A heat exchanger has a clad thin sheet material, a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material, and an inner fin held between the clad materials. The clad thick sheet material and the clad thin sheet material have Zn-containing brazing filler metal layers on their passage sides, respectively, and the post-brazing surface Zn amounts are set so as to satisfy specific conditions. Further, certain conditions concerning the compositions of each of the layers that constitute the clad materials, and the inner fin are set.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to a heat exchanger that is mounted in an electric automobile or a hybrid automobile, or on any of various electronic device circuits, and that cools a heat-generating device such as a semiconductor device.[0003]2. Description of Related Art[0004]Heat exchangers that cool heat-generating devices such as semiconductor devices are mounted in electric automobiles or hybrid automobiles, or on various electronic device circuits. One example of a conventional heat exchanger of this type is shown in FIG. 4. This heat exchanger 100 is of a water-cooled type, in which cooling water is used as the coolant, and has: a top sheet 102, which is formed of an aluminum alloy sheet, to which to attach a cooling target such as a semiconductor device; a bottom sheet 101 of an aluminum alloy sheet, which defines a passage 104 between the bottom sheet 101 and the top sheet 102; and an inner fin 103, which is held betwee...

AI Technical Summary

Benefits of technology

[0016]Even when, on the other hand, a corrosion-inhibiting potential gradient layer has been formed at the top sheet 102, i.e., the clad thin sheet material, a battery effect is produced in the neighborhood of the joint region where the individual surfaces 101a, 102a are in contact when the surface 102a of the top sheet 102 has a lower potential than the surface 101a of the bottom sheet 101 in the neighborhood 106 of the joint region between the bottom sheet 101 and the top sheet 102, and corrosion of the top sheet 102 then proceeds preferentially. This results in the problem of corrosion pitting occurring sooner than the number of years of intended durability of the top sheet 102. In addition, investigations have also been carried out into raising the cooling water flow rate in order to raise the cooling efficiency of the heat exchanger 100, but turbulent flow is produced when the cooling water flow rate is made too fast, creating the possibility for erosion or corrosion.

[0017]The inventors have acquired the following knowledge as a result of investigations directed to improving the corrosion resistance of the heat exchanger: with regard to the corrosion resistance when brazing sheets with different sheet thicknesses are combined, not only the composition of the individual brazing sheets, but also the influence of the brazing filler metal that flows in from another brazing sheet must be considered; also, the corrosion resistance of each brazing sheet can be clearly and reliably improved, regardless of the brazing conditions, by specifying the amount of surface Zn after brazing for the individual brazing sheets.

[0018]Because in the heat exchanger of the invention the clad thick sheet material has a Zn-containing brazing filler metal layer on its passage side and the clad thin sheet material has a Zn-containing brazing filler metal layer on its passage side or a Zn-containing sacrificial material layer on its passage side, the heat treatment for brazing causes the diffusion of the Zn component present in each brazing filler metal layer or present in the sacrificial material layer and thus the formation of a potential gradient layer on the individual passage sides of the clad thick sheet material and the clad thin sheet material. In addition, in the clad thick sheet material and clad thin sheet material, an excellent anticorrosion effect is produced by the potential gradient layer when the post-brazing Zn contents A1, A2, B1, and B2 of the surfaces (potential gradient layer surface) on the passage sides of the clad thick sheet material and clad thin sheet material satisfy the prescribed conditions. Due to this, corrosion can be reliably inhibited in the heat exchanger of the invention, and as a result corrosion pitting can be effectively inhibited in each clad material and in particular in the clad thin sheet material. Moreover, even when the cooling water flow rate is sped up, erosion and corrosion of each clad material can be reliably inhibited and corrosion pitting of each clad material, and particularly the clad thin sheet material, can be effectively inhibited.

[0019]Furthermore, the potential of the passage side surface of the clad thin sheet material is made nobler, or higher, than that of the passage side surface of the clad thick sheet material by setting the Zn content A2 and B2 of the passage side surface of the clad thin sheet material so that A2−0.5 and B2−0.5 are respectively smaller than the Zn contents A1 and B1 of the passage side surface of the clad thick sheet material. This serves to inhibit the battery effect-induced development of corrosion in the clad thin sheet material in the neighborhood of joint regions between individual clad materials and can thereby prevent the occurrence of corrosion pitting in this neighborhood to a joint region. With regard to the clad thick sheet material, its sheet thickness is greater than that of the clad thin sheet material, so that Cu diffusion to the brazing filler metal surface from the core material is relatively small. At the same quantity of Zn, the potential of its surface is then baser, or lower, for the clad thick sheet material than that for the clad thin sheet material. Because of this relation, the relationships of the amounts of Zn at the brazing filler metal surfaces, that is, A1>A2−0.5 and B1>B2−0.5, are adopted. Accordingly, the heat exchanger of the invention resists corrosion pitting in the clad thin sheet material even when the cooling water flow rate is raised and can simultaneously achieve a thinning down of the individual members and an improved cooling performance.

Problems solved by technology

However, the following problem can occur when the attempt has been made to use a potential gradient layer to impart corrosion resistance to a top sheet 102 made of a clad thin sheet material in a heat exchanger 100 with the structure described above: even when a heat exchanger 100 has been designed with the goal of forming a corrosion-inhibiting potential gradient layer at the top sheet 102 made of a clad thin sheet material, the intended potential gradient has not always been formed by the clad material after brazing and the anticipated corrosion-inhibiting effect has thus not always been obtained.

Images