Heat exchanger

Abstract

A heat exchanger with the ends of tubes (10) connected by being inserted into a tank (2) is disclosed. Insertion holes are formed in a protrusion (210) convex outward of the tank (2) along the tube length (X). The junction length ratio B/A is not less than 1.15, where A is the outer peripheral surface length of the tubes (10) and B the peripheral length of the junction between the tubes (10) and the tank (2). The larger the junction length ratio, the more the stress generated in the tubes (10) is distributed and reduced. Especially in the case where the junction length ratio is not less than 1.15, the stress is reduced by one half as compared with the junction length ratio of 1.0.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a heat exchanger allowing a fluid to exchange heat or, in particular, to a heat exchanger effectively applicable to an automotive radiator for radiating the heat of the cooling water of a water-cooled engine into the atmosphere.

2. Description of the Related Art

The conventional heat exchanger is configured by stacking a multiplicity of tubes and a multiplicity of corrugated fins in alternate layers to form a core portion. The longitudinal end of each tube is connected by being inserted into an insertion hole of a tank. Also, to reinforce the core portion, a side plate is arranged at each end of the core portion in the direction along the tube stack (see, for example, Japanese Utility Model Publication No. 3059971 and Japanese Unexamined Patent Publication No. 11-337290).

In the case where this heat exchanger is used as an automotive radiator, however, engine cooling water does not flow in the side plates but does flow in the tubes. The side plates are coupled to the corrugated fins and cooled by cool air. This causes a temperature difference and hence a thermal expansion difference between the tubes and the side plates.

Also, in the case where the cooling air amount varies from one part to another of the core portion, a multiplicity of the tubes develop temperature differences in accordance with the positions thereof, thereby causing thermal expansion differences between the tubes.

In the heat exchanger disclosed in Japanese Utility Model Publication No. 3059971, a deformer to absorb the thermal expansion difference between the tubes and the side plates is arranged on the side plates and, therefore, the stress due to the thermal expansion difference between the tubes and the side plates is reduced.

Nevertheless, the thermal expansion difference between the tubes may not be absorbed, and therefore the tubes develop stress due to the thermal expansion difference between them. In the case where the thickness of each tube is reduced, the tubes may be broken by the stress due to the thermal expansion differences. Thus, it is difficult to reduce the tube thickness without the risk of shortening the life of the tubes.

SUMMARY OF THE INVENTION

This invention has been achieved in view of the points described above, and the object thereof is to provide a heat exchanger in which the tubes can be reduced in thickness without shortening the service life thereof.

In order to achieve this object, according to this invention, there is provided a heat exchanger comprising a stack of a multiplicity of flat tubes, and a plurality of tanks arranged at the ends along the length (X) of the multiplicity of the tubes and communicating with the tubes, wherein the ends along the length (X) of the tubes are inserted into the insertion holes of the tanks formed at a protruded portion convex outward of the tanks along the tube length (X), and wherein the junction length ratio B/A between the outer peripheral length A of the tubes and the peripheral length B of the junction between the tubes and the tanks is not less than 1.15.

The larger the junction length ratio, the more the stress generated in the tubes is dispersed and the smaller the stress becomes. In the case where the junction length ratio is not less than 1.15, for example, the stress is reduced by about one half that of the junction length ratio of 1.0, as shown in FIG. 5. Thus, the tube thickness can be reduced without adversely affecting the service life of the tubes.

According to this invention, the junction length ratio is not more than 1.4.

In order to secure a satisfactory connection between the tubes and the tanks, the neighborhood of the tube ends may be widened by a widening jig to bring the connecting portions of the tubes and the tanks into close contact with each other after inserting the tube ends into the insertion holes of the tanks.

With the increase in the junction length ratio, the convexity of the insertion holes increases for an increased distance from the tube ends to the connecting portions, thereby making it difficult to assure close contact of the connecting portions. In the case where the junction length ratio is not more than 1.4 as in this invention, in contrast, the connecting portions can be positively brought into close contact with each other.

According to this invention, the tubes and the tanks are made of aluminum.

In the heat exchanger including the tubes of aluminum and the tanks of resin, the thermal expansion difference between the tubes and the side plates and between the tubes are absorbed by the resin tanks, and therefore the stress generated in the tubes is relaxed.

In the case where the tubes and the tanks are both made of aluminum, on the other hand, the absorption of the thermal expansion difference cannot be substantially expected. Therefore, this invention is applicable suitably to the heat exchanger including the tubes and the tanks of aluminum. The aluminum as referred to herein includes aluminum alloys.

According to this invention, the tanks are substantially rectangular as viewed from the direction along the tube stack (Y).

In the case where a large flow rate is involved, such as in a radiator, a sufficient flow path is must be secured. A tank in the form of circular tube would require a considerable diameter, thereby increasing the tank width (transverse size of the tubes).

In the case where the tanks are substantially rectangular, as in this invention, on the other hand, the tank width can be reduced by increasing the tube length in the tanks and securing a sufficient flow area.

According to this invention, each tank includes a cylindrical portion extending in the direction along the tube stack (Y) and the cylindrical portion is formed by connecting a plurality of plate members formed with insertion holes and not formed with insertion holes.

The job of bringing the connecting portions into close contact with each other is performed easily while the plate members not formed with insertion holes are not mounted, i.e. while the tube ends are not covered. As a result, the connecting portions can be positively brought into close contact with each other.

According to this invention, the tank width D is not more than 1.5 times as large as the tube width C, on the assumption that the tube width C is the outside dimension of the tubes in the direction perpendicular to both the tube length (X) and the direction of the tube stack (Y) and the tank width D is the outside dimension of the tanks in the direction perpendicular to both the tube length (X) and the direction of the tube stack (Y).

In the case where the tank width D is sufficiently large as compared with the tube width C, the thermal expansion difference of the side plates and the thermal expansion difference between the tubes are liable to be absorbed by the deformation of the sides forming the insertion holes of the tank.

In the case where the tank width D is not sufficiently large as compared with the tube width C, on the other hand, the thermal expansion difference of the side plates and the thermal expansion difference between the tubes cannot be expected to be absorbed by the deformation of the sides forming the insertion holes of the tanks. Therefore, as in this invention, the heat exchanger having the tank width D not more than 1.5 times as large as the tube width C is suitably applicable.

The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a radiator according to an embodiment of the invention.

FIG. 2 is a sectional view taken along line II-II in FIG. 1.

FIG. 3 is a view as seen from the arrow F showing the tank of FIG. 2 as a unit.

FIG. 4 is a sectional view showing a modification of the tank.

FIG. 5 is a graph showing the relation between the junction length ratio B/A and the stress generated in the tubes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention is explained. This embodiment represents an application of the heat exchanger according to the invention to a radiator for cooling the cooling water for the water-cooled engine of an automotive vehicle.

FIG. 1 is a front view of the radiator according to this embodiment, FIG. 2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 a view as seen from the arrow F showing the tank of FIG. 2 as a unit.

As shown in FIG. 1, the radiator has a parallelopipedal core portion 1 configured of a multiplicity of tubes 10 and a multiplicity of corrugated fins 11 stacked alternately.

The tubes 10 have therein a path of the cooling water for the water-cooled engine (not shown) mounted in an automotive vehicle. More specifically, the tubes 10 are each formed of an aluminum plate about 0.2 to 0.3 mm thick bent into flat form and welded or soldered.

The corrugated fins 11 are also made of aluminum in corrugated form to promote the heat exchange between the air and the cooling water.

Tanks 2, 3 communicating with the flow paths of the tubes 10 are arranged at the ends along the length (X) of the tubes of the core portion 1.

The tank 2 is made of aluminum to distribute the high-temperature cooling water flowing out of the engine to a multiplicity of the tubes 10. The tank 2 has an inlet pipe 20 of aluminum connected to the cooling water outlet of the engine through a hose (not shown).

The other tank 3, also made of aluminum, is to collect and discharge the cooling water cooled by heat exchange with the air toward the engine. The tank 3 has an aluminum outlet pipe 30 connected to the engine cooling water inlet through a hose.

Side plates 4 for reinforcing the core portion 2 are arranged at the ends along the tube stack of the core portion 1 in the direction Y. The side plates 4 are made of aluminum, and extending in the direction parallel to the tube length X, connected to the tanks 2, 3 at the ends thereof.

As shown in FIGS. 2, 3, the tank 2 extends in the direction Y along the tube stack, and includes a cylindrical portion having the shape of a substantially rectangular cylinder as viewed from the direction Y along the tube stack and an end plate portion for closing the end of the cylindrical portion. The cylindrical portion is formed by connecting a first plate member 21 having an insertion hole and a second plate member 22 having no insertion hole.

The first plate member 21 has a trapezoidal protrusion 210 convex outward of the tank 2 along the tube length X, and the insertion holes 211 are formed in the protrusion 210. After the end along the length X of the tube 10 is inserted into the insertion holes 211, the tube 10 and the first plate member 21 are connected to each other at the insertion holes 211.

The second plate member 22 is formed, integrally with each other, of a substantially L-shaped side plate portion 220 having a cross section extending in the direction Y along the tube stack and an end plate portion 221 described above. The protrusion 210, instead of being trapezoidal, may be arcuate as shown in FIG. 4.

Incidentally, the tank 3 is configured similarly to the tank 2. The end along the length X of the tube 10 is inserted into at least an insertion hole (not shown) of the tank 3, so that the tank 3 and the tube 10 are connected to each other.

For integral soldering, at least one of the tubes 10, the corrugated fins 11, the tanks 2, 3, the pipes 20, 30 and the side plates 4 are made of a member clad with a solder material.

According to this embodiment, the width D of the tank 2 is reduced by increasing the tube length X of the tank 2 and thus securing a sufficient flow path area. The tank width D is an outside dimension of the tank 2 in the direction perpendicular to both the tube length X and the direction Y of the tube stack. According to this embodiment, the direction perpendicular to both the tube length X and the direction Y of the tube stack is coincident with the direction in which the air flows through the core portion 1.

According to this embodiment, the tubes 10 and the first plate member 21 are connected to each other in satisfactory manner so that, after inserting the ends of the tubes 10 into the insertion holes 211 of the first plate member 21, the neighborhood of the ends of the tubes 10 is widened by a widening jig not shown to bring the connecting portions between the tubes 10 and the first plate member 21 into close contact with each other (hereinafter referred to as the widening process).

This widening process is executed while the second plate member 22 is not mounted on the first plate member 21, i.e. while the ends of the tubes 10 are not covered. Therefore, the widening process can be carried out easily and hence the connecting portions can be positively brought into close contact with each other.

The provision of the insertion holes 211 in the trapezoidal or arcuate protrusion 210 increases;the length of the connecting portions of the tank 2 and the tubes 10, and therefore, the stress generated in the tubes 10 is dispersed and decreased.

With regard to the radiator according to this embodiment having this configuration, the desirable range of the junction length ratio B/A is studied, where A is the outer peripheral length of the tubes 10 and B the peripheral length of the connecting portions between the tubes 10 and the tank 2 (hereinafter referred to as the junction peripheral length). The junction peripheral length B is a value measured at the central portion along the thickness of the tank 2.

This study has been made under the conditions described below. First, the tubes 10 have the width C of 16 mm and the thickness of 1.4 mm. The tank 2 has the width D of 21.8 mm and the thickness of 1.6 mm. The tube width C is an outside dimension of the tubes 10 perpendicular to both the tube length X and the direction Y along the tube stack, and the tube thickness is an outside dimension of the tubes 10 in the direction Y along the tube stack.

FIG. 5 shows the result of this study. The abscissa represents the junction length ratio (B/A) and the ordinate the stress ratio based on the assumption that the junction length ratio is 1.0 and the stress generated in the tubes 10 is 100%. The symbol of a square in FIG. 5 designates the result in the case where the protrusion 210 is trapezoidal, and the symbol of a circle designates the result in the case where the protrusion 210 is arcuate.

As obvious from FIG. 5, the stress for the junction length ratio of not less than 1.15 is reduced by one half as compared with that for the junction length ratio of 1.0. Thus, the thickness of the tubes 10 can be reduced without adversely affecting the service life of the tubes 10.

With the increase in the junction length ratio, however, the convexity of the protrusion 210 formed with the insertion holes 211 increases for an increased distance from the ends of the tubes 10 to the connecting portions. This makes it difficult to bring the connecting portions into close contact with each other in the widening process. It has been confirmed that in the case where the junction length ratio is not more than 1.4, the connecting portions can be positively brought into close contact with each other in the widening process.

In the heat exchanger having the tubes 10 of aluminum and the tanks 2 of resin, the thermal expansion difference between the tubes 10 and the side plates 4 and between the tubes 10 are absorbed by the resin tanks, thereby relaxing the stress generated in the tubes 10. In the case where the tubes 10 and the tanks 2 are both made of aluminum, on the other hand, the absorption of the thermal expansion difference by the resin tanks cannot be expected. This invention is therefore suitably applicable to a radiator having both the tubes 10 and the tanks 2 made of aluminum.

In the case where the tank width D is sufficiently large as compared with the tube width C, the thermal expansion difference of the side plates 4 and between the tubes 10 are liable to be absorbed by the deformation of the sides formed with the insertion holes 211 of the tank 2. In the case where the tank width D is not sufficiently large as compared with the tube width C, however, the thermal expansion absorption due to the deformation of the sides formed with the insertion holes 211 is not substantially expected. This invention, therefore, is suitably applicable to a radiator having the tank width D insufficiently large as compared with the tube width C in which the tank width D is not more than 1.5 times as large as the tube width C.

The embodiments described above represent an application of the invention to the radiator. Nevertheless, this invention is applicable also to heat exchangers other than a radiator with equal effect.

While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.

Claims

1. A heat exchanger comprising: a stack of a multiplicity of flat tubes; and a pair of tanks arranged at the ends along the length (X) of the tubes and communicating with the tubes; wherein the ends along the length (X) of the tubes are inserted into the insertion holes of the tanks; wherein the insertion holes are formed at a protruded portion convex outward of the tanks along the tube length (X); and wherein the junction length ratio B/A between the outer peripheral length A of the tubes and the peripheral length B of the junction between the tubes and the tanks is not less than 1.15.

2. A heat exchanger according to claim 1, wherein the junction length ratio is not more than 1.4.

3. A heat exchanger according to claim 1, wherein the tubes and the tanks are made of aluminum.

4. A heat exchanger according to claim 1, wherein the tanks are substantially rectangular as viewed from the direction along the tube stack (Y).

5. A heat exchanger according to claim 4, wherein the tanks each include a cylindrical portion extending in the direction along the tube stack (Y); and wherein the cylindrical portion is formed by connecting a plurality of plate members including those formed with insertion holes and those not formed with insertion holes.

6. A heat exchanger according to claim 4, wherein the tank width D is not more than 1.5 times as large as the tube width C, on the assumption that the tube width C is the outside dimension of the tubes in the direction perpendicular to both the tube length (X) and the direction of tube stack (Y), and that the tank width D is the outside dimension of the tank in the direction perpendicular to both the tube length (X) and the direction of the tube stack (Y).