JP2017044468A - Brazable component and heat exchanger comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat exchanger for recirculating exhaust gas of a heat engine which is resistant to corrosion.SOLUTION: The brazable component for the circulation of a fluid in a heat exchanger, in particular for a motor vehicle, includes an aluminum alloy core 4 of a flat tube of the heat exchanger. A pure aluminum protective layer 8 placed in contact with the aluminum alloy core of the flat tube is extended to protect the flat tube. The pure aluminum protective layer acts like a sacrificial protective layer. Therefore, even if the pure aluminum protective layer starts to be corroded, the core of the wall of the flat tube is not damaged.SELECTED DRAWING: Figure 2a

Description

  The present invention relates to the field of heat exchangers for motor vehicles intended to exchange heat between two fluids, and more particularly, but not exclusively, the heat engine of these vehicles. The present invention relates to an aluminum alloy heat exchanger used for cooling the exhaust gas.

  A circuit (referred to as “exhaust gas recirculation (EGR)”) for recirculating exhaust gas from a motor vehicle heat engine is known. The exhaust gas is recirculated therein to the engine inlet, where it is completely burned.

  Since the recirculation circuit extends between the exhaust circuit and the intake circuit of the heat engine and the maximum temperature is extremely high (400 ° C. to 900 ° C.), it generally includes a heat exchanger for cooling the exhaust gas. The recirculation circuit also includes a bypass passage that is not cooled, a bypass valve that selectively directs the gas flow into the heat exchanger or bypass conduit, and a control valve that controls the throughput of the gas flow in the recirculation circuit. Including.

  These exhaust gases are particularly acidic and condense into acidic liquids, especially when the vehicle engine cools. Since this acidic liquid contains, in particular, sulfates, nitrates, organic acids, chlorides and / or hydrocarbons, they cause great damage to the heat exchanger due to corrosion. Therefore, it is common to note a condensate having a pH of less than 2 and a chlorine value of 50 ppm. Some vehicles are noted even at pH 0.8 and chlorine at 200 ppm.

  Furthermore, the assembly of the various components of these exchangers utilizes brazing, and these elements are pre-covered with a solder layer. During brazing, it is observed that the silicon of the solder layer diffuses towards the core of the element. This improvement in the composition of the core makes the element more vulnerable to corrosion

  Therefore, there is a need for a corrosion resistant exchanger component.

  The document WO2006034876 proposes to propose the formation of a hydrophobic layer on the surface of the exchanger circuit so as to remove the condensate of acidic water as quickly as possible and not give time to damage the exchanger. However, this solution is not satisfactory because it does not completely prevent corrosion and significantly reduces the heat exchange capacity of the exchanger.

  The object of the present invention is to propose a component for such an exchanger that can be resistant to corrosion due to condensation of these gases, for example, and that is particularly simple and economical to manufacture.

  For this purpose, the present invention proposes a brazeable component for circulating a fluid in a heat exchanger, in particular for a motor vehicle, which component comprises an aluminum alloy core, It further includes a pure aluminum protective layer placed in contact therewith.

  Thus, after brazing, the pure aluminum layer is in contact with the corrosive gas and the component core is not in contact. The aluminum layer has better corrosion resistance than the component core, and the presence of the aluminum layer prevents the silicon of the solder from diffusing toward the core. The component is resistant to corrosion, whether by exhaust gas circulation for liquids such as glycol water, or by exhaust gas circulation for other fluids.

According to embodiments, particularly simple and convenient features both during manufacture and in use are as follows:
-The protective layer is composed of 99.5% or more aluminum weight percent-the core has a first surface on which the protective layer extends uniformly-a second core opposite the first surface A second pure aluminum protective layer having a surface and the component placed in contact with the second surface-the two protective layers have the same composition-mechanical strength and configuration after brazing of the component The product of the element thickness is 46800 MPa. in order to assemble by brazing the component with another component, the thickness of the component being between 200 μm and 530 μm, the thickness of the protective layer being between 25 μm and 80 μm, A protective layer is placed between the core and the solder layer, the ratio of the thickness of the solder layer to the thickness of the protective layer is between 0.3 and 1-the thickness of the solder layer is 4% of the total thickness Between 10%-the component is a tube or plate

  The present invention also provides for exchanging heat between a first fluid circulating in the first circuit and a second fluid circulating in the second circuit that is different from the first fluid. Particularly with regard to an exchanger for a motor vehicle, the exchanger further comprises a plurality of components disclosed above, the surface of the components including a protective layer belonging to the first circuit.

According to embodiments, particularly simple and convenient features both during manufacture and in use are as follows:
-The first fluid contains the recirculated exhaust gas-after brazing, the product of the mechanical strength of the component and the thickness of the core of the component is 46800 MPa. greater than μm-the component is a stacked plate or a parallel tube

  The features and advantages of the present invention will become apparent from the following description, given by way of preferred examples, but not by way of limitation, with reference to the accompanying drawings, in which:

FIG. 2 is a pair of partial cross-sectional views of a tube according to the invention before brazing with a pure aluminum layer only on the outer surface. 2 is a pair of partial cross-sectional views of a tube according to the invention after brazing with a pure aluminum layer only on the outer surface. FIG. FIG. 2 is a pair of views similar to FIG. 1 with a pure aluminum layer and a solder layer placed on the inner and outer surfaces of the tube. FIG. 2 is a pair of views similar to FIG. 1 with a pure aluminum layer and a solder layer placed on the inner and outer surfaces of the tube. It is a disassembled perspective view of the exchanger by this invention. FIG. 4 is a view similar to FIG. 3 with the exchanger assembled. 1 is a perspective view of a plate according to the invention before brazing, with an aluminum layer and a solder layer placed on the inner and outer surfaces of the plate. FIG. FIG. 6 is a view similar to FIG. 5 after brazing. 1 is a perspective view of a plate according to the invention before brazing with a pure aluminum layer only on one surface of the plate and a solder layer on each side. FIG.

  With reference to FIGS. 1 and 2, the components according to the invention will be described. Here, this component is a flat tube 1 intended to be part of the heat exchanger bundle 2 shown in FIG. The tube 1 includes a wall, and its cross section transverse to its longitudinal axis is elliptical with two flat parts with alternating two rounded parts, for example semicircular. The rounded part is not shown. Two parallel segments 3 of a flat wall can be seen in the figure.

  The wall thickness of the tube 1, ie the thickness of the segment 3, is between 200 μm and 530 μm.

  The wall of the tube 1 includes a core 4 made from a 3000 series aluminum alloy.

  The interior 5 of the tube 1 in FIGS. 1 and 2 is a space extending between the two segments 3. Each segment 3 has an inner surface 6 facing the interior 5 of the tube 1 and an outer surface 7 facing the inner surface 6.

  On the outer surface 7 side, the core 4 includes a first surface with a protective layer 8 of pure aluminum extending in contact therewith. Pure aluminum is taken to mean an aluminum alloy with a very high aluminum content, which content is greater than a given value of 99%. Here, this is a 1000 series aluminum alloy. The thickness of the layer 8 is 40 μm, where the proportion of aluminum is 99.5%.

  Prior to brazing the tube 1, a protective layer 8 extends between the core 4 and the solder layer 10. The thickness of the layer 10 is 30 μm. Solder is used to braze the tube 1 to another component of the bundle 2, such as a partition placed between the tubes 1, or a collector plate of the bundle 2. Since brazing is well known and is not the subject of the present invention, a detailed description of brazing or solder composition will not be given here, but the melting temperature of the solder will fix the various components together. As such, it is below the melting temperature of the exchanger components.

  Prior to brazing, on the inner surface 6 side, the core 4 includes another solder layer 10 in contact with the surface. This layer 10 is used to braze the tube 1 with perturbing elements (not shown) placed inside the tube 1.

In general, the thickness of the components, ie the wall thickness of the tube 1, the thickness of the layer 8, and the thickness of the solder layer 10 is selected from the following ranges and relationships:
The ratio of the thickness of the solder layer 10 to the thickness of the aluminum layer 8 is between 0.3 and 1 so that the solder does not move towards the core 4; Between 4% and 10% of the thickness-the thickness of the protective layer 8 is between 25 and 80 [mu] m-the wall thickness of the tube 1 is between 200 and 530 [mu] m

  After brazing of the exchanger 11 (FIGS. 3 and 4), the metal of the solder layer 10 moves toward the areas to be brazed, thereby exposing the protective layer 8 outside these areas. .

  Layer 8 contacts the fluid and forms a coating intended to act like a sacrificial protective layer. Therefore, even if this layer 8 begins to corrode, the core 4 of the wall of the tube 1 is not damaged.

  Thus, in the tube 1 of FIGS. 1 a and 1 b, there is a protective layer 8 on the outside of the tube 1 to protect the tube 1 from external corrosion that may occur under the influence of the passing fluid.

  In the tube 1 of FIGS. 2 a and 2 b, the second surface of the core on the inner surface 6 side of the tube 1 is covered with a second protective layer 8. This second layer 8 extends between the core 4 and another solder layer 10. Brazing takes place, for example, between the tubes and inside the tube, and outside the tube and inside the tube. Thanks to the protective layer 8 being outside and inside the tube 1, the latter is protected from corrosion which can occur under the influence of the fluid passing between and through the tube.

  After brazing, the product of the wall 1 mechanical strength and the core 4 thickness is 46800 MPa. Greater than μm.

  An example of the use of the tube of FIGS. 2a and 2b is shown in FIGS. The illustrated exchanger 11 includes two rows of flat tubes 1. A bundle is placed in the housing 12.

  The exchanger 11 includes a circuit for circulating EGR gas by exchanging heat with the coolant.

  A housing 12 having a substantially rectangular part and closed at one end accommodates a bundle 2 of U-tubes 1 here, ie an inlet 13 and an outlet 14 of the tube 1 are Located on the same side at the open end 15 of the housing 12.

  The end of the bundle of tubes 1 is fixed to the support plate 16. The support plate 16 has a plurality of openings 17 for attaching each tube 1.

  The housing 12 has an inlet passage 18 and an outlet passage (not shown) for EGR coolant, here the glycol water of the engine cooling circuit.

  The EGR gas enters the exchanger 11 through the inlet 13 and circulates in the tube 1 where it is cooled and then returns through the outlet 15. Glycol water enters through the inlet passage 18, soaks the bundle 2 and exits through the outlet passage. In order to cool the EGR gas, exchange of EGR gas and glycol water is performed.

  The acidity of EGR gas can be about pH 2, and in some circumstances it can contain up to 200 ppm chlorine at pH 0.8. Due to the possibility of condensation during circulation in the exchanger, the interior of the tube is exposed to corrosive conditions and is protected against this by the presence of a protective layer 8.

  Glycol water also has a corrosive action. On the other hand, the outer side of the tube is protected by the protective layer 8 on the outer side.

  According to an alternative embodiment corresponding to FIGS. 1 a and 1 b, only the fluid circulating outside the tube is corrosive so that only the outside of the tube is protected by the protective layer 8. .

  According to another alternative, a protective layer is provided only on the inside of the tube and a solder layer is provided on the outside of the tube.

  Generally, the protective layer is provided on at least one of the inner or outer surface of the tube.

  According to another alternative, no solder is provided inside the tube.

  For the manufacture of the tube 1, first the core 4 is obtained in the form of 3000 series aluminum alloy pieces. A 1000 series aluminum layer 8 is then sprayed uniformly on the outside (FIG. 1a), or on the outside and inside (FIG. 1b). Finally, solder layers are deposited on the outside and outside, for example by immersing the tube 1 in a solder bath. Solder can also be sprayed to form a layer inside the tube 1. The tube 1 is formed by closing the two edges of a flat core relative to each other. The tube 1 is formed watertight during brazing of the exchanger 11.

  According to an alternative embodiment, the core 4 of the tube 1 is formed by extrusion. A 1000 series aluminum layer 8 is then sprayed uniformly on the outside of the tube 1 or outside and inside. Finally, solder layers are deposited on the outside and inside of the tube 1.

  In both cases, a perturbation element or stirrer that perturbs the circulation of fluid in the tube may be placed inside the tube 1 to enhance heat transfer.

  Next, another embodiment will be described with reference to FIGS. For similar elements, the same number plus 100 is used. The component according to the invention is here a plate 101 comprising a core 104 covered on two sides with a protective layer 108 (FIGS. 5 and 6). According to an alternative form, only one surface of the plate 101 is covered with a protective layer (FIG. 7).

  Similar to the above embodiment, the solder layer 110 is placed on the protective layer (s) 108.

  After brazing (FIG. 6), the protective layer 108 is exposed.

  The exchanger 111 is a plate exchanger. Plates 101 are stacked on top of each other to form, for example, two fluid circuits, such as an EGR gas circuit and a coolant circuit that circulates the glycol water of the engine cooling circuit. Here, there is the plate 101 of FIGS. 5 and 6 including a protective layer on each side.

  The lamination of the plates 101 makes it possible to form a circuit for EGR and a circuit for glycol water. As in the embodiment described above, there are conditions where the risk of corrosion is high, and the protective layer 108 plays a role of protection against corrosion.

  According to an alternative embodiment (FIG. 7), the plate 108 includes only one protective layer 108 on one side. Here, the plate 108 is arranged so that the protective layers 108 of two successive plates face each other. Thus, a fluid circuit is thereby formed, the surface has protective layers alternating with the circuit, and the surface has no specific protection. This layout is suitable for exchanging heat between corrosive fluids and fluids that have little or no corrosivity.

  For the manufacture of the plate 101, first the core 104 is obtained in the form of 3000 series aluminum alloy pieces. A 1000 series aluminum layer 108 is then sprayed. Finally, a solder layer 110 is deposited. Optionally, in order to increase the exchange surface, undulations are formed on the plate 101, in particular to form a circulation passage (not shown) and protrusions 120 or depressions.

  By way of example, a 480 μm thick component comprises a core of aluminum alloy 3916 having a thickness of 360 μm, a protective layer of aluminum alloy 1050 having a thickness of 48 μm, and two solder layers 4343 having a thickness of 36 μm (one (One per side) (ie, in proportion, the core is 75%, the protective layer is 10%, and each solder layer is 7.5%). The mechanical strength of the component is 130 MPa.

  Another example consists of a core of aluminum alloy having a thickness of 300 μm, a protective layer of aluminum alloy 1050 having a thickness of 40 μm, and two solder layers 4343 having a thickness of 30 μm (one on one surface) ( That is, in terms of proportion, the core is 75%, the protective layer is 10%, and each solder layer is 7.5%. The mechanical strength of the component is 156 MPa.

  A third example is an aluminum alloy core having a thickness of 260 μm, two protective layers of aluminum alloy 1050 having a thickness of 40 μm (one on one side), and two solder layers 4343 having a thickness of 30 μm. (One in a plane) (ie, in proportion, the core is 65%, each protective layer is 10%, each solder layer is 7.5%) and is a 400 μm thick component. The mechanical strength of the component is 180 MPa.

  In each example, the product of mechanical strength and core thickness after brazing is 46800 MPa. μm.

  As an alternative to the described embodiment, the components, tubes or plates are obtained in the form of a rolled multilayer sandwich.

  Alternative embodiments may be obtained by providing a protective layer only on one side, providing a protective layer on each side, providing a solder layer only on one side, and providing a solder layer on each side. Cover the combination.

  The optional presence of the solder layer is particularly related to the need arising from the optional presence of a partition between the tubes or an agitator in the tubes.

  According to another embodiment, the claimed component (tube or plate) includes a protective layer (s) and the component has a solder layer between the tubes or between the plates. A placed partition or perturbing element.

  According to another embodiment, the component according to the invention is a collector plate comprising an aluminum alloy core assembled, for example by brazing with a tube. The collector plate includes a pure aluminum protective layer placed on the surface of the core on the side of the tube.

  According to an alternative, the component is a support plate 16 of the exchanger 11. Tube 1 and plate 16 then include a protective layer.

  According to another embodiment, the heat exchanger according to the invention comprises a first circuit in which a cooled first fluid, for example glycol water, is circulated by a second fluid, for example air. The exchanger tube or plate includes a protective layer only on the surface that is part of the first circuit.

  The present invention is not limited to the embodiments described and illustrated, but encompasses any alternative embodiment.

FIG. 2 is a pair of partial cross-sectional views of a tube according to the invention before brazing with a pure aluminum layer only on the outer surface. 2 is a pair of partial cross-sectional views of a tube according to the invention after brazing with a pure aluminum layer only on the outer surface. FIG. FIG. 2 is a pair of views similar to FIG. 1 with a pure aluminum layer and a solder layer placed on the inner and outer surfaces of the tube. FIG. 2 is a pair of views similar to FIG. 1 with a pure aluminum layer and a solder layer placed on the inner and outer surfaces of the tube. It is a disassembled perspective view of the exchanger by this invention. FIG. 4 is a view similar to FIG. 3 with the exchanger assembled. 1 is a perspective view of a plate according to the invention before brazing, with an aluminum layer and a solder layer placed on the inner and outer surfaces of the plate. FIG. FIG. 6 is a view similar to FIG. 5 after brazing. 1 is a perspective view of a plate according to the invention before brazing with a pure aluminum layer only on one surface of the plate and a solder layer on each side. FIG. It is a perspective view which shows another embodiment.

Claims (19)

A brazeable component for circulating a fluid in a heat exchanger, in particular for a motor vehicle,
Including an aluminum alloy core (4, 104);
A component further comprising a pure aluminum protective layer (8, 108) placed in contact with said core (4, 104).   2. Component according to claim 1, characterized in that the protective layer (8, 108) consists of more than 99.5% aluminum by weight.   3. Component according to claim 1 or 2, characterized in that the core has a first surface on which the protective layer (8, 108) extends uniformly. The core has a second surface opposite the first surface;
4. Component according to claim 3, characterized in that it comprises a second pure aluminum protective layer (8, 108) placed in contact with the second surface.   5. Component according to claim 4, characterized in that the two protective layers (8, 108) have the same composition.   The product of the mechanical strength of the component after brazing and the thickness of the component is 46800 MPa. The component according to claim 1, wherein the component is μm or more.   7. Component according to any one of claims 1 to 6, characterized in that it has a thickness between 200 and 530 [mu] m.   8. Component according to any one of the preceding claims, characterized in that the thickness of the protective layer (8, 108) is between 25 and 80 [mu] m. To assemble the component by brazing the component with another component, the protective layer (8, 108) is placed between the core (4, 104) and the solder layer (10, 110);
The ratio of the thickness of the solder layer (10, 110) to the thickness of the protective layer (8, 108) is between 0.3 and 1, The components described in.   10. Component according to claim 9, characterized in that the thickness of the solder layer (10, 110) is between 4% and 10% of the total thickness.   11. Component according to any one of claims 1 to 10, characterized in that it is a tube (1).   11. Component according to any one of the preceding claims, characterized in that it is a plate (101). For exchanging heat between a first fluid circulating in the first circuit and a second fluid circulating in the second circuit, which is different from the first fluid, in particular of a motor vehicle A heat exchanger for
Comprising a plurality of components (1, 101) according to any one of claims 1 to 12,
Exchange according to claim 1, characterized in that the surface of the component (1, 101) comprises a protective layer belonging to the first circuit.   14. The exchanger according to claim 13, wherein the first fluid includes recirculated exhaust gas.   After brazing, the product of the mechanical strength of the component (1, 101) and the thickness of the core (4, 104) of the component (1, 101) is 46800 MPa. The exchanger according to claim 13 or 14, characterized by being not less than µm.   16. Exchanger according to any one of claims 13 to 15, characterized in that the component is a stacked plate (101).   16. Exchanger according to any one of claims 13 to 15, characterized in that the component is a pipe (1) placed in parallel.   The exchanger according to claim 17, characterized in that the tubes are separated by a partition.   19. Exchanger according to claim 17 or 18, characterized in that a perturbation element is placed inside the tube (1).

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