Exhaust gas heat exchanger

This application is based upon Japanese Patent Application No. 2001-226409, filed on Jul. 26, 2001, the contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to an exhaust gas heat exchanger for performing heat exchange between exhaust gas generated by combustion and cooling water. Specifically, the present invention relates to an exhaust gas heat exchanger for cooling the exhaust gas in an exhaust gas recirculation system (i.e., EGR system).

2. Related Art

As shown in FIG. 1, an exhaust gas heat exchanger for cooling the exhaust gas in an EGR system (hereinafter, referred to as an EGR gas heat exchanger) is equipped with plural laminated exhaust gas tubes 301 disposed in a tank 302 . The exhaust gas tubes 301 penetrate and are attached to a core plate 330 . A peripheral portion of the core plate 330 is folded toward the tank 302 , and is attached to an outer wall of the tank 302 . The tank 302 is closed with the core plate 330 to isolate a cooling water passage formed in the tank 302 from a bonnet 306 . A cooling water inlet pipe 304 and a cooling water outlet pipe (not shown) are disposed on the tank 302 to permit the flow of the cooling water through the tank 302 .

In this EGR gas heat exchanger, an adequate contact area is necessary for ensuring contact strength between the peripheral portion of the core plate 330 and the tank 302 . Therefore, when the core plate 330 is folded toward the tank 302 as shown in FIG. 1, the cooling water inlet pipe 304 must be kept away from the core plate 330 , for example, the distance l in the figure is about 20-30 mm, to obtain the adequate contact area between the core plate 330 and the tank 302 . As a result, the cooling water becomes stuck at a portion of the tank 302 between the core plate 330 and the cooling water inlet pipe 304 or between another core plate (disposed at the other side, not shown) and the cooling water outlet pipe. Accordingly, the heat exchanging efficiency would be lowered and the boiling of the cooling water may occur at the vicinity of the core plate.

An object of the present invention is to provide an exhaust gas heat exchanger in which a cooling water pipe is disposed close to a core plate to improve the heat exchanging efficiency and resistance to boiling.

The exhaust gas heat exchanger has a tank, plural exhaust gas tubes provided in the tank through which exhaust gas flows. A water passage is defined in the tank where cooling water flows from a cooling water inlet pipe to a cooling water outlet pipe. The plurality of exhaust gas tubes are connected to core plates at an upstream side thereof and a downstream side thereof. The core plates are connected to bonnets at both sides of the tank. A peripheral portion of at least one of the core plates is folded toward the bonnet to which said at least one of the core plates is connected.

With this feature, the cooling water inlet pipe, for example, can be disposed close to the core plate at the upstream side. In this case, the cooling water can flow close to the upstream side of the plural exhaust gas tubes. As a result, the cooling water can be prevented from being stuck at the upstream side of plural exhaust gas tubes.

Preferably, the at least one of the core plates is the one disposed at the upstream side of the plural exhaust gas tubes.

Preferably, the cooling water inlet pipe or the cooling water outlet pipe is disposed on the tank at a location where the disposed distance of the pipe from the core plate is equal to or less than a diameter of the pipe.

Other features and advantages of the resent invention will become more apparent from the following detailed description made with reference to the accompanying drawings.

FIG. 1 is a partial cross sectional view showing an EGR gas heat exchanger in the related art;

FIG. 2 is a schematic view of an EGR system according to the present invention;

FIG. 3A is a partial cross sectional view of an EGR gas heat exchanger in a first embodiment of the present invention;

FIG. 3B is a partial cross sectional view of the EGR gas heat exchanger in the first embodiment of the present invention taken along line IIIB—IIIB in FIG. 3A;

FIG. 4 is a cross sectional view of a slightly different type of the EGR gas heat exchanger in the first embodiment of the present invention showing a cross sectional view of a tank and plural exhaust gas tubes taken along line IV—IV in FIG. 3A;

FIG. 5 is an enlarged cross sectional view of the EGR gas heat exchanger in the first embodiment of the present invention taken along line V—V in FIG. 4;

FIG. 6 is an enlarged cross sectional view of the EGR gas heat exchanger in the first embodiment of the present invention taken along line VI—VI in FIG. 4;

FIG. 7 is an enlarged cross sectional view similar to FIG. 5 of the EGR gas heat exchanger in the first embodiment; and

FIG. 8 is an enlarged cross sectional view similar to FIG. 6 of the EGR gas heat exchanger in the first embodiment.

Specific embodiments of the present invention will now be described hereinafter with reference to the accompanying drawings in which the same or similar component parts are designated by the same or similar reference numerals.

A first preferred embodiment of the present invention will be now described with reference to FIGS. 2 to 8 . In this embodiment, the present invention is typically applied to an EGR cooler of an exhaust gas recirculation system (EGR system) for a diesel engine 200 (internal combustion system). FIG. 2 shows an exhaust gas heat exchanger 100 (hereinafter, referred to as an EGR gas heat exchanger) of this embodiment.

The EGR system includes an exhaust gas recirculation pipe 210 through which a part of the exhaust gas discharged from the engine 200 returns to an intake side of the engine 200 . An EGR valve 220 for adjusting the amount of exhaust gas recirculation in accordance with an operational state of the engine 200 is disposed in the exhaust gas recirculation pipe 210 . The EGR gas heat exchanger 100 is disposed between an exhaust gas side of the engine 200 and the EGR valve 220 so that heat exchange is performed between the exhaust gas discharged from the engine 200 and cooling water (i.e., engine-cooling water).

Next, a structure of the EGR gas heat exchanger 100 will be described with reference to FIGS. 3A, 3 B and 4 .

EGR gas heat exchanger 100 comprises plural, in this case, four exhaust gas tubes 101 each of which has a flat rectangular cross section, and each of which is formed by joining two plates 111 a and 111 b and has an inner fin 101 b therein, which is for partitioning the space formed in each exhaust gas tube 101 to form plural small passages by being folded many times (shown in FIG. 4 as plates 111 a and 111 b , and an inner fine 101 b ).

Ribs 108 are formed, as guides for the cooling water, on both main surfaces of each exhaust gas pipe 101 at portions of both main surfaces close to the upstream side of the exhaust gas tubes 101 . Both ribs 108 formed on the exhaust gas tube 101 contact to the other ribs 108 formed on adjoining one of the exhaust gas tubes 101 . The ribs 108 formed on the outer main surfaces of the outermost exhaust gas tubes 101 contact protrusions 109 formed on an inner wall of a tank 102 in the laminated direction of the exhaust gas tubes 101 . The ribs 108 and protrusions 109 keep the width of each water passage, formed between adjacent exhaust gas tubes 101 and between the outermost exhaust gas tube 101 and the inner wall of the tank 102 , constant.

As shown in FIG. 4, the tank 102 has a flat rectangular cross sectional shape that is formed by soldering plates 102 a and 102 b.

The plates 102 a and 102 b both have a step 102 c formed at one end thereof that protrudes outward. The other flat end of the plates 102 a and 102 b are connected to the step 102 c of the other plate 102 a or 102 b . The plates 102 a and 102 b are connected to each other by soldering at connecting portions 102 d where the steps 102 c are formed. The tank 102 and plural exhaust gas tubes 101 constitute a heat exchanging core 110 by accommodating the exhaust gas tubes 101 in the tank 102 so that the longitudinal direction of the exhaust gas tubes 101 coincides the longitudinal direction of the tank 102 .

The tank 102 is closed by core plates 103 at both ends thereof. Each core plate 103 has openings through which the exhaust gas tubes 101 are connected to the core plates 103 by soldering.

As shown in FIG. 3A, a cooling water inlet pipe 104 is provided at one end of the tank 102 where an upstream side of exhaust gas tubes 101 is disposed so as to be disposed close to the core plate 103 . The cooling water flows into the tank 102 through the cooling water inlet pipe 104 . A cooling water outlet pipe 105 is connected to the other end of the tank 102 so as to be disposed close to the other core plate 103 . Accordingly, the tank 102 serves as a passage for the cooling water.

The cooling water inlet pipe 104 and outlet pipe 105 are disposed away from respective core plates 103 at substantially a distance of d/2. The “l” is a distance between the respective core plates 103 at the near side and the center of the inlet pipe 104 or the center of outlet pipe 105 as shown in FIG. 1 . Also, the “t” is a thickness of the core plates 103 , and the “d” is a diameter of the inlet pipe 104 or outlet pipe 105 , as shown in FIG. 1 .

Bonnets 106 , 107 are connected to both ends of the tank 102 by soldering so that edges of both core plates 103 are folded in opposite directions with regard to the heat exchanging core 110 as shown in the figures to surround end portions of both bonnets 106 , 107 . An exhaust gas inlet 106 a is formed in the bonnet 106 disposed at a cooling water inlet pipe side for introducing the exhaust gas to the bonnet 106 . An exhaust gas outlet 107 a is formed in the bonnet 107 disposed at a cooling water outlet pipe side for exhausting the exhaust gas from the bonnet 106 to the outside. The cooling water flows in a direction substantially identical to the stream of the exhaust gas flowing through the exhaust gas tubes 101 .

Both of the bonnets 106 , 107 have a quadrangular pyramid-like shape so that the duct cross sectional area increases toward the heat exchanging core to improve the distribution of exhaust gas to each exhaust gas tube 101 .

In this EGR gas heat exchanger 100 described above, the exhaust gas introduced from the exhaust gas inlet 106 a passes through the bonnet 106 and each of the exhaust gas tubes 101 . Then, the exhaust gas is cooled down by the cooling water flowing around each of the exhaust gas tubes 101 . After that, the cooled exhaust gas is exhausted from the exhaust gas outlet 107 a through the bonnet 107 .

The cooling water flows into the tank 102 through the cooling water inlet pipe 104 and passes through the tank 102 to cool down the exhaust gas flowing through each exhaust gas tube 101 . Finally, the cooling water flows out from the tank 102 through the cooling water outlet pipe 105 .

Next, the core plates 103 will be described in detail with reference to FIGS. 5 to 8 .

As shown in FIG. 5, the peripheral portion of each core plate 103 is folded toward the respective bonnets 106 and 107 to form a crank shape in cross sectional view. The peripheral portion of each core plate 103 has a first perpendicular wall 103 a , a flat portion 103 b and a second perpendicular wall 103 c in order from a root portion of the plate 103 where the exhaust gas tubes 101 are connected to the end of the plate 103 . The first perpendicular wall 103 a contacts the inner wall of the tank 102 as a connecting portion to the tank 102 . The plates 102 a and 102 b of the tank contact the flat portion 103 b contiguous from the wall 103 a . The second perpendicular wall 103 c , which is an outermost end portion, contacts an outer wall of the bonnet 106 or 107 as a connecting portion thereto. The end portions of plates 102 a and 102 b , which contact the flat portion 103 b , are deformed to have tapered portions 120 so that that they do not interfere with the folded radius R of a folded portion 103 d between the first wall 103 a and the flat portion 103 b . The tapered angle of the tapered portion 120 is mainly determined to satisfy the above-described condition.

Next, the manufacturing method of the EGR gas heat exchanger will be described.

The first and second plates 111 a and 111 b fit with each other with the inner fine 101 b interposed therebetween to form the tube 101 . The tubes 101 are laminated so that the ribs 108 formed on adjacent tubes 101 contact each other. After that, the laminated tubes 101 are encapsulated in the tank 102 by fitting the plates 102 a and 102 b with each other. The plates 102 a and 102 b are connected with each other at two connecting portions 102 d where steps 102 c are formed so that one end of the plate 102 a is laid on one end of the plate 102 b at one connecting portion 102 d and the other end of the plate 102 b is laid on the other end of the plate 102 a at the other connecting portion 102 d as shown in FIG. 4 . The ribs 109 are formed on the inner wall of the tank 102 . The ribs 109 contact the ribs 108 formed on the outermost tubes 101 . The core plates 103 are assembled to the tank 102 to seal the tank so that both ends of the tubes 101 are inserted through the openings formed in the core plates 103 and fixed to the core plates 103 . Moreover, the core plates 103 are assembled to the tank 102 so that the first perpendicular wall 103 a contacts the inner wall of the tank 102 and the flat portion 103 b contacts the ends of plates 102 a and 102 b . Consequently, bonnets 106 and 107 are assembled to the tank 102 so that the second perpendicular wall 103 c of the core plate 103 contacts the outer wall of the bonnet 106 or 107 . Also, the cooling water inlet pipe 104 and outlet pipe 105 are assembled on the tank 102 . After each part is assembled as described above, soldering is performed to obtain the EGR gas heat exchanger 100 .

In this embodiment, the cooling water inlet pipe 104 and outlet pipe 105 are disposed on the tank 102 at the locations close to the respective core plates 103 since the core plates 103 are folded toward the respective bonnets 106 and 107 . Moreover, the core plates 103 have the connecting portions 103 a to be connected to the inner wall of the tank 102 by soldering. Therefore, the connecting portions are secured between the core plates 103 and the tank 102 . In this embodiment, the cooling water can flow into the tank 102 along the core plate 103 at a side of the bonnet 106 , or the cooling water can flow out from the tank 103 along the core plate 103 at a side of the bonnet 107 . Therefore, the cooling water is prevented from being stuck in the tank 102 . As a result, the cooling water that does not contribute to heat exchanging with the exhaust gas can be reduced, thereby improving the heat exchanging efficiency.

Since the temperature of the exhaust gas is relatively high at the upstream side of the exhaust gas tubes 101 , the cooling water might be boiled easily if the cooling water was stuck at the upstream side of the exhaust gas tubes 101 , i.e., at a side of the cooling water inlet pipe 104 . However, in this embodiment, the cooling water inlet pipe 104 can be disposed on the tank 102 close to the core plate 103 , so that the cooling water is prevented from being stuck at the upstream side of the exhaust gas tubes 101 to restrain the boiling of the cooling water.

The peripheral portion of each core plate 103 is formed using a press process to have the first wall 103 a and second wall 103 c both of which extend in a direction perpendicular to the root portion 101 a of the tubes 101 and the flat portion 103 b . It is difficult to make a folded portion 103 d formed between the first wall 103 a and the flat portion 103 b so as to have right angle at its corner point. Therefore, the folded portion 103 d is rounded as shown in FIGS. 5 to 8 .

In this situation, as shown in FIG. 7, if a tip portion of the plate 102 ′ b at the one connecting portion 102 d (or a tip portion of the plate 102 ′ a at the other connecting portion 102 d ) is flat, the tip portion might not contact the flat portion 103 b because the rounded folded portion 103 d prevents the tip portion from contacting the flat portion 103 b when the first wall 103 a is connected to the inner wall of the tank 102 , i.e., the plate 102 ′ b ( 102 ′ a ). As a result, the gap may be formed between the tip portion of the plate 102 ′ b ( 102 ′ a ) and the flat portion 103 b . However, as shown in FIG. 5, when the tip portion of the plate 102 b ( 102 a ) in this figure is formed to have the tapered portion 120 , the tip portion of the plate 102 b ( 102 a ) does not interfere with the folded portion 103 d . Accordingly, even if the folded portion 103 d is formed to have a curve portion, the tip portion of the plate 102 b ( 102 a ) can contact the flat portion 103 b easily while the first wall 103 a contacts the inner wall of the tank 102 . As a result, the core plate 103 is fixed to the tank 102 by soldering efficiently.

Similar to the above, in the tank 102 which has two flat plates 102 a and 102 b fitted with each other to have two connecting portions 102 d shown in FIG. 4, a portion where only one plate 102 a ( 102 b ) faces the flat portion 103 b of the core plate 103 is formed at each root portion of the step 102 c as understood from FIGS. 4, 6 and 8 . In this circumstance, when the tip portion of the plate 102 ′ b ( 102 ′ a ) is formed to be flat as shown in FIG. 7, due to the same reason described above, i.e., due to the rounded folded portion 103 d , the plate 102 ′ a ( 102 ′ b ) also may not contact the flat portion 103 b of the core plate 103 at the portion where the only one plate 102 ′ a ( 102 ′ b ) faces the flat portion 103 b of the core plate 103 since the tip portion of the plate 102 ′ b ( 102 ′ a ) shown in FIG. 7 cannot contact the flat portion 103 b of the core plate 103 . In this case, the tank 102 may not be sealed by the core plate 103 at the portion where the only one plate 102 ′ a ( 102 ′ b ) faces the flat portion 103 b of the core plate 103 as shown in FIG. 8 .

Therefore, when the tip portion of the plate 102 b ( 102 a ) is formed to have the tapered portion 120 as shown in FIG. 5, this results in the tip portion of the plate 102 a ( 102 b ) contacting the flat portion 103 b of the core plate 103 to seal the tank 102 at the portion where only one plate 102 a ( 102 b ) faces the flat portion 103 b of the core plate 103 as shown in FIG. 6 .

The tip portion of the plate 102 a should be tapered at one of two connecting portions 102 d shown in FIG. 4 where the plate 102 a contacts the first wall 103 a of the core plate 103 while the plate 102 b overlaps the plate 102 a . Also, the tip portion of the plate 102 b should be tapered at the other of two connecting portions 102 d shown in FIG. 4 where the plate 102 b contacts the first wall 103 a of the core plate 103 while the plate 102 a overlaps the plate 102 b . Therefore, both of plates 102 a and 102 b are tapered at the tip portions thereof as shown in FIGS. 5 and 6.

As described above, by forming the tapered portions 120 at the tip portion of respective plates 102 a and 102 b , the core plates 103 can be securely soldered to the tank 102 , thereby preventing the cooling water from leaking from the tank 102 through the connecting portion between the tank 102 and core plates 103 .

In the above-described embodiment, although the tank is formed by fitting and soldering two plates, and the tube is formed also by fitting and soldering two plates, the tank and tube are not limited to being formed using that process. For example, welded pipe or tube can be used to form the tank or the tube. Also, the shapes of the tank and tube is not limited to those of this embodiment. Moreover, the number of laminated tubes, row of the laminated tubes are not limited to those of this embodiment. Furthermore, a louver may be provided in each tube.

While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be therein without departing from the scope of the invention as defined in the appended claims.