FR2809170A1 - Exhaust gas heat exchanger incorporating a coating lining the inner surfaces of the tubes carrying exhaust gases to prevent soot build-up - Google Patents

Abstract

A gas exhaust heat exchanger comprises several tubes (5, 7) forming the trajectory for the exhaust gas, a fluid circulating outside these tubes for heat exchange with the exhaust gas and a coating material, with an elevated resistance to temperature preventing the formation of soot, covering the inner face of at least one of the tubes forming the trajectory for the exhaust gas.

Description

The present invention relates to a heat exchanger used for an exhaust gas recirculation device such as a recirculating outlet gas cooler for cooling the recirculating exhaust gas by heat exchange between heat exchangers. recirculating exhaust gas for the exhaust gas recirculation device and the cooling water of an internal combustion engine.

Japanese Unexamined Published Patent Application No. 9-310995 provides an exhaust gas heat exchanger such as a recirculating exhaust gas cooler for recirculating exhaust gas cooling (EGR gas) used for a device. exhaust gas recirculation system, wherein an exhaust gas portion of an internal combustion engine is delivered from an outlet of an exhaust pipe and is returned to a suction pipe of the internal combustion engine, so that the portion of the exhaust gas is added to the mixture to be sucked into a cylinder. In this exhaust gas heat exchanger, heat is exchanged as indicated below. In the exhaust gas heat exchanger, a plurality of heat transfer tubes are disposed on a tube plate by forming a metal sheet which is formed at the two end sections of an inner wall of a cylindrical tube. Heat is exchanged between the exhaust gases circulating in the heat exchange tubes and the cooling water circulating inside the heat exchange tubes, so that the exhaust gases can be cooled. .

In this exhaust gas heat exchanger, soot (particles containing unburned fuel and carbon) tends to accumulate on the inner surface of the heat transfer tube of the exhaust gas recirculation device. that is, soot tends to accumulate on the heat transfer face. When soot accumulates on the heat transfer face, an exhaust path in the heat transfer tube closes and the exhaust path is obstructed by soot. When the cross-sectional area of the exhaust path is reduced in this manner, the draw resistance on the exhaust gas inlet side of the exhaust gas recirculation device increases. As a result, the flow of the EGR gases is reduced. This is why it becomes difficult to guarantee the required amount of EGR gas.

Due to the clogging of the heat transfer face in the exhaust path of the heat transfer tube, the heat exchange performance of the exhaust gas heat exchanger is impaired. To solve the aforementioned problems, published Japanese Unexamined Utility Model Application No. 1-144192 discloses a method for periodically cleaning the heat transfer face of the heat transfer tube of the heat exchanger used for heat transfer. heat recovery of the exhaust gas, with a washing solution.

However, when the heat exchanger used to recover heat from the exhaust is removed from the vehicle and washed, this is time consuming and expensive. To prevent a deposit, which occurs when fuel is burned, does not adhere to the surface of a fuel injection valve, Japanese Unexamined Published Patent Application No. 11-311168 discloses a method for depositing a fixed reactive layer of a chemical compound consisting of perfluoropolyether on the surface of the fuel injection valve.

It is possible to apply this method to the heat transfer tube of the exhaust gas heat exchanger such as EGR gas cooling, but since the heat resistance temperature of the fixed reaction layer a chemical compound formed of perfluoropolyether is equal to about 200 C, it is impossible to apply this method to a heat transfer tube of the exhaust gas heat exchanger, in which the exhaust gas circulates, of which the temperature rises to S00 C.

An object of the present invention is to provide an exhaust gas heat exchanger, wherein a plurality of exhaust path path tubes, whose heat transfer faces (inner faces) are covered by a heat transfer material. effective coating to prevent the adhesion of soot, are arranged in layers one below the other.

According to a first aspect of the invention, the coating material, whose temperature of heat resistance is high and which is effective to prevent soot adhesion, is deposited on an inner face of a path for the gases of exhausting at least one of a plurality of path tubes for the exhaust gas of an exhaust gas heat exchanger.

More specifically, the invention relates to an exhaust gas heat exchanger, characterized in that it comprises a plurality of tubes forming a path for the exhaust gases, in which a path for the exhaust gases is formed. , that heat is exchanged between the exhaust gases of an internal combustion engine flowing in the exhaust gas path tubes and a fluid flowing out of the plurality of gas path tubes exhaust and that a coating material, the heat resistance temperature of which is high and which is effective in preventing soot adhesion, covers an inner side of an exhaust path of at least one of the plurality of path tubes for the exhaust gas.

On the basis of the foregoing, it is difficult for soot to accumulate on the inner side of the tube-shaped exhaust path in the exhaust gas recirculation device. For this reason, it is possible to reduce the occurrence of exhaust path clogging in the exhaust path tube used as an exhaust gas recirculation device. Therefore, the cross-sectional area of the exhaust gas path is not reduced, and an increase in draft resistance on the exhaust gas inlet side of the exhaust gas recirculation device can be reduced. Therefore it is possible to prevent a reduction in the flow of recirculating exhaust gases.

According to a second aspect of the invention, the plurality of path tubes for the exhaust gas are made of stainless steel being shaped in a manner adapted to the workpiece profiles by means of press forming, and that the coating material is a glass film based on silicon oxide (SiO 2), the thickness of which is between a few micrometers and a few tens of micrometers and is formed on a heat transfer face of stainless steel. Since silicon oxide (Sio2) is itself glass and is incombustible, it can not burn when used in an environment with a temperature of about 00 C. This is why Silicon oxide glass can be used in a stable manner, and the soot is permanently prevented from adhering to the inner surface of the exhaust path of the exhaust path tube.

According to a third aspect of the invention, when the inner faces of the exhaust paths of a plurality of exhaust path tubes are immersed in a SiO 2 treatment solution, glass films based on Silicon oxide (SiO 2) are formed on the inner surfaces of the plurality of exhaust path tubes, so that the manufacturing cost can be reduced. According to a fourth aspect of the invention heat transfer fins serving to facilitate a heat exchange between the exhaust gas and a fluid of an internal combustion engine are arranged between two tubes forming a path for the exhaust gas, are adjacent to one another.

Other features and advantages of the present invention will become apparent from the description given with reference to the accompanying drawings, in which: - Figure 1 is a view showing a model an exhaust gas recirculation device for use in a internal combustion engine having an exhaust heat exchanger; Fig. 2 is a view showing the external appearance of an exhaust gas heat exchanger; Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2; - Figure 4 is a cross-sectional view along the line B-B in Figure 2; and - Figure 5 is a cross-sectional view taken along the line C-C in Figure 2.

With reference to the accompanying drawings, it will be explained after one embodiment of the present invention. In this case, Figure 1 is a view showing exhaust gas recirculation device for use in an internal combustion engine. In an internal combustion engine (hereinafter referred to as the engine), such as a diesel engine mounted in a vehicle such as an automobile, there is provided an exhaust gas recirculation device 15 for use therein. for the internal combustion engine and which operates as indicated below. part of the exhaust gas is taken from the exhaust pipe 13 and is returned to the intake manifold 12 engine 11, that is to say that part of the exhaust gas is added to the mixture to be sucked into In this regard, in the cylinder head of the engine 11 there is also provided an intake valve 16 for opening and closing an intake port and an exhaust valve 17 for opening and closing an exhaust port. A piston 19 connected to a crankshaft is slidably disposed within the cylinder. The exhaust gas recirculation device 15 for use in an internal combustion engine is an exhaust gas reflux device. comprising: exhaust gas reflux tubes 21-23 for guiding the recirculating exhaust gas (EGR gas), an exhaust gas recirculation control valve 24 (hereinafter referred to as an EGR valve) for controlling the flow of the EGR gas as a function of the operating state of the engine 11, and a heat exchanger used for a water cooling type exhaust gas recirculation device (designated as a heat exchanger). exhaust gas heat).

In the above-indicated structure, the EGR valve 24 comprises: a valve housing 20 disposed between the exhaust gas reflux tubes 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 rod 27, at the front end of which is fixed the valve body 26, is connected to the diaphragm 28. On one end side of the diaphragm, there is provided a vacuum chamber 29, in which a vacuum is introduced, and at the other end of the diaphragm 28 there is provided an atmospheric chamber 30, into which the atmosphere is introduced.

Next, with reference to Figures 1 to 5, the structure of the exhaust gas heat exchanger 10 of this embodiment will be briefly explained below. This exhaust gas heat exchanger 10 is EGR gas cooling for cooling the gas by heat exchange between the cooling water of the engine 11 and the EGR gas. The exhaust gas exchanger 10 comprises: a heat exchange core 3 having laminated plates which are constituted by a plurality of superimposed and brazed plates integrally in the direction of the thickness of the wall, and a core housing and a core housing 4 for housing this heat exchange core 3.

In the heat exchange core 3 a plurality of first forming plates 1 and a plurality of second forming plates 2, which are respectively formed with predetermined profiles by press forming are superimposed in the direction of the wall thickness. . because of the structure indicated above, the paths 5 of the exhaust gases in which the EGR gases flow, and the paths 6 of the cooling water, in which the cooling water of the material flows, are arranged alternately in the direction superposition.

In this context, the exhaust path 5 is formed in the exhaust path tube 7, which is arranged such that the first forming plate 1, the lower end face of which is disposed in 3 and 4, and the second forming plate 2, whose upper end face is arranged protruding in FIGS. 3 and 4, are placed against each other in the direction of the thickness. of the wall, and at least the front end section and the rear end section in the drawing are joined to each other by brazing. That is, the exhaust path 5 is formed between a pair formed by the first forming plate 1 and the second forming plate 2, which are adjacent to each other in the direction vertical (direction of wall thickness) in the drawing.

In the exhaust gas path tube 7, the inner fins 8 (which correspond to the heat transfer fins according to the present invention) are arranged to facilitate the heat exchange between the EGR gases and the cooling water, by increasing a contact surface with the EGR gases. These internal fins 8 are shift type thermal transfer fins, which are arranged to be offset relative to each other in a direction perpendicular to the flow direction of the EGR gases, so that the growth of the layer EGR gas temperature limit may be reduced in each exhaust path. In this context, the upstream side of the plurality of exhaust paths 5 communicates with the inlet reservoir section 31, which is formed between the heat exchange core 3 and the core housing 4. The downstream side of the plurality of the exhaust gas paths communicates with the outlet tank section 32 formed between the heat exchange core 3 and the core housing 4.

In this context, the cooling water path 6 is formed in the cooling water path tube 9, which is formed such that the second forming plate 2, whose lower end face is in recess in FIGS. 3 and 4 and the first forming plate 1, the upper end face of which is recessed in FIGS. 3 and 4 are placed against each other in the direction of the thickness of the wall, and at least the right end section (junction section) 33 and the left end section (junction section) in the drawings are joined together by brazing (in this example, the front end section and rear end section in the drawing are joined together by soldering). That is, the cooling water path is formed between a pair of the second forming plate 2 and the first forming plate 1, which are adjacent to each other in the vertical direction (wall thickness direction) on the drawing.

In the cooling water path tube 9, a plurality of finned sections 35, 36 are formed integrally on opposite sides of the second forming plate 2 and the first forming plate 1. These sections with fins 35, 36 serve to facilitate the heat exchange between the EGR gas cooling water by increasing the contact surface with the cooling water. In addition, these fin sections 35, 36 serve to reduce the size of a cooling path region 6, in which the cooling water is stagnant. In addition, these finned sections 35, 36 are intended to prevent the first forming plate 1 and the second forming plate 2 from being deformed by one. charge applied to the forming plates when the heat exchange core 3 brazed temporarily. Due to the role indicated above, the path for the cooling water can not be closed. In this context, an inlet side tank section (not shown) and an outlet side tank section 38, which communicate with end sections of the plurality of paths 6 of the cooling water, are provided in both sections. end of the tubes 9 forming paths for the cooling water.

The core housing 4 comprises: a receptacle 41 of the core, the profile of which is adapted to the shape of the container for accommodating the heat exchange core 3, a core cover 42 for closing a receptacle opening portion 41 of the core. After introducing an outer circumferential end section of the core cover 42 into the opening end section of the core receptacle 41, it is secured by brazing.

In the right receptacle side wall section 41 of the core there is provided an inlet 51 for the EGR gas, which is connected to the inlet container section 31 which communicates with a plurality of exhaust paths 5. The inlet 51 of the EGR gas is connected to the exhaust gas introduction junction section 52, which serves to reintroduce the EGR gas into the core receptacle 41. In the left side wall section of the core receptacle 41 is disposed an EGR gas outlet 51, which is connected to the outlet vessel section 32 which communicates with a plurality of exhaust path 5. The outlet 53 of the EGR gas is connected to the connecting section 54 which serves to evacuate the exhaust gas for the evacuation of the EGR gas, which has participated in a heat exchange with the cooling water, out of the receptacle 41 of the core. In this context, the exhaust gas introduction junction section 52 is connected to the exhaust gas reflux tube 21, and the exhaust gas junction section 54 is connected to the reflux tube 22. exhaust gas. Both are arranged with a substantially annular shape and are made of iron, the surface plated nickel. In this respect, the surfaces of the exhaust gas introduction junction section 52 and the exhaust exhaust junction section 54 may not be plated.

In the ceiling wall section on the side of the upper extremity of the receptacle 41 of the core there is provided an inlet 55a for the cooling water, which is connected to the inlet side container, which communicates with a plurality of paths 6 of the 'cooling water. The inlet 55a for the cooling water is connected to the cooling water introduction tube 55, the profile of which substantially corresponds to a tube circulating for the introduction of the cooling water into the exchange core. 3. In the hood 42 of the core is provided a cooling water discharge port 57a, which is connected to the outlet side side container section 38 and which communicates with a plurality of paths 6 for the water of the cooling water. cooling. The cover 42 of the core is connected to the cooling water discharge tube 57a, whose profile is substantially circular, to evacuate the cooling water which has participated in a heat exchange with the EGR gas, out of the core 3. In this regard, this tube 55 for introducing the cooling water and the tube 57 for discharging the cooling water are made of stainless steel, whose resistance to corrosion is high.

In this embodiment, the heat transfer faces or inner faces of the first forming plate 1, the second forming plate 2, the inner fin 8, the core receptacle 41 and the core cover 42 are exposed to EGR gas, whose temperature is not lower than 400 C and which contain a sulphide, nitric acid, sulfuric acid, ammonium ions and acetic acid. Therefore, they are formed of a stainless steel metal sheet, whose corrosion resistance is high. The joining sections of these elements, namely the first forming plate 1, the second forming plate 2, the inner fin 8, the receptacle 41 of the core and the cover 42 core, are joined by brazing, with the use of a solder formed of a copper or nickel alloy.

On the thermal transfer faces of a plurality of tubes 7 forming paths for the exhaust gases (a pair formed by the first forming plate and the second forming plate 2) and on the internal faces of the wall of the receptacle; 41 of the core, the core cowl, the exhaust gas introduction junction section 52 and the exhaust gas junction section 52 are coated with silicon oxide glass films ( Si0z) (coating material in the form of a transparent thin film), which has a high heat resistance and strongly prevents soot adhesion. In this regard, the wall thickness of the first forming plate 1 and the wall thickness of the second forming plate 2 are equal to 0.4 mm, the wall thickness of the inner fin 8 is equal to 0.2 mm, the wall thickness of the receptacle 41 of the core and the cover 42 of the core is between 1.5 and 2.0 mm and the thickness of the SiO 2 -based glass film is between a few micrometers and a few tens of micrometers. Hereinafter with reference to Figs. 1 to 5, a method of making the exhaust gas heat exchanger of this embodiment will be briefly explained.

As shown in FIGS. 3 to 5, the first forming plate 1, the second forming plate 2 and the internal fins 8 are superposed successively in the direction of height in the direction of the height in the drawing so that that the heat exchange core 3 is provisionally incorporated into the core cover 42. Then the receptacle 41 of the core is placed on the heat exchange core 3 from above in the drawing so that the receptacle 41 of the core covers the heat exchange core 3. At the same time, the receptacle 41 of the core is pushed back to the core. Using a template from the top side of the drawing so that the core cover 42, the heat exchange core 3 and the core receptacle are provisionally fixed.

Thereafter, the exhaust gas introduction junction section 52 is provisionally introduced into the right-hand side wall section of the receptacle 41 for the core, and the exhaust exhaust junction section 54 is temporarily introduced into the exhaust section. left wall of the receptacle 41 for the core. Then provisionally introduces the cooling water introduction tube into the ceiling wall section on the receptacle end end side 41 of the core and the cooling water discharge tube 57 is temporarily incorporated into the kernel hood. Otherwise, the provisional assembly can be executed as follows. The tube 55 for the cooling water and the cover 42 of the core are fixed by means of a mat between them, and the tube 55 for introducing the cooling water and the receptacle 41 of the core are fixed by means of a matting between them. Then the heat exchange core 3 is placed on the cover 42 of the core so that the receptacle 41 of the core covers this cover. This achieves the state of provisional assembly.

After introducing a solder such as a copper or nickel alloy into the junction sections of the first forming plate 1, the second forming plate 2, the inner fin 8, the receptacle 41 of the core and the bonnet From the core, the solder is heated and melted in a heating furnace such as a vacuum heating furnace at temperatures above the melting point of the solder. In this way, the heat exchange core 3, in which are superimposed a plurality of several first forming plates 1 and several second forming plates 2, and the casing 4 of the core are fixed in one piece between them by brazing. In view of the foregoing, an exhaust gas heat exchanger 10 is provided, the corrosion resistance property of which is excellent.

It is immersed inside the exhaust gas heat exchanger 10; which in this way is brazed in an integrated manner, in the SiO 2 treatment solution, that is to say that the inner wall of the casing 4 of the core and the heat transfer face of a plurality of tubes 7 forming Exhaust gas circulation paths (which are provided a pair formed by the first forming plate 1 and the second forming plate 2) of the heat exchange core 3, are immersed in the SO 2 treatment solution. In this, in order to spread the treatment solution formed of SiO 2 on all fin surfaces, whose profiles are complicated, it is preferable to depressurize the interior of the exhaust gas heat exchanger 10 by means of a vacuum pump so as to reduce the pressure to a vacuum state, corresponding to a pressure below atmospheric pressure, and then the SiO 2 treatment solution is injected. Then, excess of the SO 2 treatment solution that exists in the exhaust gas heat exchange 10 is removed, and the exhaust gas heat exchanger 10 is dried.

In view of the foregoing, the heat transfer face of the plurality of the exhaust gas flow path tubes 7 and the inner wall faces of the core receptacle 41, the core cover 42, the the exhaust gas introduction junction 52 and the exhaust gas junction section 54, by silicon oxide-based glass films (SiO 2, in which case more than one type can be provided. It is common to use a SiO 2 treatment solution as a main agent, a curing agent, a diluent and an additive, although depending on the composition, certain types of treatment solutions may be dried. At an ordinary temperature, however, when the drying temperature is increased, the drying time can be reduced, so that the working time can be reduced. drying, the drying is performed under the conditions corresponding to 150 C x 30 minutes.

The characteristic of this embodiment will be explained below. As previously described, in the exhaust gas circulation device 15 of this embodiment for use in an internal combustion engine, heat transfer face of the exhaust gas path 5 is formed. in a plurality of exhaust path tubes, the exhaust gas heat exchanger 10 and the inner faces of the core receptacle 41 and the core cover 42 are coated with a coating material, the The heat resistance temperature is not less than 500 ° C and has an excellent property preventing soot from adhering to this material. In view of the above, it is possible to increase the contact angle provided between the soot and the heat transfer face of the exhaust gas path formed in the tube 7 forming the exhaust path of the heat exchanger. exhaust gas or it is also possible to increase the contact angle formed between the soot and the inner faces of the receptacle 41 of the core and the cover 42 of the core, during use of the device 15 recirculation exhaust gas for use in an internal combustion engine.

In view of the foregoing, it becomes difficult for the soot to accumulate on the heat transfer face of the exhaust path and on the inner faces of the receptacle 41 of the core and the bonnet of the core. Therefore, it is possible to reduce the occurrence of an obstruction of the exhaust path. In this way, it is possible to prevent a reduction in the cross section of the exhaust gas path. Therefore, it is possible to reduce the increase in draw resistance on the exhaust side of the throttle tubes 21 to 23 of exhaust gas recirculation exhaust system 15, used in an engine. internal combustion. Therefore it is possible to mitigate a reduction flow of EGR gas. This is why it is possible to guarantee the required amount of EGR gas.

On the heat transfer faces of the first forming plate 1 and the second forming plate 2 made of stainless steel, which are produced with the part profiles, silicon oxide-based glass films are formed (S '). 02), whose thickness ranges from a few microns to a few tens of micrometers. Since the silicon oxide (S'02) of the glass is incombustible it can not be burned when used in an environment, the temperature of which is approximately 500 C. The silicon oxide can be used in a stable manner and soot adhesion to the inner surface of the exhaust path in the exhaust path pipe 7 is prevented in a continuous manner.

In addition, the resistance of acid-based SiO2-based glass films to the acid is excellent. Therefore, the S'O 2 formed glass films are not corroded by the high temperature exhaust gas or condensed water from the exhaust gas (strongly acidic water). Therefore, another effect can be obtained whereby the internal corrosion of the exhaust gas heat exchanger 10 is prevented since the internal corrosion of a plurality of exhaust gas tubes can be prevented. prevented.

In another embodiment, the exhaust gas heat exchanger 10, which has a heat exchange core 3, is adapted in which the tubes 3 forming exhaust gas paths consist of a cross-section formed of 1a first forming plate 1 and the second forming plate 2 and the inner fins 8 are alternately superimposed. Otherwise, it is possible to adapt an exhaust gas heat exchanger having a heat exchange core, wherein the exhaust path tubes, which are integrally formed by extrusion or drawing, and the heat transfer fins are superimposed in an alternating manner.

In this embodiment, the present invention is applied to the exhaust gas heat exchanger 10 which is mounted between the exhaust gas reflux tubes 22 of the exhaust gas recirculation device for use in an internal combustion engine, in which a part of the exhaust gases in the engine exhaust tube 13 is returned to the intake manifold 12. However, it is possible to apply the present invention to another exchanger exhaust gas heat, such as a gas heat recovery device

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