DE10124383A1 - Exhaust gas heat exchanger - Google Patents

Abstract

According to the present invention, when a transparent thin film such as a silicon oxide glass film (SiO¶2¶ glass film) whose heat resistance is high and which is effective in preventing soot from unburned fuel and carbon adheres to the Heat transfer surfaces of a plurality of exhaust path tubes 7 of the exhaust gas heat exchanger 10 is provided, which is connected in the middle of the exhaust gas recirculation line of the exhaust gas recirculation device used for a diesel engine, it becomes difficult that soot on the heat transfer surfaces of the Plurality of the exhaust gas route tubes 7 and on the inner surface of the core housing 4 collects. As a result, the cross-sectional area of the exhaust gas path 5 is not reduced. Therefore, an increase in the draft resistance on the gas side of the exhaust gas circulating device used for a diesel engine can be prevented.

Description

Background of the Invention 1. Field of the Invention

The present invention relates to a heat exchanger which is suitable for an exhaust gas Circulation device is used, for example for an EGR gas cooler for cooling circulating exhaust gas by means of heat exchange between the circulating exhaust gas for the exhaust gas circulation device and cooling water of an internal combustion engine.

2. Description of the prior art

Japanese Unexamined Patent Application No. 9-310 995 proposes an exhaust gas Heat exchanger before, for example an EGR gas cooler for cooling circulating exhaust gas (EGR gas), which ver for an exhaust gas recirculation device is used in which a part of the exhaust gas of an internal combustion engine from a Exhaust pipe removed and to an intake pipe of the internal combustion engine is recycled so that the part of the exhaust gas enters into a cylinder absorbent mixture is added. With this exhaust gas heat exchanger Heat exchanged as indicated below. In the exhaust heat exchanger is a multitude of heat transfer tubes on one tube arranged panel, which is made by forming a metal plate, the is attached to the two end portions of the inner wall of a barrel tube. Heat is between exhaust gas that flows in the heat transfer tubes and cooling water that flows outside the heat transfer tubes, exchanged so that the exhaust gas can be cooled.

With this exhaust gas heat exchanger there is a tendency for soot (parti (which contain unburned fuel and carbon) on the inner surface of the heat transfer tube of the exhaust gas recirculation device, d. H., there is a tendency for soot to build up on the heat transfer surface collects. If soot collects on the heat transfer surface, the Exhaust gas path, which is formed in the heat transfer tube, closed, and the exhaust path is clogged with soot. If the cross-sectional area of the Exhaust path is reduced in this way, the drag on the  Exhaust side of the exhaust gas recirculation device enlarged. Therefore the Strö rate of EGR gas reduced. Accordingly, it will be difficult ensure the necessary amount of EGR gas.

As a result of the clogging of the heat transfer surface in the exhaust gas path of the Heat transfer tube is the performance of the heat exchange of the Exhaust gas heat exchanger deteriorated. To solve the problems listed above solve, discloses Japanese Unexamined Utility Model Publication No. 1-144 692 a process of periodically cleaning the heat transfer surface of the heat transfer tube of the heat exchanger, which is used for the Exhaust gas heat recovery is used with a scrubbing solution.

However, if the heat exchanger is used for the exhaust gas heat recovery used, removed from a vehicle and washed, this takes away Time consuming and expensive. To prevent a low impact that is generated when fuel is burned on a surface of a Fuel injector clinging to the unexamined Japanese patent discloses Publication No. 11-311168 a method of applying one by one Reaction pinned layer of a chemical compound of perfluoropolyether as a coating on the surface of the fuel injection valve.

It is possible to apply this method to the heat transfer tube of the To use exhaust gas heat exchanger, for example an EGR gas cooler, however, it is because of the heat resistance temperature caused by a reaction pinned layer of a chemical compound of perfluoropolyether at about 200 ° C, this method is not possible for heat transfer to use tubes of the exhaust gas heat exchanger in which exhaust gas flows, whose temperature is increased to a maximum of 500 ° C.

Summary of the invention

It is an object of the present invention to provide an exhaust gas heat exchanger create a variety of exhaust gas tubes, their heat transfer bearing surfaces (inner surfaces) are covered with a covering material, which is effective in preventing soot sticking, via is layered on top of each other.

In a first aspect of the invention there is provided a coating material whose Heat resistance temperature is high and that to prevent sticking  of soot is effective on the inner surface of an exhaust path at least one Exhaust gas tubes of a plurality of exhaust gas tubes of an exhaust gas Heat exchanger applied as a coating. As a result, it is difficult that soot on the inner surface of the exhaust path of the exhaust path tube sam melt that is used in the exhaust gas recirculation device. It is therefore possible the occurrence of clogging of the exhaust gas path in the exhaust gas path tube avoid that is used for the exhaust gas recirculation device. Corresponding the cross section of the exhaust gas path is not reduced, and an increase can be made the drag on the exhaust side of the exhaust gas recirculation device that will. Consequently, it is possible to decrease the flow rate of the to prevent circulating exhaust gas.

In a second aspect of the invention, a silicon oxide glass (SiO ₂ glass) film, the film thickness of which measures a few microns to a few tens of microns, is formed on a heat transfer surface of stainless steel which is shaped into the profile of the parts. Since silicon oxide (SiO ₂ ) is itself glass and is non-flammable, it cannot be burned if it is used in an environment whose temperature is around 500 ° C. Therefore, silica glass can be used stably, and soot can be continuously prevented from adhering to the inside surface of the exhaust gas path of the exhaust gas path tube.

In a third aspect of the invention, when the inner surfaces of the exhaust gas passages of a plurality of exhaust gas passage tubes are immersed in a treatment solution of SiO ₂ , silicon oxide glass films (SiO ₂ glass films) are formed on the inner surfaces of the plurality of exhaust gas passage tubes so that the Manufacturing costs can be reduced. In a fourth aspect of the invention, heat transfer fins are arranged to facilitate the exchange of heat between exhaust gas and liquid of an internal combustion engine between two exhaust gas tubes, which are adjacent to one another.

The present invention is more preferred from the following description Embodiments of the invention when considered together with the attached drawings to be more fully understood.

Brief description of the drawings

The drawings show:

Fig. 1 is a view showing a model of an exhaust gas recirculation device for use in an internal combustion engine, with an exhaust gas heat exchanger;

Fig. 2 is a view showing the appearance of an exhaust gas heat exchanger;

Fig. 3 is a section along the line AA in Fig. 2;

FIG. 4 shows a section along the line BB in FIG. 2; and

Fig. 5 is a section along the line CC in Fig. 2.

Description of preferred embodiments

An embodiment of the present invention will be explained below with reference to the accompanying drawings. In this case, Fig. 1 is a view showing an exhaust gas recirculation device for use in an internal combustion engine.

In an internal combustion engine (hereinafter referred to as an engine), for example a diesel engine, which is installed in a vehicle, for example in an automobile, an exhaust gas recirculation device 15 is provided for use in the internal combustion engine, which operates as indicated below. Part of the exhaust gas is removed from the exhaust line 13 and returned to the intake line 12 of the engine 11 , ie this part of the exhaust gas is additionally introduced into a mixture to be sucked into the cylinder 14 . In this connection, an extension valve 16 for opening and closing an intake port and an exhaust valve 17 for opening and closing an exhaust port are provided in the cylinder head of the engine 11 . A piston 19 connected to a crankshaft is slidably provided in the cylinder 14 .

The exhaust gas recirculation device 15 for use in the internal combustion engine is an exhaust gas recirculation device, which comprises: exhaust gas recirculation lines 21 to 23 for guiding circulating exhaust gas (EGR gas); an exhaust gas circulation control valve (hereinafter referred to as an EGR valve) 24 for adjusting the flow rate of the EGR gas according to the operating state of the engine 11 ; and a heat exchanger used for an exhaust gas circulating device of the type with water cooling (hereinafter referred to as an exhaust gas heat exchanger) 10 .

In the above structure, the EGR valve 24 has : a valve housing 20 disposed between the exhaust gas recirculation lines 22 , 23 ; and a valve body (valve) 26 for opening and closing the valve hole 25 formed in the valve housing 20 . In the EGR valve 24 , the shaft 27 , at the front end of which the valve body 26 is attached, is connected to the diaphragm 28 . On one end side of the membrane 28 , a negative pressure chamber 29 is provided, into which negative pressure is introduced, and on the other end side of the membrane 28 , an atmospheric chamber 30 is provided, into which atmospheric air is introduced.

Next, the structure of the exhaust gas heat exchanger 10 of this embodiment will be briefly explained below with reference to FIGS. 1 to 5. This exhaust gas heat exchanger 10 is an EGR gas cooler for cooling EGR gas by way of heat exchange between cooling water of the engine 11 and EGR gas. The exhaust gas heat exchanger 10 has: a heat exchange core 3 with laminated plates, which is composed of a plurality of plates laminated and integrally soldered together in the thickness direction; and a core case 4 for accommodating this heat exchange core 3 .

In the heat exchange core 3 , a plurality of first mold plates 1 and second mold plates 2 , which are formed into predetermined profiles by press molding, are laminated in the wall thickness direction. Due to the above structure, the exhaust gas paths 5 in which EGR gas flows and the cooling water paths 6 in which cooling water of the engine 11 flows are alternately arranged in the lamination direction.

In this connection, the exhaust gas path 5 is formed in the exhaust gas path tube 7 , which is constructed in such a way that the first mold plate 1 , whose lower end face projects in FIGS . 3 and 4, and the second mold plate 2 , whose upper end face in FIG . 3 and 4 projecting, laid on each other in the wall thickness direction and at least the front end portion in the drawing and the rear end portion in the drawing by brazing are interconnected. That is, the exhaust gas path 5 is formed between a pair of the first mold plate 1 and the second mold plate 2 , which are adjacent to each other in the vertical direction (wall thickness direction) in the drawing.

In the exhaust gas passage tube 7 , inner fins (corresponding to the heat transfer fins of the present invention) 8 are provided to facilitate the heat exchange between the EGR gas and the cooling water by increasing the area of contact with the EGR gas. These inner fins 8 are heat transfer fins of the offset type which are displaced relative to one another in a direction at a right angle to the flow direction of the EGR gas, so that the growth of the temperature boundary layer of the EGR gas in each exhaust gas path 5 can be suppressed or avoided. In this connection, the upstream side of the plurality of exhaust gas paths 5 communicates with the introduction tank portion 31 formed between the heat exchange core 3 and the core case 4 .

In this connection, the cooling water path 6 is formed in the cooling water path tube 9 , which is constructed in such a way that the second mold plate 2 , the lower end surface of which is recessed in FIGS . 3 and 4, and the first mold plate 1 , the upper end surface of which is shown in FIG is recessed Fig. 3 and 4 are laid on each other in the wall thickness direction, and at least the right end portion (connecting portion) 33 and the left end portion (Ver connecting portion) 34 in the drawing by brazing are connected to each other (in this example are in section of the drawing front end and the rear end section in the drawing connected to each other by soldering). That is, the cooling water path 6 is formed between a pair of a second mold plate 2 and a first mold plate 1 , which are adjacent to each other in the vertical direction in the drawing (the wall thickness direction).

In the cooling water path tube 9 , a plurality of rib sections 35 ; 36 is formed in one piece on opposite surfaces of the second mold plate 2 and the first front plate 1 . These fin portions 35 , 36 have a function of facilitating heat exchange between the EGR gas and the cooling water by increasing the area of contact with the cooling water. Furthermore, these rib regions 35 , 36 have the function of reducing an area in the cooling water path 6 where cooling water is located. Further, these fin portions 35 , 36 have a function of preventing the first face plate 1 and the second face plate 2 from being deformed by a load acting on the die plates when the heat exchange core 3 is temporarily soldered. As a result of the above function, the cooling water path 6 can be prevented from being closed. In this connection, an inlet-side tank section (not shown) and an outlet-side tank section 38 are provided on the two end sections of the cooling water path tubes 9 and are connected to the end sections of the plurality of cooling water paths 6 .

The core housing 4 has: a core container 41 , the profile of which is formed into a container shape for accommodating the heat exchange core 3 ; and a core cap 42 for closing the opening portion of this core container 41st After the outer peripheral end portion of the core cap 42 is brought into contact with the opening end portion of the core container 41 , it is soldered.

In the right side wall portion of the core container 41 , an EGR gas inlet 51 is provided, which is connected to the inlet container portion 31 , which communicates with a plurality of exhaust gas paths 5 . The EGR gas inlet 51 is connected to the exhaust gas introduction connection portion 52 for introducing EGR gas into the core container 41 . In the left side wall portion of the core tank 51 , an EGR gas outlet 51 is provided, which is connected to the outlet tank section 32 , which communicates with a plurality of exhaust gas paths 5 . The EGR gas outlet 53 is connected to the exhaust gas discharge connection section 54 for discharging the EGR gas from the core tank 41 , which has completed the heat exchange with cooling water. In this connection, the exhaust gas introduction connection section 52 is connected to the exhaust gas return line 21 , and the exhaust gas discharge connection section 54 is connected to the exhaust gas return line 22 . Both are formed into a substantially annular shape made of iron, the surface of which is plated or plated with nickel. In this connection, the surfaces of the exhaust gas introduction connection portion 52 and the exhaust gas discharge connection portion 54 need not be plated.

In the ceiling wall portion on the upper end side of the core container 41 , a cooling water inlet 55 a is provided, which is connected to the inlet-side container section, which is connected to a plurality of cooling water paths 6 in connection. The cooling water inlet 55 a is connected to the cooling water introduction line 55 , the profiles is essentially a circular line or such a pipe, for introducing cooling water into the heat exchange core 3 . In the core cap 42 , a cooling water discharge connection 57 a is provided, which is connected to the outlet-side container section 38, which is connected to a plurality of cooling water paths 6 . The core cap 42 is connected to the cooling water discharge pipe 57 , the profile of which is substantially circular, for discharging cooling water from the core 3 , which has completed the heat exchange with EGR gas. In this context, these cooling water introduction pipe 55 and cooling water discharge pipe 57 are made of stainless steel, the corrosion resistance of which is high.

In this embodiment, the heat transfer surfaces or inner surfaces of the first mold plate 1 , the second mold plate 2 , the inner fin 8 , the core container 41 and the core cap 42 are exposed to the EGR gas, the temperature of which is not lower than 400 ° C and the sulfide, nitric acid , Contains sulfuric acid, ammonium ions and acetic acid. Therefore, they are made up of a metallic sheet made of a rust-proof barn with a high corrosion resistance. The connecting portions of this first mold plate 1 , this second mold plate 2 , the inner rib 8 , the core container 41 and the core cap 42 are connected by means of soldering, using a solder material made of copper or a nickel alloy.

The heat transfer surfaces of the plurality of exhaust path tubes 7 (a pair of a first mold plate 1 and a second mold plate 2 ) and the inner wall surfaces of the heater core 41 , the core cap 42 , the exhaust gas introduction connection portion 52 and the exhaust gas discharge connection portion 54 are coated with silicon oxide glass films (SiO ₂ glass films) (transparent, thin film coating material), the heat resistance of which is high and the prevention effect for the adhesion of soot is high. In this connection, the wall thickness of the first mold plate 1 and the second mold plate 2 measures 0.4 mm, the wall thickness of the inner ribs 8 measures 0.2 mm, the wall thickness of the core container 41 and the core cap 42 measures 1.5 to 2.0 mm , and measures the film thickness of the SiO ₂ glass film a few microns to a few tens of microns.

Next, referring to FIGS. 1 to 5, there follows a brief explanation of a method of manufacturing the exhaust gas heat exchanger of this embodiment.

As shown in FIGS. 3 to 5, the first mold plate 1, the second mold plate 3 and the inner ribs 8 are successively as seen in the drawing above, laminated so that the heat exchange core 3 is mounted temporarily in the core cap 42. Then, the core container 41 is attached to the heat exchange core 3 as seen from the upper side in the drawing in such a manner that the core container 41 covers the heat exchange core 3 . At the same time, the core container 41 is pressed together with a tensioning device, seen from the upper side in the drawing, so that the core cap 42 , the heat exchange core 3 and the core container 41 are temporarily fixed.

Next, the exhaust gas introduction connection portion 52 is temporarily inserted into the right side wall portion of the core container 41 , and the exhaust gas discharge connection portion 54 is temporarily inserted into the left side wall portion of the core container 41 . Next, the cooling water introduction pipe 55 is temporarily inserted into the ceiling wall portion of the upper end side of the core container 41 , and the cooling water discharge pipe 57 is temporarily inserted into the core cap 42 . Alternatively, the temporary assembly can be carried out as follows. The cooling water pipe 57 and the core cap 42 are caulked together, and the cooling water introduction pipe 55 and the core container 41 are caulked together. Thereafter, the heat exchange core 3 is attached to the core cap 42 so that the core container 41 covers it. This completes the temporary assembly.

Thereafter, under the condition that a solder material, for example copper or a nickel alloy, is introduced into the connecting portions of the first mold plate 1 , the second mold plate 3 , the inner ribs 8 , the core container 41 and the core cap 42 , the solder material is heated and melted, and in a heating furnace, for example in a vacuum heating furnace, at temperatures higher than the melting point of the soldering material. In this way, the heat exchange core 3 , in which a plurality of the first mold plates 1 and the second mold plates 2 are laminated, and the core housing 4 are soldered together in one piece. As a result, an exhaust gas heat exchanger 10 whose corrosion resistance is excellent is manufactured.

The inside of the exhaust gas heat exchanger 10 , which is thus integrally soldered, is immersed in the treatment solution of SiO ₂ , that is, the inner wall surface of the core case 4 and the heat transfer surface of the plurality of exhaust gas flow path tubes 7 (which are between a pair of the first Mold plate 1 and second mold plate 2 are provided) of the heat exchange core 3 are immersed in the treatment solution of SiO ₂ . In this case, to spread the treatment solution SiO ₂ over the entire surfaces of the fins, the profiles of which are complicated, it is preferable that the inside of the exhaust gas heat exchanger 10 is decompressed by a vacuum pump so as to lower the pressure to a vacuum state thereof Pressure is lower than the atmospheric pressure, and then the treatment solution of SiO _{2 is} injected. Thereafter, the redundant treatment solution of SiO ₂ present in the exhaust gas heat exchanger 10 is removed, and the exhaust gas heat exchanger 10 is dried.

As a result, the heat transfer surface of the plurality of exhaust gas flow path tubes 7 and the inner wall surfaces of the core container 41 , the core cap 42 , the exhaust gas introduction connection section 52 and the exhaust gas discharge connection section 54 are covered with thin films of silicon oxide glass (SiO ₂ Glass). In this case, various types of SiO ₂ treatment solution can be provided. It is common practice to use a treatment solution of SiO ₂ which contains a main agent, a hardening agent, a solvent and an additive. Although it depends on the composition, various types of the treatment solution can be dried at an ordinary temperature. However, if the drying temperature is increased, the drying time can be shortened, so that the working time can be shortened. In this embodiment, drying is carried out under the condition of 150 ° C at 30 minutes.

The properties of this embodiment are explained below. As described above, in the exhaust gas circulating device 15 of this embodiment for use in an internal combustion engine, the heat transfer surface of the exhaust gas path 5 formed in the plurality of exhaust gas path tubes 7 of the exhaust gas heat exchanger 10 and the inner surfaces of the core container 41 and the core cap 42 with a coating material whose heat resistance temperature is not less than 500 ° C and which has an excellent property in preventing soot from adhering. As a result, it is possible to increase the contact angle formed between soot and the heat transfer surface of the exhaust path 5 formed in the exhaust path tube 7 of the exhaust gas heat exchanger 10 , or it is also possible to increase the contact angle formed between soot and the inner surfaces of the core container 41 and the core cap 42 are formed while the exhaust gas circulating device 15 is used for use in an internal combustion engine.

As a result, it becomes difficult for soot to collect on the heat transfer surface of the exhaust path 5 and the inner surfaces of the core container 41 and the core cap 42 . Accordingly, the occurrence of clogging of the exhaust gas path 5 can be avoided. In this way, it is possible to prevent the cross section of the exhaust gas path 5 from being reduced. Therefore, an increase in the drag on the gas side of the exhaust gas recirculation line 21 to 23 of the exhaust gas circulating device 15 for use in an internal combustion engine can be avoided. Accordingly, it is possible to prevent the EGR gas flow rate from being decreased. Accordingly, it is possible to ensure the necessary amount of EGR gas.

Silicon oxide glass films (SiO ₂ glass films), the thickness of which measures a few microns to a few tens of microns, are formed on the heat transfer surfaces of the first mold plate 1 and the second mold plate 2 , which are made of stainless steel and are formed into the profiles of parts. Because silicon oxide (SiO ₂ ) is itself glass and non-flammable, it cannot be burned if used in an environment the temperature of which is around 500 ° C. Therefore, silicon oxide glass can be used stably, and soot can be continuously prevented from adhering to the inner surface of the exhaust pipe 7 .

The acid resistance of SiO ₂ glass films is also excellent. Therefore, SiO ₂ glass films are not corroded by the exhaust gas with high temperature and exhaust gas condensed water (strongly acidic water). Therefore, another effect can be provided in which internal corrosion of the exhaust gas heat exchanger 10 is prevented because the internal corrosion of the plurality of exhaust gas tubes 7 can be prevented.

In a further embodiment, an exhaust gas heat exchanger 10 is used which has a heat exchange core 3 in which the exhaust gas path tubes 7 , which consist of a pair of a first molding plate 1 and a second molding plate 2 , and the inner fins 8 are alternately laminated. Alternatively, it is possible to use an exhaust gas heat exchanger having a heat exchange core in which the exhaust gas path tubes, which are integrally formed by extrusion or drawing, and the heat transfer fins are alternately laminated.

In this embodiment, the present invention finds application in an exhaust gas heat exchanger 10 , which is connected between the exhaust gas recirculation lines 21 , 22 of the exhaust gas recirculation device which is intended for use in an internal combustion engine, in which part of the exhaust gas in the Exhaust line 13 of the engine 11 is returned to the intake line 12 . However, it is possible to apply the present invention to another exhaust gas heat exchanger, for example an exhaust gas heat recovery device which is arranged in a silencer, for recovering the thermal energy of an exhaust gas.

Although the invention is reference with reference to for illustrative purposes selected particular embodiments have been described, but is apparent Lich that numerous modifications are carried out by a person skilled in the art can write without the basic concept and scope of the invention.

Claims (4)

1. exhaust gas heat exchanger comprising a multiplicity of exhaust gas path tubes, in which an exhaust gas path is formed, wherein heat between the exhaust gas Internal combustion engine flowing in the exhaust pipe and a fluid is exchanged, which flows on the outside of the multiplicity of exhaust gas path tubes, and a coating material whose heat resistance is high in view is effective in preventing soot from adhering to the inner surface an exhaust gas path as at least one of the plurality of exhaust gas path tubes Coating is applied. 2. Exhaust gas heat exchanger according to claim 1, wherein the plurality of exhaust gas path Tube made of stainless steel that goes to the profiles of parts in the Ways of press molding are formed, and the coating material is a sili cium oxide glass film, the film thickness of which measures a few microns to a few tens of microns and which is formed on the heat transfer surface of the stainless steel. 3. The exhaust gas heat exchanger according to claim 2, wherein the silicon oxide glass film is formed when the inner surface of the exhaust gas path of the exhaust gas path pipe is immersed in a treatment solution of SiO ₂ . 4. Exhaust gas heat exchanger according to any one of claims 1 to 3, wherein Heat transfer fins to facilitate heat exchange between Exhaust gas and a fluid of an internal combustion engine between two each other adjacent exhaust gas tubes are arranged.