Core structure of heat exchanger

In a core structure of a heat exchanger, tubes and corrugated fins are alternately arranged between seat plates arranged opposite to each other with a predetermined space interposed therebetween. End portions of the tubes are inserted into tube holes formed respectively in each of the top and bottom seat plates to be fixed. On the seat plates, there are provided connection portions having wall portions slanting from main body portions thereof toward the tube holes. When a thickness of the tubes is 0.13 mm to 0.23 mm, a slant angle θ of the wall portions of the connection portions is set to satisfy: slant angle θ (°)≧25χ(thickness (mm) of sheet plate)+(−125χ(thickness (mm) of tube)+25).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a core structure of corrugated fins of a heat exchanger having tubes through which coolant flows being fixed to seat plates, the core structure of corrugated fins used for a heat exchanger such as a radiator for a vehicle or the like.

2. Description of the Related Art

A core structure of a conventional heat exchanger is, for example, disclosed in Japanese Patent Laid-open No. Tokkaihei 11-14285 and in Japanese Patent Laid-open No. Tokkaihei 9-318292. This core structure of a conventional heat exchanger has seat plates arranged opposite to each other with a predetermined space interposed therebetween, tubes and corrugated fins arranged alternately between the seat plates, and reinforcements which couple and reinforce both end portions of the seat plates.

FIG. 10shows an example of the core structure of the conventional heat exchanger. As shown inFIG. 10, two seat plates101are coupled and reinforced at their both end portions by reinforcements104, and tubes102and corrugated fins103are alternately arranged between the seat plates101.

Further, as shown inFIG. 11, on the seat plates101, tube holes105for fixing the tubes102by insertion and connection portions106having wall portions slanting toward the tube holes105are formed by burring.

On the other hand, in recent years, as the tubes102, tubes having partitions104inside as shown inFIG. 12have become the mainstream. Examples of these tubes are disclosed in Japanese Patent Laid-open No. 2002-303496 for example.

Further, seat plates and tubes in recent years are desired to be made thinner in order to improve a heat exchange rate of a heat exchanger.

However, in the core structure of the conventional heat exchanger, when coolant flowing from an engine into a radiator rapidly changes in temperature from low to high as will be described later, large thermal expansion of the tubes102and the seat plates101occurs, which may cause the connection portions106to press the tubes102to crack/break root portions of the tubes102. This has been an obstruction to make the seat plates101and the tubes102thinner.

Further, since the tubes102in which the partitions104are formed have a particularly small allowable amount of deformation against an external pressure, a countermeasure has been urgently needed against thermal stress applied by the connection portions106of the seat plates101to the tubes102.

Here, the rapid change of coolant flowing from an engine into a radiator in temperature from low to high occurs, for example, in a case when an engine is started in a cold region. In this case, a state that coolant of the engine increases gradually in temperature but does not flow into a radiator continues until it reaches a valve-opening temperature of a thermostat, and then the temperature of the coolant becomes high enough to cause a valve of the thermostat to open, so that the coolant of high temperature flows into the radiator for the first time, or in a case that a so-called hunting phenomenon occurs such that a thermostat repeats opening and closing when driving in a cold region.

The present invention has been made in light of the above-described problems, and an object thereof is to provide a core structure of a heat exchanger capable of preventing a crack and a breakage of root portions of tubes fixed to seat plates due to thermal stress of the seat plates against the tubes when coolant flowing from an engine into a heat exchanger, such as a radiator, rapidly changes in temperature from low to high.

SUMMARY OF THE INVENTION

A core structure of a heat exchanger according to the present invention includes: tubes in which a heat exchange medium flows; corrugated fins adhering to the tubes to radiate heat from the heat exchange medium; and seat plates arranged opposite to each other with a predetermined space interposed therebetween and having the tubes and the corrugated fins arranged alternately therebetween, the sheet seat plates being provided with connection portions having wall portions slanted with a predetermined slant angle from main body portions thereof toward the tubes and tube holes through which the tubes are inserted to be fixed, in which when the tubes have a thickness of 0.13 mm to 0.23 mm, a slant angle θ of the connection portions is: slant angle θ (°)≧25χ(thickness (mm) of sheet plate)+(−125χ(thickness (mm) of tube)+25).

Therefore, in this core structure of the heat exchanger, the slant angle θ of the connection portions is optimally set according to the thickness of the seat plates and the thickness of the tubes so as to satisfy the above-described formula, so that cracking and breaking of the tubes due to thermal stress of the connection portions can be prevented as much as possible, thereby allowing the seat plates and the tubes to be made thinner.

Further, a correlation among the slant angle of the connection portions, the thickness of the seat plates, and the thickness of the tubes can be comprehended using the above-described formula, so that development of thinner seat plates and tubes can be facilitated.

Furthermore, when a burring apparatus for forming the tube holes and the connection portions is not able to form connection portions having a desired slant angle, a thickness of the tubes or the seat plates which is optimum for a slant angle of connection portions formed by the burring apparatus can be set, so that thin tubes with betters durability, as compared to conventional tubes, can be used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of a core structure of a heat exchanger according to the present invention will be described.

Incidentally, in these embodiments, a case that the heat exchanger is an automotive radiator will be described.

As shown inFIG. 1, the core structure of a heat exchanger of a first embodiment of the present invention has a pair of seat plates2and2arranged opposite to each other with a predetermined distance interposed therebetween at top and bottom positions of a radiator1.

Reinforcements5are arranged respectively at both end portions2aof the seat plates and couple the top and bottom seat plates2. Between the seat plates2and the reinforcements5, tubes3and corrugated fins4are alternately arranged with a predetermined space interposed therebetween in a direction of the width of the radiator1.

As shown inFIG. 2toFIG. 4, on the seat plates2, tube holes2bcorresponding to arrangement positions of the respective tubes3are formed by burring. Incidentally, inFIG. 2toFIG. 4, only top side portions of the seat plates2, the tubes3, and so on are drawn and bottom side portions thereof are not shown. Regarding the bottom side portions, the bottoms seat plate2and the lower end portions of the tubes3are fixed in a vertically reverse state of the upper side portions.

As shown inFIG. 2, on main body portions2hof the seat plates2, connection portions2chaving the tube holes2bare formed with a predetermined space. The connection portions2chave wall portions2fin a cup shape slanted toward the tube holes2binto which the tubes3are inserted from the main body portions2h, and vulnerable portions2don side ends of the tube holes2bof the wall portions2fand vulnerable portions2eon end portions of bottom portions2gformed between the tube holes2bare formed in series, respectively. These vulnerable portions2dand2eare thinner than the wall portions2fwhich have the same thickness as that of the seat plates2and are formed with the wall portions2fsimultaneously at the time of burring.

The connection portions2cfunction as a guide to insert a tip of the tube3into the tube hole2bwhen the tubes3are assembled with the seat plates2, and when the seat plates2thermally expand, the connection portions2cact so as to absorb thermal stress of the connection portions2capplied to the tubes3by bending of the vulnerable portions2dand2e.

In the tube holes2b, both end portions3cof the tubes3are fixed by brazes R1in a state that the both end portions3care inserted therethrough.

Further, both end portions5aof the reinforcements5are fixed by brazes R2in a state that the both end portions5aare inserted through reinforcement holes5bformed in the seat plates2.

Incidentally, as shown inFIG. 4, on the outside of the seat plates2, a tank8is arranged with seals9interposed therebetween, and lower outer periphery portions8athereof are fixed to the seat plates2by caulking.

Further, in this embodiment, the seat plates2, the tubes3, the corrugated fins4, and the reinforcements5are all made of aluminum and integrally assembled in advance, and thereafter they are brazed integrally in a not-shown heat treatment furnace.

Hereinafter, a slant angle of the connection portions2cwill be described usingFIG. 5.

For the connection portions2cof the first embodiment, a slant angle θ becomes θ=tan−1(LB/(LA/2)) when the bottom portion2gof the connection portions2cat the center position of a distance LA between the adjacent tubes3and3is an origin O, a distance in a horizontal direction from this origin O to the tubes3is LA/2, and a distance from the origin O to the highest positions of the connection portions2cis LB, and the connection portions2care formed in a shape which satisfies the following relationship: slant angle θ (°)≧25χ(thickness(mm) of sheet plate)+(−125χ(thickness (mm) of tube)+25) . . . formula 1.

Incidentally, the thickness of the tube in the formula 1 is 0.13 mm to 0.23 mm, for example.

Here, for example, in a first case of a combination of sheet plates (thickness: 1.3 mm) and tubes (thickness: 0.18 mm) made thinner than conventional ones, the connection portions2care formed to have a slant angle θ of 35° or larger by the formula 1.

Hereinafter, results of experiments performed regarding combinations of other seat plates2and tubes3with various thicknesses including the first case will be described.

FIG. 6shows measurement results of thermal stress received by the tubes when a slant angle θ of each connection portion2cis varied regarding the combinations of other various seat plates2and tubes3including the first case.

As shown inFIG. 6, in the first case, when the slant angle is larger than 35°, the thermal stress became substantially 15 N/mm2or lower, which proves that the combination is capable of adequately enduring a normal usage of a heat exchanger.

Further, as shown in the same view, the same results were obtained by slant angles calculated by the formula 1 for the respective combinations regarding the combinations of other various sheet plates and tubes.

Note that in this first embodiment, the vulnerable portions2ebend to absorb the thermal stress of the connection portions against the tubes, thereby contributing to alleviation of the thermal stress.

FIG. 7shows measurement results of performing heat and impact durability tests in which warm water and cool water are repeatedly made to flow through combinations of tubes (thickness: 0.18 mm) made thinner than conventional ones and seat plates2with various thicknesses.

As shown inFIG. 7, in the first case, when the slant angle is larger than 35°, the combination passed the durability tests of approximately 7000 times, which proves that the combination, is capable of adequately enduring a normal usage of a heat exchanger.

Further, as shown in the same view, the same results were obtained by slant angles calculated by the formula 1 for each combination regarding combinations of other seat plates having various thicknesses.

Furthermore, as shown inFIG. 8, a correlation of optimum slant angles of the connection portions of specific sheet plates and tubes can be graphed, which enables the easy obtaining of the optimum slant angle for making the seat plates2and the tubes3thinner to thereby prevent cracking/breaking of the tubes due to the thermal stress of the connection portions.

Therefore, for the core structure H of the heat exchanger in this embodiment, the formula 1 can be used to easily obtain an optimum slant angle of the connection portions2caccording to an average thickness of the connection portions including the vulnerable portions of the seat plates2and the thickness of the tubes3, and in this case, cracking/breaking of the tubes3due to the thermal stress of the connection portions2ccan be prevented, so that the durability of tubes3can be increased as compared to conventional tubes.

Further, by the formula 1, a correlation among the slant angle of the connection portions2c, the thickness of the seat plates2, and the thickness of the tubes3can be comprehended to thereby facilitate making the seat plates2and the tubes3thinner.

FIG. 9shows portions in the vicinity of connection portions2cof a core structure of a heat exchanger according to a second embodiment of the present invention. For these connection portions2c, a bottom portion2gis formed as a flat portion.

In this case, similarly to the case described withFIG. 5, an origin O is taken at a position in between adjacent tubes3and3and in contact with the bottom face of the seat plate2to measure a slant angle θ.

Thus, even when the connection portions2care formed to have a flat portion, the formula 1 is satisfied.

In the foregoing, the embodiments of the present invention have been described, but the specific structure of the present invention is not limited to these embodiments. The present invention includes any change of design in the range not departing from the gist of the invention.