JP2000213425A - Egr cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a serious engine trouble by preventing cooling water from leaking to a passage side of exhaust gas. SOLUTION: In this EGR cooler, cooling water is supplied and exhaust inside a shell 1, and heat exchange between exhaust gas and the cooling water is carried out through the exhaust gas inside a tube 3. An end part of the tube 3 penetrated to a plate 2 is a tapered part 14 whose bore diameter increases toward a side opposite to the shell 1, and whole region of the tapered part 14 is welded to the plate 2 by laser irradiation L from the side opposite to the shell 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR cooler which is attached to an EGR device for recirculating exhaust gas of an engine to reduce the generation of nitrogen oxides and cools the exhaust gas for recirculation.

[0002]

2. Description of the Related Art Conventionally, an EGR device for reducing the generation of nitrogen oxides by recirculating a part of exhaust gas from an engine of an automobile or the like to the engine has been known.
In the device, when the exhaust gas recirculated to the engine is cooled, the temperature of the exhaust gas is reduced and its volume is reduced, so that the combustion temperature is reduced without significantly lowering the output of the engine and the nitrogen oxidation is effectively performed. In order to reduce the generation of substances, some engines are equipped with an EGR cooler for cooling the exhaust gas in the middle of a line for recirculating the exhaust gas to the engine.

FIG. 7 is a cross-sectional view showing an example of the EGR cooler. In FIG. 7, reference numeral 1 denotes a shell formed in a cylindrical shape. The plates 2 and 2 are fixed to each other, and both ends of a large number of tubes 3 are fixed to the respective plates 2 and 2 in a penetrating state.
Extends in the axial direction.

In the vicinity of one end of the shell 1,
A cooling water inlet pipe 4 is attached from the outside, and a cooling water outlet pipe 5 is attached from the outside near the other end of the shell 1, and cooling water 9 flows from the cooling water inlet pipe 4 into the shell 1. The supplied water flows outside the tube 3 and is discharged from the cooling water outlet pipe 5 to the outside of the shell 1.

Further, bonnets 6 and 6 formed in a bowl shape are fixed to the opposite sides of the shells 1 of the plates 2 and 2 so as to cover the end faces of the plates 2 and 2, respectively. The exhaust gas inlet 7 is provided at the center of the bonnet 6, and the exhaust gas outlet 8 is provided at the center of the other bonnet 6, respectively.
After the exhaust gas 10 of the engine enters the inside of one bonnet 6 from the exhaust gas inlet 7 and is cooled by heat exchange with the cooling water 9 flowing outside the tubes 3 while passing through a number of tubes 3, the other one is cooled. The exhaust gas is discharged into the bonnet 6 and recirculated from the exhaust gas outlet 8 to the engine.

[0006]

However, in such a conventional EGR cooler, the end of the tube 3 is fixed to the plate 2 through the brazing portion 11 as shown in an enlarged view in FIG. In particular, on the outlet side of the exhaust gas 10 as shown in the figure, when the exhaust gas 10 is cooled in the tube 3, a condensate containing a sulfuric acid component is generated and flows out from the outlet of the tube 3. There is a possibility that the brazing material (generally nickel brazing) forming the brazing portion 11 may be corroded by the condensed liquid. If the cooling water 9 leaks from the condensed liquid, the cooling water 9 is transferred to the engine side. There was a fear that it would lead to serious trouble.

At present, as shown in FIG.
It is considered that the end of the tube 3 is welded to the plate 2 by laser irradiation L. However, when this kind of laser welding is adopted, a laser welded portion 12 resistant to corrosion by condensate is obtained, Since the penetration by the laser irradiation L does not reach the deep part, it is difficult to sufficiently increase the welding depth D, and only the laser welded part 12 having a low bonding strength can be obtained. In such a case, there is a possibility that the laser weld 12 is damaged and the cooling water 9 leaks out.

That is, when the end of the tube 3 is laser-welded to the plate 2, the laser irradiation L is performed from the side opposite to the shell 1 of the plate 2 in parallel with the axial direction of the tube 3.
Since it is common to weld the boundary between the end face of the tube 3 and the plate 2 at a welding depth D approximately equal to the thickness of the tube 3, only the laser welded portion 12 having a strength lower than the strength of the tube 3 itself is obtained. Did not.

In the actual operation, since the laser irradiation L is performed from directly above with the tube 3 in an upright state, even if the laser intensity is simply increased to increase the penetration depth, the tube 3 is melted. There is a high risk that the part will flow into the tube 3 and narrow the flow path,
There was naturally a limit in increasing the laser intensity.

Further, as described above, in the laser welded portion 12 having a shallow welding depth D, the tube 3 is welded to the through hole 13 on the plate 2 only in a small area on the side opposite to the shell 1, so A minute gap is formed in most of the portion between the hole 13 and the tube 3, and cavitation occurs due to water pressure fluctuation caused by minute vibration of the tube 3 in the gap. Crevice corrosion occurred at the innermost portion (the portion that abuts on the laser welded portion 12), and there was a possibility that the end of the tube 3 was damaged and the cooling water 9 leaked out.

The present invention has been made in view of the above circumstances, and has as its object to prevent the occurrence of serious engine trouble by preventing cooling water from leaking to the exhaust gas passage side.

[0012]

According to a first aspect of the present invention, there is provided a shell having a cylindrical shape, plates fixed to both ends of the shell in the axial direction so as to close the shell end faces, A bonnet fixed to the side opposite to the shell of the plate so as to enclose the end face of the plate; and a tube extending in the axial direction inside the shell and having both ends fixed to the respective plates. An EGR cooler for supplying and discharging cooling water therein and passing heat through the exhaust gas from one bonnet side to the other bonnet side in the tube to exchange heat between the exhaust gas and the cooling water, The end of the tube penetrating into the shell is tapered so that the diameter gradually increases toward the anti-shell side, and the entire area of the tapered part is welded to the plate by laser irradiation from the anti-shell side. The one in which the features.

If the end of the tube is formed in a tapered portion whose diameter gradually increases toward the anti-shell side, the inner peripheral surface of the tapered portion forms a mortar-shaped slope toward the anti-shell side. It becomes an open shape, and it becomes possible to easily perform laser irradiation on the entire inner peripheral surface from the side opposite to the shell.

The resulting laser weld has a high bonding strength with the welding depth increased to an extent corresponding to the thickness of the plate, and has a very small gap between the through hole of the plate and the tube. No gap is formed, and no gap corrosion occurs.

The invention according to claim 2 of the present invention provides:
A shell formed in a cylindrical shape, a plate fixed to both ends in the axial direction of the shell so as to close the shell end surface, a bonnet fixed to cover the plate end surface on the side opposite to the shell of the plate; Tubes extending axially through the inside of the shell and having both ends fixed to the respective plates to supply and discharge cooling water to the inside of the shell, and inside the tubes from one bonnet side to the other. An EGR cooler configured to exchange heat between the exhaust gas and the cooling water through the exhaust gas toward the bonnet side,
A notch was formed on the shell side of the through hole of the plate through which the end of the tube penetrated, and the end of the tube was welded to the plate by laser irradiation from the opposite side of the shell so that the laser welded portion reached the notch. It is characterized by the following.

If the notch is formed on the shell side of the through hole of the plate, the end of the tube is welded to the plate by laser irradiation from the opposite side of the shell so that the laser welded portion reaches the notch. In addition, since a portion that is not welded remains as a notch portion in a state of being largely open to the shell side, a minute gap is not formed between the through hole of the plate and the tube, so that crevice corrosion does not occur. Under conditions where crevice corrosion does not occur, increase the laser intensity to such an extent that the melted part due to laser irradiation does not flow into the tube and narrow the flow path, and increase the penetration depth as much as possible to join the laser weld It is possible to make the structure as strong as possible.

According to a third aspect of the present invention, there is provided a shell formed in a cylindrical shape, a plate fixed to both ends of the shell in the axial direction so as to close a shell end face, and a plate opposite to the shell. A bonnet fixed so as to enclose the end face of the plate, and a tube extending in the axial direction inside the shell and having both ends penetratingly fixed to the respective plates, and supplying cooling water to the inside of the shell. An EGR cooler that discharges exhaust gas from the one bonnet side to the other bonnet side and exchanges heat between the exhaust gas and the cooling water in the tube, and one end of the EGR cooler has a required length with respect to the plate. A sub-plate is provided so as to extend through the tube and fixed through a brazed portion, and penetrate the end of the extended tube and fixed through a laser welded portion. It is characterized in that it has configured to cover the braze by the plate.

If the plate is covered with the sub-plate as described above, even if condensate containing a sulfuric acid component is generated by cooling the exhaust gas in the tube and flows out from the outlet of the tube, the condensate flowing out is The brazing material forming the brazing portion is corroded by the condensed liquid because the sub-plate fixing the tube through the corrosion-resistant laser welding portion is isolated from the brazing portion of the plate so as not to contact the brazing portion. This is reliably avoided, and the bonding strength of the tube to the plate is kept high by the brazing portion. Even if the brazing portion cracks and water leaks, the cooling water Is blocked by the sub-plate and accumulates between the sub-plate and the plate.

According to a fourth aspect of the present invention, there is provided a shell formed in the shape of a cylindrical container, and the inside of the shell extends in the axial direction and both ends thereof are fixed through both ends of the shell in the axial direction. An EG for supplying cooling water to the inside of the shell and passing exhaust gas into the tube to exchange heat between the exhaust gas and the cooling water.
An R cooler, characterized in that the diameter and thickness of the tube are increased so as to increase the cross-sectional area and the strength of the flow path, and that a gas flange is provided at the tip of each tube protruding outside the shell. is there.

In this way, the number of tubes can be reduced to the minimum necessary, and a line for recirculating exhaust gas is appropriately branched to the gas flange at the tip of each tube that protrudes outside the shell. Even if condensate containing a sulfuric acid component is generated by cooling the exhaust gas in the tube, the condensate may adversely affect the penetration fixing portion of the tube to the shell, such as corrosion, etc. And even if a leak occurs due to a crack in the through-fixed portion of the tube with respect to the shell, the leaked cooling water simply leaks out of the shell, This prevents the exhaust gas from entering the flow path side.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an example of an embodiment for carrying out the invention according to claim 1 of the present invention. The same parts as those in FIGS. 7 to 9 are denoted by the same reference numerals.

In the present embodiment, an EGR cooler having substantially the same configuration as the EGR cooler described above with reference to FIG.
The end of the tube 3 penetrating the plate 2 is formed as a tapered portion 14 whose diameter gradually increases toward the side opposite to the shell 1,
The entire area of the tapered portion 14 is welded to the plate 2 by laser irradiation L from the side opposite the shell 1.

As described above, the end of the tube 3 is connected to the shell 1
If the tapered portion 14 gradually increases in diameter toward the side, the inner peripheral surface of the tapered portion 14 becomes a shape that is opened in a mortar-shaped slope toward the side opposite to the shell 1, and The laser irradiation L can be easily performed on the entire region from the side opposite to the shell 1.

The resulting laser welded portion 12 has a high bonding strength with the welding depth D increased to an extent corresponding to the thickness of the plate 2, and has a through hole 13 of the plate 2 and a tube. 3, no minute gap is formed and no gap corrosion occurs.

Therefore, according to the above embodiment, the welding depth D is made larger than before by the laser welding portion 12 which is resistant to corrosion, so that the plate 2 and the tube 3 can be fixedly penetrated with high bonding strength. Since the formation of minute gaps between the through holes 13 of the plate 2 and the tubes 3 can be avoided to prevent the occurrence of crevice corrosion, the cooling water 9 leaks to the flow path side of the exhaust gas 10. Can be reliably prevented, whereby the possibility that the cooling water 9 is guided to the engine side can be eliminated, and serious engine trouble can be prevented from occurring.

FIGS. 3 and 4 show an embodiment of the invention according to claim 2 of the present invention. In this embodiment, a plate 2 through which an end of a tube 3 penetrates is shown.
A notch 15 is formed in the through hole 13 on the shell 1 side, and the end of the tube 3 is welded to the plate 2 by laser irradiation L from the opposite side of the shell 1 so that the laser welding portion 12 reaches the notch 15. I have.

If the notch 15 is formed on the shell 1 side of the through hole 13 of the plate 2 in this manner, the end of the tube 3 is irradiated with the laser beam L from the opposite side of the shell 1 to the laser welding portion
2 is welded to the plate 2 so as to reach the notch 15, a portion that is not welded is formed as a notch 15 in the shell 1.
As a result, a small gap is not formed between the through hole 13 of the plate 2 and the tube 3 so that no crevice corrosion occurs. In the above, the laser intensity is increased to such an extent that the portion melted by the laser irradiation L does not flow into the tube 3 and narrow the flow path, and the penetration depth D is increased as much as possible to increase the bonding strength of the laser weld 12 as much as possible. It is possible to have an enhanced structure.

Therefore, also in this embodiment, the plate 2
The formation of minute gaps between the through hole 13 and the tube 3 can be avoided to prevent the occurrence of crevice corrosion, so that the cooling water 9 leaks to the flow path side of the exhaust gas 10 without fail. Thus, there is no possibility that the cooling water 9 is guided to the engine side, and a serious engine trouble can be prevented from occurring.

FIG. 5 shows an example of an embodiment for carrying out the invention according to claim 3 of the present invention. In this embodiment, the tube 3 has one end extending from the plate 2 by a required length. Through the brazing portion 11 and through the tip of the extended tube 3 to form the laser welded portion 1
A sub-plate 16 is provided, which is fixed through the sub-plate 2, and the brazing portion 11 is covered with the sub-plate 16.

In this embodiment, the plate 2
Is bent toward the axial direction of the tube 3 with a step portion interposed therebetween, and the shell 1 and the bonnet 6 are butt-welded with the outer periphery of the plate 2 interposed therebetween.

When the plate 2 is covered with the sub-plate 16 in this manner, the exhaust gas 10 is cooled in the tube 3 to generate a condensate containing a sulfuric acid component and flows out from the outlet of the tube 3. However, the condensate that has flowed out is isolated from the brazing portion 11 of the plate 2 by the sub-plate 16 that penetrates and fixes the tube 3 through the corrosion-resistant laser welded portion 12 so as not to contact the brazing portion 11 of the plate 2. Corrosion of the brazing material forming the brazing portion 11 by the condensed liquid is reliably avoided, and the bonding strength of the tube 3 to the plate 2 is maintained higher by the brazing portion 11. Even if a crack occurs in the brazing portion 11 and water leakage occurs, the cooling water 9 is blocked by the sub-plate 16 and accumulates between the sub-plate 16 and the plate 2. It will be.

Therefore, according to the above embodiment, the plate 2
While maintaining the bonding strength of the tube 3 with respect to the
6 protects the condensate of the exhaust gas 10 from corrosion, so that the occurrence of corrosion in the brazing portion 11 can be prevented. Even if water is leaked due to cracks, the cooling water 9 can be blocked by the sub-plate 16 and stored between the sub-plate 16 and the plate 2, so that the cooling water 9 is guided to the engine side. It is possible to prevent a serious engine trouble from occurring.

FIG. 6 shows an example of an embodiment for carrying out the invention according to claim 4 of the present invention. In this embodiment, the shell 1 is formed in a cylindrical container shape, and the inside of the shell 1 is formed. The two ends of a tube 3 extending in the axial direction
The diameter of the tube 3 and the wall thickness of the tube 3 are increased as compared with the conventional case, and the number of tubes 3 is increased by increasing the cross-sectional area and strength of the flow path. Is reduced to a necessary minimum (for example, about three tubes), and a gas flange 17 is provided at the end of each tube 3 projecting outside the shell 1.

That is, in the case of the conventional EGR cooler,
Since the diameter of the tube 3 and the thickness of the tube 3 have been reduced so that the recirculated exhaust gas 10 can be efficiently cooled by the cooling water 9, the flow path cross-sectional area per tube 3 is reduced, and Tubes 3 are required, and a structure in which these are supported by the plate 2 and all the tubes 3 communicate with each other in the bonnet 6 has to be adopted. However, in the present embodiment, the diameter and the wall thickness of the tubes 3 are conventionally reduced. The number of tubes 3 is reduced to a necessary minimum by further increasing the flow path cross-sectional area and strength.

However, it is needless to say that it is necessary to appropriately increase the lengths of the shell 1 and the tube 3 in order to maintain the same cooling efficiency as the conventional one.

In this way, if the number of tubes 3 is reduced to the necessary minimum and the ends of the tubes 3 are fixed through the ends of the shell 1 in the axial direction, the tubes 3 projecting outside the shell 1 3 against the gas flange 17 at the tip
Since the line for recirculating the exhaust gas 10 can be appropriately branched and connected directly, even if a condensate containing a sulfuric acid component is generated by cooling the exhaust gas 10 in the tube 3, the condensation The liquid is prevented from adversely affecting the through-fixed portion of the tube 3 with respect to the shell 1 such as corrosion.
In addition, even if a crack occurs in the portion where the tube 3 penetrates and is fixed to the shell 1 and water leaks, the leaked cooling water 9 only leaks out of the shell 1 and exhaust gas 10 Is prevented from invading the flow path side.

Therefore, according to the above embodiment, the exhaust gas 1
0 can reliably prevent the condensate of the exhaust gas 10 from adversely affecting the through-fixed portion of the tube 3 with respect to the shell 1. Even if water is leaked due to cracks, it is possible to reliably prevent the leaked cooling water 9 from entering the flow path side of the exhaust gas 10.
Eliminates the possibility that the cooling water 9 is guided to the engine side,
Serious engine troubles can be prevented from occurring.

Incidentally, the EGR cooler of the present invention is not limited to the above-described embodiment, but the exhaust gas outlet side is shown in the figure, but a similar structure is adopted on the exhaust gas inlet side. It goes without saying that various changes may be made without departing from the spirit of the present invention.

[0040]

According to the EGR cooler of the present invention described above, it is possible to reliably prevent the cooling water from leaking to the exhaust gas passage side, and the cooling water is guided to the engine side. An excellent effect of eliminating the fear and preventing the occurrence of serious engine trouble can be achieved.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing an example of an embodiment for carrying out the invention described in claim 1 of the present invention.

FIG. 2 is an enlarged sectional view showing a state where the tube of FIG. 1 is laser-welded to a plate.

FIG. 3 is an enlarged sectional view showing an example of an embodiment for carrying out the invention described in claim 2 of the present invention.

FIG. 4 is an enlarged sectional view showing a state where the tube of FIG. 3 is laser-welded to a plate.

FIG. 5 is an enlarged sectional view showing an example of an embodiment for carrying out the invention described in claim 3 of the present invention.

FIG. 6 is an enlarged sectional view showing an example of an embodiment for carrying out the invention described in claim 4 of the present invention.

FIG. 7 is a sectional view showing an example of a conventional EGR cooler.

FIG. 8 is an enlarged sectional view showing details of a through-fixing portion between the tube and the plate in FIG. 7;

FIG. 9 is an enlarged cross-sectional view showing another example of a penetration fixing portion between a tube and a plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shell 2 Plate 3 Tube 6 Bonnet 9 Cooling water 10 Exhaust gas 11 Brazing part 12 Laser welding part 13 Through hole 14 Tapered part 15 Notch part 16 Sub plate 17 Gas flange L Laser irradiation

Claims (4)

[Claims] 1. A shell formed in a cylindrical shape, a plate fixed to both ends in the axial direction of the shell so as to close a shell end face, and a plate fixed to the opposite side of the plate to cover the plate end face. And a tube extending axially through the inside of the shell and having both ends penetratingly fixed to the respective plates, for supplying and discharging cooling water to the inside of the shell and having one inside the tube. An EGR cooler for exchanging heat between the exhaust gas and the cooling water through the exhaust gas from the bonnet side to the other bonnet side, wherein the diameter of the tube penetrating the plate is gradually increased toward the anti-shell side. An EGR cooler characterized in that a tapered portion is formed, and the entire region of the tapered portion is welded to a plate by laser irradiation from the opposite side of the shell. 2. A shell formed in a cylindrical shape, a plate fixed to both ends in the axial direction of the shell so as to close a shell end surface, and a plate fixed to the opposite side of the plate to cover the plate end surface. And a tube extending axially through the inside of the shell and having both ends penetratingly fixed to the respective plates, for supplying and discharging cooling water to the inside of the shell and having one inside the tube. An EGR cooler configured to exchange heat between the exhaust gas and the cooling water by passing exhaust gas from the bonnet side to the other bonnet side, wherein a notch is formed in a shell side of a through hole of a plate through which an end of a tube passes. An EGR cooler, wherein an end of the tube is welded to a plate by laser irradiation from an opposite side of the shell so that a laser welded portion reaches the notch. . 3. A shell formed in a cylindrical shape, a plate fixed to both ends in the axial direction of the shell so as to close a shell end surface, and a plate fixed to the opposite side of the plate to cover the plate end surface. And a tube extending axially through the inside of the shell and having both ends penetratingly fixed to the respective plates, for supplying and discharging cooling water to the inside of the shell and having one inside the tube. An EGR cooler for exchanging heat between the exhaust gas and the cooling water through the exhaust gas from the bonnet side to the other bonnet side, wherein one end of the EGR cooler extends through a tube so as to extend a required length to the plate. A sub-plate fixed through a brazing portion and penetrating the tip of the extended tube and fixed through a laser welding portion is provided, and the brazing portion is fixed by the sub-plate. An EGR cooler characterized by being configured to cover. 4. A shell formed in a cylindrical container shape, and a tube extending in the axial direction inside the shell and having both ends fixed to both end surfaces in the axial direction of the shell,
An EGR cooler that supplies and discharges cooling water to the inside of the shell and exchanges heat between the exhaust gas and the cooling water through an exhaust gas in the tube. An EGR cooler characterized in that the diameter and thickness of the tube are increased and a gas flange is provided at the end of each tube protruding outside the shell.