Brazed structure and method of manufacturing the same

Abstract

In a brazed structure, a first member has a first portion defined by one of a recessed portion and a hole, and a second member has a second portion brazed to the first portion with a copper brazing material. The first member has a coefficient of thermal expansion that is smaller than that of the second member.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Applications No. 2005-139112 filed on May 11, 2005 and No. 2005-337626 filed on Nov. 22, 2005, the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a brazed structure and a method of manufacturing the same, which is for example employed to connecting portions between a header tank and tubes of a heat exchanger.

BACKGROUND OF THE INVENTION

A heat exchanger in which longitudinal ends of tubes are connected to header tanks is for example known in Japanese Unexamined Patent Publication No. 2002-286395 (U.S. Pat. No. 6,736,197). In such a heat exchanger, the header tank is generally constructed of a tank body and a header plate formed with tube holes. The longitudinal ends of the tubes are inserted in the tube holes and brazed to the header plate. The tubes and the header tanks are for example made of aluminum.

In general, the quality of brazing is determined based on how well a brazing material is drawn into a clearance of a joint between connecting portions by capillary action. As shown in FIG. 7 and the following formula 1, it is known that the capillarity generally has an inverse proportion with respect to a density ρ of a brazing material BM and a clearance d of the joint. In the formula 1, h denotes a drawn height of the brazing material BM by capillary action, γ denotes a surface tension of the brazing material BM, and g denotes gravitational acceleration.
[Formula 1] h=2γ/dρg

To improve the quality of brazing, it is required to reduce the clearance as small as possible. If a material having high density is selected as a material of the heat exchanger, it is required to further reduce the clearance of the joint for an increase of the density of the brazing material. With this, it is required to improve dimensional accuracy of parts. However, there is a limitation to improve the dimensional accuracy while processing the parts.

Further, it is for example proposed to mechanically expand the tube after the tube is inserted to the tube hole of the header plate so as to reduce the clearance between the tube end and the tube hole. However, if the tube is made of a material having a high coefficient of elasticity (e.g., copper), it does not easily deform and may cause a spring back. Accordingly, it is difficult to reduce the clearance.

SUMMARY OF THE INVENTION

The present invention is made in view of the foregoing matter, and it is an object of the present invention to provide a brazed structure with an improved brazing quality and a method of manufacturing the same without precisely setting an initial clearance between brazing portions.

According to an aspect of the present invention, a brazed structure has a first member having a first portion defined by one of a recessed portion and a hole, and a second member having a second portion brazed to the first portion of the first member with a copper brazing material. The first member has a coefficient of thermal expansion smaller than that of the second member.

During brazing, the second member more expands than that the first member expands. Thus, the second portion relatively becomes close to the first portion of the first member during the brazing. Namely, the initial clearance defined between the first portion and the second portion is reduced by the difference of coefficient of thermal expansion between the first member and second members. Accordingly, the quality of brazing improves without requiring to precisely set the initial clearance between the brazing portions.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a front view of an intercooler according to a first example embodiment of the present invention;

FIG. 2 is a cross-sectional view of the intercooler taken along line II-II in FIG. 1;

FIG. 3A is a cross-sectional view of a part of the intercooler denoted by an arrow III in FIG. 1;

FIG. 3B is a cross-sectional view of the part of the intercooler for showing a coating on a header plate of the intercooler according to the first example embodiment;

FIG. 4 is a cross-sectional view of the intercooler taken along line IV-IV in FIG. 3;

FIG. 5 is a cross-sectional view of the intercooler as a modification of the first example embodiment shown in FIG. 1;

FIG. 6 is a cross-sectional view of a tube of the intercooler according to a second example embodiment of the present invention; and

FIG. 7 is an explanatory view of a model for explaining capillary action of a brazing material.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

A first example embodiment of the present invention will now be described with reference to FIGS. 1 to 4. In the first example embodiment, a brazed structure of the present invention is for example employed to a base portion (connecting portion) 101 of an air cooling type intercooler 100.

The intercooler 100 is a heat exchanger for performing heat exchange between an intake air to be sucked in an engine of a vehicle for combustion and an external cooling air for cooling the intake air. The intercooler 100 has a core portion 110 and a pair of header tanks 120. The intercooler 100 is a large heat exchanger and is for example mounted on a large vehicle such as trucks. Respective parts of the intercooler 100, which will be described later, are made of materials such as copper, copper alloy, or iron to have sufficient thermal conduction and durability.

Further, connecting portions between respective parts are connected by brazing or welding. For example, a copper brazing material containing 75% copper, 15% tin, 5% nickel, and 5% phosphorous and having resolution at a low melting point is used as a brazing material.

In the core portion 110, tubes 11 and outer fins 112 are alternately layered and side plates 113 are provided at outermost ends of the core portion 110 in a layering direction. Further, inner fins 114 are interposed in the inside of the tubes 111.

The tube (second member) 111 is a flat pipe member through which the intake air flows. The tube 111 has a substantially rectangular cross-section so as to increase a flow area of the intake air as much as possible and reduce a flow resistance of the intake air. The tube 111 is for example formed by joining two tube plates.

Here, the tube 111 is made of copper alloy containing 15% zinc and 0.8% iron. The copper alloy has a coefficient of linear expansion (thermal expansion) of 19×10⁻⁶ m/K.

The inner fin 114, which is interposed in the tube 111, is made of pure copper plate and is corrugated to disturb the flow of the intake air, to thereby improve thermal conduction of the intake air. Since the tube 111 has the rectangular cross-section, the inner fin 114 is housed in the tube 111 by effectively using the space inside of the tube 111.

Likewise, the outer fin 112 is made of pure copper plate and is corrugated. Further, flat portions of the corrugated outer fin 112 are cut to have sloping pieces 112a as louver portions. Accordingly, a heat radiating area of the cooling air is increased by the louver portions 112a. Also, the louver portions 112a provide a turbulent effect to the cooling air to enhance heat exchange between the cooling air and the intake air.

The side plates 113 is made of brass and provided as reinforcement members. Each of the side plates 113 extends in a longitudinal direction of the tubes 111. The side plate 113 has a substantially U-shaped cross-section. Also, the side plate 113 has a rib that extends in the longitudinal direction of the side plate 113 at a substantially middle portion of the U-shape.

Each of the tubes 111 is formed by brazing two tube plates. A paste brazing material, which is a mixture of the brazing material and binder, is applied to both surfaces of the tube plate before brazing. Further, the outer fins 112 and the inner fins 114 are brazed to the tubes 111 with the brazing material applied on the tube plates.

Likewise, the paste brazing material is applied to a surface of the side plate 113, which faces the outermost fin 112 before brazing. Thus, the side plates 113 are brazed to the outermost outer fins 112 with the brazing material.

Instead of the paste brazing material, a foil brazing material can be used. In this case, the foil brazing material is interposed between the respective connecting portions such as between the tubes 111 and the outer fins 112, between the tubes and the inner fins 114, and between the side plates 113 and the outer fins 112.

The longitudinal ends 111a of the tubes 111 are connected to header tanks 120 to have communication with cavities of the header tanks 120. Each of the header tanks 120 extends in a direction perpendicular to the longitudinal direction of the tubes 111. The header tank 120 is constructed of a header plate 121, a tank body 122 and a pipe 123.

As shown in FIG. 4, the header plate (first member) 121 has a substantially U-shaped cross-section and includes a longitudinal plate portion and side portions 121b extending from longitudinal edges of the plate portion. Also, the plate portion forms an expanding portion 1211c that expands toward the tubes 111 in a domed shape.

Further, the plate portion of the header plate 121 forms tube holes 121a at positions corresponding to the tube ends 111a. Each of the tube holes 121a has a hole size (inner dimension) that is slightly larger than a cross-sectional area (outer dimension) of the tube 111 and a perimeter of the tube hole 121a on a side of the tube 111 is chamfered so that the tube 111 is easily inserted in the hole 121a.

The header plate 121 is made of an iron material, such as stainless steel or steel. Both surfaces of the header plate 121, around the tube holes 121a and except the side portions 121b, are coated or covered with pure copper, as shown in FIG. 3B. The iron material of the header plate 121 has a coefficient of linear expansion (thermal expansion) of 12×10⁻⁶ m/K. Namely, the header plate 121 has the coefficient of linear expansion smaller than that of the tube 111.

In a condition that the tube ends 111 are inserted in the tube holes 121a, a paste brazing material, which is a mixture of the brazing material, flux and binder, is applied to connecting portions between the tube ends 111a and the tube holes 121a. Accordingly, the tubes 111 and the header plate 121 are brazed at contact portions 101a between them through the brazing material. The brazed contact portions 101a correspond to the base portions 101. Further, the longitudinal ends of the side plates 113 are brazed to the header plates 121 by the brazing material applied to contact portions between the side plates 113 and the header plates 121.

The tank body 122 is made of the iron material, which is the same as the material of the header plate 121. The tank body 122 has a semi-tubular shape having an opening on one side. The header plate 121 is joined to the opening of the tank body 122. The side portions 121b of the header plate 121 are welded to edges of the openings of the tank body 122. Accordingly, the header tank 120 defining the cavity therein is formed.

The pipe 123 is made of iron material. The pipe 123 is welded to a longitudinal end of the tank body 122 so that a pipe space in the pipe 123 communicates with the cavity of the header tank 120.

In FIG. 1, the intake air flowing in one header tank (right tank) 120 through the pipe 123 is distributed into tubes 111. The intake air passing through the tubes 111 is collected in the remaining header tank (left tank) 120, and then discharged to an external device through the pipe 123.

Next, a method of manufacturing the intercooler 100 will be briefly described. First, tube plates for the tubes 111, side plates 113, and the header plates 121 are formed by pressing. Also, the outer fins 112 and the inner fins 114 are shaped by using a roller.

Then, the paste brazing material is applied to the both surfaces of the tube plates, and one surface of each side plate 113. Next, by using a layering jig (not shown) as a guide, the core portion 110 is assembled. For example, one of the side plates 113 is laid at a bottom. On the side plate 113, predetermined numbers of the outer fin 112, the tube plate 111, the inner fin 114, and the tube plate 111 are repeatedly alternately layered in this order. Further, the remaining side plate 113 is placed on the uppermost outer fin 112. In this assembly, the tube 111 interposing the inner fin 114 therein is formed by layering the inner fin 114 between the tube plates.

Then, the tube ends 111a are inserted to the tube holes 121a of the header plate 121 and the paste brazing material, containing the brazing material, flux and binder, is applied to the connecting portions between the tube ends 111a and the tube holes 121a. In a condition that the tube ends 111a are inserted to the tube holes 121b, a predetermined clearance D (initial clearance) is defined between an outer wall of the tube end 111a and an inner wall of the tube hole 121a. The predetermined clearance D is defined by initial dimensions of the tube ends 111a and the tube holes 121a. The initial clearance D is for example 0.15 mm. Also, another jig such as a wire can be used to hold the assembled core portion 110, if necessary.

Next, grease or oil is removed from the assembled core portion 110. Then, the assembled core portion 110 is placed in a furnace. The core portion 110 is integrally brazed at a brazing temperature e.g., 625° C.

Then, the pipe 123 is welded to the tank body 122, which is formed by pressing. Further, the edges of the opening of the tank body 122 is welded to the side portions 121b of the header plate 121. Thus, the tank body 122 and the header plate 121 are connected.

Then, a predetermined check, such as a leak check for checking the quality of brazing and welding and a size check, is performed to the intercooler 100. In this way, the intercooler 100 is manufactured.

In the first example embodiment, the tubes 111 expands more than that the header plate 121 expands during the brazing because of the difference of the coefficient of linear expansion between the tubes 111 and the header plate 121. At the base portion 101, particularly, the tube 111 expands in a direction to reduce the initial clearance D (e.g., 0.15 mm) between the tube end 111a and the tube hole 121a.

For example, the amount (ΔD) of change of the clearance D with the change of temperature from a normal temperature of 25° C. to the brazing temperature of 625° C. will be calculated as follows.
ΔD=0.15−(19−12)×10⁻⁶×56/2×(625−25)=0.03

Here, value 56 is a width L of the tube 111.

Accordingly, the initial clearance D is reduced by the difference of the coefficient of thermal expansion between the tube 111 and the header plate 121. Therefore, the quality of brazing is improved without precisely setting the initial clearance D.

The intercooler 100, which is manufactured in the above condition, is cut at the base portion 101 and the quality of brazing is checked in the cross-section of the base portion 101. In the cross-section of the base portion 101, the clearance D after brazing is 0.05 mm, and is sufficiently filled with the brazing material.

Further, the above quality of brazing is compared to that of a comparison heat exchanger, which is manufactured by using a tube made of copper alloy having a coefficient of linear expansion of 10×10⁻⁶ m/k and a header plate made of brass having a coefficient of linear expansion of 21×10⁻⁶ m/k. In the comparison heat exchanger, the header plate having tube holes expands more than the tube. Accordingly, the clearance D between the tube and the tube hole after brazing is 0.25 mm, and is not sufficiently filled with the brazing material.

In the first example embodiment, the tube 111 and the header plate 121 are made of dissimilar materials (e.g., copper alloy and iron material), and the header plate 121 is previously coated with the material (e.g., pure copper), similar to the material of the tube 111. Accordingly, flexibility for choosing the materials of the tubes 111 and the header plate 121 so as to have the difference of the coefficient of linear expansion improves. Further, since the material that is similar to the material of the tube 111 is used as the brazing material, the tube 111 and the header plate 121 are easily and sufficiently brazed according to diffusion of the brazing material into the coating.

In the heat exchanger such as the intercooler 100, the quality of brazing at the base portion 101 is important to maintain air-tightness. By employing the brazed structure of the present invention to the base portions 101 of the intercooler 100, the quality of brazing at the base portions 101 improves.

Also, the inner fin 114 is interposed in the tube 111 without mechanically expanding the tube 111. If the inner fin 114 is inserted in the tube 111 by mechanically expanding the tube 111, it is likely to separate from an inner wall of the tube 111. In the first example embodiment, the inner fin 114 is sandwiched between the tube plates and integrally brazed. Accordingly, the inner fin 114 is sufficiently brazed to the tube 111.

As shown in FIG. 5, the header plate 121 can have burring portions 121d at the perimeters of the tube holes 121a so that a brazing area between the header plate 121 and the tube 111 increases. In this case, the expanding portion 121c can be eliminated due to a matter of forming the burring portions 121d.

A second example embodiment of the present invention will now be described with reference to FIG. 6. In the second embodiment, the brazed structure of the present invention is employed to the tubes 111 of the intercooler 100.

The tube 111 is constructed of a first tube member (first member) 111A and a second tube member (second member) 111B, as shown in FIG. 6 Each of the tube members 111A, 111B has a substantially U-shaped cross-section and is formed by bending a plate. In the U-shape of the cross-section, the middle portion between the bent side portions has a width larger than a length of each side portion. The first tube member 111A forms a recessed portion inside of the U-shape. The first tube member 111A and the second tube member 111B are brazed in a condition that the side portions of the second tube member 111B are arranged in the recessed portion defined by the side portions of the first tube member 111A, as shown in FIG. 6.

The first tube member 111A is made of the iron material, and both surfaces of the first tube member 111A are coated or covered with pure copper before brazed to the second tube member 111B. The first tube member 111A has a coefficient of linear expansion (thermal expansion) of 12×10⁻⁶ m/K. The second tube member 111B is made of copper alloy containing 15% zinc and 0.8% iron, similar to the tube 111 of the first example embodiment. The second tube member 111B has a coefficient of linear expansion (thermal expansion) of 19 ×10⁻⁶ m/K. Thus, the first tube member 111A has the coefficient of thermal expansion smaller than that of the second tube member 111B.

In the second example embodiment, the connecting portion of the tube 111 provides effects similar to those of the connecting portions between the tubes 111 and the header plate 121 of the first example embodiment. Namely, during the brazing, the second tube member 111B expands more than the first tube member 111A because of the difference of the coefficient of the linear expansion between the first tube member 111A and the second tube member 111B. Thus, an initial clearance D1 (e.g., 0.15 mm) defined between the first tube member 111A and the second tube member 111B is reduced.

For example, the amount (ΔD1) of change of the clearance D1 when the temperature changes from the normal temperature (e.g., 25° C. ) to the brazing temperature (e.g., 625° C. ) during the brazing is calculated as follows.
ΔD1=0.15−(19−12)×10⁻⁶ ×60/2×(625−25)=0.024

Here, value 60 is a width L1 of the tube 111.

Accordingly, the clearance D1 between the first side member 111A and the second side member 111B is reduced by the difference of the coefficient of thermal expansion between the first and second side members 111A, 111B. Therefore, the quality of brazing can be improved without precisely setting the initial clearance D1.

In the second example embodiment, the first tube member 111A and the second tube member 111B are made of different materials (e.g., iron material, and copper alloy), and the first tube member 111A is previously coated with the material (e.g., pure copper), which is similar to the material of the second tube member 111B. Accordingly, flexibility of choosing the materials of the first and second tube members 111A, 111B so as to have the difference of the coefficient of linear expansion increases.

Further, since the brazing material (e.g., copper brazing material), which is similar to the material of the second tube member 111B is used, the first tube member 111A and the second tube member 111B are easily brazed with diffusion of the brazing material into the coating on the first tube member 111A. Furthermore, the inner fin 114 is sufficiently brazed to the inner walls of the tube 111 by the difference of coefficient of thermal expansion between the first tube member 111A and the second tube member 111B.

The brazing structure of the present invention is employed to the connecting portions between the tube plates 111A, 111B of the intercooler 100. Accordingly, the quality of brazing, which is important to maintain air-tightness in the heat exchanger, improves.

The above first and second example embodiments can be modified as follows.

In the first example embodiment, the header plate (first member) 121 has the coefficient of linear expansion smaller than that of the tube (second member) 111. In the second example embodiment, the first tube member (first member) 111A has the coefficient of liner expansion smaller than that of the second tube member (second member) 111B. As a modification of the first example embodiment, the header plate 121 can be made of pure copper, instead of the iron material. Likewise, the first tube member 111A of the second example embodiment can be made of pure copper, instead of the iron material. In these cases, it is not necessary to coat the surfaces of the header plate 121 and the first tube member 111A with copper, because the members 121, 111A are brazed with copper brazing material.

In the above first and second example embodiments, the intercooler 100 is mainly made of copper or copper alloy. Alternatively, the brazing structure of the present invention may be employed to another heat exchanger made of another material.

In the above first and second example embodiments, the brazed structure of the present invention is applied to the base portion 101 between the header plate 121 and the tube 111, and to the connecting portion between the tube plate members 111A, 111B. In addition, the brazed structure of the present invention can be applied to connecting portions between plate-shaped outer fins (first member) forming tube holes and tubes (second member) inserted to the tube holes. In this case, the outer fin has a coefficient of linear expansion smaller than that of the tube.

Further, the brazed structure of the present invention can be employed to fix an additional member such as a fixing member (second member) to the header tank (first member) 120. In this case, a recessed portion is formed on the surface of the header tank 120 and the fixing member is partly inserted in the recessed portion and brazed therein. Here, the header tank 120 has a coefficient of linear expansion that is smaller than that of the fixing member.

Further, the brazed structure of the present invention can be employed in a body of a shell-and-tube heat exchanger. For example, ends of pipe members (second member) are inserted in a recessed portion defined by a rising edge formed at a periphery of a cover member (first member) and brazed thereto. In this case, the cover member has a coefficient of linear expansion smaller than that of the pipe member.

Also, the heat exchanger to which the present invention is applied is not limited to the intercooler 100. The brazed structure of the present invention can be employed to another heat exchanger such as a radiator or a condenser.

Furthermore, the use of the brazed structure of the present invention is not limited to the heat exchanger. The brazing structure can be employed to another device other than the heat exchanger as long as the first member having a recessed portion or a hole and the second member is inserted in the recessed portion or the hole and brazed therein.

In the first example embodiment, the tube 111 is made of copper alloy. Alternatively, the tube 111 can be made of pure copper. Likewise, the second tube member 111B of the second example embodiment can be made of pure copper, instead of copper alloy.

In the first example embodiment, the brazing portion of the header plate 121, which is made of the iron material, is coated with pure copper before the brazing, so that it is brazed to the tube 111 with diffusion of the copper brazing material into the coating. Instead of pure copper, the header plate 121 can be coated with nickel. Likewise, the first tube member 111A of the second example embodiment can be coated with nickel instead of pure copper.

The example embodiments of the present invention are described above. However, the present invention is not limited to the above example embodiment, but may be implemented in other ways without departing from the spirit of the invention.

Claims

1. A brazed structure comprising:

a first member having a first portion that is defined by one of a recessed portion and a hole; and

a second member having a second portion brazed to the first portion with a copper brazing material, wherein the first member has a coefficient of thermal expansion smaller than that of the second member.

2. The brazed structure according to claim 1, wherein

the first member and the second member are made of different materials,

one of the first member and the second member has a coating, and

the coating is made of a material that is brazed to the other one of the first and second member with diffusion of the copper brazing material.

3. The brazed structure according to claim 2, wherein the material of the coating contains one of copper and nickel.

4. The brazed structure according to claim 1, wherein

the first member and the second member are included in members of a heat exchanger that performs heat exchange between an internal fluid flowing therein and an external fluid flowing outside thereof.

5. The brazed structure according to claim 4, wherein

the first member is included in a header tank of the heat exchanger in which the internal fluid flows, the header tank forms a hole as the first portion,

the second member is a tube of the heat exchanger in which the internal fluid flows, and the tube has a tube end brazed in the hole of the header tank as the second portion.

6. The brazed structure according to claim 5, wherein the tube encloses an inner fin.

7. The brazed structure according to claim 4, wherein

the first member and the second member are made of one of copper and copper alloy, respectively.

8. The brazed structure according to claim 4, wherein

the first member is made of one of stainless steel and steel and has a coating containing one of copper and nickel, and

the second member is made of one of copper and copper alloy.

9. The brazed structure according to claim 4, wherein

the first member forms a first tube member of a tube of the heat exchanger, the first tube member has a substantially U-shaped cross-section and includes a main portion and side portions extending from sides of the main portion, to define the recessed portion therein,

the second member forms a second tube member of the tube, the second tube member has a substantially U-shaped cross-section and includes a main portion and side portions extending from sides of the main portion, and

the side portions of the second tube member are brazed to the side portions of the first tube member in an inside of the recessed portion.

10. The brazed structure according to claim 9, wherein the first tube member and the second tube member interpose an inner fin therebetween.

11. A method of manufacturing a brazed structure, the brazed structure having a first member having a first portion defined by one of a recessed portion and a hole and a second member having a second portion brazed in the first portion, the method comprising steps of:

arranging the second portion of the second member in the first portion of the first member; and

brazing the second portion of the second member to the first portion of the first member while thermally expanding the second member more than the first member.

12. The method according to claim 11, wherein

in the arranging the first member and the second member define an initial clearance between the first portion and the second portion, and

in the brazing the initial clearance is reduced by a difference of coefficient of thermal expansion of the first member and the second member.